Method for obtaining cellulose-rich material from xylitol residues

Abstract

The invention provides a method for obtaining a cellulose-rich material from xylitol residues, which comprises the following steps: cleaning and crushing the xylitol residues, and mixing the xylitol residues with a composite ionic liquid system comprising an ionic liquid I and an ionic liquid II, the ionic liquid II is ionic liquid which has no dissolving capacity to cellulose or has very low dissolving capacity to cellulose, dissolving the xylitol residue, adding a cleaning agent, carrying out solid-liquid separation to obtain a solution residue, and washing and drying the solution residue to obtain the cellulose-rich material. According to the method for extracting the cellulose from the xylitol residues, the yield of the obtained cellulose is not lower than 91%, and the purity is not lower than 73%. Different from a mixed system of amino acid or modified amino acid and ionic liquid, the two types of ionic liquid disclosed by the invention can be mutually dissolved better, and amino acid ions in the ionic liquid can play a role in inhibiting cellulose degradation, so that the cellulose degradation rate in the extraction process is low, and the cellulose yield is improved to a great extent.

Description

Technical Field

[0001] The present invention belongs to the field of comprehensive utilization of biomass, and particularly relates to a method for separating and obtaining cellulose-rich materials from xylitol residues. Background Art

[0002] China is a major producer of xylitol, with rich resources of xylitol residues, and the annual output is about ten million tons on average. However, the utilization rate of xylitol residues is relatively low. Currently, a large amount of xylitol residues are stacked in the open air or incinerated centrally, which not only seriously pollutes the environment but also causes waste of resources. Therefore, improving the comprehensive utilization rate of xylitol residues plays an important role in improving environmental quality and promoting the green development of the economic society.

[0003] Cellulose is the most abundant renewable resource on the earth. It has a wide range of sources, is green and environmentally friendly, and is biodegradable. It is widely used in industrial fields such as pharmaceuticals and textiles. With the increasing shortage of non-renewable resources such as petroleum and coal and the increasing attention paid to the pollution problems generated during their use, the development and utilization of cellulose resources have become particularly important.

[0004] Xylitol residues are mainly composed of cellulose, lignin, and a very small amount of hemicellulose. Cellulose molecules form a basic skeleton in a crystalline structure through hydrogen bonds between molecular chains, and the skeleton is filled with lignin and a small amount of hemicellulose. The high crystallinity of cellulose and the large number of hydrogen bonds existing between and within molecules make it insoluble in traditional solvents, which has become the biggest obstacle to the development and utilization of cellulose. Therefore, how to efficiently separate biomass to obtain cellulose has become the focus of attention in the academic and industrial circles.

[0005] Ionic liquid is a new type of efficient green solvent, which has the advantages of good thermal stability, adjustable structure, and reusable. The emergence of ionic liquid provides a new idea for people to develop and utilize biomass resources sustainably, and is of great significance to solving the energy crisis and environmental pollution problems.

[0006] There are many studies in the existing literature on the extraction of cellulose using ionic liquid solvent systems, such as I. Semerci, F. Güler, [Protic ionic liquids as effective agents for pretreatment of cottonstalks at high biomass loading], Industrial Crops and Products, 125 (2018) 588 - 595; F. J. V. Gschwend, F. Malaret, S. Shinde, A. Brandt-Talbot, J. P. Hallett, [Rapid pretreatment of Miscanthus using the low-cost ionic liquid triethylammonium hydrogen sulfate at elevated temperatures], Green Chemistry 20 (15) (2018) 3486 - 3498; V. Rigual, A. Ovejero-Pérez, S. Rivas, J. C. Domínguez, M. V. Alonso, M. Oliet, F. Rodriguez, [Protic, Aprotic, and Choline-Derived Ionic Liquids: Toward Enhancing the Accessibility of Hardwood and Softwood], ACS Sustainable Chemistry & Engineering, 8 (3) (2020) 1362 - 1370; E. Liu, M. Li, L. Das, Y. Pu, T. Frazier, B. Zhao, M. Crocker, A. J. Ragauskas, J. Shi, Engineering, [Understanding lignin fractionation and characterization from engineered switchgrass treated by an aqueous ionic liquid], ACS Sustainable Chem. Eng, 6 (5) (2018) 6612 - 6623, etc. It is recorded that the ionic liquid solvent systems used mainly include [HBIM][HSO 4 -water, [TEA][HSO 4- water, [Mim][Cl], [OHEtAm][OAc], [Ch][Ser], [Ch][Lys]-water, etc., mainly used for separating and extracting cellulose-rich materials from biomass raw materials such as cotton stalks, Miscanthus giganteus, pinewood, eucalyptus, and switchgrass. The cellulose yield is 50-78%, and the cellulose purity is 40-60%.

