Production method of high-whiteness non-wood unbleached pulp

Abstract

The invention provides a production method of high-whiteness non-wood unbleached pulp. The production method of the high-whiteness non-wood unbleached pulp comprises the following steps: reacting a hydrogen bond donor with a hydrogen bond acceptor to obtain a ternary eutectic solvent; the method comprises the following steps: dispersing dried 60-80-mesh non-wood raw material powder into a ternary eutectic solvent, reacting, filtering, washing, dehydrating and drying to obtain the high-whiteness non-wood unbleached pulp. The green ternary eutectic solvent is adopted to treat non-wood raw materials to produce the high-whiteness unbleached paper pulp, and the production method is simple, low in cost, green, safe, efficient and suitable for industrialization; the obtained paper pulp has high whiteness without being bleached, and reliable guarantee is provided for chlorine-free bleaching of straw pulp and production of high-whiteness unbleached paper pulp; and the pulping by-product lignin can be effectively recovered, and a new strategy is provided for lignocellulose biomass refining.

Description

Technical Field

[0001] The invention belongs to the field of pulping and papermaking, and particularly relates to a method for producing high-whiteness non-wood natural color pulp. Background Art

[0002] At present, there are many methods for producing pulp, such as chemical method, chemical-mechanical method, mechanical method, etc. Among the chemical methods, the alkali method and the sulfite method dominate the many pulping methods. The pulp obtained by chemical cooking is called natural pulp. Unbleached pulp has a low whiteness characteristic (generally less than 30% ISO). Its bleaching process requires the implementation of multiple processes and relies on high-dose chlorine-containing bleaching agents, which causes the toxic components of papermaking wastewater to exceed the standard, forming a significant environmental load. In order to meet the use requirements of paper, the pulp must be bleached to give the paper a higher whiteness. If the whiteness of the pulp can be improved during the pulping process, it can not only save the subsequent bleaching process and solve the black liquor problem that may exist in the pulping process, but also greatly reduce costs and ensure environmentally friendly production, simplify the production process, reduce production costs, and further expand the processing and utilization of natural pulp.

[0003] Chinese patent document CN107090730A uses bamboo as raw material and produces natural pulp through two steps of pretreatment, washing, dehydration, refining, screening, and purification. Chinese patent document CN103924470A pretreats plant fiber raw material with sodium percarbonate, then cooks it in a mixed organic solvent of formic acid, acetic acid, and acetone. The cooked pulp is then washed with formic acid and hot water to produce natural pulp. Chinese patent document CN1238816A treats lignocellulosic biomass with formic acid at a reaction temperature greater than 85°C. After the reaction, the pulp is rinsed with formic acid and finally bleached with alkaline hydrogen peroxide.

[0004] However, the existing technologies mentioned above still have the following drawbacks. The preparation method is cumbersome, and the raw materials need to be pretreated twice, which increases operating costs. When using organic acids to produce natural pulp, the liquid strong acid is highly dangerous and difficult to recycle. In addition, the acid and alkaline solutions used in the washing and bleaching of pulp can cause problems such as corrosion of equipment and environmental pollution. The washed pulp needs to be further bleached to produce natural pulp, which increases the process flow and limits the development of industrialization. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention provides a method for producing high-whiteness, natural-color non-wood pulp. This method uses a green ternary deep eutectic solvent to treat non-wood raw materials to produce high-whiteness, natural-color pulp. The production method is simple, low-cost, environmentally friendly, safe, and efficient, making it suitable for industrialization. The resulting pulp exhibits high whiteness without the need for bleaching, providing a reliable guarantee for chlorine-free bleaching of straw pulp and the production of high-whiteness, natural-color pulp. Furthermore, the method can effectively recover lignin, a byproduct of pulping, providing a new strategy for refining lignocellulosic biomass.

[0006] The technical solutions of the present invention are as follows:

[0007] A method for producing high-whiteness non-wood natural color pulp comprises the following steps:

[0008] (1) A hydrogen bond donor and a hydrogen bond acceptor react to obtain a ternary deep eutectic solvent;

[0009] (2) Dispersing dry 60-80 mesh non-wood raw material powder in a ternary low eutectic solvent, reacting, filtering, washing, dehydrating and drying to obtain a high-whiteness non-wood natural color pulp.

[0010] According to the present invention, preferably, in step (1), the hydrogen bond acceptor is one or a combination of two or more of choline chloride, guanidine hydrochloride, benzyltetramethylammonium chloride, benzyltriethylammonium chloride, tetramethylammonium chloride or tetramethylammonium bromide, preferably guanidine hydrochloride.

