Fluorinated Hollow Fiber Membranes Based on Matrimid 5218 and Their Application in the Process of Helium Recovery from Natural Gas

Abstract

New data have been obtained on the influence of the conditions of modification of Matrimid 5218 asymmetric hollow fibers by direct gas-phase fluorination directly in laboratory membrane modules on their gas separation properties. It has been shown that direct gas-phase fluorination significantly increases the selectivity of gas separation, in particular, for the He/CH₄ pair. Stability of the fluorination effect has been studied for a long time (up to 10 years). It is noted that over the first days after modification, the modules modified using an He/F₂ mixture with a high F₂ content (10 vol %) exhibit the greatest ideal He/CH₄ selectivity (~8000). However, a high degree of fluorination leads to the degradation of hollow fiber membranes in the module with time, whereas fluorination with a mixture with a low F₂ content (2 vol %) also results in a high He/CH₄ selectivity of the modified membranes (~800), which increases to 4600 with time, the thin selective layer remaining undamaged. The mathematical modeling of the single-stage process of helium recovery from natural gas using modified hollow fiber membranes on the basis of Matrimid 5218 shows a high potential for their practical application in this field.