[0007] CN114808510A discloses a method for extracting high-purity cellulose materials from xylitol residues. Using xylitol residues as raw materials for extracting cellulose, sulfamic acid and ionic liquid are uniformly mixed and then added to xylitol residues. The resulting mixed solution is centrifuged. After the supernatant is uniformly mixed with an acetone aqueous solution, it is centrifuged again to obtain regenerated cellulose. The obtained regenerated cellulose is washed with water multiple times until the washing liquid is clear, and then freeze-dried to obtain high-purity cellulose. Its high purity is mainly because the sulfamic acid used destroys the hemicellulose and lignin complex, making cellulose dissolve into the ionic liquid. However, overall, the cellulose yield is relatively low. Summary of the Invention

[0008] At present, there is still much room for improvement in the efficiency of extracting cellulose from biomass using the current ionic liquid system. Through the research of the inventor, on the one hand, this is due to the low dissolution selectivity of the current ionic liquid system for the three components of lignocellulose, and on the other hand, cellulose degrades during the extraction process, both of which result in a low cellulose yield. Although substances such as amino acids can inhibit the degradation of cellulose in ionic liquids to a certain extent, the poor solubility of amino acids in ionic liquids weakens their effect of inhibiting cellulose degradation in ionic liquids. Therefore, in the present invention, the inventor uses amino acid ionic liquids and combines them with ionic liquids that have no or very low solubility in cellulose to dissolve lignin and a small amount of hemicellulose to achieve the purpose of extracting cellulose, greatly improving the extraction rate of cellulose, and all solvents can be simply recycled.

[0009] In order to achieve the above technical objectives, the technical solution of the present invention is as follows:

[0010] A method for obtaining cellulose-rich materials from xylitol residues, comprising the following steps:

[0011] After cleaning and crushing the xylitol residues, they are mixed with a composite ionic liquid system including ionic liquid I and ionic liquid II. The ionic liquid I is an amino acid ionic liquid, and the ionic liquid II is an ionic liquid that has no or very low solubility in cellulose. After mixing, the xylitol residues are dissolved, and then a cleaning agent is added. After solid-liquid separation, the residue is obtained. After washing and drying the residue, the cellulose-rich material is obtained.

[0012] The residue in the present invention refers to the insoluble matter after the xylitol residues are fully dissolved.

[0013] Further, the cation of the ionic liquid I is selected from alkyl quaternary ammonium ions [NR X H 4-X + , alkyl quaternary phosphonium ions [PR x H 4-x + , alkyl-substituted imidazolium ions, N-alkyl-substituted pyridinium ions, or at least one of them. More preferably, it is at least one of alkyl quaternary ammonium ions [NR X H 4-X + , alkyl-substituted imidazolium ions, N-alkyl-substituted pyridinium ions; further preferably, it is at least one of 1-ethyl-3-methylimidazolium ion and N-ethyl-2-methylpyridinium ion. Its anion is selected from at least one of arginine ion, histidine ion, lysine ion, threonine ion, and proline ion. More preferably, it is arginine ion.

[0014] Further, the ionic liquid I is preferably at least one of 1-ethyl-3-methylimidazolium arginate, 1-ethyl-3-methylimidazolium lysinate, 1-ethyl-3-methylimidazolium threonate, 1-ethyl-3-methylimidazolium histidinate, and N-ethyl-2-methylpyridinium arginate.

