CN110354909B

CN110354909B - Catalyst system for preparing L-menthol and preparation method and application thereof

Info

Publication number: CN110354909B
Application number: CN201910648765.9A
Authority: CN
Inventors: 方文娟; 董菁; 王亚新; 于磊; 王联防; 于斌成; 张永振; 黎源
Original assignee: Wanhua Chemical Group Co Ltd; Wanhua Chemical Ningbo Co Ltd
Current assignee: Wanhua Chemical Group Co Ltd; Wanhua Chemical Ningbo Co Ltd
Priority date: 2019-07-18
Filing date: 2019-07-18
Publication date: 2022-01-07
Anticipated expiration: 2039-07-18
Also published as: CN110354909A

Abstract

The invention discloses a catalyst system for preparing L-menthol, a preparation method and application thereof. Under the action of the catalyst, L-menthol is converted from L-menthone to generate L-menthol, and through the synergistic effect of the components of the heterogeneous catalyst, the reaction can be efficiently and rapidly carried out under mild conditions, the reaction conversion rate and the chemical selectivity can reach over 99.5 percent at most, the service life of the catalyst is long, the activity is basically stable after being applied for 20 times, and the application can reach 50 times at most.

Description

Catalyst system for preparing L-menthol and preparation method and application thereof

Technical Field

The invention belongs to the field of menthol preparation, relates to a method for preparing and synthesizing chiral L-menthol from L-menthone, and particularly relates to a catalyst system for preparing L-menthol, and a preparation method and application thereof.

Background

Menthol, also known as menthol, is a natural cyclic terpene alcohol which exists in nature, the menthol molecule has 3 chiral centers, so 8 stereoisomers as shown below exist, 4 pairs of racemic compounds, wherein D, L-menthol has a cooling effect, other isomers have no cooling effect, the odors of L-menthol and D-menthol are obviously different, L-menthol is a light sweet pungent odor and has a unique mint flavor, and D-menthol is a spicy pungent odor with slight camphor odor. L-menthol has a cooling effect and D-menthol does not, so L-menthol has a higher industrial value and can be used in daily-use and edible essences, medicines, tobacco and oral products.

The menthol is mainly extracted from plants, the yield is influenced by uncontrollable factors such as seasons, planting areas and the like, so that the price fluctuation is large, the chemical molecular formula of the synthetic menthol is consistent with that of natural menthol, and the synthetic menthol and the natural menthol can be completely interchanged in sense.

Patent CN200880125808.5 discloses a method for preparing chiral citronellal by asymmetrically hydrogenating citral, followed by cyclization and hydrogenation to obtain L-menthol, but the method has a complex process route, and the asymmetric hydrogenation reaction usually uses a catalyst system prepared by matching rhodium heavy metal and chiral ligand, which is expensive and has high cost.

Patent CN 105254475A discloses a synthesis method for obtaining racemic menthol and isomer derivatives thereof from citronellal in a solvent under the action of a peroxide radical initiator, but the menthol obtained by the method has bad smell, and other solvents need to be introduced into a catalyst system, which has adverse effects on post-treatment and increases the complexity of process operation.

In Journal of Molecular CatalyssiA: Chreical, 2006,256:216-218, a method for preparing L-menthol by hydrogen reduction under catalysis of beta-cyclodextrin and nickel is disclosed, but the method has low yield and poor selectivity, and the catalyst is not easy to recycle.

In summary, the problems of complex synthetic route, difficult recovery and reuse of homogeneous catalysts, complex post-treatment and the like in the existing preparation process of L-menthol are urgently needed to be solved, and the L-menthol needs to be greatly improved in the aspects of preparation process, catalysts, economy, environmental protection and the like.

Disclosure of Invention

The invention aims to provide a catalyst and a method for preparing L-menthol, thereby solving a plurality of problems in the existing process for preparing L-menthol.

In natural peppermint oil, the content of L-menthone is about 30%. From the following molecular structure, the molecular structure of the L-menthone is similar to that of the L-menthol, and due to the C-4S configuration of the L-menthone, more L-menthol can be obtained after reduction under the steric hindrance effect of isopropyl. Thus, L-menthol can be obtained by simple transformation using the natural chiral precursor L-menthone.

The invention firstly provides nickel-phosphomolybdic acid-epigallocatechin oxide gallate-graphene and a preparation method thereof. And secondly, the method for preparing the L-menthol from the L-menthone by adopting the catalyst is carried out under mild reaction conditions, can recover the catalyst in a convenient and fast manner, and has the advantages of simpler reaction process, lower reaction cost, good environmental friendliness and good industrial prospect.

