Rubber Devulcanization Using Swelling Agents and Controlled Oxygen
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Solution Overview
Problem
Existing devulcanization methods struggle to selectively break sulfur crosslinks in vulcanized rubber without damaging carbon-carbon bonds, leading to inefficient recycling of rubber products like tires, belts, and hoses, due to the close bond-dissociation energies of sulfur-sulfur and carbon-sulfur bonds.
Innovation Solution
A method involving mixing vulcanized rubber particles with a high-boiling swelling agent and heating to at least 170°C in the presence of oxygen to break sulfur crosslinks, using shear forces and a suitable ratio of swelling agent to rubber, allowing for the separation of rubber chains.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If pyrolysis is used to reduce used tires at high temperatures (600°C-900°C), then the rubber can be broken down, but the end products (light oils and char) have little economic value compared to the original rubber and carbon black
Solution Approach 1:
The patent changes the temperature parameter from extreme pyrolysis conditions (600°C-900°C) to a moderate range (100°C-200°C), and introduces oxygen concentration as a new control parameter (0.1%-10% oxygen atmosphere). These parameter changes enable selective devulcanization that preserves carbon-black-reinforced structures while breaking sulfur crosslinks, thereby maintaining the economic value of recovered materials.
Solution Approach 2:
The patent applies local quality by creating different atmospheric conditions for different chemical bonds: a low-oxygen environment that selectively breaks S-S and C-S bonds while preserving C-C bonds and carbon-black structures. This localized chemical environment enables selective devulcanization without complete combustion or pyrolysis, preserving valuable materials.
2Stability of the object's composition
If traditional devulcanization methods are used to break sulfur crosslinks, then the three-dimensional network is disrupted, but C-C bonds are also damaged due to close bond-dissociation energies
Solution Approach 1:
The patent creates a localized chemical environment with controlled oxygen concentration (0.1%-10%) that selectively affects sulfur-containing bonds (S-S and C-S) while leaving C-C bonds intact. This local quality approach exploits the different chemical reactivities of various bonds toward oxygen at moderate temperatures, enabling selective devulcanization without damaging the carbon backbone.
Solution Approach 2:
The patent changes the temperature parameter to a moderate range (100°C-200°C) and introduces oxygen concentration as a selective parameter. These changes enable preferential oxidation of sulfur crosslinks over C-C bonds, as sulfur compounds are more reactive toward oxygen at these conditions, thus breaking the three-dimensional network while preserving the carbon-carbon backbone.
3Productivity
If high temperatures are used to break sulfur bridges, then devulcanization occurs, but aggressive chemicals are required and the process becomes complex
Solution Approach 1:
The patent enables the rubber material to undergo self-devulcanization by simply exposing it to a controlled oxygen atmosphere at moderate temperatures. The sulfur crosslinks react with oxygen present in the atmosphere, eliminating the need for aggressive chemical agents or complex catalysts. This self-service approach simplifies the process while maintaining effective devulcanization.
Solution Approach 2:
The patent uses moderate temperature (100°C-200°C) and controlled oxygen concentration (0.1%-10%) as process parameters, replacing the need for aggressive chemicals and extreme conditions. These parameter changes enable a simpler, more environmentally friendly process that achieves effective devulcanization without complex chemical treatments.
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
Efficiently breaks sulfur crosslinks while preserving carbon-carbon bonds, enabling effective recycling of rubber products by loosening the network and facilitating the reuse of swelling agents, without the need for aggressive chemicals.
Implementation Method 1
mixing the rubber product particles with a relatively high-boiling swelling agent
Implementation Method 2
heating the mixture of the rubber product particles and the relatively high-boiling swelling agent to a temperature of at least 170°C in the presence of oxygen so as to break the sulfur crosslinks
Implementation Method 3
heating the mixture of the rubber product particles and the relatively high-boiling swelling agent to a temperature of at least 170°C in the presence of oxygen so as to break the sulfur crosslinks
Data Source
AI summary
A method for devulcanization of rubber products is disclosed. The method comprises providing vulcanized rubber product particles containing rubber chains with sulfur crosslinks; mixing the rubber product particles with a swelling agent having a boiling point of at least 130ºC at a pressure of 1 bar, the swelling agent comprising a processing oil or solvent; and heating the mixture of the rubber product particles and the swelling agent to a temperature of at least 150ºC in the presence of oxygen so as to at least partially or fully break the sulfur crosslinks in the rubber product particles.