CN113214497A - Method for recovering lignin from enzymolysis residues of lignocellulose - Google Patents
Method for recovering lignin from enzymolysis residues of lignocellulose Download PDFInfo
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Classifications
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08H—DERIVATIVES OF NATURAL MACROMOLECULAR COMPOUNDS
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Abstract
The invention relates to the technical field of biochemical engineering, and discloses a method for recovering lignin from enzymolysis residues of lignocellulose, which comprises the following steps: s1, carrying out anaerobic digestion on the enzymolysis residues to obtain digestion residues; s2, performing reflux extraction on the digestion residues to obtain a mixture; s3, sequentially centrifuging, filtering and separating the mixture to obtain extract liquor and extract residues; s4, sequentially concentrating, precipitating, centrifuging and filtering and separating the extract liquor to obtain solid lignin; according to the invention, a composite process of anaerobic digestion and reflux extraction is constructed, firstly, lignin is enriched from enzymolysis residues by adopting the biological method of anaerobic digestion, then the reflux extraction is utilized to purify the lignin from the digestion residues and remove impurities such as protein, ash and the like, and the effect of separating the high-purity lignin with a natural structure from the enzymolysis residues of lignocellulose is achieved.
Description
Technical Field
The invention relates to the technical field of biochemical engineering, in particular to a method for recovering lignin from enzymolysis residues of lignocellulose.
Background
The lignocellulose is biologically refined and converted into clean energy and chemical products, so that the application prospect is good, the development of the industry is restricted by high production cost and environmental problems generated in each link of biological refining, and the problem that how to make biological refining more economical, feasible and environment-friendly is always puzzling the head of experts and the like.
Among the reasons for the high cost of the biorefinery industry, the first time is the accumulated enzymolysis residues accounting for about 30% of the total substrate weight in the enzymatic hydrolysis process, and the problems of low utilization rate of sugar, resource waste, environmental pollution and the like caused by the accumulated enzymolysis residues. A large amount of lignin is contained in the enzymolysis residues, and the lignin is a natural aromatic compound, so that the method has a far-reaching high-value utilization prospect, and the cost of the biorefinery industry can be effectively reduced by reasonably utilizing the lignin after the lignin is separated. Unfortunately, there is currently no systematic and effective separation and utilization of the enzymatic residues, which are generally regarded as by-products and inhibitors of the enzymatic hydrolysis process and discarded. Firstly, for biorefineries, an effective and reasonable separation method for the lignin is lacked at present, so that excessive enzymolysis residue precipitation accumulation can obviously influence the sugar yield and the hydrolysis efficiency in the enzymatic hydrolysis process; secondly, the key of high-value utilization of the lignin is to obtain the lignin which has high purity, does not contain binding sugar, retains natural functional groups and is low in modification, and the enzymolysis residues contain a large amount of difficultly-degradable sugar, protein, fat and ash, so that the lignin is difficult to meet the requirement of high-value utilization; moreover, in the lignin separation process, the natural active structure of lignin is easily destroyed, so a large amount of enzymolysis residues are only used for simple incineration heat generation by a biorefinery, which undoubtedly causes huge waste of resources. Therefore, if we can separate high-quality lignin from the enzymolysis residues while further improving the utilization rate of sugar in the enzymolysis residues, and use the lignin for producing high-value products, the economic pressure and corresponding environmental problems of a biorefinery can be relieved undoubtedly, and the problem of restricting the development of the biorefinery industry can be solved fundamentally.
