Influence of starch content on the properties of low-cost microfiltration ceramic membranes

The use of starch as pore former is frequent in the fabrication of porous ceramic membranes, since starches are cheap, innocuous and environmentally friendly. A study has been conducted to evaluate the influence of potato starch content (0–30 wt%) and sintering temperature (1100 and 1400 °C) on low-cost ceramic microfiltration membranes. The raw materials were a mixture of kaolin, alumina and starch, from which membrane specimens were shaped by uniaxial dry pressing. The results indicated that the percentage of potato starch did affect the properties of the membrane. Thus, an increase of starch content provoked a reduction of bulk density (an increase of porosity) a rise of water permeability and a substantial modification (coarsening) of the pore size distribution. This effect deals with the role as pore former of starch, which burns out when fired. More interestingly, it was experimentally observed that the effect of starch was particularly effective for starch percentages higher than 10 wt% once a connected coarse pore network is developed. On the other hand, an increase in sintering temperature from 1100 to 1400 °C also influenced membranes׳ characteristics but the effect was much less significant than that of starch content. A percolation analysis based on the Effective Medium Approximation (EMA) contact model allowed to conclude that the critical porosity calculated corresponds to a starch content of 10.2 wt%, which agrees quite well with the estimation from experimental results. Finally, tortuosity was calculated with a simple model derived from the Hagen–Poiseuille equation. The obtained data showed that tortuosity factor decreased as the starch content or sintering temperature increased. These findings are consistent with SEM analysis and pore size determination.The authors thank Spanish Ministerio de Economía y Competitividad their support for the development of this research (Plan Nacional de I+D, ref. CTQ2012-37450-C02-02

On the underestimated effect of the starch ash on the characteristics of low cost ceramic membranes

Starches are commonly used as a pore generator in the fabrication of low-cost ceramic membranes, since they are cheap, innocuous, environmentally friendly and easy to burn. Nevertheless, the influence of starches residues (ashes) generated during its burning off is dismissed. The present study analyses the influence of the starch ashes, generated by six different starches of similar particle size, on the characteristics of low-cost ceramic supports. The results indicated that starches gave rise to different amounts of ashes ranging from 0.17 to 0.71 wt%. In addition, these ashes contained some chemical elements in their composition, such as sodium, potassium or calcium, which can act as fluxes in the ceramic composition, modifying the characteristics of the obtained supports (mainly open porosity, water permeability and pore size distribution). It has also been observed that when the ash content grows the effect of the fluxing elements on the evolution of the microstructural features of the ceramic membrane (porosity, pore size or permeability) becomes more significant. Finally, tortuosity was calculated with a simple model derived from the Hagen–Poiseuille equation; the obtained data showed that tortuosity factor and its evolution with dwelling time were also affected by the starch ashes.This material is based upon work supported by the Spanish Ministry of Science and Innovation through the National Plan for Scientific Research, Development and Technology Innovation 2008–2011 (INNPACTO programme, project IPT-2011–1069-310000)

Low-cost ceramic membranes: A research opportunity for industrial application

Obtaining low-cost ceramic membranes has attracted great interest in the scientific community in last years, as it allows to preserve the advantages of ceramic materials while significantly reduce their manufacturing costs. This type of membranes is mainly based on the use of raw materials and manufacturing processes typical of traditional ceramic materials, i.e silicate-based ceramics. This work exhaustively reviews the raw materials, ceramic compositions and variables of the manufacturing processes used in the development of these membranes, with special emphasis on their numerous potential industrial applications

Preparation of chamott es as raw material for low - cost ceramic membranes

Low cost ceramic membranes are usually prepared fro m a mixture of natural raw materials and some organic porogen agent, as starch . The fact that the porogen must be completely eliminated during firing, leaving an int erconnected porous structure, impose large firing times, increasing the final price. A s tudy about the synthesis of porous chamottes as an alternative to organic pore formers was conducted to reduce firing costs. Chamottes were obtained from mixtures of a c lay and starch. Different starches were used and the influence of the composition and processing variables were studied. The viability of the porous chamottes was demonstra ted.Supported by the Spanish Ministerio de Economía y C ompetitividad (Plan Nacional de I+D, ref. CTQ2012 37450 C02 02)

Mejora del comportamiento en la extrusión de pastas cerámicas de baja plasticidad.

