Patent Application
20130074874
The disclosure is directed to certain diesel fuel additives and to diesel fuels and diesel fuel additive concentrates that include the additive. In particular the disclosure is directed to a diesel fuel additive that is effective to enhance the performance of fuel injectors for diesel engines, particularly for low sulfur and ultra low sulfur diesel fuels.
It has long been desired to maximize fuel economy, power and driveability in diesel fuel powered vehicles while enhancing acceleration, reducing emissions, and preventing hesitation. While it is known to enhance gasoline powered engine performance by employing dispersants to keep valves and fuel injectors clean, such gasoline dispersants are not necessarily effective in diesel fuel applications. The reasons for this unpredictability lie in the many differences between how diesel engines and gasoline engines operate and the chemical differences between diesel fuel and gasoline.
Furthermore, low sulfur diesel fuels, ultra low sulfur diesel fuels and high pressure common rail (HPCR) engines are now common in the marketplace. A “low sulfur” diesel fuel means a fuel having a sulfur content of 50 ppm by weight or less based on a total weight of the fuel. An “ultra low sulfur” diesel fuel (ULSD) means a fuel having a sulfur content of 15 ppm by weight or less based on a total weight of the fuel. Fuel injectors in an HPCR engine perform at much higher pressures and temperatures compared to older style engines and fuel injection systems. The combination of low sulfur or ULSD and HPCR engines have resulted in a change to the type of injector deposits and frequency of formation of injector deposits now being found in the marketplace.
Over the years, dispersant compositions for diesel fuel have been developed. Dispersant compositions known in the art for use in diesel fuel include compositions that may include polyalkylene succinimides, which are the reaction products of polyalkylene succinic anhydrides and amines. Dispersants are suitable for keeping soot and sludge suspended in a fluid, however dispersants are not particularly effective for cleaning surfaces once deposits have formed on the surfaces. Hence, diesel fuel compositions containing low sulfur diesel fuels or ULSD used in new engine technologies often still produce undesirable deposits in diesel engine injectors. Accordingly, improved compositions that can prevent deposit build up, maintaining “as new” cleanliness for the vehicle life are desired. Ideally, the same composition that can clean up dirty fuel injectors restoring performance to the previous “as new” condition would be equally desirable and valuable in the attempt to reduce air borne exhaust emissions.
In accordance with the disclosure, exemplary embodiments provide a diesel fuel, a diesel fuel additive concentrate and a method for improving the performance of fuel injectors for a diesel engine are provided. The diesel fuel includes a major amount of middle distillate fuel having a sulfur content of 50 ppm by weight or less; and a reaction product of (a) a hydrocarbyl substituted dicarboxylic acid or anhydride, and (b) an amine compound or salt thereof of the formula
wherein R is selected from a hydrogen and a hydrocarbyl group containing from about 1 to about 15 carbon atoms, and R1 is selected from hydrogen and a hydrocarbyl group containing from about 1 to about 20 carbon atoms, wherein the reaction product contains less than one equivalent of an amino triazole group per molecule of reaction product, and wherein the reaction product is present in an amount sufficient to improve the performance of diesel direct and/or indirect fuel injectors.
Another embodiment of the disclosure provides a method of improving the injector performance of a fuel injected diesel engine. The method includes operating the diesel engine on a fuel composition that includes a major amount of diesel fuel having a sulfur content of 50 ppm by weight or less and a minor amount of a reaction product derived from (a) a hydrocarbyl carbonyl compound of the formula
wherein R2 is a hydrocarbyl group having a number average molecular weight ranging from about 200 to about 3000 and (b) an amine compound or salt thereof of the formula
wherein R is selected from hydrogen and a hydrocarbyl group containing from about 1 to about 15 carbon atoms, and R1 is selected hydrogen and a hydrocarbyl group containing from about 1 to about 20 carbon atoms. The reaction product is characterized by an FTIR spectrum having a peak intensity in a region of from about 1630 cm1 to about 1645 cm−1 that ranges from about 5 to about 45% of peak intensities of other peaks in a region of from about 1500 cm−1 to about 1800 cm−1.
