Analytical hierarchy process-based preliminary screening of rice husk-derived calcium silicate synthesis parameters using lauric acid adsorption

Abstract

With the increasing global demand for cleaner fuels, the use of biodiesel has grown steadily. As a potential feedstock, waste frying oil (WFO) is highlighted due to its availability and suitability for mild transesterification processing. As a low-cost and eco-friendly adsorbent, rice husk-derived silicates offer a promising strategy for waste frying oil polishing, specifically free fatty acid (FFA) content reduction. Upon this, lauric acid (LA) was used as a simplified model FFA to evaluate the calcium silicate performance under controlled conditions. Considering both production yield and adsorption capacity, the Analytical Hierarchy Process (AHP) was used as a decision-support tool to screen and prioritise all OFAT-based experimental data from four potential calcium silicate synthesis parameters, including sodium hydroxide concentration (0.5 – 2.5 M), calcium nitrate concentration (0.5 – 2.5 M), leaching temperature (60 – 100 °C), and leaching time (1 – 5 hours). The screening analysis revealed that sodium hydroxide concentration (1.5 – 2.5 M), calcium nitrate concentration (1.5 – 2.5 M), and leaching temperature (80 – 100 °C) strongly influenced both production yield and adsorption performance of calcium silicate. Under these highly prioritised ranks of synthesis conditions, the production yield of calcium silicates ranged from 58.77% to 83.48%, while the adsorption capacity ranged from 10.24 to 12.52 mmol/g. These results highlight the effectiveness of the OFAT analysis and AHP integration as a systematic preliminary screening-based method in prioritising the key parameters for subsequent synthesis condition optimisation. Indeed, it established a rational framework for the high-performance calcium silicate production for future WFO purification.