A method for hydrogenating chloride using supercritical separation method

Abstract

The invention discloses a method for hydrogen chloride oxidation using a supercritical separation method, comprising the following steps: pre-treating HCl-containing reaction gas and co-heating and mixing it with an oxygen-containing gas to perform a catalytic oxidation reaction to obtain a chlorine-containing reaction gas A; quenching the chlorine-containing reaction gas A to obtain a chlorine-containing reaction gas B; drying and dehydrating the chlorine-containing reaction gas B, and pressurizing it before sending it to a liquid chlorine refining unit to collect liquid chlorine and a mixed gas C; sending the mixed gas C to an HCl purification unit to separate it by supercritical extraction to obtain a chlorine-containing supercritical stream D and a chlorine-free supercritical stream E; refluxing the chlorine-containing supercritical stream D to a catalytic oxidation unit for cyclic treatment; absorbing the tail gas of the chlorine-free supercritical stream E and then discharging it, or partially refluxing it to the catalytic oxidation unit as circulating gas. The method can reduce HCl loss and waste gas discharge, reduce power consumption and equipment size, and increase the operating cycle of the device.

Description

Technical Field

[0001] The invention relates to a hydrogen chloride oxidation method, in particular to a hydrogen chloride oxidation method using a supercritical separation method. Background Art

[0002] As an important basic chemical, chlorine is widely used in the production process of chemical raw materials, agricultural chemicals, building materials, pharmaceutical preparations and other products. However, in most chlorine-related reaction processes, the utilization rate of chlorine resources is very low, and most of the by-products are hydrochloric acid in the form of HCl. Especially when producing large-scale products such as isocyanates, methane chloride, and epichlorohydrin, the amount of by-product HCl is very large.

[0003] The most commonly used methods for treating HCl and the problems they have are: 1) direct absorption with alkali solution will cause a large waste of chlorine resources; 2) manufacturing products such as vinyl chloride, but the product profit is low and uncompetitive; 3) direct oxidation of HCl into chlorine gas through Deacon catalytic oxidation can achieve the recycling of chlorine resources. Therefore, currently, converting HCl into chlorine gas for recycling is a relatively green chlorine balance treatment method.

[0004] The oxidation of hydrogen chloride to produce chlorine is an equilibrium reaction, and HCl cannot be completely converted into chlorine. The traditional treatment method is: after the reaction, most of the unreacted HCl is absorbed by water to obtain hydrochloric acid, and chlorine is refined. Then, in order to improve the conversion rate and reduce the loss of chlorine, a large amount of non-condensable gas containing oxygen, nitrogen, carbon dioxide, unreacted HCl and residual chlorine is recycled, resulting in the actual circulating gas volume being much larger than the required circulating gas volume, the equipment size is large, and the energy consumption is very high.

[0005] In view of the above process difficulties, it is urgent to develop a hydrogen chloride oxidation process that can reduce HCl loss and waste gas emissions and reduce the energy consumption of the device. Summary of the invention

[0006] In order to solve the above technical problems, the present invention proposes a method for hydrogenation of chloride using a supercritical separation method. In view of the problem that the hydrogen chloride reaction is incomplete and the residual chlorine content in the reaction gas is high during the process of hydrogenation of chloride to prepare chlorine, the present invention uses CO2 carried by the reaction gas to separate and purify the residual chlorine through a supercritical separation method, and directly reuses it in the hydrogenation of chloride reaction, thereby greatly reducing HCl loss and circulating gas volume, reducing equipment size and energy consumption, and thus solving the above technical problems.

