ABSTRACT
In the past two decades, supercritical fluid (SCF) extraction technology has attracted considerable attention from chemists and engineers for its potential applications as an environmentally friendly solvent for chemical processing (1,2). Supercritical fluids exhibit gas-like mass transfer properties yet have liquid-like solvation capabilities. Because of its high diffusivity and low viscosity, an SCF is capable of penetrating into porous solid materials to dissolve organic compounds. Since the density of an SCF can be altered continuously by manipulating pressure and temperature, the solvation strength of the fluid is tunable. Thus, selective dissolution of certain groups of solutes in an SCF may be achieved by optimizing density of the fluid phase. This tunable solvation capability is a unique property that makes SCFs different from conventional liquids. Another major advantage of SCF extraction is rapid separation of solutes that can be easily achieved by reduction of pressure. Carbon dioxide is one of the most widely used gas for SCF applications because of its moderate critical constants (Tc=31.1°C, Pc= 72.8 atm, and φc=0.47 g cm
−3), nontoxic nature, low cost, and availability in pure form. Examples of large-scale industrial applications of the SCF CO2 extraction technology include the preparation of decaffeinated coffee and hop extracts.
