CN112941117A - Method for synthesizing L-lactide from chiral L-lactic acid produced by using lignocellulose biomass as raw material - Google Patents
Method for synthesizing L-lactide from chiral L-lactic acid produced by using lignocellulose biomass as raw material Download PDFInfo
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Abstract
The invention belongs to the field of biorefinery, and relates to a method for synthesizing L-lactide by producing chiral L-lactic acid from a lignocellulose raw material. The method comprises the following steps: (1) removing inhibitors from the pretreated lignocellulose raw material in a final biodegradation mode; (2) high-solid content synchronous saccharification and co-fermentation are carried out on the lignocellulose raw material to obtain cellulose L-lactic acid with high concentration, high handiness and extremely low residual sugar; (3) preparing polymer-grade L-lactic acid; (4) and dehydrating, polycondensing, depolymerizing and purifying the purified cellulose chiral L-lactic acid to obtain the L-lactide. The biodegradation method adopted in the invention removes the influence of inhibitors on L-lactic acid fermentation and L-lactic acid purity, the adopted high-solid-content full-sugar co-fermentation method obtains cellulose chiral L-lactic acid with high concentration and extremely low residual sugar, and the steps of purification, polycondensation, depolymerization and the like are carried out on the cellulose chiral L-lactic acid, thereby realizing the synthesis of L-lactide from lignocellulose raw materials.
Description
Technical Field
The invention relates to the field of biorefinery, in particular to research on synthesis of L-lactide by using renewable resource lignocellulose biomass raw material to produce chiral L-lactic acid.
Background
Polylactic acid (PLA) is a biodegradable plastic, which has been widely used in the fields of packaging materials, biomedical materials, and the like as a substitute for petroleum-derived polymers. The synthesis mode of polylactic acid is mainly realized by a two-step method, firstly, chiral lactic acid monomers are polycondensed into low molecular weight polylactic acid, and then, the low molecular weight polylactic acid is depolymerized to obtain lactide; then lactide is used as a polymerization monomer to polymerize and synthesize the high molecular weight polylactic acid. Wherein the synthesis of lactide is a key step of polylactic acid. At present, lactide is mainly prepared from chiral lactic acid obtained by fermenting starch raw materials, and the production cost and the future growth space of the lactide form potential barriers for large-scale application of polylactic acid.
Lignocellulosic biomass is an important chiral lactic acid feedstock due to its low cost, abundant resources and renewability. The technology for synthesizing lactide by purifying and refining chiral lactic acid produced by starch raw materials has already been industrially applied. The method for obtaining polymer-grade chiral L-lactic acid and L-lactide from cellulose chiral L-lactic acid produced by taking lignocellulose as a raw material has not found any research paper or patent publication so far. The synthesis of L-lactide from cellulose chiral L-lactic acid produced by using lignocellulose as a raw material mainly has the following obstacles: (1) inhibitors (furfural, 5-hydroxymethylfurfural, vanillin, syringaldehyde and the like) generated after pretreatment of the lignocellulose raw material can seriously inhibit the growth and lactic acid fermentation performance of a fermentation strain, and the residual inhibitors make the purification of polymerization-grade L-lactic acid very difficult; (2) the utilization rate of the cellulose lactic acid fermentation strain on non-glucose monosaccharides (xylose, arabinose, galactose, mannose and the like) which account for 40 percent of the total monosaccharides in lignocellulose is low, so that the yield and the yield of cellulose lactic acid are low, and the separation and the purification of post-polymerization-grade lactic acid are seriously influenced by residual monosaccharides. The above two key obstacles make it difficult to synthesize chiral L-lactic acid from lignocellulosic biomass as a feedstock for L-lactide synthesis.
The information disclosed in this background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.