[0007] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0008] A method for hydrogen chloride oxidation using a supercritical separation method comprises the following steps:

[0009] Step a), using the HCl-containing reaction gas from which organic impurities have been removed as a raw material, co-heating and mixing with an oxygen-containing gas in a catalytic oxidation unit, and performing a catalytic oxidation reaction to obtain a chlorine-containing reaction gas A;

[0010] Step b), sending the chlorine-containing reaction gas A to a quenching unit, and recovering industrial hydrochloric acid and chlorine-containing reaction gas B through quenching;

[0011] Step c), drying and removing water from the chlorine-containing reaction gas B and sending it to a compression and liquefaction unit, and then further sending it to a liquid chlorine refining unit after pressurization to collect liquid chlorine and mixed gas C;

[0012] Step d), sending the mixed gas C into the HCl purification unit, increasing the pressure until CO2 enters the supercritical state, and using supercritical extraction to separate to obtain chlorine-containing supercritical stream D and chlorine-free supercritical stream E;

[0013] Step e), returning the chlorine-containing supercritical stream D to the catalytic oxidation unit for circulation treatment; sending the chlorine-free supercritical stream E to the tail gas absorption unit to eliminate CO2 and then discharge it, or partially returning it to the catalytic oxidation unit as circulating gas.

[0014] As a preferred embodiment, in step a), the HCl-containing reaction gas comes from the HCl reaction gas generated in a diphenylmethane diisocyanate production unit, a special isocyanate production unit, a hydrochloric acid analysis unit, a chloropropylene unit or a fluorine chemical production process. The HCl content in the raw gas after removing organic matter is substantially 100%, and the content of organic matter and other impurities is 0-10ppm.

[0015] Preferably, the oxygen-containing gas contains at least 95% O2 and 1% CO2. The composition of the oxygen-containing gas must ensure the oxygen concentration required for the catalytic oxidation reaction on the one hand, and on the other hand, provide the CO2 required for HCl purification. Of course, the content of CO2 in the oxygen-containing gas can also be appropriately adjusted according to the CO2 contained in the HCl-containing reaction gas. If the HCl-containing reaction gas itself contains a certain concentration of CO2, the CO2 content in the oxygen-containing gas can be reduced as appropriate.

[0016] As a preferred embodiment, in step a), the catalytic oxidation reaction is carried out in the presence of an oxidation catalyst, and the oxidation catalyst is preferably a copper-based catalyst and / or a ruthenium-based catalyst, which can be any copper- and / or ruthenium-containing catalyst known in the prior art that has HCl catalytic oxidation effect, such as the catalysts disclosed in patents CN102000583B, CN109718789B, CN107684927B, etc.

[0017] Preferably, the amount of the oxidation catalyst used is 45-700 L / (kg-cat) / h based on the space velocity of the reaction gas containing HCl.

[0018] As a preferred embodiment, in step a), the catalytic oxidation reaction temperature is 280-450°C, the reaction pressure is 0.2-0.5 MPaG, and the residence time is 0.1-15 min; preferably, the raw reaction gas is preheated to 80-200°C before the reaction.

[0019] Preferably, in the catalytic oxidation reaction of step a), the raw material ratio is 4-0.5:1 in terms of the molar ratio of HCl to oxygen.

[0020] In a preferred embodiment of the present invention, the chlorine-containing reaction gas A exiting the catalytic oxidation unit has a gas composition including, for example, O2 9-20%, N2 1-5%, CO2 2-8%, HCl 7-30%, Cl2 25-40%, and H2O 20-35%.

[0021] In the present invention, as a preferred embodiment, the catalytic oxidation unit adopts a reactor, which can be a fixed bed reactor, a fluidized bed reactor, a trickle bed reactor, etc.

[0022] As a preferred embodiment, in step a), the method for removing organic impurities is selected from any one or more combinations of cryogenic treatment, physical adsorption, chemical adsorption, and distillation removal, and those skilled in the art can make a conventional selection based on known methods and physical properties of impurities;

[0023] Preferably, the organic impurities are one or more of chlorobenzene, o-dichlorobenzene, benzene compounds, propylene, allyl chloride, and HF.

[0024] As a preferred embodiment, in step b), the quenching operation temperature is 30-80°C and the operation pressure is 0.1-0.45MPaG;

[0025] Preferably, the quenching process is adjusted so that the concentration of industrial hydrochloric acid is 25-31%;

[0026] Preferably, the chlorine-containing reaction gas B contains at least 30-65% chlorine and 3-12% CO2.

