A method for improving the yield of alkali impregnation of fiber raw material

Abstract

The application discloses a method for improving the alkali impregnation yield of fiber raw materials, wherein after qualified wood chips are obtained by screening the fiber raw materials, at least one dry heat treatment is performed on the washed and dehydrated fiber raw materials before alkali impregnation, the treatment temperature is 105 DEG C to 130 DEG C, and the total treatment time is 10 min to 60 min. According to the method, under the condition of not being chemically modified, only by using relatively mild heat treatment, the precursor small molecules originally in the cell cavity are connected with the main structure of the fiber raw materials by free radical condensation as much as possible, so that the alkali impregnation yield of pulping of the chemical mechanical pulp is improved, the subsequent paper pulp performance is ensured, the pulping cost is saved, and the emission of pollutants is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of pulping process, in particular to a pretreatment method for improving the alkali impregnation yield of fiber raw material by heat treatment. BACKGROUND

[0002] With the continuous increase of chemi-mechanical pulp production capacity, domestic wood resources are in short supply. Large-scale chemi-mechanical pulp production lines are difficult to ensure stable supply of fiber raw materials, and have to use a large amount of young wood, branch wood, small-diameter wood and processing residues, etc. These raw materials are still in the growth period of the life cycle, and contain a large amount of lignin precursors (small molecule water-soluble phenylpropanoid structure monomers and polymers) and hemicellulose, cellulose precursors (small molecule water-soluble polysaccharides, monosaccharide molecules) in the cell cavity of the plant body when the life activity stops. (Jiaotang, Beiping Zhu, Wenliang Guo, et al. Study on the antioxidant activity of hot water extractives of three kinds of lignocellulosic materials [J]. China pulp and paper, 2024, 39(03): 63-70), these precursors are rich in active groups, have small molecular weight and relatively unstable structure, which not only increases the consumption of chemicals in the pulping process, but also increases the pollution load of pulping wastewater.

[0003] Pre-impregnation is a key step in the process of chemi-mechanical pulp production, and its mechanism is to use the nucleophilicity of hydroxide to moderately destroy various types of linkages in fiber raw materials, so as to achieve the purpose of swelling and softening the fiber raw materials. Otherwise, the fiber raw materials that are too hard will be cut off during the subsequent disc mill processing, affecting the strength of the subsequent pulp. In the pre-impregnation process, the pulp yield is inevitably lost. The pre-impregnation extract mainly includes the small molecule precursors originally contained in the raw materials as described above, and the water-soluble small molecules formed after the reaction of the relatively unstable lignin structure with sodium hydroxide. At present, the increase of pulp yield is mainly realized by reducing the chemical dosage of alkali pre-impregnation, but due to the limitation of the subsequent process on the strength index of the pulp, the adjustment range of the chemical dosage is limited. SUMMARY

[0004] The technical problem to be solved by the present application is to provide a pretreatment method for improving the alkali impregnation yield of fiber raw material by heat treatment, which solves the problems of the prior art.

[0005] The various linkages present in the fiber raw material are mainly carbon-carbon bonds and carbon-oxygen ether bonds, both of which can be synthesized by free radical condensation reaction. If the main structure of the fiber raw material (lignin, cellulose and hemicellulose) and various precursor small molecules can be excited into free radicals by mild heat treatment, and the free radical condensation reaction is initiated during the cooling process, the originally water-soluble small molecules can be stably connected to the main structure of the fiber raw material, the mass loss in the pre-impregnation process can be reduced, and the pulp yield can be improved. Based on this principle, the present application activates various groups or active sites in the extractives (cellulose, hemicellulose and lignin precursors) and the main structure of the fiber raw material by short-time and relatively mild heat treatment of the pulp, so that free radicals are formed, and the free radical condensation reaction is initiated during the cooling process. The condensation reaction establishes the linkages between various precursor small molecules and the main structure of the fiber raw material, so that these originally water-soluble small molecules become difficult to dissolve, thereby achieving the purpose of increasing the pulp yield, thereby reducing the cost of pulping and increasing the profit of enterprises.

