Due to the rise in demand for energy and the limited supplies of
fossil fuel available, more attention has recently been focused on
developing clean and renewable sources of alternative energy
[1,2]. Among the possible candidates for an alternative energy
source, biodiesel has attracted much attention because its physical
and chemical properties and energy content are similar to those of
petroleum diesel [3]. In addition, the emission of particulates, CO,
and unburned hydrocarbons from biodiesel combustion in a diesel
engine are all lower than that those from petroleum diesel [4–6].
Biodiesel could be produced by transesterification of triglycerides.
Transesterification is conventionally performed by alkaline or acid
catalysis, which is restricted by impurities such as water and free
fatty acids [7–10]. Another method to produce biodiesel is to use
supercritical reactions, although these are usually performed at
high temperature and pressure, thus requiring significant energy
consumption and high operating costs. A last method is to utilize
enzymatic reactions by using lipase. Lipase can perform the esterification
of free fatty acids and transesterification of triglycerides
without the formation of soaps. The main products when using lipase
as the catalyst in transesterification are biodiesel and glycerol,
resulting in the easy removal of lipase [11,12], which is an important
issue when choosing a catalyst.
The major barrier to the wider use of enzymatic transesterification
is the cost of lipases, but the enzyme cost can be reduced by
the enzyme immobilization, which enables repeated uses of the
enzyme [13]. Moreover, the stability, activity, and reusability of