RU2140896C1 - Method of purification of recovery ethylbenzene from low-boiling hydrocarbon fraction in production of propylene oxide and styrene - Google Patents

Abstract

FIELD: chemical technology. SUBSTANCE: invention relates to production of propylene oxide and styrene, in part, a method of purification of recovery ethylbenzene from low-boiling fraction of the total recycle current. Recovery ethylbenzene is formed at the stages of oxidation of ethylbenzene, epoxidation of propylene with ethylbenzene hydroperoxide and separation of epoxidation products. Method of purification is based on the use of hydroperoxide method. Method involves the use of ethylbenzene current isolated from exhaust air in ethylbenzene oxidation, current from the stage of separation of epoxidate heavy fraction after reaction of propylene epoxidation with ethylbenzene hydroperoxide obtained by an alkaline washing out an epoxidate heavy fraction from acid impurities and ethylbenzene isolation from this fraction by rectification. Current or its part of recovery ethylbenzene isolated from exhaust air in the process of ethylbenzene oxidation is purified after washing out from low-boiling hydrocarbons by rectification and ethylbenzene from the stage of separation of epoxidate heavy fraction after an alkaline washing out is isolated by rectification using a single fractionating column. It is desirable to perform the purification of ethylbenzene current isolated from exhaust air in the process of oxidation from low-boiling hydrocarbons by rectification at 150 C, not above, in the column vat and the isolation of recovery ethylbenzene to perform by rectification at 145-155 C in the column vat. The most efficient procedure involves the purification of 5-10% of recovery ethylbenzene isolated from exhaust air in the process of oxidation from low-boiling hydrocarbons. EFFECT: improved method of purification. 3 cl, 2 tbl, 1 dwg, 3 ex

Description

 The invention relates to the production of propylene oxide with styrene. In particular, the invention relates to a method for purification of the low-boiling fraction of the total ethylbenzene-recycle recycle stream formed at the stages of ethylbenzene oxidation, epoxidation of propylene with ethylbenzene hydroperoxide and separation of epoxidation products.

The known process for producing ethylbenzene hydroperoxide (US patent N 3592857, MKI C 07 C 73/06, publ. 07/13/1971), in which the oxidation of ethylbenzene with molecular oxygen takes place at 165 ^o C. A vapor-air mixture containing exhaust air, light hydrocarbons and unreacted ethylbenzene exits from the top of the reactor, passes alkaline washing, where ethylbenzene is cooled to a liquid state. Excess flushing fluid is discharged to a separator, where the liquid is separated into a layer of ethylbenzene and a layer of water. A layer of water containing neutralized acidic by-products leaves the separator. On the other hand, the exhaust non-condensing gas is diverted to combustion. The ethylbenzene layer after the separator is dried using alumina or silica gel and recycled to the oxidation reactor. Oxide containing ethylbenzene hydroperoxide, unreacted ethylbenzene and oxidation by-products is discharged from the bottom of the reactor. The oxidate can be concentrated and alkaline washed. Ethylbenzene evaporated during concentration is sent to alkaline washing, then to dried and recycled to the oxidation reactor.

 The closest in technical essence is the process of joint production of styrene and propylene oxide (Album of technological schemes of the main industries of the synthetic rubber industry. P. Kirpichnikov, V.V. Berestnev, L.M. Popova - L .: Chemistry, 1986, p. 102 -112), in which alkali is used to purify the ethylbenzene return stream consisting of the stream obtained from the ethylbenzene oxidation stages, the stream from the concentration column of ethylbenzene hydroperoxide and the stream from the stage of separation of the heavy fraction of the epoxide after epoxidation washing the heavy fraction epoksidata from acidic impurities and recovering low-boiling fraction (toluene, benzene, etc.) in the step of separation of the heavy fraction by sequential isolation epoksidata first low-boiling fraction of a two column distillation scheme, then ethylbenzene-return and benzaldehyde.

 The disadvantage of this method is the increased cost of energy when separating a low-boiling fraction from the return ethylbenzene according to a two-column rectification scheme, which is associated with a low concentration of the highly volatile fraction in it up to 0.04 wt.% And the need for its concentration in the distillate of the first column to 0.25 wt. % and up to 37 wt.% in the distillate of the second column.

