Vinyl chloride whole-process green synthesis system and method based on mercury-free catalyst

Abstract

The invention discloses a whole-process green synthesis system and method for vinyl chloride based on a mercury-free catalyst. The system comprises a synthesis unit, a purification unit, a condensation unit, a rectification unit and a hydrogen chloride recovery unit. A ruthenium-based mercury-free catalyst is used in the synthesis unit. The purification unit comprises a combined absorption tower. The combined absorption tower absorbs hydrogen chloride in the crude vinyl chloride gas to form concentrated hydrochloric acid and conveys the concentrated hydrochloric acid to the hydrogen chloride recovery unit. And the hydrogen chloride recovery unit separates hydrogen chloride gas and conveys the hydrogen chloride gas to the synthesis unit for reuse. And the vinyl chloride gas purified by the purification unit is condensed into vinyl chloride condensate by the condensation unit and then is conveyed to the rectification unit. The rectification unit comprises a low-boiling tower, a high-boiling tower, a vaporizer and a catalytic cracking furnace. And the vinyl chloride condensate is treated by the low-boiling tower and the high-boiling tower in sequence to obtain the final vinyl chloride. High-boiling raffinate generated by the high-boiling tower is conveyed to a vaporizer for vaporization treatment and then conveyed to a catalytic cracking furnace for cracking treatment. The waste liquid and the tail gas are further recycled.

Description

Technical Field

[0001] The invention relates to the technical field of vinyl chloride synthesis, and in particular to a full-process green synthesis method of vinyl chloride based on a mercury-free catalyst. Background Art

[0002] Vinyl chloride (C2H3Cl), with a boiling point of -13.4°C, is slightly soluble in water and is an important monomer in polymer chemical industry. At present, the production of vinyl chloride monomer (VCM) mainly includes the acetylene method and the ethylene method. Although the ethylene oxychlorination method for preparing VCM is relatively less polluting, based on the characteristics of domestic energy endowment (rich in coal, poor in oil and little gas) and the need to balance a large amount of chlorine resources in the chlor-alkali industry, my country's VCM production route is still dominated by the calcium carbide acetylene method, which accounted for 81.3% of the market in 2019. The calcium carbide acetylene method produces VCM, that is, acetylene gas and hydrogen chloride gas are reacted under the action of mercuric chloride catalyst to generate crude vinyl chloride gas, and then purified, compressed and refined to obtain high-purity VCM. This route has a high reaction conversion rate, few side reactions, and simple equipment. However, the acetylene production process will produce mercury-containing waste liquid, high-boiling residual liquid, etc. If not handled properly, it will not only cause waste of resources, but also bring great pollution risks to the environment. Therefore, the development of mercury-free catalysts, resource processing of high-boiling residual liquid, and recovery and utilization of hydrogen chloride have become the key to the green production of VCM by the calcium carbide acetylene method, and are related to the sustainable development and market competitiveness of my country's VCM production.

[0003] Patent CN110227507B "A high-stability ultra-low mercury catalyst and its preparation method and application" discloses that the ultra-low mercury catalyst can effectively catalyze the preparation of VCM monomer, with an acetylene conversion rate of more than 97.2% and a VCM selectivity of more than 99.5%. However, the catalyst still cannot avoid the loss of mercuric chloride (<3.0%) during the reaction process, and fails to solve the treatment problems of mercury-containing waste liquid and high-boiling residual liquid.

[0004] Patent CN108558596B "An Improved Calcium Carbide Process for Synthesizing VCM" uses calcium carbide slag slurry instead of alkali solution to alkali wash the crude VCM gas, reducing the discharge of waste liquid. The main component of calcium carbide slag slurry is calcium hydroxide, which has a low solubility in water. During alkali washing, there will be problems such as incomplete washing and the need to regularly replace the alkali solution.

[0005] Patent CN104211563B "A VCM high boiling point recovery process and equipment" uses a packed distillation tower and its ancillary equipment to reduce and recycle high boiling points under normal pressure and pressurized conditions. The patent recovers 1,1-dichloroethane from high boiling liquid, while 1,2-dichloroethane, trichloroethane and other components are not further recycled.

[0006] In summary, it is necessary to develop a green synthesis method for vinyl chloride based on a mercury-free catalyst to completely solve the pollution problems such as mercury-containing waste liquid in the acetylene production process and realize the green production of VCM in the whole process of calcium carbide acetylene method. Summary of the invention

[0007] In order to solve the above problems existing in the existing VCM production process of the carbide acetylene method, the present invention provides a green synthesis method of vinyl chloride based on a mercury-free catalyst, which not only ensures the quality of VCM, but also reduces and recycles the by-product waste liquid and waste gas generated in the synthesis process.

