Polymer foams belong to the solid foams family which are versatile materials, extensively used for a large number of applications such as automotive, packaging, sport products, thermal and acoustic insulators, tissue engineering or liquid absorbents. Composed of air bubbles entrapped in a continuous solid network, they combine the properties of the polymer with those of the foam to create an intriguing and complex material. Incorporating a foam into a polymer network not only allows one to use the wide range of interesting properties that the polymer offers, but also permits to profit from the advantageous properties of foam including lightness, low density, compressibility and high surface-to-volume ratio. Generally, the properties of polymer foams are strongly related to their density and their structure (bubble size and size distribution, bubble arrangement, open vs closed cells). Having a good control over foam properties is thus achieved by first controlling its density and structure.We developed a technique in which solid foams are generated essentially in a two-step process: a sufficiently stable liquid foam with well-controlled structural properties is generated in a first step, and then solidified in a second one. With such a two-step approach, the generation of solid foams can be divided into a number of well-separated sub-tasks which can be controlled and optimised separately. The transition from liquid to solid state is a sensitive issue of a great importance and therefore needs to be controlled with sufficient accuracy. It is essentially composed of three key steps: foam generation, mixing of reactants and foam solidification and requires the optimisation of foam stability in conjunction with an appropriate choice of both foaming time and solidification time. Furthermore, a good homogeneity of the polymer foam calls for a good mixing of the different reactants involved in the foaming and the polymerisation.A particularly powerful demonstration of the advantages of this approach is given by solidifying monodisperse liquid foams generated using millifluidic technique, in which all bubbles have the same size. In a liquid foam, equal-volume bubbles self-order into periodic, close-packed structures under gravity or confinement. As such, monodisperse foams provide simultaneous control over the size and the organisation of the pores in the final solid with an accuracy which is expected to give rise to a better understanding of the structure-property relationship of porous solids and to the development of new porous materials.We therefore aim to explore the new spectrum of properties, which polymer foams offer when we introduce an ordered structure into them since the most widely used polymer foams nowadays have disordered structures. The goal of our study is to demonstrate the feasibility of this two-step approach for different classes of polymers, including biomolecular hydrogel, superabsorbent polymer and polyurethane.For the generation of the structured polymer foams we use Lab-on-a-Chip technologies which allow the "shrinking" of large-scale set-ups to micro/millimetic scale. It permits also to perform "flow chemistry" in which the various liquid and gaseous ingredients of the foam are injected and mixed in a purpose-designed network of the micro- and millifluidic Lab-on-a-Chip. We adjust this approach according to the requirements of each polymer system, i.e. the foaming and the mixing techniques are chosen to fit the properties of each system, and can be exchanged to fit the properties of the studied systems.

The utilisation of waste process grease (WPG) as feedstock for biodiesel production was investigated in this study. WPG is a lubrication oil used in the metalworking industry and is considered a hazardous waste material. WPG contains vegetable oil and animal fat which are used as base oils in the lubricant formulation. Three different production routes were followed to produce biodiesel using WPG as feedstock. The first production route involved the conventional two-step production process comprising the acid esterification of the free fatty acids, followed by alkaline transesterification. The second production route involved the extraction of free fatty acids in the WPG by means of liquid-liquid extraction and the production of biodiesel from the extracted free fatty acids through acid esterification. The produced biodiesel was purified by means of chromatography. A third process route was the saponification of the WPG using aqueous sodium hydroxide followed by acidulation with hydrochloric acid. The resulting acid oil was purified by means of column chromatography, using a hydrophobic resin as the stationary phase prior to esterification through acid catalysis to produce biodiesel. The crude biodiesel was purified using column chromatography with silica gel as stationary phase. The optimum reaction conditions for the reduction of the free fatty acid content of WPG in route 1 to 0.5% were a methanol to oil ratio of 8:1 and a reaction temperature of 65 °C with a catalyst loading of 4 wt%. Acetonitrile was found to be the most effective extraction solvent for the reduction of sulphur compounds in the free fatty acid feedstock in route 2. A reverse phase chromatographic system with a hydrophobic stationary phase and methanol as the mobile phase was found to be an effective system to reduce the sulphur to below 10 ppm as specified by the SANS 1935 biodiesel standard in route 3. Both the conventional two-step process (route 1) and the liquid-liquid extraction process (route 2) were found not to be suitable for the production of biodiesel from WPG as the sulphur content of the produced biodiesel for routes 1 and 2 was 8 141 ppm and 4 888 ppm, respectively. The sulphur content of the produced biodiesel following route 3 was 9 ppm. The latter approach reduced the sulphur content of the biodiesel to acceptable levels that conform to the SANS 1935 standard to be used in a B10 biodiesel blend. A biodiesel yield of 45%, calculated as the mass of biodiesel produced as a percentage of the total mass of dried WPG used, was achieved with route 3. The biodiesel conformed to most of the specifications in the SANS1935 standard for biodiesel. The presence of a relatively high concentration of saturated fatty acids reflected in the higher cetane number of 74.7, the high cold filter plugging point of +10 and the oxidative stability of > 6 hours. A comparative cost analysis for route 3 indicated that the production cost of biodiesel, compared to the cost of petroleum diesel is marginally higher at the current Brent crude oil price of $102.41 per barrel. The production of biodiesel from WPG will be economically viable once the crude oil price has risen to about $113 per barrel. / Thesis (PhD (Chemical Engineering))--North-West University, Potchefstroom Campus, 2013.

