US2722510A - Process of preparing alkali metal-titanium fluoride - Google Patents

Description

, tioned copending application.

that his in a frozen state.

United States Patent O M PROCESS OF PREPARING ALKALI METAL-TITANIUM FLUORIDE James C. Schaefer, Parma, Ohio, assignor to Republic Steel Corporation, Cleveland, Ohio, a corporation of New Jersey No Drawing. Application April 28, 1954, Serial No. 426,278

Claims. (Cl. 204-64) The present invention relates to a process of preparing an alkali metal-titanium fluoride, and more particularly for preparing either sodium-titanium fluoride (NazTiFs) or potassium-titanium fluoride (KzTiFe). The present process is further adapted to prepare either of these alkali metal fluorides in admixture with an alkali metal chloride.

The alkali metal-titanium fluorides above referred to are both known to the art. The methods heretofore vknown for preparing these compounds are, however,

with an alkali metal chloride, is useful and usable when in a fused state as the electrolyte for a cell for the deposition of metallic titanium at the cathode due to electrolytic action. The provision of such a cell andthe process of obtaining metallic titanium therein is no part of the present invention and is embodied in a copending application Serial No. 448,473, filed August 9, 1954.

I Summarizing the present invention, it comprises starting with titanium tetrachloride (TiCl4) as a source of .titanium and reacting this material with the desired alkali metal fluoride according to the equation:

wherein alk means an alkali metal which is either sodium or potassium, when making the pure alkali metal titanium fluoride, or according to the equation:

TiCl +6 alkF-l-(x) alkCl= alkzTiFs+(4+x alkCl 2 when making the admixture of alkali metal-titanium fluoride and alkali metal chloride. It may be explained that 'the quantity x is so chosen that the resultant mixture of 'alkzTiFs+(4+x) alkCl is of such composition as to be especially suitable for use as an electrolyte in an electrolytic process, which is described in my aforemen- In such a composition, the vsalts are present essentially in the weight ratio of 5.0 parts KzTiFs to 17.6 parts KCl. In either event, the

titanium tetrachloride, which is highly hygroscopic and tends to hydrolyze in the presence of atmospheric water vapor to form HCl and a white powder of titanium hydroxide, is preferably brought to such a low temperature This occurs atand below about 30 C. The frozen titanium tetrachloride is then put into an aqueous solution of the alkali metal fluoride (when making the alkali metal-titanium chloride alone) or an aqueous solution of the alkali metal fluoride 2,722,510 Patented Nov. 1, 1955 aforesaid). In either case, there must be at least the stoichiometric proportion of the alkali metal fluoride in accordance with the respectively pertinent one of the equations given above.

When making the pure alkali metal-titanium fluoride (not the admixture), the amount of water used in making up the aqueous solution should be only about enough to keep in solution all the alkali metal chloride which is present at the termination of the reaction. When making the admixture, the amount of water used is determined only by the amount required to dissolve the reactant fluoride. The water is evaporated from all the material remaining at the completion of the reaction and all the salts are crystallized together, so that it is not even necessary to retain all the alkali metal chloride in solution. Preferably, the amount of water initially present is minimized for reasons which will appear hereinafter.

Considering now the details of the present process, there will be discussed first the several ingredient materials.

The first of these ingredient materials is titanium tetrachloride (TiCl4). This material is a known chemical compound which is a liquid at ordinary temperatures. Its freezing point is 30 C. and its boiling point at atmospheric pressure is 136.4 C. It is a liquid vesicant. Liquid TiCLl fumes strongly in air due to an hydrolysis reaction with the moisture in the air, forming titanium hydroxide and gaseous hydrogen chloride.

Titanium tetrachloride may be formed, for example, by reacting titanium dioxide (TiOz) with carbon and chlorine in a furnace. The process of preparation of titanium tetrachloride in this way is known to the prior art and forms no necessary part of the present invention. It may also be prepared by the chlorination of ilmenite ore (FeTiOa) yielding titanium tetrachloride (TiClt), ferric chloride (FeCls) and CO2. Since FeCla condenses at about 315 C., it may be easily separated from TiCl4, which condenses at about 136 C.

While the process of the present invention, i. e. the reaction between 'TiCl4 and an alkali metal fluoride is carried out in accordance with the present invention by first freezing the TiCl4, the reaction will take place to some extent without resorting to this freezing step. However, when the reaction is so carried out, the volatile and hydrolyzable character of the TiCl4 cause such loss of this material by volatilization and/ or decomposition that it is uneconomical as well as being highly objectionable from the point of view of any persons in the vicinity.

plus alkali metal chloride (when making the admixture Another reason for carrying on this reaction with the TiCl4 frozen is so as to provide a predetermined and usually substantially stoichiometric proportions of the ingredient materials required for the reaction. In the event that the freezing step were not resorted to, the loss of T iCl4 might well be so great that the desired proportion of the several ingredients would not be had and the resulting 'product either lower in amount or indeterminate as to purity.

