Fluids, supercritical

Liquid phase chromatography can use a supercritical fluid as an eluent. The solvent evaporates on leaving the column and allows detection by FID. At present, there are few instances in the petroleum industry using the supercritical fluid technique. 

Figure A2.5.28. The coexistence curve and the heat capacity of the binary mixture 3-methylpentane + nitroethane. The circles are the experimental points, and the lines are calculated from the two-tenn crossover model. Reproduced from [28], 2000 Supercritical Fluids—Fundamentals and Applications ed E Kiran, P G Debenedetti and C J Peters (Dordrecht Kluwer) Anisimov M A and Sengers J V Critical and crossover phenomena in fluids and fluid mixtures, p 16, figure 3, by kind pemiission from Kluwer Academic Publishers.

Anisimov M A and Sengers J V 2000 Critical and crossover phenomena in fluids and fluid mixtures Supercritical Fluids-Fundamentals and Applications ed E Kiran, P G Debenedetti and C J Peters (Dordrecht Kluwer) pp 1-33... 

As it has appeared in recent years that many hmdamental aspects of elementary chemical reactions in solution can be understood on the basis of the dependence of reaction rate coefficients on solvent density [2, 3, 4 and 5], increasing attention is paid to reaction kinetics in the gas-to-liquid transition range and supercritical fluids under varying pressure. In this way, the essential differences between the regime of binary collisions in the low-pressure gas phase and tliat of a dense enviromnent with typical many-body interactions become apparent. An extremely useful approach in this respect is the investigation of rate coefficients, reaction yields and concentration-time profiles of some typical model reactions over as wide a pressure range as possible, which pemiits the continuous and well controlled variation of the physical properties of the solvent. Among these the most important are density, polarity and viscosity in a contimiiim description or collision frequency. 

Schwarzer D, Schroeder J and Schroder Ch 2000 Quantum yields for the photodissociation of iodine in compressed liquids and supercritical fluids Z. Phys. Chem. 214... 

Panagiotopoulos A Z 1994 Moleoular simulation of phase equilibria Supercritical Fluids—Fundamentals for Application NATO ASI Series ed E Kiran and J M H Levelt Sengers (Dordreoht Kluwer)... 

Catalysis in a single fluid phase (liquid, gas or supercritical fluid) is called homogeneous catalysis because the phase in which it occurs is relatively unifonn or homogeneous. The catalyst may be molecular or ionic. Catalysis at an interface (usually a solid surface) is called heterogeneous catalysis, an implication of this tenn is that more than one phase is present in the reactor, and the reactants are usually concentrated in a fluid phase in contact with the catalyst, e.g., a gas in contact with a solid. Most catalysts used in the largest teclmological processes are solids. The tenn catalytic site (or active site) describes the groups on the surface to which reactants bond for catalysis to occur the identities of the catalytic sites are often unknown because most solid surfaces are nonunifonn in stmcture and composition and difficult to characterize well, and the active sites often constitute a small minority of the surface sites. 

A separation technique in which the mobile phase is a supercritical fluid. 

The most common mobile phase for supercritical fluid chromatography is CO2. Its low critical temperature, 31 °C, and critical pressure, 72.9 atm, are relatively easy to achieve and maintain. Although supercritical CO2 is a good solvent for nonpolar organics, it is less useful for polar solutes. The addition of an organic modifier, such as methanol, improves the mobile phase s elution strength. Other common mobile phases and their critical temperatures and pressures are listed in Table 12.7. 

Typical Properties of Gases, Liquids, and Supercritical Fluids ... 

Supercritical fluid chromatography has found many applications in the analysis of polymers, fossil fuels, waxes, drugs, and food products. Its application in the analysis of triglycerides is shown in Figure 12.38. 

Example of the application of supercritical fluid chromatography to the analysis of triglycerides. (Chromatogram courtesy of Alltech Associates, Inc. Deerfield, IL). 

Palmieri, M. D. An Introduction to Supercritical Fluid Ghromatography. Part 1 Principles and Applications, ... 

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

Jinno, K., Hyphenated Techniques in Supercritical Fluid Chromatography and Extraction, Elsevier, Amsterdam, 1992. 

---