A Study On The Microchannel Reactor For The Direct Ammoxidation Of Propane To Acrylonitrile

Acrylonitrile(ACN)is an important chemical raw material for synthesizing fibers,resins,rubbers,and so on.Replacing propylene with less expensive and more abundant propane has tremendous advantages in reducing the ACN production cost.However,propane ammoxidation(PAO)is a highly exothermic reaction.Efficient heat transfer and elimination of hot spots in the catalyst bed are keys to the successful practice of PAO.This work systematically investigated the potential application of a microchannel reactor in PAO to produce ACN by taking the advantage of the efficient heat transfer of microchannel reactor.In the PAO reaction,it was found that the catalytic selectivity and the stability of the MoVTeNb oxide catalysts are very sensitive to the reaction temperature.To obtain a higher yield of ACN while maintaining high catalyst stability,the reaction temperature should be precisely controlled in a narrow temperature window of 440-450?.At a reaction temperature of 440 ?(0.3 g;C3H8:NH3:O2:He = 6:7:17:70;60 mL/min),the temperature gradient in a conventional fixed bed tubular reactor(CFBTR)with an inner diameter of 4 mm is as high as 43.2 ?.The hot spots formed in CFBTR lead to rapid catalyst deactivation and decreased selectivity to ACN.However,the temperature gradients in a microchannel reactor(0.5 x 12.7 x 80 mm)can be maintained at less than 0.5 ? to ensure the stable and efficient operation of PAO reaction,owing to efficient heat transfer of a microchannel reactor.By taking the advantage of the excellent heat transfer of a microchannel reactor,the PAO reaction be operated even under harsh conditions.It was found that the space time yield of ACN increases from 169.0 kmol/(m3 h)to 189.9 kmol/(m3·h)when the gas hourly space velocity increases from 12000 mL/(h·g)to 18000 mL/(h·g).Meanwhile,the space time yield of ACN increases from 169.0 kmol/(m3·h)to 360.5 kmol/(m3·h)when the content of helium in the feed gas reduces from 70%to 40%.At the same time,the temperature gradient in the catalyst bed is less 1 ? at such harsh reaction conditions.These results indicate that a microchannel reactor has potential applications for the PAO reaction.However,due to the harsh reaction conditions,especially at the high oxygen partial pressure,the M2 phase in the MoVTeNb oxide catalysts is unstable.Even though the M1 phase in the MoVTeNb oxide catalysts is stable at high oxygen partial pressure,the selectivity of ACN is too low over to limit its applications in microchannel reactor under harsh conditions.P doped M1 phase MoVTeNb oxide catalyst was systematically studied aiming to address the issue of its low selectivity to ACN.Experimental results show that the introduction of P can reduce the amount of the lattice oxygen on the catalyst surface and weaken its ability of oxidation.Compared with the pure M1 phase catalyst,the P doped pure M1 phase catalyst can efficiently suppress the deep oxidation of PAO at a similar conversion of propane.Under low content of He inert gas and high content of oxygen reaction condition,good catalyst stability and high selectivity to ACN(65.4%)can be achieved,leading to space time yield of ACN as high as 397.9 kmol/(m3·h)?Hence,combination of the P doped pure M1 phase catalyst and microchannel reactor technologies may offer potential opportunities for the industrial practice of the PAO reaction.In summary,a microchannel reactor can effectively solve the problem of the high exothermicity in the PAO reaction thanks to its efficient heat transfer.Furthermore,combination of the P doped pure M1 phase catalyst and microchannel reactor technologies may offer potential opportunities for the commercial practice of the PAO reaction.