Permeation Tube Equilibration Times and Long-Term Stability
SourceThe time required to reach permeation rate equilibrium after a temperature change, and the long-term rate stability were investigated for fluorinated ethylene propylene (FEP) and tetrafluoroethylene (TFE) Teflon permeation tubes filled with sulfur dioxide, hydrogen sulfide, methyl mercaptan, and dimethyl sulfide. The effect of repeated temperature changes on the repeatability of permeation rates was determined for permeation tubes filled with ammonia, nitrogen dioxide, and sulfur compounds. A two-stage process to equilibrium was observed for tubes made of FEP Teflon. Permeation through TFE Teflon requires one fifth the time to reach equilibrium and does not exhibit the same two-stage equilibration process. Long-term stability was good for both FEP and TFE membranes. Permeation rates were reproducible after repeated temperature cycles.