Search

Spiral jet mills utilise high-pressure gas jets, which induce particle breakage by collisions. Appropriately angled jets force particles to circulate in dense phase near the wall due to the centrifugal field. Moving radially inwards towards the mill centre, the two-phase dense flow is transformed into a lean phase and fine particles are entrained out by the fluid drag. Here we analyse the effect of grinding nozzles pressure on the particle dynamics and fluid flow by numerical simulation. The average velocity gradient in the radial direction is very steep for low mass loadings, indicative of rapid shearing, but it decreases significantly as the particle mass loading is increased. The dissipated collisional energy, accountable for size reduction, is strongly influenced by the jet penetration through the circulating bed, which in turn depends on the mass loading and operating pressure of grinding gas nozzles. As a result of jet penetration, the grinding gas nozzles pressure becomes less effective at high pressures. The analysis developed here elucidates the coupled effect of mass loading and grinding nozzles pressure on the dissipated collisional energy, which accounts for particle breakage.

Cystinuria is the most common cause of inherited stone disease and is caused by the failure of absorption of filtered dibasic amino acids including cystine in the proximal tubules. It is associated with a very high recurrence rate in affected patients, with the potential for significant morbidity in such patients due to the need for repeated surgical interventions. A multimodal and multispecialty approach in a dedicated centre is the key to improving treatment outcomes and patient adherence to the treatment. This article reviews the latest knowledge on the clinical and diagnostic features and summarises key developments to aid clinicians in diagnosis and management options, together with future directions for the care of these patients.

Cyclones are commonly used in the process industry to separate entrained particles from gas streams. Particles entering a cyclone are subjected to a centrifugal force field, driving them to the cyclone walls, where they experience collisional and rapid shearing stresses. Consequently, particle attrition and erosion of the cyclone walls occur, depending on the mechanical properties of the particles and cyclone walls. In this work, the attrition of manganese oxide particles, intended for use in the Chemical Looping Combustion (CLC) process, flowing through a standard design cyclone (Stairmand design) is analysed as an example by considering surface damage processes of chipping and wear. A new methodology is developed, whereby Computational Fluid Dynamics-Discrete Element Method (CFD-DEM) simulations are used to analyse the particle motion and interactions with the cyclone walls. The approach is then coupled with breakage models of chipping and wear to predict the extent of attrition. The impact breakage due to chipping is evaluated experimentally first as a function of particle size and impact angle and velocity. The data are fitted to the chipping model of Ghadiri and Zhang. The model is then coupled with the frequency of collisions and impact velocity, obtained from the CFD-DEM simulation, to work out the particle attrition by chipping. For surface wear the model of Archard is used to account for particle wear by shearing against the walls. The outcome of the work provides a methodology for describing the extent of attrition in different regions of the cyclone.

Homogenous iridium complexes with asymmetric ligands and different tether lengths have been solid‐supported and prepared in multi‐gram quantities. Packed in a fixed‐bed, they have been used in continuous flow for up to 120 hours in the asymmetric transfer hydrogenation of APs in 2‐propanol to make 1‐phenethyl alcohols in > 95 % conversion and ee. The CsDPEN ligand and C5 tether showed higher performance than TsDPEN and the C14 tether, whilst the ketone feed concentration and reaction temperature were optimized to enable the catalyst to be used at 5 mol‐% loading with a residence time of 39 minutes. The total amount iridium leaching of from the support during sustained operation was 58–147 ppm. The flow system gives higher catalyst turnover numbers than the related batch reactions, but the nature and concentration of the base were found to influence strongly the catalyst's performance, with the finding that triethylamine maintains high enantioselectivity but slowly deactivates the catalyst, whilst potassium tert‐butoxide does the opposite. The utility of the system is shown in the high ee's and good conversions achieved for a range of aryl alcohols.

Crystal growth rates are notoriously difficult to predict and even experimental data are often inconsistent. By allowing for mass and energy diffusion through the molecular and thermal layers surrounding a growing crystal and for the heat effect of crystallization, a new model of crystal growth from solution is proposed and applied to crystallization of potassium chloride from aqueous solution. The driving force for crystal growth was calculated using the solubility at the interface temperature in contrast to the conventional one based on bulk temperature. A positive heat effect at the crystal interface as well as the resistances to the mass and energy transfer processes to and from the crystal surface can reduce the conventional driving force for crystal growth by more than 20 %.

