CN118698439A - A method for synthesizing 2,3,3,3-tetrafluoropropene - Google Patents

Abstract

The invention discloses a method for synthesizing 2,3,3,3-tetrafluoropropylene. The method comprises the following steps: continuously introducing 1,1,2,3,3,3-hexafluoropropylene, hydrogen and a diluent into a first reactor, reacting and separating to obtain 1,1,1,2,3,3-hexafluoropropane; introducing 1,1,1,2,3,3-hexafluoropropane into a second reactor, reacting and separating to obtain 1,2,3,3,3-pentafluoropropylene; introducing 1,2,3,3,3-pentafluoropropylene into the first reactor, and reacting with 1,1,2 ,3,3,3-hexafluoropropylene, hydrogen and a diluent react to obtain a mixture of 1,1,1,2,3,3-hexafluoropropane and 1,1,1,2,3-pentafluoropropane; after separation, 1,1,1,2,3,3-hexafluoropropane returns to the second reactor, and 1,1,1,2,3-pentafluoropropane enters the third reactor, and the final product 2,3,3,3-tetrafluoropropylene is obtained after reaction and separation. The present invention has the advantages of simple process, high reaction efficiency, low cost and green environmental protection.

Description

A kind of synthesis method of 2,3,3,3-tetrafluoropropene

Technical Field

The invention relates to a method for preparing fluorine-containing olefins, and in particular to a method for synthesizing 2,3,3,3-tetrafluoropropylene.

Background Art

It is urgent to develop and research green, efficient and low GWP refrigeration technology.

The fourth generation of new refrigerants mainly refers to fluorinated olefins (HFOs), which have the advantages of zero ODP and extremely low GWP. The representative product is 2,3,3,3-tetrafluoropropylene (HFO-1234yf, also known as R1234yf). HFO-1234yf has a boiling point of -29°C, an ODP value of 0, a GWP value of 4, and an atmospheric life of 11 days. It can be used as a refrigerant to replace HFC-134a for automotive air-conditioning systems. There are three main methods for the preparation of HFO-1234yf with industrial prospects: 3,3,3-trifluoropropylene method, 1,1,2,3,3,3-hexafluoropropylene (HFP) method and 1,1,2,3-tetrachloropropylene (TCP) method. Among them, the hexafluoropropylene process undergoes four steps, namely two steps of hydrogenation and two steps of dehydrofluorination, and has the advantages of easy raw materials, few by-products, and simple process, and is widely used in research.

For example, CN107011114A discloses a method for preparing HFO-1234yf from 1,1,2,3,3,3-hexafluoropropylene: (1) reacting HFP with hydrogen in the presence of a catalyst to produce 1,1,1,2,3,3-hexafluoropropane (HFC-236ea); (2) reacting HFC-236ea with an alkaline aqueous solution to obtain 1,2,3,3,3-pentafluoropropylene (HFO-1225ye); (3) in the presence of a catalyst, HFO-1225ye is reacted with hydrogen to produce 1,1,1,2,3-pentafluoropropane (HFC-245eb); (4) HFC-245eb is purified, and the purification step is to remove compounds having a boiling point that differs from the boiling point of HFO-1234yf by ±10°C; (5) HFC-245eb is reacted with an alkaline aqueous solution and purified to obtain HFO-1234yf. Although the liquid phase dehydrofluorination method is easy to operate, it has a long operation cycle, high product energy consumption, and high investment costs.

For example, CN101553453A, CN102026947A, CN102267869A, etc. disclose that HFO-1234yf is obtained by using hexafluoropropylene as the starting material through four steps of hydrogenation, dehydrofluorination, hydrogenation, dehydrofluorination, etc. The disadvantage is that the prior art has many and complicated process steps, large equipment investment, high separation cost, high energy consumption, or more three wastes.

Summary of the invention

In view of the deficiencies in the prior art, the present invention provides a method for synthesizing 2,3,3,3-tetrafluoropropylene which has simple process, low cost and is environmentally friendly.

