Method for removal of phenolic polymerization inhibitors from liquid conjugated olefin hydrocarbon by contacting said liquid hydrocarbon with a sorbent material comprising particulate acidified active carbon which sorbent has previously been oxidized by contact with a highly acidic oxidizing fluid. Optionally, after contact with the highly acidic oxidizing fluid the sorbent may be further treated in an alkaline environment with compounds of at least one of alkali metals, alkaline earth metals and ammonia. The sorbent material may be regenerated by heating, or by passing a heated non-oxidizing gas e.g., superheated stream there through.