Products from a high pressure processing system are separated and purified. The processing system is adapted for pressurizing and heating a feed mixture comprising carbonaceous material(-s) in the presence of homogeneous catalysts and liquid organic compounds to produce a converted feed mixture. The converted feed mixture is cooled and depressurized, and then separated into: a gas phase, an oil phase, and a water phase comprising liquid organic compounds and dissolved homogeneous catalysts comprising potassium and/or sodium. The liquid organic compounds and dissolved homogenous catalysts are at least partly recovered from said water phase, thereby producing a first water phase stream enriched in liquid organic compounds and homogeneous catalysts and a second water phase stream depleted in liquid organic compounds and homogeneous catalysts. The first water phase is at least partly recycled to the feed mixture, with a bleed stream being withdrawn therefrom prior to recycling.