Systems and methods for wet air oxidation regeneration of catalysts with atmospheric switching

A method for producing a regenerated hydrogenation catalyst from a fouled hydrogenation catalyst, the method comprising:

• catalytically reacting a feedstock stream having at least one sulfur-containing impurity in the presence of a hydrogenation catalyst to produce the fouled hydrogenation catalyst, wherein the fouled hydrogenation catalyst comprises an amount of sulfur derived from the at least one sulfur-containing impurity of the feedstock stream, and
• subjecting the fouled hydrogenation catalyst to a regeneration cycle to produce a regenerated hydrogenation catalyst, the regeneration cycle comprising:
• (a) contacting the catalyst with a first flushing medium for an air-treatment duration to produce an air-treated catalyst, wherein the first flushing medium comprises, measured at 25° C. and 1 atmospheric pressure, liquid water and a gaseous phase comprising oxygen, and
• (b) contacting the air-treated catalyst with a second flushing medium for a nitrogen-treatment duration to produce a nitrogen-treated catalyst, wherein the second flushing medium comprises, measured at 25° C. and 1 atmospheric pressure, liquid water and a gaseous phase comprising at least 90% nitrogen by volume,
• wherein the amount of sulfur in the nitrogen-treated hydrogenation catalyst is reduced relative to the fouled hydrogenation catalyst.