RU2252207C1 - Method for isolation of fine dispersed, gummy and high boiling by-products from dichloroethane pyrolysis reaction gases from vinylchloride production - Google Patents

Abstract

FIELD: chemical technology, in particular method for vinylchloride production.

SUBSTANCE: claimed method includes fast gas cooling in quenching column followed by separation of pyrolysis products. Quenching and separation are carried out by barbotage through the layer of liquid concentrated by-products of these gases in quenching column cube. Then steam/gas mixture is brought into contact with returning condensate in regular filling layer of rectification tower with simultaneous purification of steam/gas mixture in rectification zone upstream. Liquid concentrated by-products are additionally rectified in vacuum with isolating and recovery of products having boiling point higher than the same for dichloroethane and distillate recycling. Method of present invention also makes it possible to produce perchloroethylene and tricloroethylene.

EFFECT: vinylchloride of high quality; reduced effort and energy consumption.

2 tbl, 4 dwg, 2 ex

Description

The invention relates to the technology of basic organic synthesis and can be used in the separation of finely divided solid, tarry and high boiling point by-products from the reaction gases of dichloroethane pyrolysis in the production of vinyl chloride used to produce polymeric materials, in particular polyvinyl chloride.

There is a method of separating finely dispersed resinous and high boiling point by-products from dichloroethane pyrolysis reaction gases in the production of vinyl chloride having a temperature of 440-520 ° C and a pressure of 10-28 atm by rapidly cooling them in a quenching column followed by separation of dichloroethane pyrolysis products (patent DE 3147310, C 07 C 21/06, 01/18/90).

The quenching of the reaction gases by this method (Fig. 1) is carried out at a temperature of 105-200 ° C in a column 1 operating according to the principle of a mixing condenser by spraying a quenching liquid 2 cooled by means of a pump 4 and generated by condensation of the reaction gases. Next, part 7a of the reaction products condensed in the condenser 6 is returned to column 1, and the remaining part 7b together with gaseous products 8 and quenching liquid are subjected to rectification in a distillation column system, which provides for the distillation of initially hydrogen chloride, then vinyl chloride, and then “low-boiling” by-products pyrolysis products and, finally, unreacted dichloroethane returned to pyrolysis, which is released together with "high boiling point by-products". Separation of the dichloroethane returned to the pyrolysis from the "high-boiling" by-products is carried out in conjunction with the separation of the "high-boiling" by-products from the "direct" dichloroethane synthesized from ethylene and chlorine by the initial distillation of pure dichloroethane and then residual dichloroethane from the bottoms.

This classical scheme of quenching by cooling and separation of reaction products by sequential separation of light components has a number of serious drawbacks:

- difficult operating conditions of the rectification system, including the column for quenching the reaction gases, due to the presence of highly viscous products and solid resinous particles in the bottom quenching liquid. This forces the installation of special filters 3 on the bottoms liquid lines to separate these impurities. At the same time, the presence of such impurities in still liquids of distillation columns helps to reduce the duration of the run of boilers between cleanings;

- the presence in the technological scheme of the hardening column of the circulation pump and the need for circulation of a large stream of highly tarred liquid;

- bottoms of dichloroethane rectification after separation of dichloroethane returned to pyrolysis cannot be used for processing into other target products and must be destroyed. As a result, valuable products, such as higher chloroethanes, are irretrievably lost.

The closest analogue of this invention (prototype) is a method for the separation of finely divided solid, tarry and high boiling point by-products from dichloroethane pyrolysis reaction gases in the production of vinyl chloride, which is as follows (patent RU 2153486 C 07 C 7/09, 7/11, 17/25 , 21/06).

The reaction gases (temperature 440-520 ° C) from the coil of the dichloroethane pyrolysis furnace (Fig. 2) are fed into the cube of the quenching column 1 through a bubbler into a layer of concentrated concentrated by-products at a boiling point of 120-200 ° C. The resulting vapor-gas mixture passes through the drop-off 19 and mass transfer 20 plates of the distillation zone of the quenching column 1 and enters as a vapor-gas mixture 3 freed from high-boiling components into the refrigerator 4. Part of the condensate of this vapor-gas mixture is returned to the quenching column 1 in the form of reflux 5a, and part in the form distillate 5b together with the non-condensed stream 6 is fed to a further separation.

The liquid 2 taken from the bubbling layer is fed into the evaporation circuit, which includes a container 7, a forced circulation device 8 and an evaporator 9. The vapor-gas mixture from the evaporation circuit is fed to a distillation column 11 with a boiler 12, a condenser 13 and a reflux tank 14 to separate the target dichloroethane in the form of a distillate, part of which is returned to the distillation column 11 in the form of reflux using a pump 15, and part is sent to the quenching column 1 using a pump 16. The bottom product 18 from the column 11 ovmestno with concentrated products osmol 17 discharged from the system.

