Kinetics of the Reaction of CO2/CO Gas Mixtures with Iron Oxide

Abstract

The kinetics of the oxygen exchange reaction between carbon dioxide and carbon monoxide were measured on iron, wu¨stite, and magnetite surfaces. This was done through the use of an isotope exchange technique. The measured rate constants are dependent on the oxygen activity. This dependence is expressed by k a = k o a O Àm . The parameter m was found to have values between 0 and 1. It was found that, in the iron region, the apparent rate constant was independent of the oxygen partial pressure (i.e., m = 0) at 1123 K (850°C) and that it was inversely dependent on the oxygen partial pressure (i.e., m = 1) for the magnetite region at 1123 K (850°C) and 1268 K (995°C). In the wu¨stite region, m was found to be equal to 0.51, 0.66, and 1.0 for the w 1 , w 2 , and w 3 pseudo phases, respectively, at 1268 K (995°C). At 1123 K (850°C), in wu¨stite, m was found to be equal to 0.59 and to 1.0 for the w 1 ¢ and w 3 ¢ pseudo phases, respectively.

Interfacial Rate of CO2^|^ndash;CO Reaction with the Solid Iron and Iron Oxide by Isotope Exchange Technique at 1273 K

“…The values of the slopes of the lines in this study and other researches 1,20,24) were shown in Table 3. It can be found that the slopes from this work are different from the other results by Grabe, 1) Meschter and Grabke, 24) and Worral and Coley.…”

“…Worral and Coley 20) reported there are three straight lines in wüstite region, but the results in w1 and w2 were so close, if the error of ±0.03-0.05 was considered, the difference between 0.51 and 0.66 will become smaller. In w3 region near magnetite phase, their results were similar to the present work.…”

“…It can be found that the slopes from this work are different from the other results by Grabe, 1) Meschter and Grabke, 24) and Worral and Coley. 20) To explain the relationship between rate constant and CO 2 /CO ratio, Grabke 1,2) proposed a theory of defect structure according to the electron transfer mechanism for the CO 2 reaction with iron oxide. However, it is difficult to accurately describe the interfacial kinetics because the defect structure of iron oxide such as wüstite and magnetite is much more complicated than assumed by Grabke. According to the usual understanding, CO 2 dissociation on the surface of metal and oxides containing iron oxide can be expressed as follows: If the electron can be considered as a chemical entity, 25) the rate of CO 2 dissociation will be expressed as Eq.…”

“…Therefore, the kinetics of CO2-CO reaction with the solid iron oxide became more important. However, the research works using the isotope exchange method were only carried out by Grabke 1,2) and Worral and Colley 20) up to now, and their results are not fully consistent.…”

“…From the 1960s, the isotope exchange technique, as an effective experimental method to study the interfacial kinetics between gas and iron oxide, has been extensively used by many researchers in metallurgical field. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] Recently, in order to meet the strong demand on the utilization of low grade iron ores and reduction of CO2 emission, the direct reduction of fine iron ore, as an innovative ironmaking process, has been given more attention. Therefore, the kinetics of CO2-CO reaction with the solid iron oxide became more important.…”