A method for preparing all-biobased n-decanol using rhamnose waste liquid as raw material and all-biobased n-decanol prepared thereby

Abstract

The present invention discloses a method for preparing all-biobased n-decanol using rhamnose waste liquid as raw material and all-biobased n-decanol prepared thereby. The method comprises the following steps: using rhamnose waste liquid containing 3-hydroxydecanoic acid dimer and 3-hydroxydecanoic acid produced in the rhamnose production process as raw material, using alkanes or aromatic hydrocarbons as solvent, and under the combined action of an acidic catalyst and a hydrogenation catalyst, obtaining all-biobased n-decanol in a single step. The present invention aims to prepare all-biobased n-decanol from rhamnose waste liquid. On the one hand, the oil phase waste liquid in the rhamnose production process can be reused, reducing the cost of three wastes treatment and increasing the added value of the product. On the other hand, a new method for preparing all-biobased n-decanol is provided. The obtained all-biobased n-decanol product is more in line with the current demand for safe, green and natural products.

Description

Technical Field

[0001] The invention relates to a new method for preparing fully bio-based n-decanol by using rhamnose waste liquid as raw material. Background Art

[0002] Rhamnose is a substance widely found in plant polysaccharides, glycosides, plant gums, and bacterial polysaccharides. Rhamnose is an important chemical used in food additives, health supplements, personal care products, and pharmaceuticals. Currently, the hydrolysis of rhamnolipids is an important and viable industrial route for producing rhamnose. However, this route produces an oily wastewater during the hydrolysis of rhamnolipids, resulting in poor atom economy, reduced economic value, and decreased competitiveness. The rhamnose wastewater produced by the rhamnose hydrolysis method generally contains a large amount of hydroxyalkyl acids, such as 3-hydroxydecanoic acid dimer, 3-hydroxydecanoic acid, and 3-hydroxyoctanoic acid. Treating this wastewater as wastewater not only increases wastewater treatment costs but also wastes significant resources. Therefore, developing a new method for repurposing rhamnose wastewater is of great significance.

[0003] Decanol, with its sweet floral aroma, is a common spice. It is primarily used in the formulation of flavors such as orange, lemon, coconut, and mixed fruits. GB 2760-96 stipulates that it is a permitted flavoring agent and can be used in food, soap, and daily cosmetics. It is also used in the manufacture of surfactants, plasticizers, defoamers, synthetic fibers, herbicides, lubricant additives, and ink solvents. It has a wide range of applications and is an important fine chemical.

[0004] Currently, n-decanol is synthesized primarily through the following methods: 1) Natural coconut oil is hydrogenated at high temperature and high pressure in the presence of mixed oxides. The resulting mixed alcohols with even carbon atoms (ranging from lower alcohols to octadecanol) are then fractionated under reduced pressure. The C8-C12 fraction is refined using borate esterification and hydrolyzed before fractionation under reduced pressure. This approach currently suffers from unstable raw material sources, large price fluctuations, a long synthesis route, difficulty in product separation, and high costs. 2) Propylene is polymerized in the presence of phosphoric acid or boron fluoride to produce nonene, which is then reacted with carbon monoxide and hydrogen in a liquid phase. This approach currently suffers from a long reaction route, harsh reaction conditions, and the resulting product is not biobased.

[0005] In summary, the current industrial route for synthesizing n-decanol has many shortcomings, so it is of great significance to develop a new route to synthesize all-biobased n-decanol with high yield and high selectivity. Summary of the Invention

[0006] In light of this, the present invention proposes a method for preparing all-biobased n-decanol using rhamnose wastewater as a raw material. This method aims to produce all-biobased n-decanol from rhamnose wastewater. This method, on the one hand, reuses the oily wastewater from the rhamnose production process, reducing the cost of treating the three wastes and increasing the added value of the product. It also provides a new method for preparing all-biobased n-decanol. The resulting all-biobased n-decanol product better meets current demand for safe, green, and natural products.

[0007] To achieve the above object, the technical solutions adopted by the present invention are as follows:

[0008] A method for preparing fully bio-based n-decanol using rhamnose waste liquid as raw material comprises the following steps:

[0009] With rhamnose waste liquid containing 3-hydroxydecanoic acid dimer and 3-hydroxydecanoic acid as raw material and hydrogen as hydrogen source, fully bio-based n-decanol is obtained through a one-step reaction under the combined action of an acid catalyst and a hydrogenation catalyst.

