Clean zero-emission HCFC-22 production method for byproduct HFC-23

Abstract

The invention provides an HCFC-22 production method with net zero emission of by-product HFC-23, a production process system integrates a conversion and utilization process system of the by-product HFC-23 in the HCFC-22 production process, the HCFC-22 production process is coupled with a conversion process of HFC-23 and CHCl3, the by-product HFC-23 generated in the HCFC-22 production process is directly converted into HCFC-22 and HCFC-21 in the system, and the HCFC-22 and CHCl3 are converted into HCFC-22 and CHCl3. Through further separation and purification and raw material index control, the HFC-23 conversion catalyst keeps good activity, selectivity and stability, HFC-23 generated in the HCFC-22 production process can be effectively converted, and zero emission of HFC-23 in a system is achieved. The method is simple in process, low in investment cost, low-carbon, environment-friendly, efficient in emission reduction and capable of realizing net zero emission of the byproduct HFC-23 of the HCFC-22 production system.

Description

Technical Field

[0001] The present invention relates to a method for producing HCFC-22 with net-zero emission of by-product HFC-23, and particularly to a method for efficiently recycling by-product HFC-23 in an HCFC-22 production system. Background Art

[0002] Chlorodifluoromethane CHClF2 (HCFC-22) is a main raw material for preparing plastic monomers such as tetrafluoroethylene (TFE) and hexafluoropropylene (HFP). Its consumption as a raw material for producing fluorohydrocarbons such as TFE accounts for more than 40% of the consumption of HCFC-22. During the production of HCFC-22, trifluoromethane CHF3 (HFC-23) is an inevitable by-product. According to different process flows, the production amount of HFC-23 is 2-5% of HCFC-22 [Journal of Fluorine Chemistry, 2012, 140:7-16]. The main reaction equations are as follows:

[0003] Main reaction: CHCl3 + 2HF → CHClF2 + 2HCl

[0004] Side reaction: CHClF2 + HCl → CHF3 + HCl

[0005] HFC-23 is a strong greenhouse gas with a global warming potential (GWP) as high as 14,800, and it is a greenhouse gas that is key-controlled for emissions in the Kigali Amendment. Therefore, achieving net-zero emission of by-product HFC-23 in the production of HCFC-22 and realizing energy conservation and emission reduction is a very important topic.

[0006] Currently in industry, the by-product HFC-23 generated during the production of HCFC-22 is generally treated by high-temperature plasma incineration. This method is simple and efficient, but the operation and equipment costs are relatively high. Therefore, the resource conversion of HFC-23 has always been a research hotspot.

[0007] US3009966 discloses that HFC-23 can be pyrolyzed at 700-1090 °C to prepare TFE and hexafluoropropylene (HFP). WO96 / 29296 and US Patent US2003 / 0166981 disclose methods for co-pyrolyzing with fluoroalkanes to prepare macromolecular fluoroalkanes. Chinese Patent CN104628514A reports a series of methods for co-pyrolyzing with CH4 to prepare vinylidene fluoride, etc. These technologies can convert the resource of by-product HFC-23 into some high-value-added products, but these technologies require very high reaction temperatures, have many by-products, the catalyst is prone to carbon deposition and deactivation, the products are numerous and complex and difficult to separate, and the industrialization is difficult.

[0008] The method disclosed in CN104628513 for converting HFC-23 and CHCl3 into HCFC-22 under the action of a catalyst directly reacts HFC-23 with CHCl3, the raw material for industrial production of HCFC-22. The product is also HCFC-22, and the reaction conditions are mild and the product composition is simple, but no specific production process is mentioned. CN103467239 introduces a process for preparing chlorodifluoromethane by pyrolysis of trifluoromethane. The pyrolysis reaction of trifluoromethane and methyl chloride produces a mixture containing trifluoromethane, methyl chloride, chlorodifluoromethane and chlorodifluoromethane. Chlorodifluoromethane is directly separated, and the separated dichlorofluoromethane reacts with hydrogen fluoride to produce chlorodifluoromethane. The trifluoromethane and methyl chloride in the mixture are separated and recovered and then continue to be used as the reaction mixture. However, the above solutions cannot be coupled with the existing HCFC-22 production process, and the separation process is relatively complex.

