AU2020102427A4 - Method for refining and upgrading paper grade chemical pulp to dissolving pulp - Google Patents

Abstract

The present invention discloses a method for refining and upgrading a paper grade chemical pulp to a dissolving pulp. The chemical pulp is treated with y-valerolactone to dissolve hemicellulose in the chemical pulp, to obtain an c-cellulose pulp with high purity, which is the dissolving pulp. The y-valerolactone is an important solvent for cleanly producing biomass and also is a novel, highly-efficient, green organic solvent with excellent characteristics. The y-valerolactone can be miscible with water in any ratio, does not produce peroxide with air, is a stable chemical substance, and can be recycled and reused. The y-valerolactone effectively removes a large amount of hemicellulose in the chemical pulp to obtain a refined chemical pulp of high-purity cellulose. The resultant chemical pulp achieves all critical property indexes of a commercially available dissolving pulp, thus alleviating the increasing demand for the dissolving pulp to a certain extent and playing an important role in the clean and simplified production for the dissolving pulp.

Description

METHOD FOR REFINING AND UPGRADING PAPER GRADE CHEMICAL PULP TO DISSOLVING PULP

Technical Field The present invention belongs to the technical field of paper pulp treatment, and in particular relates to a

method for refining and upgrading a paper grade chemical pulp to a dissolving pulp.

Background Art As a refined chemical pulp, dissolving pulp has the following characteristics: high content ofu-cellulose, good

reaction property, low content of pentosan, high whiteness, low ash content, low dirt count, etc. The dissolving

pulp is usually used to prepare viscose fibers, and can also be used as a raw material for preparing cellulose

derivative products. Removal of hemicellulose from the dissolving pulp is beneficial to the production of

viscose acetal fibers. In order to obtain a cellulose pulp with a higher purity, lignin and hemicellulose therein

need to be removed as impurities.

Conventional bleached paper grade chemical pulps have the characteristics of high whiteness and high content

of cellulose. Generally, their lignin has been fundamentally removed, but there is still a small amount of

hemicellulose, and the purity of cellulose does not meet the basic requirements of the dissolving pulp.

A method for removing hemicellulose from a paper grade pulp in the prior art mainly involves extraction of

alkali and treatment of hemicellulase. However, extraction of alkali needs to consume a lot of alkali, thereby

causing severe environmental burden. At the same time, the reaction conditions for strong alkali lead to a

change in the ultrastructure of cellulose and lower reactivity, and also the purification efficiency of

hemicellulase is poor, which restricts industrial application.

As a biomass-based platform compound molecule, y-valerolactone can be catalytically converted from

cellulose and hemicellulose, and has non-toxic and biodegradable characteristics. The physical and chemical

properties of the y-valerolactone comprises a molecular weight of 100 g/mol, a density of 1.05 g/mL, a melting

point of -31°C and a boiling point of 207°C, and the y-valerolactone is miscible with water in any ratio.

Meanwhile, the y-valerolactone has a unique smell, which made the leakage detection becomes much easier,

and is extremely suitable for large-scale storage, transportation and use. At present, the y-valerolactone is

mainly used as an additive for gasoline, diesel and other such fuels, for the preparation of liquid fuels, as an

intermediate product or solvent in chemical and pharmaceutical industries, and also for the preparation of

high-molecular materials like biomass-based nylon. Its use in papermaking has just begun. For example, in the

publication No. CN109811585A, the inventor of the present application discloses a method for improving the

strength of boxboard paper. For the first time, use of the y-valerolactone in papermaking is disclosed.

The y-valerolactone can effectively enhance a binding force between fibers, and ultimately achieve the purpose

of improving the papermaking strength of waste paper pulp. However, it is not mentioned in this patent

whether the y-valerolactone has other influences on paper pulp.

