Patent Grant
6897628
1. Field of the Invention
This invention resides in the field of process equipment used in the treatment of materials in liquid media by ultrasound.
2. Description of the Prior Art
The use of ultrasound for driving chemical reactions is well known. Examples of publications that describe chemical uses of ultrasound are Suslick, K. S., Science, vol. 247, p. 1439 (1990), and Mason, T. J., Practical Sonochemistry, A User's Guide to Applications in Chemistry and Chemical Engineering, Ellis Norwood Publishers, West Sussex, England (1991). Of the various sonicating systems that have been developed, those known as “probe”-type systems include an ultrasonic transducer that generates ultrasonic energy and transmits that energy to an ultrasonic horn for amplification.
Ultrasound generators are generally of limited energy output due to the power needed to drive the vibrations and the heat generated by ultrasonic transducers. Because of these limitations, the use of ultrasound for large-scale chemical processes has met with limited success. One means of achieving ultrasonic vibrations at a relatively high power is by the use of magnetostriction-driven ultrasound transducers, but frequencies attainable by magnetostriction drives are still only moderate in magnitude. Disclosures of the magnetostriction ultrasound transducers and their use in chemical reactions appear in Ruhman, A. A., et al. U.S. Pat. No. 6,545,060 B1 (issued Apr. 8, 2003), and its PCT counterpart WO 98/22277 (published May 28, 1998), as well as Yamazaki, N., et al. U.S. Pat. No. 5,486,733 (issued Jan. 23, 1996), Kuhn, M. C., et al. U.S. Pat. No. 4,556,467 (issued Dec. 3, 1985), Blomqvist, P., et al. U.S. Pat. No. 5,360,498 (issued Nov. 1, 1994), and Sawyer, H. T., U.S. Pat. No. 4,168,295 (issued Sep. 18, 1979). The Ruhman et al. patent discloses a magnetostriction transducer that produces ultrasonic vibrations in a continuous-flow reactor in which the vibrations are oriented radially relative to the direction of flow and the frequency range is limited to a maximum of 30 kHz. The Yamazaki et al. patent discloses a small-scale ultrasonic horn operating at relatively low power, in which magnetostriction is listed as one of a group of possible vibration-generating sources together with piezoelectric elements and electrostrictive strain elements. The Kuhn et al. patent discloses a continuous-flow processor that includes a multitude of ultrasonic horns and generators supplying frequencies less than 100 kHz. The Blomqvist et al. patent discloses an ultrasonic generator utilizing a magnetostrictive powder composite operating at a resonance frequency of 23.5 kHz. The Sawyer et al. patent discloses a flow-through reaction tube with three sets of ultrasonic transducers, each set containing four transducers and delivers ultrasound at a frequency of 20 to 40 kHz. These systems are not suitable for high-throughput reactions where a high reaction yield is required.
It has now been discovered that ultrasound can be supplied to a reaction system at high energy and high frequency by an ultrasound generator driven by a magnetostriction ultrasound transducer that includes a driving electromagnet formed from a pair of magnetostrictive prongs wound with coils that are oriented to produce an oscillating magnetostrictive force that produces ultrasonic vibrations in the prongs when an oscillating voltage is applied. The vibrations in the driving magnet produce magnetic field changes in the sensing magnet by a reverse magnetostrictive effect known in the art as the Villari effect, and these magnetic field changes generate a voltage in a coil that is wound around the sensing magnet. The voltage is representative of the amplitude of the oscillating magnetostrictive force in the driving magnet, and is compared to a target value in a control circuit that makes appropriate adjustments to the oscillating voltage applied to the driving magnet. The ultrasonic vibrations in the prongs of the driving magnet are also transmitted to an ultrasonic horn that is immersed in the liquid reaction medium to provide direct contact with the reactant(s). The prongs of the driving magnet are large enough to withstand a voltage as high as 300 volts and frequencies that are well into the megahertz range. The generator can be configured for use in a continuous-flow reactor, where it will accommodate a high-throughput reaction system, and a single such generator is preferably used as the sole source of ultrasound energy supplied to the reactor.
It has also been discovered that a highly efficient conversion of electrical energy to ultrasonic energy is achieved when the applied voltage is a pulsewise voltage with a rectangular waveform that consists of periods of positive voltages separated by periods of negative voltage rather than a zero voltage baseline.
