KR102559550B1 - Method for producing pulp for dissolution and pulp for dissolution - Google Patents

Abstract

A method for producing pulp for dissolving includes the steps of S1) steaming and cooking wood chips to obtain a brown stock; S2) subjecting the brown stock to oxygen delignification to obtain an oxygen-delignified stock; S3) performing enzymatic hydrolysis by mixing the oxygen-delignified stock and hemicellulose to obtain an enzyme-hydrolyzed stock; and S4) bleaching the enzyme-hydrolyzed stock and subjecting the enzyme-hydrolyzed stock to papermaking to obtain pulp for dissolution. Hemicellulase is added after oxygen delignification to remove hemicellulose in the stock, so that lignin can also be easily removed, thereby promoting bleaching of the dissolving pulp, reducing the amount of bleach used, and causing a mild reaction. In addition, cellulose is retained to the maximum extent during the removal of hemicellulose and lignin, improving the pulp fiber content and performance of the dissolving pulp and reducing contamination caused by wastewater.

Description

Method for producing pulp for dissolution and pulp for dissolution

[0001] This application claims priority to Chinese Patent Application No. 201810751437.7, entitled "DISSOLVING PULP PREPARATION METHOD AND DISSOLVING PULP", filed with the Chinese Intellectual Property Office on July 10, 2018, the entire content of which is incorporated herein by reference.

Field

[0002] The present invention belongs to the field of pulping and papermaking, and specifically relates to a manufacturing method for dissolving pulp and to dissolving pulp.

[0003] Cellulosic fibers, along with natural fibers and synthetic fibers, are the three main types of fibers. Fiber is an essential material for cloth textiles. In recent years, the demand for cellulosic fibers has increased rapidly. Both dissolving pulp and cotton pulp are the main raw materials for producing viscose staple fibers, a common product from cellulosic fibers.

[0004] In existing processes, pulp is produced using cotton linters as a raw material, but linters for pulp production are in significant short supply as world cotton cultivation declines. Since the process using dissolving pulp (wood pulp for viscose fiber) has advantages such as low pollution, wide resources and low price, and the price of cotton pulp is rising rapidly due to cotton shortage, dissolving pulp is increasingly used as a raw material for producing viscose staple fibers.

[0005] In view of the foregoing, the present invention relates to a manufacturing method for a dissolving pulp and to providing a dissolving pulp. These methods use biological enzymes for oxygen delignification.

[0006] The present invention is a manufacturing method for dissolving pulp,

S1) obtaining a brown stock by cooking wood chips;

S2) subjecting the brown stock to oxygen delignification to obtain an oxygen-delignified stock;

S3) performing enzymatic digestion by mixing the oxygen-delignified stock with hemicellulase to obtain an enzymatically digested stock; and

S4) bleaching the enzymatically digested stock and subjecting the enzymatically digested stock to papermaking to obtain pulp for dissolution.

[0007] Preferably, hemicellulase is used in an amount of 0.05 to 0.25 kg/adt.

[0008] Preferably, the oxygen delignification comprises a first oxygen delignification stage and a second oxygen delignification stage, wherein the stocks fed to the first oxygen delignification stage and the second oxygen delignification stage each independently have a concentration of 7 to 12% by weight.

[0009] Preferably, during the first oxygen delignification stage, oxygen is used in an amount of 5 to 25 kg/adt and alkali is used in an amount of 10 to 25 kg/adt; During the second oxygen delignification stage, oxygen is used in an amount of 5 to 20 kg/adt and alkali is used in an amount of 0 to 15 kg/adt.

[0010] Preferably, step S1) is specifically

by prehydrolysis of wood chips followed by cooking to obtain a brown stock, wherein the prehydrolysis is carried out at a temperature of 140° C. to 170° C. with a P-index of 450 to 650, and the hydrolyzate has an electrical conductivity of 140 to 170 S/cm during prehydrolysis.

[0011] Preferably, the cooking is carried out in white liquor, wherein the white liquor is a mixed solution of sodium hydroxide and sodium sulfide, contains 100 to 140 g/L of usable alkali and 110 to 160 g/L of total alkali, and has a sulfidity of 20% to 40%; Cooking is carried out with an H-index of 1300 to 1600.

