US2399096A - Production of magnesium-containing mixtures - Google Patents

Description

Patented Apr. 23, 1946 2,399,099 FlCE PRODUCTION OF MAGNESIUM-CONTAINING MIXTUR Alva C. Byrns, Oakland, Calif., assignor, by .mcsne assignments, to

The Permanente Metals Corporation, a corporation of Delaware No Drawing. Application February 21, 1944,

Serial'No. 523,361

11 Claims. (Cl. 75-4) This invention relates to a method for preparing a magnesium-containing mixture, particularly a mixture to be used for the preparation of magnesium metal by reduction.

A number of methods have been devised for recovering magnesium from its ores or from com pounds containing magnesium and there are included in these methods reduction processes wherein materials containing magnesium in combination with oxygen are reduced to yield the free metal. One of these processes, known in the art as the carbothermic process, comprises the reduction of a magnesium-oxygen compound with a carbonaceous reducing agent, yielding entirely gaseous products of reaction from which the magnesium is condensed and recovered.

The method of producing the mixture of the" magnesium compound and the carbonaceous reducing agent has been the subject of considerable investigation. It has been known to mix finely ground or'powdered magnesia, or other source of magnesium, with finely ground or powdered solid carbonaceous material such as coke, charcoal, graphite. In an attempt to obtain more intimate admixture of the magnesium compound and the reducing agent it has also been known to add a binding agent, such as tar, pitch, tar oil, asphalt or the like to the primary mixture of ore, or other compound, and the coke or charcoal. This binder has then been carbonized prior to reduction. It has been considered preferable to form the mixture into briquets and then to carbonize the binder. This is believed to be a more effective way of holding the magnesia, for example, and the carbonaceous reducing agent in intimate contact in the heated zone during the reducing operation.

It is a two-fold object in preparing carbothermic feed to get the magnesium compound and the carbonaceous reducing agent into intimate contact, one with the other, and to maintain this intimate contact as, for instance, by making the mixture into a briquet which will be strong and stable under handling or heating. It' has been found in practice that mixtures or briquets made as described above have had less than the desired strength and stability andthe components have tended to burst apart upon heating,

as when rapidly heated to the temperatures required for reduction. This has led to incomplete reaction and decreased yield of the desired magnesium metal. Particles of small size, which break off, are-carried out of the furnace before reaction takes place, for example, and thus signiflcant amountsof unreacted MgO and reducingv agent are carried over with the eiiluent vapors from the reaction zone.

I haie now found that the aforesaid objects can be attained and the above disadvantages overcome by admixing finely divided magnesium compound with a liquefiable, thermoplastic car I bonaceous reducing agent and then subjecting to destructive distillation to form a carbonized or preferably a coked, matrix having the magnesium compound dispersed therethru.

In one method of practicing my invention, themagnesium compound, such as magnesia, magnesium hydroxide; magnesite, brucite, basic carbonate or the like issuitably made into a dispersion or suspension in a llquefiable carbonaceous material such as bituminous or coking coal, bitumens, tar, pitch, residual fuel oil, crude petroleum, heavy petroleum residue, cracked petroleum residue, molasses or the like, or mixtures l of such materials. This suspension or dispersion is then heated to cause coking or carbonization,

-without attaining conditions under which the magnesiumcompound would be reduced. The coked mass may then be broken up into pieces of suitable size and used directly, or it may be ground and formed into the desired agglomerate, using a binder, for example, tar, pitch, or the like, I if necessary. However, pellets may be formed by the use of pressure alone if high enough pressures are employed. Alternatively, briquets, pellets, nodules or other shapes may be formed of the magnesium compound-liqufiable, thermoplastic hydrocarbon mixture and these formed pieces then coked. It is found in practical operations that formed pieces are more conveniently handled both before and during reduction.

The mixtures of reactants formed as described above react smoothly, uniformly and quickly in the reducing zone and excel in these characteristics over the furnace feeds produced according to former methods. This is shown more clearly by the examples in the table below, wherein the term "furnace feed is used to described a feed made by combining MgO and petroleum coke,

both finely divided, with a binder of coal tar pitch and baking to carbonize the binder. The "fuel oil and M coke" describes a feed made by coking a mixture of a fuel oil which was a heavy liquid hydrocarbon having a density of 13.4" A. P. I. and finely divided MgO with stirring to prevent segregation' These tests were carried out in a small induction furnace and Kw. represents the input in kilowatts. Helium was passed through the furnace, to maintain an 0 inert atmosphere, at the rate of 2 liters per minute.

Pellet Tom .0! Sublima- Feed Pellet No. weight. reacton, Kw. tiontime' 0 grams 'C. lnminutes Furnaeefeed" Aveil'iligtea of 6 0.6163 1940 8.9 9.13 Fuel oil and Average oi 4 .em 1894 a4 1.2:;- MgO coke. pellets.

