Method for removing lignin in straw

Abstract

The invention discloses a method for removing lignin in straw. The method comprises the following steps: S1, cleaning and drying: cleaning corn straw, and drying for later use; s2, crushing and screening: crushing the dried corn straws, screening corn straw particles with proper particle sizes, and sealing and storing for later use; s3, mixing and heating: fully mixing the corn straw particles with a reagent, putting the mixture into a salt bath reactor, heating to a certain temperature, and reacting for a period of time; and S4, filtering and washing: filtering to remove lignin after the reaction is finished, washing filter residues with deionized water until the filter residues are neutral, and drying to obtain solid residues. Compared with the prior art, the method has the beneficial effects that the mixed solution of NaOH and urea is adopted to soak and treat the corn straw, and urea is easy to decompose and release ammonia in alkali liquor, so that the alkalization effect on the corn straw is enhanced, ester bonds among lignin, cellulose and hemicellulose are easier to break, and the removal rate of lignin in the corn straw is increased.

Description

Technical Field

[0001] The invention relates to the technical field of lignin removal, and in particular to a method for removing lignin from straw. Background Art

[0002] Lignin is a complex organic compound that is widely present in nature and is mainly extracted from the cell walls composed of cellulose and hemicellulose in plants. It is one of the important characteristics of plants adapting to terrestrial environments and is also a major component of vascular plants.

[0003] Lignin in corn straw is an important biomass component, and its content and structure have a significant impact on the utilization efficiency of corn straw. Lignin is present in high levels in the secondary cell walls of corn straw, usually accounting for between 14.2% and 15.8%, which makes corn straw a crop straw with a high lignin content. The presence of lignin has a negative impact on the enzymatic hydrolysis process of corn straw. Due to the tight carbohydrate structure of lignin, it hinders the contact of cellulase with cellulose, thereby affecting the adsorption and hydrolysis efficiency of cellulase. Therefore, removing or degrading lignin is one of the key steps to improve the conversion and utilization efficiency of corn straw.

[0004] There are many methods for removing lignin, mainly including chemical method, biological method and physical method. Chemical method includes sodium chlorite method, alkaline hydrogen peroxide method and ionic liquid method; biological method includes microbial method and electrochemical oxidation and biodegradation combined method; physical method includes steam explosion pretreatment and pyrolysis method.

[0005] A Chinese invention patent with application number 202310489465.7 discloses a method for removing lignin from straw. Although the invention improves the dissolution rate of lignin in straw through a simple process, has little damage to cellulose, and facilitates the recovery of lignin products, reduces pollution, is environmentally friendly and green, causes little damage to equipment, and has low cost, the optimal conditions for removing lignin from corn straw with urea in the invention are: adding 9wt% of urea and ten times the mass of water to the corn straw powder, oscillating and hydrolyzing it at a temperature of 60°C for 4 hours, the lignin dissolution rate is 60%, and the lignin removal effect is not ideal and needs to be further improved. Summary of the invention

[0006] The purpose of the present invention is to provide a method for removing lignin from straw, so as to solve the technical problem that the removal effect of lignin in the prior art is not ideal and needs to be further improved.

[0007] To achieve the above object, the present invention is implemented by adopting the following technical solutions:

[0008] A method for removing lignin from straw comprises the following steps:

[0009] S1. Cleaning and drying: Clean the corn stalks and dry them for later use;

[0010] S2. Crushing and screening: crushing the dried corn stalks, screening corn stalk particles of suitable particle size, and sealing and storing them for later use;

[0011] S3, mixing and heating: the corn stalk particles are fully mixed with the reagents, and placed in a salt bath reactor and heated to a certain temperature to react for a period of time;

[0012] S4, filtering and washing: after the reaction is completed, lignin is removed by filtering, and the filter residue is washed with deionized water until it is neutral, and then dried to obtain a solid residue.

[0013] Furthermore, the particle size range of the corn stalk particles screened in step S2 is 0.5 to 0.9 mm.

[0014] Furthermore, in step S3, the solid-liquid ratio of the corn stalk particles to the reagent is 1:10.