The present invention, therefore, is limited to the freezing of the TiCl4 prior to reacting it with the alkali metal fluoride, so as to avoid the loss of the titanium compound by volatilization and also so assubstantially to prevent fuming thereof with accompanying discomfort for persons in the vicinity.

The other ingredient entering into the reaction is the aqueous solution of alkali metal fluoride, or a mixture of this fluoride with one or more of the alkali metal chlorides. In respect to this ingredient per se, the only variable to be considered in accordance with the present invention is the concentration of the aqueous solution, or from another point of view, the amount of water to be present. In general, the amount of water to be used in the present case should be substantially a minirnum,-a-s-the efliciene'y of the process is progressively less as the amo nt of W r is increased over such minimum. There is, however, no sharp line of demarcation on one side of which the process is wholly inoperative, while it is operative on the other side; but the increase in the amount of water over the aforesaid minimum progressively decreases the efficiency of the process, for reasons which will now be set forth.

When the process is carried on to form pure alkali metal-titanium fluoride (as distinguished from the mixture thereof with alkali metal chloride), it is necessary to separate the alkali metal-titanium fluoride from the other materials present in the system at the termination of the reaction. This is effected in accordance with the present process due to the relatively lower solubility of the double fiuoridethan the chloride, which is present as a result of the reaction and/or that resulting from the reaction plus any alkali metal chloride initially present in the solution. Thus,

in order, to effect this separation, it is necessary that there be sufficient water to maintain in solution all the alkali metal chloride present in the system at the end of the reaction, whether that chloride is present as a result of the reaction and as a product thereof, or whether it is present due to being present initially and being unchanged throughout the reaction, or both. This provides or establishes the minimum amount of water when the substantially pure double salt is to be made as aforesaid.

The reasons for minimizing the amount of water are, first, that the alkali metal-titanium fluorides are both somewhat soluble, even though they are, in practice, in accordance with the present invention, thrown out of solution at the termination of the reaction. The solubility of potassium-titanium fluoride (K2TiFs) at 2022 C. is about 1.3 grams per hundred cc. of saturated solution. The corresponding solubility of sodium-titanium fluoride (NaaTiFs) at 20-22 C. is about 6.5 grams per hundred cc. of saturated solution. From the above it will be obvious that as the amount of water is increased, a correspondingly increasing amount of the double salt to be produced is lost in the solution and cannot easily be recovered due to the simultaneous presence in the solution of the alkali metal chloride formed as a product of the reaction.

Asecond and independent reason for minimizing the amount of water is if too much water is present, the double salt to be formed tends to hydrolyze therein, producing an hydroxide of titanium.

A further reason particularly applicable to the specific process, wherein it is desired to make the mixture of alkali metal-titanium fluoride and one or more of the alkali metal chlorides, is that the more water present, the more must be evaporated in order to bring the slurry prescut at the termination of the reaction down to the condition of a substantially anhydrous mixture of salts. Even here, it will be seen that an amount of water somewhat in excess of the minimum is not narrowly critical, but rather presents a condition which is progressively more undesirable as the amount of water is progressively increased above the The present invention, therefore, is intended to cover the use of the minimum amount of water as herein defined and also a reasonable margin greater than and approaching this minimum.

The next factor to be considered is the temperature for the reaction and the reactants.

The titanium tetrachloride should be frozen as aforesaid into a solid state. This may be conveniently effected, for example, by putting the titanium tetrachloride in'liquid form into a vessel, for example a plastic container or one made of rubber or similar material, then abstracting suflicient heat therefrom so as to freeze it either by the use of Dry Ice surrounding the container or by the use of conventional refrigeration means and methods. .On a

' labora ory scal Dry Ice serves admirably for this purpose and has een so used. The cooling of the titanium tetrachloride substantially below its freezing point is not at all critical and merely serves further to slow down the rate of reaction according as the reactants are introduced to the presence of each and in a cooler and cooler state.

The aqueous solution of the other one or two ingredients as aforesaid is preferably brought to a temperature not higher than room temperature, and, from a particularly preferred point of view, to about 10 C. Here again, the exact temperature of the aqueous solution is not narrowly critical, except that the temperature of a given amount of solvent shall be high enough to keep the reactant fluoride and/or chlorides in solution. As the temperature of the reacting materials, or either of them, is raised up to or beyond room temperature, the tendency for the reaction to proceed too fast is increased. It has been found that when the aqueous solution is brought to about 10 C. and when the TiCLr is frozen as aforesaid, the reaction will take place with amounts as hereinafter given in the particular examples in about one minute and with a desirable minimum of bumping. The reaction itself is exothermic in character; so that in order to keep it under desired control, it is usually preferred that the ingredient materials shall be introduced into the presence of each other in a relatively cool state. It has further been found that the expedient of freezing the TiCl-t into a single solid block reduces the surface of such material available for reaction with the dissolved alkali metal fluoride, and hence controls the rate of reaction from this point of view. With the exception of the principles above given, temperature is not a critical factor in the reaction.

