Method for preparing liquid phenolic products, cellulose and bio-based carbon black from wood xylan residues

Abstract

The present application relates to a method for preparing liquid phenolic product, cellulose and bio-based carbon black from wood sugar residue, comprising the following steps: first, mixing wood sugar residue with alkaline catalyst, phenolic protective agent, low-carbon alcohol and water in a certain proportion, placing them in a closed pressure-resistant reactor, making lignin dissolve, ether bond break and side chain cleavage under the catalysis of alkali, and preventing the formation of new carbon-carbon crosslinking polymerization through phenolic protective agent; second, filtering and separating after cooling after the reaction, distilling or vacuum distilling the filtrate to recover alcohol solvent and water, thereby obtaining high-concentration liquid phenolic product, and the recovered alcohol solvent and water can be recycled for preparing liquid phenolic product from wood sugar residue. The method can direct the conversion of lignin components in wood sugar residue into phenolic product, the obtained phenolic product can be used for synthesizing bio-based phenolic resin, wood adhesive, antioxidant, flame-retardant material or other bio-based chemicals, and has the advantages of wide raw material source, simple process, high utilization rate and high added value of product.

Description

Technical Field

[0001] This invention belongs to the field of biomass resource utilization and bio-based chemical preparation technology. Specifically, it relates to a method for preparing liquid phenolic products by directional depolymerization of lignin using xylose residue as raw material through the synergistic effect of alkali catalysis and phenolic protective agents, and a method for further preparing bio-based cellulose products and bio-based carbon black from solid residue. Background Technology

[0002] Xylose residue is the solid residue remaining after hemicellulose hydrolysis of raw materials such as corn cobs, straw, and lignocellulose to produce xylose and xylitol. This type of residue typically contains a high proportion of lignin, cellulose, and ash, and usually also contains up to 50% moisture. It is characterized by concentrated sources, large output, high moisture content, and complex composition. If it is only treated as low-value fuel through low-value processing such as stockpiling, drying, and then incineration, not only will the resource utilization efficiency be low, but it will also easily lead to problems such as dust, odor, wastewater, toxic exhaust gases, and carbon emissions.

[0003] Lignin, with its aromatic ring structure, is an important potential source for the preparation of phenolic compounds. Compared to unprocessed biomass materials, xylose residue contains a higher lignin content due to the removal of hemicellulose, and it is easily separated from cellulose. Therefore, recovering lignin and obtaining phenolic compounds from xylose residue is an efficient and low-cost approach.

[0004] Existing chemical processes for separating lignin and cellulose from biomass materials typically lead to further carbon-carbon crosslinking and polymerization of lignin into polymers with larger molecular weights. This results in a decrease in the proportion of phenolic or alcoholic hydroxyl groups, making subsequent use and modification difficult and reducing their application value.

[0005] Therefore, it is necessary to establish a utilization method suitable for the characteristics of xylose residue raw materials: on the one hand, converting lignin-enriched components into monomers or small molecular weight soluble liquid phenolic products to facilitate subsequent conversion and utilization; on the other hand, converting solid residues into bio-based cellulose products and bio-based carbon black or carbon black substitute fillers, thereby improving the overall resource utilization rate and product added value of xylose residue. Summary of the Invention

[0006] This invention provides a method for preparing liquid phenolic products from xylose residue, aiming to achieve directional depolymerization of lignin components and enrichment of phenolic products in xylose residue, while also enabling high-value utilization of the solid residue after the reaction.

[0007] The method includes the following steps: S1, Xylose residue, alkaline catalyst, phenolic protective agent, low-carbon alcohol solvent, and water are mixed to obtain a reaction raw material system. The alkaline catalyst comprises 5-10 parts by mass of 100 parts by mass of dry xylose residue, 5-30 parts by mass of phenolic protective agent, 50-700 parts by mass of alcohol solvent, and 50-300 parts by mass of water. The alkaline catalyst comprises one or more of sodium hydroxide, potassium hydroxide, sodium carbonate, and potassium carbonate, preferably sodium hydroxide. The alcohol solvent comprises one or more of methanol, ethanol, isopropanol, and ethylene glycol, preferably methanol. The phenolic protective agent comprises one or more of phenol, p-tert-butylphenol, and p-tert-octylphenol.

