A method for preparing cotton pulp for medical and food grade cellulose ether

Abstract

The present invention relates to the field of cotton pulp technology, and in particular to a method for preparing cotton pulp for pharmaceutical and food-grade cellulose ether. The cotton pulp of the present invention is prepared by material selection, cotton opening, impurity removal; cellulose purification with the help of biological enzymes; alkali preparation, impregnation, selective removal of hemicellulose and lignin cooking; pre-sanding; pre-pulping; concentration; hydrogen peroxide bleaching; acid treatment; post-sanding; post-pulping; and papermaking. The cotton pulp has a degree of polymerization of 2500-2600 and a whiteness of ≥84%, which can make the pharmaceutical and food-grade cellulose ether have ultra-high viscosity, high degree of substitution, excellent solubility, and improve the quality of the pharmaceutical and food-grade cellulose ether. The use of the cooking technology for selective removal of hemicellulose and lignin and the cellulose purification technology with the help of biological enzymes to produce cotton pulp for pharmaceutical and food-grade cellulose ether can also make the COD discharge of wastewater in the entire pulping process between 6000 and 10000 mg / L, reducing the pressure on sewage treatment.

Description

Technical Field

[0001] The invention relates to the technical field of cotton pulp, in particular to a method for preparing cotton pulp for medical and food grade cellulose ether. Background Art

[0002] Cellulose ether is a general term for a variety of derivatives obtained through the etherification of natural cellulose. It is widely used in the pharmaceutical and health care, daily chemical, papermaking, food, construction, materials, and oil drilling industries, and is commonly known as "industrial MSG." Pharmaceutical and food-grade cellulose ether is a high-end product among cellulose ethers. The higher the degree of polymerization and whiteness, the wider its application range. The viscosity of pharmaceutical and food-grade cellulose ethers is not only related to the etherification process, but also primarily determined by the degree of polymerization of the fiber raw material itself. The higher the degree of polymerization of the fiber raw material, the higher the viscosity of the resulting pharmaceutical and food-grade cellulose ether. The most challenging aspect of cotton pulp for pharmaceutical and food-grade cellulose ethers is achieving both high degree of polymerization and high whiteness, which impacts both production and performance. Traditional cotton pulp is typically cooked at high temperatures and high alkali levels, making it difficult to achieve high degrees of polymerization and high whiteness. Furthermore, the cooking process produces a large amount of black liquor, which has a high alkali concentration, dark color, high organic content, and poor biodegradability. This constitutes a highly polluting and difficult-to-treat industrial wastewater. Therefore, how to provide a production process for high-polymerization-degree, high-whiteness cotton pulp for pharmaceutical and food-grade cellulose ether has become a technical problem to be solved urgently by those skilled in the art. Summary of the Invention

[0003] The object of the present invention is to provide a method for preparing cotton pulp for medical and food grade cellulose ether, so as to solve the problems existing in the prior art.

[0004] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0005] The present invention provides a method for preparing cotton pulp for medical and food-grade cellulose ether, comprising the following preparation steps:

[0006] 1) Material selection, cotton opening, and impurity removal; 2) Enzyme-assisted cellulose purification; 3) Alkali preparation, impregnation, selective hemicellulose removal, and lignin cooking; 4) Pre-sand removal; 5) Pre-pulping; 6) Concentration; 7) Hydrogen peroxide bleaching; 8) Acid treatment; 9) Post-sand removal; 10) Post-pulping; 11) Pulping.

[0007] Preferably, in the step 2) of cellulose purification with the aid of biological enzymes, pectinase, xylanase, and ammonium chloride are added to the slurry for purification, the purification time is 30 to 120 minutes, and the temperature is 30 to 80° C. to obtain a slurry;

[0008] The slurry has a concentration of 1-10% and a pH value of 4-6.

[0009] The usage ratio of the pectinase, xylanase, ammonium chloride and absolute dry pulp is 0.1-1kg: 0.1-1kg: 0.1-1kg: 1t.

[0010] Preferably, it is characterized in that the alkali preparation in step 3) is carried out at 80-85° C., and the alkali solution is prepared according to the ratio of NaOH to water = 1:3.7-4.2 to obtain alkali solution;

[0011] The impregnation step is to fully immerse the slurry obtained by purification in step 2) into a mixed solution of alkali solution, Na2SO3, NaBO2 and fatty alcohol polyoxyethylene ether phosphate;

[0012] The alkali solution is calculated as NaOH at 10.5-12.5% of the absolute dry pulp weight, Na2SO3 at 0.1-1% of the absolute dry pulp weight, NaBO2 at 0.1-1% of the absolute dry pulp weight, and fatty alcohol polyoxyethylene ether phosphate at 0.1-1% of the absolute dry pulp weight.

[0013] The selective removal of hemicellulose and lignin is carried out by cooking at a temperature of 100 to 160° C. for 60 to 240 minutes.

[0014] Preferably, in the step 1) of selecting materials, opening cotton and removing impurities, the third-class first-class cotton linters with a maturity of ≥80% are selected, the cotton linters are torn, and then loosened, impurities are removed, and impurities are carefully selected and removed.