At present, the traditional methods for separating lignin comprise acid separation, alkaline separation, organic solvent extraction and the like, but the separation methods all have some defects which are difficult to overcome:
1. the acid method separation is one of the most widely used lignin separation modes in industrial utilization at present, the extraction efficiency is high, but the acidolysis process inevitably leads to lignin modification, the chemical properties of the lignin are influenced after the lignin modification, and the high-value utilization requirement is difficult to meet; in addition, hydrolysis liquid needs to be neutralized for extracting the acid lignin, and the acid liquid cannot be recovered, so that the cost is high;
2. the alkaline method is mild in separation, relatively small in modification on lignin, but capable of dissolving a large amount of impurities, and influencing the purity of a substrate to hardly meet the requirement of high-value utilization of the substrate; in addition, the inevitable steps of alkali liquor neutralization, extra washing and extraction and the like greatly increase the extraction cost of the alkali lignin;
3. the organic solvent extraction method has small modification on lignin, can retain most of natural active structures of the lignin, but has low yield and purity of the lignin, and the organic solvent is generally expensive and has certain toxicity.
The method for treating the corn straw enzymatic hydrolysis residue by anaerobic digestion is disclosed in Zhao Kung, Gao Xionghui, wishing its li and Tang Xiao Yu, the polysaccharide content in the digestion residue is obviously reduced, the total amount of lignin is basically unchanged, and the structure of the lignin is slightly different before and after the anaerobic digestion, so that the structure of the lignin can be well reserved. However, the introduction of inoculum during anaerobic processes leads to an increase in digestion residue lignin ash and it remains difficult to meet high value substrate utilization requirements.
In view of the above, there is a need for a method for separating lignin with high purity and natural structure from enzymolysis residues of lignocellulose.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provide a method for recovering lignin from lignocellulose enzymolysis residues, so as to at least achieve the effect of separating the lignin with high purity and a natural structure from the lignocellulose enzymolysis residues.
The purpose of the invention is realized by the following technical scheme: the method for recovering lignin from the enzymolysis residues of lignocellulose comprises the following steps:
s1, carrying out anaerobic digestion on the enzymolysis residues to obtain digestion residues;
s2, performing reflux extraction on the digestion residues to obtain a mixture;
s3, sequentially centrifuging, filtering and separating the mixture to obtain extract liquor and extract residues;
and S4, sequentially concentrating, precipitating, centrifuging and filtering and separating the extract liquor to obtain the solid lignin.
In certain embodiments, the extractant employed in the reflux extraction in S2 is acetic acid.
In certain embodiments, the extractant employed in the reflux extraction in S2 is acetic acid and water.
In certain embodiments, the volume ratio of acetic acid to water is 1 to 2: 1.
In certain embodiments, the volume ratio of acetic acid to water is 2: 1.
In certain embodiments, in S2, the extractive agents used for the reflux extraction are ethanol and water.
In certain embodiments, the volume ratio of ethanol to water is 0-2: 1.
In certain embodiments, the volume ratio of ethanol to water is 2: 1.
In some embodiments, S2 further comprises, before the reflux extraction, a step of mixing the digestion residue with deionized water, and then sequentially performing centrifugal washing, drying, grinding and sieving to obtain the extract.
In certain embodiments, the weight to volume ratio of the extract to the extractant is ≧ 1:20(g: mL).
In certain embodiments, the spin rate of the centrifugal water wash is 12000rpm or more and the time is 10min or more.
In some embodiments, in S2, the temperature of the reflux extraction is 85 to 110 ℃, and the time of the reflux extraction is 24 hours.
In some embodiments, in S1, the anaerobic digestion is to inoculate the enzymolysis residue, adjust the pH of the system to 6.8-7.5, and perform anaerobic digestion under the anaerobic condition at the temperature of 30-40 ℃ until no gas is produced, thereby obtaining the digestion residue.
In certain embodiments, the inoculum is kitchen waste anaerobically digested sludge.
In certain embodiments, the mass ratio of the inoculum to the enzymolysis residue is 1-2: 1.
In certain embodiments, in S3, the rotation speed of the centrifugation is more than or equal to 10000rpm, and the time of the centrifugation is more than or equal to 10 min.
In certain embodiments, S3, further comprising the step of sequentially subjecting the raffinate to centrifugal water washing, drying, and grinding.