[0012] Preferably, the bleaching in step S4) comprises successively chlorine dioxide bleaching, alkali bleaching, a first bleaching stage and a second bleaching stage;

[0013] During chlorine dioxide bleaching, chlorine dioxide is used in an amount of 10 to 15 kg/adt;

[0014] During alkaline bleaching, the bleaching agent comprises sodium hydroxide, oxygen and hydrogen peroxide, wherein sodium hydroxide is used in an amount of 10 to 30 kg/adt, oxygen is used in an amount of 1 to 10 kg/adt, and hydrogen peroxide is used in an amount of 1 to 10 kg/adt;

[0015] During the first bleaching stage, the bleaching agent is chlorine dioxide used in an amount of 3 to 8 kg/adt;

[0016] During the second bleaching stage, the bleaching agent is chlorine dioxide used in an amount of 1 to 3 kg/adt.

[0017] Preferably, during chlorine dioxide bleaching, the stock has a pH value of 1 to 3; During alkaline bleaching, the stock has a pH value between 10 and 12; During the first bleaching stage, the stock has a pH value between 3.5 and 4; During the second bleaching stage, the stock has a pH value between 2.5 and 3.

[0018] Preferably, the wood chips have a packing density of 140 to 250 kg/m 3 and a moisture content of 30 to 60% by weight.

[0019] The present invention also relates to dissolving pulp, wherein the dissolving pulp contains alpha-cellulose of 93.0% or more, pentosans of 3.0% or less, extract components by DCM of 0.15% or less, ash of 0.10% or less, Fe of 10.0 ppm or less, and SiO of 50 mg/kg or less, when the dissolving pulp is a dissolving pulp from softwood.₂and has a viscosity of 380 to 560 ml/g, a brightness of 90.0% or more based on ISO standards and a dirt count of 3.0 ppm or less, when the dissolving pulp is a dissolving pulp from hardwood, alpha-cellulose of 94.5% or more, pentosans of 3.0% or less, extract components by DCM of 0.15% or less, ash of 0.10% or less, 10. Fe less than 0 ppm, and SiO less than 60 mg/kg₂and a viscosity of 400 to 530 ml/g, a brightness of 90.0% or more based on ISO standards, and a dirt count of 3.0 ppm or less.

[0020] The present invention is a manufacturing method for dissolving pulp, S1) digesting wood chips to obtain a brown stock; S2) subjecting the brown stock to oxygen delignification to obtain an oxygen-delignified stock; S3) performing enzymatic digestion by mixing the oxygen-delignified stock with hemicellulase to obtain an enzymatically digested stock; and S4) bleaching the enzymatically digested stock and subjecting the enzymatically digested stock to papermaking to obtain pulp for dissolution. Compared with the prior art, in the present invention, hemicellulase is added after oxygen delignification to remove hemicellulose from the stock, and therefore, lignin can also be easily removed to promote bleaching of the obtained stock, reduce the amount of bleach used, and cause the reaction to be mild. In addition, cellulose is maximally retained during the removal of hemicellulose and lignin, improving the alpha-cellulose content in the pulp and the performance of the dissolving pulp and reducing contamination caused by wastewater.

[0021] Figure 1 is a schematic diagram illustrating a device used in Example 1.

[0022] The solutions in the embodiments of the present invention will be clearly and completely described below together with the embodiments. It is clear that the described embodiments include only a few, but not all, embodiments of the present invention. All other embodiments obtained by a person skilled in the art based on the embodiments of the present invention without creative efforts fall within the scope of the present invention.

[0023] The present invention comprises the steps of S1) digesting wood chips to obtain a brown stock; S2) subjecting the brown stock to oxygen delignification to obtain an oxygen-delignified stock; S3) performing enzymatic digestion by mixing the oxygen-delignified stock with a hemicellulase to obtain an enzymatically digested stock; and S4) bleaching the enzymatically digested stock and subjecting the enzymatically digested stock to papermaking to obtain pulp for dissolution.

[0024] In the present invention, the source of any raw material is not particularly limited, and can be commercially available or manufactured.

