Asha Immanuel Raju Chaduvula1, Sarat Babu Imandi2, Kiran Kumar Nalla3, Sita Kumari Karanam4, and Gangadhar Madabathula3. (1) Chemical Engg, Andhra University, Visakhapatnam, AP, India, Andhra University, Visakhapatnam - 530 003, AP, INDIA, visakhapatnam, 530003, India, (2) Chemical Engg, Center for Biotechnology, Room No: 109, Andhra University, Visakhapatnam, 530003, India, (3) Chemical Engg, Center for Energy Engg, Room No: 109, Andhra University, visakhapatnam, 530003, India, (4) Pharmaceutical Sciences, M.R. P.G. College,, Pool Bagh, Vijayanagaram, 530002, India
A central composite rotatable design was used to study the effect of methanol quantity, acid concentration and reaction time on the reduction of free fatty acids content of waste frying oil during its pretreatment for making biodiesel. All the three variables significantly affected the acid value of the product, methanol being the most elective followed by reaction time and acid catalyst concentration. Using response surface methodology, a quadratic polynomial equation was obtained for acid value by multiple regression analysis. Verification of experiments confirmed the validity of the predicted model. The optimum combinations for reducing the acid level of waste frying oil to less than 1% after pretreatment was 6:1 mole ratio of methanol-to-oil, H2SO4 catalyst of 1.5 wt % of oil and 1 h reaction time at 60–650 C. After the pretreatment of waste frying oil, transesterification reaction was carried out with 6:1 mole ratio of methanol-to-oil and 1 wt % of KOH as an alkaline catalyst to produce biodiesel. Fire point, flash point, cetane index, distillation characteristics, kinematic viscosity, sulphur content and carbon residue are also addressed in the paper.