RU2648754C1 - Method of purification of the return solvent - Google Patents

Abstract

FIELD: technological processes.

SUBSTANCE: invention refers to the production of synthetic rubbers that are obtained by means of solution polymerization, in particular to the regeneration of the return solvent from the rubber separation step. Method includes rectification of the return solvent on the column, cooling of vapors in the dephlegmator, collecting distillate in the vessel, feeding the reflux with the alkaline agent into the rectification column, pumping out heavy hydrocarbons from the bottom of the column. In this case, the return of 10–90 % of the bottom product which contains the unspent alkaline agent that has the reaction of the aqueous extracting medium with pH 10–12, to the rectification column into the middle part of it above the feed stream.

EFFECT: invention allows to purify the recycled solvent during the production of synthetic rubber from halogen-containing impurities, to maintain the alkaline environment in it in order to avoid corrosion of the equipment, to increase the safety of production of solution polymers.

1 cl, 1 dwg, 5 tbl, 1 ex

Description

The invention relates to the production of synthetic rubbers obtained by solution polymerization, in particular to the regeneration of a return solvent from the rubber separation step.

A known method of purification of a return solvent in the production of diene polymers by distillation [T.V. Bashkatov, Y.L. Zhigalin. Synthetic rubber technology. L .: Chemistry. 1987, p. 170, 174]. It is used in industry, however, it does not allow cleaning the return solvent from halogen-containing impurities, and eliminates the formation of hydrogen chloride, which causes corrosion of equipment.

A known method of cleaning the return solvent, where for cleaning the return solvent, heavy hydrocarbons are pre-concentrated to a content of 0.5-25 wt.% By partially evaporating the hydrocarbon layer due to the heat of degassing vapors and sent to the rectification, where the evaporated part is fed in a separate stream [Return processing method solvent. USSR copyright certificate No. 1147714 A, cl. С08С 2/06 ,. 1985, Bull. No. 12]. In the proposed method, due to the heating of the feed stream, the number of contact steps on the mass exchange devices of the distillation column is reduced, and accordingly, the penetration of hydrogen chloride vapor into the upper part of the column becomes possible, which will lead to corrosion of the reflux condenser and condensate collection tanks.

A known method of cleaning the return solvent, in which to regulate the process of cleaning the solvent from impurities in the production of synthetic rubber by extraction with an aqueous solution of alkali, part of the solvent at the outlet of the installation is recycled to its input [Method for controlling the process of cleaning the solvent from impurities in the production of synthetic rubber. Copyright certificate No. 1361154 A1. Cl. C08F 136/04. 1987. Bull. No. 47]. The solvent extraction extraction installation does not imply its heating and it becomes impossible to completely decompose the halogenated hydrocarbons. The extractant is an aqueous solution of an alkaline agent, which determines the course of the mass transfer process at the interface.

In the known method, the regulation of the solvent cleaning process is proposed to be carried out on a distillation column. The parameters governing the purification of the solvent are the reflux ratio and steam flow rate in the boiler of the column [Method for controlling the purification of the solvent. Copyright certificate No. 1306928 A1. Cl. C08F 136/04, G05D 27/00. 1987. Bull. No. 16]. Regulation of the solvent purification process by reflux ratio and heating of the bottom part of the column prevents the ingress of C ₅ hydrocarbons into the toluene fraction and vice versa - the ingress of toluene into the C ₅ hydrocarbon distillate, and does not solve the problem of neutralizing the resulting hydrogen chloride.

The objective of this invention is the cleaning of the return solvent in the production of synthetic rubber from halogen-containing impurities, maintaining an alkaline environment in it to prevent equipment corrosion, improving the safety of production of solution polymers.

To solve this problem, a method for cleaning the return solvent is proposed, including rectification of the return solvent on the column, cooling the vapors in a reflux condenser, collecting distillate in a tank, feeding reflux with an alkaline agent to the distillation column, pumping out heavy hydrocarbons from the bottom of the column to the toluene separation stage, while bottled product is returned from 10 to 90%, containing unused alkaline agent, to the distillation column in the middle part of the column, above the feed level flow, while the bottom product of the column cleaning the return solvent, containing unused alkaline agent, has a reaction of an aqueous medium pH 10.0 ÷ 12.0.

