Acid Wash of the PD-Series Dryer Element
NOTE: This was an older procedure written many years ago to allow for customer cleaning of the PD element. Today, we don’t recommend this procedure, as it is not only dangerous but does not provide repeatable, predictable results. Today, we don’t recommend cleaning our dryers for these reasons. We present the procedure here for reference only.
If oily residues are present, the dryer should be washed with acid to remove the residues and to recondition the Nafion (restore it to its original sulfonic acid form).
- Prepare a bath of 10% nitric acid (HNO3) in a suitable container. The container should withstand exposure to nitric acid and heating.
- Immerse the Nafion tubing into the nitric acid bath taking care not to wet the epoxy headers. About 1.5 inches (4cm) of tubing as well as the header should remain out of the acid.
NOTE: Do not sharply bend the Nafion tubing during this cleaning process. The bath should be large enough to allow the Nafion to flex gradually. A magnetic stirring hotplate should be used if available. If not, the acid container should be heated in some fashion and stirred periodically.
Caution: Heating of the acid bath will generate noxious fumes. The cleaning process should be performed in a fume hood or very well ventilated area. Covering the container with a loose plastic lid will minimize the fumes.
Caution: Rubber gloves and protective eyewear must be worn. Nitric acid at this concentration will stain and/or irritate the skin and injure the eyes if splashed.
- Heat the acid bath to 70°C to 80°C, and soak the Nafion dryer element for one hour with occasional stirring (a magnetic stirring bar set on low if possible).
- Remove the dryer from the acid bath. The acid bath may be covered and reused until it shows significant discoloration.
- Rinse the outside of the tubing and headers with de-ionized (DI) water at room temperature to remove the nitric acid residues.
- Briefly force De-ionized water through the inside of the tubing. This may be accomplished with a plastic squeeze bottle or syringe. Do not immerse the headers of the dryer element in water or excessively wet the tubing inside the headers. Nafion tubing swells when exposed to water. If the tubing inside the epoxy headers becomes too wet, it may swell sufficiently to crack the rigid epoxy header.
- Quickly blow clean, dry air through the dryer element to remove any residual water.
- Continue to blow air through the dryer for several minutes. This will reduce any swelling and restore the dryer to normal length.