Abstract: A process for reacting titanium tetrachloride vapors with oxygen including a first oxygen preheat assembly for preheating oxygen to a first predetermined temperature and a titanium tetrachloride preheat assembly for preheating titanium tetrachloride to a relatively low, temperature. The process includes adding a second oxygen preheat assembly for preheating oxygen to a second temperature substantially below the first temperature, and includes a second reaction zone adapted for receiving the mixture from the first reaction zone, the oxygen at the second temperature being reacted with the titanium tetrachloride in the mixture from the first reaction zone to produce titanium dioxide. Also provided is a process for the preparation of titanium dioxide comprising reacting titanium tetrachloride with oxygen at an elevated pressure and at a temperature above about 1750.degree. F.