Method for improving the emulsification performance of nonionic alkoxylated surfactants

Abstract

A method of improving the emulsification performance of nonionic alkoxylated surfactants, for example when used as fuel additives. The method involves a) providing a composition comprising at least one nonionic alkoxylated surfactant; and b) prior to the addition of said composition to an aircraft fuel, thermally cycling said composition by (i) chilling the composition from a first temperature to a second temperature that causes metal ions and/or associated ions contained therein to precipitate as ionic salts; (ii) filtering the chilled composition to remove the precipitated ionic salts; and (iii) heating the filtered composition to the first temperature.

Claims

1. A method of improving the emulsification performance of nonionic alkoxylated surfactants in a fuel additive composition, said method comprising, prior to the addition of said fuel additive composition to an aircraft fuel, the steps of: a) providing a composition comprising at least one nonionic alkoxylated surfactant; and b) thermally cycling said composition by (i) chilling the composition from a first temperature of 30° C. to 10° C. to a second temperature of 20° C. to −60° C. that causes metal ions and/or associated ions contained therein to precipitate as ionic salts, wherein the thermal cycling comprises from 2 to 15 cycles of heating and chilling; (ii) filtering the chilled composition to remove the precipitated ionic salts; and (iii) heating the filtered composition to the first temperature.

2. The method of claim 1, wherein the at least one nonionic alkoxylated surfactant is at least one nonionic ethoxylated surfactant.

3. The method of claim 2, wherein the at least one nonionic alkoxylated surfactant is at least one C.sub.6-C.sub.15-alkanol ethoxylate.

4. The method of claim 2, wherein the at least one nonionic alkoxylated surfactant is selected from C.sub.6-alkanol ethoxylates, C.sub.7-alkanol ethoxylates, a C.sub.8-alkanol ethoxylates, C.sub.9-alkanol ethoxylates, C.sub.10-alkanol ethoxylates, C.sub.11-alkanol ethoxylates, C.sub.12-alkanol ethoxylates, C.sub.13-alkanol ethoxylates, C.sub.14-alkanol ethoxylates, and C.sub.15-alkanol ethoxylates.

5. The method of claim 1, wherein the at least one C.sub.6-C.sub.15-alkanol ethoxylate is one C.sub.6-C.sub.15-alkanol ethoxylate selected from C.sub.6-alkanol ethoxylates, C.sub.7-alkanol ethoxylates, C.sub.8-alkanol ethoxylates, C.sub.9-alkanol ethoxylates, C.sub.10-alkanol ethoxylates, C.sub.11-alkanol ethoxylates, C.sub.12-alkanol ethoxylates, C.sub.13-alkanol ethoxylates, C.sub.14-alkanol ethoxylates, and C.sub.15-alkanol ethoxylates.

6. The method of claim 1, wherein the at least one nonionic alkoxylated surfactant is a mixture of C.sub.6-C.sub.15-alkanol ethoxylates with different carbon numbers for the alkanol unit species and 2 to 5 moles of ethylene oxide units on average per mole of alkanol, wherein the carbon numbers for the two C.sub.6-C.sub.15-alkanol ethoxylates which have the highest share in weight in the mixture being at least 1.5 carbon numbers distant from each other, and wherein the carbon number for one of the two C.sub.6-C.sub.15-alkanol ethoxylates which have the highest share in weight in the mixture is in the range of 9 to 11 and the other is in the range of 12 to 14.

7. The method of claim 1, wherein the thermal cycling comprises from 2 to 5 cycles of heating and chilling.

8. The method of claim 1, wherein the thermal cycling comprises from 6 to 10 cycles of heating and chilling.

9. The method of claim 1, wherein the thermal cycling comprises from 11 to 15 cycles of heating and chilling.

10. The method of claim 1, wherein in step (b) the first temperature is ambient temperature.

11. The method of claim 1, wherein in step (b) the second temperature is from 10° C. to −40° C.

12. The method of claim 11, wherein in step (b) the second temperature is from 0° C. to −20° C.

13. The method of claim 1, wherein in step (c) the chilled composition comprising at least one nonionic alkoxylated surfactant is filtered through a filter having a mesh size of less than 150 microns.

14. The method of claim 13, wherein the chilled composition is filtered through a filter having a mesh size of less than 25 microns.

