Improving the circularity of waste tyres: Activated carbon development for carbon-capture applications
File(s)
Author(s)
Bowles, Alex
Type
Thesis
Abstract
Tyres are one of the world’s most abundant, problematic, and unrecycled wastes. This thesis provides investigation of their recovery by pyrolysis, demineralisation, and activation. The final outcome was a tyre-derived activated carbon which showed potential as an effective CO2 adsorbent for carbon capture and storage from the flue gas stream of a cement kiln.
The superior performance of low temperature (450-550°C) mechanically mixed tyre pyrolysis systems, specifically rotary kilns, was shown by a literature analysis of 181 experiments from 37 pyrolysis reactors. A bootstrapping algorithm indicated that feedstock control can reduce recovered carbon black (RCb) ash content by over 50%. A laboratory pyrolysis analysis showed that a pyrolysis temperature of 550°C, and high ratios of gas to rubber pyrolysed, were most appropriate for high quality RCb production (77.7 m2/g, 0.2% volatile matter, 17.0% ash, 94.8% transmissibility of toluene extract). Demineralisation improved the physiochemical characteristics of RCb, whilst economic analysis showed a high value ($ 103 to 257/tonne) of the removable metallic fraction, potentiating recycling.
A comprehensive meta-analysis of waste derived pyrogenic activated carbons (343 samples) elucidated the determinants (ultramicropores, 750 to 1500 m2/g surface area) and activation conditions (KOH) for high CO2 adsorption capacities. Ultramicropore morphologies in the 343 activated carbons were best represented by a numerical model assuming trapezoidal geometries.
A KOH activation reactor was commissioned to produce highly tailored (>800 m2/g) tyre derived activated carbons with an improved CO2 adsorption capacity (>80 mg CO2/g at 25°C and 1 bar). Physiochemical characterisation results supported the trapezoidal pore model. This hydrophobic material had a high working CO2/N2 selectivity (200+) at realistic (50 to 150°C) CO2 capture conditions. The π-electrons in the sp2-bonded carbon structure allowed rapid and efficient regeneration via electricity. This study demonstrates how carbonaceous wastes can be converted to high-performance materials, thereby fulfilling zero-pollution objectives.
The superior performance of low temperature (450-550°C) mechanically mixed tyre pyrolysis systems, specifically rotary kilns, was shown by a literature analysis of 181 experiments from 37 pyrolysis reactors. A bootstrapping algorithm indicated that feedstock control can reduce recovered carbon black (RCb) ash content by over 50%. A laboratory pyrolysis analysis showed that a pyrolysis temperature of 550°C, and high ratios of gas to rubber pyrolysed, were most appropriate for high quality RCb production (77.7 m2/g, 0.2% volatile matter, 17.0% ash, 94.8% transmissibility of toluene extract). Demineralisation improved the physiochemical characteristics of RCb, whilst economic analysis showed a high value ($ 103 to 257/tonne) of the removable metallic fraction, potentiating recycling.
A comprehensive meta-analysis of waste derived pyrogenic activated carbons (343 samples) elucidated the determinants (ultramicropores, 750 to 1500 m2/g surface area) and activation conditions (KOH) for high CO2 adsorption capacities. Ultramicropore morphologies in the 343 activated carbons were best represented by a numerical model assuming trapezoidal geometries.
A KOH activation reactor was commissioned to produce highly tailored (>800 m2/g) tyre derived activated carbons with an improved CO2 adsorption capacity (>80 mg CO2/g at 25°C and 1 bar). Physiochemical characterisation results supported the trapezoidal pore model. This hydrophobic material had a high working CO2/N2 selectivity (200+) at realistic (50 to 150°C) CO2 capture conditions. The π-electrons in the sp2-bonded carbon structure allowed rapid and efficient regeneration via electricity. This study demonstrates how carbonaceous wastes can be converted to high-performance materials, thereby fulfilling zero-pollution objectives.
Version
Open Access
Date Issued
2023-04-12
Date Awarded
01/01/2024
License URL
Advisor
Fowler, Geoffrey
Sponsor
Engineering and Physical Sciences Research Council Great Britain
Pyrenergy Limited (Firm)
Grant Number
EP/R513052/1
Publisher Department
Civil and Environmental Engineering
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)