GB791657A - Improvements in or relating to the preparation of titanium dioxide - Google Patents

Abstract

In the production of rutile titanium dioxide pigment by reacting titanium tetrachloride vapour and oxygen or oxygen containing gases in a reaction chamber, the molar proportion of titanium tetrachloride and oxygen is from 1 : 1 to 1:6, one or both of these being pre-heated to produce when mixed and irrespective of the heat of reaction, a temperature not below 300 DEG C. The reaction gases are passed in two separate streams in the same direction in the reaction chamber, the titanium tetrachloride stream being within the oxygen stream and the ports for the titanium tetrachloride have a perimeter per unit cross-section area greater than 26 cm.-1. The velocity ratio of oxygen to titanium tetrachloride is less than unity and the velocity of each gas is maintained so that the Reynolds flow number does not exceed 1800 and 500 respectively for the titanium tetrachloride and oxygen in the feed ports immediately prior to admission to the reactor. The oxygen may contain 0 to 5 per cent water vapour and the titanium tetrachloride may contain 0 to 25 per cent of silicon tetrachloride. It is preferred that the titanium tetrachloride feed ports are retracted relative to the oxygen feed ports and the ratio of the velocity of oxygen to titanium tetrachloride is preferably from 0.1 to 0.2: 1. The reaction gases are preferably admitted to the reactor through parallel and preferably concentric ducting, such ducting being straight sided and parallel for a length at least 20 times the hydraulic radius when the gas velocities are associated with a Reynolds flow number of 1800. Shorter lengths of straightsided and parallel ducting may be tolerated for lower gas velocities. The reaction chamber may be constructed of silica alumina refractory concrete or fired steatite. The latter may be advantageously employed for the construction of the burner ports by shaping it in its raw mineral state. The reaction chamber is preferably such that a ratio of at least 10 to 1 between the diameter of the reaction chamber and the external diameter of the feed ports is obtained. Liquid cooling devices may be employed around the burner tips. A number of examples and comparative examples are provided.