Lubricating base oils

Abstract: Lubricating base oils of enhanced aromaticity and high viscos ity index are manufactured by dehydrogenation of a high viscosity index base oil over a suitable catalyst and, optionally, subsequent hydrotreating of the dehydrogenated product.

Description: This invention relates to lubricating base oils and is particularly concerned with a process for the manufacture of such base oils with a high viscosity index and to lubricating base oils which can be obtained by that process. Lubricating base oils are derived from various mineral crude oils by a variety of refining processes, generally directed to obtaining a lubricating base oil with a suitable viscosity index for the intended end use. The preparation of high viscosity index lubricating base oils can be carried out as follows. A crude oil is separated by distillation at atmospheric pressure into a number of distillate fractions and a residue, known as long residue. The long residue is then separated by distillation at reduced pressure into a number of vacuum distillates and a vacuum residue known as short residue. From the vacuum distillate fractions lubricating base oils are prepared by refining processes which include wax removal from the vacuum distillate fractions. From the short residue asphalt can be removed by known deasphalting processes to give a deasphalted oil from which wax can subsequently be removed to yield a residual lubricating base oil, known as bright stock. The wax obtained during refining of the various lubricating base oil fractions is designated as slack wax. Such slack waxes can be catalytically hydrotreated to yield high viscosity index lubricating base oils using processes such as those described in GB 1,429,494 and European patent application No. 324 528. The high viscosity index base oils obtained by such processes have excellent characteristics in many respects, especially as they obviate the need for the addition of polymeric viscosity index improvers. However, as a result of the processing involved in their manufacture, they have a low aromaticity when compared with lubricating base oils of lower viscosity index. Thus they have a reduced ability to solubilize other materials, for example materials resulting from oxidation reactions which occur in the commercial lubricants prepared therefrom. In United States patent specification No. 3,530,061 a process is described in which a lubricating base oil obtained from a hydrocracking process and comprising polycyclic hydrocarbons, is made resistant to deterioration upon exposure to light and air by contacting the lubricating base oil with a catalyst having dehydrogenation/hydrogenation activity. The feed to the process described in this publication, is a hydrocracked dewaxed distillate feed not having a high viscosity index as defined hereinbelow, and already containing a relatively high percentage of aromatic compounds. In United States patent specification No. 3,880,747 a process is described for hydro-aromatisation of a lubricating base oil distillate stock. The product of this process contains an increased weight percentage of monocyclic and total aromatics. Nowhere in this document reference is made to a viscosity index (VI). The preferred feedstock is a naphthenic distillate which is generally characterised by a viscosity index well below 100. In French patent specification No. 1,593,929 a process is described for the preparation of a lubricating base oil, having a VI of at least 80 from a paraffinic-naphthenic feed, low in aromatics and having a VI of from 80 to 122. In this process the saturated rings of the naphthenes are opened to give paraffins and naphthenes with a lower number of condensed rings. Apart from this, dehydrogenation of the naphthenes to aromatics also takes place. If it is desired to prepare very high viscosity index lubricating base oils, the aromatics have to be removed from the product by conventional methods. The present invention is directed to the preparation of novel lubricating base oils having a high viscosity index together with comparatively high aromaticity. Surprisingly it has been found that such aromatics-containing base oils can be obtained by dehydrogenating and optionally selectively rehydrogenating a high viscosity index lubricating base oil while still maintaining the desired high viscosity index. Accordingly, one aspect of the present invention provides a novel process for introducing aromaticity to a lubricating base oil comprising contacting a lubricating base oil feedstock having a high viscosity index with a dehydrogenating catalyst and recovering a high viscosity index product having enhanced aromaticity therefrom. By high viscosity index is understood a viscosity index of at least 125 as determined by ASTM D-567. The feedstock preferably has an extra high viscosity index of at least 135. At least a portion of the product having enhanced aromaticity may be subjected, in accordance with a further aspect of the present invention, immediately downstream of the dehydrogenation or after further processing and/or transportation, to hydrotreating in the presence of hydrogen and a suitable catalyst and recovering a hydrotreated product therefrom. It has also surprisingly been found that the hydrotreating does not substantially decrease the aromaticity, so that there is obtained a product of increased aromaticity from which olefinic unsaturation has substantially been removed by the hydrotreatment. Furthermore, the product has been found to maintain a high viscosity index, together with an increased aromatic content. Suitably, the aromatic content is increased by contact with the dehydrogenating catalyst by an amount of at least 3 mmol/100 g. Therefore, in accordance with a still further aspect of the invention, there are provided, as novel products, lubricating base oils having an extra high viscosity index of at least 135 and an aromatic content of at least 3 mmol/100 g. These base oils may be the direct products of the dehydrogenation, containing some olefinic unsaturation, or the products of the subsequent hydrotreatment to give base oils from which the olefinic unsaturation has substantially been removed. The lubricating base oil feedstock having a high viscosity index may be obtained for example by the processes described in GB 1,429,494 and EP 324 528. The viscosity index as determined by ASTM D-567 is at least 125 and is preferably at least 135, more preferably above 140. The base oils suitably also have a low pour point below -10 °C (as determined by ASTM D-27). The dehydrogenating catalyst employed to introduce aromaticity to the lubricating base oil is preferably a composite catalyst comprising a Group VIII noble metal component, a Group IVA metal component and a refractory oxide support. The Group VIII noble metal component is preferably platinum and is preferably present in an amount of 0.1 to 1 %wt, preferably 0.3 to 0.5 %wt. The Group IVA metal component is preferably tin and is preferably present in an amount of 0.1 to 1 %wt, preferably 0.3 to 0.5 %wt. The refractory oxide support is preferably alumina but may also be materials such as silica, silica-alumina, magnesia, zirconia, titania or mixtures thereof. It is possible, though not essential, to neutralize the catalyst support, for example with an alkali metal or alkaline earth metal component, preferably lithium, or, alternatively potassium. Suitable catalysts are described, for example, in US Patent No. 4,672,146. The dehydrogenation reaction is normally carried out at a relatively high temperature and moderate pressure. Suitable temperatures are in the range of 300 °C to 600 °C, preferably from 400 to 500 °C, with a hydrogen partial pressure of 1 to 30 bar, preferably from 5 to 15 bar. Suitable space velocities range from 0.2 to 20, preferably from 2 to 10 kg/l catalyst.h. A suitable gas/feedstock ratio ranges from 200 to 2500 Nl/kg, preferably from 500 to 1200 Nl/kg. The product having increased aromaticity may be subjected to subsequent hydrotreating immediately downstream of the dehydrogenation and with or without removal of, for example, gaseous products. Alternatively the product may be subjected to further processing, such as deep dewaxing, solvent extraction and/or transportation to a separate station for subsequent hydrotreatment. The catalyst used in the hydrotreatment contains at least one hydrogenating metal component. The metal component is suitably selected from the Groups VIB and/or VIII of the Periodic Table of the Elements. These Groups include the noble metals platinum and palladium. It is however preferred to use nickel and/or cobalt, and molybdenum and/or tungsten compounds. The amount of nickel and/or cobalt present in the catalyst can suitably vary between 1 and 20% by weight, calculated as metal on total catalyst, preference being given to amounts in the range of 1.5 to 12% by weight. The amounts of molybdenum and/or tungsten may advantageously vary between 5 and 40% by weight, calculated as metal on total catalyst, preference being given to amounts in the range of 8 to 30% by weight. The metal components may be incorporated on a support by any conventional technique, such as impregnation, dry-impregnation, precipitation or a combination thereof. Any suitable support material may be used, such as the refractory oxides silica, alumina, silica-alumina, magnesia, zirconia, titania or mixtures thereof. Silica, silica-alumina and alumina are preferred support materials, in particular alumina. Natural and synthetic crystalline aluminosilicates can also be used, such as faujasite-type zeolites, in particular zeolite Y, mordenite-type zeolites and ZSM-5 type zeolites, or mixtures containing such a zeolite. The catalysts are normally sulphided and may be fluorided by techniques known in the art. The catalyst preferably further comprises phosphorus, advantageously in an amount of from 0.5 to 12% by weight calculated as elemental phosphorus, based on total catalyst. The hydrotreating reaction is suitably carried out under comparatively mild conditions. Suitable temperatures are in the range of 100-400 °C, preferably from 200-300 °C with a hydrogen partial pressure in the range of 20 to 150 bar, preferably from 40 to 60 bar. Suitable space velocities range from 0.1 to 5 kg/l catalyst.h, preferably from 0.5 to 2 kg/l catalyst.h, while a suitable gas/feedstock ratio ranges from 200 to 2000 Nl/kg, preferably from 400 to 1000 Nl/kg. The invention will now be illustrated by means of the following examples. EXAMPLE 1 A high viscosity index lubricating base oil was used as feedstock. This oil had the following characteristics: The feedstock was used for a series of dehydrogenation experiments in an automated one-reactor trickle-flow unit under gas once-through mode of operation and using temperatures as given in Table 1, a hydrogen pressure of 10 bar, a gas/feedstock ratio of 700 Nl/kg, and a space velocity of 4 kg/1.h. The catalyst employed was a platinum/tin catalyst on a lithium-neutralized alumina support and contained 0.40 %wt platinum and 0.41 %wt tin, with an initial pore volume of 0.93 cm³/g and an initial surface area of 131 m²/g. Aromatics content was determined by UV absorption. The results of the experiments are given in Table 1. It will be seen from the above results that aromaticity has been introduced to the lubricating base oil while maintaining a high viscosity index over a range of operating temperatures. The products were found to have a content of olefinic unsaturation (by determination of the bromine number in accordance with ASTM D-1159-82) of from 1 to 6. EXAMPLE 2 A high viscosity index, high aromatics lubricating base oil obtained as described in Example 1 and having the properties given in Table 2 below was hydrotreated in a one-reactor micro-flow unit under gas once-through mode of operation. The conditions of operation were a temperature of 260 °C, a hydrogen pressure of 50 bar, a gas/feedstock ratio of 500 Nl/kg and a space velocity of 1 kg/l.h. The catalyst employed was a hydrotreating catalyst comprising 2.5% by weight of nickel, 13.5% by weight of molybdenum and 2.9% by weight of phosphorus on alumina, the percentages being based on total catalyst. Aromatics content was determined by UV absorption. The results are given in Table 2. The yield of > 370 °C, %wt on feedstock, was 99%. It will be seen from the above results that hydrotreatment of the aromatized lubricating base oil has given a product in which the aromaticity and the viscosity index have not been adversely affected. The product was found to have a low content of olefinic unsaturation by determination of the bromine index (ASTM D-1491-78) which was found to be 20 mg/100 g.