To improve the purification of ethylbenzene return and reduce the energy consumption for the extraction of the boiling fraction formed at the stage of ethylbenzene oxidation, we propose the following method for purification of the low boiling fraction of hydrocarbons from ethylbenzene returning the production of propylene oxide and styrene using the hydroperoxide method, consisting of a stream of ethylbenzene oxidation stream extracted from the exhaust air, from the stage of concentration of ethylbenzene hydroperoxide and ethylbenzene stream from the separation of heavy fra fraction of epoxide after the reaction of epoxidation of propylene with ethylbenzene hydroperoxide obtained by alkaline washing of the heavy fraction of the epoxide from acidic impurities and the separation of ethylbenzene from this fraction by distillation. The stream or part of the stream of ethylbenzene recycle, extracted from the exhaust air of the ethylbenzene oxidation process, is purified by distillation after washing, and ethylbenzene from the separation of the heavy fraction of the epoxide after alkaline washing of the fraction is isolated by distillation using one distillation column. It is possible to clean the boiling stream of ethylbenzene extracted from the exhaust air of the oxidation process by distillation at a column bottom temperature of not more than 150 ^o C, and recover ethylbenzene from the heavy fraction of the epoxide by distillation at a column bottom temperature of 145-155 ^o C. It is most rational to use volatile hydrocarbons to clean 5-10 wt.% the return stream of ethylbenzene isolated from the exhaust air of the oxidation process.

 According to the proposed method (see drawing), a mixture consisting of ethylbenzene rectified (line 1) and recycled streams of recycled ethylbenzene 2,3,4,5a is sent to unit I - II to produce ethylbenzene hydroperoxide by oxidation of ethylbenzene with atmospheric oxygen.

 Return ethylbenzene from unit I - II (unit for the oxidation of ethylbenzene to hydroperoxide, washing the oxidate and strengthening oxidized ethylbenzene) is sent for cleaning to the subsequent units of the technological scheme in two streams. Stream 5 is ethylbenzene isolated from the exhaust air of the oxidation process. This stream of ethylbenzene after alkaline treatment on line 5b returns to the oxidation stage. Another part of stream 5 along line 5a is directed to the separation of a fraction of low-boiling hydrocarbons from it into a distillation column K-1. The distillate of the K-1 column - the fraction of "low-boiling products" after the T-1 condensers is collected in a tank E-1, from where, after separation of the phases into a hydrocarbon and water pump N-1, it is fed to fire neutralization or used as a fuel additive. The aqueous phase is pumped by pump N-1a to fire neutralization in a specially prepared furnace, and / or in a bioreactor, and / or to treatment facilities. The bottoms liquid K-1 is sent through line 3 as a recycle to the ethylbenzene oxidation reactor.

 The second stream formed during the concentration of ethylbenzene hydroperoxide is directed along line 2 to oxidation.

 On line 6, concentrated ethylbenzene hydroperoxide is sent to unit III - IV (washing and separation units of heavy epoxide) for epoxidation of propylene with ethylbenzene hydroperoxide and separation of epoxidation products into light and heavy epoxide fractions.

 From node III - IV, stream 7 from the washing stage of the heavy epoxide is fed to the K-2 column for distillation of the ethylene benzene recovery. The distillate of the K-2 column — ethylbenzene return after condensers K-2 and K-3 — is collected in a tank E-2, from where it is fed by a pump N-2 through line 4 to the common recycle stream of ethylbenzene-return to the charge of the oxidation process. The bottoms liquid K-2 is directed to the further isolation of benzaldehyde and the methyl phenyl carbinol fraction.

 The proposed method for the separation of low-boiling fraction from ethylbenzene-return obtained at the stage of cooling and condensation from the exhaust air stream after oxidation reactors in one distillation column simplifies the process flow diagram and also allows to reduce steam consumption by about 4 t / h and electricity by 11 kWh

 Example 1 (see drawing).

 200 t / h of a mixture of ethylbenzene streams are continuously fed into the cascade of ethylbenzene oxidation reactors with atmospheric oxygen, which includes: 1 - 16 t / h fresh from the warehouse, 2 - 100 t / h recycle from the stage of concentration of oxidized ethylbenzene, 3 - 60 t / h recycle from the stage of separation of epoxidation products and 4-24 t / h recycle from the stage of separation of hydrocarbons from the exhaust air stream after oxidation reactors. The ethylbenzene return extracted from the exhaust air stream contains 1.51 wt.% Light hydrocarbons, which include benzene, toluene and more boiling hydrocarbons, the presence of which is undesirable at the stage of ethylbenzene oxidation, since they reduce the selectivity of the formation of hydroperoxide.

