US2456918A - Distillation of volatilizable metals - Google Patents

Description

Dec. 21, 1948. H. CHURCH i ADISTILIIATION oF voLATI-LIZABLE METAL Filed sept.' 5. 1945 H. R m TC N wm mA W o H Patented Dele. 21, 194s STATES GFFICE '1 l l 2,2:ia91s- 'l DISTILILATION "or voLA'iiLIZALEL'METALs;

Howard'Churchgwlios'.r Gatos; Calif.; assignorsto I The Pe-rmanente fMetals Gorproratiomaldand, Calif., a corporation of"Delaware Applicaton'septeinber 5, 1945",- SerialNo.` 614,5 21

rms--invenuonrennes1-tothe: production ofy Sincetlisreactionis reversible" it 'isnecessary to" cool 'then magnesium and carbon monoxide to a7 pointwliere they'are' stable in the presence of eachother? This coolingjor chillingoperation is-v rapidly' effected WithA the' aid" of Hlarge quantities" of an inertA chilling; medium, such as', natural gas; hydrogen; or` certain of' theF noble gases: However," even` when` good chillingj effi'-l ciency" ist achieved there isYI some reversion of tliiefsreaction` so-"that theA product recovered 'comi prises" aAv mass" of about fty percent metallic magnesium with the remainder magnesium oxide and carbon'in' thefratioof about Gte-40.` There are* also`l relatively" small amounts of carbides present; The-mate1ial'is finely divided andthe individual particlesy are for the most part less thank one micron= in" size: In theendustry this product isn usuallyv referred to as magnesium dust."

Thesrenementoffthis magnesiumv dust in order tof recover? solidE metallic magnesium' of high purityfis a difficult"problem'.` The dusts highly pyrophoric in air, apparently dueto thefcarbidsflpresent; andimust be handled' in an inert atmosphere" or b'e' Wet' down with hydrocarbon liquidi it. isnot' readily pelletedv without`V the use of tspecial, equipment; andl as; a` consequence it must'v liefliandled' withY considerable4 careA and precaution;A

The most widely usedv method for recovering solidi metalfrom-magnesium dustis `a batch. sublimation'A process' wherein pelletsi of magnesium dust; either.' inf. dryV form orw'etted with@ liquid hydrocarbons;areintroducedintofalretortwhich ist thereafter,- subjected toi ai vacuum and i' heated toxa temperature'. of about 1450 F. 'Ihe niag- Ireslurrx vapoi-'izese and 1 flows' out` ofi'. the'.I hot sec:

ber.: wher-edi?. may" beirecoveredv; asfs'olid metallic magnesium'. Although.n fair.: yields? can: -bevob-4 tained'"byythisy processdf; sutdcientlyt large retorts employed; it;v ist noti economic because if-of; the toV rstfrpurge the atmosphere: within denim.- (cms-sr);-

L the retort with inertfgas 2y l es;I thediilcultyof'-'c11avtt` ingrai suflicientlyfhigh vacuum' within the retort;l the '.sloWf rate'=off' heat transfer Within r they retort charge?l due 'f to': the 4poortA thermal conductivity; of

l the magnesiumn containingy charge, thel large capital investment? andthe high operatingr and maintenance costs"of"theapparatus' used.

Continuous processes for the. distillationf` of magnesium. have: never been. successful. Up?. to the -present'tlme the art'ha's not knotvnzanyfsuceA cessiully operated.` production'I scale continuous distillation.; process: This' has :beenA due fto yniucli the samedii'culties'fas are encounteredzin` the batclr process; particularly: in,;so fari asi theiheat transfer and dusti handling problems are con cerned; Eurthermore, the; continuousf distillationisystems :of the?. prior artzcannot lbeioperated att atmospheric; pressures because itis f necessary to go` tcry temperatures which.v are tooA high'cfor the materials ,ofi construction. Itgiszalso-unsatse factory to operate at vacuum or reducedi:pres. sure because of mechanical vdifiiculties in achieving; the" rdesiredn vacuum and A the'.v condensation of magnesiumiirtheesolidlstate.

Itfisamong the objects of the-present invent tionto' overcome-theabove difficulties: and. to provide a process for the'continuous distillation of i metallicy magnesium; which isIv economic: and which can' befperformed readily. on largeqscalet These andotherl objects willber apparent from the:y description of vthe invention which follows; According to: theiinvention, a method isrpros vided for the continuous distillation of'mage nesiumyrdust-r or :the- `like -Wherein i the magnesium dust' Iis,.introduced into aistream of ay hoty gas inert,tozthe'magnesium-1 .The dust is entrained Withinf the: hot: gasesiwhich vaporize thevv mage nesium; as;1 the: dust is: propelledl, through; the system. 'I'hewtemperature of thegasisnotA high enough to' reacta the :magnesiumv oxidei;l andL car.-i bonand they` remain in the.; solidiy state.` The oWing` mixturev of gas, vapors; and solids' is passedxtor. oneL l or more separators `Where .af sub= stantial. proportion of z the solids arearemoved.' 'Thereafterthe mixture of` vapors, gas, landany entrainedisolids, if theyrarepresent, are passed to. a-condensor andthe-magnesium-is recovered iny either: liquid' or solid,l form'. The inert gas isreadily separated for reuse or discard.

