Purpose and characteristics of the rectification process. Description of the rectification process. B) chemical processing of raw alcohol

Alcohols have firmly 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 distillation a second time. In fact, this is a multiple run 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 alcohol is. The word was borrowed from the Latin language and means "spirit". If all normal conditions are maintained, it will be a colorless, transparent liquid with a sharp taste and a characteristic aroma. Pure alcohol will be strong in the range from 95.6 to 100%.

Mankind has been familiar with alcoholic beverages for a long time, as with the fermented juice of natural berries and fruits. Then it was drinks with a low alcohol content. But with the development of chemical knowledge, people received more and more strong drinks. But only at the very end of the 18th century they were able to get 100% rectified alcohol. The author of the invention was the Russian chemist T. E. Lovitz.

What is rectification

The word came into our language from the Latin language and means correction, straightening. This is one of the methods used in industry, laboratories or at home to separate liquids mixed with each other.

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

In the process of meeting the flows, the ascending vapor flow absorbs all the volatile components, and the flowing liquid absorbs the less volatile ones. As in the process of distillation - another process for obtaining alcohol - the energy costs of rectification are the same, but the extraction of the desired component (in our case, alcohol) is much more efficient. That's what rectification is.

In order for the liquid and vapor to interact more successfully, contact elements are used in the installations - plates or nozzles. They increase the efficiency and area of interaction of two oncoming flows. The principle of their operation is as follows: upward steam passes through the contact element and the liquid accumulated on it, exchanging mass and heat more intensively. The more elements are installed in the design, the faster the equilibrium between the vapor and liquid fraction will be achieved.

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

The difference between rectification and distillation

difference	Distillation	Alcohol rectification
The resulting strength of the drink	Depends on the number of distillations and the quality of the apparatus, it can vary from 40 to 65 vol.	Can reach 96 rpm.
Drink quality	The aroma and aftertaste of the used raw materials are preserved.	Rectified alcohol, without other impurities.
Obtaining pure fractions	Extremely poor separation quality, the substances are mixed, and there is no way to fix this.	If substances are contained that boil at different temperatures, then they will be clean at the exit.
Removal of substances harmful to health	A minimum of two distillations is required for the qualitative removal of fusel oils.	If all technologies are observed, they are removed completely.
Alcohol losses	Even if you follow all the rules, only 80% of the total will be extracted.	Virtually lossless. Only 1 to 3% can be lost.
Explosion and fire hazard	The device is quite simple, but the risk is still there.	The equipment is quite complex, and if a mistake is made, an explosion is possible.

Equipment for rectification

Two types of equipment can be used for this process: continuous and batch plant. The first type is used in industry, since automation is used to regulate the work - expensive and complex. For laboratories, the second, simpler and cheaper type of equipment is used. It is equipped with elementary means for adjusting the selection - a thermometer and a manometric meter for pressure changes on the column.

The structure of the distillation column

The classic scheme looks like this. A vertical column is installed on the evaporation cube (it is also called a tsarga) and a reflux condenser with a limit switch. Such an installation does not require complex mechanisms, only a tap for sampling, 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 will be the mass and heat transfer of the two flows. And the rectification of alcohol will be better.

How the column works

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

It is important to know: you should never close two fittings (rectificate extraction and water supply) at the same time, because of this the column can simply explode under the influence of the resulting excess pressure!

The heater brings the liquid poured into the cube to a boil, and the resulting steam rises. Then, once in the dephlegmator, it condenses and flows down the walls, again in contact with the new steam rising up. It hits 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. At the bottom - from high (fusel oils). Now they can be selected.

Equilibrium is determined by maintaining the temperature for 10 minutes. Until this moment, the device does not need to be touched.

Column selection unit

What is a selection node? Most often, this is a small side that slows down, preventing phlegm (liquid condensed from steam) from draining. 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 stay on the side flows further down to repeat the cycle again. IN industrial plants you can set the ratio between rectified and phlegm, which returns (reflux number) with a tap. The purity and percentage of alcohol depend on this number. The higher it is, the purer the alcohol.

It happens that such an unpleasant phenomenon occurs as the choking of a distillation column. The information that this happened is shown by a strong gurgling type noise inside the structure itself. There may be several reasons why the choke occurred, consider them.