[0015] Preferably, the desanding pressure before step 4) is controlled at 0.1-0.9 MPa, the desanding rate is 10-30 min / t, and the slurry concentration is 0.1-1%;

[0016] The beating current of the pre-beating in step 5) is 150-200A, the beating rate is 10-30min / t, and the slurry concentration is 0.5-1.5%;

[0017] The step 6) of concentration is to concentrate the slurry to a concentration of 5-15%.

[0018] Preferably, the step 7) hydrogen peroxide bleaching comprises the following preparation steps:

[0019] a. In a medium-consistency mixer, add diethylenetriamine pentaacetic acid and hydrogen peroxide to the slurry, introduce steam, mix at 90-110°C for 10-30 minutes, and transfer to a hydrogen peroxide bleaching tower;

[0020] The diethylenetriamine pentaacetic acid is 0.07-0.25% by weight relative to the absolute dry pulp; the hydrogen peroxide is 0.5-3% by weight relative to the absolute dry pulp;

[0021] b. In the hydrogen peroxide bleaching tower, the temperature is set at 90-110°C. After bleaching for 50-120 minutes, the pulp is diluted with deionized water to a concentration of 0.5-3%. The pulp is then sent to a vacuum pulp washer and washed with deionized water until it becomes neutral.

[0022] Preferably, the acid treatment in step 8) is carried out at room temperature for 10 to 60 minutes, followed by washing with deionized water for 1 to 3 hours;

[0023] The acid comprises hydrochloric acid; the mass concentration of the hydrochloric acid is 20-30%; and the acid is 0.5-4% relative to the absolute dry pulp.

[0024] Preferably, the pressure of sand removal after step 9) is ≥0.3 MPa, the sand removal rate is 10-30 min / t, and the concentration of the slurry is 0.5-0.7%.

[0025] Preferably, the current during beating after step 10) is 160-180 A, the beating rate is 10-30 min / t, and the concentration of the slurry is 2.5-2.7%.

[0026] Preferably, in the step 11), when pulping, the concentration of the pulp when sizing the paper on the Fourdrinier web is 8-12 g / L, the drying cylinder pressure is ≤0.20 MPa, and the pulping rate is 1-5 h / t, so as to obtain cotton pulp for medical and food grade cellulose ether.

[0027] This invention utilizes enzyme-assisted cellulose purification technology to purify cotton linters, thereby reducing cooking conditions during the cooking process and, in turn, COD in the wastewater. The principle is that through the decomposition of pectinase and xylanase, combined with the addition of ammonium chloride as an auxiliary agent, the enzymatic hydrolysis of pectin releases bound metal ions such as calcium and iron. Xylanase selectively decomposes the alkali-resistant hemicellulose in the cellulose matrix, improving the reactivity of the cotton pulp during the etherification process. Furthermore, within the pH range of 4 to 6, the probability of acidic hydrolysis of the cellulose in the cotton pulp is very low. This removes impurities while maintaining the degree of polymerization of the cotton pulp, improving the whiteness of the subsequent bleaching process.

[0028] The present invention utilizes selective hemicellulose removal and lignin cooking technology to cook cotton linters, ensuring a high degree of polymerization while improving product whiteness. The principle is as follows: low-temperature cooking reduces the degradation reaction rate of cellulose, allowing residual fat, pectin, and other substances in the cotton linters to undergo chemical reactions such as saponification and emulsification to generate water-soluble substances. Simultaneously, the sodium sulfite addition process is optimized to cleave the difficult-to-remove non-phenolic β-aryl ether bonds in lignin macromolecules, thereby increasing the delignification rate. The sodium borate addition process is optimized to allow complexation and dissolution of difficult-to-extract polyglucose mannose in hemicellulose, thereby increasing the hemicellulose removal rate. The use of the surfactant fatty alcohol polyoxyethylene ether phosphate accelerates the dissolution rate of water-soluble substances in the fiber, further weakening the cooking conditions, preventing oxidative degradation of cellulose macromolecules, ensuring the degree of polymerization of the cotton pulp, and improving product whiteness. Furthermore, the COD discharge of wastewater from the entire pulping process is below 10,000 mg / L, reducing the pressure on wastewater treatment.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] The present invention provides a method for preparing high-polymerization-degree, high-whiteness cotton pulp for pharmaceutical and food-grade cellulose ethers. The resulting cotton pulp has a degree of polymerization of 2500-2600 and a whiteness of 84% or greater. This method provides pharmaceutical and food-grade cellulose ethers with ultra-high viscosity, a high degree of substitution, and excellent solubility, thereby enhancing the quality of the pharmaceutical and food-grade cellulose ethers. The production of pharmaceutical and food-grade cellulose ethers using a cooking technique that selectively removes hemicellulose and lignin and a bio-enzyme-assisted cellulose purification technique also reduces wastewater COD emissions from the pulping process to 6000-10000 mg / L, reducing the burden on wastewater treatment. DETAILED DESCRIPTION

[0031] The present invention provides a method for preparing cotton pulp for medical and food-grade cellulose ether, comprising the following preparation steps:

[0032] 1) Material selection, cotton opening, and impurity removal; 2) Enzyme-assisted cellulose purification; 3) Alkali preparation, impregnation, selective hemicellulose removal, and lignin cooking; 4) Pre-sand removal; 5) Pre-pulping; 6) Concentration; 7) Hydrogen peroxide bleaching; 8) Acid treatment; 9) Post-sand removal; 10) Post-pulping; 11) Pulping.

