CN118698439A

CN118698439A - Synthesis method of 2, 3-tetrafluoropropene

Info

Publication number: CN118698439A
Application number: CN202410399197.4A
Authority: CN
Inventors: 葛文锋; 洪江永; 童超丽; 张彦; 任亚文; 赵阳; 吴斌; 余慧梅; 熊显云
Original assignee: Zhejiang Quhua Fluor Chemistry Co Ltd
Current assignee: Zhejiang Quhua Fluor Chemistry Co Ltd
Priority date: 2024-04-03
Filing date: 2024-04-03
Publication date: 2024-09-27

Abstract

The invention discloses a method for synthesizing 2, 3-tetrafluoropropene, continuously introducing 1,2, 3-hexafluoropropylene, hydrogen and a diluent into a first reactor, reacting and separating to obtain 1,2, 3-hexafluoropropane; 1,2, 3-hexafluoropropane is introduced into a second reactor, and 1,2, 3-pentafluoropropene is obtained through reaction and separation; 1,2, 3-pentafluoropropene is introduced into a first reactor, with 1,2, 3-hexafluoropropylene reacting the hydrogen and the diluent to obtain a mixture containing 1,2, 3-hexafluoropropane and 1,2, 3-pentafluoropropane; after separation, the 1,2, 3-hexafluoropropane returns to the second reactor, the 1,2, 3-pentafluoropropane enters the third reactor, the final product 2, 3-tetrafluoropropene is obtained through reaction and separation, and the method has the advantages of simple process, high reaction efficiency, low cost and environment friendliness.

Description

Synthesis method of 2, 3-tetrafluoropropene

Technical Field

The invention relates to a preparation method of fluorine-containing olefin, in particular to a synthesis method of 2, 3-tetrafluoropropene.

Background

Development and research of green and efficient low GWP refrigeration technology is urgent.

The fourth generation novel refrigerant mainly refers to fluorine-containing olefins (HFOs), has the advantages of zero ODP, extremely low GWP value and the like, represents 2, 3-tetrafluoropropene (HFO-1234 yf, also can be written as R1234 yf), has the boiling point of-29 ℃, has the ODP value of 0, has the GWP value of 4 and has the atmospheric service life of 11 days, and can be used as a refrigerant to replace HFC-134a for an automobile air conditioning system. The preparation method of HFO-1234yf has industrialized prospect mainly comprises three steps: 3, 3-trifluoropropene process, 1,2, 3-Hexafluoropropylene (HFP) process, and 1,2, 3-Tetrachloropropene (TCP) process. The hexafluoropropylene process has the advantages of easily available raw materials, less byproducts and simple process through four steps of reactions, namely two steps of hydrogenation and two steps of dehydrofluorination, and is widely applied and researched.

A process for preparing HFO-1234yf from 1,2, 3-hexafluoropropylene is disclosed as CN107011114 a: (1) Reacting HFP with hydrogen in the presence of a catalyst to produce 1,2, 3-hexafluoropropane (HFC-236 ea); (2) Reacting HFC-236ea with an aqueous alkaline solution to produce 1,2, 3-pentafluoropropene (HFO-1225 ye); (3) Reacting HFO-1225ye with hydrogen in the presence of a catalyst to produce 1,2, 3-pentafluoropropane (HFC-245 eb); (4) Purifying HFC-245eb by removing a compound having a boiling point that differs from the boiling point of HFO-1234yf by + -10 ℃; (5) HFC-245eb is reacted with an aqueous alkaline solution and purified to yield HFO-1234yf. Although the liquid phase dehydrofluorination method is convenient to operate, the operation period is long, the product energy consumption is high, and the investment cost is high.

Also, for example, CN101553453A, CN102026947A, CN102267869A discloses that HFO-1234yf is obtained from hexafluoropropylene as the starting material by four steps of hydrogenation, dehydrofluorination, hydrogenation, dehydrofluorination and the like. The defects of the prior art are that the process steps are more and complex, the equipment investment is large, the separation cost is high, the energy consumption is high, the three wastes are discharged more, and the like.

Disclosure of Invention

Aiming at the defects of the prior art, the invention provides a synthesis method of 2, 3-tetrafluoropropene, which has the advantages of simple process, low cost and environmental protection.

