Olefin/Paraffin Separation in Open Metal Site Cu-BTC Metal-Organic Framework

Adsorption in metal-organic frameworks with coordinatively unsaturated sites (CU's) offers a cost-effective alternative to cryogenic processes for olefin/paraffin separation. Since experiments on adsorption equilibrium of gas mixtures are challenging, molecular simulation methods can be exploited to characterize the adsorption at CU's. This work computationally addresses the adsorptive olefin/paraffin separation using Cu-BTC. To this end, we developed a parametrization of specific interactions between hydrocarbon molecules and the CU's, which is of great interest for the modeling community. We obtain the host-guest interacting parameters for linear hydrocarbons by fitting to experimental single-component adsorption isotherms of ethane, ethene, propane, and propene and examine their transferability to larger hydrocarbons. In addition, we propose force field parameters for branched isobutane and isobutene. We then predict the adsorption selectivity of the binary alkane/alkene mixtures for chains from two to five carbon atoms. Cu-BTC was found potential candidate for the separation, especially for isobutane/isobutene (iC4) mixtures. Besides, our results allowed the rationalization of the difference in the uptakes experimentally observed between both iC4 hydrocarbons.