A stream of 10 wt.% Recycled ethylbenzene, isolated from the exhaust air of the oxidation process, is sent to a K-1 distillation column having 20 theoretical plates, in which at a top temperature of 110 ^° C, a cube temperature of 148 ^° C and a reflux ratio of 30, a fraction is isolated from it low boiling hydrocarbons. As a top product of K-1 column, a stream of 0.32 t / h is isolated, which is then separated into aqueous and hydrocarbon layers. After separation of the water, a hydrocarbon layer having a composition (wt.%): Low boiling hydrocarbons 0.63; benzene 9.2; toluene 34; water 0.21 and the rest ethylbenzene, is sent to combustion or used as a high-octane additive to motor fuel. The aqueous layer of the separated fraction is sent to treatment plants, and / or to the bioreactor, and / or to combustion.

 The bottom product of the column along the line K-1 is sent to the site for the preparation of the charge of the oxidation of ethylbenzene.

The heavy fraction of the epoxide from line 7 is sent to the K-2 column, in which at a cube temperature of 150 ^o C and a pressure in it of 0.19 MPa, a fraction of recycled ethylbenzene is released. The selected recycle ethylbenzene (stream N4) is mixed with other recycle streams N2,3,5b and stream N1 of fresh ethylbenzene and is sent for oxidation, having the composition (wt.%):
Name of the component - wt.%
1. Benzene - 0.02
2. Toluene - 0.2
3. Water - 0.08
4. Ethylbenzene - 99.28
5. Styrene - 0.01
6. Benzaldehyde - 0.007
7. Acetophenone - 0.14
8. Methylphenylcarbinol - 0.06
9. Ethylbenzene hydroperoxide - 0.2
Total: - 100,000
As a result of non-catalytic oxidation at a temperature of 155 ^o C get an oxidate containing 11.3 wt. % ethylbenzene hydroperoxide. The selectivity of the formation of hydroperoxide 82 mol.%. The content of organic acids in the calculation of benzoic 0.23 wt.%.

 Example 2

 260 t / h of a mixture of ethylbenzene streams are continuously fed into the cascade of ethylbenzene oxidation reactors with atmospheric oxygen, which includes: 1 - 35 t / h fresh from stock, 2 - 120 t / h recycle from the stage of concentration of oxidized ethylbenzene, 3 - 55 t / h recycle from the stage of separation of epoxidation products and 4-50 t / h of recycled ethylbenzene isolated from the exhaust air stream after the oxidation reactors. Ethylbenzene return isolated from the exhaust air stream contains 1.83% of light hydrocarbons, the presence of which at the stage of oxidation of ethylbenzene to hydroperoxide is undesirable, since they reduce the selectivity of the formation of the target product.

In order to improve the quality of ethylbenzene entering the oxidation reactors, a recycle ethylbenzene stream separated from oxidation exhaust air containing 1.83 wt.% Low boiling hydrocarbons is sent in an amount of 5.5 wt.% Of the total flow to the K-1 distillation column, having 70 theoretical plates, in which at a top temperature of 110 ^o C, a cube temperature of not more than 150 ^o C and a reflux ratio of 80, a fraction of low-boiling hydrocarbons is isolated from it. As a top product of K-1 column, a stream of 0.32 t / h is isolated, which is then separated into aqueous and hydrocarbon layers. After separation of the water, a hydrocarbon layer having a composition (wt.%): Low boiling hydrocarbons 0.6; benzene 9.3; toluene 32; water 0.23 and the rest ethylbenzene in an amount of 0.29 t / h, sent to combustion or used as a high-octane additive to motor fuel. The aqueous layer of the separated fraction is sent to treatment plants, and / or to the bioreactor, and / or to combustion.

 The bottom product of the column along the K-1 line is sent for mixing with fresh ethylbenzene and other recycle streams returned to the oxidation stage.

The heavy fraction of the epoxide from line 7 is sent to the K-2 column, in which at a cube temperature of 148 ^o C and a pressure of 0.2 MPa in it, a fraction of recycled ethylbenzene is released. Dedicated recycled ethylbenzene is sent to the oxidation unit.

