Process efficiency simulation for key process parameters in biological methanogenesis

• Main Authors: Sébastien Bernacchi, Michaela Weissgram, Walter Wukovits, Christoph Herwig
• Format: Article
• Language: English
• Published: AIMS Press 2014-09-01
• Series: AIMS Bioengineering
• Subjects: process simulation; biological methanogenesis; CO₂ fixation; overall process efficiency; bioprocess
• Online Access: http://www.aimspress.com/Bioengineering/article/156/fulltext.html

New generation biofuels are a suitable approach to produce energy carriers in an almost CO₂ neutral way. A promising reaction is the conversion of CO₂ and H₂ to CH₄. This contribution aims at elucidating a bioprocess comprised of a core reaction unit using microorganisms from the <em>Archaea</em> life domain, which metabolize CO₂ and H₂ to CH₄, followed by a gas purification step. The process is simulated and analyzed thermodynamically using the Aspen Plus process simulation environment. The goal of the study was to quantify effects of process parameters on overall process efficiency using a kinetic model derived from previously published experimental results. The used empirical model links the production rate of CH₄ and biomass to limiting reactant concentrations. In addition, Aspen Plus was used to improve bioprocess quantification. Impacts of pressure as well as dilution of reactant gas with up to 70% non-reactive gas on overall process efficiency was evaluated. Pressure in the reactor unit of 11 bar at 65℃ with a pressure of 21 bar for gas purification led to an overall process efficiency comprised between 66% and 70% for gaseous product and between 73% and 76% if heat of compression is considered a valuable product. The combination of 2 bar pressure in the reactor and 21 bar for purification was the most efficient combination of parameters. This result shows Aspen Plus potential for similar bioprocess development as it accounts for the energetic aspect of the entire process. In fact, the optimum for the overall process efficiency was found to differ from the optimum of the reaction unit. High efficiency of over 70% demonstrates that biological methanogenesis is a promising alternative for a chemical methanation reaction.