NO770924L - FUEL MIXTURE. - Google Patents

Description

"Fuel mixture".

The invention relates to a middle distillate fuel mixer which comprises an additive which improves the fuel's filterability at low temperature.

Middle distillate fuels are fuels that have a boiling range usually in the range from approx. 120 to 48o°C at atmospheric pressure and cloud point usually in the range from -40 to +8°C. Such fuels can be so-called "straight run" products or catalytically or thermally cracked products or hydrotreated products or mixtures thereof, and they find use as fuel oil, diesel oil or jet fuel.

A middle distillate fuel suffers, unlike a light distillate fuel such as gasoline, from the problem that cooling it causes crystallization of paraffin wax until eventually a solid mass of fuel and paraffin wax crystals is formed. The crystallization of this paraffin wax is a serious problem when fuels must be pumped and filtered at low temperatures, since deposits of paraffin wax crystals in fuel lines and on filters make it difficult to transfer the fuel to the combustion site.

It is already known to add oil insoluble additives to middle distillate fuels in an attempt to improve their flowability and filterability at low temperatures. Additives that improve the flowability of the fuel by lowering its pour point are generally referred to as pour point depressants, while such additives that improve the filterability of the fuel are generally referred to as filterability improvers or nucleating agents.

Combinations of additives claimed to improve the flowability and filterability of fuels are described in U.S. Patent No. 3,275,427 (combination of an ethylene/vinyl acetate copolymer and polylauryl acrylate); B.R.D. Off. document no. 2,156,425

(combinations of different copolymers, eg ethylene/vinyl acetate, and such additives as sorbitan tristearate) and Dutch Application No. 7201824 (combinations of two different ethylene/vinyl acetate copolymers).

The applicant has now discovered a new type of additive that improves the filterability of middle distillate fuels at low temperatures.

According to the invention, a middle distillate fuel mixture comprises a major proportion of a middle distillate fuel and a small proportion of an additive which can be considered to be a C-^q 4q~ hydrocarbyl ester of a hydroxycarboxylic acid.

The filterability-improving agents for use in the above-mentioned mixtures can be mono- or polyesters, with diesters being preferred, and can contain one or more hydroxyl groups, with those containing one hydroxyl group being preferred. The esters preferably contain a hydroxyl group of ot-, /3- , Y~ or the 6 carbon atom in relation to the carbonyl carbon atom in an ester group, a hydroxyl group on the a or /3 carbon atom being particularly preferred.

The filterability-improving agents can be produced by various techniques, e.g. by reaction of a suitable alcohol with a hydroxycarboxylic acid (direct esterification) or with a lactone or lactide (indirect esterification) or with e.g. a C 1-6 alkyl hydroxycarboxylic acid ester (transesterification). It can thus be seen that although the filterability-improving agents do not have to be derived directly from a hydroxycarboxylic acid, they have such a structure that they can be considered to be esters of hydroxycarboxylic acids. The following discussion relates to filterability enhancers derived from direct esterification.

Suitable hydroxycarboxylic acids from which the filterability-improving agents can be prepared by direct esterification include mono- or polycarboxylic acids, with dicarboxylic acids being preferred, and may contain one or more hydroxyl groups, with those containing one hydroxyl group being preferred. The acids preferably contain a hydroxyl group on the a-, /3-, y- or - carbon atom in the carboxyl group, a hydroxyl group on the Gj- or /3-carbon atom being particularly preferred. The acids preferably contain 2-10 carbon atoms.

The acids may be hydroxyalkyl, alkenyl, alkynyl, aralkyl or alkarylcarboxylic acids with hydroxyalkylcarboxylic acids being the preferred. The acids may contain non-hydrocarbyl groups other than hydroxyl or carboxyl groups. The acids can be linear or branched.

Examples of suitable hydrocarboxylic acids are hydroxy-acetic acid, 2-hydroxypropionic acid, 2-hydroxy-n-butyric acid, 2-hydroxy-n-valeric acid, 2-hydroxy-n-caproic acid, 2-hydroxy-3-butenoic acid, phenylhydroxyacetic acid, 2 -hydroxy-3-phenylpropionic acid, 3-hydroxy-propionic acid, 3-hydroxy-n-butyric acid, 3-hydroxy-n-valeric acid, 3-hydroxy-n-caproic acid, 4-hydroxybutyric acid, 4-hydroxy-n-valeric acid, 4 -hydroxy-n-caproic acid, 5-hydroxy-n-valeric acid, 5-hydroxy-n-caproic acid, 2-hydroxypropanedic acid (hydroxymalonic acid), 2-hydroxysuccinic acid (malic acid), 2-hydroxy-3T-methylsuccinic acid (citramalic acid), 2-hydroxypentanedioic acid (2-hydroxyglutaric acid), 3-hydroxy-3-carboxylpentanedioic acid (citric acid), dihydroxysuccinic acids, e.g. 2,3-dihydroxysuccinic acid, dihydroxypentanoic acids, e.g. 2,3-dihydroxy-n-pentanoic acid, hexanoic acids, e.g. 2,3-dihydroxy-n-hexanoic acid, 2,3-dihydroxysuccinic acid (tartaric acid) and 2,3,4-trihydroxypentanedioic acid. A particularly preferred acid is 2-hydroxysuccinic acid (malic acid).

