Preparation method of norbornene

Abstract

The present invention provides a norbornene preparation method, which comprises that ethylene and cyclopentadiene are subjected to a reaction in an ionic liquid to prepare the norbornene. The preparation method of norbornene provided by the invention has the characteristics of lower reaction pressure and higher safety.

Description

Technical Field

[0001] This invention belongs to the field of chemical engineering, and specifically relates to a method for preparing norbornene. Background Technology

[0002] Norbornene is an important monomer for the production of cyclic olefin copolymers and cyclic olefin polymers. Cyclic olefin copolymers and cyclic olefin polymers are high-performance thermoplastic engineering plastics with excellent light transmittance, water and oxygen barrier properties, chemical resistance, and low leaching characteristics. They are widely used in fields with strict quality standards, such as medical devices, optical lenses, and electronic components, for products like vaccine vials, pre-filled syringes, and mobile phone lenses.

[0003] Norbornene monomer can be prepared via a Diels-Alder reaction between cyclopentadiene and ethylene. The process requires no catalyst; under thermal influence, electrons flow from the HOMO orbital of the diene-containing cyclopentadiene (containing a conjugated double bond) to the LUMO orbital of the diene-loving ethylene, resulting in a cycloaddition reaction and the formation of norbornene. Depending on the state of the dicyclopentadiene or cyclopentadiene during the reaction, the synthesis process of norbornene can be divided into two types: liquid-phase reaction and gas-phase reaction. In the gas-phase reaction process, the dicyclopentadiene or cyclopentadiene is heated to a gaseous state during the reaction, then mixed with ethylene gas before entering the reactor for further reaction. The resulting norbornene product is also gaseous. In the gas-phase reaction process, the material concentration is lower, the residence time is shorter, and the mixing is more uniform and thorough, resulting in high selectivity for the target product, norbornene, and fewer byproducts. However, gas-phase reaction processes involve large reactant volumes, resulting in low reaction efficiency and a lower final conversion rate. Furthermore, the temperature of gas-phase reactions is approximately 100°C higher than that of liquid-phase reactions, leading to more engineering safety issues. Therefore, liquid-phase reactions are still more commonly used in actual production. In liquid-phase reactions, dicyclopentadiene or cyclopentadiene is in a liquid state during the reaction, and ethylene gas dissolves in the liquid mixture, producing norbornene, which is also in a liquid state. Liquid-phase reactions include solvent-free and solvent-based processes. In solvent-free processes, uneven mixing of materials leads to excessively high local concentrations of cyclopentadiene, numerous side reactions, low selectivity for norbornene, and a high tendency to form large amounts of carbon and resin, clogging reactors and related equipment. In solvent-based processes, the reaction takes place in a solvent, which dissolves oligomers or polymers, prevents polymer deposition, inhibits carbon or resin formation, and improves reaction selectivity. Therefore, solvent-based liquid-phase reactions are the primary method used in the actual preparation of norbornene.

[0004] Chinese patent CN117964441A discloses a synthesis process for norbornene. A certain proportion of ethylene, dicyclopentadiene, and a solvent are mixed and preheated to 120-180℃. A low-temperature tubular reaction is carried out at 160-220℃ and 10-40 MPa to obtain the reaction product. Subsequently, a high-temperature tubular reaction is carried out at 210-300℃ and 10-50 MPa. The reaction product is then flash-distilled and purified to obtain norbornene. While this process can improve the yield of norbornene to some extent, it uses toluene as a solvent, which is flammable, explosive, and prone to producing toxic substances. Furthermore, the reaction is carried out under high pressure, posing a greater challenge to the safe and stable operation of the process.

[0005] As can be seen from the above, the current methods for preparing norbornene require high reaction pressures, posing safety risks. Therefore, developing a safer method for preparing norbornene with lower reaction pressures has become a research direction in this field. Summary of the Invention

[0006] This invention provides a method for preparing norbornene, achieving the technical effect of lower reaction pressure and greater safety.

[0007] The present invention provides a method for preparing norbornene, comprising reacting ethylene with cyclopentadiene in an ionic liquid to obtain the norbornene.

