阅读说明：本技术 一种阔叶木溶解浆的制备方法及其应用 (Preparation method and application of broadleaf wood dissolving pulp ) 是由 董翠华 沈珮琰 王凯月 庞志强 吉海瑞 于 2021-05-20 设计创作，主要内容包括：本发明属于溶解浆制备技术领域,具体涉及一种阔叶木溶解浆的制备方法及其应用,所述制备方法包括用对甲苯磺酸、次氯酸钠和亚氯酸钠的混合溶液对挤压木片进行预处理得到未漂浆。该制备方法具有反应条件温和、时间短、漂白段数低、绿色低能耗的特点。(The invention belongs to the technical field of dissolving pulp preparation, and particularly relates to a preparation method and application of broadleaf wood dissolving pulp. The preparation method has the characteristics of mild reaction conditions, short time, low bleaching stage number, greenness and low energy consumption.)

1. The preparation method of the hardwood dissolving pulp is characterized by comprising the step of pretreating extruded wood chips by using a mixed solution of p-toluenesulfonic acid, sodium hypochlorite and sodium chlorite to obtain unbleached pulp.

2. The method for preparing hardwood dissolving pulp as recited in claim 1, wherein the unbleached pulp is subjected to two-stage oxygen delignification treatment; further, carrying out chlorine dioxide bleaching treatment on the pulp subjected to oxygen delignification; further, carrying out bleaching treatment on the pulp by adopting intensified alkali extraction to obtain dissolved pulp; the pulp concentration in each bleaching stage is 8-15%, preferably 10%.

3. The method of preparing hardwood dissolving pulp as recited in claim 1 wherein the extruding comprises: soaking broad-leaved wood chips in water at normal temperature for 4-6 hours, and then carrying out extrusion treatment; the compression ratio of the extrusion treatment was 3: 1-5: 1; preferably, the ratio is 4: 1.

4. the method for preparing hardwood dissolving pulp as recited in claim 1, wherein the pretreatment solution comprises p-toluenesulfonic acid 75-80 wt%, sodium hypochlorite 0.7-1.6% (calculated by available chlorine), and sodium chlorite 0.5-1.25%; the solid-liquid ratio of the wood chips to the treatment liquid is 1: 20-1.5: 20 (g: mL), the pretreatment temperature is 90-105 ℃, and the pretreatment time is 60-90 min.

5. The method for preparing hardwood dissolving pulp as recited in claim 1, wherein the unbleached pulp is treated by ultrasonic dispersion, washed and filtered to neutrality, and then treated by oxygen delignification; and carrying out ultrasonic dispersion treatment for 5-10s, wherein the ultrasonic frequency is 40 KHZ.

6. The method for preparing hardwood dissolving pulp as claimed in claim 2, wherein the two oxygen delignification stages are carried out by holding the temperature at 105-125 ℃ with 5.5-6.5 bar oxygen pressure using sodium hydroxide and magnesium sulfate, wherein the amount of sodium hydroxide is 2.5-3.5% (based on the absolute dry pulp) and the amount of magnesium sulfate is 2.5-3.5% (based on the absolute dry pulp); the first stage heat preservation time is 25-35 min, and the second stage heat preservation time is 40-50 min.

7. The method for preparing hardwood dissolving pulp as claimed in claim 2, wherein the chlorine dioxide bleaching comprises secondary bleaching of pulp after oxygen delignification by chlorine dioxide and sulfuric acid at 70-85 deg.C for 45-60 min, at pH 3.5-4, with chlorine dioxide 0.55-0.65% (based on oven dry pulp) and sulfuric acid 0.1-0.2% (based on oven dry pulp).

8. The method as claimed in claim 2, wherein the enhanced alkaline extraction comprises bleaching unbleached pulp with sodium hydroxide and hydrogen peroxide under an oxygen pressure of 4.0-5.0 bar at 90-100 deg.C for 90-100 min, with NaOH in an amount of 2-2.5% (based on oven dry pulp) and H₂O₂The amount is 0.5-0.6% (based on oven-dried pulp).

