Abstract
In this study a kinetic model was developed to represent the kinetics of transesterificiation of
waste vegetable oil (frying oil) in a batch reactor at different isothermal conditions of 313 K, 323
K, 333 K and 338 K. The reaction occurs in series of 3 steps. Solution to the model was derived
using MATLAB the method for solving was done by applying ode solver ode15s which makes
use of backward differential formulas known as Gear method was used to solve the equations
derived and to simulate kinetic data from literature. The effect of temperature on concentration
profile of species and the reaction rate constant was studied for the selected isothermal
conditions. Temperature had no effect on formation of triglyceride, alcohol and Methyl ester
because the concentration at 313 K, 323 K, 333 K and 338 K were close but temperature
favoured the formation of Diglyceride and Monoglyceride. High temperature did not favour
formation of glycerol which is the undesired product. The maxi
1.0 INTRODUCTION
Transesterificiation is the general term used to describe the important class of organic reactions
where an ester is transformed into another ester through interchange of the alcohol to glycerol
moiety. This is also described as chemical process by which biodiesel is produced. It is primarily
the displacement of alcohol from an ester by another alcohol; the reaction reduces the high
viscosity of triglycerides usually present vegetable oil and animal fat. (Orificia et al., 2013). The
transesterificiation reaction is an equilibrium reaction and the transformation occurs essentially
by mixing the reactants. However, the presence of a catalyst (strong acid, base or alkali metal)
accelerates considerably the adjustment of the equilibrium. In order to achieve a high yield of the
ester, the alcohol has to be used in excess.
Vegetable oils are oils from feedstock and plants are usually found to contain long chain alkyl
(methyl, propyl and ethyl) esters. For this study used frying oil would be used as the oil of
interest for the transesterificiation reaction. Some vegetable oils may be in form of a colorless
liquid and could be a pale yellow liquid sometimes with distinct taste and odor, their boiling
point ranges from 313 0C to 350 and likewise the density is from 800kg/m3
.to 961kg/m3
they
contain triglyceride in which most of their fatty acids chains are ricinoleate. Oleate and linoleates
and other components vegetable oils can be used for domestic purposes and commercial
purposes like in the production of soaps, brake fluids and hydraulic, paints, dyes, inks, coatings
etc. (Leonor and Forero, 2012).
Vegetable oils are a good source of ricinoleic and oleic acid, this acid is a mono unsaturated, 18-
carbon fatty acid ricinoleic acid has a unique characteristic in which its hydroxyl functional
2
group lies on the 12th carbon. This unique feature causes it to be more bipolar than most fats
(Leonor and Forero, 2012).
To carry out a transesterificiation reaction, this is achievable with the use of a Batch reactor,
continuous stirred tank reactors (CSTR), tubular reactors, fixed bed catalytic reactors etc. In this
study, the research will be focused on modeling a Batch for the transesterificiation of castor oil
with methanol. The concept of batch reactors is readily applied in chemical industries.
In a batch reactor some catalyst like silica gel, sodium hydroxide could be used to aid certain
reaction whilst perfect mixing of the fluids is being carried out by the stirrer, this concept is
applied to different operations such as esterification, saponification, transesterificiation, alcohol
synthesis etc In all these applications size of the reactor is usually estimated and design equations
are usually obtained to also estimate the pressure drop of fluids flowing in the reactor In a batch
reactor the catalyst placed inside in a position in such a way that reacting fluids must make an
appreciable contact with the catalyst. Energy balances together with material balances are carried
out on both the fluid in contact with catalyst particles and the catalyst particles in the reactor
(Levenspiel, 1999).
Generally in reactors the following steps of a reaction usually takes place;
1. Reactants are continuously stirred to ensure proper mixing.
2. Reactants are transported as well as energy from bulk fluid to the catalyst external
surface.
3. Reactants transported with energy from external surface into the porous pellets,
4. Adsorption of reactants chemical reactions and desorption of newly formed products at
the active sites of catalyst.
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5. Products are transported from the internal pores of catalyst to the external surface of the
pellet.
6. Product is transported into the bulk fluid.( Levenspiel,1999)
Chemical reactions in a reactor are either exothermic or endothermic and require that energy may
either be removed or added to the reactor to maintain a constant temperature. The batch reactor is
normally run such that the temperature and concentration are the same throughout the fluid. The
batch reactor is generally modeled as having no special variations in concentration and
temperature or reaction rate throughout the vessel. In the case of using a batch reactor for
transesterificiation reaction, the fluids are to be perfectly mixed and operated at isothermal or
non isothermal conditions and products to be withdrawn after a certain time interval.
In theory, ideal batch reactors are assumed to have a constant volume; therefore equal volume of
reactor content is expected to be withdrawn after a certain time interval. These contents are
usually accounted for by using lumped parameters of material and energy balances with
mathematical equations which is being described by a set of ordinary differential equations (Hill,
2011).
In a batch reactor the reactants are charged and reaction is allowed to take place for a given time.
Batch reactors are usually best used for liquid solid reactions and liquid phase reactions it is
majorly used in heterogeneous reactions with a catalyst. The major advantage of using a batch
reactor is that it facilitates good quality for the product and reaction occurs faster within less
resident time compared to CSTR through provision of greater constancy in reaction conditions.
(Hill, 2011).
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1.1 Aim and Objectives of Study
The aim of this study is to obtain a kinetic model for transesterificiation reaction of frying oil.
The objectives include the following
? Apply model to fit that of a batch reactor at isothermal conditions
? Simulate the reaction using computational software package MATLAB
? Study the effects of temperature on the kinetic rate constant and concentrations of
components.
MATLAB is the application applied in this study because it is can be applied to solve complex
differential equations It is most suitable for solving differential equations of any kind.
Using MATLAB and the derived model equations can be solved and simulated to obtain results
that can be compared to existing results in literature. In obtaining a suitable model of a batch
reactor to carry out this reaction certain parameters such as different temperature only at
isothermal condition would be considered, therefore to achieve this mass balance equations
coupled with rate kinetic rate constants for both the forward and backward reaction will be
greatly employed in this study.
1.2 Scope of Work
The scope of this work will cover the following:
? Mass balances on the reacting species
? It will also cover reaction kinetics involved in the transesterificiation reaction of used
vegetable oil and methanol.
? Deriving a model which describes the reaction in the batch reactor.
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? Use of MATLAB to simulate reaction.
1.3 Justification of Study
This research work is adopted as a result of the increase in need of suitable reactors for reactions
like esterification reaction, saponification reaction, hydro-cracking and transesterificiation
reaction which is essential in the production of bio fuel.
There has been a major concern about the high rate of exploitation of oil reserves In Nigeria and
around the world and the need for alternative fuels arises.
As a new form of energy is been explored, reactors and technology are needed to harness it, this
will in turn improve lifestyle of the people, increased productivity in agriculture, improved
health care and also a stable economy, therefore there is a need to bring about new reactors that
will enhance the exploitation of a new form of energy, .therefore the significance of this study is
that it would give a model which describes the reaction in the batch reactor. It would also save
the time of carrying out multiple experiments and model would serve a good purpose in the
production of biodiesel.
1.4 Problem Statement
The Transesterificiation reaction process of vegetable oil and methanol is applied in the
production of Biodiesel, the process is to be optimized to fit the reaction occurring in Batch
reactor. The problem to be solved is to obtain the kinetic model and study the effects of
temperature on the rate constants (k).