Carbon dioxide-negative composite materials: an economically viable solution for CO2 sequestration†

Abstract

Anthropogenic emissions of CO₂ have nearly exhausted our carbon budget, putting the world on a trajectory toward irreversible climate change. CO₂ emissions must be reversed in coming decades to avoid global warming past the 2 °C target. Recent approaches have focused on recycling CO₂ into fuels and chemicals to create sufficient financial incentives to pay for CO₂ removal and geological sequestration. These technologies aim to produce fuels and chemicals at quantities relevant to global markets while also recycling a meaningful amount of CO₂. While promising, these technologies are CO₂-neutral at best. Truly negative emission technologies will require significant quantities of durable, fungible products that sequester hundreds of millions of tonnes of CO₂. We present an economically viable approach to sequestering hundreds of thousands of tonnes of CO₂ per year in polymer composites made from CO₂-functionalized lignin or lignite fillers mixed with a high-density polyethylene (HDPE) matrix. CO₂ is chemically fixed to polymeric phenols via C–C bond formation at the lignin or lignite surface, storing about 2–4.2 wt% of CO₂. Composites produced with the CO₂-functionalized fillers and HDPE have mechanical properties that meet international building code standards for decking, a multi-billion-dollar market. A techno-economic analysis and life cycle assessment suggest that CO₂-functionalized lignin and lignite fillers have favorable economic potential. These composites could reduce greenhouse gas emissions up to 62% over conventional wood plastic composites or be CO₂-negative within 20 years when manufactured with renewable electricity, recycled high-density polyethylene and if extra CO₂ is captured and sequestered in the ground. The composites can achieve a net-negative global warming potential after 54 years for the CO₂ solely stored in the composites.