MXPA00008012A - Pure titanium dioxide hydrate and a process for the production thereof - Google Patents

Abstract

Titanium dioxide hydrate which contains less than 250 ppm sulfate ions and less than 50 ppm ammonium or alkali metal ions with respect to Tio2 is obtained by producing an aqueous suspension with sulfate-containing titanium dioxide hydrate with 2 to 18%by weight, preferably 5 to 15%by weight solid calculated as Tio2, the sulfate content of the suspension calculated as H2SO4 is determined, 95 to 100.1 mol%of the stoichiometric amount of ammonia or alkali metal hydroxide necessary for the neutralization of the calculated H2SO4 amount is added under stirring, the suspension is filtered after stirring period of 5 to 60 minutes, preferably 10 to 30 minutes, and is washed with low-salt, preferably deionized, water and a diffusion wash with deionized water is carried out at a pressure of 3 to 5 bar is then performed.

Description

\ PURE TITANIUM DIOXIDE HYDRATE AND PROCESS FOR THE PRODUCTION OF THE SAME FIELD OF THE INVENTION The invention relates to a process for the production of titanium dioxide hydrate with low sulfate content from a hydrolyzate which was obtained by hydrolysis of titanyl sulfate as well as particularly pure titanium dioxide hydrate. BACKGROUND OF THE INVENTION It is well known how to produce a hydrolyzed titanium dioxide hydrate, which still contains sulfate ions chemically bound after the removal of the diluted sulfuric acid containing metal sulphate, from solutions of titanyl sulfate in sulphurous acid containing metal sulphate, solutions which are obtained by digestion of crude materials of titanium with concentrated sulfuric acid. East The hydrolyzate still contains 5 to 10% by weight of S042"ions with respect to Ti02 after intensive washing with water or diluted acid and an optional reducing treatment (so-called bleached) (Ullmanns Encyclopaedia of Technical Chemistry, 4th Edition, Vol. 18 (1979), pages 574-576).

This sulfate ion content is a great disadvantage for most uses of the hydrolyzate. In the production of Ti02 or mixed oxides containing Ti02 by calcination of the hydrolyzate, the sulfate ions are separated as sulfuric acid and S03, which is partially decomposed to S02, 02 and H20 at high temperatures. This requires large-scale gas purification measures. In the production of catalysts, its activity is frequently negatively influenced by sulfate ions. Therefore, many attempts have been made to produce sulfate-free titanium dioxide hydrate. According to US-A 3 518 053, a sulfate-poor hydrate is created by treating a bleached hydrolyzate with ammonia, hydroxide or ammonium carbonate and washing the ammonium sulfate. The hydrate obtained in this way still contains 0.5 to 2.0% sulphate. Even though many of the ammonium compounds are aggregated according to US-A 3 658 539 so that the pH value of the suspension is increased to 8.0 the S content of the washed hydrate is still 0.3% by weight corresponding to 0.9% by weight of S042 ~. DE-A 43 21 555 describes a process for the production of mixed oxide powders for denaturing catalysts in which the suspension of titanium dioxide hydrate containing sulfur ions is partially neutralized with bleach at a pH value of between 4.0 and 6.0, filtered and the filter cake is washed intensively. The starting material is preferably a suspension of bleached titanium dioxide hydrate of 20 to 40% by weight solids. In this manner, a hydrate with a content of about 2.5% S042"and 20 ppm Na20 can be produced.A further reduction of the sulfate content with a simultaneously low Na20 content is possible according to US-A 5,527,469. As a consequence, the sulfate-containing hydrate suspension is mixed with 0.1 to 2 parts by weight of alkali metal hydroxide or carbonate and stirred at 60 to 120 ° C for 30 to 60 minutes After washing the alkali metal compounds, the The pH value of the hydrate suspension should be decreased with organic acids to below 6, preferably below 4.5, to remove alkali metal ions chemically bound to the hydrate.The residual organic acids are decomposed by calcination. of titanium dioxide created with this very extensive process contain between 110 and 480 ppm of S corresponding to 330 and 440 ppm of S042"as well as up to 293 ppm of Na +. Consequently, according to the technique, it has not previously been possible to produce titanium dioxide hydrate with a very low sulfate and alkali and / or ammonium content despite numerous attempts.

