Process for preparing cyclohexane-1, 2-dioctyl phthalate

Abstract

The invention provides a process for preparing cyclohexane-1, 2-dioctyl phthalate, which adopts a loop reaction process to perform hydrogenation reaction of dioctyl phthalate, and comprises the following steps: under the condition of excessive hydrogen atmosphere, firstly putting a catalyst, a solvent and a target product into a reaction tank to form a circulating material; when reaction liquid passes through the Venturi ejector, hydrogenation reaction can be carried out, the Venturi reactor can provide a high gas-liquid mixing ratio, the reaction rate is high, and the production efficiency is high. The catalyst and the reaction mixed liquid are separated by combining a membrane separation process, so that the catalyst is recycled, and the cost is reduced. The target product is added into the system to maintain material balance in the system, so that stable production is ensured. Compared with the traditional technical process, the method has the advantages that the reaction time is shortened, the energy consumption of the device and the investment cost are reduced, the high conversion rate of reactants and the high selectivity of target products can be kept, the operation period of the device is long, and continuous and stable production is realized.

Description

Technical Field

[0001] The invention relates to the field of preparing cyclohexane plasticizers by hydrogenating ortho-phthalate plasticizers, and in particular to a process for preparing dioctyl cyclohexane-1,2-dicarboxylate. Background Art

[0002] Dioctyl phthalate (DOP) is a type of plasticizer and softener commonly used in industry. It is also widely added to commonly used polymer rubber and plastic products, such as children's toys, food packaging materials, medical materials, and household and automotive decorative materials. Studies have shown that dioctyl phthalate (DOP) contains benzene rings, which are toxic and harmful to human health. It is restricted or prohibited by many countries from being used in plastic products such as medical devices, food, and children's toys. With the deepening of environmental protection concepts, this type of plasticizer no longer meets the needs of current industrial development. Cyclohexane 1,2-dioctyl dicarboxylate (DEHCH), the hydrogenation product of dioctyl phthalate (DOP), is an environmentally friendly, non-toxic plasticizer. Compared with dioctyl phthalate (DOP), cyclohexane 1,2-dicarboxylate (DEHCH) has excellent plasticizing properties and is biodegradable in the natural environment. It is considered to be an environmentally friendly plasticizer that can replace dioctyl phthalate (DOP).

