High-shear wet granulation of alumina with expanded Microspheres: Role of bio-based binders

Abstract

This study reports co-granulation of alumina (density = 3.95 g/cm³) and expanded hollow microspheres (EHMs, density = ∼ 60 mg/cm³) using various bio-based binders in a high-shear wet granulator. The significant density difference between alumina and EHMs posed a challenge for uniform mixing, which was effectively addressed by bio-based binders through hydrogen bonding and uniform film formation. Key granulation parameters, such as liquid-to-solid ratio and binder viscosity, were optimized to produce granules with desirable properties. The study systematically evaluated the effect of binder type, amount, and concentration on granule properties such as shape, size distribution, flowability, density, and compressive strength. Among the tested binders (chitosan, sucrose, and cellulose nanocrystals), granules with sucrose binder proved to be the strongest (∼120 kPa at 8 % strain), most flowable (angle of repose ∼28°) and narrow size distribution (90 % granules have a diameter between 3 and 6 mm). The excellent water solubility, hydrogen bonding capacity, and film-forming ability of sucrose primarily contributed to the cohesion between alumina and expanded hollow microspheres, although different in density and particle size, forming high-quality granules. After calcinating at 1200 °C, these granules maintained good compressive strength (∼350 kPa at 13 % strain) and exhibited desirable open and closed macroporosity, making them promising candidates for applications such as catalyst supports, separation etc. This research highlights the potential of sucrose as an optimal binder to produce alumina-based composite materials and porous ceramic granules, paving the way for further exploration in sustainable and eco-friendly material applications in e.g., the energy and the building sector.