[0011] According to the preferred embodiment of the present invention, in step (1), the hydrogen bond donors are lactic acid and p-toluenesulfonic acid, and the molar ratio of lactic acid to p-toluenesulfonic acid is 2:0.04-0.1, preferably 2:0.06.

[0012] According to the preferred embodiment of the present invention, in step (1), the molar ratio of the hydrogen bond donor to the hydrogen bond acceptor is 2.04-2.1:1, preferably 2.06:1.

[0013] Preferably, according to the present invention, in step (1), the reaction temperature is 50-70° C., the reaction time is 1-2 h, and the reaction is carried out under stirring conditions.

[0014] According to the present invention, in step (2), the non-wood raw material is selected from one or a combination of two or more of Qigang, moso bamboo, rice straw, wheat straw, sugarcane bagasse or xylose residue, preferably Qigang or moso bamboo.

[0015] Preferably, according to the present invention, in step (2), the volume ratio of the mass of the non-wood raw material powder to the ternary deep eutectic solvent is 1:10-20 g / mL.

[0016] According to the preferred embodiment of the present invention, in step (2), the reaction temperature is 80-120° C., preferably 100-120° C.; the reaction time is 5-60 minutes, preferably 5-15 minutes; and the reaction is carried out under stirring conditions.

[0017] According to the preferred embodiment of the present invention, in step (2), the filtrate obtained by filtration is subjected to reverse precipitation with a hydrochloric acid aqueous solution having a pH of 2, and the by-product lignin is obtained by filtration and drying.

[0018] According to the preferred embodiment of the present invention, the obtained high-whiteness non-wood natural color pulp does not need to be bleached, and natural color paper is obtained through further pulping, screening, and papermaking. The pulping, screening, and papermaking processes can be carried out according to existing methods.

[0019] The technical features and beneficial effects of the present invention are as follows:

[0020] (1) The reaction raw materials of the present invention are non-wood resources, which makes up for the shortage of pulping raw materials, avoids excessive deforestation, and protects the ecological environment.

[0021] (2) The ternary deep eutectic solvent used in the present invention is easier to design and synthesize, is inexpensive, low-toxic, biocompatible, biodegradable, and recyclable, eliminating the need for a complex preparation process. The ternary deep eutectic solvent is recyclable, and the wastewater is free of sulfides and AOX (adsorbable organic halides), with a COD value 80% lower than that of conventional pulping.

[0022] (3) The method of the present invention has a short processing time, a simple production process, and an easy-to-control reaction. It does not require the use of acid or alkali, and does not require a bleaching process. It is green, safe, and environmentally friendly, effectively reduces energy consumption, reduces costs, and is suitable for industrialization.

[0023] (4) The method of the present invention does not require a bleaching process, and the obtained pulp also has a high whiteness, which provides a reliable guarantee for the chlorine-free bleaching of straw pulp and the production of high-whiteness natural pulp.

[0024] (5) The method of the present invention can effectively recover lignin, a by-product of pulping, and provides a new strategy for the refining of lignocellulosic biomass.

[0025] (6) Guanidine hydrochloride is a strong hydrogen bond acceptor, containing guanidinium cations and Cl-, forming a highly polar solvent environment, destroying the hydrogen bond network in the lignin-carbohydrate complex (LCC), and selectively dissolving lignin. The high charge density of the guanidinium cation (higher than choline) can more effectively destroy the hydrogen bond network of LCC, and its Cl- forms a strong ion pair with the phenolic hydroxyl group of lignin. Lactic acid (hydrogen bond donor) provides protons (H + ) and carboxylic acid groups, protonating the lignin ether bond, causing it to break and inhibiting the formation of quinone-type chromophores. The α-hydroxycarboxylic acid structure of lactic acid can chelate metal ions (such as Fe 3+), preventing the oxidative degradation of cellulose caused by the Fenton reaction. p-Toluenesulfonic acid, a strongly acidic hydrogen bond donor, contains a sulfonic acid group and a hydrophobic benzene ring, which enhances solvent acidity and catalyzes the cleavage of lignin's β-O-4 bonds. The benzene rings stack with lignin in a π-π pattern, leading to the directional exfoliation of lignin fragments. The strong acidity of the sulfonic acid group (pKa = -2.8) allows it to catalyze the cleavage of β-O-4 bonds at low temperatures (80°C) (compared to temperatures >150°C traditionally). Its benzene rings also have a better match with the hydrophobic regions of lignin than other sulfonic acids (such as benzenesulfonic acid).