Disclosure of Invention
In view of the technical problems faced by the synthesis of lactide from cellulose lactic acid, the present invention provides a method for synthesizing L-lactide from chiral L-lactic acid produced by using lignocellulosic biomass as a raw material. The method completely removes inhibitors (furfural, 5-hydroxymethyl furfural, vanillin, syringaldehyde and the like) influencing lactic acid fermentation in the lignocellulose raw material by utilizing a solid biodegradation method, simultaneously uses a fermentation strain Pediococcus acidilactici ZY271 to synchronously metabolize five main fermentable monosaccharides (glucose, xylose, arabinose, mannose and galactose) generated by the lignocellulose raw material, and realizes the fermentation of cellulose L-lactic acid with high concentration and extremely low residual sugar. The difficulty of purifying L-lactic acid to the polymerization grade purity is greatly reduced due to the thorough removal of inhibitors and the extremely low residual sugar content, and the L-lactide is successfully synthesized by using the cellulose chiral L-lactic acid obtained by the method.
The invention aims to provide a method for synthesizing L-lactide by using chiral L-lactic acid produced by using lignocellulose biomass as a raw material, which comprises the following specific steps:
(1) removing inhibitors from the pretreated lignocellulose raw material in a final biodegradation mode, inoculating a biodegradation strain into the pretreated lignocellulose raw material for solid biodegradation for 24-72h, wherein the inoculation amount is 5% -15%, the ventilation amount is 0.1-1.0vvm, and the temperature is kept at 20-37 ℃; the biodegradable strain includes but is not limited to Cladosporium arboreum Amorphotheca resinae ZN1(CGMCC 7452), Paecilomyces variotii FN89(CGMCC 17665);
(2) performing high-solid-content synchronous saccharification and co-fermentation on a lignocellulose raw material to obtain cellulose L-lactic acid with high concentration, high handiness and extremely low residual sugar; the fermentation strain used for lactic acid fermentation includes but is not limited to Pediococcus acidilactici ZY271(CGMCC 13611); the pH neutralizing agent used includes but is not limited to one or more of calcium hydroxide and calcium carbonate.
(3) Removing solid residues, decoloring, crystallizing, washing crystals, carrying out acidolysis and desalting on the cellulose chiral L-lactic acid obtained by fermentation to obtain polymer-grade L-lactic acid;
(4) dehydrating, polycondensing, depolymerizing and purifying the purified cellulose chiral L-lactic acid to obtain L-lactide; the dehydration temperature in the dehydration stage is 100-120 ℃, and the absolute pressure is controlled to be 0.05MPa to 0.1 MPa;
in the polycondensation and depolymerization stages, the temperature is controlled at 200-260 ℃, the absolute pressure is controlled at 0-0.05 MPa, and the used catalyst includes but is not limited to one or more of stannous octoate, zinc oxide and the like.
Further, the step (1) is used for removing inhibitors from the pretreated lignocellulose raw material in a final biodegradation mode: adding biodegradable strains (such as Acremonium chrysogenum Amorphotheca resinae ZN1, Paecilomyces variotii FN89 and the like) into the pretreated lignocellulose raw material in an inoculation amount of 5-15% (w/w), carrying out solid biodegradation in a 15L reactor for 24-72h, wherein the ventilation amount is 0.1-1.0vvm, the temperature is kept at 20-37 ℃, completely converting inhibitors such as furfural, 5-hydroxymethyl furfural, vanillin and syringaldehyde into carbon dioxide and water, and eliminating the influence of the inhibitors on L-lactic acid fermentation and L-lactic acid purification;
the step (2) is to carry out high solid content synchronous saccharification and co-fermentation on the lignocellulose raw material to produce chiral L-lactic acid with high concentration and extremely low residual sugar: carrying out high-solid-content (20-35%) synchronous saccharification and co-fermentation on the pretreated and detoxified lignocellulose raw material for 72-96h in a 5L reactor, wherein the fermentation conditions are as follows: 37-45 ℃, 100-200 rpm and pH 5.0-6.0. The simultaneous saccharification and co-fermentation can convert all fermentable monosaccharides (glucose, xylose, arabinose, mannose and galactose) generated by lignocellulose into high-concentration chiral L-lactic acid, and eliminate the influence of residual monosaccharides on the purification of the L-lactic acid.
