Critical evaluation of process parameters for direct biodiesel production from diverse feedstock

Bottlenecks on the development of biodiesel production could be eliminated using direct transesterification (DT). This review presents a comprehensive overview for DT from oleaginous seed crops (edible and non-edible), microalgal and fungal/yeast biomass. Effects of key operational parameters, affecting the yield of biodiesel, such as feedstock, feedstock processing technologies, feedstock water content, catalyst choice, temperature, co-solvent and reaction time are summarised and critically assessed. 15% and 68% of published data showed high fatty acid (FA) yields and FA to fatty acid methyl ester (FAME) conversion efficiencies, respectively. Highest fatty acid yielding feedstock were Jatropha and a novel non-edible Mediterranean crop, Cynara cardunculus, the microalgae Chlorella and Nannochloropsis, and the fungi/yeast Trichosporon oleaginosus, Rhodosporidium toruloides, Lipomyces starkeyi, Mortierella isbellina, and Pichia guilliermondi. For wet micmalgal biomass, a preference for acidcatalysed direct transesterification was determined, while base-catalysed DT was more suitable for dry biomass, except for turbo-thin film-assisted DT of microalgal biomass. The data highlight that DT operational parameters and technologies need optimisation for feedstock and water content and outcomes may be strongly straindependent for micmalgal feedstock. To bring commercial biodiesel potential of some high-yielding feedstock to reality, comprehensive life cycle - and techno-economic analyses are required for intensified and nonintensified DT processing, taking feedstock production and possibilities of biorefinery concepts into account whilst also focussing on those processing platforms that can esterify fatty acids in wet biomass.