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 high-temperature liquid water (HTW) that is first order in H⁺ concentration. These calculations suggest that CO₂ is most effective as a rate-...

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Bibliographic Details
Published in:AIChE journal 2008-02, Vol.54 (2), p.516-528
Main Authors: Hunter, Shawn E, Savage, Phillip E
Format: Article
Language:English
Subjects:
acid catalysis
Applied sciences
Catalysis
Catalytic reactions
Chemical engineering
Chemistry
Exact sciences and technology
General and physical chemistry
green engineering
reaction kinetics
Reactors
supercritical processes
Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry
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Summary: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 high-temperature 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 (150-200°C). 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, 2008
ISSN:0001-1541
1547-5905
DOI:10.1002/aic.11392