Biocatalysis of Plant Derived Oils for Biodiesel Production

 
 
Assoc Prof JP Obbard (Division of Environmental Science and Engineering)
 
 
orld energy consumption is projected to increase by 50 percent from 2005 to 2030, with over 80% of this demand anticipated to be derived from fossil fuels. However, the rise of crude oil prices, limited reserves

and environmental concerns relating to carbon emissions and climate change has sparked a worldwide quest to develop sustainable alternatives for liquid fuels.

Therefore, biodiesel has gained widespread importance in recent years as an alternative, renewable transportation fuel. Biodiesel is mainly produced via the transesterification of triglycerides in plant derived oil (PDO). Alcohols that can be used in the transesterification process include methanol, ethanol, propanol and butanol, where methanol and ethanol are most frequently used, especially methanol, because of its low cost and distinct physical and chemical advantages i.e. it is polar and is the shortest chain alcohol.

Our research group is studying the production of biodiesel via the biocatalytic transesterification of PDOs. The aim of the study is to develop a laboratory-scale reactor system for the whole-cell biocatalysis of PDOs using an immobilized fungus and the enzyme lipase to convert PDOs into fatty acid methyl ester (FAME) i.e. biodiesel. The study comprises fundamental research on two key objectives: i) the development of enzymatic transesterification of PDOs using lipase, under whole-cell biocatalysis; and ii) the development of a packed bed reactor system for batch and continuous enzymatic transesterification of PDOs. The lipase biocatalyst is derived from a locally isolated strain of fungus immobilized onto biological support particles (BSPs). BSPs consist of 8 mm cubes of reticulated polyurethane foam with a particle voidage beyond 97% and a pore size of 50 pores per linear inch. Fungal mycelia became well immobilized within the BSPs during shake flask cultivation as can be observed from the scanning electron microscope (SEM) images, shown in Figure 1.

  Figure 1: SEM image (magnification: ×50) of the fungus immobilized onto the BSPs.  

Figure 2 shows the effect of buffer content and temperature on FAME production from PDO using the fungal immobilized BSPs. An 86% yield of FAME is achievable at 10% buffer and 30°C temperature in 72 hours.

From investigations conducted to date, it is known that BSP immobilized whole-cell lipase can be used as a biocatalyst in a packed bed reactor (PBR) for transesterification of both pure and used (i.e. that used for food cooking) PDO (see Figure 3). To date, a yield of 50% FAME within 72 hours has been achieved in the PBR, where further optimization of the reactor is ongoing to increase yields to above 90% in a shorter time period. Efficient use of mycelium-bound whole-cell biocatalysis in the PBR will lead to a more environmentally benign process for producing biodiesel, with significant cost reduction.
 
  Figure 2: FAME production from used PDOs.  

  Figure 3(a): Bench-scale packed bed biodiesel reactor. (b): Production of FAME in the packed bed reactor with intermittent addition of methanol for transesterification of PDO.  


Jeff is an Associate Professor in the Division of Environmental Science & Engineering and a Project Director (Bioenergy & Carbon Capture) at the Tropical Marine Science Institute, NUS. He also holds a joint appointment with the Science & Engineering Research Council (SERC) of the Agency for Science Technology & Research (A*STAR), Singapore as Principal Scientist and Manager of its Bioenergy Program. His research group’s work on bioenergy is funded by the Academic Research Fund and A*STAR.

Email: esejpo@nus.edu.sg
 
     
 

Engineering Research · Special Focus
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