Methane/nitrogen separation by SMB using UiO - 66(Zr)_(COOH)2

Nowadays, natural gas (NG) has been widely studied as an alternative to petroleum-based fuels. However, when extracted from unconventional sources, it is contaminated with N 2 . Its removal is industrially done by cryogenic distillation, which is an extremely energy-intensive process. Therefore, adsorption-based methods are of particular interest, and the application of metal–organic frameworks (MOFs) in adsorption-based processes focus on separating different mixtures. This way, the goal of this work was to test a functionalized zirconium-based MOF, the UiO-66(Zr) _ (COOH) 2 , to be used in a gas-phase simulated moving bed (SMB) process for the purification of nitrogen contaminated methane streams, which is the case of methane obtained from shale gas, landfill gas and coalbeds. The adsorbent material was supplied by KRICT (Korea Research Institute of Chemical Technology) as granules. Firstly, the adsorption isotherms of pure C 2 H 6 were determined at 303, 333, and 373 K. The dual-site Langmuir (DSL) isotherm was used to fit the experimental results. The equilibrium data for ethane was compared with previously measured data for CH 4 , N 2, and CO 2 . The affinity of the gas towards the adsorbent has the following order, CO 2 > C 2 H 6 ≫ CH 4 > N 2 , from the most adsorbed to the less adsorbed at 303 K and 1.5 bar. At 333 K and 1.5 bar, C 2 H 6 exhibits the highest uptake. Single, binary, and pseudo-ternary breakthrough curves were performed at 333 K and 1.5 bar. These experimental results allowed experimental validation of adsorption equilibrium predicted by the multicomponent extension of the DSL isotherm and the validation of the fixed-bed mathematical model, as well as the evaluation of the ability of the eluent of displacing the mixture and its own displacement by the mixture. Lastly, a gas-phase SMB process was designed, based on the simulation of the separation regions for each one of the target desorbents, operating at 303 K and 1.5 bar, using four-zone unit configuration (2–3–2–1), in a closed-loop. This process allows the production of a methane stream with 99.56% purity and 99.65% recovery and a nitrogen stream with 99.73% purity and a recovery of 99.58%, showing the potential of this technology for the separation of CH 4 /N 2 mixtures.