venturi [14]. When the local pressure falls below the vapour
pressure of
fluid, cavities are created [3]. High intensity of micro
level turbulence generated by oscillating cavities with high
interfacial area in a hydrodynamic cavitation reactor is very
effective to eliminate the mass transfer resistance during the
reaction [15]. Hydrodynamic cavitation has been widely used in
wastewater treatment, but only a few works have been done since
2006 in biodiesel production. There is only one report [16] in the
published literature on the effects of operating parameters, such as
molar ratio and catalyst concentration, but it does not include
temperature and reaction time on the transesterification process
with respect to the conversion performance under hydrodynamic
cavitation. Also, even when these conditions were tested,
evaluation of the
final product quality was not reported. With
regard to the raw materials, Ghyal et al. [17] and Maddikeri et al.
[18] have studied the effect of geometry and upstream pressure of a
cavitating orifice plate assisted centrifugal pump upon methyl
ester conversion derived from used frying oil in a 10 L and 15 L
capacity reactor. In addition, their work did not focus on cavitating
orifice plate assisted by a double diaphragm pump that was
presented in this work at a pilot plant. The main focus of this study
is the optimisation of the reaction parameters for the alkali
transesterification on the methyl ester conversion derived from
waste cooking oil by using a 50 L of hydrodynamic cavitation
reactor with optimised plate and inlet pressure assisted by a
double diaphragm pump. In the present work, mechanical stirring
was also applied in the same capacity of reactor to synthesise the
biodiesel derived from waste cooking oil in order to make a
comparison with hydrodynamic cavitation in terms of conversion,
reaction time and yield efficiency. In addition, qualities of biodiesel
produced via hydrodynamic cavitation compared to petroleum
based diesel fuel have been investigated according to the ASTM D
6751 and EN 14214 standards [19]. Such waste cooking oil derived
from the palm olein was chosen because they are the ones mostly
produced and consumed in Malaysia. Therefore, utilisation of low
cost waste cooking oil has been considered as one of the promising
non-edible feedstock in reducing the total biodiesel production
cost especially under hydrodynamic cavitation in Malaysia.