A process system and method for synthesizing vinyl chloride using mercury-free catalyst

Abstract

The invention discloses a process system for synthesizing vinyl chloride with mercury-free catalyst, comprising a mixer, the mixer is connected to a first preheater and a precompressor, the first preheater is connected to a front converter, the front converter is connected to a first cooler, the first cooler is connected to an intermediate compressor, the intermediate compressor is connected to a second cooler, the second cooler is connected to a first gas-liquid separator, the first gas-liquid separator is connected to a second preheater, the second preheater is connected to a back converter, the back converter is connected to a third cooler, the third cooler is connected to a second gas-liquid separator, the second gas-liquid separator is connected to a low boiling tower and a pressure swing adsorption device, and the pressure swing adsorption device is connected to a purification device. A method for synthesizing vinyl chloride is also disclosed, in which in the early stage of operation of the mercury-free catalyst, the mixed gas is preheated and then enters the front converter; in the late stage of operation, the mixed gas is pre-pressurized and then preheated and then enters the front converter, which can give full play to the catalytic ability of the mercury-free catalyst in the front converter and extend the operating life of the catalyst.

Description

Technical Field

[0001] The invention belongs to the technical field of acetylene-based vinyl chloride synthesis methods, and specifically relates to a process system for synthesizing vinyl chloride using a mercury-free catalyst, and also relates to a method for synthesizing vinyl chloride using a mercury-free catalyst. Background Art

[0002] There are two main mature synthetic routes for vinyl chloride in industry: the acetylene method (calcium carbide method) and the ethylene method. In China, the coal-based acetylene method is the mainstream process for vinyl chloride synthesis, that is, acetylene and hydrogen chloride are mixed in a mixer in a certain proportion (usually the molar ratio of acetylene to hydrogen chloride is 1:1.05-1.1), heated to 80-100°C by a preheater, and then enter two converters in series equipped with mercuric chloride catalysts, namely the front converter and the back converter, for vinyl chloride synthesis. The crude vinyl chloride produced by the reaction exits the conversion device and enters the subsequent purification and distillation treatment system. The core catalytic link almost entirely uses mercuric chloride catalysts supported by activated carbon. However, the loss of mercury is causing serious environmental problems.

[0003] In recent years, although great progress has been made in the research of mercury-free catalysts in China, there is still a certain gap in performance compared with low-mercury catalysts. It is difficult to meet the application requirements of new mercury-free catalysts using the existing low-mercury catalyst synthesis process. The development of supporting application process technology for mercury-free catalysts will help to break through the technical bottleneck of mercury-free catalyst application as soon as possible and realize the industrialization of mercury-free catalysts. Summary of the invention

[0004] The purpose of the present invention is to provide a process system for synthesizing vinyl chloride with a mercury-free catalyst, which solves the problem of the influence of hydrogen in hydrogen chloride gas on the operating life of the mercury-free catalyst.

[0005] The present invention also aims to provide a method for synthesizing vinyl chloride using a mercury-free catalyst, thereby improving the utilization rate of the mercury-free catalyst and the acetylene conversion rate and reaction efficiency.

[0006] The first technical solution adopted by the present invention is a process system for synthesizing vinyl chloride with a mercury-free catalyst, comprising a mixer, wherein the mixer is respectively connected to a first preheater and a precompressor inlet, the precompressor outlet is connected to the inlet of the first preheater, the outlet of the first preheater is connected to the material inlet of a front-end converter, the material outlet of the front-end converter is connected to the inlet of a first cooler, the outlet of the first cooler is connected to an intermediate compressor, the intermediate compressor is connected to the inlet of a second cooler, the outlet of the second cooler is connected to the inlet of a first gas-liquid separator, the gas phase outlet of the first gas-liquid separator is connected to the inlet of the second preheater, the outlet of the second preheater is connected to the material inlet of a back-end converter, the material outlet of the back-end converter is connected to the inlet of a third cooler, the outlet of the third cooler is connected to the inlet of a second gas-liquid separator, the gas phase outlet of the second gas-liquid separator is respectively connected to the inlet of the intermediate compressor and the inlet of a pressure swing adsorption device, the outlet of the pressure swing adsorption device is connected to the inlet of a purification device, and the outlet of the purification device is connected to the inlet of the intermediate compressor.

[0007] The present invention is also characterized in that:

[0008] The mixer outlet is connected to the intermediate compressor inlet.

[0009] The liquid phase outlet of the first gas-liquid separator and the liquid phase outlet of the second gas-liquid separator are also connected to the inlet of the low boiling tower. The liquid phase outlet of the low boiling tower is connected to the high boiling tower, and the gas phase outlet of the low boiling tower is connected to the inlet of the pressure swing adsorption device.

