Rectification is an industrial method for obtaining alcohol. What is rectification

Behind the terrible word "rectification" are complex chemical processes. They consist in the fact that a complex substance is divided into simple components due to their different boiling points. That is, pure elements are taken away from the mixture by their evaporation and condensation.

Many novice distillers are wondering: what is the difference between distillate and rectified? At first glance, both of these processes seem similar, but in fact, the principle of their work, purpose and end result are different.

Distillation at home produced through alcohol mashine. Fermented raw materials are poured into alembic and heat up. Ethanol starts to evaporate first. The steam passes through the tube to the refrigerator, where it cools and condenses. Thus, alcohol with a strength of about 40 ° is extracted from the mash, which for the most part consists of water.

The process of rectification is more complicated. For it, a distillation column is used. This time, not mash is poured into the distillation cube, but a ready-made distillate. The liquid heats up and turns into steam. At the top of the column, it is cooled by the heat removal system and condenses. There is an interaction between the steam tending upwards and the phlegm flowing down the walls.

Throughout the cylinder there are plates or nozzles that provide an increase in the area of \u200b\u200bcontact between these two phases . Mass transfer takes place on each plate. In this case, the steam is saturated with volatile substances and gives off non-volatile liquids. So it passes through all the plates, and as a result, the lowest boiling component of the mixture accumulates at the top of the column. It is then withdrawn from the column and condensed. This produces pure 96% alcohol.

From what has been written above, it is clear that the purpose of distillation is to obtain alcohol from mash, and the task of rectification is to remove impurities from it. Rectified alcohol is widely used in various fields, but in the alcohol industry it is suitable only for making vodka and diluting other drinks. Unlike distillate, rectified has no taste and smell of raw materials created due to impurities.

So what is better - a distillation column or a moonshine still? It all depends on the goals and available means of the distiller. Rectification at home is more difficult and dangerous, but the output is a clean, less toxic product. The distillate contains more harmful impurities, but with the right approach, you can create high-quality and tasty alcohol.

Equipment

In the previous paragraph, it was discussed that distillation and rectification are not interchangeable actions. First, the raw material is distilled, and then, if necessary, the resulting moonshine is purified from impurities. Now it's time to figure out how the equipment for these processes is arranged and how to make them at home.

Alcohol mashine

For distillation in handicraft industry even the most primitive device assembled from improvised means will do. It consists of a distillation cube, a refrigerator and connecting tubes.

After making sure that all parts of the distiller are sealed and there are no leaks anywhere, you can safely begin to operate. It is recommended to clean the unit thoroughly with water and detergents before and after use. This will have a beneficial effect on the taste. alcohol and prolong the life of the device.

When moonshine is driven, not pure alcohol is obtained, which contains components that simply worsen the taste, as well as poisonous analogues. Therefore, rectification is used to improve the organoleptic and type of moonshine, as well as for complete purification from harmful impurities. This procedure is mandatory when making a rectificate at home. How does the rectification process go, and what are the key differences between the final product and moonshine?

Rectification is a rather complex process, which is based on the heterogeneity of the mixture of primary moonshine, the presence of liquids of various densities in the composition of the drink. This is the difference from the rectified product, which has a pronounced homogeneous alcohol structure.

Moonshine contains three different fractional parts, namely:

The first is the fractional part, which has a low density and a boiling point. It consists of methyl alcohol, toxic esters, makes up 15% of the volume of moonshine. This is a poisonous part, which, if ingested, will disable the pancreas and lead to poisoning. Immediately rectification begins with the removal of this fraction. It can also be used in practice, for example, as an organic dirt cleaner, but an unpleasant odor should be taken into account.
The second fractional part, which is fundamental for this process, consists of ethyl alcohol and makes up 75% of moonshine. This is the most numerous and safest part, which is the final product of distillation of moonshine. To give taste and presentation, you can paint and remove unpleasant odors.
The third fractional part consists of fusel oils. A characteristic feature is the boiling point, which is higher than that of the previous fractions - 87 degrees. It is represented by various components, the main of which are isobutyl alcohol and isoamyl alcohol, as well as fatty acid. It does not adversely affect health, but has an unpleasant odor and the effects of a severe hangover after consumption.

Which is better: rectified or moonshine?

Moonshine, as you know, is obtained by distillation, while the product does not lose its original taste properties and becomes completely free of harmful substances. Of the benefits: a pleasant delicate taste of the drink, which does not completely disappear with this cleaning method. The fortress is 50%. At home, cooking will require a little effort. For better separation into fractions, you will have to distill more than once.

Rectified does not retain taste properties, and chemical composition pure alcohol - without the presence of organic compounds, it is clear that in this case no taste can be achieved. This species is completely purified after the first distillation. These are the main differences between the two alcoholic beverages cooked at home. There is a percentage of alcohol, which is 90. There are people who prefer a certain type of drink, everyone decides for himself.

It is worth remembering that the rectification process is technologically more difficult to implement than traditional distillation.

Fundamentals of the rectification process

To begin with, bring the fortress of the initial volume of moonshine, which was going to be rectified, up to 40%, this is an acceptable parameter. Now we choose a substance for cleaning moonshine from unpleasant odors, it can be either coal with potassium permanganate or milk.

Let's start with the rectification:

The first and main stage is the disposal of the solution from poisonous "heads". We start setting on an active fire, but when the temperature reaches 55 degrees, we weaken and try to increase the temperature. Upon reaching 65 degrees, this stage begins: the deposition of harmful substances that made up the “heads” on the dry-evaporating part of the apparatus. We wash this part well.
The most interesting and responsible operation is the evaporation of the main part, which consists entirely of ethyl alcohol. At the same time, the procedure is simple: we bring the temperature regime to 80 degrees and then reduce the fire, constantly monitoring the temperature.
The final stage is getting rid of the oils that give an unpleasant odor. Here the cloudy structure of alcohol is removed, and if desired, then it is added to enhance the strength of the moonshine or give it natural aromatic properties. These oils require care when adding them, as they can cause a hangover. Nevertheless, such legends of alcoholic beverages as bourbon and cognac are impossible without the use of this type of oil.

With sufficient skill and the ability to distinguish between products, rectified products can be recognized by the pronounced smell of alcohol, and the rest of the parts by a strong unpleasant odor. There are two methods of distillation, one of them is the distillation column, which is an effective way to de-flavor the drink and give a pure product. And the second method is with the help of distillers.

If you work with an electronic temperature comparator, then you can more accurately determine the end of the stabilization of the column by the temperature difference.

C) Selection of head fractions.

For the correct organization of selection at this difficult period of rectification, we can recommend the following approach, which consists in breaking down the stage " IN» , for three successive equal time intervals ( absolute values time and selection are indicated for the example of conditional RUM-1).

Interval Duration Selection

"B" % min % ml/h ml/min

initial 33 7 10% enom 100 1,66

medium 33 7 30% enom 300 5

transitional 33 7 50% enom 500 8,3

Such a scheme for organizing the selection of head fractions guarantees you:

Complete separation of the head fractions from the cube, and their complete absence in the food fraction SR following them;

The minimum volume of the head fraction and the absence of the CP food fraction in it;

Approach to the main fraction of SR with a small 50% productivity.

In practice, the most accurate instrument for deciding on the end of the period of selection of head fractions and the beginning of the selection of food SR is the usual "human nose".

The odor control of the obtained distillate is carried out as follows:

- put a few drops of the selected distillate into the palm of your hand;

- rub this puddle over the entire surface of the palm;

- bring your palm to your face and inhale the distillate evaporated from your palm through your nose.

Such an instant and fairly accurate analysis will always be of some help to you in the rectification of alcohol.

The total amount of head fractions obtained during this period is 1...3% of the expected amount of alcohol and depends on the quality of the feedstock. REMEMBER! that the distillate obtained by distillation of the head fractions is not food product, since it consists mainly of ethers, acetones, aldehydes and other toxic substances, and can ONLY be used for technical needs, for example, as a solvent.

D) Selection of the food alcohol fraction.

Install a new, clean and large receiving container. Increase selection to enom(for conditional RUM-1 this is 1l/h=16.6ml/min), which will remain until the end of the entire rectification process. Let's check this selection with a stopwatch and a graduated cylinder. After 5-10 minutes, check the thermometer readings. If everything was done correctly, then the thermometer readings will not change. Moreover, this temperature will remain unchanged during the entire period of selection of the food fraction.

The SR obtained from this point on is a high-quality food product. However, its composition (indistinguishable by many even by smell) gradually changes and can be divided into three parts:

The first 5% of the total volume of SR will still contain traces of head fractions (for conditional RUM-1, this is ≈200 ml);

The central part - about 80% of the total volume of SR will be absolutely pure (for conditional RUM-1, this is ≈3360 ml);

And 5% of the total volume of SR before the end of this mode will begin to acquire traces of tail fractions (for conditional RUM-1, this is ≈200 ml).

But remember - the smaller the selection, the higher the quality!

This rectification mode does not require constant presence near the apparatus, and the receiving containers are replaced as they are filled.

Such a technique allows, in case the moment of temperature increase is missed (admission of SR with a higher concentration of heavy alcohols and fusel oils), to prevent “bad” alcohol from getting into “good” alcohol.

The selection of SR is completed when the temperature reaches 0.1 ... 0.05˚С above the temperature tc. Conventionally, it is considered that the amount of heavy-boiling impurities present in the SR at that moment and causing such an increase in the boiling point corresponds to acceptable food standards.

The approach and end of this moment can be "predicted" by the amount of SR already produced (for conventional RUM-1, this is ≈3760 ml) or by the smell of its last portion.

E) Selection of tail fractions (residue).