Summary of the Invention An object of the present invention is to provide a method for refining and upgrading a paper grade chemical pulp to a dissolving pulp. According to the method, y-valerolactone is employed to treat and dissolve hemicellulose in the chemical pulp to obtain an c-cellulose pulp with high purity. The present invention provides a brand-new method for removing hemicellulose from paper grade pulp, which overcomes the problem of environmental pollution caused by chemical treatments in the prior art. This method is simple and pollution-free. In order to achieve the above object, the present invention adopts the following technical solution. A method for refining and upgrading a chemical pulp to a dissolving pulp is provided. The chemical pulp is treated with y-valerolactone to dissolve hemicellulose in the chemical pulp, to obtain an c-cellulose pulp with high purity, which is the dissolving pulp. After measurement, the viscosity, alkali solubility and Fcok reaction property of the dissolving pulp basically reach the indexes of a commercially available dissolving pulp. Preferably, the y-valerolactone has the following treatment conditions: the y-valerolactone has a concentration of 20-80%, a treatment temperature of 80-140°C, and a time of 0.5-2h and a liquid ratio of 1:10. More preferably, the y-valerolactone has the following treatment conditions: the y-valerolactone has a concentration of 60%, a treatment temperature of 120°C, a time of 2h, and a liquid ratio of 1: 10. Preferably, before treatment with the y-valerolactone, the chemical pulp is first soaked in deionized water, and then dispersed with a fiber dissociator for later use. The chemical pulp is a bleached chemical kraft pulp. The bleached chemical kraft pulp comprises a commonly used bleached softwood kraft pulp and a bleached hardwood kraft pulp, at which the experiments of the present invention mainly aim. Measurement of u-cellulose of the present invention: 2 g of pulp was soaked in 30mL of 17.5% NaOH solution at a constant temperature for 45 minutes, washed with 9.5% NaOH solution, dipped in 2 mol/L of acetic acid for 5 minutes and then washed with water, dried, and weighed. Measurement of viscosity: the oven dried pulp samples equivalent to 0.2 g were weighed, placed into a 50 mL white vial, added with 25 mL of deionized water, 25mL of cuprous diamine were added. Finally, it was tested by viscometer. Measurement of alkali solubility: 1.5 g oven dried pulp was accurately weighed, placed into a 200 ml high-shaped reactor, added with 100 ml of 10% NaoH (Sio) or 18% NaoH (S1 8 ), wetted and swelled for 2 minutes and then stirred for 1 minute to dissolve the fibers. From the time when the sample of the pulp came into contact with the sodium hydroxide solution, the pulp was kept in a 20°C water bath for 60 minutes. After 60 minutes, the pulp was stirred and filtered with a G2 filter. 40mL of the filtrate was collected for experimental uses. 10 mL of the filtrate was drawn into a 250 mL Erlenmeyer flask, slowly added with 10 mL of potassium dichromate solution, and finally slowly added with 30 mL of concentrated sulfuric acid. The solution was heated to 120°C and kept at this temperature for 10 minutes, cooled to room temperature, added with 50 mL of distilled water, then added with two drops of a Ferroin indicator, and titrated with a calibrated ammonium ferrous sulfate solution until purple appeared.

Measurement of Fock reactivity: (0.500.01) g of oven dried pulp was accurately weighed, placed into a 250

