Professor Jonathan Seville

The Birmingham positron camera for tracking positron-emitting particles has been successfully used in a wide range of fundamental researches and industrial applications. The technique was originally developed to track a single positron-emitting tracer particle. However, tracking multiple particles would provide more information on the physical processes taking place in a system. In this paper, a new method that is able to track more than one particle is presented. The accurate spatial locations of multiple tracers are calculated by taking account of the radioactivity concentration of each tracer and by discarding corrupted y-ray trajectories. The potential applications of the multiple-particle tracking technique are illustrated through an example by tracking two moving particles in a fluidised bed.

The flow behaviour of powders during die filling was investigated using the positron emission particle tracking (PEPT) technique, from which quantitative information on the flow of individual particles was obtained. Two grades of spherical microcrystalline cellulose powders with different particle sizes were used as the model powder systems. It is shown that the trajectories of tracked particles at different initial positions are consistent with the overall flow patterns observed using a high-speed video system and linear kinematics (i.e. displacement and velocity) of the tracked particles in the moving direction of the feed shoe correspond very well with the specified shoe motion. Furthermore, a close examination of the vertical velocity component (i.e. in the gravitational direction) of the tracked particles that were deposited into the die reveals that for the system with large particles, the particles flow into the die at a higher falling velocity, compared to the system with small particles. This is primarily due to the effect of the presence of air in the die, which can significantly inhibit the flow of small particles, while its effect on the flow of large particles is small.

The effects of a high shear blending process on lactose ±-monohydrate have been investigated and important process parameters identified. Total energy input (kJ/kg), blade design and the conditions in which lactose was stored prior to blending were found to have the most significant effect on the particle size distribution, which may affect final formulation performance. The power settings used during blending, equipment temperature and humidity of the headspace above the powder were not found to have a significant effect. A simple energy balance model has also been produced that predicts the temperature of the blend with time. Although the temperature has no effect on the particle size distribution, it will affect the relative humidity in the blend which is known to have an impact on the drug-lactose interaction.

The novel traveling fluidization column, designed and built to assure identical operating conditions, was deployed to compare alternate experimental measurement techniques for hydrodynamic characterization of gas-fluidized beds. This paper compares measurements of particle velocity obtained by radioactive particle tracking (RPT ? non-invasive at the Ecole Polytechnique), positron emission particle tracking (PEPT ? non-invasive at University of Birmingham), optical fibre probes (invasive at UBC) and borescopic high speed particle image velocimetry (invasive at PSRI) carried out with FCC particles of mean diameter 107 ¼m. All of the techniques provided similar trends with respect to time-average particle velocity profiles, but significant differences were observed in some cases. Analysis of the results, focusing on the physical principles of each measurement technique, provides valuable insights into the reasons for the observed discrepancies. The results also add to a unique hydrodynamic database for validation of CFD and other mechanistic models.© 2015 Elsevier B.V. All rights reserved.

Better understanding, design and operation of engineering processes demand visualisation of the material flows within them under realistic conditions. Methods based on radioactive tracers enable visualisation to be performed on real processes taking place within opaque walls. Positron emission methods rely on detecting the pairs of back-to-back gamma rays produced when a positron (emitted in radioactive decay) annihilates with an electron, and are variants of positron emission tomography (PET) which is widely used in medicine for determining the distribution in 3D of a labelled fluid. In chemical engineering applications, extensive use has been made of the alternative technique of positron emission particle tracking (PEPT), invented at the University of Birmingham, in which a single tracer particle is radioactively labelled and can be accurately tracked at high speed. This has now been developed to the point where it has the capability to track tracer particles down to approximately 60 ¼m in size, moving at up to 10 m/s, yielding locations to within ±1 mm at frequencies better than 100 Hz. Most importantly, gamma rays are sufficiently penetrating that good location data can be obtained within real process vessels. Applications have been extremely diverse, and include both gas-phase-continuous and liquid-phase-continuous systems. Particularly strong contributions have been made to the study of mixing processes and applications of fluidisation. Hitherto, the method has been confined to the laboratory. However, a modular transportable positron camera has now been developed and has been used for the first time on large-scale plant at an industrial site. © 2009 Elsevier Inc. All rights reserved.

