CN116815528A - Lignin removing method for straw - Google Patents
Lignin removing method for straw Download PDFInfo
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- CN116815528A CN116815528A CN202310489465.7A CN202310489465A CN116815528A CN 116815528 A CN116815528 A CN 116815528A CN 202310489465 A CN202310489465 A CN 202310489465A CN 116815528 A CN116815528 A CN 116815528A
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- Polysaccharides And Polysaccharide Derivatives (AREA)
Abstract
The embodiment of the disclosure provides a lignin removal method of straw, which is applied to the field of lignin removal, and comprises the following steps: cleaning and drying the straw, crushing, sieving, and drying for the second time to obtain straw powder; weighing straw powder, adding the straw powder into mixed liquid of urea and distilled water, and placing the mixed liquid into a water bath constant temperature oscillator for oscillation; and after the oscillation is finished, carrying out suction filtration on the mixed solution to remove lignin dissolved in the filtrate, thereby obtaining a cellulose filter cake. The method improves the dissolution rate of lignin in the straw through a simple process, has small harm to cellulose, is convenient for recycling lignin products, reduces pollution, is environment-friendly and green, has small damage to equipment and has low cost.
Description
Technical Field
The disclosure relates to the field of lignin removal, in particular to a method for removing straw lignin by urea.
Background
Since the 70 s of the 20 th century, global oil consumption has increased by a factor of two, and future energy demands will continue to increase. In addition, the consumption of non-renewable energy sources such as petroleum also causes problems such as energy crisis and environmental pollution, so that the human eye turns to renewable energy sources. Biomass energy is one of the key points in research on renewable resources, and the preparation of clean fuels and bio-based chemicals from lignocellulosic biomass as a raw material to supplement or replace petrochemicals is attracting attention.
The theoretical resource amount of the straws in 2022 is 9.77 hundred million tons, wherein 2.2 hundred million tons of straws, 1.75 hundred million tons of wheat straws and 3.4 hundred million tons of corn straws respectively account for 22.52 percent, 17.91 percent and 34.80 percent of the total yield of the crop straws, and the proportion of the three accounts for more than 75 percent. The theoretical resource amount of straw in 2023 is estimated to reach 10.14 hundred million tons, and the collectable resource amount is estimated to reach 7.37 hundred million tons. The straw is used as biomass resource with wide sources and abundant resources, and about 70% of the straw is carbohydrate, namely cellulose and hemicellulose, and can be converted into fermentable sugar, and the biomass resource is further used for preparing ethanol, biogas, single-cell protein, microbial metabolites and the like.
The pretreatment process of biomass cellulose is a key step in converting lignocellulose into fermentable sugars. The cellulose is protected by lignin and hemicellulose to limit the specific surface area and accessibility of the cellulose, so that the cellulose biodegradation efficiency is low, and biomass raw materials such as straw and the like are difficult to directly use. The pretreatment of the straw aims at removing lignin and partially degrading hemicellulose by destroying the wrapping effect of the lignin and the hemicellulose on cellulose, so that the cellulose is de-crystallized and the cellulose porosity is improved, thereby promoting the contact of enzyme or yeast and a substrate and improving the yield of fermentable sugar.
The traditional separation method of lignin is an inorganic acid-base method, but the inorganic acid-base method requires a large amount of water to wash and desalt the pretreated substrate, detoxicates the pretreated substrate, and the wastewater is not easy to recycle and has great influence on soil environment. The inorganic acid method is corrosive to equipment, and increases the running and maintenance cost of the equipment. Therefore, there is a need for a method for removing lignin that is environmentally friendly, has low pollution, is simple to operate, and has a certain feasibility.
Disclosure of Invention
In view of the problems in the prior art, according to the embodiment of the disclosure, a lignin removing method for straw is provided, the dissolution rate of lignin in straw is improved through a simple process, the harm to cellulose is small, the recovery of lignin products is convenient, the pollution is reduced, the environment is protected, the damage to equipment is small, and the cost is low.
