Wax isomerate having a reduced pour point

Abstract: A combination of a low and a high molecular weight polyalkylmethacrylate has been found to be effective in reducing the pour point of a wax isomerate to a level that cannot be obtained with conventional pour point depressants. In a preferred embodiment, the wax isomerate is a slack wax isomerate.

Description: This invention relates to reducing the pour point of wax isomerates, alone or in combination with a conventional lubricating oil basestock. According to one aspect of the present invention a wax isomerate having a reduced pour point comprises : (a) a major amount of a wax isomerate, and (b) a minor amount of an additive combination of (i) a low molecular weight polyalkylmethacrylate having a weight average molecular weight of from 10,000 to 50,000, and (ii) a high molecular weight polyalkylmethacrylate having a weight average molecular weight of from 70,000 to 150,000. In another aspect, the invention provides a lubricating oil containing a major amount of the slack wax isomerate and a minor amount of a lubricating oil basestock. The addition of polyalkylmethacrylates to lubricating oils is known. For example, U.S.P.-A-2,628,225 discloses that polyalkylmethacrylates can be used as VI improvers and pour point depressants in lubricating oils. EP-0140247 discloses that the pour point of a lubricating oil can be reduced by adding a mixture of acrylate or methacrylate polymers. Each polymer contains several acrylate or methacrylate esters. The molecular weight of both polymers ranges from 50,000 to 500,000. FR-A-2407259 relates to the reduction in pour point of hydrocracked lubricating oils using a mixture of two polyalkylmethacrylates, one having VI improving properties and the other pour point depressant properties. Both have number average molecular weights from 10³ to 10⁶; all the VI improvers illustrated have higher molecular weights than the pour point depressants. The present invention is, however, concerned with reducing the pour point of wax isomerates preferably slack wax isomerates, which are the lubes fraction remaining following dewaxing the isomerate formed from isomerizing wax in the presence of a suitable catalyst under isomerization conditions. The invention enables the reduction of the pour point of such isomerates by employing a synergistic mixture of low and high molecular weight polyalkylmethacrylates has been found to be effective in reducing the pour point of wax isomerates In a preferred embodiment, the wax isomerate is a slack wax isomerate. The wax which is isomerized may originate from any number of sources. Synthetic waxes from Fischer-Tropsch processes may be used, as may be waxes recovered from the solvent or autorefrigerative dewaxing of conventional hydrocarbon oils, or mixtures of these waxes. Waxes from dewaxing conventional hydrocarbon oils are commonly called slack waxes and usually contain an appreciable amount of oil. The oil content of these slack waxes can range anywhere from 0 to 45% or more, but usually from 5 to 30% oil. Isomerization is conducted over a catalyst containing a hydrogenating metal component--typically one from Group VI, or Group VIII, or mixtures thereof, preferably Group VIII, more preferably noble Group VIII, and most preferably platinum on a halogenated refractory metal oxide support. The catalyst typically contains from 0.1 to 5.0 wt.%, preferably 0.1 to 1.0 wt.%, and most preferably from 0.2 to 0.8 wt.% metal. The halogenated metal oxide support is typically an alumina ( e . g . gamma or eta) containing chlorides (typically from 0.1 to 2 wt.%, preferably 0.5 to 1.5 wt.%) and fluorides (typically 0.1 to 10 wt.%, preferably 0.3 to 0.8 wt.%). Isomerization is conducted under conditions of temperatures between about 270 to 400°C (preferably betweem 300 to 360°C), at pressures of from 3.45 to 20.7 MPa (500 to 3000 psi) H₂ (preferably 6.9 to 10.35 MPa (1000-1500 psi) H₂), at hydrogen gas rates of from 178 to 1780 m³/m³ (1000 to 10,000 SCF/bbl), and at a space velocity in the range of from 0.1 to 10 v/v/hr, preferably from 1 to 2 v/v/hr. Following isomerization, the isomerate may undergo hydrogenation to stabilize the oil and remove residual aromatics. The resulting product may then be fractionated into a lubes cut and fuels cut, the lubes cut being identified as that fraction boiling in the 330°C⁺ range, preferably the 370°C⁺ range, or even higher. This lubes fraction is then dewaxed to reduce the pour point, typically to between about -15 to about -24°C. This fraction is the "wax isomerate" to which the high and low polyalkylmethacrylates combination of this invention is added. The polyalkylmethacrylate combination may also be added to a lubricating oil comprising a major amount of wax isomerate and a minor amount of a lubricating oil basestock (such as described in U.S.P.-A-4,906,389). The low molecular weight polyalkylmethacrylate used in this invention have a weight average molecular weight ranging from 10,000 to 50,000, preferably from 30,000 to 45,000, as measured by gel permeation chromatography (GPC) using polystyrene as the calibrant. The amount of low molecular weight polyalkylmethacrylate added can range from 0.01 up to 5 wt.% or more. Practically, however, the amount of low molecular weight polyalkylmethacrylate will range from 0.1 to 1 wt.%, most preferably from 0.3 to 0.7 wt.%, based on weight of the final product. The high molecular weight polyalkylmethacrylate have a weight average molecular weight ranging from 70,000 to 150,000, preferably from 90,000 to 120,000, as measured by GPC. The amount of high molecular weight polyalkylmethacrylate can range from 0.01 up to 3 wt.% or more. Practically, however, the amount of high molecular weight polyalkylmethacrylate will range from 0.1 to 1 wt.%, most preferably from 0.2 to 0.6 wt.%, based on weight of the final product. The alkyl group comprising the low and high polyalkylmethacrylates used in this invention may be straight chained or branched and should preferably contain from 6 to 22, more preferably from 8 to 19, carbon atoms. These polyalkylmethacrylates are known articles of commerce and, as such, are readily available in the marketplace. Frequently, the polyalkylmethacrylates are available from vendors in mixture with a solvent. The invention is illustrated by the following examples: Example 1 - Use of Low and High MW Polyalkylmethacrylates in Slack Wax Isomerate Basestock The pour points of several samples of a slack wax isomerate (SWI) basestock containing various combinations of low and high molecular weight (MW) polyalkylmethacrylates (PMA) were determined using ASTM D-97. The results of these tests are shown in Table 1 below: The data in Table 1 show that the pour point of the SWI basestock can be depressed to -33°C with 0.5% of the high MW PMA (Sample B). However, increasing the concentration of high MW PMA (Sample F) does not depress the pour point further. The low MW PMA also acts as a pour depressant (Samples C and D), but even at a concentration of 3.0% (Sample D), the pour point is still only -33°C. However, addition of the low MW PMA to Sample B reduced the pour point to -42°C (Sample E), which clearly illustrates the synergistic effect of the combination of low and high MW PMA's. Example 2 - Use of Low and High MW Polyalkylmethacrylates in Fully Formulated Slack Wax Isomerate The pour point of several samples of a fully formulated SWI containing various combinations of low and high molecular weight polyalkylmethacrylates were determined using ASTM D-97. The results of these tests are summarized in Table 2 below. The data in Table 2 show that the combination of the high MW PMA and the low PMA in a fully formulated oil resulted in a pour point of -42°C (Sample H) compared to -36°C (Sample G) for the blend containing only the high MW PMA. Increasing the concentration of the low MW PMA to very high levels (Sample J) can result in even lower pour points. Example 3 - Use of Various High MW VI Improvers The pour point of several samples of a SWI basestock in combination with various high molecular weight polymer commercial VI improvers were determined using ASTM D-97. The results of these tests are shown in Table 3 below. The data in Table 3 show that not all combinations of the high MW PMA of this invention and other high molecular weight VI improvers are effective in depressing the pour point. Only the combination of low and high molecular weight polyalkylmethacrylates effectively depressed the pour point.

