KR810001007B1 - Process for treating unreacted 1,2-dichloroethane from 1,2-dichloroethane cracking - Google Patents

Abstract

A process for the recovery of unreacted 1,2-dichloroethane from the cleavage of 1,2-dichloroethane was described. Thus, unreacted 1,2-dichloroethane contg. EtCl 10,2-chloro-1,3-butadiene 1,500, and 1-chloro-1,3-butadiene 150 Wt. ppm, then cl2(g)(1,1,2-trichloroethane content increased only to 176 ppm), finally ethylene (to remove cl2 1,2-dichloroethane without increasing the EtCl level) to give 1,2-dichloroethane contg. 2 ppm Cl2 with ethylene conversion of 99.6 %.

Description

A process for treating undigested 1,2-dichloroethane in pyrolysis of 1,2-dichloroethane.

Vinyl chloride is produced from the pyrolysis of 1,2-dichloroethane on a large scale. The higher the pyrolysis temperature, the higher the decomposition rate and the greater the amount of unwanted cracking by-products appearing during the cracking process. After removing the chloride and vinyl chloride and simultaneously separating the boiling by-products such as 1,3-butadiene, acetylene, monovinylacetylene and ethyl chloride, 1,2-dichloroethane that was not decomposed during cracking was still 1, 1-dichloroethylene, 1,2-dichloroethylene, chloroform, carbon tetrachloride, butychloroethylene, benzle, and especially higher amounts of 2-chloro-1,3-butadiene and small amounts of 1-chloro-1,3-butadiene It contains. The by-products must be removed during recycling of undigested 1,2-dichloroethane to avoid a rapid increase in soot coke in the cracking furnace. However, the separation of the aforementioned by-products by distillation causes chloroprene to accumulate in the distiller followed by polymerization of chloroprene, thereby causing the process to stop.

It is known from French Patent No. 2,080,645 to add a small amount of chlorine of 1,2-dichloroethane containing pyrolysis gas before separating vinyl chloride and hydrogen chloride. After adding chlorine, the liquid reaction mixture should be placed in the reservoir for some time before further treatment. Incomplete decomposition of the process is a problem and it is inevitable that corrosion of the storage container is inevitable. In order to prevent this, measures such as the use of new or expensive instruments are necessary.

According to German Patent DT-AS 2,307,736, if chlorine is added from 0.01% to 1% of the original weight of dichloroethane dissolved in 1,2-dichloroethane before the vinyl chloride is separated, a portion of the added chlorine It is disadvantageous that 1,, 12-trichloroethane is reacted or partially substituted 1,2-dichloroethane which is not converted under the above-mentioned reaction conditions. Therefore, quantitative chlorination of chloroprene cannot be observed.

According to German patent DT-AS 2,416,786, when treating the reaction product of 1,2-dichloroethane pyrolysis after separating hydrogen chloride and vinyl chloride, the chlorine of gas into the sorting vessel to separate the boiling product at high temperature under the catalyst auxiliary Is introduced. The reduction of chloroprene due to these conditions can increase the operation time of the pyrolysis furnace by one step, but the pyrolysis of chloroprene, which is indispensable for optimum operating conditions, cannot be achieved. At temperatures of approximately 100 ° C. to 110 ° C., chlorine is also included in the distillate mixture, so it is changed to 1,1,2-trichloroethane boiling at high temperatures with a clear chlorine substitution of 1,2-dichloroethane. It leads to ineffectiveness of the process.

It is an object of the present invention, before recycling 1,2-dichloroethane which is not decomposed in 1,2-dichloroethane pyrolysis, in particular unnecessary by-products, namely 2-chloro-1,3-butadiene and 1-chloro-1,3 -Butadiene is quantitatively removed in a simple manner as desired to reduce the disadvantages of the methods known to date and also to achieve an optimum operating time for the pyrolysis furnace and for the product distiller.

It is an object of the present invention to provide a method for treating undigested 1,2-chloroethane before recycling from 1,2-dichloroethane pyrolysis.

