Preparation method of cotton pulp with high alpha-cellulose content

Abstract

The present invention relates to the technical field of cotton pulp production, and particularly to a preparation method of cotton pulp with a high content of alpha cellulose. The present invention obtains the finished cotton pulp through processes such as raw material selection, cotton opening, dry impurity removal, hot water extraction of hemicellulose, cooking for selective delignification and hemicellulose removal, pre-sand removal, pre-beating, concentration, hydrogen peroxide bleaching, acid treatment, post-sand removal, post-beating, pulp making. By adopting the hot water extraction technology for hemicellulose removal, hemicellulose is selectively removed, and the content of alpha cellulose is increased. By adopting the cooking technology for selective delignification and hemicellulose removal, pure cotton cellulose is further refined and the content of alpha cellulose is increased. The content of alpha cellulose in the cotton pulp is ≥98%. The prepared cellulose ether has a uniform degree of substitution, stable viscosity, and good compatibility, improving the quality of the cellulose ether.

Description

Technical Field

[0001] The present invention relates to the technical field of cotton pulp production, and particularly relates to a method for preparing cotton pulp with a high content of alpha-cellulose. Background Art

[0002] Cellulose ether is a general term for a variety of derivatives obtained by etherifying natural cellulose, and is widely used in industries such as lithium batteries, medicine and health, daily chemical industry, food, construction, materials, and oil drilling, commonly known as "industrial monosodium glutamate". As the raw material for producing cellulose ether, the quality of cotton pulp determines the quality of cellulose ether. The content of alpha-cellulose is an important indicator for measuring the quality of cotton pulp, and the level of alpha-cellulose content affects the quality of cellulose ether. Increasing the content of alpha-cellulose is beneficial to improving the yield of cellulose ether products, enhancing the production capacity of equipment, reducing chemical consumption, and improving the quality of cellulose ether products. Currently, the alpha-cellulose content of refined cotton and cotton pulp used in cellulose ether production in China is between 92% and 98%, which greatly restricts the improvement of the quality of cellulose ether.

[0003] Therefore, how to provide a method for preparing cotton pulp with a high content of alpha-cellulose, so that the alpha-cellulose content of the prepared cotton pulp is ≥ 98% has become an urgent technical problem to be solved by those skilled in the art. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for preparing cotton pulp with a high content of alpha-cellulose, so that the alpha-cellulose content of the prepared cotton pulp is ≥ 98%, and the prepared cellulose ether has a uniform degree of substitution, stable viscosity, and good compatibility, thereby improving the quality of cellulose ether.

[0005] In order to achieve the above-mentioned invention purpose, the present invention provides the following technical solutions:

[0006] The present invention provides a method for preparing cotton pulp with a high content of alpha-cellulose, comprising the following steps: 1) material selection, cotton opening, and dry impurity removal process; 2) hot water delignification of hemicellulose process; 3) cooking process for selective delignification and hemicellulose removal; 4) pre-sand removal process; 5) pre-beating process; 6) concentration process; 7) hydrogen peroxide bleaching process; 8) acid treatment process; 9) post-sand removal process; 10) post-beating process; 11) pulp making process.

[0007] Optionally, in the step 2) hot water delignification of hemicellulose process: the selected cotton linters and the surfactant fatty alcohol polyoxyethylene ether phosphate are mixed and heated to obtain a slurry;

[0008] 0.5 kg to 1 kg of the surfactant fatty alcohol polyoxyethylene ether phosphate is added per ton of the selected cotton linters;

[0009] The heating temperature is 130°C to 150°C, and the time is 60 min to 120 min.

[0010] Optionally, the cooking process for selectively delignifying and hemicellulosing in step 3) is as follows: Add lye, Na 2 SO 3 and Na 2 B 4 O 7 to the pulp obtained in step 2) and carry out cooking.

[0011] The method for preparing the lye is to prepare the lye at 45°C to 50°C, and configure the lye solution according to the weight ratio of NaOH: water = 1:3.7 to 4.2. The total alkali is 6% to 10% of the weight of the absolute dry pulp based on NaOH.

[0012] Na 2 SO 3 is 0.4% to 0.8% of the weight of the absolute dry pulp; Na 2 B 4 O 7 is 0.3% to 0.5% of the weight of the absolute dry pulp.

[0013] The cooking temperature is 120°C to 135°C, and the time is 100 min to 150 min.

[0014] Optionally, the processes of material selection, cotton opening, and dry impurity removal in step 1) are as follows: Select the third-class first-grade cotton linter with a maturity of ≥80%. After tearing the cotton linter, loosen, remove impurities, and then carry out fine impurity removal to obtain the selected cotton linter.

