Environment Benign Technology For Lignin Degradation

With the development of human society, the resource crisis and environmental pollution have become the two major challenges faced by the human community. The exploitation and utilization of biomass is very important to resolve the crisis. The importance of the resources based on wood material, is gradually being known. The resources will be exploited and utilized as basical raw material in chemical industry. The study of environment benign technology for lignin degradation has achieved good future prospects. This article attempts to clarity the mechanisms of lignin treated by imidazolium ionic liquids as well as laccase, and to further obtain related information of products.Results obtained were as follows:1-. The research on liquefaction conditions of wood powder treated by [Bmim]ClThe research on liquefaction conditions of wood powder treated by [Bmim]Cl was done under atmospheric conditions. The results showed that temperature, time, the impurities of [Bmim]Cl, and solid-liquid ratio affected the efficiency of liquefaction. Higher temperature, longer treating time, smaller Solid-liquid ratio and higher concentration of [Bmim]Cl increased the efficiency of liquefaction. When the liquefaction conditions included as follows:the solid-liquid ratio was3:100,and the temperature was80℃, and the time was24h, as well as [Bmim]Cl was pure, the efficiency of liquefaction was99%. The liquefaction of wood powder reported before was often carried out at high temperature and pressure.2,Establishment of lignin content determination methods and lignin solubility determinationThe standard absorption curve of lignin dissolved in the co-solvent of Ionic Liquid [Bmim]Cl and water was set up. The content of CEL in solvent was obtained. Compared with the traditional method for the determination (sulfate determination of lignin content), the experimental results showed that this method was more accurate, and more reliable. Through this mothed, the maximum lignin content in60%and45% [Bmim]Cl water solution was143.5mg/ml and95.8mg/ml, respectively,which demonstrated that ionic liquid [Bmim]Cl had a very strong ability of dissolving CEL.3,[Bmim]Cl lignin extraction and validation[Bmim]Cl lignin was extracted and the conditions affecting its yield were analyzed. The acetone was better extractant than others solves and when acetone-water volume ratio was1:1, the yield of lignin was higher than the control. Compared with CEL, FTIR spectra showed the extracted [Bmim]Cl lignin had the characteristics of lignin absorption peaks.'H-NMR spectra showed that the Proton-type in [Bmim]Cl lignin was basically the same as CEL, but the Proton numbers was different to CEL, especially proton numbers in methoxy were significantly different.13C NMR spectra showed that [Bmim]Cl lignin lost a lot of integral signals. The primary reasons may be that [Bmim]Cl lignin was suffered destruction of ionic liquids, and some changes in the structure of the benzene ring occurred, which needs to be further discussed. All in all, the preparation method of [Bmim]Cl lignin has some advantages as follows:the preparation process is simple, and [Bmim]Cl may be recycled. Without repeated dissolution of strong acid or alkali, Bmim] Cl lignin structure obtained was less damaged. Thus, the method may be used as a new method for lignin preparation.4,Determination of stability of laccase in ionic liquidsThe laccase from Trametes hirsuta1g-9was produced and its stability in [Bmim]Cl and in organic solvents were tested. The results showed that the laccase activity is persistent in organic solvents, as well as in [Bmim]Cl. The laccase in certain [Bmim]Cl concentration can often maintain high stability. In the presence of high [Bmim]Cl content, the laccase activity lost fast. But the time is enough for laccase to cause some changes of the substrate before its activity completely was lost. The laccase activity was determinated in the45%[Bmim]Cl under different pH, and the results showed that the laccase activity remains still high when pH was5to7.5,The effect of laccase on CEL in two different solution systemsWe chose CEL as the substrate and laccase from Trametes hirsuta1g-9as the research object. The purpose of this study was to prove whether laccase catalytic efficiency is far higher in a [Bmim]1/H2O homogeneous solution than in a water heterogeneous solution. Results obtained were as follows:After laccase treatment of CEL in the heterogeneous water solution, CEL was then compared with control sample A. UV spectra showed that the total absorbance of sample B increased at205and280nm; FTIR spectra showed that the carbonyl group obviously appeared; and13C-NMR spectra showed that the C-y signals disappeared, the C-a signals significantly increased, and the methoxyl content decreased. After laccase treatment of CEL in the homogeneous [Bmim]Cl/H20solution, CEL was compared with control sample C. UV spectra showed that the total absorbance of sample D decreased at280nm; HPLC analysis showed that some small absorption peaks disappeared; and13C-NMR spectra showed that the C-y signals obviously increased, the C-a signals slightly decreased, and the methoxyl content increased. From the above discussions, the laccase from our laboratory could clearly act on CEL whether in the water heterogeneous solution or in the [Bmim] Cl/H2O homogeneous solution. Due to the different dissolution degrees, the results were significantly different. For insoluble CEL in the heterogeneous water solution, laccase partly oxidized the hydroxyl group into a carbonyl group. Consequently, CEL was degraded which increased its solubility. On the other hand, for soluble CEL in the [Bmim] Cl/H2O homogeneous solution, laccase primarily polymerized small molecule fragments of CEL with the CEL macromolecule and increased the methoxyl content of CEL, so accordingly it played a role in lignin polymerization.6,The effect of other ionic liquid on CELCEL was completely dissolved in [Emim]Ac and [Pmim]Ac at80℃respectively. After24h, the distilled water was added into the solution. The supernant and the precipitation were obtained, respectively. The supernant was extracted with toluene, methylene chloride, and ethyl acetate, respectively. The precipitation was lyopHilized and analyzed. The results showed that the dissolution products in [Emim] Ac received higher yields with ethyl acetate extraction, while the dissolution products in [Pmim]Ac received higher yields with methylene chloride extraction. In all of the products from the former, the main products are Methyl-(2-hydoxy-3-ethoxy-benzyl) ether (120mg) and vanillin (21.5mg); while from the latter, the main products are Methyl-(2-hydoxy-3-ethoxy-benzyl) ether(180mg) and3-hydroxy-4-methoxy-Benzaldehyde (79.5mg).1H NMR spectra showed that the proton number in the functional group of lignin after being treated by the two ionic liquids had small changes compared with the control. After being treated with [Pmim] Ac, both the carboxyl group and the aldehyde of lignin lost a proton. One proton was added to guaiacylpropanoid(G) after the two Ils treated, and One proton was added to syringylpropanoid (S) after [Emim]Ac treated. In addition, the proton number in methoxyl increased after [Emim] Ac treated. These showed that the cation type in Ils can affect the mechanisms of dissolving lignin.13C NMR spectra showed that the methoxyl content in G or S has increased significantly compared with the control; the C-γ and C5G signals increased obviously after being treated with [Pmim] Ac. In addition, the C6G (G') signals increased after being treated with [Pmim] Ac, while the signals disappeared after being treated with [Pmim] Ac.