Method for preparing cyclohexane-1, 4-dioctyl phthalate through continuous catalytic hydrogenation

Abstract

The invention provides a method for preparing diisooctyl cyclohexane-1, 4-dicarboxylate through continuous catalytic hydrogenation, which is characterized in that a Venturi reactor is used for reaction, and the diisooctyl cyclohexane-1, 4-dicarboxylate is continuously produced by combining a membrane separation process and a vacuum distillation process. Wherein the Venturi reactor can provide a higher gas-liquid mixing ratio, the contact area of gas, solid and liquid phases is large, the mixing effect is good, the mass transfer efficiency is high, and the reaction rate is high. And the membrane separation process can separate the mixed liquid from the catalyst, so that efficient utilization of the catalyst is realized. The energy consumption can be effectively reduced through the vacuum distillation process, and the equipment investment and the operation cost are reduced. According to the present invention, the hydrogenation reaction can be performed under the mild hydrogenation operation condition, and in the whole loop reaction system, the temperature distribution is uniform, the local overheating phenomenon does not exist, and the side reaction is effectively reduced. The method is simple in process, mild in reaction condition, short in reaction time and high in production efficiency, the reactant conversion rate and the target product selectivity are up to 99% or above, and the method is suitable for industrial production.

Description

Technical Field

[0001] This invention belongs to the field of organic chemical synthesis technology, specifically relating to a method for the continuous catalytic hydrogenation preparation of diisooctyl cyclohexane-1,4-dicarboxylate. Background Technology

[0002] Phthalate plasticizers such as dioctyl terephthalate (DOTP) and diisooctyl phthalate (DOP) are frequently used as primary plasticizers in polyvinyl chloride (PVC) plastic products. They improve the ductility, durability, and plasticity of these products and are widely used in industries such as medical devices, food packaging, and children's products. However, research has shown that phthalate plasticizers, due to the presence of benzene rings in their molecular structure, can cause endocrine disorders in the human body and harm human health. Currently, many countries have enacted regulations explicitly prohibiting the use of phthalate plasticizers in plastic products that come into direct contact with the human body. Cyclohexane esters, such as diisooctyl cyclohexane-1,4-dicarboxylate, are considered one of the most likely environmentally friendly plasticizers to replace phthalates in the future due to their benzene-free, non-toxic, and environmentally friendly characteristics, as well as their excellent plasticizing properties. Therefore, the synthesis of this type of compound has attracted widespread attention.

[0003] Current technologies often employ the hydrogenation of phthalate esters to prepare the environmentally friendly plasticizer cyclohexane-1,4-dicarboxylate (CDI). However, the hydrogenation of phthalate esters to CDI is a heterogeneous reaction, requiring increased contact area between the gas, liquid, and solid phases to improve mass transfer efficiency. Furthermore, the hydrogenation process generates significant heat, raising the reactor temperature and inhibiting the forward reaction, thus reducing reactant conversion. Therefore, researchers are continuously improving the process to enhance both mass transfer efficiency and reactant conversion. For example, patent CN103130648A discloses an apparatus and method for preparing dioctyl 1,4-cyclohexanedicarboxylate. The method involves esterifying terephthalic acid with octanol at 220–230°C to obtain dioctyl terephthalate, followed by hydrogenation of the obtained dioctyl terephthalate at 12.9 MPa and 200°C to obtain dioctyl 1,4-cyclohexanedicarboxylate. This technical solution uses a relatively simple and safe method of esterification followed by hydrogenation to prepare dioctyl 1,4-cyclohexanedicarboxylate. However, the hydrogenation of the esterification product requires high pressure conditions, and the single-pass conversion rate and yield of dioctyl 1,4-cyclohexanedicarboxylate using this method are significantly limited. Furthermore, the post-processing is cumbersome and generates wastewater. Patent CN1356973A discloses a method for preparing cyclohexane-1,4-dicarboxylate compounds by catalytic hydrogenation of terephthalic acid esters using a noble metal Ru catalyst, wherein the hydrogen pressure is 20 MPa, the reaction time is 3.5 h, and the product yield is 97%. This method has a long reaction time, is an intermittent reaction, has low production efficiency, and the high hydrogen pressure of 20 MPa places high demands on the strength and sealing of the equipment, posing significant safety hazards. Patent CN111269119A discloses a guide gas stirrer with extraction, exhaust, and stirring functions. In a reaction vessel equipped with this stirrer, the hydrogenation of dioctyl terephthalate to prepare diisooctyl cyclohexane-1,4-dicarboxylate is carried out at a reaction temperature of 120–135 °C, a hydrogen pressure of 20–98 bar, and a reaction time of 4–15 h, with a product selectivity of over 99.0%. This method is simple in process and has high product selectivity. It also enhances the mass transfer effect by adding a stirrer to increase the contact area between the gas and liquid phases. However, the mixing capacity of the impeller structure is limited, the structure is complex, the equipment cost is high, and the hydrogenation reaction time is long, resulting in low production efficiency.