In the step (2), the used lignocellulose raw material includes but is not limited to one or more of corn stover, wheat straw, rice straw, bagasse, cotton straw, corn fiber, wood or wood chips, bamboo or bamboo chips.
In the step (2), after the fermentation is finished, all known fermentable monosaccharides including glucose, xylose, arabinose, mannose and galactose of the lignocellulose source are converted into chiral L-lactic acid, the concentration of glucose residual sugar is not more than 0.2g/L, the concentration of xylose residual sugar is not more than 0.5g/L, and the concentration of total reducing sugar residual sugar is not more than 1.0 g/L.
In the step (2), the pretreated and detoxified lignocellulose raw material is subjected to high-solid-content synchronous saccharification and co-fermentation to obtain L-lactic acid with an optical purity of not less than 99.89% and an L-lactic acid content of not less than 120g/L, wherein the fermentation mode includes but is not limited to one or more of fractional saccharification and fermentation, synchronous saccharification and co-fermentation.
And (3) removing solid residues, decoloring, crystallizing, washing crystals, carrying out acidolysis and desalting on the chiral L-lactic acid obtained by fermentation to obtain polymer-grade L-lactic acid: removing lignocellulose biomass residues from L-lactic acid fermentation mash obtained by 72-96h of synchronous saccharification and co-fermentation in one or more modes of centrifugation, filter pressing, suction filtration and the like, adding 0.3-15% of active carbon or diatomite into the cellulose chiral L-lactic acid fermentation liquor, and decoloring for 0.5-2.5h in a water bath shaking table at 50-90 ℃; concentrating the obtained basically colorless L-lactic acid fermentation liquid to 100-200g/L, and then crystallizing at the temperature of minus 20 ℃ to 37 ℃; washing calcium lactate crystals with water or absolute ethyl alcohol to remove impurities attached to the surface of calcium lactate; then, heating and dissolving the calcium lactate solid, and carrying out acidolysis on the calcium lactate solution by using a sulfuric acid solution or cation exchange resin until the pH value is 0-3 to obtain crude cellulose L-lactic acid; desalting and refining the obtained crude cellulose L-lactic acid by one or more of ion exchange method, extraction method, electrodialysis method, etc. to obtain cellulose L-lactic acid with purity of not less than 90%. The mass purity of the cellulose chiral L-lactic acid finally obtained in the step (3) is not less than 98 percent
And (4) dehydrating, polycondensing, depolymerizing and purifying the purified L-lactic acid to synthesize L-lactide: dehydrating the obtained high-purity and polymer-grade cellulose chiral L-lactic acid at the temperature of 120 ℃ and the absolute pressure of 0.05-0.1 MPa, adding a catalyst into a reaction kettle, controlling the temperature at 260 ℃ and the absolute pressure at 0-0.05 MPa, and carrying out polycondensation and depolymerization reaction to obtain crude L-lactide; refining the crude L-lactide by adopting one or more of recrystallization method, membrane separation method, sublimation method and rectification method to obtain the high-purity L-lactide.
The biodegradation method adopted in the invention removes the influence of the inhibitor on L-lactic acid fermentation and L-lactic acid purity, the adopted high solid content total sugar co-fermentation method obtains cellulose chiral L-lactic acid with high concentration and extremely low residual sugar, and the difficulty of purifying the L-lactic acid to the polymerization grade purity is greatly reduced due to the complete removal of the inhibitor and the extremely low residual sugar content. The cellulose chiral L-lactic acid obtained by the method is subjected to the steps of purification, polycondensation, depolymerization and the like, so that the L-lactide is synthesized from the lignocellulose raw material.
