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Carrying out Rectification (practice) with the formula - “Moonshine. Practical distillation How alcohol rectification occurs

Carrying out Rectification (practice) with the formula - “Moonshine. Practical distillation How alcohol rectification occurs

Making alcoholic beverages at home is accompanied by the term distillation or rectification. Some suggest that these are absolutely identical processes, because the result is an alcohol-containing liquid, but this is not entirely true. There are differences in the principle of producing alcohol, in the equipment and in the quality of the final product itself, including its strength, the presence of impurities, and foreign flavors.

Knowledge about the essence of these processes will be useful for those who plan to prepare various alcoholic drinks based on moonshine at home. The quality of the final product will depend on the technology.

The operation of the classic moonshine still is based on the distillation process, which is relatively simple and affordable, which explains its popularity. The principle of obtaining moonshine is as follows:

  • Heating the mash to a temperature at which steam begins to form;
  • Steam entering the cooler. The system can be supplemented with a settling tank and equipped with other auxiliary devices to capture some of the impurities, but the distillate itself is produced through condensation in a special refrigeration element.

The resulting liquid has a strength of no more than 50%, contains a certain amount of impurities, including fusel oils, and may have a peculiar taste of raw materials. The solution is passed through once, which explains the low strength and purity of moonshine.

If we consider distillation equipment, it is quite simple and has previously been successfully constructed at home. Now you can purchase more advanced analogues with good performance and easy to use.

Features of rectification

To understand the rectification process, it is enough to look at the equipment itself, which is a column, a drawer or a special tube with a nozzle, a cooler. The design may have different dimensions, shapes and volumes of the devices included in the system, but the unchanged principle is the reaction of the separation of the working fluid into individual components through repeated evaporation.

Conventionally, this action can be represented as follows:

  1. Heating the initial alcohol-containing liquid or mash to the evaporation temperature;
  2. The entry of steam into the distillation column, passing through which the working medium enters the refrigerator;
  3. Return of condensed liquid (reflux) to the upper plate of the column by irrigation;
  4. Partial selection of the distillate, obtaining a more concentrated solution due to the countercurrent of steam moving upward and the distillate falling down.

This kind of circulation allows the steam to “absorb” alcohol compounds and the final condensate has a strength of at least 93%. Along with saturation with alcohol vapor, the suspension is also purified from impurities, which only has a positive effect on the quality of the alcohol. The rectification process makes it possible to get rid of the specific smell of moonshine and the flavor shades of raw materials. Also, no additional cleaning will be required, which is practically always used if a standard moonshine still is used.

Braga can be used as the initial raw material, but it is better if it is raw alcohol or moonshine of the first distillation. Such recommendations are associated with excessive foaming during distillation due to the presence of impurities. During the rectification period, temperature stability is also important, therefore, in addition to constant heating, it is sometimes advisable to insulate the column so that even minor changes do not occur.

Equipment for alcohol rectification is even visually significantly different from a moonshine still, since it includes a rectification column and a built-in reflux condenser. Dimensions, volumetric indicators, the number of built-in planes (plates) to increase the evaporation surfaces may differ, which affects the performance and functionality of the system.

While experiments with homemade moonshine systems can sometimes be successful, creating a rectification system at home can be difficult for many.

Apparatus based on distillation or distillation column

Despite the more familiar moonshine still, which operates on the principle of one-time distillation, rectification makes it possible to obtain alcoholic products of higher strength, practically free of impurities. Sometimes it is the alcohol obtained using the rectification system that is used for medicinal tinctures, as a basis for elite drinks.

The cost of a set of equipment to make rectification possible at home differs to a certain extent from moonshine stills, which is related to the principle of operation of the system. After several procedures for obtaining alcohol, the price is compensated by the good yield of the final product and the ease of use of the device.

A regular moonshine still is suitable for those who do not have particularly high demands on alcoholic beverages and who have time to use additional purification methods. For some types of alcohol, the use of the distillation principle is preferable, for example, when you need to leave the taste of raw materials, because rectification allows you to completely remove it. In addition, mash, of which there are many recipes, can be used as the initial solution, but for the column it is better to use a processed analogue, for example, first distillation alcohol or “pervach”.

Regardless of the chosen type of production, whether it is rectification of alcohol or distillation of moonshine, any equipment can be purchased at specialized points. The times of “handicraft” production of distillation devices are over, as there are various designs on sale that differ in operating principle, cost, and output volumes. For cubes, columns, reflux condensers, connecting elements and other structures included in the rectification or distillation system, only safe, chemically neutral compounds are used. Engineers combine all components in such a way that the technology for producing alcohol-containing liquid itself is not disrupted. You just need to make a choice and you can start making high-quality and safe moonshine yourself.

Rectification or rectification is a process where the raw material can be separated into two pure phases such as liquid and vapor. This process occurs for reasons that are determined by the physical properties of alcohol and water. These components boil at different temperatures. Thus, during rectification, both liquids make repeated contact with each other, due to the fact that the liquid evaporates and the vapor condenses. And these processes are repeated more than once.

With such a circulation, there is a constant exchange of not only heat, but also mass exchange. In these processes, the most important component is isolated - ethyl alcohol, which will subsequently be purified from harmful aldehydes, as well as fusel oils.

Very often the process of rectification can be confused with distillation. This is a big mistake. During the distillation process, ordinary distillation occurs, where the collected condensate is already the immediate final product. Which can be diluted to achieve the required strength level.

In the rectification process, the final product is ethyl alcohol. This pure product mainly serves as a base for medicinal tinctures or liqueurs. In this case, it is customary to use entire distillation columns, which often consist of a special refrigerator, drawer and fittings through which the final product is discharged. If this device is equipped with an air fitting, it will enable the device to operate not only in rectification mode, but also in distillation mode.