[0008] S2, the reaction raw material system is placed in a closed pressure-resistant reactor and alkali-catalyzed conversion is carried out under stirring conditions. The stirring speed is 50-500 r / min, the reaction temperature is 150-260℃, the holding time is 1.0-2.5h, and the reaction pressure is 1-9MPa. The preferred reaction conditions are 200±10℃, holding time 1.5-2.5h, and stirring speed 100-150 r / min. In this process, the lignin in the xylose residue dissolves, ether bonds break, and side chains are cracked under alkali catalysis. The active intermediates formed during the reaction are stabilized by phenolic protective agents, inhibiting the formation of new carbon-carbon cross-linked structures, thereby obtaining small molecule phenolic compounds or phenolic oligomers.

[0009] S3. After the reaction is completed, the mixture is cooled and filtered to separate the reaction liquid and solid residue. The reaction liquid contains a solvent composed of low-carbon alcohols and water, as well as phenolic products and non-phenolic organic compounds. The non-phenolic organic compounds mainly include saturated or unsaturated hydrocarbons, aromatic hydrocarbons, and compounds such as alcohols, esters, and ketones.

[0010] S4, the reaction solution is distilled or subjected to vacuum distillation to recover the alcohol solvent and water, which can be reused in step S1 according to the component ratio to separate and obtain liquid phenolic products. The liquid phenolic products include phenol, 2-methoxyphenol, 4-ethylphenol, 4-ethyl-2-methoxyphenol, 2-methoxy-4-vinylphenol, 2,6-dimethoxyphenol, 4-(3-hydroxy-1-propenyl)phenol, 4-ethyl-2,6-dimethoxyphenol, 2,6-dimethoxy-4-propylphenol, bisphenol E, acetone compounds, and hydroxyphenyl acrylate compounds, etc. The area ratio of phenolic compounds is more than 30%, preferably more than 40%, based on GC-MS peak area normalization. The obtained liquid phenolic products can be used to synthesize bio-based phenolic resins, wood adhesives, antioxidants, flame retardants, or other bio-based chemicals.

[0011] Preparation of bio-based cellulose products from solid-phase residues (optional steps): S5A, the solid residue obtained in step S3 is washed with deionized water and / or methanol until the pH of the filtrate is close to neutral.

[0012] S5B involves bleaching the washed solid residue to obtain a bio-based cellulose product with a whiteness greater than or equal to 80, which is used to prepare cellulose products such as carboxymethyl cellulose (CMC). The bleaching process can be carried out using a 4% sodium hypochlorite solution with a liquid-to-solid ratio of 10 mL / g based on the mass of the solid residue, and rinsing at 50°C for 60 min.

[0013] Preparation of bio-based carbon black or carbon materials from solid-phase residues (optional step): S5C, wash the solid residue obtained in step S3 until the pH of the filtrate is close to neutral, and dry it at 80-105℃ to constant weight; the washing includes adding deionized water at 5-10 times the mass of the solid residue, stirring and washing for 10-20 minutes, filtering and measuring the pH of the filtrate, repeating the water washing 3-6 times until the pH of the filtrate is 6.5-8.0, then washing with methanol 1-2 times, and optionally washing with deionized water once more to reduce methanol residue.

[0014] S5D involves pyrolyzing and carbonizing the dried solid residue under one or more inert atmospheres, namely nitrogen, argon, or carbon dioxide. The pyrolysis and carbonization temperature is 500-900℃, the heating rate is 2-20℃ / min, and the holding time is 0.5-3h. Before pyrolysis and carbonization, inert gas is introduced for 20-30min to remove air from the furnace tube, and the inert gas flow rate is 100-300mL / min. Preferably, the temperature is raised to 600-800℃ at a heating rate of 5-10℃ / min and held for 1-2h. After the holding time is completed, the product is cooled to below 50℃ under the protection of an inert atmosphere before being removed.

