Reduced vapor pressure gelled fuels and solvents
The present invention relates generally to gelled fuels and solvents. Specifically the invention relates to gel thickeners that reduce vapor pressure in fuels and solvents and are shear thinning (pseudoplastic or thixotropic) or are shear thickening and remain pourable and flowable. Still more specifically, the invention relates to nonaqueous gels made with diblock copolymers that reduce the Reid Vapor Pressure of gelled gasoline and lower the total volatility of gelled hydrocarbon solvents. These gels may contain secondary amino acid or triblock polymer gelling agents. The invention includes gel compositions and methods of making gels.
1. Field of the Invention
The present invention relates generally to gelled fuels and solvents in US class 44, subclass 272. Specifically the invention relates to gel thickeners that reduce vapor pressure in fuels and solvents and are shear thinning (pseudoplastic or thixotropic) or are shear thickening and remain pourable and flowable. Still more specifically, the invention relates to nonaqueous gels made with diblock copolymers that reduce the Reid Vapor Pressure of gelled gasoline and lower the total volatility of gelled hydrocarbon solvents. These gels may contain secondary amino acid or triblock polymer gelling agents. The invention includes gel compositions and methods of making gels.
2. Background Information
The vapor pressure of hydrocarbon fuels such as gasoline is controlled by both state and federal regulations. The purpose of these regulations is to reduce the production of environmental pollutants including ozone that cause smog. The economics of refining favors adding cheap butane fractions to the blend to produce high vapor pressure gasoline. Environmental regulations require refineries to produce reduced vapor pressure gasoline that contains less butane. This is expensive. Oxygenates, which are oxygen containing compounds such as ethanol, are sometimes blended into gasoline to lower undesirable emissions. These oxygenates are expensive and do not remove the need to control the gasoline's vapor pressure. Currently oxygenates are government subsidized and some studies report that oxygenates do not significantly reduce ozone formation. It is still necessary to reducing the amount of butane in the blend to lower the gasoline's vapor pressure.
Like gasoline, industrial and consumer hydrocarbon solvents contribute to the volatile organic compounds released into the environment that produce ozone and cause smog. These solvents are not as highly regulated as gasoline, but their control regime is getting tougher and it would certainly be desirable to lower their total volatility to reduce the amount of volatile organic compounds released into the atmosphere.
When the amount of butane in gasoline is reduced, the octane rating of the gasoline goes down, which makes engines knock and hard to start. It would be desirable to be able to lower the vapor pressure of gasoline and hydrocarbon solvents without removing as much butane from the blended gasoline.
Gel thickeners have been tested to lower the vapor pressure of gasoline, especially in aviation fuels. The prior art teaches that gelled gasoline does have lower vapor pressure. The high viscosity of the gelled fuel required that the gel be degraded by in-line degraders in the fuel lines before the fuel was pumped, filtered or injected into an engine. This requirement for the use of in-line degraders made the use of gelled fuels economically impractical.
To better understand the present invention, it is helpful to understand vapor pressure. Vapor pressure is the measure of how volatile a compound is; the lower the vapor pressure, the less volatile the compound. From the standpoint of petroleum characterization, lighter hydrocarbons (i.e. butane) have a higher vapor pressure than heavier hydrocarbons.
The volatility of a blended gasoline is characterized by its Reid Vapor Pressure (RVP.) There is a direct correlation between the ability of a gasoline to operate an engine in both cold and hot start situations and its RVP. Also, the ideal RVP for a blended gasoline depends on the season (approximately 13 psi RVP in winter, 8.5 psi RVP in summer). Furthermore, the change in atmospheric pressure with altitude and variations in temperature means that the RVP of a blended gasoline must be localized. This means that the RVP of gasoline sold in Denver is different than the gasoline sold in Death Valley.
Gasoline, from a refinery point of view, it is a mix of hydrocarbons that, when combined, meet vapor pressure specifications. These hydrocarbons fall in the C4 to C12 range. Only isobutane and normal butane have RVPs above the limit of 13 psi. Therefore, addition or removal of these butane blending components is used to adjust the gasoline's RVP to meet vapor pressure requirements. The procedure for estimating the volume of butane required is outlined in Petroleum Refining in Nontechnical Language (Pennwell Nontechnical Series) by William L. Leffler. It should also be noticed that these butanes are the lowest cost components in the gasoline blend. Their elimination to lower RVP increases the price of the final gasoline product.
