US2251906A

US2251906A - Condensation of magnesium vapor

Info

Publication number: US2251906A
Application number: US316199A
Authority: US
Inventors: Joseph D Hanawalt
Original assignee: Dow Chemical Co
Current assignee: Dow Chemical Co
Priority date: 1940-01-29
Filing date: 1940-01-29
Publication date: 1941-08-12
Anticipated expiration: 1958-08-12

Description

Aug. 12, 1941. J. D. HANAWALT.

CONDENSATION OF MAGNESIUM VAPOR Filed Jan. 29, 1940 r/ 0 Z m 2 fi T 5 H j W a ODD DDDDQ" m K {W 3% 1w 5 A e w n, v r? Occcoooc w ATTORNEYS Patented Aug. 12, 1941 CONDENSATION 0F MAGNESIUM VAPOR Joseph- D. Hanawalt, Midiand, Michr, assignor to The Dow Chemical Company, Mi

dhnd, Mich,

a corporation of Michigan Application January 29, 1940, Serial No. 316,199

SCIaims.

The invention relates to an improved method of condensing magnesium vapor.

The condensation of magnesium vapor to recover the metal substantially all in liquid form involves a number of serious practical diiiiculties,

all resulting from the fact that liquid magnesium dust, even if collected, cannot satisfactorily be melted down, but must be converted to massive magnesium by expensive methods.

An object of the present invention is to provide an improved method of condensing magnesium vapor. Another object isto provide a method in which the metal is substantially all converted into liquid form, even though the vapor is supplied under such conditions that the vapor pressure of the condensed liquid magnesium is an appreciable fraction of the partial pressure of the magnesium vapor.

According to the invention, magnesium vapor to be condensed is passed successively into two condensing zones, which are maintained at temperatures respectively above and below the melting point of magnesium. In the first zone most of the vapor is condensed to liquid magnesium, and in the second zone the remaining vapor is condensed to solid magnesium, usually in powder form. All the magnesium condensed is recoverable. If desired, condensate from the second zone may be returned into contact with the liquid condensate in the first zone where it melts and coalesces with the main body of condensed magnesium. In this way, substantially all the vapor condensed in both zones is finally obtained in the liquid state. i

The invention may be explained in detail with reference to the accompanying drawing, in

which:

Figure l is a vertic one form of appar view, partly in section, of adapted to carrying out th process of the invention; and

Figure 2 is a similar view of another form of apparatus.

The magnesium condenser. shown in Figure 1 consists of a vertical elongated metal cylinder ii provided with a vapor inlet l2 near its lower end and terminated at the bottom by a closed reservoir it, which may be heated by an electric resistance element i4, and from which liquid metal can be withdrawn through double valves It and it with an intermediate receiver ii. The apparatus is closed at the top by a cover ll provided with a gas outlet is. The condenser ii is divided into a lower zone A and an upper zone B which are cooled by radiation, and may be heated, if desired, by independent electric re- In operation, the reservoir i3 and the lower condensing zone A are raised to a temperature slightly above the melting point of magnesium by passing electric currents of suitable magnitime through their respective resistance windings i4 and 20. -A stream oi magnesium vapor is then introduced through the inlet i2. Most of the vapor is condensed in'the lower zone A to a liquid metal, which flows down the walls of the condenser into the reservoir I3. vapor rises into the upper cooler condensing zone B where it deposits on the walls as a fine duct, some of which falls back into the pool of molten magnesium in the reservoir I3. Much of the magnesium dust being condensed clings to the wall of the condensing zone B, forming a deposit which increases in thickness and gradually lowers the rate of condensation in the zone. The deposit may be removed from time to time as necessary by passing electric current through the upper resistance winding 2i, thus heating the walls of the zone B sufliciently to permit melting of the dust particles nearest the wall, causing the solid metal deposit to slide down the condenser into the reservoir i3. The dust, on reaching the reservoir fuses and coalesees satisiactorily with the main body of molten metal. Substantially all the magnesium vapor entering the condenser is recovered in liquid form, and may be tapped oii as desired through the double valves i5 and it. Any fixed gases present in the entering magnesium vapor escape through th upper outlet is, to which suction may be ap plied ii vacuum operation is desired.

In an alternative form of the apparatus shown in Figure 2, the magnesium dust depositing on the wall of the upper condensing zone B is continuously removed from the wall by means of a scraper 23 secured to a reciprocable shaft 24 The remainin mounted through the cover i8, and falls into the reservoir i3. In this case, an upper heating element adapted to dislodge the condensed powder is unnecessary.

