Method for separating and purifying 3-chloropropene

Abstract

The invention relates to a method for separating and purifying 3-chloropropene. Comprising the following steps: 1) carrying out rectification separation on a raw material chloropropene to obtain refined chloropropene; and 2) feeding the tower bottoms into a dimerization reactor to polymerize the 1, 5-hexadiene. 3) carrying out rectification separation on the polymerization reaction liquid, and circularly feeding light components into a chloropropene refining tower; by adopting the method for refining the chloropropene serving as the raw material of the epoxy chloropropane, the content of 1, 5-hexadiene in 3-chloropropene can be reduced, and the epoxidation reaction effect can be improved; by adding the polymerization reaction, the 1, 5-hexadiene is effectively separated, and the consumption of 3-chloropropene in the chloropropene refining process is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of epichlorohydrin separation and recovery, and specifically relates to a method for refining 3-propylene chloride, a raw material of epichlorohydrin using a hydrogen peroxide process, and a polymerization catalyst. Background Art

[0002] Epichlorohydrin (ECH) is mainly used in the production of epoxy resins, glycerol, epichlorohydrin rubber and other derivatives. It can also be used as a solvent, plasticizer, flame retardant and surfactant. It is an important organic chemical raw material and an important intermediate in petrochemicals and has a wide range of uses.

[0003] Epichlorohydrin is the epoxy compound monomer with the largest market capacity besides EO and PO, with a global demand of 2.5 million tons / year. China's apparent consumption is about 900,000-1 million tons / year, and it is growing at an annual rate of 5%-6%. As the product with the largest downstream consumption of epichlorohydrin, epoxy resin consumption is highly positively correlated with economic development. The per capita consumption of epoxy resin in developed countries is about 1.5 kg, and the per capita consumption in China is 0.9 kg, which shows that China's epoxy resin market has great development potential. Among the current mainstream processes of epichlorohydrin, the hydrogen peroxide process is green and environmentally friendly, and is an innovative process encouraged by the state, so it is currently being studied more.

[0004] Chinese patent CN 201110319618.0 discloses a method for purifying epichlorohydrin containing olefin impurities. In order to eliminate the impurity 1,2-epoxy-5-hexene which is difficult to separate in the product, halogen is introduced into the crude epichlorohydrin after separation of allyl chloride, and the impurity 1,2-epoxy-5-hexene is added to other high-boiling substances, the boiling point difference between 1,2-epoxy-5-hexene and epichlorohydrin is increased, and the two are separated by conventional separation means. This method can efficiently remove the impurity 1,2-epoxy-5-hexene in epichlorohydrin, but a relatively large amount of halogen is introduced, which not only increases the cost of raw materials but also greatly enhances the corrosiveness and is difficult to operate.

[0005] Chinese patent CN 201480022879.8 introduces a method for removing 1,2-epoxy-5-hexene from epichlorohydrin. This patent also adds halogen to convert 1,2-epoxy-5-hexene into other addition products. This patent controls the molar ratio of halogen to 1,2-epoxy-5-hexene to 0.5-1:1 to minimize the content of 1,2-epoxy-5-hexene in the product. This patent also adds halogen to reduce the content of 1,2-epoxy-5-hexene, which is difficult to avoid the problems of raw material cost and corrosiveness.

[0006] The production of epichlorohydrin by hydrogen peroxide method includes three steps: high-temperature chlorination of propylene to produce allyl chloride; cyclization reaction of allyl chloride and hydrogen peroxide in the presence of a catalyst to produce epichlorohydrin; and separation and purification of epichlorohydrin. In the process of high-temperature chlorination of propylene to produce allyl chloride, 1,5-hexadiene byproduct will be produced, and its content is greater than 1000ppm. This byproduct will undergo cyclization reaction to produce 1,2-epoxy-5-hexene. The boiling point of this product is consistent with that of epichlorohydrin, and it cannot be separated by distillation. The content of high-quality epichlorohydrin needs to be greater than 99.9%, and when the content of 1,5-hexadiene in the raw material is greater than 1000ppm, high-quality epichlorohydrin cannot be obtained, which affects the downstream application of epichlorohydrin. It is necessary to develop a suitable separation method for the production of 1,5-hexadiene to obtain high-quality epichlorohydrin. Therefore, it is very important to develop a simple and easy-to-implement separation method to obtain high-quality epichlorohydrin. Summary of the invention

[0007] The present invention aims at the problem that the high content of 1,5-hexadiene in the hydrogen peroxide method epichlorohydrin process affects the purity of the product, and develops a method for separating and purifying 3-chloropropene. 3-chloropropene is refined by distillation + polymerization. First, conventional distillation is used to achieve preliminary separation of 1,5-hexadiene by distillation at a relatively low temperature, thereby reducing the loss of 3-chloropropene.

