1. Where does alcohol as a chemical substance come from
Ethyl alcohol (ethanol, wine alcohol) – C2H5OH – colorless liquid with a characteristic odor. It turns out by fermentation of food raw materials, hydrolysis of plant materials and synthetically – hydration of ethylene. Cleared by rectification. The synthetic way of producing ethanol is rather complicated, and the result is a technical rectified alcohol containing a large amount of impurities that are not separated by rectification. This path is widely used in industry. Another way of obtaining alcohol is more accessible and is associated with the technology of fermentation of simple sugars by yeast. This is how ordinary wine turns out 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:
(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 it can be concluded that from 180kg of sugar, 92kg of alcohol and 88kg of carbon dioxide are obtained. Thus, the theoretical alcohol yield from sugar is
1kg (apples) =>
Most often, alcohol is obtained from starch-containing raw materials (potatoes, corn and
and then it is fermented. As in the previous case, it can be calculated that, theoretically, 1.11 kg of sugar is obtained from 1 kg of starch. Knowing the starch content in raw materials, it is easy to determine the alcohol yield from a particular product. For example, if wheat contains 60% starch, then the theoretical alcohol yield from such grain will be 0.426 l / kg:
1kg (wheat) => 0.6 kg (starch) => 0.666 kg (sugar) => 0,426l (alcohol).
The practical alcohol yield is always 10 … 15% less than the theoretical one. Such losses are considered normal and, mainly, are connected with: unkind, that is, with the situation when part of the sugar remains in the mash and does not turn into alcohol; improper fermentation, that is, when part of the sugar is converted not into alcohol, but into some other substances impurities; direct losses, when part of the alcohol simply disappears along with carbon dioxide during fermentation, or is lost during distillation and rectification.
2. Thermophysical properties of water-alcohol solutions.
The properties of absolutized 100% ethyl alcohol (ES) are of little interest from the practical point of view (tboil = 78.3 ° C at
Everyone knows that ES is very soluble in water forming a binary water-alcohol mixture (solution), which may contain any amount of alcohol. In the case of the use of certain reference data, it is necessary to clearly distinguish between two concepts of the concentration of alcohol in an aqueous-alcoholic solution — mass and volume concentration. 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). The concept of volume concentration of alcohol is often and traditionally used – it is the volume of alcohol in the solution volume (indicated as% vol., Or m3 / m3, or l / l, or ml / ml). This certain “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 figures of volume and mass concentrations of the same solution is significant, therefore then we will use only the concept of the volume concentration of alcohol. To determine the volume content of alcohol in the solution – the concentration of alcohol in the liquid (X) special alcohol meters are used: АСП-3 0 … 40%, АСП-3 40 … 70%, АСП-3 70 … 100%, АСП 95 … 105%, АСП-2 96 … 101%, with the thermometer АСТТ 60 … 100% . It should be noted that the density of the water-alcohol solution strongly depends on its temperature, and all these devices measure the density of the solution (using the power of Archimedes). Therefore, the actual alcohol content in the solution coincides with the readings of these devices only at 20ºC, as indicated on the scales of these devices. The most well-known solutions are vodka – 40% and rectified spirit – 96.4%. By the way, the alcohol content in the mash is within 7 … 12%, but it is impossible to measure this concentration using alcohol meters because of 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 fumes also dissolve well in water vapor and form with them a single steam mixture with the concentration of alcohol in them Y, which can only be determined after the condensation of these vapors –
Naturally, the boiling point of a solution of two substances is water (tkip = 100 ° C at
The equilibrium state of the phases (liquid and vapor) is their coexistence, in which no visible qualitative or quantitative changes of these phases occur. The phase equilibrium is considered to be achieved only in the case when two conditions are simultaneously satisfied: the temperatures of the phases are equal and the partial pressures of each component are equal in the vapor and liquid phases. The second condition means that the process of transition through the interface between the phases of each component from the liquid phase to the vapor phase and back is completed.
