CN108179647B

CN108179647B - Preparation method of chlorine-free slightly-bleached softwood pulp

Info

Publication number: CN108179647B
Application number: CN201810161399.XA
Authority: CN
Inventors: 孙曰平; 李伟东; 张玉全; 王吉祥
Original assignee: Rizhao Huatai Paper Co ltd
Current assignee: Rizhao Huatai Paper Co ltd
Priority date: 2018-02-27
Filing date: 2018-02-27
Publication date: 2021-03-23
Anticipated expiration: 2038-02-27
Also published as: CN108179647A

Abstract

The invention provides a preparation method of chlorine-free slightly-bleached softwood pulp, belonging to the field of slurry preparation, and the method takes softwood as a raw material, and firstly dissolves out lignin through a DDS replacement cooking production process; then, carrying out primary oxygen removal on the slurry obtained by DDS replacement cooking, softening fibers and removing lignin; and finally, carrying out treatment by two-stage oxygen removal and biological enzyme bleaching assistance to degrade LCC (cellulose C) connecting bonds between lignin and carbohydrates, degrading xylan adsorbed and precipitated on the surface of the fiber in the cooking process, and destroying colored groups in the lignin structure. The invention adopts DDS replacement cooking production process and is matched with OAB + biological enzyme micro-bleaching technology to produce environment-friendly pulp, and the produced product not only performs micro-bleaching to change color, but also realizes chlorine-free. The variety produced by using the chlorine-free slightly-bleaching environment-friendly unbleached pulp can replace imported high-end products, all indexes reach the export European Union standard, and the pulp can be used for producing high-grade packing paper, paper for industrial technology and paper for natural color or primary color living.

Description

Preparation method of chlorine-free slightly-bleached softwood pulp

Technical Field

The invention relates to the technical field of slurry preparation, in particular to a preparation method of chlorine-free slightly-bleached softwood pulp.

Background

Pulp bleaching is an important process in pulping processes, and aims to improve the brightness of wood pulp to meet the requirements of different papers. The raw material for paper making is mainly wood, which contains considerable lignin in addition to cellulose. The lignin contains a certain amount of chromophoric groups and a great number of active reaction sites, and in the bleaching process, certain active reaction groups can be converted into chromophors besides a certain amount of chromophors cannot be destroyed. Thus, the presence of lignin greatly limits pulp brightness and its bleachability.

Delignification bleaching is the main mode of pulp bleaching. The traditional delignification bleaching mainly uses hypochlorite as a bleaching agent, usually combines chlorination and alkali treatment to carry out multi-stage bleaching, and the bleaching mode produces a large amount of organic halides in waste liquid, thereby causing great environmental pollution.

Disclosure of Invention

The technical task of the invention is to provide a preparation method of chlorine-free slightly-bleached softwood pulp aiming at the defects of the prior art, and solve the problem of environmental pollution caused by chlorine bleaching in the prior art.

The method uses needle-leaved wood as a raw material, utilizes a DDS replacement cooking production process and is matched with an OAB + biological enzyme micro-bleaching technology to produce environment-friendly pulp, thoroughly changes the color of original unbleached pulp, achieves micro-bleaching and chlorine-free, paper made of the environment-friendly pulp replaces high-end products imported from abroad, and all indexes reach the export European Union standard.

Firstly, the DDS replacement cooking process is a new technology developed on the basis of an RDH (rapid replacement cooking) intermittent cooking technology, thoroughly eliminates odor pollution, reduces steam consumption, reduces sewage discharge load, improves product quality, and has obvious energy-saving and environment-friendly effects.

Secondly, in the OAB micro-bleaching technology, in order to realize chlorine-free micro-bleaching, oxygen and alkali are added to soften fiber and remove lignin.

And thirdly, the biological enzyme bleaching assisting technology simply depends on OAB micro-bleaching technology to meet the requirements of the brightness of pulp and partial paper variety, the biological enzyme technology is combined, the addition of the biological enzyme can selectively degrade the connecting bond between the lignin and the somnolence compound, the LCC structure is damaged, xylan adsorbed and settled on the surface of the fiber in the degradation cooking process is degraded, phenolic hydroxyl groups and syringyl groups in the lignin structure are damaged, the chemical structure of the cellulose is not damaged at the same time, the gaps among the fibers are increased, and the bleaching effect is achieved.

