CN110256226B

CN110256226B - Method for preparing D-lactic acid from C3, xylose, glucose and corn straw in one step

Info

Publication number: CN110256226B
Application number: CN201910366350.2A
Authority: CN
Inventors: 胡常伟; 许曙光; 李建梅; 何婷; 黄志铭
Original assignee: Sichuan University
Current assignee: Sichuan University
Priority date: 2019-04-30
Filing date: 2019-04-30
Publication date: 2021-07-13
Anticipated expiration: 2039-04-30
Also published as: CN110256226A

Abstract

A one-step method for preparing D-lactic acid from C3, xylose, glucose and corn stalks comprises the steps of taking C3 compounds (dihydroxyacetone, glyceraldehyde and pyruvaldehyde), xylose, glucose and corn stalks as raw materials, taking water as a reaction solvent, taking MgO and D-lactic acid (D-LaA) as catalysts, and reacting in a high-pressure reactor (Parr) under a nitrogen atmosphere to prepare the lactic acid. The MgO-D-LaA catalytic system has high catalytic activity, the yield of lactic acid respectively reaches 78.5%, 80.2%, 88.3%, 89.1%, 90.1% and 57.9% under the optimal condition, and the corresponding D-lactic acid ee values respectively reach 72.0%, 70.3%, 76.5%, 75.1%, 77.2% and 49.8%.

Description

Method for preparing D-lactic acid from C3, xylose, glucose and corn straw in one step

Technical Field

The invention relates to a method for preparing D-lactic acid by taking renewable biomass as a raw material in a non-fermentation and non-traditional chemical synthesis mode.

Background

Lactic acid (LaA) has wide application in food, medicine, cosmetics, chemical industry and other industries. Lactic acid has two chiral enantiomers (D-lactic acid and L-lactic acid) in nature, and the two lactic acids with different conformations have different applications due to the difference of chemical properties, for example, L-lactic acid can be absorbed by human body and used as food additive. With the development of society, the application of lactic acid has been expanding in recent years. Polylactic acid (PLA) is gaining favor as a degradable plastic, and due to its good biodegradability, biocompatibility and mechanical properties, it has a good application potential in medicine and medical treatment, such as drug delivery systems, surgical implant devices, orthopedic devices, etc., and is considered to be one of the most promising candidates for replacing petroleum-based plastics. However, commercially available poly-L-lactic acid (PLLA) generally has the disadvantages of small deformation, easy breakage and slow crystal growth. In recent years, studies have shown that PLLA and PDLA (poly-D-lactic acid) are produced in combination to form a polylactic acid stereocomplex (sc-PLA) having a stereocomplex structure, and that the melting point, thermochemical and physical properties, and biodegradation rate of the polylactic acid stereocomplex (sc-PLA) are greatly improved, thereby overcoming the above-mentioned disadvantages of PLLA.

