CN110467525B - Method for preparing lactic acid by selective catalytic conversion of biomass polyol - Google Patents

Abstract

The invention belongs to the technical field of fine chemicals, and particularly relates to a method for preparing lactic acid by selective catalytic conversion of biomass polyol. The method comprises the steps of taking biomass polyol as a raw material, taking alkali metal or alkaline earth metal hydroxide as alkali, taking alcohols as a solvent and taking nitrogen heterocyclic carbene iridium complex as a catalyst, and carrying out closed reaction for 6-24 hours at 100-200 ℃ to obtain the lactic acid. Compared with the prior art, the method takes alcohols as a solvent, takes cheap and easily-obtained biomass polyol as a substrate, and performs catalytic oxidation reaction under mild conditions to obtain almost quantitative lactic acid yield, has high reaction conversion efficiency, is simple and convenient to operate, can obtain high-purity lactic acid without complex post-treatment, and is suitable for large-scale industrial application.

Description

A kind of method for preparing lactic acid by selective catalytic conversion of biomass polyol

technical field

The invention belongs to the technical field of fine chemicals, and in particular relates to a method for preparing lactic acid by selective catalytic conversion of biomass polyols.

Background technique

As a common metabolite of organisms, lactic acid is widely distributed in nature and is one of the three recognized organic acids. It is the smallest chiral molecule existing in nature and a class of industrial products with high added value. At present, the annual production capacity of lactic acid in the world is about 370,000 tons, and the annual production capacity growth rate is about 12%, while the total demand for lactic acid is about 500,000 tons per year, and it is increasing at a rate of about 16% per year. Especially in recent years, polylactic acid, as a degradable bio-based polymer material, has been recognized as an ideal plastic material due to its excellent thermoplasticity and safety. Therefore, the contradiction between supply and demand of lactic acid will become increasingly serious.

At present, the production of lactic acid mainly includes two ways: biological fermentation method and chemical conversion method. Traditional fermentation processes are also becoming more and more difficult to meet relevant needs. Although biological fermentation has the advantages of mild reaction conditions and good selectivity, it has disadvantages such as high price of enzyme catalysts, easy poisoning, long fermentation cycle, dilute product concentration, and difficult purification. , its large-scale production is subject to certain restrictions.

The Chinese patent application with the application number of 201510161476.8 discloses a class of azacyclic carbene metal coordination polymers, its preparation method and application as a catalyst. It is used to catalyze the oxidative dehydrogenation reaction of alcohol and its derivatives, sugar compounds, cellulose or lignin, and the oxidative dehydrogenation reaction is used for the preparation of lactic acid or its derivatives. However, the applicant found that in this type of oxidative dehydrogenation reaction, for biomass polyols other than glycerol, such as sorbitol, when potassium hydroxide is used as an alkali and water is used as a solvent, the conversion rate of the raw materials generally does not exceed 60%, The yield of lactic acid is generally below 20%. There is therefore a need to develop an efficient and highly selective process for the oxidative dehydrogenation of biomass polyols other than glycerol to lactic acid.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a method for preparing lactic acid by selective catalytic conversion of biomass polyols with cheap and easy-to-obtain raw materials, high efficiency and high yield.

The method for preparing lactic acid by selective catalytic conversion of biomass polyols provided by the invention uses biomass polyols as raw materials, alkali metal or alkaline earth metal hydroxides as alkalis, alcohols as solvents, and nitrogen heterocyclic carbene metal compounds as a solvent. The position polymer is used as a catalyst, and the closed reaction is carried out at 100 to 200° C. for 6 to 24 hours to obtain lactic acid. The chemical reaction process is as follows:

Here, n is 3 to 6 and 12.

Compared with the prior art, the present invention provides a method for preparing lactic acid with high efficiency and high selectivity, which uses biomass polyols that are cheap and easy to obtain as raw materials, and obtains lactic acid through catalytic oxidation reaction under alkaline conditions. In previous studies, it was found that the addition of solvent (mainly water) would reduce the concentration of reactants, resulting in a slower reaction rate, so most of the reactions were solvent-free. In addition, the addition of alcoholic solvents tends to convert the product into the corresponding lactate ester, which increases the post-treatment steps, and is also considered to react with the catalyst, resulting in a decrease in the activity of the dehydrogenation catalyst. Therefore, alcohol solvents were not added to the reaction in the past. However, the applicant detected a series of alcohols as by-products, such as methanol, ethanol and ethylene glycol, in the reaction of sorbitol catalyzed conversion of lactic acid. By adding these alcohols to the reaction system, the applicant found that the addition of alcohols not only did not generate the corresponding lactate, but could effectively inhibit the generation of by-products, so that the selectivity of lactic acid was greatly improved. The applicant has found that, in the method provided by the present invention, biomass polyols are also used as raw materials, alkali metal or alkaline earth metal hydroxides are used as alkalis, and nitrogen heterocyclic carbene metal coordination polymers are used as catalysts. Polyols are selectively catalytically converted to prepare lactic acid. When alcohols are used as solvents, the conversion rate of biomass polyols and the yield of lactic acid are substantially improved compared with water as the solvent. Specifically, the conversion rate of biomass polyols can reach more than 99%, and the yield of lactic acid can reach more than 97%.

