Definitions & Terms
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Purification
Purification is removing contamination, either solid, liquid, or dissolved and returning the material to a state where it can be re-used for it’s original purpose.
Recycling
This is the re-use of the product for any other purpose than the original use and covers such things as conversion to fuel programs.
Re-Refining
Re-Refining uses severe physical and chemical process’s, or separation of the oil fraction by distillation. The old, now obsolete technology, was to contact the oil with Sulphuric acid, separate the acid sludge, then clay contact the oil at high temperature. This produced a relatively low grade basestock of some average viscosity that was generally only suited to making low grade industrial oils, such as lubes and cutting oils. Nowadays the preferred process is demetalization followed by vacuum distillation of the various oil fractions. Distillation is followed by Hydrotreating, which further purifies the basestock fraction. There are other process’s based on Solvent Extraction which are presently being commercialized.
Oils produced by distillation and Hydrotreating are typically pure enough to be used in high quality products and are indistinguishable in performance from virgin oils produced by the major oil companies. Two or three viscosity grades are typically produced.
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Waste Oil
Used oils are of either industrial origin or from automotive crankcase oils. No attempt is made to separate or segregate any part of the sources. These wastes may contain almost any organic liquid not deemed "Hazardous Waste" and large amounts of aqueous wastes.
Waste oils generally are disposed of by burning as fuel in waste heat generation, cement kilns or by re-refining to produce industrial oil Basestocks. None is presently used for dust control on roads. At present only a relatively small percentage is sent for re-refining.
Industrial Oils
Industrial oils are described by some of the following general classes:
Lubricating,
Hydraulic,
Gear,
Cutting,
Soluble,
Drawing,
Phosphate ester fluids
Segregation
The process of separating various wastes from others, by containing the different waste streams as close as possible to the source of the waste. Each waste should be identified and stored separately from all others.
Filtration
The removal of solid particles by passing the fluid through a "Filter" where the solid particles are removed from the fluid stream by collection on a "Filter Media". The filter media may be paper, fibrous material (felts etc.), filter aid, diatomaceous earth, or man made materials.
The filter may be a cartridge, belt, or filter press.
Centrifuge
A Centrifuge removes insoluble materials by spinning the fluid at high speed. The high ‘G’ forces generated have the effect of increasing the effects of specific gravity differences of the impurities. In an oil, water being generally heavier flows to the outside of the spinning bowl. Dirt particles heavier than the water, collect at the bottom of the water layer. Centrifuges will not give complete separation of either water or dirt, but can be useful for preliminary treatments to remove gross contamination. Centrifuges are generally only useful for low viscosity fluids, the higher the viscosity and the specific gravity of the oil, the less effective they are.
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Vacuum Dehydration
Water boils at 100 deg C at atmospheric pressure. Many additives present in industrial oils will be degraded relatively rapidly if heated to 100 deg C in the presence of water. When removing water it is very important to find ways to lower the process temperature as much as possible.
As the pressure is reduced, the boiling point is also reduced. A high vacuum of about 25 millibars allows the water to be distilled off at a temperature of about 50 deg C. This reduces the "Stress" on the oils and additives, so that there is no degradation of either during this process.
Distillation
Distillation is a process where a fluid is heated above it’s boiling point and turned to a vapour. The vapour passes into a condenser and is turned back into a liquid. Impurities present in the original fluid remain behind, allowing the distilled fluid to be purified. Distilled oil will usually require further treatment before it can be re-used as a useful lubricant.
Oxidation
In simple terms, oxidation is the reaction of Oxygen with oil components. The higher the temperature of an oil, the faster oxidation reactions will take place. They can never be completely eliminated, but can be slowed down tremendously by the use of the proper "Antioxidant additive" and also controlling temperatures and contamination that the oil is exposed to in use.
The first effect of oxidation is generally an increase in "Total Acid Number" (TAN), then as a second stage a rise in viscosity. Along with these effects there will probably be sludge’s and varnishes formed which may separate out in the oil reservoirs, or coat the surfaces of metal components and cause all kinds of mechanical problems.
Additive Degradation
Additives in industrial oils are very often compounds that will react with water, oxygen or system metals to form reaction, or hydrolysis products which may not be completely soluble in the oil phase. The presence of water together with high temperatures will accelerate this process. These reaction products quite often are responsible for deposits, sludge’s and the formation of varnish like deposits and the accelerated wear of components. Deposits and varnishes are commonly associated with oxidation by-products when in fact the deposits MAY be from degraded additives.
The reduction of additive concentration will also reduce the antiwear, or EP properties of the oil.
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Filter Aid
Filter Aids are normally a "Diatomaceous Earth" or "Pearlite Mineral" which are mined, heated to remove organic materials then ground and classified into various size ranges.
