Method for enhancing catalytic activity

Claim 1

In a process for preparing a high quality lube base stock oil having a predetermined pour point in the range of about -25° to +30° F. from waxy crude oil, which process comprises: extracting a distillate fraction that boils within the range of 450° to 1100° F. or a deasphalted short residuum fraction of said waxy crude with a solvent selective for aromatic hydrocarbons to yield a raffinate from which undesirable compounds have been removed; contacting the raffinate and hydrogen gas with a dewaxing catalyst under dewaxing conditions effective to impart said predetermined pour point, said catalyst comprising a first crystalline zeolite having a dry crystal framework density of not less than about 1.6 grams per cubic centimeter and a constraint index of about 1 to about 12, thereby converting wax contained in the raffinate to lower boiling hydrocarbons; and, topping the dewaxed raffinate to remove therefrom components of a low molecular weight; the improvement, whereby the resistance to oxidation of said dewaxed raffinate is increased, which comprises: pretreating said raffinate, prior to dewaxing, with a sorbent comprising a second crystalline zeolite having an effective pore diameter equal to or larger than said first crystalline zeolite, said pretreating being conducted under a combination of conditions selected from a temperature of about 35° to about 350° F., a pressure of 0 to 3000 psig, and a contact time equivalent to a LHSV of 0.1 to 100 hr. -1 , said combination being effective to provide a pretreated raffinate characterized by an initial equilibrium temperature not exceeding about 675° to 700° F. and at least 25° F. lower than that obtained with said raffinate without pretreatment when dewaxed at about 1 LHSV; and dewaxing said raffinate at a temperature not to exceed the lesser of said equilibrium temperature of said raffinate without pretreatment minus 25° F., or 700° F.