This invention thus resides in an ultrasonic vibration generator as well as a continuous-flow reactor which incorporates the ultrasonic vibration generator, and also in a method for performing a chemical reaction with the assistance of ultrasound by passing a reaction medium in liquid form through a flow-through reactor that incorporates the ultrasonic vibration generator. This invention is useful in any chemical reaction whose yield and/or reaction rate can be enhanced by ultrasound, and is particularly useful in the desulfurization of crude oil and crude oil fractions, in processes disclosed in commonly owned U.S. Pat. No. 6,402,939 (issued Jun. 11, 2002), U.S. Pat. No. 6,500,219 (issued Dec. 31, 2002), U.S. Published Patent Application No. US 2003-0051988 A1 (published Mar. 20, 2003), U.S. patent application Ser. No. 10/279,218 (filed Oct. 23, 2002), and U.S. patent application Ser. No. 10/326,356 (filed Dec. 20, 2002). All patents, patent applications, and publications in general that are cited in this specification are incorporated herein by reference in their entirety for all legal purposes that are capable of being served thereby.
In accordance with this invention, ultrasonic vibrations are transmitted to an ultrasonic horn by a transducer that converts periodically varying voltages to mechanical vibrations in the ultrasound range by way of magnetostriction. The drive prongs in the transducer thus operate as electromagnets and are preferably formed of a material that is a soft magnetic alloy as well as a magnetostrictive material. A soft magnetic alloy is one that becomes magnetic in the presence of an electric field but retains little or no magnetism after the field is removed. Soft magnetic alloys are well known, and any such alloy is suitable for use in the present invention. Examples are iron-silicon alloys, iron-silicon-aluminum alloys, nickel-iron alloys, and iron-cobalt alloys, many of these containing additional alloying elements such as chromium, vanadium, and molybdenum. Examples of trade names under which these alloys are sold are HIPERCO® 27, HIPERCO® 35, 2V PERMENDUR®, and SUPERMENDUR. A presently preferred alloy is H ERCO® Alloy 50A (High Temp Metals, Inc., Sylmar, Calif., USA). A magnetostrictive material is one that undergoes a physical change in size or shape as the result of the application of a magnetic field. Magnetostrictive materials are likewise well known in the art, as are materials that are both magnetostrictive and soft magnetic alloys. The sensing magnet is made of the same types of materials as the drive prongs, and both can be made of the same alloy.
The size of each drive prong can vary depending on the energy needed to achieve the conversion or yield sought in the chemical reaction. In most cases, suitable drive prongs will be from about 5 to about 50 cm in length, and preferably from about 10 to about 25 cm in length, with volumes of from about 100 to about 1,000 cm3 per prong, and preferably from about 250 to about 500 cm3 per prong. The sensing magnet is preferably made of a pair of sensing prongs, whose size may vary as well, and in most cases, suitable sensing prongs will have the same length ranges as the drive prongs, whereas suitable volumes of the sensing prongs will most often range from about 10 to about 300 cm3 and preferably from about 30 to about 100 cm3. Due to the limitations of the properties of soft magnetic alloys that are commercially available and to the desirability of having the magnetic moments in proper and uniform alignment in these alloys, the prongs are preferably manufactured from thin plates stacked together. Individual plates may for example range in thickness from about 0.1 cm to about 1.0 cm, or preferably from about 0.25 cm to about 0.6 cm, and can be joined by any conventional adhesive that is strong enough to withstand the high localized temperatures and mechanical stresses that the vibrations can generate. Ceramic adhesives are particularly useful in this regard. For convenience in manufacturing, each pair of prongs is preferably connected by a crossbar to form a unitary U-shaped piece similar in appearance to a horseshoe magnet, i.e., the drive prongs preferably form a U-shaped drive magnet and the sensing prongs preferably form a U-shaped sensing magnet.
The windings around the various prongs are arranged and oriented to serve the drive and sensing functions of the prongs. The windings around the drive prongs, for example, are preferably in opposing directions so that when a voltage is applied across both windings the magnetic polarities arising from the resulting current are in opposite directions and magnetostrictive forces are created in a direction parallel to the axes of the prongs. Conversely, the windings around the sensing prongs are preferably a single winding that encircles one prong and continues to the other prong, i.e., the windings around the two prongs are in series. Both prongs are preferably wound to have the same magnetic polarity and the sensing magnet as a whole will respond to the vibrations produced by the driving magnet with a reverse magnetostrictive effect that generates magnetic field changes in the sensing prongs. These magnetic field oscillations then produce a voltage in the coils around the sensing prongs.
