Pseudo-boehmite (PB) is often used as a precursor for hydrotreating catalyst support (gamma-Al-2 O-3) in the petroleum refining process. Recently, continuous-carbonation process was proposed to prepare PB in order to meet the increasing demand for macroporous gamma-Al2O3, but the highly dispersed particle size of PB in this process limited its development. To obtain the PB with monodispersed particle size, a 10 mm mini-hydrocyclone was designed by 3D printing technology and used to the classification for PB. Then a high-performance zone for classification with Re of 4000-5000 was obtained. The volume ratio of particles (>10 mu m) was increased from 56.3% to 83.5% at a split ratio of 15%, and the mean particle size was increased from 12.91 mu m to 45.7 mu m, which indicated that the highly dispersed particle size could be efficiently concentrated into monodispersed one by hydrocyclone classification. Under optimal operating conditions (Re of 4360 and R-f of 15%), the hydrocyclone was unprecedentedly applied to the continuous-carbonation preparation process of PB, and the volume ratio of particles (>10 mu m) was significantly increased from 53.1% to 75.6% in the pilot test. This finding contributed to optimize continuous-carbonation process and improve product performance. (C) 2019 Published by Elsevier B.V. on behalf of Institution of Chemical Engineers.