US3607221A

US3607221A - Carbothermic production of aluminum

Info

Publication number: US3607221A
Application number: US799672A
Authority: US
Inventors: Robert M Kibby
Original assignee: Reynolds Metals Co
Current assignee: Reynolds Metals Co
Priority date: 1969-02-17
Filing date: 1969-02-17
Publication date: 1971-09-21
Anticipated expiration: 1988-09-21

Abstract

A carbothermic process for the production of substantially pure aluminum metal comprising (a) introducing a feed comprising an aluminum oxide and aluminum carbide and/or carbon into a heating zone; (b) maintaining the heating zone at an elevated temperature sufficient to quickly vaporize all products to essentially only gaseous aluminum and carbon monoxide; (c) containing the vaporous mixture in the absence of a reactive environment with a layer of liquid aluminum at a temperature sufficiently low that the vapor pressure of the liquid aluminum is less than the partial pressure of the aluminum vapor in contact with it and sufficiently high to prevent the reaction of carbon monoxide and aluminum; and (d) recovering the substantially pure aluminum.

Description

United States Patent Inventor [72] Robert M. Kibby 3,136,627 6/1964 Caldwell... 75/68 Florence, Ala. 3,168,394 2/1965 Johnson 75/68 [21] Appl. No. 799,672 3,186,832 6/1965 Sparwald 75/68 [22] Filed 5:1). 17, 19969 O N PATENTS [45] Patented pt. 21,1 71

943,589 1963 Great Britain 75/68 73 Assignee gzeg rs lgs a Company 964,792 1964 Great Britain 75/68 Primary Examiner-Winston A. Douglas Assistant ExaminerPeter D. Rosenberg Att0rneyGlenn,'Palmer, Lyne, Gibbs & Thompson [54] CARBOTHERMIC PRODUCTION OF ALUMINUM 17 Claims 1 Drawing ABSTRACT: A carbothermlc process for the production of substantially pure aluminum metal comprising (a) introducing [52] US. Cl 75/10, a f d comprising an aluminum oxide and aluminum carbide 75/68 and/0r carbon into a heating zone; (b) maintaining the heating 1 Int.

zone at an elevated temperature sufficient to vaporize C22!) 2 H02 all products to essentially only gaseous aluminum and carbon [50] Field 01' Search 75/10, 68, monoxide; (c) containing the vapomus mixture i h absence 933 23/301-312 ofa reactive environment with a layer of liquid aluminum at a temperature sufficiently low that the vapor pressure of the [56] References Cited liquid aluminum is less than the partial pressure of the alu- UNITED STATES PATENTS minum vapor in contact with it and sufficiently high to prevent 2,408,278 9/1946 Stroup 75/68 the reaction of carbon monoxide and aluminum; and ((1) 2,974,032 3/1961 Grunert 75/89 recovering the substantially pure aluminum.

C CH4 2 ELECTRODE 4 PREPARATION 7 6 1 3 ZONE A I I I I, /5

H H2 l 2 I42 Condensin S rf coo Q U 068 1 L ZONE c ZONE 8 MHD/ STEAM POWER GENERATOR PATENTED8EP21 I971 Condensing Surface ELECTRODE PREPARATION COOL- ZONE C ZONE 8 0 17 lllllllll 1/1 MHD/ STEAM POWER GENERATOR ELECTRIC INVENTOR ROBERT M. KIBB Y l8 WASTE QM,mm, /1&,GALK2 2LT ATTORNEY) CARBOTHERMIC PRODUCTION OF ALUMINUM BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a new and improved process for producing substantially pure aluminum metal under carbothermic conditions from aluminum oxides and carbon.

2. Description of the Prior Art The prior art is aware of various methods of attempting to produce aluminum in a carbothermic process from an aluminum oxide such as alumina. Generally, however, the

methods of the prior art have not provided means by which this process can be carried out successfully.