[0008] The present invention also provides a 1,5-hexadiene selective polymerization catalyst, which can realize high-selective polymerization of 1,5-hexadiene, further improve the dechlorination of 1,5-hexadiene in the raw material, and reduce the consumption of 3-chloropropylene.

[0009] In order to achieve the above-mentioned object of the invention, the technical solution of the present invention is as follows:

[0010] A method for separating and purifying 3-chloropropylene comprises the following steps:

[0011] 1) using a first refining tower to purify the 3-chloropropylene raw material to obtain a tower top liquid and a tower bottom liquid, wherein the tower top liquid is crude 3-chloropropylene, and the 1,5-hexadiene content in the epoxidation raw material 3-chloropropylene is reduced by distillation separation in a first distillation tower;

[0012] 2) introducing crude 3-chloropropylene into a polymerization reactor, and in the presence of a polymerization catalyst, 1,5-hexadiene undergoes a dimerization reaction to convert 1,5-hexadiene into a dimer, and the conversion rate of 3-chloropropylene is extremely low due to the steric hindrance effect of chlorine;

[0013] 3) The dimerization reaction liquid is separated in a second distillation tower to obtain a bottom liquid and a top liquid. The bottom liquid has a high content of 1,5-hexadiene dimer, part of which is recycled to the feed inlet of the first distillation tower to recover 3-chloropropylene, and part of which is treated as waste liquid. The top liquid is 3-chloropropylene with a low 1,5-hexadiene content after purification.

[0014] In step 1) of the present invention, the content of 1,5-hexadiene in the 3-chloropropylene raw material is 500-5000 ppm.

[0015] In step 1) of the present invention, the first refining tower is operated by atmospheric distillation, the bottom temperature of the distillation separation tower is 60-80°C, the top temperature of the distillation separation tower is 35-52°C, the theoretical separation plate number is 30-50, and the reflux ratio is 0.5-2.5.

[0016] In step 2) of the present invention, the dimerization reaction temperature is 80-120°C, the pressure is 1-3.5Mpa, and the reaction liquid processing volume is 0.3-1.5h -1 .

[0017] In step 3) of the present invention, the second refining tower is atmospheric distillation, the bottom temperature of the distillation separation is 70-100°C, the top temperature of the distillation separation is 35-50°C, the theoretical separation plate number is 15-30, and the reflux ratio is 0.5-2.0.

[0018] In step 2) of the present invention, the method for preparing the polymerization catalyst comprises the following steps:

[0019] 1) placing ZSM-5 in an aqueous solution of oxalic acid and nickel oxalate, and placing the solution in a crystallization kettle, and performing crystallization treatment at 110-140° C. for 48 hours to obtain a carrier;

[0020] 2) Add nickel salt, copper salt and zirconium salt into deionized water to prepare a 0.5-1.5M salt solution for later use;

[0021] 3) The carrier is immersed in a salt solution, adsorbed in a crystallization kettle at 120-150°C, then aged at 120-150°C for 4-6 hours, heated to 150-180 hours, further aged for 4-6 hours, filtered, and dried.

[0022] The present method can reduce the 1,5-hexadiene content in 3-chloropropene to less than 200 ppm, preferably reduce the 1,5-hexadiene content to less than 100 ppm.

[0023] In step 2) of the present invention, the nickel salt is selected from one or more of nickel nitrate, nickel carbonate, nickel acetate and nickel oxalate.

[0024] In step 2) of the present invention, the copper salt is selected from one or more of copper nitrate, copper chloride, copper acetate and copper sulfate.

[0025] In step 2) of the present invention, the zirconium salt is selected from one or more of zirconium nitrate, zirconium oxychloride, zirconium acetate or zirconium sulfate.

[0026] In step 1) of the present invention, the amount of nickel oxalate used is 1-3wt%, based on the weight of the catalyst.

