Aromatic compounds, supercritical

One example of normal-phase liquid chromatography coupled to gas chromatography is the determination of alkylated, oxygenated and nitrated polycyclic aromatic compounds (PACs) in urban air particulate extracts (97). Since such extracts are very complex, LC-GC is the best possible separation technique. A quartz microfibre filter retains the particulate material and supercritical fluid extraction (SPE) with CO2 and a toluene modifier extracts the organic components from the dust particles. The final extract is then dissolved in -hexane and analysed by NPLC. The transfer at 100 p.1 min of different fractions to the GC system by an on-column interface enabled many PACs to be detected by an ion-trap detector. A flame ionization detector (PID) and a 350 p.1 loop interface was used to quantify the identified compounds. The experimental conditions employed are shown in Table 13.2. 

The heat of decomposition (238.4 kJ/mol, 3.92 kJ/g) has been calculated to give an adiabatic product temperature of 2150°C accompanied by a 24-fold pressure increase in a closed vessel [9], Dining research into the Friedel-Crafts acylation reaction of aromatic compounds (components unspecified) in nitrobenzene as solvent, it was decided to use nitromethane in place of nitrobenzene because of the lower toxicity of the former. However, because of the lower boiling point of nitromethane (101°C, against 210°C for nitrobenzene), the reactions were run in an autoclave so that the same maximum reaction temperature of 155°C could be used, but at a maximum pressure of 10 bar. The reaction mixture was heated to 150°C and maintained there for 10 minutes, when a rapidly accelerating increase in temperature was noticed, and at 160°C the lid of the autoclave was blown off as decomposition accelerated to explosion [10], Impurities present in the commercial solvent are listed, and a recommended purification procedure is described [11]. The thermal decomposition of nitromethane under supercritical conditions has been studied [12], The effects of very high pressure and of temperature on the physical properties, chemical reactivity and thermal decomposition of nitromethane have been studied, and a mechanism for the bimolecular decomposition (to ammonium formate and water) identified [13], Solid nitromethane apparently has different susceptibility to detonation according to the orientation of the crystal, a theoretical model is advanced [14], Nitromethane actually finds employment as an explosive [15],... 

Supercritical carbon dioxide extraction (SCDE) is an ex situ process currently being researched for the treatment of soil and debris contaminated with polychlorinated biphenyls (PCBs) and polycyclic aromatic compounds (PAHs) as well as for the removal of solvents from low-level solid mixed wastes and land disposal restricted (LDR) wastes. 

Ding ZY, Aki NVSK, Abraham MA. Catalytic supercritical water oxidation an approach for complete destruction of aromatic compounds. Presented at the Symposium on Supercritical Fluids, AIChE Meeting, San Francisco, CA, 1994. 

Gonzalez, Bueno, and Medina [Ind. Eng. Chem. Res. 40,3711 (2001)] measured diffusivities of aromatic compounds in C02 under supercritical conditions and compared them to the Wilke-Chang [Eq. (5-218)], Hayduk-Minhas [Eq. (5-226)], and other equations. They recommended the Wilke-Chang equation (which yielded a relative error of 10.1 percent) but noted that the He-Yu equation provided the best fit (5.5 percent). 

Figure 11 shows a typical example of the temperature-dependent behavior for the reactions of OH radical with aromatic compounds. The measured bimolecular rate constants of OH radical with nitrobenzene showed distinctly non-Arrhenius behavior below 350°C, but increased in the slightly subcritical and supercritical region. Feng a succeeded in modeling these data with a three-step reaction mechanism originally proposed by Ashton et while Ghandi etal. claimed to have developed a so-called multiple collisions model to predict the rates for the reactions of OH radical in sub- and super-critical water. 

The crude black, viscous pyrolysis oil product requires an upgrading step to make it suitable as a refinery feedstock. This is accomplished by high-pressure hydrogenation in a manner very similar to the upgrading step used for the coking products in tar sands processing. The influence of overall process conditions on the polycyclic aromatic compounds found in the product has been examined [62], and the supercritical water extract of the pyrolytic product has been characterized [63]. 

The threshold density is that density of solvent gas at which a solute begins to dissolve in a supercritical fluid (or dense gas) at levels that are detectable (11). In Bowman s work it was UV detection using a mercury lamp for aromatic compounds the solute solubilities corresponding to threshold densities of carbon dioxide were on the order of micrograms-to-nanograms per milliliter of carbon dioxide. 

Shariff, S. M., Robson, M. M., and Bartle, K. D., Supercritical fluid chromatography of polycyclic aromatic compounds a review. Polycyclic Aromat. Compel., 12, 147-185, 1997. 

Anacleto, J. E., Ramaley, L., Boyd, R. K., Ploeasance, S., QuiUiam, M. A., Sim, P. G., and Benoit, F. M., Analysis of polycychc aromatic compounds by supercritical fluid chromatography mass spectrometry using atmospheric-pressure chemical ionization. Rapid Commun. Mass Spectrom., 5, 149-155,1991. Mansoori, B. A., Isomeric identification and quantification of polycychc aromatic hydrocarbons in environmental samples by liquid chromatography tandem mass spectrometry using a high pressure quadrupole collision cell, Rapid Common. Mass Spectrom., 12, 712-728, 1998. 

The Pd nanoparticles synthesized in the CO2 microemulsion are effective for hydrogenation of C02-soluble and water-soluble olefins but are not effective for hydrogenation of aromatic compounds. Hydrogenation of arenes is conventionally carried out with heterogeneous catalysts. Bonilla et al. recently reported a Rh catalyzed hydrogenation of arenes in a water/supercritical ethane biphasic system (35). Hydrogenation occurred well in this biphasic system with excellent results obtained for a number of arenes after 62 hours of reaction... 

Trace Level Extraction. To provide a challenging sample for evaluation of off-line SEE, activated carbon was spiked at 50 ppm with several polar and higher molecular weight polycyclic aromatic compounds. A one-gram sample was subjected to 16 h of Soxhlet extraction using carbon disulfide and then followed with a second similar extraction using methylene chloride. Another sample was extracted for 1 h with supercritical carbon dioxide at 125 and 400 bar. As shown in Table I, no detectable levels of the compounds were recovered in the combined Soxhlet extracts. However, low levels of the compounds were recovered with supercritical carbon dioxide extraction of the activated carbon. Although only low levels of the... 

Inclusion complexes. Solubility of poorly soluble drugs, such as piroxicam, can be enhanced by forming inclusion complexes with cyclodextrins. For many non-polar drugs, previously established inclusion complex preparation methods involved the use of organic solvents that were associated with high residual solvent concentration in the inclusion complexes ]. Cyclodextrins had previously been used for the entrapment of volatile aromatic compounds after supercritical extraction ]. On the basis of this principle. Van Hees employed SCFs for producing piroxicam and j8-cyclodexhin inclusion... 

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