Production of renewable fuels and chemicals from fats, oils, and grease (FOG) using homogeneous and heterogeneous catalysts: Design, validation, and optimization

Abstract

Fats, oils, and grease (FOG) is a waste which collected from the kitchen and restaurant wastes. This waste causes sewer blockage in many countries because of the rising of human activities. The new FOG waste-to-chemicals processes for producing biodiesel and side products of glycerol and K2HPO4 are developed in Aspen Plus®, where thermodynamic and kinetic models are successfully validated. To address the trade-off process design of two-step esterification and transesterification reactions with different homogeneous and heterogeneous catalysts, (i) the esterification reaction [Step-1] by using homogenous catalyst is specified as Est-Design-1 and by using heterogenous catalyst is specified as Est-Design-2, (ii) the transesterification reaction [Step-2] by using homogenous catalyst are specified as TransEst-Design-1 and TransEst-Design-2, and by using heterogeneous catalyst is specified as TransEst-Design-3, (iii) five frameworks of FOG waste-to-chemicals processes (Scheme-1 to Scheme-5) are presented. As compared to Scheme-1 (H2SO4 and KOH catalysts for Est-Design-1 and TransEst-Design −1, respectively), Scheme-2 (H2SO4 and KOH catalysts for Est-Design-1 and TransEst-Design-2, respectively) and Scheme-5 (Amberlyst-15 and KOH catalysts for Est-Design-2 and TransEst-Design-2, respectively) could reduce 29.63% and 22.34% of energy duties, respectively. From the environmental aspects, Scheme-5 is superior to Scheme-2 due to Est-Design-1 discharging acidic wastewater. The Box-Behnken design combined with response surface methodology (RSM) is employed to maximize the biodiesel yield and free fatty acid (FFA) conversion of Scheme-5, the optimum operating conditions of Est-Design-2 and TransEst-Design-2 are 100 °C of reaction temperature at 480 min, and the molar ratio of methanol to oleic acid with 9:1, and 75 °C of reaction temperature at 63 min, and the molar ratio of methanol to triolein with 3.84:1, respectively.