US 3067025 A
Description (OCR text may contain errors)
Dec. 4, 1962 D. s. CHISHOLM CONTINUOUS PRODUCTION OF TITANIUM SPONGE Filed April 5, 1957 vi i l 52 i4 r LP! INVENTOR. 0009/06 62 C/nlsAo/m estates T This invention relates to the production of titanium metal from a titanium tetrahalide. More particularly it relates to a method and apparatus for the production of titanium sponge from the tetrahalide by the action of a reducing metal which is comminuted and at an advanced temperature when contacting the tetrahalide.
it is known to produce titanium sponge from a titanium tetrahalide in a batch process by reacting therewith a metal more electropositive than titanium, e.g., a reducing metal such as magnesium. Heretofore, titanium sponge thus produced has been extremely difficult to free from the reactor in which the reaction has taken place. It has usually been necessary to chip or drill the titanium from the reactor, or to collapse or destroy the reactor to free the titanium. An additional objection to such methods is that the titanium thus produced has been contaminated to an undesirable extent by the materials composing the contacting surfaces of the reactor. Furthermore, these methods have not been of a type which permitted continuous operation.
To overcome the difficulties associated with removing the titanium in a satisfactory state from the reactor and to provide a continuous process, it has been proposed to introduce the reducing metal, e.g., magnesium, in a molten state through a constricted opening which forms the molten metal into droplets or globules which fall into the boiling titanium tetrahalide therebelow to produce titanium granules at the bottom of the reactor. Attempts to introduce a molten reducing metal according to this proposal have created additional problems among which are repeated plugging of the necessarily constricted feed opening for the molten reducing metal and the fact that considerable quantities of the molten metal droplets fall through the titanium tetrahalide vapor above the boiling liquid tetrahalide and on through the titanium tetrahalide liquid without reacting therewith. In fact, attempts to employ a molten metal, e.g., magnesium, in this manner have often resulted in the reaction becoming almost entirely quenched.
There is a desideratum in the art of titanium production for a continuous process for producing titanium from its tetrahalides by a reducing metal wherein the resulting titanium and the by-product metal halide are readily removed from the reacting vessel relatively free from contaminants acquired from the contacting surfaces of the vessel.
An object of the invention is to provide a continuous process and apparatus for the production of titanium metal sponge by the action of a reducing metal such as an alkali or alkaline earth metal on a titanium tetrahalide which is made to exist in the vapor phase above the ignition temperature of the reducing metal therein and in the liquid phase above the boiling point of the titanium tetrahalide.
Another object of the invention is to provide a process of the foregoing character which is relatively free from vexing interruptions due to clogging of openings in the reacting vessel.
A further object is to provide a process which produces titanium which is relatively uncontaminated by the materials composing the con-tacting surfaces of the reactor and which is readily removable from the reactor.
3,067,025 Patented Dec. 4, 1962 duced to metallic titanium and the liquid sustains the reduction reaction until it is satisfactorily completed and then serves as a quence to prevent undesirable reactions, e.g., T i+ 3TiCl 4TiCl These and other objects are accomplished by the meth- 0d hereinafter described and particularly pointed out in the claims.
According to the invention, a comminuted solid reducing metal is introduced together with an inert gas into the upper part of a reaction chamber, provided with a' heating means, and containing a titanium tetrahalide vapor in the upper part of the chamber and the titanium tetrahalide in liquid form in the lower part of the chamber below the vapor. The comminuted reducing metal is; dropped through the heated titanium tetrahalide vapor into the titanium tetrahalide liquid. A comminuted al-- kali or alkaline earth metal, e.g., sodium, calcium, magnesium or calcium-magnesium alloy may be employed; as the reducing metal. Although TiBr or TiI may be; employed after first converting it into a liquid, the properties and availability of TlClq, make it the preferred titanium tetrahalide to employ, the preferred reducing; metal being magnesium.
The temperature of the titanium tetrahalide vapor usually employed is one sufiicient to heat the reducing: metal particles, e.g., magnesium, to a temperature above their ignition temperature in the vapor of the titanium tetrahalide as they fall therethrough. The ignition temperature is that temperature at which the reaction between the falling metallic particles and the tetrahalide vapor is sufliciently intense to cause the particles to glow. The ignition temperature of comminuted magnesium which contains not over about 5 percent of particles larger than 200 mesh (US. Bureau of Standards Sieve Series) while falling through TiCl vapor is between 450 and 550 C.
