An insight on the influence of ethyl benzoate (EB) and diisobutyl phthalate (DIBP) as internal donors, differing in coordination nature on the structural aspects of MgCl2 matrix in high‐performance MgCl2‐supported titanium catalysts was developed using FTIR spectroscopy and WAXD studies. The analysis of the >CO stretching IR band of internal donors showed their coordination to (104) and (110) lateral cuts of MgCl2 matrix. Transformation of magnesium ethoxide {Mg(OEt)2} to MgCl2 during catalyst preparation resulted in different MgCl2 phases, namely the α‐form, β‐form, and the disordered δ‐form, which were analyzed by WAXD studies. The results from WAXD showed the relative preference of α‐form over β‐form in case of DIBP‐based catalysts, which might be due to interlayer bridging between adjacent layers due to the bidendate nature of DIBP. This can be one of the reasons for the high productivity of dialkyl‐phthalate‐based catalysts in comparison to ethyl‐benzoate‐based catalyst systems.magnified image

The increasing demand for plastics for their widespread applications has ultimately resulted in accumulation of substantial plastic waste, which remains a concern due to limited efforts, inadequacy, and environmental distresses of conventional techniques for waste plastics remediation. The enhanced production of raw materials for polymer syntheses has a dual impact on our ecosystem by causing rapid depletion of nonrenewable petroleum resources and waste generation. To address this situation, researchers have adopted advanced thermochemical recycling processes to produce intermediate products of the petrochemical industries including monomers, fuels, and other value-added products. Such practices can potentially serve the purpose of a circular economy. This review aims to cover the recent highlights in the field of waste plastics pyrolysis including critical observations from the past to provide precise understanding. Consequently, the reactivities and product distributions for plastic feeds, pyrolysis reactors, roles of catalysts, and effects of operating parameters on reactivity and selectivity have been covered. Coprocessing of plastic waste with radioactive materials, biomass, and heavy petroleum residue is also discussed. Furthermore, an overview on kinetics and mechanistic aspects of plastic pyrolysis is presented with a discussion on relevant analytical techniques. The applications of pyrolysis oil as a fuel or fuel additive are comprised in a separate section. Lastly, comparisons of existing chemical recycling technologies, summaries of commercial operations, and future projections are provided.

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We present a computational study, using density functional theory, of the role of internal and external donors in supported heterogeneous Ziegler-Natta polymerization catalyst systems. The focus of the investigation is the ability of the donors to stabilize the MgCl 2 support through the zip mode of coordination. Phthalates and alkoxy benzoates have been considered as representative internal and external donors, respectively. Models for the R (ccp) and the (hcp) phases of the (110) MgCl 2 lateral cut have been considered. Studies were first done with a "Fully Fixed Model", where the atoms in the MgCl 2 lateral cuts were kept fixed. The studies indicated that the phthalate donors would preferentially stabilize the R phase of MgCl 2 , while the alkoxy benzoate donors would stabilize the phase more, corroborating experimental results. A comparison of the zip coordination mode with other modes of coordination (mono, chelate, and bridge) indicates that it would be preferred over the mono and chelate coordination modes and be competitive with the bridge coordination mode. The validity of the Fully Fixed Model was then tested by doing calculations with the Partially Relaxed (some of the magnesium and chlorine atoms unfixed) and the Fully Relaxed (all atoms free) Models. The results from the latter two models corrected some of the discrepancies that had been observed for the Fully Fixed Model in comparison to previous experimental and computational investigations but were in general agreement with the Fully Fixed Model, indicating that the overall conclusions drawn with the earlier model are correct. Insertion studies done on an octahedrally coordinated titanium site flanked by two zip-coordinated phthalate donor molecules indicated that the zip-coordinating donors can confer exceptional regioselectivity to the titanium center. A list of potential donors that could serve as external donors, with di-iso-butyl phthalate (DIBP) as the internal donor, was investigated, and it was found that 1,3-diethers would serve as the best external donors to DIBP.