Shaping by extrusion may be used for the manufacture of tiles, bricks, and also refractory products. The three fundamental aspects that must be considered to achieve ideal extrusion conditions are the nature of the material, particle size and Plastic behaviour. Of these, obtaining a mass of adequate plasticity is essential during the processing in order to prevent defects such as cracks, laminations or migrations of the liquid phase [1]. Plastic behaviour depends on numerous factors [2]: size and shape of the particle, mineralogical composition, presence of electrolytes, organic matter, etc. With regard to traditional ceramics, as is the case of the manufacture of ceramic tiles, clay materials are those with the necessary plasticity to carry out the extrusion process. However, in the absence of clays with sufficient plasticity or when the composition incorporates a high proportion of other non-plastic ingredients, the extrusion operation may be seriously compromised, particularly for the manufacture of large or complex tiles. In these cases it is necessary to add plasticizers or binders to the pastes to achieve rheological behaviour and plasticity enabling correct processing of the composition [3]. In this report the influence of different additives in different proportions on the plasticity index of a ceramic composition was evaluated and the variation of the plasticity index was related to the behaviour of the paste during extrusion.El conformado por extrusión se puede utilizar para la fabricación de baldosas, ladrillos, tejas o también productos refractarios. Los tres aspectos fundamentales que se deben considerar para lograr unas condiciones de extrusión idóneas son la naturaleza del material, el tamaño de partícula y el comportamiento plástico. De éstas, obtener una masa de plasticidad adecuada es fundamental durante el procesado, para evitar la aparición de defectos tales como grietas, laminaciones o migraciones de la fase líquida [1]. El comportamiento plástico depende de numerosos factores [2]: tamaño y forma de la partícula, composición mineralógica, presencia de electrolitos, materia orgánica, etc. En lo que concierne a las cerámicas tradicionales, como es el caso de la fabricación de baldosas cerámicas, los materiales arcillosos son los que confieren la plasticidad necesaria para llevar a cabo el proceso de extrusión. Sin embargo, cuando no se dispone de arcillas con la plasticidad suficiente o cuando la composición incorpora otros ingredientes no plásticos en elevada proporción, la operación de extrusión se puede ver seriamente comprometida, sobre todo en la fabricación de baldosas de gran formato o de geometría compleja. En estos casos es necesario añadir a las pastas aditivos plastificantes o ligantes para conseguir un comportamiento reológico y plasticidad que permitan un correcto procesado de la composición [3]. En este trabajo se evaluó la influencia de la incorporación de diferentes aditivos en distintas proporciones sobre el índice de plasticidad de una composición cerámica y se relacionó la variación del índice de plasticidad con el comportamiento de la pasta durante la extrusión

Comparison of extruded and pressed low cost ceramic supports for microfiltration membranes

A comparison has been made between ceramic supports for microfiltration membranes of the same composition obtained by pressing and by extrusion in terms of microstructure and properties. The extruded supports displayed lower porosity and smaller pore size than pressed supports. The higher the clay content in the starting composition, the clearer this tendency became. In contrast, the difference tended to disappear when starch was added to the initial composition. The mechanical strength values followed a decreasing exponential variation with porosity, which was influenced by the starting composition and the shaping method. Water permeability reflected the strong effect of the mean pore size. The supports synthesised from the composition with the higher clay content showed the lowest permeability, while those obtained from the composition including starch showed the highest value. A model derived from the Hagen–Poiseuille equation enabled the tortuosity values to be calculated.This material is based upon work supported by the Spanish Ministry of Science and Innovation through the National Plan for Scientific Research, Development and Technology Innovation 2008–2011 (INNPACTO programme, project IPT-2011-1069-310000). The authors wish to thank the personnel of FACSA (Fomento Agricola Castellonense S.A., Castellón, Spain), especially José Guillermo Berlanga, Ernesto Santateresa and Anna Gozalbo for their helpful aid and discussion during the execution of the present work

Eco-friendly ceramic membranes for water reuse in a membrane bioreactor (MBR)

The main objective of this study is to develop and validate ceramic membranes at lower cost than the commercial ones, by including agricultural and industrial wastes in the composition, together with raw materials typically used in the ceramic tile industry

Ecological low-cost ceramic membranes based on olive stones as pore former

They will address the obtained results so far regarding the manufacturing and validation of the REMEB ceramic membranesSe abordarán los resultados obtenidos hasta el momento con respecto a la fabricación y validación de las membranas cerámicas de REME

Reactores catalíticos de membrana para la eliminación de nitratos

El objetivo del proyecto es desarrollar un sistema eficaz para eliminar los nitra­tos presentes en aguas subterráneas, en procesos de potabilización, transfor­mándolos en nitrógeno mediante una reacción de hidrogenación realizada en reactores catalíticos de membrana. Es necesario precisar que las actuales tec­nologías de tratamiento de nitratos (ós­ mosis inversa, intercambio iónico, etc.) no eliminan estas sales, sino que las concentran, no solucionándose de for­ma completa la problemática que plan­tean los nitratos en el medio ambiente. En cambio, las membranas catalíticas, mediante el proceso de desnitrificación llevado a cabo por los catalizadores en superficie, eliminan los nitratos de las aguas a tratar transformándolos en ni­trógeno gaseoso.El proyecto con número de expediente IPT- 2012-0126-310000 está financiado con un importe total de 870.455,39 euros por el Mi­nisterio de Economía y Competitividad y cofinanciado por el Fondo Europeo de Desa­rrollo Regional (FEDER) de la Unión Europea, a través del programa INNPACTO, a los que mostramos nuestro más sincero agradecimiento

Wastes from industrial processes introduced as chamottes in ceramic membranes

In the present work, chamottes generated as subproducts by different industrial processes have been used to obtain low-cost ceramic membranes