Catalytic Vapor Phase Epoxidation of Propene with Nitrous Oxide as an Oxidant: Investigations on Catalyst Composition and Reaction Conditions

Abstract

The vapor phase epoxidation of propene with nitrous oxide (N 2 O) was experimentally investigated in a fixed bed reactor using different Cs x /Fe y /SiO 2 catalysts. This was done with a systematic approach which comprises the derivation of kinetic parameters for directly comparing catalyst performance. Therefore, kinetic measurements were made for each catalyst by variation of the residence time. It was found that the addition of an alkali promoter to the Fe y /SiO 2 catalyst is essential for the formation of propylene oxide and a proper alkali/Fe molar ratio is crucial for both activity and selectivity. Maxima in both activity and selectivity were observed for alkali/Fe ratios in the region 1.2-1.7. A further increase in activity without any loss in selectivity was obtained by adjusting the calcination temperature to 783 K. The conversion of PO was used as a tool to measure the product stability and a minimum reaction rate was also found for alkali/Fe ratios in the region 1.2-1.7. The promoter is responsible for the formation of active centers and it reduces surface acidity which leads to an increased stability of PO through the inhibition of the consecutive conversion. Maximum selectivities to PO of about 40% at 5-10% conversion were achieved at moderate reaction temperatures of 648 K. Because of parallel and consecutive formation of carbonaceous deposits on the catalyst, the catalyst deactivated within 2 h of operation to a remaining activity of around 40%. Neglecting the carbonaceous deposits as a reaction product and considering only the vapor phase products, PO selectivity is more than 75% at 5-10% propene conversion. The attempt to slow down the deactivation through the addition of supplementary gases (H 2 , O 2 , NH 3 , H 2 O) was partially successful, but unfortunately this is always accompanied by lower PO selectivity.

Effect of size of catalytically active phases in the dehydrogenation of alcohols and the challenging selective oxidation of hydrocarbons

“…159 The FeO x -catalysed C 3 H 6 epoxidation by N 2 O was further studied by several research groups. [160][161][162][163][164][165][166][167][168][169][170][171] An interesting phenomenon is the significant shift of reaction route from allylic oxidation to epoxidation due to modification of FeO x nanoclusters or nanoparticles by alkali metal ions. 161,162 For example, over the 1 wt% FeO x / SBA-15, the oxidation of C 3 H 6 by N 2 O produced mainly acrolein and CO x at 598 K, and almost no PO was formed.…”

Chemical and Technical Aspects of Propene Oxide Production via Hydrogen Peroxide (HPPO Process)

“…Several catalysts and several reaction conditions have been tested until now, but the results are very far from the industrial targets. − Duma and Hönicke in 2000 have proposed the use of N 2 O as oxidant for propene epoxidation to PO in gaseous phase, using silica supported iron oxide promoted with Na . However, this route suffers of low selectivity due to the formation of both carbonaceous deposits and other high molecular weight products …”

“…8 However, this route suffers of low selectivity due to the formation of both carbonaceous deposits and other high molecular weight products. 9 The most ancient industrial process developed to produce PO from propene is based on the dehydrochlorination of chlorohydrins (Chlorohydrin Route) (see scheme 1).…”

Visible light-triggered vanadium-substituted molybdophosphoric acids to catalyze liquid phase oxygenation of cyclohexane to KA oil by nitrous oxide

“…Furthermore, N2O is more conductive to selective oxidation than traditional air or O2 [1,21]. Considerable progress, therefore, has been achieved in catalytic oxygenations based on using N2O as an oxidant, which includes gaseous or liquid phase oxidation of aliphatic and aromatic hydrocarbons [21][22][23][24][25][26][27][28][29][30], alkenes [31][32][33][34], alcohols [23] and phosphines [35] under heterogeneous or homogeneous conditions. In these catalytic transformations, the use of a N2O-containing stream for hydroxylation of benzene to phenol catalyzed by Fe-ZSM-5 zeolite [24][25][26][27][28] is highly appreciated because its product phenol can be hydrogenated into cyclohexanol to complete N2O cycle [29].…”