CN112048929A - Method for separating hemicellulose from wood and bamboo raw materials by low-solid prehydrolysis - Google Patents
Method for separating hemicellulose from wood and bamboo raw materials by low-solid prehydrolysis Download PDFInfo
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Abstract
The invention belongs to the technical field of hemicellulose treatment, and discloses a method for removing wood and bamboo raw material hemicellulose by adopting low solid matter prehydrolysis separation. The prehydrolysis liquid is extracted in the prehydrolysis process, and simultaneously, the same amount of water with the same temperature is added to replace the prehydrolysis liquid, so that the concentration of hemicellulose degradation products in the prehydrolysis liquid is reduced, and the low solid content prehydrolysis is realized. Compared with the traditional wood and bamboo water prehydrolysis method, the method has the advantages of short prehydrolysis time, low prehydrolysis temperature, low prehydrolysis energy consumption, good prehydrolysis selectivity, high hemicellulose removal rate and the like. The method for separating the hemicellulose from the wood and bamboo raw materials by low-solid-content prehydrolysis can be directly used for industrial production, and is beneficial to reducing the production energy consumption of dissolving pulp, improving the quality of the dissolving pulp and improving the production efficiency of the dissolving pulp.
Description
Technical Field
The invention relates to the technical field of hemicellulose treatment, in particular to a method for separating hemicellulose from wood and bamboo raw materials by low-solid prehydrolysis.
Background
Due to the wide application of dissolving pulp products in the industries of textile, construction, tobacco, war industry, medical treatment, food, water treatment and the like, the global dissolving pulp yield is increased year by year, reaches 1010 ten thousand tons in 2018, the productivity is mainly concentrated in China, America and Europe, and the dissolving pulp is a main dissolving pulp production base in the world. The apparent capacity of the dissolving pulp in 2019 years in China reaches 260 million tons (10 million tons in each of stone inkstone paper industry, Qingshan paper industry and Anhui Huatai, 30 million tons in Juntai paper industry, 30 million tons in Hubei morning song, 50 million tons in Taiyang paper industry and 120 million tons in Asian Tai mountain), the dissolving pulp accounts for 25 percent of the total global production capacity, and the dissolving pulp becomes a large world for producing the global dissolving pulp.
The current dissolving pulp production technology mainly comprises an acid sulfite method and a prehydrolysis sulfate method. Among them, the acidic sulfite process is gradually replaced by the prehydrolysis sulfate process because of long cooking time, low system pH, severe corrosion to equipment, and unsuitability for wood raw materials with high resin content. The prehydrolysis sulfate process removes hemicellulose by prehydrolysis, and then the sulfate process is used for cooking to remove lignin, so as to obtain cellulose fibers, namely dissolving pulp products (the content of alpha-cellulose is more than 90%, the content of hemicellulose is less than 5%, and trace residual lignin, organic extracts and inorganic salts). The method adds a prehydrolysis process, the prehydrolysis process comprises two types of steam prehydrolysis and water prehydrolysis, and the steam prehydrolysis and the water prehydrolysis have the bottleneck problems of long prehydrolysis time, high temperature, high energy consumption, low hemicellulose removal rate, poor prehydrolysis selectivity and the like.
The method develops a new prehydrolysis technology, shortens the prehydrolysis time, reduces the prehydrolysis temperature, saves the prehydrolysis energy consumption, improves the hemicellulose removal rate and the prehydrolysis selectivity, and has important practical significance for improving the purity and the reactivity of the dissolving pulp and the subsequent product quality, realizing the clean production of the dissolving pulp, saving energy and reducing emission. However, at present, the technology research and development of the prehydrolysis section of the process for producing dissolving pulp by the wood and bamboo prehydrolysis sulfate method are less, and the literature reports are few.
Disclosure of Invention
The invention aims to solve the technical problems of long prehydrolysis time, high temperature, high energy consumption, low hemicellulose removal rate and poor prehydrolysis selectivity when a prehydrolysis sulfate method is used for preparing dissolving pulp in the prior art, and firstly provides a method for separating hemicellulose from wood and bamboo raw materials by low solid matter prehydrolysis.
