Processes for the direct alkylation of ethylene with isobutane or isopentane using a highly active ionic liquid alkylation catalyst are described. Ethylene is sent to a high-temperature alkylation reactor loop, and C3, C4, and C5 olefins are routed to a low temperature alkylation reactor loop. In each reactor, the olefins are contacted with an excess of isobutane or isopentane in the presence of a highly active ionic liquid catalyst. Portions of the reactor effluent streams are fed to a common downstream catalyst separation and product fractionation sections. The remainder of the reactor effluent is recycled back to the respective alkylation reactor.