In some embodiments, in S3, the rotation speed of the centrifugal water washing is more than or equal to 10000rpm, and the time of the centrifugal water washing is more than or equal to 10 min.
In certain embodiments, in S4, the step of concentrating and precipitating is: and concentrating the extract liquid to 30-60 mL, and adding plasma water with the same volume to precipitate lignin.
In certain embodiments, in S4, the rotation speed of centrifugation is 12000rpm or more, and the time of centrifugation is 20min or more.
In certain embodiments, the enzymatic residue is a residue of lignocellulosic material that has been enzymatically hydrolyzed and comprises lignin, glucan, xylan and ash.
In certain embodiments, the lignocellulose comprises one or more of crop straw, wood, and energy plants.
It is worth noting that the present invention enriches lignin from enzymatic digestion residue by the biological method of anaerobic digestion, and then purifies lignin from the digestion residue by solvent extraction. The enzymolysis residues can convert residual glycan into biogas in the anaerobic digestion process, so that lignin is enriched and clean energy is produced, and the utilization efficiency of raw materials is improved; meanwhile, the anaerobic digestion biological method has mild reaction conditions, and is beneficial to retaining the natural structure of lignin; on the basis, the reflux extraction can effectively remove impurities such as protein, ash and the like, thereby obtaining the high-purity lignin.
It should be understood that, although the prior art has been studied on the extraction of lignin from enzymatic residues by means of organic solvent extraction, it is fundamentally different from the method of the invention:
in the prior art, an organic solvent is adopted to directly extract enzymolysis residues, and lignin becomes relatively small molecules to be dissolved in a polar solvent by breaking alpha-aromatic ether bonds and beta-aromatic ether bonds in part of lignin, so that the aim of separating the lignin from the enzymolysis residues is fulfilled; the method adopts the organic solvent to extract the digestion residues and removes impurities such as protein, ash and the like, thereby achieving the purpose of separating high-purity lignin with a natural structure from the digestion residues; in Zhao Kung, Gao Xionghui, Zhu Li, Tang Xiao Yu, it has been clearly shown that the introduction of inoculum during anaerobic treatment leads to an increase in lignin ash content in digestion residues. Thus, it can be seen that:
1) the extraction substrate in the prior art is enzymolysis residue; the extraction substrate in the invention is digestion residue, and compared with enzymolysis residue, the content of glycan is obviously reduced, the content of ash is obviously increased, and the components are more complex;
2) the extraction in the prior art is only to break a part of alpha-aryl ether bonds and beta-aryl ether bonds in the lignin, so that the lignin becomes relatively small molecules to be dissolved in a solvent; the extraction in the present invention is to remove impurities such as protein and ash and to separate lignin having a high purity and a natural structure by retaining the natural structure of lignin.
Therefore, the prior art is completely different from the present invention in terms of extraction substrate and extraction purpose, and the prior art does not have any reference to the present invention.
The invention has the beneficial effects that: the composite process of anaerobic digestion and reflux extraction constructed by the invention can effectively separate lignin from the enzymolysis residues, has mild conditions, can effectively retain the natural structure and the main functional groups of the lignin, and simultaneously obtains a high-purity lignin product.
Drawings
FIG. 1 is a TGA analysis of lignin and lignin in digestion residue of examples 2-4 in section 3 of the test results;
FIG. 2 is a 2D-HSQC NMR spectra of lignin of examples 2 and 4 and lignin in digestion residue in Experimental Effect section 4 (where a is lignin in digestion residue, b is lignin of example 4, and c is lignin of example 2);
FIG. 3 shows the results of the lignin in part 4 of the test1H-13C signal attribution table.
Detailed Description
The technical solutions of the present invention are further described in detail below with reference to the accompanying drawings, but the scope of the present invention is not limited to the following.
