A method for producing lyocell fibers using papermaking bamboo pulp

Abstract

The application discloses a method for producing lyocell fibers by using papermaking bamboo pulp, and belongs to the field of lyocell fiber production, wherein the preparation method of pulp used as raw material for producing lyocell fibers comprises the following steps: once impregnation by using papermaking bamboo pulp as raw material, twice impregnation by adding depolymerization auxiliary agent nickel salt and resin auxiliary agent, washing, ash removal, press drying and the like; the application can reduce the polymerization degree of bamboo pulp raw material, remove resin, reduce wastewater discharge, reduce equipment investment and equipment land occupation by adding two special catalytic auxiliary agents; the use of bamboo pulp as raw material can effectively reduce production cost, solve the problem of raw material shortage, and broaden the types of raw materials; the application can obviously reduce the amount of wastewater, further improve the content of methyl cellulose, further improve the brightness of pulp, and further reduce the content of hemicellulose.

Description

Technical Field

[0001] This invention relates to the field of lyocell fiber production, and more particularly to a method for producing lyocell fiber using papermaking bamboo pulp. Background Technology

[0002] Cotton, polyester, and cellulose fiber are the three main materials used in the textile industry. However, cotton's development is significantly limited by its competition with grain for land. Polyester, on the other hand, is derived from petroleum, making its entire production process subject to environmental constraints. Furthermore, environmental governance has long plagued the domestic cellulose fiber industry, with the pollution from viscose fiber's "three wastes" (waste gas, wastewater, and solid waste) and water consumption becoming bottlenecks for industry development. Lyocell fiber, produced using an N-methylmorpholine-N-oxide (NMMO) aqueous solution as a solvent, dissolves cellulose pulp and then spins it, employing a solvent method to produce regenerated cellulose fiber without chemical reactions. The NMMO solvent used in lyocell fiber production is environmentally friendly, can be recycled and refined for reuse, and the entire production system forms a closed-loop recycling system with no waste discharge and no environmental pollution, achieving clean production of regenerated cellulose fiber.

[0003] In the production of lyocell, pulp is first swollen and dissolved into a solution (i.e., dissolving pulp) before subsequent production. The properties of the pulp are crucial to lyocell production and the quality of the fiber products. Dissolving pulp raw materials are widely available; most biomass materials with high lignocellulose content can be used as raw materials for dissolving pulp production. Currently, due to the shortage of domestic timber resources, the inconvenience of large-scale logging, and production cost constraints, the supply of high-quality dissolving pulp in China is insufficient. Currently, domestic lyocell fiber manufacturers all use imported wood dissolving pulp as raw material. However, China is a major bamboo-producing country with widely distributed and rapidly growing bamboo resources. Therefore, promoting the application of bamboo dissolving pulp in the lyocell fiber industry can effectively solve the raw material sourcing problem.

[0004] To use bamboo pulp in lyocell production, the following difficulties generally need to be overcome: Bamboo pulp fiber has a low α-cellulose (also known as "methylcellulose") content, generally around 80%; a high degree of polymerization, generally around 800-1000; a high ash content, generally around 0.2-0.3 wt%; and a high resin content (see Table 1, which mainly includes four components: resin acids, fatty acids, unsaponifiables, and esters). Among these, resin acids and fatty acids have a negative impact on viscose production, and a high proportion of these substances can be found in spinneret deposits. Unsaponifiables and esters cause difficulties in viscose filtration; when the resin content is 1.4%, the filtration time is 1.45-3.4 hours; while when the resin content is 0.12 wt%, the filtration time is shortened to 0.5-1 hour. Currently, the industry-recognized performance indicators for lyocell-specific pulp are: degree of polymerization 450-600, ISO whiteness ≥92%, methylcellulose ≥90%, R... 10 ≥90%, R 18 ≥93%, R 18 -R 10 The content of bamboo pulp used in papermaking is ≥2.8%, ash ≤0.1%, Fe ≤2.0ppm, Ca ≤50ppm, and Mg ≤50ppm. Therefore, bamboo pulp used in papermaking requires relevant treatment for lyocell production.