The preparation method provided by the invention uses biomass polyols that are cheap and easy to obtain as substrates, and uses alcohols as solvents to carry out catalytic oxidation reaction under mild conditions, so that almost quantitative lactic acid yield can be obtained, and the reaction conversion efficiency is high. , the operation is simple, and high-purity lactic acid can be obtained without complicated post-processing, which is suitable for large-scale industrial application.

Preferably, the alcohols are selected from one or more of methanol, ethanol, n-propanol, isopropanol, n-butanol, tert-butanol, and benzyl alcohol.

Preferably, the alkali metal or alkaline earth metal hydroxide is selected from one or more of sodium hydroxide, potassium hydroxide, calcium hydroxide, barium hydroxide octahydrate and cesium hydroxide monohydrate.

Further preferably, the alkali metal hydroxide is barium hydroxide octahydrate. The applicant found that the conversion of biomass polyols and the yield of lactic acid were further improved when barium hydroxide octahydrate was used as the alkali metal hydroxide to participate in the reaction.

Preferably, the nitrogen heterocyclic carbene metal coordination polymer has the structure represented by the general formula (I):

(I)

in:

M is a transition metal;

V and W are each independently N or CH;

X and Y are each independently O, N-G, CH, -CH=CH-, -C≡C-, an alkane group having 0 to 8 carbon atoms, p-phenyl, m-phenyl, o-phenyl, 1, 4-divinylphenyl, 1,4-diethynylphenyl, biphenyl, 1,4-methylenephenyl or 9,10-anthryl; the G is a protecting group, the protecting The group is: a chain alkane group with a carbon number of 1-12, a cyclic alkane group with a carbon number of 5-7, benzyl, aryl, tert-butoxycarbonyl, benzoyl or benzyl chloroformate;

Z is an anion halide, tetrafluoroborate, hexafluorophosphate or hexafluoroantimonate;

L is an auxiliary ligand;

R is a chain alkane group with a carbon number of 1-12, a cyclic alkane group with a carbon number of 5-7, a benzyl group or an aryl group;

m represents the number of repeating units in the linker, m is 0 or a natural number;

n represents the number of monomers contained in the azacyclic carbene metal coordination polymer, and n is a natural number greater than or equal to 2.

Further preferably, the transition metal is selected from Ag, Au, Fe, Ir, Mn, Ni, Pd, Rh or Ru; the auxiliary ligand is halogen, carbonyl, benzene ring, locene ring, cyclooctadiene, hydroxyl , water, carbonate, acetate, acetylacetonate anion or phosphine ligand.

Further preferably, the nitrogen heterocyclic carbene metal coordination polymer catalyst is a homogeneous nitrogen heterocyclic carbene iridium catalyst or a nitrogen heterocyclic carbene iridium solid molecular catalyst.

Preferably, the biomass polyol is selected from the group consisting of glycerol, erythritol, threitol, arabitol, xylitol, adonitol, sorbitol, mannitol, galactitol, maltitol and lactitol one or more of them.

Preferably, the molar ratio of the nitrogen heterocyclic carbene metal coordination polymer catalyst to the biomass polyol is 1/10,000 to 1%; the alkali metal or alkaline earth metal hydroxide and the biomass The molar ratio of the substance polyol is 0.5 to 10; the molar ratio of the alcohol solvent to the biomass polyol is 0 to 50; the molar ratio of the alkali metal or alkaline earth metal hydroxide to the biomass polyol The ratio is 1.1-2; the molar ratio of the alcohol solvent to the biomass polyol is 5-15.

Preferably, the nitrogen heterocyclic carbene iridium complex catalyst is recovered by centrifugal separation after the reaction. The catalyst can be separated from the reaction solution by centrifugation. After washing and drying, the next catalytic reaction can be carried out without additional activation; the reaction solution is acidified and the solvent is removed to obtain high-purity lactic acid. Sorbitol conversion and lactic acid yield were measured using high performance liquid chromatography.