mL Erlenmeyer flask, and added with 50 mL of 9% NaOH solution. The Erlenmeyer flask was placed into a shaker under operation conditions of 250 rpm and 19°C for 10 minutes before taken out. The Erlenmeyer flask was placed in a fume cupboard, added with 1.3 mL of CS 2, quickly sealed, placed into the shaker under the above operation conditions of the shaker, and shaken for 3 hours to complete the reaction. After 3 hours, the Erlenmeyer flask was taken out, added with 43.14 g of deionized water, and shaken uniformly. Thereafter, 50mL of solution was taken and placed in a centrifuge tube for centrifugation at 4500 rpm for 15 minutes. 10 mL of supernate was taken and placed in the Erlenmeyer flask, and then added with 3 mL of 20% H 2SO4. The Erlenmeyer flask was placed in the fume cupboard under open conditions and allowed to stand for 18 hours. After standing for 18 hours, 20 mL of 68% H 2SO4 was added to the Erlenmeyer flask. The Erlenmeyer flask was placed in the shaker for shaking for 10 minutes. 10 minutes later, the Erlenmeyer flask was taken out, added with 10 mL of0.1M K2Cr207 solution, then placed on a heating board, and installed with a reflux condensing tube. After the solution was slowly heated to a boiling state, a timing of 1 hour was initiated and the temperature was adjusted to 140°C. After the heating was completed, the Erlenmeyer flask was cooled to room temperature and the liquid in the flask was transferred to a 100 mL volumetric flask, and the volume of the liquid was metered to a standard scale line. After the volume was completely metered, 40 mL of the liquid was placed in the Erlenmeyer flask, then added with 5 mL of 10% KI solution, and quickly titrated with a 0.1 M of sodium thiosulfate sodium solution. A starch indicator was added when the color of the solution became lighter, and finally titration was carried out until the color of the solution became bright blue, which means that the measurement ended. It can also be concluded that the y-valerolactone can dissolve hemicellulose. Therefore, use of the y-valerolactone comprises the treatment of the hemicellulose in the chemical pulp. Further, use of the y-valerolactone in dissolving hemicellulose in other pulps also falls within the protection scope of the present invention, and the treatment conditions of the y-valerolactone can be adjusted according to different pulps. The present invention has the following advantages. The method of the present invention uses y-valerolactone (GVL) as an organic solvent to purify the chemical pulp. The solvent is an important solvent for cleanly producing biomass and also is a novel, highly-efficient, green organic solvent with excellent characteristics. The solvent can be miscible with water in any ratio, does not produce peroxide with air, is a stable chemical substance, and can be recycled and reused. The solvent effectively removes a large amount of hemicellulose in the chemical pulp to obtain a refined chemical pulp of high-purity cellulose. The resultant chemical pulp achieves all critical property indexes of a commercially available dissolving pulp, thus alleviating the increasing demand for the dissolving pulp to a certain extent and playing an important role in the clean and simplified production for the dissolving pulp. For the first time, the present invention discloses use of the y-valerolactone in dissolving hemicellulose and expands the range of application of the y-valerolactone.

Detailed Description of the Invention The present invention will be further explained through specific examples below, but it should be understood that the present invention can be implemented in various forms and should not be limited by the examples set forth herein. Rather, these examples are provided to enable a more thorough understanding of the invention, and to fully convey the scope of the invention to those skilled in the art. As mentioned throughout the description and claims, "include" or "comprise" is an open-ended term and should be construed as "including but not limited to". Preferred examples for implementing the present invention are described below, but the following are for the general principles of the description, and not intended to limit the scope of the present invention. The protection scope of the present invention shall be determined by the scope defined by the appended claims. Unless otherwise specified, various methods adopted in the present invention are conventional methods, and various materials and reagents can be commercially available. In order to prove the effects of the present invention, the inventor conducted the following experiments. Experiment 1: Effect of a change in GVL concentration on c-cellulose and pentosan The purification treatment of a bleached chemical kraft pulp was as follows: a paper pulp used was a chemical pulp board, which was torn into small pieces, soaked in deionized water, and finally dispersed with a fiber dissociator for later use. Five individual sets of experiment were carried out. 5 g pulp (equivalent to oven dried base) was weighed and placed in a round bottom flask. A certain amount of y-valerolactone solvent and a certain amount of deionized water were added at a liquid ratio of 1: 10, and mixed uniformly. The amounts of the y-valerolactone for a single factor experiment were as follows, respectively: 0, 20%, 40%, 60% and 80%. The y-valerolactone was

