RU2179546C1 - Method of preparing vinyl chloride - Google Patents

Abstract

FIELD: chemical industry. SUBSTANCE: described is method of preparing vinylchloride by thermal pyrolysis of dichloroethane. Process comprises feeding pyrogas through waste heat recovery boiler into hardening column from top of which gaseous phase containing vinyl chloride dichloroethane and hydrogen chloride is withdrawn. After cooling, partial condensation and separation of reflux liquid, the remaining products of said phase are fed into rectification columns for isolation of hydrogen chloride, vinyl chloride and dichloroethane. Pyrogas in waste heat recovery boiler is cooled with water preheated with gaseous phase of hardening column to produce high-pressure steam. Waste heat recovery boiler top is connected with sectionized container and preheated water is fed into upper portion of said container. Gaseous phase partially cooled with said water is then cooled in heat exchanger with initial dichloroethane which is then fed into pyrolysis furnace. Vinyl chloride prepared process gives full use of heat of reaction gases. EFFECT: more efficient preparation method. 3 cl, 1 tbl

Description

 The invention relates to the chemical industry in terms of obtaining a chlorine-containing monomer - vinyl chloride from dichloroethane.

A known method of producing vinyl chloride by thermal pyrolysis of dichloroethane with subsequent hardening of the resulting mixture and its rectification [application of Germany 2925720, MKI C 07 C 21/06]. From the pyrolysis furnace, a mixture containing dichloroethane formed during decomposition at a temperature of 480-560 ^o C and a pressure of 1.5-2.5 MPa vinyl chloride and other products are introduced into the heat exchanger. The latter is cooled with liquid and gaseous substances to drastically reduce the temperature to 120-220 ^o C (preferably up to 100-150 ^o C). For this purpose, for example, water, mineral oil, diphenyl, silicone oil are used. Further cooling is carried out using a mixture containing more than 50% dichloroethane, which is injected into the gas stream or in contact with it in a countercurrent quenching column. The cooling rate of the gas mixture should be ( ^o C / s) 1 / 4-1 / 9 (preferably 1 / 5-1 / 7) of the temperature of the gas entering the cooling system. The heat taken from the gas mixture is used to heat the cube of the distillation column. Typically, two-stage cooling is used: at the first stage, the gas from the furnace is cooled to 120-220 ^{o C.} , at the second - to 60-100 ^o C.

 The disadvantages of the method include the insufficient full utilization of the heat of the reaction gases.

Closest to the proposed technical solution is a method for producing vinyl chloride by thermal pyrolysis of dichloroethane [application Germany 3135242, MKI C 07 With 21/06, 17/34], in accordance with which the process is as follows. The gas leaving the reaction zone of the furnace with a temperature of about 500 ^° C and a pressure of 15 atm is cooled to 160-200 ^° C by mixing with dichloroethane. The latter is taken from a quenching column with a temperature of 140 ^o C. This dichloroethane contains up to 15% of high boiling compounds. Then the pyrogas is cooled in a quenching column to 130-150 ^o With the simultaneous separation of high-boiling compounds, coke and tar from the reaction gas. The gas leaving the top of the quenching column containing vinyl chloride, dichloroethane and hydrogen chloride is cooled to 90-110 (preferably 100) ^o С in the condenser of the column using water. This gives 0.4 tons of process steam with a pressure of 1.7 atm per 1 ton of vinyl chloride. Part of the condensate obtained is returned to the quenching column in the form of reflux, and the other part, together with the gas, is fed to the heat exchanger. Gas and condensate from a heat exchanger with a temperature of 40-60 ^o With are subjected to rectification on two columns and get hydrogen chloride, vinyl chloride and dichloroethane. A mixture of high boiling compounds and resins taken from the cube of the quenching column is distilled in a distillation column. Part of the obtained distillation with a boiling point of 130 ^o C and below, containing dichloroethane, after condensation is returned to the distillation column in the form of reflux. The other part is introduced into the cube of the quenching column. Fresh dichloroethane is periodically added to dichloroethane to be returned to the distillation column to control the butadiene impurity content of the resulting vinyl chloride. The latter contains not more than 1400 ppm of chlorine and not more than 40 ppm of iron. The consumption of this dichloroethane is not more than 1 (preferably 0.05-0.2) mol% of the amount of dichloroethane fed to the furnace. Such dichloroethane is obtained, for example, by chlorination of ethylene in the presence of iron compounds.