The method of the invention uses alcohols as solvents, uses cheap and easily available biomass polyols as substrates, and carries out catalytic oxidation reaction under relatively mild conditions, so that almost quantitative lactic acid yield can be obtained, the reaction conversion efficiency is high, and the operation It is simple and can obtain high-purity lactic acid without complicated post-processing, which is suitable for large-scale industrial application.

Description of drawings

1 is a high-performance liquid chromatogram of the reaction solution obtained in Example 8.

Fig. 2 is the cycle performance diagram of nitrogen heterocyclic carbene iridium solid molecular catalyst.

Detailed ways

In order to make the objectives, technical solutions and advantages of the present invention clearer, each embodiment of the present invention will be described in detail below. However, those of ordinary skill in the art can appreciate that, in the various embodiments of the present invention, many technical details are set forth in order for the reader to better understand the present application. However, even without these technical details and various changes and modifications based on the following embodiments, the technical solutions claimed in the claims can be realized.

1. Preparation of nitrogen heterocyclic carbene metal coordination polymer catalyst (see Chinese patent application with application number 201510161476.8)

Embodiment 1, the preparation of nitrogen heterocyclic carbene iridium solid molecular catalyst 2a:

Under nitrogen, tetraimidazolium salt (azacyclic carbene precursor) 1 (0.4 g), [Ir(COD)Cl] ₂ (0.33 g), DMF (5 mL), LiHMDS in tetrahydrofuran were sequentially added to a 50 mL standard Schlenk flask The solution (1M, 2mL) was stirred evenly and heated under reflux for 12 hours. A large amount of yellow solid was precipitated. The heating was stopped and the reaction system was cooled to room temperature. 10 mL of deionized water was added to the reaction system and filtered, the solid was washed with deionized water, and dried in vacuo to obtain a brownish-yellow solid, namely azacyclic carbene iridium solid molecular catalyst 2a, yield: 0.5 g, 98%.

Embodiment 2, the preparation of nitrogen heterocyclic carbene iridium solid molecular catalyst 2b:

Under nitrogen, tetraimidazolium salt (azacyclic carbene precursor) 1 (0.4 g), Ir(CO) ₂ (acac) (0.35 g), DMF (5 mL), LiHMDS in tetrahydrofuran were sequentially added to a 50 mL standard Schlenk flask The solution (1M, 2mL) was stirred evenly and heated under reflux for 12 hours. A large amount of yellow solid was precipitated. The heating was stopped and the reaction system was cooled to room temperature. 10 mL of deionized water was added to the reaction system, followed by filtration, the solid was washed with deionized water, and dried under vacuum to obtain a brownish yellow solid, which is azacyclic carbene iridium solid molecular catalyst 2b, yield: 0.54 g, 99%.

2. Selective catalytic conversion of biomass polyols to prepare lactic acid

Embodiment 3, nitrogen heterocyclic carbene iridium solid molecular catalyst 2a is used for catalyzing oxidation of sorbitol to prepare lactic acid:

Under the protection of nitrogen atmosphere, nitrogen heterocyclic carbene iridium solid molecular catalyst 2a (0.003g, 0.2mol%), potassium hydroxide (0.34g, 6mmol), sorbitol (0.54g) were successively added to the 15mL thick-walled pressure bottle. , 3 mmol), water (2 mL). After sealing the thick-walled pressure bottle, it was put into an oil bath, heated to 140° C. and reacted for 12 hours. After the reaction, cooled to room temperature, diluted the reaction solution with 10 mL of deionized water, transferred the diluted reaction solution to a centrifuge tube, centrifuged at 10,000 r/min for 10 minutes, took the supernatant, added 1M H ₂ SO ₄ dilution. After dilution, the liquid was subjected to high performance liquid chromatography to measure the conversion rate of sorbitol and the yield of lactic acid. The conversion of sorbitol was 89%, and the yield of lactic acid was 25%.

Embodiment 4, nitrogen heterocyclic carbene iridium solid molecular catalyst 2a is used for catalyzing oxidation of sorbitol to prepare lactic acid:

Under the protection of nitrogen atmosphere, nitrogen heterocyclic carbene iridium solid molecular catalyst 2a (0.003g, 0.2mol%), sodium hydroxide (0.24g, 6mmol), sorbitol (0.54g) were successively added to a 15mL thick-walled pressure bottle. , 3 mmol), water (2 mL). After sealing the thick-walled pressure bottle, it was put into an oil bath, heated to 140° C. and reacted for 12 hours. After the reaction, cooled to room temperature, diluted the reaction solution with 10 mL of deionized water, transferred the diluted reaction solution to a centrifuge tube, centrifuged at 10,000 r/min for 10 minutes, took the supernatant, added 1M H ₂ SO ₄ dilution. After dilution, the liquid was subjected to high performance liquid chromatography to measure the conversion rate of sorbitol and the yield of lactic acid. The conversion of sorbitol was 94%, and the yield of lactic acid was 29%.