The technical scheme adopted by the invention for solving the technical problems is as follows:

a method for preparing chlorine-free slightly-bleached softwood pulp, which takes softwood as a raw material,

firstly, dissolving out lignin by a DDS replacement cooking production process;

then, carrying out primary oxygen removal on the slurry obtained by DDS replacement cooking, softening fibers and removing lignin;

and finally, carrying out treatment by two-stage oxygen removal and biological enzyme bleaching assistance to degrade LCC (cellulose C) connecting bonds between lignin and carbohydrates, degrading xylan adsorbed and precipitated on the surface of the fiber in the cooking process, and destroying colored groups in the lignin structure.

As a further improvement of the invention, the needle-leaved wood is taken as a raw material, and the method comprises the following steps:

1) the wood chips are taken out after the processes of screening, washing and presoaking, and the softened wood chips after presoaking are sent to the cooking process to dissolve out lignin in the wood chips;

the cooking procedure adopts DDS replacement cooking production process to cook, the cooking liquor used in the wood chip cooking procedure accounts for 2-3 wt% of the absolutely dry raw materials, and the cooking liquor is fed into a cooking pot in stages along with the cooking process;

2) washing the pulp after cooking, retaining fibers, separating and removing waste liquid from the pulp, purifying and screening the washed pulp, and separating out non-cooked materials and impurities which are not cooked and become pulp completely;

3) feeding the purified and screened pulp into a first-stage oxygen removal process, and adding sodium hydroxide and oxygen into a first-stage oxygen removal tower to perform first-stage oxygen delignification, wherein the sodium hydroxide accounts for 1.0-2.0 wt% of the oven-dried pulp, and the oxygen accounts for 1.0-2.0 wt% of the oven-dried pulp;

4) feeding the pulp subjected to the first-stage oxygen removal into a second-stage oxygen removal process, and adding sodium hydroxide, oxygen, hydrogen peroxide, bleaching promoting enzyme, scale inhibitor and chelating agent into a medium-concentration mixer to perform second-stage oxygen delignification, wherein the sodium hydroxide accounts for 0.8-1.0 wt% of the oven-dry pulp, the oxygen accounts for 1.0-1.5 wt% of the oven-dry pulp, the hydrogen peroxide accounts for 1-2 wt% of the oven-dry pulp, the bleaching promoting enzyme accounts for 0.01-0.04 wt% of the oven-dry pulp, the scale inhibitor accounts for 0.05-0.08 wt% of the oven-dry pulp, and the chelating agent accounts for 0.02-0.04 wt% of the oven-dry pulp;

5) and washing, dehydrating, concentrating, conveying and storing the slurry after the second-stage oxygen removal.

As a further improvement of the invention, the DDS replacement cooking production process in the step 1) comprises the following steps:

a) heating and preserving heat in the cooking process, replacing low-temperature black liquor in a cooking pot by using warm black liquor and hot black liquor, heating to 156-163 ℃, then heating to 170-172 ℃ of the highest cooking temperature by using 0.8MPa steam, and preserving heat, wherein the heating and preserving heat are controlled at 100 ℃ for 120 minutes;

b) after the temperature is raised and preserved, the hot black liquor in the digester is replaced by the low-temperature black liquor, and then the black liquor enters the hot black liquor tank, the warm black liquor tank and the recovery tank in sequence from high to low until the temperature in the digester is reduced to be below 100 ℃, and the process lasts for 30-40 minutes.

As a further improvement of the present invention, the cooking liquor in step 1) comprises: 16 to 20 percent of sodium hydroxide, 5 to 8 percent of sodium sulfide, 0.02 to 0.05 percent of assistant A and 0.05 to 0.08 percent of assistant B.

Wherein sodium hydroxide, sodium sulfide and non-fibrous matters such as lignin in the fiber material react with the liquid medicine to generate compounds dissolved in the cooking liquid, so that the compounds are removed from the fiber to dissociate the fiber.

As a further improvement of the invention, the additive A is a dispersant which has the function of reducing the surface tension of the cooking liquor, so that the cooking liquor is uniformly distributed on the surface of the wood chip to help the liquor to permeate, such as cellulose derivatives and fatty acid polyglycol ester, and the additive B is a catalyst which has the function of the cooking additive to promote the dissolution of lignin and protect fibers, such as anthraquinone and derivatives thereof.