The titanium tetrahalide vapor is required to be heated by an exterior source to somewhat above the temperature necessary to initiate the reaction, i.e., above the ignition temperature of reducing metal particles. The rate of flow, the particle size, and the length of the fall of the reducing metal through the titanium tetrahalide vapor determine the temperature to which the tetrahalide vapor must be heated. The ignition temperature of the falling metal particles is manifested by their glowing brightly as they fall. After the reaction has begun, its highly exothermic character generates sufiicient heat to sustain the reaction thereafter. The solid particles of reducing metal do not become molten immediately upon entering the reaction chamber but remain discrete solid particles until they have fallen away from the feed opening. It is immaterial for the purposes of the invention whether or not they become molten later as they fall through the titanium tetrahalide vapor. It is preferable that the temperature in the vicinity of the feed opening be below the fusion temperature of the reducing metal employed, e.g., 651 C. for magnesium. However, due to the rate of fall, the rise in temperature of the particles required and the admission of inert gas enveloping the comminuted reducing metal as it enters. the reaction chamber, no difficulties are usually en-. countered in maintaining the particles in a non-molten state in the vicinity of their entrance. An ambient tem-' perature in the vicinity of the entrance of the reducing; metal particles of 900 to 1000 C. or even higher mayusually be tolerated. It is preferred, however, to provide a means for cooling the interior of the upper reaction chamber as 'by introducing liquid titanium tetrahalide at the top of the reactor so as to provide a cooling film of titanium tetrahalide on the interior. of the walls thereof.
The comminuted, reducing metal shouldpreferably be su'fiiciently fine to pass through a. number 200 mesh screen, although somewhat larger particles may be employed. As the particles of comminuted reducing metal such as an alkali or alkaline-earth metal fall through the heated titanium tetrahalide vapor, there is some reaction with the titanium tetrahalide vapor whereby titanium sponge and the by-product halide of the reducingmetal are formed.
It is thought that titanium sponge forms on the surface of the discrete reducing metal particles and comprises aifcoating or envelope of titanium sponge about each particle. As the partially reacted heated particles strike the liquid titanium tetrahalide, the reaction therewith becomes more intense. Heat is generated by the reaction vaporizingsome titanium tetrahalide immediately about the particle. The thus-vaporized titanium. tetrahalide appears to serve as a buoyant cushion to hold the particles of reacting reducing metal afioat until consumed in forming titanium sponge and the by-product halide.
When the reaction ceases, particles of mixed solid titanium sponge and the by-product halide settle and accumulate at the bottom of the titanium tetrahalide liquid.
Although not limited thereto, the invention will be described in reference to the drawing wherein TiCl is reduced by comminuted magnesium metal. The reaction may be represented by the equation:
Referring to the drawingthere is shown comminuted magnesium supply reservoir IO -haVing removable cover 11 thereon and hopper-shaped bottom 12. Leading from an opening provided in bottom 12 is connecting tube 13 opening into barrel'14 in which is screw 15 for advancing comminutedmagnesium into vertical feed tube 16 which is substantially centrally positionedin chamber 17 forming annular passageway 18a and gas-enveloping section-18b therebelow in chamber 17. Inert gas cylinder 21 is connected to gas line 19 leading into reservoir and to gas line '20 leading into annular passageway 138a]. Valves'55 and 56 control the passage of inert gasthrough lines 19 and 20, respectively. Sight glass 22 secured to the top of feed tube 16 provides a meansfor observing the action of inert gas and the comminuted magnesium in section 1812 of chamber 17.
