A purification and distillation method for by-products of vinyl chloride production by calcium carbide method

Abstract

The present invention provides a method for purifying and distilling byproducts of vinyl chloride production using a calcium carbide process, belonging to the technical field of vinyl chloride purification and distillation. The method solves the problem that the purified distillation products of vinyl chloride production byproducts have low purity and cannot be efficiently recovered. The device used in the present invention includes an ethylene dichloride storage tank and at least two purification units. The purification units include a distillation tower, a first cooler is provided at the top of the distillation tower, the first cooler is connected to a reflux tank, a reboiler is provided at the bottom of the distillation tower, 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 ethylene dichloride enters each purification unit in sequence for purification treatment until the last purification unit transports the purified liquid ethylene dichloride to the finished product tank for storage. The present invention solves the problem that the ethylene dichloride removed by the traditional distillation system has low purity, resulting in waste of production resources, while also achieving efficient recovery and recycling, thereby improving resource utilization.

Description

Technical Field

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

[0002] In the current carbide-based vinyl chloride production process, calcium carbide may contain impurities such as sulfur and phosphorus. These impurities react with water to generate corresponding impurity gases, such as hydrogen sulfide and phosphine, which enter the vinyl chloride conversion system. Simultaneously, while calcium carbide and water react to produce acetylene, other side reactions may also occur: impurities in the calcium carbide react with water, or acetylene reacts further under certain conditions to produce other organic or inorganic compounds. Furthermore, during the vinyl chloride synthesis stage, catalysts such as mercuric chloride are used to promote the reaction between acetylene and hydrogen chloride. In addition to catalyzing the main reaction, these catalysts may also promote side reactions, generating byproducts such as ethylene dichloride and ethylene bis(dichloroethane).

[0003] To ensure the purity of vinyl chloride monomer, the production unit must be equipped with a purification unit for water and alkali washing to remove inorganic compounds contained in the vinyl chloride monomer and then be stored in a vinyl chloride gas tank. The vinyl chloride in the gas tank is then transported to a distillation unit via a compressor for purification to remove organic compounds such as acetylene and high-boiling substances. The final product, vinyl chloride monomer with qualified purity, is then used as a feed for the polymerization reaction. High-boiling substances such as ethylene dichloride removed at the end of the unit need to be loaded onto trucks for off-take processing. On the one hand, the low purity of ethylene dichloride removed by traditional distillation systems results in a low off-take price, resulting in a waste of production resources. On the other hand, because ethylene dichloride is a flammable and explosive hazardous chemical, the long-distance transportation of low-purity ethylene dichloride presents significant safety risks. Explosions and fires during transportation are very likely to occur, which can easily cause casualties and property damage. Summary of the Invention

[0004] The purpose of the present invention is to provide a purification and distillation method for by-products of vinyl chloride production by the calcium carbide process, so as to solve the problem that the purity of the purified distillation products of vinyl chloride production by-products is low 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: comprising a dichloroethane storage tank and at least two purification units, the purification units being connected in series in sequence, each purification unit comprising a distillation tower, a first cooler being provided at the top of the distillation tower, the first cooler being connected to a reflux tank, the reflux tank being connected to the distillation tower, a reboiler being provided at the bottom of the distillation tower, the first cooler of each purification unit being commonly connected to a vinyl chloride gas holder; the dichloroethane storage tank being connected to the first purification unit, the reboiler of the preceding purification unit being connected to the distillation tower of the succeeding purification unit, the reflux tank of the last purification unit being connected to a finished product tank, the reboiler of the last purification unit being connected to a residue tank, the residue tank being provided with a jacket, the jacket being connected to a steam pipe, the residue tank being connected to the distillation tower of the last purification unit via a recovery pipe;

[0006] The outlet of the finished product tank is connected to a second cooler, which is connected to a dichloroethane loading crane; the third cooler is connected between the residue tank and the reboiler of the last purification unit, and the outlet of the residue tank is connected to a residue loading crane;

[0007] The method comprises the following steps:

[0008] Step 1: The ethylene dichloride storage tank transports ethylene dichloride to the first purification unit. In this purification unit, ethylene dichloride is purified in a distillation tower. The ethylene dichloride is separated by heat exchange through countercurrent contact with the rising airflow generated by heating in the reboiler. The vapor flowing out of the tower is cooled by the first cooler. The uncondensed gas is sent to the vinyl chloride gas tank for recycling. The condensed liquid flows to the reflux tank and then to the distillation tower for further purification.

