As with engineering, a clear and concise definition that captures the essence of chemical engineering is not readily available. The American Institute of Chemical Engineers (AIChE), the professional society of chemical engineers in the United States, defines chemical engineers as follows:
Individuals who use science and mathematics, especially chemistry, biochemistry, applied mathematics, and engineering principles, to take laboratory or conceptual ideas and turn them into value added products in a cost effective, safe (including environmental) and cutting-edge processes.
This definition is clearly broad enough to cover all the activities that a chemical engineer engages in and yet not specific enough to distinguish it from other engineering disciplines. By specifically mentioning biochemistry, the definition also tends to show a bias toward biological or life sciences, which is not reflective of the occupation of a vast majority of chemical engineers.
An alternative, more concise definition of chemical engineering is presented by Morton M. Denn [12]:
Chemical engineering is the field of applied science that employs chemical, physical and biochemical rate processes for the betterment of humanity.
The term applied science carries the meaning of taking laboratory or conceptual ideas to a larger scale. Chemical engineering differs from other engineering in having the scientific basis in chemistry in addition to physics and mathematical sciences. The concept of rate processes is at the heart of the previous definition. Chemical engineering, according to this definition, is the field dealing with the rates of physicochemical processes involving transformations of molecular species. The definition places emphasis on processes and the rates thereof. Although the process or the rate of transformation is of critical importance, affecting the economics of the engineering endeavor, it is ultimately the result of the transformation that is usually the desired outcome. In other words, the consumer or the society is interested in the product that can provide a needed service and not in the specifics of how that product is obtained.
The benefit or betterment of humanity is a common theme in most of the definitions of engineering. As previously mentioned, the term is too general, and engineering is not the only occupation working for the betterment of humanity. Despite the shortcomings, a combination of both definitions does convey the essence of chemical engineering as a profession. An individual can be identified as a chemical engineer, if the following descriptors can adequately describe his/her activities:
• The individual is engaged in an engineering enterprise; that is, he/she is working to apply scientific knowledge to make products, both tangible and intangible, commercially available to the general society.
• The engineering enterprise is based on the transformation of species, involving restructuring of bonds (forces) between them. This restructuring is typically at the atomic level, that is, involving chemical reactions yielding products that are distinct from initial species. However, the transformation may simply involve separations, or restructuring of physical bonds between different species. No new molecular species are generated in such transformations. In other words, the transformations involve altering the affinities between elemental and/or molecular species.
Chemical engineering thus deals generally with systems where chemical reactions take place. These chemical reactions are invariably accompanied by physical separations. These physical separations, as explained in subsequent chapters, often play the dominant role in determining the economics of the process. Chemical engineers use their knowledge of science and mathematics to ensure that laboratory reactions and separations are scaled up to the industrial level.
Historically, one can argue that individuals who fermented various brews were the earliest chemical engineers, predating even civil engineers. However, chemical engineering came into being as a distinct profession toward the end of the 19th century and beginning of the 20th century [12]. The development of the discipline resulted from increased demand for chemicals and fuels for both peacetime (fertilizers, consumer goods) and wartime (explosives) activities. Many of the technologies and products developed during the world wars led to additional industrial chemicals. Subsequent developments and societal needs have seen chemical engineering encompass myriad industries ranging from semiconductor, textile, pharmaceutical, agriculture, and food to energy, biotechnology, and medicine [13]. Chemical engineering is a highly versatile field full of challenges and opportunities in practically all facets of human activity.
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