Embodiments of a hydrocarbon conversion apparatus are provided, as are embodiments of a hydroprocessing conversion process. In one embodiment, the hydrocarbon conversion apparatus includes a reaction vessel having a reaction chamber and a feed distribution chamber. A riser fluidly couples the feed distribution chamber to the reaction chamber, and a catalyst recirculation standpipe fluidly couples the reaction chamber to the feed distribution chamber. The catalyst recirculation standpipe forms a catalyst recirculation circuit with the reaction chamber, the feed distribution chamber, and the riser. A catalyst is circulated through the catalyst recirculation circuit during operation of the hydrocarbon conversion apparatus.