15. The method of claim 14, wherein the chilled composition is filtered through a filter having a mesh size of less than 10 microns.

Description

DESCRIPTION OF THE DRAWINGS

(1) The present application includes FIGS. 1 to 7. In the drawings:

(2) FIG. 1 shows pre-filtered SURFAC™ UN30 surfactant (see Example 1).

(3) FIG. 2 shows the SURFAC™ UN30 surfactant composition after having been filtered through 1 micron glass fibre paper (see Example 1).

(4) FIG. 3 shows pre-filtered SYNPERONIC™ 91-2.5 surfactant (see Example 3).

(5) FIG. 4 shows the SYNPERONIC™ 91-2.5 surfactant composition after having been filtered through the 0.45 micron filter membrane (see Example 3).

(6) FIG. 5 shows jet fuel with water droplets at the bottom of the container (see Example 4).

(7) FIG. 6 shows the fuel after 17 ml of the additive system has been added (see Example 4).

(8) FIG. 7 shows the fuel after 19.4 ml of the additive system has been added (see Example 4).

DETAILED DESCRIPTION OF THE INVENTION

(9) The present invention provides a method for improving the emulsification performance of nonionic alkoxylated surfactants, for example when used as fuel additives.

(10) Liquid hydrocarbon fuel, especially jet fuel, can be contaminated in a fuel tank of a turbine engine aircraft with small quantities of water from condensation arising from the changes in temperature due to altitude changes. On the ground the fuel/tank temperature can range from about −20° C. to +50° C. (depending on location), whilst in flight it typically ranges from −22° C. to −39° C. It is believed a Boeing 777 aircraft lost sufficient power to cause an emergency landing at Heathrow in January 2008 due to the formation of ice reducing the flow of fuel from the fuel tanks to the engines (AAIB interim report No 2 G-YMMM).

(11) Water exists in fuel as either free water or dissolved water. The term “free water” refers to water present as a separate visible liquid phase in a two phase liquid fuel and water mixture, while the term “dissolved water” refers to water that is dissolved in the liquid fuel phase. This may arise from entrained water or water that is dissolved in the liquid fuel phase. Dissolved water becomes free water with lower temperatures due to the reduction in solubility of the water in liquid fuel.

(12) Such free water exists in or is introduced into the liquid fuel as a contaminant i.e. it is not water, which has been deliberately added to the liquid fuel, such as water, added to a liquid fuel in the preparation of a water-in-oil emulsion or microemulsion. The free water exists or is introduced as a contaminant in the liquid fuel or water when e.g. water is added to the liquid fuel accidentally or inadvertently, or the water is ambient moisture such as from rain or condensation water derived from changes in humidity levels in the atmosphere whilst the liquid fuel is in a tank vented to atmospheric conditions or in a tank subject to wide temperature changes such as that on an aircraft.

(13) Whilst in extreme conditions the amount of free water which may be introduced as a contaminant could comprise 0.5% by weight or more of the combined weight of water and liquid fuel, it will be apparent to those skilled in the art that in practice the amount of free water contaminant will typically comprise significantly less than 0.5 wt % of the combined weight of free water and liquid fuel. For example, typically the amount of free water contaminating the liquid fuel will be less than 0.2 wt % and more typically less than 0.1 wt %, such as 0.05 wt % or less, by weight of the combined weight of water and liquid fuel.

(14) Diethylene glycol monomethyl ether (DiEGME) is often added to fuel, especially jet fuel, to minimise the formation of ice in the fuel. However DiEGME is known to form a gel at low temperatures that is commonly known in the industry as “apple jelly”. The formation of apple jelly in jet fuel has been attributed to causing several aviation accidents.

(15) Nonionic alkoxylated surfactants are useful in fuel additives, especially in fuel additive systems that are known to prevent or at least minimise the formation of ice and “apple jelly” in fuel, especially jet fuel cooled to temperatures in the range of from 0 to −50° C., for example during storage before on during flight. International patent applications WO 2011/095825 A1 and WO 2011/0445334 A1 disclose such fuel additive systems that include nonionic alkoxylated surfactants.

(16) Nonionic alkoxylated surfactants are also useful in fuel additives systems that are known to partition particulate solids, e.g. rust and dust particles, from water in the fuel. United Kingdom patent GB 2463030 B discloses such fuel additive systems that include nonionic alkoxylated surfactants.

