(182f) Syngas Mass Transfer Analysis in a Hollow Fiber Reactor

Biofuel production via fermentation is produced primarily by fermentation of simple sugars. Besides the sugar fermentation route, there exists a promising alternative process that uses syngas (CO, H₂, CO₂) produced from biomass as building blocks for biofuels. Although syngas fermentation has many benefits, there are several challenges that still need to be addressed in order for syngas fermentation to become a viable process for producing biofuels on a large scale. One challenge is mass transfer limitations due to low solubilities of syngas species. The hollow fiber reactor (HFR) is one type of reactor that has the potential for achieving appropriate mass transfer rates for biofuels production, but a better understanding of mass transfer limitations associated with all syngas species is critical for assessing syngas usage during fermentation.

Mass transfer coefficients for O₂ and CO₂ have been typically assessed for HFRs using dissolved gas probes. In limited cases, CO has been studied using myoglobin assays. Though there are many reports on mass transfer coefficients in HFRs, studies are lacking that compare mass transfer coefficients of syngas species, including comparisons obtained from different measurement methods. Such comparisons are important to verify the accuracy of the experimental methods and to provide an increased understanding of the competing mass transfer limitations associated with syngas species.

In this study, we measured the mass transfer coefficient for O₂ in a PDMS hollow fiber reactor as a function of Reynolds number (flow rate) using a dissolved O₂ probe. The data was fit to a model characterizing O₂ mass transfer and the model was used to predict the mass transfer coefficients for CO and H₂. In order to verify the model predictions for these latter species, a second measurement technique using GC analysis was developed to measure CO and H₂ mass transfer coefficients. The GC technique was validated by comparing the mass transfer coefficient of O₂ from both GC and dissolved O₂ probe analysis. The mass transfer coefficients of both H₂ and CO in a HFR will be compared and the impact of such coefficients on syngas utilization will be presented. This study will greatly enhance the knowledge necessary to assess syngas usage and mass transfer limitations in a HFR used for syngas fermentation.