US2048112A - Process for reduction of metaloxygen compounds - Google Patents

Description

July 21, 1936.- GAHL 2,048,112

PROCESS FOR REDUCTION OF METAL OXYGEN COMPOUNDS Filed July 31, 1935 INVENTOR. flu 0 0 65/7 BY KM A4- ATTORN Patented July 21, 1936 PATENT. OFFICE PROCESS FOR REDUCTION OF METAL- OXYGEN COMPOUNDS Rudolf Gahl, Berkeley, Calif.

Application July 31, 1933, Serial No. 683,031

2 Claims. (CL 75-90) homologs, by ethylene. acetylene, benzene and their respective homologs, by the various naphthenes etc., as well as byv mixtures of various hydrocarbons with other substances. I have referred to the hydrocarbons available as chemical 0 individuals, but do not want to imply that the mixtures to be used for my reduction process have to be made up from the individual hydrocarbons. Commercial mixtures like natural gas, refinery gas, cracked gas etc. will as a rule be used for commercial applications of the process.

By low temperature reduction I mean reduction at a temperature at which no appreciable fusion of the reacting or resulting substances takes place. Such processes may be resorted to for economic reasons. For instance the unavail ability of cokezof a suitable quality may prevent. the use of the common blast furnace and suggest the use ofin'ethods not requiring coke. 0n the other hand non-fusion methods may be desirable on accountof the fact that the metals produced without fusion have properties which make them particularly useful for certain purposes. The diiference in the properties is due to the fact that the removal oi. the non-metallic constituents of the ore particularly oxygen (which takes place during the reduction process) at temperatures sufllciently low to exclude fusion and even sintering results in the production of metal of a spongy nature. The material is therefore naturally more reactive than solid metal and is preferable for purposes where reactivity is desired, for instance the so-called sponge iron is a much quicker precipitant of copper from copper solutions than solid iron and its. reactivity with gases is indicated by the fact that, at least when it has been reduced at very low temperatures, it develops heat due to rapid oxidation when exposedto the air.

It has been established that some of the hydrocarbons enumerated'above particularly methane are relatively inactive which makes them unsuited for reduction processes at temperatures below those at which they can be decomposed. It is furthermore a well known fact that when hydrocarbons particularly the higher ones are used as reducing agents by themselves the reduction is accompanied by the liberation of carbon and other by-products which interfere with the reduction and make the reduced metal impure and unsuited for many applications. Another drawback connected with the direct reduction of metaloxygen compounds by hydrocarbons is that the reaction at least where the oxides of iron and other base metals are concerned is strongly endothermic and requires the supply of considerable heat for the maintenance of the reaction temperature which is undesirable both from an operative and economic standpoint.

It is true that these difficulties may be largely avoided bysubiecting the hydrocarbons to a partial oxidation before letting them react with the metal-oxygen compounds, but this procedure also has drawbacks. Should air or oxygen be used to effect the oxidation, part of the reducing power is destroyed which seriously impairs the economic possibilities of the process not mentioning the fact that oxygen in the form of air on account of its dilution with nitrogen slows down the reaction and takes up heat units that otherwise could be utilized. There is further the danger of carrying the oxidation too far that is to a point where the altered hydrocarbons become oxidizing to the metal involved and there is the danger of explosions taking place when the hydrocarbons are mixed with air or oxygen for the purpose of carrying out the reaction. These arguments against a preliminary oxidation of the hydrocarbons apply with less force when steam or carbon dioxide are used as oxidizing agents but they are still valid to some extent. It is the object of this patent specification to describe a method by which the oxygen content of the oxygen-metal compound with which this application is concerned may be used to promote the reduction of the metals involved. The process eliminates the objections that exist against processes as those referred to. It will easily be understood by reference to the attached figures which illustrate its essential principles in sectional elevation.

In the drawing accompanying and forming a part hereof, Figure 1 is a diagram, partly in section, illustrating one apparatus arrangement which I can employ.

Figure 2 is a variation on the apparatus shown in Figure 1, this figure particularly relating to a recovery and re-cycle operation.

