The objective of this research was to develop technique to prepare biodiesel from WPO (Waste palm oil) with high free fatty acid contents using a two-step. The process consists of esterification and transesterification steps. RSM (Response surface methodology) was applied for investigating the experimental design for esterification step. These were 20 experiments involving the three investigated variables of methanol to FFA (Free fatty acid) of WPO ratio, amount of sulfuric acid catalyst and

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... ction time that were studied on esterification to optimize the condition for decreasing FFA in WPO to less than 2% wt.. The WPO with low FFA was further experimented in transesterification step to obtain fatty acid methyl ester. The investigated results showed that the WPO containing 48.62% wt. of high FFA and the optimum condition of esterification step was 28 mol of methanol to FFA in WPO molar ratio, 5.5% sulfuric acid concentration in 90 min of reaction time and 60 º C of reaction temperature. Waste palm oil biodiesel with optimized condition in two-step catalyzed process gave methyl ester content at 84.05% according to EN (European standard) 14103 method. The properties of waste palm oil methyl ester met the standards of Thai community biodiesel.