Production of lubricant base stocks with controlled aromatic contents

Abstract

Methods are provided for producing Group II and Group III base stocks with a controlled or consistent aromatics content. An aromatics-rich base stock, such as a Group I base stock or an alkylated aromatic base stock, can be added to the catalytically treated base stock in a minimal amount after the final catalytic treatment step but prior to fractionation. At the beginning of a processing run for forming lubricant base stock products, about 0.25 wt % to about 1.25 wt % of the Group I base stock can be added to a catalytically processed feed after the final catalytic processing stage but prior to fractionation to form the Group II and/or Group III base stock. During the course of the processing run, the amount of Group I base stock added can be reduced roughly in correspondence with the increase in aromatics caused by catalyst deactivation. This can allow a catalytically processed lubricant base stock product to be generated that contains at least about a threshold (minimum) aromatics content during the course of a processing run. Alternatively, this can allow a catalytically processed lubricant base stock product to be generated that has consistent aromatics content during the course of the processing run.