Electrical Device for Conversion of Molecular Weights

1. Field of the Invention

The present invention relates to the conversion of the size of hydrocarbon molecules in a process stream, using an electrical method, and can be used either to combine small molecules into larger molecules or to separate larger molecules into smaller molecules.

2. Description of Prior Art

In the petroleum process industries, for many decades a thermal separation process has been applied to crude oil, which is a mixture of hydrocarbons, to separate out various fractions which are subsequently used for specific purposes. For example, diesel fuel, gasoline, lubricating oils, and asphalts are separated by vaporization and subsequent condensation at appropriate different temperatures and heights in a tower. The resulting yields of refined products are dependent upon the characteristics of the crude oil supplied, which will be different for each petroleum reservoir. The market demand for each category of refined products is variable in time, and therefore the adjustment of the petroleum refining process to changes in input composition and output demand can be difficult and challenging.

One remedy which has been recognized for many years is to convert larger molecules into smaller ones, a process called cracking, which has been normally accomplished by catalytic action on special surfaces at high temperatures. In this way, for example, an extra quantity of heavy oils can be converted into gasoline, which may be more marketable. Limitations of this approach include the cost of catalysts, the range of input molecules for which they are effective, and the thermal energy required for the process, which is difficult to recover.

On the other hand, the world supply of liquid hydrocarbons is also being consumed, and within only a few decades the known reserves will be exhausted. Two obvious alternatives involve the utilization of other natural sources of hydrocarbons which are in abundant supply: natural gas, and heavy oil. Keeping in mind that the majority of uses of petroleum in equipment use in our era have been for fuels in liquid form (such as gasoline, diesel fuel, jet fuel, and the like), and the transport of liquid fuel at normal atmospheric temperature and pressure is a decided advantage and has been designed into equipment in use today, it is clear that an important advantage would be derived from methods to convert natural gas (typically methane and ethane, CH.sub.4 and C.sub.2 H.sub.6) into liquids (C.sub.4 H.sub.x to C.sub.10 H.sub.y, for example). Natural gas is easily withdrawn from reservoirs, and, if converted into higher molecular weight species, could readily be transported from remote source locations to consumers via existing liquid petroleum pipelines or ships, whereas in it's natural gaseous form or refrigerated liquid form, special-purpose pipelines and ships must be constructed, and the use of natural gas as a vehicle fuel by the consumer would require substantial investment in new equipment on vehicles. A process has in fact been built and operated commercially by the New Zealand government which produces some 14,450 barrels of gasoline per day using natural gas as a feedstock. It is a three stage process; the first producing hydrogen and carbon monoxide, the second producing methanol, and the third producing gasoline via the Mobil MTG (methanol-to-gasoline) process which uses a synthetic zeolite catalyst ZSM-5 (U.S. Pat. No. 3,702,886, Argauer and Landolt). The incorporation of zeolites into various reactor geometries is considered in U.S. Pat. Nos. 4,058,576 (Chang and Grover), U.S. Pat. No. 3,928,483 (Chang, Silvestri, and Smith), U.S. Pat. No. 3,931,349 (Kuo), U.S. Pat. No. 4,138,440 (Chang, Jacob, Silvestri, and Zahner), U.S. Pat. No. 4,197,418 (Lee and Yurchak), U.S. Pat. No. 4,046,825 (Owen and Venuto), and U.S. Pat. No. 4,251,484 (Daviduk and Haddad). Two difficulties with all of the processes based upon these patents are, firstly, that a multi-stage conversion process from natural gas to gasoline is involved, and, secondly, that high operating temperatures are involved (315 degrees C. to 450 degrees C.). Both difficulties lead to loss of energy and to high cost of initial equipment. An approach which involves a single-stage direct conversion, and in which the energy which is to be supplied to the reaction is specifically used to accomplish the molecular conversion, with a minimum waste as heat, would represent an improvement. Furthermore, the MTG process is limited as to the size of large molecules which may be formed, by the interior dimensions of the columns of the synthetic zeolite molecule. A process which allows the combination of molecules with virtually unlimited larger sizes would have additional uses in the production of lubricating oils and heavier fluids. The principle of molecular conversion thus has wide application.

Although the foregoing discussion of molecular conversion is oriented towards hydrocarbon gaseous-to-liquid conversion, it is obvious that compound gases containing other elements, such as oxygen, chlorine, flourine, bromine, nitrogen, sulfur, hydrogen, silicon, and other elements could be changed in composition in order to accomplish certain benefits, such as the diminution of toxicity prior to release into the natural environment, or the alteration of composition so as to render harmful gases into harmless liquids or gases prior to release into the environment. The chloroflourocarbon gases, for example, which interact with naturally-available ultraviolet radiation when they are present in the atmosphere, could be transformed into liquid forms in combination with other elements which would be relatively harmless. Accordingly, it is the object of this invention to provide an electrical device which will accomplish the function of combining molecules of low molecular weight into molecules of higher molecular weight. A further object of the invention is to provide an electrical device for separating molecules of higher molecular weight into other molecules of lower molecular weight. Moreover, an additional object of the invention is to provide an electrical device for combining two or more different molecular species into new molecular species.