[0033] In the present invention, in the step 2) of cellulose purification with the aid of biological enzymes, pectinase, xylanase, and ammonium chloride are added to the slurry for purification. The purification time is 30 to 120 minutes, preferably 40 to 100 minutes, more preferably 50 to 80 minutes, and the temperature is 30 to 80° C., preferably 40 to 70° C., more preferably 50° C.; and a slurry is obtained.

[0034] The concentration of the slurry is 1-10%, preferably 2-8%, more preferably 4-6%, and even more preferably 5%; the pH value is 4-6, preferably 5;

[0035] The usage ratio of the pectinase, xylanase, ammonium chloride and the absolute dry pulp of the pulp is 0.1~1kg:0.1~1kg:0.1~1kg:1t, preferably 0.2~0.8kg:0.2~0.8kg:0.15~0.6kg:1t, further preferably 0.3~0.7kg:0.3~0.7kg:0.18~0.4kg:1t, and further preferably 0.5kg:0.5kg:0.2kg:1t.

[0036] In the present invention, the alkali preparation in step 3) is performed at 80-85° C., preferably 81-84° C., more preferably 82-83° C., and the alkali solution is prepared according to the ratio of NaOH: water = 1:3.7-4.2, preferably 1:3.9-4.1, more preferably 1:4, to obtain an alkali solution;

[0037] The slurry obtained by purification in step 2) is fully immersed in a mixed solution of alkali solution, Na2SO3, NaBO2 and fatty alcohol polyoxyethylene ether phosphate, and is driven into a steaming ball through a ball shaft and fully mixed with cotton linters by cold rotation;

[0038] The alkali solution is calculated as NaOH in an amount of 10.5-12.5% by weight relative to the absolute dry pulp, preferably 11-12%; the Na2SO3 is calculated as 0.1-1% by weight relative to the absolute dry pulp, preferably 0.2-0.8%, more preferably 0.4-0.6%; the NaBO2 is calculated as 0.1-1% by weight relative to the absolute dry pulp, preferably 0.2-0.8%, more preferably 0.4-0.6%; the fatty alcohol polyoxyethylene ether phosphate is calculated as 0.1-1% by weight relative to the absolute dry pulp, preferably 0.2-0.8%, more preferably 0.4-0.6%;

[0039] The selective removal of hemicellulose and lignin is carried out by cooking at a temperature of 100-160°C, preferably 11-150°C, more preferably 120-140°C, and further preferably 125-135°C, for 60-240 min, preferably 80-200 min, more preferably 100-180 min, and further preferably 120-140 min.

[0040] In the present invention, the step 1) of selecting materials, opening cotton and removing impurities is to select Class III first-class cotton linters with a maturity of ≥80%, tear the cotton linters with a cotton opener, loosen and remove impurities with an impurity remover, and then transfer them to a cotton squeezer. After the impurities are carefully selected and removed, they are sent to a cellulose purification process coordinated by a biological enzyme through a cyclone separator.

[0041] In the present invention, the pressure of sand removal before step 4) is controlled at 0.1-0.9 MPa, preferably 0.2-0.7 MPa, more preferably 0.3-0.5 MPa; the sand removal rate is 10-30 min / t, preferably 20 min / t, and the slurry concentration is 0.1-1%, preferably 0.3-0.7%, more preferably 0.4-0.6%;

[0042] The beating current of the pre-beating in step 5) is 150-200A, preferably 160-190A, more preferably 170-180A, the beating rate is 10-30min / t, preferably 20min / t, and the slurry concentration is 0.5-1.5%, preferably 0.8-1.2%, and preferably 0.9-1.1%;

[0043] The step 6) of concentration is to concentrate the slurry to a concentration of 5 to 15%, preferably 6 to 13%, and more preferably 8 to 10%.

[0044] In the present invention, the step 7) hydrogen peroxide bleaching comprises the following preparation steps:

[0045] a. In a medium-consistency mixer, add diethylenetriamine pentaacetic acid and hydrogen peroxide to the slurry, introduce steam, mix at 90-110°C, preferably 100°C for 10-30 minutes, preferably 20 minutes, and transfer to a hydrogen peroxide bleaching tower;

[0046] The diethylenetriamine pentaacetic acid is 0.07-0.25% by weight relative to the absolute dry pulp, preferably 0.08-0.2%, more preferably 0.1-0.15%; the hydrogen peroxide is 0.5-3% by weight relative to the absolute dry pulp, preferably 1-2.5%, more preferably 1.5-2%;

[0047] b. In the hydrogen peroxide bleaching tower, the temperature is set at 90-110°C, preferably 100°C, and the bleaching reaction is 50-120 minutes, preferably 60-110 minutes, and more preferably 80-10 minutes. Then, the slurry is diluted with deionized water to a concentration of 0.5-3%, preferably 1-2.5%, and more preferably 1.5-2%. The slurry is sent to a vacuum pulp washer and washed with deionized water until it is neutral.

[0048] In the present invention, the acid treatment in step 8) is carried out at room temperature for 10 to 60 minutes, preferably 20 to 50 minutes, more preferably 30 to 40 minutes, and then washed with deionized water for 1 to 3 hours, preferably 2 hours;

[0049] The acid comprises hydrochloric acid; the mass concentration of the hydrochloric acid is 20-30%, preferably 30%; the acid is 0.5-4% relative to the absolute dry pulp amount, preferably 1-3.5%, more preferably 1.5-3%, and even more preferably 2-2.5%.

