Tuning the selectivity of light hydrocarbons in natural gas in a family of isoreticular MOFs

Abstract

Purification of methane from other light hydrocarbons in natural gas is a topic of intense research due to its fundamental importance in the utilization of natural gas fields. Porous materials have emerged as excellent alternative platforms to conventional cryogenic methodologies to perform this task in a cost- and energy-efficient manner. Here we report a new family of isoreticular chiral MOFs, prepared from oxamidato ligands derived from natural amino acids L-alanine, L-valine and L-leucine, where, by increasing the length of the alkyl residue of the amino acid, the charge density of the MOF's channels can be tuned (1 > 2 > 3), decreasing the adsorption preference towards methane over light hydrocarbons thus improving this purification process. The validity of our rational design strategy has been proved by a combination of single-component adsorption isotherms, adsorption kinetics of CH4, C2H6, C3H8 and n-C4H10, and breakthrough experiments of binary CH4/C2H6 and CH4/C3H8 mixtures. ; This work was supported by the mineco (Spain) (Projects CTQ2013-46362-P, MAT2013-45008-P, MAT2016-81732-ERC, CTQ2016-75671-P and Excellence Unit "Maria de Maeztu" MDM-2015-0538), the Generalitat Valenciana (Spain) (Project PROMETEOII/2014/070, PROMETEOII/2014/004) and the Ministero dell'Istruzione, dell'Università e della Ricerca (Italy). T. G. and M. M. thank the Universitat de València and the mineco for predoctoral contracts. Thanks are also extended to the Ramón y Cajal Program (E. P. and E. V. R.-F. (RYC-2012-11427)). B. S. and J. G. acknowledge the financial support of the European Research Council under the European Union's Seventh Framework Programme (FP/2007-2013)/ERC Grant Agreement no. 335746, CrystEng-MOF-MMM.