A second object of the invention is to provide the use of the above method for the preparation of dissolving pulp products.
The third purpose of the invention is to provide the application of the method in shortening the prehydrolysis time, reducing the energy consumption of the prehydrolysis and improving the hemicellulose removal rate.
The purpose of the invention is realized by the following technical scheme:
a method for separating hemicellulose from wood and bamboo materials by low solid content prehydrolysis comprises the steps of extracting prehydrolysis liquid in the prehydrolysis process, and simultaneously adding water with the same amount and temperature as the prehydrolysis liquid for replacement so as to reduce the concentration of hemicellulose degradation products in the prehydrolysis liquid.
The prehydrolysis liquid is extracted for many times in the prehydrolysis process, and hot water with the same quantity and the same temperature is added for replacement at the same time, so that the concentration of hemicellulose degradation products in the prehydrolysis liquid is reduced, and the generation amount of the hemicellulose degradation products converted into the pseudolignin at high temperature is reduced. The prehydrolysis liquid contains less pseudolignin, so that the adsorption capacity of the prehydrolysis liquid on the surfaces of wood and bamboo is low, the blocking effect of the pseudolignin on the dissolution of the hemicellulose degradation products is relieved, and the dissolution of the hemicellulose degradation products is facilitated.
The solid is the low molecular weight degradation product generated by the degradation reaction of cellulose, hemicellulose and lignin in the pulping raw material in the prehydrolysis process, and is dissolved in water liquid, and the solid is called as solid. In the prehydrolysis process, the solid matters in part of the prehydrolysis liquid are separated by repeatedly replacing the prehydrolysis liquid with clear water, so that the concentration of the solid matters in the prehydrolysis liquid is at a lower level in the whole prehydrolysis process, namely the low-solid-matter prehydrolysis.
As a preferable technical scheme, the ratio of the prehydrolysis solution is 1: 3.5-4.0; the heating process in the prehydrolysis process sequentially comprises the following steps: first-stage heating, first-stage small steam release, second-stage heating, second-stage small steam release, third-stage heating and heat preservation;
the first-stage temperature rise comprises the following steps: heating from the initial temperature to 120 ℃, wherein the heating rate is 7-10 ℃/10min, and the heating time is 90-125 min; the period of small steam release time is 10-15 min; the second-stage heating comprises the following steps: heating from 120 ℃ to 140 ℃, wherein the heating rate is 7-10 ℃/10min, and the heating time is 20-30 min; the two-stage small steam release time is 15-20 min; the three-stage heating comprises the following steps: heating from 140 ℃ to 160-165 ℃, wherein the heating rate is 7-10 ℃/10min, and the heating time is 20-30 min; the heat preservation is carried out at 160-165 ℃, and the heat preservation time is 30-60 min;
the replacement is respectively carried out when the first section of small air release, the second section of small air release and the third section of heating to the highest temperature.
As a more preferable technical solution, in the prehydrolysis process, the displacement operation of the prehydrolysis liquid is:
(1) one-section small air release: pumping out 15-25% of prehydrolysis liquid from the bottom of the cooking vertical pot, and pumping and adding the same amount of water which is preheated to 120 ℃;
(2) two-stage small air release: pumping out 20-30% of prehydrolysis liquid from the bottom of the cooking vertical pot, and pumping and adding equivalent water which is preheated to 140 ℃;
(3) and when the temperature is raised to the highest temperature in the third section: pumping out 20-30% of prehydrolysis liquid from the bottom of the cooking vertical pot, and pumping and adding equivalent water which is preheated to 160-165 ℃.