Briefly, the present invention consists of a plurality of tubes, made of glass or ceramic, which have electrically semi-conductive inner walls. By applying a voltage from one end of this array of tubes to the opposite end, an electric field is established which is parallel with the interior surfaces. A weak source of electrons is located at or just outside of the negatively-connected side of the array, and these electrons are accelerated along the interior regions of the tubes, eventually striking the walls with energies which may range from several electron volts to more than a hundred electron volts. For electron flow, gas pressures less than 1 Torr are usually used, although operation at pressures several orders of magnitude higher is possible if volume electron/ion interaction effects are to be used as a supplemental improvement in operation. The gas which is to be converted is admitted into the chamber on the side of the tubular array which is opposite the electron source. Diffusion of the source gas into the tubular array takes place, with absorption of the gas molecules on the interior walls of the tube. Upon grazing impact of the electrons upon the interior walls of the tube, several processes take place, the most obvious of which is the disruption of molecular bonding of the absorbed gas. In the case of methane source gas, a hydrogen ion is created, H.sup.+, which immediately is separated from its parent molecule by the action of the electric field. Hydrogen ions thus created are accelerated along the tube towards the negative end, striking the walls along the way and, upon impact, disrupting the bonding of the methane molecules and, as well, serving as an additional electron source via ion-induced secondary electron emission. The impact of electrons also creates secondary electron emission, with a net gain in electron flux along the length of the tube. Furthermore, once methane molecules are stripped of one or more hydrogen atoms, they have a net negative charge which, if they have been released from the wall surface by the energy associated with electron impact, causes them to be accelerated back towards the positive end of the tube. In such a state of activation, they will bond readily to other similar species upon collision with them, and the formation of carbon-carbon bonds is probable. Thus, by the repeated application of this process, formation of higher-order mixtures of paraffins, aromatics, olefins, and polyenes takes place, and a physical separation of the available hydrogen from the newly-formed higher-order hydrocarbon products is made possible by the electric field. Charge exchange is possible because of the flow of electrons through space, and the flow of electrical current through the semiconducting substrate. Energy for the dissociation is provided by the electric field which accelerates electrons, hydrogen ions, and complex hydrocarbon ions. Energy transfer is by direct impact at the interior surfaces of the tubes; volume interaction effects also take place at higher pressures, with similar results. Both chemi-absorbed molecules and physically absorbed molecules at the surface are affected and transformed by the electron impact process. The higher-order molecules are electrically moved to the region of higher inlet gas pressure, where they are carried by the inlet gas pressure gradient laterally to an outlet stream. A condensation stage then removes the higher-order species and the methane is recirculated through the device. The same device, if operated in a high electron flux mode, could decompose higher-order hydrocarbon molecules deposited on the walls of the tube near the output end, and a separate collecting electrode held at a greater positive voltage would attract such fragments. In this mode, lower molecular weight species could be produced from large molecules. It is clear that the admission of gaseous mixtures into this apparatus would result in a variety of output compounds, with a very large number of possibilities which could be considered, among which the detoxification of certain gases or liquids could take place. It is also clear that the hydrogen ions emerging from the negative-polarity ends of the tubes could be used to fragment large-molecular-weight hydrocarbon molecules in either a surface interaction or a volume interaction, and could combine with the fragments so that molecules of medium weight (for example C.sub.3 H.sub.x to C.sub.10 H.sub.y) would be formed. Even pure carbon (such as coal) could be gasified in this way and the resulting hydrocarbons pumped away.

FIG. 1 is a section view of a simplified reaction chamber.

FIG. 2 is an end section view of part of the parallel array of tubes.

FIG. 3 is a section view of one such tube.

FIG. 4 is a section view of one such tube with an angle between electric field and tube axis.

FIG. 5 is a section view of an axial-flow reaction chamber with quad-symmetric tube mounting.

FIG. 6 is an end section view of part of the reaction chamber of FIG. 5.