[0025] In the present invention, it is preferable to use softwood or hardwood as a raw material. The softwood is preferably a radiata pine, more preferably a 15 to 40 year old radiata pine, even more preferably a 15 to 40 year old Australian radiata pine. The hardwood is preferably eucalyptus, more preferably 15 to 25 year old eucalyptus nitens, even more preferably 15 to 25 year old Australian eucalyptus nitens. Preferably, the wood chips have a packing density of 140 to 250 kg/m 3 and a moisture content of 30 to 60% by weight.

[0026] According to the invention, the wood chips are preferably prehydrolyzed and then cooked. The prehydrolysis method is not particularly limited, and any method well known to those skilled in the art may be used, but hot water prehydrolysis is preferred. In the present invention, the prehydrolysis is preferably carried out with a P-index ranging from 450 to 650, more preferably from 500 to 650, even more preferably from 500 to 600, and most preferably from 550. The temperature for prehydrolysis preferably ranges from 140°C to 170°C, more preferably from 150°C to 160°C. The prehydrolysis is preferably carried out at a heating rate of 3 to 10° C./min, more preferably 4 to 7° C./min. According to the present invention, the prehydrolysis is preferably carried out in a hydrolysis tower, wherein the temperature of the liquid phase preferably ranges from 140 °C to 170 °C, more preferably from 150 °C to 160 °C, even more preferably from 155 °C, and the temperature of the gas phase is preferably from 140 °C to 220 °C, more preferably from 150 °C to 165 °C, even more preferably from 155 °C to 160 °C. is the range of During prehydrolysis, the hydrolyzate preferably has an electrical conductivity in the range of 140 to 170 S/cm 2 , more preferably 150 to 170 S/cm 2 , even more preferably 155 to 165 S/cm 2 and most preferably 160 S/cm 2 . The duration of prehydrolysis is preferably 1 to 3 hours, more preferably 1.5 to 2.5 hours, and even more preferably 2 hours.

[0027] After prehydrolysis, cooking is performed to obtain a brown stock. The cooking method is not particularly limited, and any method widely known to those skilled in the art may be used, but the kraft cooking process is preferred in the present invention. Cooking is preferably carried out in white liquor, which is a mixed solution of sodium hydroxide and sodium sulfide. The white liquor preferably contains 100 to 140 g/L, more preferably 110 to 135 g/L, even more preferably 120 to 135 g/L, even more preferably 120 to 130 g/L, most preferably 135 g/L of usable alkali. The white liquor preferably contains 110 to 160 g/L, more preferably 120 to 150 g/L, even more preferably 130 to 140 g/L, most preferably 140 g/L of total alkali. The white liquor preferably has a degree of sulfidation between 20% and 40%, more preferably between 25% and 40%, even more preferably between 28% and 38%, even more preferably between 30% and 35%, and most preferably between 32%. The cook preferably has an H-index ranging from 1300 to 1600, more preferably from 1350 to 1550, even more preferably from 1400 to 1500, most preferably from 1450.

[0028] The brown stock is preferably subjected to oxygen delignification after screening and washing, wherein the washing is preferably carried out at a dilution factor of 2 to 2.5 m 3 /adt. The oxygen delignification method is not particularly limited, and any method well known to those skilled in the art may be used, but in the present invention, a method comprising a first oxygen delignification stage and a second oxygen delignification stage is preferred. During the first oxygen delignification stage, the stock is preferably fed at a concentration of 7 to 12 wt%, more preferably 8 to 11 wt%, even more preferably 8.5 to 10 wt%, most preferably 8.5 to 9.5 wt%; Oxygen is preferably used in an amount of 5 to 25 kg/adt, more preferably 10 to 25 kg/adt, even more preferably 10 to 20 kg/adt, most preferably 10 to 15 kg/adt; The alkali is preferably used in an amount of 10 to 25 kg/adt, more preferably 15 to 25 kg/adt, even more preferably 15 to 23 kg/adt. During the first oxygen delignification stage, the pressure preferably ranges from 600 to 800 kPa, the temperature preferably ranges from 80 °C to 90 °C, more preferably from 80 °C to 88 °C, and the duration preferably ranges from 20 to 40 minutes, more preferably from 25 to 35 minutes, even more preferably from 30 minutes. During the second oxygen delignification stage, the stock is preferably fed at a concentration of 7 to 12% by weight, more preferably 8 to 11% by weight, even more preferably 8 to 10% by weight, most preferably 8 to 9% by weight; Oxygen is preferably used in an amount of 5 to 20 kg/adt, more preferably 8 to 18 kg/adt, even more preferably 10 to 15 kg/adt; The alkali is preferably used in an amount of 0 to 15 kg/adt, more preferably 2 to 10 kg/adt. During the second oxygen delignification stage, the pressure preferably ranges from 300 to 600 kPa, the temperature preferably ranges from 90 °C to 100 °C, more preferably from 90 °C to 95 °C, and the duration preferably ranges from 40 to 80 minutes, more preferably from 50 to 70 minutes, even more preferably from 60 minutes.

