Preparation and application of a modified palladium-carbon catalyst

Abstract

The invention provides a preparation method and application of a modified palladium-carbon catalyst, and particularly describes its application in the conversion of vitamin A isomers. The catalyst uses activated carbon as an initial template, undergoes oxidation, deep reduction, and activated carbon modification, then adsorbs palladium metal, and is made into an isomerization catalyst after drying and calcination. The catalyst is used to catalyze the conversion reaction of vitamin A cis isomer to all-trans isomer, which can effectively reduce the loss of metal during the reaction, and the catalyst has excellent tolerance to the reaction, and the activity of the catalyst does not change significantly after 20 times of application.

Description

Technical Field

[0001] The invention belongs to the technical field of catalyst and compound preparation, and particularly relates to a method for preparing a modified palladium-carbon catalyst and a method for catalyzing double bond isomerization conversion of vitamin A isomers. Background Art

[0002] Vitamin A (VA) is one of the essential vitamins for humans and animals. It is a basic substance required for growth, development, reproduction and vision, and affects the regulatory function of cell proliferation and differentiation. In addition to being used clinically to treat night blindness, conjunctivomalacia, and keratitis sicca, it is also used as a food nutritional enhancer and animal feed additive. The structural formula is as follows.

[0003]

[0004] VA has a polyene structure with four conjugated double bonds on the side chain, of which the all-trans isomer has the highest biological activity. However, a large number of cis isomers are inevitably produced in the process of industrial synthesis of vitamin A, among which the most important are 9-cis isomers, 11-cis isomers and 13-cis isomers. In order to improve the recovery rate of all-trans vitamin A and reduce the cost of the route, converting the cis isomers produced in the reaction process into all-trans isomers has always been an important research direction for vitamin A manufacturers.

[0005] At present, the most commonly used method for converting vitamin A isomers in industry is to use a heterogeneous Pd catalyst as an isomerization catalyst. Taking patent US04051174 as an example, the reaction uses a Pd catalyst, which can efficiently convert the 11-cis isomer to the all-trans isomer, but the reaction process will be accompanied by the generation of the 9-cis isomer, and this method cannot convert the 13-cis isomer. In addition, the reaction process will be accompanied by the loss of Pd metal, which will lead to a gradual decrease in the subsequent catalyst application effect, increase the industrialization cost, and the residual Pd in ​​the product VA crystal is a great hidden danger in the subsequent application of VA in food and feed.

[0006] Therefore, in order to solve the problems of catalyst loss and decreased application activity during the isomerization process, it is necessary to develop a new catalyst to replace it in order to save industrial costs and improve product quality. Summary of the invention

[0007] The purpose of the present invention is to provide a preparation method and application of a modified palladium-carbon catalyst, so as to solve the problems of Pd metal loss and reduced catalyst activity after the Pd catalytic isomerization process in the art, so that the prepared catalyst not only has reaction activity for multiple cis isomers at the same time, but also effectively solves the problem of Pd loss during the reaction process.

[0008] Another object of the present invention is to provide a method for converting cis-trans isomers of vitamin A. The modified palladium-carbon catalyst can not only convert the 11-cis isomer to the all-trans isomer that can be achieved by conventional palladium catalysts, but also can achieve the conversion of the 9-cis isomer to the all-trans isomer that is difficult to achieve by conventional palladium catalysts, and the reaction balance is all-trans isomer:9-cis isomer>12:1.

[0009] In order to achieve the above-mentioned purpose and technical effect, the technical solution of the present invention is as follows:

[0010] A method for preparing a modified palladium-carbon catalyst comprises the following steps:

[0011] S1: Activated carbon oxidation: Activated carbon is oxidized and modified using nitric acid to obtain oxidized activated carbon; the number of carboxyl, lactone and hydroxyl functional groups on the surface of the oxidized activated carbon increases significantly;

[0012] S2: Deep reduction: The oxidized activated carbon is reduced with lithium aluminum hydride to obtain deeply reduced activated carbon; the oxidized activated carbon is further reduced with lithium aluminum hydride, wherein the lactone and carboxyl functional groups are deeply reduced, and the number of hydroxyl functional groups on the surface of the activated carbon is further increased;