Compared with the prior art, the invention has the following positive effects:
the inhibitor biodegradation method can completely remove inhibitors (furfural, 5-hydroxymethyl furfural, vanillin, syringaldehyde and the like) which influence the fermentation of cellulose lactic acid, and simultaneously, glucose, xylose, arabinose, mannose and galactose which are derived from lignocellulose and are synchronously co-fermented by the strain Pediococcus acidilactici ZY271, so that the fermentation of cellulose L-lactic acid with high concentration, extremely low residual sugar and high handiness is realized. The complete removal of the inhibitor and the extremely low residual sugar content greatly reduce the influence of the inhibitor on the separation, purification and polymerization of the lactic acid, reduce the operation difficulty of the separation and purification of the lactic acid and have obvious economic benefit. The invention improves the existing separation and purification method of starch lactic acid, and is very beneficial to the acceptance, popularization and application of the market.
1. Classification name: amorphotheca resinae ZN1
The name of the depository: china general microbiological culture Collection center (CGMCC)
The address of the depository: xilu No.1 Hospital No. 3 of Beijing market facing Yang district
The preservation number is: CGMCC NO.7452
The preservation date is as follows: 2013.04.12
2. Classification name: paecilomyces variotii FN89
The name of the depository: china general microbiological culture Collection center (CGMCC)
The address of the depository: xilu No.1 Hospital No. 3 of Beijing market facing Yang district
The preservation number is: CGMCC NO.17665
The preservation date is as follows: 2019.05.08
3. Classification name: pediococcus acidilactici ZY271
The name of the depository: china general microbiological culture Collection center (CGMCC)
The address of the depository: xilu No.1 Hospital No. 3 of Beijing market facing Yang district
The preservation number is: CGMCC NO.13611
The preservation date is as follows: 2017.01.13
Drawings
FIG. 1: the wheat straw is subjected to synchronous saccharification and co-fermentation to produce chiral L-lactic acid.
FIG. 2: the corn straws are subjected to synchronous saccharification and co-fermentation to produce the chiral L-lactic acid.
FIG. 3: separating and purifying the chiral L-lactic acid of the cellulose.
FIG. 4: polymerizing and purifying the cellulose chiral L-lactic acid.
FIG. 5: l-lactide nuclear magnetic resonance hydrogen spectrogram of lignocellulose source.
FIG. 6: DSC profile of L-lactide of lignocellulosic origin.
FIG. 7: a lignocellulose derived L-lactide Fourier transform infrared spectrogram.
FIG. 8: a mass spectrum of L-lactide from lignocellulose.
Detailed Description
The following examples are intended to describe the present invention in further detail, but the present invention is not limited to the scope defined by the examples.
Example 1: method I for synthesizing L-lactide by using chiral L-lactic acid produced by using wheat straws as raw material, and finally biodegrading pretreated wheat straws to remove inhibitors
After wheat straws are pretreated by dry dilute acid, the pH value of the materials is adjusted to 5 by using 20% (w/w) of calcium hydroxide or calcium carbonate, 10% (w/w) of Cladosporium arboreum Amorphotheca resinae ZN1 seeds are inoculated, 3 kg of uniformly mixed wheat straws and Cladosporium arboreum seeds are put into a 15L bioreactor, and solid-state biodegradation is carried out under the conditions that the ventilation volume is 0.5vvm and the temperature is 28 ℃. In the biodegradation process, the content of main inhibitors in the material is measured by using a high performance liquid chromatography, and furfural, 5-hydroxymethyl furfural, vanillin and syringaldehyde are completely consumed in 36 hours.