[0015] S5E involves cooling the pyrolysis and carbonization products, followed by grinding or ball milling and sieving to obtain bio-based carbon black or carbon materials. The carbonization products can also undergo secondary water washing, dilute acid washing, or activation treatment based on ash content, pH, and residual Na, K, Ca, and Si elements. The dilute acid washing can be performed by washing or soaking in 0.1 mol / L hydrochloric acid for 30-60 minutes, followed by washing with deionized water until the pH of the filtrate is 6.5-7.5. The ball milling speed is 300-500 r / min, the ball milling time is 1-3 hours, and the product is graded by 100-mesh, 200-mesh, or 325-mesh sieves.

[0016] Beneficial effects (1) Using industrial by-product xylose residue as raw material reduces raw material costs and solves the problems of waste accumulation and environmental pollution at the same time; (2) Through the synergistic effect of "alkali catalysis + phenolic protectant", the repolymerization of lignin can be effectively blocked. The area ratio of phenolic compounds in the liquid product can reach more than 30%, and under preferred conditions it can reach more than 40% or even more than 50%, which has the potential to replace bio-based phenolic sources. (3) The filter residue is no longer discarded as waste residue, but can be converted into bio-based cellulose products (whiteness ≥ 80) or bio-based carbon black to improve the utilization rate of carbon resources; (4) The reaction temperature is mainly concentrated in 150-260℃, and the process conditions are relatively mild; (5) By adjusting the composition of liquid-phase phenolic products with different protective agents, the composition can be directionally adjusted according to the needs of downstream resins, adhesives or carbon materials; (6) After the solid residue is washed to near neutral, it can meet the needs of two high-value-added pathways: cellulose products and carbon materials. (7) Bio-based carbon black can reduce the residue of alkali and inorganic salts after secondary water washing, dilute acid washing or activation treatment, and improve its stability and applicability in rubber, plastics and other fields. Detailed Implementation

[0017] The present invention will be further described below with reference to the experimental scheme. It should be understood that the following examples are for illustrative purposes only and should not be construed as limiting the scope of protection of the present invention. Without departing from the concept of the present invention, those skilled in the art can adjust the moisture content of the raw materials, the type of solvent, the type of catalyst, the type of protective agent, the reaction temperature, the holding time, the pyrolysis and carbonization conditions, etc.

[0018] Comparative Example 1 268g of xylose residue (with a moisture content of 20.33%), 13.5g of NaOH, 949mL of methanol, and 450mL of water were weighed and added to a high-pressure reactor without the addition of any exogenous phenolic preservative. The temperature was raised to 200℃, and the reaction was carried out for 2.5h. After that, cooling water was introduced to lower the temperature to room temperature within 30min. The pressurized liquefaction product was filtered to separate the solid and liquid phases. The dry weight of the filter residue was 140.66g. The filtrate was subjected to vacuum distillation at 60℃ under a vacuum of 0.09MPa to recover methanol and water, yielding the reaction solution. GC-MS analysis showed that the total phenolic compound content in the reaction solution was 21.58%. The specific composition is shown in Table 1.

[0019] Example 1 Weigh out the same mass of xylose residue, NaOH, methanol, and water as in Comparative Example 1, add 50g of phenol protective agent, and add to a high-pressure reactor. Heat to 200℃ and react for 2.5h. Then, introduce cooling water to cool to room temperature within 30min. Filter the pressurized liquefaction product to separate the solid and liquid phases. The dry weight of the filter residue is 135.37g. Distill the filtrate under reduced pressure at 0.09MPa and 60℃ to recover methanol and water, obtaining the reaction solution. GC-MS analysis shows that the total phenolic compound content in the reaction solution after deducting the protective agent is 53.31%. The specific composition is shown in Table 1.

[0020] Example 2 238g of xylose residue (same as in Example 1), 13.5g of NaOH, 630mL of methanol, 200mL of water, and 50g of phenol were weighed and added to a high-pressure reactor. The temperature was raised to 260℃, and the reaction was carried out for 1.5h. Cooling water was then introduced to lower the temperature to room temperature within 30min. The pressurized liquefaction product was filtered to separate the solid and liquid phases. The dry weight of the obtained filter residue was 57.11g. The filtrate was subjected to vacuum distillation at 0.09MPa and 60℃ to recover methanol and water, yielding the reaction solution. GC-MS analysis showed that the total phenolic compound content in the reaction solution after deducting the protective agent was 43.68%. The specific composition is shown in Table 1.

