Field of the Disclosure

The present invention relates to the use of amphoteric surfactants in oil-in-water diesel fuel emulsions.

Background

A diesel emulsion and its use as a fuel in combustion engines is known. US 4,744,796, for example, suggests to make microemulsions of a hydrocarbon fuel, water and/or methanol and a combination of tertiary butyl alcohol (TBA) and a surfactant. However, the known diesel emulsions have not been fully commercialized and the known emulsions still suffer from too low water content, resulting in too high NOx emissions upon combustion, and/or insufficient stability, and/or use surfactants with an undesirable eco-toxicity profile.

US 201 1/0296746 suggests the use of N-alkyl or N-alkenyl or N-cycloalkyl or N-aryl amino or imino propionic acids, at ppm levels, as corrosion inhibitors to protect and prevent the corrosion of ferrous metal in contact with crude oil and liquid fuels.

JPS49108106 (abstract) discloses to use gel-like fuels containing 2-20% water. Such fuels are undesired since they contain too little water to give the desired NOx emissions and a gel-like behavior is undesired since it requires extra measures to be taken to prevent gelation during the actual use of the fuel.

Eco toxicity (including aquatic toxicity and eye irritation profile) of a chemical is classified according to the Directive 91 /325/EEC [2] as well as 1999/45/EC. Limits are specified for the application of risk phrases and the "N" symbol (sometimes shown as dead-fish-dead-tree symbol). Conventional surfactants proposed for fuel emulsions currently require the labelling with the dead-fish-dead-tree symbol. Hereinafter a good ecotoxicity (profile) is used for surfactants that do not need to be labelled with the "N" symbol. It is desired to find an adjuvant or mixture of adjuvants that give the desired fuel emulsions while having a very mild ecotoxicity, such that they do not require the product to be labelled with the dead-fish-dead-tree symbol per the Directive. Summary

The present disclosure relates to the use of one or more particular amphoteric surfactants. These surfactants have an isoelectric point and outside this point they are either in the cationic or anionic state. In an embodiment they are used at a pH which is not the isoelectric point. The amphoteric surfactants as claimed were found to perform very well as surfactants in oil-in-water diesel fuel emulsions.

The surfactants for use in the claimed diesel emulsions have the following general structure:

each X is, independently, -H, -COOM or -S0 ₃ M, with at least one X, in one embodiment all X, in the molecule being COOM or S0 ₃ M ,

R is a C5-C22 linear or branched, saturated or non-saturated, substituted or unsubstituted hydrocarbon group ,

each R ² , independently, is H, CH ₃ , or C ₂ H ₅ , suitably H or CH ₃ ,

k = 0-3, suitably 0 or 1 ,

each m, independently, is 2-6, suitably 2-4, suitably 2 or 3,

each n, independently, is 1-6, suitably 1-3, suitably 1 or 2, whereby if n>1 the alkylene group— [-C-] _n - may be substituted with alkyl groups,

o = 0-40, suitably 0-20, suitably 0-10,

each M is, independently, selected from H and any cation M ⁺ , suitably an alkaline (earth) metal ion, such as Mg ²⁺ ,Ca ²⁺ , NH ₄ ⁺ , K ⁺ or Na ⁺ , whereby the oxygen attached to said cation is negatively charged and whereby any 2-valent ions or mixtures of ions comprising 2-valent ions, are used in an amount such that the sum of all positive and the sum of all negative charges is the same, suitably M is selected from K ⁺ or Na ⁺ for economic reasons and to avoid complex formation.

In an embodiment at least one M is not H.

In an embodiment RA- is from a natural source, such as derived from oleyl, coco, castor, or tallow fatty acids.

In an embodiment RA is lauryl, (iso)tridecyl or (iso)dodecyl.

In an embodiment RA is a C6-C10 linear or branched, saturated or non-saturated hydrocarbon group because such products were found to be easily synthesized, very effective and have a favourable ecotoxicity profile.

In an embodiment the surfactant is used at a pH<7 where the product is in the cationic form with all M=H and one or more of the nitrogen atoms being protonated. At this pH a suitable counter ion X is present, which can be any negatively charged ion, for example Cl , CH ₃ -0-S0 ₃ , C0 ₃ ² , or HC0 ₃ in an amount to have a formulation wherein the total of positive and negative charges is equal.

The products can be made in a conventional way by reacting an amine or polyamine, suitably a (poly)amine with a primary amine group, with acrylic acid (such that n=2 and the ethylene moiety defined by n is not substituted), methacrylic acid (n=2 and the ethylene group is substituted with a methyl group), typically followed by adjusting the pH. Products produced in this way have the advantage that they are salt-free, which is a benefit since it makes aqueous formulations of the products less corrosive, which is an advantage, particularly in fuel emulsions.

