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.
Siloxane adsorption on activated carbons: Role of the surface chemistry on sorption properties in humid atmosphere and regenerability issues
Abstract Commercial activated carbons (ACs) have been studied in dynamic adsorption of octamethylcyclotetrasiloxane (D4) in both dry and wet conditions. 1000 ppm (v/v) D4 with N2 as carrier gas and relative humidity (RH) up to 70% were used. Samples were characterized by physicochemical techniques such as N2 and H2O adsorption/desorption at −196 and 20 °C, respectively, XPS, Boehm titration, chemical and elemental analysis, thermogravimetric measurements. No correlation between adsorption capacity in dry conditions and textural properties could be established. In wet conditions, the presence of hydrophilic sites preferentially adsorbing H2O strongly decreases the ability of ACs to adsorb D4. The regenerability by thermal treatment after D4 adsorption in dry conditions was also addressed and followed by gas chromatography and in situ DRIFTS. The D4 polymerization into polysiloxanolate/PDMS was found to proceed on ACs containing alkali metals (K, Na) as revealed by the observed release of their decomposition products during the thermodesorption treatment. This property is detrimental to the regenerability of the AC by blockage of its porosity. The eventual formation of polysiloxanalolate type species during the adsorption could also be responsible for limiting the D4 uptake by partial blockage of the AC porosity.
Failure analysis for poor solderability of Au surface of PCB
Nonwetting is one of the common problems and is always rejected in electronic assemblies. ENIG pads of a PCBA exhibited nonwetting after lead-free reflow soldering. With the aid of stereomicroscope, SEM&EDS and XRF, a series of analysis was performed. And after visual inspection, surface and cross section analysis, thickness measurement and solderability test, it can be inferred that oxidation of plating surface was the main reason for nonwetting, and corrosion in Ni plating caused an adverse impact on solderalibity.