https://orcid.org/0000-0002-2812-9813
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ABSTRACT
Absorption of carbon dioxide (CO2) by solvents is an important process in many practical applications such as capture of greenhouse gases from flue gas, gas processing in the chemical and petroleum industries, capture of radioactive isotopes in the nuclear cycle, etc. High pH alkaline solutions were used in this research project to capture CO2. The chemical reaction between CO2 and the hydroxyl ion is known to significantly increase the absorption rate compared to the same process without chemical reaction. The goal of this work is to study the influence of the chemical reaction on the absorption rate. For this purpose, the gas-liquid mass transfer coefficient was measured under reactive and nonreactive conditions. Reactive mass transfer coefficient values were higher than similar ones without chemical reaction. Under the operating conditions used in this work, the mass transfer process was found to be controlled by the liquid phase resistance.
Nomenclature
| av | = | Mass-transfer specific area for the packing (m2 m−3) |
| aw | = | Wet packing specific area (m2 m−3) |
| at | = | Dry packing specific area (m2 m−3) |
| ci | = | Liquid-phase molar concentration at point I (mol m−3) |
| ct | = | Total molar concentration in liquid phase (mol m−3) |
| Ch | = | Packing constant for liquid hold-up (-) |
| Cl | = | Packing constant for liquid phase (-) |
| COH | = | Hydroxyl ion concentration (mol m−3) |
| DCO2 | = | CO2 diffusion coefficient (m2 s−1) |
| Dl | = | Solute diffusion coefficient in liquid-phase (m2 s−1) |
| Dp | = | Packing particle equivalent sphere diameter (m) |
| dz | = | Column differential height (m) |
| E | = | Enhancement factor (-) |
| g | = | Gravitational constant (m s−2) |
| ht | = | Liquid hold-up per unit volume (-) |
| H | = | Column height (m) |
| Ha | = | Hatta number (-) |
| Hcc | = | Concentration-based Henry’s constant (-) |
| HTU | = | Height of a transfer unit (m) |
| ki | = | Mass-transfer coefficient for phase I (m s−1) |
| KOL | = | Overall liquid-side mass-transfer coefficient (m s−1) |
| kR | = | Specific reaction rate (m3 mol−1 s−1) |
| L | = | Liquid molar flowrates (mol s−1) |
| L’ | = | Solute free molar flows (mol s−1) |
| Lm | = | Liquid molar flux (mol m−2 s−1) |
| NTU | = | Number of transfer units (-) |
| P | = | Pressure (Pa) |
| Qg | = | Gas-phase flow rate (m3 s−1) |
| Ql | = | Liquid-phase flow rate (m3 s−1) |
| Rei | = | Reynolds number of phase I (-) |
| ui | = | Superficial velocity of phase I (m s−1) |
| V | = | Gas molar flowrates (mol s−1) |
| V’ | = | Solute-free gas molar flows (mol s−1) |
| x | = | Liquid-phase molar fractions (-) |
| X | = | Solute-free liquid-phase molar fractions (-) |
| y | = | Gas-phase molar fractions (-) |
| Y | = | Solute-free gas-phase molar fractions (-) |
Greek Letters
| ε | = | Void fraction (-) |
| ρi | = | Density of phase I (kg m−3) |
| μl | = | Dynamic viscosity of the liquid phase (kg m−1 s−1) |
Acknowledgments
Notice: This manuscript has been authored by UT-Battelle, LLC under Contract No. DE-AC05-00OR22725 with the US Department of Energy. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a nonexclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes. The Department of Energy will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan (http://energy.gov/downloads/doe-public-access-plan).
Funding for this research provided by the Office of Nuclear Energy of the U.S. Department of Energy, under the Nuclear Energy University Program (Grant # NFE-12-03822), is gratefully acknowledged by the authors. This study was conducted at Prairie View A&M University in collaboration with the Oak Ridge National Laboratory (ORNL).