Process for the production of high quality base oils

A method for hydroprocessing a hydrocarbon feedstock which produces a stream of unconverted oil of sufficient quality for use as a base oil feed for the production of Group III oils, white oils and low BMCI ethylene plant feed, said method employing multiple reaction zones within a single reaction loop, comprising the following steps:

• (a) passing a hydrocarbonaceous feedstock to a first hydroprocessing zone, the hydroprocessing zone having one or more beds containing hydroprocessing catalyst, the hydroprocessing zone being maintained at hydroprocessing conditions, including a pressure in the range from 500 to 5000 psig, wherein the feedstock is contacted with catalyst and hydrogen;
• (b) passing the effluent of step (a) directly to a hot high pressure stripper, wherein the effluent is contacted with a hydrogen-rich stripping gas to produce a vapor stream comprising hydrogen, hydrocarbonaceous compounds boiling at a temperature below the boiling range of the hydrocarbonaceous feedstock, hydrogen sulfide, ammonia, and a bottoms stream comprising hydrocarbonaceous compounds boiling in approximately the same range of said hydrocarbonaceous feedstock along with a portion of the hydrocarbonaceous compounds boiling in the diesel boiling range;
• (c) passing the overhead vapor stream from the hydrogen stripper of step (b) to a first cold high pressure separator where hydrogen, hydrogen sulfide and light hydrocarbonaceous gases are removed overhead and a liquid stream comprising naphtha, middle distillates and unconverted oil is passed to fractionation, thereby removing most of the ammonia and some of the hydrogen sulfide (as ammonium bi-sulfide in the sour water stream as it leaves the cold high-pressure separator);
• (d) combining the liquid stream from the hydrogen stripper of step (b) with a portion of the unconverted oil of the fractionation step of step (c) and passing the combined stream to a bed of hydroprocessing catalyst in a second reactor zone, wherein the liquid is contacted under hydroprocessing conditions with the catalyst, in the presence of hydrogen, and under a pressure in the range from 500 to 5000 psig;
• (e) passing the overhead from the cold high pressure separator of step (c) to an amine absorber, where hydrogen sulfide is removed before hydrogen is compressed and recycled to hydroprocessing vessels within the loop;
• (f) passing the effluent of step (d), after cooling, to a second cold high pressure separator where hydrogen, hydrogen sulfide and light hydrocarbonaceous gases are removed overhead and a liquid stream comprising naphtha, middle distillates and unconverted oil is passed to fractionation, thereby removing most of the ammonia and some of the hydrogen sulfide (as ammonium bi-sulfide in the sour water stream as it leaves the second cold high-pressure separator);
• (g) passing the vapor stream from step (f) after further cooling and separation of condensate, to the recycle gas hydrogen compressor;
• (h) passing the compressed hydrogen from the recycle gas hydrogen compressor to the primary reactor loop;
• and
• (i) passing at least a portion of the unconverted oil from the fractionator of steps (c) and (f) to facilities for the preparation of Group III oil, white oil, or BMCI ethylene feed.