It is very easy to make pure alcohol at home. You just need to purchase special equipment that is completely freely available. In addition, there will be no need for special financial costs.

The rectification process takes place in several stages:

First, we need what exactly we are going to distill and from which to obtain the rectified product, that is, raw materials. It can easily be sugar, fruit or any other mash. It is important here that the alcohol concentration is not higher than 30%, otherwise the yeast will not work.

For example, you need to get 96% alcohol, that is, its strength will be about 40%, at this percentage the yeast will simply die. What should you do in this case? Here you will need your moonshine still, where you will distill this mash, separating the head and tail. This is how the alcohol will undergo the first purification.

Next, we assemble the rectification column according to the instructions. If there is an atmospheric fitting, be sure to keep it open until the raw material begins to boil, otherwise rectification will safely turn into distillation.

Another important point is the still, which should be filled to 2/3 or 3/4. Here, on the contrary, the fitting will be closed until it boils.

The first fraction must be separated from the head fraction. This is approximately 2.5%. It will contain acetone and other toxic substances. An excellent solvent.



At 78-80 degrees, the release of pure ethyl alcohol begins. At 45 revolutions, this process ends and the tail begins, which is also not recommended for ingestion.

When the temperature reaches 100, we turn off the heating of the entire column and drain the liquid; the tailings can be stored until the next stage.

Rectification at home is a very simple process that does not require special skills.

Start of the process.
Filled in a cube with a volume of 25 liters, 17 liters of raw alcohol 40%. The warm-up time before reaching the operating mode was 35 minutes. Then, using a switch, the heating power was reduced to 933 W and remained unchanged almost until the very end of the distillation. Only at the very end we had to increase it to 1.25 kW. You will understand why after reading to the end. First the temperature rose to 78 degrees. and even stayed at 78-79 degrees for some time. Then it started to fall and stopped at 75g. The column stabilization process was carried out for 15 minutes, without distillate selection. Then he began to make selections at minimum speed. The result was:
1. The first 150 ml, it smells terrible, like acetone, and some other crap. The temperature at first is from 75 degrees. up to 77g., at the end, sometimes 78g appears. Will be used for technical needs. I put another container.
2. Next 300 ml. At first there is clearly a foreign smell. I keep it in a separate container until the smell stops being noticeable. The temperature at the end stabilized at 78 degrees. Unfortunately, the thermometer does not show tenths of a degree. And I also forgot to measure the strength of the head, but in principle this is not important. It will go to the third distillation as it accumulates.
Next comes the process of selecting the middle (food fraction). Using a stopwatch and a graduated cylinder, I adjusted the withdrawal rate to 1 liter per hour, let's see how much actually comes out.
3. In the first hour, 950 ml of 96% alcohol was obtained. The volume turned out to be a little less than planned, but oh well, I won’t change anything, let it remain as it is.
4. For the second hour, the same thing
5. For the third hour, the same thing
6. For the fourth hour, the same
7. For the fifth hour, the same thing
8. For the sixth hour, the same thing, just in case I put another container.
Total 5700 ml.
9. Soon after this, the temperature began to jump 78-79, I pour it into a separate container until the temperature rises from 78 to 85 degrees, the pasture is 450 ml, the strength is about 90% total. Will go for the third stage. There is some strange smell.
10. Next the temperature increases, I will take it until the temperature rises to 98 as an experiment. After 95 gr. the output speed begins to decrease, air bubbles begin to appear in the receiving tube, the distillate strength is about 42%. The smell of fusel is clearly noticeable. The temperature rises very slowly. After 96 gr. To speed up the process, I increase the power to 1.25 kW, since the dripping is very slow, the temperature has practically stopped rising. My patience is reaching its limit, I would have turned it off long ago, but it’s an experiment. Five minutes after increasing the power, the temperature is still 96 degrees. The strength is about 38%, the release rate has increased slightly and is approximately 450 ml per hour. After about another five minutes, the strength is still 38%, the yield weakens again, air bubbles appear in the receiving tube. Sometimes the thermometer flashes 97g. and again returns to 96g. Then after 10 minutes everything was finally stable at 97 degrees. In the tube the distillate is interspersed with air bubbles, the yield has decreased, the strength is 28%. The smell of fusel has noticeably increased. After 10 minutes the temperature is 98 degrees. About 20% ABV, tastes disgusting. The smell of fusel dulled and became less noticeable, but something different was added. I turn everything off, there’s no point in driving it any further, the water will start flowing soon. Yield 900 ml with a total strength of 40%. The distillate has lost a little transparency and some whitishness is noticeable in the light. On top of the surface of the distillate you can see small, fatty droplets of something, probably fusel oil.
This is the layout I have in practice.

1. Where does alcohol come from as a chemical substance?

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

C 12 H 22 O 11 + H 2 0 = 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: hydrogen into the previous chemical formula H=1, carbon С=12 and oxygen О=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 taking into account the density of ethyl alcohol (ρ = 0.8 kg/l), it will be equal to 0.64 l/kg.
If alcohol is obtained not from sugar, but from sugar-containing raw materials (grapes, sugar beets, Jerusalem artichoke, etc.), then, knowing the sugar content of the product, it is easy to determine the alcohol yield 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:

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

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

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

and then it is fermented.
As in the previous case, we can calculate that 1.11 kg of sugar is theoretically obtained from 1 kg of starch. Knowing the starch content in the raw material, you can easily determine the alcohol yield 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) => 0.6 kg (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 associated with:
unfermentation, that is, a situation where some 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 evaporates along with carbon dioxide during fermentation, or is lost during distillation and rectification.

