Synchronous zeolite shaping and pore-size regulation for effective selective adsorption of thiophene from crude benzene

Abstract

Shaping technology using the binder is critical to the application of the powdered material. However, the binder wrapping and blockage usually decrease the performance of the powder material. This work thus investigates a method forming a binder-free monolith Y zeolite by citric-acid treatment. The powdered and monolith zeolites are compared in selective adsorption of thiophene from crude benzene. Ce modification results in the best adsorption capacity of 13.5 mg g⁻¹ for thiophene among all transition-metal modifications. After the shaping, the adsorption capacity is even increased to 14.9 mg g⁻¹. Moreover, its adsorption selectivity of thiophene from benzene is bigger than 84 % at 30–60 °C. In the cyclic adsorption for three turns, the capacity maintains a stable value between 14.6 and 14.9 mg g⁻¹. According to the mechanism investigation, pore sizes of the powdered and monolith zeolites are concentrated at 0.48–0.8 nm and 0.6 nm, respectively. The size of the monolith zeolite allows diffusion in of thiophene (0.53 nm) but excludes the toluene (0.65 × 0.68 nm), which results in the high selectivity. Thiophene is both adsorbed by Brönsted acidic sites and Ce(OH)₂²⁺ sites. The main result of this work thus puts forward a useful route for the zeolite shaping.