The process of the invention may advantageously be applied to the condensation of magnesium vapor at any pressure, with or without the presence of accompanying gases such as hydrogen, helium, nitrogen, carbon monoxide, or hydrocarbon vapor. such mixtures are formed in the production of magnesium by thermal reduction processes, and in the purification of magnesium metal by distillation. The new method is especially useful, however, when the magnesium vapor is supplied under such conditions of temperature, pressure, or dilution that the vapor pressure of the liquid magnesium in the condenser, even at its solidification temperature, is an appreciable fraction, say 3 per cent or more,

of the pressure or partial pressure of magnesium in the vapor or vapor mixture to be condensed. It is under these conditions, especially when a vapor mixture is supplied at an absolute pressure below 100 mm. of mercury, that dust formation lsmost serious.

In practice the lower or liquid condensing zone A is maintained at any suitable condensing temperature above the melting point of magnesium (650 (3.), usually in the range 660 C. to 750 C.

The upper or solid condensing zone Bis held preferably at a temperature suificiently below the freezing point of -magnesium that the vapor pressure of the solid condensed metal is negligible, temperatures of 50 C. to 500 C. being usual, and below 300 C. preferable.

It is not essential to the invention in the broadest form that the solid condensed magnesium dust be combined with the liquid condensate. Even when the two portions are separately withdrawn from the condenser, the recovery of magneslum is still higher than that attained in ordinary condensers. However, return of the solid dust to the liquid condense e is a very great advantage, since it permits recovery of substantially all of the condensate in the liquid state.

It is to be understood that the foregoing descrlption is illustrative rather than strictly limitative, and that the invention is co-extensive in scope with the following claims.

I claim as my invention:

1. A method of condensing magnesium vapor which comprises passing the vapor successively into two condensation zones maintained at condensation temperatures respectively above and below the melting temperature of magnesium, whereby the major portion of the vapor is condensed in the first zone directly to a liquid and the remaining vapor is condensed in the second zone as a solid, and combining the condensate from the second zone with that formed in the first zone, whereby substantially all the magnesium condensed is recovered in the liquid state.

2. In a method of condensing magnesium vapor wherein the vapor is supplied under such conditions oi temperature and pressure that the vapor pressure of the condensed liquid magnesium formed in the process is an appreciable fraction "of the partial pressure of the magnesium vapor to be condensed, the steps which comprise passing the vapor successively into two condencation zones, the first being maintained at a condensing temperature above the melting temperature of magnesium and the second maintained at a temperature such that the vapor pressure of magnesium at that temperature is negligible, and combining the condensate from the second zone with that formed in the first zone, whereby substantially all the magnesium condensed is recovered in the liquid state.

3. In a method of condensing magnesium vapor from admixture with fixed gases, the mixture being supplied under such conditions of temperature and pressure that the vapor pressure of the condensed liquid magnesium formed in the procass is an appreciable fraction of the partial pressure of the magnesium vapor to be condensed, the steps which comprise passing the vapor successively into two condensation zones, the first being maintained at a condensing temperature above the melting temperature or magnesium,

and the second maintained at a temperature such that the vapor pressure of magnesium at that temperature is negligible, and combining the condensate from the second zone with that formed in the first zone, whereby substantially all the magnesium condensed is recovered in the liquid s to.

4. A method of condensing magnesium vapor from admixture with fixed gases, the mixture being supplied at an absolute pressure below 100 mm. of mercury, which comprises passing the mixture successively into two condensation Zones.

the first being maintained at a temperature between about 660 C. and about 750 C., and the second at a temperature between about 50 C. and about 500 0., and combining the condensate from the second zone with that formed in the first zone, whereby substantially all the magnesium condensed is recovered in the liquid state.

5. In a method of condensing magnesium vapor, the steps which comprise passing the vapor successively into two condensation zones, the first being maintained at a temperature between about 660 and about 750 C. and the second at a temperature between about 50 and about 500 C.,

whereby the major portion of the vapor is condensed in the first zone directly to a liquid and the remaining vapor is condensed in the second zone as a solid, and combining the condensate from the second zone with that from the first zone, whereby substantially all of the magnesium condensed is recovered in the liquid state.

JOSEPH D. HANAWALT.