(668a) Development CO Sensor for Syngas Fermentation for Production of Fuels and Chemicals

Syngas fermentation is an emerging technology to produce fuels and chemicals from gasified biomass, coal, petcoke and solid wastes. This technology can also be used to make fuels and chemicals from gas streams that contain syngas components (CO, CO₂ and H₂). Some acetogens can convert these gases to organic acids and alcohols via the acetyl-CoA pathway. Challenges for commercialization of syngas fermentation technology include mass transfer limitations and low alcohol productivity associated with low cell mass concentration in the bioreactor and inhibition effects of high CO concentrations on key enzymes such as hydrogenase. Our recent results showed that the control of syngas feed rate to match the kinetics requirements of cells resulted in a stable operation of syngas fermentation (US Patent Application Publication, US 2016/0281114 A1 and International Patent Application No. PCT/US2015/60720). However, this required the use of gas chromatography and mathematical models to estimate the dissolved CO concentration in the medium, which was time consuming. Direct monitoring of dissolved CO and H₂ concentrations in the fermentation medium is a key to improve productivity and process stability. A real-time monitoring system for the dissolved CO and H₂ concentrations is being developed, which includes a built in-house dissolved CO sensor, a sample handling unit, a central control unit and an off-the-shelf dissolved H₂ sensor. The dissolved CO sensor was developed based on the spectral responses of CO in the mid infrared range (MIR). The CO sensor was housed in a designed cage with a careful alignment between a MIR LED as a light source and a photodetector as a signal receiver. A preamplifier and a lock-in-amplifier were used to preprocess the raw signal before being collected by the central control unit. The CO sensor was tested with gas samples containing CO concentration range generally found in bioreactors at typical operating pressures and achieved a sensitivity of over 10 mV/ppm CO. The central control unit was also developed for data acquisition and process control. The dissolved H₂ sensor was calibrated to measure 0 to 3 ppm of dissolved H₂ in the fermentation medium. Both CO and H₂ sensors were integrated in the bioreactor control platform to allow efficient delivery of these gases to the biocatalysts to enhance conversion efficiency, productivity and operation stability of syngas fermentation. Preliminary results showed the feasibility of the use of continuous mentoring of CO and H₂ concentrations in the bioreactor. Further work is focused on improving the sensors’ performance and its integration with the bioreactor control for efficient continuous syngas fermentation.