Fermentation Sulfur Additives for Butanol Production
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Solution Overview
Problem
Current methods for producing butanol and other C4 oxygenates through anaerobic fermentation using syngas face challenges in providing biologically available sulfur to microorganisms efficiently and cost-effectively, particularly due to the volatility and toxicity issues associated with hydrogen sulfide.
Innovation Solution
The use of sulfur additives such as sulfurous acid, bisulfite, metabisulfite, and thiosulfate, which provide sulfur oxyanions or hydrosulfur oxyanions in a bioavailable and highly soluble form, allowing microorganisms to assimilate hydrosulfide and minimize hydrogen sulfide emissions, thereby supporting the production of butanol and butyrate while maintaining a favorable pH that inhibits contaminant growth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If hydrogen sulfide is used as a sulfur source for microorganisms, then sulfur nutrition is provided, but volatility and toxicity issues arise
Solution Approach 1:
The patent uses cysteine as an intermediary compound to transfer sulfur from inorganic sources (sodium sulfide, sulfur dioxide) to the microorganisms. Instead of directly using hydrogen sulfide which causes volatility and toxicity problems, the system converts inorganic sulfur to cysteine, which then serves as the bioavailable sulfur source for microorganisms, eliminating the harmful effects while maintaining sulfur nutrition
Solution Approach 2:
The patent changes the chemical form of sulfur from gaseous hydrogen sulfide (H2S) to stable inorganic forms (sodium sulfide Na2S, sulfur dioxide SO2) and then to organic cysteine. This parameter change in sulfur's chemical state eliminates volatility and toxicity while maintaining biological availability through the established conversion pathway
2Ease of manufacture
If inorganic sulfur compounds are used to replace cysteine, then cost is reduced, but microbial growth may be inhibited
Solution Approach 1:
The patent applies preliminary action by pre-converting inorganic sulfur compounds to cysteine before introducing them to the fermentation system. The inorganic sulfur (sodium sulfide or sulfur dioxide) is first transformed into the bioavailable organic form (cysteine) through chemical or biological conversion, ensuring that when microorganisms encounter the sulfur source, it is already in the appropriate form for growth, thus maintaining reliability while achieving cost reduction
3Manufacturing precision
If pH is maintained to inhibit contaminants, then product purity is improved, but sulfur bioavailability may be reduced
Solution Approach 1:
The patent uses cysteine as an intermediary that bridges the conflict between pH control and sulfur bioavailability. Cysteine, being an organic sulfur compound, maintains stability and bioavailability across a broader pH range compared to inorganic sulfur forms. This allows the system to maintain pH levels that inhibit contaminants while ensuring sulfur remains in a bioavailable form through the cysteine intermediary
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables high titers of butanol production with improved alcohol-to-acid ratios and reduced cysteine requirements, minimizing process costs and volatility issues, while maintaining microbial viability and productivity.
Implementation Method 1
The invention uses the higher oxidation state sulfur in the microorganism as the means to reduce the oxidation state of the sulfur to the usable form
Implementation Method 2
allowing microorganisms to assimilate hydrosulfide
Implementation Method 3
METHOD FOR PRODUCING C4 OXYGENATES BY FERMENTATION USING HIGH OXIDATION STATE SULFUR
Data Source
AI summary
The invention relates to improvements in the production of butanol and butyrate by microbial fermentation, particularly to production of alcohols by microbial fermentation of a substrate comprising CO and the addition of an inorganic sulfur additive. It more particularly relates to the provision of an inorganic organic sulfur source to a fermentation system such that one or more micro-organisms convert a substrate comprising CO to butanol. In one aspect the invention uses a sulfur additive comprising inorganic sulfur compounds having a +2 to a +4 sulfur oxidation state that produces sulfur oxoanions and hydrosulfur oxoanions in an aqueous fermentation medium.