Plastic plays an important role in our daily lives due to its versatility, light weight and low production cost. Plastics became essential in many sectors such as construction, medical, engineering applications, automotive, aerospace, etc. In addition, economic growth and development also increased our demand and dependency on plastics which leads to its accumulation in landfills imposing risk on human health, animals and cause environmental pollution problems such as ground water contamination, sanitary related issues, etc. Hence, a sustainable and an efficient plastic waste treatment is essential to avoid such issues. Pyrolysis is a thermo-chemical plastic waste treatment technique which can solve such pollution problems, as well as, recover valuable energy and products such as oil and gas. Pyrolysis of plastic solid waste (PSW) has gained importance due to having better advantages towards environmental pollution and reduction of carbon footprint of plastic products by minimizing the emissions of carbon monoxide and carbon dioxide compared to combustion and gasification. This paper presents the existing techniques of pyrolysis, the parameters which affect the products yield and selectivity and identify major research gaps in this technology. The influence of different catalysts on the process as well as review and comparative assessment of pyrolysis with other thermal and catalytic plastic treatment methods, is also presented.

Molecular oxygen is without doubt the greenest oxidant for redox reactions, yet aerobic oxidation is one of the most challenging to perform with good chemoselectivity, particularly on an industrial scale. This collaborative review (between teams of chemists and chemical engineers) describes the current scientific and operational hurdles that prevent the utilisation of these reactions for the production of speciality chemicals and active pharmaceutical ingredients (APIs). The safety aspects of these reactions are discussed, followed by an overview of (continuous flow) reactors suitable for aerobic oxidation reactions that can be applied on scale. Some examples of how these reactions are currently performed in the industrial laboratory (in batch and in flow) are presented, with particular focus on the scale-up strategy. Last but not least, further challenges and future perspectives are presented in the concluding remarks

Over the past few decades, life cycle assessment (LCA) has been established as a critical tool for the evaluation of the environmental burdens of chemical processes and materials cycles. The increasing amount of plastic solid waste (PSW) in landfills has raised serious concern worldwide for the most effective treatment. Thermochemical post-treatment processes, such as pyrolysis, seem to be the most appropriate method to treat this type of waste in an effective manner. This is because such processes lead to the production of useful chemicals, or hydrocarbon oil of high calorific value (i.e. bio-oil in the case of pyrolysis). LCA appears to be the most appropriate tool for the process design from an environmental context. However, addressed limitations including initial assumptions, functional unit and system boundaries, as well as lack of regional database and exclusion of socio-economic aspects, may hinder the final decision. This review aims to address the benefits of pyrolysis as a method for PSW treatment and raise the limitations and gaps of conducted research via an environmental standpoint.

The city of London, UK, has seen in recent years an increase in the number of high-rise/multi-storey buildings ("skyscrapers") with roof heights reaching 150 m and more, with the Shard being a prime example with a height of ∼310 m. This changing cityscape together with recent plans of local authorities of introducing Combined Heat and Power Plant (CHP) led to a detailed study in which CFD and wind tunnel studies were carried out to assess the effect of such high-rise buildings on the dispersion of air pollution in their vicinity. A new, open-source simulator, FLUIDITY, which incorporates the Large Eddy Simulation (LES) method, was implemented; the simulated results were subsequently validated against experimental measurements from the EnFlo wind tunnel. The novelty of the LES methodology within FLUIDITY is based on the combination of an adaptive, unstructured, mesh with an eddy-viscosity tensor (for the sub-grid scales) that is anisotropic. The simulated normalised mean concentrations results were compared to the corresponding wind tunnel measurements, showing for most detector locations good correlations, with differences ranging from 3% to 37%. The validation procedure was followed by the simulation of two further hypothetical scenarios, in which the heights of buildings surrounding the source building were increased. The results showed clearly how the high-rise buildings affected the surrounding air flows and dispersion patterns, with the generation of "dead-zones" and high-concentration "hotspots" in areas where these did not previously exist. The work clearly showed that complex CFD modelling can provide useful information to urban planners when changes to cityscapes are considered, so that design options can be tested against environmental quality criteria.

A Teflon AF-2400 tube-in-tube microreactor is investigated for the continuous, solvent-free, catalytic oxidation of benzyl alcohol with oxygen. The semipermeable Teflon AF-2400 tube acts as the interface between the gaseous oxidant and the liquid substrate. Because of the inherent safety of this contacting method, the use of pure oxygen is possible. The semipermeable tube was packed with 1 wt % Au−Pd/TiO 2 catalyst particles and placed inside a PTFE tube to provide an annular region which was pressurized with pure oxygen. This design allowed continuous penetration of oxygen through the inner tube during the reaction, resulting in higher oxygen concentration in the catalyst bed and significantly improved conversion compared to a reactor operating with an oxygen presaturated feed. The amount of oxygen available for reaction in the tube-in-tube microreactor was 2 orders of magnitude higher than that in a nonpermeable reactor with oxygen presaturated feed. The semipermeable tube reactor performance in terms of both conversion and selectivity was enhanced by increasing the gas pressure, the catalyst contact time and by dilution of the catalyst. The highest conversion of benzyl alcohol obtained for the range of conditions investigated was 44.1%, with 73.0% selectivity to benzaldehyde, at 120°C; catalyst contact time, 115 g cat ·s/g alcohol ; and catalyst dilution factor, 4.

