This invention relates to fuel oils with improved low temperature properties. More particularly, this invention relates to narrow boiling distillate

(NBD) fuels which have a relatively high wax content which have their flow and filterability properties improved through treatment with a three component additive system.

It is known in the art that NBD fuels having a relatively high wax content, i.e., 3-6% by weight, are difficult to treat effectively with conventional flow improver additives, such as ethylene vinyl acetate copolymers.

One object of this invention is to treat NBD fuels having 3-6%, especially 3-4% by weight, waxy hydrocarbons at 10° below cloud point with an additive system so as to provide the fuel with a pour point (ASTM) of at least -12°C and a CFPP (Cold Flow Plugging Point) value of at least -9°C at a treatment level of 200 ppm (parts per million) or less, so satisfying a commercial manufacturing target typical of this type of fuel.

A second object is to optimise the combination of flow improver additives required for effective treatment of NBD fuels.

For the purpose of this invention NBD fuels are those having a boiling range of from about 200°C (+ or - 50°C) to about 340°C (+ or - 30°C). Thus, such fuel oils have a relatively higher initial boiling point and a relatively lower final boiling point, as compared with middle distillate fuels which have a boiling point range of about 120°C to 500°C, especially 160°C to 400°C. NBD fuels also typically have one or more of the following distillation characteristics;

(i) a 90% to FBP temperature range of <30°C; (ii) a 20% to 90% temperature range of < 100°C; (iii) a 95% distillation point < 360°C.

Each of the flow improver additives used in the three component blend of this invention is known in the art and is disclosed in European Application 93905284.1 published December 21 , 1994, as EP Publication No. 629231.

In accordance with the invention, there has been discovered narrow boiling distillate fuel oil compositions having improved low temperature properties which contain about 0.0001 to about 0.5 wt.% of a blend of three flow improver additives consisting of:

(A) a polyoxyalkylene ester, ether or ether/ester mixture,

(B) a comb polymer, and

(C) a fatty dialkylamine-polycarboxylic acid or anhydride reaction product, the blend containing 0.5 to 2 parts by weight of the (B) component and 0.5 to 5 parts by weight of the (C) component per each part by weight of the (A) component.

Preferably, the blend contains 0.5 to 1 part by weight of each of components (B) and (C) for each part by weight of component (A), such as 0.5 to 0.8 parts by weight of each of the (B) and (C) components per part by weight of (A).

The (A) component of the additive blend used in the invention are polyoxyalkylene esters, ethers, ester/ethers and mixtures thereof, particularly those containing at least one, preferably at least two C-JO to C30 linear saturated alkyl groups and a polyoxyalkylene glycol group of molecular weight up to 5,000 preferably 200 to 5,000, the alkyl group in said polyoxyalkylene glycol containing from 1 to 4 carbon atoms.

The preferred esters, ethers or ester/ethers which may be used may be structurally depicted by the formula

R-0(A)-0-R ²

where R and R2 are the same or different and may be

(a) n-alkyl

0

(b) n-alkyl — C

0

II (c) n-alkyl — Q -C— - < ^c ^>ή

O O

(d) n-alkyl — O- C— (CH ₂ )|T ^c"

n being, for example, 1 to 30, the alkyl group being linear and saturated and containing 10 to 30 carbon atoms, and A representing the polyalkylene segment of the glycol in which the alkylene group has 1 to 4 carbon atoms, such as a polyoxymethylene, polyoxyethylene or polyoxythmethylene moiety which is substantially linear; some degree of branching with lower alkyl side chains (such as in polyoxypropylene glycol) may be present but it is preferred that the glycol is substantially linear. A may also contain nitrogen.

Examples of suitable glycols are substantially linear polyethylene glycols (PEG) and polypropylene glycols (PPG) having a molecular weight of about 100 to 5,000, preferably about 200 to 2,000 such as a blend of polyethylene glycols of 200, 400 and 600 molecular weights. Esters are preferred and fatty acids containing from 10-30 carbon atoms are useful for reacting with the glycols to form the ester additives, it being preferred to use a C18-C24 fatty acid, especially behenic acid. The esters may also be prepared by esterifying polyethoxylated fatty acids or polyethoxylated alcohols.

