Lubricant production process

Abstract

A process for producing lubricant oils of low pour point and high viscosity index by first carrying out a partial dewaxing of a lubricant base stock in an initial catalytic dewaxing operation, followed by a selective dewaxing step. The initial catalytic dewaxing step is carried out using a large pore, high silica zeolite dewaxing catalyst such as high silica Y or zeolite beta which dewaxes by isomerizing the waxy components of the base stock to less waxy brance chain isoparaffins but the severity of the operation is controlled so as to effect only a partial removal of the waxy components. Further removal of the waxy components is effected during the subsequent dewaxing step which is selective for the removal of the more waxy n-paraffin components, leaving the branched chain isoparaffins which contribute to a high VI in the product. The selective dewaxing step may be either a solvent, e.g. MEK dewaxing operation or a catalytic dewaxing using a highly shape selective zeolite such as ZSM-22 or ZSM-23. The severity of the initial catalytic dewaxing operation may be controlled so as to effect a net increase in the content of isoparaffins and because of the selective nature of the solvent dewaxing step, this increased isoparaffins concentration may be retained, producing a product of high VI. The pour point of the feedstock is preferably reduced during the initial catalytic dewaxing step to a value which is no lower than 10.degree. F. and preferably no lower than 20.degree. F., above the target pour point for the products. Generally, this will entail a reduction of at least 10.degree. F. and preferably at least 20.degree. F. in the pour point of the feed.