Black Liquor Gasification with Direct Causticization Using Titanates - Recycling Effects on the Solid Sodium Titanates

摘要

One promising alternative recovery process is black liquor gasification with direct causticization using titanates where not only the recovery boiler is replaced by a gasifier but also the conventional lime cycle is replaced by a titanate cycle with direct causticization in the gasifier. In this study, the recycling effects on the solid sodium titanates in the titanate process have been studied. Repeated recycling has been carried out, i.e. the same material has passed through several cycles of high temperature reactions (850℃, atmospheric pressure in N_2 atmosphere) and leaching (100℃ and atmospheric pressure). Analyses to study the chemical composition, surface changes and particle size changes were performed and evaluated. The analyses showed that sodium penta-titanate was the main product formed in the heat treatment and, tri- and hexa-titanate were the main species found after the leaching procedure. The surface area of the particles decreased during the high temperature reaction, while it was regained somewhat upon leaching. In addition, the sintering of the particles increased with the number of recycles. A change in the crystal structure occurred during the heat treatment: a needle-like structure was obtained after the first leaching steps and could hardly be seen after the final recycles.