In order to achieve the purpose of the invention, the technical scheme adopted by the invention is as follows:

a catalyst system for preparing L-menthol has a structure of nickel-phosphomolybdic acid-epigallocatechin oxide gallate-graphene (Ni-HMoP-OEGCG-GN), wherein the content of each component is 9-34 wt% of nickel, 5-16 wt% of phosphomolybdic acid, 4-15 wt% of epigallocatechin oxide gallate and 35-82 wt% of graphene, and the total mass of the catalyst system is 100%.

Preferably, the catalyst system for preparing the L-menthol comprises 17-26 wt% of nickel, 8-13 wt% of phosphomolybdic acid, 7-11 wt% of epigallocatechin gallate oxide and 50-68 wt% of graphene, wherein the total mass of the catalyst system is 100%.

The preparation method of the catalyst system comprises the following preparation steps:

1) preparation of Graphene Oxide (GO);

2) preparation of phosphomolybdic acid-graphene oxide (HMoP-GO);

3) preparation of nickel-phosphomolybdic acid-epigallocatechin gallate oxide-graphene (Ni-HMoP-OEGCG-GN).

In the invention, the Graphene Oxide (GO) in the step 1) can be prepared by any available method, preferably by a Hummers oxidation method, and the GO is obtained by taking natural graphite powder as a raw material;

the granularity of the graphite powder ranges from 500 meshes to 5000 meshes, and 1500 meshes to 3000 meshes are preferred.

Preferably, the method employed in the exemplified embodiments of the invention is: adding a solid mixture of graphite powder and sodium nitrate into concentrated sulfuric acid (such as 98%) under stirring, adding potassium permanganate for multiple times (such as 6 times), controlling the reaction temperature to be not more than 20 ℃, stirring for reaction for 1-3 hours, heating to 33-38 ℃, continuously stirring for 25-35 minutes, adding deionized water, continuously heating to above 98 ℃, heating for 15-25 minutes (the solution is brown yellow at the moment), adding hydrogen peroxide, continuously stirring for 10-20 minutes, filtering, washing and drying to obtain Graphene Oxide (GO).

In the enumerated method, the dosage of the concentrated sulfuric acid is 21-25 mL/g graphite powder; the mass ratio of the graphite powder to the sodium nitrate in the solid mixture of the graphite powder and the sodium nitrate is 1: 0.4 to 0.6; the mass ratio of the graphite powder to the potassium permanganate to the hydrogen peroxide is 1: 2.5-3.5: 4.5-5.5;

in the method listed, the filtration, washing and drying are all conventional operations, and the following methods are preferably adopted: the hot solution is filtered and washed with 5wt% aqueous HCl and deionized water until the filtrate is free of sulfate radicals, and the filter cake is dried under full vacuum at 60 ℃.

In the present invention, the phosphomolybdic acid-graphene oxide (HMoP-GO) in step 2) can be prepared by any available method, preferably by an impregnation method, and in the specific embodiments of the present invention, the method is: and dissolving phosphomolybdic acid in the graphene oxide water dispersion, performing ultrasonic dispersion for 25-35 min, and drying to obtain phosphomolybdic acid-graphene oxide (HMoP-GO).

In the enumerated method, the dispersion concentration of the aqueous dispersion of graphene oxide is 5-6 mg/mL; the addition amount of the phosphomolybdic acid is 3-10 wt% of the mass of Graphene Oxide (GO), and preferably 5-8 wt%;

among the listed methods, the drying is a conventional operation, and the following method is preferably employed: and (3) naturally airing the mixture after being placed for about 24 hours, then drying the mixture in vacuum at 65-75 ℃ until free water is removed, and then drying the mixture for about 5 hours at about 120 ℃.

In the present invention, the preparation method of nickel-phosphomolybdic acid-epigallocatechin gallate oxide-graphene (Ni-HMoP-OEGCG-GN) in step 3) comprises the steps of:

(1) adding phosphomolybdic acid-graphene oxide (HMoP-GO) into an epigallocatechin gallate (EGCG) aqueous solution, and stirring and reacting at 70-180 ℃, preferably 90-130 ℃, for 0.5-6 hours, preferably 2-4 hours, in a nitrogen environment with 3-8 MPaG, preferably 4-6 MPaG;

(2) adding water-soluble nickel salt into the reaction system in the step (1), and stirring and reacting for 0.5-6 hours, preferably 2-4 hours, at 70-180 ℃, preferably 90-130 ℃ in a nitrogen environment with 3-8 MPaG, preferably 4-6 MPaG;

(3) and (3) washing and drying the reaction system in the step (2) to obtain the nickel-phosphomolybdic acid-epigallocatechin oxide gallate-graphene.

