Supercritical fluid media

We report on steady-state and time-resolved fluorescence of pyrene excimer emission in sub- and supercritical C02. Our experimental results show that, above a reduced density of 0.8, there is no evidence for ground-state (solute-solute) interactions. Below a reduced density of 0.8 there are pyrene solubility complications. The excimer formation process, analogous to normal liquids, only occurs for the excited-state pyrene. In addition, the excimer formation process is diffusion controlled. Thus, earlier reports on pyrene excimer emission at rather "dilute pyrene levels in supercritical fluids are simply a result of the increased diffusivity in the supercritical fluid media. There is not any anomalous solute-solute interaction beyond the diffusion-controlled limit in C02. 

Investigations of Solute—Cosolvent Interactions in Supercritical Fluid Media... 

Hutchenson KW. Organic chemical reactions and catalysis in supercritical fluid media. In Sun Y-P, ed. Supercritical Fluid Technology in Materials Science and Engineering. New York Marcel Dekker, 2002 87-187. 

Many chemical reactions carried out in supercritical fluid media were discussed in the first edition, and those developments are included in total here after some recent work is described. In the epilogue (chapter 13) of the first edition we made reference to one of the author s work in enzyme catalyzed reactions in supercritical fluids that was (then) soon to appear in the literature. The paper (Hammond et al., 1985) was published while the first edition was in print, and as it turned out, there was a flurry of other activity in SCF-enzyme catalysis many articles describing work with a variety of enzymes, e.g., alkaline phosphatase, polyphenol oxidase, cholesterolase, lipase, etc., were published starting in mid 1985. Practical motivations were a potentially easier workup and purification of a product if the solvent is a gas (i.e., no liquid solvent residues to contend with), faster reaction rates of compounds because of gas-like transport properties, environmental advantages of carbon dioxide, and the like. 

Recent studies in our laboratory, as well as cost considerations, suggest that there would be a great advantage to employing sub- and supercritical fluid media for multiple processing operations in a sequential feshion in a production plant. This is bas on the iQ thesis that the capital equipment costs are relatively high to implement a critical fluid-based process, hence multiple applications should stribute the initial costs over an entire production sequence, rather than concentrate the economics on just one unit process. 

Prior studies utilizing adsorbents in the presence of supercritical fluid media have been reviewed by King (3), who has commented on the lack of fundamental knowledge on adsorbate(sorbate)/adsorbent(sorbent)/supercritical fluid systems. Indeed, with the exception of the sorbent regeneration studies performed at Critical Fluid Systems in the last... 

Only limited work has been reported on microemulsion-mediated synthesis of aluminum hydroxide [44,45]. In the two publications available [44,45], AOT served as the surfactant. It is possible to form reverse micelles in supercritical fluid media [130], and Matson et al. [44] used such a medium and the microemulsion-plus-reactant technique to synthesize A1(0H)3 particles at 110°C. With supercritical propane as the continuous phase, anhydrous ammonia was injected into the reversed micellar solution containing solubilized Al + [as an aqueous A1(N03)3 solution]. Referring to Fig. 1 and Table 2, the resulting precipitation process followed reaction path AP3 the added ammonia reacted with water molecules in the aqueous pseudophase of the microemulsion to generate hydroxide ions ... 

Even though not as extensive as chain addition polymerization, polymerization by step growth mechanisms in supercritical fluid media is also gaining attention. 

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