Example 1
A method for carrying out anaerobic digestion on lignocellulose enzymolysis residues comprises the following specific steps:
219.38g of kitchen waste anaerobic digestion sludge concentrated by a sieve of 80 meshes is used as an inoculum and inoculated into 100g of enzymolysis residues obtained by enzymatic hydrolysis of lignocellulose, the pH value of the system is adjusted to 7.2, anaerobic digestion is carried out under the anaerobic condition of 35 ℃, an anaerobic bottle with the total volume of 610mL is adopted for fermentation, the fermentation volume is 250mL, and 293.99 +/-5.38 g of digestion residues are obtained after gas production is completely stopped.
Wherein, the inoculum comprises: 8.44 +/-0.08 g of glucan, 4.18 +/-0.09 g of xylan, 64.68 +/-0.44 g of lignin and 4.44 +/-0.1 g of ash; the enzymolysis residue comprises: 6.47 plus or minus 0.04g of glucan, 4.67 plus or minus 0.04g of xylan, 50.54 plus or minus 0.94g of lignin and 68.35 plus or minus 0.11g of ash; the digestion residues include: 7.27 +/-0.63 g of glucan, 6.35 +/-0.52 g of xylan, 116.36 +/-1.80 g of lignin and 63.15 +/-0.14 g of ash.
Example 2
A method for recovering lignin from lignocellulosic digestate comprising the steps of:
s1, carrying out centrifugal water washing on the digestion residue obtained in the example 1 and deionized water according to the proportion of 1:10(g: mL) at 12000rpm to remove a small amount of ash, drying overnight at 80 ℃, and then grinding and sieving by a sieve of 80 meshes to obtain an extract to be extracted;
s2, mixing the extract to be extracted with acetic acid according to the proportion of acetic acid to be extracted to 1:20(g: mL), adding the mixture into a double-neck flask, adding a magnetic stirring rotor, carrying out condensation reflux extraction heated by an oil bath at 105 ℃ under the state of starting magnetic stirring, and taking out the mixture after condensation reflux is carried out for 24 hours;
wherein, the heater used for the condensation reflux extraction is a DF-101S heat collection type magnetic stirring heater (produced by Yineng laboratory instruments and factories in Changzhou city) provided with a temperature probe, the heating medium is methylene silicon oil, circulating cold water is used as a coolant, the temperature of the oil bath is monitored by the temperature probe, and a thermometer is inserted into the flask to monitor the temperature of the acetic acid solvent;
s3, centrifuging the mixture at 10000rpm for 10min, filtering and separating, and performing solid-liquid separation to obtain an extraction liquid and extraction residue;
s4, carrying out centrifugal washing on the extraction residue and deionized water according to the mass ratio of 1:2 at 10000rpm for 10min, and drying and grinding for later use;
s5, concentrating the extract at 60 ℃ under reduced pressure to 30mL by using a rotary evaporator, adding equal volume of deionized water to precipitate lignin, centrifuging the mixed solution at 12000rpm for 20min, and carrying out solid-liquid separation to obtain solid lignin (the yield is 35.2%).
Example 3
A method for recovering lignin from lignocellulosic digestate comprising the steps of:
s1, carrying out centrifugal water washing on the digestion residue obtained in the example 1 and deionized water according to the proportion of 1:10(g: mL) at 12000rpm to remove a small amount of ash, drying overnight at 80 ℃, and then grinding and sieving by a sieve of 80 meshes to obtain an extract to be extracted;
s2, adopting acetic acid and water with a volume ratio of 2:1 as an extracting agent, mixing the extract to be extracted with the extracting agent according to the proportion of the extract to be extracted to the extracting agent of 1:20(g: mL), adding the mixture into a double-neck flask, adding a magnetic stirring rotor, carrying out condensation reflux extraction heated by an oil bath at 105 ℃ under the state of starting magnetic stirring, and taking out the mixture after condensation reflux is carried out for 24 hours;
wherein, the heater used for the condensation reflux extraction is a DF-101S heat collection type magnetic stirring heater (produced by Yineng laboratory instruments and factories in Changzhou city) provided with a temperature probe, the heating medium is methylene silicon oil, circulating cold water is used as a coolant, the temperature of the oil bath is monitored by the temperature probe, and a thermometer is inserted into the flask to monitor the temperature of the acetic acid solvent;
s3, centrifuging the mixture at 10000rpm for 10min, filtering and separating, and performing solid-liquid separation to obtain an extraction liquid and extraction residue;
s4, carrying out centrifugal washing on the extraction residue and deionized water according to the mass ratio of 1:2 at 10000rpm for 10min, and drying and grinding for later use;
s5, concentrating the extract at 60 ℃ under reduced pressure to 45mL by using a rotary evaporator, adding equal volume of deionized water to precipitate lignin, centrifuging the mixed solution at 12000rpm for 20min, and carrying out solid-liquid separation to obtain solid lignin (the yield is 37.37%).