Generally, these carbothermic processes comprise heating the aluminum oxide and a carbon-contalning compound such as aluminum carbide or elemental carbon in a heating zone under extremely high temperatures so as to form a vaporous mixture of aluminum and carbon monoxide. After this vaporous mixture is formed, various attempts have been made to condense the vaporous mixture in order to recover the elemental aluminum therefrom. However, in all the prior art processes embodying this concept, it has not been possible to recover substantially pure aluminum in this manner because when approaching condensation, the aluminum combines with carbon and carbon gases present at the condensing surfaces to form aluminum carbide so that free aluminum heretofore has not been successfully obtained.

In variations on this process, attempts have been made to circumvent the condensation problem by conducting the reduction steps so that the aluminum is not completely vaporized, which process would have the effect of separating the aluminum metal which remains in the condensed state from the reactants from which it is made. However, the results of this technique have similarly been unsatisfactory because of back reactions of aluminum with carbon-bearing materials derived from the reactants.

One process for the carbothermic reduction of metal oxides is that disclosed in US. Pat. No. 2,9 79,449. In this patented process, in which the metal to be recovered may be aluminum, a mixture of the metal oxides to be reduced and carbon is converted to a highly energized jet of elemental vapors consisting initially of carbon, the free metal and oxygen, all primarily in the form of monatomic gases. As the carbon is present in sufficient quantities to fix all the oxygen as carbon monoxide, the vapors will thereafter shortly consist of a mixture of carbon monoxide gas and metal vapor. The vapors are then condensed according to the patent as such a rate that, at the proper rate of cooling, the metal values are recovered in powder form while the carbon remains attached to the oxygen. This, of course, presupposes close control of the carbon content contained in the vapor, that is, the amount of carbon present must be such that all of it remains in combination with the oxygen present must be such that all of it remains in combination with the oxygen present. As a practical matter, however, the procedure disclosed in this patent does not operate successfully because of the difficulty in control of the carbon values present and the fact that condensation is on a cool surface. Thus, very little pure ahiminum can be recovered because as the gases cool, the aluminum recombines with carbon and/or carbon monoxide present to form aluminum carbide. The

paragraph bridging columns

4 and 5 in this patent alludes to this problem but fails to offer any solution except to say if a proper rate of cooling is established the metal values may be recovered in powder form while the carbon seizes all the oxygen.

These patentees further note that they cool the mixture of gases down to a nonreactive temperature quickly enough that the back reaction cannot take place, column 5, lines 22-27. However, as mentioned, it is impossible to cool the gases sufficiently fast to obviate the back reaction as the. laws of nature require that the cooling pass through a very reactive stage where the back'reaction, or combination of aluminum and carbon, will take place. Hence, as a practical matter, very little aluminum will be recovered. Hence, this patent merely states the problem.

A similar process is disclosed in US. Pat. No. 3,230,072 in which aluminum oxide and carbon are vaporized to form a vaporous mixture of carbon monoxide and aluminum vapor of extremely high temperatures. However, the inventors in this patent attempt to circumvent the condensation problem by utilizing the lower specific gravity of aluminum as compared with fused aluminum oxide, by floating the aluminum on the aluminum oxide fusion. This is effected by maintaining a zone of cooled carbon monoxide gas above the liquid aluminum to maintain what is stated to be reduced conditions over the aluminum and means for feeding into the reduction zone of an electric furnace a granular or coherent mixture of aluminum oxide in fused state free of loose fines or powder. However, this patent is similarly unsatisfactory as the process disclosed therein, where the condensation is effected in a reactive atmosphere, negates any suitable recovery of aluminum metal.

In summary, the prior art has sought to produce aluminum in the condensed state without providing means to separate aluminum from reactive materials, or else has sought to condense aluminum from mixtures of aluminum and carbon monoxide vaporsby rapid cooling to avoid back reactions. Neither approach has produced a commercially successful process.

