Study Of The Deactivated Titanosilicate Zeolite Catalyst For The Methanol To Propylene Reaction

Propylene is an important bulk chemical.Methanol to propylene（MTP）reaction is an effective method through non-crude oil route to produce propylene using methanol as a platform molecule.Effective catalyst is the core of the methanol to propylene process.In this paper,we developed the process of methanol to propylene using deactivated TS-1 zeolite（De-TS）as catalyst.The structure of the active site was explored and modified by phosphorus.The influence of the Lewis acid site was discussed.The research content is divided into the following three aspects.1.Process conditions like reaction temperature,space velocity and partial pressure were investigated.The results showed that high reaction temperature was beneficial for the conversion of methanol,and it was unfavorable for the hydrogen transfer side reaction.But high temperature would promote the formation of aromatics and lead to rapid coke and deactivation of the catalyst.High space velocity and low partial pressure can reduce the secondary reaction,but they are not conducive to the long-term conversion of methanol.The appropriate reaction parameters are:reaction temperature=450℃,mass space velocity=3 h^-1 and methanol partial pressure=40 KPa.2.The structure of the active site was studied combined with nitric acid washing,K⁺exchange experiment and IR spectra in the OH vibration region.It was proved that there were two kinds of Br（?）nsted acid centers in the De-TS zeolite:Ti O₂-Si O₂ binary oxide and Si-OH（Ti）in the zeolite framework.The experimental results showed that the Si-OH（Ti）was the active center for the MTP process.We further developed phosphorus impregnation on the De-TS zeolite.It was found that both the acid amount and strength were weakened.The modified zeolite showed higher propylene selectivity and longer lifetime.The result of the Py-IR spectra,XPS and ³¹P MAS NMR characterization showed that the phosphoric acid not only interacted with the Br（?）nsted acid center Si-OH and formed a new weaker Br（?）nsted acid site,but also interacted with the Lewis acid center Ti-OH and transformed the Ti（Ⅳ）into Ti（Ⅵ）.Therefore,both the amount of Br（?）nsted acid site and Lewis acid site decreased.3.Based on the discrepancy between K⁺exchange and phosphorus modification in adjusting the Br（?）nsted and Lewis acid sites,the influence of Lewis acid site on the MTP process was studied.It was indicated that although the Lewis acid site may have an inhibiting effect on the aromatic cycle,it can contribute to the formation of formaldehyde,which is toxic for the lifetime of the catalyst in the MTP process.