DE4033047C2 - Process for the separation of benzene from the 1,2-dichloroethane recovered in the production of vinyl chloride - Google Patents

Description

The present invention relates to a method for Ben zole separation from that in the production of vinyl chloride recovered 1,2-dichloroethane.

The technical production of vinyl chloride is based on the thermal cracking of 1,2-dichloroethane at temperatures from 450 to 600 ° C under increased pressure. Here, about 40 to 65% of the 1,2-dichloroethane used is split into vinyl chloride and hydrogen chloride. In this thermal cleavage, 2-chlorobutadiene (1,3), butadiene (1,3), 1,1-dichloroethane, 1,1-dichloroethylene, chloroform, trichlorethylene, ethyl chloride, carbon tetrachloride and Benzene, which are named in the literature as low boilers (bp ₇₆₀ <83.7 ° C).

When working up the cleavage products, the hydrogen chloride is first separated off as a top product in a distillation. In a further column, the vinyl chloride column, the vinyl chloride is distilled off as the top product. The bottom of this column consists of non-cleaved 1,2-dichloroethane which, in addition to the low boilers, also contains high-boiling products (bp ₇₆₀ <83.7 ° C) and coke particles.

It has been found that the by-products of 1,2-dichloroethane when cleaved again in the canning Verko kung arise, the butadiene (1,3) formation is increased and the gap temperature increases with increasing benzene content increases, causing the by-product formation in the thermal  Cleavage of the 1,2-dichloroethane undesirably white ter increases, cf. DE-PS 6 68 336, column 2, lines 15 to 27 and DE-PS 9 59 211, column 1, lines 19 to 31.

In DE-PS 6 68 336 has been proposed, undesirable tes 2-chlorobutadiene (1,3) and benzene from 1,2-dichloro separate ethane by mixing the 1,2-dichloroethane with aluminum Select minium chloride at 70 to 150 ° C in a closed vessel heated for 24 to 48 hours. This time consuming order constant cleaning does not lead to one satisfactory depletion of the byproducts in the 1,2-dichloroethane.

In DE-PS 9 59 211, a cleaning process for extensive separation of 2-chlorobutadiene (1,3) 1,2-dichloroethane proposed, in which the low boilers in 1,2-dichloroethane at the top of a distillation column be enriched and the one enriched with low boilers Fraction is gassed with chlorine under UV light. Through the The low boilers are converted into high boilers by chlorination delt, which then in a distillation column from 1,2-Di chloroethane can be separated.

According to the procedure of DE 31 40 447 A1, undesirable Chloroprene and 1,3-butadiene through a chlorine treatment of the 1,2-dichloroethane converted into and in high boilers Form can be removed. About a benzene separation not spoken here.

According to the procedure of DE 29 03 640 A1 low boilers converted to high boilers by chlorination. A benzene separation is not reached here.

According to the procedure of DE 19 17 933 C3 is also no benzene separation from the 1,2-dichloroethane was achieved.

With the known methods, the low boilers can Except for the benzene satisfactory from the 1,2-dichloro be removed ethane. For a benzene separation So far, 1,2-dichloroethane has not been found in the prior art Procedure specified.

It was therefore the task of a procedure for Ben zole separation from that in the production of vinyl chloride recovered 1,2-dichloroethane, after the removal of the Vinyl chloride and hydrogen chloride.  

The method according to the invention is now known records that the purified product stream in the presence of metallic iron at a temperature of 30 to 85 ° C with 1.5 to 15 grams of chlorine per kilogram of 1,2-dichloroethane treated and this product stream with the unpurified Product stream reunited and together in another Purification step the 1,2-dichloroethane from high boilers separates.