[0004] In view of the above problems, simplifying the preparation process, reducing production costs, and using mild reaction conditions, while ensuring high conversion rate of reactants and high selectivity of target products, and shortening reaction time to improve production efficiency are the research priorities of researchers. Summary of the Invention

[0005] The purpose of this invention is to provide a highly efficient and continuous method for the preparation of diisooctyl cyclohexane-1,4-dicarboxylate, which features mild reaction conditions, simple process, high reactant conversion rate, and high selectivity for target product.

[0006] This invention utilizes a loop reaction process, employing a Venturi reactor in conjunction with membrane separation and vacuum distillation to continuously produce diisooctyl cyclohexane-1,4-dicarboxylate. The Venturi reactor leverages the high-speed liquid-phase entrainment of the gas phase, breaking the liquid into fine droplets, increasing the contact area between the gas, solid, and liquid phases, resulting in high mass transfer efficiency, fast reaction rate, and high production efficiency. Furthermore, the membrane separation process separates the mixture from the catalyst, achieving efficient catalyst utilization. The vacuum distillation process lowers the boiling point of substances within the distillation column, effectively reducing separation energy consumption and purifying the product. High-purity products are collected from the side stream of the vacuum distillation column, significantly reducing energy consumption, equipment investment, and operating costs compared to traditional distillation processes. This invention features mild reaction conditions, a safe, continuous, and stable reaction system, and a simple process with high reactant conversion and target product selectivity, making it suitable for industrial production.

[0007] The technical solution of this invention is:

[0008] A method for the continuous catalytic hydrogenation preparation of diisooctyl cyclohexane-1,4-dicarboxylate, characterized in that the method comprises the following steps:

[0009] Step 1: Add the catalyst and solvent to the buffer tank in a certain proportion to form a circulating material. Then, replace the material with nitrogen and hydrogen in sequence. After the replacement is completed, turn on the circulating pump and heat and pressurize the circulating material in the buffer tank to the reaction conditions.

[0010] Step 2: Add a reaction solution consisting of dioctyl terephthalate and solvent to the circulation line after the separator. When the dioctyl terephthalate and hydrogen in the reaction solution pass through the Venturi reactor, a hydrogenation reaction occurs to generate a mixture of cyclohexane-1,4-dicarboxylate and diisooctyl terephthalate.

[0011] Step 3: Start the membrane separator to discharge the product. Separate the cyclohexane-1,4-dicarboxylic acid diisooctyl ester mixture generated in Step 2 from the catalyst through the membrane separation system to obtain the separated mixture. Control the pressure of the reaction system by controlling the pressure of hydrogen.

[0012] Step 4: The cyclohexane-1,4-dicarboxylic acid diisooctyl ester solution obtained in Step 3 is transferred to a vacuum distillation system to obtain high-purity cyclohexane-1,4-dicarboxylic acid diisooctyl ester and solvent.

[0013] Step 5: Mix the solvent obtained in Step 4 with dioctyl terephthalate in a certain proportion to form a reaction solution, and then enter the circulation pipeline.

[0014] Specifically, the active component of the catalyst mentioned in step 1 is Ru, Rh, Pd, or Pt; the reaction pressure is 4–8 MPa, and the reaction temperature is 80–160°C. The reaction conditions of this invention are mild, eliminating the need for hydrogenation under high temperature and high pressure conditions, thus effectively reducing energy consumption and cost. By employing a loop reaction process, the internal temperature distribution of the system is uniform, with no localized overheating, ensuring stable reaction.