Example 4
A method for recovering lignin from enzymolysis residues of lignocellulose comprises the following steps:
s1, carrying out centrifugal water washing on the digestion residue obtained in the example 1 and deionized water according to the proportion of 1:10(g: mL) at 12000rpm to remove a small amount of ash, drying overnight at 80 ℃, and then grinding and sieving by a sieve of 80 meshes to obtain an extract to be extracted;
s2, adopting ethanol and water with a volume ratio of 2:1 as an extracting agent, mixing the to-be-extracted substance and the extracting agent according to a ratio of the to-be-extracted substance to the extracting agent of 1:20(g: mL), adding the mixture into a double-neck flask, adding a magnetic stirring rotor, carrying out condensation reflux extraction heated by an oil bath at 105 ℃ under the state of starting magnetic stirring, and taking out the mixture after condensation reflux is carried out for 24 hours;
wherein, the heater used for the condensation reflux extraction is a DF-101S heat collection type magnetic stirring heater (produced by Yineng laboratory instruments and factories in Changzhou city) provided with a temperature probe, the heating medium is methylene silicon oil, circulating cold water is used as a coolant, the temperature of the oil bath is monitored by the temperature probe, and a thermometer is inserted into the flask to monitor the temperature of the acetic acid solvent;
s3, centrifuging the mixture at 10000rpm for 10min, filtering and separating, and performing solid-liquid separation to obtain an extraction liquid and extraction residue;
s4, carrying out centrifugal washing on the extraction residue and deionized water according to the mass ratio of 1:2 at 10000rpm for 10min, and drying and grinding for later use;
s5, concentrating the extract at 60 ℃ under reduced pressure by using a rotary evaporator to 60mL, adding equal volume of deionized water to precipitate lignin, centrifuging the mixed solution at 12000rpm for 20min, and carrying out solid-liquid separation to obtain solid lignin (the yield is 21.57%).
Comparative example 1
The method in the embodiments 2 to 4 of the invention is compared with the comparative example 1, wherein the comparative example 1 adopts the method of Chinese patent document cn200610143889.4, and specifically comprises the following steps:
weighing 10g of enzymolysis residues obtained by hydrolyzing lignocellulose with enzyme, putting the enzymolysis residues into a 500mL three-neck flask, adding 200mL of mixed organic solvent of ethanol and water (the volume ratio of the ethanol to the water is 2:1), stirring for 12min to promote the enzymolysis lignin to be dissolved in the organic solvent, heating to 81 ℃, keeping the temperature at normal pressure for 1.5h, separating the enzymolysis lignin solution from other impurities insoluble in the organic solvent by filtering, and distilling the solution to remove the solvent to obtain 3.6g of crude lignin.
Comparative example 2
The method in the embodiments 2 to 4 of the invention is compared with the comparative example 2, wherein the comparative example 2 adopts the method of Chinese patent document cn200610143889.4, and specifically comprises the following steps:
weighing 10g of enzymolysis residues obtained by hydrolyzing lignocellulose with enzyme, putting the enzymolysis residues into a 500mL three-neck flask, adding 200mL of mixed organic solvent of acetic acid and water (the volume ratio of the acetic acid to the water is 2:1), stirring for 12min to promote the enzymolysis lignin to be dissolved in the organic solvent, heating to 100 ℃, keeping at normal pressure for 1.5h, separating the enzymolysis lignin solution from other impurities insoluble in the organic solvent by filtering, and distilling the solution to remove the solvent to obtain 7.8g of crude lignin.