[0015] Optionally, the pre-desanding process in step 4) is as follows: Desand the pulp obtained in step 3) in a desander. The desanding pressure is 0.30 Mpa to 0.32 Mpa, the pulp concentration is 0.4% to 0.6%, and the desanding rate is 10 min / t to 30 min / t.

[0016] The pre-beating process in step 5) is as follows: Beat the pulp obtained in step 4) in the first large-taper refiner. The beating current is 180 A to 200 A, the pulp concentration is 1.0% to 1.8%; the beating rate is 10 min / t to 30 min / t.

[0017] Optionally, the concentration process in step 6) is as follows: Concentrate the pulp obtained in step 5) in a side-pressure cylinder screen concentrator. The pulp concentration is 10% to 12%.

[0018] Optionally, the hydrogen peroxide bleaching process in step 7) is as follows:

[0019] a. Transfer the slurry obtained in step 6) to a medium consistency mixer, add diethylenetriaminepentaacetic acid and hydrogen peroxide, introduce steam, control the temperature at 90°C - 110°C, mix for 20 min - 30 min, and then transfer it to a hydrogen peroxide bleaching tower;

[0020] The diethylenetriaminepentaacetic acid is 0.17% - 0.22% of the weight of the absolutely dry pulp; the hydrogen peroxide is 2% - 2.8% of the weight of the absolutely dry pulp;

[0021] b. In the hydrogen peroxide bleaching tower, control the temperature at 90°C - 110°C, after the bleaching reaction for 100 min - 120 min, dilute with water, the concentration of the slurry is 1% - 1.5%, and send it to a vacuum pulp washer to wash with water until neutral;

[0022] The acid treatment process in step 8) is as follows: Feed the slurry obtained in step 7) into an acid treatment tank, add hydrochloric acid accounting for 2% - 2.5% of the weight of the absolutely dry pulp, conduct acid treatment for 20 min - 40 min, and then wash with water for 2 h - 3 h; the concentration of the hydrochloric acid is 300 g / L - 400 g / L.

[0023] Optionally, the post - sand - removal process in step 9) is as follows: Remove sand from the slurry obtained in step 8) in a post - sand - remover, the pressure for sand removal ≥ 0.3 Mpa, the concentration of the slurry is 0.5% - 0.7%, and the sand - removal rate is 10 min / t - 30 min / t.

[0024] Optionally, the beating process in step 10) is as follows: Beat the slurry obtained in step 9) in a second large - conicity refiner, the beating current is 160 A - 180 A, the concentration of the slurry is 2.5% - 2.7%, and the beating rate is 10 min / t - 30 min / t.

[0025] Optionally, the pulp - making process in step 11) is as follows: Place the slurry obtained in step 10) on the long - wire of a paper machine in a pulp - making machine, the concentration of the slurry is 8 g / L - 12 g / L, the dryer cylinder pressure ≤ 0.20 Mpa, and after the pulp - making is completed, cotton pulp sheets with a high content of alpha - cellulose are obtained.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] The present invention adopts the hot - water hydrolysis technology to remove hemicellulose selectively, thereby increasing the content of alpha - cellulose. The principle is as follows: During the hot - water hydrolysis process, the main mechanism of polysaccharide hydrolysis is the proton - catalyzed cleavage of glycosidic bonds: H 3 O +Combined with the fact that cotton linters can obtain greater kinetic energy at high temperatures, the acetyl groups and uronic acids in hemicellulose are catalyzed to fall off and form organic acids in-situ, and continue to act as catalysts to maintain a higher level of reaction, promoting the selective hydrolysis of glycosidic bonds between the monomeric units of the hemicellulose polymer chain. Adding surfactants to emulsify cotton linters to reduce surface tension is more conducive to the removal of hemicellulose.

[0028] The present invention adopts a cooking technology for selective delignification and hemicellulose removal to further purify cotton cellulose and increase the content of alpha-cellulose. The principle is as follows: adding the auxiliary agent sodium sulfite to break the difficult-to-remove non-phenolic beta-aryl ether bonds in the lignin macromolecule, thereby increasing the delignification rate; adding the auxiliary agent sodium borate to complex and dissolve the difficult-to-extract glucomannan in hemicellulose, further increasing the removal rate of hemicellulose. Detailed implementation manners

[0029] Now, various exemplary implementation manners of the present invention will be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, characteristics, and implementation schemes of the present invention.

[0030] It should be understood that the terms used in the present invention are only for describing specific implementation manners and are not used to limit the present invention. Additionally, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded from the range.

[0031] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention pertains. Although the present invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein can also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In case of conflict with any incorporated document, the content of this specification shall prevail.