The demand for sc-PLA is rapidly increasing due to its excellent properties, and development of a new strategy for economically and efficiently producing D-lactic acid is urgently required. The method for commercially producing the lactic acid is commercializedChemical synthesis and fermentation of carbohydrates. Among them, the chemical synthesis method requires the use of a highly toxic substance, hydrocyanic acid, as a raw material, which causes severe environmental pollution, and produces lactic acid as a racemic mixture, thus limiting its large-scale industrial application. At present, the main production mode of lactic acid is that edible biomass starch is used as a raw material, a biological fermentation method is adopted for production, and as the bacterial colony for producing the L-lactic acid is relatively low in price, about 90 percent of products obtained by the fermentation method are the L-lactic acid. Production of D-lactic acid by fermentation is more challenging due to the limited number of colonies and high cost of producing D-lactic acid compared to L-lactic acid. Although a small amount of related documents have reported the production of D-lactic acid by fermentation, the methods still suffer from problems such as low yield, long production period, inability to produce continuously, and generation of large amounts of waste salts (CaSO)₄) And limitations on raw materials (typically edible biomass as a fermentation). The chemical catalysis method can not only use edible biomass as raw material, but also use non-edible cellulose, even cheap lignocellulose from agriculture and forestry as raw material, thus greatly reducing the production cost of lactic acid. Therefore, in recent years, the chemical catalytic method for producing lactic acid has been receiving attention from many researchers. For example, Lisha Yang et al (Applied Catalysis B: Environmental,2015,162,149-157) use xylose and xylan as raw materials, ZrO₂As a catalyst, the lactic acid can be obtained with yields of 42% and 30% respectively by reacting at 200 ℃ for 40 min. Ayumu Onda et al (Catalysis Communications,2008,9, 1050-. Cristina S-nchez et al (Chemical Engineering Journal,2012, (181-182),655-660) use cellulose and hemicellulose as raw materials, 0.7M Ca (OH)₂The reaction is carried out for 30min at 300 ℃ as a catalyst, and 44.76% of lactic acid can be obtained. Ye Wang et al (Nature communications,2013,4,2141) selectively obtain-70% lactic acid at 463K using glucose as raw material and a small amount of lead (II) ions as catalyst; they have further studied (Al)^III-Sn^II) A catalytic system (Green chemistry,2018,20,735-744) catalyzes the conversion of cellulose to lactic acid and was found to be available at 453KLactic acid yield of 65%. Our previous work found that more lactic acid was obtained using hemicellulose dissolved from corn stover as a feedstock than using xylose as a feedstock, under the catalytic action of MgO (Scientific Reports,2016,6, 38623). Our recent studies found that D-excess lactic acid could be obtained from monosaccharides and primary biomass under the catalytic action of Y (III), which demonstrates that D-excess lactic acid could be directly prepared from primary biomass, unfortunately the ee value of the obtained D-lactic acid is still low (I), (II), (III)<20%) (iSience, 2019,12, 132-. However, other researchers reported at present hardly mention the chiral distribution of lactic acid in the relevant documents of preparing lactic acid by a chemical catalysis method by using pentose and hexose as raw materials, and do not report that D-lactic acid with high optical purity is obtained by directly converting primary biomass. Therefore, the development of an efficient catalytic system to obtain the high-yield and high-chiral-selectivity D-lactic acid has important significance for reducing the production cost of the D-lactic acid and meeting the wide market demands of the D-lactic acid, and simultaneously can provide a new direction and thought for high-value utilization of xylose, glucose and even native biomass, thereby promoting the transition of biomass chemistry from the production of a common platform compound to the synthesis of a more refined chiral product with high optical purity.

Disclosure of Invention

The invention aims to provide a method for preparing D-lactic acid with high yield and high manual selectivity from a C3 compound, xylose, glucose and corn straws, wherein the method uses renewable biomass as a raw material, and overcomes the defect that the traditional chemical synthesis method uses highly toxic substances as the raw material; the method utilizes a chemical catalysis method, and overcomes the defects that the lactic acid prepared by a fermentation method has long period, can not be continuously produced, generates a large amount of waste salt and the like; the method uses cheap and easily-obtained metal oxide as a catalyst, and has the characteristics of good catalytic activity, recoverability and reusability; the method takes the product as the chiral ligand, does not additionally add other chiral ligands, and has the characteristic of continuous production.

The invention is characterized in that: adding C3 compounds (dihydroxyacetone, glyceraldehyde and methylglyoxal), xylose, glucose or cornstalks into 50mL of water as reactants, adding MgO and D-lactic acid as catalysts, and carrying out heating reaction in a closed high-pressure kettle reactor under the initial nitrogen atmosphere of 2.0MPa, wherein the mass ratio of MgO to a substrate is 0.25-1, the mass ratio of D-lactic acid to MgO is 0.6-1.8, the reaction time is 10-120 min, and the reaction temperature is 120-220 ℃. After the reaction is finished, the reaction system is naturally cooled to room temperature, white precipitate is separated by suction filtration, and the precipitate is roasted at 600 ℃ and used for the next catalytic reaction. And detecting the small molecular compound in the solution and the lactic acid configuration by HPLC.

In the present invention, the mass ratio of MgO to xylose is preferably 0.5 to 1. The mass ratio of xylose to MgO is too small, the conversion of the product lactic acid is incomplete, the yield of the lactic acid is not obviously increased, and the chiral selectivity of the D-lactic acid is not obviously increased; as the mass ratio of xylose to MgO is increased, the yield of lactic acid is also obviously increased, and the chiral selectivity of D-lactic acid is also obviously increased. However, when the mass ratio is more than 0.75, the yield of lactic acid and the chiral selectivity of D-lactic acid hardly increase.