In order to solve the above technical problems, the technical solution adopted by the present invention is: a method for synthesizing 2,3,3,3-tetrafluoropropene, comprising a synthesis device, the synthesis device comprising a first reactor, a second reactor, a third reactor, a first separation unit, a second separation unit and a third separation unit, the first reactor is provided with a basic raw material inlet, the outlet of the first reactor is connected to the inlet of the first separation unit, the first separation unit is provided with a first separation outlet, a second separation outlet and a third separation outlet, the first separation outlet is connected to the basic raw material inlet, the second separation outlet is connected to the inlet of the second reactor, the outlet of the second reactor is connected to the inlet of the second separation unit, the second separation unit is provided with a fourth separation outlet, a fifth separation outlet and a sixth separation outlet, the fourth separation outlet is connected to the basic raw material inlet, the third separation outlet is connected to the inlet of the third reactor, the outlet of the third reactor is connected to the inlet of the third separation unit, the third separation unit is provided with a seventh separation outlet, an eighth separation outlet and a ninth separation outlet, the specific synthesis method comprises the following steps:

(a) continuously introducing raw materials 1,1,2,3,3,3-hexafluoropropylene, hydrogen, and a diluent into the first reactor through the base raw material inlet, reacting under the action of a first catalyst to obtain a first reaction product;

(b) separating the first reaction product through the first separation unit to obtain 1,1,1,2,3,3-hexafluoropropane, a diluent and unreacted hydrogen;

(c) returning the diluent and unreacted hydrogen obtained in step (b) to the first reactor through the first separation outlet, and introducing 1,1,1,2,3,3-hexafluoropropane into the second reactor through the second separation outlet, and reacting the 1,1,1,2,3,3-hexafluoropropane under the action of the second catalyst to obtain a second reaction product;

(d) separating the second reaction product by the second separation unit to obtain 1,2,3,3,3-pentafluoropropylene, hydrogen fluoride and unreacted 1,1,1,2,3,3-hexafluoropropane;

(e) introducing the 1,2,3,3,3-pentafluoropropylene obtained in step (d) into the first reactor through the fourth separation outlet to react with 1,1,2,3,3,3-hexafluoropropylene, hydrogen and a diluent under the action of a first catalyst to obtain a reaction product;

(f) separating the reaction product obtained in step (e) by the first separation unit to obtain 1,1,1,2,3,3-hexafluoropropane, 1,1,1,2,3-pentafluoropropane, a diluent and unreacted hydrogen;

(g) returning the diluent and unreacted hydrogen obtained in step (f) to the first reactor through the first separation outlet, introducing 1,1,1,2,3,3-hexafluoropropane into the second reactor through the second separation outlet, introducing 1,1,1,2,3-pentafluoropropane into the third reactor through the third separation outlet, reacting under the action of a third catalyst to obtain a third reaction product;

(h) separating the third reaction product through the third separation unit to obtain a final product of 2,3,3,3-tetrafluoropropene, hydrogen fluoride and unreacted 1,1,1,2,3-pentafluoropropane, and outputting the final product 2,3,3,3-tetrafluoropropene through the seventh separation outlet.

As a preferred embodiment of the present invention, the first catalyst has Pd or Pt as a main component, and one or more selected from Ni, Fe, Au, Cu, and Al as auxiliary components. The main component and the auxiliary components are loaded on a carrier, and the carrier is one of activated carbon, titanium dioxide, alumina, and silicon dioxide. The loading amount of the main component is 0.01 to 0.3 wt% (wt%, mass percentage), and the loading amount of the auxiliary component is 0.001 to 0.5 wt%.

As a preferred embodiment of the present invention, the second catalyst has chromium as a main component and one or more selected from Zn, Co, Fe, In as auxiliary components. The main component and auxiliary components are loaded on _γ - _Al2O3 and/or _AlF3 carriers. The loading amount of chromium is 5-20wt%, and the loading amount of the auxiliary components is 1-5wt%.

As a preferred embodiment of the present invention, the third catalyst has chromium as a main component and one or more selected from Mg, Zn, Co, and Ga as auxiliary components. The main component and the auxiliary components are loaded on γ- _Al2O3 and/or _{AlF3 carriers} . The loading amount of chromium is 5 to 15 wt%, and the loading amount of the auxiliary components is 0.5 to 3 wt%.

As a preferred embodiment of the present invention, the molar ratio of 1,1,2,3,3,3-hexafluoropropylene, hydrogen and diluent in step (a) is 1:1-30:1-30, the temperature of the first reactor is 80-200°C, the pressure is 0.1-1.5 MPa, and the space velocity is 300-2000 h ^-1 .

As a preferred embodiment of the present invention, the temperature of the second reactor in step (c) is 150-400° C., the pressure is 0.1-1.5 MPa, and the space velocity is 30-1000 h ^-1 .

As a preferred embodiment of the present invention, the temperature of the third reactor in step (g) is 150-400° C., the pressure is 0.1-1.5 MPa, and the space velocity is 30-1000 h ^-1 .