[0015] Furthermore, the reagent in step S3 includes NaOH in a mass ratio (W / W) of 0.5% to 1.0% and urea in a mass ratio of 0.1% to 0.3%.

[0016] Furthermore, in step S3, the reaction temperature is 35-55° C. and the reaction time is 12-20 h.

[0017] The beneficial effects of the present invention are as follows:

[0018] The invention soaks corn stalks by using a mixed solution of NaOH and urea. Urea is easily decomposed in an alkali solution to release ammonia, thereby strengthening the alkalization effect on the corn stalks, making it easier to break the ester bonds between lignin and cellulose and hemicellulose, thereby improving the removal rate of lignin in the corn stalks. Moreover, a large amount of lignin and a part of hemicellulose in the corn stalks are removed, so that the wrapping effect of lignin and hemicellulose is weakened. Meanwhile, the crystal state of cellulose can be changed by swelling of the mixed solution of dilute alkali and urea, which is more conducive to subsequent enzymolysis and fermentation. DETAILED DESCRIPTION

[0019] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

[0020] Example 1

[0021] A method for removing lignin from straw comprises the following steps:

[0022] S1. Cleaning and drying: The corn stalks were cleaned and dried for use. The corn stalks were taken from Zhengzhou City, Henan Province, and their components were: cellulose 38.51%, hemicellulose 21.55%, lignin 18.11%, ash 4.71%, and other components 17.12%; the analysis method of the components in the corn stalks adopted a two-step hydrolysis method, the high performance liquid chromatograph adopted an RI differential detector, the chromatographic column adopted BioRad Aminex HPX-87H (300×7.8mm), the column temperature was maintained at 65°C, the mobile phase was 5mmol / L H2SO4 solution, and the flow rate was 0.6mL / min;

[0023] S2. Crushing and screening: crushing the dried corn stalks, screening corn stalk particles of suitable particle size, and sealing and storing them for later use;

[0024] S3, mixing and heating: the corn stalk particles are fully mixed with the reagents, and placed in a salt bath reactor and heated to a certain temperature to react for a period of time;

[0025] S4, filtration and washing: After the reaction is completed, lignin is removed by filtration, and the filter residue is washed with deionized water until neutral, and then dried to obtain solid residue. The cellulose, hemicellulose and lignin contents in the solid residue are weighed and determined, and the cellulose and hemicellulose recovery rates and lignin removal rates are calculated. The calculation formula is as follows:

[0026] Cellulose recovery rate = cellulose mass in solid residue / cellulose mass in original straw × 100%;

[0027] Hemicellulose recovery rate = mass of hemicellulose in solid residue / mass of hemicellulose in original straw × 100%;

[0028] Lignin removal rate = (1 - lignin mass in solid residue / lignin mass in original straw) × 100%.

[0029] As an optional technical solution of the present invention: the particle size range of the corn stalk particles screened in step S2 is 0.5 to 0.9 mm.

[0030] As an optional technical solution of the present invention: in step S3, the solid-liquid ratio of the corn stalk particles to the reagent is 1:10.

[0031] As an optional technical solution of the present invention: in step S3, the reagents include 0.5% NaOH and 0.1% urea in a mass ratio (W / W), and urea is easily decomposed in the alkali solution to release ammonia, which strengthens the alkalization effect on the corn stalks, makes the ester bonds between lignin and cellulose and hemicellulose more easily broken, and increases the removal rate of lignin;

[0032] As an optional technical solution of the present invention: the reaction temperature in step S3 is 35° C. and the reaction time is 12 h.

[0033] Through calculation, it is known that the removal rate of lignin in this embodiment is 63.82%.

[0034] Example 2

[0035] A method for removing lignin from straw comprises the following steps:

[0036] S1. Cleaning and drying: Clean the corn stalks and dry them for later use;

[0037] S2. Crushing and screening: crushing the dried corn stalks, screening corn stalk particles of suitable particle size, and sealing and storing them for later use;

[0038] S3, mixing and heating: the corn stalk particles are fully mixed with the reagents, and placed in a salt bath reactor and heated to a certain temperature to react for a period of time;

[0039] S4, filtering and washing: After the reaction is completed, lignin is removed by filtering, and the filter residue is washed with deionized water until it is neutral, and then dried to obtain a solid residue.