[0009] Currently, the production of HCFC-22 and the conversion process of HFC-23 are independent related reports. If the two processes are directly connected together, there are many devices, the separation is relatively complex, and the investment cost is high. More importantly, if the raw material indicators and the coupling process are not well controlled, it is difficult to achieve the connection of the two processes. Therefore, there is still no report on directly achieving net-zero emissions of by-product HFC-23 in the HCFC-22 production system. Coupling the process of efficiently converting HFC-23 into HCFC-22 in the existing industrial process of producing HCFC-22 from CHCl3 to achieve the resource recycling of by-product HFC-23 in the HCFC-22 production process can not only meet the net-zero emission requirements of low-carbon emission reduction, but also greatly simplify the HFC-23 conversion and separation process flow, save reaction equipment and investment, and achieve zero emission of by-product HFC-23 in the HCFC-22 system, which is a technical difficulty in this field. Summary of the Invention

[0010] The object of the present invention is to establish a method for producing HCFC-22 with net-zero emissions of by-product HFC-23, achieving a by-product rate of HFC-23 of 0 and zero emission of HFC-23 in the HCFC-22 production process system. The object of the present invention is achieved by the following technical solutions:

[0011] A method for producing HCFC-22 with net-zero emissions of by-product HFC-23, characterized in that it includes the following steps:

[0012] (1) CHCl3 and HF react in a liquid-phase fluorination reactor, and the reaction gas continuously enters a condenser for separation. The reaction gas includes products HCFC-22, HCFC-21, HFC-23, HCl, and partial raw materials HF, CHCl3, and catalyst vapor. The product gas is extracted; the condensate is refluxed to the reactor for continuous reaction. The product gas includes HCFC-22, HFC-23, HCl, and contains a small amount of intermediate HCFC-21 and HF; after the condenser, there is an HCl separation system. In the HCl separation system, the product gas is washed with water to remove HCl and HF. The preliminarily purified product gas is passed through a first rough separation tower to remove the heavy component HCFC-21, and then through a first rectification tower to separate the bottom product HCFC-22 and the top by-product HFC-23. The top by-product after preliminary separation by the first rectification tower is further separated by a second rectification tower to ensure that the purity of HFC-23 is ≥97%.

[0013] (2) The separated HFC-23 and raw material CHCl3 are preheated and mixed and then enter the reactor for an intermolecular fluorochlorination exchange reaction to produce products HCFC-22 and HCFC-21. The single-pass conversion rate of HFC-23 is ≥25% or more, the total selectivity of the main products HCFC-22 and HCFC-21 is ≥99.0%, and the by-product selectivity is ≤1.0%; after passing through the reactor, the unreacted raw materials HFC-23, CHCl3, and products HCFC-22, HCFC-21 are condensed by a condenser and then enter the second rough separation tower. The low-boiling HFC-23, HCFC-22, and a small amount of HCFC-21 enter the condenser from the top for condensation, and HCFC-21 is condensed and refluxed. The high-boiling CHCl3 and product HCFC-21 enter the crude product tank from the bottom of the second rough separation tower.

[0014] (3) In the HFC-23 conversion product, HCFC-21 and CHCl3 are not separated and are directly pumped to the liquid-phase fluorination reactor in the HCFC-22 production section for continuous fluorination reaction to produce product HCFC-22; the HFC-23 and HCFC-22 at the top of the second rough separation tower in the HFC-23 conversion section and the HFC-23 and HCFC-22 at the top of the first rough separation tower in the HCFC-22 production section all enter the first rectification tower. The bottom HCFC-22 enters the product tank, and the top HFC-23 contains a small amount of HCFC-22 and continues to enter the second rectification tower for refined separation, with the purity reaching more than 97%. The bottom HCFC-22 and HFC-23 enter the first rectification tower for cyclic separation.

