Processes for the anaerobic bioconversion of syngas to oxygenated organic compound with in situ protection from hydrogen cyanide

A process anaerobic bioconversion of a gas substrate comprising carbon monoxide, hydrogen and carbon dioxide to an oxygenated organic compound in a fermentation broth wherein said gas substrate may contain from time to time hydrogen cyanide comprising:

• a. continuously introducing said gas substrate into a fermentation broth by injection using a motive fluid, said fermentation broth containing microorganisms suitable for bioconverting said substrate to the oxygenated organic compound, said fermentation broth being maintained under anaerobic fermentation conditions, and the gas substrate having sufficient contact with the fermentation broth to provide an oxygenated organic compound-containing fermentation broth and a substrate-depleted gas phase;
• b. maintaining the pH of the fermentation broth between about 4 and 6;
• c. continuously or intermittently supplying to said motive fluid a metal cation of one or more of iron, cobalt, nickel and zinc capable of forming a substantially water insoluble complex with cyanide anion, to provide said metal cation dissolved in said fermentation broth in an amount at least stoichiometrically sufficient to form, under said anaerobic fermentation conditions and pH, said water insoluble complex with the cyanide anion if introduced with said gas substrate into said fermentation broth;
• d. continuously withdrawing the substrate-depleted gas phase from the fermentation broth having a substantial absence of the hydrogen cyanide;
• and
• e. continuously or intermittently withdrawing a portion of the fermentation broth for recovery of said oxygenated organic compound, said withdrawal being sufficient to maintain the oxygenated organic compound in said fermentation broth below a concentration that unduly adversely affects the microorganisms.