Low-energy synthesis of kaliophilite catalyst from circulating fluidized bed fly ash for biodiesel production

Abstract

Circulating fluidized bed fly ash (CFBFA) was used to synthesize kaliophilite catalyst via a facile and low-energy two-step process: fabrication of amorphous CFBFA geopolymer and hydrothermal transformation of CFBFA-based geopolymer into kaliophilite. X-ray diffraction and scanning electron microscopy results demonstrated that CFBFA was successfully converted into kaliophilite with short prismatic crystals having size of ~1 μm. Temperature-programmed desorption of CO2 analysis results indicated the presence of abundant weak, medium-strength and high-strength basic sites on the kaliophilite catalyst, which were respectively assigned to hydroxyl groups, K-O ion pairs, and O2− ions. When kaliophilite was used as a heterogeneous catalyst for biodiesel production, the highest biodiesel yield of 99.2% was obtained under transesterification conditions of 5 wt% catalyst concentration, methanol:canola oil mole ratio of 15:1, reaction temperature of 85 °C, and reaction time of 6 h. The kaliophilite catalyst could be easily recovered and reused for four cycles without significant deactivation. Further, a solid base catalysis mechanism for transesterification over kaliophilite catalyst was proposed.