Method for preparing 2, 3, 3, 3-tetrafluoropropene

Abstract

The invention relates to the technical field of preparation of hydrofluoroolefin, in particular to a method for preparing 2, 3, 3, 3-tetrafluoropropene, which comprises the following steps: carrying out fluorination reaction on 3, 3, 3-trifluoro-2-chloropropene and excessive hydrogen fluoride under the action of a catalyst to generate a first mixture flow containing 1, 1, 1, 2, 2-pentafluoropropane (245cb), and separating the first mixture flow from the first mixture flow to obtain the 2, 3, 3, 3, 3-tetrafluoropropene. Then directly introducing the first mixture flow into a dehydrofluorination reactor for gas phase dehydrofluorination reaction to generate a second mixture flow containing 2, 3, 3, 3-tetrafluoropropene, hydrogen fluoride and unreacted raw materials, finally condensing the second mixture to remove hydrogen chloride, condensing and recycling hydrogen fluoride to obtain a third mixture flow, and rectifying the third mixture flow to obtain 2, 3, 3, 3-tetrafluoropropene. And 3, 3, 3, 3-tetrafluoropropene. According to the invention, unavoidable process wastes in the prior art are converted into recyclable reaction raw materials, the environmental protection and economic pressure of by-product treatment in the prior art is eliminated, meanwhile, the purpose of continuous flow reaction is effectively realized, and the process control difficulty and the process cost are reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of preparation of hydrofluoroolefins, and in particular to a method for preparing 2,3,3,3-tetrafluoropropylene. Background Art

[0002] 2,3,3,3-Tetrafluoropropene (HFO-1234yf), an environmentally friendly refrigerant with zero ozone depletion potential (ODP) and low global warming potential (GWP), is widely used in automotive air conditioning and commercial refrigeration equipment, replacing the traditional HFC-134a, which has a significant greenhouse effect. In compliance with the United Nations Kigali Amendment, the industrial production of HFO-1234yf has become a key development direction in the global fluorine chemical industry.

[0003] The current mainstream industrialization route of 1234yf is divided into two steps: first, 3,3,3-trifluoro-2-chloropropene (1233xf, CH2CClCF3) is reacted with hydrogen fluoride (HF) under gas-liquid catalytic conditions to generate the intermediate 2-chloro-1,1,1,2-tetrafluoropropane (244bb, CF3CFClCH3), and then 244bb is further dechlorinated and fluorinated to prepare 2,3,3,3-tetrafluoropropene (HFO-1234yf).

[0004] Although the existing synthetic routes have been industrialized, the following key issues still exist: (1) The by-products in the process of generating the intermediate 244bb are difficult to control: The addition reaction of 1233xf with HF requires precise control of the raw material ratio. For example, when HF is in excess, the proportion of the by-product 1,1,1,2,2-pentafluoropropane (245cb, CF3CF2CH3) increases significantly. Since 245cb is difficult to be converted into the target product through subsequent reactions, it can only be discharged as waste gas, resulting in a waste of raw materials and a burden on the environment. For example, US 2009 / 0182179 A1, US 2011 / 0270000 A1, WO 2013 / 071024 A1 disclose that whether liquid or gas phase reaction conditions are used, in the case of SbCl 5， SbCl 3， SbCl 5， SbF 5， TiCl 4，The presence of Cr2O3 and fluorinated Cr2O3 as catalysts in the fluorination step of 1233xf can produce byproduct 245cb, which can reach levels exceeding 10%. To reduce the formation of 245cb, existing technologies require complex process adjustments (such as gradual addition of HF and low-temperature suppression of side reactions), significantly increasing operational complexity and costs. To address this issue, U.S. Patent No. 9,399,609 B2 specifically discloses a patented method for suppressing the formation of 245cb. The specific implementation involves adding a small amount of catalyst during the initial reaction of 1233xf with HF, using a gradual, small, and multiple additions of catalyst. Even with this approach, selectivity for 244bb can only be maintained above 80%, while selectivity for 245cb can only be maintained below 20%.

[0005] (2) Low economic efficiency of fluorine atoms: The utilization rate of HF in this route is not high, resulting in the need to supplement excess HF in the production of 1234yf, which significantly increases the cost.

[0006] Other companies have explored improvements to address these shortcomings. For example, European Patent EP 2636165 B1 attempts to optimize the catalyst system to increase 244bb selectivity, but the byproduct 245cb remains high. Patent applications WO2010 / 123154, WO2014 / 10750, and US2012 / 330073 also propose multi-stage reactions to control impurities, but this requires the introduction of chlorine suppression technology, increasing process complexity.

[0007] In summary, the existing technology still has the disadvantages of great difficulty in controlling the selectivity between 244bb and 245cb, and the by-product 245cb cannot be economically utilized, resulting in low fluorine atom economy and high process costs. Summary of the Invention

[0008] The present invention aims to overcome the defects of the prior art methods for preparing 2,3,3,3-tetrafluoropropene, such as the difficulty in controlling the selectivity and the inability to economically utilize the by-products. Therefore, a method for preparing 2,3,3,3-tetrafluoropropene is provided to overcome the above-mentioned shortcomings.

[0009] To achieve the above-mentioned purpose, the present invention is implemented through the following technical solutions: A method for preparing 2,3,3,3-tetrafluoropropene comprises the following steps: (a) in a fluorination reactor, reacting 3,3,3-trifluoro-2-chloropropene with excess hydrogen fluoride in the presence of a catalyst to produce a first mixed stream containing 1,1,1,2,2-pentafluoropropane (245cb); (b) directly introducing the first mixed stream into a dehydrofluorination reactor to undergo a gas-phase dehydrofluorination reaction to generate a second mixed stream containing 2,3,3,3-tetrafluoropropene, hydrogen fluoride and unreacted raw materials; (c) introducing the second mixed stream into a condensing device to reduce the temperature of the second mixed stream, thereby condensing the hydrogen fluoride and recycling it to step (a) to obtain a third mixed stream containing 2,3,3,3-tetrafluoropropene, a small amount of hydrogen fluoride and unreacted raw materials, and washing the third mixed stream with water and alkali and then distilling it to obtain 2,3,3,3-tetrafluoropropene.

