Absorption Volatile organic compound (VOC) Emulsion Gas-liquid Mass transfer coefficient a b s t r a c t This study outlines a volatile organic compounds (VOCs) removal spray tower consisting of an empty cylindrical vessel and nozzles spraying an oil/water emulsion into the vessel. Spraying an emulsion into a spray tower absorbs both lipophilic and hydrophilic compounds, facilitates oil transport, improves the interfacial area (oil coats water droplets) and increases the turbulent flow regime enhancing mass transfer. Toluene was chosen as the synthetic lipophilic pollutant. The choice of the organic absorbent, silicone oil (47v350 Rhordorsil ® ), was made by considering several properties: thermal and mechanical stability, non-biodegradable nature, insolubility in water and low value of Henry's constant. Gas-liquid mass transfer and the hydrodynamics of the gas-liquid contactor were thoroughly investigated. It was observed that emulsion spraying allowed the dual absorption of hydro-and lipophylic VOCs (efficiency around 90% for both) and strongly enhanced the liquid mass transfer coefficient. Finally, a model describing the efficiency of the process as a function of time was developed. The predicted values are in good agreement with the experimental results.
A wide range of siloxanes exist but the most abundant in biogas are Hexamethyldisiloxane (L2) and Octamethyltrisiloxane (L3) as linear siloxanes and Octamethylcyclotetrasiloxane (D4) as a cyclic siloxane. In order to remove volatile organic compound from biogas, different processes can be used. A promising process for siloxane removal is their absorption in an organic solvent. In this work, three oils were tested to absorb the selected siloxanes: silicone oil 47V20, Seriola 1510 and Polyalphaolefin. Initially, the characterization of these oils was realized by measuring their viscosities and densities, depending on temperature. The second time, the absorption capacity of the siloxanes by selected oils was characterized through the determination of their Henry's constants, but also owing to the implementation of a wet-wall column. Both Henry's constants and removal efficiencies in continuous regime revealed that silicone oil (47V20) can be considered as the most efficient oil among the three selected siloxanes. Moreover, the cyclic siloxane (D4) showed more affinity with oils than linear siloxanes. Silicone oil 47V20 appeared to be the best oil (intermediate price 14 euro/L, low viscosity, low volatility, chemical inertness (no corrosion) and resistance to high and low temperatures).
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