Study On The Catalytic Liquefaction Of Industrial Kraft Lignin For The Production Of Phenols

The lignin is the second largest aromatic polymer material only inferior to cellulose in amount. Industrial kraft lignin, a waste polymer by product from kraft pulping process in the pulp and paper industry was usually burnt off. Biomass is an important part of renewable energy resource. Effective conversion of biomass energy is the hot point in the research and industry. We can work it out with the method of catalytic liquefaction. This atmospheric liquefaction process is energy saving without high pressure equipment and has has development potential. The technological parameters and machanismof catalytic of industrial kraft lignin to phenols were studied for commercial process.After comparing the catalytic effects of different kinds of inorganic and organic acid, SiO₂ Al₂O₃ and FeS were chosen and used in experiments creatively. The optimal reaction conditions were researched including catalyst dosage, heating time, heating temperature, solvent glycerol volume. The material was industrial kraft lignin and solvent was glycerol. SiO₂ Al₂O₃ and FeS were used in experiments as to find the similarities and differences during the reaction between them.When SiO₂ Al₂O₃ was the catalyst, the optimal reaction conditions were catalyst dosage 4%, heating time 1h, heating temperature 240℃, liquor solid ratio 4 ml g^-1. The yield of phenolic compounds approached 54.10% under opimal conditions. While FeS was employed as catalyst, the optimal parameters were catalyst dosage 4%, heating time 1h, heating temperature 240℃, liquorsolid ratio 3 ml g^-1. The yield of phenols approached 55.18%. The chemical structure and categories of liquefaction products were studied in detail, byusing the methods of elemental analysis, FTIR, 1H NMR, GPC, HPLC, GC MS and GC. The main phenolic products were 2,6 dimethoxy phenol（15.73 wt%）, 2 methoxy phenol（12.26 wt%） and phenol（13.65 wt%） with the catalyst SiO₂ Al₂O₃. While the main phenols were 2 methoxy phenol（15.82 wt%）, 4 methyl 2 methoxy phenol（14.78 wt%） and 2,6 dimethoxy phenol（12.47 wt%） by FeS. The result of the liquefaction experiments was more desired than that of traditional liquefaction with inorganic acid.Furthermore, the kinetic analysis showed that these two liquefaction processes followed first order reaction. The reaction velosity constant was 0.0158 min^-1 and activation energy was 44.2028 KJ mol^-1 with SiO₂ Al₂O₃ and that of FeS were 0.0212 min^-1, 35.7251 KJ mol^-1.Takes the lead to study the structural changes of kraft lignin during liquefaction. When using SiO₂ Al₂O₃ as the catalyst, theα-O-4 andβ-O-4 ether bonds and C-C_αbonds of lignin units were prone to break, forming 2,6 -dimethoxy phenol, 2 -methoxy phenol, phenol and other phenols, aicds compound.While FeS action was more difficult, theαO 4 andβO 4 ether bonds and parts of C_α-C bonds broke down. Then, the introduction of additional hydroxyl groups from glycols consequently increased the solubility of other parts. At the same time, C_β–C_γbond of the phenylpropane linkage was broken to produce phenolic chemicals. Third, C_γdeprivation and structural rearrangement occurred. So the content of 2 methoxy 4 methyl phenol and the yield of cyclopentanone were high. Other kinds of industrial lignin were also well liquefied with this method. The technology for separation and recovery of phenols from liquefaction products was also discussed for industrialized determination.