The Clean Air Act amendments of 1990 require the use of reformulated gasoline with oxygen additives such as ethanol (sometimes just called “alcohol”) and methyl tertiary butyl ether (MTBE) in areas of the United States that have substantial ozone pollution. These gasolines are sold in cities on the East Coast, in the Midwest, Texas, and California—particularly during the summer months, when near-ground ozone is most prevalent. This ozone is formed when pollutants from many different sources, including automobiles, react chemically in the presence of sunlight. Reformulated gasolines are designed to lower the emissions of vehicle pollutants, including those that contribute to ozone formation. In addition to oxygen additives, the fuels have a number of other characteristics that lower emissions.
But the oxygen additives in reformulated gasolines have raised environmental concerns. MTBE, for example, has leaked into drinking water in California, leading the state to phase out the use of this additive. Other states will probably also phase out the use MTBE. Because questions persist over which types of reformulated gasolines are preferable in improving air quality, the Environmental Protection Agency (EPA) recently asked the National Research Council (NRC) to study methods for certifying gasoline blends with oxygen additives.
The NRC found that, compared with MTBE blends, ethanol blends result in more pollutants evaporating from vehicle gas tanks. Ethanol blends also increase the overall potential of emissions to form ozone. Recent test data indicate that the potential for either additive to lower smog levels is small and will continue to decrease as other measures to reduce vehicle emissions take effect.
The EPA has established a two-phase reduction in summertime commercial gasoline volatility. These rules reduce gasoline emissions of volatile organic compounds (VOC) that are a major contributor to ground-level ozone (smog). Phase I was applicable to calendar years 1989 through 1991. Depending on the state and month, gasoline RVP was not to exceed 10.5 psi (pounds per square inch), 9.5 psi, or 9.0 psi. Phase II is applicable to 1992 and later calendar years. Depending on the state and month, gasoline RVP may not exceed 9.0 psi or 7.8 psi.
The prior art in gasoline RVP control is the production of low RVP gasoline. To make low RVP gasoline, refiners simply lower the vapor pressure by removing high vapor pressure components, i.e. the cheap butanes. Low RVP gasoline has a lower vapor pressure and thus a lower evaporation rate and lower volatility than conventional gasoline, but it costs more to make.
Lowering the vapor pressure of gasoline also reduces the evaporative emissions generated during vehicle refueling and therefore decreases the emissions of volatile organic compounds (VOCs) and other ozone-forming emissions.
Currently, the Regional Low RVP Gasoline program requires that low RVP gasoline be used in 95 central and eastern Texas counties during the summer months when ozone pollution is at its worst. The program, which began May 1, 2000, requires that all gasoline sold from retail gasoline-dispensing facilities within the affected counties have a maximum Reid vapor pressure of 7.8 pounds per square inch (psi) from June 1 through October 1 of each year. Gasoline suppliers are required to supply low RVP gasoline to the affected counties from May 1 through October 1 of each year.
BRIEF SUMMARY OF THE INVENTIONThe present invention is a gelled fuel or solvent, for example gasoline, containing an effective amount of at least one diblock copolymer. The effective amount of copolymer may be determined on a case by case basis by those skilled in the art. It will be the type and amount of diblock copolymer that results in the gelled gasoline having a desired RVP and viscosity and also being pseudoplastic shear thinning so it can pass though fuel filters, pumps and injectors. In the case of gelled hydrocarbon solvents it may be sometimes desirable to add amino acid gelling agent or triblock, radial or star copolymers to the gel to lower the total amount of polymer required to produce an acceptable gel. The addition of these gelling agents and non diblock copolymers will cause the gel to become Newtonian or shear thickening, but not so much as the prior art and the gelled solvent will still be flowable. Flowable means that it can be poured easily and will flow through pipes.