In the invention, the mass ratio of the D-lactic acid to the MgO in the catalytic system is preferably 1.0-1.8. The mass ratio of the D-lactic acid to the MgO is too small, the yield of the product lactic acid is not obviously increased, and the chiral selectivity of the D-lactic acid is not obviously increased; as the mass ratio of the D-lactic acid to the MgO is increased, the yield of the lactic acid is also obviously increased, and the chiral selectivity of the D-lactic acid is also obviously increased. However, when the mass ratio is more than 1.4, the yield of lactic acid and the chiral selectivity of D-lactic acid hardly increase.

In the invention, the reaction time is preferably 60 to 120 minutes. The reaction time is too short, xylose is not completely converted, and the yield of lactic acid and the chiral selectivity of D-lactic acid do not reach the maximum value. The yield of lactic acid and the chiral selectivity of D-lactic acid increase with the increase of the reaction time; however, when the reaction time exceeds 60 minutes, the yield of lactic acid and the chiral selectivity of D-lactic acid do not increase any more.

In the invention, the reaction temperature is preferably 140-220 ℃. The reaction temperature is too low, and the yield of the lactic acid is low. As the reaction temperature increases, the yield of lactic acid also increases; however, when the reaction temperature exceeds 160 ℃, the yield of lactic acid D-lactic acid shows little change or even a decrease in the chiral selectivity.

The invention has the beneficial effects that:

1) the invention uses C3 intermediate, xylose, glucose and corn stalk as raw materials, and adopts a chemical catalysis method to prepare lactic acid. The method is suitable for a wide variety of biomass raw materials, and overcomes the defects of the chemical synthesis method and the fermentation method for preparing the lactic acid, such as: the raw materials are toxic and harmful substances, the period is long, the continuous production cannot be realized, a large amount of waste salt is generated, the cost is high, and the like.

2) The catalyst used in the invention is common commercially available MgO, has wide source and low price, has higher catalytic activity for the generation of lactic acid, exists in a solid form after the reaction is finished, and is easy to separate and recycle.

3) The method uses the product D-lactic acid as a chiral ligand, does not additionally add other chiral ligands, generates the complex with the chiral environment in situ, avoids the complex synthetic process of the traditional chiral catalyst, and simplifies the separation and purification of subsequent products.

4) The invention accurately analyzes the distribution of two configurations (D-lactic acid/L-lactic acid) in the product lactic acid, and finds that the content of the D-lactic acid in the product lactic acid is greatly higher than that of the L-lactic acid.

Detailed Description

1. Reaction condition optimization

Example 1:

1) a100 mL closed autoclave reactor (Parr) was charged with 0.2g of xylose, 0.15g of MgO, and 0.27g of 0.27g D-lactic acid as catalysts, and 50mL of high purity water was added. After the autoclave was sealed, nitrogen gas was introduced thereinto for 3 minutes, and the atmosphere in the autoclave was purged and pressurized to 2 MPa. Stirring and heating to 200 ℃, reacting for 1 hour, lifting the autoclave out of the heating device, and naturally cooling to room temperature. Opening the autoclave, pouring out all the products, washing the autoclave with high-purity water for 3 times, merging the washing liquid into the reaction products, and filtering the products through a microporous filter membrane to obtain a little solid residue and filtrate.

2) And washing the collected filter residue with deionized water, and roasting the filter residue in a muffle furnace at 600 ℃ for 4 hours to be used as a catalyst for the next reaction. Then, the by-products and lactic acid in the aqueous phase were separately subjected to HPLC, and the results are shown in Table 1. (yield in table is molar carbon yield based on xylose%).

TABLE 1

Examples 2 to 5:

the procedure of example 1 was followed except that the MgO to xylose mass ratio was different and the other reaction conditions were the same as in example 1, and the specific results are shown in Table 2. (yield in table is molar carbon yield based on xylose%).

TABLE 2

Example of the implementation	Mass ratio of MgO to raw material	Xylose	Total yield of lactic acid	D-lactic acid	L-lactic acid	Glycolic acid	Formic acid	Furfural
									2	0.25	1.2	35.3	25.5	9.8	9.4	3.6	10.6
3	0.5	0	53.4	41.1	12.3	6.7	3.3	8.9
									4	0.75	0	74.9	62.1	12.8	4.5	2.1	2.4
5	1	0	73.6	59.2	14.4	4.0	2.5	2.1

Examples 6 to 9:

the procedure of example 1 was followed except that the mass ratio of D-lactic acid to MgO was different, the other reaction conditions were the same as in example 1, and the specific results are shown in Table 3. (yield in table is molar carbon yield based on xylose%).

