Aviation gasolines containing mesitylene and isopentane

Abstract

Describe are preferred formulations for Avgas meeting the requirements for use in aircraft, including requirements established under ASTM standards and by the Federal Aviation Administration. In one embodiment, a binary mixture of 1,3,5-trimethyl benzene (mesitylene) and isopentane is used to provide a MON of at least 100, and more preferably at least 102. In other embodiments, the amounts of mesitylene and/or isopentane may be changed, and other fuel components are included. These various Avgas formulations are thereby adjusted to meet a variety of requirements as to octane rating, RVP, cold start, and other fuel characteristics.

Claims

1. A motor fuel having a MON of at least 100 and an RVP of 38-49 kPa at 38° C. comprising 70-80 wt % mesitylene, isopentane in an amount up to 20 wt %, and isooctane in an amount up to 15 wt %.

2. The motor fuel of claim 1 in which the isooctane is provided as a component of aviation alkylate.

3. The motor fuel of claim 1 and further comprising butane in an amount up to 2 wt %.

4. The motor fuel of claim 1 comprising 75-80 wt % mesitylene, 15-20 wt % isopentane, and alkylate in an amount up to 10 wt %, the alkylate comprising isooctane.

5. The motor fuel of claim 1 comprising 10-20 wt % isopentane, alkylate in an amount up to 10 wt %, and butane in an amount up to 2 wt %.

6. A motor fuel having a MON of at least 100 and an RVP of 38-49 kPa at 38° C. comprising 56-88 wt % mesitylene, 10-20 wt % isopentane, isooctane in an amount up to 15 wt %, butane in an amount up to 2 wt %, and alkylate.

7. A motor fuel having a MON of at least 100 and an RVP of 38-49 kPa at 38° C. comprising 70-88 wt % mesitylene, 10-20 wt % isopentane, isooctane in an amount up to 25 wt %, butane in an amount up to 2 wt %, and alkylate in an amount up to 10 wt %.

8. A motor fuel having a MON of at least 100 and an RVP of 38-49 kPa at 38° C. comprising about 10.0 wt % mesitylene, 15.0 wt % isopentane, 61.3 wt % isooctane, and 13.7 wt % alkylate.

9. The motor fuel of claim 1 comprising 2 wt % butane.

10. The motor fuel of claim 5 comprising 10 wt % isopentane, alkylate in an amount of up to 10 wt. %, and 2 wt % butane.

11. The motor fuel of claim 6 comprising 56-88 wt. % mesitylene, isooctane in an amount of up to 15 wt. %, 10 wt % isopentane and 2 wt % butane.

12. The motor fuel of claim 7 comprising 70-88 wt. % mesitylene, isooctane in an amount of up to 25 wt. %, alkylate in an amount of up to 10 wt. %, 10 wt % isopentane and 2 wt % butane.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a graph showing the distillation curve with the temperature plotted against the volume. The horizontal bars on the graph correlate to the ASTM specification number D7547 and the permissible limits of that specification.

(2) FIG. 2 is a graph showing the MON of various compositions graphed against the percentage of mesitylene present in the composition.

DETAILED DESCRIPTION OF THE INVENTION

(3) For the purposes of promoting an understanding of the principles of the invention, reference will now be made to certain embodiments and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications, and such further applications of the principles of the invention as described herein, being contemplated as would normally occur to one skilled in the art to which the invention relates.

(4) The fuel formulations of the present invention are characterized herein in several respects. The included components are identified and ranges of those components are indicated. In making these indications of ranges, it is intended that the specific amounts of each component used in a particular formulation are selected based on certain additional criteria as already discussed. It is within the ordinary skill in the art, given the teachings herein, to determine whether particular formulations satisfy the criteria as set forth in the claims.

(5) The inventive fuels are formulated to qualify as motor fuels, and particularly aviation gasoline, and they therefore satisfy criteria established for such. Thus, a starting point is that the amounts of the various fuel components are selected to provide a minimum MON as established for the applicable use in aviation gasoline. At present, the minimum MON is considered to be 100, although a MON of at least 102 is preferred herein. Similarly, a second important criteria is that the volatility of the fuel satisfy established requirements for aviation gasoline. The Reid vapor pressure (RVP) of the inventive formulations is within the range of 38-49 kilopascals (kPa), as determined in accordance with applicable ASTM standards.

