Cleaning of an inorganic ultrafiltration membrane has been quantified through hydraulic, physicochemical, and spectroscopic (infrared and x-photoelectron spectroscopy) analyses. An efficient cleaning sequence of nitric acid followed by sodium hypochlorite has been proposed for cleaning of defatted whey protein concentrate and milk ultrafiltration membranes. The influence of reversed sequence and time reduction are discussed together with the action of both cleaning chemicals. In spite of residual fouling left after every cleaning sequence studied, hydraulic cleanliness of the membrane was achieved, particularly after the standard procedure.
The interaction between zirconia and polyethyleneimine (PEI) has been characterized using Fourier
transform infrared analysis (FTIR) and X-ray photoelectron spectroscopy (XPS). For FTIR, polyvinylimidazole
with an aromatic amine group and tetraethylenepentamine were added for an in-depth study: two new
broad bands due to nitrogen coordinated with zirconium are seen in the 1580−1560 cm-1 region and
1450−1350 cm-1 region, respectively. XPS shows that both ZrOH and N+ were involved in a minor part
only, in good accordance with FTIR. After a cross-linking step of the adsorbed PEI on zirconia, a ratio of
about one molecule of cross-linker to five PEI units was obtained by both methods. From XPS Zr 3d signal
attenuation, the PEI thickness on plates is about 1.2 and 3.5 nm before and after the cross-linking step,
respectively; the cross-linked PEI thickness on zirconia membrane is larger because of the procedure of
coating or porous and tubular character of membranes.
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