Optimization of biodiesel production from Chlorella sp through in-situ microwave-Assisted acid-catalyzed trans-esterification

Microalgae is one of the potential raw materials in producing the third generation biodiesel thanks to its high lipid contents and the fact that it requires relatively small space for cultivation. Microalgae in the form of Chlorella sp. was used as a raw material in this study due to its high oil content, i.e. up to 30% of the dry algae weight. The use of microwave irradiation in this process would accelerate the in-situ trans-esterification reaction by extracting microalgae lipids and simultaneously converting them into Methyl-Esters. This study aims to investigate the methyl ester production through the in-situ trans-esterification process by studying the effect of acid catalyst concentration (0.2-0.5 mol/L), microwave power (300-600 W) and reaction time (30-90 minutes). The experiment was carried out in a 500 ml flat bottom flask made of pyrex, under the influence of microwave irradiation in which homogeneous sulfuric acid (H₂SO₄) was introduced as a catalyst. The experiment was carried out in atmospheric pressure with the following operating variables: catalyst concentration, microwave power and reaction time, respectively. Prior to running the experiment, the response surface methodology using Box Behnken Design (3 factors and 2 levels) was conducted beforehand in order to minimize the number of runs. It is suggested from the analysis that the optimum conditions for the in-situ microwave-Assisted trans-esterification of Chlorella sp. with sulfuric acid catalyst are as follows: microwave power (370 W), concentration of catalyst (0.2 mol/L), and trans-esterification time (82.7 min) with yield of 63.36 %. The predicted yield values generated from the response surface methodology with Box-Behnken design exhibit a high degree of confirmation with the actual yield from the experiment, suggesting that the optimization methodology carried out has made the experiment more effective and efficient by focusing only on certain specific parameters in order to get the best results, in terms of both quality and quantity.