Catalyst and method for hydrogenation amination of by-products containing benzene and cyclohexane

Abstract

The invention discloses a catalyst and a method for hydrogenation amination of by-products containing benzene and cyclohexane. The catalyst carrier is diatomite, the active component is Ni, and the auxiliary agent is selected from one or more of platinum, palladium, cerium, molybdenum and zirconium. The catalyst prepared by the method is high in activity and good in selectivity, benzene and cyclohexane byproducts can be recycled to generate cyclohexylamine and dicyclohexylamine, and the method is mild in process condition, simple to operate, safe, environment-friendly and suitable for industrial large-scale production.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for resource utilization of benzene and cyclohexane byproduct, more particularly to a method for resource utilization of benzene and cyclohexane byproduct to prepare cyclohexylamine and dicyclohexylamine. BACKGROUND

[0002] Cyclohexylamine and dicyclohexylamine are important organic fine chemical intermediates, widely used in rubber additives, food additives, corrosion prevention, papermaking, plastic processing and textile industry and many other fields. The most commonly used synthesis process at home and abroad at present is to use aniline to prepare by catalytic hydrogenation at high temperature and low pressure. This method is simple, easy to operate, high in safety and automation, and the raw materials are easy to obtain and stable in quality. However, in the production process, light component byproducts such as benzene and cyclohexane are generated. These byproducts are mixtures and have little utilization value, and are usually incinerated, which will cause waste of resources. How to effectively utilize these light component byproducts to realize resource recycling and reduce the emission of three wastes is a technical problem to be solved.

[0003] CN113149846A discloses a device for re-hydrogenation utilization of byproducts (cyclohexyl aniline, cyclohexene aniline, etc.) in the production process of cyclohexylamine, which converts the byproducts into dicyclohexylamine. The patent process is simple in operation, has few equipment, high efficiency and less three wastes.

[0004] CN119114095A discloses a method for resource utilization of industrial aniline waste liquid, which converts the industrial aniline waste liquid (containing aniline, cyclohexylamine, cyclohexanol, chlorobenzene, biphenyl, diphenylamine, cyclohexyl aniline, N-p-anilino aniline, etc.) into cyclohexylamine and dicyclohexylamine under certain process conditions. The patent has mild reaction conditions, simple operation, safety and environmental protection, and can realize the reuse of waste liquid.

[0005] CN103480380B discloses a catalyst for resource utilization of aniline rectification residue in fixed bed and a preparation method thereof, which can utilize the aniline rectification residue (containing aniline, cyclohexyl aniline, diphenylamine, p-anilino aniline, phenol, N-cyclohexyl-1,2-diphenylamine, 2-phenyl aniline, etc.) to generate cyclohexylamine and dicyclohexylamine. The catalyst has high activity and stability, and has industrialization potential.

[0006] The above prior arts all disclose some methods for resource utilization of byproducts or waste liquid, but there is little report on the method for resource utilization of benzene and cyclohexane byproduct to generate cyclohexylamine and dicyclohexylamine, so it is necessary to develop a method for utilization of benzene and cyclohexane byproduct to realize the utilization of waste and the value-added of products. SUMMARY

[0007] In order to solve the above technical problems, the application provides a catalyst and a method for resource utilization of benzene and cyclohexane by-product, which can be used for preparing cyclohexylamine and dicyclohexylamine.

[0008] The application has found that the benzene and cyclohexane by-products produced in the process of preparing cyclohexylamine and dicyclohexylamine by hydrogenation of aniline can be returned to the reactor inlet, and further catalytic hydrogenation and amination of part of the by-products can be realized to produce cyclohexylamine and dicyclohexylamine products, thereby realizing the reuse of by-products, reducing the generation of three wastes, and having good economic and environmental benefits.

[0009] In order to achieve the above application purposes, the application adopts the following technical solutions.

[0010] In one aspect of the application, a hydrogenation amination catalyst for resource utilization of benzene and cyclohexane by-products is provided, which comprises a carrier, an active component and an additive.

[0011] The carrier is diatomite, the active component is Ni, and the additive is selected from one or more of platinum, palladium, cerium, molybdenum and zirconium, preferably platinum and / or cerium.

[0012] In a specific embodiment, the content of the active component Ni is 35-60wt%, preferably 45-55wt%, and the content of the additive is 0.05-3wt%, preferably 0.1-2wt%, based on the weight of the catalyst.

