Field of the Invention

The disclosure herein relates to the production of titanium dioxide. More specifically, the disclosure herein provides for scour medium to produce titanium dioxide.

Background of the Invention
Titanium dioxide (TiO2) pigments are produced either by chloride route or sulphate route. The properties of TiO2 pigment produced in chloride route are superior compared to the pigment produced in sulphate route. The “Q” grade Ilmenite contains around 60% of TiO2. The TiO2 content is enriched to 90-92% by following Benalite process and the product produced is called synthetic rutile. The synthetic rutile titanium dioxide is subjected to chlorination at elevated temperature followed by purification done by distillation and partial condensation to produce titanium tetrachloride (TiCl4). As a general practice, titanium tetrachloride is oxidized with oxygen at a temperature around 900o C in an oxidation reactor to produce titanium dioxide (TiO2). The freshly formed titanium dioxide particles grow together to form small aggregates in the oxidizer itself and stick on the walls of the rector tube experiencing chocking and there by developing high pressure in the oxidizer zone. At present, silica sand is used as the scouring material to remove the adhered TiO2particles in the reaction tube. Silica sand must be separated from titanium dioxide pigment before subjected for surface coating to produce final grade titanium dioxide pigments for different applications. The carryover of silica sand along with the titanium dioxide pigments has disadvantages such as poor quality of titanium dioxide produced, abrasion of the downstream equipment. In addition, silica sand wears off the inner walls of the reactor by generating holes in the reactor which as a result requires replacement of the reactor, thus hampering the production process. Moreover, silica sand particle are easily crushed which contaminates the reaction mixture, thereby reducing the quality of the titanium dioxide produced. The separation of silica sand from the final titanium dioxide pigment not only increases the production costs but also increases the cost of service and maintenance of the equipment.

As a result, there arises a need for substituting silica sand with other materials or minimizing the usage of silica sand as a scouring medium. The commercial available zirconium beads, alumina beads, silicon carbide beads, cannot be employed as scouring material for the production of rutile titanium dioxide, as they like silica sand have to be removed from the final titanium dioxide pigment after scouring. Moreover, the scouring material to be used should have sufficient heat withstanding capacity and heat absorption capacity since the reaction between TiCl4 and O2 takes place is an exothermic reaction and takes place at a higher temperature inside the oxidizer, thus producing TiO2.

US Patent No. 3,511,308, discloses the cooling efficiency of externally cooled conduits through which a hot gaseous suspension of fine solids is passed for cooling, is improved by introducing into the hot suspension a minor amount of particulate, solid, water-soluble salt and after cooling, separating the fine particles from the salt by solution. However, using salt as scouring media have disadvantages such as the introduction of salt enhances the viscosity of TiO2 slurry in water thereby, affecting the surface treatment procedures. In addition, the titanium dioxide pigment produced is of poor quality with a smaller particle size, making it undesirable for commercial use.

US Patent No 4,784,841 describes an invention to develop a process for the production of coarse TiO2 scrubbing solids. However, the calcined titanium dioxide particles used as scouring material are larger than the finished titanium dioxide pigment particles and are difficult to remove from the titanium dioxide pigment thereby affecting its quality.

US patent No. 5,266,108 describes a method of using titanium dioxide, of compacted particles of uncalcined titanium dioxide pigment as the scrubbing material and said compacted particles of titanium dioxide pigment being produced by subjecting titanium dioxide pigment to sufficient pressure to form same.

A method of preparing grinding media consisting essentially of sintered titanium dioxide (TiO2) particles was disclosed in US patent No. 6,036,999. However, the TiO2 granules produced possess a low surface area, thereby making it difficult to control the size and shape of the scrub.

US patent No. 7,119,039 B2discloses a scouring media effective in removing titanium dioxide buildup on the walls of a titanium dioxide reaction vessel.

A method of making TiO2 based scrubbing granules using salt binders including sodium aluminate was revealed in US patent No 2015/0078985 A1. TiO2-based scrubbing granules, and methods of making and using such TiO2-based scrubbing granules are described in this patent.