[0006] In order to solve the above technical problems, the present application discloses a method for improving the alkali impregnation yield of fiber raw material, characterized in that after washing and dewatering the fiber raw material, at least one dry heat treatment is carried out on the washed and dewatered fiber raw material before alkali impregnation, the treatment temperature is 105-130 DEG C, and the total treatment time is 10-60 min. The heat treatment temperature is very important for the alkali treatment yield and the subsequent grinding energy consumption and pulp uniformity, because the glass transition temperature of lignin structure is about 135 DEG C, and exceeding this temperature will cause the lignin in the fiber raw material to become a liquid fluid, which may be excessively enriched in some parts. After the heat treatment is completed, the temperature is lower than 135 DEG C, which will re-condense, resulting in excessive lignin on the outer layer of the microfibril of the fiber raw material, which will increase the subsequent grinding energy consumption and affect the uniformity of the stress of the pulp. At the same time, the degree of heat treatment cannot be excessive, otherwise the free radical condensation reaction will be too much, which will cause the carbonization or even combustion of the fiber raw material, and qualified pulp cannot be prepared. Due to the large difference in the structure of the fiber raw material, the optimal value of the heat treatment degree of each raw material needs to be designed and optimized by experiment. Generally, the pulp yield before and after heat treatment (i.e. the ratio of the mass difference after heat treatment to the original mass, because the free radical condensation reaction mainly forms ether bonds in air atmosphere, so the mass change is positive) should not be higher than 105%.

[0007] Preferably, the dry heat treatment is any one or a combination of hot air drying, baking and infrared heat treatment.

[0008] Preferably, the dry heat treatment is any one or a combination of hot air drying, baking and infrared heat treatment.

[0009] The fiber raw material is any one or several of eucalyptus, poplar, acacia, pine and bamboo.

[0010] In one embodiment, the step of alkali impregnation is that the dry heat pretreated pulp is subjected to alkali impregnation under the condition of 20% pulp consistency based on the absolute dry pulp, the amount of sodium hydroxide is 30 kg / t of the absolute dry pulp, the reaction temperature is 95°C, and the reaction time is 1h.

[0011] The steps of the above alkali impregnation treatment, subsequent pulping treatment and papermaking are all conventional chemical mechanical method pulping processes, and the process parameters are different according to the structure of the raw material. The present method only lists the conventional operation.

[0012] The present application further provides a papermaking method, characterized in that comprising the following steps:

[0013] (1) screening, washing and dewatering the fiber raw material;

[0014] (2) subjecting the raw material obtained in step (1) to at least one dry heat treatment, the treatment temperature is 105-130°C, and the total treatment time is 10-60min;

[0015] (3) subjecting the fiber raw material obtained in step (2) to alkali impregnation treatment, the treatment condition is that the dry heat pretreated pulp is subjected to alkali impregnation under the condition of 20% pulp consistency based on the absolute dry pulp, the amount of sodium hydroxide is 30 kg / t of the absolute dry pulp, the reaction temperature is 95°C, and the reaction time is 1h;

[0016] (4) subjecting the alkali impregnated pulp obtained in step (3) to high consistency disc mill grinding under the condition of 20% to obtain a coarse pulp, subjecting the coarse pulp to secondary alkali treatment under the condition of 20% pulp consistency, the amount of sodium hydroxide is 50 kg / t, the reaction temperature is 95°C, and the reaction time is 1h. After the reaction, the dissolved substance is washed and subjected to medium consistency disc mill treatment under the condition of 10% pulp consistency to grind to a Canadian freeness of about 300mL CSF to obtain a fine pulp;

[0017] (5) washing the fine pulp obtained in step (4) and then performing papermaking.

[0018] 7. The papermaking method according to claim 6, characterized in that in step (2), the dry heat treatment is any one or a combination of several of hot air drying, baking and infrared heat treatment.

