Chemical engineering is an applied science. Where the science of chemistry tends to focus on developing and understanding new molecules, reactions, etc., chemical engineering takes what is already known and applies it on an industrial scale. Chemical engineers are responsible for bringing new materials to market, always considering safety, efficiency, and even profitability.
For illustrative purposes, imagine that Bob, a chemist, developed a new reaction that occurs in two steps. This reaction produces a new, transparent and lightweight material that has strength near that of steel. Bob sells his discovery to an automotive company who plans to use it to make lighter, stronger, safer windshields. Bob is now fairly rich, and the automotive company has a chemical process that has never been performed in anything bigger than a few glass flasks in Bob’s lab. The company hands the project over to chemical engineers, who are told to scale the reaction up so that they can produce enough of the product to fit 500 windshields daily.
SAFETY is always a concern when working with chemicals. It becomes even more paramount when working with large amounts of chemicals. Aside from the obvious fact that some chemicals are toxic on their own, chemical engineers must also consider the hazards that appear when the chemicals are mixed, processed, stored, heated, cooled, pumped, etc. Chemical pipes, tanks, and reactors all have to be designed so that they are resistant to the chemicals within, able to withstand any pressures that are generated, and can handle any temperature changes that are anticipated – all without losing integrity. Beyond that, facilities have to be designed so that if something does go wrong, the hazards are minimized. Dikes may be used to contain spills, fire suppression systems are a must with anything flammable, and blast-proof walls may even be installed if there is explosive potential.
Looking at the example case, Sue has been assigned as the lead engineer. Under her guidance, the team has identified that step one of the reaction is very exothermic – it produces a lot of heat. Too much heat is known to cause one of the reactants to degrade into an explosive gas. They solve this problem by designing a heat-exchange mechanism that pumps a highly conductive liquid through pipes inside the reactor. Heat is rapidly removed, eliminating the process during normal operations. To be sure, a fail-safe is installed, so that if the temperature ever exceeds a preset temperature, the flow of reactants into the reactor is shut off. A few degrees higher and a second trigger will switch on a spray of cold water to cool the tank from the outside. All systems are designed with a back-up power source, so that even in the event of a power outage, the reaction temperature can be controlled.
EFFICIENCY is perhaps the central premise of chemical engineering. Whereas any lab monkey might be able to mix the right chemicals together to get product, it takes a great deal of math and creativity to find just the right balance of how to mix the chemicals to maintain production on a large scale, safely. From a business standpoint, it is almost always preferable to operate on a continuous basis rather than having to start and stop constantly. It is also desirable not to waste chemical feedstocks – the raw materials going into production. The chemical engineer has to consider chemical kinetics (rate of reaction), thermodynamics (heat and energy transfer), flow properties (both into and out of reactors, tanks, pipes, etc.), potential bottlenecks (like a slow filtration step), and other related factors. When working on an industrial scale, chemistry is no longer a matter of “mix A with B”. Every little detail is considered and calculated, and even a small oversight can cost a company greatly, either in terms of equipment downtime, wasted materials, or even employee injuries.
Sue’s team found a challenge awaiting them during the second step of the reaction. They were able to make the reaction continuous easily enough, pumping the product from the first step and an acid mixture in the proper ratio into a mixing chamber that feeds into an outlet pipe. They face two problems here – the product has to be filtered, but it hardens and clogs the pipes if the flow is stopped. The filtration has to be done in-line with this step, but filters have to be changed regularly. If they just put one filter into the system, they will have to stop the reaction every time they want to change the filter. Instead, Sue has them split the pipe into two parallel sections, each with a filter. Flow is directed through only one of the two pipes at a time, and the filter in the other pipe can then be changed without interrupting the reaction.
PROFITABILITY is arguably the domain of businessmen and not engineers, but since the businessmen tend to be the engineer’s employers, it ends up being a part of engineering as well. There’s no point to making a product if it can’t be brought to market at a price that customers will pay. As a result, costs have to be kept as low as practical. This may mean finding a low-cost source for the starting chemicals, installing energy-efficient components, recycling where possible, automating systems to reduce the number of people required for operation, and ensuring that the work is of high quality so that money isn’t wasted fixing things needlessly later on.
When Sue’s team discovered that the second step of the reaction worked better when heated, one of her subordinates had a great idea. Rather than installing a heater, they could just use the excess heat that was removed from the first step. The pipes carrying heat from the first reactor feed into the second reactor, warming the reactants and speeding the reaction along. Over time, this innovation saves the company thousands of dollars, and Sue’s subordinate gets a nice bonus check that year.
That’s a general overview of what chemical engineering is about. Admittedly, it is quite a bit simplified, especially since the math was left out entirely. On the bright side, modern engineers have computers to help them with the math and to simulate the processes they design, so one might argue that their job has gotten a bit simplified as well. Have no fear, it’s still a complex and challenging profession.