Direct Causticization of Kraft Black Liquor with Recycled Sodium Titanate, 1998 International Chemical Recovery Conference Proceedings

The present paper deals with the reaction of recycled sodium titanate with either pure Na2 CO3 or the sodium salts in kraft black liquor solids (KBLS) in a semi-continuously operated pilot fluidized bed reactor. With Na2CO3 as feed the The titanate bed was fluidized by nitrogen, while air war introduced into the bed when KBLS was used. Na2 CO3 or KBLS were fed continuously to the preloaded and preheated fluidized bed of recycled sodium titanate particles. The recycled titanate was prepared by hydrolysing the sodium titanate product generated in the fluidized bed by earlier experiments with TiO2 and Na2 CO3. Solid samples were taken from the bed during an experiment and analysed quantitatively using wet chemistry, atomic emission spectrophotometry, X-ray fluorescence and ion chromatography techniques. Based on these analyses, the development of the different sodium titanate species were determined as a function of Na2 O/TiO2 molar ratio. The results show that a high causticization efflciency is obtained with KBLS as feed because the KBLS coats the recycled titanate, while a significant fraction of the Na2 CO3 particles remain intact in the bed of recycled titanate when Na2 CO3 is fed. Defluidization due to agglomeration is experienced with KBLS at a Na2 O/TiO2 molar ratio of about 0.5. Theoretical and visual evidence suggests that the increased diffusion resistance into the recycled titanate particles causes accumulation of an eutectic mixture on the surface of the particles which induces agglomeration. The bridging between agglomerated particles due to crystal growth at the interface may also play an important role in the agglomeration process.