Method for preparing phenolic monomer through separation and purification of black liquor lignin and catalytic hydrogenolysis
The hydrogenolysis reaction of the combination of Ru/C catalyst by acid-extraction and dichloromethane purification was solved by the complex structure of black liquid lignin, the preparation of phenolic monomers and the high-value utilization of resources were realized, and the environment was provided. Friendly process and efficient preparation methods for monophenol compounds.
Patent Information
- Application Number
- CN202411221178.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-09-02
- Publication Date
- 2024-12-13
AI Technical Summary
The lignin structure of black liquid is complex and difficult to integrate and utilize, and the existing technology is difficult to effectively extract and separate its small molecule fractions. The method of catalytic hydrogenolysis to prepare monophenol aromatic compounds has not been fully explored, resulting in waste and high lignin resources. Value-based utilization challenges.
The black liquor lignin was extracted by acidolysis, and purified by dichloromethane extraction, combined with Ru/C catalyst to carry out hydrogenolysis reaction to prepare phenolic monomers, and the solid precipitated components were obtained by hydrochloric acid solution treatment and freeze-drying, followed by the two The chloromethane is mixed and mechanically stirred and filtration is performed. Finally, hydrogen is introduced into the sealed reaction kettle for catalytic reaction.
Successfully retained the β-O-4' structure of black liquid lignin, improved the monomer yield, realized the high-value utilization of lignin, and provided an environmentally friendly process, reducing equipment corrosion and pollution, and opened up Important application prospects of monophenol compounds in chemicals.
Smart Images
Figure FT_1 
Figure FT_2 
Figure BDA0005023090890000051
Abstract
Description
Technical Field
[0001] The invention relates to the field of high-value utilization of black liquor lignin, in particular to a method for separating and purifying black liquor lignin and preparing phenolic monomers by catalytic hydrogenolysis. Background Art
[0002] Lignin is a natural, renewable aromatic polymer with great potential for producing a variety of chemicals such as functional materials, coatings and fuels. It exists between the microfibrils of plant cell walls and is a three-dimensional polymer composed of phenylpropane (p-hydroxyphenyl (H), guaiacyl (G) and syringyl (S)) connected by C–O and C–C bonds. Among these unit connections, the β-O-4' structure has the highest content and relatively low bond energy, which provides the premise and basis for the conversion of lignin into low-molecular aromatic chemicals.
[0003] Pulping and papermaking is a process of removing lignin to obtain high-quality cellulose pulp. Lignin undergoes structural rearrangement during the pulping process, and most of the β-O-4' bonds with lower bond energy are broken to form irreversible C-C bonds. At the same time, this process is accompanied by various chemical reactions, such as macromolecular degradation and condensation reactions, which lead to the structural rearrangement of lignin and the random reorganization of lignin fragments, thereby forming non-natural C-C bonds and a completely different three-dimensional structure. The resulting black liquor contains a large number of low molecular weight aromatic fragments and high molecular weight polymers of known or unknown composition, which makes the structure of black liquor lignin more uneven and complex, bringing challenges to its value-added application.
[0004] In addition, in the research stage, the use of organic solvents to fractionate black liquor lignin can fractionate complex lignin mixtures into relatively uniform fractions for the separate utilization of each fraction. However, only very limited research has touched on the description of the small molecular fraction of hardwood industrial lignin (ACS Sustainable Chem. Eng., 2016, 5, 835–842.).
[0005] In view of the above problems, it is necessary to focus on the extraction of black liquor lignin, retain the structure of macromolecular lignin and small molecular black liquor lignin derivatives in the black liquor as much as possible, and further propose a method for catalytic hydrogenolysis of black liquor lignin to prepare monophenolic aromatic compounds based on the β-O-4' structure of black liquor lignin. Monophenolic aromatic compounds can be widely used in the preparation of new materials such as thermoplastics, coatings and resin materials. This strategy can not only reduce the waste of lignin resources, but also provide high-value platform chemicals. Summary of the invention
[0006] The purpose of the present invention is to provide a method for separating and purifying liquid lignin and preparing phenolic monomers by catalytic hydrogenolysis, so as to solve the defects of black liquor lignin being complex in structure and difficult to be comprehensively utilized. The complete black liquor lignin structure is retained by extraction and purification, and the monophenol aromatic compounds are successfully prepared by catalytic hydrogenolysis reaction, which not only deepens the understanding of lignin structure research, but also realizes the resource utilization and high-value utilization of black liquor lignin.
