A plant for producing hydrogen peroxide and using the hydrogen peroxide so made for manufacturing an oxirane by reaction between an olefin and said hydrogen peroxide, wherein the hydrogen peroxide is manufactured by an alkylanthrahydroquinone (AO) process in which an aqueous hydrogen peroxide solution is obtained by extraction, with substantially pure water, of a mixture derived from the oxidation of at least one alkylanthrahydroquinone, without a subsequent washing, purification treatment or combination thereof.