[0040] As an optional technical solution of the present invention: the particle size range of the corn stalk particles screened in step S2 is 0.5 to 0.9 mm.

[0041] As an optional technical solution of the present invention: in step S3, the solid-liquid ratio of the corn stalk particles to the reagent is 1:10.

[0042] As an optional technical solution of the present invention: in step S3, the reagent includes NaOH and urea at a mass ratio (W / W) of 0.75%;

[0043] As an optional technical solution of the present invention: the reaction temperature in step S3 is 45° C. and the reaction time is 16 h.

[0044] Calculation revealed that the removal rate of lignin in this embodiment was 69.71%.

[0045] Example 3

[0046] A method for removing lignin from straw comprises the following steps:

[0047] S1. Cleaning and drying: Clean the corn stalks and dry them for later use;

[0048] S2. Crushing and screening: crushing the dried corn stalks, screening corn stalk particles of suitable particle size, and sealing and storing them for later use;

[0049] S3, mixing and heating: the corn stalk particles are fully mixed with the reagents, and placed in a salt bath reactor and heated to a certain temperature to react for a period of time;

[0050] S4, filtering and washing: after the reaction is completed, lignin is removed by filtering, and the filter residue is washed with deionized water until it is neutral, and then dried to obtain a solid residue.

[0051] As an optional technical solution of the present invention: the particle size range of the corn stalk particles screened in step S2 is 0.5 to 0.9 mm.

[0052] As an optional technical solution of the present invention: in step S3, the solid-liquid ratio of the corn stalk particles to the reagent is 1:10.

[0053] As an optional technical solution of the present invention: in step S3, the reagent includes NaOH and urea at a mass ratio (W / W) of 1.0%;

[0054] As an optional technical solution of the present invention: the reaction temperature in step S3 is 55° C. and the reaction time is 20 h.

[0055] Calculation revealed that the removal rate of lignin in this embodiment was 67.53%.

[0056] It can be seen from the above examples that increasing the NaOH concentration, extending the reaction time, and increasing the reaction temperature are all helpful for the removal of lignin. Among them, when the NaOH concentration is 0.75%, the urea concentration is 0.2%, the temperature is 45°C, and the time is 16h, the removal effect of lignin in corn straw is the best, and the large-scale removal of lignin and the removal of part of hemicellulose in corn straw weaken the wrapping effect of lignin and hemicellulose. At the same time, the swelling of the mixed solution of dilute alkali and urea can change the crystal state of cellulose, which is more conducive to subsequent enzymatic hydrolysis and fermentation.

[0057] Comparative Example 1

[0058] A method for removing lignin from straw comprises the following steps:

[0059] S1. Cleaning and drying: Clean the corn stalks and dry them for later use;

[0060] S2. Crushing and screening: crushing the dried corn stalks, screening corn stalk particles of suitable particle size, and sealing and storing them for later use;

[0061] S3, mixing and heating: the corn stalk particles are fully mixed with the reagents, and placed in a salt bath reactor and heated to a certain temperature to react for a period of time;

[0062] S4, filtering and washing: after the reaction is completed, lignin is removed by filtering, and the filter residue is washed with deionized water until it is neutral, and then dried to obtain a solid residue.

[0063] As an optional technical solution of the present invention: the particle size range of the corn stalk particles screened in step S2 is 0.5 to 0.9 mm.

[0064] As an optional technical solution of the present invention: in step S3, the solid-liquid ratio of the corn stalk particles to the reagent is 1:10.

[0065] As an optional technical solution of the present invention: in step S3, the reagent uses urea with a mass ratio (W / W) of 0.1%.

[0066] As an optional technical solution of the present invention: the reaction temperature in step S3 is 35° C. and the reaction time is 12 h.

[0067] It was calculated that the removal rate of lignin in this comparative example was 43.22%.

