KR20010072550A - Pure titanium dioxide hydrate and a process for the produciton thereof - Google Patents

Abstract

The present invention is an ammonium or alkali metal ions present invention relates to titanium dioxide hydrate which contains less than 50 ppm sulfate ion and less than 250 ppm, which is a solid 2 to 18 5 to 15% by weight, preferably calculated as TiO ₂ for TiO ₂ Obtained by producing an aqueous suspension with a sulfate-containing titanium dioxide hydrate comprising% by weight, measuring the sulfate content of the calculated suspension as H ₂ SO ₄ , and ammonia or alkali metal hydroxide required for the neutralization reaction of the calculated H ₂ SO ₄ content. 95 to 100.1 mol% of the stoichiometric content of is added under stirring, the suspension is filtered after stirring for 5 to 60 minutes, preferably 10 to 30 minutes, washed with water with a low salt content, preferably deionized water and After that, the diffusion washing is performed with deionized water at a pressure of 3 to 5 bar.

Description

PURE TITANIUM DIOXIDE HYDRATE AND A PROCESS FOR THE PRODUCITON THEREOF

Titanium Dioxide Hydrate Hydrolyzate, which still contains chemically bound sulfate ions after removal of metal sulfate-containing diluted sulfuric acid from a solution of titanyl sulfate in sulfuric acid containing metal sulfate, and the solution is obtained by digestion of the titanium crude material It is well known to produce. The hydrolyzate still contains 5-10% by weight of SO ₄ ^2- ion to TiO ₂ after a strong wash with water or dilute acid and any reduction (so-called bleaching) treatment. References Ullmanns Encyclopaedia of Technical Chemistry , 4th edition, Vol. 18 (1979), 574-576.

This sulfate ion content is not very beneficial for the use of most hydrolyzates. In the production of TiO ₂ or TiO ₂ -containing mixed oxides by calcination of the hydrolyzate, sulfate ions are separated as SO ₃ or sulfuric acid, which partially decomposes into SO ₂ , O ₂ and H ₂ O at high temperatures.

This requires a large amount of gas purification measurements. In the preparation of a catalyst, its activity is often affected in a negative way by sulfate ions. Thus, many attempts have been made to produce titanium dioxide hydrates that do not contain sulfate.

According to US Pat. No. 3,518,053, the bleached lysate is treated with ammonia, ammonium hydroxide or ammonium carbonate and washed off to remove ammonium sulphate to produce less sulfate hydrate. Hydrates obtained in this way still contain 0.5-2.0% of sulfate. According to US-A-3,658,539, even when a certain amount of ammonium compound is added to increase the pH value of the suspension to 8.0, the S-content of the washed hydrate is still 0.3, corresponding to SO ₄ ^2- 0.9 wt%. It becomes weight%.

DE-A-43 21 555 describes the denitrification of a catalyst comprising partially neutralizing a sulfur ion-containing titanium dioxide hydrate suspension to pH 4.0-6.0 using an alkaline solution, followed by filtration. The preparation of the mixed oxide powder for this is described. The starting material is preferably a bleached titanium dioxide hydrate suspension having a solids content of 20-40% by weight. In this way, a hydrate may be produced with about 2.5% SO ₄ ²⁻ and 20 ppm Na ₂ O.

According to US Pat. No. 5,527,469, it is possible that the sulfate content is further reduced while at the same time having a low Na ₂ O content. Thus, the sulfate-containing hydrate dispersion is mixed with 0.1 to 2 parts by weight of alkali metal hydroxide or carbonate and then stirred at 60 ° C. to 120 ° C. for 30 to 60 minutes.

After washing away the alkali metal compound, the pH value of the hydrate suspension must be lowered to pH 6 or lower, preferably 4.5 or lower, using an organic acid to remove chemically bound alkali metal ions from the hydrate. Residual organic acids are decomposed by calcination. The large titanium dioxide hydrate produced by using a method of the same contains a S 110~480 ppm or less, as well as Na ⁺ 293 ppm, corresponding to SO ₄ ^2- 330~1,440 ppm.

In conclusion, according to the art, it has not been possible in the past to produce very small amounts of sulfate and titanium dioxide hydrates with very low alkali and / or ammonium content despite these various attempts.

The present invention relates not only to titanyl sulfate, but also to a process for the production of titanium sulfate hydrates with a low sulfate content from lysates obtained by hydrolysis of pure titanium dioxide hydrates.

