Scaling up continuous eutectic freeze crystallization of lactose from whey permeate: A pilot plant study at sub-zero temperatures

Abstract

Eutectic freeze crystallization is explored as an alternative to the state-of-the-art evaporation process for the recovery of lactose from whey permeate. At the so-called eutectic freezing point, both water (the solvent) and lactose (the solute) crystallize and can be removed continuously while continuously feeding whey permeate. This continuous process is demonstrated on a pilot scale at sub-zero temperatures. In the first instance, only freeze concentration of whey permeate took place at -4 °C. It was possible to reach a lactose concentration of 30 wt% and hardly any nucleation was observed. The resulting ice had high purity, with a lactose concentration of ±2 wt%. Next, the eutectic phase was reached, and lactose and ice crystallized simultaneously and were continuously removed from the system, the resulting crystals had parallelogram morphology with an average size of 10 µm. Ice was recovered at a rate of 60 kg/h and lactose was recovered at a rate of 16 kg/h, yielding over 80% of the feed lactose. A conceptional design was proposed for an improved yield and reduction of energy. Yields of at least 80% and up till 95% could be achieved. Compared to the state-of-the-art mechanical vapor recompression (MVR), EFC is 80% more energy efficient.

Keywords: Continuous crystallization; Eutectic freeze crystallization; Freeze concentration; Lactose; Mechanical vapor recompression; Pilot plant; Whey permeate.