Method for co-producing HFO-1234ze and HFO-1336mzz through dehydrogenation-fluorination of R152a

Abstract

The invention provides a method for co-production of HFO-1234ze and HFO-1336mzz through dehydrogenation and fluorination of R152a (R152a). The method comprises the following steps: carrying out adsorption pretreatment on R152a (the purity is greater than or equal to 99.5%), and carrying out dehydrogenation in the presence of a CrO / AlO catalyst to generate HFO-1132a; the product is shunted according to the volume ratio of 40-60%, and HFO-1234ze (at the temperature of 300-400 DEG C and the pressure of 0.2-0.4 MPa) is prepared through SnCl / activated carbon catalytic fluorination, and HFO-1336mz (at the temperature of 250-350 DEG C and the pressure of 0.15-0.35 MPa) is prepared through ZnCl / gamma-AlO catalytic dimerization; and finally, carrying out water washing, alkali washing and rectification purification to obtain a product with the purity of more than or equal to 99.0%. The method is high in integration level and low in energy consumption, the total yield reaches 65-70%, and the problems of redundancy and low yield of traditional process equipment are solved.

Description

Technical Field

[0001] This invention belongs to the field of organofluorine chemical technology, specifically relating to a process for preparing 2,3,3,3-tetrafluoropropylene (HFO-1234ze) and 1,1,1,4,4,4-hexafluoro-2-butene (HFO-1336mzz) from 1,1-difluoroethane (R152a) via a dehydrogenation-fluorination combined reaction. Background Technology

[0002] With increasingly stringent global environmental protection requirements, the Montreal Protocol and its amendments have continuously strengthened restrictions on ozone-depleting substances (ODS), while the Paris Agreement has also promoted global efforts to control greenhouse gas emissions. The refrigeration and air conditioning industry, as a major application area for fluorochemical products, is urgently seeking new-generation low global warming potential (GWP) refrigerants to replace traditional high-GWP refrigerants, such as the widely used R134a (GWP=1300).

[0003] Hydrofluoroolefins (HFOs) have become a promising area of ​​research and development for refrigerant alternatives due to their excellent environmental performance (typically GWP values ​​less than 10, ODP=0), good thermodynamic properties, and safety. Among them, HFO-1234ze (2,3,3,3-tetrafluoropropylene) and HFO-1336mzz (1,1,1,4,4,4-hexafluoro-2-butene) are two highly promising HFO products. HFO-1234ze, with its low GWP value (approximately 6), good thermal stability, and cycle performance, is considered an ideal replacement for R134a and is widely used in heat pumps, refrigerators, and blowing agents. HFO-1336mzz also exhibits extremely low GWP values ​​and good non-flammability, showing broad prospects in medium- and low-temperature refrigeration and organic Rankine cycles (ORC).

[0004] Current processes for preparing HFO-type refrigerants face several challenges. Firstly, most processes focus solely on the preparation of a single HFO product. For instance, HFO-1234ze is often prepared from HFC-245fa or HFC-245eb via hydrogen defluorination, while HFO-1336mzz is typically prepared from HFO-1132a or HFC-134a via dimerization or similar reactions. This single-product approach results in poor production flexibility, hindering efficient adjustments to the product structure based on market demand changes. Furthermore, each unit can only serve one product, limiting equipment utilization and return on investment.

[0005] On the other hand, traditional preparation methods are often cumbersome, involving multiple independent reaction units and separation and purification systems. For example, the separate preparation of HFO-1234ze and HFO-1336mzz requires two independent sets of raw material pretreatment, reaction, separation, and purification equipment. This not only results in high equipment investment costs but also inefficient material transfer and energy utilization between units, leading to high overall production costs. Furthermore, the complex process increases operational difficulty and the risk of failure, hindering large-scale, stable industrial production.