[0008] In the above-described method for preparing norbornene, the reaction temperature is 180-240℃, the reaction pressure is 0.5-2.5 MPa, and the reaction time is 10-40 min.

[0009] In the method for preparing norbornene as described above, the Henry's law constant of ethylene in the ionic liquid is ≤8 MPa during the reaction.

[0010] In the method for preparing norbornene as described above, the boiling point of the ionic liquid at atmospheric pressure is greater than or equal to 260°C.

[0011] In the method for preparing norbornene as described above, the ionic liquid is selected from at least one of 1-methyl-3-octylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium nitrate, 1-butyl-3-methylimidazolium hexafluorophosphate, 1-hexyl-3-methylimidazolium hexafluorophosphate, and 1-octyl-3-methylimidazolium hexafluorophosphate.

[0012] In the method for preparing norbornene as described above, the molar ratio of ethylene to cyclopentadiene is (1-3):1; and / or,

[0013] The mass ratio of the cyclopentadiene to the ionic liquid is 1:(0.8-6).

[0014] In the method for preparing norbornene as described above, the Henry's law constant of ethylene in the ionic liquid is ≤6 MPa; and / or,

[0015] The boiling point of the ionic liquid at normal pressure is greater than or equal to 280℃.

[0016] In the method for preparing norbornene as described above, the reaction temperature is 200-240°C; and / or,

[0017] The reaction pressure is 0.5-1.5 MPa; and / or,

[0018] The reaction time is 20-35 min.

[0019] The method for preparing norbornene as described above involves continuously feeding a liquid-phase mixture comprising ethylene, cyclopentadiene, and an ionic liquid into a stirred reactor to obtain the norbornene.

[0020] In the method for preparing norbornene as described above, the temperature of the liquid phase mixture is 50-110°C.

[0021] The method for preparing norbornene provided by this invention uses an ionic liquid with good thermal stability, low vapor pressure, and low volatility to replace traditional organic solvents, eliminating the need to increase reaction pressure to prevent solvent vaporization, thereby achieving a lower reaction pressure and a safer technical effect. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0023] In existing technologies, the preparation methods for norbornene often suffer from high reaction pressures, posing safety hazards. The inventors analyzed that the reason for this phenomenon lies in the low boiling points of the organic solvents used in existing technologies. To reduce solvent vaporization, the reaction pressure needs to be increased, resulting in high reaction pressures in the norbornene preparation methods. Through research, the inventors discovered that ionic liquids with higher boiling points can be used as solvents to replace traditional organic solvents. Because ionic liquids have higher boiling points, the required reaction pressure is significantly reduced compared to traditional organic solvents, thus achieving a lower reaction pressure and greater safety in the norbornene preparation method.

[0024] Based on this, the first aspect of the present invention provides a method for preparing norbornene. This method involves reacting ethylene with cyclopentadiene in an ionic liquid to obtain norbornene. Specifically, an ionic liquid is used as a solvent to accommodate a Diels-Alder reaction between ethylene and cyclopentadiene to generate norbornene.

[0025] Ionic liquids refer to salts composed entirely of cations and anions that are liquid at or near room temperature. This invention does not limit the specific type of ionic liquid; it only requires that the liquid be suitable as a solvent to accommodate the Diels-Alder reaction of ethylene and cyclopentadiene to produce norbornene.

[0026] This invention does not limit the specific reaction conditions for the Diels-Alder reaction between ethylene and cyclopentadiene; any reaction that produces norbornene is acceptable. In one embodiment, the reaction temperature is greater than or equal to 180°C, the reaction pressure is greater than or equal to 0.5 MPa, and the reaction time is greater than or equal to 10 min.