[0005] To address the aforementioned issues, there have been numerous reports on the preparation of Lyocell-specific pulp using papermaking bamboo pulp. Examples include Chinese patent applications CN1383965A, CN1190531C, CN1544223A, CN1760412A, CN18511115A, and CN112853796A. These existing reports generally suffer from the following problems:

[0006] (1) Pretreatment of pulp often requires special equipment, which is expensive; (2) The process is complicated and cumbersome, often requiring multiple washing steps, generating a large amount of alkaline and COD wastewater, resulting in high treatment costs and environmental pressure; (3) Repeated pressing is often required, consuming electricity, increasing factory area, and increasing equipment; (4) The processing temperature is high, for example, the processing temperature of CN112853796A is 150-175℃, resulting in high energy consumption. Summary of the Invention

[0007] The purpose of this invention is to provide a method for producing lyocell fiber using papermaking bamboo pulp, in order to solve the above-mentioned problems.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows: a method for producing lyocell fiber using papermaking bamboo pulp, comprising swelling, dissolving, filtering, and spinning the pulp, characterized in that the pulp is prepared by the following method:

[0009] (1) Using papermaking bamboo pulp as raw material, the papermaking bamboo pulp is impregnated in a mixing tank. The concentration of the papermaking bamboo pulp is <5wt%, the alkali content of the pulp is 50-110g / l, the temperature is 40-60℃, the impregnation time is 30-60min, and then it is pressed to control the water content of the pulp to be below 50wt%.

[0010] (2) Soak the pulp after pressing in step (1) in a mixing tank, add 5-10 ppm of depolymerization aid nickel salt and 5-10 ppm of resin additive by weight of oven-dry pulp respectively, pulp concentration < 5 wt%, temperature 40-60℃, time 30-60 min, and press the pulp after soaking to control the water content of the pulp to be below 50 wt%.

[0011] It should be noted that "oven-dry pulp" refers to papermaking bamboo pulp with a water content of 0 wt%, while general pulp contains 5-10 wt% water.

[0012] (3) Wash the pulp porridge after pressing in step (3) until it is neutral;

[0013] (4) Place the washed porridge from step (3) into a mixing tank, add oxalic acid and iron removal agent (such as sodium hexametaphosphate), control the pH of the porridge to 1-2, the porridge concentration to 5-10 wt%, the temperature to 40-60℃, and the stirring time to 30-60 min. After stirring, press the porridge to control the water content to be below 50 wt%. Wash the pressed porridge with water until it is neutral. The water used is preferably demineralized water.

[0014] It should be noted that "deionized water" refers to the finished water obtained after removing suspended solids, colloids, and inorganic cations and anions from water using various water treatment processes.

[0015] (5) The pulp is dried to obtain pulp for the production of lyocell fiber.

[0016] Through extensive experimentation, the inventors of this invention employed nickel salt as a polymerization depolymerization aid. The nickel salt in this invention acts only as a catalyst, providing empty orbitals as a transition metal, generating feedback bonds, etc., ultimately leading to a reduction in the activation energy of the reaction. This allows the degree of polymerization of bamboo pulp raw materials to be reduced and resin to be removed without requiring a relatively harsh environment.

[0017] The depolymerization aid can also be added in step (1), which is mainly to remove hemicellulose. The effect of the depolymerization aid will be weakened after it is added in this step.

[0018] As a preferred technical solution: in step (2), the depolymerization aid nickel salt is selected from at least one of nickel chloride and nickel sulfate.

[0019] As a preferred technical solution: In step (2), the resin removal agent is an ether. The resin removal agent can remove resin from the pulp and dissolve it.

[0020] As a further preferred technical solution: the ether is diethyl ether.

[0021] As a preferred technical solution, the stirring speed in steps (1), (2), and (4) is 70-150 rpm, and more preferably 120 rpm.

[0022] As a preferred technical solution: In step (3), the washing method involves conveying the slurry to the mixing and washing tank via a conveyor belt for 1-2 hours. The degree of depolymerization is controlled and adjusted by controlling the conveying time.

[0023] As a preferred technical solution, the alkaline solution removed by the press in step (4) is introduced into a nanofiltration system to separate low molecular weight monosaccharides and oligosaccharides. The purpose is to purify the alkaline solution containing waste alkali and extract the valuable components (xylooligosaccharides).

[0024] Compared with existing technologies, the advantages of this invention are as follows: By adding two special catalytic aids, this invention can reduce the degree of polymerization of bamboo pulp raw materials and remove resin without the need for a harsh environment, thereby reducing wastewater discharge, equipment investment, and equipment footprint; the use of bamboo pulp as raw material can effectively reduce production costs, solve the problem of raw material scarcity, and broaden the types of raw materials that can be used; this invention can significantly reduce wastewater generation, further increase cellulose content, further increase pulp whiteness, and further reduce hemicellulose content; this invention can also solve the negative impacts of resin and polysaccharides during dissolution, filtration, and spinning.

