Optimizing Host–Guest Selectivity for Ethylbenzene Capture Toward Superior Styrene Purification

The
separation of ethylbenzene (EB) and styrene (ST) mixtures to
obtain pure ST has been an enduring challenge for the petrochemical
industry. So far, adsorptive separation using porous materials has
mainly focused on capturing ST rather than EB, where high temperatures
are needed to reactivate the sieving materials and collect the product.
Here, we tuned the host–guest interactions in thienothiophene-based
trianglimine (ThT-TI) macrocycles to selectively adsorb
the unreacted EB over ST, after a dehydrogenation reaction, to readily
provide pure ST without the need for further thermal treatments. This
is the first report on the selective adsorptive separation of EB over
ST using macrocycles as molecular hosts. Both crystalline and amorphous ThT-TI can be used to separate EB with 96% uptake capacity.
Single-crystal and powder X-ray diffraction patterns suggest that
this selective adsorption arises from a guest-induced structural reordering
and involvement of the sulfur atoms in host/guest C–H···π
interactions. We believe that this work paves the way for a new generation
of molecular sieves that are designed to afford high-purity products
by in situ capturing of the unreacted starting materials.