Modification of zeolite via acid-etching and coke-deposition for the selective transformation of propylene glycol and butylene glycol in ethylene glycol

Abstract

Biomass-derived ethylene glycol (EG) contains 1,2-propylene glycol (PG) and 1,2-butylene glycol (BG), which are difficult to isolate via traditional techniques. This paper presents a modification strategy of a zeolite catalyst through acid-etching and coke-deposition to achieve selective transformation of these diols. The diameters of mesopores were increased after the treatment with HCl, significantly enhancing the transport of the substrate and improving the conversions of PG and BG. According to the FTIR, Raman, NH₃-TPD, and titration results, the coke contained ether, aromatic, and phenolic groups. The coke selectively deactivated the strong Lewis acid sites over zeolite, suppressing the acetalization and ketalization reactions of EG. Meanwhile, the dehydration reactions of PG and BG as well as ring-closure and oligomerization reactions of EG were less dependent on these Lewis acid sites, and thereby these reactions were less affected by the deposition of coke. Therefore, the undesirable conversion of EG was inhibited without suppressing the reactivity of PG and BG. The reaction products were efficiently isolated from EG via a single-stage distillation process, and the purity and recovery of EG reached 90.3% and 93%. This modified catalyst demonstrated excellent stability over multiple reaction cycles, and it can be regenerated via simple calcination.