CN115246770B

CN115246770B - Method for preparing glycolic acid by catalytic conversion of glycerol

Info

Publication number: CN115246770B
Application number: CN202110457991.6A
Authority: CN
Inventors: 李建梅; 许曙光; 张文瑜; 胡常伟
Original assignee: Sichuan University
Current assignee: Sichuan University
Priority date: 2021-04-26
Filing date: 2021-04-26
Publication date: 2023-11-17
Anticipated expiration: 2041-04-26
Also published as: CN115246770A

Abstract

A method for preparing glycolic acid by glycerin catalytic conversion. Firstly, copper magnesium oxide with a certain copper-magnesium ratio is prepared by a coprecipitation method, and the obtained catalyst is used for subsequent catalytic reaction. Glycerin is used as a raw material, water is used as a reaction solvent, copper magnesium oxide is used as a catalyst, and the glycolic acid is prepared by reacting in an autoclave reactor under the oxygen atmosphere. The copper-magnesium coprecipitation catalytic activity is high, and the conversion rate of glycerin and the yield of glycolic acid respectively reach 89.2% and 60.3% under the optimal conditions.

Description

Method for preparing glycolic acid by catalytic conversion of glycerol

Technical Field

The invention relates to a method for preparing a catalyst for preparing glycolic acid by catalytic conversion of glycerin and catalyzing the reaction of the glycerin to generate the glycolic acid.

Background

Glycolic Acid (GA) is the simplest alpha-hydroxycarboxylic acid known at present, is an important bulk fine chemical intermediate, can be used for synthesizing ethylene glycol, glycine, menthol, quinine and other pharmaceutical intermediates, and is widely applied to industries such as fine chemical engineering, pharmacy, cosmetics, biomedical engineering and the like. In recent years, with increasing attention to ecological environment problems, traditional plastics are difficult to degrade to form 'white pollution', and the traditional plastics cause more and more harm to the environment, so that the search for biodegradable plastics is one of the current hot research subjects. Among them, polyglycolic acid (PGA), which is a very promising candidate for replacing petroleum-based plastics, is widely used in drug controlled-release systems, as well as in internal fixation of fractures of humans or animals, repair of bone defects, repair of tendons, suturing of blood vessels, muscles and other tissues of humans or animals, because it has excellent gas barrier properties, biocompatibility and biodegradability, and can be completely decomposed into non-toxic and harmless water and carbon dioxide in nature. In addition, recent researches indicate that GA has the capability of inducing proliferation of collagen synthesis cells in organisms, can be used as a surface corrosive agent of enamel and dentin, and is also widely applied to biomedical engineering. In addition, lactic acid-glycolic acid copolymer (PLGA) obtained by copolymerizing GA and lactic acid (LaA) is approved by the united states Food and Drug Administration (FDA) and is formally recorded in the united states pharmacopeia as a pharmaceutical excipient. Compared with PGA and PLA (polylactic acid), the PLGA degradation speed is more controllable, and has better solubility and higher mechanical strength; thus having wider application potential.

The excellent properties of PLGA have led to a rapid increase in demand. There are studies reporting that its global demand will increase from dollars 3 billion in 2017 to dollars 4.06 billion in 2023. There is therefore a need to develop new strategies that enable cost-effective production of GA. The current production methods of glycolic acid include traditional chemical synthesis methods, enzyme catalysis methods and microbial oxidation glycol methods. DuPont in the United states has been working on the development and process optimization of glycolic acid. In 1939, they proposed a chemical continuous production method for preparing glycolic acid by using formaldehyde, water and excess carbon monoxide as raw materials and sulfuric acid as a catalyst. The process is complex in process, high in energy consumption and relatively low in production efficiency, and large-scale industrial application of the process is limited. In addition, chloroacetic acid is taken as a raw material, hydrolysis reaction is carried out in NaOH solution, and glycolic acid can also be obtained; however, the process uses a large amount of alkali liquor, which causes corrosion of equipment. In 2004, duPont developed enzyme catalysis. First, formaldehyde and hydrogen cyanide flow react to form acetonitrile of high purity at 90-150 ℃. Subsequently, acetonitrile was further enzymatically catalyzed to obtain an aqueous solution of ammonium glycolate, and finally GA having a purity of 99.9% was recovered from the aqueous ammonium glycolate solution by ion exchange. The adoption of the enzyme catalysis process reduces energy consumption and has certain economic advantages; however, the process uses highly toxic acetonitrile, which causes a certain pollution to the environment, and the adopted chemical enzymes depend on certain known irritant and carcinogenic chemical substances, so that the industrial development of the chemical enzymes is greatly limited. The microorganism oxidation glycol method can obtain glycolic acid with high selectivity, but the method needs to maintain the pH of the system to be about 7.0, so that alkali is required to be continuously added to neutralize the generated glycolic acid, and subsequent separation is difficult.

