Purification of brown cane sugar solutions by ultrafiltration with ceramic membranes: Investigation of membrane fouling

This paper describes the purification and decoloration of brown cane sugar solutions by ultrafiltration with multichannel 2.5 mm inner diameter ceramic membranes of 15 kDa cutoff. Filtration tests were carried out at concentrations of 30, 40, and 50 degrees Brix, a temperature of 60 degrees C, and 3 and 5 m/s velocities. The permeate flux at 100 kPa decays continuously during 8 hours, reaching at the end 20 L/h.m(2) at 30 degrees Bx and 6 L/h-m(2) at 50 degrees Bx. Higher fluxes were obtained at 300 kPa. The permeate coloration stabilized at 1000 I.U. (ICUMSA units) from a retentate at 2400 I.U., representing a 58% decoloration rate. A comparison was made with microfiltration using a 0.1-mu m ceramic membrane. The permeate flux in this case was much higher, decaying from 140 to 100 L/h.m(2) in 8 hours for 30 degrees Bx. In order to reduce membrane fouling, other ultrafiltration tests were performed by superimposing velocity and pressure pulsations of 1 Hz frequency at the membrane inlet. A gain in permeate flux became significant (20%) after 3 hours of filtration. The permeate coloration was not augmented by the pulsations. Attempts to characterize this fouling and to determine its origin were made by comparing the variation of permeate flux or filtered volume versus time with existing fouling models. Best fits were achieved with cake filtration and pore narrowing models.