[0009] Step 2: The dichloroethane treated in the first purification unit enters the subsequent purification units in sequence for purification treatment;

[0010] Step 3: Until the last purification unit transports the purified liquid dichloroethane to the finished product tank for storage, the reboiler of the purification unit transports the residue generated at the bottom of the distillation tower to the residue tank for recovery.

[0011] 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.

[0012] 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.

[0013] 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.

[0014] 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.

[0015] The beneficial effects of the present invention are as follows: the dichloroethane purification device designed and used in the present invention is purified by setting up multiple purification units, each purification unit is used in conjunction with a distillation tower and a cooler, a reboiler and a reflux tank arranged thereon, the distillation tower is heated by the reboiler at the bottom of the tower and the condensate of the first cooler at the top of the tower is reversely contacted and heat exchanged in the tower, and the difference in boiling point and volatility of the by-products at the end of the distillation is utilized to perform mass transfer and heat transfer on the materials, and the separation of each component is achieved by controlling the pressure, reflux amount, etc., to purify the dichloroethane product after the distillation of vinyl chloride, so that the dichloroethane The ethane purity index meets the requirements, and finally dichloroethane with a purity of 99% is produced. It is transported to downstream pesticide and pharmaceutical intermediate production equipment over short distances by tank trucks as raw material. This solves the problem that the dichloroethane removed by traditional distillation systems has low purity, resulting in waste of production resources. Long-distance transportation of low-purity dichloroethane poses a major safety hazard and is very likely to cause casualties and property damage. At the same time, the present invention also achieves efficient recovery and 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

[0016] Figure 1 Schematic diagram of the structure of the device used in the present invention.

[0017] In the figure: 1-dichloroethane storage tank; 2-distillation tower; 3-first cooler; 4-reflux tank; 5-reboiler; 6-vinyl chloride gas holder; 7-finished product tank; 8-second cooler; 9-third cooler; 10-residue tank; 101-jacket; 11-dichloroethane 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

[0018] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0019] like Figure 1 As shown, a purification and distillation method for by-products of vinyl chloride production by the calcium carbide process, the device structure used is as follows, including a dichloroethane 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 dichloroethane storage tank 1 is connected to the first purification unit 27, the reboiler 5 of the previous purification unit 27 is connected to the next purification unit The distillation tower 2 of the unit 27 is connected, the reflux tank 4 of the last purification unit 27 is connected to the finished product tank 7, and the reboiler 5 of the last purification unit 27 is connected to the residue tank 10; the residue tank 10 is provided with a jacket 101, the jacket 101 is connected to the steam pipe, and the residue tank 10 is connected to the distillation tower 2 of the last purification unit 27 through the recovery pipe 23; the outlet of the finished product tank 7 is connected to the second cooler 8, and the second cooler 8 is connected to the 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 the residue loading crane 12;

[0020] The method comprises the following steps:

[0021] Step 1: The ethylene dichloride storage tank 1 delivers 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 vapor flowing out 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.

[0022] Step 2: The dichloroethane treated in the first purification unit 27 enters the subsequent purification units 27 for purification treatment in sequence;

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] Example 1

[0028] 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 substances of different components have different vapor partial pressures, and uses the reverse contact heat exchange of the bottom heating steam and the top condensate in the tower to achieve separation, which has the characteristic 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.

[0029] The front end of the system is equipped with a stainless steel storage tank for the dichloroethane storage tank 1. A feed pipe is set on the top of the dichloroethane storage tank 1 to send the dichloroethane after distillation to the dichloroethane storage tank 1 for temporary storage. An outlet pipe is set at the bottom of the dichloroethane storage tank 1 to connect the feed pump 24. The dichloroethane is pumped to the previous purification unit 27 for purification. The top of the distillation tower 2 of the purification unit 27 is connected to the first cooler 3 through a pipe. The shell side of the first cooler 3 is heat-exchanged by a heat exchange pipe with 5°C water. The heat exchange pipe is provided with a first regulating valve 1. 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 provided on the inlet pipeline of the reflux tank 4 and is interlocked with the first regulating valve 15. A pipeline is provided at the bottom of the reflux tank 4 and is connected to a reflux pump 25 to send the vinyl chloride in the reflux tank 4 to the distillation tower 2 for further heat exchange. The reboiler 5 provided at the bottom of the distillation tower 2 is fed with steam through the shell side of the steam pipeline. A fourth regulating valve 18 is provided on the steam pipeline. The fourth regulating valve 18 is interlocked with the thermometer 14 at the bottom of the distillation tower 2 for temperature regulation.

