Method for extracting vinyl chloride and dichloroethane from vinyl chloride rectification residual liquid

Abstract

The invention discloses a method for extracting chloroethylene and dichloroethane from chloroethylene rectification residual liquid, and belongs to the technical field of chloroethylene production. A three-tower rectifying tower is additionally arranged behind a vinyl chloride rectifying high-boiling tower, the tower is intermittently operated to respectively recover vinyl chloride, dichloroethane and product high-boiling residues with higher purity, a vinyl chloride monomer and dichloroethane are recovered by utilizing an efficient guide sieve plate and a computer simulation and optimization technology, and the high-boiling residues finally obtained by two times of separation can also be sold. According to the technology, high-added-value products can be recycled, remarkable economic benefits can be obtained, and environmental pollution can be reduced.

Description

Technical Field

[0001] The invention relates to the technical field of vinyl chloride production, in particular to a method for extracting vinyl chloride and ethylene dichloride from vinyl chloride rectification residue. Background Art

[0002] At present, the treatment of the residual liquid in the tower of vinyl chloride distillation tower of calcium carbide PVC enterprises in China is simple. The method is to further remove vinyl chloride from the high-boiling residual liquid obtained by distillation of the high-boiling tower in the recovery device, so that its quality is partially improved and then sold as a product. After filtering, oil-water separation, decolorization, removal of water and impurities, the residual liquid is recovered downstream, and most of the substances are used as mixed solvents. The existing process only recovers vinyl chloride monomer, and the high-boiling residual liquid with a dichloroethane content of more than 90% is directly loaded and sold. Due to the high content of impurities in high-boiling substances, there is no price advantage. The price of high-boiling substances of this purity is sold at a high price, and the monomers contained therein are also sold at a lower price, resulting in waste. Summary of the invention

[0003] The object of the present invention is to provide a method for extracting vinyl chloride and ethylene dichloride from vinyl chloride rectification residue, so as to solve the problems raised in the above-mentioned background technology.

[0004] To achieve the above object, the present invention provides the following technical solutions:

[0005] A method for extracting vinyl chloride and ethylene dichloride from vinyl chloride distillation residue, wherein the vinyl chloride distillation residue is heated by a three-tower reboiler, and the vinyl chloride and a small amount of ethylene dichloride and other raw materials are gasified in the first distillation and then condensed and controlled by a three-tower condenser, and the condensed ethylene dichloride condensate is used as a reflux liquid for in-tower distillation. Uncondensed vinyl chloride gas is recovered as a crude monomer to a vinyl chloride gas holder. The ethylene dichloride and high-boiling substances in the tower kettle are pumped into a dichloroethane storage tank by an intermittent extraction method using a discharge pump.

[0006] The bottom liquid of the three towers includes ethylene dichloride and other high-boiling impurities, which are first stored in the ethylene dichloride storage tank. The second distillation also adopts atmospheric distillation, and the residual liquid in the ethylene dichloride storage tank enters the three distillation towers through the feed pump for further separation and purification. The relatively pure ethylene dichloride is obtained at the top of the tower and enters the ethylene dichloride product tank. The other mixed liquid flows out from the bottom of the tower and enters the high-boiling product tank as the product high-boiling product.

[0007] As a further solution of the present invention: the bottom temperature of the three distillation towers for the first extraction of vinyl chloride is controlled to 45°C to 65°C, and the bottom temperature of the three distillation towers for the second extraction of ethylene dichloride is controlled to 70°C to 85°C.

[0008] As a further solution of the present invention: the temperature of the tower bottom is automatically adjusted by a steam automatic control valve.

[0009] As a further solution of the present invention: the two distillations inside the three distillation towers are both atmospheric pressure distillations.

[0010] As a further solution of the present invention: when the bottom temperature of the tower exceeds 95 degrees, the feed pump will be interlocked and stopped, and the feed quick-cut valve and the steam quick-cut valve will be interlocked and closed; when the water pressure of the cooling brine of the three distillation towers is lower than 0.05MPa, the reboiler steam cut-off valve will be interlocked and closed; when the liquid level in the bottom of the three distillation towers is lower than 20%, the discharge pump of the three distillation towers will be stopped; when the liquid level in the bottom of the three distillation towers exceeds 85%, the feed pump of the three distillation towers will be interlocked and stopped, and the feed quick-cut valve will be closed.

