Nanofiltration studies of larger organic microsolutes in methanol solutions

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Multistep organic solvent-based pharmaceutical syntheses of larger organic microsolutes having molecular weights (MW) in the range of 300-1000 generally require athermal separation processes because the active molecules and the intermediates are thermally labile. To that end, nanofiltration (NF) of methanol solutions of three selected solutes, safranin O (MW 351), brilliant blue R (MW 826) and vitamin B12 (MW 1355) has been studied in a batch stirred cell for a dilute solution of each individual solute at 3034kPa (440psig). The solvent-resistant membranes investigated and their manufacturer-specified molecular weight cut-offs (MWCO) are MPF-44 (250), MPF-50 (700) and MPF-60 (400). During an initial transient period, the solvent flux decreased with time and the solute rejection increased with time for every membrane reaching a steady state after about 12h. This behavior resulting from membrane compaction and pore size reduction was partially reversible. Additional studies using higher feed solute concentrations (1 and 3wt.%) show considerable reduction in solvent flux and increase in solute rejection; the effect appears to be far more than that due to an increase in osmotic pressure and possible reasons for such a behavior have been suggested. The observed solute rejection values are generally significantly lower than the manufacturer-specified MWCO values. Additional studies varying the feed solution pressure through the membrane MPF-60 indicate that the variation of the percent rejection of solutes safranin O and brilliant blue R with the solvent flux tends to follow the relation suggested by the Finely Porous Model. (C) 2000 Elsevier Science B.V.

Original languageEnglish (US)
Pages (from-to)159-172
Number of pages14
JournalJournal of Membrane Science
Issue number2
StatePublished - May 31 2000

All Science Journal Classification (ASJC) codes

  • Biochemistry
  • General Materials Science
  • Physical and Theoretical Chemistry
  • Filtration and Separation


  • Membrane reactor
  • Methanol solution
  • Nanofiltration
  • Organic separations


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