In recent years, the chemical catalytic method for preparing the glycolic acid has been attracting attention of more and more researchers because of short production period and wide production raw materials (edible sugar, polyalcohol, cellulose, raw biomass and the like). For example, feng Shi et Al (Angewandte Chemie International Edition,2019,58 (16): 5251-5255) utilize dihydroxyacetone as a starting material, cu/Al ₂ O ₃ As catalyst in equimolar H ₂ O ₂ The reaction is carried out for 8 hours at 25 ℃ in the presence of the catalyst to obtain the glycolic acid with 85 percent yield. Raghunath V.Chaudhari et al (Industrial)&Engineering Chemistry Research,2019,58,18561-18568) with ethylene glycol as raw material, pt-Fe/CeO ₂ O at 1atm as catalyst ₂ Under the atmosphere, the reaction is carried out for 12 hours at 70 ℃, and the hydroxyacetic acid with the selectivity of 60 percent can be obtained. Yi Tang et al (ACS Sustainable Chemistry)&Engineering,2019,7,17559-17564) using ethylene glycol as the starting material, [ Cp ] Ir (bpyO)]OH ^- As a catalyst, the hydroxyacetic acid with the selectivity of 70% can be obtained when the reaction is carried out for 10 hours at 100 ℃ in the presence of equimolar NaOH. Skrzy ń ska et al (Catalysis Science&Technology,2016,6 (9): 3182-3196) starting from glycerol, ag/Al ₂ O ₃ As a solid catalyst, glycolic acid with 24% yield is obtained by reacting for 3 hours at 100 ℃ in the presence of NaOH with the same mole as glycerol and under the oxygen atmosphere of 0.5 MPa. Fangming Jin et al (Industrial)&Engineering Chemistry Research,2014,53 (19): 7939-7946) uses cellulose as raw material, cuO as catalyst, and under the action of 1mol/L NaOH, the reaction is carried out for 5min at 300 ℃, so that glycolic acid with 14.9% yield can be obtained; yu Han et al (ACS Catalysis,2012,2 (8): 1698-1702) reacted at 180℃for 1 hour under an oxygen atmosphere of 0.6MPa with cellulose and bagasse as raw materials and phosphomolybdic heteropolyacid as a catalyst to obtain glycolic acid in 49% and 30% yields, respectively.

Glycerol is used as a byproduct for producing biodiesel, and has the advantage of higher economic advantage compared with dihydroxyacetone, ethylene glycol and other raw materials; although it has been reported at present that biomass feedstocks can also catalyze the production of glycolic acid, it is often difficult to obtain glycolic acid with high selectivity due to the complexity of its structure, increasing the difficulty of post-treatment. In view of the above, glycerol has a simple structure, a controllable reaction process and low cost, and is an ideal raw material for preparing glycolic acid.

Therefore, the chemical catalytic method for preparing the glycolic acid has good application prospect, but the following two problems still exist in the preparation process: (1) Most of the reaction processes need to introduce NaOH as a reaction auxiliary agent, and the introduction of NaOH can corrode reaction equipment; (2) When cheap and easily available biomass raw materials or biodiesel byproduct glycerol is used as a reaction substrate, the obtained glycolic acid has lower yield. Aiming at the two problems, the invention selects the low-cost glycerin as a substrate, the copper magnesium oxide as a catalyst and the water as a solvent, does not need to additionally add NaOH auxiliary agent, and obtains the glycolic acid at a milder reaction temperature; and the catalyst can be directly separated from the liquid-phase product through reduced pressure suction filtration, so that the subsequent separation of the product and the recycling of the catalyst are facilitated.

Disclosure of Invention

The invention prepares a cheap copper-magnesium oxide catalyst which is used for preparing glycolic acid and formic acid by catalyzing glycerol to convert; the method overcomes the defects of complex process, high energy consumption and low production efficiency of the traditional chemical method; substances harmful to human bodies in the process of enzyme catalysis are overcome; overcomes the defects of long period, incapability of continuous production and the like of a microbial oxidation glycol method; the method takes water as a solvent, does not need to additionally add NaOH auxiliary agent, and has green and environment-friendly production process; the method uses cheap copper magnesium oxide as a catalyst and has the characteristics of high catalytic activity, recoverability and reusability.

