Johnson Matthey Technology Review - Volume 68, Issue 3, 2024

Neutron scattering methods such as quasielastic neutron scattering (QENS) and inelastic neutron scattering (INS) have been used to study the reactivity of propene and 1-octene over the acid zeolite catalyst H-ZSM-5. The high activity of the catalyst causes the alkenes to form linear oligomers below room temperature. INS has shown that the reaction proceeds through a hydrogen-bonded intermediate. Studies using propane as an inert analogue for propene have found that the adsorbed C3 molecules spend much of their time undergoing short jumps within the pore channels of the zeolite. Hydrothermal dealumination plays an important role in determining the activity of zeolite catalysts. Dealumination was found to delay the onset of catalytic activity for oligomerisation to higher temperatures and increase the mobility of hydrocarbons within the zeolite, both due to reduced acid-hydrocarbon interactions.

End-of-life plastics present a significant challenge to achieving a sustainable economy. It is crucial to develop environmentally friendly technologies to process the waste streams beyond landfilling. This review provides a detailed overview of end-of-life plastics management, covering mechanical recycling, pyrolysis and hydrocracking methods. Mechanical recycling is the predominant technique employed on a large scale in recycling end-of-life plastics, and this review discusses the technoeconomic assessment and life cycle assessment (LCA) of mechanical recycling. This review also summarises key studies concentrating on chemical recycling techniques for handling end-of-life plastics. Among these, pyrolysis and hydrocracking are discussed in depth. Recent advancements and fundamentals of these two techniques are covered, highlighting their significance in tackling the plastic waste challenge. The prospects of scaling up pyrolysis and hydrocracking technologies are interpreted in terms of technical and economic feasibility. The discussion concludes with recommendations for future research to commercialise chemical recycling of end-of-life plastics.

Activated carbon (AC) is an effective material for various environmental and industrial applications. The characteristics and performance of AC is a result of interaction between source and method of preparation. In the current work, AC has been prepared from date seed waste using microwave heating under nitrogen using basic medium such as potassium hydroxide and acidic medium such as sulfuric acid as chemical activating agents. The AC was characterised using X-ray diffraction (XRD), scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX), transmission electron microscopy (TEM) and thermogravimetric analysis (TGA) with differential scanning calorimetry (DSC). XRD patterns of the AC in both cases exhibited three peaks corresponding to the crystalline graphite form of carbon. Scanning electron microscopy (SEM) images of the freshly prepared carbons showed that the samples contained particles of various sizes including both nanoparticles as well as millimetre-range particles. DSC analysis showed that the samples exhibited endothermic reaction in low temperature ranges until 300°C and exothermic reaction above this temperature. SEM analysis of the AC, separated into three different size ranges, showed significant etching of the surface of the carbon to yield porous structures. The AC produced using sulfuric acid showed better adsorption capacity (9.2 g g⁻¹) when compared to that produced using potassium hydroxide (7.7 g g^–1). We conclude that the AC prepared from date seeds can find potential application in water purification and oil spill clean-up.

Removal of sulfur compounds from transportation fuels is a requirement in the worldwide effort to reduce emissions from transportation fuels. Refineries use the hydrodesulfurisation (HDS) process to reduce sulfur compounds in fuels. However, the HDS process requires high hydrogen pressure and temperature, making it costly. An alternative to the HDS process is oxidative desulfurisation via solvent extraction, which requires low-temperature operating conditions. In this regard, deep eutectic solvents (DESs) are attractive for researchers to desulfurise transportation fuels via solvent extraction due to their low-cost. In our study, DESs were synthesised using phenylacetic acid (PAA) and salicylic acid (SAA) as hydrogen bond acceptors (HBAs) and tetraethylene glycol (TTEG) as hydrogen bond donor (HBD) in the mole ratio of 1:2. DESs were characterised by using Fourier transform infrared (FTIR) spectroscopy. Physicochemical properties of DESs, such as density, viscosity and refractive index, were also measured. The synthesised DESs were used to extract organosulfur compounds from model fuel and actual diesel. An oxidation study was carried out for model fuel and diesel, followed by solvent extraction using these synthesised DESs. The extraction efficiency for PAA/TTEG(1:2) and SAA/TTEG(1:2) was achieved as 50.16% and 38.89% for model fuel at a temperature of 30°C using a solvent to feed ratio of 1.0 while for diesel, it was 38% and 37%. However, it increased to 77%, 68% and 54%, 73%, respectively, for PAA/TTEG(1:2) and SAA/TTEG(1:2) when the feedstocks were oxidised. These results showed better extraction performance of DES PAA/TTEG(1:2) than that of SAA/TTEG(1:2) at low temperature 30°C using combined extractive catalytic oxidative desulfurisation. Hence, the DES synthesised using SAA and TTEG in the molar ratio of 1:2 works better as an extraction solvent for removing organic sulfur compounds from fuels at low temperatures.

