Effect of the evaporation time and of the annealing on the morphology and performance of cellulose acetate membranes

ROMERO DONDIZ, ESTELA M.; ALMAZÁN, JORGE E.; RAJAL, VERÓNICA B.; CASTRO VIDAURRE, ELZA F.

Amsterdam, The Netherlands

Congreso; International Congress on Membranes and Membrane Processes (ICOM 2011).; 2011

University of Twente

In  this  work,  we  report  about  cellulose  acetate  (CA)  ultrafiltration  (UF)  and nanofiltration (NF) membrane preparation according to the phase inversion process and post-treatment (annealing). The effect of tempo of evaporation (0 and 90 seconds) and  annealing  temperature  (75  to  88  ºC)  on  the  morphology  of  the  synthesized membranes  were  investigated.  The  morphology  and  structure  of  the  resulting membranes were observed by scanning electron microscope (SEM). The permeation performances  of  the  membranes  were  evaluated  in  terms  of  pure  water  flux (PWF),equilibrium water content (EWC), hydraulic permeability, and salts rejection rate (R) NaCl and Na2SO4 . Using cross-sectional images obtained by SEM, we observed that the membranes have an asymmetric structure, a decrease in the size of the macro-pores in sub-cape and pore size with increasing evaporation time. In all cases, the increasing evaporation time produces a decrease in the thickness of the membrane, the equilibrium water content and porosity.The effect of annealing on the membrane performance was investigated by changing the annealing temperature in distillation water. The annealing had great influence on reducing pore size of membrane (Wang, 1994; Kim, 2002). In hydraulic permeability tests  during  the  compaction  stage  there  was  a  decrease  in  permeate  flux  with increasing temperature post-treatment. A linear correlation between the permeate flux and operating pressure was also observed. The salt rejection rate increased sharply in the membranes synthesized with longer evaporation times. On the other hand, the increase  in  annealing  temperatures  increases  the  percent  rejection  of  salts  and reduces the pure water and salts fluxes. This study showed that evaporation time and annealing temperature have significant effects on morphology and permeation flux.ReferencesKim  I.-C.,  Yun  H.-G.,  Lee  K.-H.  (2002).  Preparation  of  symmetric  polyacrylonitrile membrane with small pore size by phase inversion and post-treatment process. J. Membr. Sci. 199, 75-84.Wang Y., Lau WWY, Sourirajan S. (1994). Effects of pre-treatments of morphology and performance of CA (formamide type) membranes. Desalination 95, 155-169.