[0010] In the present invention, the mass percentage composition of the rhamnose waste liquid includes: 65-85wt% of 3-hydroxydecanoic acid dimer, for example, 65, 70, 75, 80, 85wt%, 5-8wt% of 3-hydroxydecanoic acid, for example, 5, 6, 7, 8wt%, 1-3wt% of rhamnolipid, for example, 1, 2, 3wt%, 3-hydroxyoctanoic acid 3-7wt% for example, 3, 4, 5, 6, 7wt%, 3-hydroxydodecanoic acid 3-7wt% for example, 3, 4, 5, 6, 7wt%, and 3-10wt% of other components, for example, 3, 5, 7, 9, 10wt%, based on the total mass of the waste liquid as 100%. In the present invention, the rhamnose waste liquid mainly comes from the industrial route of preparing rhamnose by hydrolysis of rhamnolipid, which produces an oily waste liquid that cannot be treated, which generally contains a large amount of hydroxyalkyl acids, such as 3-hydroxydecanoic acid dimer, 3-hydroxydecanoic acid, 3-hydroxyoctanoic acid, etc.

[0011] In the present invention, the reaction is preferably carried out in a solvent;

[0012] Preferably, the solvent is selected from one or more of n-heptane, n-octane, n-decane, toluene, o-xylene, m-xylene, p-xylene, ethylbenzene, n-propylbenzene, and N,N-dimethylformamide, preferably toluene and / or xylene;

[0013] Preferably, the amount of the solvent is 0.5-20 times the mass of the rhamnose waste liquid, such as 0.5, 4, 8, 12, 16, 20 times, preferably 2-5 times.

[0014] In the present invention, the hydrogen pressure is 1-10 MPa(G), such as 1, 3, 5, 7, 9, 10 MPa(G), preferably 2-4 MPa(G).

[0015] In the present invention, the acidic catalyst is selected from one or more of sulfuric acid, nitric acid, hydrochloric acid, acetic acid, formic acid, p-toluenesulfonic acid, and trifluoromethanesulfonic acid, preferably trifluoromethanesulfonic acid.

[0016] In the present invention, the hydrogenation catalyst is selected from a metal salt hydrogenation catalyst, and the metal salt is selected from one or more salts of metals Ru, Rh, Pt, Pd, Ir, Ni, Cu and Co, preferably a metal salt containing Co;

[0017] Preferably, the metal salt hydrogenation catalyst includes but is not limited to one or more of cobalt chloride, cobalt oxalate, cobalt carbonate, cobalt sulfate, cobalt nitrate, cobalt acetate, and cobalt tetrafluoroborate hexahydrate, more preferably cobalt tetrafluoroborate hexahydrate;

[0018] In the present invention, the amount of the acidic catalyst is 0.1-5wt% of the mass of the rhamnose waste liquid, such as 0.1, 1, 2, 3, 4, 5wt%, preferably 0.5-1wt%;

[0019] The amount of the hydrogenation catalyst used is 0.1-5 wt% of the mass of the rhamnose waste liquid, such as 0.1, 1, 2, 3, 4, 5 wt%, preferably 0.2-0.5 wt%.

[0020] In the present invention, the reaction temperature is 100-200°C, such as 100, 120, 140, 160, 180, 200°C, preferably 130-150°C; the reaction time is 1-18h, such as 1, 4, 8, 12, 16, 18h, preferably 3-6h.

[0021] After the reaction of the present invention is completed, further post-processing processes such as cooling, recovery of formaldehyde, and distillation are included, which are conventional operations in the field and have no special requirements in the present invention.

[0022] Another object of the present invention is to provide a fully bio-based n-decanol.

[0023] A fully bio-based n-decanol is prepared by adopting the above-mentioned method for preparing fully bio-based n-decanol.

[0024] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0025] 1) The fully bio-based n-decanol is synthesized through a one-step reaction, and the raw material rhamnose waste liquid is all derived from natural raw materials, which is fully bio-based, safer and greener, meeting people's demand for natural products;

[0026] 2) The use of rhamnose waste liquid to synthesize fully bio-based decanol not only solves the problem of waste liquid treatment, but also realizes waste utilization and increases the added value of rhamnose products. DETAILED DESCRIPTION

[0027] The method of the present invention is further described below by means of specific examples. However, the present invention is not limited to the examples listed, but also includes any other known changes within the scope of the claims of the present invention.

