Hydroconversion process for making lubricating oil basestocks

A process for producing a lubricating oil basestock meeting at least 90 wt. % saturates and VI of at least 105 by selectively hydroconverting a raffinate produced from solvent refining a lubricating oil feedstock which comprises:

• (a) conducting the lubricating oil feedstock, said feedstock being a distillate fraction, to a solvent extraction zone and under-extracting the feedstock to form an under-extracted raffinate whereby the yield of raffinate is maximized;
• (b) stripping the under-extracted raffinate of solvent to produce an under-extracted raffinate feed having a dewaxed oil viscosity index from about 85 to about 105 and a final boiling point of no greater than about 650.degree. C.;
• (c) passing the raffinate feed to a first hydroconversion zone and processing the raffinate feed in the presence of a non-acidic catalyst having an acidity value less than about 0.5, said acidity being determined by the ability of the catalyst to convert 2-methylpentyl-2-ene to 3-methylpent-2-ene and 4-methylpent-2-ene and is expressed as the mole ratio of 3-methylpent-2-ene to 4-methylpent-2-ene at a temperature of from 340 to 420.degree. C., a hydrogen partial pressure of from 1000 to 2500 psig (7.0 to 17.3 mPa), space velocity of 0.2 to 3.0 LHSV and a hydrogen to feed ratio of from 500 to 5000 Scf/B (89 to 890 m.sup.3 /m.sup.3) to produce a first hydroconverted raffinate;
• (d) passing the hydroconverted raffinate from the first hydroconversion zone to a second hydroconversion zone and processing the hydroconverted raffinate in the presence of a non-acidic catalyst having an acidity value less than about 0.5, said acidity being determined by the ability of the catalyst to convert 2-methylpent-2-ene to 3-methylpent-2-ene and 4-methylpent-2-ene and is expressed as the mole ratio of 3-methylpent-2-ene to 4-methylpent-2-ene at a temperature of from 340 to 400.degree. C. provided that the temperature in second hydroconversion is not greater than the temperature in the first hydroconversion zone, a hydrogen partial pressure of from 1000 to 2500 psig (7.0 to 17.3 mPa), a space velocity of from 0.2 to 3.0 LHSV and a hydrogen to feed ratio of from 500 to 5000 Scf/B (89 to 890 m.sup.3 /m.sup.3) to produce a second hydroconverted raffinate;
• (e) passing the second hydroconverted raffinate to a hydrofinishing reaction zone and conducting cold hydrofinishing of the second hydroconverted raffinate in the presence of a hydrofinishing catalyst which is at least one Group VIB or Group VIII metal oxide or metal sulfide on a refractory metal oxide support at a temperature of from 260 to 360.degree. C., a hydrogen partial pressure of from 1000 to 2500 psig (7.0 to 17.3 mPa), a space velocity of from 0.2 to 5 LHSV and a hydrogen to feed ratio of from 500 to 5000 Scf/B (89 to 890 m.sup.3 /m.sup.3) to produce a hydrofinished raffinate;
• (f) passing the hydrofinished raffinate to a separation zone to remove products having a boiling less than about 250.degree. C.;
• and
• (g) passing the hydrofinished raffinate from the separation zone to a dewaxing zone to produce a dewaxed basestock having a viscosity index of at least 105 provided that the basestock has a dewaxed oil viscosity index increase of at least 10 greater than the raffinate feed, a NOACK volatility improvement over raffinate feedstock of at least about 3 wt. % at the same viscosity in the range of viscosity from 3.5 to 6.5 cSt viscosity at 100.degree. C., and a saturates content of at least 90 wt. % and a basestock with low toxicity by passing the IP346 or FDA(c) tests.