After mixing the recycle streams N2,3,4 and 5b with the stream N1 of "fresh" ethylbenzene, the charge fed to the oxidation had the composition (wt.%):
Name of the component - wt.%
1. Low boiling hydrocarbons - 0.01
2. Benzene - 0.02
3. Toluene - 0.22
4. Water - 0.09
5. Ethylbenzene - 99.21
6. Styrene - 0.01
7. Benzaldehyde - 0.007
8. Acetophenone - 0.14
9. Methylphenylcarbinol - 0.07
10. Ethylbenzene hydroperoxide - 0.23
Total: - 100,000
As a result of oxidation at a temperature of 148 ^o C in the presence of a Na - catalyst, oxidized ethylbenzene containing 10 wt.% Ethylbenzene hydroperoxide is obtained. The selectivity of the formation of hydroperoxide 89 mol.%. The content of organic acids in the calculation of benzoic 0.2 wt.%.

 Example 3

 The experiment is carried out according to the method of example 1. In the cascade of ethylbenzene oxidation reactors with atmospheric oxygen, 170 t / h of a mixture of ethylbenzene streams are continuously fed, which includes: 1 - 26 t / h of fresh stock, 2 - 80 t / h of recycle from the concentration of oxidized ethylbenzene, 3-30 t / h of recycle from the stage of separation of epoxidation products and 4-24 t / h of recycled ethylbenzene isolated from the exhaust air stream after oxidation reactors.

In order to improve the quality of ethylbenzene entering the oxidation reactors, a stream of recycled ethylbenzene extracted from oxidation exhaust air containing 1.3 wt.% Low-boiling hydrocarbons is sent to a K-1 distillation column having 10 theoretical plates, in which at a top temperature of 110 ^o C and reflux number 100, a fraction of low-boiling hydrocarbons is isolated from it. As the top product of K-1 column, a flow of 2.5 t / h is isolated, which is then separated into aqueous and hydrocarbon layers. After separation of the water, the hydrocarbon layer is sent to combustion or used as a high-octane additive to motor fuel. The aqueous layer of the separated fraction is sent to treatment plants, and / or to the bioreactor, and / or to combustion.

The heavy fraction of the epoxide from line 7 is sent to the K-2 column, in which at a cube temperature of 145 ^o C and a pressure in it of 0.2 MPa, a fraction of recycled ethylbenzene is released. The recycle ethylbenzene recovered is mixed with fresh ethylbenzene and sent for oxidation.

As a result of oxidation at a temperature of 155 ^o C get oxidized ethylbenzene containing 10 wt.% Ethylbenzene hydroperoxide. The selectivity of the formation of hydroperoxide 89.5 mol.%. The content of organic acids in the calculation of benzoic 0.19 wt.%.

Claims (3)

 1. The method of purification from the boiling fraction of hydrocarbons of the return ethylbenzene production of propylene oxide with styrene by the hydroperoxide method, consisting of a stream extracted from the exhaust air of the ethylbenzene oxidation process, a stream from the stage of concentration of ethylbenzene hydroperoxide and a stream of ethylbenzene from the stage of separation of the heavy fraction of epoxide after the propylene epoxidation reaction ethylbenzene obtained by alkaline washing of the heavy fraction of the epoxide from acidic impurities and the allocation of ethyl benzene from this fraction by distillation, characterized in that the stream or part of the ethylbenzene recycle stream extracted from the exhaust air of the ethylbenzene oxidation process after washing is purified from boiling hydrocarbons by rectification, and the ethylbenzene stream from the stage of separation of the heavy epoxide fraction after alkaline washing of the heavy epoxide fraction is recovered using one distillation column. 2. The method according to claim 1, characterized in that the purification from low-boiling hydrocarbons of the ethylbenzene stream extracted from the exhaust air of the ethylbenzene oxidation process is carried out by distillation at a column bottom temperature of not higher than 150 ^o C, and the recovery of ethylbenzene from the heavy epoxide fraction is carried out by distillation under vacuum at a temperature of cube columns 145 - 155 ^o C.  3. The method according to claims 1 and 2, characterized in that 5-10 wt.% Of the ethylbenzene return stream extracted from the exhaust air of the ethylbenzene oxidation process is purified from boiling hydrocarbons by distillation.