[0015] The specific reaction equations are as follows:

[0016] CHCl3 + 2HF → CHClF2 + 2HCl

[0017] CHClF2 + HF → CHF3 + HCl

[0018] CHF3 + CHCl3 → CHClF2 + CHCl2F

[0019] CHCl2F + HF → CHClF2 + HCl

[0020] As described above, in the present invention, during the fluorination of CHCl3 to produce HCFC-22, by-product HFC-23 is generated. After purification, it reacts with the raw material CHCl3 for producing HCFC-22 under the action of a catalyst through a fluorochloride exchange reaction to obtain the product HCFC-22 and HCFC-21, and HCFC-21 is further fluorinated to be converted into HCFC-22. The raw materials for the conversion of HFC-23 and the produced products are exactly the same as those in the HCFC-22 production device. The process is simple, suitable for coupling with the HCFC-22 production process, with a relatively low investment cost. The entire process achieves zero emission of HFC-23. The specific process is as follows:

[0021] (1) CHCl3 and HF carry out a liquid-phase fluorination reaction in a reaction kettle. The gaseous products of the reaction, HCFC-22, HCFC-21, HFC-23, and HCl, together with some raw material HF, CHCl3, and catalyst vapor continuously enter a condenser for separation. After condensation and reflux, most of the high-boiling-point vapors (HF, CHCl3, HCFC-21) and all the catalyst become liquids and reflux to the reactor to continue the reaction. The uncondensed mixed gas is the product gas (HCFC-22, HFC-23, HCl) and a small amount of intermediate HCFC-21 and HF. This mixed gas is washed with water in the HCl separation system to remove HCl and HF. After preliminary separation, the crude product mixture (HCFC-22, HCFC-21, HFC-23) is sent to a first rough separation tower to remove the heavy component HCFC-21, and then separated by a first rectification tower to obtain HCFC-22 (at the bottom of the tower) and by-product HFC-23 (at the top of the tower). The refined HCFC-22 can be directly packaged. The initially separated by-product HFC-23 contains a small amount of HCFC-22, and HCFC-22 is further separated by a second rectification tower to ensure that the purity of HFC-23 is ≥97%;

[0022] (2) The separated HFC-23 and raw material CHCl3 are preheated and mixed, then enter a shell-and-tube reactor for fluoro-chloro exchange reaction to produce the products HCFC-22 and HCFC-21. The single-pass conversion rate of HFC-23 is ≥25%. The total selectivity of the main products HCFC-22 and HCFC-21 is ≥99.0%, and the by-product selectivity is ≤1.0%. After passing through the reactor, the unreacted raw materials HFC-23, CHCl3 and the products HCFC-22, HCFC-21 are condensed by a condenser, and then enter the second rough separation column. The low-boiling HFC-23, HCFC-22 and a small amount of HCFC-21 enter the condenser from the top of the column for condensation. HCFC-21 is condensed and refluxed. The high-boiling CHCl3 and the product HCFC-21 enter the crude product tank from the bottom of the rough separation column;

[0023] (3) Without separation, the HCFC-21 and CHCl3 in the above-mentioned HFC-23 conversion products are directly pumped to the liquid-phase fluorination reactor for producing HCFC-22 to continue the reaction to produce the product HCFC-22. The HFC-23 and HCFC-22 at the top of the second rough separation column of the HFC-23 conversion products are combined with the HFC-23 and HCFC-22 at the top of the first rough separation column of the HCFC-22 production products and enter the first distillation column together. The HCFC-22 at the bottom of the column enters the product tank. The HFC-23 at the top of the column contains a small amount of HCFC-22 and continues to enter the second distillation column for refining separation. The purity reaches more than 97%. The HCFC-22 and HFC-23 at the bottom of the column enter the first distillation column for cyclic separation.

[0024] Among them, in step (1), the HCFC-22 is prepared by the fluoro-chloro exchange reaction of CHCl3 and anhydrous AHF. The catalyst is antimony fluorochloride SbCl 5- xFx (x = 1 - 5), and SbCl4F has the highest activity. Introducing an appropriate amount of chlorine into the reaction system helps to improve the reaction activity of the catalyst. In the method provided by the present invention, in the reaction stage, the reaction temperature only needs to satisfy that the reaction proceeds smoothly.

[0025] It is found that HCFC-22 and HCFC-21 are prone to disproportionation reaction under the action of the catalyst. The specific reaction formulas are as follows:

[0026] 3CHClF2 → 2CHF3 + CHCl3

[0027] 2CHClF2 → CHF3 + CHFCl2

[0028] 2CHCl2F → CHCl3 + CHClF2

[0029] In step (2), a small amount of HCFC-22 is entrained in the by-product HFC-23 after preliminary separation. Further refining of HFC-23 will increase production costs and energy consumption. Since the fluorine-chlorine exchange reaction between HFC-23 and CHCl3 is an equilibrium reaction and the product contains HCFC-22, too high a content of HCFC-22 in HFC-23 is not conducive to the conversion of HFC-23. To ensure the efficient conversion of HFC-23, the content of HCFC-22 in HFC-23 is preferably controlled within the range of 0 to 1.5%.

