Introduction to Chemical Engineering E-Book

C. M. van't Land

• Herausgeber: John Wiley & Sons
• Kategorie: Fachliteratur
• Sprache: Englisch

Seitenzahl: 687

Veröffentlichungsjahr: 2023

Beschreibung

Introduction to Chemical Engineering An accessible introduction to chemical engineering for specialists in adjacent fields Chemical engineering plays a vital role in numerous industries, including chemical manufacturing, oil and gas refining and processing, food processing, biofuels, pharmaceutical manufacturing, plastics production and use, and new energy recovery and generation technologies. Many people working in these fields, however, are nonspecialists: management, other kinds of engineers (mechanical, civil, electrical, software, computer, safety, etc.), and scientists of all varieties. Introduction to Chemical Engineering is an ideal resource for those looking to fill the gaps in their education so that they can fully engage with matters relating to chemical engineering. Based on an introductory course designed to assist chemists becoming familiar with aspects of chemical plants, this book examines the fundamentals of chemical processing. The book specifically focuses on transport phenomena, mixing and stirring, chemical reactors, and separation processes. Readers will also find: * A hands-on approach to the material with many practical examples * Calculus is the only type of advanced mathematics used * A wide range of unit operations including distillation, liquid extraction, absorption of gases, membrane separation, crystallization, liquid/solid separation, drying, and gas/solid separation Introduction to Chemical Engineering is a great help for chemists, biologists, physicists, and non-chemical engineers looking to round out their education for the workplace.

Leseprobe

Introduction to Chemical Engineering

C.M. van ’t Land

Enschede, The Netherlands

Copyright © 2024 by John Wiley & Sons, Inc. All rights reserved.

Published by John Wiley & Sons, Inc., Hoboken, New Jersey.Published simultaneously in Canada.

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Library of Congress Cataloging‐in‐Publication Data

Names: C.M. van 't Land, 1937– author.Title: Introduction to chemical engineering / C.M. van 't Land.Description: 1st edition. | Hoboken, NJ : Wiley, 2024. | Includes bibliographical references and index.Identifiers: LCCN 2021035195 (print) | LCCN 2021035196 (ebook) | ISBN 9781119634089 (hardback) | ISBN 9781119634096 (adobe pdf) | ISBN 9781119634126 (epub)Subjects: LCSH: Chemical engineering.Classification: LCC TP155 .L26 2024 (print) | LCC TP155 (ebook) | DDC 660–dc23LC record available at https://lccn.loc.gov/2021035195LC ebook record available at https://lccn.loc.gov/2021035196

Cover Design: WileyCover Image: Courtesy of C.M. van ’t Land

Preface

After graduation as a chemical engineer at the University of Twente in The Netherlands in 1971 I worked in research for the multinational company Akzo Nobel. My retirement started in 2000. In 2005, I proposed the Dutch organization PAO Techniek en Management to organize a seminar “Introduction to Chemical Engineering”. The goal was to enable chemists in the process industry to acquire knowledge of chemical engineering. The seminar was given successfully in The Netherlands between 2005 and 2015 and its scope was gradually extended. Material from standard textbooks was combined with material obtained while at work. The seminar appeared to be attractive also for, e.g., mechanical engineers and physicists. The seminar was written in English as that is the “lingua franca” of the process industry. Then, in 2015, the interest declined. It is possible that internet information is the cause. I then proposed John Wiley & Sons to publish a book containing the material of the seminar. An agreement was made and the present book is the result. I am grateful for the permissions obtained for the incorporation of material from various sources. The sources are mentioned in the book. I wish to thank especially the following publishers:

Delft Academic Press/VSSD at Delft in The Netherlands,

Elsevier at Amsterdam in The Netherlands,

McGraw‐Hill at New York in the U.S.A.,

John Wiley & Sons at Hoboken in the U.S.A.,

Taylor and Francis Group at Abingdon in the U.K., and

Wolters Kluwer at Alphen aan den Rijn in The Netherlands.

I am greatly indebted to my wife, Annechien, for her constant encouragement and patience.

C.M. van ’t Land

Prologue

1. A Typical Chemical Production System

Introduction

The production system for crystalline ethylene diamine tetra‐acetic acid (EDTA) within Nouryon Industrial Chemicals will be described. Nouryon is a multinational company manufacturing chemicals. The company employs at present approximately 10,000 employees and is active in more than 80 countries. The activities of Nouryon were part of the multinational company AkzoNobel till 2019. EDTA is a chelate, it is also called a sequestering agent. The commercial name of the product is Dissolvine Z.

