the present invention relates to polymer membranes for separating olefins from paraffins which have the similar molecular size and close boiling point . more particularly , it relates to a silver salt - containing facilitated transport membrane for olefin separation , and also a method for producing the same . an object of the present invention is to provide a silver salt - containing facilitated transport membrane for olefin separation having improved stability , and also a method for preparing the same , which exhibits no deterioration in membrane performance even when operated for an extended period of time . the facilitated transport membrane for olefin / paraffin separation of the present invention comprises a polymer , a silver salt , and a phthalate compound represented by the following formula wherein r denotes an alkyl group of 2 to 8 carbon atoms or a phenyl group .