Abstract
The separation of styrene (St) and ethylbenzene (EB) mixtures is important in the chemical industry. Here, we explore the St and EB adsorption selectivity of two pillar-shaped macrocyclic pillar[n]arenes (EtP5 and EtP6; n = 5 and 6). Both crystalline and amorphous EtP6 can capture St from a St-EB mixture with remarkably high selectivity. We show that EtP6 can be used to separate St from a 50:50 v/v St:EB mixture, yielding in a single adsorption cycle St with a purity of >99%. Single-crystal structures, powder X-ray diffraction patterns, and molecular simulations all suggest that this selectivity is due to a guest-induced structural change in EtP6 rather than a simple cavity/pore size effect. This restructuring means that the material “self-heals” upon each recrystallization, and St separation can be carried out over multiple cycles with no loss of performance.
Highlights
Styrene (St) is an important aromatic feedstock in the chemical industry.[1]
St is mainly produced by dehydrogenation of ethylbenzene (EB):[2] after dehydrogenation, the product stream still contains a large fraction (20−40%) of unreacted EB that must be removed.[3]
Pillar[n]arenes (n = 5−15) were first reported in 2008 as a novel class of supramolecular host.[12−22] The host−guest properties of pillar[n]arenes have been investigated intensively and they have been applied in the fabrication of various supramolecular systems, such as interlocked structures, molecular machines, supramolecular polymers, and supramolecular amphiphiles.[12−20] There are only a few occasions where pillar[n]arenes have been used as solid materials
Summary
Styrene (St) is an important aromatic feedstock in the chemical industry.[1]. More than 80% of St production is used for polymerization or copolymerization to produce thermoplastics, synthetic rubbers, and resins. We investigate two pillararenes with different cavity sizes, perethylated pillar[5]arene (EtP5) and pillar[6]arene (EtP6) (Figure 1b), as adsorptive separation materials to separate St and EB. The adsorption of St or EB by EtP6α triggers a crystal transformation from EtP6α to St@EtP6 or EB@EtP6, respectively
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