WO1990015775A1

WO1990015775A1 - Method of hydrolyzing metal halides

Info

Publication number: WO1990015775A1
Application number: PCT/US1990/003369
Authority: WO
Inventors: John R. Peterson
Original assignee: Teledyne Industries, Inc.
Priority date: 1989-06-13
Filing date: 1990-06-12
Publication date: 1990-12-27
Also published as: AU5935290A; EP0429638A1; JPH04500355A; EP0429638A4; CA2034004A1; BR9006805A; US5080880A

Abstract

A process for hydrolyzing a preselected metal halide comprising the steps of adding the metal halide to water in an amount sufficient to observe that there is no longer a positive heat of reaction or solution in amounts up to the stoichiometric quantity for the hydrolysis product obtained. Example reactions include: NbCl5? + H2?O $m(8) NbOCl3? + 2HCl, 2NbOCl3? + 3H2?O + HEAT $m(8) Nb2?O5? + 6HCl.

Description

METHOD OF HYDROLYZING METAL HALIDES

BACKGROUND OF THE INVENTION

The present invention relates to the hydrolysis of metal halides and more particularly to the production 5 of the corresponding metal oxides by the hydrolysis of

^■ the chloride and calcining the hydrolysis product.

Current practice for the production of Nb₂0₅ and TaCls utilizes for example, NbCl₅ from a ferroniobium (FeNb) chlorinator as the feed for Nb₂0₅ production. The 10 NbCl₅ is mixed with H₂0 forming a hydrolysed NbOCl₃.xH₂0 in a highly acidified (HC1) solution. This solution is pH adjusted with ammonia to further convert the NbOCl₃.xH₂0 to hydrolysed Nb₂0₅. The solution is then filtered and calcined at high temperature to produce dry 15 Nb₂θ5- The addition of ammonia is expensive and produces a waste disposal problem. Further, the addition or loading of NbCls to water is limited in the present practice to about 2 lbs of NbCl₅ per gallon of water. The filtration of the ammoniated NbCls water mixture is 20 required to eliminate excess water and decrease the mass of material going to the kiln which typically would then contain only 15% to 20% solids. Finally the prior use of ammonia produced ammonium chloride in the off gases from the kiln which required a large flue gas scrubbing 25 capacity.

It is therefore an object of the present invention to eliminate the use of ammonia in the production of Nb₂0₅ by the hydrolysis of NbCl₅.

It is a further object of the present invention 30 to increase the production of Nb₂θ5 while decreasing the volume of water required.

It is also an object of the present invention to provide a more energy efficient process for the production of Nb₂0₅. SUMMARY OF THE INVENTION

It has been discovered that the hydrolysis of NbCl5 if done at a loading greater than about 3 pounds per gallon of water produces a fluid mixture which can be directly charged into a calcining kiln to produce Nb₂0₅.

DETAIUED DESCRIPTION OF THE INVENTION

Conventionally the hydrolysis of the chlorides of niobium, tantalum vanadium and titanium have all employed a neutralizing step, e.g. ammonia to produce a solid suitable after filtering for charging into a kiln. As previously described, the process steps thought to be necessary limited the loading of the chloride in the water and produced further process complications and inefficiencies. The process steps shown in Table 1 compare the prior process to the process of the present invention when hydrolyzing NbCls-

Table 1

Old Process Process of This Invention

1.8# NbCl₅ 15# to 20# NbCl₅

+ +

1 gal H₂0 1 gal H₂0

+ NH₄OH i

Kiln ( 750°C)

Filtration 400 to 600#/hr A waste 1

HC1 liquor ψ to

> ^N-°2°5 scrubber Kiln ( 1000-C) for

200 to 400# recovery and

Nb₂0₅/hr sale or use

• s. waste 1 ^» NH₄CI to

> r scrubber

Nb₂0₅ It will be clearly seen that the steps of adding ammonia and filtering have been eliminated. Likewise, since the niobium loading or concentration is so much higher in the process of the present invention, the evaporative loading of the kiln is lower and therefore the overall process efficiency increases since the kiln can process more oxide with less fuel, at lower temperatures.

