What are "Unit Operations"?

A typical process which a chemical engineer might work with is the production of gasoline from crude oil

Process = sequence of "unit operations" (physical changes) + chemical reactors

Any process can be subdivided into a number of steps which are performed in sequence to go from some initial starting material (crude oil, in this case) to some final material (gasoline). For example, we might start by heating the crude oil to lower its viscosity, then pump the oil to the distillation column, where we then separate various components of the crude. A unit operation is one of the steps of this sequence. Usually the term refers to steps intended primarily to perform some physical transformation (as opposed to chemical transformation) of the input stream.

Examples of unit operations:

• heat exchange (change temperature of a stream)
• fluid flow (transportation)
• distillation (separation of mixture into multiple streams which are richer in some components that original)
• evaporation (remove water from liquid)
• humidification (increase water content of gas)
• gas absorption (remove one component of a gas mixture)
• sedimentation (separate solid from liquid)
• classification (divide mixture of particles into different "classes" on the basis of size)