The mixing of powders is a long established practice and is undertaken in most industrial applications where powders are handled. The quality of the mixture has a significant impact on the end product; for example the efficacy of Pharmaceuticals or the strength of a sintered metal component. The measurement of the quality of a mixture is not without debate, and many ways of determining 'mixedness' have been proposed. Tomographic techniques have been used extensively to follow process behaviour in dynamic solid/liquid and solid/gas systems, but the evaluation of batch solid/solid blending systems has been under represented. This paper presents some initial tomographic studies to evaluate mixedness in batch blenders with a view to developing comparisons with established techniques for evaluation of blend quality and determination of end point.

Circulating Fluidized Beds (CFB) are attracting increasing interest for both gas-solid and gas-catalytic reactions, although operating modes differ completely. To model the reactor, the knowledge of the solids residence time is an important parameter. Previous studies mostly assess operations at moderate values of the solids circulation rates (d 100 kg/m2s), whereas gas-catalytic reactions and biomass pyrolysis require completely different operating conditions. Positron Emission Particle Tracking (PEPT) is used to study the movement and population density of particles in the CFB-riser. Transformation of the PEPT results define (i) the vertical particle movement and population density in a cross sectional area of the riser; (ii) the required transport gas velocity (Utr) to operate in a fully established circulation mode; (iii) the overall particle movement mode (plug flow vs. core/annulus flow); and (iv) the particle slip velocity. Only in a plug flow mode can the particle slip velocity be estimated from the difference of superficial gas velocity and particle terminal velocity. The slip velocity is lower than U - Utr outside the plug flow mode. To operate in plug flow, the superficial gas velocity should exceed Utr by 1 m/s and the solids circulation rate should exceed 200 kg/m2s.

The novel travelling fluidization column, designed and built to assure identical operating conditions, was deployed to compare alternate experimental measurement techniques for hydrodynamic characterization of gas-fluidized beds. This study compares measurements of particle velocity obtained by radioactive particle tracking (RPT ? non-invasive at the Ecole Polytechnique), positron emissi on particle tracking (PEPT ? non-invasive at University of Birmingham), optical fibre prob es (invasive at UBC) and borescopic high speed particle image velocimetry (invasive at PSRI) carried out with FCC and sand particles. Analysis ofthe time-average particle velocity profiles, focusing on the physical principles of each measurement technique provides valuable insights into the reasons of the discrepancy between the results.

We have enhanced the radio-activation efficiency of SiC (silicon carbide) particles, which by nature have a poor affinity towards 18F ions, to be employed as tracers in studies using PEPT (Positron Emission Particle Tracking). The resulting SiC-Al2O3 core-shell structure shows a good labelling efficiency, comparable to ³-Al2O3 tracer particles, which are commonly used in PEPT. The coating of the SiC particles was carried at 27 ± 3 °C and 1 bar in a fluidized bed reactor, using trimethyl aluminium and water as precursors, by a gas phase technique similar to atomic layer deposition. The thickness of the alumina films, which ranged from 5 to 500 nm, was measured by elemental analysis and confirmed with FIB-TEM (focus ion beam ? transmission electron microscope), obtaining consistent results from both techniques. By depositing such a thin film of alumina, properties that influence the hydrodynamic behaviour of the SiC particles, such as size, shape and density, are hardly altered, ensuring that the tracer particle shows the same flow behaviour as the other particles. The paper describes a general method to improve the activation efficiency of materials, which can be applied for the production of tracer particles for many other applications too.

A dense particle suspension, also called an upflow bubbling fluidized bed, is an innovative alternative to the heat transfer fluids commonly used in concentrated solar power plants. An additional advantage of this technology is that it allows for direct thermal storage due to the large heat capacity and maximum temperature of the particle suspension. The key to the proposed process is the effective heat transfer from the solar heated surfaces to the heat transfer fluid, i.e. the circulating solid suspension. In order to better understand the process and to optimise the design of the solar receiver, it is of paramount importance to know how particles behave inside the bundle of small tubes. To access to the particle motion in the solar receiver, two different techniques are carried out: experimental using positron emission particle tracking (PEPT) and 3D numerical simulation via an Eulerian n-fluid approach with NEPTUNE_CFD code. Both numerical predictions and PEPT measurements describe an upward flow at the centre of the transport tube with a back-mixing flow near the wall which influences the heat transfer mechanism. Comparisons between experiment and computation were carried out for the radial profiles of the solid volume fraction, and vertical and radial time-averaged and variance velocities of solid, and demonstrating the capability of NEPTUNE_CFD code to simulate this peculiar upflow bubbling fluidized bed.