[0050] In the present invention, the pressure of sand removal after step 9) is ≥0.3 MPa, preferably ≥0.5 MPa, and more preferably ≥0.6 MPa; the sand removal rate is 10-30 min / t, preferably 20 min / t, and the slurry concentration is 0.5-0.7%, preferably 0.6%.

[0051] In the present invention, the current of the beating after step 10) is 160-180A, preferably 165-175A, the beating rate is 10-30min / t, preferably 20min / t, and the concentration of the slurry is 2.5-2.7%, preferably 2.6%.

[0052] In the present invention, in the step 11), when pulping, the concentration of the pulp when sizing the paper on the Fourdrinier web is 8-12 g / L, preferably 9-11 g / L, and more preferably 10 g / L; the drying cylinder pressure is ≤0.20 MPa, preferably ≤0.15 MPa, and more preferably ≤0.10 MPa; the pulping rate is 1-5 h / t, preferably 2-4 h / t, and more preferably 3 h / t, to produce cotton pulp for medical and food grade cellulose ether.

[0053] The technical solutions provided by the present invention are described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0054] Example 1

[0055] (1) Material selection, cotton opening, and impurity removal process: Class III first-grade cotton linters with a maturity of ≥80% are selected, and the linters are torn with a cotton opener, loosened and impurities are removed by a cotton remover, and then transferred to a cotton squeezer. After the impurities are removed, the linters are sent to a screw press and impregnation through a cyclone separator;

[0056] (2) Bio-enzyme-assisted cellulose purification process: pectinase, xylanase, and ammonium chloride are added, the purification time is 60 min, the purification temperature is 45°C, the obtained slurry concentration is 5%, and the pH value is 4. The slurry is transported to the next process via a screw;

[0057] The dosage ratio of pectinase, xylanase, ammonium chloride and slurry is 0.5kg:0.5kg:0.2kg:1t.

[0058] (3) Alkali preparation, impregnation, selective removal of hemicellulose and lignin cooking process: the alkali preparation temperature is controlled at 85 °C, NaOH: water = 1:4.2;

[0059] The slurry obtained by purification in step 2) is fully immersed in a mixed solution of alkali solution, Na2SO3, NaBO2 and fatty alcohol polyoxyethylene ether phosphate, and is driven into a steaming ball through a ball shaft and fully mixed with cotton linters by cold rotation;

[0060] The alkali solution is calculated as NaOH, which is 10.5% of the weight of the absolute dry pulp; Na2SO3 is 0.5% of the weight of the absolute dry pulp; NaBO2 is 0.3% of the weight of the absolute dry pulp; and fatty alcohol polyoxyethylene ether phosphate is 0.3% of the weight of the absolute dry pulp.

[0061] The selective removal of hemicellulose and lignin was carried out at a cooking temperature of 135°C for 120 min.

[0062] (4) Pre-sand removal process: carried out in the desander, the pressure is controlled at 0.30 MPa, the slurry concentration is controlled at 0.4%, and the desanding rate is 20 min / t;

[0063] (5) Pre-beating process: It is carried out in the first large-taper refiner, with the beating current controlled at 180A, the pulp concentration controlled at 1.0%, and the beating rate at 20min / t;

[0064] (6) Concentration process: carried out in a side pressure rotary screen concentrator, and the slurry concentration is controlled at 10%;

[0065] (7) Hydrogen peroxide bleaching process:

[0066] a. In a medium-consistency mixer, add 0.17% of diethylenetriamine pentaacetic acid relative to the absolute dry pulp and 2% of hydrogen peroxide relative to the absolute dry pulp, introduce steam, control the temperature at 90°C, mix for 20 minutes, and then transfer to a hydrogen peroxide bleaching tower;

[0067] b. In the hydrogen peroxide bleaching tower, the temperature is controlled at 90°C. After bleaching reaction for 100 minutes, the pulp is diluted with deionized water and the pulp concentration is controlled at 1%. The pulp is sent to a vacuum washer and washed with deionized water until it is neutral. After washing, it enters the acid treatment tank;

[0068] (8) Acid treatment process: Add hydrochloric acid to the acid treatment tank at a concentration of 2% relative to the absolute dry pulp, with a mass concentration of 30%. Treat with acid at room temperature for 30 minutes, then wash with deionized water for 2 hours, and transfer to the desander;

[0069] (9) Post-sand removal process: The pressure of the post-sand remover is controlled at 0.35 MPa, the sand removal rate is 20 min / t, and the slurry concentration is controlled at 0.5%. After sand removal, the slurry is transferred to the second large-taper refiner;

[0070] (10) Post-beating process: The current of the second large-tapered pulping machine is controlled at 160A, the pulp concentration is controlled at 2.5%, the pulping rate is 20min / t, and the pulping machine is transferred to the pulping machine;

[0071] (11) Pulping process: The pulping concentration on the long wire of the pulping machine is controlled at 8g / L, and the drying cylinder pressure is 0.18Mpa. After the pulping is completed, the finished product is obtained.

