Optimization of biodiesel production from spent cooking oil: a Malawi refinery case study

Thesis Abstract

Optimization of biodiesel production from spent cooking oil a Malawi refinery case study The rapid growth of biodiesel production in Sub-Saharan Africa is constrained by feedstock variability, process inefficiencies, and quality control challenges, particularly in small to medium-scale refineries relying on spent cooking oil (SCO) as a feedstock. This study addresses the critical gap in understanding how process optimization can enhance biodiesel yield, fuel quality, and economic viability within a Malawi refinery context, where volatile supply chains and limited technical capacity interact with environmental compliance requirements. The aim is to develop a robust, scalable optimization framework for converting SCO into high-quality biodiesel, aligned with local feedstock characteristics and market demands. Specific objectives are (i) to characterize SCO feedstock variability and its impact on transesterification efficiency; (ii) to optimize reaction parameters (methanol-to-oil ratio, catalyst type and loading, temperature, and reaction time) using Response Surface Methodology (RSM); (iii) to evaluate product quality against international standards (ASTM D6751 and EN 14214) and assess storage and stability parameters; (iv) to perform a techno-economic analysis and life-cycle assessment to determine the parameter sensitivity and overall sustainability; and (v) to propose a practical implementation roadmap for the refinery under local regulatory and infrastructure constraints. The study adopts a mixed-methods research design, integrating experimental optimization with economic and environmental assessment. The population comprises SCO collected from three major food service clusters in Blantyre and Lilongwe over six months, with a stratified sampling approach yielding 120 SCO batches for characterization and 60 batches for controlled transesterification experiments. Data collection instruments include gas chromatography–mass spectrometry (GC-MS) for fatty acid methyl ester (FAME) profiling, Fourier-transform infrared spectroscopy (FTIR) for functional group analysis, Karl Fischer titration for moisture content, and standard ASTM methods for biodiesel quality (including oxidation stability and cold soak performance). The experimental framework applies a central composite design (CCD) to optimize transesterification conditions, supported by ANOVA to assess factor significance and regression models to describe response surfaces. Supplementary qualitative insights are obtained through structured interviews with refinery technicians to capture operational constraints and maintenance considerations, analyzed via thematic analysis. Validity and reliability are ensured by calibration against certified reference standards, duplicate measurements, and cross-validation of models using a hold-out dataset (n=20). The analytical framework integrates a process-based model for biodiesel yield with a financial model incorporating capital expenditure, operating costs, feedstock variability, and policy incentives. Theoretical grounding draws on the Theory of Constraints to identify bottlenecks in the conversion process and the Technology Acceptance Model to assess operator adoption of optimized procedures. Expected findings include a quantified relationship between SCO variability and biodiesel yield, identification of optimal transesterification conditions yielding >95% FAME purity and meeting EN 14214 criteria, and a break-even analysis indicating sensitivity to feedstock price fluctuations and methanol utilization efficiency. The study anticipates that a moderate reduction in methanol loop losses and improved catalyst dispersion can increase yield by up to 18% and reduce production cost per liter by 12–15%, while maintaining environmental compliance. The contribution to knowledge lies in providing a context-specific optimization framework that links feedstock characterization, process parameters, product quality, and economic viability for Malawi’s refining sector, with transferable insights for similar developing-country settings. The conclusion will emphasize the feasibility of implementing the optimized process in existing refinery facilities, given appropriate scale-up and operator training, and will propose a staged implementation plan aligned with regulatory approvals and supplier arrangements. Recommendations include adopting the CCD-derived operating envelope, establishing SCO pre-processing protocols to reduce moisture and free fatty acids, implementing routine quality control using GC-MS and FTIR, and pursuing partnerships for feedstock sourcing, catalyst reuse, and potential access to finance through climate-focused incentives.