[0010] Traditionally, 245cb has been viewed as an unavoidable waste material, leading to process designs focused solely on suppressing its production through strict control of reaction conditions (e.g., controlling the absolute excess of HF), forcing the company to endure the negative impacts of material imbalance. The inventors of this application have discovered that 245cb itself has potential value as a reaction intermediate. Rather than requiring its complete elimination, it can be utilized as a resource by regulating its conversion pathway.

[0011] To this end, the present invention emphasizes a two-step process from 1233xf to 245cb and then from 245cb to 1234yf. This process is characterized by completely converting 1233xf to 245cb in a liquid or gas phase, and then converting 245cb to 1234yf in a liquid or gas phase.

[0012] Therefore, the reaction condition combination of the present invention comprises the following four embodiments: The reaction in step (a) is carried out under liquid phase conditions, and the reaction in step (b) is carried out under liquid phase conditions; The reaction in step (a) is carried out under liquid phase conditions, and the reaction in step (b) is carried out under gas phase conditions; The reaction in step (a) is carried out under gas phase conditions, and the reaction in step (b) is carried out under liquid phase conditions; The reaction in step (a) is carried out under gas phase conditions, and the reaction in step (b) is carried out under gas phase conditions.

[0013] Among them, the most preferred solution is that both steps (a) and (b) are gas-phase reactions, which facilitates the implementation of continuous reactions.

[0014] Among them, it is also preferred that step (a) is a liquid phase reaction and (b) is a gas phase reaction, and a continuous reaction can be carried out.

[0015] Specifically, the use of a highly efficient fluorine-chlorine addition exchange catalyst in step (a) of this application allows and ensures that 245cb is primarily produced during the reaction. Simultaneously, through step (b), it is directly introduced into the HF removal reaction link in the gas phase along with excess HF, essentially constructing a reaction system with 245cb as the core intermediate. The breakthrough of this technical solution lies in overturning the traditional process logic of only solidifying the 244bb intermediate, and reinjecting 245cb, which was originally blocked in the waste treatment chain, into the main reaction network. This means that the new reaction sequence essentially transforms the original "process waste" into a recyclable reaction raw material, fundamentally eliminating the environmental and economic pressures of by-product disposal in existing technologies.

[0016] Of particular note is that conventional techniques, to avoid byproduct formation, are forced to employ a limited, low molar ratio of HF to 1233xf, requiring continuous and strict control of the HF feedstock amount. However, the present invention significantly broadens the process window for step (a) by adding excess HF in step (a) and utilizing a highly efficient fluorine-chlorine addition-exchange catalyst to convert the byproduct 245cb into the primary product and establish a subsequent conversion pathway.

[0017] Furthermore, through the targeted conversion in steps (b) and (c), the fluorine atoms in 245cb can still be effectively recovered into the product stream. In step (c) of this application, a condensation step is creatively employed to recover HF, which is then reused in step (a), thereby establishing a hydrogen fluoride recycling channel and significantly improving the economic efficiency of fluorine atoms.

[0018] Furthermore, step (b) involves the dehydrofluorination of the first mixed stream of 245cb containing a large amount of hydrogen chloride to produce 2,3,3,3-tetrafluoropropene. The inventors discovered that the presence of hydrogen chloride can be addressed by optimizing the catalytic system to achieve efficient dehydrofluorination of the 245cb stream containing hydrogen chloride.

[0019] Finally, in the present application, only one separation and purification step is required at the end of the reaction to achieve the collection and reuse of the end material. Therefore, this operation not only reduces the consumption of unnecessary intermediate purification steps in the reaction process in the prior art, but also improves the utilization rate and added value of the material.

[0020] Preferably, the fluorination reaction in step (a) is a gas phase fluorination reaction, the molar ratio of hydrogen fluoride to 3,3,3-trifluoro-2-chloropropene is 3:1 to 6:1, the reaction temperature is 100-200°C, and the pressure is 0.2-1.8 MPa; The catalyst is a novel SbF5 / ZnCr / AlF3 composite catalyst, and the catalyst is pre-activated by nitrogen containing 5-10% hydrogen fluoride at 250-300°C.

[0021] Preferably, the preparation method of the SbF5 / ZnCr / AlF3 composite catalyst in this application is as follows: (1) Immerse Al2O3 in a 20% hydrofluoric acid (HF) solution for 8-12 hours, dry at room temperature, and calcine at 800°C for 2-5 hours to form an AlF3 carrier; (2) dissolving a zinc precursor (e.g., Zn(NO3)2·6H2O) and a chromium precursor (e.g., Cr(NO3)3·9H2O) in deionized water at a Zn:Cr molar ratio of 1:0.5-2 to form a mixed solution; (3) Using the equal volume impregnation method, the AlF3 carrier is saturated with adsorption (liquid-solid ratio 3:1, impregnation time ≥ 8h), then dried to remove free water, and then heated to 300-500℃ for calcination and maintained in air atmosphere for 3-5 hours to form a ZnCr2O4 spinel structure; (4) The Zn / Cr / AlF3-loaded carrier was placed in a closed reactor, SbCl5 vapor was introduced, and anhydrous HF gas (flow rate 50 mL / min) was introduced into the system. The reaction was carried out at room temperature and vacuum was evacuated to remove the by-product HCl (maintaining the pressure ≤ 0.1 bar). After stabilization for 6 hours, SbF5 / ZnCr / AlF3 was obtained.

[0022] Preferably, step (4) can also be prepared by an impregnation method: SbF5 was dissolved in anhydrous tetrahydrofuran (THF, concentration 0.5 M), and the calcined Zn / Cr / AlF3 was immersed in the solution (stirring for 24 h, temperature -20 ° C) to avoid SbF5 hydrolysis. The solvent was removed by vacuum drying (pressure <1 Pa, temperature 25 ° C) to retain the SbF5 loading layer.

