In−depth insights into the kinetic and thermodynamic parameters of synergistic coffee residue pyrolysis of sugar industry sludge and biochar characterization

Abstract

This study elucidated the thermal behavior, biochar, kinetics and thermodynamics parameters of sugar industry sludge (SS), coffee residue (CR) and their mixtures (SC31: mass ratio of 3:1 and SC21: mass ratio of 2:1) using high‐precision thermogravimetric analysis (TGA) and Fourier transform infrared (FTIR) spectroscopy, combined with advanced non−isothermal conversion methods. The ultimate analysis reveals that the feedstocks contain high carbon content and low levels of nitrogen and sulfur, underscoring their potential as sources for producing clean carbon resources. The TGA result indicates that (co-)pyrolysis proceed via a three−stage process, encompassing moisture removal, devolatilization, and char formation. The kinetic results demonstrated that the non−isothermal conversion methods have good agreement on kinetic parameters, the average E_a of sugar industry sludge, coffee residue, CS31 and SC21 were 241.18, 207.35, 247.89 and 218.36 kJ/mol, respectively. At a mass ratio of sugar industry sludge to coffee residue at 2:1, the experimental E_a dips below its theorized value. SS and CR (co-)pyrolysis follows the Avrami−Erofeev (SC31) and power−law (SC21) mechanisms. The thermodynamic results indicate that co−pyrolysis exhibits higher reactivity. FTIR findings revealed that SS and CR had similar functional groups and that the co−pyrolysis chars not only incorporated ketones, aldehydes and acids, but also H₂O and CO₂. SEM images underscore the potential of co−pyrolyzed biochar as a significant feedstock for fabricating porous nanosheet biochar.

Graphical Abstract