The steps taken following the reaction per se differ in accordance with the particularly desired products. When the product desired is substantially pure alkali metal-titanium fluoride, this material is separated from the alkali metal chloride in the solution due to its relatively lower solubility. This results in a major part of the alkali metal-titanium fluoride being thrown out of solution as a precipitate (the total produced, less, of course, the amount thereof required to saturate the solution present). The precipitate may then be separated from the supernatant liquor by decantation or filtration. Either step may be resorted to. In washing the precipitate, it is usually preferred to use several small amounts of water, minimizing the amount in each instance, so as not to lose too much of the desired product by solution in the wash water. In practice, the wash water itself may be used to make up a new batch of solution for the next succeeding batch operation as will be obvious to those skilled in the art, thus minimizing the losses of the desired product material in this way.

When the double salt of titanium is to be recovered in admixture with alkali metal chloride, the slurry, including the precipitate and the mother liquor, is not separated, but rather is evaporated to dryness and then is further heated at a temperature suflicient to remove the water of hydration. It has been found that a temperature of about -120 C. is quite satisfactory for this purpose.

When the process is operated to form an admixture of salts, it is unnecessary that the alkali metal of the alkali metal-titanium fluoride to be formed be the same as the alkali chloride initially present in the salt solution in addition to the alkali metal fluoride required to form the double salt with the titanium. Thus, for example, it would be possible and is contemplated as one embodiment of the invention that titanium tetrachloride (TiClt) may be reacted with an aqueous solution of potassium fluoride (KF) with which is also dissolved (x) NaCl. Such a composition would be considerably cheaper than using solely KCl as the admixed chloride. By the same token, it is contempla ed to make a salt mix ure of NaaTiFs-i- (rt-+4) KCl.

The process of the present invention is f rther illustrated by the following examples.

. v,: E am l I This example illustrates thepreparation of relatively pure potassium-titanium fluoride (KzTiFs).

400 grams or 229 ml. of TiCl4 were cooled with Dry Ice to a temperature somewhat lower'than -30 C. causing the solidification thereof into a solid block. 728 grams of KF (or when KF-2H2O was used, then 1180 grams thereof) was dissolved in 3 liters of water. The resulting solution was cooledto about C. The frozen block of TiCl4 was placed in the bottom of the reactor containing the KF solution and held there (it would float otherwise) until the reaction was completed, which took about one minute. The resultant slurry contained about 500 grams of KzTiFs andabout 621 grams KCl. The precipitate of KaTiFs was allowed to settle and the supernatant liquor was decanted. Water was added suflicient only to form-a slurry, which was thoroughly agitated and the precipitate again allowed to settle, the supernatant liquor being decanted. This washing was repeated two or more times and then the KzTiFs was filtered and dried.

Example II This example illustrates the making of a mixed salt material containing KzTiFs-I- (x) KCl.

400 grams of TiCl4 was frozen into a solid block as in Example I. This solid block was then added to 5 liters of an aqueous solution containing 111 grams per liter KCl and 146 grams per liter KF, the aqueous solution being cooled to about 10 C. prior to introducing the frozen 1 This example illustrates the making of pure sodiumtitanium fluoride (NazTiFs) corresponding to the product of Example I. In accordance with this example, 400

grams of TiCl4 were first cooled to a temperature somewhat lower than C. to cause the freezing thereof into a solid block. The frozen TiCl4 was held in the bottom of a reaction vessel containing an aqueous solution of 532 grams of sodium fluoride (NaF) dissolved in 10 kilograms of water. The solution was initially maintained at a temperature of 23 C. Based upon complete reaction which is substantially attained in practice, there was produced 494 grams of sodium chloride (NaCl) and 438 grams of sodium-titanium fluoride (NazTiFs). The temperature of the solution at the completion of the reaction was 39 C. This solution was reduced by evaporation to a volume of approximately 3 liters, cooled and the precipitate of NazTiFs allowed to settle, after which the supernatant liquid was decanted. The remaining precipitate was washed and dried in the manner described in Example I. The amount of chloride-free NazTiFs was 370 grams, indicating a yield of 84%. The recovery in this case is lower than in Example I as a result of the greater solubility of sodium-titanium fluoride as aforesaid.

It is noted that in this connection the solution volume and the temperature are both substantially greater than those values respectively given in connection with Example I. This was found to be necessary in order to cause complete solution of the required amount of sodium fluoride (NaF). Either a smaller amount of Water or a lower temperature would have caused some of the NaF to crystallize or would have failed to dissolve it, as the case might be.