It is accordingly clear that a need remains in the art for a process by which the vaporous mixture of aluminum and carbon monoxide can be condensed so as to recover substantial amounts of the free aluminum without combining with the other elements present in the vaporous mixture.

SUMMARY OF THE INVENTION It is accordingly one object of the present invention to provide a process for the production of substantially pure aluminum under carbothermic reduction.

A further object of the invention is to provide a process for the production of substantially pure aluminum metal by the reaction of aluminum oxide and a carbon containing material to form a completely vaporous mixture with subsequent condensation of the resulting vaporous mixture to recover substantially pure aluminum.

A still further object of the present invention is to provide a procedure wherein the vaporous mixture is condensed in a nonreactive environment such that the aluminum is recovered in substantially uncombined form.

Other objects and advantages of the present invention will become apparent as the description thereof proceeds.

In satisfaction of the foregoing objects and advantages, there is provided by this invention a carbothermic process for the production of substantially pure aluminum metal which comprises; (a) introducing a feed comprising an aluminum oxide and at least one material selected from the group consisting of aluminum carbide and carbon into a heating zone; (b) maintaining the heating zone at an elevated temperature sufficient to quickly vaporize all products to essentially only gaseous aluminum and carbon monoxide; (c) contacting said vaporous mixture in the absence of a reactive environment with liquid aluminum at a temperature sufficiently low such that the vapor pressure of the liquid aluminum is less than the partial pressure of the aluminum vapor in contact with it and a high enough temperature to prevent the reaction of carbon monoxide and aluminum and (d) recovering substantially pure aluminum therefrom.

DESCRIPTION OF THE DRAWING Reference is now made to the drawing accompanying this application wherein there is illustrated one type of apparatus suitable for conducting the process of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS As indicated above, the present invention is concerned with the production of commercial grade aluminum of at least 99 percent purity or better from metallurgical grade alumina or aluminum oxides by carbothermic reduction, and particularly to the temperature and pressure conditions under which the aluminum can be condensed from a gaseous mixture consisting essentially of carbon monoxide and aluminum.

The invention is also concerned with processes and apparatus by which this reaction may be conducted.

In this reaction, mixtures of aluminum carbide and/or carbon and an aluminum oxide, such as alumina (A1 are heated to a temperature suflicient to produce a stoichiometric ratio or mixture of carbon monoxide and aluminum vapor by means known in the art. The temperature for forming this gaseous mixture is extremely high, being in the range of about 2,600 K. or higher, for example, 2,700 K. up to as high as 5,000 K. A highly preferred temperature is 2,600 K. to 2,800 K.

In one procedure for conducting this initial step of the reaction, the alumina and carbon or aluminum carbide are mixed together in the preferred ratios and formed into baked electrodes by means known to those skilled in the art. One method comprises reacting the alumina and carbon in a resistance or electrically heated fluidized bed reactor to produce aluminum carbide and a carbon monoxide off-gas, the latter taken to the combustion chamber of a Magneto-Hydrodynamic (MI-ID) power unit. The aluminum carbide is then cooled and mixed with alumina to make electrodes. In one method, the carbon is in the form of graphite sleeves and the alumina and aluminum carbide are compacted within the sleeve. If methane is employed in the reaction, as described hereinafter, a duct or opening is left within the sleeve for methane introduction.

These electrodes are then operated against each other to form an electric arc and achieve the temperature desired of above about 2,600 K. As a result of this step, the off gas produced will be a vaporous mixture of carbon monoxide and aluminum, the carbon monoxide combining as the oxygen is released from the alumina at these temperatures. Generally, ratios of starting materials should be employed so as to achieve an off gas ratio such that all of the carbon and oxygen present will be combined or at least only aluminum and carbon monoxide are present except for inert materials, the latter being present as a separate embodiment of the invention.

