Lubricant compositions, their preparation and use

Abstract

A lubricating composition that has improved air release characteristics is based on a lubricating base oil comprising an oil or mixture of oils derived from waxy hydrocarbons produced in an F-T synthesis process. The composition is substantially free of a viscoelastic fluid having a shear stress greater than 11 kPa and a viscosity greater than 30 cSt at 100° C. It is further characterized as entraining less than 1.7% air in 2 minutes and having an air release rate greater than 0.3% / min. when measured at 50° C. by ASTM D 3427.

Description

[0001]This application claims priority of Provisional Application 60 / 833,871 filed Jul. 28, 2006.FIELD OF THE INVENTION[0002]The present invention relates to lubricant compositions with good air release characteristics, their preparation and use.BACKGROUND OF THE INVENTION[0003]Lubricating oils, including hydraulic oils and crankcase oils, often are used in environments in which the oil is subject to mechanical agitation in the presence of air. As a consequence, the air becomes entrained in the oil and also forms a foam.[0004]Foam appears on the surface of an oil as air bubbles greater than 1 mm in diameter. Air entrainment refers to the dispersion within the oil of air bubbles less than 1 mm in diameter.[0005]Air entrainment and foaming in lubricating compositions are undesirable phenomena. For example, air entrainment reduces the bulk modules of the fluid resulting in spongy operation and poor control of a hydraulic system's response. It can result in reduced viscosity of a lubric...

AI Technical Summary

Benefits of technology

[0018]A key advantage of the present invention is that it provides a method to control the air release characteristics of a lubricating composition by formulating the composition with a base oil derived from a waxy hydrocarbon produced in an F-T synthesis process.

[0019]As is known to those skilled in the art, in an F-T synthesis process, a synthesis gas comprising a mixture of H2 and CO is catalytically converted into hydrocarbons and preferably liquid hydrocarbons. The mole ratio of the hydrogen to the carbon monoxide may broadly range from about 0.5 to 4, but which is more typically within the range of from about 0.7 to 2.75 and preferably from about 0.7 to 2.5.

[0020]As is well known, F-T synthesis processes include processes in which the catalyst is in the form of a fixed bed, a fluidized bed or as a slurry of catalyst particles in a hydrocarbon slurry liquid. The stoichiometric mole ratio for an F-T synthesis reaction is 2.0, but there are many reasons for using other than a stoichiometric ratio as those skilled in the art know. In cobalt slurry hydrocarbon synthesis process the feed mole ratio of the H2 to CO is typically about 2.1 / 1.

[0021]The synthesis gas comprising a mixture of H2 and CO is bubbled up into the bottom of the slurry and reacts in the presence of the particulate F-T synthesis catalyst in the slurry liquid at conditions effective to form hydrocarbons, a portion of which are liquid at the reaction conditions and which comprise the hydrocarbon slurry liquid. The synthesized hydrocarbon liquid is separated from the catalyst particles as filtrate by means such as filtration, although other separation means such as centrifugation can be used. Some of the synthesized hydrocarbons pass out the top of the hydrocarbon synthesis reactor as vapor, along with unreacted synthesis gas and other gaseous reaction products. Some of these overhead hydrocarbon vapors are typically condensed to liquid and combined with the hydrocarbon liquid filtrate. Thus, the initial boiling point of the filtrate may vary depending on whether or not some of the condensed hydrocarbon vapors have been combined with it.

[0022]Slurry hydrocarbon synthesis process conditions vary somewhat depending on the catalyst and desired products. Typical conditions effective to form hydrocarbons comprising mostly C5+ paraffins, (e.g., C5+-C200) and preferably C10+ paraffins, in a slurry hydrocarbon synthesis process employing a catalyst comprising a supported cobalt component include, for example, temperatures, pressures and hourly gas space velocities in the range of from about 320-850° F., 80-600 psi and 100-40,000 V / hr / V, expressed as standard volumes of the gaseous CO and H2 mixture (0° C., 1 atm) per hour per volume of catalyst, respectively. The term “C5+” is used herein to refer to hydrocarbons with a carbon number of greater than 4, but does not imply that material with carbon number 5 has to be present.

[0023]Similarly other ranges quoted for carbon number do not imply that hydrocarbons having the limit values of the carbon number range have to be present, or that every carbon number in the quoted range is present. It is preferred that the hydrocarbon synthesis reaction be conducted under conditions in which limited or no water gas shift reaction occurs and more preferably with no water gas shift reaction occurring during the hydrocarbon synthesis. It is also preferred to conduct the reaction under conditions to achieve an alpha of at least 0.85, preferably at least 0.9 and more preferably at least 0.92, so as to synthesize more of the more desirable higher molecular weight hydrocarbons. This has been achieved in a slurry process using a catalyst containing a catalytic cobalt component. Those skilled in the art know that by alpha is meant the Schultz-Flory kinetic alpha. While suitable F-T reaction types of catalyst comprise, for example, one or more Group VIII catalytic metals such as Fe, Ni, Co, Ru and Re, it is preferred that the catalyst comprise a cobalt catalytic component. In one embodiment the catalyst comprises catalytically effective amounts of Co and one or more of Re, Ru, Fe, Ni, Th, Zr, Hf, U, Mg and La on a suitable inorganic support material, preferably one which comprises one or more refractory metal oxides. Preferred supports for Co containing catalysts comprise titania. Particularly useful catalysts and their preparation are known and illustrative, but nonlimiting examples may be found, for example, in U.S. Pat. Nos. 4,568,663; 4,663,305; 4,542,122; 4,621,072 and 5,545,674.

Problems solved by technology

Air entrainment and foaming in lubricating compositions are undesirable phenomena.

For example, air entrainment reduces the bulk modules of the fluid resulting in spongy operation and poor control of a hydraulic system's response.

Air entrainment, however, is more problematic than foaming.

These additives expedite the breakup of a foam, but they do not inhibit air entrainment.

Indeed, some antifoamants, such as silicone oils typically used in diesel and automotive crankcase oils, are known to retard air release.

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