[0023] The preferred technical solution in this application further optimizes the structure and performance matching of the catalytic medium within the framework of the high-activity reaction established above, thereby essentially enhancing the high efficiency and stability of the SbF5 / ZnCr / AlF3 composite catalyst. The activation treatment is not a simple surface activation process, but is essentially a preset adaptation to the subsequent high-temperature fluorination process environment. When pretreated at 250-300°C with nitrogen containing 5-10% hydrogen fluoride, a controllable degree of fluorination reconstruction occurs on the catalyst surface: nitrogen as a diluent carrier gas avoids excessive etching caused by a sudden increase in HF concentration, and the precisely controlled passivation temperature window (between the melting point of the active component and the structural collapse temperature) ensures the directional breaking of the Cr-O bonds in the chromium oxide skeleton and the step-by-step formation of Cr-F bonds.

[0024] Preferably, the fluorination reaction in step (a) may also be a liquid phase fluorination reaction, wherein the molar ratio of hydrogen fluoride to 3,3,3-trifluoro-2-chloropropene is (2.5-4):1, the reaction temperature is 80-100°C, and the pressure range is 0.5-1.1 MPa; The catalyst for the liquid-phase fluorination reaction in step (a) is any one or more of SbF5, SbCl5, SbCl3, TiCl4, FeCl3, and SnCl4; the amount of the catalyst is 20wt%-50wt% of the total mass of hydrogen fluoride (HF) and 3,3,3-trifluoro-2-chloropropene (1233xf), and the fluorination reaction time is 3-8 hours.

[0025] In the present application, during the process of dehydrofluorinating a first mixed stream containing 245cb to prepare 2,3,3,3-tetrafluoropropene, due to the presence of a large amount of hydrogen chloride component in the first mixed stream, during the process of removing hydrogen fluoride from 245cb, the presence of hydrogen chloride will cause the active components of the catalyst in this step (such as Cr, Al) to react with hydrogen chloride irreversibly to form chlorides (such as CrCl3, AlCl3), thereby destroying the crystal structure of the catalyst and causing the active site to deactivate. For example: CrF3 active center + HCl → CrCl3 + HF, and the poor thermal stability of CrCl3 makes it unable to maintain catalytic activity. Secondly, the strong acidity of HCl will lead to the formation of isomerization side reactions by changing the proton transfer direction of the reaction pathway, and induce the formation of byproducts such as 1234ze (trans isomer). At the same time, HCl combines with incompletely defluorinated intermediates, promoting the cracking of organic matter at high temperatures, thereby accelerating the formation of coke and chlorine-containing polymers (tar). Once this coke coats the catalyst surface, it significantly reduces the catalyst's catalytic efficiency. Therefore, the catalyst's hydrogen chloride resistance requires additional consideration in this step.

[0026] To eliminate the effects of HCl, the conventional process typically involves subjecting the resulting mixture from the fluorination of 3,3,3-trifluoro-2-chloropropene to at least one purification step to remove the majority of the hydrogen chloride. However, these additional purification steps inevitably prolong the reaction path.

[0027] In response to the above-mentioned technical problems, the inventors of the present application have discovered that they can optimize the catalytic system to achieve efficient dehydrofluorination of the 245cb stream containing hydrogen chloride components.

[0028] Among them, with regard to the improvement of the catalyst, the present application found that the dehydrofluorination reaction under the conditions of Fe-doped Cr-Zr / Al2O3 composite catalyst can effectively prolong the catalytic efficiency and service life of the catalyst in the presence of hydrogen chloride. Among them, zirconium (Zr) is doped in the conventional Cr catalyst, which can make Zr and HCl preferentially form ZrCl4, thereby avoiding the reaction of HCl and Cr, and then protecting the main active phase Cr, reducing the impact of the loss of the main active phase Cr on the decline in the conversion efficiency of the main reaction. Secondly, the present application also doped a certain amount of transition metal Fe in the catalyst, through Fe 3+ Oxidation at high temperature can promote the Cl in ZrCl4 - The removal of ZrCl4 reduces the ZrCl4 to its original state and removes the byproduct tar formed by the reaction. Ultimately, the doping of Zr and Fe results in a 1234yf selectivity of >95% and a significant reduction in byproduct content.

[0029] Preferably, the catalyst used in step (b) is a Fe-Cr-Zr / Al2O3 composite catalyst, which contains 65-75% Cr2O3, 12-18% ZrO2, and 7-22% Al2O3 in terms of the mass percentage of metal oxides, and is doped with less than or equal to 3wt% Fe2O3, and the catalyst surface is pre-passivated with hydrogen fluoride.

[0030] Preferably, the catalyst used in step (b) comprises at least one or more combinations of oxides or fluorides of alkaline earth metals and / or transition metals.

[0031] Preferably, the catalyst used in step (b) comprises one or a combination of at least two of the oxides or fluorides of magnesium, calcium, barium, chromium, zinc, zirconium, zinc, iron, nickel, and copper.

[0032] Specifically, the catalyst may include fluorides of magnesium, calcium, barium, chromium, zirconium, and mixtures thereof, and may also include oxides of zirconium, zinc, chromium, iron, nickel, copper, and cobalt. Furthermore, the catalyst may be supported on a carrier such as graphite or alumina to enhance its catalytic activity.

[0033] Preferably, the dehydrofluorination reaction in step (b) is controlled in two stages, the temperature of the first stage is 350-370°C and the residence time is 1-30 seconds, and the temperature of the second stage is 370-450°C and the residence time is 0.5-10 seconds, and the two stages are connected by an adiabatic transition stage.

[0034] In the dehydrofluorination reaction of step (b), the front low-temperature zone (350-370°C) and the rear high-temperature zone (370-450°C) and their respective residence times are specifically set as follows based on the balance between reaction kinetics and mass transfer optimization: The front low temperature zone (350-370℃): promotes HCl to separate from the catalyst surface and reduces the poisoning of HCl to the catalyst; The high-temperature zone in the latter part (370-450°C) accelerates the main HF removal reaction and ensures that 245cb is fully converted into 1234yf at the temperature with the highest catalytic activity, maximizing the main reaction conversion rate while controlling the formation of by-products.