We replace the receiving container or leave the intermediate one (in which the “tail” has already been missed). We do not change the column setting - power Wt; selection Enom.

The process of selecting the residue is completed when the temperature level reaches about 82...85˚С, or is stopped due to odor control.

ATTENTION! The selected residue still contains a sufficient amount of ethyl alcohol. It can be considered a special SS with a high content of impurities of fusel oils and heavy alcohols. It, like SS, is not a food product, therefore it is strictly prohibited to use it for food purposes. The resulting residue can be recycled with a new portion of the SS. Or, what is more preferable, to carry out its rectification separately, having previously accumulated 10…20 residues (not less than 30% of the volume of the evaporation tank).

5.4. Re-rectification.

Re-rectification is carried out only in the following cases:

A) there is a need to obtain alcohols of the "Extra" and "Lux" types with the smallest content impurities from very poor raw materials;

b) unsatisfactory quality of SR obtained during the first rectification (reasons: non-compliance with the recommendations of this instruction during the training process).

To carry out re-rectification, the entire food SR (and in case of very low quality only its central part) is necessary, after diluting it with water to a concentration of 40-45%, pour it into a well-washed evaporator tank and repeat the rectification as indicated in section 5.

Note to Section 5

Do not increase this concentration!

The indicated SS strength can also be achieved with the usual (direct) distillation of the mash on the simplest distillation apparatus. Thus, if you already have such a device, it is very convenient to use RUM only for rectification, and receive CC on your device. This will significantly increase their joint productivity without reducing the quality of the final product.

6. Chemical treatment of mash and raw alcohol.

A) chemical treatment of the mash.

Subject to the technology of preparing the mash, the wort gradually increases its acidity during fermentation - and this is normal. In this case, no chemical treatment is required.

Sometimes the acidity of the mash can rise above the norm. This can happen for a variety of reasons related to the violation of technology:

The wort was not sterilized, and the fermentation process was "captured" by wild yeast;

By chance, the temperature in the room dropped sharply, and the mash cooled down and “stopped” and its fermentation turned into vinegar.

In such cases, before distillation, it is recommended to artificially reduce the acidity with alkalis. If such treatment is not carried out, then during the heating process in the mash, chemical reactions increase sharply, which may (or may not) cause the formation of new accompanying impurities that affect the purity of the SR.

B) chemical processing of raw alcohol.

If all the previous steps were correct, then the chemical treatment of raw alcohol is not required.

If raw alcohol is obtained from fruit raw materials (bad wine) or mistakes were made in the previous steps (you can find out about this only after correct rectification), then raw alcohol should be chemically processed. Accurate data for this procedure can only be obtained after very precise and fine analyzes of the raw materials. We can only give general recommendations as outlined in our instructions.

GENERAL REMARK - it is better to follow the previous technology than to "get carried away" with chemical processing.

The main task of this treatment is to neutralize acids in the SS and carry out esterification reactions, as a result of which some acids and alcohols with a volatility close to ES are converted into more volatile (esters) and less volatile (heavy alcohols) chemical compounds, which significantly improves the quality of SR in rectification process.

To do this, 1 ... 2 g / l of alkali (KOH or NaOH) is added to the SS, after diluting them in a small amount of water. Usually such processing is sufficient to start rectification.

In case of very poor quality of the SS (unfortunately, this becomes clear only after the rectification process), it is additionally treated with potassium permanganate (potassium permanganate), which, after diluting in a small amount of water, is added to the SS in the amount of 1.5 ... 2 g per liter alcohol, located in the SS. The solution is thoroughly mixed and left for 15-20 minutes to complete the chemical reaction. After that, alkali is added again (in the same amount) and left for clarification for 8 ... 12 hours. Then the SS is filtered and rectified.

7. Checking the quality of alcohol.

Alcohol quality control includes the following tests:

Determination of color and transparency.

The test alcohol is poured into a clean dry cylinder of colorless and transparent glass with a capacity of 100-150 ml and the color, shade and presence of mechanical impurities in the alcohol are observed in transmitted scattered light.

Determination of smell and taste.

A small amount of the test alcohol is placed in a vessel with a well-closing stopper, diluted with 2.5 ... 3.0 volumes of cold drinking water, and immediately after preliminary strong mixing, a smell and taste test is performed.

Determination of ethyl alcohol content (strength).

The alcohol concentration must be determined at 20 ° C with an alcohol meter (ASP 95-105, ASP-2 96-101, an alcohol meter with an ASPT 60-100% thermometer or an N16 densimeter 0.76-0.82).

Cleanliness test.

For the accuracy of the test, the contents of the flask are poured (after cooling) into a special cylinder (test tube) with a ground stopper and, using a camera tripod, observe the color of the mixture, comparing with alcohol, as well as acid, taken in equal volumes and poured into separate cylinders (test tubes) the same size and glass quality. The test result is considered positive if the mixture is as colorless as alcohol and acid.

Oxidation test.

When standing, the red-violet color of the mixture gradually changes and reaches the color of a special standard solution, the appearance of which is taken as the end of the test.

To observe the change in color of the test mixture, a sheet of white paper is placed under the cylinder. The time during which the oxidation reaction occurs is expressed in minutes. The test result is considered positive if the color persists for 20 minutes.

Determination of furfural content.

If the solution remains colorless within 10 minutes, the alcohol is considered to have passed the test. The appearance of red coloring characterizes the presence of furfural.

The purpose of the article is to analyze the theoretical and some practical aspects of the work of a home distillation column aimed at obtaining ethyl alcohol, as well as dispel the most common myths on the Internet and clarify the points that equipment sellers are “silent about”.

Alcohol rectification– separation of a multicomponent alcohol-containing mixture into pure fractions (ethyl and methyl alcohol s, water, fusel oils, aldehydes, and others), having different boiling points, by repeated evaporation of the liquid and condensation of steam on contact devices (trays or nozzles) in special countercurrent tower apparatus.

From a physical point of view, rectification is possible, since initially the concentration of individual components of the mixture in the vapor and liquid phases is different, but the system tends to equilibrium - the same pressure, temperature and concentration of all substances in each phase. Upon contact with a liquid, the vapor is enriched with volatile (low-boiling) components, while the liquid, in turn, is enriched with low-volatile (high-boiling) ones. Simultaneously with enrichment, heat exchange takes place.

circuit diagram

The moment of contact (interaction of flows) between vapor and liquid is called the process of heat and mass transfer.

Due to the different directions of movements (steam rises, and the liquid flows down), after the system reaches equilibrium in the upper part of the distillation column, it is possible to separately select practically pure components that were part of the mixture. First, substances with a lower boiling point (aldehydes, esters and alcohols) come out, then with a high one (fusel oils).

A state of balance. Appears at the very boundary of the phase separation. This can only be achieved if two conditions are met simultaneously:

Equal pressure of each individual component of the mixture.
The temperature and concentration of substances in both phases (vapor and liquid) is the same.

The more often the system comes into equilibrium, the more efficient the heat and mass transfer and the separation of the mixture into individual components.

Difference between distillation and rectification

As you can see in the graph, from a 10% alcohol solution (mash) you can get 40% moonshine, and during the second distillation of this mixture, a 60-degree distillate will come out, and during the third - 70%. The following intervals are possible: 10-40; 40-60; 60-70; 70-75 and so on up to a maximum of 96%.

Theoretically, to get pure alcohol, 9-10 successive distillations are required on a moonshine still. In practice, distillation of alcohol-containing liquids with a concentration above 20-30% is explosive, moreover, due to the high energy and time costs, it is economically unprofitable.

From this point of view, the rectification of alcohol is a minimum of 9-10 simultaneous, stepwise distillations that occur on different contact elements of the column (packings or plates) along the entire height.

difference	Distillation	Rectification
Organoleptics of the drink	Keeps aroma and taste of initial raw materials.	It turns out pure alcohol without smell and taste (the problem has a solution).
Fortress at the exit	Depends on the number of distillations and the design of the apparatus (usually 40-65%).	Up to 96%.
The degree of separation into fractions	Low, substances even with different boiling points are mixed, it is impossible to fix this.	High, pure substances can be isolated (only with different boiling points).
Ability to clean harmful substances	Low or medium. To improve the quality, a minimum of two distillations with separation into fractions in at least one of them is required.	High, with the right approach, all harmful substances are cut off.
Alcohol loss	High. Even with the right approach, you can extract up to 80% of the total amount, while maintaining an acceptable quality.	Low. Theoretically, it is possible to extract all the ethyl alcohol without loss of quality. In practice, at least 1-3% losses.
The complexity of the technology for implementation at home	Low and medium. Even the most primitive apparatus with a coil is suitable. Equipment improvements are possible. The technology of distillation is simple and clear. A moonshine still does not usually take up much space in working order.	High. Special equipment is required, which is impossible to manufacture without knowledge and experience. The process is more difficult to understand, preliminary at least theoretical preparation is needed. The column takes up more space (especially in height).
Danger (compared to each other), both processes are flammable and explosive.	Due to the simplicity of the moonshine still, distillation is somewhat safer (subjective opinion of the author of the article).	Because of complex equipment, when working with which there is a risk of making more mistakes, rectification is more dangerous.

Operation of the distillation column

Distillation column- a device designed to separate a multicomponent liquid mixture into separate fractions according to the boiling point. It is a cylinder of constant or variable section, inside which there are contact elements - plates or nozzles.

Also, almost every column has auxiliary units for supplying the initial mixture (raw alcohol), controlling the rectification process (thermometers, automation) and distillate extraction - a module in which the vapor of a certain substance extracted from the system is condensed and then taken out.