However, the method has several significant disadvantages:

- distillation column 11 operates under atmospheric pressure, which leads to a high boiling point in the evaporator and, as a result, the grinding of products and the formation of solid deposits on the heating surface;

- high (about 20 wt.%) concentration of dichloroethane in waste sent for disposal;

- the presence of the evaporation circuit, including the tank 7, the device for forced circulation 8 and the evaporator 9 makes the node for the additional separation of liquid by-products cumbersome and metal-intensive.

The essence of the invention lies in the fact that in the method of separating finely divided solid, tarry and high boiling point by-products from dichloroethane pyrolysis reaction gases in the production of vinyl chloride by rapidly cooling them in a quenching column and subsequent separation of the pyrolysis products by sparging them through a layer of concentrated liquid by-products of these gases into cube of the quenching column with subsequent contact of the gas mixture with the return condensate of these gases in the distillation zone, providing m cleaning the vapor-gas mixture from high-boiling products, withdrawing by-products and their further distillation with separation and withdrawal of finely dispersed solid, tarry particles and products boiling above dichloroethane, and returning the distillate to the process, additional distillation is carried out under vacuum in a distillation column equipped with regular nozzle and high-speed evaporator with the withdrawal of finely dispersed solid, tarry particles and high boiling point by-products with still bottoms of the column.

When carrying out the invention, the following technical result is achieved:

- reduced to ~ 5 wt.% loss of dichloroethane due to a decrease in its content in the waste sent for disposal by lowering the boiling point and eliminating the polymerization processes in the evaporator of the additional distillation column;

- provides high quality vinyl chloride;

- conditions are created for the possible qualified use of C ₂ fraction polychlorides formed during the synthesis of dichloroethane, for example, for the production of perchlorethylene, trichlorethylene, etc.

- provides the concentration of coke, tarry and high-boiling by-products of the dichloroethane pyrolysis reaction and their withdrawal from the separation system of the gas-vapor mixture with the still residue of the additional distillation column;

- the overall dimensions and metal consumption of the installation are reduced by eliminating the evaporation circuit and supplying the liquid directly to the distillation column.

The presence of one new distinctive feature in comparison with the prototype determines the conformity of the claimed technical solution to the criterion of "novelty."

The compliance of the claimed technical solution with the criterion of “inventive step” is due to the appearance in the aggregate of essential features of a new technical result, which consists in reducing the loss of dichloroethane in waste sent for disposal by lowering the boiling point and eliminating the polymerization processes in the evaporator of the rectification column. Figure 3 shows the dependence of the boiling point of the waste sent for disposal on pressure at different concentrations of dichloroethane. It can be seen that at a pressure of P = 1 at the boiling point of the mixture with a concentration of dichloroethane X = 20 wt.% (The dashed line corresponding to the operation of the column according to the prototype) is ~ 120 ° C. If you lower the pressure to P = 0.1 atm, then the mixture with a lower concentration of dichloroethane X = 5 wt.% Will have a boiling point t = 105 ° C (curve 1). It follows from this that without exceeding the permissible temperatures, it is possible to reduce the loss of dichloroethane with waste by more than three times.

The process of distillation in a column under vacuum allows you to reduce the boiling point of the mixture in the evaporator and to dispose of the mixture with a higher content of high boiling impurities. This, in turn, leads to a reduction in waste dichloroethane. Figure 3 (curve 4) shows the dependence of the boiling point of the liquid on the content of high-boiling impurities at a pressure in the cube of the column P = 0.5 atm. It is seen that the boiling point of 113 ° C corresponds to a concentration of high-boiling impurities of 90 wt.% And, accordingly, a dichloroethane concentration of less than 3 wt.%.

The list of figures in the drawings:

Figure 1 - diagram of a method for the separation of finely resinous and high boiling point by-products from the reaction gases of dichloroethane pyrolysis in the production of vinyl chloride by analogy to DE 3147310.

Figure 2 is a diagram of a method for the separation of finely dispersed resinous and high boiling point by-products from the reaction gases of dichloroethane pyrolysis in the production of vinyl chloride according to the prototype.

Figure 3 - dependence of the boiling point of the waste sent for disposal, on pressure at different concentrations of dichloroethane.

4 is a diagram of the proposed method for the separation of finely dispersed tarry and high boiling point by-products from the reaction gases of dichloroethane pyrolysis in the production of vinyl chloride.

The method is as follows. The reaction gases (temperature 440-520 ° C) from the coil of the dichloroethane pyrolysis furnace are fed into the cube of the quenching column 1 through a bubbler into a layer of liquid concentrated by-products at a boiling point of 120-200 ° C. The resulting vapor-gas mixture passes through a layer of a regular packing 2 of the distillation zone of the quenching column 1 and enters the refrigerator 4, freed from the high-boiling components of the vapor-gas mixture 3.

Part of the condensate of this vapor-gas mixture is returned to column 1 in the form of reflux 5a, and part in the form of distillate 5b together with non-condensed stream 6 is fed for further separation.

