Quantifying rate enhancements for acid catalysis in CO2-enriched high-temperature water
✍ Scribed by Shawn E. Hunter; Phillip E. Savage
- Publisher
- American Institute of Chemical Engineers
- Year
- 2008
- Tongue
- English
- Weight
- 296 KB
- Volume
- 54
- Category
- Article
- ISSN
- 0001-1541
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✦ Synopsis
Abstract
Thermodynamic calculations revealed that 10 to 100‐fold increases in reaction rate are obtainable with added CO~2~ (0.1–1 MPa) for an acid‐catalyzed reaction in high‐temperature liquid water (HTW) that is first order in H^+^ concentration. These calculations suggest that CO~2~ is most effective as a rate‐enhancing additive in HTW at lower temperatures (150–200°C). When compared with increased temperature as a competitive option for accelerating acid‐catalyzed reactions in HTW, CO~2~ 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 CO~2~ 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 CO~2~. This behavior is consistent with previous results for these reactions wherein mineral acid, rather than CO~2~, was added to lower the pH. A summary of experimental results reported for reactions in CO~2~‐enriched HTW revealed that product yields of some reactions can be increased by a factor of 23 with added CO~2~. Taken collectively, these results suggest that CO~2~ 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, 2008