[0026] The deep eutectic solvent forms a dynamic cross-linked network through hydrogen bonding. Lactic acid (pKa = 3.86) provides mild acidity, while p-toluenesulfonic acid (pKa = -2.8) enhances the local strong acid microenvironment, forming a gradient of proton attack, precisely severing the β-O-4 bonds in lignin (requires pH < 3) while preventing excessive hydrolysis of cellulose. The guanidinium cations form an ion-hydrogen bond cross-linked network with the anions of lactic acid and p-toluenesulfonic acid (Cl-, lactate, and p-toluenesulfonate), creating a "molecular clamp" effect that selectively encapsulates lignin fragments. The benzene rings of p-toluenesulfonic acid stack with the phenylpropane units of lignin through π-π stacking, preferentially stripping the hydrophobic lignin while retaining the cellulose due to its hydrophilicity.

[0027] The reducing properties of lactic acid inhibit the formation of quinone structures. The sulfonic acid groups of p-toluenesulfonic acid react with the phenolic hydroxyl groups of lignin, blocking the formation of conjugated double bonds and inhibiting the formation of lignin chromophores. Guanidine hydrochloride stabilizes the type I crystal structure of cellulose through hydrogen bonds, inhibiting the hydrolysis of amorphous regions. Residual hemicellulose fills the interfiber gaps, reducing light scattering and improving pulp brightness.

[0028] As described above, the components of the ternary deep eutectic solvent of the present invention work together as a whole to achieve the dual functions of directional oxidation of chromophores and protection of cellulose, thereby improving the whiteness of pulp.

[0029] (7) The ternary deep eutectic solvent of the present invention has a significantly higher lignin solubility than traditional solvents (e.g., NaOH removal rate of 75-85%). Ionic liquid ([EMIM]Ac): has a high solubility for cellulose (>40%) and consumes a lot of energy for recovery. Binary deep eutectic solvent (choline chloride / lactic acid): lacks the strong acidity and π-π interaction of p-toluenesulfonic acid, resulting in a low delignification rate and insufficient whiteness. Organic acid (formic acid / acetic acid): is too acidic, leading to cellulose hydrolysis (DP decrease >30%), and has no directional solubility. DETAILED DESCRIPTION

[0030] The present invention will be further described below by way of specific examples, but is not limited thereto.

[0031] The experimental methods described in the examples are conventional methods unless otherwise specified; the reagents and materials used are commercially available unless otherwise specified.

[0032] Example 1

[0033] A method for producing high-whiteness non-wood natural color pulp comprises the following steps:

[0034] (1) Guanidine hydrochloride, lactic acid, and p-toluenesulfonic acid were mixed uniformly in a molar ratio of 1:2:0.06, and heated and stirred at 60°C for 1.5 h to obtain a homogeneous and transparent solution, namely, a ternary deep eutectic solvent.

[0035] (2) The Qigang raw material powder with a particle size of 60-80 mesh was obtained, which was composed of 40.7% cellulose, 20.1% xylan, and 24.8% lignin. 1 g of the 60-80 mesh Qigang raw material powder was weighed, and 15 mL of a guanidine hydrochloride / lactic acid / p-toluenesulfonic acid low eutectic solvent was added. The mixture was treated at 100°C and a stirring speed of 500 rpm for 5 minutes. Through the strong hydrogen bond breaking effect of guanidine hydrochloride, the protonation ability of lactic acid, and the synergistic catalytic effect of p-toluenesulfonic acid, the lignin-carbohydrate complex was efficiently dissociated (the removal rates of lignin and hemicellulose were 62.4% and 58.2%, respectively). After the reaction, the mixture was hot filtered, washed alternately with deionized water and ethanol, and vacuum dried at 60°C to obtain cellulose pulp, the cellulose content of which was increased to 58.3% (an increase of 17.6% compared to the raw material), and the pulp brightness was 40.7% ISO. The reaction mixture was then hot-filtered, and the resulting filtrate was subjected to reverse precipitation with a hydrochloric acid solution at a pH of 2. The lignin byproduct was recovered by filtration and drying at a yield of 40.9% (based on the lignin content in the raw material). FT-IR and compositional analysis confirmed the product to be sulfur-free, high-purity lignin with a purity of 95.4%.

[0036] Example 2

[0037] A method for producing high-whiteness non-wood natural color pulp comprises the following steps:

[0038] (1) Guanidine hydrochloride, lactic acid, and p-toluenesulfonic acid were mixed uniformly in a molar ratio of 1:2:0.06, and heated and stirred at 60°C for 1.5 hours to obtain a homogeneous and transparent solution, namely, a ternary deep eutectic solvent.