[0072] Example 2

[0073] (1) Material selection, cotton opening, and impurity removal process: Class III first-grade cotton linters with a maturity of ≥80% are selected, and the linters are torn with a cotton opener, loosened and impurities are removed by a cotton remover, and then transferred to a cotton squeezer. After the impurities are removed, the linters are sent to a screw press and impregnation through a cyclone separator;

[0074] (2) Bio-enzyme-assisted cellulose purification process: pectinase, xylanase, and ammonium chloride are added, the purification time is 60 min, the purification temperature is 45°C, the obtained slurry concentration is 5%, and the pH value is 4. The slurry is transported to the next process via a screw;

[0075] The dosage ratio of pectinase, xylanase, ammonium chloride and slurry is 0.5kg:0.5kg:0.2kg:1t.

[0076] (3) Alkali preparation, impregnation, selective removal of hemicellulose and lignin cooking process: the alkali preparation temperature is controlled at 85 °C, NaOH: water = 1:4.2;

[0077] The slurry obtained by purification in step 2) is fully immersed in a mixed solution of alkali solution, Na2SO3, NaBO2 and fatty alcohol polyoxyethylene ether phosphate, and is driven into a steaming ball through a ball shaft and fully mixed with cotton linters by cold rotation;

[0078] The alkali solution is calculated as NaOH, which is 10.5% of the weight of the absolute dry pulp; Na2SO3 is 0.5% of the weight of the absolute dry pulp; NaBO2 is 0.3% of the weight of the absolute dry pulp; and fatty alcohol polyoxyethylene ether phosphate is 0.3% of the weight of the absolute dry pulp.

[0079] The selective removal of hemicellulose and lignin was carried out at a cooking temperature of 130°C for 120 min.

[0080] (4) Pre-sand removal process: carried out in the desander, the pressure is controlled at 0.30 MPa, the slurry concentration is controlled at 0.4%, and the desanding rate is 20 min / t;

[0081] (5) Pre-beating process: It is carried out in the first large-taper refiner, with the beating current controlled at 180A, the pulp concentration controlled at 1.0%, and the beating rate at 20min / t;

[0082] (6) Concentration process: carried out in a side pressure rotary screen concentrator, and the slurry concentration is controlled at 10%;

[0083] (7) Hydrogen peroxide bleaching process:

[0084] a. In a medium-consistency mixer, add 0.17% of diethylenetriamine pentaacetic acid relative to the absolute dry pulp and 2% of hydrogen peroxide relative to the absolute dry pulp, introduce steam, control the temperature at 90°C, mix for 20 minutes, and then transfer to a hydrogen peroxide bleaching tower;

[0085] b. In the hydrogen peroxide bleaching tower, the temperature is controlled at 90°C. After bleaching reaction for 100 minutes, the pulp is diluted with deionized water and the pulp concentration is controlled at 1%. The pulp is sent to a vacuum washer and washed with deionized water until it is neutral. After washing, it enters the acid treatment tank;

[0086] (8) Acid treatment process: Add hydrochloric acid to the acid treatment tank at a concentration of 2% relative to the absolute dry pulp, with a mass concentration of 30%. Treat with acid at room temperature for 30 minutes, then wash with deionized water for 2 hours, and transfer to the desander;

[0087] (9) Post-sand removal process: The pressure of the post-sand remover is controlled at 0.35 MPa, the sand removal rate is 20 min / t, and the slurry concentration is controlled at 0.5%. After sand removal, the slurry is transferred to the second large-taper refiner;

[0088] (10) Post-beating process: The current of the second large-tapered pulping machine is controlled at 160A, the pulp concentration is controlled at 2.5%, the pulping rate is 20min / t, and the pulping machine is transferred to the pulping machine;

[0089] (11) Pulping process: The pulping concentration on the long wire of the pulping machine is controlled at 8g / L, and the drying cylinder pressure is 0.18Mpa. After the pulping is completed, the finished product is obtained.

[0090] Example 3

[0091] (1) Material selection, cotton opening, and impurity removal process: Class III first-grade cotton linters with a maturity of ≥80% are selected, and the linters are torn with a cotton opener, loosened and impurities are removed by a cotton remover, and then transferred to a cotton squeezer. After the impurities are removed, the linters are sent to a screw press and impregnation through a cyclone separator;

[0092] (2) Bio-enzyme-assisted cellulose purification process: pectinase, xylanase, and ammonium chloride are added, the purification time is 60 min, the purification temperature is 45°C, the obtained slurry concentration is 5%, and the pH value is 4. The slurry is transported to the next process via a screw;

[0093] The dosage ratio of pectinase, xylanase, ammonium chloride and slurry is 0.5kg:0.5kg:0.2kg:1t.

[0094] (3) Alkali preparation, impregnation, selective removal of hemicellulose and lignin cooking process: the alkali preparation temperature is controlled at 85 °C, NaOH: water = 1:4.2;

[0095] The slurry obtained by purification in step 2) is fully immersed in a mixed solution of alkali solution, Na2SO3, NaBO2 and fatty alcohol polyoxyethylene ether phosphate, and is driven into a steaming ball through a ball shaft and fully mixed with cotton linters by cold rotation;

[0096] The alkali solution is calculated as NaOH, which is 10.5% of the weight of the absolute dry pulp; Na2SO3 is 0.5% of the weight of the absolute dry pulp; NaBO2 is 0.3% of the weight of the absolute dry pulp; and fatty alcohol polyoxyethylene ether phosphate is 0.3% of the weight of the absolute dry pulp.

