Coprecipitation Synthesis of Large-Pore-Volume γ-Alumina Nanofibers by Two Serial Membrane Dispersion Microreactors with a Circulating Continuous Phase
Zhiyuan Yu, Chengyu Guo, Xinmei Pang, Yuge Shen, Mingtang Gao, Shenyuan Zhao, Yujun Wang, Guangsheng Luo
Abstract
A coprecipitation method was developed for the synthesis of fibrous γ-alumina using serial membrane dispersion microreactors with a circulating continuous phase and high concentrations of NaAlO 2 and Al 2 (SO 4 ) 3 as reactants. Owing to the ultra-high mixing intensity and reduction of supersaturation due to the large circular phase ratio, a large pore volume and specific surface area and an extremely narrow pore diameter distribution were realized using the high-concentration and high-viscosity precipitation system. The influence of the phase ratio, dispersion order of reactants, Al 2 (SO 4 ) 3 residence time, and the precipitation reaction pH and time were investigated, and the nanofiber formation mechanism was explored employing theoretical calculations. By controlling the Al 2 (SO 4 ) 3 residence time of 3 s, phase ratio of 16, and pH of 8.0, γ-Al 2 O 3 nanofibers with a pore volume of 1.36 cm 3 /g, a specific surface area of 376 m 2 /g, and a length/diameter ratio in the range of 30–54 were obtained without any organic reagents. This study provides an economical and readily scalable method for the synthesis of fibrous γ-Al 2 O 3 with excellent pore properties and a large specific surface area, which can potentially be applied as an excellent catalyst support for diesel and bio-oil hydrogenation.