As a preferred embodiment of the present invention, the diluent is one or more of 1,1-difluoroethane (HFC-152a), 1,1,1-trifluoroethane (HFC-143a), 1,1,1,2-tetrafluoroethane (HFC-134a), 1,1,1,2,2-pentafluoroethane (HFC-125), and 1,1,1,2,3,3,3-heptafluoropropane (HFC-227ea).

As a preferred embodiment of the present invention, the first separation unit adopts distillation operation, and the second separation unit and the third separation unit adopt acid removal and distillation operation.

As a preferred embodiment of the present invention, the unreacted 1,1,1,2,3,3-hexafluoropropane described in step (d) is circulated to the second reactor through the sixth separation outlet, and the unreacted 1,1,1,2,3-pentafluoropropane described in step (h) is circulated to the third reactor through the ninth separation outlet.

The present invention realizes the synthesis of HFO-1234yf using HFP as a raw material through three reactors. The first reactor mainly undergoes a hydrogenation reaction of HFP to obtain 1,1,1,2,3,3-hexafluoropropane (HFC-236ea) and a hydrogenation reaction of 1,2,3,3,3-pentafluoropropylene (HFO-1225ye) to obtain 1,1,1,2,3-pentafluoropropane (HFC-245eb). The second reactor mainly undergoes a dehydrofluorination reaction of HFC-236ea to obtain HFO-1225ye. The third reactor mainly undergoes a dehydrofluorination reaction of HFC-245eb to obtain HFO-1234yf. The main equations are as follows:

CF ₂ =CFCF ₃ (HFP) + H ₂ →CF ₂ HCHFCF ₃ (HFC-236ea)

CHF＝CFCF ₃ (HFO-1225ye)+H ₂ →CH ₂ FCHFCF ₃ (HFC-245eb)

CF ₂ HCHFCF ₃ (HFC-236ea)→CHF＝CFCF ₃ (HFO-1225ye)+HF

CH ₂ FCHFCF ₃ (HFC-245eb)→CH ₂ =CFCF ₃ (HFO-1234yf)+HF

The boiling points of some substances in the present invention are as follows:

name Abbreviation Molecular weight Boiling point/℃ 1,1,2,3,3,3-Hexafluoropropylene HFP 150 -29.6 1,1,1,2,3,3-Hexafluoropropane HFC-236ea 152 6.2 1,2,3,3,3-Pentafluoropropylene HFO-1225ye 132 -18.0 1,1,1,2,3-Pentafluoropropane HFC-245eb 134 23.0 2,3,3,3-Tetrafluoropropene HFO-1234yf 114 -29.4 hydrogen _H2 2 -252.7 Hydrogen fluoride HF 20 19.5

In the present invention, the first reactor can be a gas phase reactor. The starting raw materials HFP, _H2 and diluent are continuously introduced into the first reactor to obtain a mixture containing HFC-236ea, _H2 and diluent. The mixture is introduced into the first separation unit. The first separation unit can use at least two distillation towers according to actual production conditions. When two distillation towers are used, _H2 and diluent are separated from the top of the first distillation tower. H2 can be used as the diluent. ₂ and the diluent are returned to the first reactor for continued use, the HFC-236ea obtained in the bottom of the first distillation tower is passed into the second distillation tower, and the HFC-236ea separated at the top of the second distillation tower is passed into the second reactor; HFC-236ea undergoes dehydrofluorination reaction in the second reactor to obtain a mixture containing HFO-1225ye, HF and a small amount of HFC-236ea, and the mixture is passed into the second separation unit; the second separation unit can use at least one acid removal tower and one distillation tower according to actual production conditions. When one acid removal tower and one distillation tower are used for operation, HF is discharged from the bottom of the acid removal tower, and the top of the acid removal tower is a mixture containing HFC-236ea and HFO-1225ye. The mixture containing HFC-236ea and HFO-1225ye is passed into the distillation tower for separation, and the HFC-236ea obtained in the bottom of the distillation tower can be returned to the second reactor for continued reaction, and the HFO-1225ye obtained at the top of the tower is passed into the first reactor; HFO-1225ye and the starting raw materials HFP, H ₂ The mixture is introduced into a first separation unit (which can be operated by two distillation towers), and _H2 and diluent are separated at the top of the first distillation tower. _{The H2} and diluent can be returned to the first reactor for continued use. The HFC-236ea and HFC-245eb obtained in the bottom of the first distillation tower are introduced into a second distillation tower, and the HFC-236ea separated at the top of the second distillation tower is introduced into a second reactor, and the HFC-245eb separated in the bottom of the second distillation tower is introduced into a third reactor; HFC-245eb is subjected to a dehydrofluorination reaction in the third reactor to obtain a mixture containing HFO-1234yf, HF and a small amount of HFC-245eb, and the mixture is introduced into the third distillation tower. The third separation unit can adopt at least one acid removal tower and one distillation tower according to the actual production situation. When one acid removal tower and one distillation tower are used for operation, HF is discharged from the bottom of the acid removal tower, and the top of the acid removal tower is a mixture containing HFC-245eb and HFO-1234yf. The mixture containing HFC-245eb and HFO-1234yf is passed into the distillation tower for separation, and HFC-245eb is obtained in the distillation tower kettle, which can be returned to the third reactor for further reaction, and the target product HFO-1234yf is obtained at the top of the tower.