[0027] The inventors have discovered that the preparation method for norbornene by reacting ethylene with cyclopentadiene in an ionic liquid exhibits advantages such as lower reaction pressure and a higher safety factor. The inventors believe this is due to several factors: First, the cations and anions in ionic liquids interact through strong electrostatic attraction (Coulomb forces), which are far stronger than intermolecular van der Waals forces. These stronger Coulomb forces require higher energy to transform them from a liquid to a gaseous state, thus increasing the boiling point. Second, ionic liquids are typically non-volatile, meaning they are less likely to produce gaseous molecules upon heating. Most ionic liquids do not boil directly at high temperatures but decompose. This low volatility makes them less prone to sublimation or evaporation upon heating. Finally, the complex and asymmetric ionic structure of ionic liquids makes it difficult for them to form an ordered structure in crystals, thereby lowering the melting point. Simultaneously, the asymmetry in the liquid state makes it more difficult to break intermolecular forces, further increasing the boiling point. Because ionic liquids have higher boiling points, the reaction pressure required by traditional organic solvents is significantly reduced, resulting in a lower reaction pressure and greater safety in the norbornene preparation method.

[0028] Meanwhile, this invention uses cyclopentadiene as a raw material to prepare norbornene monomer, avoiding the slow reaction process of depolymerizing dicyclopentadiene into cyclopentadiene, thereby reducing the reaction residence time and preventing further polymerization of cyclopentadiene monomer. Furthermore, the ample supply of ethylene in the reaction system reduces, to some extent, the related side reactions of further polymerization of cyclopentadiene into polymers, thus improving the selectivity of norbornene monomer in the reaction process.

[0029] Furthermore, ionic liquids, while having a high boiling point, also possess good thermal stability and are green and safe. Compared to traditional organic solvents such as toluene, which are prone to producing toxic substances and explosives, the preparation method of norbornene provided by this invention is safer and more environmentally friendly.

[0030] To further improve the reaction rate, feedstock conversion rate, product selectivity, and yield of the norbornene preparation method provided by this invention, in one embodiment, the reaction temperature can be controlled at 180-240°C, the reaction pressure at 0.5-2.5 MPa, and the reaction time at 10-40 min. A suitable reaction pressure allows for the dissolution of more ethylene in the ionic liquid. By increasing the reactant concentration, and in conjunction with appropriate reaction temperature and reaction events, the reaction rate, feedstock conversion rate, product selectivity, and yield can be improved.

[0031] To achieve both lower reaction pressure and higher raw material conversion rate in the norbornene preparation method provided by this invention, an ionic liquid with a specific Henry's Law coefficient can be selected. Specifically, under the reaction conditions, the Henry's Law coefficient of ethylene in the ionic liquid is ≤8 MPa. The Henry's Law coefficient describes the solubility of a gas in a liquid; it indicates that the concentration of a gas in the liquid at a constant temperature is proportional to the partial pressure of that gas in the gas phase above the liquid phase. The smaller the Henry's Law coefficient, the lower the partial pressure required to dissolve a certain amount of ethylene gas in the ionic liquid. In traditional norbornene preparation methods, cyclopentyl monomer and ethylene monomer are usually dissolved in an organic solvent for reaction, which is a typical gas-liquid reaction process. Due to the low solubility of ethylene in traditional organic solvents, the reaction rate is low, and it is necessary to increase the reaction pressure to increase the solubility of gaseous ethylene in the liquid-phase reaction bulk to improve the reaction rate. This invention uses an ionic liquid as a solvent to react cyclopentadiene with ethylene. Regarding the dissolution process of ethylene, on the one hand, the physical dissolution of ethylene in the ionic liquid conforms to the generalized Henry's Law to a certain extent. In the ionic liquid used in this invention, the Henry's coefficient of ethylene in the ionic liquid under reaction conditions is ≤8 MPa, thus ensuring a sufficient supply of ethylene even at low pressure. Therefore, when an ionic liquid with a smaller Henry's coefficient relative to ethylene is selected, the pressure required to dissolve the same concentration of ethylene is also lower, thus further highlighting the advantage of low reaction pressure in the preparation method of norbornene provided by this invention. Furthermore, selecting an ionic liquid with a Henry's coefficient ≤8 MPa relative to ethylene at a reaction temperature of 180-240℃ and a reaction pressure of 0.5-2.5 MPa further enhances the advantage of low reaction pressure in the preparation method provided by this invention.

[0032] On the other hand, the double bonds in ethylene can form complexes with ions in ionic liquids, thereby increasing the solubility of ethylene in ionic liquids through chemical dissolution. Based on this significant increase in ethylene solubility, it is ultimately possible to achieve an increased reaction rate, a reduced reaction pressure, and an improved conversion rate of cyclopentadiene.

