Rapid Expansion of a Supercritical Solution RESS

RESS was the first technique devised to exploit SCFs as precipitation media. It received wide attention from the chemical engineering community especially in the late 1980s and early 1990s. Two important review papers are a general one by Tom and Debenedetti [18] and a second, tailored to pharmaceutical processes, by Phillips and Stella [19]. 

Note that RESS is a semibatch operation, as the SCF is flowing continuously through the apparatus. 

The size and morphology of the product can be tuned by changing the process parameters, namely the concentration of the supercritical solution, the temperature of the expanding orifice, and the temperature and pressure of the expansion vessel. Details on the effects of these variables are extensively discussed by Reverchon [20]. 

Although the literature about RESS is rich, it mainly consists of scientific papers rather than industrial applications. This can be explained by a number of reasons  

Note that the part of the apparatus under high pressure must be designed for 

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Kikic I, Lora M, Bertucco A. Thermodynamic analysis of three phase equilibria in binary and ternary systems for applications in rapid expansion of a supercritical solution (RESS) particles from gas-saturated solutions (PGSS) and supercritical antisolvent (SAS). Ind Eng Chem Res 1997 36 5507-5515. 

Kikic, I., Lora, M. and Bertucco, A. (1997) A Thermodynamic Analysis of Three-Phase Equilibria in Binary and Ternary Systems for Applications in Rapid Expansion of a Supercritical Solution (RESS), Particles from Gas-Saturated Solutions (PGSS), and Supercritical Antisolvent (SAS), Ind. Eng. Chem. Res. 36,5507-5515. 

Figure C.2. Photograph of the supercritical fluid system used for nanoparticle synthesis. Shown is the 300-mL high-pressure reactor (A), with pressure/temperature controllers (B). The system is rated for safe operation at temperatures and pressures below 200°C and 10,000psi, respectively. The vessel may be slowly vented, or exposed to a dynamic CO2 flow, using a multiturn restrictor valve (C), which provides a sensitive control over system depressurization, allowing for the collection of C02-solvated species in the stainless steel collector (D). For deposition using the rapid expansion of tlie supercritical solution (RESS), nanoparticles were blown onto a TEM grid that was placed under the stopcock below D. Also shown is the cosolvent addition pump (E) used for the synthesis of aluminum oxide nanoparticles, capable of delivering liquids into the chamber against a back-pressure of <5,000 psi.

A number of crystallization and precipitation techniques using SCFs have been considered, with special respect to the rapid expansion of a supercritical solution method (RESS) and to the SCF antisolvent processes (GASP). 

In our laboratory, we have modified the supercritical fluid processing method known as RESS (Rapid Expansion of Supercritical Solution) (7 J-7S) by expanding the supercritical solution into a liquid solvent, or RESOLV (Rapid Expansion of a Supercritical Solution into a Liquid SOLVent), to produce nanoscale semiconductor and metal particles (7, 9, 19-22). For the solubility of metal salts, supercritical ammonia, THF, and acetone were used in the rapid expansion at relatively higher temperatures. The nanoparticles thus obtained were small (less than 10 nm), with relatively narrow size distributions. In an effort to replace the organic solvents with C02-based systems for RESOLV at ambient temperatures, we used a water-in-C02... 

The basic RESS process has been further modified to produce nanoparticles with tight particle size control and minimal agglomeration. Rapid expansion of a supercritical solution into a liquid solvent (RESOLV Pathak et al. 2004) and rapid expansion from supercritical to aqueous solution (RESAS Young et al. 2004 Tozuka et al. 2010) are the most notable ones. In RESOLV, the supercritical solution is allowed... 

Besides the supercritical fluid extraction (SFE) for preparation of medicines and materials processing, supercritical fluid technology involves processes such as supercritical anti-solvent (SAS), rapid expansion supercritical solutions (RESS), rapid expansion of a supercritical solution into a liquid solvent (RESOLV), supercritical assisted atomization (SAA), impregnation and solution enhanced dispersion by supercritical CO2 (SEDS) that involves the supercritical fluid in drug processing to drug delivery systems. 

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. 

Repeat step 1 using ethanol for both copper and phenylenediamine solutions. This time, when you vent the system after 45 min, place a carbon TEM grid at the base of the collector vessel (the instmctor will point this out). This technique, known as RESS (rapid expansion of the supercritical solution), is a unique benefit of performing reactions in supercritical fluids. When the system is vented, the gas/liquid carbon dioxide expands, being rapidly converted from its original... 

RESS has been particularly popular for the processing of polymeric materials. According to the original report by Krukonis (55), rapid expansion of a polypropylene solution in supercritical propylene resulted in the formation of fiber-like particles. The report marked the beginning of an extensive discussion on the issue of particles vs. fibers involving the use of RESS with polymers. 

In the first method, the drug is dissolved in the SF and followed by rapid expansion of the SF solution across a heated orifice to cause a reduction in the density of the solution and reducing the salvation power of the SF, which leads to the precipitation of the drug [16]. This process is termed the rapid expansion of supercritical solution (RESS). 

As described in Chapter 3, several SCF techniques are available for the preparation of drug delivery systems. These include rapid expansion of supercritical solutions (RESS), gas antisolvent recrystallization (GAS), supercritical antisolvent recrystallization (SAS), supercritical antisolvent with enhanced mass transfer (SAS-EM), solution-enhanced dispersion by supercritical fluids (SEDS), supercritical fluid nucleation (SFN), precipitation with compressed antisolvent (PCA), and aerosolized supercritical extraction of solvents (ASES). While RESS and SFN involve the expansion of a supercritical fluid solution of a drug to form drug particles, GAS, SAS, SAS-EM, SEDS, PCA, and ASES use a supercritical fluid as an antisolvent to precipitate particles of a drug dissolved in an organic solvent (5). General RESS and GAS processes are further elaborated in Sections 1.1.1 and 1.1.2. 

Another inorganic particle that has been prepared via RESS is iron oxide (Fe203) (75). The preparation involved rapid expansion of a Fe(N03)3 solution in supercritical water. The expansion was at 500°C and 100 MPa through 50-to 200-p,m-diameter orifices into an evacuated chamber. The Fe203 particles thus obtained were small and exhibited exceptional reactivities. In addition to inorganic oxides, several neutral metal carbonyls (chromium hexacarbonyl, dimanganese decacarbonyl, and triiron dodecacarbonyl) were processed via RESS to form micrometer-sized particles (76). The solubility of these compounds allowed the use of supercritical CO2 in the RESS processing. 

RESS was also used as an alternative to the conventional chemical vapor deposition (CVD) process in the preparation of thin films (77-79). A general procedure involved rapid expansion of an SCF solution onto a heated substrate in a vacuum chamber. For example, palladium thin films were prepared via the rapid expansion of a bis-(2,2,7-trimethyl-3,5-octanedionato)palladium(II) solution in supercritical pentane at 205°C and 1200 psia onto a silicon substrate heated to 515-740°C (77,78). High-quality InP films were obtained by a similar procedure (79). 

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]. 

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]. 

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... 

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. 

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. 

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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