Extraction Of Lignin From Bamboo Residues Using Glycerine And Study Of Lignin Alcoholysis With Solid Acid Catalyst

As the problem of global fossil resources shortage and the environmental concerns getting serious, it is necessary to explore new renewable resources in place of fossil resources. Lignin which is the only renewable aromatic compounds from non-fossil resources, has been paid extensive attentions in both academia and industry.Natural lignin is one of three polymer materials in the lignocellulosic biomass. Industrial lignin which is a kind of by-product from paper industry has been burned as fuel. Speed of research and development in lignin utilization can not keep up with the needs of industrial development, so lignin usually is burned which not only waste the resouce but also pollute the environment seriously. One of the main reasons is that industrial lignin mainly contains alkali lignin and ligin sulfonates, the functional groups in the lignin had suffered serious damage during the processing, and the reaction activity of the lignin was greatly reduced. Separation and purification of the lignin is very difficult. Solvent pulping could get the high-purity lignin with the natural structure of the lignin being well-preserved. Lignin obtained from solvent pulping could be decomposed into a variety of small organic molecules of aromatic or aliphatic compounds under proper conditions. As a result, lignin can be considered a functional renewable resources in place of petroleum chemical products.As the by-product of the booming biodiesel industry, glycerol is cheap renewable green chemical raw materials. Glycerol is a solvent with high reactivity and high boiling point, with which as a solvent, pulping can been accomplished at atmospheric pressure. Although more research on the use of glycerol solvent in the pulping process and the use of obtained lignin need to be done.In this study, conditions of the lignin preparation with glycerin pulping under atmospheric pressure and the effect of lignin under different alcohol degradation reagent had been studied. One of solid acid catalyst had been selected form three green solid acid catalysts, which could be suitable for industrial mass production. Tubular reactor was used in the alcoholysis of lignin in an attempt to provide a new direction for lignin green manufacturing with solvent pulping. The results of study obtained are as follows:1. According to the results of the single-factor test of glycerol pulping at atmospheric pressure, the orthogonal experiment was designed and tested to determine the optimal conditions for the glycerol lignin preparation. Under the conditions of270℃cooking for3h, with solid-liquid ratio of1:14, the catalyst (sulfuric acid) amount to0.1%, lignin yield could reach20.6%.2. According to the analysis of the physical and chemical properties of the glycerin lignin, the content of phenolic group in the glycerin lignin was3.04%, the content of total hydroxyl was13.01%, the content of alcohol hydroxyl was9.97%, all were better than those from other kind of industrial lignin. Through the ultraviolet and infrared scanning map analysis, lignin and MWL (spell out)had similar chemical structures. Percentage of small molecules was6.2%in glycerol lignin and the average molecular weight of the glycerin lignin was665.5.3. Alcoholysis of the glycerin lignin with ethanol, n-Pentanol, n-octyl alcohol, ethanol and n-octyl alcohol mixture, ethanol, n-octyl alcohol and phenol mixture were investigated, and the content of phenolic hydroxyl and total hydroxyl in different lignin alcoholysis liquid were determined. The change in n-Pentanol alcoholysis liquid was the most significant, with the content of total hydroxyl and phenolic hydroxyl being0.082mol/L and0.024mol/L, respectively, indicated an increase of25.6%and54.1%, respectively. Percentage of small molecules were9.2%、8.6%、4.5%、8.9%、8.5%, and the average molecular weight were643.2、197.7、114.1、629.5、635.2, respectively, for the alcoholysis solvents used. Through FT-IR and UV analysis of the process of alcoholysis of the lignin, it was found that the guaiac base was degraded first, and the syringyl were not easy to be alcoholyzed. The molecular weights of the different alcoholysis product were also determined to be643.2,197.7,114.1,629.5,635.2, respectively when ethanol, n-Pentanol, n-octyl alcohol, ethanol n-octyl alcohol mixture, or ethanol n-octyl alcohol and phenol mixture were used as the alcoholysis solvent. Phenols were tested in different alcoholysis product using GC-MS, the results showed that lignin carbon chain was ruptured during the process of alcoholysis. 4. Alcoholysis was conducted with n-pentanol as the alcoholysis solvent. Using the content of phenolic hydroxyl as an index, the solid acid catalysts of SiO2-Al2O3, WO3-ZrO2, and Fe3O4-Al2O3were compared and selected. The concentration of the phenolic hydroxyl group increased by101.7%,104%,90.2%in the alcohol solution, respectively with the solid acid catalysts of SiO2-Al2O3,WO3-ZrO2、Fe3O4-Al2O3WO3-ZrO2and SiO2-Al2O3had same catalytical effect according to the GC-MS analysis, and Fe3O4-Al2O3had obviously lower effect than the other two. Since W and Zr is expensive, the SiO2-Al2O3was chosen for in-depth study to explore the best preparation process parameters for the SiO2-Al2O3solid acid catalyst. The structural characterization of the SiO2-Al2O3solid acid catalyst was studied using X-ray diffraction, thermogravimetric analysis and FT-IR. Results indicated that the tubular reactor with the SiO2-Al2O3solid acid catalyst bed could be used for the alcoholysis of the glycerol lignin, and the alcoholysis products were also analyzed. This study should help develop a new low cost green chemical process for phenolic compounds production from the pulping lignin and enhance the overall profitability of the solvent pulping industry.