[0010] The second technical solution adopted by the present invention is a method for synthesizing vinyl chloride using a mercury-free catalyst, and the specific operating steps are as follows:

[0011] Step 1, loading mercury-free catalysts in the tubes of the front converter and the back converter, mixing acetylene and hydrogen chloride in a mixer and preheating them or pressurizing them and then preheating them, and then entering the front converter to generate crude vinyl chloride;

[0012] Step 2, the crude vinyl chloride generated after the reaction is cooled to 10-30° C. by a first cooler, then pressurized to 300-600 KPa by an intermediate compressor, then cooled to -30-30° C. by a second cooler, and finally enters a first gas-liquid separator for gas-liquid phase separation;

[0013] Step 3, the liquid vinyl chloride separated by the first gas-liquid separator enters the low-boiling tower, and the vinyl chloride rectified by the low-boiling tower is further rectified by the high-boiling tower to form finished vinyl chloride; the separated gas phase gas is preheated by the second preheater and enters the background converter to continue the synthesis of vinyl chloride under the action of a mercury-free catalyst, and the crude vinyl chloride obtained by the reaction is cooled to -30 to 30° C. by the second cooler, and finally enters the second gas-liquid separator for gas-liquid phase separation;

[0014] Step 4, the liquid vinyl chloride separated by the second gas-liquid separator enters the low-boiling tower, and a part of the separated gas phase gas enters the pressure swing adsorption device together with the low-boiling substances distilled out from the top of the low-boiling tower. After passing through the purification device, it is recycled with the other part to the inlet of the intermediate compressor for pressurization, and further circulates the reaction to improve the acetylene conversion rate.

[0015] The second technical solution of the present invention is also characterized in that:

[0016] In step 1, specifically, in the early stage of operation of the mercury-free catalyst, that is, when the activity of the mercury-free catalyst is relatively high, the raw gas acetylene and hydrogen chloride are mixed in a mixer and then enter the first preheater to be preheated to 80-100° C. The preheated gas directly enters the front converter to react and generate crude vinyl chloride;

[0017] In the later stage of mercury-free catalyst operation, when the activity of mercury-free catalyst decreases and the acetylene conversion rate decreases, the raw gas acetylene and hydrogen chloride are mixed in the mixer and enter the compressor for pre-pressurization to 60-200KPa, and then preheated to 80-100℃ in the first preheater. The preheated gas directly enters the front converter to react and generate crude vinyl chloride.

[0018] The molar ratio of acetylene to hydrogen chloride is 1:0.90-1.10; the purity of acetylene is greater than 99.5%; and the purity of hydrogen chloride is more than 99%.

[0019] The beneficial effects of the present invention are:

[0020] 1. This process system solves the impact of hydrogen in hydrogen chloride gas on the operating life of mercury-free catalysts, and compared with the existing low-mercury catalyst process, it improves the hydrogen recovery rate and further improves the economic efficiency of the device operation;

[0021] 2. The process system recycles unreacted acetylene, hydrogen chloride, and unseparated vinyl chloride, which is beneficial to reducing the operating cost of mercury-free catalysts;

[0022] 3. The process system performs preliminary separation of crude vinyl chloride at the outlet of the front converter, thus preventing a large amount of vinyl chloride gas from entering the back converter to inhibit the catalytic efficiency of the mercury-free catalyst, and preventing vinyl chloride from continuing to add to form ethylene dichloride, thereby reducing the yield of ethylene dichloride by-products;

[0023] 4. This process system reduces the possibility of increased carbon deposition of mercury-free catalysts during long-term operation and increases the service life of the catalyst;

[0024] 5. The process system can adopt two operating modes: conventional process and pre-pressurization. It can flexibly adjust the molecular ratio according to the performance requirements and operating conditions of the mercury-free catalyst, effectively improving the service life and operating economy of the foreground catalyst. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a structural schematic diagram of a process system for synthesizing vinyl chloride with a mercury-free catalyst according to the present invention;

[0026] Figure 2 The present invention is a flow chart of a method for synthesizing vinyl chloride using a mercury-free catalyst.

[0027] In the figure, 1. mixer, 2. first preheater, 3. precompressor, 4. front-end converter, 5. first cooler, 6. intermediate compressor, 7. second cooler, 8. second preheater, 9. first gas-liquid separator, 10. back-end converter, 11. third cooler, 12. second gas-liquid separator, 13. low boiling tower, 14. high boiling tower, 15. pressure swing adsorption device, 16 purification device. DETAILED DESCRIPTION

[0028] The present invention is described in detail below in conjunction with specific implementation modes and accompanying drawings.

