To understand "physics" alcohol rectification Consider the main properties of absolute 100% ethyl alcohol:
- boiling point \u003d 78.3 ° C at 760 mm Hg
- liquid density \u003d 790 kg / m3 at 20 ° С

It is known that ethyl alcohol is perfectly soluble in water, forming a binary water-alcohol mixture with any amount of alcohol. Here it is necessary to indicate the difference between the mass and volume concentration of ethanol in a water-alcohol solution. The mass concentration of alcohol is the mass of alcohol in the mass of the solution (denoted as g / g or% mass).

The concept of volumetric concentration is most often used - this is the volume of alcohol in the volume of the mixture (denoted as ml / ml or% vol.). Due to the significant difference in the density of alcohol (0.79 g / ml) and water (1 g / ml), the values \u200b\u200bof volumetric and mass concentrations can differ significantly. Hereinafter, we will only use the concept of volumetric concentration.

It is clear that the boiling point of a solution of two liquids should be between their individual boiling points - 100 ° C for water and 78.3 ° C for ethyl alcohol (at 760 mm Hg). The dependence of the boiling point (vaporization) of this solution, or, which is the same, the temperature of saturated water-alcohol vapor on the concentration of alcohol in the vapor is shown in Fig. one.

Point A with a concentration of 96.4% and a boiling point less than the boiling point of 100% ethyl alcohol deserves special attention in this graph.

Processes distillation and rectification of ethanol explain by the phase equilibrium curve of a binary water-alcohol mixture (see Fig. 2).

It can be seen from the diagram that practically the entire equilibrium curve is above the diagonal Y \u003d X, that is, upon evaporation of an aqueous-alcoholic solution, the concentration of alcohol in the vapor is greater than in the original liquid. This is what underlies the processes of distillation and rectification of ethanol.

Of great importance is the point (A, X \u003d Y \u003d 97.2% by volume) of the intersection of the phase equilibrium curve with the diagonal. This is a special "azeotrope point" - an inseparably boiling liquid mixture of two pure components, which cannot be separated into components by distillation or rectification. The water-alcohol mixture as close as possible to the azeotrope point is called rectified alcohol.

Using the equilibrium curve and the diagonal Y \u003d X (see Fig. 2), you can see that a simple distillation of 10% mash first produces moonshine with a concentration of about 53% by volume. Further, after step 10-53, you can build the following ones - 53-82, 82-88, 88-92, etc. The vertical component of the step shows an increase in the percentage of ethanol in the vapor phase until the onset of phase equilibrium (point A). The horizontal component of the step shows the condensation of these vapors (the point of intersection of the horizontal with the diagonal Y \u003d X). The diagram shows that in order to obtain rectified alcohol from the mash with an initial concentration of 10%, theoretically, more than a dozen of such successive distillations should take place. In practice, there should be much more of them, so as the concentration of alcohol in the distillation still decreases, the concentration of the distillate decreases accordingly. For example, on the first step, 53% vol. corresponds only to the initial moment of distillation. After some time, the concentration of alcohol in the brew decreases and we already have less than 10% alcohol in it, as a result of which, by the end of the first distillation, the selected moonshine has an average strength of not 53% vol., But 35-40% vol.

It should be noted that the boiling point of ethanol depends on atmospheric pressure (see Fig. 3). Moreover, this dependence is quite significant for the rectification process, when every tenth of a degree matters.

In a very, very simplified formulation, the "steps" of individual distillations described above, but carried out not separately, but collected together in one apparatus, constitute alcohol rectification process... Such a rectification unit has another huge "plus" - in parallel with the task of obtaining rectified alcohol, it also solves the problem of purifying it from impurities that have a boiling point different from alcohol (see the table in the article Physics - Simple distillation).

Going beyond our goal of obtaining alcohol, any substance can be isolated in its pure form with the help of a rectification column (this will be especially easy if you know its boiling point). For example, distilling an infusion of spruce needles, you can try to isolate the component that controls the smell of needles, or from the infusion of rose petals, isolate the substance responsible for this floral smell. From a moonshiner to a perfumer, one step; o).