One of the most common home designs

Raw alcohol- a product of the distillation of mash by the classical distillation method, which can be "filled" into a distillation column. In fact, this is moonshine with a strength of 35-45 degrees.

Reflux- steam condensed in the dephlegmator, flowing down the walls of the column.

Phlegm number- the ratio of the amount of reflux to the mass of the sampled distillate. There are three streams in the alcohol distillation column: steam, phlegm and distillate (end goal). At the beginning of the process, the distillate is not withdrawn so that there is enough reflux in the column for heat and mass transfer. Then part of the alcohol vapor is condensed and taken from the column, and the remaining alcohol vapor continues to create a reflux flow, ensuring normal operation.

For the operation of most installations, the reflux ratio must be at least 3, that is, 25% of the distillate is taken, the rest is needed in the column for irrigating the contact elements. As a general rule, the slower the alcohol is withdrawn, the higher the quality.

Distillation column contact devices (trays and packings)

They are responsible for the multiple and simultaneous separation of the mixture into liquid and vapor, followed by the condensation of vapor into a liquid - the achievement of an equilibrium state in the column. Ceteris paribus, the more contact devices in the design, the more effective distillation in terms of alcohol purification, since the surface of phase interaction increases, which intensifies the entire heat and mass transfer.

theoretical plate- one cycle of exit from the equilibrium state with its repeated achievement. To obtain high-quality alcohol, a minimum of 25-30 theoretical plates is required.

physical plate- a real working device. The vapor passes through the liquid layer in the plate in the form of many bubbles, creating an extensive contact surface. In the classical design, the physical plate provides about half of the conditions for reaching one equilibrium state. Therefore, for the normal operation of the distillation column, two times more physical plates are required than the theoretical (calculated) minimum - 50-60 pieces.

Nozzles. Often, plates are placed only on industrial installations. In laboratory and home distillation columns, nozzles are used as contact elements - specially twisted copper (or steel) wire or dishwashing nets. In this case, the phlegm flows down in a thin stream over the entire surface of the nozzle, providing the maximum contact area with steam.

Washcloth nozzles are the most practical

There are a lot of structures. The disadvantage of home-made wire nozzles is the possible damage to the material (blackening, rust), factory counterparts are devoid of such problems.

Properties of distillation column

Material and dimensions. The column cylinder, nozzles, cube and distillers must be made of a food-grade, stainless, heat-safe (expands evenly) alloy. In home-made designs, cans and pressure cookers are most often used as a cube.

The minimum length of the pipe of a home distillation column is 120-150 cm, diameter is 30-40 mm.

heating system. In the process of rectification, it is very important to control and quickly adjust the heating power. Therefore, the most successful solution is heating with the help of heating elements built into the bottom of the cube. Heat input through gas stove not recommended, because it does not allow you to quickly change the temperature range (high inertia of the system).

Process control. During rectification, it is important to follow the instructions of the column manufacturer, which must indicate the features of operation, heating power, reflux ratio and model performance.

The thermometer allows precise control of the sampling process

It is very difficult to control the rectification process without two simple devices - a thermometer (helps determine the correct degree of heating) and an alcohol meter (measures the strength of the resulting alcohol).

Performance. It does not depend on the size of the column, since the higher the side (pipe), the more physical plates are inside, therefore, the cleaning is better. The performance is affected by the heating power, which determines the speed of steam and reflux flows. But with an excess of supplied power, the column chokes (stops working).

The average performance of home distillation columns is 1 liter per hour with a heating power of 1 kW.

Influence of pressure. The boiling point of liquids depends on pressure. For successful distillation of alcohol, the pressure at the top of the column should be close to atmospheric - 720-780 mm Hg. Otherwise, when the pressure decreases, the vapor density will decrease and the evaporation rate will increase, which may cause flooding of the column. If the pressure is too high, the evaporation rate drops, making the operation of the device inefficient (there is no separation of the mixture into fractions). To maintain the correct pressure, each distillation column is equipped with an atmospheric connection tube.

About the possibility of self-made assembly. Theoretically, a distillation column is not a very complex device. Designs are successfully implemented by craftsmen at home.

But in practice, without understanding the physical foundations of the rectification process, correct calculations of equipment parameters, selection of materials and high-quality assembly of units, the use of a home-made distillation column turns into a dangerous occupation. Even one mistake can lead to fire, explosion or burns.

In terms of safety, factory columns that have been tested (have supporting documentation) are more reliable, and they are also supplied with instructions (must be detailed). The risk of a critical situation comes down to only two factors - proper assembly and operation according to the instructions, but this is a problem for almost all household appliances, and not just columns or moonshine stills.

The principle of operation of the distillation column

The cube is filled with a maximum of 2/3 of the volume. Before turning on the installation, it is imperative to check the tightness of the connections and assemblies, shut off the distillate extraction unit and supply cooling water. Only after that you can start heating the cube.

The optimal strength of the alcohol-containing mixture fed into the column is 35-45%. That is, in any case, distillation of the mash is required before rectification. The resulting product (raw alcohol) is then processed on a column, obtaining almost pure alcohol.

This means that a home distillation column is not a complete replacement for the classic moonshine still (distiller) and can only be considered as an additional purification step that replaces re-distillation (second distillation) with better quality, but levels the organoleptic properties of the drink.

In fairness, I note that most modern models of distillation columns involve working in the moonshine still mode. To proceed to distillation, it is only necessary to close the connection to the atmosphere and open the distillate selection unit.

If both nozzles are closed at the same time, then the heated column may explode due to excess pressure! Don't make these mistakes!

In continuous industrial plants, mash is often distilled immediately, but this is possible due to its gigantic size and design features. For example, a pipe 80 meters high and 6 meters in diameter is considered a standard, in which many more contact elements are installed than on distillation columns for a house.

Size matters. The possibilities of distilleries in terms of cleaning the cube are greater than with home distillation

After switching on, the liquid in the cube is brought to a boil by the heater. The resulting vapor rises up the column, then enters the reflux condenser, where it condenses (phlegm appears) and returns in liquid form along the walls of the pipe to the lower part of the column, on the way back coming into contact with the rising steam on plates or nozzles. Under the action of the heater, the phlegm again becomes steam, and the steam at the top is again condensed by a dephlegmator. The process becomes cyclic, both streams are in continuous contact with each other.

After stabilization (steam and phlegm are sufficient for an equilibrium state), pure (separated) fractions with the lowest boiling point (methyl alcohol, acetaldehyde, ethers, ethyl alcohol) accumulate in the upper part of the column, with the highest (fusel oils) at the bottom. As the selection of the lower fractions gradually rise up the column.

In most cases, a column in which the temperature does not change for 10 minutes is considered stable (you can start sampling) (the total warm-up time is 20-60 minutes). Up to this point, the device works "on its own", creating flows of steam and phlegm that tend to balance. After stabilization, the selection of the head fraction containing harmful substances begins: esters, aldehydes and methyl alcohol.

The distillation column does not eliminate the need to separate the output into fractions. As in the case of a conventional moonshine still, you have to assemble the “head”, “body” and “tail”. The difference is only in the purity of the output. During rectification, the fractions are not “lubricated” - substances with a close, but at least a tenth of a degree, different boiling point do not intersect, therefore, when the “body” is selected, almost pure alcohol is obtained. During conventional distillation, it is physically impossible to separate the yield into fractions consisting of only one substance, no matter what design is used.

If the column is brought to the optimal mode of operation, then there are no difficulties during the selection of the “body”, since the temperature is stable all the time.

The lower fractions (“tails”) are selected during rectification, guided by temperature or smell, but unlike distillation, these substances do not contain alcohol.

Return to alcohol of organoleptic properties. Often, "tails" are required to return the "soul" to rectified alcohol - the aroma and taste of the raw material, for example, apples or grapes. After the process is completed, a certain amount of collected tail fractions is added to pure alcohol. The concentration is calculated empirically by experimenting on a small amount of product.

The advantage of rectification is the ability to extract almost all the alcohol contained in the liquid without losing its quality. This means that the “heads” and “tails” obtained on a moonshine still can be processed on a distillation column and ethyl alcohol safe for health can be obtained.

Flooding of distillation column

Each design has a maximum speed of steam movement, after which the flow of reflux in the cube first slows down, and then stops altogether. The liquid accumulates in the distillation part of the column and "flooding" occurs - the termination of the heat and mass transfer process. Inside there is a sharp pressure drop, extraneous noise or gurgling appears.

Causes of flooding of the distillation column:

exceeding the permissible heating power (most common);
clogging the bottom of the device and overflowing the cube;
very low atmospheric pressure (typical for high mountains);
the voltage in the network is higher than 220V - as a result, the power of the heating elements increases;
design errors and failures.