(6) In one embodiment, the present invention comprises 79-85 wt % mesitylene and 15-21 wt % isopentane. This fuel formulation is further characterized by having a MON of at least 100, more preferably at least 102, and an RVP of 38-49 kPa, equivalent to 5.5-7.1 psi. It has been found that the presence of mesitylene supports the high MON of the formulation, while the isopentane contributes to the desired RVP.

(7) To exemplify one aspect of the present invention, tests have been carried out according to ASTM D5191 to determine the Reid vapor pressure as a function of concentration (wt %) of mesitylene for a binary mixture of mesitylene and isopentane. The Reid vapor pressure requirement of 100 LL octane aviation fuel is between 5.5 and 7.1 psi. Mesitylene concentrations of about 70-85 wt % in combination with isopentane were found to meet the Reid vapor pressure requirement for 100 LL octane aviation fuel. By comparison, neither pure mesitylene nor pure isopentane meet this specification.

(8) Further tests were conducted according to six ASTM standards to determine various characteristics of pure mesitylene, pure isopentane, Swift 702 pure fuel according to the present invention (comprised of 83 wt % mesitylene and 17 wt % isopentane) and conventional 100 LL aviation fuel. The results of these comparative tests are illustrated below:

(9) TABLE-US-00001 ASTM Swift 100 LL Method Test Mesitylene Isopentane 702 spec D2700 Motor Octane 136 90.3 104.9 ≥99.6 Number D909 Supercharge ON 170 92.3 133.0 130.0 D5191 Vapor Pressure ≤5.5 ≥7.1 5.7 5.5 to 7.1 D2386 Freezing Pt −49 −161 −63 ≤58 D86 10% Distillation 165 28 65 ≤75 Pt. D86 End Distillation 165 28 165 ≤170 Pt.

(10) It has unexpectedly been discovered from these tests that adding isopentane to mesitylene in certain concentrations as called for herein increases the vapor pressure, lowers the freezing point, and lowers the 10% distillation point of the fuel to within the ASTM standard. It was also unexpectedly discovered that adding mesitylene to isopentane to form a 100 octane aviation fuel, as compared to pure isopentane, raises the motor octane number, raises the supercharge octane number, and lowers the vapor pressure to within the ASTM D910 specification.

(11) Variations of the inventive formulations involve the inclusion of one or more fuel components, generally with a modification of the amounts of mesitylene and/or isopentane. In each instance, the components are included in amounts, again, to meet the criteria of the final formulation as having a MON of at least 100, more preferably at least 102, and an RVP of 38-49 kPa. These formulations are further described hereafter.

(12) Certain alkanes are particularly useful for adjusting the MON or RVP of the formulations and to meet cold start requirements. The inclusion of isooctane and/or butane provides the following formulations in accordance with the present invention:

(13) TABLE-US-00002 Mesitylene Isopentane Isooctane Butane 1 70-80 wt % 15-20 wt % 0-15 wt % — 1 70-88 wt % 10-20 wt % 0-15 wt % 0-2 wt %

(14) In refining, the alkylation process transforms low molecular-weight alkenes and iso-paraffin molecules into larger iso-paraffins with a high octane number. The product is referred to as an “alkylate”, and includes a mixture of high-octane, branched-chain paraffinic hydrocarbons. This “alkylate” product may contain many hydrocarbon compounds typically in the C4 to C12 range, but particularity isooctane. “Aviation alkylate” is a premium gasoline blending stock because it has exceptional anti-knock properties and is clean burning with a final boiling point appropriate for aviation use. The octane number of the aviation alkylate depends mainly upon the kind of alkenes used and upon refinery operating conditions. For example, isooctane results from combining butylene with isobutane and has an octane rating of 100 by definition. There are other products in the alkylate, so the octane rating will vary accordingly.