It is a first object of the present invention to provide a simple process for the preparation of low sulfate content titanium dioxide hydrate from any bleached hydrate produced by hydrolysis of other metal sulfates and titanyl sulfate solution containing any free sulfuric acid. I would like to.

Further, the second object of the present invention is to provide a pure titanium dioxide hydrate containing an ammonium or alkali metal ion less than 50 ppm and less than 250 ppm SO ₄ ^2- to the TiO _2.

These objects according to the invention are surprisingly achieved by a neutralization reaction of 2-18% by weight titanium dioxide hydrate suspension.

SUMMARY OF THE INVENTION The present invention relates to a process for the preparation of pure titanium dioxide hydrates comprising less than 25 ppm ammonium or alkali metal ions and less than 100 ppm SO ₄ ^2- ions from titanium dioxide hydrates produced by titanyl sulfate hydrolysis, The aqueous suspension is produced as a sulfate-containing titanium dioxide hydrate comprising 2-18% by weight solids, preferably 5-15% by weight calculated as TiO ₂ and measuring the sulfate content of the suspension calculated as H ₂ SO ₄ , 95 to 101.1 mol% of the stoichiometric content of ammonia or alkali metal hydroxide required for the neutralization reaction of the calculated H ₂ SO ₄ content is added under stirring, and the suspension is stirred for 5 to 60 minutes, preferably 10 to 30 minutes. Filtration, washing with low salt water, preferably deionized water, followed by diffusion washing with deionized water at a pressure of 3 to 5 bar. The.

Typically, the raw titanium material, such as titanium iron ore or titanium slag, is decomposed into concentrated sulfuric acid to obtain sulfate containing hydrates. The metal sulfate thus obtained is dissolved in water or dilute sulfuric acid. The undissolved solids are separated and the appropriate Ti ³⁺ concentration is adjusted, followed by hydrolysis of the titanyl sulfate in the presence of hydrolysis nuclei at the time of formation of sulfate-containing titanium dioxide hydrate and sulfuric acid. The metal sulfate-containing sulfuric acid is separated by filtration and the filter cake is washed, after which the filter cake is colored heavy metal ions such as Fe ³⁺ by dissolution in dilute acid (" bleaching ") or by dissolution in sulfuric acid if necessary. , Cr ³⁺ , V ³⁺ can be removed and the hydrolysis reaction in the presence of Ti ³⁺ ions can be started again.

Titanium dioxide hydrate filter cake containing 5 to 10% by weight of SO ₄ ^2- ion to TiO ₂ obtained by the conventional technique by hydrolysis of titanyl sulfate is obtained by pure titanium dioxide hydrate and drying or calcination according to the present invention. It is a starting material for the preparation of the product produced therefrom.

According to the invention, an aqueous suspension comprising from 2 to 18% by weight of solids, preferably from 5 to 15% by weight of solids, calculated as TiO ₂ , is produced from a titanium dioxide hydrate filter cake. Of the suspension calculated as H ₂ SO ₄ SO ₄ ^2- ion content were measured, 95~100.1 mole% of the stoichiometric amount of ammonium or alkali metal hydroxide required for neutralization of the calculated H ₂ SO ₄ content, preferably 99.5-100.1 mol%, most preferably 99.8-100.05 mol% are added at 20 degreeC-100 degreeC, Preferably it is 30 degreeC-80 degreeC under stirring. The suspension mixed with hydroxide is stirred for 5 to 60 minutes, preferably 10 to 30 minutes, then filtered and washed with hot water at 30 ° C to 100 ° C, preferably 50 ° C to 95 ° C. The washing is carried out with low brine, preferably deionized water. According to the invention, filtration and washing with a vacuum filter or preferably a pressure filter is carried out at pressures up to 3 bar or less. If the conductivity of the filtrate is clearly lowered to preferably about 300 mS / cm, removal of residual sulfate is carried out on a pressure filter by diffusion washing at a pressure of 3 to 5 bar at 30 ° C. to 100 ° C. with brine. This is preferably washed until the conductivity of the wash filtrate is 100 μS / cm or less. When using a membrane filter press as the preferred filter agglomerate, the mother liquor was squeezed off at a pressure of 3-5 bar before initiating the diffusion wash. Partial removal of water from the filter cage can be performed with increasing compression pressure after complete diffusion washing.