Particle size reduction in spiral jet mills is induced by high velocity gas jets, causing interparticle and particle wall collisions leading to breakage. Despite extensive research on the design and operational parameters, the underlying mechanics of size reduction is still poorly understood. Discrete Element Method and Computational Fluid Dynamics are used here to analyse particle and fluid motions. A fast shearing dense particle bed is formed on the wall, with a transition to lean phase towards the centre of the mill. This necessitates four-way coupling of fluid and particle interactions for analysis. It is shown that increasing the depth of the particle bed reduces the fluid phase tangential velocity in the proximity of the classifier, as momentum is exchanged with circulating particles. The energy dissipation through particle collisions occurs mainly along the bed surface and in front of the grinding jet nozzles.

Characterisation of anodic aluminium oxide coatings and measurement of their thickness using microscopic techniques is valuable for analysing the effectiveness of the prior anodising process. Three different methods for preparing samples to view the coating cross-section (mechanical fracturing, cryogenic fracturing and metallography) were trialled and assessed for speed of implementation, simplicity and achievable measurement accuracy. Cryogenic fracturing was found to be destructive to samples. Mechanical fracturing yielded relatively accurate coating thickness measurements and coating structural information. Metallography provided the most accurate coating thickness measurement at the expense of coating structural information.

A spiral jet mill was simulated using Discrete Element Method modelling and Computational Fluid Dynamics. The particle behaviour and fluid motion were analysed as a function of hold-up and grinding pressure. Particle collision energy was predicted to be prevalent along the bed surface and in front of the grinding jets, as shown through the collision data recorded. The bed itself affects the fluid flow field, as momentum is transferred to the particles. Increasing the grinding pressure does not result in a proportional increase in the kinetic energy of the particle system, as the high pressure jets begin to penetrate the bed with greater ease. The particle bed moves as ‘plug-flow’, with the layers of the bed closest to chamber wall.

A polythermal methodology to assess the mechanisms and the kinetics of solution crystallisation is described and used in connection with a recently proposed model for the dependence of the critical undercooling for crystallisation on the cooling rate (D. Kashchiev, A. Borissova, R. B. Hammond, K. J. Roberts, J. Cryst. Growth, 312 (2010) 698–704; J. Phys. Chem. B, 114 (2010) 5441–5446). This first principles model allows determination of crystallisation parameters that could otherwise only be obtained by combined application of both the isothermal and the polythermal methods. The methodology is validated through analysis of experimental data measured for methyl stearate crystallising from kerosene solutions with concentrations from 200 to 350 g l−1. The analysis reveals a progressive heterogeneous nucleation mechanism and crystallite interfacial tension values between 1.64 and 1.79 with no obvious dependence on the solution concentration, in good agreement with values derived by isothermal methods. Sensitivity analysis leads to the conclusion that a minimum of four different cooling rates spanning at least one order of magnitude together with at least five repeats for crystallisation temperature values at each cooling rate are appropriate. Extensive supplementary material provides a mathematical description of the above authors' model, insight into the relationship between this model and the empirical Nyvlt model, and further detail concerning the results of the sensitivity analysis carried out on the experimental methodology used.

Among the various methods for the solution of population balances (PB) equations, the moments based methods are some of the most successful and popular. Moment based methods have demonstrated advantages such as reduced computational effort especially for applications that couple population balance (PB) simulation with computational fluid dynamics (CFD). The methods, however, suffers from two main drawbacks: the inability to yield the number density directly and limitation to system models that only consider size independent growth expression and certain breakage and aggregation kernels. This article presents an extension to the standard MOM (SMOM), the extended method of moment (EMOM), which not only allows the prediction of the number density directly in most cases, but also makes it applicable to systems with size dependent growth and any particle aggregation and breakage kernels. The method is illustrated and tested by reference to case studies that were well studied systems in the literature.

Crystallization modelling is limited by the availability of methods to reliably predict mixing, temperature and concentration distributions, supersaturation, nucleation and growth kinetics for crystallization systems of industrial size. A new software environment for modelling batch cooling crystallization has been developed integrating crystallization and fluid dynamics. The mathematical model can reliably predict mixing in stirred vessels of a given geometry and its effect on the crystallization kinetics and crystal product properties thus reducing the cost and time required for the design and scale-up of industrial crystallizers. The paper describes the development and application of crystSim for modelling industrial crystallization in stirred tanks. The software is developed in Visual C# making full use of Object Oriented Programming (OOP) and multithreading.

Crystallization in solutions under steady cooling is considered in the case of progressive nucleation, in which new crystallites are continuously nucleated among the already growing ones. Expressions are obtained for the total volume and number of crystallites as functions of the steadily increasing undercooling. These expressions are employed for determining the dependence of the relative critical undercooling u c for crystallization on the cooling rate q . The resulting u c ( q ) formula reveals that in the case of crystallization by progressive nucleation, the often used semi-empirical Nyvlt equation is an approximation which contains only the linear terms in the relationship between ln u c and ln q . The results obtained are also directly applicable to overall crystallization of melts at sufficiently small undercoolings.

