Sulfite Absorption for Anaerobic Fermentation Sulfur Management
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Solution Overview
Problem
The commercial viability of anaerobic fermentation processes for converting hydrogen and carbon oxides to alcohols is hindered by low mass transfer rates due to low solubility of gases in aqueous media, high costs associated with sulfur removal from bioreactor off-gases, and excessive alkali consumption, which also poses environmental concerns and operational inefficiencies.
Innovation Solution
A continuous process that removes hydrogen sulfide from bioreactor off-gases using an aqueous sulfite solution to produce sulfur compounds beneficial to microorganisms, recycling them back into the bioreactor to meet sulfur demands, thereby enhancing conversion efficiency and reducing waste and chemical consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If alkali is used to recover sulfide from bioreactor off gas, then sulfide recovery is achieved, but alkali consumption becomes excessive due to the acidic nature of the off gas
Solution Approach 1:
The patent converts the harmful acidic nature of the off gas (which causes excessive alkali consumption) into a beneficial feature by using the acid to protonate sulfite ions, forming bisulfite ions that selectively absorb hydrogen sulfide. This transforms the acid from a problem into the mechanism that enables efficient sulfide recovery without requiring excessive alkali.
Solution Approach 2:
The patent introduces sulfite as an intermediary substance that mediates between the acidic off gas and the hydrogen sulfide removal process. The sulfite reacts with the acid to form bisulfite, which then serves as the active species that absorbs hydrogen sulfide, avoiding direct alkali consumption while achieving effective sulfide recovery.
2Object-affected harmful factors
If hydrogen sulfide is removed from off gas, then environmental concerns are addressed, but sulfur compounds needed by microorganisms are lost
Solution Approach 1:
The patent recovers sulfur compounds from the off gas stream by using sulfite to absorb hydrogen sulfide, then regenerates the sulfite and releases sulfur dioxide which can be converted back to sulfite. This creates a cyclic process where sulfur is continuously recovered and reused, preventing loss while maintaining effective hydrogen sulfide removal.
Solution Approach 2:
The patent implements a feedback mechanism where the sulfur-containing products of hydrogen sulfide removal are fed back into the bioreactor system. The sulfur dioxide generated during the process is converted back to sulfite and returned to the absorption system, creating a closed-loop feedback that maintains sulfur availability for microorganisms while continuously removing harmful hydrogen sulfide.
3Productivity
If mass transfer is enhanced for gas conversion, then conversion efficiency improves, but capital and operating costs increase
Solution Approach 1:
The patent employs self-service principles by using the natural acidic nature of the off gas to drive the sulfite absorption process. The acid in the off gas automatically protonates sulfite ions without requiring external energy input or complex control systems, enabling efficient mass transfer while keeping the system simple and cost-effective.
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 process achieves high conversion efficiencies of carbon to alcohols, minimizes sulfur removal and disposal costs, and operates at atmospheric pressure with low chemical consumption, addressing environmental concerns and improving the economic viability of the fermentation process.
Implementation Method 1
contacting the off gas with an aqueous sulfite solution so as to produce sulfur compounds
Data Source
AI summary
High conversion efficiency processes are disclosed for the anaerobic bioconversion of syngas to alcohol by microorganisms having metabolic processes that utilize sulfur in limited amounts. The processes remove hydrogen sulfide from the gas leaving the bioreactor assembly by forming sulfur compounds that are beneficial to the microorganisms. The sulfur compounds can be returned to the bioreactor assembly to meet a portion of microorganism sulfur demand.