Bituminous binders, often referred to as asphalt, play a pivotal role in the construction and maintenance of flexible pavements. As the demand for durable and sustainable infrastructure continues to rise, a thorough understanding of the physical and rheological properties of bituminous binders becomes imperative. This manuscript presents a comprehensive review of various mechanical tests used to assess bituminous binder properties, including penetration (Pen), softening point (SP), penetration ratio (PR), penetration index (PI), ductility tests and absolute and kinematic viscosities. These mechanical tests serve as fundamental tools for evaluating binder consistency, hardness, ductility and flow behaviour. SP and Pen measurements are employed to grade bituminous binders based on their response to temperature. Additionally, PR and PI provide valuable insights into binder performance under varying environmental conditions. Ductility tests offer critical information about a binder’s ability to elongate without breaking, a crucial factor in withstanding the stresses imposed by traffic. In parallel, the manuscript underscores the significance of understanding the rheological properties of bituminous binders. Dynamic shear rheometry (DSR) is introduced as a method for characterising complex modulus (G*), fail temperature and phase angle (δ) behaviour under different temperature and loading conditions. These tests are well established in the USA based on Strategic Highway Research Program (SHRP) specifications. Their relevance in the Indian context is discussed, with recent inclusion of rheological parameters in the Bureau of Indian Standards (BIS) specification. The manuscript highlights the role of instrumental analysis techniques, including Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR) and scanning electron microscopy (SEM), in uncovering the molecular and microstructural aspects of bituminous binders. FTIR aids in identifying functional groups within the binder, elucidating chemical composition and aging effects, while NMR provides insights into molecular mobility and heterogeneity. SEM is instrumental in revealing the binder’s microstructure and its interaction with aggregates. In conclusion, this manuscript offers a comprehensive analysis of both mechanical and rheological testing, emphasising their significance in evaluating bituminous binder properties. It also stresses the growing importance of instrumental analysis techniques, particularly for chemically modified bitumen. The primary aim is to provide a valuable resource for researchers, engineers and practitioners in the field of civil engineering and infrastructure development.

Recent progress has been made towards decarbonisation of transport, which accounts for one quarter of global carbon dioxide emissions. For the short to medium term, new European Union (EU) and national energy and climate plans agree on a strategy based on the combination of increasing shares of electric vehicles with the promotion of sustainable fuels, especially if produced from residual feedstock and routes with low or zero net carbon emission. Hydrogen stands out among these fuels for its unique properties. This work analyses the potential of using hydrogen in a dual-fuel, compression ignition (CI) engine running with three diesel-like fuels (conventional fossil diesel, advanced biodiesel (BD) and hydrotreated vegetable oil (HVO)) and different hydrogen energy substitution ratios. The results were confronted with conventional diesel operation, revealing that dual-fuel combustion with hydrogen demands higher exhaust gas recirculation (EGR) rates and more advance combustion, leading to a remarked reduction of NOx emission at the expense of a penalty in energy consumption due mainly to unburnt hydrogen and wall heat losses. Unreacted hydrogen was ameliorated at high load. At low load, the use of BD dual combustion permitted higher hydrogen substitution ratios and higher efficiencies than diesel and HVO.

