Preparation and characterization of agarose–nickel nanoporous composite particles customized for liquid expanded bed adsorption

Agarose–nickel nanoporous composite matrices with a series of densities, named Ag–Ni, were prepared herein for expanded bed adsorption of nanobioproduct/bioproduct by a water-in-oil emulsification method. The optical microscope (OM), scanning electronic microscope (SEM) and particle size analyzer (PSA) were utilized in order to characterize the structure and morphology of the agarose–nickel composite. The results indicated that the matrices prepared had a spherical appearance, appropriate wet density of 1.73–2.56 g/ml, water content of 32.2–58.5% and porosity of 79.4–96.37% and pore size of about 100–150 nm. All the Ag–Ni beads follow logarithmic normal size distribution with the range of 60–230 μm and average diameter of 133.68–148.4 μm. One of the useful properties of the Ag–Ni particles is the high wet density up to 2.56 g/ml, which shows a potential for the operation in an expanded bed at high flow rate. The impact of nickel powder addition on the physical and hydrodynamic properties was also investigated. In addition, the fluidization behavior of the Ag–Ni particles under various conditions was characterized by the measurement of bed expansion and axial dispersion coefficients for the liquid phase when operated in a standard fluidized bed contactor. It was observed that the expansion factors were decreased with the increasing matrix density under the same velocity. The bed expansion and fluid velocity were correlated with Richardson–Zaki equation for all particles prepared and the correlation parameters (the terminal settling velocity Ut and expansion index n) were investigated. Using measurements of residence time distributions, hydrodynamic properties in the expanded beds were investigated and were compared with reported matrices in other literatures. In addition, the impact of the flow velocity, bed expansion degree and density of adsorbent on hydrodynamic properties in the expanded beds were investigated. The results indicated that the expansion factor showed little effect on the hydrodynamic properties while the fluid velocity was the most essential factor on this regard. Furthermore, the results indicated that the heavy matrices of Ag–Ni-3, Ag–Ni-4 and Ag–Ni-5, were more suited for high operation fluid velocity. In addition, even the light matrices, i.e. Ag–Ni-1 and Ag–Ni-2, seem to be superior to other matrices in hydrodynamic properties, which made them promising adsorbents for further use in EBA processes.