In conducting this reaction, insofar as apparatus is concerned, it is necessary to exclude other possible reactants, particularly those which would contain elemental carbon and for that reason, the walls of the container are preferably constructed of an inert refractory material which contains no free carbon such as calcium oxide, titanium carbide or zirconium oxide. As indicated above, as a result of the amounts and materials present, the resulting vaporous material will consist essentially of only gaseous aluminum and carbon monoxide, the carbon monoxide being formed under these extremely high temperature conditions from the carbon present and oxygen derived from the aluminum oxide.

in a separate embodiment of the invention, as mentioned above, there may also be introduced into the heating zone a quantity of an inert gas, such as argon or hydrogen or any hydrocarbon which decomposes to produce hydrogen. If a hydrocarbon is used, its quantity should be controlled with corresponding less use of carbon or aluminum carbide to insure that all carbon present will become combined as carbon monoxide in the arc heating stage. Hydrocarbon gas is thus useful as an additional source of carbon and also provides means by which the pressure in the heating zone can be controlled at will with the hydrogen thus obviating the need for removing the gases by pulling a vacuum on the system.

In a further embodiment for the initial step of the reaction, the raw materials, carbon and/or aluminum carbide and the aluminum oxide, may be converted to highly energized jets consisting initially of the carbon, aluminum and oxygen vapors, all of which are primarily in the form of monatomic gases. This technique is fully described in U.S. Pat. No. 2,979,449, discussed above. In this technique, which in itself provides a self-contained reaction zone characterized by the temperatures specified and further is constrained in free space to a specific geometry, whether the surrounding atmosphere is at high pressure or at high vacuum, the problem of maintaining furnace walls is eliminated. In conducting this technique, the reactants are introduced into a'resistance-heated or electrically heated fluidized bed reactor where they react at a temperature of about 2,300 K. to produce aluminum carbide, CO and if methane is present, hydrogen. In a preferred aspect, two reactors are used and they cycle between the production of hydrogen and carbon in the bed and the production of carbon monoxide. However, the use of two fluidized bed reactors can be avoided by introducing the methane directly to the plasma jet and adjusting the amounts of carbon introduced with alumina to the fluidized bed reactor. The introduction of methane directly to the plasma jet has the advantage that only one fluidized bed reactor is required before the second reduction furnace and would eliminate the necessity of handling hydrogen. Then alumina, aluminum carbide and hydrogen (or hydrocarbon gas) are introduced to an electrically heated plasma are where they react at a temperature equal to or greater than a temperature of 2,600 K. Wall temperatures above the condensing surface are maintained at temperatures equal to or greater than 2,400 K. Those parts of the wall below 2,600 K. are constructed of materials containing no elemental carbon, such as calcium oxide, titanium carbide or zirconium oxide.

Use of the plasma are or jet method constitutes a particularly important aspect as the plasma arc is a gas envelope which does not need to contact equipment walls at 2,600 K. and, therefore, the refractories would be less expensive.

After the vaporous gas is formed at the elevated temperatures, the mixture is then condensed in the absence of a reactive environment over a layer of liquid aluminum under conditions such that the vapor pressure of the liquid aluminum is less than the partial pressure of the aluminum vapor in contact with it and the partial pressure of carbon monoxide is low enough to prevent the reaction of any carbon monoxide present and aluminum. In conducting this aspect of the process, the aluminum vapor is condensed over a surface of liquid aluminum maintained at a temperature which depends on the pressure and amount of inert gas in the chamber, and is preferably as high as refractories will permit. In the examples shown, the condensing surface is maintained at 2,400 K. No elemental carbon is permitted in the condensing area and as indicated no elemental carbon is permitted in the refractory sources in contact with the aluminum and carbon monoxide vapors when the temperatures of the surfaces are below the temperature of 2,600 K. The pressure maintained in the condensing region is below that which gives a partial pressure of carbon monoxide sufficient to cause a reverse reaction to form aluminum oxide, aluminum carbide and/or aluminum oxy carbide mixtures. Under these conditions, the condensing recovery of aluminum depends on the mole ratio of carbon monoxide to aluminum produced in the heating reaction. At these pressures, all of the gases except for aluminum vapor are removed from the condensing zone which gases comprise carbon monoxide, hydrogen, if methane gas is used and a portion of the aluminum vapor. For example, based on 8 moles of aluminum and 4 moles of carbon monoxide produced in the heating zone, it will be found in this example that about 1.5 moles of the aluminum vapor leaves the condensing zone with the carbon monoxide. Hence, a chemically stable mixture of the carbon monoxide, hydrogen and aluminum vapor is removed from the system at a temperature of at least 2,400 K.

