Isoconversional Kinetic Analysis and ANN-Based Prediction of Metformin Pyrolysis for Sustainable Waste Management

Abstract

Pharmaceutical waste poses a growing environmental concern due to its persistence and potential ecological impacts, necessitating effective and sustainable management strategies. This study investigates the pyrolysis of metformin as a means to valorize pharmaceutical waste within a circular economy framework. Pyrolysis experiments conducted on 500 mg of metformin demonstrated the formation of liquid-phase products, characterized by GC–MS, which revealed a high concentration of the active pharmaceutical ingredient (API) alongside carbonaceous, nitro, and acidic compounds. Comprehensive thermogravimetric analyses at heating rates of 10, 20, 30, and 40 °C/min were performed to evaluate the thermal decomposition behavior. Kinetic parameters were determined using four isoconversional methods, namely KAS, FWO, Starink, and FRD, yielding average activation energies of 101.4, 105.8, 101.4, and 111.1 kJ/mol, respectively. Thermodynamic parameters (ΔG, ΔH, and ΔS) were also calculated to gain further insights into the decomposition process. Additionally, an ANN model was developed using temperature and heating rate as inputs to predict mass loss, achieving accurate estimations with an optimized architecture comprising two hidden layers. GC–MS analysis of the pyrolysis liquid identified a high concentration of the API, along with carbonaceous, nitro, and acidic compounds. These findings highlight the potential for API recovery and reuse, as well as the valorization of byproducts for energy or chemical synthesis. The potential recovery of APIs for reuse and the utilization of byproducts as fuels or chemical precursors underscore pyrolysis as a promising route for sustainable pharmaceutical waste management and circular economy integration.