That is, the present invention relates to a method for treating 1,2-dichloroethane which is not decomposed in thermal decomposition of 1,2-dichloroethane, wherein the decomposition is not carried out at a temperature of about 0 ° to 80 ° C. and a pressure of about 5 to 6 bar. 1,2-dichloroethane in an amount of about 0.001-0.01% by weight of 0-crazol, m-crasol type hydroxyl-containing aromatic compound or derivative thereof or mixture thereof, wherein the undecomposed 1,2 A stream comprising dichloroethane is brought into contact with chlorine to produce a chlorine content of up to 800 ppm in the fluid by chlorination (step a), and at a temperature of about 0 ° to 80 ° C. and about 5 to 6 Under pressure of the bar, the chlorine-containing fluid from step (a) is contacted with ethylene in an amount equivalent to chlorine to dechlorination (step b), which is separated in the pyrolysis of 1,2-dichloroethane. Undiluted 1,2-dichloroethane It is about a method of processing.

The best way to achieve this process is by mixing 1% by volume of oxygen with chlorine.

The advantage of the process of the present invention is that there is no loss, in particular there is little loss of ethylene and chlorine. A surprising fact is found in that the trace amount of aromatic compounds with hydroxyl groups mentioned above is satisfied only by quantitative chlorination of chlorobutadiene with different characteristics, and in a short time the excess chlorine in the chlorination process is removed with ethylene. . Even without adding the aforementioned aromatic compound with a hydroxyl group, the same mole of ethylene in the dilute solution by iron chloride, known as a chlorination catalyst, reacts only about 40% of insoluble chlorination. Dichloroethane will be replaced with 1,1,2-trichloroethane.

After the pyrolysis reaction, undecomposed 1,2-dichloroethane is taken out from the collector with impurities and the reaction temperature of 0 ° to 80 ° C, preferably 20 ° to 30 ° C, and 0.5 to 6 bar bar). The addition of a single or a mixture of 0.00001 to 0.1 [sic] weight% of undecomposed dichloroethane by ortho- or meta-cresol type hydroxyl-containing aromatic compound or gmono- or di-chloro derivative is 1, It is suitably done by means of a dosing pump from a reservoir with a corresponding amount of said hydroxyl-containing aromatic compound previously dissolved in 2-dichloroethane.

The addition may also be carried out before the control of the above-mentioned undigested 1,2-dichloroethane. The selective chlorination of the chlorobutadiene isomers in undigested 1,2-dichloroethane can be done in empty or filled reaction tubes, but the dechlorination reactor is used to make the separation of ethylene better. Preferred are reaction tubes. As a chlorine charge, liquid chlorine is evaporated or chlorine obtained by electrolysis is suitable, and these are combined with a sufficient amount of oxygen so that the maximum content of oxygen is 1% by volume. The higher the oxygen content, the greater the risk of the formation of explosive mixtures in the reservoir. According to the present invention, expensive special steel is not required for the reaction tube, and ordinary C-steel is sufficient. The residence time in the reaction tube for the chlorination reaction is about 20-50 seconds and the residence time for the dechlorination reaction is about 10-40 seconds. Although the relationship between the length and diameter of the reaction tube is not absolute, it is best to use a mechanism in which the relationship is selected such that the sum of the reaction gases in the tube outside the residence time is obtained. Rasching-rings used in dechlorination reactors are made of iron.

Aromatic compounds with OH groups added suitably to the present invention are more effective in mixed distillers, which are partially chlorinated and boil difficult to boil materials with boiling materials at high temperatures. Thereby, there is no loading amount of a dichloroethane circulation at the time of recycling in a pyrolysis reaction.

In the chlorination process, after chlorination of 1-chloro-1,3-butadiene or 2-chloro-1,3-butadiene, chlorine excess of up to 800 ppm by weight is generated, and chlorine excess is measured. 1,2-1,7 moles of chlorination per mole of undigested 1,2-dichloroethane with 2-chloro-1,3-butadiene, unreacted 1,2 with 1-chloro-1,3-butadiene Add 2,1-2,3 moles of chlorine per mole of dichloroethane.

