A method for preparing higher whiteness pulp and high activity lignin

Abstract

The present invention belongs to the field of pulping and papermaking engineering, and provides a method for preparing high-whiteness pulp and high-activity lignin, that is, a method for obtaining high-whiteness pulp by adding lignin parent small molecules and short-chain polyols during the raw material cooking process, and belongs to the field of pulping and papermaking industry. In the method, in the delignification process, the lignin parent small molecules and short-chain polyols form a nucleophilic combination (including active organic small molecules containing short chains and aromatic bodies), and a saturated condensation reaction occurs on the side chain position of lignin, aiming to reduce the activity of lignin molecules, stabilize lignin molecules, and reduce their disordered reactions, that is, reduce the relative molecular mass of dissolved lignin, thereby promoting the dissolution of lignin from the cell wall of the raw material, thereby reducing the residual lignin in the cellulose pulp, improving the purity of cellulose, and increasing the number of lignin molecular functional groups, directly obtaining high-whiteness unbleached pulp and high-activity lignin. The method has a simple operation process, and the solvent is easy to recycle and reuse, which can effectively reduce production energy consumption and operating costs.

Description

Technical Field

[0001] The invention belongs to the field of pulping and papermaking engineering, and particularly relates to a method for obtaining high-whiteness pulp and high-activity lignin by adding lignin parent small molecules and short-chain polyols during raw material cooking. Background Art

[0002] The information disclosed in this background technology section is only intended to enhance the understanding of the overall background of the invention, and should not necessarily be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to a person skilled in the art.

[0003] The pulp and paper industry is a huge consumer of wood fiber raw materials. The traditional pulping process mainly utilizes cellulose in wood fiber raw materials, while the other two main components, hemicellulose and lignin, are not fully utilized. Based on the concept of biomass refining, exploring efficient separation technology for all components of wood fiber raw materials is both a severe challenge and a rare development opportunity for the traditional pulp and paper industry. Based on the concept of biomass refining, the development of new and efficient wood fiber separation technology should meet two principles: (1) selectively and efficiently separate the main components of wood fiber raw materials to obtain products such as cellulose pulp, hemicellulose sugars and lignin; (2) the separated components are easy to further process into high value-added products. On this basis, a biomass refining platform for high-value utilization of wood fiber is constructed.

[0004] In the pulp and paper industry that uses a large amount of wood fiber raw materials, about 80% to 90% of the lignin is removed from the raw materials and dissolved in the cooking liquid during the pulping and papermaking process. The unremoved lignin remains in the cellulose pulp, which causes the pulp to be brown in color and white at 20% to 30% ISO. The high-value application of cellulose pulp often requires a higher cellulose purity or whiteness, such as dissolving-grade pulp. The existing conventional preparation process of dissolving-grade pulp includes three stages: pretreatment, cooking and bleaching. The natural pulp obtained after cooking needs to go through 4-6 bleaching stages to further remove the lignin remaining in the pulp to improve the purity or whiteness of the cellulose pulp. The bleaching process of pulp consumes a large amount of chemicals such as hypochlorite, chlorine dioxide, sodium hydroxide and hydrogen peroxide. According to statistics, hydrogen peroxide used for pulp bleaching accounts for 50% of the total production (about 1.1 million tons) worldwide each year. In addition, a large amount of wastewater is produced during the bleaching process, which is the main source of wastewater in the pulp and paper industry and the main target of environmental risk management.

[0005] Therefore, by improving the existing cellulose separation technology, the lignin removal rate can be increased, the residual lignin content in the pulp can be reduced, and pulp with higher whiteness can be directly obtained through separation. The subsequent bleaching process and the amount of bleaching chemicals used can be effectively reduced, while highly active lignin and hemicellulose can be obtained. This is of great significance for realizing the high value and industrialization of biomass resource utilization.