The ultrasonic horn can be of any conventional shape and size that may be known in the prior art for ultrasonic horns in general. The horn may for example be rod-shaped, preferably of circular cross section, and suitable lengths may range from about 5 cm about 10 cm, depending on the reactor size, and preferably from about 10 cm to about 50 cm, with a diameter of from about 3 cm to about 30 cm, and preferably from about 5 cm to about 15 cm. The drive prongs are operatively joined to the horn, i.e., by a mechanical connection that transmits the mechanical vibrations of the prongs to the horn. Metals from which the horn can be made are well known in the art of ultrasound. Examples are steel, stainless steel, nickel, aluminum, titanium, copper, and various alloys of these metals. Aluminum and titanium are preferred.
The transducer can be powered by any oscillating voltage. The oscillations can be a continuous waveform oscillation such as sinusoidal wave or a series of pulses such as rectangular waveform pulses. By “rectangular waveform” is meant a direct current voltage that alternates between a constant positive value and a baseline with stepwise voltage changes in between. Rectangular waveforms that are preferred in the practice of this invention are those in which the baseline is a negative voltage rather than a zero voltage, and preferably those in which the alternating positive and negative voltages are of the same magnitude. Preferred voltage is from about 140 volts to about 300 volts, and preferably about 220 volts single-phase, and the preferred wattage is from about 12 kilowatts to about 20 kilowatts. The frequency of the voltage oscillation will be selected to achieve the desired ultrasound frequency. Preferred frequencies are in the range of about 10 to about 30 megahertz, with a range of about 17 to about 20 megahertz more preferred.
Ultrasound transducers in accordance with this invention will typically require cooling during use. Cooling of the drive and sensing prongs can conveniently be achieved by surrounding these prongs in a jacket or housing through which a coolant is passed or circulated. The ultrasound generator is preferably mounted to a reaction vessel with the ultrasound horn protruding into the vessel interior and the drive and sensing prongs and the coolant jacket resides outside the vessel. Water is generally an acceptable and convenient coolant medium and is preferably circulated through the coolant jacket in a circulation loop that is separated from the reaction mixture passing through the reactor.
Ultrasound generators in accordance with this invention can be used in either batch reactors on a batch basis or in continuous-flow reactors in a continuous process. Continuous-flow reactors are preferred.
While this invention is susceptible to a variety of implementations and configurations, a detailed study of specific embodiments will provide the reader with a full understanding of the concepts of the invention and how they can be applied. One such embodiment is shown in the Figures.
The windings are shown in the side views of the prongs presented in
The windings around the drive prongs are visible in
The windings around the sensing prongs 42 are visible in
The power components, including the power supply, the amplifier, and the controller, are conventional components available from commercial suppliers and readily adaptable to perform the functions described above. In currently preferred embodiments, an arbitrary waveform generator such as Agilent 33220A, Agilent 3325A, or Advantek 712 with multifunction DAC 4-channel and AC 15 single-ended channels can be used, together with A/D temperature sensors to detect faults and power surges. Other components are a high-power push-pull amplifier with two Mitsubishi-QM200HA-2H Darlington transistors, rated 200A and 1,000V, or an IGBT (insulated gate bipolar transistor). An NPN configuration at 220V DC and 100A is used to generate power in the drive coils at 25 kW, and two positive pulse trains are used for driving the NPN transistors separately. Two transistors with NPN characteristics can be used in a push-pull amplifier. A PNP inverting state is used before the gate of the negative power transistor to develop a true push-pull power amplifier that will drive the driving electromagnet circuit. The pulse that drives the high-power amplifier can be adjusted to maximize the ultrasonic power. For the sensing components, a magnetic deflection circuit powers a transducer tip deflection foil with dc power and measures an ac return pulse. The arbitrary waveform generator is auto-tuned by a DAC and AD card in a Lab-View computer, in which pulse software controls the arbitrary waveform generator to maximize the ultrasonic output by adjusting the pulse frequency to the transducer resonance frequency. The positive and negative pulse components can also be adjusted to give an overall DC component that will maximize the magnetostrictive effect.
