Noura Dawass

6 126 S OLUBILITY OF G ASES IN M ONOETHYLENE G LYCOL Table 6.3: Henry coefficient of CO 2 in MEG at different temperatures obtained from experiments (this work) and molecular simulation. H CO 2 ,MEG , bar/(mol CO 2 /mol EG) T /[K] Experimental MC Simulations 333.15 634 ± 2 445 ± 20 353.15 736 ± 2 576 ± 15 373.15 843 ± 2 730 ± 21 ionic liquid [bmim][TF 2 N] were reported to be 68 bar and 66 bar, respectively. At the same temperature, experimental Henry coefficient of CO 2 in MEG is 634 bar (Table 6.3) . From the knowledge of solubility of CO 2 at different temperature, the heat of absorption q of CO 2 in MEG can be calculated using − q R = ∂ ln( H CO 2 ,MEG / P o ) ∂ (1/ T ) (6.6) where R is the ideal gas constant and P o is a reference pressure to make the ar- gument of the logarithm dimensionless. Using solubilities of CO 2 in MEG from MC simulations of this work, q was found to be equal to -12.8 kJ/mol, indicating that the absorption of CO 2 is an exothermic process. This value is in good agree- ment with experimental findings. In a study by Wanderley et al. [229] , where the heat of absorption was measured using calorimetric experiments resulting in -14 kJ/mol at 343.15 K. The differences between theoretical and experimental solubilities can be at- tributed to the force field used to describe MEG. From our simulations, it is ob- served that the TraPPE-UA force field underpredicts the density of pure MEG (see Table 6.2) . Lower MEG densities can potentially lead to higher absorption capac- ities of solutes. Moreover, the force field parameters of TraPPE-UA [199] were obtained using VLE experimental data of MEG at high temperatures ( > 400 K), as a result inaccuracies at lower temperatures can be expected as we move outside the fitting range of the TraPPE force field. Figure 6.3 shows that deviations between experiments and simulations are larger at lower temperatures. While deviations can be reduced by optimising the force field parameters of MEG, force field parameters of the solute have to be considered as well. For CO 2 , TraPPE force field parameters are obtained using pure component data and not data of multi–component systems. Predictions of MC simulations can be improved by revising force field parameterisation or considering different force field combinations. Alternatively, one might consider