(15) This alkylate product from the refineries is also useful in the formulations to address the problem of cold starts. Formulations of the present invention meeting the MON and RVP criteria include the following:

(16) TABLE-US-00003 Mesitylene Isopentane Alkylate Butane 2 75-80 wt % 15-20 wt % 0-10 wt % — 2A 70-88 wt % 10-20 wt % 0-10 wt % 0-2 wt %

(17) Whether from the alkylate product of the refineries, or in more isolated form, the inclusion in the inventive fuel formulations of high volatility/low boiling point components (including the isopentane) contributes to achieving the desired RVP range, while also allowing the engines to start in cold temperature situations (cold weather or high altitude).

(18) With the addition of C7 to C9 methyl aromatics other than the mesitylene (e.g. toluene and/or any mixture of xylenes including ortho-, meta- or para-xylene), further fuel formulations are available in accordance with the present invention, as follows:

(19) TABLE-US-00004 Mesitylene Isopentane Toluene Xylenes Butane Isooctane Alkylate 4B 44-88 wt % 10-20 wt % 0-44 wt % — 0-2 wt % 4C 36-88 wt % 10-20 wt % 0-44 wt % 0-35 wt % 0-2 wt % 3C 68-88 wt % 10-20 wt % 0-24 wt % 0-2 wt % 0-15 wt % 0-5 wt % 3D 56-88 wt % 10-20 wt % 0-24 wt % 0-30 wt % 0-2 wt % 0-15 wt % 0-5 wt %

(20) Certain organometallic additives, when included in the formulations shown below, have been found to positively affect other fuel characteristics and provide the resulting MON and RVP that meet the foregoing criteria. For example, iron pentacarbonyl and/or ferrocene may be added in low amounts, e.g., 0 up to 2,000 ppm, to these listed formulations and others resulting in an unexpected increase in the MON. For example, lab results indicate that about 500 ppm of iron pentacarbonyl unexpectedly boosts octane for the base fuel up to 2.5 MON.

(21) TABLE-US-00005 Mesitylene Isopentane Isooctane Butane Alkylate Toluene Xylenes 3 70-80 wt % 15-20 wt % 0-15 wt % — 3A 70-88 wt % 10-20 wt % 0-15 wt % 0-2 wt % 3B 70-88 wt % 10-20 wt % 0-25 wt % 0-2 wt % 0-10 wt % 2 75-80 wt % 15-20 wt % 0-10 wt % 4B 44-48 wt % 10-20 wt % 0-2 wt % 0-44 wt % 3C 68-88 wt % 10-20 wt % 0-15 wt % 0-2 wt %  0-5 wt % 0-24 wt % 3D 56-88 wt % 10-20 wt % 0-15 wt % 0-2 wt %  0-5 wt % 0-24 wt % 0-30 wt % 4C 36-88 wt % 10-20 wt % — 0-2 wt % — 0-44 wt % 0-35 wt %

(22) It will be appreciated by those skilled in the art that the described formulations can be adjusted to meet various MON ratings and RVP based on the teachings herein. Requirements for aviation gasoline are established by the FAA and other sanctioning bodies in the US and throughout the world. The present invention notes that the basic combination of mesitylene and isopentane provides a fuel formulation which can be adjusted to meet various MON and RVP requirements. Various other characteristics of the Avgas may thereby also be accommodated, such as cold starting and reduced carbon smoke. The fuel formulations may also be optimized in regard to the availability and cost of the various components which may be included, while still meeting the criteria for aviation gasoline.

(23) Accordingly, for purposes herein applicant refers to an “established” criteria or requirement as one that is determined at any point in time to apply to the characteristics of an aviation gasoline in a given country. For example, the “established” minimum MON rating for aviation gasoline based upon ASTM D910 is currently 99.6 for 100 LL fuel. However, it is recognized that a newly “established” minimum MON rating for unleaded aviation gasoline in the future may differ, e.g., be set at a MON of 102. The present invention is therefore directed also to meeting such changed or new criteria, particularly as to the required MON or RVP for the Avgas.

(24) Throughout this disclosure various components for the inventive fuel formulations have been identified. It will be appreciated that it is not necessary for these components to be in a pure form. It is only necessary that the formulations not include a deleterious amount of other components, particularly so as to cause the MON or RVP to fall outside the stated ranges. At the same time, the present invention may use materials which satisfy these conditions and are less expensive and/or more readily available than more pure grades of components. By way of example, mesitylene may be obtained as a mixture with minor amounts of pseudocumene, and such product may be usefully employed in accordance with the present invention.

