FIELD OF THE INVENTION

The present invention, in general, relates to the production of nano crystalline TiO2 from titanium oxychloride. Particularly, the invention relates to the synthesis of rutile and anatase nano-size titanium dioxide from titanium oxychloride solution. More particularly, the present invention relates to the process for the synthesis of nano rutile, and nanoanatase, of 98% TiO2 content and particle size less than 50nm, from lower and higher gpl TiOCl2 solutions respectively.

DESCRIPTION OF RELATED ART

In the prior art literature, a number of methods have been found, relating to the production of titanium dioxide. More specifically, in the known art, two main manufacturing processes dominate the TiO2 Industry - the sulfate process and the chloride process. The sulfate process was the first to provide TiO2, with high hiding power, using hydrolysis of a titanyl sulfate solution, by boiling and dilution, followed by high-temperature calcination. The chloride process, on the other hand, uses chlorination of a titanium ore or an intermediate product to form TiCl4 followed by oxidation to form pure TiO2.

Titanium dioxide exists mostly in two crystalline phases: rutile and anatase. TiO2 mostly precipitates in anatase phase from titanyl sulphate solutions, and in rutile phase from titanium oxychloride (TiOCl2) solutions, under normal conditions.

TiO2 is used in a variety of applications; in most of these applications, particular crystal structures and particle sizes are needed to provide the desired properties. There are only few methods disclosed in prior-art for the production of crystalline TiO2 with reduced particle size.

For example, the U.S. patent 4923682 (Robert et al) describes a process for making anatase titanium dioxide, in which precipitation was done from a titanyl chloride solution in presence of sorbitol & seed nuclei, at the boiling point of the solution and finally calcining the hydrolysate. In this process, the control over the particle size of the product is not accomplished.

Another U.S. Patent (No.4944936) {Lawhome et al) discloses a process for the production of titanium dioxide with high purity and unifonn particle size, in which the calcination temperature is very high (600-1100°C) and the particle size varies from 10-40 micrometers.

Nano anatase and rutile having particle size less than 100nm can be prepared from titanyl chloride solution by hydrothermal reaction conducted at 85-220°C for 1-4 h in an autoclave. The product obtained is crystalline and there is no need of calcination. It was also reported that high acidity and high concentration of TiCU favors formation of rutile phase; the product was mainly anatase at the pH of 1; addition of mineralizers like NH4CI, NaCI and SnCI4 etc to the solution decreases the particle size (Humin Cheng et.al, Chem. Mater. 1995,7,663-671).

Few alternative methods for the preparation of nano Ti02 also have been developed, but none provides an economical process for the production of high-grade nano rutile/anatase. For example, the U.S. Patent No. 6001326 (Kim et.al) discloses a homogeneous precipitation method, WO 2008036176 provides a low temperature process by producing an intermediary compound called Ti-peroxo complex {Kim Insoo et al), WO 2008/088312 describes a hydrothermal process, and WO 2009062608 discloses a method for producing nano-sized TiOa powder using hot gas stream, in which the mtile content of the final product is only 50% (Put stijn et al)

Further, according to US Patents viz US7344591 and US7326399, the Ti02 nanoparticles with desired size, shape, and uniformity can be prepared from titanyl chloride solution, by adding dispersing agents like glycolic acid, glycine, L-alanine and beta alanine. The process includes microwave heating (Zhou et al). Also, the US Publication No. 2007/0173405 {Karvinen et.al) describes a process for the preparation of nanorutile by precipitating TiOa from titanium oxy chloride solution (>90 gpl). The seeding agent added in this process is a dilute suspension of rutile nanoTi02. According to their process, the final product is predominantly rutlle (above 90%) having the particle size of 5-30nm.

Of late, the prior art document, US 20080279760 disclosed a process for preparing nanocrystalline TiOz using a separable filtering agent, in which titanium dioxide particles are predominantly rutile. (Torardi, Carmine).

However, in comparison with the prior-art literature, the present invention discloses a process wherein crystalline nano Titanium dioxide having high Ti02 content (greater than 98%) is prepared from titanium oxy chloride solution. Also, the said process achieves its results within a relatively lower temperature range, for low gpl and high gpl solutions respectively. Moreover, it is apparent from the prior-art literature that titanium oxy chloride tends to precipitate In rutile fonn only, Irrespective of the temperature variation. But, herein claimed Invention also describes the process for the precipitation of anatase TiOa from titanium oxy chloride at the temperature below the boiling point of the solution.