Suitable C^0_^0 hydrocarbyl alcohols are those having at least one continuous chain with at least 8 methylene groups, i.e. at least one uninterrupted —f-CI^—chain where n is at least 8, preferably at least 10 methylene groups and most preferably at least 12 methylene groups. Such alcohols can be alkyl, alkenyl or aralkyl alcohols, alkyl alcohols being preferred. The 3-hydrocarbyl alcohols preferably contain 15-30 carbon atoms. The c'^0 ^0-hydrocarbyl alcohols may be natural or synthetic, and linear or branched, with substantially linear alcohols being preferred, and they may be primary, secondary or tertiary, with primary alcohols being preferred. Suitable alcohols include natural alcohols, e.g. . decyl (Cl0)-, lauryl (C12)-, myristyl (C14)-, palmityl (C16)-, stearyl (C1Q)-, arakidyl (C2o)-, behenyl (<C>22)-, lignoceryl (C24)- or cerotyl (C2_b,) alcohols and mixtures thereof, and synthetic alcohols, e.g. hydroformylation alcohols and alcohols derived from Ziegler-type catalysts pg olefins (eg "Alfol" or "EPAL" alcohols).

Most preferred filterability-improving agents are alkyl malic diesters, e.g. di-C-^^_2Q-alkyl malic diesters.

The direct esterification of one or more of the aforementioned hydroxycarboxylic acids with. one or more C10-40-hydrocarbyl alcohols can be carried out by conventional techniques. The amount of alcohol used can be such that a monoester is obtained or, in the case of polycarboxylic acids, a polyester. Excess alcohol can be used. In the case of polycarboxylic acids, the acid can be partially decarboxylated during the esterification process so that the fully esterified product contains fewer ester groups than could be expected from theoretical considerations. The hydroxycarboxylic acids can also form small amounts of self-esterification polymers during the esterification process. The esterification process can be carried out at elevated temperatures and/or in the presence of an acidic catalyst. The esterified products can be processed by known techniques, e.g. by washing with water. The products may contain small amounts of unreacted alcohols or

of completely or partially unconverted acids.

The filterability-improving agents should be soluble

in the middle distillate fuel, which means that they are capable of being dissolved to the desired extent in the middle distillate fuel. The concentration of the filterability-improving agent in middle distillate fuel can vary within wide limits, whereby 1-2500 ppm is common and 10-800 ppm is preferred.

The product according to the invention may contain a pour point depressant. Suitable pour point depressants include copolymers of ethylene and vinyl esters (eg ethylene/vinyl acetate copolymers), alkyl (meth)acrylates or alkyl fumarates; chlorinated polyethylene; alkylated aromatics; alkylated polystyrene; fully or partially hydrogenated polymers or copolymers of olefins, e.g. butadiene or mixtures of butadiene and styrene; polyalkyl(meth)acrylates and mixtures thereof.

Suitable polyalkyl(meth)acrylates are those with molecular weights in the range 2,000-1,000,000 and preferably 2.0O0-5O0.OO0,

in which the alkyl groups are C-^ 2Q~ alkyl groups, e.g. C§_ 2Q~ groups. Preference is given to those which have an average number of carbon atoms in the alkyl groups of 10-17.

Suitable hydrogenated styrene/butadiene copolymers are those which have an average molecular weight of 2,500-1,000,000, a styrene content of 5-50% and a butadiene content of 50-95%.

The concentration of pour-point depressant in the middle distillate fuel can be varied within wide limits, whereby 1-2,500 ppm is common and 15-800 ppm is preferred, the weight ratio between pour-point depressant and filterability-improving agent can also vary within wide limits, f .ex. from 99:1 to 1:99, but preferably lies within the range from 75:25 to 25:75.

The additives can be added to the middle distillate fuel by various methods, but it is convenient to form a solution, dispersion or emulsion of the additives in a suitable solvent, e.g. toluene, benzene or a small amount of middle distillate fuel which is then added as a concentrate to middle distillate fuel fat.

In what follows, the invention will be illustrated by means of examples.

In the examples, the filterability of the middle distillate fuel substance or middle distillate fuel mixture was measured by the test according to DIN 51428 which concerns the so-called cold filter plugging point (CFPP).

In this test, 45 cm 3 of the sample material is cooled, and after each °C cooling, 20 ml is filtered through a 350 mesh filter at a 20 cm 1^0 pressure difference. If this 20 ml of the sample material cannot pass through the filter within 1 minute, then the test is considered to have failed at the specified temperature. For example, a CFPP result of -10°C means that the sample is unable to pass through the filter during. 1 minute at temperatures below -9°C.

in the examples, the pour point of the middle distillate fuel or middle distillate fuel mixture was measured by a standardized laboratory test which involved placing the sample material in a test tube which is then cooled until the test tube can be held horizontally for 5 sec. without the contents (a crystalline wax mass) starting to flow. This temperature is called the solidification point of the sample material. During the cooling of the test tube, it is lifted out of the cooling bath for every temperature drop of 3°C. The temperature reading immediately before the solidification point is reached is the lowest temperature observed at which the wax mixture does not flow. This temperature is called the pour point of the sample material.

