Fermentation method for producing high concentration carbon dioxide product

Abstract

A method for producing carbon dioxide at a flow rate is disclosed. The method comprises several steps including the provision of an oxidant fluid to a fermentation broth, use of oxygen from the oxidant fluid to promote fermentation and microbial growth in a fermenter while producing carbon dioxide within the broth, passing a fermentation broth stream out from the fermenter, and then through a heat exchanger, and then back into the fermenter via a recirculation loop, bubbling carbon dioxide out therefrom the broth creating a gas mixture containing a carbon dioxide concentration of 97.5 mole percent and recovering the gas mixture as product carbon dioxide. The oxidant fluid is provided to the fermentation broth at a flow rate such that the amount of oxygen provided to the fermentation broth is not more than 5 weight percent of the total amount of carbon dioxide being produced. The oxidant fluid contains an oxygen concentration of at least 40 mole percent. The oxidant fluid may be provided to the broth downstream of the heat exchanger, and also can be provided in either the fermenter or in the recirculation loop. Also the oxygen is provided to the broth at a flow rate within the range of 0.0003 to 0.0015 vvm. Ethanol may also be produced during fermentation in addition to carbon dioxide. The carbon dioxide can be subjected to purification which may include distillation and/or solvent absorption.