REACTORS, KINETICS, AND CATALYSIS Quantifying Rate Enhancements for Acid Catalysis in CO2-Enriched High-Temperature Water

Thermodynamic calculations revealed that 10 to 100-fold increases in reaction rate are obtainable with added CO2 (0.1–1 MPa) for an acid-catalyzed reaction in hightemperature liquid water (HTW) that is first order in H concentration. These calculations suggest that CO2 is most effective as a rate-enhancing additive in HTW at lower temperatures (150–2008C). When compared with increased temperature as a competitive option for accelerating acid-catalyzed reactions in HTW, CO2 addition generally carries a lower pressure penalty (and no temperature penalty) for the model acid-catalyzed reaction with activation energies of up to 35 kcal/mol. An experimental survey revealed that CO2 addition is effective for achieving increased reaction rates for dibenzyl ether hydrolysis in HTW, but that bisphenol A cleavage, methyl benzoate hydrolysis, and o-phthalic acid decarboxylation were not significantly impacted by added CO2. This behavior is consistent with previous results for these reactions wherein mineral acid, rather than CO2, was added to lower the pH. A summary of experimental results reported for reactions in CO2-enriched HTW revealed that product yields of some reactions can be increased by a factor of 23 with added CO2. Taken collectively, these results suggest that CO2 addition may be a practical technique for making HTW more attractive as a reaction medium for acid-catalyzed organic synthesis. 2007 American Institute of Chemical Engineers AIChE J, 54: 516–528, 2008