A further embodiment of the disclosure provides a method of cleaning fuel injectors of a fuel injected diesel engine. The method includes operating the diesel engine on a fuel composition including a major amount of diesel fuel having a sulfur content of 50 ppm by weight or less and a minor amount of a reaction product derived from (a) a hydrocarbyl carbonyl
wherein R2 is a hydrocarbyl group having a number average molecular weight ranging from about 200 to about 3000 and (b) an amine compound or salt thereof of the formula
wherein R is selected from hydrogen and a hydrocarbyl group containing from about 1 to about 15 carbon atoms, and R1 is selected from hydrogen and a hydrocarbyl group containing from about 1 to about 20 carbon atoms. The reaction product contains less than one equivalent of an amino triazole group per molecule of reaction product.
An advantage of the fuel additive described herein is that the additive may not only reduce the amount of deposits forming on direct and/or indirect diesel fuel injectors, but the additive may also be effective to clean up dirty fuel injectors.
Additional embodiments and advantages of the disclosure will be set forth in part in the detailed description which follows, and/or can be learned by practice of the disclosure. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the disclosure, as claimed.
The compositions of the present application may be used in a minor amount in a major amount of diesel fuel and may be made by reacting an amine compound or salt thereof of
wherein R is selected from the group consisting of hydrogen and a hydrocarbyl group containing from about 1 to about 15 carbon atoms, and R1 is selected from the group consisting of hydrogen and a hydrocarbyl group containing from about 1 to about 20 carbon atoms with a hydrocarbyl carbonyl compound of the formula
wherein R2 is a hydrocarbyl group having a number average molecular weight ranging from about 200 to about 3000 wherein the reaction product contains less than one equivalent of amino triazole group per molecule of reaction product. The reaction product is characterized by an FTIR spectrum having a peak intensity in a region of from about 1630 cm−1 to about 1645 cm−1 that ranges from about 5 to about 45% of peak intensities of other peak in a region of from about 1500 cm−1 to about 1800 cm−1.
For comparison purposes,
As used herein, the term “hydrocarbyl group” or “hydrocarbyl” is used in its ordinary sense, which is well-known to those skilled in the art. Specifically, it refers to a group having a carbon atom directly attached to the remainder of a molecule and having a predominantly hydrocarbon character. Examples of hydrocarbyl groups include:
As used herein, the term “major amount” is understood to mean an amount greater than or equal to 50 wt. %, for example from about 80 to about 98 wt. % relative to the total weight of the composition. Moreover, as used herein, the term “minor amount” is understood to mean an amount less than 50 wt. % relative to the total weight of the composition.
Suitable amine compounds of the formula
may be chosen from guanidines and aminoguanidines or salts thereof wherein R and R1 are as defined above. Accordingly, the amine compound may be chosen from the inorganic salts of guanidines, such as the halide, carbonate, nitrate, phosphate, and orthophosphate salts of guanidines. The term “guanidines” refers to guanidine and guanidine derivatives, such as aminoguanidine. In one embodiment, the guanidine compound for the preparation of the additive is aminoguanidine bicarbonate. Aminoguanidine bicarbonates are readily obtainable from commercial sources, or can be prepared in a well-known manner.
The hydrocarbyl carbonyl reactant compound of the additive may be any suitable compound having a hydrocarbyl moiety and a carbonyl moiety, and that is capable of bonding with the amine compound to form the additives of the disclosure. Non-limiting examples of suitable hydrocarbyl carbonyl compounds include, but are not limited to, hydrocarbyl substituted succinic anhydrides, hydrocarbyl substituted succinic acids, and esters of hydrocarbyl substituted succinic acids.
In some aspects, the hydrocarbyl carbonyl compound can be a polyalkylene succinic anhydride reactant having the following formula:
wherein R2 is a hydrocarbyl moiety, such as for example, a polyalkenyl radical having a number average molecular weight of from about 100 to about 5,000. For example, the number average molecular weight of R2 may range from about 200 to about 3,000, as measured by GPC. Unless indicated otherwise, molecular weights in the present specification are number average molecular weights.
The R2 hydrocarbyl moiety may comprise one or more polymer units chosen from linear or branched alkenyl units. In some aspects, the alkenyl units may have from about 2 to about 10 carbon atoms. For example, the polyalkenyl radical may comprise one or more linear or branched polymer units chosen from ethylene radicals, propylene radicals, butylene radicals, pentene radicals, hexene radicals, octene radicals and decene radicals. In some aspects, the R2 polyalkenyl radical may be in the form of, for example, a homopolymer, copolymer or terpolymer. In one aspect, the polyalkenyl radical is isobutylene. For example, the polyalkenyl radical may be a homopolymer of polyisobutylene comprising from about 10 to about 60 isobutylene groups, such as from about 20 to about 30 isobutylene groups. The polyalkenyl compounds used to form the R2 polyalkenyl radicals may be formed by any suitable methods, such as by conventional catalytic oligomerization of alkenes.
