(667f) Sustainable Production of Biodiesel from Waste Biomass Utilising Intensified Reactors: A Kinetic, CFD and Scale-up Approach

To achieve net-zero emissions by 2050, a significant contribution from bioenergy will be required while other renewable alternatives are still under development ^[1]. Biofuels offer a viable solution in decarbonising the transport sector (heavy road traffic, shipping, and aviation) since they are adaptable to current engine designs and perform very well in most conditions. Over the past decade, biofuel production has increased at an annual rate of ~11% ^[2]. However, challenges related to production costs, availability, and ethical considerations – such as competition with food crops – limit their widespread adoption. Waste-derived biofuels combined with advanced processing technologies, present a promising alternative to overcome these limitations.

Process intensification has delivered dramatic improvements in process and chemical industries and has resulted in more efficient, cleaner, and cost-effective systems ^[3]. Among the different strategies for process intensification, microreactor technology stands out of its ability to improve biodiesel production by enhancing heat and mass transfer rates, increasing surface-to-volume ratios, controlling flow dynamics, and improving selectivity ^[4]. However, their uptake in the energy industry remains slow, often hampered by regulation or the misconception that microfluidic systems cannot handle large-scale energy production. Addressing these barriers is crucial for advancing biofuel production through intensified processes.

This study investigates the transesterification of waste cooking oil (WCO) using a base catalyst in a microreactor system. WCO is an attractive feedstock due to its sustainability and low cost, but its high free fatty acid (FFA) content introduces challenges such as side reactions and mass transfer limitations. To address these challenges, we performed a kinetic analysis using pseudo-homogeneous and biphasic models to determine the mass transfer effects and model accuracy. It was found that a biphasic approach provided a more accurate model as it accounts the mass transfer resistances of the immiscible liquids. The microreactor system was optimized to determine ideal operating conditions whilst assessing scalability by increasing the microtube diameter. Results showed that increasing the diameter to 3.2 mm enabled high biodiesel in under 6 minutes. Additionally, computational fluid dynamics (CFD) simulations were used to model flow behaviour, mass transfer, mixing, and reaction kinetics, with experimental results validating the predictions within a 10% deviation in slug size, slug velocity and film thickness.

References

[1] Department for Energy Security & Net Zero, 2023. Biomass Strategy 2023. London.

[2] International Energy Agency (IEA), 2023. World Energy Outlook 2023. [Online].

[3] Vapourtec, 2022, Process Intensification (PI), Vapourtec. [Online].

[4] Natarajan, Y., Nabera, A., Salike, S., Tamilkkuricil, V. D., Pandian, S., Karuppan, M., Appusamy, A., 2019. An overview on the process intensification of microchannel reactors for biodiesel production. Chemical Engineering & Processing: Process Intensification 136, 163-176