Polyoxyalkylene diesters, diethers, ether/esters and mixtures thereof are also suitable as the (A) component. In particular, stearic or behenic diesters of polyethylene glycol, polypropylene glycol or polyethylene/polypropylene glycol mixtures are preferred.

The (B) component of the triblend additive system is a comb polymer flow improver additive. Comb polymers are those in which hydrocarbyl groups are pendant from a polymer backbone.

Advantageously, the comb polymer is a homopolymer having side chains containing at least 6, and preferably at least 10, carbon atoms or a copolymer having at least 25 and preferably at least 40, more preferably at least 50, molar per cent of units having side chains containing at least 6, and preferably at least 10, carbon atoms.

As examples of preferred comb polymers there may be mentioned those of the general formula

where D R ¹ , COOR 1 , OCOR ¹ , R ¹² COOR ¹ 1 or ORH E H, CH ₃ , D or R ¹² G H or D J H, R ¹² , R^COOR ^{1 1} , or an aryl or heterocyclic group K H, COOR ² , OCORl ² , OR ¹² or COOH L H, R ² , COOR ¹² , OCOR ¹² or aryl

R11 > C-J O hydrocarbyl R12 > Ci hydrocarbyl

and m and n represent mole ratios, m being within the range of from 1.0 to 0.4, n being in the range of from 0 to 0.6. R ^{1 1} advantageously represents a hydrocarbyl group with from 10 to 30 carbon atoms, and R ¹² advantageously represents a hydrocarbyl group with from 1 to 30 carbon atoms.

The comb polymer may contain units derived from other monomers if desired or required. It is within the scope of the invention to include two or more different comb copolymers.

These comb polymers may be copolymers of maleic anhydride or fumaric acid and another ethylenically unsaturated monomer, e.g. an α-olefin or an unsaturated ester, for example, vinyl acetate. It is preferred but not essential that equimolar amounts of the comonomers be used although molar proportions in the range of 2 to 1 and 1 to 2 are suitable. Examples of olefins that may be copolymerized with e.g. maleic anhydride, include 1-decene, 1- dodecene, 1-tetradecene, 1-hexadecene, and 1-octadecene.

The copolymer may be esterified by any suitable technique and although preferred it is not essential that the maleic anhydride or fumaric acid be at least 50% esterified. Examples of alcohols which may be used include n-decan-1-ol, n-dodecan-1-ol, n-tetradecan-1-ol, n-hexadecan-1-ol, and n- octadecan-1-ol. The alcohols may also include up to one methyl branch per chain, for example, 1-methylpentadecan-1-ol, 2-methyltridecan-1-ol. The alcohol may be a mixture of normal and single methyl branched alcohols. It is preferred to use pure alcohols rather than the commercially available alcohol mixtures but if mixtures are used the R ¹² refers to the average number of carbon atoms in the alkyl group; if alcohols that contain a branch at the 1 or 2 positions are used R ¹² refers to the straight chain backbone segment of the alcohol.

These comb polymers may especially be fumarate or itaconate polymers and copolymers such as for example those described in U.S. Patent 5,478,368 (1995) which is incorporated by reference.

Particularly preferred fumarate comb polymers are copolymers of alkyl fumarates and vinyl acetate, in which the alkyl groups have from 12 to 20 carbon atoms, more especially polymers in which the alkyl groups have 14 carbon atoms or in which the alkyl groups are a mixture of C-14/C15 alkyl groups, made, for example, by solution copolymerizing an equimolar mixture of fumaric acid and vinyl acetate and reacting the resulting copolymer with the alcohol or mixture of alcohols, which are preferably straight chain alcohols. When the mixture is used it is advantageously a 1 :1 by weight mixture of normal C-14 and C<|6 alcohols. Furthermore, mixtures of the C14 ester with the mixed C-14/C16 ester may advantageously be used. In such mixtures, the ratio of C14 to C14/C-16 is advantageously in the range of from 1:1 to 4:1,

preferably 2:1 to 7:2, and most preferably about 3:1 , by weight. The particularly preferred fumarate comb polymers may, for example, have a number average molecular weight in the range of 1 ,000 to 100,000, preferably 1 ,000 to 30,000, as measured by Vapour Phase Osmometry (VPO).