[0027] The dimerization catalyst of the present invention comprises the following components: based on the weight of the catalyst, 5-15wt% of nickel oxide, 1-5wt% of zirconium oxide, and 2-8wt% of copper oxide.

[0028] The polymerization catalyst uses nickel oxalate and oxalic acid to expand the pores and modify the catalyst. After the modification, the internal pores of the catalyst are larger. After the inside of the catalyst pores are first loaded with nickel oxalate, the binding force between the salt and the carrier inside the pores can be effectively increased during the subsequent impregnation process. The addition of zirconium additives can further improve the polymerization reaction activity, and while increasing the diffusion rate, highly selective polymerization of 1,5-hexadiene is achieved, effectively achieving the removal of 1,5-hexadiene.

[0029] The method of the present invention can effectively reduce the content of 1,5-hexadiene in 3-chloropropylene. First, 3-chloropropylene is concentrated and enriched under relatively low distillation conditions by using a first distillation tower, and 3-chloropropylene and 1,5-hexadiene are separated under relatively mild conditions to reduce separation energy consumption. Subsequently, a polymerization catalyst is creatively used to selectively polymerize 1,5-hexadiene, and the pore size of the catalyst is increased through the pore expansion effect during the crystallization and impregnation of the molecular sieve, which accelerates the diffusion rate of 1,5-hexadiene. The loading of nickel oxalate in the early stage effectively increases the binding force between the salt and the carrier inside the pore during the subsequent impregnation process, and the addition of a zirconium additive can further improve the polymerization reaction activity and polymerize 1,5-hexadiene with high selectivity. Subsequently, the 1,5-hexadiene polymer and 3-chloropropylene are further separated by a second distillation tower to improve the yield of 3-chloropropylene during the separation process.

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

[0031] 1) Through the separation method of the invention, 3-chloropropene with low 1,5-hexadiene impurity content can be obtained, which not only improves the epoxidation reaction activity, but also eliminates the need to further separate 1,2-epoxy-5-hexene from the product after the epoxidation reaction to obtain superior epichlorohydrin.

[0032] 2) A selective polymerization reaction is creatively introduced and used together with distillation separation. When the concentration of 1,5-hexadiene in the bottom liquid increases, a specially treated molecular sieve is used to selectively react 1,5-hexadiene to generate a dimer, thereby increasing the boiling points of 1,5-hexadiene dimer and 3-chloropropylene, further recovering 3-chloropropylene in the bottom liquid, and improving the recovery rate of 3-chloropropylene during the refining process. DETAILED DESCRIPTION

[0033] In order to better understand the technical solution of the present invention, the following examples will further illustrate the method provided by the present invention, but the present invention is not limited to the listed examples, and should also include any other known changes within the scope of the claims of the present invention.

[0034] Chromatographic analysis conditions: PONA (30m×0.25mm×0.25μm) column was used for analysis. The specific operating conditions were: 50°C for 2 minutes, heating to 200°C at 15°C / min, and holding for 5 minutes. The injector temperature was 220°C, and the detector temperature was 240°C.

[0035] Methanol is produced by the company's methanol plant, and the product purity is >99.5%.

[0036] Allyl chloride was provided by Aladdin Reagent Co., Ltd., and the product purity was >99%.

[0037] Nickel sulfate was provided by Xilong Chemical Reagent Co., Ltd., and the product purity was >98%.

[0038] Copper nitrate trihydrate was provided by Xilong Chemical Co., Ltd., and the product purity was >98%.

[0039] Zirconium nitrate pentahydrate was provided by Xilong Chemical Reagent Co., Ltd., and the product purity was >98%.

[0040] Ammonia water was provided by Xilong Chemical Reagent Co., Ltd., with a product purity of 25-28%.

[0041] ZSM-5 was provided by China Catalyst Co., Ltd.

[0042] Example 1

[0043] Dissolve 1.97g nickel oxalate and 16.80g oxalic acid in 500ml water, place 91g ZSM-5 in the prepared oxalic acid / nickel oxalate aqueous solution, and place in a rotary crystallization reactor for crystallization at 110°C for 48h;

[0044] Weigh 19.52 g of nickel nitrate hexahydrate, 2.62 g of zirconium oxychloride octahydrate, and 6.04 g of copper nitrate trihydrate, dissolve them in 200.5 g of water to prepare a 0.5 M salt solution, mix well and set aside.

