| dc.description.abstract | The MixAlco process, a proprietary technology owned by Texas A&M
University, converts biomass (e.g., municipal solid waste, sewage sludge, paper,
agricultural residues, and energy crops) into usable chemicals (e.g., acetic acid) and fuels
(e.g., ethanol). Historically, calcium carbonate has been used as the buffer. Recently, it
was found that using ammonium bicarbonate as the buffering agent enhances the
fermentation conversion. In this case, fermentation broth contains ammonium salts (e.g.,
ammonium acetate, propionate, butyrate, pentanoate). Therefore, the downstream
processing steps (including extraction, purification, esterification, and product
separation) must be compatible with the ammonium carboxylate salts formed in the
fermentation.
This research focuses on converting fermentation broth carboxylate salts into
their corresponding acids via "acid springing." Reactive extraction and thermal
conversion (distillation) are crucial parts of the acid springing process. Because the components of the fermentation broth are over 80% ammonium
acetate and 20% other ammonium carboxylate salts (ammonium propionate, butyrate,
pentanoate, etc.), all the initial experiments in this study were performed using reagentgrade
ammonium acetate to simplify the reaction. Later, actual fermentation broth was
employed.
The primary objective of this study was to provide the optimal operating
conditions to make the downstream processing steps of the MixAlco process compatible
with ammonium carboxylate salts formed in the fermentation. The optimal initial
concentration for reactive extraction should be 150-200 g/L and the volume ratio of
aqueous phase and extractant should be 1:1. The distribution coefficient reaches the
maximum value when the concentration of TOA is 20% (vol %) in n-octanol. The batch
distillation study shows that there are two reaction stages: (1) water leaves the system at
100-106 °C and (2) the acid-amine complex decomposes at 160-180 °C. | en |