[0029] After oxygen delignification, it is preferred to perform washing and add hemicellulase for enzymatic digestion to obtain an enzymatically digested stock. Washing is preferably carried out with a dilution factor of 2 to 2.5 m 3 /adt. The hemicellulose is not particularly limited, and any hemicellulases well known to those skilled in the art can be used. In the present invention, the hemicellulase is preferably a hemicellulase based on xylanase, and more preferably a Buckman bleaching enzyme of Vybrant701. Hemicellulase is preferably used in an amount of 0.05 to 0.25 kg/adt, more preferably 0.1 to 0.2 kg/adt, even more preferably 0.15 kg/adt. The enzymatic digestion is carried out at a temperature of preferably 70°C to 90°C, more preferably 75°C to 85°C, even more preferably 80°C over a period of preferably 1 to 3 hours, more preferably 1.5 to 2.5 hours, even more preferably 2 hours.

[0030] The enzymatically digested stock is bleached to obtain a bleached stock. The bleaching method is not particularly limited, and any method well known to those skilled in the art may be used. In the present invention, a method comprising successively chlorine dioxide bleaching, alkali bleaching, a first bleaching stage and a second bleaching stage is preferred. During chlorine dioxide bleaching, it is preferred to add a chlorine dioxide solution and a sulfuric acid solution, and the chlorine dioxide is preferably used in an amount of 10 to 15 kg/adt, more preferably 11 to 14 kg/adt, even more preferably 12 to 13 kg/adt. During chlorine dioxide bleaching, the stock preferably has a pH value of 1 to 3, more preferably 1.5 to 2.5, even more preferably 2. Chlorine dioxide bleaching is preferably carried out at a temperature of 60°C to 80°C, more preferably 65°C to 75°C, even more preferably 70°C. The bleaching agent used in alkaline bleaching preferably comprises sodium hydroxide, oxygen and hydrogen peroxide, wherein the sodium hydroxide is preferably used in an amount of 10 to 30 kg/adt, more preferably 10 to 25 kg/adt, even more preferably 10 to 20 kg/adt, most preferably 12 to 15 kg/adt; Oxygen is preferably used in an amount of 1 to 10 kg/adt, more preferably 4 to 10 kg/adt, even more preferably 4 to 8 kg/adt, even more preferably 5 to 7 kg/adt, most preferably 6 kg/adt; Hydrogen peroxide is preferably used in an amount of 1 to 10 kg/adt, more preferably 3 to 8 kg/adt, even more preferably 4 to 7 kg/adt and most preferably 5 kg/adt. During alkaline bleaching, the stock preferably has a pH of 10 to 12, more preferably 10.5 to 11.5, even more preferably 11. Alkaline bleaching is preferably carried out at a temperature of 70°C to 90°C, more preferably 75°C to 85°C, even more preferably 80°C. The bleaching agent used in the first bleaching stage is preferably chlorine dioxide, and the chlorine dioxide is preferably used in an amount of 3 to 8 kg/adt, more preferably 4 to 7 kg/adt, even more preferably 5 to 6 kg/adt. During the first bleaching stage, the stock preferably has a pH value of 3.5 to 4, and the temperature is preferably in the range of 70°C to 90°C, more preferably 75°C to 85°C, even more preferably 80°C. The bleaching agent used in the second bleaching stage is preferably chlorine dioxide, and the chlorine dioxide is preferably used in an amount of 1 to 3 kf/adt, more preferably 1.5 to 2.5 kg/adt, even more preferably 2 kg/adt. During the second bleaching stage, the stock preferably has a pH value of 2.5 to 3 and the temperature is preferably in the range of 70°C to 90°C, more preferably 75°C to 85°C, even more preferably 80°C.