1. Where does alcohol come from as a chemical

Ethyl alcohol (ethanol, wine alcohol) - C2H5OH is a colorless liquid with a characteristic odor. It is obtained by fermentation of food raw materials, hydrolysis of plant materials and synthetically - ethylene hydration. Purified by rectification.
The synthetic way of obtaining ethanol is quite complicated, and the result is technical rectified alcohol containing a large amount of impurities that cannot be separated by rectification. This way is widely used in industry.
Another way to obtain alcohol is more accessible and is associated with the technology of fermentation of simple sugars by yeast. This is how ordinary wine is obtained, and that is why the first name of ethyl alcohol is wine spirit. The chemical formula for this transformation in a very simplified form looks like this:

C 12 H 22 O 11 + H 2 0 \u003d 4 C 2 H 5 OH + 4 CO 2 + HEAT

Those. from one molecule of sugar, with the help of yeast cells, two molecules of ethyl alcohol, two molecules of carbon dioxide are formed and a decent amount of heat is released.
To determine the ratio of mass transformations, it is enough to substitute the molar masses of atoms into the previous chemical formula: hydrogen H=1, carbon C=12 and oxygen O=16:

(12 12+1 12+16 11)+ (1 2+16)= 4 (12 2+1 5+16+1) + 4 (12+ 16 2),
or 342 + 18 = 184 + 176 ;

and then we can conclude that from 180 kg of sugar, 92 kg of alcohol and 88 kg of carbon dioxide are obtained. Thus, the theoretical yield of alcohol from sugar is 0.511 kg/kg, and given the density of ethyl alcohol (ρ = 0.8 kg/l), it will be 0.64 l/kg.
If alcohol is obtained not from sugar, but from sugar-containing raw materials (grapes, sugar beet, Jerusalem artichoke, etc.), then, knowing the sugar content of the product, it is easy to determine the yield of alcohol from it. So, for example, if apples contain 12% sugar, then the theoretical yield of alcohol from the juice of this raw material (the yield of juice from apples is 70%) will be 54 ml/kg:

1kg (apples) =>0.7kg (juice) => 0.084kg (sugar) => 0.054l (alcohol).

Most often, alcohol is obtained from starch-containing raw materials (potatoes, grains, etc.). Then, in the technological chain of the preparation of alcohol, the process of starch saccharification appears - the transformation (hydrolysis) of raw starch under the influence of certain enzymes into sugar

(C 6 H 10 O 5)n + n H 2 O +ENZYME\u003d n C 6 H 12 O 6,

and then fermentation takes place.
As in the previous case, it can be calculated that 1.11 kg of sugar is theoretically obtained from 1 kg of starch. Knowing the starch content in raw materials, one can easily determine the yield of alcohol from a particular product. So, for example, if wheat contains 60% starch, then the theoretical yield of alcohol from such grain will be 0.426 l / kg:

1kg (wheat) => 0.6kg (starch) => 0.666kg (sugar) => 0.426l (alcohol).

The practical yield of alcohol is always 10 ... 15% less than the theoretical one. Such losses are considered normal and are mainly due to:
unkindness, that is, with a situation where part of the sugar remains in the mash and does not turn into alcohol;
improper fermentation, that is, when part of the sugar turns not into alcohol, but into some other impurity substances;
direct losses, when part of the alcohol simply escapes with carbon dioxide during fermentation, or is lost during distillation and rectification.

2. Warmth physical properties water-alcohol solutions.

The properties of absolute 100% ethyl alcohol (ES) are of little interest from a practical point of view ( tbp=78.3°C at 760mm Hg, ρ=790κg/m3). Therefore, here we will deal with the properties of a binary (double) mixture of ES + water, which give a complete picture of the operation of distillation equipment and the production of rectified ethyl alcohol on it.

2.1 Alcohol concentration.

Everyone knows that ES dissolves very well in water, forming a binary water-alcohol mixture (solution), which can contain any amount of alcohol.
In the case of using certain reference data, it is necessary to clearly distinguish between two concepts of the concentration of alcohol in a water-alcohol solution - mass and volume concentrations. The mass concentration of alcohol is used only for physical calculations, analysis of combustion processes, etc. Mass concentration is the mass of alcohol in the mass of the solution (denoted as % mass, or kg / kg, or g / g). More often and traditionally, the concept of the volumetric concentration of alcohol is used - this is the volume of alcohol in the volume of the solution (denoted as% vol., or m3 / m3, or l / l, or ml / ml). This some “confusion” in concentrations arises due to the different density of alcohol ( ρ=790κg/m3=0.79g/ml) and water ( ρ=1000κg/m3=1g/ml). The difference in the numbers of volume and mass concentrations of the same solution is significant, therefore In what follows, we will use only the concept of the volumetric concentration of alcohol.
To determine the volumetric content of alcohol in a solution - the concentration of alcohol in a liquid ( X) special alcohol meters are used: ASP-3 0…40%, ASP-3 40…70%, ASP-3 70…100%, ASP 95…105%, ASP-2 96…101%, with a thermometer ASPT 60…100% . It is worth noting that the density of a water-alcohol solution strongly depends on its temperature, and all these devices measure the density of the solution (they use the Archimedes force). Therefore, the real alcohol content in the solution coincides with the readings of these devices only at 20ºC, which is indicated on the scales of these devices.
The most famous solutions are vodka - 40% and rectified alcohol - 96.4%. By the way, the alcohol content in the mash is in the range of 7 ... 12%, but it is impossible to measure this concentration using alcohol meters due to the presence of residual sugar and other impurities in the mash that affect the density of the solution and, accordingly, distort the readings of the device.
ES vapors are also well soluble in water vapor and form a single vapor mixture with them with an alcohol concentration in them Y, which can be determined only after the condensation of these vapors - i.e. in a liquid (as in the previous case) or according to the temperature of their vaporization at 760 mm Hg. (see below).

2.2 Boiling point of a water-alcohol mixture.

Naturally, the boiling point of a solution of two substances - water ( tbp=100°C at 760 mm Hg) and ethanol ( tbp=78.3°C at 760 mm Hg) must be between the boiling points of the individual substances. The dependence of the temperature of a saturated water-alcohol vapor or the boiling point (vaporization) of this binary mixture on the concentration of alcohol in vapor Y shown in Fig.1.
It is worth noting that there is some point on this graph A with a concentration of 96.4%, the temperature at which is even lower than the boiling point of 100% ethanol.

Fig.1 The temperature of saturated water-alcohol vapor or the boiling point of a water-alcohol mixture (at a pressure of 760 mm Hg)

2.3 Phase balance.

The equilibrium state of the phases (liquid and vapor) is their coexistence, in which there are no visible qualitative or quantitative changes in these phases. Phase equilibrium is considered to be achieved only when two conditions are simultaneously satisfied: the phase temperatures are equal and the partial pressures of each component in the vapor and liquid phases are equal. The second condition means that the process of transition through the phase boundary of each component from the liquid phase to the vapor phase and vice versa is completed. Those. the compositions of the liquid and vapor phases have stabilized, and the concentrations of the components in a single phase are the same at each point of its volume.
For a binary water-alcohol mixture, this theoretical statement means a very simple thing. If you pour a small amount of a water-alcohol mixture with a concentration Xzh and heat to the boiling point of this mixture, then the concentration of alcohol in the resulting vapor will be Yp. Then, if you quickly close the flask and shake vigorously (mix the vapor and liquid phases), then the temperature inside the flask will even out, and the vapor and liquid will come to an equilibrium state - with alcohol concentrations in them Y And X respectively.
If such experiments are carried out for different concentrations of water-alcohol solutions, then it is possible to obtain a certain dependence of the phase equilibrium - the phase equilibrium curve. The graph of the phase equilibrium curve for a binary mixture of pure alcohol + pure water is shown in Fig.2.

Fig.2 Equilibrium curve of the phases of a binary water-alcohol mixture (at a pressure of 760 mm Hg)

The theoretical and practical significance of the phase equilibrium curve from the point of view of the alcohol distillation process is very high, but we will return to this later in the “Rectification” section, and now we will show how to use this curve.
For example, during the usual distillation of mash with an alcohol concentration X= 10% vapor is formed with a concentration of alcohol in it Y\u003d 42%, and after its condensation we get “moonshine” (condensate, distillate) of the same “strength”. Thus, if the moonshine is not equipped with any additional “bells and whistles”, then theoretically it is simply impossible to get stronger moonshine in this way. In the same way, it is possible to “predict” using the same curve the result of repeated distillation of “pervacha” - from a 40% distillate, a 60% “moonshine” can be obtained by a second distillation.
Considering this graph, it is worth paying attention to the diagonal Y=X. It is due to the fact that almost the entire equilibrium curve lies above this diagonal that it is possible, when evaporating a water-alcohol mixture, to obtain a concentration of alcohol in vapors greater than its concentration in the original liquid. The only exception is the point A- intersection of the equilibrium curve with the diagonal, where X=Y=96.4%. This is the singular point of the azeotrope.
Azeotropic or inseparably boiling mixtures are called mixtures in which the vapor, which is in equilibrium with the liquid, has the same composition as the liquid mixture ( X=Y). During the distillation of azeotropic mixtures, a condensate of the same composition as the original mixture is formed. The separation of such mixtures by distillation and rectification is excluded.
A water-alcohol mixture at a special point of the azeotrope is called “rectified ethyl alcohol (SR)”. It is to this point that the rectification process tends, it is it that is the limiting concentration of alcohol in this process, and it is at this point that the water-alcohol mixture has a minimum boiling point ( tbp=78.15°C at 760 mm Hg see fig.1).

2.4 The main properties of rectified alcohol

For this product, there is GOST 5962-67, which regulates the concentration of alcohol in rectified alcohol from 96% to 96.4% and its composition.
Here are some physical properties of rectified ethyl alcohol
Liquid density (at 20ºС)…………….……….…. 812 kg/m3 (≈0.8kg/l)
Vapor density (at 760 mmHg)………….……….. 1.601 kg/m3
Boiling point (at 760 mm Hg)……………… 78.15 ºC
Specific heat of vaporization……………………. 925 kJ/kg
These data are the basis for the design of alcohol distillation equipment. And for you they will be the usual reference information.

2.5 Rectified alcohol boiling point and atmospheric pressure.

It should be noted that the boiling point of SR depends significantly on atmospheric pressure. Moreover, this dependence is so strong (see Fig. 3) that when distilling alcohol by temperature, recorded, for example, with an electronic thermometer, you can determine the exact value of atmospheric pressure at a given moment and calibrate a regular home barometer using the following dependence.

