Achilleas Constantinou

A review on thermal and catalytic pyrolysis of plastic solid waste (PSW)

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.

Aerobic oxidations in flow: opportunities for the fine chemicals and pharmaceuticals industries

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 aerobic oxidation 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.

CO2 absorption in flat membrane microstructured contactors of different wettability using aqueous solution of NaOH

Abstract CO2 absorption in solutions of sodium hydroxide (NaOH) was performed in three membrane/mesh microstructured contactors: a single-channel polytetrafluoroethylene (PTFE) membrane contactor, a nickel mesh contactor and an eight-channel PTFE membrane contactor. A membrane/mesh was used to achieve gas/liquid mass transfer without dispersion of one phase within the other. The PTFE membrane consisted of a pure PTFE layer 20 μm thick laminated onto a polypropylene (PP) layer of 80 μm thickness. The pure PTFE layer contained pores of ~0.5 to 5 μm diameter and was hydrophobic, while the PP layer consisted of rectangular openings of 0.8 mm×0.324 mm and was hydrophilic. The nickel mesh was 25 μm thick and contained pores of 25 μm diameter and was hydrophilic. Experiments were performed with a 2 m NaOH solution and an inlet feed of 20 vol % CO2/N2 gas mixture. Numerical simulations matched reasonably well the experimental data. CO2 removal efficiency increased by increasing the NaOH concentration, the gas residence time and the exchange area between gas and liquid. Higher removal of CO2 was achieved when the PP was in the gas side rather than in the liquid side, due to lower mass transfer resistance of the gas phase. For the same reason, CO2 removal efficiency was higher for the eight-channel PTFE contactor compared to the nickel mesh contactor. Average CO2 flux was higher for the eight-channel contactor (8×10−3 mol/min·cm2 with PP on the gas side) compared to the nickel mesh contactor (3×10−3 mol/min·cm2) for the same gas and liquid residence times. The eight-channel PTFE membrane contactor removed around 72% of CO2 in 1.2 s gas residence time, demonstrating the potential for CO2 absorption using flat membrane contactors.