[0032] Without departing from the scope or spirit of the present invention, various improvements and changes can be made to the specific implementation manners of the present invention specification, which are obvious to those skilled in the art. Other implementation manners obtained from the specification of the present invention are obvious to those skilled in the art. The specification and embodiments of this application are only exemplary.

[0033] Regarding "comprising", "including", "having", "containing", etc. used herein, they are all open-ended terms, meaning including but not limited to.

[0034] In the present invention, unless otherwise specified, the "room temperature" and "normal temperature" are both calculated as 25 ± 2 °C.

[0035] All raw materials used in the following examples of the present invention are obtained commercially.

[0036] The present invention provides a method for preparing cotton pulp with a high content of alpha-cellulose, comprising the following steps: 1) material selection, cotton opening, and dry impurity removal process; 2) hot water extraction of hemicellulose process; 3) cooking process for selective delignification and hemicellulose removal; 4) pre-sand removal process; 5) pre-beating process; 6) concentration process; 7) hydrogen peroxide bleaching process; 8) acid treatment process; 9) post-sand removal process; 10) post-beating process; 11) sheet forming process.

[0037] In the present invention, in the step 2) hot water extraction of hemicellulose process: the selected cotton linter is mixed with the surfactant fatty alcohol polyoxyethylene ether phosphate, and heated to obtain a slurry;

[0038] 0.5 kg to 1 kg of the surfactant fatty alcohol polyoxyethylene ether phosphate is added per ton of selected cotton linter, for example, it can be 0.5 kg, 0.6 kg, 0.7 kg, 0.8 kg, 0.9 kg, 1 kg, etc., and the optimal addition amount is 1 kg;

[0039] The heating temperature is 130 °C to 150 °C, for example, it can be 130 °C, 135 °C, 140 °C, 145 °C, 150 °C, etc., the optimal temperature is 150 °C, and the time is 60 min to 120 min, for example, it can be 60 min, 70 min, 80 min, 90 min, 100 min, 110 min, 120 min, etc., and the optimal time is 90 min.

[0040] In the present invention, in the step 3) cooking process for selective delignification and hemicellulose removal: the alkali liquor, Na 2 SO 3 and Na 2 B 4 O 7 are added to the slurry obtained in step 2) for cooking;

[0041] The method for preparing the alkali liquor is to prepare the alkali liquor at 45 °C to 50 °C, and the alkali solution is prepared according to the weight ratio of NaOH: water = 1: 3.7 to 4.2, and the total alkali calculated as NaOH is 6% to 10% of the weight of the absolute dry pulp;

[0042] The most preferred way to prepare the alkali liquor is: prepare the alkali liquor at 45 °C, and the alkali solution is prepared according to the weight ratio of NaOH: water = 1: 4.2, and the total alkali calculated as NaOH is 6% of the weight of the absolute dry pulp;

[0043] Na 2 SO 3 is 0.4% - 0.8% of the weight of absolutely dry pulp, for example, it can be 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, etc., and the optimal value is 0.4%; Na 2 B 4 O 7 is 0.3% - 0.5% of the weight of absolutely dry pulp, for example, it can be 0.3%, 0.4%, 0.5%, etc., and the optimal value is 0.4%;

[0044] The cooking temperature is 120°C - 135°C, for example, it can be 120°C, 125°C, 130°C, 135°C, etc., and the optimal temperature is 120°C; the time is 100 min - 150 min, for example, it can be 100 min, 110 min, 120 min, 130 min, 140 min, 150 min, etc., and the optimal time is 120 min.

[0045] In the present invention, the procedures of step 1) material selection, cotton opening, and dry impurity removal are as follows: Select the third-class first-grade cotton linter with a maturity of ≥80%. After tearing the cotton linter, loosen and remove impurities, and then conduct fine selection and impurity removal to obtain the fine-selected cotton linter.

[0046] In the present invention, the pre-desanding procedure of step 4) is as follows: Desand the pulp obtained in step 3) in a desander. The desanding pressure is 0.30 Mpa - 0.32 Mpa, for example, it can be 0.30 Mpa, 0.31 Mpa, 0.32 Mpa, etc., and the preferred value is 0.30 Mpa; the pulp concentration is 0.4% - 0.6%, for example, it can be 0.4, 0.5%, 0.6%, etc., and the preferred value is 0.4%. The desanding rate is 10 min / t - 30 min / t, for example, it can be 10 min / t, 15 min / t, 20 min / t, 25 min / t, 30 min / t, etc., and the preferred value is 30 min / t;

[0047] The pre-beating procedure of step 5) is as follows: Beat the pulp obtained in step 4) in the first large-taper refiner. The beating current is 180 A - 200 A, for example, it can be 180 A, 185 A, 190 A, 195 A, 200 A, etc., and the preferred value is 180 A; the pulp concentration is 1.0% - 1.8%, for example, it can be 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, etc., and the preferred value is 1.0%; the beating rate is 10 min / t - 30 min / t, for example, it can be 10 min / t, 15 min / t, 20 min / t, 25 min / t, 30 min / t, etc., and the preferred value is 30 min / t.

