Siloxane Adsorption Research Articles

Adsorption characteristics of activated carbon for siloxanes

The adsorption capacity of several kinds of activated carbons (ACs) for octamethylcyclotetrasiloxane (D4) in simulated landfill gas (LFG) was investigated and the main textural characteristics for AC adsorptive removal of siloxanes were studied. It was found that most of the ACs employed in this work showed good D4 adsorption capacity, and the D4 adsorption capacities of them ranged from 21.94mg/g to 224.63mg/g. Positive correlation was observed between D4 adsorption capacity and the BET surface area and the micropore volume of these ACs. Through analyzing nitrogen adsorption isotherms of these ACs, a conclusion was made that the super micropores and small mespores (pores of diameter∼1.7–3.0nm) in the ACs are the most favorable pores for siloxane adsorption.

Analysis of Siloxane Adsorption Characteristics Using Response Surface Methodology

A central composite design and response surface methodology were applied to investigate the optimum conditions for maximum adsorption capacity in activated alumina as an adsorbent. The optimized conditions were determined for adsorption capacity using variables of flow rate and temperature. It was found that flow rate and temperature greatly influenced the adsorption capacity, as determined by analysis of variance analysis of these variables. Statistical checks indicated that second order polynomial equations were adequate for representing the experimental values. The optimum conditions for adsorption capacity were 0 o C and 2,718 mL/min, with the estimated maximum adsorption capacity of 17.82%. The experimental adsorption capacity was 17.75% under these optimum conditions, which was in agreement with the predicted value of 17.82%.

Molecular simulations of the competitive adsorption of siloxanes and water on amorphous silica surfaces as a function of temperature

Molecular simulations of individual and competitive adsorption of water and PDMS (polydimethylsiloxane) on an amorphous silica surface in the temperature range 300–1500K show that the presence of PDMS does not appear to change the adsorption behavior of water significantly but that the presence of water has a substantial effect on the adsorption behavior of PDMS at temperatures below approximately 600K. Water adsorbs adjacent to and penetrates into the silica surface while PDMS adsorbs adjacent to the water layer. Finally, the vapor pressure is enhanced at low temperatures because of the formation of nanoclusters on the surface as a consequence of the Gibbs–Thomson effect.

Stability of siloxane couplers on pure and fluorine doped SnO 2 (110) surface: A first principles study

Siloxane is a favorable candidate as an anchor group that can be used to bind organic molecules to SnO 2 surfaces, with a wide range of practical applications. Therefore, adsorption geometries and energies of siloxane coupler on the SnO 2 (110) surface have been investigated in this study using quantum-chemical periodic density functional theory (DFT) calculations. We present a comparative study of different siloxane adsorption arrangements on pristine and fluorine doped SnO 2 surface. According to the calculations, the surface doping with fluorine leads to stabilization of the siloxane network at the stannic oxide surface. The trend is analyzed in terms of additional charge provided by F impurities to the chemisorbed oxygen atoms thus increasing the ionicity of their bonding. Implications of the current findings for the design of organic-metal oxide interface with better thermo-stability and improved electronic properties are discussed.

Behaviour and adsorptive removal of siloxanes in sewage sludge biogas

We investigated the behaviour of siloxanes, which adversely affect biogas engines, as well as their concentration levels in sewage sludge biogas in Japan. We also performed experiments on the absorptive removal of siloxanes using various adsorbents and determined the main adsorbent characteristics required for the removal of siloxanes. The results of our study on the concentration and composition of siloxanes in biogas were similar to previous reports. Moreover, we found that the concentration of siloxanes changes in relation to the outside air temperature based on real-time measurements of siloxanes using a continuous analyser. We further speculated that the continuous analyser would accurately indicate the siloxane concentration in model biogas but overestimate the siloxane concentration in actual biogas because of positive interference by VOCs and other biogas components. In the siloxane adsorption experiment, the equilibrium uptake of both cyclic siloxanes, D4 and D5, was positively related to the BET-specific surface area of the adsorbents and the fraction of the external surface area taken up by relatively large diameter pores. We attributed the adsorption results to the fact that the siloxane molecules are generally larger than micropores; therefore, they are less susceptible to adsorption to micropores. Based on these results, we concluded that adsorbents with large BET-specific surface areas, especially those with a high external specific surface area and pores of relatively large diameters, are desired for the removal of siloxanes.

Study of the Adsorption of Siloxane and Hydrocarbon Contaminants onto the Surfaces at the Head/Disk Interface of a Hard Disk Drive by Thermal Desorption Spectroscopy

The adsorption of siloxanes and hydrocarbons, which are common harmful contaminants found on hard disk drives (HDDs), has been investigated by thermal desorption spectroscopy (TDS). The desorption energy of each molecule from various modeled surfaces at the head/disk interface (HDI) was determined. The surfaces studied in this literature were (a) hydrogenated amorphous carbon (a-C:H), (b) a-C:H with perfluoropolyether (PFPE) and (c) a nascent surface of a-C:H. Considerable variations in the monolayer desorption energy of a siloxane model compound were observed. The monolayer desorption energy of a siloxane model compound from a plain a-C:H surface is higher than that from an a-C:H surface with perfluoropolyether, while that from a nascent a-C:H surface is far higher than that from an a-C:H surface. Meanwhile, the monolayer desorption energy of a hydrocarbon model compound from a-C:H is a little bit higher than that from a-C:H with perfluoropolyether. These results suggest that the adsorption of these harmful contaminants can be decreased by the control of HDI surfaces, and therefore we can reduce the risk of failure of HDDs.