A process for injecting an immiscible liquid stream comprising a co-catalyst for a hydrocarbon conversion into a larger liquid stream that is an ionic liquid catalyst for the hydrocarbon conversion, comprising: a. feeding the immiscible liquid stream towards one or more injection quills in an additive delivery system comprising a transfer drum; b. transferring the immiscible liquid stream from the additive delivery system to the one or more injection quills in a solvent flushing system, fluidly connected downstream from the additive delivery system, wherein the solvent flushing system injects a solvent into one or more additive addition lines in the solvent flushing system; and c. continuously injecting the immiscible liquid stream into the larger liquid stream in an additive injection and mixing system comprising the one or more injection quills.