During on-line monitoring and control of batch cooling crystallization using ATR-FTIR spectroscopy, appropriate calibration procedures are indispensable to the conversion of the spectroscopic measurements into useful and informative in-situ concentration predictions. The commonly used empirical transmittance ratio models cannot effectively handle complicated systems where the absorption bands appearing from solute and solvent overlap each other or the characteristic absorption bands of solute are rather weak and prone to noise. The conventional multivariate bilinear calibration modelling approaches of PCR and PLS are not capable of explicitly modelling with acceptable accuracy the temperature-induced spectral variations, the scaling effect resulting from the use of concentration units in mass–mass/mass–volume ratio rather than molarity, and the multiplicative effects caused by potential variations in optical path-length. In this contribution, an advanced chemometric methodology, termed extended loading space standardization, is presented and shown to be able to explicitly address the above issues. This is demonstrated by application to the on-line monitoring of the batch cooling crystallization of two organic compounds, monosodium glutamate and L-glutamic acid respectively using ATR-FTIR spectroscopy. The results showed that using extended loading space standardization has enhanced predictive performance than conventional multivariate bilinear calibration methods due to its ability in efficiently handling the impact of temperature and multiplicative effects.

The in situ measurement of solution supersaturation associated with the batch cooling crystallization of l-glutamic acid (LGA) at 500 mL and 20 L scale sizes is assessed via ATR-FTIR spectroscopy. A partial least squares chemometric calibration model was developed for the online prediction of LGA concentration from measured FTIR absorbance spectra overcoming some significant challenges related to the low sensitivity of LGA in the mid-IR frequency range, its low solubility in water, and its complex speciation chemistry. The solubility data of LGA in water over the temperature range from 40 to 80 °C, using ATR-FTIR, reveals excellent agreement with those obtained both from using a gravimetric method and literature data. The metastable zone width determined using the turbidimetric methods as a function of heating/cooling rates and solute concentration is found to increase with increasing cooling rate while it decreases with increasing solution concentration. Monitoring online crystallization via both spontan...

A new insight for quantitative determination of the complex interaction of kinetics of reactive crystallization is gained by a study of the acidification of monosodium glutamate with hydrochloric acid in a semi-batch reactor. The dynamic equilibrium of the l-glutamic acid ions, their simultaneous presence in the solution, and the effect on the crystal size and size distribution are simulated using a mathematical model based on integration of the population balance equation with the crystallization kinetics and thermodynamics of the process. The model includes equations of chemical reactions, pH, nucleation, size-independent growth, and population balance. This allows a precise determination of the driving force for the reactive crystallization and the parameters of the nucleation and crystal growth rate expressions. The model considers the effect of the controlling parameters such as the rate of addition of the acid and the initial concentrations of ionic species and can be used to predict the concentrati...

In-process ATR FTIR spectroscopy is used to measure concentration and supersaturation in drowning-out of benzophenone from methanol/water solution and to study the effect of the rate of the aqueous antisolvent addition. A selected peak ratio in terms of IR transmittance or absorbance is monitored on-line and used to develop calibration equations for the concentration of the solute in the mixed solvent as a function of the ratio and the quantity of the antisolvent added. The benzophenone solubility in the mixed methanol/water solvent is found to be a nonlinear function of the respective solubilities of the solvents accounting not only for the dilution effect, but also for the binding of solvent molecules by the antisolvent molecules.

Closed-loop computer control of solution supersaturation based on in-process measurements of the concentration using ATR-FTIR spectroscopy and adaptive determination of the corresponding temperature profile has been applied to control the crystallization of monosodium glutamate from an aqueous solution. The crystal size and its distribution are varied and optimized by applying different control strategies such as rapid desupersaturation, constant supersaturation, and step-changing supersaturation profiles.

Crystallization in solutions under steady cooling is considered in the case of instantaneous nucleation, in which all crystallites appear at once in the solution and grow in the absence of crystallites born subsequently. Expressions are obtained for the total crystallite volume as a function of the steadily increasing undercooling. These expressions are employed for determining the dependence of the relative critical undercooling u(c) for crystallization on the cooling rate q. The resulting u(c)(q) formula reveals the physical meaning of the parameters in the linear relationship, often reported experimentally, between u(c) and q in double logarithmic coordinates. The results obtained are also directly applicable to overall crystallization of melts at sufficiently small undercoolings.