Biosourced, highly porous, carbon xerogel microspherest

The first tannin-based carbon xerogel microspheres were prepared and characterised. The materials were synthesised by inverse emulsion polymerisation in sunflower oil, based on the same formulation but using two main independent variables: stirring speed and surfactant amount. The resultant sol–gel spheres were then washed, dried in air, and pyrolysed. The effect of stirring speed and surfactant amount on carbon microsphere size distribution and porous texture was investigated in detail. Depending on the cases, ultramicroporous carbon microspheres with extremely narrow pore size distributions centred at 0.4–0.5 nm, zero mesoporosity, negligible macroporosity and median diameters close to 40 mm, could be obtained. These characteristics are typical of expensive commercial carbon molecular sieves, whereas the present materials were prepared with cheap and renewable precursors using a very simple method

Integrated catalytic process for obtaining liquid fuels from renewable lignocellulosic biomass

International audienceAn integrated process for obtaining liquid biofuels is reported. The process is based on the separation of a lignocellulosic feedstock into cellulose and low-molecular-weight lignin (LMWL) followed by their conversion into two types of liquid biofuels, namely, hydrocarbon mixtures and bioalcohols. Different methods of wood fractionation into cellulose and LMWL-mechanical, steam explosion, and selective oxidation methods and their combinations-are compared. The amount of cellulose derived from wood and the amount of hydrolysate obtained from this cellulose for ethanol biosynthesis are determined by the efficiency of the method used for the fractionation of the lignocellulosic material. The best results are achieved by combining mechanical activation and subsequent catalytic oxidation of wood. Use of the resulting high-quality glucose solution, which are free of pentoses-sugars inhibiting ethanol biosynthesis-allows the alcohol yield to be increased by 30-35%. Liquid hydrocarbon mixtures enriched with phenols and products of their alkylation with ethanol have been obtained by thermal processing of LMWL in ethanol at an elevated pressure

Biosourced, highly porous, carbon xerogel microspherest

The first tannin-based carbon xerogel microspheres were prepared and characterised. The materials were synthesised by inverse emulsion polymerisation in sunflower oil, based on the same formulation but using two main independent variables: stirring speed and surfactant amount. The resultant sol–gel spheres were then washed, dried in air, and pyrolysed. The effect of stirring speed and surfactant amount on carbon microsphere size distribution and porous texture was investigated in detail. Depending on the cases, ultramicroporous carbon microspheres with extremely narrow pore size distributions centred at 0.4–0.5 nm, zero mesoporosity, negligible macroporosity and median diameters close to 40 mm, could be obtained. These characteristics are typical of expensive commercial carbon molecular sieves, whereas the present materials were prepared with cheap and renewable precursors using a very simple method

Lignin-phenol-formaldehyde aerogels and cryogels

International audienceHighly porous organic aerogels have been prepared for the first time from a mixed lignin-phenol-form-aldehyde (LPF) resin. Six different P/L weight ratios and two (L + P)/F weight ratios have been tested, leading most of times to nice and reproducible hydrogels which were subsequently either supercritically of freeze-dried. A broad family of aerogels and cryogels, respectively, was thus obtained. These materials were thoroughly investigated in terms of porous structure, based on pycnometry, adsorption and electron microscopy studies. The pore-size distributions were found to depend strongly on the initial composition, but not on the method of drying. The thermal conductivity of aerogels and cryogels has been measured and found to be minimal in materials combining both high mesopore volume and ideal pore sizes

Biosourced, highly porous, carbon xerogel microspheres

The first tannin-based carbon xerogel microspheres were prepared and characterised.</p

Rubber-like materials derived from biosourced phenolic resins

The present work describes new gels derived from cheap, abundant and non-toxic wood bark extracts of phenolic nature, behaving like elastomers. Especially, we show that these materials might be used as rubber springs. Such amazing properties were obtained by a quite simple synthesis based on the autocondensation of flavonoid tannins in water at low pH in the presence of a plasticizer. After gelation and drying, the materials presented elastic properties that could be tuned from hard and brittle to quite soft and deformable, depending on the amount of plasticizer in the starting formulation. Not only the materials containing the relevant amount of plasticizer had stress-strain characteristics in quasi-static and cyclic compression similar to most commercial rubber springs, but they presented outstanding fire retardance, surviving 5 min in a flame at 1000°C in air. Neither flame propagation nor drips were noticed during the fire test, and the materials were auto-extinguishable. These excellent features make these materials potential substitutes to usual organic elastomers