[0011] As a further solution of the present invention: the liquid level of the three vinyl chloride distillation towers is controlled at 25% to 80%, the liquid level control is automatically adjusted by the steam regulating valve of the reboiler, and the automatic control feeding parameter is 0.3-1.5t / h.

[0012] Compared with the prior art, the present invention has the following beneficial effects:

[0013] 1. Add a three-distillation tower after the high-boiling tower of vinyl chloride distillation. The tower operates intermittently to recover vinyl chloride, ethylene dichloride and higher-purity product high-boiling products respectively. Use high-efficiency guide sieve plates and computer simulation and optimization technology to recover vinyl chloride monomer and ethylene dichloride. The high-boiling products obtained after two separations can also be sold. This technology can not only recover high-value-added products and achieve significant economic benefits, but also reduce environmental pollution.

[0014] 2. The above materials were simulated and calculated using Aspen plus chemical simulation software, and the calculation results were optimized to obtain ethylene dichloride with a purity level higher than 98%, which was sold directly as a product. The product vinyl chloride contains a small amount of light impurities such as acetaldehyde, which is sent to the vinyl chloride distillation section as recovered vinyl chloride monomer to remove light impurities and then recover vinyl chloride, which not only recovers vinyl chloride in high-boiling products, but also does not affect the overall quality of vinyl chloride monomer.

[0015] 3. The present invention adopts three distillation towers, which have high separation efficiency and strong anti-blocking ability in actual use. At the same time, the structure is simple and the cost is low, which is convenient for reducing the actual production cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a process flow chart for recovering high boiling points of vinyl chloride;

[0017] Figure 2 This is the composition diagram of high-boiling substances in vinyl chloride. DETAILED DESCRIPTION

[0018] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0019] Example 1

[0020] This embodiment provides a method for extracting vinyl chloride and ethylene dichloride from vinyl chloride distillation residue. The vinyl chloride distillation residue is heated by a three-tower reboiler. The vinyl chloride and a small amount of ethylene dichloride and other raw materials are gasified in the first distillation and then condensed and controlled by a three-tower condenser. The condensed ethylene dichloride condensate is used as reflux liquid for in-tower distillation. Uncondensed vinyl chloride gas is recovered as crude monomer to the vinyl chloride gas cabinet. The ethylene dichloride and high-boiling products in the tower are pumped into the ethylene dichloride storage tank by an intermittent extraction method using a discharge pump.

[0021] The bottom liquid of the three towers includes ethylene dichloride and other high-boiling impurities, which are first stored in the ethylene dichloride storage tank. The second distillation also adopts atmospheric distillation, and the residual liquid in the ethylene dichloride storage tank enters the three distillation towers through the feed pump for further separation and purification. The relatively pure ethylene dichloride is obtained at the top of the tower and enters the ethylene dichloride product tank. The other mixed liquid flows out from the bottom of the tower and enters the high-boiling product tank as the product high-boiling product.

[0022] Furthermore, the bottom temperature of the three distillation towers for the first extraction of vinyl chloride is controlled to 45°C to 65°C, and the bottom temperature of the three distillation towers for the second extraction of ethylene dichloride is controlled to 70°C to 85°C.

[0023] Furthermore, the temperature of the tower bottom is automatically adjusted by a steam automatic control valve.

[0024] Furthermore, the two distillations inside the three distillation towers are both atmospheric pressure distillations.

[0025] Furthermore, when the bottom temperature of the tower exceeds 95 degrees, the feed pump will be interlocked to stop, and the feed quick-cut valve and the steam quick-cut valve will be interlocked to close; when the water pressure of the cooling brine of the three distillation towers is lower than 0.05MPa, the reboiler steam cut-off valve will be interlocked to close; when the bottom liquid level of the three distillation towers is lower than 20%, the discharge pump of the three distillation towers will be stopped; when the bottom liquid level of the three distillation towers exceeds 85%, the feed pump of the three distillation towers will be interlocked to stop, and the feed quick-cut valve will be closed.

[0026] Furthermore, the liquid level of the three vinyl chloride distillation towers is controlled at 25% to 80%, and the liquid level control is automatically adjusted by the steam regulating valve of the reboiler, and the automatic control feeding parameter is 0.3-1.5 t / h.