Claims: A wax isomerate having a reduced pour point, which comprises: (a) a major amount of a wax isomerate, and (b) a minor amount of an additive combination of (i) a low molecular weight polyalkylmethacrylate having a weight average molecular weight of from 10,000 to 50,000, and (ii) a high molecular weight polyalkylmethacrylate having a weight average molecular weight of from 70,000 to 150,000. The wax isomerate of claim 1 wherein the low molecular weight polyalkylmethacrylate has a weight average molecular weight of from 30,000 to 45,000. The wax isomerate of claim 1 or 2 wherein the high molecular weight polyalkylmethacrylate has a weight average molecular weight of from 90,000 to 120,000. The wax isomerate of any preceding claim wherein the alkyl group in the low and high molecular weight polyalkylmethacrylates has from 6 to 22 carbon atoms. The wax isomerate of any preceding claim wherein the amount of low molecular weight polyalkylmethacrylate is from 0.01 to 5 wt.% and the amount of high molecular weight polyalkylmethacrylate is from 0.01 to 3 wt.%. The wax isomerate of any preceding claim wherein the amount of low molecular weight polyalkylmethacrylate is from 0.3 to 0.7 wt.% and the amount of high molecular weight polyalkylmethacrylate is from 0.2 to 0.6 wt.%. The wax isomerate of any preceding claim which also contains a minor amount of a lubricating oil basestock. A wax isomerate according to any of preceding claims 1 to 6, which is a slack wax isomerate. A lubricating oil containing a major amount of the slack wax isomerate of claim 8 and a minor amount of a lubricating oil basestock.

Inventors: ASSELIN ANDRE ERNEST, HALLS PATRICK MICHAEL ERNEST, MACALPINE GERALD ARTHUR, ASSELIN, ANDRE ERNEST, HALLS, PATRICK MICHAEL ERNEST, MACALPINE, GERALD ARTHUR
Applicants: EXXON RESEARCH ENGINEERING CO, EXXON RESEARCH AND ENGINEERING COMPANY
Application year: 1991
Main classification: C10M145
IPC codes: C10M169, C10N30, C10N70, C10M145