US2238908A - Method of condensing magnesium vapor - Google Patents

Description

April 22, 1941. T. H. McCONiCA, so

METHOD OF CONDENSING MAGNESIUM VAPOR Filed Feb. 21, 1940 7 M [0 M/xfure Pomp Air/2005;

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roduc/ 4/ (b Mix/are ATTORNEYS Patented Apr. 22, 1941 'METHOD OF CONDENSING MAGNESIUM VAPOR Thomas H. McConica, III, Midland, Mich., as-

signor to The Dow Chemical Company, Midland, Mich., a corporation of Michigan Application February 21, 1940, Serial No. 320,085

7 Claims.

This invention relates to an improved method of condensing metallic magnesium from vaporphase admixture with carbon monoxide.

In the preparation of metallic magnesium by the thermal reduction of magnesia-containing materials using carbonaceous reducing agents, the magnesium is liberated in the vapor state in admixture with carbon monoxide and at a. temperature well above that at which any substantial interaction between magnesium and carbon monoxide occurs; it can be recovered only by condensation. Unfortunately, since magnesium, in both vapor and liquid states, is vigorously attacked by carbon monoxide at ordinary condensing temperatures, it is inevitable that some loss of magnesium must occur in any-condensation. To minimize this loss, it is customary to subject the vapor mixture to be condensed to drastic chilling so as to condense and then cool the magnesium to temperatures below its freezing point in as short a time as possible.

As methods of effecting shock-condensation and chilling, the art has recommended either that large volumes of cold hydrogen or finelydivided salts be injected into the vapor mixture, or that the mixture be caused to impingeupon extensive cold surfaces. These procedures, although operable, are not wholly successful in preventing appreciable reversion of the liberated magnesium to magnesia, so that frequently as high as 40-50 per cent of the oxide is found in the metal condensate.

In view of this situation, it is an object of the present invention to provide an improved condensing process which permits an even more rapid rate of condensation than that existing in prior processes, and hence produces a metal condensate containing a considerably lower percentage of magnesia than has been customary heretofore.

According to the invention, the vapor mixture 7 of magnesium and carbon monoxide to be condensed is first chilled suddenly by injecting a controlled small proportion of a relatively cool tion or settling.

quence, within a fraction of a second, that they are almost simultaneous.

The gaseous cooling of the first step may be efiected by any gas which does not oxidize magnesium under the reaction conditions, e. g., hydrogen, helium, or hydrocarbon vapors. The gas is supplied at such a temperature that it is cool relative to the magnesium vapor; temperatures up to 650 C. are satisfactory, although in practical operation the gas is usually not far above room temperature. The gas is injected into the magnesium-carbon monoxide mixture in a proportion suflicient to cause a sudden and considerable drop in temperature, but not sufficient to cool the mixture below the temperature at which magnesium condenses at the existing pressure. It is preferable to chill the vapor mixture just to the point of incipient condensation, although it is difficult in practice to achieve temperature control of this precision. It is better to inject too little rather than too much gas, since the process of the invention does not contemplate injecting enough cool gas to cause any substantial condensation of the magnesium.

Immediately after the gas chilling step, the magnesium-carbon monoxide vapor mixture is passed into contact with a non-gaseous condensing means maintained at a condensing temperature below 650 C. The condensing means may be either liquid or solid; if liquid, it is preferably supplied in a proportion sufficient to absorb the entire heat of condensation of the magnesium. The most suitable liquid condensing agents are hydrocarbon oils, preferably paraflins of high boiling point, from which the condensed magnesium can be recovered in solid form by filtra- However, molten metals and alloys which dissolve magnesium at temperatures below 650 C., e. g. lead, may also be used, the condensed magnesium being subsequently recovered from solution by distillation. The magnesium-carbon'monoxide vapor mixture may be introduced into contact with the liquid condensing agent in any desired way, for'instance by bubbling it into abody of the latter, or by injecting it into a spray of the liquid.

Among the solid condensing means which may be used are ordinary surface condensers, made of any suitable material of construction and provided with adequate coolingmapacity Alternatively, the'chilled vapor mixture may be con densed by introducing it into a shower of fine metal particles supplied in a quantity sufllcient to absorb the heat of condensation and cooling,

as disclosed in my co-pending application Serial No. 316,628, filed January 31, 1940.

It is important that the non-gaseous condensing means be maintained at a temperature below 650 C. In this way, the condensed metal is cooled at once to below its freezing temperature; any substantial interaction of the condensate with carbon monoxide is avoided and the purity of the magnesium iskept high.

A probable explanation of the improved 'efliciency of the process of the invention as compared to prior processes is found in theoretical considerations. The condensation of magnesium vapor can be considered as occurring in four steps: (1) cooling of the magnesium-carbon monoxide mixture from its temperature of formation down to a temperature of incipient condensation (dew point) (2) condensation to the liquid phase; (3) cooling of the liquid to its freezing point; and (4) freezing of the liquid condensate. Of these stages, the first inyolves abstraction of heat from a wholly gaseous mixture, Whereas the other three require that heat be removed. from a liquid, either during or after its formation. An analysis of the molecular kinetics involved seems to show that by far the most effective way of cooling a hot gas is to inject therein a cold gas, whereas except under very unusual conditions a liquid is cooled much more readily by contact with a cooler liquid or solid than by contact with a cold gas. These principles are employed in the present-process, which uses gas cooling to chill the gaseous magnesium-carbon mixture to near its condensing temperature, and then uses liquid or solid cooling to effect the condensation, cooling, and freezing of the magnesium. Optimum heat transfer conditions are maintained at every stage in the process; condensation and cooling is accordingly accomplished. in a shorter time, and attack of the magnesium by the carbon monoxide is mini mized.

