A method for preparing cyclopentene by selective hydrogenation of dicyclopentadiene depolymerization

Abstract

This invention belongs to the field of catalytic reaction engineering and relates to a method for the selective hydrogenation of dicyclopentadiene to produce cyclopentene via depolymerization. Dicyclopentadiene undergoes continuous liquid-phase depolymerization in the bottom of a reactive distillation column. A mixture of decahydronaphthalene and ethylcyclohexane in the bottom of the column serves as the heating medium, directly contacting, mixing, and transferring mass and heat with the dicyclopentadiene. The heating medium inhibits the polymerization of DCPD and CPD to form other polymers. The depolymerization product, cyclopentadiene, and the entrained dicyclopentadiene are mixed with H2 and CO2 and enter the stripping section. The dicyclopentadiene continues to depolymerize. After depolymerization, it contacts, transfers mass and heat with the cyclopentane fraction refluxed from the rectification section, and undergoes selective hydrogenation on a hydrogenation catalyst (Pd-Pt-Ag@Al2O3) packed in the reactive distillation section. The product after selective hydrogenation passes through the rectification section, and cyclopentene with a purity greater than 99.5% is collected from the top of the column. This invention can achieve high selectivity and yield of the target product, cyclopentadiene.

Description

Technical Field

[0001] This invention belongs to the field of catalytic reaction engineering and relates to a method for selective hydrogenation of dicyclopentadiene to produce cyclopentene. Background Technology

[0002] Cyclopentene and its downstream products are important applications of dicyclopentadiene. Producing these products not only consumes dicyclopentadiene but also, through further processing, can increase the added value of dicyclopentadiene, leading to its widespread use in the pharmaceutical industry, organic synthesis, and synthetic rubber. Currently, most cyclopentadiene is produced by the depolymerization of dicyclopentadiene, followed by catalytic selective hydrogenation. During this process, the main byproducts include cyclopentane, dicyclopentadiene, dihydrodicyclopentadiene, and tetrahydrodicyclopentadiene.

[0003] The hydrogenation of cyclopentadiene proceeds in two stages: the first stage hydrogenates to cyclopentene, and the second stage further hydrogenates to cyclopentane. During the reaction, cyclopentadiene polymerization and dicyclopentadiene hydrogenation also occur. Kinetic and thermodynamic studies reveal that controlling the hydrogenation reaction entirely within the cyclopentene stage is difficult, and the final product, cyclopentane, is always present. For the selective hydrogenation of dicyclopentadiene, palladium catalysts are commonly used, often modified with other metals to reduce the adsorption capacity of active sites for mono-olefins, thereby improving the selectivity for mono-olefin formation. This process requires selecting a suitable support and its structure to ensure the rapid removal of the generated mono-olefin from the catalyst surface, preventing further hydrogenation to alkanes. Eggshell-type catalysts, where the active metal is concentrated on the support surface, effectively reduce the amount of precious metal active components needed, increasing catalyst activity. Furthermore, the eggshell-shaped catalyst distribution facilitates the desorption of reaction products from the catalyst surface, preventing further reaction of the target product and improving the selectivity of intermediate products in irreversible cascade reactions.

[0004] The hydrogenation of cyclopentadiene is a strongly exothermic reaction. If cyclopentadiene is introduced directly into the reaction bed without dilution, the bed temperature will rise excessively, which will not only reduce the selectivity of cyclopentadiene but, more seriously, accelerate the dimerization of cyclopentadiene and deactivate the catalyst. Catalytic distillation technology can improve the selectivity for mono-olefin formation and reduce separation processes. Currently, the liquid-phase depolymerization of dicyclopentadiene involved in reactive distillation for cyclopentadiene production requires the addition of a large amount of polymerization inhibitor, a deficiency present in known existing technologies.

[0005] US6100435A discloses "Use of catalytic distillation to produce cyclopentane or cyclopentene", which uses catalytic distillation to prepare cyclopentene or cyclopentane with a purity of 97-98%. However, due to the failure to effectively control the temperature of the reactive distillation section, i.e., the depth of the hydrogenation reaction cannot be controlled, the main product is decacyclopentane.

[0006] The publication number CN102911001A discloses a method for preparing cyclopentene from dicyclopentadiene. The method uses a catalytic distillation process to produce cyclopentene. A recyclable diluent is introduced at the lower 1 / 4 of the catalytic distillation section to control the outlet temperature of the reaction distillation section. A polymerization inhibitor is added to dicyclopentadiene to prevent polymerization and the formation of polymers, but this reduces the product yield.

