Due to similar properties, it is hard to separate corresponding olefins and paraffins. Currently, high-pressure distillation is used as purification method, which is energy-intensive and expensive. A cheaper, more efficient, less energy-intensive and cleaner method for separating olefins from paraffins would be very desirable. One of these alternative separation methods is adsorption, which is still in the research-phase. Commonly, it is the olefin that is preferentially adsorbed using this separation method, because of the strong interaction between the unsaturated bond of the olefin and a metal ion on the surface of the adsorbent material, forming a p-complex. Because the olefin is preferably adsorbed, it is the paraffin that is easily obtained in its pure form. Unfortunately, in industrial processes the desired product is the olefin (raw material for polymers) and not the paraffin. Therefore, adsorption is not an option to replace the current distillation columns (yet). However, when it is the paraffin that is selectively adsorbed, the olefin can be easily obtained in its pure form, which would make the adsorption process a very attractive alternative. Recently, for the first time, an adsorption material was found that was able to selectively adsorb the paraffin instead of the olefin. This research involved the selective absorption of ethyl chloride compared to vinyl chloride using the hybrid inorganic-organic material aluminum methylphosphonate polymorph alpha (AlMePO-a)1. The study was performed by a combined experimental-molecular simulation approach. However, it is still unclear why AlMePO-a selectively adsorbs the ethyl chloride compared to the vinyl chloride, and whether this material is also suited for other olefin/paraffin separations. We are using molecular simulations in order to understand the key factors determining the selective paraffin adsorption by AlMePO-a (molecular interactions, steric effects, rigidity) and to investigate the suitability of this material for other olefin/paraffin separations. The molecular model used for the material is the same developed in previous work2, while appropriate force fields are used for the different olefin and paraffins under consideration. Results will be presented and discussed at the conference.

This work is partially funded by the Spanish government (CTQ2005-00296/PPQ) and the Catalan government (SGR2005-00288). Supercomputing time from CESCA is also acknowledged.

References

1. Herdes, C.; Valente, A.; Lin, Z.; Rocha, J.; Coutinho, J. A. P.; Medina, F.; Vega, L. F.; Langmuir 2007, 23 (13), 7299-7305.

2. Herdes, C.; Lin, Z.; Valente, Z.; Coutinho, J.A.P.; Vega, L.F., Langmuir 2007, 22, 3097-3104.