Continuous Carbonation for Synthesis of Pseudo-Boehmite by Using Cross-Flow Rotating Packed Bed through the Reaction of NaAlO(2) Solution with CO(2) Gas

This research established a novel method for the preparation of pseudo-boehmite (PB) via a continuous carbonation of CO(2) gas and a NaAlO(2) solution in a cross-flow rotating packed bed (CF-RPB). In the CF-RPB, the NaAlO(2) solution can be sheared into fine liquid filaments and droplets, and react in full contact with the CO(2) gas. Effects of synthesis parameters, including the concentration of the NaAlO(2) solution, the gas–liquid ratio, the rotating speed of the CF-RPB, and the final pH of the solution on the crystal structure of PB, were fully investigated. A series of characterizations, including X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Brunauer–Emmett–Teller (BET) analysis, were carried out to explain the evaluation results and to find the relationship between PB properties and the synthetic conditions. The results showed that PB with a high specific surface area (495 m(2)/g) and large pore volume (2.125 cc/g) can be obtained when the concentration of the NaAlO(2) solution was 0.1 mol/L, the gas–liquid ratio was 3:1, the rotating speed of RPB was 600 rpm, and the final pH was around 10.5. PB obtained by this method had a higher quality compared with that using a stirred tank reactor. Moreover, the continuous carbonation can be efficiently batch-produced, which provided a new idea for an industrial application.