[0015] Specifically, the solvent mentioned in step 1 is a mixture of methanol or ethanol and diisooctyl cyclohexane-1,4-dicarboxylate in a mass ratio of 1:(1-5); the mass ratio of the solvent to the catalyst is (10-100):1.

[0016] Specifically, the solvent in step 2 is methanol or ethanol; the mass ratio of the solvent to dioctyl terephthalate is 1:(1-5); and the flow rate ratio of the reaction solution to the circulating liquid is 1:20 to 1:100.

[0017] Specifically, the membrane separator mentioned in step 3 is a cross-flow filtration system.

[0018] Specifically, the operating pressure of the vacuum distillation system described in step 4 is 0.001–0.005 MPa, the top temperature is 120–140°C, and the bottom temperature is 230–250°C. This invention employs vacuum distillation, which lowers the boiling point of substances within the vacuum distillation column, effectively reducing separation energy consumption and thus separating and purifying the product, yielding a high-purity product from the side stream of the vacuum distillation column.

[0019] Specifically, the solvent mentioned in step 5 is methanol or ethanol; the ratio of the solvent to dioctyl terephthalate is the same as that mentioned in step 2.

[0020] The beneficial effects of this invention are as follows:

[0021] (1) This invention utilizes a loop reaction process, with a Venturi reactor for reaction, combined with membrane separation process and vacuum distillation system to continuously produce diisooctyl cyclohexane-1,4-dicarboxylate. The material composition, temperature and pressure in the reaction system remain unchanged, ensuring safety, stability and high production efficiency.

[0022] (2) The present invention uses a Venturi reactor for hydrogenation reaction, which has a high gas-liquid mixing ratio and high mass transfer efficiency. When dioctyl terephthalate and hydrogen in the reaction liquid pass through the Venturi reactor, hydrogenation reaction can occur. The reaction rate is fast and the reaction liquid does not need to stay in the reactor for a long time, resulting in high production efficiency.

[0023] (3) The present invention maintains the material balance of the system by adding the target product cyclohexane-1,4-dicarboxylic acid diisooctyl ester to the reaction system, so that the reaction is continuous and stable.

[0024] (4) The present invention separates the reaction mixture from the catalyst through a membrane separator, thereby achieving efficient utilization of the catalyst and saving costs.

[0025] (5) The present invention uses a vacuum distillation process to separate and purify the product, which can effectively reduce reaction energy consumption compared with the traditional distillation process.

[0026] (6) The process of this invention is simple, the reaction conditions are mild, the reaction rate is fast, and the production efficiency is high, which can realize industrial production. Attached Figure Description

[0027] Figure 1 This is a process flow diagram for the production of diisooctyl cyclohexane-1,4-dicarboxylate.

[0028] The components include: 1. Raw material feed tank; 2. Raw material feed pump; 3. Buffer tank; 4. Venturi reactor; 5. Circulation pump; 6. Membrane separator; 7. Circulation pipeline; and 8. Vacuum distillation column. Detailed Implementation

[0029] The present invention will be further described in detail below with reference to specific embodiments, but the present invention is not limited to the following embodiments. The implementation conditions used in the embodiments can be further adjusted according to different requirements of specific use, and the implementation conditions not specified are conventional conditions in this industry.

[0030] Example 1

[0031] Step 1: Add Ru-based catalyst and solvent in a buffer tank at a mass ratio of 1:60 to form circulating material. The solvent is a mixture of methanol and diisooctyl cyclohexane-1,4-dicarboxylate in a mass ratio of 1:5. Nitrogen and hydrogen are used for purging. After purging, the circulating pump is turned on, and the circulating material in the buffer tank is heated to 120°C and pressurized to 7 MPa. Step 2: Add a reaction solution composed of methanol and dioctyl terephthalate in a mass ratio of 1:5 to the circulating pipeline after the separator. When dioctyl terephthalate and hydrogen in the reaction solution pass through the Venturi reactor, a hydrogenation reaction occurs to generate a mixture of diisooctyl cyclohexane-1,4-dicarboxylate. The feed flow rate of the reaction solution is 46 g / min, and the flow ratio of the reaction solution to the circulating solution is 1:20.

