Reactivity, Kinetic, and Thermodynamic Analysis of Ionic Liquid-Assisted Thermal Degradation of Spent Coffee Ground

In this work, the impact of Ionic Liquid (IL) pretreatment of Spent Coffee Grounds (SCG)  is assessed using three analytical techniques. Four different classes of ILs were employed to compare the effect of cations and anions. Thermogravimetric analysis under the N2 environment was done to collect analytical data at 20 °C/min. Reactivity analysis evaluated mean relative reactivity (Rm) and pyrolysis factor (PF), kinetic analysis determined activation energy (Ea) and pre-exponential factor (A), while thermodynamic analysis helped to find enthalpy change (ΔH), Gibbs free energy change (ΔG), and entropy change (ΔS). IL treatment aided thermal breakdown by increasing the mass loss % from 93% for untreated SCG to 97% after IL treatment. The decomposition rate for the IL-treated samples was calculated to be in the range of 6.7-7% min-1. All the ILs increased Rm, with the largest increase from 2.42*102 to 2.57*102 % min-1°C-1; they also decreased the Ea of SCG from 42.25 to as low as 29.91 kJ/mole. This might be induced by the breakdown of the lignin structure of SCG by IL treatment leaving it sensitive to heat treatment. IL-treated SCG ΔS values indicate increased disorder and thermal instability. Among the studied ILs, relatively inexpensive and infrequently used [P66614] [Cl] and [N1444] [Cl] fared better than imidazolium-based ILs. This study could provide useful knowledge in finding effective cations for designing task-specific ILs for the thermochemical conversion process.