The diblock copolymer should have a molecular weight between about 100,000 and about 500,000. The molecular weight of the diblock polymer, or diblock polymers, is a function of the desired viscosity of the gelled fuel or solvent, the resulting vapor pressure of the gelled fuel and its ability to be flowable or shear thinning for use with fuel injectors, pumps and filters so as to avoid the requirement of in line degraders.
In the present invention, the embodiment of the invention comprising gasoline gelled with diblock copolymer is pseudoplastic. The gelled gasoline has a viscosity higher than the base ungelled gasoline, which lowers the vapor pressure and the gelled fuel exhibits a significant instantaneous reduction in viscosity when it flows through a small orifice, such as the fuel injector of an automotive engine. One benefit of the present invention is to allow formation of useful gels from a wide range of gasoline and solvent products, including by way or example, and not of limitation: Conosol® and Drakeol® hydrocarbon oils and solvents made by Penreco of Houston, Tex.; gasoline and other hydrocarbon containing fuels and lubricants such as diesel oil, jet fuel; and low viscosity specialty hydrocarbon products including penetrating oils and solvents sold under the trademarks Liquid Wrench® and WD-40®.
The vapor pressure reducing gelled fuels and solvents taught by the present invention may use one or more of a wide variety of diblock copolymers such as the hydrogenated and unhydrogenated diblock copolymers manufactured under the trademark Kraton®. The preferred embodiment of the present invention for use with gasoline and Conosol solvents uses Kraton® G-1702 diblock copolymer. This material is sold by Kraton Polymers of Houston, Tex.
The gelled hydrocarbon fuels and solvents taught by the present invention may also contain small amounts of amino acid gelling agents and triblock, radial or star copolymers in addition to the primary diblock copolymer. These low amounts of secondary gelling agents are useful in the range of about 0.1 to 5.0 weight percent to increase the viscosity of the gelled solvent while still allowing the gelled solvent to be pourable and flowable.
Yet a further benefit of the present invention is reduction in hydrocarbon product vapor pressure lowers the total amount of volatile organic compounds (VOC) that are released by the product into to the environment at a given temperature and pressure. One example of this benefit is that gelled fuel in an empty gas tank would have a lower vapor pressure, i.e. less VOC per unit volume of the gas tank, and thus would release less VOC pollution into the atmosphere during refueling, when the VOC vapor in the gas tank is forced out of the tank by the fuel flowing into the tank.
Yet another advantage of the pseudoplastic shear thinning gelled gasoline taught by the present invention is that the lower vapor pressure of the present invention lowers the risk of hydrocarbon-air explosion, while at the same time providing a gelled gasoline or solvent product that can flow through pumps, filters and small orifices, such as the jets in pores in fuel filters and fuel injectors in reciprocating gasoline or diesel engines, which may be stationary or may be in a car, truck or other mobile machinery. This advantage includes use of the present invention to provide a sprayable hydrocarbon containing gel with reduced vapor pressure to make fuel air explosion less likely while retaining the ability to flow properly through fuel spray nozzles in an aircraft reciprocating or turbojet engine or through the fuel injector plate orifices in an expendable or reusable rocket engine.
Numerous commercially available block copolymers can be used in embodiments of the invention. For example, various grades of copolymers sold under the trade name of Kraton® from Kraton Polymers, Houston, Tex. can be used. In some embodiments, the diblock copolymers are one or more of Kraton® G-1701 and Kraton® G-1702. Both Kraton® G-1701 and Kraton® G-1702 are diblock copolymers comprising hard styrene blocks and saturated poly(ethylene/propylene) blocks. Kraton® G-1701 has a specific gravity of about 0.91, and is reported to have a tensile strength of about 300 psi as measured on films cast from toluene, with Instron jaw separation of 10 inches per minute at a temperature of 25° C. and dumbbell specifications cut with ASTM die D. The styrene to rubber content of Kraton® G-1701 is reported by the manufacturer to be about 37:63, and the Brookfield viscosity is about greater than 50,000 cps (toluene solution, cps at 77° F., 25% by weight). The Shore A hardness is about 72. Kraton® G-1702 has a styrene content of about 28% and a Shore A hardness of about 75.