treated in a constant-temperature oil bath pan at the temperature of 120°C for 2h. 5 kinds of 2g pulps were weighed respectively, placed into a 100-150 mL beaker, and added with about 30 mL of 175 g/L NaOH solution for sample dipping. At the time of adding lye, about 15 mL of the lye was first added and stirred carefully with a flat-head glass rod for 2 to 3 minutes to disperse the pulp into a uniform paste. Then, the remaining lye was added, and stirred evenly and carefully for 1 min to dissolve fibers. The beaker was then covered with watch glass and placed in a constant-temperature water bath at (20±0.5)°C for mercerizing treatment. After 45 minutes, about 30 mL of distilled water was added to the beaker and stirred carefully for 2 minutes. Finally, the pulp in the beaker was slowly moved into a glass filter with constant weight, evenly spread in the filter, and then subjected to suction filtration with a vacuum pump. The pulp was washed with 25 mL of 95g/L NaOH solution, and this was repeated three times. The pulp was then washed with about 400 mL of the distilled water. In the case where no vacuum filtration is performed, 2 mol/L acetic acid solution was added into the filter so that the treated pulp was completely immersed. After 5 minutes, the acetic acid solution was sucked away by means of vacuum filtration, and then washed with water until the washing solution was not acidic. Upon completion of the washing, the filter was removed, placed in an oven, and dried at (105±2)°C to constant weight. The contents ofu-cellulose and pentosan were measured at different concentrations of the y-valerolactone, see Table 1.

Table 1 Effect of a change in GVL concentration on c-cellulose and pentosan

GVL Concentration 0 200% 400% 600% 800%

8 hardwood experimental group c-cellulose content 85.4% 7. 3 % 88 2 . % 9 0.0% 9 1.0% 8 86 6 88 6 89 2 hardwood control group u-cellulose content 5.0% . % 87.7% . % .

% hardwood experimental group pentosan content 12.7% 10.30% 8.76% 7.12% 5.980% hardwood control group pentosan content 12.9% 11.1% 9.55% 8.03% 7.75% 86 8 8 4 88 9 89 softwood experimental group c-cellulose content 85.1% . % 7. % . % .7% softwood control group c-cellulose content 84.3% 85.9% 86.8% 88.0% 88.8% softwood experimental group pentosan content 10.7% 8.92% 7.630% 6.52% 5.85% 9 3 8 3 6 34 softwood control group pentosan content 11.0% . 1% .05%1 7.1 % .

% It could be seen from Table 1 that after either the bleached hardwood pulp or the bleached softwood pulp was treated with a GVL/water medium, there was a significant increase in their u-cellulose. At the same time, a decrease in the content of pentosan was also seen, which verified that GVL could effectively remove hemicellulose and significantly improve the purity of cellulose in the chemical pulp. In comprehensive consideration of the experimental results and economic costs, the treatment concentration 60% of GVL was chosen. Experiment 2: Effect of different treatment temperatures on -cellulose and pentosan Five individual sets of experiment were carried out. 5 g pulp (equivalent to oven dried base) was weighed in a flask. A certain amount of y-valerolactone solvent and a certain amount of deionized water were added at a liquid ratio of 1: 10, and mixed uniformly. The concentration of GVL was fixed at 60%. The treatment temperatures for a single factor experiment were selected as follows: 80°C, 100°C, 120°C, 140°C, 160°C, and the GVL was treated with a constant-temperature oil bath for 2h. The other conditions of Experiment 2 were the same as Experiment 1. Table 2 Effect of different treatment temperatures on -cellulose and pentosane Temperature 80°C 100°C 120°C 140°C 160°C Experiment Type 9 9 92 3 92 92 2 hardwood experimental group u-cellulose content 0.0% 1.0% . % .7% . %

8 hardwood control group u-cellulose content 5. 4 % 8 5. 9 % 86 6 . % 8 7.5% 88 .0%

hardwood experimental group pentosan content 7.12% 6.92% 5.45% 4.76% 4.35%

hardwood control group pentosan content 1 2 .9 % 1 2 .9 % 1 2 .5% 1 2 .1% 11. 9 %

