Catalyst color change issue
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The catalysts in our plant’s converters have changed color after being used; some of their surfaces have turned blue while others have turned black. I’m not sure what the reason for this is
Changes in the color of sulfuric acid catalysts are often due to changes in the valence state of vanadium within the catalyst. For details, please refer to pages 593–595 of Volume 2 of the “Practical Manual on Sulfuric Acid Production Process, Equipment Installation Construction Techniques, and Quality Inspection and Testing Standards”. This book is available on this forum and can be downloaded. Personally, I think this set of books is okay overall, but there are too many spelling mistakes.
Thank you for posting! Turning blue indicates that the catalyst is damp, while turning black means scarring has formed on its surface (iron sulfate adhering to the catalyst).
The surface of the catalyst turns blue; this is mainly the color of tetravalent vanadium. Generally speaking, this color is harmless. The surface turns black; it is usually trivalent vanadium. If there is no refractory lining inside the converter and the steel plate comes into direct contact with the catalyst, then during cooling, the V2O5 in the portion of the catalyst adjacent to the steel plate is reduced by iron.
The black color is likely due to the catalyst becoming inactive, which is caused by a rapid rise in temperature during intake. The blue color probably results from the catalyst coming into contact with moisture; this shouldn’t have much effect on the catalyst itself
When a catalyst becomes damp, it usually turns green; blue or black colors may also be caused by high levels of arsenic in the smoke!
The green one is probably damaged due to moisture exposure; the white one is likely ruined because of excessive heat