In an embodiment, the surfactant is used in its pure form. However, to improve handling, a solvent can be used. The solvent is suitably selected from water, alcohols, glycols, ethers, and mixtures thereof. In an embodiment, dipropylene glycol methylether is used as a solvent. In an embodiment ethylene glycol is used as a solvent. In an embodiment a mixture of dipropylene glycol methylether and ethylene glycol is used as a solvent.

It was found that the use of the surfactants of formula (I) allows the formulation of emulsions with a higher water content than conventional diesel fuel emulsions, resulting in an even lower NOx emission upon combustion. Particularly since a large amount of surfactant is used in the fuel emulsions as claimed, it is advantageous to use a surfactant with a good ecotoxicity profile. Also, since the emulsions are to be used in fuel systems which requires precise pumping and metering, they should preferably not be gelled.

Details

The present disclosure generally relates to the use of amphoteric surfactants of the formula I above as a surfactant in oil-in-water diesel fuel emulsions. The use of the surfactants as claimed results in desired fuel emulsions, with high water content, good stability (physical stability, i.e. stability of the oil droplet size), and little corrosion, while having a very mild ecotoxicity, such that they do not require the product to be labelled with the dead-fish-dead-tree symbol per the Directive.

The fuel emulsions described herein are typically white, which sets them apart from known clear micro-emulsions. In an embodiment the emulsions are opaque. The emulsions were found to have a D[4,3] of from 0.2, 0.5, 1 , 2, 3, or 4 pm up to 50, 20, 10, 9, 8, 7, 6, or 5 pm, with a D ₅₀ (or D[v,0.5]) in the same range, when determined using a Malvern and Laser Diffraction. In an embodiment the emulsions have a stability of at least 5 minutes, 10 minutes, 20 minutes, 1 hour, 2 hours, 4 hours, 8 hours, 16 hours, 32 hours, or 48 hours. Stability is define herein to be acceptable when 250 ml of the emulsion in a graduated glass cylinder of 30 cm height is not forming a separation layer of more than 5 mm when standing at 25°C for the time indicated. Since the emulsions are easily produced, they are suitably produced right before combustion. Suitably the emulsion are produced 5 minutes, 10 minutes, 20 minutes, 1 hour, 2 hours, 4 hours, 8 hours, 16 hours, 32 hours, or 48 hours before they are combusted.

The group R is a C5-C22 linear or branched, saturated or non-saturated, substituted or unsubstituted hydrocarbon group. In an embodiment R is from a natural source, such as derived from oleyl, coco or tallow fatty acids. In an embodiment R is alkyl. In an embodiment R is lauryl, (iso)tridecyl or (iso)dodecyl. In an embodiment the group R is a hydrocarbon group substituted with one or more OH groups, as in castor oil-derived products. In an embodiment R is a C5-C10 linear or branched, saturated or non- saturated hydrocarbon group because such products were found to be easily synthesized and very effective. In an embodiment the C5-C10 hydrocarbon is alkyl.

In an embodiment R is (iso)decyl, 3-propylheptyl, or 2-ethylhexyl.

In an embodiment the moiety R-A- is a C6-23 alkyl group or an oxyalkylated C5-22 alkyl group.

In an embodiment, the surfactant is Ampholak® YCE (sodium coco propylene diamine propionate ) ex AkzoNobel®.

In an embodiment, the surfactant is Ampholak YJH (coco imino dipropionate) ex AkzoNobel.

The surfactants as claimed are considered to be readily biodegradable, mild to skin, eyes, and aquatic life when compared to other surfactants, particularly alkylamine ethoxylates. In an embodiment the surfactants as claimed need not to be labelled with the dead-fish-dead-tree symbol.

Diesel fuels are defined to be fuels suitable for use in diesel engines. In an embodiment it is a Marine Gas Oil (MGO) or Marine Diesel Oil (MDO) such as Shell® 99. Typically diesel is a mixture of various hydrocarbons, including aliphatic and cyclic hydrocarbons and paraffins with a boiling point of 150 - 600 °C, suitably 170 - 390 °C. Typically such fuels are derived from fractional distillation of petroleum. However, herein the term is also used for the diesel fuels comprising more or less biodiesel: biomass to liquid (BTL), gas to liquid (GTL) and coal to liquid (CTL) fuels.