In a first aspect of the present application, a method for removing lignin from straw is provided, comprising the steps of: cleaning and drying the straw, crushing, sieving, and drying for the second time to obtain straw powder; weighing straw powder, adding the straw powder into mixed liquid of urea and distilled water, and placing the mixed liquid into a water bath constant temperature oscillator for oscillation; and after the oscillation is finished, carrying out suction filtration on the mixed solution to remove lignin dissolved in the filtrate, thereby obtaining a cellulose filter cake.
Further, the grain size of the straw powder is 40-80 meshes.
Further, the addition amount of urea in the mixed solution of urea and distilled water accounts for 6-12wt% of the addition amount of the straw powder.
Further, the mass ratio of the added straw powder to the distilled water in the mixed liquid of urea and distilled water is 1:6-1:15.
Further, the mixed solution is placed in the water bath constant temperature oscillator to oscillate at an oscillation speed of 160-180 r/min.
Further, the mixed solution is placed in the water bath constant temperature oscillator with the water temperature set to be 40-90 ℃ for oscillation.
Further, the mixed solution is placed in the water bath constant temperature oscillator to oscillate for 3-24 hours, and then the oscillation is finished.
The second part of the application, a cellulose manufacturing method, comprises the following steps: the cellulose filter cake is obtained by adopting the lignin removal method; washing the filter cake with distilled water until the filtrate is neutral to obtain a neutral filter cake; and drying the neutral filter cake to obtain cellulose.
The method for removing lignin from straws by using urea is characterized in that corn straws in straws with highest crop yield in China are selected as lignocellulose biomass raw materials, and the operation condition for removing lignin by using environment-friendly urea is optimized. OH from hydrolysis of urea - Can weaken hydrogen bond between cellulose and hemicellulose molecules, saponify hemicellulose and lignin moleculesThe ester bond and lignin react chemically to form alkali lignin, which is separated from the surface of lignocellulose and dissolved in solution, so as to eliminate lignin and reduce cellulose crystallinity. The lignin dissolution rate of the technology is higher than that of H 2 SO 4 Method, caO method and H 2 O 2 The method has the advantages of environment friendliness, low pollution, reproducibility, simplicity in operation, reduction of cellulose loss rate, improvement of cellulose purity and certain feasibility of the process.
It should be understood that what is described in this summary is not intended to limit the critical or essential features of the embodiments of the disclosure nor is it intended to limit the scope of the disclosure. Other features of the present disclosure will become apparent from the following description.
Drawings
The above and other features, advantages and aspects of embodiments of the present disclosure will become more apparent by reference to the following detailed description when taken in conjunction with the accompanying drawings. For a better understanding of the present disclosure, and without limiting the disclosure thereto, the same or similar reference numerals denote the same or similar elements, wherein:
FIG. 1 illustrates a process flow diagram of the present disclosure;
fig. 2 shows a flow chart of the Van Soest assay method.
Detailed Description
For the purpose of making the objects, technical solutions and advantages of the embodiments of the present disclosure more apparent, the technical solutions in the embodiments of the present disclosure will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present disclosure, and it is apparent that the described embodiments are some embodiments of the present disclosure, but not all embodiments. All other embodiments, which can be made by one of ordinary skill in the art without inventive effort, based on the embodiments in this disclosure are intended to be within the scope of this disclosure.
In addition, the term "and/or" herein is merely an association relationship describing an association object, and means that three relationships may exist, for example, a and/or B may mean: a exists alone, A and B exist together, and B exists alone. In addition, the character "/" herein generally indicates that the front and rear associated objects are an "or" relationship.
