Study of the decomposition kinetics, pyrolysis products, and even reaction mechanisms plays an important role for the development of polymer recycling. In the present research, the kinetics of virgin and waste polypropylene (PP) and lowdensity polyethylene (LDPE) were studied by a modified Coats−Redfern method. Afterward, thermal cracking of them in a semibatch reactor under atmospheric pressure in nitrogen has been investigated. Both virgin and waste plastics are decomposed at 420−460 °C, and the products have been characterized using GC, FT-IR, 1 H NMR, and GC-MS. The reaction path and the degradation mechanism for the thermal cracking of polymer in this study were also discussed. The lower activation energy of waste PP and LDPE indicates that waste plastics degrade at lower initial temperature and may favor mild conditions. Due to the short residence time, the higher gaseous and liquid yields were obtained for virgin PP and LDPE. A large amount of residues for waste polymer indicates that it is a favorable way to degrade waste plastics in a semibatch reactor without further separation. Chain scission reactions are the predominant degradation mechanism in this thermal cracking process. The significant content of unsaturated hydrocarbons in PP thermal cracking products shows the intramolecular hydrogen transfer and β-scission reactions are predominant. In the case of LDPE, intermolecular hydrogen transfer and β-disproportionate reactions also occur. For thermal cracking polymer in a semibatch reactor under atmospheric pressure, the high yields of gasoline (C 6 −C 12 ) and diesel (C 13 −C 22 ) fraction in liquid products confirm that it is a desirable way to realize waste plastics recovery.
A new eight-lump kinetic model containing 19 kinetic constants is proposed to describe coal tar hydrogenation. The model contains lump 1 (>300 °C), lump 2 (250À300 °C), lump 3 (200À250 °C), lump 4 (20À200 °C), diesel, gasoline, gas, and coke as lumps. The kinetic parameters were determined using least-squares regression analysis of the experimental data, obtained in two-stage fixed beds filled with the laboratory-made catalysts at various operating conditions. The proposed model was also validated. Comparisons between the experimental data and predictions using the lumping kinetic model showed good agreement. The variation in product yields and product distribution with operating conditions and feed properties was predicted. The effects of space velocity, hydrogen/oil ratio, temperature, initial hydrogen pressure, and other reaction conditions on hydrogenation performance were also investigated.
High-quality single-crystalline NbSe2 nanosheet arrays were successfully synthesized by a salt and hydrogen co-assisted CVD method, and the crystal structure and morphology of the material were investigated by XRD, Raman...
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