[0021] Example 3 Weigh out the same mass of xylose residue, NaOH, methanol, and water as in Example 2, but reduce the mass of phenol protective agent to 25g and add it to a high-pressure reactor. Heat to 260℃ and react for 1.5h. Then, introduce cooling water and allow the mixture to cool to room temperature within 30min. Filter the pressurized liquefaction product to separate the solid and liquid phases. The resulting filter residue has a dry weight of 85.78g. Distill the filtrate under reduced pressure at 0.09MPa and 60℃ to recover methanol and water, yielding the reaction solution. GC-MS analysis showed that the total phenolic compound content in the reaction solution after removing the protective agent was 51.85%. Specific components are shown in Table 1.

[0022] Example 4 The same mass of xylose residue, NaOH, methanol, water, and phenol as in Example 3 were weighed and added to a high-pressure reactor. The reaction temperature was lowered to 230°C, and the reaction time was extended to 2 hours. After the reaction was completed, cooling water was introduced to lower the temperature to room temperature within 30 minutes. The pressurized liquefaction product was filtered to separate the solid and liquid phases. The dry weight of the obtained filter residue was 113.77 g. The filtrate was subjected to vacuum distillation at 0.09 MPa and 60°C to recover methanol and water, yielding the reaction solution. GC-MS analysis showed that the total phenolic compound content in the reaction solution after deducting the protective agent was 53.16%. The specific composition is shown in Table 1.

[0023] Example 5 The same mass of xylose residue, NaOH, methanol, water, and phenol as in Example 4 were weighed and added to a high-pressure reactor. The reaction temperature was reduced to 200°C, and the reaction time was reduced to 1.25 h. After the reaction was completed, cooling water was introduced to lower the temperature to room temperature within 30 min. The pressurized liquefaction product was filtered to separate the solid and liquid phases. The dry weight of the obtained filter residue was 109.22 g. The filtrate was subjected to vacuum distillation at 60°C under a vacuum of 0.09 MPa to recover methanol and water, yielding the reaction solution. GC-MS analysis showed that the total phenolic compound content in the reaction solution after deducting the protective agent was 51.45%. The specific composition is shown in Table 1.

[0024] Example 6 241g of xylose residue (moisture content 37.80%), 12.15g of NaOH, 996mL of methanol, 22.5g of p-tert-butylphenol, and 465.75mL of water were weighed and added to a high-pressure reactor. The temperature was raised to 200℃, and the reaction was carried out for 2.5h. Cooling water was then introduced to lower the temperature to room temperature within 30min. The pressurized liquefaction product was filtered to separate the solid and liquid phases, and 121.62g of filter residue was obtained. The filtrate was subjected to vacuum distillation at 60℃ under a vacuum of 0.09MPa to recover methanol and water, yielding the reaction solution. GC-MS analysis showed that the total phenolic compound content in the reaction solution after deducting the protective agent was 31.25%. The specific composition is shown in Table 1.

[0025] Example 7 214g of xylose residue (same as in Example 6), 10.8g of NaOH, 991mL of methanol, 40g of p-tert-butylphenol, and 468mL of water were weighed and added to a high-pressure reactor. The temperature was raised to 200℃, and the reaction was carried out for 2.5h. Cooling water was then introduced to lower the temperature to room temperature within 30min. The pressurized liquefaction product was filtered to separate the solid and liquid phases, and 106.00g of filter residue was obtained. The filtrate was subjected to vacuum distillation at 60℃ under a vacuum of 0.09MPa to recover methanol and water, yielding the reaction solution. GC-MS analysis showed that the total phenolic compound content in the reaction solution after deducting the protective agent was 36.43%. The specific composition is shown in Table 1.

