Production method of high-purity cyclopentene

Abstract

The invention provides a production method of high-purity cyclopentene, and belongs to the technical field of olefin production. According to the method, a crude cyclopentene raw material rich in cyclopentene, cyclopentane and 1, 2-pentadiene is mixed with hydrogen, the mixture is introduced into an adiabatic bubbling bed reactor for a selective hydrogenation reaction, and a catalyst is modified Pd / Al2O3. After hydrogenation reaction liquid is subjected to light component removal and refining, a high-purity cyclopentene product with the content of 99.9% or above and the content of 1, 2-pentadiene being 10 ppm or below is obtained, and the monomer requirement for producing cyclopentene rubber is met.

Description

Technical Field

[0001] This invention relates to the field of cyclopentene production technology, and specifically to a method for producing high-purity cyclopentene. Background Technology

[0002] Cyclopentene (hereinafter referred to as CPE) is an important intermediate for fine chemical products. It can be used as a raw material for the production of high-value-added pharmaceutical and fragrance intermediates such as cyclopentanol, cyclopentanone, bromocyclopentane, chlorocyclopentane, and cyclopentanoic acid. It is also an important monomer for polycyclic olefin polymers and a raw material for the production of specialty electronic chemicals.

[0003] Cyclopentene is mainly found in the C5 fraction of catalytic cracked gasoline or the C5 fraction of naphtha cracking for ethylene production. Because these C5 fractions contain many compounds with very similar boiling points, conventional distillation methods cannot produce high-purity cyclopentene products with a purity of over 99.9%. Currently, the available method is to depolymerize dicyclopentadiene (DCPD) into cyclopentadiene (CPD), and then obtain cyclopentene through selective hydrogenation and distillation.

[0004] With suitable hydrogenation catalysts and process conditions, the conversion rate of cyclopentadiene can generally reach approximately 99.5%, and the selectivity of cyclopentene is approximately 97%. The hydrogenation products contain residual trace amounts of cyclopentadiene, cyclopentene, and a small amount of the tandem hydrogenation product cyclopentane. Because the boiling points of cyclopentadiene, cyclopentene, and cyclopentane are extremely close (41.50℃, 44.23℃, and 49.25℃, respectively), obtaining high-purity cyclopentene products through distillation is very difficult.

[0005] US Patent 6153804A describes a method for producing cyclopentane and / or cyclopentene from partially hydrocracking gasoline via distillation. The method involves first collecting a low-boiling-point C5 fraction from the top of a first distillation column, collecting a heavy fraction containing six or more carbon atoms from the bottom, and collecting a side stream fraction containing at least 40% cyclopentane and cyclopentene, which is then fed into a hydrogenation reactor to convert olefins into alkanes. The hydrogenation product is then fed into a second distillation column, where a mixture of n-pentane and isopentane is separated from the top. The bottom liquid is then fed into a third distillation column to obtain cyclopentane. Alternatively, the fraction containing at least 40% cyclopentane and cyclopentene can be directly distilled to obtain cyclopentene and cyclopentane.

[0006] US Patent 6264799B1 discloses a method for producing cyclopentane and / or cyclopentene. The method involves distilling a hydrogenated C5 fraction in a first distillation column, separating the lower-boiling C5 fraction from the top of the column, and feeding the bottom fraction into a second distillation column, from which cyclopentene is separated.

[0007] The above method mainly obtains cyclopentene through selective hydrogenation and distillation separation processes. However, since it involves the separation of monoolefins with boiling points very close to cyclopentene, the energy consumption is high, and the obtained cyclopentene content is only about 99.5%, which affects its downstream chemical utilization. In particular, it cannot meet the requirements of a monomer content of more than 99.9% and a 1,2-pentadiene content of less than 10 ppm for use as polycyclopentene rubber.

[0008] Cyclopentene with a content of 99.9% or higher and 1,2-pentadiene content below 10 ppm is the key monomer for the production of cyclopentene rubber. 1,2-pentadiene content exceeding 10 ppm in cyclopentene leads to rapid deactivation of the polymerization catalyst. Cyclopentene rubber is a novel elastomer with a "linear structure" and "fully end-modified" structure. Due to its linear structure, it exhibits a low glass transition temperature of around -110°C, demonstrating excellent flexibility even at low temperatures. Furthermore, the fully end-modified structure enhances its affinity for silica and carbon black, resulting in overwhelmingly low oil consumption. In low-temperature performance evaluations at -40°C, it also shows superior low-temperature properties compared to previous rubbers. Moreover, cyclopentene rubber can be recycled from waste rubber using a closed-loop process based on catalytic depolymerization, achieving a recovery rate exceeding 90%. Summary of the Invention

[0009] To address the technical problem that existing cyclopentene production processes cannot meet purity requirements, this invention provides a method for producing high-purity cyclopentene. Using crude cyclopentene as raw material, the cyclopentene obtained through selective hydrogenation and distillation achieves a purity of over 99.9% and a 1,2-pentadiene content of less than 10 ppm.