[0031] The bleached stock is subjected to a papermaking process to obtain a pulp for dissolution.

[0032] In the present invention, hemicellulase is added in the process of oxygen delignification to remove hemicellulose from the stock, whereby the lignin can also be easily removed to promote bleaching of the stock obtained, reduce the amount of bleach used, and make it possible to milden the reaction. In addition, cellulose is maximally retained during the removal of hemicellulose and lignin, improving the alpha-cellulose content in the pulp and the performance of the dissolving pulp, and reducing contamination caused by wastewater.

[0033] The present invention also provides a pulp for dissolution produced by the method described above. When the dissolving pulp is dissolving pulp from softwood, it contains alpha-cellulose of 93.0% or more, pentosans of 3.0% or less, extract components by DCM of 0.15% or less, ash of 0.10% or less, Fe of 10.0 ppm or less, and SiO ₂ of 50 mg/kg or less, viscosity of 380 to 560 ml/g, brightness of 90.0% or more based on ISO standard , and a dirt count of less than or equal to 3.0 ppm. When the dissolving pulp is dissolving pulp from hardwood, it contains alpha-cellulose of 94.5% or more, pentosans of 3.0% or less, extract components by DCM of 0.15% or less, ash of 0.10% or less, Fe of 10.0 ppm or less, and SiO ₂ of 60 mg/kg or less, viscosity of 400 to 530 ml/g, brightness of 90.0% or more based on ISO standard , and a dirt count of less than or equal to 3.0 ppm.

[0034] To further illustrate the present invention, the manufacturing method and dissolving pulp for the dissolving pulp provided by the present invention are described in detail in conjunction with the following examples.

[0035] All of the reagents used in the examples below are commercially available.

Example 1

[0036] Wood chips from a 40-year-old Australian Radiata pine with a packing density of 149 kg/m and a water content of 55% were subjected to hot water prehydrolysis at a temperature of 165° C. for 2 hours with a P-index of 450, and the hydrolyzate had an electrical conductivity of 145 S/cm.

[0037] The prehydrolyzed wood chips were transferred to a cooking tower and cooked to an H-index of 1450 in white liquor under a pressure of 800 kPa for 4 hours, where the white liquor contained 125 g/L usable alkali and 135 g/L total alkali, and had a degree of sulfurization of 32%.

[0038] The cooked stock was first subjected to a first oxygen delignification stage and then to a second oxygen delignification stage. During the first oxygen delignification stage, the stock had a concentration of 9.5%, oxygen was used in an amount of 15 kg/adt, alkali was used in an amount of 20 kg/adt, the pressure was 650 kPa, the reaction time was 30 minutes, and the reaction temperature was 85°C. During the second oxygen delignification stage, the stock had a concentration of 9%, oxygen was used in an amount of 10 kg/adt, alkali was used in an amount of 5 kg/adt, the pressure was 400 kPa, the reaction time was 60 minutes, and the reaction temperature was 95°C.

[0039] After completion of the second oxygen delignification stage, the stock was washed with a dilution factor of 2.0 m/adt and then transferred to an enzymatic digestion tank, where Buckman bleaching enzyme from Vybrant701 was used as a biological enzyme in an oxygen delignification stage in an amount of 0.15 kg/adt, and enzymatic digestion was carried out at a temperature of 80 °C for 2 hours.

[0040] The enzymatically digested stock was bleached in ECF 4-stage bleach D0-EOP-D1-D2. During the DO stage, the temperature is 70° C., ClO ₂ is used in an amount of 12 Kg/ADT, and the pH is 2.0. During the EOP stage, the temperature is 80° C., oxygen is used in an amount of 6.0 kg/ADT, alkali is used in an amount of 12 Kg/ADT, H ₂ O ₂ is used in an amount of 5.0 Kg/ADT, and the pH is 11.0. During the D1 stage, the temperature is 80° C., ClO ₂ is used in an amount of 5 Kg/adt, and the pH is 3.5. During the D2 stage, the temperature is 80° C., ClO ₂ is used in an amount of 2 Kg/ADT, and the pH is 3.0.