[0033] As a preferred option, when an ionic liquid with a boiling point greater than or equal to 260°C at atmospheric pressure is selected as the solvent to accommodate the reaction of ethylene and cyclopentadiene, the pressure required for the reaction is further reduced due to the high boiling point of the ionic liquid. Thus, the method for preparing norbornene provided by this invention has the more prominent feature of lower reaction pressure.

[0034] In one embodiment, the ionic liquid may be selected from at least one of 1-methyl-3-octylimidazolium tetrafluoroborate ([omim][BF4]), 1-butyl-3-methylimidazolium nitrate ([bmim][NO3]), 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]), 1-hexyl-3-methylimidazolium hexafluorophosphate ([hmim][PF6]), and 1-octyl-3-methylimidazolium hexafluorophosphate ([omim][PF6]). The boiling points of the above ionic liquids are all greater than or equal to 260°C, and the Henry's law coefficient of ethylene in the above ionic liquids under reaction conditions is less than or equal to 8 MPa. This further highlights the advantage of the low reaction pressure provided by the present invention while achieving a higher raw material conversion rate.

[0035] To further increase the raw material conversion rate and product selectivity of the preparation method provided by the present invention, in one embodiment, the molar ratio of ethylene to cyclopentadiene can be controlled to be (1-3):1, or the mass ratio of cyclopentadiene to ionic liquid can be controlled to be 1:(0.8-6); in a more preferred embodiment, the molar ratio of ethylene to cyclopentadiene can be simultaneously controlled to be (1-3):1 and the mass ratio of cyclopentadiene to ionic liquid to be 1:(0.8-6). Appropriate molar ratios of ethylene to cyclopentadiene and mass ratios of cyclopentadiene to ionic liquid allow the preparation method provided by the present invention to achieve higher product selectivity by rationally controlling the proportions of the main and side reaction raw materials.

[0036] To further highlight the low reaction pressure characteristic of the norbornene preparation method provided by this invention, in one specific embodiment, the Henry's law constant of ethylene in the ionic liquid can be controlled to be ≤6 MPa or the boiling point of the ionic liquid at atmospheric pressure to be ≥280°C. In a more preferred embodiment, the Henry's law constant of ethylene in the ionic liquid can be controlled to be ≤6 MPa and the boiling point of the ionic liquid at atmospheric pressure to be ≥280°C. When an ionic liquid with a smaller Henry's law constant and a higher boiling point than ethylene is selected, the pressure required to dissolve the same concentration of ethylene is also lower, thus further emphasizing the low reaction pressure advantage of the norbornene preparation method provided by this invention.

[0037] To further improve the feed conversion rate and product selectivity of norbornene provided by this invention, the reaction temperature is 200-240℃, the reaction pressure is 0.5-1.5 MPa, and the reaction time is 20-35 min. Meeting any one or two, or all of the above conditions, will further enhance the reaction rate, feed conversion rate, product selectivity, and yield of the norbornene preparation method provided by this invention due to the catalytic effect of heat on the Diels-Alder reaction between ethylene and cyclopentadiene, and the weakening effect of the above conditions on the polymerization reaction of cyclopentadiene.

[0038] In one specific embodiment, to improve the preparation efficiency of norbornene, a liquid-phase mixture including ethylene, cyclopentadiene, and an ionic liquid can be continuously fed into a stirred reactor to obtain norbornene. The process involves the liquid-phase mixture including ethylene, cyclopentadiene, and an ionic liquid continuously entering the stirred reactor, residing in the reactor for a period of time, and then exiting the reactor. During this period, the stirred reactor continuously feeds and discharges material. The temperature of the mixed liquid inside the stirred reactor is the reaction temperature, the pressure inside the stirred reactor is the reaction pressure, and the residence time of the liquid-phase mixture in the reactor is the reaction time. In a preferred embodiment, the stirred reactor is an adiabatic reactor. The temperature rise of the ionic liquid solution containing dissolved ethylene and cyclopentadiene during feeding is used to deheat the reaction process, saving cooling costs in the norbornene preparation process. In a preferred embodiment, the temperature of the phase mixture can be controlled at 50-110°C to maximize the neutralization of the heat of reaction.