[0006] Patent CN111958730A discloses a method for inhibiting lignin condensation, replacing macromolecular lignin with small molecular phenolic organic matter, which preferentially reacts with the active sites of lignin to increase the efficiency of delignification. Patent CN109706769A discloses a method for separating lignocellulose by blending small molecular aldehyde organic matter with organic acid, mixing the small molecular aldehyde organic matter and organic acid blend with wood fiber raw material and then performing high temperature cooking to increase the lignin removal rate. However, the above method still needs to be improved in improving the whiteness of pulp. Summary of the invention

[0007] In order to solve the above problems, the present invention provides a method for preparing high-whiteness pulp and high-activity lignin, so as to improve the lignin removal rate of wood fiber biomass components and directly obtain high-whiteness pulp and high-activity lignin. The present invention adds lignin parent small molecules and short-chain polyols during the cooking process. During the delignification process, the lignin parent small molecules and the short-chain polyols form a nucleophilic combination (including active organic small molecules containing short chains and aromatic bodies), and a saturated condensation reaction occurs on the side chain position of lignin, that is, the lignin parent small molecules and the short-chain polyols form a nucleophilic combination to react with as many electrophilic active sites of the lignin intermediate as possible, and after occupying these electrophilic sites of the lignin intermediate, the lignin intermediate loses its reaction activity, thereby blocking the reaction between the electrophilic points of the lignin intermediate and the nucleophilic points of the lignin molecule itself, and preventing the condensation reaction between the lignin molecules themselves. Therefore, the relative molecular mass of dissolved lignin can be reduced, the dissolution of lignin from the cell wall of the raw material can be promoted, the residual lignin in the cellulose pulp can be reduced, the purity of cellulose can be improved, and unbleached pulp with higher whiteness can be directly obtained, while highly active lignin and hemicellulose products can be obtained.

[0008] The present invention finds that the linking bonds in the lignin structure are mainly β-O-4 aromatic ether bonds (accounting for 40-60%), and contain ether bonds such as α-O-4, 4-O-5, and carbon-carbon bonds such as β-1, 5-5, and β-β. In the process of delignification, lignin will be degraded and dissolved from the raw material into the reaction system. Its degradation reaction is the process of breaking different connecting bonds in the lignin structure. These degradation reactions occur in a disordered manner, among which the breaking of α-aromatic ether bonds and β-aromatic ether bonds in the lignin structure is the main way of lignin degradation and dissolution. In addition to the degradation reaction of fragmentation, lignin will also undergo intramolecular and intermolecular condensation reactions. These condensation reactions are mainly (1) the carbon cation at the C-α position of the lignin reaction intermediate reacts with the active sites of the benzene rings of other lignin units (C5 and C6 positions) to form an intermolecular condensation structure; (2) the carbon cation at the C-α position attacks the benzene rings of adjacent lignin units to generate new carbon-carbon bonds to form a benzofuran intramolecular condensation structure. These condensation reactions also occur in a disordered manner, in which the intermolecular condensation reaction causes the lignin fragments to be reconnected into macromolecules through carbon-carbon bonds, thereby increasing the relative molecular mass of lignin. The carbon cation at the C-α position of lignin is a key active intermediate for the degradation reaction and condensation reaction of lignin. Due to its high chemical reactivity, the lignin matrix small molecule organic matter can preferentially undergo condensation reaction with the carbon cation at the C-α position of lignin to a certain extent. The addition of short-chain polyols will further promote the condensation reaction of itself and the lignin matrix small molecule with the carbon cation at the C-α position of lignin, thereby achieving a saturated condensation reaction of the carbon cation at the C-α position of the lignin side chain. The addition of short-chain polyols will make up for the obstacles to the reaction caused by the spatial structure of the lignin matrix small molecule. In the delignification process, the nucleophilic combination of lignin parent small molecules and short-chain polyols can more effectively reduce the activity of lignin molecular intermediates (carbon cations at the C-α position of lignin), form stable lignin molecules, and reduce the condensation reaction between disordered lignin molecules, that is, reduce the relative molecular mass of dissolved lignin, thereby promoting the removal of lignin and facilitating the acquisition of low molecular weight, functional group-rich, highly active lignin.