[0007] The publication number CN108069814A discloses a method for producing cyclopentene from dicyclopentadiene. The method involves catalytic distillation, where the dicyclopentadiene feedstock is heated and partially decomposed, then fed directly into a distillation column along with hydrogen. The decomposition products of dicyclopentadiene and hydrogen flow upwards into a reactive distillation section, where they react with the light components of the refluxed distillate oil on a hydrogenation catalyst packed within the reactive distillation section, undergoing mass transfer, heat transfer, and hydrogenation reactions. The reacted products are discharged from the top of the column after passing through the distillation section. The depolymerization process of dicyclopentadiene still requires the addition of p-tert-butylcatechol as a polymerization inhibitor. Summary of the Invention

[0008] To address the aforementioned problems, this invention proposes a method for selective hydrogenation of dicyclopentadiene to produce cyclopentene. CO2 is introduced as an inert atmosphere into the liquid-phase depolymerization of dicyclopentadiene to reduce the partial pressure of cyclopentadiene and simultaneously act as a polymerization inhibitor to suppress the polymerization of dicyclopentadiene and cyclopentadiene. The byproduct cyclopentane is used as a diluent to control the temperature of the catalytic distillation section.

[0009] To achieve the above objectives, the following technical solution is adopted: a method for selective hydrogenation of dicyclopentadiene to produce cyclopentene, characterized in that the method includes,

[0010] a. Dicyclopentadiene is continuously introduced from the bottom of a reactive distillation column containing a heating medium and undergoes liquid-phase depolymerization;

[0011] b. The depolymerization product cyclopentadiene and the entrained dicyclopentadiene are mixed with H2 and CO2 and enter the stripping section for further depolymerization;

[0012] c. After complete depolymerization, the product cyclopentane is collected from the side stream of the rectification section and condensed in the condenser of the column into the reflux tank of the column. Most of it is refluxed as a diluent and comes into contact with the cyclopentadiene fraction from the stripping section for mass and heat transfer. The reaction temperature at the inlet of the reaction rectification section is controlled by controlling the reflux flow rate of the reflux tank of the column. A small portion is collected as a by-product.

[0013] d. Selective hydrogenation is carried out in the reactive distillation section filled with hydrogenation catalyst. The product cyclopentene after selective hydrogenation reaction is distilled in the distillation section, cooled in the top condenser and enters the top reflux tank. Part of it is refluxed at the top of the column, and part is collected as a reaction product. The purity of the collected cyclopentene is ensured to be greater than 99.5% by controlling the reflux ratio. The gas separated by cooling in the top reflux tank is mixed with hydrogen and recycled back into the bottom of the column to participate in the reaction.

[0014] Preferably, the heating medium in the reboiler is a mixture of decahydronaphthalene and ethylcyclohexane, with a molar ratio of decahydronaphthalene to ethylcyclohexane of 5:1-9:1. Decahydronaphthalene, as a heat medium, ensures uniform heating without localized overheating and, as a hydrogen-donating solvent, prevents the polymerization of dicyclopentadiene, thus improving its utilization rate. Ethylcyclohexane utilizes its latent and sensible heat to control the temperature of the reboiler and stripping section (160-180℃), acting as a driving force for heat transfer and ensuring good temperature distribution. The latent and sensible heat processes absorb and carry away the heat of reaction, effectively controlling the temperature of the reaction zone. The light components of the distillate oil allow the inlet temperature of the upper rectification section to be controlled at approximately 90℃.

[0015] Preferably, the reactive distillation column has a top pressure of 0.2-0.3 MPa, a bottom temperature of 180-200℃, a top temperature of 65-75℃, a top reflux ratio of 2-4, and a reflux flow rate of reflux tank in the column that is 3-4 times the feed rate of dicyclopentadiene.

[0016] Preferably, the rectification section has 12-16 trays; the stripping section is packed with ceramic stepped packing, and the distillation trays need to be 20-40.

[0017] Preferably, the inlet temperature of the reactive distillation section is 60-100℃, the molar ratio of hydrogen to dicyclopentadiene is greater than 2, and the CO2 concentration in the stripping section is maintained at 30-50%. The introduction of CO2 into the lower part of the stripping section serves three purposes: first, to reduce the polymerization of dicyclopentadiene and cyclopentadiene; second, to reduce the partial pressure of cyclopentadiene in this section and promote the depolymerization of dicyclopentadiene; and third, to serve as a dilution gas to increase the selectivity of the selective hydrogenation catalyst for cyclopentadiene.

