Catalytic synthesis method of 1, 1, 3, 3, 3-pentafluoropropylene

Abstract

The invention discloses a catalytic synthesis method of 1, 1, 3, 3, 3-pentafluoropropylene, which comprises the following steps: (1) introducing a raw material 1, 1, 1, 3, 3, 3-hexafluoropropane into a reactor, and reacting under the action of a catalyst to obtain crude 1, 1, 3, 3, 3-pentafluoropropylene, the catalyst containing Cr2O3 and one of metal oxides of Al, Bi and Co; (2) carrying out water washing, alkali washing and drying on the crude 1, 1, 3, 3, 3-pentafluoropropene, and then introducing the crude 1, 1, 3, 3, 3-pentafluoropropene into a first rectifying tower for separation to obtain a mixture containing 1, 1, 1, 3, 3-pentafluoropropene and a small amount of by-products; and (3) introducing the mixture containing 1, 1, 1, 3, 3-pentafluoropropylene and a small amount of by-products into a second rectifying tower, and separating to obtain a 1, 1, 1, 3, 3-pentafluoropropylene product. The method has the advantages of simple process, high catalyst activity, low cost and environmental protection.

Description

Technical Field

[0001] The invention relates to a method for preparing fluorine-containing olefins, and in particular to a method for catalytic synthesis of 1,1,3,3,3-pentafluoropropylene. Background Art

[0002] 1,1,3,3,3-pentafluoropropylene (HFO-1225zc) is an important chemical raw material with broad application prospects in the fields of refrigeration, foaming, solvents, etc. It has a low boiling point, low freezing point, ODP value of 0, and low GWP value, and is an environmentally friendly compound. However, the existing methods for preparing HFO-1225zc are mainly based on high-temperature cracking dehydrohalogenation or liquid-phase saponification dehydrohalogenation. These methods have high reaction temperatures, high energy consumption, many side reactions, and produce a lot of waste, which is not conducive to environmental protection and industrial production.

[0003] For example, CN101133008A discloses a method for producing 1,1,3,3,3-pentafluoropropylene from 1,1,1,3,3,3-hexafluoropropane (HFC-236fa) by non-catalytic method, using 1,1,1,3,3,3-hexafluoropropane as raw material at 700-1000°C to directly defluorinate hydrogen (HF) by high temperature pyrolysis. The method has an HFC-236fa conversion rate of 25-75% and an HFO-1225zc selectivity of 90%. The advantage of the high temperature cracking method is that HFO-1225zc can be directly prepared by high temperature cracking of HFC-236fa, and the process is relatively simple. The disadvantages are high reaction temperature, high energy consumption, high requirements for equipment and materials (such as special nickel materials), and increased production costs. In addition, the conversion rate and selectivity are limited, and the economic benefits are poor.

[0004] For example, CN102887812A discloses a method for synthesizing 1,1,3,3,3-pentafluoropropene, using pentafluorohalogenated propane (CF3CH2CF2X, where X refers to F, Cl, Br) as a raw material, saponifying and dehydrohalogenating with an inorganic base and a phase transfer catalyst at 50-90°C for 2-5h to obtain HFO-1225zc, with a product yield of 64-71%. Although liquid phase saponification is carried out at a relatively low temperature and the reaction conditions are relatively mild, a large amount of wastewater and waste solids are generated during the reaction process, causing serious environmental pollution and being unfavorable for large-scale industrial production.

[0005] Another example is CN101801894A, which discloses a method for preparing olefins containing halogens and hydrogen by using a metal fluoride catalyst. The invention uses 1,1,1,3,3-pentafluoro-3-chloropropane or 1,1,1,3,3-pentafluoro-2-chloropropane or 1,1,1,3,3,3-hexafluoropropane as a raw material, and removes hydrogen chloride or hydrogen fluoride at 50-450° C. under the catalysis of aluminum fluoride or oxyfluoride to obtain olefins containing halogens and hydrogen. Among them, when HFO-1225zc is prepared using 1,1,1,3,3,3-hexafluoropropane as a raw material, the highest selectivity (88%) can be obtained at a reaction temperature of 350° C., and the conversion rate of 1,1,1,3,3,3-hexafluoropropane is 13.5%. The disadvantages are poor catalyst activity, low conversion rate of raw material 1,1,1,3,3,3-hexafluoropropane and low selectivity of product HFO-1225zc, many by-products and poor overall economic performance. Summary of the invention

[0006] In view of the deficiencies in the prior art, the present invention provides a catalytic synthesis method for 1,1,3,3,3-pentafluoropropylene which has simple process, good catalyst activity, low cost and is environmentally friendly.