Embodiment 5, nitrogen heterocyclic carbene iridium solid molecular catalyst 2a is used for catalyzing oxidation sorbitol to prepare lactic acid:

Under the protection of nitrogen atmosphere, nitrogen heterocyclic carbene iridium solid molecular catalyst 2a (0.003g, 0.2mol%), calcium hydroxide (0.44g, 6mmol), sorbitol (0.54g) were successively added to a 15mL thick-walled pressure bottle. , 3 mmol), water (2 mL). After sealing the thick-walled pressure bottle, it was put into an oil bath, heated to 140° C. and reacted for 12 hours. After the reaction, cooled to room temperature, diluted the reaction solution with 10 mL of deionized water, transferred the diluted reaction solution to a centrifuge tube, centrifuged at 10,000 r/min for 10 minutes, took the supernatant, added 1M H ₂ SO ₄ dilution. After dilution, the liquid was subjected to high performance liquid chromatography to measure the conversion rate of sorbitol and the yield of lactic acid. The conversion of sorbitol was 99%, and the yield of lactic acid was 19%.

Embodiment 6, nitrogen heterocyclic carbene iridium solid molecular catalyst 2a is used for catalyzing oxidation of sorbitol to prepare lactic acid:

Under the protection of nitrogen atmosphere, nitrogen heterocyclic carbene iridium solid molecular catalyst 2a (0.003g, 0.2mol%), barium hydroxide octahydrate (1.89g, 6mmol), sorbitol ( 0.54 g, 3 mmol), water (2 mL). After sealing the thick-walled pressure bottle, it was put into an oil bath, heated to 140° C. and reacted for 12 hours. After the reaction, cooled to room temperature, diluted the reaction solution with 10 mL of deionized water, transferred the diluted reaction solution to a centrifuge tube, centrifuged at 10,000 r/min for 10 minutes, took the supernatant, added 1M H ₂ SO ₄ dilution. After dilution, the liquid was subjected to high performance liquid chromatography to measure the conversion rate of sorbitol and the yield of lactic acid. The conversion of sorbitol was 88%, and the yield of lactic acid was 43%.

Embodiment 7, nitrogen heterocyclic carbene iridium solid molecular catalyst 2a is used for catalyzing oxidation of sorbitol to prepare lactic acid:

Under the protection of nitrogen atmosphere, nitrogen heterocyclic carbene iridium solid molecular catalyst 2a (0.003g, 0.2mol%), cesium hydroxide monohydrate (0.9g, 6mmol), sorbitol ( 0.54 g, 3 mmol), water (2 mL). After sealing the thick-walled pressure bottle, it was put into an oil bath, heated to 140° C. and reacted for 12 hours. After the reaction, cooled to room temperature, diluted the reaction solution with 10 mL of deionized water, transferred the diluted reaction solution to a centrifuge tube, centrifuged at 10,000 r/min for 10 minutes, took the supernatant, added 1M H ₂ SO ₄ dilution. After dilution, the liquid was subjected to high performance liquid chromatography to measure the conversion rate of sorbitol and the yield of lactic acid. The conversion of sorbitol was 97%, and the yield of lactic acid was 22%.

Embodiment 8, nitrogen heterocyclic carbene iridium solid molecular catalyst 2a is used for catalyzing oxidation of sorbitol to prepare lactic acid:

Under the protection of nitrogen atmosphere, nitrogen heterocyclic carbene iridium solid molecular catalyst 2a (0.003g, 0.2mol%), potassium hydroxide (0.34g, 6mmol), sorbitol (0.54g) were successively added to the 15mL thick-walled pressure bottle. , 3 mmol), methanol (2 mL). After sealing the thick-walled pressure bottle, it was put into an oil bath, heated to 140° C. and reacted for 12 hours. After the reaction, cooled to room temperature, diluted the reaction solution with 10 mL of deionized water, transferred the diluted reaction solution to a centrifuge tube, centrifuged at 10,000 r/min for 10 minutes, took the supernatant, added 1M H ₂ SO ₄ dilution. After dilution, the liquid was subjected to high performance liquid chromatography to measure the conversion rate of sorbitol and the yield of lactic acid. The conversion of sorbitol was 89%, and the yield of lactic acid was 59%.