Fig. 3 Dependence of the boiling point of rectified ethyl alcohol on atmospheric pressure

If you operate a distillation plant without a thermometer, then this information simply expands your horizons and has no practical meaning for you, since you determine the moment of release of SR with absolute accuracy by smell. But, for those who have purchased a device with an electronic thermometer, this relationship between the boiling point of alcohol and atmospheric pressure is of immediate practical importance.
Indeed, having professional distillation equipment and an electronic thermometer capable of determining the temperature of alcohol vapors with high accuracy, you may be surprised to find that its readings differ from day to day. If yesterday you observed the boiling point of alcohol at 77.0ºC, and today - 78.0ºC, then this does not mean a change in the alcohol composition or a malfunction of the distillation device, but only a change in atmospheric pressure: yesterday it was - 730 mm Hg, and today - 755mmHg

3. Theory and practice of simple distillation of mash.

Simple distillation (distillation) is a process in which a single evaporation of the most volatile components from the bottom liquid and a single condensation of these vapors occur.

3.1 Purpose of simple distillation

The alcohol content in the mash is very low, from 6 to 12%. However, to obtain high-quality alcohol by rectification, a more concentrated alcohol solution is required, therefore, to obtain recitified alcohol, all distilleries produce an initial, rough separation of alcohol from water, as a result of which raw alcohol (SS) is obtained, and then it is rectified. The same way can be recommended for home technology for the preparation of alcohol.
The distillation of the mash can also be carried out using distillation equipment (see below). Using the same rectification technique during the distillation of the mash, you can immediately get 80 ... 85% SS from the mash. But this is not necessary, because for a clear rectification of the SS, it will still need to be diluted to a concentration of 40%. Moreover, when distilling the mash on a distillation device, the lower part of the column is very often clogged with foam.
For more efficient use of the distillation column, it is still better to carry out rectification on it, and 40% moonshine can be successfully obtained from the mash using a simple distillation apparatus.

3.2 Equipment for simple distillation

A schematic diagram of a simple distiller is shown in Fig. 4. The distiller consists of an evaporation tank - a cube 1 and a condenser-cooler 2, which are interconnected by a branch pipe 3. The cube is filled with a processed liquid 4, which is heated and evaporated by a heater 5. Cooling water constantly flows through the condenser-cooler (shown by arrows). For the convenience of working with the distiller, a thermometer 6 can be installed in the lid of the cube, which records the temperature of the vapors heading for condensation. Receiving container 7.

3.3 Operation of the simple distillation apparatus

The distiller works as follows. With the help of a heater, the bottom liquid is brought to a boil. The steam formed in the cube enters the condenser-cooler through the pipe, where it is condensed and cooled. The resulting distillate flows into the receiving tank 7.
As for the distillation of alcohol, when this device is operating, the process of obtaining a distillate basically obeys the above phase equilibrium curve (Fig. 2). Moreover, at the initial moment, when the concentration of alcohol in the solution is high (in the brew it is 10 ... 12%), the concentration of alcohol in the vapors, and, consequently, in its distillate, is also high (42 ... 45%). However, the mash is not a binary mixture of water and alcohol, but contains a large amount of associated impurities with a lower and higher boiling point in relation to the water-alcohol mixture. The vapor temperature of the alcohol-water mixture passing at this moment through the pipe is about 90 ... 94 ° C, but low-boiling impurities (ethers, acetones, aldehydes, methyl alcohol, etc.) theoretical temperature up to 65…75°C. An increased concentration of low-boiling impurities (whose density is less than the density of alcohol) in the original distillate distorts the alcohol meter readings upwards, creating the illusion of increased “strength”. That is why the first portion of the distillate obtained from the mash is called “pervach”. In fact, this is not concentrated alcohol, but a water-alcohol mixture with an increased concentration of “poison”.
In the next distillation step, the temperature change is more in line with theory. Using the readings of thermometer 6 and using the graph in Fig. 1, one can always know the concentration of alcohol vapor Y going to condensation. Gradually, the concentration of alcohol in the still decreases, and accordingly, its concentration in the distillate also decreases, which is indicated by an increase in temperature on thermometer 6. If the temperature has reached 100 ° C, this means that the alcohol in the bottom liquid has completely run out and only water evaporates from the cube.
Despite the fact that near the zero point (Fig. 2) the concentration of alcohol in vapor is 8 times greater than its concentration in liquid, the distillation process is usually completed at a vapor temperature of 97…98°C. This is due to the fact that from this moment begins a more intense evaporation of fusel oils and other tail impurities.
The average concentration of alcohol in the distillate (typical "moonshine"), obtained from the mash using simple distillation apparatus, usually does not exceed 40%. A typical graph of temperature change over time during simple distillation is schematically presented in Fig.5.

Fig. 5 Vapor temperature change during simple distillation

You can re-distill a 40% distillate and get a more concentrated ≈ 60% alcohol solution (see Fig. 2). Then you can repeat this process many times until the concentration of alcohol in the distillate is about 90 ... 94%. However, you should immediately draw your attention to the fact that the “alcohol” obtained in this way will contain all the impurities originally contained in the mash. This means that after diluting such “alcohol” with water up to 40%, you will get the same “moonshine” as after the first distillation.
With this method of extracting alcohol from the mash, in order to obtain high-quality vodka, complex, sometimes very expensive and proceeding with large losses of alcohol and electricity, cascades of purification and re-distillation are required.
That is why this way of obtaining high-quality vodka has long gone down in history!
At the moment, there is another, simpler way to obtain high-quality vodka, the essence of which is to obtain from the SS (“moonshine”) immediately 96% rectified alcohol, purified from impurities, and then diluting it with good water to a concentration of vodka solution. This method requires special and rather complex distillation equipment.

4. Theory of rectification

Rectification is a heat and mass transfer process, which is carried out in countercurrent column apparatuses with contact elements (packing, plates). In the process of distillation, there is a continuous exchange between the liquid and vapor phases. The liquid phase is enriched with a higher-boiling component, and the vapor phase is enriched with a lower-boiling one. The process of heat and mass transfer occurs along the entire height of the column between the distillate flowing down, which is formed at the top of the column (reflux), and the steam rising upward. To intensify the process of heat and mass transfer, contact elements are used that increase the surface of interaction of the phases. In the case of using a nozzle, phlegm flows down as a thin film over its developed surface. In the case of trays, steam in the form of many bubbles forming a developed contact surface passes through the liquid layer on the tray.

4.1 Purpose of rectification

The purpose of rectification in general is a clear separation of liquid mixtures into separate pure components.
When distilling alcohol, the main task is to obtain SR from 40% SS with an ES concentration of at least 96% in it with a minimum content of foreign impurities. For this, the process of rectification of the SS is carried out at a time on special rectification equipment. This equipment allows you to separate the water-alcohol mixture into separate azeotropic fractions that differ in boiling points. One of these fractions is edible rectified alcohol.

4.2 Equipment for distillation

Distillation units of continuous operation are used in industry. In these plants, 85% SS and superheated water vapor are mixed at the bottom of the column and converted into ≈40% saturated water-alcohol steam at a temperature of ≈94°C (see Fig. 1). This vapor mixture continuously enters the distillation column, stratifies along its height into separate fractions, which are continuously and at a certain rate taken from different parts of the column. To ensure the normal operation of such continuous columns, quite complex and expensive automation elements are required.
In chemical and physical laboratories, batch distillation columns are usually used, which do not require any automation. These columns are equipped with only elementary means of adjusting the selection, temperature control and a manometric meter for the pressure drop across the column.
A schematic diagram of a periodic distillation plant is shown in Fig.6. The installation consists of an evaporation tank - cube 1 and a distillation column installed vertically on the lid of the cube. The cube is filled with processed liquid 4, which is heated and evaporated by heater 5. The column includes a distillation part 9 and a column head 10. The distillation part of the column is a pipe 11, covered on the outside with thermal insulation 12 and filled inside with contact elements 13. The column head is a system branch pipes 3 to which, in accordance with the diagram, are connected: thermometer 6, condenser 2, cooler 14 and selection regulator 15. At the bottom of the distillation part of the column, a manometric tube 16 is usually mounted to measure the pressure drop in the column. Cooling water constantly flows through the cooler 14 and the condenser 2.

4.3 Operation of the distillation column.

The distillation plant works as follows. With the help of a heater, the bottom liquid is brought to a boil. The steam formed in the cube rises up through the distillation part of the column 9 and enters the condenser 2, where it is completely condensed. Part of this condensate (phlegm) returns to the distillation part of the column, and the other part passes through the cooler 14 and flows into the receiving tank 8 in the form of distillate 7. The ratio between the flow rates of phlegm and the distillate withdrawn is called the reflux ratio and is set using the selection regulator 15. Throughout At the height of the distillation part of the column, a process of heat and mass transfer occurs between the phlegm flowing down and the steam rising up. As a result, the lightest-boiling (with the lowest boiling point) component of the bottom liquid accumulates in the head of the column in the form of steam and phlegm, and after it, a “number queue” (down the height of the column) of various substances is built up by itself. The “number” in this queue is the boiling point of each component, which increases as it goes down the column. With the help of the regulator 15, a slow and sequential selection of these substances is carried out in accordance with their order. The “number” of the substance taken at each moment is recorded using thermometer 6. Knowing this temperature, taking into account atmospheric pressure, it is possible to accurately indicate the main substance of the distillate taken at a given time.
For clarification, we give the simplest and clearest example of laboratory rectification. Pour acetone (20 ml), methyl alcohol (30 ml), ethyl alcohol (50 ml) and water (100 ml) into the evaporation container. The total amount of cubic liquid will be 200 ml. We will carry out rectification with a record of the current temperature and the current volume of the resulting distillate 7. The total volume of the selected distillate will be brought to 120 ml, while the remainder of the bottom liquid (water) will be 80 ml. Based on the records, we will build a graph of temperature changes from the current volume of distillate (Fig. 7). Four horizontal sections are clearly visible on the graph. α (tk=const) and three transitional sections β between them. Plots α are the individual pure components of the initial mixture, and the transitional sections β are intermediate substances consisting of a mixture of two pure neighboring components. Let the rectification process take place at an atmospheric pressure of 760 mm Hg, then by the “height” and “length” of each step, one can easily conclude the qualitative and quantitative composition of the initial mixture:

In the process of rectification, each individual and intermediate substances can be taken into separate receiving containers 8, which allows not only to carry out a qualitative and quantitative analysis of the initial mixture, but also to obtain all its components separately.