[0007] In order to solve the above technical problems, the technical solution adopted by the present invention is: a catalytic synthesis method of 1,1,3,3,3-pentafluoropropylene, comprising the following steps:

[0008] (1) introducing the raw material 1,1,1,3,3,3-hexafluoropropane into a reactor and reacting under the action of a catalyst to obtain crude 1,1,3,3,3-pentafluoropropene, wherein the catalyst contains Cr2O3 and Al, Bi 、 , one of the metal oxides of Co;

[0009] (2) washing the crude 1,1,3,3,3-pentafluoropropene obtained in step (1) with water, alkali, and then drying it and passing it into a first distillation tower for separation, wherein unreacted 1,1,1,3,3,3-hexafluoropropane is obtained in the bottom of the first distillation tower, and a mixture containing 1,1,1,3,3-pentafluoropropene and a small amount of by-products is obtained at the top of the tower;

[0010] (3) Passing the mixture containing 1,1,1,3,3-pentafluoropropene and a small amount of by-products obtained in step (2) into a second distillation tower for separation, separating the by-products at the top of the second distillation tower, and obtaining the 1,1,1,3,3-pentafluoropropene product at the bottom of the tower.

[0011] As a preferred embodiment of the present invention, the catalyst is Al2O3-Cr2O3 or Bi2O3-Cr2O3 or CoO-Cr2O3.

[0012] As a preferred embodiment of the present invention, the mass percentage of Cr2O3 in the catalyst is 40-80%.

[0013] As a preferred embodiment of the present invention, the catalyst is added with a modified metal, and the mass percentage of the modified metal is 5 to 20%.

[0014] As a preferred embodiment of the present invention, the modified metal is one of Zn, Ni and Mg.

[0015] As a preferred embodiment of the present invention, the reaction temperature is 250-450°C.

[0016] As a preferred embodiment of the present invention, the reaction pressure is 0.1-1.0 MPa.

[0017] As a preferred embodiment of the present invention, the reaction space velocity is 50 to 500 h -1 .

[0018] As a preferred embodiment of the present invention, the unreacted 1,1,1,3,3,3-hexafluoropropane obtained in the bottom of the first distillation tower in step (2) is recycled back to the reactor.

[0019] As a preferred embodiment of the present invention, the catalyst is pretreated with hydrogen fluoride gas before the reaction.

[0020] The present invention realizes the production of HFO-1225zc using HFC-236fa as raw material through a reactor, and the reaction principle is as follows:

[0021] CF3CH2CF3(HFC-236fa)→CF2=CHCF3(HFO-1225zc)+HF

[0022] The major by-product produced in the reaction is 1,1,1-trifluoroethane, which is formed by breaking the carbon-carbon bond in HFC-236fa.

[0023] The boiling points of the main substances in the present invention are as follows:

[0024] name Abbreviation Molecular weight Boiling point / ℃ 1,1,1,3,3,3-Hexafluoropropane HFC-236fa 152 -1.4 1,1,3,3,3-Pentafluoropropylene HFO-1225zc 132 -21.0 1,1,1-Trifluoroethane HFC-143a 84 -47.6 Hydrogen fluoride HF 20 19.5