(25) The inventive fuels may “comprise” the described formulations, in which case other components may be included. However, in a preferred embodiment, the inventive fuels “consist of” the described formulations, in which no other components are present. In addition, the inventive fuels may “consist essentially of” the formulations, in which case other fuel excipients, and/or non-deleterious components, may be present. As used herein, the term “fuel excipients” refers to materials which afford improved performance when using the fuels, but which do not significantly impact the basic characteristics of the formulation—e.g., the MON and RVP. Fuel excipients thus may include, for example, antioxidants, etc.

(26) The formulations are also useful for combining with other fuel components to form blends that are useful as motor fuels, including as aviation gasoline. As used herein, the term “fuel additives” refers to materials which are themselves combustible and have varying motor octane ratings and are included primarily to provide improved combustion characteristics of the blend. In preferred embodiments, such fuel additives are present in the blend at less than 5 wt %, and more preferably less than 1 wt %.

Example 1 TA-55

(27) The fuel components of Table 1 were combined according to methods well known in the art to prepare 94 MON motor fuel and this composition was labeled TA-55.

(28) TABLE-US-00006 TABLE 1 Composition of TA-55. Fuel Components: Mass [g] Mass [%] Isopentane 6,300 15.00% Alkylates TA37 5,754 13.70% Isooctane TA44 25,746 61.30% Mesitylene 4,200 10.00%

(29) The fuel composition of TA-55 was analyzed to determine the motor octane number (MON) of the composition and the MON was found to be 94.3 and the research octane number (RON) was found to be 100. The fuel composition of TA-55 was distilled and a distillation curve was prepared with the temperature plotted against volume. The horizontal bars on the graph correlate to the ASTM specification number D7547 and the permissible limits (max or min) of that specification as shown in FIG. 1.

Example 2 TA-71

(30) In one embodiment of the present invention, the fuel components of Table 2 were combined according to methods well known in the art to prepare an aviation fuel and was labeled TA-71.

(31) TABLE-US-00007 TABLE 2 Composition of TA-71 Fuel Components: Mass [g] Mass [%] Butane 5.5 1.00% Isopentane 71.5 13.00% Toluene 165 30.00% Mesitylene 308 56.00%

(32) The fuel composition of TA-71 was analyzed to determine the motor octane number (MON) of the composition and was found to be 102.0.

Example 3 TA-73

(33) In one embodiment, the fuel components of Table 3 were combined according to methods well known in the art to prepare an aviation fuel and the composition was labeled TA-73.

(34) TABLE-US-00008 TABLE 3 Composition of TA-73 Fuel Components: Mass [g] Mass [%] Butane 5.5  1.0% Isopentane 71.5 13.0% Toluene 165 30.0% Mesitylene 308 56.0% Iron pentacarbonyl 0.275 0.05%

(35) The fuel composition of TA-73 was analyzed to determine the motor octane number (MON) of the composition and the MON was found to be 102.8.

Example 4 TA-74

(36) In one embodiment, the fuel components of Table 4 were combined according to methods well known in the art to prepare an aviation fuel and the composition was labeled TA-74.

(37) TABLE-US-00009 TABLE 4 Composition of TA-74 Fuel Components: Mass [%] Mass [g] Isopentane 15.00% 135 Alkylates TA37 13.70% 123.3 Isooctane TA44 61.30% 551.7 Mesitylene 10.00% 90 Iron pentacarbonyl 0.05% 0.450

(38) The fuel composition of TA-74 was analyzed to determine the motor octane number (MON) of the composition and the MON was found to be 96.5. This case demonstrates an unexpected increase in MON of 2.2 vs Example 1 (TA-55).

Example 5. TA-68

(39) In one embodiment, the fuel components of Table 5 were combined to prepare an aviation fuel and the composition was labeled TA-68.