There is a chance of contamination of titanium dioxide pigments while scouring with calcined TiO2 scrubs. These scrubs either fully disintegrate in the process itself after serving its scouring purpose or require an additional process step of separation from the TiO2 pigment to avoid contamination and reduction in quality of TIO2 pigment. Carryover of these scrubs in the pigment leads to increased grit content in the pigment thereby affecting the pigmentary properties of the TiO2 leading to quality issues. Hence, at present there is a need for development of suitable scouring media of required specification and properties for production of titanium dioxide.

Summary of the Invention
The disclosure herein relates to a scouring media comprising titanium dioxide and at least one binder selected from water, starch, sodium aluminate, sodium silicate, titanium oxychloride, titanium tetrachloride.

The disclosure herein also provides a method for producing a scouring media, the scouring media comprising, mixing titanium dioxide and binder selected from water, starch, sodium aluminate, sodium silicate, titanium oxychloride, titanium tetrachloride alone or in combinations thereof.

Detailed description of the Invention
The present disclosure herein relates to a scouring media comprising titanium dioxide and at least one binder selected from water, starch, sodium aluminate, sodium silicate, titanium oxychloride, titanium tetrachloride.

The binder ratio used in the scouring media as disclosed above varies from 0.5%- 10% of titanium dioxide.

According to an embodiment of the disclosure herein, the binder is preferably selected from titanium oxychloride, titanium tetrachloride either alone or in combination with other binders such as water, starch, sodium aluminate, sodium silicate.

The scouring media as disclosed above is in the form of granules having a size range of 0.5mm to 1.0mm. Further, the said scouring media has a bulk density of 1.29g/cc to 1.44g/cc. Furthermore, the scouring media as disclosed above is preferably round and spherical in shape depending on the nature of binder and binder to pigment ratio.

The present disclosure herein also provides a method of producing a scouring media comprising mixing titanium dioxide and binder selected from water, starch, sodium aluminate, sodium silicate, titanium oxychloride, titanium tetrachloride alone or in combinations thereof to form a scouring media.

The scouring media produced from the above method is further dried at a temperature of 140°C-150oC. The dried scouring media is further calcined at a temperature in the range of 900oC to 1000oC.

The scouring media disclosed herein, is used for scouring titanium dioxide during the manufacture of rutile titanium dioxide. Particularly, the scouring media is used to remove the titanium dioxide adhered to the walls of the reaction vessel, during production of rutile titanium dioxide.

The present disclosure herein, also provides a process for production of titanium dioxide the process comprising, reacting titanium tetrachloride with oxygen to produce titanium dioxide pigment and scouring the titanium dioxide pigment by means of the scouring media as disclosed above.

According to an embodiment, the process for production of titanium dioxide comprises mixing the scouring media disclosed above with silica sand in varying ratios.

The quality of the titanium dioxide produced is improved in terms of brightness, color, ease of dispersion by using the scouring media as disclosed above either alone or in partial substitution with silica. Further, the binders used in the scouring media are selected from titanium compounds like titanium tetrachloride (TiCl4) and titanium oxychloride (TiOCl2), which will not make any contaminant in the rutile titanium dioxide produced by using the said scouring media. Further, the said scouring media fully disintegrates after scouring thereby reducing further process steps of removal from the titanium dioxide.

Examples:
The following examples illustrate the invention but are not limiting thereof:
Example 1: Production of scouring media
30 kg of hydrophilic titanium dioxide powder was introduced into a rotating base vessel which was connected with a racket shaped agitator. TiO2 pigment was sprinkled with binders such as at 1 kg of titanium oxychloride and 0.5 kg of titanium tetrachloride. 0.5 kg of water was added to wet the surface of TiO2. The racket shaped agitator was rotated at 50rpm for effective mixing of titanium dioxide powder with the binder solution to produce the scouring media. Baffles provided in different areas inside the racket shaped agitator also enhanced the proper mixing and scouring media generation. The scouring media thus produced was dried under static conditions at 150oC for 5 hours to remove the moisture content and sieved to the required size of 0.5 mm to 1mm. The dried scouring media was further calcined at 900oC to 1000oC. The bulk density of the TiO2 scouring particle was found to be 1.29 to 1.44 g/cc. The flow rate of these particles through 10 cm orifice was 5 to 6 kg per minute.

