US 4,784,841 AGranted

Process for the production of coarse, scrubbing aggregates of titanium dioxide particles by oxidation of titanium tetrachloride in the vapor phase and use of said aggregates for the prevention of deposit formation in the same production process

AssigneeKronos Titan G.m.b.H.

InventorsAchim Hartmann, Hans Thumm

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Abstract

A process for the production of coarse scrubbing aggregates of TiO.sub.2 particles by vapor phase oxidation of titanium tetrachloride. The particle aggregates of sizes above 0.15 mm are separated from the TiO.sub.2 fines by wet screening on a moving screen, calcined and returned to the process. In a preferred embodiment of the process, the titanium dioxide prior to calcination is admixed with 0.01 to 0.3% by weight alkaline hydroxides (related to anhydrous TiO.sub.2), hard particle aggregates of sizes between 0.2 to 2.0 mm being generated that are returned to the hot reaction mixture and used for the prevention of deposit formation on the surfaces of the heat exchanger. The process can be carried through in such a way that the quantities of coarse scrubbing TiO.sub.2 aggregates per unit of time consumed by abrasion and newly formed by sintering are equal, their percentages in recycling TiO.sub.2 thus remaining constant which simplifies the TiO.sub.2 production process.

Claims32

Dependent claims

A process for the production of coarse scrubbing aggregates of titanium dioxide particles by vapor phase oxidation of titanium tetrachloride with an oxygen-containing gas thereby forming a hot gaseous reaction mixture contianing suspeneded TiO.sub.2, previously recovered coarse TiO.sub.2 scrubbing aggregates being commingled with the hot gaseous reaction mixture, the hot reaction mixture being cooled, the titanium dioxide being separated from the cooled reaction mixture, coarse titanium dioxide aggregates of sizes above 0.15 mm being separated from TiO.sub.2 fines of sizes below 0.15 mm, recovered and recycled as scrubbing solids in the hot reaction mixture, the process comprising:

(a) adding coarse scrubbing aggregates of TiO.sub.2 particles of sizes above 0.15 mm to the hot reaction mixture subsequent to the vapor phase oxidation;
(b) cooling the hot reaction mixture indirectly to 350.degree.-500.degree. C.;
(c) separating the titanium dioxide form the cooled reaction mixture;
(d) slurrying the separated titanium dioxide with water;
(e) using a moving screen to separate the coarse titanium dioxide aggregates having particle sizes above 0.15 mm present in the agqueous slurry of step (d) form the TiO.sub.2 fines having particle sizes below 0.15 mm so as to form a residue on the moving screen;
(f) treating the residue on the moving screen with an aqueous solution;
(g) treating the moving screen residue that has been treated with an aqueous solution with an alkaline solution;
(h) calcining the treated moving screen residue;
and
(i) returning the calcined material in the form of coarse TiO.sub.2 scrubbing aggregates to the hot reaction mixture so as to form said coarse scrubbing aggregates of TiO.sub.2 added in step (a).

7 more elements

A process for the production of coarse scrubbing aggregates of titanium dioxide particles by vapor phase oxidation of titanium tetrachloride with an oxygen-containing gas thereby forming a hot gaseous reaction mixture containing suspended TiO.sub.2, previously recovered coarse TiO.sub.2 scrubbing aggregates being commingled with the hot gaseous reaction mixture, the hot reaction mixture being cooled, the titanium dioxide being separated from the cooled reaction mixture, coarse titanium dioxide aggregates of sizes above 0.15 mm being separated form TiO.sub.2 fines of sizes below 0.15 mm, recovered and recycled as scrubbing solids in the hot reaction mixture, the process comprising:

(a) adding coarse scrubbing aggregates of TiO.sub.2 particles of sizes above 0.15 0.15 mm to the hot reaction mixture subsequently to the vapor phase oxidation;
(b) cooling the hot reaction mixture indirectly to 350.degree.-500.degree. C.;
(c) separating the titanium dioxide from the cooled reaction mixture;
(d) slurrying the separated titanium dioxide with water;
(e) using a moving screen to separate the coarse titanium dioxide aggrgates having particle sizes above 0.15 mm present in the aqueous slurry of step (d) form the TiO.sub.2 fines having particle sizes below 0.15 mm so as to form a residue on the moving screen;
(f) treating the residue on the moving screen with an aqueous solution;
(g) treating the moving screen residue that has been treated with an aqueous solution with an aqueous titanium dioxide suspension to obtain a mixture containing 70 to 90% by weight TiO.sub.2 from the screen residue and 30 to 10% by weight TiO.sub.2 from the suspension (both percentages relative to anhydrous TiO.sub.2);
(h) calcining the mixture;
and
(i) returning the calcined material in the form of coarse TiO.sub.2 scrubbing aggregates to the hot reaction mixture so as to form said coarse scrubbing aggregates of TiO.sub.2 added in step (a).

7 more elements

Dependencies are inferred from the claim text.