The key points of the invention are as follows: adding a certain amount of copper acetate and magnesium acetate into 100mL of absolute ethyl alcohol, and reacting for 2 hours at 40 ℃ in a closed autoclave reactor to obtain blue transparent liquid; transferring the blue transparent liquid into a beaker, adding 10mL of LiOH aqueous solution with the molar weight being 1.1 times based on the molar weight of copper and magnesium, and reacting for 20min in an ice water bath at the rotating speed of 400prm (magnetic stirring) to obtain blue colloid; centrifuging the blue colloid, and washing for three times (ethanol washing is carried out once and water washing is carried out twice), wherein the rotating speed is 4000rpm, so as to obtain blue precipitate; drying the blue precipitate in an oven at 80 ℃ for 12 hours to obtain a gray black solid; grinding the gray black solid, then placing the ground gray black solid into a muffle furnace for calcination at 400 ℃ for 4 hours, heating at a rate of 5 ℃/min, and cooling to obtain the copper-magnesium oxide.

Adding a glycerin reactant into 50mL of water, adding the prepared copper-magnesium catalyst, and heating to react in a closed autoclave reactor under an initial oxygen atmosphere of 1.0MPa, wherein the molar ratio of copper to magnesium in the catalyst is 1:8,1:4,1:1,4:1,8:1, a step of; the mass ratio of the catalyst to the substrate is 0.5-2.5, the reaction time is 1-12 h, and the reaction temperature is 140-220 ℃. After the reaction is completed, the reaction system is naturally cooled to room temperature, the catalyst is separated by suction filtration, and the precipitate is calcined at 400 ℃ and then used for the next catalytic reaction. The small molecule compounds in the solution were detected by HPLC.

In the invention, the copper-magnesium ratio of the catalyst is preferably 1: 8-1: 1. when the copper content is too low, the conversion rate of glycerin is low, and the yield of glycolic acid is also low; with the increase of copper content, the conversion rate of glycerin and the yield of glycolic acid are obviously increased. But when the copper content exceeds 1: after 1, the yield of glycolic acid is obviously reduced, and byproducts are increased.

In the present invention, the mass ratio of the catalyst to the substrate is preferably 1.5 to 2.5. When the amount of the catalyst is too low, the glycerol conversion rate and the selectivity of the product glycolic acid are relatively low, and with the increase of the catalyst amount, the glycerol conversion rate and the yield of the product glycolic acid are obviously increased; when the mass ratio of the catalyst to the substrate reaches 2.0, the ratio is continuously increased, and the glycerol conversion rate and the yield of the product glycolic acid are not obviously increased.

In the present invention, the reaction time is preferably 6 to 10 hours. The reaction time is too short, the glycerol conversion rate is too low, and the yield of the glycolic acid is not high. With the increase of the reaction time, the glycerol conversion rate and the yield of the product glycolic acid are increased; however, when the reaction time exceeds 8 hours, the increase in the conversion of glycerin and the yield of the product glycolic acid is not significant.

In the present invention, the reaction temperature is preferably 160 to 220 ℃. The reaction temperature is too low, and the glycerol conversion rate and the yield of the product glycolic acid are low. With increasing reaction temperature, the glycerol conversion rate and the yield of the product glycolic acid are increased; however, when the reaction temperature exceeds 200 ℃, the yield of glycolic acid is rather lowered.

The invention has the beneficial effects that:

1) The invention uses the byproduct glycerol of biodiesel as raw material, and adopts a chemical catalysis method to prepare the glycolic acid. The method overcomes the defects of the traditional chemical method, enzyme catalysis method and microorganism oxidation glycol method, such as: high energy consumption, low production efficiency, introduction of harmful substances and the like.

2) The invention does not introduce soluble inorganic strong alkali such as NaOH and the like as a reaction auxiliary agent, and can not cause corrosion to equipment in the reaction process.

3) The catalyst used in the invention is copper magnesium oxide, the preparation process is simple, the price is low, the catalyst has higher catalytic activity for preparing the glycolic acid, and the catalyst exists in a solid form after the reaction is finished, and is easy to separate and recycle.

Detailed Description

1. Optimization of reaction conditions

Example 1:

1) Into a 100mL closed autoclave reactor were charged 0.20g of glycerin and 0.20g of copper magnesium catalyst (copper: magnesium=1: 4) A further 50mL of high purity water was added. After the autoclave was sealed, oxygen was introduced for 3 minutes, and the air in the autoclave was discharged and pressurized to 1MPa. Stirring and heating to 180 ℃ and then reacting for 8 hours, lifting the autoclave out of a heating device, and naturally cooling to room temperature. Opening the autoclave, pouring out the whole product, washing the autoclave with high-purity water for 3 times, combining the washing liquid into the reaction product, and filtering the product by a microporous filter membrane to obtain solid residue and filtrate.