In an additional aspect, the hydrocarbyl moiety R2 may be derived from a linear alpha olefin or an acid-isomerized alpha olefin made by the oligomerization of ethylene by methods well known in the art. These hydrocarbyl moieties can range from about 8 carbon atoms to over 40 carbon atoms. For example, alkenyl moieties of this type may be derived from a linear C18 or a mixture of C20-24 alpha olefins or from acid-isomerized C16 alpha olefins.
In some aspects, high reactivity polyisobutenes having relatively high proportions of polymer molecules with a terminal vinylidene group may be used to form the R2 group. In one example, at least about 60%, such as about 70% to about 90%, of the polyisobutenes comprise terminal olefinic double bonds. There is a general trend in the industry to convert to high reactivity polyisobutenes, and well known high reactivity polyisobutenes are disclosed, for example, in U.S. Pat. No. 4,152,499, the disclosure of which is herein incorporated by reference in its entirety.
Specific examples of hydrocarbyl carbonyl compounds include such compounds as dodecenylsuccinic anhydrides, C16-18 alkenyl succinic anhydride, and polyisobutenyl succinic anhydride (PIBSA). In some embodiments, the PIBSA may have a polyisobutylene portion with a vinylidene content ranging from about 4% to greater than about 90%. In some embodiments, the molar ratio of the number of carbonyl groups to the number of hydrocarbyl moieties in the hydrocarbyl carbonyl compound may range from about 0.5:1 to about 5:1.
In some aspects, approximately one mole of maleic anhydride may be reacted per mole of polyalkylene, such that the resulting polyalkenyl succinic anhydride has about 0.8 to about 1 succinic anhydride group per polyalkylene substituent. In other aspects, the molar ratio of succinic anhydride groups to alkylene groups may range from about 0.5 to about 3.5, such as from about 1 to about 1.1.
The hydrocarbyl carbonyl compounds may be made using any suitable method. Methods for forming hydrocarbyl carbonyl compounds are well known in the art. One example of a known method for forming a hydrocarbyl carbonyl compound comprises blending a polyolefin and maleic anhydride. The polyolefin and maleic anhydride reactants are heated to temperatures of, for example, about 150° C. to about 250° C., optionally, with the use of a catalyst, such as chlorine or peroxide. Another exemplary method of making the polyalkylene succinic anhydrides is described in U.S. Pat. No. 4,234,435, which is incorporated herein by reference in its entirety.
The hydrocarbyl carbonyl and amine compounds described above may be mixed together under suitable conditions to provide the desired reaction product of the present disclosure. In one aspect of the present disclosure, the reactant compounds may be mixed together in a mole ratio of hydrocarbyl carbonyl compound to amine ranging from about 1:0.5 to about 1:1.5. For example, the mole ratio of the reactants may range from about 1:0.5 to about 1:0.95.
Suitable reaction temperatures may range from about 130° C. to less than about 200° C. at atmospheric pressure. For example, reaction temperatures may range from about 140° C. to about 160° C. Any suitable reaction pressures may be used, such as, including subatmospheric pressures or superatmospheric pressures. However, the range of temperatures may be different from those listed where the reaction is carried out at other than atmospheric pressure. The reaction may be carried out for a period of time within the range of about 1 hour to about 8 hours, preferably, within the range of about 2 hours to about 6 hours.
In some aspects of the present application, the dispersant products of this application may be used in combination with a diesel fuel soluble carrier. Such carriers may be of various types, such as liquids or solids, e.g., waxes. Examples of liquid carriers include, but are not limited to, mineral oil and oxygenates, such as liquid polyalkoxylated ethers (also known as polyalkylene glycols or polyalkylene ethers), liquid polyalkoxylated phenols, liquid polyalkoxylated esters, liquid polyalkoxylated amines, and mixtures thereof. Examples of the oxygenate carriers may be found in U.S. Pat. No. 5,752,989, issued May 19, 1998 to Henly et. al., the description of which carriers is herein incorporated by reference in its entirety. Additional examples of oxygenate carriers include alkyl-substituted aryl polyalkoxylates described in U.S. Patent Publication No. 2003/0131527, published Jul. 17, 2003 to Colucci et. al., the description of which is herein incorporated by reference in its entirety.
