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There are various types of plastic produced and used today in society. Depending on the plastic type and also the application, different recycling techniques are best suited to recovering as much value (in a economic but mainly environmental sense) as possible. One of the most abundant plastics in our world is polypropylene (PP). This can be a difficult plastic to recycle and as we are pushing for a circular economy we need to find ways to recycle the less pure and more mixed plastic waste streams. Chemical recycling (in this case catalytic pyrolysis) offers an opportunity to break down the polymer chains into either valuable products or to intermediate products that can be further processed by a refinery into valuable products and/or into the building blocks for new plastics. Catalytic pyrolysis in this research looks at heating up a small amount of a polymer in a reactor along with a catalyst material. As the temperature increases the polymer will first melt and then start to react with the catalyst material to produce shorter hydrocarbon chains. If these chains are short enough such that they are in a gaseous form they will diffuse outwards and be carried towards a measurement device (gas chromatography) to enable quantification of the products. The reaction pathway is highly complex as the products can also react with one another to form further products and thus the exact reactor/catalyst conditions can make a significant difference to the products leaving the reactor. The main catalyst material that we studied was a fluid catalytic cracking (FCC) catalyst. This catalyst is used industrially to crack crude oil fractions which in some ways are chemically similar to PP. The ICC research group has vast experience in characterising and studying these catalyst materials so it was a good starting point for our research. The first interesting result we found was the discarded FCC catalyst seemed to outperform the fresh FCC catalyst material in our reaction conditions.

While plastics-to-plastics recycling via melting and re-extrusion is often the preferred option due to a relatively low CO2 footprint, this technique requires a highly sorted waste stream and plastic properties can often not be maintained. Obtaining aromatics, such as benzene, toluene, and xylene (BTX), via catalytic pyrolysis of polyolefins, such as polypropylene and polyethylene, offers another attractive recycling technology. In this process, a discarded crude oil refinery catalyst (ECAT) was previously shown to lower the unwanted formation of deactivating coke species compared to a fresh crude oil refinery catalyst (FCC-cat), while yielding 20 wt% aromatics from polypropylene. In this work, we study the underlying reaction mechanism for this chemical recycling process over the fresh and used refinery catalyst as well as a model system, not containing any zeolite material, using a combination of microscopy and spectroscopy. More specifically, by using in situ fluorescence microscopy, in situ infrared spectroscopy, in situ ultraviolet-visible spectroscopy as well as ex situ solid-state nuclear magnetic resonance, we observe highly fluorescent methylated aromatic intermediates that differ for the three catalyst materials under study both in their fluorescence, IR, UV-vis, and NMR spectroscopy features. This detailed micro-spectroscopic comparison informs which potential reaction intermediates lead to increased coke formation. Our results suggests that a next generation of catalyst materials for this process would profit from a higher accessibility and a milder acidity compared to an FCC-cat and shows the great potential of using ECAT to reduce coking and obtain a BTX stream, which could be become the chemical building blocks for the manufacturing of e.g., plastics and coating materials.

Increasing the stream of recycled plastic necessitates an approach beyond the traditional recycling via melting and re-extrusion. Various chemical recycling processes have great potential to enhance recycling rates. In this Review, a summary of the various chemical recycling routes and assessment via life-cycle analysis is complemented by an extensive list of processes developed by companies active in chemical recycling. We show that each of the currently available processes is applicable for specific plastic waste streams. Thus, only a combination of different technologies can address the plastic waste problem. Research should focus on more realistic, more contaminated and mixed waste streams, while collection and sorting infrastructure will need to be improved, that is, by stricter regulation. This Review aims to inspire both science and innovation for the production of higher value and quality products from plastic recycling suitable for reuse or valorization to create the necessary economic and environmental push for a circular economy.

Windcatchers are built on the roofs of houses of hot areas of the Middle East to ameliorate the internal summer climate. The archaeological and historical record shows them to have been used since antiquity, and although they are still widely found in the region today, and regularly mentioned in the modern works on architecture o-f the region, no detailed study of their types or operation has been published. Rather architects refer continually to an accepted stereotype of their form and performance on which modern architects have to rely as a design model. This study makes an original contribution to the published record. In it the badgirs, or windcatchers of a single region, Yazd, on the Persian plateau, are described; and the distribution o-f their types in the villages of the area, and city of Yazd are reviewed in relation to the climatic and historical influences on their design and use. The functions o-F badgirs in the houses of Yazd, as airconditioners and ventilators, are investigated. General temperature limits o-F their summer performance in the context of the life-style of the Yazdi, are established and reviewed in relation to comfort and the physiology of the human body and the climatic results used to interpret the distribution of windcatchers types in the wider area of the Middle East. The research provides a unique historical record of the badgirs of Yazd, illuminates the complexity of the climatic and historical influences in their distribution, and, through analysis of their performance, provides a general climatic guide that may assist contemporary designers wishing to incorporate windcatchers in modern houses in hot areas.