Is it a wrong choice to send the wax oil produced from slurry-bed residue hydrogenation through the catalytic cracking process?

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Slurry-bed residue hydrogenation is a combination of radical cracking reactions for 540+°C fractions and metal molybdenum-catalyzed positive carbon ion reactions; the dominant mechanism in this process is the gradual separation of gums and asphaltenes to form asphaltene nuclei. As a result, the reaction products in the form of diesel and wax oil are rich in aromatic compounds. The effective utilization of these components has a direct impact on the overall process flow and economic efficiency of the plant. Unfortunately, at present, all plants in China that possess slurry-bed residue hydrogenation units follow a process flow that involves slurry-bed wax oil treatment, hydrogenation refining, catalytic cracking (or hydrocracking), and diesel hydrotreating – a approach that goes against the principle of selecting processes based on the preference for aromatic compounds. I. The short-process route in refining and chemical processing represents a low-carbon development direction. In the current approach, slurry-bed wax oil must go through processes such as slurry-bed hydrogenation, hydroprocessing, catalytic cracking, UCN hydrogenation cracking, hydrogenation saturation refining, and reforming in order to be converted from residue oil into aromatics and olefins; this involves multiple steps of hydrogen consumption and production, representing an inefficient internal cycle of hydrogen use ； II. The slurry-bed wax oil processing route undermines the advantages of the catalytic cracking process, creating a conflict between the requirements of hydrogen transfer reactions and those for polyolefin products. As a result, aromatic compounds such as those with two, three, four rings in slurry-bed wax oil undergo transformations within the family of naphthene compounds during hydrorefining and catalytic cracking reactions. In particular, the naphthene-based hydrogen donors facilitate asymmetric catalysis of saturated intermediate products such as propylene and isobutylene in catalytic riser reactions, which severely undermines the effectiveness of the catalytic process ； III. The coke-forming reaction in the slurry-bed catalytic route for wax oil is the reverse process of slurry-bed hydrogenation. Its negative effect of reducing the yield of light olefins constitutes a violation of the principle of “producing olefins when appropriate”; it also represents an inefficient utilization of hydrogen energy and internal competition between upstream and downstream processes in petroleum refining ； IV. The slurry-bed wax oil catalytic route occupies space resources in the catalytic and hydrogenation units; hydroprocessed tail oils and reduced-first-stage oils, which are low in aromatic content and suitable for catalytic cracking, cannot be used to produce olefin-rich gasoline or olefin-rich LPG through catalytic cracking, thus preventing the full realization of scale benefits such as those associated with etherification and alkylation. Personal suggestion: For the wax oil produced by slurry-bed residue hydroprocessing, abandon the catalytic cracking route and instead use bimetallic-functioned wax oil hydrocracking to achieve simultaneous hydrogenation and cracking. This approach allows for the efficient utilization of the abundant aromatic compounds to produce highly aromatic heavy naphtha and light ethylene feedstocks; it also enables the replacement of low-aromatic potential feedstocks in the overall process, ensuring a stable output of reformed aromatics and maximizing the effective capacity of the plant.