Example 2: Production of scouring media
30 kg of hydrophilic titanium dioxide powder was introduced into a rotating base vessel which was connected with a racket shaped agitator. TiO2 pigment was sprinkled with binder such as 2.0 kg of water. 0.03 kg of potassium sulphate was added to the TiO2 pigment as a softener, to adjust the hardness of the TiO2 agglomerate, so that it disintegrates after scouring purpose. Moreover, the presence of potassium ion in the scoring media controlled the particle size of TiO2 pigment produced. The racket shaped agitator was rotated at 50rpm for effective mixing of titanium dioxide powder with the binder solution to produce the scouring media. Baffles provided in different areas inside the racket shaped agitator also enhanced the proper mixing and scouring media generation. The scouring media thus produced was dried under static conditions at 140oC for 5 hours to remove the moisture content and sieved to the required size of 0.5 mm to 1mm. The dried scouring media was further calcined at 900oC to 1000oC. The bulk density of the TiO2 scouring particle was found to be 1.29 to 1.44 g/cc. The flow rate of these particles through 10 cm orifice was 5 to 6 kg per minute.

Example 3: Production of scouring media
30 kg of hydrophilic titanium dioxide powder was introduced into a rotating base vessel which was connected with a racket shaped agitator. TiO2 pigment was sprinkled with 0.25 kg of starch in 2 kg of hot water. The racket shaped agitator was rotated at 50rpm for effective mixing of titanium dioxide powder with the binder solution to produce the scouring media. Baffles provided in different areas inside the racket shaped agitator also enhanced the proper mixing and scouring media generation. The scouring media thus produced was dried under static conditions at 140oC for 5 hours to remove the moisture content and sieved to the required size of 0.5 mm to 1mm. The dried scouring media was further calcined at 900oC to 1000oC. The bulk density of the TiO2 scouring particle was found to be 1.29 to 1.44 g/cc. The flow rate of these particles through 10 cm orifice was 5 to 6 kg per minute.

Example 4: Production of scouring media
30 kg of hydrophilic titanium dioxide powder was introduced into a rotating base vessel which was connected with a racket shaped agitator. TiO2 pigment was added with1.5 kg of sodium aluminate binder (Na2O= 21% and Al2O3 =22%, Specific gravity = 1.5 g/cc. 0.5 kg of water was added to wet the surface of TiO2. The racket shaped agitator was rotated at 50rpm for effective mixing of titanium dioxide powder with the binder solution to produce the scouring media. Baffles provided in different areas inside the racket shaped agitator also enhanced the proper mixing and scouring media generation. The scouring media thus produced was dried under static conditions at 140oC for 5 hours to remove the moisture content and sieved to the required size of 0.5 mm to 1mm. The dried scouring media was further calcined at 900oC to 1000oC. The bulk density of the TiO2 scouring particle was found to be 1.29 to 1.44 g/cc. The flow rate of these particles through 10 cm orifice was 5 to 6 kg per minute.

Example 5: Production of scouring media
30 kg of hydrophilic titanium dioxide powder was introduced into a rotating base vessel which was connected with a racket shaped agitator. TiO2 pigment was added to 1.5 kg of sodium silicate binder (Na2O= 9% and SiO2 =29%, specific gravity = 1.4 g/cc).0.5 kg of water was added to wet the surface of TiO2. The racket shaped agitator was rotated at 50rpm for effective mixing of titanium dioxide powder with the binder solution to produce the scouring media. Baffles provided in different areas inside the racket shaped agitator also enhanced the proper mixing and scouring media generation. The scouring media thus produced was dried under static conditions at 140oC for 5 hours to remove the moisture content and sieved to the required size of 0.5 mm to 1mm. The dried scouring media was further calcined at 900oC to 1000oC. The bulk density of the TiO2 scouring particle was found to be 1.29 to 1.44 g/cc. The flow rate of these particles through 10 cm orifice was 5 to 6 kg per minute.

Example 6: Production of scouring media
30 kg of hydrophilic titanium dioxide powder was introduced into a rotating base vessel which was connected with a racket shaped agitator. TiO2 pigment was added to 1.5 kg of titanium oxychloride. 0.5 kg of water was added to wet the surface of TiO2. The racket shaped agitator was rotated at 50rpm for effective mixing of titanium dioxide powder with the binder solution to produce the scouring media. Baffles provided in different areas inside the racket shaped agitator also enhanced the proper mixing and scouring media generation. The scouring media thus produced was dried under static conditions at 140oC for 5 hours to remove the moisture content and sieved to the required size of 0.5 mm to 1mm. The dried scouring media was further calcined at 900oC to 1000oC. The bulk density of the TiO2 scouring particle was found to be 1.29 to 1.44 g/cc. The flow rate of these particles through 10 cm orifice was 5 to 6 kg per minute.

