Molecular sieving of linear and branched C6 alkanes by tannin-derived carbons

Two micro-mesoporous carbons (MMCs): a disordered mesoporous carbon (DMC) and an ordered mesoporous carbon (OMC), synthesized by an easy, low-cost, and green method are proposed as efficient hydrocarbon sieves for the separation of C6 isomers: n-hexane (nHEX), 2-methylpenthane (2 MP) and 2,2-dimethylbutane (22DMB). Their textural characterization reveals a highly interconnected pore network within the DMC, while a reverse hierarchy of ordered mesopores only accessible through narrow micropores is found in the OMC. The pore texture strongly affects their adsorption performance by kinetic and molecular sieving effects; the narrow constrictions in the OMC allow adsorption of nHEX and partially 2 MP but not 22DMB, whereas the highly connected pore network of DMC allows adsorption of the three isomers. Multi-component adsorption isotherms calculated from the single-component experimental results by ideal adsorbed solution theory (IAST) demonstrates that the OMC material has a remarkably high selectivity for the adsorption of nHEX and nHEX + 2 MP from binary and ternary mixtures, respectively. To the best of the authors’ knowledge, such behavior has never been reported so far for carbon materials. Hence, this study shows that tannin-derived MMCs have great potential to be used as an eco-friendly and low-cost alternative for the selective separation of di-branched C6 isomers. Jimena Castro-Gutiérrez gratefully acknowledges CONACYT-SENER for the scholarship awarded (601021/438978) to support her PhD studies, resulting in the work presented herein. This study was partly funded by the French PIA project "Lorraine Université d’Excellence”, reference ANR-15-IDEX-04-LUE, and TALiSMAN project, funded by FEDER (2019-000214). Joaquín Silvestre-Albero would like to acknowledge the financial support from MINECO (PID2019-108453GB-C21) and H2020 (MSCA-RISE-2016/NanoMed Project).