88 9 89 8 92 9 4 softwood experimental group u-cellulose content . % . % 91.1% .0% 1. %

softwood control group u-cellulose content 85.1% 85.8% 86.3% 86.9% 87.2% 6 2 64 4 3 80 4 2 3 96 softwood experimental group pentosan content .5 % 5. % . % .1 % . %

9 9 9 softwood control group pentosan content 11.0% 10.7% 10.1% . 7% .7 8 %

It could be seen from Table 2 that temperatures played a key role in the removal of the hemicellulose from the chemical pulp. Since the GVL had a higher boiling point, the temperature range from 80°C to 160°C was selected as an experimental temperature range. High temperatures were beneficial to the removal of the hemicellulose, which was more obvious when the temperature was above 100°C. High temperatures promoted the wetting and swelling of the GVL in pulp fibers. However, the removal efficiency of the hemicellulose decreased at the temperature above 140°C. The cellulose in the pulp also possibly accelerated dissolution. When the temperature was 120°C, the separation effect was significant, and the highest removal efficiency of the hemicellulose was attained. Experiment 3: Effect of different treatment time on c-cellulose and pentosan According to Experiment 2, c-cellulose in the paper pulp had the highest increase rate under the temperature of 120°C. In this experiment, five individual sets of experiment were carried out. 5 g pulp (equivalent to oven dried base) was weighed and placed in a round bottom flask. A certain amount of y-valerolactone solvent and a certain amount of deionized water were added at a liquid ratio of 1: 10, and mixed uniformly. The treatment time for a single factor experiment was 0.5h, 1h, 2h, 4h, and 6h, respectively. The other conditions of Experiment 3 were the same as Experiment 1. Table 3 Effect of different treatment time on c-cellulose and pentosane 0.5h 1h 2h 4h 6h

92 3 92 8 93 2 hardwood experimental group c-cellulose content 89.2% 90.7% . % . % .

% hardwood control group c-cellulose content 85.6% 86.0% 86.0% 86.9% 87.4% hardwood experimental group pentosan content 9.38% 7.17% 5.45% 4.93% 4.54% hardwood control group pentosan content 12.8% 12.6% 12.5% 12.4% 12.3% softwood experimental group u-cellulose content 88.3% 89.6% 91.1% 91.8% 92.0% 8 8 86 3 86 86 9 softwood control group u-cellulose content 5.0% 5.7% . % .5% . %

6 39 80 4 3 80 4 3 92 softwood experimental group pentosan content . % 5.7 % . % .17% . %