[0008] In a first aspect, the present invention provides a green synthesis system of vinyl chloride based on a mercury-free catalyst, which comprises a synthesis unit, a purification unit, a condensation unit, a distillation unit and a hydrogen chloride recovery unit. A ruthenium-based mercury-free catalyst is used in the synthesis unit. The crude vinyl chloride gas synthesized in the synthesis unit is transported to the purification unit.

[0009] The purification unit includes a combined absorption tower. The combined absorption tower is used to absorb hydrogen chloride in the crude vinyl chloride gas to form concentrated hydrochloric acid, which is then transported to a hydrogen chloride recovery unit. The hydrogen chloride recovery unit is used to separate hydrogen chloride gas from the concentrated hydrochloric acid and transport it to a synthesis unit for reuse.

[0010] The vinyl chloride gas purified by the purification unit is condensed into vinyl chloride condensate by the condensation unit and then transported to the distillation unit. The distillation unit includes a low boiling tower, a high boiling tower, a vaporizer and a catalytic cracking furnace. The vinyl chloride condensate is sequentially processed by the low boiling tower and the high boiling tower to obtain the final vinyl chloride. The high boiling residual liquid produced by the high boiling tower is transported to the vaporizer for vaporization treatment and then transported to the catalytic cracking furnace for cracking treatment.

[0011] Preferably, a heat exchanger is connected between the synthesis unit and the catalytic cracking furnace and vaporizer in the distillation unit. The heat exchanger uses a heat exchange medium to absorb the heat generated when the synthesis unit synthesizes vinyl chloride, and provides the heat to the catalytic cracking furnace and vaporizer that need to absorb heat.

[0012] Preferably, the synthesis unit comprises a front VCM converter and a rear VCM converter connected in series. The mixed gas inlet of the synthesis unit is connected to the acetylene raw material processing unit and the hydrogen chloride raw material processing unit through a mixer. The front VCM converter and the rear VCM converter both use VCM tube-type fixed bed converters equipped with mercury-free catalysts.

[0013] Preferably, the mercury-free catalyst is composed of a porous solid carrier and a ruthenium complex, metal and non-metallic additives loaded on the surface of the carrier, wherein the ruthenium complex is one or more of a polypyridine ruthenium complex, a ruthenium porphyrin ruthenium complex, and an aromatic ruthenium complex; the metal additive is ruthenium nitrate; the non-metallic additive is specifically a mixture of triphenylmethylphosphine bistrifluoromethanesulfonyl imide salt and triphenylethylphosphine bromide in a mass ratio of (2.5 to 5.5):1; and the porous solid carrier is activated carbon.

[0014] Preferably, the purification unit further comprises an alkali washing tower, a demister and a dry separator. The vinyl chloride gas output from the combined absorption tower passes through the alkali washing tower, the demister and the dry separator in sequence.

[0015] Preferably, the condensing unit comprises a condenser and a condensate storage tank. The vinyl chloride gas purified by the purification unit is transported to the condenser. The vinyl chloride condensate output by the condenser is stored in the condensate storage tank. The condensate storage tank transports liquid hydrogen chloride to the distillation unit. The gas phase outlet of the condensate storage tank and the tail gas outlet of the low boiling tower are both connected to the pressure swing adsorption unit.

[0016] Preferably, the hydrogen chloride recovery unit comprises a bidirectional heat exchanger, a concentrated acid stripping tower, a dilute acid stripping tower, a calcium chloride solution storage tank and an evaporation concentration tower. The concentrated hydrochloric acid outlet of the combined absorption tower, the bidirectional heat exchanger, the concentrated acid stripping tower and the dilute acid stripping tower are connected in sequence. The calcium chloride solution storage tank provides calcium chloride solution to the dilute acid stripping tower. The calcium chloride solution with reduced concentration at the bottom of the dilute acid stripping tower is output to the evaporation concentration tower; after the evaporation concentration tower increases the concentration of the calcium chloride solution, the calcium chloride solution is transported to the calcium chloride solution storage tank for reuse. The concentrated acid stripping tower is connected to a concentrated acid reboiler. The dilute acid stripping tower is connected to a dilute acid reboiler. The evaporation concentration tower is connected to a concentration reboiler. The water produced by the evaporation concentration tower is transported to the combined absorption tower for reuse.

