Putting two oils side by side, the easiest slide is into a discussion of which one is better, and that question has no workable answer. What has real engineering value is the difference: oils from different sources differ in base oil type, additive formulation and the composition of the degradation products, and those differences carry through to every stage of the purification process. Broken down in this way, the configuration has a basis.
The difference starts with the base oil and the additive system
The base oil type determines how readily oxidation starts and what form the products take. Mineral base oil and synthetic base oil produce different kinds of oxidation products over the same running temperature and the same length of time: the former more readily forms polar products of the varnish and sludge type, while the latter oxidises more slowly, but once it has degraded its products are harder to separate by conventional means.
The differences brought by the additive system are closer to what happens on site. Antioxidants, anti-wear agents, detergents and dispersants form a balanced system, and different formulations lose their activity at different rates at high temperature. Running in the same temperature control range of 45–80 °C, one oil may reach the point where its viscosity rises and its colour darkens a long way before or after another. This directly decides whether the oil can still be recovered by purification.
The requirements of the dehydration and degassing stage differ
Water exists in oil in two forms, dissolved water and emulsified water, and this part of the difference has nothing to do with the origin. The degradation products do differ, and they change the polarity of the oil, which changes the efficiency of vacuum degassing. When there are many polar products, the load on the medium heat-absorbing condensing system is heavier, the condensate is discharged more frequently and the automatic separation of the condensate is triggered more often. If the temperature control is still held at the upper limit, bring the limit down from 80 °C to 70 °C where the water content is high, and the processing time will be stretched.
Another easily overlooked point is dissolved gas. Different oils differ in how much gas they dissolve and release in service, and the same vacuum system works better on some oils than on others. That is why a site report that this machine gives only average results on this brand of oil is usually not an equipment problem; the oil characteristics and the process parameters simply do not match.
The requirements of the adsorption and decolouring stage differ as well
Decolouring relies on the adsorbent trapping the polar chromophores and the oxidation products in the oil. An adsorbent has a capacity limit, and once the load is saturated the oil coming out can be worse than the oil going in. The degree of degradation of the oil directly determines how often the adsorbent has to be replaced; with the same TL series machine, an oil that has run for a long time at high temperature and an oil that has run for a long time at low temperature do not have the same replacement cycle for the adsorption tank.
| Stage | Source of the difference | Effect on the configuration |
|---|---|---|
| Dehydration and degassing | Different amounts of polar oxidation products and additive residues | Load on the condensing system and the setting of the upper temperature limit |
| Adsorption and decolouring | Different composition of the chromophores and the polar products | Selection of the adsorbent and its replacement cycle |
| Staged filtration | Different characteristics of the solid particles formed during degradation | Matching of the filter element accuracies and the flushing frequency |
| Temperature control | Different rates at which the additives lose their activity | Allocation of the heating and circulation time |
How to turn the differences into one specific treatment
The most practical approach is not to judge the origin first but to take a representative oil sample and carry out a full assessment of what state it is in before and after treatment. The degree of degradation before the treatment and whether the targets can be met consistently afterwards decide directly whether the route is purification or an oil change.
- When the source or the grade of the oil changes, a fresh sample should be taken and assessed, even if the viscosity grade is the same.
- If the colour clearly darkens and the acid value rises at the same time, degradation products have usually built up; purification can improve the oil but cannot restore it.
- For a machine that runs for long periods under high temperature conditions, the adsorption stage should be put on a scheduled replacement plan rather than being changed only when the colour at the outlet deteriorates.
- Select the filter elements on the measured particle characteristics, not on an assumption based on the origin of the oil.
The differences between the oils decide where the process parameters have to be adjusted, not which drum of oil is worth using. They become useful only when they are turned into a specific temperature control range, an adsorption replacement cycle and a filter element accuracy.