[0003] At present, there are two main industrial production methods for cyclohexane 1,2-dicarboxylic acid dioctyl ester (DEHCH): 1) Olefin method, that is, butadiene and maleic anhydride are synthesized into o-cyclohexene dicarboxylic anhydride through Diels-Alder reaction, and then hydrogenated and esterified with isooctyl alcohol to synthesize cyclohexane 1,2-dicarboxylic acid dioctyl ester (DEHCH). 2) Hydrogenation method, that is, dioctyl phthalate (DOP) is directly catalyzed to hydrogenate on the benzene ring; or phthalic anhydride is first hydrogenated to synthesize 1,2-cyclohexane dicarboxylic acid, and then esterified to produce it. The hydrogenation method has a simple production process and high yield. Among them, the DOP direct hydrogenation method is the main method for the current industrial production of cyclohexane 1,2-dicarboxylic acid dioctyl ester (DEHCH). With the continuous development of industrial demand, researchers have continuously updated and improved the preparation process of the DOP direct hydrogenation method. For example, U.S. Patent US6284917 discloses a method for hydrogenating phthalate compounds to produce cyclohexane dicarboxylic acid ester plasticizers. Hydrogenation using a catalyst comprising the active metal ruthenium alone or together with at least one metal of transition group I, VII or group VII of the periodic table applied to a support having an average pore size of at least 50 nm and a specific surface area of ​​not more than 30 m 2 / g, the reaction temperature is 70-220°C, and the hydrogenation reaction is carried out at a pressure of 2-30MPa. The product yield of this method is relatively high, but the reaction conditions are relatively harsh, and the requirements for the reaction equipment are high, which increases the difficulty of industrial production. Patent CN101417950A discloses a method for preparing 1,2-cyclohexanedicarboxylic acid dibasic ester. The reaction system consists of dibasic phthalate, hydrogen and a catalyst; the reaction temperature is 100-250°C, the reaction pressure is 3.0-12.0MPa, the molar ratio of hydrogen to dibasic phthalate is 50-450, and the liquid space velocity of dibasic phthalate is 0.1-0.4h -1 . The conversion rate of the reactant phthalic acid dibasic ester and the selectivity of the target product 1,2. cyclohexane dicarboxylic acid dibasic ester in this method are relatively high, but the catalyst reduction and hydrogenation catalytic reaction time in this method is relatively long; at the same time, due to the large heat release and high reaction temperature of the phthalic acid dibasic ester hydrogenation reaction, the reaction energy consumption is high, which increases the production cost. Patent CN112174818A discloses a phthalate hydrogenation process, the process reaction system is composed of a first reactor and a second reactor in parallel, and then connected in series with a third reactor, hydrogen, part of the circulating gas, and phthalate are flowed into the first reactor and the second reactor for hydrogenation reaction; the hot hydrogen coming out of the reaction enters the gas-liquid separator after passing through the heat exchanger; the liquid coming out of the gas-liquid separator enters the third reactor; the hydrogen coming out of the gas-liquid separator and the hydrogen coming out of the third reactor are mixed and compressed and enter the first reactor and the second reactor; the reaction product of the third reactor is condensed to obtain cyclohexane 1,2-dicarboxylic acid ester. The method provides energy for preheating the reactants by heat exchange between the hot hydrogen coming out of the first and second reactors and the hydrogen coming out of the condensed third reactor, thereby reducing the energy consumption of the reaction process. However, the equipment investment is large, the floor space is large, and the equipment is difficult to maintain in the later stage. Patent CN112321427A discloses a dioctyl phthalate hydrogenation catalyst and a method for using the same. The catalyst is a loaded catalyst with alumina or silica as a carrier and loaded with precious metals. A fixed bed hydrogenation reactor is used to hydrogenate dioctyl phthalate to prepare dioctyl 1,2-cyclohexanedicarboxylate, the reaction temperature is 80-140°C, and the reaction pressure is 4-8MP. The catalyst in this method has the advantages of high activity and high selectivity, and the raw material conversion rate in the fixed bed hydrogenation reactor can reach 100%, but the catalyst cost in this method is high and the utilization rate is low, which increases the cost. CN101406840A discloses a method for preparing cyclohexanedicarboxylic acid dibasic ester, using a trickle bed high-pressure reactor, a reaction temperature of 200°C, a hydrogen partial pressure of 7.0 MPa, and a liquid hourly space velocity of 0.5 h -1, the raw material conversion rate can reach 99.9%, and the selectivity of cyclohexanedicarboxylic acid dibasic ester can reach 98.6%. The raw material conversion rate and the selectivity of cyclohexanedicarboxylic acid dibasic ester of this method are both high, but at a higher temperature, phthalic acid ester can generate benzoic acid monoester and corresponding alcohol or olefin through molecular internal elimination reaction, DOP can be decomposed into phthalic anhydride, 2-ethylhexyl alcohol and 2-ethylhexene by heating, and olefin can be further converted into alkane under hydrogen atmosphere, and one of the two ester bonds of DOP breaks to generate benzoic acid (2-ethylhexyl) ester and 2-ethylhexene, and 2-ethylhexene is hydrogenated to generate 3-methylheptane. The presence of benzoic acid monoester will reduce the performance of cyclohexane plasticizers, and low-boiling alcohols and alkanes will cause cyclohexane plasticizers to produce pungent odors, reduce the flash point of cyclohexane plasticizers, and ultimately reduce the comprehensive performance of cyclohexane plasticizers. Patent CN116715578A provides a method for hydrogenating dioctyl phthalate to produce dioctyl cyclohexanedicarboxylate. The hydrogenation reactor is provided with a circulating pump to reduce the temperature difference in the reactor and reduce the energy consumption of the device. The process is provided with an alkali washing tank to remove acid-containing impurities generated during the reaction. The process is provided with a light removal tower and a heavy removal tower, both of which are operated under negative pressure, which can effectively avoid the cracking of DOP and DEHCH at high temperature. However, this method has problems such as high equipment investment and short device operation cycle.

