Aviation fuel cold flow additives and compositions

Abstract

Aviation fuel, such as jet fuel, blends and methods for improving cold flow properties of such fuels at extremely low temperatures are disclosed. Cold flow properties of, for example, JP-8 jet fuel are improved by addition to the fuel of an oil-soluble, polar nitrogen-containing compound. Demonstratable cold flow improvement of such fuels at temperatures of about −53° C. and lower is shown.

Description

FIELD OF THE INVENTION

[0001] The invention pertains to jet fuel blends and methods in which a cold flow enhancement agent is added to the jet fuel to improve fuel flow rates and flow characteristics at low fuel temperatures.

BACKGROUND OF THE INVENTION

[0002] It is important that aviation fuel exhibits a freeze point that is sufficiently low to allow adequate fuel flow through fuel system lines and filters to the engine. It is known that fuel temperature decreases as flight time increases and that longer duration flights typically require lower freezing point fuels than do shorter duration flights.

[0003] Additionally, high altitude flights, such as those conducted under military operational conditions, also require lower freezing point fuels than do lower altitude conventional flights. Quite obviously then, there is a need to provide freeze point depressant/cold flow enhancement aids for aviation fuels, particularly for jet fuels, which will allow for sufficient fuel flow to desired combustion locations at the extremely low fuel temperatures encountered at high altitude and long duration flights. Publications WO 01/32811 A1 and WO 01/62874 A2 discuss details of aviation fuels and the need for lowered freeze point fuel blends.

[0004] One such means of enhancing the cold flow properties of wax containing hydrocarbon fluids is via use of polymeric pour point depressant additives. For example, use of poly[(meth)acrylates] as a pour point depressant for hydrocarbon lubricating oil is taught by U.S. Pat. Nos. 5,312,884 and 5,368,761. Additionally, the use of poly[&agr;-olefins] to improve the cold flow properties of gas oil is taught by E1-Gamal et al., J. of Polym. Sci. 61, pp. 1265-1272 (1966). The use of a low molecular weight highly branched polymer of normal &agr;-olefin to improve the cold flow properties of residual fuel oil is taught in U.S. Pat. No. 4,022,590.

[0005] The use of nitrogen compounds, such as amides, amine salts, and ammonium salts of carboxylic acids or anhydrides, or sulpho anhydrides, as an adjuvant to polymeric pour point additives in middle distillate fuels is also known to those skilled in the art. These compounds act as wax crystal modifiers and/or anti-agglomeration agents to provide enhanced cold flow properties relative to the polymeric pour point additive as a stand-alone treatment. For example see U.S. Pat. Nos. 3,982,909; 4,211,534; and 5,516,443; and EP applications Nos. 0 261 959 A2; 0 261 957 A2; and 0 272 889 A2.

[0006] WO 01/62874 A2 teaches the use of various chemical additives, including certain copolymers of vinyl acetate and ethylene, to lower the freeze point of aviation fuels. It is further taught that certain classes of pour point additives known to those skilled in the art for treating middle distillates, such as heating oils and diesel fuels, are not necessarily effective in the treatment of aviation fuel and actually may be detrimental.

DESCRIPTION OF THE INVENTION

[0007] Methods for improving the cold flow rate of aviation fuels, and jet fuels in particular are provided wherein the jet fuel is blended with a cold flow rate enhancement agent (CFREA). The CFREA is an oil-soluble, polar, nitrogen-containing compound.

[0008] The oil-soluble, polar nitrogen-containing compounds are set forth in U.S. Pat. No. 4,211,534 (Feldman) incorporated by reference herein. Basically, as stated in the '534 specification, these compounds are oil-soluble amine salts and/or amides that are generally formed by reaction of at least one molar proportion of hydrocarbyl acid having 1-4 carboxyl groups or their anhydrides, with a hydrocarbyl substituted primary, secondary, and/or tertiary amine.

[0009] In the case of the polycarboxylic acids, or anhydrides, all of the acid groups may be converted to amine salts or amides, or part of the acid groups may be left unreacted.

[0010] The term “hydrocarbyl” as defined in U.S. Pat. No. 4,211,534 includes groups that may be branched or straight chain, saturated or unsaturated, aliphatic, cycloaliphatic, aryl, alkaryl, substituted derivatives thereof and the like. Typically, these hydrocarbyl groups will consist from about 4-24 carbon atoms, more preferably 10-20 carbon atoms. In general, the resultant compound should contain sufficient hydrocarbyl content so as to be soluble in the fuel matrix.