[0030] When the raw material HFC-23 contains more than 1.5% of HCFC-22, HCFC-22 will compete with HFC-23 and CHCl3 for adsorption, and is more likely to occupy some of the active sites on the catalyst surface, which is not conducive to the fluorine-chlorine exchange reaction of the by-product HFC-23. At the same time, the disproportionation reaction of HCFC-22 to generate HCFC-21 and HFC-23 will shift the fluorine-chlorine exchange reaction equilibrium of HFC-23 and CHCl3 to the left, further resulting in a decrease in the conversion rate of HFC-23. At the same time, this side reaction will accelerate the coking and deactivation of the catalyst, resulting in a decrease in the catalyst life. When the content of HCFC-22 in HFC-23 is controlled within the range of 0 to 1.5%, the conversion rate of HFC-23 can reach more than 25%. When the input cost in the process related to the conversion of HFC-23 is relatively low, the HFC-23 generated in the production process of HCFC-22 can be effectively converted, realizing zero emission of HFC-23 in the system. When the conversion rate of HFC-23 tends to decrease and the production of HFC-23 gradually exceeds the conversion amount of HFC-23, the by-product rate of HFC-23 in the HCFC-22 production system will tend to increase. The catalyst maintains good activity and stability, and can maintain the conversion rate of HFC-23 ≥ 25% within a longer life cycle, realizing a long-term by-product rate of 0. By adjusting the distillation conditions of the second distillation column, the content of HCFC-22 can be effectively controlled.

[0031] In the post-system of HCFC-22 production, due to reasons such as dissolved air in the water and alkali washing, a small amount of air will be entrained in HFC-23 during the water and alkali washing process of the crude product. A relatively high air content will cause CHCl3 to decompose to generate phosgene (COCl2), etc., and will promote the formation of by-products such as CFC-12, which will affect the product quality of HCFC-22, and further increase the cost of input by increasing the separation of by-product CFC-12 in the distillation column. The air content entrained in HFC-23 needs to be controlled within the range of 0 to 1.5%, and the total selectivity of HCFC-22 and HCFC-21 can reach more than 99.0%. Further preferably, the air content is controlled within the range of 0.5 to 1.0%. By intermittently discharging air from the top of the second distillation column and collecting HFC-23 in the upper tower body, the air content can be effectively controlled.

[0032] When the raw material CHCl3 contains more than 500 ppm of water, the water will occupy some of the Lewis acid active sites to form Bronsted acid, which will inhibit the adsorption and reaction of HFC-23 and CHCl3 on the Lewis acid active sites of the catalyst, resulting in a decrease in the conversion rate of HFC-23. In the by-product HFC-23 conversion section, the water content in CHCl3 needs to be controlled within the range of 0 - 500 ppm. Further preferably, it is controlled within the range of 30 - 300 ppm.

[0033] In step (2), the catalyst for the fluorine-chlorine exchange reaction is composed of two or more components selected from chromium oxide, chromium fluoride, partially fluorinated chromium oxide, aluminum oxide, aluminum fluoride, partially fluorinated aluminum oxide, iron oxide, iron fluoride, partially fluorinated iron oxide, magnesium oxide, magnesium fluoride, partially fluorinated magnesium oxide, chromium sulfate, aluminum sulfate, chromium phosphate, and aluminum sulfate. The catalyst promoter is selected from two or more metal oxides or chlorides of Ni, Co, Zn, Cu, In, or Mn.

[0034] Among them, the total mass content of the catalyst promoter is 0.5 - 5% of the total amount of the catalyst. When using an oxide promoter, the required catalyst is prepared by molding through mechanical mixing. When using a chloride promoter, the required catalyst is prepared by molding through impregnation.

[0035] In step (2), the vaporization temperature of the CHCl3 is 90 - 150 °C, and the preheating and mixing temperature of HFC-23 and CHCl3 is 250 - 360 °C.