As indicated, at the bottom of the furnace, or initial condensation portion of the reactors, a layer of liquid aluminum is maintained at a temperature of at least about 2,400 K. This liquid or condensed aluminum is further connected below a gas seal to a cooling chamber or zone where it is cooled to a temperature of about 1,000 K. It has been found that these two different temperatures on the same aluminum layer may be effected simply by omission of insulation about the portion to be cooled. At the temperatures of the cooling zone, i.e.,

l,000 K., it has also been found that the exposed surface of the melt will be covered with a flux or crust which serves to further inhibit any reactions in the 1,000 K. cooling zone.

In the main reactor where the aluminum layer is maintained at a temperature of 2,400 K. for initial condensation, a major portion of the gaseous aluminum present will condense on the liquid bed and will then be moved in the deep bed to the 1,000 K. cooling zone out of contact with elemental carbon where it may be recovered.

As indicated above, under the conditions in the furnace, sufficient pressure is maintained to exhaust the chemically stable mixture of carbon monoxide, hydrogen and a small portion of aluminum from the condensation zone, allowing the remaining aluminum vapor to condense on the fluid layer in the absence of a reactive environment. This total pressure in the condensing region is below that sufficient to give a partial pressure of carbon monoxide sufficient to cause reversible reactions to form aluminum compounds. This total pressure may conveniently be controlled by introduction of the inert gas. While this total pressure may vary depending on other conditions and may range from about 0.5 atm. to 100 atm., it has been found that, at a temperature of 2,400 K., a pressure of about 0.5 to 5 atmospheres is adequate.

The temperature in the condensation region should be maintained such that the vapor pressure of the liquid aluminum is less than the partial pressure of the aluminum vapor, but the temperature should be high enough to prevent the reaction of carbon monoxide and aluminum. The temperatures specified herein are adequate in that respect. However, it is to be understood that as other conditions of the process are varied, the specific temperatures mentioned will also be varied.

It is to be emphasized in this respect that the higher the temperature in the condensation zone, the more efficient is the process as the higher the temperature, the less aluminum vapor will be contained in the OR gas chemically stable mixture. Hence, it is preferred to condense as much above 2,400 K. as possible under the conditions of the process.

In the cooling zone l,000 K. zone), the atmosphere above the aluminum layer is essentially an inert gas such as hydrogen, argon, nitrogen, helium or the like, to prevent further reaction of the aluminum. This may be conveniently effected by introduction of the gas via a separate conduit or line or by other suitable means such as by use of the inert gas from the condensation chamber.

The off gases from the condensation step, comprising the chemically stable mixture of CO, H, and aluminum at about 2,400 K., may be treated in any desired manner. However, in a preferred aspect, after removal from the condensation region, they are combined with the CO from the fluid bed reactor and burned in the combustion zone of an MHD generator and thus can be used to generate power.

In a preferred embodiment, the off gases are removed from the system under pressure as described. However, it is also within the scope of the invention to also pull a vacuum on the system in order to effect their removal. If this latter aspect is employed, it is of course to be understood that the system is not operated under the pressures described above.

Referring now to the drawing accompanying this invention wherein one embodiment of the present invention is shown and a suitable apparatus presented therefor, it will be seen a complete cyclic process is shown wherein all recoverable components of the system are utilized in the recovery of aluminum and generation of electricity.

