Effect of Phosphoric Acid on HZSM-5 Catalysts for Prins Condensation to Isoprene from Isobutylene and Formaldehyde

Abstract

A series of HZSM-5 zeolites modified with different amounts of phosphoric acid(P/HZSM-5) was pre-pared. The physicochemical features of the P/HZSM-5 catalysts were characterized via X-ray diffraction(XRD), N₂ adsorption-desorption, NH₃-temperature programmed desorption(NH₃-TPD) and Fourier tranform infrared(FTIR) spectra of the adsorbed pyridine, and the performances of the catalysts for Prins condensation to isoprene from iso-butylene and formaldehyde were investigated. The maximum isobutene conversion and isoprene selectivity were 10.3% and 94.6% on the HZSM-5 catalyst with a Si/Al molar ratio of 600 using 5%(mass fraction) phosphoric acid. The phosphoric acid modification not only modulated the amount of acidic sites but also regulated the acid type. An appropriate amount of weak Lewis and Brönsted acid sites served as the active sites for the condensation of isobutene with formaldehyde, and the strong acid sites could cause side reactions and coke deposition.

Keywords

Isobutylene / Isoprene / Formaldehyde / HZSM-5 catalyst / Phosphoric acid modification

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