Embodiment 9, nitrogen heterocyclic carbene iridium solid molecular catalyst 2b is used for catalyzing oxidation sorbitol to prepare lactic acid:

Under the protection of nitrogen atmosphere, nitrogen heterocyclic carbene iridium solid molecular catalyst 2b (0.003g, 0.2mol%), barium hydroxide octahydrate (1.89g, 6mmol), sorbitol ( 0.54 g, 3 mmol), methanol (2 mL). After sealing the thick-walled pressure bottle, it was put into an oil bath, heated to 140° C. and reacted for 12 hours. After the reaction, cooled to room temperature, diluted the reaction solution with 10 mL of deionized water, transferred the diluted reaction solution to a centrifuge tube, centrifuged at 10,000 r/min for 10 minutes, took the supernatant, added 1M H ₂ SO ₄ dilution. After dilution, the liquid was subjected to high performance liquid chromatography to measure the conversion rate of sorbitol and the yield of lactic acid. The conversion rate of sorbitol was 99%, and the yield of lactic acid was 97%.

Embodiment 10, homogeneous nitrogen heterocyclic carbene iridium catalyst 3 is used to catalyze the oxidation of sorbitol to prepare lactic acid:

Under the protection of nitrogen atmosphere, homogeneous nitrogen heterocyclic carbene iridium molecular catalyst 3 (0.003g, 0.2mol%), barium hydroxide octahydrate (1.89g, 6mmol), sorbitol were successively added to a 15mL thick-walled pressure bottle. (0.54 g, 3 mmol), methanol (2 mL). After sealing the thick-walled pressure bottle, it was put into an oil bath, heated to 140° C. and reacted for 12 hours. After the reaction, cooled to room temperature, diluted the reaction solution with 10 mL of deionized water, transferred the diluted reaction solution to a centrifuge tube, centrifuged at 10,000 r/min for 10 minutes, took the supernatant, added 1M H ₂ SO ₄ dilution. After dilution, the liquid was subjected to high performance liquid chromatography to measure the conversion rate of sorbitol and the yield of lactic acid. The conversion of sorbitol was 97%, and the yield of lactic acid was 82%.

Embodiment 11, nitrogen heterocyclic carbene iridium solid molecular catalyst 2b is used for catalyzing oxidation of sorbitol to prepare lactic acid:

Under the protection of nitrogen atmosphere, nitrogen heterocyclic carbene iridium solid molecular catalyst 2b (0.003g, 0.2mol%), barium hydroxide octahydrate (1.89g, 6mmol), sorbitol ( 0.54 g, 3 mmol), ethanol (2 mL). After sealing the thick-walled pressure bottle, it was put into an oil bath, heated to 140° C. and reacted for 12 hours. After the reaction, cooled to room temperature, diluted the reaction solution with 10 mL of deionized water, transferred the diluted reaction solution to a centrifuge tube, centrifuged at 10,000 r/min for 10 minutes, took the supernatant, added 1M H ₂ SO ₄ dilution. After dilution, the liquid was subjected to high performance liquid chromatography to measure the conversion rate of sorbitol and the yield of lactic acid. The conversion rate of sorbitol was 99%, and the yield of lactic acid was 85%.

Embodiment 12, nitrogen heterocyclic carbene iridium solid molecular catalyst 2b is used to catalyze the oxidation of sorbitol to prepare lactic acid:

Under the protection of nitrogen atmosphere, nitrogen heterocyclic carbene iridium solid molecular catalyst 2b (0.003g, 0.2mol%), barium hydroxide octahydrate (1.89g, 6mmol), sorbitol ( 0.54 g, 3 mmol), isopropanol (2 mL). After sealing the thick-walled pressure bottle, it was put into an oil bath, heated to 140° C. and reacted for 12 hours. After the reaction, cooled to room temperature, diluted the reaction solution with 10 mL of deionized water, transferred the diluted reaction solution to a centrifuge tube, centrifuged at 10,000 r/min for 10 minutes, took the supernatant, added 1M H ₂ SO ₄ dilution. After dilution, the liquid was subjected to high performance liquid chromatography to measure the conversion rate of sorbitol and the yield of lactic acid. The conversion rate of sorbitol was 98%, and the yield of lactic acid was 79%.