When the column is choking

The maximum speed of steam in each design is different. When it is reached, the phlegm slows down its movement in the cube, and then it can stop altogether. Its accumulation in the distillation part causes the process of heat and mass transfer to stop. The result is a pressure drop (often very sharp) and the appearance of extraneous noise.

Causes of "choke":

most often it is heating above the permissible;
overflowing the cube or clogging it with particles of an alcohol-containing composition;
in the highlands, the main reason is low atmospheric pressure;
a power surge, due to which the power of the heating element increases;
defects and design errors.

Now you know what rectification is. The alcohol obtained as a result of this process has a harsh taste (the so-called industrial alcohol). It can be used for technical purposes, but for Food Industry it will still need to be refined - diluted, filtered and insisted.

For better purification, the resulting raw material is subjected to a carbonization process (passing through Activated carbon). As a result of this procedure, the alcohol will acquire "softness", and (a small amount of them always ends up in alcohol, even if you used the fractional selection process) will be bound by carbon. In fact, this is a classic procedure for making the famous Russian vodka.

After carrying out the dilution and carbonation procedures, the drink must be given a rest. Just leave it for a few days in a glass container. Vodka will go softer, and if you don’t sort it out, then there will be no hangover.

IN modern world not infrequently, methods are used to extract individual elements from multicomponent mixtures, which can subsequently be used for industrial and many other purposes. The rectification process is one of the most efficient. Many use it for home production alcoholic products.

Rectification is a procedure for separating mixtures of a multicomponent type into individual elements. The separation is carried out due to the fact that a countercurrent exchange of mass and heat appears between the vapor and liquid. The rectification process can be carried out continuously and from time to time.

In order to be able to carry out rectification, it is necessary to have specialized equipment. It can be represented by a distillation column. It is an equipment that is very often used in industry and at home in the manufacture of highly purified alcohol for the production of alcoholic beverages or medical preparations. Also, with the help of distillation columns, you can get gasoline and other types of fuel.

A distillation column is a vertical type vessel with a constant or variable cross section. Inside this cylinder there are special auxiliary units and devices for the exchange of mass and temperature in order to be able to separate multicomponent liquids into separate fractions for their subsequent use. In the column, all separated components have a temperature close to the boiling point.

The most common column for carrying out the distillation process is a cylindrical vessel, which has built-in contact devices. They are represented by various plates and nozzles. It also has auxiliary nodes, the activity of which is aimed at leading or distributing liquid and vapor inside the vessel in the right way, so that a quality product is obtained at the output.

In the modern world, rectification is used various kinds multicomponent liquids to isolate from them the elements necessary for further use. Rectification of alcohol is quite common.

This process consists of several stages:

First of all, it is necessary to bring to a boil the liquid, which, along with other substances, contains alcohol.
After that, the vapors of the heated liquid rise up the column. They accumulate in the dephlegmator.
After that, the dephlegmator is cooled down.
After the cooling process, condensate forms on the surface of the reflux condenser.
Drops of condensate flow down the column.
At the bottom of the column, all drops of condensate accumulate in a special nozzle.
The nozzle lifts them back up.
As a result, liquid accumulates in the upper part of the column, which is easily subjected to boiling. Part of it accumulates in the condenser, and the other part enters the receiving tank.

In the modern world, oil rectification is used to obtain certain types of fuel. This process consumes a lot of time and energy. As a result, it is possible to get gasoline or gas at the output. This process is also carried out in distillation columns, which are larger than household ones. Their principle of operation is similar. The stages of oil rectification are the same as in the rectification of sprit-containing liquids. Only at the output are formed certain types fuel.

Rectification of benzene has found wide application at coke production enterprises.

In this case, substances such as:

pure benzene,
tluene,
xylene.

In the modern world, there are three types of rectification.

They are represented by the following types:

Simple rectification.

This procedure is typical for cases where a tray distillation column is used. As a result of thermal and mass exchange of vapors, a purified liquid of the desired type is obtained at the outlet.

Steam circular rectification.

