NOVELTY - Regeneration of an alkylation catalyst mixture comprises: (1) alkylating a first olefin with a first isoparaffin in the presence of the alkylation catalyst mixture having hydrofluoric acid in an alkylation reaction zone; (2) passing an alkylation reaction zone effluent to a separation zone; and (3) passing at least a portion of an alkylation catalyst mixture phase to a re-run column.    USE - For regenerating an alkylation catalyst mixture used in an alkylation process system (claimed).    ADVANTAGE - Regeneration of alkylation catalyst mixture reduces the concentration of hydrofluoric acid in the bottoms stream of an isoparaffin re-run column used in the alkylation process. It increases the ASO recovery from an alkylation process system re-run column bottoms stream.    DETAILED DESCRIPTION - Regeneration of an alkylation catalyst mixture comprises:    (1) alkylating a first olefin with a first isoparaffin in the presence of the alkylation catalyst mixture comprising hydrofluoric acid in an alkylation reaction zone to produce an alkylate product and an acid soluble oil (ASO) reaction by-product;    (2) passing an alkylation reaction zone effluent comprising the alkylation product, the ASO reaction by-product and the alkylation catalyst mixture from the reaction zone to a separation zone for separating the effluent into a hydrocarbon phase (20) comprising the alkylate product and an alkylation catalyst mixture phase comprising the alkylation catalyst mixture and the ASO reaction by-product; and    (3) passing at least a portion of the alkylation catalyst mixture phase (22) to a re-run column for contact with an upwardly flowing gas stream comprising a second olefin and a second isoparaffin to provide a re-run column (32) bottoms stream comprising at least a portion of the ASO reaction by-product, and a re-run column overhead stream comprising hydrofluoric acid, at least a portion of the gas stream and an organic fluoride.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic flow diagram of the invention.    hydrocarbon phase (20)    Alkylation catalyst mixture phase (22)    Re-run column (32)    Upper phase (50)    Lower phase (52)