Recovery and conversion of palm olein-derived used frying oil to methyl ssters for biodiesel

Frying oils (both vegetable oils and animal fats) degrade with use, and beyond the limits, the excessive free fatty acids (FFA), peroxide value (PV) and polar components preclude their further use in food applications, unless they can be purified by very effective adsorbent systems. In this study, four adsorbents: silica gel, activated carbon, aluminium oxide and acid-activated spent bleaching earth were used to reduce some of the poor quality parameters of the oils. Although pre-treatment of used frying oils with these adsorbents could improve the oil quality to a certain extent, the oils could only be used for non-food applications. The FFA and PV of the treated oils subjected to the above adsorbent treatment, were reduced as follows: 33.3% and 65.1%, 6.5% and 7.8%, 30.2% and 20.8%, and 11.8% and 46.9% respectively, and silica gel was found to be the most effective adsorbent. The treated used frying oil was converted into methyl esters as biodiesel. The methyl esters obtained had comparable fuel properties as petroleum diesel. Hence, it can be used as a diesel substitute.