This fork is based on the use of distillation columns, which operate on the principle of circulating water vapor. In this case, impurities are distributed differently between the liquid substrate and vapors.

This type of rectification is suitable for isolating desired element from raw materials, which in its composition has a minimum amount of non-aromatic hydrocarbons.

All these methods are aimed at isolating certain substances necessary for further use from liquids consisting of many components. Their choice depends on the type of distillation column and on the raw material that needs to be divided into fractions and the desired substance is isolated.

Table 1. Boiling point of a water-alcohol mixture.

Boiling point of the mixture (0 C)	Alcohol content mixed (0)	Alcohol content in pairs (0)
100	0	0
98,75	1	13
97,50	2	28
95	5	42
93,75	7	50
92,50	10	55
91,25	12	61
90	15	66
88,75	18	68
87,50	20	71
85	30	78
83,75	40	82

Table 2. The yield of alcohol and vodka from one kilogram of raw materials.

Type of raw material	Yield spiritaliter/kg	Vodka yield 40 0 liter/kg
Potato	0,11-0,18	0,35
Rye	0,4-0,43	0,88
Wheat	0,433	0,92
Rice	0,587	1,247
oats	0,358	0,895
Peas	0,408	0,767
Millet	0,413	0,876
Starch	0,716	1,521
acorns	0,25	0,558
Beet	0,082-0,12	0,212
Grape	0,09-0,14	0,247
Apples	0,064	0,138
Pears	0,052-0,10	0,165
Barley	0,344	0,724
Buckwheat	0,473	1,004
Cherry	0,045-0,06	0,121
Sugar	0,511	1,080
Chestnut	0,258	0,572

The purpose of the article is to analyze the theoretical and some practical aspects of the work of a home distillation column aimed at obtaining ethyl alcohol, as well as dispel the most common myths on the Internet and clarify the points that equipment sellers are “silent about”.

Alcohol rectification– separation of a multicomponent alcohol-containing mixture into pure fractions (ethyl and methyl alcohols, water, fusel oils, aldehydes, and others) having different boiling points by repeated evaporation of the liquid and condensation of steam on contact devices (plates or nozzles) in special counterflow tower apparatuses.

From a physical point of view, rectification is possible, since initially the concentration of individual components of the mixture in the vapor and liquid phases is different, but the system tends to equilibrium - the same pressure, temperature and concentration of all substances in each phase. Upon contact with a liquid, the vapor is enriched with volatile (low-boiling) components, while the liquid, in turn, is enriched with low-volatile (high-boiling) components. Simultaneously with enrichment, heat exchange takes place.

circuit diagram

The moment of contact (interaction of flows) between vapor and liquid is called the process of heat and mass transfer.

Due to the different directions of movements (steam rises, and the liquid flows down), after the system reaches equilibrium in the upper part of the distillation column, it is possible to separately select practically pure components that were part of the mixture. First, substances with a lower boiling point (aldehydes, esters and alcohols) come out, then with a high one (fusel oils).

A state of balance. Appears at the very boundary of the phase separation. This can only be achieved if two conditions are met simultaneously:

Equal pressure of each individual component of the mixture.
The temperature and concentration of substances in both phases (vapor and liquid) is the same.

The more often the system comes into equilibrium, the more efficient the heat and mass transfer and the separation of the mixture into individual components.

Difference between distillation and rectification

As you can see in the graph, from a 10% alcohol solution (mash) you can get 40% moonshine, and during the second distillation of this mixture, a 60-degree distillate will come out, and during the third - 70%. The following intervals are possible: 10-40; 40-60; 60-70; 70-75 and so on up to a maximum of 96%.

Theoretically, to get pure alcohol, 9-10 successive distillations are required on a moonshine still. In practice, distillation of alcohol-containing liquids with a concentration above 20-30% is explosive, moreover, due to the high energy and time costs, it is economically unprofitable.