Chelates

The word “chela” means claw in Greek. Chelates have the ability to seize metal ions and control them, making it difficult for a different substance to liberate them. EDTA and compounds derived from EDTA are chelates. For example, the calcium disodium salt of EDTA is applied to deactivate undesirable heavy metal ions that catalyze (promote) the degradation of vegetable oils and fats. By preventing this degradation, which makes food and beverages rancid, food quality is preserved and shelf life is increased. The application of EDTA in boilers, heat exchangers, and other water circulation systems present in power, brewing, sugar, and dairy industries is a further example. The compound forms stable, water‐soluble metal complexes with all potentially harmful metal ions, dissolving existing metal complexes and preventing new ones to form.

The other side of the coin is that sequestering agents can also be applied to deliberately administer a metal. For example, a Nouryon iron chelate has been approved by the World Health Organization and the Food and Agricultural Organization to be applied as an iron supplement in food. The iron chelate is soluble in water.

The Chemistry of the EDTA‐Na4 Synthesis

The tetra sodium salt of EDTA is the intermediate for the manufacture of EDTA.

The compound is made by the alkaline cyanomethylation of ethylene diamine (EDA) by means of sodium cyanide and formaldehyde:

This is an overall equation. The alkaline cyanomethylation comprises in fact a series of consecutive reactions.

The principal by‐product is NH3, ammonia, which is continuously boiled off during the reaction. The reaction is carried out batchwise. The reaction is exothermic. The reaction conditions are 100–105 °C and the pressure is atmospheric. The pH of the reaction is higher than 12, some free caustic soda is added to the reactor. The reaction rate is high, the reaction is brought to completion in seconds. The reaction does not need a catalyst. An excess of NaCN causes the formation of sodium formate. An excess of formaldehyde causes the formation of oligomeric compounds. With respect to EDA, the yield is 95–100%. For selectivity reasons, it is not possible to carry out the reaction continuously.

The removal of ammonia is key as ammonia reacts with sodium cyanide, formaldehyde, and water to the trisodium salt of nitrilo tri‐acetic acid:

NTA‐Na3:

The impurity NTA‐Na3 and other impurities (like glycolic acid salt) are not detrimental to most applications of chelating agents.

The Industrial Reaction to Produce EDTA‐Na4

See Figure 1. First, the reactor will be described. Its total volume is approximately 25 m3. The reactants are mixed by means of a proprietary stirrer. Heat is transferred indirectly to the reactor contents by means of a coil in the lower part of the reactor. The coil is heated by means of steam. The reaction is an exothermic one; however, extra heat is needed for the evaporation of water and ammonia. There are baffles in the lower part of the reactor, their height equals the height of the coil. Formaldehyde is dosed by means of a sparger around the agitator. Formaldehyde is the most critical component. An aqueous solution of sodium cyanide and EDA are dosed by means of dip‐pipes. Gaseous ammonia and water are removed overhead and are condensed in a series of two surface condensers. In the first condenser, water is condensed mainly whereas NH3‐25 is obtained in the second condenser. The saturated vapor pressure of NH3‐25 is 1 bara at 25 °C.

Figure 1 EDTA‐Na4 reactor.

Second, the manufacturing procedure will be described. A certain amount of EDA is added to the reactor. Small amounts of water and caustic soda (NaOH) are also added to adjust the alkalinity. Next, the stirrer is activated and the reactor contents are heated to 100 °C. The dosing of the aqueous solutions of sodium cyanide, formaldehyde, and EDA is started and the reaction proceeds. Ammonia and water are removed overhead. The batch time is 4–5 h. Each batch yields 15 t of a 45% by weight solution of the tetra sodium salt of EDTA in water and 4 t of a 25% by weight solution of ammonia in water. Next, the reactor contents are pumped to a second reactor to bring the reaction to completion under moderate boiling conditions. Bleaching the contents of the second reactor is the next step. The intermediate is termed Dissolvine E‐45. It can be sold as such, it can be spraydried, or it can be converted into the acid. The conversion into the acid will be described in the next section.

The aqueous solution of sodium cyanide is highly toxic to humans. Contact with an acid converts sodium cyanide to hydrogen cyanide which is a hazardous respiratory poison. Hydrogen cyanide dissolves in water and is transported via the bloodstream to the individual cells of the body where it blocks oxygen uptake by combining with the enzymes which control cellular oxidation. Oxygen uptake at the cellular level is blocked as long as the cyanide is present. Normal cellular oxygen uptake can resume if death of the cells has not already occurred. The cyanides are particularly hazardous because of their low threshold toxicity level coupled with the fact that they are odorless. Several operators are trained to be able to give an injection with an antidote if need be.

The Conversion into EDTA

See Figure 2. EDTA‐H4 (the acid) is made by means of reaction crystallization, liquid/solid‐separation on a belt filter, and drying in a thin‐film dryer, a Solidaire. A Solidaire is a horizontal cylinder equipped with a stirrer rotating at high speed.

