Process for producing a middle distillate

A process for producing a middle distillate, comprising:

• a. reacting an isobutane stream with a process stream containing butene under alkylation conditions wherein the isobutane and butene are alkylated to produce an alkylate product in the presence of a chloroaluminate ionic liquid catalyst comprising an alkyl substituted pyridinium chloroaluminate or an alkyl substituted imidazolium chloroaluminate of the general formulas A and B, respectively,
• where R═H, methyl, ethyl, propyl, butyl, pentyl or hexyl group, R′═H, methyl, ethyl, propyl, butyl, pentyl or hexyl group, X is a chloroaluminate, and R1 and R2═H, methyl, ethyl, propyl, butyl, pentyl or hexyl group and where R, R′, R1 and R2 may or may not be the same;
• b. adjusting over time a halide containing additive during the reacting step to improve the selectivity for the middle distillate;
• and
• c. separating out the middle distillate from the alkylate product, wherein the separated middle distillate fraction is from 20 wt % or higher of the total alkylate product.