[0004] In view of the problems existing in the prior art, it is particularly important to study and design a new and efficient hydrogenation process for preparing dioctyl cyclohexane-1,2-dicarboxylate with mild reaction conditions, high production efficiency, low cost, high reactant conversion rate and target product selectivity. Summary of the invention

[0005] The object of the present invention is to provide a process for preparing dioctyl cyclohexane-1,2-dicarboxylate, which reduces the energy consumption and investment cost of the device, maintains a high conversion rate of reactants and a high selectivity of target products, prolongs the operation cycle of the device, improves production efficiency, and continuously stabilizes production. The loop reaction system of the present invention is composed of a venturi ejector, a reaction tank, a heat exchanger, a membrane separator, a circulation pump, a circulation pipeline and a distillation system. The reaction liquid is hydrogenated through the venturi ejector, wherein the venturi ejector can provide a higher gas-liquid mixing ratio, a large contact area of ​​the gas, solid and liquid three phases, a fast reaction rate, and the reaction liquid does not need to stay in the reactor for a long time to achieve a high conversion rate of the reactants and a high selectivity of the target product. The mixed liquid after the hydrogenation reaction is separated from the catalyst by a membrane separation process, so as to realize the recycling of the catalyst and reduce costs. The hydrogenation reaction in the present invention is an exothermic reaction, and a large amount of reaction heat will be released during the reaction process, affecting the activity of the catalyst; at the same time, high temperature will cause dioctyl phthalate (DOP) to decompose and produce side reactions, and the heat exchanger in the system can remove the heat in time, maintain the temperature in the loop reaction system to be uniform, and make the reaction proceed continuously and stably. The present invention performs continuous catalytic hydrogenation reaction through a loop reaction process, and the temperature and pressure distribution in the whole system are uniform, ensuring safe and stable production. The present invention has a simple process, low cost, and can achieve safe, continuous and stable production.

[0006] The technical solution of the present invention is as follows:

[0007] A process for preparing dioctyl cyclohexane-1,2-dicarboxylate, characterized in that the process comprises the following steps:

[0008] Step 1: Add the catalyst and solvent into the reaction tank in a certain proportion to form a circulating material; perform nitrogen and hydrogen replacement in sequence, start the circulation pump after the replacement is completed, and then increase the temperature and pressure of the circulating material in the reaction tank to the reaction conditions;

[0009] Step 2: adding a reaction liquid consisting of dioctyl phthalate and a solvent into a circulation pipeline after the separator, and injecting the dioctyl phthalate in the reaction liquid into a reaction tank through a venturi injector, so that the gas, liquid and solid three phases are fully contacted, and the dioctyl phthalate reacts with hydrogen under the action of a catalyst to generate dioctyl cyclohexane-1,2-dicarboxylate;

[0010] Step 3: Open the membrane separator to start discharging, separate the dioctyl cyclohexane-1,2-dicarboxylate generated in the reaction in step 2 from the catalyst through the membrane separation system to obtain a mixed liquid, and control the pressure of the entire reaction system by controlling the pressure of hydrogen;

[0011] Step 4: transporting the mixed liquid separated by the membrane separator in step 3 to a distillation system to obtain high-purity dioctyl cyclohexane-1,2-dicarboxylate and solvent;

[0012] Step 5: The solvent obtained in step 4 is mixed with dioctyl phthalate in proportion to form a reaction solution, which then enters the circulation pipeline.

[0013] Specifically, the catalyst described in step 1 is a supported catalyst, the catalyst carrier is alumina, silica or activated carbon; the active component of the catalyst is Ru, Rh, Pd or Pt; the supported weight of the active component of the catalyst is 0.1 to 5% of the weight of the catalyst.

[0014] Specifically, the reaction pressure in step 1 is 5-8 MPa, and the reaction temperature is 80-170° C. In the loop reaction system of the present invention, the temperature and pressure are evenly distributed, and there is no local overheating phenomenon, which is conducive to continuous and stable reaction.

[0015] Specifically, the solvent in step 1 is a mixed solution obtained by mixing methanol, ethanol, n-hexane or cyclohexane with dioctyl cyclohexane-1,2-dicarboxylate in a mass ratio of 1: (1-5); the mass ratio of the solvent to the catalyst is (20-100): 1. The present invention maintains the material balance in the system by adding the target product dioctyl cyclohexane-1,2-dicarboxylate into the system to ensure stable production.

