EP2179014A1

EP2179014A1 - Use of a lubricating oil composition

Info

Publication number: EP2179014A1
Application number: EP08803161A
Authority: EP
Inventors: Richard Thomas Dixon; Martin Luebbers; Ralf Ortlepp
Original assignee: Shell Internationale Research Maatschappij BV
Current assignee: Shell Internationale Research Maatschappij BV
Priority date: 2007-08-23
Filing date: 2008-08-22
Publication date: 2010-04-28
Also published as: WO2009024610A1; JP5623276B2; RU2010110824A; CN101802152A; JP2010536972A; BRPI0815689B1; BRPI0815689A2; RU2486233C2

Abstract

The present invention provides the use of a lubricating oil composition comprising a base oil and one or more viscosity index improvers, wherein the lubricating oil composition has a Viscosity Index (VI; according to ASTM D2280) of at least 190 for improving the energy consumption in a hydraulic system.

Description

USE OF A LUBRICATING OIL COMPOSITION

The present invention relates to the use of a lubricating oil composition, in particular as a hydraulic fluid in a hydraulic system.

Lubricating oil compositions are widely used as hydraulic fluids in e.g. manufacturing, construction and transportation .

In formulating a "multigrade" hydraulic fluid, i.e. a fluid with a relatively high (> 150) viscosity index (VI) which can be used in equipment where operating temperatures can vary significantly, the formulator can obtain the desired VI by proper selection of type and amounts of the base oil and VI improver.

API Group I mineral oils commonly have a viscosity index of 90-100. Other types of base oils such as poly- alpha-olefin (PAOs) and esters may have a VI about 135 and 160 respectively.

"VI improvers", "VI modifiers" or "thickening agents" are used to increase the VI of the intended composition. The thickening or VI adding power of a VI modifier usually increases with its molecular weight. However, with increasing molecular weight of the VI improver shear stability decreases . "Shear stability" is the tendency of the large (usually polymer) molecules to be degraded during use as they pass around the hydraulic system.

Therefore, the formulator needs to carefully select the base oil (or base oil mixture), thickening power and shear stability in order to formulate a composition that meets the desired targets. Recently, especially for lubricating oil compositions meant for use in hydraulic systems at low temperatures (below 0°C), the trend has been to move away from formulating high VI fluids with relatively high VI index but poor shear stability to formulating fluids meeting the required minimum level of VI considering the climatic conditions of operation and optimal shear stability.

One of the reasons for this trend to move away from high VI fluids is the current assumption that energy consumption of a fluid varies inversely with the VI of the fluid. In other words, it is assumed that with increasing VI of the fluid, the energy consumption increases (as the fluid gets more viscous), resulting in that more energy is required to do work when using the fluid in a hydraulic system. See in this respect e.g. The conventional Figure 1 and associated discussion of S.N. Herzog, T. E. Marougy and P. W. Michael, "Fluid viscosity selection criteria for hydraulic pumps and motors", Technical Paper Series number 100-9.12, presented at the International Exposition for Power Transmission and Technical Conference on 4-6 April 2000. The conventional understanding is thus that a lower VI results in more desired energy consumption.

It is an object of the present invention to improve the energy consumption of a lubricating oil composition, especially at temperatures below 0°C. It is another object of the present invention to reduce the time of lifting in a hydraulically operated lifting apparatus.

One or more of the above or other objects of the present invention can be achieved by providing the use of a lubricating oil composition comprising a base oil and one or more viscosity index improvers, wherein the lubricating oil composition has a Viscosity Index (VI; according to ASTM D2280) of at least 190 for improving the energy consumption in a hydraulic system. It has been surprisingly found according to the present invention that, especially at temperatures below 0°C, the energy consumption decreases when using a fluid having a VI of above 190. As a result of this, less energy is required e.g. during lifting using a hydraulically operated lifting apparatus .

Further it has been found according to the present invention that, when using a lubricating oil composition having a VI of at least 190, that the energy consumption can be obtained in the whole temperature range of from - 60°C to +75°C, preferably from -40°C to +40°C, more preferably from -40 °C to 0°C , even more preferably from -20°C to 0°C, especially from -20°C to -5°C and most preferably from -20°C to -10⁰C. According to the present invention there are no particular limitations regarding the base oil in the lubricating oil composition of the present invention. Preferably, said base oil is petroleum-based, synthetic hydrocarbon-based and/or ester-based. If desired, mixtures of two or more base oils may be used.

The base oil in the lubricating oil composition of the present invention may be selected from mineral and/or synthetic lubricant base oils.

Said base oil is preferably present in an amount of at least 50 wt.%, more preferably at least 60 wt.%, and at most 90%, more preferably at most 80%, based on the total weight of the lubricating oil composition.

