1. An asymmetric composite membrane for selectively pervaporating alcohol from an alcohol and gasoline feed mixture, the asymmetric composite membrane comprising:a porous substrate comprising opposite first and second major surfaces, and a plurality of pores; and
a pore-filling polymer disposed in at least some of the pores so as to form a layer having a thickness within the porous substrate, with the amount of the pore-filling polymer at, or adjacent to, the first major surface being greater than the amount of the pore-filling polymer at, or adjacent to, the second major surface;
wherein the pore-filling polymer is more permeable to alcohol than gasoline;
wherein the asymmetric composite membrane further comprises
a liquid ionic compound selected from 1-ethyl-3-methyl imidazolium tetrafluoroborate (Emim-BF4), 1-ethyl-3-methyl imidazolium trifluoromethane sulfonate (Emim-TFSA), 3-methyl-N-butyl-pyridinium tetrafluoroborate, 3-methyl-N-butyl-pyridinium trifluoromethanesulfonate, N-butyl-pyridinium tetrafluoroborate, 1-butyl-2,3-dimethylimidazolium tetrafluoroborate, 1-butyl-2,3-dimethylimidazolium trifluoromethanesulfonate, 1-ethyl-3-methylimidazolium chloride, 1-butyl-3-ethylimidazolium chloride, 1-butyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium bromide, 1-methyl-3-propylimidazolium chloride, 1-methyl-3-hexylimidazolium chloride, 1-methyl-3-octylimidazolium chloride, 1-methyl-3-decylimidazolium chloride, 1-methyl-3-dodecylimidazolium chloride, 1-methyl -3-hexadecylimidazolium chloride, 1-methyl-3-octadecylimidazolium chloride, 1-ethylpyridinium bromide, 1-ethylpyridinium chloride, 1-butylpyridinium chloride, and 1-benzylpyridinium bromide, 1-butyl-3-methylimidazolium iodide, 1-butyl-3-methylimidazolium nitrate, 1-ethyl-3-methylimidazolium bromide, 1-ethyl-3-methylimidazolium iodide, 1-ethyl-3-methylimidazolium nitrate, 1-butylpyridinium bromide 1-butylpyridinium iodide, 1-butylpyridinium nitrate, 1-butyl-3-methylimidazolium hexafluorophosphate, 1 -octyl-3-methylimidazolium hexafluorophosphate, 1-octyl-3-methylimidazolium tetrafluoroborate, 1-ethyl-3-methylimidazolium ethylsulfate, 1-butyl-3-methylimidazolium acetate, 1-butyl-3-methylimidazolium trifluoroacetate, and 1-butyl-3-methyl imidazolium bis(trifluormethylsulfonyl)imide (Bmim-Tf2N).