Contents lists available at ScienceDirect Journal of Natural Gas Science and Engineering journal homepage: www.elsevier.com/locate/jngse Carbon capture and adjustment of water and hydrocarbon dew-points via absorption with ionic liquid [Bmim][NTf 2 ] in offshore processing of CO 2 - rich natural gas Lara Costa Barbosa, Ofélia de Q. Fernandes Araújo, José Luiz de Medeiros ∗ Escola de Química, Federal University of Rio de Janeiro, Av. Horacio Macedo, 2030, Bl. E, 21949–900, Rio de Janeiro, RJ, Brazil ARTICLE INFO Keywords: Ionic liquid Offshore natural gas processing Ionic liquid CO 2 capture Ionic liquid gas dehydration Supersonic separator CO 2 drying ABSTRACT Offshore oil production from huge reservoirs at deep waters with high gas-oil ratio and high carbon dioxide (CO 2 ) content is a challenging puzzle because oil extraction imposes to process a huge flow rate of raw CO 2 -rich natural gas from which CO 2 must be separated and sent to appropriate destination. Offshore gas processing comprises three steps: water dew-point adjustment (WDPA), hydrocarbon dew-point adjustment (HCDPA) and CO 2 removal to avoid transport of inert and to boost oil production by injecting CO 2 into the reservoir for enhanced oil recovery. In offshore rigs, gas is conventionally treated via TEG absorption for WDPA, Joule- Thomson expansion for HCDPA and membrane permeation for CO 2 removal. This work discloses a new concept of CO 2 -rich natural gas processing using the ionic-liquid [Bmim][NTf 2 ] for simultaneous WDPA, HCDPA and CO 2 removal. All results were obtained via rigorous simulations, including the ionic-liquid implications in vapor- liquid equilibrium and heat-effects. The main novelty of the new process is its high-pressure selective stripping of CO 2 , lowering compression power for enhanced oil recovery utilization. Economic comparison of conventional gas processing with the ionic-liquid gas processing shows that the latter has 19.3% higher revenues, 23.6% less manufacturing costs and 18% less investment, entailing a 37% higher net present value. 1. Introduction Offshore oil production in deep and ultra-deep waters, with high gas-oil ratio and high CO 2 content in the associated gas, is posing stringent constraints to natural gas (NG) processing technologies (Reis et al., 2017). Furthermore, the urge for a low-carbon energy, which pulls worldwide the expansion of environmental regulations and carbon taxes, implies that, for extracting the oil, a huge flow rate of CO 2 -rich gas must be processed and a convenient destination for the extracted CO 2 must be found. Offshore NG processing comprises sweetening, dehydration and removal of propane and heavier hydrocarbons (C3+) to avoid pipeline transportation issues such as gas-hydrates, corrosion, condensation, transportation of inert and to increase lower heating value (LHV) of sales gas (Peters et al., 2011). In offshore production of oil and CO 2 -rich NG, a common CO 2 destination is injection into the reservoir to increase oil production since CO 2 , besides pressurizing the reservoir, reduces oil viscosity and surface tension promoting enhanced oil recovery (EOR). It is worth noting that the continuous CO 2 injection increases CO 2 content of the produced gas, because more than 50% of injected CO 2 returns with the associated gas (Kwak, 2014). To meet pipeline specifications, conventional CO 2 -rich NG proces- sing in offshore rigs applies triethylene glycol (TEG) absorption or temperature swing adsorption (TSA) or pressure/temperature swing adsorption (PTSA) on molecular sieves for water dew-point adjustment (WDPA), while Joule-Thomson (JT) expansion is used for hydrocarbon dew-point adjustment (HCDPA) and membrane permeation (MP) for CO 2 removal (GPSA, 2017). CO 2 removal via TSA/PTSA on molecular sieves is not common for NG with high CO 2 contents such as 45%mol CO 2 due to excessive size, footprint and costs of such operations. As a matter of fact, the limitation of area on offshore rigs has created a technology niche for MP due to its low footprint and modularity (Araújo and de Medeiros, 2017). Currently, 178 offshore rigs are in operation worldwide at deep waters among which 44 operate in Bra- zilian Pre-Salt reserves, mostly employing MP CO 2 removal, HCDPA via JT expansion, TSA/PTSA dehydration with molecular sieves or TEG absorption dehydration for WDPA (Barton et al., 2017; Araújo et al., 2017). Since the MP driving-force is the retentate-permeate fugacity dif- ference, the main MP drawback is the power required to provide such https://doi.org/10.1016/j.jngse.2019.03.014 Received 10 November 2018; Received in revised form 5 February 2019; Accepted 17 March 2019 ∗ Corresponding author. E-mail addresses: laracb@eq.ufrj.br (L.C. Barbosa), ofelia@eq.ufrj.br (O.d.Q.F. Araújo), jlm@eq.ufrj.br (J.L. de Medeiros). Journal of Natural Gas Science and Engineering 66 (2019) 26–41 Available online 23 March 2019 1875-5100/ © 2019 Elsevier B.V. All rights reserved. T