[0007] In order to solve the above problems, the present invention adopts the following technical solutions:
[0008] A method for separating and purifying black liquor lignin and preparing phenolic monomers by catalytic hydrogenolysis, comprising the following steps:
[0009] (1) adding the prepared hydrochloric acid solution dropwise to the black liquor while stirring until the pH value is 2-3, and placing the obtained flocculent suspension in a -4°C refrigerator for 12-24 hours; the mixture is centrifuged to obtain a solid precipitate component, which is washed with deionized water several times until neutral, and freeze-dried to obtain black liquor lignin;
[0010] (2) mixing the black liquor lignin obtained in step (1) with dichloromethane at a ratio of 1 g:30-60 mL, mechanically stirring at 20-30° C. for 20-40 min, and filtering to obtain a dichloromethane soluble component (liquid) and a dichloromethane insoluble component (solid);
[0011] (3) The dichloromethane insoluble component obtained in step (2), the Ru / C catalyst and the reaction solvent are mixed and placed in a closed reactor, hydrogen is introduced and the temperature is raised to a reaction temperature of 200 to 260° C., and the reaction is carried out for 1 to 6 hours. After the reaction is completed, the reactor is cooled to room temperature and the pressure is released, and a solid product and a liquid product are obtained after filtration. The obtained liquid product is rotary evaporated and then dissolved in dichloromethane, extracted, and a lignin oil product rich in lignin depolymerization products is obtained.
[0012] Furthermore, in step (1), the black liquor is alkaline kraft pulping flax black liquor.
[0013] Furthermore, in step (1), the concentration of the hydrochloric acid solution is 2-3M.
[0014] Furthermore, in step (1), the stirring speed is 600-800 rpm.
[0015] Furthermore, in step (2), the ratio of the black liquor lignin to dichloromethane is 1 g:50 mL.
[0016] Furthermore, in step (2), the stirring speed is 600-800 rpm.
[0017] Furthermore, in step (3), the ratio of the dichloromethane insoluble component, the Ru / C catalyst and the reaction solvent is 100 mg: 1-7 mg: 2 mL.
[0018] Furthermore, in step (3), the loading amount of the Ru / C catalyst is 5 wt%.
[0019] Furthermore, in step (3), the reaction solvent is one of ethanol, methanol, isopropanol, or a mixture of several of them in any proportion.
[0020] Furthermore, in step (3), the reaction pressure of the hydrogen introduced is 0.3-3 MPa, and the reaction is carried out under stirring conditions at a stirring speed of 200-800 rpm.
[0021] Furthermore, the dichloromethane soluble component (liquid), the dichloromethane insoluble component (solid) and the depolymerized lignin oil product were structurally analyzed by two-dimensional nuclear magnetic resonance analysis, wherein flax lignin and the dichloromethane insoluble component were semi-quantitatively analyzed by two-dimensional nuclear magnetic resonance analysis.
[0022] Furthermore, the lignin oil product is extracted with dichloromethane and then qualitatively and quantitatively analyzed and determined using gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS). The qualitative properties of the product are determined using standard samples, and the quantitative properties are determined using a standard curve method.
[0023] Furthermore, the monomer yield is calculated using the following formula:
[0024] Monomer yield (wt%) = M (total monomer) / M (black liquor lignin) × 100%
[0025] Among them, M (total monomer amount) represents the mass of monomers in lignin oil, and M (black liquor lignin) represents the mass of black liquor lignin input.
[0026] The present invention extracts flax black liquor lignin by acid precipitation method, and uses dichloromethane for extraction and purification, and the obtained insoluble components still contain 40.1% of β-O-4' structure with depolymerization value. On this basis, the black liquor lignin is hydrogenated on Ru / C catalyst, and the product is qualitatively and quantitatively analyzed, and the monomer yield of lignin is 11.7wt%. The present invention provides the possibility of high-value utilization of black liquor lignin.
[0027] Compared with the prior art, the present invention has the following beneficial effects:
[0028] (1) The present invention takes the by-products of the pulp and paper industry as the research object to improve the overall utilization value of biomass resources.
[0029] (2) The reaction conditions in the present invention are mild and an environmentally friendly solvent is used, thereby avoiding corrosion to equipment and pollution to the environment during the process.
[0030] (3) The present invention is a new way to increase the value-added utilization of black liquor lignin, and the monophenolic compounds can become important raw materials for various chemicals, and have good industrial application prospects.
[0031] (4) The present invention analyzes the lignin and derived structures in black liquor, explains the changes in lignin during pulping, and provides a structural basis for further exploration of lignin. BRIEF DESCRIPTION OF THE DRAWINGS
[0032] Figure 1 The two-dimensional NMR spectra of flax lignin and dichloromethane insoluble / soluble components, where (a) is native flax lignin (flax lignin), (b) is dichloromethane insoluble, (c) is the two-dimensional NMR spectrum of dichloromethane soluble components, and (e) is the lignin connection bond type and lignin derived monomer structure.
