Process for controlling particle size and additive coverage in the preparation of titanium dioxide
The present disclosure relates to a vapor phase process for producing a substantially anatase-free titanium dioxide pigment comprising: reacting a vaporous titanium dioxide precursor and an oxygen containing gas in a reactor; and introducing a mixture of liquid titanium dioxide precursor and a liquid or finely divided solid compound comprising a element selected from the group consisting of Li, Be, B, Na, Mg, Al, P, S, K, Ca, Sc, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, As, Se, Rb, Sr, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Te, Cs, Ba, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg, Tl, and Pb, into the reactor at a point downstream of the addition of the vaporous titanium dioxide precursor, and the oxygen containing gas, and at a process temperature of about 1200° C. to about 1600° C. to produce titanium dioxide particles that are coated by the oxide formed from the element.
1. A vapor phase process for producing a substantially anatase-free titanium dioxide pigment comprising:
(a) reacting a vaporous titanium dioxide precursor and an oxygen containing gas in a reactor; and
(b) introducing a mixture of liquid titanium dioxide precursor and a liquid or finely divided solid compound comprising a element selected from the group consisting of Li, Be, B, Na, Mg, Al, P, S, K, Ca, Sc, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, As, Se, Rb, Sr, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Te, Cs, Ba, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg, Tl, and Pb, into the reactor at a point downstream of the addition of the vaporous titanium dioxide precursor, and the oxygen containing gas, and at a process temperature of about 1200° C. to about 1600° C. to produce titanium dioxide particles that are coated by the oxide formed from the element.
2. The process of claim 1 wherein the element is selected from the group of Ge, Nb, Li, Be, B, Mg, Al, P, K, Zn, Zr, Rb, Mo, Cs, and W.
3. The process of claim 2 wherein the element is selected from the group of Ge, Nb, B, P, Zn, W, and Zr.
4. The process of claim 1 wherein the titanium dioxide comprises less than about 0.7% anatase.
5. The process of claim 1 wherein the titanium dioxide precursor is titanium tetrachloride, TiCl 4 .
6. The process of claim 1 wherein the liquid compound comprises boron trichloride, phosphorous trichloride, or stannic tetrachloride.
7. The process of claim 1 wherein the finely divided solid compound comprises zirconium tetrachloride, zinc chloride, lithium chloride, cesium chloride, potassium chloride, magnesium chloride, aluminum trichloride, rubidium chloride, molybdenum pentachloride, stannous chloride, tungsten pentachloride, or tungsten hexachloride.
8. The process of claim 1 wherein the liquid or finely divided solid compound is introduced in an amount sufficient to provide the corresponding oxide content of about at least 0.1% by weight, based on the total weight of the pigment.
9. The process of claim 1 wherein an aluminum halide is added in step (a) along with the vaporous titanium dioxide precursor.
10. The process of claim 1 wherein the liquid titanium dioxide precursor is TiCl 4 , and where the mixture of liquid or finely divided solid compound and liquid TiCl 4 is added at a point in the reactor with a process temperature of about 1400° C. to about 1600° C.
11. The process of claim 1 wherein the liquid titanium dioxide precursor is TiCl 4 , and where the mixture of liquid or finely divided solid compound and liquid TiCl 4 is added about 0.002 to about 2 seconds after the addition of the vaporous titanium dioxide precursor and the oxygen containing gas.
12. The process of claim 1 wherein the liquid titanium dioxide precursor is TiCl 4 , and where the mixture of liquid or finely divided solid compound and liquid TiCl 4 is added at the point wherein oxidation of the vaporous titanium dioxide precursor is at least about 90% complete.
13. The process of claim 1 wherein an additional compound is mixed with the liquid or finely divided solid compound and liquid titanium dioxide precursor.
14. The process of claim 13 wherein the additional compound comprises at least one halide of boron, phosphorous, zirconium, tungsten, aluminum, zinc, sodium, calcium, or magnesium.
15. A durable titanium dioxide pigment coated by a metal oxide wherein at least 75% of the pigment particles are covered by a layer of amorphous metal oxide, the pigment produced by:
(a) reacting a vaporous titanium dioxide precursor and an oxygen containing gas in a reactor; and
(b) introducing a mixture of liquid titanium dioxide precursor and a liquid or finely divided solid compound comprising a element selected from the group consisting of Li, Be, B, Na, Mg, Al, P, S, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, As, Se, Rb, Sr, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Te, Cs, Ba, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg, Tl, and Pb, into the reactor at a point downstream of the addition of the vaporous titanium dioxide precursor, and the oxygen containing gas, and at a process temperature of about 1200° C. to about 1600° C. to produce titanium dioxide particles coated by the oxide formed from the element.