Process for producing ether compound

A process for continuously producing an ether compound comprising the steps of:

• subjecting a lower alcohol having 1 to 3 carbon atoms to a reaction procedure with a hydrocarbon mixture consisting of hydrocarbon compounds having 3 to 6 carbon atoms and comprising, as the major component thereof, an unsaturated hydrocarbon compound having 4 or 5 carbon atoms, to provide a reaction product mixture comprising a resultant ether compound, a non-reacted portion of the lower alcohol and a non-reacted portion of the hydrocarbon mixture;
• feeding the resultant reaction product mixture to a distillation procedure in a distillation column, to provide a bottom liquid fraction comprising the resultant ether compound and a top vapor fraction comprising the non-reacted lower alcohol portion and the non-reacted hydrocarbon mixture portion;
• collecting the bottom liquid fraction through a bottom outlet of the distillation column;
• discharging the top vapor fraction through a top outlet of the distillation column;
• liquefying the top vapor fraction by cooling;
• bringing the liquefied top fraction into contact with one side face of an aromatic polyimide asymmetric separating membrane having a separation factor, as defined below, of 200 or more, at a temperature of 50.degree. C. or more, while exposing the opposite side face of the separating membrane to an atmosphere maintained under reduced pressure, to allow a vapor fraction comprising, as a major component thereof, the non-reacted lower alcohol to selectively permeate the separating membrane, said aromatic polyimide in the asymmetric separating membrane comprises 70 to 100 molar % of at least one type of recurring unit selected from those of the formulae (I) and (II):
• ##STR3## wherein R represents a divalent aromatic group having 2 to 4 benzene ring structures and X represents a member selected from the group consisting of --S--, --SO.sub.2 --, --CO-- --O--, --C(CH.sub.3).sub.2 --, --CH.sub.2 --, and C(CF.sub.3).sub.2 -- groups, and said separation factor being determined in accordance with the equation:
• .alpha.=C.sub.1 /C.sub.2
• wherein .alpha. represents the separation factor of the separating membrane, C.sub.1 represents a proportion in weight of the non-reacted lower alcohol contained in the permeated fraction and C.sub.2 represents a proportion in weight of the non-reacted lower alcohol contained in the liquefied top fraction to the non-reacted hydrocarbon mixture contained in the liquified top fraction;
• cooling the permeated lower alcohol vapor fraction to liquefy and collect the same;
• returning the liquefied lower alcohol fraction to the reaction step.