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.

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A model is developed that allows accurate prediction of the permeability of a core sample of sedimentary rock, based on two-dimensional image analysis of its pore structure. The pore structure is idealized as consisting of a cubic network of pore tubes, with the tubes having an arbitrary distribution of cross-sectional areas and shapes. The areas and perimeters of the individual pores are estimated from image analysis of scanning electron micrographs of thin sections, with appropriate stereological corrections introduced to account for the angle between axis of the pore tube and plane of the thin section. The individual conductances of each tube are estimated from the measured areas and perimeters, using the hydraulic radius approximation. Variations in the pore diameter along the length of the tube are accounted for with a “constriction factor” whose derivation is based on laminar flow through an irregular tube. Effective-medium theory is used to find the effective single-tube conductance, based on the measured distribution of individual conductances. This procedure is applied to several consolidated North Sea reservoir sandstones, and some outcrop sandstones, with permeabilities ranging from 20 to 1400 mD. The predicted permeabilities are typically within a factor of 2 of the measured values, with an average error in logk of only 0.168.

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