[0015] Further, the solubility of the ionic liquid II in cellulose is not more than 0.05 g / 100 g of ionic liquid. As a further preference, the cation of the ionic liquid II is selected from alkyl quaternary ammonium ions [NR X H 4-X + , alkyl quaternary phosphonium ions [PR x H 4-x + , alkyl-substituted imidazolium ions, N-alkyl-substituted pyridinium ions, or at least one of them. Preferably, it is at least one of 1-ethyl-3-methylimidazolium ion and N-ethyl-2-methylpyridinium ion; its anion is tetrafluoroborate ion.

[0016] Further, the ionic liquid II is selected from at least one of 1-ethyl-3-methylimidazolium tetrafluoroborate and N-ethyl-2-methylpyridinium tetrafluoroborate.

[0017] Further, in the composite ionic liquid, by total weight, the weight percentage of the ionic liquid I is 0.8% - 20%, preferably 0.9 - 15%, more preferably 2% - 10%.

[0018] Further, the mixing ratio of xylitol residue and the composite ionic liquid is added at 0.5% - 15% of the weight of the composite ionic liquid based on the xylitol residue, preferably added at 0.9% - 10%. ​​​​​

[0019] Furthermore, the temperature for the mixed dissolution of xylitol residue and the composite ionic liquid is 90 - 150°C, preferably 130 - 150°C, and the time is 1 - 4 h.

[0020] Furthermore, for the cleaning and crushing treatment of the xylitol residue, the xylitol residue is cleaned with distilled water, crushed into powder by a pulverizer, and then sieved to obtain xylitol residue solid with a mesh size not greater than 100 meshes, preferably not greater than 120 meshes.

[0021] Furthermore, the addition of the cleaning agent is to minimize the carry - over of ionic liquid during the separation of the residue, thus facilitating the recycling of the solvent during subsequent washing. The cleaning agent is selected from lower alcohols, water, or a mixed solution of both. Further, the lower alcohol is selected from at least one of methanol, ethanol, n - propanol, and isopropanol.

[0022] Furthermore, the residue is washed successively with DMSO and methanol. The method for drying the residue is drying by baking or freeze - drying.

[0023] Adopting the technical solution of the present invention has the following beneficial effects:

[0024] (1) For the method of extracting cellulose from xylitol residue in the present invention, the cellulose yield is not less than 91%, and the purity is not less than 73%.

[0025] (2) The present invention uses amino acid ionic liquids, which is different from the mixed system of amino acids or modified amino acids and ionic liquids. The two types of ionic liquids in the present invention can be well - miscible, and the amino acid ions therein can play an inhibitory role in the degradation of cellulose, resulting in a low cellulose degradation rate during the extraction process, thereby greatly improving the cellulose yield.

[0026] (3) For the two - miscible ionic liquid system of the present invention, the solvent can be simply recycled.

[0027] Other features and advantages of the present invention will be described in detail in the subsequent specific implementation section. Specific Implementation Modes

[0028] The following non - restrictive examples can enable those of ordinary skill in the art to more comprehensively understand the present invention, but do not limit the present invention in any way.

[0029] In the present invention, the contents of cellulose, lignin, and hemicellulose in the raw material xylitol residue and the cellulose content in the product rich - cellulose material are all determined by the standard method adopted by the National Renewable Energy Laboratory (NREL) of the United States, with HPLC as the main detection means.

[0030] The extraction rate of cellulose is calculated according to formula (1):

[0031] Cellulose extraction rate = W 1 / W 0 * 100% (1)

[0032] Wherein, W 0 is the initial mass of cellulose in xylitol residue, and W 1 is the mass of the extracted cellulose.

[0033] The purity of cellulose is calculated according to formula (2):

[0034] Cellulose purity = M 1 / M 0 * 100% (2)

[0035] Wherein, M 0 is the mass of the fiber-rich material, and M 1 is the mass of cellulose in the fiber-rich material.

[0036] The weight percentages of the main components in the xylitol residue used in the following examples are as follows: cellulose 58.24%, lignin 27.12%, hemicellulose 2.19%;

[0037] Example 1

[0038] Mix 6.00 g of 1-ethyl-3-methylimidazolium tetrafluoroborate ([Emim][BF 4 ), 0.06 g of 1-ethyl-3-methylimidazolium arginate [Emim][Arg] and 0.06 g of xylitol residue evenly, heat and dissolve at 90 °C for 1 h to obtain a suspension. After adding methanol to the suspension and performing vacuum filtration, a filter cake and a filtrate are obtained. The filtrate can recover methanol and ionic liquid after rotary evaporation. Wash the filter cake 3 times with 50 mL of DMSO and methanol in sequence and then dry it to obtain a fiber-rich material; add methanol to the DMSO washing solution and perform suction filtration to obtain a filtrate. The filtrate can recover methanol and DMSO respectively after rotary evaporation. The cellulose yield obtained is 98.11%, and the purity is 74.25%.