[0033] Figure 2 This is the GC spectrum of the monomer after hydrogenolysis of the dichloromethane insoluble component in methanol solvent. DETAILED DESCRIPTION
[0034] The present invention is further described below in conjunction with specific embodiments.
[0035] Example 1
[0036] At room temperature, the prepared 2M hydrochloric acid solution was added dropwise to the flax black liquor (alkaline sulfite pulping black liquor provided by Mudanjiang Hengfeng Paper Co., Ltd.) under stirring at 800rpm until pH = 2, and the obtained flocculent suspension was left to stand overnight in a -4°C refrigerator. The mixture was centrifuged to obtain a solid precipitate component, which was washed with deionized water several times until neutral, and freeze-dried to obtain flax crude black liquor lignin. 1g of flax crude black liquor lignin was added to 50mL of dichloromethane, and mechanically stirred at 700rpm for 30min under room temperature. After filtration, 0.7275g (~73wt%) of dichloromethane soluble component (DCM SL) and 0.2711g (~27wt%) of dichloromethane insoluble component (DCM INSL) were obtained.
[0037] The two-dimensional structures of flax lignin and dichloromethane insoluble / soluble components were analyzed by two-dimensional nuclear magnetic resonance technology. Figure 1(a), (b) and (c). The preparation process of the flax lignin is as follows: 40g of flax powder after extraction and ball milling is dispersed in a buffer solution of pH = 4.8 (2.05g of sodium acetate is dissolved in 1L of deionized water containing 1mL of acetic acid), and then cellulase and xylanase are added (flax powder: buffer solution: cellulase: xylanase = 10g: 200mL: 5mL: 1mL). The mixed sample is then placed in a shaker and maintained at a speed of 150r / min and a temperature of 50°C for 72h. After centrifugation, the insoluble residue is retained, the above enzymatic hydrolysis steps are repeated and the solid components are collected by centrifugation, washed with deionized water until neutral and freeze-dried to obtain a solid product. 5g of the above product suspension is added to an acidic (HCl = 0.01mol L -1 )1,4-dioxane / water (85:15, v / v, 100 mL) mixture, reflux (azeotropic, 86°C) for 4 h under nitrogen environment. The supernatant collected by centrifugation is neutralized with sodium bicarbonate and then rotary evaporated to obtain a concentrated solution. The above concentrated solution is added dropwise to a hydrochloric acid aqueous solution (pH = 2) to form a precipitate, which is centrifuged, washed to neutrality and freeze-dried to obtain flax lignin.
[0038] After pulping with alkaline sulfite method, the structure of lignin changed significantly. Compared with flax lignin, the CO bond signal in DCM INSL component decreased, but the CC bond signal area increased, while almost no connecting bond signal was detected in DCM SL component. This result preliminarily indicates that the lignin structure was rearranged during pulping and partially depolymerized into small molecular monomers. Figure 1 As shown in (c), the two main aromatic compounds identified are vanillin (VA) composed of G units and syringaldehyde (SA) composed of S units, both of which are products of oxidative depolymerization of lignin.
[0039] Aromatic S 2 / 6 The content of lignin linkages was semi-quantitatively analyzed on the basis of volume integration, with the G2 peak as reference (Table 3-4). Compared with flax EMAL, the S / G ratio of DCM INSL (4.4) was slightly lower than that of flax EMAL (5.7), which may be due to the fact that S-type lignin is easier to remove than G-type lignin during chemical pulping. In addition, the condensed lignin structure was still as high as 32.4% (β-5: 30.5%; β-β: 1.9%), indicating that lignin underwent depolymerization during pulping, accompanied by condensation side reactions, resulting in a high degree of condensation of lignin. Surprisingly, DCM INSL still contained 40.1% of β-O-4' bonds, and the lignin CO bonds were less broken in this reaction system, which provided the prerequisite for the hydrogenolysis of black liquor lignin.
[0040] Table 1 Chemical bond content (%) and S / G value of flax lignin and dichloromethane insoluble components
[0041]
[0042] Example 2
[0043] 0.5g of the insoluble component in dichloromethane, Ru / C catalyst (5wt%, Macklin reagent) and methanol solvent were mixed in a ratio of 50mg:2mg:1mL and placed in a closed reactor. After 3MPa of hydrogen was introduced, the temperature was raised to 240°C and the reaction was carried out at 800rpm for 4h. After the reaction was completed, the reactor was cooled to room temperature and the pressure was released. After filtration, solid products and liquid products were obtained. The obtained liquid product was dissolved in 30mL of dichloromethane after rotary evaporation and extracted to obtain a lignin oil product rich in lignin depolymerization products. After the above product was spin-dried, 5mL of dichloromethane was added for dissolution and then entered into GC and GC-MS for quantitative and qualitative analysis. The analyzed products were as follows: Figure 2 The monomer yields are shown in Table 2.