[0041] The bleached stock was subjected to papermaking treatment by a pulp board machine to obtain dissolution pulp, which contained 94.5% alpha-cellulose, 2.5% pentosans, 0.11% extractables by DCM, 0.06% ash, 5.0 ppm Fe, and 30 mg/kg SiO ₂ , with a viscosity of 500 ml/g, 90.8% based on ISO standard. brightness, and a dirt count of 2.0 ppm.

Example 2

[0042] Wood chips from a 15-year-old Chilean Eucalyptus nitens with a packing density of 179 kg/m and a moisture content of 48% were subjected to hot water prehydrolysis with a P-index of 500 for 2 hours, the hydrolyzate having a temperature of 160°C and an electrical conductivity of 158 S/cm.

[0043] The prehydrolyzed wood chips were transferred to a cooking tower and cooked to an H-index of 1350 in white liquor under a pressure of 800 kPa for 4 hours, where the white liquor contained 132 g/L usable alkali and 139 g/L total alkali, and had a degree of sulfidation of 33%.

[0044] The cooked stock was first subjected to a first oxygen delignification stage and then to a second oxygen delignification stage. During the first oxygen delignification stage, the stock has a concentration of 9%, oxygen is used in an amount of 13 kg/adt, alkali is used in an amount of 15 kg/adt, the pressure is 650 kPa, the reaction time is 30 minutes, and the reaction temperature is 80°C. During the second oxygen delignification stage, the stock has a concentration of 8.5%, oxygen is used in an amount of 13 kg/adt, alkali is used in an amount of 10 kg/adt, the pressure is 400 kPa, the reaction time is 60 minutes, and the reaction temperature is 90°C.

[0045] After completing the second oxygen delignification stage, the stock was washed with a dilution factor of 2.0 m/adt and then transferred to an enzymatic digestion tank, where Buckman bleaching enzyme from Vybrant701 was used as a biological enzyme in an oxygen delignification stage in an amount of 0.05 kg/adt, and enzymatic digestion was carried out at a temperature of 80°C for 2 hours.

[0046] The enzymatically digested stock was bleached in ECF 4-stage bleach D0-EOP-D1-D2. During the DO stage, the temperature is 70° C., ClO ₂ is used in an amount of 12 Kg/ADT, and the pH is 2.0. During the EOP stage, the temperature is 80° C., oxygen is used in an amount of 6.0 Kg/ADT, alkali is used in an amount of 12 Kg/ADT, H ₂ O ₂ is used in an amount of 5.0 Kg/ADT, and the pH is 11.0. During the D1 stage, the temperature is 80° C., ClO ₂ is used in an amount of 5 Kg/adt, and the pH is 3.5. During the D2 stage, the temperature is 80° C., ClO ₂ is used in an amount of 2 Kg/ADT, and the pH is 3.0.

[0047] The bleached stock was subjected to papermaking by a pulp board machine to obtain a dissolving pulp, comprising 96.2% alpha-cellulose, 2.6% pentosans, 0.12% extractables by DCM, 0.05% ash, 4.5 ppm Fe, and 25 mg/kg SiO ₂ , with a viscosity of 550 ml/g, 91.2% based on ISO standard brightness, and a dirt count of 1.9 ppm.

Example 3

[0048] Wood chips from 15-year-old Vietnamese acacia wood with a packing density of 141 kg/m and a moisture content of 52% were subjected to hot water prehydrolysis treatment with a P-index of 550 for 2 hours, and the hydrolyzate had a temperature of 155°C and an electrical conductivity of 152 S/cm.

[0049] The prehydrolyzed wood chips were transferred to a cooking tower and cooked to an H-index of 1300 in white liquor under a pressure of 800 kPa for 4 hours, where the white liquor contained 119 g/L usable alkali and 128 g/L total alkali and had a degree of sulfidation of 30%.

[0050] The cooked stock was first subjected to a first oxygen delignification stage and then to a second oxygen delignification stage. During the first oxygen delignification stage, the stock has a concentration of 8.5%, oxygen is used in an amount of 10 kg/adt, alkali is used in an amount of 23 kg/adt, the pressure is 650 kPa, the reaction time is 30 minutes, and the reaction temperature is 88°C. During the second oxygen delignification stage, the stock has a concentration of 8%, oxygen is used in an amount of 15 kg/adt, alkali is used in an amount of 2 kg/adt, the pressure is 400 kPa, the reaction time is 60 minutes, and the reaction temperature is 92°C.

