Entropy driven separations in nanoporous materials

There are many industrially relevant separation processes which are either not feasible by conventional methods (such as distillation or crystallization), or energetically very expensive. Examples are the separation of xylene isomers (important in the petrochemical industry for the production of PET), and the purification of styrene (necessary for the production of polystyrene). In these cases, separation based on adsorption in porous materials is an important alternative, from both an economic and an environmental point of view. The overall performance in adsorption based separation processes in porous materials depends on (1) the degree of preference of the material for a given mixture component, the selectivity, and (2) the amount that the material can adsorb, the capacity. This thesis focuses on studying and developing more economic and environmentally friendly adsorption-based separation mechanisms in porous materials for industrial applications. To fulfill this, we need separation mechanisms where both the selectivity and capacity can be combined. Many relevant industrial separations work at saturation conditions, to operate cost efficiently. In this regime, the separations are entropic in nature. Several entropy effects (mechanisms) that lead to mixture separations have previously been published: configurational entropy, size entropy and length entropy. The work in this thesis shows that none of these effects can be extended to large capacity-structures (they originate from tight confinement) and also presents two new entropic mechanisms: commensurate stacking and face-to-face stacking, that can be used in large pore structures and therefore offer an alternative path in the design of nanoporous materials for industrial separations.