[0017] Preferably, during the operation of the hydrogen chloride recovery unit, concentrated hydrochloric acid enters the top of the concentrated acid stripping tower, and counter-currently transfers mass and heat with the hydrogen chloride and water vapor from the concentrated acid reboiler in the tower, and obtains aqueous hydrogen chloride gas at the top of the tower, and obtains dilute hydrochloric acid at the bottom of the tower. The hydrogen chloride temperature at the top feed port of the concentrated acid stripping tower is 90°C~95°C, and the pressure is controlled at 60KpaG~70KpaG. Dilute hydrochloric acid is fed to the top of the dilute acid stripping tower, and counter-currently transfers mass and heat with the hydrogen chloride, water vapor from the acid reboiler and the calcium chloride solution from the calcium chloride solution storage tank in the tower, and obtains aqueous hydrogen chloride gas at the top of the tower, and obtains a calcium chloride solution with reduced concentration at the bottom of the tower. The hydrogen chloride temperature at the top feed port of the dilute acid stripping tower is 90~110°C, and the pressure is controlled at 60~70 KpaG. After the reduced concentration of the calcium chloride solution is fed to the evaporation concentration tower to restore the initial concentration, it is transported to the calcium chloride solution storage tank for reuse.

[0018] In a second aspect, the present invention provides a green synthesis method of vinyl chloride throughout the process, which uses the above-mentioned green synthesis system of vinyl chloride throughout the process; the green synthesis method of vinyl chloride throughout the process comprises the following steps: Step 1: acetylene gas and hydrogen chloride gas are mixed and fed into a synthesis unit to react and convert into crude vinyl chloride gas; Step 2: sending the crude vinyl chloride gas obtained in step 1 to a combined absorption tower in a purification unit; the combined absorption tower absorbs hydrogen chloride gas in the crude vinyl chloride gas with water to obtain concentrated hydrochloric acid and purified vinyl chloride gas; Step 3: The concentrated hydrochloric acid output from the combined absorption tower is input into the hydrogen chloride recovery unit, and the generated hydrogen chloride gas is transported to the synthesis unit for reuse. The vinyl chloride gas output from the combined absorption tower is input into the condensation unit; the vinyl chloride condensate output from the condensation unit is sequentially processed by the low-boiling tower and the high-boiling tower to produce the final vinyl chloride gas. The high-boiling residual liquid produced by the high-boiling tower is vaporized and then sent to the catalytic cracking furnace for cracking treatment, and the resulting vinyl chloride and hydrogen chloride cracking gas are transported to the synthesis unit for reuse.

[0019] Preferably, in step 1, the mass ratio of hydrogen chloride / acetylene in the mixed gas fed to the synthesis unit is (1.0-1.5):1; the reaction temperature of the synthesis unit is 110-190°C, and the volume space velocity (GHSV) is 30-100 h -1 .

[0020] Preferably, in step 2, the vinyl chloride gas output from the combined absorption tower is processed in sequence by an alkali washing tower, a demister and a dry separator to remove residual impurities including hydrogen chloride and carbon dioxide.

[0021] Preferably, in step 3, the catalyst used in the catalytic cracking furnace is nitrogen-doped activated carbon; the nitrogen-doped activated carbon is obtained by nitrogen-doping activated carbon by low-temperature plasma treatment. The reaction temperature of the catalytic cracking furnace is 220°C to 280°C.

[0022] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention adopts a mercury-free catalyst (ruthenium-based catalyst) to synthesize VCM, thus avoiding mercury pollution.

[0023] 2. The present invention adopts a combined absorption tower, a concentrated acid desorption tower and a dilute acid desorption tower to recover hydrogen chloride in the crude vinyl chloride gas, thereby achieving zero discharge of waste water.

[0024] 3. The present invention uses a non-metallic catalyst to catalytically crack high-boiling residual liquid, thereby reducing waste liquid discharge and recycling it.

[0025] 4. The hydrogen chloride recovered by the present invention is returned to the VCM fluidized bed converter for reuse, thereby effectively recycling the by-product hydrogen chloride. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is the overall process flow chart of the present invention.

[0027] Figure 2 It is a schematic diagram of the combination of the purification unit and the hydrogen chloride recovery unit in the present invention.

[0028] Figure 3 It is a structural schematic diagram of the combined absorption tower in the present invention.

[0029] Figure 4 It is a schematic diagram of the distillation unit in the present invention. DETAILED DESCRIPTION

[0030] The present invention will be described in detail below through specific embodiments. The illustrative embodiments and descriptions of the present invention are used to explain the present invention but are not intended to limit the present invention.