Test effects
1. Analysis of composition
In order to verify the effect of extracting lignin by the method of the invention, the digestion residue in example 1, the extracts and the raffinate in examples 2 to 4, and the crude lignin in the comparative example were subjected to component analysis, and the content of glycan, lignin and ash in the crude lignin was determined. The measurement method is as follows:
the ash and lignin were analyzed according to standard methods established by the National Renewable Energy Laboratory (NREL) (Sluiser et al, 2008 a; Sluiser et al, 2005; Sluiser et al, 2008 b); analysis of glucose, xylose and arabinose in the acid hydrolysate using High Performance Liquid Chromatography (HPLC): the HPLC system is Agilent Technologies 1200series equipped with Aminex HPX-87H chromatographic column, the detector is RID, the temperature of the column incubator and the detector are both 35 ℃, and the mobile phase is 5mmol/L H2SO4The flow rate of the aqueous solution was 0.6 mL/min.
The results are shown in the following table:
note: the composition of the raffinate in comparative example 1 could not be analyzed for sample reasons.
From the above table, it can be seen that:
1) the lignin can be effectively separated in the embodiments 2 to 4, the digestion residues with ash content reaching 21.48% can achieve excellent removal effect on the ash content in the digestion residues, and the ash content of the lignin samples obtained after extraction is lower than 6%.
2) In the embodiments 2 to 4, the purity of the lignin extracted in the embodiment 2 is the highest, the lignin is 94.59% and the ash content is the lowest, and is only 2.44%;
3) the extracts of examples 2-4 had lower glycan content than comparative examples 1-2, because the methods of examples 2-4 can efficiently utilize glycans for conversion to biogas;
4) the lignin purity in the extract of example 2 was higher than in comparative examples 1-2.
2. Gel chromatography analysis
The molecular weight of lignin polymers is an important parameter determining their physical properties, mechanical properties and fluid behavior and is of great importance for their applications. The separation procedures such as common chemical methods or high-temperature extraction generally cause reactions such as cracking or condensation among lignin molecules, so that the molecular weight of the separated lignin is changed. The lignin obtained in examples 2 to 4 was analyzed by GPC for changes in lignin Mn, Mw and degree of dispersion (PDI) (where Mn is the number average molecular weight and Mw is the weight average molecular weight). The results are shown in the following table:
overall, after extraction with three different solvents, their molecular weights have a similar tendency: firstly, the molecular weight of lignin is greatly increased, which is caused by the condensation between lignin during the extraction and heating processes; secondly, the degree of dispersion is significantly reduced to around 1.5, which is due to the possibility of separating the lignin by solvent extraction, with some degree of selectivity for lignin fragments.
3. Thermogravimetric analysis
The thermodynamic properties of lignin are another important factor affecting its thermochemical conversion to chemicals, fuels or fuel products, and we used thermogravimetric analysis to analyze the effect of the extraction methods of examples 2-4 on lignin in the digestion residue of example 1. The results are shown in FIG. 1:
in general, the lignin obtained in examples 2-4 and the lignin in the digestion residue have similar thermal decomposition curves: the total heat loss at the first 200 ℃ is relatively small, and all lignin is thermally stable in the interval; almost most of the mass loss occurs at 200-500 ℃, and the mass loss rate reaches the maximum between 300-400 ℃; a small part of mass loss still occurs at 500-600 ℃; the residual mass after 600 ℃ is almost unchanged.