Figure 3 is another variation on Figure 1, this figure illustrating the variation and arrangement of various reaction zones. 7

Figure 4 is a section on the line 4-4 of Figure 5 while Figure 5 is a section taken on line 5-5 of Figure 4, these two views illustrating a construction of another type of apparatus useful in connection with my invention.

Figure 6 is aview, partly in section and illus- 2 trating diagrammatically another form of apparatus which I can employ.

Figure 'I is a plan view of the apparatus shown inFlgureG.

In Figure 1 the reducing agent coming from pipe it enters a heatable chamber a which may contain 'a catalyst and will be referred to as catalyst chamber. The means for heating are dis.- grammatically represented by the coils of wire s through which electric current is assumed to fiow which does not mean that the heating has to be done by such coils surrounding the chamber or has to be done electrically at all. I Any suitable means for heating may be used. The pipe 0 also discharges a gas into catalyst chamber a and a simple way applicable in many cases of injecting the gas into the chamber in question is by forcing the reducing gas coming from it through a Venturi tube e as shown in Figures 1 and 3 whereby it creates a suction which draws the gas from pipe c along with it. The nature of the gas coming through pipe c will be defined later but it may be mentioned herethat it contains reducible constituents, in other words substances which may exercise an oxidizing action on the reducing gas entering chamber a. The reaction between the two gases can be accelerated by the provision of a suitable catalyst. The gases which now contain hydrocarbon at least partially oxidized to carbon monoxide and, hydrogen (more active reducing agents than methane) go from the catalyst chamber to the main reduction chamber which is shown in the form of a vertical shaft 1) and react with the metal-oxygen compounds which will be called ore and which pass over inclined planes 0. It should be pointed out that the method by which the ore is passed through the reduction furnace and by which it is brought in contact with the reducing gases is immaterial so far as this specification is concerned and that I do not intend to limit the scope of my invention to the design of furnace indicated in the figure. When a reactiontakesplace oxygen is removed from the ore and further oxidizes the already partially oxidized reducing gas coming from d. The gas while undergoing this reaction fiows upward in the reduction chamber and it will be evident now that what enters pipe 0 at g and is transported to the catalyst chamber a is partially oxidized reducing gas.

Assuming that natural gas which is essentially methane were used as reducing agent it would on its passage through the catalyst chamber extract oxygen from the gas coming from c thus forming some carbon monoxide and hydrogen and on its way through the reduction chamber the carbon monoxide and hydrogen would react as follows while extracting oxygen from the ore:

From these equations it is evident that the gas flowing through c will contain carbon dioxide and steam. These substances in turn will react as follows with the fresh methane coming from d:

The part of the uprising gas that doesnot enter into pipe 0 on its upward course reacts with the ore spread out on the higher planes 0, thereby reducing additional .ore and being itself more completely oxidized. Ii. the zone of the reduction chamber which forms a circuit with pipe c and catalyst chamber a is called the first zone, the

indicated as being continuously discharged by the roll feeder i which may drop the metal either on railroad cars or into suitable storage bins not shown in the figure it being assumed that in the 15 design of the equipment the necessary precautions are taken to prevent the leakage of air into the reduction chamber and the oxidation of the reduced iron through contact with the air.

It is not necessary that the circulation ofvthe g0 gases be confined to the first zone of the reduction chamber, it is quite possible to circulate through the pipes k or I (having higher intakes than c) either alone or in combination with each other or with pipe 0. Circulation through these pipes may 25 if necessary be effected and controlled by fans, blowers or similar apparatus not indicated in the figures. If pipe 1:: alone is used this means that the first and second zones are combined as in Figure 2. If the circulation is confined to pipes c 30 or k and an ore like magnetite (that is an ore the reduction of which would lead directly to the metal and not to an intermediate product) is being treated, it would be impossible to produce a gas that is oxidizing to iron. That possibility 35 would exist however when gas is circulated through pipe 1 although with reasonable supervision it should; not occur easily.

It is not essential that the heat of combustion of the partly exhausted gas be utilized for preheating the ore by burning the gases in the topof the furnace. The gases'may equally well be conducted away and burnt in other places. For instance a combustion chamber could be arranged so as to provide the heat indicated in Figure 1 as produced by the coils s, for heating the reduction chamber or the gas return pipes.

