Utilisation of biomass for sustainable fuels and chemicals: Molecules, methods and metrics

The various catalytic methodologies for the utilisation of renewable biomass for the sustainable production of liquid fuels and commodity chemicals are reviewed. Attention is focused on second generation processes starting from lignocellulose as a sustainable feedstock, thus circumventing the food vs fuel dilemma, and on the green features of these new processes. Emphasis is also placed on the need for establishing a set of metrics for assessing the sustainability of different processes and products. It is concluded that one set of metrics is probably not sufficient to assess the sustainability of both biofuels and platform commodity chemicals. The latter can probably be evaluated on the basis of E factors (kgs waste/kg product) that take both the carbon dioxide derived from energy consumption and water usage into account, perhaps together with some form of life cycle assessment. With biofuels on the other hand, the sheer magnitude of the volumes involved present extra issues, such as land usage, and the goal is different, i.e. to produce a particular energy density for an economically viable price in a sustainable fashion.