In order to solve the technical problems, the invention adopts the following technical scheme: a process for the synthesis of 2, 3-tetrafluoropropene comprising a synthesis apparatus comprising a first reactor, a second reactor, a third reactor, a first separation unit, a second separation unit and a third separation unit, said first reactor being provided with a base stock inlet, said first reactor outlet being connected to said first separation unit inlet, said first separation unit being provided with a first separator outlet, a second separator outlet and a third separator outlet, said first separator outlet being connected to said base stock inlet, said second separator outlet being connected to said second reactor inlet, said second reactor outlet being connected to said second separation unit inlet, said second separation unit being provided with a fourth separator outlet, a fifth separator outlet and a sixth separator outlet, said fourth separator outlet being connected to said base stock inlet, said third separator outlet being connected to said third reactor outlet, said third separator outlet being connected to said third separator outlet, said eighth separator outlet being provided with a third separator outlet, said eighth separator outlet, said method comprising the steps of:

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

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

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

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

(e) Introducing the 1,2, 3-pentafluoropropene obtained in the step (d) into the first reactor through the fourth separator outlet, and reacting with 1,2, 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 the step (e) by the first separation unit to obtain 1,2, 3-hexafluoropropane, 1,2, 3-pentafluoropropane, a diluent and unreacted hydrogen;

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

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

As a preferred embodiment of the invention, pd or Pt is used as a main component, one or more selected from Ni, fe, au, cu, al is used as an auxiliary component, the main component and the auxiliary component are loaded on a carrier, the carrier is one of active carbon, titanium dioxide, alumina and silicon dioxide, the loading of the main component is 0.01-0.3 wt% (wt%, the mass percentage content) and the loading of the auxiliary component is 0.001-0.5 wt%.

As a preferred embodiment of the invention, the second catalyst takes chromium as a main component and one or more selected from Zn, co, fe, in as an auxiliary component, the main component and the auxiliary component are loaded on a gamma-Al ₂O₃ and/or AlF ₃ carrier, the loading of the chromium is 5-20wt%, and the loading of the auxiliary component is 1-5wt%.

As a preferred embodiment of the invention, the third catalyst takes chromium as a main component and one or more selected from Mg, zn, co, ga as an auxiliary component, the main component and the auxiliary component are loaded on a gamma-Al ₂O₃ and/or AlF ₃ carrier, the loading of the chromium is 5-15 wt%, and the loading of the auxiliary component is 0.5-3 wt%.

As a preferred embodiment of the invention, the molar ratio of the 1,2, 3-hexafluoropropylene, the hydrogen and the diluent in the step (a) is 1:1-30:1-30, the temperature of the first reactor is 80-200 ℃, 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 to 400 ℃, the pressure is 0.1 to 1.5MPa, and the space velocity is 30 to 1000h ^-1.

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

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

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

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

The invention realizes the synthesis of HFO-1234yf by taking HFP as raw material through three reactors, the first reactor mainly carries out HFP hydrogenation reaction to obtain 1,2, 3-hexafluoropropane (HFC-236 ea) and hydrogenation of 1,2, 3-pentafluoropropene (HFO-1225 ye) to produce 1,2, 3-pentafluoropropane (HFC-245 eb), the second reactor is mainly subjected to HFC-236ea dehydrofluorination reaction to obtain HFO-1225ye, and the third reactor is mainly subjected to HFC-245eb dehydrofluorination reaction to obtain HFO-1234yf, wherein the main equation is as follows:

CF₂＝CFCF₃(HFP)+H₂→CF₂HCHFCF₃(HFC-236ea)

CHF＝CFCF₃(HFO-1225ye)+H₂→CH₂FCHFCF₃(HFC-245eb)

CF₂HCHFCF₃(HFC-236ea)→CHF＝CFCF₃(HFO-1225ye)+HF

CH₂FCHFCF₃(HFC-245eb)→CH₂＝CFCF₃(HFO-1234yf)+HF

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

Name of the name	Shorthand	Molecular weight	Boiling point/. Degree.C
				1,2, 3-Hexafluoropropylene	HFP	150	-29.6
1,2, 3-Hexafluoropropane	HFC-236ea	152	6.2
				1,2, 3-Pentafluoropropene	HFO-1225ye	132	-18.0
1,2, 3-Pentafluoropropane	HFC-245eb	134	23.0
				2, 3-Tetrafluoropropene	HFO-1234yf	114	-29.4
Hydrogen gas	H₂	2	-252.7
				Hydrogen fluoride	HF	20	19.5