A process to coat particles of active pharmaceutical ingredient (API) onto microcrystalline cellulose (MCC) excipient shows promise as a new way to dosage forms showing enhanced drug release. The process consists of a fluidized bed operated at elevated pressure in which API particles are precipitated from a Supercritical Anti-Solvent process (SAS). MCC particles were used as an excipient in the fluidized bed and collect the SAS-generated API particles. Naringin was selected as the model API to coat onto MCC. A number of operational parameters of the process were investigated: fluidization velocity, coating pressure, temperature, concentration of drug solution, drug solution flow rate, drug mass, organic solvent, MCC mass and size and CO2-to-organic solution ratio. SEM and SPM analyses showed that the MCC particle surfaces were covered with near-spherical nanoparticles with a diameter of approximately 100? 200 nm, substantially smaller than the as-received API material. XRD showed that naringin changed from crystalline to amorphous during processing. The coated particles resulting from the SAS fluidized bed process have a higher loading of API, gave faster release rates and higher release ratios in comparison with those produced using a conventional fluidized bed coating process. The approach could be transferred to other industries where release is important such as agrochemical, cosmetic and food.

Ribbon milling is a critical step in dry granulation using roll compaction as it determines the properties of granules, and subsequently the properties of final products. During ribbon milling, fragmentation of ribbons or flakes (i.e. compressed agglomerates from dry powders) are induced by either impact or abrasion. Understanding these fragmentation mechanisms is critical in optimising ribbon milling processes. In the current study, the discrete element method (DEM) was used to model fragmentation at the microscopic level, providing a detailed insight into the underlying breakage mechanism. In DEM modelling, virtual ribbons were created by introducing an appropriate interfacial energy using the cohesive particle model. A set of three-dimensional parallelepiped ribbons with solid fraction Æ=0.7422 and surface energies ranging from ³=0.03 JDm^2 and ³=2 JDm^2 were created and then fractured during impacts with a plane at various impact velocities, in order to model impact dominated milling. The fragmentation rate, and the number and size of fragments (i.e. granules) resulting from the breakage of a ribbon during the impact were determined. The DEM simulations showed that the granules size distribution had a bimodal pattern and there was a strong correlation between the size of fines generated from fragmentation during impact and the size of the feed powder (i.e. the size of the primary particles in this study), which was consistent with the observation from physical experiments. Two quantities were calculated from the DEM simulations: the number of fragments p and the fraction of fines z for each breakage event which can be used as input parameters for population balance models (PBM) to develop a DEM-PBM modelling framework.

In dry granulation, fine cohesive powders are compacted into large multi-particle entities, i.e., briquettes, flakes or ribbons. The powder compaction is generally followed by milling, a size reduction process, which is crucial to obtain the desired granule size or properties. Abrasion and impact are two primary mechanisms of comminution in ribbon milling, but they are not completely understood. The aim of this paper was hence to investigate numerically the fragmentation process induced by abrasion during ribbon milling. The discrete element method (DEM) was employed to simulate abrasion tests, for which three-dimensional parallelepiped ribbons were generated using auto-adhesive elastic spheres. The fragmentation rate, and the fragments size and number were determined for various surface energies and abrasive velocities. The DEM results showed that the mass-equivalent fragment size distributions were bi-modal, similar to the experimental observations and the numerical results for impact-dominated ribbon milling reported in the literature. In addition, two quantities were determined from the DEM analysis, i.e. the number of large fragments and the fraction of fines, which was then integrated into the population balance models (PBM) so that a DEM-PBM multiscale modelling framework was developed to predict the granule size distribution during ribbon milling. The DEM-PBM results were compared with the experimental results reported in the literature, and a broad agreement was obtained, implying the proposed DEM-PBM can be used to analyse the ribbon milling behaviour.