[0013] S3: Activated carbon modification: The deeply reduced activated carbon reacts chemically with the modifying agent to form a NO chemical bond to obtain the modified activated carbon; The deeply reduced activated carbon reacts chemically with the modifying agent, and the hydroxyl functional group reacts chemically with the modifying agent to form a NO chemical bond, thereby introducing a modified functional group on the activated carbon to obtain the modified activated carbon;

[0014] S4: Metal adsorption: The modified activated carbon is subjected to palladium metal adsorption, and a modified palladium-carbon catalyst is obtained after drying and calcination.

[0015] As a specific embodiment, a method for preparing the above-mentioned modified palladium-carbon catalyst comprises the following steps:

[0016] S1: adding a certain amount of activated carbon to a certain amount of nitric acid aqueous solution, heating and refluxing for a period of time, filtering, washing the activated carbon with distilled water until neutral, and then drying in an oven to obtain oxidized activated carbon;

[0017] S2: adding the oxidized activated carbon obtained in S1 to an organic solvent, cooling to a certain temperature, adding lithium aluminum hydride, reacting at a specified temperature for a period of time, filtering, washing the activated carbon with distilled water until it is neutral, and then drying it in an oven to obtain deeply reduced activated carbon;

[0018] S3: adding the activated carbon obtained in S2 to an organic solvent, then adding a modifying agent, heating and stirring the reaction for a period of time, and then filtering the reaction solution under reduced pressure, washing the activated carbon with an organic solvent for multiple times, and then sending it to an oven for drying;

[0019] S4: The activated carbon obtained in S3 is used as a carrier, and a soluble palladium salt is used as a Pd source. The soluble palladium salt can be any palladium compound commonly used in the industry, preferably PdCl2. The palladium-carbon catalyst is prepared by a volume impregnation method. The obtained catalyst is then sent to an oven for drying, and then calcined to obtain a modified palladium-carbon catalyst.

[0020] In the present invention, the activated carbon used in S1 is selected from one or more of fruit shell activated carbon, coconut shell activated carbon and wood activated carbon, preferably wood activated carbon.

[0021] In the present invention, the nitric acid in S1 is a nitric acid aqueous solution with a concentration of 0.5-4 mol / L, preferably 2-3 mol / L.

[0022] In the present invention, the ratio of nitric acid and activated carbon in S1 is (10-50) mL: 1 g, preferably (20-30) mL: 1 g.

[0023] In the present invention, the activated carbon in S1 needs to be refluxed in the nitric acid aqueous solution for 2-10 hours, preferably 4-6 hours.

[0024] In the present invention, the activated carbon obtained in S1 is dried at 100-150° C. for 5-15 h, preferably 10-12 h, and used for subsequent reactions after cooling.

[0025] In the present invention, the reduction reaction in S2 requires the use of lithium aluminum hydride, and the mass ratio of lithium aluminum hydride to oxidized activated carbon is (0.2-1):1, preferably (0.3-0.8):1.

[0026] In the present invention, the solvent in S2 is selected from one or more of water, acetic acid, acetonitrile, toluene, ethanol, and dichloroethane, preferably acetic acid.

[0027] In the present invention, the usage ratio of the solvent and the oxidized activated carbon in S2 is (5-30) mL: 1 g, preferably (10-20) ml: 1 g.

[0028] In the present invention, the reduction reaction temperature in S2 is -20-10°C, preferably -10-0°C.

[0029] In the present invention, the reduction reaction time in S2 is 2-8 hours, preferably 3-5 hours.

[0030] In the present invention, the activated carbon obtained in S2 is dried at 100-150° C. for 5-15 h, preferably 10-12 h, and used for subsequent reactions after cooling.

[0031] In the present invention, the modifying reagent in S3 is an adenine, including one or more of adenine, adenine with a functional group and 8-azaadenine, wherein the functional group includes methyl, fluorine, chlorine, benzyl, preferably adenine.

[0032] In the present invention, the mass ratio of the modifying agent and the deeply reduced activated carbon in S3 is (0.5-2):1, preferably (0.8-1.5):1.

