published_or_final_version / Medical Sciences / Master / Master of Medical Sciences

Thèse de doctorat : Génie des procédés et des produits : INPL : 2008. / Titre provenant de l'écran-titre.

Thesis (M. Med. Sc.)--University of Hong Kong, 2008. / Includes bibliographical references (p. 53-64)

Yes / Granulation is commonly used as an enlargement process of particles produce granules with desirable characteristics and functionality. Granulation process transforms fine powders into free-flowing, dust-free granules with the presence of liquid binder at certain operating conditions. The main focus of this research is on seeded granulation of detergent powders, a new phenomenon of granulation in which a layer of fine powders surround the coarse particle. This is already proven for calcium carbonate (Rahmanian et al., 2011). Here, detergent granules were produced in a 5 L high shear Cyclomix granulator using different fine/coarse powder ratio (1/3, 1, 3) and different binder ratio of 10 %, 20 % and 30 %. The granules were then characterized for their particle size distribution, strength and structure. It was found that a high percentage (70 wt. %) of granules in the desired size range between 125 - 1,000 µm were produced using the powder ratio of 1/3 and a binder content of 10 %. Low mean crushing strength (3.0 N) with a narrow distribution was obtained using this condition. Structure characterization of the detergent granules produced in the granulator shows that consistent seeded granule structures are produced under the optimum process and formulation conditions of 1/3 powder ratio with 10 % binder.

Mémoire (M.Sc.A.)--Université du Québec à Chicoutimi, 1991. / Document électronique également accessible en format PDF. CaQCU

Yes / It has been shown that seeded granules of calcium carbonate can be produced in commercial batch high shear granulators such as the Cyclomix high-shear impact mixer. Seeded granules are attractive to the pharmaceutical industry due to their high uniformity and good mechanical properties which can assist efficient tablet manufacture. In the current study, attempts to produce seeded granules of Durcal 65 and PEG 4000 binder using hot melt granulation are reported, in response to the recent shift towards continuous pharmaceutical manufacturing. Various screw configurations and rotation speeds were investigated in a series of experiments to determine the relationship between process conditions and granule properties. Particle size analysis, strength measurement and structural characterisation were used to quantify granule properties. It was found that using a series of kneading elements arranged at a 60° staggering angle located near to the feed section of the extruder screw generated strong, spherical granules. From structural characterisation approximately 5–15% of extruded granules were found to be seeded. Twin screw melt granulation is therefore considered to be a promising technique for continuous production of seeded granules, although a more detailed investigation is required to optimise yield and quality.

No description available.

The mixing of powders and liquids is a process ubiquitous to many industrial, research and household applications, from the production of foodstuffs, pharmaceutical and cosmetic products to the preparation of hot drinks or cement. The final mixed state of powders and liquids can be broadly split into two distinct regimes identified respectively as having low- and high volume fraction, ∅. Low-∅ systems are typified by flowing suspensions whereas samples prepared with high-∅, beyond some threshold value, produce solid agglomerates which are unable to flow. These two regimes are the focus of two separate scientific disciplines; suspension rheology and granulation. Within the field of suspension rheology there has been recent advances in the understanding of a phenomena known as shear thickening, which describes the increase in a suspension's viscosity with increasing applied stress. In this thesis we aim to unify the phenomena of shear thickening and granulation within this new theoretical framework. We study shear thickening and granulation using a well characterised model system developed for this purpose, comprising polydisperse glass particles with a mean diameter of ≃ 7 μm and a glycerol-water mixture (90:10 %vol). We measured the rheological behaviour as a function of applied stress, σ, of suspensions at various volume fractions. We observed shear thickening behaviour, with divergences in the low-stress viscosity, η1(∅), and the high-stress viscosity, η2(∅), at ∅RCP = 0:662 and ∅m = 0:572 respectively. These divergences mark the transition between continuous shear thickening, discontinuous shear thickening and a state in which flow is not possible, with increasing volume fraction. Using a recently developed theory of shear thickening (Wyart and Cates, 2014), we were able to fit our rheological data quantitatively. The WC theory predicts a stress-dependent crossover in the fraction of contacts which are frictional in nature, following a stretched exponential function. In order to improve numerical agreement between our data and the model, we developed a method taking into account the volume-weighted contribution of particle sizes in our polydisperse system. Bulk mixing of the same model system in a custom-built high-shear mixer also exhibited three different mixing regimes with the change in behaviour coinciding with the location of the viscosity divergences, ∅m and ∅RCP, measured in the rheology experiments. For ∅ < ∅m suspensions are formed at both high and low stress; for ∅ ≥ ∅RCP granules are formed at all stresses; for ∅m ≤ ∅ < ∅RCP transient granules are formed, which are solid at high stresses, but can relax to a flowing suspension state at low stress. This transient behaviour is reversible with the application of high stress. This coincidence of viscosity divergence in the rheology measurements and mixing behaviour change in the high-shear mixing strongly suggests that the two phenomena are related. Thus we used the stress-dependent jamming volume fraction, ∅J(σ), predicted by the WC theory, to define the transition between the formation of suspensions and granules. We were able to calculate a quantitative phase diagram, with which the regions of the ∅-σ phase space in which granules or suspensions are formed can be easily identified, in agreement with our high-shear mixer data. Thus, using small-scale rheological measurements, requiring relatively small volumes of sample, we are able to define the parameter space in which granules can be prepared, thus eliminating the need for trial and error granulation experiments in order to define this space. We measured the volume-weighted mean granule size as a function of ∅ in the range ∅m → ∅ ≃ 0:85. Based on our observations of granule structure and measurements of granule size distributions, we modelled the granules as an ensemble of core-shell agglomerates with a log-normal size distribution. The packing in the granule cores was assumed to be ∅J(σ ), i.e. ∅m at high stress and ∅RCP at low stress. Appealing to conservation of mass arguments, our model predicts that the mean granule size decreases with increasing volume fraction and stress, in quantitative agreement with experimental data.