6 3 9 9 9 93 softwood control group pentosan content 10. % 10. % 10.1% . 7% . %

It could be seen from Table 3 that the purification time of the bleached chemical pulp in a GVL/water medium system had a certain effect on the removal of the hemicellulose. As time went on, the content ofu-cellulose in the bleached chemical pulp increased. During the time period of 0.5h to 2h, the content ofu-cellulose had a significant growth rate. During the time period from 2h to 6h, the content ofu-cellulose had a relatively slow growth rate, and the removal reaction of the hemicellulose reached the optimum. The best reaction efficiency was obtained at when the entire reaction stage lasted for 2h. Example 1 According to Experiments 1-3, the best treatment conditions obtained were as follows: the liquid ratio was 1: 10, the amount of GVL was 60%, the treatment temperature was 120°C, and the time was 2h. Under these conditions, a refined and upgraded hardwood chemical pulp (the pulp obtained in the present invention) and a control pulp without treatment with GVL (the hardwood chemical pulp) were compared with the dissolving pulp (a hardwood dissolving pulp). The content ofu-cellulose, the content of pentosan, viscosity (mL/g), alkali solubility and Fock reactivity were compared. The specific measurement steps were as follows. (1) Measurement of -cellulose: 2 g of pulp was soaked in 30mL of 17.5% NaOH solution at a constant temperature for 45 minutes, washed with 9.5% NaOH solution, dipped in 2 mol/L of acetic acid for 5 minutes and then washed with water, dried, and weighed. (2) Measurement of viscosity: the oven dried pulp samples of an original pulp, a control pulp, an upgraded pulp, and a commercially available dissolving pulp equivalent to 0.2 g were weighed respectively, placed into a 50 mL white vial, added with 25 mL of deionized water, and then added with about 4 glass beads therein. The vial was placed on a shaker. A switch was turned on to make the vial shake and disperse away all the fibers. 20 minutes later, when the fibers were fully dispersed, 25 mL of copper hexamethylenediamine was added and shaking continued for about 20 minutes to bring the dispersed fibers into full reaction with the copper hexamethylenediamine solution. After the reaction was completed, the vial was taken out and placed in a constant-temperature water tank at 20°C, and a viscometer system was turned on to prepare for testing. The vial was then taken out and placed in a suction tube of the viscometer. After being sucked to a standard line, the solution was allowed to flow out automatically and the value of viscosity was read. This operation was repeated three times and an average value was taken. (3) Measurement of alkali solubility: the oven dried pulp samples of an original pulp, a control pulp, an upgraded pulp, and a commercially available dissolving pulp equivalent to 1.5 g were weighed respectively, placed into a 200 ml high-shaped reactor, added with 100 ml of 10% NaoH (Sio) or 18% NaoH (S), wetted and swelled for 2 minutes and then stirred for 1 minute to dissolve the fibers. From the time when the sample of the pulp came into contact with the sodium hydroxide solution, the pulp was kept in a 20°C water bath for 60 minutes. After 60 minutes, the pulp was stirred and filtered with a G 2 filter. 40mL of the filtrate was collected for experimental uses. 10 mL of the filtrate was drawn into a 250 mL Erlenmeyer flask, slowly added with 10 mL of potassium dichromate solution, and finally slowly added with 30 mL of concentrated sulfuric acid. The solution was heated to 120°C and kept at this temperature for 10 minutes, cooled to room temperature, added with 50 mL of distilled water, then added with two drops of a Ferroin indicator, and titrated with a calibrated ammonium ferrous sulfate solution until purple appeared. Finally, in place of the filtrate, 10 mL of a selected sodium hydroxide solution was used for blank test. (4) Measurement of Fock reactivity: (0.500.01) g of oven dried pulp was accurately weighed from 3 pulp samples, placed into a 250 mL Erlenmeyer flask, and added with 50 mL of 9% NaOH solution. The Erlenmeyer flask was placed into a shaker under operation conditions of 250 rpm and 19°C for 10 minutes before taken out. The Erlenmeyer flask was placed in a fume cupboard, added with 1.3 mLof CS 2, quickly sealed, placed into the shaker under the above operation conditions of the shaker, and shaken for 3 hours to complete the reaction. After 3 hours, the Erlenmeyer flask was taken out, added with 43.14 g of deionized water, and shaken uniformly. Thereafter, 50mL of solution was taken and placed in a centrifuge tube for centrifugation at 4500 rpm for 15 minutes. 10 mL of supernate was taken and placed in the Erlenmeyer flask, and then added with 3 mL of 20% H2 SO 4 . The Erlenmeyer flask was placed in the fume cupboard under open conditions and allowed to stand for 18 hours. After standing for 18 hours, 20 mL of 68% H 2SO4 was added to the Erlenmeyer flask. The Erlenmeyer flask was placed in the shaker for shaking for 10 minutes. 10 minutes later, the Erlenmeyer flask was taken out, added with 10 mL of0.M K 2Cr2O7 solution, then placed on a heating board, and installed with a reflux condensing tube. After the solution was slowly heated to a boiling state, a timing of 1 hour was initiated and the temperature was adjusted to 140°C. After the heating was completed, the Erlenmeyer flask was cooled to room temperature and the liquid in the flask was transferred to a 100 mL volumetric flask, and the volume of the liquid was metered to a standard scale line. After the volume was completely metered, 40 mL of the liquid was placed in the Erlenmeyer flask, then added with 5 mL of 10% KI solution, and quickly titrated with a 0.1 M of sodium thiosulfate sodium solution. A starch indicator was added when the color of the solution became lighter, and finally titration was carried out until the color of the solution became bright blue, which means that the measurement ended. After testing, the comparison of the components of the pulp was shown in Table 4. Table 4 Comparison of the components of the pulp component hardwood hardwood hardwood softwood softwood softwood (0%) chemical refining dissolving chemical refining dissolving pulp pulp pulp pulp pulp pulp u-cellulose 85.0 92.3 93.1 84.3 91.1 91.9 pentosan 12.9 4.35 3.68 11.0 3.96 3.53