[0033] In the present invention, the modification reaction in S3 needs to be carried out in an organic solvent, and the organic solvent is selected from one or more of acetonitrile, n-hexane, toluene, and dichloroethane, preferably acetonitrile.

[0034] In the present invention, the usage ratio of the organic solvent and activated carbon in S3 is (10-50) mL:1 g, preferably (20-30) mL:1 g.

[0035] In the present invention, the reaction temperature of the modification reaction in S3 is 30-100°C, preferably 50-80°C; the reaction time is 5-20h, preferably 8-12h.

[0036] In the present invention, the activated carbon obtained in S3 is dried at 100-150° C. for 5-15 h, preferably 10-12 h, and used for subsequent reactions after cooling.

[0037] In the present invention, the metal adsorption step in S4 uses the modified activated carbon prepared in S3 as a carrier, and uses a soluble palladium salt as a Pd source. The soluble palladium salt can be any palladium compound commonly used in the industry, preferably PdCl2, and the catalyst is prepared by a volume impregnation method. The amount of modified activated carbon and palladium salt is related to the catalyst formulation to be prepared. The catalyst preparation method can prepare a palladium carbon catalyst with a Pd content of 1-10%. The amount of palladium salt is related to the palladium content therein, ensuring that the mass ratio of palladium metal to activated carbon is 1-10%, corresponding to a palladium carbon catalyst with a Pd content of 1-10%.

[0038] In the present invention, the loading of Pd in ​​the palladium carbon catalyst needs to be carried out in a solvent, and the solvent is selected from one or more of acetone, dimethyl sulfoxide, N,N-dimethylformamide, dioxane, tetrahydrofuran, acetonitrile, and ethanol, preferably ethanol; the ratio of the solvent to the modified activated carbon is (10-50) mL: 1 g, preferably (20-30) mL: 1 g.

[0039] In the present invention, the loading temperature of Pd in ​​the palladium carbon catalyst is 20-120° C., preferably 40-60° C.; the reaction time is 12-48 h, preferably 24-36 h.

[0040] In the present invention, after Pd loading is completed, the palladium carbon catalyst needs to be dried at 100-150° C. for 5-15 h, preferably 10-12 h; then calcined at 400-600° C. for 5-10 h, preferably 6-8 h, and cooled to obtain a finished catalyst.

[0041] The modified palladium-carbon catalyst of the present invention can be used to catalyze the cis-trans isomerization reaction of C=C double bond or C=N double bond, in particular, to catalyze the conversion of vitamin A cis isomer to all-trans isomer.

[0042] Another object of the present invention is to provide a method for converting the cis and trans isomers of vitamin A.

[0043] A method for converting cis-trans isomers of vitamin A, using the modified palladium-carbon catalyst to catalyze the isomerization reaction of cis-vitamin A isomers to convert them into all-trans-vitamin A isomers.

[0044] In the conversion method, the reaction substrate is one or more of various cis-vitamin A isomers and all-trans-vitamin A isomers, and does not contain only all-trans-vitamin A isomers or a single cis-isomer as a substrate.

[0045] Preferably, the content of all-trans isomer in the reaction substrate is 0-10%, the content of 11-cis isomer is 0-100%, and the content of 9-cis isomer is 0-100%, based on the total mass of crude vitamin A oil.

[0046] In the conversion method, the isomerization reaction is carried out in the presence of an organic solvent, and the organic solvent is selected from one or more of acetonitrile, N,N-dimethylformamide, hexane, pentane, heptane, benzene, toluene, methyl tert-butyl ether, tetrahydrofuran, ethanol, methanol, isopropanol, n-propanol and butanol, preferably acetonitrile.

[0047] In the conversion method, the usage ratio of the organic solvent to the reaction substrate is (1-4) L:1 kg, preferably (2-3) L:1 kg.

[0048] In the conversion method, the amount of the isomerization catalyst used in the isomerization reaction is 0.1-10% of the amount of the reaction substrate, preferably 1-5%.

