Kinetics of the Direct Causticizing Reaction between Sodium Carbonate and Titanium Dioxide or Sodium Trititanate

摘要

Gasification ofkraft black liquor increases the amount of Na_2CO_3 in green liquor. The increased causticization requirement may be eliminated by gasification in the presence of TiO_2 or sodium trititanate (Na_2O·3TiO_2) leading to the formation of sodium pentatitanate (4Na_2O·5TiO_2). Sodium pentati-tanate forms sodium hydroxide when contacted with water. The kinetics of this so-called direct causticization reaction ofNa_2CO_3 with TiO_2 or Na_2O·3TiO_2 were determinedin a novel reactor consisting of a stack ofAl_2O_3 trays. The reaction rate was determined from the CO_2 content of a carrier gas flowing over a thin layer of a mixture ofNa_2CO_3 and TiO_2 or sodium trititanate in each tray, and by continuous weight loss measurement. Excellent agreement was obtained between the two methods. Variables were the CO_2 concentration (0-10%) and temperature (630-740℃). The products were analyzed by X-ray diffraction measurements. The final yield ofNaOH was determined by titration.