[0039] The preparation method of norbornene provided by the present invention will be described in detail below through specific embodiments.

[0040] Example 1

[0041] 1-Methyl-3-octylimidazolium tetrafluoroborate [omim][BF4] was used as the reaction solvent. The boiling point of the above ionic liquid is 303℃ under normal pressure, and the Henry's law constant of ethylene in the above ionic liquid under reaction conditions is 5.9 MPa. The mass ratio of cyclopentadiene to [omim][BF4] is 1:4, and the molar ratio of ethylene to cyclopentadiene is 3:1. The ionic liquid solution containing dissolved ethylene and cyclopentadiene is continuously fed into a stirred reactor at a feed temperature of 50℃. The reaction temperature in the stirred reactor is 180℃, the pressure is 2.5 MPa, and the residence time is 40 min. The Diels-Alder reaction between cyclopentadiene and ethylene is carried out in the stirred reactor, thereby generating norbornene monomer. The composition of the reaction products is shown in Table 1.

[0042] Table 1. Component analysis of reaction products (w%)

[0043]

[0044] Example 2

[0045] 1-Butyl-3-methylimidazolium nitrate [bmim][NO3] was used as the reaction solvent. The boiling point of the above ionic liquid is 411℃ under normal pressure, and the Henry's law constant of ethylene in the above ionic liquid under reaction conditions is 7.8 MPa. The mass ratio of cyclopentadiene to [bmim][NO3] is 1:5.6, and the molar ratio of ethylene to cyclopentadiene is 2.5:1. The ionic liquid solution containing dissolved ethylene and cyclopentadiene is continuously fed into a stirred reactor at a feed temperature of 100℃. The reaction temperature in the stirred reactor is 240℃, the pressure is 1.5 MPa, and the residence time is 10 min. The Diels-Alder reaction between cyclopentadiene and ethylene is carried out in the stirred reactor to generate norbornene monomer. The composition of the reaction products is shown in Table 2.

[0046] Table 2. Component analysis of reaction products (w%)

[0047]

[0048] Example 3

[0049] 1-Butyl-3-methylimidazolium hexafluorophosphate [bmim][PF6] was used as the reaction solvent. The boiling point of the above ionic liquid is 271℃ at normal pressure, and the Henry's law constant of ethylene in the above ionic liquid under reaction conditions is 7.9 MPa. The mass ratio of cyclopentadiene to [bmim][PF6] is 1:3, and the molar ratio of ethylene to cyclopentadiene is 1.5:1. The ionic liquid solution containing dissolved ethylene and cyclopentadiene is continuously fed into a stirred reactor at a feed temperature of 70℃. The reaction temperature in the stirred reactor is 200℃, the pressure is 2.0 MPa, and the residence time is 35 min. The Diels-Alder reaction between cyclopentadiene and ethylene is carried out in the stirred reactor, thereby generating norbornene monomer. The composition of the reaction products is shown in Table 3.

[0050] Table 3. Component analysis of reaction products (w%)

[0051]

[0052] Example 4

[0053] 1-Butyl-3-methylimidazolium hexafluorophosphate [bmim][PF6] was used as the reaction solvent. The boiling point of the above ionic liquid is 271℃ at normal pressure, and the Henry's law constant of ethylene in the above ionic liquid under reaction conditions is 7.9 MPa. The mass ratio of cyclopentadiene to [bmim][PF6] is 1:6, and the molar ratio of ethylene to cyclopentadiene is 2.7:1. The ionic liquid solution containing dissolved ethylene and cyclopentadiene is continuously fed into a stirred reactor at a feed temperature of 90℃. The reaction temperature in the stirred reactor is 220℃, the pressure is 1.5 MPa, and the residence time is 30 min. The Diels-Alder reaction between cyclopentadiene and ethylene is carried out in the stirred reactor, thereby generating norbornene monomer. The composition of the reaction products is shown in Table 4.