TABLE 3

Example of the implementation	Mass ratio of D-lactic acid to MgO	Xylose	Total yield of lactic acid	D-lactic acid	L-lactic acid	Glycolic acid	Formic acid	Furfural
									6	0.6	0.9	40.1	29.9	10.2	5.9	3.4	1.5
7	1	0.1	64.7	51.7	13.0	4.7	3.0	2.2
									8	1.4	0	74.9	62.1	12.8	4.5	2.1	2.4
9	1.8	0	73.4	61.0	12.4	3.7	2.2	3.0

Examples 10 to 13:

the procedure of example 1 was followed except that the reaction time was varied, the other reaction conditions were the same as in example 1, and the specific HPLC results are shown in Table 4. (yield in table is molar carbon yield based on xylose%).

TABLE 4

Example of the implementation	Reaction time (min)	Xylose	Total yield of lactic acid	D-lactic acid	L-lactic acid	Glycolic acid	Formic acid	Furfural
									10	10	19.4	27.6	22.2	5.4	1.4	1.0	0.7
11	60	0	74.9	62.1	12.8	4.5	2.1	2.4
									12	90	0	74.1	61.2	12.9	4.7	2.4	2.0
13	120	0	73.4	60.3	13.1	5.1	2.4	3.7

Examples 14 to 18:

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 5. (yield in table is molar carbon yield based on xylose%).

TABLE 5

Example of the implementation	Reaction temperature	Xylose	Total yield of lactic acid	D-lactic acid	L-lactic acid	Glycolic acid	Formic acid	Furfural
									14	120℃	28.8	41.3	29.8	11.5	1.0	0.8	0.5
15	140℃	14.4	56.4	46.4	10.0	2.1	1.1	1.4
									16	160℃	0.5	78.5	67.5	11.0	3.3	1.6	2.3
17	180℃	0.3	78.2	65.6	12.6	3.9	2.2	2.5
									18	220℃	0	71.1	59.8	11.3	4.6	3.1	1.7

Expansion of substrates

Examples 19 to 23:

the procedure of example 1 was followed except that the reaction substrates were different, the reaction temperature of glucose was changed to 180 deg.C, the reaction temperature of corn stover was changed to 220 deg.C, the reaction temperature of the other three substrates was changed to 160 deg.C, and the other reaction conditions were the same as in example 1, with the specific results shown in Table 6. (yields in the table are molar carbon yields based on glucose, molar carbon yields based on xylose and glucose in corn stover, and molar carbon yields based on the other three substrates%).

TABLE 6

Recycling of the catalyst

Examples 24 to 26:

the procedure of example 1 was followed except that the MgO was used in different times and the reaction temperature was changed to the optimum reaction temperature of 160 ℃ and other reaction conditions were the same as in example 1, and the specific results are shown in Table 7. (yield in table is molar carbon yield based on xylose%).

TABLE 7

Example of the implementation	Number of times	Lactic acid yield (%)	Ee value of D-lactic acid
				24	1	77.6	70.8
25	2	75.3	71.5
				26	3	76.2	70.1

Claims

1. A method for preparing D-lactic acid by C3, xylose, glucose and corn stalk in one step is characterized in that C is used₃The compound comprises dihydroxyacetone, glyceraldehyde, methylglyoxal, xylose, glucose and corn straws as raw materials, MgO and D-lactic acid as catalysts, and is used for preparing lactic acid in a closed high-pressure kettle reactor under the atmosphere of nitrogen, wherein the mass ratio of MgO to the raw materials is 0.25-1, the mass ratio of D-lactic acid to MgO is 0.6-1.8, the reaction time is 10-120 min, the reaction temperature is 120-220 ℃, and the lactic acid in the product is precisely subjected to chiral quantification.

2. The method according to claim 1, wherein the mass ratio of MgO to the raw material is 0.25 to 0.75.

3. The method according to claim 1, wherein the mass ratio of D-lactic acid to MgO is 0.6 to 1.4.

4. The process according to claim 1, wherein the reaction time is 30 to 90 minutes.

5. The process according to claim 1, wherein the reaction temperature is 140 to 200 ℃.