[0010] Crude cyclopentene feedstock is the C5 fraction obtained by removing light components from isoprene, selectively hydrogenating it, and then separating it into isoprene, 1-pentene, 2-pentene, and 2-methyl-2-butene by distillation. Depending on the composition of isoprene, the crude cyclopentene feedstock typically contains 60-70% cyclopentene, 25-35% cyclopentane, and 0.01-0.3% 1,2-pentene, with the remainder being other C5 fractions.

[0011] Experiments have confirmed that distillation cannot separate cyclopentene from 1,2-pentadiene, as cyclopentene (boiling point 44.24℃) and 1,2-pentadiene (boiling point 44.86℃) have essentially the same boiling point. Therefore, this invention employs a hydrogenation process to obtain high-purity cyclopentene products, and allows 5-10% of the cyclopentene in the crude cyclopentene feedstock to be converted into cyclopentane, which can also be sold as a product.

[0012] A method for producing high-purity cyclopentene involves mixing crude cyclopentene feedstock rich in cyclopentene, cyclopentane, and 0.001-0.30% 1,2-pentadiene with hydrogen gas and then passing the mixture into an adiabatic bubbling bed reactor for selective hydrogenation. After the hydrogenated reaction liquid is purified and treated to remove light components, high-purity cyclopentene product is obtained.

[0013] By effectively adjusting the molar ratio of hydrogen to dienes in the feed and other operating parameters, 100% conversion of 1,2-pentadiene can be achieved, with some cyclopentene further converted to cyclopentane. In this invention, the molar feed ratio of hydrogen to dienes in the feed is 60~180:1, preferably 90~150:1; the volume hourly space velocity is 0.5~3.0 hr. -1 Preferred 1.0~2.0hr -1 The reaction pressure is 8~15 bar, preferably 10~12 bar; the reaction temperature is 40~60℃, preferably 50~55℃.

[0014] The catalyst for selective hydrogenation is Pd / Al2O3, with Pd as the active component and Al2O3 as the support, and the Pd loading is 0.30~0.35%. The inventors discovered in experiments that 1,2-pentadiene exhibits lower hydrogenation activity compared to other conjugated dienes such as isoprene, isoprene, and cyclopentadiene. Therefore, if conventional hydrogenation catalysts for these three dienes are used, 1,2-pentadiene cannot be completely converted when the Pd content is in the range of 0.25~0.30%.

[0015] Therefore, this invention improves the catalyst by modifying and optimizing it, increasing the Pd content from 0.25-0.30% to 0.30-0.35%, and by adding a certain amount of rare earth oxides (such as cerium oxide or lanthanum trioxide) to fine-tune the acidity and alkalinity, thereby changing the adsorption selectivity of the catalyst. As a result, while improving the catalyst activity, it still has a high selectivity for the hydrogenation of 1,2-pentadiene, and reduces the 1,2-pentadiene content to below 10 ppm.

[0016] Meanwhile, through numerous experiments and theoretical analyses, it has been found that when using an adiabatic bubbling bed reactor for hydrogenation, in order to control the temperature of the catalyst bed, a large amount of hydrogenation products need to be mixed with fresh feedstock and recycled back to the reactor for hydrogenation. The circulation of the hydrogenation liquid can remove the heat of reaction in a timely manner, thus improving the stability of temperature control or the safety of hydrogenation operation.

[0017] This invention employs a selective hydrogenation reaction by mixing raw materials rich in cyclopentene, cyclopentane, and 1,2-pentadiene with hydrogen gas and then introducing the mixture into an adiabatic bubbling bed reactor. The catalyst is modified Pd / Al₂O₃. After removal of light components and purification, the hydrogenated reaction solution yields a high-purity cyclopentene product with a content of over 99.9% and 1,2-pentadiene content below 10 ppm, meeting the monomer requirements for producing cyclopentene rubber. Detailed Implementation

[0018] The present invention will now be described in further detail with reference to specific embodiments. The embodiments of the present invention are given for illustrative and descriptive purposes only, and are not intended to be exhaustive or to limit the invention to the disclosed forms. Many modifications and variations will be apparent to those skilled in the art. The embodiments were chosen and described to better illustrate the principles and practical applications of the invention, and to enable those skilled in the art to understand the invention and design various embodiments with various modifications suitable for a particular purpose.

[0019] In this invention, unless otherwise specified, all raw material components are commercially available products well known to those skilled in the art.

[0020] Examples 1-10

[0021] The hydrogenation feedstock, rich in cyclopentene, cyclopentane, and 0.001–0.30% 1,2-pentadiene, is derived from the C5 fraction, a byproduct of ethylene production from petroleum hydrocarbons (such as naphtha and light diesel oil) via high-temperature steam cracking. In the examples, the hydrogenation feedstock contains 62% cyclopentene, 31% cyclopentane, and 0.30% 1,2-pentadiene, with the remainder being other chain-like C5 fractions.

