Combination process for the conversion of a distillate hydrocarbon to produce middle distillate product

A process for the conversion of an aromatic-rich, distillable gas oil charge stock which is essentially free from asphaltenic hydrocarbons and possesses an aromatic hydrocarbon concentration greater than about 20 volume percent to selectively produce large quantities of high quality middle distillate while minimizing hydrogen consumption which process comprises the steps of:

• (a) reacting said charge stock with hydrogen, in a catalytic hydrocracking reaction zone, at hydrocracking conditions including a maximum catalyst bed temperature in the range of about 600.degree. F. (315.degree. C.) to about 850.degree. F. (454.degree. C.) selected to convert at least a portion of said charge stock to lower-boiling hydrocarbon products including middle distillate and to convert at least 10 volume percent of the aromatic hydrocarbon compounds contained in said charge stock to provide an increased concentration of paraffin hydrocarbon compounds in the resulting hydrocracking reaction zone effluent;
• (b) separating said resulting hydrocracking reaction zone effluent to provide a middle distillate product stream and a paraffin-rich hydrocarbonaceous stream boiling at a temperature greater than about 700.degree. F. (371.degree. C.);
• (c) recovering said middle distillate product stream;
• (d) reacting said paraffin-rich hydrocarbonaceous stream recovered in step (b) in a thermal coking zone at mild thermal coking conditions including an elevated temperature from about 750.degree. F. (399.degree. C.) to about 950.degree. F. (510.degree. C.), a pressure from about 10 psig (69 kPa gauge) to about 150 psig (1034 kPa gauge) and a combined feed ratio from about 1 to about 2 to provide a thermal coking zone effluent wherein said combined feed ratio is defined as total valume of liquid charged per volume of fresh hydrocarbon charge;
• (e) separating said thermal coking zone effluent to provide a fraction boiling in the range from about 300.degree. F. (149.degree. C.) to about 700.degree. F. (371.degree. C.) and a distillable hydrocarbonaceous stream boiling in the range from about 700.degree. F. (371.degree. C.) to about 1000.degree. F. (538.degree. C.);
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• (f) recycling at least a portion of said distillable hydrocarbonaceous stream boiling in the range from about 700.degree. F. (371.degree. C.) to about 1000.degree. F. (538.degree. C.) recovered in step (e) to said catalytic hydrocracking reaction zone in step (a).