Roller Compaction: Mechanistic understanding of ribbon splitting and sticking

Roller compaction is a dry granulation technique in which the feed powder is subjected to different types of stresses, which are applied between two counter-rotating rollers. The stress applied during this process mediates both desired (intact ribbon) and undesired (ribbon splitting/sticking) bond formation. The phenomenon of ribbon splitting/sticking could originate from either process or formulation related causes; due to the imbalanced combination of material mechanical properties and stress application which has the potential to result in different types of ribbon failures i.e. cohesion and/or adhesion-related ribbon failure. Despite current research work conducted in the field of roller compaction, there remains a lack of comprehensive understanding in relation to the development of ribbon failure during roller compaction which can hinder the use of roller compaction with many formulations. Therefore, an in-depth understanding of the causes of ribbon failure during roller compaction is required to design better formulations and incorporate steps which will mitigate/stop the occurrence of ribbon splitting/sticking. The aim of this work is to build a mechanistic understanding of ribbon splitting/sticking phenomenon in terms of the ribbon-roller interactions in both the bulk and at the roller walls. A range of materials was selected to cover a wide range of powder deformability, the minimum gap between the two smooth rollers was fixed and the maximum roll stress was varied. Ribbon splitting was observed to occur either transversally (through the ribbon thickness) or longitudinally (through the ribbon width). It was observed that transverse splitting is commonly associated with sticking of the split ribbons to the rollers. Longitudinal splitting is associated with an across-width distribution of the ribbon density which may cause an adverse effect on the mechanical strength and dissolution properties of the tablets formed from the milled granules. The observed trends of ribbon splitting were rationalised in terms of a splitting index which is a measure of the residual stresses driving crack growth relative to the tensile strength of the ribbons. Furthermore, knurled rollers with higher roller/powder contact surface area have been investigated in terms of the occurrence of ribbon splitting/sticking. The predictability of the splitting index was improved by incorporating the ribbon solid fraction difference across the ribbon width. Using knurled rollers extends the range of transversal 2 splitting/roller sticking when compared with the smooth rollers and reduces the extent of longitudinal splitting. Attempts have been conducted to correlate powder and metal thermodynamic work of adhesion with its sticking tendency during roller compaction. The technology of inverse gas chromatography was utilised to characterise both powder and metal in terms of their surface energy. No clear correlation between the work of adhesion/cohesion and sticking probability was found which suggests that particle deformation is the dominant factor of sticking during compaction. However, the result could contribute to the elaboration of the lubrication mechanism of MgSt during powder compaction. Finally, a data-driven model was developed to predict the ribbon porosity distribution using the artificial neural network approach (ANN). Various process-related parameters and material properties considered as the inputs of the ANN. While the outputs of the network were the porosity which was experimentally measured by X-ray tomography across the ribbon width, powder and ribbon porosity distribution have linked together using ANN approach as a novel approach to predict the heterogeneity of ribbon in terms of its porosity distribution. Results showed that the ANN was able to successfully map various material and process parameters to the ribbon porosity distribution across the ribbon width, which is considered to be one of the most important quality attributes in the roller compaction process. Due to its short processing time This is particularly useful as it allows potentially for future powders and formulations to be modelled to understand the propensity of undesired ribbon properties to occur

Le projet d’intégration maghrébine à l’épreuve des tensions régionales

Le projet d’unification du Maghreb est un projet ancien enraciné dans la conscience des peuples de la région, puisqu’il se fonde sur des éléments de solidarité extrêmement puissants comme la culture, l’histoire et le destin communs. Cet article se propose de montrer comment les tentatives d’intégration régionale, dans le cadre du Comité Permanent Consultatif Maghrébin (CPCM) mis en place en 1964 et de l’Union du Maghreb Arabe (UMA) instituée en 1989, n’ont pas atteint les objectifs escomptés. Pourtant, la coopération au sein du CPCM et de l’UMA aurait pu constituer le cadre idéal pour la normalisation des rapports entre les pays du Maghreb