[0018] Preferably, the volume ratio of cyclopentene extracted as a reaction product to the hydrogenation catalyst loaded in the reactive distillation section is 1:2-2:1.

[0019] Preferably, the amount of cyclopentane produced as a byproduct is determined based on the results of the selected hydrogenation reaction.

[0020] Preferably, the concentration of dicyclopentadiene in the bottom of the column in step a is 85-99%. When low concentration dicyclopentadiene is used as raw material, the purity of the product cyclopentene can still be greater than 99.5%. After continuous operation for a period of time, the heat medium in the bottom of the reactive distillation column needs to be distilled to ensure the purity of decahydronaphthalene and ethylcyclohexane.

[0021] Preferably, the hydrogenation catalyst is an eggshell-type Pd-Pt-Ag@Al2O3 catalyst, wherein the molar ratio of Pd:Pt:Ag is 40:10:(1-3), and the total metal loading is 0.3-0.5%. The eggshell-type catalyst facilitates the desorption of the intermediate product cyclopentene from the catalyst surface, thus avoiding further reaction.

[0022] As can be seen from the above technical solution, this method introduces CO2 as an inert atmosphere into the liquid-phase depolymerization of dicyclopentadiene in the catalytic distillation column, reducing the partial pressure of cyclopentadiene, which is beneficial to the depolymerization of dicyclopentadiene. At the same time, CO2 can also inhibit the polymerization of dicyclopentadiene and cyclopentadiene, acting as a polymerization inhibitor. The by-product cyclopentane is used as a diluent to control the temperature of the catalytic distillation section.

[0023] To address the issue of low selectivity for hydrogenation of cyclopentene in the catalysts used in the reactive distillation section, a highly active and selective eggshell-type Pd-Pt-Ag catalyst was adopted as the selective hydrogenation catalyst. This catalyst not only exhibits good hydrogenation selectivity for cyclopentene but also possesses naphthalene thiolic properties, significantly increasing the feedstock adaptability of dicyclopentadiene.

[0024] This method involves continuous feeding of dicyclopentadiene and continuous discharge of cyclopentene, achieving continuous production. It features simple process, high dicyclopentadiene utilization, good catalyst activity, high selectivity, and high product purity. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the process flow of the present invention.

[0026] As shown in the figure: 1. Bottom of the column; 2. Stripping section; 3. Reactive distillation section; 4. Rectifying section; 5. Top condenser; 6. Top reflux tank; 7. Middle condenser; 8. Middle reflux tank. Detailed Implementation

[0027] Example 1

[0028] Eggshell-shaped Pd-Pt-Ag catalysts were prepared using a CO reaction deposition method. Spherical Al₂O₃ supports (2-6 mm in diameter) were added to a mixed metal salt solution of Pd, Pt, and Ag, with a Pd:Pt:Ag molar ratio of 40:10:(1-3). Rapid reduction of the metals with CO was used to control the deposition of Pd-Pt-Ag on the support surface. After filtration, washing, and drying under an inert atmosphere, a stable eggshell-shaped Pd-Pt-Ag catalyst was formed, with a metal shell thickness of 50-100 μm. The total noble metal loading was 0.3-0.5%. The catalyst was initially reduced with H₂ at 300 °C for 2 h. Homogeneous catalysts with the same metal ratio and loading were prepared using an impregnation method as a comparison. Comparing the hydrogenation effect of cyclopentadiene in a fixed bed, the hydrogenation reaction conditions were: reaction temperature 80℃, reaction pressure 0.2MPa, and space velocity 0.5h⁻¹. -1 (Cyclopentadiene feed rate per hour to catalyst volume ratio), hydrogen-to-oil ratio 200, hydrogenation effect is as follows:

[0029]

[0030] As shown in the table, the eggshell-type catalyst with the same metal loading exhibits extremely high activity and selectivity in the cyclopentadiene fixed-bed reaction. Even after the addition of thiophene, it still shows high activity. Compared with the homogeneous catalyst, the selectivity for the target product cyclopentene is significantly improved.