[0054] Table 4. Component analysis of reaction products (w%)

[0055]

[0056] Example 5

[0057] 1-Hexyl-3-methylimidazolium hexafluorophosphate [hmim][PF6] was used as the reaction solvent. The boiling point of the above ionic liquid is 317℃ under normal pressure, and the Henry's law constant of ethylene in the above ionic liquid under reaction conditions is 6.2 MPa. The mass ratio of cyclopentadiene to [hmim][PF6] is 1:5, and the molar ratio of ethylene to cyclopentadiene is 2:1. The ionic liquid solution containing dissolved ethylene and cyclopentadiene is continuously fed into a stirred reactor at a feed temperature of 100℃. The reaction temperature in the stirred reactor is 230℃, the pressure is 1.0 MPa, and the residence time is 30 min. The Diels-Alder reaction between cyclopentadiene and ethylene is carried out in the stirred reactor, thereby generating norbornene monomer. The composition of the reaction products is shown in Table 5.

[0058] Table 5. Component analysis of reaction products (w%)

[0059]

[0060] Example 6

[0061] 1-Octyl-3-methylimidazolium hexafluorophosphate [omim][PF6] was used as the reaction solvent. The boiling point of the above ionic liquid is 362℃ at normal pressure, and the Henry's law constant of ethylene in the above ionic liquid under reaction conditions is 5.2 MPa. The mass ratio of cyclopentadiene to [omim][PF6] is 1:4.5, and the molar ratio of ethylene to cyclopentadiene is 1.3:1. The ionic liquid solution containing dissolved ethylene and cyclopentadiene is continuously fed into a stirred reactor at a feed temperature of 105℃. The reaction temperature in the stirred reactor is 240℃, the pressure is 0.5 MPa, and the residence time is 25 min. The Diels-Alder reaction between cyclopentadiene and ethylene is carried out in the stirred reactor, thereby generating norbornene monomer. The composition of the reaction products is shown in Table 6.

[0062] Table 6. Component analysis of reaction products (w%)

[0063]

[0064] Example 7

[0065] 1-Octyl-3-methylimidazolium hexafluorophosphate [omim][PF6] was used as the reaction solvent. The boiling point of the above ionic liquid is 362℃ at normal pressure, and the Henry's law constant of ethylene in the above ionic liquid under reaction conditions is 5.2 MPa. The mass ratio of cyclopentadiene to [omim][PF6] is 1:0.8, and the molar ratio of ethylene to cyclopentadiene is 1:1. The ionic liquid solution containing dissolved ethylene and cyclopentadiene is continuously fed into a stirred reactor at a feed temperature of 110℃. The reaction temperature in the stirred reactor is 240℃, the pressure is 2.5 MPa, and the residence time is 40 min. The Diels-Alder reaction between cyclopentadiene and ethylene is carried out in the stirred reactor, thereby generating norbornene monomer. The composition of the reaction products is shown in Table 7.

[0066] Table 7. Component analysis of reaction products (w%)

[0067]

[0068] Example 8

[0069] 1-Hexyl-3-methylimidazolium hexafluorophosphate [hmim][PF6] was used as the reaction solvent. The boiling point of the above ionic liquid is 317℃ at normal pressure, and the Henry's law constant of ethylene in the above ionic liquid under reaction conditions is 6.2 MPa. The mass ratio of cyclopentadiene to [hmim][PF6] is 1:5, and the molar ratio of ethylene to cyclopentadiene is 4:1. The ionic liquid solution containing dissolved ethylene and cyclopentadiene is continuously fed into a stirred reactor at a feed temperature of 100℃. The reaction temperature in the stirred reactor is 230℃, the pressure is 1.0 MPa, and the residence time is 30 min. The Diels-Alder reaction between cyclopentadiene and ethylene is carried out in the stirred reactor, thereby generating norbornene monomer. The composition of the reaction products is shown in Table 8.