In fact, rectification columns are of different types and sometimes have a very complex structure. A deeper description of the physical and technological aspects of rectification can be found on the website of one of the oldest manufacturers

With any rectification, the temperature during home brewing is maintained within certain limits. Likewise, Water for stirring granulated sugar, and especially yeast, must be taken warm. If the yeast is dry, it is necessary to "revive". First, stir in water with a temperature not higher than 35 and not lower than 25 degrees, add a little sugar and let stand until foam forms. Then pour into a container. do not need it. The mash fermentation takes place at room temperature.

About the temperature required for distillation

• In home brewing, it is very important not to overdo it with the temperature during distillation. The boiling point of water is 100 degrees, alcohol begins to evaporate intensively a little earlier. If you do the distillation of boiling mash, then the moonshine at the exit will become cloudy.
• Moreover, it will drop sharply. All harmful impurities from the wash will get into it. A thermometer in the lid of the distillation cube will allow you to control the process. The optimum distillation temperature is 79 - 82 degrees Celsius.
• But already at 65 degrees of heating, the evaporation of light alcohols and ethers begins. This is the "head" of moonshine or "pervach" - the first liter (if the container with home brew is at least 25 - 30 liters). Drinking it is harmful due to the presence of ethers in it. And the temperature of 78 degrees "makes" ethyl alcohol to evaporate.
• It is collected in a separate vessel. The heating of the mash is reduced so that it does not boil. Then they bring it on low heat until the temperature rises again to 78. And the distillation is continued further. The exact boiling point of alcohol (100% ethanol) is 78.39 degrees. 96% of the rectified liquor boils a little earlier (78.15).

Cooling alcohol vapors

If there is no thermometer

If there is no thermometer, then the strength of the outgoing moonshine is determined by setting it on fire. Dripping a little onto a wooden surface and lighting it. A bluish flame (and almost invisible) indicates the high strength of the drink. A faint light of yellowish color indicates already 38 - 40% alcohol content. After burnout, an oily film, iridescent in the light, remains - these are fusel oils. The amount of this residue indicates the strength of the drink. Do not completely expel alcohol from the mash. If you need a "tail", that is, the moonshine is already cloudy, then it is heated over 85 degrees. If this is not needed, then you can add this residue to the next container with a new portion of the mash. The fortress in that will increase slightly. After distillation, about a quarter of the alcohol remains in the wash after distillation.

About heaters

Now let's talk about heaters for a distillation cube or other capacity. It is best to use a gas stove, on which the boiling point of the mash is easiest to regulate. The hotplate or induction oven does not allow smooth heating changes. As a last resort, a fire will do. The tank with the mash is first heated over full fire. If there is no thermometer, then the main thing in this process is not to miss the start of the hiss of the mash. Reduce heat sharply to avoid boiling. Soon, the first drops of moonshine will appear at the exit of the coil. As the container is filled, the trickle of the alcoholic beverage is monitored. If it turns into a series of drops, then the heating is slightly increased. During the rectification process, the smell of alcohol is released. The temperature regime in the distillation cube should be maintained within 76 - 82 degrees. After a while, the concentration of alcohol in the wash decreases. The process should take as long as possible. The highest quality of moonshine is achieved with the distillation of the mash at 80 degrees of heating.

About the sump

There are many varieties of devices for home brewing. For some, a sump for fusel oils is cut into the hose between the distillation cube and the coil. Their vapors are heavier than alcohol ones and settle faster. The sump in the form of a small vessel is gradually filled with harmful impurities. The higher the temperature of the mash, the faster it fills. But some of the harmful impurities still reach the exit.

Under normal atmospheric pressure, the boiling point of alcohol is 78.3 ° C (for ethanol). It should be borne in mind that this temperature always remains unchanged, even in the case when the heat supply is carried out continuously. This feature of the process is explained by the fact that the transformation of a liquid substance into vapor also occurs when a certain temperature value, fixed for a given substance, is reached - the heat of evaporation.

With an increase in molecular weight, the boiling point of alcohol rises, while the proportion is reversed for alcohols that are close in a row, starting from ethyl. Numerically, its value is much higher than that of ethers or hydrocarbons, which have the same molecular weight. Accordingly, this pattern applies to derivatives of these substances. This property is explained by the presence of molecular association in alcohols due to the presence of hydroxyl groups in the composition.