[0031] like Figure 1 As shown, a green synthesis system of vinyl chloride based on a mercury-free catalyst for the whole process includes a synthesis unit 1, a purification unit 2, a condensation unit 3, a pressure swing adsorption unit 4, a distillation unit 5 and a hydrogen chloride recovery unit 6.

[0032] The synthesis unit 1 includes a front VCM converter and a rear VCM converter connected in series. The mixed gas input port of the synthesis unit 1 is connected to the acetylene raw material processing unit and the hydrogen chloride raw material processing unit respectively through a mixer. The front VCM converter and the rear VCM converter both use VCM tube-type fixed bed converters equipped with mercury-free catalysts.

[0033] The mercury-free catalyst adopts a ruthenium-based catalyst, which is composed of a porous solid carrier and a ruthenium complex, metal and non-metallic additives loaded on the surface of the carrier. The ruthenium complex is one or more of a polypyridine ruthenium complex, a ruthenium porphyrin ruthenium complex, and an aromatic ruthenium complex; the metal additive is ruthenium nitrate; the non-metallic additive is specifically a mixture of triphenylmethylphosphine bistrifluoromethanesulfonyl imide salt and triphenylethylphosphine bromide in a mass ratio of 4:1; the porous solid carrier is activated carbon.

[0034] like Figure 2 and Figure 3 As shown, the purification unit 2 includes a combined absorption tower, an alkali washing tower, a demister and a dry separator. The combined absorption tower is provided with a gas distribution area, a filler absorption area, a gas-liquid separation area and a plate absorption area arranged in sequence from bottom to top. An air inlet is provided at the bottom of the combined absorption tower, and an air outlet is provided at the top. The combined absorption tower is also provided with a concentrated hydrochloric acid outlet; the air inlet at the bottom of the combined absorption tower is connected to the outlet of the synthesis unit 1. The air outlet at the top of the combined absorption tower, the alkali washing tower, the demister and the dry separator are connected in sequence. The outlet of the dry separator is used to output the purified vinyl chloride gas.

[0035] like Figure 2 As shown, the hydrogen chloride recovery unit 6 includes a two-way heat exchanger, a concentrated acid stripping tower, a dilute acid stripping tower, a calcium chloride solution storage tank and an evaporation and concentration tower. The concentrated hydrochloric acid output port of the combined absorption tower, the two-way heat exchanger, the concentrated acid stripping tower, and the dilute acid stripping tower are connected in sequence. The output port of the calcium chloride solution storage tank is connected to the calcium chloride input port of the dilute acid stripping tower; the low-concentration calcium chloride output port at the bottom of the dilute acid stripping tower is connected to the evaporation and concentration tower. The evaporation and concentration tower obtains a high-concentration calcium chloride solution and transports it to the calcium chloride solution storage tank for reuse. The water produced by the evaporation and concentration tower is connected to the combined absorption tower for reuse. The concentrated acid stripping tower is connected to a concentrated acid reboiler. The dilute acid stripping tower is connected to a dilute acid reboiler. The evaporation and concentration tower is connected to a concentration reboiler. The hydrogen chloride gas produced by the concentrated acid stripping tower and the dilute acid stripping tower is connected to the mixed gas input port of the synthesis unit 1 after passing through the concentrated sulfuric acid drying tower to realize the reuse of the hydrogen chloride gas. The tops of the evaporation and concentration tower, the low boiling tower and the high boiling tower are all connected with condensers.

[0036] The condensation unit 3 includes a condenser and a condensate storage tank. The output port of the dry separator, the condenser and the condensate storage tank are connected in sequence. The gas phase outlet of the condensate storage tank is connected to the pressure swing adsorption unit 4.

[0037] like Figure 4 As shown, the distillation unit 5 includes a low boiling tower, a high boiling tower, a finished product storage tank, a vaporizer, a catalytic cracking furnace and a heat exchanger. The liquid phase output port of the condensate storage tank, the low boiling tower, the high boiling tower and the finished product storage tank are connected in sequence. The pressure swing adsorption unit 4 is used to further separate useful components from the tail gas; the useful components include vinyl chloride, hydrogen and acetylene. The low-boiling tail gas outlet of the low boiling tower is connected to the pressure swing adsorption unit 4. The high-boiling tail liquid outlet of the high boiling tower, the vaporizer and the catalytic cracking furnace are connected in sequence. The catalytic cracking furnace is used to produce cracking gas to generate vinyl chloride and hydrogen chloride.

