Introduction to Adsorption: Basics, Analysis, and Applications

By Chi Tien

Introduction to Adsorption: Basics, Analysis, and Applications presents adsorption basics that are relevant and essential to its application, including data analysis, interpretation and design calculations. The book deliberately keeps background information to a minimum, instead comprehensively covering adsorption of liquid solutions, the difference between equilibrium individual solute uptake and surface excess, a general discussion of adsorbate uptake mechanisms and uptake rate expression, uptake steps, performance models and their generalizations, application of performance models, and design methods based on the constant behavior assumption and unused bed length concept.

• Includes adsorption basics and their applications
• Discusses gas adsorption equilibrium and equilibrium of liquid adsorption
• Gives the various steps of adsorbate uptake and their combination to yield adsorbate uptake rate expression
• Presents both rational and empirical design for adsorption processes
• Highlights common mistakes found in recent adsorption publications

• Language: English
• Publisher: Elsevier Science
• Release date: Nov 27, 2018
• ISBN: 9780128175125

Chi Tien

Chi Tien (BSc., National Taiwan University, 1952; MSc., 1954; PhD., Northwestern University, 1958) is professor emeritus of chemical engineering at Syracuse University. During his teaching career, Professor Tien also taught at the University of Tulsa, University of Windsor, National University of Singapore, and Nanyang Technological University. In addition, he had visiting appointments with University of Leeds, Karlsruhe University, and University of Duisburg-Essen. For over 60 years, Professor Tien has been actively engaged in fluid/particle separation and adsorption research and has published widely. He authored and coauthored a number of books including Granular Filtration of Aerosols and Hydrosols, 1st Ed. (Butterworths), Adsorption Calculations and Modeling (Butterworths-Heinemann), Kinetics of Metal Ion Adsorption from Aqueous Solutions: Models, Algorithms, and Applications (with S. Yiacoumi, Kluwer Academic Publisher), Introduction to Cake Filtration: Analyses, Experiments, and Applications (Elsevier), Granular Filtration of Aerosols and Hydrosols, 2nd Ed. (with B. V. Ramaro, Elsevier), and Principles of Filtration (Elsevier).

Book preview

Introduction to Adsorption

Basics, Analysis, and Applications

First Edition

Chi Tien

Professor Emeritus, Department of Biomedical and Chemical Engineering, Syracuse University

Table of Contents

Cover image

Title page

Copyright

Dedication

Preface

Chapter 1: Introduction

Abstract

1.1 Adsorption as a Sorption Process

1.2 Comparisons With Other Separation Processes

1.3 Operation Modes of Adsorption Processes

1.4 Applications of Adsorption

Chapter 2: Adsorbents

Abstract

2.1 Adsorbent Materials

2.2 Properties and Physical Characteristics of Adsorbents

2.3 Adsorbent Selection

2.4 Problems Associated With Contacting Adsorbents With Fluid Solutions

Chapter 3: Adsorption Equilibrium Relationships, Isotherm Expressions, Their Determinations, and Predictions

Abstract

3.1 Pure Gas Adsorption Equilibrium

3.2 Adsorption of Gas Mixtures

3.3 Adsorption from Liquid Solutions

3.4 Determination of Pure Gas/Single Solute Isotherm Expressions through Data Fitting

3.5 Prediction of Adsorption Isotherm

3.6 Is There Equivalence Between Adsorption Isotherm and Ion Exchange Equilibrium Constant?

Chapter 4: Adsorbate Uptake and Equations Describing Adsorption Processes

Abstract

4.1 Transport and Uptake of Adsorbates

4.2 Estimation of Mass Transfer Parameters

4.3 Equations Describing Adsorbate Uptake and Adsorption Performance

4.4 Governing Equations of Adsorption Processes—Adsorption Performance Models

Chapter 5: Batch Adsorption Models and Model Applications

Abstract

5.1 Single Species Batch Adsorption of Systems with Linear Adsorption Equilibrium Relationship and Adsorbate Uptake Controlled by Mass Transfer

5.2 Finite Bath Single Species Adsorption Model of Mao et al. (1993)

5.3 Empirical Models

Chapter 6: Fixed-Bed Adsorption Models and Fixed-Bed Design Calculations

Abstract

6.1 Terminologies of Fixed-Bed Adsorption

6.2 The Thomas Model of Fixed-Bed Adsorption (Thomas, 1944, 1948)

6.3 Models Based on Simple Uptake Rate Expressions

6.4 Model Applications

6.5 Constant Pattern Behavior of Breakthrough Curve of Fixed-Bed Adsorption

6.6 Other Empirical Fixed-Bed Design Methods

6.7 Is There a Preferred Design Method of Fixed-Bed Adsorption?

Author’s Suggestions on Adopting Introduction to Adsorption in Teaching

Index

Copyright

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Notices

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Dedication

To Julia C. Tien

Preface

This volume, Introduction to Adsorption: Basics, Analysis, and Applications, is prepared as a textbook for engineering students. It is also intended for self-study by practicing engineers and technologists who desire background information in adsorption for their current professional work, but did not have the opportunity to learn about adsorption in their earlier academic training.