[0029] The present invention provides a process system for synthesizing vinyl chloride with a mercury-free catalyst, such as Figure 1 As shown, the mixer 1 includes a mixer 1, the mixer 1 is respectively connected to the inlet of the first preheater 2 and the precompressor 3, the outlet of the precompressor 3 is connected to the inlet of the first preheater 2, the outlet of the first preheater 2 is connected to the material inlet of the front-end converter 4, the material outlet of the front-end converter 4 is connected to the inlet of the first cooler 5, the outlet of the first cooler 5 is connected to the intermediate compressor 6, the intermediate compressor 6 is connected to the inlet of the second cooler 7, the outlet of the second cooler 7 is connected to the inlet of the first gas-liquid separator 9, the gas phase outlet of the first gas-liquid separator 9 is connected to the inlet of the second preheater 8, the outlet of the second preheater 8 is connected to the material inlet of the back-end converter 10, the material outlet of the back-end converter 10 is connected to the inlet of the third cooler 11, the outlet of the third cooler 11 is connected to the inlet of the second gas-liquid separator 12, the gas phase outlet of the second gas-liquid separator 12 is respectively connected to the inlet of the first cooler 5 and the inlet of the pressure swing adsorption device 15, the outlet of the pressure swing adsorption device 15 is connected to the inlet of the purification device 16, and the outlet of the purification device 16 is connected to the inlet of the intermediate compressor 6;

[0030] The liquid phase outlet of the first gas-liquid separator 9 and the liquid phase outlet of the second gas-liquid separator 12 are also connected to the inlet of the low boiling tower 13. The liquid phase outlet of the low boiling tower 13 is connected to the high boiling tower 14 respectively, and the gas phase outlet of the low boiling tower 13 is connected to the inlet of the pressure swing adsorption device 15.

[0031] The acetylene gas outlet, the hydrogen chloride gas outlet, and the mixer 1 outlet are respectively connected to the inlet of the intermediate compressor 6;

[0032] The present invention provides a method for synthesizing vinyl chloride using a mercury-free catalyst, such as Figure 2 The specific steps are as follows:

[0033] Step 1, mercury-free catalyst is loaded into the tubes of the front converter 4 and the back converter 10, acetylene and hydrogen chloride are mixed in the mixer 1 and preheated or pressurized and then preheated, and then enter the front converter 4 to generate crude vinyl chloride;

[0034] Specifically, in the early stage of operation of the mercury-free catalyst, that is, when the activity of the mercury-free catalyst is relatively high, the raw gas acetylene and hydrogen chloride are mixed in the mixer 1 and then enter the first preheater 2 to be preheated to 80-100°C. The preheated gas directly enters the front converter 4 to react and generate crude vinyl chloride;

[0035] In the later stage of operation of the mercury-free catalyst, when the activity of the mercury-free catalyst decreases and the acetylene conversion rate decreases, the raw gas acetylene and hydrogen chloride are mixed in the mixer 1 and enter the compressor 3 for pre-pressurization to 60-200KPa, and then preheated to 80-100°C in the first preheater 2. The preheated gas directly enters the front-end converter 4; in this way, the catalytic capacity of the mercury-free catalyst in the front-end converter can be fully utilized, and the operating life of the mercury-free catalyst in the front-end converter 4 can be extended;

[0036] The molar ratio of acetylene to hydrogen chloride is 1:0.90-1.10; the purity of acetylene is greater than 99.5%; the purity of hydrogen chloride is more than 99%;

[0037] The hydrogen chloride used is produced by the reaction of chlorine and excess hydrogen, wherein the purity of hydrogen chloride is greater than 94% and the hydrogen content is about 5%. After separation and purification, the purity of hydrogen chloride reaches more than 99%, and the hydrogen is recycled to the hydrogen chloride synthesis process;

[0038] Step 2, the crude vinyl chloride generated after the reaction is cooled to 10-30° C. by the first cooler 5, then pressurized to 300-600 KPa by the intermediate compressor 6, then cooled to -30-30° C. by the second cooler 7, and finally enters the first gas-liquid separator 9 for gas-liquid phase separation;

[0039] Step 3, the liquid vinyl chloride separated by the first gas-liquid separator 9 enters the low-boiling tower 13, and the vinyl chloride distilled by the low-boiling tower 13 is further distilled by the high-boiling tower 14 to form finished vinyl chloride; the separated gas phase gas (a small amount of vinyl chloride, unreacted acetylene, hydrogen chloride and other gases) is preheated by the second preheater 8 and enters the background converter 10, and the synthesis of vinyl chloride is continued under the action of a mercury-free catalyst. The crude vinyl chloride obtained by the reaction is further cooled to -30 to 30° C. by the second cooler 11, and finally enters the second gas-liquid separator 12 for gas-liquid phase separation;

