Direct conversion process for enhancing biodiesel production from insect biomass waste

This study aimed to ascertain the viability of silkworm pupae as a biodiesel (BD) feedstock. The silkworm pupal extract (31.98 wt% based on the pupae) contains impurities, including free fatty acids (FFAs) and hydrocarbons (HCs). These impurities hindered the conversion of lipids into BD using conventional methods (alkali/acid-catalysed transesterification). The BD yield via conventional transesterification was below 70 wt% due to side reactions such as saponification and hydrolysis. In response to the technical constraints inherent in conventional methods, non-catalytic transesterification was introduced. Owing to the high tolerance of non-catalytic method toward the impurities, the BD yield (91.6 wt%) was significantly higher than conventional methods. This indicated that over 99 wt% of lipids in the extract were converted into BD. The reaction time of non-catalytic method (within a minute) was also shorter than acid-(24 h)/alkali-(100 min) catalysed transesterification. To enhance the BD production, silkworm pupae were directly converted to BD, yielding 103.5 wt% (lipid basis). This implied incomplete lipid extraction or lipid loss during the extraction step. This study presents a new pathway for the valorisation of waste in the textile industry, with the potential to make a significant contribution to the establishment of a circular economy. The direct conversion method would not be limited to silkworm pupae; it has the potential to be adapted for a variety of insect-based feedstocks. By expanding its application, this method would contribute to more sustainable biofuel production and also contribute to the achievement of Sustainable Development Goal: 7 (Affordable and clean energy).