[0009] In order to achieve the above object, the present invention adopts the following technical solution:

[0010] The first aspect of the present invention provides a method for preparing high brightness pulp and high activity lignin, comprising:

[0011] In the presence of lignin parent small molecule organic matter, short chain polyols and cooking reagents, the lignocellulose raw material is separated at high temperature to obtain;

[0012] The number of benzene rings of the lignin parent small molecule organic matter is 1, and the lignin parent small molecule organic matter is at least one of guaiacol, eugenol, m-methoxyphenol, p-methoxyphenol, p-hydroxybenzaldehyde, benzaldehyde, vanillin and syringaldehyde;

[0013] The dosage ratio of the lignin parent small molecule organic matter, the short-chain polyol and the cooking agent is 1-2:1-5:7-9.5.

[0014] The present invention uses a cooking liquid composed of a cooking agent and a lignin matrix small molecule organic matter in a certain ratio to perform high temperature separation on the lignocellulose raw material. The purpose of the high temperature separation can be pulping and papermaking, or it can be comprehensive utilization of biomass.

[0015] In some embodiments, the short-chain polyol is at least one of ethylene glycol, propylene glycol, butylene glycol, and glycerol.

[0016] The cooking agent can be a solvent used in conventional separation methods in the prior art and can be used in conventional concentrations. Therefore, in some embodiments, the cooking agent is at least one of formic acid, acetic acid, methanol, ethanol, sodium sulfide, sodium sulfite and sodium hydroxide.

[0017] In some embodiments, the ratio of the cooking agent to the "total mass of lignin parent small molecule organic matter and short-chain polyols" is 5-95:95-5.

[0018] Preferably, the ratio of the cooking agent to the "total mass of lignin parent small molecule organic matter and short-chain polyols" is 7-8:1-1.5.

[0019] In some embodiments, the mass ratio of the lignin parent small molecule organic matter to the short-chain polyol is 5-95:95-5.

[0020] Preferably, the mass ratio of the lignin matrix small molecule organic matter to the short-chain polyol is 1 to 2:1.

[0021] In some embodiments, the conditions for high temperature separation are: feed-liquid mass ratio of 1:4 to 1:20, preferably 1:4 to 1:10, more preferably 1:7 to 1:10;

[0022] In some embodiments, the high temperature separation temperature is 60 to 200°C, preferably 80 to 170°C, and more preferably 130 to 140°C;

[0023] In some embodiments, the high temperature separation time is 10 to 900 min, preferably 10 to 180 min, and more preferably 30 to 60 min;

[0024] In some embodiments, the heating rate is preferably 5 to 10° C. / min.

[0025] In some embodiments, the method further comprises: after the high temperature separation is completed, solid-liquid separation is performed to obtain solids and black liquor;

[0026] Using the solids to prepare pulp;

[0027] The black liquor is used to extract high-activity lignin and / or hemicellulose sugars, and to recover cooking reagents and lignin parent small molecule organic matter.

[0028] More specifically, the extraction method of lignin and / or hemicellulose sugars can adopt existing conventional extraction methods, such as evaporation and concentration under reduced pressure, and then adding water to generate a precipitate to obtain lignin, and the hemicellulose sugars dissolved in the water phase can be obtained after drying.

[0029] The recovery method of the cooking reagent is: after reduced pressure evaporation, it is obtained separately through multi-effect extraction and distillation.

[0030] In some embodiments, the lignocellulosic feedstock includes wood (such as poplar, eucalyptus, and acacia) and non-wood fiber feedstock (such as bamboo, rice straw, wheat straw, and corn stover).

[0031] The second aspect of the present invention provides pulp with higher brightness prepared by the above method.

[0032] The third aspect of the present invention provides the use of lignin-based small-molecule organic matter and short-chain polyols in improving pulp whiteness.

