The H-Oil-DC Process is a specially engineered, ebullated-bed process for the treatment of vacuum gas oils. The ebullated-bed was invented in the 1950s and was a forerunner to the commercial H-Oil^® Process, which is used to upgrade vacuum residua.

The ebullated-bed reactor system overcomes problems encountered with fixed-bed reactors when processing difficult feedstocks or when high processing severity is required. The bed of extrudate catalyst is fluidized (ebullated) by the lift of hydrogen and feed oil and recycled reactor liquid. The ebullated catalyst is well mixed and can be added and withdrawn from the reactor while at operating conditions.

Because of the ability to replace the catalyst bed incrementally, the H-Oil-DC  Reactor can operate indefinitely– typically, four to five years between turnarounds to coincide with the inspection and maintenance schedule for an FCC Unit.

The difficult processing requirements resulting from stricter environmental regulations and the processing of heavy feedstocks makes H-Oil-DC  a preferred choice for FCC pretreatment in the 21^st century. Axens has already eight commercially operating ebullated-bed reactor units.

Two additional advanced generation H-Oil processes are marketed: H-Oil-HCC and H-Oil-RC.