Burning the gases the reducing power'of whi has been more or less exhausted represents one way of making use of their remaining reducing power. Another way is removing part of the carbon dioxide and water formed during the reduction process thus restoring the reducing action of the gas. In that case the gas which has been partially freed of these constituents is returned to the lower part of the reduction chamber-either directly or by way of the catalyst chamber it. Such an arrangement is illustrated in Figure 2. The carbon dioxide may be removed for instance by triethanolamine, the water e. g. by coolso ing and condensation or by an absorbent like calcium chloride, sulfuric acid or phosphor pentoxide. A carbon dioxideabsorber is indicated as u in Figure 2 while the water absorption unit is indicated by letter 12 in Figure 2. A suitable 35 project g permits proper handling, together with valves w, of the gases, in a desired manner. A fan a is utilized to introduce the gases into pipe 11 after they have passed through the various absorption units in any desired manner. The 70 catalyst chamber can be by-passed by pipe 1 and the valves indicated.

4 It is not necessary to subject the whole return stream to absorbents for water and carbon dioxide, in fact it has been pointed out before 75 that both these substances are required for the oxidation of the hydrocarbon. Only the excess should be absorbed. For that reason Figure 2 indicates the treatment of a fraction of the return current by absorption or condensation while the remaining fraction by-passes the absorption and condensation apparatus.

It will be evident that a substantially complete utilization of the hydrocarbonsis possible by a system of this type, that the resulting chemical process represents a complete combustion of the hydrocarbon to water and carbon dioxide and that no products of incomplete combustion such as carbon monoxide are discharged when the process is conducted as indicated by Figure 2.

It should be noted that the composition of the gases entering the reduction chamber from the catalyst. chamber is controllable so far as the relation between hydrogen and carbon monoxide is concerned through the degree of thoroughness with which water and carbon dioxide in the return current are absorbed. If for instance the water were quantitatively absorbed but the carbon dioxide only partially the proportion between carbon monoxide and hydrogen would increase because in such a case the hydrogen contained in the absorbed water would disappear from circulation and would not exercise further reducing action on the ore, while some carbon dioxide would remain unabsorbed and would return to the catalyst chamber where fresh hydrocarbon would reduce it to carbon monoxide. The latter would therefore build up in the system. Since the reduction of iron oxides by carbon monoxide may be conducted exothermically, while this is impossible with hydrogen, a shift towards the carbon monoxide becomes important under conditions where an exothermic reaction is desired.

It should also be. pointed out that the system illustrated by Figure 2 as well as the other systems represented in the figures permits working within an optimum zone in regard to the' degree of oxidation. If the degree of oxidation is too low, that is if the hydrocarbon is largely unaltered, the reduction will be slow, at least where an unreactive hydrocarbon like natural gas is used. If the degree of oxidation is too high, carbon dioxide and water will be present and slow down the reduction. On account of the circulation which is a characteristic of the processes described here the degree of oxidation needs to differ only little between the points where the gas enters and leaves the furnace and can be kept at optimum conditions so far as velocity of reaction is concerned. Likewise the processes herein described permit the maintenance of an exceptionally even temperature through the whole furnace. The latter is facilitated by the fact that the heat consumption of the process is centered in the catalyst chamber and is relatively small for the furnace proper, in fact there may be a heat production as mentioned above.

Attention should also be called to the following feature of the processes herein described. If gases oxidizing to the reducing hydrocarbons were introduced from the outside and the reaction products were directly discharged after passage through the reduction chamber which is the procedure common to most other processes, it would be necessary in the interest of economy to provide for a thorough performance of the partial oxidation of the hydrocarbon employed which means that a relatively high temperature would have to be maintained in the catalyst .chamber I hydrocarbon.

and that the gases would have to be passed through slowly enough to be thoroughly converted. In my process however a gas which ordinarily is already reducing to iron is fed to the catalyst chamber. A quick passage at relatively 5 low temperature is therefore sufiicient to increase the reducing power to the desired point.