In the method, the mass ratio of the phosphomolybdic acid-graphene oxide to the epigallocatechin gallate in the step (1) to water is (3-10): 100, preferably 1 (5-8): 100, respectively;

the soluble nickel salt in the step (2) includes but is not limited to at least one of nickel acetate, nickel chloride, nickel nitrate and nickel sulfate, preferably nickel acetate and/or nickel chloride, and more preferably nickel chloride; the adding amount of the soluble nickel salt is 5-20 wt% of the weight of the phosphomolybdic acid-graphene oxide, and preferably 10-15 wt% of the weight of the phosphomolybdic acid-graphene oxide.

Preferably, the stirring speed in the steps (1) and (2) is 100-300 rpm, preferably 150-250 rpm.

Preferably, the reaction conditions of the steps (1) and (2) are the same, namely, the reaction is carried out under the same nitrogen pressure, stirring speed, temperature and time.

The water washing and drying in the step (3) are conventional operations, and preferably adopt the following method: and (3) decompressing and cooling the reaction system in the step (2), washing the reaction system for 3 times by using deionized water, removing unreacted epigallocatechin gallate (EGCG), and drying the reaction system at the temperature of 50-200 ℃ until no free water exists, preferably drying the reaction system at the temperature of 70 ℃ in vacuum until no free water exists.

In the prepared catalyst nickel-phosphomolybdic acid-epigallocatechin gallate-graphene, epigallocatechin gallate (OEGCG) oxide is detected through ultraviolet-visible spectrum, and the loading amount of the epigallocatechin gallate in the finished catalyst is 4-15 wt%.

In the catalyst system for preparing L-menthol, phosphomolybdic acid is combined with functional groups on the surface of graphene oxide and adsorbed on the graphene, and then added epigallocatechin gallate reacts with the rest exposed functional groups of the graphene oxide to reduce GO into GN, wherein the epigallocatechin gallate mainly has the following two combination forms:

1) combine with the epoxy group on GO surface, the structure is:

2) combined with the carboxyl around GO, the structure is:

the oxidized epigallocatechin gallate molecules are stacked on the surface of the graphene through Van der Waals force, and finally the added nickel salt is reduced by excessive EGCG and deposited on the surface of the graphene to become nickel particles, so that a catalyst system with high catalytic activity and capable of being used for preparing L-menthol is obtained.

A method for preparing L-menthol comprises the following steps: l-menthone is subjected to hydrogenation reaction under the action of a catalyst of nickel-phosphomolybdic acid-epigallocatechin gallate-graphene (Ni-HMoP-OEGCG-GN) to prepare L-menthol.

In the present invention, the amount of the catalyst nickel-phosphomolybdic acid-epigallocatechin gallate-graphene (Ni-HMoP-OEGCG-GN) is 0.001 to 1wt%, preferably 0.01 to 0.1wt%, based on the mass of L-menthone.

In the invention, the temperature of the hydrogenation reaction is 30-80 ℃, preferably 40-60 ℃; the reaction time is 6-24 h, preferably 8-12 h; the reaction gauge pressure is 0 to 2MPaG, preferably 0.5 to 1 MPaG.

In the invention, the hydrogenation reaction is carried out by controlling the amount of introduced hydrogen through the reaction pressure.

In the hydrogenation reaction, the conversion rate of the L-menthone is more than 95 percent and can reach more than 99.5 percent at most, and the selectivity of the L-menthol is more than 90 percent and can reach more than 99.5 percent at most.

The catalyst can be directly recycled and reused, the recycling method is simple, and the catalyst can be filtered and washed. The catalyst has long service life, basically stable activity after being recycled and reused for 20 times, and the maximum reuse time can reach 50 times.

According to the heterogeneous catalyst nickel-phosphomolybdic acid-epigallocatechin oxide-graphene, the surface smoothness of graphene oxide is reduced through doping of phosphomolybdic acid, a large number of folded protrusions are formed, so that the peripheral stress and the internal stress of a graphene oxide film are uneven, and then the graphene oxide is changed into a wavy shape due to different thermal stress and compressive stress bearing capacity and reducing capacity of each part when the graphene oxide is reduced by EGCG, so that the pi-pi aggregation capacity of the reduced graphene is reduced and tends to planar connection, the aggregation problem existing in the reduction of graphene by using a conventional reducing agent is effectively avoided, and the catalytic activity of the graphene as a heterogeneous catalyst carrier is improved. Meanwhile, the doping of phosphomolybdic acid enables the nickel salt added later to be uniformly reduced to the surface of the graphene by EGCG, so that the number and space of catalytic active sites in contact with a reaction substrate are greatly increased, and the conversion rate of the L-menthone is accelerated under the synergistic effect of the ultra-high carrier mobility of the graphene; meanwhile, partially oxidized EGCG molecules are stacked on the surface of the graphene carrier, so that the selectivity of converting L-menthone into L-menthol is greatly improved; in addition, the stability of the catalyst is also obviously improved, and the service life of the catalyst is prolonged.

