MODELLING, SIMULATION AND CONTROL OF THE REACTIVE DISTILLATION OF BIODIESEL PRODUCTION

CHAPTER ONE

1.0 INTRODUCTION

1.1 Background of Study

Due to an increased demand of energy by the world population and the non-renewability of crude oil, the development of renewable energy generation techniques for future generations has gained great importance over the century (Madhu et al., 2012). One of these renewable energy has been identified to be biodiesel.

Biodiesel is a renewable, non-toxic, biodegradable substitute for diesel produced from crude oil. Generally, it is produced by transesterification of vegetable oils and animal fat by short chained aliphatic alcohols. Commercially, the production of biodiesel from vegetable oils and fats still have various drawbacks. Both batch and continuous processes utilize almost 100% excess alcohol than the stoichiometric molar requirement (3:1) in order to drive the transesterification reaction to completion and produce the maximum amount of biodiesel per unit consumption of oil (Kiss et al., 2008). At the end of the process, unreacted alcohol must be recovered by a separate distillation column. The use of a separate distillation column for alcohol recovery increases capital as well as operating cost. Therefore, there is the need to develop alternative means for the commercial production of biodiesel which minimizes cost without reducing the yield and quality of biodiesel produced. Reactive distillation is one of such alternative means.

Reactive distillation combines separation and reaction into a single vessel to minimize operation and equipment costs (Kiss et al., 2008). In this process, the products formed are removed as soon as they are formed. This characteristic makes it possible to overcome the

equilibrium thermodynamics of a reaction, reaching high conversion and selectivity. Thus, 1

it is particularly effective for reversible reactions such as the transesterification of vegetable oil and fats to biodiesel (He et al, 2006). However, the combination of reaction and separation into a single unit that resulted in many complexities of the process has made its dynamics and control study of this process a challenge to Process Engineers.

Dynamics in chemical engineering is the study of how process variables vary with time. As all real-life process variables vary with time, it is therefore important to study the dynamics of the biodiesel production process. Control is the external intervention needed to guarantee the satisfaction of operational requirements such as safety, production specifications, environmental regulations, operational constraints, economics (Stephanopoulos, 1984). Since the structure of biodiesel reactive distillation process is complex, due the need to maximize mass and energy raw materials, there is therefore need to develop a suitable control system for the process.

This research project is aimed at providing an outlook at the dynamics of biodiesel production by reactive distillation and developing a control system for the process by means of CHEMCAD and MATLAB modelling and simulation.

1.2 Research Problem Statement

Biodiesel is a valuable renewable fuel that can supplement and replace petroleum diesel in diesel engines. However, its cost of production by the reversible transesterification of vegetable oil and fats with alcohol by conventional means to achieve high purity of the product is relatively high. This high cost is a big problem that needs to be solved through provision of an alternative, novel, route and development of a reliable control method to make the process behave efficiently.