Dirty shift catalyst

FeS also catalyzes the shift reaction, but its activity is only half that of Fe,04 [592]-[594], In principle the catalyst can tolerate up to 500 or 1000 ppm H2S, but with a considerable loss of mechanical strength, which is additionally affected by other contaminants in the gas, such as soot and traces of formic acid. For this reason the so-called dirty shift catalyst is used in this case, which was originally introduced by BASF [639]. This cobalt-molybdenum-alumina catalyst [603], [630], [640]-[644] is present under reaction conditions in sulfidized form and requires for its performance a sulfur content in the gas in excess of 1 g S/m3. Reaction temperatures are between 230 and 500 °C. COS is not hydrolyzed on dirty shift catalysts, but may be removed in the subsequent sour-gas removal stage using the Rectisol process. Separate hydrolysis on alumina based catalysts is possible at temperatures below 200 °C [603],... 

In later developments aditionally potassium carbonate promotion of the dirty shift catalysts was introduced [645], [646] which increased the activity at low temperatures to achieve CO values sufficiently low to use a methanation step after C02 removal. But according to [647] it is also possible to achieve such low CO concentrations with nonalkalized dirty shift catalyst as shown in Figure 65. 

Equations to describe reaction rate measurements on dirty shift catalyst are given in [648], [649],... 

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