Filter Aids are very useful for removal of extremely fine materials suspended in liquids, they are used for clarifying many liquids, water, beer and wine among many.
The small chambers present in the ground material allows very small particles to become trapped in them, filtration of the relatively large particle also removes all the very small particles trapped within it.
Filter Aids are generally non absorbing to oil additives, although some specific additives can be extracted and removed.
Clay Treatment
Many people become confused when talking about filter aids and various clays such as Fullers Earth used for oil treatment. They are two completely different types of materials. Filter Aids are described above.
Activated Clays and Fullers Earth are a kind of "Bentonite Clay". This type of material when properly pre-treated becomes very attracted to "polar" materials and will actually attract and chemically attach to many impurities, thus removing them from the oil.
The clays are particularly reactive to acidic materials. During the process of oil oxidation, many acidic by-products are formed, these further oxidize to give the sludge’s and varnishes typical of severely oxidized oils. It is well known in oil chemistry that these acidic materials are first formed in the oxidation process and themselves act as catalysts for the further oxidation of the oil.
Removal of these materials while they are present in small amounts and as they form, will enhance the oxidation stability of the oil and extend it’s life.
Clay Treatment is normally accomplished by mixing a known amount of SELECTED ACTIVATED CLAY with the oil in a specially equipped reactor. The oil/clay mixture is heated to a pre-determined temperature, for a very specific time period. The oil is cooled and filtered to remove all traces of the clay. Contact at too high, or too low a temperature will not remove the impurities efficiently. Contact for too long can degrade the oil quality as well as severely degrade some oil additives.
Clay treatment is particularly effective for removing very small particles of degraded oil additives. These particles are semi-plastic and have been proved to pass through even a 0.45 micron absolute filter.
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Colour Degradation
Oil companies have put much effort into producing light coloured base stocks. Removal of unstable compounds during the refining process usually removes the materials that are highly coloured as well. We have been conditioned by the oil companies to think that a light coloured oil is required for oils to have "Good Quality". As a general rule, when dealing with virgin oils, this may be so, but colour is actually a minor characteristic. The materials that give the colour are present in parts per million levels and are difficult, if not impossible to analyze for specifically.
Oils that are "Reclaimed" will always be slightly darker in colour than new oil. The more times an oil is put through the "Purification Process" the darker the colour will become. THIS IS NOT NECESSARILY A SIGN THAT THE OIL IS OXIDIZING! It only means that these "colour components" are building up slightly in the oil. Analysis of the oil is the ONLY way to determine if the oil is starting to oxidize. If the analysis indicates oxidation is NOT occurring and the oil is clean and the additives are present, the colour is irrelevant!
How bad can it get? One of our first customer’s has been recycling the oil from it’s presses for over twenty years now. They pick up and reclaim about 80% of the oil, so there is a 20% make up rate. The oil has been a very dark brown for a long time. Every reclaimed batch is analyzed by the major oil company that supplied the new oil. NOT ONE BATCH HAS BEEN REJECTED BY THE OIL COMPANY!
Total Acid Number (TAN)
This is a measure of the acidity in an oil. The number by itself does not relate to oxidation. Many additives used in oils have a significant acid number to start with. It is very important that the TAN be recorded over time, as it is this trend that indicates whether or nor an oil is oxidizing, or degrading.
I.S.O. Particle Counts (Cleanliness Rating)
In the past there have been many systems developed to measure how clean an oil is. Many of these were very time consuming and difficult. Different labs would often give non uniform results of the same sample.
The whole world is now using one measurement system. One milliliter of oil is filtered through an absolute filter and the particles counted. Only five micron and 15 micron particles are counted, all others are ignored. A typical clean hydraulic system will have an ISO rating of better than 16/14. The numbers of particles are broken into groups for each rating class, numbers falling on the line between groups moves the rating up towards the next higher group. The first number reported is the rating for five micron particles and is referred to the SILT level. The silts will cause wear by acting like an abrasive lapping compound". The second number refers to the 15 micron group rating, these are generally considered to cause abrasive wear.
Filter Ratings
Industrial filters have traditionally been rated at an arbitrary number which was supposed to be the largest size particle that would pass through the filter. In effect this rating was only achieved when the filter was loaded with particles and about ready to be thrown away.
A better way to rate filters uses the BETA RATIO. The ratio is the number of particles per ml. in the dirty stream divided by the number of particles actually passing through the filter. The number is based on particles of a particular size. A filter that passes 5000 particles of the 10,000 entering the filter of size 5 microns has a Beta5 ratio of 2. A filter passing only 100 particles of the 10,000 entering has a Beta5 ratio of 100 and is obviously a better filter. A filter can have a number of Beta ratios depending on it’s construction.
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