Alcohols tightly entered our lives. And this is not only alcohol. Get it by fermentation, followed by distillation. And often people mistakenly think that rectification is a distillation a second time. In fact, this is a multiple sweep of alcohol-containing liquids in special columns. As a result of the meeting of two streams - liquid and vapor - pure alcohol is obtained. Let's look at what rectification is, in more detail.
Alcohol and its properties
But first, let's figure out what is alcohol. The word was borrowed from the Latin language and means "spirit". If all normal conditions are met, then it will be a colorless, transparent liquid with a sharp taste and characteristic aroma. Pure alcohol will be strong in the range of 95.6 to 100%.
Mankind has known alcohol for a long time, as with fermented juice of natural berries and fruits. Then these were low alcohol drinks. But with the development of chemical knowledge, people received more and more strong drinks. But only at the very end of the XVIII century were able to get 100% rectified alcohol. The author of the invention was the Russian chemist Lovitz T. E.
What is rectification?
The word came to our language from the Latin language and means correction, rectification. This is one of the methods that are used in industry, laboratories or at home to separate mixed liquids.
The rectification process is based on the difference in the distribution of mixed components between the vapor and liquid fractions. In this process, the steam flow moves towards the fluid flow, they are in contact with each other, exchanging heat and mass until equilibrium in the system. All this happens in a special device called a distillation column apparatus.
In the process of meeting streams, the upward steam stream absorbs all the volatile components, and the flowing liquid - less volatile. As in the distillation process - another process for producing alcohol - the energy costs during rectification are the same, but the extraction of the desired component (in our case, alcohol) is much more efficient. This is what rectification is.
In order for the liquid and steam to interact more successfully, the contact elements used in the plants are plates or nozzles. They increase the efficiency and area of interaction of two oncoming flows. The principle of their operation is as follows: the steam going up passes through the contact element and the liquid accumulated on it, more intensively exchanging mass and heat. The more it is installed in the design of the elements, the faster the equilibrium between the vapor and the liquid fraction will be achieved.
How distillation differs from the distillation process, we consider in the table below.
Distillation of distillation from distillation
| Difference | Distillation | Rectification of alcohol |
| The resulting beverage strength | Depends on the number of distillations and the quality of the apparatus, can vary from 40 to 65 vol. | It can reach 96 vol. |
| Drink quality | The aroma and aftertaste of the raw materials used is preserved. | Rectified alcohol, without other impurities. |
| Getting pure fractions | An extremely poor quality of separation, the substances are mixed, and there is no way to fix this. | If there are substances boiling at different temperatures, then they will be clean at the outlet. |
| Removal of harmful substances | High-quality removal of fusel oils requires at least two distillations. | If all technologies are followed, they are completely removed. |
| Alcohol losses | Even if you follow all the rules, only 80% of the total will be recovered. | Virtually lossless. Only 1 to 3% can be lost. |
| Explosion and fire hazard | The device is quite simple, but there is still a risk. | The equipment is quite complicated, and if a mistake is made, then an explosion is possible. |
Rectification Equipment
Two types of equipment can be used for this process: a unit with continuous and batch operation. The first type is used in industry, since automation is used to regulate the work - expensive and complicated. For laboratories, a second, simpler and cheaper type of equipment is used. It contains elementary means of adjusting the selection - a thermometer and a gauge measuring pressure changes on the column.
Distillation column structure
The classical scheme of a distillation column is as follows. A vertical column (also called a tsar) and a reflux condenser with a trailer are installed on the evaporation cube. Such an installation does not require complex mechanisms, only a tap for selection, a sight glass, a thermometer, and sometimes a power regulator.
It should be remembered that the greater the height of the column, the more intense the mass and heat transfer of the two flows will be . And rectification of alcohol will be better.
The principle of operation of the column
The cube is filled to a maximum of two thirds of its volume with an alcohol-containing mixture, the joints are checked for leaks, the sampling valve is closed and a cooling element (most often water) is supplied. Only now can you turn on the heating.
It is important to know: you can never close two fittings (selection of rectified and water supply) at the same time, from this the column can simply explode under the influence of the generated excess pressure!
The heater, the liquid poured into the cube, is brought to a boil, and the resulting steam rises. Then, once in the reflux condenser, it condenses and flows down the walls, again in contact with the new steam rising upward. It falls on the heater again, becomes steam, and the process repeats.
After some time, the vapor and liquid come into equilibrium, and a fraction with a low boiling point (methanol) accumulates in the upper part. In the bottom - high (fusel oils). Now they can be selected.
Equilibrium is determined by maintaining the temperature for 10 minutes. Up to this point, the device does not need to be touched.
Column Pickup Assembly
What is a selection node? Most often, this is a small side, which slows down, preventing draining, phlegm (liquid condensed from steam). If you open the tap of the selection unit, then the delayed phlegm flows into the refrigerator, turning into rectified alcohol.
The same liquid that did not linger on the side drains further down to repeat the cycle. In industrial installations, you can set the ratio between the rectified and reflux, which is returned (reflux ratio) using a crane. The purity and percentage of alcohol depends on this number. The higher it is, the cleaner the alcohol.
It happens that such an unpleasant phenomenon as a choke of a distillation column occurs. The information that this happened is shown by a strong gurgling noise inside the structure itself. There may be several reasons why there was a choke, consider them.
When the column chokes
The maximum steam speed in each design is different. When it is achieved, phlegm slows down its movement in the cube, and then it can completely stop. Its accumulation in the distillation part causes a halt in the process of heat and mass transfer. The result is a pressure drop (often very sharp) and the appearance of extraneous noise.
The reasons for the "choke" :
- most often it is heating above permissible;
- overflow of the cube or its clogging with particles of an alcohol-containing composition;
- in highlands, the main reason is low atmospheric pressure;
- a voltage surge, due to which the power of the heating element rises;
- malfunctions and design errors.
Now you know what distillation is. The alcohol obtained as a result of this process has a hard taste (the so-called technical alcohol). It can be used for technical purposes, but for the food industry it will still need to be further developed - diluted, filtered and insisted.
For better purification, the resulting raw materials are subjected to a carbohydrate process (passing through activated carbon). As a result of this procedure, alcohol will become “soft” , and fusel oils (a small amount of them always get into alcohol, even if you used the fractional selection process) will be bound by coal. In fact, this is a classic procedure for making famous Russian vodka.
After carrying out dilution and carbohydrate procedures, the drink should be given rest. Just leave it for a few days in a glass container. Vodka will go softer, and if you do not sort it out, then there will be no hangover.