Mineral lubricant base oils that may be conveniently used include liquid petroleum oils and solvent treated or acid treated mineral lubricating oils of the paraffinic, naphthenic, or mixed paraf finic/naphthenic type which may be further refined by hydrocracking and hydrof inishing processes and/or dewaxing.

Naphthenic base oils have low viscosity index (VI) (generally 40-80) and a low pour point. Such base oils are produced from feedstocks rich in naphthenes and low in wax content and are used mainly for lubricants in which colour and colour stability are important, and VI and oxidation stability are of secondary importance. Paraffinic base oils have higher VI (generally >95) and a high pour point. Said base oils are produced from feedstocks rich in paraffins, and are used for lubricants in which VI and oxidation stability are important. Fischer-Tropsch derived base oils may be conveniently used as the lubricating oil base oil in the lubricating oil composition of the present invention, for example, the Fischer-Tropsch derived base oils disclosed in EP 776 959, EP 668 342, WO 97/21788, WO 00/15736, WO 00/14188, WO 00/14187, WO 00/14183, WO 00/14179, WO 00/08115, WO 99/41332, EP 1 029 029, WO 01/18156 and WO 01/57166.

Synthetic processes enable molecules to be built from simpler substances or to have their structures modified to give the precise properties required. Synthetic lubricant base oils include hydrocarbon oils such as olefin oligomers (also known as polyalphaolefins (PAOs)) . Synthetic hydrocarbon base oils sold by the Shell Group under the designation "XHVI" (trade mark) may be conveniently used. Preferred lubricating oil base oils for use in the lubricating oil composition of the present invention are Group I, Group II, Group III, Group IV or Group V base oils, polyalphaolefins, Fischer-Tropsch derived base oils and mixtures thereof. By "Group I -V" base oils in the present invention are meant lubricating oil base oils according to the definitions of American Petroleum Institute (API) categories I-V. Such API categories are defined in API Publication 1509, 15^th Edition, Appendix E, April 2002. Group I base oils contain less than 90 % saturates (according to ASTM D2007) and/or greater than 0.03 % sulphur (according to ASTM D2622, D4294, D4927 or D3120) and have a viscosity index of greater than or equal to 80 and less than 120 (according to ASTM D2270) .

Group II base oils contain greater than or equal to 90 % saturates and less than or equal to 0.03 % sulphur and have a viscosity index of greater than or equal to 80 and less than 120, according to the aforementioned ASTM methods.

Group III base oils contain greater than or equal to 90 % saturates and less than or equal to 0.03 % sulphur and have a viscosity index of greater than 120, according to the afore-mentioned ASTM methods . As described in US 6 180 575 and US 5 602 086, poly- alpha-olef ins and their manufacture are well known in the art. Preferred poly-alpha-olef ins that may be used in lubricating oil compositions of the present invention may be derived from C₂ to C₃₂ alpha olefins . Particularly preferred feedstocks for said poly- alpha-olef ins are 1-octene, 1-decene, 1-dodecene and 1- tetradecene .

Preferably, lubricating oil base oils that may be conveniently used in the lubricating oil compositions of the present invention have a kinematic viscosity at

100 ⁰C (according to ASTM D445) in the range of from 1 to 300 mm²/s, more preferably in the range of from 1 to 100 mm² / s .

Preferably, the lubricating oil composition of the present invention has a kinematic viscosity in the range of from 15 to 150 mm²/s at 40 ⁰C (according to ASTM D445), more preferably in the range of from 20 to 100 mm²/s, and most preferably in the range of from 25 to 68 mm² / s . A preferred lubricating base oil for use in one embodiment herein is a Group V base oil, in particular a naphthenic gas oil. Particularly suitable are naphthenic gas oils having low pour points, typically less than -50 ⁰C. An example of a suitable naphthenic gas oil is commercially available from Shell Petroleum Co. Ltd. under the tradename Risella 907.

According to the present invention there are no particular limitations regarding the viscosity index improvers in the lubricating oil composition of the present invention.

Examples of viscosity index improvers include non- dispersant-type viscosity index improvers such as polymethacrylates and olefin copolymers such as ethylene/propylene copolymer and styrene/diene copolymer, and dispersion-type viscosity index improvers such as those obtained by copolymerizing these with nitrogen- containing monomers. The amount added thereof may conveniently be from 0.1 to 35 wt%, preferably from 10 wt% to 35 wt%, more preferably from 20 wt% to 30 wt%, based on the total lubricating oil composition.

The lubricating oil composition of the present invention can further comprise one or more additives such as anti-wear additives, corrosion inhibitors, anti- oxidants, foam inhibitors, demulsifiers, pour-point depressants and the like. The amount of said additives to be present in the lubricating composition depends on the specific compounds used. As the above-mentioned and other additives are well known in the art, they are not described herein in full detail. The total amount added of the additives may conveniently be from 0.1 to 15.0 wt. %, based on the total lubricating oil composition .

Examples of anti-wear additives are zinc-based or zinc-free or ashless anti-wear additives. Examples of corrosion inhibitors are N- alkylsarcosinic acids, alkylate phenoxy acetates, imidazolines, the alkaline earth metal salts of phosphate esters disclosed in EP 0 801 116 and alkenyl succinate ester-based corrosion inhibitors.

Examples of anti-oxidants are amine-based, sulphur based, phenol-based and phosphorus-based anti-oxidants. These antioxidants can be used individually, or a plurality can be used in combination. Examples of foam inhibitors are organo-silicates such as dimethylpolysiloxane, diethyl silicate and fluorosilicone, and non-silicone foam inhibitors such as polyalkyl acrylates.

Examples of demulsifiers are polyalkylene glycol- based nonionic surfactants such as polyoxyethylene alkyl ethers, polyoxyethylene alkyl phenyl ethers and polyoxyethylene alkyl naphthyl ethers.

Examples of pour-point depressants are polymethacrylate-based polymers. The lubricating oil composition according to the present invention can be conveniently prepared by blending together one or more base oils, the one or more VI improvers and one or more further additives .

In a further aspect the present invention provides the use of the lubricating oil composition for reducing the time of lifting a weight in a hydraulically operated lifting apparatus.

Non-limiting examples of a hydraulically operated lifting apparatus are a fork-lift truck, a garbage truck, cherry picker, open cast mining equipment, etc.

Also the present invention provides a method of improving the energy consumption in a hydraulic system by using the lubricating oil composition as described herein . Furthermore the present invention provides a method of reducing the time of lifting a weight in a hydraulically operated lifting apparatus by using the lubricating oil composition as described herein. The present invention is described below with reference to the following Examples, which are not intended to limit the scope of the invention in any way. EXAMPLES

Formulations were blended in a conventional way using the base oils and additives specified in Table 1 in order to obtain the viscosity properties as outlined in Table 2.

The amounts in Table 1 are in wt.%, based on the total weight of the formulation. The base oils 1-4 as used in the formulations of

Tables 1 and 2 were the following:

Base oil 1 is an API Group V base oil, designated a "naphthenic gas oil" commercially available from Shell Petroleum Co. Ltd. under the tradename Risella 907; - Base oil 2 is an API Group V naphthenic base oil having a kinematic viscosity at 40⁰C (ASTM D445) of between 7.9 and 8.9 mm²/s;

Base oil 3 is a blend of API Group I base oils available from Shell Petroleum Co., Ltd under the trade designation "HVI 60", "HVI 100" and "HVI 160", the blend being adjusted to give the viscosities as given in Table 2; and

Base oil 4 is an API Group III base oil available from Fortnum Neste OY under the trade designation "Nextbase 3050".

The viscosity index improvers as used in the formulations of Tables 1 and 2 were those available from Rohmax GmbH under the trade designations "Viscoplex 8-238" (VI improver 1) and "Viscoplex 8-200" (VI improver 2 ) . The formulations of Tables 1 and 2 also comprised an additive combination of conventional additives in conventional amounts to act as corrosion inhibitors, demulsifiers, anti-wear agents, anti-oxidants, pour-point depressants and foam inhibitors.

Example 1 is according to the present invention whilst the remaining Examples in Tables 1 and 2 are comparative in nature (and referred to as Comparative Examples 1-4) .

TABLE 2 - Viscosities

Energy consumption test / Average lifting time test

The formulations as described in Tables 1 and 2 were tested for energy consumption.

To this end, the formulations of Tables 1 and 2 were used in the electrically powered hydraulic system of a

Jungheinrich forklift truck, model EFG-DH 12,5 330, with a lifting capability of 1.25 tonnes. The forklift controls were operated pneumatically, and controlled to ensure same operation precision for each of the formulations .

Each formulation was tested in turn on the setup by raising and lowering a standard container containing 1 tonne water and antifreeze (such that the content of container remained liquid at -20⁰C) 40 times at the following ambient temperatures: -20⁰C, -15°C, -10⁰C, -5°C, 0⁰C, 5°C, 10⁰C, 20⁰C, 40⁰C. To allow the fork lifter hydraulic system and formulations to adapt to the following temperature, the temperature sequence was split into 2 parts: a) the cold sequence starting at -20⁰C up to -5°C; and b) a warm sequence starting with +40⁰C down to 0⁰C. Each of the sequences were conducted in one day with repeat tests performed the following day.

Formulation temperature was measured continuously at the control unit, the reservoir and at the inlet to the hydraulic cylinder (the "lifting frame") . Oil pressure was measured at the control unit, pump exit and the lifting frame.