The earlier in the development of a process a design change is made, the lower the cost and the higher the impact on the final performance. This applies equally to environmental and technical performance, but in practice the environmental aspects often receive less attention. To maximise sustainability, it is important to review all of these aspects through each stage, not just after the design. Tools that integrate environmental goals into the design process would enable the design of more environmentally friendly processes at a lower cost. This paper brings together approaches based on Life Cycle Assessment (LCA) including comparisons of design changes, hotspot analysis, identification of key impact categories, environmental break-even analysis, and decision analysis using ternary diagrams that give detailed guidance for design while not requiring high quality data. The tools include hotspot analysis to reveal which unit operations dominate the impacts and therefore should be the focus of further detailed process development. This approach enables the best variants to be identified so that the basic design can be improved to reduce all significant environmental impacts. The tools are illustrated by a case study on the development of a novel process with several variants: thermal cracking of mixed plastic waste to produce a heavy hydrocarbon product that can displace crude oil, naphtha, or refinery wax or be used as a fuel. The results justified continuing with the development by confirming that the novel process is likely to be a better environmental option than landfill or incineration. The general approach embodied in the toolkit should be applicable in the development of any new process, particularly one producing multiple products.

The oral drug delivery system using bilayer tablets has become more commonly used in therapeutic strategies as it has several advantages over conventional single layer tablets such as the modified drug release, physical separation of chemically incompatible therapeutics, elongation of product patent life, etc. However, one of the common problems associated with bilayer tablets is the insufficient interfacial strength between layers, which may lead to product failure during the manufacturing process. Therefore, it is important to gain a good understanding on bilayer technology to bring bilayer design and manufacturing to similar levels of robustness as encountered in single layer tablets. In this thesis, the attributes (e.g. compressibility, elasticity, compactibility and hygroscopicity) of the commonly used pharmaceutical powders were firstly investigated to thoroughly understand how these mechanical properties affect the manufacturing performance and product quality, which built a sound scientific basis for formulation design. Based on the material property investigation, a plastic powder (MCC PH 102) and a brittle material (mannitol SD 100) were selected to produce bilayer tablets. The interfacial strength of these tablets was evaluate using two different methods: direct tensile test and terahertz pulsed imaging system. The tablet interfacial strength was used in the analysis to investigate the impacts of the different factors on tablet integrity. For instance, the influences of both powder conditions (e.g. powder formulation, mean particle size and water content) and manufacturing process conditions (e.g. compression pressure, dwell time and punch geometry) on bilayer tablet interfacial strength were examined. In addition, the elastic contact theory was also used to model the particulate contacts at the bilayer tablet interface.

It is well accepted that the technical, financial and environmental performance of a chemical process is largely determined during design. Therefore, the development of tools that integrate environmental considerations would enable the design of more environmentally friendly processes at a lower cost. This research investigates how Life Cycle Assessment (LCA) can be applied at any stage in the design process to produce useful information for design, not just after the plant is operating, which is the norm for LCA. The tools have been applied to the development of a novel process (the RT7000): thermal cracking of mixed plastic waste to produce several hydrocarbon products with the potential to displace crude oil, naphtha, or refinery wax or be used as a fuel. To allow LCA to guide the design process, a toolkit methodology was developed including comparisons of design changes, hotspot analysis, identification of key impact categories, environmental break-even analysis, and decision analysis using ternary diagrams. The results of applying these tools justified continuing with the development by confirming that the novel process is likely to be a better environmental option than landfill or incineration. At the later stages of design, advanced tools such as process simulations become attractive and allow a more accurate estimation of material and energy flows. A simulation of the RT7000 in Aspen Plus® was developed that provided data for a wide range of feed compositions. The RT7000 continued to have lower environmental impact to incineration offering a saving equivalent to 969-1305 kgCO2/tonne plastic processed. It was also ascertained that variation in feed composition does influence environmental performance, but not enough to affect the outcomes of decision making. The general approaches used in this work to assess the RT7000 should be applicable to the development of any new process. Benefits and insights similar to those obtained in the case study can realistically be expected when these methodologies are applied to any new processes. Therefore the results have been published in the Journal of Cleaner Production (Gear et al., 2018)