Fig.7 Temperature change during rectification of a 4-component liquid

4.4 What is a “theoretical plate” and how many are needed.

Let us consider more carefully the equilibrium curve of the phases of a binary water-alcohol mixture, shown in Fig.2. As indicated in the example, a 40% solution can be obtained from a 10% alcohol solution by simple distillation. Then, from a 40% solution, a 60% solution can be obtained in the same way.
It is easy to build a series of successive steps 10-40 on the phase equilibrium curve; 40-60; 60-70; 70-75; etc. and make sure that in order to achieve an alcohol concentration of 96% in the final distillate, theoretically at least 9 ... 10 such successive distillations are required.
Each such distillation-step is conditionally called theoretical plate (TT). The amount of TT physically means the number of distillations required to obtain 96% alcohol from its 10% solution of pure alcohol in pure water.
The theoretical plate is sometimes (and now increasingly) referred to as a mass transfer unit or transfer unit (TU).
In practice, we never have a pure mixture of alcohol and water (unless it's good vodka). In practice, the only source alcohol-containing liquid to obtain rectified alcohol is mash or moonshine. Both of these solutions, in addition to water and alcohol, contain a small (by volume) amount of impurities. However, about 70 different components were found in these impurities, the boiling point of which is close to the boiling point of rectified alcohol. Moreover, many of these impurities with “great pleasure” form with alcohol and water a multicomponent azeotrope of rectified alcohol with degraded taste properties.
Experience shows that in order to obtain high-quality alcohol from the above “primary sources”, it is necessary to have at least 25 ... 30 TT or, which is the same thing, 25 ... 30 EP.

4.5 The physical plate and how it differs from the theoretical one.

Trays are commonly used as contact elements in large distillation columns. Each such plate located in the column is called physical plate (FT). The purpose of such a plate, like any other contact device, is to ensure the closest contact between the liquid and vapor phases in order to achieve the maximum state of equilibrium between them.
Plates work as follows. Steam in the form of bubbles with a developed surface passes through the reflux layer located on the plate. As a result of such “bubbling”, heat and mass transfer between the liquid and vapor phases is intensified. However, after the passage of steam through one plate, the equilibrium between the phases is not achieved. A measure of the difference between the state of the vapor and liquid phases from their equilibrium state is coefficient useful action(efficiency) dishes.
For classic cymbals, the efficiency is about 50-60%. Those. it will take about two PTs to reach the state of phase equilibrium corresponding to one CT. Thus, to implement 40 HP in a distillation column, it will be necessary to install about 80 FT of a classical design in it.

4.6 Nozzle and where are the "theoretical plates" in it.

For successful interaction of phlegm flowing down the column and steam moving up, any other contact elements can be used that increase the area and efficiency of this interaction.
For distillation columns of ultra-small diameter (10-30 mm), the contact element is more efficient than a tray nozzle. The packing fills the entire internal volume of the distillation part of the column. There are many various types nozzles, for example, regular nozzles - Spraypack, Sulzer, Stedman; chaotic (bulk) - ceramic rings of Lessing, Pal, Berl, the most common - wire spiral-prismatic nozzle.
The process of heat and mass transfer on such contact elements is continuous, and the state of phase equilibrium, equivalent to one HP, occurs after the steam overcomes a certain height of the packing. And then they usually talk about the height of the packing layer, which is equivalent to one HP, i.e. for packed columns, the concept is usually used - theoretical plate height VTT or transfer unit height VEP (currently used more often).
This height is usually estimated in millimeters, which makes it easy to compare the efficiency of one or another packing by its WEP and calculate the height of the entire distillation part of the column. So, for example, with an inner diameter of a column of 30 mm, for a spiral-prismatic packing, the WEP is 20 ... 25 mm, and for a Sulzer-type packing, the WEP is 15 ... 20 mm.
For packings, the height of the transfer unit strongly depends on the column diameter and rapidly increases with its increase. That is why such effective packed contact elements are practically not used in large industrial distillation plants, but have found their use exclusively in laboratory equipment.
The appearance of this little-known contact element is perceived by many as a kind of filter, which must have a certain service life in the column. However, it is not. The packing is a heat and mass transfer contact filler of the column, through which pure distillate flows down, and pure steam rises up. Thus, if both of these components really do not contain foreign inclusions (foam from the bottom liquid does not enter the column), then this “filter” performs its functions of heat and mass transfer indefinitely inside the column.

4.7 Throughput of the column. Column flooding.

Whatever contact elements are used in the column, the operating scheme of the distillation column remains unchanged - phlegm flows down, and steam moves up.
With such a movement of the phases, there is a certain limiting speed of the steam, at which the gravitational forces that ensure the downward movement of the phlegm are not able to overcome the counter velocity pressure of the steam. Those. as the steam speed increases, phlegm first slows down its downward flow rate, and then simply stops (hangs in the column) and begins to accumulate in its distillation part. going on column flooding.
Column flooding is an off-design mode of its operation. In this state, the column can be no more than 30 ... 60 seconds. During this time, the phlegm first fills the internal cavity of the distillation part of the column, then the dephlegmator, and then it is ejected from the column through the top fitting of the dephlegmator. Column flooding can be identified by the pressure drop across the column, or can be clearly heard as a specific “gurgling” noise in the column. In order to avoid flooding of the distillation unit, it is necessary to strictly follow the operating recommendations set out in the passport for each unit.
The limiting steam velocity is determined by the contact elements themselves, which clutter up the internal section of the column. Different contact elements have their own limiting speed of alcohol vapor in the full section of the column, which is in the range of 0.5 ... 1.2 m / s. This is and maximum throughput column, which is usually expressed by the mass flow rate of steam (kg / h) through the unit area of the full section of the column (m2). Its value for different contact elements is in the range of 2000…7000(kg/h)/m2.
A column with certain contact elements can be "load" and less steam. However, the maximum efficiency of many contact elements (efficiency of the plate and EPP packing) is realized when the column is operating near the flooding state. Therefore, all distillation columns are designed for an operating mode that is as close as possible to the maximum throughput of the column.
The mass flow rate of alcohol vapor (at the heat of vaporization CP 925 kJ/kg) passing through the column is completely determined by the power supplied to the evaporation tank. So, for example, with a technological power of 1 kW, the following amount of alcohol vapor will be formed per unit of time:

Therefore, at the rectification stage, the column is loaded only with technological power (Wt), which is indicated in the passport for your installation. If you increase the input power, you will increase the amount of alcohol evaporated, and, consequently, increase its vapor velocity through the column. As a result, the column will flood with all the ensuing consequences.
It should be noted that flooding of the column can also occur at the nominal (correct) process power supplied to the evaporation tank. There are only three reasons for this unusual behavior of the column.
The first reason is either the clogging of the lower part of the column with foam, for example, from the mash or the overflow of the evaporation tank with the processed liquid. This is a direct violation of the operating instructions for filling the evaporation tank.
The second reason is the increased voltage in the network (more than 230V), which leads to an increase in the thermal power of the technological heating element.
The third reason is a strong decrease in atmospheric pressure or an attempt to operate the column in highlands. This reason deserves special attention.

4.8 Atmospheric pressure and stable operation of the column.

The operation of the column is designed for an internal pressure in the column of 720…780 mm Hg. And since Since the column necessarily has a connection with the atmosphere through the upper fitting of the dephlegmator, then this pressure is also the optimal atmospheric pressure for its operation. Let's figure out how atmospheric pressure can affect the operation of the column and how to control the operation of the column in highlands.
As was indicated in the example of the previous section (on column flooding), 1 kW of thermal power evaporates 3.89 kg / hour of alcohol vapor. This mass flow rate of steam at normal pressure of 760 mm Hg. (density of alcohol vapor - 1.6 kg / m3) corresponds to a well-defined volume flow - 2.43 m3 / h, which passes through the full section of the column (for example, Ф30mm) at a speed of 0.96 m / s. If atmospheric pressure drops to 700 mm Hg, then the density of alcohol vapor decreases to 1.47 kg/m3, the volumetric flow rate of steam increases to 2.64 m3/h, and, accordingly, its velocity in the full section of the column increases to 1.04 m /With. If this speed is limiting, then the column will flood.
With an increase in atmospheric pressure, on the contrary, a decrease in the speed of alcohol vapor occurs, which somewhat reduces the efficiency of column separation, but this is easily compensated by adjusting the reflux ratio (see below).
When designing columns, certain “reserves” are laid down in its design to ensure stable and optimal operation of the column, taking into account the accuracy of manufacturing contact elements, technological heating elements (their power spread), possible changes in atmospheric pressure, and so on. However, each distillation column has some "personality" and "burrow" that you need to feel and use correctly.
If the atmospheric pressure flooding threshold of your particular column is well below the minimum possible pressure in your area, you may never experience this problem. If this happens occasionally, then we can recommend that you do not carry out rectification on days of very low atmospheric pressure.
If the operation of the distillation column will take place only in high-mountainous areas, then it is necessary to use LATR (laboratory adjustable autotransformer) or any other voltage regulator to control the rate of evaporation of the bottom liquid.

