Influence of gas addition on crystallisation behaviour of lactose from supersaturated solution

The effect of gas (CO2 and N2) addition in supersaturated lactose solution on yield, size, shape, densities and flow behaviour indices of crystallised lactose was examined. Gas was introduced through a sintered porous metal tube at 0, 10 and 30 mL min−1 flow rates in a custom-built double jacketed glass crystalliser at 20 °C. Low power ultrasound (US; 205 kHz) was applied (0, 2 or 120 min) through a metal transducer flanged beneath the crystalliser after gassing. The whole solution was mechanically agitated at 200 rpm for 120 min at 15 °C. Recovered and dried lactose crystals were then analysed. Addition of gas alone or in combination with sonication enhanced the lactose yield due to acceleration of crystal nucleation and reduction of crystal size. The results showed that higher amounts of gas decreased lactose crystal size and due to the differences in solubility of gases, the effect on particle size, d(0.5), was more pronounced with CO2 (∼92 μm) than N2 (∼170 μm) as compared to without gas (∼178 μm). In general, the particle densities were unaffected by gas addition and similar flow behaviour indices among crystals were noted regardless of treatments.