[0027] In a preferred embodiment of the present invention, the chlorine-containing reaction gas B exiting the quenching unit has a gas composition that includes, for example, O2 12-40%, N2 1-7%, CO2 3-12%, HCl 4-30%, Cl2 30-65%, wherein the water content is reduced to below 1%, more preferably to below 0.1%.

[0028] In the present invention, as a preferred embodiment, the quenching unit adopts a heat exchanger or a quenching tower or a spray tower, more preferably a spray tower, and obtains industrial hydrochloric acid and removes most of the water in the reaction gas by controlling the spraying temperature and pressure to obtain chlorine reaction gas B.

[0029] Preferably, the drying and dehydration of the chlorine-containing reaction gas B in step c) is carried out in a drying unit, and the equipment used may be a tower or a piled bed, and the desiccant may be a desiccant that does not react with HCl, such as concentrated sulfuric acid and alumina. After being treated in the drying unit, the water content is further reduced to below 10 ppm, more preferably to below 1 ppm.

[0030] As a preferred embodiment, in step c) the compression liquefaction unit, the reaction gas is compressed to 1.0-2.0 MPaG, and after gas-liquid separation, the gas is sent to the liquid chlorine refining unit.

[0031] In the present invention, as a preferred embodiment, the equipment used in the compression liquefaction unit is, for example, a conventional compressor.

[0032] As a preferred embodiment, the liquid chlorine refining unit in step c) adopts a plate tower or a packed tower, the operating pressure in the tower is 0.8-1.8MPaG, the operating temperature is -45°C to 70°C, the number of theoretical plates is 5-40, and the spray density is 0.1-40m 3 / m 2 , the pan-point rate is 15-80%.

[0033] In a preferred embodiment of the present invention, the mixed gas C obtained by the liquid chlorine refining unit contains the following composition: O2 40-70%, N2 1-7%, CO2 8-20%, HCl 10-35%, Cl2 0-10%.

[0034] As a preferred embodiment, the HCl purification unit in step d) adopts a plate tower or a packed tower, the operating pressure in the tower is 5.0-8.0 MPaG, the operating temperature is -100°C to 50°C, the number of theoretical plates is 10-60, and the spray density is 0.1-40m 3 / m 2 , the pan-point rate is 15-80%.

[0035] As a preferred embodiment, the chlorine-containing supercritical stream D contains at least HCl, chlorine and CO2; preferably, the composition of the chlorine-containing supercritical stream D is, for example: O2 0-10%, N2 0-5%, CO2 10-40%, HCl 40-70%, Cl2 0-20%.

[0036] The chlorine-free supercritical stream E contains at least CO2 and other optional O2 and N2; preferably, the composition of the chlorine-free supercritical stream E is, for example: O2 80-96%, N2 1-5%, CO2 1-15%.

[0037] In the present invention, as a preferred embodiment, the tail gas absorption unit uses a water washing device, which can be a tank, a packed tower, a spray tower, etc., and the reverse water washing preferably uses 8-32% sodium hydroxide solution.

[0038] The present invention utilizes CO2 (preferably introduced from air) contained in the hydrogen chloride oxidation reaction gas to separate unreacted hydrogen chloride and residual chlorine through a supercritical separation method, and can reuse the residual chlorine in the catalytic oxidation reaction under a small circulating gas volume, thereby reducing HCl loss and exhaust gas discharge on the one hand, and reducing equipment size and energy consumption on the other hand, which is conducive to increasing the operation cycle of the device. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 The figure is an overall process flow chart of the method of the present invention. DETAILED DESCRIPTION

[0040] The present invention is further described below by means of specific examples. The examples described in the present invention are only used to illustrate the present invention and do not limit the scope of the present invention.

[0041] Main raw material information:

[0042] Reaction gas 1: Composition: 99.9% HCl, 0.1% chlorobenzene, sourced from Wanhua Chemical's isocyanate unit;

[0043] Reaction gas 2: Composition: 99.9% HCl, 0.1% o-dichlorobenzene, sourced from Wanhua Chemical's isocyanate unit;

[0044] Reaction gas 3: Composition: 99% HCl, 1% propylene chloride, sourced from Wanhua Chemical's epichlorohydrin unit.