Secondly, fermenting the cellulose L-lactic acid by utilizing the wheat straws after pretreatment and detoxification of high solid content
The method comprises the following steps of performing synchronous saccharification and co-fermentation on pretreated and biodegradable wheat straws with solid content of 30% (w/w): firstly, wheat straws are added into a 5L single-spiral belt stirring bioreactor containing a certain amount of water and cellulase of 4mg protein/g straw (dry basis) in batches, and pre-saccharification is carried out for 6 hours at 50 ℃ and 150 rpm; after the temperature is reduced to 42 ℃, inoculating the cultured Pediococcus acidilactici ZY271 seed solution into a fermentation tank according to the inoculation amount of 10% (v/v), simultaneously adding nutrient salts (10g/L peptone, 10g/L yeast extract, 2g/L diammonium citrate and 0.25g/L manganese sulfate monohydrate), and carrying out synchronous saccharification and co-fermentation at 42 ℃ and 150 rpm. During the fermentation, the fermentation pH was maintained at 5.5 with 25% (w/w) calcium hydroxide as neutralizing agent. As shown in figure 1, after 96h of synchronous saccharification and co-fermentation, monosaccharide derived from lignocellulose is completely converted into high-concentration chiral L-lactic acid, and through detection, the concentration of the finally obtained L-lactic acid reaches 136.6g/L, and the optical purity reaches 99.89%, wherein the residual glucose, xylose, arabinose + mannose and galactose in the fermentation liquor are only 0.17g/L, 0.43 g/L, 0g/L and 0.14g/L respectively.
Thirdly, separation and purification of the cellulose chiral L-lactic acid
After 96h of simultaneous saccharification and co-fermentation, the cellulose L-lactic acid fermentation broth is centrifuged at high speed (10,000 rpm,10min) to separate the cellulose lactic acid fermentation broth from the lignocellulosic biomass residue. The obtained calcium lactate fermentation liquor is decolorized by 10% (w/v) of activated carbon at 60 ℃ for 1.5h, and then the concentration of the calcium lactate fermentation liquor is concentrated to 200g/L by using a rotary evaporator, and then the calcium lactate fermentation liquor is placed in a refrigerator at 4 ℃ for overnight crystallization. Washing the calcium lactate crystals with ultrapure water at 0 ℃ to remove impurities attached to the surfaces of the calcium lactate crystals, and heating to melt the calcium lactate crystals into a calcium lactate solution. Adding 50% (v/v) sulfuric acid into the calcium lactate solution to replace the calcium lactate into lactic acid, forming calcium sulfate precipitate, and performing suction filtration through a Buchner funnel to obtain the crude cellulose chiral L-lactic acid. Pumping the obtained crude cellulose chiral L-lactic acid into a chromatographic column filled with cation exchange resin by using a peristaltic pump to remove metal ions such as iron, sodium and the like contained in the wood cellulose biomass, and collecting effluent liquid which is high-purity cellulose chiral L-lactic acid. FIG. 3 is a picture of the steps of separating and purifying the chiral L-lactic acid of lignocellulose according to the preferred separation and purification method.
The purity of the purified cellulose L-lactic acid was analyzed by High Performance Liquid Chromatography (HPLC), and the contents of protein, total phenol and total reducing sugar in the purified cellulose L-lactic acid were measured by Coomassie Brilliant blue G-250 method, Folin phenol reagent method and DNS method, respectively, and the results are shown in Table 1, where 1G of purified cellulose L-lactic acid contained 8.80X 10-4g acetic acid, 4.52X 10-8g protein, 8.00X 10-3g Total reducing sugar, Metal ion (Ca)2+、 Fe2+、Fe3+、Na+) The content is less than 1.00 multiplied by 10-5And g, total phenols and inhibitors are not detected, and the purity of the cellulose chiral L-lactic acid is not lower than 99.10 percent according to calculation.
TABLE 1 analysis of the purity of the chiral L-lactic acid of cellulose the quality of the substances contained in 1g of cellulose L-lactic acid after separation and purification
Analysis of L-lactic acid purity without Water
Fourthly, polymerization and characterization analysis of purified cellulose chiral L-lactic acid
Dehydrating the high-purity and polymer-grade cellulose chiral L-lactic acid obtained after purification at the temperature of 100-; the method adopts a recrystallization method to refine the crude L-lactide to obtain the high-purity L-lactide, and realizes the synthesis of the L-lactide by using the cellulose chiral L-lactic acid produced by using the lignocellulose biomass as the raw material for the first time. FIG. 4 is a picture of L-lactide obtained by polymerization of cellulose chiral L-lactic acid. FIG. 5 is a structural analysis characterization of lignocellulose-derived L-lactide by nuclear magnetic resonance apparatus (Bruker, Ascend 600, Germany), showing that the structure of L-lactide synthesized using lignocellulose-derived L-lactic acid completely conforms to the nuclear magnetic hydrogen spectrogram characteristics of known L-lactide; the melting point of lignocellulose-derived L-lactide was determined to be 96.02 ℃ (fig. 6) by differential scanning calorimetry (Perkinelmer, DSC8500, USA) with a temperature rise rate of 10 ℃/min under nitrogen protection, consistent with literature reports.