Chamber 17 opens into vertically positioned-cylindrical upperreaction chamber 23 positioned in furnace setting 24 which is provided with gasburner 25 and exhaust outlet 26. Supply line 27 leading from titanium tetrachloride reservoir 57 opens into upper supply line 28 and lower supply line 29 containing valves 36 and 31, respectively. Supply line 28 empties into annular trough 32, secured substantially horizontally'to the inner surface of upper chamber 23 near the top thereof-and containing perforations in the bottom thereofadjacent to and directed toward said inner surface to permit the titanium tetrachloride, entering trough 32, to trickle down the inner-wall of chamber 23. Supply line 29*leads into lower reaction chamber 33 which comprises an enlarged section of upper chamber 23 and which contains liquid titanium tetrachloride. Tube 34 carries inert gas together with some unreacted titanium tetrachloride vapor 'upwardly and outwardly into condenser 35. Sediment trap 36 in the bottom of condenser 35 collect solid suspended impurities carried over with the titanium tetrachloride vapor. Line 37 returns the titanium tetrachloride liquefied by condenser 35toline 29. Outlet line 38, having control valve 39 therein, provides means for the inert gas to leave the system thus to provide a continuous atmosphere of inert gas in the system. The inert gas is removed by an evacuating means which may be connected to a compressing means for placing the gas under suificient pressure for reuse according to the invention.
Screw conveyor 40 operating in barrel 41 conveys reaction product accumulated in lower chamber 33, upwardly and out of the body of liquid titanium tetrachloride, and drops it into droptube 42. Line 43, containing valve 44, connects the upper portion of barrel 4-1 and lower chamber 3-3 above the level of liquid therein thus providing a means for equalizing pressure and preventing back pressure from developing in the upper end of barrel 41 or in droptube 42. V
Receiver 45 is clamped to droptube 4-2 by means of flanged joint 46. Valve 47 in the lower portion of droptube 42 and valve 48 in the neck of receiver 35 provide a means for controlling the passage of the reaction product into receiver 45 for the removal thereof.
Chamber 23. should be at least 8 to 16 feet long and preferably should not be less than 20 feet long to provide a suflicientheight for free fall of the cornminuted metal through the halide vapor. A convenient diameter is 2 to 3 feet. The other dimensions of the apparatus are not critical so long as they are adequate to maintain the required temperatures and provide a continuous supplyof reactants according to the invention.
Tube 28 and trough 32 are provided for introducing TiCl intothe top of reactor 23 so that the walls of reactor 23 can be cooled and also washed down to discourage any tendency for the reaction to occur along the walls of the upper reactor chamber.
The pressure in the system may be atmospheric but it is preferred to be a little above atmospheric pressure, e.g., a pressure sufficient to sustain a column of water a few inches above that of atmospheric pressure. Any pressure within that which the apparatus can withstand may be employed but the highest gauge pressure for practical purposes is about pounds and the pressure usually employed is from 2 to 5 pounds per square inch.
In practicing the invention by means of the apparatus shown in the drawing, an inert gas, e.g., argon or helium, is admitted to reservoir 10 through line 19 by opening valve 55 therein and is admitted to passageway 18a in chamber 17 through line 2.9 by opening valve 56 therein.
The temperature of chamber 23 is raised above the ignition temperature of the comminuted magnesium to r be employed, say about 500 C., by means of gas burner 15, operating in barrel 14, to feed tube 16 from whence it falls through section 18b into reaction chamber 23. The inert gas entering passageway 18a enswathes or forms a generally gaseous envelope about the mass of particles 50 as they fall through 1817.
i The mass of comminuted magnesium thus enswatched with inert gas, enters and falls through chamber 23 containing titanium tetrahalide vapor which is heated to a temperature sufi iciently high to heat the magnesium particles above their ignition temperature by means of furnace 7. The so-heated magnesium particles react with the titanium tetrachloride vapor while they fall through it into the liquid titanium tetrachloride 51 in chamber 33 where they float and continue to react. The reaction between the magnesium and the titanium tetrachloride thereafter generates ample heat to make the reaction selfsustaining. T iCl is caused to flow through line 28 into trough 32 where it thereafter flows out through the perforations in trough 32 and trickles down the walls of reaction chamber 23. The TiCl thereby both cools the walls of chamber 23 and washes them down to prevent substantially any reaction along the walls. The temperature of the liquid TiCL; in chamber 33 is maintained above its boiling temperature by regulating control valve 31 in lower supply line 29.
The reacting magnesium particles maintain their discrete character although their temperature is likely above their fusion temperature when they strike the liquid titanium halide 51. it is thought that the relatively high intensity of the reaction at this point, being exothermic in nature, generates sufiicient heat to vaporize the liquid titanium tetrachloride immediately adjacent to each magnesium particle and thereby produces a cushion of vapor which supports each particle on or near the surface of the liquid until the reaction is substantially complete. Whether or not this theory is correct, particles of magnesium while they react do not coalesce to the extent that the reaction is quenched or sink too rapidly to prevent the method of the invention from progressing smoothly.
