Importance of the control mode in ultrafiltration: case of raw cane sugar remelt Original Research Article

Experiments on microfiltration of raw cane remelts with tubular mineral membranes show that rigorous methodology is required if laboratory data are to be extrapolated to an industrial setting. We studied two main variables of ultrafiltration: sugar dilution and the control mode (constant pressure or constant permeate flux). Optimal sugar dilution, on the basis of the highest dry substance flux criteria, was in the range 28–33 g DS/100 g. Comparison between the two control modes, with the remelt at 30 g DS/100 g and 80°C and tubular mineral membranes (kerasep 15 kDa, Orelis, France), showed that use of a constant permeate flux reduced fouling of the mineral membrane without altering selectivity. The optimal flux setpoint of 100 l h−1 m−2 corresponded to the maximal productivity of 2.5 m3 m−2 day−1 (permeate volume collected per membrane area and per day, including time lost to cleaning) and the lowest cleaning frequency. The permeate flux control mode was favourable in ultrafiltration, but was less influential than in microfiltration. Ultrafiltration of remelt through spiral organic membrane (S4 HFK VSF 131, 5 kDa, Koch, USA) showed that the control mode was also less important in this case. Our results confirmed that the control mode is of importance in the particular case of microfiltration through tubular mineral membranes. Few relevant studies have been published, as these membranes are not widely used.