Sunday, February 24, 2008

Lubricants

Oil is NOT for lubricants. Or is it?

Lubricants are substances that are applied between two moving surfaces to prevent them rubbing against each other and wearing down. They can be grouped into three classes: liquid lubricants (e.g. engine oil or WD40), grease and solid lubricants (e.g. graphite). Somewhat to my surprise, when researching this post it initially appeared to me that there were good non-petroleum alternatives currently available for all three.


Liquid lubricants

Even in a world where personal motor vehicles were a thing of the past, oils would still be important both for whichever vehicles were being used to transport people and goods and to keep all kinds of machinery from sewing machines to hydroelectric turbines in good working order.


Liquid lubricants are grouped by the American Petroleum Institute into five groups, where groups I - III are petroleum fractions and groups IV and V are synthetic oils made of poly-alpha olephins (PAOs) and synthetic esters respectively. Aha! I thought. Maybe we can replace all lubricating oils with group IV and V lubricants and leave petroleum-based oils behind. After all, these synthetic oils are more expensive than petroleum-based oils, but perform better, remaining effective over a higher temperature range and lasting longer before needing to be changed.

However, despite the fact that these were initially developed in response to declining oil base stocks in the 1960s, synthetic oils turn out to be ultimately synthesised from oil. The PAOs are polymerised alkenes such as 1-hexene and 1-octene. These are currently most commonly made from ethylene, although 1-octene can also be made from butadiene. Further digging confirmed that both ethylene and butadiene are produced from oil - ethylene, indeed, being the most common industrial chemical obtained from oil. It is a similar story with the synthetic esters in group V.

Thus synthetic oils are currently synthesised from oil.

This need not be the case, though. Butadiene is currently manufactured from ethanol in much of Eastern Europe and the developing world, and 1-hexene is also manufactured commerically from carbon monoxide and hydrogen using the Fischer-Tropsch process. Unfortunately, as discussed earlier, although these substances need not be sourced from petroleum most commercial hydrogen also traces back to oil. So too does carbon monoxide, although this could be generated from landfill gas. The negative impact of bioethanol on human food availability has been widely discussed elsewhere.

Are there other alternatives, then, outside the API classification system? As far as I can tell there are two further types of liquid lubricants, neither of which seem to provide a magic bullet. The first are made from agricultural products; either tallow (beef fat) or palm kernels. These oils will compete with the food supply in the same way that bioethanol does, although, as lubricating oils are not consumed at the rate that fuels are, this may not be a big issue.

The second is what we used before we had petroleum: spermaceti oil from sperm whales, or similar oils from other cold-water marine species such as orange roughy or royal penguins (1/2 litre per penguin!). Apparently wonderful lubricants, but not something I can see people going for in a big way today.


Grease

Greases are lubricants that are thick, viscous liquids. They are used where liquid lubricants are unsuitable - i.e. in high-pressure applications or where, as is the case with bicycle chains, a liquid oil would simply drip off. The earliest greases were pure animal fats, but most greases we buy today are emulsions of a jelly-like soap thinned down with a lubricating oil of the type described above. They are then spiked with various additives (usually heavy metal and/or petroleum-based) depending on the intended use. Obviously, if petroleum is needed to make lubricating oils, then it is also needed for these greases which include lubricating oils in their manufacture.

The only real exceptions are highly specialised greases, designed to function under extreme temperatures and pressures or around highly corrosive chemicals. These include fluoroether greases such as Krytox (used widely in the aerospace industry) and a variety of silicone greases (which are primarily used in semiconductors and in chemical laboratories, but have a myriad other uses). Unfortunately fluoroether greases are, chemically speaking, modified plastic, and as such are derived from petroleum. The case of silicone greases is more complex, as the silica that is their main constituent comes from rocks not petroleum, but the process of turning that rock into a liquid involves reacting it with oil-derived compounds. Back we come to petroleum. Without it, we'd either be greasing everything from bicycle chains to heavy machinery with animal fats or starting from scratch and making our greases from hydrolysed water and landfill gas in a mind-boggling number of costly and energy-intensive steps!


Solid lubricants

There are two quite distinct types of solid lubricants - teflon (the same teflon that coats non-stick cookware) and fine powders technically known as layered inorganic compounds, of which the most common is graphite.

Teflon, chemically speaking, is identical to the plastic used for plastic shopping bags, except that the hydrogen atoms in its structure have been replaced with fluorine atoms. Oil again...

The layered inorganic compounds are, at a microscopic level, composed of thin, smooth sheets that slide freely against each other, making them excellent lubricants. Many of these, including graphite, are mined and need only minimal processing to obtain a useful lubricant. As naturally occuring minerals they are a non-renewable resource, but their availability is not dependent on oil. Aside from graphite, the next most common is molybdenum disulfide (mined as the mineral molybdenite) followed by tungsten disulfide (mined as tungstenite). The remaining layered compounds are refered to as 'ceramics' and are synthetic, although their synthesis, whilst generally very energy-intensive, need not involve oil. By far the most common of these is boron nitride.

All of these layered inorganic compounds are excellent lubricants, able to function well at extremely high temperatures and pressures. They are currently only used in such extreme environments as their high price prohibits wider application, but they would be eminently suited to use in more everyday contexts as well. I am not alone in suggesting that they would be the lubricant of choice in a world of depleted oil reserves.


In summary, without oil, the readily applied liquid lubricants and greases with which we are familiar would become a thing of the past, unless we were prepared to again slaughter animals to obtain lubricants from their fat. We would, however, still be able to lubricate our machinery with slippery powders, although probably much of that machinery would need to be redesigned to accomodate this change and ball bearings in races may become more common.


As my husband has frequently said as I have been researching and writing this:

"OIL is for lubricants:
save the WHALES!"


1 comment:

Fr. Peter Doodes said...

Hi Heather,

When I was involved in motor sport, there was an oil available for the motorcycle race fraternity that was, I was told (I never used it) was vegetable based and this was called, I think, Castrol R.

Oil technology has certainly improved since I was involved and as you point out, we cannot do without oil.

Synthetic and Semi Synthetic oils have certainly changed the motor engineering world and engines now last several times longer than they did even just a few years ago, and I have no doubt that this is not simply due to improvements in metallurgy.

Thank you for the info and the links... grat stuff!