[0028] The main analytical instruments used in the examples and comparative examples of the present invention are:

[0029] 1) Liquid Chromatograph: Agilent 1200 Series, equipped with a C18 column, column temperature set at 40°C, mobile phase consisting of acetonitrile and 0.03% phosphoric acid in water, flow rate 0.8 mL / min, detection at 285 nm using a UV detector, and quantification by external standard method. Samples were diluted appropriately with acetonitrile prior to injection and analysis.

[0030] 2) Gas chromatograph: Agilent 7890, DB-5 separation column, vaporizer temperature 305°C, detector temperature 300°C, temperature ramp program: start temperature 40°C, hold temperature for 10 min, ramp to 130°C at 5°C / min, ramp to 310°C at 20°C / min, hold temperature for 5 min.

[0031] The sources of the main raw materials used in the examples and comparative examples of the present invention are as follows. Unless otherwise specified, all other raw materials are obtained from common commercial channels. The rhamnolipid aqueous solution has a content of 40% and is from Evonik Specialty Chemicals (Shanghai) Co., Ltd.

[0032] Cobalt chloride, cobalt oxalate, cobalt carbonate, cobalt sulfate, cobalt nitrate, cobalt acetate, cobalt tetrafluoroborate hexahydrate, chemical purity ≥97%, Aladdin Biochemical Technology Co., Ltd.

[0033] n-Heptane, n-octane, n-decane, toluene, o-xylene, m-xylene, p-xylene, ethylbenzene, n-propylbenzene, N,N-dimethylformamide, chemical purity ≥98%, Aladdin Biochemical Technology Co., Ltd.

[0034] Sulfuric acid, nitric acid, hydrochloric acid, acetic acid, formic acid, p-toluenesulfonic acid, trifluoromethanesulfonic acid, Aladdin Reagent Co., Ltd.;

[0035] Rhamnose oil phase waste liquid: prepared according to the method disclosed in patent CN112079709B.

[0036] Main synthesis equipment: high-pressure reactor, constant temperature oil bath.

[0037] Example 1

[0038] Preparation of all-biobased n-decanol, the steps are:

[0039] The rhamnose oil phase waste liquid was analyzed and its mass percentage composition was as follows: 3-hydroxydecanoic acid dimer 65%, 3-hydroxydecanoic acid 8%, rhamnolipid 3%, 3-hydroxyoctanoic acid 7%, 3-hydroxydodecanoic acid 7%, and other components 10%.

[0040] In pressure-resistant reactor, raw material rhamnose oil phase waste liquid (100g), sulfuric acid (0.7g), cobalt chloride (0.5g) and n-heptane (200g) are added successively under room temperature, reaction kettle is closed, nitrogen and hydrogen are replaced three times successively, then reactor is pressurized to 1MPa using hydrogen, and opening speed is 800rpm. Start temperature programming, after question reaction temperature rises to 115 DEG C, continue reaction 6h, stopped reaction. Reaction solution is down to room temperature, open reactor, reaction solution is analyzed by liquid phase external standard method, 3-hydroxydecanoic acid dimer conversion 97%, 3-hydroxydecanoic acid conversion 93%, and reaction solution is analyzed by gas phase internal standard method, and the yield of n-decanol is 91%.

[0041] The reaction system was cooled at 20 hPa and 70°C to recover n-heptane, and the residual liquid was further purified by distillation through 36 plates and a reflux ratio of 2 to obtain n-decanol product.

[0042] Example 2

[0043] Preparation of all-biobased n-decanol, the steps are:

[0044] The rhamnose oil phase waste liquid was analyzed and its mass percentage composition was as follows: 3-hydroxydecanoic acid dimer 85%, 3-hydroxydecanoic acid 5%, rhamnolipid 1%, 3-hydroxyoctanoic acid 3%, 3-hydroxydodecanoic acid 3%, and other components 3%.

[0045] In pressure-resistant reactor, raw material rhamnose oil phase waste liquid (100g), nitric acid (1g), cobalt oxalate (0.4g) and n-decane (200g) are added successively at room temperature, reactor is closed, nitrogen and hydrogen are replaced three times successively, reactor is then pressurized to 10MPa using hydrogen, and it is then opened that rotating speed is 800rpm. Start temperature programming, after the reaction temperature rises to 125 DEG C, continue reaction 5h, stopped reaction. Reaction solution is cooled to room temperature, reactor is opened, reaction solution is analyzed by liquid phase external standard method, 3-hydroxydecanoic acid dimer conversion 94%, 3-hydroxydecanoic acid conversion 96%, reaction solution is analyzed by gas phase internal standard method, and the yield of n-decanol is 92%.