[0016] Specifically, the solvent described in step 2 is methanol, ethanol, n-hexane or cyclohexane; the mass ratio of dioctyl phthalate to the solvent is 1:(1-5); the flow ratio of the reaction liquid to the circulating liquid is 1:(10-100). The present invention adopts a loop reaction process to carry out the hydrogenation reaction of dioctyl phthalate to prepare dioctyl cyclohexane-1,2-dicarboxylate. Under the condition of excess hydrogen atmosphere, the hydrogenation reaction can occur when the reaction liquid passes through the venturi injector, wherein the venturi injector can provide a higher gas-liquid mixing ratio, a large gas-solid-liquid three-phase contact area, a fast reaction rate, and the reaction liquid does not need to stay in the system for a long time. The conversion rate of the reactant dioctyl phthalate and the selectivity of the target product cyclohexane-1,2-dicarboxylic acid dioctyl ester can reach more than 99%.

[0017] Specifically, the membrane separator described in step 3 is a metal-based ceramic composite membrane cross-flow filtration system.

[0018] Specifically, the solvent described in step 5 is methanol, ethanol, n-hexane or cyclohexane; the mass ratio of dioctyl phthalate to the solvent is consistent with the ratio described in step 2.

[0019] The beneficial effects of the present invention are as follows:

[0020] (1) The present invention combines a venturi ejector, a reaction tank, a heat exchanger, a membrane separator, a circulation pump, a circulation pipeline and a distillation system to form a loop hydrogenation reaction system. The temperature and pressure in the system are evenly distributed and kept stable, ensuring that the reaction is safe, continuous and stable.

[0021] (2) The present invention uses a venturi injector to carry out hydrogenation reaction, wherein the venturi injector has a high gas-liquid mixing ratio, a large contact area of ​​the gas, solid and liquid three phases, a fast reaction rate, and the reaction liquid does not need to stay in the reactor for a long time to achieve a high conversion rate of the reactants and a high selectivity of the target product.

[0022] (3) The present invention separates the mixed liquid after the reaction from the catalyst through a membrane separation process, thereby realizing the recycling of the catalyst and reducing production costs.

[0023] (4) The present invention maintains the material balance in the system by adding the target product dioctyl cyclohexane-1,2-dicarboxylate into the system to ensure stable production.

[0024] (5) The present invention has mild reaction conditions, simple process, low equipment investment cost and floor space, can realize continuous and stable production, and has high production efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a process flow chart for preparing dioctyl cyclohexane 1,2-dicarboxylate by hydrogenating dioctyl phthalate.

[0026] Among them: 1. reaction tank; 2. Venturi ejector; 3. circulation pump; 4. heat exchanger; 5. separator; 6. distillation system; 7. circulation pipeline. DETAILED DESCRIPTION

[0027] The present invention is further described in detail below in conjunction with specific examples, but the present invention is not limited to the following examples. The implementation conditions used in the examples can be further adjusted according to different requirements of specific use, and the implementation conditions not specified are conventional conditions in the industry.

[0028] Example 1

[0029] Step 1: Put Ru / C catalyst (Ru loading weight is 0.5% of catalyst weight) and solvent in a mass ratio of 1:20 into a reaction tank to form a circulating material, wherein the solvent is a mixed solution obtained by mixing dioctyl cyclohexane-1,2-dicarboxylate and methanol in a mass ratio of 5:1, and replace with nitrogen and hydrogen successively. After the replacement is completed, start the circulation pump, and then heat the circulating material in the reaction tank to 120° C. and increase the pressure to 5 MPa;

[0030] Step 2: adding a reaction liquid composed of dioctyl phthalate and methanol in a mass ratio of 5:1 to the circulation pipeline after the separator, the dioctyl phthalate in the reaction liquid is sprayed in the reaction tank through a venturi injector, the gas, liquid and solid three phases are fully contacted, and the dioctyl phthalate reacts with hydrogen under the action of the catalyst to generate dioctyl cyclohexane-1,2-dicarboxylate, wherein the feed flow rate of the reaction liquid is 30g / min, and the flow ratio of the reaction liquid to the circulation liquid is 1:100;

[0031] Step 3: Open the membrane separator to start discharging, separate the dioctyl cyclohexane-1,2-dicarboxylate generated in the reaction in step 2 from the catalyst through the membrane separation system to obtain a mixed liquid, and control the pressure of the entire reaction system by controlling the pressure of hydrogen;

[0032] Step 4: transporting the mixed liquid separated by the membrane separator in step 3 to a distillation system to obtain high-purity dioctyl cyclohexane-1,2-dicarboxylate and methanol;

[0033] Step 5: The methanol obtained in step 4 is mixed with dioctyl phthalate in a mass ratio of 1:5 to form a reaction liquid, which then enters the circulation pipeline.

