Producing Pyridines via Thermocatalytic Conversion and Ammonization of Waste Polylactic Acid over Zeolites

In this study, polylactic acid served as raw material to produce fine chemicals (pyridines) via a thermocatalytic conversion and ammonization (TCC-A) process. Ammonia was employed as not only carrier gas but also a reactant in this process. The thermal decomposition behavior of PLA under N2 or NH3 atmosphere was investigated. Different catalysts, including MCM-41, β-zeolite, ZSM-5 (Si/Al = 50) and HZSM-5 with different Si/Al ratios (Si/Al = 25, 50, 80) were also screened. Reaction temperature and residence time, which may affect the pyridines production, were investigated systematically. It was verified that all the investigated factors, including catalyst structure, catalyst acid amounts, reaction temperature, and residence time, influenced the PLA conversion and the pyridines production. The highest pyridines yield, 24.8%, was achieved by using HZSM-5 (Si/Al = 25) at around 500 °C. The catalyst regeneration tests were carried out. It demonstrated that the catalyst was stable after five regenerations and...