[0039] Example 2

[0040] Mix 6.00 g of [Emim][BF 4, 0.08 g of 1-ethyl-3-methylimidazolium lysinate [Emim][Lys] was mixed evenly with 0.30 g of xylitol residue, heated and dissolved at 130 °C for 4 h to obtain a suspension. After adding methanol to the suspension and performing vacuum filtration, a filter cake and a filtrate were obtained. The filtrate was rotary evaporated to recover methanol and the ionic liquid. The filter cake was washed 3 times with 50 mL of DMSO and methanol in sequence and then dried to obtain a cellulose-rich material. After adding methanol to the DMSO washing solution and performing filtration, a filtrate was obtained. The filtrate was rotary evaporated to recover methanol and DMSO respectively. The cellulose yield obtained was 92.31%, and the purity was 76.15%.

[0041] Example 3

[0042] 6.00 g of [Emim][BF 4 , 0.15 g of 1-ethyl-3-methylimidazolium threoninate [Emim][Thr] was mixed evenly with 0.30 g of xylitol residue, heated and dissolved at 130 °C for 4 h to obtain a suspension. After adding ethanol to the suspension and performing vacuum filtration, a filter cake and a filtrate were obtained. The filtrate was rotary evaporated to recover methanol and the ionic liquid. The filter cake was washed 3 times with 50 mL of DMSO and methanol in sequence and then dried to obtain a cellulose-rich material. After adding methanol to the DMSO washing solution and performing filtration, a filtrate was obtained. The filtrate was rotary evaporated to recover methanol and DMSO respectively. The cellulose yield obtained was 94.13%, and the purity was 75.34%.

[0043] Example 4

[0044] 6.00 g of [Emim][BF 4 , 0.24 g of 1-ethyl-3-methylimidazolium histidinate [Emim][His] was mixed evenly with 0.30 g of xylitol residue, heated and dissolved at 130 °C for 4 h to obtain a suspension. After adding water to the suspension and performing vacuum filtration, a filter cake and a filtrate were obtained. The filtrate was rotary evaporated to recover methanol and the ionic liquid. The filter cake was washed 3 times with 50 mL of DMSO and methanol in sequence and then dried to obtain a cellulose-rich material. After adding methanol to the DMSO washing solution and performing filtration, a filtrate was obtained. The filtrate was rotary evaporated to recover methanol and DMSO respectively. The cellulose yield obtained was 93.12%, and the purity was 74.95%.

[0045] Example 5

[0046] 6.00 g of [Emim][BF 4, 0.54 g of [Emim][Arg] was mixed evenly with 0.30 g of xylitol residue, heated and dissolved at 130 °C for 4 h to obtain a suspension. After adding a mixed solution of methanol and water (volume ratio 1:1) to the suspension and then performing vacuum filtration, a filter cake and a filtrate were obtained. The filtrate was rotary evaporated to recover methanol and the ionic liquid. The filter cake was washed 3 times with 50 mL of DMSO and methanol successively and then dried to obtain a cellulose-rich material; methanol was added to the DMSO washing solution and then filtered to obtain a filtrate, and the filtrate was rotary evaporated to recover methanol and DMSO respectively. The cellulose yield obtained was 96.41%, and the purity was 76.72%.

[0047] Example 6

[0048] 6.00 g of [Emim][BF 4 , 0.60 g of [Emim][Arg] was mixed evenly with 0.60 g of xylitol residue, heated and dissolved at 150 °C for 2.5 h to obtain a suspension. After adding methanol to the suspension and then performing vacuum filtration, a filter cake and a filtrate were obtained. The filtrate was rotary evaporated to recover methanol and the ionic liquid. The filter cake was washed 3 times with 50 mL of DMSO and methanol successively and then dried to obtain a cellulose-rich material; methanol was added to the DMSO washing solution and then filtered to obtain a filtrate, and the filtrate was rotary evaporated to recover methanol and DMSO respectively. The cellulose yield obtained was 95.13%, and the purity was 78.52%.