[0019] 8. The papermaking method according to claim 6, characterized in that in step (2), the washed and dewatered fiber raw material is subjected to several dry heat treatments, the material is taken out after each treatment for 5-8min, and then subjected to the next dry heat treatment after being uniformly stirred.

[0020] 9. The papermaking method according to claim 6, wherein the fiber raw material in step (2) is any one or more of eucalyptus, poplar, acacia, pine and bamboo.

[0021] Beneficial effects: The method of the present application, under the condition of no chemical modification, only uses relatively mild heat treatment, as much as possible to establish stable connection between the precursor small molecules originally in the cell cavity and the main structure of the fiber raw material through free radical condensation, so as to improve the alkali impregnation yield of the pulp, ensure the subsequent paper pulp performance while saving the cost of pulping, and reduce the emission of pollutants. BRIEF DESCRIPTION OF DRAWINGS

[0022] The above and / or other aspects of the present application will become apparent and more readily appreciated from the following description, taken in conjunction with the accompanying drawings, in which:

[0023] Figure 1 Temperature optimization curve of pulp yield of green bamboo at hydrothermal pretreatment for 30 min (comparative example 1);

[0024] Figure 2 Time optimization curve of pulp yield of black poplar at hot air pretreatment of 110℃ (comparative example 2);

[0025] Figure 3 Temperature and time optimization curve of pulp yield of acacia mangium at hot air pretreatment (example 1);

[0026] Figure 4 Temperature and time optimization curve of pulp yield of eucalyptus grandis at baking pretreatment (example 2);

[0027] Figure 5 Temperature and time optimization curve of pulp yield of black poplar at infrared heat treatment (example 3);

[0028] Figure 6 Temperature and time optimization curve of pulp yield of green bamboo at baking pretreatment (example 4);

[0029] Figure 7 Temperature and time optimization curve of pulp yield of larch at hot air pretreatment (example 5). DETAILED DESCRIPTION

[0030] A method for improving the pulp yield of chemical mechanical pulp by dry heat pretreatment, comprising the following steps:

[0031] (1) Pretreatment of fiber raw material (including but not limited to eucalyptus, poplar, acacia, pine, bamboo and other chemical mechanical pulp raw materials): The fiber raw material is screened, washed and dehydrated.

[0032] (2) Dry heat treatment of fiber raw material: dry heat pretreatment methods include, but are not limited to, hot air drying, baking, and infrared heat treatment; the pretreatment process can be performed in multiple times, and one heat treatment method or multiple methods can be used alone or in combination, the heat treatment temperature is 105-130°C, and the reaction time is 10-60 min.

[0033] (3) Alkali impregnation treatment of fiber raw material: alkali impregnation is performed on the dry heat pretreated pulp at a pulp consistency of 20% (based on the absolute dry pulp, the same below), the sodium hydroxide dosage is 30 kg / t o.d. pulp (kg / t of absolute dry pulp, the chemical dosage unit is abbreviated as kg / t below), the reaction temperature is 95°C, and the reaction time is 1 h. After the reaction, the dissolved substance is washed, and the pulp yield A is calculated after the reaction.

[0034]

[0035] wherein M1 is the absolute dry weight of the material after pre-impregnation, g; M0 is the absolute dry weight of the material before pre-impregnation, g.

[0036] (4) Subsequent treatment of fiber raw material after chemical mechanical pulping: the pulp after alkali pre-impregnation is ground to a Canadian freeness of about 550 mL CSF using a high consistency disc refiner at a pulp consistency of 20% to obtain a coarse pulp. The coarse pulp is subjected to secondary alkali treatment at a pulp consistency of 20%, the sodium hydroxide dosage is 50 kg / t, the reaction temperature is 95°C, and the reaction time is 1 h. After the reaction, the dissolved substance is washed, and the pulp is subjected to medium consistency disc refining at a pulp consistency of 10% to grind it to a Canadian freeness of about 300 mL CSF to obtain a fine pulp.

[0037] (5) Papermaking and performance testing:

[0038] After the fine pulp is washed, papermaking and tensile strength testing are performed.