[0033] Beneficial effects of the present invention

[0034] (1) In the process of raw material cooking, the present invention reduces the molecular weight of lignin dissolved by adding lignin matrix small molecule organic matter and short-chain polyols, increases the number of lignin functional groups, promotes the dissolution of lignin, improves the purity of cellulose, and directly obtains pulp with higher whiteness and high-activity lignin.

[0035] (2) The present invention improves the removal rate of lignin in the raw material and reduces the amount of residual lignin and chemicals in the cellulose pulp.

[0036] (3) The blended cooking liquid and lignin precursor small molecule organic matter of the present invention are easy to recycle, the operation process is simple, and the production cost is low.

[0037] (4) The preparation method of the present invention is simple, practical and easy to promote. DETAILED DESCRIPTION

[0038] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0039] The present invention will be further described in detail below in conjunction with specific embodiments. It should be noted that the specific embodiments are intended to explain the present invention rather than to limit it.

[0040] Unless otherwise specified, the content of each component used below is in mass percentage.

[0041] Example 1

[0042] Wood fiber raw materials: poplar wood chips, length and width 2.0 to 4.0 cm, thickness 0.5 to 1.0 cm;

[0043] Cooking vessel: Hastelloy reactor, heated by a programmable temperature-controlled heating jacket.

[0044] Table 1 Cooking material ratio:

[0045]

[0046]

[0047] Among them, control group 4 used resorcinol to replace guaiacol, control group 5 used ethanol to replace ethylene glycol, control group 6 used propylene glycol to replace ethylene glycol, control group 7 used butylene glycol to replace ethylene glycol, control group 8 used a combination of ethylene glycol and propylene glycol to replace ethylene glycol, and the mass ratio of the two was 1:1; control group 9 used a combination of butylene glycol and propylene glycol to replace ethylene glycol, and the mass ratio of the two was 1:1.

[0048] Cooking process:

[0049] a. The blended cooking liquid (cooking agent + lignin matrix small molecules + short-chain polyols) and poplar wood chips in the above Table 1 are loaded into a reactor, heated to 140°C, and cooked at the highest temperature for 45 minutes. The heating rate during the heating process is 5.0°C / min.

[0050] b. After the cooking is completed, the solid and liquid are separated to obtain solids and black liquor. The solids are washed and screened to obtain pulp.

[0051] c. Recover chemical products such as cooking reagents, sugars and lignin from the black liquor. The lignin recovery method can be reduced pressure evaporation concentration, adding water to generate precipitation to obtain lignin.

[0052] The cooking reagents are obtained respectively through reduced pressure evaporation and multi-effect extraction and distillation, and are reused.

[0053] Table 2 Properties of the separated products

[0054]

[0055]

[0056] From the comparison of ratio 1 to ratio 3, it can be seen that with the increase in the dosage of lignin matrix small molecule organic matter and short chain polyols, the whiteness of the pulp gradually increases.

[0057] From the comparison of ratio 4 and ratio 4-3, it can be seen that when the ratio of lignin matrix small molecule organic matter and short chain polyol is 1:1, the whiteness of the pulp is the highest.

[0058] From the comparison between the ratio 3 and the ratio 5, it can be seen that, compared with the use of formic acid alone, the combination of formic acid and acetic acid has a poor effect on lignin removal and reduces the whiteness of the pulp.

[0059] From the comparison between mix 1 and mix 6, it can be seen that as the total acid dosage decreases, the whiteness of the pulp decreases.

[0060] From the comparison between mix 4, mix 7 and mix 8, it can be seen that, compared with eugenol and p-hydroxybenzaldehyde, using guaiacol as the lignin matrix small molecule organic matter can better improve the pulp whiteness.

[0061] From the comparison of ratios 9 to 12, it can be seen that among the combinations of guaiacol, eugenol and p-hydroxybenzaldehyde, the combination of guaiacol and eugenol has a better effect on improving the whiteness of pulp.