(17) The present inventor has used water filtration test to check the functionality of such fuel additives and fuel additive systems. In the test the amount of fuel additive or fuel additive system required to emulsify 1% by volume of water, by forming a clear bright microemulsion, was measured. Although the actual treat rates of these additive systems are of the order of parts per million (ppm) this test allows the emulsification potential of each system to be compared when using the same jet fuel. The lower the quantity of additive required, the more efficient the system.

(18) Commercially available nonionic alkoxylated surfactants, especially alcohol ethoxylates, are manufactured using well-known techniques that produce residual metal ions, especially monovalent alkali metal ions e.g. potassium or sodium ions, and often associated ions such as sulphate and chloride ions. The manufacturers of those nonionic alkoxylated surfactants do not remove such ions as their products are often used in conjunction with ionic surfactants, for example in dish-washing cleaners where the presence of these ions, for example monovalent metal ions, is beneficial.

(19) In order to meet stringent fuel regulations the addition of a fuel additive system must not increase the presence of these types of metal ions above certain limits. The use of standard commercially available alcohol ethoxylates does not adversely affect these metal ion concentration requirements. However, the present inventor has found that the presence of metal ions, particularly monovalent alkali metal ions, detrimentally affects the non-ionic emulsification process.

(20) During routine testing of materials it had been noted on several occasions that when commercially available nonionic alkoxylated surfactants, especially alcohol ethoxylate surfactants, have been subject to sub-zero temperatures solid material form in the additive system that once warmed up did not always get taken back into solution. Initially it was considered that this material was higher chain length by products formed in the production process. However as the material did not generally re-dissolve the present inventor postulated that the material may have resulted from contamination.

(21) The present invention provides a method of improving the emulsification performance of nonionic alkoxylated surfactants, for example when used as fuel additives.

(22) The first step, step a), of the method of the present invention comprises providing a composition comprising at least one nonionic alkoxylated surfactant.

(23) Preferably the at least one nonionic alkoxylated surfactant is at least one nonionic ethoxylated surfactant, more preferably at least one C.sub.6-C.sub.15-alkanol ethoxylate.

(24) Preferably the at least one nonionic alkoxylated surfactant is at least one C.sub.6-C.sub.15-alkanol ethoxylate is selected from one or more of C.sub.6-alkanol ethoxylates, C.sub.7alkanol ethoxylates, a C.sub.8-alkanol ethoxylates, C.sub.9-alkanol ethoxylates, C.sub.10-alkanol ethoxylates, C.sub.11-alkanol ethoxylates, C.sub.12-alkanol ethoxylates, C.sub.13-alkanol ethoxylates, C.sub.14-alkanol ethoxylates, and C.sub.15-alkanol ethoxylates. More preferably the at least one nonionic alkoxylated surfactant is at least one C.sub.6-C.sub.15-alkanol ethoxylate selected from C.sub.6-alkanol ethoxylates, C.sub.7alkanol ethoxylates, C.sub.8-alkanol ethoxylates, C.sub.9-alkanol ethoxylates, C.sub.10-alkanol ethoxylates, C.sub.11-alkanol ethoxylates, C.sub.12-alkanol ethoxylates, C.sub.13-alkanol ethoxylates, C.sub.14-alkanol ethoxylates, and C.sub.15-alkanol ethoxylates.

(25) In certain embodiments the at least one nonionic alkoxylated surfactant is a mixture of C.sub.6-C.sub.15-alkanol ethoxylates. Preferably it is preferably a mixture of C.sub.9-C.sub.14 alcohol ethoxylates, such as a mixture of C.sub.9 to C.sub.11 alcohol ethoxylates or a mixture of C.sub.12-C.sub.14 alcohol ethoxylates. The distribution of any of the components in the mixture can range from 0 to 50% by weight, and are preferably distributed in a Gaussian format.

(26) In certain embodiments the at least one nonionic alkoxylated surfactant is a mixture of C.sub.6-C.sub.15-alkanol ethoxylates with different carbon numbers for the alkanol unit species and 2 to 5 moles of ethylene oxide units on average per mole of alkanol, wherein the carbon numbers for the two C.sub.6-C.sub.15-alkanol ethoxylates which have the highest share in weight in the mixture being at least 1.5 carbon numbers distant from each other, and wherein the carbon number for one of the two C.sub.6-C.sub.15-alkanol ethoxylates which have the highest share in weight in the mixture is in the range of 9 to 11 and the other is in the range of 12 to 14.