2. Thermophysical properties of water-alcohol solutions.

The properties of absolute 100% ethyl alcohol (EA) are of little interest from a practical point of view ( boiling point=78.3°C at 760mmHg, ρ=790κg/m3). Therefore, here we will deal with the properties of a binary (double) mixture of ES + water, which gives a complete understanding of the operation of rectification equipment and the production of rectified ethyl alcohol using 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.
When using certain reference data, it is necessary to clearly distinguish between two concepts of alcohol concentration in an aqueous-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 % wt., or kg/kg, or g/g). The concept of volumetric alcohol concentration is more often and traditionally used - this is the volume of alcohol in the volume of solution (denoted as % vol., or m3/m3, or l/l, or ml/ml). This some “confusion” in concentrations arises due to the different densities 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 further we will use only the concept of volumetric alcohol concentration.
To determine the volumetric alcohol content in a solution - the concentration of alcohol in the 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 an ASPT thermometer 60...100% . It is worth noting that the density of an aqueous-alcohol solution strongly depends on its temperature, and all these devices measure precisely the density of the solution (using the Archimedes force). Therefore, the actual 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 well-known 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 this concentration cannot be measured 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 vapor also dissolves well in water vapor and forms a single vapor mixture with it with the alcohol concentration in it Y, which can only be determined after the condensation of these vapors - i.e. in liquid (as in the previous case) or by 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 ( tboil=100°C at 760mmHg) and ethanol ( boiling point=78.3°C at 760 mm Hg) should be between the boiling temperatures of individual substances. Dependence of the temperature of saturated water-alcohol vapor or the boiling point (vaporization) of this binary mixture on the concentration of alcohol in the vapor Y is presented in Fig. 1.
It is worth noting that on this graph there is a certain point A with a concentration of 96.4%, the temperature in which is even less than the boiling point of 100% ethanol.

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

2.3 Phase equilibrium.

The equilibrium state of phases (liquid and vapor) is their coexistence in which no visible qualitative or quantitative changes occur in these phases. Phase equilibrium is considered achieved only when two conditions are simultaneously satisfied: the temperatures of the phases 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 across the interface of each component from the liquid phase to the vapor phase and back 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 in 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 into an ordinary flask (schematically drawn inside the graph in Fig. 2) Xf and heat this mixture to the boiling point, then in the resulting vapor the alcohol concentration will be Yп. Then, if you quickly close the flask and shake vigorously (mix the vapor and liquid phases), the temperature inside the flask will equalize, and the vapor and liquid will come to an equilibrium state - with the concentrations of alcohol in them Y And X respectively.
If such experiments are carried out for different concentrations of aqueous-alcohol solutions, then it is possible to obtain a certain dependence of the phase equilibrium - a phase equilibrium curve. The graph of the phase equilibrium curve for a binary mixture of pure alcohol + pure water is presented in Fig. 2.


Fig. 2 Phase equilibrium curve 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 rectification process is very great, but we will return to this later in the “Rectification” section, and now we will show how to use this curve.
For example, during normal distillation of mash with an alcohol concentration X= 10% vapor is formed with an alcohol concentration in it Y=42%, and after its condensation we get “moonshine” (condensate, distillate) of the same “strength”. Thus, if the moonshine still is not equipped with any additional “bells and whistles,” then it is theoretically simply impossible to obtain stronger moonshine in this way. In the same way, you can “predict” using the same curve the result of repeated distillation of the “primary” - from a 40% distillate, you can get a 60% “moonshine” by the second distillation.
When looking at this graph, you should pay attention to the diagonal Y=X. It is precisely due to the fact that almost the entire equilibrium curve lies above this diagonal that, when evaporating a water-alcohol mixture, it is possible to obtain a concentration of alcohol in the vapor that is 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 a special point in the azeotrope.
Azeotropic or inseparably boiling mixtures are those in which the vapor in equilibrium with the liquid has the same composition as the liquid mixture ( X=Y). When distilling 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.
The water-alcohol mixture at a special point in the azeotrope is called “rectified ethyl alcohol (RE)”. It is this point that the rectification process tends to, it is the maximum concentration of alcohol in this process, and it is at this point that the water-alcohol mixture has a minimum boiling point ( tboil=78.15°C at 760mmHg see Fig.1).

2.4 Basic properties of rectified alcohol

There is GOST 5962-67 for this product, which regulates the alcohol concentration in rectified spirit 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 rectification equipment. And for you they will be regular reference information.

2.5 Boiling point of rectified alcohol and atmospheric pressure.

It is worth noting that the boiling point of CP significantly depends on atmospheric pressure. Moreover, this dependence is so strong (see Fig. 3) that when rectifying alcohol using the temperature recorded, for example, by an electronic thermometer, you can determine the exact value of atmospheric pressure at a given moment and calibrate an ordinary home barometer using the dependence below.


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

If you operate a distillation unit without a thermometer, then this information simply expands your horizons and has no practical significance for you, since you determine the moment of release of the CP by the smell with absolute accuracy. But, for those who have purchased a unit with an electronic thermometer, this connection between the boiling point of alcohol and atmospheric pressure has immediate practical significance.
Indeed, if you have professional distillation equipment and an electronic thermometer capable of accurately determining the temperature of alcohol vapor, you may be surprised to find that its readings differ from day to day. If yesterday you observed the boiling point of alcohol 77.0ºC, and today - 78.0ºC, then this does not mean a change in the alcohol composition or a malfunction of the rectification device, but only a change in atmospheric pressure: yesterday it was 730 mmHg, 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 occurs.

