TECHNOLOGY FOCUS - CHEMICAL ENGINEERING - Preferred Method: In method (M1), the upwardly directed flow of molecular hydrogen at least partially distributes the slurry catalyst in the cellulosic biomass solids. The cellulosic biomass solids are distributed laterally within the hydrothermal digestion unit by floating the cellulosic biomass solids on the fluid phase digestion medium. The cellulosic biomass solids are introduced to the hydrothermal digestion unit at several locations disposed laterally about upper surface of the hydrothermal digestion unit. The cellulosic biomass solids are distributed laterally within the hydrothermal digestion unit by a solids transport mechanism located in it. The solids transport mechanism comprises screw impeller. The cellulosic biomass solids are distributed laterally within the hydrothermal digestion unit by circulating the fluid phase digestion medium and the slurry catalyst laterally through it. The method (M1) further involves removing at least a portion of the fluid phase digestion medium and the slurry catalyst from the hydrothermal digestion unit, after the alcoholic component has been formed; and further involves returning at least a portion of the fluid phase digestion medium and the slurry catalyst to the hydrothermal digestion unit; and circulating at least a portion of the fluid phase digestion medium and the slurry catalyst laterally through the hydrothermal digestion unit. The fluid phase digestion medium and the slurry catalyst are circulated laterally through the hydrothermal digestion unit in the same direction in which the cellulosic biomass solids are being distributed in the hydrothermal digestion unit. The method (M1) further involves recirculating at least a portion of the molecular hydrogen from a headspace of the hydrothermal digestion unit to a source of the upwardly directed flow of molecular hydrogen. The fluid phase digestion medium comprises organic solvent and water. The alcoholic component is formed by catalytic reduction reaction of soluble carbohydrates, the soluble carbohydrates being derived from the cellulosic biomass solids. The slurry catalyst comprises poison-tolerant catalyst. The poison-tolerant catalyst comprises sulfided catalyst. In method (M2), the upwardly directed flow of molecular hydrogen at least partially distributes the slurry catalyst in the cellulosic biomass solids or partially digested cellulosic biomass solids. The second hydrothermal digestion unit has height that is greater than its length or its width. The bottom of the first hydrothermal digestion unit is fluidly coupled to the top of the second hydrothermal digestion unit. The second hydrothermal digestion unit has length or width that is greater than its height. The first hydrothermal digestion unit and the second hydrothermal digestion unit are fluidly coupled to one another end-to-end. The method (M2) further involves removing at least a portion of the fluid phase digestion medium and the slurry catalyst from the second hydrothermal digestion unit, after the alcoholic component has been formed; and further involves returning at least a portion of the fluid phase digestion medium and the slurry catalyst to the first hydrothermal digestion unit; and circulating at least a portion of the fluid phase digestion medium and the slurry catalyst laterally through the first hydrothermal digestion unit. The fluid phase digestion medium and the slurry catalyst are circulated from the second hydrothermal digestion unit to the first hydrothermal digestion unit. The method (M2) further involves recirculating at least a portion of the molecular hydrogen from a headspace of either hydrothermal digestion unit to the same hydrothermal digestion unit or different hydrothermal digestion unit, the molecular hydrogen being recirculated to source of the upwardly directed flow of molecular hydrogen in it. Preferred System: The system (S1) further comprises gas recycle line configured to establish fluid communication between headspace of the hydrothermal digestion unit and the gas distribution system; and solids transport mechanism within the hydrothermal digestion unit. In system (S2), the second hydrothermal digestion unit has height that is greater than its length or its width. The second hydrothermal digestion unit has length or a width that is greater than its height. The system (S2) further comprises solids transport mechanism located within the first hydrothermal digestion unit. The first hydrothermal digestion unit and the second hydrothermal digestion unit are fluidly coupled to one another at two or more locations. The system (S2) further comprises gas recycle line configured to establish fluid communication between headspace of the first hydrothermal digestion unit and the gas distribution system in the first hydrothermal digestion unit or the second hydrothermal digestion unit. The system (S2) further comprises gas recycle line configured to establish fluid communication between headspace of the second hydrothermal digestion unit and the gas distribution system in the first hydrothermal digestion unit or the second hydrothermal digestion unit. The fluid conduit is configured to convey fluid from the second hydrothermal digestion unit to the first hydrothermal digestion unit. EXAMPLE - No suitable example given.