Method for dehydrating alcohols into olefins comprising the recycling of alcohols

A method for simultaneously dehydrating and isomerizing a feedstock comprising 40 to 100% by weight of a primary alcohol substituted in position 2 by an alkyl group, the method comprising:

• a) compressing said feedstock, mixing a fraction of said compressed feedstock with an alcohol-rich organic effluent obtained from step h) and with a fraction of an aqueous effluent obtained from step f) to obtain a feedstock mixture, and then preheating said feedstock mixture to produce a partially vaporized feedstock and a residual compressed feedstock, wherein the residual compressed feedstock fraction is sent to step h);
• b) superheating said partially vaporized feedstock at a temperature of between 250 and 375° C. in such a way as to produce a vaporized feedstock;
• c) dehydrating said vaporized feedstock in at least one dehydration reactor operating in gas phase at a weighted mean temperature of between 250 and 375° C., at a pressure of between 0.2 MPa and 1 MPa, and at a WHSV of between 1 and 18 h−1, in the presence of a catalyst, to produce a dehydration effluent, wherein said catalyst comprises a zeolite having at least one series of channels with a pore opening defined by a ring with 8 oxygen atoms (8 MR) and wherein said catalyst is coked in advance in-situ or ex-situ;
• d) cooling said dehydration effluent obtained from step c) to a temperature of between 30 and 50° C. to produce a cooled effluent;
• e) separating said cooled effluent by decanting into an aqueous phase and an organic phase;
• f) distilling said aqueous phase obtained from step e) to produce a light hydrocarbon effluent and an aqueous effluent, wherein the light hydrocarbon effluent comprises at least 50% by weight of hydrocarbons comprising at most 4 carbon atoms, and wherein a part of said aqueous effluent is purged and another part of said aqueous effluent is recycled to step a);
• g) distilling said organic phase obtained from step e) to produce an olefinic effluent and a heavy hydrocarbon effluent, wherein said olefinic effluent comprises at least 50% by weight of olefins corresponding to said primary alcohol(s) substituted in position 2 by an alkyl group and wherein said olefins comprise linear olefins;
• and
• h) mixing the heavy hydrocarbon effluent obtained from step g) with the residual compressed feedstock fraction obtained from step a) at a ratio by mass of flow rates of the residual compressed feedstock fraction to unconverted alcohol(s) in the heavy hydrocarbon effluent of between 2:1 and 10:1 to produce a heavy effluent mixture, and then distilling said heavy effluent mixture to produce a C5-C6 hydrocarbon effluent, an alcohol-rich organic effluent comprising unconverted alcohol(s), and a C6+hydrocarbon effluent and recycling said alcohol-rich organic effluent to step a).