Cation exchange resin catalysed biodiesel production from used cooking oil (UCO): Investigation of impurities effect

Converting used cooking oil (UCO) into biodiesel using solid acid catalysts shows good prospective for renewable and clean bio-fuel production. However, impurities (metal ion, water, etc.) contained in UCO will have effect on its biodiesel production as well as to affect the activity of solid acids. These effects were explored by selecting two UCOs and their model oils (same AV, without impurities) as feedstock, two typical kinds of cation exchange resins Amberlyst 15 and Amberlyst BD20 as solid acid catalysts. The result indicated that metal ion (Fe3+) not only showed deactivation effect on resin catalyst by cationic exchange but also exhibited catalytic activity as Lewis acid when it is in free form. The deactivation effect of water formed hydrated proton (–H3O+–SO3−) on resin catalyst cannot be alleviated by increasing methanol concentration but can be reduced through increasing reaction temperature. The organic acids, highly active in catalysing esterification reaction, showed synergistic effect with cation exchange resin. Under the co-effect of organic acid (UCO-1, 0.19 mmol H+ g−1; UCO-2, 0.12 mmol H+ g−1), metal ions (UCO-1, Fe: 0.6 ppm, etc.; UCO-2, Fe: 9.4 ppm, etc.) and other impurities, UCO-1/UCO-2 showed a FFA conversion of 1.2–14.1%/4.5–13.5%, compared with −4.35–9.36%/0.96–8.09% for their model oils at reaction condition of catalyst-free, 70–110 °C, 3 h, methanol-to-FFA molar ratio of 15:1.