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 a first catalyst layer and a second catalyst layer, the second catalyst layer disposed vertically below the first catalyst layer in the downflow supercritical upgrading reactor,
• where the first catalyst layer comprises a catalyst having a first void volume ratio and the second catalyst layer comprises a catalyst having a second void volume ratio, and
• where the second void volume ratio differs from the first void volume ratio;
• passing the combined feed stream through the first catalyst layer and the second catalyst layer, where light hydrocarbons in the combined feed stream at least partially flow through the first catalyst layer and the second catalyst layer while heavy hydrocarbons in the combined feed stream are at least partially sifted in voids of the first catalyst layer, voids of the second catalyst layer, or both;
• at least partially converting the sifted heavy hydrocarbons to light hydrocarbons in the first catalyst layer or the second catalyst layer in the presence of the supercritical water;
• and
• passing upgraded product comprising light hydrocarbons and the converted light hydrocarbons out of the downflow supercritical upgrading reactor.