[0006] Therefore, developing a process technology that can efficiently co-produce multiple high-value-added HFO products (such as HFO-1234ze and HFO-1336mzz) from a single raw material in a single production line is of great practical significance and economic value for simplifying processes, reducing energy consumption, improving raw material utilization, enhancing production flexibility, and increasing market competitiveness. This invention is proposed based on this need. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of existing technologies, such as simple preparation processes for HFO refrigerants, large equipment investment, high energy consumption, and low raw material utilization. This invention provides a method for the efficient co-production of HFO-1234ze and HFO-1336mzz using R152a as a single raw material through a dehydrogenation-fluorination-dimerization reaction.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: A method for the dehydrogenation-fluorination co-production of HFO-1234ze and HFO-1336mzz using R152a includes the following steps: a) Raw material pretreatment: The R152a (1,1-difluoroethane) raw material undergoes adsorption pretreatment to achieve a purity of over 99.5%. Specifically, the R152a raw material is passed into a fixed-bed adsorption tower containing adsorbent (such as 5A molecular sieve or other high-efficiency desiccant and adsorbent), with the gas flow rate controlled at 0.5-1.0 m³ / h and the adsorption temperature at 20-30℃. This removes trace amounts of moisture (target residue <50 ppm), oxygen (target residue <100 ppm), and other trace organic impurities that may be present in the raw material, ensuring the smooth progress of the subsequent catalytic reaction and extending the catalyst's lifespan.

[0009] b) Dehydrogenation reaction: Pretreated high-purity R152a is introduced into a dehydrogenation reactor and undergoes a dehydrogenation reaction with a dehydrogenation catalyst under specific temperature and pressure conditions, mainly producing HFO-1132a (CH2=CHF, 1,1-difluoroethylene). The dehydrogenation reactor is a tubular reactor. The reaction conditions are: temperature 550-650℃, pressure 0.1-0.3MPa. The dehydrogenation catalyst is Cr2O3 / Al2O3, with Cr2O3 loading at 10-15wt%. In the dehydrogenation reaction, the flow rate of R152a is 0.5-1.0 m³ / h, and the reactor inner diameter is 25-35 mm to control the residence time of the reactant gas in the reactor to be 5-10 s. Under these conditions, R152a undergoes a dehydrogenation reaction: CH2F-CH3 → CH2=CHF + H2, with a conversion rate of 80-85% and a selectivity of 93-96% for HFO-1132a.

[0010] Preparation of dehydrogenation catalyst Cr2O3 / Al2O3: γ-Al2O3 support was impregnated in chromium nitrate solution, dried at 120℃ for 4 h, and calcined at 600℃ for 3 h, with the Cr2O3 loading controlled at 10-15 wt%.

[0011] c) Product splitting and conversion: The reaction product mixture gas containing HFO-1132a (mainly including HFO-1132a, hydrogen, and a small amount of unreacted R152a) from the dehydrogenation reactor is split at a volume ratio of 40-60% and fed into the subsequent fluorination and dimerization reaction units respectively. c1) Fluorination Reaction: A portion of the diverted HFO-1132a (40-60% by volume) enters the fluorination reactor, where it undergoes an addition fluorination reaction with anhydrous hydrogen fluoride (HF) under specific temperature and pressure conditions in the presence of a fluorination catalyst, producing HFO-1234ze. The fluorination reactor is preferably a fluidized bed reactor. The reaction conditions are: temperature 300-400℃, pressure 0.2-0.4 MPa. The preferred molar ratio of HFO-1132a to anhydrous hydrogen fluoride is 1:2-1:3. The fluorination catalyst is SnCl4 / activated carbon, with a SnCl4 loading of 8-12 wt%. Under these conditions, HFO-1132a undergoes an addition fluorination reaction with HF: CH2=CHF + 2HF → CF3CH=CHF (HFO-1234ze, mainly the trans isomer) + H2 (or other side reactions). The selectivity of HFO-1234ze in this step can reach 85-90%.

[0012] c2) Dimerization Reaction: Another portion of the diverted HFO-1132a (60-40% by volume, i.e., the remaining portion) enters the dimerization reactor, where it undergoes a dimerization reaction with the dimerization catalyst under specific temperature and pressure conditions to generate HFO-1336mzz. The dimerization reactor is preferably a fixed-bed reactor. The reaction conditions are: temperature 250-350℃, pressure 0.15-0.35MPa. The dimerization catalyst is preferably ZnCl2 / γ-Al2O3, with a ZnCl2 loading of 6-10wt%. Under these conditions, two molecules of HFO-1132a undergo a dimerization reaction: 2 CH2=CHF → CF3CH=CHCF3 (HFO-1336mzz). The selectivity of HFO-1336mzz in this step can reach 80-85%.

