Separation Process Essentials

Alan M. Lane

• Éditeur: CRC Press
• Année: 2019
• ISBN:
  9781351618137
• Édition: 1
• Sujet: Physical Sciences
• Sous-sujet: Industrial & Technical Chemistry

Separation Process Essentials provides an interactive approach for students to learn the main separation processes (distillation, absorption, stripping, and solvent extraction) using material and energy balances with equilibrium relationships, while referring readers to other more complete works when needed. Membrane separations are included as an example of non-equilibrium processes.

This book reviews and builds on material learned in the first chemical engineering courses such as Material and Energy Balances and Thermodynamics as applied to separations. It relies heavily on example problems, including completely worked and explained problems followed by "Try This At Home" guided examples. Most examples have accompanying downloadable Excel spreadsheet simulations. The book also offers a complementary website, http://separationsbook.com, with supplementary material such as links to YouTube tutorials, practice problems, and the Excel simulations.

This book is aimed at second and third year undergraduate students in Chemical engineering, as well as professionals in the field of Chemical engineering, and can be used for a one semester course in separation processes and unit operations.

Part I

Introduction

The book is divided into several parts. This part needs no introduction. It is the introduction!

But as long as you are here, Chapter 1 “Introduction” will show you how I think about separation processes, my teaching philosophy and methods, important features to look for, and how the book is laid out. A bit of that is in the Preface too. The Preface was never assigned when I was an undergraduate and I rarely read it. I hope you go back and read those few pages.

Chapter 2 “A Look Inside Your Chemical Engineering Toolbox” is an essential review of the skills you learned in previous courses, especially the first chemical engineering course in material and energy balances. You already possess almost every tool you need for this subject. We are simply going to apply them to the specific process of separations.

1

Introduction to Separation Processes

So, here you are, in the third year of your chemical engineering studies and ready for a course on separation processes. Congratulations! That’s awesome! Questions?

Q: Why should I learn from your book?

A: There are plenty of other good books on separation processes. Some are listed in Table 1.1 with the first four being the most popular in the United States. Why use this new book Separation Process Essentials by Professor Emeritus Alan M. Lane?

My book is just for you, a chemical engineering student being introduced to separations for the very first time. I do not cover all separation processes, just the most common ones. So, it won’t be a great reference book for specialists. I limit the content to what you can reasonably learn in one semester. So, it won’t be appropriate for advanced or graduate studies. Most chemical engineering students no longer study computer programming, so I limit the computer tools you need to spreadsheets and (optionally) CAD software. I am a big believer in learning with examples, and you will find lots of thoroughly explained exercises throughout. As I write this, I try to imagine you sitting in my office and informally discussing the topic. I hope you find it easy to read, even humorous in parts. After 30 years of teaching this stuff, I have a pretty good feel for what you can learn well in one semester.

When and if you need a broader or deeper knowledge of separation processes, you can always take an advanced or graduate course, read a more comprehensive book, work with your company’s design group, and talk to vendors of separation equipment.

TABLE 1.1
Some Textbooks on Separation Processes

Separation Process Engineering (4th Edition) by Phillip C. Wankat (2016) Separation Process Principles (4th Edition) by J. D. Seader, Ernest J. Henley, and D. Keith Roper (2015) Transport Processes and Separation Process Principles (5th Edition) by Christie John Geankoplis, A. Allen Hersel, and Daniel H. Lepek (2018) Unit Operations of Chemical Engineering (7th Edition) by Warren L. McCabe, Julian C. Smith, and Peter Harriott (2004) Separation Processes (2nd Edition) by C. Judson King (2013) Mass Transfer and Separation Processes (2nd Edition) by Diran Basmadjian (2007) Principles and Modern Applications of Mass Transfer Operations (3rd Edition) by Jaime Benitez (2016)

Q: What do you mean by “separation processes?”

A: I think you already have a pretty decent idea of what separation processes are. You’ve passed by (or maybe even worked in) chemical plants with those giant distillation towers you can see from the road. You studied partial evaporation – flash distillation – in the material and energy balance and thermodynamics courses. You even have run across separation processes in your everyday living, like brewing a tasty cup of coffee!

Separation processes are important and ubiquitous in the chemical industry. Most chemical processes are centered on a reactor or some device that converts raw materials into more valuable products. Before the reactor, separators are used to purify the raw materials. After the reactor, separators are used to recycle raw materials back into the process, purify the products, and remove environmental pollutants.

You probably know that distillation is the most common separation process. It is used for materials with reasonable differences in volatility. But many other types exist, as shown in the brief listing in Table 1.2. The choice depends on the physical and chemical differences that you can exploit between the materials to be separated.

Q: How do separations fit into the chemical engineering curriculum?

TABLE 1.2
Examples of Separation Processes

A: I’ll explain with the chemical engineering building blocks shown in Figure 1.1. In the first year, you learn the science fundamentals that form the foundation for chemical engineering. These include chemistry, physics, biology, and math. In the second year, you become skilled at material and energy balances, thermodynamics, and transport phenomena. Material and energy balances allow you to count what goes into a process and what comes out (or accumulates!). Sounds simple but can get quite challenging, as you discovered! Thermodynamics shows how far a process can go, and transport shows how fast it can get there. In the third year, you apply all these skills toward the analysis and design of the major unit operations: fluid flow, heat transfer, chemical reactions, and the topic at hand, separations. Finally, in the fourth year you get to practice chemical engineering in the lab and design courses, including design and operation of separation equipment.

FIGURE 1.1
Chemical engineering building blocks.

Q: What is the basic idea behind separation processes?

A: Most separation processes consist of mixing two separable phases like gas with liquid; gas or liquid with solid; or even two immiscible liquids. The contact area between phases should be large enough and maintained long enough for transfer of chemicals to occur between them. The distribution of the chemicals between phases approaches thermodynamic phase equilibrium. Finally, the two phases are physically separated.

Think of a simple tank containing a liquid mixture of chemicals. Add heat to partially evaporate the liquid and the more volatile chemicals will concentrate in the vapor (distillation). Bubble a gas through the liquid and some chemicals will pass from the liquid to the gas (stripping) or from the gas to the liquid (absorption). Add a second immiscible liquid and the chemicals will distribute according to their relative solubility in the two liquid phases (solvent extraction).

Maybe you had a delicious cup of hot coffee this morning? You (or maybe a barista) added hot water to ground up coffee beans and some of the chemicals dissolved from the beans into the water (extraction). Then the solids and liquids were separated by passing the mixture through a paper filter (filtration). All sorts of separation processes occur after that in your digestive system – but we won’t get into that!

Think about the process variables that affect coffee brewing. How do temperature, mixing, contact time, particle size, amounts, etc. affect the extraction? What are the underlying physical reasons? Close the book and think about that for a moment. Make a list of these variables and their effects. Discuss this in class or with your study group.

FIGURE 1.2
A series of equilibrium stages.

Now take a similar look at carbonation of sof...