Nor Asrina, Sairi (2011) Physical properties of guanidinium trifluoromethanesulfonate-methyldiethanolamine aqueous mixtures and their CO2 absorption capacities / Nor Asrina Sairi. PhD thesis, University of Malaya.
Abstract
In this work, the physical properties i.e. density, viscosity and CO2 solubility studies were conducted on the aqueous systems of N-methyldiethanolamine (MDEA) and guanidinium trifluoromethanesulfonate [gua][OTf]. The studies were carried out at various concentration of MDEA (1 – 4 M) and [gua][OTf] (0.1 – 2 M). The temperature and pressure were also varied depending on the study involved. The studies on densities and viscosities of binary ([gua][OTf] - H2O) and ternary ([gua][OTf] - MDEA - H2O) systems were carried out at a wide temperature range from 293 to 363 K and at atmospheric pressure. The results show that the density and viscosity were strongly affected by the presence of water. Correlations for both viscosity and density for binary and ternary systems were ± 3.5 % in temperature ranges from 293 and 363 K except 2M2G and 1M3G have shown deviation up to 9.587 %. Also, binary systems of [gua][OTf] – H2O i.e. 0M0.1G, 0M0.3G, 0M0.5G, 0M0.7G, 0M0.9, 0M1G and 0M4G showed higher deviation in viscosities which is up to 8.442 %. As for solubility studies, this work was focused in determining the ability of aqueous binary ([gua][OTf] – H2O) and ternary (MDEA – [gua [OTf] – H2O) systems in capturing CO2 at high pressures. The experiments were conducted at CO2 partial pressures from 500 to 3000 kPa and temperatures at 303, 323 and 333 K. It has been found that the effect of partial pressures was most pronounced for 1 M aqueous [gua][OTf] (0M1G) which showed a competitive performance in capturing CO2, up to 1.63 mol CO2/ total mol system at 323.2 K and 3000 kPa, as compared to other pure ionic liquids such as [emim][C2N3], [emim][MDEGSO4] and [emim][OTf] with 0.8132, 0.9587 and 1.0753 mol CO2/ total mol system, respectively, which were also recorded in the same environments. The solubility to pressure data also supported that 0M1G is involved mainly in physical absorption and the effect of partial pressure was more significant at lower alkanolamine concentration. Correlations of solubility as a function of pressure and temperature have been determined with difference of ± 0.957 %. The solubility was also measured at lower partial pressure of CO2 at 10, 50 and 100 kPa and temperature 303.2 K. This experiment was predominantly on chemical absorption and it showed that the addition of 1 M [gua][OTf] induced 14 % of CO2 solubility at 303.2 K and 100 kPa of the CO2 partial pressure as compared to 1 M [bmim][BF4], in 4 M MDEA. Also, the solubility of CO2 in 4 M [gua][OTf] gave 27.5 % higher CO2 loading compared to 1 M [gua][OTf]. Compared to 4 M MDEA, the CO2 loading of blended system 4M1G was found to be slightly lower i.e. 0.6498 mol CO2/ total mol system at 100 kPa. The presence of [gua][OTf] could not make up the loss of the CO2 absorption capacity of MDEA due to the reducing amount of water with increasing amount of [gua][OTf] as physical absorption of CO2 will only play a significant role at high operating pressure. The R2 values from plot of PCO2 versus (aCO2 2/ 1 - aCO2) range from 0.94232 to 0.96272 for partial pressure between 0 - 100 kPa. These R2 values were finely fitted.
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