Anaerobic Oxidation of Propene to Acrolein in a CFBR Reactor

Anaerobic Oxidation of Propene to Acrolein in a CFBR Reactor 

Elf Atochem (now Arkema) and Du Pont have claimed a cycle process for the oxidation of propene to acrolein [70a]. In a first transport-bed reactor (a riser, where the catalyst is transported upwards by the gas) propene is put in contact with the catalyst, a Bi/Mo/W/ 

Co/ Fe mixed oxide, while in the second one, a fluidized-bed reactor, the catalyst that in the first step has been reduced by the olefin is reoxidized with air. The catalyst is continuously transported from the first reactor to the regenerator, by means of a C FB R. 

The best per pass yield to C2 + C3 products (aldehydes plus acids with two and three C atoms) with the said catalyst was obtained at a propene conversion of 61.3% (selectivity to acrolein 83.7%), at the reaction temperature of 355 °C, with the following feed composition C3H6/H20/N2 11.6 10.0 78.4 (mol.%), with a gas contact time of 2.4 s. A decrease in solids circulation rate, while keeping gas residence time constant, led to a considerable decrease in propene conversion, while selectivity to C2 + C3 oxygenated products was not much affected by circulation rate. With a less concentrated feed, the amount of solid to be circulated for a defined olefin conversion is lower, but productivity also becomes lower. Other catalysts based on Bi/Mo/O or on V/Mo/W/Cu/O [72c] afforded conversions 70% and selectivity 90% industrial 

Although the reaction is very selective, the re-oxidation step remains a crucial point that limits the overall productivity of the process. In this regard, it was found that it is possible to obtain a high selectivity to menadione even when starting from the partially oxidized catalyst, instead of the fully oxidized one. In other words, there is no need to re-oxidize the reduced POM (a = 0) completely, but a partial reoxidation (a = 0.25) is sufficient to obtain a POM that can be used for the successive synthetic step by contact with 2-methyl-l-naphthol [75]. This is an advantage compared to the 

Several papers describe the anaerobic ODH of alkanes to olefin with catalysts based on metal oxides [77-83]. In many cases, an improved selectivity to the olefin as compared to the co-feed operation has been aciiieved in other cases, no effective improvement has been reported. For instance, catalysts made of V20s-Si02 showed a remarkably improved selectivity to propene with respect to the co-feed conditions for propane ODH, whereas the same remarkable effect was not observed with catalysts 

One condition for obtaining an improved selectivity with the cycle operation is the presence of catalysts in which V sites are highly dispersed this was achieved by preparing vanadium oxide-silica co-gels, with a V2O5 content lower than 10% [77b,ej. The improvement in selectivity to propene was around 30 percentage points (60% selectivity in cyclic mode versus 30% in co-feed mode) for a propane conversion of 35%. 

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