As a further improvement of the invention, in the step 4), the bleaching-promoting enzyme is a biological enzyme which is used for promoting lignin dissolution and reducing pulp hardness, such as xylitol enzyme and hemicellulase, the scale inhibitor is used for preventing the formation of sediment including calcium oxalate, such as organic phosphate, and the chelating agent is a masking agent which is used for masking heavy metal ions, such as organic phosphoric acid and polycarboxylic acid compound.

As a further improvement of the present invention, in step 1), the DDS replacement cooking production process comprises:

filling into a pot LC, adding 2.0-3.0 wt% of alkali (for the cooking liquid medicine, the weight of the added alkali is the sum of sodium hydroxide and sodium sulfide, the same applies below), and controlling the temperature to be 70-80 ℃;

secondly, primarily cooking the IC, adding 4.0-4.3 wt% of alkali, controlling the temperature to be 128-133 ℃, and simultaneously adding 0.3 kg/ton of additive A;

thirdly, middle-level cooking MC, adding the rest of alkali at the temperature of 156-163 ℃, and simultaneously adding 0.5 kg/ton of auxiliary agent B;

fourthly, heating the FC to 172 ℃ by using fresh steam of 0.8MPa, and starting heat preservation, wherein the cooking H factor reaches 1550 liters and the heat preservation is finished;

fifth, recovering and replacing RC, replacing the black liquor in the cooking with low-temperature black liquor, and reducing the temperature in the pot to be below 100 ℃;

sixthly, putting the pot DC, and conveying the slurry in the pot to a spraying pot by using a pot-putting pump.

Compared with the prior art, the preparation method of the chlorine-free slightly-bleached softwood pulp has the following beneficial effects:

the invention adopts DDS replacement cooking production process and is matched with OAB + biological enzyme micro-bleaching technology to produce environment-friendly pulp, and the produced product not only performs micro-bleaching to change color, but also realizes chlorine-free. The variety produced by using the chlorine-free slightly-bleaching environment-friendly unbleached pulp can replace imported high-end products, and all indexes reach the export European Union standard. The product can be used for producing high-grade packing paper, industrial and technical paper and natural or primary color paper for daily use.

Detailed Description

The process for producing chlorine-free slightly bleached softwood pulp of the present invention is described in detail below.

Example one

The invention relates to a preparation method of chlorine-free slightly-bleached softwood pulp, which takes softwood as a raw material and comprises the following steps:

1) the wood chips are taken out after the processes of screening, washing and presoaking, and the softened wood chips after presoaking are sent to the cooking process to dissolve out lignin in the wood chips; [ due to the fact that the wood chips are softened after being presoaked, the wood chips can be loosened and loosened, cooking liquor can be soaked into the wood chips easily, pulping time is shortened, and residue sieving rate is reduced. "C (B)

The cooking procedure adopts DDS replacement cooking production process to cook, the cooking liquor used in the wood chip cooking procedure accounts for 2 wt% of the absolutely dry raw materials, and the cooking liquor is fed into a cooking pot in stages along with the cooking process;

the related cooking liquor comprises the following components: 16 wt% of sodium hydroxide, 5 wt% of sodium sulfide, 0.03 wt% of assistant A and 0.05 wt% of assistant B, wherein the weight percentage of the assistant A is less than that of the assistant B;

the assistant A is cellulose derivative used as dispersant to lower the surface tension of the cooking liquor and to distribute the cooking liquor homogeneously on the surface of the wood chip to assist in permeating the liquor. The assistant B is anthraquinone, is used as a catalyst and has the functions of digesting the assistant, promoting the dissolution of lignin and protecting fibers.

