Thermal recovery of diclofenac and valorization of excipients via pyrolysis

Abstract

In this study, pyrolysis is investigated as a sustainable waste treatment method for pharmaceuticals within the context of the circular economy. Pyrolysis experiments were conducted on four different diclofenac sodium drug product formulations, including two gastro-resistant tablets, one capsule, and one suppository. The resultant gases and liquids were analyzed by chromatography. The pyrolysis liquids of the tablets and capsules, with liquid yields up to 32.93 %, contained large amounts of the active pharmaceutical ingredient (API) itself, with relative abundance values up to 94.76 %, as well as compounds typically found in bio-oil, such as phenols, esters, and ketones, owing to multiple lignocellulosic-based excipients in the formulations. Gases consisted mostly of CO up to 79.77 mol%, with smaller quantities of CO₂, H₂, CH₄, and ethylene. The suppositories produced a high liquid yield of 79.73 % with composition similar to those resultants from pyrolysis of fatty materials, containing acids, esters, and long-chain alkanes and alkenes, and gases rich in H₂, CH₄, and ethylene. DSC data was used to conduct an energy balance during the pyrolysis of each formulation. All products gave a net positive energy output with the capsule form producing the highest net energy of +14,566.77 J/g. The findings highlight the potential of pyrolysis to recover high-value APIs and generate energy-rich byproducts to support the overall sustainability of the process.