In the invention, a gas phase reactor can be adopted as the first reactor, the starting materials HFP, H ₂ and the diluent are continuously introduced into the first reactor to obtain a mixture containing HFC-236ea, H ₂, the diluent and the like, and the mixture is introduced into the first separation unit; The first separation unit can adopt at least two rectifying towers according to actual production conditions, when the two rectifying towers are adopted for operation, H ₂ and a diluent are separated from the top of the first rectifying tower, H ₂ and the diluent can be returned to the first reactor for continuous use, HFC-236ea obtained from the bottom of the first rectifying tower is introduced into the second rectifying tower, HFC-236ea is separated from the top of the second rectifying tower and introduced into the second reactor; Dehydrofluorination of HFC-236ea in a second reactor to obtain a mixture comprising HFO-1225ye, HF and a small amount of HFC-236ea, and passing the mixture to a second separation unit; the second separation unit can adopt at least one acid removal tower and one rectifying tower according to actual production conditions, when the acid removal tower and the rectifying tower are adopted for operation, HF is discharged from the bottom of the acid removal tower, 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 introduced into the rectifying tower for separation, HFC-236ea obtained from the tower bottom of the rectifying tower can be returned to the second reactor for continuous reaction, and HFO-1225ye obtained from the tower top is introduced into the first reactor; The HFO-1225ye and the starting materials HFP, H ₂ and the diluent are subjected to hydrogenation reaction in a first reactor to obtain a mixture containing HFC-236ea, HFC-245eb, H ₂, the diluent and the like, the mixture is fed into a first separation unit (which can be operated by two rectifying towers), H ₂ and the diluent are separated from the top of the first rectifying tower, H ₂ and a diluent can be returned to the first reactor for continuous use, HFC-236ea and HFC-245eb obtained from the tower kettle of the first rectifying tower are introduced into the second rectifying tower, HFC-236ea separated from the top of the second rectifying tower is introduced into the second reactor, and HFC-245eb separated from the tower kettle of the second rectifying tower is introduced into the third reactor; Dehydrofluorination of HFC-245eb in a third reactor to obtain a mixture comprising HFO-1234yf, HF and a small amount of HFC-245eb, and passing the mixture to a third separation unit; the third separation unit can adopt at least one acid removal tower and one rectifying tower according to actual production conditions, when the acid removal tower and the rectifying tower are adopted for operation, HF is discharged from the bottom of the acid removal tower, 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 introduced into the rectifying tower for separation, HFC-245eb is obtained at the bottom of the rectifying tower, and the mixture can be returned to the third reactor for continuous reaction, and the target product HFO-1234yf is obtained at the top of the rectifying tower.

In the invention, the first reactor mainly generates HFP hydrogenation reaction and HFO-1225ye hydrogenation reaction, the reaction is strong exothermic reaction, and the diluent is added to take away the heat released by the reaction, thereby reducing the temperature of the system, leading the reaction to be more stable and controllable, and preventing the catalyst from coking and inactivating due to overhigh local temperature of the reaction. The choice of an appropriate diluent is one of the keys to achieve efficient and smooth progress of the strongly exothermic reaction. In the invention, fluorine-containing substances with lower boiling points are selected as diluents, preferably 1, 1-difluoroethane (HFC-152 a), 1-trifluoroethane (HFC-143 a), 1, 2-tetrafluoroethane (HFC-134 a) 1, 2-pentafluoroethane (HFC-125) one or more of 1,2, 3-heptafluoropropane (HFC-227 ea).