In the present invention, the first reactor mainly undergoes HFP hydrogenation reaction and HFO-1225ye hydrogenation reaction, and the reaction is a strong exothermic reaction. Adding a diluent can take away the heat released by the reaction, thereby reducing the temperature of the system, making the reaction more stable and controllable, and preventing the local temperature of the reaction from being too high, causing the catalyst to coke and deactivate. Selecting an appropriate diluent is one of the keys to achieving a strong exothermic reaction to be carried out efficiently and smoothly. In the present invention, a fluorinated substance with a lower boiling point is selected as a diluent, preferably one or more of 1,1-difluoroethane (HFC-152a), 1,1,1-trifluoroethane (HFC-143a), 1,1,1,2-tetrafluoroethane (HFC-134a), 1,1,1,2,2-pentafluoroethane (HFC-125), and 1,1,1,2,3,3,3-heptafluoropropane (HFC-227ea).

In the present invention, the reaction temperature of the first reactor has a great influence on the activity of the catalyst and the selectivity of the product. The increase in reaction temperature is conducive to the improvement of the activity of the catalyst. However, since hydrogenation is easier to carry out, the conversion rate of the raw material and the selectivity of the product can reach 100% at a lower temperature. Considering the industrial application value of the catalyst, while ensuring the high activity of the catalyst, the reaction temperature should be reduced as much as possible to reduce energy consumption. Therefore, the reaction temperature of the first reactor is preferably 80-200°C, and the reaction temperature is more preferably 90-150°C. With the increase of the space velocity, the contact time between the reactant and the catalyst bed is reduced, and the activity of the catalyst decreases. To ensure that the raw material is completely converted, the space velocity is preferably 300-2000h ^-1 , and more preferably 500-1000h ^-1 . The molar ratio of HFP, _H2 and diluent has a great influence on the reaction. Increasing the molar ratio of _H2 and HFP can effectively improve the selectivity and stability of the catalyst, and gradually increase the activity of the catalyst to completely convert HFP. At the same time, excessive _H2 and diluent can take away the heat of the reaction, which helps to prevent carbon deposition on the catalyst. The diluent can play a role in regulating the reaction heat, improving the catalyst dispersibility and preventing the catalyst from carbonizing, but excessive diluent will reduce the efficiency of the reaction. Therefore, the molar ratio of HFP, _H2 and diluent is preferably 1:1-30:1-30, more preferably 1:1-20:1-20.

In the present invention, the second reactor mainly undergoes gas phase dehydrofluorination reaction of HFC-236ea. The temperature is high and the conversion rate of HFC-236ea is high, 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 150-400°C, more preferably 180-300°C; the space velocity is preferably 30-1000h ^-1 , more preferably 100-800h ^-1 .

In the present invention, the third reactor mainly undergoes gas phase dehydrofluorination of HFC-245eb. The reaction temperature of the third reactor is preferably 150-400°C, more preferably 180-300°C; the space velocity is preferably 30-1000h ^-1 , more preferably 100-800h ^-1 .

The first reactor of the present invention is filled with a precious metal Pd or Pt and an auxiliary metal composite catalyst. The precious metal loading is too low, the catalytic activity is insufficient, and there is an optimal balance between the precious metal content and the activity of the catalyst. The selection of the carrier is more important for the catalyst. Activated carbon, titanium dioxide, aluminum oxide or silicon dioxide are selected as the carrier. The addition of auxiliary metals such as Ni, Fe, Au, Cu, Al, etc. is conducive to making the loaded catalytic active centers Pd and Pt have high dispersion, so as to obtain a high-activity catalyst. It is found through experiments that the catalyst precious metal Pd or Pt loading in the first reactor is preferably 0.01-0.3%, and the auxiliary metal loading is preferably 0.001-0.5%.