The disclosure provides a lignin removal method for straw, the specific flow is shown in fig. 1, and the lignin removal method comprises the following steps:
s1: cleaning and drying the straw, crushing, sieving, and drying for the second time to obtain straw powder;
in the above embodiment, the particle size of the powder of the straw is 40-80 mesh, and the size of the particle size directly determines the lignin removal effect. Theoretically, the higher the degree of pulverization, the better the lignin removal effect. However, the straw is not easy to infiltrate due to the overlarge grain size, and certain difficulty is brought to subsequent processing; the particle size is too small, the substrate concentration is high, but the energy consumption is large, the processing cost is high, and the method is uneconomical. In this embodiment, the straw is selected from corn straw with highest yield in crops, and straw of crops such as wheat and rice can be used as raw material.
S2: weighing straw powder, adding the straw powder into mixed liquid of urea and distilled water, and placing the mixed liquid into a water bath constant temperature oscillator for oscillation;
in the above embodiment, the amount of urea added in the mixed liquid of urea and distilled water is 6wt% to 12wt% of the amount of straw powder added. Along with the change of the mass concentration of urea, the content of hemicellulose, cellulose and lignin in the corn straw can also change. Along with the continuous increase of the mass concentration of the urea, the content of hemicellulose is reduced more rapidly, the cellulose content is gradually increased, and the lignin content is also reduced to some extent, which indicates that the urea is firstly degraded to generate peeling reaction, along with the rapid dissolution of the hemicellulose, the lignin is exposed more, the lignin has the characteristic of alkali solubility, and the increase of the urea leads to the OH - The concentration is increased, the lignin in the straw is swelled, and the crystallinity and the polymerization degree are reduced simultaneously, so that the lignin is matched with OH - Is increased, the degradation rate is increased; when the mass concentration of the urea is higher than 12wt%, along with the continuous increase of the mass concentration of the urea, OH in the mixed solution - The concentration increases, at which time the lignin dissolution has reached a levelThe balance is that hemicellulose is dissolved out more, OH-in the solution reacts with cellulose in a peeling reaction, so that the reducing glucose terminal groups of cellulose macromolecules are peeled one by one and dissolved in the solution, and the structure of the cellulose is destroyed; when the mass concentration of urea is lower than 6wt%, the OH-concentration in the mixed solution is insufficient, and the dissolution of lignin cannot be ensured, so that the dissolution rate is lower. The urea added is preferably chemically pure. In the whole experiment, the application only adopts urea to remove lignin, and compared with the general method of removing acid-base solution or organic substances, the application not only can obtain good removing efficiency, but also can remove lignin without damaging reaction filtrate along with the environment, has better environmental friendliness, is milder to cellulose and removed lignin, does not influence the quality of the cellulose and removed lignin, and can recycle the removed lignin.
In the above embodiment, the mass ratio of the added straw powder to the distilled water in the mixed liquid of urea and distilled water is 1:6-1:15, because when the solid-to-liquid ratio is lower than 1:6, the addition amount of distilled water in the solution is too small, resulting in non-dispersion of straw powder in the solution and insufficient reaction; when the water content is too small, the concentration of OH-dissolved in the distilled water is too high, and the OH-can be preferentially contacted with hemicellulose, so that the degradation rate of the hemicellulose is higher than that of lignin; along with the increase of the amount of distilled water added, the dispersity of straw powder also starts to become larger, the OH-concentration in the solution gradually decreases, the hemicellulose degradation rate is lower than the reaction when the solid-liquid ratio is 1:6, and more abundant time and OH are given to lignin - Carrying out reaction; when the solid-liquid ratio is 1:10, the dispersity of the straw powder is optimal, and the lignin content is the lowest and the cellulose content is the highest; with further increase of the solid-to-liquid ratio, the increase of the water amount leads to OH in the solution - Further decrease in concentration, when the solid-to-liquid ratio exceeds 1:15, OH in the solution - The concentration is too low, the dispersion degree of the straw powder is too high, and the straw powder cannot generate chemical reaction, so that the purpose of dissolution is lost.
In the above embodiment, the value range of the oscillating speed of the water bath constant temperature oscillator for oscillating the mixed solution is 160-180r/min, because the oscillating speed higher than 180r/min can damage the stability of the solution system and also damage the cellulose structure; and the oscillation speed is lower than 160r/min, so that the distribution in the system is uneven, and the dissolution efficiency of lignin is reduced.
