RU2114812C1 - Dichloroethane production process - Google Patents

Abstract

FIELD: industrial organic synthesis. SUBSTANCE: dichloroethane is produced by chlorination of ethylene in liquid reaction product medium in several reaction zones involving reactant straight flow and recycle of reaction mass from upper reaction zone into lower one caused by natural circulation of reaction mass. Method is distinguished by that reaction mass is picked out from several upper reaction zones and introduced into at least two reaction zones. EFFECT: intensified process and improved its safety.

Description

 The invention relates to a method for producing dichloroethane, which finds use as a solvent, as well as an intermediate for the production of vinyl chloride.

 To obtain dichloroethane in industry, the method of chlorination of gaseous ethylene with gaseous chlorine in the medium of liquid reaction products consisting mainly of dichloroethane is used. The process is carried out at the boiling point of dichloroethane with the removal of the reaction heat due to the evaporation of the reaction products. The range of operating temperatures varies widely depending on the pressure and amount of inert gases in chlorine and ethylene (patent 2929852, 260-660, 1960).

 The closest analogue of this invention is the current production of dichloroethane. The chlorination process is carried out in the environment of the reaction products in the presence of ferric chloride, which is formed due to corrosion of the equipment or injected in the form of a solution in dichloroethane from the bottom of the column as a corrosion product of pipelines and apparatuses, in several reaction zones during the direct flow of reactants with recycling of the reaction mixture from the upper reaction zone to the lower due to the natural circulation of the reaction mass. The reaction unit is a column filled with liquid reaction products and divided in height into 7 reaction zones by means of 6 sectional sieve plates with a live section of 36%. The reactor is equipped with an external circulation pipe that connects the upper and lower reaction zones (Fig. 1).

 The natural circulation of the reaction mass from the upper to the lower zone is due to the difference in the specific gravities of the gas-filled reaction mass in the column and the gas-free reaction mass in the circulation pipe (Technological Regulation of Dichloroethane, Sterlitamak, 1990).

 The process is carried out at a pressure at the top of the reactor 0.11 MPa at the boiling point of dichloroethane with ethylene (stream 1) and chlorine (stream 2) introduced into the lower reaction zone and the reaction product is withdrawn in the form of vapors together with inert gases and unreacted ethylene and chlorine from the vapor space upper reaction zone (stream 3). In the upper reaction zone, a constant level of liquid reaction mass is maintained by introducing a portion of the condensed dichloroethane vapor into the lower reaction zone (stream 4), because in terms of heat balance, the amount of dichloroethane vapor discharged from above significantly exceeds the amount of dichloroethane synthesized in the reactor.

 The disadvantage of this method of producing dichloroethane is the danger of combustion and explosion of a gas mixture of chlorine and ethylene when the circulation ceases if the liquid level in the upper zone decreases below the level of selection of the circulating reaction mass. The cessation of circulation leads to the formation of "gas cushions" under the partitioning plates. The formation of "gas cushions" - zones free of the liquid phase - is explained by the fact that the circulating stream 5 is one or two orders of magnitude larger than the condensate stream 4, and when the circulation ceases, the mechanical entrainment of the liquid from the underlying zone to the overlying one slightly exceeds the value of stream 4. When In this case, under the sectioning plate, a zone is formed free of liquid of such a height at which equilibrium is established: the entrainment of the liquid becomes equal to the arrival.

 The formation of liquid-free zones is unacceptable, because leads to the reaction of chlorine and ethylene in the gas phase, which can lead to combustion and explosion with large volumes of "gas cushions".

 With the existing method of producing dichloroethane to ensure safety conditions, taking into account the possibility of a decrease in the level due to a failure of the level control system or a failure of the flow supply system 4, the process is conducted at a high height of the liquid layer above the level of withdrawal of the circulating reaction mass and at large live sections of the sectioning plates. A large live section of the plates in the range of 10–40% at low gas velocities in the plate openings ensures a “dip” of the liquid through the plate from the overlying zone to the underlying one. In this case, the fluid flow from the overlying zone to the underlying (“dip”) compensates for the mechanical entrainment from the underlying zone to the overlying one, the height and volume of the “gas cushion” are reduced and the risk of explosion is reduced. Operation at low gas speeds in the openings of the plates, due to the need to have a large live section of the plates, leads to a decrease in the overall speed of the process, since the rate of the dichloroethane synthesis process is determined by the mass transfer rate.

 The objective of the invention is to provide safe conditions for the preparation of dichloroethane by chlorination of ethylene in the environment of liquid reaction products while enhancing the process.

 The problem is solved by obtaining dichloroethane by chlorination of ethylene in the liquid reaction products in several reaction zones during the direct flow of reactants with recycle of the reaction mass from the upper reaction zone to the lower due to the natural circulation of the reaction mass during the selection of the circulating reaction mass from several upper zones with the introduction of the circulating reaction mass in at least two reaction zones.

