Transient dynamic of hydrogen permeation through a palladium membrane is studied in the present study. Three different pressure differences between the two sides of the membrane are considered; they are 3, 5 and 8 atm. The experimental results indicate that the variation in the hydrogen permeation process is notable at the selected pressure differences. When the pressure difference is relatively low (i.e. 3 atm), the hydrogen permeation process proceeds from a time-lag period, then to a concave up period and eventually to a concave down period. Therefore, the transient hydrogen permeation is characterized by a three-stage mass transfer process. When the pressure difference is increased to 5 atm, the time-lag period disappears, thereby evolving the three-stage mass transfer process into a two-stage one. However, the concave up period withers significantly. Once the pressure difference is as high as 8 atm, the transient hydrogen permeation is completely characterized by a concave down curve, yielding a single-stage mass transfer process. A quasi-steady state of hydrogen permeation is defined to evaluate the period of the transient mass transfer process. It suggests that, within the investigated conditions of operation, the time required for hydrogen permeation to reach the steady value is around or over 1 h. For the low pressure difference cases, the transient period is especially long, resulting from the time-lag characteristic. Once the hydrogen permeation is in the steady state, over 80% of hydrogen can be recovered from the membrane.
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