The hemicellulose of wood and bamboo is hydrolyzed into various oligosaccharides, monosaccharides, organic acids, furfural and the like by autocatalysis acid hydrolysis, and the oligosaccharides, the monosaccharides, the organic acids, the furfural and the like are dissolved in the prehydrolysis liquid, and the hemicellulose in the wood and bamboo raw materials can be removed by separating the prehydrolysis liquid after the prehydrolysis is finished. Therefore, as a preferred technical solution, the method further comprises a step of separating the prehydrolysis liquid after the prehydrolysis is completed: pumping the pre-hydrolysis waste liquid to an acid liquid tank by using a pump so as to separate and remove hemicellulose degradation products dissolved in the pre-hydrolysis waste liquid.
As a preferred technical scheme, the method further comprises the steps of preparing materials and filling in a pot before prehydrolysis, wherein the material preparation refers to that wood and bamboo raw materials are sequentially subjected to chipping, screening, washing and dewatering for later use; the step of pot filling refers to that the wood and bamboo raw materials which are reserved after dehydration are sent to a liquid pot filling device and then are filled into a stewing vertical pot through the liquid pot filling device for prehydrolysis.
In a preferred embodiment, the wood or bamboo material is selected from masson pine, radiata pine, caribbean pine, eucalyptus globulus, eucalyptus grandis, poplar, moso bamboo, green bamboo, dendrocalamus latiflorus, Sasa albo-marginata, and Tabason bamboo; of course, the wood and bamboo pulp can also be other wood and bamboo materials which are not listed and are commonly used in the field of pulping and papermaking.
As a specific technical scheme, the method for separating the hemicellulose from the wood and bamboo raw materials by low-solid-content prehydrolysis comprises the following steps:
s1, preparing materials: selecting wood and bamboo raw materials, and chipping the raw materials by using a chipping machine to obtain wood and bamboo chips with the length size of 20-30 mm; after chipping, screening by using a disc type wood chip screen or a double-layer cylinder type bamboo chip screen to remove large pieces, long strips, wood knots, wood and bamboo chips; after screening, washing the wood and bamboo chips by a drum washing machine to remove impurities such as stones, silt, metal and the like mixed in the wood and bamboo chips; after washing, the wood and bamboo chips are dewatered by an inclined screw dewaterer to remove free water brought by the wood and bamboo chips. Conveying the dewatered wood and bamboo chips to a storage bin by a rubber belt conveyor for use in a prehydrolysis working section;
s2, filling in a pot: conveying the wood and bamboo chips treated by the S1 in the storage bin to a liquid pot filling device through a rubber belt conveyor, and filling the wood and bamboo chips into a cooking vertical pot through the liquid pot filling device for pre-hydrolysis treatment;
s3, prehydrolysis: when the vertical cooking pot is filled with wood and bamboo chips, the automatic self-pressing pot cover is tightly covered, and clean water is introduced. The amount of the clean water is determined according to the liquid ratio set by the prehydrolysis process, the amount of the clean water used for filling the liquid into the pot by the pot filling device and the water content of the wood and bamboo chip raw materials. After adding the clean water required by the prehydrolysis, starting to heat to the temperature set by the prehydrolysis process through a liquid medicine circulation and heating system, and preserving the heat for the time set by the prehydrolysis process; the ratio of the prehydrolysis solution is 1: 3.5-4.0; the heating process in the prehydrolysis process sequentially comprises the following steps: first-stage heating, first-stage small steam release, second-stage heating, second-stage small steam release, third-stage heating and heat preservation;
s4, replacing prehydrolysis liquid: when the first-stage small steam release, the second-stage small gas release and the third-stage temperature rise reach the highest temperature, extracting part of prehydrolysis liquid from the bottom of the vertical boiler, pumping and adding the same amount of water preheated to the same temperature, and replacing the prehydrolysis liquid;
s5, separation of prehydrolysis liquid: after the prehydrolysis is finished, the degradation products of the wood and bamboo hemicellulose are dissolved in the prehydrolysis waste liquor. Pumping the prehydrolysis waste liquor to an acid liquor tank through a liquor inlet at the bottom of the cooking vertical pot by using a pump so as to separate and remove hemicellulose degradation products dissolved in the prehydrolysis waste liquor.