[0031] The effect of reaction conditions on the hydrogenation of eggshell-type Pd-Pt-Ag selective hydrogenation catalyst cyclopentadiene in a fixed bed was investigated. The hydrogenation reaction conditions were: reaction temperature 60-100℃, reaction pressure 0.2MPa, and space velocity 0.5-2h⁻¹. -1 (Cyclopentadiene feed rate per hour to catalyst volume ratio), hydrogen-to-oil ratio 200, the effects of reaction temperature and space velocity on hydrogenation were investigated as follows:

[0032]

[0033] The table shows that low temperature and high air velocity are conducive to the formation of cyclopentene.

[0034] The stability of selective hydrogenation of cyclopentadiene using an eggshell-type Pd-Pt-Ag catalyst was investigated. The hydrogenation reaction conditions were: reaction temperature 80℃, reaction pressure 0.2 MPa, and space velocity 0.5 h⁻¹. -1 (Cyclopentadiene feed rate per hour to catalyst volume ratio), hydrogen-to-oil ratio 200, the results of catalyst stability investigation are shown in the table below:

[0035]

[0036]

[0037] As shown in the table, the eggshell-type Pd-Pt-Ag catalyst exhibits extremely high stability in the selective hydrogenation of cyclopentadiene to cyclopentene.

[0038] Example 2

[0039] The column of the catalytic distillation column is divided into three sections, each containing hydrogenation catalyst and separation packing. The inner diameter of the column is 4 cm. Specifically, the upper section is the rectification section (4), which is filled with rectification separation packing; the middle section is the reactive distillation section (3), which is filled with 200 mL of eggshell-type Pd-Pt-Ag catalyst with a diameter of 2 mm that has selective hydrogenation function; and the lower section is the stripping section (2), which is filled with separation packing. The raw material dicyclopentadiene is preheated to 100°C and then continuously fed into the bottom (10 L) of the catalytic distillation column containing a pre-filled heat medium (5 L). The bottom (1) is heated by external heat transfer oil. Here, dicyclopentadiene mixes with the heat medium and undergoes liquid-phase depolymerization. The depolymerized dicyclopentadiene, along with some dicyclopentadiene, mixes with H2 and CO2 and enters the stripping section (2) filled with ceramic stepped packing for further depolymerization and rectification separation. The stripping section (2) theoretically requires 20-40 distillation trays. The cyclopentadiene from the stripping section (2) contacts, transfers mass and heat with the cyclopentane fraction collected from the side stream of the rectification section and refluxed. The inlet reaction temperature of the reactive rectification section is controlled by the reflux flow rate of the reflux tank (8) in the control column, and the two fractions enter the reactive rectification section (3) together for selective hydrogenation and distillation separation. In the reactive rectification bed, the reaction products absorb the heat of reaction and vaporize, allowing the heat released by the reaction to be removed from the reaction bed in a timely manner and ensuring a uniform temperature distribution in the bed. In addition, cyclopentane can both dilute the concentration of cyclopentadiene and absorb and carry away the heat of reaction using its latent and sensible heat, thus controlling the temperature of the reaction zone. This controls the outlet temperature of the reactive rectification section to be around 80-90℃. The hydrogenated product is selected to enter the rectification section (4), which has 12-16 theoretical plates. The top product, cyclopentene, is collected from the top of the column at a temperature of 65°C. It is condensed in the top condenser (5) and enters the top reflux tank (6). A portion is refluxed at the top (reflux temperature of 40°C) with a reflux ratio of 2-4 to maintain a stable temperature at the top of the column; the other portion is collected as a reaction product. The volume ratio of cyclopentene collected to the hydrogenation catalyst loading is 1:2. A cyclopentane fraction is extracted from the middle of the rectification section (4). After condensation, a portion is used as a diluent and enters the inlet of the reactive rectification section (3), while a small portion is collected as a byproduct cyclopentane. After the system reaches equilibrium, the feed space velocity for dicyclopentadiene is 0.5 h⁻¹. -1 (Feed to catalyst volume hourly space velocity). With a CO2 concentration of 30-50% in the system, the effect of the composition of the heat transfer medium on the depolymerization of dicyclopentadiene was investigated. Specific results are shown in the table below.

[0040]

[0041] Under the condition that the system operating conditions remain unchanged, the effect of introducing CO2 on depolymerization and hydrogenation was investigated. The specific results are shown in the table below.

[0042]

[0043]

[0044] Note: [1] Liquid feed volume hourly space velocity: the volume hourly space velocity of the feed relative to the catalyst.

