Development and validation of a continuous-flow biodiesel production process using heterogeneous catalysts

Thesis Abstract

The study addresses the persistent challenges of conventional biodiesel production, including limited catalyst recyclability, energy-intensive processing, and variability in product quality when using homogeneous catalysts. It aims to design, implement, and validate a continuous-flow biodiesel production process that employs robust heterogeneous catalysts to enhance reaction efficiency, catalyst longevity, and product quality while reducing energy input and wastewater generation. Specific objectives include (i) to synthesize and characterize a family of heterogeneous catalysts (CaO-supported Al2O3, MgO-ZnO mixed oxides, and sulfonated carbonaceous catalysts) for transesterification of mixed feedstocks (palm olein, waste cooking oil, and virgin rapeseed oil) under continuous-flow conditions; (ii) to optimize process parameters (temperature 60–180°C, residence time 2–20 minutes, methanol-to-oil molar ratio 41 to 91, and catalyst loading 0.5–5 wt%) using response surface methodology; (iii) to evaluate catalyst stability, fouling tendencies, and separation efficiency via accelerated aging tests and live-feed throughput monitoring; (iv) to validate ester yield, purity, and compliance with EN 14214 specifications through analytical measurement; and (v) to perform techno-economic and environmental life-cycle assessment to compare with conventional batch processes. The methodology adopts a mixed-methods framework anchored in a design, implementation, and evaluation approach. The experimental population comprises commercially sourced vegetable oils and waste cooking oil streams, with a sample size of at least 12 distinct feedstock batches analyzed over three replicate runs per condition. Catalyst synthesis follows solvothermal and impregnation routes, with characterization by X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) surface area analysis, temperature-programmed desorption (TPD) of ammonia, scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS). Transesterification experiments are conducted in a modular microreactor platform enabling continuous-flow operation, monitored by online GC-FID for methyl ester concentrations and GC-MS for impurity profiling. Process optimization employs central composite design (CCD) within response surface methodology to identify optimum temperature, residence time, methanol/Oil ratio, and catalyst loading. Catalyst stability is assessed through 100-hour continuous operation, coke formation analysis by thermogravimetric analysis (TGA), and post-run catalyst characterization to evaluate deactivation mechanisms. Data analysis integrates regression modeling, ANOVA for parameter significance, and multivariate PCA for product quality variation. A conceptual framework incorporating the Theory of Planned Behavior and the Process Intensification paradigm guides the interpretation of implementation feasibility and operational performance. Key expected findings include (i) heterogeneous catalysts achieving methyl ester yields ? 95% with reduced by-product formation under optimized conditions; (ii) significant reductions in reaction time and temperature relative to batch processes, enabled by enhanced mass transfer and surface active sites in the flow reactor; (iii) robust catalyst stability with minimal leaching and facile regeneration, maintaining activity over 500 cycles or 100 hours of operation with less than 8% performance decline; (iv) consistent compliance with EN 14214 specifications across feedstock variability; and (v) favorable techno-economic indicators (net present value, internal rate of return, and payback period within 2–4 years) and a lower environmental footprint quantified by a cradle-to-gate life-cycle assessment demonstrating reductions in energy use and wastewater generation. The study contributes knowledge by providing a validated design framework for continuous-flow biodiesel production using heterogeneous catalysts, including catalyst selection criteria, process parameter windows, and scaling considerations for industrial implementation. It offers a transferable methodology for integrating catalyst development with process intensification to achieve sustainable, high-purity biodiesel production. The main conclusion anticipates that continuous-flow processes with optimized heterogeneous catalysts can outperform conventional batch systems in yield stability, energy efficiency, and environmental impact, supporting policy and industry adoption. Recommendations include further scale-up validation in pilot plants, long-term catalyst durability studies under varying feedstock compositions, and integration with in-line product quality monitoring and automated process control.