Preferably, in the liquid pot filling device in the step S2, the amount of the fresh water for filling the pot is 0.1 to 0.2 ton/ton of the oven-dried raw material.
The invention also provides the use of the method in the preparation of dissolving pulp products. The viscosity of the dissolving pulp prepared by the method is improved by more than 10 percent (the intrinsic viscosity is increased from 490mL/g to more than 540 mL/g); the method not only improves the reaction performance of the dissolving pulp, but also improves the viscosity of the dissolving pulp, and has important significance for improving the product quality of the dissolving pulp.
Compared with the traditional bamboo water prehydrolysis method, the prehydrolysis method has the advantages that the prehydrolysis time is short (shortened from 180-210 min to 150min), the prehydrolysis temperature is low (reduced from 165-175 ℃ to 160 ℃), the prehydrolysis steam consumption is reduced by more than 15% (reduced from 0.6-0.7 ton of steam/ton of pulp to less than 0.5 ton of steam/ton of pulp), and the energy-saving effect is obvious.
Therefore, the invention also provides the application of the method in shortening the prehydrolysis time, reducing the energy consumption of prehydrolysis and improving the removal rate of hemicellulose.
Compared with the prior art, the invention has the following beneficial effects:
the invention provides a method for separating hemicellulose from wood and bamboo raw materials by low solid content prehydrolysis, which is characterized in that prehydrolysis liquid is extracted in the prehydrolysis process, and meanwhile, water with the same amount and temperature is added for replacement with the prehydrolysis liquid so as to reduce the concentration of hemicellulose degradation products in the prehydrolysis liquid; .
Compared with the traditional bamboo water prehydrolysis method, the method disclosed by the invention has the following advantages: (1) the prehydrolysis time is short (shortened from 180-210 min to 150min), the prehydrolysis temperature is low (reduced from 165-175 ℃ to 160 ℃), the prehydrolysis steam consumption is reduced by more than 15% (reduced from 0.6-0.7 ton of steam/ton of pulp to less than 0.5 ton of steam/ton of pulp), and the obvious energy-saving effect is achieved; (2) the hemicellulose removal rate is improved by more than 5 percent (55-60 percent is increased to more than 65 percent), the viscosity of the dissolving pulp is improved by more than 10 percent (the intrinsic viscosity is increased to more than 540mL/g from 490 mL/g); the reaction performance of the dissolving pulp is improved, the viscosity of the dissolving pulp is also improved, and the dissolving pulp has important significance for improving the product quality of the dissolving pulp; (3) due to the fact that the prehydrolysis temperature is low, the prehydrolysis time is short, the prehydrolysis liquid is replaced in batches, the degradation degree of the hemicellulose in the prehydrolysis liquid is low, and the development of subsequent hemicellulose high value-added products is facilitated.
Drawings
FIG. 1 is the temperature profile of prehydrolysis of low-solid tamarindus pole in example 1.
Detailed Description
The following further describes the embodiments of the present invention. It should be noted that the description of the embodiments is provided to help understanding of the present invention, but the present invention is not limited thereto. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
The test methods used in the following experimental examples are all conventional methods unless otherwise specified; the materials, reagents and the like used are, unless otherwise specified, commercially available reagents and materials.
Example 1 pretreatment separation of hemicellulose from bamboo Material
The method comprises the following steps:
(1) taking a 2-year-old punt bamboo raw material, and chipping bamboo materials by using a Pallmann chipping machine (the moisture content of the bamboo chips is 61.31%) to obtain the bamboo chips with the length dimension of 20-30 mm. After chipping, screening by using a double-layer cylindrical bamboo chip screen to remove broken bamboo joints, bamboo chips and uncut bamboo strips. After screening, the bamboo chips are washed by a drum washing machine to remove impurities such as stones, silt and metals mixed in the bamboo chips. After washing, the bamboo chips are dewatered by an inclined screw dewaterer to remove free water brought by the bamboo chips. The dehydrated bamboo chips are conveyed to a storage bin by a rubber belt conveyor for use in a prehydrolysis working section.
