A process for producing phenol and/or cyclohexanone by cleaving cyclohexylbenzene hydroperoxide in a loop cleavage reactor comprising multiple reaction zones connected in series. In desirable embodiments, fresh cyclohexylbenzene hydroperoxide feed(s) are supplied to reaction zones the final reaction zone, and fresh acid catalyst is supplied only to the final reaction zone. In desirable embodiments, a portion of the effluent exiting the final reaction zone is recycled to the first reaction zone. Each reaction zone is equipped with a heat exchanger downstream of the feed port to extract heat generated from the cleavage reaction.