Recovery of α-lactose monohydrate crystals with favorable shape from dairy by-product using membrane crystallization

This study evaluates membrane crystallization (MCr) as a process-intensified route to recover α -lactose monohydrate crystals with controllable morphology from dairy by-products while simultaneously producing reusable high-purity water (EC < 5 μS/cm). The effects of operating conditions (i.e., feed temperature, feed flow rate, water recovery, and co-existing mineral impurities) on MCr performance and lactose crystal properties were systematically assessed. Feed temperature exerted a stronger influence on the process than flow rate, and together with water recovery governed crystal morphology. Elevated feed temperatures promoted the formation of larger rectangular crystals with smoother surfaces, particularly at 58% water recovery. In contrast, 30 °C and/or high water recovery (≥60%) at feed temperatures ≥40 °C favored tomahawk-shaped crystals. The presence of mineral impurities delayed the onset of crystallization, shifting crystal formation to higher supersaturation and also promoting tomahawk morphology. X-ray diffraction (XRD) confirmed the recovered solids as α -lactose monohydrate, with no detectable anhydrous β -lactose. Overall, the results demonstrate that MCr can couple lactose valorization with water reuse and provides an operational lever set to tailor lactose crystal habit, supporting more compact and sustainable dairy processing. Future work can be focused on validation with real whey matrices and broader compositional effects. • MCr recovered α -lactose monohydrate crystals with tunable morphology. • Salts delayed crystallization; T and RF enabled lactose morphology control. • Rectangular crystals dominated at elevated T, especially at 58% RF. • Tomahawk crystals formed at 30 °C or ≥60% RF ( T ≥ 40 °C). • MCr co-produced high-purity water (EC < 5 μS/cm) for reuse in dairy processing.