Originally Posted By: pev223
Your first post also said PAO was the ultimate paraffinic oil,completely wrong. Just the opposite is true, that's PAO greatest strength. Only mineral based oils have paraffin in them. This is one of the impurities they are forever trying to remove.
You are correct in a way
-- as they do want to remove
certain paraffins from oil, just not all paraffins. There are 3 general types of paraffins …
1) linear paraffins -- straight chain hydrocarbons or normal paraffins
2) iso-paraffins -- branched chain paraffins
3) cyclo-paraffins -- hydrocarbon chains with ring structures (naphthenes)
It turns out that you don't want the linear paraffins (1) in your base oil, so they are removed. The longer chain (C20+) linear paraffins can line up and crystallize too easily to form wax -- even at room temperature. So you either remove them by solvent dewaxing, or, you rearrange them by isomerization (isodewaxing = Chevrons name for technology) into more appropriate isoparaffins for use in your base oil. You keep the other paraffins (2,3) which make up your Group II/III base oils.
PAO's are hydrocarbon chains just as are Group II and III base oils are. It's just that PAO's have a different hydrocarbon structure compared to II/III. In other words, the C-H molecules in PAO are just chained together differently than for GII/III base oils. So a PAO is technically a paraffin (isoparaffin) too.
Interestingly enough, Group III+ base oils are made from paraffin wax and have an isoparaffin structure (branched chain structure) in many ways very similar to PAO's (that's why they have similar performance). Group III+ have a longer backbone with shorter varying length chains, whereas PAO's have a short backbone with longer C-H chains sticking out. It's the particular C-H chaining structure of PAO's that gives them a nice low pour point (they don't line up easily to crystallize). PAO can crystallize (form wax) -- they just do so at a very low temperature, much lower than the typical C-H chain in a Group II or even III base oils.