TECHNOLOGY FOCUS - INSTRUMENTATION AND TESTING - Preferred System: The biomass conversion system further comprises: a porous retention structure within the first zone; a liquids removal line connected to the first zone; a reactor housing a condensation catalyst in fluid communication with the liquids removal line; and a liquid phase separation unit in fluid communication with the liquids removal line, where the liquid phase separation unit is located between the hydrothermal digestion unit and the reactor housing the condensation catalyst. Preferred Components: The hydrothermal digestion unit comprises a fluid conduit external that is configured to convey the continuous liquid phase from a lower portion of the hydrothermal digestion unit to an upper portion of the hydrothermal digestion, where the continuous gas phase is located.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Method: In the method, once released, the continuous liquid phase and the slurry catalyst migrate downward through the second portion of cellulosic biomass solids as a discontinuous phase within the continuous gas phase. The method further involves: adding slurry catalyst to the portion of the continuous liquid phase being conveyed to the location within the continuous gas phase; and supplying an upwardly directed liquid stream into the continuous liquid phase. At least a portion of the slurry catalyst in the continuous liquid phase is upwardly conveyed into at least a portion of the first portion of cellulosic biomass solids by the upwardly directed flow of molecular hydrogen. At least a portion of the cellulosic biomass solids reside on a porous retention structure that is configured to allow the upwardly directed flow of molecular hydrogen to pass through its. After being released, at least a portion of the continuous liquid phase and the slurry catalyst adheres to the cellulosic biomass solids. The first portion of cellulosic biomass solids and the second portion of cellulosic biomass solids are located in a hydrothermal digestion unit. The method involves providing cellulosic biomass solids in a hydrothermal digestion unit, a first portion of the cellulosic biomass solids being contacted by a continuous liquid phase and a second portion of the cellulosic biomass solids being contacted by a continuous gas phase; supplying an upwardly directed flow of molecular hydrogen through the cellulosic biomass solids; heating the cellulosic biomass solids and the continuous liquid phase in the presence of the molecular hydrogen, thereby forming an alcoholic component derived from the cellulosic biomass solids; conveying at least a portion of the continuous liquid phase and at least a portion of the slurry catalyst through a fluid conduit external to the hydrothermal digestion unit to a location within the continuous gas phase that is above at least a portion of the cellulosic biomass solids; and after conveying the continuous liquid phase and the slurry catalyst, releasing them such that they migrate downward through the second portion of cellulosic biomass solids as a discontinuous phase within the continuous gas phase. Supplying an upwardly directed liquid stream into the continuous liquid phase comprises circulating the continuous liquid phase through the first portion of cellulosic biomass solids in an upwardly directed manner. At least a portion of the cellulosic biomass solids accumulate below the porous retention structure in the continuous liquid phase. Preferred Components: The continuous liquid phase comprises liquid phases, where the liquid phases comprise phenolics liquid phase comprising lignin or product formed from its, aqueous phase comprising the alcoholic component and/or light organics phase. The slurry catalyst comprises a poison-tolerant catalyst. EXAMPLE - No suitable example given.