[0026] Example 8 (Preparation of bio-based cellulose products from solid-phase residues) Take 30g of the solid residue obtained from filtration in Example 1 and add 5-10 times its weight of deionized water. Stir and wash for 10-20 minutes, then filter. Repeat washing with water until the pH of the filtrate is 6.5-8.0. Then add a 4% sodium hypochlorite solution, with a liquid-to-solid ratio of 10mL / g based on the weight of the solid residue. Rinse at 50°C for 60 minutes. After rinsing, filter and wash with deionized water until near neutral. After drying, the bio-based cellulose product is obtained. After rinsing with sodium hypochlorite, the color of the solid residue changes significantly from brown to grayish-white to near white. The whiteness of the final bio-based cellulose product is greater than 80, and it can be further used as a raw material for industrial carboxymethyl cellulose (CMC) and other bio-based cellulose products.

[0027] Example 9 (Preparation of bio-based carbon black from solid residue) The solid residue obtained from filtration in Example 2 was washed until nearly neutral, dried at 80-105°C to constant weight, heated to 700°C at 5°C / min under nitrogen protection, held at that temperature for 1.5 hours, cooled, ground, and passed through a 200-mesh sieve to obtain bio-based carbon black. Based on 100 parts by weight of natural rubber, 5 parts by weight of bio-based carbon black were added to the control formulation for rubber performance testing, and the results were compared with a control group without added bio-based carbon black.

[0028] The main performance comparisons are shown in Table 2. After adding 5 parts of bio-based carbon black, the Mooney viscosity of the rubber compound decreased from 67.65 MU to 63.17 MU, a decrease of 6.62%, indicating improved processing performance. The 10% modulus increased by 5.56%, the elongation at break increased by 8.32%, and the tensile product increased by 3.22%, indicating that the mechanical response and overall tensile properties of the material under low strain were enhanced to a certain extent. Meanwhile, the tensile strength decreased only from 19.52 MPa to 18.60 MPa, a decrease of 4.71%; the hardness decreased by 1.39%, and the springback decreased by 1.12%, neither showing a significant reduction; the DIN abrasion loss decreased from 0.3049 g to 0.3040 g, and the abrasion resistance remained basically unchanged. The minimum and maximum torques of the vulcanizer were close to those of the control group, indicating that the overall vulcanization characteristics of the rubber compound did not change significantly after adding 5 parts of bio-based carbon black.

[0029] The results above show that, while maintaining the basic stability of tensile strength, hardness, resilience and abrasion resistance, the addition of 5 parts of bio-based carbon black can improve the elongation at break, low strain elongation and tensile product, and reduce the Mooney viscosity of the rubber compound. This indicates that the obtained bio-based carbon black has the potential to be used as a bio-based filler for rubber.

Claims

1. A method for preparing liquid phenolic products from xylose residue, characterized in that, Includes the following steps: S1, xylose residue, alkaline catalyst, phenolic protective agent, low-carbon alcohol solvent and water are mixed to obtain the reaction raw material system; S2, the reaction raw material system is placed in a closed pressure-resistant reactor, heated and kept at a temperature for a period of time under stirring conditions, so that the xylose residue undergoes lignin dissolution, ether bond cleavage and side chain pyrolysis under alkaline catalysis, and the active intermediates formed during the reaction are stabilized by phenolic protective agents to inhibit the formation of new carbon-carbon cross-linked structures, and a liquid-phase mixture of small molecule phenolic compounds or oligomers and saturated and unsaturated hydrocarbons and aromatic hydrocarbons, alcohols, esters and ketones is obtained; S3, after the reaction is complete, cool and filter to separate the reaction liquid and solid residue; S4, the reaction solution is distilled or vacuum distilled to recover the alcohol solvent and water, and a high concentration of liquid phenolic product is obtained. The recovered alcohol solvent and water can be reused in step S1 according to the composition ratio.

2. The method according to claim 1, characterized in that, In step S1, based on 100 parts by weight of dry xylose residue, the alkaline catalyst comprises 5-10 parts by weight, the phenolic protective agent comprises 5-30 parts by weight, the alcohol solvent comprises 50-700 parts by weight, and the water comprises 50-300 parts by weight; the alkaline catalyst comprises one or more of sodium hydroxide, potassium hydroxide, sodium carbonate, and potassium carbonate; the alcohol solvent comprises one or more of methanol, ethanol, isopropanol, and ethylene glycol; and the phenolic protective agent comprises one or more of phenol, p-tert-butylphenol, and p-tert-octylphenol.