(27) Known nonionic alkoxylated surfactant products include SYNPERONIC™ brand surfactants from Croda including SYNPERONIC™ 91-2.5 surfactant, SURFAC™ brand surfactants from Surfachem including SURFAC™ UN30, and NEODOL™ brand surfactants from Shell such as NEODOL™ 91-6 surfactant.

(28) The second step, step b), of the method of the present invention comprises thermally cycling said composition by (i) chilling the composition from a first temperature to a second temperature that causes metal ions and/or associated ions contained therein to precipitate as ionic salts; (ii) filtering the chilled composition to remove the precipitated ionic salts; and (iii) heating the filtered composition to the first temperature. As mentioned above, commercially available nonionic alkoxylated surfactants, especially alcohol ethoxylates, often contain metal ions, especially monovalent alkali metal ions, which are innocuous or sometimes advantageous to their typical uses. However the present applicant has found these metal ions, especially monovalent alkali metal ions such as potassium and sodium ions, are detrimental when formulating fuel additives so they should be removed from or at least their concentration should be minimised. These metal ions are typically associated with other ions such as sulphate and chloride ions. Those ions may also be detrimental when formulating fuel additives and may also precipitate as ionic salts with the metal ion salts.

(29) Chilling a composition means lowering the temperature of that composition, typically from ambient temperature to below ambient temperature and often below 0° C.

(30) This can be achieved by various art-known methods and equipment. For example chilling a composition means lowering the temperature of the composition by relocating it from one area that has a certain temperature to another area when temperature is lower than that of the first area, for example by moving a vessel containing the composition into a fridge or chiller. Alternatively, one can chill a composition by placing a cooling device within the composition.

(31) The chilling needs to be sufficient in terms of temperature to cause all or substantially metal ions and/or associated ions contained in the composition to precipitate out of the composition as ionic salts. The rate by which the temperature of the composition is lowered will often determine when the metal ions and/or associated ions contained in the composition will form ionic salts and precipitate out of the composition as ion salts. One skilled in the art can readily determine the optimal chilling temperature for a given composition and a given environment. For example the ambient temperature in many parts of Australia will generally much higher than the ambient temperature of most parts of Norway.

(32) The third step, step c), of the method of the present invention comprises filtering the chilled composition to remove the precipitated ionic salts.

(33) The filtering can carried out using any suitable art-known filtering/filtration method. Preferably the filtering is performed at room temperature. Filtration can be carried out using any suitable art type of filter, for example a mesh filter. Preferably the chilled composition comprising at least one nonionic alkoxylated surfactant is filtered through a filter having a mesh size of less than 150 microns, preferably less than 25 microns, more preferably less than 10 microns, even more preferably less than 1 micron, or yet more preferably less than 0.45 microns.

(34) Multiple filtration stages may be needed to obtain a desired filtration.

(35) If desired, the concentration of metal ions and/or associated ions can be measured in the composition at any time before, during or after the method of the present invention is performed to verify the removal of metal ions and/or associated ions. Suitable methods for measuring the concentration of metal ions and/or associated ions in a compositions are well known in the art, for example Inductively Coupled Plasma Mass Spectrometry (ICP-MS) analysis.

(36) If desired, the temperature of the filtered composition is raised to room temperature by any suitable means before it is used in the formulation of a fuel additive system, for example any of the fuel additive systems disclosed in the international patent applications WO 2011/095825 A1, WO 2011/0445334 A1 and WO 2013/150274 A2 or in United Kingdom patent GB 2463030 B.

(37) Industrially, filtration can be performed in conjunction with the chilling step.

(38) One skilled in the art would appreciate that the viscosity of a given nonionic alkoxylated surfactant will increase with decreasing temperature so for best results it is may be necessary to optimize the chilling temperature and the filtration mesh size.

(39) Various modifications and variations of the described methods and uses of the present invention will be apparent to those skilled in the art. Although the invention has been described in connection with specific preferred embodiments, it should be understood that the invention as claimed should not be unduly limited to such specific embodiments.

