A method for the liquefaction of an industrial gas by integration of a methanol plant and an air separation unit (ASU) is provided. The method can include the steps of: (a) providing a pressurized natural gas stream (24, 27), a pressurized purge gas stream (48) originating from a methanol plant, and a pressurized air gas stream (132) comprising an air gas originating from the ASU; (b) expanding three different pressurized gases to produce three cooled streams (32, 62, 142), wherein the three different pressurized gases are the pressurized natural gas stream, the pressurized purge gas stream, and the pressurized air gas stream; and (c) liquefying the industrial gas (44) in a liquefaction unit against the three cooled streams to produce a liquefied industrial gas stream (46). The industrial gas to be liquefied is selected from the group consisting of a first portion of the pressurized natural gas stream, a nitrogen gas stream, hydrogen and combinations thereof.