In the above embodiment, the water temperature of the water bath constant temperature oscillator for oscillating the mixed solution is set to be 40-90 ℃, because urea is not basically hydrolyzed to generate OH-at the temperature below 40 ℃, the solution is neutral, and lignin is not degraded. When the temperature is increased to 40 ℃, urea starts to hydrolyze slowly to generate ammonia, and the ammonia is dissolved in water to generate OH < - > and then reacts with lignin. When the temperature reached 60 ℃, lignin dissolution reached equilibrium. When the temperature exceeds 90 ℃, urea is severely hydrolyzed, cellulose can undergo peeling reaction, the polymerization degree is reduced, and the strength is reduced.
In the above embodiment, the value range of the oscillation time of the water bath constant temperature oscillator for oscillating the mixed solution is 3-24 hours, and when the oscillation time is lower than 3 hours, the lignin is not dissolved, and the dissolution rate is lower; after more than 24 hours, the dissolution for too long time not only causes alkaline hydrolysis of cellulose, but also the dissolution of lignin is balanced, so that unnecessary capacity is wasted and efficiency is reduced.
S3: and after the oscillation is finished, carrying out suction filtration on the mixed solution to remove lignin dissolved in the filtrate, thereby obtaining a cellulose filter cake. Because urea is only adopted for removal, the components in the filtrate are simple, the lignin recovery is easier to operate, the filtrate can be directly utilized, excessive treatment is not needed, and the whole process is strong in environmental protection.
In a second aspect of the application, a method for producing cellulose is provided, wherein the lignin removal method is adopted to obtain a cellulose filter cake; washing the filter cake with distilled water until the filtrate is neutral to obtain a neutral filter cake; and drying the neutral filter cake to obtain the cellulose with stable properties.
In the above embodiment, a large amount of water is needed for cleaning the filter cake to obtain a neutral filter cake, for example, inorganic acid and alkali or organic substances are used for removing lignin to obtain the filter cake, a large amount of water is needed for cleaning the filter cake, waste water for cleaning the filter cake is discharged after being treated, and the environment is polluted and water source is wasted.
In the above examples, alkali lignin in the filtrate was recovered. Specifically, lignin is dissolved in a filtrate containing urea, and the filtrate can be treated to recover the alkali lignin produced. Because lignin has the characteristic of alkali solubility, under the alkaline condition, the lignin can be mixed with OH in the solution - The alkali lignin is generated by reaction and separated from the surface of lignocellulose, and is dissolved in the solution. The alkali lignin is a natural polymer surfactant, has strong surface activity, and can be chemically modified and applied, so that the alkali lignin can be recovered from filtrate, and the utilization rate of straw is improved.