3.1 Purpose of simple distillation

The alcohol content in the mash is very low, ranging from 6 to 12%. However, to obtain high-quality alcohol by rectification, a more concentrated alcohol solution is required, therefore, to obtain rectified alcohol, all distilleries perform 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 method can be recommended for home technology for preparing alcohol.
Distillation of mash can also be carried out using distillation equipment (see below). Using the same rectification technique when distilling mash, you can immediately obtain 80...85% CC from the mash. But this is not necessary, since for clear rectification of the SS, it will still need to be diluted to a concentration of 40%. Moreover, when distilling mash in a distillation device, very often the lower part of the column becomes clogged with foam.
To use a distillation column more efficiently, it is still better to carry out rectification on it, and 40% moonshine can be successfully obtained from mash using a simple distillation apparatus.

3.2 Equipment for simple distillation

The 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 connected to each other by a pipe 3. The cube is filled with a processed liquid 4, the heating and evaporation of which is carried out by a heater 5. Cooling water constantly flows through the condenser-cooler (shown by arrows). For 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 capacity 7.

3.3 Operation of a simple distillation apparatus

The distiller works as follows. Using a heater, the still liquid is brought to a boil. The steam formed in the cube passes through the pipe into the condenser-cooler, where it is condensed and cooled. The resulting distillate flows into receiving container 7.
As for the distillation of alcohol, when this device operates, the process of obtaining a distillate mainly 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 vapor is also high, and therefore in its distillate (42...45%). However, the mash is not a binary mixture of water and alcohol, but contains a large number of associated impurities with lower and higher boiling points in relation to the water-alcohol mixture. The temperature of the vapor of the alcohol-water mixture passing through the pipe at this moment is about 90...94 ° C, but low-boiling impurities (ethers, acetones, aldehydes, methyl alcohol, etc.) are included in a larger proportion in the composition of the initial steam, lowering this theoretical temperature up to 65...75°C. An increased concentration of low-boiling impurities (the density of which is less than the density of alcohol) in the initial distillate distorts the alcohol meter readings upward, creating the illusion of increased “strength”. That is why the first portion of distillate obtained from the mash is called “pervach”. In reality, this is not concentrated alcohol, but a water-alcohol mixture with an increased concentration of “poison”.
In the next stage of distillation, the temperature change is more consistent with theory. Using the readings of thermometer 6 and using the graph in Fig. 1, you can always know the concentration of alcohol vapor Y going to condensation. Gradually, the concentration of alcohol in the still decreases, and its concentration in the distillate decreases accordingly, which is indicated by an increase in temperature on thermometer 6. If the temperature reaches 100°C, this means that the alcohol in the still liquid is completely gone and only water evaporates from the still.
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 more intense evaporation of fusel oils and other tail impurities begins.
The average concentration of alcohol in the distillate (typical “moonshine”) obtained from mash using simple distillation apparatus usually does not exceed 40%. A typical graph of temperature changes over time during simple distillation is shown schematically in Fig. 5.


Fig.5 Change in vapor temperature during simple distillation

You can re-distill the 40% distillate and obtain a more concentrated ≈ 60% alcohol solution (see Fig. 2). Then you can repeat this process many times until the alcohol concentration 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 mash in order to obtain high-quality vodka, complex, sometimes very expensive cascades of purifications and re-distillations that occur with large losses of alcohol and electricity are required.
That is why this way of obtaining high-quality vodka has long since become a thing of history!
At the moment, there is another, simpler way to obtain high-quality vodka, the essence of which is to immediately obtain 96% rectified alcohol from SS (“moonshine”), purified from impurities, and then dilute it with good water to the concentration of a vodka solution. This method requires special and rather complex distillation equipment.

4. Rectification theory

Rectification is a heat and mass transfer process that is carried out in counterflow column devices with contact elements (packing, plates). During the rectification process, 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 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, 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 between the phases. When using a nozzle, phlegm flows down as a thin film over its developed surface. In the case of using trays, vapor in the form of many bubbles forming a developed contact surface passes through the layer of liquid on the tray.

4.1 Purpose of rectification

The purpose of rectification in general is the clear separation of liquid mixtures into individual pure components.
When rectifying alcohol, the main task is to obtain SR from 40% SS with a concentration of ES in it of at least 96% with a minimum content of foreign impurities. To do this, the SS rectification process 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 rectified food alcohol.

4.2 Equipment for rectification

Continuous distillation units are used in industry. In these units, 85% CC and superheated steam are mixed at the bottom of the column and converted into ≈ 40% hydroalcoholic saturated steam at a temperature of ≈ 94°C (see Fig. 1). This steam mixture continuously enters the distillation column, is stratified 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, rather 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 only with rudimentary means of adjusting the extraction, temperature control and a manometric meter for the pressure drop across the column.
A schematic diagram of a periodic distillation unit is shown in Fig. 6. The installation consists of an evaporation tank - cube 1 and a distillation column mounted vertically on the lid of the cube. The cube is filled with a processed liquid 4, the heating and evaporation of which is carried out by a heater 5. The column includes a rectification part 9 and a column head 10. The rectification 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 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 cooler 14 and condenser 2.

