The method of separation of finely dispersed solid, resinous and high-boiling by-products from the reaction gases of the pyrolysis of dichloroethane in the production of vinyl chloride

 

(57) Abstract:

The invention relates to a method for separation of the products of pyrolysis of dichloroethane in the production of vinyl chloride. The described method of separation of finely dispersed solid, resinous and high-boiling stream of products from the reaction gases of the pyrolysis of dichloroethane in the production of vinyl chloride having a temperature of 440 - 520oC and a pressure of 10 - 28 ATM. The method is rapid cooling of these gases in the quenching column and subsequent separation of the products of pyrolysis. Quenching and separation are bubbling through the layer of concentrated liquid by-products of these gases in the cube hardening of the column at the temperature of boiling 120 - 200oC. Then the gas-vapor mixture in contact with return condensation of these gases on kapitbisig and mass transfer plates of a distillation zone with the cleaning gas mixture at the height of the zone of rectification. The final stage is the feed gas mixture to the secondary rectification with the selection and output of the process products boiling above dichloroethane, and the return of the distillate of the distillation process. The technical result - obtaining vinyl chloride high quality, creation of conditions for receipt.

The invention relates to the technology of basic organic synthesis and relates to a method of selection of finely dispersed solid, resinous and high-boiling by-products from the reaction gases of the pyrolysis of dichloroethane in the production of vinyl chloride. The vinyl chloride is used to produce different polymer materials.

The known method of separation of chlorohydrocarbons and by-products in the production of perforoperation quenching in condensation and Stripping columns, the first step is cooling the source of the reaction gas to the boiling point of the bottom liquid, for example, by sparging through the layer of the liquid and subsequent contacting the cooled gases from flowing phlegm on rectifying plates with a corresponding decrease in the concentration of high-boiling products in steam and gas phases at the height of condensation and Stripping columns [1].

The use of this method for quenching and separation of the reaction gases of the pyrolysis of dichloroethane in the production of vinyl chloride requires a relatively high temperature in the condensation-Stripping column due to the relatively high pressure of the pyrolysis process and raises concerns in parts of higher education is of current manufacture vinyl chloride, in particular the process of separating fine solid, resinous and high-boiling by-products from the reaction gases.

The closest way to the same destination to the claimed invention by the combination of features of the method of separation of finely dispersed solid, resinous and high-boiling by-products from the reaction gases of the pyrolysis of dichloroethane in the production of vinyl chloride having a temperature of 440-520oC and pressure of 10-18 ATM, by rapid cooling in the quenching column with subsequent separation of the products of pyrolysis of dichloroethane is a technical solution is described in [2].

Quenching of the reaction gases by this method is carried out at a temperature 105-200oC in column 1, acting on the principle of capacitor mixing by spraying the circulating pump 4 hardening liquid 2, formed during cooling of the reaction gases (Fig. 1). Next part 7a condensed in the condenser 6 of the reaction products are returned to the column 1, and the remaining part 7b together with gaseous products 8 and hardening the liquid is subjected to distillation in a system of distillation columns, providing for the allocation in the form of distillate original chloris is, the finally, the unreacted dichloroethane, returned to the pyrolysis. The selection is returned to the pyrolysis of dichloroethane carried out in conjunction with selection of the "high-boiling" by-products of direct dichloroethane, synthesized from ethylene and chlorine by original distillation of pure dichloromethane and then the residual dichloroethane from distillation products.

This classical scheme of hardening by cooling and separation of the reaction products by successive selection of light components has a number of serious drawbacks:

- heavy-duty system rectification, including the column quenching of the reaction gases, due to the presence in the bottom hardening liquid of high viscosity products (coke, tar), forcing to install on the lines of still liquids special filters 3 (Fig. 1) (only seven pairs of alternately operating apparatus for the separation of these impurities. Simultaneously, the presence of such impurities in the distillation of liquids distillation columns helps to reduce the duration of pre-owned boilers between cleanings. All of this involves significant use of manual labor for removal of the filters and boilers accumulating harmful products increased Stev difficult conditions due to the necessity of large circulation flow strongly pitched fluid with solid particles of coke;

- residual rectification dichloroethane after the selection is returned to the pyrolysis of dichloroethane may not be used for processing in other target products, for example in the production of perchloroethylene, trichloroethylene, and others , and shall be destroyed due to the presence of impurities chlorohydrocarbons fraction C4-C6(dichlorobutenes, chlorobenzene), which are formed during the pyrolysis of dichloroethane. The destruction of the bottoms is permanently lost and such relatively valuable for the synthesis of perchloroethylene and other products, as the highest haratani formed during the synthesis of dichloroethane.