Specific examples of the above lignin removal method are as follows:
selecting corn straw for experiments, wherein the main components of the corn straw are as follows: hemicellulose with mass fraction of 33.33%, cellulose with mass fraction of 40.34%, lignin with mass fraction of 11.14% and ash with mass fraction of 5.3%, the total content of cellulose and hemicellulose of the corn straw is higher, and the corn straw is a preferential straw raw material. The determination method of each component adopts Van Soest test, and specifically comprises the following steps: corn stalk sample (m) 1 ) Washing with 3% sodium dodecyl sulfate neutral detergent to obtain neutral washing fiber comprising hemicellulose, cellulose, lignin and silicate, oven drying, cooling, and weighing (M 1 ) The method comprises the steps of carrying out a first treatment on the surface of the Re-weighing the corn stalk sample (m) 2 ) Washing with 2% hexadecyl trimethyl ammonium bromide acid detergent to obtain acid washing fiber comprising cellulose, lignin and silicate, oven drying, cooling, and weighing (M 2 ) The method comprises the steps of carrying out a first treatment on the surface of the Treating the acidic washed fiber with 72% concentrated sulfuric acid to obtain residue including lignin and silicate, washing the residue with distilled water to neutrality, oven drying, cooling, and weighing (M 3 ) Acid washing fiber value (M 2 ) Subtracting outResidue value after 72% sulfuric acid treatment (M 3 ) Is the cellulose content of the corn stalk powder; ashing the residue after 72% sulfuric acid treatment, drying and cooling to obtain residue (M) 4 ) The part escaping in the ashing process is the content of the acidic washing lignin. The calculation formula for hemicellulose, cellulose and lignin content can be obtained as follows:
the specific experimental process is as follows: cleaning corn straw, drying, crushing, sieving with a 60-mesh sieve, and drying again to obtain corn straw powder; weighing a certain weight of corn straw powder, and adding the corn straw powder into a mixed solution of urea accounting for 6-12wt% of the weight of the straw powder and distilled water with the solid-liquid ratio of the weight of the straw to the weight of water being 1:6-1:15; placing the mixed solution in a water bath constant temperature oscillator with the speed of 170r/min and the temperature of 40-90 ℃ for reaction for 3-24 hours, and carrying out suction filtration by using a G3 glass sand core funnel to remove lignin dissolved in the filtrate; washing the filter residue with distilled water until the filtrate is neutral, and drying the filter residue at 105 ℃ for 6 hours to obtain cellulose.
Specific experimental conditions and experimental results are shown in the following table:
table 1 lignin dissolution rates of the examples under different conditions
From the experimental data in the above table, comparative examples 1-8 and comparative examples 1, 2 give: when the urea content accounts for 9wt% of the mass of the straw powder, the dissolution rate of lignin is 40% -60% when the solid-to-liquid ratio of the mass of the corn straw powder to the mass of distilled water is 1:6-1:15; when the solid-liquid ratio is 1:10, the dissolution rate of lignin is highest.
Comparative example 1, examples 9 to 13 and comparative examples 3 and 4 gave: when the urea content accounts for 9wt% of the mass of the straw powder, the dissolution rate of lignin is 42% -60% when the oscillation temperature is 40-90 ℃; when the oscillation temperature is 60 ℃ and above, the dissolution rate of lignin is the highest. When the temperature exceeds 90 ℃, the dissolution of lignin reaches equilibrium, but the high temperature causes peeling reaction of cellulose, the polymerization degree is reduced, and the strength is reduced. Based on the principle of protecting the cellulose structure and saving resources, the conclusion that the lignin dissolution rate is highest when the oscillation temperature is 60 ℃ is obtained.
Comparative example 1, examples 14-20 and comparative examples 5, 6 give: when the urea content accounts for 9wt% of the mass of the straw powder, the dissolution rate of lignin is 45-60% when the oscillation time is 3-24 hours; when the oscillation time is 4 hours and above, the dissolution rate of lignin is the highest. However, when the shaking time exceeds 4 hours, the cellulose starts to undergo alkaline hydrolysis, and the loss rate increases with time. Based on the principle of protecting the cellulose structure, the conclusion that the lignin dissolution rate is highest when the oscillation time is 4 hours is obtained.
Comparative example 1, examples 21 to 26 and comparative examples 7 and 8 gave: when the mass concentration of urea is 6-12wt%, the dissolution rate of lignin is 43% -60%; when the mass concentration of urea is 9% or more, the dissolution rate of lignin is highest. However, when the mass concentration of urea exceeds 12%, the dissolution of lignin has reached equilibrium, at which time the cellulose undergoes a peeling reaction, the polymerization decreases, and the strength decreases. Based on the principle of protecting the cellulose structure and saving resources, the conclusion that the lignin dissolution rate is highest when the mass concentration of urea is 9% is obtained.
The best conditions for removing lignin in corn straw by urea can be obtained by combining the above embodiments: adding 9wt% of urea and ten times of water into the corn straw powder, and carrying out oscillation hydrolysis for 4 hours at the temperature of 60 ℃ to obtain the lignin dissolution rate of 60%. It will be appreciated that the above embodiments may also be applied in the lignin removal of wheat straw, barley straw, oat straw, sorghum straw.