[0062] From the comparison between the ratio 3 and the control groups 1-3, it can be seen that the addition of lignin-based small molecule organic matter and short-chain polyols effectively improves the whiteness of the pulp. Compared with the addition of lignin-based small molecule organic matter or short-chain polyols alone, the nucleophilic combination composed of the simultaneous addition of the two can significantly improve the whiteness of the pulp.

[0063] From the comparison between the ratio 3 and the control group 4, it can be seen that after the use of resorcinol instead of guaiacol, the whiteness of the pulp decreased significantly.

[0064] From the comparison between the ratio 3 and the control group 5, it can be seen that after the ethylene glycol is replaced by ethanol, the whiteness of the pulp is significantly reduced.

[0065] From the comparison between ratio 3 and control groups 6-9, it can be seen that the addition of short-chain polyols, such as ethylene glycol, propylene glycol, butanediol, and ethylene glycol blended with propylene glycol and butanediol blended with propylene glycol can reduce the relative molecular mass of lignin to a certain extent and improve the whiteness of pulp, among which ethylene glycol has the best effect.

[0066] In summary, it can be seen that compared with the cooking process without adding additives or adding a single additive, the addition of lignin matrix small molecules and short-chain polyol composite solution can significantly reduce the relative molecular mass of lignin and improve the whiteness of pulp, indicating that it effectively reduces the content of residual lignin in pulp and obtains pulp with higher whiteness.

[0067] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing high-brightness pulp and high-activity lignin, characterized in that: include: In the presence of lignin parent small molecule organic matter, short chain polyols and cooking reagents, the lignocellulose raw material is separated at high temperature to obtain; The number of benzene rings of the lignin parent small molecule organic compound is 1, and the compound is selected from at least one of guaiacol and eugenol; The mass ratio of the lignin precursor small molecule organic matter, the short-chain polyol and the cooking agent is (1-2): (1-5): (7-9.5); The short-chain polyol is selected from at least one of ethylene glycol, propylene glycol and butanediol; The cooking agent is selected from at least one of formic acid and acetic acid.

2. The method for preparing higher brightness pulp and high activity lignin according to claim 1, characterized in that: The mass ratio of the lignin parent small molecule organic matter to the short-chain polyol is (1-2):

1.

3. The method for preparing higher brightness pulp and high activity lignin according to claim 1, characterized in that: The conditions for the high-temperature separation are: a feed-liquid mass ratio of (1:4) to (1:20), a high-temperature separation temperature of 60 to 200° C., and a high-temperature separation time of 10 to 900 min.

4. The method for preparing higher brightness pulp and high activity lignin according to claim 1, characterized in that: Also includes: After high temperature separation is completed, solid and liquid are separated to obtain solids and black liquor; using the solids to prepare pulp; The black liquor is used to extract high-activity lignin and / or hemicellulose sugars, and to recover cooking reagents and lignin parent small molecule organic matter.

5. The method for preparing higher brightness pulp and high activity lignin according to claim 1, characterized in that: Lignocellulosic feedstocks include wood and non-wood fiber feedstocks.

6. The method for preparing higher brightness pulp and high activity lignin according to claim 5, characterized in that: The wood is selected from at least one of poplar, eucalyptus and acacia.

7. The method for preparing higher brightness pulp and high activity lignin according to claim 5, characterized in that: The non-wood fiber raw material is selected from at least one of bamboo, rice straw, wheat straw and corn stalks.

8. Pulp with higher brightness and high-activity lignin prepared by the method according to any one of claims 1 to 7.

9. Application of lignin matrix small molecule organic matter and short chain polyols in improving pulp whiteness and lignin activity, characterized in that: Prepared by the method according to any one of claims 1 to 7; The number of benzene rings of the lignin parent small molecule organic matter is 1, and the lignin parent small molecule organic matter is at least one selected from guaiacol and eugenol.

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