In addition, copolymers sold under the trade name of Vector® available from Dexco and Septon® from Kuraray also may be used. Table I lists some commercially available block copolymers which may be used in embodiments of the invention.
Kraton® G-1702 is used with gasoline and solvents in the examples set out below. However the remaining examples of diblock polymers, as well as other diblock copolymers having similar characteristics, may be used depending on the values of pseudoplasticity, viscosity and RVP desired in the final gelled solvent or fuel.
Penreco Conosol 260 is a high-purity, low-odor aliphatic solvent that is composed primarily of C13-C20 isoparaffinic and cycloparaffinic hydrocarbons. It is a low-toxicity product that contains less than 0.5% aromatics, and it has a higher solvent strength than competitive aliphatic solvents. Conosol 260 is environmentally friendly and meets numerous FDA regulations (21 CFR) for direct and indirect food additives. Penreco has determined that this product meets the low vapor pressure (LVP) VOC exemption for consumer products as set by the California Air Resources Board.
The chemical composition of Penreco Drakesols is predominantly saturated hydrocarbons. These compounds may be branched, straight chain or saturated cyclic structures. The aromatic content is very low and olefins are almost nonexistent.
Any hydrocarbon fuel or solvent with similar properties may be used in the present invention. The weight percent of the copolymer is selected in order to yield the desired viscosity, shear thinning and RVP. In the preferred embodiment of the invention, the weight percent of copolymer is from about half a weight percent to about twently weight percent. This yields a gelled fuel or solvent that has a viscosity range from about 100 SUS to about 2000 SUS, whereby the gelled fuel can be used fuel injector. The injection pressure ranges in, for example, a Jaguare engine, is from 230 bar (3,380 psi) at low engine speeds to 1,500 bar (22,000 psi) when engine speed exceeds 2,000 rev/min.
The gelled fuels and solvents taught by the present invention may contain any well known additive used in gasoline (discussed in more detail below), chemical and physical stabilizers, long chain alcohols, fragrances, insecticides, waxes, other solvents, oils and long chain organic acids, long chain organic bases, mineral oils, oils derived from vegetables and fruits, and animal derived oils and fats, long chain esters, and generally any organic material that contains hydrocarbons, having carbon chain length preferably from about C6 up to about C40. These additional materials may be blends from natural or synthetic feedstocks or may be pure chemicals.
The gelled gasoline taught by the present invention may contain gasoline additives. Additives are gasoline-soluble chemicals that are mixed with gasoline to enhance certain performance characteristics or to provide characteristics not inherent in the gasoline. Typically, they are derived from petroleum-based raw materials and their function and chemistry are highly specialized. They produce the desired effect at the parts-per-million (ppm) concentration range. (One ppm is 0.0001 mass percent.)
Oxidation inhibitors, also called antioxidants, are aromatic amines and hindered phenols. They prevent gasoline components from reacting with oxygen in the air to form peroxides or gums. They are needed in virtually all gasolines, but especially those with a high olefins contents. Peroxides can degrade antiknock quality and attack plastic or elastomeric fuel system parts, soluble gum can lead to engine deposits, and insoluble gums can plug fuel filters. Inhibiting oxidation is particularly important for fuels used in modern fuel-injected vehicles, as their fuel recirculation design may subject the fuel to more temperature and oxygen-exposure stress.
Corrosion inhibitors are carboxylic acids and carboxylates. The facilities—tanks and pipelines—of the gasoline distribution and marketing system are constructed primarily of uncoated steel. Corrosion inhibitors prevent free water in the gasoline from rusting or corroding these facilities. Corrosion inhibitors are less important once the gasoline is in the vehicle. The metal parts in the fuel systems of today's vehicles are made of corrosion resistant alloys or of steel coated with corrosion-resistant coatings. In addition, service station systems and operations are designed to prevent free water from being delivered to a vehicle's fuel tank.
Metal deactivators are chelating agents—chemical compounds which capture specific metal ions. More-active metals, like copper and zinc, effectively catalyze the oxidation of gasoline. These metals are not used in most gasoline distribution and vehicle fuel systems. However, when they are present, metal deactivators inhibit their catalytic activity.