[0013] Preparation of fluorinated catalyst SnCl4 / activated carbon: After pretreatment with 5% nitric acid, activated carbon is impregnated with SnCl4 ethanol solution and dried at 80℃ under nitrogen protection, with the SnCl4 loading controlled at 8-12wt%.

[0014] Preparation of the dimerizing catalyst ZnCl2 / γ-Al2O3: γ-Al2O3 was impregnated in ZnCl2 aqueous solution, dried at 110℃ for 6 h, activated at 500℃ for 2 h, and the ZnCl2 loading was controlled to be 6-10 wt%.

[0015] d) Product Separation and Purification: The product mixtures from the fluorination and dimerization units undergo subsequent separation and purification. Specific steps include: Water Washing: The product gas after the reaction first enters a water washing tower to remove acidic impurities (such as unreacted excess HF, small amounts of HCl generated during the reaction). The water washing temperature is controlled at 20-30℃, and the liquid-to-gas ratio (wash water volume to gas volume ratio) is 1:3-1:5. Alkali Washing: The water-washed gas then enters an alkaline washing tower, where 5-10% (mass percentage) sodium hydroxide (NaOH) solution is used to further neutralize any remaining trace acidic substances, ensuring the product's pH meets standards. The liquid-to-gas ratio in the alkaline washing tower is 1:4-1:6. Distillation: The gas after water washing and alkali washing (mainly containing the target product HFO-1234ze or HFO-1336mzz, as well as unreacted feed gas, by-products, and inert gases, etc.) enters a distillation column. After distillation, based on the difference in boiling points between HFO-1234ze and HFO-1336mzz and other by-products, the corresponding fractions are collected to obtain HFO-1234ze and HFO-1336mzz with a purity greater than 99.0%. Unreacted feed gas (such as HFO-1132a, R152a, HF) can be recovered and recycled as appropriate to improve feed utilization.

[0016] The core innovation of this invention lies in: 1. Innovative Reaction Path Integration: A groundbreaking staged reaction system was designed using R152a as a single raw material. This system, involving "one-time dehydrogenation, product splitting, and separate fluorination and dimerization," ingeniously integrates the generation of HFO-1132a and its conversion into HFO-1234ze (fluorination) and HFO-1336mzz (dimerization) within the same production line. This integrated design achieves highly efficient synergistic preparation from a single basic raw material to two high-value-added HFO products with different structures, breaking the limitations of traditional single-product preparation.

[0017] 2. Precise reaction control and catalyst matching: By precisely controlling key parameters such as temperature, pressure, material ratio, and residence time in each reaction step (dehydrogenation, fluorination, and dimerization), and by selecting catalysts with specific loadings (Cr2O3 / Al2O3 dehydrogenation catalyst, SnCl4 / activated carbon fluorination catalyst, and ZnCl2 / γ-Al2O3 dimerization catalyst) for each reaction step, the efficient generation of HFO-1132a and its reasonable distribution and highly selective conversion between fluorination and dimerization reactions are ensured, thereby guaranteeing high yields of the two target products.

[0018] 3. High-efficiency separation and energy optimization: A unified separation and purification unit (water washing, alkali washing, and distillation) is used to process the products of two different reactions, simplifying the process. Simultaneously, the entire process facilitates the recovery and utilization of reaction heat (e.g., using the high-temperature reaction heat generated by the dehydrogenation reaction to preheat raw materials or other units requiring heating), further reducing energy consumption.

[0019] Compared with the prior art, the present invention has the following significant advantages: 1. High process integration and strong production flexibility: This invention enables the simultaneous production of two high-demand HFO products (HFO-1234ze and HFO-1336mzz) on a single production line. The splitting ratio of the two HFO-1132a streams can be flexibly adjusted according to market demand, thereby optimizing the yield ratio of the two products. Compared to traditional step-by-step, independent preparation processes, this significantly improves production flexibility and the ability to respond quickly to the market.