The invention has the positive effects that: under the action of a heterogeneous catalyst of a catalyst nickel-phosphomolybdic acid-epigallocatechin gallate-graphene oxide (Ni-HMoP-OEGCG-GN), L-menthol can be prepared from L-menthone at a high yield under mild reaction conditions, and the method has remarkable operability and economy; and in addition, other solvents are not involved in the system, so that the introduction of other impurities is reduced, and the method has good environmental friendliness. Finally, the heterogeneous catalyst has the advantages of easy recovery, high catalytic activity and the like.

Detailed Description

The invention is further illustrated by the following examples which are intended to be illustrative of the invention but not limiting in any way, and which include any novel feature or any novel combination disclosed in the specification, as well as any novel method or process steps or any novel combination disclosed.

An analytical instrument:

gas chromatograph: agilent 7890, chromatographic column INNO-WAX, inlet temperature: 300 ℃; the split ratio is 50: 1; carrier gas flow: 30 mL/min; temperature rising procedure: 80-230 ℃, 5 ℃/min, detector temperature: 280 ℃.

Uv-vis spectrophotometer: and (3) dissolving a proper amount of a dried sample into distilled water by Schimadazu UV 1700, and scanning within the range of 190-500 nm by taking the distilled water as a reference.

Main raw materials and reagents:

graphite powder with the granularity of 1500-3000 meshes, the content of more than 95 wt%, the carbon content of 99.85 wt%, Aldrich company;

phosphomolybdic acid, 99 wt%, Aldrich;

epigallocatechin gallate, 99 wt%, Aldrich corporation;

95-98 wt% of sulfuric acid, national drug group chemical reagent limited;

99 wt% potassium permanganate, chemical reagents of national drug group, ltd;

99 wt% of sodium nitrate, chemical reagents of national drug group, ltd;

30 wt% of hydrogen peroxide, national medicine group chemical reagent company Limited;

hydrochloric acid, 37 wt%, chemical reagents of national drug group, ltd;

barium chloride, 99 wt%, chemical reagents of national drug group, ltd;

99 wt% of nickel acetate, chemical reagents of national drug group, ltd;

99 wt% of nickel chloride, chemical reagents of national drug group, ltd;

phosphotungstic acid, 99 wt%, Aladdin reagent, Inc.;

sodium borohydride, 99 wt%, alatin reagent ltd;

tea polyphenols, 98 wt%, alatin reagent ltd;

5A molecular sieves, Sichuan Kanglong chemical Co., Ltd;

l-menthone, 99.9 wt%, Allatin reagent, Inc.

The preparation process of the catalyst comprises the following steps:

example 1

Placing a 250mL reaction bottle in an ice water bath, adding 23mL98 wt% concentrated sulfuric acid, adding a solid mixture of 1g of graphite powder and 0.5g of sodium nitrate under stirring, adding 3g of potassium permanganate 6 times, controlling the reaction temperature to be not more than 20 ℃, stirring for reaction for 2 hours, then heating to 35 ℃, continuing to stir for 30 minutes, slowly adding 46mL of deionized water, raising the temperature to 98 ℃, continuing to heat for 20 minutes to obtain a brownish yellow solution, adding 5g of hydrogen peroxide, continuing to stir for 15 minutes, taking down the reaction bottle, filtering while the solution is hot, and washing with a 5wt% HCl aqueous solution and deionized water until no sulfate radical is detected in the filtrate. And finally, putting the filter cake into a vacuum drying oven at 60 ℃ for full drying to obtain GO, and dispersing the GO into a deionized water solution with the concentration of 5 mg/mL.

Example 2

Adding 0.05g of phosphomolybdic acid (the addition amount is 5wt% of the mass of the graphene oxide) into 200mL of GO solution prepared in example 1, mixing and adsorbing, ultrasonically dispersing for 30min, standing for 24 hours, naturally airing, then drying in vacuum at 65 ℃ until free water is removed, and drying at 120 ℃ for 5 hours to prepare phosphomolybdic acid-graphene oxide (HMoP-GO);

dissolving 1g of HMoP-GO and 10g of epigallocatechin gallate (EGCG) in 100g of water (the mass ratio of HMoP-GO to EGCG: water is 1:10:100), transferring the mixture into a reaction kettle, filling nitrogen to 6MPaG, heating to 90 ℃, stirring at the speed of 150rpm for 4 hours, adding 0.22g of nickel chloride (the addition of nickel is 10wt% of HMoP-GO) into the reaction kettle, stirring at 90 ℃ and 150rpm in nitrogen for 4 hours, then decompressing and cooling, washing the mixed solution with deionized water for 3 times, drying in vacuum at 70 ℃ until free water does not exist, preparing a No. 1 catalyst, and measuring the weight of the EGCG after oxidation by using an ultraviolet visible spectrum (OEGCG with the absorption intensity of 13 at 276 nm) to be 15wt% of the No. 1 catalyst.