[0045] The crystallized carrier was placed in a rotatable crystallization kettle, and 0.5M salt solution was poured into the crystallization kettle. The impregnation liquid was evenly adsorbed on the carrier surface by turning the kettle. After the catalyst was aged at 120°C for 6 hours, the temperature was raised to 150 hours for further crystallization for 6 hours, and then dried at 120°C for 4 hours to obtain polymerization catalyst A.

[0046] Example 2

[0047] Dissolve 3.94g nickel oxalate and 15.59g oxalic acid in 500ml water, place 80g ZSM-5 in the prepared oxalic acid / nickel oxalate aqueous solution, and place in a rotary crystallization reactor for crystallization at 125°C for 48h;

[0048] Weigh 39.03 g of nickel nitrate hexahydrate, 7.86 g of zirconium oxychloride octahydrate, and 15.1 g of copper nitrate trihydrate, dissolve them in 291.8 g of water to prepare a 0.75 M salt solution, mix well and set aside.

[0049] The crystallized carrier was placed in a rotatable crystallization kettle, and 0.75M salt solution was poured into the crystallization kettle. The impregnation liquid was evenly adsorbed on the carrier surface by turning it over. After the catalyst was aged at 135°C for 5h, the temperature was raised to 165h for further crystallization for 5h, and then dried at 120°C for 4h to obtain polymerization catalyst B.

[0050] Example 3

[0051] Dissolve 5.91g nickel oxalate and 14.38g oxalic acid in 500ml water, place 65g ZSM-5 in the prepared oxalic acid / nickel oxalate aqueous solution, and place in a rotary crystallization reactor for crystallization at 140°C for 48h;

[0052] Weigh 58.55 g of nickel nitrate hexahydrate, 13.1 g of zirconium oxychloride octahydrate, and 24.16 g of copper nitrate trihydrate, dissolve them in 342.0 g of water to prepare a 1.0 M salt solution, mix well and set aside.

[0053] The crystallized carrier was placed in a rotatable crystallization kettle, 1.0M salt solution was poured into the crystallization kettle, and the impregnation liquid was evenly adsorbed on the carrier surface by turning it over. After the catalyst was aged at 150°C for 4 hours, the temperature was raised to 180 hours for further crystallization for 4 hours, and then dried at 120°C for 4 hours to obtain polymerization catalyst C.

[0054] Example 4

[0055] The crude 3-chloropropylene feedstock with a 1,5-hexadiene content of 1560 ppm enters the first distillation tower, the bottom temperature of the first distillation tower is 60°C, the top temperature is 39°C, the theoretical plate number of the distillation tower is 50, and the top reflux ratio is 0.5. The top of the distillation tower is refined crude chloropropylene, which goes to the dimerization reactor, the 1,5-hexadiene in the crude chloropropylene is reduced to 815 ppm, and the bottom liquid is discharged as waste liquid.

[0056] The dimerization reactor uses catalyst A, the reaction temperature is 80°C, the reaction pressure is 3.5Mpa, and the reaction liquid processing capacity is 0.3h -1 The dimerization reaction liquid enters the second distillation tower.

[0057] The bottom temperature of the second distillation tower is 70°C, the top temperature is 41°C, the theoretical plate number of the distillation tower is 15, and the top reflux ratio is 0.5. The top liquid is the refined 3-chloropropylene, in which the 1,5-hexadiene content is reduced to 85ppm. 1 / 3 of the bottom liquid is discharged as waste liquid, and 2 / 3 is recycled to the inlet of the first distillation tower to recover 3-chloropropylene.

[0058] Example 5

[0059] The crude 3-chloropropylene feedstock with a 1,5-hexadiene content of 1560ppm enters the first distillation tower, the first distillation tower has a bottom temperature of 70°C, a top temperature of 40°C, a theoretical plate number of 40, and a top reflux ratio of 1.5. The top of the distillation tower is refined crude chloropropylene, which goes to the dimerization reactor. The 1,5-hexadiene in the crude chloropropylene is reduced to 862ppm, and the bottom liquid is discharged as waste liquid. The dimerization reactor uses catalyst B, the reaction temperature is 100°C, the reaction pressure is 2.0Mpa, and the reaction liquid processing capacity is 1.0h -1 The dimerization reaction liquid enters the second distillation tower.

