No abstract

Plastic production has been increasing at enormous rates. Particularly, the socioenvironmental problems resulting from the linear economy model have been widely discussed, especially regarding plastic pieces intended for single use and disposed improperly in the environment. Nonetheless, greenhouse gas emissions caused by inappropriate disposal or recycling and by the many production stages have not been discussed thoroughly. Regarding the manufacturing processes, carbon dioxide is produced mainly through heating of process streams and intrinsic chemical transformations, explaining why first-generation petrochemical industries are among the top five most greenhouse gas (GHG)-polluting businesses. Consequently, the plastics market must pursue full integration with the circular economy approach, promoting the simultaneous recycling of plastic wastes and sequestration and reuse of CO2 through carbon capture and utilization (CCU) strategies, which can be employed for the manufacture of olefins (among other process streams) and reduction of fossil-fuel demands and environmental impacts. Considering the previous remarks, the present manuscript’s purpose is to provide a review regarding CO2 emissions, capture, and utilization in the plastics industry. A detailed bibliometric review of both the scientific and the patent literature available is presented, including the description of key players and critical discussions and suggestions about the main technologies. As shown throughout the text, the number of documents has grown steadily, illustrating the increasing importance of CCU strategies in the field of plastics manufacture.

Pyrolysis is a chemical recycling technology that is experiencing fast development, is complementary to mechanical recycling, and is used to avoid incorrect disposal of postconsumer plastics (mainly polyolefins) and decrease environmental impacts related to the production of virgin plastic. However, although it has been widely accepted that pyrolysis can constitute an essential technology for the present and the future, discussions regarding the increase of scale, process sustainability, and other aspects needed for the circular economy must be carried out more thoroughly. For this reason, in this work, life cycle assessments (LCAs) of pyrolytic processes are discussed, showing that available LCA studies still lack holistic consistency and representativeness, based on a short review of previously published studies and proposed approaches and limitations.

Bibliometric studies allow to collect, organize and process information that can be used to guide the development of research and innovation and to provide basis for decision-making. Paraffin/olefin separations constitute an important industrial issue because cryogenic separation methods are frequently needed in industrial sites and are very expensive. As a consequence, the use of membrane separation processes has been extensively encouraged and has become an attractive alternative for commercial separation processes, as this may lead to reduction of production costs, equipment size, energy consumption and waste generation. For these reasons, a bibliometric survey of paraffin/olefin membrane separation processes is carried out in the present study in order to evaluate the maturity of the technology for this specific application. Although different studies have proposed the use of distinct alternatives for olefin/paraffin separations, the present work makes clear that consensus has yet to be reached among researchers and technicians regarding the specific membranes and operation conditions that will make these processes scalable for large-scale commercial applications.

Pollution by plastics constitutes an urgent problem that demands immediate actions, including development of efficient polymer recycling technologies. In this scenario, the catalytic degradation of plastic wastes constitutes a promising technology, as suitable catalysts can be used to perform cracking reactions and controlled plastic degradation, yielding high quality end products. Catalyst investments are expected to be recovered by benefits related to reduction of reaction temperature and time and by manufacture of higher valued products. However, proper environmental assessment of catalyst usage has yet to be performed in most plastics chemical recycling processes. For these reasons, in the present study, life cycle assessment (LCA) based on system expansion methodologies is carried out to determine the environmental impacts of catalytic pyrolysis transformations of high‐impact polystyrene (HIPS) and high‐density polyethylene (HDPE) using zeolite H‐USY (ultrastable Y) and SO4/SnO2 catalysts, respectively, based on actual collected experimental data to represent conversions and yields. Surprisingly, the obtained results indicate that the use of catalysts for plastic waste degradation reactions can be environmentally disadvantageous sometimes, depending on the blend of obtained products. Therefore, the environmental impact of catalysts on plastics chemical recycling should be carefully assessed to avoid problems derived from positive bias, which assumes that the catalytic process is necessarily better than the noncatalytic counterpart. However, the positive impacts of styrene and olefins recovery can indeed contribute with positive environmental performances of both catalytic and non‐catalytic processes, particularly regarding global warming, acidification, human toxicity, ecotoxicity, eutrophication, and ozone layer depletion.

An experimental and theoretical study was performed to analyze the evolution of droplet size distribution and phase separation in water-in-oil emulsions under the effect of the electric field in a batch vessel. The effects of electrostatic time, initial water content, and electric potential on the efficiency of separation were studied in the experiments. Moreover, a mathematical model based on population, mass, and momentum balance equations for dispersed, oil, and free phases was developed to interpret the experimental data. A coalescence kernel was proposed to predict the aggregation of droplets. Furthermore, a capture term was added to the balance equations to address the creation of free water. The parameters of the coalescence and capture models were estimated using the experimental data. The estimation of the parameters was done using parallel execution of the particle swarm optimization algorithm. The results of the simulation showed a decent performance of the model in predicting the profiles of water content inside the vessel.