It is surmised that the prior process was designed with the highly acidic nature of the chlorides in mind and the perceived need to protect downstream process equipment. These concerns then dictated the use of a large volume of water and the step of neutralizing the solution. Further, loading NbCl₅ into water at the level of one to two pounds per gallon produced a significant heat of reaction and heat of solution which raised concerns about the containment of the materials when the mixture became hot enough to boil out liquid HCl above its dew point and perhaps even NbCls-

Surprisingly, it has been discovered that continued additions of the chloride does not continue to heat the solution. Initial additions, i.e. up to two to three pounds per gallon will raise the temperature of the water to 70°C to 90°C. At this point the temperature stopped rising as further additions were made and there were indications that the heats of reaction and/or solution had indeed ceased being positive and even turned from positive to negative, permitting substantial additions up to a point where one half of the stoichiometric amount of NbCls to available water was reached. In addition to this phenomenon the solution which was becoming more viscous at the two to three pounds per gallon level began to become more fluid and would accept up to about 25 pounds of NbCl₅ per gallon of water before the viscosity again rose sufficiently to pose a problem for continued stirring and pumping. The liquid after mixing was capable of being fed directly into the kiln even though it was highly acidic i.e. a pH less than 1, with respect to HCl. Large volumes of HCl are given off in the mixing of bCls with water as well as in the direct firing in the kiln by a variety of reactions which would include, but not be limited to: NbCl₅ + H₂0 NbOCl₃ + 2HC1 2NbOCl₃ + 3H₂0 + HEAT Nb₂0₅ + 6HC1 HCl gas with water is very corrosive at temperatures below the dew point or approximately 100"C. Care should then be taken in the selection of materials for the mixing tank and any scrubber over the tank using materials that are not attacked by warm HCl. Likewise the scrubber on the kiln has to be designed so that hot kiln off gas will reach the scrubber before cooling to the dew point, but will operate at a cool enough temperature so that the materials selected are not harmed by heat from the kiln. It was found that the HCl gas or acid is more easily scrubbed with water or HCl acid than the prior scrubbing required to remove the NH₄C1 of the ammonia neutralization process system. The following experiments were designed and conducted to evaluate the prospect of increasing the NbCl₅ loading in the conventional process.

Experiment 1

The first experiment was to see how much NbCl₅ could be added to water, since an obvious disadvantage of the prior process was the large amounts of water involved.

The experimental design was simply to add 222 g

NbCl₅ to 500 ml of water, or double the normal loading, in 10 g increments. At the same time, any temperature variations would be noted along with general observation of the changing nature of the mixture.

The procedure was as follows for two times the usual concentration of 1.85 pounds/gal: A 2000 ml beaker with 500 ml of H₂0 was packed in an ice bath with a stirrer to assist mixing and/or dissolution of the NbCls-

After adding about half the 222 g of NbCl₅, the mixture became so thick, like mud, that it stopped the stirrer motor and the temperature had risen to 57°C.

Adding more NbCls up to 222 g the temperature reached 69^βC but the mixture became thin and watery and stayed that way down to 10^βC. After standing overnight without stirring, it looked like a thick lemon milk shake.

Experiment 2

A second experiment gave the following results: Objective: To add three times normal, or 333 g,

NbCl₅ to 500 mis water. As the experiment proceeded, it was decided to add more NbCls.

Table 2

Total Temperature NbCl₅ of

NbCl₅ Addition Added Mixture ^βC Observations 0 0 10^βC In ice bath 135 g 135 g 60 Thick like mud + 178 g 313 g 60 Thin, watery + 43 g 356 g 75 More watery + 97 g 453 g 26 Still watery + 350 g 803 g + 92 g 895 g 31 NbCl₅ would sit on top for a while before mixing in. Ice completely melted.