[0034] Example 2

[0035] Step 1: Rh / Al2O3 catalyst (Rh loading weight is 0.1% of catalyst weight) and solvent are put into a reaction tank at a mass ratio of 1:50 to form a circulating material, wherein the solvent is a mixed solution obtained by mixing dioctyl cyclohexane-1,2-dicarboxylate and ethanol at a mass ratio of 3:1, and nitrogen and hydrogen are replaced successively. After the replacement is completed, a circulating pump is turned on, and the circulating material in the reaction tank is heated to 100°C and the pressure is increased to 6MPa;

[0036] Step 2: adding a reaction liquid composed of dioctyl phthalate and ethanol in a mass ratio of 3:1 to the circulation pipeline after the separator, the dioctyl phthalate in the reaction liquid is sprayed in the reaction tank through a venturi injector, the gas, liquid and solid three phases are fully contacted, and the dioctyl phthalate reacts with hydrogen under the action of the catalyst to generate dioctyl cyclohexane-1,2-dicarboxylate, wherein the feed flow rate of the reaction liquid is 50g / min, and the flow ratio of the reaction liquid to the circulation liquid is 1:10;

[0037] Step 3: Open the membrane separator to start discharging, separate the dioctyl cyclohexane-1,2-dicarboxylate generated in the reaction in step 2 from the catalyst through the membrane separation system to obtain a mixed liquid, and control the pressure of the entire reaction system by controlling the pressure of hydrogen;

[0038] Step 4: transporting the mixed liquid separated by the membrane separator in step 3 to a distillation system to obtain high-purity dioctyl cyclohexane-1,2-dicarboxylate and ethanol;

[0039] Step 5: The ethanol obtained in step 4 is mixed with dioctyl phthalate in a mass ratio of 1:3 to form a reaction liquid, which then enters the circulation pipeline.

[0040] Example 3

[0041] Step 1: Pd / C catalyst (the loading weight of Pd is 5% of the weight of the catalyst) and solvent are added into a reaction tank at a mass ratio of 1:100 to form a circulating material, wherein the solvent is a mixed solution obtained by mixing dioctyl cyclohexane-1,2-dicarboxylate and n-hexane at a mass ratio of 1:1, and nitrogen and hydrogen are replaced successively. After the replacement is completed, a circulating pump is turned on, and then the circulating material in the reaction tank is heated to 80° C. and the pressure is increased to 8 MPa;

[0042] Step 2: adding a reaction liquid composed of dioctyl phthalate and n-hexane in a mass ratio of 1:1 to the circulation pipeline after the separator, the dioctyl phthalate in the reaction liquid is sprayed in the reaction tank through a venturi injector, the gas, liquid and solid three phases are fully contacted, and the dioctyl phthalate reacts with hydrogen under the action of the catalyst to generate dioctyl cyclohexane-1,2-dicarboxylate, wherein the feed flow rate of the reaction liquid is 46 g / min, and the flow ratio of the reaction liquid to the circulation liquid is 1:30;

[0043] Step 3: Open the membrane separator to start discharging, separate the dioctyl cyclohexane-1,2-dicarboxylate generated in the reaction in step 2 from the catalyst through the membrane separation system to obtain a mixed liquid, and control the pressure of the entire reaction system by controlling the pressure of hydrogen;

[0044] Step 4: transporting the mixed liquid separated by the membrane separator in step 3 to a distillation system to obtain high-purity dioctyl cyclohexane-1,2-dicarboxylate and n-hexane;

[0045] Step 5: The n-hexane obtained in step 4 is mixed with dioctyl phthalate in a mass ratio of 1:1 to form a reaction liquid, which then enters the circulation pipeline.