Claims: Claims for the following Contracting States : BE, DE, FR, GB, IT, NL A process for the manufacture of a lubricating base oil of enhanced aromaticity comprising contacting a lubricating base oil feedstock having a high viscosity index that is a VI of at least 125 as determined by ASTM D-567 with a dehydrogenating catalyst at dehydrogenation conditions and recovering a high viscosity index product having enhanced aromaticity therefrom. A process according to claim 1, wherein the aromaticity is increased by an amount of at least 3 mmol/100 g. A process according to claim 1 or 2, wherein the viscosity index of the feedstock is at least 135. A process according to claim 1, 2 or 3, wherein the dehydrogenating catalyst comprises a Group VIII noble metal component, a Group IVA metal component and a refractory oxide support, preferably platinum, tin and an alumina support. A process according to any one of the preceding claims, wherein the reaction temperature is from 300 to 600 °C and the hydrogen partial pressure is from 1 to 30 bar. A process according to any one of the preceding claims, wherein at least a portion of the product of enhanced aromaticity is subjected to hydrotreating in the presence of hydrogen and a suitable catalyst and a hydrotreated product is recovered therefrom, preferably using a hydrotreating catalyst which comprises nickel and/or cobalt and molybdenum and/or tungsten, especially a hydrotreating catalyst which further comprises phosphorus. A process according to claim 6, wherein the hydrotreating is carried out at a temperature of 100 to 400 °C and a hydrogen partial pressure of 20 to 150 bar. A lubricating base oil having a viscosity index of at least 135 and an aromatic content of at least 3 mmol/100 g. A lubricating base oil according to claim 8 having an aromatic content of at least 10 mmol/100 g. A lubricating base oil according to claim 8 or 9 containing olefinic unsaturation. A lubricating base oil according to claim 8 or 9 from which the olefinic unsaturation has been substantially removed by selectively hydrotreating. Claims for the following Contracting State : ES A process for the manufacture of a lubricating base oil of enhanced aromaticity comprising contacting a lubricating base oil feedstock having a high viscosity index (that is a VI of at least 125 as determined by ASTM D-567) with a dehydrogenating catalyst at dehydrogenation conditions and recovering a high viscosity index product having enhanced aromaticity therefrom. A process according to claim 1, wherein the aromaticity is increased by an amount of at least 3 mmol/100 g. A process according to claim 1 or 2, wherein the viscosity index of the feedstock is at least 135. A process according to claim 1, 2 or 3, wherein the dehydrogenating catalyst comprises a Group VIII noble metal component, a Group IVA metal component and a refractory oxide support, preferably platinum, tin and an alumina support. A process according to any one of the preceding claims, wherein the reaction temperature is from 300 to 600 °C and the hydrogen partial pressure is from 1 to 30 bar. A process according to any one of the preceding claims, wherein at least a portion of the product of enhanced aromaticity is subjected to hydrotreating in the presence of hydrogen and a suitable catalyst and a hydrotreated product is recovered therefrom, preferably using a hydrotreating catalyst which comprises nickel and/or cobalt and molybdenum and/or tungsten, especially a hydrotreating catalyst which further comprises phosphorus. A process according to claim 6, wherein the hydrotreating is carried out at a temperature of 100 to 400 °C and a hydrogen partial pressure of 20 to 150 bar.

Inventors: BEAL FRANCOIS, CABIN PHILIPPE, MARSEU ROBERTE, MISSIAEN ROLAND, BEAL, FRANCOIS, CABIN, PHILIPPE, MARSEU, ROBERTE, MISSIAEN, ROLAND
Applicants: SHELL INT RESEARCH, SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ B.V.
Application year: 1990
Main classification: C10G45
IPC codes: C10G65, C10G45, C10G69, C10G50, C10M101, C10G71, C10N60