Abstract
In this work, the modelling, simulation and optimization of a reactive distillation column
for the production of Fatty Acid Methyl Ester (FAME) has been carried out. The FAME
considered was methyl palmitate, which was produced from an esterification reaction
between palmitic acid and methanol. The reactive distillation column used was set up in
Aspen HYSYS environment using Distillation Column Sub-Flowsheet and the fluid
package employed was Wilson model. The column had 17 stages, excluding the condenser
and the reboiler, and it was divided into seven sections, viz, condenser section, rectifying
section, upper feed section, reaction section, lower feed section, stripping section and
reboiler section. Palmitic acid (fatty acid) entered the column through the upper feed section
while methanol (alcohol) was fed at the lower feed section of the column. The developed
model was simulated to convergence using Sparse Continuation Solver. Furthermore, the
optimizer tool of Aspen HYS
1.0 INTRODUCTION
Reactive distillation process has been given special attention in the past two decades because
of its potential for process intensification for certain types of chemical reactions (Popken et
al., 2001; Murat et al., 2003).
Reactive distillation process is a growing chemical unit operation that involves the
integration of a reactor and a distillation column in one unit i.e. it merges two different unit
operations in a single apparatus. In other words, reactive distillation involves simultaneous
chemical reaction and multi-component distillation. The chemical reaction usually takes
place in the liquid phase or at the surface of a solid catalyst in contact with the liquid phase
(Seader et al., 2006). General application of reactive distillation is the separation of a closeboiling or azeotropic mixture (Terril et al., 1985).
The most interesting application involves combining chemical reactions and separation by
distillation in a single distillation apparatus. The most important benefit of reactive
distillation technology is a reduction in capital investment, because two unit operations can
be carried out in the same device. Such integration leads to lower costs in pumps, piping
and instrumentation. For exothermic reaction, the reaction heat can be used for vaporization
of liquid. This leads to savings of energy costs by the reduction of reboiler duties. Reactive
distillation process is also advantageous when the reactor product is a mixture of species
that can form several azeotropes with each other. Reactive distillation conditions can allow
the azeotropes to be “reacted away” through reaction. But the combination of reaction and
distillation is only possible if the conditions of both unit operations can be combined (Taylor
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and Krishna, 2000).
Reactive distillation can be used with a variety of chemical reactions e.g. acetylation, aldol
condensation, alkylation, amination, dehydration, esterification, etherification, hydrolysis,
isomerization, oligomerization, transesterification of fatty acids etc.
Fatty acid methyl esters (FAMEs) are a type of fatty acid ester derived by trans-esterification
of fats with methanol. They are used to produce detergents and biodiesel. Fatty acid esters
are produced by vegetable oils and animal fats trans-esterification with short chain aliphatic
alcohols. This process reduces significantly the vegetable oils viscosities without affecting
its calorific power, thereby, allowing their use as fuel. Fatty acid methyl esters are typically
produced by an alkali-catalyzed reaction between fats and methanol in the presence of base
such as sodium hydroxide or sodium meth-oxide. The physical properties of Fatty acid esters
are closer to fossil diesel fuel than pure vegetable oils, but the properties depend on the type
of vegetable oil (FAME fact sheet, 2011). A mixture of different fatty acid methyl esters is
commonly referred to as biodiesel, which is a renewable alternative fuel. Biodiesel is known
for being a clean-burning diesel fuel with minimum negative environmental impacts and
potential to greatly reduce greenhouse gas emissions. It is a biodegradable fuel with
negligible sulfur content and ultra-low sulfur emissions. It has similar physical properties as
fossil diesel fuel, which makes it compatible for combustion in internal combustion engines
and boilers. Biodiesel can be used as a blending component or a direct replacement for diesel
fuel in the diesel engines. It is defined as a mixture of monoalkyl esters of long chain fatty
acids (FAME) derived from a renewable lipid feedstock, such as vegetable oil or animal fat.
The scarcity of conventional fossil fuels, growing emissions of combustion- generated
pollutants, and their increasing costs will make biomass sources more attractive (Sensoz et
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al., 2000). Petroleum-based fuels have limited reserves concentrated in certain regions of
the world. These sources are on the verge of reaching their peak production. The fossil fuel
resources are shortening day by day. The scarcity of known petroleum reserves will make
renewable energy sources more attractive (Sheehan et al., 1998).
According to Demirbas, An alternative fuel to petro-diesel must be technically feasible,
economically competitive, environmentally acceptable and easily available. Biodiesel is one
of the current alternative diesel fuels, which has high heating value a little bit lower than
gasoline (46 MJ/kg), petro-diesel (43 MJ/kg) or petroleum (42 MJ/kg), but higher than coal
(32–37 MJ/kg). Biodiesel is also a good lubricant and can improve the lubrication properties
of the diesel fuel blend (Extension, 2010). The production of biodiesel can be simulated
using a software package known as Aspen HYSYS.
Aspen HYSYS is a program that offers a complete integrated solution to chemical process
industries. This software package can be used in almost every aspect of process engineering
from design stage to cost and profitability analysis. It has a built-in model library for
distillation columns, separators, heat exchangers, reactors etc. custom models can extend its
model library. Aspen HYSYS can interactively change specifications such as flow sheet
configuration, operating conditions and feed compositions to run new cases and analyze
process alternatives. Aspen HYSYS software allows us to perform a wide range of tasks
such as estimating and regressing physical properties, generating custom graphical and
tabular output results, fitting plant data to simulation models, optimizing process and
interfacing results to spreadsheets.
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1.1 Problem Statement
Crude oil has limited reserves and is the backbone of Nigeria’s economy. Also, it is not a
renewable source and contributes to the unwanted effect to the world environment.
Alternative, renewable, clean and environmentally friendly energy is sought after to support
the availability of crude oil fractions.
1.2 Aim
This research project is aimed at determining the optimum parameters required for obtaining
fatty acid methyl ester (FAME) of high purity with the aid of Aspen HYSYS.
1.3 Objectives
The objectives of this work are:
? To study, simulate and understand fatty acid methyl ester reactive distillation process
using Aspen HYSYS software package.
? To determine optimal parameters for high purity of the desired product (fatty acid
methyl ester).
1.4 Scope of Study
This work is limited using Aspen HYSYS to modelling, simulating and optimizing a
reactive distillation process used for the production of fatty acid methyl ester.
1.5 Motivation of Study
This work is embarked upon in order to have better understanding of how reactive
distillation process can be simulated with the aid of Aspen HYSYS.
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1.6 Justification
FAMEs are versatile products covering a wide range of product uses which include;
lubricants, working fluids, solvents, fuels, agriculture, surfactants, polymers, coatings and
food.
Simulating the RD process can help in understanding the behavior of this process, which
can be applied in practice