[0070] Table 8. Component analysis of reaction products (w%)

[0071]

[0072] Example 9

[0073] 1-Octyl-3-methylimidazolium hexafluorophosphate [omim][PF6] was used as the reaction solvent. The boiling point of the above ionic liquid is 362℃ under normal pressure, and the Henry's law constant of ethylene in the above ionic liquid under reaction conditions is 5.2 MPa. The mass ratio of cyclopentadiene to [omim][PF6] is 1:0.8, and the molar ratio of ethylene to cyclopentadiene is 1:1. The [omim][PF6] solution containing dissolved ethylene and cyclopentadiene is continuously fed into a stirred reactor at a feed temperature of 110℃. The reaction temperature in the stirred reactor is 240℃, the pressure is 0.5 MPa, and the residence time is 40 min. The Diels-Alder reaction between cyclopentadiene and ethylene is carried out in the stirred reactor to generate norbornene monomer. The composition of the reaction products is shown in Table 9.

[0074] Table 9. Analysis of reaction product composition (w%)

[0075]

[0076] Comparative Example 1

[0077] Toluene was used as the reaction solvent. Toluene has a boiling point of 111℃ at ambient pressure, and the Henry's law constant for ethylene in toluene under reaction conditions is 46.7 MPa. The mass ratio of cyclopentadiene to toluene was 1:0.8, and the molar ratio of ethylene to cyclopentadiene was 1:1. The toluene solution containing dissolved ethylene and cyclopentadiene was continuously fed into a stirred reactor at a feed temperature of 110℃. The reaction temperature inside the stirred reactor was 240℃, the pressure was 2.5 MPa, and the residence time was 40 min. The Diels-Alder reaction between cyclopentadiene and ethylene occurred in the stirred reactor, resulting in norbornene monomer. The composition of the reaction products is shown in Table 10.

[0078] Table 10. Analysis of reaction product composition (w%)

[0079]

[0080] Comparative Example 2

[0081] Toluene was used as the reaction solvent. Toluene has a boiling point of 111℃ at ambient pressure, and the Henry's law constant for ethylene in toluene under reaction conditions is 27.1 MPa. The mass ratio of cyclopentadiene to toluene was 1:4, and the molar ratio of ethylene to cyclopentadiene was 3:1. The toluene solution containing dissolved ethylene and cyclopentadiene was continuously fed into a stirred reactor at a feed temperature of 50℃. The reaction temperature inside the stirred reactor was 180℃, the pressure was 2.5 MPa, and the residence time was 40 min. The Diels-Alder reaction between cyclopentadiene and ethylene occurred in the stirred reactor, resulting in norbornene monomer. The composition of the reaction products is shown in Table 11.

[0082] Table 11. Component analysis of reaction products (w%)

[0083]

[0084] Comparative Example 3

[0085] Sulfolane was used as the reaction solvent. Sulfolane has a boiling point of 287℃ at ambient pressure, and the Henry's law constant for ethylene in sulfolane under reaction conditions is 189.6 MPa. The mass ratio of cyclopentadiene to sulfolane was 1:4.5, and the molar ratio of ethylene to cyclopentadiene was 1.3:1. The sulfolane solution containing dissolved ethylene and cyclopentadiene was continuously fed into a stirred reactor at a feed temperature of 105℃. The reaction temperature inside the stirred reactor was 240℃, the pressure was 0.5 MPa, and the residence time was 25 min. The Diels-Alder reaction between cyclopentadiene and ethylene was carried out in the stirred reactor, resulting in norbornene monomer. The composition of the reaction products is shown in Table 12.

[0086] Table 12 Analysis of reaction product composition (w%)

[0087]

[0088] Comparative Example 4

[0089] 1-Hexyl-3-methylimidazolium hexafluorophosphate [hmim][PF6] was used as the reaction solvent. The boiling point of the above ionic liquid is 317℃ under normal pressure, and the Henry's law constant of ethylene in the above ionic liquid under reaction conditions is 6.2 MPa. The mass ratio of dicyclopentadiene to [hmim][PF6] is 1:5, and the molar ratio of ethylene to dicyclopentadiene is 4:1. The ionic liquid solution containing dissolved ethylene and dicyclopentadiene is continuously fed into a stirred reactor at a feed temperature of 100℃. The reaction temperature in the stirred reactor is 230℃, the pressure is 1.0 MPa, and the residence time is 30 min. In the stirred reactor, dicyclopentadiene first depolymerizes to cyclopentadiene, followed by a Diels-Alder reaction between cyclopentadiene and ethylene, which then generates norbornene monomer. The composition of the reaction products is shown in Table 13.