9. The dissolving pulp prepared by the method for preparing hardwood dissolving pulp as recited in any claim 1-8, wherein the dissolving pulp has an alpha cellulose content of 89-95%, a degree of polymerization of 510-530, a whiteness of 91-95% ISO and a kappa number of 0.2-0.5.

10. Use of the dissolving pulp according to claim 9 in the textile industry, food packaging.

Technical Field

The disclosure belongs to the technical field of dissolving pulp preparation, and particularly relates to a preparation method and application of broadleaf wood dissolving pulp.

Background

The information in this background section is only for enhancement of understanding of the general background of the invention and is not necessarily to be construed as an admission or any form of suggestion that this information forms the prior art that is already known to a person of ordinary skill in the art.

In recent years, the growing amount of cotton is becoming smaller and smaller globally, and the supply of cotton linters for pulp production is becoming markedly insufficient. In view of the above, the use of dissolving pulp (wood pulp) prepared from wood as a raw material instead of cotton pulp has been receiving increasing attention. At present, the preparation of dissolving pulp is common in acid sulfite pulping and prehydrolysis sulfate pulping processes, and the pulping process conditions required by the methods are severe and can be realized only under the conditions of high temperature and high pressure; the number of bleaching stages is more, generally five or more bleaching stages are provided; high production cost, difficult recovery of chemicals and great environmental pollution. Therefore, the development of a mild and efficient separation technique of wood components in a green solvent system, and the bleaching of purified fibers to produce high quality dissolving pulp has become a major direction of the current technological development.

Disclosure of Invention

In order to solve the problems in the prior art, the disclosure provides a preparation method of hardwood dissolving pulp and an application thereof.

Specifically, the technical scheme of the present disclosure is as follows:

in a first aspect of the disclosure, a method of making hardwood dissolving pulp includes pretreating extruded wood chips with a mixed solution of p-toluenesulfonic acid, sodium hypochlorite, and sodium chlorite to obtain unbleached pulp.

In the second aspect of the disclosure, the dissolving pulp prepared by the method for preparing hardwood dissolving pulp has the alpha cellulose content of 89-95%, the polymerization degree of 510-530, the whiteness of 91-95% ISO and the kappa number of 0.2-0.5.

In a third aspect of the present disclosure, the dissolving pulp is applied to textile industry and food packaging.

One or more technical schemes in the disclosure have the following beneficial effects:

(1) the method takes a p-toluenesulfonic acid (p-TsOH) solution as a reaction solvent system, the efficiency of converting sodium hypochlorite into hypochlorous acid in an acidic environment is improved, the oxidizability is enhanced, and the existence of the hypochlorous acid accelerates the release of ClO from sodium chlorite₂Improving the oxidative bleaching capacity of the reaction solvent system.The three components have synergistic effect, so that unbleached pulp obtained after the broad-leaved wood chips are treated by a mixed solution system of p-toluenesulfonic acid, sodium hypochlorite and sodium chlorite is subjected to short-time ultrasonic treatment (5-10s) and then is subjected to three-stage bleaching process ((OO) D)₀E_op) A dissolving pulp is obtained.

(2)、p-TsOH/NaClO/NaClO₂The mixed solution system has good lignin and hemicellulose removal effect, and the lignin and hemicellulose removal rates are 89.02% and 87.16% respectively. The existence of sodium hypochlorite and sodium chlorite in the solution can enhance and promote the removal of lignin and hemicellulose. The preparation method of dissolving pulp disclosed by the invention has the advantages of mild reaction conditions, low temperature, short treatment time and few bleaching stages ((OO) D)₀E_op) Accords with the concept of green and low energy consumption, and provides a production method with high efficiency and low energy consumption for the preparation of dissolving pulp.