Aerobic sludge granulation is a new technology that has been developed for biological wastewater treatment. Compared with conventional activated sludge, aerobic granules allow better sludge-water separation and a higher biomass concentration. However, the mechanism of the transformation from sludge flocs to granular sludge under the aerobic condition is still unclear. Deterioration of aerobic granules in long-term operation is also a concern for its scale-up application. The present study was conducted to investigate the crucial factors for aerobic granulation and its underlying mechanism. In addition, the stability of aerobic granules under unfavorable conditions and the recovery of deteriorated granules in bioreactors were also studied. For formation of aerobic granules, gelation-facilitated biofilm growth was proposed as a new mechanism for the granulation process. Simulation of granule formation was performed in a well-controlled chemical system to provide an experimental proof for the proposed aerobic granulation theory. Granule formation was achieved in a particle suspension with latex microspheres for bacterial cells and alginate and peptone for extracellular polymeric substances (EPS), together with the cation addition and floc discharge. In the mixture with the dosing of alginate and a small amount of peptone, artificial gels and granules could be well formed, and the artificial granules share the similar micro-structure as the aerobic bacterial granules. However, as the dose of peptone increased, gels were not formed and only large particle flocs were produced. The formation of artificial granules proves that effective EPS interactions with cations and the subsequent gelation are crucial to aerobic granulation in bioreactors. In relation to granulation, the effect of the substrate feeding pattern on the microbial yield was tested. The results show that the bioreactor with a more frequent substrate feeding interval had a lower sludge yield than the reactor (0.45 vs. 0.55) with a less frequent feeding. The sludge fed less frequently was able to store more substrates as intracellular substances, resulting in more biomass growth. Moreover, a long feeding interval would force the biomass into the feast-famine regime, which was found to enhance microbial growth and granulation, producing granules with a compact and stable structure. For the stability of aerobic granules, various factors that would been countered in biological wastewater treatment were experimented. The results show that granules deteriorated in structure under unfavorable conditions, such as a low solution pH (pH~6.0), a high loading rate, and feed of starch instead of glucose into the bioreactors. In some deterioration cases, filamentous bacterial growth became more dominant and the granules became loose and fluffy flocs. Compared to mature granules, fresh granules were less stable and more vulnerable to the unfavorable conditions. As the granules deteriorated in structure, their surface roughness values increased considerably from 35 or less to more than 230. Under a favorable condition with a feed of sodium acetate, the deteriorated granules could be recovered in some reactors. However, deterioration of the granules caused by filamentous growth at a low pH or high loading rate could hardly be recovered. / published_or_final_version / Civil Engineering / Master / Master of Philosophy

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