Th. doct.--Chim. phys. et génie des procédés--Nancy--INPL, 1995. / Bibliogr. p. 305-312. Résumé en français et en anglais.

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Charles University, Faculty of Pharmacy in Hradec Králové Department of Pharmaceutical Technology Candidate: Veronika Skalická Supervisor: Dr. Georgios Paraskevopoulos, Ph.D.; Michael Binnefeld Title of Diploma thesis: Up-scaling and further development of matrix liposomes The thesis evaluates novel matrix liposomes formed by dual asymmetric centrifugation technology. Particles' parameters (size, size distribution and ζ-potential) were analyzed by dynamic light scattering method using ZetaSizer device. Encapsulation efficacy was determined by size exclusion chromatography using carboxyfluorescein as fluorescent encapsulation marker. The overall results support that the most beneficial formulation parameters are 15 min of speed mixing process with ceramic beads of diameter 1,0-1,2 mm. Up-scaling of the procedure didn't drastically affect liposomal parameters up to a lipid batch load of 700 mg. Furthermore, the usage of different types of gelatin or glycerinated gelatin didn't significantly influenced particles' characteristics. It is noteworthy that the matrix composed of 50% glycerinated gel sustained the ability to form liposomes by dispersion of vesicular phospholipid gels in phosphate buffer saline even after 31 days. Other matrices showed a damage of liposomes as confirmed by size and size...

Sediment Oxygen Demand (SOD) is the fluctuation of dissolved oxygen between the sediment from the overlying water. The method to acquire SOD values is inefficient and troubled by unreliable equipment. Diffusion gradients in thin film (DGT) are proposed as a potential method to collect geochemical proxy measures that can be used as SOD predictors. Field deployment of the DGTs was conducted at two locations to compare recovery and accuracy against ex-situ centrifuge methods. The results indicated DGT can be used as a statistically significant geochemical method. A principle component analysis was used to determine if reduced iron and manganese collected using DGTs clustered with SOD. Results indicated reduced iron and manganese cannot be used to predict SOD. Sulfide measurement by microelectrode from the same matrix of geochemical methods however did cluster with SOD. A stepwise multiple linear regression concluded sulfide measurement by microelectrode is a statistically significant predictor of SOD.

The solid-solid separation processes employed by modern coal preparation plants require large amounts of process water that must be removed from the surfaces of particles using mechanical dewatering equipment. Unfortunately, the existing processes that are used to dewater fine particles are inefficient in terms of moisture reduction and/or solids recovery. Many coal preparation plants are forced to discard fine coal particles because of the inability of existing technologies to reduce the moisture content of this product to an acceptable level. In light of this problem, a new ultrafine dewatering process called hyperbaric filter centrifugation (HFC) has been developed. This novel method combines centrifugation and pressure filtration within a single process to substantially reduce moistures over what can be achieved using conventional dewatering systems. In the current study, steady-state and dynamic dewatering models were developed in order to be able to simulate the behavior of the HFC technology. The steady-state model, which was based on grain-size properties, used empirical expressions to predict product moistures. On the other hand, the dynamic model was based on fundamental theories of filtration and centrifugation. Although the dynamic model provided a better understanding of the working principles of the process, the steady-state grain model produced more accurate equilibrium moisture predictions. Therefore, the steady-state model was used to further investigate the effects of several parameters on cake moistures. As such, the steady-state model was useful for scale up and design purposes. The steady-state dewatering model was also used to perform an economical analysis of potential applications of the HFC technology. The model was used to investigate a variety of new circuit designs that have the potential to be commercially applied in the coal industry. The results clearly showed that this new technology would allow coal companies to process difficult-to-dewater ultrafines using the HFC process, while coarser solids would be more appropriately dewatered using conventional technologies such as vacuum filters or screenbowl centrifuges. This "split dewatering" concept would provide substantially higher profitability due to lower moistures and higher recoveries of ultrafine solids than could be achieved using a single dewatering process. Laboratory- and pilot-scale versions of this technology has been constructed and tested at the facilities of Mining & Minerals Engineering Department of Virginia Tech. Results of this testing program showed that 30-50% lower moisture values than the ones obtained using conventional mechanical dewatering processes could be achieved with the HFC technology. Based on these promising results, a pilot-scale prototype unit, which was tested successfully at several commercial U.S. coal plants, was also constructed by Decanter Machine, Inc. Finally, the process of developing of this novel technology was successfully completed with the sale of the first full-scale commercial unit by Decanter Machine, Inc. to a major U.S. coal producer. / Ph. D.

