In Situ Transesterification of Spirulinamicroalgae to produce Biodiesel using microwave irradiation

Abstract

The present technology of transesterification of vegetable oils to produce biodiesel that is suited to replace petro-diesel has economic challenges and therefore alternative sources are being explored. Microalgae, a renewable, third-generation biofuel resource have the potential to become a viable feedstock due to their high oil content and environmentally friendly nature. The main objective of this work was to produce fatty acid methyl esters (FAME) from Spirulina microalgae by in-situ catalytic transesterification using microwave irradiation. Specific objectives being quantifying and characterizing algae lipid, studying effect of reaction variables on FAME yield in a batch reactor, and FAME characterization. Simultaneous extraction and conversion of oil from algae biomass to biodiesel was studied in a batch reaction system using methanol and sulphuric acid catalyst. The microwave synthesis unit comprised of a 3-necked round bottom flask inside a 1300-watt microwave, fitted with a quick-fit condenser and having an external stirrer. Response Surface methodology (RSM) was used to analyze the influence of process variables; dry algae to methanol ratio (1: 4 − 1: 14 g/ml), algae biomass to catalyst ratio (1: 0.0032 − 1: 0.0368 wt %), and reaction time (1 − 11 min) at 500 rpm stirring rate on the FAME conversion. Biodiesel was analyzed for FAME using a gas chromatography (GC) fitted with flame ionization detector. Nitrogen was used as a carrier gas. The column used was a 30m by 0.25m by 0.25μm Zebron ZB-FAME column. Methyl Heptadecanoate (C17: 0), was used as an internal standard for analysis. The total lipid content of Spirulina-Platensis microalgae biomass was 10.7% by weight. The algae biomass also contained a large amount of proteins at 51.83%, moisture content at 7.8% and ash content 14.30% by weight basis. From Response Surface Methodology (RSM) using Central Composite Design, the optimum process conditions were determined as follows: dry algae biomass feed to methanol (wt/Vol) ratio of 1:9, catalyst concentration of 2 wt%, and reaction time of 7 minutes giving a maximum FAME yield of 83.43 wt%. FAME was analyzed for fatty acid composition and characteristic fuel properties. From GC analysis, palmitic (30.83%), linoleic(43.83%), and linolenic (19.41%), acids were found to be the major fatty acids inferring that Spirulina-Platensisis a promising feedstock for biodiesel production. FAME properties obtained according to EN 14214 and ASTM D 6751 standards were: flash point (164 o C) calorific value (32,911 kJ/kg), acid value (0.475KOH/g), viscosity (4.45 mm 2 /s) and specific gravity (0.868). Study showed that AthrospiraSpirulina-Platensis microalgae lipid FAME met biodiesel standards (EN 14214 and ASTM D 6751), and has potential to replace petrodiesel. Process variables for optimal FAME yield were identified. Microwave irradiation was found to be a superior heating mode as compared to conventional heating. It increased reaction rate resulting into a reduced reaction time of 7 minutes, as compared to 8 hours for conventional heating. Approaches for making Spirulina microalgae biodiesel be economically competitive in comparison with petrodiesel are discussed. It was found out that Spirulinamicroalgae biomass exhibits good properties for biodiesel production. Further research on the in-situ microwave irradiation transesterification of microalgae for a flow reactor should be carried out to increase FAME production rate.