a process unit for the zeolite - catalyzed conversion of light refinery olefins from an fcc unit such as ethylene , propylene , and butylene to gasoline boiling range motor fuels comprises at least two sequential , serially connected reactors connected in parallel to a fractionation section with at one or two fractionators for separating the reactor effluents into product fraction with an optional recycle stream or streams . the configurations according to this scheme allow the adjustment of reactor temperature and / or pressure and / or space velocity to be based on the reactivities of the olefin compounds present in the lpg streams so that the gasoline produced in each reactor will be separated immediately , to reduce over - polymerization of the gasoline in the low severity reactor and to ensure that gasoline formed in the low severity reactor will not be sent to the higher severity reactor e . g . with a higher reactor temperature , where excessive polymerization to undesirable higher molecular with products may take place .