Expansion of supercritical

Tsutsumi, A., Nakmoto, S., Mineo,T., and Yoshida, K., A Novel Fluidized-Bed Coating of Fine Particles by Rapid Expansion of Supercritical Fluid Solutions, Proc. 1st Int. Particle Technol. Forum, pp. 452-455, Denver, CO (1994)... 

RESS [Rapid Expansion of Supercritical Solutions] A process for depositing a film of solid material on a surface. The substance is dissolved in supercritical carbon dioxide. When the pressure is suddenly reduced, the fluid reverts to the gaseous state and the solute is deposited on the walls of the vessel. Used for size-reduction, coating, and microencapsulation. First described in 1879. Developed in 1983 by R. D. Smith at the Battelle Pacific Northwest Laboratory. 

A number of techniques are based on supercritical fluid technology. Three are of particular pharmaceutical interest, namely the supercritical antisolvent (SAS) system, the rapid expansion of supercritical solution (RESS) method, and the gas antisolvent (GAS) technique [126]. 

Rapid expansion of supercritical solutions containing dissolved dmg, and... 

Journal of Applied Polymer Science 11, No.7, 15th Aug.2000, p. 1478-87 MORPHOLOGIES OF BLENDS OF ISOTACTIC POLYPROPYLENE AND ETHYLENE COPOLYMER BY RAPID EXPANSION OF SUPERCRITICAL SOLUTION AND ISOBARIC CRYSTALLIZATION FROM SUPERCRITICAL SOLUTION... 

By rapid expansion of supercritical propane solution (RESS), and isobaric crystallisation (ICSS), isotactic polypropylene and ethylene-butylene copolymers were precipitated from the supercritical solution. The RESS process produced microfibres with a trace of microparticles, while the ICSS process produced microcellular products. Improvement in thermal stability was achieved by first synthesising a thermoplastic vulcanisate from polypropylene and ethylene-propylene-diene terpolymer from a supercritical propane solution, followed by RESS. 28 refs. 

The Chinese scientists [123] have reported the preparation of nanoscale RDX (-50 nm) and nanoscale HMX (=70 nm) by an impinging method [124]. Researchers from China have also reported preparation and characterization of n-NTO and their data indicate that it decomposes at a lower temperature and at the same time, it is less sensitive to impact compared with m-NTO. This property of n-NTO is likely to be of tremendous significance for insensitive munitions [125]. The preparation of n-RDX particles with a mean size (=110-120 rim) but narrow distribution has also been reported by a novel method known as rapid expansion of supercritical solution (RESS) [126]. 

By utilizing the rapid expansion of supercritical solutions, small-size particles can be produced from materials which are soluble in supercritical solvents. In this process, a solid is dissolved in a pressurized supercritical fluid and the solution is rapidly expanded to some lower pressure level which causes the solid to precipitate. This concept has been demonstrated for a wide variety of materials including polymers, dyes, pharmaceuticals and inorganic substances. 

By varying the process parameters that influence supersaturation and the nucleation rate, particles can be obtained which are quite different in size and morphology from the primary material. Extremely high supersaturation can be obtained from cooling by depressurization and density reduction owing to the expansion of supercritical solutions. 

Turk, M., B. Helfgen, P. Hils, R. Lietzow, and K. Schaber. 2002. Micronization of pharmaceutical substances by rapid expansion of supercritical solutions (RESS) Experiments and miRtetio ... 

Vemavarapu, C., M. J. Mollan, andT. E. Needham. 2002. Crystal doping aided by rapid expansion of supercritical solutions APS Pharm Sci TedBi1-15. 

Deryagin, B. M. Levi, S. M. Film Coating Theory, The Focal Press New York, 1964. Domingo, C. Berends, E. Van Rosmalen, G. M. Precipitation of Ultrafine Organic Crystals from the Rapid Expansion of Supercritical Solutions over a Capillary and a Frit Nozzle. J. Supercrit. Fluids, 1997, 10, 35-55. 

Kim, J.-H. Paxton, T. E. Tomasko, D. L. Microencapsulation of Naxopren Using Rapid Expansion of Supercritical Solutions. Biotechnol. Prog. 1996, 12, 650-661. 

Kwauk, X. Debenedetti, P. G. Mathematical Modeling of Aerosol Formation by Rapid Expansion of Supercritical Solutions in a Converging Nozzle. J. Aerosol Sci. 1993, 24, 445-469. 

Matson, D. W. Petersen, R. C. Smith, R. D. Formation of Silica Powders from the Rapid Expansion of Supercritical Solutions. Adv. Ceram. Mater. 1986a, 1, 242-246. 

A novel fluidized-bed coating process using the rapid expansion of supercritical solutions (RESS) is described for the encapsulation of fine particles [2,3]. This process exploits the capability of supercritical fluids to act as a selective solvent. Supercritical fluids are noteworthy in that their... 

D.W. Matson, J.L. Fulton, R.C. Petersen, R.D. Smith, Rapid expansion of supercritical fluid solutions solute formation of powders, thin films and fibers, Ind. Eng. Chem. Res. 26 (1987) 2298-2306. 

H. Krober, U. Teipel, H. Krause, Manufacture of submicron particles via expansion of supercritical fluids, Chem. Eng. Technol. 23 (2000) 763-765. 

A. Tsutsumi, S. Nakamoto, T. Mineo, K. Yoshida, A novel fluidized-bed coating of fine particles by rapid expansion of supercritical fluid solutions, Powder Technol. 85 (1995) 275-278. 

The rapid expansion of supercritical solutions (RESS) has been explored recently as a novel route for the production of small and monodispersed particles (1-2.). Particle formation involves nucleation, growth and agglomeration. In RESS, nucleation is induced by a rapid decompression growth and agglomeration occur within the expanding solution. The thermodynamics of the supercritical mixture influences the relative importance of these mechanisms, and thus play a key role in sizes or size distribution of final particles. 

Several new processes for formation of solid particles with defined particle size and particle size distribution using supercritical fluids were developed in the past years. Examples are crystallisation from supercritical fluids, rapid expansion of supercritical solutions (RESS), gas antisolvent recrystallisation (GASR), and PGSS (Particles from Gas Saturated Solutions)-process [1,2]. 

Production of fine, solvent free powders is of great importance in the pharmaceutical industry /5/. Conventional techniques produce particles with broad particle size distributions. Moreover, particles may be irregular or contain solvents. Hence the development of procedures such as Rapid Expansion of Supercritical Solutions (RESS) or the Gas Antisolvent Recrystallisation (GAS) is in progress /5, 6/... 

Solids Formation by Rapid Expansion of Supercritical Solutions... 

A pilot plant is presented, which has been built to prepare fine particles (< 4 pm) by the Rapid Expansion of Supercritical Solutions (RESS - process). In this study carbon dioxide loaded with anthracene was used. By varying process parameters, the particle size distribution can be influenced. Changes of the post-expansion pressure have no provable influence on the particle size distribution. 

The rapid expansion of supercritical solutions (RESS) was explored by several authors as a novel route to the formation of microparticles. Ohgaki [1] produces fine stigmasterin particles by the rapid expansion of a supercritical C02 solution. Amorphus fine particle and whisker-like crystals (0,05 - 3 pm) were obtained with different preexpansion pressures. Johnston [2] obtained submicron particles from different polymers. Loth [3] described the mirconisation of phenacetin with supercritical fluids. 

A pilot plant was built to study the influence of different process parameters on the particle size produced by RESS-process (Rapid Expansion of Supercritical Solutions). Particles smaller than 4 pm were obtained for the system carbon dioxide-anthracene. 

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