[0090] Table 13 Analysis of reaction product composition (w%)

[0091]

[0092] The conversion rates of cyclopentadiene monomers and the selectivity of norbornene monomers after the reaction in each example and comparative example were statistically analyzed and entered into Table 14.

[0093] The conversion rate of cyclopentadiene monomer is calculated as follows:

[0094]

[0095] in:

[0096] X CPD Conversion rate of cyclopentadiene monomer, %

[0097] m CPDin : Mass of cyclopentadiene monomer entering the reactor;

[0098] m CPDout : Mass of cyclopentadiene monomer leaving the reactor;

[0099] m DCPDout Mass of dicyclopentadiene monomer leaving the reactor.

[0100] The method for calculating the selectivity of norbornene monomer is as follows:

[0101]

[0102] in:

[0103] S NB Selectivity of norbornene monomer, %

[0104] m NBout : Mass of norbornene monomer leaving the reactor;

[0105] m TCPDout : Mass of tetracyclododecene monomer leaving the reactor;

[0106] m TCPDout Mass of heavy monomer components such as tricyclopentadiene leaving the reactor.

[0107] Table 14. Statistical analysis of the conversion rate of cyclopentadiene monomers and the selectivity of norbornene monomers.

[0108]

[0109] As can be seen from the above, the embodiments using the norbornene preparation method provided by this invention exhibit higher conversion rates and selectivity of cyclopentadiene monomers compared to the comparative examples. Specifically, Example 7 and Comparative Example 1 are identical except for the solvent. Table 14 shows that Example 7 exhibits higher conversion rates and selectivity of cyclopentadiene monomers compared to Comparative Example 1. Furthermore, comparing Example 9 and Comparative Example 1, except for the solvent, the reaction pressure of Example 9 (0.5 MPa) is significantly lower than that of Comparative Example 1 (2.5 MPa), yet Example 9 also exhibits higher conversion rates and selectivity of cyclopentadiene monomers compared to Comparative Example 1. This demonstrates that the norbornene preparation method provided by this invention, compared to preparation methods using conventional organic solvents, achieves both lower reaction pressure and higher conversion rates and selectivity of cyclopentadiene monomers.

[0110] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing norbornene, characterized in that, The norbornene is prepared by reacting ethylene with cyclopentadiene in an ionic liquid.

2. The preparation method according to claim 1, characterized in that, The reaction temperature is 180-240℃, the reaction pressure is 0.5-2.5 MPa, and the reaction time is 10-40 min.

3. The preparation method according to claim 1 or 2, characterized in that, In the reaction, the Henry's law constant of ethylene in the ionic liquid is ≤8 MPa.

4. The preparation method according to any one of claims 1-3, characterized in that, The boiling point of the ionic liquid at normal pressure is greater than or equal to 260℃.

5. The preparation method according to any one of claims 1-4, characterized in that, The ionic liquid is selected from at least one of 1-methyl-3-octylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium nitrate, 1-butyl-3-methylimidazolium hexafluorophosphate, 1-hexyl-3-methylimidazolium hexafluorophosphate, and 1-octyl-3-methylimidazolium hexafluorophosphate.

6. The preparation method according to any one of claims 1-5, characterized in that, The molar ratio of ethylene to cyclopentadiene is (1-3):1; and / or, The mass ratio of the cyclopentadiene to the ionic liquid is 1:(0.8-6).

7. The preparation method according to any one of claims 1-6, characterized in that, The Henry's law constant of ethylene in the ionic liquid is ≤6 MPa; and / or, The boiling point of the ionic liquid at normal pressure is greater than or equal to 280℃.

8. The preparation method according to any one of claims 1-7, characterized in that, The reaction temperature is 200-240℃; and / or, The reaction pressure is 0.5-1.5 MPa; and / or, The reaction time is 20-35 min.

9. The preparation method according to any one of claims 1-8, characterized in that, The norbornene is prepared by continuously feeding a liquid-phase mixture including ethylene, cyclopentadiene, and an ionic liquid into a stirred reactor.

10. The preparation method according to claim 9, characterized in that, The temperature of the liquid mixture is 50-110℃.

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