Continuous preparation of titanium dioxide seed suspensions

Claim 2

The process as defined in claim 1 wherein the titanium concentration in said stream of aqueous feed solution ranges from about 0.3 to about 0.42 gram-atoms per liter.

Claim 3

The process as defined in claim 1 wherein said hydrogen concentration in said stream of aqueous feed solution is such that twice the titanium concentration plus the hydrogen concentration ranges from about 0.36 to about 0.6 gram-atoms per liter.

Claim 4

The process as defined in claim 1 wherein the stream of aqueous feed solution is heated to a temperature of from about 85* to about 100* C. and maintained at said temperature for from about 5 to about 20 minutes to form said seed suspension.

Claim 5

A continuous process for preparing an opalescent seed suspension of colloidal titanium dioxide particles which comprises: a. heating a stream of an aqueous feed solution having a titanium concentration at the maximum of about 0.6 gram-atoms per liter, a chloride to titanium gram-mole ratio of at least 1.8, a hydrogen concentration such that twice the titanium concentration plus the hydrogen concentration at the maximum is about 1.2 gram-atoms per liter and not more than 0.1 gram-atoms per liter of multivalent anions to a temperature of from about 80* C. to about 125* C. while flowing said stream upwardly in laminar flow, said flow characterized as having a Reynolds number of less than about 2,100, through a substantially vertical heating zone to form a heated feed solution; b. conducting the flowing stream of heated solution at a temperature of from about 80* to about 125* C. through a reaction zone, said stream being maintained at said temperature for a total period of from about 1 to about 30 minutes, at a flow rate adjusted to prevent bulk back-mixing of reacted portions of the flowing stream containing titanium dioxide particles with the unreacted portion of the flowing stream which does not contain said titanium dioxide particles; and c. continuously removing said titanium dioxide particles from said reaction zone.

Claim 6

The process as defined in claim 6 wherein said stream of heated feed solution from said heating zone is conducted at a temperature not greater than the temperature of the stream from the heating zone downwardly in laminar flow through a substantially vertical reaction zone to form said seed suspension said reaction zone being characterized as designed to prevent bulk back-mixing of portions of the stream which differ substantially as to the degree of reaction attained therein and said laminar flow is characterized as having a Reynolds number of less than about 2,100.

Claim 7

The process as defined in claim 6 wherein said stream of heated feed solution is conducted at said temperature through a reaction zone having a sufficiently restricted cross-sectional area such that at the volume flow rate of the stream turbulent flow characterized as having a Reynolds number of greater than about 2,100 results, thereby forming said seed suspension while preventing bulk back-mixing of portions of said stream differing substantially as to the degree of completion of the reaction attained therein.

Claim 8

The process as defined in claim 1 including continuously mixing a stream of a concentrated aqueous solution with a stream of water in a mixing zone in turbulent flow in proportions required to form said aqueous feed solution.

Claim 9

The process as defined in claim 9 wherein said concentrated aqueous feed solution contains at least about 4.2 gram-atoms per liter of titanium and a chloride to titanium gram-mole ratio of at least 2.

Claim 10

A continuous process for preparing an opalescent seed suspension of colloidal titanium dioxide particles which comprises: a. mixing a stream of concentrated aqueous solution, containing at least about 4.2 gram-atoms per liter of titanium and a chloride to titanium gram-mole ratio of at least 2 and having a temperature of less than about 70* C., with a sufficient quantity of a stream of water having a temperature of from about 80* to 140* C. to provide a heated flowing stream of aqueous feed solution having a temperature of from about 80* to about 125* C., the flow of said stream being characterized by an average Reynolds number of greater than about 2,100; b. conducting said heated stream at said temperature through a reaction zone, said stream being maintained at said temperature for a total period of from about 1 to about 30 minutes, at a flow rate adjusted to prevent bulk back-mixing of reacted portions of the flowing stream containing titanium dioxide particles with the unreacted portion of the flowing stream which does not contain said titanium dioxide particles; and c. continuously removing said seed suspension from said reaction zone.

Claim 11

A continuous process for preparing an opalescent seed suspension of colloidal titanium dioxide particles which comprises: a. heating a stream of an aqueous feed solution having a titanium concentration at the maximum of about 0.6 gram-atoms per liter, a chloride to titanium gram-mole ratio of at least 1.8, a hydrogen concentration such that twice the titanium concentration plus the hydrogen concentration at the maximum is about 1.2 gram-atoms per liter and not more than 0.1 gram-atoms per liter of multivalent anions, by flowing said stream through a heating zone in turbulent flow, said flow characterized as having a Reynolds number of greater than about 2,100, to a temperature of from about 80* to about 125* C; b. conducting the flowing stream of heated solution at a temperature of from about 80* to about 125* C. through a reaction zone, said stream being maintained at said temperature for a total period of from about 1 to about 30 minutes, at a flow rate adjusted to prevent bulk back-mixing of reacted portions of the flowing stream containing titanium dioxide particles with the unreacted portion of the flowing stream which does not contain said titanium dioxide particles; and c. continuously removing said seed suspension from said reaction zone.

Claim 12

The process as defined in claim 11 wherein the heated stream of aqueous feed solution is flowed downwardly in laminar flow characterized as having a Reynolds number of less than about 2,100 through a substantially vertical reaction zone, while maintained at a temperature not greater than the temperature thereof when entering the reaction zone.

Claim 13

The process as defined in claim 12 wherein said stream of heated feed solution at said temperature is conducted through said reaction zone in turbulent flow characterized as having a Reynolds number of greater than about 2,100 so that back-mixing of portions of the flowing stream which differ substantially as to the degree of reaction attained therein is avoided, thereby forming said seed suspension.

Claim 14

The process as defined in claim 12 wherein said stream of heated reaction solution at said temperature is conducted downwardly in laminar flow characterized as having a Reynolds number of less than about 2,100 through a substantially vertical reaction zone to form said seed suspension, said reaction zone being designed to prevent bulk back-mixing of portions of the flowing stream which differ substantially as to the degree of reaction attained therein.