The DDS replacement cooking production process comprises the following steps:

filling into a pot LC, adding 2.0 wt% of alkali (for the cooking liquid medicine, the weight of the added alkali is the sum of sodium hydroxide and sodium sulfide, the same applies below) and controlling the temperature at 70 ℃;

secondly, primarily cooking the IC, adding 4.0 wt% of alkali, controlling the temperature to be 133 ℃, and simultaneously adding 0.3 kg/ton of additive A;

③ carrying out middle-grade cooking MC, adding the rest of alkali at the temperature of 156 ℃, and simultaneously adding the auxiliary agent B with the addition of 0.5 kg/ton;

replacing and heating up the low-temperature black liquor in the digester by adopting the warm black liquor and the hot black liquor;

fourthly, heating to 172 ℃ by using fresh steam of 0.8MPa, starting heat preservation, controlling the temperature of the heat preservation to be 100 minutes, and finishing the heat preservation when the cooking H factor reaches 1550 liters;

recovering and replacing RC, replacing the cooking internal hot black liquor with low-temperature black liquor, and sequentially feeding the black liquor into a hot black liquor tank, a warm black liquor tank and a recovery tank from high temperature to low temperature to reduce the temperature in the pot to be below 100 ℃, wherein the process is carried out for 30 minutes;

2) Washing the cooked pulp, retaining fibers, separating and removing waste liquid from the pulp, sending the waste liquid to a recovery system for recovery to prevent pollution, purifying and screening the washed pulp, and separating out non-digested matters and impurities which are not cooked and become pulp completely;

for softwood pulp, the non-digested matter is mainly wood blocks which are not well digested, and the impurities are mainly sand, metal substances and the like;

3) feeding the purified and screened slurry into a first-stage oxygen removal process, adding sodium hydroxide and oxygen into a first-stage oxygen removal tower to perform first-stage oxygen delignification: wherein, the sodium hydroxide accounts for 1.0 wt% of the oven dry pulp, and the oxygen accounts for 1.0 wt% of the oven dry pulp;

4) feeding the pulp subjected to the first-stage oxygen removal into a second-stage oxygen removal process, and adding sodium hydroxide, oxygen, hydrogen peroxide, bleaching promoting enzyme, scale inhibitor and chelating agent into a medium-concentration mixer to perform second-stage oxygen delignification, wherein the sodium hydroxide accounts for 0.8 wt% of the oven-dried pulp, the oxygen accounts for 1.0 wt% of the oven-dried pulp, the hydrogen peroxide accounts for 1 wt% of the oven-dried pulp, the bleaching promoting enzyme accounts for 0.01 wt% of the oven-dried pulp, the scale inhibitor accounts for 0.05 wt% of the oven-dried pulp, and the chelating agent accounts for 0.02 wt% of the oven-dried pulp;

the bleaching promoter is xylitol enzyme, is used as biological enzyme and has the function of promoting lignin to dissolve out to reduce pulp hardness. The scale inhibitor is an organophosphate which acts to prevent the formation of deposits including calcium oxalate. The chelating agent is organic phosphoric acid and is used as a masking agent, and the function of the chelating agent is to mask heavy metal ions.

In the present invention, oxygen delignification is the use of alkali and oxygen to remove most of the lignin remaining after cooking.

The comparative example is the preparation method of the softwood pulp in the prior art, the softwood is taken as a raw material, and the method comprises the following steps: RDH kraft cooking + hypochlorite bleaching.

Example two

The cooking procedure adopts DDS replacement cooking production process to cook, the cooking liquor used in the wood chip cooking procedure accounts for 2.5 wt% of the absolutely dry raw materials, and the cooking liquor is fed into a cooking pot in stages along with the cooking process;

the related cooking liquor comprises the following components: 18 wt% of sodium hydroxide, 7 wt% of sodium sulfide, 0.02 wt% of assistant A and 0.07 wt% of assistant B, wherein the weight percentage of the assistant A is the same as that of the sodium sulfide;

the additive A is fatty acid polyglycol ester and is used as dispersant to lower the surface tension of the cooking liquor and to make the cooking liquor distributed homogeneously on the surface of the wood chip to help the liquor to permeate. The assistant B is anthraquinone derivative used as catalyst and has the functions of digesting assistant to promote the leaching of lignin and protect fiber.