[0013] In another aspect of the application, a preparation method of the catalyst is provided, which comprises the following steps.

[0014] S1: impregnating the carrier with an aqueous solution containing a nickel salt and an additive corresponding metal salt, drying, calcining to obtain a catalyst precursor;

[0015] S2: tabletting and forming the catalyst precursor, and activating.

[0016] In the application, the nickel salt and metal salt in S1 are selected from corresponding soluble salts, preferably nitrate salts.

[0017] In the application, as a preferred scheme, in S1, the drying temperature is 80-120℃, preferably 100-110℃, and the drying time is 4-12h, preferably 6-8h.

[0018] In the application, as a preferred scheme, in S1, the calcination temperature is 300-600℃, preferably 400-500℃, and the time is 6-12h, preferably 8-10h.

[0019] In the present application, as a preferred scheme, in S2, the activated atmosphere is hydrogen, the activation pressure is normal pressure, the activation temperature is 300-450 DEG C, preferably 350-400 DEG C, and the activation time is 24-96 h, preferably 48-72 h.

[0020] Another object of the present application is to provide a method for preparing cyclohexylamine and dicyclohexylamine by utilizing benzene and cyclohexane byproduct resources, comprising the following steps:

[0021] The hydrogenation raw material prepared by blending the benzene and cyclohexane byproduct is subjected to hydrogenation reaction under the action of hydrogen and a catalyst to obtain cyclohexylamine and dicyclohexylamine.

[0022] In the present application, the hydrogenation raw material prepared by blending the benzene and cyclohexane byproduct comprises the following components:

[0023] benzene and cyclohexane byproduct 0.5-5wt%;

[0024] pure benzene 0-5wt%;

[0025] aniline 90-99.5wt%.

[0026] In the present application, the benzene and cyclohexane byproduct is a byproduct produced in the process of preparing cyclohexylamine and dicyclohexylamine by hydrogenation of aniline, which is collected from the top of a light-removing column as a light component.

[0027] As a preferred scheme, the benzene and cyclohexane byproduct comprises benzene 40-60wt%, cyclohexane 35-55wt%, cyclohexene 0.2-5wt%, and water 0.01-0.2wt%.

[0028] In the present application, the hydrogenation raw material prepared by blending the benzene and cyclohexane byproduct is prepared by mixing the benzene and cyclohexane byproduct with optional pure benzene and aniline, and is used as the hydrogenation raw material of the present application. The three raw materials, i.e. the benzene and cyclohexane byproduct, the pure benzene and the aniline, can be mixed simultaneously or in a certain order, for example, the benzene and cyclohexane byproduct is mixed with optional pure benzene, and then mixed with aniline, which does not have special limitation on the technical scheme of the present application.

[0029] In the present application, the reaction temperature of the hydrogenation reaction is 150-210 DEG C, preferably 160-190 DEG C.

[0030] In the present application, the reaction pressure of the hydrogenation reaction is 50-400 KPaG, preferably 100-300 KPaG.

[0031] In the present application, the molar ratio of hydrogen to the sum of the molar amounts of benzene and aniline in the hydrogenation raw material is 8-20:1, preferably 10-15:1.

[0032] In this invention, the mass hourly space velocity (MSV) of the hydrogenation feedstock is 0.05-0.4 g / g(cat) / h, preferably 0.1-0.3 g / g(cat) / h.

[0033] In this invention, the hydrogenation reaction is illustrated as follows:

[0034]

[0035] Without any theoretical limitations, the possible reaction mechanism of this invention is as follows: benzene and cyclohexane byproducts are selectively hydrogenated to generate cyclohexene under the action of the catalyst and hydrogen in this invention. The cyclohexene then reacts with ammonia, a byproduct of the hydrogenation of aniline to dicyclohexylamine, to generate cyclohexylamine. Part of the cyclohexylamine undergoes a deamination reaction to generate dicyclohexylamine.

[0036] The beneficial effects of this invention are:

[0037] (1) Surprisingly, the catalyst and / or platinum in the catalyst and additives used in this invention can effectively improve the selective hydrogenation of benzene to cyclohexene, thereby improving the utilization rate of by-products; at the same time, additives such as cerium, molybdenum, and zirconium can improve the acidity of the catalyst, promote the main reaction of aniline hydrogenation to cyclohexylamine and dicyclohexylamine, and synergistically promote the reaction of cyclohexene with ammonia to produce cyclohexylamine and dicyclohexylamine.

