| Popis: |
In this study, a separation cascade was developed for the recovery of medium-chained fatty acids (MCFAs) from fermentation broth (FB) using membrane technologies. The MCFAs were produced by the fermentation of maize silage in a mixed-culture chain-elongation process. The separation cascade consists of a basket press for solid-liquid separation, ultrafiltration (UF) for the removal of suspended solids and macromolecules, and nanofiltration (NF) to concentrate the MCFAs. Two ceramic UF membranes and three polymeric flat-sheet NF membranes were trialled in a technical-scale crossflow filtration. Investigations to establish the ideal process conditions were based on yield, flux and energy expenditure and included: thermal pretreatment, filtration parameter studies, UF and NF membrane screening, diafiltration, and membrane fouling analysis. In UF, permeate fluxes of >50 kgm‑2h‑1 and volume reductions of ~0.9 were achieved. Pretreatment and membrane pore size had no considerable influence on permeate flux and the limiting factor was concluded to be the formation of a cake layer on the membrane surface. In NF, volume reductions of >0.6 were attained, and the Tricep TS80 membrane had the highest MCFA retentions (>90%). Although initial NF permeate fluxes with this membrane were high (60-80kgm‑2h‑1), flux decline due to membrane fouling occurred rapidly, and near-total blockage limited the final concentration of MCFAs. While direct industrial application is restricted by the inadequate MCFA concentration, characterisation and reduction of NF membrane foulants could make this process viable. As it stands, this membrane filtration cascade provides an improved feedstock for the final purification of MCFAs by extraction or distillation. |
