Processing Pharmaceuticals, Natural Products, Specialty Chemicals, and Waste Streams

Processing Pharmaceuticals, Natural Products, Specialty Chemicals, and Waste Streams 

A large body of experimental data has been accumulated on the solubility and extractability of natural products, such as steroids, alkaloids, anticancer agents, oils from seeds, and caffeine from coffee beans, in various SCF solvents such as CO2, ethane, ethylene, and N2O. Carbon dioxide is probably the most widely investigated SCF solvent since its critical temperature T = 31.1°C) makes it an ideal solvent for extracting materials that are thermally labile. Also, CO2 is nontoxic, nonflammable, environmentally acceptable, and inexpensive. 

To determine the solubility characteristics of compounds in SCFs Stahl and coworkers (Stahl and Quirin, 1983 Stahl et al., 1980) have developed a microextraction apparatus that they directly couple with thin-layer chromatography. They find that a number of variables control the solubility of natural products in supercritical CO2. They corroborate some of the trends detailed in the preceding pages. For instance, they report that  

Fractionation of liquids or solids is possible if the constituents of the mixture exhibit large differences in vapor pressure, mass, and polarity. Low molecular weight hydrocarbons and lipophilic organic compounds, such as esters, ethers, and lactones, are easily extractable. 

Hydroxyl and carboxyl substituent groups on the mixture constituents reduce the solubility of the substance in the SCF and therefore make the extraction extremely difficult. 

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