Claims:1. A process for synthesizing crystalline nano titanium dioxide of particle size 10-40 nm by vapor phase oxidation of titanium tetra chloride and oxygen in presence of liquefied petroleum gas, said process characterized in that:
• performing first stage heating of titanium tetrachloride at a temperature range of 120oC to 135oC;
• performing second stage heating of said heated titanium tetra chloride to 145oC to 190oC by passing it through a plurality of nickel tube bundles;
• further heating of said pre-heated titanium tetrachloride vapours to 330oC-370oC using liquefied petroleum gas burners;
• pre-heating oxygen to 940oC to 980oC in an oxygen preheater;
• feeding silica sand mixture into an oxidizer, followed by simultaneous introduction of said obtained titanium tetrachloride vapours, pre-heated oxygen, and liquefied petroleum gas into said oxidiser; and
• collecting the nano rutile titanium dioxide formed, wherein it is filtered, cleaned and stored.

2. The process as claimed in claim 1, wherein the silica sand mixture comprises of a seed quantity of 3-5% by weight of nano rutile titanium dioxide, wherein said seed quantity is computed based on the Ti content present in the titanium tetrachloride.

3. The process as claimed in claim 1, wherein pre-heated titanium tetrachloride vapour, pre-heated oxygen, and liquefied petroleum gas are simultaneously passed into the oxidiser in order to raise the reaction temperature to 1200oC.

4. The process as claimed in claims 1 or 3, wherein titanium tetrachloride vapour is fed into the oxidizer at a flow rate of 3T/Hr, and liquefied petroleum gas at the rate 9.2 nm3 and pre-heated oxygen at a flow rate of 415 nm3 respectively.

5. The process as claimed in claim 2, wherein the seed acts as nuclei wherein the nano rutile titanium dioxide particles is subsequently formed at a particle size same as that of the seed (<40nm).

6. The process as claimed in claim 1 is a continuous process.
, Description:[0016] The preferred embodiments of the present invention will now be explained in detail. 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.

[0017] The preferred embodiment of the present invention discloses a continuous process for synthesizing nanorutile titanium dioxide of particle size 10-40 nm by vapor phase oxidation of titanium tetra chloride and oxygen in presence of liquefied petroleum gas at 1200oC. Referring to FIG.1, the titanium tetrachloride from storage tank is pumped through a heater set at a temperature of 120oC to 135oC.The titanium tetrachloride is then further heated to 145oC to 190oC by passing it through a plurality of nickel tube bundles. Further, these vapours are preheated at 330oC-370oC using liquefied petroleum gas burners, wherein said vapour is then send to an oxidizer. In the preferred embodiment of the present invention, the oxidizer is an inconel tube of 10 cm diameter and 2 metre length.

[0018] Meanwhile, oxygen is preheated to 940oC to 980oC in an oxygen preheater, wherein said pre-heated oxygen is passed to the oxidizer, as shown in the figure. Silica sand mixture is also fed into oxidizer to erase the pigment from the oxidizer whereas liquefied petroleum gas is also passed simultaneously through the oxidiser for attaining the reaction temperature of 1200oC. Specifically, the silica sand mixture is slowly released to the oxidizer, followed by simultaneous introduction of titanium tetra chloride, liquefied petroleum gas and pre-heated oxygen into the oxidizer. The reaction between titanium tetrachloride and oxygen to form titanium dioxide is exothermic, wherein the heat generated by said reaction is sufficient for the sustainability of the reaction.

TiCl4 + O2 ------? TiO2 + 2Cl2

[0019] The silica sand mixture comprises of silica sand mixed with 3-5% by weight of nano rutile titanium dioxide, wherein it is added to the oxidizer. Said seed quantity (3-5%) is computed based on the Ti content present in the titanium tetrachloride. The seed will act as nuclei and the nano rutile particles will be formed of particle size same as the seed (i.e. less than 40 nm).

[0020] The reaction temperature is 1200oC. After the reaction is completed, the nano rutile titanium dioxide obtained is cooled and chlorine is collected from top of pigment separator and is stored. The nano rutile titanium dioxide formed is then filtered, washed and stored. The particle size of the product was analysed by TEM and was found to be between 10-40 nm. The XRD data showed that crystallinity was of rutile in nature.

Example

[0021] Three tonnes of tickle (TiCl4) is vaporized to a temperature of 350oC, wherein it was heated in three stages as mentioned in the description above. Oxygen is pre-heated at 950oC, whereas the sand scouring mixture prepared comprises of 50 kg of nano titanium dioxide mixed with silica sand. Said silica sand mixture is slowly released to the oxidizer, followed by simultaneous addition of titanium tetra chloride, liquefied petroleum gas and pre-heated oxygen into the oxidizer. Tickle vapour is fed into the oxidizer at a flow rate of 3T/Hr, and liquefied petroleum gas at the rate 9.2 nm3 and pre-heated oxygen at flow rate of 415 nm3 respectively. The chemical reaction inside the oxidizer takes place at 1200oC wherein the nano rutile titanium dioxide of particle size 10 to 40 nm subsequently formed is filtered, washed and stored. The chlorine is collected from top of pigment separator and is stored.

[0022] Although the present invention has been described in connection with the preferred embodiments thereof, 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 unless they depart there from.