[0039] Papermaking: according to GB 7981-1999, Laboratory Preparation of Paper Sheet from Pulp, Conventional Sheet Former Method;

[0040] Quantitative: according to GB / T 451.2-2002, Determination of the Mass Per Unit Area of Paper and Paperboard;

[0041] Tensile strength: according to GB / T 12914-2002, Determination of Tensile Strength of Paper and Paperboard (Constant Rate of Extension Method).

[0042] The steps (3), (4), and (5) in the above method are all conventional mechanical pulping processes, and the process parameters will be different according to the structure of the raw material. The present method only lists the conventional operation.

[0043] The advantageous effects of the present application will be described below by means of specific examples.

[0044] Example 1

[0045] Using Acacia mangium as raw material, after being treated by a chipper and passing through a wood chip screen, wood chips with a length of 50 mm to 100 mm, a width of 2.5 mm to 10 mm, and a thickness of 4.5 mm to 6 mm were obtained. After washing and dewatering, the wood chips were dried by hot air at 120°C for 30 min. During the drying process, the material was taken out every 5 min, stirred evenly, and then continuously sent into the hot air dryer. The final heat treatment yield was 103.76%. The obtained material was subjected to pre-impregnation (alkali impregnation was performed on the pulp after dry heat pretreatment under the condition of a pulp consistency of 20% (based on absolute dry pulp), the sodium hydroxide dosage was 30 kg / t, the reaction temperature was 95°C, and the reaction time was 1 h). The pulp after alkali impregnation was ground to a Canadian freeness of 550 mL CSF using a high-consistency disc grinder under the condition of a pulp consistency of 20% to obtain a coarse pulp. The coarse pulp was subjected to secondary alkali treatment (sodium hydroxide dosage was 50 kg / t, reaction temperature was 95°C, and reaction time was 1 h) under the condition of a pulp consistency of 20%, and the yield of the material was 88.80%. After the reaction was completed, the dissolved material was washed and subjected to medium-consistency disc grinding under the condition of a pulp consistency of 10% to grind it to a Canadian freeness of about 300 mL CSF to obtain fine pulp. After washing the fine pulp, papermaking was performed to obtain hand sheets with a tensile strength of 0.69 kN / m. The raw material without hot air drying treatment had an alkali treatment yield of 85.72% and a tensile strength of 0.68 kN / m. The yield was increased by 3.59%, and the strength was almost unchanged.

[0046] Example 2

[0047] Using Eucalyptus dura as raw material, after the chipper treatment, the wood chips are obtained by wood chip screen with length of 50mm-100mm, width of 2.5mm-10mm, and thickness of 4.5mm-6mm. After washing and dehydrating, the wood chips are treated by 110°C drying for 50min, and every 5min, the material is taken out, stirred and then put into the drying oven. The final heat treatment yield is 102.12%. The obtained material is subjected to alkali pre-impregnation (under the condition of pulp consistency of 20% (based on absolute dry pulp), the dry heat pretreated pulp is subjected to alkali impregnation, the sodium hydroxide dosage is 30kg / t, the reaction temperature is 95°C, and the reaction time is 1h). The alkali impregnated pulp is ground by high consistency disc grinder to Canadian freeness of 550mL CSF under the condition of 20% pulp consistency, to obtain the coarse pulp. The coarse pulp is subjected to secondary alkali treatment under the condition of 20% pulp consistency (the sodium hydroxide dosage is 50kg / t, the reaction temperature is 95°C, and the reaction time is 1h), and the material yield is 85.54%. After the reaction, the dissolved material is washed, and the medium consistency disc grinding is performed under the condition of 10% pulp consistency, to grind the material to Canadian freeness of about 300mL CSF, to obtain the fine pulp. After washing the fine pulp, papermaking is performed, and the tensile strength of the obtained hand sheet is 0.84kN / m. The raw material without drying treatment has alkali treatment yield of 80.39%, and the tensile strength is 0.84kN / m, the yield is increased by 6.41%, and the strength is unchanged.

