ABSTRACT This research aims to simulate the process of natural gas sweetening using an imidazoliumbased ionic liquid solvent called 1-butyl 3-methyl imidazolium bis(trifluoromethylsulfonyl)imide [bmim][NTf2] and comparing it with natural gas sweetening using an Amine-based solvent. The comparison includes an economic analysis and an eva‎luation of the energy consumption of both systems. The PC-SAFT model, based on the molecular structure of the ionic liquid, was used as the equation of state, and relevant parameters were calculated for this study. The critical properties of pure ionic liquid were calculated using the Group Contribution Method. Laboratory data were used to determine the physical properties of the ionic liquid solvent including density, thermal conductivity, heat capacity, surface tension, viscosity, vapor pressure and ideal gas heat capacity, and these data were then fitted by relevant DIPPR equation for each property and input into the Aspen Plus. Laboratory data related to the solubility of natural gas in the ionic liquid solvent were collected and screened based on the research condition and then the binary interaction parameters of each component with the ionic liquid was determined using a flash calculation simulation. The Aspen Plus software version 10 was then used to simulate the sweetening of natural gas with the ionic liquid solvent. The sweetening was carried out in two different ways. In the initial approach to sweetening, adjustments were made to the system pressure, a heat load was applied, and the circulation rate of the solvent was increased. On the other hand, in the alternate approach the system pressure was modified and the solvent was increased without any additional heating load. The results show that to sweeten about 500 tons per hour of South Pars natural gas feed and reach the limit of 4 parts per million of hydrogen sulfide in the sweetened gas, significant and unusual quantities of 26,600 and 89,600 tons per hour of ionic liquid solvent are needed for the first and second approaches, respectively. The economic comparison between the two processes of sweetening with ionic liquid solvent in the first approach and sweetening with amine solvent also shows that the investment costs and annual operating costs of the sweetening process with ionic liquid are 3.05 and 2.82 times the corresponding costs in the sweetening process, respectively with an amine solvent. In previous researches by others, it has been stated that for absorbing 99% of acid gases, ionic liquid solvent can be a promising substitute for amine-based solvents. This fact was also examined. The obtained results show that the energy required to absorb 99% of the acid gases of the feed gas by the ionic liquid solvent [bmim][NTf2] is 79.3% lower than the energy required for the same process with the amine solvent. Besides, in the process of absorbing 99% of acid gases, the annual operating costs of the process with ionic liquid solvent is 22.8% of the operating costs of the process with amine solvent. Keywords: Process Simulation, Ionic Liquid, Natural Gas Sweetening, Aspen Plus

محمدرضا احساني , علي تقي ذوقي

اميرحسين جليلي

محسن محمدي , احمد محب