(2) The bamboo chips in the bin are conveyed to a liquid pot filling device by a rubber belt conveyor and then are filled into a cooking vertical pot by the liquid pot filling device.
(3) After the vertical cooking pot is filled with bamboo chips, the automatic self-pressing pot cover is tightly covered, and clean water is introduced. The dosage of the clean water is 0.13 ton/ton of oven-dried bamboo chips, and the liquid ratio is 1: 3.5. After adding the clean water required by the prehydrolysis, starting to carry out the prehydrolysis by a liquid medicine circulation and heating system, wherein the prehydrolysis process comprises the following steps:
firstly, raising the temperature for the first time: heating from the initial temperature to 120 ℃, wherein the heating rate is 10 ℃/10min, and the heating time is 100 min;
II, one-stage small steam release: the time is 15 min;
③ two-stage heating: heating from 120 ℃ to 140 ℃, wherein the heating rate is 10 ℃/10min, and the heating time is 20 min;
fourthly, two-stage small steam release: the time is 15 min;
third-stage heating: heating from 140 ℃ to 162 ℃, wherein the heating rate is 10 ℃/10min, and the heating time is 22 min;
sixthly, heat preservation after temperature rise is finished: the heat preservation temperature is 162 ℃, and the heat preservation time is 50 min.
Replacing prehydrolysis liquid: in the prehydrolysis process, when the first-stage small steam release, the second-stage small air release and the third-stage heating are carried out to the highest temperature, part of prehydrolysis liquid is extracted from the bottom of the cooking vertical boiler, and then the same amount of hot water which is preheated to the same temperature is added by pumping to carry out replacement on the prehydrolysis liquid, wherein the specific prehydrolysis liquid replacement process comprises the following steps of:
firstly, when the first stage of small steam release is carried out, 15 percent of prehydrolysis liquid is pumped out from the bottom of the vertical boiler, and then the same amount of hot water which is preheated to 120 ℃ is added by a pump;
secondly, when the steam is discharged in the second stage, 20 percent of prehydrolysis liquid is pumped out from the bottom of the vertical boiler, and then the same amount of hot water which is preheated to 140 ℃ is pumped and added;
thirdly, when the temperature is raised to the highest temperature in the three sections, 30 percent of prehydrolysis liquid is pumped out from the bottom of the cooking vertical boiler, and then equivalent hot water which is preheated to 162 ℃ is added by a pump.
(4) After the prehydrolysis is finished, pumping the prehydrolysis waste liquor to an acid liquor tank through a liquor inlet at the bottom of the cooking vertical pot by using a pump so as to separate and remove bamboo wood hemicellulose degradation products dissolved in the prehydrolysis waste liquor.
After the prehydrolysis process is finished, the prehydrolysis yield of the bamboo chips is 79.41%, and the removal rate of the hemicellulose is 76.38%.
Example 2 pretreatment separation of hemicellulose from pine wood raw material
The method comprises the following steps:
(1) taking imported radiata pine chips, washing the chips by a drum type washing machine, and removing impurities such as stones, silt, metal and the like mixed in the chips. After washing, the chips were dewatered by an inclined screw dewaterer to remove the free water carried by the chips. The dewatered wood chips are conveyed to a storage bin by a rubber belt conveyor for use in a prehydrolysis working section.
(2) The wood chips in the storage bin are conveyed to a liquid pot filler by a rubber belt conveyor, and then are filled into a cooking vertical pot by the liquid pot filler.
(3) After the vertical cooking pot is filled with wood chips, the automatic self-pressing pot cover is tightly covered, and clean water is introduced. The amount of clean water is 0.15 ton/ton of oven-dried wood chips; the liquid ratio was 1: 3.6. After adding the clean water required by the prehydrolysis, starting to carry out the prehydrolysis by a liquid medicine circulation and heating system, wherein the prehydrolysis process comprises the following steps:
firstly, raising the temperature for the first time: heating from the initial temperature to 120 ℃, wherein the heating rate is 8 ℃/10min, and the heating time is 125 min;
II, one-stage small steam release: the time is 10 min;
③ two-stage heating: heating from 120 ℃ to 140 ℃, wherein the heating rate is 8 ℃/10min, and the heating time is 25 min;
fourthly, two-stage small steam release: the time is 10 min;
third-stage heating: heating from 140 ℃ to 165 ℃, wherein the heating rate is 8 ℃/10min, and the heating time is 20 min;
sixthly, heat preservation after temperature rise is finished: the heat preservation temperature is 165 ℃, and the heat preservation time is 60 min.