Rubber-like materials derived from biosourced phenolic resins

The present work describes new gels derived from cheap, abundant and non-toxic wood bark extracts of phenolic nature, behaving like elastomers. Especially, we show that these materials might be used as rubber springs. Such amazing properties were obtained by a quite simple synthesis based on the autocondensation of flavonoid tannins in water at low pH in the presence of a plasticizer. After gelation and drying, the materials presented elastic properties that could be tuned from hard and brittle to quite soft and deformable, depending on the amount of plasticizer in the starting formulation. Not only the materials containing the relevant amount of plasticizer had stress-strain characteristics in quasi-static and cyclic compression similar to most commercial rubber springs, but they presented outstanding fire retardance, surviving 5 min in a flame at 1000°C in air. Neither flame propagation nor drips were noticed during the fire test, and the materials were auto-extinguishable. These excellent features make these materials potential substitutes to usual organic elastomers

New tannin-lignin aerogels

International audienceHighly porous organic aerogels based on tannin and lignin have been prepared and characterized for the first time. Hydrogels were first described, which were prepared at constant solid weight fraction and constant pH, but with different tannin/lignin and (tannin + lignin)/formaldehyde weight ratios. A phase diagram has been drawn, showing the range of compositions in which nice hydrogels may be obtained. The porosity of the resultant aerogels, dried with supercritical CO2, has been systematically investigated in terms of surface area, macro (pore width > 50 nm), meso (2-50 nm) and microporosity (<2 nm). The impact of the composition on the porous properties was thoroughly discussed and supported by electron microscopy studies. We show how the gradual substitution of tannin by lignin modified the pore size distribution, although the aerogels remained almost purely mesoporous materials. Values of thermal conductivity and mechanical resistance are also given, which are compared with those of much more expensive, non renewable, aerogels derived from resorcinol-formaldehyde

Fire-resistant tannin–ethylene glycol gels working as rubber springs with tuneable elastic properties

Non-flammable, tannin-based gels with tuneable elastic properties acting as rubber springs.</p

Geles de carbón de origen natural

[EN] Most carbon gels investigated so far and reported in the literature were prepared from resorcinol crosslinked with formaldehyde in water, and were generally dried with supercritical CO2 before being pyrolysed. In the present paper, through some selected examples, we show how valuable carbon gels can be derived from other phenolic resources having a natural origin. Special emphasis is given to tannin and lignin, both derived from wood, as potential precursors of carbon aero- and cryogels. However, natural compounds not obeying the usual concepts of sol-gel chemistry may also be used for preparing carbon gels, such as cellulose, and even glucose. In the latter case, hydrothermal treatment forces the phase separation to occur, and leads to monoliths which can be advantageously converted into carbon aerogels by supercritical drying and subsequent pyrolysis.[ES] La mayoría de los geles de carbón investigados hasta ahora y citados en la literatura han sido preparados a partir de resorcinol reticulado con formaldehído en agua, y generalmente secados con CO2 supercrítico antes de ser pirolizados. En este manuscrito, hemos seleccionado algunos ejemplos y mostramos como se pueden preparar excelentes geles de carbón a partir de compuestos fenólicos que tienen un origen natural. Especial mención merecen los taninos y ligninas, extraídos de la madera, como potenciales precursores de aero- y criogeles de carbón. Sin embargo, otros compuestos naturales que no obedecen al concepto habitual de la química de sol-gel también pueden ser usados para preparar geles de carbón, como la celulosa y la glucosa. En este último caso, el tratamiento hidrotermal fuerza la separación de fase, y conduce a monolitos que pueden ser convertidos en aerogeles de carbón por secado supercrítico y posterior pirólisisThe authors gratefully acknowledge the financial support of the CPER 2007–2013 “Structuration du Pôle de Compétitivité Fibres Grand’Est” (Competitiveness Fiber Cluster), through local (Conseil Général des Vosges), regional (Région Lorraine), national (DRRT and FNADT) and European (FEDER) funds. We also thank the French Foreign Ministry (MAE) and the Région Lorraine, especially one of us (L.I.G) for her grant through the Lorraine-Russia ARCUS cooperation programPeer reviewe