Elimination Of Siloxanes By Adsorption ProcessAs A Way Of Upgrading Biogas
Biogas is increasingly being investigated as a source of renewable energy, however its utilisation requires an improvement of its quality. Certain biogases contain compounds called siloxanes; these compounds are the origin of some problems when using biogas. At high temperatures siloxanes are transformed to silicate oxides which can damage equipment (i.e. engines corrosion, the clogging of fuel cell membranes.). This paper provides details of the research done in the treatment of siloxane by adsorption process of adsorption. Different porous materials were studied in order to evaluate adsorption capacities. Influences of humidity and temperature on the mass transfer were evaluated. Moreover, reactors were filled with a mixture of methane and carbon dioxide (principal compounds on the biogas) in order to evaluate the impact of the gas composition in the adsorption capacities. Finally the capacity of adsorption is also evaluated in the presence of an organic volatile compound (VOC). Activated carbon cloth was chosen to continue with the experiences realised for the adsorption – desorption process. This porous material has shown good adsorption capacities. Furthermore, desorption process can be performed in situ and their implementation in industrial process is more easy. Adsorption-desorption cycles were performed and the possibilities of the material regeneration evaluated. Joule effect was employed in the desorption process in order to reduce the duration of regeneration. First cycles have been accomplished. Results are promising, even if the operational conditions of the process must be optimised.
Purification du biogaz pour sa valorisation énergétique : adsorption de siloxanes sur charbons actifs
Le biogaz issu de la degradation anaerobie de matieres organiques peut remplacer le gaz naturel dans plusieurs applications. Pour une meilleure valorisation energetique du biogaz, ce travail s’interesse a l’elimination des composes organiques volatils du silicium (siloxanes) dans biogaz par l’adsorption sur des materiaux poreux. Trois charbons actifs (CA) commerciaux ont ete utilises pour l’adsorption des siloxanes. Leurs proprietes physicochimiques sont caracterisees par plusieurs techniques. Un CA montre excellent capacite d’adsorption d’octamethylcyclotetrasiloxane (D4) ce qui est bien superieur que l’autre. En presence de la vapeur, les capacites d’adsorption des CA peuvent etre reduites plus ou moins fort dependant de degree d’humidite relative et la presence des sites hydrophiles sur la surface de CA. Ainsi, la capacite des echantillons possedant ces sites specifiques est reduite apres la thermodesorption a cause de la formation des especes non volatiles sur la surface de CA. Tests avec d’autres siloxanes ont montre que le phenomene de polymerisation s’est produit avec de reactivite et de mecanisme different, dependant de la nature du CA et de siloxane. La polymerisation est toujours plus importante pour le CA qui present plus de sites hydrophiles, conduisant egalement a sa plus faible regenerabilite
Adsorption onto Activated Carbon Cloths and Electrothermal Regeneration: Its Potential Industrial Applications
Activated carbon cloths (ACCs) are recently developed adsorbents that could be used in many air treatment applications. The use of the Joule effect heating as a regeneration process offers many possibilities in terms of desorption operating conditions to adapt the cloth process to the constraints of particular industrial applications. Hence, this paper presents ACC physical properties and adsorption–desorption cycles performed on a pilot plant to determine the influence of the desorption conditions on the desorbate quality. Two examples of activated carbon cloth processes for specific industrial applications are then presented. The role of the first one is to concentrate an industrial effluent upstream of recovery facilities. The second application is for indoor air treatment, where the desorbate quality is not the major interest but rather the development of a very simple system with an easily handled filter.