EXAMPLES

(40) The following Examples illustrate the method of the present invention:

Example 1

(41) A commercial sample of SURFAC™ UN30 surfactant (C.sub.9-11alcohol ethoxylate with 2.5 moles ethylene oxide available from Surfachem Group Ltd supplied as a 100% active liquid) was placed in a chiller to reduce its temperature to −5° C. and thermally cycled over 2 cycles. The resulting opaque additive system was then filtered using 1 micron glass fibre filter material. The resulting recovered fluid was then warmed to ambient temperature and used in the preparation of a fuel additive system (described in WO 2011/095825 A1 and WO 2011/0445334 A1).

(42) FIG. 1 shows pre-filtered SURFAC™ UN30 surfactant.

(43) FIG. 2 shows the SURFAC™ UN30 surfactant composition after having been filtered through 1 micron glass fibre paper.

Example 2

(44) The commercial sample of SURFAC™ UN30 surfactant prepared in Example 1 was used in a fuel additive system noted in Example 1. It was tested using the 1% volume water titration test (described below). This was compared to an additive system from Example 1 using a SURFAC™ UN30 that was not thermally cycled and filtered.

(45) The additive system using the thermally cycled SURFAC™ UN30 alcohol ethoxylate reduced the quantity of additive required by 10% volume.

Example 3

(46) A commercial sample of SYNPERONIC™ 91-2.5 surfactant (C.sub.9-11alcohol ethoxylate with 2.5 moles ethylene oxide available from Croda Ltd supplied as a 100% active liquid) was thermally cycled from −23° C. to ambient over 10 cycles. The resulting fluid was then passed through a 0.45 micron filter membrane at 23° C. The resulting recovered liquid was used to prepare a fuel additive system per Example 1.

(47) FIG. 3 shows pre-filtered SYNPERONIC™ 91-2.5 surfactant. The solution is hazy.

(48) FIG. 4 shows the SYNPERONIC™ 91-2.5 surfactant composition after having been filtered through the 0.45 micron filter membrane. The solution is clear/transparent.

Example 4

(49) The additive system prepared in Example 3 was tested using the 1% volume water titration test and compared to an additive system from Example 3 using a version of the SYNPERONIC™ 91-2.5 surfactant that was not thermally cycled and filtered.

(50) The additive system using the thermally cycled SYNPERONIC™ 91-2.5 alcohol ethoxylate reduced the quantity of additive required by 10.2% volume.

(51) FIG. 5 shows jet fuel with water droplets at the bottom of the container. The solution is clear/transparent.

(52) FIG. 6 shows the fuel after 17 ml of the additive system has been added. The solution is hazy.

(53) FIG. 7 shows the fuel after 19.4 ml of the additive system has been added. The solution is clear/transparent.

Example 5

(54) The recovered liquid from Example 3 was also used to prepare a second additive system for another fuel additive as described in GB 2463030 B.

Example 6

(55) The additive system prepared in Example 5 was tested using the 1% volume water titration test and compared to an additive system from Example 5 using a version of the SURFAC™ UN30 surfactant that was not thermally cycled and filtered.

(56) The additive system using the thermally cycled SURFAC™ UN30 alcohol ethoxylate reduced the quantity of additive required by 9% volume.

Example 7

(57) The additive system prepared in Example 5 was tested using the 1% volume water titration test and compared to an additive system from Example 5 using a version of the SYNPERONIC™ 91-2.5 surfactant that was not thermally cycled and filtered.

(58) The additive system using the thermally cycled SYNPERONIC™ 91-2.5 alcohol ethoxylate reduced the quantity of additive required by 9.4% volume.

(59) Water Titration Test Protocol

(60) 1% volume water titration test is a standard test for examining the emulsification capacity of a surfactant system.

(61) Place 99 ml of jet fuel into a suitable container such as a 250 ml conical flask with a magnetic stirrer set at rpm or value (5). In order to maintain consistency of results the magnetic stirrer should be used at a set rpm or value (0-9) on the equipment.

(62) Add 1 ml water.

(63) From a burette add the fuel additive system in aliquots of 1 ml allowing 30 seconds between each addition. As with any type of titration, drop wise additions are carried out once the end point is near.

(64) The fluid in the container will become a white opaque emulsion. Continue to add the additive system until the fluid clears i.e. becomes transparent and free of haze. The results are taken from an average of 3 tests.

(65) To check the clarity of the final fluid, samples of the fuel can be placed into a quartz cuvette and the % transmission of light can be measured at a given wavelength using a spectrophotometer or colorimeter.