Supercritical reactor systems and processes for petroleum upgrading

A process for upgrading a petroleum-based composition comprising:

• combining a supercritical water stream with a pressurized, heated petroleum-based composition in a mixing device to create a combined feed stream;
• introducing the combined feed stream into an upgrading reactor system comprising at least one downflow supercritical upgrading reactor operating at a temperature greater than a critical temperature of water and a pressure greater than a critical pressure of water,
• where the downflow supercritical upgrading reactor comprises at least one catalyst layer and one or more purging fluid inlets disposed on one or more side locations of the downflow supercritical upgrading reactor proximate the catalyst layer;
• passing the combined feed stream through the at least one catalyst layer to at least partially convert the combined feed stream to an upgraded product comprising light hydrocarbons;
• injecting purging fluid through the purging inlets to contact the at least one catalyst layer to reduce plugging;
• and
• passing upgraded product out of the downflow supercritical upgrading reactor.