Synergy and evolved gas analysis of spent coffee ground with plastic waste in pyrolysis environment

• Online TG-IR-GCMS system was utilized to identify and analyze evolved gases that mimic a real-life scenario. • Synergistic effects during SCG-PET co-pyrolysis were calculated. • Co-pyrolysis promotes formation of more aromatic compounds at a higher temperature range. • Evolved gas analysis shows the formation of fuel-grade hydrocarbons and aromatics which pose a potential candidate for transportation fuels. • The positive interaction between SCG and PET during co-pyrolysis led to notable changes in degradation products. The growth in coffee consumption is directly linked to the generation of vast amounts of solid waste such as coffee husk, coffee pulp, coffee silver skin, and spent coffee grounds. Numerous environmental issues and ecotoxicological concerns arise from directly disposing of this waste in landfills or incineration, attributable to organic constituents such as dioxin, furan, polyaromatic hydrocarbons, volatile organic compounds, and persistent organic pollutants. There is a need for a suitable alternative strategy to resolve these issues and utilize this waste as a functional product, as it is a carbon-rich source with high energy content. This work includes synergetic studies and utilization of online TG-FTIR and Py-GC/MS systems to investigate spent coffee ground (SCG) and plastic bottles (PET) co-pyrolysis characteristics and mechanisms. This study examined the product distribution, emission of pollutants, and change in functional groups and composition with temperature during the process to evaluate the right proportion and nature of bio-oil and gaseous products. The kinetic and thermodynamic parameters were also calculated to understand the behavior of SCG-PET blend pyrolysis using a model-free approach and to optimize the process to scale up to the industrial level. The results revealed that co-pyrolysis of spent coffee grounds (SCG) and PET at high temperatures yields a condensed bio-oil enriched with energy-dense aromatic hydrocarbons, highlighting its potential as a promising drop-in transportation fuel, chemical feed stocks, intermediates, and solvent in different industries. During synergy analysis, positive synergy was observed throughout the temperature range (25-800°C), indicating the lower energy requirement and enhanced product quality; however, the oxygenated compounds can be further removed by catalytic cracking or hydro-treatment to make it more feasible.