 The main disadvantage of this method is the insufficiently rational use of high potential (high temperature) heat of the reaction gases and the deposition of coke and resins on plates and in the boiler of a distillation column.

 The objective of the invention is to obtain vinyl chloride by pyrolysis of dichloroethane with a more rational and full use of the heat of the reaction gases.

 The problem is solved by the proposed method for the production of vinyl chloride by pyrolysis of dichloroethane, including cooling the resulting pyrogas and directing it into the quenching column to separate the gaseous phase containing vinyl chloride, hydrogen chloride and dichloroethane and the quenching column discharged from above, and high-boiling compounds concentrated in the column cube. The gaseous mixture from the quenching column is sent for cooling to obtain condensate, which is partially returned as reflux to the quenching column, and the remaining condensate, together with the gas phase, is sent to successive distillation columns to isolate hydrogen chloride, vinyl chloride and dichloroethane. The high boiling bottoms fraction from the quenching column is directed to the separation of dichloroethane from it, which is returned to the process, and the resinous ones are removed.

 According to the proposed method, the cooling of the pyrogas is carried out in a recovery boiler, which in the upper part is connected to a sectioned tray with a tank, the upper part of which is supplied with water pre-heated in the first downstream heat exchanger-utilizer, leaving the quenching column, by evaporation of which high vapor is produced pressure, while the initial dichloroethane is preheated before being fed to the pyrolysis furnace in a second heat exchanger-utilizer due to the residual heat cooled in it the gaseous mixture of the quenching column, and further cooling of the gaseous mixture is carried out in the third heat exchanger-utilizer with air, which, after heating, is fed to the burners of the pyrolysis furnace to burn gaseous or liquid fuel.

 In addition, according to the proposed method, bottoms liquid from the quenching column is withdrawn to a clarification system to separate dichloroethane vapors from the liquid phase containing resins and coke, and dichloroethane vapors are sent to a hydrogen chloride distillation column. The clarification system includes a tank, a pump and an evaporator, through which the still liquid of the quenching column is passed with a linear velocity of 10-100 m / s.

The process of thermal pyrolysis or dehydrochlorination of dichloroethane consists in the decomposition of dichloroethane by heating to a temperature of 480-520 ^o With vinyl chloride and hydrogen chloride.

 The dichloroethane pyrolysis stage includes a pyrolysis furnace, a pyrogas quenching column, a condensation unit for the vapors leaving the top of this column, a clarification unit for the bottom quenching columns, a distillation column designed to isolate the fraction of dichloroethane returned to the process, and the fraction of high-boiling by-products sent for combustion .

 The proposed method differs from the known one in that the cooling of the pyrogas is carried out in a recovery boiler, which is connected at the top to a sectioned plate with a tank, the top of which is supplied with water preheated in the heat exchanger-utilizer due to the heat of the gaseous mixture leaving the quenching column, as a result vaporization of which high-pressure steam is obtained, while the initial dichloroethane is preheated before being fed to the pyrolysis furnace in a heat exchanger-utilizer due to residual heat hlazhdaemoy therein a gaseous mixture vakadki column.

 In addition, further cooling of the gaseous mixture is carried out in the next (third) heat exchanger-utilizer with air, which, after heating, is fed into the burners of the pyrolysis furnace for burning fuel.

 The bottom liquid from the quenching column is passed through a clarification system, including a tank, pump and evaporator, at a speed of 10-100 m / s to separate the liquid phase containing resins and coke from dichloroethane vapors sent to the distillation column for the separation of hydrogen chloride.

 The drawing shows a diagram of the production of vinyl chloride by thermal pyrolysis of dichloroethane according to the proposed method. Dichloroethane rectified with a basic substance content of at least 99.3% is fed into the coil of the dichloroethane R-1 pyrolysis furnace.

 The pyrolysis furnace consists of 3 chambers - radiant, transitional (shock) and convective, united by a common frame, a chimney mounted in the side walls of the burner furnace, duct systems and fuel supply to the burners, as well as a coil located inside the furnace. The latter is conditionally divided into several zones.