The utilisation of waste process grease (WPG) as feedstock for biodiesel production was investigated in this study. WPG is a lubrication oil used in the metalworking industry and is considered a hazardous waste material. WPG contains vegetable oil and animal fat which are used as base oils in the lubricant formulation. Three different production routes were followed to produce biodiesel using WPG as feedstock. The first production route involved the conventional two-step production process comprising the acid esterification of the free fatty acids, followed by alkaline transesterification. The second production route involved the extraction of free fatty acids in the WPG by means of liquid-liquid extraction and the production of biodiesel from the extracted free fatty acids through acid esterification. The produced biodiesel was purified by means of chromatography. A third process route was the saponification of the WPG using aqueous sodium hydroxide followed by acidulation with hydrochloric acid. The resulting acid oil was purified by means of column chromatography, using a hydrophobic resin as the stationary phase prior to esterification through acid catalysis to produce biodiesel. The crude biodiesel was purified using column chromatography with silica gel as stationary phase. The optimum reaction conditions for the reduction of the free fatty acid content of WPG in route 1 to 0.5% were a methanol to oil ratio of 8:1 and a reaction temperature of 65 °C with a catalyst loading of 4 wt%. Acetonitrile was found to be the most effective extraction solvent for the reduction of sulphur compounds in the free fatty acid feedstock in route 2. A reverse phase chromatographic system with a hydrophobic stationary phase and methanol as the mobile phase was found to be an effective system to reduce the sulphur to below 10 ppm as specified by the SANS 1935 biodiesel standard in route 3. Both the conventional two-step process (route 1) and the liquid-liquid extraction process (route 2) were found not to be suitable for the production of biodiesel from WPG as the sulphur content of the produced biodiesel for routes 1 and 2 was 8 141 ppm and 4 888 ppm, respectively. The sulphur content of the produced biodiesel following route 3 was 9 ppm. The latter approach reduced the sulphur content of the biodiesel to acceptable levels that conform to the SANS 1935 standard to be used in a B10 biodiesel blend. A biodiesel yield of 45%, calculated as the mass of biodiesel produced as a percentage of the total mass of dried WPG used, was achieved with route 3. The biodiesel conformed to most of the specifications in the SANS1935 standard for biodiesel. The presence of a relatively high concentration of saturated fatty acids reflected in the higher cetane number of 74.7, the high cold filter plugging point of +10 and the oxidative stability of > 6 hours. A comparative cost analysis for route 3 indicated that the production cost of biodiesel, compared to the cost of petroleum diesel is marginally higher at the current Brent crude oil price of $102.41 per barrel. The production of biodiesel from WPG will be economically viable once the crude oil price has risen to about $113 per barrel. / Thesis (PhD (Chemical Engineering))--North-West University, Potchefstroom Campus, 2013.