[0045] [Example 1]

[0046] The production system used includes:

[0047] Pretreatment unit: Use activated carbon to physically adsorb the reaction gas to remove organic impurities.

[0048] Catalytic oxidation unit: A fixed bed reactor is used and loaded with 20 t of copper-based catalyst (the copper-based catalyst is prepared by the method in Example 1 of patent CN102000583B).

[0049] Rapid cooling unit: using spray tower.

[0050] Drying unit: uses a pile bed containing aluminum oxide desiccant.

[0051] Compression liquefaction unit: using compressor.

[0052] Liquid chlorine refining unit: using packed tower.

[0053] HCl purification unit: using packed tower.

[0054] Tail gas absorption unit: A packed tower is used, and a 16% sodium hydroxide aqueous solution is used as the absorption alkali solution.

[0055] A method for hydrogen chloride oxidation using a supercritical separation method comprises the following steps:

[0056] Step a), the reaction gas 1 is allowed to enter the raw material processing unit at a flow rate of 980 kmol / h, and chlorobenzene is adsorbed and removed under the conditions of 40°C and 0.6 MPaG pressure. After adsorption by activated carbon, the chlorobenzene content in the HCl gas is reduced to below 1 ppm, and the gas is preheated to 200°C before entering the catalytic oxidation unit; at the same time, an oxygen-containing gas (containing 98% oxygen, 1.7% carbon dioxide, and 0.5% nitrogen) with a total flow rate of 275 kmol / h is preheated to 200°C before entering the catalytic oxidation unit, and is mixed with the reaction gas 1 to undergo a catalytic oxidation reaction to generate chlorine, thereby obtaining a chlorine-containing reaction gas A; in this step, the reaction temperature is 380°C, the reaction pressure is 0.5 MPaG, the residence time is 2 min, and the chlorine-containing reaction gas A at the reactor outlet is composed of O2 18%, N2 1.0%, CO2 4%, HCl15%, Cl2 32%, and H2O 30%.

[0057] Step b), sending the chlorine-containing reaction gas A to a quenching unit, performing quenching spraying at 30°C and 0.45MPaG, obtaining about 11t / h of 31% hydrochloric acid at the bottom of the tower, and obtaining 918kmol / h of chlorine-containing reaction gas B at the top of the tower, whose composition is O2 32%, N21%, CO2 6%, HCl 12%, Cl2 48.5%, and the water content is reduced to less than 0.1%.

[0058] Step c), the chlorine-containing reaction gas B enters the drying unit, is dried under the conditions of 30°C and 0.4MPaG, and the water content is reduced to below 1ppm; then enters the compression liquefaction unit, and is pressurized to 1.8MPaG before gas-liquid separation, wherein the gas phase enters the liquid chlorine refining unit at a flow rate of 918kmol / h, at an operating pressure of 1.6MPaG, an operating temperature of -45°C to 50°C, a theoretical plate number of 40, and a spray density of 40m 3 / m 2, liquid chlorine is refined under the condition of 75% flooding rate, 99.6% liquid chlorine is obtained in the bottom of the tower, and 484kmol / h mixed gas C is obtained at the top of the tower, whose composition is O2 58%, N2 2%, CO2 11%, HCl 24%, Cl2 5%.

[0059] Step d), the mixed gas C is sent to the HCl purification unit at an operating pressure of 5.2 MPaG, an operating temperature of -85°C to 10°C, a theoretical plate number of 45, and a spray density of 30m 3 / m 2 , under the condition of 80% flooding rate, CO2 is made into supercritical state, and supercritical extraction is used to separate to obtain 285kmol / h chlorine-containing supercritical stream D and 199kmol / h chlorine-free supercritical stream E; wherein, the composition of chlorine-containing supercritical stream D is O2 7%, N2 0.5%, CO2 23%, HCl 59.5%, Cl2 10%; the composition of chlorine-free supercritical stream E is O2 93%, N2 3%, CO2 4%.