[0048] Example 3

[0049] Using Populus nigra as raw material, after the chipper treatment, the wood chips are obtained by wood chip screen with length of 50mm-100mm, width of 2.5mm-10mm, and thickness of 4.5mm-6mm. After washing and dehydrating, the wood chips are treated by 115°C infrared drying for 50min, and every 10min, the material is taken out, stirred and then put into the infrared lamp box. The final heat treatment yield is 102.55%. The obtained material is subjected to alkali pre-impregnation (under the condition of pulp consistency of 20% (based on absolute dry pulp), the dry heat pretreated pulp is subjected to alkali impregnation, the sodium hydroxide dosage is 30kg / t, the reaction temperature is 95°C, and the reaction time is 1h). The alkali impregnated pulp is ground by high consistency disc grinder to Canadian freeness of 550mL CSF under the condition of 20% pulp consistency, to obtain the coarse pulp. The coarse pulp is subjected to secondary alkali treatment under the condition of 20% pulp consistency (the sodium hydroxide dosage is 50kg / t, the reaction temperature is 95°C, and the reaction time is 1h), and the material yield is 89.34%. After the reaction, the dissolved material is washed, and the medium consistency disc grinding is performed under the condition of 10% pulp consistency, to grind the material to Canadian freeness of about 300mL CSF, to obtain the fine pulp. After washing the fine pulp, papermaking is performed, and the tensile strength of the obtained hand sheet is 1.21kN / m. The raw material without hot air drying treatment has alkali treatment yield of 87.65%, and the tensile strength is 1.22kN / m, the yield is increased by 2.21%, and the strength is almost unchanged.

[0050] Example 4

[0051] Using green bamboo as raw material, after being treated by a chipper and passing through a chip screen, qualified wood chips with a length of 50mm-100mm, a width of 2.5mm-10mm, and a thickness of 4.5mm-6mm were obtained. After washing and dewatering, the wood chips were baked at 110°C for 40min, during which the material was taken out every 5min, stirred evenly, and then continuously fed into the oven. The final heat treatment yield was 101.98%. The obtained material was subjected to alkali pre-impregnation (alkali impregnation of the dry heat pretreated pulp at a pulp consistency of 20% (based on absolute dry pulp), with a sodium hydroxide dosage of 30kg / t, a reaction temperature of 95°C, and a reaction time of 1h). The alkali-impregnated pulp was ground to a Canadian freeness of 550mL CSF using a high-consistency refiner at a consistency of 20% to obtain a coarse pulp. The coarse pulp was subjected to secondary alkali treatment at a consistency of 20% (sodium hydroxide dosage of 50kg / t, reaction temperature of 95°C, and reaction time of 1h), and the yield of the material was 90.76%. After the reaction was completed, the dissolved substances were washed and subjected to medium-consistency refiner treatment at a consistency of 10% to grind the pulp to a Canadian freeness of about 300mL CSF to obtain fine pulp. After washing the fine pulp, papermaking was performed, and the hand sheet obtained had a tensile strength of 0.83kN / m. The raw material without baking treatment had an alkali treatment yield of 87.82% and a tensile strength of 0.84kN / m, with a yield increase of 3.35% and almost no change in strength.

