Preface

Distillation is one of the most used processes for industrial separation, and is responsible for a great part of energy consumption. The correct design and operation of a distillation column can lead to large savings of energy. Having sufficient knowledge to make an efficient column project and establish the best operational conditions needs experience and many tests. These types of tests can be very expensive, and is one of the reasons why it is justified to use process simulation tools, because with simulation tools various virtual tests and process changes can be evaluated at a reduced cost.

A mathematical model is necessary for making a simulation and consequently many simulations are necessary for the optimization of a process. However, the mathematical model must correctly represent the quantities and reflect the state of the studied system, so that simulation and optimization can succeed. During mathematical model construction an engineer must attempt to make the model simpler. This can be done without significant loss of capacity of system properties behavior.

The book is divided into four main sections. The first section contains the introductory chapter. The second section has two chapters dealing with the modeling of the distillation process using solar distillation and batch distillation. The third section has two chapters that discuss topics related to phase equilibrium modeling and simulation, very important steps of distillation process modeling. The last section deals with the modeling, simulation, and optimization of reactive distillation processes, a technique combining both reaction and separation in a single unit operation.

The importance of distillation can be reflected by the number of variations of the process, e.g., batch distillation, solar distillation, vacuum distillation, steam distillation, and fractional distillation. In some cases the mixture being distillated creates a problem in the separation process leading to modifications such as extractive distillation, azeotropic distillation, etc. Attempts to improve product quality can be done by the addition of, e.g., pump-around, side-stripper, etc. Energy saving can be attained by strategies such as vapor compression and vapor recompression. One of the most successful variants of distillation is reactive distillation (also known as reactive distillation with side reactors), a process intensification that has been applied successfully to lots of applications and has been revealed as a promising strategy for recent challenges. This book presents just a small part of the large scientific field involving modeling, simulation, and optimization of distillation.

**II**

**Section 4**

*by Vandana Sakhre*

Reactive Distillation **89**

**Chapter 6 91**

Reactive Distillation: Modeling, Simulation, and Optimization

**Vilmar Steffen** Departamento Acadêmico de Engenharia Química, Universidade Tecnológica Federal do Paraná, Francisco Beltrão, Paraná, Brazil

**1**

Section 1

Introduction

Section 1 Introduction

**3**

formation.

**Chapter 1**

*Vilmar Steffen*

economically viable [1].

model, with little loss in the result quality [2].

Introductory Chapter: Distillation

**1. Modelling, simulation, and optimization of distillation processes**

Obtaining a phenomenological model of a process consists on applying law conservations, like mass, energy, and momentum balances and constitutive relations, like vapor-liquid equilibrium, chemical reaction rate, chemical equilibrium relation, etc. A mathematical model, developed to represent (approximately) the real behavior of a process, is very important to analyze an existing plant or to evaluate the technical viability of a new chemical process plant. These analyses and evaluations normally are carried out by making changes in some process parameter and measuring the results of the respective change, in other words, carry out lots of "what if" relations. The analysis of a plant, by simulation, within the development of new processes may frequently show beforehand whether it is technically and

The solution process of a mathematical model is known as simulation (nowadays, simulation is synonymous of computational simulation). Analyzing a process based only in the mathematical model, is a task almost impossible, but the numerical results of simulation can be easier analyzed. The mathematical model is very important, beyond for simulation and analyses, for the optimization of a process. The mathematical model must correctly represent the quantities and reflect the state of the studied system, only so the simulation and optimization will succeed. In the step of the mathematical model construction, the engineer must analyze if some simplifications, which can make the model simpler (or much simpler), can be adopted without a significant loss in the prediction capacity of system property behavior. However complex a model may be, it cannot represent exactly the real behavior, so some simplifications can be accepted, resulting in a much more simpler

The complexity of a distillation column is not due to the material and energy balances that normally are simple equations. This complexity comes from the constitutive relations of chemical reaction (for the case of reactive distillation), mass transfer relation (in a more simplified way, phase equilibrium), and relations to compute the enthalpy. The chemical reaction must be analyzed for chemical equilibrium limitation and chemical reaction rates to evaluate if, in the column dimensions and operation conditions, the desired conversion will be reached. The enthalpies must be precisely evaluated, because it has influence on the heat duties of the condenser and reboiler. And, the thermodynamic property that has the greatest influence on the simulation of separation processes are those related to phase equilibria, for this part is necessary the non-idealities prediction of vapor phase (usually performed with equations of state) and liquid phase (associated with the excess Gibbs energy models). A good phase equilibrium modelling can predict limitations on the separation like those ones caused by azeotrope

The distillation process is the most commonly used in industry to separate chemical mixtures; its applications range from cosmetic and pharmaceutical to
