Noura Dawass

6 116 S OLUBILITY OF G ASES IN M ONOETHYLENE G LYCOL force field is used, without any modifications. In the case of the solubility of H 2 S, we test the performance of an additional force field developed by Kristóf and Liszi [207] which was used in a number of solubility studies [208, 209] . Solubility calculations are validated by comparing with experimental data. For this pur- pose, we have collaborated with the research group of Prof. Hanna Knuutila at The Norwegian University of Science and Technology to experimentally measure the solubility of CO 2 in MEG. In their labs, calorimetric measurements were per- formed using a CPA 122 calorimeter purchased from ChemiSens AB. In this de- vice, gas from a compartment with a fixed known volume is absorbed to the sam- ple. By accurately measuring the changes in pressure and temperature of the gas in this compartment and using the Peng-Robinson equation of state [210] , the amount of absorbed material in the sample can be calculated. For details related to the experimental setup and methods, the reader is referred to Ref. [171] . For the binary system CO 2 –MEG, absorption isotherms from MC simulations and experiments are compared for the temperatures 333.15 K, 353.15 K, and 373.15 K. The solubilities of CH 4 , N 2 , and H 2 S in MEG are computed at 373.15 K and compared to experimental data from literature, when available. In addition to absorption isotherms, Henry coefficients are computed using CFCMC simula- tions. From the knowledge of Henry coefficients of different solutes in MEG, se- lectivities are also computed. The chapter is organised as follows. In section 6.2, the MC simulation meth- ods used to compute the solubilities inMEG are explained. Results are presented and discussed in section 6.3. In section 6.3.1, MC calculations of absorption isotherms of CO 2 in MEG are compared to the experimental data obtained from Ref. [171] . MC simulations results of the solubility of CH 4 , N 2 , and H 2 S in MEG are shown in section 6.3.2. In section 6.4, the main findings of this chapter are summarized. 6.2. M ETHODS 6.2.1. F ORCE FIELDS Classical force fields were used to describe the interactions of the molecules studied in this work. For MEG, all interaction potentials and parameters fol- low from TraPPE-UA force field [199] . The TraPPE force field adequately pre- dicts densities and vapor-liquid equilibria (VLE) of many species such as normal alkanes [198] , branched alkanes [211] , glycols, and ketones [199] . To accurately represent the molecular structure of MEG, Stubbs et al. [199] added an additional repulsive term ( r − 12 ) for interactions between a hydroxyl hydrogen and an oxy- gen atom separated by four bonds. In our study, the TraPPE–UA force field was also used to represent CO 2 , CH 4 , H 2 S, and N 2 as rigid objects. We also tested an-