Hydrogen Production and Byproducts Separation

Abstract

For an economical and ecological acetone–butanol–ethanol (ABE) biorefinery, the valorization of all streams and produced components is necessary. The main products are the solvents ABE. In the fermentation effluent, the intermediates, butyric and acetic acids, are present, as well as the microbial cell constituents. The fermentation off-gas contains around 52–67% hydrogen and 33–48% carbon dioxide, representing significant amounts of interesting gases for further use. After completion of the fermentation process, the cell mass of the microorganism is often separated from the fermentation broth, prior to further treatment of the fermentation broth, using solid-liquid separation processes such as centrifugation, filtration or membrane filtration. In developing biorefinery concepts, the complexity of the whole process increases due to interconnection of various production processes. The increase in investment costs needs to be paid off by the value of the additional products. Successful combinations of ABE fermentation and anaerobic digestion, as well as the combination of dark fermentation for additional hydrogen production, ABE fermentation, anaerobic digestion, and cogeneration have been already developed. Such process combination reduces water demand significantly, avoids waste, and closes the cycles with the feedstock production in agriculture and reduces the amount of artificial fertilizer needed. This approach counts as double positive for the environmental impact of the process. Calculations, based on experimental data, have shown that the revenues for hydrogen from the fermentation off-gas can be in the range of those for the ABE solvents and can contribute around 50% each to the total revenues.