The present invention relates to a process for the preparation of a green multilayer sol-gel ceramic membrane for the separation of gaseous CO.sub.2 from natural gas. For being composed solely of ceramic materials (silica and alumina), the ceramic membrane developed by the proposed process has high chemical, physical and mechanical stability as its main characteristics. These characteristics ensure its usefulness in the process of separating CO.sub.2 from natural gas, even in streams having high CO.sub.2 concentrations and under high pressure; the developed membrane further enables backwashing operations to be carried out, when needed.