BRIEF DESCRIPTION OF THE INVENTION It is an object of the present invention to provide a simple process for the production of titanium dioxide hydrate with a low sulfate content from an optionally bleached hydrolyzate which was produced by hydrolysis of titanyl sulfate solutions which contains other metal sulfates and optionally free sulfuric acid. AdditionallyIt is an object of the invention to provide a pure titanium dioxide hydrate containing less than 250 ppm of SO42"and less than 50 ppm of ammonia or alkali metal ions with respect to TiO2 The objects according to the invention could not Surprisingly by neutralizing 2 to 18% by weight of the titanium dioxide hydrate suspension.

DETAILED DESCRIPTION OF THE INVENTION The subject matter of the invention is a process for the production of pure titanium dioxide hydrate with less than 100 ppm of S042"and less than 25 ppm of ammonia or alkali metal ions from dioxide hydrate of titanium produced by the hydrolysis of titanyl sulfate, characterized in that an aqueous suspension is produced with the titanium dioxide hydrate containing sulphate with 2 to 18% by weight, preferably 5 to 15% by weight, of solids calculated as Ti02, the sulfate content of the suspension calculated as S042_ was determined, 95 to 101.1 mol% of the stoichiometric amount of ammonia or alkali metal hydroxide required for neutralization of the amount of H2SO4 calculated under agitation was added, the suspension was filtered after a stirring time of 5 to 60 minutes, preferably 10 to 15 minutes, and washed with water with a low salt content, preferably to deionized water, and then washing by diffusion with deionized water at a pressure of 3 to 5 bar. The sulfate-containing hydrate is obtained in a conventional manner so that crude titanium materials such as ilmenite or titanium slag are decomposed with concentrated sulfuric acid. The metal sulfates obtained are therefore dissolved in water or dilute sulfuric acid. After separation of the undissolved solids and adjustment of a suitable Ti3 + concentration, the titanyl sulfate was hydrolysed from 90 to 110 ° C in the presence of hydrolysis cores under the formation of the titanium dioxide hydrate containing sulfate and sulfuric acid. After the separation of the sulfuric acid containing metal sulphate by filtration and wash the filter cake, the filter cake can be liberated from heavy metal ions dyes such as Fe3 +, Cr3 +, V3 + if required by means of a reducing treatment in dilute acid ("bleached") or dissolving in sulfuric acid and renewed hydrolysis in the presence of T3 + ions. This filtration cake of titanium dioxide hydrate containing from 5 to 10% by weight of S042_ ions with respect to Ti02 is obtained according to the technique by hydrolysis of titanyl sulfate represents the initial material for the production of dioxide hydrate of titanium according to the invention and the products produced from the same concentrate or by calcination. According to the invention, a suspension with a solids content such as Ti02 of 12 to 18% by weight, preferably with a solids content of 5 to 15% by weight, was produced from the filter cake of titanium dioxide hydrate obtained. It was determined that the S04 ~~ ion content, calculated as H2S04, of this suspension is from 95 to 100.1 mol%, preferably from 99.5 to 100.1 mol%, more preferably from 99.8 to 100.05 mol% of the stoichiometric amount of ammonium hydroxide or alkali metal required for the neutralization of the amount of circulated H2SO4 added under agitation from 20 to 100 ° C, preferably from 30 to 80 ° C. After the suspension mixed with hydroxide had been stirred for 5 to 60 minutes, preferably 10 to 30 minutes, it was filtered and washed with hot water of 30 to 100 ° C, preferably 50 to 95 ° C. The washing occurred with low salt water, preferably deionized. According to the invention, the filtration and washing with vacuum filters or preferably pressure filters was carried out at pressures up to a maximum of 3 bar. If the conductivity of the filtrate clearly decreased, preferably to approximately 300 mS / cm, then the removal of the residual sulfate was carried out on a pressure filter by diffusion washing with salt-free water of 30 to 100 ° C and a pressure from 3 to 5 bar. Preferably, this was washed until the conductivity of the washed filtrate was less than 100 μs / cm. If a membrane filter press is used as the aggregate of the preferred filter, then the mother liquor is pressed with a pressure of 3 to 5 bar before starting the washing by diffusion. Advantageously, a partial removal of the water from the filter cake can occur with the increase of the compaction pressure after completing the diffusion wash. The filter cake obtained by applying the process according to the invention generally contains less than 1% by weight of sulphate ions and less than 10 ppm of ammonium or alkali metal ions, each with respect to Ti02. When the preferred amounts of ammonium hydroxide or alkali metal are used, titanium dioxide hydrate according to the invention is obtained which contains less than 250 ppm of S042 ~ ions and less than 50 ppm of ammonium or alkali metal ions. , especially less than 100 ppm of S042"ions and less than 25 ppm of ammonia ions or alkali metal ions, each with respect to Ti02.This titanium hydroxide hydrate is distinguished by a particularly large reaction capacity, high capacity of adsorption of ions and cations and, depending on the degree of removal of water, a high catalytic activity The subject matter of the invention is also a method for the production of titanium dioxide and / or titanium dioxide hydrate of the composition of Ti02 x nH20 1 >; n > 0 containing less than 250 ppm, preferably less than 100 ppm, of sulfate ions and less than 50 ppm, preferably less than 25 ppm, of ammonium ions and alkali metal, each with respect to Ti02, which is it can be obtained by drying and / or calcining the titanium dioxide hydrate according to claim 5 at temperatures in the range of 50 to 750 ° C. These products can not be produced from the titanium dioxide hydrate containing conventional sulphate because first the thermal cleavage of the sulfate ions occurs at higher temperatures. The invention is illustrated by the examples without limiting the scope of the invention to them.