The catalyst used in the second reactor and the third reactor of the present invention can be a catalyst with chromium as an active component known in the art, with γ-Al ₂ O ₃ and/or AlF ₃ as the carrier, and one or more auxiliary metals of Mg, Zn, Co, Fe, In, and Ga are added to increase the dispersion of chromium. The preparation method of the catalyst can adopt the conventional method in the art: for example, chromium and the nitrate of the auxiliary metal 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, calcined, granulated, and tableted into a precursor, and the catalyst is obtained after fluorination. The pretreatment of the catalyst can be carried out in other reactors.

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

1. The process is simple and the reaction efficiency is high. The present invention improves the reaction efficiency by optimizing the reaction process, catalyst and material ratio, reaction temperature and pressure, space velocity and other parameters. The reaction temperature and reaction pressure are relatively low, the reaction conditions are mild and easy to control, the operation is significantly simplified, and the energy consumption is reduced. At the same time, the reaction temperature can be controlled by adding a diluent, so that the reaction is more stable and controllable, the temperature inside the equipment is reduced, the thermal damage to the catalyst and the equipment is reduced, and the reaction efficiency is further improved.

2. Small investment in equipment and low operating cost. The raw materials HFP and _H2 used in the present invention are widely available, which significantly reduces the cost of raw materials in the production process. By optimizing the process, the hydrogenation reaction of HFP and the hydrogenation reaction of HFO-1225ye are carried out in the same reactor. Compared with two-step reactions in two independent reactors, the use of the same reactor can save space and reduce equipment and operating costs.

3. Green and environmentally friendly, with less three wastes. The raw materials and intermediate products that have not reacted completely can be recycled into the reactor to continue the reaction, which can not only improve production efficiency and resource utilization, but also has significant environmental advantages, reducing the discharge of three wastes such as waste water, waste gas and waste residue, and helping to achieve green production and sustainable development.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a process flow chart of the present invention.

In the figure: 1 is the first reactor, 2 is the second reactor, 3 is the third reactor, 4 is the first distillation tower, 5 is the second distillation tower, 6 is the first acid removal tower, 7 is the third distillation tower, 8 is the second acid removal tower, and 9 is the fourth distillation tower.