[0038] The catalyst in the catalytic cracking furnace is nitrogen-doped activated carbon, which uses coconut shell, fruit shell or coal-based activated carbon. The nitrogen doping modification adopts low-temperature plasma technology, the discharge power is 30W, the discharge gas is 1:1 Ar / N2 mixed gas, the flow rate is 30 ml / min, and the discharge time is 30 minutes.

[0039] A heat exchanger is provided between the front VCM converter, the rear VCM converter, the catalytic cracking furnace and the vaporizer. The heat exchanger uses heptane refrigerant to absorb the heat generated by the front VCM converter, the rear VCM converter and the catalytic oxidation furnace, and provides the heat to the catalytic cracking furnace and the vaporizer that need to absorb heat.

[0040] The following are some key points of this embodiment: (a) Synthesis of vinyl chloride using mercury-free catalysts (ruthenium-based catalysts); (b) using a combined absorption tower, a concentrated acid stripping tower and a dilute acid stripping tower to recover by-product hydrogen chloride in the crude vinyl chloride gas; (c) The recovered hydrogen chloride is returned to the VCM tube-in-tube fixed bed converter for reuse; (d) The high-boiling residual liquid is converted into gaseous state by the action of the vaporizer and enters the catalytic cracking furnace for cracking to generate vinyl chloride and hydrogen chloride cracking gas, which is then recycled after purification; (e) Use heptane refrigerant, water or heat transfer oil as medium to absorb and transfer heat from the entire VCM production process.

[0041] like Figure 1 As shown, a green synthesis method of vinyl chloride without mercury catalyst comprises the following steps: 1) If Figure 2 As shown in the figure, acetylene gas and hydrogen chloride gas are mixed in a mixer and then passed into the front VCM converter and the rear VCM converter in turn to be converted into crude vinyl chloride gas, and then enter the purification unit. The mass ratio of hydrogen chloride / acetylene in the mixed gas input to the front VCM converter is 1.0~1.5 / 1, the reaction temperature is 110~190℃, and the volume space velocity (GHSV) is 30~100 h -1 .

[0042] 2) If Figure 3 As shown, crude vinyl chloride gas enters from the bottom of the combined absorption tower, and concentrated hydrochloric acid is obtained at the bottom of the tower after the water in the upper part absorbs hydrogen chloride. After the gas is discharged from the top of the tower, it enters the alkali washing tower, demister and dry separator in sequence to further purify the impurities such as hydrogen chloride and carbon dioxide in the gas, and obtains separated purified gas and concentrated hydrochloric acid.

[0043] 3) The purified gas obtained in step 2) is pressurized and sent to a condenser for condensation to obtain vinyl chloride condensate; the condensed tail gas is sent to a pressure swing adsorption unit for further separation of useful components; the useful components include vinyl chloride, hydrogen and acetylene.

[0044] 4) If Figure 4 As shown, the vinyl chloride condensate obtained in step 3) is passed through a low boiling tower to remove low boiling point components, and then enters the pressure swing adsorption unit of step 3) for treatment. The kettle liquid after the low boiling tower treatment enters a high boiling tower for treatment to obtain refined vinyl chloride gas, and at the same time, a high boiling residual liquid (main component: ethylene dichloride) is produced in the distillation tower kettle.

[0045] 5) The concentrated hydrochloric acid obtained in step 2) enters the top of the concentrated acid stripping tower, and counter-currently transfers mass and heat with the high-temperature hydrogen chloride and water vapor from the concentrated acid reboiler in the tower, and obtains hydrous hydrogen chloride gas at the top of the tower, and obtains constant boiling acid (dilute hydrochloric acid solution) at the bottom of the tower. The hydrogen chloride temperature at the top feed inlet of the concentrated acid stripping tower is 90~95℃, and the pressure is controlled at 60~70 KpaG. The dilute hydrochloric acid solution is sent to the dilute acid stripping tower for desorption to obtain hydrous hydrogen chloride gas. When the dilute acid stripping tower is desorbed, calcium chloride solution is added to make the high-temperature hydrogen chloride, water vapor and calcium chloride from the dilute acid reboiler to counter-currently transfer mass and heat in the tower, and hydrous hydrogen chloride gas is obtained at the top of the tower, and a low-concentration calcium chloride solution is obtained at the bottom of the tower. After the low-concentration calcium chloride solution is sent to the evaporation and concentration tower to restore the initial concentration, it is sent to the dilute acid stripping tower for use, and the water vapor evaporated from the evaporation and concentration tower is condensed and returned to the combined absorption tower for reuse. The temperature of hydrogen chloride at the top feed inlet of the dilute acid stripping tower is 90~110℃, and the pressure is controlled at 60~70 KpaG.