By visual observation thru a sight-hole in the induction furnace it is evident that the start of reaction is slower with the "furnace feed than with the fuel oil-MgO coke, that the reactionis then quite rapid in the case of the furnace feed, after which it slows down to the end, and that the reaction with the fuel oil-M30 coke, in contrast, is smooth and uniform. The table above is an example of the speedier over-all reaction with the latter material.

It is believed that these advantages are derived from the circumstances that the carbonaceous materials of my invention become plastic upon heating and fiow about, over and around and in the interstices between the fine M30 particles and are carbonized in stronger and more intimate contact with the MgO particles than has heretofore been possible. By my invention, it is believed that there is produced a continuous phase of carbon having finely divided M80 dispersed therethru and that the carbon is formed adhering to the surface of the M80 particle, so

that it forms a sort of a jacket for the small MgO particle. Such firm contact makes it possible for reaction to proceed even after the jacketed MgO particle may have split off from the main briquet, or other, mass. Processes which have hitherto been known have produced a bindind phase of coke containing particles of MgO and also discrete particles of the coke or carbon originally added as the reducing agent. My process avoids the presence of these discrete carbon particles and produces a strongly bonded mix ture wherein the surface to surface forces act between the M80 particles and the continuous carbon phase. The mixture obtained by my process has a uniformly black appearance and, even when finely subdivided, a by thorough grinding. no light-colored magnesium compound particles are evident. This is true even upon microscopic examination.

As a specific example of the method of preparing the magnesium-containins'mixture having a content of carbonaceous reducing material, I place BOOgallons of 13.4 A. P. I. fuel oil (6523 lbs.) in atank equippedwith a paddle agitator and circulating pump, and add thereto 3025 lbs. of finely ground MgO. The whole is thorous ly mixed to give a uniform suspension and is then transferred to the coking zone. This zone is a shell still suitable for carryin out destructive distillation of the heavy fuel oil and is. in this instance, a horizontal drum, externally fired, equipped for circulation of the oil-M30 mixture by-pumping out of the bottom of the drum at one end and back into the drum at the other end. The still is also provided with a vapor exit line, and with a suitable condenser, and collector for the condensate, as well as an exit line for noncondensible gases. The still is also fitted with an inlet for sweeping gases.

The oil mixture is introduced into the heated drum and heating continued while the oil mixture coke mixture shows a content of 21.4% fixed carbon and 73.9% of ash, principally MgO. v The solid coked mass is broken up into pieces of suiters can be installed in the coking zone to maintain agitation and prevent segregation of the magnesium compound. Where the carbonaceous material is solid or sufliciently viscous, as for instance in the case of suitable coal or high melting point pitch, the components of the mix can be finely divided, thoroughly mixed, and heated is circulated to cause agitation and prevent settlins out of the M30. Circulation is continued until the oil becomes so viscous that pumping is diiilcult and at this stage it is viscous enough to hold the'MgO in suspension. Distillation is continued for 22.5 hours or until the production of condensate has practically ceased. Natural gas is now admitted to the drum to sweep out residual heavy vapors and. these are collected by way of thacondenser and condensate collector also.

There are obtained'4050 lbs. of MgO-coke mixture and 669 gals. (5024 lbs.) of distillate. The

to coke with little or no agitation.

Pitch, however, foams upon heating and tends to produce a final coked product having a very spongy appearance. This may be desirable in some cases but where it is not desired, it is advantageous to prepare thecoking mixture by admixing a proportion of a fuel oil or heavy petroleum residue to reduce this tendency and to pro-' duce a denser, uniformly coked final mass. As

an example of this procedure, I mix together 437-' parts by weight of fuel oil, parts by weight of a coal tar pitchhaving a melting point of about 330 F., and 478 parts by weight of magnesia. 987 parts by weight of this mixture are destructively distilled by heating to 1030 F. over a period of minutes, with mechanical agitation for about half this time. The distillate recovered amounts to 342 partsby weight. The coke mix-' ture obtained contains 19.5% of fixed carbon. A quite dense final mass .can also advantageously be obtained by coking MgO with a liquid hydrocoking carbon having a proportion of powdered coal admixed therewith.

Other inert gases may be used to sweep'the residual heavy. vaporizable materials out of the coking drum at the end of the distillation. Other types of coking stills may of course be used. In coking a mixture or low viscosity, for example, the mixture may be partially distilled-in one zone as by the recirculation by pumping as described,

for instance, and the partially distilled mixture then transferred to another piece of equipment,

such as a coking oven or other device, for final coking.

I The condensate collected is useful in a number of ways, or it may be fractionated to recover components having specific desired boiling point ranges, or the like.

Alternatively, in making the coked mixture,

segregation may be prevented by mixing MgO which has been heated to a high temperature, for

example to incandescence, with pitch, petroleum residue or other suitable carbonaceous material.