Unnecessary by-products of 1-chloro-1,3-butadiene and 2-chloro-1,3-butadiene in 1,2-dichloroethane, not decomposed into 1,2-dichloroethanol 1,1,2-trichloroethane In a trace amount of ferric ions precipitated on steel equipment, ethylene reacts with trace amounts of ethylene and hydrogen chloride to chlorinate to boiling materials at moderately high temperatures.

Example 1

10 ppm by weight of ethyl chloride, 1500 ppm by weight of 2-chloro-1,3-butadiene and 150 ppm by weight of 1-chloro-1,3-butadiene produced at a pressure of 5 bar and a temperature of 152 ° C. in a vinyl chloride fractionator. 30 t / h of undecomposed 1,2-dichloroethane was evaporated at 0.843 kmol / h by cooling to 30 ° C. through a cooler with a 10 weight ppm 0-clesol additive dissolved in 1,2 di-chloroethane. The mixed liquid chlorine is mixed with gas in an empty reaction tube (250 mm in diameter and 5000 mm in length). At the end of the chlorination process through the reaction tube, isochlorobutadiene is removed less than 1 ppm by weight of undigested 1,2-dichloroethane. In the meantime, the concentration of 1,1,2-trichloroethane is increased by 176 ppm by weight in an insoluble chlorine excess of 460 ppm by weight. 1,2-dichloroethane, which is not reacted immediately after the chlorination process, flows through a tube (220 mm in diameter and 3800 mm in length) filled with iron-lashing. In this, 1,2-dichloroethane is mixed with 0.1944 kmol / h of ethylene gas so that the concentration of ethyl chloride in undecomposed 1,2-dichloroethane does not increase, and insoluble chlorine is almost decomposed into 1,2-dichloroethane. Done. Only 2 weight ppm of insoluble chlorine in the released dechlorinated undigested 1,2-dichloroethane resulted in a change of 99.6% ethylene.

Example 2 (Comparative Example)

As in Example 1, without addition of 0-cresol initially, 30 t / h of undigested 1,2-dichloroethane was evaporated with 1.247 kmol / h of liquid chlorine and 0.1944 kmol / h of ethylene under the same reaction conditions. Mix As a result, 460 ppm by weight of insoluble chlorine is produced in the chlorination process, but 20-dichlorobutadiene is converted into 1,1,2-trichloroethane from 1,2-dichloroethane which is not decomposed after chlorination. Chlorine substitution yields 2000 ppm by weight of 1,1,2-trichloroethane. And in the undecomposed 1,2-dichloroethane, the concentration of 1,1,2-trichloroethane increased to 2140 ppm by weight after the dechlorination process and was blown off after the dechlorination process, 30, which occurred in the reaction between ethylene and hydrogen chloride, It contains about 400 ppm by weight of ethylene chloride, and still contains about 110 ppm by weight of ethylene of 200 ppm by weight of insoluble chlorine (40% change in ethylene, but this ethylene is produced in large quantities in a pressureless buffer vessel. Release and lose). The remaining insoluble chlorine is substituted with 1,2-dichloroethane or chlorinated with extra 2-chloro-1,3-butadiene during the reaction time to nearly 100 ppm by weight. As a result, the concentration of 1,1,2-dichloroethane in undigested 1,2-dichloroethane is increased to 2300 ppm by weight in a buffer container. Due to the presence of insoluble chlorine and a large amount of hydrogen chloride produced during the chlorine substitution of 1,2-dichloroethane, a serious pollution problem and soluble problem occur when discarded in a buffer container, thus requiring a tank waste washing station.