As a separation process, adsorption is a longstanding engineering practice, and is widely used in many fields. Its importance has grown recently because of its relevance to sustainable development and green technology. However, because of time constraints imposed on our engineering curriculum, its coverage as a separate course in teaching has not been possible, except in a few exceptional situations. In most cases, adsorption has only been taught as part of a class such as unit operations, water and waste water treatment, air pollution control engineering, separation processes, and so forth. Generally speaking, the coverage afforded with the present arrangement tends to be brief and often incomplete, and in many cases, even of questionable value. This is one of the reasons that prompted the writing of this book.

The purpose of this book is to present an introductory treatment of certain adsorption basics, and their applications in analysis and design of adsorption processes. The topics discussed include adsorption basics (Chapters 3 and 4), analysis of adsorption processes (Chapter 4), and applications including identifying adsorbate uptake mechanisms, derivation of adsorbate uptake rate expressions, developing conservation equations of relevant quantities leading to the establishment of adsorption performance models, and adsorption process design. The treatment is based on physical reasoning and simple mathematics, and to the extent possible, free of any sophisticated mathematical envelopment. It, therefore, can be easily comprehended by average fourth year undergraduates, or first year graduate students, as well as practicing engineers.

As a text, the book is probably best suited for fourth year undergraduates, or first year graduate students. The materials presented in this book can also be easily incorporated into courses in which adsorption represents part of the coverage. A more detailed discussion on this point is given in Author’s Suggestions on Adopine and Introduction to Adsorption attached at the end of this volume.

In the course of preparing this book, I have enlisted assistance from a number of friends and colleagues, including Professor Cary Chiou (National Chen Kung University, Taiwan), Professor L.S. Fan (Ohio State University), Professor Rolf Gimbel (Duisburgh University, Germany), Professor C.P. Huang (University of Delaware), Professor William P. Johnson (University of Utah), Professor Yongwon Jung (Inha University, South Korea), Professor Graeme J. Millar (Queensland University of Technology, Australia), Professor H. Moon (National Chonnam University, South Korea), Professor B.V. Ramarao (ESF, State University of New York at Syracuse), Professor M.B. Ray (University of Western Ontario, Canada), Professor Kean Wang (Khalifa University of Science and Technology, Abu Dhabi), and Professor S. Yiacoumi (Georgia Tech). Their criticisms and comments about the book’s content and its writing are greatly appreciated. I am particularly grateful to R. Gimbel, H. Moon, Mita Ray, and Kean Wang, who, despite their busy schedules, have taken the tedious job of reading the entire manuscript in order to identify any mistakes and omissions, and offer changes and corrections. I am also thankful to my editors, Kostas Marinakis and Bellie Fernandez, for their help and efforts in making the prompt publication of this volume possible, to Jennifer Puthota for preparing some of the figures, to Anne Rauh for her assistance with a literature survey, and to Kathy Datthyn-Madigan for her keyboard skills in assembling the manuscript. Finally, to my wife, Julia, I thank her for her love, patience, and help of the past five plus decades. This book is dedicated to her.

Chapter 1

Introduction

Abstract

Adsorption as a separation process is widely applied in the manufacturing economy and everyday life. Adsorption performance is strongly influenced by mass transfer of the species between the solution and the adsorbent surfaces and the adsorption reaction rate. Therefore, adsorption can be considered an equilibrium-diffusion reaction process. This chapter outlines the basic operating principle of adsorption and then draws a comparison between adsorption and other separation processes. The modes of operation of adsorption processes are described and, finally, different applications of adsorption are presented.

Keywords

Adsorption; Sorption; Absorption; Equilibrium-diffusion reaction; Continuous-flow tank; Fixed-bed adsorption; Moving-bed adsorption

As a separation process, adsorption is widely applied in our manufacturing economy and in our daily life. Adsorption operations exploit certain solids’ ability to preferentially concentrate specific substances from solutions (gaseous or liquid) onto their surfaces. Thus, by contacting fluids with such solids, the desired objective of purification or separation may be achieved.

The extent of adsorption of a given situation is reached once equilibrium is established between the adsorbent and its contacting solution. In practice, adsorption performance is also strongly influenced by the mass transfer of the species between the solution and the adsorbent surfaces and the adsorption reaction rate. Technically, adsorption is, therefore, an equilibrium-diffusion-reaction process.

1.1 Adsorption as a Sorption Process

The basic operating principle of adsorption: the preferential concentration of species onto surfaces of adsorbing solids also operates in two other processes; namely, chromatography and ion exchange. In fact, adsorption, ion exchange, and chromatography are often grouped together under the title of sorption processes in engineering textbooks. Similar to most adsorption operations, chromatography operates in fixed-bed mode, but is devised for separating liquid mixtures through an intermittent feed of the solution to be separated, followed by the passage of an elution solution. In ion exchange, the solid substance used contains charged groups that interact with the charged ions present in the liquid solution. If one views adsorption as an exchange process involving a fictitious species, the equivalence between adsorption and ion exchange becomes obvious. In fact, much of the information presented in this volume may be applied to ion exchange as well.

