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Quantum Chemical Studies on Solvents for Post-Combustion Carbon Dioxide Capture: Calculation of pKa and Carbamate Stability of Disubstituted Piperazines

Authors

  • Satesh Gangarapu,

    1. Laboratory of Organic Chemistry, Wageningen University, Dreijenplein 8, 6703 HB Wageningen (The Netherlands)
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  • Gerben J. Wierda,

    1. Laboratory of Organic Chemistry, Wageningen University, Dreijenplein 8, 6703 HB Wageningen (The Netherlands)
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  • Dr. Antonius T. M. Marcelis,

    1. Laboratory of Organic Chemistry, Wageningen University, Dreijenplein 8, 6703 HB Wageningen (The Netherlands)
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  • Prof. Han Zuilhof

    Corresponding author
    1. Laboratory of Organic Chemistry, Wageningen University, Dreijenplein 8, 6703 HB Wageningen (The Netherlands)
    2. Department of Chemical and Materials Engineering, King Abdulaziz University, Jeddah (Saudi Arabia)
    • Laboratory of Organic Chemistry, Wageningen University, Dreijenplein 8, 6703 HB Wageningen (The Netherlands)===

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Abstract

Piperazine is a widely studied solvent for post-combustion carbon dioxide capture. To investigate the possibilities of further improving this process, the electronic and steric effects of [BOND]CH3, [BOND]CH2F, [BOND]CH2OH, [BOND]CH2NH2, [BOND]COCH3, and [BOND]CN groups of 2,5-disubstituted piperazines on the pKa and carbamate stability towards hydrolysis are investigated by quantum chemical methods. For the calculations, B3LYP, M11L, and spin-component-scaled MP2 (SCS-MP2) methods are used and coupled with the SMD solvation model. The experimental pKa values of piperazine, 2-methylpiperazine, and 2,5-dimethylpiperazine agree well with the calculated values. The present study indicates that substitution of [BOND]CH3, [BOND]CH2NH2, and [BOND]CH2OH groups on the 2- and 5-positions of piperazine has a positive impact on the CO2 absorption capacity by reducing the carbamate stability towards hydrolysis. Furthermore, their higher boiling points, relative to piperazine itself, will lead to a reduction of volatility-related losses.

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