[0051] After completion of the second oxygen delignification stage, the stock was washed with a dilution factor of 2.0 m/adt and then transferred to an enzymatic digestion tank, where Buckman bleach enzyme of Vybrant701 was used as a biological enzyme in an oxygen delignification stage in an amount of 0.25 kg/adt, and enzymatic digestion was carried out at a temperature of 80° C. for 2 hours.

[0052] The enzymatically digested stock was bleached in ECF 4-stage bleach D0-EOP-D1-D2. During the DO stage, the temperature is 70° C., ClO ₂ is used in an amount of 12 Kg/ADT, and the pH is 2.0. During the EOP stage, the temperature is 80° C., oxygen is used in an amount of 6.0 Kg/ADT, alkali is used in an amount of 12 Kg/ADT, H ₂ O ₂ is used in an amount of 5.0 Kg/ADT, and the pH is 11.0. During the D1 stage, the temperature is 80° C., ClO ₂ is used in an amount of 5 Kg/adt, and the pH is 3.5. During the D2 stage, the temperature is 80° C., ClO ₂ is used in an amount of 2 Kg/ADT, and the pH is 3.0.

[0053] The bleached stock was subjected to papermaking by a pulp board machine to obtain a dissolving pulp, comprising 96.8% alpha-cellulose, 2.1% pentosans, 0.09% extractables by DCM, 0.04% ash, 3.6 ppm Fe, and 19 mg/kg SiO ₂ , with a viscosity of 525 ml/g, 91.5% based on ISO standard brightness, and a dirt count of 1.3 ppm.

comparative example

[0054] Wood chips from 15-year-old Vietnamese acacia wood with a packing density of 141 kg/m and a moisture content of 52% were subjected to hot water prehydrolysis with a P-index of 550 for 2 hours, and the hydrolyzate had a temperature of 155°C and an electrical conductivity of 152 S/cm.

[0055] The prehydrolyzed wood chips were transferred to a cooking tower and cooked to an H-index of 1300 in white liquor under a pressure of 800 kPa for 4 hours, where the white liquor contained 119 g/L usable alkali and 128 g/L total alkali, and had a degree of sulfidation of 30%.

[0056] The cooked stock was first subjected to a first oxygen delignification stage and then to a second oxygen delignification stage. During the first oxygen delignification stage, the stock has a concentration of 8.5%, oxygen is used in an amount of 10 kg/adt, alkali is used in an amount of 23 kg/adt, the pressure is 650 kPa, the reaction time is 30 minutes, and the reaction temperature is 88°C. During the second oxygen delignification stage, the stock has a concentration of 8%, oxygen is used in an amount of 15 kg/adt, alkali is used in an amount of 2 kg/adt, the pressure is 400 kPa, the reaction time is 60 minutes, and the reaction temperature is 92°C.

[0057] After completing the second oxygen delignification stage, the stock was washed with a dilution factor of 2.0 m 3 /adt, and then the washed stock was bleached in ECF 4-stage bleach DO-EOP-D1-D2. During the DO stage, the temperature is 70° C., ClO ₂ is used in an amount of 15 Kg/ADT, and the pH is 2.0. During the EOP stage, the temperature is 80° C., oxygen is used in an amount of 6.0 Kg/ADT, alkali is used in an amount of 12 Kg/ADT, H ₂ O ₂ is used in an amount of 5.0 Kg/ADT, and the pH is 11.0. During the D1 stage, the temperature is 80° C., ClO ₂ is used in an amount of 5 Kg/adt, and the pH is 3.5. During the D2 stage, the temperature is 80° C., ClO ₂ is used in an amount of 5 Kg/ADT, and the pH is 3.0.

[0058] The bleached stock was subjected to papermaking by a pulp board machine to obtain a dissolving pulp, comprising 94.6% alpha-cellulose, 2.3% pentosans, 0.10% extractables by DCM, 0.06% ash, 3.3 ppm Fe, and 21 mg/kg SiO ₂ , with a viscosity of 494 ml/g, 90.2% based on ISO standard brightness, and a dirt count of 1.2 ppm.