The reaction crystallization occurs continuously in a cascade of two well‐mixed reactors. The process occurs at atmospheric pressure and approximately 80 °C. The reaction occurs between the 45% by weight solution of the tetra sodium salt of EDTA and an aqueous 30% by weight solution of hydrochloric acid. The pH in the first reactor is 2.3 whereas the pH in the second reactor is 1.45. At a pH of 2.3, relatively large crystals are formed. The reaction is brought to completion at a pH of 1.45. Reacting at a pH of 1.45 would lead to a good yield rightaway; however, the filter cake would be relatively wet. Accomplishing the bulk of the crystallization at a pH of 2.3 and finishing the reaction crystallization at a pH of 1.45 results in a filter cake having a relatively low moisture content. That means that the drying effort is relatively modest. Liquid/solid‐separation is carried out on an Outotec Larox RT belt filter. See Figure 3. The stages on the belt filter are mother liquid removal, washing, and steaming. The latter step lowers the moisture content of the cake, probably through a viscosity decrease. 18% water by weight is a typical cake moisture content.

Next, hot air (155 °C) and product travel concurrently through a dryer that is depicted in Figure 4. The air cools down to 70 °C and thereby accomplishes convective drying. At the same time, a jacket achieves contact drying. The jacket temperature is 160–170 °C (condensing steam). The Solidaire dryer has been selected because the product tends to form incrustations during the drying process. The vigorously rotating agitator prevents this from happening. Solidaire is a Bépex (Hosokawa) trade name.

Figure 2 EDTA‐H4 reactors.

Figure 3 Belt filter. Source: Courtesy of Outotec Oyj, Espoo, Finland.

Figure 4 Thin‐film dryer. Source: Courtesy of Bepex International LCC, Minneapolis, U.S.A.

The Chemical Plant

The Prologue started with a description of the manufacture of EDTA‐Na4. The chemistry, mixing, heat transfer, and stripping appeared to be important. Next, the manufacture of EDTA was treated. Mixing occurs at the reaction crystallization. The acidification is followed by liquid/solid separation, leaching (washing), and drying.

2. Chemical Reactors and Unit Operations

A distinction is made between chemical reactors and unit operations. Unit operations are steps common to most industrial processes such as heat transfer, distillation, fluid flow, filtration, crushing and grinding, and crystallization.

In response to the rapid rise of commercial manufacturing of chemicals used in industry, Lewis Mills Norton founded a course of study in chemical engineering in the chemistry department of MIT in 1888 [1]. The Report to the President of MIT at the time stated: “The chemical engineer is a mechanical engineer who has given special attention to the problems of chemical manufacture.” This is a prophetic statement of chemical engineering’s duality between the “plumbers” and the “chefs”. In 1888, the course of instruction focused on descriptive industrial chemistry with an extended study of mechanical engineering. The educational method used at the time was the case method. One wonders, however, how the study of the manufacture of soda ash would help to, for example, separate gasoline and fuel oil from crude oil.

Arthur D. Little stated in 1915 in a Visiting Committee Report to the President of MIT that the core of the chemical engineering education should be centered on the “unit operations.” Walker, Lewis, and McAdams wrote the textbook “Principles of Chemical Engineering” in 1923. The authors said: “We have selected for treatment basic operations common to all chemical industries, rather than details of specific processes, and so far as is now possible, the treatment is mathematically quantitative as well as qualitatively descriptive.”

The results were dramatic. All chemical engineering educators in the United States learned unit operations from this textbook, and they taught it to generations of students.

In 1945, it became clear that technological advances were made largely by scientists who had not studied engineering. The development of atomic energy, laser, and radar are examples. A fundamental approach appeared to be successful. The textbook “Transport Phenomena” was published in 1960 [2]. The authors remarked: “Herein we present the subjects of momentum transport (viscous flow), energy transport (heat conduction, convection, and radiation), and mass transport (diffusion)… Because of the current demand in engineering education to put more emphasis on understanding basic physical principles than on the blind use of empiricism, we feel there is a very definite need for a book of this kind.”

This publication and other aspects caused a dramatic change in the chemical engineering curriculum: a new standard of research based on more advanced mathematics and fundamental physics and physical chemistry. The latter approach became a great success.

References

1.

Wei, J. (1996). A century of changing paradigms in chemical engineering.

CHEMTECH

, 26 (5), 16–18.

2.

Bird, R. B., Stewart, W. E., and Lightfoot, E. N. (1960).

Transport Phenomena

. Hoboken, NJ: Wiley.

Part ITransport Phenomena

Part I Content

1 Mass Balances

2 Energy Balances

3 Viscosity

4 Laminar Flow

5 Turbulent Flow

6 Flow Meters

7 Case Studies Flow Phenomena

8 Heat Conduction

9 Convective Heat Transfer

10 Heat Transfer by Radiation

11 Case Studies Heat Transfer

12 Steady‐state Diffusion

13 Convective Mass Transfer

14 Case Studies Mass Transfer

Notation I