Ultrafiltration behaviors of pectin-containing solution extracted from citrus peel on a ZrO<sub>2</sub> ceramic membrane pilot unit
Ultrafiltration experiments on a solution of pectin, hesperidin, and other mixtures extracted from citrus peels have been performed on a 500 l /min pilot scale crossflow ceramic membrane unit. A 30,000 molecular weight cut-off (MWCO) zirconia (ZrO 2 ) ceramic membrane with a total effective flow area of 0.5 m 2 was used in the process. The permeate flux for pure water and hesperidin showed linear relationship with transmembrane pressure (ΔP), but the flux for pectin solutions showed a curvilinear relationship with ΔP and represented a rapid increase with increasing ΔP before leveling-off. Similar behavior was observed by adding different amounts of hesperidin to these pectin solutions, but with much lower permeate flows. The formation of gel layers on the membrane surface is mainly responsible for the lower permeate fluxes. In addition, the permeate flux decrease faster at higher ΔP, since higher ΔP brought bigger flux at lower pectin concentration. Compared with the more than 90% retention rate of macromolecular pectin, pigment and other component have less than 20% retention rate. So, the decolorization, the separation and purification of pectin preparations could be achieved simultaneously through ultrafiltration with a ceramic membrane.