The present invention proposes a low cost and simple process for large-scale production of nanorutile, and nanoanatase, from titanium oxychloride solution. Accordingly, herein discloses a more advantageous method for industrial scale of operation, in which the particle size of the final product is less than 50nm, and the Ti02 content being above 98%.

SUMMARY OF INVENTION

It is therefore the primary objective of the present Invention to propose a process for the synthesis of high-grade nano rutile, and nanoanatase, from low and high gpl titanium oxychloride solutions respectively, at temperatures below the boiling point of the said solutions, with or without external heating.

It is another objective of the invention is to produce rutile and anatase nano titanium dioxide having high Ti02 content.

It is a further object of the Invention to propose a low cost and simple process for large-scale production of nanorutile and nanoanatase.

Accordingly, the present Invention proposes a process for the preparation of rutile nano titanium dioxide, having 98%Ti02 content and particle size less than 50nm, from titanium oxychloride solution the said process comprising,
• Precipitating rutile from the titanium oxychloride solution, by adding 1 - 5 % nanorutile crystalline powder of particle size 20-50nm to the said solution as seeding agent, and slowly stirring the mixture until the precipitate is obtained.
• Neutralizing the pH of the precipitated rutile TiOa using sodium hydroxide.
• Calcining the said precipitate to obtain rutile nano Titanium dioxide.

Also, the present invention proposes another process for preparing crystalline anatase, having 98% TiOa content and particle size less than 50nm, from titanium oxychloride solution, the said process comprising,
• Seeding the titanium oxychloride solution using crystalline nano anatase titanium dioxide powder, of particle size 15-50nm.
• Precipitating anatase Ti02 by further adding suitable organic additives such as a 1% solution of iso-octyl phenoxy polyethoxy ethanol to the said solution, and slowly stirring the mixture until the precipitate is obtained.
• Neutralizing the pH of the precipitated anatase Ti02 using sodium hydroxide.
• Calcining the resultant amorphous TiOa to obtain crystalline nanoanatase.

These and other objects, features, and advantages of the present invention will become more apparent from the ensuing detailed description of the invention, taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS

Figure 1 is a high-resolution transmission electron microscopy showing the size and shape of titanium dioxide (rutile) prepared by this invention.

Figure 2 depicts the X-ray diffraction pattern of titanium dioxide (rutile) prepared by this invention.

Figure 3 is a high-resolution transmission electron microscopy showing the size and shape of titanium dioxide (anatase) prepared by this invention.

Figure 4 depicts the X-ray diffraction pattern of titanium dioxide (anatase) prepared by this invention

BRIEF DESCRIPTION OF INVENTION

The preferred embodiments of the present invention will now be explained with reference to the accompanying drawings. It should be understood however that the disclosed embodiments are merely exemplary of the invention, which may be embodied in various forms. The following description and drawings are not to be construed as limiting the invention and numerous specific details are described to provide a thorough understanding of the present invention, as the basis for the claims and as a basis for teaching one skilled in the art how to make and/or use the invention. However in certain instances, well-known or conventional details are not described in order not to unnecessarily obscure the present invention in detail.

The present invention discloses the process for the preparation of rutile and anatase nano-size titanium dioxide, from titanium oxychloride solution.

As per one of the preferred embodiments of the present invention, a given quantity of titanium oxychloride solution (300gpl) is diluted to a 90-120 gpl solution, by adding sufficient quantity of water to it, and to the said diluted mixture, 1 - 5 % of crystalline TIO2 powder of particle size 20-50nm (nanorutlle) is added immediately as nucleating agent, to precipitate rutile titanium dioxide. (The addition of seeding agent in the form of crystalline powder helps to achieve the precipitation at a lower temperature). The said reaction proceeds without any external heating, under ambient pressure, as the heat generated (>40''C) during the mixing of titanium oxychloride solution with water (which is exothermic) is sufficient to maintain the optimal reaction temperature, even though the temperature may slightly drop after 1-2 hours of continuous operation (however, the temperature does not drop below 30°C).

The precipitation can be obtained with a solution containing not more than 150g Ti02, in one litre of the solution. The precipitated titanium dioxide of the above process is neutralized using sodium hydroxide and is further processed (filtered, dried, and calcined) using various methods known in the art. Figure 1 represents a high resolution transmission microscopy image, showing the size and shape of titanium dioxide (rutile) prepared by the above said procedure. The X-ray diffraction pattern of titanium dioxide (Rutile) obtained is depicted in Figure 2.