From this point of view, the rectification of alcohol is a minimum of 9-10 simultaneous, stepwise distillations that occur on different contact elements of the column (packings or plates) along the entire height.

difference	Distillation	Rectification
Organoleptics of the drink	Keeps aroma and taste of initial raw materials.	It turns out pure alcohol without smell and taste (the problem has a solution).
Fortress at the exit	Depends on the number of distillations and the design of the apparatus (usually 40-65%).	Up to 96%.
The degree of separation into fractions	Low, substances even with different boiling points are mixed, it is impossible to fix this.	High, pure substances can be isolated (only with different boiling points).
Ability to remove harmful substances	Low or medium. To improve the quality, a minimum of two distillations with separation into fractions in at least one of them is required.	high, at right approach all harmful substances are removed.
Alcohol loss	High. Even with the right approach, you can extract up to 80% of the total amount, while maintaining an acceptable quality.	Low. Theoretically, it is possible to extract all the ethyl alcohol without loss of quality. In practice, at least 1-3% losses.
The complexity of the technology for implementation at home	Low and medium. Even the most primitive apparatus with a coil is suitable. Equipment improvements are possible. The technology of distillation is simple and clear. A moonshine still does not usually take up much space in working order.	High. Special equipment is required, which is impossible to manufacture without knowledge and experience. The process is more difficult to understand, preliminary at least theoretical preparation is needed. The column takes up more space (especially in height).
Danger (compared to each other), both processes are flammable and explosive.	Due to the simplicity of the moonshine still, distillation is somewhat safer (subjective opinion of the author of the article).	Because of complex equipment, when working with which there is a risk of making more mistakes, rectification is more dangerous.

Operation of the distillation column

Distillation column- a device designed to separate a multicomponent liquid mixture into separate fractions according to the boiling point. It is a cylinder of constant or variable section, inside which there are contact elements - plates or nozzles.

Also, almost every column has auxiliary units for supplying the initial mixture (raw alcohol), controlling the rectification process (thermometers, automation) and distillate extraction - a module in which the vapor of a certain substance extracted from the system is condensed and then taken out.

One of the most common home designs

Raw alcohol- a product of the distillation of mash by the classical distillation method, which can be "filled" into a distillation column. In fact, this is moonshine with a strength of 35-45 degrees.

Reflux- steam condensed in the dephlegmator, flowing down the walls of the column.

Phlegm number- the ratio of the amount of reflux to the mass of the sampled distillate. There are three streams in the alcohol distillation column: steam, phlegm and distillate ( final goal). At the beginning of the process, the distillate is not withdrawn so that there is enough reflux in the column for heat and mass transfer. Then part of the alcohol vapor is condensed and taken from the column, and the remaining alcohol vapor continues to create a reflux flow, ensuring normal operation.

For the operation of most installations, the reflux ratio must be at least 3, that is, 25% of the distillate is taken, the rest is needed in the column for irrigating the contact elements. General rule: The slower the alcohol is withdrawn, the higher the quality.

Distillation column contact devices (trays and packings)

They are responsible for the multiple and simultaneous separation of the mixture into liquid and vapor, followed by the condensation of vapor into a liquid - the achievement of an equilibrium state in the column. Ceteris paribus, the more contact devices in the design, the more effective distillation in terms of alcohol purification, since the surface of interaction of phases increases, which intensifies the entire heat and mass transfer.

theoretical plate- one cycle of exit from the equilibrium state with its repeated achievement. To obtain high-quality alcohol, a minimum of 25-30 theoretical plates is required.

physical plate- a real working device. The vapor passes through the liquid layer in the plate in the form of many bubbles, creating an extensive contact surface. In the classical design, the physical plate provides about half of the conditions for reaching one equilibrium state. Therefore, for the normal operation of the distillation column, two times more physical plates are required than the theoretical (calculated) minimum - 50-60 pieces.

Nozzles. Often, plates are placed only on industrial installations. In laboratory and home distillation columns, nozzles are used as contact elements - specially twisted copper (or steel) wire or dishwashing nets. In this case, the phlegm flows down in a thin stream over the entire surface of the nozzle, providing the maximum contact area with steam.

Washcloth nozzles are the most practical

There are a lot of structures. The disadvantage of home-made wire nozzles is the possible damage to the material (blackening, rust), factory counterparts are devoid of such problems.

Properties of distillation column

Material and dimensions. The column cylinder, nozzles, cube and distillers must be made of a food-grade, stainless, heat-safe (expands evenly) alloy. In home-made designs, cans and pressure cookers are most often used as a cube.