[0049] In this conversion method, the temperature of the isomerization reaction is 30-120°C, preferably 40-90°C; the reaction time is 5-20h, preferably 8-10h;

[0050] In the present conversion method, the isomerization reaction is carried out under an inert gas, preferably nitrogen and / or argon.

[0051] In the conversion method, after the isomerization reaction is completed, the temperature of the reaction solution is lowered to 25° C., the reaction solution is filtered and washed, and the catalyst is recovered.

[0052] Compared with the existing disclosed technology, the present invention has the following significant advantages:

[0053] 1. A method for preparing a novel modified palladium-carbon catalyst is provided, wherein the modified palladium-carbon catalyst has high activity for converting the cis-isomer of vitamin A to the all-trans-isomer.

[0054] 2. The modified palladium-carbon catalyst effectively avoids the loss of Pd during the isomerization reaction. After multiple applications, the activity of the catalyst does not decrease significantly (the catalyst activity does not decrease significantly after 25 applications, and the Pd content of the catalyst does not change), which greatly reduces the cost of the isomerization reaction. DETAILED DESCRIPTION

[0055] The technical solution of the present invention is further described below, but is not limited thereto. Any modification or equivalent replacement of the technical solution of the present invention without departing from the scope of the technical solution of the present invention should be included in the protection scope of the present invention.

[0056] Liquid chromatography analysis: Agilent 1260 liquid chromatograph, chromatographic column Sphersorb C18 column (φ4.6×250mm), UV-visible spectrophotometer Hitachi L7420, chromatographic workstation data processing system Chomatopac C-RIA, stationary phase Zorbax-SIL. Chromatographic conditions: mobile phase is methanol / acetonitrile = 9 / 1 (v / v) mixture, detection temperature is 40°C, flow rate is 1mL / min, wavelength is 455nm. Qualitative and quantitative analysis of product composition was performed.

[0057] Catalyst Pd elemental analysis: using inductively coupled plasma emission spectrometer, the relevant parameters are:

[0058] Power / kW 1.20 Plasma gas flow / L / min 15.0 Auxiliary gas flow / L / min 1.50 Atomizing gas flow rate / L / min 0.80 One reading time / s 5.00 Instrument stabilization time / s 15 Injection delay / s 50 Pump speed / rpm 15 Cleaning time / s 50 Number of readings 3

[0059] Table 1 Specifications and sources of some reagents in the examples and comparative examples

[0060]

[0061] Example 1

[0062] Preparation of modified catalyst:

[0063] Activated carbon oxidation: 10 g of wood activated carbon was added to a 500 mL three-necked flask, followed by 200 mL of 2 mol / L nitric acid aqueous solution. After heating and refluxing at 100 °C for 6 h, the activated carbon was filtered and washed with distilled water until neutral. The activated carbon was then dried in an oven at 120 °C for 10 h to obtain oxidized activated carbon.

[0064] Activated carbon reduction: add 10g of oxidized activated carbon and 100mL of acetic acid into a 500mL three-necked flask, cool to -10°C, add 3g of lithium aluminum hydride, react at -10°C for 5h, filter, wash the activated carbon with distilled water until neutral, and then put it into an oven to dry at 120°C for 10h to obtain deeply reduced activated carbon;

[0065] Modification of activated carbon: 10 g of deep reduced activated carbon, 8 g of adenine and 200 mL of acetonitrile were added to a 500 mL three-necked flask, reacted at 50 °C for 12 h, filtered, the activated carbon was washed with distilled water until neutral, and then dried in an oven at 120 °C for 10 h to obtain modified activated carbon;

[0066] Pd loading: 200 mL of ethanol, 10 g of modified activated carbon and 0.84 g of PdCl2 were added to a 500 mL three-necked flask, stirred at 60 ° C for 24 h, filtered, and the catalyst was washed with distilled water until neutral, then sent to an oven to dry at 120 ° C for 10 h, and then calcined at 500 ° C for 6 h. After cooling, the finished catalyst was obtained, and the catalyst Pd content was 5.0 wt%.