[0030] 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 provided 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 provided 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 provided for control and adjustment. The system is in a fully open state during operation.

[0031] A three-way connecting pipe is provided 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 provided 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%. By opening the sixth regulating valve 20, the dichloroethane purified in the front distillation tower 2 is continuously transported 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 during operation 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 during operation 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.

[0032] The reboiler 5 is a shell-and-tube heat exchanger, the tube side of which is connected to the bottom of the distillation tower 2 via 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. It exchanges heat with the rising airflow generated by the heating of the reboiler 5 in the reverse direction, achieving heat exchange separation. The first cooler 3 is a shell-and-tube heat exchanger, and the shell side is controlled by a 5°C water heat exchange pipeline through the first regulating valve 15 to control the condensation temperature. 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 via 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.

[0033] The inlet pipe of the reflux tank 4 of the rear purification unit 27 is equipped with a three-way pipe to transport part of the liquid dichloroethane to the finished product tank 7 for storage. The eighth regulating valve 22 is installed on the delivery pipe for regulation and control. The outlet of the finished product tank 7 is connected to the loading pump 26 through the pipe of the loading pump 26. 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, ensuring the safety of low-temperature loading. The shell side of the second cooler 8 is equipped with a 5°C water pipe, and a second regulating valve 16 is installed on the pipe. A thermometer 14 is installed on the material outlet pipe of the second cooler 8 and is interlocked with the second regulating valve 16. The temperature index is required to be ≤30°C. The cooled dichloroethane can be loaded and transported through the dichloroethane loading crane 11. The main benefits of using the loading crane include improved safety, reduced environmental pollution, and improved loading and unloading efficiency and flexibility.

[0034] A three-way pipe is installed at the bottom of the reboiler 5 of the second purification unit 27 to transport the bottom residue of the second distillation tower 2 to the residue tank 10 via the third cooler 9. A sixth regulating valve 20 is installed on this pipe, interlocked with the liquid level at the bottom of the second distillation tower 2, to control the liquid level between 60% and 80%. The shell side of the third cooler 9 is cooled by a 5°C water heat exchange pipe. The 5°C water pipe is equipped with a third regulating valve 17. A thermometer 14 is installed on the outlet pipe of the third cooler 9, interlocked with the third regulating valve 17, and the cooled residue is transported to the residue tank 10 for storage.

[0035] Before the residue tank 10 is loaded onto a truck, the dichloroethane inside needs to be recovered again. Therefore, a jacket 101 is provided in the residue tank 10, and steam is introduced to heat the residue tank 10 before the residue is loaded onto a truck to recover the dichloroethane. A fifth regulating valve 19 is provided on its steam pipe to be interlocked with a 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 pipe 23 is provided at the top of the residue tank 10 to continue to send the recovered dichloroethane to the subsequent distillation tower 2 for processing. A loading pump 26 is provided at the bottom of the residue tank 10, and the residue is loaded and transported using a residue loading crane 12.

[0036] 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 rectification method for by-products of vinyl chloride production by the calcium carbide process, characterized in that: The device structure used is as follows, comprising a dichloroethane storage tank (1) and at least two purification units (27), the purification units (27) are sequentially connected in series, each purification unit (27) comprises 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 dichloroethane storage tank (1) and The first purification unit (27) is connected, 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 the finished product tank (7), the reboiler (5) of the last purification unit (27) is connected to the residue tank (10), the residue tank (10) is provided with a jacket (101), the jacket (101) is connected to a steam pipe, and 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 (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); The method comprises the following steps: Step 1: The dichloroethane storage tank (1) transports the dichloroethane to the first purification unit (27). In the purification unit (27), the dichloroethane is purified in the distillation tower (2). The dichloroethane 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 dichloroethane 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) transports the purified liquid dichloroethane to the finished product tank (7) for storage, the reboiler (5) of the purification unit (27) transports the residue generated at the bottom of the distillation tower (2) to the residue tank (10) for recovery.

2. The method for purifying and rectifying by-products of vinyl chloride production by the calcium carbide process according to claim 1, wherein: 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).

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 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).

4. The method for purifying and rectifying by-products of vinyl chloride production by the calcium carbide process according to claim 3, wherein: 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).

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 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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