[0025] Table 1 shows a comparison of the performance of the raw materials before and after treatment using the method of this invention.

[0026] Table 1 Comparison of performance indicators before and after the treatment of this invention.

[0027] project Before processing After processing Degree of aggregation (DP) 800～1000 450～510 ISO whiteness / % 78-85 93.1 <![CDATA[R 18 / %]]> 82-88 95.2 <![CDATA[R 10 / %]]> 78-85 90.3 α-cellulose / wt% 78-87 92.6 Ash content / wt% 0.2-0.3 0.1 Iron content (mg / L) 10-30 5 Calcium content (mg / L) 10-50 30 Magnesium content (mg / L) 10-50 10 Resin content / % 0.05-0.1 0.03 Detailed Implementation

[0028] The present invention will be further described below with reference to embodiments.

[0029] Example 1

[0030] A method for producing lyocell fiber using papermaking bamboo pulp includes the following steps:

[0031] (1) Place the papermaking bamboo pulp board into the mixing tank, control the pulp concentration <5wt%, total alkali: 10wt%, control the stirring speed at 120rpm, control the pulp temperature at 40℃, and stir for 30min; after stirring, use a press to press the pulp.

[0032] (2) Soak the pressed pulp in a depolymerization tank, control the pulp concentration to <5wt%, add nickel chloride (addition amount: 5ppm (relative to oven-dry pulp)), add diethyl ether (addition amount: 6ppm (relative to oven-dry pulp)), control the stirring speed to 120rpm, control the pulp temperature to 40℃, stir for 30min, after stirring, use a press to press the pulp, control the moisture content to be less than 50wt%;

[0033] (3) The pressed pulp is conveyed to the washing and mixing tank by a conveyor belt. The conveying time shall not exceed 1 hour. Deionized water is added to wash the pulp until it is neutral (pH=7). After washing, the pulp is pressed to control the moisture content to be less than 50wt%.

[0034] (4) Put the pressed pulp into a mixing tank, add oxalic acid and sodium hexametaphosphate as an iron removal agent, and control the pH to about 1.5; control the stirring speed to 120 rpm, control the temperature of the pulp to 40℃, and stir for 30 minutes; after stirring, use a press to press the pulp.

[0035] (5) The above-mentioned press removes the alkaline solution and enters the nanofiltration system to separate small molecular weight monosaccharides and oligosaccharides.

[0036] (6) The pulp is air-dried and hot-dried to control the moisture content to <10wt% to obtain processed pulp, which is then fed into the Lyocell fiber production line and mixed with NMMO solvent. After swelling, dissolving, filtering and spinning processes, Lyocell fiber is produced.

[0037] Table 2 shows a comparison of the performance of the raw materials before treatment using the method of this embodiment and the pulp after treatment in step (6).

[0038] Table 2 Comparison of performance indicators before and after treatment in Example 1

[0039] project Before processing After processing Degree of aggregation (DP) 1000 510 ISO whiteness / % 85.2 93.2 <![CDATA[R 18 / %]]> 88.1 95.2 <![CDATA[R 10 / %]]> 85.1 90.4 α-cellulose / % 87.2 92.3 Ash content / % 0.32 0.12 Iron content (mg / L) 30 5 Calcium content (mg / L) 50 30 Magnesium content (mg / L) 50 10 Resin content / % 0.1 0.03

[0040] The measurement methods used in the various tests of this invention are common methods in this industry, such as:

[0041] R 18 / R 10 FZ / T50010.4—2011

[0042] Ash content FZ / T50010.5—1998

[0043] Iron content FZ / T50010.6—1998

[0044] ISO Whiteness FZ / T50010.7—1998

[0045] Resin content FZ / T50010.8—1998

[0046] Calcium and magnesium ions FZ / T50010.8—1998.

[0047] Example 2

[0048] A method for producing lyocell fiber using papermaking bamboo pulp includes the following steps:

[0049] (1) Place the papermaking bamboo pulp board into the mixing tank, control the pulp concentration <5wt%, the total alkali 10wt%, control the stirring speed at 120rpm, control the pulp temperature at 50℃, and the stirring time at 40min. After stirring, use a press to press the pulp.