In the above-mentioned reaction, the precipitation obtained is found to be in the rutile form. In other words, under the experimented conditions of concentration, pH, pressure and temperature, the precipitation obtained is in the rutile form.

Similarly, the precipitation can be obtained from a 200gpl solution (i.e. at higher gpl values) by heating at 35-45X to obtain nanorutlle, the other steps in the reaction being the same as above.

Further, according to another preferred embodiment of the present invention, anatase fonn of nano-size Ti02 is made to precipitate from titanium oxychloride solution using suitable organic additives, with or without external heating. That is, nano-size anatase Ti02 is precipitated from TiOCl2 solution by adding organic additives such as a less than 1% (0.3 to 0.6% depending on Ti02 content) solution of iso-octyl phenoxy polyethoxy ethanol to the said solution, the said precipitation being achieved at a temperature below the boiling point of the solution (at 60-yoX) for higher gpl values (200-230gpl) or without any external heating for low gpl values (below 120gpl) of the TiOCl2 solution, as in the case of rutile preparation (slightly heating the solution (at 40''C) however helps to achieve the precipitation above 95%).

Here, an aqueous solution of titanium oxychloride, of required concentration, is prepared by passing TICI4 vapours over a dilute solution of TiOCb. To the said solution, anatase Ti02 as crystal nuclei in the form of highly crystalline powder, or seeding suspension, of particle size 15-50 nm is optionally added in order to facilitate the reaction without heating. That is, by adding seeding agent, precipitation of anatase from lower gpl solution of TiOCb can be achieved with no external heating; alternatively, if no seeding agent is added, still appreciable precipitation can be achieved by heating the mixture at 35-45''C. In case of higher gpl solution also, homogenous precipitation without seeding is apparent at the temperature below the boiling point of the solution (at 60-70X) and within 2-5 hours (high gpl with seeding agent at the same temperature can be done).

The Ti02 precipitate obtained in the above said processes are acidic. Hence, it is filtered and washed using the common procedures used in the titanium dioxide industry, after making the pH to neutral at 7 using sodium hydroxide. The resultant product obtained is amorphous Ti02, which is then calcined to obtain crystalline nanoanatase. The calcination process is done at 400°C -SOCC, for 4-5 hours. The final product has particle size in the range of 20-50nm. A high resolution transmission microscopy image showing the size and shape of titanium dioxide (anatase) obtained by the above said process is depicted in Figure 3. The X-ray diffraction pattern of titanium dioxide (anatase) obtained is shown in Figure 4.

The percentage of rutile and anatase content obtained in the processes, described in the preferred embodiments of the present invention, are above 98%.

Here, it should be noted that the addition of isooctyl phenoxy polyethoxy ethanol facilitates the precipitation of anatase from highly acidic titanium oxy chloride solutions.

The invention is described in detail in the following examples, which are provided by way of illustration only and should not be construed to limit the scope of the invention.

Example 1

To 100 ml of titanium oxychloride solution, containing greater than 310 gpl of Ti02 was added 500 ml of water, to make it a 65 gpl solution. To this mixture was added 1.5 gm (5% based on Ti02 content) of crystalline nano rutile titanium dioxide powder. The temperature of the mixture is 30 to 40°C, and the mixture is slowly stirred at 25 rpm for 5 hours. The yield of the process is above 95%. The pH of the solution was neutralized using sodium hydroxide. And the filtrate was dried and calcined at 500°C for 5 hours. The rutile content of the product obtained was more than 99.5%, and the crystal size by TEM was found to be 20-50nm.

Example 2

To 100 ml of titanium oxychloride solution containing greater than 310 gpl of TiOa, was added 200ml of water, to make it a 148 gpl solution. To this mixture was added 0.9 gm (3% based on Ti02 content) of crystalline nano titanium dioxide powder. The temperature of the mixture is maintained between 30 and 40°C, and the mixture is slowly stirred at 25 rpm for 5 hours. The yield of the said process is above 95%. The pH of the solution was neutralized using sodium hydroxide. And the filtrate was dried and calcined at 500°C for 5 hours. The rutile content of the product obtained was more than 99,5% and the crystal size by TEM was found to be 20-50nm.