[0060] Step e), all the chlorine-containing supercritical stream D is refluxed to the catalytic oxidation unit for circulation treatment; the chlorine-free supercritical stream E is sent to the tail gas absorption unit, and after absorbing CO2 with alkaline solution under the conditions of 40°C and 1.0MPaG, it is divided into two parts, of which stream E with a flow rate of 50kmol / h is directly discharged, and the total flow rate is 430kmol / h, which is circulated to the catalytic oxidation unit to ensure that the molar ratio of HCl to oxygen is 2, and a cycle is established.

[0061] [Example 2]

[0062] The hydrogenation of hydrogen chloride is carried out using a production system substantially the same as in Example 1, specifically comprising the following steps:

[0063] Step a), the reaction gas 2 enters the raw material processing unit at a flow rate of 980 kmol, adsorbs and removes o-dichlorobenzene under 40° C. and 0.6 MPaG pressure conditions, and the o-dichlorobenzene content in the HCl gas is reduced to below 1 ppm after adsorption by activated carbon, and enters the catalytic oxidation unit after preheating to 80° C.; at the same time, the oxygen-containing gas (containing 95.4% oxygen, 4.5% carbon dioxide, and 0.1% nitrogen) with a total flow rate of 275 kmol / h is preheated to 80° C. and enters the catalytic oxidation unit, and is mixed with the reaction gas 1 to undergo a catalytic oxidation reaction to generate chlorine, thereby obtaining a chlorine-containing reaction gas A; in this step, the reaction temperature is 300° C., the reaction pressure is 0.2 MPaG, the residence time is 12 min, and the chlorine-containing reaction gas A at the reactor outlet is composed of O2: 12%, N2: 0.4%, CO2: 10%, HCl: 15%, Cl2: 32%, and H2O: 30.6%.

[0064] Step b), sending the chlorine-containing reaction gas A into a quenching unit, performing quenching spraying at 80°C and 0.18MPaG, obtaining about 11t / h of 31% hydrochloric acid at the bottom of the tower, and obtaining 886kmol / h of chlorine-containing reaction gas B at the top of the tower, wherein the composition is O2: 19%, N2: 0.6%, CO2: 16%, HCl: 14%, Cl2: 50.4%, and the water content is reduced to below 0.5%.

[0065] Step c), the chlorine-containing reaction gas B enters the drying unit, is dried at 50°C and 0.15MPaG, and the water content is reduced to below 10ppm; then enters the compression liquefaction unit, and is pressurized to 1.0MPaG before gas-liquid separation, wherein the gas phase enters the liquid chlorine refining unit at a flow rate of 918kmol / h, at an operating pressure of 0.8MPaG, an operating temperature of -45°C to 30°C, a theoretical plate number of 15, and a spray density of 5m 3 / m 2 , liquid chlorine is refined under the condition of 30% flooding rate, 99.6% liquid chlorine is obtained in the bottom of the tower, and 445kmol / h mixed gas C is obtained at the top of the tower, whose composition is O2: 37%, N2: 1%, CO2: 32%, HCl: 27%, Cl2: 3%.

[0066] Step d), the mixed gas C is sent to the HCl purification unit, at an operating pressure of 8.2 MPaG, an operating temperature of -60°C to 50°C, a theoretical plate number of 20, a spray density of 10m 3 / m 2 , under the condition of 70% flooding rate, CO2 is made into supercritical state, and supercritical extraction is used to separate and obtain 263kmol / h chlorine-containing supercritical stream D and 182kmol / h chlorine-free supercritical stream E; wherein, the composition of chlorine-containing supercritical stream D is O2: 0.5%, N2: 0%, CO2: 51%, HCl: 44%, Cl2: 4.5%; the composition of chlorine-free supercritical stream E is O2: 90%, N2: 3%, CO2: 5%, HCl: 2%.

[0067] Step e), all the chlorine-containing supercritical stream D is refluxed to the catalytic oxidation unit for circulation treatment; the chlorine-free supercritical stream E is sent to the tail gas absorption unit, and after absorbing CO2 with alkaline solution under the conditions of 40°C and 1.0MPaG, it is divided into two parts, of which stream E with a flow rate of 58kmol / h is directly discharged, and the total flow rate of 378kmol / h is circulated to the catalytic oxidation unit to ensure that the molar ratio of HCl to oxygen is 2.8, and a cycle is established.