[0046] 6) The high-boiling residual liquid obtained in step 4) is vaporized in the vaporizer and then enters the catalytic cracking furnace, where it is cracked into crude vinyl chloride gas and hydrogen chloride under the action of the catalyst. The gas is mixed with the crude vinyl chloride gas from the post-VCM converter and enters the purification unit. The reaction temperature of the catalytic cracking furnace is 220°C-280°C.

[0047] 7) The water-containing hydrogen chloride gas obtained in step 5) is sent to a sulfuric acid drying tower to remove moisture, and then returned to the front VCM converter and the rear VCM converter for reuse.

[0048] 8) Heptane refrigerant is used to absorb the heat generated by the front VCM converter and the rear VCM converter, and the heat is used in the catalytic cracking furnace, the purification unit and the distillation unit in turn through water or heat transfer oil heat exchange medium.

[0049] The following provides three specific reaction condition examples of the synthesis unit 1 and the catalytic cracking furnace. In the following examples, the catalysts used are shown in Table 1 below.

[0050] Table 1 Catalyst usage in examples use Acetylene hydrochlorination Catalytic cracking reaction catalyst A: Ru / C C: Ni / molecular sieve <![CDATA[B: Ru1 / C]]> <![CDATA[D: Ni1 / molecular sieve]]> Among them, Ru1 / C means that Ru is loaded in the form of a single atom; Ru / C means that Ru is loaded in a common form. Ni1 / molecular sieve means that Ni is loaded in the form of a single atom; Ni / molecular sieve means that Ni is loaded in a common form.

[0051] Example 1 Catalyst A was applied to a VCM tube-type fixed-bed reactor at 190 °C, 0.1 MPa, HCl / C2H2 molar ratio = 1.1 / 1.0, and acetylene space velocity 300 h -1The acetylene hydrochlorination reaction was carried out under the reaction conditions of . In the initial stage of the reaction, the acetylene conversion rate reached 89.5% and the VCM selectivity was 99.9%. After 200 h of reaction, the acetylene conversion rate was 88.3% and the VCM selectivity was 99.9%.

[0052] Catalyst C was used in a catalytic cracking furnace at 280 °C, 0.1 MPa, and a gas space velocity of 300 h -1 The high boiling residue was gasified and cracked under the reaction conditions of . In the initial stage of the reaction, the conversion rate of the high boiling residue after vaporization was 73.1%, and the VCM selectivity was 95.1%. After 200 h of reaction, the conversion rate of the high boiling residue after vaporization was 70.2%, and the VCM selectivity was 78.9%.

[0053] Example 2 Catalyst B was applied to a VCM tube-type fixed-bed reactor at 190 °C, 0.1 MPa, HCl / C2H2 molar ratio = 1.3 / 1.0, and acetylene space velocity 300 h -1 The acetylene hydrochlorination reaction was carried out under the reaction conditions of . In the initial stage of the reaction, the acetylene conversion rate reached 91.5% and the VCM selectivity was 99.9%. After 200 h of reaction, the acetylene conversion rate was 89.7% and the VCM selectivity was 99.9%.

[0054] Catalyst D was used in a catalytic cracking furnace at 280 °C, 0.1 MPa, and a gas space velocity of 300 h -1 The high boiling residue was gasified and cracked under the reaction conditions of . In the initial stage of the reaction, the conversion rate of the high boiling residue after vaporization was 70.4%, and the VCM selectivity was 99.6%. After 200 h of reaction, the conversion rate of the high boiling residue after vaporization was 61.2%, and the VCM selectivity was 80.6%.

[0055] Example 3 Catalyst A was applied to a VCM tube-type fixed-bed reactor at 220 °C, 0.1 MPa, HCl / C2H2 molar ratio = 1.2 / 1.0, and acetylene space velocity 400 h -1 The acetylene hydrochlorination reaction was carried out under the reaction conditions of . In the initial stage of the reaction, the acetylene conversion rate reached 90.5% and the VCM selectivity was 99.9%. After 200 h of reaction, the acetylene conversion rate was 88.2% and the VCM selectivity was 99.8%.

