The present invention involves the catalytic conversion of hydrocarbons in a multiple-stage process. More particularly, the present invention is directed toward the production of lubricating oil base stocks having viscosity indices above 100. A lubricating oil base stock is synonymously referred to in the art as a "neutral oil," and is, in effect a dewaxed hydrocarbon mixture, boiling in the lubricating oil boiling range, which does not contain viscosity improvers or other additives. That is, a "lubricating oil" denotes in the art a dewaxed product containing various additives. Through the utilization of the present invention, there is produced a waxy lubricating oil base stock having a viscosity index of above about 100. Following dewaxing, a standard prior art technique, the viscosity index remains above 100, and the resulting neutral oil is highly desirable for the production of multi-graded lubricating oils.
The prior art is replete with references to crude oils containing hydrocarbon components suitably adaptable for use as lubricating oils. In general, those lubricating oils derived from highly paraffinic crude stocks are utilized in the production of high quality motor oils, aviation oils and turbine oils. This type of lubricating oil is characterized by a relatively high viscosity index (V.I.), although, it actually is a blend of relatively low and relatively high viscosity index components. Lubricating oil base stocks which are derived from highly naphthenic crudes are employed in the production of lubricating oils having exceptionally desired properties with respect to a heavy duty use such as that found in diesel engines. Desirable components of lubricating oil base stocks, or neutral oils, are iso-paraffins and molecules containing single rings, whether naphthenic or aromatic. However, essentially all heavy hydrocarbonaceous fractions, derived from crude oils, contain condensed-ring as well as straight-chain hydrocarbons. Characteristically, condensed-ring hydrocarbons have low viscosity indices and relatively poor resistance to oxidation. Therefore, they are undesirable as components of the various types of lubricating oils.
A perusal of the prior art procedures and techniques for producing lubricating oil base stocks indicates that relatively high viscosity index lubricating oils may be produced through the use of a combination of solvent extraction techniques and clay-treating, acid-treating, etc. Some heavy duty lubricating oils are obtained by way of vacuum distillation followed by alkali-treating for the removal of naphthenic acids. The complex nature of high viscosity index lubricating oil production presents a challenge to the petroleum industry in the form of significant processing problems which are not easily solved through the use of present-day operating techniques. For example, solvent extraction of the undesirable components is inefficient in view of the fact that the available solvents are not highly selective for the components which must be removed from the lubricating oil base stock. Furthermore, immense, complicated equipment is required for contacting the lubricating oil with the solvent and for the recovery of the solvent in order to make the process economically attractive. With respect to acid-treating and clay-treating techniques, problems involve disposal of clay and loss of hydrocarbon yield, as well as an acidic sludge disposal problem when strong acids, such as sulfuric acid, are employed. By way of brief summation, it might be said that the prior art schemes are severely hampered in their capability to produce pure lubricating oils having high viscosity indices, and are tedious and expensive to operate in an acceptably efficient manner.
Candor compels recognition of the fact that certain prior art techniques are required if satisfactory lubricating oils are to be produced. Thus, it is necessary to subject a crude oil to one or more distillation techniques in order to provide a crude oil bottoms product concentrated in lubricating oil base stock. Another prior art scheme which may be required as a preliminary processing step, with respect to some crude oil bottom product, is a deasphalting process. The crude oil bottoms, containing asphaltenic constituents, is intimately admixed with a light hydrocarbon solvent such as propane, butane or hexane, at conditions of temperature and pressure under which the asphaltenic constituents are precipitated. In view of the fact that the preliminary processing techniques of distillation and deasphalting are well known to those skilled in the art of petroleum refining technology, and form no essential part of our invention, further description thereof is not believed required herein.
Another prior art technique is necessary in order to produce a suitable lubricating oil base stock. Waxy constituents must be removed to improve the overall quality of the ultimate lubricating oil. The dewaxing technique is accomplished by a well known method which generally employs solvents such as propane, methyl isobutyl ketone, methylethyl ketone, toluene, etc. The waxy lubricating oil base stock and solvent are heated to a temperature sufficiently high to render the solvent and base stock substantially miscible. The resulting mixture is then chilled to precipitate the wax from the solution. As hereinafter indicated, the dewaxing step adversely affects the viscosity index of the dewaxed product. Through the utilization of the present invention, a waxy lubricating oil base stock, having a viscosity index above 100 is produced.
Until now, there has been no facile method for producing superior lubricating lube oil base stocks while at the same time producing maximum non-lube oil distillate. Examples of non-lube oil distillate are LPG, gasoline and kerosene.