Other preferred comb polymers for use in this invention are C^2 to C- _| β alkyl poly-methacrylates, such as C-(4 alkyl polymethacrylate, particularly when used in combination with a di-hydrogenated tallow amine reacted with phthalic anhydride.

Other suitable comb polymers are the polymers and copolymers of α- olefins and esterified copolymers of styrene and maleic anhydride, and esterified copolymers of styrene and fumaric acid; mixtures of two or more comb polymers may be used in accordance with the invention and, as indicated above, such use may be advantageous.

For this invention the preferred comb polymers are (1) C12-C14 alkyl fumarate vinyl acetate copolymer or (2) a polymethacrylate C14 ester comb polymer.

The (C) component of the additive blend is the reaction product of a fatty dialkylamine with a polycarboxylic acid or its anhydride. Suitable amines are dialkyi amines wherein each alkyl has 12 to 40 carbon atoms. Preferred is di-coconut (C12- 14) fatty amines or di-hydrogenated tallow amines, which has the general formula HNR ¹ R ² wherein R ¹ and R ² are alkyl groups derived from hydrogenated tallow fat and are composed of about 4% C14 alkyl, 31 % C16 alkyl and 59% C^s alkyl- Coconut oil fatty amine has about 50% C-12 alkyl amines, 18% C14 alkyl amines and about 7% unsaturated C-JS fatty amines.

Examples of suitable carboxylic acids and their anhydrides for preparing the nitrogen compounds include cyclohexane 1 ,2 dicarboxylic acid, cyclohexene 1,2 dicarboxylic acid, cyclopentane 1 ,2 dicarboxylic acid and naphthalene dicarboxylic acid, and 1 ,4-dicarboxylic acids including dialkyi spirobislactone. Generally, these acids have about 5-13 carbon atoms in the

cyclic moiety. Other suitable acids include alkyl and alkenyl succinic acids, e.g. dodecyl or dodecenyl succinic acids, or nitrogen-containing acids such as EDTA (ethylenediamine tetraacetic acid). Preferred acids useful in the present invention are benzene dicarboxylic acids such as phthalic acid, isophthalic acid, and terephthalic acid. Phthalic acid or its anhydride is particularly preferred. The particularly preferred compounds are the amide- amine salts formed by reacting 1 molar portion of phthalic anhydride with 2 molar portions of dihydrogenated tallow amine or di-coconut amine.

The triblend additive system of this may generally be used in fuels in the range of 0.0001 to 0.5 wt.% of the fuel. But an advantage of the invention is the particular effectiveness of the additive system of the invention in NBD fuels at treatment fuels of about 150 to 350, preferably 150-250 ppm, especially at 200 ppm.

The additive may be incorporated into bulk oil by methods such as those known in the art. Components (A), (B) and (C) may be incorporated into the oil together or separately in any combination.

A concentrate comprising the additive dispersed in carrier liquid (e.g. in solution) is convenient as a means of incorporating the additive. The concentrates of the present invention are convenient as a means for incorporating the additive into bulk oil such as distillate fuel, which incorporation may be done by methods known in the art. The concentrates may also contain other additives as required and preferably contain from 3 to 75% wt.%, more preferably 3 to 60 wt.%, most preferably 10 to 50 wt.% of the three component additive of this invention, preferably in solution in oil. Examples of carrier liquid are organic solvents including hydrocarbon solvents, for example, petroleum fractions such as naphtha, kerosene, diesel and heater oil; aromatic hydrocarbons such as aromatic fractions, e.g. those sold under the 'SOLVESSO' tradename; and paraffinic hydrocarbons such as hexane and pentane and isoparaffins. The carrier liquid must, of course, be selected having regard to its compatibility with the additive and with the fuel.

The additives of the invention may be incorporated into bulk oil by other methods such as those known in the art. If co-additives are required,

they may be incorporated into the bulk oil at the same time as the additives of the invention or at a different time.