[0040] Step 4, the liquid phase vinyl chloride separated by the second gas-liquid separator 12 enters the low-boiling tower 13, and a part of the separated gas phase gas (a small amount of vinyl chloride, unreacted acetylene, hydrogen chloride and other by-product gases) enters the pressure swing adsorption device 15 together with the low-boiling substances distilled from the top of the low-boiling tower 13 to avoid the enrichment of inert gas in the device. After passing through the purification device 16, it is recycled with another part to the inlet of the intermediate compressor 6 for pressurization, and further circulates the reaction to improve the acetylene conversion rate;

[0041] The low-boiling substances separated from the low-boiling tower 13 and part of the gas phase gas from the background converter 10 are mixed and then enter the pressure swing adsorption device 15. The separated inert gas (such as methane, nitrogen, other hydrocarbon substances, oxygen, carbon monoxide, etc.) is discharged, and the separated recyclable gas (such as acetylene, hydrogen chloride, vinyl chloride, etc.) is recycled to the inlet of the intermediate compressor 6 after passing through the purification device 16 for pressurization and subsequent process treatment, and then enters the background converter 10 to continue the reaction.

[0042] The existing low-mercury catalyst adopts the process of front and back converters in series operation. Its synthesis and purification process cannot meet the performance requirements of mercury-free catalysts. The main reason is that the initial mercury-free catalyst has high activity and high acetylene conversion rate. When the front and back converters are in series operation mode, the back converter cannot play a role; but as the operation time increases, the acetylene conversion rate of the back converter gradually decreases, the subsequent purification process processing load increases, the equipment investment cost increases, and the operating cost increases. The acetylene hydrochlorination reaction is a volume contraction reaction, that is, two volumes of acetylene and hydrogen chloride react to generate one volume of vinyl chloride. The use of pressurization to increase the pressure of the raw gas entering the converter is conducive to improving the acetylene conversion rate and reaction efficiency.

[0043] The method of the present invention can flexibly adjust the molecular ratio of acetylene and hydrogen chloride entering the front-end converter according to different mercury-free catalyst performances and operating process requirements; it can also flexibly adjust the molecular ratio entering the back-end converter according to the operating conditions of the mercury-free catalyst at different stages, the composition of the circulating return gas and the composition of the gas at the outlet of the front-end converter, so as to meet the requirements for the operation of the mercury-free catalyst in the back-end converter.

[0044] Implementation Case 1: In the early stage of operation of the catalyst in the foreground converter 4, the catalyst activity is relatively high. According to the performance of the mercury-free catalyst, acetylene with a purity greater than 99.5% and hydrogen chloride with a purity greater than 99% are mixed in the mixer 1 (the molar ratio of acetylene to hydrogen chloride is 1:1), and then preheated to 80-100°C by the first preheater 2; then enter the foreground converter 4 and synthesize crude vinyl chloride by the mercury-free catalyst. The crude vinyl chloride synthesized by the foreground converter 4 is cooled to 10-60°C by the first cooler 5, pressurized to 100-600KPa by the intermediate compressor 6, and then cooled to -30-30°C by the second cooler 7, and then separated into gas and liquid by the first gas-liquid separator 9. The separated liquid vinyl chloride enters the low-boiling tower 13, and the separated gaseous phase gas (a small amount of vinyl chloride, unreacted acetylene, hydrogen chloride and other gases) is preheated by the second preheater 8 and enters the background converter 10 to continue the synthesis of vinyl chloride under the action of a mercury-free catalyst. The crude vinyl chloride obtained by the reaction is cooled to -30 to 30°C by the third cooler 11 and then separated into gas and liquid by the second gas-liquid separator 12. The separated liquid vinyl chloride enters the low-boiling tower 13, and a part of the separated gaseous phase gas (a small amount of vinyl chloride, unreacted acetylene, hydrogen chloride and other gases) enters the pressure swing adsorption device 15 together with the low-boiling substances distilled from the low-boiling tower 13 for adsorption separation. The inert gas separated by adsorption is emptied, and the recyclable gas separated by adsorption (acetylene, hydrogen chloride, vinyl chloride, etc.) enters the intermediate compressor 6 together with another part of the gaseous phase gas separated by gas-liquid condensation at the outlet of the background converter 10 after passing through the purification device 16 for pressurization and subsequent process treatment, and then enters the background converter 10 to continue the reaction.

