Method of continuously producing ethanol from sugar-containing substrates

• US 4,876,196 A
• Filed: 01/27/1988
• Issued: 10/24/1989
• Est. Priority Date: 10/18/1984
• Status: Expired due to Term

• Current Assignee: Vogelbusch GmbH
• Original Assignee: Vogelbusch GmbH
• Inventors: Steiner, Eva, Salzbrunn, Wolfgang, Wohrer, Wilfried, Meixner, Otto
• Primary Examiner(s): Warren, Charles F.
• Assistant Examiner(s): Marx, Irene
• Application Number:
  US07/149,955
• Time in Patent Office: 636 Days
• Field of Search: 435/161, 435/162, 435/813, 435/822
• US Class Current: 435/161
• CPC Class Codes: C12P 7/065 with microorganisms other than yeasts
• CPC Class Codes: Y02E 50/10 Biofuels, e.g. bio-diesel
• CPC Class Codes: Y02P 20/582 Recycling of unreacted starting or intermediate materials
• CPC Class Codes: Y10S 435/813 Continuous fermentation
• CPC Class Codes: Y10S 435/822 using bacteria or actinomycetales

Abstract

In a method of continuously producing ethanol from sugar-containing substrates by fermentation of sugars by means of a flocculating strain of Zymomonas mobilis under anaerobic conditions and at a pH of from 4.5 to 7 a substrate is led commonly with Zymomonas mobilis cells through at least three fermentation stages without preceding sterilization, a concentration of at least 4% by volume of ethanol is maintained in each fermentation stage, a residence time of the fermentation medium in the entire system of maximally 31/3 h corresponding to a dilution rate of the fermentation medium in the entire system of at least 0.3 h^-1 is adjusted, the Zymomonas mobilis cells are separated by sedimentation after the final fermentation stage, the Zymomonas mobilis cells are recycled into the first fermentation stage, and the ethanol-containing substrate separated from the Zymomonas mobilis cells is drawn off.

Claims

1. A method of continuously producing ethanol from sugar-containing substrates comprising fermentation of the sugar in said substrates by a flocculating strain of Zymomonas mobilis cells under anaerobic conditions, the method consisting essentially of:

flowing a fermentation medium comprising said substrates and said Zymomonas mobilis cells through at least three fermentation stages of a fermentation system without preceding sterilization;

maintaining a concentration of at least 4% by volume of ethanol and a pH of about 5 in each of said fermentation stages;

maintaining a residence time of said fermentation medium in said fermentation stages of up to about 3 h., corresponding to a dilution rate of said fermentation medium in said fermentation stages of at least about 1/3h^-1 ;

separating the Zymomonas mobilis cells after the final fermentation stage by sedimentation to form ethanol-containing substrates, and recycling said Zymomonas mobilis cells into the first fermentation stage; and

removing said ethanol-containing substrates separated from said Zymomonas mobilis cells.

2. A method as set forth in claim 1, wherein said residence time of said fermentation medium in said fermentation stages is adjusted to from 0.8 to 2.5 h corresponding to a dilution rate of said fermentation medium in said fermentation stages of from 0.4 to 1.25 h^-1.

3. A method as set forth in claim 1, wherein CO₂ is formed in each one of said at least three fermentation stages and wherein at least a part of the CO₂ formed is circulated in the respective stage.

4. A method as set forth in claim 1, wherein ethanol is recovered from said drawn-off ethanol-containing substrate and distillery slops remain, and wherein at least a part of said distillery slops is recycled into the first one of said at least three fermentation stages.

5. A method as set forth in claim 1 wherein additional substrate is added to each stage as required to adapt the ratio of microorganism population to the alcohol and sugar concentration in each stage.

6. A method as set forth in claim 1 wherein a pH adjusting dent is added to each stage as required to control the pH.

7. A method as set forth in claim 6 wherein said substrate contains ammonium sulfate, the ammonium ions being taken up by the Zymomonas mobilis organisms, and said pH adjusting agent is lye.