The components may be mixed by spraying simultaneouslydnto a heated tower or in any other-- desired way. Immediate, intimate contact be--- tween incandescent MgO and the reducing agents described, in this manner, causes very rapid car- I bonization and produces good distribution.

The mixture prepared may be used in carbotrier-mic reduction processes described above or in other processes, such as a process for preparinti MsCl: by treatment in the presence ofchlorine-.2 when used in the carbothermic process for making magnesium, lioweventhe're are a'number of specific advantages. It is noted that the metal content of the condensate from this process is hisher by about 5% thanith'at heretofore obtainable. The reduction furnace is found to operate smoothly at lower temperatures with consequent asaaoae it is not necessary to feed in as much of such coke as formerly.

In orderto make a dense, hard and highly reactive product it is advantageous in some cases to add a relatively small proportion of the coked mixture, finely ground, to thestarting material.

For instance, I may admix about to of coked MgO-fuel oil fines to a starting mixture of MgO and fuel oil, and coke the mass to obtain a very hard, dense coke mass. This mass also' contains the magnesium compound in firm and intimate contact with the reducing agent andshows increased strength and increased reactivity. The table below indicates the increase in re-' activity.

. Pellet as... of Sublima- Feed Pellet weight, reaction, Kw. tion time No. grams C. inminuies Furnace feed 9 5.50 1056-2000 11. ii 20 Fuel oil, MgO, and

fines, coked 5.60 1070-2010 11.5

It is to be understood that the above detailed description has been given for the purpose of illustration and that modifications and variationscan be made therein without departing from the spirit and scope of the appended claims.

Having now described my invention what I Wish toclaimis.

1. Process for preparing a magnesium-containing mixture which comprises uniformly dispersing a magnesium compound in a liquefiable, thermoplastic carbonaceous material containing substantially no non-coking solid carbonaceous material, and heating to destructively distil said carbonaceous material whereby there is produced a .liquid hydrocarbon containing substantially no continuous'carbon phase having the magnesium compound dispersed therethrough.

2. Process for preparing a magnesium-containing mixture for the recovery of Mg by reduction of an oxide compound thereof which comprises uniformly dispersing a magnesium oxide compound in a liquefiable,.thermoplastic carbonaceous reducing agent containing substantially no non-coking solid carbonaceous material, and

heating to coke said reducing agent.

3. Process for preparing a magnesium-containing mixture for the recovery of magnesium by reduction of an oxide thereof which comprises uniformly dispersing a finely divided magnesium oxide and finely divided coking coal in a heavy liquid hydrocarbon containing substantially no noncoking solid carbonaceous material, and coking said coal and said hydrocarbon with agitation during the first part of the distillation period, whereby there is produced a continuous carbon phase having finely divided MgQ dispersed therea through.

4. Process for preparing a magnesium-containing for the recovery of magnesium by reduction of an oxide thereof comprising uniformly dispersing magnesium oxide in a heavy non-coking solid carbonaceous material, destructively distilling said hydrocarbon with agitation during the first part'of the distillation, and re- I covering a cooked mass containing said magnesium oxide in dispersion in a continuous carbon non-coking solid carbonaceous material, and,

heating said mixture to recover a coitcd mass comprising a continous carbon phase having fine- .ly divided MgO dispersed therethrough.

6.. Process for preparing a magnesium-containing mixture for the recoveryof magnesium by reduction of an oxide thereof which comprises preparing an intimate mixture of finely divided M80. finely divided high melting point pitch and heavy liquid hydrocarbon, said mixture containing substantially no non-coking solid carbonaceous material and destructively distilling said mixture with agitation during the first part of the distillation to recover a coked mass. a

7. Process for preparing a magnesium-containing mixture for the recovery of magnesium by reduction of an oxide thereof which comprises preparing a uniform suspension of MgO in heavy liquid hydrocarbon containing substantially no noncoking solid carbonaceous material, heating with ing mixture which comprises preparing an inti-,

mate mixture of a liquefiable, thermoplastic car'- bonaceous agent and MgO said mixture'contain- 1 ing substantially no non-coking solid carbonaceous material, heating to obtain a coked mass.

finely dividing said coked mass, preparing a. secondintimate mixture containing a liquefiable,

thermoplastic carbonaceous agent. MgO and said finely divided coked mass, and heating to coke said second intimate mixture.

9. Process for preparing a magnesium-containing mixture which comprises preparing an intimate mixture of a liquefiable, thermoplastic car-' bonaceous agent and MgO, said mixture containing substantially no non-coking solid carbonaceous material, heating to obtain a coked mass,

' taining said MgO. and separately condensing and recovering the distillate from said carbonaceous agent.

11. Process for preparing a magnesium-con taining mixture which comprises preparing a uniform suspension of M30 in fuel oil containing substantially no. non-cok'ed solid carbonaceous material, heating to partially destructively distil while recirculating to maintain said mo in sussnvs c. ems.