[0045] Implementation Case 2: In the later stage of the operation of the catalyst in the front-end converter 4, the activity of the catalyst is relatively low. According to the performance of the mercury-free catalyst, acetylene with a purity greater than 99.5% and hydrogen chloride with a purity greater than 99% are mixed in the mixer 1 (the molar ratio of acetylene to hydrogen chloride is 1:1), pre-pressurized to 100-200 KPa by the compressor 3, and then preheated to 80-100°C by the first preheater 2 before entering the front-end converter 4, where crude vinyl chloride is synthesized by the mercury-free catalyst, and then cooled to 10-60°C by the first cooler 5, pressurized to 100-600 KPa by the intermediate compressor 6, and then cooled to -30-30°C by the second cooler 7 before being separated into gas and liquid by the first gas-liquid separator 9. The separated liquid vinyl chloride enters the low-boiling tower 13, and the separated gaseous phase gas (a small amount of vinyl chloride, unreacted acetylene, hydrogen chloride and other gases) is preheated by the second preheater 8 and enters the background converter 10 to continue the synthesis of vinyl chloride under the action of a mercury-free catalyst. The crude vinyl chloride obtained by the reaction is cooled to -30 to 30°C by the third cooler 11 and then separated into gas and liquid by the second gas-liquid separator 12. The separated liquid vinyl chloride enters the low-boiling tower 13, and a part of the separated gaseous phase gas (a small amount of vinyl chloride, unreacted acetylene, hydrogen chloride and other gases) enters the pressure swing adsorption device 15 together with the low-boiling substances distilled from the low-boiling tower 13 for adsorption separation. The inert gas separated by adsorption is emptied, and the recyclable gas separated by adsorption (acetylene, hydrogen chloride, vinyl chloride, etc.) enters the intermediate compressor 6 together with another part of the gaseous phase gas separated by gas-liquid condensation at the outlet of the background converter 10 after passing through the purification device 16 for pressurization and subsequent process treatment, and then enters the background converter 10 to continue the reaction.

[0046] Implementation Case 3: In the early stage of operation of the catalyst in the foreground converter 4, the catalyst activity is relatively high. According to the performance of the mercury-free catalyst, acetylene with a purity greater than 99.5% and hydrogen chloride with a purity greater than 99% are mixed in the mixer 1 (the molar ratio of acetylene to hydrogen chloride is 1:0.90), and then preheated to 80-100°C by the first preheater 2; then enter the foreground converter 4 and synthesize crude vinyl chloride by the mercury-free catalyst. The crude vinyl chloride synthesized by the foreground converter 4 is cooled to 10-60°C by the first cooler 5, pressurized to 100-600Kpa by the compressor, and then cooled to -30-30°C by the second cooler 7, and then separated into gas and liquid by the first gas-liquid separator 9. The separated liquid vinyl chloride enters the low-boiling tower 13, and the separated gaseous phase gas (a small amount of vinyl chloride, unreacted acetylene, hydrogen chloride and other gases) is preheated by the second preheater 8 and enters the background converter 10 to continue the synthesis of vinyl chloride under the action of a mercury-free catalyst. The crude vinyl chloride obtained by the reaction is cooled to -30 to 30°C by the third cooler 11 and then separated into gas and liquid by the second gas-liquid separator 12. The separated liquid vinyl chloride enters the low-boiling tower 13, and a part of the separated gaseous phase gas (a small amount of vinyl chloride, unreacted acetylene, hydrogen chloride and other gases) enters the pressure swing adsorption device 15 together with the low-boiling substances distilled from the low-boiling tower 13 for adsorption separation. The inert gas separated by adsorption is emptied, and the recyclable gas separated by adsorption (acetylene, hydrogen chloride, vinyl chloride, etc.) enters the intermediate compressor 6 together with another part of the gaseous phase gas separated by gas-liquid condensation at the outlet of the background converter 10 after passing through the purification device 16 for pressurization and subsequent process treatment, and then enters the background converter 10 to continue the reaction.

[0047] Implementation Case 4: In the early stage of operation of the catalyst in the foreground converter 4, the catalyst activity is relatively high. According to the performance of the mercury-free catalyst, acetylene with a purity greater than 99.5% and hydrogen chloride with a purity greater than 99% are mixed in the mixer 1 (the molar ratio of acetylene to hydrogen chloride is 1:1.10), and then preheated to 80-100°C by the first preheater 2; then enter the foreground converter 4 and synthesize crude vinyl chloride by the mercury-free catalyst. The crude vinyl chloride synthesized by the foreground converter 4 is cooled to 10-60°C by the first cooler 5, pressurized to 100-600KPa by the intermediate compressor 6, and then cooled to -30-30°C by the second cooler 7, and then separated into gas and liquid by the first gas-liquid separator 9. The separated liquid vinyl chloride enters the low-boiling tower 13, and the separated gaseous phase gas (a small amount of vinyl chloride, unreacted acetylene, hydrogen chloride and other gases) is preheated by the second preheater 8 and enters the background converter 10 to continue the synthesis of vinyl chloride under the action of a mercury-free catalyst. The crude vinyl chloride obtained by the reaction is cooled to -30 to 30°C by the third cooler 11 and then separated into gas and liquid by the second gas-liquid separator 12. The separated liquid vinyl chloride enters the low-boiling tower 13, and a part of the separated gaseous phase gas (a small amount of vinyl chloride, unreacted acetylene, hydrogen chloride and other gases) enters the pressure swing adsorption device 15 together with the low-boiling substances distilled from the low-boiling tower 13 for adsorption separation. The inert gas separated by adsorption is emptied, and the recyclable gas separated by adsorption (acetylene, hydrogen chloride, vinyl chloride, etc.) enters the intermediate compressor 6 together with another part of the gaseous phase gas separated by gas-liquid condensation at the outlet of the background converter 10 after passing through the purification device 16 for pressurization and subsequent process treatment, and then enters the background converter 10 to continue the reaction.