[0020] 2. Significantly reduced equipment investment and operating costs: Due to the adoption of integrated processes, shared raw material pretreatment, some utilities, and uniformly designed separation units, compared to building two separate independent units to produce HFO-1234ze and HFO-1336mzz, this invention can significantly reduce equipment investment costs (expected to be reduced by more than 40%), save production space, simplify factory layout, and reduce operating and maintenance costs.

[0021] 3. Low energy consumption and high energy utilization efficiency: Through reasonable heat recovery and utilization of reaction (such as preheating raw materials with high-temperature dehydrogenation reaction products) and precise temperature and pressure control, the energy consumption of this invention can be reduced by 30-50% compared with traditional separate step-by-step preparation processes.

[0022] 4. High raw material utilization and good atom economy: R152a, as a single raw material, achieves efficient atom utilization through staged reactions. The total yield (based on R152a, the sum of the yields of HFO-1234ze and HFO-1336mzz) can reach 65-70%, which is higher than the sum of the total yields of the two products prepared separately in the traditional process, effectively reducing raw material costs and waste emissions.

[0023] 5. Reliable product quality and high purity: After strict raw material pretreatment and product separation and refining processes, the final HFO-1234ze and HFO-1336mzz products have a purity of more than 99.0%, which can meet the stringent requirements of high-end refrigeration, foaming, heat pump and other industries for high-quality HFO products, and broaden the application fields of the products.

[0024] In summary, the method and process provided by this invention are novel, highly integrated, energy-efficient, have high raw material utilization, and produce high-quality products. It effectively overcomes many defects of traditional preparation processes and provides an innovative, efficient, and feasible technical solution for the industrial production of HFO refrigerants. It is of great significance and has promising application prospects for promoting the green and sustainable development of the organic fluorine chemical industry. Detailed Implementation

[0025] To better understand the present invention, the present invention will be further described in detail below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0026] Example 1 Raw material pretreatment: R152a with a purity of 99.6% was selected and fed into a fixed-bed adsorption tower (inner diameter 50 mm, height 1.5 m) packed with 5A molecular sieves. The gas flow rate was controlled at 0.8 m³ / h, the adsorption temperature at 25℃, and the pressure at 0.1 MPa. After pretreatment, the purity of R152a was increased to 99.7%, with the moisture content reduced to <30 ppm, the oxygen content <50 ppm, and the total impurity content <0.2%.

[0027] Dehydrogenation reaction: Pretreated R152a was fed into a tubular reactor (30 mm inner diameter) packed with a dehydrogenation catalyst Cr2O3 / Al2O3 (Cr2O3 loading 12 wt%). The reaction conditions were: temperature 600℃, pressure 0.2 MPa, and R152a residence time in the reactor 8 s. The main reaction product was HFO-1132a. Gas chromatography analysis showed that the conversion rate of R152a was 83%, and the selectivity for HFO-1132a was 95%.

[0028] Separation and Reaction: a. Fluorination Reaction: The HFO-1132a mixed gas generated from the dehydrogenation reaction is separated at a volume ratio of 45%. This portion of the gas enters a fluidized bed reactor packed with a fluorination catalyst SnCl4 / activated carbon (SnCl4 loading of 10 wt%). Anhydrous hydrogen fluoride (purity 99.9%) is simultaneously introduced, controlling the molar ratio of HFO-1132a to HF at 1:2.5. The reaction conditions are: temperature 350℃, pressure 0.3 MPa. The main reaction product is HFO-1234ze. Analysis shows that the conversion rate of HFO-1132a in this step is 88%, and the selectivity of HFO-1234ze is 89%. b. Dimerization Reaction: The remaining 55% volume of the HFO-1132a mixed gas enters a fixed bed reactor packed with a dimerization catalyst ZnCl2 / γ-Al2O3 (ZnCl2 loading of 8 wt%). The reaction conditions were: temperature 300℃, pressure 0.25MPa. The main reaction product was HFO-1336mzz. Analysis showed that the conversion rate of HFO-1132a in this step was 82%, and the selectivity of HFO-1336mzz was 84%.