One or more other additives can be present in the fuel emulsions containing the surfactants of the present invention. They are stabilizers, defoamers, diluents (particularly for heavy fuels to ensure that the fuel is liquid), compatibility agents, biocides (particularly in biodiesel formulations), thickeners, dyes, fragrances, detergents (for injector or valve cleaning), and chelating agents.

The use of a compatibility agent is particularly important if the nitrogen containing surfactant of the present invention is not very compatible with the diesel fuel. When using a compatibility agent, it is advantageous that the compatibility agent is a surfactant which also acts as a detergent. The compatibility agent is suitably selected from C6-C12 dimethylamidopropylamines, which is different from the surfactants as claimed, with quaternary ammonium groups. Compatibility agents are suitably used in an amount up to 50, 25, 15, or 10% by weight, based on the weight of the surfactant. Stabilizers suitable for use in the emulsions as claimed were found to be cellulose ethers. The cellulose ethers can be methyl cellulose (MC), hydroxyethyl cellulose (HEC), methyl hydroxyethyll cellulose (MHEC), ethyl hydroxyethyl cellulose (EHEC), carboxymethyl cellulose (CMC), methyl ethyl hydroxyethyl cellulose (MEHEC), methyl ethyl hydroxypropyl cellulose (MEHPC), methyl hydroxypropyl cellulose (MHPC), ethyl hydroxypropyl cellulose (EHPC), methyl ethyl hydroxypropyl cellulose (MEHPC), methyl carboxymethyl cellulose (MCMC), ethyl carboxymethyl cellulose (ECMC), methyl ethyl carboxymethyl cellulose (MECMC), aminated derivatives of any of these cellulose ethers which can be quaternized, any hydrophobically modified derivate of any of these compounds, and mixtures of any of all of these cellulose ethers. The cellulose ethers are suitably not crosslinked. The use of a stabilizer was found to be very effective in prolonging the time after which the emulsion shows phase separation. However, because of their polymeric nature they are preferably used in a small amount. The stabilizers are suitably used in an amount of from 0.001 , or 0.002, or 0.005 up to 0.05, 0.1 , 0.2, 0.5, 1 , 2, 5, 7.5 or 10% by weight of the final fuel emulsion. In an embodiment the amount of surfactant is from 0.002, or 0.005 % by weight of the final fuel emulsion. In an embodiment the amount of surfactant is up to 2 or 5% by weight of the final fuel emulsion.

Defoamers, as used in accordance with the invention, are typically silicon-based products, such as siloxane polymers. Suitable defoamers are commercially available and include all conventional defoamers. Suitably it is a defoamer selected from the SAG products from Momentive Performance Chemicals, USA, the BC Antifoam products of KCC Brasilon, Foamaster of Cognis, Rhodisol of Rhodia, Break Thru of Degussa, and/or the Surfynol® DF series and the Airase® SSDL™ products of Air Products. The defoamers are suitably used in an amount of from 0.01 to 10, in an embodiment from 0.05 to 1 , in another embodiment from 0.1 to 0.5 g/l in the concentrated compositions.

Unlike many other prior art surfactants, the surfactants of the present invention showed excellent emulsification of the diesel droplets in water. Nevertheless it can be desired to choose the concentration of the surfactant of the present invention in the diesel emulsion to be quite high. The concentration of the surfactants, particularly of surfactants of formula (I), is suitably from 0.025, 0.05, 0.1 , 0.2 or 0.3% up to about 10, 7.5, 5, 3, 2, or 1.5%, wherein % means weight percent of the surfactant in the final fuel emulsion. In an embodiment the amount of surfactant of formula I is from 0.2, or 0.3 % by weight in the final fuel emulsion. In an embodiment the amount of surfactant of formula I is up to 7.5 or 10% by weight in the final fuel emulsion. Higher surfactant concentrations of greater than 0.5% by weight are suitably used for emulsions with a fuel concentration of 50% by weight or more.

The amount of water in the emulsion is from 35, 45, 50, 55, 60, or 65% up to 85, 82.5, 80, 77.5, or 75%, wherein % means weight percent of the water in the total emulsion.

In an embodiment the amount of water in the fuel emulsion is from 50 or 55 % by weight. In an embodiment the amount of water in the fuel emulsion is up to 85 or 82.5% by weight in the total fuel emulsion.

The remainder is diesel and optional further additives. The diesel content of the final emulsion is suitably from 15, 17.5, 20, 22.5, or 25 up to 40, 45, 50, 55, 60 or 65 percent by weight of the emulsion. In an embodiment the amount of diesel in the fuel emulsion is from 15 or 17.5 up to 45 or 50% by weight since such formulations require lower levels of surfactants and achieve very good NOx reductions upon combustion.