The minimum length of the pipe of a home distillation column is 120-150 cm, diameter is 30-40 mm.

heating system. In the process of rectification, it is very important to control and quickly adjust the heating power. Therefore, the most successful solution is heating with the help of heating elements built into the bottom of the cube. The supply of heat through a gas stove is not recommended, because it does not allow you to quickly change the temperature range (high inertia of the system).

Process control. During rectification, it is important to follow the instructions of the column manufacturer, which must indicate the features of operation, heating power, reflux ratio and model performance.

The thermometer allows precise control of the sampling process

It is very difficult to control the rectification process without two simple devices - a thermometer (helps determine the correct degree of heating) and an alcohol meter (measures the strength of the resulting alcohol).

Performance. It does not depend on the size of the column, since the higher the side (pipe), the more physical plates are inside, therefore, the cleaning is better. The performance is affected by the heating power, which determines the speed of steam and reflux flows. But with an excess of supplied power, the column chokes (stops working).

The average performance of home distillation columns is 1 liter per hour with a heating power of 1 kW.

Influence of pressure. The boiling point of liquids depends on pressure. For successful distillation of alcohol, the pressure at the top of the column should be close to atmospheric - 720-780 mm Hg. Otherwise, when the pressure decreases, the vapor density will decrease and the evaporation rate will increase, which may cause flooding of the column. If the pressure is too high, the evaporation rate drops, making the operation of the device inefficient (there is no separation of the mixture into fractions). To maintain the correct pressure, each distillation column is equipped with an atmospheric connection tube.

About the possibility of self-made assembly. Theoretically, a distillation column is not very complex device. Designs are successfully implemented by craftsmen at home.

But in practice, without understanding the physical foundations of the rectification process, correct calculations of equipment parameters, selection of materials and high-quality assembly of units, the use of a home-made distillation column turns into a dangerous occupation. Even one mistake can lead to fire, explosion or burns.

In terms of safety, factory columns that have been tested (have supporting documentation) are more reliable, and they are also supplied with instructions (must be detailed). The risk of a critical situation comes down to only two factors - proper assembly and operation according to the instructions, but this is a problem for almost all household appliances, and not just columns or moonshine stills.

The principle of operation of the distillation column

The cube is filled with a maximum of 2/3 of the volume. Before turning on the installation, it is imperative to check the tightness of the connections and assemblies, shut off the distillate extraction unit and supply cooling water. Only after that you can start heating the cube.

The optimal strength of the alcohol-containing mixture fed into the column is 35-45%. That is, in any case, distillation of the mash is required before rectification. The resulting product (raw alcohol) is then processed on a column, obtaining almost pure alcohol.

This means that a home distillation column is not a complete replacement for the classic moonshine still (distiller) and can only be considered as an additional purification step that replaces re-distillation (second distillation) in a better quality, but leveling the organoleptic properties of the drink.

In fairness, I note that most modern models distillation columns suggest working in the moonshine still mode. To proceed to distillation, it is only necessary to close the connection to the atmosphere and open the distillate selection unit.

If both nozzles are closed at the same time, then the heated column may explode due to excess pressure! Don't make these mistakes!

In continuous industrial plants, mash is often distilled immediately, but this is possible due to its gigantic size and design features. For example, a pipe 80 meters high and 6 meters in diameter is considered a standard, in which many more contact elements are installed than on distillation columns for a house.

Size matters. The possibilities of distilleries in terms of cleaning the cube are greater than with home distillation

After switching on, the liquid in the cube is brought to a boil by the heater. The resulting steam rises up the column, then enters the reflux condenser, where it condenses (phlegm appears) and returns in liquid form to the lower part of the column along the pipe walls, on the way back contacting the rising steam on plates or nozzles. Under the action of the heater, the phlegm again becomes steam, and the steam at the top is again condensed by a dephlegmator. The process becomes cyclic, both streams are in continuous contact with each other.

After stabilization (steam and phlegm are sufficient for an equilibrium state), pure (separated) fractions with the lowest boiling point (methyl alcohol, acetaldehyde, ethers, ethyl alcohol) accumulate in the upper part of the column, with the highest (fusel oils) at the bottom. As the selection of the lower fractions gradually rise up the column.