Referring now to the drawings and in particular to FIG. 1, there is shown an electrical device 10 for conversion of hydrocarbon molecular weights, comprising a chamber 12 with walls constructed of glass, ceramic, or metal, with an inlet gas source 27, an outlet gas port 28, and a hydrogen outlet gas port 29. Disposed upon or near the inside wall of chamber 12 is an electrode 26 constructed of metal, and on the opposite side of chamber 12 is another electrode 22 constructed of metal or a suitable semiconducting material, which can serve as an electron source. Within the central part of chamber 12 is mounted a plurality of tubular elements 32 which are joined together along their outer boundaries in an array 30 so that the axis of each tubular element 32 is disposed parallel with each other. The tubular elements 32 are composed of appropriate glass, glass ceramic, or ceramic, and are bound together by direct fusion of their boundaries 36 as shown in FIG. 2, or may also be bound together by means of a lower-softening-point glass applied at the boundaries 36. The interior of the tubes 32 are open cylinders 33 with interior surfaces 34 which have secondary-electron-emitting properties, and which have a zone of semiconducting material disposed just beneath the surfaces 34. Details of construction as described in U.S. Pat. No. 3,260,876 (Manley et. al.) could be used, for example. The plurality 30 of tubular elements is coated with metallic electrode material 38 and 40 such as gold, nickel, or aluminum on the faces 38 and 40, with the open cylinders 33 penetrating the metallic electrode material. Three potential sources are required, source 42 being connected between the faces 38 and 40 of the plurality 30 of tubular elements, source 44 being connected from electrode 40 to electrode 26, and source 45 being connected from electrode 22 to electrode 38. Connection of these sources through a glass or ceramic chamber 12 is shown, whereas if a metallic chamber wall is used, separate insulative feed-through connections through the chamber wall would be required.

Briefly describing the operation of the device in the mode which increases hydrocarbon molecular weights, the input gas such as methane CH.sub.4 or ethane C.sub.2 H.sub.6 is admitted through port 27 into the chamber 10, with an ambient pressure of 10.sup.-6 to 1 Torr, for example. Diffusion of the gas into tubes 32 occurs, with some of the gas absorbIng on the interior walls 34. Electrons originating either from the electron source 22, or from field emission from the edges of the metallic coating on face 38, or from cosmic rays, photoemission, or other natural sources, are accelerated along the length of the regions from source 22 to face 38, and onward towards face 40, striking the interior walls 34 enroute with substantial energies such as 10 to 100 electron volts. The range of energy values is adjustable with potential source 42. A sequence of cascading impacts takes place, which will be described below in detail, which removes hydrogen ions from the absorbed molecules, and allows hydrogen ions to move in the open cylinders 33 towards face 38, while at the same time allows negatively-charged hydrocarbon ions to move in the open cylinders 33 towards face 40. Subsequent impact of these hydrocarbon ions with other similar charged or neutral species causes combination into larger hydrocarbon molecules, which emerge from face 40 and are pumped away into outlet 28. Concurrently, the extracted hydrogen ions are carried by the electric field past face 38 where they combine with others of the same species and are pumped away into outlet 29. Some of the inlet methane will pass, by diffusion, directly into outlet port 28 and will be separated in subsequent condensation stages from the heavier hydrocarbon molecules formed by the device operation, after which the methane may be recirculated back into the inlet stream which feeds port 27.

To further elaborate upon the details of the separation and recombination mechanism, with reference to FIG. 3, the methane molecules 55 may be considered to be absorbed upon the interior walls 34 in a strong, chemi-sorbed bond with silica or alumina, which pertains to a surface monolayer, and also in a weaker, multi-molecular-layer bond for additional molecules. When interior wall 34 is struck by an incident electron 51 with energy in the range 10 to 100 electron volts, a variety of processes are initiated. Some of the incident electron 51 energy goes to create secondary electrons 57 which ar emitted from the wall 34 and which are accelerated in parabolic trajectories to perpetuate the process at the next impact with wall 34 producing ion 54. Some of the incident electron 51 energy goes to separate a positive hydrogen ion 52 from an absorbed gas molecule 55, also creating a negatively-charged hydrocarbon ion 53, for example CH.sub.3 or CH.sub.2. Some of the incident electron 51 energy imparts sufficient kinetic energy to these ions 52 and 53 so that they depart from their surface creation site and are accelerated along the electric field direction, in parabolic paths. The hydrogen ion 52 will subsequently strike the wall 34 with sufficient energy to create secondary electrons which will contribute to the electron cascade required for the process; this is a positive ion feedback effect. The same impact of hydrogen ion 52 on wall 34 will also provide sufficient energy to disrupt the bonding of one or several gas molecules 55 absorbed at that site, thus creating more positive hydrogen ions and negative hydrocarbon ions which are released from that site and which are accelerated in opposite directions along the electric field direction, thus contributing to the process. The hydrocarbon ion 53, acquiring kinetic energy along it's parabolic path, strikes the wall 34 with energy sufficient to disrupt bonds of molecules 55 at the site of impact, permitting the formation of a carbon-carbon bond at that site, and thus the creation of a higher weight hydrocarbon molecule 56, which is shown in a negatively-charged ion state in FIG. 3 as it emerges from face 40 of the tube. At the site of formation of the carbon-carbon bond, other processes such as secondary electron production, and hydrogen ion production also may be expected to take place. In some cases, the higher-weight hydrocarbon may not leave the wall 34 immediately upon creation but will be dislodged by a subsequent electron or ion impact. The net trend of these processes may be summarized by noting that (a) electron and ion kinetic energy is applied to the surface zone where the hydrocarbon molecules are absorbed; (b) rupture of at least one of the hydrocarbon bonds leads to a species separation by means of the electric field; (c) the arrival of an energetic hydrocarbon ion at the surface zone further disrupts absorbed molecules and causes them to form carbon-carbon bonds; (d) higher weight molecules are moved, as ions, in a direction opposite that of the excess hydrogen, to the end of the device where they are pumped out.

