A method for preparing composite membranes based on MOF-199 with copper ions and tricarboxylate ligands via creating nucleation sites on the surface of the ceramic substrate, followed by grafting tricarboxylic acid to the surface of the ceramic porous substrate (γ-Al2O3), is developed. The permeability of the membranes is measured and the separation of a mixture of ethane and methane on them is performed. The influence of the method of forming a metal-organic framework structure (MOF) on the sorption properties of composite membranes is ascertained.