[0045] [2] Product yield = [cyclopentene (alkane) / (moles of dicyclopentadiene added * 2)] * 100%. Example 2: Using dicyclopentadiene (DPCD) of different concentrations (85% and 95%) as raw materials, the purity and yield of the products cyclohexene and cyclohexane under the same operating conditions of reactive distillation process are shown in the following table:

[0046] 85％ 96.7 93.12 3.46 95％ 98.2 95.16 2.54

[0047] This invention is not limited to this embodiment. Any equivalent concept or modification within the technical scope disclosed in this invention shall be included within the protection scope of this invention.

Claims

1. A method for selectively hydrogenating dicyclopentadiene to produce cyclopentene via depolymerization, characterized in that, The method includes, a. Dicyclopentadiene is continuously introduced from the bottom (1) of a reactive distillation column containing a heating medium and undergoes liquid-phase depolymerization; b. The depolymerization product cyclopentadiene and the entrained dicyclopentadiene are mixed with H2 and CO2 and enter the stripping section (2) for further depolymerization; c. After complete depolymerization, the product cyclopentane is collected from the side stream of the rectification section (4) and condensed in the condenser (7) of the tower and enters the reflux tank (8) of the tower. Most of it is refluxed as a diluent and comes into contact with the cyclopentadiene fraction from the stripping section for mass and heat transfer. The reaction temperature at the inlet of the reaction rectification section is controlled by controlling the reflux flow rate of the reflux tank in the tower. A small part is collected as a by-product. d. Selective hydrogenation is carried out in the reaction distillation section (3) filled with hydrogenation catalyst. The product cyclopentene after selective hydrogenation reaction is distilled in the distillation section (4), cooled by the top condenser (5) and enters the top reflux tank (6). Part of it is refluxed at the top of the column, and part of it is collected as a reaction product. The purity of the collected cyclopentene is ensured to be greater than 99.5% by controlling the reflux ratio. The gas separated by cooling in the top reflux tank (6) is mixed with hydrogen and recycled back into the bottom of the column (1) to participate in the reaction.

2. The method for selective hydrogenation of dicyclopentadiene to cyclopentene according to claim 1, characterized in that, The heating medium of the tower (1) is a mixture of decahydronaphthalene and ethylcyclohexane, with a molar ratio of decahydronaphthalene to ethylcyclohexane of 5:1-9:

1.

3. The method for selective hydrogenation of dicyclopentadiene to cyclopentene according to claim 2, characterized in that, The pressure at the top of the reactive distillation column is 0.2-0.3 MPa, and the temperature of the bottom (1) is 180-200 °C. o C, the temperature at the top of the tower is 65-75°C. o C, the top reflux ratio is 2-4, and the reflux flow rate of the reflux tank (8) in the tower is 3-4 times the feed rate of dicyclopentadiene.

4. The method for selective hydrogenation of dicyclopentadiene to cyclopentene according to claim 3, characterized in that, The rectification section (4) has 12-16 trays; the stripping section (2) is packed with ceramic stepped packing and requires 20-40 trays.

5. The method for selective hydrogenation of dicyclopentadiene to cyclopentene according to claim 4, characterized in that, The inlet temperature of the reactive distillation section (3) is 60-100°C. o C, the molar ratio of hydrogen to dicyclopentadiene is greater than 2, and the CO2 concentration in the stripping section (2) is maintained at 30-50%.

6. The method for selective hydrogenation of dicyclopentadiene to cyclopentene according to claim 5, characterized in that, The volume ratio of the amount of cyclopentene extracted as a reaction product to the amount of hydrogenation catalyst loaded in the reaction distillation section (3) is 1:2-2:

1.

7. The method for selective hydrogenation of dicyclopentadiene to cyclopentene according to claim 6, characterized in that, The amount of cyclopentane extracted as a byproduct is determined based on the results of the selected hydrogenation reaction.

8. The method for selective hydrogenation of dicyclopentadiene to cyclopentene according to claim 7, characterized in that, The concentration of dicyclopentadiene entering the bottom of the column (1) ranges from 85% to 99%.

9. The method for selective hydrogenation of dicyclopentadiene to cyclopentene according to any one of claims 1-8, characterized in that, The hydrogenation catalyst is an eggshell-type Pd-Pt-Ag@Al2O3 catalyst, wherein the molar ratio of Pd:Pt:Ag is 40:10:(1-3), and the total metal loading is 0.3-0.5%.

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