Absolute Pressure – This is the gauge pressure plus Atmospheric Pressure
Absorption – Process for separating mixtures into their constituents by taking advantage of the fact that some components are more readily absorbed than others. See also PSA.
ACEA– Association des Constructeurs Europeens d’Automobiles.
ACGIH – The American Conference of Governmental and Industrial Hygienists.
Acid Number– In lubricants and base oils their acidity is defined in terms of Acid Number (Strong acid number and total acid number, or TAN).
Acid Treating – An old refining process in which unfinished petroleum or petrochemical products (including base oils) were contacted with sulphuric acid to improve their colour, odour and other properties. May result in acidic by-products (acid-tar).
Additive – Chemical added to a product to improve its properties.
ADOS – Process for the neutralisation of naphthenic acids.
Adsorption – Certain types of molecules (generally impurities) fix to the surface of highly porous materials, e.g. nitrogen components absorb to the surface of base oil hydroprocessing catalysts, deactivating them.
After-Filter – A filtration unit typically using cartridge filters and generally the last unit in the MDU to prevent contamination of the base oil due to the formation of pinholes in the upstream rotary vacuum filters.
Aniline Point – The lowest temperature at which an oil product is completely miscible with aniline in a 1:1 volumetric ratio.
API – The API(American Petroleum Institute) is the trade association incorporated in the US representing the entire (US) petroleum industry: exploration and production, transportation, refining, and marketing.
API “Donut” – API licensed “Service Symbol” indicating the oil “Performance Level” of engine oils.
API “Starburst” – API licensed Certification Mark indicating compliance with minimum performance requirements of a particular specification.
API Gravity – An arbitrary scale used to report the gravity, or density, of a petroleum product. Related to specific gravity scale (15°C/15°C) by: °API = 141.5/SpGrav – 131.5.
API-I – Base oils that fall into the 1st group of the API Interchangeability guidelines (PAOs).
API-II – Base oils that fall into the 2nd group of the API Interchangeability guidelines (low aromatic content base oils).
API-III – Base oils that fall into the 3rd group of the API Interchangeability guidelines (PAOs).
API-IV – Base oils that fall into the 4th group of the API Interchangeability guidelines (extremely high VI base oils).
API-V – Base oils that fall into the 5th group of the API Interchangeability guidelines (other base oils, esters, etc.)
Appearance – Base oil quality test to define quality of base oils. General specification is ‘bright and clear’, off-specification products may have a haze.
Aromatics Content – See TPC, total polar content.
Aromatics – Hydrocarbons with a ring structure, generally with a distinctive aromatic odour, and good solvent properties (e.g. BTX).
Asphalt – By-product from the PDU, i.e. those components in the short residue soluble in the solvent (propane), thus propane-asphalt. Also, mixture of bitumen and aggregate used for road surfaces and synonym for bitumen (US terminology).
Asphaltenes – Petroleum compounds that are soluble in toluene (or carbon disulphide) but insoluble in pentane (C5-asphaltenes) or heptane (C7-asphaltenes).
ASTM – American Society for Testing & Materials. An association incorporated in the US for promoting knowledge of the properties of engineering materials and standardising specifications and methods of testing.
ATIEL – Association Technique de l’Industrie Europeenne des Lubrifiants.
Atmospheric Pressure – The weight of the atmosphere on the surface of the Earth. At sea level this is approximately 1.013 bars, 101,300 Newtons per square metre, 14.7 pounds per square inch or 30 inches of mercury.