BACKGROUND OF THE INVENTION 1. Field of the Invention
This invention resides in the field of petroleum and petroleum fractions, and is concerned in particular with reformation processes for upgrading petroleum by converting high-boiling components to lower-boiling products with ultrasound.
2. Description of the Prior Art
Petroleum is the largest and most widely used natural resource in the world. Fuels for consumer and industrial use are derived from petroleum, as are the chemicals used as raw materials in a vast array of consumer and industrial products. The utility of petroleum is often expanded by upgrading the petroleum to remove sulfur in its various forms and to convert some of its high-boiling components to species of lower boiling points and lower molecular weight. One of the methods in the literature for achieving these conversions is the use of ultrasound. Disclosures of the treatment of petroleum and petroleum fractions by ultrasound are found in Yen et al., U.S. Pat. No. 6,402,939, issued Jun. 11, 2002; Gunnerman, U.S. Pat. No. 6,500,219, issued Dec. 31, 2002; Gunnerman, U.S. Pat. No. 6,652,992, issued Nov. 25, 2003; Gunnerman, U.S. Pat. No. 6,827,844, issued Dec. 7, 2004; and United States Published Patent Application No. US 2004-0227414 A1, published Nov. 18, 2004 (and its PCT equivalent, Published International Patent Application No. WO 2004/105085 A1, publication date Dec. 5, 2004).
The ultrasound treatment in these disclosures is performed on aqueous emulsions of the petroleum. While petroleum in its natural form is typically an emulsified mixture of oils, waxes, tars, salt, and mineral-laden water, the emulsions in the disclosures referenced above are formed by adding water or an aqueous solution to the natural petroleum or to fractions of the petroleum. As a result, the emulsion on which ultrasound is performed contains considerably more water than is typically present in the native material. Ultrasound is typically applied to emulsions in which the organic:aqueous phase ratio is from about 25:1 to about 1:5 on a volume basis.
Of further possible relevance to this invention is literature disclosing the use of microwave energy for separating emulsions. Examples of these disclosures are found in Hudgins et al., U.S. Pat. No. 4,810,375, issued Mar. 7, 1989; Wolf et al., U.S. Pat. No. 4,853,119, issued Aug. 1, 1989; Samardzija et al., U.S. Pat. No. 4,853,507, issued Aug. 1, 1989; Samardzija et al., U.S. Pat. No. 4,855,695, issued Aug. 8, 1989; Hudgins et al., U.S. Pat. No. 4,889,639, issued Dec. 26, 1989; and Kartchner, U.S. Pat. No. 6,077,400, issued Jun. 20, 2000. The disclosures of all patents and published applications listed in this specification are incorporated herein by reference in their entirety. The typical material that is treated in these disclosures is a mixture of liquid, gas, and solids, the liquid phase being crude oil that contains water at the low levels naturally present from the source.
It has now been discovered that petroleum and petroleum fractions, which are intended herein to encompass fossil fuels, crude oil, any distillation fractions of crude oil, and petroleum residua, can be efficiently upgraded by first adding water or an aqueous liquid to the petroleum or petroleum fraction to form an emulsion, then exposing the emulsion to ultrasound to cause the chemical conversions that result in the upgrading, and then exposing the treated emulsion to microwave energy to break the emulsion and separate the organic and aqueous phases. The organic phase is then recovered from the aqueous phase by conventional separation units. The result is an efficient recovery of an upgraded petroleum product without the need for costly de-emulsifying agents. These and other objects, advantages, features, and embodiments of the invention will become apparent from the description that follows.