4.3 Operation of the distillation column.

The rectification plant operates as follows. Using a heater, the still liquid is brought to a boil. The steam formed in the cube rises upward through the distillation part of column 9 and enters condenser 2, where it is completely condensed. Part of this condensate (reflux) returns to the distillation part of the column, and the other part passes through cooler 14 and flows into the receiving tank 8 in the form of distillate 7. The ratio between the flow rates of reflux and the selected distillate 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 reflux flowing down and the steam rising up. As a result, the lowest boiling (with the lowest boiling point) component of the bottom liquid accumulates in the form of steam and reflux at the head of the column, and after it, a “numbered queue” (down the height of the column) of different substances is built by itself. The “number” in this queue is the boiling point of each component, which increases as it goes down the column. Using the regulator 15, a slow and consistent selection of these substances is carried out in accordance with their order. The “number” of the substance sampled at each moment is recorded using thermometer 6. Knowing this temperature, taking into account atmospheric pressure, one can quite accurately indicate the main substance of the distillate sampled at a given point in time.
For clarification, we give the simplest and most illustrative example of laboratory rectification. Pour acetone (20ml), methyl alcohol (30ml), ethyl alcohol (50ml) and water (100ml) into the evaporation container. The total amount of still liquid will be 200 ml. We will carry out rectification by recording the current temperature and the current volume of the resulting distillate 7. We will bring the total volume of the selected distillate to 120 ml, while the remainder of the bottom liquid (water) will be 80 ml. Using the records, we will construct a graph of temperature changes from the current volume of distillate Fig. 7. The graph clearly shows four horizontal sections α (tк=const) and three transition sections β between them. Sites α are the individual pure components of the original mixture, and the transition sections β - These 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 from the “height” and “length” of each step one can easily draw a conclusion about the qualitative and quantitative composition of the initial mixture:

During the rectification process, each individual and intermediate substances can be selected into separate receiving containers 8, which allows not only to carry out a qualitative and quantitative analysis of the original 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 of them are needed.

Let us take a closer look at the equilibrium curve of the phases of a binary water-alcohol mixture, presented in Fig. 2. As indicated in the example, it is possible to obtain a 40% solution from a 10% alcohol solution using simple distillation. Then, from a 40% solution, a 60% solution can be obtained using the same method.
It is easy to construct a series of successive steps 10-40 on the phase equilibrium curve; 40-60; 60-70; 70-75; etc. and make sure that to achieve an alcohol concentration of 96% in the final distillate, theoretically at least 9...10 such successive distillations will be required.
Each such distillation step is conventionally called theoretical plate (TT). The quantity 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 nowadays increasingly) called a mass transfer unit or transfer unit (TU).
In practice, we never have a pure mixture of alcohol and water (unless it is good vodka). In practice, the only source of alcohol-containing liquid for producing 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 deteriorated taste properties.
Experience shows that 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 Physical plate and how it differs from the theoretical one.

Trays are usually used as contact elements in large distillation columns. Each such plate located in a column is called physical plate (PT). The purpose of such a plate, like any other contact device, is to ensure the closest contact of the liquid and vapor phases to maximize the achievement of a state of equilibrium between them.
The plates work as follows. Steam in the form of bubbles with a developed surface passes through a layer of phlegm located on the plate. As a result of this “bubbling”, heat and mass transfer between the liquid and vapor phases is intensified. However, after steam passes through one plate, equilibrium between the phases is not achieved. The measure of the difference between the state of the vapor and liquid phases from their equilibrium state is coefficient of performance (efficiency) dishes.
Classic plates have an efficiency of about 50-60%. Those. To achieve a state of phase equilibrium corresponding to one CT, about two FTs will be required. Thus, to implement 40 TP in a distillation column, it will be necessary to install about 80 FT of a classical design in it.

4.6 The nozzle and where the “theoretical plates” are in it.

For successful interaction of reflux flowing down the column and steam moving upward, you can use any other contact elements that increase the area and efficiency of this interaction.
For distillation columns of ultra-small diameter (10-30mm), the contact element is more effective than a plate. nozzle. The nozzle fills the entire internal volume of the distillation part of the column. There are many different types of nozzles, for example, regular nozzles - Spraypack, Sulzer, Stedman; chaotic (bulk) - ceramic rings of Lessing, Pahl, Berle, the most common is a wire spiral-prismatic nozzle.
The process of heat and mass transfer on such contact elements occurs continuously, and a state of phase equilibrium, equivalent to one CT, occurs after the steam has overcome a certain height of the nozzle. And then they usually talk about the height of the packing layer, equivalent to one CT, i.e. for packed columns the concept is usually used - theoretical plate height VTT or transfer unit height VEP (nowadays used more often).
This height is usually estimated in millimeters, which makes it easy to compare the efficiency of a particular packing by its EEP and calculate the height of the entire distillation part of the column. So, for example, with an internal diameter of the column of 30 mm, the VEP of a spiral-prismatic nozzle is 20...25 mm, and for a Sulzer-type nozzle, the VEP is 15...20 mm.
For packings, the height of the transfer unit strongly depends on the diameter of the column and increases rapidly as it increases. That is why such effective packed contact elements are practically not used in large industrial distillation plants, but have found their application exclusively in laboratory equipment.
The appearance of this little-known contact element is perceived by many as some kind of filter, which must have a certain service life in the column. However, it is not. The nozzle 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 (no foam from the bottom liquid gets into the column), then this “filter” performs its functions of heat and mass transfer for an unlimited time inside the column.

