Method for dehydrating alcohols into olefins comprising the recycling of alcohols

Method for isomerizing dehydration of a feedstock comprising 40 to 100% by weight of primary alcohol substituted in position 2 by an alkyl group comprising at least the following steps:

• a) Pressurization of said feedstock, followed by the mixing of a fraction of said feedstock, compressed, with the alcohol-rich organic effluent obtained from step h) and with a fraction of the aqueous effluent obtained from step f), and then preheating of said mixture, in such a way as to produce a partially vaporized feedstock, with the residual compressed feedstock fraction being sent to step h);
• b) Vaporization and final superheating of said partially vaporized feedstock at a temperature of between 250 and 375° C. in such a way as to produce a vaporized feedstock;
• c) Dehydration of said vaporized feedstock in at least one dehydration reactor that operates in the 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 PPH of between 1 and 18 h−1, in the presence of a catalyst that comprises a zeolite that has at least one series of channels whose opening is defined by a ring with 8 oxygen atoms (8 MR), with said catalyst being coked in advance in-situ or ex-situ, in such a way as to produce a dehydration effluent;
• d) Cooling of said dehydration effluent obtained from step c) to a temperature of between 30 and 50° C., in such a way as to produce a cooled effluent;
• e) Separation by decanting of said cooled effluent into an aqueous phase and an organic phase;
• f) Separation by distilling of said aqueous phase obtained from step e) in such a way as to produce a light hydrocarbon effluent comprising at least 50% by weight of hydrocarbons comprising at most 4 carbon atoms and an aqueous effluent, with a fraction of said aqueous effluent being purged, and the other part being recycled to step a);
• g) Separation by distilling of said organic phase obtained from step e) in such a way as to produce an olefinic effluent comprising at least 50% by weight of olefins corresponding to primary alcohol(s) substituted in position 2 by an alkyl group that is fed in said feedstock and a heavy hydrocarbon effluent;
• h) Mixing of the heavy hydrocarbon effluent obtained from step g) with the residual compressed feedstock fraction obtained from step a), with the flow rate of said residual fraction being adjusted in such a way that the ratio by mass of the flow rates of residual fraction to unconverted alcohol in a heavy hydrocarbon effluent is between 2:1 and 10:1, and then separation by distilling of said mixture in such a way as to produce a C5-C6 hydrocarbon effluent, an alcohol-rich organic effluent, and a C6+ hydrocarbon effluent, and recycling of said alcohol-rich organic effluent to step a).