[0048] In the present invention, the concentration process in step 6) is as follows: the slurry obtained in step 5) is concentrated in a side-pressurized cylinder screen concentrator, and the concentration of the slurry is 10% - 12%, for example, it can be 10%, 11%, 12%, and preferably 10%.

[0049] In the present invention, the hydrogen peroxide bleaching process in step 7) is as follows:

[0050] a. The slurry obtained in step 6) is conveyed to a medium-consistency mixer, and diethylenetriaminepentaacetic acid and hydrogen peroxide are added, and steam is introduced. The temperature is controlled at 90°C - 110°C, for example, it can be 90°C, 95°C, 100°C, 105°C, 110°C, etc., and preferably 90°C. After mixing for 20 min - 30 min, preferably after mixing for 20 min, it is transferred to a hydrogen peroxide bleaching tower;

[0051] The diethylenetriaminepentaacetic acid is 0.17% - 0.22% of the weight of the absolutely dry pulp, for example, it can be 0.17%, 0.18%, 0.19%, 0.20%, 0.21%, 0.22%, etc., and preferably 0.17%; the hydrogen peroxide is 2% - 2.8% of the weight of the absolutely dry pulp, for example, it can be 2%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, etc., and preferably 2%;

[0052] b. In the hydrogen peroxide bleaching tower, the temperature is controlled at 90°C - 110°C, for example, it can be 90°C, 95°C, 100°C, 105°C, 110°C, etc., and preferably 90°C. The bleaching reaction is carried out for 100 min - 120 min, for example, it can be 105 min, 110 min, 115 min, 120 min, etc., and preferably after bleaching for 100 min, it is diluted with water, and the concentration of the slurry is 1% - 1.5%, for example, it can be 1%, 1.2%, 1.3%, 1.4%, 1.5%, etc., and preferably 1%. Then it is sent to a vacuum pulp washer and washed with water until neutral;

[0053] The acid treatment process in step 8) is as follows: the slurry obtained in step 7) is fed into an acid treatment tank, and hydrochloric acid accounting for 2% - 2.5% of the weight of the absolutely dry pulp is added. After acid treatment for 20 min - 40 min, it is washed with water for 2 h - 3 h;

[0054] The preferred solution is to add hydrochloric acid accounting for 2% of the weight of the absolutely dry pulp, carry out acid treatment for 30 min, and then wash it with deionized water for 2 hours;

[0055] The concentration of the hydrochloric acid is 300 g / L - 400 g / L, for example, it can be 300 g / L, 320 g / L, 330 g / L, 350 g / L, 360 g / L, 380 g / L, 400 g / L, and preferably 350 g / L;

[0056] In the present invention, the sand removal process after step 9) is as follows: the slurry obtained in step 8) is subjected to sand removal in a post-sand remover. The pressure for sand removal is ≥0.3 Mpa, the concentration of the slurry is 0.5% - 0.7%, for example, it can be 0.5%, 0.6%, 0.7%, etc., preferably 0.5%. The sand removal rate is 10 min / t - 30 min / t, for example, it can be 10 min / t, 15 min / t, 20 min / t, 25 min / t, 30 min / t, etc., preferably 30 min / t.

[0057] In the present invention, the beating process after step 10) is as follows: the slurry obtained in step 9) is beaten in a second large-taper refiner. The beating current is 160 A - 180 A, for example, it can be 160 A, 170 A, 180 A, etc., preferably 160 A. The concentration of the slurry is 2.5% - 2.7%, for example, it can be 2.5%, 2.6%, 2.7%, etc., preferably 2.5%. The beating rate is 10 min / t - 30 min / t, for example, it can be 10 min / t, 15 min / t, 20 min / t, 25 min / t, 30 min / t, etc., preferably 30 min / t.

[0058] In the present invention, the pulp-making process in step 11) is as follows: the slurry obtained in step 10) is placed on the long wire of the paper machine in the pulp-making machine. The concentration of the slurry is 8 g / L - 12 g / L, for example, it can be 8 g / L, 9 g / L, 10 g / L, 11 g / L, 12 g / L, preferably 8 g / L. The pressure of the drying cylinder is ≤0.20 Mpa. After the pulp-making is completed, cotton pulp sheets with a high content of alpha cellulose are obtained.

