Journal of Industrial and Engineering Chemistry, Vol.46, 266-272, February, 2017
Synthesis of potassium glyceroxide catalyst for sustainable green fuel (biodiesel) production
Metal hydroxides and alkoxides are used as base catalysts for biodiesel production. When metal hydroxides are dissolved in alcohol, they produce water, which can react with triglycerides (TGs) and produce free fatty acids (FFAs) rather than the desired fatty acid alkyl esters. Metal alkoxides are more expensive to produce and their transportation is hazardous. In this study, potassium alkoxide catalysts were synthesized from potassium hydroxide (KOH) solution and glycerol, which is by-product of biodiesel production process, by heating 50% KOH solution and glycerol at different mole ratios, temperatures and vacuum pressures. These operating parameters were optimized and their interactive effect on catalyst synthesis was studied by using response surface methodology (RSM). This study also focused on the development of a correlation relating the effects of these variables with drying behavior of reagents during catalyst synthesis. The results indicated that KOH to glycerol mole ratio and vacuum pressure had the most significant effects (P < 0.0001) on free water mass loss during catalyst synthesis. The optimum reaction condition was KOH to glycerol mole ratio of 2:1, reaction temperature 130 °C and vacuum pressure 113 mbar. X-ray powder diffraction showed that glycerol derived alkoxide compounds were predominantly monopotassium substituted alkoxides that occur as adducts with potassium hydroxide. The glyceroxide catalyst prepared at 3:1 mole ratio of KOH:glycerol has improved biodiesel yield to that of conventional potassium methoxide (KOCH3) catalyst.