Abstract
Carboxylic acid could be produced by anaerobic digestion of waste biomass and used as feedstocks for various chemical processes. The recovery of carboxylic acid and the optimization of organic acid producing are the challenges of this bioconversion. In this study, MCM-41 type amine functionalize mesoporous silica (MPS) was used as an adsorbent to separate carboxylic acids. The experimental data fitted with a modified Langmuir model. At an amine density of 3.14 mol N kg -1 , the highest acid adsorption capacity experienced was 3.38 mol kg -1 . The reaction was exothermic and favored at low temperature. More than 90% of maximum adsorption would be achieved at pH < 4. By increasing pH above 10.5 using alkali chemicals, the desorption/regeneration completed within 1 minute. The interferences such as ethanol, glucose and protein did not affect organic acid adsorption significantly. However, anions at the high concentration might compete acetic acid to adsorb at the same site of adsorbent. MPS has a high selectivity for carboxylic acid. The pseudo-second-order rate constant for acetic acid adsorption on MPS was 0.41 kg mol -1 min -1 which is higher than that of anion exchange resin and activated carbon. The maximum organic acid yield from serum-bottle test using corn stover as a sole substrate was 0.25±0.02 g/gVS and decreased when the substrate concentration increased. Acid inhibition might play an important role in this phenomenon. With dilution rate of 0.5 d -1 in leaching bed reactor study, the highest organic acid yield and productivity were 0.14 g/gVS and 0.70 g/L/d, respectively. On the other hand, the maximum organic acid yield from semi-batch reactor in this study was 0.056 g/gVS at substrate concentration of 70 gVS/L and hydraulic retention time of 5 days. The maximum organic acid productivity obtained from this study is 1.319 g/L/d at substrate
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