A preferred form of the process of the invention may be explained in detail with reference to the accompanying drawing, in which:

Figure l is a diagrammatic elevation, in partial section, of one arrangement of apparatus adapted to carry out the invention; and

Figure 2 illustrates another arrangement of apparatus.

The apparatus shown in Figure 1 includes a short vapor supply tube 3 which is incommunication at one end with an electric reduction furnace (not shown) or other source of magnesiumcarbon monoxide vapor mixture, and within which is mounted a gas inlet consisting of a hollow ring 4 having an inlet nipple 5 on its periphery, and gas ports 6 around its inner circumference. At its other end, the'vapor tube 3 leads into a spray chamber 1 provided at the top with a spray nozzle 8 and a gas outlet 9, and at the bottom with a drain III. This drain leads to a settling tank ll having a vent l2 and a bottom outlet 13 fitted with a discharge lock l4. The tank II also has a side outlet l5 leading to a circulating pump I6 which is connected by suitable piping through a cooler I! to the nozzle 8 in the spray chamber 1.

In operation, the separating tank II is filled with a hydrocarbon oil; the cooler I1 is turned on, and the pump I6 is set in motion so as to force cool oil to the nozzle 8, from which it falls recovering the condensed magnesium.

as a spray through the tower I back to the tank I I. If operation at reduced pressure is desired,

suction is applied to the gas outlets 9 and I2.

I 20 fitted with a discharge lock 2|.

A cool non-oxidizing gas, such as hydrogen is introduced into the vapor tube 3, through the I inlet nozzle 4. The magnesium-carbon monoxide vapor is then admitted into the vapor tube 3, where it passes through the gas nozzle 4, and is cooled sharply, and then passes immediately into the spray chamber I, where it is quenched by the oil spray and condensed. The uncondensed carbon monoxide and hydrogen escape through the outlet 9. The oil and condensed magnesium run into the separator II, where the metal settles out and may be withdrawn through the lock M; the oil is recirculated through the pump l6 and cooler l'l back to the spray nozzle 8. .As already explained, the rate of gas introduction through the nozzle 4 is controlled so that the magnesium-carbon monoxide mixture is chilled approximately to the temperature of incipient condensation, and the cooler I1 is adjusted to maintain the temperature of the oil being recirculated well below 650 C,

An alternative form of apparatus shown in Figure 2 also consists of a vapor delivery tube 3 provided with a gas nozzle 4. After the nozzle, the tube 3 leads to a condensing chamber l8 having an upper gas outlet I9 and a hopper bottom Mounted within the chamber l8 opposite the vapor tube 3 are a rotatable drum 22, which is equipped with adjustable cooling means (not shown), and a scraper 23 placed so that any scrapings removed from the drum fall into the hopper 20. In operation, the magnesium-carbon monoxide vapor mixture introduced into the inlet tube 3 is subjected to chilling by cool non-oxidizing gas injected through the nozzle 4, and then passes directly into contact with the drum 22, which is maintained at a temperature below650" C, and is rotated at a slow rate. The magnesium condenses on the drum 22 in solid form and then, as the drum revolves, is scraped into the hopper 20, from which it may be withdrawn.

It is to be understood that the foregoing description is illustrative only, and that the invention is co-extensive in scope with the following claims.

I claim: I

1. The method of condensing magnesium from the vapor phase which comprises injecting a relatively cool non-oxidizing gas into the said vapor in a proportion sufllcient to cause substantial cooling but insuilicient to chill the vapor to a temperature below that at which condensation of magnesium occurs at the existing pressure, immediately passing the cooled vapor into contact with non-gaseous condensing means maintained at a condensing temperature below 650 (2., and

2. The method of condensing magnesium from a vapor-phase admixture with carbon monoxide which is at a temperature above that at which any substantial reactionbetween magnesium and carbon monoxide occurs, which comprises injecting a relatively cool non-oxidizing gas into the said mixture in a proportion suflicient to cause substantial cooling but insuflicient to chill the mixture to a temperature below that at which condensation of magnesium occurs at the existing pressure, immediately passing the cooled vapor mixture into contact with non-gaseous condensing means maintained at a condensing temperature below 650 0., and recovering the condensed magnesium.

3. A process according to claim 2 in which the non'-gaseous condensing means is 'a'liquid'com" which is at a temperature above that at which densing medium supplied in a proportion sulficient to absorb the heat of condensation.

4. A process according to claim 2 in which the non-gaseous condensing means is a hydrocarbon oil. A

5. A process according to claim 2 in which the non-gaseous condensing means is a solid condensing surface.

6. A method according to claim 2 in which the non-gaseous condensing means is a shower of metal particles supplied in a quantity sufllcient to absorb the heat of condensation and cooling.

7. The method of condensing magnesium from a vapor-phase admixture with carbon monoxide,

any substantial reaction between magnesium and carbon monoxide occurs, which comprises injecting a relatively cool non-oxidizing gas into the said mixture in a proportion sufiicient to chill the mixture approximately to the temperature at which condensation of magnesium occurs at the existing pressure, but insuflicient to cause any substantial condensation, passing the-chilled vapor mixture into contact with non-gaseous conden sing means maintained at a condensing temperature below 650 C., and recovering the condensed magnesium.

THOMAS H. McCONICA, III..

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