[0025] In the present invention, the reactor may be a gas phase reactor, and HFC-236fa is introduced into the reactor to obtain a mixture containing unreacted HFC-236fa, HFO-1225zc, HF and a small amount of HFC-143a. The mixture is passed through a water washing tower to absorb HF generated by the reaction to form aqueous acid, and the mixture at the outlet of the water washing tower is continuously passed through an alkali washing tower to remove the trace HF that is not completely removed by the water washing tower, and then the obtained mixture containing unreacted HFC-236fa, HFO-1225zc and a small amount of HFC-143a is passed through a drying tower for drying, and the dried mixture containing unreacted HFC-236fa, HFO-1225zc and a small amount of HFC-143a is passed through a first distillation tower, and the unreacted HFC-236fa is separated from the bottom of the first distillation tower. HFC-236fa is returned to the reactor as a raw material to continue the reaction, and the top of the first distillation tower is a mixture of HFO-1225zc and a small amount of HFC-143a. The mixture at the top of the first distillation tower is passed through a second distillation tower, and the HFC-143a low-boiling substances are separated from the top of the second distillation tower, and the target product HFO-1225zc is obtained at the bottom of the second distillation tower.

[0026] The dehydrofluorination of HFC-236fa to prepare HFO-1225zc is an endothermic reaction, and the increase in reaction temperature is conducive to the reaction. The higher the temperature, the higher the conversion rate of HFC-236fa, but the selectivity of the target product is low. According to the performance of the catalyst and the conversion rate and selectivity verification, the reaction temperature is preferably 250-450°C, more preferably 300-400°C.

[0027] As the space velocity increases, the contact time between the reactants and the catalyst bed decreases, and the activity of the catalyst decreases. To ensure complete conversion of the raw materials, the space velocity is preferably 50-500 h -1 , more preferably 100 to 400 hours -1 .

[0028] The dehydrofluorination of HFC-236fa to prepare HFO-1225zc is a volume-enhancing reaction, and the reaction pressure is preferably 0.1 to 1.0 MPa, more preferably 0.1 to 0.5 MPa.

[0029] The catalyst used in the present invention contains Cr2O3 and Al, Bi 、 , Co metal oxides, and a small amount of modified metals, such as Zn, Ni, Mg and other metals, may also be added. The preparation method of the catalyst in the present invention can adopt conventional methods in the art: for example, the nitrates of various metals are mixed in a certain ratio to prepare a dilute solution of a certain concentration, a precipitant is added to react, and then filtered, washed, dried, roasted, granulated, and tableted into a precursor, and the catalyst is obtained after pre-treatment with HF fluorination. The pre-treatment of the catalyst can be carried out in other reactors.

[0030] Compared with the prior art, the present invention has the following advantages:

[0031] 1. The catalyst has high activity. The present invention optimizes the catalyst formula and the components in the catalyst work synergistically to effectively increase the active sites and greatly improve the catalytic efficiency. The conversion rate of the raw material HFC-236fa is above 45%, and can reach up to 56%; the selectivity of the product HFO-1225zc is above 99.1%, and can reach up to 99.8%.

[0032] 2. The process is simple and the reaction conditions are mild. The present invention does not require high temperature and high pressure, thereby reducing production costs and energy consumption. The catalyst used is a solid catalyst, which has good stability and recyclability and is easier to separate and recycle than a liquid catalyst. There are few by-products, which significantly reduces the separation process, making the production process more efficient and economical.

[0033] 3. Low cost and good economic benefits. The HF generated in the reaction process of the present invention is absorbed by water to form aqueous acid which can be sold, thereby increasing additional economic benefits. The unreacted 1,1,1,3,3,3-hexafluoropropane raw material can be recycled back to the reactor, thereby further reducing the production cost.

[0034] 4. Green and environmentally friendly. The present invention reduces the generation of by-products, improves atomic utilization, reduces the risk of environmental pollution, and conforms to the development trend of green and environmental protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a process flow chart of the present invention.