Detailed Description

The disclosure is further illustrated with reference to specific examples. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present disclosure. The experimental procedures, in which specific conditions are not noted in the following examples, are generally carried out according to conventional conditions or according to conditions recommended by the manufacturers.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. The reagents or starting materials used in the present invention can be purchased from conventional sources, and unless otherwise specified, the reagents or starting materials used in the present invention can be used in a conventional manner in the art or in accordance with the product specifications. In addition, any methods and materials similar or equivalent to those described herein can be used in the methods of the present invention. The preferred embodiments and materials described herein are intended to be exemplary only.

It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments according to the present disclosure. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of the stated features, steps, operations, and/or combinations thereof, unless the context clearly indicates otherwise.

At present, the existing dissolving pulp preparation method has a series of problems of severe reaction conditions, more bleaching stages, high energy consumption and the like, and in order to solve the problems, the disclosure provides a preparation method of broadleaf wood dissolving pulp and application thereof.

In one embodiment of the present disclosure, a method for preparing hardwood dissolving pulp includes pretreating extruded wood chips with a mixed solution of p-toluenesulfonic acid, sodium hypochlorite and sodium chlorite to obtain unbleached pulp.

The preparation method uses p-TsOH/NaClO under mild conditions₂The system is used for pretreating extruded broad-leaved wood chips, and has synergistic effects of extraction and acidolysis of toluenesulfonic acid, nucleophilic addition of chloride, active free radical oxidation and the like, so that ether bond breakage among lignin units can be enhanced, lignin can be effectively dissolved out, lignin polycondensation can be inhibited, and the proportion of connecting bonds such as beta-5 and beta-beta is reduced. The unbleached pulp has low ratio of residual lignin to hemicellulose, good bleaching performance, p-TsOH/NaClO₂After the pretreatment of the solution system, the unbleached pulp whiteness value is 47.5, and the lignin removal rate is 89.02%.

Generally, hardwood species contain higher levels of beta-O-4' linkages than softwood species, and the p-TsOH/NaClO as described in this disclosure is used₂The system can realize selective breakage of beta-O-4' bonds in lignin, and bleach pulp while removing lignin and hemicellulose. Therefore, the preparation method provided by the disclosure can selectively and efficiently remove lignin, and the yield of dissolving pulp prepared from hardwood is improved.

Further, the unbleached pulp is subjected to two-stage oxygen delignification treatment, and the extruded broad-leaved wood chips are subjected to p-TsOH/NaClO₂After the pretreatment system removes most of the hemicellulose and lignin, the residual lignin is further bleached to increase the whiteness of the dissolving pulp. The present disclosure found that p-TsOH/NaClO was utilized₂The system is pretreated to obtain unbleached pulp, and the contents of hemicellulose and lignin in the unbleached pulp respectively account for the components3.0-3.5% and 2.2-2.8%, a whiteness value of 47-50, and a Kappa value of 6.5-7.5. p-TsOH/NaClO₂The pretreatment system can efficiently remove lignin and hemicellulose and simultaneously improve the whiteness of the pulp. Therefore, the unbleached pulp is treated by a simple three-stage bleaching mode, and the required dissolving pulp can be obtained.

The unbleached pulp which is not subjected to dust removal treatment is subjected to two-stage oxygen delignification, so that fiber dust can be reduced, and the consumption of chemicals used for subsequent bleaching is reduced; the chlorine dioxide has active property, has the performance of dissolving lignin and pectin, has strong impurity removal capacity, and can be compensated in the bleaching stage although the reduction degree of the kappa number is reduced. The shortening of the bleaching stage of the bleaching process can reduce the consumption of chemicals and also reduce the degradation of cellulose. The whiteness of the slurry after the oxygen delignification stage was 69.3% ISO, the Kappa number 2.66, and the degree of polymerization 624.