The DDS replacement cooking production process comprises the following steps:

filling into a pot LC, adding 2.5 wt% of alkali (for the cooking liquid medicine, the weight of the added alkali is the sum of sodium hydroxide and sodium sulfide, the same applies below), and controlling the temperature to be 75 ℃;

secondly, primarily cooking the IC, adding 4.3 wt% of alkali, controlling the temperature to be 128 ℃, and simultaneously adding 0.2 kg/ton of additive A;

thirdly, middle-level cooking MC, adding the rest of alkali at 160 ℃, and simultaneously adding 0.7 kg/ton of auxiliary agent B;

fourthly, heating to 170 ℃ by using fresh steam with the pressure of 0.8MPa, starting heat preservation, controlling the temperature of the heat preservation to be 110 minutes, and finishing the heat preservation when the cooking H factor reaches 1550 liters;

recovering and replacing RC, replacing the cooking internal hot black liquor with low-temperature black liquor, and sequentially feeding the black liquor into a hot black liquor tank, a warm black liquor tank and a recovery tank from high temperature to low temperature to reduce the temperature in the pot to be below 100 ℃, wherein the process is carried out for 35 minutes;

3) feeding the purified and screened slurry into a first-stage oxygen removal process, adding sodium hydroxide and oxygen into a first-stage oxygen removal tower to perform first-stage oxygen delignification: wherein, the sodium hydroxide accounts for 1.5 percent of the weight of the oven dry pulp, and the oxygen accounts for 1.5 percent of the weight of the oven dry pulp;

4) feeding the pulp subjected to the first-stage oxygen removal into a second-stage oxygen removal process, and adding sodium hydroxide, oxygen, hydrogen peroxide, bleaching promoting enzyme, scale inhibitor and chelating agent into a medium-concentration mixer to perform second-stage oxygen delignification, wherein the sodium hydroxide accounts for 0.9 wt% of the oven-dry pulp, the oxygen accounts for 1.2 wt% of the oven-dry pulp, the hydrogen peroxide accounts for 1.5 wt% of the oven-dry pulp, the bleaching promoting enzyme accounts for 0.03 wt% of the oven-dry pulp, the scale inhibitor accounts for 0.06 wt% of the oven-dry pulp, and the chelating agent accounts for 0.03 wt% of the oven-dry pulp;

the bleaching promoter is hemicellulase, is used as biological enzyme and has the function of promoting lignin to be dissolved out to reduce the hardness of pulp. The scale inhibitor is an organophosphate which acts to prevent the formation of deposits including calcium oxalate. The chelating agent is a polycarboxylic acid complex, which acts as a sequestering agent, and its function is to sequester heavy metal ions.

EXAMPLE III

The cooking procedure adopts DDS replacement cooking production process to cook, the cooking liquor used in the wood chip cooking procedure accounts for 3 wt% of the absolutely dry raw materials, and the cooking liquor is fed into a cooking pot in stages along with the cooking process;

the related cooking liquor comprises the following components: 20 wt% of sodium hydroxide, 8 wt% of sodium sulfide, 0.05 wt% of assistant A and 0.08 wt% of assistant B, wherein the weight percentage of the assistant B is the same as that of the sodium hydroxide;

the assistant A is a mixture of cellulose derivatives and fatty acid polyglycol ester, is used as a dispersant, and has the function of reducing the surface tension of the cooking liquor, so that the cooking liquor is uniformly distributed on the surface of the wood chips to help the liquor to permeate. The assistant B is the mixture of anthraquinone and its derivative and is used as catalyst for digestion assistant to promote the digestion of lignin and protect fiber.

The DDS replacement cooking production process comprises the following steps:

filling into a pot LC, adding 3.0 wt% of alkali (for the cooking liquid medicine, the weight of the added alkali is the sum of sodium hydroxide and sodium sulfide, the same applies below) at the temperature of 80 ℃;

secondly, primarily cooking the IC, adding 4.2 wt% of alkali, controlling the temperature to be 130 ℃, and simultaneously adding 0.5 kg/ton of additive A;

③ carrying out middle-grade cooking MC, adding the rest of alkali at 163 ℃, and simultaneously adding the auxiliary agent B at the amount of 0.8 kg/ton;

fourthly, heating to 171 ℃ by using fresh steam of 0.8MPa, and beginning to preserve heat, wherein the temperature preservation is controlled at 110 minutes, and the heat preservation is finished when the cooking H factor reaches 1550 liters;

recovering and replacing RC, replacing the cooking internal hot black liquor with low-temperature black liquor, and sequentially feeding the black liquor into a hot black liquor tank, a warm black liquor tank and a recovery tank from high temperature to low temperature to reduce the temperature in the pot to be below 100 ℃, wherein the process is carried out for 40 minutes;

