Closing the loop: Valorizing pyrolyzed waste tyre residue into functional carbon materials, SiO₂ with exceptionally...

This study aims to identify suitable processing conditions for converting pyrolytic solid residue from off-the-road tyres (OTR) to improve carbon materials properties that can be used in multiple applications and the recovery of minerals from OTR. Pyrolysis of OTR at 800 °C and a heating rate 2 °C.min^-1 gave a carbon material with the highest surface area, most defective carbon structures, and the highest micro-porosity. This operating condition was used to compare the conventional three-step carbonization approach, which involves a demineralization stage that produces high volumes of toxic wastewater, with a two-step approach that bypasses this stage. Analysis of the carbon structures showed that the quality of the carbon material from the two-step approach is similar to the three-step approach. This two-step approach resulted in a solid and a liquid phase, in which ∼ 93.4% of Zn was selectively fractionated to the liquid phase. The wastewater from the acid wash of the carbonized OTR was neutralized to recover the SiO₂, of which 55.5% was reactive SiO₂. The SiO₂ was found to have an exceptionally high cross-linking ratio of 5.94, achievable only when SiO₂ is reacted with silane groups. The study demonstrated that the engineered carbon material from OTR has a H₂ uptake of 1.03 wt% at 77 K and 1.2 bar, and the sulfonated counterpart was an effective catalyst (64% conversion) for the Aldol condensation of levunilic acid to two dimer products [tetrahydro-2- methyl-5,γ-dioxo-2-furanpentanoic acid (TMDFA) and 3-(2-methyl-5-oxo- tetrahydrofuran-2-yl)-4-oxopentanoic acid (MOTOA)] that are precursors for fuels and chemicals.