Abstract
This research established a novel method for the preparation of pseudo-boehmite (PB) via a continuous carbonation of CO2 gas and a NaAlO2 solution in a cross-flow rotating packed bed (CF-RPB). In the CF-RPB, the NaAlO2 solution can be sheared into fine liquid filaments and droplets, and react in full contact with the CO2 gas. Effects of synthesis parameters, including the concentration of the NaAlO2 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 m2/g) and large pore volume (2.125 cc/g) can be obtained when the concentration of the NaAlO2 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.
Highlights
Pseudo-boehmite (PB) is a kind of aluminum hydroxides with poor crystallization, which possesses high mechanical strength, a large specific surface area, and abundant pore volume
It could be the precursor of γ-Al2 O3 and the binder for a Fluid Catalytic Cracking (FCC) catalyst [1,2]
When the concentration of the NaAlO2 solution was 0.1 mol/L, the specific surface area and pore volume were the largest, with 455 m2 /g and 0.589 cc/g, respectively. This may be due to the fact that when the concentration of NaAlO2 solution increases from 0.05 mol/L to 0.1 mol/L, the gas–liquid is fully reacted with the increase of the solution concentration, the crystallinity of the product becomes better, and the specific surface area and pore volume increase
Summary
Pseudo-boehmite (PB) is a kind of aluminum hydroxides with poor crystallization, which possesses high mechanical strength, a large specific surface area, and abundant pore volume. It could be the precursor of γ-Al2 O3 and the binder for a Fluid Catalytic Cracking (FCC) catalyst [1,2]. With the increasing proportion of residue in FCC (Fluid Catalytic Cracking) feed stock, traditional PB, due to a low specific surface area and narrow pore size distribution, cannot meet the request for actual production. The low-cost preparation method for PB with a large pore volume and high specific surface area needs to be developed [3]. According to a previous study, the carbonation of a NaAlO2 solution and CO2 gas has become one of the most economical technologies to produce PB owing to its green manufacturing process and low cost
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