smbr is kept at temperature from about 10 u00b0 c to about 70 u00b0 c in the process of the present invention the inlet outlet streams are shifted periodically from the position p u2032 to the position p being that time named switching time the operation of the smbr allows that the inlet outlet streams shift either forward or backward in a synchronous or asynchronous way within a switching period the simulated moving bed reactor utilized in the present invention is a known apparatus u s pat no 2 985 589 comprising several columns connected in series each column is packed with a solid or a mixture of solids two or three streams are introduced in the unit one of them is the desorbent that is normally the alcohol used as reactant to form acetal the desorbent is used to regenerate the solid in the first zone the reactants alcohol and aldehyde could be introduced in a single feed stream fig1 or in two feed streams fig2 the products acetal and water are removed from the simulated moving bed reactor in two liquid streams a first liquid stream comprising a solution of acetal in the desorbent raffinate and a second liquid stream comprising.