Acrylamide production in an ultrafiltration-membrane bioreactor using cells of Brevibacterium imperialis CBS 489-74

Both differential and integral UF-membrane reactors were tested for the bioconversion of acrylonitrile into acrylamide. Use was made of the commercially available flat membrane cell Amicon Mod.52 and the UF-membranes FS81PP, GR81PP, and YM100. The enzymatic reaction was catalyzed by the nitrile hydratase (NHase) present in resting cells of Brevibacterium imperialis CBS 489-74. The system was operated at 4°C and 10°C. Acrylonitrile concentration ranged from 50 to 500 mM. The membrane resistance to chemicals was complete at acrylonitrile and acrylamide concentrations up to 800 mM and 2 M, respectively. No rejection of solute was determined. Membranes totally retained the resting cells and no fouling was observed working with 2 and 16 mg of biocatalyst in stirred systems. Membrane compaction was apparently responsible for roughly 35% flux loss during the first 3–4 h of operation. The laboratory scale membrane bioreactor, continuously operating, allowed to show the dependence of enzyme deactivation on acrylonitrile concentration and process time. Substrate concentration higher than 100 mM were highly detrimental for NHase stability. The acrylamide yield reached in the multi-cycle process operating with 5.6 g/l of resting cells was 93.7% and the product concentration during roughly 450 h of bioconversion attained 8.3% (w/v). Decay of specific membrane flux was 98% of the initial value.