Chemical Engineering Essentials from Academic Authors - Session Six: Separations - What You Probably Did Not Learn as an Undergraduate

Since 40 to 70 % of the cost of most industrial plants is in separations, the field is obviously important. However, because of the large number of different separation operations, it is impossible to cover everything in an undergraduate education. The most important separations for a chemical engineer depend heavily upon the industry he/she works in. Since distillation is the most important separation in the general chemical industry, in petroleum and in petrochemicals; distillation is extensively covered in most undergraduate chemical engineering programs. Two important aspects of distillation that often receive little coverage – the optimum operating pressure and balancing the column diameter – are covered in the first part of the presentation.

Membrane separations including gas permeation, reverse osmosis (RO) and ultrafiltration (UF) are included in some undergraduate curricula but not in others. These membrane separations are becoming more important in industry because they often require relatively small amounts of energy for a given separation. These three membrane processes are briefly described and important aspects of each process are discussed.

Although adsorption and chromatography are seldom included in undergraduate curricula, they are very important in industry for gas separations, pollution control, and separation of fine chemicals and pharmaceuticals. In the vast majority of applications the separation is based on equilibrium differences, although the spreading caused by mass transfer resistances is important. The theory for these separations appears mathematically formidable since operation is usually at cyclic steady state instead of steady state. A simple equilibrium model is discussed that allows understanding of a large variety of adsorption and chromatography processes including pressure swing adsorption (PSA), temperature swing adsorption (TSA) and simulated moving beds (SMB). Mass transfer and scale-up are also briefly discussed.