Microbial Desulfurization of Crumb Rubber for Bitumen Compatibility
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Solution Overview
Problem
Rubber bitumen separation in asphalt pavements is a challenge due to crosslinked sulfur bonds in crumb rubber, leading to poor dispersion and segregation, which affects the durability and performance of rubberized asphalt.
Innovation Solution
Microbial desulfurization using sulfur-oxidizing microorganisms to break crosslinked sulfur bonds in crumb rubber, reducing sulfur content and disulfide bonds, thereby increasing the surface energy and improving interaction with bitumen, resulting in a modified bitumen with enhanced rheological properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If crumb rubber is used in asphalt, then durability and noise reduction are improved, but rubber-bitumen separation occurs due to crosslinked sulfur bonds
Solution Approach 1:
The patent extracts and removes sulfur from the crumb rubber through flotation separation processes, breaking the crosslinked sulfur bonds that cause rubber-bitumen separation. This extraction of sulfur maintains the durability benefits of rubberized asphalt while eliminating the separation problem.
Solution Approach 2:
The patent changes the sulfur content parameter in crumb rubber from high (crosslinked) to low (desulfurized) through chemical and physical treatment processes. This parameter change transforms the rubber's interaction with bitumen, preventing separation while maintaining performance benefits.
2Reliability
If crumb rubber is added to bitumen, then pavement performance is improved, but poor dispersion occurs due to sulfur content
Solution Approach 1:
The patent extracts sulfur from crumb rubber using flotation and other separation techniques, removing the substance that causes poor dispersion. This results in improved distribution and mixing of rubber particles throughout the bitumen matrix.
Solution Approach 2:
The patent introduces intermediate processing steps (flotation, chemical treatment) that mediate between the crumb rubber and bitumen, facilitating better compatibility and dispersion by reducing sulfur content before final mixing.
3Strength
If crosslinked sulfur bonds are present in crumb rubber, then rubber structure is maintained, but interaction with bitumen is reduced
Solution Approach 1:
The patent applies local quality changes by selectively modifying the sulfur content in specific regions of the rubber particles while maintaining the overall rubber structure. This localized desulfurization improves bitumen interaction without compromising the rubber's structural integrity.
Solution Approach 2:
The patent changes the sulfur bonding parameter from crosslinked to reduced states, transforming the chemical properties of rubber surfaces to enhance interaction with bitumen while preserving the fundamental rubber polymer structure.
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
The process reduces rubber-bitumen segregation by 68%, improves stiffness and stress relaxation capacity by 10% and 5% respectively, and increases elastic recovery by 6%, leading to better pavement performance and durability.
Implementation Method 1
microbially desulfurized crumb rubber is produced by combining crumb rubber and microorganisms that oxidize sulfur to break crosslinked bonds in the rubber
Implementation Method 2
microorganisms that oxidize sulfur as part of their metabolism (e.g., soil or waste activated sludge microorganisms)
Implementation Method 3
heating the precursor to yield the microbially desulfurized crumb rubber
Data Source
AI summary
Preparing a microbially desulfurized crumb rubber includes combining microorganisms capable of breaking crosslinked sulfur bonds, sulfur-containing crumb rubber, and a salt solution to yield a mixture; combining a buffer with the mixture to yield a buffered mixture, thereby adjusting a pH of the mixture; providing oxygen to the buffered mixture; incubating the buffered mixture for a length of time to yield a microbially desulfurized mixture; combining the microbially desulfurized mixture with bitumen to yield a precursor; and heating the precursor to yield the microbially desulfurized crumb rubber. The microbially desulfurized crumb rubber can be combined with bitumen to yield a modified bitumen. The modified bitumen can be combined with asphalt to yield a modified asphalt.