Biodiesel Production From Waste Materials: Process Development and Performance Evaluation

Abstract

World energy crisis is a definite truth, and the rising fuel price is evidence of it. Implementation of renewable energy to overcome the energy crisis is essential. The requirement of energy, especially for road transportation sector can meet through renewable energy. Biodiesel is an appropriate alternative of fossil diesel to run an internal combustion engine efficiently. Currently, vegetable oil is the predominantly accepted feedstock for biodiesel around the globe. However, it is not a feasible biodiesel feedstock due to its insufficient availability and potential food security issues. Current research work explored possible potential biodiesel feedstocks, i.e., rice mill waste, sewage sludge, and kitchen food waste. Appropriate lipid extraction process and transesterification method were developed for waste feedstocks such as rice mill waste, sewage sludge, and kitchen food waste. Reaction parameters of lipid extraction and transesterification were optimized through Taguchi optimization technique. Taguchi model improved the lipid yield by 8.5% (dry wt%) and rice bran methyl ester (RBME) yield by 4.3% (dry weight%) as compared to manually obtained maximum yield. The relevance of Taguchi model for optimization of biodiesel production was verified. Impact of raw material processing on biodiesel properties was established. Influence of co-solvent such as methyl tert butyl ether and tetrahydrofuran on transesterification of sewage sludge lipid was demonstrated through Taguchi generated plots. The present study also developed a closed vessel microwave irradiation process for rapid formation of fatty acid methyl ester (FAME) from kitchen food waste. Traditional transesterification process face difficulties with sample moisture content. But, modified microwave technique utilizes excess moisture to produce a by-product without interrupting the transesterification process. Significantly less energy consumption of 0.088 kWh per liter FAME production was measured. Maximum FAME yield of 96.89 wt% was achieved at microwave cell pressure: 2.2 MPa, temperature: 170 0C, reaction time: 4 min and catalyst concentration: 0.5 wt% with single phase blend ratio 1:6:30 (oil: co-solvent: methanol). Microwave irradiation method and conventional heating in combination with cosolvent-acid catalyzed transesterification resulted in 2.7 and 2.6 times less energy consumption, respectively than the conventional acid catalyzed transesterification process. Selection of appropriate co-solvent for modified microwave process delivered a novel transesterification byproduct glycerol tert butyl ether (GTBE) instead of traditional glycerol. This GTBE is a potential fuel additive that can boost ignition characteristics during engine analysis. Present work also developed an ultrasonic reactor for biodiesel production. The study introduced the reaction parameter kinematic viscosity that significantly eases the process and accelerates the transesterification duration maximum by 4-5 times for sample with free fatty acid (FFA) content greater than 7%. Ultrasonic irradiation in combination with co-solvent improved the reaction output (95.56%), brought down the catalyst demand and smoothened product separation process. The product separation is much easier and faster than the microwave and conventional transesterification based FAME mixture. Commercialization of this method can be done effortlessly due to the simplicity of method and ability to process a wide range of raw material (in terms of FFA content and kinematic viscosity) with minimal modification to the process. Obtained breakeven price of biodiesel is found to be less than current fossil diesel cost. Performance and emission analysis of produced biodiesel were performed to examine the fuel efficiency. Engine performance and emission properties of sewage sludge-derived biodiesel (SSB) were assessed. Major concern behind SSB implementation is the change in fuel properties with geographical and seasonal variation. However, the current study established the positive aspect of SSB. It contains low polyunsaturated fatty acid irrespective of geography and season. Specifically, fewer C18:2 and C18:3 percentages studied for worldwide SSB assures the fuel of better stability, reduced auto-oxidation, and fewer pollutant emissions. Moreover, SSB can also blend with biodiesel derived from other feedstocks with higher polyunsaturated fatty acids, resulting in reduced auto-oxidation by lowering C18:2 and C18:3 concentrations. Finally, the optimum fatty acid profile was prepared through dual biodiesel blend (biodiesel-biodiesel) to ensure enhanced fuel property for better ignition and reduced carbon monoxide (CO), hydrocarbon (HC) and nitrogen oxide (NOx) emissions. GTBE, the by-product of modified microwave irradiation process was used to prepare blend with biodiesel (GTBE-biodiesel blend). GTBE-biodiesel blend in combination with modified injection pressure resulted with higher brake thermal efficiency than fossil diesel and reported a maximum, 10.5% and 20% reduction in NOx and CO emission, respectively. GTBE as a fuel additive is economical as well as environmentally friendly as it is prepared from the dissociation of methyl term butyl ether, i.e., potentially hazardous to dispose of and banned by some countries. Multi-objective optimization on the basis of ratio analysis method (MOORA) was used to optimize fatty acid profile, GTBE-biodiesel blend proportion and injection pressure for improved engine performance and reduced emission.