Overview

In the polymer industry supercritical fluids are currently the subjects of intense research and commercial interest. They can be used for a variety of processes, for example as solvents in polymer synthesis, as plasticising agents or for chemical recycling. Supercritical fluids of materials such as carbon dioxide and water also offer a 'green' solution, in that they do not harm the earth's environment (181).

The development and application of supercritical fluid (SCF) technology has actually been quite slow, however it is unlikely that the pioneering researchers into supercritical fluid properties in the early 1900s envisioned the wide-ranging impact supercritical materials would have later in the century, with applications in a variety of industries. Interest really began in the 1960s and 1970s with research into extraction techniques. These experiments used mainly supercritical carbon dioxide in their research and concentrated in the food industry for the extraction of flavours and essential oils from materials such as hops and herbs and for decaffeinating coffee and tea.

The decaffeination of coffee is the process most commonly associated with supercritical fluids and was first carried out on a large production scale, in Germany in 1978. Here, the combined properties of the supercritical fluid carbon dioxide were realised in a cost competitive and environmentally superior process. The major driver for the development of the SCF process was in the elimination of residual solvents in the products, especially methylene chloride, which had previously been used to decaffeinate coffee. Increasing regulatory attention to solvent residues in food...