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Research

Fundamentals

Technique Development

Quantitative magnetic resonance (MR) data acquisition underlies all the work at the MRRC. We have expertise in a very wide variety of MR techniques (including imaging, diffusion, solids and liquids NMR) and this enables us to fully exploit the advantages of applying MR to chemical engineering applications; development of MR techniques forms a fundamental part of this. Our development of MR techniques is primarily focused on speeding up the acquisition of data whilst retaining quantification and an understanding of any errors. Examples of this include ultra-fast velocity imaging of single and two phase flows where 2-D images are acquired in as little as 10 ms and 3 component velocity vectors can be acquired in under 50 ms to quantitative 1-D imaging of conversion in reactors in times of ~5 minutes using polarisation enhancement techniques – an experiment which would takes days without these techniques. We have also developed a number of spectroscopic techniques that enable the acquisition of 2-D and 3-D correlation plots. Recently, in collaboration with Microsoft, we have been developing methods of sparse data acquisition in which the number of data points is significantly reduced, thereby reducing acquisition times further whilst retaining quantification of the relevant reconstructed data.

Transport in Porous Media

Porous materials are ubiquitous in both the natural world and in many industrial processes; they feature prominently in most of the application areas we consider. We apply a range of MR techniques to probe the physics dictating single and multi-phase fluid transport through a range of porous media, including oil-field reservoir rocks. Previously we have applied imaging and velocimetry extensively to probe pore space hydrodynamics. More recently we have made use of pulsed field gradient (PFG) measurements of diffusion and displacement propagators along with relaxometry (in particular multi-dimensional experiments), for porous systems where pore size and/or magnetic susceptibility contrast precludes direct imaging of the pore space. A key focus is the inclusion of chemical selectivity into the above measurements, exploiting as appropriate chemical shift, relaxation or diffusion contrast or a multi-nuclear approach (e.g. carbon-13 nuclei detection). We also consider the effect of pore space modification due to, for example, CO2 entrapment.

Single and Multiphase flow

An understanding of transport processes and fluid flow is at the heart of many chemical engineering applications and as such forms a fundamental part of the activities at the MRRC. Single phase flow projects include investigating complex flows of simple fluids (e.g. flow of water through an expansion at a flow rate transition) and simple flows of complex fluids (e.g. acceleration of a viscoelastic fluid in a couette cell), both of which are of fundamental interest to theoreticians. Multiphase systems examined include gas/liquid, liquid/liquid, or gas/solid phases. This work will often link into specific applications. For example, experiments elucidating the fundamentals of gas bubble shape, dispersion, coalescence and break-up in a liquid are being used to optimise reactor modelling of two-phase bubbly flows, and fundamental studies of particle dynamics and wave propagation in a vibrating particulate bed backup fluidised bed studies.

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Applications

Catalysis

Magnetic resonance is perhaps the single most powerful analytical technique that provides fundamental insights into catalytic processes because of its quantitative non-invasive nature. The magnetic resonance techniques used within our group probe physical phenomena over a hierarchy of length scales, which enables us to apply our research to areas such as fundamental catalyst powder screening and real life working catalyst pellets. For example, we can study the fundamental thermodynamic and kinetic aspects of powdered catalysis at the nanometer scale using a combination of techniques such as wideline deuterium NMR, solid state multinuclear magic angle spinning (MAS) NMR, and NMR relaxometry. Multi-nuclear pulsed field gradient (PFG) diffusion NMR can then be used to probe the transport properties of adsorbates, over micron length scales, through the porous network of millimeter sized pelletised/extruded catalysts.

Reaction Engineering

It is now quite common to talk about the magnetic resonance ‘toolkit’ as applied to studying heterogeneous catalytic reactors. The ultimate objective is to develop magnetic resonance techniques that can be used to spatially map chemical composition, concentration gradients, temperature, and gas and liquid flow profiles within a working reactor. In many cases we work with scaled-down versions of industrial reactors, but the same techniques can be used to map flow and reaction in microchannel reactors at their natural size-scale. Our research not only addresses the development of new magnetic resonance techniques to image catalytic processes occurring in the reactor environment, but also how we use these data to develop and validate numerical simulation codes, such as lattice-Boltzmann (LB) and computational fluid dynamics, of reactor performance. In the context of chemical mapping we are particularly interested in using parahydrogen and other signal enhancement techniques to advance this field of research.

Pharmaceuticals

Until recently pharmaceutical research into controlled drug delivery devices has largely relied upon offline analysis techniques such as high pressure liquid chromatography (HPLC) and Ultra Violet-Visible (UV-vis) spectroscopy. While these are both useful techniques in their own right they fail to provide any information regarding the dynamic processes that occur inside a controlled drug release matrix during drug dissolution. Our group is amongst the world leaders in the development and application of quantitative, ultrafast MR imaging protocols, to study industrial dissolution apparatus. Here we are able to localise information, such as drug concentration and diffusivity, from within the delivery matrix as well as the dissolution media hydrodynamics during an experiment in a industry standard dissolution apparatus. Recently, we have adopted a multi-modal imaging approach to pharmaceutical research by combining both magnetic resonance and Terahertz measurements on the same systems. These two techniques provide complimentary information making them powerful research tools for pharmaceutical research.

Biofilms

Biofilms are colonies of micro-organisms that anchor themselves onto a variety of support structures using a self-developed polymer matrix. We utilise a range of NMR and MRI techniques to explore their development and subsequent behaviour non-invasively. We are particularly interested in quantifying bio-colloid transport through porous support structures, nutrient and metabolic product concentration fields in the vicinity of biofilms, biofilm crystallisation of surface nano-layers and transport in the biofilm structures themselves. Our interests include the occurrence of biofilms as both friend (e.g. bio-remediation, bio-barriers) and foe (e.g. bio-fouling of reverse osmosis membranes). Data are also used to validate and help develop novel 3D Lattice Boltzmann (LB) simulations of biofilm formation and development on such complex support structures.

Micro-structure Processing Relationships

Magnetic resonance techniques are used to explore the relationship between processing conditions and micro-structure development for a range of materials including soft solids (e.g. soap), emulsions (e.g. agrochemicals, oil field emulsions), crystalline materials (e.g. gypsum) and food products (e.g. biscuit wafers). Imaging and velocimetry are used to explore velocity/shear fields inside processing equipment (e.g. extruders, humidification chambers, mixing cells, drying units) whilst micro-imaging, diffusion and relaxation measurements are used to quantify the micro-structure; correlations are then sought. This theme features the extensive use of rheo-NMR (in particular to study transient flow processes), Single Point Imaging (SPI) techniques, emulsion droplet sizing using pulsed fiend gradient (PFG) techniques and relaxation - diffusion correlation/exchange measurements.

Fluidisation

Fluidised beds are used throughout the processing industries, perhaps most commonly in the cracking and reforming of hydrocarbons. However, the development of commercially successful fluidised beds requires many stages of scale-up and often results in embarrassing failures. The challenges in designing large scale fluidised bed reactors stems from a lack of reliable knowledge about what goes on inside these systems. Fluidised beds are inherently visually opaque, making observations difficult inside three-dimensional (3D) systems. We have developed ultra-fast (viz. acquisition times of 1-25 ms) magnetic resonance techniques to study the gas and particle dynamics of fluidised beds. These measurements have been used to investigate the design and operation of gas distributors and to validate numerical simulations of these complex systems.

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