[0035] Therefore, the present application uses segmented temperature-time synergistic optimization to efficiently remove the HCl protective catalyst, ensure high conversion rate and selectivity of the main reaction, and avoid runaway side reactions.

[0036] Preferably, in step (c), the temperature of the second mixed stream is reduced to below 15° C., thereby condensing the hydrogen fluoride.

[0037] Therefore, this application has the following beneficial effects: 1) This application breaks the passive disposal model of by-products in existing processes and realizes "turning waste into treasure" through targeted conversion of by-products; 2) It avoids the need for multiple purification and separation steps in the preparation process of 2,3,3,3-tetrafluoropropene, thereby effectively reducing the difficulty of process control in the preparation process of 2,3,3,3-tetrafluoropropene. DETAILED DESCRIPTION

[0038] The present invention will be further described below with reference to specific embodiments. Those skilled in the art will be able to implement the present invention based on these descriptions. Furthermore, the embodiments of the present invention described below generally represent only a portion of the present invention, rather than all of the embodiments. Therefore, all other embodiments derived by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

[0039] Example 1 A method for preparing 2,3,3,3-tetrafluoropropene comprises the following steps: (a) Fluorination Reaction: In a fluorination reactor, hydrogen fluoride (HF) and 3,3,3-trifluoro-2-chloropropene (1233xf) in a molar ratio of 4:1 were mixed and contacted with a 50 wt% SbF5 catalyst (relative to the total mass of hydrogen fluoride and 3,3,3-trifluoro-2-chloropropene) at 80°C and a pressure of 0.8 MPa for 5 hours to complete the liquid-phase fluorination reaction. The generated hydrogen chloride was discharged during the reaction. Finally, the temperature was increased to evaporate the reaction materials in the fluorination reactor to obtain a first mixed stream containing 1,1,1,2,2-pentafluoropropane (245cb), HF, and a small amount of 2,3,3,3-tetrafluoropropene. GC analysis showed a 1233xf conversion of approximately 96% and a 245cb selectivity of approximately 93%.

[0040] (b) lowering the temperature of the first mixed stream to 10° C. to obtain a liquid phase formed by condensing HF and a gas phase containing 1,1,1,2,2-pentafluoropropane (245cb), and then recycling the liquid phase to step (a), while the gas phase is sequentially washed with water and then with alkali to remove residual HF and HCl in the gas phase to obtain 1,1,1,2,2-pentafluoropropane (245cb) containing a small amount of 2,3,3,3-tetrafluoropropene.

[0041] (c) The above-mentioned 1,1,1,2,2-pentafluoropropane (245cb) is introduced into a deacidification reactor, so that the 1,1,1,2,2-pentafluoropropane contacts a deacidification agent composed of a 40 wt % sodium hydroxide aqueous solution, and reacts at a temperature of 60° C. and a pressure of 0.8 MPa to eliminate hydrogen fluoride to produce 2,3,3,3-tetrafluoropropene (GC analysis shows that the selectivity of 1234yf is approximately 95%). The 2,3,3,3-tetrafluoropropene is collected in a storage tank and purified by distillation to obtain finished tetrafluoropropene.

[0042] Example 2 A method for preparing 2,3,3,3-tetrafluoropropene comprises the following steps: (a) Fluorination Reaction: In a fluorination reactor, hydrogen fluoride (HF) and 3,3,3-trifluoro-2-chloropropene (1233xf) in a molar ratio of 2.5:1 were mixed with 15 wt% SbCl5 catalyst and 5 wt% FeCl3 (relative to the total mass of hydrogen fluoride and 3,3,3-trifluoro-2-chloropropene) at 80°C and 0.5 MPa for 8 hours to complete the liquid-phase fluorination reaction. The generated hydrogen chloride was discharged during the reaction. Finally, the temperature was increased to evaporate the reaction materials in the fluorination reactor to obtain a first mixed stream containing 1,1,1,2,2-pentafluoropropane (245cb), HF, and a small amount of 2,3,3,3-tetrafluoropropene. GC analysis showed a 1233xf conversion of approximately 95% and a 245cb selectivity of approximately 88%.

[0043] Step (b) and step (c) are the same as in Example 1.

[0044] Example 3 A method for preparing 2,3,3,3-tetrafluoropropene comprises the following steps: (a) Fluorination Reaction: In a fluorination reactor, hydrogen fluoride (HF) and 3,3,3-trifluoro-2-chloropropene (1233xf) in a molar ratio of 3.5:1 were mixed with 45 wt% SbF5 catalyst and 5 wt% TiCl4 catalyst (relative to the total mass of hydrogen fluoride and 3,3,3-trifluoro-2-chloropropene) at 100°C and 1.1 MPa for 3 hours to complete the liquid-phase fluorination reaction. During the reaction, generated hydrogen chloride was discharged. Finally, the temperature was increased to evaporate the reaction materials in the fluorination reactor to obtain a first mixed stream comprising 1,1,1,2,2-pentafluoropropane (245cb), HF, and a small amount of 2,3,3,3-tetrafluoropropene. GC analysis showed a conversion of 1233xf of approximately 94% and a selectivity of 245cb of approximately 92%.

[0045] Step (b) and step (c) are the same as in Example 1.

[0046] Example 4 A method for preparing 2,3,3,3-tetrafluoropropene comprises the following steps: Step (a) is the same as in Example 1.