DETAILED DESCRIPTION

The synthesis device and process of the present invention are shown in Figure 1. The synthesis device includes a first reactor 1, a second reactor 2, a third reactor 3, a first separation unit consisting of a first distillation tower 4 and a second distillation tower 5, a second separation unit consisting of a first acid removal tower 6 and a third distillation tower 7, and a third separation unit consisting of a second acid removal tower 8 and a fourth distillation tower 9. A reaction raw material inlet is arranged at the top of the first reactor 1, a product outlet at the bottom of the first reactor 1 is connected to the material inlet of the first distillation tower 4, a tower bottom material outlet of the first distillation tower 4 is connected to the material inlet of the second distillation tower 5, a tower top material outlet of the first distillation tower 4 is connected to the reaction raw material inlet of the first reactor 1, a tower top material outlet of the second distillation tower 5 is connected to the material inlet of the second reactor 2, and a product outlet at the bottom of the second reactor 2 is connected to the The material inlet of the first acid-removal tower 6 is connected, the bottom of the first acid-removal tower 6 is provided with an HF outlet, the top material outlet of the first acid-removal tower 6 is connected to the material inlet of the third distillation tower 7, the top material outlet of the third distillation tower 7 is connected to the reaction raw material inlet of the first reactor 1, the bottom material outlet of the third distillation tower 7 is connected to the material inlet of the second reactor 2, the bottom material outlet of the second distillation tower 5 is connected to the material inlet of the third reactor 3, the material outlet of the third reactor 3 is connected to the material inlet of the second acid-removal tower 8, the bottom of the second acid-removal tower 8 is provided with an HF outlet, the top material outlet of the second acid-removal tower 8 is connected to the material inlet of the fourth distillation tower 9, the top of the fourth distillation tower 9 is provided with a product outlet, and the bottom material outlet of the fourth distillation tower 9 is connected to the material inlet of the third reactor 3. The specific process flow of synthesizing 2,3,3,3-tetrafluoropropene is as follows: starting raw materials HFP, _H2 , and diluent are continuously introduced into the first reactor 1 through the reaction raw material inlet to obtain a mixture containing HFC-236ea, _H2 , and diluent, etc., and the mixture is introduced into the first distillation tower 4, and the diluent and unreacted _H2 are separated from the top of the first distillation tower 4, and the diluent and unreacted H2 are separated from the top of the first distillation tower 4. ₂ is returned to the first reactor 1 for continued use, the HFC-236ea obtained in the bottom of the first distillation tower 4 is passed into the second distillation tower 5; the HFC-236ea separated at the top of the second distillation tower 5 is passed into the second reactor 2 for dehydrofluorination reaction to obtain a mixture containing HFO-1225ye, HF and a small amount of HFC-236ea, and the mixture is passed into the first acid removal tower 6; the HF separated in the bottom of the first acid removal tower 6 can be discharged regularly, and a mixture containing HFC-236ea and HFO-1225ye is separated at the top of the first acid removal tower 6, and the mixture containing HFC-236ea and HFO-1225ye is passed into the third distillation tower 7 for separation, and the HFC-236ea obtained at the bottom of the third distillation tower 7 is returned to the second reactor 2 for continued reaction, and the HFO-1225ye obtained at the top of the third distillation tower 7 is passed into the first reactor 1; HFO-1225ye is mixed with the starting raw materials HFP and H ₂ The mixture is introduced into a first distillation tower 4, and _H2 and the diluent are separated from the top of the first distillation tower 4. _{The H2} and the diluent can be returned to the first reactor 1 for continued use. The HFC-236ea and HFC-245eb obtained in the bottom of the first distillation tower 4 are introduced into a second distillation tower 5, and the HFC-236ea separated from the top of the second distillation tower 5 is introduced into a second reactor 2, and the HFC-245eb separated from the bottom of the tower is introduced into a third reactor 3. The HFC-245eb is subjected to a dehydrofluorination reaction in the third reactor 3 to obtain a mixture containing HFO-1234yf, HF and a small amount of HFC-245eb. The mixture is passed into the second acid removal tower 8; HF is discharged from the bottom of the second acid removal tower 8, and a mixture containing HFC-245eb and HFO-1234yf is separated at the top of the second acid removal tower 8. The mixture containing HFC-245eb and HFO-1234yf is passed into the fourth distillation tower 9 for further separation, and the target product HFO-1234yf is obtained at the top of the fourth distillation tower 9, and HFC-245eb is obtained in the bottom of the fourth distillation tower 9. HFC-245eb is returned to the third reactor 3 to continue the reaction.

The technical solutions in the present invention are further described clearly and completely in combination with the embodiments below. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments in 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.

Example 1

First, 200 ml of Pd-Ni/C catalyst (the mass percentage of Pd is 0.01% and the mass percentage of Ni is 0.001%) is loaded into the first reactor, 300 ml of Cr-In/γ- _{Al2O3 catalyst} (the mass percentage of Cr is 5% and the mass percentage of In is 1%) is loaded into the second reactor, and ₃₀₀ ml of Cr-Mg/γ- _Al2O3 catalyst (the mass percentage of Cr is 5% and the mass percentage of Mg is 0.5%) is loaded into the third reactor.

Then, each reactor began to heat up, and after the heating was completed, nitrogen was introduced to dry for 2 hours; then the feeding reaction began, and HFP, _H2 and diluent (HFC-152a) were continuously introduced into the first reactor. The reaction conditions of each reactor are shown in Table 1.

After the reaction stabilized, samples were taken from the outlets of the first reactor, the second reactor, and the third reactor. The organic composition was analyzed by gas chromatography, and is shown in Table 2.

Table 1 Reaction conditions of each reactor in Example 1

Table 2 Composition of organic matter at the outlet of each reactor in Example 1

Example 2

First, 200 ml of Pd-Fe/ _TiO2 catalyst (the mass percentage of Pd is 0.1% and the mass percentage of Fe is 0.01%) is loaded into the first reactor, 300 ml of Cr-Zn/ _AlF3 catalyst (the mass percentage of Cr is 10% and the mass percentage of Zn is 2%) is loaded into the second reactor, and 300 ml of Cr-Zn/ _AlF3 catalyst (the mass percentage of Cr is 8% and the mass percentage of Zn is 1%) is loaded into the third reactor.

Then, each reactor began to heat up, and after the heating was completed, nitrogen was introduced to dry for 2 hours; then the feeding reaction began, and HFP, _H2 and diluent (HFC-143a) were continuously introduced into the first reactor. The reaction conditions of each reactor are shown in Table 3.