The boiling point of alcohol is largely determined by its chemical structure. There is such a universal pattern: the more the composition of alcohol differs from the classical structure, the lower its boiling point.

When comparing the boiling points of various alcohols with the boiling points of their derivatives, a unique regularity is revealed - alcohols are practically abnormal in magnitude, very

The dependence of the boiling point on the value of the molecular weight of a particular alcohol is more natural. For example, the boiling point is 78.15 ° C with a molecular weight of 46.069 amu. e. m. At the same time, similar indicators for methyl are respectively 64.7 ° C and 32.04 a. e. m. The same pattern is typical for all alcohols.

Hydrolysis of alcohol, as a rule, is carried out when it reaches it, this is a rather long process, lasting about ten hours.

Such a parameter as the combustion temperature of alcohol largely determines the breadth of application of these compounds in industry and everyday life. However, here one should take into account such an aspect as the type of combustion. classified into four groups. The first type includes all combustion processes that occur due to the incoming oxygen contained in the ambient air. It includes the reactions of burning oil, as well as alcohol. This process is expressed by the following formula: C2H5OH + 3O2 + 11.3 N2 \u003d 2CO2 + 3H2O + 11.3N2.

Investigating this formula, it should be borne in mind that it does not fully reflect all chemical transformations that occur with substances participating in the combustion reaction. The formula is made on the basis that air consists only of oxygen and nitrogen, the presence of inert gases in it is taken to be zero.

The parameter we are considering - the boiling point of alcohol - determines its versatile use. This use is best known to us as the use of alcohols as combustible materials and a constituent substance of various types of motor fuels. For these purposes, as a rule, methanol, ethanol and butanol are used, which are produced worldwide on an industrial scale. Such production volumes are due to their commercial availability and high market conditions; moreover, in some cases these industries are used as criteria for indicators of the state's technological level. Separate technological areas are the production of biodiesel, solvents, paints and many other products, which are simply impossible to list in one small article.

We come across the concept of "alcohol", "alcohol solution" for the first time in school years, when we set up experiments in chemistry lessons. But over time, the knowledge gained during the period of study "evaporates" due to the lack of the possibility of application in practice.

Meanwhile, some of this school knowledge may come in handy. So the freezing and boiling point is useful for anyone who wants to learn how to distinguish high-quality vodka from fakes, as well as ... motorists. Let's talk about this in more detail.

In most cases, when we talk about alcohol, we mean ethyl alcohol - the same type that is used in the production of alcohol. Its characteristics are freezing point and boiling point. So, if we take into account pure ethyl alcohol, it will freeze at a very low temperature: -110 ° C.

What does "freeze" mean? If we go to the languages \u200b\u200bof chemistry, it means “ will go from liquid to solid". The freezing point is also called the melting point. Of course, it is impossible to achieve such values \u200b\u200bin a domestic environment.

Why sometimes, after taking out a bottle of vodka, long forgotten there, from the freezer, we are surprised to find pieces of ice in it?

Water-alcohol solution

The fact is that vodka is not pure alcohol, but is a solution of water, in which there is a fraction of alcohol. The freezing point changes depending on what this fraction is.

The "spread" of values \u200b\u200bat which vodka undergoes crystallization is from -27 ° C to -34 ° C. These are approximate figures. The more ethanol in vodka, the lower the limit will be when it can transform from liquid alcohol into, so to speak, "alcoholic ice cream".

The following is interesting: the freezing process proceeds gradually, vodka thickens, turning into a kind of jelly, and only after that, if the temperature does not change, it becomes solid. And it almost never freezes entirely.

Cause: first, particles of water change their characteristics - they become small pieces of ice. The concentration of alcohol in the bottle becomes higher, so the solution now needs a lower temperature to become ice.

It is unlikely that conditions can be created in the refrigerator when the degree drops to -33 or -40. It is simply technically impossible in everyday life, even if the freezer is working properly. Therefore, you are unlikely to observe the complete transformation into ice, but pieces of ice in a bottle are quite likely.