[0067] Isomerization reaction:

[0068] A 2000mL reaction bottle was equipped with a mechanical stirrer, a reflux condenser, and nitrogen replacement three times. Under nitrogen protection, 10 g of an isomerization catalyst, 1000 mL of acetonitrile and VA crude oil raw material (1000 g, 11-cis content 100 wt%, Wanhua Chemical Group Co., Ltd.) were added in sequence, and the solution was stirred to mix. The reaction solution was then reacted at 90°C for 8 h. After the reaction was completed, liquid chromatography analysis was performed to obtain a reaction solution with an all-trans content of 94.02 wt%, a 9-cis content of 5.20 wt%, and an 11-cis content of 0.78 wt%, and the Pd content in the reaction solution was not detected.

[0069] Catalyst Application:

[0070] After the reaction liquid was cooled to 20°C, it was stirred at 800 rpm for 3 hours, and then filtered under reduced pressure. The catalyst was washed with fresh n-hexane and dried to obtain a solid catalyst for the next batch of isomerization experiments. The reaction conditions were the same as the above isomerization reaction. The catalyst was used for 20 batches in total. The results of the applied products are listed in Table 2:

[0071] Table 2 Catalyst application results

[0072]

[0073]

[0074] Example 2

[0075] Preparation of modified catalyst:

[0076] Activated carbon oxidation: 10 g of wood activated carbon was added to a 500 mL three-necked flask, followed by 300 mL of 3 mol / L nitric acid aqueous solution. After heating and refluxing at 100 °C for 4 h, the activated carbon was filtered and washed with distilled water until neutral. The activated carbon was then dried in an oven at 120 °C for 5 h to obtain oxidized activated carbon.

[0077] Activated carbon reduction: add 10g of oxidized activated carbon and 200mL of acetic acid into a 500mL three-necked flask, cool to 0°C, add 8g of lithium aluminum hydride, react at 0°C for 3h, filter, wash the activated carbon with distilled water until neutral, and then put it into an oven to dry at 120°C for 5h to obtain deeply reduced activated carbon;

[0078] Modification of activated carbon: 10 g of deep reduced activated carbon, 15 g of 2-fluoroadenine and 300 mL of toluene were added to a 500 mL three-necked flask, reacted at 80 °C for 8 h, filtered, the activated carbon was washed with distilled water until neutral, and then dried in an oven at 120 °C for 5 h to obtain modified activated carbon;

[0079] Pd loading: 300 mL of acetone, 10 g of modified activated carbon and 0.84 g of PdCl2 were added to a 500 mL three-necked flask, stirred at 40 ° C for 36 h, filtered, and the catalyst was washed with distilled water until neutral, then sent to an oven to dry at 120 ° C for 5 h, and then calcined at 500 ° C for 8 h. After cooling, the finished catalyst was obtained, and the Pd content of the catalyst was 5.0 wt%.

[0080] Isomerization reaction:

[0081] A 5000mL reaction bottle was equipped with a mechanical stirrer, a reflux condenser, and nitrogen replacement three times. Under nitrogen protection, 50 g of isomerization catalyst, 2000 mL of n-hexane and VA crude oil raw material (1000 g, 9-cis content 100 wt%) were added in sequence, and the solution was stirred to mix. The reaction solution was then reacted at 40°C for 10 h. After the reaction was completed, liquid chromatography analysis was performed to obtain a reaction solution with an all-trans content of 95.12 wt%, a 9-cis content of 4.20 wt%, and an 11-cis content of 0.68 wt%.

[0082] Example 3

[0083] Preparation of modified catalyst:

[0084] Activated carbon oxidation: 10 g of wood activated carbon was added to a 1000 mL three-necked flask, followed by 500 mL of 4 mol / L nitric acid aqueous solution. After heating and refluxing at 100 °C for 10 h, the activated carbon was filtered and washed with distilled water until neutral. The activated carbon was then dried in an oven at 120 °C for 15 h to obtain oxidized activated carbon.

