M.D. Mantle

Structure and Dynamics of 1-Ethyl-3-methylimidazolium Acetate via Molecular Dynamics and Neutron Diffraction

The liquid state structure of the ionic liquid, 1-ethyl-3-methylimidazolium acetate ([C(2)mim][OAc]), an excellent nonderivitizing solvent for cellulosic biomass, has been investigated at 323 K by molecular dynamics (MD) simulation and by neutron diffraction using the SANDALS diffractometer at ISIS to provide experimental differential neutron scattering cross sections from H/D isotopically substituted materials. Ion-ion radial distribution functions both calculated from MD and derived from the empirical potential structure refinement (EPSR) model to the experimental data show the alternating shell structure of anions around the cation, as anticipated. Spatial probability distributions reveal the main anion-to-cation features as in-plane interactions of anions with the three imidazolium ring hydrogens and cation-cation planar stacking above/below the imidazolium rings. Interestingly, the presence of the polarized hydrogen-bond acceptor (HBA) anion (acetate) leads to an increase in anion-anion tail-tail structuring within each anion shell, an indicator of the onset of hydrophobic regions within the anion regions of the liquid. MD simulations show the importance of scaling of the effective ionic charges in the basic simulation approach to accurately reproduce both the observed experimental neutron scattering cross sections and ion self-diffusion coefficients.

Superior performance of a chiral catalyst confined within mesoporous silica

A chiral catalyst from the ligand 1,1′-bis(diphenylphosphino)ferrocene (dppf) anchored to the inner walls of the mesoporous support MCM-41 and co-ordinated to PdII has been shown to exhibit a degree of regioselectivity and enantiomeric excess, in the allylic amination of cinnamyl acetate, which is far superior to that of its homogeneous counterpart or that of a surface-bound analogue attached to a non-porous silica.

Magnetic Resonance Imaging of Catalysts and Catalytic Processes

Magnetic resonance (MR), in the form of solid-state nuclear magnetic resonance (NMR) spectroscopy, is well established as a research tool for investigations of the structures of solid catalysts and molecular species adsorbed on them. However, during the past decade there has been increasing interest in using magnetic resonance imaging (MRI) techniques to study, in particular, flow fields inside reactors. These studies have recently been extended to measurements of chemical conversion within model reactor systems. The real power of MR techniques is that by bringing together spectroscopy, diffusion, micro-imaging, and flow imaging, they provide a non-invasive, chemically specific measurement technique which can characterize a system over length scales ranging from the angstrom- to the centimeter scale. In this review, recent developments in MRI pulse sequences are summarized and applications to investigations of both hydrodynamics and catalytic conversion within catalysts and catalytic reactors are presented.

A one-step, enantioselective reduction of ethyl nicotinate to ethyl nipecotinate using a constrained, chiral, heterogeneous catalyst

A chiral catalyst derived from n1,1′-bis(diphenylphosphino)ferrocene and anchored within MCM-41 ndisplays remarkable increases in both enantioselectivity and activity, in nthe hydrogenation of ethyl nicotinate to ethyl nipecotinate, when compared nto an analogous homogeneous model compound.

Glycerol eutectics as sustainable solvent systems

In this work the use of glycerol as a hydrogen bond donor in Deep Eutectic Solvents is studied. The physical properties of choline chloride mixtures with glycerol are quantified and it is shown that eutectic mixtures can circumvent some of the difficulties of using glycerol as a solvent viz. high viscosity and high melting point. The solvent properties are characterised using polarity parameters and the values are similar to other ionic liquids although it is shown that this procedure is a poor method of characterising Lewis basicity. The application of these liquids to the esterification of glycerol is used as a demonstration of the ability to tune a reaction with the quaternary ammonium halide acting as a quasi-protecting group. The liquids represent a sustainable way of preparing non-toxic, tuneable solvent systems.

Application of magnetic resonance imaging techniques to particulate systems

Magnetic resonance imaging (MRI) is a well-established technique in the medical field, typically for imaging liquid water in the human body, but it is increasingly being used in the field of engineering and materials science. A particular section of this is in the area of particulate systems and granular material flows. MRI is being used to provide a unique insight into particle distribution and motion with in situ measurements. In this paper we discuss how judicious choice and development of imaging technique applied to various different granular systems can provide us with valuable new data on the processes occurring in granular flows. Experimental results focus on rotating bed segregation, velocity imaging in vertical fluidized beds and phase-resolved velocity distributions within vertical vibro-fluidized beds. A discussion of the various imaging techniques used to acquire these data is also given.

NMR measurements and hydrodynamic simulations of phase-resolved velocity distributions within a three-dimensional vibrofluidized granular bed

We report the results of nuclear magnetic resonance imaging experiments on vertically vibrated granular beds of mustard grains. A novel spin-echo velocity profiling technique was developed that allows granular temperature, mean velocity and packing fraction distributions within the three-dimensional cell to be measured as a function of both vertical position and vibration phase. Bimodal velocity distributions were observed at certain portions of the vibration cycle, and in general the ability to acquire time-resolved data demonstrated the significant distortions to the velocity distributions and the systematic errors in calculated temperature distributions that may arise with time-averaged measurements. The experimental behaviour was compared with predictions from a time-varying one-dimensional hydrodynamic model using the experimental parameters as input to the code. In both cases, damping of longitudinal sound waves was linked to significant volume heating effects, which contrasts with the usual heat transport mechanism (i.e. diffusion from the boundaries) currently assumed in most steady-state models. This leads to a new explanation for the counterintuitive upturn in granular temperature in vibrofluidized granular beds, based on amplification and damping of sound waves in the high-altitude region.

Magnetic resonance imaging of fluidized beds: Recent advances

Recent developments in magnetic resonance (MR) imaging techniques give measurements of particle velocities and voidage fractions in a bubbling fluidized bed, with a spatial resolution of approximately 0.6 mm and a time resolution of approximately 2 ms. The particles contained liquid, whose mobile molecules have more favorable relaxation times (T1, T2 and T2*), than for solids, facilitating rapid MR measurements. Seeds 0.5–2 mm in diameter containing oil and hollow, plastic spheres 1–10 mm in diameter filled with water were used.