[0049] Example 7

[0050] 6.00 g of N-ethyl-2-methylpyridinium tetrafluoroborate ([EMPy]BF4), 0.08 g of N-ethyl-2-methylpyridinium arginate [EMPy][Arg] was mixed evenly with 0.30 g of xylitol residue, heated and dissolved at 130 °C for 4 h to obtain a suspension. After adding methanol to the suspension and then performing vacuum filtration, a filter cake and a filtrate were obtained. The filtrate was rotary evaporated to recover methanol and the ionic liquid. The filter cake was washed 3 times with 50 mL of DMSO and methanol successively and then dried to obtain a cellulose-rich material; methanol was added to the DMSO washing solution and then filtered to obtain a filtrate, and the filtrate was rotary evaporated to recover methanol and DMSO respectively. The cellulose yield obtained was 92.41%, and the purity was 76.25%.

[0051] Example 8

[0052] 6.00 g of benzyltriethylammonium tetrafluoroborate ([Nbz222]BF4), 0.15 g of [Emim][Arg], and 0.30 g of xylitol residue were put into a reactor, mixed evenly, and heated and dissolved at 130 °C for 4 h. Methanol was added to the suspension, and after vacuum filtration, a filter cake and a filtrate were obtained. The filtrate was rotary evaporated to recover methanol and ionic liquid. The filter cake was washed three times with 50 mL of DMSO and methanol in sequence and then dried to obtain a cellulose-rich material; methanol was added to the DMSO washing solution, and after filtration, a filtrate was obtained. The filtrate was rotary evaporated to recover methanol and DMSO respectively. The cellulose yield was 91.90%, and the purity was 74.37%.

[0053] Example 9

[0054] 6.00 g of 1-ethyl-3-methylimidazolium tetrafluoroborate ([Emim][BF 4 ), 1.2 g of 1-ethyl-3-methylimidazolium arginate [Emim][Arg], and 0.06 g of xylitol residue were mixed evenly and heated and dissolved at 90 °C for 1 h to obtain a suspension. Methanol was added to the suspension, and after vacuum filtration, a filter cake and a filtrate were obtained. The filtrate was rotary evaporated to recover methanol and ionic liquid. The filter cake was washed three times with 50 mL of DMSO and methanol in sequence and then dried to obtain a cellulose-rich material; methanol was added to the DMSO washing solution, and after filtration, a filtrate was obtained. The filtrate was rotary evaporated to recover methanol and DMSO respectively. The cellulose yield was 97.68%, and the purity was 73.13%.

[0055] Comparative Example 1

[0056] Except that only [Emim][BF 4 was used as the ionic liquid, other conditions were the same as in Example 2:

[0057] 6.00 g of [Emim][BF 4 and 0.30 g of xylitol residue were mixed evenly and heated and dissolved at 130 °C for 4 h to obtain a suspension. Methanol was added to the suspension, and after vacuum filtration, a filter cake and a filtrate were obtained. The filtrate was rotary evaporated to recover methanol and ionic liquid. The filter cake was washed three times with 50 mL of DMSO and methanol in sequence and then dried to obtain a cellulose-rich material; methanol was added to the DMSO washing solution, and after filtration, a filtrate was obtained. The filtrate was rotary evaporated to recover methanol and DMSO respectively. The cellulose yield was 72.32%, and the purity was 65.15%.

[0058] Comparative Example 2

[0059] Except that only [Emim][Lys] was used as the ionic liquid, other conditions were the same as in Example 2:

[0060] 6.00 g of [Emim][Arg] was mixed evenly with 0.30 g of xylitol residue, heated and dissolved at 130 °C for 4 h to obtain a suspension. Methanol was added to the suspension, and after vacuum filtration, a filter cake and a filtrate were obtained. The filtrate was rotary evaporated to recover methanol and ionic liquid. The filter cake was washed three times with 50 mL of DMSO and methanol in sequence and then dried to obtain a cellulose-rich material; methanol was added to the DMSO washing solution and then filtered to obtain a filtrate, and the filtrate was rotary evaporated to recover methanol and DMSO respectively. The cellulose yield obtained was 71.21%, and the purity was 67.72%.

