For a mechanical engineer such as myself, the amount of technical chemistry knowlege required to get a good grasp of refinery units from Leffler's "Petroleum Refining in Nontechnical Language" was just about right. It is well written with perhaps high school or first year university chemistry required. It just walks you step by step from simple distillation through the more complex units. Easily one of the best three work related books I've bought.