In most cases, a column is considered stable (it is possible to start sampling) in which the temperature does not change for 10 minutes ( total time warm-up - 20-60 minutes). Up to this point, the device works "on its own", creating flows of steam and phlegm that tend to balance. After stabilization, the selection of the head fraction containing harmful substances begins: esters, aldehydes and methyl alcohol.

The distillation column does not eliminate the need to separate the output into fractions. As in the case of a conventional moonshine still, you have to assemble the “head”, “body” and “tail”. The difference is only in the purity of the output. During rectification, the fractions are not “lubricated” - substances with a close, but at least a tenth of a degree, different boiling point do not intersect, therefore, when the “body” is selected, almost pure alcohol is obtained. During conventional distillation, it is physically impossible to separate the yield into fractions consisting of only one substance, no matter what design is used.

If the column is brought to the optimal mode of operation, then there are no difficulties during the selection of the “body”, since the temperature is stable all the time.

The lower fractions (“tails”) are selected during rectification, guided by temperature or smell, but unlike distillation, these substances do not contain alcohol.

Return to alcohol of organoleptic properties. Often, "tails" are required to return the "soul" to rectified alcohol - the aroma and taste of the raw material, for example, apples or grapes. After the process is completed, a certain amount of collected tail fractions is added to pure alcohol. The concentration is calculated empirically by experimenting on a small amount of product.

The advantage of rectification is the ability to extract almost all the alcohol contained in the liquid without losing its quality. This means that the “heads” and “tails” obtained on a moonshine still can be processed on a distillation column and ethyl alcohol safe for health can be obtained.

Flooding of distillation column

Each design has a maximum speed of steam movement, after which the flow of reflux in the cube first slows down, and then stops altogether. The liquid accumulates in the distillation part of the column and "flooding" occurs - the termination of the heat and mass transfer process. Inside there is a sharp pressure drop, extraneous noise or gurgling appears.

Causes of flooding of the distillation column:

exceeding the permissible heating power (most common);
clogging the bottom of the device and overflowing the cube;
very low atmospheric pressure (typical for high mountains);
the voltage in the network is higher than 220V - as a result, the power of the heating elements increases;
design errors and failures.

The principle of the rectification process.

The device of distillation columns.

Causes of damage to distillation columns and measures to prevent them.

Fire hazard of distillation plants. Fire prevention measures.

Question 1. The principle of rectification

The processes of distillation of solutions, in other words, the separation of solutions into their constituent components, are very common in modern technology.

For example, the separation of natural petroleum hydrocarbons in order to obtain motor fuels and lubricating oils.

Separation of individual gases from their mixtures occurs by their preliminary liquefaction with subsequent distillation of the liquid mixture.

The vast majority of flammable liquids and liquid liquids (alcohol, acetone, acetic acid, benzene and its homologues, gasoline, kerosene and many other products) are also obtained using distillation processes.

Distinguish between simple distillation and rectification.

Simple distillation is the process of partial evaporation of a solution and complete condensation of the resulting vapors.

Rectification is the process of separating liquid homogeneous mixtures into their constituent components as a result of repeated countercurrent interaction of vapor with liquid.

According to According to Konovalov's first law, the vapor is enriched with that component, the addition of which to the liquid increases the vapor pressure above it or lowers the boiling point.

Ideal mixtures obey Raoult's law, according to which the partial pressure of a component in a system is equal to the vapor pressure of a pure component multiplied by its mole fraction in solution:P partz =P pair m

And according to Dalton's law, the partial pressure of a component in a gas mixture is equal to the total pressure multiplied by the mole fraction of this component in the mixture:P partz =P common m

Schematically, the rectification process can be represented as follows.

Where m 1 , m 2 , m 3 - the amount of the mixture received for rectification, the resulting distillate and the remaining residue;

X 1 , X 2 , X 3 is the content (mole fraction) of the volatile component in them, respectively.

Question 2. The device of distillation plants

So, rectification is the process of separating liquid homogeneous mixtures into their constituent components as a result of repeated countercurrent interaction of vapor with liquid.

