Upcycling mixed-material waste with elemental sulfur: applications to plant oil, unseparated biomass, and raw post-consumer food waste

Abstract

Herein we report the preparation of high sulfur-content materials (HSMs) using food waste and elemental sulfur. Peanut hulls and peanut oil were combined with sulfur to yield H_xO_yS₉₀ (x = wt% peanut hulls, y = wt% peanut oil) to enable systematic investigation of the relationship between unsaturated oil content and HSM properties. Next, post-consumer food wastes cooked in peanut oil, specifically fresh as well as desiccated French fries, were combined with elemental sulfur to afford WFFS₉₀ and DFFS₉₀, respectively. Differential scanning calorimetry revealed all HSMs in this study were readily remeltable and provided evidence for the presence of oligo/polysulfide chains crosslinking the food waste-derived organic matter. Impressively, the compressive strengths of H_xO_yS₉₀, WFFS₉₀, and DFFS₉₀ were comparable or superior to that of ordinary Portland cement. Quantitative assessment of the HSMs described in this study using the environmental metrics of atom economy, E-factor, and global warming potential (GWP) yielded values ranging from 93.5% to 100% for atom economy, 0 to 0.07 for E-factor, and −0.574 to +0.608 kg CO₂ eq. per kg for GWP. Moreover, the syntheses of these HSMs achieved 8 of the 12 Principles of Green Chemistry and 5 of the 17 UN Sustainable Development Goals. Collectively, the findings reported in this work provide strong evidence that H_xO_yS₉₀, WFFS₉₀, and DFFS₉₀ will function as thermally-recyclable, mechanically-robust sustainable alternatives to concretes.