[0046] The reaction system was maintained at 20 hPa and 100° C. to recover n-decane, and the residual liquid was further purified by distillation through 36 plates and a reflux ratio of 2 to obtain n-decanol product.

[0047] Example 3

[0048] Preparation of all-biobased n-decanol, the steps are:

[0049] The rhamnose oil phase waste liquid was analyzed and its mass percentage composition was as follows: 3-hydroxydecanoic acid dimer 75%, 3-hydroxydecanoic acid 6%, rhamnolipid 2%, 3-hydroxyoctanoic acid 4%, 3-hydroxydodecanoic acid 5%, and other components 8%.

[0050] In pressure-resistant reactor, raw material rhamnose oil phase waste liquid (100g), p-toluenesulfonic acid (0.5g), cobalt acetate (0.3g) and toluene (300g) are added successively under room temperature, reaction kettle is closed, nitrogen and hydrogen are replaced three times successively, then reactor is pressurized to 2MPa using hydrogen, and it is then opened that rotating speed is 800rpm. Start temperature programming, after the reaction temperature rises to 150 DEG C, continue reaction 3h, stopped reaction. Reaction solution is down to room temperature, reactor is opened, reaction solution is analyzed by liquid phase external standard method, 3-hydroxydecanoic acid dimer conversion 97%, 3-hydroxydecanoic acid conversion 97%, reaction solution is analyzed by gas phase internal standard method, and the yield of n-decanol is 94%.

[0051] Toluene was recovered from the reaction system at 20 hPa and 80° C., and the residual liquid was further purified by distillation through 36 plates and a reflux ratio of 2 to obtain n-decanol product.

[0052] Example 4

[0053] Preparation of all-biobased n-decanol, the steps are:

[0054] The rhamnose oil phase waste liquid was analyzed and its mass percentage composition was as follows: 3-hydroxydecanoic acid dimer 65%, 3-hydroxydecanoic acid 8%, rhamnolipid 3%, 3-hydroxyoctanoic acid 7%, 3-hydroxydodecanoic acid 7%, and other components 10%.

[0055] In pressure-resistant reactor, raw material rhamnose oil phase waste liquid (100g), trifluoromethanesulfonic acid (0.5g), cobalt tetrafluoroborate hexahydrate (0.2g) and o-Xylene (500g) are added successively under room temperature, reaction kettle is closed, nitrogen and hydrogen are replaced three times successively, then reactor is pressurized to 3MPa using hydrogen, and it is then opened that rotating speed is 800rpm. Start temperature programming, after question reaction temperature rises to 130 DEG C, continue reaction 5h, stopped reaction. Reaction solution is down to room temperature, open reactor, reaction solution is analyzed by liquid phase external standard method, 3-hydroxydecanoic acid dimer conversion 99%, 3-hydroxydecanoic acid conversion 99%, and reaction solution is analyzed by gas phase internal standard method, and the yield of n-decanol is 97%.

[0056] The reaction system was cooled to 20 hPa and 80°C to recover o-xylene, and the residual liquid was further purified by distillation through 36 plates and a reflux ratio of 2 to obtain n-decanol product.

[0057] Example 5

[0058] Preparation of all-biobased n-decanol, the steps are:

[0059] The rhamnose oil phase waste liquid was analyzed and its mass percentage composition was as follows: 3-hydroxydecanoic acid dimer 65%, 3-hydroxydecanoic acid 8%, rhamnolipid 3%, 3-hydroxyoctanoic acid 7%, 3-hydroxydodecanoic acid 7%, and other components 10%.

[0060] In pressure-resistant reactor, raw material rhamnose oil phase waste liquid (100g), trifluoromethanesulfonic acid (0.1g), palladium acetate (0.1g) and m-xylene (300g) are added successively at room temperature, reactor is closed, nitrogen and hydrogen are replaced three times successively, reactor is then pressurized to 4MPa using hydrogen, and it is then opened that rotating speed is 800rpm. Start temperature programming, after the reaction temperature rises to 200 DEG C, continue reaction 1h, stopped reaction. Reaction solution is cooled to room temperature, reactor is opened, reaction solution is analyzed by liquid phase external standard method, 3-hydroxydecanoic acid dimer conversion 96%, 3-hydroxydecanoic acid conversion 98%, reaction solution is analyzed by gas phase internal standard method, and the yield of n-decanol is 93%.

[0061] The reaction system was maintained at 20 hPa and 80°C for the recovery of meta-xylene, and the residual liquid was further purified by distillation through 36 plates and a reflux ratio of 2 to obtain the n-decanol product.