Located in the convection chamber of the furnace, the part of the coil is a dichloroethane heating zone, where it is heated to a temperature of 215-245 ^o С and fed to the evaporation zone. A part of the coil is located in the shock chamber, which is the overheating zone and where dichloroethane vapors overheat to 320-370 ^o С. The part of the coil located in the radiant chamber is reactionary. The process of pyrolysis of dichloroethane takes place directly in it.

It is known that coke formation occurs at a noticeable rate upon contact of liquid hydrocarbons with a metal surface heated to a temperature above 300 ^o C.

The dichloroethane pyrolysis is carried out at a temperature of 320-370 ^o C at the inlet and 480-520 ^o C at the outlet and an inlet pressure of 20-25 kgf / cm ² and an exit of 16-24 kgf / cm ^{2 of the} reaction zone.

Pyrolysis reaction gases with a temperature of 480-520 ^o C are fed into a recovery boiler KU-1, during passage through which the gas temperature decreases to a temperature that excludes condensation of organochlorine products due to heat transfer from boiler water preheated to 140-150 ^{o C.} A recovery boiler is an apparatus in which pyrolysis gas passes at high speed through pipes immersed in a layer of liquid water condensate. The top of the recovery boiler is a bowl-partitioned container. In this tank, water vapor is saturated due to its bubbling through a layer of water. In addition, using this tank, the water level in the waste heat boiler can be kept constant even with sharp changes in the flow rate of the supplied pyrogas.

 The installation of the recovery boiler KU-1 immediately after the pyrolysis furnace makes it possible to regenerate most of the heat of the pyrolysis gases to produce water vapor at a pressure of 12 atm.

The pyrolysis reaction gases after the KU-1 waste heat boiler with a temperature of 150-300 ^o C are fed to the lower part of the K-1 quenching column, where they are bubbled through a liquid layer to quickly reduce the temperature to a level of 170-200 ^o C. The gaseous mixture is first cleaned from carried away drops of quenching liquid on failure plates and further rectification in the upper part of the column on plates due to contact with flowing reflux.

The reflux temperature is maintained within the range of 50-80 ^o C, and the temperature of the column cube is 170-200 ^o C. As a result of rectification, the bulk of the high boiling organic and organochlorine by-products and resins are separated from the pyrolysis products, removing them from the column with bottoms flow.

The gaseous mixture leaving the top of the K-1 column, not containing coke and tar, with a temperature of 160-170 ^o С is first fed to a counterflow heat exchanger-heat exchanger TU-1, where it is cooled with boiler water. The latter is heated to 100-140 ^o With and then served in a waste heat boiler KU-1 to obtain water vapor.

The vapor-liquid mixture of pyrolysis products from the TU-1 heat exchanger is sent to the TU-2 heat exchanger-heat exchanger, where it is cooled to a temperature of 100-120 ^o C. The refrigerant - dichloroethane supplied to this heat exchanger is heated to a temperature of 80-100 ^o C and then introduced into the coil located in the convection zone of the pyrolysis furnace.

 The vapor-liquid mixture of pyrolysis products leaving the second heat exchanger-utilizer TU-2 is separated into gaseous and liquid streams.

Further cooling to 50-70 ^o With a gaseous mixture with condensation of the main part of dichloroethane and a significant part of vinyl chloride is carried out in a heat exchanger-utilizer TU-3 with air, which after heating fall into the burners of the pyrolysis furnace to burn fuel.

 The cooled liquid from the last two heat exchangers TU-2 and TU-3 is sent to the reflux tank E-1, from which part of the liquid is fed to the top of the quenching column K-1 as reflux, and the remaining part of the liquid is sent for separation into the hydrogen chloride K separation column -2.

 The non-condensed gas stream from the TU-3 heat exchanger-heat exchanger is fed to the T-1 heat exchanger, which is cooled by a cooled gaseous hydrogen chloride, which is removed from the top of the K-2 hydrogen chloride evolution column. The vapor-liquid mixture from the heat exchanger T-1 is sent to the tank E-2, in which the gas and liquid phases are separated. Both phases from the tank E-2 are sent to the separation in a column of the allocation of hydrogen chloride in separate streams.

 The bottoms product of the K-1 hardening column, containing coke, tar products and high boiling point by-products, is purified on a clarification system. From the tank E-3, using the pump N-1, the bottled product is pumped at a linear speed of 10-100 m / s through a T-2 type pipe-to-pipe evaporator to heat the circulating mixture to a boiling point. For this purpose, heating steam with a pressure of 1.2 MPa is used. The vapor-liquid mixture from the T-2 evaporator is returned to the E-3 tank, where in the expander installed above the tank, the vapor phase is separated from the liquid phase. The vapor phase that does not contain coke and tar products is fed to a K-2 distillation column. The liquid containing tar and coke from the tank E-3 periodically removed for combustion.

 The distillation column K-2 is designed to isolate hydrogen chloride. The K-2 column is equipped with a T-3 condenser and a T-4 boiler. The bottom liquid of this column is sent to a K-3 column to separate vinyl chloride and dichloroethane that did not react during pyrolysis. The distillation column K-3 has a T-5 condenser and a T-6 boiler.

 Thus, the proposed scheme of the unit for quenching pyrolysis gases makes it possible to utilize high-potential and low-grade heat of reaction gases, which will lead to additional savings in operating costs.

EXAMPLE: In accordance with the proposed process (see drawing), the initial dichloroethane in the amount of 54.6 t / h is preheated to 140 ^o C in a heat exchanger-utilizer TU-2 due to the heat of the pyrolysis gases leaving the heat exchanger-utilizer TU-1. Then, the heated initial dichloroethane is evaporated and overheated in the part of the coil located in the convection chamber of the P-1 pyrolysis furnace. Superheated vapors of dichloroethane enter the reaction zone of the pyrolysis furnace with a temperature of 360 ^o C and a pressure of 25 kgf / cm ² . Pyrolysis reaction gases with a temperature of 500 ^o C and a pressure of 21 kgf / cm ^{2 are} sent to a recovery boiler KU-1. The condensate boiler KU-1 is supplied with water condensate preheated to 140 ^o C in the heat exchanger-utilizer TU-1 due to the heat of the pyrolysis gases leaving the top of the K-1 quenching column. When passing through the recovery boiler KU-1, the temperature of the gases decreases to 300 ^o C due to the transfer of heat to the water condensate heated to 150 ^{o C.} The result is steam with a pressure of 12 kgf / cm ² (1.2 MPa).

 The KU-1 waste heat boiler is a two-section apparatus in which pyrolysis gases pass at a speed of 33 m / s through pipes located in the lower section and immersed in water condensate. Obtained by evaporation of the last pair is used to heat the rectification columns of dichloroethane and vinyl chloride.

Cooled pyrolysis products not containing condensed organochlorine products are fed to the bottom of the K-1 quenching column. By bubbling through a liquid layer, the pyrolysis products are cooled to a bottom liquid temperature of 178 ^° C. The gaseous mixture is cleaned of entrained droplets of quenching liquid on 2 failure plates and then rectified in the upper part of the column on 16 mesh plates due to contact with flowing reflux. The reflux temperature is maintained at 60 ^{° C.} , and the top temperature of the column is 160 ^° C.

The gaseous mixture that does not contain coke and tarry coming out from the top of the K-1 column is fed into a counter-current heat exchanger-heat exchanger TU-1, where it is cooled with water condensate to a temperature of 150 ^o C. The condensate in an amount of 7 m ³ / h is heated at that from 20-30 to 140 ^o C and served in a recovery boiler for steam. Excess superheated condensate in an amount of 0.2 m ³ / h is returned to the condensate preparation system.

The vapor-liquid mixture of pyrolysis products after the first heat exchanger-utilizer TU-1 is fed into the second countercurrent heat exchanger-utilizer TU-2 for preheating to 140 ^o With the source of dichloroethane fed to the pyrolysis furnace R-1.

Further cooling to 60 ^o With a gas mixture of pyrolysis products with condensation of the main part of dichloroethane and a significant part of vinyl chloride is carried out in a heat exchanger-utilizer TU-3, cooled by air. The latter, after heating, is used to burn fuel in the burners of the pyrolysis furnace.

 The liquid from the heat exchangers TU-1, TU-2 and TU-3 is sent to the reflux tank E-1. From the E-1 tank, 22.6 t / h of liquid is supplied to the upper part of the quenching column as reflux, and the remaining part of the liquid is removed for separation into the K-2 hydrogen chloride evolution column.

The non-condensed gas stream from the TU-3 heat exchanger is sent to the T-1 heat exchanger, which is cooled with gaseous hydrogen chloride cooled to a temperature of minus 27 ^{° C.} supplied from the reflux collector of the hydrogen chloride evolution column. The vapor-liquid mixture from the heat exchanger T-1 is sent to the tank E-2, in which the mixture is divided into gas and liquid phases. After depressurizing up to 1.3 MPa, both phases are fed from the vessel to the separation of hydrogen chloride in separate streams into the column.

The bottoms product of the hardening column, containing 9.2% coke, tar products and high boiling point by-products, is continuously discharged into the E-3 container in an amount of 1370 kg / h. The liquid from the E-3 tank is pumped with a pump at a speed of 100 m / s through the pipe-in-pipe evaporator pipe, where the circulating mixture is heated to a temperature of 134 ^o C. The pressure on the pump is maintained at 0.5 MPa. Heating is carried out by heating steam with a pressure of 1.2 MPa. The vapor-liquid mixture from the evaporator is returned to the tank E-3, where in the expander mounted above the tank, the vapor phase is separated from the liquid.

 The vapor phase, not containing coke and tar products, is fed into the distillation column of the allocation of hydrogen chloride K-2. The concentrated product containing resins and coke from the E-3 tank is periodically removed for burning in an amount of, on average, 120 kg / h.

In the table. 1 shows the comparative results of the technological mode for two options for the operation of the unit for hardening pyrolysis gases:
Option 1 - prototype;
Option 2 - the proposed process, implemented according to the drawing.

 To facilitate the evaluation of the results in table. 1 performance in the second embodiment is reduced to the value specified in the prototype.

 In both cases, coke and resinous coke and resinous products from the pyrolysis products are quenched together with the bottom product of the quenching column.

However, in the proposed process utilize 3.7 Gcal / h of high potential and 2.9 Gcal / h of low potential heat, while in the prototype only 2.1 Gcal / h of low potential heat is utilized. As a result, when implementing the proposed process, 4.3 t / h of water vapor with a pressure of 1.2 MPa are obtained. In addition, 30,000 kg / h of the initial dichloroethane is heated in a heat exchanger-heat exchanger TU-2 to 140 ^o C. For comparison, in the process carried out according to the prototype, only 4 t / h of water vapor are obtained under a pressure of 0.17 MPa.

 The use of a clarification system for bottoms hardening columns makes it possible to reduce by more than 4.3 times the amount of high boiling compounds and resins in the feed of the high-boiling and resinous K-2 recovery column and thus significantly facilitate the operation of this column.

Claims (3)

 1. A method of producing vinyl chloride by thermal pyrolysis of dichloroethane followed by cooling of the pyrogas and feeding it into the quenching column to separate high-boiling compounds from the gaseous phase containing vinyl chloride, dichloroethane and hydrogen chloride, which is supplied for cooling to separate the condensate formed, which is partially returned to the quenching column in the form of reflux , and feeding another part of the condensate, together with the vapor phase, into distillation columns to isolate hydrogen chloride, vinyl chloride and dichloroethane, with the outlet from the cube an alkaline column of a mixture of high-boiling compounds and resinous ones, separation of a fraction enriched with dichloroethane from it and returned to the process, characterized in that the pyrogas are cooled in a recovery boiler, which is connected in the upper part to a sectioned tank, to the upper part of which is preheated in a heat exchanger -utilizer leaving the quenching column with a gaseous mixture of water, which results in the evaporation of which high-pressure steam is obtained, while the initial dichloroethane is fed to the pyrolysis furnace and preheated in another heat exchanger-utilizer due to the residual heat of the gaseous mixture of the quenching column cooled in it.  2. The method according to p. 1, characterized in that the gaseous mixture of the quenching column after cooling with the starting dichloroethane is subjected to further cooling in the heat exchanger-utilizer with air, which, after heating, is fed to the burners of the pyrolysis furnace to burn fuel.  3. The method according to p. 1, characterized in that the still liquid from the quenching column is passed through a clarification system including a tank, pump and evaporator at a speed of 10-100 m / s to separate the liquid phase containing resins and coke from dichloroethane vapor returned to the process.

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