[0011] Exemplary hydrocarbyl substituted acids and anhydrides include, but are not limited to, hexanoic acid, lauric acid, palmitic acid, steric acid, behenic acids, benzoic acids, 1,2,4,5-benzenetetracarboxylic dianhydride, 1,2-cyclohexanedicarboxylic anhydride, ethylenediaminetetraacetic dianhydride, salicylic acid, succinic acid, succinic anhydride, alkenyl succinic anhydrides, polyisobutenyl succinic anhydrides (PIBSA), phthalic acids, phthalic anhydride, naphthenic acids, naphthenic anhydrides, and the like. Particularly preferred is phthalic anhydride.

[0012] The hydrocarbyl substituted amines may be primary, secondary, or tertiary; preferably primary or secondary.

[0013] Exemplary hydrocarbyl substituted primary amines include, but are not limited to, coco amine, tallow amine, hydrogenated fatty primary amine, 2-ethylhexylamine, n-dodecyl amine, C12-14 or C16-22 tertiary alkyl primary amines from Rohm and Haas Company marketed under the trade name Primene®, mixtures thereof and the like. Particularly preferred is the C16-22 tertiary alkyl primary amine marketed by Rohm and Haas Company under the trade name Primene® JM-T.

[0014] Exemplary hydrocarbyl substituted secondary amines include, but are not limited to, dicocoalkylamine, didecylamine, dioctadecylamine, ditallowamine, dihydrogenated tallowalkylamine, mixtures thereof and the like. Particularly preferred is dihydrogenated tallowalkylamine which is commercially available from Akzo Nobel Corporation under the trade name Armeen® 2HT.

[0015] As would be understood by one skilled in the art in view of the present disclosure, it is intended that the aforementioned examples do not in any way limit the description of the nitrogen-containing compounds. Furthermore, it is to be understood that ester analogs derived from a hydrocarbyl alcohol, and hydrocarbyl sulfo acid analogs such as those derived from o-sulphobenzoic acid or its anhydride, are also within the purview of the present invention.

[0016] An especially preferred group of polar nitrogen-containing compounds are mixed amine salt/amides derived from reaction of hydrocarbyl acid (having two or more carboxyl groups) or its anhydrides as set forth above with a hydrocarbyl secondary amine. The resulting intermediate amide acid is then neutralized with a primary amine.

[0017] Generally, the preferred group of polar nitrogen containing compounds can be represented by the formula 1

[0018] wherein Z is a divalent organic radical, and R1, R2 and R3 are independently chosen from C10-C40 hydrocarbyl groups. The hydrocarbyl groups include straight or branched chain, saturated or unsaturated aliphatic, cycloaliphatic, aryl or alkylaryl moieties. These hydrocarbyl groups may contain other groups or atoms such as hydroxy groups, carbonyl groups, ester groups, oxygen, sulfur, or chlorine groups. As stated above, the hydrocarbyl groups may be on the order of C10-C40 with the range of C14-C24 even more preferred. The R1, R2, and R3 groupings can also represent mixtures of different hydrocarbyl groups. Preferably, R3≠R1 or R2.

[0019] The resulting compound should contain sufficient hydrocarbon content to be oil-soluble.

[0020] The preferred oil-soluble, polar nitrogen-containing compound is prepared by initial reaction of a hydrocarbyl acid or its anhydride and a secondary amine, such as the Armeen® 2HT. Then, the resulting mixed amine salt/amide is neutralized with a primary amine such as the commercially available Primene® JM-T product. Approximately equimolar amounts of the reactants are used, resulting in a mixed substituted amide/amine salt.

[0021] The most preferred polar nitrogen containing compound is an oil-soluble mixed amide/amine salt formed via reaction of equimolar amounts of phthalic anhydride with the secondary amine, Armeen® 2HT. The product of this reaction is then further reacted with an equimolar amount of the primary amine, Primene® JM-T to form benzoic acid, 2-[(bis(hydrogenated tallow alkyl)amino) carbonyl]-C16-C22 tert-alkyl amine salt having the structural formula: 2

[0022] wherein R1 and R2 are mixtures of C16 and C18 hydrocarbons from the commercially available tallowamine product, and R3 is a mixture of C18-22 hydrocarbons from the commercially available Primene® JM-T product.

[0023] The CFREAs of the present invention should be added to an aviation fuel, for which improved cold flow performance is desired, in an amount effective for the purpose. In the preferred embodiment of the invention, the aviation fuel is selected from Jet Fuel A, Jet Fuel A-1, Jet Fuel B, JP-4, JP-8, and JP-8+100. Most preferably the jet fuel is a JP-8 based fuel such as neat JP-8 or the formulated JP-8+100.

