Production of biodiesel from waste cooking oil by immobilized lipase in pva-alginate-sulfate beads

Abstract

With the huge varieties of oil produced worldwide, management and disposal are the major challenges facing the production. This is due to contamination of water bodies and land resources as a result of incessant disposal. Thus embarking on waste oil utilization in biodiesel production by immobilized enzymatic transesterification is a triple step forward towards the waste management. Therefore in these studies, Candida rugosa (Type VII, 1176 units/mg) was immobilized in PVA-Alginate- Sulphate beads by entrapment and cross linking method. Transesterification process was conducted using the immobilized lipase. 32 treatment combinations were generated by the Design Expert software version 6.0.4 using 2 level fractional factorial designs. The treatment combination; 1:6 oil to methanol, 2.5 v/v, 60 U at 50 °C under 200 rpm was found to be the optimum condition that gave the highest production of 4.516g/L, 1.65 g/L and 1.6 g/L, corresponding to 45 %, 10.65 %, 10.6 %, oleic acid methyl ester, palmitic acid methyl ester and linoleic acid methyl ester respectively. In another vain the treatment combination used for the optimum production using immobilized lipase was applied to the free lipase resulting to 0.234 g/L, 0.130 g/L, 0.049 g/L, corresponding to 2.34%, 1.30%, 0.49 %, oleic acid methyl ester, palmitic acid methyl ester and linoleic acid methyl ester respectively. Approximately, the immobilized lipase performed 15 folds better than the free lipase. Enzyme assay was conducted and compared between free lipase and immobilized lipase over 3 hours of reaction using spectrophotometer, absorbance was read at 410nm. Immobilized lipase in general maintained their activity after an hour of the reaction. In other higher concentrations, both the free and the immobilized showed a steep fall with time. FESEM-EDX was also carried out to study the immobilization matrix morphology which revealed the native structure of the entrapped Candida rugosa lipase. Furthermore, reusability test of the immobilized lipase was conducted and found capable of maintaining a production of five consecutive cycles.