A process for producing propylene or butene is disclosed, comprising passing a stream comprising 10-70 wt % of diisopropyl ether or 30-95 wt % of di-sec butyl ether over an acid catalyst at a temperature of 180-300° C. and a pressure of 0.01-3 bar g. Also disclosed is a process for producing either isopropanol or 2-butanol, comprising contacting water and a propylene- or butene-containing feedstock in a hydration reaction zone with a hydration catalyst to produce a stream comprising either isopropanol and a by-product stream or 2-butanol and a by-product stream, passing said by-product stream over an acid catalyst at a temperature of 180-300° C. and a pressure of 0.01-3 bar g to produce either propylene or butene, and then recycling said propylene or butene to the hydration reaction zone.