[0060] The second distillation tower has a bottom temperature of 85°C, a top temperature of 42°C, a theoretical plate number of 25, and a top reflux ratio of 1.0. The top liquid is refined 3-chloropropylene, in which the 1,5-hexadiene content is reduced to 92 ppm. One-third of the bottom liquid is discharged as waste liquid, and 2 / 3 is recycled to the inlet of the first distillation tower to recover 3-chloropropylene.

[0061] Example 6

[0062] The crude 3-chloropropylene feedstock with a 1,5-hexadiene content of 1560ppm enters the first distillation tower, the bottom temperature of the first distillation tower is 80℃, the top temperature is 42℃, the theoretical number of plates of the distillation tower is 30, and the top reflux ratio is 2.5. The top of the distillation tower is refined crude chloropropylene, which goes to the dimerization reactor. The 1,5-hexadiene in the crude chloropropylene is reduced to 877ppm, and the bottom liquid is discharged as waste liquid. The dimerization reactor uses catalyst C, the reaction temperature is 120℃, the reaction pressure is 1.0Mpa, and the reaction liquid processing capacity is 1.5h -1 The dimerization reaction liquid enters the second distillation tower.

[0063] The second distillation tower has a bottom temperature of 100° C., a top temperature of 43° C., a theoretical plate number of 35, and a top reflux ratio of 2.0.

[0064] The top liquid is the refined 3-chloropropene, in which the 1,5-hexadiene content is reduced to 99 ppm. 1 / 3 of the bottom liquid is discharged as waste liquid, and 2 / 3 is recycled to the inlet of the first distillation tower to recover 3-chloropropene.

[0065] Comparative Example 1

[0066] The crude 3-chloropropene raw material with a 1,5-hexadiene content of 1700ppm is used in a chloropropene distillation tower. The temperature of the distillation tower kettle is 80°C, the temperature of the tower top is 42°C, the theoretical number of plates of the distillation tower is 30, and the reflux ratio of the tower top is 2.5. The top of the distillation tower is the refined chloropropene, which goes to the epoxidation unit. The 1,5-hexadiene in the refined chloropropene is reduced to 800ppm, and then enters the epoxidation reactor. The concentration of 1,2-epoxy-5-hexene is 830ppm. The purity of epichlorohydrin obtained through the separation process is only 99.8%, and it is impossible to obtain a superior epichlorohydrin.

[0067] Comparative Example 2

[0068] Weigh 58.55 g of nickel nitrate hexahydrate, 13.1 g of zirconium oxychloride octahydrate, and 24.16 g of copper nitrate trihydrate, dissolve them in 342.0 g of water to prepare a 1.0 M salt solution, mix well and set aside.

[0069] 65 g of zsm-5 carrier was placed in a rotatable crystallization kettle, and 1.0 M salt solution was poured into the crystallization kettle. The impregnation liquid was evenly adsorbed on the surface of the carrier by turning it over. After the catalyst was aged at 150°C for 4 hours, the temperature was raised to 180 hours for further crystallization for 4 hours, and then dried at 120°C for 4 hours to obtain polymerization catalyst D.

[0070] The crude 3-chloropropylene feedstock with a 1,5-hexadiene content of 1560 ppm enters the first distillation tower, the first distillation tower has a bottom temperature of 80°C, a top temperature of 42°C, a theoretical plate number of 30, and a top reflux ratio of 2.5. The top of the distillation tower is refined crude chloropropylene, which goes to the dimerization reactor. The 1,5-hexadiene in the crude chloropropylene is reduced to 877 ppm, and the bottom liquid is discharged as waste liquid. The dimerization reactor uses catalyst D, the reaction temperature is 120°C, the reaction pressure is 1.0 MPa, and the reaction liquid processing capacity is 1.5 h -1 The dimerization reaction liquid enters the second distillation tower.

[0071] The second distillation tower has a bottom temperature of 100° C., a top temperature of 43° C., a theoretical plate number of 35, and a top reflux ratio of 2.0.

[0072] The top liquid is the refined 3-chloropropene, in which the 1,5-hexadiene content is reduced to 670ppm. 1 / 3 of the bottom liquid is discharged as waste liquid, and 2 / 3 is recycled to the inlet of the first distillation tower to recover 3-chloropropene.

[0073] Comparative Example 3

[0074] Weigh 58.55 g of nickel nitrate hexahydrate and 24.16 g of copper nitrate trihydrate, dissolve them in 342.0 g of water to prepare a 1.0 M salt solution, mix well and set aside.