[0038] (2) This invention adds benzene and cyclohexane byproducts to the aniline feedstock. On the one hand, benzene consumes the ammonia generated in the reaction system to carry out a coupling reaction, thereby promoting the equilibrium reaction of aniline hydrogenation to dicyclohexylamine to proceed to the right, which can increase the single-pass yield of dicyclohexylamine by ≥1%. In addition, cyclohexane, as an inert substance, has a certain diluting effect on the aniline feedstock, which can significantly reduce the hot spot of the reaction, thereby reducing the formation of benzene, cyclohexane, and biphenyl compounds as byproducts, further improving the reaction yield. Furthermore, cyclohexane is also a good solvent, which is very effective in removing heavy components from the catalyst surface and can improve the catalyst lifetime. In addition, the addition of benzene and cyclohexane to the feedstock can also effectively inhibit the formation of benzene and cyclohexane byproducts due to the reaction equilibrium.

[0039] (3) The catalyst prepared by the present invention can utilize benzene and cyclohexane byproducts to generate cyclohexylamine and dicyclohexylamine. The reaction conditions are mild, the operation is simple, safe and environmentally friendly, and it is suitable for large-scale industrial production. Detailed Implementation

[0040] The present invention will be further described through the following embodiments, but the present invention is not limited to the listed embodiments.

[0041] The conditions for gas chromatography analysis in the following examples were as follows: Agilent DB-5 column, injection port temperature 280°C, FID detector temperature 300°C, column flow rate 1.5 ml / min, hydrogen flow rate 40 ml / min, air flow rate 400 ml / min, and temperature program mode: 60°C held for 5 min, then increased to 280°C at 15°C / min and held for 5 min.

[0042] Unless otherwise specified, all raw materials used in the following examples or comparative examples are reagent-grade materials from Inokai. Some of these raw materials are described below:

[0043] Benzene and cyclohexane byproducts: Industrial grade, Wanhua Chemical

[0044] Aniline: Industrial grade, Wanhua Chemical

[0045] The main equipment information is as follows:

[0046] Fixed-bed reactor: Manufacturer is Beijing Tuochuan;

[0047] Horizontal flow pump: manufactured by Beijing Satellite.

[0048] Example 1

[0049] Preparation of catalyst precursor #1:

[0050] Prepare an impregnation solution containing 45g nickel, 3g platinum, and 0.2g zirconium nitrates using 300ml of deionized water. Add 51.8g diatomaceous earth using the impregnation method. After impregnation for 24 hours, dry at 110℃ for 6 hours, calcine at 500℃ for 8 hours, and then compress into tablets to obtain catalyst precursor #1.

[0051] Hydrogenation reaction:

[0052] Take 50g of the No. 1 catalyst precursor and pack it in the middle of a fixed-bed reactor. Activate it at 400℃, atmospheric pressure, and pure hydrogen for 48h. After activation, lower the temperature to the reaction temperature to obtain the No. 1 catalyst.

[0053] The industrially produced benzene and cyclohexane byproducts (composition: 45wt% benzene + 53.9wt% cyclohexane + 1wt% cyclohexene + 0.1wt% water) were blended with pure benzene and aniline in a mass ratio of 0.5wt% + 2.5wt% + 97wt% to obtain the feedstock for the hydrogenation reaction. The reaction was carried out at a temperature of 170℃, a pressure of 150 kPaG, a hydrogen-to-feedstock molar ratio of 15:1, and a feedstock mass hourly space velocity of 0.2 g / g(cat) / h. After 24 hours of reaction, samples were taken for analysis. The conversion rate of aniline was 100%. The mother liquor contained 1.30% benzene + cyclohexane, 24.70% cyclohexylamine, and 73.90% dicyclohexylamine, with the remainder being other impurities. These results show that the content of benzene + cyclohexane in the mother liquor was lower than that in the feedstock, indicating that partial conversion of benzene occurred.

[0054] Example 2

[0055] Preparation of catalyst precursor #2:

[0056] Prepare an impregnation solution containing 55g nickel, 2g palladium, and 0.05g cerium nitrate in 300ml deionized water. Add 42.95g diatomaceous earth by impregnation method. After impregnation for 24h, dry at 120℃ for 8h, calcine at 400℃ for 10h, and then compress into tablets to obtain catalyst precursor #2.