Reaction product 52, composed of particles of titanium sponge and magnesium chloride particles, falls to the bottom of chamber 33 where it may be removed by known methods. A particularly suitable method is to convey it upwardly and outwardly as shown by conveyor screw 40 to the opening in the upper end of drop tube 42. Due to the clearance between screw 40 and barrel 41, TiCl 51 does not rise above the level in chamber 33 and is left behind. Reaction product 52 drops into droptube 42. When receiver 45 is clamped into position, as shown, valves 47 and 48 are opened so product 52 may pass directly into receiver 45. Upon closing valves 47 and 48, receiver 42 may be disengaged and removed for emptying reaction product 52 or be replaced by an evacuated similar vessel as desired Without admission of air into any part of the apparatus including receiver 45 while thus disengaged.
In place of receiver 45 a continuous means of removing reaction product 52 may be employed whereby the product is conveyed directly to a purification means.
The titanium sponge is thereafter separated from the magnesium halide by known processes of removing halide salts including vacuum distillation or leaching with an aqueous-acidic solution.
The method of producing titanium sponge according to the invention otters a number of advantages among which are: a continuous operation relatively free from irregularities due to clogging of constricted openings; a particularly valuable economic process because the inert gas, and the unreacted titanium tetrahalide which is carried along with the inert gas, may be conveniently recycled back into the process; the process of the invention is easily controlled; the liquid titanium halide inherently provides a means for completing the reaction of reducing metal with the halide and thereafter quenching undesirable reactions involving the reduced titanium; the temperatures are not diflicult to maintain; the product is produced free from adhesion to the reacting vessel; and the process provides easy removal of the reaction product from which the titanium sponge can be readily separated.
Although the process of the invention has been det3 scribed more fully for the use of TiCl and comminuted magnesium metal, it is understood that titanium tetrabromide and tetraiodide may be used, and that other metals than magnesium which are known chemically to reduce titanium tetrahalides may be employed according to the invention.
Having described the invention, what is claimed and desired to be protected by Letters Patent is:
1. The process of producing titanium sponge from a titanium tetrahalide by reacting therewith a reducing metal selected from the class consisting of alkali and alkaline earth metals which comprises boiling a liquid titanium tetrahalide so as to provide a vapor phase in contact with the liquid phase, heating said vapor phase sufficiently to raise the temperature of discrete particles of the reducing metal above their ignition temperature when dropped therethrough, introducing the comminuted reducing metal in the solid state, and dropping the discrete particles of the reducing metal through said vapor phase into the liquid titanium tetrahalide to form a reaction product mixture of titanium sponge and the halide of the reducing metal.
2. The process of producing titanium sponge which consists of confining a titanium tetrahalide selected from the class consisting of titanium tetrabromide and titanium tetrachloride, maintaining said tetrahalide in an ebullient state to maintain the tetrahalide in a vapor phase superimposed on a liquid phase, introducing comminuted solid magnesium metal having a particle size not greater than about 200 mesh in a pressurized inert gas into said vapor phase, passing said comminuted magnesium metal downwardly therethrough while heating said vapor sufliciently high to maintain the temperature of said particulate magnesium, while being passed therethrough, at a temperature of between 450 and 550 C., to cause said particulate magnesium to be ignited by surface reaction with the titanium tetrahalide vapor while being passed therethrough, and immersing the thus ignited particles in said liquid phase to complete substantially the reaction of the titanium tetrahalide and particulate magnesium to yield a reaction product of titanium sponge and magnesium halide, and separating the reaction mixture from a substantial portion of liquid titanium tetrahalide entrained therein by elevating the reaction mixture, and allowing the tetrahalide to drain therefrom.
References Cited in the file of this patent UNITED STATES PATENTS 2,567,838 Blue Sept. 11, 1951 2,607,674 Winter Aug. 19, 1952 2,621,121 Winter Dec. 9, 1952 2,708,158 Smith May 10, 1955 2,760,858 Findlay et al. Aug. 28, 1956 2,763,542 Winter Sept. 18, 1956 FOREIGN PATENTS 1,088,006 France Sept. 1, 1954