[0052] Example 5

[0053] Using larch as raw material, after the chipper processing, the wood chips are screened through the wood chip screen to obtain qualified wood chips with a length of 50mm-100mm, a width of 2.5mm-10mm, and a thickness of 4.5mm-6mm. After washing and dewatering the wood chips, hot air drying is used at 120℃ for 60min, wherein every 5min of processing, the material is taken out, stirred evenly, and then continuously sent into the hot air box. The final heat treatment yield is 101.30%. The obtained material is subjected to alkali pre-impregnation (alkali impregnation of the pulp material after dry heat pretreatment under the condition of pulp consistency of 20% (based on absolute dry pulp), sodium hydroxide dosage of 30kg / t, reaction temperature of 95℃, and reaction time of 1h), and the alkali-impregnated pulp material is ground to Canadian freeness of 550mL CSF using a high-consistency disc grinder under the condition of 20% to obtain the coarse pulp. The coarse pulp is subjected to secondary alkali treatment (sodium hydroxide dosage of 50kg / t, reaction temperature of 95℃, and reaction time of 1h) under the condition of pulp consistency of 20%, and the material yield is 85.40%. After the reaction is completed, the dissolved material is washed and subjected to medium-consistency disc grinding under the condition of 10% pulp consistency to grind to Canadian freeness of about 300mL CSF to obtain fine pulp. After washing the fine pulp, papermaking is performed to obtain hand sheets with a tensile strength of 1.34kN / m. The raw material without hot air drying treatment has an alkali treatment yield of 81.83% and a tensile strength of 1.34kN / m, and the yield is increased by 4.36% and the strength remains unchanged.

[0054] The present application provides a kind of to improve the yield of fiber raw material alkali impregnation mentality and method, the method and approach for specifically realizing this technical scheme are many, above-mentioned only is the preferred embodiment of the present application, it should be pointed out, for the ordinary skill in the art of this technical field, without departing from the principle of the present application, can also make several improvements and refinements, these improvements and refinements also should be considered as the protection scope of the present application. The components not explicitly described in the embodiment can be realized by existing technology.

[0055] Comparative Example 1

[0056] Comparative Example 1 uses green bamboo as raw material, which is processed by chipper and then passed through a chip screen to obtain qualified wood chips with length of 50mm-100mm, width of 2.5mm-10mm and thickness of 4.5mm-6mm. After washing and dewatering, the wood chips are treated by hydrothermal reaction at 130°C for 30min, and the final heat treatment yield is 98.77%. The obtained material is pre-impregnated (the hydrothermally pretreated pulp is impregnated with alkali under the condition of pulp consistency of 20% (based on absolute dry pulp, the same below), the amount of sodium hydroxide is 30kg / t, the reaction temperature is 95°C, and the reaction time is 1h). The alkali-impregnated pulp is ground to Canadian freeness of 550mL CSF using a high consistency refiner under the condition of 20% to obtain coarse pulp. The coarse pulp is subjected to secondary alkali treatment (the amount of sodium hydroxide is 50kg / t, the reaction temperature is 95°C, and the reaction time is 1h) under the condition of 20% to obtain a material yield of 87.30%. After the reaction, the dissolved substance is washed and subjected to medium consistency refiner treatment under the condition of 10% to grind it to Canadian freeness of about 300mL CSF to obtain fine pulp. After washing the fine pulp, papermaking is performed to obtain hand sheets with tensile strength of 0.85kN / m. The raw material without hydrothermal treatment has an alkali treatment yield of 87.82% and a tensile strength of 0.84kN / m, and the yield and strength are almost unchanged.

[0057] It can be seen that, by using hydrothermal (i.e. non-dry heat treatment) to pretreat the fiber raw material, because the water content in the system is too high, the heat of heat treatment is used for water evaporation, which cannot effectively stimulate free radicals, and thus cannot form stable connection between the precursor small molecules and the fiber raw material, so as to increase the yield of pulping.

[0058] Comparative Example 2

[0059] Comparative Example 3 used black poplar as raw material, which was processed by chipper and then passed through a wood chip screen to obtain qualified wood chips with a length of 50 mm to 100 mm, a width of 2.5 mm to 10 mm, and a thickness of 4.5 mm to 6 mm. After washing and dewatering, the wood chips were dried by hot air at 110 °C for 5 min, and the final heat treatment yield was 99.27%. The obtained material was subjected to pre-impregnation (the pulp after hot air drying was subjected to alkali impregnation at a pulp consistency of 20% (based on absolute dry pulp, the same below), the amount of sodium hydroxide was 30 kg / t, the reaction temperature was 95 °C, and the reaction time was 1 h). The pulp after alkali impregnation was ground by a high consistency refiner to a Canadian freeness of 550 mL CSF at a pulp consistency of 20% to obtain a coarse pulp, and the coarse pulp was subjected to secondary alkali treatment (the amount of sodium hydroxide was 50 kg / t, the reaction temperature was 95 °C, and the reaction time was 1 h) at a pulp consistency of 20%, and the yield of the material was 87.01%. After the reaction, the dissolved substance was washed and subjected to medium consistency refiner treatment at a pulp consistency of 10% to grind it to a Canadian freeness of about 300 mL CSF to obtain fine pulp. After washing the fine pulp, papermaking was performed to obtain hand sheets with a tensile strength of 1.20 kN / m. The raw material without hydrothermal treatment had a yield of 87.65% after alkali treatment, and the tensile strength was 1.22 kN / m, and the yield and strength were almost unchanged.