The method of the invention can also optionally still be designed in that

• a) 30 to 35% by weight of the total 1,2-dichloroethane to be purified than cleaned from high-boiling compounds Product stream available;
• b) the separation of the purified from high-boiling compounds Product flow in the manner of flash evaporation (flash) from the bottom of the column of the vinyl chloride column carries out;
• c) the column bottom under a pressure of 5 to 7 bar the vinyl chloride column expanded against normal pressure and the gas phase formed here for high-boiling Compounds condensed purified product stream;
• d) the chlorine treatment of high-boiling compounds purified product stream with 5 to 7 g of chlorine per kg Performing 1,2-dichloroethane;
• e) in addition, the uncleaned remaining product stream treated with chlorine at a temperature of 30 to 85 ° C, then the two treated product streams again united and together in a further cleaning step separates the 1,2-dichloroethane from high boilers;  
• f) the product stream purified from high-boiling compounds in the presence of metallic iron with 1 to 10, in particular 3 to 4 g of chlorine per kg of 1,2-dichloroethane and the uncleaned remaining product stream without further Additives with 0.5 to 5, especially 2 to 3 g of chlorine per kg 1,2-dichloroethane in separate treatment zones fumigated;
• g) an average treatment time of 2 to 10, in particular especially adheres to chlorination for 3 to 6 minutes;
• h) the reunited two product streams before Separation of 1,2-dichloroethane from high boilers in one Allows reaction zone to react;
• i) the reunited two product streams 2 to 10, especially 4 to 6 minutes in the residence zone at one Allows temperature from 50 to 85 ° C to react.

The method according to the invention allows with little techni effort and without additional energy input nigem 1,2-dichloroethane, which in this form in the split is introduced. It contains as an impurity still <1000 ppm benzene, <50 ppm carbon tetrachloride and <20 ppm 2-chlorobutadiene (1.3). It is taken into account that the 1,2-dichloroethane portion reacted in the cleavage by 1,2-dichloroethane from direct and oxychlorination is replaced. Another advantage of the invention The procedure is that the combustion of the High boilers separated from 1,2-dichloroethane have no disturbing deposits be deposited on the heat exchanger surfaces if the heat of combustion of the high boilers for steam generation is used.

The flash evaporation of the 1,2-dichloroethane can through a throttle valve in the sump outlet of the vinyl chlo rid column. That is 150-170 ° C and under one Pressure from 5 to 7 bar standing bottom product is  Normal pressure and a temperature of 84 ° C relaxed. Here evaporates about 1/3 of the bottom product after the condensation is referred to as a purified product stream; not that one evaporated bottom product is the unpurified product stream. The Low boilers are distributed over both product streams, whereby the purified product stream a larger proportion Low boiling has as the unpurified product stream. The coloring High boilers and the coke remain in the unpurified Product stream.

Performs the chlorine treatment both in the cleaned as well through in the unpurified product stream, so only a very small one Chlorinated 1,2-dichloroethane to high boilers. Disadvantageous here is that then 2 chlorinations installed and must be operated.

If, on the other hand, the total amount of chlorine is only carried out in the purified one Product stream, so a small part of the 1,2-dichloroethane chlorinated to high boilers.

The dwell zone consists of an empty volume. Through the Preceding a dwell zone before further cleaning step, a 1,2-dichloroethane is obtained which is chlorine-free is.

The process according to the invention is illustrated by the examples explained.

example 1

A plant for the thermal cleavage of 1,2-dichloroethane is hourly charged with 36 t dichloroethane, of which 54% split become. The recovered after the split, not implemented 1,2-dichloroethane is 16.56 t / h. It falls after separation of HCl and vinyl chloride in the bottom of the vinyl chloride column a pressure of 5 bar and a temperature of 155 ° C.  

By relaxing this bottom product, the vinyl chloride ko 5.4 t / h are evaporated at normal pressure and condensed and cooled to approx. 65 ° C. With a pump this is done cleaned product stream through an with iron-shaped bodies filled chlorination reactor and pumped at 65 ° C 3.5 g Chlorine per 1 kg of 1,2-dichloroethane added. After a ver 99% benzene, 2-chlorine 100% butadiene (1.3) and carbon tetrachloride with chlorine implemented. The product flows out of the chlorination reactor current, without the interposition of a dwelling zone, in a Distillation column.

The chemical composition of the cleaned product stream mes is noted in Table 1.

The unpurified 1,2-Di left behind when relaxing chloroethane is used in a quantity of 11.16 t / h in a second Chlorination passed and with 2.4 g of chlorine per kg 1,2-dichloroethane gassed. After a dwell time of 6 Minutes have carbon tetrachloride and 2-chlorobuta dien- (1,3) reacted with chlorine up to the detection limit. Out the chlorinated unpurified chlorine reactor flows Product stream, also without the intermediary of a ver because zone, into the distillation column, into which the chlorinated purified product stream flows.

The chemical analysis of the unpurified product stream is noted in Table 2. The benzene content changes only insignificant.

The chemical analysis of the combined product flows the distillation is shown in Table 3.  