[0068] [Example 3]

[0069] The hydrogenation of hydrogen chloride is carried out using a production system substantially the same as in Example 1, specifically comprising the following steps:

[0070] Step a), the reaction gas 3 enters the raw material processing unit at a flow rate of 1000 kmol, and is deep-cooled to remove allyl chloride at -40°C and 0.5 MPaG pressure conditions, the allyl chloride content in the HCl gas is reduced to below 1 ppm, and the gas is preheated to 150°C before entering the catalytic oxidation unit; at the same time, an oxygen-containing gas (containing 98.5% oxygen, 1.2% carbon dioxide, and 0.3% nitrogen) with a total flow rate of 275 kmol / h is preheated to 150°C before entering the catalytic oxidation unit, and is mixed with the reaction gas 1 to undergo a catalytic oxidation reaction to generate chlorine, thereby obtaining a chlorine-containing reaction gas A; in this step, the reaction temperature is 350°C, the reaction pressure is 0.4 MPaG, the residence time is 6 min, and the chlorine-containing reaction gas A at the reactor outlet is composed of O2: 20%, N2: 2%, CO2: 4%, HCl: 15%, Cl2: 32%, and H2O: 30%.

[0071] Step b), sending the chlorine-containing reaction gas A into a quenching unit, performing quenching spraying at 50°C and 0.35MPaG, obtaining about 11t / h of 31% hydrochloric acid at the bottom of the tower, and obtaining 820kmol / h of chlorine-containing reaction gas B at the top of the tower, wherein the composition is O2: 34%, N2: 1%, CO2: 8%, HCl: 5%, Cl2: 52%, and the water content is reduced to below 0.3%.

[0072] Step c), the chlorine-containing reaction gas B enters the drying unit, is dried at 50°C and 0.32MPaG, and the water content is reduced to below 10ppm; then enters the compression liquefaction unit, and is pressurized to 1.5MPaG before gas-liquid separation, wherein the gas phase enters the liquid chlorine refining unit at a flow rate of 820kmol / h, at an operating pressure of 1.0MPaG, an operating temperature of -45°C to 40°C, a theoretical plate number of 25, and a spray density of 20m 3 / m 2 , liquid chlorine was refined under the condition of 40% flooding rate, 99.6% liquid chlorine was obtained in the bottom of the tower, and 394kmol / h of mixed gas C was obtained at the top of the tower, whose composition was O2: 37%, N2: 1%, CO2: 32%, HCl: 27%, Cl2: 3%.

[0073] Step d), the mixed gas C is sent to the HCl purification unit, at an operating pressure of 6.0 MPaG, an operating temperature of -60°C to 50°C, a theoretical plate number of 30, and a spray density of 20m 3 / m 2, under the condition of 40% flooding rate, CO2 is made into supercritical state, and supercritical extraction is used to separate and obtain 250kmol / h chlorine-containing supercritical stream D and 194kmol / h chlorine-free supercritical stream E; wherein, the composition of chlorine-containing supercritical stream D is O2: 0.5%, N2: 0%, CO2: 51%, HCl: 44%, Cl2: 4.5%; the composition of chlorine-free supercritical stream E is O2: 90%, N2: 3%, CO2: 5%, HCl: 2%.

[0074] Step e), all the chlorine-containing supercritical stream D is refluxed to the catalytic oxidation unit for circulation treatment; the chlorine-free supercritical stream E is sent to the tail gas absorption unit, and after absorbing CO2 with alkaline solution under the conditions of 40°C and 1.0MPaG, it is divided into two parts, of which stream E with a flow rate of 60kmol / h is directly discharged, and the total flow rate is 420kmol / h, which is circulated to the catalytic oxidation unit to ensure that the molar ratio of HCl to oxygen is 2, and a cycle is established.

