Abstract
Biodiesel
is the most commonly used liquid biofuel for several reasons; it is less toxic,
biodegradable, and renewable, reduces greenhouse gases emissions. In the
present study mixture of edible and non-edible oils (linseed, palm, karanja and
thumba oil) was converted in to biodiesel in a reverse flow helical coil
reactor (RFHR) through transesterification. Both homogeneous and heterogeneous
catalyst i.e. KOH and KF impregnated
snail shell (KF/SS) were used as catalysts. The heterogeneous catalyst was characterized
using FT-IR, XRD, SEM-EDS, XPS, and TGA. The best calcination conditions were
observed at 850ºC for 4 hours based on biodiesel yield. Response surface
Methodology based Box Behnken Design was used to optimize the reaction
variables such as residence time, reaction temperature and catalyst
concentration for biodiesel synthesis in RFHR using mixture of oils for both
KOH and KF/SS catalysts. A quadratic
model was created for the prediction of the biodiesel yield. The R2 value
of the model for RFHR was 0.98 for homogeneous catalyst which indicates the
satisfactory accuracy of the model. Residence time due to reverse flow mixing
shows the positive effect on biodiesel yield. The optimum combinations of the
findings include residence time of 5 min, the reaction temperature of 63°C, and
catalyst concentration of 2.1 gm for homogeneous catalyst. At these reaction
conditions, the predicted and observed biodiesel yield was 99.9% and 99.8%. In
the case of heterogeous catalyst the optimal conditions were as follows:
catalyst concentration of 3.7 wt%, time 22.8min, reactor temperature 61.72oC
with biodiesel yield of 97%. Based on the optimum condition, the predicted
biodiesel conversion was 98% while the actual experimental value was 97.03%.
The comparison of result with homogeneous and heterogeous catalyst shows that
heterogeous catalyst requires more residence time compare to homogeneous one.