Embodiment 13, nitrogen heterocyclic carbene iridium solid molecular catalyst 2b is used for catalyzing oxidation of sorbitol to prepare lactic acid:

Under the protection of nitrogen atmosphere, nitrogen heterocyclic carbene iridium solid molecular catalyst 2b (0.003g, 0.2mol%), barium hydroxide octahydrate (1.89g, 6mmol), sorbitol ( 0.54 g, 3 mmol), tert-butanol (2 mL). After sealing the thick-walled pressure bottle, it was put into an oil bath, heated to 140° C. and reacted for 12 hours. After the reaction, cooled to room temperature, diluted the reaction solution with 10 mL of deionized water, transferred the diluted reaction solution to a centrifuge tube, centrifuged at 10,000 r/min for 10 minutes, took the supernatant, added 1M H ₂ SO ₄ dilution. After dilution, the liquid was subjected to high performance liquid chromatography to measure the conversion rate of sorbitol and the yield of lactic acid. The conversion rate of sorbitol was 98%, and the yield of lactic acid was 75%.

Embodiment 14, nitrogen heterocyclic carbene iridium solid molecular catalyst 2b is used to catalyze the oxidation of sorbitol to prepare lactic acid:

Under the protection of nitrogen atmosphere, nitrogen heterocyclic carbene iridium solid molecular catalyst 2b (0.003g, 0.2mol%), barium hydroxide octahydrate (1.89g, 6mmol), sorbitol ( 0.54 g, 3 mmol), benzyl alcohol (2 mL). After sealing the thick-walled pressure bottle, it was put into an oil bath, heated to 140° C. and reacted for 12 hours. After the reaction, cooled to room temperature, diluted the reaction solution with 10 mL of deionized water, transferred the diluted reaction solution to a centrifuge tube, centrifuged at 10,000 r/min for 10 minutes, took the supernatant, added 1M H ₂ SO ₄ dilution. After dilution, the liquid was subjected to high performance liquid chromatography to measure the conversion rate of sorbitol and the yield of lactic acid. The conversion rate of sorbitol was 98%, and the yield of lactic acid was 79%.

Embodiment 16, nitrogen heterocyclic carbene iridium solid molecular catalyst 2b is used to catalyze the oxidation of mannitol to prepare lactic acid:

Under the protection of nitrogen atmosphere, nitrogen heterocyclic carbene iridium solid molecular catalyst 2b (0.003g, 0.2mol%), barium hydroxide octahydrate (1.89g, 6mmol), mannitol ( 0.54 g, 3 mmol), methanol (2 mL). After sealing the thick-walled pressure bottle, it was put into an oil bath, heated to 140° C. and reacted for 12 hours. After the reaction, cooled to room temperature, diluted the reaction solution with 10 mL of deionized water, transferred the diluted reaction solution to a centrifuge tube, centrifuged at 10,000 r/min for 10 minutes, took the supernatant, added 1M H ₂ SO ₄ dilution. After dilution, the liquid was subjected to high performance liquid chromatography to measure the mannitol conversion rate and the lactic acid yield. The yield of mannitol was 99% and the yield of lactic acid was 95%.

Embodiment 17, nitrogen heterocyclic carbene iridium solid molecular catalyst 2b is used to catalyze the oxidation of galactitol to prepare lactic acid:

Under the protection of nitrogen atmosphere, nitrogen heterocyclic carbene iridium solid molecular catalyst 2b (0.003g, 0.2mol%), barium hydroxide octahydrate (1.89g, 6mmol), galactitol were successively added to a 15mL thick-walled pressure bottle. (0.54 g, 3 mmol), methanol (2 mL). After sealing the thick-walled pressure bottle, it was put into an oil bath, heated to 140° C. and reacted for 12 hours. After the reaction, cooled to room temperature, diluted the reaction solution with 10 mL of deionized water, transferred the diluted reaction solution to a centrifuge tube, centrifuged at 10,000 r/min for 10 minutes, took the supernatant, added 1M H ₂ SO ₄ dilution. After dilution, the liquid was subjected to high performance liquid chromatography to measure the conversion rate of galactitol and the yield of lactic acid. The conversion of galactitol was 99% and the yield of lactic acid was 99%.

Embodiment 18, nitrogen heterocyclic carbene iridium solid molecular catalyst 2b is used to catalyze the oxidation of xylitol to prepare lactic acid:

Under the protection of nitrogen atmosphere, add nitrogen heterocyclic carbene iridium solid molecular catalyst 2b (0.003g, 0.2mol%), barium hydroxide octahydrate (1.89g, 6mmol), xylitol to 15mL thick-walled pressure bottle successively (0.45 g, 3 mmol), methanol (2 mL). After sealing the thick-walled pressure bottle, it was put into an oil bath, heated to 140° C. and reacted for 12 hours. After the reaction, cooled to room temperature, diluted the reaction solution with 10 mL of deionized water, transferred the diluted reaction solution to a centrifuge tube, centrifuged at 10,000 r/min for 10 minutes, took the supernatant, added 1M H ₂ SO ₄ dilution. After dilution, the liquid was subjected to high performance liquid chromatography to measure the conversion rate of xylitol and the yield of lactic acid. The conversion rate of xylitol was 99%, and the yield of lactic acid was 92%.

