| Summary: | ABSTRACT
Biodiesel has been identified as a good complement and plausible replacement of fossil diesel
because of the overwhelming characteristic properties similar to fossil diesel in addition to its
good lubricity, biodegradability, non-toxicity and eco-friendliness when used in diesel engines.
The production of biodiesel from edible vegetable oils competes with food sources, thereby
resulting in high cost of food and biodiesel. Studies have shown that rubber seed contains 35
45 % oil, which portrays a better competitor to other non-edible oil bearing plants in biodiesel
production. In this study, non-edible vegetable oils from underutilized Nigerian NIG800 clonal
rubber seeds were extracted from 0.5 mm kernel particle size using n-hexane as solvent to
obtain a yield of 43 wt.% over an extraction time of 1 h. The oil was characterized for fatty
acids by using gas chromatography-mass spectrometry (GC-MS), and for structural properties
by Fourier transform-infrared (FT-IR) and nuclear magnetic resonance (NMR) analyses.
The optimization of the process conditions of the vegetable oil extraction was evaluated using
response surface methodology (RSM) and artificial neural network (ANN) techniques both of
which, were based on a statistically designed experimentation via the Box-Behnken design
(BBD). A three-level, three-factor BBD was employed using rubber seed powder (X1), volume
of n-hexane (X2) and extraction time (X3) as process variables. The RSM model predicted
optimal oil yield of 42.98 wt. % at conditions of X1 (60 g), X2 (250 mL) and X3 (45 min) and
experimentally validated as 42.64 wt. %. The ANN model predicted optimal oil yield of 43 wt.
% at conditions of X1 (40 g), X2 (202 mL) and X3 (49.99 min) and validated as 42.96 wt. %.
Both models were effective in describing the parametric effect of the considered operating
variables on the extraction of oil from the rubber seeds. On further examinations of the
potentials of the vegetable oil, the kinetics of thermo-oxidative degradation of the oil was
investigated. The kinetics produced a first-order reaction, with activation energy of 13.07
kJ/mol within the temperature range of 100 250 oC. In a bid to attain enhanced yield of
biodiesel produced via heterogeneous catalysis, coupled with the carbonaceous potentials of
the pericarp and mesocarp of rubber seed shell casing as a suitable catalytic material, the rubber
seed shells (RSS) were used to develop a heterogeneous catalyst. RSS was washed 3 4 times
with hot distilled water, dried at 110 oC for 5 h, ground to powder, and calcined at 800 oC at a
heating rate of 10 oC/min as a catalyst and analyzed for thermal, structural, and textural
properties using thermogravimetric analyzer, x-ray diffractometer, and nitrogen
adsorption/desorption analyzer, respectively. The catalyst was further analyzed for elemental
compositions and surface morphology by x-ray fluorescence and scanning electron
microscopy, respectively. The catalyst was then applied in biodiesel production from rubber
seed oil. A central composite design (CCD) was employed together with RSM and ANN to
obtain optimal conditions of the process variables consisting of reaction time, methanol/oil
ratio, and catalyst loading on biodiesel yield. The optimum conditions obtained using RSM
were as follows: reaction time (60 min), methanol/oil ratio (0.20 vol/vol), and catalyst loading
(2.5 g) with biodiesel yield of 83.11% which was validated experimentally as 83.06 0.013%.
Whereas, those obtained via ANN were reaction time (56.7 min), methanol/oil ratio (0.21
vol/vol), and catalyst loading (2.2 g) with a biodiesel yield of 85.07%, which was validated
experimentally as 85.03 0.013%. The characterized biodiesel complied with ASTM D 6751
and EN 14214 biodiesel standards and was used in modern diesel test engine without technical
modifications. Though the produced biodiesel has a lower energy content compared with
conventional diesel fuel, in all the cases of blends considered, the optimal engine speed for
higher performance and lower emissions was observed at 2500 rpm. In this study, the B20
blend has best engine performance with a lower emission profile, and was closely followed by
B50 blend. === EM2018
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