Making 1 kt of cheese produces 9 kt of cheese whey permeate, a waste with 5% lactose, which is either discarded or dried for animal feed. One pathway to add value to this waste is to convert it to lactic acid (LA), a monomer for polylactic acid, the largest bioplastic produced in the world. Lactose hydrolyses to glucose and galactose. While Brønsted acidity enhances lactose hydrolysis, Lewis acidity favours the formation of lactic acid. For the first time, we tested both industrial whey permeate and purified lactose as feedstocks for LA over a heterogeneous catalyst–Er2O3/Al2O3. LA Yield from whey permeate reached 14%, while the maximum yield with purified lactose was 22%. LA yield was invariant with respect to mixing speed while increasing temperature accelerates the time it takes to reach quasi-equilibrium. Yield was also independent of pressure with either air, He, N2, or H2 in the vapour space above the liquid phase in the autoclave. LA yield over spent catalyst with fresh lactose was only 11%, which indicates that the catalyst deactivates. Based on XRF analyses, the Er2O3 mass fraction dropped from 15% to 5%, with 6.4% leaching into the aqueous phase after the first step but only 0.8% after the second test.
Houndedoke et al. (Sun,) studied this question.