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

Abstract

On the basis of non-isothermal experiments in an integral pilot-scale reactor, the heterogeneously catalyzed gas phase oxidation of propylene to acrolein was investigated at industrial relevant process conditions. From an extensive experimental data set both reaction scheme and reaction rates were derived. Beside the main components propylene, oxygen, acrolein, and water, the proposed reaction network includes a variety of side products. The reaction rates were modeled by a semi-mechanistical approach given by Mars and van Krevelen. On the basis of a two-dimensional, pseudohomogeneous reactor model, the kinetic parameters were estimated successfully by introducing a systematic procedure for a stepwise determination using different regions with different characteristics to estimate the pre-exponential factors and activation energies individually, i.e., separate from each other. The model is able to predict the data included in the parameter estimation and independent data measured at different process conditions as well. Furthermore, it provides reliable results for an industrial plant.

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

“…However, with decreasing temperature along the catalyst bed also a decreasing gradient in acrylic acid selectivity was observed. This indicates that after ignition of the reaction and hotspot formation within the first 6 mm of the bed, high temperatures promote the further oxidation of acrolein to acrylic acid, which is in line with the results of Ganzer and Freund 27 . Moreover, as the profiles in the present study match quite well with the pilot plant data 27 , it seems that on such a small lab reactor data close to pilot/industrial plants can be derived.…”

“…This indicates that after ignition of the reaction and hotspot formation within the first 6 mm of the bed, high temperatures promote the further oxidation of acrolein to acrylic acid, which is in line with the results of Ganzer and Freund 27 . Moreover, as the profiles in the present study match quite well with the pilot plant data 27 , it seems that on such a small lab reactor data close to pilot/industrial plants can be derived. Notably, similar profiles for all quantified gas phase species were obtained and the temperature profile including the location of the hotspot could be reproduced.…”

“…On one hand, formation of CO and CO 2 started at the beginning of the catalyst bed resulting in similar amounts. Thus, both are initially formed from propylene with nearly similar rates, confirming the results of Ganzer and Freund 27 . On the other hand, the yield profiles of CO and CO 2 differed along the bed, which reveals the presence of consecutive reactions attributing to their formation.…”

“…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.…”

“…29 In general, such data is rare in the case of selective oxidation of hydrocarbons. 41 Nevertheless, Ganzer and Freund 27 recently showed that spatially resolved, non-isothermal data enables the development of detailed reaction networks for selective propylene oxidation. The data was obtained during complex experiments on a pilot plant with irregularly positioned side-inserted sampling devices.…”