Replacing prehydrolysis liquid: in the prehydrolysis process, when the first-stage small steam release, the second-stage small air release and the third-stage heating are carried out to the highest temperature, part of prehydrolysis liquid is extracted from the bottom of the cooking vertical boiler, and then the same amount of hot water which is preheated to the same temperature is added by pumping to carry out replacement on the prehydrolysis liquid, wherein the specific prehydrolysis liquid replacement process comprises the following steps of:
firstly, when the first stage of small steam release is carried out, 20 percent of prehydrolysis liquid is pumped out from the bottom of the vertical boiler, and then the same amount of hot water which is preheated to 120 ℃ is added by a pump;
secondly, when the steam is discharged in the second stage, 30 percent of prehydrolysis liquid is pumped out from the bottom of the vertical boiler, and then the same amount of hot water which is preheated to 140 ℃ is pumped and added;
thirdly, when the temperature is raised to the highest temperature in the three sections, 30 percent of prehydrolysis liquid is pumped out from the bottom of the cooking vertical pot, and then equivalent hot water which is preheated to 165 ℃ is pumped in.
(4) And after the prehydrolysis is finished, pumping the prehydrolysis waste liquor to an acid liquor tank through a liquor inlet at the bottom of the cooking vertical pot by using a pump so as to separate and remove wood hemicellulose degradation products dissolved in the prehydrolysis waste liquor.
After the prehydrolysis process was completed, the prehydrolysis yield of pine wood chips was found to be 78.61% and the hemicellulose removal rate was found to be 77.54%.
Example 3 pretreatment separation of Eucalyptus globulus raw Material hemicellulose
The method comprises the following steps:
(1) taking imported eucalyptus globulus wood chips, washing the wood chips by using a drum washing machine, and removing impurities such as stones, silt, metal and the like mixed in the wood chips. After washing, the chips were dewatered by an inclined screw dewaterer to remove the free water carried by the chips. The dewatered wood chips are conveyed to a storage bin by a rubber belt conveyor for use in a prehydrolysis working section.
(2) The wood chips in the storage bin are conveyed to a liquid pot filler by a rubber belt conveyor, and then are filled into a cooking vertical pot by the liquid pot filler.
(3) After the vertical cooking pot is filled with wood chips, the automatic self-pressing pot cover is tightly covered, and clean water is introduced. The amount of clean water is 0.16 ton/ton of oven-dried wood chips; the liquid ratio was 1: 4.0. After adding the clean water required by the prehydrolysis, starting to carry out the prehydrolysis by a liquid medicine circulation and heating system, wherein the prehydrolysis process comprises the following steps:
firstly, raising the temperature for the first time: heating from the initial temperature to 120 ℃, wherein the heating rate is 10 ℃/10min, and the heating time is 100 min;
II, one-stage small steam release: the time is 15 min;
③ two-stage heating: heating from 120 ℃ to 140 ℃, wherein the heating rate is 10 ℃/10min, and the heating time is 20 min;
fourthly, two-stage small steam release: the time is 15 min;
third-stage heating: heating from 140 ℃ to 160 ℃, wherein the heating rate is 10 ℃/10min, and the heating time is 20 min;
sixthly, heat preservation after temperature rise is finished: the heat preservation temperature is 160 ℃, and the heat preservation time is 55 min.