 Distinctive features of the proposed method is the selection of a circulating reaction mass from several upper zones with the introduction of a circulating reaction mass in at least two reaction zones.

 The selection of the circulating reaction mass from several upper zones with the introduction of the circulating reaction mass into at least two reaction zones, preferably the middle and lower, allows the natural circulation of the reaction mass to fall when the liquid level in the upper circulation zone falls below the level of withdrawal of the circulating reaction mass from this reaction zones. Preservation of circulation ensures the safety of the process, allows you to conduct the process at higher speeds in the holes of the plates, using plates with a small live section, which intensifies the chlorination process by increasing the mass transfer coefficient. The increase in mass transfer coefficient is also due to an increase in the circulation flow in the upper reaction zones due to the formation of at least two circulation circuits.

 In FIG. 1 is a flow diagram of a known dichloroethane production process. Chlorination is carried out in several reaction zones, in this example, in 9, with the introduction of ethylene (stream 1), chlorine (stream 2) and dichloroethane condensate (stream 4) in the lower zone. The reaction products in the form of vapors and unreacted gases are removed from the vapor space of the upper zone (stream 3). The circulation of the reaction mass is carried out during the selection of the circulating stream from the upper reaction zone with its input into the lower reaction zone (stream 5).

 In FIG. 2 shows a flow diagram of the proposed method for the preparation of dichloroethane. Chlorination is carried out in several reaction zones, in this case at 9, with the introduction of ethylene (stream 1), chlorine (stream 2) and dichloroethane condensate (stream 4) into the lower zone. The reaction products in the form of vapors and unreacted gases are removed from the vapor space of the upper zone (stream 3). The reaction mass is circulated during the selection of the circulating stream both from the upper zone (stream 5) and from several lower located zones (stream 6) with the introduction of the circulating stream both in the lower zone (stream 7) and in one of the middle zones (stream eight). The magnitude of the stream 7 can be both greater and less than the stream 5. At the same time, at least two circulation circuits are realized: a general circulation circuit covering all reaction zones, and a local circulation circuit covering several upper reaction zones.

 Example 1. In an industrial reactor for the production of dichloroethane with a diameter of 3200 mm and a liquid layer height of 9000 mm, divided into 9 reaction zones by sieve plates with a live section of 6% in the upper part and 16% in the lower part, chlorine is continuously fed into the lower reaction zone (chlorine concentration - 80%) in an amount of 2120 nm / h and ethylene (ethylene concentration of 99.9%) in an amount of 1825 nm / h. The reaction mass is circulated with selection from the 4 upper reaction zones and with entry into the reaction zones 1 and 6, counting from the bottom, as shown in FIG. 2.

 The chlorination process is carried out at the boiling point of the reaction mixture at a pressure at the top of the reactor 0.11 MPa. The reaction products, mainly dichloroethane, are discharged in the form of vapors and unreacted gases from the vapor space of the upper zone, cooled in a condenser, part of the condensate is returned to the lower zone to maintain a constant liquid level in the reactor, the remaining condensate in an amount of 7500 kg / h enters the finished tank product, chlorine conversion is 100%, ethylene conversion is 93%, i.e. slip ethylene is 7% of the filed.

 Example 2 (prototype). In an industrial reactor for the production of dichloroethane with a diameter of 3200 mm and a liquid layer height of 9000 mm, divided into 9 zones by sieve plates with a live section of 36%, chlorine (chlorine concentration of 80.5%) in the amount of 2108 nm / h and ethylene are continuously fed into the lower reaction zone (ethylene concentration 99.9%) in an amount of 2020 nm / h. The reaction mass is circulated, withdrawn from the upper reaction zone and introduced into the lower reaction zone, as shown in FIG. one.

 The chlorination process is carried out at the boiling point of the reaction mixture at a pressure at the top of the reactor 0.11 MPa. The reaction products, mainly dichloroethane, in the form of vapors and unreacted gases are removed from the vapor space of the upper zone, cooled in a condenser, part of the condensate is taken to the lower zone to maintain a constant liquid level in the reactor, the rest of the condensate in the amount of 7500 kg / h enters the ready-made tank product. Chlorine conversion is 100%, ethylene conversion is 84%, i.e. slip ethylene is 16% of the filed.

 Thus, the preparation of dichloroethane by the proposed method allows to reduce the leakage of chlorine by more than two times while ensuring the conditions for a safer chlorination process.

Claims (1)

 The method of producing dichloroethane by chlorination of ethylene in the liquid reaction products in the presence of ferric chloride at a boiling point of the reaction mass in several reaction zones during the direct flow of reactants with recycle of the reaction mass from the upper reaction zone to the lower reaction zone due to the natural circulation of the reaction mass, characterized in that the selection the circulating reaction mass is carried out from several upper reaction zones with the introduction of a circulating reaction mass in at least two reaction zones .

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