The theoretical and practical significance of the phase equilibrium curve from the point of view of the alcohol rectification process is very large, but we will return to this later in the section “Rectification”, and now we will show how to use this curve. For example, in the usual distillation of the brew with the concentration of alcohol X =10% steam is produced with the concentration of alcohol in it Y= 42%, and after its condensation we get “moonshine” (condensate, distillate) of the same “fortress”. Thus, if the moonshine still is not equipped with any additional “bells and whistles”, then it is theoretically impossible to get a stronger moonshine in this way. In the same way, it is possible to “predict” using the same curve and the result of the re-distillation of the “first distillate” – from the 40% distillate by the second distillation it is possible to obtain 60% “moonshine”. Considering this chart, you should pay attention to the diagonal Y = x. Due to the fact that almost the entire equilibrium curve lies above this diagonal, when the water-alcohol mixture evaporates, the concentration of alcohol in the vapor is greater than its concentration in the original liquid. The only exception is the point. BUT – intersection of the equilibrium curve with the diagonal, where X = Y = 96.4%. This is a special point azeotrope. Mixtures that have a vapor that is in equilibrium with a liquid have the same composition as the liquid mixture (X = y). During the distillation of azeotropic mixtures, condensate of the same composition as the initial mixture is formed. The separation of such mixtures by distillation and distillation is excluded. The water-alcohol mixture at a particular point of the azeotrope is called “rectified ethyl alcohol (CP)”. It is to this point that the process of rectification tends, it is she who is the ultimate 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
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. We give some physical properties of rectified ethyl alcohol The density of the liquid (at 20ºС) ……………. ……….…. 812 kg / m3 (≈
It is worth noting that the boiling point of the CP strongly depends on atmospheric pressure. Moreover, this dependence is so strong (see
If you operate a distillation unit without a thermometer, then this information simply broadens your horizons and has no practical significance for you, since you determine the time of CP release with absolute precision by smell. But, for those who have purchased an installation with an electronic thermometer, this connection between the boiling point of alcohol and atmospheric pressure is of immediate practical importance. Indeed, with professional rectification equipment and an electronic thermometer that can accurately determine the temperature of alcohol vapors, you may be surprised to find that its readings differ from day to day. If yesterday you observed an alcohol boiling point of 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 was
3. Theory and practice of simple distillation of the brew.
Simple distillation (distillation) is a process in which the single evaporation of the most volatile components from the bottom of the liquid and the single condensation of these vapors occur.
The alcohol content in the mash is very low from 6 to 12%. However, to obtain high-quality alcohol by distillation, a more concentrated alcohol solution is required, therefore, to obtain alcohol-rectified, all distilleries produce an initial, crude separation of alcohol from water, resulting in raw alcohol (CC), and then rectifying it. The same way can be recommended for home alcohol preparation technology. Distillation of the mash can be carried out using distillation equipment (see below). Using the same rectification technique in 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 SS, it will still need to be diluted to a concentration of 40%. Moreover, distilling the mash on the rectification device, very often the lower part of the column becomes clogged with foam. For more efficient use of the distillation column, all the same, it is better to carry out the rectification on it, and 40% of the moonshine can be successfully obtained from the mash with the help of the simplest distillation apparatus.
A schematic diagram of a simple distiller is presented in
The distiller works as follows. With the help of a heater, the bottom liquid is brought to a boil. The resulting vapor in the pipe enters the condenser-cooler, where it condenses and cools. The resulting distillate flows into the receiving tank 7. With regard to the distillation of alcohol, when operating this device, the process of obtaining distillate mainly obeys the above phase equilibrium curve (
Already 40% distillate can be re-distilled to obtain a more concentrated ≈ 60% alcohol solution (see
4. The theory of rectification
Rectification – heat and mass transfer process, which is carried out in counter-current column apparatus with contact elements (nozzle, plates). In the rectification process, there is a continuous exchange between the liquid and vapor phase. The liquid phase is enriched with a higher boiling component, and the vapor phase with a lower boiling point. The process of heat and mass transfer occurs over the entire height of the column between the distillate flowing downwards, which is formed at the top of the column (reflux), and the steam rising upwards. In order to intensify the process of heat and mass transfer, contact elements are used, which increase the surface interaction of the phases. In the case of the nozzle, the phlegm flows down with a thin film over its developed surface. In the case of plates, steam in the form of a set of bubbles forming a developed contact surface passes through a layer of liquid on the plate.
The purpose of the rectification is generally a clear separation of liquid mixtures into individual pure components. When alcohol is rectified, the main task is to obtain SR from a 40% SS with an ES concentration of at least 96% with a minimum content of impurities. To do this, the process of rectification of the SS is carried out at once on a special rectification equipment. This equipment allows to divide the water-alcohol mixture into separate azeotropic fractions, which differ in boiling points. One of these fractions is food rectified alcohol.
In industry, continuous distillation units are used. In these installations, 85% SS and superheated water vapor are mixed at the bottom of the column and turn into ≈ 40% water-alcohol saturated steam at ≈ 94 ° C (see
Distillation plant works as follows. With the help of a heater, the bottom liquid is brought to a boil. Formed in a cube steam rectification of the column 9 rises up and enters the condenser 2, where it is fully condensed. A part of this condensate (reflux) is returned to the distillation part of the column, and the other part passes through the cooler 14 and flows as a distillate 7 into the receiving tank 8. The ratio between the reflux consumption and the distillate being taken is called reflux number and is set using the selection controller 15. Throughout at the height of the distillation part of the column, a process of heat and mass transfer takes place between the downward reflux and the rising steam. As a result, the most lightly boiling (with the lowest boiling point) component of the bottom liquid is accumulated in the column head in the form of vapor and phlegm, followed by a “number line” (down the height of the column) of different substances. The “number” in this queue is the boiling point of each component, increasing as it descends over the column. Using the controller 15 is a slow and consistent selection of these substances in accordance with their order. The “number” of the substance selected at each moment is recorded with the help of a thermometer 6. Knowing this temperature, taking into account the atmospheric pressure, one can sufficiently accurately indicate the main substance of the distillate that is selected at a given time. For clarification, we present the simplest and most illustrative example of laboratory rectification. Pour acetone (20 ml), methyl alcohol (30 ml), ethyl alcohol (50 ml) and water (100 ml) into the evaporating capacity. The total amount of bottoms liquid will be 200 ml. We will carry out the rectification with the record of the current temperature and the current volume of distillate 7. The total volume of the selected distillate will be brought to 120ml, while the remainder of the bottom liquid (water) will be 80ml. According to the records we construct a graph of temperature change from the current volume of distillate
In the process of rectification, each individual and intermediate substances can be selected in separate receptacles 8, which allows not only to conduct a qualitative and quantitative analysis of the initial mixture, but also to obtain all of its components separately.
