Mopec Fume Exhaust Replacement Filters
Evaluating Potassium Permanganate Filters for Replacement
Filters contain alumina pellets impregnated with potassium permanganate (KMnO4), which is a fast oxidizer. Formaldehyde passing through the filter is converted to carbon dioxide and water. The filter’s life depends entirely on the amount of formaldehyde fumes passing through the filter.
The pellets are bright purple when new and become dark brown when exhausted. Once the inner part of the pellet is brown it is totally exhausted and must be replaced.
This media is very effective and essentially removes all formaldehyde as long as there is active potassium permanganate available. The efficiency drops off as you approach the end of the life of the pellet. The last 15% capacity will exhibit some pass through of formaldehyde.
Procedure: One corner of the filter will have a small tab which can be bent open just enough to allow one or two pellets to be removed. To determine when the potassium permanganate has been exhausted, remove a pellet and crush it in half.
The usefulness of the filter is approximately 80% diminished when the purple color first disappears from the core.
Place the crushed pellet(s) on a paper towel and add a few drops of water. The water running off the pellet(s) should be initially purple and then turn a deep iodine color. If no purple coloration is present, the potassium permanganate is totally exhausted.
When the purple color first disappears from the core of the pellet as described above, the rate at which formaldehyde is removed from the air stream is slowed considerably.
From a practical standpoint, it may be desirable to perform these tests more frequently during initial usage of the filters to determine when the purple first begins to disappear from the core of the sliced pellet. Based on these early observations, the user can establish a replacement testing cycle involving occasional re-checks.