[0039] (2) The Qigang raw material powder with a particle size of 60-80 mesh was obtained, which was composed of 40.7% cellulose, 20.1% xylan, and 24.8% lignin. 1 g of the 60-80 mesh Qigang raw material powder was weighed, and 15 mL of a low eutectic solvent of guanidine hydrochloride / lactic acid / p-toluenesulfonic acid was added. The mixture was treated at 100°C and a stirring speed of 500 rpm for 10 minutes. The strong hydrogen bond breaking effect of guanidine hydrochloride, the protonation ability of lactic acid, and the synergistic catalytic effect of p-toluenesulfonic acid effectively dissociated the lignin-carbohydrate complex (the removal rates of lignin and hemicellulose were 84.5% and 78.3%, respectively). After the reaction, the mixture was hot filtered, washed alternately with deionized water and ethanol, and vacuum dried at 60°C to obtain cellulose pulp. The cellulose content was increased to 71.7% (30.0% higher than the raw material) and the pulp brightness was 45.3% ISO. The reaction mixture was then hot-filtered, and the resulting filtrate was subjected to reverse precipitation with a hydrochloric acid solution at a pH of 2. The lignin byproduct was recovered by filtration and drying at a yield of 47.6% (based on the lignin content in the raw material). FT-IR and compositional analysis confirmed the product to be sulfur-free, high-purity lignin with a purity of 98.9%.

[0040] Example 3

[0041] A method for producing high-whiteness non-wood natural color pulp comprises the following steps:

[0042] (1) Guanidine hydrochloride, lactic acid, and p-toluenesulfonic acid were mixed uniformly in a molar ratio of 1:2:0.06, and heated and stirred at 60°C for 1.5 hours to obtain a homogeneous and transparent solution, namely, a ternary deep eutectic solvent.

[0043] (2) Qigang is dried and crushed to obtain a Qigang raw material powder with a particle size of 60-80 mesh, which is composed of: 40.7% cellulose, 20.1% xylan, and 24.8% lignin. 1 g of the 60-80 mesh Qigang raw material powder is weighed, 15 mL of a guanidine hydrochloride / lactic acid / p-toluenesulfonic acid low eutectic solvent is added, and the mixture is treated at 100°C and a stirring speed of 500 rpm for 15 minutes. Through the strong hydrogen bond breaking effect of guanidine hydrochloride, the protonation ability of lactic acid, and the synergistic catalytic effect of p-toluenesulfonic acid, the lignin-carbohydrate complex is efficiently dissociated (the removal rates of lignin and hemicellulose are 91.6% and 88.7%, respectively). After the reaction, the mixture is hot filtered, washed alternately with deionized water and ethanol, and vacuum dried at 60°C to obtain cellulose pulp, the cellulose content of which is increased to 74.3% (33.6% higher than the raw material), and the pulp brightness is 51.5% ISO. The reaction mixture was then hot-filtered, and the resulting filtrate was subjected to reverse precipitation with a hydrochloric acid solution at a pH of 2. The lignin byproduct was recovered by filtration and drying at a yield of 56.9% (based on the lignin content in the raw material). FT-IR and compositional analysis confirmed the product to be sulfur-free, high-purity lignin with a purity of 99.2%.

[0044] Example 4

[0045] A method for producing high-whiteness non-wood natural color pulp comprises the following steps:

[0046] (1) Guanidine hydrochloride, lactic acid, and p-toluenesulfonic acid were mixed uniformly in a molar ratio of 1:2:0.06, and heated and stirred at 60°C for 1.5 hours to obtain a homogeneous and transparent solution, namely, a ternary deep eutectic solvent.

[0047] (2) Qigang is dried and crushed to obtain a Qigang raw material powder with a particle size of 60-80 mesh, which is composed of: 40.7% cellulose, 20.1% xylan, and 24.8% lignin. 1 g of the 60-80 mesh Qigang raw material powder is weighed, and 15 mL of a guanidine hydrochloride / lactic acid / p-toluenesulfonic acid low eutectic solvent is added. The mixture is treated at 110°C and a stirring speed of 500 rpm for 5 minutes. The strong hydrogen bond breaking effect of guanidine hydrochloride, the protonation ability of lactic acid, and the synergistic catalytic effect of p-toluenesulfonic acid effectively dissociate the lignin-carbohydrate complex (the removal rates of lignin and hemicellulose are 77.3% and 71.7%, respectively). After the reaction, the mixture is hot filtered, washed alternately with deionized water and ethanol, and vacuum dried at 60°C to obtain cellulose pulp, the cellulose content of which is increased to 78.3% (37.6% higher than the raw material), and the pulp brightness is 43.6% ISO. The reaction mixture was then hot-filtered, and the resulting filtrate was subjected to reverse precipitation with a hydrochloric acid solution at a pH of 2. The lignin byproduct was recovered by filtration and drying at a yield of 51.4% (based on the lignin content in the raw material). FT-IR and compositional analysis confirmed the product to be sulfur-free, high-purity lignin with a purity of 96.4%.