[0027] like Figure 1As shown, the high-boiling materials of the raw materials extracted from the bottom of the high-boiling tower in the distillation station are stored in the raw material tank V-101. The intermittent distillation method is adopted. The first distillation adopts atmospheric distillation. The raw materials are pumped into the high-boiling material recovery tower T-101 through the raw material pump. The light components containing vinyl chloride, acetaldehyde, etc. are evaporated from the top of the tower and directly sent to the crude vinyl chloride gas tank in the gas phase to recover the vinyl chloride monomer. The condensed liquid is used as the reflux liquid of the recovery tower; the bottom liquid is mainly ethylene dichloride and other high-boiling impurities, which are first stored in the intermediate product tank V-106. The second distillation adopts atmospheric distillation. The mixed liquid in the intermediate product tank V-106 is pumped into the high-boiling material recovery tower T-101 for further separation and purification. A relatively pure ethylene dichloride is obtained at the top of the tower and enters the ethylene dichloride product tank V-104. The other mixed liquid flows out from the bottom of the tower and enters the high-boiling product tank V-105 as the product high-boiling material.

[0028] Aspen plus chemical simulation software was used to simulate the above materials. Figure 2 As shown, in the design calculation, the components of high-boiling vinyl chloride products use the data shown in the table below. The calculation results are optimized to obtain ethylene dichloride with a purity level higher than 98%, which is sold directly as a product. The product vinyl chloride contains a small amount of light impurities such as acetaldehyde. As the recovered vinyl chloride monomer, it is sent to the vinyl chloride distillation section to remove light impurities and then recover vinyl chloride. This not only recovers the vinyl chloride in the high-boiling products, but also does not affect the overall quality of the vinyl chloride monomer. The specific operating data can be adjusted and optimized accordingly according to the actual situation.

[0029] The specific operation steps of this process are as follows:

[0030] 1. In the production of vinyl chloride distillation process, the distillation residue (high boiling products) at the bottom of the high boiling tower is regularly placed in the residual liquid storage tank. When the liquid level in the storage tank reaches about 80%, the staff on duty shall open the three distillation towers to purify the vinyl chloride in the residual liquid. The remaining residual liquid after removing the vinyl chloride is first stored as high boiling products such as ethylene dichloride. The high boiling products such as ethylene dichloride in the residual liquid are further distilled twice, and the last high boiling products after the extraction of ethylene dichloride enter the high boiling product storage tank.

[0031] 2. Feeding of three distillation towers

[0032] Before feeding the three towers, start passing cooling water through the automatic control valve on the top of the distillation tower to ensure the normal operation of the condensation system. Control the feed amount through the regulating valve. According to the flow meter indication, slowly feed until there is a certain liquid level (50%-80%) at the bottom of the tower, stop feeding, and slowly open the steam automatic control valve for heating. At this time, heat slowly until there is condensate on the top of the tower to establish the balance of the whole tower, then open the feed. According to a certain feed amount (100-300Kg / h), stabilize the feed and put it into automatic control operation.

[0033] 3. Discharge from three distillation towers

[0034] The discharge from the bottom of the three-tower distillation tower is intermittent and can be remotely operated through the DCS control valve. When the temperature of the bottom of the three-tower distillation tower reaches a certain value, which is initially set to 65°C (this temperature is a provisional reference value for the process and can be adjusted according to actual operating conditions), and the bottom liquid level reaches 80%, the discharge pump is automatically turned on, and the bottom liquid level is discharged from 80% to 20% through the discharge pump, and the discharge pump is automatically turned off.

[0035] The three distillation towers have a high degree of automation during operation, which enables unmanned operation on site, and the main indicators can be adjusted automatically. After the tower kettle temperature is set, the amount of steam added can be automatically adjusted through the steam automatic control valve and the feed automatic control valve, that is, these two automatic control valves can be automatically adjusted according to the tower kettle set temperature. The tower kettle liquid level is set at 50%, and the discharge automatic control valve is adjusted. After the tower top temperature is set, it can be automatically adjusted through the tower top cooling water control valve.

[0036] In order to improve the safety factor of operation, the operation program of the three towers has set up a complete set of interlocking relationships: when the tower kettle temperature exceeds 125℃, the feed pump will be interlocked to stop, the feed quick-cut valve and the steam quick-cut valve will be interlocked to close; when the cooling water pressure of the three towers is lower than 0.05MPa, the reboiler steam cut-off valve will be interlocked to close. When the liquid level of the three distillation tower kettle is lower than 20%, the discharge pump of the three distillation towers will be stopped; when the liquid level of the three distillation tower kettle exceeds 85%, the feed pump of the three distillation towers will be interlocked to stop and the feed quick-cut valve will be closed.

