A membrane separation assembly that includes an integrated filter element and at least one membrane module housed within a first vessel and a second vessel containing at least one membrane module, which is stacked or aligned adjacent to the first vessel. The first vessel is configured to allow liquids to be trapped and removed from the assembly, and gases to flow to and through the membrane modules of the first vessel and the membrane modules of the second vessel, which are ultimately withdrawn from the assembly. The assembly is useful in the conditioning of fuel gas to separate methane from C2+ hydrocarbons.