[0048] Example 5

[0049] A method for producing high-whiteness non-wood natural color pulp comprises the following steps:

[0050] (1) Guanidine hydrochloride, lactic acid, and p-toluenesulfonic acid were mixed uniformly in a molar ratio of 1:2:0.06, and heated and stirred at 60°C for 1.5 hours to obtain a homogeneous and transparent solution, namely, a ternary deep eutectic solvent.

[0051] (2) Qigang is dried and crushed to obtain a Qigang raw material powder with a particle size of 60-80 mesh, which is composed of: 40.7% cellulose, 20.1% xylan, and 24.8% lignin. 1 g of the 60-80 mesh Qigang raw material powder is weighed, and 15 mL of a guanidine hydrochloride / lactic acid / p-toluenesulfonic acid low eutectic solvent is added. The mixture is treated at 110°C and a stirring speed of 500 rpm for 10 minutes. The strong hydrogen bond breaking effect of guanidine hydrochloride, the protonation ability of lactic acid, and the synergistic catalytic effect of p-toluenesulfonic acid effectively dissociate the lignin-carbohydrate complex (the removal rates of lignin and hemicellulose are 81.3% and 79.5%, respectively). After the reaction, the mixture is hot filtered, washed alternately with deionized water and ethanol, and vacuum dried at 60°C to obtain cellulose pulp, the cellulose content of which is increased to 80.3% (39.6% higher than the raw material), and the pulp brightness is 49.4% ISO. The reaction mixture was then hot-filtered, and the resulting filtrate was subjected to reverse precipitation with a hydrochloric acid solution at a pH of 2. The lignin byproduct was recovered by filtration and drying at a yield of 54.9% (based on the lignin content in the raw material). FT-IR and compositional analysis confirmed the product to be sulfur-free, high-purity lignin with a purity of 98.6%.

[0052] Example 6

[0053] A method for producing high-whiteness non-wood natural color pulp comprises the following steps:

[0054] (1) Guanidine hydrochloride, lactic acid, and p-toluenesulfonic acid were mixed uniformly in a molar ratio of 1:2:0.06, and heated and stirred at 60°C for 1.5 hours to obtain a homogeneous and transparent solution, namely, a ternary deep eutectic solvent.

[0055] (2) Qigang is dried and crushed to obtain a Qigang raw material powder with a particle size of 60-80 mesh, which is composed of: 40.7% cellulose, 20.1% xylan, and 24.8% lignin. 1 g of the 60-80 mesh Qigang raw material powder is weighed, and 15 mL of a guanidine hydrochloride / lactic acid / p-toluenesulfonic acid low eutectic solvent is added. The mixture is treated at 110°C and a stirring speed of 500 rpm for 15 minutes. The strong hydrogen bond breaking effect of guanidine hydrochloride, the protonation ability of lactic acid, and the synergistic catalytic effect of p-toluenesulfonic acid effectively dissociate the lignin-carbohydrate complex (the removal rates of lignin and hemicellulose are 93.4% and 90.7%, respectively). After the reaction, the mixture is hot filtered, washed alternately with deionized water and ethanol, and vacuum dried at 60°C to obtain cellulose pulp, the cellulose content of which is increased to 86.2% (45.5% higher than the raw material), and the pulp brightness is 55.3% ISO. The reaction mixture was then hot-filtered, and the resulting filtrate was subjected to reverse precipitation with a hydrochloric acid solution at a pH of 2. The lignin byproduct was recovered by filtration and drying at a yield of 61.6% (based on the lignin content in the raw material). FT-IR and compositional analysis confirmed the product to be sulfur-free, high-purity lignin with a purity of 99.3%.

[0056] Example 7

[0057] A method for producing high-whiteness non-wood natural color pulp comprises the following steps:

[0058] (1) Guanidine hydrochloride, lactic acid, and p-toluenesulfonic acid were mixed uniformly in a molar ratio of 1:2:0.06, and heated and stirred at 60°C for 1.5 hours to obtain a homogeneous and transparent solution, namely, a ternary deep eutectic solvent.

