Kinetics and performance studies of a switchable solvent TMG (1,1,3,3-tetramethylguanidine)/1-propanol/carbon dioxide system


Abstract: The rate constants and the activation energies of the reaction between carbon dioxide and 1,1,3,3-tetramethylguanidine (TMG) in 1-propanol solution were measured by a stopped-flow technique at a temperature range of 288--308 K and at a TMG concentration range of 2.5--10.0 wt %. Based on the pseudo-first-order reaction for CO_2, the reaction was modeled by a termolecular reaction mechanism, which resulted in a rate constant of 199.30 m^3 kmol^{-1} s^{-1} at 298 K. The activation energies were 5.19 kJ/mol and 5.26 kJ/mol at 2.5 and 5.0 wt % TMG, respectively. In addition, carbon dioxide absorption capacity was investigated using a gas--liquid contact system. Absorption capacity of the 10.0 wt % TMG/1-propanol system was found to be 0.035 mol CO_2/0.035 mol TMG, indicating a favorable loading ratio of 1:1. Repeatability and potential performance losses of this system were analyzed by Fourier transform infrared spectrometry (FTIR) in the range of 400--4000 cm^{-1}. It was found that the FTIR spectra of the rich solvent became virtually identical to the spectra of the lean solvent upon thermal desorption, promising efficient regeneration. It is therefore concluded that the TMG/1-propanol/CO_2 system is easily switchable and can be used both for carbon dioxide capture and for other applications that require rapid change of medium from nonionic to ionic liquid.

Keywords: Binding organic liquids, carbon capture, reaction kinetics, reaction mechanism, stopped-flow method, switchable solvents, 1,1,3,3-tetramethylguanidine

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