[0036] For the method provided by the present invention, in the reaction stage, the reaction temperature and pressure only need to meet the requirement for the smooth progress of the reaction.

[0037] Preferably, the reaction temperature of the fluorine-chlorine exchange reaction in step (2) is 250 - 400 °C. Further preferably, the reaction temperature is 300 - 360 °C.

[0038] Preferably, the reaction pressure of the fluorine-chlorine exchange reaction in step (2) is 0 - 1 MPa. Further preferably, the reaction pressure is 0.2 - 0.8 MPa.

[0039] For the method provided by the present invention, in the reaction stage, the residence time only needs to meet the requirement for the smooth progress of the reaction.

[0040] Preferably, the reaction residence time of the fluorine-chlorine exchange reaction in step (2) is 0.5 - 100 s. Further preferably, the residence time is 4 - 50 s.

[0041] For the method provided by the present invention, in the fluorine-chlorine exchange reaction of step (2), the ratio between the raw materials HFC-23 and CHCl3 only needs to meet the requirement for the smooth progress of the reaction.

[0042] Preferably, the molar ratio of HFC-23 to CHCl3 is 1:1 to 3. More preferably, the molar ratio of HFC-23 to CHCl3 is 1:1.2 to 2.2.

[0043] In step (3), to ensure that the content of HFC-23 exceeds 97%, the top temperature, bottom temperature and pressure of the distillation column need to meet certain conditions.

[0044] The top temperature of the first distillation column is 5 to 30 °C, more preferably 10 °C to 25 °C.

[0045] The bottom temperature of the first distillation column is 20 to 60 °C, more preferably 30 °C to 50 °C.

[0046] The pressure of the first distillation column is 0.8 to 2.2 MPa, more preferably 1.0 to 2.0 MPa.

[0047] The top temperature of the second distillation column is -30 to -10 °C, more preferably -25 °C to -15 °C.

[0048] The bottom temperature of the second distillation column is 0 to 30 °C, more preferably 5 °C to 25 °C.

[0049] The pressure of the second distillation column is 0.5 to 2 MPa, more preferably 0.8 to 1.7 MPa.

[0050] In the present invention, the by-product HFC-23 generated in the process of fluorinating CHCl3 to produce HCFC-22 is separated, subjected to fluorine-chlorine exchange and recycled. The product HCFC-22 is prepared. The purified HFC-23 and the raw material CHCl3 for producing HCFC-22 react under the action of a catalyst through a fluorine-chlorine exchange reaction to produce the products HCFC-22 and HCFC-21, and HCFC-21 is further fluorinated and converted into HCFC-22. The raw materials for the conversion of HFC-23 and the products produced are exactly the same as those in the HCFC-22 production device. The process is simple and suitable for coupling with the HCFC-22 production process.

[0051] The beneficial effects of the present invention:

[0052] 1. The present invention is a system that integrates the process for the conversion and utilization of the by-product HFC-23 during the production of HCFC-22, which ingeniously solves the problem of the treatment of the by-product HFC-23 in the original HCFC-22 production process, meets the requirements of low-carbon emission reduction, and improves the production efficiency of HCFC-22.

[0053] 2. The present invention couples the resource conversion process of HFC-23 and CHCl3 in the HCFC-22 production process. Since the raw material CHCl3 is the same as the product HCFC-22, the whole process is simple, with low construction cost and high feasibility.

[0054] 3. After the conversion products of HFC-23 and CHCl3 are roughly separated, the unreacted HFC-23 at the top of the tower and the product HCFC-22 directly enter the HCFC-22 rectification and recovery system for separation and purification. The purified HFC-23 continues to circulate and react for conversion. The unreacted CHCl3 and the intermediate HCFC-21 coming out from the bottom of the rough separation tower are directly refluxed to the HCFC-22 liquid-phase fluorination reactor to continue the reaction to produce HCFC-22. The whole process is cyclically coupled, rather than a simple superposition of two process systems, which simplifies the process systems such as separation, purification and collection, and further greatly reduces the investment cost of the device.

[0055] 4. Under the condition of controlling the separation cost, by simultaneously controlling the content of HCFC-22, air content and water content of CHCl3 in HFC-23, it is beneficial for the HFC-23 conversion catalyst to maintain good activity, selectivity and stability, and achieve zero emission of by-product HFC-23.

