Facilitated olefin transport by reversible olefin coordination to silver ions in a dry cellulose acetate membrane

The highly selective dry complex membrane AgBF4-cellulose acetate (CA) was prepared and tested for the separation of ethylene/ethane and propylene/pro pane mixtures. The maximum selectivity Cor olefin over paraffin was found t o be 280 for the ethylene/ ethane mixture and 200 for the propylene/propane mixture. Solid-state interactions of AgBF4 with cellulose acetate (CA) and /or olefins have been investigated by using FT-IR, UV, and X-ray photoelect ron spectroscopy (XPS). FT-IR and XPS studies clearly show that the silver ions are coordinated by carbonyl oxygen atoms among three different types o f oxygen atoms present in CA - two in thc acetate group and one in the ethe r linkage. Upon incorporation of AgBF4 into CA, the carbonyl stretching fre quency of the free cellulose acetate at 1750 cm(-1) shifts to a lower frequ ency by about 41 cm(-1). The binding energy corresponding to a carbonyl oxy gen atom in the O 1s XPS spectrum shifts to a more positive binding energy by the incorporation of AgBF4. Reversible olefin coordination to silver ion s has been observed by FT-IR and UV studies. Treat ment of the AgBF4-CA mem brane placed in a gas cell with propylene produces a propylene-coordinated membrane in which coordinated propylene is easily replaced by other olefins such as 1,3-butadiene.