After the reaction stabilized, samples were taken from the outlets of the first reactor, the second reactor, and the third reactor. The organic composition was analyzed by gas chromatography, and is shown in Table 4.

Table 3 Reaction conditions of each reactor in Example 2

Table 4 Composition of organic matter at the outlet of each reactor in Example 2

Example 3

First, 200 ml of Pd-Cu/Al ₂ O ₃ catalyst (the mass percentage of Pd is 0.3% and the mass percentage of Cu is 0.1%) is loaded into the first reactor, 300 ml of Cr-Co/γ-Al ₂ O ₃ catalyst (the mass percentage of Cr is 15% and the mass percentage of Co is 4%) is loaded into the second reactor, and 300 ml of Cr-Co/γ-Al ₂ O ₃ catalyst (the mass percentage of Cr is 12% and the mass percentage of Co is 2%) is loaded into the third reactor.

Then, each reactor began to heat up, and after the heating was completed, nitrogen was introduced to dry for 2 hours; then the feeding reaction began, and HFP, _H2 and diluent (HFC-134a) were continuously introduced into the first reactor. The reaction conditions of each reactor are shown in Table 5.

After the reaction stabilized, samples were taken from the outlets of the first reactor, the second reactor, and the third reactor. The organic composition was analyzed by gas chromatography, as shown in Table 6.

Table 5 Reaction conditions of each reactor in Example 3

Table 6 Composition of organic matter at the outlet of each reactor in Example 3

Example 4

First, 200 ml of Pt-Al/ _SiO2 catalyst (the mass percentage of Pt is 0.2% and the mass percentage of Al is 0.5%) is loaded into the first reactor, 300 ml of Cr-Fe/ _AlF3 catalyst (the mass percentage of Cr is 20% and the mass percentage of Fe is 5%) is loaded into the second reactor, and 300 ml of Cr-Ga/ _AlF3 catalyst (the mass percentage of Cr is 15% and the mass percentage of Ga is 3%) is loaded into the third reactor.

Then, each reactor began to heat up, and after the heating was completed, nitrogen was introduced to dry for 2 hours; then the feeding reaction began, and HFP, _H2 and diluent (HFC-125) were continuously introduced into the first reactor. The reaction conditions of each reactor are shown in Table 7.

After the reaction stabilized, samples were taken from the outlets of the first reactor, the second reactor, and the third reactor. The organic composition was analyzed by gas chromatography, as shown in Table 8.

Table 7 Reaction conditions of each reactor in Example 4

Table 8 Organic matter composition at the outlet of each reactor in Example 4

Claims (10)