In other aspects, compositions of the present application may not contain a carrier. For example, some compositions of the present application may not contain mineral oil or oxygenates, such as those oxygenates described above.
One or more additional optional compounds may be present in the fuel compositions of the disclosed embodiments. For example, the fuels may contain conventional quantities of cetane improvers, corrosion inhibitors, cold flow improvers (CFPP additive), pour point depressants, solvents, demulsifiers, lubricity additives, friction modifiers, amine stabilizers, combustion improvers, dispersants, antioxidants, heat stabilizers, conductivity improvers, metal deactivators, marker dyes, organic nitrate ignition accelerators, cyclomatic manganese tricarbonyl compounds, and the like. In some aspects, the compositions described herein may contain about 10 weight percent or less, or in other aspects, about 5 weight percent or less, based on the total weight of the additive concentrate, of one or more of the above additives. Similarly, the fuels may contain suitable amounts of conventional fuel blending components such as methanol, ethanol, dialkyl ethers, and the like.
In some aspects of the disclosed embodiments, organic nitrate ignition accelerators that include aliphatic or cycloaliphatic nitrates in which the aliphatic or cycloaliphatic group is saturated, and that contain up to about 12 carbons may be used. Examples of organic nitrate ignition accelerators that may be used are methyl nitrate, ethyl nitrate, propyl nitrate, isopropyl nitrate, allyl nitrate, butyl nitrate, isobutyl nitrate, sec-butyl nitrate, tert-butyl nitrate, amyl nitrate, isoamyl nitrate, 2-amyl nitrate, 3-amyl nitrate, hexyl nitrate, heptyl nitrate, 2-heptyl nitrate, octyl nitrate, isooctyl nitrate, 2-ethylhexyl nitrate, nonyl nitrate, decyl nitrate, undecyl nitrate, dodecyl nitrate, cyclopentyl nitrate, cyclohexyl nitrate, methylcyclohexyl nitrate, cyclododecyl nitrate, 2-ethoxyethyl nitrate, 2-(2-ethoxyethoxy)ethyl nitrate, tetrahydrofuranyl nitrate, and the like. Mixtures of such materials may also be used.
Examples of suitable optional metal deactivators useful in the compositions of the present application are disclosed in U.S. Pat. No. 4,482,357, issued Nov. 13, 1984, the disclosure of which is herein incorporated by reference in its entirety. Such metal deactivators include, for example, salicylidene-o-aminophenol, disalicylidene ethylenediamine, disalicylidene propylenediamine, and N,N′-disalicylidene-1,2-diaminopropane.
Suitable optional cyclomatic manganese tricarbonyl compounds which may be employed in the compositions of the present application include, for example, cyclopentadienyl manganese tricarbonyl, methylcyclopentadienyl manganese tricarbonyl, indenyl manganese tricarbonyl, and ethylcyclopentadienyl manganese tricarbonyl. Yet other examples of suitable cyclomatic manganese tricarbonyl compounds are disclosed in U.S. Pat. No. 5,575,823, issued Nov. 19, 1996, and U.S. Pat. No. 3,015,668, issued Jan. 2, 1962, both of which disclosures are herein incorporated by reference in their entirety.
When formulating the fuel compositions of this application, the additives may be employed in amounts sufficient to reduce or inhibit deposit formation in a diesel engine. In some aspects, the fuels may contain minor amounts of the above described reaction product that controls or reduces the formation of engine deposits, for example injector deposits in diesel engines. For example, the diesel fuels of this application may contain, on an active ingredient basis, an amount of the reaction product in the range of about 5 mg to about 200 mg of reaction product per Kg of fuel, such as in the range of about 20 mg to about 120 mg of reaction product per Kg of fuel. In aspects, where a carrier is employed, the fuel compositions may contain, on an active ingredients basis, an amount of the carrier in the range of about 1 mg to about 100 mg of carrier per Kg of fuel, such as about 5 mg to about 50 mg of carrier per Kg of fuel. The active ingredient basis excludes the weight of (i) unreacted components such as polyalkylene compounds associated with and remaining in the product as produced and used, and (ii) solvent(s), if any, used in the manufacture of the reaction product either during or after its formation but before addition of a carrier, if a carrier is employed.