[0044] Table 2 Monomer yield of dichloromethane insoluble components in methanol solvent
[0045]
[0046] Example 3
[0047] The same as Example 2, only the reaction solvent was replaced with ethanol, isopropanol, 1,4-dioxane, and the monomer yields were shown in Table 3.
[0048] Table 3 Monomer yields of dichloromethane insoluble components hydrogenolysis in different solvents
[0049]
[0050]
[0051] Example 4
[0052] Same as Example 2, only the reaction temperature was changed to 200, 220, 260°C, and the monomer yields are shown in Table 4.
[0053] Table 4 Effect of different temperatures on the monomer yield of hydrogenolysis of dichloromethane insoluble components
[0054]
[0055] Example 5
[0056] The same as Example 2, except that the reaction time was changed to 1, 2, and 6 h, the monomer yields are shown in Table 5.
[0057] Table 5 Effect of different time on the monomer yield of hydrogenolysis of dichloromethane insoluble components
[0058]
[0059] Example 6
[0060] The same as Example 2, only the amount of Ru / C catalyst was changed, 0.5 g of dichloromethane insoluble component, Ru / C catalyst and methanol solvent were mixed according to 50 mg: (0.5, 1, 3 or 3.5) mg: 1 mL, that is, 0.5 g of dichloromethane insoluble component and 10 mL of methanol solvent, the amount of Ru / C catalyst added was 5, 10, 30, 35 mg, respectively, and compared with the amount of Ru / C catalyst added (20 mg) in Example 2, the monomer yield is shown in Table 6.
[0061] Table 6 Effect of different catalyst dosages on the monomer yield of hydrogenolysis of dichloromethane insoluble components
[0062]
[0063]
Claims
1. A method for separating and purifying black liquor lignin and preparing phenolic monomers by catalytic hydrogenolysis, characterized in that: The following steps are involved: (1) adding hydrochloric acid solution dropwise to black liquor while stirring until pH=2-3, and placing the obtained flocculent suspension in a -4°C refrigerator for 12-24 hours; the mixture is centrifuged to obtain a solid precipitate component, which is washed with deionized water several times until neutral, and freeze-dried to obtain black liquor lignin; (2) mixing the black liquor lignin obtained in step (1) with dichloromethane in a ratio of 1 g:30-60 mL, mechanically stirring at 20-30° C. for 20-40 min, and then filtering to obtain a dichloromethane soluble component and a dichloromethane insoluble component; (3) The dichloromethane insoluble component obtained in step (2), the Ru / C catalyst and the reaction solvent are mixed and placed in a reactor, hydrogen is introduced and the temperature is raised to a reaction temperature of 200 to 260° C., and the reaction is carried out for 1 to 6 hours. After the reaction is completed, the reactor is cooled to room temperature and the pressure is released, and a solid product and a liquid product are obtained after filtration. The obtained liquid product is rotary evaporated and then dissolved in dichloromethane, extracted, and a lignin oil product rich in lignin depolymerization products is obtained.
2. The method for separating and purifying black liquor lignin and preparing phenolic monomers by catalytic hydrogenolysis according to claim 1, characterized in that: In step (1), the black liquor is alkaline kraft pulping flax black liquor.
3. The method for separating and purifying black liquor lignin and preparing phenolic monomers by catalytic hydrogenolysis according to claim 1, characterized in that: In step (1), the concentration of the hydrochloric acid solution is 2-3M.
4. The method for separating and purifying black liquor lignin and preparing phenolic monomers by catalytic hydrogenolysis according to claim 1, characterized in that: In steps (1) and (2), the stirring speed is 600 to 800 rpm.
5. The method for separating and purifying black liquor lignin and preparing phenolic monomers by catalytic hydrogenolysis according to claim 1, characterized in that: In step (3), the ratio of the dichloromethane insoluble component, the Ru / C catalyst and the reaction solvent is 100 mg: 1-7 mg: 2 mL.
6. The method for separating and purifying black liquor lignin and preparing phenolic monomers by catalytic hydrogenolysis according to claim 1, characterized in that: In step (3), the loading amount of the Ru / C catalyst is 5 wt %.
7. The method for separating and purifying black liquor lignin and preparing phenolic monomers by catalytic hydrogenolysis as claimed in claim 1, characterized in that: In step (3), the reaction solvent is one or a mixture of ethanol, methanol, isopropanol, and 1,4-dioxane.
8. The method for separating and purifying black liquor lignin and preparing phenolic monomers by catalytic hydrogenolysis as claimed in claim 1, characterized in that: In step (3), the reaction pressure is 0.3-3 MPa, and the reaction is carried out under stirring conditions at a stirring speed of 200-800 rpm.