[0047] (b) The temperature of the first mixed stream is reduced to 10°C, thereby obtaining a liquid phase formed by condensation of HF and a gas phase containing 1,1,1,2,2-pentafluoropropane (245cb). The liquid phase is then recycled to step (a), while the gas phase is passed into a two-stage dehydrofluorination reactor for a two-stage reaction in the presence of a Mg / Al2O3 composite catalyst, thereby dehydrofluorinating 1,1,1,2,2-pentafluoropropane (245cb) to obtain 2,3,3,3-tetrafluoropropene, thereby forming a second mixed stream containing 2,3,3,3-tetrafluoropropene, hydrogen fluoride, and unreacted 1,1,1,2,2-pentafluoropropane (245cb). The selectivity of 2,3,3,3-tetrafluoropropene in the product is approximately 66%, and some unknown components are generated in the reactor during the dehydrofluorination process, including a trace amount of tar.

[0048] The specific temperature parameters, residence time and catalyst conditions of the two-stage dehydrofluorination reaction are as follows: The reaction conditions in the first stage were: temperature 350 °C, residence time 30 seconds; The reaction conditions of the latter stage were as follows: temperature 410°C, residence time 5 seconds; The Mg / Al2O3 composite catalyst comprises 75% MgO and 25% Al2O3 in terms of the mass percentage of metal oxides, and its surface is pre-passivated with hydrogen fluoride.

[0049] (c) introducing the second mixed stream into a condensing device and reducing the temperature of the second mixed stream to below 15° C., thereby condensing the hydrogen fluoride and recycling it to step (a) to obtain a third mixed stream containing 2,3,3,3-tetrafluoropropene and unreacted 1,1,1,2,2-pentafluoropropane (245cb), and washing the third mixed stream with water and alkali to remove residual acidic substances such as hydrogen fluoride, and then distilling it to obtain 2,3,3,3-tetrafluoropropene.

[0050] Example 5 A method for preparing 2,3,3,3-tetrafluoropropene comprises the following steps: (a) Fluorination reaction: In a fluorination reactor, hydrogen fluoride (HF) and 3,3,3-trifluoro-2-chloropropene (1233xf) in a molar ratio of 6:1 were reacted at a temperature of 200°C and a pressure of 0.2 MPa, as well as SbF 5 / A vapor-phase fluorination reaction occurs over the ZnCr / AlF3 composite catalyst to produce 1,1,1,2,2-pentafluoropropane (245cb), thereby forming a first mixed stream containing 1,1,1,2,2-pentafluoropropane (245cb), HF, and hydrogen chloride. Simultaneously, trace amounts of tar and a small amount of 2,3,3,3-tetrafluoropropene are produced in the reactor during the dehydrofluorination process. GC analysis shows a 1233xf conversion of approximately 99% and a 245cb selectivity of approximately 92%.

[0051] Wherein, the SbF 5 / The ZnCr / AlF3 composite catalyst was pre-passivated by nitrogen containing 5% hydrogen fluoride at 250 °C for 30 min.

[0052] (b) Two-stage dehydrofluorination reaction: The first mixed stream produced in step (a) is introduced into a two-stage dehydrofluorination reactor and subjected to a two-stage reaction in the presence of a Mg / Al2O3 composite catalyst, thereby dehydrofluorinating 1,1,1,2,2-pentafluoropropane (245cb) to produce 2,3,3,3-tetrafluoropropene, thereby forming a second mixed stream containing 2,3,3,3-tetrafluoropropene, hydrogen fluoride, hydrogen chloride, and unreacted 3,3,3-trifluoro-2-chloropropene and 1,1,1,2,2-pentafluoropropane. The selectivity for 2,3,3,3-tetrafluoropropene in the product is approximately 63%, and some unknown components are produced in the dehydrofluorination reactor, including a trace amount of tar.

[0053] The specific temperature parameters, residence time and catalyst conditions of the two-stage dehydrofluorination reaction are as follows: The reaction conditions in the first stage were: temperature 350 °C, residence time 7 seconds; The reaction conditions of the latter stage were as follows: temperature 450°C, residence time 0.5 seconds; The Mg / Al2O3 composite catalyst comprises 75% MgO and 25% Al2O3 in terms of the mass percentage of metal oxides, and its surface is pre-passivated with hydrogen fluoride.

[0054] (c) introducing the second mixed stream into a condensing device and reducing the temperature of the second mixed stream to below 15° C., thereby condensing the hydrogen fluoride and recycling it to step (a) to obtain a third mixed stream containing 2,3,3,3-tetrafluoropropene, hydrogen chloride and unreacted raw materials, and washing the third mixed stream with water and alkali to remove hydrogen chloride and residual hydrogen fluoride, and then distilling it to obtain 2,3,3,3-tetrafluoropropene.

[0055] Example 6 A method for preparing 2,3,3,3-tetrafluoropropene comprises the following steps: (a) Fluorination reaction: In a fluorination reactor, hydrogen fluoride (HF) and 3,3,3-trifluoro-2-chloropropene (1233xf) in a molar ratio of 5:1 are reacted at a temperature of 100°C and a pressure of 1.8 MPa, as well as SbF 5 / A vapor-phase fluorination reaction occurs over the ZnCr / AlF3 composite catalyst to produce 1,1,1,2,2-pentafluoropropane (245cb), thereby forming a first mixed stream containing 1,1,1,2,2-pentafluoropropane (245cb), HF, and hydrogen chloride. Simultaneously, a trace amount of tar and a small amount of 2,3,3,3-tetrafluoropropene are produced in the reactor during the dehydrofluorination process. GC analysis shows that the conversion of 1233xf is approximately 98%, and the selectivity of 245cb is approximately 90%. Wherein, the SbF 5 / The ZnCr / AlF3 composite catalyst was the same as that in Example 5 and was pre-passivated with nitrogen containing 10% hydrogen fluoride at 300°C for 30 minutes.

[0056] (b) Two-stage dehydrofluorination reaction: The first mixed stream produced in step (a) is introduced into a two-stage dehydrofluorination reactor and subjected to a two-stage reaction in the presence of a Cr / Al2O3 composite catalyst, thereby dehydrofluorinating 1,1,1,2,2-pentafluoropropane (245cb) to produce 2,3,3,3-tetrafluoropropene, thereby forming a second mixed stream containing 2,3,3,3-tetrafluoropropene, hydrogen fluoride, hydrogen chloride, and unreacted 3,3,3-trifluoro-2-chloropropene and 1,1,1,2,2-pentafluoropropane. The selectivity for 2,3,3,3-tetrafluoropropene in the product is approximately 70%, and a portion of unknown components is produced in the dehydrofluorination reactor, including a trace amount of tar.