(40) TABLE-US-00010 TABLE 5 Composition of TA-68 Fuel Components: Mass [%] Mass [g] Isopentane 10.00% 55 Butane 2.00% 11 Toluene 13.00% 71.5 Mesitylene 75.00% 412.5

(41) The fuel composition of TA-68 had a MON of 105. The fuel composition of TA-68 was distilled and a distillation curve was prepared with the temperature plotted against volume. The fuel composition was found to meet the distillation requirements of ASTM specification number D7719.

Example 6. TA-80

(42) In one embodiment, the fuel components of Table 6 were combined to prepare an aviation fuel and the composition was labeled TA-80.

(43) TABLE-US-00011 TABLE 6 Composition of TA-80 Fuel Components: Mass [%] Mass [g] Isopentane 18.00% 126 Isooctane 27.00% 189 Toluene 10.00% 70 m-Xylene 10.00% 70 Mesitylene 30.00% 210 m-Toluidiene 5.00% 35

(44) The fuel composition of TA-80 had a MON of 102.1. The fuel composition of TA-80 was distilled and a distillation curve was prepared with the temperature plotted against volume. The fuel composition was found to meet the distillation requirements of ASTM specification number D7719.

Example 7. TA-81

(45) In one embodiment, the fuel components of Table 7 were combined to prepare an aviation fuel and the composition was labeled TA-81.

(46) TABLE-US-00012 TABLE 7 Composition of TA-81 Fuel Components: Mass [%] Mass [g] Isopentane 13.00% 91 Butane 2.00% 14 Isooctane 15.00% 105 ETBE 15.00% 105 Toluene 10.00% 70 m-Xylene 10.00% 70 Mesitylene 30.00% 210 Aniline 5.00% 35

(47) The fuel composition of TA-81 had a MON of 102.3. The fuel composition of TA-81 was distilled and a distillation curve was prepared with the temperature plotted against volume. The fuel composition was found to meet the distillation requirements of ASTM specification number D7719.

Example 8. TA-82

(48) In one embodiment, the fuel components of Table 8 were combined to prepare an aviation fuel and the composition was labeled TA-82.

(49) TABLE-US-00013 TABLE 8 Composition of TA-82 Fuel Components: Mass [%] Mass [g] Isopentane 10.00% 70 Butane 2.00% 14 Isooctane 18.00% 126 ETBE 15.00% 105 Toluene 10.00% 70 m-Xylene 10.00% 70 Mesitylene 35.00% 245

(50) The fuel composition of TA-81 had a MON of 102.2. The fuel composition of TA-82 was distilled and a distillation curve was prepared with the temperature plotted against volume. The fuel composition was found to meet the distillation requirements of ASTM specification number D7719.

Example 9

(51) In an effort to better understand how additional components of aviation fuel affect the MON of a fuel composition comprising mesitylene, the MON of various compositions was graphed against the percentage of mesitylene present in the composition, and is shown in FIG. 2.

(52) It is a further purpose and advantage of the present invention to provide Avgas formulations which have preferred components for other reasons. For example, the present formulations may be accurately referred to as comprising high aromatics and being hydrocarbon based. While other components may be included, preferred formulations are substantially free, or even completely free, of such other materials as sulfur components and aromatic amines.

(53) Further, it has been common in the prior art to include TEL (tetraethyl lead) in motor fuels to provide anti-knock properties. Such fuels have generally been referred to as low lead or “LL”. It is another feature of the present invention that the formulations and blends do not require the use of TEL, a known carcinogen. Therefore, in a preferred embodiment the inventive formulations and blends are unleaded, i.e., free of TEL. This is made possible, at least in part, by the presence of the 1,3,5-trimethylbenzene, which provides sufficiently high MON performance and anti-knocking characteristics under stress to offset the absence of TEL in the aviation gasoline.

(54) All component percentages expressed herein refer to percentages by weight of the formulation, unless indicated otherwise. The term “substantially free” of a component refers to the fact that less than 5 wt % of that component is present, and preferably less than 1 wt % is present.

(55) The uses of the terms “a” and “an” and “the” and similar references in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein.

(56) Any methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.

(57) While the invention has been illustrated and described in the foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only certain preferred embodiments have been described and that all changes and modifications that come within the spirit of the invention are desired to be protected. In addition, all references cited herein are indicative of the level of skill in the art and are hereby incorporated by reference in their entirety.