Titre de l'écran-titre (visionné le 14 août 2023) / Le grand rapport surface/volume et la morphologie spéciale des nanofibres leur confèrent d'excellentes propriétés mécaniques, une capacité de transfert de chaleur et des caractéristiques électriques. Bien qu'il existe diverses techniques de fabrication conventionnelles pour produire des nanofibres, celles-ci souffrent généralement de plusieurs inconvénients, tels que de faibles taux de production, des restrictions sur les matériaux, des complexités de processus et des coûts de production élevés limitant la production de masse de nanofibres. La demande croissante de nanofibres, d'autre part, motive les efforts pour éliminer ces barrières, car ces matériaux trouvent de plus en plus d'applications dans les secteurs de l'énergie et de la santé, par exemple pour produire des nano-filtres à air et à eau, des capteurs, des batteries et des masques chirurgicaux de protection. La technique de filage centrifuge (CS) a récemment permis la fabrication de nanofibres, avec beaucoup moins de limitations. Dans le procédé CS, une solution / fusion de polymère est placée dans un réservoir à rotation rapide (également appelé lière) avec plusieurs buses, extrudant le polymère en fibres incurvées très fines et longues (ou jets incurvés) sous la force centrifuge ; ces jets fortement courbés se prolongent alors dans l'espace jusqu'à atterrir sur des collecteurs placés à l'écart du centre de rotation. En conséquence, de grands volumes de fibres polymères avec des diamètres moyens de quelques centaines de nanomètres sont produits. Le procédé CS est une technique alternative très prometteuse pour produire des nanofibres. Cependant, la compréhension, l'amélioration et l'optimisation du processus CS ont été limitées, principalement en raison de la présence de nombreux paramètres affectant la dynamique d'écoulement complexe du jet courbe, par exemple les forces de rotation (centrifuge et de Coriolis), inertielles, visqueuses, rhéofluifidiantes, élastiques, de tension superficielle et gravitationnelles, ainsi que les effets de diffusion de masse, de diffusion thermique, d'aérodynamique et de rapport de viscosité. Pour avoir un compréhension fondamental du processus CS, dans ce thèse de doctorat, nous considérons mathématiquement et expérimentalement les effets des paramètres susmentionnés sur la dynamique du jet courbe. Pour généraliser nos résultats, nous les présentons en termes de nombres adimensionals, y compris les nombres de Rossby (Rb), de Reynolds (Re), de Weber (We), de Froude (Fr), de Weissenberg ( Wi), de Péclet de polymère (Pe), de Péclet l'air (Pe*), et de Reynolds de l'air (Re*), ainsi que l'indice de loi de puissance (m), le rapport de viscosité (δₛ) et la position radiale du collecteur (R). Dans le Chapitre 1, nous développons un modèle général régularisé de fibres minces (string) pour prédire les effets des forces centrifuges, de Coriolis, d'inertie, visqueuses, de fluidification par cisaillement, de tension superficielle et gravitationnelles sur la trajectoire en régime permanent et l'amincissement du rayon de la fibre. Nous montrons que pour de grandes vitesses de rotation (petit Rb), le rayon de la fibre diminue rapidement sur de petites longueurs d'arc, ce qui devient plus prononcé lorsque Re et We augmentent ou que m diminue. En fin, nous constatons que la force gravitationnelle (quantifiée via Fr) n'affecte l'angle vertical de la fibre qu'aux petites longueurs d'arc. Dans le Chapitre 2, motivés par nos observations expérimentales, nous développons un modèle mathématique complet pour la formation de nanofibres dans le processus CS, mais pour les fluides newtoniens. Par rapport au chapitre précédent, notre modèle inclut des paramètres supplémentaires, tels que la diffusion de masse dans le jet, la diffusion de masse dans l'air et les effets aérodynamiques. Nos résultats, y compris la comparaison avec les expériences, révèlent que les effets aérodynamiques doivent être pris en compte pour permettre une prédiction correcte de la trajectoire et du rayon du jet. Augmenter Re*, Re et R conduit à un jet plus long. La diminution de We force le jet à s'enrouler plus étroitement autour de la filière, mais cela montre des effets insignifiants sur l'évaporation du solvant. Les changements de Pe et Pe* n'affectent pas de manière significative la trajectoire du jet. Dans le Chapitre 3, nous étendons notre travail pour développer un modèle mathématique intégré supérieur, qui peut également tenir compte de la dynamique transitoire de la fibre. Notre modèle nous permet d'analyser les paramètres d'écoulement critiques couvrant une large gamme, en incorporant les équations de moment cinétique, le modèle constitutif viscoélastique de Giesekus, les effets de traînée air-fibre et l'équation d'énergie dans les équations du modèle. En utilisant le modèle, nous pouvons analyser le comportement dynamique des jets de polymère fondu/solution. Nous constatons que la rhéologie non linéaire affecte remarquablement la trajectoire, le rayon et les contraintes normales des fibres. L'augmentation de Wi conduit à une fibre plus épaisse, tandis que l'augmentation de δₛ montre une tendance opposée. De plus, en augmentant Wi, la courbure de la fibre est améliorée, amenant la fibre à se rapprocher du centre de rotation. Le Chapitre 4 combine en outre expériences et modélisation. Dans nos expériences, nous obtenons les données expérimentales à l'aide d'une combinaison unique d'outils : ceux-ci incluent notre dispositif CS interne, des caractérisations de rhéométrie et des tests au microscope électronique à balayage. Nos expériences sont couplées et apportent des validations à un puissant modèle mathématique, développé sur la base des équations constitutives viscoélastiques du modèle de Maxwell convecté supérieur. Cela nous permet d'examiner le processus CS en fonction des paramètres qui sont généralement importants dans les expériences à l'échelle du laboratoire, notamment la concentration en polymère, la vitesse de rotation, le diamètre de la buse, le rayon de la filière et l'angle de la buse.