[0075] [Comparative Example 1]

[0076] The HCl purification unit and the tail gas absorption unit are eliminated, and the rest of the production system is basically the same as that in Example 1 for hydrogenation of chloride, which specifically includes the following steps:

[0077] Step a), allowing the reaction gas 1 to enter the raw material processing unit at a flow rate of 980 kmol / h, adsorb and remove chlorobenzene under 40°C and 0.6 MPaG pressure conditions, and the chlorobenzene content in the HCl gas is reduced to below 1 ppm after adsorption by activated carbon, and enters the catalytic oxidation unit after preheating to 200°C; at the same time, an oxygen-containing gas (containing 98% oxygen, 1.7% carbon dioxide, and 0.5% nitrogen) with a total flow rate of 275 kmol / h is preheated to 200°C and enters the catalytic oxidation unit, mixed with the reaction gas 1 to undergo a catalytic oxidation reaction to generate chlorine, thereby obtaining a chlorine-containing reaction gas A; in this step, the reaction temperature is 380°C, the reaction pressure is 0.5 MPaG, the residence time is 2 min, and the chlorine-containing reaction gas A at the reactor outlet is composed of O2: 25%, N2: 0.7%, CO2: 4%, HCl: 14%, Cl2: 29.3%, and H2O: 27%.

[0078] Step b), sending the chlorine-containing reaction gas A into a quenching unit, performing quenching spraying at 30°C and 0.45MPaG, obtaining about 11t / h of 31% hydrochloric acid at the bottom of the tower, and obtaining 1070kmol / h of chlorine-containing reaction gas B at the top of the tower, wherein the composition is O2: 38%, N2: 1%, CO2: 5%, HCl: 12%, Cl2: 44%, and the water content is reduced to below 0.5%.

[0079] Step c), the chlorine-containing reaction gas B enters the drying unit, is dried under the conditions of 30°C and 0.4MPaG, and the water content is reduced to below 1ppm; then enters the compression liquefaction unit, and is pressurized to 1.8MPaG before gas-liquid separation, wherein the gas phase enters the liquid chlorine refining unit at a flow rate of 1070kmol / h, at an operating pressure of 1.6MPaG, an operating temperature of -45°C to 50°C, a theoretical plate number of 40, and a spray density of 40m 3 / m 2 , the liquid chlorine is refined under the condition of 75% flooding rate, 99.6% liquid chlorine is obtained in the tower bottom, and 610kmol / h mixed gas C is obtained at the top of the tower, and its composition is O2: 64%, N2: 2%, CO2: 9%, HCl: 20%, Cl2: 5%. The gas discharge rate is about 100kmol / h, and part of it is recycled back to the catalytic oxidation unit. In order to ensure that the ratio of HCl to oxygen is 2, the circulation rate is 520kmol / h.

[0080] In this implementation case, the amount of the circulating stream is 520 kmol / h, the amount of exhaust gas discharged is 100 kmol / h, and chlorine-containing substances account for 25%, resulting in a partial waste of chlorine.

[0081] The above is only a preferred embodiment of the present invention. It should be pointed out that ordinary technicians in this field can make several improvements and supplements without departing from the method of the present invention. These improvements and supplements should also be regarded as the scope of protection of the present invention.

Claims

1. A method for hydrogen chloride oxidation using supercritical separation, characterized in that: The following steps are involved: Step a), using the HCl-containing reaction gas from which organic impurities have been removed as a raw material, co-heating and mixing with an oxygen-containing gas in a catalytic oxidation unit, and performing a catalytic oxidation reaction to obtain a chlorine-containing reaction gas A; Step b), sending the chlorine-containing reaction gas A to a quenching unit, and recovering industrial hydrochloric acid and chlorine-containing reaction gas B through quenching; Step c), drying and removing water from the chlorine-containing reaction gas B and sending it to a compression and liquefaction unit, and then further sending it to a liquid chlorine refining unit after pressurization to collect liquid chlorine and mixed gas C; Step d), sending the mixed gas C into the HCl purification unit, increasing the pressure until CO2 enters the supercritical state, and using supercritical extraction to separate to obtain chlorine-containing supercritical stream D and chlorine-free supercritical stream E; Step e), returning the chlorine-containing supercritical stream D to the catalytic oxidation unit for circulation treatment; sending the chlorine-free supercritical stream E to the tail gas absorption unit to eliminate CO2 and then discharge it, or partially returning it to the catalytic oxidation unit as circulating gas; In step a), the HCl-containing reaction gas comes from the HCl reaction gas generated in a diphenylmethane diisocyanate production unit, a special isocyanate production unit, a hydrochloric acid analysis unit, a chloropropylene unit or a fluorine chemical production process.