[0036] As shown in the figure: 1 is a reactor, 2 is a water washing tower, 3 is an alkali washing tower, 4 is a drying tower, 5 is a first distillation tower, and 6 is a second distillation tower. DETAILED DESCRIPTION

[0037] The process of the present invention is as follows Figure 1As shown, the raw material HFC-236fa is introduced into the reactor 1 to obtain a mixture containing unreacted HFC-236fa, HFO-1225zc, HF and a small amount of HFC-143a, and the mixture is introduced into the water washing tower 2 to absorb the HF generated by the reaction to form aqueous acid, and the mixture at the outlet of the water washing tower 2 is continuously introduced into the alkali washing tower 3 to remove the trace HF that is not completely removed by the water washing tower 2, and then the obtained mixture containing unreacted HFC-236fa, HFO-1225zc and a small amount of HFC-143a is introduced into the drying tower 4 for drying, and the dried mixture containing unreacted HFC-236fa is dried. a, a mixture of HFO-1225zc and a small amount of HFC-143a is passed into a first distillation tower 5 for separation, unreacted HFC-236fa is separated from the bottom of the first distillation tower 5, and HFC-236fa is returned to the reactor 1 as a raw material to continue the reaction, and the top of the first distillation tower 5 is a mixture containing HFO-1225zc and a small amount of HFC-143a. The top mixture of the first distillation tower 5 is passed into a second distillation tower 6 for further separation, low boiling substances containing HFC-143a are separated from the top of the second distillation tower 6, and the target product HFO-1225zc is obtained at the bottom of the second distillation tower 6.

[0038] The technical scheme of the present invention is further clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0039] Example 1

[0040] 200 mL of Al2O3-Cr2O3 (Cr2O3 mass percentage is 40%) catalyst was introduced into HF for fluorination at 350°C for 30 hours to obtain an activated Al2O3-Cr2O3 catalyst. The activated Al2O3-Cr2O3 catalyst was then loaded into a reactor. The reactor was heated to 250°C and HFC-236fa was introduced into the reactor at a space velocity of 50 h -1 The reaction pressure was 0.1 MPa. The mixture at the reactor outlet was alkali washed and sampled for gas chromatography analysis. The HFC-236fa conversion rate was 47% and the HFO-1225zc selectivity was 99.0%.

[0041] Example 2

[0042] 200 mL of Bi2O3-Cr2O3 (Cr2O3 mass percentage is 50%) catalyst was introduced into HF for fluorination at 350°C for 30 hours to obtain an activated Bi2O3-Cr2O3 catalyst. The activated Bi2O3-Cr2O3 catalyst was then loaded into a reactor. The reactor was heated to 300°C and HFC-236fa was introduced into the reactor at a space velocity of 200 h / min. -1 The reaction pressure was 0.3 MPa. The mixture at the reactor outlet was alkali washed and sampled for gas chromatography analysis. The HFC-236fa conversion rate was 45% and the HFO-1225zc selectivity was 99.8%.

[0043] Example 3

[0044] 200 mL of CoO-Cr2O3 (Cr2O3 mass percentage is 60%) catalyst was introduced into HF for fluorination at 350°C for 30 hours to obtain an activated CoO-Cr2O3 catalyst. The activated CoO-Cr2O3 catalyst was then loaded into a reactor. The reactor was heated to 380°C and HFC-236fa was introduced into the reactor at a space velocity of 350 h -1 The reaction pressure was 0.6 MPa. The mixture at the reactor outlet was alkali washed and sampled for gas chromatography analysis. The HFC-236fa conversion rate was 48% and the HFO-1225zc selectivity was 99.4%.

[0045] Example 4

[0046] 200 mL of CoO-Cr2O3 (Cr2O3 mass percentage is 80%) catalyst was introduced into HF for fluorination at 350°C for 30 hours to obtain an activated CoO-Cr2O3 catalyst, and then the activated CoO-Cr2O3 catalyst was loaded into a reactor, the reactor was heated to 450°C, and HFC-236fa was introduced into the reactor at a space velocity of 500h -1 The reaction pressure was 1.0 MPa. The mixture at the reactor outlet was alkali washed and sampled for gas chromatography analysis. The HFC-236fa conversion rate was 52% and the HFO-1225zc selectivity was 99.1%.