The diesel emulsions as claimed can be produced in any conventional way. Suitably a high shear mixer is used to combine water, diesel, surfactant, and optional further additives. In a suitable process, water and surfactants are first mixed, during which (part or all of) the surfactant can dissolve, in any conventional matter followed by mixing this aqueous stream with diesel fuel in a high shear mixer. Optional additives can be combined with either the aqueous feed or the diesel feed, depending on the ease of processing and the compatibility with either stream. If desired, part of the aqueous stream and part of the diesel stream can be added in any sequence and quantity to the mixer. In an embodiment all, or part of, the aqueous feed and the diesel feed are added to the mixer simultaneously. In an embodiment all, or part of, the aqueous stream or the diesel stream is premixed with part of the other stream before entering the high shear mixer.

The high shear mixer can be a colloid mill, containing a rotor and a stator, where the water/surfactant stream is mixed together with the hydrocarbon stream just before entering the mill head. Those of ordinary skill in the art will realize that there are other ways of creating a high shear mixing, such as for instance in high-pressure homogenizers, such as Manton Gaulin homogenizers, or ultrasonic homogenizers, and the invention is not limited to the mixer type. The formation of the emulsion can be in batch, semi-continuous or continuous, as for instance in in-line operations wherein an aqueous stream and a diesel-containing-stream are mixed and the resulting emulsion is directly fed to the engine. For batch operations, high shear mixers from Silverson®, Ultra-Turrax®, and the like, can be used.

The surfactants of the invention may also be used with one or more other surfactants such as alkylamine alkoxylates and quaternary compounds derived therefrom, anionic surfactants such as sulfates and sulfonates from alcohols and alkoxylated alcohols, phosphate esters and ethoxylated phosphate esters, nonionic surfactants such as alcohol alkoxylates and alkyl (C6-C18) polyglucosides, and silicone surfactants. In an embodiment the surfactants of formula I are combined with one or more other surfactants such that the resulting mixture does not need to be labelled with the dead- fish-dead-tree symbol.

It was found that a further advantage of any of the surfactants/adjuvants of formula I is that they can be used without any other surfactant, thus simplifying the formulation. In one embodiment of the invention therefore the one or more surfactants as defined in claim 1 make up at least 20, 40, 50, 60, 70, 75, 80, 85, 90, 95, or 100% of all nitrogen- containing surfactants used in the formulation. In an embodiment the one or more surfactant as defined in claim 1 make up at least 20, 40, 50, 60, 70, 75, 80, 85, 90, 95, or 100% of all surfactants used in the formulation.

In the case that another surfactant is used together with the surfactants of the present invention, it is advantageous that the mixture of the surfactants have low aquatic toxicity and low irritation profiles. Employing the surfactants of formula I, with low aquatic toxicity and low irritation profiles, can reduce the total toxicity of a blend while keeping the efficacy more or less the same even if a not-so favorable surfactant in terms of the aquatic toxicity and irritation profiles is contained in the blend.

All of the surfactants as described herein were found to have the property of allowing the preparation of desirable fuel emulsions, while having a very mild ecotoxicity. In one embodiment, the fuel emulsions as claimed are used in a conventional combustion engine capable of burning diesel fuels. Suitably they are used in car engines, ship engines, steam engines, and engines in power plants, such as co- generation plants. In one embodiment the fuel emulsions are diesel emulsions and used in ship engines.

In another embodiment they are burned to heat up water or any other medium, merely to generate heat, such as, for instance, in boilers and heaters.

In either embodiment, the emulsions as claimed are suitably diluted with water or any other liquid, such as alcohol, before being burned.

Because of the accurate metering of the fuel emulsion that is needed, the fuel emulsions are preferably non-gelled, meaning that at 25 °C they do not have a storage modulus (G’) that is higher than the loss modulus (G”) at a shear frequency in the range of 0.1 to 1000 Hz using a conventional rheometer, such as a piezorheometer. Furthermore, gelling of the fuel emulsion could also have an influence on the burning characteristics of the fuel, which is undesired.

Throughout this document, when a ratio or amount is given, it is by weight, unless mentioned differently. Throughout this document, unless indicated differently, the weight percentages of the compositions are based on the total weight of the emulsion, whereby the total weight of the emulsion is 100 wt%. The term water-soluble is used for materials that dissolve in an amount of at least 1 g per liter of demineralized water at 25 °C. Where used, the term“consisting” also embraces“consisting substantially”, but may optionally be limited to its strict meaning of “consisting entirely”. It shall be pointed out that when an amphoteric surfactant appears in the text as a general name without specifying the counterions, it means both its protonated and deprotonated form and salts thereof.