The content of each component in the No. 1 catalyst is 14 wt% of nickel, 6wt% of phosphomolybdic acid, 15wt% of epigallocatechin gallate oxide and 65 wt% of graphene, and the total mass of the catalyst system is 100%.

Example 3

Adding 0.06g of phosphomolybdic acid (the addition amount is 6wt% of the mass of the graphene oxide) into 200mL of GO solution prepared in example 1, mixing and adsorbing, ultrasonically dispersing for 35min, standing for 24 hours, naturally airing, then drying in vacuum at 70 ℃ until free water is removed, and drying at 120 ℃ for 5 hours to prepare phosphomolybdic acid-graphene oxide (HMoP-GO);

dissolving 1g of HMoP-GO and 7g of epigallocatechin gallate (EGCG) in 100g of water (the mass ratio of HMoP-GO to EGCG: water is 1:7:100), transferring the mixture into a reaction kettle, filling nitrogen to 5MPaG, heating to 110 ℃, stirring at the speed of 200rpm for 3 hours, then adding 0.264g of nickel chloride (the addition of nickel is 12 wt% of HMoP-GO) into the reaction kettle, stirring at 110 ℃ and 200rpm in nitrogen for 3 hours, then decompressing and cooling, washing the mixed solution with deionized water for 3 times, drying in vacuum at 70 ℃ until free water does not exist, preparing a 2# catalyst, and measuring the weight percentage of the EGCG after oxidation by using an ultraviolet visible spectrum (OEGCG with the absorption intensity of 8 at 276 nm) to be 10wt% of the 2# catalyst.

The content of each component in the No. 2 catalyst is 20wt% of nickel, 10wt% of phosphomolybdic acid, 10wt% of epigallocatechin gallate oxide and 60 wt% of graphene, and the total mass of the catalyst system is 100%.

Example 4

Adding 0.08g of phosphomolybdic acid (the addition amount is 8wt% of the mass of the graphene oxide) into 200mL of GO solution prepared in example 1, mixing and adsorbing, ultrasonically dispersing for 25min, standing for 24 hours, naturally airing, then drying in vacuum at 75 ℃ until free water is removed, and drying at 120 ℃ for 5 hours to prepare phosphomolybdic acid-graphene oxide (HMoP-GO);

dissolving 1g of HMoP-GO and 3g of epigallocatechin gallate (EGCG) in 100g of water (the mass ratio of HMoP-GO to EGCG: water is 1:3:100), transferring the mixture into a reaction kettle, filling nitrogen to 4MPaG, heating to 130 ℃, stirring at the speed of 250rpm for 2 hours, adding 0.33g of nickel chloride (the addition of nickel is 15wt% of HMoP-GO) into the reaction kettle, stirring at the temperature of 130 ℃ and 250rpm in nitrogen for 2 hours, then decompressing and cooling, washing the mixed solution with deionized water for 3 times, drying in vacuum at 70 ℃ until free water does not exist, preparing a catalyst 3#, wherein EGCG after oxidation accounts for 4wt% of the catalyst 3# measured by ultraviolet visible spectrum (OEGCG with absorption intensity of 2 at 276 nm).

The content of each component in the No. 3 catalyst is 22 wt% of nickel, 11wt% of phosphomolybdic acid, 4wt% of epigallocatechin gallate oxide and 63 wt% of graphene, and the total mass of the catalyst system is 100%.

Comparative example 1

Weighing 1g of 5A molecular sieve, dissolving in 200mL of deionized water, adding 0.06g of phosphomolybdic acid (the addition is 6wt% of the molecular sieve), mixing and adsorbing, ultrasonically dispersing for 30min, standing for 24 hours, naturally drying, then drying at 70 ℃ in vacuum until free water is removed, and drying at 120 ℃ for 5 hours to obtain the phosphomolybdic acid-molecular sieve;

dissolving 1g of phosphomolybdic acid-molecular sieve and 6g of epigallocatechin gallate (EGCG) in 100g of water (the mass ratio of the phosphomolybdic acid-molecular sieve to the EGCG: the water is 1:6:100), transferring the mixture into a reaction kettle, introducing nitrogen to 5MPaG, heating to 120 ℃, stirring at the speed of 230rpm for 3 hours, then adding 0.264g of nickel chloride (the addition of nickel is 12 wt% of the phosphomolybdic acid-molecular sieve) into the reaction kettle, stirring at 120 ℃ and 230rpm in the nitrogen for 3 hours, after the treatment is finished, releasing pressure and cooling, washing the mixed solution with deionized water for 3 times, drying in vacuum at 70 ℃ until free water does not exist, preparing a 4# catalyst, wherein the EGCG after oxidation accounts for 9 wt% of the 4# catalyst by using an ultraviolet visible spectrum (OEGCG has an absorption intensity of 7 at 276 nm).

