English abstract
Carbon dioxide (CO2) emissions are viewed as the main contributor to global
warming. Therefore, CO2 capture technologies have become vital to mitigate the CO2
emissions. Recently, deep eutectic solvents (DESs) emerged among the several existing
solvents, owing to their harmonizing qualities, low cost, high CO2 absorption, and being
environmentally friendly.
In this work, two different Eutectic Solvent (ES) with a common hydrogen bond
acceptor of Imidazole (IM) and two different hydrogen bond donors, including
diethylenetriamine (DETA) and tetraethylenepentamine (TEPA) were prepared with
molar ratios of 1:1, 1:2, and 1:3. The prospect for CO2 loading in prepared ESs was studied
experimentally using the drop pressure method at molar ratios of 1:1, 1:2, and 1:3,
temperature ranging from 303.15K to 333.15K and pressure of 4 to 16 bar. The design of
experiment (DOE) was applied to study the effect of independent variables that includes
the pressure, temperature, and molar ratios on the CO2 loading of the solvents. The CO2
loading results were correlated based on response surface methodology (RSM) and
analysis of variance (ANOVA). The results revealed that molar ratios, temperature, and
pressure have a significant effect on the loading of CO2. The CO2 loading increased with
increasing pressure and molar ratio, while decreased with increasing temperature. Similar
trend was reported in the literature for several other solvents. Generally, IM:TEPA showed
higher CO2 loading compared to IM:DETA. The maximum CO2 absorption in IM:DETA
of 0.5115 (mol CO2/mol solvent) was observed at 303.15 K, 16 bar, and a 1:2 molar ratio,
while the minimum CO2 loading was 0.1567 (mol CO2/mol solvent) at 313.15 K, 4 bar
and a 1:1 molar ratio. However, the highest CO2 absorption in IM:TEPA was 0.5668 (mol
CO2/mol solvent) at 303.15 K and 16 bar, with a 1:2 molar ratio, while the minimum CO2
loading of 0.1978 (mol CO2/mol solvent) was observed at 313.15K, 4 bar, and a 1:1 molar
ratio. The Fourier transform infrared (FTIR) was used to identify the presence or absence
of specific functional groups as well as the formation of the new functional group after
the mixing. The results revealed that all functional groups of pure components were
present in the spectra, and no new functional groups were observed, indicating the absence
of chemical reactions.
The CO2 loading of prepared Eutectic Solvents with a 1:2 molar ratio was further
investigated with water content of 10, 20, 30, 40, and 50% volume% at temperature and
pressure of 303.15 K and 16 bar respectively. The results showed that the water content
had a significant effect on CO2 loading. It was remarkable to find that the introduction of
water significantly boosted the CO2 loading in both studied systems.
The physical properties, including density(ρ), viscosity(µ), and refractive index
(nD), of IM:DETA and IM:TEPA were measured at atmospheric pressure with 1:1, 1:2,
and 1:3 molar ratios and temperature ranging from 298.15 to 333.15K with a 5 K interval.
The results obtained showed that the density and refractive index decrease directly with
increasing temperature and molar ratio, while the viscosity decreases exponentially with
increasing temperature. The density data of IM:DETA and IM:TEPA ranged between
(1.0219-0.9607g/cc) and (1.0335-0.9779g/cc) respectively.
The thermodynamic properties, including enthalpy, entropy, and Gibbs free
energy, were calculated based on experimental data. The enthalpies of studied solvents
were compared with those of MEA 30wt%. The results reveal that the proposed Eutectic
Solvents required a lower regeneration energy.