[0032] Step 3: Start the membrane separator to discharge the product. Separate the cyclohexane-1,4-dicarboxylic acid diisooctyl ester mixture generated in Step 2 from the catalyst through the membrane separation system to obtain the separated mixture. The pressure of the reaction system is maintained at 7 MPa by controlling the pressure of hydrogen.

[0033] Step 4: The cyclohexane-1,4-dicarboxylic acid diisooctyl ester solution obtained in Step 3 is transferred to a vacuum distillation system to obtain high-purity cyclohexane-1,4-dicarboxylic acid diisooctyl ester and methanol. The vacuum distillation system operates at a pressure of 0.005 MPa, a top temperature of 140°C, and a bottom temperature of 230°C.

[0034] Step 5: Mix the methanol obtained in Step 4 with dioctyl terephthalate at a mass ratio of 1:5 to form a reaction solution, and then enter the circulation pipeline.

[0035] Example 2

[0036] Step 1: Rh-based catalyst and solvent are added to a buffer tank at a mass ratio of 1:10 to form circulating material. The solvent is a mixture of ethanol and diisooctyl cyclohexane-1,4-dicarboxylate at a mass ratio of 1:1. Nitrogen and hydrogen are purged successively. After the purging is completed, the circulating pump is turned on, and the circulating material in the buffer tank is heated to 140°C and pressurized to 4MPa.

[0037] Step 2: Add a reaction solution consisting of ethanol and dioctyl terephthalate in a mass ratio of 1:1 to the circulation line after the separator. When the dioctyl terephthalate and hydrogen in the reaction solution pass through the Venturi reactor, a hydrogenation reaction occurs to generate a mixture of cyclohexane-1,4-dicarboxylic acid diisooctyl ester. The feed flow rate of the reaction solution is 30 g / min, and the flow ratio of the reaction solution to the circulation solution is 1:100.

[0038] Step 3: Start the membrane separator to begin discharging. The cyclohexane-1,4-dicarboxylic acid diisooctyl ester mixture generated in Step 2 is separated from the catalyst through the membrane separation system to obtain the separated mixture. The pressure of the reaction system is maintained at 4 MPa by controlling the hydrogen pressure.

[0039] Step 4: The cyclohexane-1,4-dicarboxylic acid diisooctyl ester solution obtained in Step 3 is transferred to a vacuum distillation system to obtain high-purity cyclohexane-1,4-dicarboxylic acid diisooctyl ester and ethanol. The vacuum distillation system operates at a pressure of 0.001 MPa, a top temperature of 120°C, and a bottom temperature of 250°C.

[0040] Step 5: Mix the ethanol obtained in Step 4 with dioctyl terephthalate in a mass ratio of 1:1 to form a reaction solution, and then enter the circulation pipeline.

[0041] Example 3

[0042] Step 1: Pd-based catalyst and solvent are added to a buffer tank at a mass ratio of 1:100 to form a circulating material. The solvent is a mixture of methanol and diisooctyl cyclohexane-1,4-dicarboxylate at a mass ratio of 1:3.5. Nitrogen and hydrogen are used for purging. After purging, the circulating pump is turned on, and the circulating material in the buffer tank is heated to 80°C and pressurized to 8MPa. Step 2: A reaction solution composed of methanol and dioctyl terephthalate at a mass ratio of 1:3.5 is added to the circulating pipeline after the separator. When dioctyl terephthalate and hydrogen in the reaction solution pass through the Venturi reactor, a hydrogenation reaction occurs to generate a mixture of diisooctyl cyclohexane-1,4-dicarboxylate. The feed flow rate of the reaction solution is 35g / min, and the flow ratio of the reaction solution to the circulating solution is 1:50.

[0043] Step 3: Start the membrane separator to discharge the product. Separate the cyclohexane-1,4-dicarboxylic acid diisooctyl ester mixture generated in Step 2 from the catalyst through the membrane separation system to obtain a mixed solution. Control the pressure of the reaction system at 8 MPa by controlling the pressure of hydrogen.

[0044] Step 4: The cyclohexane-1,4-dicarboxylic acid diisooctyl ester solution obtained in Step 3 is transferred to a vacuum distillation system to obtain high-purity cyclohexane-1,4-dicarboxylic acid diisooctyl ester and methanol. The vacuum distillation system operates at a pressure of 0.003 MPa, a top temperature of 130°C, and a bottom temperature of 245°C.