Further, the pulp after oxygen delignification is carried out chlorine dioxide bleaching treatment. The whiteness of the dissolving pulp can be further improved by adopting the chlorine dioxide bleaching treatment, and the adsorbable organic halide generated by the chlorine dioxide bleaching is 1/5 bleached by chlorine gas under the same effective chlorine dosage, and the delignification is not influenced. The whiteness value of the dissolving pulp after the chlorine dioxide bleaching stage is 85.3 percent ISO, the Kappa value is 1.06, and the dissolving pulp after the chlorine dioxide bleaching has the advantages of good whiteness stability, low Kappa value and the like.

Further, the pulp after the chlorine dioxide bleaching treatment is bleached by adopting enhanced alkali extraction to obtain the dissolved pulp with the alpha cellulose content of 89-95%, the polymerization degree of 510-530, the whiteness of 91-95% ISO and the kappa number of 0.2-0.5.

Further, the concentration of the pulp in the unbleached pulp and in each bleaching stage is 8 to 15%, preferably 10%.

Further, the pressing comprises: soaking broad-leaved wood chips in water at normal temperature for 4-6 hours, and then carrying out extrusion treatment;

further, the compression ratio of the extrusion process was 3: 1-5: 1; preferably, the ratio is 4: 1, the compression ratio is controlled, so that the removal degree of lignin and hemicellulose in the pretreatment process can be controlled.

Furthermore, the concentration of the used pretreatment liquid p-toluenesulfonic acid is 75-80 wt%, the concentration of sodium hypochlorite is 0.7-1.6% (calculated by available chlorine), and the concentration of sodium chlorite is 0.5-1.25%; the solid-liquid ratio of the wood chips to the treatment liquid is 1: 20-1.5: 20 (g: mL), the pretreatment temperature is 90-105 ℃, and the pretreatment time is 60-90 min. Control of p-TsOH/NaClO₂In the system, the concentrations of different components can efficiently exert the synergistic effect of the three components, thereby improving the quality and yield of dissolving pulp.

Further, carrying out ultrasonic dispersion treatment on the obtained unbleached pulp, and then carrying out oxygen delignification treatment; and carrying out ultrasonic dispersion treatment for 5-10s, wherein the ultrasonic frequency is 40KHZ, and ensuring uniform dispersion of the slurry through short ultrasonic dispersion treatment.

Further, performing two-stage oxygen delignification treatment by using sodium hydroxide and magnesium sulfate, and performing heat preservation at 105-125 ℃ by using an oxygen pressure of 5.5-6.5 bar, wherein the using amount of the sodium hydroxide is 2.5-3.5% (based on oven-dried pulp), and the using amount of the magnesium sulfate is 2.5-3.5% (based on oven-dried pulp);

furthermore, the first section of heat preservation time is 25-35 min, and the second section of heat preservation time is 40-50 min. The oxygen delignification treatment is carried out under the condition, so that the bleaching of the dissolving pulp can be completed in a short time, and the violent degradation of cellulose in the dissolving pulp is not caused, thereby being beneficial to protecting the polymerization degree of the dissolving pulp. Also, the oxygen delignification of the unbleached pulp prior to the oxygen delignification stage reduces fiber dustiness and induces xylan removal from the fiber surface, and reduces the lignin content of 1/3-1/2 in the dissolving pulp to reduce consumption of chemicals for subsequent bleaching.

Further, the chlorine dioxide bleaching comprises the steps of bleaching the pulp subjected to oxygen delignification by using chlorine dioxide and sulfuric acid at the temperature of 70-85 ℃, reacting for 45-60 min, wherein the pH value is 3.5-4, the dosage of the chlorine dioxide is 0.55-0.65% (based on the oven-dried pulp), and the dosage of the sulfuric acid is 0.1-0.2% (based on the oven-dried pulp).

