Acid-catalyzed esterification of waste edible oils (WEOs) assisted by microwave heating

• Main Author: Thant, Amie
• Format: text
• Language: English
• Published: Animo Repository 2011
• Subjects: Esterification; Microwave heating; Oils and fats, Edible; Chemical Engineering
• Online Access: https://animorepository.dlsu.edu.ph/etd_masteral/7014
• Institution: De La Salle University

Biodiesel was produced from waste edible oil (WEO) by the two-step catalyzed process. The WEO samples from three fast food restaurants near De La Salle University, Manila, in the Philippines, were classified as high-, medium-, and low-FFA WEOs. The fatty acid composition of these WEOs was analyzed by gas chromatography using the AOAC method 969.33. Esterification of free fatty acids (FFAs) in waste cooking oil catalyzed by sulfuric acid and assisted by microwave heating was studied as a pre-treatment step for biodiesel production. After optimizing the esterification process, the alkali-catalyst transesterification step was performed. The five important parameters that were investigated in relation to FFA reduction were acid value (6.71mgKOH/g, 1.67mgKOH/g), reaction time (5min, 8min), methanol-to-oil ratio (30:1, 45:1), catalyst concentration (1wt%, 4wt%), and temperature (50°C, 60°C). Software (MINITAB 14) was used to analyze statistically the effect of these variable parameters on the reduction of FFA. Results revealed the significant effects of acid value and reaction time on % FFA reduction. The calculated optimum % FFA reduction was obtained at 84.95% by using 3.92mgKOH/g acid value, 2.5wt% sulfuric acid catalyst, 37.5:1 methanol-to-oil molar ratio, 55°C reaction temperature, and 8min reaction time. Thereby, acid value was reduced from 3.92mgKOH/g to 0.59 ±0.11mgKOH/g (0.295 ±0.055%). In the alkali-catalyst transesterification process, the optimum yield of the biodiesel at 92.73% based on the esterified oil, 89.20% based on the crude oil and a conversion of 96.40% were obtained by using 6:1 methanol-to-oil molar ratio, 0.75% NaOH catalyst based on the weight of the esterified oil, 55°C temperature, and 6.5min reaction time at 60% or 540W microwave power. Analyses of the biodiesel produced yielded acceptable results that meet ASTM standards.