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Kinetics of the reaction of carbon dioxide with aqueous hydroxide solutions

Kinetics of the reaction of carbon dioxide with aqueous hydroxide solutions. Presented by: Shahla Gondal Date:07-06-2013. Outline. Objective Introduction Experimental set-up Evaluation procedure Results Conclusions Future work. Introduction.

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Kinetics of the reaction of carbon dioxide with aqueous hydroxide solutions

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  1. Kinetics of the reaction of carbon dioxide with aqueous hydroxide solutions Presented by: ShahlaGondal Date:07-06-2013

  2. Outline • Objective • Introduction • Experimental set-up • Evaluation procedure • Results • Conclusions • Future work

  3. Introduction • The rate of absorption of CO2 into aqueous solutions of LiOH, NaOH, KOH (0.01–2.0 kmol m−3), and blends of hydroxides (0.5–3.0 kmol m−3) with carbonates for a range of temperatures (25–62 °C) has been studied in a string of discs contactor (SDC) under conditions where, the reaction of CO2 could be assumed pseudo-first-order. • The dependence of the reaction rate constant on temperature and concentration has been presented for the reaction of CO2 with hydroxyl ions in aqueous electrolyte solutions.

  4. The reactions occurring during absorption of CO2 into aqueous solutions of hydroxides: • Reaction (1) represents the process of physical dissolution of gaseous CO2 into the liquid solution. As the rate of this process is comparatively very high, at the interface the equilibrium described by Henry’s law can be assumed (Pohorecki and Moniuk, 1988). • The reaction (3) is a proton transfer reaction and thus fast. • Hence, reaction (2) governs the overall rate of the process and the rate of this second-order reaction (2) can be expressed by the equation:

  5. Experimental set-up • The absorption rate of CO2 into hydroxide / carbonate solutions and their blends was measured for different concentrations and temperatures. • The difference in CO2 pressure in and out was calculated from a material balance based on the CO2 mass flow controller. String of Discs Contactor used for kinetics measurements

  6. Evaluation procedure • The overall mass transfer coefficient, using CO2 balance over the entire system can be calculated for the whole string of discs by the equation • By use of experimentally determined Kov,G , liquid phase enhancement factor, apparent Henry’s law constant, gas side film coefficient and diffusivity, the pseudo first order reaction rate constant can be calculated from • In Eq. (7), k1 is the pseudo first order rate constant (1/s) and the second order kinetic constant can be calculated by

  7. Results for 2 molar hydroxides Both and depend on counter ion: K+ > Na+ > Li+

  8. Results for 1 molar Hydroxides and show different trends for counter ion, mainly due to Henry’s law constant value and physical properties.

  9. Results for concentrations < 1M • No clear trend based on counter ion is observed but concentration dependence of is very obvious. • While shows no dependence either on concentration or on counter ion.

  10. Conclusions • For hydroxide systems, the reaction rate “constant”, based on the use of concentrations in the kinetic expression depends both on the counter ion in the solution and the ionic strength. • The dependence of 2nd order rate constant, ()on concentration and counter ion increases by increasing ionic strength.

  11. Future Work • The experiments will be interpreted using a new activity based kinetic rate expression instead of the traditional concentration-based rate expression. • In an activity based expression like: the kinetic constant,, should be independent of concentration level of ions in solution and only be an Arhenius type temperature function. • The activities of the reactants should take care of possible changes in reaction rate with composition.

  12. References • Haubrock, Jens, J. Hogendoorn, and Geert F. Versteeg. "The Applicability Of Activities In Kinetic Expressions: a More Fundamental Approach To Represent the Kinetics Of the System CO (-OH-) In Terms Of Activities." International Journal of Chemical and Reactor Engineering 3.3 (2005): 1290. • Knuutila, Hanna, Olav Juliussen, and Hallvard F. Svendsen. "Kinetics of the reaction of carbon dioxide with aqueous sodium and potassium carbonate solutions." Chemical Engineering Science 65.23 (2010): 6077-6088. • Luo, Xiao. Experimental and numerical study of carbon dioxide mass transfer and kinetics in amine solutions. Diss. Norwegian UniversityofScience and Technology, 2012. • Pohorecki, Ryszard, and Wa̵dysa̵wMoniuk. "Kinetics of reaction between carbon dioxide and hydroxyl ions in aqueous electrolyte solutions." Chemical Engineering Science 43.7 (1988): 1677-1684.

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