Filter cakes obtained using the process according to the invention generally contain less than 100 ppm of ammonia and alkali metal ions and less than 1% by weight of sulfate ions, respectively, for TiO ₂ . When using the preferred amount of the preferred ammonia or alkali metal hydroxide, respectively, of ammonium and alkali metal ions for the TiO ₂ is less than 50 ppm and the SO ₄ ^2- ions less than 250 ppm, in particular less than each of an ammonium or alkali metal ions for the TiO ₂ 25 ppm And pure titanium dioxide hydrate according to the invention containing less than 100 ppm of SO ₄ ^2- ion. These titanium dioxide hydrates are particularly characterized by their high reaction capacity, high absorption capacity for anions and cations, and high catalytic activity due to the removal of water.

The subject matter of the present invention also relates to a process for producing titanium dioxide and / or to titanium dioxide hydrate, wherein the titanium dioxide hydrate is less than 50 ppm of ammonium and alkali metal ions, preferably less than 25 ppm and sulfate ions, respectively, for TiO ₂ . Titanium dioxide hydrate of composition TiO ₂ × nH ₂ O (1 ≧ n ≧ 0) containing less than 250 ppm, preferably less than 100 ppm, according to claim 5 at a temperature within the range of 50 ° C. to 750 ° C. Obtainable by drying and / or calcination of titanium dioxide hydrate.

Such products cannot be produced from conventional sulfate-containing titanium dioxide hydrates because thermal decomposition of sulfate ions occurs primarily at high temperatures.

The invention is illustrated by the following examples, which are not intended to limit the scope of the invention.

Industrial sulfate-containing titanium dioxide hydrate is produced by hydrolysis of sulfuric acid, metal sulfate-containing titanyl sulfate solution. The washed filter cake is "bleached" by a reduction treatment. The washed filter cake of "bleached" titanium dioxide hydrate was mashed with water. The suspension obtained in this way contains 25.24% by weight of titanium dioxide hydrate calculated by TiO ₂ and 2.14% by weight of sulfate ions calculated by H ₂ SO ₄ .

Suspensions serve as starting materials for all examples.

Comparative Example 1

6,240 kg of this suspension was mixed with 50% by weight of 213 kg of NaOH under vigorous stirring. This NaOH content is sufficient to neutralize 97.7 mol% of H ₂ SO ₄ contained in the suspension such that a residual content of 1,950 ppm of H ₂ SO ₄ is expected after washing away the Na ₂ SO ₄ . After 30 minutes of NaOH addition, the suspension is pumped to the membrane filter press. After filtration was complete, the mother liquor was compressed to a membrane pressure of 4 bar and then washed with deionized water for 180 minutes. The conductivity of the filtrate was reduced to 122 μS. The filter cake was suspended in deionized water and the samples analyzed. The sample contains 266 ppm Na ₂ O and 3184 ppm H ₂ SO ₄ for TiO ₂ .

Comparative Example 2

After completion of filtration, the mother liquor was carried out similarly to Comparative Example 1, except that the mother liquor was not compressed and instead washed through the slurry channel with deionized water for 30 minutes instead. Thereafter, only 75 minutes of compression and washing were carried out through the washing tube of the filter press, so that the conductivity of the filtrate dropped to 97 µS. The suspended and homogenized filter cake thus contained 2730 ppm H ₂ SO ₄ and 28 ppm Na ₂ O.

Example 1

4,340 kg of the sulfate-containing suspension was mixed with 6,653 L of deionized water at 80 ° C. 213 kg of 50% NaOH sufficient for the neutralization reaction of 97.7 mol% of H ₂ SO ₄ contained and a suspension containing 9.96% by weight of titanium dioxide hydrate calculated as TiO ₂ were mixed under vigorous stirring. After 30 minutes, the suspension was pumped with a membrane filter press and filtered for about 20 minutes, thus increasing the pressure to 2.5 bar. It was then washed with deionized water through a slurry tube at a water pressure of 2.5 bar for 15 minutes. Thus the conductivity of the wash filtrate dropped to 290 mS / cm. The filter cake was then compressed to a membrane pressure of 5 bar and washed with deionized water at 5 bar water pressure through a wash tube of the membrane filter press until the conductivity of the wash filtrate was 81 μS / cm. The filter cake was removed and suspended in deionized water. The homogenized titanium dioxide hydrate suspension contained 5 ppm Na ⁺ and SO ₄ ^2- 2,030 ppm for each of the TiO _2.

