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Bioseparations are critical to the field of biochemical engineering. Each bioseparation process must be tailored to separate, purify, or recover the desired bioproduct. This article gives an introductory overview of filtration and chromatography - two key bioseparation unit operations.
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Modem biotechnology is built on genetic engineering - the genetic manipulation of organisms to produce commercial products. Bioproducts are derived by extraction from plants or animals or by synthesis in bioreactors containing cells or enzymes.
Bioproducts are sold for their chemical activity: methanol for its solvent activity, ethanol for its neurological activity (or as a fuel), penicillin for its antibacterial activity, streptokinase (an enzyme) for its blood-clot-dissolving activity, hexose isomerase for its sugar-converting activity, and whole Bacillus thuringiensis cells for their insecticide activity, to name a few very different examples. The wide variety represented by this tiny list suggests that bioseparations must encompass a correspondingly wide variety of methods. The choice of separation method depends on the nature of the product, as well as purity, yield, and - most importantly - activity requirements.
Bioproducts have unique properties. For bioseparation purposes, important properties include thermal stability, solubility, diffusivity, charge, and isoelectric pH, among others. A considerable amount of process planning is based on the lability, or susceptibility to change, of most bioproducts. Temperature, pH, and concentration must be maintained within specific ranges to assure product bioactivity.
Purification of bioproducts by a bioseparations process typically involves a long sequence of steps, and each step requires the use of one or more unit operations, such as filtration, extraction, chromatography, and drying. This article provides an overview of bioseparation and discusses the basic principles and theory of two key unit operations - filtration and chromatography.
Developing a sequence of bioseparations
The development of a flowsheet for the recovery and purification of a biological product is a creative process that draws on the engineer's experience and imagination. Attempts have been made to capture that experience in computer software (1-4) and automate, to some extent, the process synthesis tasks.
Experienced engineers rely heavily on certain rules of thumb, or heuristics, for putting together the skeleton of a recovery and purification process (5). A few such heuristics include:
* Remove the most plentiful impurities first.
* Remove...