It could be seen from Table 4 that after either the hardwood chemical pulp or the softwood chemical pulp was treated with the y-valerolactone of the present invention, the contents ofu-cellulose of the hardwood chemical pulp and the softwood chemical pulp were increased from 85.0% and 84.3% to 92.3% and 91.1%, respectively, which were close to the contents of hardwood and softwood dissolving pulps. It is thus clear that the treated chemical pulp could decrease the hemicellulose in the pulp (a decrease in hemicellulose content was reflected by an increase in c-cellulose content), so the content ofu-cellulose in the chemical pulp could be increased. The comparison results of the property indexes of the pulp were shown in Table 5. Table 5 Comparison of the property indexes of the pulp property hardwood hardwood hardwood softwood softwood softwood chemical refining dissolving chemical refining dissolving pulp pulp pulp pulp pulp pulp viscosity 658 595 582 643 568 536 (mL/g) Fock( %) 40 54.6 56.7 42.8 57.8 60.1 Sio) 13.5 8.9 7.7 12.7 8.7 6.7 Si8 (c%) 10.7 5.7 4.8 9.5 5.2 4.2

It could be seen from Table 2 that after either the hardwood chemical pulp or the softwood chemical pulp was treated with the y-valerolactone of the present invention, the viscosity index of the hardwood chemical pulp or the softwood chemical pulp as well as Sie and Sis were decreased, and the Fock reactivity were increased.

They were all close to the properties of the dissolving pulp and met the standards of the dissolving pulp. Although the present invention has been described in detail with general descriptions and specific examples, it is obvious for those skilled in the art that some modifications or improvements can be made based on the present invention. Therefore, these modifications or improvements made without departing from the spirit of the present invention all fall within the scope of protection of the present invention.

Claims (7)

Claims

1. A method for refining and upgrading a chemical pulp to a dissolving pulp, wherein the chemical pulp is treated with y-valerolactone to dissolve hemicellulose in the chemical pulp, to obtain an c-cellulose pulp with high purity, which is the dissolving pulp.

2. The method according to claim 1, wherein the y-valerolactone has the following treatment conditions: the y-valerolactone has a concentration of 20-80%, a treatment temperature of 80-140°C, and a time of 0.5-2h and a liquid ratio of 1:10.

3. The method according to claim 2, wherein the y-valerolactone has the following treatment conditions: the y-valerolactone has a concentration of 60%, a treatment temperature of 120°C, a time of 2h, and a liquid ratio of 1: 10.

4. The method of claim 1, wherein the chemical pulp is a bleached chemical kraft pulp.

5. The method according to claim 4, wherein the bleached chemical kraft pulp comprises a bleached softwood kraft pulp and a bleached hardwood kraft pulp.

6. The method according to claim 1, wherein before treatment with the y-valerolactone, the chemical pulp is first soaked in deionized water, and then dispersed with a fiber dissociator for later use.

7. Use of y-valerolactone in dissolving hemicellulose.