The additives of the present application, including the reaction product described above, and optional additives used in formulating the fuels of this invention may be blended into the base diesel fuel individually or in various sub-combinations. In some embodiments, the additive components of the present application may be blended into the diesel fuel concurrently using an additive concentrate, as this takes advantage of the mutual compatibility and convenience afforded by the combination of ingredients when in the form of an additive concentrate. Also, use of a concentrate may reduce blending time and lessen the possibility of blending errors.
The diesel fuels of the present application may be applicable to the operation of both stationary diesel engines (e.g., engines used in electrical power generation installations, in pumping stations, etc.) and ambulatory diesel engines (e.g., engines used as prime movers in automobiles, trucks, road-grading equipment, military vehicles, etc.). For example, the fuels may include any and all middle distillate fuels, diesel fuels, biorenewable fuels, biodiesel fuel, gas-to-liquid (GTL) fuels, jet fuel, alcohols, ethers, kerosene, low sulfur fuels, synthetic fuels, such as Fischer-Tropsch fuels, liquid petroleum gas, bunker oils, coal to liquid (CTL) fuels, biomass to liquid (BTL) fuels, high asphaltene fuels, fuels derived from coal (natural, cleaned, and petcoke), genetically engineered biofuels and crops and extracts therefrom, and natural gas. “Biorenewable fuels” as used herein is understood to mean any fuel which is derived from resources other than petroleum. Such resources include, but are not limited to, corn, maize, soybeans and other crops; grasses, such as switchgrass, miscanthus, and hybrid grasses; algae, seaweed, vegetable oils; natural fats; and mixtures thereof. In an aspect, the biorenewable fuel can comprise monohydroxy alcohols, such as those comprising from 1 to about 5 carbon atoms. Non-limiting examples of suitable monohydroxy alcohols include methanol, ethanol, propanol, n-butanol, isobutanol, t-butyl alcohol, amyl alcohol, and isoamyl alcohol.
Accordingly, aspects of the present application are directed to methods for reducing the amount of injector deposits of a diesel engine having at least one combustion chamber and one or more direct fuel injectors in fluid connection with the combustion chamber. In another aspect, the improvements may also be observed in indirect diesel fuel injectors. In some aspects, the methods comprise injecting a hydrocarbon-based compression ignition fuel comprising the reaction product additive of the present disclosure, through the injectors of the diesel engine into the combustion chamber, and igniting the compression ignition fuel. In some aspects, the method may also comprise mixing into the diesel fuel at least one of the optional additional ingredients described above.
In one embodiment, the diesel fuels of the present application may be essentially free, such as devoid, of conventional succinimide dispersant compounds. The term “essentially free” is defined for purposes of this application to be concentrations having substantially no measurable effect on injector cleanliness or deposit formation.
In yet other aspects of the present application, the fuel additive may be free or substantially free of 1,2,4-triazoles. For example, the compositions may be substantially free of
wherein R4 and R5 are independently chosen from hydrogen and hydrocarbyl groups, with the proviso that at least one of R4 and R5 is not hydrogen. Examples of hydrocarbyl groups include C2 to C50 linear, branched or cyclic alkyl groups; C2 to C50 linear, branched or cyclic alkenyl groups; and substituted or unsubstituted aryl groups, such as phenyl groups, tolyl groups and xylyl groups.
The following examples are illustrative of exemplary embodiments of the disclosure. In these examples as well as elsewhere in this application, all parts and percentages are by weight unless otherwise indicated. It is intended that these examples are being presented for the purpose of illustration only and are not intended to limit the scope of the invention disclosed herein.
A 950 molecular weight polybutenyl succinic anhydride (295 grams) was mixed with 86 grams (2 equivalents) aminoguanidine bicarbonate (AGBC) and 416 grams of aromatic solvent 150. The mixture was heated under vacuum to 165° C. and held at that temperature for about 4 hours, removing water and carbon dioxide. The resulting mixture was filtered. An FTIR spectrum of the product shows a peak at 1636 cm−1 that dominates the peaks in a region from 1500 cm−1 to 1800 cm−1 as shown in
A flask was charged with 950 molecular weight polybutenyl succinic anhydride (553 g), aromatic solvent 150 (210 g), aminoguanidine bicarbonate (AGBC) (79.5 g, 1 equivalent), and toluene (145 g). The reaction mixture was heated up to 145° C. and held for about 2 hrs. No more water was removed through azeotrope distillation. A sample was removed and diluted with about an equal weight of heptane. The resulting mixture was filtered through Celite 512 and concentrated by a rotary evaporator to give desired product as a brownish oil. An FTIR spectrum of the product showed peaks at 1724, 1689, 1637, 1588 cm−1 with the peak at 1637 cm−1 being the smallest.