The term “petroleum or petroleum fraction” is used herein to denote any carbonaceous liquid that is derived from petroleum and that is used to generate energy for any kind of use, including industrial uses, agricultural uses, commercial uses, governmental uses, and consumer uses. Included among these liquids are whole crude oil itself, automotive fuels such as gasoline, diesel fuel, jet fuel, and rocket fuel, and petroleum residuum-based fuel oils including bunker fuels and residual oils. Bunker fuels are heavy residual oils used as fuel by ships and industry and in large-scale heating installations. No. 6 fuel oil, which is also known as “Bunker C” fuel oil, is used in oil-fired power plants as the major fuel and is also used as a main propulsion fuel in deep draft vessels in the shipping industry. No. 4 fuel oil and No. 5 fuel oil are used to heat large buildings such as schools, apartment buildings, and office buildings, and as a power source for large stationary marine engines. The heaviest fuel oil is the vacuum residuum from the fractional distillation, commonly referred to as “vacuum resid,” with a boiling point of 565° C. and above, which is used as asphalt and coker feed. The present invention is useful in reducing the sulfur content and lowering the molecular weights of any of these fuels and fuel oils.
The properties of crude oil, resides, and other petroleum-derived oils that have been treated by ultrasound followed by microwave irradiation in accordance with this invention are significantly improved as a result of the combined ultrasound and microwave treatments. Included among these improved properties are the boiling point range and the API gravity. The term “API gravity” is used herein as it is among those skilled in the art of petroleum and petroleum-derived fuels. In general, the term represents a scale of measurement adopted by the American Petroleum Institute, the values on the scale increasing as specific gravity values decrease.
The application of ultrasound in the practice of this invention is performed on an emulsion of the oil in an aqueous fluid. The aqueous fluid can be water or any aqueous solution. The relative amounts of the oil and aqueous phases in the emulsion may vary, and while the proportion may affect the efficiency of the process or the ease of handling the fluids, the relative amounts are not critical to this invention. In most cases, however, best results will be achieved when the volume ratio of organic phase to aqueous phase is from about 25:1 to about 1:5, preferably from about 20:1 to about 1:2, and most preferably from about 12:1 to about 1:1. A ratio that is presently preferred is 10:1.
A hydroperoxide can be included in the emulsion as an optional additive, but is not critical to the success of the conversion. When a hydroperoxide is present, the amount can vary. In most cases, best results will be achieved with a hydroperoxide concentration of from about 10 ppm to about 100 ppm by weight, and preferably from about 15 ppm to about 50 ppm by weight, of the aqueous solution, particularly when the hydroperoxide is H2O2. Alternatively, when the H2O2amount is calculated as a component of the combined organic and aqueous phases, best results will generally be achieved in most systems with an H2O2concentration within the range of from about 0.0003% to about 0.03% by volume (as H2O2), and preferably from about 0.001% to about 0.01%, of the combined phases. For hydroperoxides other than H2O2, the preferred concentrations will be those of equivalent molar amounts.
In certain embodiments of this invention, a surface active agent or other emulsion stabilizer is included to stabilize the emulsion as the organic and aqueous phases are being prepared for the ultrasound exposure. Certain petroleum fractions contain surface active agents as naturally-occurring components of the fractions, and these agents may serve by themselves to stabilize the emulsion. In other cases, synthetic or non-naturally-occurring surface active agents can be added. Any of the wide variety of known materials that are effective as emulsion stabilizers can be used. These materials are listed in various references such as McCutcheon's Volume 1: Emulsifiers & Detergents—1999 North American Edition, McCutcheon's Division, MC Publishing Co., Glen Rock, N.J., USA, and other published literature. Cationic, anionic and nonionic surfactants can be used. Preferred cationic species are quaternary ammonium salts, quaternary phosphonium salts and crown ethers. Examples of quaternary ammonium salts are tetrabutyl ammonium bromide, tetrabutyl ammonium hydrogen sulfate, tributylmethyl ammonium chloride, benzyltrimethyl ammonium chloride, benzyltriethyl ammonium chloride, methyltricaprylyl ammonium chloride, dodecyltrimethyl ammonium bromide, tetraoctyl ammonium bromide, cetyltrimethyl ammonium chloride, and trimethyloctadecyl ammonium hydroxide. Quaternary ammonium halides are useful in many systems, and the most preferred are dodecyltrimethyl ammonium bromide and tetraoctyl ammonium bromide.