[0029] Product separation and purification: The mixed gas after the reaction was successively washed with water (liquid-to-gas ratio 1:4), washed with alkali (8% NaOH, liquid-to-gas ratio 1:5), and distilled to finally obtain HFO-1234ze with a purity of 99.2% and HFO-1336mzz with a purity of 99.1%. The total yield of HFO-1234ze based on R152a was 36%, and the total yield of HFO-1336mzz was 32%.

[0030] Example 2 Raw material pretreatment: R152a raw material with a purity of 99.7% was selected and fed into a fixed-bed adsorption tower packed with 5A molecular sieves. The R152a gas flow rate was controlled at 0.8 m³ / h, and the adsorption temperature was 25℃. After adsorption treatment, the moisture content in R152a was reduced to <30 ppm, the oxygen content was reduced to <50 ppm, and the purity reached 99.8%.

[0031] Dehydrogenation reaction: Pretreated R152a was fed into a tubular reactor (25 mm inner diameter) packed with a dehydrogenation catalyst Cr2O3 / Al2O3 (Cr2O3 loading 14 wt%). The reaction conditions were: temperature 620℃, pressure 0.15 MPa, and residence time of R152a in the reactor 6 s. The main reaction product was HFO-1132a. Gas chromatography analysis showed that the conversion rate of R152a was 83%, and the selectivity of HFO-1132a was 93%.

[0032] Fluorination and dimerization reaction: 50% by volume of HFO-1132a was introduced into a fluidized bed reactor with SnCl4 activated carbon (SnCl4 loading 11wt%) and mixed with HF at a molar ratio of 1:2. The reaction temperature was 380℃ and the pressure was 0.25MPa. The remaining HFO-1132a was introduced into a fixed bed reactor with ZnCl2γ-Al2O3 (ZnCl2 loading 7wt%) and the temperature was 320℃ and the pressure was 0.3MPa.

[0033] Product separation and purification: After washing with water (liquid-to-gas ratio 1:4), washing with alkali (8% NaOH, liquid-to-gas ratio 1:5), and distillation, HFO-1234ze with a purity of 99.3% and HFO-1336mzz with a purity of 99.0% were obtained. The total yield of HFO-1234ze was 38%, and the total yield of HFO-1336mzz was 30%.

[0034] Example 3 Raw material: R152a with a purity of 99.5% was selected and fed into a fixed-bed adsorption tower packed with 5A molecular sieves. The R152a gas flow rate was controlled at 0.8 m³ / h, and the adsorption temperature was 25℃. After adsorption treatment, the moisture content in R152a was reduced to <30 ppm, the oxygen content was reduced to <50 ppm, and the purity reached 99.6%.

[0035] Dehydrogenation reaction: Cr2O3 / Al2O3 (Cr2O3 loading 10wt%) was used as the dehydrogenation catalyst. The R152a flow rate was 0.9 m³ / h, and it was introduced into a tubular reactor with an inner diameter of 35 mm. The temperature was 580℃, the pressure was 0.25 MPa, the residence time of the reaction gas was 9 s, the conversion rate of R152a was 80%, and the selectivity of HFO-1132a was 96%.

[0036] Fluorination and dimerization reaction: 40% by volume of HFO-1132a was introduced into a SnCl4 / activated carbon (SnCl4 loading 9wt%) fluidized bed reactor and mixed with HF at a molar ratio of 1:3. The reaction temperature was 320℃ and the pressure was 0.35MPa. The remaining HFO-1132a was introduced into a ZnCl2 / γ-Al2O3 (ZnCl2 loading 9wt%) fixed bed reactor at a temperature of 340℃ and a pressure of 0.15MPa.

[0037] Product separation and purification: After washing with water (liquid-to-gas ratio 1:4), washing with alkali (8% NaOH, liquid-to-gas ratio 1:5), and distillation, HFO-1234ze with a purity of 99.0% and HFO-1336mzz with a purity of 99.2% were obtained. The total yield of HFO-1234ze was 34%, and the total yield of HFO-1336mzz was 33%.