[0085] Activated carbon reduction: add 10g of oxidized activated carbon and 50mL of acetonitrile to a 500mL three-necked flask, cool to 10°C, add 10g of lithium aluminum hydride, react at 10°C for 8h, filter, wash the activated carbon with distilled water until neutral, and then put it into an oven to dry at 120°C for 15h to obtain deeply reduced activated carbon;

[0086] Modification of activated carbon: 10 g of deep reduced activated carbon, 5 g of 9-methyladenine and 100 mL of n-hexane were added to a 500 mL three-necked flask, reacted at 100 °C for 5 h, filtered, and the activated carbon was washed with distilled water until neutral, and then dried in an oven at 120 °C for 15 h to obtain modified activated carbon;

[0087] Pd loading: 100 mL of ethanol, 10 g of modified activated carbon and 0.84 g of PdCl2 were added to a 500 mL three-necked flask, stirred at 20 ° C for 48 h, filtered, and the catalyst was washed with distilled water until neutral, then sent to an oven to dry at 120 ° C for 15 h, and then calcined at 500 ° C for 5 h. The finished catalyst was obtained after cooling, and the catalyst Pd content was 5.0 wt%.

[0088] Isomerization reaction:

[0089] A 5000mL reaction bottle was equipped with a mechanical stirrer, a reflux condenser, and nitrogen replacement three times. Under nitrogen protection, 100 g of an isomerization catalyst, 3000 mL of toluene and VA crude oil raw material (1000 g, with an all-trans isomer content of 10%, an 11-cis isomer content of 40%, and a 9-cis isomer content of 50 wt%) were added in sequence, and the solution was stirred to mix. The reaction solution was then reacted at 120°C for 5 h. After the reaction was completed, liquid chromatography analysis was performed to obtain a reaction solution with an all-trans content of 96.11 wt%, a 9-cis content of 3.28 wt%, and an 11-cis content of 0.61 wt%.

[0090] Example 4

[0091] Preparation of modified catalyst:

[0092] Activated carbon oxidation: 10 g of wood activated carbon was added to a 500 mL three-necked flask, followed by 100 mL of 0.5 mol / L nitric acid aqueous solution. After heating and refluxing at 100 °C for 2 h, the activated carbon was filtered and washed with distilled water until neutral. The activated carbon was then dried in an oven at 120 °C for 12 h to obtain oxidized activated carbon.

[0093] Activated carbon reduction: add 10g of oxidized activated carbon and 100mL of acetic acid into a 500mL three-necked flask, cool to -20°C, add 2g of lithium aluminum hydride, react at -20°C for 2h, filter, wash the activated carbon with distilled water until neutral, and then put it into an oven to dry at 120°C for 12h to obtain deeply reduced activated carbon;

[0094] Modification of activated carbon: 10 g of deep reduced activated carbon, 20 g of adenine and 500 mL of acetonitrile were added to a 1000 mL three-necked flask, reacted at 30 °C for 20 h, filtered, the activated carbon was washed with distilled water until neutral, and then dried in an oven at 120 °C for 12 h to obtain modified activated carbon;

[0095] Pd loading: 500 mL of dimethyl sulfoxide, 10 g of modified activated carbon and 0.84 g of PdCl2 were added to a 1000 mL three-necked flask, stirred at 120°C for 12 h, filtered, the catalyst was washed with distilled water until neutral, then sent to an oven to dry at 120°C for 12 h, and then calcined at 500°C for 10 h. After cooling, the finished catalyst was obtained, with a Pd content of 5.0 wt% in the catalyst.

[0096] Isomerization reaction:

[0097] A 10L reaction bottle was equipped with a mechanical stirrer, a reflux condenser, and nitrogen replacement three times. Under nitrogen protection, 1.0 g of an isomerization catalyst, 4000 mL of acetonitrile and VA crude oil raw material (1000 g, with an all-trans isomer content of 5 wt%, an 11-cis isomer content of 20 wt%, and a 9-cis isomer content of 75 wt%) were added in sequence, and the solution was stirred to mix. The reaction solution was then reacted at 30°C for 20 h. After the reaction was completed, liquid chromatography analysis was performed to obtain a reaction solution with an all-trans content of 95.33 wt%, a 9-cis content of 4.10 wt%, and an 11-cis content of 0.57 wt%.

[0098] Comparative Example 1

[0099] In comparison with Example 1, VA isomerization reaction was carried out using 5% Pd / C purchased from Xi'an Kaili as a catalyst.