[0060] As can be seen, when the treatment time is too short, the lower heat treatment temperature is not enough to provide sufficient energy to the fiber raw material to excite various types of precursor small molecules into free radicals, so that the free radical condensation reaction cannot occur, and the pulp yield and paper strength are not significantly changed.

Claims

1. A method for improving the yield of alkali impregnation of a fiber raw material, characterized by, After the fiber raw material is screened to obtain qualified wood chips, the fiber raw material after washing and dehydration is subjected to at least one dry heat treatment before alkali impregnation, the treatment temperature is 105 DEG C ~ 130 DEG C, and the total treatment time is 30 min ~ 60 min; the fiber raw material after washing and dehydration is subjected to several times of dry heat treatment, the material is taken out after each treatment for 5 min ~ 8 min, and the next dry heat treatment is carried out after uniform stirring; the fiber raw material is any one or several of eucalyptus, poplar, acacia, pine and bamboo.

2. The method of claim 1, wherein, The dry heat treatment is any one or a combination of several of hot air drying, baking and infrared heat treatment.

3. The method of claim 1, wherein, The alkali impregnation step is: alkali impregnation of the dry heat pretreated pulp under the condition that the pulp consistency is 20% based on the absolute dry pulp, the sodium hydroxide dosage is 30 kg / t of absolute dry pulp, the reaction temperature is 95 DEG C, and the reaction time is 1 h.

4. A papermaking process characterized by, Comprising the following steps: (1) screening, washing and dewatering the fiber raw material; (2) subjecting the raw material obtained in step (1) to at least one dry heat treatment, the treatment temperature is 105 DEG C ~ 130 DEG C, and the total treatment time is 30 min ~ 60 min; (3) alkali impregnation treatment of the fiber raw material obtained in step (2), the treatment conditions are: alkali impregnation of the dry heat pretreated pulp under the condition that the pulp consistency is 20% based on the absolute dry pulp, the sodium hydroxide dosage is 30 kg / t of absolute dry pulp, the reaction temperature is 95 DEG C, and the reaction time is 1 h; (4) using a high consistency disc grinder to grind the alkali impregnation treated pulp obtained in step (3) to a Canadian freeness of 550 mL CSF under the condition of 20% to obtain a rough pulp, and then performing secondary alkali treatment on the rough pulp under the condition of 20% pulp consistency, the sodium hydroxide dosage is 50 kg / t, the reaction temperature is 95 DEG C, and the reaction time is 1 h, after the reaction, the dissolved substance is washed and cleaned, and a medium consistency disc grinding treatment is performed under the condition of 10% pulp consistency to grind it to a Canadian freeness of 300 mL CSF to obtain a fine pulp; (5) washing the fine pulp obtained in step (4) and then performing papermaking; In step (2), the fiber raw material after washing and dehydration is subjected to several times of dry heat treatment, the material is taken out after each treatment for 5 min ~ 8 min, and the next dry heat treatment is carried out after uniform stirring; the fiber raw material is any one or several of eucalyptus, poplar, acacia, pine and bamboo.

5. The papermaking process according to claim 4, characterized in that, In step (2), the dry heat treatment is any one or a combination of several of hot air drying, baking and infrared heat treatment.

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