Physical aging of polyetherimide membranes

• Physical aging of PEI membranes are investigated.
• The effects of PDMS coating, heat treatment temperature, PEI wt%, and the method of storage are studied.
• New first-order empirical models that predict membrane permeance and selectivity are proposed.

This paper presents a study of the physical aging of asymmetric polyetherimide (PEI) flat membranes. The effects of storage type (under vacuum, atmospheric air, and pure argon), the presence of polydimethylsiloxane (PDMS) coating, membrane heat-treatment temperature, and membrane-preparation PEI wt% on the physical aging were investigated over 240 days by monitoring CO2 permeance and CO2/CH4 selectivity of the membranes. The feed was a 10/90 V/V CO2/CH4 binary gas mixture. Physical aging was quantified in terms of CO2 permeance ultimate change and aging time constant, as well as CO2/CH4 selectivity ultimate change and aging time constant. New first-order physical-aging models were proposed and shown to predict the physical aging accurately. This study indicates that physical aging decreases the permeance but increases the selectivity. The membranes age less when (a) they have a PDMS coating, (b) they are prepared with a higher PEI wt%, and (c) they have a higher annealing temperature, especially above the glass transition temperature. Membranes stored under vacuum age at a slower rate than those stored under atmospheric air or pure argon.