[0024] Jet Fuel A and Jet Fuel A-1 are kerosene-type fuels with Jet Fuel B being a “wide cut” fuel. Jet A is used for many domestic commercial flights in the U.S. Most preferably, the CFREAs of the invention are used to increase the cold flow characteristics of military jet fuels such as JP-5, JPTS, JP-7, JP-8, and JP-8+100. JP-5 is currently used by the U.S. Navy with JP-8 and JP-8+100 used by the Air Force.

[0025] These fuel types are described in the following Table 1. 1 TABLE 1 U.S. Military Jet Fuel Year Freeze Point Flash Fuel Introduced Type ° C. Max Point Comments JP-5 1952 kerosene −46 60 U.S. Navy obsolete JPTS 1956 kerosene −53 43 High thermal stability JP-7 1960 kerosene −43 60 Lower higher thermal stability JP-8 1979 kerosene −47 38 U.S. Air Force JP-8 + 100 1998 kerosene −47 38 U.S. Air Force contains additives for improved thermal stability JP = jet propulsion Source: Chevron “Aviation Fuels” Technical Review.

[0026] On a 100% actives basis, the CFREA is preferably added to the jet fuel in an amount of about 1-7,500 mg/L of the jet fuel. More preferably, the CFREA is added in an amount of between about 200-5,000 mg/L, most preferably about 4,000 mg/L. The jet fuel/CFREA blend is capable of improving the cold flow rate of jet fuel, specifically, JP-8 based jet fuel, at fuel temperatures on the order of about −53° C. and below. Experimental results have indicated that the CFREAs when blended with JP-8 based jet fuel in accordance with the invention improve cold flow rates of the fuel so that they are, as measured in accordance with Table 2 and the test system described, on the order of about 0.60 (g/s) and greater at fuel temperatures of about −53° C. and lower.

[0027] The CFREAs of the invention can be employed in combination with conventional fuel additives such as dispersants, antioxidants, and metal deactivators. Such additives are known to those skilled in the art, for example see U.S. Pat. Nos. 5,596,130 and 5,614,081.

[0028] The invention will be described further in conjunction with the following examples that are included for illustrative purposes only and should not be construed to limit the invention.

EXAMPLE 1

Preparation of Benzoic Acid, 2-[(bis(hydrogenated tallow alkyl)amino)carbonyl]-C16-C22 tert-alkyl Amine Salt

[0029] To a four-necked reaction flask equipped with a mechanical overhead stirrer, thermocouple, reflux condenser, nitrogen sparge tube, addition port with septum and a heating mantle was added phthalic anhydride (99%, 5.0 g, 0.03342 mole) and Armeen® 2HT (17.0 g, 0.03342 mole amine). The resulting wax mixture was then heated to 90° C. under nitrogen with mixing and held for four hours. Primene® JM-T (10.9 g, 0.03342 mole amine) was then added to the reactor at 90° C. over an eight-minute period, after which the batch was maintained at 90° C. for an additional four hours before cooling to room temperature to yield a wax like material. This was then diluted in Aromatic 100 to yield a 25 wt % solution of the nitrogen-containing compound.

EXAMPLE 2

Preparation of Benzoic Acid, 2-[(bis(hydrogenated tallow alkyl)amino)carbonyl]-C16-C22 tert-alkyl Amine Salt

[0030] This preparation was a scaleup of Example 1 (basis: phthalic anhydride, 99%, 344.74 g, 2.30 mole) except the hold times after the Armeen® 2HT and Primene® JM-T additions were decreased to one-hour each.

Cold Flow Additive Testing

[0031] JP-8 jet fuel was then treated with a known amount of additive solution and subjected to cold flow testing. Cold flow tests were conducted utilizing a Cold Additive Screening Test (CAST) and low temperature viscometer apparatus.

[0032] In general, the CAST apparatus consists of two 500 ml flasks, one at atmospheric pressure and one sealed, connected via a ¼″ Teflon tube. A known amount of fuel is charged to the flask at atmospheric pressure, and the apparatus is cooled to the desired test temperature in an environmental chamber. Once cooled to the desired temperature vacuum (2″ Hg) is applied to the sealed flask. The to the desired temperature vacuum (2″ Hg) is applied to the sealed flask. The effectiveness of an additive is determine by measuring the time it takes for the fuel to flow to the sealed flask, and the amount of fuel remaining in the atmospheric flask after the fuel flow ceases.