Demulsifiers are polyglycol derivatives. An emulsion is a stable mixture of two mutually insoluble materials. A gasoline-water emulsion can be formed when gasoline passes through the high-shear field of a centrifugal pump if the gasoline is contaminated with free water. Demulsifiers improve the water separating characteristics of gasoline by preventing the formation of stable emulsions.
Antiknock compounds are lead alkyl, tetraethyl lead (TEL) and tetramethyl lead (TML) and methylcyclopentadienyl manganese tricarbonyl (MMT). Antiknock compounds increase the antiknock quality of gasoline. Because the amount of additive needed is small, they are a lower cost method of increasing octane than changing gasoline chemistry. Gasoline containing tetraethyl lead was first marketed in 1923. The average concentration of lead in gasoline gradually was increased until it reached a maximum of about 2.5 grams per gallon (g/gal.) in the late 1960s. After that, a series of events resulted in the use of less lead: new refining processes which produced higher octane gasoline components, steady growth in the population of vehicles requiring unleaded gasoline, and EPA regulations requiring the reduction of the lead content of gasoline in phased steps beginning in 1979. The EPA completely banned the addition of lead additives to onroad gasoline in 1996 and the amount of incidental lead may not exceed 0.05 g/gal.
MMT was commercialized in 1959 and was used in gasoline alone or in combination with the lead alkyls. The Clean Air Act Amendments of 1977 banned the use of manganese antiknock additives in unleaded gasoline unless the EPA granted a waiver. MMT continued to be extensively used in unleaded gasoline in Canada. In 1996, after several waiver requests and court actions by the manufacturer, the courts ordered the EPA to grant a waiver for MMT. Its use is limited to a maximum of 0.031 g/gal. California regulations continue to ban the addition of manganese to gasoline.
Anti-icing additives are surfactants, alcohols, and glycols. They prevent ice formation in the carburetor and fuel system. The need for this additive is disappearing as older-model vehicles with carburetors are replaced by vehicles with fuel injection systems.
Dyes are oil-soluble solids and liquids used to visually distinguish batches, grades, or applications of gasoline products. For example, gasoline for general aviation, which is manufactured to different and more exacting requirements, is dyed blue to distinguish it from motor gasoline for safety reasons.
Markers are a means of distinguishing specific batches of gasoline without providing an obvious visual clue. A refiner may add a marker to their gasoline so it can be identified as it moves through the distribution system.
Any of these additives may be used in the reduced vapor pressure pseudoplastic gelled fuels and solvents taught by present invention without departing from the scope of the invention.
EXAMPLESThe following are examples of gelled fuel and solvent made according to an embodiment of the present invention. These examples should be taken as illustrative of the invention and not as limiting its scope. All values are in weight percent.
Gelled Hydrocarbon Solvent
The first example is a gelled solvent. The base hydrocarbon solvent is Penreco Conosol C-145. This solvent is made and sold by Penreco of Houston, Tex. Conosol C-145 is a high-purity, low-odor aliphatic solvent composed primarily of C10-C13 cycloparaffinic and isoparaffinic hydrocarbons. It is a low-toxicity product that contains less than 0.5% aromatics, and it has a higher solvent strength than competitive 140+ flash aliphatic solvents.
The Conosol solvent is gelled by the addition of 9.5 weight percent of Kraton 1702 diblock copolymer and 0.5 Kraton 1650 triblock copolymer. These polymers are produced and sold by Kraton Polymers of Houston, Tex.
The control solvent and the gelled solvent were then tested for volatility by an evaporation test conducted at the Penreco Technology Center in the Woodlands, Tex.
Evaporation Test Procedure
Instruments: Square glass dish 4″/4′/1″ (2); Fume hood; Room thermometer; Scale that can accurately measure 100 g product
Materials: Conosol C-145, Gelled Conosol
Procedure: 1. Weigh 100 g of Conosol C-145 directly in a square glass dish previously tarred. Repeat with gelled Conosol.; 2. Record products' weight and ambient temperature. 3. Place the two dishes side-by-side in the fume hood. 4. Pull the dishes out and weigh them every day for the two weeks. 5. Record products' weight and ambient temperature. 6. After the two weeks, when the evaporation rate has slowed down, weigh the dishes only once a week. 7. Record products' weight and ambient temperature.