[0056] Catalyst D was used in a catalytic cracking furnace at 270 °C, 0.1 MPa, and a gas space velocity of 100 h -1 The high boiling residue was gasified and cracked under the reaction conditions of . In the initial stage of the reaction, the conversion rate of the high boiling residue after vaporization was 77.8%, and the VCM selectivity was 99.6%. After 200 h of reaction, the conversion rate of the high boiling residue after vaporization was 69.8%, and the VCM selectivity was 99.5%.

[0057] The present invention is not limited to the above-mentioned embodiments. On the basis of the technical solution disclosed in the present invention, technicians in this field may make some substitutions and improvements to some technical features therein according to the disclosed technical content without departing from the principles of the present invention. These substitutions and improvements should also be regarded as within the protection scope of the present invention.

Claims

1. A green synthesis system for vinyl chloride based on a mercury-free catalyst, comprising a synthesis unit (1), a purification unit (2), a condensation unit (3) and a distillation unit (5); characterized in that: It also includes a hydrogen chloride recovery unit (6); a ruthenium-based mercury-free catalyst is used in the synthesis unit (1); the crude vinyl chloride gas synthesized in the synthesis unit (1) is transported to the purification unit (2); The purification unit (2) comprises a combined absorption tower; the combined absorption tower is used to absorb hydrogen chloride in the crude vinyl chloride gas to form concentrated hydrochloric acid, which is then transported to a hydrogen chloride recovery unit (6); the hydrogen chloride recovery unit (6) is used to separate hydrogen chloride gas from the concentrated hydrochloric acid and transport it to the synthesis unit (1) for reuse; The vinyl chloride gas purified by the purification unit (2) is condensed into vinyl chloride condensate by the condensation unit (3) and then transported to the distillation unit (5); the distillation unit (5) comprises a low boiling tower, a high boiling tower, a vaporizer and a catalytic cracking furnace; the vinyl chloride condensate is sequentially treated by the low boiling tower and the high boiling tower to obtain the final vinyl chloride; the high boiling residual liquid produced by the high boiling tower is transported to the vaporizer for vaporization treatment and then transported to the catalytic cracking furnace for cracking treatment.

2. A green synthesis system of vinyl chloride based on mercury-free catalyst according to claim 1, characterized in that: A heat exchanger is connected between the synthesis unit (1) and the catalytic cracking furnace and vaporizer in the distillation unit (5); the heat exchanger uses a heat exchange medium to absorb the heat generated when the synthesis unit (1) synthesizes vinyl chloride, and provides the heat to the catalytic cracking furnace and vaporizer that need to absorb heat; the synthesis unit (1) includes a front VCM converter and a rear VCM converter connected in series; the mixed gas input port of the synthesis unit (1) is connected to the acetylene raw material processing unit and the hydrogen chloride raw material processing unit through a mixer; the front VCM converter and the rear VCM converter both use VCM tube-type fixed bed converters equipped with mercury-free catalysts.

3. The green synthesis system of vinyl chloride based on mercury-free catalyst according to claim 1, characterized in that: The mercury-free catalyst is composed of a porous solid carrier and a ruthenium complex, metal and non-metal additives loaded on the surface of the carrier. The ruthenium complex is one or more of a polypyridine ruthenium complex, a ruthenium porphyrin ruthenium complex and an aromatic ruthenium complex; the metal additive is ruthenium nitrate; the non-metal additive is specifically a mixture of triphenylmethylphosphine bistrifluoromethanesulfonyl imide salt and triphenylethylphosphine bromide in a mass ratio of (2.5 to 5.5):1; the porous solid carrier is activated carbon.

4. The green synthesis system of vinyl chloride based on mercury-free catalyst according to claim 1, characterized in that: The purification unit (2) further comprises an alkali washing tower, a demister and a dry separator; the vinyl chloride gas outputted from the combined absorption tower passes through the alkali washing tower, the demister and the dry separator in sequence; the condensation unit (3) comprises a condenser and a condensate storage tank; the vinyl chloride gas purified by the purification unit (2) is transported to the condenser; the vinyl chloride condensate outputted from the condenser is stored in the condensate storage tank; the condensate storage tank transports the liquid hydrogen chloride to the distillation unit (5); the gas phase outlet of the condensate storage tank and the tail gas outlet of the low boiling tower are both connected to the pressure swing adsorption unit (4).