A further class of surface active agents are liquid aliphatic C15-C20hydrocarbons and mixtures of such hydrocarbons, preferably those having a specific gravity of at least about 0.82, and most preferably at least about 0.85. Examples of hydrocarbon mixtures that meet this description and are particularly convenient for use and readily available are mineral oils, preferably heavy or extra heavy mineral oil. The terms “mineral oil,” “heavy mineral oil,” and “extra heavy mineral oil” are well known in the art and are used herein in the same manner as they are commonly used in the art. Such oils are readily available from commercial chemicals suppliers throughout the world. The amount of mineral oil can vary and the optimal amount may depend on the grade of mineral oil, the composition of the petroleum or fraction being treated, the relative amounts of the aqueous and organic phases, and the operating conditions. Appropriate selection will be a matter of routine choice and adjustment to the skilled engineer. In the case of mineral oil, best and most efficient results will generally be obtained using a volume ratio of mineral oil to the organic phase of from about 0.00003 to about 0.003.
Another additive that is useful in forming and stabilizing the emulsion is a dialkyl ether. Preferred dialkyl ethers are those having a normal boiling point of at least 25° C. Both cyclic and acyclic ethers can be used, and are thus represented by the formula R1OR2in which R1and R2are either separate monovalent alkyl groups or are combined into a single divalent alkyl group, in either case either saturated or unsaturated but preferably saturated. The term “alkyl” is used herein to include both saturated and unsaturated alkyl groups. Whether R1and R2are two separate monovalent groups or one combined divalent group, the total number of carbon atoms in R1and R2is from 3 to 7, preferably 3 to 6, and most preferably 4 to 6. In an alternative characterization, the dialkyl ether is one whose molecular weight is at most about 100. Examples of dialkyl ethers that would be preferred in the practice of this invention are diethyl ether, methyl tertiary-butyl ether, methyl-n-propyl ether, and methyl isopropyl ether. The most preferred is diethyl ether.
When a dialkyl ether is used, its amount can vary. In most cases, however, best results will be obtained with a volume ratio of ether to the resid or other material to be treated that is within the range of from about 0.00003 to about 0.003, and preferably within the range of from about 0.0001 to about 0.001. The dialkyl ether can be added directly to either the resid or to the aqueous phase, but can also be first diluted in an appropriate solvent to facilitate the addition of the ether to either phase. In a presently preferred method, the ether is first dissolved in kerosene at 1 part by volume ether to 9 parts by volume kerosene, and the resulting solution is added to the resid prior to forming the emulsion.
Another optional component of the system is a metallic catalyst. Examples are transition metal catalysts, preferably metals having atomic numbers of 21 through 29, 39 through 47, and 57 through 79. Particularly preferred metals from this group are nickel, silver, tungsten (and tungstates), and combinations thereof. In certain systems within the scope of this invention, Fenton catalysts (ferrous salts) and metal ion catalysts in general such as iron (II), iron (III), copper (I), copper (II), chromium (III), chromium (VI), molybdenum, tungsten, and vanadium ions, are useful. Of these, iron (II), iron (III), copper (II), and tungsten catalysts are preferred. For some systems, Fenton-type catalysts are preferred, while for others, tungstates are preferred. Tungstates include tungstic acid, substituted tungstic acids such as phosphotungstic acid, and metal tungstates. The metallic catalyst when present will be used in a catalytically effective amount, which means any amount that will enhance the progress of the reactions by which the resid or oil components are upgraded. The catalyst may be present as metal particles, pellets, screens, or any form that has high surface area and can be retained in the ultrasound chamber.