Let us consider more closely the equilibrium curve of the phases of a binary water-alcohol mixture, presented in
Plates are commonly used as contact elements in large distillation columns. Each such plate located in a column is called physical plate (FT). The purpose of such a dish, like of any other contact device, is to ensure the closest contact between the liquid and vapor phases in order to maximize the state of equilibrium between them. Plates work as follows. The vapor in the form of bubbles with a developed surface passes through a layer of phlegm 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 a single plate, the equilibrium between the phases is not reached. The measure of the difference between the state of the vapor and liquid phases from their equilibrium state is coefficient of performance (COP) plates. In classical plates, the efficiency is about 50-60%.
For successful interaction of phlegm flowing down the column, and the pair moving upwards, 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 efficient than the 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 – Spreypak, 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 takes place continuously, and the phase equilibrium state, equivalent to one TT, occurs after the steam overcomes a certain height of the packing. And then they usually talk about the height of the nozzle layer, equivalent to one TT,
Whatever contact elements are used in the column, the scheme of operation of the distillation column remains unchanged – the reflux flows downwards and the steam moves upwards. With such a phase movement, there is a certain limiting vapor velocity at which the gravitational forces ensuring the downward movement of phlegm are not able to overcome the oncoming velocity head of steam.
Therefore, at the rectification stage, the column is loaded only with that technological capacity (Wt), which is specified in the passport for your installation. If you increase the input power, you will increase the amount of evaporated alcohol, and, consequently, increase the speed of its vapor in the column. As a result, the column will be flooded, with all the ensuing consequences. It is worth noting that the flooding of the column can occur at the nominal (correct) technological power supplied to the evaporative tank. There are only three reasons for this unconventional column behavior. The first reason is either the blockage of the lower part of the column with foam, for example, from a mash or the overflow of the evaporative tank with the processed liquid. This is a direct violation of the instruction manual, about filling the evaporating tank. The second reason is the increased voltage in the network (over 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 a column in high-mountainous areas. This reason should be paid special attention.
The work of the column is designed for internal pressure in the column 720 …
In the design mode of the column, the internal contact elements provide design resistance to the movement of alcohol vapors in the column.
At the stage of rectification, only that technological capacity should be supplied to the column (Wt), which is listed in the passport for your installation. In this case, the column works without flooding and provides maximum separation efficiency. For example, with a technological capacity of 1 kW, a definite amount of alcohol vapor will theoretically evaporate:
after 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 total distillate formed in the reflux condenser, which is Emax = 1.2 l / h This value is the ultimate theoretical performance of the plant on the alcohol mode with a power input of 1 kW. Our company underestimates somewhat the value of theoretical performance and recommends that in order to guarantee a positive result, we do not select more Enom = 1 l / h. This is due to the fact that not all thermal technological capacity works for vaporization, since there are thermal losses. These losses are mainly related to the size of the evaporating capacity and usually do not exceed 10 … 15%. However, if you greatly increase the volume of the evaporative capacity, then these losses can exceed our 20% performance 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 capacity can produce only 1 l / hour of high-quality rectified alcohol. This rule is reflected in the names of our installations,
5. Practice of alcohol rectification
As already noted, in the impurities in the mash, about 70 different components were found: acids, acetons, esters, aldehydes, light and heavy alcohols, fusel oils and
a) Assemble the distillation unit as indicated in its passport. b) For distillation, fill the evaporation tank with 2/3 of its volume with the mash if distillation is carried out using a distillation column. For rectification, fill the evaporating tank with 3/4 of its volume with raw alcohol, with a strength of no more than 35-45%. c) Close the selection. d) Check the tightness of the assembly. e) Turn on the flow of cooling water. f) Turn on the heating of the bottom liquid. The total time of preparation of the column for work usually takes no more than 5-20 minutes and depends on the skill and readiness of all equipment to work (the place where the installation is connected to the power grid and water cooling network).
The rectification process is monitored and regulated according to the thermometer reading. Typical temperature variation t on time presented on