Selective oxidation of colour-inducing constituents in raw sugar cane juice with potassium permanganate

Colour removal in raw sugar remains a crucial but expensive process in the sugar industry. In this report, permanganate (MnO₄^-) oxidation is explored as an alternative method to remove colour-inducing constituents in sugar cane juice/produced raw sugar. Experiments indicated alum, an inexpensive coagulant, was able to remove residual Mn species produced after MnO₄^- treatment. The optimal dosages of MnO₄^- and alum for decoloration of a 17 wt% raw sugar solution (70 °C) was found to be 4 mM and 2 g/l, respectively. Removal of colour and Mn removal were further improved at ambient temperature. Sucrose, the major component of raw sugar, was not affected during treatment with MnO₄^- and alum. Two-phase kinetic behaviour for MnO₄^- oxidation was observed, where an initial rapid oxidation phase is followed by a second slower reaction phase. These results suggest permanganate oxidation is a promising alternative for accomplishing the decoloration of raw sugar solutions.