Tian, Qingyu; (2021) Towards the development of an energy efficient microalgae biodiesel process. Masters thesis (M.Phil), UCL (University College London).

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Abstract

Biofuel is a powerful energy source to replace fossil fuels and has received much attention in recent years. This project used microalgae Chlorella Sorokiniana UTEX-1230 to produce the biodiesel. The process included cell cultivation, harvesting, lipid extraction, and transesterification. There are two different processes that have been evaluated in this project: the base line and the modified process. These two processes have the same biofuel production steps including cultivation, harvesting, lipid extraction, and transesterification. In this project, different conditions were used in cultivation and the highest lipid content obtained was ~50% (w/w) after eight cultivation days. After cultivation, the biomass was harvested for the lipid extraction and the transesterification. The base line process, which was the benchmark, was established using centrifugation followed by ultrasonication, and acid catalysed transesterification. This process can reach high lipid extraction yield (~50%) and conversion performance (90%), but the energy requirement was relatively high. Thus, a modified processes were established. A flocculation step was added before centrifugation to reduce the sample volume, which can reduce the energy requirement. Enzymes or ethanol were used in cell breaking stage and lipid conversion stage to decrease the energy input. Moreover, chloroform was replaced by hexane in the modified process during lipid extraction due to the low cost, easy of recovery, and low toxicity. Then, enzyme transesterification was used to replace the acid transesterification. The modified process aimed to have the same process performance and lower energy input than the base line. Two modified process where established in this project to reduce the energy input with wet biomass and have a similar FAME produce performance. The base line performance was 48.26%. The modified process 1 performance was 17.57% and modified process 2 performance was 17.26%. The performances of modified processes were still lower than that of base line. However, the energy requirements of modified process 1 (11.40% of base line) and modified process 2 (12.08% of base line) were much lower than base line. Besides, when not considering about the waste of cultivation material and with the same energy input, the power output ratio of modified process 1 to baseline was 325%. The power output ratio of modified process 2 to baseline was 275%. The power output ratio of modified process 2 was lower than modified process 1 and both modified processes were higher than the baseline. These results indicated that in this project, both modified processes can have higher energy output than the baseline when under same energy input.

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