Although butanol is a promising biofuel, its fermentative production suffers from inhibition caused by end product toxicity. The in situ removal of butanol from cultures via expanded bed adsorption offers an effective strategy for mitigating the effects of product toxicity while eliminating the need to clarify cultures via microfiltration. The hydrophobic polymer resin Dowex Optipore L-493 was found to be both an effective butanol adsorbent and suitable for use in expanded bed adsorption. Recirculation rates through the adsorption column were strongly correlated with and ultimately controlled rates of butanol uptake from the media which, reaching as high as 41.1 g/L h, easily exceed those of its production in a typical fermentation. Vacuum application with vapor collection was found to be an effective means of adsorbent regeneration, with an average of 81% butanol recovery possible, with butanol concentrations in the cold trap reaching as high as 85.8 g/L. Integration of expanded bed adsorption with a fed-batch Clostridium acetobutylicum ATCC 824 fermentation and its continuous operation for 38.5 h enabled the net production (i.e., in solution and adsorbed) of butanol and total solvent products at up to 27.2 and 40.7 g/L of culture, respectively, representing 2.2- and 2.3-fold improvements over conventional batch culture. While adsorbent biofouling was found to be minimal, further investigation of biofouling in longer-term studies will provide useful and further insight regarding the robustness of the process strategy.
The hydrophobic silica aerogel Cabot
Nanogel TLD302 was evaluated as an adsorbent for recovering 2–5
carbon n-alcohols from aqueous solutions. Whereas
intraparticle transport limitations restricted adsorption under dilute
conditions, at higher concentrations, improved surface wetting resulted
in facile “pore intrusion” and ∼5-fold increases
in adsorption capacity for all alcohols. To promote surface wetting
and pore intrusion at lower concentrations, partial oxidation of TLD302
was performed by heat treatment to create a series of novel aerogel
materials with tunable surface hydrophobicities. An optimum surface
oxidation state was found to exist wherein pore intrusion under dilute
conditions was achieved while still balancing high adsorption affinity.
Lastly, the optimized aerogel adsorbent was used to recover n-butanol from a Clostridium acetobutylicum ATCC 824 fermentation broth. Relative to model solutions, no loss
of adsorption affinity or capacity was observed, indicating that competitive
coadsorption by other media components was not a performance-limiting
factor.
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