4.9 Column pressure drop and how to measure it.

When the design mode of operation of the column, the internal contact elements provide a calculated resistance to the movement of alcohol vapor along the column. Those. in the lower part of the column, the pressure is higher than in its upper part (reflux condenser). And since the pressure in the dephlegmator is equal to atmospheric, they usually talk about pressure drop across the column ∆P.
The magnitude of this ∆P(resistance) is easy to observe by the height of the liquid column in a special manometric tube located at the bottom of the column (see Fig. 6). If the column is not working, then the liquid in this tube is at the lower level. It is necessary to bring the column to the operating mode, the pressure at the bottom of the column will increase, and the liquid column, balancing the differential ∆P, rise to a certain height H, related to the difference in the ratio ∆P = ρgΝ(Where: ρ - fluid density, g = 9.81 m/s2). During normal operation of the column, the liquid column must be at a certain and constant height. H. The magnitude of this pressure drop - the height of the liquid column does not exceed 350 mm.
Using this column, it is very convenient to set the calculated power supplied to the evaporation tank, i.e. you can clearly set the optimal load on the column by pressure drop.
With this "measuring device" you can easily determine the moment of flooding of the column. The column of liquid in the manometric tube at the moment of flooding of the column begins to grow rapidly due to the accumulation of reflux inside the column, which instantly increases the resistance to steam movement.

4.10 Reflux number and how to set it correctly.

Figure 8 shows the main mass flows in the distillation column. Evaporated in a cube of steam Mn=M passes through the distillation part of the column upwards, completely condenses in the reflux condenser, and turns into a distillate Md=M. Part of this distillate E taken away, and the other part of it is returned back to the column and is called phlegm R. They also say that phlegm is sent back to the column for irrigation(wetting) of its contact elements.
It is worth noting that M=R+E.
Reflux ratio: V=R/E is the ratio of the amount of phlegm R returned to the column to the amount of distillate withdrawn E.
If there is no alcohol selection E=0, then the whole distillate in the form of reflux R=M returns back to the column. Then they say that the column works for itself, and the reflux number of the column in this state is equal to infinity - V=∞. In this state, the column has a maximum separating capacity, and the number of theoretical plates in it increases.
If fully open selection E=M, then there will be no return of reflux to the column R=0. Then the reflux number is zero. In this case, due to the absence of phlegm in the column, its contact elements are completely “dry out”, heat and mass transfer processes stop, and the distillation column turns into a conventional “moonshine still”. Naturally, this transformation is temporary and reversible - without physical disturbances in the column.
To obtain high-quality alcohol, the phlegm number must be at least V≥3. This means that out of 4 parts of the distillate formed in the dephlegmator, only 1 part can be taken away, and 3 parts must be sent back to the column to irrigate its contact elements. Only in this case there will be no violation of heat and mass transfer processes in the column.
Emax= ¼M.
Remember! that by reducing the selection of alcohol, you improve its quality.
If the reflux ratio is so important to the correct operation of the column, then I would like to give a clear and simple recommendation for setting it with a selection regulator.
SELECTION RULE:
Option 1 (main):
With the help of a stopwatch and a measuring cylinder, set the selection recommended in the passport.
Option 2 (testing for any faction):
The selection was chosen correctly if the temperature in the column did not decrease 2–3 min after its termination.

4.11 Power, performance, reserves.

At the stage of distillation, only that technological capacity should be supplied to the column ( Wt), which is indicated in the passport for your installation. In this case, the column operates without flooding and provides maximum separation efficiency.
So, for example, at a technological power of 1 kW, theoretically, quite a certain amount of alcohol vapor will evaporate:

after the condensation of these vapors in the reflux condenser, 4.86 l / h of distillate is formed.
To implement the rectification process, as noted above, we can theoretically select only ¼ of the entire distillate formed in the reflux condenser, which is Emax = 1.2 l/hour. This value is the limiting theoretical performance of the installation in the alcohol mode with an input power of 1 kW.
Our company slightly underestimates the value of theoretical productivity and recommends to make a selection of no more than enom= 1 l/hour. This is due to the fact that not all of the thermal technological capacity works for vaporization, since there are heat losses. These losses are mainly related to the size of the evaporation vessel and usually do not exceed 10...15%. However, if the volume of the evaporator tank is greatly increased, these losses can exceed our 20% capacity reserve.
Thus, for your column there is a well-defined technological capacity and a well-defined selection regulated by the rectification process. this implies PERFORMANCE RULE:
1 kW of technological power can produce only 1 liter/hour of high-quality rectified alcohol.
This rule is reflected in the names of our installations, because. testing and testing of our universal equipment is carried out on this typical and most studied liquid - ethyl alcohol.

5. The practice of distillation of alcohol

As already noted, about 70 different components were found in the impurities in the mash: acids, acetones, esters, aldehydes, light and heavy alcohols, fusel oils, etc. Impurities are formed at the time of preparation of the wort, but most of all accumulate during fermentation, and during distillation, the mash almost completely enters the SS.
The main task of rectification is a clear separation of impurities from rectified alcohol.
The amount of impurities in the dehydrated distillate (i.e. in the distillate minus water) usually does not exceed 6%. The specific amount of “waste” usually depends on the accuracy of observing the technology for preparing the mash. Many of these impurities are difficult to separate from SR, and only correct work on distillation equipment allows you to get rid of them in the commercial part of rectified alcohol.
From a practical point of view, all impurities present in the SS (the previously mentioned 6%) can be divided into two groups with respect to the boiling point of the SR ( tboil = 78.15°C at 760mm Hg):
- head (≈ 2.5%);
- tailings (≈ 3.5%).
Head impurities include all substances having a boiling point less than 78.15°C and preceding (by the time of the distillation process) the appearance of SR from the distillation column. It is these impurities that occupy the first (head) line for selection from the distillation column, and it is precisely behind them that the SR stands in turn. Among these substances, the best known are methyl alcohol ( tbp=64.7°C) and an aldehyde group of impurities, in which tboil somewhat smaller, but very close to tboil SR.
Tail impurities include all substances with a boiling point greater than 78.15°C these substances are distilled off immediately after SR. It is they who take their place at the tail of the general queue for the CP. Among these substances, the most famous is the group of fusel oils ( tboil slightly larger, but very close to tboil SR).

5.1 Preparing the column for work.

a) Assemble the distillation unit as indicated in its passport.
b) For distillation, fill the evaporation tank to 2/3 of its volume with mash, if distillation is carried out using a distillation column.
For rectification, fill the evaporation tank to 3/4 of its volume with raw alcohol, with a strength of not more than 35-45%.
c) Close the selection.
d) Check the tightness of the assembly.
e) Turn on the cooling water flow.
f) Turn on the heating of the bottom liquid.
The total time for preparing the column for operation usually takes no more than 5-20 minutes and depends on the skill and readiness of all equipment for operation (the place where the unit is connected to the power supply and water cooling network).

5.2 Process of rectification.

The process of rectification is controlled and regulated according to the indication of a thermometer. Typical dependence of temperature change t in time is shown in Fig. 9, indicating five periods:

Fig.9 Temperature change during distillation of alcohol.

A) heating.

The SS in the evaporation tank is heated by all the heating elements installed in it with a total power - w. After some time, the SS in the cube begins to boil, and the gradual heating of the column by rising steam begins. At this point, you must immediately switch to technological capacity Wt specified in the installation passport.
If such a switch is not made, then after a few seconds the column will choke. REMEMBER that the column can be in this state for no more than 30-60 seconds, otherwise the column and dephlegmator will overflow with distillate and its emergency discharge will begin through the top fitting of the dephlegmator to the outside. If you still missed the moment of the beginning of boiling, and the column choked, then you will have to put up with the loss of alcohol and turn off the column. Then wait for the choking process to stop and turn on Wt.
After the column is warmed up, a temperature jump is observed, which is noted by a thermometer.

B) Stabilization.

The column operates at technological capacity Wt. Selection blocked E=0. The column works for itself, reflux number V=∞. Watching the thermometer readings, wait for the temperature to decrease and stabilize at the lowest level.
At this moment, the process of separation and accumulation of head (low-boiling) fractions in the upper part of the column takes place. After 10-15 minutes, this process is completed, and the temperature in the upper part of the column reaches its minimum value and stabilizes 3-5°C below the expected boiling point CP. The value of this difference depends on the composition and amount of low-boiling fractions in the SS. Expected boiling point CP tc can be determined by the atmospheric pressure at the moment using the graph in Fig. 3.
If you don't have a thermometer, just let the column run on its own for 15 minutes. If this process drags on for more time, then it will only get better. You will more accurately be able to separate all the head impurities that have accumulated in the column by this point.
If you work with an electronic temperature comparator, then you can more accurately determine the end of the stabilization of the column by the temperature difference.

C) Selection of head fractions.

The selection of head fractions should be carried out as slowly as possible (with a large reflux number). Slow selection does not “smear” a fraction along the column and does not take with it the fractions following it. Due to the small amount, but a wide variety of substances in the head fraction, this part of the distillate is actually one large transitional area ( β in Fig. 7) from the set of head impurities to pure SR.
For the correct organization of selection at this difficult period of rectification, we can recommend the following approach, which consists in breaking down the stage “ IN” , for three consecutive periods of equal time.

Such a scheme for organizing the selection of head fractions guarantees you:

complete separation of the head fractions from the cube, and their complete absence in the food fraction SR following them;
the minimum volume of the head fraction and the absence of the CP food fraction in it;
approach to the main fraction of SR with a small 50% productivity.

