PROCEEDING 19 th Regional Symposium on Chemical Engineering ISBN: 978-602-9494-30-3 The Enhancement of waste cooking oil esterfication catalyzed by sulfated zirconia and assisted by the addition of silica gel Agus Adhiatma a , Chahyo Purbo Anshory a , Agus Purwanto a and Wirawan Ciptonugroho a* a Department of Chemical Engineering, Sebelas Maret University, Jalan Ir.Sutami No 36A, Surakarta57126, Indonesia * Corresponding Author’s e-mail: w_ciptonugroho@uns.ac.id Abstract Waste cooking oil (WCO) is commonly known containing higher free fatty acids (FFA) compared to fresh oil. The high FFA content has a detrimental effect in transesterification process for biodiesel production because it can deactivate the base catalyst during the reaction. In this paper, an inconventional approach has been employed to trim down the FFA content by esterifying WCO over heterogeneous sulfated zirconia catalyst (SZ). The zirconia particles was succesfully prepared by means of precipitation technique. XRD, BET, and SEM analysis were then employed to characterize the prepared zirconia. Furthermore, the prepared zirconia was activated by soaking into sulfuric acid solution. The presence of sulfate ions on zirconia surface was investigated using FTIR analysis. The activity test of the activated zirconia was conducted by esterifying WCO with ethanol. The enhancement towards higher FFA conversion was performed by the addition of ground silica gel (SG) into the reaction mixture. As the result, the highest conversion (80%) was achieved within 2 hours by the reaction system of 1 %w SZ, 4 %w SG and weight ratio of WCO and ethanol was 1. Keywords:sulfated zirconia; free fatty acid ; waste cooking oil ; esterification ; silica gel 1. Introduction WCO is a potential raw material for biodiesel production. It is unused and available in huge amount. Therefore, it offers a solution to minimize a rivalry between food and energy. However, high FFA content in WCO can disrupt transesterification reaction for biodiesel generation since it extinguishes active alkali catalyst during the process. To supress FFA content, high FFA biodiesel feed is conventionally saponified to form soap. However, the presence of considerable soap makes the separation of glycerol and the formed biodiesel being more difficult. One alternative route to lessen FFA in WCO can be done by esterifying FFA with alcohol before transesterification or so called pre- transesterification step (as shown on Equation 1). Interestingly, by carrying out esterification, FFA can also be converted to biodiesel. Thus, in addition to lowering FFA concentration, this method is also benificial in rising the yield of biodiesel. R 1 -COOH + R 2 -OH   ⇔        R 1 -COO-R 2 +H 2 O (1) FFA alcohol FAME water In order esterification to perform rapidly, acid catalyst should be added during the reaction. Liquid acid catalysts such as sulfurinc acid[Yadav, Singh and Singh 2010], [Resitoglu, Keskin and Guru 2012], and heteropolyacids [Cardoso, Augusti and Da Silva 2008] are commonly used in esterification. Nevertheless, they are difficult to separate from the product mixture, require high quality construction materials to avoid corrosion, and provoke a serious environmental impact. Heterogeneous solid acid catalysts propose a solution to figure out the problems encountered in homogeneous ones. FFA has succesfully been converted by polyacids immobilized on silica[Caetano, et al. 2008], polymeric resin amberlyst catalyst [Park, Kim and Lee 2010],mesoporous regime zeolite faujasite catalyst [Sanchez, Martinez and Aracil 1997]. Another promising solid catalyst in esterification is modified zirconia. Modified zirconia such as sulfated zirconia is claimed possesing highly acidic sites. Therefore, it is potential to initiate acid catalyzed reaction. Esterification acetyl salicylic acid, which is widely recognized as aspirin, has fruitfully been synthesized using nano-crystaline SZ[Tyagi, Mishra and Jasra 2010]. The activity of SZ towards benzoic acid esterification has also been examined by Ardizzone [Ardizzone, et al. 1999]. Liu and coworkers reported that sulfated TiO 2 -ZrO 2 could actively catalyze the esterification of terephthalic acid (TPA) and 1,3-Propanediol (PDO) to Poly-trimethylene terephthalate (PTT) which A-33-1