[0097] The selective removal of hemicellulose and lignin was carried out at a cooking temperature of 125°C for 120 min.

[0098] (4) Pre-sand removal process: carried out in the desander, the pressure is controlled at 0.30 MPa, the slurry concentration is controlled at 0.4%, and the desanding rate is 20 min / t;

[0099] (5) Pre-beating process: It is carried out in the first large-taper refiner, with the beating current controlled at 180A, the pulp concentration controlled at 1.0%, and the beating rate at 20min / t;

[0100] (6) Concentration process: carried out in a side pressure rotary screen concentrator, and the slurry concentration is controlled at 10%;

[0101] (7) Hydrogen peroxide bleaching process:

[0102] a. In a medium-consistency mixer, add 0.17% of diethylenetriamine pentaacetic acid relative to the absolute dry pulp and 2% of hydrogen peroxide relative to the absolute dry pulp, introduce steam, control the temperature at 90°C, mix for 20 minutes, and then transfer to a hydrogen peroxide bleaching tower;

[0103] b. In the hydrogen peroxide bleaching tower, the temperature is controlled at 90°C. After bleaching reaction for 100 minutes, the pulp is diluted with deionized water and the pulp concentration is controlled at 1%. The pulp is sent to a vacuum washer and washed with deionized water until it is neutral. After washing, it enters the acid treatment tank;

[0104] (8) Acid treatment process: Add hydrochloric acid to the acid treatment tank at a concentration of 2% relative to the absolute dry pulp, with a mass concentration of 30%. Treat with acid at room temperature for 30 minutes, then wash with deionized water for 2 hours, and transfer to the desander;

[0105] (9) Post-sand removal process: The pressure of the post-sand remover is controlled at 0.35 MPa, the sand removal rate is 20 min / t, and the slurry concentration is controlled at 0.5%. After sand removal, the slurry is transferred to the second large-taper refiner;

[0106] (10) Post-beating process: The current of the second large-tapered pulping machine is controlled at 160A, the pulp concentration is controlled at 2.5%, the pulping rate is 20min / t, and the pulping machine is transferred to the pulping machine;

[0107] (11) Pulping process: The pulping concentration on the long wire of the pulping machine is controlled at 8g / L, and the drying cylinder pressure is 0.18Mpa. After the pulping is completed, the finished product is obtained.

[0108] Example 4

[0109] (1) Material selection, cotton opening, and impurity removal process: Class III first-grade cotton linters with a maturity of ≥80% are selected, and the linters are torn with a cotton opener, loosened and impurities are removed by a cotton remover, and then transferred to a cotton squeezer. After the impurities are removed, the linters are sent to a screw press and impregnation through a cyclone separator;

[0110] (2) Bio-enzyme-assisted cellulose purification process: pectinase, xylanase, and ammonium chloride were added, the purification time was 60 min, the purification temperature was 50°C, the obtained slurry concentration was 5%, the pH value was 4, and it was transported to the next process by screw conveyor;

[0111] The dosage ratio of pectinase, xylanase, ammonium chloride and slurry is 0.5kg:0.5kg:0.2kg:1t.

[0112] (3) Alkali preparation, impregnation, selective removal of hemicellulose and lignin cooking process: the alkali preparation temperature is controlled at 85 °C, NaOH: water = 1:4.2;

[0113] The slurry obtained by purification in step 2) is fully immersed in a mixed solution of alkali solution, Na2SO3, NaBO2 and fatty alcohol polyoxyethylene ether phosphate, and is driven into a steaming ball through a ball shaft and fully mixed with cotton linters by cold rotation;

[0114] The alkali solution is calculated as NaOH, which is 10.5% of the weight of the absolute dry pulp; Na2SO3 is 0.5% of the weight of the absolute dry pulp; NaBO2 is 0.3% of the weight of the absolute dry pulp; and fatty alcohol polyoxyethylene ether phosphate is 0.3% of the weight of the absolute dry pulp.

[0115] The selective removal of hemicellulose and lignin was carried out at a cooking temperature of 125°C for 120 min.

[0116] (4) Pre-sand removal process: carried out in the desander, the pressure is controlled at 0.30 MPa, the slurry concentration is controlled at 0.4%, and the desanding rate is 20 min / t;

[0117] (5) Pre-beating process: It is carried out in the first large-taper refiner, with the beating current controlled at 180A, the pulp concentration controlled at 1.0%, and the beating rate at 20min / t;

[0118] (6) Concentration process: carried out in a side pressure rotary screen concentrator, and the slurry concentration is controlled at 10%;

[0119] (7) Hydrogen peroxide bleaching process:

[0120] a. In a medium-consistency mixer, add 0.17% of diethylenetriamine pentaacetic acid relative to the absolute dry pulp and 2% of hydrogen peroxide relative to the absolute dry pulp, introduce steam, control the temperature at 90°C, mix for 20 minutes, and then transfer to a hydrogen peroxide bleaching tower;

[0121] b. In the hydrogen peroxide bleaching tower, the temperature is controlled at 90°C. After bleaching reaction for 100 minutes, the pulp is diluted with deionized water and the pulp concentration is controlled at 1%. The pulp is sent to a vacuum washer and washed with deionized water until it is neutral. After washing, it enters the acid treatment tank;