[0033] Screening results of the additives of the present invention in the CAST apparatus are provided in Table 2 below. At approximately −53° C. the untreated fuel has solidified and exhibited 100% holdup and essentially no fuel flow. Addition of the additives of the present invention to the fuel dramatically improved the cold flow properties at approximately −53° C. as evidenced by a substantial decrease in hold up and increase in fuel flow. 2 TABLE 2 CAST Testing Results Conc. Fuel Temp Holdup Flow Rate Additive 1 (mg/L)* (° C.) (%) (g/s) None N/A −53.5 100 N/A Example 1  8000 −52.7 10 1.34 Example 1 16000 −53.3 9 0.93 Example 2 12000 −57.8 25 0.47 Example 2 12000 −55.1 7 0.85 Example 2 14000 −57.0 13 0.83 Example 2 14000 −55.2 10 1.06 Example 2 16000 −57.1 8 0.82 Example 2 16000 −55.2 8 0.93

[0034] Low temperature viscosity studies of the treated fuel were carried out using a scanning Brookfield Viscometer in the temperature range of −5° C. to −60° C. as described by S. Zabarnick and M. Vangsness, Petroleum Chemistry Preprints 2002, 47(3), pp. 243-246 (2002). The results of this testing are given in Table 2. The knee temperature is defined as the temperature at which a rapid viscosity increase occurs due to crystal formation. It is desirable to have the “knee temperature” for a treated fuel to be shifted to a lower temperature relative to the neat fuel. It is also highly desirable to minimize the rate of viscosity increase as the fuel is cooled below the knee temperature.

[0035] Table 3 summarizes the results for the low temperature viscosity studies. The letter designation corresponds to the viscosity curve for that treatment in the companion graph presented in FIG. 1. It can be seen from the data presented that the additives of the present invention lower the knee temperature of the fuel. Additionally, as shown in FIG. 1, addition of the additives of the invention significantly reduces the rate of viscosity increase. The effect is pronounced to the extent that at higher additive levels there was no obvious knee temperature (curve “C” of FIG. 1). 3 TABLE 3 Low TemperatureViscosity Results-Knee Temperature in JP-8 Fuel Conc. Ledtter Additive 1 (mg/L)* Knee Temp (° C.) A None N/A −52.0 B Example 2 12000 −55.2 C Example 2 16000 None Observed

[0036] While the specification above has been drafted to include the best mode of practicing the invention as required by the patent statutes, the invention is not to be limited to that best mode or to other specific embodiments set forth in the specification. The breadth of the invention is to be measured only by the literal and equivalents constructions applied to the appended claims.

Claims

1. Method of improving the cold flow rate of jet fuel comprising adding to said jet fuel an effective amount of the purpose of a cold flow rate enhancement agent (CFREA) comprising an oil-soluble, polar, nitrogen-containing compound.

2. Method as recited in claim 1 comprising adding from a 1-7,500 mg of said CFREA to said jet fuel, based upon 1 liter of said jet fuel.

3. Method as recited in claim 1 wherein said jet fuel is a JP-8 based jet fuel.

4. Method as recited in claim 1 wherein said oil-soluble, polar nitrogen compound comprises an amine salt or amide.

5. Method as recited in claim 4, wherein said oil-soluble, polar nitrogen compound comprises a reaction product formed from reaction of a hydrocarbyl acid having two or more carboxyl groups or anhydride thereof, and a hydrocarbyl secondary amine followed by neutralization of the resulting product with a hydrocarbyl primary amine.

6. Method as recited in claim 1 wherein said oil-soluble, polar nitrogen compound is benzoic acid, 2-[(bis(hydrogenated tallow alkyl)amino)carbonyl]-C16-C22 tert-alkyl amine salt.

7. Method as recited in claim 2 wherein said oil-soluble, polar nitrogen-containing compound is represented by the formula

3

wherein Z is a divalent organic radical, and R1, R2, and R3 are independently chosen from C10-C40 hydrocarbyl groups.

8. Method as recited in claim 2 wherein said oil-soluble, polar, nitrogen-containing compound is formed from a reaction of a hydrocarbyl acid having from about 1 to about 4 carboxyl groups or anhydrides thereof with a hydrocarbyl substituted primary, secondary, or tertiary amine.

9. Method as recited in claim 8 wherein said hydrocarbyl acid or anhydride and hydrocarbyl substituted primary, secondary, and tertiary amines each have from about 4 to about 24 carbon atoms.

10. Method as recited in claim 9 wherein said hydrocarbyl acid or anhydride and hydrocarbyl substituted primary, secondary, and tertiary amines each have from about 10-24 carbon atoms.