1.2 Comparisons With Other Separation Processes

1.2.1 Adsorption Versus Absorption

Because of their similarity in spelling, the two terms; adsorption and absorption, are often used interchangeably by lay people. However, there are significant differences between them. Gas absorption is an operation in which a gas mixture is brought into contact with a liquid for the purpose of dissolving one or more components of the mixture into the liquid. Absorption, therefore, is a bulk phenomenon, and the extent of separation is limited by the solubilities of the gases involved. In contrast, adsorption is a surface phenomenon, and the extent of adsorption is limited by the relevant adsorption isotherm relationship.

Absorption may be carried out by passing the gas and liquid streams through a packed column concurrently or counter-currently. The operation consists of two moving phases (gas and liquid) and a stationary phase (column packing), which provides the interfacial area for liquid/gas contact. In fixed-bed adsorption, the fluid to be treated passes through a bed packed with adsorbent. The process involves two phases, a moving fluid and a stationary solid phase of adsorbents. Absorption, therefore, may be treated as a steady-state process, while adsorption in a fixed-bed operation is an inherently non-steady state. As a result, the computational effort required for the design of fixed-bed adsorption is more extensive than that of absorption. This point will be discussed later.

A cartoonist's version of the difference between adsorption and absorption is shown in Fig. 1.1.

Fig. 1.1 Difference between absorption and adsorption.

1.2.2 Adsorption Versus Distillation

Distillation, like adsorption and absorption, also belongs to the equilibration-diffusion category of separation processes, and is used for the separation of homogeneous liquid mixtures. However, unlike adsorption or absorption, separation by distillation is effected by using energy instead of material as an agent of separation.

Distillation is perhaps the most widely used separation process in processing engineering and operates on the principle of the difference in volatilities of substances to be separated. In a hypothetical study comparing distillation versus adsorption, Ruthven (1984) showed that for separating an A-B mixture, the use of distillation becomes impractical if the relative volatility of A to B is less than 1.2. To separate light gas mixtures, adsorption was found to be preferential to cryogenic distillation, even when the relative volatility is high.

1.2.3 Adsorption Versus Deep-Bed Filtration

Deep-bed filtration is a process designed for the removal of fine particles from diluted fluid suspensions. Its operation is carried out by passing the suspension to be treated through a column packed with granular or fibrous substances (filter media). Generally speaking, deep-bed filtration and fixed-bed adsorption share many common features, such as equipment configuration and modes of operation. Because of their similarities, the words ‘adsorption’ and ‘filtration’ are often used interchangeably. The removal of submicron colloidal particles from fluid to solid surfaces may be described as either filtration or deposition (Hirtzel and Rajagopalan, 1985). Carbon columns used to remove dissolved organic solutes in water treatment are often referred to as ‘carbon filters’ by water engineers. Similarly, the term ‘charcoal filter’ is used to denote cartridges filled with granular activated carbon for personal protection.

In spite of these similarities, the analogy between deep-bed filtration and fixed-bed adsorption is limited. A major difference between them resides in the fact that in deep-bed filtration, removal of particles from the suspension to be treated results in particle deposition over the exterior surfaces of the filter media. In contrast, the adsorbed dissolved species in fixed-bed adsorption covers mainly the interior surfaces of adsorbents. As stated before, the extent of separation achieved in adsorption is limited by the adsorption equilibrium relationship. On the other hand, particle retention in deep-bed filtration depends strongly upon the nature of particle-collector interaction forces, but there is no clear-cut limit on the extent of deposition (Tien and Ramarao, 2007). As adsorption processes may cease operation once the adsorbents become saturated, for deep-bed filtration, due to increasing particle retention, the pressure drops required for maintaining a specified throughput increase with time. The duration of operation is limited by the maximum allowable pressure drop.

1.3 Operation Modes of Adsorption Processes

Separation by adsorption is effected by contacting solutions to be treated with selected adsorbents. There are numerous ways of bringing about fluid/solid contact, as shown in Fig. 1.2. A brief description of is given as follows:

a.Adsorption in agitated vessels. Batch adsorption in agitated vessel represents perhaps the simplest way of bringing about fluid/adsorbent contact. A fixed amount of adsorbent of a known state is added to a volume of solution of a known solute concentration in a closed vessel. Agitation is provided by rotating stirrers in order to insure that adsorbent particles are fully suspended, and the adsorbate concentration is kept uniform throughout the solution. The data collected are the temporal evolution of the solute concentration of the solution. While batch operation is not suitable for treating large volumes of solution (such as water supplies), in general, batch adsorption test data are often used in characterizing new adsorbents for applications.

b.Adsorption in continuous-flow tanks. This type of