[0122] (8) Acid treatment process: Add hydrochloric acid to the acid treatment tank at a concentration of 2% relative to the absolute dry pulp, with a mass concentration of 30%. Treat with acid at room temperature for 30 minutes, then wash with deionized water for 2 hours, and transfer to the desander;

[0123] (9) Post-sand removal process: The pressure of the post-sand remover is controlled at 0.35 MPa, the sand removal rate is 20 min / t, the slurry concentration is controlled at 0.5%, the sand removal rate is 20 min / t, and the slurry is transferred to the second large-taper refiner;

[0124] (10) Post-beating process: The current of the second large-tapered pulping machine is controlled at 160A, the pulp concentration is controlled at 2.5%, the pulping rate is 20min / t, and the pulping machine is transferred to the pulping machine;

[0125] (11) Pulping process: The pulping concentration on the long wire of the pulping machine is controlled at 8g / L, and the drying cylinder pressure is 0.18Mpa. After the pulping is completed, the finished product is obtained.

[0126] Example 5

[0127] (1) Material selection, cotton opening, and impurity removal process: Class III first-grade cotton linters with a maturity of ≥80% are selected, and the linters are torn with a cotton opener, loosened and impurities are removed by a cotton remover, and then transferred to a cotton squeezer. After the impurities are removed, the linters are sent to a screw press and impregnation through a cyclone separator;

[0128] (2) Bio-enzyme-assisted cellulose purification process: pectinase, xylanase, and ammonium chloride were added, the purification time was 60 min, the purification temperature was 60°C, the obtained slurry concentration was 5%, the pH value was 4, and it was transported to the next process by screw conveyor;

[0129] The dosage ratio of pectinase, xylanase, ammonium chloride and slurry is 0.5kg:0.5kg:0.2kg:1t.

[0130] (3) Alkali preparation, impregnation, selective removal of hemicellulose and lignin cooking process: the alkali preparation temperature is controlled at 85 °C, NaOH: water = 1:4.2;

[0131] The slurry obtained by purification in step 2) is fully immersed in a mixed solution of alkali solution, Na2SO3, NaBO2 and fatty alcohol polyoxyethylene ether phosphate, and is driven into a steaming ball through a ball shaft and fully mixed with cotton linters by cold rotation;

[0132] The alkali solution is calculated as NaOH, which is 10.5% of the weight of the absolute dry pulp; Na2SO3 is 0.5% of the weight of the absolute dry pulp; NaBO2 is 0.3% of the weight of the absolute dry pulp; and fatty alcohol polyoxyethylene ether phosphate is 0.3% of the weight of the absolute dry pulp.

[0133] The selective removal of hemicellulose and lignin was carried out at a cooking temperature of 125°C for 120 min.

[0134] (4) Pre-sand removal process: carried out in the desander, the pressure is controlled at 0.30 MPa, the slurry concentration is controlled at 0.4%, and the desanding rate is 20 min / t;

[0135] (5) Pre-beating process: It is carried out in the first large-taper refiner, with the beating current controlled at 180A, the pulp concentration controlled at 1.0%, and the beating rate at 20min / t;

[0136] (6) Concentration process: carried out in a side pressure rotary screen concentrator, and the slurry concentration is controlled at 10%;

[0137] (7) Hydrogen peroxide bleaching process:

[0138] a. In a medium-consistency mixer, add 0.17% of diethylenetriamine pentaacetic acid relative to the absolute dry pulp and 2% of hydrogen peroxide relative to the absolute dry pulp, introduce steam, control the temperature at 90°C, mix for 20 minutes, and then transfer to a hydrogen peroxide bleaching tower;

[0139] b. In the hydrogen peroxide bleaching tower, the temperature is controlled at 90°C. After bleaching reaction for 100 minutes, the pulp is diluted with deionized water and the pulp concentration is controlled at 1%. The pulp is sent to a vacuum washer and washed with deionized water until it is neutral. After washing, it enters the acid treatment tank;

[0140] (8) Acid treatment process: Add hydrochloric acid to the acid treatment tank at a concentration of 2% relative to the absolute dry pulp, with a mass concentration of 30%. Treat with acid at room temperature for 30 minutes, then wash with deionized water for 2 hours, and transfer to the desander;

[0141] (9) Post-sand removal process: The pressure of the post-sand remover is controlled at 0.35 MPa, the sand removal rate is 20 min / t, and the slurry concentration is controlled at 0.5%. After sand removal, the slurry is transferred to the second large-taper refiner;

[0142] (10) Post-beating process: The current of the second large-tapered pulping machine is controlled at 160A, the pulp concentration is controlled at 2.5%, the pulping rate is 20min / t, and the pulping machine is transferred to the pulping machine;

[0143] (11) Pulping process: The pulping concentration on the long wire of the pulping machine is controlled at 8g / L, and the drying cylinder pressure is 0.18Mpa. After the pulping is completed, the finished product is obtained.