Example I

A filterability-improving agent was prepared

(A) by melting a mixture of 13.4 g of malic acid and 62.4 g of a mixture of natural C^g-C22 alcohols with an average

molecular weight of 312 (average C2^). The melt was stirred for 4.75 hours at 180°C while purging with nitrogen. The product was then cooled so that mart obtained a 95% yield of the filterability-improving agent with an acid content of 0.14 mg-eq/g, an unconverted alcohol content of 9% by weight and a melting range of 61.1-62.3°C .

Example II

A filterability-improving agent was prepared

(B) by melting 272.8 g of a mixture of synthetic, substantially straight chain, primary C^0-C26 alcohols (''Alfol" alcohols) having an average molecular weight of 341 (average ^ 23^'°9addition of 53.6 g of malic acid to the melt. The melt was stirred for 4.5 hours at 140 C under a nitrogen purge. The product was then cooled and a 97% yield of the filterability-improving agent was obtained with an acid content of 0.21 mg- eq/g, an unconverted alcohol content of 10% by weight and a melting range similar to the product in example I.

Examples III-XV

Middle distillate fuel mixtures were prepared by adding solutions of the filterability-improving agents A and B in toluene to the middle distillate fuels described

in Table I.

The amounts of filterability enhancer used (parts per million by weight of middle distillate fuel (ppm)) and CFPP values for the mixture are given in Table II.

Examples XV-XX

Middle distillate fuel mixtures were prepared by adding to the fuels in Table I., solutions in toluene of the filterability-improving agent A and a hydrogenated styrene/butadiene copolymer pour-point depressant (molecular weight 96,000; styrene content 27% by weight; butadiene content 63 % by weight; agent A) or a polyalkyl methacrylate pour point depressant (molecular weight 99,700; the number of carbon atoms in the alkyl groups varied from 9 to 18; agent B). The additive amounts that were used, the CFPP values and the pour points of the mixtures are reproduced in Table III. For the sake of comparison, the table also includes data regarding the effect of agent B alone on CFPP and the pour point of the fuels.

Claims (17)

1. Middle distillate fuel mixture, characterized in that it comprises a major proportion of a middle distillate fuel and a smaller proportion of a filterability-improving agent which can be considered to be a C^Q -C^Q -hydrocarbyl ester of a hydroxycarboxylic acid. 2. Mixture as stated in claim 1, characterized in that the C^Q -C^Q hydrocarbyl group of the ester includes at least one uninterrupted chain of at least 8 methylene groups. 3. Mixture as stated in claim 1 or 2, characterized in that the filterability-improving agent is a diester. 4. Mixture as set forth in any one of claims 1 to 3, characterized in that the filterability-improving agent contains one hydroxyl group. 5.. Mixture as stated in claim 4, characterized in that the hydroxyl group is on the a- or /3-carbon atom in relation to the carbonyl carbon atom in an ester group. 6. Mixture as set forth in any one of claims 1 to 5, characterized in that the filterability-improving agent is prepared by reacting a c^0 -C4o <-> hydrocarbyl alcohol with a hydroxycarboxylic acid. 7. Mixture as stated in claim 6, characterized in that the hydrocarbyl alcohol is a C 1 -C 2 -hydrocarbyl alcohol. 8. Mixture as stated in claim 6 or 7, characterized in that the hydrocarbyl alcohol is an alkyl alcohol. 9. A mixture as set forth in any one of claims 6 to 8, characterized in that the hydroxycarboxylic acid is a dicarboxylic acid. 10. Mixture as stated in any one of claims 6 to 9, characterized in that the hydroxycarboxylic acid is an α- or β-hydroxycarboxylic acid. 11. Mixture as set forth in any one of claims 6 to 10, characterized in that the hydroxycarboxylic acid is malic acid. 12. Mixture as stated in any one of the preceding claims, characterized in that the filterability-improving agent is a di-C 1 -C 4 -alkyl malic acid diester. 13. Mixture as stated in any of the preceding claims, characterized in that the amount of filterability-improving agent is 1-2,500 ppm. 14. Mixture as stated in any of the preceding claims, characterized in that the mixture additionally comprises a pour-point depressant. 15. Mixture as stated in claim 14, characterized in that the pour point depressant is a hydrogenated styrene/butadiene copolymer or a polyalkyl (meth)acrylate. 16. Mixture as stated in claim 14 or 15, characterized in that the amount of the pour-point depressant is 1-2,500 ppm. 17. A mixture as set forth in any one of claims 14 to 16, characterized in that the weight ratio between pour point depressant and filterability improving agent is from 75:25 to 25:75.