[0057] The specific temperature parameters, residence time and catalyst conditions of the two-stage dehydrofluorination reaction are as follows: The reaction conditions in the first stage were: temperature 350 °C, residence time 7 seconds; The reaction conditions of the latter stage were as follows: temperature 370°C, residence time 10 seconds; The Cr / Al2O3 composite catalyst contains 75% Cr2O3 and 25% Al2O3 in terms of the mass percentage of metal oxides, and its surface is pre-passivated with hydrogen fluoride.

[0058] (c) introducing the second mixed stream into a condensing device and reducing the temperature of the second mixed stream to below 15° C., thereby condensing the hydrogen fluoride and recycling it to step (a) to obtain a third mixed stream containing 2,3,3,3-tetrafluoropropene, hydrogen chloride and unreacted raw materials, and washing the third mixed stream with water and alkali to remove hydrogen chloride and residual hydrogen fluoride, and then distilling it to obtain 2,3,3,3-tetrafluoropropene.

[0059] Example 7 A method for preparing 2,3,3,3-tetrafluoropropene comprises the following steps: (a) Fluorination reaction: In a fluorination reactor, hydrogen fluoride (HF) and 3,3,3-trifluoro-2-chloropropene (1233xf) in a molar ratio of 3:1 were reacted at a temperature of 150°C and a pressure of 0.8 MPa, as well as SbF 5 / A vapor-phase fluorination reaction occurs over the ZnCr / AlF3 composite catalyst to produce 1,1,1,2,2-pentafluoropropane (245cb), thereby forming a first mixed stream containing 1,1,1,2,2-pentafluoropropane (245cb), HF, and hydrogen chloride. Simultaneously, a portion of tar and a small amount of 2,3,3,3-tetrafluoropropene are produced in the reactor during the dehydrofluorination process. GC analysis shows that the conversion of 1233xf is approximately 99%, and the selectivity of 245cb is approximately 93%. Wherein, the SbF 5 / The ZnCr / AlF3 composite catalyst was the same as that in Example 5 and was pre-passivated by nitrogen containing 7% hydrogen fluoride at 275°C for 30 minutes.

[0060] (b) Two-stage dehydrofluorination reaction: The first mixed stream produced in step (a) is introduced into a two-stage dehydrofluorination reactor and subjected to a two-stage reaction in the presence of a Zn-Cr / Al2O3 composite catalyst, thereby dehydrofluorinating 1,1,1,2,2-pentafluoropropane (245cb) to produce 2,3,3,3-tetrafluoropropene, thereby forming a second mixed stream containing 2,3,3,3-tetrafluoropropene, hydrogen fluoride, hydrogen chloride, and unreacted 3,3,3-trifluoro-2-chloropropene and 1,1,1,2,2-pentafluoropropane. The selectivity for 2,3,3,3-tetrafluoropropene in the product is approximately 79%, and some unknown components are produced in the dehydrofluorination reactor, including a trace amount of tar.

[0061] The specific temperature parameters, residence time and catalyst conditions of the two-stage dehydrofluorination reaction are as follows: The reaction conditions for the first stage were: temperature 370°C, residence time 1 second; The reaction conditions of the latter stage were as follows: temperature 410°C, residence time 5 seconds; The Zn-Cr / Al2O3 composite catalyst contains 50% ZnO, 25% Cr2O3 and 25% Al2O3 in terms of the mass percentage of metal oxides, and its surface is pre-passivated with hydrogen fluoride.

[0062] (c) introducing the second mixed stream into a condensing device and reducing the temperature of the second mixed stream to below 15° C., thereby condensing the hydrogen fluoride and recycling it to step (a) to obtain a third mixed stream containing 2,3,3,3-tetrafluoropropene, hydrogen chloride and unreacted raw materials, and washing the third mixed stream with water and alkali to remove hydrogen chloride and residual hydrogen fluoride, and then distilling it to obtain 2,3,3,3-tetrafluoropropene.

[0063] Comparative Example 1 A method for preparing 2,3,3,3-tetrafluoropropene comprises the following steps: (a) Fluorination Reaction: In a fluorination reactor, hydrogen fluoride (HF) and 3,3,3-trifluoro-2-chloropropene (1233xf) in a molar ratio of 6:1 undergo a vapor phase fluorination reaction at 200°C and a pressure of 0.5 MPa over a conventional zinc / chromium oxide catalyst to produce 1,1,1,2,2-pentafluoropropane (245cb), thereby forming a first mixed stream containing 1,1,1,2,2-pentafluoropropane (245cb), HF, and hydrogen chloride. In addition, trace amounts of tar and a small amount of 2,3,3,3-tetrafluoropropene are also formed in the fluorination reactor. GC analysis shows that the conversion of 1233xf is approximately 85%, and the selectivity of 245cb is approximately 73%.

[0064] Step (b) and step (c) are the same as in Example 5.

[0065] Wherein, the preparation method of zinc / chromium oxide catalyst is as follows: (1) Dissolve zinc nitrate (Zn(NO3)3·6H2O) and chromium nitrate (Cr(NO3)3·9H2O) in water at a Zn:Cr molar ratio of 1:1 to prepare a precursor solution with a total metal concentration of 1.0 mol / L; (2) Ammonia water (NH3·H2O) and sodium carbonate (Na2CO3) were prepared in a molar ratio of 1:0.2 to prepare a precipitant solution with a pH of 8.0-9.0; (3) The precursor solution was added dropwise to the precipitant solution at a rate of 10 mL / min at 60 °C. After the addition was completed, the solution was aged for 2 hours, filtered, and washed with hot water (60 °C) until there was no NO3 - The residue was dried at 110 °C for 12 h to obtain a precursor powder; (4) The precursor powder was gradually heated to 500°C in an air atmosphere and kept at this temperature for 4 hours to obtain a zinc / chromium oxide catalyst.