This period ends with the temperature reaching 0.1-0.05˚C lower tc. Conventionally, it is considered that the amount of low-boiling impurities present in the SR at this moment and causing such a decrease in the boiling point of the SR corresponds to acceptable food standards.
In practice, the most accurate instrument for making a decision about the end of the period of selection of head fractions and the beginning of the selection of food SR is the usual “human nose”.
The odor control of the obtained distillate is carried out as follows:

put a few drops of the selected distillate into the palm of your hand;
rub this puddle over the entire surface of the palm;
bring your palm to your face and inhale the distillate evaporated from your palm through your nose.

Such an instant and fairly accurate analysis will always be of some help to you in the rectification of alcohol.
The total amount of head fractions obtained during this period is 1...3% of the expected amount of alcohol and depends on the quality of the feedstock. REMEMBER! that the distillate obtained by distillation of the head fractions is not a food product, as it consists mainly of ethers, acetones, aldehydes and other toxic substances, and can be used ONLY for technical needs, for example, as a solvent.

D) Selection of the food alcohol fraction.

Install a new, clean and large receiving container. Increase selection to enom, which will remain until the end of the entire rectification process. Let's check this selection with a stopwatch and a graduated cylinder. After 5-10 minutes, check the thermometer readings. If everything was done correctly, then the thermometer readings will not change. Moreover, this temperature will remain unchanged during the entire period of selection of the food fraction.
The SR obtained from this point on is a high-quality food product. However, its composition (indistinguishable by many even by smell) gradually changes and can be divided into three parts:

the first 5% of the total volume of SR will still contain traces of head fractions
the central part - about 80% of the total volume of SR will be absolutely pure
and 5% of the total volume of SR before the end of this mode will begin to acquire traces of tailings. Considering the last remark, it can be recommended to prepare two separate labeled containers for the selection of the food fraction, which are used to select the first 10% and the last 10% portion of SR.

Upon receipt of the central part of the SR, you can choose the maximum selection Emax(reflux value is close to V=2.5 ). Meaning Emax mainly depends on the quality of the processed SS, so it needs to be clarified with each rectification. However, the search and refinement of it can be recommended only after the full development of the rectification process according to these instructions. For finding Emax it is necessary to use the second variant of the selection rule.
But remember - the smaller the selection, the higher the quality!
This rectification mode does not require constant presence near the apparatus, and the receiving containers are replaced as they are filled.
When receiving the third part of the food SR, it is recommended to use an intermediate container, from which periodically, after making sure that the thermometer readings correspond to the boiling point of the SR, pour alcohol into the main container.
Such a technique allows, in case the moment of temperature increase is missed (admission of SR with a higher concentration of heavy alcohols and fusel oils), to prevent “bad” alcohol from getting into “good” alcohol.
The selection of SR is completed when the temperature reaches 0.1 ... 0.05˚С above the temperature tc. Conventionally, it is considered that the amount of heavy-boiling impurities present in the SR at that moment and causing such an increase in the boiling point corresponds to acceptable food standards.
The approach and end of this moment can be "predicted" by the amount of SR already produced.

E) Selection of tail fractions (residue).

We replace the receiving container or leave the intermediate one (in which the “tail” has already been missed). We do not change the column setting - power Wt; selection Enom.
The process of selecting the residue is completed when the temperature level reaches about 82...85˚С, or is stopped due to odor control.
ATTENTION! The selected residue still contains a sufficient amount of ethyl alcohol. It can be considered a special SS with a high content of impurities of fusel oils and heavy alcohols. It, like SS, is not a food product, therefore it is strictly prohibited to use it for food purposes. The resulting residue can be recycled with a new portion of the SS. Or, what is more preferable, to carry out its rectification separately, having previously accumulated 10…20 residues (not less than 30% of the volume of the evaporation tank).

5.3 Re-rectification.

Re-rectification is carried out only in the following cases:
A) there is a need to obtain alcohols of the "Extra" and "Lux" types with the lowest content of impurities from very poor raw materials;
b) unsatisfactory quality of SR obtained during the first rectification (reasons: non-compliance with the recommendations of this instruction during the training process).
To carry out re-rectification, the entire food SR (and in case of very low quality only its central part) is necessary, after diluting it with water to a concentration of 40-45%, pour it into a well-washed evaporator tank and repeat the rectification as indicated in section 5.

Note to Section 5

You probably noticed that the strength of the SS used for the rectification process is recommended in the range of 35-45%. It is at this concentration of SS that the highest quality of the resulting SR is ensured.
Do not increase this concentration!
The indicated SS strength can also be achieved with the usual (direct) distillation of the mash on the simplest distillation apparatus.

6. Chemical treatment of mash and raw alcohol.

A) chemical treatment of the mash.

Subject to the technology of preparing the mash, the wort gradually increases its acidity during fermentation - and this is normal. In this case, no chemical treatment is required.
Sometimes the acidity of the mash can rise above the norm. This can happen for a variety of reasons related to the violation of technology:

the must was not sterilized, and the fermentation process was “captured” by wild yeast;
by chance, the temperature in the room dropped sharply, and the mash cooled down and “stopped” and its fermentation turned into vinegar.

B) chemical processing of raw alcohol.

If all the previous steps were correct, then the chemical treatment of raw alcohol is not required.
If raw alcohol is obtained from fruit raw materials (bad wine) or mistakes were made in the previous steps (you can find out about this only after correct rectification), then raw alcohol should be chemically processed. Accurate data for this procedure can only be obtained after very precise and fine analyzes of the raw materials. Only general recommendations are given here.
GENERAL REMARK - it is better to follow the previous technology than to “get carried away” with chemical processing.
The main task of this treatment is to neutralize acids in the SS and carry out esterification reactions, as a result of which some acids and alcohols with a volatility close to ES are converted into more volatile (esters) and less volatile (heavy alcohols) chemical compounds, which significantly improves the quality of SR in rectification process.
To do this, 1 ... 2 g / l of alkali (KOH or NaOH) is added to the SS, after diluting them in a small amount of water. Usually such processing is sufficient to start rectification.
In case of very poor quality of the SS (unfortunately, this becomes clear only after the rectification process), it is additionally treated with potassium permanganate (potassium permanganate), which, after diluting in a small amount of water, is added to the SS in the amount of 1.5 ... 2 g per liter alcohol, located in the SS. The solution is thoroughly mixed and left for 15-20 minutes to complete the chemical reaction. After that, alkali is added again (in the same amount) and left for clarification for 8 ... 12 hours. Then the SS is filtered and rectified.

7. Checking the quality of alcohol.

Alcohol quality control includes the following tests:

Determination of color and transparency.

Determination of smell and taste.

Determination of ethyl alcohol content (strength).

The alcohol concentration must be determined at 20 ° C with an alcohol meter (ASP 95-105, ASP-2 96-101, an alcohol meter with an ASPT 60-100% thermometer or an N16 densimeter 0.76-0.82).

Cleanliness test.

10 ml of the test alcohol is poured into a narrow-necked flask with a capacity of 70 ml and quickly added in 3 ... 4 doses with constant shaking 10 ml of sulfuric acid (density 1.835). The resulting mixture is immediately heated on an alcohol stove, which gives a flame 4–5 cm high and about 1 cm in diameter in the lower wide part. During heating, the liquid in the flask is rotated all the time so that the fire does not touch the flask above the boundary of the heated liquid. Heating of the mixture is stopped when the bubbles come to the surface of the liquid, forming foam; the heating process lasts 30 ... 40 seconds, after which the mixture is allowed to cool quietly. After cooling, the mixture in the flask should be completely colorless.
For the accuracy of the test, the contents of the flask are poured (after cooling) into a special cylinder (test tube) with a ground stopper and, using a camera tripod, observe the color of the mixture, comparing with alcohol, as well as acid, taken in equal volumes and poured into separate cylinders (test tubes) the same size and glass quality. The test result is considered positive if the mixture is as colorless as alcohol and acid.

Oxidation test.

A cylinder with a ground stopper and a 50 ml mark is rinsed with alcohol, filled with the same alcohol to the mark and immersed for 10 minutes in water at a temperature of 15 ° C, poured into a glass bath above the level of alcohol in the cylinder. Then 1 ml of a solution of potassium permanganate (0.2 g solution in 1 liter of water) is added to the cylinder, the cylinder is closed with a cork and, after mixing the liquid, is again immersed in a bath of water.
When standing, the red-violet color of the mixture gradually changes and reaches the color of a special standard solution, the appearance of which is taken as the end of the test.
To observe the change in color of the test mixture, a sheet of white paper is placed under the cylinder. The time during which the oxidation reaction occurs is expressed in minutes. The test result is considered positive if the color persists for 20 minutes.

Determination of furfural content.

10 drops of pure aniline, 3 drops of hydrochloric acid (density 1.1885 kg / l) are poured into a cylinder with a ground stopper with a capacity of 10 ml using a dropper, and the volume is adjusted to the mark with the test alcohol.
If the solution remains colorless within 10 minutes, the alcohol is considered to have passed the test. The appearance of red coloring characterizes the presence of furfural.

Rectification is an industrial method for obtaining alcohol. What is rectification

Equipment

Alcohol mashine

Which is better: rectified or moonshine?

Fundamentals of the rectification process

C) Selection of head fractions.

D) Selection of the food alcohol fraction.

E) Selection of tail fractions (residue).

5.4. Re-rectification.

6. Chemical treatment of mash and raw alcohol.

7. Checking the quality of alcohol.

Difference between distillation and rectification

Operation of the distillation column

Distillation column contact devices (trays and packings)

Properties of distillation column

The principle of operation of the distillation column

Flooding of distillation column

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