Les mousses polymères appartiennent à la famille des mousses solides qui sont des matériaux polyvalents, largement utilisés dans un grand nombre d'applications telles que l'automobile, l'emballage, produits de sport, isolants thermiques et acoustiques ou l'ingénierie tissulaire. Composé de bulles d'air piégées dans un réseau continu solide, elles allient les propriétés du polymère avec ceux de la mousse pour créer un matériau intéressant et complexe. L'intégration d'une mousse dans un réseau de polymère permet non seulement d'utiliser la vaste gamme de propriétés intéressantes offertes par les polymères, mais permet aussi de profiter des propriétés avantageuses des mousse telles que la légèreté, la faible densité, la compressibilité et un rapport surface/volume grande surface élevé. En général, les propriétés des mousses polymères sont fortement liées à leur densité et leur structure (la taille des bulles, l’arrangement des bulles dans l’espace, la structure des cellules ouvertes ou fermées). Le contrôle des propriétés finales de ces mousses est donc régi par le contrôle de sa densité et sa structure.Nous avons développé une technique dans laquelle des mousses solides sont générées essentiellement suivant un processus à deux étapes dans lequel une mousse liquide suffisamment stable ayant des propriétés bien contrôlées est générée dans une première étape, puis solidifiée. Avec une telle approche, la production des mousses solides peut être divisé en un certain nombre de sous-tâches qui peuvent être contrôlées et optimisées séparément.Le passage de l'état liquide à l'état solide est essentiellement composé de trois étapes principales: la production de la mousse, le mélange des réactifs et la solidification de la mousse. Ce dernier nécessite l'optimisation de la stabilité de la mousse et des paramètres expérimentaux tels que le choix du temps de moussage et de solidification. En outre, une bonne homogénéité de la mousse polymère appelle à un bon mélange des différents réactifs impliqués dans la formulation de la mousse et de la polymérisation.Une illustration des avantages de cette approche est donnée par la solidification de mousses liquides monodisperses générées à l’aide de la technique millifluidique. Dans une telle mousse, des bulles de volume égal, s’auto-organisent sous l’effet de la gravité et du confinement pour former des structures cristallines. Ainsi, les mousses monodisperses permettent d’avoir un contrôle simultanément sur la taille et la distribution des bulles du matériau poreux final, ce qui donne lieu à une meilleure compréhension de la corrélation entre sa structure et ses propriétés. L’objectif de cette étude est donc d'explorer le nouveau spectre de propriétés, que des mousses polymère offrent lorsque l’on y introduit une structure ordonnée et de démontrer la faisabilité de cette approche à deux étapes pour différentes classes de polymères (hydrogel, polymère super-absorbant et polyuréthane).La génération de ces mousses polymères structurées a été réalisée à l’aide d’un laboratoire sur puce qui permet le rétrécissement des dispositifs expérimentaux à l'échelle micro / millimétrique. Il permet également l’injection et le mélange divers ingrédients liquides et gazeux de la mousse. / Polymer foams belong to the solid foams family which are versatile materials, extensively used for a large number of applications such as automotive, packaging, sport products, thermal and acoustic insulators, tissue engineering or liquid absorbents. Composed of air bubbles entrapped in a continuous solid network, they combine the properties of the polymer with those of the foam to create an intriguing and complex material. Incorporating a foam into a polymer network not only allows one to use the wide range of interesting properties that the polymer offers, but also permits to profit from the advantageous properties of foam including lightness, low density, compressibility and high surface-to-volume ratio. Generally, the properties of polymer foams are strongly related to their density and their structure (bubble size and size distribution, bubble arrangement, open vs closed cells). Having a good control over foam properties is thus achieved by first controlling its density and structure.We developed a technique in which solid foams are generated essentially in a two-step process: a sufficiently stable liquid foam with well-controlled structural properties is generated in a first step, and then solidified in a second one. With such a two-step approach, the generation of solid foams can be divided into a number of well-separated sub-tasks which can be controlled and optimised separately. The transition from liquid to solid state is a sensitive issue of a great importance and therefore needs to be controlled with sufficient accuracy. It is essentially composed of three key steps: foam generation, mixing of reactants and foam solidification and requires the optimisation of foam stability in conjunction with an appropriate choice of both foaming time and solidification time. Furthermore, a good homogeneity of the polymer foam calls for a good mixing of the different reactants involved in the foaming and the polymerisation.A particularly powerful demonstration of the advantages of this approach is given by solidifying monodisperse liquid foams generated using millifluidic technique, in which all bubbles have the same size. In a liquid foam, equal-volume bubbles self-order into periodic, close-packed structures under gravity or confinement. As such, monodisperse foams provide simultaneous control over the size and the organisation of the pores in the final solid with an accuracy which is expected to give rise to a better understanding of the structure-property relationship of porous solids and to the development of new porous materials.We therefore aim to explore the new spectrum of properties, which polymer foams offer when we introduce an ordered structure into them since the most widely used polymer foams nowadays have disordered structures. The goal of our study is to demonstrate the feasibility of this two-step approach for different classes of polymers, including biomolecular hydrogel, superabsorbent polymer and polyurethane.For the generation of the structured polymer foams we use Lab-on-a-Chip technologies which allow the “shrinking” of large-scale set-ups to micro/millimetic scale. It permits also to perform “flow chemistry” in which the various liquid and gaseous ingredients of the foam are injected and mixed in a purpose-designed network of the micro- and millifluidic Lab-on-a-Chip. We adjust this approach according to the requirements of each polymer system, i.e. the foaming and the mixing techniques are chosen to fit the properties of each system, and can be exchanged to fit the properties of the studied systems.