Example 2: method I for synthesizing L-lactide by using chiral L-lactic acid produced by using corn straws as raw material and for finally biodegrading pretreated corn straws to remove inhibitors
After the corn stalks are pretreated by dry dilute acid, the pH value of the material is adjusted to 4.8 by using 25 percent (w/w) of calcium hydroxide or calcium carbonate, the cultured Paecilomyces variotii FN89(CGMCC17665) seeds are inoculated into the material according to the proportion of 20 percent (w/w), the mixture is evenly mixed, 4kg of the mixture of the corn stalks and the cladosporium resinatum seeds is filled into a plastic box, and the static biodegradation is carried out in a constant temperature incubator (37 ℃). In the biodegradation process, the content of main inhibitors in the material is measured by using a high performance liquid chromatography, and furfural, 5-hydroxymethyl furfural, vanillin and syringaldehyde are completely consumed in 48 hours by detection.
Secondly, carrying out fermentation of cellulose L-lactic acid by utilizing 30% (w/w) solid content of pretreated and detoxified corn straw
The method comprises the following steps of performing synchronous saccharification and co-fermentation by using 30% (w/w) of corn straws with solid content after pretreatment and biodegradation, and specifically comprises the following steps: firstly, adding corn straws into a 5L single-spiral belt stirring bioreactor containing a certain amount of water in batches, adding cellulase of 5mg protein/g straw (dry basis), and carrying out pre-saccharification for 6h at 50 ℃ and 150 rpm; after the pre-saccharification is finished, inoculating the cultured Pediococcus acidilactici ZY271 seed solution into a fermentation tank according to the inoculation amount of 10% (v/v), and simultaneously adding nutrient salts (10g/L peptone, 10g/L yeast extract, 2g/L diammonium hydrogen citrate, and 0.25g/L manganese sulfate monohydrate). During the fermentation, the temperature was maintained at 42 ℃ and the stirring speed was 150rpm, 25% (w/w) calcium carbonate was used as neutralizing agent to maintain the fermentation pH at 5.5. As shown in FIG. 2, after 96h of simultaneous saccharification and co-fermentation, the residual glucose, xylose, arabinose + mannose and galactose in the fermentation broth are only 0.18, 0.45, 0 and 0.32g/L respectively. The fermentable monosaccharide in the corn straw is completely converted into high-concentration L-lactic acid, the L-lactic acid finally reaches 130.17g/L, and the optical purity of the L-lactic acid reaches 99.89%.
Thirdly, separation and purification of the cellulose chiral L-lactic acid
After 96h of synchronous saccharification and co-fermentation, carrying out suction filtration on the cellulose L-lactic acid fermentation liquor, so that the cellulose L-lactic acid fermentation liquor is separated from the lignocellulose biomass residues. Decolorizing the obtained calcium lactate fermentation liquor at 70 ℃ for 1h by using 12% (w/v) activated carbon, concentrating the concentration of the calcium lactate fermentation liquor to 200g/L by using a rotary evaporator, and then placing the calcium lactate fermentation liquor in a refrigerator at 20 ℃ below zero for crystallization. Washing the calcium lactate crystals with absolute ethyl alcohol to remove impurities attached to the surfaces of the calcium lactate crystals, and heating to melt the calcium lactate crystals into a calcium lactate solution. Pumping the obtained calcium lactate solution with high purity into a chromatographic column filled with cation exchange resin by using a peristaltic pump, acidifying the calcium lactate solution, removing metal ions such as iron, sodium and the like contained in the wood cellulose biomass, repeating for 2-3 times, and collecting effluent liquid which is high-purity cellulose chiral L-lactic acid.
