Base Oil Groups – A relook

UNDERSTANDING BASE OIL

Base Oils

Lubricants have been around since ancient times. The Petroleum-based Lubricants business started in mid 1800′s. The initial processing was limited to separation by boiling point. Most people know the key driver of the production for lubricants are Base Oils.

Mineral Base Oil

Modern mineral base oils are the result of a long and complex distillation and refining processes. The feedstock used is crude oil. This substance is not of uniform quality but consists of several thousands of hydrocarbon compounds in which the elements carbon and hydrogen are present in all molecules and, in part, are bound to other elements.

The hydrocarbons can be divided into three main groups: paraffinic, naphthenic and aromatic.

Paraffinic hydrocarbons can be further divided into two subgroups: normal paraffinic and isoparaffinic.

Paraffinic hydrocarbons are the best lubricants. The distillation process in the refinery separates the hydrocarbons contained in the crude into cuts based on the molecule size.

Furthermore, as many unwanted substances as possible are removed in the process, such as sulphur, aromatic hydrocarbons, paraffin wax, etc. In other words the mineral oil production process is physical cleaning and the end product is so-called paraffinic base oil.

Most of the hydrocarbons in the base oil are paraffinic, but it also contains naphthenic and aromatic molecules. When the finished lubricant, such as motor oil, is made of these, several additive compounds are used to improve the base oil properties.

The final outcome can also be so-called naphthenic base oil, where most of the hydrocarbons are naphthenic. Their cold properties are excellent.

Groups

Base stocks are called by several names:
Neutrals (100N, 150N, 600N, …),
Bright Stocks, Grades (SAE 5, 10…; ISO 22, 32..).

The most common names are for group I (SN: Solvent Neutral), for group II (N: Neutrals) and group III grade names refer to the viscosity (4cst, 6cst, 8cst …). Grade names can also refer to trademarks.

Group Viscosity Index Saturates Sulphur in > 0.03% Conventional (Solvents)
II 80-120 0.9 0.0003 Requires Hydroprocessing
III >120 0.9 0.0003 Requires severe Hydroprocessing, often special feedstocks
IV — PolyAlphaOlefins (PAO)
V — All other basestocks not in Group I – IV including other synthetics

Base Oil Production

The quality of Base Oil has evolved with the process technology. The first generation of process technology was developed to remove aromatics and other impurities.

With the Solvent Processing Technology, it was possible to recover wax as a by-product and lower the pour-point and the simply hydro-fining also added to the further reduction of impurities.

In third phase the Hydro-processing Technology was developed and this changed the base oil business from “Physical separations” to “Chemical transformations”. The technology could produce lighter viscosity grades, which was a popular option for the refineries. Some refineries use also Wax Isomeration to produce very high quality base oils.

Production Flow Chart

” Feedstock is separated into distillates and vacuum gas oils
” Vacuum gas oil is sent through the hydrocracker for conversion
” To saturate the molecules and remove impurities such as nitrogen, sulphur, oxygen and heavy metals, Hydrogen is introduced.
” Under extreme temperature and pressure in the presence of a catalyst, hydro-cracking converts aromatics molecules into saturated Paraffin.
” This process yields stock with ighter in colour since the absence of contaminants.
” Long waxy paraffin molecules are restructured into shorter ones , so-Paraffin that resist gelling and improve low temperature pump-ability.
” Hydrogen is introduced again to clean up the remaining and impurities thus enhancing the oxidation and thermal stability of the final product.

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