Example 2

4,340 kg of the sulfate-containing suspension was mixed with 4550 L of deionized water (TiO ₂ content of suspension: 12.3 wt%). 335 liters of an aqueous ammonia solution using 10 wt% of NH ₃ sufficient to neutralize 99.5 mol% of the H ₂ SO ₄ contained are added to the strongly stirred suspension. After 20 minutes of stirring time, the suspension is filtered and washed similarly to Example 1. The diffusion wash is terminated when the conductivity of the wash filtrate is 72 μS / cm. The suspension is homogenized titanium dioxide hydrate filter cake containing SO ₄ ^2- 217 ppm for TiO _2. Ammonium ions were not detected.

Example 3

4,340 kg of the sulfate-containing suspension was mixed with 6,500 L of deionized water, and 705 L of 10% by weight of NaOH sufficient for the 99.95 mol% neutralization reaction of H ₂ SO ₄ contained was mixed at 80 ° C. under vigorous stirring. Filtration and filter cake washing were performed similarly to Example 1. The diffusion wash is terminated when the conductivity of the wash filtrate is 64 μS / cm. The homogenized titanium dioxide hydrate suspension contained 16 ppm each of Na ⁺ and SO ₄ ^2- is less than 16 ppm for the TiO _2.

Example 4

The sulfate containing suspension was mixed similarly to Example 3 and mixed with 706 L of 10% by weight of NaOH corresponding to 100.1 mol% of the content required for the neutralization reaction of H ₂ SO ₄ contained. Filtration and filter cake washing were performed similarly to Example 1 until the conductivity of the wash filtrate was 83 μS / cm. In the homogenized titanium dioxide hydrate suspension, SO ₄ ^2- <50 ppm was present for TiO ₂ , so no sulfate was detected. Na ⁺ content was 86 ppm relative to TiO ₂ .

Claims (7)

A process for the preparation of pure titanium dioxide hydrates comprising less than 25 ppm of ammonium or alkali metal ions and less than 100 ppm of SO ₄ ^2- ions from titanium dioxide hydrates produced by titanyl sulfate hydrolysis, wherein the aqueous suspension is calculated as TiO ₂ . the solids 2-18% by weight, preferably is produced by sulfate-containing titanium dioxide hydrate containing 5 to 15% by weight, and measuring the sulfate content of the calculated suspension as H ₂ SO _4, calculated H ₂ SO ₄ content 95 to 101.1 mol% of the stoichiometric content of ammonia or alkali metal hydroxide required for the neutralization reaction of the solution is added under stirring, the suspension is filtered after stirring for 5 to 60 minutes, preferably 10 to 30 minutes, and the salt content is low. Washing with water, preferably deionized water, followed by diffusion washing with deionized water at a pressure of 3 to 5 bar. The method according to claim 1, wherein 99.5 to 100.1 mol%, preferably 99.8 to 100.05 mol%, of the stoichiometric content of ammonium or alkali metal hydroxide required to neutralize the calculated H ₂ SO ₄ content It is added to suspension, The manufacturing method characterized by the above-mentioned. The process according to claim 1 or 2, wherein the filter cake is washed with water at a maximum pressure of 3 bar until the conductivity of the filtrate is reduced to 300 mS / cm or less. The process according to any one of claims 1 to 3, wherein the diffusion washing is carried out at 3 to 5 bar until the conductivity of the filtrate is reduced to 100 μS / cm or less. Titanium dioxide hydrate obtainable by claim 1 containing less than 50 ppm of ammonium or alkali metal ions and less than 250 ppm of sulfate ions for each TiO ₂ . The titanium dioxide hydrate of claim 5 which contains less than 25 ppm of ammonium or alkali metal ions and less than 100 ppm of sulfate ions, respectively, for TiO ₂ . Less than 50 ppm, preferably less than 25 ppm, of ammonium and alkali metal ions, respectively, for TiO ₂ , obtainable by drying and / or calcination of the titanium dioxide hydrate according to claim 5 at a temperature in the range from 50 ° C. to 750 ° C. and Titanium dioxide hydrate and / or titanium dioxide of composition TiO ₂ xnH ₂ O (1 ≧ n ≧ 0) containing less than 250 ppm of sulfate ions, preferably less than 100 ppm.