Lipid extraction and biodiesel production from microalgae and recovery of free lutein by-product

Abstract

The thesis is divided into three studies whose purposes are set out to determine various ways to improve the production of biodiesel from microalgae, focusing particularly on the downstream processes in which more than half of overall process energy is consumed. The first part of the thesis involved solvent extraction of lipid from microalgae. The results revealed that the mixture of chloroform/MeOH, 2:1 (v/v) could extract the highest amount of total lipid from algae, while hexane was a good solvent, concerning the selectivity for targeted lipids. In addition, application of ultrasound and microwave to the process caused cell disruption, which could then accelerate the rate of lipid extraction especially from algae with tough cell walls such as Chlorella vulgaris In part 2, pulsed microwave was applied to transesterification of Chlorella lipid and algal biomass to enhance the production of biodiesel. Considerable enhancement in the biodiesel yield was observed for reaction under pulsed microwave over that under conventional heating. Especially for the single-step process, in which extraction and transesterification took place simultaneously, as high as 62% enhancement in biodiesel yield was found. Furthermore, in microwave irradiated reaction, the amount of MeOH and catalyst seemed to affect the biodiesel yields. Apart from reaction variables such as MeOH and catalyst amounts, biodiesel production was also found to be affected by the power settings of the pulsed microwave system. The highest biodiesel yield resulted from transesterification for 10 min at 60oC was found at the power setting of 250 W instead of at higher power settings (500 W or 1000 W). The highest efficiency (biodiesel yield per unit energy) was also the highest at 250 W. It could be suggested by the characteristic power profiles that the yield and the efficiency did not correlate with the power input, but rather, with the pulse frequency and intensity during the entire reaction, which was the most uniform at 250 W. In the last part, different route to enhance the production of algal biodiesel is taken. Herein, we emphasized on improving the economic feasibility of the biodiesel production process by producing a high-valued co-product. That is, biodiesel and valuable free lutein were demonstrated to be simultaneously produced from Chlorella lipid extracts. The alkali catalyst used in the transesterification of triglycerides acted as a reactant in converting lutein fatty acid esters to free lutein. A maximum biodiesel yield of 33.6% by weight of the algal lipids was obtained after a 4-h reaction with MeOH at the MeOH/biomass ratio of 16:1using 6% alkali catalyst. The excess of alkali and MeOH employed in the production of biodiesel ensured the complete saponification of all lutein fatty acid esters to free lutein, giving a maximum yield of 2.3% by weight of the algal lipids. In addition, a process for the separation of the biodiesel and free lutein products from the reaction mixture was proposed. A preliminary economic assessment was also conducted, which suggested that the process for the simultaneous production of biodiesel and lutein from C. vulgaris may be economically feasible.