Integrated processes for anaerobic conversion of hydrogen and carbon oxides to alcohol

An alcohol derived from the anaerobic bioconversion of a gas substrate by a process comprising:

• a) steam reforming a carbonaceous gas from a non-renewable source to produce a reformed gas having an electron carbon ratio of greater than 7:1 and at least 90% of the available electrons from the methane in the carbonaceous gas;
• b) combining the reformed gas a with renewable gas derived from a renewable carbon source to provide a gas substrate comprising hydrogen, carbon monoxide, and carbon dioxide in which between about 20 and 70 percent of the carbon in the gas substrate is from renewable carbon in the renewable gas, the balance of the gas substrate stream is made from non-renewable carbon in the reformed gas, and the electron to carbon (e/C) ratio of the gas substrate is in a range from 5.5:1 to 6.7:1;
• c) continuously contacting said substrate gas with an aqueous menstruum containing anaerobic microorganisms to bioconvert the substrate gas to alcohol and provide an alcohol-containing menstruum and a substrate depleted gas phase, wherein said contacting is in a bioreactor assembly containing said menstruum;
• d) continuously withdrawing a substrate depleted gas phase from said aqueous menstruum, said depleted gas phase having a lower mass quantity of CO2 than the mass quantity of CO2 in the combined gas stream;
• and,
• e) continuously or intermittently withdrawing a portion of said menstruum for recovery of said alcohol, said withdrawal being sufficient to maintain the alcohol in said menstruum below a concentration that unduly adversely affects the microorganisms.

An integrated process for reducing the greenhouse gas release associated with making alcohol from natural gas that uses a combined gas substrate of 1) a CO2 rich gas from an anaerobic fermentation of carbohydrates and 2) a reformed natural gas that provides a substrate comprising carbon monoxide, hydrogen and carbon dioxide, the process comprising:

• a. a carbohydrate substrate to alcohol process comprising:
• i. bioconverting the carbohydrate substrate under fermentation conditions—including the presence of a first biocatalyst and an aqueous broth containing the carbohydrate substrate—to provide an alcohol-containing broth containing the biocatalyst and a carbon dioxide gas;
• ii. removing the carbon dioxide gas from the alcohol-containing broth and recovering at least a portion of the carbon dioxide as a carbon dioxide stream;
• iii. separating alcohol by distillation from said alcohol-containing broth and providing a whole stillage containing water, unconverted carbohydrates and at least a portion of the biocatalyst;
• iv. separating the whole stillage by centrifugation to provide a thin stillage and distillers grains;
• v. evaporating water from the thin stillage to provide a concentrate containing unconverted carbohydrates;
• and,
• b. a reformed gas to alcohol process comprising:
• i. continuously introducing said combined gas substrate into a bioreactor assembly containing an aqueous menstruum and a second biocatalyst to bioconvert the combined gas substrate to alcohol and providing an alcohol-containing menstruum and a depleted gas phase;
• ii. continuously withdrawing the depleted gas phase from said aqueous menstruum;
• iii. continuously or intermittently withdrawing a portion of said menstruum for recovery of said alcohol,
• iv. separating the withdrawn portion of said menstruum by distillation to provide alcohol and an aqueous stillage,
• wherein at least a portion of the carbon dioxide stream from step (a)(ii) is used as a portion of the gas substrate in step (b)(i) to provide a gas substrate having an electron to carbon atom ratio of between about 5.2:1 and 6.8:1.