[0068] Comparative Example 2

[0069] A method for removing lignin from straw comprises the following steps:

[0070] S1. Cleaning and drying: Clean the corn stalks and dry them for later use;

[0071] S2. Crushing and screening: crushing the dried corn stalks, screening corn stalk particles of suitable particle size, and sealing and storing them for later use;

[0072] S3, mixing and heating: the corn stalk particles are fully mixed with the reagents, and placed in a salt bath reactor and heated to a certain temperature to react for a period of time;

[0073] S4, filtering and washing: After the reaction is completed, lignin is removed by filtering, and the filter residue is washed with deionized water until it is neutral, and then dried to obtain a solid residue.

[0074] As an optional technical solution of the present invention: the particle size range of the corn stalk particles screened in step S2 is 0.5 to 0.9 mm.

[0075] As an optional technical solution of the present invention: in step S3, the solid-liquid ratio of the corn stalk particles to the reagent is 1:10.

[0076] As an optional technical solution of the present invention: in step S3, the reagent uses urea with a mass ratio (W / W) of 0.2%.

[0077] As an optional technical solution of the present invention: the reaction temperature in step S3 is 45° C. and the reaction time is 16 h.

[0078] It was calculated that the removal rate of lignin in this comparative example was 44.56%.

[0079] Comparative Example 3

[0080] A method for removing lignin from straw comprises the following steps:

[0081] S1. Cleaning and drying: Clean the corn stalks and dry them for later use;

[0082] S2. Crushing and screening: crushing the dried corn stalks, screening corn stalk particles of suitable particle size, and sealing and storing them for later use;

[0083] S3, mixing and heating: the corn stalk particles are fully mixed with the reagents, and placed in a salt bath reactor and heated to a certain temperature to react for a period of time;

[0084] S4, filtering and washing: after the reaction is completed, lignin is removed by filtering, and the filter residue is washed with deionized water until it is neutral, and then dried to obtain a solid residue.

[0085] As an optional technical solution of the present invention: the particle size range of the corn stalk particles screened in step S2 is 0.5 to 0.9 mm.

[0086] As an optional technical solution of the present invention: in step S3, the solid-liquid ratio of the corn stalk particles to the reagent is 1:10.

[0087] As an optional technical solution of the present invention: in step S3, the reagent uses urea with a mass ratio (W / W) of 0.3%.

[0088] As an optional technical solution of the present invention: the reaction temperature in step S3 is 55° C. and the reaction time is 20 h.

[0089] It was calculated that the removal rate of lignin in this comparative example was 45.37%.

[0090] It can be seen from the above comparative examples that increasing urea concentration, prolonging reaction time and raising reaction temperature are all helpful for removing lignin.

[0091] The following table shows the lignin removal rates of various embodiments and comparative examples under different conditions:

[0092]

[0093] In summary: the components of corn straw after soaking in a mixture of NaOH and urea were analyzed and compared with the corn straw soaked in urea alone. The removal rate of lignin in the corn straw after soaking in a mixture of NaOH and urea was higher than that in the corn straw soaked in urea alone.

[0094] Although the present invention has been described in detail with reference to the aforementioned embodiments, it will be possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments, or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for removing lignin from straw, comprising the following steps: S1. Cleaning and drying: Clean the corn stalks and dry them for later use; S2. Crushing and screening: crushing the dried corn stalks, screening corn stalk particles of suitable particle size, and sealing and storing them for later use; S3, mixing and heating: the corn stalk particles are fully mixed with the reagents, and placed in a salt bath reactor and heated to a certain temperature to react for a period of time; S4, filtering and washing: after the reaction is completed, lignin is removed by filtering, and the filter residue is washed with deionized water until it is neutral, and then dried to obtain a solid residue.

2. The method for removing lignin from straw according to claim 1, characterized in that: The particle size range of the corn stalk particles screened in step S2 is 0.5 to 0.9 mm.

3. The method for removing lignin from straw according to claim 1, characterized in that: In step S3, the solid-liquid ratio of the corn stalk particles to the reagent is 1:

10.

4. The method for removing lignin from straw according to claim 1, characterized in that: The reagents in step S3 include NaOH and urea in a weight ratio (W / W) of 0.5% to 1.0% and 0.1% to 0.3%.

5. The method for removing lignin from straw according to claim 1, characterized in that: In step S3, the reaction temperature is 35-55° C. and the reaction time is 12-20 hours.

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