[0046] Example 4

[0047] Step 1: Pt / SiO2 catalyst (Pt loading weight is 1% of catalyst weight) and solvent are put into a reaction tank at a mass ratio of 1:60 to form a circulating material, wherein the solvent is a mixed liquid obtained by mixing dioctyl cyclohexane-1,2-dicarboxylate and cyclohexane at a mass ratio of 2.5:1, and nitrogen and hydrogen are replaced successively. After the replacement is completed, the circulation pump is turned on, and the circulating material in the reaction tank is heated to 170°C and the pressure is increased to 5MPa;

[0048] Step 2: adding a reaction liquid composed of dioctyl phthalate and cyclohexane in a mass ratio of 2.5:1 to the circulation line after the separator, the dioctyl phthalate in the reaction liquid is sprayed in the reaction tank through a venturi injector, the gas, liquid and solid three phases are fully contacted, and the dioctyl phthalate reacts with hydrogen under the action of the catalyst to generate dioctyl cyclohexane-1,2-dicarboxylate, wherein the feed flow rate of the reaction liquid is 40g / min, and the flow ratio of the reaction liquid to the circulation liquid is 1:80;

[0049] Step 3: Open the membrane separator to start discharging, separate the cyclohexane-1,2-dioctyl dicarboxylate generated in the reaction in step 2 from the catalyst through the membrane separation system to obtain a mixed liquid, and control the pressure of the entire reaction system by controlling the pressure of hydrogen;

[0050] Step 4: transporting the mixed liquid separated by the membrane separator in step 3 to a distillation system to obtain high-purity dioctyl cyclohexane-1,2-dicarboxylate and cyclohexane;

[0051] Step 5: The cyclohexane obtained in step 4 is mixed with dioctyl phthalate in a mass ratio of 2:5 to form a reaction liquid, which then enters the circulation pipeline.

[0052] Comparative Example 1

[0053] This comparative example provides a method for preparing dioctyl cyclohexane-1,2-dicarboxylate (DEHCH) in a 2L stirred reactor, with a reaction temperature of 80°C, a reaction pressure of 8MPa, a stirring blade speed of 1200r / min, and a Pd / C catalyst the same as in Example 3 above. 1500g of the reaction solution is put into the reactor at one time, wherein the mass ratio of the catalyst to dioctyl phthalate (DOP) and the solvent is 1:100:100. After a reaction time of 7h, the hydrogen pressure no longer decreases, and sampling is performed for analysis.

[0054] The collected sample of the reaction product was analyzed for components by chromatography, and the conversion rates of dioctyl phthalate (DOP) and dioctyl cyclohexane-1,2-dicarboxylate (DEHCH) were calculated.

[0055] The following table summarizes the conversion rate of dioctyl phthalate (DOP) and dioctyl cyclohexane-1,2-dicarboxylate (DEHCH) in Examples 1 to 4 and Comparative Example 1.

[0056]

[0057] Comparing Example 3 with Comparative Example 1, in Comparative Example 1, 1500 g of the reaction solution was put into the reactor for reaction. After 7 hours of reaction, the amount of DOP in the reaction was 748.43 g. However, in Example 3, under the same reaction conditions such as reaction temperature and pressure, after 7 hours of reaction, the amount of DOP in the reaction was 9657.10 g. The present invention has continuous and stable reaction and high production efficiency.

[0058] Comparing Examples 1 to 4 with Comparative Example 1, we can see that Comparative Example 1 uses a fixed-volume stirred tank reactor, and the reaction materials are put into the reactor at one time for reaction. The reaction time requires more than 7 hours, and the reactant conversion rate and target product selectivity can reach more than 99%. In addition, the reaction temperature of the tank reactor is not easy to control and the heat and mass transfer effects are poor, which affects the catalyst activity and produces side reactions.

[0059] The present invention adopts a loop hydrogenation reaction system, the reaction conditions are mild, the temperature and pressure remain unchanged during the entire reaction process, and it is a safe, continuous and stable reaction. In the present invention, the hydrogenation reaction can occur when the reaction liquid passes through the venturi injector, the reaction rate is fast, and the reaction liquid does not need to stay in the reactor for a long time to obtain a high conversion rate of the reactants and a high selectivity of the target product, and the production efficiency is high. The sample collected from the reaction product is analyzed by chromatography to analyze the components, and the conversion rate of the reactants and the selectivity of the target product can reach more than 99%.