It is reasonably assured from the foregoing that the production of the mixed salt, i. e. NazTiFs plus a chloride of an alkali'metal (either-sodium oi potassium ems rideor a mixture of both) would present no difficulties in'viewof the data found in tests actually'made and set forth hereinabove in Examples II and III.

While there is herein disclosed in considerabledetail the process of making relatively pure alkali "metal-titan nium fluorides alone or admixed with either one or both aikalimetal chlorides, and certain limitations on the process and the requirements thereof have. been set out in some detail, further modifications will occur to those skilled in the art from the foregoing. I do not wish tobe limited, therefore, except by the scope of the appended claims, which are'to' beconstrued validly as broadly as the state of the art permits.

I claim: I

1. The process of preparing an alkali metal-titanium fluoride according to the. equation:

TiCl4+6 alkF=alk2TiFe+4 alkCl wherein alk is an alkali metal selected from the group consisting of potassium and sodium, comprising the steps of cooling a predetermined amount of TiCl4 to bring it to a solid frozen state, introducing the frozen TiCl4 into an aqueous solution of an alkali metal fluoride, the alkali metal of which is selected from the group consisting of potassium and sodium, and in which there is at least suificient of said alkali metal fluoride to be stoichiometrically equivalent to said predetermined amount of TiCl4 in accordance with the equation above.

2. The process in accordance with claim 1, in which said alkali metal is potassium.

3. The process in accordance with claim 1, in which said alkali metal is sodium.

4. The process in accordance with claim 1, in which a the frozen body of TiCl4 is positively held beneath the surface of said aqueous solution substantially throughout the reaction aforesaid.

5. The process of preparing an alkali metal-titanium fluoride according to the equation:

wherein alk is an alkli metal selected from the group consisting of potassium and sodium, comprising the steps of cooling at predetermined amount of TiCl4 to bring it to a solid frozen state, introducing the frozen TiCl4 into an aqueous solution of an alkali metal fluoride, the alkali metal of which is selected from the group consisting of potassium and sodium, in which there is at least sufficient of said alkali metal fluoride to be stoichiometrically equivalent to said predetermined amount of TiCl4 in accordance with the equation above, and in which aqueous solution there is only about enough water to keep in solution all the alkali metal chloride present at the completion of the reaction.

6. The process in accordance with claim 5 particularly for the preparation of separated alkali metaltitanium fluoride, comprising the additional steps of filtering the precipitate of alkali metal-titanium fluoride from the supernatant liquor following the reaction aforesaid, and drying said precipitate.

7. The process in accordance with claim 5 particularly for the preparation of separated and purified alkali metal-titanium fluoride, comprising the additional steps of separating and washing the precipitate of alkali metaltitanium fluoride by repeated settling and decantation of the supernatant liquor, and washing with small amounts of water, followed by drying the separated and washed precipitate of alkali metal-titanium fluoride.

8. The process in accordance with claim 5 for making KzTiFe, wherein TiCh is first frozen by bringing it to a temperature at least as low as -30 C., wherein the frozen TiCl4 is positively held beneath the surface of said aqueous solution throughout the reaction, and wherein the material supplied to the reaction is supplied in the proportion of 400 grams TiCl4 to 728 grams of KF (calculated as such), dissolved in about 3 liters of water, and wherein said \aqueousflsolution is cooled to about 10 C. prior tolthe introduction thereinto of the frozen Tick.

9. The process .of preparing an alkali metal-titanium fluoride mixed with the corresponding alkali chloride, according to the equation:

wherein alk in each instance is an alkali metal selected from the group consisting of potassium and sodium, comprising the steps of cooling ,a predetermined amount of TiCl4 to bring it to a solid frozen state, introducing the frozen TiCl4 into an aqueous solution of an alkali metal fluoride mixed with an alkali metal chloride, saidlalkali metal in each instance being selected from the group consisting of potassium and sodium, and in which there is at least sufiicient of said alkali metal fluoride to be stoichiometrically equivalent to said predetermined amount of TiCl4 in accordance with the equation above.

1'0. The process inaccordance with claim 9 for making KzTiFs mixed (x') K01, in which the ingredients bnonght togethm in the reaction are used in the propomion of 400 grams TiCh to 5 liters of said aqueous solution, in which aqueous vsolution there is 111 grams per liter of KCl and 146 grams per liter of KF, andin which said aqueous solution is cooled to about 10 'C. prior to the introduction of the frozen TiCli thereinto.

References Citedinthe file of this patent UNITED STATES PATENTS Kawecki et a1. Sept. 18, 1951

Claims (1)

1. THE PROCESS OF PREPARING AN ALKALI METAL-TITANIUM FLUORIDE ACCORDING TO THE EQUATION: