Fuel and related compositions – Liquid fuels – Containing organic -c
Reexamination Certificate
2000-01-14
2001-09-04
Howard, Jacqueline V. (Department: 1714)
Fuel and related compositions
Liquid fuels
Containing organic -c
C044S390000, C044S405000, C044S412000
Reexamination Certificate
active
06284008
ABSTRACT:
This invention relates to fuel oils, and to the use of additives to improve the characteristics of fuel oils, more especially of diesel fuel and kerosene.
Environmental concerns have led to a need for fuels with reduced sulphur content, especially diesel fuel and kerosene. However, the refining processes that produce fuels with low sulphur contents also result in a product of lower viscosity and a lower content of other components in the fuel that contribute to its lubricity, for example, polycyclic aromatics and polar compounds. Furthermore, sulphur-containing compounds in general are regarded as providing anti-wear properties and a result of the reduction in their proportions, together with the reduction in proportions of other components providing lubricity, has been an increase in reported failures of fuel pumps in diesel engines using low-sulphur fuels, the failure being caused by wear in, for example, cam plates, rollers, spindles and drive shafts.
This problem may be expected to become worse in future because, in order to meet stricter requirements on exhaust emissions generally, high pressure fuel pumps, including in-line, rotary and unit injector systems, are being introduced, these being expected to have more stringent lubricity requirements than present equipment, at the same time as lower sulphur levels in fuels become more widely required.
At present, a typical sulphur content in a diesel fuel is about 0.25% by weight. In Europe maximum sulphur levels are being reduced to 0.20%, and are expected to be reduced to 0.05%; in Sweden grades of fuel with levels below 0.005% (Class 2) and 0.001 % (Class 1) are already being introduced. A fuel oil composition with a sulphur level below 0.20% by weight is referred to herein as a low-sulphur fuel.
The present invention is based on the observation that a cold flow improver enhances the lubricity of a low-sulphur fuel.
In a first aspect of the invention, there is provided the use of a cold flow improver to enhance the lubricity of a fuel oil composition having a sulphur content of at most 0.2% by weight, more especially of at most 0.05% by weight.
In a second aspect of the invention, there is provided a process for the manufacture of a petroleum based fuel oil of enhanced lubricity, which comprises refining a crude oil to produce a fuel oil of low sulphur content, and blending a cold flow improver with the refined product to provide a fuel oil composition with a sulphur content of at most 0.2% by weight, preferably of at most 0.05% by weight, and having a lubricity such as to give a wear scar diameter, as measured by the HFRR test (as hereinafter defined) at 60° C. of at most 500 &mgr;m, such as at most 450 &mgr;m, preferably at most 380 &mgr;m, more preferably at most 350 &mgr;m.
Advantageously, the petroleum-based fuel oil is a middle distillate fuel oil.
In a third aspect of the invention, there is provided a composition comprising a major proportion of a petroleum-based fuel oil and a minor proportion of a cold flow improver comprising an oil-soluble polar nitrogen compound carrying one or more substituents of the formulae >NR
13
, where R
13
represents a hydrocarbyl group containing 8 to 40 carbon atoms, which substituent or one or more of which substituents may be in the form of a cation derived therefrom, the sulphur content of the composition being at most 0.2% by weight. Advantageously, the sulphur content is at most 0.05% by weight.
Advantageously, the petroleum-based fuel is a middle distillate fuel oil.
Said polar nitrogen compound may be used in combination with an ethylene-unsaturated ester copolymer flow improver.
Advantageously, the composition resulting from the use of the first aspect, and the composition of the third aspect of the invention have a lubricity as defined with reference to the second aspect.
As used herein, the term “cold flow improver” refers to any additive which will lower the vehicle operability temperature relative to untreated base fuel, as evidenced, for example by lowering the pour point, the cloud point, the wax appearance temperature, the cold filter plugging point (hereinafter CFPP) or the Low Temperature Flow Test (LTFT) temperature of a fuel, or will reduce the extent of wax settlement in a fuel, especially a middle distillate fuel.
