Decomposition, supercritical fluid

SFC/MS. supercritical fluid chromatography and mass spectrometry used as a combined technique SID. surface-induced dissociation (or decomposition)... 

Minowa, T. Zhen, F. Ogi, T., Cellulose decomposition in hot-compressed water with alkali or nickel catalyst. Journal of Supercritical Fluids 1998,13, 253. 

Rate of complex formation between chiral alcohols and DBTA monohydrate in hexane suspension is quite slow (see Figure 1) and numerous separation steps are necessarry for isolation of the alcohol isomers (filtration of the diastereoisomeric complex then concentration of the solution, decomposition of the complex, separation of the resolving agent and the enantiomer, distillation of the product). To avoid these problems, alternative methods have been developed for complex forming resolution of secondary alcohols. In a very first example of solid phase one pot resolution [40] the number of separation steps was decreased radically. Another novel method [41] let us to increase the rate of complex forming reaction in melt. Finally, first examples of the application of supercritical fluids for enantiomer separation from a mixture of diastereoisomeric complexes and free enantiomers [42, 43] are discussed in this subchapter. 

In this table, we provide solubility parameters for some liquid solvents that can be used as modifiers in supercritical fluid extraction and chromatography. The solubility parameters (in MPa1/2) were obtained from reference 3, and those in cal1/2cm 3/2 were obtained by application of Equation 4.1 for consistency. It should be noted that other tabulations exist in which these values are slightly different, since they were calculated from different measured data or models. Therefore, the reader is cautioned that these numbers are for trend analysis and separation design only. For other applications of cohesive parameter calculations, it may be more advisable to consult a specific compilation. This table should be used along with the table on modifier decomposition, since many of these liquids show chemical instability, especially in contact with active surfaces. 

Although C02 is the most common solvent for supercritical extraction processes because of it s abundance, non-toxicity and non-flammability, other compounds may prove to be better solvents in certain instances. In choosing a solvent, a balance between solubility and selectivity has to be struck. In the case of solutes with a melting point well below the decomposition temperature, it is usually desirable to perform a liquid-supercritical fluid extraction to circumvent the problems associated with handling solids at high pressures. In... 

Supercritical fluid extraction processes are particularly appropriate for the separation and isolation of biochemicals where thermal decomposition, chemical modification, and physiologically-active solvents are undesirable. Examples of these bioseparations include the extraction of oils from seeds using carbon dioxide (1), of nicotine from tobacco using carbon dioxide-water mixtures (2), and of caffeine from coffee beans again using carbon dioxide-water mixtures (3). 

While the inherent thermal decomposition of some additives such as light stabilizers has initiated the development of less destructive techniques like supercritical fluid extraction (SFE), it does not preclude the use of thermal desorption methods. Actually, the thermal decomposition products of the additives can be used to assign an identity to a particular compound. 

As mentioned earlier, the stationary phase must also be rendered nonextractable under supercritical fluid conditions. This has been accomplished by in situ free-radical crosslinking. Excellent results have been obtained using azo-t-butane as free-radical generator ( ). Azo-t-butane is superior to peroxides because its decomposition products are nonpolar (nitrogen gas and t-butane), and it does not promote oxidation of susceptible stationary phases with consequent activity and deterioration ( ). Other azo compounds are currently under investigation as well. Using azo-t-butane, both apolar and polar nonextractable phases have been produced for small-bore columns. 

Debenedetti, P. (2000) Phase separation by nucleation and by spinodal decomposition fundamentals. In Kiran, E. et al. (eds). Supercritical Fluids, pp 123-166. Kluwer Academic Publishers, The Netherlands. 

Several other chemists were active in the field of supercritical fluid reactions at the beginning of the twentieth century. For example, Briner studied the decomposition and reactivity of supercritical fluids such as scNO and scCO (e.g., eq 1.1-6) [119-122]. He also investigated the system N2-H2 and reported that N2 and H2 do not combine at room temperature and 900 bar [122]. At the Chemical Institute of the University of Berlin, Arthur Stabler studied the reactions of alkyl halides such as chloroethane with SCNH3 (eq 1.1-7) [123]. One of the earliest attempts to utilize SCFs for the selective synAesis of low molecular weight organic products dates to the early 1940s, when Patat at the University of Innsbruck studied the hydrolysis of aniline under supercritical conditions (eq 1.1-8) [124]. 

Because the extraction efficiency was determined by the direct comparison of dye concentration in the spiked dyebadi before and after the extraction, the higher SFE recoveries (e.g. efficiency >99%) should have relative standard deviations <1%. For the purpose of this study, >99% of recovery is sufficient to illustrate the effectiveness of the SFE technique. According to our experiments, no decomposition or breakdown of these disperse dyes was observed during SFE at the specified experimental conditions described atove. The restrictor flow rates of SC-CO2 often dominate the success of SFE, and can be varied to provide information on the dynamics of the extraction process. It is known that if the flow of supercritical fluid is sufficient to sweep the ceil void volume, the effectiveness of the extraction is enhanced. In fact, changing the flow rate is a simple way to determine the extraction efficiency (7). In this study, no obvious difference in extraction efficiency was observed at the SC-C02 flow rate of 2.0, and S.O mL/min. It is also noted that SFE of samples with high concentrations of water tends to plug fused silica restrictors 19). Therefore, a restrictor temperature controller was used in our experiments to avoid restrictor plugging. 

Althou various supercritical fluids have been found useful as solvents for fatty acids and their esters, carbon dioxide is thus far the most commonly used extractant because of its inherent advantages. Extraction with carbon dioxide is effective at moderately low tenperatures, vhich limits autoxidation, decomposition and polymerization of the hi ily xmsaturated fatty... 

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