In the invention, the reaction temperature of the first reactor has a larger influence on the activity of the catalyst and the selectivity of the product, the reaction temperature is increased, which is favorable for improving the activity of the catalyst, but the hydrogenation is easier to carry out, the conversion rate of raw materials and the selectivity of the product can reach 100 percent at lower temperature, the industrial application value of the catalyst is considered, the reaction temperature is reduced as much as possible while the high activity of the catalyst is ensured, and the energy consumption is reduced, so the reaction temperature of the first reactor is preferably 80-200 ℃, and the reaction temperature is more preferably 90-150 ℃. With the increase of the space velocity, the contact time of the reactant and the catalyst bed is reduced, the activity of the catalyst is reduced, the space velocity is preferably 300-2000H ^-1, more preferably 500-1000H ^-1.HFP、H₂, and the molar ratio of the diluent has great influence on the reaction, the increase of the molar ratio of H ₂ and HFP can effectively improve the selectivity and stability of the catalyst, the activity of the catalyst is gradually increased, and the HFP is completely converted. Meanwhile, the excessive H ₂ and the diluent can take away the heat of reaction, thereby being beneficial to preventing the carbon deposition of the catalyst. The diluent may play a role in adjusting the reaction heat, improving the catalyst dispersibility, preventing catalyst carbon deposition, etc., but an excessive amount of the diluent may reduce the efficiency of the reaction, so that the molar ratio of HFP, H ₂ and the diluent is preferably 1:1 to 30:1 to 30, more preferably 1:1 to 20:1 to 20.

In the invention, the second reactor mainly generates HFC-236ea gas phase dehydrofluorination reaction, the temperature is high, the conversion rate of HFC-236ea is high, but the selectivity of a target product is low, the reaction temperature is preferably 150-400 ℃, more preferably 180-300 ℃ according to the performance of the catalyst and the verification of the conversion rate and the selectivity; the space velocity is preferably from 30 to 1000h ^-1, more preferably from 100 to 800h ^-1.

In the invention, the third reactor mainly carries out HFC-245eb gas phase dehydrofluorination reaction, and the reaction temperature of the third reactor is preferably 150-400 ℃, more preferably 180-300 ℃; the space velocity is preferably from 30 to 1000h ^-1, more preferably from 100 to 800h ^-1.

The first reactor is filled with the noble metal Pd or Pt and auxiliary metal composite catalyst, the noble metal loading is too low, the catalytic activity is insufficient, and the content of the noble metal and the activity of the catalyst have an optimal balance point. The selection of the carrier is important for the catalyst, and the addition of the auxiliary metal Ni, fe, au, cu, al and the like is favorable for making the dispersion degree of the supported catalytic active center Pd and Pt high to prepare the high-activity catalyst by selecting the active carbon, titanium dioxide, alumina or silicon dioxide as the carrier. It is found through experiments that the loading of the noble metal Pd or Pt of the catalyst in the first reactor is preferably 0.01-0.3%, and the loading of the auxiliary metal is preferably 0.001-0.5%.

The catalysts used in the second and third reactors of the present invention may employ catalysts known in the art having chromium as the active component, gamma-Al ₂O₃ and/or AlF ₃ as the support, and one or more auxiliary metals in Mg, zn, co, fe, in, ga to increase the dispersity of the chromium. The catalyst may be prepared by conventional methods in the art: for example, chromium and nitrate of auxiliary metal are mixed according to a certain proportion to prepare a dilute solution with a certain concentration, a precipitator is added for reaction, and then the solution is filtered, washed, dried, roasted, granulated and tabletted to form a precursor, and the precursor is fluorinated to prepare the catalyst, and the pretreatment of the catalyst can be carried out in other reactors.

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

1. The method has the advantages of simple process and high reaction efficiency, improves the reaction efficiency by optimizing parameters such as the reaction flow, the catalyst and material ratio, the reaction temperature, the reaction pressure, the airspeed and the like, has relatively low reaction temperature and reaction pressure, is mild and easy to control, remarkably simplifies the operation and reduces the energy consumption; meanwhile, the reaction temperature can be controlled by adding the 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. The invention has the advantages of low equipment investment and low operation cost, and the sources of the used raw materials HFP and H ₂ are wide, so that the raw material cost in the production process is obviously reduced; by optimizing the process, the HFP hydrogenation reaction and the HFO-1225ye hydrogenation reaction are carried out in the same reactor, and compared with the two-step reaction carried out in two independent reactors, the use of the same reactor can save space and reduce equipment and operation cost;

3. The method is environment-friendly, has few three wastes, can recycle unreacted raw materials and intermediate products into the reactor for continuous reaction, can improve the production efficiency and the resource utilization rate, has obvious environment-friendly advantages, reduces the discharge of the three wastes such as waste water, waste gas, waste residues and the like, and is favorable for realizing green production and sustainable development.

Drawings

FIG. 1 is a process flow diagram of the present invention.