Throughout the description and claims of this specification, the words“comprise” and “contain” and variations of the words, for example“comprising” and“comprises”, mean “including but not limited to”, and do not exclude other moieties, additives, components, integers or steps. Moreover the singular encompasses the plural unless the context otherwise requires: in particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise. Where upper and lower limits are quoted for a property, for example for the concentration of a component, then a range of values defined by a combination of any of the upper limits with any of the lower limits may also be implied.

It will also be appreciated that features from different aspects and embodiments of the invention may be combined with features from any other aspect and embodiment of the invention.

The following non-limiting examples are presented to further illustrate and explain the present invention.

Examples

Materials used:

Ampholak YCE, sodium cocopropylene diamine propionate

Ampholak XCE, coco imino diglycinate

Ampholak YJH-40, C12-imino dipropionate

Lakeland AMA ex Lakeland Chemicals India Ltd, and Librateric AA-30 ex Libra Spec

Chem, both coco imino dipropionate disodium salt

Bermocoll® EM 7000FQ, a MEHEC ex AkzoNobel

Water, tap water with a hardness of 10°dH, unless indicated differently.

A fuel emulsion was made at room temperature using 69.75% by weight water, 29.75 % by weight of a marine diesel fuel, and 0.50 % by weight of surfactant, unless specified differently. Each test was done on samples with a size of 100 ml. First surfactant and water were mixed in a beaker while stirring. Depending on the test, the pH was subsequently controlled. Thereafter the diesel was added while stirring for 20 minutes. Then the resulting mixture was emulsified with a Silverson L4R with a general purpose head for 60 seconds.

Experiment set 1 : Test of pH influence.

Surfactant used : Ampholak YCE.

The pH of the water/surfactant mixture was adapted with a little NaOH or HCI to be in the range from 1 to 13. The test showed all emulsions to be suitable since they all had the desired physical properties for at least 15 minutes. However, when stored overnight without stirring, the products with pH 2-8 showed least separation, with pH <7 being the best, and these pH ranges may therefore be preferred for emulsions as claimed.

Experiments 2-4 : Test of influence of water hardness.

Surfactant used : Ampholak YCE.

Three experiment were done using tap water (soft water, 3°dH), medium-hard water (10°dH) and hard water (17°dH).

The test showed all emulsions to be suitable since they all had the desired physical properties for at least 15 minutes. However, when stored overnight without stirring, the emulsions made with hard water showed separation and a water hardness from 3- 10°dH may therefore be preferred for emulsions as claimed.

Experiments 5 and 6 : Test of influence of salt.

Surfactant used : Ampholak YCE and Ampholak XCE.

An emulsion was made with each of the surfactants. Both emulsions performed satisfactory, showing that salt (present in the Ampholak XCE) has little influence on the emulsions.

Experiments 7-9 : Test of influence of water content.

Surfactant used : Ampholak YCE.

The ratio of diesel : water was varied in these tests. A ratio of 60:40, 50: 50, 40:60, and 20:80 was used. Surprisingly it showed that a product with a water content of 50% or more was stable for 15 minutes, whereas products with less water were not stable for 15 minutes. More surprisingly, the best stability (least separation in 15 minutes) was observed in emulsions containing 60% by weight or more of water. The higher amount of water will lead to less NOx formation upon combustion of the emulsion. The product with 80% water showed foaming.

Experiment 10 : Test of surfactant concentration.

Experiment 5 was repeated using 0.3% by weight of Ampholak YCE instead of 0.5%. The emulsion was satisfactory, showing that the concentration of the surfactant can be varied to optimize cost/performance. Experiments 11-12 : Test of influence of stabilizer.

Two emulsion were made using 54.5 % water 44.5% diesel; and 1% Ampholak YJH-40. In one example 0.1% by weight of the stabilizer Bermocoll EM 7000FQ was added. Both emulsions performed satisfactory. However, the one containing the stabilizer showed better properties showing that the use of a stabilizer may be preferred.

Experiments 13-14 : T est of influence of amphoteric

Lakeland AMA,and Librateric AA-30 were used as the surfactant in these examples in an amount of 0.4% by weight. The pH was not controlled.

Good emulsions resulted with a particle size distribution (d 10, d50, d90 by volume) of 2.2, 4.9, 8.8 micron and 2.1 , 4.7, 8.6 micron, respectively, which foamed a little. In such formulations a little defoamer is suitably added to reduce the foaming.