Process for the conversion of an alcohols mixture comprising about 20 w% to 100% isobutanol to make essentially propylene, comprising: a) introducing in a reactor (also called the first reaction zone or low temperature reaction zone) a stream comprising the mixture, optionally water, optionally an inert component, b) contacting said stream with a catalyst in said reactor at conditions effective to dehydrate: at least a portion of the isobutanol to essentially butenes, at least a portion of other alcohols, if any, to essentially olefins other than butene having the same carbon number as the alcohol precursor, c) recovering from said reactor an effluent comprising: butenes, optionally olefins other than butene, water, optionally unconverted alcohols of the mixture, various hydrocarbons, and the optional inert component of step a), d) fractionating said effluent of step c) to remove a portion or all the water, unconverted alcohols, optionally the inert component, and optionally the whole or a part of the various hydrocarbons to get a stream comprising essentially olefins and optionally the inert component, e) introducing at least a part of said stream in an OCP reactor (also called the second reaction zone or high temperature zone), f) contacting said stream comprising at least a part of, optionally in combination with a stream comprising olefins having 4 carbon atoms or more (C4+ olefins), in said OCP reactor with a P-modified zeolite catalyst which is selective towards light olefins in the effluent, to produce an effluent with an olefin content of lower molecular weight than that of the feedstock, g) fractionating said effluent of step f) to produce at least an ethylene stream, a propylene stream and a fraction consisting essentially of hydrocarbons having 4 carbon atoms or more, optionally recycling ethylene in whole or in part at the inlet of the OCP reactor of step f), or at the inlet of the reactor or at the inlet of both the OCP reactor of step f) and the reactor, optionally recycling the fraction consisting essentially of hydrocarbons having 4 carbon atoms or more at the inlet of the OCP reactor. a) introducing in a reactor (also called the first reaction zone or low temperature reaction zone) a stream comprising the mixture, optionally water, optionally an inert component, b) contacting said stream with a catalyst in said reactor at conditions effective to dehydrate: at least a portion of the isobutanol to essentially butenes, at least a portion of other alcohols, if any, to essentially olefins other than butene having the same carbon number as the alcohol precursor, at least a portion of the isobutanol to essentially butenes, at least a portion of other alcohols, if any, to essentially olefins other than butene having the same carbon number as the alcohol precursor, c) recovering from said reactor an effluent comprising: butenes, optionally olefins other than butene, water, optionally unconverted alcohols of the mixture, various hydrocarbons, and the optional inert component of step a), d) fractionating said effluent of step c) to remove a portion or all the water, unconverted alcohols, optionally the inert component, and optionally the whole or a part of the various hydrocarbons to get a stream comprising essentially olefins and optionally the inert component, e) introducing at least a part of said stream in an OCP reactor (also called the second reaction zone or high temperature zone), f) contacting said stream comprising at least a part of, optionally in combination with a stream comprising olefins having 4 carbon atoms or more (C4+ olefins), in said OCP reactor with a P-modified zeolite catalyst which is selective towards light olefins in the effluent, to produce an effluent with an olefin content of lower molecular weight than that of the feedstock, g) fractionating said effluent of step f) to produce at least an ethylene stream, a propylene stream and a fraction consisting essentially of hydrocarbons having 4 carbon atoms or more,