Base Oil (Group I / II / III)

Base Oil is not a single chemical compound but a refined, closely specified mixture of saturated paraffinic and naphthenic hydrocarbons recovered from the heavier fractions of crude oil. What distinguishes one API group from another is less the starting crude and more the depth of refining applied: the proportion of saturated hydrocarbons, the sulphur content, and the resulting viscosity index (a measure of how little the oil's viscosity changes with temperature) all increase as refining moves from Group I through Group II to Group III.

At room temperature it is a pale yellow to water-white, oily liquid, essentially odourless in its higher grades. It is blended, almost never sold neat to the end consumer, with an additive package — detergents, dispersants, antioxidants, viscosity-index improvers, anti-wear agents — to produce the finished engine oils, industrial lubricants, hydraulic fluids and greases the market actually uses.

Where it fits in the value chain

Base Oil is the single largest-volume raw material in the lubricants industry. Group I, produced by solvent refining, is still widely used in general industrial oils, process oils and less performance-demanding automotive applications where cost is the main driver. Group II, produced by hydrotreating or mild hydrocracking, offers better oxidation stability and a cleaner, lower-sulphur, lower-aromatic composition, and has become the dominant base stock for modern passenger-car and heavy-duty engine oils. Group III, produced by severe hydrocracking and hydroisomerisation (sometimes marketed as 'hydrocracked synthetic' or 'VHVI' base oil), achieves a viscosity index of 120 or higher from mineral feedstock, approaching the performance of true synthetic polyalphaolefin base stocks at a lower cost, and is widely used in full-synthetic and synthetic-blend engine oils.

Grades we supply

Chelora Chemicals offers Base Oil across Group I, Group II and Group III, in the standard viscosity grades used across industrial and automotive lubricant formulation. Each grade is supplied with a batch-wise certificate of analysis covering viscosity, viscosity index, pour point, flash point and sulphur content.

Base Oil production begins with vacuum distillation of the atmospheric residue left after crude oil's lighter fractions (naphtha, kerosene, diesel) have already been distilled off, which separates the residue into several lubricating-oil-range distillate cuts by boiling range, plus a vacuum residue used for asphalt or further processing. Each lube distillate cut is then refined by one of two broad routes. The conventional (Group I) route uses solvent extraction, typically with furfural or N-methylpyrrolidone, to remove aromatic and polar compounds, followed by solvent dewaxing (commonly with a methyl ethyl ketone/toluene solvent mixture) to remove wax and reach the target pour point, and a final hydrofinishing step to improve colour and stability.

The hydroprocessing (Group II and Group III) route instead uses catalytic hydrotreating or hydrocracking to saturate aromatics and remove sulphur and nitrogen compounds, followed by catalytic dewaxing (isomerising or cracking the wax molecules rather than solvent-extracting them) to reach the target pour point. Group III base oil takes this hydroprocessing further still, with more severe hydrocracking and hydroisomerisation conditions that convert a larger share of the feed into highly branched, highly saturated iso-paraffins, which is what pushes the viscosity index up to 120 and beyond.