[0050] (2) Soak the pressed pulp in a depolymerization tank, control the pulp concentration to <5wt%, add nickel chloride (addition amount: 8ppm (for oven-dry pulp)), add diethyl ether (addition amount: 7ppm (for oven-dry pulp)), control the stirring speed to 120rpm, control the pulp temperature to 50℃, stir for 40min, after stirring, use a press to press the pulp, control the moisture content to be less than 50wt%;

[0051] (3) The pressed pulp is conveyed to the washing and mixing tank by a conveyor belt. The conveying time shall not exceed 1.5 hours. Deionized water is added to wash the pulp until it is neutral (pH=7). After washing, the pulp is pressed to control the moisture content to be less than 50wt%.

[0052] (4) Put the pressed pulp into a mixing tank, add oxalic acid and sodium hexametaphosphate as an iron removal agent, and control the pH to 1-2; control the stirring speed to 120 rpm, control the temperature of the pulp to 50℃, and stir for 40 min; after stirring, use a press to press the pulp.

[0053] (5) The above-mentioned press removes the alkaline solution and enters the nanofiltration system to separate small molecular weight monosaccharides and oligosaccharides.

[0054] (6) The pulp is air-dried and hot-dried to control the moisture content to <10% to obtain processed pulp, which is then fed into the Lyocell fiber production line and mixed with NMMO solvent. After swelling, dissolving, filtering and spinning processes, Lyocell fiber is produced.

[0055] Table 3 shows a comparison of the performance of the raw materials before treatment using the method of this embodiment and the pulp after treatment in step (6).

[0056] Table 3 Comparison of performance indicators before and after treatment in Example 2

[0057] project Before processing After processing Degree of aggregation (DP) 900 480 ISO whiteness / % 82.3 93.7 <![CDATA[R 18 / %]]> 85.6 95.6 <![CDATA[R 10 / %]]> 82.1 90.7 α-cellulose / % 82.2 92.3 Ash content / % 0.25 0.11 Iron content (mg / L) 20 5 Calcium content (mg / L) 30 30 Magnesium content (mg / L) 30 10 Resin content / % 0.08 0.03

[0058] Example 3

[0059] A method for producing lyocell fiber using papermaking bamboo pulp includes the following steps:

[0060] (1) Place the papermaking bamboo pulp board into the mixing tank, control the pulp concentration <5wt%, the total alkali 10%, control the stirring speed at 120rpm, control the pulp temperature at 60℃, and the stirring time at 60min. After stirring, use a press to press the pulp.

[0061] (2) Soak the pressed pulp in a depolymerization tank, control the pulp concentration to <5%, add nickel chloride (addition amount: 10ppm (for oven-dry pulp)), add diethyl ether (addition amount: 10ppm (for oven-dry pulp)), control the stirring speed to 120rpm, control the pulp temperature to 60℃, stir for 60min, after stirring, use a press to press the pulp, control the moisture content to be less than 50wt%;

[0062] (3) The pressed pulp is conveyed to the washing and mixing tank by a conveyor belt. The conveying time shall not exceed 2 hours. Deionized water is added to wash the pulp until it is neutral (pH=7). After washing, the pulp is pressed to control the moisture content to be less than 50%.

[0063] (4) Put the pressed pulp into a mixing tank, add oxalic acid and iron removal agent, and control the pH to 1-2; control the stirring speed to 120 rpm, control the temperature of the pulp to 60℃, and stir for 60 min; after stirring, use a press to press the pulp.

[0064] (5) The above-mentioned press removes the alkaline solution and enters the nanofiltration system to separate small molecular weight monosaccharides and oligosaccharides.

[0065] (6) The pulp is air-dried and hot-dried to control the moisture content to <10wt% to obtain processed pulp, which is then fed into the Lyocell fiber production line and mixed with NMMO solvent. After swelling, dissolving, filtering and spinning processes, Lyocell fiber is produced.

[0066] Table 4 shows a comparison of the performance of the raw materials before treatment using the method of this embodiment and the pulp after treatment in step (6).

[0067] Table 4 Comparison of performance indicators before and after treatment in Example 3

[0068] project Before processing After processing Degree of aggregation (DP) 800 450 ISO whiteness / % 78.1 93.5 <![CDATA[R 18 / %]]> 82.3 95.4 <![CDATA[R 10 / %]]> 78.2 90.3 α-cellulose / % 78.9 92.3 Ash content / % 0.21 0.11 Iron content (mg / L) 10 5 Calcium content (mg / L) 10 30 Magnesium content (mg / L) 10 10 Resin content / % 0.05 0.03

[0069] Comparative Example 1

[0070] This comparative example is based on Example 2, except that in step (2), the amount of nickel chloride added is changed from 8 ppm to 2 ppm, while the other raw materials and process conditions remain unchanged. The performance comparison of the raw materials before treatment and the pulp after treatment in step (6) using the method of this comparative example is shown in Table 5.

