Characterization, activity and process optimization with a biomass-based thermal power plant's fly ash as a potential catalyst for biodiesel production

Abstract

A typical thermal power plant operated using a solid biomass mixture as fuel, which comprised 70–80% gram straw, 10–15% cotton straw, 5–10% wheat straw and leaves (2%) with a small quantity of coal (1–2%) initially used for smooth ignition, produces a residue called Biomass-Based Thermal Power Plant Fly Ash (BBTPFS). BBTPFS was investigated for composition and structural characterization using different techniques. The versatile composition of the BBTPFS was confirmed by XRF analysis that indicated the weight percent of different components viz. CaO (30.74%), SiO₂ (27.87%), K₂O (13.96%), MgO (6.67%), SO₃ (4.83%), Cl (3.36%), Al₂O₃ (2.83%), Fe₂O₃ (2.36%), P₂O₅ (1.34%), Na₂O (1.14%), small quantities of TiO₂, SrO, MnO, BaO, ZrO₂, ZnO, Rb₂O, Br, Cr₂O₃, CuO, NiO and As₂O₃ as active ingredients. The SEM and TEM image analysis showed the surface morphology of the BBTPFS which was found to be mixed in nature, having 1 to 500 nm range particles with meso, micro and macro porosity. BBTPFS was used as a catalyst for transesterification of Jatropha curcas oil having a high percentage of free fatty acids and appropriate process optimization was achieved using the Taguchi-ANOVA method. It was observed that at a temperature of 225 °C and an internal vapour pressure of 3.2 MPa in a batch reactor with 5% catalyst loading, 1 : 9 mol mol⁻¹ of oil–alcohol and 3 h reaction time, the optimum yield of biodiesel obtained was ∼93.9%, which is in agreement with the theoretical value. The product quality was assessed and found to conform to ASTM and EN-standards.