Further, the intensified alkali extraction comprises bleaching unbleached pulp with sodium hydroxide and hydrogen peroxide at an oxygen pressure of 4.0-5.0 bar and a temperature of 90EThe reaction time is 90-100 min at 100 ℃, the consumption of NaOH is 2-2.5 percent (based on absolute dry pulp), and H₂O₂The amount is 0.5-0.6% (based on oven-dried pulp). Wherein, the stage H₂O₂Free radicals or anions (HOO-) generated under alkaline conditions act on chromophoric groups, carbon-carbon double bonds, and carbonyl or quinoid structures remaining in lignin to react. The hydroxyl free radical, the perhydroxyl free radical and the perhydroxyl anion can react with lignin to accelerate the removal of the lignin and improve the whiteness of the slurry, and H₂O₂The damage to the cellulose is small, and the polymerization degree of the cellulose is protected.

The cooking temperature is 155-. The cooking temperature in the process of producing dissolving pulp by the acid sulfite method is 125-145 ℃, the cooking time is about 7 hours, and the total time is about 9-10 hours. The pretreatment temperature for preparing the dissolving pulp is less than or equal to 105 ℃, the time is less than or equal to 90min, and the total pulping time is about 4-5h from the pretreatment stage to the preparation of the dissolving pulp. Compared with the method for preparing dissolving pulp by pre-hydrolyzing sulfate and acidic sulfite, the method disclosed by the invention has the advantages that a pressure-resistant container is not required for pretreatment under normal pressure, the bleaching process is short, the pollution load and the cost of bleaching wastewater are low, the activity of extracting lignin is high, the processing is easy, the product value is high, and the pretreatment liquid is easy to recycle. The temperature is reduced and the time is shortened in the pulping process, so that the energy consumption in the pulping process is reduced, and the concept of green and low energy consumption is met. The dissolving pulp prepared by the pulping method disclosed by the invention has the yield of 40.3%, which is about 2-6% higher than that prepared by a prehydrolysis sulfate method and an acidic sulfite method. The improvement of the yield of the dissolving pulp is beneficial to improving the utilization efficiency of the lignocellulose.

In one embodiment of the disclosure, the dissolving pulp prepared by the above preparation method has an alpha cellulose content of 89-95%, a polymerization degree of 510-530, a whiteness of 91-95% ISO, and a kappa number of 0.2-0.5.

In one embodiment of the present disclosure, the dissolving pulp is used in textile industry, food packaging, and the like.

In order to make the technical solutions of the present disclosure more clearly understood by those skilled in the art, the technical solutions of the present disclosure will be described in detail below with reference to specific embodiments.

Example 1

3g of wood chips having a size of not more than 50X 40X 8mm (length X width X thickness) were screened, and the screened wood chips were soaked at normal temperature for 4 hours and then subjected to an extrusion treatment. The concentration of the used pretreatment solution p-toluenesulfonic acid solution is 75 wt%, the concentration of sodium hypochlorite solution is 0.7% (calculated by available chlorine), and the content of sodium chlorite is 0.5%. The wood chips are put into 60mL of pretreatment solution and are kept warm for 60min at 90 ℃ to obtain unbleached pulp. And (4) filtering the unbleached pulp to be neutral, and performing ultrasonic treatment for 7s at the stirring speed of 300rpm/min to obtain the unbleached pulp subjected to ultrasonic treatment. Unbleached pulp is subjected to washing-free staged oxygen delignification, the dosage of sodium hydroxide in the first stage is 2.5 percent (based on oven dry pulp), the dosage of magnesium sulfate is 2.5 percent (based on oven dry pulp), and the unbleached pulp is subjected to heat preservation for 25min at 105 ℃ by using the oxygen pressure of 5.5 bar; the second stage sodium hydroxide was used in an amount of 2.5% (based on oven dried pulp) and magnesium sulfate was used in an amount of 2.5% (based on oven dried pulp), and the resulting slurry was washed to neutrality using an oxygen pressure of 5.5bar at 105 ℃ for 40 min. The oxygen delignified pulp was subjected to chlorine dioxide bleaching at a pH of 3.5, with chlorine dioxide in an amount of 0.55% (based on oven dried pulp) and sulfuric acid in an amount of 0.1% (based on oven dried pulp). Keeping the temperature at 70 ℃ for 45min to obtain slurry, and washing the slurry to be neutral. And (3) performing alkali extraction on the pulp bleached by the chlorine dioxide, wherein the using amount of sodium hydroxide is 2 percent (based on oven dry pulp) and the using amount of hydrogen peroxide is 0.5 percent (based on oven dry pulp), and performing heat preservation for 90min at 90 ℃ by using 4.0bar oxygen pressure to obtain dissolved pulp and washing the dissolved pulp to be neutral. The resulting dissolving pulp had a whiteness of 95% ISO, a degree of polymerization of 519, a kappa number of 0.32 and an alpha cellulose content of 93%.

