CS268005B1 - Method of separation of aqueous and alcoholic mixtures - Google Patents

Abstract

The solution relates to the separation of water-alcohol mixtures, especially azeotropic mixtures by extractive rectification. Its essence lies in the fact that the extraction effect is achieved by increasing the concentration of one of the components of the separation of the mixture, for example water, fed to the top of the column. If the more volatile component does not form an azeotrope with the component fed as a feed to the top of the column, it is obtained directly in a single operation in a pure state by connecting the extractive reactivation column with a normal rectification column. If the more volatile component is immiscible or only to a limited extent miscible with the feed, the less volatile components are separated only to a greater extent and the remaining portion in the still is removed in a normal liquid extraction column, where the feed is used as the extraction agent.

Description

Separation of aqueous-alcoholic mixtures, especially azeotropic mixtures, is usually a difficult technological matter. In many cases, the azeotropic mixture can be separated by extraction between two immiscible phases and the individual components isolated by distillation of these phases. Often, the addition of another component can affect the relative volatility of the individual components so that the mixture can be separated by rectification. Depending on the nature of the added component, azeotropic rectification, extractive rectification or rectification extraction can be distinguished.

A common disadvantage of these methods is that foreign components are introduced into the separated mixture, which must be additionally isolated from the individual fractions. The complete division of the mixture into pure components therefore represents several independent operations, which adversely affects the economics of production.

These shortcomings are largely eliminated by the process for separating aqueous-alcoholic mixtures according to the invention. Its essence lies in the fact that the extraction effect is achieved by increasing the concentration of one of the components of the separation of the mixture, e.g. water, fed to the top of the column. If the more volatile component does not form an azeotrope with the component fed as a feed to the column head, the more volatile component is obtained directly in one operation in a pure state, by combining an extraction rectification column with a normal rectification column. If the more volatile component is immiscible with the feed component, only the most volatile component or components are separated in the extraction reactivation column and only the remainder in the distillate is removed in a normal liquid extraction column, where the extractant is used as the extractant. injection onto the head of the extraction rectification column.

It is essentially an extractive rectification, but instead of the additional component fed, the least volatile component of the separated mixture is fed to the top of the column, which strongly associates with the second component and entrains it as it passes through the column, so that it accumulates in the reboiler. Increasing the concentration of the least volatile component will increase the relative volatility of the third, least associated component, which leaves the column head as a distillate. If this component does not form a binary azeotrope with the additional component, it can be obtained directly in the pure state by extending the column by the enrichment part. If a binary azeotrope is formed, it must be processed separately either by extraction or by azeotropic distillation.

By not introducing another auxiliary component into the separated mixture, the cost of separating the mixture is considerably lower, since in most cases the least volatile component is water, which after gradual distillation of both components remains in the boiler and is not distilled further. If it is necessary to separate the intermediate fraction in order to separate the components sharply, this is processed together with the next batch. The process is particularly suitable for separating aqueous-alcoholic mixtures, eg an acetone-methanol-water mixture; ethyl acetate - ethanol - water, etc. The principle consists in the additional supply of water to the head or to a certain floor of the column, so that alcohol, which strongly associates with water, accumulates in the boiler, while the unassociated component or only slightly associated passes into the distillate.

CS 268005 Bl

Example 1

Separation of acetone-methanol-water mixture

The acetone-methanol-water mixture cannot be separated by direct rectification because a binary acetone-methanol azeotrope is formed. Divide this mixture by extraction rectification on a laboratory column with a diameter of 25 mm, packed with Raschiga 3 x 4 mm and a packing height of 1 m.

Place 800 ml of a mixture of %0% acetone, 14% methanol, 6% water in a 1 L distillation flask. After the column has been heated to total reflux, water is started at the top of the column at a rate of 10 ml / min and the total distillate is started at the same time. After distilling off 650 ml, the water injection is stopped and, after discarding a small intermediate fraction, methanol is distilled off at reflux. Practically pure water remains in the distillation flask. The wet acetone is then worked up on the same apparatus. 550 ml of pure acetone are obtained.

Example 2

Separation of ethyl acetate-ethanol-water

Apparatus - enamelled duplicator 250 1, equipped with a rectification column ls-150 with a Raschig glass packing with a total packing length of 2.5 m. Water is fed under the head of the column via a rotameter. The extraction is carried out with total distillate collection.

145 kg of a mixture of approximately the azeotrope composition are introduced into the duplicator. After tempering the column at total reflux, water is injected at a rate of about 54 1 / min. After about 5 minutes, the total collection of distillate begins. Gradually, the temperature in the boiler is increased so that the distillation rate is approximately constant throughout the extraction. as soon as the temperature at the top of the column starts to rise, the distillate is transferred to the second well and the water injection is stopped. The intermediate fraction and then the wet ethanol are then distilled off at reflux. 98 kg of binary ethyl acetate-water, 12.5 kg of fraction are obtained, m.p. 70.5-77 ° C and 33 kg of aqueous ethanol. The total operation time is 5.5 h. The distilled binary is easily azeotropically dewatered, which is proof of perfect extraction.

Claims (3)

OBJECT OF THE INVENTION A process for separating aqueous-alcoholic mixtures, in particular azeotropic mixtures, by extraction rectification, characterized in that the extraction effect is obtained by increasing the concentration of one of the components of the separated mixture, for example water, fed to the column head. 2. The process according to item 1, characterized in that if the more volatile component does not form an azeotrope with the component fed as a feed to the column head, the more volatile component is obtained directly in one operation in a pure state by combining an extraction reactivation column with a normal rectification column. 3. The process according to item 1, characterized in that if the more volatile component is immiscible or only to a limited extent miscible with the component fed to the column head, the extraction of the less volatile component or components is carried out in the extraction rectification column only for the most part. of the distillate is removed in a normal liquid extraction column, where the component used as feed to the head of the extraction reaction column is used as the extraction agent.