Rectification processes are carried out in distillation plants.

Distillation columns are classified:

by design: dish-shaped; packed.

depending on working pressure: working under vacuum; working at atmospheric pressure; working under pressure.

Cymbals Distinguish : valve; jet; sieve; cap.

Let's take a look at how the rectification process is carried out.

In the middle of the column the raw material subject to rectification arrives heated to a certain temperature.

The feed may be supplied to the column as a liquid, vapor, or a mixture of vapor and liquid.

When raw materials enter the column, a single evaporation process occurs, as a result of which vapors and a liquid of a certain composition are formed, which are in equilibrium.

To ensure rectification, it is necessary to the top of the column towards the vapors to organize the flow of liquid (phlegm, irrigation). To do this, heat is removed at the top of the column in one way or another (heat of the partial condenser). Due to this, part of the vapor rising from the upper plate is condensed, forming the necessary downward flow of liquid.

Phlegm number is the ratio of the amount of distillate (phlegm) returned to the column to the amount of distillate withdrawn as a product.

A schematic diagram of a distillation column is shown in the figure.

Receipt of raw materials

The flow of phlegm

Vapor outlet to dephlegmator

boiler

Yield of VAT residue

An ascending vapor flow must be provided at the bottom of the column. To do this, heat is supplied to the bottom of the column in one way or another (the heat of the boiler). In this case, part of the liquid flowing down from the bottom plate evaporates, forming a vapor stream.

In this mode: the lowest temperature will be at the top of the column and the highest at the bottom of the column.

The product taken from the top of the column, enriched with a low-boiling component, is called rectified (or distillate). And from the bottom of the column, the sampled product, enriched with a high-boiling component, is called residue or bottom (bottom) product.

The part of the column where the raw material is introduced is called feeding section or evaporative space. Part of the distillation column located above the input of raw materials - upper, concentration or firming, and below the input of raw materials - lower, distant or exhaustive .

The same distillation process takes place in both parts of the column.

This figure shows a diagram of a simple (I) and complex (II) columns:

but - complete; b- strengthening; in - distillate; G - with the selection of additional products from above and below from the main column; d - with the selection of additional product from the top of the stripping column.

Introduction

rectification thermal reflux insulation

Rectification has been known since the beginning of the twentieth century as one of the most important technological processes mainly alcohol and oil industries. At present, rectification is increasingly used in various fields of chemical technology, where the isolation of components in a pure form is very important (in the production of organic synthesis, isotopes, polymers, semiconductors, and various other high-purity substances). Thus, the process of distillation makes it possible to solve one of the main problems of chemical technology - the isolation of target products of the required purity.

Rectification is the process of separating liquid mixtures, which is reduced to simultaneous and repeatedly repeated processes of partial evaporation and condensation of the mixture being separated on the phase contact surface. Distillation columns are designed for carrying out mass transfer processes in chemical, petrochemical industry. Depending on the diameter, column apparatuses are manufactured with various types of trays.

As well as general requirements(high intensity per unit volume of the apparatus, its cost, etc.) a number of requirements can be determined by the specifics of production: a large interval of stable operation when loads change, the ability of the plate to work in contaminated liquids, protection against corrosion, etc. Often these qualities become prevailing, determining the suitability of the design for use in each particular process.

The calculation of a distillation column is reduced to the determination of the main geometric dimensions of the diameter and height. Both parameters are largely determined by the steam and liquid loads, the type of plate, and the properties of the interacting phases.

Theoretical foundations of the rectification process

Rectification is a mass transfer process of separation of a homogeneous mixture of volatile components, carried out by countercurrent multiple interaction of vapors formed during distillation with a liquid formed during the condensation of these vapors. The separation of a liquid mixture is based on the different volatility of the substances. During rectification, the initial mixture is divided into two parts: distillate - a mixture enriched with a low-boiling component (NC), and VAT residue - a mixture enriched with a high-boiling component (HC). The rectification process is carried out in a distillation unit. The main apparatus is a distillation column, in which the vapors of the distilled liquid rise from below, and the liquid flows towards the vapors, supplied in the form of reflux to the upper part of the apparatus. The distillation process can proceed at atmospheric pressure, as well as at pressures above and below atmospheric pressure. Under vacuum, rectification is carried out when high-boiling liquid mixtures are to be separated. Elevated pressure is used to separate mixtures that are in the gaseous state at a lower pressure. Atmospheric pressure is used when separating a mixture of liquids into constituent components and the purity of the resulting distillate and distillation residue depends on how developed the phase contact surface is, on the amount of phlegm supplied for irrigation and on the device of the distillation column.

