Partial Oxidation of n-Butane in a Solid Electrolyte Membrane Reactor

Abstract

The partial oxidation of n-butane to maleic anhydride ͑MA͒ in a solid electrolyte membrane reactor was studied in three different operation modes: electrochemical membrane reactor ͑EMR͒, cofeed membrane reactor ͑CR͒, and mixed-feed membrane reactor ͑MMR͒. The EMR operation exhibited lower selectivity to MA but higher conversion of oxygen than the CR operation. The electrochemical oxygen pumping in the MMR operation led to decrease in the MA selectivity compared to the CR operation. By means of comparing the three operation modes, the electrochemically pumped oxygen was found to be more reactive but less selective to MA than gas-phase oxygen, which is directly related to the different reaction mechanisms between the CR and EMR operations. The butane oxidation occurred in the EMR involved not only the same catalytic reaction mechanism as in the CR but also an electrocatalytic reaction. A simplified catalytic and electrocatalytic reaction-mechanism scheme was proposed for the butane oxidation carried out in the EMR.Maleic anhydride ͑MA͒, produced by partial oxidation of n-butane over vanadium phosphorous oxide ͑VPO͒ catalyst, is a versatile monomer and an important chemical intermediate with many uses such as unsaturated polyester resins, lubricating oil additives, agricultural products, and pharmaceuticals. The oxidation of n-butane to MA is recognized as one of the most complex reactions involving light alkanes, 1-4 which includes eight hydrogen atoms abstraction and three oxygen atoms insertion with 14 electrons transferring. VPO catalyst is the unique catalyst used in this reaction. It is commonly accepted that the vanadium oxidation state of VPO catalyst plays an important role in the catalyst selectivity and activity and that the best VPO catalyst for MA production should possess an optimal V 4+ /V 5+ ratio. [5][6][7][8] Despite the fact that the oxidation of butane to MA has been intensively studied by numerous scientists, the respective roles of oxygen species in the selective and nonselective oxidations are still far from clear. 1 Gas-phase oxygen, lattice oxygen, and activated chemisorbed oxygen have been proposed as the possible active species in the formation of the desired product MA and undesired products CO x . [9][10][11][12][13] Though MA production processes have been commercialized in fixed-bed and fluidized-bed reactors, all these reactors still suffer from disadvantages such as the demand of high attrition resistance of the catalyst in fluidzed-bed reactors and the possible hot spots and explosive mixtures in fixed-bed reactors. Recently, in order to increase the MA selectivity and also to overcome the limitations of these conventional reactors, Mallada et al. 14,15 have intensively studied the application of inert porous membrane reactors to butane partial oxidation. In our previous work, 16,17 we have demonstrated the feasibility of MA synthesis in an electrochemical membrane reactor ͑EMR͒ using a dense solid oxide electrolyte membrane, where the oxygen required for the butane oxidation was su...

Reaction induced current generation by butane oxidation in high temperature electrochemical membrane reactor

“…The observed current increase with butane containing feed gas in the anodic feed could be explained by immediate oxidation reactions on the Au electrode which lowered the oxygen concentration. However, this observation is not in a direct agreement with the observation of Ye et al where only negligible reactions of butane were observed on the Au anode in the membrane reactor Au|YSZ|Pt-Ag [24]. It should be noticed here that the measurements by Ye et al were carried out under oxygen pumping mode (EOP), which is not directly comparable with our present study.…”

“…York et al [6] investigated the electrochemical butane oxidation with an Au|YSZ|Ag cell. At reaction temperature of 723 K and an applied current of 4.5 mA, no MA was detected under electrochemical oxygen pumping conditions, which is in agreement with the observations of Ye et al [24] with Au|YSZ|Pt-Ag reactor at 753 K. Based on these literature reportings and our own results, we might conclude that the formation of MA is not occurring on the Au electrode surface.…”

“…8 As we see all the reactions are highly exothermic including remarkable release of Gibbs free energy, and therefore highly interesting to electrochemical processing. It is to be expected that it is not only the MA formation which induces the detected current in our investigations, but also the total oxidation of butane to CO/CO 2 is highly probable, as observed as competitive reactions to the formation of MA by numerous investigations by Ye et al under oxygen pumping conditions [15,24,26]. Furthermore, the current might be induced also by the overoxidation of MA to CO/CO 2 according to reactions (4) and (5) as well.…”

“…The maximum reaction induced current in the present investigation, 0.3 mA, corresponds to the oxygen flow of 7.77 × 10 −10 mol/s (2.98 × 10 −11 mol/(s cm 2 )). The operation in EMR with measurable quantitative results is only possible with applied voltage in the EOP modus as reported in [15,24,26]. The applied voltage between the electrodes increased the current more than one order of magnitude (up to 120 mA in the studies of Ye et al) at the temperatures from 720 to 790 K, where quantitative measurable MA amounts were synthesized.…”

Bulk and Surface Properties of a VPO Catalyst Used in an Electrochemical Membrane Reactor: Conductivity-, XRD-, TPO- and XPS-study

“…In our EMR application, however, the catalyst is fixed on the electrolyte membrane in the anodic compartment, where the oxygen is supplied in a very low concentration. We have shown before [9,10,21,22], that under these conditions part of the transported oxygen ions is converted neither to MA nor to CO 2 or CO, but is recombined to gaseous dioxygen. Due to these parallel processes, the oxygen concentration in the anodic compartment can vary, which in turn might influence the conductivity.…”