For heavy petroleum fractions, a further improvement in efficiency is often achievable by preheating the fraction, the aqueous fluid, or both, prior to forming the emulsion or to exposing the emulsion to ultrasound. The degree of preheating is not critical and can vary widely, the optimal degree depending on the particular starting material and the ratio of aqueous to organic phases. In general, best results will be obtained by preheating to a temperature within the range of from about 50° C. to about 100° C. For fuels with an API gravity of from about 20 to about 30, preheating is preferably done to a temperature of from about 50° C. to about 75° C., whereas for fuels with an API gravity of from about 8 to about 15, preheating is preferably done to a temperature of from about 85° C. to about 100° C.
Ultrasound consists of soundlike waves at a frequency above the range of normal human hearing, i.e., above 20 kHz (20,000 cycles per second). Ultrasonic energy with frequencies as high as 10 gigahertz (10,000,000,000 cycles per second) has been generated, but for the purposes of this invention, useful results will be achieved with frequencies within the range of from about 10 kHz to about 100 MHz, and preferably within the range of from about 10 kHz to about 30 MHz. Ultrasonic waves can be generated from mechanical, electrical, electromagnetic, or thermal energy sources. The intensity of the sonic energy may also vary widely. For the purposes of this invention, best results will generally be achieved with an intensity ranging from about 30 watts/cm2to about 300 watts/cm2, or preferably from about 50 watts/cm2to about 100 watts/cm2. The typical electromagnetic source is a magnetostrictive transducer which converts magnetic energy into ultrasonic energy by applying a strong alternating magnetic field to certain metals, alloys and ferrites. The typical electrical source is a piezoelectric transducer, which uses natural or synthetic single crystals (such as quartz) or ceramics (such as barium titanate or lead zirconate) and applies an alternating electrical voltage across opposite faces of the crystal or ceramic to cause an alternating expansion and contraction of crystal or ceramic at the impressed frequency. Ultrasound has wide applications in such areas as cleaning for the electronics, automotive, aircraft, and precision instruments industries, flow metering for closed systems such as coolants in nuclear power plants or for blood flow in the vascular system, materials testing, machining, soldering and welding, electronics, agriculture, oceanography, and medical imaging. The various methods of producing and applying ultrasonic energy, and commercial suppliers of ultrasound equipment, are well known among those skilled in ultrasound technology. In the presently preferred practice of the invention, ultrasound is administered by used of an ultrasonic transducer and an ultrasonic horn. Examples of ultrasonic transducers are disclosed in pending United States Published Patent Application No. US 2004-0227414 A1, published Nov. 18, 2004 (and its published PCT equivalent WO 2004/105085 A1, published Dec. 5, 2004); and pending U.S. patent application Ser. No. 10/994,166, filed Nov. 18, 2004, both of which are co-owned herewith.
The exposure time of the emulsion to ultrasound is not critical to the practice or the success of the invention, and the optimal exposure time will vary according to the material being treated. In general, however, effective and useful results can be achieved with a relatively short exposure time. Best results will generally be obtained with exposure times ranging from about 8 seconds to about 150 seconds. For starting materials with API gravities of from about 20 to about 30, the preferred exposure time is from about 8 seconds to about 20 seconds, whereas for fuels with API gravities of from about 8 to about 15, the preferred exposure time is from about 100 seconds to about 150 seconds.
Improvements in the efficiency and effectiveness of the process can in many cases be achieved by exposing the emulsion to ultrasound in a continuous process in a flow-through ultrasound chamber, and even further improvement can be achieved by recycling the organic phase to the chamber with a fresh supply of water. Recycle can be repeated for a total of three passes through the ultrasound chamber for even better results. Alternatively, the organic phase emerging from the ultrasound chamber can be subjected to a second stage ultrasound treatment in a separate chamber, and possibly a third stage ultrasound treatment in a third chamber, with a fresh supply of water to each chamber.
Ultrasound typically generates heat, and in certain embodiments of this invention it is preferable to remove some of the generated heat to maintain control over the reaction. Heat can be removed by conventional means, such as a liquid coolant jacket or a coolant circulating through a cooling coil in the interior of the ultrasound chamber. Water at atmospheric pressure is an effective coolant for this process. When cooling is achieved by immersing the ultrasound chamber in a coolant bath or by use of a circulating coolant, the coolant may be at a temperature of about 50° C. or less, preferably about 20° C. or less, and more preferably within the range of from about −5° C. to about 20° C. Suitable cooling methods or devices will be readily apparent to those skilled in the art.