No definitive rules can be laid down regarding the percentage of the gas circulated. The

Figure 3 shows a variation of the arrangement indicated in Figure 1. It illustrates that the intake 9 of the return pipe c may be located below the discharge point of gases into the furnace so the zones I and 2 and 3 are separated. This is 25 different from the arrangement of Figure 1. What is above and below for a vertical furnace can easily be translated into the equivalent terms for horizontal reduction furnaces which are not illustrated.

In the figures so far illustrated catalyst chambers were indicated as forming part of the required apparatus and as a matter of fact such chambers when filled with a suitable catalyst satisfactorily eifect the partial oxidation of the reducing gas for which they are intended. Metallic catalysts such as for instance nickel and iron are quite satisfactory and as the present process is meant for the production of those among other metals the metal produced can be utilized to perform the catalytic function. As in that case in a sense the catalyst chamber is located inside the furnace the necessary circulation may also be effected inside the furnace. It should be pointed out however that operation without a separate catalyst chamber requires that the reduction be accomplishedat a temperature at least as high as that required for the catalysis and it should likewise be pointed out that the combination of the catalyst chamber for the oxidation of the hydrocarbon with the reduction chamber for the the circulation to extend over the higher zones is separated from the second zone by a partition 1: except for a passage way m for the uprising gases. It will be evident that this passage way may also be utilized for the passage of the ore from the upper to the lower compartment. Only a few of the planes over which the ore travels are indicated and other details illustrated in the preceding figures left out in this figure in order to show the circulation of the gases with greater clarity. If the gases enter the chamber with a suflicient velocity the required circulation can be provided by the gas current which does away with the fan.

Itis even possible in certain cases to rely on 'diifusion and convection alone for effecting the circulation. In Figure 6 the surface of contact 75 removal oi water between the upper and lower layers of the first zone is shown as considerably increased by use of a chamber I so that diflusion and convection will be 's'uihcient to insure partly oxidized gases to reach the lower strata of the first zone. 7

A number or possible variations of the processes previously described will beevident to those ismiliar with the art. Such variations will naturally fall within the spirit of my invention although not having been described in detail. To a few such variations attention may be called.

I have illustrated the absorption of water and C02 only in connection with DQ688868 which utilize a separate catalyst chamber for the oxidation of the hydrocarbon. Obviously the absorption or condensationtreatment may also be used in those cases where no separate catalyst chamber is employed. In such a case the outside circulation of a certain portion of the gases for the d CO: is required.

I have also sai that the catalyst chamber should be heatable. It will be evident that the gases entering the catalyst chamber may be heated in place of the chamber itself. The use or the gases resulting from the, reduction of metal-oxygen compounds for the oxidation of the reducing hydrocarbons is characteristic of my process, but this does not mean that I have to rely on them exclusively for the oxidation. It is entirely possible to introduce an outside oxidizing agent like oxygen, air, water or carbon-' dioxide and to utilize it for the oxidation in addition to the return gases.

. I claim: a

l. A process for reduction oi an oxygen containing finely divided solid characterized by reduction at a temperature whereat any appreciable 'sintering of said solid is avoided, said process 5 consisting essentially in passing a reducing gas consisting essentially of C0 and H in contact with a stream of said solid to reduce said solid at a temperature whereat any appreciable sintering of said solid is avoided and to oxidize said gas to 10 form CO: and 11:0, imparting heat to said oxi-- dized gas and said gas together with a reducing gas over a catalyst to reduce CO: and

H and form aireahsupplyot reducing gas and then returning said heated reducing gas to con- 18* tact with more of said solid.

2. A process for reduction of an oxygen containing finely divided solid c by reduction at a temperature whereat any appreciable sintering of said solid is avoided,'said process con- 20.

sistingessentially in a reducing gas consisting essentially of CO and Bin contact with'a stream of said solid to reduce said solid at a temperature whereat any appreciable sintering of said solid is avoided and to oxidize said gas to form CO: and H20, imparting heat to said oxidized gas sis-substantially the only heat input supply for said process-and passing said gas together with a reducing gas ov r a catalyst to reduce CO: and IhO'and to a fresh supp y of reducing gas and then returning said heated reducing gas to contact with more oi. said solid.

RUDOLF GAHL.

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