Natural Extracts Using Supercritical Carbon Dioxide

Supercritical fluid extraction (SCFE) is an advanced extraction technique that utilizes a supercritical fluid as the solvent to extract valuable chemical compounds and natural products. A supercritical fluid is any substance above its critical temperature and pressure, giving it unique properties that are intermediate between those of a gas and liquid. This allows a supercritical fluid to dissolve both non-polar and polar solutes. 

Carbon dioxide is the most commonly used supercritical fluid solvent due to its favorable critical temperature and pressure of 31°C and 73 atmospheres, respectively. In its supercritical state, carbon dioxide can be easily manipulated to have solvent strengths ranging from gas-like to liquid-like densities by adjusting the operating pressure and temperature. This tunable solvating power enables carbon dioxide to effectively extract a wide variety of compounds with differing polarities from plant and agricultural materials.

The solubility behavior of solutes in supercritical fluids also exhibits distinctive characteristics like retrograde solubility and exponential increases in solubility with pressure. Cosolvents can be added to supercritical carbon dioxide to further enhance its solvent capabilities and selectivity for certain compounds. All of these unique properties allow supercritical fluid extraction to gently and efficiently separate valuable chemicals from complex biological matrices.

In a typical SCFE system, the raw material is loaded into an extractor vessel and pressurized with liquid carbon dioxide. By carefully controlling the temperature and pressure above carbon dioxide's critical point, the supercritical fluid can selectively dissolve the desired compounds from the sample matrix. The enriched supercritical fluid stream containing the extracted compounds is then expanded to lower pressure through a valve, causing the solutes to precipitate out of solution. 

The resulting extract is separated from the carbon dioxide in downstream collection vessels as the gas is depressurized and recondensed back to a liquid. The carbon dioxide solvent is recycled in a closed loop process. Additional equipment includes separators, heat exchangers, CO2 storage tanks, and control systems. Through continuous circulation of liquid carbon dioxide and precise regulation of operating conditions, SCFE enables highly efficient, non-toxic extractions.

This advanced extraction technology was pioneered by researchers at the Indian Institute of Technology Delhi. It offers numerous advantages over traditional solvent extraction methods for natural products. SCFE using carbon dioxide produces extracts of superior quality and purity with minimal thermal degradation. No residual solvent contamination occurs and extracts have longer shelf lives than those obtained through other techniques. 

The process is also very flexible, as extraction selectivity can be finely tuned by adjusting the pressure and temperature profile. Carbon dioxide is inexpensive, non-flammable, and environmentally friendly. SCFE technology shows strong potential for use in food, fragrance, pharmaceutical and other industries requiring high value plant extracts and isolates. It allows production of cholesterol-free and decaffeinated products.

The researchers have developed laboratory, pilot and commercial-scale SCFE systems up to 10 tons per day in capacity. They provide comprehensive process design, equipment, and technical support services to help companies adopt this green extraction technology. SCFE using supercritical carbon dioxide is poised to transform natural products manufacturing.