Abstract
Cyanide is a minor constituent of crude syngas whose content depends on the feedstock and gasification procedure. It is a known poison to metal catalysts and inhibits iron-containing enzymes like carbon monoxide dehydrogenase of acetogenic organisms. Therefore, it is considered a component that has to be removed from the gas stream prior to use in chemical synthesis or syngas fermentation. We show that the growth rate and maximum biomass concentration of Clostridium ljungdahlii are unaffected by cyanide at concentrations of up to 1.0 mM with fructose as a carbon source and up to 0.1 mM with syngas as a carbon source. After the culture is adapted to cyanide it shows no growth inhibition. While the difference in growth is an increasing lag-phase with increasing cyanide concentrations, the product spectrum shifts from 97% acetic acid and 3% ethanol at 0 mM cyanide to 20% acetic acid and 80% ethanol at 1.0 mM cyanide for cultures growing on (fructose) and 80% acetic acid and 20% ethanol at 0.1 mM cyanide (syngas).
Highlights
Hydrogen, carbon monoxide, and carbon dioxide are the main constituents of gas yielded by gasification of coal or biomass, called syngas
Cells do not start to grow until 168 h but from on they consume the same amount of fructose as the other cultivations within the following 96 h
Another effect of increasing cyanide concentrations can be found with the formed products
Summary
Carbon monoxide, and carbon dioxide are the main constituents of gas yielded by gasification of coal or biomass, called syngas. The gas composition varies depending on gasifier type, feedstock, and process mode but consists mainly of CO, CO2, H2, and N2, if air is used as the gasification medium In addition to these main constituents, crude syngas contains variable amounts of methane (CH4) and C2-compounds such as ethane (C2H6), ethylene (C2H4), and acetylene (C2H2); tar components like benzene, toluene, xylene, and naphthalene; halogens such as hydrogen chloride (HCl) and hydrogen fluoride (HF); sulfur compounds like hydrogen sulfide (H2S), carbonyl sulfide (COS), and carbonyl disulfide (CS2); and nitrogen species such as nitrogen oxides (NOx), ammonia (NH3), and hydrogen cyanide (HCN) as well as oxygen (O2) and reactive oxygen species (ROS) (Hofbauer et al, 2009). Cyanide levels of crude syngas, for example, range from below 25 (Boerrighter et al, 2013) to 2500 ppm (Broer et al, 2015)
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