Fine solid, resinous products from the reaction gases of pyrolysis are trapped in the bubble layer of the quenching column. The liquid 7 taken from the bubbling layer together with finely dispersed resinous products is fed through a reducing valve 8 to the middle part of the distillation column 9, equipped with a regular nozzle 10 and 11, a high-speed evaporator 12, which works together with a circulation pump 13, a condenser 14 and a reflux tank 15. Vacuum in the column 9 is created by condensation of vapors and is supported by a vacuum pump 16. A part of the condensate from the tank 15 is returned by the pump 17 to the column 9 in the form of reflux 18a, and a part 186 by the pump 19 is sent to the quench th column 1.

The bottoms product from the column 9, together with the finely divided resinous products 20, is removed from the system for disposal.

The use of a regular nozzle and a high-speed evaporator, working in conjunction with a circulation pump, makes the distillation column 9 insensitive to the presence of solid finely dispersed substances in the liquid, which are discharged together with concentrated high-boiling components. The composition of the material flows are presented in table 1.

Table 1 The approximate composition of the flows in the circuit (figure 4) The concentration of components,% of the mass. No. p / p Mixture components Pyrogas Stream 3 (pairs from the quenching column) Stream 7 (quench column fluid) Stream 20 (waste from a vacuum distillation column) 1 Hydrogen chloride 18.14 18.28 - - 2 Acetone 0.04 0.04 - - 3 Vinyl chloride 30.95 31,0 - - 4 1,1-Dichloroethane 0.15 0.15 - - 5 Carbon tetrachloride 0.05 0.05 - - 6 Benzene 0.72 0.70 - - 7 1,2-Dichloroethane 49.58 49.76 89.0 5,0 8 Trichlorethylene 0.15 0.02 4.3 38.9 nine 1,1,2-Trichloroethane 0.01 0.02 0.3 2.7 10 M-Dichlorobenzene 0.06 0.02 1.7 15.4 eleven Tetrachlorethylene 0.15 0.02 4.2 38,0 12 Fine solid products + - + +

Example 1 of the method.

From the bubbling layer, liquid in the amount of 1600 kg / h is supplied to the middle part of the vacuum distillation column 9, equipped with a regular nozzle and refluxed at the top in the amount of 1450 kg / h. To prevent polymerization of the separation products in a high-speed evaporator, it is necessary to maintain a temperature of about 120 ° C.

When carrying out the process at atmospheric pressure, a boiling point of 120 ° C has a mixture with a dichloroethane content of 20 wt.% (Fig. 3, point A). Lowering the pressure in the column to 0.4 atm ensures at a permissible temperature of 120 ° C the boiling of the mixture with a dichloroethane content of 5 wt.% (Fig. 3, point B). This leads to a decrease in losses of dichloroethane with high-boiling waste by 44 kg / h and to a decrease in waste sent for disposal by 16% (see table).

table 2 No. p / p The name of the indicator and its dimension The value of indicators prototype by the proposed method 1 The amount of fluid taken from the column 1, kg / h 1600 1600 2 The concentration of dichloroethane in the liquid taken from the column 1,% of the mass. 86 86 3 The boiling point of the mixture in evaporators, ° C 120 120 4 The concentration of dichloroethane in waste sent for disposal,% of the mass. twenty 5 5 The amount of waste sent for recycling, kg / h 280 236 6 The amount of dichloroethane in waste sent for disposal, kg / h 56 12 7 Reducing the loss of dichloroethane compared with the prototype, kg / h - 44

Example 2 of the method.

In contrast to the conditions of example 1, the pressure in the vacuum column 9 is reduced to 0.1 at. This leads to a decrease in the boiling point of the mixture with a dichloroethane content of 5 wt.% To 105 ° C. Lowering the boiling point from 120 ° C to 105 ° C (Fig. 3, points C) will slow down the polymerization of the separation products in the evaporator circuit and, therefore, reduce the pollution of the heating surface during operation.

In this case, the performance of the installation will remain the same as in example 1.

Claims (1)

The method of separation of finely dispersed solid, tarry and high boiling point by-products from dichloroethane pyrolysis reaction gases in the production of vinyl chloride by rapidly cooling them in a quenching column and subsequent separation of the pyrolysis products by bubbling them through a layer of concentrated liquid by-products of these gases in a cube of the quenching column with subsequent contact of a vapor-gas mixture with the return condensate of these gases in the distillation zone, ensuring the cleaning of the gas mixture from high-boiling products, the withdrawal of by-products and their additional distillation with the separation and withdrawal from the process of fine solid, tarry particles and products boiling above dichloroethane, and returning the distillate to a process, characterized in that the additional distillation is carried out under vacuum in a distillation column equipped with a regular packing and high-speed evaporator with the withdrawal of finely divided solid, tarry particles of high-boiling by-products with still bottom of the column.

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