[0075] 65 g of zsm-5 carrier was placed in a rotatable crystallization kettle, 1.0 M salt solution was poured into the crystallization kettle, and the impregnation liquid was evenly adsorbed on the surface of the carrier by turning it over. After the catalyst was aged at 150°C for 4 hours, the temperature was raised to 180 hours for further crystallization for 4 hours, and then dried at 120°C for 4 hours to obtain polymerization catalyst E.

[0076] The crude 3-chloropropylene feedstock with a 1,5-hexadiene content of 1560ppm enters the first distillation tower, the bottom temperature of the first distillation tower is 80℃, the top temperature is 42℃, the theoretical number of plates of the distillation tower is 30, and the top reflux ratio is 2.5. The top of the distillation tower is refined crude chloropropylene, which goes to the dimerization reactor. The 1,5-hexadiene in the crude chloropropylene is reduced to 877ppm, and the bottom liquid is discharged as waste liquid. The dimerization reactor uses catalyst E, the reaction temperature is 120℃, the reaction pressure is 1.0Mpa, and the reaction liquid processing capacity is 1.5h -1 The dimerization reaction liquid enters the second distillation tower.

[0077] The second distillation tower has a bottom temperature of 100° C., a top temperature of 43° C., a theoretical plate number of 35, and a top reflux ratio of 2.0.

[0078] The top liquid is the refined 3-chloropropene, in which the 1,5-hexadiene content is reduced to 620ppm. 1 / 3 of the bottom liquid is discharged as waste liquid, and 2 / 3 is recycled to the inlet of the first distillation tower to recover 3-chloropropene.

Claims

1. A method for separating and purifying 3-chloropropylene, comprising the following steps: 1) using a first refining tower to purify the 3-chloropropylene raw material to obtain a tower top liquid and a tower bottom liquid, wherein the tower top liquid is crude 3-chloropropylene; 2) introducing crude 3-chloropropylene into a polymerization reactor, and causing 1,5-hexadiene to dimerize in the presence of a polymerization catalyst; 3) The dimerization reaction liquid is separated in a second distillation tower to obtain a bottom liquid and a top liquid. Part of the bottom liquid is recycled to the feed inlet of the first distillation tower to recover 3-chloropropylene, and part of it is treated as waste liquid. The top liquid is 3-chloropropylene with a low 1,5-hexadiene content.

2. The method according to claim 1, characterized in that: In the step 1), the 1,5-hexadiene content in the 3-chloropropylene raw material is 500-5000 ppm.

3. The method according to claim 1, characterized in that In the step 1), the first refining tower is operated by atmospheric distillation, the bottom temperature of the distillation separation tower is 60-80°C, the top temperature of the distillation separation tower is 35-52°C, the theoretical separation plate number is 30-50, and the reflux ratio is 0.5-2.

5.

4. The method according to claim 1, characterized in that In the step 2), the dimerization reaction temperature is 80-120°C, the pressure is 1-3.5Mpa, and the reaction liquid processing volume is 0.3-1.5h -1 .

5. The method according to claim 1, characterized in that In the step 3), the second refining tower is atmospheric distillation, the bottom temperature of the distillation separation tower is 70-100°C, the top temperature of the distillation separation tower is 35-50°C, the theoretical separation plate number is 15-30, and the reflux ratio is 0.5-2.

0.

6. The method according to claim 1, characterized in that In the step 2), the method for preparing the polymerization catalyst comprises the following steps: 1) placing ZSM-5 in an aqueous solution of oxalic acid and nickel oxalate, and placing the solution in a crystallization kettle, and performing crystallization treatment at 110-140° C. for 48 hours to obtain a carrier; 2) Add nickel salt, copper salt and zirconium salt into deionized water to prepare a 0.5-1.5M salt solution for later use; 3) The carrier is immersed in a salt solution, adsorbed in a crystallization kettle at 120-150°C, then aged at 120-150°C for 4-6 hours, heated to 150-180 hours, further aged for 4-6 hours, filtered, and dried.

7. The method according to claim 6, characterized in that The dimerization catalyst comprises the following components: based on the weight of the catalyst, 5-15 wt% nickel oxide; 1-5 wt% zirconium oxide; and 2-8 wt% copper oxide.