Background: Biodiesel is a green fuel consisting of long chain fatty acid monoalkyl esters, which
can be blended with diesel or used alone which is usually produced from vegetable oils/fats by either lipasecatalyzed
transesterification. In this investigation, an enzyme (Novozym 435) catalyzed process was optimized
to prepare methyl esters from crude Citrullus colocynthis oil (CCO) by transesterification of CCO with methanol.
However, as per our knowledge, lipase-catalyzed transesterification have not been used for biodiesel production
from Citrullus colocynthis.
Objective: The purpose of this work was to transesterify the CCO in the presence of Candida antarctica lipase
as catalyst and methanol. Additionally, the physicochemical parameters/fuel properties of the Citrullus colocynthis
methyl ester (CCME) were assessed and compared.
Methods: Lipase-catalyzed reactions were carried out in three necked flask (50 mL) attached with reflux condenser
and thermometer, immersed in oil bath at constant stirring speed (400 rpm). The reaction mixture was
consisted of CCO and varying the calculated amount of methanol, tert-butyl alcohol, and Novozym 435. The
experimental parameters reaction time, methanol/oil molar ratio, reaction temperature, tert-butanol content,
Novozym 435 content and water content were optimized for the transesterification reaction. The CCME yield
was measured using gas chromatograph. The fuel properties of the produced CCME were determined as per
American Society for Testing and Materials (ASTM) and European (EN) biodiesel standard methods.
Results: In this study, an enzymatic catalyst was employed to synthesize the CCME from CCO via transesterification.
Several variables affecting the CCME yield were optimized as lipase quantity (4%), water content
(0.5%), methanol/oil molar ratio (5:1), reaction temperature (43 °C), reaction medium composition (80% tertbutanol/
oil), and reaction time (3.7 h). A CCME yield of 97.8% was achieved using enzyme catalyzed transesterification
of CCO under optimal conditions. The significant biodiesel fuel properties of CCME, i.e. cloud
point (0.70 °C); cetane number (49.07); kinematic viscosity (2.27 mm2/s); flash point (143 °C); sulfur content (2
ppm) density (880 kg/m3) and acid value (0.076 mg KOH/g) were appraised. CCME also exhibited long-term
storage stability (4.80 h) and all the biodiesel fuel properties were within the range of standards (ASTM D6751
and EN 14214).
Conclusion: The lipase-catalyzed transesterification produced better conversion than the base-catalyzed reaction.
The fuel properties of CCME were within the limits of the ASTM D6751 and EN14214 standards. Furthermore,
CCME showed good oxidative stability and a long shelf life due its high natural antioxidant content.
CCME showed better fuel properties and long-term storage stability due to which it can be used as a potential