Example 7: Production of scouring media
30 kg of hydrophilic titanium dioxide powder was introduced into a rotating base vessel which was connected with a racket shaped agitator. TiO2 pigment was added to 0.5 kg of titanium tetrachloride. 1.5 kg of water was added to wet the surface of TiO2. The racket shaped agitator was rotated at 50rpm for effective mixing of titanium dioxide powder with the binder solution to produce the scouring media. Baffles provided in different areas inside the racket shaped agitator also enhanced the proper mixing and scouring media generation. The scouring media thus produced was dried under static conditions at 140oC for 5 hours to remove the moisture content and sieved to the required size of 0.5 mm to 1mm. The dried scouring media was further calcined at 900oC to 1000oC. The bulk density of the TiO2 scouring particle was found to be 1.29 to 1.44 g/cc. The flow rate of these particles through 10 cm orifice was 5 to 6 kg per minute.

Example 8: Production of titanium dioxide using scouring media of Examples 1-7
TiO2 pigment is produced by admixing Titanium tetrachloride (TiCl4) and O2 as shown by the below reaction scheme:
TiCl4 + O2 TiO2 + Cl2
The pre-heated TiCl4 and pre-heated O2 were admitted to a reaction tube to produce TiO2 and chlorine. Additional LPG firing system was included in the reaction chamber to enhance the chemical reaction between TiCl4 and O2. The titanium dioxide along with chlorine produced in the reaction vessel was transported to the pigment separator (which separated the solids from gas) through jacketed cooling tube with water to reduce the temperature of the pigment produced. The TiO2 pigment was separated from chlorine gas by using bag filters in the pigment separating system. The chlorine separated from TiO2 pigment was recycled to chlorination unit where TiCl4 was produced. Water jacketed cooling system were provided in the transporting tubes for decreasing the temperature of the TiO2 pigment. The freshly produced TiO2 were adhered on the inner side of the reaction tube.
The scouring media of Examples 1-7 of size (0.5 to 1mm) was introduced in to the scouring system in the production plant making titanium dioxide pigment. The process conditions during the stage wise enhancement of percentage of scouring media in silica sand are given below in the Table1.
Table 1: Process parameters with different ratio of silica sand and scouring media of Example 2
Scouring material TiCl4 Flow
Flow
(NM³/hr) By pass TiCl4 Flow
(NM³/hr) Oxygen Flow
(NM³/hr) Nitrogen pressure
(NM³/hr) Fluter Pressure
(Kg/cm²) Pigment seperator
Temp (°C) Bag Filter
Outlet Temperature (°C) Bag Filter DP (mmwc)
sand
(%) Scouring media of Example 2
(%)
100 0 800 150 940 0.40 0.39 373 170 280
90 10 800 150 940 0.40 0.39 379 170 297
80 20 800 150 940 0.42 0.38 384 170 298
70 30 800 150 940 0.39 0.41 412 175 280
60 40 800 150 940 0.40 0.39 442 180 260
50 50 800 150 940 0.41 0.40 440 177 240

It was observed that, there was no chocking or pressure build up in the system by using the scouring media of Example 1 along with silica sand when said components were mixed in the ratio of 1:1 Further, there was no process parameter variation by partial substitution of silica sand with the scouring media of Example 2. The bag filter temperature (maximum limit 200 oC), which is a very crucial process parameter, also lies below 200oC, for all different proportion of scouring media of Example 2 in silica sand as used scouring material for production of titanium dioxide.
Example 3: Quality of titanium dioxide produced using Scouring media of Example 2 and silica sand mixture.
The quality of titanium dioxide produced using scoring media of example 2 along with silica sand mixture in varying ratios is given below in Table 2.
Table 2: Quality of titanium dioxide produced with different ratio of silica sand and scouring media of Example 2
Scouring material Brightness (L) Colour (b) Carbon Black under tone value (CBU) Oil Absorption (OA) (%)
Sand
(%) Scouring media of Example 2
(%)
100 0 97.67 1.62 -3.45 22.8
90 10 97.76 1.40 -4.04 22.8
80 20 97.77 1.43 -2.44 23.6
70 30 97.77 1.64 -3.46 23.4
60 40 97.88 1.55 -3.44 23.4
50 50 97.94 1.54 -3.42 23.6