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

Detailed Description

The synthesis device and the flow are shown in figure 1, the synthesis device comprises a first reactor 1, a second reactor 2, a third reactor 3, a first separation unit formed by a first rectifying tower 4 and a second rectifying tower 5, a second separation unit formed by a first deacidification tower 6 and a third rectifying tower 7, and a third separation unit formed by a second deacidification tower 8 and a fourth rectifying tower 9, wherein the top of the first reactor 1 is provided with a reaction raw material inlet, a product outlet at the bottom of the first reactor 1 is connected with a material inlet of the first rectifying tower 4, a tower bottom material outlet of the first rectifying tower 4 is connected with a material inlet of the second rectifying tower 5, a tower top material outlet of the first rectifying tower 4 is connected with a reaction raw material inlet of the first reactor 1, The top material outlet of the second rectifying tower 5 is connected with the material inlet of the second reactor 2, the product outlet at the bottom of the second reactor 2 is connected with the material inlet of the first acid removing tower 6, the tower kettle of the first acid removing tower 6 is provided with an HF outlet, the top material outlet of the first acid removing tower 6 is connected with the material inlet of the third rectifying tower 7, the top material outlet of the third rectifying tower 7 is connected with the reaction raw material inlet of the first reactor 1, the tower kettle material outlet of the third rectifying tower 7 is connected with the material inlet of the second reactor 2, the tower kettle material outlet of the second rectifying tower 5 is connected with the material inlet of the third reactor 3, the material outlet of the third reactor 3 is connected with the material inlet of the second acid removing tower 8, The tower kettle of the second acid removal tower 8 is provided with an HF outlet, the tower top material outlet of the second acid removal tower 8 is connected with the material inlet of the fourth rectifying tower 9, the tower top of the fourth rectifying tower 9 is provided with a product outlet, and the tower kettle material outlet of the fourth rectifying tower 9 is connected with the material inlet of the third reactor 3. The specific process flow for synthesizing the 2, 3-tetrafluoropropene comprises the following steps: continuously introducing the starting materials HFP, H ₂ and a diluent into a first reactor 1 through a reaction raw material inlet to obtain a mixture containing HFC-236ea, H ₂, the diluent and the like, introducing the mixture into a first rectifying tower 4, separating the diluent and unreacted H ₂ from the top of the first rectifying tower 4, Returning the diluent and unreacted H ₂ to the first reactor 1 for continuous use, and introducing HFC-236ea obtained from the tower bottom of the first rectifying tower 4 into the second rectifying tower 5; Introducing HFC-236ea separated from the top of the second rectifying tower 5 into a second reactor 2 for dehydrofluorination reaction to obtain a mixture containing HFO-1225ye, HF and a small amount of HFC-236ea, and introducing the mixture into a first acid removal tower 6; the HF separated from the tower bottom of the first acid removal tower 6 can be discharged periodically, the top of the first acid removal tower 6 is separated to obtain a mixture containing HFC-236ea and HFO-1225ye, the mixture containing HFC-236ea and HFO-1225ye is introduced into a third rectifying tower 7 for separation, the HFC-236ea obtained from the tower bottom of the third rectifying tower 7 is returned to the second reactor 2 for continuous reaction, and the HFO-1225ye obtained from the tower top of the third rectifying tower 7 is introduced into the first reactor 1; The HFO-1225ye, the starting materials HFP, H ₂ and the diluent are subjected to hydrogenation reaction in the first reactor 1 to obtain a mixture containing HFC-236ea, HFC-245eb, H ₂, the diluent and the like, the mixture is introduced into the first rectifying tower 4, H ₂ and the diluent are separated from the top of the first rectifying tower 4, H ₂ and a diluent can be returned to the first reactor 1 for continuous use, HFC-236ea and HFC-245eb obtained from the tower bottom of the first rectifying tower 4 are introduced into the second rectifying tower 5, HFC-236ea separated from the tower top of the second rectifying tower 5 is introduced into the second reactor 2, HFC-245eb separated from the tower bottom is introduced into the third reactor 3, the HFC-245eb undergoes dehydrofluorination reaction in the third reactor 3 to obtain a mixture containing HFO-1234yf, HF and a small amount of HFC-245eb, Passing the mixture to a second acid removal column 8; HF is discharged from the tower bottom of the second acid removal tower 8, the tower top of the second acid removal tower 8 is separated to obtain a mixture containing HFC-245eb and HFO-1234yf, the mixture containing HFC-245eb and HFO-1234yf is introduced into a fourth rectifying tower 9 for further separation, a target product HFO-1234yf is obtained from the tower top of the fourth rectifying tower 9, HFC-245eb is obtained from the tower bottom of the fourth rectifying tower 9, and the HFC-245eb is returned to the third reactor 3 for continuous reaction.

