What is rectification? Process description and application in industry

Alcohols tightly entered our lives. And it's not just alcohol. It is obtained by fermentation followed by distillation. And often people mistakenly think that rectification is a second distillation. In fact, this is a multiple run of alcohol-containing liquids in special columns. As a result of a meeting between two streams - fluid and steam - pure alcohol is obtained. Let's see what the rectification is, in more detail.

Alcohol and its properties

But first let's see what alcohol is. The word was borrowed from the Latin language and means "spirit." If all normal conditions are maintained, then it will be a colorless, transparent liquid with a sharp taste and characteristic aroma. Net alcohol will be strong in the range from 95.6 to 100%.

With alcoholic beverages, mankind is familiar long ago, as with fermented juice of natural berries and fruits. Then it was drinks with a low alcohol content. But with the development of chemical knowledge, people were getting more and more strong drinks. But only at the very end of the XVIII century they were able to get 100% distilled spirit. The author of the invention was the Russian chemist Lovits TE

What is rectification?

The word came into our language from the Latin language and means correction, correction. This is one of the methods that are used in industry, laboratories or at home to separate mixed fluids.

The rectification process is based on the difference in the distribution of the mixed components between the vapor and liquid fractions. In this process, the flow of steam moves towards the flow of liquid, they contact each other, exchanging heat and mass before the equilibrium in the system. All this happens in a special device, called the rectification column apparatus.

In the process of the meeting of the streams, the ascending vapor stream absorbs all volatile components, and the flowing liquid is less volatile. еще одного процесса получения спирта, — затраты энергии при ректификации одинаковы, но извлечение нужного компонента (в нашем случае спирта) гораздо эффективнее. As in the process of distillation - another process of obtaining alcohol - the energy expenditure for rectification is the same, but extracting the desired component (in our case, alcohol) is much more effective. That's what rectification is.

тарелки или насадки. In order for the liquid and vapor to interact more successfully, the units use contact elements - plates or nozzles. They increase the efficiency and area of interaction of the two counter flows. The principle of their work is as follows: steam, going up, passes through the contact element and accumulated liquid on it, more intensively exchanging mass and heat. The more will be established in the design of the elements, the faster the equilibrium between the vapor and the liquid fraction will be achieved.

How the rectification differs from the distillation process, we consider in the following table.

The difference between rectification and distillation

Equipment for rectification

Two types of equipment can be used for this process: a plant with a continuous and a periodic action. дорогая и сложная. The first type is used in industry, since automation is used to adjust the work - expensive and complex. For laboratories, a second, simpler and cheaper type of equipment is used. градусник и манометрический измеритель изменения давления на колонне. It has elementary selection controls - a thermometer and a gauge pressure gauge on the column.

The structure of the distillation column

The classical scheme of the distillation column is as follows. On the evaporative cube is installed a vertical column (also called a king) and a reflux condenser with a tailpiece. Such an installation does not require complicated mechanisms, only a tap for sampling, a sight glass, a thermometer, and sometimes a power regulator.

- и теплообмен двух потоков . It should be remembered that the higher the height of the column, the more intensive will be the mass and heat transfer of the two streams . And rectification of alcohol will be better.

Principle of operation of the column

The cube is filled with two-thirds of its volume with an alcohol-containing mixture, the joints are sealed, the tap is closed and the cooling element (most often water) is supplied. Only now you can turn on the heating.

It is important to know: it is never possible to close two fittings (rectification and water supply) simultaneously, from which the column can simply explode under the action of the excess pressure generated!

The liquid is poured into the cube by the heater, it is brought to a boil, and the steam is raised. Then, after getting into the reflux condenser, it condenses and flows down the walls, again contacting the rising steam rising up. Again it gets on the heater, it becomes steam, and the process repeats.

After a while, the vapor and liquid come into equilibrium, and a fraction with a low boiling point (methanol) accumulates in the upper part. с высокой (сивушные масла). In the lower - with high (fusel oil). Now they can be selected.

The equilibrium is determined by maintaining the temperature for 10 minutes. Until then, the device should not be touched.

Column picking assembly

What is the selection site? Most often, this is a small side, which inhibits, without letting off, phlegm (condensed from the vapor liquid). If you open the tap of the selection node, the delayed phlegm flows into the refrigerator, turning into an alcohol-rectificate.

The same fluid, which did not linger on the rim, flows down further to repeat the cycle. In industrial installations it is possible to establish the ratio between rectificate and reflux, which is returned (reflux ratio) by means of a crane. The purity and percentage of alcohol depends on this number. The higher it is, the more pure the alcohol.

It happens that such an unpleasant phenomenon occurs as the choking of the distillation column. The information that this happened shows a strong buzzing noise inside the structure itself. The reasons why there was a choking, maybe a few, consider them.

When the column chokes

Maximum speed of steam in each design is different. When it is reached, the phlegm slows down its movement in the cube, and then at all it can stop. Accumulation of it in the rectifying part causes the heat and mass transfer process to stop. перепад давления (зачастую очень резкий) и появление посторонних шумов. The result is a pressure drop (often very abrupt) and the appearance of extraneous noise.

: The reasons for "zahleba" :

• More often this heating is higher than permissible;
• Overflow of the cube or clogging it with particles of alcohol-containing composition;
• In the highlands, the main cause is low atmospheric pressure;
• A voltage jump, because of which the power of the heating element rises;
• Faults and design errors.

Now you know what rectification is. The alcohol obtained as a result of this process has a hard taste (the so-called technical alcohol). разбавлять, фильтровать и настаивать. It can be used for technical purposes, but for the food industry it will need to be further developed - dilute, filter and insist.

For better purification, the resulting raw material is subjected to the carbonation process (transmission through activated carbon). , а сивушные масла (небольшое их количество всегда попадает в спирт, даже если вы использовали процесс дробного отбора) будут связаны углем. As a result of this procedure, alcohol will acquire "softness" , and fusel oils (a small amount of them always get into alcohol, even if you used the process of fractional selection) will be connected by coal. In fact, this is a classic procedure for preparing famous Russian vodka.

After carrying out the dilution and carbonation procedures, the drink should be given a rest. Just leave it for a few days in a glass container. Vodka will go softer, and if you do not touch, then there will not be a hangover either.