mixture to a more dense catalyst phase in a particular way to improve yield of desirable isoparaffinic alkylate while reducing the required catalyst inventory feedstocks useful in the present alkylation process include at least one isoparaffin and at least one olefin the isoparaffin reactant used in the present alkylation process has from about 4 to about 8 carbon atoms representative examples of such isoparaffins include isobutane isopentane 3 methylhexane 2 methylhexane 2 3 dimethylbutane and 2 4 dimethylhexane the olefin component of the feedstock includes at least one olefin having from 2 to 12 carbon atoms representative examples of such olefins include butene 2 isobutylene butene 1 propylene ethylene hexene octene and heptene merely to name a few the preferred olefins include the c 4 olefins for example butene 1 butene 2 isobutylene or a mixture of one or more of these c 4 olefins with butene 2 being the most preferred suitable feedstocks for the process of the present invention are described in u s pat no 3 862 258 to huang et al at column 3 lines 44 56 the disclosure of which is incorporated by reference as if set forth at length herein isoparaffin olefin ratios in the reactor feed typically range from about 1 5 1 to about 15 1 to produce a high octane isobutane butene alkylate product at industrially useful yields higher isoparaffin olefin ratios may also be used however limited availability of produced isoparaffin within the refinery coupled with the relatively high cost of purchased isoparaffin favor isoparaffin olefin ratios within the ranges listed above in the process and apparatus of the present invention alkylate product further dilutes the isoparaffin olefin feed to the reactor as alkylate is drawn into a longitudinally extensive draft tube traversing the interface between.