The content of each component in the No. 4 catalyst is 10wt% of nickel, 4.6 wt% of phosphomolybdic acid, 9 wt% of epigallocatechin gallate oxide and 76.4 wt% of molecular sieve, wherein the total mass of the catalyst system is 100%.

Comparative example 2

Dissolving 1g of GO prepared in example 1 and 5g of epigallocatechin gallate (EGCG) in 100g of water (GO: EGCG: water mass ratio is 1:5:100), transferring into a reaction kettle, introducing nitrogen to 5MPaG, heating to 100 ℃, stirring at 190rpm for 3 hours, adding 0.264g of nickel chloride (nickel addition is 12 wt% of GO) into the reaction kettle, stirring at 190rpm and 100 ℃ under 5MPaG in nitrogen for 3 hours, after the treatment is finished, releasing pressure and cooling, washing the mixed solution with deionized water for 3 times, drying in vacuum at 70 ℃ until free water does not exist, preparing a 5# catalyst, and measuring the weight of the EGCG after oxidation to 7 wt% of the 5# catalyst by using an ultraviolet visible spectrum (OEGCG with 276nm absorption intensity of 5).

The content of each component in the No. 5 catalyst is 20wt% of nickel, 7 wt% of epigallocatechin gallate oxide and 73 wt% of graphene, and the total mass of the catalyst system is 100%.

Comparative example 3

dissolving 1g of HMoP-GO and 7g of sodium borohydride in 100g of water (the mass ratio of HMoP-GO to sodium borohydride to water is 1:7:100), transferring the mixture into a reaction kettle, filling nitrogen into the reaction kettle until 5MPaG is reached, heating the mixture to 110 ℃, stirring at the speed of 200rpm, stirring for 3 hours, then adding 0.264g of nickel chloride (the addition of nickel is 12 wt% of HMoP-GO) into the reaction kettle, stirring for 3 hours at the speed of 200rpm under the condition of 5MPaG in nitrogen, relieving pressure and reducing temperature after the treatment is completed, washing the mixed solution for 3 times by deionized water, and drying the mixed solution in vacuum at the temperature of 70 ℃ until no free water exists to obtain the No. 6 catalyst.

The content of each component in the No. 6 catalyst is 20wt% of nickel, 10wt% of phosphomolybdic acid and 70 wt% of graphene, and the total mass of the catalyst system is 100%.

Comparative example 4

Adding 0.06g of phosphomolybdic acid (the addition amount is 6wt% of the mass of the graphene oxide) into 200mL of GO solution prepared in example 1, mixing and adsorbing, ultrasonically dispersing for 25min, standing for 24 hours, naturally airing, then drying in vacuum at 70 ℃ until free water is removed, and drying at 120 ℃ for 5 hours to prepare phosphomolybdic acid-graphene oxide (HMoP-GO);

dissolving 1g of HMoP-GO and 7g of tea polyphenol in 100g of water (the mass ratio of HMoP-GO to tea polyphenol to water is 1:7:100), transferring the mixture into a reaction kettle, filling nitrogen into the reaction kettle until 5MPaG is reached, raising the temperature to 110 ℃, stirring at the speed of 200rpm, stirring for 3 hours, then adding 0.264g of nickel chloride (the addition of nickel is 12 wt% of HMoP-GO) into the reaction kettle, stirring for 3 hours at the speed of 200rpm under the condition of 5MPaG in nitrogen, releasing pressure and reducing temperature after the treatment is completed, washing the mixed solution for 3 times by deionized water, and drying in vacuum at 70 ℃ until no free water exists to obtain the 7# catalyst.

The content of each component in the No. 7 catalyst is 20wt% of nickel, 10wt% of phosphomolybdic acid, 6wt% of tea polyphenol and 64 wt% of graphene, and the total mass of the catalyst system is 100%.

The application of the catalyst comprises the following steps:

examples 5 to 7

Preparing L-menthol:

0.1g of 1#, 2#, and 3# catalysts are respectively put into a dry 500mL high-pressure reaction kettle replaced by nitrogen, 99% purity hydrogen is used for stamping to 0.5MPaG, the pressure is released to normal pressure, and the step is repeated for 3 times to complete gas replacement. 200g of L-menthone is conveyed into a kettle by using an advection pump, the temperature is maintained at 50 ℃, the pressure of the reaction kettle is kept at 0.7MPaG, the stirring is started, the uniform stirring is ensured, and the reaction lasts for 10 hours.

