Conversion Of Lignin Into Aromatic Compounds Over Silica-alumina Solid Acid

Biomass is a significant feedstock for renewable production of fuels, chemical and energy. Currently, in the investigation and industrialization of biomass conversion, cellulose and hemicellulose can be converted and utilized efficiently. However, most lignin was difficult to be converted because of its compacted and steady structure. Simultaneously 2000t of industrial lignin were generated every year, which could be feedstock for aromatic compounds. Hence, the depolymerization of lignin is important.In this work, we used a series of silica-alumina solid acid (SiO2-AL2O3, HY, Hβ and HZSM-5) to degrade lignin into arenes and phenols. The effect of structure, acidity and pore size of catalyst on lignin depolymerization was investigated. The results showed that both acidity and pore size of the catalyst could influence the conversion of lignin. SiO2-Al2O3 with moderate acidity and larger was the most efficient catalyst. In the liquid product, phenols were identified as the main phenolic monomers via Gas Chromatography-Mass Spectrometer (GC-MS). SiO2-AlO3 was the most efficient catalyst, giving 12.91% yield of phenols and 2.41% yield of arenes in ethanol at 280℃ for 4 h. The Fourier Transform Infrared Spectroscopy (FT-IR) and’H Nuclear Magnetic Resonance Spectroscopy (1H-NMR) analysis demonstrated that deoxygenation and alkylation occurred in the catalytic process.Also, the depolymerization of other lignin (dealkali lignin, alkali lignin and sodium ligonosulfonate) was investigated and the effect of their structure was discussed. However, SiO2-Al2O3 was not efficient enough for depolymerization of alkali lignin, so a series of Ni supported SiO2-Al2O3, Ni/SiO2-Al2O3, was prepared. The effect of Ni loading, reaction temperature, reaction time and catalyst dosage was investigated. Using 0.1 g 15% Ni/SiO2-Al2O3,9.10% yield of arenes and 17.54% yield of phenolic monomers were obtained in ethanol, at 300℃ for 8 h. Via The Fourier Transform Infrared Spectroscopy (FT-IR) and Liquid Chromatograph Mass Spectrometer (LCMS) analysis, in this process, the transformation of lignin structure and molecular weight was investigated. Also the catalyst was involved in depolymerization of solid residues from hydrolysis of biomass, where 2.01% yield of arenes and 3.10% yield of phenolic monomers were obtained.The investigation in this work can give a novel approach to lignin conversion and data basis on utilization of solid acid in process of lignin depolymerization.