Bei der Behandlung organische Abfälle werden zunehmend Feststoff-Vergärungsverfahren mit Perkolation eingesetzt. Sie werden bevorzugt, wenn eine Vorab-Zerstörung der Feststoffstruktur nachteilig für die Gärrest-Verwendung oder sich daraus keine ökonomischen Vorteile ergeben. Das trifft auch bei strohartiger Biomasse zu. Zur satzweisen Vergärung wurden zahlreiche Erkenntnisse publiziert. Zeitgleich wurde das Sauter-Verfahren für den kontinuierlichen Betrieb zur Anwendungsreife entwickelt sowie am Leibniz-Institut für Agrartechnik und Bioökonomie e.V. (ATB) Forschungen einer zweistufigen Variante publiziert. Erstmalig erfolgt unter Verwendung von Silagen ein Vergleich der Varianten. Einflüsse der Perkolationsintensität auf Zusammensetzung und Eigenschaften der Feststoffe und der Prozessflüssigkeit sowie auf die Kinetik der Gasbildung werden untersucht. Die Perkolatzusammensetzung variiert variantenabhängig. OTS-Belastungs-Grenzen lassen sich in erster Näherung bestimmen. Geeignete Vergleichsparameter werden dargestellt. Betreiberbefragungen und messtechnische Begleitung einer Sauter-Anlage ergänzen die Arbeit. Eine differenzierte Beurteilung der Perkolationsverfahren ist nun möglich. Betrachtet werden die Feststoffdichte im Fermenter, die TS-Gehalte im Gärstock sowie der Schwimmschicht. Die Verweilzeit der partikulären Biomasse im Fermenter ist erheblich kürzer als bisher angenommen. Das beeinflusst direkt die Hydrolyserate und mittelbar die Mikroflora im Fermenter. Nähere Untersuchungen sind erforderlich. Auch bei Perkolationsverfahren beeinflusse Substratzusammensetzung und Mahlgrad die Kinetik der Gasbildung. Die Methanausbeuten unterscheiden sich nur unwesentlich von Rührkessel-Systemen. Die Erweiterung der perkolierten Vergärung durch eine Perkolat-Methanisierungsstufe sind höhere Raum-Zeit-Ausbeuten möglich. Das erlaubt eine zeitlich gesteuerte Methanerzeugung, wobei Ausmaß und Leistungsgradient weiterer Forschung bedürfen. / Numerous research findings and experience on the batchwise fermentation of stacked biomass are available. At the same time, the percolated and continuously operated Sauter-process was developed to market maturity. Research on a two-stage variant has been carried out and published by the Leibnitz Institute for Agricultural Engineering and Bioeconomics e.V. (ATB). This paper provides for the first time a direct comparison of the above-mentioned percolated process variants using maize and sedge silages. The effects of percolation intensity on composition and properties of the solids and the process fluid as well as on the gas formation kinetics are investigated in particular. Furthermore, suitable benchmarks of the variants are identified and evaluated. The link to practice is a operators questioning and a one year lasting monitoring of a Sauter plant. The findings allow a differentiated assessment of percolation processes. Findings on solid matter density as well as on dry matter content in the fermenting stock or floating layer are presented in detail. During continuous operation, particulate biomass retention time is considerably shorter than would result from usual calculation of hydraulic retention time. It is indicated that the microflora in the fermenter is also indirectly affected. This requires further research work. It is shown that in percolation processes substrate composition and extent of grinding also dominate the gas formation kinetics, albeit to different extents. Methane yields differ under comparable load and operating parameters only marginally from yields of stirred tank systems. Composition of percolate also varies variant-specific. Findings can be used to define in a first approximation limits of volatile solid load. It has been proven that percolated solid-state fermentation with an additional percolate methanization stage allows higher space-time yields. This extra stage suits also for controlled flexible methane production.