4.7 Column capacity. Column choking.

Whatever contact elements are used in the column, the operation 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 steam, at which the gravitational forces ensuring the downward movement of phlegm are not able to overcome the oncoming high-speed pressure of the steam. Those. when the steam speed increases, the reflux first slows down its flow rate downwards, and then simply stops (hangs in the column) and begins to accumulate in its distillation part. Happening column drowning.
Column flooding is an off-design mode of its operation. The column can remain in this state for 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 reflux condenser, and then it is released into an emergency from the column through the upper fitting of the reflux condenser. Column flooding can be determined by the pressure drop in the column, or can be clearly heard as a specific “gurgling” noise in the column. To avoid flooding of the rectification installation, you must strictly follow the operating recommendations set out in the passport for each installation.
The limiting steam velocity is determined by the contact elements themselves, which clutter the internal cross-section of the column. Different contact elements have their own limiting speed of alcohol vapor in the full cross-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/hour) per unit area of ​​the total cross-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 flow. However, the maximum efficiency of many contact elements (efficiency of the tray and EEP of the nozzle) is realized when the column operates 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 a heat of vaporization CP of 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 time:

Therefore, at the rectification stage, the column is loaded only with that technological power (Wt), which is indicated in the passport for your installation. If you increase the power input, you will increase the amount of alcohol evaporated, and, therefore, increase the speed of its vapor through the column. As a result, the column will flood with all the ensuing consequences.
It is worth noting that flooding of the column can occur even at the rated (correct) process power supplied to the evaporation tank. There are only three reasons for this non-standard behavior of the column.
The first reason is either clogging of the lower part of the column with foam, for example, from mash, or overfilling of the evaporation tank with the processed liquid. This is a direct violation of the operating instructions regarding 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 high mountains. This reason is worth paying special attention to.

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 because the column necessarily has a connection with the atmosphere through the upper fitting of the reflux condenser, then this pressure is also the optimal atmospheric pressure for its operation. Let's figure out how atmospheric pressure can affect the operation of a column and how to control the operation of a column in high mountains.
As indicated in the example of the previous section (about flooding of the column), 1 kW of thermal power evaporates 3.89 kg/hour of alcohol vapor. This mass flow rate of steam at a normal pressure of 760 mm Hg. (alcohol vapor density - 1.6 kg/m3) corresponds to a very specific volumetric flow rate - 2.43 m3/h, which passes through the full cross-section of the column (for example, Ф30mm) at a speed of 0.96 m/s. If atmospheric pressure drops to 700 mmHg, 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 speed in the full cross-section of the column increases to 1.04 m /With. If this speed is maximum, then the column will flood.
With an increase in atmospheric pressure, on the contrary, the speed of alcohol vapor decreases, 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 included in its design to ensure stable and optimal operation of the column, taking into account the precision of manufacturing of contact elements, technological heating elements (their power variations), possible changes in atmospheric pressure, etc. However, each distillation column has some “individuality” and “noise” that you need to feel and use correctly.
If the atmospheric pressure threshold for your specific column instance is significantly lower than the minimum possible pressure in your area, you may never encounter this problem. If this happens occasionally, then we can recommend that you not carry out rectification on days of very low atmospheric pressure.
If the operation of the distillation column will take place only in high mountains, then it is necessary to use LATR (adjustable laboratory autotransformer) or any other voltage regulator to control the rate of evaporation of the bottom liquid.

4.9 Pressure drop in the column and how to measure it.

Under the design operating conditions of the column, the internal contact elements provide the design 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 reflux condenser is equal to atmospheric pressure, they usually talk about pressure drop across the column ∆P.
The magnitude of this ∆P(resistance) can be easily observed 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. Once the column is brought into operating mode, the pressure at the bottom of the column will increase, and the liquid column, balancing the difference ∆P, will rise to a certain height N, associated with the difference in ratio ∆P = ρgΝ(Where: ρ - liquid density, g = 9.81 m/s2). During normal operation of the column, the liquid column must be at a certain and constant height N. The magnitude of this pressure difference - 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 based on the pressure drop.
Using this “measuring device” you can easily determine the moment of flooding of the column. The liquid column 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 the movement of steam.

4.10 Reflux ratio and how to set it correctly.

Figure 8 shows the main mass flows in the distillation column. Steam evaporated in a cube Mn=M passes through the distillation part of the column upward, completely condenses in the reflux condenser, and turns into a distillate Md=M. Part of this distillate E is taken away, and the other part 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) 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 taken E.
If there is no alcohol selection E=0, then the entire distillate is in the form of reflux R=M returns back to the column. Then they say that the column works on itself, and the reflux ratio of the column in this state is equal to infinity - V=∞. In this state, the column has maximum separation capacity, and the number of theoretical plates in it increases.
If you open the selection completely E=M, then there will be no return of phlegm to the column R=0. Then the reflux ratio is zero. In this case, due to the absence of reflux in the column, its contact elements are completely “dried up”, heat and mass transfer processes stop, and the distillation column turns into an ordinary “moonshine still”. Naturally, this transformation is temporary and reversible - without physical disturbances in the column.
To obtain high-quality alcohol, the reflux ratio must be at least V≥3. This means that out of 4 parts of the distillate formed in the reflux condenser, only 1 part can be selected, and 3 parts must be sent back to the column to irrigate its contact elements. Only in this case there will be no disruption 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 make a clear and simple recommendation for setting it using an extraction regulator.
SELECTION RULE:
Option 1 (main):
Using a stopwatch and a graduated cylinder, set the selection recommended in the passport.
Option 2 (test for any faction):
The selection was chosen correctly if, 2-3 minutes after its termination, the temperature in the column did not decrease.

4.11 Power, performance, reserves.

At the rectification stage, only that technological power 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 ensures maximum separation efficiency.
So, for example, with a technological power of 1 kW, a very certain amount of alcohol vapor will theoretically evaporate:

after condensation of these vapors in the reflux condenser, 4.86 l/hour of distillate is formed.
To implement the rectification process, as noted above, we can theoretically select only ¼ of the total distillate formed in the reflux condenser, which is Emax = 1.2 l/hour. This value is the maximum theoretical productivity of the installation in alcohol mode with an input power of 1 kW.
Our company somewhat underestimates the value of theoretical productivity and recommends that in order to guarantee a positive result, selection should be no more than Enom= 1 l/hour. This is due to the fact that not all thermal technological power is used for steam generation, since there are heat losses. These losses are mainly related to the size of the evaporation tank and usually do not exceed 10...15%. However, if the volume of the evaporation tank is greatly increased, then these losses can exceed our 20% reserve in terms of productivity.
Thus, for your column there is a completely defined technological capacity and a completely defined selection regulated by the rectification process. this implies PRODUCTIVITY RULE:
1 kW of technological power can produce only 1 l/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 using this typical and most studied liquid - ethyl alcohol.