[0038] Comparative Example (Traditional Stepwise Preparation Method) A two-step method was employed. First, HFO-1234ze was prepared separately using HFC-245eb as a raw material. Under the action of an AlF3 catalyst, hydrogen fluoride was removed at 350°C and 2.0 MPa, achieving a raw material conversion rate of 70%, a target product selectivity of 80%, and an overall yield of 56%. Then, HFO-1336mzz was prepared separately using a separate apparatus. Using HFO-1132a as a raw material, dimerization was achieved under the action of a Pd / C catalyst at 400°C and 1.5 MPa, achieving a raw material conversion rate of 60%, a target product selectivity of 75%, and an overall yield of 45%. The investment cost of these two apparatuses is approximately 1.8 times that of the present invention, and the energy consumption is on average 50% higher than that of the embodiments of the present invention.

Claims

1. A method for the co-production of HFO-1234ze and HFO-1336mzz by dehydrogenation-fluorination of R152a, characterized in that, Includes the following steps: a) Raw material pretreatment: The R152a raw material is subjected to adsorption pretreatment to achieve a purity of over 99.5%; b) Dehydrogenation reaction: The pretreated R152a is contacted with a dehydrogenation catalyst at 550-650℃ and 0.1-0.3MPa to undergo a dehydrogenation reaction, generating HFO-1132a; c) Fluorination and dimerization reaction: The generated HFO-1132a is split at a volume ratio of 40-60%. A portion of the split HFO-1132a undergoes a fluorination reaction with anhydrous hydrogen fluoride at 300-400℃ and 0.2-0.4MPa under the action of a fluorination catalyst to generate HFO-1234ze; the other portion of the split HFO-1132a undergoes a dimerization reaction with a dimerization catalyst at 250-350℃ and 0.15-0.35MPa to generate HFO-1336mzz. d) Product separation and purification: The products after fluorination and dimerization were successively washed with water, washed with alkali and distilled to obtain high-purity HFO-1234ze and HFO-1336mzz.

2. The method according to claim 1, characterized in that, Step a) The adsorption pretreatment involves passing the R152a raw material into a fixed-bed adsorption tower containing adsorbent, controlling the gas flow rate at 0.5-1.0 m³ / h and the adsorption temperature at 20-30℃, so that the moisture content in the raw material is <50 ppm and the oxygen content is <100 ppm.

3. The method according to claim 1 or 2, characterized in that, The dehydrogenation catalyst in step b) is Cr2O3 / Al2O3, wherein the loading of Cr2O3 is 10-15 wt%.

4. The method according to any one of claims 1-3, characterized in that, In step b), the flow rate of R152a is 0.5-1.0 m³ / h, and it is introduced into a tubular reactor with an inner diameter of 25-35 mm. The residence time of the reaction gas is 5-10 s.

5. The method according to claim 1, characterized in that, The fluorination catalyst in step c) is SnCl4 / activated carbon, wherein the loading of SnCl4 is 8-12 wt%.

6. The method according to claim 1 or 5, characterized in that, In step c), the molar ratio of HFO-1132a to anhydrous hydrogen fluoride is 1:2-1:

3.

7. The method according to claim 1, characterized in that, The dimerizing catalyst in step c) is ZnCl2 / γ-Al2O3, wherein the loading of ZnCl2 is 6-10 wt%.

8. The method according to claim 1, characterized in that, In step d), the temperature of the water washing is controlled at 20-30℃, and the liquid-to-gas ratio is 1:3-1:5; the alkaline washing uses a 5-10% sodium hydroxide solution, and the liquid-to-gas ratio of the alkaline washing tower is 1:4-1:

6.

9. The method according to claim 1, characterized in that, In step b), the conversion rate of the dehydrogenation reaction is 80-85%, and the selectivity of HFO-1132a is ≥93%; in step c), the selectivity of the fluorination reaction is 85-90%, and the selectivity of the dimerization reaction is 80-85%.

10. The method according to claim 1, characterized in that, The purities of HFO-1234ze and HFO-1336mzz obtained in step d) were both greater than 99.0%.