Example 2:

7.5g of wood chips having a size of not more than 50X 40X 8mm (length X width X thickness) were screened, and the screened wood chips were soaked at normal temperature for 6 hours and then subjected to an extrusion treatment. The concentration of the used pretreatment solution p-toluenesulfonic acid solution is 80 wt%, the concentration of sodium hypochlorite solution is 1.6% (calculated by available chlorine), and the content of sodium chlorite is 1.25%. Placing the wood chips into 100mL of pretreatment solution, preserving the heat for 90min at 105 ℃, filtering the obtained unbleached pulp to be neutral, and performing ultrasonic treatment for 5s at the stirring speed of 100rpm/min to obtain unbleached pulp. And (4) filtering the unbleached pulp to be neutral, and performing ultrasonic treatment for 7s at the stirring speed of 300rpm/min to obtain the unbleached pulp subjected to ultrasonic treatment. Unbleached pulp is subjected to washing-free staged oxygen delignification, the dosage of the first stage sodium hydroxide is 3.5 percent (based on oven dry pulp), the dosage of the magnesium sulfate is 3.5 percent (based on oven dry pulp), and the unbleached pulp is subjected to heat preservation for 35min at 125 ℃ by using the oxygen pressure of 6.5 bar; the second stage sodium hydroxide was used in an amount of 3.5% (based on oven dried pulp) and magnesium sulfate was used in an amount of 3.5% (based on oven dried pulp), and the resulting slurry was washed to neutrality at 125 ℃ for 50min using 6.5bar oxygen pressure. The oxygen delignified pulp was subjected to chlorine dioxide bleaching at a pH of 4, with a chlorine dioxide content of 0.65% (based on oven dried pulp) and a sulphuric acid content of 0.2% (based on oven dried pulp). Keeping the temperature at 85 ℃ for 60min to obtain slurry, and washing the slurry to be neutral. And (3) performing alkali extraction on the pulp bleached by the chlorine dioxide, wherein the using amount of sodium hydroxide is 2.5 percent (based on oven dry pulp), the using amount of hydrogen peroxide is 0.6 percent (based on oven dry pulp), and performing heat preservation for 100min at 100 ℃ by using 5.0bar oxygen pressure to obtain dissolved pulp and washing the dissolved pulp to be neutral. The resulting dissolving pulp had a whiteness of 94% ISO, a degree of polymerization of 521, a kappa number of 0.4 and an alpha cellulose content of 94.5%.

Example 3:

