A rapid and scalable synthesis of six new imine-linked highly porous and crystalline COFs is presented that feature exceptionally high chemical stability in harsh environments including conc. H₂SO₄ (18 m), conc. HCl (12 m), and NaOH (9 m). This is because of the presence of strong interlayer C−H⋅⋅⋅N hydrogen bonding among the individual layers, which provides significant steric hindrance and a hydrophobic environment around the imine (−C=N−) bonds, thus preventing their hydrolysis in such an abrasive environment. These COFs were further converted into porous, crystalline, self-standing, and crack-free COF membranes (COFMs) with extremely high chemical stability for their potential applications for sulfuric acid recovery. The as-synthesized COFMs exhibit unprecedented permeance for acetonitrile (280 Lm⁻² h⁻¹ bar⁻¹) and acetone (260 Lm⁻² h⁻¹ bar⁻¹).