[0059] (2) Qigang is dried and crushed to obtain a Qigang raw material powder with a particle size of 60-80 mesh, which is composed of: 40.7% cellulose, 20.1% xylan, and 24.8% lignin. 1 g of the 60-80 mesh Qigang raw material powder is weighed, and 15 mL of a guanidine hydrochloride / lactic acid / p-toluenesulfonic acid low eutectic solvent is added. The mixture is treated at 120°C and a stirring speed of 500 rpm for 5 minutes. The strong hydrogen bond breaking effect of guanidine hydrochloride, the protonation ability of lactic acid, and the synergistic catalytic effect of p-toluenesulfonic acid effectively dissociate the lignin-carbohydrate complex (the removal rates of lignin and hemicellulose are 76.2% and 71.3%, respectively). After the reaction, the mixture is hot filtered, washed alternately with deionized water and ethanol, and vacuum dried at 60°C to obtain cellulose pulp, the cellulose content of which is increased to 76.3% (35.6% higher than the raw material), and the pulp brightness is 49.4% ISO. The reaction mixture was then hot-filtered, and the resulting filtrate was subjected to reverse precipitation with a hydrochloric acid solution at a pH of 2. The lignin byproduct was recovered by filtration and drying at a yield of 56.7% (based on the lignin content in the raw material). FT-IR and compositional analysis confirmed the product to be sulfur-free, high-purity lignin with a purity of 97.5%.

[0060] Example 8

[0061] A method for producing high-whiteness non-wood natural color pulp comprises the following steps:

[0062] (1) Guanidine hydrochloride, lactic acid, and p-toluenesulfonic acid were mixed uniformly in a molar ratio of 1:2:0.06, and heated and stirred at 60°C for 1.5 hours to obtain a homogeneous and transparent solution, namely, a ternary deep eutectic solvent.

[0063] (2) Qigang is dried and crushed to obtain a Qigang raw material powder with a particle size of 60-80 mesh, which is composed of: 40.7% cellulose, 20.1% xylan, and 24.8% lignin. 1 g of the 40-80 mesh Qigang raw material powder is weighed, and 15 mL of a low eutectic solvent of guanidine hydrochloride / lactic acid / p-toluenesulfonic acid is added. The mixture is treated at 120°C and a stirring speed of 500 rpm for 10 minutes. The strong hydrogen bond breaking effect of guanidine hydrochloride, the protonation ability of lactic acid, and the synergistic catalytic effect of p-toluenesulfonic acid effectively dissociate the lignin-carbohydrate complex (the removal rates of lignin and hemicellulose are 82.3% and 86.5%, respectively). After the reaction, the mixture is hot filtered, washed alternately with deionized water and ethanol, and vacuum dried at 60°C to obtain cellulose pulp, the cellulose content of which is increased to 84.5% (43.8% higher than the raw material), and the pulp brightness is 53.9% ISO. The reaction mixture was then hot-filtered, and the resulting filtrate was subjected to reverse precipitation with a hydrochloric acid solution at a pH of 2. The lignin byproduct was recovered by filtration and drying at a yield of 65.8% (based on the lignin content in the raw material). FT-IR and compositional analysis confirmed the product to be sulfur-free, high-purity lignin with a purity of 99.6%.

[0064] Example 9

[0065] A method for producing high-whiteness non-wood natural color pulp comprises the following steps:

[0066] (1) Guanidine hydrochloride, lactic acid, and p-toluenesulfonic acid were mixed uniformly in a molar ratio of 1:2:0.06, and heated and stirred at 60°C for 1.5 hours to obtain a homogeneous and transparent solution, namely, a ternary deep eutectic solvent.

[0067] (2) Qigang is dried and crushed to obtain a Qigang raw material powder with a particle size of 60-80 mesh, which is composed of: 40.7% cellulose, 20.1% xylan, and 24.8% lignin. 1 g of the 60-80 mesh Qigang raw material powder is weighed, 15 mL of a guanidine hydrochloride / lactic acid / p-toluenesulfonic acid low eutectic solvent is added, and the mixture is treated at 120°C and a stirring speed of 500 rpm for 15 minutes. Through the strong hydrogen bond breaking effect of guanidine hydrochloride, the protonation ability of lactic acid, and the synergistic catalytic effect of p-toluenesulfonic acid, the lignin-carbohydrate complex is efficiently dissociated (the removal rates of lignin and hemicellulose are 94.6% and 95.5%, respectively). After the reaction, the mixture is hot filtered, washed alternately with deionized water and ethanol, and vacuum dried at 60°C to obtain cellulose pulp, the cellulose content of which is increased to 90.2% (49.5% higher than the raw material), and the pulp brightness is 58.4% ISO. The reaction mixture was then hot-filtered, and the resulting filtrate was subjected to reverse precipitation with a hydrochloric acid solution at a pH of 2. The lignin byproduct was recovered by filtration and drying at a yield of 71.9% (based on the lignin content in the raw material). FT-IR and compositional analysis confirmed the product to be sulfur-free, high-purity lignin with a purity of 99.5%.