[0059] These above descriptions are only preferred embodiments of the present invention. It should be noted by those skilled in the art that various improvements and modifications may be made without departing from the principles of the present invention, and such improvements and modifications should be regarded as falling within the protection scope of the present invention.

Claims (10)

S1) obtaining a brown stock by cooking wood chips;
S2) subjecting the brown stock to oxygen delignification to obtain an oxygen-delignified stock;
the oxygen delignification comprises a first oxygen delignification stage and a second oxygen delignification stage; the stocks fed to the first oxygen delignification stage and the second oxygen delignification stage each independently have a concentration of 7 to 12% by weight;
During the first oxygen delignification stage, oxygen is used in an amount of 5 to 25 kg/adt and alkali is used in an amount of 10 to 25 kg/adt; during the second oxygen delignification stage, oxygen is used in an amount of 5 to 20 kg/adt and alkali is used in an amount of 0 to 15 kg/adt;
S3) mixing the oxygen-delignified stock with hemicellulase to perform enzymolysis to obtain an enzymatically digested stock; hemicellulase is used in an amount of 0.05 to 0.25 kg/adt; and
S4) immediately after enzymatic digestion, bleaching the enzymatically digested stock and subjecting the enzymatically digested stock to papermaking to obtain a dissolving pulp. The method of claim 1, wherein step S1) is specifically,
by prehydrolysis of wood chips, followed by cooking to obtain a brown stock, wherein the prehydrolysis is carried out at a temperature of 140 ° C to 170 ° C with a P-index of 450 to 650, and the hydrolyzate has an electrical conductivity of 140 to 170 S / cm 2 during the prehydrolysis. According to claim 2,
Cooking is carried out in white liquor; The white liquor is a mixed solution of sodium hydroxide and sodium sulfide, contains 100 to 140 g/L of usable alkali and 110 to 160 g/L of total alkali, and has a sulfidity of 20% to 40%; The cooking method is performed with an H-index of 1300 to 1600. According to claim 1,
In step S4), bleaching successively includes chlorine dioxide bleaching, alkali bleaching, a first bleaching stage and a second bleaching stage;
During the chlorine dioxide bleaching, chlorine dioxide is used in an amount of 10 to 15 kg/adt;
During the alkaline bleaching, the bleaching agent comprises sodium hydroxide, oxygen and hydrogen peroxide, wherein the sodium hydroxide is used in an amount of 10 to 30 kg/adt, the oxygen is used in an amount of 1 to 10 kg/adt, and the hydrogen peroxide is used in an amount of 1 to 10 kg/adt;
During the first bleaching stage, the bleaching agent is chlorine dioxide used in an amount of 3 to 8 kg/adt;
During the second bleaching stage, the bleaching agent is chlorine dioxide used in an amount of 1 to 3 kg/adt. According to claim 4,
During chlorine dioxide bleaching, the stock has a pH value of 1 to 3;
During alkaline bleaching, the stock has a pH value between 10 and 12;
During the first bleaching stage, the stock has a pH value between 3.5 and 4;
During the second bleaching stage, the stock has a pH value of 2.5 to 3. According to claim 1,
wherein the wood chips have a packing density of 140 to 250 kg/m 3 and a moisture content of 30 to 60% by weight. A pulp for dissolution prepared according to claim 1,
When the dissolving pulp is a dissolving pulp from softwood, it comprises not less than 93.0% alpha-cellulose, not more than 3.0% pentosans, not more than 0.15% extractables by DCM, not more than 0.10% ash, not more than 10.0 ppm Fe, and not more than 50 mg/kg SiO ₂ , and has a viscosity of 380 to 560 ml/g, based on ISO standard of 9 has a brightness of 0.0% or greater, and a dirt count of 3.0 ppm or less;
When the dissolving pulp is a dissolving pulp from hardwood, it comprises not less than 94.5% alpha-cellulose, not more than 3.0% pentosans, not more than 0.15% extractables by DCM, not more than 0.10% ash, not more than 10.0 ppm Fe, and not more than 60 mg/kg SiO ₂ , and has a viscosity of 400 to 530 ml/g, 90.0 based on ISO standard A pulp for dissolution, having a brightness of 3.0 ppm or less, and a dirt count of 3.0 ppm or less.
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