A process for making phenol and/or cyclohexanone, the process comprising: providing a cleavage reactor having a plurality of reaction zones connected in series, the reaction zones comprising a first reaction zone, a final reaction zone and optionally one or more intermediate reaction zone(s) between the first reaction zone and the final reaction zone; wherein: each of the reaction zones comprises a processed feed port, a fresh feed port, a heat exchanger at least partly downstream of the processed feed port and the fresh feed port in the same reaction zone, and an effluent port, except that the heat exchanger for the final reaction zone is optional; the effluent port of any given reaction zone other than the final reaction zone is in fluid communication with the processed feed port of the immediately following reaction zone in the series; and the effluent port of the final reaction zone is in fluid communication with the processed feed port of the first reaction zone; supplying a fresh cleavage reaction feed comprising cyclohexylbenzene hydroperoxide to each reaction zone other than the final reaction zone via the fresh feed port of the reaction zone and producing an effluent at the effluent port of the reaction zone; supplying at least a portion of the effluent exiting the effluent port of each of the reaction zones other than the final reaction zone to the processed feed port of the immediately following reaction zone in the series; supplying an acid catalyst feed to the final reaction zone via the fresh feed port of the final reaction zone and producing a final effluent exiting the effluent port of the final reaction zone; recycling a portion of the final effluent to the first reaction zone via the processed feed port of the first reaction zone; and obtaining phenol and/or cyclohexanone from a portion of the final effluent. providing a cleavage reactor having a plurality of reaction zones connected in series, the reaction zones comprising a first reaction zone, a final reaction zone and optionally one or more intermediate reaction zone(s) between the first reaction zone and the final reaction zone; wherein: each of the reaction zones comprises a processed feed port, a fresh feed port, a heat exchanger at least partly downstream of the processed feed port and the fresh feed port in the same reaction zone, and an effluent port, except that the heat exchanger for the final reaction zone is optional; the effluent port of any given reaction zone other than the final reaction zone is in fluid communication with the processed feed port of the immediately following reaction zone in the series; and the effluent port of the final reaction zone is in fluid communication with the processed feed port of the first reaction zone; each of the reaction zones comprises a processed feed port, a fresh feed port, a heat exchanger at least partly downstream of the processed feed port and the fresh feed port in the same reaction zone, and an effluent port, except that the heat exchanger for the final reaction zone is optional; the effluent port of any given reaction zone other than the final reaction zone is in fluid communication with the processed feed port of the immediately following reaction zone in the series; and the effluent port of the final reaction zone is in fluid communication with the processed feed port of the first reaction zone; supplying a fresh cleavage reaction feed comprising cyclohexylbenzene hydroperoxide to each reaction zone other than the final reaction zone via the fresh feed port of the reaction zone and producing an effluent at the effluent port of the reaction zone; supplying at least a portion of the effluent exiting the effluent port of each of the reaction zones other than the final reaction zone to the processed feed port of the immediately following reaction zone in the series; supplying an acid catalyst feed to the final reaction zone via the fresh feed port of the final reaction zone and producing a final effluent exiting the effluent port of the final reaction zone; recycling a portion of the final effluent to the first reaction zone via the processed feed port of the first reaction zone; and obtaining phenol and/or cyclohexanone from a portion of the final effluent.