Advanced biofuels are required to play a key role in the transition to a sustainable global fuel economy. In the European Union, the revised Renewable Energy Directive (2018) aims to increase the share of renewable energy in transport to at least 14%, including a minimum share of 3.5% of advanced biofuels.

It has previously been shown that gasoline and diesel compatible drop-in advanced biofuel additives can be produced via the acid catalysed hydrolysis of lignocellulosic biomass in alcohol solvent.

A parameterised study into the effect of various reaction conditions (reaction time, feedstock loading, acid concentration and temperature) on the chemical composition of the advanced biofuel products is reported with the aim of informing reaction kinetics process simulation. Reactions are initially performed using a constant concentration of sulphuric acid (0.5% mass) as the catalyst, ethanol as the alcohol, and glucose, cellulose, and corn cob as the feedstocks. The concentrations of the ethanol consumed and of the diethyl ether and ethyl levulinate formed are quantitatively determined using gas-chromatography.

It is found that the yield of the ethyl levulinate increases with increasing feedstock concentrations and with increasing reaction times, until a steady state is reached. This is true for glucose and cellulose. However, the yield of ethyl levulinate does not scale with feedstock concentration for the real biomass used (corn cob). Further investigation concluded that this effect is due to the changing feedstock/acid ratio as the feedstock loading in increased. It is observed that for a maximum yield of ethyl levulinate from real biomass, the acid concentration must be scaled with the feedstock concentration. We hypothesise that this is due to the hydrogen cation from the acid catalyst being consumed in some irreversible process so that the reaction cannot proceed. This is consistent with observations of increased rate and yield when the ratio of biomass/acid is fixed.

The experimental data was used to train a mass-conserved chemical kinetic model for the ethanolysis of glucose, cellulose, and corncob involving a simplified reaction network of 21 species. The reaction network is hierarchical in structure to capture the incremental effects of complexity in feedstock molecular composition, from glucose, to cellulose, to corn cob. Optimal conditions for the yields of diethyl ether and ethyl levulinate are identified.

Conall McNamara

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