In the schematic drawing shown, alumina (A1 (1.0 mole) and carbon (1.5 moles) from zone 1 are prepared into electrodes in preparation zone 2. The

electrodes

3 and 4 are then operated against each other in furnace 5 heated by elec tricity generated at 6. In the electrode preparation, a duct is left in electrode 3 for the introduction of 1.5 moles of methane.

The electrodes are operated against each other in zone A at a temperature of at least 2,700 K. and a pressure of 1.86 atmospheres. From this reaction, there is formed a vapor consisting of 3 moles carbon monoxide, 2 moles aluminum and 3 moles hydrogen. Under these conditions most of the aluminum vapor condenses on the condensing surface 8 of liquid aluminum layer 9, the temperature at the condensing surface being about 2,400 K. The condensed aluminum in zone B then connects below a gas seal to zone C maintained at about 1,000 K. In this zone liquid aluminum layer 9 is covered with a flux or crust 10. Above the flux 10, an inert atmosphere is provided in area 11 to prevent any reaction of the aluminum, in this case by the introduction of hydrogen gas through line 12. The substantially pure aluminum is then recovered from zone C by line 13. Using the molar ratios given, about 1.52 moles of aluminum are recovered.

From the condensation area, after the aluminum has condensed, the gases comprising a chemically stable mixture of 3 moles carbon monoxide, 3 moles hydrogen and 0.48 moles of the aluminum vapor, is removed from the system through line 14 by the pressure in the reactor, and sent to combustion zone l5 where it is burned in air at about 2,400 K. This combustion zone 15 is the combustion zone of a MHD steam power generator 16, shown schematically. These hot gases are sufficient to generate about 2.6 kw.-h of electricity per pound of aluminum from line 17, with about 1.7 kw.-h electricity per pound of aluminum being shown as waste in 18.

From MHD generator 16, the aluminum from the burned off gas mixture is recovered as aluminum oxide, about 0.24 moles, which may be returned to the system via line 19 to be made up into fresh electrodes.

It is thus apparent that the process of the invention provides a means whereby substantially pure aluminum can be produced from aluminum oxide and the byproducts utilized to generate electricity to operate the process and recovered M 0 can be recycled to the system. It is clear that many variations can be made in this process including use of the jets and plasma are described herein. It is also apparent that other variables may be incorporated into operation of the process but all such variables are considered to be within the scope of the invention. For example, the off gases need not be utilized to power a MHD generator but may be processed in any desired manner as by passing them through a filter.

The following examples are presented to illustrate certain specific embodiments of the present invention, however, the invention is not to be considered as limited thereto.

EXAMPLE 1 One mole of aluminum oxide and 1.5 moles of carbon are mixed and formed into baked electrodes. These electrodes are then operated against one another to form an electric arc achieving a temperature in excess of 2,700 K. as illustrated in the drawing and 1.5 moles of methane are introduced. In the heating zone, the vapor produced is in the ratio of 3 moles CO to 2 moles aluminum. The vessel or furnace walls below 2,700 K. are made of material containing no elemental carbon, in this example, calcium oxide. The condensing surface of liquid aluminum is maintained at 2,400 K. and, of the two moles of alumina to be condensed, 0.48 mole leaves with the CO. The condensed aluminum connects below a gas seal to a cooling chamber where it is cooled to l,000 K. under a hydrogen atmosphere. The surface of the melt in the cooling zone is covered with a flux. The off gases from the condensation consisting of CO, H and 0.48 mole A1 are burned with air to produce power in a MHD unit at an efficiency of 60 percent recovery of the heat value of the gases entering the power unit. A pressure of 1.86 atmospheres is maintained in the heating zone in order to have sufficient pressure in the combustion zone to drive the MHD duct. This pressure, which is above the equilibrium partial pressures of CO plus aluminum, is achieved by introducing methane through a duct in one of the electrodes as shown in the drawing.

