(544l) Transesterification of Waste Cooking Oil for Biodiesel Production Using Lithium Metasilicate Prepared from Fumed Silica

In
this study, as-prepared lithium metasilicate (Li₂SiO₃)
was used as a heterogeneous base catalyst to catalyze the transesterification
reaction of waste cooking oil (WCO) in excess methanol for biodiesel
production. Waste cooking oil, collected from the food-court of a local
hospital, was found to have an acid value at 1.89 mg KOH/g oil. Lithium
metasilicate was synthesized hydrothermally by using fumed silica as a starting
material with an addition of LiOH_(aq) at 150^oC for 2 h. After
the hydrothermal reaction, the products were washed thoroughly by de-ionized
water, dried in the oven and then calcined at 500^oC in the air for 6
h. The catalysts were characterized by XRD, TGA, FTIR, SEM and BET. The
basicity test was also conducted. The factors influencing the yield of
biodiesel such as reaction temperature, reaction time, alcohol quantity, and
catalyst amount were studied. The yield of biodiesel achieved 85% under the
following optimal conditions: methanol to oil molar ratio 54:1, catalyst amount
10 wt% at 65^oC for 4 h. According to the Arrhenius equation, the
activation energy of transesterification reaction using lithium metasilicate is
near 82.61 kJ/mol. Furthermore, the acid value of the biodiesel was found to be
0.41 mg KOH/g oil, which is within the limits of ASTM standards.

Fig.1 comparison of biodiesel yield of
different source of Li₂SiO₃ under optimal reaction
conditions (methanol to oil molar ratio 54:1, catalyst amount 10 wt% at 65^oC)