Embodiment 19, nitrogen heterocyclic carbene iridium solid molecular catalyst 2b is used for catalytic oxidation of adonitol to prepare lactic acid:

Under the protection of nitrogen atmosphere, nitrogen heterocyclic carbene iridium solid molecular catalyst 2b (0.003g, 0.2mol%), barium hydroxide octahydrate (1.89g, 6mmol), adonose were successively added to a 15mL thick-walled pressure bottle. Alcohol (0.45 g, 3 mmol), methanol (2 mL). After sealing the thick-walled pressure bottle, it was put into an oil bath, heated to 140° C. and reacted for 12 hours. After the reaction, cooled to room temperature, diluted the reaction solution with 10 mL of deionized water, transferred the diluted reaction solution to a centrifuge tube, centrifuged at 10,000 r/min for 10 minutes, took the supernatant, added 1M H ₂ SO ₄ dilution. After dilution, the liquid was subjected to high performance liquid chromatography to measure the conversion rate of adonit and the yield of lactic acid. The conversion rate of Adonit was 99%, and the yield of lactic acid was 93%.

Embodiment 20, nitrogen heterocyclic carbene iridium solid molecular catalyst 2b is used to catalyze the oxidation of arabitol to prepare lactic acid:

Under the protection of nitrogen atmosphere, nitrogen heterocyclic carbene iridium solid molecular catalyst 2b (0.003g, 0.2mol%), barium hydroxide octahydrate (1.89g, 6mmol), adonose were successively added to a 15mL thick-walled pressure bottle. Alcohol (0.45 g, 3 mmol), methanol (2 mL). After sealing the thick-walled pressure bottle, it was put into an oil bath, heated to 140° C. and reacted for 12 hours. After the reaction, cooled to room temperature, diluted the reaction solution with 10 mL of deionized water, transferred the diluted reaction solution to a centrifuge tube, centrifuged at 10,000 r/min for 10 minutes, took the supernatant, added 1M H ₂ SO ₄ dilution. After dilution, the liquid was subjected to high performance liquid chromatography to measure the conversion rate of adonit and the yield of lactic acid. The conversion rate of Adonit was 99%, and the yield of lactic acid was 99%.

Embodiment 21, nitrogen heterocyclic carbene iridium solid molecular catalyst 2b is used for catalyzing oxidation erythritol to prepare lactic acid:

Under the protection of nitrogen atmosphere, the nitrogen heterocyclic carbene iridium solid molecular catalyst 2b (0.003g, 0.2mol%), barium hydroxide octahydrate (1.89g, 6mmol), erythrose were successively added to the 15mL thick-walled pressure bottle. Alcohol (0.36 g, 3 mmol), methanol (2 mL). After sealing the thick-walled pressure bottle, it was put into an oil bath, heated to 140° C. and reacted for 12 hours. After the reaction, cooled to room temperature, diluted the reaction solution with 10 mL of deionized water, transferred the diluted reaction solution to a centrifuge tube, centrifuged at 10,000 r/min for 10 minutes, took the supernatant, added 1M H ₂ SO ₄ dilution. After dilution, the liquid was subjected to high performance liquid chromatography to measure the erythritol conversion rate and the lactic acid yield. The conversion rate of erythritol was 99%, and the yield of lactic acid was 67%.

Embodiment 22, nitrogen heterocyclic carbene iridium solid molecular catalyst 2b is used to catalyze the oxidation of threitol to prepare lactic acid:

Under the protection of nitrogen atmosphere, nitrogen heterocyclic carbene iridium solid molecular catalyst 2b (0.003g, 0.2mol%), barium hydroxide octahydrate (1.89g, 6mmol), threitol were successively added to a 15mL thick-walled pressure bottle. (0.36 g, 3 mmol), methanol (2 mL). After sealing the thick-walled pressure bottle, it was put into an oil bath, heated to 140° C. and reacted for 12 hours. After the reaction, cooled to room temperature, diluted the reaction solution with 10 mL of deionized water, transferred the diluted reaction solution to a centrifuge tube, centrifuged at 10,000 r/min for 10 minutes, took the supernatant, added 1M H ₂ SO ₄ dilution. After dilution, the liquid was subjected to high performance liquid chromatography to measure the threitol conversion rate and lactic acid yield. The conversion rate of threitol was 99%, and the yield of lactic acid was 68%.