The technical scheme of the present invention will be further clearly and completely described in the following examples. It will be apparent that the described embodiments are only some, but not all, embodiments of the invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.

Example 1

200Ml of Pd-Ni/C catalyst (0.01% by mass of Pd, 0.001% by mass of Ni) was charged into the first reactor, 300ml of Cr-In/gamma-Al ₂O₃ catalyst (5% by mass of Cr, 1% by mass of In) was charged into the second reactor, and 300ml of Cr-Mg/gamma-Al ₂O₃ catalyst (5% by mass of Cr, 0.5% by mass of Mg) was charged into the third reactor.

Then each reactor starts to heat up, and nitrogen is introduced to dry for 2 hours after the temperature is raised; the batch reaction was then started and HFP, H ₂ and diluent (HFC-152 a) were continuously fed into the first reactor, each reactor having the reaction conditions shown in Table 1.

After the reaction was stabilized, the mixture at the outlets of the first reactor, the second reactor and the third reactor was sampled, and the organic composition thereof was analyzed by gas chromatography and shown in table 2.

TABLE 1 reaction conditions for each reactor in example 1

TABLE 2 organic composition at the outlet of each reactor in example 1

Example 2

200Ml of Pd-Fe/TiO ₂ catalyst (0.1% by mass of Pd, 0.01% by mass of Fe) was charged into the first reactor, 300ml of Cr-Zn/AlF ₃ catalyst (10% by mass of Cr, 2% by mass of Zn) was charged into the second reactor, and 300ml of Cr-Zn/AlF ₃ catalyst (8% by mass of Cr, 1% by mass of Zn) was charged into the third reactor.

Then each reactor starts to heat up, and nitrogen is introduced to dry for 2 hours after the temperature is raised; the batch reaction was then started and HFP, H ₂ and diluent (HFC-143 a) were continuously fed into the first reactor, each reactor having the reaction conditions shown in Table 3.

After the reaction was stabilized, the mixture at the outlets of the first reactor, the second reactor and the third reactor was sampled, and the organic composition thereof was analyzed by gas chromatography and shown in table 4.

TABLE 3 reaction conditions for each reactor in example 2

TABLE 4 organic composition at the outlet of each reactor in example 2

Example 3

200Ml of Pd-Cu/Al ₂O₃ catalyst (Pd 0.3% by mass, cu 0.1% by mass) was charged into the first reactor, 300ml of Cr-Co/gamma-Al ₂O₃ catalyst (Cr 15% by mass, co 4% by mass) was charged into the second reactor, and 300ml of Cr-Co/gamma-Al ₂O₃ catalyst (Cr 12% by mass, co 2% by mass) was charged into the third reactor.

Then each reactor starts to heat up, and nitrogen is introduced to dry for 2 hours after the temperature is raised; the batch reaction was then started and HFP, H ₂ and diluent (HFC-134 a) were continuously fed into the first reactor, each reactor having the reaction conditions shown in Table 5.

After the reaction was stabilized, the mixture at the outlets of the first reactor, the second reactor and the third reactor was sampled, and the organic composition thereof was analyzed by gas chromatography and shown in table 6.

TABLE 5 reaction conditions for each reactor in example 3

TABLE 6 organic composition at the outlet of each reactor in example 3

Example 4

200Ml of Pt-Al/SiO ₂ catalyst (0.2% by mass of Pt and 0.5% by mass of Al) was charged into the first reactor, 300ml of Cr-Fe/AlF ₃ catalyst (20% by mass of Cr and 5% by mass of Fe) was charged into the second reactor, and 300ml of Cr-Ga/AlF ₃ catalyst (15% by mass of Cr and 3% by mass of Ga) was charged into the third reactor.

Then each reactor starts to heat up, and nitrogen is introduced to dry for 2 hours after the temperature is raised; the feed reaction was then started and HFP, H ₂ and diluent (HFC-125) were continuously fed into the first reactor, each reactor having the reaction conditions shown in Table 7.