The purity of the refined cellulose L-lactic acid was analyzed by High Performance Liquid Chromatography (HPLC), and the contents of protein, total phenol and total reducing sugar in the refined cellulose L-lactic acid were measured by Coomassie Brilliant blue G-250 method, Folin phenol reagent method and DNS method, respectively, and the results were substantially the same as those in Table 1.
Fourthly, polymerization and characterization analysis of purified cellulose chiral L-lactic acid
Dehydrating the high-purity and polymer-grade cellulose chiral L-lactic acid obtained after purification at the temperature of 100 ℃ and 120 ℃ under the absolute pressure of 0.05-0.1 MPa, adding a catalyst into a reaction kettle, controlling the absolute pressure of 0-0.05 MPa, rapidly heating to 200 ℃ and 260 ℃, and carrying out polycondensation and depolymerization reactions to obtain crude L-lactide; the method adopts a recrystallization method to refine the crude L-lactide to obtain the high-purity L-lactide, and realizes the synthesis of the L-lactide by using the cellulose chiral L-lactic acid produced by using the lignocellulose biomass as the raw material for the first time. FIG. 7 is a structural analysis and characterization of lignocellulose-derived L-lactide by Fourier transform infrared spectrometer (Nicolet,6700, USA), showing that the structure of L-lactide synthesized using lignocellulose-derived lactic acid completely conforms to the infrared spectrogram characteristics of known L-lactide; FIG. 8 is a graph showing that molecular weight of lignocellulose-derived L-lactide was measured by ESI-high resolution time-of-flight mass spectrometer (Waters, XEVO G2 TOF, USA), and the molecular weight was 199.0587 after sodium addition treatment using methanol as a solvent, which is completely consistent with the results of molecular weight measurement of purchased L-lactide; in addition, a certain mass of L-lactide derived from lignocellulose was weighed, and the C, H element content thereof was measured by an element analyzer (ELEMENTAR, Vario EL cube, germany), and the results showed that: the cellulose L-lactide contains 49.71 +/-0.16% of C element and 5.67 +/-0.33% of H element, and basically conforms to theoretical values (C: 50.00%, H: 5.60%).
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, several modifications and decorations can be made without departing from the concept of the present invention, and these modifications and decorations should also be regarded as being within the protection scope of the present invention.
Claims (11)
1. A method for synthesizing L-lactide by using chiral L-lactic acid produced by using lignocellulose biomass as a raw material comprises the following specific steps:
(1) removing inhibitors from the pretreated lignocellulose raw material in a final biodegradation mode, inoculating a biodegradation strain into the pretreated lignocellulose raw material for solid biodegradation for 24-72h, wherein the inoculation amount is 5% -15%, the ventilation amount is 0.1-1.0vvm, and the temperature is kept at 20-37 ℃; the biodegradable strain includes but is not limited to Cladosporium arboreum Amorphotheca resinae ZN1(CGMCC 7452), Paecilomyces variotii FN89(CGMCC 17665);
(2) performing high-solid-content synchronous saccharification and co-fermentation on a lignocellulose raw material to obtain cellulose L-lactic acid with high concentration, high handiness and extremely low residual sugar; fermentation strains used for lactic acid fermentation include, but are not limited to Pediococcus acidilactici ZY271(CGMCC 13611); the pH neutralizing agent used includes but is not limited to one or more of calcium hydroxide and calcium carbonate.
