Absorption of a linear (L2) and a cyclic (D4) siloxane using different oils: application to biogas treatment

Abstract

Hydrophobic volatile methyl siloxanes (VMS), such as hexamethyldisiloxane (L2) and octamethylcyclotetrasiloxane (D4), present a low solubility in water. An alternative treatment by absorption into hydrophobic absorbents was therefore studied. For this purpose, three different absorbents, motor oil, cutting oil and a water-cutting oil mixture, were selected with the aim of re-using a waste product. The set of experiments was carried out in a bubble column, where parameters such as inlet concentration, residence time and temperature were studied. The best performance for the removal of both siloxanes, in terms of absorption capacity, was observed for motor oil, particularly for D4. In fact, motor oil removal efficiency for D 4 was 80%, whereas for L2 it was 60%, indicating that D 4 is more easily absorbed than L2. In the case of water-cutting oil, this showed a mass transfer enhancement from the gas phase to the liquid phase compared with water alone. Furthermore, a removal efficiency of 70% was observed for D 4, showing that the addition of an oil fraction to a water system improves the absorption of VMS. These results show that VMS absorption into oils could be a promising way to achieve their abatement.

Environmental Chemistry of Organosiloxanes

“…Volatile siloxanes such as D 4 or L 2 can be removed from gas by absorption in organic liquids, preferentially PDMS. , Another recent possibility for siloxane removal from a gas stream, diffusion through a PDMS rubber membrane, suffers from low selectivity …”

Removal of siloxanes from biogas using acetylated silica gel as adsorbent

“…Biogas is produced by the anaerobic digestion of organic matter in landfill and sewage plants. Biogas is primarily comprised of methane CH 4 (50%-70%) and carbon dioxide CO 2 (30%-50%), as well as trace amounts of other components, such as hydrogen sulfide, halogenated compounds, volatile organic compounds (VOCs) and siloxanes (Kougias and Angelidaki 2018;Devia and Subrenat 2013). Currently, the use of biogas as a renewable energy sources is complicated due to the presence of siloxane contaminants, which are transformed into microcrystalline SiO 2 at high temperatures, whose abrasiveness and thermoelectric insulating properties can severely damage heat exchangers, turbines and gas engines (Turkin et al 2014;Lee and Rittmann 2016;Allen et al 1997).…”

“…Currently, the use of biogas as a renewable energy sources is complicated due to the presence of siloxane contaminants, which are transformed into microcrystalline SiO 2 at high temperatures, whose abrasiveness and thermoelectric insulating properties can severely damage heat exchangers, turbines and gas engines (Turkin et al 2014;Lee and Rittmann 2016;Allen et al 1997). Consequently, it is necessary to reduce the amount of siloxanes in biogas below a threshold level (e.g., 10 mg siloxane/m 3 of methane) if it is to be used as a biofuel for energy applications (Devia and Subrenat 2013;Lee and Rittmann 2016;Dewil et al 2006). Several methods are used in industry to remove siloxanes from biogas, including adsorption by porous materials (Sigot et al 2015;Jiang et al 2016;Jafari et al 2016) and oils (Devia and Subrenat 2013); however, their performance is often unsatisfactory, because they employ expensive or non-recyclable materials, involve long treatment time and high energy consumption, Edited by Xiu-Qin Zhu and Xiu-Qiu Peng Handling editor: Runduo Zhang Electronic supplementary material The online version of this article (doi:https ://doi.org/10.1007/s1218 2-019-0336-4) contains supplementary material, which is available to authorized users.…”

“…Consequently, it is necessary to reduce the amount of siloxanes in biogas below a threshold level (e.g., 10 mg siloxane/m 3 of methane) if it is to be used as a biofuel for energy applications (Devia and Subrenat 2013;Lee and Rittmann 2016;Dewil et al 2006). Several methods are used in industry to remove siloxanes from biogas, including adsorption by porous materials (Sigot et al 2015;Jiang et al 2016;Jafari et al 2016) and oils (Devia and Subrenat 2013); however, their performance is often unsatisfactory, because they employ expensive or non-recyclable materials, involve long treatment time and high energy consumption, Edited by Xiu-Qin Zhu and Xiu-Qiu Peng Handling editor: Runduo Zhang Electronic supplementary material The online version of this article (doi:https ://doi.org/10.1007/s1218 2-019-0336-4) contains supplementary material, which is available to authorized users. and only afford low saturation adsorption levels (Kajolinna et al 2015;Ajhar et al 2010).…”