In FIG. 1 presents the claimed scheme for cleaning the return solvent:

I - feed stream to the column for cleaning the return solvent

II - pairs of the hydrocarbon fraction With ₅

III - condensate of the hydrocarbon fraction With ₅

IV - alkaline agent

V - toluene fraction with heavy hydrocarbons

VI - toluene for polymerization

VII - heavy hydrocarbons

VIII - recycle stream from the bottom product of the column cleaning purification of return solvent

1 - solvent cleaning column

2 - column for the purification of toluene from heavy hydrocarbons

3 - reflux condenser

4 - distillate collection tank

6 - capacity with phenols of alkali metals

5, 7, 8 - pumps

9 - boiler

The cleaning of the return solvent in accordance with the proposed method on the site of cleaning the solvent is as follows.

The flow of return solvent through pipeline I as a raw material enters the middle or lower middle part of column 1. The temperature in the cube of the exhaustive part of column 1 is 125–135 ° С, and on the top of the reinforcing part of column 1 is 70–80 ° С. The temperature regime in the exhaustive part of the column is a sufficient condition for the evaporation of C ₅ hydrocarbons, decomposition of primary and tertiary isoprene hydrochlorides and the evolution of hydrogen chloride. Stream II of a pair of C ₅ hydrocarbon fraction with hydrogen chloride through a reflux condenser 3 is collected in a tank 4. From tank 4, part of stream III by pump 5 is directed as reflux to the upper plate of the strengthening part of the column, and the balance excess of hydrocarbon stream III is sent to the C ₅ hydrocarbon separation stage. An alkaline agent IV is supplied to a stream III moving along the reflux line from a tank 6 by a pump 7. Due to the high density of the alkaline agent, it completely flows into the bottoms of column 1 and, with a stream of toluene and heavy hydrocarbons with a pH of 10–12, flows through pipe V to pump 8 to clean the toluene 2. On distillation column 2, separation into toluene fraction VI and heavy hydrocarbons VII. A portion of stream V from 10 to 90% is sent to the purification column of the return solvent 1 through line VIII to a point above the feed point of the return solvent.

The feed point of the bottoms product into the column is due to the difference in the physicochemical parameters of the feed stream and the hydrocarbons of the bottoms product, including density. The creation of a homogeneous hydrocarbon liquid phase on the plates of the distillation column will occur as it flows onto the lower plates and, accordingly, the distribution of the alkaline agent over the section of the plates will occur unevenly. In accordance with the proposed method, the hydrocarbons of the bottoms product must be supplied above the point of entry of the feed stream.

Example. At the laboratory distillation unit, the rectification conditions of the return solvent formed after the polymerization of isoprene on a Ziegler-Natta catalyst and containing isoprene and isoamylene hydrochlorides with the addition of hydrocarbons, a bottoms product of the column containing an alkaline agent, were simulated. The ratio of miscible hydrocarbon feedstocks per column: bottoms was 4: 1 by volume. Characteristics of hydrocarbons are presented in table 1, the results of the experiment in tables 2-5.

With an increase in the temperature of distillation from 70 to 110 ° С, the concentration of water-soluble chlorides in the distillate obtained from raw materials to the column without adding bottoms is higher than in the distillate obtained by distillation of a mixture of raw materials into the column and bottoms from the column for cleaning the return solvent. An increase in the concentration of water-soluble chlorides in the distillate correlates with a decrease in the pH level of the aqueous extract.

The proposed method allows to neutralize the released hydrogen chloride to maintain the reaction of the medium in evaporating hydrocarbons at a neutral level of pH = 7.0, to prevent corrosion of the reflux condenser, pipes and distillate collection capacity, which will affect the safety of production of solution polymers, the return of unused alkaline agent in the bottoms product leads to savings in alkaline agent.

Claims (1)

A method for purifying a return solvent, including rectification of a return solvent on a column, cooling vapors in a reflux condenser, collecting distillate in a tank, feeding reflux with an alkaline agent to a distillation column, pumping out heavy hydrocarbons from the bottom of the column to the toluene separation stage, characterized in that the bottoms are returned a product from 10 to 90%, containing an unspent alkaline agent, to the distillation column in the middle of the column, above the feed level of the feed stream, while the bottom product solvent refluxing columns containing an unspent alkaline agent have a reaction of an aqueous extract medium of pH 10-12.

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