Ammonia is emerging as a promising alternative fuel for longer range decarbonised heavy transport, particularly in the marine sector due to highly favourable characteristics as an effective hydrogen carrier. This is despite generally unfavourable combustion and toxicity attributes, restricting end use to applications where robust health and safety protocols can be upheld. In the currently reported work, a spark ignited thermodynamic single cylinder research engine equipped with gasoline direct injection was upgraded to include gaseous ammonia port injection fuelling, with the aim of understanding maximum viable ammonia substitution ratios across the speed load operating map. The work was conducted under overall stoichiometric conditions with the spark timing re-optimised for maximum brake torque at all stable logged sites. The experiments included industry standard measurements of combustion, performance and engine-out emissions (including ammonia ‘slip’). With a geometric compression ratio of 12.4:1, it was possible to run the engine on pure ammonia at low engine speeds (1000–1800 rpm) at low to moderate engine loads in a fully warmed up state. When progressively dropping down below a threshold load limit, an increasing amount of gasoline co-firing was required to avoid engine misfire. Due to the favourable antiknock characteristics, pure ammonia operation was up to 5% more efficient than pure gasoline operation under stable operating regions. A maximum net indicated thermal efficiency (ITE) of 40% was achieved, with efficiency tending to increase with speed and load. For the co-fuelling of gasoline and ammonia in a pure ammonia attainable operating region, it was found that addition of gasoline improved the combustion, but these improvements were not sufficient to translate into improved thermal efficiency. Emissions of ammonia slip reduced with increased gasoline co-fuelling, albeit with increased NOx. However, the reduction in ammonia slip was nearly ten times the increase in NOx emissions. Comparing pure ammonia and pure gasoline operation, NOx reduced by ~60% when switching from pure gasoline to pure ammonia (as the latter is associated with longer and cooler combustion). Results were finally compared to those obtained a modern multicylinder Volvo ‘D8’ turbo-diesel engine modified for dual-fuel operation with ammonia port fuel injection (PFI), with the focus of the comparison being ammonia slip and NOx emissions.

This experimental study investigates the palladium/rhodium based three-way catalyst (TWC) in a hydrogen-gasoline dual-fuel spark ignition (SI) engine under stoichiometric and lean conditions. The work focused on lean-burn engine operating conditions with the aim of reducing nitrogen oxides (NOx) emissions during the combustion process, where the TWC is not effective, while improving the thermal efficiency of the engine. Under these lean-burn engine conditions, the combustion promoting properties of hydrogen allowed for maintained engine combustion stability as determined by the cycle-to-cycle variation (COVimep) values even up to ultra lean conditions (λ= 2.0). It was found that by reducing the combustion temperature through the application of lean conditions, engine-out NOx emissions could be reduced or even eliminated, while under these conditions the TWC was effective in reducing engine-out carbon-based gaseous emissions.

Fossil fuel price continuous growth invites to look for alternative solutions to fuel for internal combustion engines. One of the most accepted options is biodiesel. In the present study, the multifrequency ultrasound-assisted synthesis of Sinapis alba oil biodiesel has been tested. For this purpose, an ultrasonic probe working at 20 kHz and an ultrasonic reactor with interchangeable transducers of discrete frequencies (195 kHz, 578 kHz, 861 kHz and 1136 kHz) have been used. For the probe, a multi-response optimisation has been carried out, setting methanol-to-oil molar ratio at 5.5:1. Optimal results were provided by 1.42 percentage weight (wt%) of catalyst after approx. 10 min of ultrasonication. In case of transducers, oil-to-biodiesel conversion needed an ultrasonication time of 15 min. Overall, when ultrasound frequency increases, oil-to-biodiesel conversion slightly improves. In conclusion, this work provides a predictive method to produce biodiesel under ultrasonication conditions, at different frequencies, in batch mode. Resulting biodiesel meets European standard requirements.

The evolution of three dimensional (3D) printed porous metallic biomaterials and their clinical applications are currently receiving much consideration. Many research works have been focused on the shaping by 3D printing of lightweight metal implants with improved mechanical properties. In the same way, the effect of surface finishes on roughness and porosity distribution on biological properties is still debated. Therefore, several factors need to be addressed and revisited in this context. This review focuses on the importance of porous metallic implant design and its relationship with biological and mechanical properties. First, the additive manufacturing (AM) techniques for bio-inert metals and alloys will be discussed. The review will then introduce the most efficient surface treatments and coating approaches for biomedical porous metals to enhance bone tissue regeneration, prevent corrosion, reduce revision surgery and improve implant lifetime. A critical study of the various parameters impacting the biological properties will also be carried out in this review.