In Situ Transesterification of Spirulina Microalgae to Produce Biodiesel Using Microwave Irradiation

Abstract

The present technology of transesterification of vegetable oils to produce biodiesel, which is suited to replace petrodiesel, 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 present study investigates the effect of microwave irradiation on the simultaneous extraction and transesterification of algae lipids to produce fatty acid methyl ester (FAME), in a batch reaction system using sulphuric acid catalyst. In situ transesterification combines the two steps of lipid extraction and transesterification into a single step. The microwave synthesis unit comprised of a 3-neck round bottom flask inside a 1300-Watt microwave oven, fitted with a quick-fit condenser and having an external stirrer. Response surface methodology (RSM) was used to analyse the influence of process variables, dry algae to methanol ratio $\left(1:4-1:14\text{g}/\text{ml}\right),$ algae biomass to catalyst ratio $\left(1:0.0032-1:0.0368\text{wt}\%\right),$ and reaction time $\left(1-11\min \right),$ at $500$  rpm stirring rate for in situ reaction. FAME was analysed using gas chromatography (GC). The total lipid content of Arthrospira Spirulina platensis microalgae biomass was found to be $10.7\%$ by weight. The algae biomass also contained proteins at $51.83\%$ , moisture content at $7.8\%$ , and ash content $14.30\%$ by weight. RSM gave the optimum process conditions as dry algae biomass feed to methanol $\left(\text{wt}/\text{vol}\right)$ ratio of 1 : 9, catalyst concentration of $2\text{wt}\%,$ and reaction time of $7\text{minutes}$ for a maximum FAME yield of $83.43\text{wt}\%.$ The major fatty acid composition of FAME was palmitic $43.83\%$ , linoleic $38.83\%$ , and linolenic $19.41\%$ . FAME properties obtained according to European Standards (EN 14214) and American Society for Testing and Materials (ASTM D 6751) standards were as follows: flash point $164^{\text{o}}\text{C}$ calorific value $\mathrm{32,911}\text{kJ}/\text{kg},$ acid value $0.475\text{KOH}/\text{g},$ viscosity $4.45\text{m}{\text{m}}^2/\text{s}$ , and specific gravity $0.868$ . The study showed that Arthrospira Spirulina platensis microalgae lipid FAME met the biodiesel standards (EN 14214 and ASTM D 6751) and h