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 ð1 : 4 − 1 : 14 g/mlÞ, algae biomass to catalyst ratio ð1 : 0:0032 − 1 : 0:0368 wt%Þ, and reaction time ð1 − 11 minÞ,
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 ðwt/volÞ ratio of 1 : 9, catalyst concentration of 2 wt%, and reaction time of 7 minutes for a maximum
FAME yield of 83:43 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 o C calorific value 32,911 kJ/kg, acid value 0:475KOH/g, viscosity 4:45 mm 2 /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 has the potential to replace petrodiesel. Microwave irradiation increased the reaction
rate resulting in a reduced reaction time of 7 minutes (as compared to 8 hours for conventional heating) and therefore was found
to be a superior heating mode as compared to conventional heating.