Analytical results

Table 1

Benzene chlorination of the purified 1,2-dichloroethane (purified product stream)

Catalyst: iron rings
Use of chlorine: 3.5 g Cl₂ / kg 1,2-dichloroethane

Table 2

Chlorination of the unpurified 1,2-dichloroethane (unpurified product stream)

Use of chlorine: 2.4 g Cl₂ / kg 1,2-dichloroethane

Table 3

United product streams after distillation

Example 2

A plant for the thermal cracking of 1,2-dichloroethane 36 t dichloroethane are fed every hour, of which 54% to be split. The recovered after the split, unreacted 1,2-dichloroethane is 16.56 t / h. It falls after the removal of HCl and vinyl chloride in the sump Vinyl chloride column at a pressure of 5 bar and one Temperature of 155 ° C.

By relaxing this bottom product of the vinyl chloride column 5.4 t / h are evaporated to atmospheric pressure and condensed and cooled to approx. 65 ° C. This is by means of a pump cleaned product stream through an with iron-shaped bodies filled chlorination reactor and 6.0 g of chlorine per 1 kg 1,2-dichloroethane added. From the chlorination reactor the chlorinated purified product stream flows into one 1 m³ container as a dwell zone. Chemical analysis of this Product is shown in Table 4.

The unpurified 1,2-dichloroethane left behind when relaxing is also in an amount of 11.6 t / h promoted the 1 m³ container. Flows out of the 1 m³ container the mixed 1,2-dichloroethane in a distillation column, in which the high boilers are separated. The chemical Analysis of the product after distillation is in the Table 5 listed.  

Table 4

Benzene chlorination of the purified 1,2-dichloroethane (purified product stream)

Catalyst: iron rings
Chlorine use: 6.0 g Cl₂ / kg 1,2-dichloroethane

Table 5

United product streams after distillation

Claims (10)

1. A process for the separation of benzene from the 1,2-dichloroethane recovered in the production of vinyl chloride, after the separation of the hydrogen chloride and vinyl chloride and division of the 1,2-dichloroethane from the bottom of the column of the vinyl chloride column into one purified from high-boiling compounds and one unpurified remaining product stream, thereby characterized in that the said purified product stream is treated in the presence of metallic iron at a temperature of 30 to 85 ° C with 1.5 to 15 grams of chlorine per kilogram of 1,2-dichloroethane and this product stream is combined again with the unpurified product stream and together in a further purification step which separates 1,2-dichloroethane from high boilers. 2. The method according to claim 1, characterized in that 30th up to 35% by weight of the total 1,2-dichloroethane to be purified as a product stream purified from high-boiling compounds available. 3. The method according to claim 1 or 2, characterized in that the separation of high-boiling compounds purified product stream in the manner of flash evaporation (flash) from the bottom of the column of the vinyl chloride column carries out.   4. The method according to any one of claims 1 to 3, characterized ge indicates that one under a pressure of 5 to 7 bar standing column bottom of the vinyl chloride column against Normal pressure relaxes and the gas phase formed to the product stream cleaned of high-boiling compounds condensed. 5. The method according to any one of claims 1 to 4, characterized ge indicates that the chlorine treatment of high-boiling Connections of purified product stream with 5 up to 7 g of chlorine per kg of 1,2-dichloroethane. 6. The method according to any one of claims 1 to 5, characterized ge indicates that you also add the uncleaned Product flow at a temperature of 30 to Treated at 85 ° C with chlorine, then the two treated Product streams reunited and together in one Another purification step is the 1,2-dichloroethane from high boilers separates. 7. The method according to claim 6, characterized in that the product stream cleaned of high-boiling products in the presence of metallic iron with 1 to 10, in particular 3 to 4 g of chlorine per kg of 1,2-dichloroethane and the uncleaned remaining product stream without further Additives with 0.5 to 5, especially 2 to 3 g of chlorine per kg 1,2-dichloroethane in separate treatment zones fumigated. 8. The method according to any one of claims 1 to 7, characterized ge indicates that one has an average duration of treatment of 2 to 10, especially 3 to 6 minutes in chlorine compliance.   9. The method according to any one of claims 1 to 8, characterized ge indicates that the reunited two product streams before separating the 1,2-dichloroethane from High-boilers can react in a dwell zone. 10. The method according to claim 9, characterized in that the reunited two product streams 2 to 10, especially 4 to 6 minutes in the residence zone at one Allows temperature from 50 to 85 ° C to react.