Ind. Eng. Chem. Res. 2002, 41, 1917-1919
1917
COMMENTARIES Molecular Structure and Property: Product Engineering Engineers make useful things for people, and chemical engineers do it with chemistry. The two main tasks of chemical engineers are as follows: what should we make, or product engineering, and how should we make it, or process engineering. Both tasks are critically important if we are to make what people want. From the introduction of Unit Operations in 1923, the chemical engineering curriculum has concentrated on process engineering, which prepares the graduates for efficient plant design and production and for reducing cost and improving safety. However, our prosperity must not depend exclusively on the process side, and we have to keep an eye on the product side to ensure that we always have something worth making. The modern chemical industry was created in 1856 by William Perkin when he introduced synthetic dyes, which brightened a drab world with brilliant and affordable colors. Another burst of creativity revitalized the chemical industry in the 1920s when Thomas Midgley, Jr., introduced tetraethyllead, which led to powerful and efficient automobile and airplane engines without knocking, and chlorofluoro carbons, which led to safe home refrigerators and air conditioning. All of these miraculous new products, as well as dichlorodiphenyltrichloroethane and cellophane, have now been replaced with better substitute products that are more effective to the customers or less threatening to the environment. Remember the golden age of applied chemistry when consumers waited eagerly for the introduction of miraculous new chemical products that transformed their lives, such as celluloid, nylon, penicillin, synthetic rubber, Teflon, and Kevlar. However, for the past decade, the parade of new chemical products seemed to have halted. Instead, information technology has held center stage and captured the attention of the public with new products such as the personal computer, cellular telephone, word processors, spreadsheets, and the Internet. We need new and improved chemical products to rejuvenate the industry and to help customers to lead better lives. The business landscape is littered with the wreckage of once-successful companies that neglected to develop new products. We are also in danger of losing the competition for the most capable and ambitious engineering students, who seek challenges and opportunities to work for an industry with high growth and profit and are not attracted to stagnant commodities such as sulfuric acid and common salt. In February 2002, DuPont announced selling the fabled nylon and fibers business build by Carothers. CEO Charles Holliday said DuPont aims to generate enough new products so that one-third of profits will come from products that are less than five years old. Business analysts commented DuPont had squandered its R&D capabilities: instead of inventing blockbusters, they got bogged down in making fibers a penny cheaper. It is sometimes said that chemical engineers wait for
the chemists to invent new products and then are summoned to manufacture them in large quantity with economy and safety. Indeed the most ambitious among the newly recruited chemical engineers often gravitate toward the process departments because what they have learned in their curriculum seems more relevant to solving process problems. There is no emphasis in the chemical engineering curriculum to teach them how to design a more environmentally benign refrigerant or gasoline, a longer life battery suitable for laptop computers and cellular phones, or a missile fuel for increased range. Actually, both the chemistry and the chemical engineering departments do not teach product design, but all of the other engineering departments have capstone product design courses. Thomas Midgley, Jr., invented both tetraethyllead and Freon, two of the most celebrated products in the 20th century, but he only had a bachelor’s degree in mechanical engineering. He had exposure to product design but had to learn about product chemistry on his own and made major contributions to the methods of product engineering that we use today. At the same time, there are many chemical engineers who do creative research in product engineering, and the people in the polymer and biotechnology fields are used to the study of structure-property relations. We should teach the art and science of product engineering to all chemical engineering students and to chemical engineers currently working in industry on product assignments. Their work would be much more innovative and productive if they had been given appropriate toolboxes of theories and methods that are generally applicable as well as triumphant cases of historical developments as guides to future successes. Past successes in the introduction of new products and improvement of existing products can be divided into accidental discoveries and planned innovations. An example of accidental discovery is the synthesis and discovery of the properties of the dye mauve by Perkin, and an example of planned innovation is the invention of tetraethyllead and chlorofluoro carbons by Midgley. The art of being opportunistic in accidents is important for a lucky few, but the science of planned innovations is more systematic and dependable. Midgley has shown that the central science of product engineering is an understanding of molecular structure-property relations. The starting point is specification of the target properties essential to the performance of the product and how these properties are affected by manipulations, such as addition or substitution of groups, isomerization and skeletal rearrangements, additives, and blending. Many research and development groups in academia and industry are working on ways to come up with new products, with improvement of existing products, and with repositioning of existing products into new markets. The oil companies need to re-engineer gasoline to
10.1021/ie0200398 CCC: $22.00 © 2002 American Chemical Society Published on Web 03/13/2002
1918
Ind. Eng. Chem. Res., Vol. 41, No. 8, 2002
meet new federal clean air regulations and to anticipate greenhouse gas restrictions, and the polymer companies are developing packaging for ever-changing electronic devices and for biodegradable bags. The most scientifically based and successful recent progress is computeraided drug design, which has used very sophisticated computer tools to model and design drug molecules that would interact and dock with target proteins. Many industrial and academic leaders have spoken out on the need for better product design. In 2001, Cussler and Moggridge produced the first textbook on Chemical Product Design, which represents the start of a new movement. Product engineers should be knowledgeable about the five basic phases in the development of a new product: exploration and definition of a product, specification of product properties and price target, search for appropriate components, design and testing of products, and manufacturing and marketing. Engineers are found in all five phases, but an engineering education is most valued in research and development and in manufacturing. An effective engineer should have an appreciation of how his or her work fits in the context of the overall effort, what the various tasks of the team are, and how to prepare for leadership in the entire enterprise. A very beneficial part of the education of a product engineer is an introduction to marketing, which studies the characteristics and the needs of the customers, the current products available that fulfill some of the needs, the levels and trends of the prices and the volumes of production, and the current producers and their strengths. You have to know who you have to beat and what the rewards are if you do. The intellectual core of product engineering is the science of molecular structure-property relations. A product needs to have certain properties, which are required for it to function with satisfaction. The success of each product, such as a refrigerant, depends on an appropriate boiling point, adequate heat of vaporization, inert chemical reactivity so that it is nontoxic and nonflammable, and affordable pricing. The principal intellectual challenge is, how does an innovative product engineer find or design a molecular structure or compound a mixture with the required properties? The research and development division is concerned with ways to improve the properties of existing products, to find other materials that are not currently used for this market, or less frequently to synthesize of a brand new material. The toolbox of molecular structure-property relations is based on the maturity of current scientific understanding. The first stage of knowledge is the collection of experimental results as a memory bank, such as a handbook or database. The second stage is the coalescence of many memories to obtain qualitative rules of practice, such as the trend of paraffins to have boiling points generally increasing with molecular weights. The third stage is the development of quantitative rules resting on theoretical principles, such as the formula relating the boiling points of paraffins with the cohesive energy. The last stage is the theoretical knowledge of cause and effects, leading to the exact computation of molecular orbitals from quantum mechanics. The product engineers need the ability to predict the effects of a proposed change in molecular structures on the molecular properties, so that they would be able to manipulate the material to converge the desired proper-
ties to the target values and to know where to look for new material with desired properties. Design involves making choices among possible components and arriving at a product with a slate of properties that is optimal, which is mainly dominated by profit maximization. The methods available include using additives and blending, adding and substituting functional groups, isomerizing and rearranging the skeleton of the molecules, and cross-linking molecular chains. The proposed product has to be tested for its laboratory properties and field tested to ensure customer satisfaction, often under the watchful eye of a federal government agency. A successful product development requires constant cooperation and frequent consultation in an interdisciplinary team. The most promising techniques are built around the recent advances of the information revolution and of computational chemistry. The current information revolution has provided many powerful new tools that have revolutionized our ability to access information, to analyze information, to do creative work, and to store and disseminate information. This speeds up the scientific method enormously, from observations to hypothesis, predictions, tests against all known data, revision of the hypothesis, further predictions, and tests against data. It is quite easy now to access databases of experimental observations compiled in CD-ROM and on the Internet, including the encyclopedic Beilstein and Gmelin and the National Institute of Science and Technology website. There are many fast computer software programs that help us to visualize the threedimensional structure of a molecule, to calculate the structural parameters of a molecule, to visualize the molecular collisions and condensations that take place in an ensemble of molecules, and to calculate the predicted properties from the hypothesis and derived equations. At the present time, the successes of computational chemistry in predicting useful molecular properties from molecular structure are modest and are limited to a few fundamental properties of small molecules. From a foundation of quantum mechanics and statistical mechanics, most of the important properties of industrial chemicals are out of reach. Many quantitative methods of correlation, using structural parameters with or without theoretical justifications, must be added to the toolbox if we are to make reasonable progress. We need much more theoretical knowledge on the reasons why structure affects properties, and we need many more practical prediction methods. We are particularly in need of improvement in predictions of the properties of a mixture, starting from the properties of the individual components. Another great challenge in product engineering concerns the discovery of unusual and desired properties of many natural and synthetic products being discovered everyday. When we walk into a rainforest, how would we know that the bark of Pacific yew trees contains substances that would yield Taxol, which has a therapeutic value for cancer? What other plants may have even more potent effects or greater yields? What about the myriad substances produced by combinatorial chemistry? We do not have enough time and money to make laboratory tests and field evaluations of every substance for every property. The answer may go back to the need for more theoretical understanding and predictive power
Ind. Eng. Chem. Res., Vol. 41, No. 8, 2002 1919
to develop leads, so we can concentrate on measuring a few high-potential materials and thus increase productivity. Most of my contemporary chemical engineering educators and I have spent our lives teaching students how to solve problems in process engineering. The skills of process engineering alone are insufficient to ensure the prosperity of chemical engineers, and careers in processing engineering alone are not enough to compete for the best engineering students today. There is now a
market push for innovations in new product development and a technical pull from the revolution in information technology and computation chemistry. They need to be synthesized into the subject of product engineering and molecular structure-property relations, and we need a burst of new creativity. In the terminology of Thomas Kuhn, the case method of historic product development and the toolbox of molecular structure-property relations can become the third paradigm of chemical engineering.
James Wei School of Engineering & Applied Science, Princeton University, Princeton, New Jersey 08544-5263 IE0200398
