Abstract
Chlorella vulgaris is one of the promising microalgae strains that can produce high yield of bio-oils. The C. vulgaris was pretreated with microwave irradiation prior to extraction using supercritical carbon dioxide (SCCO2). Fourier transform infrared spectroscopy (FTIR) analysis showed microwave irradiation pretreatment does not affect the material composition of C. vulgaris. Scanning electron microscopy (SEM) of the microwave irradiation pretreated microalgae showed an agglomeration of the cells with the cells shape became distorted due to rupturing of the cell walls. Optimization of the SCCO2 process parameters (pressure, temperature and CO2 flow rate) was performed by using response surface methodology (RSM) with central composite design (CCD). Two factors significantly affecting the extraction yield were temperature and pressure. The model equation also predicted the optimum condition for the SCCO2 (without microwave pretreatment) at 70 , 5676 psi and 7 sL/ min while optimum condition for SCCO2 (microwave irradiation pretreatment) at 63 , 5948 psi and 10 sL/ min. High amount of saturated fatty acids (SFA), monounsaturated fatty acids (MUFA), -linolenic acid and palmitoleic acid were found in the extracted oil with microwave irradiation pre-treatment sample. In addition, the polyunsaturated fatty acids (PUFA) content in the microwave irradiation pretreated oil was considerably low and is desirable for biodiesel production.
Highlights
Biodiesel is defined as alkyl monoesters of long-chain fatty acids derived from triglycerides which have been used in transportation [1]
The bio-oil extracted from the microwave irradiation pretreated microalgae using SCCO2 was analysed and comparison was made with the untreated microalgae in terms of extraction yield and composition of fatty acids content
The model equation had predicted the optimum condition for the SCCO2-WM was at 70, 5479 psi and 8 sL/ min while optimum condition for SCCO2 with microwave irradiation pretreatment (SCCO2-M) was at 65, 5857 psi and 9 sL/min
Summary
Biodiesel is defined as alkyl monoesters of long-chain fatty acids derived from triglycerides which have been used in transportation [1]. Extraction of bio-oil from microalgae imposed several challenges due to the toughness of their cell walls that may reduce the efficiency of the extraction process. In another study, autoclaving, bead-beating, microwave irradiation and ultrasonication in 10% NaCl solution were used on microalgae as pretreatment method prior to extraction process using a mixture of chloroform and methanol. Cheng et al [7] have made comparison studies between conventional solvent extraction and SCCO2 and found that the latter was proven to be more effective and provide higher selectivity for triglycerides extraction. The bio-oil extracted from the microwave irradiation pretreated microalgae using SCCO2 was analysed and comparison was made with the untreated microalgae in terms of extraction yield and composition of fatty acids content. The optimization on extraction process parameters (i.e. temperature, pressure and CO2 flow rate) of microalgae using SCCO2 with and without microwave irradiation pretreatment was conducted using response surface methodology (RSM) with CCD model and the results were discussed
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