After the reaction was completed, the solution after the reaction was subjected to gas phase detection using a gas chromatograph.

Comparative examples 5 to 8

Preparing L-menthol:

0.1g of 4#, 5#, 6#, and 7# catalysts are respectively put into a dry 500mL high-pressure reaction kettle replaced by nitrogen, 99% purity hydrogen is used for stamping to 0.5MPaG, the pressure is released to normal pressure, and the step is repeated for 3 times to complete the gas replacement. 200g of L-menthone is conveyed into a kettle by using an advection pump, the temperature is maintained at 50 ℃, the pressure of the reaction kettle is kept at 0.7MPaG, the stirring is started, the uniform stirring is ensured, and the reaction lasts for 10 hours.

In examples 5 to 7 of the present invention and comparative examples 5 to 8, the results of the conversion and selectivity of the reaction are shown in Table 1:

TABLE 1 reactivity of different catalysts

Catalyst numbering	L-menthone conversion/%)	L-menthol selectivity/%)	D-neomenthol selectivity/%)
				1#	95.2	94.7	3.7
2#	99.7	99.6	0.1
				3#	96.4	95.0	2.9
4#	85.1	92.1	6.3
				5#	75.9	90.5	7.6
6#	96.1	62.3	22.4
				7#	96.3	85.3	11.6

The reaction condition evaluation process:

example 8

0.02g of catalyst 2# was placed in a dry 500ml autoclave purged with nitrogen, pressurized to 0.5MPaG using 99% pure hydrogen, depressurized to normal pressure, and the process was repeated 3 times to complete gas purging. 200g of L-menthone is conveyed into the kettle by using an advection pump, the temperature is maintained at 60 ℃, the pressure of the reaction kettle is kept at 0.5MPaG, the stirring is started, the uniform stirring is ensured, and the reaction lasts for 8 hours.

After the reaction was completed, the solution after the reaction was subjected to gas phase detection using a gas chromatograph. The conversion of L-menthone was 95.6%, the selectivity of the reaction was 97.5% for L-menthol and 2.4% for D-neomenthol.

Example 9

0.2g of catalyst 2# was placed in a dry 500ml autoclave purged with nitrogen, pressurized to 0.5MPaG using 99% pure hydrogen, depressurized to normal pressure, and the process was repeated 3 times to complete gas purging. 200g of L-menthone is conveyed into a kettle by using an advection pump, the temperature is maintained at 40 ℃, the pressure of the reaction kettle is kept at 1MPaG, the stirring is started, the uniform stirring is ensured, and the reaction lasts for 12 hours.

After the reaction was completed, the solution after the reaction was subjected to gas phase detection using a gas chromatograph. The conversion of L-menthone was 98.1%, the selectivity of the reaction was 98.7% for L-menthol and 1.2% for D-neomenthol.

Example 10

0.1g of catalyst 2# was placed in a dry 500ml high-pressure reaction vessel previously subjected to nitrogen substitution, pressurized to 0.5MPaG using 99% pure hydrogen, depressurized to normal pressure, and the step was repeated 3 times to complete the gas substitution. 200g of L-menthone is conveyed into a kettle by using an advection pump, the temperature is maintained at 50 ℃, the pressure of the reaction kettle is kept at 0.8MPaG, the stirring is started, the uniform stirring is ensured, and the reaction lasts for 10 hours.

After the reaction was completed, the solution after the reaction was subjected to gas phase detection using a gas chromatograph. The conversion of L-menthone was 99.8%, the selectivity of the reaction was 99.6% for L-menthol and 0.1% for D-neomenthol.

Example 11

The application experiment was carried out on catalyst # 2 under the conditions described in example 10, with the results shown in table 2 below:

TABLE 22 # catalyst application experiment

Number of times of application	5	10	15	20	50
						Conversion rate/%	99.7	99.7	99.5	99.1	98.9
L-menthol selectivity/%)	99.5	99.4	99.2	99.1	99.0
						D-neomenthol selectivity/%)	0.2	0.1	0.2	0.3	0.3

Claims

1. A catalyst system for the preparation of L-menthol, characterized in that: the catalyst is characterized by having a structure of nickel-phosphomolybdic acid-epigallocatechin gallate-graphene, wherein the content of each component is 9-34 wt% of nickel, 5-16 wt% of phosphomolybdic acid, 4-15 wt% of epigallocatechin gallate and 35-82 wt% of graphene, and the total mass of the catalyst system is 100%.