An apparatus which is particularly -usefulin carryilfig`A out ther process ofT this. invention?i is show-nir1 theI accompanying drawing entitled l Referring-,5to thezdrawngs, a horizontally diss posed elongated retortftypefurnace-Ill` isr pro coil I5 is adapted to carry an inert gas which is'.

introduced at a point I6 extending outside of the retort. y'At its upper end I1 the coil is`connected to ahorizontally disposed tube I8 preferably of similar material, which runs` the length of the retort. Located immediately beyond the conn'ec` tion I'I there is a connection I9,at which point the magnesium dust to be treated is introduced from tube I4. Tube I8 terminates at the end of theretort adjacent burner section I2 and discharges into aA cyclone separator 20.' f- A pipe 2I leading from the top of separator discharges into a settling chamber 2-2. Suitable means (not shown) are provided for the removal of the solids collected in the separator 20; Leading from the settling chamber 22 is pipe 23 which isprovided With a cooling jacket 24. 'The pipe 23 discharges intoa bag 'lter 25, preferably of Woven glass.

In' operation, hydrogenor` other inert gas, such as the noble gases, helium and argon, is introduced at I6 to the coil I5 located in the burner section II. The gas is heated to a' temperature in the neighborhood of 1600 F. while it is in the coil I5.; It then passes into pipe I8 and is mixed with magnesium dust entering at I9. The hot into pipe 2| and on into the collecting chamber 22 where partial condensation occurs. The remaining magnesium vapors are condensed inthe cooled pipe 23 and the gas ilovvs` on to the bag lter Where entrained' solids are readily separated. The gas maythereafter be discardedor reused in circuit. v

The system disclosed herein is adapted to operate at approximately 1600 F. and at atmospheric ,f

pressure. However, under any conditions the temperature of the carrier gas is maintained at a'rate so that for any given ratio'of gas to mage l vnesium vapor the gas remains unsaturated. Ad'- vantageously, operating under normal conditions, that is at atmospheric pressure and with gener-v ally available materials, the temperature ofthe system should lie in a range of from 1400 to 1900i F. Higher temperatures can be employed if more highly refractory materials are employedfin the apparatus. Lower temperatures can also be employed if greater quantities of carrier gas are used or if precautions are taken to seal the appal ratus from the atmosphere so that it is Ypossible to operate at reduced pressure.

, yAlthough a 'cyclone separator has been A1:iis closed as the mean'sforcarrying out the separation of the vapors and gases from the solidsl itis to be understoodthat-any other means'capable of Iperforming the separation operation may also be employed. In this connection it is to be noted that the process of this invention can be carried out in any suitable apparatus and is not intended to be limited to the embodiment disclosed herein.

There are several advantages to the process of this invention which may be apparent from the above description and which will now be pointed out.r .f r

According to the process it is possible to utilize a carrier gas for the materials to be treated which also serves as a heat transfer medium. This is a distinct advantageand eliminates many of the difficulties of previous schemes which have been proposed by the prior art. It also makes it possible to take advantage of the small particle size of the dust to obtain better heat transfer rates.

Other advantages include the ability to utilize generally available equipment which achieves considerable saving and the avoidance of the necessity for pelleting the magnesium dust which is an operation =requiringg fspecialI equipment.

Furthermorethe dust can be-employed 'immediately as it issuesfrom the furnace and-,is.vsepa rated from the chilling gas and carbonmonoxide. It isjunnecessary to treat it for the purposezpf decreasing its pyrophoric qualities `because-itv-remains in a closed system throughout. j f l It is possible by judicious operation of thecon'- densation step to control the physical state ofthe condensed product so asto meet 4the :requireyr ments for subsequent treatment ror uses, i. e., it may be recovered as a solid in the form of either large orv small particles as desired, or as ailiquid. Any carbides present as impurities in the original dust are removed by the vdistillation step since theyare unstable at the temperatures employed and break down to form carbon and magnesium Vapor. Furthermore, no problem is encountered from sodium formed in the vreduction step and it can even be recovered separatelyas a by-produ'ct vby fractional condensation. As a consequence,v

the product recovered by this process is ,consider ably less pyrophoric than the Original magnesium dust., In operations according to the processV1 ofthe invention it has been possible'to obtainl acon-v densate having as much as90 .per centmage nesium when using only one cyclone vseparating means. When employing additional.;separating means in series it is possible to ,achieve even better separation so that for certain uses-'the magnesium recovered can bre-fabricated directly, as by extrusion or the like. Where it is `desirable to use magnesium of higher purity vthan that obtained directly from this process, the confA densed product may be refined by melting-and iluxing, or batch sublimation, yor otherwise. Batch sublimation is not rineicient in this case because the high magnesium content .of the con-y densed product results in increased heat transfer during the vaporization step and increasedref coveries of condensed metal.`

