Kinetic experiments for pyrolytic recycling of solid plastic waste

Pyrolysis is a promising strategy to convert plastic wastes to valuable liquid products that can be used as fuels, chemicals and platform molecules. An understanding of the pyrolysis chemistry and kinetics of neat polymers and contaminated waste plastics is valuable to design and optimize the pyrolysis reactors for maximum recovery and selectivity to valuable organics in the liquid pyrolysis oil. Thermogravimetric analysis (TGA) is a popular analytical technique to obtain mass loss data, which can then be used to obtain the decomposition regimes and kinetics of polymer pyrolysis. Owing to the limitations of TGA such as slow heating rate and the influence of heat and mass transfer on kinetics and pyrolysate evolution, a number of analytical pyrolyzers have captured the attention of researchers for accurate estimation of product yields and fast pyrolysis kinetics. This article provides an overview of the different pyrolyzers including TGA, Pyroprobe, Curie point pyrolyzer, Frontier micropyrolyzer, Pyrola and PHASR (Pulse Heated Analysis of Solid Reactions), analyzes their capabilities, and pros and cons of each of them for the kinetics of plastic decomposition. Salient results from the literature on the use of the above pyrolysis systems are highlighted. While Pyroprobe and Frontier micropyrolyzer have extended capabilities to analyze the time evolution of pyrolysate composition in seconds timeframe and obtain non-isothermal kinetics using the evolved gas analysis, respectively, the PHASR reactor is gaining popularity owing to its accuracy in obtaining product evolution data in milliseconds timeframe. Finally, the challenges and opportunities in obtaining kinetic data in heat and mass transport-free conditions are outlined, which would eventually pave way for a mechanistic understanding of polymer pyrolysis.