Monitoring Reactions in Supercritical Media

Thierry Meyer, Sophie Fortini, and Charalampos Mantelis 

Chemical reactions in supercritical fluids (SCF) have been extensively studied during the past 30 years. Although many of these studies have been performed on a small scale ( 60 mL), recent developments tend to attain the liter scale in order to gain engineering as well as chemical and physical information. To carry out chemical reactions on an industrial scale requires a detailed and comprehensive understanding of the energetics of exothermic reactions. The development of an intrinsically safe process requires data on kinetics, physicochemical properties, thermicity, and safety aspects [1], 

On-line monitoring of chemical reactions encompasses on-stream and on-reactor applications of analytical methods to 

On-line analysis of physical parameters, such as temperature, pressure, volume, density, etc., may also reflect the extent of a chemical reaction in addition to revealing the state of the reactor. 

Supercritical Carbon Dioxide in Polymer Reaction Engineering 

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MM Hoffmann, MS Conradi. Hydrogen exchange reactions in supercritical media monitored by in situ NMR. J Supercrit Fluids 14 31-40, 1998. 

Because of the rapidly growing number of reactions which can be carried out in supercritical fluids, there is an increasing demand for in situ techniques to monitor the course of chemical syntheses in these reaction media. There is a growing need to have efficient analytical techniques in order to determine chemical properties (like concentration and chemical species), physicochemical parameters (Uke heat capacities, conductivity, density, refractive index, and solu-bihty), thermodynamical information (like phase behavior and boundaries, partitioning, and critical points) and/or engineering information (like transfer phenomena, mixing, and scale-up). 

Fisher at al. [17] reported the use of on-line NMR spectroscopy with a flow probe for supercritical fluid chromatography (SFC) used for reaction monitoring purposes. They monitored aliphatic amines in SCCO2. A typical NMR spectrum reahzed both in classical media and in SCCO2 is presented in Fig. 5.6. 

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