Specifically, the total heat loss of lignin in example 4 was greater than that of the remaining lignins from 320 ℃ and reached the maximum difference at about 500 ℃ (about 20% more than that of the remaining lignins), while 21% of the lignin remained in example 4 by mass at the end of heating, about 40% of the lignin remained in example 2, about 35% of the lignin remained in example 3, and about 35% of the lignin remained in the digestion residue. The thermal stability of the lignin is the worst in example 4, and the lignin in examples 2-3 and the lignin in the digestion residue have very similar heat loss curves, that is, they have very similar thermochemical properties. The thermogravimetric curves of different extracted lignins are similar to the results reported under similar extraction conditions (Meyer et al, 2018; Da Costa et al, 2016).
By comprehensive analysis, it can be seen that: the lignin obtained in the examples 2-3 has thermochemical properties more similar to those of lignin in the digestion residue, while the lignin obtained in the example 4 has better thermal properties; the thermochemical properties of lignin are closely related to its molecular weight and acetyl number, and the ethanol solvent extracts are reported to have a low acetyl content according to related studies (Qianzhi et al, 2002; Kubo et al, 1996), and are likely to be ethanol: this change is caused by the low amount of lignin acetyl groups upon water extraction.
4. Two-dimensional nuclear magnetic resonance analysis
The influence of the extraction mode on lignin was determined by two-dimensional nuclear magnetic resonance analysis (2D-HSQC NMR). Considering the lower purity after extraction in example 3, and according to the relevant report (Meyer et al, 2018) AcOH: H2The HSQC spectra of O2: 1 and AcOH extracted lignin were not different, so I chose to HSQ only lignin obtained in examples 2 and 4And C, analyzing. The results are shown in FIG. 2(Δ C/Δ H:50-100ppm/2.8-6.0ppm for side chain block package; Δ C/Δ H:90-150ppm/5.8-8.3ppm for aromatic region, signals are shown in FIG. 3):
in general, the spectra of example 2 and example 4 were from similar sources before and after extraction, but were different in some regions. First, the strongest signal of the lignin extracted with different solvents in the side chain region (Δ c/Δ H:50-100ppm/2.8-6.0ppm) still comes from methoxy groups (OCH)3δ c/δ H:55.9/3.72ppm) and β aryl ether linkages (A)β(S),δc/δH:85.8/4.10ppm；Aβ(G),δc/δH:83.4/4.42ppm；Aα,δc/δH:72.0/4.85ppm；A'γ,δc/δH:63.4/4.16ppm；AγDelta c/Delta H62.53/4.40 ppm). It can be seen that the lignin obtained by the example 2 and the example 4 still retains a large amount of methoxyl; the main difference between the two is the β -O-4 related region, the lignin β -O-4 related linkages are reduced after the extraction of example 2 (acetic acid), while a large amount of β -O-4 related signals remain after the extraction of example 4 (ethanol: water), which is similar to the report of similar conditions (Meyer et al, 2018; Da Costa et al, 2016). The phenomenon of beta-O-4 reduction is likely to be due to the acidic conditions and higher temperatures of acetic acid extraction causing condensation of the lignin aryl ether linkages (Azadi et al, 2013; Zhujialiang et al, 2018), resulting in a reduction of the beta-O-4 related signal in the spectra.
Secondly the most intense signal in the aromatic region (. delta.C/. delta.H: 90-150ppm/5.8-8.3ppm) is still from lignin units of type G (G'6,δc/δH:122.8/7.12ppm；G6,δc/δH:118.8/6.75ppm；G5,δc/δH：115.2/6.75ppm；G2δ c/δ H:110.1/6.92ppm), S-type lignin unit (S'2,6,δc/δH:106.1/7.28ppm；S2,6δ c/δ H103.7/6.69 ppm). The signal for lignin extraction of example 4 (ethanol: water) is more pronounced, and the signal for extraction of example 2 (acetic acid) is reduced. According to the study of Meyer et al (2018) on the extraction of lignin by acetic acid, they believe that this reduction in aromatic rings is due to the phenomenon caused by the large amount of acetylation of acetic acid with lignin during the extraction of acetic acid.