The objective of the invention is the separation of finely dispersed solid, resinous and high-boiling by-products from the reaction gases of the pyrolysis of dichloroethane at the stage of hardening. When carrying out the invention may be obtained from the technical result:

- obtain the desired vinyl chloride of high quality;

- creation of conditions for a possible qualified using the side polyvinyl chloride fraction C2(the highest chloretone), formed during the synthesis of dichloroethane, for example, to obtain perchloroethylene, trichloroethylene, and others;

the concentration of COCs is we split gas mixture and consequently the exclusion of their falling into the boilers of the rectification column and labor costs for cleaning the latter.

This technical result is achieved by the fact that in the present method of selection of finely dispersed solid, resinous and high-boiling by-products from the reaction gases of the pyrolysis of dichloroethane in the production of vinyl chloride having a temperature of 440-520oC and pressure 10-28 ATM, by rapid cooling in the quenching column and subsequent separation of the products of pyrolysis, the peculiarity lies in the fact that quenching and separation of the pyrolysis gases is carried out by bubbling them through the layer of concentrated liquid by-products of these gases in the cube hardening of the column at the temperature of boiling 120-200oC and the subsequent contact of the gas mixture with return condensation of these gases on kapitbisig and mass transfer plates of a distillation zone hardening of the column with the cleaning gas mixture from the high-boiling components at the height of the zone of rectification, output of the accumulating liquid by-products, followed by additional separation and preconcentration by a single distillation and the feed gas mixture to the secondary rectification, allocation and output from the process products boiling above dichloroethane, and the return of the distillate of this rectify the district of gases is in contact with the return condensate (phlegm) 5 to 10 theoretical stages of mass transfer.

As shown by calculations, confirmed by practical experiments, setting just 15 real plates (about 8 theoretical stages of separation) allows to reduce the concentration of high-boiling by-products in the exhaust gas mixture to a value of less than 0.02%, and in the hardening liquid concentration increases, up to 10%. The increase in the number of theoretical stages of separation to 15-20 allows the value to increase to 30-40%. This complication technology is justified by the fact that the subsequent rectification raw "reverse" of dichloroethane together with direct dichloroethane allows its use distillation residues for processing into products such as perchlorethylene, etc. because they practically do not contain impurities chlorohydrocarbons C4-C6, giving such processing of a large number of by-products (Hexachlorobutadiene, hexachlorobenzene).

The method is as follows.

The reaction gases (temperature 440-520oC) of the coil of the furnace pyrolysis of dichloroethane served in the cube quenching column 1 (Fig.2) through a bubbler in a layer of concentrated liquid by-products at the temperature of boiling 120-200oC. the resulting pairs of the h-1 and arrives in the form 3 in the refrigerator 4. The condensate part of this gas mixture are returned to the quenching column 1 in the form of phlegmy 5A and part in the form of distillate 5B together with neskondensirovannyh flow 6 serves to further separate.

Taken from the bubble layer, the liquid 2 is served in the evaporator circuit, which includes a capacity of 7, a device for forced circulation 8 and the evaporator 9. Gas-vapor mixture from the evaporator served in the distillation column 11 and a heater 12, a condenser 13 and the reflux tank 14 for discharge from her target dichloroethane in the form of distillate, part of which is returned to distillation column 11 in the form of phlegmy by a pump 15, and a portion is directed into the quenching column 1 by a pump 16. CBM product 18 from the column 11 together with concentrated products osmola 17 is removed from the system.

Example 1. The reaction gases from the pyrolysis furnace which is supplied with dichloroethane 54 t/h to pyrolysis at a temperature of 500oC and a pressure of 20 ATM, proceed through the bubbler in the cube quenching column with a diameter of 2200 mm, the resulting gas-vapor mixture passes through two capleton and ten massoobmennyh plates and enters the refrigerator, where it is cooled to 80oC, and then the plate quenching column. The remainder of the condensate is directed to the rectification together with the exhaust gas-vapor mixture.

