CHEMICAL REACTORS

The chemical reactor is the heart of any chemical process. Chemical processes turn inexpensive chemicals into valuable ones, and chemical engineers are the only people technically trained to understand and handle them. While separation units are usually the largest components of a chemical process, their purpose is to purify raw materials before they enter the chemical reactor and to purify products after they leave the reactor. Here is a very generic flow diagram of a chemical process.

Raw materials from another chemical process or purchased externally must usually be purified to a suitable composition for the reactor to handle. After leaving the reactor, the unconverted reactants, any solvents, and all byproducts must be separated from the desired product before it is sold or used as a reactant in another chemical process. The key component in any process is the chemical reactor; if it can handle impure raw materials or not produce impurities in the product, the savings in a process can be far greater than if we simply build better separation units. In typical chemical processes the capital and operating costs of the reactor may be only 10 to 25% of the total, with separation units dominating the size and cost of the process. Yet the performance of the chemical reactor totally controls the costs and modes of operation of these expensive separation units, and thus the chemical reactor largely controls the overall economics of most processes. Improvements in the reactor usually have enormous impact on upstream and downstream separation processes. Design of chemical reactors is also at the forefront of new chemical technologies. The major challenges in chemical engineering involve


1. Searching for alternate processes to replace old ones,
2. Finding ways to make a product from different feedstocks, or
3. Reducing or eliminating a troublesome byproduct

The search for alternate technologies will certainly proceed unabated into the next century as feedstock economics and product demands change. Environmental regulations create continuous demands to alter chemical processes. As an example, we face an urgent need to reduce the use of chlorine in chemical processes. Such processes (propylene
to propylene oxide, for example) typically produce several pounds of salt (containing considerable water and organic impurities) per pound of organic product that must be disposed of in some fashion. Air and water emission limits exhibit a continual tightening that shows no signs of slowing down despite recent conservative political trends.