[0057] Hydrogenation reaction:

[0058] Take 50g of the No. 2 catalyst precursor and pack it in the middle of the fixed bed reactor. Activate it at 450℃, atmospheric pressure and pure hydrogen for 24h. After activation, lower the temperature to the reaction temperature to obtain the No. 2 catalyst.

[0059] The industrially produced benzene and cyclohexane byproducts (composition: 60wt% benzene + 36.8wt% cyclohexane + 3wt% cyclohexene + 0.2wt% water) were blended with pure benzene and aniline in a mass ratio of 5wt% + 2.5wt% + 92.5wt% to obtain the feedstock for the hydrogenation reaction. The reaction was carried out at a temperature of 160℃, a pressure of 100 kPaG, a hydrogen-to-feedstock molar ratio of 20:1, and a feedstock mass hourly space velocity of 0.1 g / g(cat) / h. Samples were taken for analysis after 24 hours of reaction. The conversion rate of aniline was 100%. The mother liquor contained 2.50% benzene + cyclohexane, 25.60% cyclohexylamine, and 71.84% dicyclohexylamine, with the remainder being other impurities.

[0060] Example 3

[0061] Preparation of catalyst precursor #3:

[0062] Prepare an impregnation solution containing 50g nickel, 3g platinum, and 0.1g molybdenum nitrates using 300ml of deionized water. Add 46.9g diatomaceous earth using the impregnation method. After impregnation for 24 hours, dry at 100℃ for 10 hours, calcine at 300℃ for 12 hours, and then compress into tablets to obtain catalyst precursor #3.

[0063] Hydrogenation reaction:

[0064] Take 50g of catalyst precursor #3 and pack it in the middle of a fixed-bed reactor. Activate it at 350℃, atmospheric pressure, and pure hydrogen for 72h. After activation, lower the temperature to the reaction temperature to obtain catalyst #3.

[0065] The industrially produced benzene and cyclohexane byproducts (composition: 40wt% benzene + 54.99wt% cyclohexane + 5wt% cyclohexene + 0.01wt% water) were mixed with aniline at a mass ratio of 0.5wt% + 99.5wt% to obtain the feedstock for the hydrogenation reaction. The reaction was carried out at a temperature of 190℃, a pressure of 300 kPaG, a hydrogen-to-feedstock molar ratio of 12:1, and a feedstock mass hourly space velocity of 0.3 g / g(cat) / h. Samples were taken for analysis after 24 hours of reaction. The conversion rate of aniline was 100%. The mother liquor contained 1.05% benzene + cyclohexane, 23.55% cyclohexylamine, and 75.25% dicyclohexylamine, with the remainder being other impurities.

[0066] Example 4

[0067] Preparation of catalyst precursor #4:

[0068] Prepare an impregnation solution containing 35g nickel, 1.5g platinum, and 1g cerium nitrates using 300ml of deionized water. Add 62.5g diatomaceous earth using the impregnation method. After impregnation for 24 hours, dry at 80℃ for 12 hours, calcine at 600℃ for 6 hours, and then compress into tablets to obtain catalyst precursor #4.

[0069] Hydrogenation reaction:

[0070] Take 50g of the No. 4 catalyst precursor and pack it in the middle of a fixed-bed reactor. Activate it at 300℃, atmospheric pressure, and pure hydrogen for 96h. After activation, lower the temperature to the reaction temperature to obtain the No. 4 catalyst.

[0071] The byproducts of industrially produced benzene and cyclohexane (composition: 50wt% benzene + 49.65wt% cyclohexane + 0.2wt% cyclohexene + 0.15wt% water) were mixed with pure benzene and aniline in a mass ratio of 5wt% + 5wt% + 90wt% to obtain the feedstock for the hydrogenation reaction. The reaction was carried out at a temperature of 210℃, a pressure of 400 kPaG, a hydrogen-to-feedstock molar ratio of 8:1, and a feedstock mass hourly space velocity of 0.05 g / g(cat) / h. Samples were taken for analysis after 24 hours of reaction. The conversion rate of aniline was 100%. The mother liquor contained 3.54% benzene + cyclohexane, 20.75% cyclohexylamine, and 75.44% dicyclohexylamine, with the remainder being other impurities.