[0071] Comparative Example 2

[0072] This comparative example is based on Example 2, except that in step (2), the amount of nickel chloride added is changed from 8 ppm to 12 ppm, while the other raw materials and process conditions remain unchanged. The performance comparison of the raw materials before treatment and the pulp after treatment in step (6) using the method of this comparative example is shown in Table 5.

[0073] Comparative Example 3

[0074] This comparative example is based on Example 2, except that in step (2), the amount of ether added is changed from 7 ppm to 2 ppm, while the other raw materials and process conditions remain unchanged. The performance comparison of the raw materials before treatment and the pulp after treatment in step (6) using the method of this comparative example is shown in Table 5.

[0075] Comparative Example 4

[0076] This comparative example is based on Example 2, except that in step (2), the amount of ether added is changed from 7 ppm to 12 ppm, while the other raw materials and process conditions remain unchanged. The performance comparison of the raw materials before treatment and the pulp after treatment in step (6) using the method of this comparative example is shown in Table 5.

[0077] Comparative Example 5

[0078] This comparative example is based on Example 2, except that in step (2), the traditional depolymerization method is used (the traditional depolymerization method is: after alkali soaking, it is pressed and then naturally degraded in the air). The rest is the same as Example 2. The results are shown in Table 5.

[0079] Table 5 Comparison of performance indicators before and after treatment for each comparative example

[0080]

[0081] As can be seen from Table 5, if the amount of nickel chloride depolymerization aid added is too small, the degree of polymerization of the fiber will decrease only slightly, which cannot meet the pulp requirements for Lyocell fiber.

[0082] If the amount of nickel chloride, a depolymerization aid, is too high, the degree of polymerization of the fiber will be reduced significantly, and it will not be able to meet the minimum degree of polymerization requirement of 450 for lyocell fiber.

[0083] If the amount of ether added is too low, the resin content is only slightly removed. If the amount of ether added is further increased, the resin removal effect no longer increases significantly.

[0084] Without the addition of polymerization aids, the degree of polymerization of the fiber is reduced to 400 using the traditional depolymerization method, which cannot meet the minimum degree of polymerization requirement of 450 for lyocell fiber. At the same time, the R18 content is reduced to 93.2% and the α-cellulose content is reduced to 91.3%.

[0085] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for producing lyocell fiber using papermaking bamboo pulp, comprising swelling, dissolving, filtering, and spinning the pulp, characterized in that, The pulp is prepared using the following method: (1) Using papermaking bamboo pulp as raw material, the papermaking bamboo pulp is impregnated in a mixing tank. The concentration of the papermaking bamboo pulp is <5wt%, the alkali content of the pulp is 50-110g / l, the temperature is 40-60℃, the stirring time is 30-60min, and then pressing is used to control the water content of the pulp to be below 50wt%. (2) The pulp porridge after pressing in step (1) is soaked in a mixing tank, and 5-10 ppm of the dry pulp mass of nickel depolymerization aid and 5-10 ppm of the dry pulp desulphurization aid are added respectively. The pulp concentration is <5 wt%, the temperature is 40-60℃, and the stirring time is 30-60 min. The soaked pulp porridge is pressed to control the water content of the pulp porridge to be less than 50 wt%. The nickel depolymerization aid is selected from at least one of nickel chloride and nickel sulfate. The desulphurization aid is an ether. (3) Wash the pulp porridge after pressing in step (2) until it is neutral; (4) Put the porridge washed in step (3) into a mixing tank, add oxalic acid and iron removal agent, control the pH of the porridge to 1-2, the porridge concentration to 5-10wt%, the temperature to 40-60℃, the stirring time to 30-60min, and after stirring, press it to control the water content of the porridge to be less than 50wt%. The pressed porridge is washed with water until it is neutral. (5) The pulp is dried to obtain pulp for the production of lyocell fiber.

2. The method according to claim 1, characterized in that: The ether is diethyl ether.

3. The method according to claim 1, characterized in that: The stirring speed in steps (1), (2), and (4) is 70-150 rpm.

4. The method according to claim 1, characterized in that: In step (3), the washing method is to transport the porridge to the mixing and washing tank via a conveyor belt, and the transport time is 1-2 hours.

5. The method according to claim 1, characterized in that: The alkaline solution removed after pressing in step (4) is introduced into a nanofiltration system to separate low molecular weight monosaccharides and oligosaccharides.

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