[0045] Step 5: Mix the methanol obtained in Step 4 with dioctyl terephthalate at a mass ratio of 1:3.5 to form a reaction solution, and then enter the circulation pipeline.

[0046] Example 4

[0047] Step 1: Pt-based catalyst and solvent are added to a buffer tank at a mass ratio of 1:30 to form a circulating material. The solvent is a mixture of ethanol and diisooctyl cyclohexane-1,4-dicarboxylate at a mass ratio of 1:2. Nitrogen and hydrogen are used for purging. After purging, the circulating pump is turned on, and the circulating material in the buffer tank is heated to 160°C and pressurized to 5MPa. Step 2: A reaction solution composed of ethanol and dioctyl terephthalate at a mass ratio of 1:2 is added to the circulating pipeline after the separator. When dioctyl terephthalate and hydrogen in the reaction solution pass through the Venturi reactor, a hydrogenation reaction occurs to generate a mixture of diisooctyl cyclohexane-1,4-dicarboxylate. The feed flow rate of the reaction solution is 50g / min, and the flow ratio of the reaction solution to the circulating solution is 1:30.

[0048] Step 3: Start the membrane separator to discharge the product. Separate the cyclohexane-1,4-dicarboxylic acid diisooctyl ester mixture generated in Step 2 from the catalyst through the membrane separation system to obtain a mixed solution. Control the pressure of the reaction system at 5 MPa by controlling the pressure of hydrogen.

[0049] Step 4: The cyclohexane-1,4-dicarboxylic acid diisooctyl ester solution obtained in Step 3 is transferred to a vacuum distillation system to obtain high-purity cyclohexane-1,4-dicarboxylic acid diisooctyl ester and ethanol. The vacuum distillation system operates at a pressure of 0.004 MPa, a top temperature of 135°C, and a bottom temperature of 240°C.

[0050] Step 5: Mix the ethanol obtained in Step 4 with dioctyl terephthalate in a mass ratio of 1:2 to form a reaction solution, and then enter the circulation pipeline.

[0051] Comparative Example 1

[0052] This comparative example provides a method for preparing diisooctyl cyclohexane-1,4-dicarboxylate using a fixed-bed process with an Rh-based catalyst. The reactants, dioctyl terephthalate and ethanol, are mixed at a mass ratio of 1:1 and fed into a fixed-bed reactor through the catalyst bed. The feed flow rate is 2.1 g / min, the residence time is 9 h, the reaction pressure is 4 MPa, and the reaction temperature is 140 °C.

[0053] The samples collected from the products of Examples 1-4 and the sample collected from Comparative Example 1 were analyzed by chromatography, and the conversion rate of diisooctyl terephthalate and the selectivity of diisooctyl cyclohexane-1,4-dicarboxylate were calculated. The table below summarizes the conversion rate of diisooctyl terephthalate and the selectivity of diisooctyl cyclohexane-1,4-dicarboxylate in Examples 1-4 and Comparative Example 1.

[0054]

[0055] Comparing Example 2 and Comparative Example 1, we can see that in Comparative Example 1, the feed flow rate in the fixed-bed reactor was 2.1 g / min, the residence time was 9 h, and the amount of diisooctyl terephthalate reacted was 561.9 g. In contrast, in Example 2 of this invention, under the same reaction conditions (temperature, pressure, etc.), the amount of diisooctyl terephthalate reacted after 9 h was 8091.9 g. This invention demonstrates continuous and stable reaction, resulting in high production efficiency.

[0056] Comparing Examples 1-4 with Comparative Example 1, we can see that Comparative Example 1 uses a fixed-bed process with a residence time as long as 9 hours. Fixed-bed reactors have poor mass and heat transfer, easily causing overheating and runaway phenomena, affecting catalyst activity, and also generating side reactions. In contrast, this invention uses a Venturi reactor, which has a large gas-solid-liquid three-phase contact area, a high gas-liquid mixing ratio, a fast reaction rate, and high production efficiency. This invention is a continuous and stable reaction; the temperature and pressure remain constant throughout the entire reaction process, resulting in high reactant conversion rate and high selectivity for the target product.