Replacing prehydrolysis liquid: in the prehydrolysis process, when the first-stage small steam release, the second-stage small air release and the third-stage heating are carried out to the highest temperature, part of prehydrolysis liquid is extracted from the bottom of the cooking vertical boiler, and then the same amount of hot water which is preheated to the same temperature is added by pumping to carry out replacement on the prehydrolysis liquid, wherein the specific prehydrolysis liquid replacement process comprises the following steps of:
firstly, when the first stage of small steam release is carried out, 20 percent of prehydrolysis liquid is pumped out from the bottom of the vertical boiler, and then the same amount of hot water which is preheated to 120 ℃ is added by a pump;
secondly, when the steam is discharged in the second stage, 30 percent of prehydrolysis liquid is pumped out from the bottom of the vertical boiler, and then the same amount of hot water which is preheated to 140 ℃ is pumped and added;
thirdly, when the temperature is raised to the highest temperature in the three sections, 30 percent of prehydrolysis liquid is pumped out from the bottom of the cooking vertical pot, and then the equivalent amount of hot water which is preheated to 160 ℃ is added by a pump.
(4) And after the prehydrolysis is finished, pumping the prehydrolysis waste liquor to an acid liquor tank through a liquor inlet at the bottom of the cooking vertical pot by using a pump so as to separate and remove wood hemicellulose degradation products dissolved in the prehydrolysis waste liquor.
After the prehydrolysis process is finished, the prehydrolysis yield of the eucalyptus globulus wood chips is 77.36%, and the hemicellulose removal rate is 79.93%.
Comparative example 1 separation of hemicellulose from wood and bamboo raw materials by traditional prehydrolysis process
The starting materials and the process were essentially the same as in example 1, the only difference being that the prehydrolysis process of this comparative example: the liquid ratio is 1:3.5, the prehydrolysis temperature is 162 ℃, and the heat preservation time is 50 min.
Experimental examples preparation of dissolving pulp
The raw materials obtained by the prehydrolysis process of example 1 and the raw materials obtained by the prehydrolysis process of comparative example 1 were respectively used for preparing dissolving pulp, and the preparing of the dissolving pulp included the following steps:
(1) pre-hydrolysis of the raw material.
(2) The sulfate cooking process comprises the following steps: the alkali amount is 23% (calculated by NaOH), the liquid ratio is 1:4.0, the cooking temperature is 170 ℃, and the heat preservation time is 120 min.
(3) The bleaching process comprises the following steps: the bleaching sequence is OD1EopD2。
The oxygen delignification process comprises the following steps: the pulp concentration is 10%, the sodium hydroxide dosage is 4%, the magnesium sulfate dosage is 0.5%, the temperature is 100 ℃, the time is 60min, and the oxygen pressure is 0.8 MPa.
D1A section bleaching process: the pulp concentration is 10%, the chlorine dioxide dosage is 2%, the sodium hydroxide dosage is 1%, the temperature is 75 ℃, and the time is 90 min.
The Eop bleaching process comprises the following steps: the pulp concentration is 10%, the sodium hydroxide dosage is 1%, the magnesium sulfate dosage is 0.5%, the hydrogen peroxide dosage is 0.5%, the oxygen pressure is 0.4MPa, the temperature is 75 ℃, and the time is 60 min.
D2A section bleaching process: the pulp concentration is 10%, the chlorine dioxide dosage is 0.4%, the sodium hydroxide dosage is 0.2%, the temperature is 75 ℃, and the time is 90 min.
The results show that: the intrinsic viscosity of the dissolving pulp obtained from the raw material of example 1 was 489.2 mL/g; the intrinsic viscosity of the resulting dissolving pulp of the raw material of comparative example 1 was 541.6 mL/g.
Claims (9)
1. A method for separating hemicellulose from wood and bamboo raw materials by low solid content prehydrolysis is characterized in that prehydrolysis liquid is extracted in the prehydrolysis process, and meanwhile, water with the same amount and temperature is added to replace the prehydrolysis liquid, so that the concentration of hemicellulose degradation products in the prehydrolysis liquid is reduced.