Embodiment 23, nitrogen heterocyclic carbene iridium solid molecular catalyst 2b is used to catalyze the oxidation of maltitol to prepare lactic acid:

Under the protection of nitrogen atmosphere, nitrogen heterocyclic carbene iridium solid molecular catalyst 2b (0.003g, 0.2mol%), barium hydroxide octahydrate (1.89g, 6mmol), maltitol ( 0.52 g, 1.5 mmol), methanol (2 mL). After sealing the thick-walled pressure bottle, it was put into an oil bath, heated to 140° C. and reacted for 12 hours. After the reaction, cooled to room temperature, diluted the reaction solution with 10 mL of deionized water, transferred the diluted reaction solution to a centrifuge tube, centrifuged at 10,000 r/min for 10 minutes, took the supernatant, added 1M H ₂ SO ₄ dilution. After dilution, the liquid was subjected to high performance liquid chromatography to measure the conversion rate of maltitol and the yield of lactic acid. The conversion rate of maltitol was 99%, and the yield of lactic acid was 51%.

Embodiment 24, nitrogen heterocyclic carbene iridium solid molecular catalyst 2b is used to catalyze the oxidation of lactitol to prepare lactic acid:

Under the protection of nitrogen atmosphere, nitrogen heterocyclic carbene iridium solid molecular catalyst 2b (0.003g, 0.2mol%), barium hydroxide octahydrate (1.89g, 6mmol), lactitol ( 0.52 g, 1.5 mmol), methanol (2 mL). After sealing the thick-walled pressure bottle, it was put into an oil bath, heated to 140° C. and reacted for 12 hours. After the reaction, cooled to room temperature, diluted the reaction solution with 10 mL of deionized water, transferred the diluted reaction solution to a centrifuge tube, centrifuged at 10,000 r/min for 10 minutes, took the supernatant, added 1M H ₂ SO ₄ dilution. After dilution, the liquid was subjected to high performance liquid chromatography to measure lactitol conversion and lactic acid yield. The lactitol conversion rate was 99%, and the lactic acid yield was 55%.

Embodiment 25, the nitrogen heterocyclic carbene iridium solid molecular catalyst 2b is recycled for the preparation of lactic acid by catalytic oxidation of sorbitol:

The experimental procedure is the same as that in Example 8. The solid obtained by centrifugation after the reaction is recovered, washed with deionized water, methanol and dichloromethane for 5 times in turn, and dried in vacuum at 80° C. for 8 hours. The recovered solid catalyst was used in a cycle experiment to investigate the repeatability of the catalyst, and the results are shown in Figure 2. It can be seen from Figure 2 that the catalyst has good reusability, and after 10 cycles, the yield of lactic acid can still reach 95%.

Those skilled in the art can understand that the above-mentioned embodiments are specific examples for realizing the present invention, and in practical applications, various changes in form and details can be made without departing from the spirit and the spirit of the present invention. scope.

Claims (2)

1. A method for preparing lactic acid by selective catalytic conversion of biomass polyol is characterized in that: taking biomass polyol as a raw material, taking alkali metal or alkaline earth metal hydroxide as alkali, taking alcohol as a solvent, and carrying out a closed reaction for 6-24 hours at 100-200 ℃ under the action of a catalyst to obtain lactic acid;

the molar ratio of the catalyst to the biomass polyol is one ten thousandth to one hundredth; the molar ratio of the alkali metal or alkaline earth metal hydroxide to the biomass polyol is 0.5 to 10; the molar ratio of the alcoholic solvent to the biomass polyol is more than 0 and less than or equal to 50;

the alcohol is selected from one or more of methanol, ethanol, n-propanol, isopropanol, n-butanol, tert-butanol and benzyl alcohol;

the alkali metal or alkaline earth metal hydroxide is selected from one or more of sodium hydroxide, calcium hydroxide, barium hydroxide octahydrate and cesium hydroxide monohydrate;

the catalyst is as follows:

、

or

；

Wherein n represents the number of monomers contained in the N-heterocyclic carbene metal coordination polymer, and n is a natural number which is more than or equal to 2.

2. The method for selective catalytic conversion of biomass polyol to lactic acid according to claim 1, wherein said biomass polyol is selected from one or more of glycerol, erythritol, threitol, arabitol, xylitol, adonitol, sorbitol, mannitol, galactitol, maltitol, and lactitol.

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