E. T. White

Mutarotation of D-fructose in aqueous-ethanolic solutions and its influence on crystallisation

Abstract The mutarotation of d -fructose in aqueous-ethanolic solutions was studied between 24 and 50 °C. The ethanol:water mass ratios of the solvent were 3:1, 6:1, and 9:1. The principal tautomers found in the solution were β- d -fructopyranose. β- d -fructofuranose, and α- d -fructofuranose, as is found with aqueous solutions of d -fructose. The furanose tautomers were more strongly favoured in the aqueous-ethanolic solutions, comprising approximately 60% of the fructose in solution for the range of solvent conditions studied, in comparison to 27% in aqueous solution at 24 °C. The rate of mutarotation from β- d -fructopyranose to the furanose tautomers was fivefold slower in solutions of ethanol:water ratio of 9:1 than in aqueous solutions. The tautomeric composition of d -fructose in aqueous-ethanolic solutions was shown to affect the crystallisation of the sugar, due to the slow rate of mutarotation of furanose forms to β- d -fructopyranose.

Control of the quality of fluidization in a tall bed using the variance of pressure fluctuations

A quantitative relation was established experimentally between the excess gas flow above minimum fluidization and the variance of the differential pressure fluctuations in a bed. The measured variance was used as part of a computer control scheme to maintain a tall fluidized bed very close to minimum fluidization throughout its length. This was achieved by bleeding gas from the fluidized bed at several different levels. The control strategy has been successfully demonstrated using a 200-mm dia., 3.2-m tall fluidized bed.

Growth Rate Kinetics for Struvite Crystallization

The crystallisation of struvite is one means of removing phosphate (and nitrogen) from nutrient-rich wastewater. As with all crystallisation processes, the growth rate of the crystals and its dependence on supersaturation is of considerable interest in designing processing equipment Modelling of struvite solubility using the computer package MINTEQA2 showed that struvite exhibits a minimum solubility in moderately alkaline conditions, with increasing solubility in acidic and strongly alkaline solutions, while temperature has only a minimal effect on struvite solubility. To measure the growth rate of struvite crystals, laboratory measurements were conducted in an isothermal batch I L stirred seeded crystallizer. Experiments were performed in aqueous solution at three pH levels (7.5, 8.0 and 8.5) and three temperatures (25, 35 and 40 degrees C) for similar initial ionic concentrations with phosphate being the limiting ion. These conditions were chosen to cover the pH values at which struvite readily crystallises without excessive adjustment of the wastewater pH, and at temperatures typical of many wastewaters. The increase in crystal size with time together with the decrease in the concentration of the ionic species in solution were followed. Rapid crystallisation kinetics were observed in the solution, with growth rates over 20 mu m/min at pH 8.5. A second order dependence of growth rate on supersaturation (as phosphate concentration) was observed, and the growth rate constant increased as pH increased but was insensitive to temperature over the range of conditions used. Results from a 200 L pilot-scale trial of struvite crystallisation at a local abattoir were consistent with the laboratory results.

Correlation of second virial coefficient with solubility for proteins in salt solutions

In this work, osmotic second virial coefficients (B22) were determined and correlated with the measured solubilities for the proteins, α‐amylase, ovalbumin, and lysozyme. The B22 values and solubilities were determined in similar solution conditions using two salts, sodium chloride and ammonium sulfate in an acidic pH range. An overall decrease in the solubility of the proteins (salting out) was observed at high concentrations of ammonium sulfate and sodium chloride solutions. However, for α‐amylase, salting‐in behavior was also observed in low concentration sodium chloride solutions. In ammonium sulfate solutions, the B22 are small and close to zero below 2.4 M. As the ammonium sulfate concentrations were further increased, B22 values decreased for all systems studied. The effect of sodium chloride on B22 varies with concentration, solution pH, and the type of protein studied. Theoretical models show a reasonable fit to the experimental derived data of B22 and solubility. B22 is also directly proportional to the logarithm of the solubility values for individual proteins in salt solutions, so the log‐linear empirical models developed in this work can also be used to rapidly predict solubility and B22 values for given protein–salt systems.

Porosity and water retention in coarse coking coal

At two Queensland mines producing high-rank coking coals, seam borecores and corresponding samples of product from the coarse coal centrifuges of the preparation plants were examined by mercury porosimetry. The dull (inertinite) particles were found to be much more porous than the bright (vitrinite), and to show greater variability in properties. Optical micrographs suggest that some of the variation is due to clays deposited in the pores of some inertinite particles. The pore water content predicted by assuming that all the particle porosity is filled with water was in good agreement with the internal moisture value determined experimentally by a centrifuge technique. The total porosity was estimated from the sum of the volume occupied by equilibrium moisture (micropores) and volume measured by mercury porosimetry (meso- and macropores). The mercury porosimetry results must be corrected for the compressibility of the coal.

