Dynamic thin film-intensified direct transesterification of oleaginous biomass to biodiesel

Author: Eko K. Sitepu

Sitepu, Eko K., 2020 Dynamic thin film-intensified direct transesterification of oleaginous biomass to biodiesel, Flinders University, College of Medicine and Public Health

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Utilization of liquid renewable energy is rising to satisfy increasing demands in the transport sector, as fossil fuel reserves are rapidly depleting. Although bioethanol can contribute to biofuel blends for the general transport sector, biodiesel is the only suitable biofuel for heavy machinery and in the shipping industry; yet high biodiesel production costs limit its uptake. Traditional biodiesel production is a multiple step process which is not cost-effective, and especially requires drying or dewatering of oleaginous biomass, oil extraction and purification, high temperature and prolonged reaction times. Direct transesterification (DT) of oleaginous biomass to biodiesel can significantly reduce production costs which can be further reduced by using wet biomass. The effectiveness of the DT process using some oleaginous biomass has been demonstrated and is predominantly conducted under high temperature and pressure, particularly when using wet biomass to avoid negative effects of water. Maintaining these conditions under prolonged reaction times increases the biodiesel price which therefore requires subsidy and tax exemption to compete with petro-diesel fuel. This research investigated the suitability, energy efficiency and green chemistry pathway attributes of DT assisted by novel microfluidic platforms, the vortex fluidic device (VFD) and the turbo thin film device (T2FD), for biodiesel production from a range of representative oleaginous biomass, such as Chloroparva pannonica (microalga), Mucor plumbeus (fungus) and soybean seeds under room temperature and atmospheric pressure conditions.

Fatty acid extraction and fatty acid to FAME conversion efficiencies were used at different parameter settings to evaluate performance of the processing technology in continuous flow - and in confined mode for the VFD. Single factor experiments evaluated the effects of catalyst concentration and water content of biomass, while factorial experimental designs determined the interactions between catalyst concentration and biomass to methanol ratio, flow rate, and rotational speed. For the VFD-assisted DT of C. pannonica biomass, a response surface method based on Box-Behnken experimental design was used to determine effects of water content, ratio of biomass to methanol and residence time. The success of the VFD microfluidic platform led to the design of high throughput, higher shear T2FD. The presence of high shear stress in the thin film of liquid with the adjustable thickness of 100 to 200 μm in T2FD is the result of high rotational speed of internal surfaces; that is a titanium blade is moving relative to a stationary stainless-steel block, which also improves the interaction of reactants. Irrespective of raw materials and process-intensification technology, conversion efficiencies were >90%, showing a broad tolerance to parameter settings and water content.

Finally, process performance was evaluated by determining energy efficiency and green chemistry process metrics. Compared to the traditional two-step, one step, and one-step microwave- and ultrasound-assisted biodiesel production pathways, VFD and T2FD-assisted base-catalysed DT of microalgal biomass saved ~98, 60, 98 and 94% of energy, respectively, with the processing occurring at room temperature and ambient pressure, while the environmental factor improved by ~80%. These outcomes are promising for directing biodiesel process pathway development for scale-up to commercial production. Outcomes of this research also identified promising future research avenues that can further improve environmental and economic metrics, particularly for the T2FD-intensified DT of oleaginous biomass, using novel green chemistry-generated re-usable catalysts and less toxic substances that serve both purposes of being solvents and reactants.

Keywords: Biodiesel, Oleaginous Biomass, Vortex Fluidic Device, Turbo Thin Film Device

Subject: Biotechnology thesis

Thesis type: Doctor of Philosophy
Completed: 2020
School: College of Medicine and Public Health
Supervisor: Wei Zhang