Manufacture of hydrocracked low pour lubricating oils

Claim 1

A continuous process for producing a dewaxed lubricating oil base stock characterized by good stability on exposure to light and air from a hydrocarbon feedstock boiling above about 650° F. (343° C.), which process comprises: hydrocracking said feedstock in a hydrocracker section containing a hydrocracking zone at hydrocracking conditions including a pressure of 1000 to 3000 psig, said conditions being effective to convert at least 20 volume percent of said feedstock to materials boiling below the initial boiling point of said feedstock, said conversion being accompanied by the consumption of hydrogen and the formation of hydrogen sulfide and ammonia contaminants; passing the hydrocracker effluent comprising hydrocrackate and contaminated hydrogen gas to a sorption section wherein a substantial fraction of said hydrogen sulfide and ammonia contaminants are removed; passing the effluent from said sorption section, including purified hydrogen gas, to a catalytic dewaxing section wherein the hydrocrackate is catalytically dewaxed in a high pressure dewaxing zone; passing the effluent from the catalytic dewaxing section, comprising dewaxed hydrocrackate and hydrogen gas to a high pressure hydrotreating zone operated at conditions effective to stabilize the lube base stock in said hydrocrackate; passing the hydrotreater effluent to a high pressure separator section thereby recovering hydrogen gas and hydrocarbons comprising said dewaxed, stable lubricating oil base stock; passing makeup hydrogen gas into at least one of said sections and in an amount at least equal to the hydrogen consumed in the hydrocracker section; recycling said recovered hydrogen gas to said hydrocracker; and maintaining the circulation of said gas in said process by repressuring said gas by not more than about 750 psi.