Noura Dawass

6.3. R ESULTS AND DISCUSSION 6 127 changes to the used combination rules. To improve the predictions of MC sim- ulations, deviations from the Lorentz–Berthelot rules can be used. For instance, other combination rules can be considered and/or adjustable parameter(s) can be added to fine–tune solute–solvent interactions. 6.3.2. S OLUBILITY OF CH 4 , H 2 S AND N 2 IN MONOETHYLENE GLYCOL MC simulations were used to compute the solubility of other pure gases in MEG at 373.15 K. MC simulation results were compared to experimental data from literature. In Figure 6.5 the absorption isotherm of CH 4 in MEG is shown for T = 373.15 K and pressures ranging from 1 to 10 bar. At this pressure range, low load- ings of CH 4 are obtained from MC simulations. To validate computational re- sults, experimental solubilities [225] at higher pressures are shown in Figure 6.5. At P = 17.9 bar, MC simulations overpredicts the solubility of CH 4 in MEG by ca. 25%. As discussed earlier in section 6.3.1, higher absorption of solutes is due to the underestimated densities of MEG when using the TraPPE-UA force field. In Figure 6.6, solubilities of H 2 S in MEG at T = 373.15 K from MC simula- tions using two different H 2 S force fields are compared to experimental solu- bilities from Ref. [186] . A reasonable agreement between MC simulations and experiments is obtained for the two force fields, but larger deviations appear at high pressures. The H 2 S-TraPPE force field underpredicts loadings of H 2 S, while the H 2 S-KL force field overpredicts loadings at the studied conditions. At atmo- spheric pressure, solubilities computed using H 2 S-KL were found to be closer to the experimental value reported by Jou et al. [186] , compared to the solubility computed using H 2 S-TraPPE. In Figure 6.7, the absorption isotherm of N 2 in MEG at T = 373.15 K is shown. The loading of N 2 is computed using MC simulations and is compared to exper- imental data from Zheng et al. [177] . Since the absorption of N 2 in MEG is neg- ligible at atmospheric pressures, simulations were performed at pressures rang- ing from 10 bar to 100 bar. From Figure 6.7 it can be seen that the computed loadings deviate considerably from experimental values, and that the deviations increase systematically with pressure. As discussed earlier, differences between MC simulations and experimental data at high pressures data can be improved by modifying the used force fields, or fine–tune solute–solvent interactions. In Table 6.4, Henry coefficients computed using MC simulations of CH 4 , H 2 S, and N 2 are listed. Experimental Henry coefficients of CH 4 and H 2 S are also shown. Average differences between experimental and computational values are around 25%. From the Henry coefficients at T = 373.15 K, the following order of