Operating conditions in general for the practice of this invention can vary widely, depending on the material being treated and the manner of treatment. The pH of the emulsion, for example, may range from as low as 1 to as high as 10, although best results are presently believed to be achieved within a pH range of 2 to 7. The pressure of the emulsion as it is exposed to ultrasound can likewise vary, ranging from subatmospheric (as low as 5 psia or 0.34 atmosphere) to as high as 3,000 psia (214 atmospheres), although preferably less than about 400 psia (27 atmospheres), and more preferably less than about 50 psia (3.4 atmospheres), and most preferably from about atmospheric pressure to about 50 psia.
The microwave radiation that follows the ultrasound treatment can be achieved using conventional microwave generators can be used, and the frequency and power level are not critical. Increases in both frequency and power will provide greater speed in breaking the emulsion. In general, however, adequate results will be obtained using microwave radiation at a frequency of from about 900 MHz to about 2,500 MHz. Particularly preferred frequencies are 915 MHz and 2,450 MHz. In terms of the microwave power level, preferred levels are from about 100 watts to about 10,000 watts, and most preferably from about 500 watts to about 5,000 watts. The exposure time to the microwave radiation can vary as well, although preferred exposure times are from about 0.03 second to about 30 seconds, most preferably from about 0.1 second to about 1 second. In a currently preferred process, a microwave power level of 1,000 watts is used for an exposure time of 0.1 second to 1 second.
With the organic and aqueous phases thus exposed to microwave radiation, the organic phase is readily isolated and recovered from the aqueous phase by conventional means, examples of which are centrifuges, hydrocyclones, or simple decanting. The resulting organic phase is essentially water-free and the remaining aqueous phase can be recycled for treatment of fresh quantities of petroleum.
The use of microwave radiation allows the phases to be separated without the addition of chemical de-emulsifying agents that are typically used in petroleum processing. These agents are typically hydrophilic surfactants and synthetic or natural flocculants. Examples are quaternary ammonium siloxanes, tannin, sodium silicate, sodium pentahydrate, and high molecular weight amines, acrylamies, acrylic acids, acrylates, and acrylate salts. The emulsion on which the processing stages of this invention are performed is generally a liquid-liquid emulsion of the petroleum and the aqueous liquid. Solids and gases that are often found in crude oil are preferably removed prior to the processing, although some gas will be formed during the ultrasound exposure due to the cavitation caused by the ultrasound.
The various stages of the process as a whole can be performed either in a batchwise manner or in a continuous-flow operation. Continuous-flow operations are preferred. In a currently preferred system, the ultrasound exposure is performed in a flow-through reactor with a cylindrical ultrasound horn extending into the reactor interior and the incoming emulsion impinging a flat end surface of the horn then flowing radially outward to the edges of the end surface and along the sides of the horn before leaving the reactor. A reactor of this description is disclosed in Gunnerman et al., United States Published Patent Application No. US 2004-0227414 A1, published Nov. 18, 2004 and its PCT equivalent, Published International Patent Application No. WO 2004/105085 A1, publication date Dec. 5, 2004. Microwave exposure is also preferably performed in a continuous manner by passing the ultrasound-treated emulsion through a plastic pipe positioned in a microwave chamber. A presently preferred pipe is 1.5 inch (3.8 cm) internal diameter, and 18 inches (46 cm) in length. Crude oil at a throughput rate of 1,000 barrels per day, in the form of an emulsion of which 90% is the crude oil and 10% is water (by volume), is successfully treated in a unit of these dimensions.
The foregoing is offered primarily for purposes of illustration. Further variations and modifications that still embody the concepts of the invention will be readily apparent to those skilled in the art.