[0144] The present invention tested the polymerization degree, whiteness, methyl cellulose, ash content, metal content and cooking black liquor of the cotton pulp prepared in Examples 1-5. The test results are shown in Table 1:

[0145] Table 1 Test results of cotton pulp properties prepared in Examples 1-5

[0146]

[0147] As can be seen from the above examples, the present invention provides a method for producing pharmaceutical and food-grade cotton pulp for cellulose ethers. The resulting cotton pulp has a degree of polymerization (DP) of 2580 and a whiteness of 86.8%, resulting in pharmaceutical and food-grade cellulose ethers with ultra-high viscosity, a high degree of substitution, and excellent solubility, thereby enhancing the quality of the pharmaceutical and food-grade cellulose ethers. Furthermore, the use of a steaming technology that selectively removes hemicellulose and lignin and a bio-enzyme-assisted cellulose purification technology to produce pharmaceutical and food-grade cotton pulp for cellulose ethers also reduces COD emissions from the entire pulping process to between 6,000 and 10,000 mg / L, reducing the burden on wastewater treatment.

[0148] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for preparing cotton pulp for medical and food grade cellulose ether, characterized in that: The method comprises the following preparation steps: 1) Material selection, opening, and impurity removal; 2) Enzyme-assisted cellulose purification; 3) Alkali preparation, impregnation, selective hemicellulose removal, and lignin cooking; 4) Pre-sand removal; 5) Pre-pulping; 6) Concentration; 7) Hydrogen peroxide bleaching; 8) Acid treatment; 9) Post-sand removal. 10) Post-beating; 11) Papermaking; In the step 2) of cellulose purification with bio-enzyme collaboration, pectinase, xylanase, and ammonium chloride are added to the slurry for purification. The purification time is 30-120 minutes and the temperature is 30-80° C. to obtain a slurry. The slurry has a concentration of 1-10% and a pH of 4-6; The usage ratio of the pectinase, xylanase, ammonium chloride and the absolute dry pulp of the pulp is 0.1~1kg:0.1~1kg:0.1~1kg:1t; In step 3), the alkali solution is prepared at 80-85° C. according to the ratio of NaOH to water (1:3.7-4.2) to obtain an alkali solution; The impregnation step is to fully immerse the slurry obtained by purification in step 2) into a mixed solution of alkali solution, Na2SO3, NaBO2 and fatty alcohol polyoxyethylene ether phosphate; Among them, the alkali solution is calculated as NaOH at 10.5-12.5% of the absolute dry pulp weight, Na2SO3 at 0.1-1% of the absolute dry pulp weight, NaBO2 at 0.1-1% of the absolute dry pulp weight, and fatty alcohol polyoxyethylene ether phosphate at 0.1-1% of the absolute dry pulp weight; The selective removal of hemicellulose and lignin is carried out by cooking at a temperature of 100-160°C for 60-240 minutes.

2. The method for preparing cotton pulp for medical and food grade cellulose ether according to claim 1, characterized in that: In the step 1) of selecting materials, opening cotton and removing impurities, three types of first-grade cotton linters with a maturity of ≥80% are selected, the cotton linters are torn, and then loosened, impurities are removed, and impurities are carefully selected and removed.

3. The method for preparing cotton pulp for medical and food grade cellulose ether according to claim 2, characterized in that: In step 4), the pressure before sand removal is controlled at 0.1-0.9 MPa, the sand removal rate is 10-30 min / t, and the slurry concentration is 0.1-1%; The beating current of the pre-beating in step 5) is 150-200A, the beating rate is 10-30min / t, and the slurry concentration is 0.5-1.5%; The step 6) concentration is to concentrate the slurry to a concentration of 5-15%.

4. The method for preparing cotton pulp for medical and food grade cellulose ether according to claim 1 or 3, characterized in that: The step 7) hydrogen peroxide bleaching comprises the following preparation steps: a. In a medium-consistency mixer, add diethylenetriamine pentaacetic acid and hydrogen peroxide to the slurry, introduce steam, mix at 90-110°C for 10-30 minutes, and transfer to a hydrogen peroxide bleaching tower; The diethylenetriamine pentaacetic acid is 0.07-0.25% by weight relative to the absolute dry pulp; the hydrogen peroxide is 0.5-3% by weight relative to the absolute dry pulp; b. In the hydrogen peroxide bleaching tower, set the temperature to 90~110℃. After bleaching for 50~120min, dilute the pulp with deionized water to a concentration of 0.5~3%. Send the pulp to a vacuum washer and wash it with deionized water until it is neutral.

5. The method for preparing cotton pulp for medical and food grade cellulose ether according to claim 4, characterized in that: The acid treatment in step 8) is carried out at room temperature for 10 to 60 minutes, followed by washing with deionized water for 1 to 3 hours; The acid comprises hydrochloric acid; the mass concentration of the hydrochloric acid is 20-30%; and the acid is 0.5-4% relative to the absolute dry pulp.

6. The method for preparing cotton pulp for medical and food grade cellulose ether according to claim 5, characterized in that: The pressure of the sand removal after step 9) is ≥0.3 MPa, the sand removal rate is 10-30 min / t, and the slurry concentration is 0.5-0.7%.

7. The method for preparing cotton pulp for medical and food grade cellulose ether according to claim 1 or 6, characterized in that: The current of the beating after step 10) is 160-180 A, the beating rate is 10-30 min / t, and the concentration of the slurry is 2.5-2.7%.

8. The method for preparing cotton pulp for medical and food grade cellulose ether according to claim 7, characterized in that: In the step 11), when pulping, the concentration of the pulp on the papermaking machine is 8-12 g / L, the drying cylinder pressure is ≤0.20 MPa, and the pulping rate is 1-5 h / t, thereby producing cotton pulp for medical and food grade cellulose ether.

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