[0100] A 2000mL reaction bottle was equipped with a mechanical stirrer, a reflux condenser, and nitrogen replacement three times. Under nitrogen protection, 10 g of Pd / C catalyst, 1000 mL of acetonitrile and VA crude oil raw material (1000 g, 11-cis content 100 wt%) were added in sequence, and the solution was stirred to mix. The reaction solution was then reacted at 90°C for 8 h. After the reaction was completed, liquid chromatography analysis was performed to obtain a reaction solution with an all-trans content of 39.0%, an 11-cis content of 35.2 wt%, and a 9-cis content of 25.8 wt%. The Pd content in the reaction solution was 20 ppm, and the Pd loss rate was 7.2 wt%.

[0101] From Comparative Example 1, it can be seen that when the unmodified Pd / C catalyst with a substrate mass fraction of 1% isomerization reaction is used, under the same conditions, the conversion rate of the 11-cis isomer is slow, the all-trans selectivity is poor, and there is a loss of 7.2 wt% of Pd.

[0102] Those skilled in the art will appreciate that, based on the teachings of this specification, some modifications or adjustments may be made to the present invention, and these modifications or adjustments should also be within the scope defined by the claims of the present invention.

Claims

1. A method for preparing a modified palladium-carbon catalyst, characterized in that: The following steps are involved: S1: Activated carbon oxidation: oxidative modification of activated carbon using nitric acid to obtain oxidized activated carbon; S2: Reduction: The oxidized activated carbon is further reduced using lithium aluminum hydride; S3: Activated carbon modification: The reduced activated carbon reacts chemically with the modification reagent to form a NO chemical bond to obtain modified activated carbon; S4: Metal adsorption: The modified activated carbon is subjected to palladium metal adsorption, and a modified palladium-carbon catalyst is obtained after drying and calcination; Among them, the modification reagent described in S3 is one or more of adenine, adenine with a functional group, and 8-azaadenine; the modification reaction described in S3 needs to be carried out in an organic solvent, and the organic solvent is selected from one or more of acetonitrile, n-hexane, toluene, and dichloroethane.

2. The method for preparing a catalyst according to claim 1, characterized in that: The activated carbon used in S1 is selected from one or more of fruit shell activated carbon, coconut shell activated carbon and wood activated carbon; And / or, the nitric acid in S1 is an aqueous nitric acid solution with a concentration of 0.5-4 mol / L; And / or, the ratio of nitric acid to activated carbon is (10-50) mL: 1 g.

3. The method for preparing a catalyst according to claim 2, characterized in that: The activated carbon used in S1 is wood activated carbon.

4. The method for preparing a catalyst according to claim 2, characterized in that: The nitric acid described in S1 is a nitric acid aqueous solution with a concentration of 2-3 mol / L.

5. The method for preparing a catalyst according to claim 2, characterized in that: The ratio of the nitric acid to the activated carbon is (20-30) mL:1 g.

6. The method for preparing a catalyst according to claim 2, characterized in that: The activated carbon in S1 needs to be refluxed in the nitric acid aqueous solution for 2-10 hours.

7. The method for preparing a catalyst according to claim 6, characterized in that: The activated carbon in S1 needs to be refluxed in the nitric acid aqueous solution for 4-6 hours.

8. The method for preparing a catalyst according to claim 1, characterized in that: The mass ratio of lithium aluminum hydride and oxidized activated carbon in S2 is (0.2-1):1; And / or, the reduction reaction temperature in S2 is -20-10°C; And / or, the reaction time is 2-8h.

9. The method for preparing a catalyst according to claim 1, characterized in that: The reduction reaction in S2 is carried out in a solvent, and the solvent is selected from one or more of water, acetic acid, acetonitrile, toluene, ethanol, and dichloroethane; and / or, the amount ratio of the solvent to the oxidized activated carbon is (5-30) mL: 1 g.

10. The method for preparing a catalyst according to claim 9, characterized in that: The dosage ratio of solvent and oxidized activated carbon in S2 is (10-20) ml:1 g.

11. The method for preparing a catalyst according to claim 8, characterized in that: The reduction reaction temperature in S2 is -10-0°C.

