FAQ: What oils should we avoid mixing?
March 23, 2018
A Q&A with Thomas Knight, Summit’s Development Chemist
Can we mix oils? What can we mix? What can’t we mix?
There are many different types of base stocks or oils out there. The most common oil is mineral oil, so let's just start there. We have Group 1, which is higher in sulfur and higher in aromatics. And then we have Group 2, which has less aromatic or less saturates and less sulfur, therefore it's a cleaner oil. Those mix fine together. There's not an issue with mineral oils because any mineral oil can mix with any other mineral oil. Additionally, they also now have Group 3 oils (which are highly refined Group 2 oils). Mineral oils, which we just described, come out of the ground and are then refined.
Synthetics, on the other hand, are produced. You have polyalphaolefins (PAO), which are chemically made synthetic hydrocarbons. PAO oils have the same basic ingredients as a mineral oils, except that they're made under tight conditions where they can be highly branched. They can have absolutely no saturates.
That's why we consider them synthetics, right?
Yes. PAO oils are actually produced synthetically from a gas stream, and they mix fine with mineral oils because they are basically carbon and hydrogen just like mineral oils. The difference is that the PAO oils are highly refined, therefore they work at both higher and lower temperatures and they have less of a tendency to oxidize.
Additionally, there are other oils, like esters, that can be mixed with this group. A lot of esters are used as plasticizers in industry. We use esters in our oils to give the oil solvency. There also base stocks, like alkylated naphthalenes, which are a little bit new but can be mixed as well. For example, one that's come along that will mix well with oil is a product called oil soluble polyglycols (OSP). Oil soluble polyglycols, like esters and alkylated naphthalenes, are polar and have a solvency to them.
Everything I’ve talked about thus far mix with oil and do fine. Whether you should mix them or not depends on the application and the desired result, but at the very least it’s not unsafe.
The ones that don't mix well, the ones you have to be concerned with, are silicone oils and perfluorinated types (PFAE). These are also synthetic oils, but silicone oils will not mix with standard oils like PAO oils, mineral oils, esters, alkylated naphthalenes, polyglycols and OSP.