[0066] From the above results, we can see that the present application can achieve good fluorination effect through step (a) whether it is performed by gas phase method or liquid phase method. In addition, by comparing Example 5 with Comparative Example 1 by single factor variables, we found that SbF 5 / The conversion rate of 1233xf and the selectivity of 245cb in the gas phase process embodiment (Example 5) of the ZnCr / AlF3 composite catalyst are significantly higher than those of the comparative example 1 of the ordinary zinc / chromium oxide catalyst, indicating that SbF 5 / Application potential of ZnCr / AlF3 composite catalyst.

[0067] Furthermore, from Examples 5 to 7 above, we can see that the type of catalyst selected in step (b) has a significant impact on the selectivity of the final product. Therefore, to explore the relationship between different dehydrofluorination reaction catalysts in step (b) and product selectivity, the applicant conducted an experimental investigation using a controlled variable method (individually controlling the type of dehydrofluorination reaction catalyst). The specific experimental process was basically the same as that of Example 5, except that the catalyst in step (b) of Example 5 was replaced by the dehydrofluorination reaction catalyst shown in Table 1 below. All other conditions were the same.

[0068] The preparation methods of the dehydrofluorination reaction catalysts in Table 1 are as follows: Cr / Al2O3 composite catalyst (Cr2O3 75%, Al2O3 25%): (1) Select γ-Al2O3 spherical particles and immerse them in 5% oxalic acid (H2C2O4) solution at 80℃ and stir for 2 hours to remove inorganic impurities (mainly Na + plasma) and weakly acidic sites, and then washed with a large amount of deionized water until the pH of the washing solution was ≈ 7 and no oxalate ions were detected. It was then dried at 110°C for 6-12 hours, and the dried support was calcined at 500°C in an air atmosphere for 4 hours to obtain an Al2O3 support.

[0069] (2) Cr(NO3)3·9H2O is dissolved in deionized water to obtain a solution with a concentration of 1.5 mol / L. The Al2O3 carrier pretreated in step (1) is placed in an impregnation container, and the prepared chromium salt impregnation solution is slowly and evenly added dropwise to the carrier while continuously stirring or rolling the carrier to ensure that the impregnation solution is evenly absorbed. The container is then sealed and allowed to stand at room temperature for 8-12 hours or overnight to allow the solution to fully diffuse into the pores inside the carrier. The catalyst is then dried in air at 110°C for 8-12 hours. After drying, the catalyst precursor is placed in a tube furnace or a muffle furnace and heated to 500-550°C at a heating rate of 1-2°C / min, and calcined at a constant temperature for 4-6 hours to obtain a Cr / Al2O3 composite catalyst.

[0070] (3) The calcined catalyst (Cr / Al2O3) is placed in an inert material reactor resistant to HF corrosion, and then an HF / N2 mixed gas with an HF concentration of 2 vol% is introduced as a passivation medium. The temperature is raised to 250-300°C (preferably 275°C) at a rate of 1-2°C / min and passivated for 3-8 hours. After the passivation is completed, N2 is purged and continued to be purged at the passivation temperature for 1-2 hours to remove physically adsorbed or weakly bound HF.

[0071] Mg / Al2O3 composite catalyst (MgO 75%, Al2O3 25%): The preparation method is similar to that of the Cr / Al2O3 composite catalyst, except that Cr(NO3)3·9H2O is replaced by an equal amount of magnesium nitrate hexahydrate (Mg(NO3)2·6H2O).

[0072] Fe-Cr / Al2O3 composite catalyst (Cr2O372%, Al2O325%, Fe2O33%): The preparation method is similar to that of the Cr / Al2O3 composite catalyst, except that 3% of ferric nitrate based on Fe2O3 is additionally added in step (2).

[0073] Zn-Cr / Al2O3 composite catalyst (ZnO 50%, Cr2O3 25%, Al2O3 25%): The calculated amount of Zn(NO3)2·6H2O and Cr(NO3)3·9H2O was dissolved in deionized water, and 5–10wt% citric acid (chelating agent) was added. The solution containing Zn and Cr salts was then slowly and evenly dripped onto the Al2O3 support while continuously stirring or rolling the support to ensure that the impregnation solution was evenly absorbed. The container was then sealed and allowed to stand at room temperature for 8–12 hours or overnight to allow the solution to fully diffuse into the pores inside the support. The catalyst was then dried in air at 110°C for 8–12 hours. After drying, the catalyst precursor was placed in a tube furnace or muffle furnace and heated to 400–450°C at a heating rate of 1–2°C / min. It was then calcined at this constant temperature for 4–6 hours to obtain a Zn-Cr / Al2O3 composite catalyst.

[0074] Zr-Cr / Al2O3 composite catalyst (Cr2O3 72%, ZrO2 18%, Al2O3 10%): (1) Using zirconium oxychloride (ZrOCl2·8H2O) as the zirconium source, the target weight of ZrOCl2·8H2O was weighed and dissolved in dilute hydrochloric acid to prepare a zirconium precursor solution. The zirconium precursor solution was slowly and evenly added dropwise to the Al2O3 support, dried at 110°C for 12 hours, and then heated to 550°C and calcined for 4 hours (in air) to form a ZrO2-Al2O3 composite support; (2) Cr(NO3)3·9H2O was used as the Cr source. The target weight of Cr(NO3)3·9H2O was weighed to prepare a Cr precursor solution. The Cr precursor solution was slowly and evenly added dropwise to the ZrO2-Al2O3 composite support. The temperature was then raised to 250°C at a rate of 2°C / min and kept warm for 2 h. The temperature was then raised to 500°C at a rate of 1°C / min and kept warm for 4 h to obtain a Zr-Cr / Al2O3 composite catalyst.

