Upgrading of hydrocarbons by hydrothermal process

A method of upgrading a hydrocarbon feedstock, the method comprising the steps of:

• supplying a mixed stream comprising the hydrocarbon feedstock, water and a hydrogen donating composition to a hydrothermal reactor, wherein the mixed stream is maintained at a pressure greater than the critical pressure of water and a temperature greater than the critical temperature of water, and wherein the hydrogen donating composition is pre-heated in a heater to a temperature of greater than about 50° C. and maintained at said temperature for a period of at least about 10 minutes,
• wherein the hydrogen donating composition is selected from the group consisting of tetralin, alkylated tetralin, extracts of liquefied coal, petroleum refinery distillates, cracked products from a petroleum refinery product stream, residue from a petroleum refinery, and combinations of the same;
• reacting the mixed stream in the hydrothermal reactor in the absence of catalyst;
• reacting the mixed stream in the hydrothermal reactor for a residence time sufficient to convert the mixed stream into a modified stream, said modified stream comprising upgraded hydrocarbons relative to the hydrocarbon feedstock;
• separating the modified stream into a gas stream and a liquid stream;
• and
• separating the liquid stream into a water stream and an upgraded hydrocarbon product stream.