1. A method for synthesizing 2,3,3,3-tetrafluoropropene, comprising a synthesis device, characterized in that the synthesis device comprises a first reactor, a second reactor, a third reactor, a first separation unit, a second separation unit and a third separation unit, the first reactor is provided with a basic raw material inlet, the outlet of the first reactor is connected to the inlet of the first separation unit, the first separation unit is provided with a first separation outlet, a second separation outlet and a third separation outlet, the first separation outlet is connected to the basic raw material inlet, the second separation outlet is connected to the inlet of the second reactor, the outlet of the second reactor is connected to the inlet of the second separation unit, the second separation unit is provided with a fourth separation outlet, a fifth separation outlet and a sixth separation outlet, the fourth separation outlet is connected to the basic raw material inlet, the third separation outlet is connected to the inlet of the third reactor, the outlet of the third reactor is connected to the inlet of the third separation unit, the third separation unit is provided with a seventh separation outlet, an eighth separation outlet and a ninth separation outlet, and the specific synthesis method comprises the following steps: (a) continuously introducing raw materials 1,1,2,3,3,3-hexafluoropropylene, hydrogen, and a diluent into the first reactor through the base raw material inlet, reacting under the action of a first catalyst to obtain a first reaction product; (b) separating the first reaction product through the first separation unit to obtain 1,1,1,2,3,3-hexafluoropropane, a diluent and unreacted hydrogen; (c) returning the diluent and unreacted hydrogen obtained in step (b) to the first reactor through the first separation outlet, and introducing 1,1,1,2,3,3-hexafluoropropane into the second reactor through the second separation outlet, and reacting the 1,1,1,2,3,3-hexafluoropropane under the action of the second catalyst to obtain a second reaction product; (d) separating the second reaction product by the second separation unit to obtain 1,2,3,3,3-pentafluoropropylene, hydrogen fluoride and unreacted 1,1,1,2,3,3-hexafluoropropane; (e) introducing the 1,2,3,3,3-pentafluoropropylene obtained in step (d) into the first reactor through the fourth separation outlet to react with 1,1,2,3,3,3-hexafluoropropylene, hydrogen and a diluent under the action of a first catalyst to obtain a reaction product; (f) separating the reaction product obtained in step (e) by the first separation unit to obtain 1,1,1,2,3,3-hexafluoropropane, 1,1,1,2,3-pentafluoropropane, a diluent and unreacted hydrogen; (g) returning the diluent and unreacted hydrogen obtained in step (f) to the first reactor through the first separation outlet, introducing 1,1,1,2,3,3-hexafluoropropane into the second reactor through the second separation outlet, introducing 1,1,1,2,3-pentafluoropropane into the third reactor through the third separation outlet, reacting under the action of a third catalyst to obtain a third reaction product; (h) separating the third reaction product through the third separation unit to obtain a final product of 2,3,3,3-tetrafluoropropene, hydrogen fluoride and unreacted 1,1,1,2,3-pentafluoropropane, and outputting the final product 2,3,3,3-tetrafluoropropene through the seventh separation outlet. 2. The method for synthesizing 2,3,3,3-tetrafluoropropene according to claim 1, characterized in that the first catalyst has Pd or Pt as a main component and one or more selected from Ni, Fe, Au, Cu, and Al as an auxiliary component, the main component and the auxiliary component are loaded on a carrier, the carrier is one of activated carbon, titanium dioxide, aluminum oxide, and silicon dioxide, the loading amount of the main component is 0.01 to 0.3 wt%, and the loading amount of the auxiliary component is 0.001 to 0.5 wt%. 3. The method for synthesizing 2,3,3,3-tetrafluoropropene according to claim 1, characterized in that the second catalyst has chromium as a main component and one _or more selected from Zn, Co, Fe, In as auxiliary components, the main component and the auxiliary component are loaded on γ- _Al2O3 and/or _AlF3 carriers, the loading amount of chromium is 5-20wt%, and the loading amount of the auxiliary component is 1-5wt%. 4. The method for synthesizing 2,3,3,3-tetrafluoropropene according to claim 1, characterized in that the third catalyst has chromium as a main component and one _or more selected from Mg, Zn, Co, and Ga as auxiliary components, the main component and the auxiliary component are loaded on γ- _Al2O3 and/or _AlF3 carriers, the loading amount of chromium is 5 to 15wt%, and the loading amount of the auxiliary component is 0.5 to 3wt%. 5. The method for synthesizing 2,3,3,3-tetrafluoropropene according to claim 1, characterized in that the molar ratio of 1,1,2,3,3,3-hexafluoropropene, hydrogen and diluent in step (a) is 1:1-30:1-30, the temperature of the first reactor is 80-200°C, the pressure is 0.1-1.5 MPa, and the space velocity is 300-2000 h ^-1 . 6 . The method for synthesizing 2,3,3,3-tetrafluoropropene according to claim 1 , characterized in that the temperature of the second reactor in step (c) is 150-400° C., the pressure is 0.1-1.5 MPa, and the space velocity is 30-1000 h ⁻¹ . 7. The method for synthesizing 2,3,3,3-tetrafluoropropene according to claim 1, characterized in that the temperature of the third reactor in step (g) is 150-400°C, the pressure is 0.1-1.5 MPa, and the space velocity is 30-1000 h ^-1 . 8. The method for synthesizing 2,3,3,3-tetrafluoropropene according to claim 1, characterized in that the diluent is one or more of 1,1-difluoroethane, 1,1,1-trifluoroethane, 1,1,1,2-tetrafluoroethane, 1,1,1,2,2-pentafluoroethane, and 1,1,1,2,3,3,3-heptafluoropropane. 9. The method for synthesizing 2,3,3,3-tetrafluoropropene according to claim 1, characterized in that the first separation unit adopts distillation operation, and the second separation unit and the third separation unit adopt acid removal and distillation operations. 10. The method for synthesizing 2,3,3,3-tetrafluoropropene according to claim 1, characterized in that the unreacted 1,1,1,2,3,3-hexafluoropropane described in step (d) is circulated to the second reactor through the sixth separation outlet, and the unreacted 1,1,1,2,3-pentafluoropropane described in step (h) is circulated to the third reactor through the ninth separation outlet.