[0068] Comparative Example 1

[0069] A method for producing non-wood natural color pulp comprises the following steps:

[0070] The Qigang raw material powder with a particle size of 60-80 mesh was obtained, which was composed of 40.7% cellulose, 20.1% xylan, and 24.8% lignin. 1 g of the 60-80 mesh Qigang raw material powder was weighed, 15 mg of caustic soda / sodium sulfite / anthraquinone (the mass ratio of caustic soda, sodium sulfite, and anthraquinone was 240:160:1) was added, and then water was added (the ratio of Qigang raw material powder to water was 1:15 kg / L). The mixture was treated at 160° C. and a stirring speed of 400 rpm for 150 minutes. The removal rates of lignin and hemicellulose were 50.6% and 68.6%, respectively. The reaction mixture was hot filtered, washed alternately with deionized water and ethanol, and vacuum dried at 60° C. to obtain cellulose pulp. The cellulose content in the pulp was 64.3% (increased by 23.6% compared with the raw material), and the pulp brightness was 28.4% ISO. The reaction mixture was then hot-filtered, and the resulting filtrate was subjected to reverse precipitation with a hydrochloric acid solution at pH 2. The filtrate was then filtered, dried, and recovered to yield a lignin byproduct with a yield of 10.5% (based on the lignin content in the feedstock). FT-IR and compositional analysis confirmed the product to be sulfur-containing lignin with a purity of 76.3%.

[0071] Compared to the caustic soda / sodium sulfite / anthraquinone composite solvent used in Comparative Example 1, the deep eutectic solvent used in the present invention is inexpensive, environmentally friendly, and produces unbleached pulp under mild reaction conditions and in a short reaction time, with high pulp brightness and a high yield of the byproduct lignin. This pulping method not only effectively reduces energy consumption but also effectively improves the whiteness of unbleached pulp, providing a reliable guarantee for the production of high-whiteness paper. Furthermore, the byproduct lignin can be effectively recovered, providing more possibilities for refining lignocellulosic biomass.

[0072] Comparative Example 2

[0073] A method for producing non-wood natural color pulp, comprising the following steps:

[0074] (1) Guanidine hydrochloride and lactic acid were mixed uniformly in a molar ratio of 1:2, and heated and stirred at 60°C for 1.5 h to obtain a deep eutectic solvent.

[0075] (2) The Qigang raw material powder with a particle size of 60-80 mesh was dried and crushed to obtain a Qigang raw material powder with a composition of 40.7% cellulose, 20.1% xylan, and 24.8% lignin. 1 g of the Qigang raw material powder with a particle size of 60-80 mesh was weighed, 15 mL of guanidine hydrochloride / lactic acid low eutectic solvent was added, and the mixture was treated at 120°C and a stirring speed of 500 rpm for 15 minutes. The removal rates of lignin and hemicellulose were 40.3% and 57.5%, respectively. The reaction mixture was hot filtered, washed alternately with deionized water and ethanol, and vacuum dried at 60°C to obtain cellulose pulp with a cellulose content of 54.1% (13.4% higher than the raw material) and a pulp brightness of 21.9% ISO. At the same time, the filtrate obtained by hot filtration of the reaction mixture was reverse precipitated with a hydrochloric acid aqueous solution with a pH of 2, filtered, dried and recovered to obtain a lignin by-product with a yield of 8.5% (based on the lignin content in the raw material). FT-IR and component analysis proved that it was sulfur-containing lignin with a purity of 85.7%.

[0076] Compared with the guanidine hydrochloride / lactic acid deep eutectic solvent used in Comparative Example 2, the present invention can effectively remove more lignin and hemicellulose, and the whiteness of the pulp is increased by 36.5% ISO. In addition, the by-product lignin has a higher yield and purity.

[0077] Comparative Example 3

[0078] A method for producing high-whiteness non-wood natural color pulp comprises the following steps:

[0079] (1) Guanidine hydrochloride, lactic acid, and p-toluenesulfonic acid were mixed uniformly in a molar ratio of 1:2:0.01, heated and stirred at 60°C for 1.5 h to obtain a homogeneous and transparent solution, namely, a ternary deep eutectic solvent.