(3) Removing solid residues, decoloring, crystallizing, washing crystals, carrying out acidolysis and desalting on the cellulose chiral L-lactic acid obtained by fermentation to obtain polymer-grade L-lactic acid;
(4) dehydrating, polycondensing, depolymerizing and purifying the purified cellulose chiral L-lactic acid to obtain L-lactide; the dehydration temperature in the dehydration stage is 100-120 ℃, and the absolute pressure is controlled to be 0.05MPa to 0.1 MPa; in the polycondensation and depolymerization stages, the temperature is controlled at 200-260 ℃, the absolute pressure is controlled at 0-0.05 MPa, and the used catalyst includes but is not limited to one or more of stannous octoate, zinc oxide and the like.
2. The method for synthesizing L-lactide from chiral L-lactic acid produced from lignocellulosic biomass as claimed in claim 1, wherein in step (1), the biodegradation strain completely converts inhibitors such as furfural, 5-hydroxymethylfurfural, vanillin and syringaldehyde into carbon dioxide and water.
3. The method for synthesizing L-lactide from chiral L-lactic acid produced from lignocellulose biomass as raw material according to claim 1, wherein in the step (2), the lignocellulose raw material used includes but is not limited to one or more of corn stover, wheat straw, rice straw, bagasse, cotton stover, corn fiber, wood or wood dust, bamboo or bamboo dust.
4. The method for synthesizing L-lactide from chiral L-lactic acid produced from lignocellulose biomass as a raw material according to claim 1, wherein in the step (2), the pretreated and detoxified lignocellulose raw material is used for high-solid content synchronous saccharification and co-fermentation to obtain L-lactic acid with a concentration of not less than 120g/L and an optical purity of not less than 99.89%, and the fermentation mode includes but is not limited to one or more of fractional saccharification and fermentation, synchronous saccharification and co-fermentation.
5. The method for synthesizing L-lactide by using chiral L-lactic acid produced by using lignocellulose biomass as a raw material according to claim 1, wherein in the step (2), the solid content of the lignocellulose raw material used for lactic acid fermentation is 20-35%, all known fermentable monosaccharides such as glucose, xylose, arabinose, mannose and galactose from lignocellulose are converted into the chiral L-lactic acid after the fermentation is finished, the concentration of glucose residual sugar is not more than 0.2g/L, the concentration of xylose residual sugar is not more than 0.5g/L, and the concentration of total reducing sugar residual sugar is not more than 1.0 g/L.
6. The method for synthesizing L-lactide from chiral L-lactic acid produced from lignocellulose biomass as raw material according to claim 1, wherein the solid biomass residue removal mode in step (3) includes but is not limited to one or more of centrifugation, pressure filtration, suction filtration and the like.
7. The method for synthesizing L-lactide from chiral L-lactic acid produced from lignocellulosic biomass as raw material according to claim 1, wherein in the cellulose lactic acid separation and purification method in step (3), the material used for decolorization includes but is not limited to one or more of activated carbon, diatomite, etc.; the addition amount of the substance for decolorization is 0.3-15%, the temperature for decolorization is 50-90 ℃, and the time for decolorization is 0.5-2.5 h.
8. The method for synthesizing L-lactide from chiral L-lactic acid produced from lignocellulosic biomass as claimed in claim 1, wherein in the step (3), the crystalline concentration of the fermentation broth of cellulose chiral L-lactic acid is 100-200g/L, and the crystallization temperature is-20 to 37 ℃.
9. The method for synthesizing L-lactide from chiral L-lactic acid produced from lignocellulosic biomass as claimed in claim 1, wherein in the step (3), the medium for acid hydrolysis includes but is not limited to one or more of sulfuric acid, ion exchange resin, etc., and the pH after acid hydrolysis is controlled at 0-3.
10. The method for synthesizing L-lactide from chiral L-lactic acid produced from lignocellulose biomass as raw material according to claim 1, wherein in the step (3), the desalting method includes but is not limited to one or more of ion exchange method, extraction method, electrodialysis method and the like.
11. The method for synthesizing L-lactide from chiral L-lactic acid produced from lignocellulose biomass as recited in claim 1, wherein in the method for purifying L-lactide after cellulose L-lactic acid polymerization described in step (4), the purification method includes but is not limited to one or more of recrystallization, membrane separation, sublimation and distillation.
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