5. Practice of rectification of alcohol

As already noted, about 70 different components were found in the impurities in the mash: acids, acetones, ethers, aldehydes, light and heavy alcohols, fusel oils, etc. Impurities are formed during the preparation of the wort, but most of all accumulate during fermentation, and during distillation, the mash almost completely ends up in the SS.
The main task of rectification is to clearly separate impurities from rectified alcohol.
The amount of impurities in the dehydrated distillate (that is, the distillate minus water) usually does not exceed 6%. The specific amount of “waste” usually depends on the accuracy of the mash preparation technology. Many of these impurities are difficult to separate from CP, and only correct working on rectification equipment allows you to get rid of them in the commercial part of the rectified alcohol.
From a practical point of view, all impurities existing in SS (the previously mentioned 6%) can be divided into two groups in relation to the boiling point of CP ( boiling point = 78.15°C at 760mmHg):
-head (≈ 2.5%);
- tail (≈ 3.5%).
Head impurities include all substances that have a boiling point less than 78.15°C and preceding (in the time of the rectification 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 behind them that the SR comes in turn. Among these substances, the best known are methyl alcohol ( tboil=64.7°C) and the aldehyde group of impurities, in which tboil somewhat less, 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. They are the ones who take their place at the back of the general queue for SR. Among these substances, the most famous is the group of fusel oils ( tboil somewhat more, 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 2/3 of its volume with mash, if distillation is carried out using a distillation column.
For rectification, fill the evaporation tank 3/4 of its volume with raw alcohol, at a strength of no more than 35-45%.
c) Stop 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 to prepare the column for operation usually takes no more than 5-20 minutes and depends on the skill and readiness of all equipment for operation (where the installation is connected to the electrical network and the water cooling network).

5.2 Rectification process.

The rectification process is controlled and regulated according to the thermometer reading. Typical temperature dependence t in time is presented in Fig. 9, indicating five periods:


Fig.9 Temperature change during alcohol rectification.

A) Heating.

The SS in the evaporation tank is heated by all heating elements installed in it with a total power - Wу. After some time, the SS in the cube begins to boil, and gradual heating of the column begins with rising steam. At this moment it is necessary to 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 remain 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 upper fitting of the dephlegmator to the outside. If you nevertheless missed the moment of the beginning of boiling, and the column choked, then you will have to come to terms with the loss of alcohol and turn off the column. Then wait until the drowning process stops and turn on Wt.
After heating the column, a temperature jump is observed, noted by a thermometer.

B) Stabilization.

The column operates at technological capacity Wt. Selection blocked E=0. The column works on its own, reflux ratio V=∞. While observing the thermometer readings, wait until the temperature decreases and stabilizes at the lowest level.
At this moment, the process of separation and accumulation of the head (low-boiling) fractions takes place in the upper part of the column. After 10-15 minutes, this process is completed, and the temperature at the top of the column reaches its minimum value and stabilizes 3-5˚C below the expected boiling point of CP. The magnitude of this difference depends on the composition and amount of low-boiling fractions present in the CC. Expected boiling point CP tс 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 takes longer, it will only be better. You will be able to more accurately separate all the main impurities that have accumulated in the column at this point.
If you work with an electronic temperature comparator, then you can more accurately determine the moment when the column stabilizes by the temperature difference.

C) Selection of head fractions.

The selection of the head fractions must be carried out as slowly as possible (with a high reflux ratio). Slow selection does not “spread” a fraction throughout the column and does not take with it the following fractions. Due to the small amount but wide variety of substances in the head fraction, this part of the distillate is actually one large transition section ( β in Fig. 7) from many head impurities to pure CP.
To properly organize selection during this difficult rectification period, we can recommend the following approach, consisting of a breakdown of the stage “ IN” , for three successive equal periods of time.

This 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 following food fraction of the CP;
  • minimum volume of the head fraction and the absence of the CP food fraction in it;
  • approach to the main CP fraction with a low 50% productivity.

This period ends with reaching a temperature 0.1-0.05˚C lower tс. It is conventionally considered that the amount of low-boiling impurities present in the CP at this moment and causing such a decrease in the boiling point of the CP corresponds to acceptable food standards.
In practice, the most accurate device for making a decision about the end of the period of selection of the head fractions and the beginning of the selection of food CP is the usual “human nose”.
Control of the resulting distillate by smell is carried out as follows:

  • place a few drops of the selected distillate onto your palm;
  • rub this puddle over the entire surface of your palm;
  • bring your palm to your face and inhale through your nose the distillate that has evaporated from your palm.

Such an instant and fairly accurate analysis will always be of some help to you when rectifying 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. PLEASE REMEMBER! that the distillate obtained by distilling off the head fractions is not a 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 edible alcohol fraction.

We will install a new, clean and larger receiving tank. Let's increase the selection to Enom, which will remain until the end of the entire rectification process. Let's check this selection using a stopwatch and a graduated cylinder. After 5-10 minutes we will check the thermometer readings. If everything was done correctly, the thermometer readings will not change. Moreover, this temperature will remain unchanged throughout the entire period of food fraction selection.
The resulting CP from this moment is a high-quality food product. However, its composition (indistinguishable by many even by smell) is gradually changing and can be divided into three parts:

  • the first 5% of the total volume of SR will still contain traces of the leading fractions
  • central part - about 80% of the total volume of SR will be absolutely clean
  • and 5% of the total volume of SR before the end of this regime will begin to acquire traces of tail. Taking into account the last remark, it can be recommended to prepare two separate marked containers for collecting the food fraction, which are used to select the first 10% and the last 10% portion of SR.

