RESUMO
The acid-catalyzed pre-treatment esterification process is required for low-cost feedstock with high free fatty acids (FFAs) to avoid the saponification that occurs during alkali-catalyzed transesterification for the production of fatty acid alkyl esters (FAAE). Reverse hydrolysis in acid-catalyzed esterification causes a decrease in fatty acid methyl ester (FAME) yield. Therefore, the esterification process must be intensified. This study aims to develop and optimize a low-temperature intensification process to enhance biodiesel yield and reduce energy consumption. Three intensification systems were studied: co-solvent technique, co-solvent coupled with adsorption of water using molecular sieves, and entrainer-based continuous removal of water. The process variables of esterification reaction in co-solvents without the adsorption system were optimized by using central composite design (CCD). The study showed that the co-solvent without the adsorption system was effective in intensifying the FFA conversion (XFFA) at low temperatures, compared to the other two systems, due to the dilution effect at high co-solvent/entrainer amount required for sufficient vapors in the adsorption system. Optimized process variables have achieved 95% XFFA within 75 min at 55 °C, 20 mL/100 g of oil DEE, 9 MR, 3 wt % H2SO4, and 320-350 RPM in a co-solvent without the adsorption system.
RESUMO
To produce biodiesel cost-effective, low-cost, high free fatty acid (FFA) oil feedstock is desirable. But high FFA creates difficulty during the base-catalyzed transesterification process by yield loss due to the formation of soap. However, these problems are overcome by the use of an acid catalyst. The acid catalysts can directly convert both triglycerides and FFAs into biodiesel without the formation of soaps or emulsions. The shortcomings of mostly used inorganic acids are that they work well for esterification of FFA present in low-cost oil, but their kinetics for transesterification of triglycerides present in oils is considerably slower. Corrosion of equipment is another major problem associated with an inorganic acid catalyst. The usage of an organic acid catalyst of the alkyl benzene sulfonic type, like 4-dodecyl benzene sulfonic acid (DBSA) minimizes these disadvantages of inorganic acid-catalyzed transesterification. The aim of the present investigation was to reduce the reaction time of transesterification of triglycerides further by using microwaves as a heating source in the presence of DBSA catalyst to achieve higher conversions under mild operating conditions. To optimize the transesterification variables for the higher conversion of biodiesel, the response surface methodology was employed to design the experiment. By using the DBSA catalyst under microwave heating at a temperature of 76 °C, conversion close to 100% in only 30 min of reaction time was obtained using a 0.09 molar ratio of catalyst to oil and 9.0 molar ratio of methanol to oil. A modified polynomial model was developed and was adequately fitted with the experimental data and could be used for understanding the effect of various process parameters. The catalyst to oil molar ratio and reaction temperature created a stronger effect on the biodiesel production than that exhibited by the methanol to oil molar ratio. It was observed that the microwave heating process outperformed conventional heating, providing a rapid, easy method for biodiesel synthesis from triglycerides in the presence of DBSA, an organic acid catalyst. The produced biodiesel was of good quality, as all the properties were within the prescribed limits of the ASTM D6751 standard.