Reactions of n-decene with ozone and subsequent quenching of the formed ozonides were carried out under flow conditions using the standard Vapourtec flow system equipped with a cooled flow cell. The reactions were performed continuously and in the annular flow regime within the circular cross-section channels. Typical flow rates were 0.25À1 mL min À1 for liquid and 25À100 mL min À1 for gas, reactor volumes were 0.07À10 mL formed of 1 mm ID PFA tubing. The reaction temperature was À10°C. The flow was not always smooth, while waves in the liquid film and droplets in the gas core were observed. Liquid residence times were found to be independent of gas flow rates and increasing with decreasing liquid flow rates. Substrate residence times in the ozonolysis reactor ranged between 1 and 80 s, and complete conversion could be achieved at ∼1 s residence time. Two common reductants, triethylphosphite and triphenylphosphine, were examined as to their suitability under flow conditions. Triphenylphosphine achieved faster reduction of the intermediate ozonides, resulting in a greater than 10:1 selectivity for the aldehyde over the corresponding acid. The cooling system provided a safe and efficient control of the highly exothermic reaction system. The configuration of the system allowed the production of chemically significant amounts (1.8 g h À1 at 1.3 ozone equivalents), with minimal amounts of ozonides present at any time. ' INTRODUCTIONOzone is an oxidant that has been used for decades in organic synthesis 1 and in the purification/deodorisation of water. 2 Ozonolysis is the addition of ozone to a substance, resulting initially in a primary ozonide which then usually rearranges to a more stable secondary ozonide in the case of alkenes. 3 The most common substrates for ozonolysis are unsaturated species containing either double or triple carbonÀcarbon bonds, which result usually in aldehydes/ketones and acids. This transformation has great utility in synthesis both in a research and an industrial setting. Ozone can also be used to oxidise phosphorus 1,4 and sulphur 1,5 compounds as well as organometallics 6 and other inorganic species. 6 The advantages of using ozone over other oxidants is the low cost and toxicity of the byproduct, i.e. DMSO from DMS, Ph 3 PO from PPh 3 as compared with high oxidation level metallic oxidants, e.g. chromium. Some of the drawbacks of using ozone at scale are the high exotherms associated with the initial reaction of substrates with ozone. 7 Also the intermediate ozonides are unstable (although some can be isolated at room temperature) and are an explosion risk due to the instability of the OÀO single bond; the build-up of these materials must be avoided. The use of continuous flow can alleviate both the exotherm problem and the build-up of potentially explosive materials (if suitable reagents are used to quench them in flow).Microreactors have shown several benefits in the past years. Microstructured devices provide short diffusion pathways, improved heat and mass transfer rates, and increa...

Virgin linear low-density polyethylene was subjected to pyrolysis in a fluidized bed reactor pilot plant segmented into three heating zones with both sand and Magnofil BT 80 catalyst as bed materials. The pyrolysis oil and wax products were extracted at an average bed temperature of 600 and 700 °C. The oil yield decreased between 600 (8.7 wt %) and 700 °C (8.1 wt %) in an inverse relationship with the reaction time (358 and 384 min, respectively). This was attributed to an increase in the vibration of the polyolefin polymer matrix as a result of the absorbed thermal energy with an increase in temperature. The experiments performed at 700 °C showed no wax formation but high yields of gaseous products and oils, which are more lucrative in managing accumulated plastic waste, of which polyethylene constitutes large proportions, via thermochemical conversion technologies. The estimated calorific value at 600 °C was 45.5 MJ kg–1, which is in the acceptable range for both diesel and gasoline fuel market specifications. The sulfur content in the pyrolysis oil was estimated to be 0.013% and was not affected by changes in the temperature of the fluidized reactor. However, desulfurization will be required in the future to obtain oil within acceptable ranges of clean fuels. In addition, to support this work’s results in obtaining fuels from such feedstock materials, the fuel range hydrocarbons were also analyzed. The diesel fuel hydrocarbon range (C10–C19) was between 37 and 60% in the pyrolysis oils examined. The results determined experimentally from the pilot-plant work herein are quite promising for sustainable fuel integration plans in the near future with existing petroleum refining complexes.

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