[0059] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0060] Example 1

[0061] (1) Material selection, cotton opening, and impurity removal process: Select the third-class first-grade cotton linter with a maturity ≥80%. After tearing the cotton linter with a cotton opener, it is loosened and impurities are removed through an impurity remover, and then transferred to a cotton squeezer. After fine selection and impurity removal, it is sent to a screw press and impregnation through a cyclone separator;

[0062] (2) Hot water hydrolysis to remove hemicellulose process: The temperature is 130 °C, the surfactant fatty alcohol polyoxyethylene ether phosphate is 1 kg / ton, and the treatment time is 90 min. It is sent to the next process through a screw conveyor;

[0063] (3) Cooking process for selective delignification and hemicellulose removal: The temperature for alkali preparation is controlled at 45 °C. The total alkali, calculated as NaOH, is 6% of the weight of the absolute dry pulp. The ratio of alkali preparation liquid is 1:3.7, Na 2 SO 3is 0.4% of the weight of absolute dry pulp, Na 2 B 4 O 7 is 0.4% of the weight of absolute dry pulp, cooking time is 120 min, cooking temperature is 120 °C. After cooking is completed, it enters the next process;

[0064] (4) Pre-desanding process: carried out in a desander, pressure is controlled at 0.30 Mpa, pulp consistency is controlled at 0.4%, desanding rate is 30 min / t;

[0065] (5) Pre-beating process: carried out in the first large-taper refiner, beating current is controlled at 180 A, pulp consistency is controlled at 1.0%, beating rate is 30 min / t;

[0066] (6) Concentration process: carried out in a side-pressure cylinder screen concentrator, pulp consistency is controlled at 10%;

[0067] (7) Hydrogen peroxide bleaching process:

[0068] a. In a medium-consistency mixer, add diethylenetriaminepentaacetic acid at 0.17% of the absolute dry pulp weight, add hydrogen peroxide at 2% of the absolute dry pulp weight, introduce steam, control the temperature at 90 °C, after mixing for 20 min, transfer to a hydrogen peroxide bleaching tower;

[0069] b. In the hydrogen peroxide bleaching tower, control the temperature at 90 °C, after the bleaching reaction for 100 min, dilute with deionized water, control the pulp consistency at 1%, send to a vacuum washer and wash with deionized water until neutral, after washing, enter the acid treatment tank;

[0070] (8) Acid treatment process: In the acid treatment tank, add hydrochloric acid (concentration of hydrochloric acid is 350 g / L) at 2% of the absolute dry pulp weight, carry out acid treatment for 30 min, then wash with deionized water for 2 hours, transfer to a post-desander;

[0071] (9) Post-desanding process: Control the pressure of the post-desander at 0.3 Mpa, pulp consistency at 0.5%, desanding rate at 30 min / t, after desanding, transfer to the second large-taper refiner;

[0072] (10) Post-beating process: Control the current of the second large-taper refiner at 160 A, pulp consistency at 2.5%, beating rate at 30 min / t, after refining, transfer to a sheet former;

[0073] (11) Sheet forming process: Control the pulp consistency on the wire of the sheet former at 8 g / L, drying cylinder pressure at 0.20 Mpa, after sheet forming, the finished product is obtained.

[0074] Example 2

[0075] (1) Raw material selection, cotton opening, and impurity removal process: Select the third-class first-grade cotton linter with a maturity of ≥80%. After tearing the cotton linter with a cotton opener, loosen and remove impurities through an impurity remover, then transfer it to a cotton squeezing machine. After fine selection and impurity removal, send it to a spiral press and impregnation through a cyclone separator;

[0076] (2) Hot water extraction of hemicellulose process: Temperature is 140°C, surfactant fatty alcohol polyoxyethylene ether phosphate is 1 kg / ton, treatment time is 90 min, and transfer to the next process through a screw conveyor.

[0077] (3) Cooking process for selective delignification and hemicellulose removal: The alkali preparation temperature is controlled at 45°C, the total alkali (calculated as NaOH) is 6% of the weight of the absolute dry pulp, the alkali preparation liquor ratio is 1:3.7, Na 2 SO 3 is 0.4% of the weight of the absolute dry pulp, Na 2 B 4 O 7 is 0.4% of the weight of the absolute dry pulp, the cooking time is 120 min, and the cooking temperature is 120°C. After cooking, enter the next process.