When obtaining the central part of the SR, you can select the maximum selection Emax(reflux ratio is close to V=2.5 ). Meaning Emax mainly depends on the quality of the processed SS, so it requires clarification at each rectification. However, searching and clarifying it can only be recommended after fully mastering the rectification process according to these instructions. To find Emax it is necessary to use the second option of the selection rule.
But remember - the less selection, the higher the quality!
In this rectification mode, a constant presence near the device is not required, and the receiving containers are replaced as they are filled.
When receiving the third part of the food CP, it is recommended to use an intermediate container, from which periodically, after making sure that the thermometer reading corresponds to the boiling point of the CP, pour the alcohol into the main container.
This technique allows, if the moment of temperature increase is missed (the arrival of CP with a higher concentration of heavy alcohols and fusel oils), to prevent the “bad” alcohol from entering the “good” one.
Selection of CP is completed when the temperature reaches 0.1...0.05˚С above the temperature tс. It is conventionally considered that the amount of heavy-boiling impurities present in the CP at this 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 CP already produced.

D) Selection of tail fractions (residue).

We replace the receiving container or leave an intermediate one (in which the “tail” has already been lost). We do not change the column settings - power Wt; selection Enom.
The residue selection process 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 its use for food purposes is strictly prohibited. The resulting residue can be reprocessed with a new portion of CC. Or, what is more preferable, rectify it separately, having previously accumulated 10...20 residues (at least 30% of the volume of the evaporation tank).

5.3 Repeated rectification.

Repeated rectification is carried out only in the following cases:
A) there is a need to obtain “Extra” and “Lux” type alcohols with the least amount of impurities from very poor raw materials;
b) unsatisfactory quality of the SR obtained during the first rectification (reasons: non-compliance with the recommendations of this instruction during the training process).
To carry out repeated rectification, it is necessary to fill the entire food CP (and in case of very low quality, only its central part) with water to a concentration of 40-45%, pour it into a well-washed evaporation container and repeat the rectification as indicated in section 5.

Note to Section 5

You probably noticed that the strength of the CC used to carry out the rectification process is recommended within the range of 35-45%. It is at this concentration of SS that the highest quality of the resulting CP is ensured.
Do not increase this concentration!
The indicated SS strength can also be achieved by conventional (direct) distillation of the mash using simple distillation apparatus.

6. Chemical treatment of mash and raw alcohol.

A) chemical treatment of mash.

If you follow the mash preparation technology, the wort gradually increases its acidity during the fermentation process - and this is normal. In this case, no chemical treatment is required.
Sometimes the acidity of the mash can increase above normal. This can happen due to a variety of reasons related to technology violations:

  • the wort was not sterilized, and the fermentation process was “taken over” by wild yeast;
  • By chance, the temperature in the room dropped sharply, and the brew cooled and “stopped” and its fermentation turned into vinegar.

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

B) chemical treatment of raw alcohol.

If all previous steps were correct, then chemical treatment of raw alcohol is not required.
If raw alcohol is obtained from fruit raw materials (bad wine) or mistakes were made in previous steps (you can find out about this only after correct rectification), then chemical treatment of the raw alcohol should be carried out. Accurate data for this procedure can only be obtained after very precise and subtle analyzes of the raw materials. Only general recommendations are given here.
GENERAL NOTE - 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, which have a volatility close to ES, are converted into more volatile (ethers) and less volatile (heavy alcohols) chemical compounds, which significantly improves the quality of the SS in rectification process.
To do this, add 1...2 g/l of alkali (KOH or NaOH) to the SS, having previously diluted them in a small amount of water. Usually such processing is sufficient to begin rectification.
In the 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, having previously been diluted in a small amount of water, is added to the SS in an amount of 1.5...2 g per liter alcohol present in CC. The solution is thoroughly mixed and left for 15...20 minutes to complete the chemical reaction. After this, alkali is added again (in the same amount) and left to clarify for 8...12 hours. Then the CC is filtered and rectified.

7. Checking the quality of alcohol.

Testing the quality of alcohol includes the following tests:

Determination of color and transparency.

The test alcohol is poured into a clean, dry cylinder made 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 stirring, 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 a densimeter N16 0.76-0.82).

Test for purity.

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 lamp, producing a flame 4...5 cm high and with a diameter in the lower wide part of about 1 cm. During heating, the liquid in the flask is constantly rotated so that the fire does not touch the flask above the border of the heated liquid. Heating of the mixture is stopped when bubbles reach 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-in stopper and, using a tripod camera, the color of the mixture is observed, comparing with alcohol and acid, taken in equal volumes and poured into separate cylinders (test tubes). same size and quality glass. 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 alcohol level in the cylinder. Then 1 ml of a solution of potassium permanganate (a solution of 0.2 g in 1 liter of water) is added to the cylinder, the cylinder is closed with a stopper and, after mixing the liquid, it 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 color change of the test mixture, place a sheet of white paper under the cylinder. The time during which the oxidation reaction occurs is expressed in minutes. The test result is considered positive if the color remains for 20 minutes.

Determination of furfural content.

Into a cylinder with a ground stopper with a capacity of 10 ml, add 10 drops of pure aniline, 3 drops of hydrochloric acid (density 1.1885 kg/l) 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 a red color characterizes the presence of furfural.


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