Controllable and scalable synthesis of hollow-structured porous aromatic polymer for selective adsorption and separation of HMF from reaction mixture of fructose dehydration

The hollow-structured porous aromatic polymers (H-PAP) with cavity diameter from 228 ± 11 to 464 ± 15 nm were controllably prepared through surface coating and template-etching method under scalable synthesis conditions from standard scale to 20-fold scale-up. It is found that the fill factor (f) of reactor is an important parameter for determining the scalability of synthesis. Benefiting from the favorable textural properties, chemical and thermal stability, surface hydrophobicity and π electrons, the well-developed H-PAP as adsorbent was investigated in selective adsorption of 5-hydroxymethylfurfural (HMF) under static batch mode from the single-component and multi-component aqueous solutions. The H-PAP shows an exclusive adsorption for HMF, without adsorption of fructose, levulinic acid (LA) and formic acid (FA), and can be recycled three times without significant decrease in adsorption capacity. Structure-performance relationship points out that the apparent amount of HMF adsorbed on H-PAP is related to micropore surface area, micropore volume and cavity diameter, while HMF selectivity depends on surface hydrophobicity. In the case of HMF adsorption from the real reaction mixture of acid-catalyzed fructose dehydration, the HMF constituent with high purity (ca.94.4%) can be recovered. Combining the adsorption isotherms with DFT calculation reveals adsorption mechanism that HMF adsorption on H-PAP proceeds initially via π-π stacking interaction, and then assembles into regular array around spherical surface to form monolayer coverage following modified Langmuir model, and finally diffuses into interior cavity until adsorption saturation.