12. The method for preparing a catalyst according to claim 8, characterized in that: The reduction reaction time in S2 is 3-5h.

13. The method for preparing a catalyst according to claim 1, characterized in that: The functional group of the adenine with a functional group in the modification reagent described in S3 is selected from methyl, fluorine, chlorine, and benzyl.

14. The method for preparing a catalyst according to claim 1, characterized in that: The modifying reagent in S3 is adenine.

15. The method for preparing a catalyst according to claim 1, characterized in that: In S3, the ratio of the organic solvent to the reduced activated carbon is (10-50) mL: 1 g; and / or, the mass ratio of the modifying agent to the reduced activated carbon is (0.5-2): 1; And / or, the reaction temperature of the modification reaction in S3 is 30-100° C.; the reaction time is 5-20 h.

16. The method for preparing a catalyst according to claim 15, characterized in that: The usage ratio of the organic solvent and the reduced activated carbon is (20-30) mL:1 g.

17. The method for preparing a catalyst according to claim 14, characterized in that: The mass ratio of the modifying agent to the reduced activated carbon is (0.8-1.5):

1.

18. The method for preparing a catalyst according to claim 14, characterized in that: The reaction temperature of the modification reaction in S3 is 50-80°C, and the reaction time is 8-12h.

19. The method for preparing a catalyst according to claim 1, characterized in that: The metal adsorption step described in S4 uses the modified activated carbon prepared in S3 as a carrier, uses a soluble palladium salt as a Pd source, and adopts a volume impregnation method to prepare a modified palladium-carbon catalyst.

20. The method for preparing a catalyst according to claim 19, characterized in that: In S4, the soluble palladium salt is PdCl2.

21. The method for preparing a catalyst according to claim 19, characterized in that: In S4, the prepared modified palladium-carbon catalyst has a Pd content of 1-10%.

22. Use of a modified palladium-carbon catalyst prepared by the catalyst preparation method according to any one of claims 1 to 21 in catalyzing the conversion of vitamin A cis isomer to all-trans isomer.

23. A method for converting cis and trans isomers of vitamin A, characterized in that: The modified palladium-carbon catalyst prepared by the preparation method described in any one of claims 1 to 21 catalyzes the isomerization reaction of cis-vitamin A isomers to convert them into all-trans-vitamin A isomers.

24. The method according to claim 23, characterized in that The reaction substrate is a mixture of 11-cis vitamin A isomer, 9-cis isomer and all-trans vitamin A isomer or a single cis isomer is used as a substrate.

25. The method according to claim 24, characterized in that The content of all-trans isomer in the reaction substrate is 0-10%, the content of 11-cis isomer is 0-100%, and the content of 9-cis isomer is 0-100%, based on the total mass of crude vitamin A oil.

26. The preparation method according to claim 23, characterized in that: The isomerization reaction is carried out in the presence of an organic solvent, and the organic solvent is selected from one or more of acetonitrile, N,N-dimethylformamide, hexane, pentane, heptane, benzene, toluene, methyl tert-butyl ether, tetrahydrofuran, ethanol, methanol, isopropanol, n-propanol and butanol; And / or, the usage ratio of the organic solvent to the reaction substrate is (1-4) L:1 kg.

27. The preparation method according to claim 26, characterized in that: The usage ratio of the organic solvent to the reaction substrate is (2-3) L: 1 kg.

28. The preparation method according to claim 23, characterized in that: The amount of palladium carbon catalyst used in the isomerization reaction is 0.1-10% of the amount of the reaction substrate; And / or, the temperature of the isomerization reaction is 30-120°C; the reaction time is 5-20h; And / or, the isomerization reaction is carried out under an inert gas and in the absence of light.

29. The preparation method according to claim 28, characterized in that: The amount of palladium-carbon catalyst used in the isomerization reaction is 1-5% of the amount of the reaction substrate.

30. The preparation method according to claim 28, characterized in that: The isomerization reaction temperature is 40-90° C., and the reaction time is 8-10 h.

31. The preparation method according to claim 28, characterized in that: The isomerization reaction was carried out under nitrogen and / or argon in the absence of light.

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