Abstract
Biofuel produced from microalgae is considered as one of potential renewable energies. To effectively produce biodiesel, lipid in microalgae is required to be extracted first before transesterification. However, the microalgal biofuel production is still not so economical until now, mainly due to large energy consumed in the lipid extraction from algal cells stage. Therefore, an effectivet extraction method is needed to propose. In this study, CO2-expanded ethanol is used as the extraction solvent in a continuous operation mode. Microalgae named Schizochytrium sp. was chose as the biomass for lipid extraction. The so-called CO2-expanded ethanol is that the volume of ethanol would be expanded after the dissolution of pressurized CO2. Because CO2-expanded ethanol possesses higher mass transfer coefficient as well as lower surface tension and viscosity as compared with ethanol itself, it can easily penetrate into microalgal cell to extract lipid. The experimental results show that the yield of lipid from 10 g of the microalgae sample at 313 K is 7 wt% within 10 minutes when pure ethanol is used as the extraction solvent. The yield of lipids, however, is increased to 70 wt% using CO2-expanded ethanol with 1000 psi of CO2 in ethanol extraction at 313 K within 10 minutes. The factorial design technique with the variables as pressure, temperature, ethanol flow rate and CO2 flow rate is used to determine the most dominant variables affecting the extraction outcomes. The extracted lipids can be pressurized and heated to the desired pressure and temperature to carry out transesterification to produce biodiesel after the extraction stage. The proposed technique is proven to be promising to produce biodiesel with less operation time and less energy consumption.