Taken from the bubble layer fluid in the number of 1600 kg/h emptied into a container, where at normal pressure is the partial evaporation by the heat of overheating, and also carry out the distillation by circulating pump through the evaporator "pipe in pipe" in the same capacity. Outgoing couple with a temperature of about 120oC is sent to distillation column with a diameter of 600 mm, equipped with 20 plates, irrigated from above phlegm in the amount of 1450 kg/h

Vapors from the upper part of the distillation column fed to the condensation in the refrigerator. Part of the condensate is returned to the rectification column, and the part with the pump returns to the fifth plate of the distillation zone hardening of the column.

Flow characteristics of the node quenching and separation are given in table 1.

Example 2. Unlike example 1, in the quenching column was established twenty-mass transfer plates (about 10 theoretical stages of mass transfer). The selection of the bottom liquid was 1400 kg/h

Characteristics of the work site hardening and separation are given in table 1.

Note the critical stages of mass transfer). The selection of the bottom liquid was 1200 kg/h

Description of site hardening and separation are given in table 1.

According to the estimates generated by overheating of the reaction gases evaporating liquid (flegma) enough to be distinguished from them with the required degree and components boiling above vinyl chloride.

Work hardening apparatus equipped with a distillation zone, accompanied by the production of condensate from the exhaust gas mixture, characterized by almost no coke and products osmola. This, in particular, have followed from the fact that phlegm is a colorless transparent liquid without mechanical impurities. As a consequence, the mileage of boilers between cleanings increased, at least up to one year, which can be seen from the following table 2.

Low content of coke and Asmolov in products coming to the division, follows also from the practical absence of these impurities in the filters installed on the supply lines of these columns.

For this reason, managed to reduce the content of residual dichloroethane in the bottom liquid of up to 10% against the hardly reached 20% when the hardening is their quenching column with a distillation zone allows processing bottoms last column separation of the products of rectification system dichloroethane (distillation residual dichloroethane) in the production of perchloroethylene.

The achievement of these positive effects is relatively easy to predict in the case of knowledge of the behavior of vinyl chloride in the considered conditions. Job new installation quenching the reaction gases of the pyrolysis of dichloroethane showed an unexpected positive result, such as enhancement of the quality of the final vinyl chloride and, correspondingly, of polyvinyl chloride, as compared with the product produced by using a mixture condenser for quenching the reaction gases of the pyrolysis of dichloroethane. The content of propylene in the vinyl chloride decreased from 4 to a maximum of 2 ppm (is 0.0002%), i.e. to the product requirements of the highest quality, 1,3-butadiene with 10-12 ppm up to 6 ppm (0,0006%) at the rate of 8 ppm, and the methyl chloride from 100 ppm to 60 ppm (at a rate of 80 ppm).

Literature

1. Tichinin C. N., Vasiliev B. N., Abdrashitov J. M. and other use of the heat of reaction gases for their separation in the production of perforoperation //Chemical industry - 1984.- # 4. page 7-9.

2. Patent DE 31 47 310 C2. C 07 C 21/06. 18.01.90.

1. The method of separation of finely dispersed solid, resinous and high-boiling by-products from the reaction gases of the pyrolysis of dichloroethane in the production of vinyl chloride having a temperature I of pyrolysis products, characterized in that the quenching and separation is carried out by bubbling them through the layer of concentrated liquid by-products of these gases in the cube hardening of the column at the temperature of boiling 120 - 200oC and the subsequent contact of the gas mixture with return condensation of these gases on kapitbisig and mass transfer plates of a distillation zone with the cleaning gas mixture from the high-boiling components at the height of the zone of rectification with the output of the accumulating liquid by-products, followed by additional separation and preconcentration by a single distillation and the feed gas mixture to the secondary rectification with the selection and output of the process products boiling above dichloroethane, and the return of the distillate of this rectification in the process.

2. The method according to p. 1, characterized in that the gas-vapor mixture after quenching the reaction gases in contact with the return condensate (phlegm) 5 to 10 theoretical stages of mass transfer.

 

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