Process for producing an ether and an olefin from a hydrocarbon cut containing at least one tertiary olefin by synthesizing then decomposing an ether, comprising a first step for purifying the olefin by washing with water

A process for the production of a tertiary olefin and/or a tertiary alkyl ether from a hydrocarbon cut containing at least one etherifiable tertiary olefin, the process comprising:

• a) a step for forming at least one tertiary alkyl ether by bringing at least one hydrocarbon cut containing at least one etherifiable tertiary olefin into contact with at least one alcohol, in a reaction zone containing an etherification catalyst, under conditions for transforming at least a portion of the tertiary olefin into a tertiary alkyl ether;
• b) a fractionation step for separating the major portion of the product from step a) into an organic fraction (O1) which is depleted in tertiary alkyl ether and an organic fraction (E1), enriched in the tertiary alkyl ether;
• c) a step for decomposing at least a portion of the tertiary alkyl ether contained in the organic fraction (E1) from step b), in a reaction zone (R1) containing a catalyst for decomposing said ether, into a product (P1) containing at least one alcohol and at least one tertiary olefin;
• d) a step for purifying at least a portion of product (P1) from step c) in a water washing extraction zone (L1) from which an aqueous fraction (A1) containing the major portion of the alcohol initially present in said portion of product (P1) and a fraction (B1) containing the major portion of the tertiary olefin initially present in product (P1) are obtained, said fraction (B1) containing said tertiary olefin, water, possibly ether and possibly light compounds;
• said process being characterized in that it comprises a step e) in which at least a portion of fraction (B1) is sent to a separation zone (Co1), from which a liquid aqueous fraction (La1) and a liquid organic fraction (Lb1) containing the major portion of the tertiary olefin initially present in said portion of the fraction (B1) are recovered, said fraction (Lb1) containing said tertiary olefin and possibly ether, possibly light compounds and possibly heavy compounds.