2) And washing the collected filter residues with deionized water, and then placing the filter residues into a muffle furnace to be roasted for 4 hours at 400 ℃ to be used as a catalyst for the next reaction. The aqueous phase small molecules were checked by HPLC and the results are shown in table 1. (mol% yield except for the noted conversion in the table, mol% carbon yield is represented, and the ratio in the table is the molar ratio).

TABLE 1

Description of the preferred embodiments	Glycerol conversion	Glycolic acid	Lactic acid	Hydroxymalonic acid	Formic acid	Oxalic acid
							1	70.1	47.0	5.6	1.7	18.8	0.9

Examples 2 to 5:

the procedure of example 1 was followed except that the copper-magnesium ratio in the catalyst was varied, and the other reaction conditions were the same as in example 1, and the specific results are shown in Table 2. (mol% yield except for the noted conversion in the table, mol% carbon yield is represented, and the ratio in the table is the molar ratio).

TABLE 2

Description of the preferred embodiments	Cu:Mg	Glycerol conversion	Glycolic acid	Lactic acid	Hydroxymalonic acid	Formic acid	Oxalic acid
								2	1：8	51.7	31.9	2.3	0.4	12.5	0.3
3	1：1	73.1	43.8	4.8	1.9	16.7	1.1
								4	4：1	68.9	33.9	3.3	1.2	13.4	1.1
5	8：1	57.2	23.1	3.9	1.3	11.0	1.4

Examples 6 to 9:

the procedure of example 1 was followed except that the reaction temperature was varied, and the other reaction conditions were the same as in example 1, and the specific results are shown in Table 3. (mol% yield except for the noted conversion in the table, mol% carbon yield is represented, and the ratio in the table is the molar ratio).

TABLE 3 Table 3

Description of the preferred embodiments	Reaction temperature	Glycerol conversion	Glycolic acid	Lactic acid	Hydroxymalonic acid	Formic acid	Oxalic acid
								6	140℃	8.4	4.9	0.7	--	1.3	--
7	160℃	45.2	32.5	3.8	0.3	10.6	0.5
								8	200℃	84.7	52.2	7.4	2.4	23.9	1.3
9	220℃	98.8	50.1	7.2	2.6	24.5	0.8

Examples 10 to 13:

the procedure of example 8 was followed except that the mass ratio of catalyst to substrate was varied, and the other reaction conditions were the same as in example 8, and the specific results are shown in Table 4. (mol% yield except for the noted conversion in the table, mol% carbon yield is represented, and the ratio in the table is the molar ratio).

TABLE 4 Table 4

Examples 14 to 19:

the procedure of example 12 was followed except that the reaction time was varied and the other reaction conditions were the same as in example 12, and the specific HPLC results are shown in Table 5. (mol% yield except for the noted conversion in the table, mol% carbon yield is represented, and the ratio in the table is the molar ratio).

TABLE 5

Examples 20 to 22:

recycling of catalyst

The procedure of example 1 was followed except that the catalyst was used in different numbers, and the other reaction conditions were the same as in example 1, and the specific results are shown in Table 6.

TABLE 6

Description of the preferred embodiments	Number of times	Glycolic acid yield (%)
			20	2	58.8
21	3	57.5
			22	4	58.9

Claims

1. A method for preparing glycolic acid by glycerin catalytic conversion is characterized in that copper acetate and magnesium acetate are respectively used as a copper source and a magnesium source, liOH is used as a precipitator, copper magnesium oxide with different copper-magnesium ratios is prepared by changing the proportion of the copper acetate to the magnesium acetate and adopting a coprecipitation method, and the prepared catalyst is used for subsequent catalytic reaction; glycerol is taken as a raw material, water is taken as a solvent, a catalyst is added, and glycolic acid is prepared in a closed autoclave reactor under the oxygen atmosphere, wherein the copper-magnesium ratio in the catalyst is 1: 8. 1: 4. 1:1. 4:1 or 8:1, the mass ratio of the catalyst to the substrate is 0.5-2.5, the reaction time is 1-12 hours, and the reaction temperature is 160-220 ℃.

2. The method according to claim 1, wherein the copper-magnesium ratio in the catalyst is 1: 8-1: 1.

3. the process according to claim 1, wherein the mass ratio of catalyst to substrate is from 1.5 to 2.5.

4. The process according to claim 1, wherein the reaction time is from 6 to 10 hours.