The results of this experimental example is shown in Table 2 below and is presented graphically in
The gelled solvent is shear thickening, but it remains pourable and flowable and needs no in line gel degrading to be used in industrial processing. The amount of triblock copolymer can be from about 0.10 to about 3.0 weight percent.
Gelled Fuel
The second example is a gelled fuel—gasoline v. ungelled gasoline. This test was conducted by Intertek Testing Services—Caleb Brett of Houston, Tex. according to ASTM D323, the Reid Vapor Pressure test.
Materials: Gasoline: Lab ID # 1004-2-0; Gelled Gasoline: Lab ID # 1004-2-1
The gelled gasoline was prepared by adding 10 weight percent of Kraton 1702 diblock copolymer to the base gasoline in a cold mix.
Test Procedure Reid Vapor Pressure ASTM D323; Vapor Pressure Test Results: Gasoline: 10.30 psi; Gelled Gasoline: 9.50 psi.
The gelled gasoline is pseudoplastic and shear thinning. At a shear rate of 25 the viscosity is 1.456; at shear rate of 50, the viscosity is 1.185; at a shear rate of 75, the viscosity is 1.062; and at a shear rate of 100, the viscosity is 1.019. Please see
While the invention has been described with respect to a limited number of embodiments, the specific features of one embodiment should not be attributed to other embodiments of the invention. No single embodiment is representative of all aspects of the inventions. In some embodiments, the gel compositions may include numerous compounds not mentioned herein. In other embodiments, the gel compositions do not include, or are substantially free of, any compounds not enumerated herein. Moreover, variations and modifications therefrom exist. For example, various additives may also be used to further enhance one or more properties of the gel compositions and fuels or solvents made therefrom. Cross-linking within the gel may be either enhanced or reduced, as desired, by physical or chemical methods in order to modify the properties of the composition. It should also be understood that uses of the gel compositions are not limited to retail fuel or solvent products, but also encompass industrial solvents and fuels. While the processes are described as comprising one or more steps, it should be understood that these steps may be practiced in any order or sequence unless otherwise indicated. These steps may be combined or separated. Finally, any number disclosed herein should be construed to mean approximate, regardless of whether the word “about” or “approximate” is used in describing the number. The appended claims intend to cover all such variations and modifications as falling within the scope of the invention. The appended claims intend to cover all such variations and modifications as falling within the scope of the invention.
Claims
1. A method for reducing the vapor pressure a liquid hydrocarbon comprising adding an effective amount of diblock copolymer to the liquid hydrocarbon to form a shear thinning hydrocarbon gel having a vapor pressure lower than the vapor pressure of said liquid hydrocarbon.
2. The method of claim 1, wherein the diblock copolymer has a molecular weight of from 100,000 to 500,000 and the effective amount of diblock copolymer added to the liquid hydrocarbon is from about 0.5 to about 20 weight percent.
3. The method of claim 2, wherein the liquid hydrocarbon is an aliphatic solvent that is composed primarily of C13-C20 isoparaffinic and cycloparaffinic hydrocarbons.
4. The method of claim 3, including adding 0.1 to 3.0 weight percent of a triblock copolymer gelling agent to the liquid hydrocarbon.
5. The method of claim 3, including adding 0.1 to 3.0 weight percent of an amino acid gelling agent to the liquid hydrocarbon.
6. The method of claim 3, wherein the liquid hydrocarbon is a petroleum fuel.
7. The method of claim 6, wherein the petroleum fuel is gasoline and the effective amount of diblock copolymer is from 5 to 15 weight percent,
8. The method of claim 7, wherein the gasoline contains additives selected from the group consisting of: oxygenates, corrosion inhibitors, chelating agents, emulsifiers, antiknock compounds, surfactants, alcohols, dyes and markers.
Type: Application
Filed: Jul 2, 2008
Publication Date: Oct 30, 2008
Inventor: Steluta Gina Butuc (Woodlands, TX)
Application Number: 12/217,324
International Classification: C10L 1/192 (20060101);