The fork lift operation speed and lift height was measured with a high precision distance sensor. Each cycle of raising the container was timed, and the DC current through the pump motor and voltage across it measured. The product of the time (in seconds), current (amperes) and voltage (volts) gives the total energy consumption in kWh as follows :

Energy = Current xVoltage x (kWh)

3600 ^V The test apparatus was conditioned at the test temperature until the formulation reservoir was at the target temperature. In later testing, the test apparatus was conditioned until all three temperature points were within ±2°C of the target. Re sult s

Table 3 below shows the cumulative electrical energy consumption (in Wh) after lifting the container ten times for each formulation.

Table 4 shows the data expressed as a percentage difference, whilst using Comparative Example 1 (VI = 95) as a reference baseline

Further Table 5 shows the average lifting time over ten cycles in seconds.

TABLE 3 - Cumulative energy consumption [Wh]

TABLE 4 - Cumulative energy consumption as percentage difference with respect to Comparative Example 1 (VI = 95) [%]

TABLE 5 - Average lifting time over 10 lift cycles [s]

Ambient Ex. 1 Comp. Ex Comp. Ex. Comp . Ex. Comp . Ex . test 1 2 3 4 temperature [⁰C]

-20 14.6 17.8 16.3 16.1 15.3

-15 14.0 14.9 14.4 14.6 14.2

-10 13.7 14.4 14.0 14.0 13.6

-5 13.0 13.8 13.6 13.7 13.2

0 12.9 13.3 13.3 13.0 13.0

13.0 13.0 13.0 13.0 13.0

10 13.0 13.0 12.9 13.0 13.0

20 13.0 13.0 13.0 13.0 12.9

40 13.0 13.0 13.0 13.0 13.0

Discussion

It can be seen in Tables 3 and 4 that no simple linear correlation exists between viscosity or viscosity index and energy consumption, as has been assumed in the field. As an example, Comparative Examples 2, 3 and 4 show a trend whereby at some temperatures (above 0⁰C) a benefit in energy consumption is observed and at some temperatures (above 0⁰C) a detriment, or within the precision of the test method no discernible benefit (0.1%) .

However, Example 1 according to the present invention shows a benefit over the entire temperature range tested (-20 to +40⁰C) .

It has been found according to the present invention that at most temperatures a viscosity index above 190 surprisingly improves the energy consumption. The trend is most pronounced below 0⁰C.

Turning to the average lifting time data of Table 5, representing the time it would take for a fork-lift truck to lift a load (in a warehouse for example), a surprising benefit is also seen. Although it would be expected that, in order to do work more quickly more energy would be required, the data in Table 5 show that the formulation having the highest VI (Example 1) does the work quickest, in particular at temperatures below O⁰C.

The person skilled in the art will readily understand that it is highly advantageous to reduce lifting time for such an operation in e.g. a warehouse and hence increase productivity.

Claims

C L A I M S

1. Use of a lubricating oil composition comprising a base oil and one or more viscosity index improvers, wherein the lubricating oil composition has a Viscosity Index (VI; according to ASTM D2280) of at least 190 for improving the energy consumption in a hydraulic system.

2. Use according to claim 1, wherein the lubricating oil composition has a VI of at least 200, preferably at least 210.

3. Use according to claim 1 or 2, wherein the lubricating oil composition has a VI of at most 350, preferably at most 310, more preferably at most 300.

4. Use according to any one of claim 1 to 3, in the temperature range of -60°C to +75°C.

5. Use according to any one of claims 1 to 4, in the temperature range of from -40 °C to 0°C.

6. Use according to any one of Claims 1 to 5 in the temperature range of from -20 °C to 0°C.

7. Use according to any one of claims 1 to 6, for reducing the time of lifting a weight in a hydraulically operated lifting apparatus.

8. Method of improving the energy consumption in a hydraulic system by using the lubricating oil composition as described in any one of claims 1 to 6.

9. Method of reducing the time of lifting a weight in a hydraulically operated lifting apparatus by using the lubricating oil composition as described in any one of claims 1 to 6.

10. Lubricating oil composition comprising from 50wt% to 90wt% a base oil and from 10wt% to 35wt% of one or more viscosity index improvers, wherein the lubricating oil composition has a Viscosity Index (VI; according to ASTM D2280) of at least 190 and wherein the base oil is a Group V base oil.

11. Lubricating oil composition according to Claim 10 wherein the Group V base oil is a naphthenic gas oil.

12. Lubricating oil composition according to Claim 10 or 11 wherein the base oil is present at a level of from 50wt% to 80wt%.

13. Lubricating oil composition according to any of Claims 10 to 12 wherein the viscosity index improvers are present at a total level of from 20wt% to 30wt%.