The following examples are offered for purposes of illustration only.
This example illustrates the use of an ultrasound generator in accordance with the present invention in the treatment by crude oil.
A reactor having the configuration shown in the Figures with a diameter of 8 inches (20 cm) and a length of 12 inches (30 cm) was used, with inlet and outlet ports having diameters of approximately 2 inches (5 cm), an ultrasound generator with a solid aluminum horn measuring 5.5 inches (14.0 cm) in length and 3.75 inches (9.5 cm) in diameter. The drive and sensing magnets were made from plates of PERMENDUR® (Hiperco Alloy 50A), each prong measuring 5.8 inches (14.8 cm) in length (total length, including crossbar, of 9 inches or 23 cm), 1.36 inch (2.4 cm) in width, and 0.14 inch (0.37 cm) in thickness, with seventeen such plates forming the drive prongs and three such plates forming the sensing prongs. The plates were annealed at approximately 1,600° F. (870° C.) for several hours, then cooled in a vacuum, prior to bonding. The block was annealed at 1,700° F. (930° C.) for several hours before the plates were silver-soldered into the block. The wire used for winding around the drive prongs was 12-14 gauge wire, and the wire used for winding around the sensing magnets was 14-16 gaueg wire, both with high-temperature insulation. The drive magnets were driven by a power supply at 4 kW at 220 V single-phase, and a positive-negative pulse at a frequency of 17-20 mHz. The feed to the reactor was a 50:50 (volume ratio) emulsion of crude oil and water, supplemented with diethyl ether and kerosene (2.2:19.8 volume ratio), at a total flow rate of 0.97 gallons per second (3.7 L/sec) with the diethyl ether and kerosene mixture supplied at 22 mL per second.
The reaction mixture leaving the reactor was separated into aqueous and organic phases by centrifuge, and the organic phase was washed once-through with water in a shear mixer at 3100 rpm for thirty seconds, then separated again. The starting material, first-run product (prior to washing), and wash product were each fractionated to determine the relative amounts of gasoline (C4-C14), diesel (C9-C24), and oil (C18-C34) fractions, and the results in volume percents are listed in Table I.
Elemental analyses for C, H, N, and S were performed on the starting material, first-run product, and wash product, on a Perkin-Elmer elemental analyzer, with results shown in Table II.
Sulfur analyses were also performed by oxidizing a 0.1 g sample with 50 mL of 50% hydrogen peroxide (diluted to 500 mL), refluxing for 6 hours until clear, then analyzing the oil fractions for sulfate by ionic chromatography and the water fractions by ICP (inductively coupled plasma spectroscopy). The results, expressed as elemental sulfur, are listed in Table III.
The foregoing is offered primarily for purposes of illustration. Further variations in the components of the apparatus and system, their arrangement, the materials used, the operating conditions, and other features disclosed herein that are still within the scope of the invention will be readily apparent to those skilled in the art.
| Number | Name | Date | Kind |
|---|---|---|---|
| 4168295 | Sawyer | Sep 1979 | A |
| 4531934 | Kossovsky et al. | Jul 1985 | A |
| 4556467 | Kuhn et al. | Dec 1985 | A |
| 4563837 | Ono | Jan 1986 | A |
| 4579000 | Sudo | Apr 1986 | A |
| 5057182 | Wuchinich | Oct 1991 | A |
| 5208787 | Shirley | May 1993 | A |
| 5238335 | Nomura | Aug 1993 | A |
| 5360498 | Blomqvist et al. | Nov 1994 | A |
| 5486733 | Yamazaki et al. | Jan 1996 | A |
| 5854589 | How et al. | Dec 1998 | A |
| 6188186 | Kong et al. | Feb 2001 | B1 |
| 6545060 | Ruhman et al. | Apr 2003 | B1 |
| 6720684 | Czimmek | Apr 2004 | B2 |
| Number | Date | Country |
|---|---|---|
| 08 318419 | Dec 1996 | JP |
| WO 9524999 | Sep 1995 | WO |
| WO 9822277 | May 1998 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 20040227414 A1 | Nov 2004 | US |