[0080] (2) Qigang is dried and crushed to obtain a Qigang raw material powder with a particle size of 60-80 mesh, which is composed of: 40.7% cellulose, 20.1% xylan, and 24.8% lignin. 1 g of the 60-80 mesh Qigang raw material powder is weighed, and 15 mL of a guanidine hydrochloride / lactic acid / p-toluenesulfonic acid low eutectic solvent is added. The mixture is treated at 120°C and a stirring speed of 500 rpm for 15 minutes. The strong hydrogen bond breaking effect of guanidine hydrochloride, the protonation ability of lactic acid, and the synergistic catalytic effect of p-toluenesulfonic acid effectively dissociate the lignin-carbohydrate complex (the removal rates of lignin and hemicellulose are 51.6% and 67.5%, respectively). After the reaction, the mixture is hot filtered, washed alternately with deionized water and ethanol, and vacuum dried at 60°C to obtain cellulose pulp with a cellulose content of 71.8% (31.1% higher than the raw material) and a pulp brightness of 34.3% ISO. The reaction mixture was then hot-filtered, and the resulting filtrate was subjected to reverse precipitation with a hydrochloric acid solution at pH 2. The filtrate was then filtered, dried, and recovered to yield a lignin byproduct with a yield of 28.5% (based on the lignin content in the feedstock). FT-IR and compositional analysis confirmed the product to be sulfur-containing lignin with a purity of 91.7%.

[0081] Compared with Comparative Example 3, the present invention can effectively remove more lignin and hemicellulose, and the whiteness of the pulp is increased by 24.1% ISO. In addition, the by-product lignin has a higher yield and purity.

[0082] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as a preferred embodiment, it is not intended to limit the present invention. Any person skilled in the art can, without departing from the scope of the technical solution of the present invention, make slight changes or modifications to the technical content disclosed above into equivalent embodiments. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A method for producing high-whiteness non-wood natural color pulp, comprising the steps of: (1) A hydrogen bond donor and a hydrogen bond acceptor react to obtain a ternary deep eutectic solvent; (2) Dispersing dry 60-80 mesh non-wood raw material powder in a ternary low eutectic solvent, reacting, filtering, washing, dehydrating and drying to obtain a high-whiteness non-wood natural color pulp.

2. The method for producing high-whiteness non-wood natural color pulp according to claim 1, characterized in that: In step (1), the hydrogen bond acceptor is one or a combination of two or more of choline chloride, guanidine hydrochloride, benzyltetramethylammonium chloride, benzyltriethylammonium chloride, tetramethylammonium chloride or tetramethylammonium bromide, preferably guanidine hydrochloride.

3. The method for producing high-whiteness non-wood natural color pulp according to claim 1, characterized in that: In step (1), the hydrogen bond donors are lactic acid and p-toluenesulfonic acid, and the molar ratio of lactic acid to p-toluenesulfonic acid is 2:0.04-0.1, preferably 2:0.

06.

4. The method for producing high-whiteness non-wood natural color pulp according to claim 1, characterized in that: In step (1), the molar ratio of the hydrogen bond donor to the hydrogen bond acceptor is 2.04-2.1:1, preferably 2.06:

1.

5. The method for producing high-whiteness non-wood natural color pulp according to claim 1, characterized in that: In step (1), the reaction temperature is 50-70° C., the reaction time is 1-2 h, and the reaction is carried out under stirring.

6. The method for producing high-whiteness non-wood natural color pulp according to claim 1, characterized in that: In step (2), the non-wood raw material is selected from one or a combination of two or more of Qigang, moso bamboo, rice straw, wheat straw, sugarcane bagasse or xylose residue, preferably Qigang or moso bamboo.

7. The method for producing high-whiteness non-wood natural color pulp according to claim 1, characterized in that: In step (2), the volume ratio of the mass of the non-wood raw material powder to the ternary deep eutectic solvent is 1:10-20 g / mL.

8. The method for producing high-whiteness non-wood natural color pulp according to claim 1, characterized in that: In step (2), the reaction temperature is 80-120° C., preferably 100-120° C.; the reaction time is 5-60 minutes, preferably 5-15 minutes; and the reaction is carried out under stirring.

9. The method for producing high-whiteness non-wood natural color pulp according to claim 1, characterized in that: In step (2), the filtrate obtained by filtration is subjected to reverse precipitation with a hydrochloric acid aqueous solution with a pH of 2, and the by-product lignin is obtained by filtration and drying.