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- ~ MAGINE A WORLD where penicillin and other antibiotics are rarer and more expensive than the finest diamonds. Imagine countries gripped by famine as dwin- dling supplies of natural guano and saltpeter cause fertilizers to become increasingly scarce. Imagine hospitals and clinics where kidney dialysis is as risky and as uncertain over the long term as today's artificial heart program. Imagine serving on a police force or in the infantry without a lightweight bulletproof vest. Imagine your closet with no wash-and-dry, wrinkle-free synthetic garments, or your home without durable, easy-cleaning, mothproof syn- thetic rugs. Imagine cities choked with smog and soot from millions of residential coal fur- naces and millions of automobiles without emis- sion controls. Imagine an "information society" trying to function on vacuum tubes and ferrite core storage for data processing. Imagine paying $25 or more for a gallon of gasoline, if you can even buy it. This world, in which few of us would want to live, is what a world without chemical engineering would be like. Chemical engineers have made so many im- portant contributions to society that it is hard FROA'T{~{AIN C}~'/~L ~1~-~'.''Wi~ to visualize modern life without the large-vol- ume production of antibiotics, fertilizers and agricultural chemicals, special polymers for biomedical devices, high-strength polymer com- posites, and synthetic fibers and fabrics. How would our industries function without environ- mental control technologies; without processes to make semiconductors, magnetic disks and tapes, and optical information storage devices; without modern petroleum processing? All these technologies require the ability to produce spe- cially designed chemicals and the materials based on them economically and with a min- imal adverse impact on the environment. De- veloping this ability and implementing it on a practical scale is what chemical engineering is all about. The products that depend on chemical engi- neering emerge from a diverse array of indus- tries that play a key role in our economy (Table 2.11. These industries produce most of the materials from which consumer products are made, as well as the basic commodities on which our way of life is built. In 1986, they shipped products valued at nearly $585 billion. They had a payroll of 3.3 million employees, or TABLE 2.1 The Chemical Processing Industries in the United Statesa Number of Value ofValue Added by Employees ShipmentsManufacture Industryb(thousands) ($ millions)($ millions) Food and beverages378 73,63324,370 Textiles99 7,6492,897 Paper322 51,14519,871 Chemicals1,023 197,93295,258 Petroleum169 129,36517,112 Rubber and plastics340 31,07815,390 Stone, clay, and glass354 34,37217,449 Nonferrous metals49 21,920524 Other nondurables577 37,59424,291 TOTAL Chemical processing industries' share of total manufacturing a Data for employment and value of shipments are for 1986. Data for value added by manufacture are for 1985. SOURCE: Data Resources, Inc. b The definition of the chemical processing industries (CPI) used in this table is the one used by Data Resources and Chemical Engineering in compiling their statistics on these industries. For several of the industries listed, only a part is considered to be in the CPI and data are presented for this part only. A list of the Standard Industrial Classification codes used to define the CPI for this table is given in Appendix C. 3,321 584,689 217,161 17.5% 25.7% 21.7%

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WHAT IS CHEMICAL ENGINEERING? 17.5 percent of all U.S. manufacturing employ- ees. They generated over $217 billion in value added in 1985, or 21.7 percent of all U.S. manufacturing value added. The chemicals por- tion of the CPI is one of the most successful U.S. industries in world competition, producing an export surplus of $7.8 billion in 1986, in contrast to the overall U.S. trade deficit of $152 billion. But chemical engineering is more than a group of basic industries or a pile of economic statis- tics. As an intellectual discipline, it is deeply involved in both basic and applied research. Chemical engineers bring a unique set of tools and methods to the study and solution of some of society's most pressing problems. TRADITIONAL PARADIGMS OF CHEMICAL ENGINEERING Every scientific discipline has its character- istic set of problems and systematic methods for obtaining their solution that is, its para- digm. Chemical engineering is no exception. Since its birth in the last century, its fundamental intellectual model has undergone a series of dramatic changes. When the Massachusetts Institute of Tech- nology (MIT) started a chemical engineering program in 1888 as an option in its chemistry department, the curriculum largely described industrial operations and was organized by spe- cific products. The lack of a paradigm soon became apparent. A better intellectual founda- tion was required because knowledge from one chemical industry was often different in detail from knowledge from other industries, just as the chemistry of sulfuric acid is very different from that of lubricating oil. Unit Operations The first paradigm for the discipline was based on the unifying concept of "unit operations" proposed by Arthur D. Little in 1915. It evolved in response to the need for economic large-scale manufacture of commodity products. The con- cept of unit operations held that any chemical manufacturing process could be resolved into a coordinated series of operations such as pul 1i verizing, drying, roasting, crystallizing, filter- ing, evaporating, distilling, electrolyzing, and so on. Thus, for example, the academic study of the specific aspects of turpentine manufacture could be replaced by the generic study of distillation, a process common to many other industries. A quantitative form of the unit op- erations concept emerged around 1920, just in time for the nation's first gasoline crisis. The rapidly growing number of automobiles was severely straining the production capacity for naturally occurring gasoline. The ability of chemical engineers to quantitatively character- ize unit operations such as distillation allowed for the rational design of the first modern oil refineries. The first boom of employment of chemical engineers in the oil industry was on. During this period of intensive development of unit operations, other classical tools of chem- ical engineering analysis were introduced or were extensively developed. These included studies of the material and energy balance of processes and fundamental thermodynamic studies of multicomponent systems. Chemical engineers played a key role in helping the United States and its allies win World War II. They developed routes to syn- thetic rubber to replace the sources of natural rubber that were lost to the Japanese early in the war. They provided the uranium-235 needed to build the atomic bomb, scaling up the man- ufacturing process in one step from the labo- ratory to the largest industrial plant that had ever been built. And they were instrumental in perfecting the manufacture of penicillin, which saved the lives of potentially hundreds of thou- sands of wounded soldiers. An in-depth look at this latter contribution shows the sophistication that chemical engineering had achieved by the 1940s.' Penicillin was discovered before the war, but could only be prepared in highly dilute, impure, and unstable solutions. Up to 1943, when chem- ical engineers first became involved with the project, industrial manufacturers used a batch purification process that destroyed or inacti- vated about two-thirds of the penicillin pro- duced. Within 7 months of their involvement, chemical engineers at an oil company (Shell Development Company) had applied their

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q ~ knowledge of generic engineering principles to build a fully integrated pilot plant that processed 200 gallons of fermentation broth per day and achieved nearly 85 percent recovery of penicil- lin. When this process was installed by four penicillin producers, production soared from a rate in 1943 capable of sustaining the treatment of 4,100 patients per month to a rate in the second half of 1944 equivalent to treatments for nearly 250,000 patients per month. A second challenge in getting penicillin to the front was its instability in solution. A stable form was needed for storage and shipment to hospitals and clinics. Freeze drying- in which the penicillin solution was frozen to ice and then subjected to a vacuum to remove the ice as water vapor seemed to be the best solution, but it had never been implemented on a pro- duction scale before. A crash project by chem- ical engineers at MIT during 1942-1943 estab- lished enough understanding of the underlying phenomena to allow workable production plants to be built. The Engineering Science Movement The high noon of American dominance in chemical manufacturing after World War II saw the gradual exhaustion of research problems in conventional unit operations. This led to the rise of a second paradigm for chemical engi- neering, pioneered by the engineering science movement. Dissatisfied with empirical descrip- tions of process equipment performance, chem- ical engineers began to reexamine unit opera- tions from a more fundamental point of view. The phenomena that take place in unit opera- tions were resolved into sets of molecular events. Quantitative mechanistic models for these events were developed and used to analyze existing equipment, as well as to design new process equipment. Mathematical models of processes and reactors were developed and applied to capital-intensive U.S. industries such as com- modity petrochemicals. THE CONTEMPORARY TRAINING OF CHEMICAL ENGINEERS Parallel to the growth of the engineering science movement was the evolution of the core >~ ~ ~ tY A' 'rS I`/\ ~ Delphi i CAL ~1\'6 [~RA;161JO chemical engineering curriculum in its present form. Perhaps more than any other develop- ment, the core curriculum is responsible for the confidence with which chemical engineers in- tegrate knowledge from many disciplines in the solution of complex problems. The core curriculum provides a background in some of the basic sciences, including math- ematics, physics, and chemistry. This back- ground is needed to undertake a rigorous study of the topics central to chemical engineering, including: ~ multicomponent thermodynamics and ki- netics, transport phenomena, unit operations, . . . reaction englneerlng, process design and control, and plant design and systems engineering. This training has enabled chemical engineers to become leading contributors to a number of interdisciplinary areas, including catalysis, col- loid science and technology, combustion, elec- trochemical engineering, and polymer science and technology. A NEW PARADIGM FOR CHEMICAL ENGINEERING Over the next few years, a confluence of intellectual advances, technological challenges, and economic driving forces will shape a new model of what chemical engineering is and what chemical engineers do (Table 2.21. A major force behind this evolution will be the explosion of new products and materials that will enter the market during the next two decades. Whether from the biotechnology in- dustry, the electronics industry, or the high- performance materials industry, these products will be critically dependent on structure and design at the molecular level for their usefulness. They will require manufacturing processes that can precisely control their chemical composition and structure. These demands will create new opportunities for chemical engineers, both in product design and in process innovation. A second force that will contribute to a new chemical engineering paradigm is the increased

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WHAT IS CHEMICAL E~-~NEERt\G? TABLE 2.2 Enduring and Emerging Characteristics of Chemical Engineering Enduring Characteristics ~3 Emerging Characteristics Serves industries whose products are quickly superseded in the marketplace by improved ones Serves industries that compete on the basis of quality and product performance Serves industries whose products remain unchanged on the market for long periods Serves industries that compete mainly on the basis of price and availability Expertise in the manufacture of homogeneous materials from small molecules Expertise in the manufacture of commodity materials Expertise in process design Expertise in designing large-volume processes Expertise in designing continuous processes Expertise in designing industrial plants dedicated to a single product or process Practitioners use simple models and approximations to solve problems Practitioners have access to only a few simple analytical instruments Practitioners build their careers around a single product line or process Expertise in the manufacture of composite and structured materials from large molecules Expertise in the manufacture of high-performance and specialty materials Expertise in designing products with special performance characteristics Expertise in designing small-scale processes Expertise in designing batch processes Expertise in designing flexible manufacturing plants Practitioners use more complete models. better approximations, and large computers to solve problems rigorously Practitioners have access to many sophisticated analytical instruments Practitioners have multiple career changes Academic research is mostly performed by single principalAcademic research is also performed by multidisciplinary investigators within chemical engineering departmentsgroups of principal investigators, sometimes in centers or other organizational environments Research and education focus on the mesoscale (equipment level) Research and education also include the microscale (molecular level) and macroscale (systems level) competition for worldwide markets. Product quality and performance are becoming more important to global competition than ever be- fore. If the United States is to remain compet- itive in world chemical markets, it must find new ways to lower costs and improve product quality and consistency. Similarly, a strong domestic energy-producing industry is needed to preclude foreign domination of this vital sector of the economy. The key to meeting these challenges is innovation in process design, control, and manufacturing operations. It is particularly important that the United States maintain a vigorous presence in commodity chemical markets. Commodities are at the base of industries that employ millions of Americans, provide basic necessities for our society, and generate valuable export earnings. Thriving commodity businesses are also vital to specialty chemical businesses. The technical expertise and financial resources that commodities pro- vide is crucial to the long-term research and development efforts that specialties require. The third force shaping the future of chemical engineering is society's increasing awareness of health risks and environmental impacts from the manufacture, transportation, use, and ulti- mate disposal of chemicals. This will be an important source of new challenges to chemical engineers. Modern society will not tolerate a continuing occurrence of such incidents as the release of methyl isocyanate at Bhopal (in 1985) and the contamination of the Rhine (in 1986~. It is up to the chemical engineering profession to act as the cradle-to-grave guardian for chem- icals, ensuring their safe and environmentally sound use. The fourth and most important force in the development of tomorrow's chemical engineer- ing is the intellectual curiosity of chemical engineers themselves. As they extend the limits of past concepts and ideas, chemical engineering researchers are creating new knowledge and tools that will profoundly influence the training and practice of the next generation of chemical engineers.

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When a discipline adopts a new paradigm, exciting things happen, and the current era is probably one of the most challenging and po- tentially rewarding times to be entering chemical engineering. How can the unfolding pattern of change in the discipline be described? The focus of chemical engineering has always been industrial processes that change the phys- ical state or chemical composition of materials. Chemical engineers engage in the synthesis, design, testing, scale-up, operation, control, and optimization of these processes. The traditional level of size and complexity at which they have worked on these problems might be termed the mesoscale. Examples of this scale include re- actors and equipment for single processes (unit operations) and combinations of unit operations in manufacturing plants. Future research at the mesoscale will be increasingly supplemented by studies of phenomena taking place at molecular dimensions the microscale and the dimen- sions of extremely complex systems the ma- croscale (see Table 2.31. Chemical engineers of the future will be integrating a wider range of scales than any other branch of engineering. For example, some may work to relate the macroscale of the en- vironment to the mesoscale of combustion sys- tems and the microscale of molecular reactions and transport (see Chapter 7~. Others may work to relate the macroscale performance of a com- posite aircraft to the mesoscale chemical reactor in which the wing was formed, the design of the reactor perhaps having been influenced by TABLE 2.3 Microscale-Mesoscale-Macroscale: Illustrations FROAYTIERS IN CHEMICAL .~INEERING studies of the microscale dynamics of complex liquids (see Chapter 54. Thus, future chemical engineers will conceive and rigorously solve problems on a continuum of scales ranging from microscale to macroscale. They will bring new tools and insights to re- search and practice from other disciplines: mo- lecular biology, chemistry, solid-state physics, materials science, and electrical engineering. And they will make increasing use of computers, artificial intelligence, and expert systems in problem solving, in product and process design, and in manufacturing. Two important developments will be part of this unfolding picture of the discipline: ~ Chemical engineers will become more heavily involved in product design as a com- plement to process design. As the properties of a product in performance become increasingly linked to the way in which it is processed, the traditional distinction between product and process design will become blurred. There will be a special design challenge in established and emerging industries that produce proprietary, differentiated products tailored to exacting per- formance specifications. These products are characterized by the need for rapid innovation, as they are quickly superseded in the market- place by newer products. ~ Chemical engineers will be frequent partic- ipants in multidisciplinary research efforts. Chemical engineering has a long history of fruitful interdisciplinary research with the chem Microscale (~10-3 m) Atomic and molecular studies of catalysts Chemical processing in the manufacture of integrated circuits Studies of the dynamics of suspensions and microstructured fluids Mesoscale (10-3-102 m) Improving the rate and capacity of separations equipment Design of injection molding equipment to produce car bumpers made from polymers Designing feedback control systems for bioreactors Macroscale (>10 m) Operability analysis and control system, synthesis for an entire chemical plant Mathematical modeling of transport and chemical reactions of combustion-generated air pollutants Manipulating a petroleum reservoir during enhanced oil recovery through remote sensing of process data, development and use of dynamic models of underground interactions, and selective injection of chemicals to improve efficiency of recovery

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~T IS CHEMICAL E~.VEERiA-~? ical sciences, particularly in industry. The po- sition of chemical engineering as the engineering discipline with the strongest tie to the molecular sciences is an asset, since such sciences as chemistry, molecular biology, biomedicine, and solid-state physics are providing the seeds for tomorrow's technologies. Chemical engineering has a bright future as the "interracial discipline" that will bridge science and engineering in the multidisciplinary environments where these new technologies will be brought into being. Some things, though, will not change. The underlying philosophy of how to train chemical engineers emphasizing basic principles that are relatively immune to changes in field of application must remain constant if chemical engineers of the future are to master the broad spectrum of problems that they will encounter. At the same time, the way in which this philos- ophy finds concrete expression in course offer- ings and requirements must be responsive to changing needs and situations. NOTE 1. Additional background and references on chemical engineers and the effort to win World War II may be found in Separation and Purification: Critical Needs and Opportunities (Washington, D.C.: Na- tional Academy Press, 1987), pp. 92-100.

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