[0056] In summary, this method has a simple process, low investment cost, low carbon and environmental protection, high emission reduction efficiency, and can achieve net zero emission of by-product HFC-23 in the HCFC-22 production system. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] Figure 1 It is a schematic diagram of the HCFC-22 production process flow for the net zero emission of by-product HFC-23 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0058] The present invention will be further described below in conjunction with specific embodiments, but the present invention is not limited to these specific embodiments. Those skilled in the art should recognize that the present invention covers all alternative solutions, improvement solutions and equivalent solutions that may be included within the scope of the claims.

[0059] Example 1

[0060] In this example, a system for converting and utilizing by-product HFC-23 is integrated in the HCFC-22 production process. The HCFC-22 production process is coupled with the HFC-23 conversion process to form a HCFC-22 production process system with a net zero emission of high GWP by-products. The specific operations are as follows:

[0061] (1) The raw materials CHCl3 and HF enter the liquid-phase fluorination reactor, and in SbCl 5-The fluorochloride exchange reaction occurs under the action of the xFx catalyst, where the reaction temperature is 70 °C and the pressure is 5 atm. The gaseous products of the reaction, HCFC-22, HCFC-21, HFC-23, and HCl, after condensation, most of the high-boiling-point vapors (HF, CHCl3, HCFC-21) and the catalyst become liquid and flow back to the reactor to continue the reaction. The uncondensed mixed gas is the product gas (HCFC-22, HFC-23, HCl) and a small amount of low-boiling-point intermediate HCFC-21 and HF. This mixed gas is washed with water in the HCl separation system to remove HCl and HF. After the preliminary separation, the crude product mixture (HCFC-22, HCFC-21, HFC-23) is stripped of the heavy component HCFC-21 in the first crude fractionation column, and then separated in the first rectification column to obtain HCFC-22 (bottom of the column) and the by-product HFC-23 (top of the column). The refined HCFC-22 is collected using a storage tank, and the HFC-23 and CHCl3 after rectification separation further react. The content of HCFC-22 in HFC-23 is 0.2%, the entrained air content is 1%, and the water content in CHCl3 is 120 ppm.

[0062] (2) After the raw material CHCl3 is vaporized in the vaporizer at a temperature of 120 °C, purified HFC-23 for HCFC-22 production enters the vaporizer and the preheater together. The preheating temperature is 300 °C, and then it enters the reactor, where a fluorochloride exchange reaction occurs under the action of a 1% NiO / AlF3-Cr2(SO4)3 catalyst to produce the product HCFC-22 and the intermediate HCFC-21. Among them, the reaction temperature is 320 °C, the pressure is 0.4 MPa, the residence time is 9 s, and HFC-23:CHCl3 = 1:2.2.

[0063] (3) After the reaction of HFC-23 and CHCl3, the unreacted raw materials HFC-23, CHCl3 and the products HCFCF-22, HCFC-21 are condensed by a condenser and then enter the second rough separation tower for separation. The high-boiling CHCl3 and HCFC-21 enter the rough product tank from the bottom of the second rough separation tower for collection and are pumped to the liquid-phase fluorination reactor for the production of HCFC-22 to continue the fluorination reaction to produce HCFC-22. After the low-boiling HFC-23, HCFC-22 and a small amount of HCFC-21 are separated by the first rough separation tower to remove the heavy component HCFC-21, HFC-23, HCFC-22 and other low-boiling substances enter the first rectification and recovery system of HCFC-22 and are mixed with the gas after the reaction in the production of HCFC-22. After washing with water, drying, separation, purification, the product HCFC-22 at the bottom of the rectification tower is transported to the product tank for storage. The low-boiling HFC-23 at the top of the tower is refined so that the HCFC-22 content is 0.2% and then recycled to the HFC-23 conversion reactor to continue the reaction with CHCl3 to produce the product HCFC-22 and the intermediate HCFC-21, and continue the above cycle.

[0064] The HFC-23 conversion catalyst remains stable after a single-pass reaction for 4500 h. The average conversion rate of HFC-23 is 26.5%, the total selectivity of HCFC-22 and HCFC-21 is 99.2%, and the selectivity of other by-products such as CFC-12 is 0.8%. All the by-product HFC-23 generated during the production of HCFC-22 can be effectively converted in the HFC-23 reactor, and the HFC-23 by-product rate of the HCFC-22 system is 0.