2. The method for separating hemicellulose from wood and bamboo raw materials by low-solid-content prehydrolysis according to claim 1, wherein the ratio of prehydrolysis liquid is 1: 3.5-4.0; the heating process in the prehydrolysis process sequentially comprises the following steps: first-stage heating, first-stage small steam release, second-stage heating, second-stage small steam release, third-stage heating and heat preservation;
the first-stage temperature rise comprises the following steps: heating from the initial temperature to 120 ℃, wherein the heating rate is 7-10 ℃/10min, and the heating time is 90-125 min; the period of small steam release time is 10-15 min; the second-stage heating comprises the following steps: heating from 120 ℃ to 140 ℃, wherein the heating rate is 7-10 ℃/10min, and the heating time is 20-30 min; the two-stage small steam release time is 15-20 min; the three-stage heating comprises the following steps: heating from 140 ℃ to 160-165 ℃, wherein the heating rate is 7-10 ℃/10min, and the heating time is 20-30 min; the heat preservation is carried out at 160-165 ℃, and the heat preservation time is 30-60 min;
the replacement is respectively carried out when the first section of small air release, the second section of small air release and the third section of heating to the highest temperature.
3. The method for separating hemicellulose from wood and bamboo materials by low-solid-content prehydrolysis according to claim 2, wherein the displacement operation of the prehydrolysis liquid is as follows:
(1) one-section small air release: pumping out 15-25% of prehydrolysis liquid from the bottom of the cooking vertical pot, and pumping and adding the same amount of water which is preheated to 120 ℃;
(2) two-stage small air release: pumping out 20-30% of prehydrolysis liquid from the bottom of the cooking vertical pot, and pumping and adding equivalent water which is preheated to 140 ℃;
(3) and when the temperature is raised to the highest temperature in the third section: pumping out 20-30% of prehydrolysis liquid from the bottom of the cooking vertical pot, and pumping and adding equivalent water which is preheated to 160-165 ℃.
4. The method for low-solids prehydrolysis separation of hemicellulose in wood and bamboo materials according to claim 1, wherein said wood and bamboo materials are selected from masson pine, radiata pine, caribbean pine, eucalyptus globulus, eucalyptus grandis, poplar, phyllostachys pubescens, green bamboos, dendrocalamus latiflorus, Sasa albo-marginata, and Sasa albo-marginata.
5. The method for separating hemicellulose from wood and bamboo materials by low-solid prehydrolysis according to claim 1, further comprising the step of separating the prehydrolysis liquid: and after the pre-hydrolysis is finished, pumping the pre-hydrolysis waste liquid to an acid liquid tank by using a pump so as to separate and remove the hemicellulose degradation products dissolved in the pre-hydrolysis waste liquid.
6. The method for separating hemicellulose from wood and bamboo raw materials by low-solid prehydrolysis according to claim 1, further comprising the steps of preparing materials and loading in a pot before prehydrolysis, wherein the material preparation refers to that the wood and bamboo raw materials are sequentially sliced, screened, washed and dehydrated for later use; the step of pot filling refers to that the wood and bamboo raw materials which are reserved after dehydration are sent to a liquid pot filling device and then are filled into a stewing vertical pot through the liquid pot filling device for prehydrolysis.
7. The method for separating hemicellulose from wood and bamboo raw materials by low-solid prehydrolysis according to claim 6, wherein the amount of fresh water used for filling a pot in the liquid pot filling device is 0.1-0.2 ton/ton of absolutely dry raw materials.
8. The application of the method for separating hemicellulose from wood and bamboo raw materials by low-solid-content prehydrolysis according to any one of claims 1-7 in preparation of dissolving pulp products.
9. The method for separating hemicellulose from wood and bamboo raw materials by low-solid-content prehydrolysis according to any one of claims 1 to 7, and is applied to shortening prehydrolysis time, reducing prehydrolysis energy consumption and improving hemicellulose removal rate.
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| CN101701431A (en) * | 2008-07-16 | 2010-05-05 | 中国制浆造纸研究院 | Method for producing bleached pulp for viscose fibers from bamboo |
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