Reaction Kinetics, Catalyst Development, and Reaction Networks for Hydrothermal Hydrodeoxygenation.

Abstract

This dissertation examines issues related to producing a hydrocarbon biocrude from wet algal biomass. It first reports on the hydrothermal liquefaction (HTL), a high-temperature (>250 °C) and high-pressure (>40 bar) aqueous treatment, of Nannochloropsis sp. to produce a bio-oil. Determining the elemental and molecular composition of the bio-oil, aqueous, gaseous, and solid products produced by HTL at 350 °C revealed how these product compositions are affected by the choice of solvent used to extract the bio-oil. Hexadecane and decane provided the highest gravimetric yields of bio-oil (39 wt% each). Furthermore, quantifying 19 individual molecular components in the bio-oil showed that many of the heteroatoms (N, S, and O) were present in free fatty acids and heterocyclic molecules. The removal of oxygen from the bio-oil increases the energy density and stability of the oil, while decreasing the viscosity. Studying the effect of process variables on hydrothermal hydrodeoxygenation (HDO) of benzofuran over Pt/C at 380 °C provided the reaction network and kinetics for benzofuran HDO. The kinetic analysis revealed that benzofuran had an inhibitory effect on the dehydration of ethylphenol to ethylbenzene. Studying the hydrothermal HDO of o-cresol in a flow reactor at 380 °C showed that Pt/C, Raney Ni, and 10 wt% Raney NiCu were stable under the hydrothermal reaction conditions, but only Pt/C and Raney NiCu were selective for the production liquid hydrocarbons. The Raney NiCu catalyst increased the liquid hydrocarbon yield by a factor of 3.4 when compared with the unmodified Raney Ni. Raney NiCu catalysts doped with more than 10 wt% Cu showed a significant decrease in gasification activity and an increase in liquid oxygenated products, but no change in the desired liquid hydrocarbons. The addition of acid sites to the NiCu catalysts, either by supporting NiCu on Al2O3 or by calcining the Raney Ni catalyst to convert Al in the catalyst to Al2O3, increased the liquid hydrocarbon yield significantly. In flow reactions, two catalysts, calcined 5% Raney NiCu and 10%, 0.5% NiCu/Al2O3, achieved a high (~70%) and stable yield of liquid hydrocarbons. These catalysts provided the highest known stable yields of liquid hydrocarbons for hydrothermal HDO.