This chapter focuses on chemical devices which measure, make, or purify chemicals on a much smaller scale than the commodity chemicals described in the previous chapter. For example, we may wish to make oxygen-enriched air for a single emphysema patient, not for making steel. We may seek to remove water from the lubricating oil in one truck, not from a feed in an oil refinery. We may seek a ten-minute analysis of blood cholesterol from one drop of a patient's blood so the doctor has the analytical result before the patient's appointment is over.

In each of these cases, the device itself will be our desired product. The best device will not necessarily be the cheapest. This is a major change from commodity process design, where cost is king. The device which we seek to design will normally be much smaller than a conventional process: our device will usually be smaller than a meter and may be as small as a few hundred micrometers. However, the tools which we use will still assume that the chemicals involved form continua. We will still base our thinking on thermodynamics, chemical kinetics, and unit operations, just as we did in designing a process for chemical commodities.

As in the earlier chapters, we will base our designs on a four-step design template of needs, ideas, selection, and manufacture. As before, we will rewrite our needs as specifications, which will be quantitative.