(284d) Solvent Effects On Reactions in Supercritical Fluids

The high compressibility of supercritical water near its critical point allows for the controlled manipulation of the related solvent properties through adjustments of the prevailing system pressure. This, in turn, permits the use of pressure to optimize rates and selectivities for reactions susceptible to solvent effects. Transition state theory was used to organize these solvent effects quantitatively in terms of an apparent activation volume that had contributions from mechanical pressure effects, solvent compressibility, diffusion limitations, electrostatic interactions and phase behavior. Experimental results for the reactions of the lignin model compounds phenethylphenyether and guaiacol and the coal model compound dibenzyl ether are used to illustrate these effects.