EXPERIMENTAL STUDY OF THE PRODUCTION OF SOLAR HYDROGEN IN ALGERIA

<p>Hydrogen is a sustainable fuel option and one of the potential solutions for the current energy and environmental problems. In this study hydrogen is produced using a hydrogen generator with a Proton Exchange Membrane (PEM) electrolyser. An experimental study is done in the Center of Development of the Renewable Energy, Algiers, Algeria.</p><p>The experimental device contains essentially a photovoltaic module, a PEM electrolyser, a gasometer and the devices of measures of characteristics of the PEM electrolyser as well as two pyranometers for the horizontal and diffuse global radiance registration. This system in pilots scale is permitted on the one hand, to measured and analyzed the characteristics: of the PEM electrolyser for two different pressures of working (Patm and P=3 bar), on the other hand, to study the volume of hydrogen produces in the time with different sources of electrical power (generator, photovoltaic module, fluorescent lamp), the efficiency for every case is calculated and compared. We present in this paper the variation of the solar hydrogen flow rate produced according to the global radiance and according to the time for a typical day’s of August.</p

Water heating control for efficiency enhancement of Proton Exchange Membrane Electrolyser using Photovoltaic panels and MPPT

International audienceThe studied system consists of a 59 kW Proton Exchange Membrane (PEM) electrolyser 6 powered by a photovoltaic (PV) generator through a boost converter for H2 production. The PV panels were sized to 63 kW according to the Belfort region in France, and controlled using Maximum Power Point Tracking (MPPT) technique allowing the extraction of the maximum available power. It is also shown that the produced H2 flow is increased if the input water is heated. The optimal input water temperature is investigated in order to maximize the produced H2 by taking into account the physical constraints when using a maximal temperature in a given system and the limitation to avoid the transformation of the water into vapor. Fuzzy Logic (FL) control is used to determine the instantaneous optimal water temperature and a simple proportional integral (PI) controller heats the inlet water to the optimal temperature. It is also shown that the pressure affects the system efficiency and temperature, and the proposed controller manages the water temperature and pressure. The proposed system design allows the production of H2 and the extraction of the maximal available solar power. The electrolyser efficiency is substantially increased as a result of using MPPT for the PV panels and FL with PI as water heating controllers

Roller compaction : ribbon splitting and sticking

Roller compaction is the main technique employed in dry granulation. Ribbon sticking and splitting are among the major factors that can hinder the use of this process for some formulations. Ribbon splitting can occur either transversally (through the ribbon thickness) or longitudinally (through the ribbon width). It was observed that transverse splitting is commonly associated with sticking of the split ribbons to the rollers and results in an inferior performance of the process. Longitudinal splitting is associated with an across-width distribution of the ribbon density so that there may an adverse effect on the mechanical strength and dissolution properties of the tablets formed from the milled granules. The aim of the current work was to elucidate the mechanisms of splitting by an experimental study involving single component powders with a range of yield strengths, including those that are commonly used as excipients. Both smooth and knurled rollers were employed without and with lubrication by applying magnesium stearate to the rollers. The minimum gap was fixed and the maximum roll stress was varied. The observed trends for the smooth rollers were rationalised in terms of a splitting index, which is a measure of the residual stresses driving crack growth relative to the tensile strength of the ribbons. There was a lower limit at which splitting was observed but the occurrence of transverse splitting decreased and that for longitudinal splitting increased with increasing values of the index, which was accompanied by an increase in mixed transverse-longitudinal splitting. Transverse splitting was always associated with sticking to the rollers and was prevented by external lubrication. The main difference with the knurled rollers was that in some cases transverse splitting occurred without sticking to the rollers. A detailed discussion of the mechanisms involved is presented

La gestion thermique dans les piles à combustible PEMFC

International audienceDans la pile à combustible à membrane échangeuse de protons PEMFC, certaines difficultés techniques restent à surmonter pour convaincre les principaux acteurs de l'intérêt du développement d'une économie de l'hydrogène, tels que la gestion de la chaleur et de l'eau dans la cellule, le module de stack et le système de cette pile PEMFC. En réalité, les piles à combustible sont formées d'un empilement de cellules élémentaires (stack) connectées en série afin d'obtenir des puissances plus élevées. Les stacks peuvent être composés au maximum d'une centaine de cellules, une augmentation du nombre de cellules engendre des difficultés pour la gestion thermique. Cet article présente une approche électrochimique pour comprendre la cinétique d'échauffement qui est trop important dans certaines parties (régions) de la pile et pour réduire les contraintes thermiques manifestées