Converting lignocellulose feedstock into potential replacements for petroleum-derived products

Abstract

Biomass can be used as a renewable energy source to reduce the over-reliance on fossil fuels. Lignocellulose, which is non-edible and the most abundant biomass in the world, comprises two carbohydrate polymers (cellulose and hemicellulose) and one aromatic polymer (lignin). This thesis examines work done to convert lignocellulose biomass to liquid fuels and solvents that are currently derived from fossil fuels. The work is mainly divided into two sections. In the first section, the attempts to make transportation fuel range alkanes (C8-C22) using hydroxymethylfurfural (HMF) oligomers are described. The second section of the thesis explains the attempts to synthesize cyclohexyl methyl ether mixture from lignin to replace fossil fuel derived solvents. Under acidic conditions, HMF, a compound obtained by processing carbohydrate polymers, polymerizes to form an insoluble polymer called humin. In this work, oligomerization of HMF has been used as an opportunity to increase the carbon chain length of HMF. Simultaneous oligomerization and hydrodeoxygenation of HMF were shown to make long-chain alkanes (>C9). Completion of hydrodeoxygenation was confirmed by 1H NMR spectroscopy. According to mass spectroscopy, long chain alkanes up to about 600 m/z were present. Alkanes from C9-C18 were analyzed by GC-MS. Different straight, branched, and cyclic alkanes with C10-C12 were observed. From these n-dodecane had the highest concentration. Most of the major peaks were consistent with the alkanes obtained through dimers from oligomerization and self-condensation reactions of HMF. A mixture of cyclohexyl methyl ethers was prepared from Kraft lignin pyrolysis oil for use as a biomass-derived aliphatic solvent. Using Kamlet–Taft solvatochromic parameters, it was determined that the solvent mixture is somewhat more basic and polar than cyclopentyl methyl ether. Neither the biomass- derived solvent nor pure cyclohexyl methyl ether formed any detectable peroxides in 12 weeks of exposure to air, even though THF forms peroxides rapidly under such conditions. This mixture can be used as a biomass-derived aliphatic ether solvent and as a potential replacement for THF, dioxane, ethyl acetate, acetone and 2-butanone.