Biodiesel production from algae through in situ transesterification technology

Abstract

Biodiesel, a promising renewable biofuels, is receiving increased attentions. Due to the high price of vegetable oils and the land use competition of biodiesel feedstock production and food production, it is necessary to find other ways to lower the biodiesel production cost and reduce the pressure on food and feed supplies. One possibility to overcome these problems is to produce biodiesel from microalgae feedstock using advanced conversion process. The conventional biodiesel production involves a two-step process in which oil is first extracted from oil feedstock and then subjected to transesterification step. Unfortunately, it is hard to extract oil from algae, making algae based biodiesel production very costly. In this thesis project, an innovative in situ direct transesterification method was investigated. In situ direct transesterification method combines the oil extraction and transesterification process into one step. In this project, microalgae (Chlorella Vulgaris) were used as the feedstock and several factors affecting the final lipid conversion rate were tested and optimized. At room temperature, the best conditions for the in situ transesterification process are: concentration of catalyst (KOH), 2% of the lipid content, reaction time, 10 h, and the methanol amount, 16.4 ml. At temperatures above 45 °C, the optimal reaction time was 4 h. It was found that 60 °C was better than 45 and 75 °C. Almost all the pretreatments tested were able to improve lipid conversion rate. The best pretreatment was the combination of methanol soaking and microwave irradiation, which increased the rate of conversion by 14.8%. The two-step traditional transesterification method was also tested for comparison purpose. The result suggested that in situ direct transesterification produced higher lipid conversion rate than the conventional transesterification process, and could be an alternative, efficient and economical process for algal biodiesel production.