Example 3

5 weight ppm 1,1,2-trichloroethane, 7 weight ppm ethyl chloride, 1000 weight ppm 2-chloro-1,3-butadiene and 120 contained with vinyl chloride and hydrogen chloride as in Example 1 To 20 t / h of 1,2-dichloroethane undecomposed by 1,2-dichloroethane pyrolysis in 1 ppm of 1-chloro-1,3-butadiene, 15 ppm by weight of m-cresol was added continuously. Cool to 32 ° C. Next, unreacted 1,2-dichloroethane and 0.404 kmol / h of chlorine obtained from electrolysis containing approximately 0.6% by weight of oxygen are mixed in an empty reactor as described in Example 1. Thus, at the end of the chlorination process, isochlorobutadiene is removed less than 1 ppm in undigested 1,2-dichloroethane. In the meantime, the concentration of 1,1,2-trichloroethane is increased by 165 ppm by weight in the excess of 350 ppm by weight insoluble chlorine. Immediately after the chlorination process, undigested 1,2-dichloroethane was flowed into the same tube as in Example 1. In this, 1,2-dichloroethane is mixed with 0.099 kmol / h of ethylene, so that the concentration of ethyl chloride in undecomposed 1,2-dichloroethane does not increase, and the substituted moles of 1,2-dichloroethane are no longer present. Increasingly, insoluble chlorine changes almost completely to 1,2-dichloroethane. Only 1 ppm by weight of insoluble chlorine in the dechlorinated, undigested 1,2-dichloroethane released represents 99.99% change in ethylene.

Example 4 (Comparative Example)

Without adding m-cresol, as in Example 3, undigested 20 t / h of 1,2-dichloroethane was mixed with 0.565 kmol / h of chlorine obtained by electrolysis and then 0.384 kmol / h of ethylene Mix with The resulting undigested 1,2-dichloroethane after chlorination was approximately 550 ppm by weight of insoluble chlorine, 900 ppm by weight of 1,1,2-trichloroethane and 40 ppm by weight of 2-chloro-1,3-butadiene. Will be included. The same amount of ethylene adducts, however, react stoichiometrically with insoluble chlorine, so that subsequent dechlorination cannot remove 2-chloro-1,3-butadiene. For 1,2-chloroethane unreacted at the end of the dechlorination process, 5 ppm by weight of insoluble chlorine, 25 ppm by weight of ethylene chloride, 960 ppm by weight of 1,1,2-trichloroethane and 0.238 kmol / h of ethylene It is released as a large amount of gas from the pressureless buffer, the change of which is 37.6%. Since chlorine and 2-chloro-1,3-butadiene require a long time to react, ethylene must be added after dechlorination to remove almost all chloroprene.

Example 5

30 t / h unreacted 1,2 with 5 weight ppm 0-crasol and 5 weight ppm m-clesol at a temperature of 20 ° C. and pressure from 1 bar to 3 bar as in Example 1 Mixture of dichloroethane is first mixed with 0.927 kmol / h of liquid chlorine evaporated and then 0.302 kmol / h of ethylene. Undecomposed 1,2-dichloroethane from the dechlorination process includes the following compounds.

10 ppm by weight of ethylene chloride,

2-chloro-1,3-butadiene up to 1 ppm by weight,

1-chloro-1,3-butadiene up to 1 ppm by weight,

74 ppm by weight of 1,1,2-trichloroethane,

1 ppm by weight insoluble chlorine,

0 weight ppm ethylene.

Claims (1)

As described above in the text, in the method for treating 1,2-dichloroethane which is not decomposed in the thermal decomposition of 1,2-dichloroethane, the above method is carried out at a temperature of about 0 ° C. to 80 ° C. and a pressure of about 5 to 6 bar. In the presence of about 0.0001 to 0.01% by weight of undecomposed 1,2-dichloroethane, 0-cresol, m-cresol type hydroxyl-containing aromatic compound or derivative thereof or mixtures thereof, A chlorination (step a) of a stream comprising 2-dichloroethane in contact with chlorine produces a chlorine content of up to 80 ppm in the fluid and a temperature of about 0 ° C. to 80 ° C. and about 5 to 6 ° C. Dehydrochlorination (step b) by contacting the chlorine-containing fluid from step (a) with ethylene in an amount equal to the chlorine content under pressure of a bar. Does 1,2D Method of processing a furnace and ethane.