quote:Chevron has announced that they're going to produce more Group II+ base stock and less Group II at their Richmond refinery. The GR-II+ has the higher viscosity index/better cold crank numbers. I don't know if this means that Chevron is reformulating their own products or just producing more GR-II+ for sale to other customers. Note that Chevron describes Havoline as their "internal" customer, and Havoline, as well as other users, needs more GR-II+ base stock for more 5W-30 production. Ken
Originally posted by Drstressor: ..... Chevron may now be using a more aggressive hydro-cracking method that improves the VI to the point where extensive wax isomerization (the iso-syn process) is no longer necessary. Just a guess.
quote:...mmmmm, drstressor, could you explain everything after the part where you say, "Sure."
Originally posted by Drstressor: Sure. Waxes are long linear hydrocarbon chains. So a wax molecule that is say 24 carbons long is a pretty long molecule that can easily interact with other long molecules to form a network once the temperature gets low enough so that molecular motions doesn't pull everything apart. Chevron's iso-dewaxing procedure uses a chemical catalyst attached to a solid matrix that re-arranges the wax molecules into branched structures which have a smaller radius. So a 24 carbon linear molecule might be converted to a 24 carbon branched molecule. Since they have the same mass, but different structures, they are said to be isomers. The branched molecules don't form networks as easily as long linear molecules so you get a base stock with a low pour point. Severe hydrocracking treats a base stock with hydrogen at high temperature and pressure in the presence of different catalysts. Chemical bonds are saturated with hydrogen, broken, and often rearranged into branched structures. The resulting molecules have a much more uniform mass range than the feed stock and thus a higher VI. So, wax molecules are rearranged by hydrocracking as well. In fact, some of the best Group III base oils start out by treating "slack wax", which is essentially obtained by cooling down crude feed stock oil and allowing the wax to congeal.