In summary, example 4 (ethanol: water) retains more β -aromatic ether linkages in lignin and has less effect on aromatic rings in lignin than example 2 (acetic acid) extraction.
The foregoing is illustrative of the preferred embodiments of this invention, and it is to be understood that the invention is not limited to the precise form disclosed herein and that various other combinations, modifications, and environments may be resorted to, falling within the scope of the concept as disclosed herein, either as described above or as apparent to those skilled in the relevant art. And that modifications and variations may be effected by those skilled in the art without departing from the spirit and scope of the invention as defined by the appended claims.
Claims (10)
1. The method for recovering lignin from the enzymolysis residues of lignocellulose is characterized by comprising the following steps:
s1, carrying out anaerobic digestion on the enzymolysis residues to obtain digestion residues;
s2, performing reflux extraction on the digestion residues to obtain a mixture;
s3, sequentially centrifuging, filtering and separating the mixture to obtain extract liquor and extract residues;
and S4, sequentially concentrating, precipitating, centrifuging and filtering and separating the extract liquor to obtain the solid lignin.
2. The method of claim 1, wherein in S2, the extractant used in the reflux extraction is acetic acid.
3. The method of claim 1, wherein in S2, the extractant used in the reflux extraction is acetic acid and water;
preferably, the volume ratio of the acetic acid to the water is 1-2: 1;
more preferably, the volume ratio of acetic acid to water is 2: 1.
4. The method of claim 1, wherein in S2, the extracting agents used in the reflux extraction are ethanol and water;
preferably, the volume ratio of the ethanol to the water is 0-2: 1;
more preferably, the volume ratio of ethanol to water is 2: 1.
5. The method according to any one of claims 2 to 4, wherein in S2, before the reflux extraction, the method further comprises the steps of mixing the digestion residue with deionized water, and then sequentially carrying out centrifugal washing, drying, grinding and screening to finally obtain an extract to be extracted;
preferably, the weight volume ratio of the extract to be extracted to the extracting agent is more than or equal to 1:20(g: mL);
more preferably, the rotation speed of the centrifugal water washing is more than or equal to 12000rpm, and the time is more than or equal to 10 min.
6. The method according to claim 1, wherein in S2, the temperature of the reflux extraction is 85-110 ℃, and the time of the reflux extraction is 24 h.
7. The method according to claim 1, wherein in S1, the anaerobic digestion is to inoculate an inoculum into the enzymolysis residue, adjust the pH value of the system to 6.8-7.5, and carry out anaerobic digestion under the anaerobic condition at the temperature of 30-40 ℃ until gas is not produced any more, so as to obtain the digestion residue;
preferably, the inoculum is kitchen waste anaerobic digestion sludge;
more preferably, the mass ratio of the inoculum to the enzymolysis residues is 1-2: 1.
8. The method according to claim 1, wherein in S3, the rotation speed of the centrifugation is more than or equal to 10000rpm, and the time of the centrifugation is more than or equal to 10 min;
preferably, in S3, the method further comprises the steps of sequentially performing centrifugal washing, drying and grinding on the extraction residue;
more preferably, in S3, the rotation speed of the centrifugal washing is not less than 10000rpm, and the time of the centrifugal washing is not less than 10 min.
9. The method of claim 1, wherein in S4, the concentrating and precipitating steps are: concentrating the extract liquid to 30-60 mL, and adding plasma water with the same volume to precipitate lignin;
preferably, in S4, the rotating speed of the centrifugation is more than or equal to 12000rpm, and the time of the centrifugation is more than or equal to 20 min.
10. The method of claim 1, wherein the enzymatic residue is a residue obtained by enzymatic hydrolysis of lignocellulose, and the components of the residue comprise lignin, glucan, xylan and ash;
preferably, the lignocellulose comprises one or more of crop straw, wood and energy plants.
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