[0047] Example 5

[0048] The operation method and reaction conditions are the same as those in Example 1. The difference is that the catalyst is different. Zn element is added to the Al2O3-Cr2O3 (Cr2O3 mass percentage is 40%) catalyst used in Example 1, and the mass percentage of Zn is 5%. The mixture at the reactor outlet is sampled after alkali washing and analyzed by gas chromatography. The HFC-236fa conversion rate is 50%, and the HFO-1225zc selectivity is 99.3%.

[0049] Example 6

[0050] The operation method and reaction conditions are the same as those in Example 2. The difference is that the catalyst is different. Ni element is added to the Bi2O3-Cr2O3 (Cr2O3 mass percentage is 50%) catalyst used in Example 1, and the mass percentage of Ni is 15%. The mixture at the reactor outlet is sampled after alkali washing and analyzed by gas chromatography. The HFC-236fa conversion rate is 56%, and the HFO-1225zc selectivity is 99.8%.

[0051] Example 7

[0052] The operation method and reaction conditions are the same as those in Example 3. The difference is that the catalyst is different. Mg element is added to the CoO-Cr2O3 (Cr2O3 mass percentage is 60%) catalyst used in Example 1, and the mass percentage of Mg is 20%. The mixture at the reactor outlet is sampled after alkali washing and analyzed by gas chromatography. The HFC-236fa conversion rate is 53%, and the HFO-1225zc selectivity is 99.2%.

Claims

1. A catalytic synthesis method of 1,1,3,3,3-pentafluoropropylene, characterized in that: The following steps are involved: (1) introducing a raw material 1,1,1,3,3,3-hexafluoropropane into a reactor and reacting under the action of a catalyst to obtain crude 1,1,3,3,3-pentafluoropropene, wherein the catalyst contains Cr2O3 and one of metal oxides of Al, Bi, and Co; (2) washing the crude 1,1,3,3,3-pentafluoropropene obtained in step (1) with water, alkali, and then drying it and passing it into a first distillation tower for separation, wherein unreacted 1,1,1,3,3,3-hexafluoropropane is obtained in the bottom of the first distillation tower, and a mixture containing 1,1,1,3,3-pentafluoropropene and a small amount of by-products is obtained at the top of the tower; (3) Passing the mixture containing 1,1,1,3,3-pentafluoropropene and a small amount of by-products obtained in step (2) into a second distillation tower for separation, separating the by-products at the top of the second distillation tower, and obtaining the 1,1,1,3,3-pentafluoropropene product at the bottom of the tower.

2. The catalytic synthesis method of 1,1,3,3,3-pentafluoropropylene according to claim 1, characterized in that: The catalyst is Al2O3-Cr2O3 or Bi2O3-Cr2O3 or CoO-Cr2O3.

3. The catalytic synthesis method of 1,1,3,3,3-pentafluoropropylene according to claim 2, characterized in that: The mass percentage of Cr2O3 in the catalyst is 40-80%.

4. The catalytic synthesis method of 1,1,3,3,3-pentafluoropropylene according to claim 1, 2 or 3, characterized in that: The catalyst is added with a modified metal, and the mass percentage of the modified metal is 5-20%.

5. The catalytic synthesis method of 1,1,3,3,3-pentafluoropropylene according to claim 4, characterized in that: The modified metal is one of Zn, Ni and Mg.

6. The catalytic synthesis method of 1,1,3,3,3-pentafluoropropylene according to claim 1, characterized in that: The reaction temperature is 250-450°C.

7. The catalytic synthesis method of 1,1,3,3,3-pentafluoropropylene according to claim 1, characterized in that: The reaction pressure is 0.1-1.0 MPa.

8. The catalytic synthesis method of 1,1,3,3,3-pentafluoropropylene according to claim 1, characterized in that: The reaction space velocity is 50 to 500 h -1 .

9. The catalytic synthesis method of 1,1,3,3,3-pentafluoropropylene according to claim 1, characterized in that: The unreacted 1,1,1,3,3,3-hexafluoropropane obtained in the bottom of the first distillation tower in step (2) is recycled back to the reactor.

10. The catalytic synthesis method of 1,1,3,3,3-pentafluoropropylene according to claim 1, characterized in that: The catalyst is pretreated with hydrogen fluoride gas before the reaction.

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