The invention is further illustrated by the following examples. The responsiveness of the fuels to the additives is measured by the Cold Flow Plugging Point (CFPP) test.

The procedure is described in detail in "Journal of the Institute of Petroleum", Volume 52, Number 510, June 1966 pp 173-185. In brief, a 40 ml sample of the oil to be tested is cooled in a bath to about -34°C. Periodically, (at each one degree Centigrade drop in temperature starting from at least 2°C. above the cloud point) the cooled oil is tested for its ability to flow through a fine screen in a prescribed time period using a test device which is a pipette to whose lower end is attached an inverted funnel which is positioned below the surface of the oil to be tested. Stretched across the mouth of the funnel is a 350 mesh green having an area of about 12 mm diameter. The periodic tests are each initiated by applying a vacuum to the upper end of the pipette whereby oil is drawn through the screen up into the pipette to a mark indicating 20 ml of oil. The test is repeated with each one degree drop in temperature until the oil fails to fill the pipette within 60 seconds. The results of the test are reported as the temperature (the plugging point) in °C. at which the oil fails to fill the pipette in one minute.

For the example below:

Additive Description:

Additive A: Polyethylene glycol (mixed number average molecular weights of 200, 400, 600) dibehenate [Note that the glycols are in an approximate weight ratio of 1 :1 :1]

Additive B1 : A 1 :1 fumarate vinyl acetate copolymer. The fumarate is a mixed C 12/14 fumarate obtained by a reaction of a 50:50 weight mixture of normal C12 and C14 alcohols with fumaric acid. The solution copolymerisation of a 1 :1 molar mixture of fumarate and vinyl acetate is carried out at 60°C using azo diisobutylene as a catalyst.

Additive B2: A poly n-tetradecyl methacrylate ester comb polymer of about 30,000 molecular weight.

Additive C1 : An N,N-dialkylammonium salt of 2-N',N'-dialkylamido-benzoate, being the reaction product of reacting one mole of phthalic anhydride with two moles of di-coconut (C 12-14) amine to form a half amide/half amine salt.

Additive C2: An N,N-dialkylammonium salt of 2-N',N'-dialkylamido-benzoate, being the reaction product of reacting one mole of phthalic anhydride with two moles of dihydrogenated tallow amine to form a half amide/half amine salt.

The properties of the fuels tested are listed below:

Description FueM Fuel 2 Fuel 3_ Fuel 4 Fuel 5

CP (Cloud Point) 1 -3 -4 -5 -5

Wax content 10 deg 3.7 4 3.9 4.15 3.7

C below CP

Base PP (Pour Point) -6 -6 -9 -6 -9

Base CFPP -5 -6 -4 -6 -5

Distillation D86

IBP% 175 196 201 164 179

10% 221 230 240 229 229

20% 247 244 251 251 251

30% 265 257 262 265 269

50% 290 281 280 284 292

70% 310 303 300 302 311

80% 321 314 314 314 321

90% 337 328 332 331 333

95% 348 342 345 344 343

FBP 359 354 359 359 350

The tables below show the performance of the additives of this invention in Fuels 1-5.

Fuel No. 1 - Cold Flow Performance

Fuel No. 4

Sample No. Component/Amounts. CFPP. °C Pour Point. °C ppm

A B2 C1

1 60 120 100 -9/10 -15

2 60 120 150 -9 -15

3 60 120 200 -10/9 -15

4 60 120 300 -8 -15

Fuel No. 5

Sample No. Component/Amounts, CFPP. °C Pour Point. °C ppm

A B2 C1

Comparison 100 450 450 -12 -21 1

2 200 400 400 -13 -21

3 350 350 350 -13 -21

4 400 300 300 -16 -21

5 500 250 250 -16 -21

Comparison 600 200 200 -10 -21 2

The results in Fuel 5 illustrate that optimal results are obtained when the ratio of components A:B:C falls within the stated range of 0.5 to 2 parts by weight of the (B) component and 0.5 to 5 parts by weight of the (C) component per part by weight of the (A) component. Particularly good results are seen where the ratio of components A:B:C falls within the range of 1 :0.5 to 1 :0.5 to 1