EXAMPLE 2 Alumina and carbon are reacted in a resistance-heated fluidized bed reactor to produce aluminum carbide, with an off gas of CO, the latter taken to the combustion chamber of a MHD power unit. The aluminum carbide is cooled and mixed with alumina to make electrodes. The carbon is introduced in the form of graphite sleeves. The alumina and aluminum carbide are compacted within the sleeve having a duct for methane introduction. The reactants are present in the amount of 2 moles of alumina, l mole of aluminum carbide, 3 moles of methane and 3 moles of carbon. In the heating zone, the electrodes are then operated against one another to produce a temperature in excess of 2,700 K. forming a gas in the mole ratio 8 aluminum to 6 CO. As in Example 1, all walls above the condensing surface are in excess of 2,400 K. and those walls below 2,700 K. are made of materials containing no elemental carbon in this example, calcium oxide. The condensing surface is maintained at 2,400 K. The condensed aluminum is moved in the deep aluminum bed to the cooling zone where the temperature is reduced to l,00O K. out of contact with elemental carbon and under nitrogen atmosphere. A flux covers the aluminum layer in the cooling zone. The off gas from the condensing surface is a mixture of CO, hydrogen, and a portion of the aluminum chemically stable with the CO at 2,400 K. This mixture of gases is combined with the CO from the fluid bed reactor and burned in the combustion zone of a MHD power generator. In order to provide pressure sufficient to drive the MHD duct, methane is introduced through the electrodes into the heating zone to give a pressure of 1.86 atmospheres.

EXAMPLE 3 Alumina, methane, and carbon are introduced to a resistance-heated fluidized bed reactor where they react at a temperature of 2,300 K. to produce aluminum carbide, CO, and hydrogen. Two reactors are used and they cycle between the production of hydrogen and carbon in the bed and the production of CO. One mole of alumina, one mole of aluminum carbide, and 3 moles of hydrogen are then introduced to an electrically heated plasma arc where they react at a temperature equal to or greater than 2,700 K. to provide a gas mixture in the mole ratio 6 aluminum to 3 CO. Wall temperatures above the condensing surface are maintained at temperatures equal to or greater than 2,400 K. Those parts of the wall below 2,600 K. are of materials containing no elemental carbon, in this example, calcium oxide. The condensing surface of the aluminum layer is maintained at 2,400 K. Condensed aluminum is then moved to the cooling zone where it is cooled as in Examples 1 and 2 under hydrogen gas. Refractories in the cooling zone contain no elemental carbon. The off gas from the condensing zone is burned in the combustion zone of an MHD power generating unit as in Examples 1 and 2. In this example, use of two fluidized bed reactors could be avoided by introducing the methane directly to the plasma jet and adjusting the amounts of carbon introduced with alumina to the fluidized bed reactor. introducing methane directly to the plasma jet has the advantage that only one fluidized bed reactor is required before the second reduction furnace and eliminates the necessity of handling hydrogen. As in examples l and 2 the hydrogen or methane is used to achieve pressures in the heating zone sufficient to remove the off gases and drive the MHD power duct.

EXAMPLE 4 This example is the same as Example 1 except that the off gases are not used to generate power but are merely removed from the heating zone discarded.

The process has been described herein with reference to certain specific embodiments. However, as obvious variations thereof will become apparent to those skilled in the art, all

What is claimed is: 1. A carbothermic process for the production of pure aluminum metal which comprises:

at. introducing a feed comprising an aluminum oxide and at least one material selected from the group consisting of aluminum carbide, carbon and mixtures thereof into a heating zone;

b. maintaining the heating zone at a temperature of from about 2,600 K. to 5,000 K. to completely vaporize all products to essentially only gaseous aluminum and carbon monoxide;

c. contacting the vaporous mixture in the absence of a reactive environment with liquid aluminum at a temperature low enough so that the vapor pressure of the liquid aluminum is less than the partial pressure of aluminum vapor in contact with it and high enough to prevent the reaction of carbon monoxide and aluminum and;

d. recovering the substantially pure aluminum.