[0048] Implementation Case 5: In the early stage of operation of the catalyst in the foreground converter 4, the catalyst activity is relatively high. According to the performance of the mercury-free catalyst, acetylene with a purity greater than 99.5% and hydrogen chloride with a purity greater than 99% are mixed in the mixer 1 (the molar ratio of acetylene to hydrogen chloride is 1:1.10), and then preheated to 80-100°C by the first preheater 2; then enter the foreground converter 4 and synthesize crude vinyl chloride by the mercury-free catalyst. The crude vinyl chloride synthesized by the foreground converter 4 is cooled to 10-60°C by the first cooler 5, mixed with a certain amount of acetylene gas, pressurized to 100-600KPa by the intermediate compressor 6, and then cooled to -30-30°C by the second cooler 7, and then separated into gas and liquid by the first gas-liquid separator 9. The separated liquid vinyl chloride enters the low-boiling tower 13, and the separated gaseous phase gas (a small amount of vinyl chloride, unreacted acetylene, hydrogen chloride and other gases) is preheated by the second preheater 8 and enters the background converter 10 to continue the synthesis of vinyl chloride under the action of a mercury-free catalyst. The crude vinyl chloride obtained by the reaction is cooled to -30 to 30°C by the third cooler 11 and then separated into gas and liquid by the second gas-liquid separator 12. The separated liquid vinyl chloride enters the low-boiling tower 13, and a part of the separated gaseous phase gas (a small amount of vinyl chloride, unreacted acetylene, hydrogen chloride and other gases) enters the pressure swing adsorption device 15 together with the low-boiling substances distilled from the low-boiling tower 13 for adsorption separation. The inert gas separated by adsorption is emptied, and the recyclable gas separated by adsorption (acetylene, hydrogen chloride, vinyl chloride, etc.) enters the intermediate compressor 6 together with another part of the gaseous phase gas separated by gas-liquid condensation at the outlet of the background converter 10 after passing through the purification device 16 for pressurization and subsequent process treatment, and then enters the background converter 10 to continue the reaction.

[0049] Implementation Case 6: In the early stage of operation of the catalyst in the foreground converter 4, the catalyst activity is relatively high. According to the performance of the mercury-free catalyst, acetylene with a purity greater than 99.5% and hydrogen chloride with a purity greater than 99% are mixed in the mixer 1 (the molar ratio of acetylene to hydrogen chloride is 1:0.90), and then preheated to 80-100°C by the first preheater 2; then enter the foreground converter 4 and synthesize crude vinyl chloride by the mercury-free catalyst. The crude vinyl chloride synthesized by the foreground converter 4 is cooled to 10-60°C by the first cooler 5, mixed with a certain amount of hydrogen chloride gas, pressurized to 100-600Kpa by the compressor intermediate 6, and then cooled to -30-30°C by the second cooler 7, and then separated into gas and liquid by the first gas-liquid separator 9. The separated liquid vinyl chloride enters the low-boiling tower 13, and the separated gaseous phase gas (a small amount of vinyl chloride, unreacted acetylene, hydrogen chloride and other gases) is preheated by the second preheater 8 and enters the background converter 10 to continue the synthesis of vinyl chloride under the action of a mercury-free catalyst. The crude vinyl chloride obtained by the reaction is cooled to -30 to 30°C by the third cooler 11 and then separated into gas and liquid by the second gas-liquid separator 12. The separated liquid vinyl chloride enters the low-boiling tower 13, and a part of the separated gaseous phase gas (a small amount of vinyl chloride, unreacted acetylene, hydrogen chloride and other gases) enters the pressure swing adsorption device 15 together with the low-boiling substances distilled from the low-boiling tower 13 for adsorption separation. The inert gas separated by adsorption is emptied, and the recyclable gas separated by adsorption (acetylene, hydrogen chloride, vinyl chloride, etc.) enters the intermediate compressor 6 together with another part of the gaseous phase gas separated by gas-liquid condensation at the outlet of the background converter 10 after passing through the purification device 16 for pressurization and subsequent process treatment, and then enters the background converter 10 to continue the reaction.