5. The green synthesis system of vinyl chloride based on mercury-free catalyst according to claim 1, characterized in that: The hydrogen chloride recovery unit (6) comprises a bidirectional heat exchanger, a concentrated acid desorption tower, a dilute acid desorption tower, a calcium chloride solution storage tank and an evaporation and concentration tower; the concentrated hydrochloric acid output port of the combined absorption tower, the bidirectional heat exchanger, the concentrated acid desorption tower and the dilute acid desorption tower are connected in sequence; the calcium chloride solution storage tank provides calcium chloride solution to the dilute acid desorption tower; the calcium chloride solution with reduced concentration at the bottom of the dilute acid desorption tower is output to the evaporation and concentration tower; after the evaporation and concentration tower increases the concentration of the calcium chloride solution, the calcium chloride solution is transported to the calcium chloride solution storage tank for reuse; the concentrated acid desorption tower is connected to a concentrated acid reboiler; the dilute acid desorption tower is connected to a dilute acid reboiler; the evaporation and concentration tower is connected to a concentration reboiler; and the water generated by the evaporation and concentration tower is transported to the combined absorption tower for reuse.

6. The green synthesis system of vinyl chloride based on mercury-free catalyst according to claim 1, characterized in that: During operation of the hydrogen chloride recovery unit (6), concentrated hydrochloric acid enters the top of the concentrated acid stripping tower, and conducts countercurrent mass transfer and heat transfer with the hydrogen chloride and water vapor from the concentrated acid reboiler in the tower, and water-containing hydrogen chloride gas is obtained at the top of the tower, and dilute hydrochloric acid is obtained at the bottom of the tower; the hydrogen chloride temperature at the top feed inlet of the concentrated acid stripping tower is 90°C to 95°C, and the pressure is controlled at 60KPaG to 70KPaG; Dilute hydrochloric acid is fed into the top of the dilute acid stripping tower, and countercurrently transfers mass and heat with hydrogen chloride, water vapor from the acid reboiler and the calcium chloride solution from the calcium chloride solution storage tank in the tower, and aqueous hydrogen chloride gas is obtained at the top of the tower, and a calcium chloride solution with reduced concentration is obtained at the bottom of the tower; the hydrogen chloride temperature at the top feed inlet of the dilute acid stripping tower is 90-110°C, and the pressure is controlled at 60-70 KpaG; the calcium chloride solution with reduced concentration is fed into the evaporation and concentration tower to restore the initial concentration, and then transported to the calcium chloride solution storage tank for reuse.

7. A green synthesis method of vinyl chloride throughout the entire process, characterized in that: Using the green synthesis system of vinyl chloride as claimed in claim 1; the green synthesis method of vinyl chloride comprises the following steps: Step 1: Acetylene gas and hydrogen chloride gas are mixed and fed into a synthesis unit (1) to react and convert into crude vinyl chloride gas; Step 2: sending the crude vinyl chloride gas obtained in step 1 to a combined absorption tower in a purification unit (2); the combined absorption tower uses water to absorb hydrogen chloride gas in the crude vinyl chloride gas to obtain concentrated hydrochloric acid and purified vinyl chloride gas; Step 3: The concentrated hydrochloric acid output from the combined absorption tower is input into the hydrogen chloride recovery unit (6), and the generated hydrogen chloride gas is transported to the synthesis unit (1) for reuse; the vinyl chloride gas output from the combined absorption tower is input into the condensation unit (3); the vinyl chloride condensate output from the condensation unit (3) is sequentially processed through a low boiling tower and a high boiling tower to generate final vinyl chloride gas; the high boiling residual liquid generated in the high boiling tower is vaporized and then sent to a catalytic cracking furnace for cracking treatment, and the obtained vinyl chloride and hydrogen chloride cracking gas is transported to the synthesis unit (1) for reuse.

8. A green synthesis method of vinyl chloride throughout the entire process according to claim 7, characterized in that: In step 1, the mass ratio of hydrogen chloride / acetylene in the mixed gas fed into the synthesis unit (1) is (1.0-1.5):1; the reaction temperature of the synthesis unit (1) is 110-190°C, and the volume space velocity is 30-100 h -1 .

9. The green synthesis method of vinyl chloride according to claim 7, characterized in that: In step 2, the vinyl chloride gas output from the combined absorption tower is processed in sequence by an alkali washing tower, a demister and a dry separator to remove residual impurities including hydrogen chloride and carbon dioxide.

10. The green synthesis method of vinyl chloride according to claim 7, characterized in that: In step three, the catalyst used in the catalytic cracking furnace is nitrogen-doped activated carbon; the nitrogen-doped activated carbon is obtained by nitrogen-doping activated carbon by low-temperature plasma treatment; the reaction temperature of the catalytic cracking furnace is 220°C to 280°C.

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