NOVELTY - Treating (P1) a spent adsorbent, involves (a) contacting the spent adsorbent with a basic solution under adsorbent dechlorination conditions, where the spent adsorbent includes at least one halogenated component; and b) via step a), removing at least a portion of the halogenated component from the spent adsorbent to provide a dechlorinated adsorbent.    USE - For treating spent adsorbent; for producing rejuvenated adsorbent, where the adsorbent comprises molecular sieve (preferably large pore zeolites, intermediate pore zeolites, and/or small pore zeolites), a refractory oxide, and/or an activated carbon, and the adsorbent comprises 13x molecular sieve; and for providing purified hydrocarbon product, where the hydrocarbon product is selected from alkylate gasoline, diesel fuel, jet fuel, and/or base oil (all claimed).    ADVANTAGE - The method improves the operability and economics of ionic liquid catalyzed hydrocarbon conversion processes; and provides efficient purification of hydrocarbon products. The purified hydrocarbon product has chloride content less than 50 parts per million (ppm). The rejuvenated adsorbent subsequently undergoes repetitive cycles of adsorption and rejuvenation to greatly extend the useful lifetime of the adsorbent.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the followings:    (1) producing (P2) rejuvenated adsorbent, involving (a') contacting a hydrocarbon product comprising an organic halide with an adsorbent under organic halide adsorption conditions in an adsorption zone to provide a purified hydrocarbon product and a spent adsorbent, where a first chloride content of the hydrocarbon product is greater than a second chloride content of the purified hydrocarbon product; (b') contacting the spent adsorbent with a basic solution under adsorbent dechlorination conditions to provide a dechlorinated adsorbent; and (c') activating the dechlorinated adsorbent to provide a rejuvenated adsorbent; and    (2) providing (P3) a purified hydrocarbon product, involving (a1) contacting at least one hydrocarbon reactant with an ionic liquid catalyst in a hydrocarbon conversion zone under hydrocarbon conversion conditions to provide a hydrocarbon product comprising an organic halide contaminant; (b1) contacting the hydrocarbon product with an adsorbent in an adsorption zone under organic halide adsorption conditions to provide the purified hydrocarbon product and a spent adsorbent; (c1) contacting the spent adsorbent with a basic solution under adsorbent dechlorination conditions to provide a dechlorinated adsorbent; and (d1) activating the dechlorinated adsorbent to provide a rejuvenated adsorbent.