A free radical catalyzed depolymerization process to convert intact lignocellulosic biomass to hydrocarbon fuel precursors and purified cellulose

Current sugar-platform biorefinery research has mainly focused on the degradation of polysaccharides while leaving the lignin as a waste product. In this study, a novel one-pot catalytic process was developed to selectively depolymerize the lignin fraction of intact lignocellulosic biomass to hydrocarbon fuel precursors, while leaving the solid cellulosic fraction in high purity. The catalysis was driven by free radical reactions that selectively degraded lignin through demethoxylation and subsequent beta-ether bond cleavage between subunits resulting in low weight aromatics and aliphatic acids (hydrocarbon precursors). The degradation to the cellulose was minimal. The catalyst’s free radical mechanism was discovered through previous work in which hydrocarbon precursors were obtained from pure lignin in yields up to 66%. The one-pot reaction produced a biphasic liquid that included water solubles and organic oil. The organic phase was extracted by dichloromethane and consisted of the target hydrocarbon precursors. The water soluble phase was mainly monomer or oligomer sugars from hemicellulose. The residual solid fraction was highly purified cellulose, which could be directly used for materials or further hydrolyzed to produce fuels or chemicals. The catalysts chosen for experimentation were composed of low-cost metals and oxidants. This new research successfully demonstrates a controlled free radical depolymerization of the lignin fraction of intact lignocellulosic biomass.