Replenishment of methane molecules 55 on the surface will take place rapidly by diffusion and deposition from the gas phase present in the tube. Some degree of interaction between charged particles and neutral molecules in the volume space of the tube will also take place, with charge-separation and species separation trends as described for the walls 34, further enhancing the process.

The proper amount of charge required for electron current conservation at each impact site is provided by a small current flowing in a semiconducting layer just a few hundred Angstroms, or less, beneath the surface 34. Such a layer is easily formed by a prior high-temperature hydrogen reduction treatment of a lead-oxide aluminosilicate glass, for example.

The parabolic paths of the electrons and of the ions, as described above, have a length which depends upon the electric field strength and also upon the initial kinetic energy of the particles and their direction of emission from the surface. Inasmuch as the impact-creation of these charged particles involves the combination of many random processes within the wall 34, the direction and initial kinetic energy of the particles will follow a statistical distribution function. Some of these particles will follow trajectories which are very long, enabling them to acquire hundreds of electron volts of kinetic energy. This may lead to complete removal of hydrogen upon impact, with deposition of elemental carbon. Although this may be removed by subsequent impacts, it would be useful to contrive both a lower and an upper limit upon the range of impact energies, and for this reason the geometry of inclined channel axes as shown in FIG. 4 will be discussed.

With reference to FIG. 4, an angle is introduced between the electric field and the tube axis, by preparing the bundle of tubes and then slicing the bundle at such an angle. Molecules 55 are not shown in FIG. 4 for purposes of reducing complexity, but are present along the wall 34. Impact of electron 51 creates hydrogen ion 52, hydrocarbon ion 53, and secondary electrons 58. Since there is an angle between electric field and tubular axis the length of the parabolic paths is sharply limited. For example, if the electric field is 10 volts per diameter, path lengths of three diameters or less, with resulting impact energies of 30 electron volts or less can be arranged. Many more impacts along the length are thus possible, creating larger molecular ions 54, 56 and 57. The length of these tubes may extend from 10 diameters to 1000 diameters or more, and the combination of angle, electric field strength, length/diameter ratio, and total length can be chosen to optimize the conversion process in each particular case, depending upon input molecular species, flow rates, and desired spectrum of output molecular species,

Various geometries can be utilized to expose an input molecular stream to many millions of the electrical reaction tubes. One possible configuration is illustrated in FIG. 5, where plurality of tubular elements 32b are disposed facing a central core region in an array 30b, with the most positive electrode 26b in the form of a rod at the center of the core region. The quad symmetry of this axial flow reactor is shown also in FIG. 6, which illustrates that the electrode 26b provides the electric field to draw the larger negatively-charged molecules from the tubular elements exit surface electrodes 40b. The potential sources 42, 44, 45 have deliberately been omitted from FIGS. 5 and 6 in the interest of drawing clarity, but are nonetheless essential to the operation and are connected as mentioned above. Inlet molecules from port 27b are converted in tubular elements 32b and higher-weight molecules are extracted at port 28b, with hydrogen extracted at port 29b. The flow of gas from inlet port 27b to outlet port 28b can be augmented by a magnetic field if desired to force converted charged molecules towards port 28b. In that case, one configuration could be a magnetic field of cylindrical symmetry which would be produced by a large current in the rod 26b, which would in such an instance penetrate the chamber wall 10b in two locations and which would be attached to a suitable current source. In accordance with well-known principles, the magnetic force on the charged particles would be in the direction of the axial flow. Such a magnetic field would also extend into the tubular elements 32b where it would increase the number of collisions of charged particles with the walls and in certain circumstances improve the conversion efficiency.

Inasmuch as the present invention is subject to many variations, modifications, and changes in detail, it is intended that all subject matter discussed above or shown in the accompanying drawings be interpreted as illustrative and not in a limiting sense. Such modifications and variations are included within the scope of this invention as defined by the following claims.