The distillation process is used to separate liquids with different boiling points by countercurrent multiple contacting of vapors and liquids. To create close contact between vapor and liquid, distillation columns are equipped with special devices - packing or distillation plates.

Packed columns are used in small-scale production and are used in cases where a low pressure drop is required. Packed columns are filled with Raschig rings made of various materials, Pal rings, hires from elements of a saddle-shaped profile (Intallox and Berl saddles).

Tray columns are widely used in refineries. Trays are distinguished by the method of transferring liquid from a tray to a tray (failure and with special transfer devices), by the nature of the movement of phases on a tray (bubbling and jet), by the design of devices for introducing steam into a liquid (contact, cap, valve, etc.). In table. 5.7 provides information on the main types of plates used in the chemical and oil refining industries.

Technological calculation of a distillation column consists of the following operations: 1) drawing up a material balance; 2) determination of pressure in the column; 3) calculation of the temperature regime (temperature of raw material inlet, top and bottom of the column, selection of side strips in complex columns); 4) determination of the reflux ratio (irrigation ratio), i.e. the ratio of the amount of reflux supplied to the top of the column to the amount of distillate; 5) compilation of heat balance; 6) definition of internal material flows; 7) calculation of the number of theoretical plates; 8) determination of the number of real (valid) plates.

For the continuous flow of the rectification process, it is necessary that the mixture entering the separation come into contact with the oncoming steam flow with a higher concentration of the hardly volatile (high-boiling) component than in the mixture. Therefore, in installations for continuous distillation (Fig. 1), the columns are made of two parts: the lower (exhaustive) and the upper (strengthening). In the exhausting part of the column, the volatile component is removed from the liquid flowing down, and in the upper part, the ascending vapors are enriched with the volatile component.

The schematic diagram of the distillation plant is shown in Figure 1:

Figure 1. - Schematic diagram of the distillation plant:

1 - container for the initial mixture; 2.9 - pumps; 3 - heat exchanger-heater; 4 - boiler; 5 - distillation column; 6 - dephlegmator; 7 - distillate cooler; 8 - container for collecting distillate; 10 - bottom liquid cooler; 11 - container for bottom liquid.

The initial mixture from the intermediate tank 1 centrifugal pump 2 fed into the heat exchanger 3 where it is heated to boiling point. The heated mixture is fed to separation in distillation column 5, where the composition of the liquid is equal to the composition of the original mixture.

Flowing down the column, the liquid interacts with the rising vapor formed during the boiling of the bottom liquid in the boiler 4. The initial composition of the steam is approximately equal to the composition of the VAT residue X W , those. depleted in a volatile component. As a result of mass exchange with the liquid, the vapor is enriched with a highly volatile component. For a more complete enrichment, the upper part of the column is irrigated in accordance with a given reflux number with a liquid (reflux) , obtained in the dephlegmator 6 by condensing the steam leaving the column. Part of the condensate is removed from the reflux condenser in the form of a finished separation product - distillate, which is cooled in the heat exchanger 7 and sent to the intermediate tank 8. From the bottom of the column by a pump 9 bottom liquid is continuously removed - a product enriched with a non-volatile component, which is cooled in a heat exchanger 10 and goes to container 11.

Thus, in the distillation column, a continuous non-equilibrium process of separation of the initial mixture into a distillate (with a high content of a volatile component) and a distillation residue (enriched with a non-volatile component) is carried out.

Rectification has been known since the beginning of the 19th century as one of the most important technological processes, mainly in the alcohol and oil industries. Currently, rectification is increasingly used in various areas of chemical technology, where the isolation of components in a pure form is very important (in the production of organic synthesis, isotopes, polymers, semiconductors, and various other high-purity substances).

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