As used herein, the term “middle distillate” refers to fuel oils obtainable in refining crude oil as the fraction from the lighter, kerosene or jet fuel, fraction to the heavy fuel oil fraction. The fuel oils may also comprise atmospheric or vacuum distillate, cracked gas oil or a blend, in any proportions, of straight run and thermally and/or catalytically cracked distillate. Examples include kerosene, jet fuel, diesel fuel, heating oil, visbroken gas oil, light cycle oil, vacuum gas oil, light fuel oil and fuel oil. Such middle distillate fuel oils usually boil over a temperature range, generally within the range of 100° C. to 500° C., as measured according to ASTM D86, more especially between 150° C. and 400° C.
It is within the scope of the invention to include as a component of the composition a vegetable-based fuel oil, or “biofuel”, for example a rapeseed methyl ester or vegetable oil.
The HFRR, or High Frequency Reciprocating Rig, test is that described according to CEC F-06-T-94 and ISO TC22/SC7/WG6N180.
The CFPP test is defined in “Journal of the Institute of Petroleum”, 52 (1966) pp 173 to 185.
The cold flow improvers usable in the present invention will now be described in further detail. Numerous classes of flow improvers, especially middle distillate flow improvers, are suitable for use in the present invention. Among these there may be mentioned:
(A) An ethylene-unsaturated ester copolymer.
More especially one having, in addition to units derived from ethylene, units of the formula
—CR
1
R
2
—CHR
3
—
wherein R
I
represents hydrogen or methyl, R
2
represents COOR
4
, wherein R
4
represents an alkyl group having from 1 to 9 carbon atoms, which is straight chain or, if it contains 3 or more carbon atoms, branched, or R
2
represents OOCR
5
, wherein R
5
represents R
4
or H, and R
3
represents H or COOR
4
.
These may comprise a copolymer of ethylene with an ethylenically unsaturated ester, or derivatives thereof. An example is a copolymer of ethylene with an ester of a saturated alcohol and an unsaturated carboxylic acid, but preferably the ester is one of an unsaturated alcohol with a saturated carboxylic acid. An ethylene-vinyl ester copolymer is advantageous; an ethylene-vinyl acetate, ethylene-vinyl propionate, ethylene-vinyl hexanoate, or ethylene-vinyl octanoate copolymer is preferred. Preferably, the copolymer contains from 5 to 40wt % of the vinyl ester, more preferably from 10 to 35wt % vinyl ester. A mixture of two copolymers, for example as described in U.S. Pat. No. 3,961,916, may be used. The number average molecular weight of the copolymer, as measured by vapour phase osmometry, is advantageously 1,000 to 10,000, preferably 1,000 to 5,000. If desired, the copolymer may contain units derived from additional comonomers, e.g. a terpolymer, tetrapolymer or a higher polymer, for example where the additional comonomer is isobutylene or disobutylene.
The copolymers may be made by direct polymerization of comonomers, or by transesterification, or by hydrolysis and re-esterification, of an ethylene unsaturated ester copolymer to give a different ethylene unsaturated ester copolymer. For example, ethylene-vinyl hexanoate and ethylene-vinyl octanoate copolymers may be made in this way, e.g., from an ethylene-vinyl acetate copolymer.
(B) A Comb Polymer.
Such polymers are polymers in which branches containing hydrocarbyl groups are pendant from a polymer backbone, and are discussed in “Comb-Like Polymers. Structure and Properties”, N. A. Plate and V P Shibaev, J. Poly. Sci. Macromolecular Revs., 8, p 117 to 253 (1974).
Generally, comb polymers have one or more long chain hydrocarbyl branches, e.g., oxyhydrocarbyl branches, normally having from 10 to 30 carbon atoms, pendant from a polymer backbone, said branches being bonded direc
Exxon Chemical Patents Inc.
Howard Jacqueline V.
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