Comparative Studies On The Production Of Biodiesel Using Various Heterogeneous Catalysts
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Date
2015-05
Authors
Ezebor, Francis
Journal Title
Journal ISSN
Volume Title
Publisher
Universiti Sains Malaysia
Abstract
Heterogeneous acid catalysts were prepared by incomplete carbonisation and
sulphonation of oil palm trunk (OPT) and sugarcane bagasse (SCB) and
characterised. The catalysts consisted of high densities of strong acid sites (-SO3H)
and weak acid sites (COOH and phenolic OH groups). The performance of the
catalysts was influenced by incomplete carbonisation and the grafting time for the
Brønsted acid sites. The catalysts exhibited similarities in process behaviour to the
basic reaction parameters (acid:methanol molar ratio, catalyst loading, reaction time
and temperature). The activity of the catalysts was independent of total acidity and
textural properties (surface area, pore volume and pore width). However, activity of
the catalysts strongly correlated with the strong Brønsted acid sites density. The
catalysts exhibited longer reaction time and selectivity towards esterification reaction
under reflux at 65 to 130 oC. The catalysts are active in many cycles of usage with
gradual decrease in activity during successive cycles. Elemental analysis of used
catalysts showed a decrease in sulphur content from 2.89 to 2.65 % for the SCB
catalyst and from 2.66 to 2.37 % for the OPT catalyst after the seventh cycle in
esterification under the pseudo-infinite methanol. The decreased in activity was due
to the leaching of small -SO3H bearing polycyclic compounds. Catalysts prepared by
one-step synthesis showed very significant homogeneous contribution due to the
leaching of the active sites. Remarkable improvement in catalytic activity and
decrease in selectivity towards esterification is dependent on the control of the
adsorption-desorption equilibria of predominant adsorbates. Under the pseudoxxvi
infinite methanol, catalysts deactivation and dissolution effect of methanol over
kinetic effect were minimised. The catalysts demonstrated rapid activity, reducing
the time for optimum conversion of fatty acids to FAME from 5 h to 45 mins. In
esterification, it gave 6.53 to 6.97 fold increase over conventional method. In
transesterification of waste oil containing 42% FFA, the catalysts gave FFA
conversion of 98.6 to 99.1% after 30 mins and FAME yield of 80.6 to 83.0% after 4
h. In contrast, the conventional method gave FAME yield of 43.7 to 45.0% after 6 h
at the same temperature. The CaO-La2O3 mixed oxide catalysts showed basicity of
1.310 to 1.400 mmol/g and basic strength of 15.0<H_<18.4. Coupling of the pseudoinfinite
methanol esterification with transesterification by the mixed oxide catalysts
gave FAME yield of 97 to 98.2% within 60 to 100 mins of the transesterification
step, thereby simplified the processing of high FFA oils. The reaction rate constants
of the catalysts showed strong dependency on the temperature and were proportional
to the concentration of the unconverted substrate but the equilibrium constant was
weakly dependent on the temperature. The catalysed reactions of the OPT and SCB
heterogeneous acid catalysts are strongly endothermic but surface effects
predominate over kinetic reaction as the concentration of the products increases.
Description
Keywords
The Production of biodiesel using , Various heterogeneous Catalysts.