The specification value of brightness (L value) for the titanium dioxide pigment is 97.5 (minimum) [based on CIE color measurement values, L = 0 for the darkest black, and L = 100 for the brightest white].
From the above Table 2, it can be shown that with a gradual increase in the percentage of the scouring media of Example 2 in the scouring material, the brightness of the titanium dioxide produced increased. Particularly, when the scoring material contained 50% of the scouring media of Example 1 along with silica sand (50%), the brightness value of the titanium dioxide produced was 97.94, in contrast to when silica sand (100%) was used as the scouring material, the brightness of titanium dioxide was 97.67. Thus, it is inferred that the brightness value of the titanium dioxide produced increased with an increase in percentage of scouring media of Example 2 in the scouring material used.
Further, the color of the titanium dioxide pigment was determined by measuring the color values (b). The b value is negative for blue tone and positive for yellow tone. The color value (b) fixed in the specification for the titanium dioxide pigment was below 1.8 (< 1.8). The use of scouring media of Example 1, in the scouring material improved the color value of the titanium dioxide produced.
From the above Table 2, it can be inferred that when the scoring material contained 50% of the scouring media of Example 2 along with silica sand (50%), the color value (b) of the titanium dioxide produced was 1.54, in contrast to when silica sand (100%) was used as the scouring material, the color value (b) of titanium dioxide was 1.62 Thus, it is inferred that the use of the scouring media of Example 2 in the scouring material improved the color value of the titanium dioxide.
Furthermore, the particle size of the pigment was determined by measuring the carbon black under tone value (CBU) of pigment. The range for CBU value fixed for titanium dioxide pigment lies between -2 to -4. From Table 2, it can be inferred that the CBU values lie within this standard range by using scouring media of Examples 1-7 in the scouring material.

There was an enhancement of oil absorption (OA) value upon using the scouring media of Example 1 in the scoring material. The standard value fixed for OA for titanium dioxide pigment was 22%. From table 2, it can be inferred that when the scoring material contained 50% of the scouring media of Example 2 along with silica sand (50%), the OA value of the titanium dioxide produced was 23.6%, in contrast to when silica sand (100%) was used as the scouring material, the OA value of titanium dioxide was 22.8%. The enhancement in OA value is due to the decreased silica grit in the titanium dioxide produced while using scouring media of Example 2 in the scouring material.

Further, there was a total disintegration of the scouring media of Example 2 after scouring, and hence no further separation step was required to remove the scouring media granules from raw titanium dioxide produced, before subjecting to finishing process step.

Claims:We Claim:

1. A scouring media comprising titanium dioxide and at least one binder selected from water, starch, sodium aluminate, sodium silicate, titanium oxychloride, titanium tetrachloride.

2. The scouring media as claimed in claim 1, wherein the size of scouring media is in the range of 0.5mm to 1.0mm.

3. The scouring media as claimed in claim 1, wherein the scouring media has a bulk density of 1.29g/cc to 1.44g/cc.

4. The scouring media as claimed in claim 3, wherein the scouring media is in a form of granules.

5. A method for producing a scouring media, the scouring media comprising:
mixing titanium dioxide and binder selected from water, starch, sodium aluminate, sodium silicate, titanium oxychloride, titanium tetrachloride alone or in combinations.

6. The method as claimed in claim 5 comprising drying the scouring media at a temperature of 140°C-150oC.

7. The method as claimed in claim 6 comprising calcining the dried scouring media at a temperature in the range of 900oC to 1000oC.

8. A method for scouring titanium dioxide, the method comprising scouring the titanium dioxide by means of the scouring media as claimed in claim 1.

9. A process for producing titanium dioxide, the process comprising:
producing titanium dioxide by chloride process; and
removing the titanium dioxide adhered to the reaction vessels by the scouring media as claimed in claim 1.

10. A process for producing rutile titanium dioxide, the process comprising:
reacting titanium tetrachloride and oxygen to produce titanium dioxide pigment; and
scouring the titanium dioxide pigment by means of the scouring media as claimed in claim 1.