Purification and rectification method for by-product in production of vinyl chloride by calcium carbide method

Abstract

The invention provides a purification and rectification method for by-products in production of vinyl chloride by a calcium carbide method, belongs to the technical field of purification and rectification of vinyl chloride, and solves the problems that purification and rectification products of by-products in production of vinyl chloride are low in purity and cannot be efficiently recovered. Each purification unit comprises a rectifying tower, a first cooler is arranged at the top of the rectifying tower, the first cooler is connected with a reflux tank, a reboiler is arranged at the bottom of the rectifying tower, the reflux tank of the last purification unit is connected with a finished product tank, and the reboiler of the last purification unit is connected with a residue tank; dichloroethane sequentially enters each purification unit for purification treatment until the last purification unit conveys purified liquid-phase dichloroethane to a finished product tank for storage. According to the invention, the problem of production resource waste caused by low purity of dichloroethane removed by a traditional rectification system is solved, meanwhile, efficient recovery and cyclic recovery are also realized, and the resource utilization rate is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of vinyl chloride purification and distillation, and specifically relates to a method for purifying and distilling by-products of vinyl chloride production by the calcium carbide process. Background Art

[0002] In the current production process of vinyl chloride by calcium carbide, since calcium carbide may contain impurities such as sulfur and phosphorus during the production process, these impurities will generate corresponding impurity gases, such as hydrogen sulfide and phosphine, when calcium carbide reacts with water and enters the vinyl chloride conversion system. At the same time, when calcium carbide reacts with water to generate acetylene, other side reactions may also occur. Impurities in calcium carbide react with water, or acetylene further reacts under certain conditions to generate other organic or inorganic compounds. In addition, in the vinyl chloride synthesis stage, catalysts such as mercuric chloride are used to promote the reaction of acetylene and hydrogen chloride. In addition to catalyzing the main reaction, the catalyst may also promote some side reactions to generate by-products, such as ethylene dichloride and ethylene dichloride.

[0003] In order to ensure the purity of vinyl chloride monomer, the production unit needs to be equipped with a purification device for water washing and alkali washing, and the inorganic substances contained in the vinyl chloride monomer are removed and sent to the vinyl chloride gas tank for storage. The vinyl chloride in the gas tank is then sent to the distillation device through a compressor for purification to remove organic compounds, such as acetylene and high-boiling substances, and finally the vinyl chloride monomer with qualified product purity is obtained for polymerization feed reaction. The high-boiling substances such as ethylene dichloride removed at the end of the device need to be loaded and transported for takeaway treatment. On the one hand, the purity of ethylene dichloride removed by the traditional distillation system is low, resulting in a low takeaway price, resulting in a waste of production resources. On the other hand, since ethylene dichloride is a flammable and explosive hazardous chemical, there are great safety hazards in the long-distance transportation of low-purity ethylene dichloride, and it is very easy to cause explosion and fire accidents during transportation, which is very easy to cause casualties and property losses. Summary of the invention

[0004] The purpose of the present invention is to provide a method for purifying and distilling by-products of vinyl chloride production by the calcium carbide process, so as to solve the problem that the products of the purification and distillation of by-products of vinyl chloride production have low purity and cannot be efficiently recovered.

[0005] The technical solution of the present invention is: a method for purifying and distilling by-products of vinyl chloride production by the calcium carbide process, the device structure used is as follows, including a dichloroethane storage tank and at least two purification units, the purification units are connected in series in sequence, each purification unit includes a distillation tower, the top of the distillation tower is provided with a first cooler, the first cooler is connected to a reflux tank, the reflux tank is connected to the distillation tower, a reboiler is provided at the bottom of the distillation tower, the first cooler of each purification unit is commonly connected to a vinyl chloride gas holder; the dichloroethane storage tank is connected to the first purification unit, the reboiler of the previous purification unit is connected to the distillation tower of the next purification unit, the reflux tank of the last purification unit is connected to a finished product tank, and the reboiler of the last purification unit is connected to a residue tank; The method comprises the following steps: Step 1: The ethylene dichloride storage tank transports the ethylene dichloride to the first purification unit, in which the ethylene dichloride is purified in a distillation tower, and the ethylene dichloride is separated by heat exchange through reverse contact with the rising airflow generated by heating in the reboiler, the steam flowing out of the tower top is cooled by the first cooler, the uncondensed gas is sent to the vinyl chloride gas holder for recycling, and the condensed liquid flows to the reflux tank and then sent to the distillation tower for further purification; Step 2: The ethylene dichloride treated by the first purification unit enters the subsequent purification units in sequence for purification treatment; Step 3: until the last purification unit delivers the purified liquid dichloroethane to the finished product tank for storage, the reboiler of the purification unit delivers the residue produced at the bottom of the distillation tower to the residue tank for recovery.