6g of wood chips having a size of not more than 50X 40X 8mm (length X width X thickness) were screened, and the screened wood chips were soaked at normal temperature for 5 hours and then subjected to an extrusion treatment. The concentration of the used pretreatment solution p-toluenesulfonic acid solution is 80 wt%, the concentration of sodium hypochlorite solution is 1.2% (calculated by available chlorine), and the content of sodium chlorite is 1%. Placing the wood chips into 100mL of pretreatment solution, preserving the heat at 100 ℃ for 75min to obtain unbleached pulp, filtering the unbleached pulp to be neutral, and performing ultrasonic treatment for 10s at the stirring speed of 200rpm/min to obtain the unbleached pulp after ultrasonic treatment. Unbleached pulp is subjected to washing-free staged oxygen delignification, the dosage of sodium hydroxide in the first stage is 3 percent (based on oven dry pulp), the dosage of magnesium sulfate is 3 percent (based on oven dry pulp), and the unbleached pulp is subjected to heat preservation for 30min at 115 ℃ by using oxygen pressure of 6 bar; the second stage sodium hydroxide amount is 3% (based on oven dried pulp), magnesium sulfate amount is 3% (based on oven dried pulp), and the pulp is washed to neutrality at 115 deg.C by maintaining the temperature with 6bar of oxygen pressure for 45 min. The oxygen delignified pulp is bleached by chlorine dioxide, the pH is 4, the using amount of the chlorine dioxide is 0.6 percent (based on the oven dry pulp) and the using amount of the sulfuric acid is 0.15 percent (based on the oven dry pulp), and the pulp is kept warm for 50min at 80 ℃ to be washed to be neutral. And (3) performing alkali extraction on the pulp bleached by the chlorine dioxide, wherein the using amount of sodium hydroxide is 2.2 percent (based on oven dry pulp), the using amount of hydrogen peroxide is 0.55 percent (based on oven dry pulp), and performing heat preservation for 95min at 95 ℃ by using 4.5bar oxygen pressure to obtain dissolving pulp and washing the dissolving pulp to be neutral.

The wood chips after the extrusion treatment are subjected to p-TsOH/NaClO₂The pretreatment system separates lignin and hemicellulose to obtain unbleached pulp. The unbleached pulp obtained is then subjected to a three-stage bleaching ((OO) D)₀E_op) Obtaining the broadleaf wood dissolving pulp after the process flow. The whiteness of the dissolving pulp is 91.1 percent ISO, the polymerization degree is 517, the kappa number is 0.33, and the content of alpha cellulose is 89.6 percent.

Comparative example 1:

the difference compared with example 1 is that the pretreatment solution used was a p-toluenesulfonic acid solution having a concentration of 80% by weight. The resulting dissolving pulp had a whiteness of 84.2% ISO, a degree of polymerization of 567, a kappa number of 3.7 and an alpha cellulose content of 85.7%. The pretreatment solution used was a p-toluenesulfonic acid solution which was subjected to ((OO) D)₀E_op) The dissolving pulp prepared after the bleaching stage has low whiteness value and alpha cellulose content, and does not meet the standard of commercial dissolving pulp. Other pretreatment means are needed to increase the whiteness and alpha cellulose content values.

Comparative example 2:

the difference from example 1 is that the pretreatment solution used had a concentration of 75 wt% in p-toluenesulfonic acid solution and a concentration of 0.7% in sodium hypochlorite solution (in terms of available chlorine). The resulting dissolving pulp had a whiteness of 87.3% ISO, a degree of polymerization of 533, a kappa number of 1.6 and an alpha cellulose content of 87.5%. The adding of the sodium hypochlorite solution has certain effect of improving the whiteness and the alpha cellulose content of the dissolving pulp, but the adding of the single sodium hypochlorite solution cannot mutually promote the sodium chlorite, and the quality of the dissolving pulp is not as good as p-TsOH/NaClO₂Dissolving pulp prepared as a pretreatment solution.

Comparative example 3:

compared with example 1, the difference is that the conventional method for preparing dissolving pulp comprises a prehydrolysis sulfate process and an acid sulfite process, and the dissolving pulp produced by the method has the alpha cellulose content of 90-97%, the whiteness of 90-95% ISO, the polymerization degree of 400-900 and the kappa number content of 0.2-0.6.

Although the present invention has been described in detail with reference to the foregoing embodiments, it will be apparent to those skilled in the art that changes may be made in the embodiments and/or equivalents thereof without departing from the spirit and scope of the invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.