Thermal Deoxygenation of Levulinate and Formate Salts for the Production of Transportation Fuels
Thermal deoxygenation (TDO) refers to a simple, non-catalytic, reaction scheme for the removal of oxygen from cellulosic feedstock. The primary reaction is a single-step decomposition which converts neutralized biomass-derived acids at 450°C under inert atmosphere and ambient pressure to chars, water and volatile organic products. For simple acid salts, ketonic decarboxylation yields volatile ketones and metal carbonates. Recently, TDO was applied to levulinic acid and formic acid mixtures yielding a complex mixture of aromatic compounds with low oxygen content (<4 >wt%). The crude oils offer opportunities for the displacement of fossil fuels in transportation applications. This dissertation describes the chemistry and kinetics of TDO reactions involving alkaline-earth metal levulinate and formate salts. Considerations are made for the role of the neutralization cation, feedstock contaminants and formate addition.
The salts are shown to undergo a series of material changes resulting in two volatilization regimes. In Stage I volatilization, between 200-350°C, melt-phase condensation reactions involving levulinate methylketone functionality leads to a poly-salt of increasing molecular weight and reduced oxygen content. Above 400°C, Stage II volatilization results from decarboxylation reactions yielding condensable aromatic species of broad boiling point distribution (75-585°C). Stage I and Stage II reaction yields and kinetics are reported and a two-step reaction model is presented describing mass volatilization rates for levulinate and levulinate formate mixed salts of the alkaline-earth metals; magnesium, calcium and strontium. This research identified TDO process improvements demonstrated to improve crude oil yields and material handling operations.