2. The catalyst system for the preparation of L-menthol according to claim 1, characterized in that: the catalyst system comprises 17-26 wt% of nickel, 8-13 wt% of phosphomolybdic acid, 7-11 wt% of epigallocatechin gallate oxide and 50-68 wt% of graphene, wherein the total mass of the catalyst system is 100%.

3. A process for preparing a catalyst system according to claim 1 or 2, characterized in that the process comprises the steps of:

1) preparing graphene oxide;

2) preparing phosphomolybdic acid-graphene oxide;

3) preparing nickel-phosphomolybdic acid-epigallocatechin oxide gallate-graphene.

4. The preparation method according to claim 3, wherein the step 3) of preparing the nickel-phosphomolybdic acid-epigallocatechin gallate-graphene oxide comprises the following steps:

(1) adding phosphomolybdic acid-graphene oxide into an epigallocatechin gallate aqueous solution, and stirring and reacting for 0.5-6 hours at 70-180 ℃ in a nitrogen environment of 3-8 MPaG;

(2) adding water-soluble nickel salt into the reaction system in the step (1), and stirring and reacting for 0.5-6 hours at 70-180 ℃ in a nitrogen environment of 3-8 MPaG;

5. The preparation method according to claim 4, wherein in the step (1), the reaction is carried out in a nitrogen environment of 4-6 MPaG at a temperature of 90-130 ℃ for 2-4 hours with stirring;

in the step (2), the reaction is carried out for 2-4 hours at 90-130 ℃ in a nitrogen environment of 4-6 MPaG under stirring.

6. The preparation method according to claim 4, wherein the weight ratio of the phosphomolybdic acid-graphene oxide to the epigallocatechin gallate in the step (1) to water is 1 (3-10): 100.

7. the preparation method according to claim 6, wherein the weight ratio of the phosphomolybdic acid-graphene oxide to the epigallocatechin gallate to the water is 1 (5-8): 100.

8. the method according to claim 4, wherein the water-soluble nickel salt in the step (2) is at least one selected from the group consisting of nickel acetate, nickel chloride, nickel nitrate and nickel sulfate.

9. The method according to claim 8, wherein the water-soluble nickel salt is nickel acetate and/or nickel chloride.

10. The preparation method according to claim 4, wherein the water-soluble nickel salt in the step (2) is added in an amount of 5 to 20wt% based on the weight of the phosphomolybdic acid-graphene oxide in terms of nickel element.

11. The method according to claim 10, wherein the water-soluble nickel salt is added in an amount of 10 to 15 wt%.

12. The production method according to claim 3,

step 1), adopting a Hummers oxidation method for the graphene oxide, and taking natural graphite powder as a raw material, wherein the particle size of the graphite powder is 500-5000 meshes; the preparation method of the phosphomolybdic acid-graphene oxide in the step 2) comprises the following steps: dissolving phosphomolybdic acid in the graphene oxide water dispersion, performing ultrasonic dispersion for 25-35 min, and drying to obtain phosphomolybdic acid-graphene oxide; the dispersion concentration of the graphene oxide aqueous dispersion is 5-6 mg/mL; the addition amount of the phosphomolybdic acid is 3-10 wt% of the mass of the graphene oxide.

13. The production method according to claim 12,

the granularity of the graphite powder in the step 1) is 1500-3000 meshes;

in the step 2), the addition amount of the phosphomolybdic acid is 5-8 wt% of the mass of the graphene oxide.

14. A preparation method of L-menthol is characterized by comprising the following steps: l-menthone is subjected to hydrogenation reaction under the action of the catalyst system of claim 1 or 2 or the catalyst system prepared by the method of any one of 3 to 13, namely nickel-phosphomolybdic acid-epigallocatechin oxide gallate-graphene, so as to prepare L-menthol.

15. The method according to claim 14, wherein the catalyst nickel-phosphomolybdic acid-epigallocatechin oxide gallate-graphene is used in an amount of 0.001 to 1wt% based on the mass of L-menthone.

16. The method according to claim 15, wherein the catalyst nickel-phosphomolybdic acid-epigallocatechin oxide gallate-graphene is used in an amount of 0.01 to 0.1wt% based on the mass of L-menthone.

17. The method according to claim 14, wherein the hydrogenation reaction is carried out at a temperature of 30 to 80 ℃ for 6 to 24 hours, and the reaction gauge pressure is 0 to 2 MPaG.

18. The method according to claim 17, wherein the hydrogenation reaction is carried out at a temperature of 40 to 60 ℃ for 8 to 12 hours, and the reaction gauge pressure is 0.5 to 1 MPaG.

19. The method of claim 14, wherein the catalyst is recyclable, and has substantially stable activity for 20 uses, up to 50 uses.