[0022] The hydrogenation reaction was carried out in a tubular fixed-bed reactor with dimensions of φ25mm × 1500mm. The reactor was loaded with 100mL of catalyst, with Pd as the active component and rare-earth-modified Al₂O₃ as the support. The Pd content was 0.35wt%, and the catalyst was purchased from the manufacturer. Inert ceramic balls were packed at the bottom of the reactor. Fresh catalyst was activated with hydrogen before feeding. Platinum resistance thermometers were installed at the top, middle, and bottom of the catalyst bed. The feed rate was controlled by a feed pump, and the system pressure was regulated by a back pressure valve.

[0023] After the hydrogenation feedstock is mixed with hydrogen, it is introduced into the catalyst bed from the bottom of the reactor, and the hydrogenation reaction is carried out according to the set reaction conditions. The hydrogenated material flowing out from the top of the hydrogenation reactor goes to a gas-liquid separator. The liquid phase material enters the product storage tank, and the unreacted hydrogen is depressurized by a regulating valve, metered by a wet gas meter, and then vented, or compressed and returned to the reaction system.

[0024] The hydrogenation reaction products obtained in the examples were analyzed by chromatography, and the conversion rate and product selectivity were calculated. The reaction conditions and results for each example are shown in Table 1. The 100% conversion rate of 1,2-pentadiene directly indicates that the 1,2-pentadiene content is below 10 ppm.

[0025] Comparative Example 1

[0026] The hydrogenation apparatus and operation of Comparative Example 1 were the same as those of Examples 1-10, but the catalyst was Pd as the active component and Al2O3 as the support (unmodified), with a Pd content of 0.35 wt%. The reaction conditions and results of Comparative Example 1 are also recorded in Table 1.

[0027] Table 1

[0028] <![CDATA[Mass space velocity (hr -1 ).]]> reaction temperature Reaction pressure (bar) <![CDATA[H2 / Diolefin molar ratio]]> 1,2-Pentadiene conversion CPE conversion rate Example 1 0.5 40℃ 8.0 60:1 100％ 6.4％ Example 2 3.0 60℃ 15.0 180:1 100％ 7.8％ Example 3 6.0 55℃ 10.0 90:1 100％ 8.6％ Example 4 4.5 50℃ 11.6 95:1 100％ 8.8％ Example 5 1.0 55℃ 12.0 100:1 100％ 6.2％ Example 6 1.5 50℃ 11.5 120:1 100％ 7.0％ Example 7 1.2 53℃ 10.5 112:1 100％ 8.5％ Example 8 2.0 52℃ 12.0 120:1 100％ 9.4％ Example 9 1.5 50℃ 11.0 140:1 100％ 8.6％ Example 10 1.6 51℃ 10.8 130:1 100％ 7.2％ Comparative Example 1 1.6 51℃ 10.8 130:1 80% 12.5%

[0029] The comparison shows that the conversion rate of 1,2-pentadiene is significantly increased to 100% using the rare earth modified Pd / Al2O3 catalyst. Analysis shows that in addition to changing the acidity of the support, the rare earth oxides also improve the stability of the palladium crystals, thereby improving the activity stability of the catalyst.

[0030] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for producing high-purity cyclopentene, characterized in that, Crude cyclopentene feedstock rich in cyclopentene, cyclopentane, and 0.001–0.30% 1,2-pentadiene is mixed with hydrogen and then fed into an adiabatic bubbling bed reactor for selective hydrogenation. The molar ratio of hydrogen to dienes in the feedstock is 60–180:1, and the volume hourly space velocity (VHSV) is 0.5–3.0 hr. -1 The reaction pressure is 8~15 bar and the reaction temperature is 40~60℃; after the hydrogenation reaction solution is purified and treated to obtain high-purity cyclopentene product.

2. The method for producing high-purity cyclopentene according to claim 1, characterized in that, In step 1, the molar feed ratio of hydrogen to diene in the material is 90~150:

1.

3. The method for producing high-purity cyclopentene according to claim 2, characterized in that, In step 1, the volumetric hourly space velocity is 1.0~2.0 hr. -1 The reaction pressure is 10~12 bar, and the reaction temperature is 50~55℃.

4. The method for producing high-purity cyclopentene according to claim 1, characterized in that, The catalyst for the selective hydrogenation reaction is Pd / Al2O3, where Pd is the active component and Al2O3 is the support, with a Pd loading of 0.30~0.35%.

5. The method for producing high-purity cyclopentene according to claim 4, characterized in that, The acidity and alkalinity of Pd / Al2O3 catalysts are fine-tuned by adding rare earth oxides.