[0050] Implementation Case 7: In the late stage of catalyst operation of the foreground converter 4 and the background converter 10, the catalyst activity is low. According to the performance of the mercury-free catalyst, acetylene with a purity greater than 99.5% and hydrogen chloride with a purity greater than 99% are mixed in the mixer 1 (the molar ratio of acetylene to hydrogen chloride is 1:1), and then preheated to 80-100° C. by the first preheater 2; then enter the foreground converter 4 and synthesize crude vinyl chloride by the mercury-free catalyst. The crude vinyl chloride synthesized by the foreground converter 4 is cooled to 10-60° C. by the first cooler 5, mixed with a certain amount of hydrogen chloride gas, pressurized to 100-600 KPa by the intermediate compressor 6, and then cooled to -30-30° C. by the second cooler 7, and then separated into gas and liquid by the first gas-liquid separator 9. The separated liquid vinyl chloride enters the low-boiling tower 13, and the separated gaseous phase gas (a small amount of vinyl chloride, unreacted acetylene, hydrogen chloride and other gases) is preheated by the second preheater 8 and enters the background converter 10 to continue the synthesis of vinyl chloride under the action of a mercury-free catalyst. The acetylene content at the outlet is relatively high. The crude vinyl chloride obtained by the reaction is cooled to -30 to 30°C by the third cooler 11 and then separated by gas and liquid phase by the second gas-liquid separator 12. The separated liquid vinyl chloride enters the low-boiling tower 13, and a part of the separated gaseous phase gas (a small amount of vinyl chloride, unreacted acetylene, hydrogen chloride and other gases with a relatively high content) enters the pressure swing adsorption device 15 together with the low-boiling substances distilled from the low-boiling tower 13 for adsorption separation. The inert gas separated by adsorption is emptied, and the recyclable gas separated by adsorption (acetylene, hydrogen chloride, vinyl chloride, etc.) enters the compressor 6 together with another part of the gaseous phase gas separated by gas-liquid condensation at the outlet of the background converter 10 after passing through the purification device 16 for intermediate pressurization and subsequent process treatment, and then enters the background converter 10 to continue the reaction.

[0051] Implementation Case 8: In the early stage of operation of the catalyst in the foreground converter 4, the catalyst activity is relatively high. According to the performance of the mercury-free catalyst, acetylene with a purity greater than 99.5% and hydrogen chloride with a purity greater than 99% are mixed (the molar ratio of acetylene to hydrogen chloride is 1:1), and then preheated to 80-100°C by the first preheater 2; then enter the foreground converter 4 and synthesize crude vinyl chloride by the mercury-free catalyst. The crude vinyl chloride synthesized by the foreground converter 4 is cooled to 10-60°C by the first cooler 5, and mixed with a certain amount of acetylene with a purity greater than 99.5% and hydrogen chloride with a purity greater than 99% (the molar ratio of acetylene to hydrogen chloride is 1:1), pressurized to 100-600KPa by the intermediate compressor, and then cooled to -30-30°C by the second cooler 7, and then separated into gas and liquid by the first gas-liquid separator 9. The separated liquid vinyl chloride enters the low-boiling tower 13, and the separated gaseous phase gas (a small amount of vinyl chloride, unreacted acetylene, hydrogen chloride and other gases) enters the background converter 10 after being preheated by the second preheater 8 to continue the synthesis of vinyl chloride under the action of a mercury-free catalyst. The crude vinyl chloride obtained by the reaction is then cooled to -30 to 30°C by the third cooler 11 and then separated into gas and liquid phases by the second gas-liquid separator 12. The separated liquid vinyl chloride enters the low-boiling tower 13, and a part of the separated gaseous phase gas (a small amount of vinyl chloride, unreacted acetylene, hydrogen chloride and other gases) enters the pressure swing adsorption device 15 together with the low-boiling substances distilled from the low-boiling tower 13 for adsorption separation. The inert gas separated by adsorption is emptied, and the recyclable gas separated by adsorption (acetylene, hydrogen chloride, vinyl chloride, etc.) enters the intermediate compressor 6 together with another part of the gaseous phase gas separated by gas-liquid condensation at the outlet of the background converter 10 after passing through the purification device 16 for pressurization and subsequent process treatment, and then enters the background converter 10 to continue the reaction.