Another significant advantage of'this inventtion is that the solids separatedfrom the vapors and gases comprise a mixture chieiiyot magnesium oxide and carbon which has several useful purposes, particularly in compounding-rubber. lThis process may be used inrecovering any readily volatilizable metals including sodium-and is not intended to be limited to the manufacture of metallicmagnesium,'although it is particularly advantageous in recovering the ilatter metal since several of the diiiiculties encountered with .mag-.i

.nesium are vnot encountered .withlall'othery readily volatilizable-metals. The proces'sis useful.' re' fining any such materials when they are of a particle size possible to be conveyed in suspension in a carrier gas.

What is claimed is:

1. In the method of rening a, mixture of a volatilizable metal and less volatile solid impurity, wherein the mixture is heated to a temperature suiicient to vaporize the meta1 but insuflicient to vaporize the impurity, and the metal vapor is separated from the unvaporized impurity, the improvement which comprises supplying at least the major portion of the heat of vaporization of the metal by means of a preheated inert gas yby adding the said mixture of metal and impurity in nely divided form to the preheated gas in proportions such that a suspension of the solids in the gas is formed in which the metal at thermal equilibrium exerts a substantial partial pressure, and causing a turbulent flow of the resulting suspension thereby rapidly vaporizing the metal from the suspended solids by virtue of the heat transferred from the preheated gas to the solids suspended therein, and separating the suspended solid impurity from the gaseous mixture of inert gas and metal vapor.

2. In the method of refining a mixture of a volatilizable metal and less volatile solid impurity, wherein the mixture is heated to a temperature sufficient to vaporize the metal but insuiflcient to vaporlze the impurity, and the metal Vapor is separated from the unvaporized impurity, the improvement which comprises supplying at least the major portion of the heat of vaporization of the metal by means of a preheated inert gas by adding the said mixture of metal and impurity in finely divided form to the preheated gas in proportions such that a suspension of the solids in the gas is formed in which the metal at thermal equilibrium exerts a substantial partial pressure under a total pressure of about one atmosphere, and causing a turbulent flow of the resulting suspension thereby rapidly vaporizing the metal from the suspended solids under to total pressure of about one atmosphere by virtue of the heat transferred'from the preheated gas to the solids suspended therein, and separating the suspended solid impurity from the gaseous mixture of inert gas and metal vapor.

3. The improvement of claim 2, wherein said less volatile impurity is composed largely of the oxide of the volatilizable metal and a. reducing agent capable of reducing the oxide to the metal at a high temperature, and the temperature of the mixture of inert gas and finely divided solids is well below temperatures at which substantial reduction of the oxide by the reducing agent oc curs but is sufficiently high to produce substantial vaporization of the metal.

4. The improvement of claim 2, wherein said metal is magnesium, said impurity is composed largely of magnesium oxide and carbon, and the inert gas is preheated to about 1400 to 1900 F.

5. The improvement of claim 2, wherein said gas is hydrogen.

6. The method of refining a solid mixture of volatilizable metal and less volatile impurity, which comprises establishing a cyclic ow of a gas which is inert with respect to the metal, heating the gas during the course of its flow to a temperature at which the metal exerts a substantial vapor pressure but below the temperatures of substantial vaporization of said impurity, adding the solid mixture of metal and impurity in nely divided form to the owing gas after it has -been thus heated so as to cause a co-current flow of hot gas and solids suspended therein, continuing turbulent flow of the solids in gas suspension for a sufcient length of time to eifect substantial heat transfer from the gas to the solids and to effect substantial Vaporization of the metal, separating unvaporized solids from the gaseous mixture of metal vapor and inert gas, then condensing metal vapor from the inert gas and recycling the inert gas.

HOWARD CHURCH.

REFERENCES CITED The following references are of record in the le oi this patent:

UNITED STATES PATENTS Number Name Date 1,943,601 Hansgirg Jan. 16, 1934 2,025,740 Hansgirg Dec. 31, 1935 2,160,969 Hansgirg June 6, 1939 2,393,704 Ogorzaly Jan. 29, 1946 2,398,443 Munday Apr, 16, 1946

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