Lubricants [2]

A lubricant (colloquially, lube, although this usually refers to personal lubricants) is a substance (usually a liquid) introduced between two moving surfaces to reduce the friction and wear between them. Worldwide, more than 50 million tonnes of lubricants are consumed annually. Many lubricants are oils or greases. Automotive engine lubricants comprise approximately 50% and hydraulic fluids with transmission oils 30% of lubricants volume-wise.

In developed nations, lubricants contribute to nearly 1/4 of total pollution released to environment. Spent lubricants are referred to as used oil or waste oil. As a liquid waste, one liter of used oil can contaminate one million liters of water. In most countries, there are efficient collection processes for used lubricants and the majority of this is used directly as a heavy fuel oil. Air emissions of heavy metals have been identified as a problem₁ with this recycling method. Other recycling methods include regeneration for re-use as a lubricant base oil, or in a more recent technology development, thermally cracked to produce gasoil or diesel fuel. The Aldwich processing plant at Kemaman, Malaysia uses thermal cracking technology in conjunction with the ROBYS(tm) aftertreatment process to purify the diesel fuel.

Typically lubricants contain 90% base oil (most often petroleum fractions, called mineral oils) and less than 10% additives. Vegetable oils or synthetic liquids such as hydrogenated polyolefins, esters, silicone, fluorocarbons and many others are sometimes used as base oils. Additives deliver reduced friction and wear, increased viscosity, resistance to corrosion and oxidation, aging or contamination, etc.

Non-liquid lubricants include grease, powders (dry graphite, PTFE, Molybdenum disulfide, etc.), teflon tape used in plumbing, air cushion and others. Alternative way to reduce friction and wear is to use bearings such as ball bearings, roller bearings or air bearings or to use sound, in the case of acoustic lubrication.

In addition to automotive and industrial applications, lubricants are used for many other purposes, including personal hygiene, e.g. K-Y Jelly, often used as a sexual lubricant, bio-medical applications (e.g. lubricants for artificial joints) and others.

Reference

[1] Boughton and Horvath, 2003, Environmental Assessment of Used Oil Management Methods, California Environmental Protection Agency, Department of Toxic Substances Control