Antisolvent precipitations

Methods for isolation of the product polycarbonate remain trade secrets. Feasible methods for polymer isolation include antisolvent precipitation, removal of solvent in boiling water, spray drying, and melt devolatization using a wiped film evaporator. Regardless of the technique, the polymer must be isolated dry, to avoid hydrolysis, and essentially be devoid of methylene chloride. Most polycarbonate is extmded, at which point stabiUzers and colors may be added, and sold as pellets. 

In an industrial application dissolution/reprecipitation technology is used to separate and recover nylon from carpet waste [636]. Carpets are generally composed of three primary polymer components, namely polypropylene (backing), SBR latex (binding) and nylon (face fibres), and calcium carbonate filler. The process involves selective dissolution of nylon (typically constituting more than 50wt% of carpet polymer mass) with an 88 wt % liquid formic acid solution and recovery of nylon powder with scCC>2 antisolvent precipitation at high pressure. Papaspyrides and Kartalis [637] used dimethylsulfoxide as a solvent for PA6 and formic acid for PA6.6, and methylethylketone as the nonsolvent for both polymers. 

Reverchon, E. (1999) Supercritical antisolvent precipitation of micro- and nano-particles. Journal of Supercritical Fluids, 15 (1), 1-21. 

Gas anti-solvent processes (GASR, gas anti-solvent recrystallization GASP, gas antisolvent precipitation SAS, supercritical anti-solvent fractionation PCA, precipitation with a compressed fluid anti-solvent SEDS, solution-enhanced dispersion of solids) differ in the way the contact between solution and anti-solvent is achieved. This may be by spraying the solution in a supercritical gas, spraying the gas into the liquid solution. 

Chapter Eight is concerned with a major question connected with the development of high pressure technologies in the process and chemical industry, i.e., the economic evaluation of production carried out at high pressures. In this case, also, the matter is discussed in relation to three important examples dense gas extraction, polymerization and supercritical antisolvent precipitation processes. 

Fusaro, F., M., M. Flanchen, M. Mazzotti, G Muhrer, and B. Subramaniam. 2005. Dense gas antisolvent precipitation A comparative investigation of the GAS and PCAtechnidpi ng Chem Res44 1502-1509. 

Antisolvent precipitation is a bottom-up method wherein two phases are involved the initial creation of crystal nuclei of drugs and the subsequent growth. Formation... 

Matteucci, M. E., Hotze, M. A., Johnston, K. P., and Williams, III. R. O. (2006), Drug nanoparticles by antisolvent precipitation Mixing energy versus surfactant stabilization, Langmuir, 22, 8951-8959. 

Novel methods of preparation of vanadium phosphate catalysts have been explored by several groups these methods include hydrothermal synthesis, gas-phase s)mthesis, supercritical antisolvent precipitation, and the use of templates and structure-directing agents to modify the bulk... 

Hutchings and coworkers (78-83) pioneered the use of supercritical antisolvent precipitation to prepare a number of catalyst and support materials including vanadium phosphates. Vanadium phosphate precursor solutions were prepared from VOCI3 and H3PO4 refluxed in isopropanol. In the supercritical antisolvent precipitation method, a solution of the material to be precipitated and supercritical CO2 are pumped through a coaxial nozzle at temperatures and pressures above the critical point of... 

Hutchings and coworkers (78,149,150) prepared vanadium phosphate catalysts by using supercritical antisolvent precipitation. These materials were found to be amorphous by XRD and by electron diffraction, but they showed activity about twice as high as that of the standard vanadium phosphate catalysts. 

FIGURE 28 TEM and electron diffraction pattern (insert) of the vanadium phosphate catalyst prepared via supercritical antisolvent precipitation. 

At present, the most promising process seems to be the supercritical antisolvent precipitation, which is the most widely applied " and has been recently proposed on a semi-industrial scale. However, despite the fact that many works have been published on SAS precipitation, only a limited number of them have focused on the mechanisms controlling particle formation and on the role of the process parameters on the morphology and on the dimensions of the precipitated powders. This lack of information can be one of the main factors hampering the industrial application of this process. 

Based on the previous considerations, some authors proposed thermodynamic-based approaches to SAS. De la Fuente Badilla et al attempted to develop a thermodynamic-based criterion for optimum batch antisolvent precipitation (GAS) using a definition of the volume expansion that takes into account the molar volume of the system studied. They analyzed various binary and ternary systems and concluded that the pressure corresponding to a minimum value of the liquid-phase volume expansion coincides with the pressure at which the solute precipitates. In a subsequent work, Shariati and Peters further highlighted the role of SC-CO2 in GAS. It acts as a co-solvent (cosolvency effect) at lower concentrations, whereas at higher concentrations it acts as an antisolvent. 

Case e is the result of precipitation under conditions above the ternary MCP and is the true supercritical antisolvent precipitation. The formation of very small particles indicates that characteristic times for surface tension disappearance are very short, droplets are not formed at the exit of the injector and the very small particles are released from the fluid phase. These aspects have been studied in the previously cited works of Werling and Debenedetti," which underline the interplay among the different consecutive or simultaneous process that characterize SAS, mainly mass transfer under sub-critical and supercritical conditions. The characteristic times... 

Debenedetti, P.G. Lim, G.B. Prud homme, R.K. Formation of protein microparticles by antisolvent precipitation. Princeton University. Eur, 542314, 1993. 

Gas antisolvent processes can be performed in a semicontinuous mode. In this case the solution and the antisolvent are continuously introduced in the system until the desired amount of the product is formed. The introduction of the solution is then stopped and the DG flux extracts the residual solvent from the system. The system is then depressurized to enable collection of the product. The solution is generally introduced through an atomization nozzle that favors the prompt expansion of the solution and the formation of small particles. Different process configurations have been utilized, i.e., co- and countercurrent introduction of the solution and antisolvent fluxes and various nozzles have been designed. The process is referred to by different acronyms such as ASES (aerosol solvent extraction system), SAS (supercritical antisolvent), SEDS (solution enhanced dispersion by supercritical fluids), PCA (precipitation with a compressed fluid antisolvent), GASR (gas antisolvent recrystallization), GASP (gas antisolvent precipitation). 

The effect of processing technique on the aerosol performance of insulin formulations prepared by DG antisolvent precipitation and spray drying has been investigated. Two types of insulin formulations were produced. They were 1 20 insulin-mannitol (IM) and 1 20 8 insulin-mannitol-citric acid (IMC). Mannitol is an excipient commonly used to improve aerodynamic performance of powders for inhalation delivery. Citric acid has been found effective in improving insulin absorption in the lungs. ... 

Debenedetti, P.G Lim, G.B Prud homme, R.K Formation of Protein Microparticles by Antisolvent Precipitation. European Patent 5423141, Nov 13, 1992... 

Reverchon, E. De Marco, L Caputo, G. Della Porta, G. Pilot scale micronization of amoxicillin by supercritical antisolvent precipitation. J. Supercrit. Fluids 2003, 26 (1), 1-7. 

Reverchon E. Supercritical antisolvent precipitation its applications to microparticle generation and products fractionation. Proceedings of the 5th Meeting on Supercritical Fluids, Materials, and Natural Products Processing. Vol. 1. Nice France, 1998 221-236. 

Table 2 Qualitative Description of the Effect of Different Process Parameters on the Size and Morphology of Particles Obtained by Antisolvent Precipitation "...

Shekunov BY, Baldyga J, Sun Y, Astrakcharchik E, York P. Optical characterization and mechanism of antisolvent precipitation in turbulent flow. Proceedings of the 7th Meeting on Supercritical Fluids 2000 1 65-70. 

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