Degradation of Oil during Frying and Its Effect on Biodiesel Production

The effects of frying unripe plantain and sweet potato (separately) in soyabean oil on the properties of the oil were investigated. Also, the effect of the degradation of the oil on biodiesel yield obtained from the oil was considered. Physico-chemical properties of soyabean oil (acid value, saponification value, viscosity, density, colour) were measured daily after being used for frying for days. The fatty acid profile of the oil was analysed daily using GC/MS and biodiesel was produced daily from the oil sample. The results of the frying process showed increase in oil Acid values in the two cases; sweet potato (1.10 – 1.16mgKOH/g) and unripe plantain (1.12 – 1.71mgKOH/g). And increase in oil saponification values (146 – 271mgKOH/g for sweet potato and 175 – 340mgKOH/g for unripe plantain). The oil became less dense, less viscous and darker in colour for both batches during repeated frying. Five day Frying process reduced the percentage unsaturated fatty acid contents of oil (for unripe plantain from 81.94% to 36.80% and for sweet potato from 82.46% to 40.10%) and increased the percentage saturated fatty acid composition of the oil (unripe plantain from 12.18% to 34.70% and sweet potato from 12.24% to 27.50%). As frying progress, there was reduction in biodiesel yield, though insignificant difference in yield was observed between the biodiesel obtained from unripe plantain frying process and that obtained from the sweet potato frying process.