3) feeding the purified and screened slurry into a first-stage oxygen removal process, adding sodium hydroxide and oxygen into a first-stage oxygen removal tower to perform first-stage oxygen delignification: wherein the dosage of the sodium hydroxide accounts for 2.0 wt% of the oven dry pulp, and the dosage of the oxygen accounts for 2.0 wt% of the oven dry pulp;

4) feeding the pulp subjected to the first-stage oxygen removal into a second-stage oxygen removal process, and adding sodium hydroxide, oxygen, hydrogen peroxide, bleaching promoting enzyme, scale inhibitor and chelating agent into a medium-concentration mixer to perform second-stage oxygen delignification, wherein the sodium hydroxide accounts for 1.0 wt% of the oven-dry pulp, the oxygen accounts for 1.5 wt% of the oven-dry pulp, the hydrogen peroxide accounts for 2 wt% of the oven-dry pulp, the bleaching promoting enzyme accounts for 0.04 wt% of the oven-dry pulp, the scale inhibitor accounts for 0.08 wt% of the oven-dry pulp, and the chelating agent accounts for 0.04 wt% of the oven-dry pulp;

the bleaching promoter is a mixture of xylitol enzyme and hemicellulase, is used as biological enzyme, and has the function of promoting lignin to dissolve out to reduce pulp hardness. The scale inhibitor is an organophosphate which acts to prevent the formation of deposits including calcium oxalate. The chelating agent is a mixture of organic phosphoric acid and polycarboxylic acid complex, and is used as a masking agent, and the function of the masking agent is to mask heavy metal ions.

While the preferred embodiments of the present application have been described, additional variations and modifications in those embodiments may occur to those skilled in the art once they learn of the basic inventive concepts. Therefore, it is intended that the appended claims be interpreted as including preferred embodiments and all alterations and modifications as fall within the scope of the application.

It will be apparent to those skilled in the art that various changes and modifications may be made in the present application without departing from the spirit and scope of the application. Thus, if such modifications and variations of the present application fall within the scope of the claims of the present application and their equivalents, the present application is intended to include such modifications and variations as well.

In addition to the technical features described in the specification, the technology is known to those skilled in the art.

Claims

1. A preparation method of chlorine-free slightly-bleached softwood pulp is characterized in that softwood is taken as a raw material,

firstly, dissolving out lignin by a DDS replacement cooking production process;

finally, two-stage oxygen removal and biological enzyme bleaching are carried out to degrade LCC connecting bonds between lignin and carbohydrates, xylan adsorbed and precipitated on the surface of fiber in the cooking process is degraded, and colored groups in the lignin structure are damaged;

the method comprises the following steps:

1) the wood chips are taken out after screening, washing and presoaking processes, and the wood chips softened after presoaking are sent to a cooking process;

the cooking procedure adopts DDS replacement cooking production process to cook, the alkali of cooking liquor used in the wood chip cooking procedure accounts for 2-3 wt% of the absolute dry raw material, and the cooking liquor is fed into a cooking pot in stages along with the cooking process;

wherein the cooking liquor comprises the following components: 16 to 20 percent of sodium hydroxide, 5 to 8 percent of sodium sulfide, 0.02 to 0.05 percent of assistant A and 0.05 to 0.08 percent of assistant B; the auxiliary agent A is a dispersing agent and comprises a cellulose derivative and fatty acid polyglycol ester, and the auxiliary agent B is a catalyst and comprises anthraquinone and derivatives thereof;

the DDS replacement cooking production process comprises the following steps:

filling LC in a pot, adding 2.0-3.0 wt% of alkali, and controlling the temperature to be 70-80 ℃;

fifthly, recovering and replacing the RC, replacing hot black liquor in the digester with low-temperature black liquor, and reducing the temperature in the digester to be below 100 ℃;

sixthly, putting the pot DC, and conveying the slurry in the pot to a spraying pot by using a pot pump;

2. The method for preparing chlorine-free slightly bleached softwood pulp according to claim 1, wherein in the step 4), the bleaching promoting enzyme is a biological enzyme comprising xylitol enzyme and hemicellulase, the scale inhibitor is an organic phosphate, and the chelating agent is a masking agent comprising an organic phosphate and polycarboxylic acid compound.