[0037] The three distillation towers have the following advantages during use:

[0038] (1) High separation efficiency: The bubbling area on the tower plate is enlarged, thereby increasing the gas-liquid mass transfer opportunities and improving the tower plate efficiency; the high-efficiency guide sieve plate effectively overcomes the liquid phase backmixing and improves the tower plate efficiency; the liquid surface gradient is eliminated, the leakage volume and mist entrainment are reduced, and the tower plate efficiency is improved.

[0039] (2) Strong anti-blocking ability. The gas ejected from the guide hole pushes the material to move horizontally on the tower plate, which can strengthen the flow of liquid on the tower plate. For viscous materials, more guide holes can be set, especially for the distillation of fermented mash and self-polymerizing systems.

[0040] (3) Simple structure and low cost. Since the high-efficiency guide screen plate is just a few screen holes and guide holes on the steel plate without other components, it has a simple structure, light weight and is easy to disassemble and assemble. The cost of the high-efficiency guide screen plate is also low.

[0041] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions. The sentence "includes an element defined by ... does not exclude the existence of other identical elements in the process, method, article or device including the element".

[0042] In the present invention, unless otherwise clearly stipulated and limited, the terms such as "installation", "setting", "connection", "fixation" and "screw-on" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral one; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can be the internal connection of two elements or the interaction relationship between two elements. Unless otherwise clearly defined, ordinary technicians in this field can understand the specific meanings of the above terms in the present invention according to the specific circumstances.

[0043] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for extracting vinyl chloride and ethylene dichloride from vinyl chloride rectification residue, characterized in that: The residual liquid of vinyl chloride distillation is heated by the three-tower reboiler. The first distillation vaporizes the vinyl chloride and a small amount of ethylene dichloride and other raw materials, and then condenses and controls them through the three-tower condenser of the distillation. The condensed ethylene dichloride condensate is used as reflux liquid for distillation in the tower. The uncondensed vinyl chloride gas is recovered as crude monomer to the vinyl chloride gas cabinet. The ethylene dichloride and high-boiling products in the tower kettle are pumped into the ethylene dichloride storage tank by the discharging pump through intermittent extraction. The bottom liquid of the three towers includes ethylene dichloride and other high-boiling impurities, which are first stored in the ethylene dichloride storage tank. The second distillation also adopts atmospheric distillation, and the residual liquid in the ethylene dichloride storage tank enters the three distillation towers through the feed pump for further separation and purification. The relatively pure ethylene dichloride is obtained at the top of the tower and enters the ethylene dichloride product tank. The other mixed liquid flows out from the bottom of the tower and enters the high-boiling product tank as the product high-boiling product.

2. The method for extracting vinyl chloride and ethylene dichloride from vinyl chloride rectification residue according to claim 1, characterized in that: The bottom temperature of the three distillation towers for the first extraction of vinyl chloride is controlled to be between 45°C and 65°C, and the bottom temperature of the three distillation towers for the second extraction of ethylene dichloride is controlled to be between 70°C and 85°C.

3. The method for extracting vinyl chloride and ethylene dichloride from vinyl chloride rectification residue according to claim 2, characterized in that: The temperature of the tower kettle is automatically adjusted by a steam automatic control valve.

4. The method for extracting vinyl chloride and ethylene dichloride from vinyl chloride rectification residue according to claim 1, characterized in that: The two distillations inside the three distillation towers are both atmospheric pressure distillations.

5. The method for extracting vinyl chloride and ethylene dichloride from vinyl chloride rectification residue according to claim 1, characterized in that: When the bottom temperature of the tower exceeds 95 degrees, the feed pump will be interlocked to stop, and the feed quick-cut valve and the steam quick-cut valve will be interlocked to close; when the water pressure of the cooling brine of the three distillation towers is lower than 0.05MPa, the reboiler steam cut-off valve will be interlocked to close; when the bottom liquid level of the three distillation towers is lower than 20%, the discharge pump of the three distillation towers will be stopped; when the bottom liquid level of the three distillation towers exceeds 85%, the feed pump of the three distillation towers will be interlocked to stop, and the feed quick-cut valve will be closed.

6. The method for extracting vinyl chloride and ethylene dichloride from vinyl chloride rectification residue according to claim 1, characterized in that: The liquid level of the three vinyl chloride distillation towers is controlled at 25% to 80%, and the liquid level control is automatically adjusted by the steam regulating valve of the reboiler, and the automatic control feeding parameter is 0.3-1.5t / h.

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