[0072] Example 5

[0073] Preparation of catalyst precursor #5:

[0074] Prepare an impregnation solution containing 40g nickel, 2.0g palladium, and 0.5g zirconium nitrates using 300ml deionized water. Add 57.5g diatomaceous earth using the impregnation method. After impregnation for 24 hours, dry at 105℃ for 9 hours and calcine at 450℃ for 9 hours. Then, compress the solution into tablets to obtain catalyst precursor #5.

[0075] Hydrogenation reaction:

[0076] Take 50g of the 5# catalyst precursor and pack it in the middle of a fixed-bed reactor. Activate it at 375℃, atmospheric pressure, and pure hydrogen for 60h. After activation, lower the temperature to the reaction temperature to obtain the 5# catalyst.

[0077] The industrially produced benzene and cyclohexane byproducts (composition: 52.4 wt% benzene + 45 wt% cyclohexane + 2.5 wt% cyclohexene + 0.1 wt% water) were mixed with pure benzene and aniline in a mass ratio of 2.5 wt% + 2.5 wt% + 95 wt% to obtain the feedstock for the hydrogenation reaction. The reaction was carried out at a temperature of 200℃, a pressure of 50 kPaG, a hydrogen-to-feedstock molar ratio of 10:1, and a feedstock mass hourly space velocity of 0.15 g / g(cat) / h. After 24 hours of reaction, samples were taken for analysis. The conversion rate of aniline was 100%. The mother liquor contained 2.15% benzene + cyclohexane, 23.28% cyclohexylamine, and 74.37% dicyclohexylamine, with the remainder being other impurities.

[0078] Comparative Example 1

[0079] Hydrogenation reaction:

[0080] Take 50g of the No. 2 catalyst precursor and pack it in the middle of the fixed bed reactor. Activate it at 450℃, atmospheric pressure and pure hydrogen for 24h. After activation, lower the temperature to the reaction temperature to obtain the No. 2 catalyst.

[0081] Aniline was used exclusively as the feedstock for the hydrogenation reaction. The reaction was conducted at 160℃, 100 kPaG, with a hydrogen-to-feedstock molar ratio of 20:1 and a feedstock mass hourly space velocity (MHV) of 0.1 g / g(cat) / h. Samples were taken and analyzed after 24 hours. The conversion rate of aniline was 100%. The mother liquor contained 0.75% benzene + cyclohexane, 28.10% cyclohexylamine, and 70.65% dicyclohexylamine, with the remainder being other impurities. The results indicate that even without the addition of benzene and cyclohexane byproducts, as well as pure benzene, a net formation of benzene and cyclohexane byproducts would still occur in the feedstock.

[0082] Comparative Example 2

[0083] Preparation of catalyst precursor #6:

[0084] Prepare an impregnation solution containing 55g nickel and 0.05g cerium nitrate in 300ml deionized water. Add 44.95g diatomaceous earth by impregnation method. After impregnation for 24h, dry at 120℃ for 8h, calcine at 400℃ for 10h, and then compress into tablets to obtain catalyst precursor #6.

[0085] Hydrogenation reaction:

[0086] Take 50g of the 6# catalyst precursor and pack it in the middle of a fixed-bed reactor. Activate it at 450℃, atmospheric pressure, and pure hydrogen for 24h. After activation, lower the temperature to the reaction temperature to obtain the 6# catalyst.

[0087] The industrially produced benzene and cyclohexane byproducts (composition: 60wt% benzene + 36.8wt% cyclohexane + 3wt% cyclohexene + 0.2wt% water) were blended with pure benzene and aniline in a mass ratio of 5wt% + 2.5wt% + 92.5wt% to obtain the feedstock for the hydrogenation reaction. The reaction was carried out at a temperature of 160℃, a pressure of 100 kPaG, a hydrogen-to-feedstock molar ratio of 20:1, and a feedstock mass hourly space velocity of 0.1 g / g(cat) / h. Samples were taken for analysis after 24 hours of reaction. The conversion rate of aniline was 100%. The mother liquor contained 2.98% benzene + cyclohexane, 25.12% cyclohexylamine, and 71.75% dicyclohexylamine, with the remainder being other impurities.

