The reaction network for the oxidation of propylene over a bismuth molybdate catalyst

Abstract

An initial-rate study was conducted to determine the kinetics of the oxidation of acrolein over a bismuth molybdate catalyst. The results were combined with results from a previous initial-rate study of propylene oxidation on the same catalyst to develop a quantitative description of the reaction network for propylene oxidation.The redox steady-state model with half-order in oxygen which provided the best fit to the propylene oxidation data also provided the best fit to the acrolein oxidation data. The disappearance of propylene occurs through parallel reactions to acrolein, carbon oxides, and acetaldehyde, with subsequent oxidation of the acrolein to carbon oxides.Une Ctude de vitesse initiale a it6 effectuCe afin de determiner la cinktique de I'oxydation de I'acrolCine sur un catalyseur de rnolybdate de bismuth. Les rksultats ont CtC combinks h des donnCes antCrieures sur I'Ctude de vitesse initiale de I'oxydation du propyltne sur le rn&rne catalyseur pour rnettre au point une description quantitative du rCseau de rtaction pour I'oxydation du propyltne.Le modtle permanent d'oxydo-rCduction d'un demi-ordre en oxygtne qui concorde le mieux avec les donntes d'oxydation du propykne, est celui qui prCsente Cgalernent la rneiUeure concordance avec les donnks d'oxydation de I'acroltine. Le propyltne disparait lors de rCactions paralleles produisant I'acroltine, les oxydes de carbone et I'acCtaldChyde, suivies de I'oxydation de I'acrolCine en oxydes de carbone.he overall objective of this research was to develop a T quantitative description of the reaction network for the oxidation of propylene over a bismuth molybdate catalyst. An initial-rate study of propylene oxidation was completed first (Tan et al., 1988), using a joint criterion design for model discrimination and parameter estimation (Tan et al., 1989). The present paper reports the results of the final two stages of the work, namely, an initial-rate study of the oxidation of the intermediate acrolein, and the combination of propylene and acrolein results to develop a quantitative description of the reaction network.The first point to be resolved when modelling a reaction network is whether the individual steps can be adequately described by the same kinetic model form. Different model forms can be used for each step but the network model is simpler if this is not necessary. In the case of propylene and acrolein there are reports of different models being required for each (Cartlidge et al., 1975, using bismuth molybdate, and Forissier et al., 1979, using iron molybdate).

Kinetic Modeling of the Partial Oxidation of Propylene to Acrolein: A Systematic Procedure for Parameter Estimation Based on Non-isothermal Data

“…The formation of acetaldehyde seems to take place in a parallel reaction from propylene ( r 5 ) by C–C bond scission, as can be concluded from the nonzero initial slope of the yield–time curve. This is also in good agreement to a variety of experimental data reported elsewhere. − ,,,,, Since the selectivity to acetaldehyde increased or stayed almost constant with an increasing conversion of propylene, it is concluded that acetaldehyde is also produced by an additional consecutive reaction. In this regard, it can be assumed that a further oxidation step of acrolein ( r 6 ) results in acetaldehyde. ,, In both reactions, oxidation of propylene and oxidation of acrolein, the C–C bond scission to form acetaldehyde leads to carbon oxides as additional byproducts.…”

“…This behavior indicates that acetaldehyde is formed by a parallel reaction from propylene which is in very good agreement to studies reported in literature. [2][3][4]7,8,35,36,47 The strong increase of the formation at conversion levels higher than 80% further provides evidence for a consecutive reaction. The results from the variation of the feed composition (molar ratios) further substantiate the conclusion that acetaldehyde is formed in a parallel as well as consecutive reaction.…”

“…This is also in good agreement to a variety of experimental data reported elsewhere. [2][3][4]7,8,35,36,47 Since the selectivity to acetaldehyde increased or stayed almost constant with an increasing conversion of propylene, it is concluded that acetaldehyde is also produced by an additional consecutive reaction. In this regard, it can be assumed that a further oxidation step of acrolein (r 6 ) results in acetaldehyde.…”

“…This two-step mechanism (reduction and reoxidation) is well-known as a redox mechanism and can be modeled by the reaction rate approach proposed by Mars and van Krevelen (MvK). Even though the mechanism of oxidation reactions on metal oxide catalysts is understood quite well, only a few kinetic models for the catalytic propylene oxidation are based on the MvK approach. − …”

Spatial activity profiling along a fixed bed of powder catalyst during selective oxidation of propylene to acrolein

“…14,20 Beside the target product acrolein, various by-products originating from parallel and/or consecutive reactions are known. Thus, complex reaction networks [20][21][22][23][24][25][26][27] have been proposed to elucidate the origin of by-products including carbon monoxide, carbon dioxide, acrylic acid, acetic acid, acetaldehyde, formaldehyde, and others. From an industrial point of view, knowledge of reaction networks is essential to understand the processes taking place inside the reactor.…”