[0061] Comparative Example 3

[0062] L-arginine was used instead of 1-ethyl-3-methylimidazolium arginate, and the others were the same as in Example 1:

[0063] 6.00 g of 1-ethyl-3-methylimidazolium tetrafluoroborate ([Emim][BF 4 )), 0.06 g of L-arginine and 0.06 g of xylitol residue were mixed evenly, heated and dissolved at 90 °C for 1 h to obtain a suspension. Methanol was added to the suspension, and after vacuum filtration, a filter cake and a filtrate were obtained. The filter cake was washed three times with 50 mL of DMSO and methanol in sequence and then dried to obtain a cellulose-rich material. The cellulose yield obtained was 83.52%, and the purity was 70.18%.

Claims

1. A method for obtaining cellulose-rich materials from xylitol residues, comprising the following steps: After cleaning and crushing the xylitol residues, they are mixed with a composite ionic liquid system comprising ionic liquid I and ionic liquid II. The ionic liquid I is an amino acid ionic liquid, and the ionic liquid II is an ionic liquid having no or very low solubility in cellulose. After mixing, the xylitol residues are dissolved, and then a cleaning agent is added. Solid-liquid separation is carried out to obtain the residue. After washing and drying the residue, the cellulose-rich material is obtained.

2. The method according to claim 1, wherein, The cation of the ionic liquid I is selected from alkyl quaternary ammonium ions [NR X H 4-X + , alkyl quaternary phosphonium ions [PR x H 4-x + , alkyl-substituted imidazolium ions, N-alkyl-substituted pyridinium ions, and the anion is selected from at least one of arginine ions, histidine ions, lysine ions, threonine ions, and proline ions.​​ 3. The method according to claim 2, wherein, The cation of the ionic liquid I is selected from at least one of 1-ethyl-3-methylimidazolium ion and N-ethyl-2-methylpyridinium ion.

4. The method according to claim 2, wherein, The ionic liquid I is selected from at least one of 1-ethyl-3-methylimidazolium arginate, 1-ethyl-3-methylimidazolium lysinate, 1-ethyl-3-methylimidazolium threonate, 1-ethyl-3-methylimidazolium histidinate, and N-ethyl-2-methylpyridinium arginate.

5. The method according to claim 1, wherein, The cation of the ionic liquid II is selected from alkyl quaternary ammonium ions [NR X H 4-X + , alkyl quaternary phosphonium ions [PR x H 4-x + , at least one of alkyl-substituted imidazolium ions and N-alkyl-substituted pyridinium ions, and the anion is a tetrafluoroborate ion.​​ 6. The method according to claim 5, wherein, The cation of the ionic liquid II is selected from at least one of 1-ethyl-3-methylimidazolium ion and N-ethyl-2-methylpyridinium ion.

7. The method according to claim 5, wherein, The ionic liquid II is selected from at least one of 1-ethyl-3-methylimidazolium tetrafluoroborate and N-ethyl-2-methylpyridinium tetrafluoroborate.

8. The method according to claim 1, wherein, In the composite ionic liquid, by total weight, the weight percentage of the ionic liquid I is 0.8% - 20%.

9. The method according to claim 1, wherein, The mixing ratio of the xylitol residues and the composite ionic liquid is added at 0.5% - 15% of the weight of the composite ionic liquid based on the xylitol residues.

10. The method according to claim 1, wherein, The temperature for mixing and dissolving the xylitol residues and the composite ionic liquid is 90 - 150 °C, and the time is 1 - 4 h.

11. The method according to claim 1, wherein, The cleaning agent is selected from lower alcohols, water, or a mixed solution of both.

12. The method according to claim 1, wherein, The cleaning and crushing treatment of the xylitol residues is to wash the xylitol residues with distilled water, crush them into powder by a pulverizer, and then sieve to obtain xylitol residue solids not larger than 100 mesh.

13. The method according to claim 1, wherein, The washing of the residue is carried out successively with DMSO and methanol, and the method for drying the residue is drying by baking or freeze-drying.