[0057] As can be seen from the results of the above embodiments and comparative tests:

[0058] (1) This invention utilizes a loop reaction process, employing a Venturi reactor combined with membrane separation and vacuum distillation, to achieve efficient and continuous production of diisooctyl cyclohexane-1,4-dicarboxylate. Compared to conventional fixed-bed reactors, this invention offers better mixing of reactants, higher mass transfer efficiency, faster reaction rate, and higher production efficiency. The reaction does not require prolonged residence time in the reactor, and the conversion rate of the reactants to diisooctyl phthalate and the selectivity of the target product, cyclohexane-1,4-dicarboxylate, can reach over 99%.

[0059] (2) The present invention has a simple process, mild reaction conditions, fast reaction rate, high production efficiency and low energy consumption, and can realize industrial production.

[0060] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for preparing diisooctyl cyclohexane-1,4-dicarboxylate by continuous catalytic hydrogenation, characterized in that: The method comprises the following steps: Step 1: Add the catalyst and solvent into a buffer tank in a certain proportion to form a circulating material, and replace them with nitrogen and hydrogen in turn. After the replacement is completed, start the circulating pump, and then increase the temperature and pressure of the circulating material in the buffer tank to the reaction conditions; Step 2: adding a reaction liquid consisting of dioctyl terephthalate and a solvent into a circulation pipeline after the separator, and the dioctyl terephthalate and hydrogen in the reaction liquid undergo a hydrogenation reaction when passing through a venturi reactor to generate a cyclohexane-1,4-dicarboxylic acid diisooctyl ester mixed liquid; Step 3: opening the membrane separator to start discharging, separating the cyclohexane-1,4-dicarboxylic acid diisooctyl ester mixed liquid generated in the reaction in step 2 from the catalyst through the membrane separation system to obtain a separated mixed liquid, and controlling the pressure of the reaction system by controlling the pressure of hydrogen; Step 4: conveying the diisooctyl cyclohexane-1,4-dicarboxylate solution obtained in step 3 to a vacuum distillation system to obtain high-purity diisooctyl cyclohexane-1,4-dicarboxylate and a solvent; Step 5: The solvent obtained in step 4 is mixed with dioctyl terephthalate in proportion to form a reaction solution, which then enters the circulation pipeline.

2. The method for preparing diisooctyl cyclohexane-1,4-dicarboxylate by continuous catalytic hydrogenation according to claim 1, characterized in that: The active component of the catalyst in step 1 is Ru, Rh, Pd or Pt; the reaction pressure is 4-8 MPa, and the reaction temperature is 80-160°C.

3. The method for preparing diisooctyl cyclohexane-1,4-dicarboxylate by continuous catalytic hydrogenation according to claim 1, characterized in that: The solvent described in step 1 is a mixed solution of methanol or ethanol and diisooctyl cyclohexane-1,4-dicarboxylate in a mass ratio of 1:(1-5); the mass ratio of the solvent to the catalyst is (10-100):

1.

4. The method for preparing diisooctyl cyclohexane-1,4-dicarboxylate by continuous catalytic hydrogenation according to claim 1, characterized in that: The solvent described in step 2 is methanol or ethanol; the mass ratio of the solvent to dioctyl terephthalate is 1:(1-5); and the flow ratio of the reaction liquid to the circulating liquid is 1:20-1:

100.

5. The method for preparing diisooctyl cyclohexane-1,4-dicarboxylate by continuous catalytic hydrogenation according to claim 1, characterized in that: The membrane separator described in step 3 is a cross-flow filtration system.

6. The method for preparing diisooctyl cyclohexane-1,4-dicarboxylate by continuous catalytic hydrogenation according to claim 1, characterized in that: The operating pressure of the vacuum distillation system described in step 4 is 0.001-0.005 MPa, the tower top temperature is 120-140°C, and the tower bottom temperature is 230-250°C.

7. The method for preparing diisooctyl cyclohexane-1,4-dicarboxylate by continuous catalytic hydrogenation according to claim 1, characterized in that: The solvent described in step 5 is methanol or ethanol; the ratio of the solvent to dioctyl terephthalate is consistent with the ratio described in step 2.

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