Claims

1. A method for synthesizing vinyl chloride using a mercury-free catalyst, which is implemented by using a process system for synthesizing vinyl chloride using a mercury-free catalyst, and has a specific structure: comprising a mixer (1), wherein the mixer (1) is respectively connected to the inlets of a first preheater (2) and a precompressor (3), wherein the outlet of the precompressor (3) is connected to the inlet of the first preheater (2), wherein the outlet of the first preheater (2) is connected to the material inlet of a front-end converter (4), wherein the material outlet of the front-end converter (4) is connected to the inlet of a first cooler (5), wherein the outlet of the first cooler (5) is connected to an intermediate compressor (6), wherein the intermediate compressor (6) is connected to the inlet of a second cooler (7), wherein the outlet of the second cooler (7) is connected to the inlet of a first gas-liquid separator (9), wherein the gas phase outlet of the first gas-liquid separator (9) is connected to the inlet of a second preheater (8), wherein the outlet of the second preheater (8) is connected to the inlet of a second preheater (8), wherein the outlet of the second preheater (8) is connected to the inlet of a second preheater (9), wherein the outlet of the first preheater (8) is connected to the inlet of a second preheater (8), wherein the outlet of the second preheater (8) is connected to the inlet of a second preheater (8), wherein the outlet of the first preheater (2 ... The material inlet of the background converter (10) is connected to the material outlet of the background converter (10) and the inlet of the third cooler (11). The outlet of the third cooler (11) is connected to the inlet of the second gas-liquid separator (12). The gas phase outlet of the second gas-liquid separator (12) is respectively connected to the inlet of the intermediate compressor (6) and the inlet of the pressure swing adsorption device (15). The outlet of the pressure swing adsorption device (15) is connected to the inlet of the purification device (16). The outlet of the purification device (16) is connected to the inlet of the intermediate compressor (6). The liquid phase outlet of the first gas-liquid separator (9) and the liquid phase outlet of the second gas-liquid separator (12) are also connected to the inlet of the low boiling tower (13). The liquid phase outlet of the low boiling tower (13) is connected to the inlet of the high boiling tower (14). The gas phase outlet of the low boiling tower (13) is connected to the inlet of the pressure swing adsorption device (15). The invention is characterized in that: The specific steps are as follows: Step 1, loading mercury-free catalysts in the tubes of the front converter (4) and the back converter (10), mixing acetylene and hydrogen chloride in the mixer (1) and preheating them or pressurizing them and then preheating them, and then entering the front converter (4) to generate crude vinyl chloride by reaction; Step 2, cooling the crude vinyl chloride generated after the reaction to 10-30° C. through a first cooler (5), then pressurizing it to 300-600 KPa through an intermediate compressor (6), then cooling it to -30-30° C. through a second cooler (7), and finally entering a first gas-liquid separator (9) for gas-liquid phase separation; Step 3, the liquid vinyl chloride separated by the first gas-liquid separator (9) enters the low-boiling tower (13), and the vinyl chloride distilled by the low-boiling tower (13) passes through the high-boiling tower (14) to form finished vinyl chloride; the separated gas phase gas is preheated by the second preheater (8) and enters the background converter (10), where vinyl chloride synthesis is continued under the action of a mercury-free catalyst, and the crude vinyl chloride obtained by the reaction is cooled to -30 to 30° C. by the second cooler (7), and finally enters the second gas-liquid separator (12) for gas-liquid phase separation; In step 4, the liquid vinyl chloride separated by the second gas-liquid separator (12) enters the low-boiling tower (13), and a part of the separated gas phase gas enters the pressure swing adsorption device (15) together with the low-boiling substances distilled from the top of the low-boiling tower (13), and after passing through the purification device (16), it is recycled with the other part to the inlet of the intermediate compressor (6) for pressurization, and further circulates the reaction to improve the acetylene conversion rate.

2. The method for synthesizing vinyl chloride using a mercury-free catalyst according to claim 1, characterized in that: In the step 1, specifically, in the early stage of operation of the mercury-free catalyst, that is, when the activity of the mercury-free catalyst is relatively high, the raw gas acetylene and hydrogen chloride are mixed in a mixer (1) and then enter a first preheater (2) to be preheated to 80-100° C., and the preheated gas directly enters a front converter (4) to react and generate crude vinyl chloride; In the later stage of operation of the mercury-free catalyst, when the activity of the mercury-free catalyst decreases and the acetylene conversion rate decreases, the raw gas acetylene and hydrogen chloride are mixed in the mixer (1) and enter the pre-compressor (3) to be pre-pressurized to 60 to 200 KPa, and then preheated to 80 to 100° C. in the first preheater (2). The preheated gas directly enters the front converter (4) to react and generate crude vinyl chloride.

3. The method for synthesizing vinyl chloride using a mercury-free catalyst according to claim 2, characterized in that: The molar ratio of acetylene to hydrogen chloride is 1:0.90-1.10; the purity of acetylene is greater than 99.5%; the purity of hydrogen chloride is more than 99%.

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