Fine coal constitutes a relatively small portion of a product stream in a coal cleaning plant. However, its processing cost is approximately three times higher than the cost of processing coarse coal. Therefore, many coal companies chose to discard the fines to refuse ponds, causing a loss of profit and creating environmental concerns. This problem can be solved by developing more efficient fine coal dewatering processes, since bulk of the cost associated with processing fine coal is due to dewatering. For this reason, Virginia Tech has developed new chemicals that can increase the efficiency of mechanically dewatering coal fines. To determine the performance of the novel reagents on fine coal dewatering, laboratory vacuum filtration and centrifugation tests were conducted. The utilization of the novel dewatering aids in the dewatering systems decreased the final moisture contents of the filter cakes to sufficiently low values. There was approximately 50% reduction in the cake moisture of many coal samples with the usage of the novel dewatering aids. The tests were performed on various coal samples from different coal preparation plants. This gave the advantage of testing the novel dewatering aids at many different conditions since each sample had its own characteristics. The vacuum filtration tests were extensively used to compare the efficiency of each novel reagent in dewatering. The best performing dewatering aids were determined and they were further utilized to analyze the effects of operational variables, such as; drying cycle time, cake thickness, vacuum pressure level and slurry temperature on dewatering. A statistical analysis was also performed to observe the effect of each factor quantitatively. The analyses were very useful in terms of determining the synergistic effects of these factors in dewatering of fine coal. The centrifuge tests were conducted to examine the efficiency of the novel reagents in a different dewatering application. The experimental results showed a significant improvement in centrifuge dewatering with the usage of proper coal sample. The moisture contents of fairly thick cakes decreased down to 5-10%. This outcome was very satisfactory since most of the dewatering aids commonly used in the coal industry were observed to increase the final cake moisture in centrifuge dewatering instead of decreasing it. Finally, surface chemistry analyses were performed on the coal samples and slurries to analyze the changes in the chemistry of the dewatering system in the presence of the novel dewatering aids. It was observed that there was a favorable improvement in the system chemistry, which was helpful in terms of decreasing the cake moisture content. These observations were also consistent with the results of the dewatering tests. The combined effect of the novel additives in decreasing the surface tension of the slurry and increasing the contact angle of the coal surface at the same time was concluded to be the reason for their significant performance as dewatering aids. / Master of Science

Thesis (Ph. D.)--University of Chicago, Department of Chemistry, December 2003. / Includes bibliographical references. Also available on the Internet.

Factors affecting the centrifugal separation of apple parenchyma cell serum were investigated for three important cultivars from the Okanagan Valley of British Columbia; Mcintosh, Red Delicious, and Winesap. The factors studied included cultivar, maturity, maceration treatment, and centrifugation time and speed. Observations included yield of cell serum, relative serum clarity, pulp and serum viscometric properties, alcohol insoluble solids, soluble solids, serum pH, particle size and tissue firmness. The pulp viscometric property, viscosity at a shear rate of 100 sec⁻¹, was the observation which primarily influenced juice yields. The increased separation obtained for Mcintosh > Red Delicious > Winesap was attributed to pulp viscosity values. Relative serum clarity was influenced by serum soluble solids when centrifugation time was constant at six minutes or by the serum pH and pulp viscosity at maturity one (0 storage). Increased centrifugation speed and time markedly improved the yield of cell serum for the factors evaluated. Maceration treatments reduced the average particle diameter from 330 μm to 229 μm and the pulp viscosity values. At 5,500 and 8,000 rpm, higher yields were obtained when the particle size was small. At 10,500 rpm or 14,500 rpm, higher serum yields were obtained with larger particle sizes. Consideration of the particle size (> 100 μm) and shape (non-spherical), along with sedimentation theory indicated the separation followed Newton's Law. The high yields obtained with the larger particle size at high rpm confirmed a low drag force coefficient (C[sub D] = .5). Although a slight reduction in particle size and viscosity was observed when parenchyma tissue was subjected to ultrasonic vibration, no improvement was obtained in serum yield or clarity. The centrifugal separation of apple parenchyma cell serum was shown to be feasible. The efficiency of the separation improved as pulp viscosity decreased and speed or time of centrifugation increased. The tissue particle size evaluated was of secondary importance for the separations observed. / Land and Food Systems, Faculty of / Graduate