Formed Activated Alumina for Adsorptive Water Separation from Compressed Air: A Critical Review of Material–Bed–Cycle Evidence and Failure Diagnosis

Water-vapor removal from compressed air is governed by the product pressure dew point (PDP), dynamic bed utilization, hydraulic loss, regeneration demand, and cyclic reliability, yet activated-alumina studies are often interpreted from powder Brunauer–Emmett–Teller (BET) area or equilibrium uptake alone. This critical narrative review evaluates where evidence can and cannot be transferred across material, formed-particle, packed-bed, cycle, and field scales. It distinguishes equilibrium capacity, static test capacity, dynamic breakthrough capacity, and usable cycle capacity; conditionally compares desiccants and regeneration modes; and links PDP-defined breakthrough, mass-transfer-zone (MTZ)/length-of-unused-bed (LUB) measures, non-spherical-particle pressure drop, thermal waves, and regeneration endpoints. The available evidence supports several directional conclusions but not universal design values: alkali modification can increase uptake despite lower surface area; forming and binder chemistry alter accessible pores and strength; wall effects and particle geometry require measured hydrodynamic validation; and reported regeneration savings of approximately 27–40% are architecture-specific relative results rather than matched absolute energy benchmarks. A baseline-normalized diagnostic framework separates reversible regeneration faults and feed contamination from material aging and particle/bed degradation. The review identifies the central evidence gap as the absence of matched datasets reporting formed-body properties, adiabatic breakthrough, segmented pressure drop, regeneration energy, and long-cycle failure for the same material. It concludes with a standards-coverage map, a transparent screening sensitivity analysis, and a prioritized validation agenda.