Development and evaluation of a green solvent-free biodiesel synthesis process

Thesis Abstract

The increasing demand for sustainable and low-emission energy sources has intensified the search for eco-friendly biodiesel production routes that minimize solvent use and environmental impact while maintaining fuel quality. This study addresses the gap in scalable, solvent-free biodiesel synthesis by developing and evaluating a green process that leverages catalytic transesterification under solvent-free conditions, coupled with in situ reaction heat management to improve energy efficiency. The aim is to establish a robust synthesis route that achieves high conversion, high iodine value compliance, and favorable process economics without conventional organic solvents. Specific objectives include (i) identifying an effective heterogeneous catalyst system compatible with solvent-free transesterification of waste cooking oil (WCO) and non-edible vegetable oils; (ii) optimizing reaction parameters (temperature, catalyst loading, molar ratio, and agitation) using a central composite design to maximize biodiesel yield and minimize free glycerol content; (iii) assessing the environmental performance through life cycle assessment (LCA) and quantifying process intensification benefits; (iv) evaluating product quality against ASTM D6751 and EN 14214 specifications; and (v) conducting a techno-economic analysis (TEA) to compare solvent-free versus conventional solvent-based processes. The methodological approach combines experimental design and analytical evaluation with a systems optimization framework. A mixed-methods design is employed, integrating quantitative experimental data (n = 5 oils, each replicated in triplicate transesterification runs) with qualitative process observations to inform scale-up feasibility. The population consists of commercially sourced WCO and non-edible oils (rapeseed and jatropha) with characterized free fatty acid contents below 2.5%. Sample sizes are determined via factorial screening followed by response surface methodology, yielding a minimum of 60 experimental runs for optimization. Data collection instruments include gas chromatography with flame ionization detection (GC-FID) for fatty acid methyl ester (FAME) quantification, Fourier-transform infrared spectroscopy (FTIR) for functional group verification, differential scanning calorimetry (DSC) for product property assessment, high-performance liquid chromatography (HPLC) for glycerol content, and a structured energy meter for real-time thermal analysis. Validity and reliability are ensured through calibration with certified biodiesel standards, repeatability tests (n = 3 runs per condition), and instrument validation against standard reference materials. Data analysis employs regression analysis and analysis of variance (ANOVA) to model yield and ester content as functions of process variables, with response surface methodology used to identify optimal conditions. A conceptual framework drawing on Green Chemistry principles and the Theory of Constraints informs the design, while the Ecological Scarcity and Waste Management theories underpin the LCA and TEA components. The study anticipates achieving biodiesel yields above 96% within a solvent-free regime at moderate temperatures (55–65°C) with catalyst loadings in the range of 3–5 wt% and methanol-to-oil molar ratios adjusted via in situ methanol generation within the reaction matrix. It is expected that the absence of bulk organic solvents will reduce process environmental footprint by at least 25% (global warming potential and nonrenewable energy consumption) and improve overall energy efficiency by 15–20% compared with conventional solvent-based methods, after accounting for catalyst regeneration and glycerol separation. The contribution to knowledge includes empirical evidence for solvent-free transesterification using robust heterogeneous catalysts, a validated optimization model for eco-friendly biodiesel synthesis, and a framework for integrating LCA and TEA into process design. The study concludes that green solvent-free biodiesel synthesis is technically feasible at pilot scale with competitive environmental and economic performance, recommending continued development toward modular reactor systems, catalyst lifecycle assessment, and integration with waste valorization pathways to support industrial adoption.