The urea removal method can improve the dissolution rate of lignin in the straw, has the advantages of simple operation, small pollution, low cost and high feasibility of the process, and simultaneously, the dissolution of lignin is Cheng Wenhe without damaging the performance of lignin, thereby improving the maximum possibility of lignin recovery, and being economical and practical.
The above is only a preferred embodiment of the present application, and is not intended to limit the present application, but various modifications and variations can be made to the present application by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included in the protection scope of the present application.
Claims (8)
1. A lignin removal method for straw, comprising:
cleaning and drying the straw, crushing, sieving, and drying for the second time to obtain straw powder;
weighing straw powder, adding the straw powder into mixed liquid of urea and distilled water, and placing the mixed liquid into a water bath constant temperature oscillator for oscillation;
and after the oscillation is finished, carrying out suction filtration on the mixed solution to remove lignin dissolved in the filtrate, thereby obtaining a cellulose filter cake.
2. The method of claim 1, wherein the straw powder has a particle size in the range of 40-80 mesh.
3. The method according to claim 1, wherein the amount of urea added in the mixture of urea and distilled water is 6 to 12wt% of the amount of straw powder added.
4. The method according to claim 1, characterized in that the mass ratio of added straw powder to distilled water in the mixture of urea and distilled water is 1:6-1:15.
5. The method according to claim 1, wherein the mixed liquor is placed in the water bath thermostatic oscillator to oscillate at an oscillation speed of 160-180 r/min.
6. The method according to claim 1, wherein the mixed liquor is placed in the water bath thermostatic oscillator with water temperature set to 40-90 ℃ for oscillation.
7. The method according to claim 1, wherein the mixing solution is placed in the water bath thermostatic oscillator for oscillation for 3-24 hours, and then the oscillation is ended.
8. A method for producing cellulose, comprising the steps of:
obtaining a cellulose filter cake by the lignin removal method according to any one of claims 1 to 7;
washing the filter cake with distilled water until the filtrate is neutral to obtain a neutral filter cake;
and drying the neutral filter cake to obtain cellulose.
Priority Applications (1)
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Citations (4)
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| CN109988797A (en) * | 2019-04-19 | 2019-07-09 | 哈尔滨工业大学 | A kind of method of the pretreatment of low temperature high solid-liquid ratio alkalinuria solution and its enzymatic hydrolysis conversion of agricultural crop straw |
| CN110092947A (en) * | 2018-01-30 | 2019-08-06 | 山东省圣泉生物质石墨烯研究院 | A kind of micro-nano cellulose compound, and its preparation method and application |
| CN110607334A (en) * | 2019-10-11 | 2019-12-24 | 中国农业大学 | Lignocellulose pretreatment method in fluid shear-driven urea/alkali system and application thereof |
| CN112626903A (en) * | 2020-12-18 | 2021-04-09 | 安徽工业大学 | Method for extracting lignin from urea-assisted low-temperature alkali liquor |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN110092947A (en) * | 2018-01-30 | 2019-08-06 | 山东省圣泉生物质石墨烯研究院 | A kind of micro-nano cellulose compound, and its preparation method and application |
| CN109988797A (en) * | 2019-04-19 | 2019-07-09 | 哈尔滨工业大学 | A kind of method of the pretreatment of low temperature high solid-liquid ratio alkalinuria solution and its enzymatic hydrolysis conversion of agricultural crop straw |
| CN110607334A (en) * | 2019-10-11 | 2019-12-24 | 中国农业大学 | Lignocellulose pretreatment method in fluid shear-driven urea/alkali system and application thereof |
| CN112626903A (en) * | 2020-12-18 | 2021-04-09 | 安徽工业大学 | Method for extracting lignin from urea-assisted low-temperature alkali liquor |
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