3. The method according to claim 1, characterized in that, The reaction conditions in step S2 are: stirring speed 50-500 r / min, reaction temperature 150-260℃, holding time 1.0-2.5h, and reaction pressure 1-9MPa; the preferred conditions are reaction temperature 200±10℃, holding time 1.5-2.5h, and stirring speed 100-150 r / min.

4. The method according to claim 1, characterized in that, In addition to the solvent composed of low-carbon alcohols and water, the reaction solution obtained in step S3 also contains phenolic products and non-phenolic organic compounds. The non-phenolic organic compounds mainly include alcohols, esters, and ketones of saturated or unsaturated alkanes and aromatic hydrocarbons. The liquid phenolic products obtained in step S4 include one or more of the following: phenol, 2-methoxyphenol, 4-ethylphenol, 4-ethyl-2-methoxyphenol, 2-methoxy-4-vinylphenol, 2,6-dimethoxyphenol, 4-(3-hydroxy-1-propenyl)phenol, 4-ethyl-2,6-dimethoxyphenol, 2,6-dimethoxy-4-propylphenol, bisphenol E, ethyl ketone compounds, and hydroxyphenyl acrylate compounds. In the liquid phenolic products obtained in step S4, the area ratio of phenolic compounds is more than 30% based on GC-MS peak area normalization.

5. The method according to claim 1, characterized in that, It also includes the step of preparing bio-based cellulose products from the solid residue obtained in step S3: S5A, the solid residue is washed with deionized water and / or methanol until the pH of the filtrate is close to neutral. S5B involves bleaching the washed solid residue to obtain a bio-based cellulose product with a whiteness of ≥80, which is used to prepare cellulose products such as carboxymethyl cellulose (CMC).

6. The method according to claim 5, characterized in that, The washing process described in step S5A includes: adding deionized water at a ratio of 5-10 times the mass of the solid residue, stirring and washing for 10-20 minutes, filtering and measuring the pH of the filtrate, repeating the water washing 3-6 times until the pH of the filtrate is 6.5-8.0, then washing with methanol 1-2 times, and optionally washing with deionized water once more to reduce methanol residue.

7. The method according to claim 1, characterized in that, It also includes the step of preparing bio-based carbon black or carbon materials from the solid residue obtained in step S3: S5C, the solid residue is washed until the pH of the filtrate is close to neutral, and then dried at 80-105℃ to constant weight; S5D involves pyrolyzing and carbonizing the dried solid residue under an inert atmosphere. S5E involves cooling the pyrolysis and carbonization products, followed by grinding or ball milling and sieving to obtain bio-based carbon black or carbon materials.

8. The method according to claim 7, characterized in that, The washing process described in step S5C includes: adding deionized water at a ratio of 5-10 times the mass of the solid residue, stirring and washing for 10-20 minutes, filtering and measuring the pH of the filtrate, repeating the water washing 3-6 times until the pH of the filtrate is 6.5-8.0, washing with methanol 1-2 times, and optionally washing with deionized water once more to reduce methanol residue.

9. The method according to claim 7, characterized in that, In step S5D, the inert atmosphere is one or more of nitrogen, argon, or carbon dioxide; the pyrolysis carbonization temperature is 500-900℃, the heating rate is 2-20℃ / min, and the holding time is 0.5-3h; before pyrolysis carbonization, inert gas is introduced for 20-30min to remove air from the furnace tube, and the inert gas flow rate is 100-300mL / min; preferably, the temperature is raised to 600-800℃ at 5-10℃ / min and held for 1-2h, and after the holding is completed, the product is cooled to below 50℃ under the protection of an inert atmosphere before being removed.

10. The method according to claim 7, characterized in that, In step S5E, the carbonized product may also undergo secondary water washing, dilute acid washing, or activation treatment based on the ash content, pH, or residual Na, K, Ca, and Si elements. The dilute acid washing includes washing or soaking in 0.1 mol / L hydrochloric acid for 30-60 min, followed by washing with deionized water until the pH of the filtrate is 6.5-7.

5. The ball milling speed is 300-500 r / min, the ball milling time is 1-3 h, and the product is classified through 100 mesh, 200 mesh, or 325 mesh sieves.