I got into an interesting discussion on Twitter about the difference between engineering and science and thought about this that I wrote a few years ago….
“You know what women are like; once they hear you have a PhD in chemical engineering, they’re all over you”. So said a minor character in an episode of the classic eighties television series, Moonlighting, the show that launched the career of Bruce Willis. Obviously the scriptwriters were being ironic and having a little chuckle at a profession that they saw as being the epitome of ‘nerdiness’.
Throughout my life, when I have had to tell people that I am a chemical engineer, I have been met with either a blank stare or some comment or other about that person not liking chemistry, or being useless at maths. Very occasionally, people have seemed rather impressed, believing for some unknown reason that all chemical engineers are geniuses, a very satisfying response indeed. The dread is always that they ask the follow-up question: “What’s chemical engineering?” I usually mumble something like this: “Think of the production of a new drug, an antibiotic perhaps. Scientists have discovered the drug and devised methods for making grams of it. Chemical engineers figure out how to make hundreds of kilos of it – economically.” Moving from the laboratory scale to the industrial scale – process scale-up– is, indeed, an important part of chemical engineering. Chemical engineers routinely apply the sciences of physics, chemistry and, increasingly, biology to bring processes from the laboratory scale to the industrial scale.
But chemical engineers don’t just apply science; they create it as well. Indeed, chemical engineering could be described as the most ‘scientific’ of the engineering disciplines. It is certainly the most molecular. Cornell University’s chemical engineering department even has the title of “School of Chemical and Biomolecular Engineering”.
Chemical engineers have contributed to our understanding of the thermodynamics of both gases and liquids; to our ability to calculate reaction rates of catalytic chemical reactions involving highly complex mixtures of petrochemicals; to the creation of mathematical models of metabolic pathways in bacterial cells; to our understanding of the mechanisms of solute transport through the nanofiltration membranes used in wastewater treatment processes.
Chemical engineers must create the science because there are many areas of science where scientists don’t, or won’t, go. It’s not so much that there are places where scientists fear to tread, but places where scientists have no interest in treading. Chemical engineers have to work with physical, chemical and biological systems that arise, not so much in nature, as in the man-made environment of a production process. Thus, physicists don’t take the same interest in the fluid dynamics of bubbles or drops rising in a chemical reactor as engineers do. Chemists are not so interested in the vapour-liquid equilibrium of mixtures of hundreds of hydrocarbons. Biologists are not so interested in metabolic engineering to improve the yield of a genetically engineered product.
The systems that chemical engineers study are complex and messy. They often defy a purely theoretical approach. Even the simple problem of predicting the pressure drop for flow of water in a pipe network cannot be done theoretically. Therefore, the chemical engineering approach is to combine theory and experiment. Chemical engineering science, for that is what many chemical engineers do, is ultimately driven by the need to find practical answers. The goal is to devise methods, especially mathematical methods, to analyse, design and optimise physical, chemical and biological processes. In that sense, chemical engineering is not a search for ‘truth’ but a search for a workable solution. The art of chemical engineering is in finding the optimum balance between theory and experiment to arrive at that solution.
In the early days of engineering, when the slide rule was at the cutting edge of computation, chemical engineering analysis and design was a wonderful mix of theory and art. Even simplified theoretical analyses required complicated, repetitive calculations, often involving the use of trial-and-error methods. Extraordinarily creative and beautiful – yes, beautiful – graphical techniques were developed that made it possible to do complex calculations in minutes. The famous method for the design of distillation columns, devised by McCabe and Thiele, is a wonderful example of the computational creativity of chemical engineers. It is hard to believe that McCabe and Thiele were both postgraduate students when they unveiled their famous method.
In the age of powerful computers, all scientists and engineers can push the purely theoretical approach a little bit further. But the environments encountered by chemical engineers are just too complicated and the need to combine theoretical and experimental knowledge remains. Chemical engineering is not a dying art.
As a youngster and avid viewer of Carl Sagan’s famous television series, Cosmos, I had dreamed of being an astrophysicist. I settled for chemical engineering because I thought I’d be more likely to get a job! I have no regrets, even if the Moonlighting character was talking nonsense.