[0075] Fe-Cr-Zr / Al2O3 composite catalyst (Cr2O3 72%, ZrO2 16.2%, Al2O3 10%, Fe2O3 1.8%): The preparation method is similar to that of the Zr-Cr / Al2O3 composite catalyst, except that step (2) further contains 1.8% of ferric nitrate based on Fe2O3.

[0076] Subsequently, the product of step (b) obtained according to the catalyst conditions in Table 1 below was subjected to gas phase analysis, the selectivity of the product was calculated, and the results were compared to compare the catalytic effects of the catalysts. The comparison results are shown in Table 1 below.

[0077] Table 1 Relationship between catalyst type and product selectivity

[0078] As shown in Table 1 above, this application screened various catalysts for their catalytic performance in step (b). The screening results showed that several existing dehydrofluorination catalysts exhibited excellent catalytic activity for step (b), with selectivity for 1234yf in the product from step (b) exceeding 80%. After comprehensively considering factors such as catalytic performance, we unexpectedly discovered that the Fe-Cr-Zr / Al2O3 composite catalyst exhibited exceptionally high selectivity for 1234yf, along with high tolerance to hydrogen chloride and minimal tar production, demonstrating long-term stability.

[0079] In addition, for the Fe-Cr-Zr / Al2O3 composite catalyst with the highest selectivity for 1234yf, the applicant conducted a detailed gas phase analysis of its product, and the selectivity of each component in the product was as follows: 1234yf selectivity was 96%, 244bb selectivity was 0.3%, 1243zf selectivity was 1.2%, TFPY selectivity was 0.7%, 1234ze selectivity was 0.2%, and unknown components were 1.6%.

[0080] Therefore, in summary, the present application innovatively discovered a technical route for sequentially converting 3,3,3-trifluoro-2-chloropropene (1233xf) into 1,1,1,2,2-pentafluoropropane (245cb) and 1234yf, thereby transforming the "process waste" considered unavoidable in the prior art into a recyclable reaction raw material, fundamentally eliminating the environmental and economic pressures of by-product disposal in the prior art. At the same time, it avoids the various negative effects caused by the imbalance of strictly restricted reaction conditions to suppress the generation of "process waste." Furthermore, the technical route in the present application can reuse the excess hydrogen fluoride raw material in step (a), thereby significantly reducing the loss of hydrogen fluoride and effectively reducing the preparation cost of 2,3,3,3-tetrafluoropropene (1234yf).

[0081] The specific embodiments described herein are merely illustrative of the spirit of the present invention. Persons skilled in the art may make various modifications, additions, or substitutions to the described specific embodiments without departing from the spirit of the present invention or exceeding the scope of the appended claims.

Claims

1. A method for preparing 2,3,3,3-tetrafluoropropene, characterized in that: The following steps are involved: (a) in a fluorination reactor, reacting 3,3,3-trifluoro-2-chloropropene with excess hydrogen fluoride in the presence of a catalyst to produce a first mixed stream containing 1,1,1,2,2-pentafluoropropane; (b) directly introducing the first mixed stream into a dehydrofluorination reactor to undergo a gas-phase dehydrofluorination reaction to generate a second mixed stream containing 2,3,3,3-tetrafluoropropene, hydrogen fluoride and unreacted raw materials; (c) introducing the second mixed stream into a condensing device to reduce the temperature of the second mixed stream, thereby condensing the hydrogen fluoride and recycling it to step (a) to obtain a third mixed stream containing 2,3,3,3-tetrafluoropropene, a small amount of hydrogen fluoride and unreacted raw materials, and washing the third mixed stream with water and alkali and then distilling it to obtain 2,3,3,3-tetrafluoropropene.

2. The method according to claim 1, characterized in that The fluorination reaction in step (a) is a gas phase fluorination reaction, the molar ratio of hydrogen fluoride to 3,3,3-trifluoro-2-chloropropene is 3:1 to 6:1, the reaction temperature is 100-200° C., and the pressure is 0.2-1.8 MPa.

3. The method according to claim 2, characterized in that The catalyst for the gas-phase fluorination reaction in step (a) is a SbF5 / ZnCr / AlF3 composite catalyst, and the catalyst is pre-activated by nitrogen containing 5-10% hydrogen fluoride at 250-300°C.

4. The method according to claim 1, wherein The fluorination reaction in step (a) is a liquid phase fluorination reaction, the molar ratio of hydrogen fluoride to 3,3,3-trifluoro-2-chloropropene is (2.5-4):1, and the reaction temperature is 80-100°C.

5. The method according to claim 4, characterized in that The catalyst for the liquid-phase fluorination reaction in step (a) is any one or more of SbF5, SbCl5, SbCl3, TiCl4, FeCl3, and SnCl4; the catalyst dosage is 20wt%-50wt%, and the fluorination reaction time is 3-8 hours.

6. The method according to claim 1, characterized in that The catalyst used in step (b) comprises at least one or more combinations of oxides or fluorides of alkaline earth metals and / or transition metals.

7. The method according to claim 6, characterized in that The catalyst used in step (b) comprises one or a combination of at least two of the oxides or fluorides of magnesium, calcium, barium, chromium, zinc, zirconium, zinc, iron, nickel, and copper.

8. The method according to claim 6, characterized in that The catalyst used in step (b) is a Fe-Cr-Zr / Al2O3 composite catalyst, which contains 65-75% Cr2O3, 12-18% ZrO2, and 7-22% Al2O3 in terms of the mass percentage of metal oxides, and is doped with less than or equal to 3wt% Fe2O3. The catalyst surface is pre-passivated with hydrogen fluoride.

9. The method according to claim 1, characterized in that The dehydrofluorination reaction in step (b) is controlled in two stages, the temperature of the first stage is 350-370°C and the residence time is 1-30 seconds, and the temperature of the second stage is 370-450°C and the residence time is 0.5-10 seconds, and the two stages are connected by an adiabatic transition stage.

10. The method according to claim 1, characterized in that In step (c), the temperature of the second mixed stream is reduced to below 15° C., thereby condensing the hydrogen fluoride.

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