EXAMPLES Technical sulfate-containing titanium dioxide hydrate was produced by hydrolysis of a sulfuric acid, titanyl sulfate solution containing metal sulfate. The washed filter cake was "bleached" by means of a reducing treatment. The washed filter cake of the "bleached" titanium dioxide hydrate was sucked with water. The suspension obtained in this manner had 25.24% by weight of titanium dioxide hydrate calculated as Ti02 and 2.14% by weight of sulfate ions calculated as H2SO4. The suspension served as the starting material for all the examples.

Comparative Example 1 6240 kg of suspension was mixed with 213 kg of 50% by weight NaOH under intensive agitation. The amount of NaOH was sufficient for the neutralization of 97.7 mol% of the H2S04 contained in the suspension, so that the residual content of 1950 ppm of H2SO4 was expected after washing the Na2SO4. 30 minutes after the addition, the suspension was pumped to a membrane filter press. After completing the filtration, the mother liquor was pressed with a membrane pressure of 4 bar and washed for 180 minutes with deionized water.

The conductivity of the filtrate therefore fell to 133 μS. The filter cake was suspended in deionized water and a sample was analyzed. The sample contained 3184 ppm of H2SO4 and 266 ppm of Na20 with respect to Ti02.

Comparative Example 2 This was carried out analogously to Comparative Example 1, except that the mother liquor was not pressed after completing the filtration, but was washed for 30 minutes with deionized water through the suspension channel. The pressing and washing for 75 minutes through the washing channels of the filter press was carried out only after this, so that the conductivity of the filtrate dropped to 97 μS. The filter cake suspended and homogenized thereafter had 2370 ppm of H2SO4 and 28 ppm of Na20.

Example 1 4340 kg of sulfate-containing suspension was mixed with 6653 1 of deionized water at a temperature of 80 ° C. The suspension containing 9.96% titanium dioxide hydrate calculated as Ti02 was mixed under intensive agitation with 213 kg of 50% NaOH which is sufficient for the neutralization of 99.7 mol% of the contained H2SO4. 30 minutes later, the suspension was pumped into a membrane filter press and filtered for approximately 20 minutes, whereby the pressure was increased to 2.5 bar. Subsequently, it was washed for 15 minutes with deionized water through a suspension channel at a water pressure of 2.5 bar. Therefore, the conductivity of the filtrate dropped to 290 mS / cm. After the filter cake had been pressed with a membrane pressure of 5 bar, it was washed with deionized water through the washing channels of the membrane filter press at a water pressure of 5 bar until the The conductivity of the washed filtrate was 81 μS / cm. The filter cake was removed and suspended in deionized water. The suspension of homogenized titanium dioxide hydrate was 2030 ppm of S042 ~ and 5 ppm of Na + each with respect to Ti02.