[0065] Comparative Example 1

[0066] The operation of this example is the same as that of Example 1. The main difference is that the separated by-product HFC-23 does not enter the HFC-23 conversion reactor, and the HFC-23 by-product rate of the HCFC-22 production system is 2.5%.

[0067] Comparative Example 2

[0068] The operation of this example is the same as that of Example 1. The main difference is that the HCFC-22 content in the raw material HFC-23 used in the HFC-23 conversion reaction is 2.2%. The HFC-23 by-product rate in the whole process system production is 0.3%. Among them, the single-pass conversion rate of HFC-23 in the HFC-23 conversion reaction is 22.6%, and the total selectivity of HCFC-22 and HCFC-21 is 98.1%.

[0069] Comparative Example 3

[0070] The operation of this example is the same as that of Example 1. The main difference is that the content of HCFC-22 in the raw material HFC-23 used in the HFC-23 conversion reaction is 4.0%. The by-product rate of HFC-23 in the production of the whole process system is 0.7%. Among them, the single-pass conversion rate of HFC-23 in the HFC-23 conversion reaction is 18.3%, and the total selectivity of HCFC-22 and HCFC-21 is 97.2%.

[0071] Comparative Example 4

[0072] The operation of this example is the same as that of Example 1. The main difference is that the air content in the raw material HFC-23 used in the HFC-23 conversion reaction is 2.5%. The by-product rate of HFC-23 in the production of the whole process system is less than 0.1%. Among them, the conversion rate of HFC-23 in the HFC-23 conversion reaction is 25.9%, the total selectivity of HCFC-22 and HCFC-21 in the single-pass reaction is 95.1%, and the by-product selectivity is 4.9%.

[0073] Comparative Example 5

[0074] The operation of this example is the same as that of Example 1. The main difference is that the water content in the raw material CHCl3 used in the HFC-23 conversion reaction is 550 ppm. The by-product rate of HFC-23 in the production of the whole process system is 0.5%. Among them, the conversion rate of HFC-23 in the HFC-23 conversion reaction is 19.8%, the total selectivity of HCFC-22 and HCFC-21 in the single-pass reaction is 98.9%, and the by-product selectivity is 1.1%.

Claims

1. A production method of HCFC-22 with net-zero emission of by-product HFC-23, characterized in that: It includes the following steps: (1) CHCl3 and HF react in a liquid-phase fluorination reactor, and the reaction gas continuously enters a condenser for separation. The reaction gas includes products HCFC-22, HCFC-21, HFC-23, HCl, and partial raw materials HF, CHCl3, and catalyst vapor. The product gas is extracted, and the condensate is refluxed to the reactor for continuous reaction. The product gas includes HCFC-22, HFC-23, and HCl, and contains a small amount of intermediate HCFC-21 and raw material HF. A HCl separation system is connected after the condenser. In the HCl separation system, the product gas is washed with water to remove HCl and HF. The preliminarily purified product gas is sent to a first rough separation tower to remove the heavy component HCFC-21, and then separated by a first rectification tower to obtain the bottom product HCFC-22 and the top by-product HFC-23. The top by-product after preliminary separation by the first rectification tower is further separated by a second rectification tower to ensure that the purity of HFC-23 is ≥97%, and the air content is controlled at the top of the second rectification tower; (2) The separated HFC-23 and raw material CHCl3 are preheated and mixed and then enter the reactor for an intermolecular fluorine-chlorine exchange reaction. After passing through the reactor, the unreacted raw materials HFC-23, CHCl3, and products HCFC-22, HCFC-21 enter a second rough separation tower after condensation. The low-boiling HFC-23, HCFC-22, and a small amount of HCFC-21 enter the condenser for condensation from the top of the tower, and HCFC-21 is refluxed after condensation. The high-boiling CHCl3 and product HCFC-21 enter the crude product tank from the bottom of the second rough separation tower; (3) HCFC-21 and CHCl3 in the HFC-23 conversion product are directly pumped to the liquid-phase fluorination reactor for producing HCFC-22 without separation to produce the product HCFC-22. HFC-23 and HCFC-22 at the top of the second rough separation tower of the HFC-23 conversion product and HFC-23 and HCFC-22 at the top of the first rough separation tower of the HCFC-22 production product all enter the first rectification tower. The bottom HCFC-22 enters the product tank, and the top HFC-23 contains a small amount of HCFC-22 and continues to enter the second rectification tower for refined separation with a purity of over 97%. The bottom HCFC-22 and HFC-23 enter the first rectification tower for cyclic separation.

2. The production method of HCFC-22 with by-product HFC-23 achieving net-zero emissions as claimed in claim 1, wherein: After further separating HCFC-22 by the second rectification tower, the HCFC-22 content is controlled within the range of 0 - 1.5%.

3. The production method of HCFC-22 with by-product HFC-23 achieving net-zero emissions as claimed in claim 1, wherein: After further separating HCFC-22 by the second rectification tower, the air content entrained in HFC-23 needs to be controlled within the range of 0 - 1.5%.

4. The production method of HCFC-22 with by-product HFC-23 achieving net-zero emissions as claimed in claim 1, wherein: The water content in the raw material CHCl3 added in the by-product HFC-23 conversion reaction needs to be controlled within the range of 0 - 500 ppm.

5. The production method of HCFC-22 with by-product HFC-23 achieving net-zero emissions according to claim 1, characterized in that: In step (2), the catalyst for the fluorine-chlorine exchange reaction is composed of two or more components selected from chromium oxide, chromium fluoride, partially fluorinated chromium oxide, aluminum oxide, aluminum fluoride, partially fluorinated aluminum oxide, iron oxide, iron fluoride, partially fluorinated iron oxide, magnesium oxide, magnesium fluoride, partially fluorinated magnesium oxide, chromium sulfate, aluminum sulfate, chromium phosphate, and aluminum sulfate. The catalyst promoter is selected from two or more metal oxides or chlorides of Ni, Co, Zn, Cu, In, or Mn.

6. The production method of HCFC-22 with by-product HFC-23 achieving net-zero emissions as claimed in claim 5, wherein: In step (2), the total mass content of the catalyst promoter is 0.5-5% of the total amount of the catalyst. When using an oxide promoter, the required catalyst is formed by mechanical mixing. When using a chloride promoter, the required catalyst is formed by impregnation.

7. The production method of HCFC-22 with by-product HFC-23 achieving net-zero emissions as claimed in claim 1, wherein: In step (2), the preheating and mixing temperature of HFC-23 and CHCl3 is 250-360°C.

8. The production method of HCFC-22 with by-product HFC-23 achieving net-zero emissions as claimed in claim 1, wherein: The reaction temperature of the fluorine-chlorine exchange reaction in step (2) is 250-400°C; The reaction pressure of the fluorine-chlorine exchange reaction in step (2) is 0-1 MPa; preferably, the reaction pressure is 0.2-0.8 MPa.

9. The production method of HCFC-22 with by-product HFC-23 achieving net-zero emissions as claimed in claim 1, wherein: The reaction residence time of the fluorine-chlorine exchange reaction in step (2) is 0.5-100 s; preferably, the residence time is 4-50 s.

10. A method for producing HCFC-22 with by-product HFC-23 achieving net-zero emissions, as described in claim 1, wherein: The molar ratio of the raw materials HFC-23 and CHCl3 in the fluorine-chlorine exchange reaction in step (2) is 1:1-3; preferably, the molar ratio of HFC-23 and CHCl3 is 1:1.2-2.

2.

11. A method for producing HCFC-22 with net-zero emission of by-product HFC-23 according to claim 1, characterized in that: The temperature at the top of the first distillation column is 5-30°C, and more preferably 10°C-25°C; The temperature at the bottom of the first distillation column is 20-60°C, and more preferably 30°C-50°C; The pressure of the first distillation column is 0.8-2.2 MPa, and more preferably 1.0-2.0 MPa; The temperature at the top of the second distillation column is -30 to -10°C, and more preferably -25°C to -15°C; The temperature at the bottom of the second distillation column is 0-30°C, and more preferably 5°C-25°C; The pressure of the second distillation column is 0.5-2 MPa, and more preferably 0.8-1.7 MPa.

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