Supercritical processing

Supercritical processing may use relatively nonhazardous materials such as water or carbon dioxide as reaction and extraction... 

Sethia S, and Squillante E (2004) In vitro-in vivo evaluation of supercritical processed solid dispersions Permeability and viability assessment in Caco-2 cells. J. Pharm. Sci. 93 2985-2993. 

In former days in the US the subcritical process was used, but in the new plants, which are located in the hops areas, the supercritical process is applied. 

In addition, our design has eliminated the use of a restrictor. Restrictors are the most common means of controlling the pressure or density of a supercritical process. With no restriction, flow is dead-ended (i.e. restricted) via a switching valve in our invention. Supercritical fluid extractions are then conducted in a static mode (no flow). 

Micronized cocoa butter particles produced by a supercritical process... 

Particle production is an important process of particle technology. The paper of J. Toth et al discusses the results of investigation on salting-out precipitation of glycine and sodium chloride. In another paper, production of micronized cocoa butter particles by supercritical process was reported by J.-J Letourneau et al. 

The cocoa butter powder obtained by supercritical process was able to seed using the following conditions. 

Robey, R. J. Sunder, S. "Application of Supercritical Processing to the Concentration of Citrus Oil Fractions", Annual Meeting of American Institute of Chemical Engineers, San Francisco, 1984. 

This paper deals with the degradation of substances like PVC, Tetrabromobisphenol A, y-HCH and HCB in supercritical water. This process is called "Supercritical Water Oxidation", a process which gained a lot of interest in the past. The difference between subcritical and supercritical processes is easy to recognize in the phase diagram of water. The vapor pressure curve of water terminating at the critical point, i.e. at 374 °C and 221 bar. The relevant critical density is 0.32 g/cm3. This corresponds to approx. 1/3 of the density of normal liquid water. Above the critical point, a compression of water without condensation, i.e. without phase transition is possible. It is within this range that supercritical hydrolysis and oxidation are carried out. The vapor pressure curve is of special importance in subcritical hydrolysis as well as in wet oxidation. 

Winters, M. A., Debenedetti, P. G., Carey, J., Sparks, H. G., Sane, S. U., and Przybycien, T. M. (1997), Long-term and high-temperature storage of supercritically-processed microparticulate protein powders, Pharm. Res., 14,1370-1378. 

In addition to the process benefits, there are cost and environmental benefits associated with the supercritical process. The supercritical fluid process has low operating energy costs when compared to other alternative solvent processes and the cost of the carbon dioxide used to supply the system is orders of magnitude less than the purchase costs of chlorofluorocarbons, especially with the added taxes imposed by the federal government. In addition, carbon dioxide is a more environmentally friendly material and does not have the disposal costs associated with other alternatives. 

Shekunov BY, Chow AHL, Fecley JC, Tong HHY, York P, Aerosolisation behaviour of micronised and supercritically-processed powders. Aerosol Sci 2003 34 553-68. 

Richard A. Novak and Raymond J. Robey Supercritical Processing, Inc., 966 Postal Road, Allentown, PA 18103... 

Supercritical COj is used in different procedures for the formation of small particles, and also as an antisolvent to precipitate substances out of a solution in conventional solvents. Such small particles improve the dissolving kinetics of pharmaceuticals and are a precondition for inhalative applications. Dense CO2 is applied as a solvent for reactions and chemical synthesis, e.g. for hydrogenation of vegetable oils, and it is increasingly important for preparative-scale chromatographic separations which require large amounts of solvent that can be simply recycled in the supercritical process. 

Process equipment has to operate over wide ranges of temperature, pressure, and fluid composition. Volatile hydrocarbons are stored at temperatures well below -100°C, and furnace tubes may be required to operate at temperatures above 1000°C. Crude oil distillation equipment operates commonly under vacuum, whereas supercritical processes operate at pressures of several hundred atmospheres. Aqueous solutions of mineral acids, alkalis, and salts can be extremely corrosive toward metallic materials, whereas plastic materials are much more vulnerable to organic solvents. The wide diversity of commercial chemical process conditions dictates that all classes of engineering materials find use in chemical process equipment. 

Many chemical processes are conducted at elevated pressures, particularly those processes that involve a reduction in the number of moles present as the reaction proceeds (e.g., hydrogenation) and those that benefit from increased solvent effects (e.g., supercritical processing). The safe application of these processes requires adequately designed pressure vessels. Vessels intended for use at elevated pressure need to have sufficient strength to safely contain the pressure. This is achieved by the careful selection of material and providing adequate wall thickness to support the intended pressure at the temperature of application. Numerous bodies of experts have developed such design criteria. The criteria discussed below are primarily that of the ASME. 

The improved reaction rates achieved in the SC-CO2 medium combined with the variety of substrates considered so far illustrate the potential of this technology. As an indication of the economic viability of CO2 processing in the fine chemical industry, a plant has been constructed at Thomas Swan and Co. in the The plant has been built for hydrogenation processes to produce fine chemicals and pharmaceutical intermediates to a rating of 1000 kg hr of CO2 at pressures up to 500 bar. However, the significant capital cost of supercritical processes, combined with the complex production and expensive nature of chiral products, demand that SC-CO2 be considered for asymmetric hydrogenation. 

---