EXAMPLE 2 4340 kg of suspension containing sulfate was mixed with 4550 1 of deionized water (content of Ti02 of the suspension, 12.3% by weight). 337 1 of an aqueous solution of ammonia with 10% by weight of NH 3 sufficient for the neutralization of 99.5 mol% of the acid H2S04 contained in the suspension agitated intensively was added. After a stirring time of 20 minutes, the suspension was filtered in a manner analogous to Example 1 and washed. The diffusion was completed when the conductivity of the filtration was 72 μS / cm. The suspended and homogenized titanium dioxide hydrate filter cake had 217 ppm of S042 ~ with respect to Ti02. No ammonium ions could be detected.

EXAMPLE 3 4340 kg of sulfate-containing suspension were mixed with 6500 1 of deionized water and mixed under intensive agitation at 80 ° C with 705 1 of 10% by weight NaOH sufficient for the neutralization of 99.95 mol% of the contained H2SO4. The filtration and the washing of the filter cake were carried out analogously to example 1. The washing by diffusion was completed when the conductivity of the filtrate was 60 μS / cm. The homogenized titanium dioxide hydrate suspension contained less than 50 ppm S04 of at least 16 ppm Na + each with respect to Ti0.

Example 4 The suspension containing sulphate was mixed in a manner analogous to Example 3 and mixed with 706 1 of 10% by weight NaOH corresponding to 100.1 mole% of the amount required for the neutralization of the contained H2SO4. The filtration and washing of the cake were carried out analogously to Example 1 until the conductivity of the filtrate was 83 μS / cm. In the suspension of homogenized titanium dioxide hydrate, no sulfate could be detected, so that they become present < 50 ppm of S04 ~ 2 with respect to Ti02. The Na + content was 86 ppm with respect to Ti02.

It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Claims (7)

1. CLAIMS Having described the invention as above, the content of the following claims is claimed as property. 1. A process for the production of pure titanium dioxide hydrate with less than 100 ppm of S04 ~ 2 ions and less than 25 ppm of ammonium or alkali metal ions of the titanium dioxide hydrate produced by the hydrolysis of titanium sulfate , characterized in that an aqueous suspension is produced with the titanium dioxide hydrate containing sulphate with 2 to 18% by weight, preferably 5 to 15% by weight, of solids calculated as TiO2, the sulfate content of the suspension calculated as H2SO4, 95 to 101.1 mole% of the stoichiometric amount of ammonia or alkali metal hydroxide was added to neutralize the amount of H2SO4 calculated, added under stirring, the suspension was then filtered at a stirring time of 5 hours. to 60 minutes, preferably 10 to 30 minutes, and washed with water with a low salt content, preferably deionized water, and washing by diffusion with deionized water was carried out. a pressure of 3 to 5 bars.
2. 2. The process according to claim 1, characterized in that from 99.5 to 101.1 mole%, preferably from 99.8 to 100.5 mole% of the stoichiometric amount of ammonium hydroxide hydroxide or alkali metal hydroxide is required for the neutralization of the amount of H2SO4 calculated, added to the suspension of the titanium dioxide hydrate containing sulfate in water.
3. 3. The process according to claim 1 and 2, characterized in that the filter cake was washed with water at a maximum pressure of 3 bar until the conductivity of the filtrate decreased below 300 mS / cm.
4. The process according to any of claims 1 to 3, characterized in that the diffusion washing was carried out from 3 to 5 bar until the conductivity of the filtrate decreased to below 100 μS / cm.
5. 5. The titanium dioxide hydrate obtainable according to claim 1, characterized in that it contains less than 250 ppm sulfate ions and less than 50 ppm of ammonium or alkali metal ions each with respect to Ti02.
6. 6. The titanium dioxide hydrate according to claim 5, characterized in that it contains less than 100 ppm sulfate ions and less than 25 ppm of ammonium or alkali metal ions each with respect to Ti02.
7. 7. A titanium dioxide and / or titanium dioxide hydrate of the composition Ti02 x nH20 with 1 > n > 0, characterized in that it contains less than 250 ppm, preferably less than 100 ppm, of alkali metal ammonium ions, each with respect to Ti02 obtainable by drying and / or calcining titanium dioxide substrate according to claim 1 at temperatures in the range of 50 to 750 ° C.