[0006] As a further improvement of the present invention, a jacket is provided in the residue tank, the jacket is connected to a steam pipeline, and the residue tank is connected to the distillation tower of the last purification unit through a recovery pipeline.

[0007] As a further improvement of the present invention, the finished product tank outlet is connected to a second cooler, and the second cooler is connected to a dichloroethane loading crane pipe; a third cooler is connected between the residue tank and the reboiler of the last purification unit, and the residue tank outlet is connected to a residue loading crane pipe.

[0008] As a further improvement of the present invention, thermometers are respectively provided on the top and bottom of the distillation tower, the inlet pipe of the reflux tank, the outlets of the second cooler and the third cooler, and the residue tank.

[0009] As a further improvement of the present invention, the first cooler, the second cooler and the third cooler are respectively provided with heat exchange pipes, the heat exchange pipe on the first cooler is provided with a first regulating valve, the heat exchange pipe on the second cooler is provided with a second regulating valve, and the heat exchange pipe on the third cooler is provided with a third regulating valve; the reboiler is provided with a steam pipe, the steam pipe is provided with a fourth regulating valve; the steam pipe connected to the jacket is provided with a fifth regulating valve.

[0010] As a further improvement of the present invention, the thermometer on the inlet pipe of the reflux tank is interlocked with the first regulating valve; the thermometer at the bottom of the distillation tower is interlocked with the fourth regulating valve.

[0011] As a further improvement of the present invention, the thermometer on the outlet of the second cooler is interlocked with the second regulating valve, and the temperature index is ≤30°C; the thermometer on the outlet of the third cooler is interlocked with the third regulating valve; the thermometer on the residue tank is interlocked with the fifth regulating valve, and the temperature index is 60-75°C.

[0012] The beneficial effects of the present invention are as follows: the ethylene dichloride purification device designed and used in the present invention performs purification treatment by arranging a plurality of purification units, each of which is composed of a distillation tower and a cooler, a reboiler and a reflux tank arranged thereon, the distillation tower performs reverse contact heat exchange in the tower through the heating steam of the reboiler at the bottom of the tower and the condensate of the first cooler at the top of the tower, utilizes the difference in boiling point and volatility of the by-products at the end of the distillation, performs mass transfer and heat transfer on the materials, and separates the components by controlling the pressure, the reflux amount, etc., to purify the ethylene dichloride product after the distillation of vinyl chloride, so that the ethylene dichloride The ethane purity index meets the requirements, and finally ethylene dichloride with a purity of 99% is produced. It is transported to downstream pesticide and pharmaceutical intermediate production equipment as raw materials by tank trucks over short distances, which solves the problem that the ethylene dichloride removed by the traditional distillation system has low purity, resulting in waste of production resources. There are major safety hazards in the long-distance transportation of low-purity ethylene dichloride, which is very likely to cause casualties and property losses. At the same time, the present invention also realizes efficient recovery and circular recycling, improves resource utilization, reduces raw material costs, and enhances the market competitiveness of products, thereby bringing better economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is a schematic diagram of the structure of the device used in the present invention.

[0014] In the figure: 1-ethylene dichloride storage tank; 2-distillation tower; 3-first cooler; 4-reflux tank; 5-reboiler; 6-ethylene chloride gas holder; 7-finished product tank; 8-second cooler; 9-third cooler; 10-residue tank; 101-jacket; 11-ethylene dichloride loading crane pipe; 12-residue loading crane pipe; 13-pressure gauge; 14-thermometer; 15-first regulating valve; 16-second regulating valve; 17-third regulating valve; 18-fourth regulating valve; 19-fifth regulating valve; 20-sixth regulating valve; 21-seventh regulating valve; 22-eighth regulating valve; 23-recovery pipeline; 24-feed pump; 25-reflux pump; 26-loading pump; 27-purification unit. DETAILED DESCRIPTION

[0015] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0016] like Figure 1As shown, a method for purifying and distilling by-products of vinyl chloride production by the calcium carbide process, the device structure used is as follows, including an ethylene dichloride storage tank 1 and at least two purification units 27, the purification units 27 are connected in series in sequence, each purification unit 27 includes a distillation tower 2, the top of the distillation tower 2 is provided with a first cooler 3, the first cooler 3 is connected to a reflux tank 4, the reflux tank 4 is connected to the distillation tower 2, the bottom of the distillation tower 2 is provided with a reboiler 5, the first cooler 3 of each purification unit 27 is commonly connected to a vinyl chloride gas holder 6; the ethylene dichloride storage tank 1 is connected to the first purification unit 27, the reboiler 5 of the previous purification unit 27 is connected to the distillation tower 2 of the next purification unit 27, the reflux tank 4 of the last purification unit 27 is connected to a finished product tank 7, and the reboiler 5 of the last purification unit 27 is connected to a residue tank 10; The method comprises the following steps: Step 1: The ethylene dichloride storage tank 1 transports the ethylene dichloride to the first purification unit 27. In the purification unit 27, the ethylene dichloride is purified in the distillation tower 2. The ethylene dichloride is separated by heat exchange by reverse contact with the rising airflow generated by heating in the reboiler 5. The steam flowing out of the top of the tower is cooled by the first cooler 3. The uncondensed gas is sent to the vinyl chloride gas holder 6 for recycling. The condensed liquid flows to the reflux tank 4 and is then sent to the distillation tower 2 for further purification. Step 2: The ethylene dichloride treated by the first purification unit 27 enters the subsequent purification units 27 in sequence for purification treatment; Step 3: until the last purification unit 27 delivers the purified liquid dichloroethane to the finished product tank 7 for storage, the reboiler 5 of the purification unit 27 delivers the residue produced at the bottom of the distillation tower 2 to the residue tank 10 for recovery.

[0017] A jacket 101 is provided in the residue tank 10, and the jacket 101 is connected to a steam pipe. The residue tank 10 is connected to the distillation tower 2 of the last purification unit 27 through a recovery pipe 23; the outlet of the finished product tank 7 is connected to a second cooler 8, and the second cooler 8 is connected to a dichloroethane loading crane pipe 11; a third cooler 9 is connected between the residue tank 10 and the reboiler 5 of the last purification unit 27, and the outlet of the residue tank 10 is connected to a residue loading crane pipe 12; thermometers 14 are respectively provided on the top and bottom of the distillation tower 2, the inlet pipe of the reflux tank 4, the outlets of the second cooler 8 and the third cooler 9, and the residue tank 10.

[0018] The first cooler 3, the second cooler 8 and the third cooler 9 are respectively provided with heat exchange pipes, the heat exchange pipe on the first cooler 3 is provided with a first regulating valve 15, the heat exchange pipe on the second cooler 8 is provided with a second regulating valve 16, and the heat exchange pipe on the third cooler 9 is provided with a third regulating valve 17; the reboiler 5 is provided with a steam pipe, and the steam pipe is provided with a fourth regulating valve 18; the steam pipe connected to the jacket 101 is provided with a fifth regulating valve 19.

[0019] The thermometer 14 on the inlet pipe of the reflux tank 4 is interlocked with the first regulating valve 15; the thermometer 14 at the bottom of the distillation tower 2 is interlocked with the fourth regulating valve 18; the thermometer 14 on the outlet of the second cooler 8 is interlocked with the second regulating valve 16, and the temperature index is ≤30°C; the thermometer 14 on the outlet of the third cooler 9 is interlocked with the third regulating valve 17; the thermometer 14 on the residue tank 10 is interlocked with the fifth regulating valve 19, and the temperature index is 60-75°C.

[0020] Embodiment 1, Taking the setting of two purification units 27 as an example, the distillation tower 2 in the device used in the present invention is a vertically oriented sieve plate tower, which utilizes the principle that different components of substances have different vapor partial pressures, and uses the reverse contact heat exchange between the bottom heating steam and the top condensate in the tower to achieve separation, and has the characteristics of high efficiency. Therefore, in this embodiment, two distillation towers 2 are set to meet production needs. Pressure gauges 13 are also provided at the top and bottom of the distillation tower 2 for monitoring during operation to ensure normal operation.

[0021] The front end of the system is provided with a stainless steel storage tank for the dichloroethane storage tank 1. A feed pipeline is provided at the top of the dichloroethane storage tank 1 to deliver the dichloroethane after distillation to the dichloroethane storage tank 1 for temporary storage. An outlet pipeline is provided at the bottom of the dichloroethane storage tank 1 to connect the feed pump 24. The dichloroethane is delivered to the previous purification unit 27 for purification by pumping. The top of the distillation tower 2 of the purification unit 27 is connected to the first cooler 3 through a pipeline. The shell side of the first cooler 3 is heat-exchanged by a heat exchange pipeline with 5°C water. The first regulating valve 1 is provided on the heat exchange pipeline. 5 for regulating heat exchange, the bottom of the first cooler 3 is connected to the reflux tank 4 through a pipeline, a thermometer 14 is arranged on the inlet pipeline of the reflux tank 4 and is interlocked with the first regulating valve 15, a pipeline is arranged at the bottom of the reflux tank 4, and a reflux pump 25 is connected to send the vinyl chloride in the reflux tank 4 to the distillation tower 2 for further heat exchange, the reboiler 5 arranged at the bottom of the distillation tower 2 is introduced with steam through the shell side of the steam pipeline, and a fourth regulating valve 18 is arranged on the steam pipeline, and the fourth regulating valve 18 is interlocked with the thermometer 14 at the bottom of the distillation tower 2 for temperature regulation.

[0022] The latter purification unit 27 is provided with a distillation tower 2, a first cooler 3, a reflux tank 4, a reboiler 5, a first regulating valve 15, a fourth regulating valve 18 and a reflux pump 25 with the same connection relationship and working principle as the former purification unit 27. Similarly, a thermometer 14 is arranged on the inlet pipe of the reflux tank 4 of the purification unit 27. The distillation tower 2 of the purification unit 27 is interlocked with the first regulating valve 15 arranged on the first cooler 3. The thermometer 14 at the bottom of the distillation tower 2 is interlocked with the fourth regulating valve 18 on the reboiler 5 connected thereto for temperature adjustment. The uncondensed gas phase in the first cooler 3 on the distillation tower 2 is transported to the vinyl chloride gas holder 6 through a pipeline. On the pipelines connecting the first coolers 3 of the two purification units 27 to the vinyl chloride gas holder 6, seventh regulating valves 21 are respectively arranged for control and adjustment. The system is in a fully open state during operation.

[0023] A three-way connecting pipe is arranged at the bottom of the reboiler 5 of the front purification unit 27, which is connected to the distillation tower 2 of the rear purification unit 27. A sixth regulating valve 20 is arranged on the connecting pipe and is interlocked with the bottom liquid level gauge of the front distillation tower 2 to control the bottom liquid level index to be 60%-80%. The sixth regulating valve 20 is opened to continue to transport the dichloroethane purified by the front distillation tower 2 to the rear distillation tower 2 for further processing. The designed bottom temperature index range of the distillation tower 2 of the first purification unit 27 is 80-90°C, the bottom pressure index is 0.12-0.2MPa, the top temperature index is ≤60°C, and the top pressure index is 0.1-0.18MPa; the designed bottom temperature index range of the distillation tower 2 of the second purification unit 27 is 62-75°C, the bottom pressure index is 0-0.04MPa, the top temperature index is 62-75°C, and the top pressure index is 0-0.05MPa. The interlocking settings of various valves and thermometers can improve safety, reduce energy waste, enhance automatic control and improve production efficiency.

[0024] The reboiler 5 is a shell-and-tube heat exchanger, and the tube side is connected to the bottom of the distillation tower 2 through a pipeline. The feed pump 24 delivers ethylene dichloride from the top of the distillation tower 2 of the previous purification unit 27 into the tower, and heat is exchanged by reverse contact with the rising airflow generated by the heating of the reboiler 5 to achieve heat exchange separation. The first cooler 3 is a shell-and-tube heat exchanger, and the shell side controls the condensation temperature through the 5°C water heat exchange pipeline through the first regulating valve 15. The steam flowing out of the top of the tower is cooled by the first cooler 3, and the uncondensed gas is sent to the vinyl chloride gas holder 6 for recycling. The condensed liquid flows to the reflux tank 4 through the bottom pipeline of the first cooler 3. The reflux tank 4 is connected to the reflux pump 25 through the bottom pipeline, and the liquid phase in the reflux tank 4 is sent to the previous distillation tower 2 for further purification. The function of the reflux device of the previous distillation tower 2 is to reflux part of the condensate, adjust the liquid phase composition in the tower, maintain the concentration gradient of the distillation section in the tower, and improve the separation efficiency.

[0025] A three-way pipe is provided on the inlet pipe of the reflux tank 4 of the rear purification unit 27 to transport part of the liquid dichloroethane to the finished product tank 7 for storage, and an eighth regulating valve 22 is provided on its transport pipe for regulation and control. A pipe is provided at the outlet of the finished product tank 7 to connect to the loading pump 26, and the outlet pipe of the loading pump 26 is connected to the second cooler 8 to cool the dichloroethane in the finished product tank 7 before loading the dichloroethane to ensure the safety of low-temperature loading. A 5°C water pipe is provided on the shell side of the second cooler 8, and a second regulating valve 16 is provided on the pipe. A thermometer 14 is provided on the material outlet pipe of the second cooler 8 to interlock with the second regulating valve 16, and the temperature index is required to be ≤30°C. The cooled dichloroethane can be loaded and transported through the dichloroethane loading crane pipe 11. The main benefits of using the loading crane pipe include improved safety, reduced environmental pollution, and improved loading and unloading efficiency and flexibility.

[0026] A three-way pipeline is set at the bottom of the reboiler 5 of the rear purification unit 27, and the bottom residue of the rear distillation tower 2 is transported to the residue tank 10 through the third cooler 9. The sixth regulating valve 20 is set on the transport pipeline and interlocked with the bottom liquid level of the rear distillation tower 2 to control the liquid level index at 60%-80%. The shell side of the third cooler 9 is cooled by setting a 5℃ water heat exchange pipeline, and the third regulating valve 17 is set on the 5℃ water pipeline. The thermometer 14 is set on the outlet pipeline of the third cooler 9, which is interlocked with the third regulating valve 17, and the cooled residue is transported to the residue tank 10 for storage.

[0027] Before loading the residue tank 10, the internal ethylene dichloride needs to be recovered again. Therefore, a jacket 101 is set in the residue tank 10, and steam is introduced to heat the residue tank 10 before loading the residue to recover the ethylene dichloride. A fifth regulating valve 19 is set on its steam pipeline to interlock with the thermometer 14 at the top of the residue tank 10. The recovery temperature index is 60-75°C and the loading temperature is ≤40°C. A recovery pipeline 23 is set at the top of the residue tank 10 to continue to send the recovered ethylene dichloride to the next distillation tower 2 for treatment. A loading pump 26 is set at the bottom of the residue tank 10, and the residue is loaded and transported by the residue loading crane 12.

[0028] The pumps used in the device of the present invention are all shielded pumps, and the design requirements are in accordance with the explosion-proof grade of vinyl chloride; the control valve accuracy must meet the requirements of ANSI / FCI70-2, and the adjustment accuracy is ±1%; the device used in the present invention contains a device for recovering flammable and explosive media, and the design and installation must comply with the chemical fire and explosion protection requirements, and the system must be replaced with nitrogen before operation.

Claims

1. A purification and distillation method for by-products of vinyl chloride production by the calcium carbide process, characterized in that: The device used has the following structure, comprising a dichloroethane storage tank (1) and at least two purification units (27), wherein the purification units (27) are connected in series in sequence, each purification unit (27) comprises a distillation tower (2), a first cooler (3) is provided at the top of the distillation tower (2), the first cooler (3) is connected to a reflux tank (4), the reflux tank (4) is connected to the distillation tower (2), a reboiler (5) is provided at the bottom of the distillation tower (2), and the first cooler (3) of each purification unit (27) is commonly connected to a vinyl chloride gas holder (6); the dichloroethane storage tank (1) is connected to the first purification unit (27), the reboiler (5) of the first purification unit (27) is connected to the distillation tower (2) of the next purification unit (27), the reflux tank (4) of the last purification unit (27) is connected to a finished product tank (7), and the reboiler (5) of the last purification unit (27) is connected to a residue tank (10); The method comprises the following steps: Step 1: The ethylene dichloride storage tank (1) transports the ethylene dichloride to the first purification unit (27). In the purification unit (27), the ethylene dichloride is purified in the distillation tower (2). The ethylene dichloride is separated by heat exchange by countercurrent contact with the rising airflow generated by heating in the reboiler (5). The steam flowing out of the tower top is cooled by the first cooler (3). The uncondensed gas is sent to the vinyl chloride gas holder (6) for recycling. The condensed liquid flows to the reflux tank (4) and is then sent to the distillation tower (2) for further purification. Step 2: The ethylene dichloride treated in the first purification unit (27) enters the subsequent purification units (27) in sequence for purification treatment; Step 3: until the last purification unit (27) delivers the purified liquid dichloroethane to the finished product tank (7) for storage, the reboiler (5) of the purification unit (27) delivers the residue generated at the bottom of the distillation tower (2) to the residue tank (10) for recovery.

2. The method for purifying and distilling by-products of vinyl chloride production by the calcium carbide process according to claim 1, characterized in that: The residue tank (10) is provided with a jacket (101), the jacket (101) is connected to a steam pipeline, and the residue tank (10) is connected to the distillation tower (2) of the last purification unit (27) through a recovery pipeline (23).

3. The method for purifying and rectifying by-products of vinyl chloride production by the calcium carbide process according to claim 1 or 2, characterized in that: The outlet of the finished product tank (7) is connected to a second cooler (8), and the second cooler (8) is connected to a dichloroethane loading crane (11); a third cooler (9) is connected between the residue tank (10) and the reboiler (5) of the last purification unit (27), and the outlet of the residue tank (10) is connected to a residue loading crane (12).

4. The method for purifying and rectifying by-products of vinyl chloride production by the calcium carbide process according to claim 3, characterized in that: Thermometers (14) are respectively provided on the top and bottom of the distillation tower (2), the inlet pipe of the reflux tank (4), the outlets of the second cooler (8) and the third cooler (9), and the residue tank (10).

5. The method for purifying and rectifying by-products of vinyl chloride production by the calcium carbide process according to claim 4, characterized in that: The first cooler (3), the second cooler (8) and the third cooler (9) are respectively provided with heat exchange pipes, the heat exchange pipe on the first cooler (3) is provided with a first regulating valve (15), the heat exchange pipe on the second cooler (8) is provided with a second regulating valve (16), and the heat exchange pipe on the third cooler (9) is provided with a third regulating valve (17); the reboiler (5) is provided with a steam pipe, and the steam pipe is provided with a fourth regulating valve (18); the steam pipe connected to the jacket (101) is provided with a fifth regulating valve (19).

6. The method for purifying and rectifying by-products of vinyl chloride production by the calcium carbide process according to claim 5, characterized in that: The thermometer (14) on the inlet pipe of the reflux tank (4) is interlocked with the first regulating valve (15); and the thermometer (14) at the bottom of the distillation tower (2) is interlocked with the fourth regulating valve (18).

7. The method for purifying and rectifying by-products of vinyl chloride production by the calcium carbide process according to claim 6, characterized in that: The thermometer (14) on the outlet of the second cooler (8) is interlocked with the second regulating valve (16), and the temperature index is ≤30°C; the thermometer (14) on the outlet of the third cooler (9) is interlocked with the third regulating valve (17); the thermometer (14) on the residue tank (10) is interlocked with the fifth regulating valve (19), and the temperature index is 60-75°C.

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