[0062] Example 6

[0063] Preparation of all-biobased n-decanol, the steps are:

[0064] The rhamnose oil phase waste liquid was analyzed and its mass percentage composition was as follows: 3-hydroxydecanoic acid dimer 65%, 3-hydroxydecanoic acid 8%, rhamnolipid 3%, 3-hydroxyoctanoic acid 7%, 3-hydroxydodecanoic acid 7%, and other components 10%.

[0065] In pressure-resistant reactor, raw material rhamnose oil phase waste liquid (100g), trifluoromethanesulfonic acid (1g), nickelous chloride (5g) and n-heptane (50g) are added successively at room temperature, reactor is closed, nitrogen and hydrogen are replaced three times successively, reactor is then pressurized to 6MPa using hydrogen, and it is then opened that rotating speed is 800rpm. Start temperature programming, after the reaction temperature rises to 120 ℃, continue reaction 4h, stopped reaction. Reaction solution is cooled to room temperature, reactor is opened, reaction solution is analyzed by liquid phase external standard method, 3-hydroxydecanoic acid dimer conversion 95%, 3-hydroxydecanoic acid conversion 96%, reaction solution is analyzed by gas phase internal standard method, and the yield of n-decanol is 94%.

[0066] The reaction system was cooled at 20 hPa and 70°C to recover n-heptane, and the residual liquid was further purified by distillation through 36 plates and a reflux ratio of 2 to obtain n-decanol product.

[0067] Example 7

[0068] Preparation of all-biobased n-decanol, the steps are:

[0069] The rhamnose oil phase waste liquid was analyzed and its mass percentage composition was as follows: 3-hydroxydecanoic acid dimer 65%, 3-hydroxydecanoic acid 8%, rhamnolipid 3%, 3-hydroxyoctanoic acid 7%, 3-hydroxydodecanoic acid 7%, and other components 10%.

[0070] In a pressure-resistant reactor, the raw material rhamnose oil phase waste liquid (100g), trifluoromethanesulfonic acid (2g), tris(2,2-bipyrimidine)dichlororuthenium (1g) and p-xylene (1000g) were added in sequence at room temperature, the reactor was closed, and nitrogen and hydrogen were used to replace three times in sequence. Then, the reactor was pressurized to 8MPa with hydrogen, and the speed was turned on to 800rpm. The temperature was programmed to rise. After the reaction temperature rose to 120°C, the reaction was continued for 3h and the reaction was stopped. The reaction solution was cooled to room temperature, the reactor was opened, and the reaction solution was analyzed by liquid phase external standard method. The conversion rate of 3-hydroxydecanoic acid dimer was 95%, the conversion rate of 3-hydroxydecanoic acid was 96%, and the reaction solution was analyzed by gas phase internal standard method. The yield of n-decanol was 93%.

[0071] The reaction system was maintained at 20 hPa and 80°C to recover p-xylene, and the residual liquid was further purified by distillation through 36 plates and a reflux ratio of 2 to obtain n-decanol product.

[0072] Example 8

[0073] Preparation of all-biobased n-decanol, the steps are:

[0074] The rhamnose oil phase waste liquid was analyzed and its mass percentage composition was as follows: 3-hydroxydecanoic acid dimer 65%, 3-hydroxydecanoic acid 8%, rhamnolipid 3%, 3-hydroxyoctanoic acid 7%, 3-hydroxydodecanoic acid 7%, and other components 10%.

[0075] In pressure-resistant reactor, raw material rhamnose oil phase waste liquid (100g), trifluoromethanesulfonic acid (5g), platinum chloride (3g) and toluene (2000g) are added successively under room temperature, reaction kettle is closed, nitrogen and hydrogen are replaced three times successively, then reactor is pressurized to 10MPa using hydrogen, and it is then opened that rotating speed is 800rpm. Start temperature programming, after question reaction temperature rises to 100 DEG C, continue reaction 18h, stopped reaction. Reaction solution is down to room temperature, open reactor, reaction solution is analyzed by liquid phase external standard method, 3-hydroxydecanoic acid dimer conversion 98%, 3-hydroxydecanoic acid conversion 97%, and reaction solution is analyzed by gas phase internal standard method, and the yield of n-decanol is 96%.

[0076] Toluene was recovered from the reaction system at 20 hPa and 80° C., and the residual liquid was further purified by distillation through 36 plates and a reflux ratio of 2 to obtain n-decanol product.

