Process to make rutile pigment from aqueous titanium solutions
A process to make rutile pigment from aqueous titanium solutions. The process involves the addition of a catalyst and is conducted under low temperature conditions using comparatively short calcinations times.
1 . A low-temperature process for producing pigment-grade rutile titanium dioxide from an aqueous solution comprising the following sequential steps:
a. preparing an aqueous feed solution comprising a titanium compound;
b. adding an effective amount of a catalyzing salt to the solution;
c. optionally adding a chemical control agent to the solution;
d. evaporating the solution to produce a dry amorphous intermediate that includes a mixture of titanium compounds; and
e. calcining the intermediate to form TiO 2 rutile pigment base.
2 . The process of claim 1 further comprising washing the salt from the calcined TiO 2 rutile pigment base.
3 . The process of claim 2 further comprising milling and dispersing the TiO 2 rutile pigment.
4 . The process of claim 1 wherein the titanium compound is selected from the group of titanium chloride, titanium oxychloride, and mixtures thereof.
5 . The process of claim 1 wherein the titanium compound is titanium oxychloride.
6 . The process of claim 1 wherein the catalyzing salt is a salt of an alkali metal.
7 . The process of claim 1 wherein the catalyzing salt is selected from the group consisting of chloride salts.
8 . The process of claim 7 wherein the chloride salts are selected from the group consisting of NaCl, KCl, LiCl and mixtures thereof.
9 . The process of claim 7 wherein the chloride salts comprise a eutectic mixture of NaCl, KCl, and LiCl.
10 . The process of claim 7 wherein the chloride salts comprise a eutectic mixture of LiCl and KCl.
11 . The process of claim 7 wherein the chloride salts comprise a eutectic mixture of LiCl and NaCl.
12 . The process of claim 1 wherein the catalyzing salt is present in the feed solution in an amount from about 3 weight % of the equivalent amount of TiO 2 present in the feed solution and the amount corresponding to the saturation point of the catalyzing salt in the feed solution.
13 . The process of claim 1 wherein the catalyzing salt present in the feed solution is from about 10 weight % and about 50 weight % of the equivalent amount of TiO 2 present in the feed solution.
14 . The process of claim 1 wherein the amount of the catalyzing salt is between about 15 weight % and about 30 weight % of the equivalent amount of TiO 2 present in the feed solution.
15 . The process of claim 1 wherein the catalyzing salt does not significantly chemically react with titanium oxide through the process.
16 . The process of claim 1 wherein the catalyzing salt does not significantly change chemical composition.
17 . The process of claim 1 wherein the catalyzing salt is recycled.
18 . The process of claim 1 , wherein the TiO 2 rutile pigment base comprises an open network of rutile crystals.
19 . The process of claim 1 wherein the catalyzing salt has a melting point of less than 800° C.
20 . The process of claim 1 wherein the calcining is conducted at a temperature less than 800° C.
21 . The process of claim 1 wherein the calcining is conducted at a temperature less than 700° C.
22 . The process of claim 1 wherein the calcining is conducted at a temperature less than 600° C.
23 . The process of claim 1 wherein the calcining is conducted at a temperature less than 500° C.
24 . The process of claim 1 wherein the calcining is conducted at a temperature less than 400° C.
25 . The process of claim 1 wherein the calcination time is between the time needed to melt the catalyzing salt and about 24 h.
26 . The process of claim 1 wherein the calcination time is less than about two hours.
27 . The process of claim 1 wherein the calcination time is less than about 30 minutes.
28 . The process of claim 1 wherein the calcination time for is less than about one minute.
29 . The process of claim 1 wherein the chemical control agent is added before evaporating.
30 . The process of claim 27 wherein the chemical control agent is a water-soluble salt of tin.
31 . The process of claim 27 wherein the chemical control agent is tin chloride.
32 . The process of claim 1 wherein the evaporating is conducted in a spray drier.
33 . The process of claim 1 wherein the evaporation temperature is between about 100° C. and about 300° C.
34 . The process of claim 1 wherein the amorphous intermediate comprises a homogeneous mixture of titanium, oxygen, chlorine, and hydrogen compounds, with a homogeneous distribution of salts through the titanium intermediate.
35 . The process of claim 32 wherein the product after calcination comprises TiO 2 rutile crystallites bound in a structure of hollow spheres or parts of spheres.
36 . The process of claim 33 wherein the spheres have a diameter of about 0.1 to about 100 μm.
37 . The process of claim 33 wherein the crystallites have a particle size between about 10 nm and 1000 nm.
38 . The process of claim 33 wherein the crystallites have a particle size between about 50 nm and 500 nm.
39 . The process of claim 33 wherein the crystallites forming the hollow spheres have a particle size between about 100 nm and 300 nm.
40 . The process of claim 1 wherein the washing is conducted with water to provide an aqueous salt solution and the TiO 2 rutile pigment base.
41 . The process of claim 40 further comprising recycling the salts in the aqueous salt solution.
42 . The process of claim 41 further comprising milling the washed TiO 2 rutile pigment base product.
43 . The process of claim 1 wherein a thermodynamically unstable brookite phase is formed as an intermediate during the early stages of calcination.