+ 105 g 1000 g 26 very liquid

Net weight of the mixture 1250 g volume 625 cc density 2 g/cc The mixture was then poured into a quartz tray heated on a hot plate for preliminary drying. When there was no apparent moisture in the mix, it was then calcined at 1000^βC for 1 1/2 hours in a muffle furnace.

Experiment #3

This experiment was a repeat of Experiment 2 but without the ice bath and more rapid addition of the NbCls up to 1.5 times as much, or 1550 g, for 500 ml of water.

Table 3

Total Temperature

NbCl₅ NbCl₅ of additions Added Mixture °C Observations

0 0 23

375 g 375 g 85 No thickening like occurred in the ice bath experiments.

375 g 750 g 45 NbCl₅ floating on top and dissolving slowly.

250 g lOOO g 37 Long dissolving time, minutes.

500 g 1500 g 18 Mixture is thickening but still very fluid.

As soon as stirring stops, a skin forms on the top. Considerable fuming is evident during mixing, which is largely HCl.

Net weight 1450 g

Volume 575 cc

Density 2.5 g/cc The mixture was then dried in a quartz tray on a hot plate and calcined at 1000°C in a muffle furnace for 1 1/2 hours.

In an experiment to check recoveries of Nb₂0₅ from NbCl₅, the mixing, drying and calcining were done in one vessel with a resulting recovery of 97.5%.

Further laboratory experiments show that the high loading of Tad.5 into water exhibits much the same behavior as bCls. At the first additions of TaCl₅, there is a rapid rise of both temperature and viscosity as the loading of TaCl₅ continued. The following are two experiments conducted in the laboratory.

Experiment #1

TaCl₅ Temperature

Time Added Before-After

Min. crrams ^βC

0 5 20.5 - 32 Bright yellow solution

2 5 — __. 41

4 5 38 - 48

6 5 41 - 50

8 5 46 - 45 Solution became thick, and as it cooled, even thicker

Stir Motor Failed <and \ Was Changed

23 5 26 - 31 Consistency of cream cheese — bright yellow

2 277 5 5 25 - 38

— 5 5 37

— — 5 5 33 - 39

3 344 5 5 35 - 37 Darker yellow color l ike mustard — same consistency

3 366 5 5 34 - 37

3 388 5 5 35 - 36 Looking watery

4 400 5 5 35 - 35 Thinner and more watery

4 422 5 5 35 - 33 Thinner still

4 444 5 5 33 - 32 D a r k y e l l ow , consistency of mustard

4 477 5 5 26 - 27

4 499 5 5 26 - 27 Turned greenish

— — 1 100 26 - 28 Starting to thicken again

54 10 21 - 26 Skin forming on top of solution

56 10 24 - 24

— 10 21 - 21

—— 1100 19.5 - 17 Getting very thick, turning green gray

— 10 17 - 15 Stalled stir motor, looks like glue

64 10 15.5 - 16 Semi solid lump

1100 16 - 13.5 Thick blob

69 10 15 - 15 TaCls did not mix in at this point

Total 175

About 3.3 g of TaCl₅ per ml of water was the maximum loading reached. In terms of having a pumpable slurry, mix or solution, the optimum loading appears to be 1.5 to

1.9 g of TaCl₅ per ml of water. This is a lower loading than was obtained with NbCl₅ in water, but still exhibits a similar and useful cooling effect with a more watery consistency.

Recovery is approximately 94%.

Experiment #2

In this experiment, the additions of TaCls were larger and more rapid to a total of 150 g in 50 mis of water.