[0078] (4) Pre-desanding process: Conduct in a desander, with the pressure controlled at 0.30 Mpa, the pulp concentration controlled at 0.4%, and the desanding rate of 30 min / t;

[0079] (5) Pre-beating process: Conduct in the first large-taper refiner, with the beating current controlled at 180 A, the pulp concentration controlled at 1.0%, and the beating rate of 30 min / t;

[0080] (6) Concentration process: Conduct in a side-pressure cylinder screen concentrator, with the pulp concentration controlled at 10%;

[0081] (7) Hydrogen peroxide bleaching process:

[0082] a. In a medium-consistency mixer, add diethylenetriaminepentaacetic acid at 0.17% of the absolute dry pulp amount, add hydrogen peroxide at 2% of the absolute dry pulp amount, introduce steam, control the temperature at 90°C, mix for 20 min, and then transfer to a hydrogen peroxide bleaching tower;

[0083] b. In the hydrogen peroxide bleaching tower, control the temperature at 90°C. After 100 min of bleaching reaction, dilute with deionized water, control the pulp concentration at 1%, send it to a vacuum pulp washer and wash with deionized water until neutral, and then enter the acid treatment tank after washing;

[0084] (8) Acid treatment process: In the acid treatment tank, add hydrochloric acid (the concentration of hydrochloric acid is 350 g / L) at 2% of the absolute dry pulp amount, conduct acid treatment for 30 min, then wash with deionized water for 2 hours, and transfer to the post-desander;

[0085] (9) Post-desanding process: The pressure of the post-desander is controlled at 0.3 Mpa, the pulp consistency is controlled at 0.5%, the desanding rate is 30 min / t. After desanding, it is transferred to the second large-taper refiner.

[0086] (10) Post-beating process: The current of the second large-taper refiner is controlled at 160 A, the pulp consistency is controlled at 2.5%, the beating rate is 30 min / t. After refining, it is transferred to the paper-making machine.

[0087] (11) Paper-making process: The pulp consistency on the long wire of the paper-making machine is controlled at 8 g / L, the pressure of the dryer cylinder is 0.20 Mpa. After paper-making, the finished product is obtained.

[0088] Example 3

[0089] (1) Material selection, cotton opening and impurity removal process: Select the third-class first-grade cotton linter with a maturity of ≥80%. After tearing the cotton linter with a cotton opener, it is loosened and impurity-removed by an impurity remover, and then transferred to a cotton squeezer. After selective impurity removal, it is sent to a screw press and impregnation through a cyclone separator.

[0090] (2) Hot water delignification of hemicellulose process: The temperature is 150 °C, the surfactant fatty alcohol polyoxyethylene ether phosphate is 1 kg / t, the treatment time is 90 min, and it is transported to the next process through a screw conveyor.

[0091] (3) Cooking process for selective delignification and hemicellulose removal: The alkali mixing temperature is controlled at 45 °C, the total alkali calculated as NaOH is 6% of the weight of the absolute dry pulp, the alkali mixing liquor ratio is 1:4.2, Na 2 SO 3 is 0.4% of the weight of the absolute dry pulp, Na 2 B 4 O 7 is 0.4% of the weight of the absolute dry pulp, the cooking time is 120 min, and the cooking temperature is 120 °C. After cooking, it enters the next process.

[0092] (4) Pre-desanding process: It is carried out in a desander, the pressure is controlled at 0.30 Mpa, the pulp consistency is controlled at 0.4%, and the desanding rate is 30 min / t;

[0093] (5) Pre-beating process: It is carried out in the first large-taper refiner, the beating current is controlled at 180 A, the pulp concentration is controlled at 1.0%, and the beating rate is 30 min / t;

[0094] (6) Concentration process: It is carried out in a side-pressure cylinder screen concentrator, and the pulp consistency is controlled at 10%;

[0095] (7) Hydrogen peroxide bleaching process:

[0096] a. In the medium consistency mixer, add diethylenetriaminepentaacetic acid at 0.17% based on the weight of absolutely dry pulp, add hydrogen peroxide at 2% based on the weight of absolutely dry pulp, introduce steam, control the temperature at 90°C, mix for 30 min, and then transfer to the hydrogen peroxide bleaching tower.

[0097] b. In the hydrogen peroxide bleaching tower, control the temperature at 90°C. After the bleaching reaction for 100 min, dilute with deionized water, control the pulp concentration at 1%, send it to the vacuum pulp washer and wash with deionized water until neutral, and then enter the acid treatment tank after washing.

[0098] (8) Acid treatment process: In the acid treatment tank, add hydrochloric acid (the concentration of hydrochloric acid is 350 g / L) at 2% based on the weight of absolutely dry pulp, carry out acid treatment for 30 min, then wash with deionized water for 2 hours, and transfer to the post-desander.

[0099] (9) Post-desanding process: Control the pressure of the post-desander at 0.3 Mpa, control the pulp concentration at 0.5%. After desanding, transfer to the second large-taper refiner.

[0100] (10) Post-beating process: Control the current of the second large-taper refiner at 160 A, control the pulp concentration at 2.5%, the beating rate is 30 min / t. After refining, transfer to the sheet former.

[0101] (11) Sheet forming process: Control the pulp concentration on the wire of the sheet former at 8 g / L, the pressure of the drying cylinder at 0.20 Mpa. After sheet forming, the finished product is obtained.

[0102] Comparative Example 1

[0103] 1) Material selection, cotton opening, and dry impurity removal process. Select the third-class first-grade cotton linter with a maturity of ≥80%. After tearing the cotton linter with a cotton opener, loosen and remove impurities through a multi-roll loosener and a heavy-duty trash remover respectively, and then transfer to a cotton squeezing machine and send it to the alkali preparation, impregnation, and cooking processes through a cyclone separator.

[0104] 2) Alkali preparation, impregnation, and cooking processes. Control the alkali preparation temperature at 45°C, the total alkali calculated as NaOH is 6% of the weight of absolutely dry pulp, and Na 2 SO 3 is 0.4% of the weight of absolutely dry pulp; and add Na 2 SO 3 to the alkali solution to obtain the prepared alkali solution; then pump the prepared alkali solution into the digester and fully mix it with the loaded cotton linter through cold rotation for impregnation; then heat up and cook the materials in the digester, the cooking temperature is 120°C, the cooking time is 120 min, and after cooking, enter the next process.

[0105] (3) Pre-desanding process. The cooked pulp is put into a desander for desanding. The pressure is controlled at 0.30 Mpa, the pulp concentration is controlled at 0.4%, and the desanding rate is 30 min / t.

[0106] (4) Pre-desanding process: Conducted in a desander, with the pressure controlled at 0.30 Mpa, the pulp consistency controlled at 0.4%, and the desanding rate at 30 min / t;

[0107] (5) Pre-beating process: Conducted in the first large-taper refiner, with the beating current controlled at 180 A, the pulp concentration controlled at 1.0%, and the beating rate at 30 min / t;

[0108] (6) Concentration process: Conducted in a side-pressure cylinder screen concentrator, with the pulp concentration controlled at 10%;

[0109] (7) Hydrogen peroxide bleaching process:

[0110] a. In a medium-consistency mixer, add diethylenetriaminepentaacetic acid at 0.17% based on the absolutely dry pulp weight, add hydrogen peroxide at 2% based on the absolutely dry pulp weight, introduce steam, control the temperature at 90 °C, mix for 30 min, and then transfer to a hydrogen peroxide bleaching tower;

[0111] b. In the hydrogen peroxide bleaching tower, control the temperature at 90 °C. After 100 min of bleaching reaction, dilute with deionized water, control the pulp concentration at 1%, send it to a vacuum pulp washer and wash with deionized water until neutral, and then enter the acid treatment tank after washing;

[0112] (8) Acid treatment process: In the acid treatment tank, add hydrochloric acid (with a concentration of 350 g / L) at 2% based on the absolutely dry pulp weight, conduct acid treatment for 30 min, then wash with deionized water for 2 hours, and transfer to a post-desander;

[0113] (9) Post-desanding process: Control the pressure of the post-desander at 0.3 Mpa, the pulp concentration at 0.5%, and the desanding rate at 30 min / t. After desanding, transfer to the second large-taper refiner;

[0114] (10) Post-beating process: Control the current of the second large-taper refiner at 160 A, the pulp concentration at 2.5%, and the beating rate at 30 min / t. After refining, transfer to a sheet-forming machine;

[0115] (11) Sheet-forming process: Control the pulp concentration on the wire of the sheet-forming machine at 8 g / L and the dryer cylinder pressure at 0.20 Mpa. After sheet-forming, the finished product is obtained.

[0116] The degree of polymerization, whiteness, alpha cellulose, dirt, ash content, and metal content of the finished products prepared in Examples 1 - 3 were detected. After detection, the specific indicators of the products are shown in Table 1 below:

[0117] Performance test table of the products prepared in Examples 1-3 and Comparative Example 1

[0118]

[0119]

[0120] As can be seen from Table 1, by using the cotton pulp production process with a high content of alpha-cellulose provided by the present invention, the alpha-cellulose content of the obtained cotton pulp reaches 99.2%. The prepared cellulose ether has a uniform degree of substitution, stable viscosity and good compatibility, improving the quality of the cellulose ether.

[0121] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing cotton pulp with high methylcellulose content, characterized in that: The following steps are involved: 1) Material selection, cotton opening, and dry impurity removal process; 2) Hot water dehesicellulose process; 3) Selective delignification and hemicellulose cooking process; 4) Pre-sand removal process; 5) Pre-pulping process; 6) Concentration process; 7) Hydrogen peroxide bleaching process; 8) Acid treatment process; 9) Post-sand removal process; 10) Post-pulping process; 11) Pulping process; The step 2) of hot water dehemicellulose removal comprises: mixing selected cotton linters and surfactant fatty alcohol polyoxyethylene ether phosphate, and heating to obtain a slurry; wherein 0.5 kg to 1 kg of the surfactant fatty alcohol polyoxyethylene ether phosphate is added per ton of selected cotton linters; the heating temperature is 130° C. to 150° C., and the heating time is 60 min to 120 min; The selective delignification and hemicellulose cooking process of step 3) is as follows: adding alkali solution, Na2SO3 and Na2B4O7 to the slurry obtained in step 2) for cooking.

2. The method for preparing cotton pulp with high methylcellulose content according to claim 1, characterized in that: The preparation method of the alkali solution is to prepare the alkali solution at 45°C to 50°C according to the weight ratio of NaOH to water = 1:3.7 to 4.2, and the total alkali is 6% to 10% of the relative weight of the absolute dry pulp in terms of NaOH; Na2SO3 is 0.4% to 0.8% relative to the absolute dry pulp weight; Na2B4O7 is 0.3% to 0.5% relative to the absolute dry pulp weight; The cooking temperature is 120°C to 135°C, and the cooking time is 100min to 150min.

3. The method for preparing cotton pulp with high methylcellulose content according to claim 1, characterized in that: The process of material selection, cotton opening and dry impurity removal in step 1) is as follows: selecting three types of first-class cotton linters with a maturity of ≥80%, tearing the cotton linters, loosening and removing impurities, and then selecting and removing impurities to obtain selected cotton linters.

4. The method for preparing cotton pulp with high methylcellulose content according to claim 1, characterized in that: The desanding process before step 4) is as follows: desanding the slurry obtained in step 3) in a desander, the desanding pressure is 0.30MPa to 0.32MPa, the concentration of the slurry is 0.4% to 0.6%, and the desanding rate is 10min / t to 30min / t; The pulping process before step 5) is as follows: the pulp obtained in step 4) is pulped in the first large-tapered pulping machine, the pulping current is 180A-200A, the pulp concentration is 1.0%-1.8%; the pulping rate is 10min / t-30min / t.

5. The method for preparing cotton pulp with high methylcellulose content according to claim 1, characterized in that: The concentration process in step 6) is as follows: the slurry obtained in step 5) is concentrated in a side pressure rotary screen concentrator, and the concentration of the slurry is 10% to 12%.

6. The method for preparing cotton pulp with high methylcellulose content according to claim 1, characterized in that: The step 7) of bleaching with hydrogen peroxide is as follows: a. The slurry obtained in step 6) is conveyed to a medium-consistency mixer, diethylenetriamine pentaacetic acid, hydrogen peroxide, steam is introduced, the temperature is controlled at 90 ℃ ~ 110 ℃, mixed for 20min ~ 30min, and then transferred to a hydrogen peroxide bleaching tower; The diethylenetriaminepentaacetic acid is 0.17% to 0.22% by weight relative to the absolute dry pulp; the hydrogen peroxide is 2% to 2.8% by weight relative to the absolute dry pulp; b. In the hydrogen peroxide bleaching tower, the temperature is controlled at 90℃~110℃. After the bleaching reaction lasts for 100min~120min, the pulp is diluted with water to a concentration of 1%~1.5%, and then sent to a vacuum pulp washer for washing with water until it becomes neutral; The acid treatment process in step 8) is as follows: the slurry obtained in step 7) is sent to an acid treatment tank, 2% to 2.5% hydrochloric acid relative to the absolute dry pulp weight is added, the slurry is treated with acid for 20 minutes to 40 minutes, and then washed with water for 2 hours to 3 hours; the concentration of the hydrochloric acid is 300g / L to 400g / L.

7. The method for preparing cotton pulp with high methylcellulose content according to claim 1, characterized in that: The post-sand removal process of step 9) is as follows: the slurry obtained in step 8) is desanded in a post-sand remover, the desanding pressure is ≥0.3MPa, the concentration of the slurry is 0.5% to 0.7%, and the desanding rate is 10min / t to 30min / t.

8. The method for preparing cotton pulp with high methylcellulose content according to claim 1, characterized in that: The pulping process after step 10) is as follows: the pulp obtained in step 9) is pulped in a second large-taper refiner, the pulping current is 160A-180A, the pulp concentration is 2.5%-2.7%, and the pulping rate is 10min / t-30min / t.

9. The method for preparing cotton pulp with high methylcellulose content according to claim 1, characterized in that: The pulping process in step 11) is as follows: placing the pulp obtained in step 10) on the long wire of a pulping machine, wherein the concentration of the pulp is 8 g / L to 12 g / L, and the drying cylinder pressure is ≤0.20 MPa. After the pulping is completed, cotton pulp with a high content of type A cellulose is obtained.

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