[0077] Comparative Example 1

[0078] The preparation method was prepared with reference to Example 1, except that sulfuric acid catalyst was not added, and other operations and conditions remained unchanged. The reaction solution was analyzed by liquid phase external standard method, and the conversion rate of 3-hydroxydecanoic acid dimer was 5%, and the conversion rate of 3-hydroxydecanoic acid was 6%. The reaction solution was analyzed by gas phase internal standard method, and the yield of n-decanol was 2%.

[0079] Comparative Example 2

[0080] The preparation method was prepared with reference to Example 1, except that no cobalt chloride catalyst was added, and other operations and conditions remained unchanged. The reaction solution was analyzed by liquid phase external standard method, and the conversion rate of 3-hydroxydecanoic acid dimer was 94%, and the conversion rate of 3-hydroxydecanoic acid was 86%. The reaction solution was analyzed by gas phase internal standard method, and the yield of n-decanol was 0%.

Claims

1. A method for preparing all-biobased n-decanol using rhamnose waste liquid as raw material, characterized in that: The following steps are involved: Using rhamnose wastewater containing 3-hydroxydecanoic acid dimer and 3-hydroxydecanoic acid as raw material and hydrogen as hydrogen source, fully bio-based n-decanol is obtained through a one-step reaction under the combined action of an acid catalyst and a hydrogenation catalyst. The acidic catalyst is selected from one or more of sulfuric acid, nitric acid, hydrochloric acid, acetic acid, formic acid, p-toluenesulfonic acid, and trifluoromethanesulfonic acid; and the hydrogenation catalyst is selected from metal salt hydrogenation catalysts.

2. The method according to claim 1, characterized in that The mass percentage composition of the rhamnose waste liquid includes: 65-85% of 3-hydroxydecanoic acid dimer, 5-8% of 3-hydroxydecanoic acid, 1-3% of rhamnolipid, 3-7% of 3-hydroxyoctanoic acid, 3-7% of 3-hydroxydodecanoic acid and 3-10% of other components.

3. The method according to claim 1, characterized in that The reaction is carried out in a solvent.

4. The method according to claim 3, characterized in that The solvent is selected from one or more of n-heptane, n-octane, n-decane, toluene, o-xylene, m-xylene, p-xylene, ethylbenzene, n-propylbenzene, and N,N-dimethylformamide.

5. The method according to claim 4, characterized in that The solvent is selected from toluene and / or xylene.

6. The method according to claim 3, characterized in that The amount of the solvent used is 0.5-20 times the mass of the rhamnose waste liquid.

7. The method according to claim 6, characterized in that The amount of the solvent used is 2-5 times the mass of the rhamnose waste liquid.

8. The method according to claim 1, characterized in that The hydrogen pressure is 1-10 MPa G.

9. The method according to claim 8, characterized in that The hydrogen pressure is 2-4 MPaG.

10. The method according to claim 1, characterized in that The acidic catalyst is trifluoromethanesulfonic acid.

11. The method according to claim 1, characterized in that The metal salt hydrogenation catalyst is selected from one or more salts of metals Ru, Rh, Pt, Pd, Ir, Ni, Cu and Co.

12. The method according to claim 11, characterized in that The metal salt hydrogenation catalyst is selected from metal salts containing Co.

13. The method according to claim 1, wherein The metal salt hydrogenation catalyst is selected from one or more of cobalt chloride, cobalt oxalate, cobalt carbonate, cobalt sulfate, cobalt nitrate, cobalt acetate, and cobalt tetrafluoroborate hexahydrate.

14. The method according to claim 13, characterized in that The metal salt hydrogenation catalyst is cobalt tetrafluoroborate hexahydrate.

15. The method according to claim 1, wherein The amount of the acidic catalyst used is 0.1-5 wt% of the mass of the rhamnose waste liquid.

16. The method according to claim 15, characterized in that The amount of the acidic catalyst used is 0.5-1 wt% of the mass of the rhamnose waste liquid.

17. The method according to claim 1, wherein The amount of the hydrogenation catalyst used is 0.1-5 wt% of the mass of the rhamnose waste liquid.

18. The method according to claim 17, characterized in that The amount of the hydrogenation catalyst used is 0.2-0.5 wt% of the mass of the rhamnose waste liquid.

19. The method according to claim 1, wherein The reaction temperature is 100-200° C. and the reaction time is 1-18 h.

20. The method according to claim 19, characterized in that The reaction temperature is 130-150° C. and the reaction time is 3-6 hours.