[0088] Comparative Example 3

[0089] Preparation of catalyst precursor #7:

[0090] Prepare an impregnation solution containing 55g nickel and 2g palladium nitrates using 300ml deionized water. Add 43g diatomaceous earth using the impregnation method. After impregnation for 24 hours, dry at 120℃ for 8 hours, calcine at 400℃ for 10 hours, and then compress into tablets to obtain catalyst precursor #7.

[0091] Hydrogenation reaction:

[0092] Take 50g of the 7# catalyst precursor and pack it in the middle of a fixed-bed reactor. Activate it at 450℃, atmospheric pressure, and pure hydrogen for 24h. After activation, lower the temperature to the reaction temperature to obtain the 7# catalyst.

[0093] The industrially produced benzene and cyclohexane byproducts (composition: 60wt% benzene + 36.8wt% cyclohexane + 3wt% cyclohexene + 0.2wt% water) were blended with pure benzene and aniline in a mass ratio of 5wt% + 2.5wt% + 92.5wt% to obtain the feedstock for the hydrogenation reaction. The reaction was carried out at a temperature of 160℃, a pressure of 100 kPaG, a hydrogen-to-feedstock molar ratio of 20:1, and a feedstock mass hourly space velocity of 0.1 g / g(cat) / h. Samples were taken for analysis after 24 hours of reaction. The conversion rate of aniline was 99.75%. The mother liquor contained 3.24% benzene + cyclohexane, 24.83% cyclohexylamine, and 71.43% dicyclohexylamine, with the remainder being other impurities.

Claims

1. A hydrogenation amination catalyst containing benzene and cyclohexane byproducts, comprising a support, an active component, and an auxiliary agent; in, The carrier is diatomaceous earth, the active component is Ni, and the additives are selected from one or more of platinum, palladium, cerium, molybdenum, and zirconium, with platinum and / or cerium being preferred.

2. The catalyst according to claim 1, characterized in that, The active component Ni has a content of 35-60 wt%, preferably 45-55 wt%, and the additive has a content of 0.05-3 wt%, preferably 0.1-2 wt%, based on the weight of the catalyst.

3. The catalyst according to claim 1, characterized in that, The method for preparing the catalyst includes the following steps: S1: Impregnate the support with an aqueous solution containing nickel salt and the corresponding metal salt of the additive, dry, and calcine to obtain the catalyst precursor; S2: The catalyst precursor is compressed into tablets and activated.

4. The catalyst according to claim 1, characterized in that, In S1, the calcination temperature is 300-600℃, preferably 400-500℃, and the time is 6-12h, preferably 8-10h.

5. The catalyst according to claim 4, characterized in that, In S2, the activation atmosphere is hydrogen, the activation pressure is atmospheric pressure, the activation temperature is 300-450℃, preferably 350-400℃, and the activation time is 24-96h, preferably 48-72h.

6. A method for hydrogenating and amination of benzene and cyclohexane byproducts, comprising the following steps: The hydrogenation feedstock, which is prepared by blending benzene and cyclohexane byproducts, is subjected to a hydrogenation reaction in the presence of hydrogen and the catalyst described in any one of claims 1-5 to obtain cyclohexylamine and dicyclohexylamine.

7. The method according to claim 6, characterized in that, The hydrogenation feedstock obtained by blending benzene and cyclohexane byproducts, It includes the following components: Contains 0.5-5 wt% benzene and cyclohexane byproducts; Pure benzene 0-5 wt%; Aniline 90-99.5 wt%.

8. The method according to claim 7, characterized in that, The composition of the benzene and cyclohexane byproducts is: benzene 40-60 wt%, cyclohexane 35-55 wt%, cyclohexene 0.2-5 wt%, and water 0.01-0.2 wt%.

9. The method according to claim 7 or 8, characterized in that, The reaction temperature of the hydrogenation reaction is 150-210℃, preferably 160-190℃; and / or, the reaction pressure of the hydrogenation reaction is 50-400 kPaG, preferably 100-300 kPaG.

10. The method according to any one of claims 7-9, characterized in that, The molar ratio of hydrogen gas in the hydrogenation reaction to the sum of the molar amounts of benzene and aniline in the hydrogenation feedstock is 8-20:1, preferably 10-15:1; and / or the mass hourly space velocity (MSV) of the hydrogenation feedstock is 0.05-0.4 g / g(cat) / h, preferably 0.1-0.3 g / g(cat) / h.

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