2. The method for hydrogen chloride oxidation using supercritical separation according to claim 1, wherein: The oxygen-containing gas contains at least 95% O2 and 1% CO2.

3. The method for hydrogen chloride oxidation using supercritical separation according to claim 1, characterized in that: In step a), the catalytic oxidation reaction is carried out in the presence of an oxidation catalyst.

4. The method for hydrogen chloride oxidation using supercritical separation method according to claim 3, characterized in that: The oxidation catalyst is a copper-based catalyst and / or a ruthenium-based catalyst.

5. The method for hydrogen chloride oxidation using supercritical separation method according to claim 3, characterized in that: The amount of the oxidation catalyst used is 45-700 L / (kg-cat) / h based on the space velocity of the reaction gas containing HCl.

6. The method for hydrogen chloride oxidation using supercritical separation according to claim 3, characterized in that: In step a), the catalytic oxidation reaction temperature is 280-450° C., the reaction pressure is 0.2-0.5 MPaG, and the residence time is 0.1-15 min.

7. The method for hydrogen chloride oxidation using supercritical separation according to claim 6, characterized in that: In the step a) catalytic oxidation reaction, the raw material ratio is 4-0.5:1 in terms of the molar ratio of HCl to oxygen.

8. The method for hydrogen chloride oxidation using supercritical separation according to claim 6, characterized in that: In step a), the method for removing organic impurities is selected from any one or more combinations of cryogenic treatment, physical adsorption, chemical adsorption, and distillation removal.

9. The method for hydrogen chloride oxidation using supercritical separation according to claim 8, characterized in that: The organic impurities are one or more of chlorobenzene, o-dichlorobenzene, benzene compounds, propylene, allyl chloride, and HF.

10. The method for hydrogen chloride oxidation using supercritical separation method according to any one of claims 1 to 9, characterized in that: In step b), the quenching operation temperature is 30-80° C. and the operation pressure is 0.1-0.45 MPaG.

11. The method for hydrogen chloride oxidation using supercritical separation according to claim 10, characterized in that: The quenching process is adjusted so that the concentration of industrial hydrochloric acid is 25-31%.

12. The method for hydrogen chloride oxidation using supercritical separation according to claim 10, characterized in that: The chlorine-containing reaction gas B contains at least 30-65% chlorine and 3-12% CO2.

13. The method for hydrogen chloride oxidation using supercritical separation method according to any one of claims 1 to 9, characterized in that: Step c) In the compression liquefaction unit, the reaction gas is compressed to 1.0-2.0 MPaG, and after gas-liquid separation, the gas is sent to the liquid chlorine refining unit.

14. The method for hydrogen chloride oxidation using supercritical separation according to claim 13, characterized in that: In step c), the liquid chlorine refining unit adopts a plate tower or a packed tower, the operating pressure in the tower is 0.8-1.8MPaG, the operating temperature is -45°C to 70°C, the theoretical number of plates is 5-40, and the spray density is 0.1-40m 3 / m 2 , the pan-point rate is 15-80%.

15. The method for hydrogen chloride oxidation using supercritical separation method according to any one of claims 1 to 9, characterized in that: In the step d), the HCl purification unit adopts a plate tower or a packed tower, the operating pressure in the tower is 5.0-8.0 MPaG, the operating temperature is -100°C to 50°C, the number of theoretical plates is 10-60, and the spray density is 0.1-40m 3 / m 2 , the pan-point rate is 15-80%.

16. The method for hydrogen chloride oxidation using supercritical separation according to claim 15, characterized in that: The chlorine-containing supercritical stream D contains at least HCl, chlorine and CO2; the chlorine-free supercritical stream E contains at least CO2 and other optional O2 and N2.

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