[0060] From the results of the above examples and comparative examples, it can be seen that:

[0061] (1) The present invention performs hydrogenation reaction in a loop reaction system, and the temperature and pressure in the system are uniform, thereby ensuring continuous and stable operation of the reaction.

[0062] (2) In the present invention, a venturi ejector is used for the reaction. Under the condition of an excess hydrogen atmosphere, a hydrogenation reaction can occur when the reaction liquid passes through the venturi ejector. The reaction rate is fast, and a high conversion rate of the reactants and a high selectivity of the target product can be obtained without staying in the reactor for a long time, and the production efficiency is high.

[0063] (3) The present invention separates the catalyst and the reaction mixture through a membrane separation process, thereby realizing the recycling of the catalyst and reducing production costs.

[0064] (4) The present invention maintains the material balance in the system by adding the target product dioctyl cyclohexane-1,2-dicarboxylate into the system to ensure stable production.

[0065] (5) The present invention has mild reaction conditions, simple process, low equipment investment cost, small footprint, and is suitable for industrial production.

Claims

1. A process for preparing dioctyl cyclohexane-1,2-dicarboxylate, characterized in that: The process includes the following steps: Step 1: Add the catalyst and solvent into the reaction tank in a certain proportion to form a circulating material: nitrogen and hydrogen replacement are carried out in sequence, and after the replacement is completed, the circulation pump is turned on, and then the circulating material in the reaction tank is heated and pressurized to the reaction conditions; Step 2: adding a reaction liquid consisting of dioctyl phthalate and a solvent into a circulation pipeline after the separator, and injecting the dioctyl phthalate in the reaction liquid into a reaction tank through a venturi injector, so that the gas, liquid and solid three phases are fully contacted, and the dioctyl phthalate reacts with hydrogen under the action of a catalyst to generate dioctyl cyclohexane-1,2-dicarboxylate; Step 3: Open the membrane separator to start discharging, separate the dioctyl cyclohexane-1,2-dicarboxylate generated in the reaction in step 2 from the catalyst through the membrane separation system to obtain a mixed liquid, and control the pressure of the entire reaction system by controlling the pressure of hydrogen; Step 4: transporting the mixed liquid separated by the membrane separator in step 3 to a distillation system to obtain high-purity dioctyl cyclohexane-1,2-dicarboxylate and solvent; Step 5: The solvent obtained in step 4 is mixed with dioctyl phthalate in proportion to form a reaction solution, which then enters the circulation pipeline.

2. A process for preparing dioctyl cyclohexane-1,2-dicarboxylate according to claim 1, characterized in that: The catalyst described in step 1 is a supported catalyst, and the catalyst carrier is alumina, silica or activated carbon; the active component of the catalyst is Ru, Rh, Pd or Pt; the supported weight of the active component of the catalyst is 0.1-5% of the weight of the catalyst.

3. A process for preparing dioctyl cyclohexane-1,2-dicarboxylate according to claim 1, characterized in that: The reaction pressure in step 1 is 5-8 MPa, and the reaction temperature is 80-170°C.

4. A process for preparing dioctyl cyclohexane-1,2-dicarboxylate according to claim 1, characterized in that: The solvent described in step 1 is a mixed solution obtained by mixing methanol, ethanol, n-hexane or cyclohexane with dioctyl cyclohexane-1,2-dicarboxylate in a mass ratio of 1:(1-5); the mass ratio of the solvent to the catalyst is (20-100):

1.

5. A process for preparing dioctyl cyclohexane-1,2-dicarboxylate according to claim 1, characterized in that: The solvent described in step 2 is methanol, ethanol, n-hexane or cyclohexane; the mass ratio of dioctyl phthalate to the solvent is 1:(1-5); the flow ratio of the reaction liquid to the circulating liquid is 1:(10-100).

6. A process for preparing dioctyl cyclohexane-1,2-dicarboxylate according to claim 1, characterized in that: The membrane separator described in step 3 is a metal-based ceramic composite membrane cross-flow filtration system.

7. A process for preparing dioctyl cyclohexane-1,2-dicarboxylate according to claim 1, characterized in that: The solvent described in step 5 is methanol, ethanol, n-hexane or cyclohexane; the mass ratio of dioctyl phthalate to the solvent is consistent with the ratio described in step 2.

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