After the reaction was stabilized, the mixture at the outlets of the first reactor, the second reactor and the third reactor was sampled, and the organic composition thereof was analyzed by gas chromatography and shown in table 8.

TABLE 7 reaction conditions for each reactor in example 4

TABLE 8 organic composition at the outlet of each reactor in example 4

Claims

1. A process for the synthesis of 2, 3-tetrafluoropropene comprising a synthesis apparatus, characterized in that said synthesis apparatus comprises a first reactor, a second reactor, a third reactor, a first separation unit, a second separation unit and a third separation unit, said first reactor being provided with a base stock inlet, said first reactor outlet being connected to said first separation unit inlet, said first separation unit being provided with a first separator outlet, a second separator outlet and a third separator outlet, said first separator outlet being connected to said base stock inlet, said second separator outlet being connected to said second reactor inlet, said second reactor outlet being connected to said second separator inlet, said second separation unit being provided with a fourth separator outlet, a fifth separator outlet and a sixth separator outlet, said fourth separator outlet being connected to said base stock inlet, said third separator outlet being connected to said third reactor outlet, said third separator outlet being provided with a seventh separator outlet, said eighth separator outlet, said third separator outlet being provided with a ninth separator outlet, said third separator outlet being provided with said third separator outlet, and said eighth separator outlet being provided with said third separator outlet:

2. The method for synthesizing 2, 3-tetrafluoropropene according to claim 1, wherein the first catalyst uses Pd or Pt as a main component and one or more selected from Ni, fe, au, cu, al as an auxiliary component, the main component and the auxiliary component are supported on a carrier, the carrier is one of activated carbon, titanium dioxide, alumina and silica, the loading of the main component is 0.01-0.3 wt%, and the loading of the auxiliary component is 0.001-0.5 wt%.

3. The method for synthesizing 2, 3-tetrafluoropropene according to claim 1, wherein the second catalyst uses chromium as a main component and one or more selected from Zn, co, fe, in as an auxiliary component, the main component and the auxiliary component are supported on gamma-Al ₂O₃ and/or AlF ₃ carriers, the load of chromium is 5-20wt%, and the load of the auxiliary component is 1-5wt%.

4. The method for synthesizing 2, 3-tetrafluoropropene according to claim 1, wherein the third catalyst uses chromium as a main component and one or more selected from Mg, zn, co, ga as an auxiliary component, the main component and the auxiliary component are supported on gamma-Al ₂O₃ and/or AlF ₃ carriers, the load of chromium is 5-15 wt%, and the load of the auxiliary component is 0.5-3 wt%.

5. The method for synthesizing 2, 3-tetrafluoropropene according to claim 1, wherein the molar ratio of 1,2, 3-hexafluoropropylene, hydrogen and diluent in step (a) is 1:1 to 30:1 to 30, the temperature of the first reactor is 80 to 200 ℃, the pressure is 0.1 to 1.5MPa, and the space velocity is 300 to 2000h ^-1.

6. The process for the synthesis of 2, 3-tetrafluoropropene according to claim 1, wherein the temperature of the second reactor in step (c) is 150 to 400 ℃, the pressure is 0.1 to 1.5MPa, and the space velocity is 30 to 1000h ^-1.

7. The process for the synthesis of 2, 3-tetrafluoropropene according to claim 1, wherein the temperature of the third reactor in step (g) is 150 to 400 ℃, the pressure is 0.1 to 1.5MPa, and the space velocity is 30 to 1000h ^-1.

8. The method for synthesizing 2, 3-tetrafluoropropene according to claim 1, wherein, the diluent is 1, 1-difluoroethane, 1-trifluoroethane, 1, 2-tetrafluoroethane 1, 2-pentafluoroethane one or more of 1,2, 3-heptafluoropropane.

9. The method for synthesizing 2, 3-tetrafluoropropene according to claim 1, wherein the first separation unit employs a rectification operation, and the second separation unit and the third separation unit employ an acid removal and rectification operation.

10. The process for the synthesis of 2, 3-tetrafluoropropene according to claim 1, wherein the unreacted 1,2, 3-hexafluoropropane in step (d) is recycled to the second reactor through the sixth separator outlet, recycling the unreacted 1,2, 3-pentafluoropropane obtained in step (h) to the third reactor via said ninth separator outlet.