Freezing table of water-alcohol solution

Do you have anything to add to our article? We are ready to post your comments on the topic - they will be useful for everyone. Write, we will share our knowledge!

To understand alcohol rectification Consider the main properties of absolute 100% ethyl alcohol:
- boiling point \u003d 78.3 ° C at 760 mm Hg
- liquid density \u003d 790 kg / m3 at 20 ° С

It is known that ethyl alcohol is perfectly soluble in water, forming a binary water-alcohol mixture with any amount of alcohol. Here it is necessary to indicate the difference between the mass and volume concentration of ethanol in a water-alcohol solution. The mass concentration of alcohol is the mass of alcohol in the mass of the solution (denoted as g / g or% mass).

The concept of volumetric concentration is most often used - this is the volume of alcohol in the volume of the mixture (denoted as ml / ml or% vol.). Due to the significant difference in the density of alcohol (0.79 g / ml) and water (1 g / ml), the values \u200b\u200bof volumetric and mass concentrations can differ significantly. Hereinafter, we will only use the concept of volumetric concentration.

It is clear that the boiling point of a solution of two liquids should be between their individual boiling points - 100 ° C for water and 78.3 ° C for ethyl alcohol (at 760 mm Hg). The dependence of the boiling point (vaporization) of this solution, or, which is the same, the temperature of saturated water-alcohol vapor on the concentration of alcohol in the vapor is shown in Fig. one.

Point A with a concentration of 96.4% and a boiling point less than the boiling point of 100% ethyl alcohol deserves special attention in this graph.

Processes distillation and rectification of ethanol explain by the phase equilibrium curve of a binary water-alcohol mixture (see Fig. 2).

It can be seen from the diagram that practically the entire equilibrium curve is above the diagonal Y \u003d X, that is, upon evaporation of an aqueous-alcoholic solution, the concentration of alcohol in the vapor is greater than in the original liquid. This is what underlies the processes of distillation and rectification of ethanol.

Of great importance is the point (A, X \u003d Y \u003d 97.2% by volume) of the intersection of the phase equilibrium curve with the diagonal. This is a special "azeotrope point" - an inseparably boiling liquid mixture of two pure components, which cannot be separated into components by distillation or rectification. The water-alcohol mixture as close as possible to the azeotrope point is called rectified alcohol.

Using the equilibrium curve and the Y \u003d X diagonal (see Fig. 2), you can see that a simple distillation of a 10% mash first produces moonshine with a concentration of about 53% vol. Further, after step 10-53, you can build the following ones - 53-82, 82-88, 88-92, etc. The vertical component of the step shows an increase in the percentage of ethanol in the vapor phase until the onset of phase equilibrium (point A). The horizontal component of the step shows the condensation of these vapors (the point of intersection of the horizontal with the diagonal Y \u003d X). The diagram shows that in order to obtain rectified alcohol from the mash with an initial concentration of 10%, theoretically, more than a dozen of such successive distillations should take place. In practice, there should be much more of them, so as the concentration of alcohol in the distillation still decreases, the concentration of the distillate decreases accordingly. For example, on the first step, 53% vol. corresponds only to the initial moment of distillation. After some time, the concentration of alcohol in the brew decreases and we already have less than 10% alcohol in it, as a result of which, by the end of the first distillation, the selected moonshine has an average strength of not 53% vol., But 35-40% vol.

It should be noted that the boiling point of ethanol depends on atmospheric pressure (see Fig. 3). Moreover, this dependence is quite significant for the rectification process, when every tenth of a degree matters.

In a very, very simplified formulation, the "steps" of individual distillations described above, but carried out not separately, but collected together in one apparatus, constitute the process of alcohol rectification. Such a rectification unit has one more additional "plus" - in parallel with the task of obtaining rectified alcohol, it also solves the task of cleaning it from impurities that have a boiling point different from alcohol (see the diagram on the forum

Going beyond our goal - obtaining alcohol using a rectification column, you can isolate any substance in its pure form (it will not be difficult if you know its boiling point). For example, distilling an infusion of pine needles, you can try to isolate the component that controls the smell of needles, or from the infusion of violet petals, isolate the substance responsible for this floral smell. One step from a moonshiner to a perfumer