A membrane based separation method is for the separation or enrichment of one or more unsaturated compounds from mixtures of chemically similar organic compounds having a different degree of unsaturation, using a membrane, such as an inorganic membrane, functionalized with a metal, such as silver. An inorganic membrane, preferably modified or grafted with an organic functional group, is further functionalized with a metal, such as silver, for use in the membrane based separation methods.