In the following example, an injector deposit test was performed on a diesel engine using a conventional diesel engine fuel injector test as described below.
A DW10 test that was developed by Coordinating European Council (CEC) was used to demonstrate the propensity of fuels to provoke fuel injector fouling and was also used to demonstrate the ability of certain fuel additives to prevent or control these deposits. Additive evaluations used the protocol of CEC F-98-08 for direct injection, common rail diesel engine nozzle coking tests. An engine dynamometer test stand was used for the installation of the Peugeot DW10 diesel engine for running the injector coking tests. The engine was a 2.0 liter engine having four cylinders. Each combustion chamber had four valves and the fuel injectors were DI piezo injectors have a Euro V classification.
The core protocol procedure consisted of running the engine through a cycle for 8-hours and allowing the engine to soak (engine off) for a prescribed amount of time. The foregoing sequence was repeated four times. At the end of each hour, a power measurement was taken of the engine while the engine was operating at rated conditions. The injector fouling propensity of the fuel was characterized by a difference in observed rated power between the beginning and the end of the test cycle.
Test preparation involved flushing the previous test's fuel from the engine prior to removing the injectors. The test injectors were inspected, cleaned, and reinstalled in the engine. If new injectors were selected, the new injectors were put through a 16-hour break-in cycle. Next, the engine was started using the desired test cycle program. Once the engine was warmed up, power was measured at 4000 RPM and full load to check for full power restoration after cleaning the injectors. If the power measurements were within specification, the test cycle was initiated. The following Table 1 provides a representation of the DW10 coking cycle that was used to evaluate the fuel additives according to the disclosure.
Various fuel additives were tested using the foregoing engine test procedure in an ultra low sulfur diesel fuel containing zinc neodecanoate, 2-ethylhexyl nitrate, and a fatty acid ester friction modifier (base fuel). A “dirty-up” phase consisting of base fuel only with no additive was initiated, followed by a “clean-up” phase consisting of base fuel with additive. All runs were made with 8 hour dirty-up and 8 hour clean-up unless indicated otherwise. The percent power recovery was calculated using the power measurement at end of the “dirty-up” phase and the power measurement at end of the “clean-up” phase. The percent power recovery was determined by the following formula
Percent Power recovery=(DU−CU)/DU×100
wherein DU is a percent power loss at the end of a dirty-up phase without the additive, CU is the percent power at the end of a clean-up phase with the fuel additive, and power is measured according to CEC F98-08 DW10 test. The conventional succinimide dispersant was made generally in accordance with the disclosure of U.S. Pat. No. 5,752,989.
1Engine run 16 hours without additive and 16 hours with additive
2Engine run 32 hours without additive and 32 hours with additive
As shown by the foregoing example, the reaction product of Runs 5-9 provided substantially greater power recovery after dirty up in an ultra low sulfur diesel fuel than the reaction product of Comparative Example 1. The results were surprising and totally unexpected. Accordingly, it is believed that the reaction product as described herein may be effective for keeping surfaces of fuel injectors for diesel engines clean and in cleaning up dirty fuel injectors.
It is noted that, as used in this specification and the appended claims, the singular forms “a,” “an,” and “the,” include plural referents unless expressly and unequivocally limited to one referent. Thus, for example, reference to “an antioxidant” includes two or more different antioxidants. As used herein, the term “include” and its grammatical variants are intended to be non-limiting, such that recitation of items in a list is not to the exclusion of other like items that can be substituted or added to the listed items
For the purposes of this specification and appended claims, unless otherwise indicated, all numbers expressing quantities, percentages or proportions, and other numerical values used in the specification and claims, are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by the present disclosure. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.
While particular embodiments have been described, alternatives, modifications, variations, improvements, and substantial equivalents that are or can be presently unforeseen can arise to applicants or others skilled in the art. Accordingly, the appended claims as filed and as they can be amended are intended to embrace all such alternatives, modifications variations, improvements, and substantial equivalents.