Example 3

To 100 ml of titanium oxychloride solution, containing greater than 310 gpl of TiOa, was added 500 ml of water, to make it a 65 gpl solution. To this mixture was added 0.9 gm (3% based on Ti02 content) of crystalline nano anatase titanium dioxide powder. Further, to this solution was added 0.3% of iso-octyl poly ethoxy ethanol and precipitation was done. The temperature of the mixture was 30 to 40°C and the mixture is slowly stirred at 25 rpm for 5 hours. The yield of the process is above 70%. The pH of the solution was neutralized using sodium hydroxide. And the filtrate was dried and calcined at 500°C for 5 hours. The anatase content of the product was more than 99.5% and the crystal size by TEM was found to be 20-50nm.

Example 4

To 100 ml of titanium oxychloride solution, containing greater than 310 gpl of TiOa,
was added 100 ml of water, to make it a 250 gpl solution. To this mixture was added 0.9 gm (3% based on TiOa content) of crystalline nano anatase titanium dioxide powder. Further, 0.6 % of iso-octyi poly ethoxy ethanol was added to the said solution, and precipitation was done. The temperature of the mixture was below the boiling point of the solution (preferably at 60 to 7(fC), and the mixture is slowly stirred at 25 rpm for 5 hours. The yield of the process was found to be above 96%. The pH of the solution was neutralized using sodium hydroxide, and the filtrate was dried and calcined at SOO^C for 5 hours. The anatase content of the product was more than 99.5%, and the crystal size by TEM was found to be 20-60nm,

Although, the present invention has been fully described in connection with the preferred embodiments there of with reference to the accompanying drawings, it is to be noted that various changes and modifications are possible and are apparent to those skilled in the art. Such changes and modifications are to be understood as included within the scope of the present invention as defined by the appended claims unless they depart there from.

We Claim

1. A process for the preparation of rutile nano titanium dioxide, having 98% TiO2 content and particle size less than 50nm, from titanium oxychloride solution, the said process comprising,
• Precipitating titanium dioxide from the titanium oxychloride solution, by adding 1 - 5 % nanorutile crystalline powder of particle size 20-50nm to the said solution as seeding agent, and slowly stirring the mixture until the precipitate is obtained.
• Neutralizing the pH of the precipitated rutile TiO2 using sodium hydroxide.
• Calcining the said precipitate to obtain rutile nano titanium dioxide.

2. A process for preparing crystalline anatase, having 98% TiO2 content and particle size less than 50nm, from titanium oxychloride solution, the said process comprising,
• Seeding the titanium oxychloride solution using crystalline nano anatase titanium dioxide powder, of particle size 15-50nm.
• Precipitating anatase TiO2 by further adding suitable organic additives such as a 1% solution of iso-octyl phenoxy polyethoxy ethanol to the said solution, and slowly stirring the mixture until the precipitate is obtained.
• Neutralizing the pH of the precipitated anatase TiO2 using sodium hydroxide.
• Calcining the resultant amorphous TiO2 to obtain crystalline nanoanatase.

3. The process as claimed in claim 1, wherein the precipitation is obtained by externally heating the titanium oxychloride solution at about 35-40˚C , for higher gpl values (200 gpl) of the said solution.

4. The process as claimed in claim 2, wherein the precipitation is achieved at a temperature below the boiling point (at 60-70˚C ), for titanium oxychloride solutions of higher gpl values (200-230gpl).

5. The process as claimed in claim 4, wherein the requisite heat for the reaction is provided by an external source.

6. The process as claimed in claim 4, wherein the addition of seeding agent is an optional step.

7. The process as claimed in claim 2, wherein the seeding agent is not a prerequisite if sufficient heat (35-45˚C) is applied through external means, for titanium oxychloride solutions of lower gpl values (below 120 gpl).

8. The process as claimed in claims 1 & 2, wherein the calcination process is done at 400˚C - 500˚C, for 4-5 hours.

9. The process as claimed in claims 1 & 2, wherein the aqueous solution of titanium oxychloride is prepared by passing TiCl4 vapours over a dilute solution of TiOCl2.

10.A process for the preparation of rutile nano Titanium dioxide, and crystalline nanoanatase, having the TiO2 content of over 98% and particle size less than 50nm, from lower and higher gpl titanium oxychloride solutions respectively, substantially as herein described with respect to the accompanying drawings.