2. A process according to claim 1 wherein aluminum carbide is reacted with aluminum oxide.

3. A process according to claim 1 wherein carbon is reacted with the aluminum oxide.

4. A process according to claim 1 wherein the aluminum oxide and aluminum carbide and/or carbon are formed into baked electrodes and then operated against one another at a temperature in excess of 2,600 K. to form the vaporous mixture of gaseous aluminum and carbon monoxide.

5. A process according to claim 1 wherein the aluminum oxide and aluminum carbide and/or carbon are introduced into the heating zone of a plasma arc producing a temperature in excess of 2,600 K.

6. A process according to claim 1 wherein the aluminum vapor is condensed on liquid aluminum maintained at a temperature of above about 2,400 K.

7. A process according to claim 6 wherein an inert gas is introduced into the heating zone to control the pressure therein.

8. A process according to claim 7 wherein the inert gas is a hydrocarbon.

9. A process according to claim 8 wherein a chemically stable mixture consisting of carbon monoxide, hydrogen and a small proportion of aluminum vapor is removed from the condensation zone and sent to an electric power generator to generate electricity.

10. The process according to claim 9 wherein at least one stage of the electric power generator is an MHD generator.

11. A process according to claim 9 wherein the condensed aluminum on the liquid aluminum surface is removed to a cooling zone maintained at a temperature of about l,000 K.

12. A process according to claim 11 wherein the layer of aluminum in the cooling zone has a layer of flux thereon.

13. A process according to claim 12 wherein the atmosphere in the cooling zone above the aluminum layer comprises an inert gas.

14. A process according to claim 13 wherein the substantially pure aluminum is recovered from the cooling zone beneath the flux.

15. A process according to claim 11 wherein aluminum oxide is removed from the electric power generator and returned to the system for reaction with carbon and/or aluminum carbide.

Claims

2. A process according to claim 1 wherein aluminum carbide is reacted with aluminum oxide.
3. A process according to claim 1 wherein carbon is reacted with the aluminum oxide.
4. A process according to claim 1 wherein the aluminum Oxide and aluminum carbide and/or carbon are formed into baked electrodes and then operated against one another at a temperature in excess of 2,600* K. to form the vaporous mixture of gaseous aluminum and carbon monoxide.
5. A process according to claim 1 wherein the aluminum oxide and aluminum carbide and/or carbon are introduced into the heating zone of a plasma arc producing a temperature in excess of 2,600* K.
6. A process according to claim 1 wherein the aluminum vapor is condensed on liquid aluminum maintained at a temperature of above about 2,400* K.
7. A process according to claim 6 wherein an inert gas is introduced into the heating zone to control the pressure therein.
8. A process according to claim 7 wherein the inert gas is a hydrocarbon.
9. A process according to claim 8 wherein a chemically stable mixture consisting of carbon monoxide, hydrogen and a small proportion of aluminum vapor is removed from the condensation zone and sent to an electric power generator to generate electricity.
10. The process according to claim 9 wherein at least one stage of the electric power generator is an MHD generator.
11. A process according to claim 9 wherein the condensed aluminum on the liquid aluminum surface is removed to a cooling zone maintained at a temperature of about 1,000* K.
12. A process according to claim 11 wherein the layer of aluminum in the cooling zone has a layer of flux thereon.
13. A process according to claim 12 wherein the atmosphere in the cooling zone above the aluminum layer comprises an inert gas.
14. A process according to claim 13 wherein the substantially pure aluminum is recovered from the cooling zone beneath the flux.
15. A process according to claim 11 wherein aluminum oxide is removed from the electric power generator and returned to the system for reaction with carbon and/or aluminum carbide.
16. A process according to claim 1 wherein the carbon monoxide/aluminum chemically stable mixture is removed from the reactor by pulling a vacuum on the system.