Experimental analysis on products distribution, characterization and mechanism of waste polypropylene (PP) and polyethylene terephthalate (PET) degradation in sub-/supercritical water.

Supercritical water (SCW) treatment of plastics is a clean technology in the 'waste-to-energy' path. In this work, PP and PET plastics were processed by sub-/supercritical water. The results showed that temperature was the most important factor of the PP and PET degradation. The influence of factors on the degradation of plastics follows the following order: temperature > residence time > plastic/water ratio. These factors influenced the yield of gas products by promoting or inhibiting various reactions (such as reverse water gas shift reaction, methylation reaction, and Fischer-Tropsch synthesis reaction). Besides, the composition of liquid oil was also analyzed. The main composition of the liquid oil produced by PET was benzoic acid and acetaldehyde, which were generated from the decarboxylation of terephthalic acid (TPA) and dehydration reaction of ethylene glycol (EG). The liquid oil from PP was mainly long-chain olefins, long-chain alkanes, cycloalkanes, etc., which were formed by the interaction of various methyl, alkyl, hydroxyl, and other free radicals. This study could build fundamental theories of plastic mixture treatment.

The interactions between mixed waste from discarded surgical masks and face shields during the degradation in supercritical water.

The widespread use of surgical masks made of polyolefin and face shields made of polyester during pandemics contributes significantly to plastic pollution. An eco-friendly approach to process plastic waste is using supercritical water, but the reaction of mixed polyolefin and polyester in this solvent is not well understood, which hinders practical applications. This study aimed to investigate the reaction of waste surgical masks (SM) and face shields (FS) mixed in supercritical water. Results showed that the optimal treatment conditions were 400 °C and 60 min, achieving a liquid oil yield of 823.03 mg·g-1 with 25 wt% FS. The interaction between polypropylene (PP), polyethylene terephthalate (PET), and iron (Fe) in SM and FS mainly determined the production of liquid oil products such as olefins and benzoic acid. The methyl-branched structure of PP enhanced PET hydrolysis, resulting in higher production of terephthalic acid (TPA). The degradation of PP was facilitated by the acidic environment created by TPA and benzoic acid in the reaction. Moreover, the hydrolysis of PET produced carboxylic acid, which coordinated with Fe3+ to form Fe-H that catalyzed the polymerization of small olefins, contributing to higher selectivity for C9 olefins. Therefore, this study provides valuable insights into the degradation mechanism of mixed PPE waste in supercritical water and guidance for industrial treatment.

Fast pyrolysis kinetics of waste tires and its products studied by a wireless-powered thermo-balance.

Fast pyrolysis is commonly used in industrial reactors to convert waste tires into fine chemicals and fuels. However, current thermogravimetric analyzers are facing limitations that prevent the acquisition of kinetic information. To better understand the reaction kinetics, we designed a novel thermo-balance device that was capable of in-situ weight measurement during rapid heating. The results showed that the reaction rate substantially increased, with significant reductions in reaction time and apparent activation energy compared to slow pyrolysis. The change of reaction mechanism from the reaction order model to the nucleation and growth model was responsible for the increase in the degradation rate. Fast pyrolysis led to the generation of more trimers of isoprene as primary pyrolytic volatiles, which we further supported through density functional theory calculations. The findings suggested that fast pyrolysis has a higher chance of overcoming the high energy barrier to form trimers of isoprene. This comprehensive and in-depth understanding of fast pyrolysis kinetics and product distribution could reveal a more realistic process of waste pyrolysis, which benefited the industry.

Effective Ultrasound Acoustic Measurement to Monitor the Lithium-Ion Battery Electrode Drying Process with Various Coating Thicknesses.

The electrode drying process (DP) is a crucial step in the lithium-ion battery manufacturing chain and plays a fundamental role in governing the performance of the cells. The DP is extremely complex, with the dynamics and their implication in the production of electrodes generally being poorly understood. To date, there is limited discussion of these processes in the literature due to the limitation of the existing in situ metrology. Here, ultrasound acoustic measurements are demonstrated as a promising tool to monitor the physical evolution of the electrode coating in situ. These observations are validated by gravimetric analysis to show the feasibility of the technique to monitor the DP and identify the three different drying stages. A possible application of this technique is to adjust the drying rates based upon the ultrasound readings at different drying stages and to speed up the drying time. These findings prove that this measurement can be used as a cost-effective and simple tool to provide characteristic diagnostics of the electrode, which can be applied in large-scale coating manufacturing.

In Situ Ultrasound Acoustic Measurement of the Lithium-Ion Battery Electrode Drying Process.

The electrode drying process is a crucial step in the manufacturing of lithium-ion batteries and can significantly affect the performance of an electrode once stacked in a cell. High drying rates may induce binder migration, which is largely governed by the temperature. Additionally, elevated drying rates will result in a heterogeneous distribution of the soluble and dispersed binder throughout the electrode, potentially accumulating at the surface. The optimized drying rate during the electrode manufacturing process will promote balanced homogeneous binder distribution throughout the electrode film; however, there is a need to develop more informative in situ metrologies to better understand the dynamics of the drying process. Here, ultrasound acoustic-based techniques were developed as an in situ tool to study the electrode drying process using NMC622-based cathodes and graphite-based anodes. The drying dynamic evolution for cathodes dried at 40 and 60 °C and anodes dried at 60 °C were investigated, with the attenuation of the reflective acoustic signals used to indicate the evolution of the physical properties of the electrode-coating film. The drying-induced acoustic signal shifts were discussed critically and correlated to the reported three-stage drying mechanism, offering a new mode for investigating the dynamic drying process. Ultrasound acoustic-based measurements have been successfully shown to be a novel in situ metrology to acquire dynamic drying profiles of lithium-ion battery electrodes. The findings would potentially fulfil the research gaps between acquiring dynamic data continuously for a drying mechanism study and the existing research metrology, as most of the published drying mechanism research studies are based on simulated drying processes. It shows great potential for further development and understanding of the drying process to achieve a more controllable electrode manufacturing process.