An Approach for the Laboratory Investigation of Coarse Coal Dewatering by Centrifugation

In many coal preparation plants, basket centrifuges are used for dewatering coarse coal after it has been cleaned. As part of a large Australian Minerals Industries Research Association (AMIRA) project, a laboratory batch centrifuge test has been developed to provide a reproducible procedure to quantify the moisture retention properties of black coals. The final moisture content after prolonged centrifugation, termed the non-centrifugable moisture, NCM, has been found to be independent of the batch size and the amount of initial moisture. It only varies slightly with the magnitude of the applied centrifugal force. The rate of drainage falls exponentially with time, and can be described by a time constant, τ, and an exponentially centrifugable moisture, ECM. Both NCM and ECM vary markedly with the particle size of the coal, being linearly related to the specific surface area. This allows the NCM to be divided into one component for the internal moisture, NCMi. and another for the external film moisture, wh...

Factors Influencing the Moisture Content of Coarse Coal After Centrifugation

High moisture contents in export coals increase transport and handling costs and can result in contract penalties. Considerable efforts have been focussed on fine coal dewatering, but the significant variations in the moisture content of the coarse product are also important. Very little work has been carried out to determine the magnitude and causes of these variations. An AMIRA funded project has been conducted to investigate this problem. An on-line moisture monitor was installed on the product belt immediately after the first coarse coal centrifuge at two coal preparation plants to continuously measure the moisture content of the coal from a single centrifuge. Samples were taken over a range of operating conditions and at times of low and high product moisture contents. The coal samples were characterised by a range of techniques and those properties correlating with moisture content variations have been identified. Basic studies were also conducted with a laboratory centrifuge specifically designed to characterise various coarse coal samples in terms of their water retention capacity. It has been established for the plants investigated, that the moisture of the coarse coal (typically 6 to 9%) can vary by at least one percent at a particular plant, and a number of percentage points between plants. An empirical model has been developed which can explain about 80% of the variation of the moisture content of the coarse coal from the 25 samples investigated. The rank of the coals ranged from 0.7 to 1.65 mean reflectance. The model identified four principle controlling factors: (i) The amount of moisture held internally within the coal, as measured by the new laboratory centrifuge technique. (ii) The specific surface area of the coal being presented to the centrifuge. (iii) The rank of the coal as measured by reflectance. (iv) The amount of ultra-fine (slimes) material associated with the coarse coal, which can affect the drainage of water from the coal particle surface. The hydrophobicity (rank) of the coal and the ultra-fine particles hinder the water flow from the coarse particles. This model provides an estimate of the moisture level which can be achieved by centrifugation of coarse coal.

Quantifying CVD diamond growth and morphology: a useful technique for studying growth kinetics

We present formulae for determining alpha and the average growth rate in the and directions (V-100 and V-111) from a micrograph of a single diamond crystal. The growth-rate equations provide a simple and powerful tool for studies into the kinetics of diamond chemical vapour deposition (CVD), as alternative measures of the growth rate are based on polycrystalline films. A large part of the film kinetics is confounded with issues such as nucleation, film evolution, and differences between the crystallographic faces. Our measure of growth rate avoids these issues. The alpha equation provides a simpler and more accurate method to determine its value than other methods described in literature. The derivation of the equations is based on the progressive truncation of cubic and octahedral crystals by removing prisms from the corners to leave cubo-octahedral crystals. A worked example of the application of the equations is presented

Estimating crystal growth rates using computed tomography

It has been observed that sugar crystals growing in solution exhibit growth rate dispersion, that is, variation in growth rate from one crystal to the next. We consider the problem of estimating the distribution of growth rates in batch-grown crystals, given only samples of their sizes at a number of fixed points in time. The problem can be expressed as a tomographic image reconstruction problem, in which we try to reconstruct the joint density of initial size and growth from a set of marginal densities obtained by integrating the joint density in a number of different directions.

Crystallization kinetics of ibuprofen from ethanol and aqueous ethanol

Ibuprofen [2-(4-isobutyl-phenyl)-propionic acid] is a common analgesic pharmaceutical. It is substantially insoluble in water but quite soluble in organic solvents. Ibuprofen here has been crystallized from ethanol and aqueous ethanol. Batch experiments were undertaken from 10 to 40 oC to measure the solubility, the width of the metastable zone and the growth kinetics. The solubility in ethanol varies markedly with temperature. Generally solubilities fall as the water content increases for aqueous ethanol. At 40 oC, saturated solutions with solvent water contents from 35 to 65 % w/w show a phase separation into two liquid layers. The metastable zone width for primary nucleation is substantial, but is much narrower for secondary nucleation. None the less, growth rates in this narrow secondary metastable zone are still significant and this region, with care, can be used for non-nucleating seeded batch crystallizations. Crystal growth rates were found to be first order with supersaturation, with growth rate constants increasing with temperature [activation energy = 23.4 (±50%) kJ/mol] and within the accuracy of measurement not changing with the solvent water content.