TaCl₅ Temperature

Time Added Before-After Min. σrams °C

0 25 21 - 71 Thick yellow paste

25 57 - 65 6 25 55 - 53 Looks watery—greenish in color

8 25 46 - 42 Stir motor stalled, chunky yellow-green

13 25 42 - 34 Dry looking mud, stirred by hand

— 25 32 - 24 Almost solid Total 150

The rapid heating and thickening are at first evident at

0.5 g per ml of water, then at 1.5 g TaCl₅/ml water it is obviously watery and cooling. The temperature drops rapidly at 2.0 g TaCls ml water and the mix thickens.

It is apparent from the foregoing that the same advantages exist in producing Ta₂0₅ from TaCls as described for NbCl₅ to Nb₂05 conversion even though the loading figures are somewhat lower.

The foregoing descriptions of the present invention demonstrates several important differences and advantages over the prior conventional practice. First, only water and a kiln are required to form Nb 0₅ from NbCl₅. This elimination of the neutralization step produces several important advantages, including cost savings in material, labor and equipment in both the running of the process and the handling of by-product waste from the process.

Finally, the calcined oxide produced by the practice of the present invention exhibits a higher bulk density without further processing than the product of the prior process. This property makes the product more suitable for subsequent processing into the pure metal or use in niobium containing ceramics.

The invention has been described in terms of its preferred embodiments, however, it will be appreciated that the process is applicable to the hydrolysis of any metal chloride with or without subsequent conversion to the oxide. It is therefore contemplated that the invention is not limited to the embodiments described and should only be limited in scope to the scope of the appended claims interpreted in view of the pertinent prior art.

Claims

1. A process for hydrolyzing a preselected metal halide comprising the steps of adding the metal halide to water in an amount sufficient to observe that there is no longer a positive heat of reaction or solution and then adding more metal halide to the solution in amounts up to the stoichiometric quantity for the hydrolysis product obtained.

2. A process for hydrolyzing a preselected metal chloride comprising the steps of adding the metal chloride to water in an amount sufficient to observe that there is no longer a positive heat of reaction or solution and then adding more metal chloride to the solution in amounts up to the stoichiometric quantity for the hydrolysis product obtained.

3. The process of claim 2 wherein the metal chloride is selected from the group consisting of chlorides niobium, tantalum, vanadium, titanium and mixtures thereof.

4. The process of claim 2 wherein the metal chloride is niobium pentachloride.

5. The process of claim 2 wherein the metal chloride is tantalum pentachloride.

6. The process of claim 4 wherein the niobium pentachloride is charged into water in amounts up to about 25 pounds per gallon of water.

7. A hydrolyzed product produced by the addition of preselected metal chlorides into water in amounts as great or greater than the amount required to reach the concentration where there is no longer a positive heat of reaction or solution.

8. The product of claim 7 wherein the metal chloride is selected from the group consisting of chlorides of niobium, tantalum vanadium, titanium and mixtures thereof.

9. The product of claim 8 wherein the metal chloride is niobium pentachloride.

10. The product of claim 8 wherein the metal chloride is tantalum pentachloride.

11. A process for producing a metal oxide from a metal chloride comprising the steps of: a) charging sufficient metal chloride into water to reach the point where the heat of reaction or solution of the metal chloride with the solution is no longer positive to produce a hydrolysis product; b) calcining the product of step a) at an elevated temperature for a sufficient time to produce the corresponding metal oxide.

12. The process of claim 11 wherein the metal chloride is selected from the group consisting of chlorides of niobium, tantalum, vanadium titanium and mixtures thereof.

13. The process of claim 12 wherein the metal chloride is niobium pentachloride.

14. The process of claim 12 wherein the metal chloride is tantalum pentachloride.

15. A process for producing hydrochloric acid from a metal chloride comprising the steps of: a) charging sufficient metal chloride into water to reach the point where the heat of reaction or solution of the metal chloride with the solution is no longer positive to produce a hydrolysis product; b) calcining the product of step a) at an elevated temperature for a sufficient time to produce the corresponding metal oxide; and c) recovering hydrochloric acid from the off gases of steps a and b) .