To describe in one sentence what a Chemical Engineer does is a sheer impossibility, as it is one of the most diverse engineering disciplines. However, the description in my Webster's at least forms a nice introduction to the traditional field of Chemical Engineering (Chem. Eng.):
The branch of engineering that deals with the manufacture of chemicals on a large scale, esp. with the design and operation of the plan and equipment involved.

To clear up one misconception: chemical engineering is not chemistry although it originated from this discipline. Also, chemical engineering has an overlap with chemistry and other disciplines such as mechanical engineering, materials science, and physics.

At the end of the nineteenth century, the industrial revolution was in full swing in Europe. Germany was a major center for the production of chemicals, such as explosives, dyes, drugs, and metals. Plants were operated by mechanical engineers and industrial chemists.

Around that time, the United States only had a very limited chemical industry, and relied mainly on the import of chemicals from Europe. But in the years leading up to World War I, the US was cut off almost completely from European imports, and this triggered the rise of the chemical industry in the US. There were only few chemists in the US, most of them working in academic laboratories. These chemists were more comfortable with test-tubes, erlenmeyers, and beakers and had no experience with large scale production processes. On the other hand, American mechanical engineers did not have the proper training in chemistry to take on a leading role in the chemical industry.

As a result, the fundamental skills for designing and operating chemical plants were first formulated at MIT around 1910, and were further developed to what would become known as chemical engineering. These early chemical engineers postulated the concept of breaking down a chemical process into physical operations that they called Unit operations, a term that is used up to this day. Typical unit operations are distillation, evaporation, filtration, heat transfer. As the chemical industry and the chemical processes themselves became more complex, a second classification for these type of operations was suggested: the Unit processes. Typical unit processes are oxidation, sulfonation, nitration, hydrogenation, chlorination, etc.

The chemical industry or Chemical Process Industries (CPI) as it is commonly called have grown to an immensely diverse field, affecting everyone's lives. Chemical engineers play a vital role in this field, serving as designers, consultants and operators of chemical plants. Chemical engineers also play major roles in research and development, and on the business side of the industries: forecasting demands, consulting on product use, and marketing. The chemical engineer is truly a polymath in the world of the engineering sciences.

The diversity of the discipline is reflected in the variety of the academic curriculum. Following are some of the courses that the prospective chemical engineer will encounter:

  • Mathematics: the swiss army knife of the chemical engineer. One cannot study Chem. Eng. without a thorough knowledge of mathematics. However, the focus is very much on applied mathematics. For instance, differential equations are essential for solving problems related to heat transfer, mass transfer. Numerical analysis is important for process design calculations. Statistical analysis is often used for design of experiments and process failure analysis.
  • Chemistry: so Chem. Eng. is not chemistry, but you must have a solid basis in many branches of chemistry: general, analytical, physical, inorganic and organic chemistry. My inorganic chemistry text book was one-thousand pages with reaction mechanisms, nomenclature, and formulas; we finished it in one semester. On top of that, the curriculum requires extensive practical laboratory experience.
  • Thermodynamics: not only the thermodynamics of gases, but also that of liquids, since many chemical reactions yield liquid products and side products.
  • Separations: in this course, the student learns about multi-stage operations, such as distillation, extraction, evaporation. These processes play an essential role in the CPI.
  • Heat Transfer: An essential course for the design of chemical process equipment: reactors, heat exchangers, and condensers. All forms of heat transfer (convection, conduction, radiation) are studied.
  • Mass Transfer: this course is another fundamental course, because it plays an important role in chemical reactions, and the way the reactions are executed (e.g. diffusion processes).
  • Fluid Mechanics: flow through pipes, orifices, etc. The CPI deals mainly with fluids (whether that being gases or liquids). Fluid mechanics is a method to describe and quantify the flow of liquids.
  • Reactor Design: say, we have a reaction of a -> b. Or a - > d + u1 + u2 +..., where d is a desired product, and u is an undesired sideproduct. What is the ideal size for a chemical reactor for a certain flow rate, how much heat do we need to add or remove to gain the best yield, conversion, and a minimal amount of side products? A batch reactor or continuous? What happens to a steady state when the temperature, pH, or concentration is changed?
  • Process Design: this course focuses on the design of entire chemical plants, or process lines. All the required equipment is evaluated based on performance and costs. For instance, a reaction could be done at low temperature and low conversion, or at high temperature and high conversion. The former would be cheaper, but requires additional costs for separation of reactants and products. Thus, the overall costs of the latter may be cheaper.
  • Process Control: this course deals with maintaining process parameters, such as temperature, pressure, pH, concentration etc. Typically, these are feedback processes: we measure a temperature (an output signal), and based on this, we add or remove heat to the reactor (an input). Small deviations from the setpoint can have disastrous effects, such as an explosion of the reactor.
  • Many other courses: there is simply not enough space to list all these courses in detail, but a few I have been exposed to include: Technical drawing, biotechnology, plastics, environmental engineering, computer programming, economics, mechanical engineering laboratory...

A typical chemical engineering job would be to take a discovery from a chemical laboratory, and turn it into a commercial scale process. Chemists work on small scales using test tubes, small batch reactors, and erlenmeyers. The chemical engineer works with very large, expensive equipment: their reactors can hold 1000 to 10000 gallons or more. Translating a small scale process to these huge proportions is not a trivial task. And the associated costs are tremendous: the capital investment for one single process sometimes exceeds $100 million.

But chemical engineering has expanded to many non-traditional fields. For instance, the Chem. Eng. department of my school does research on aerosol droplet formation, catalysis and surface science, imaging bacteria and biopolymers using atomic force microscopy, nanostructured materials, and fuel cells. Chemical engineers will continue to expand into fields that traditionally belong to other engineering disciplines, as well as new disciplines. But technology keeps getting more and more complex, and many of today's challenges can only be solved by interdisciplinary teams of scientists and engineers. With their diverse skill sets, chemical engineers will maintain their leading role in the development of advanced technology.

Chemical Engineer's salaries are among the highest of all engineering disciplines (but I'm deep in the red figures). Because of the wide diversity of the field, there has been an increasing demand for Chemical Engineers, although the market has also known its ups and downs.


Sources:

William L. Luyben and Leonard A. Wenzel, Chemical Process Analysis - Mass and Energy Balances, Prentice-Hall, 1988.
George T. Austin, Shreve's Chemical Process Industries, McGraw- Hill, 1984


The professional society for chemical engineers in the US is called American Institute of Chemical Engineers (AIChE). Their webpage is at:
http://www.aiche.org

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