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A silicone manufacturing process yields two-phase wastewater, of which the aqueous phase flashes at 2°C primarily due to hexamethyldisiloxane (HMDSO). To be classified as non-hazardous and immediately disposable, it must flash above 60°C. Project objectives entailed identifying a method and then designing a prototype for on-site aqueous phase treatment, removing enough HMDSO for non-hazardous disposal. The previous team’s proposal was gravity separation, NaCl extraction, and feeding through an activated carbon packed bed. Extraction proved ineffective, packed bed outlet samples flashed at 52°C, and HMDSO quantification methodology was incorrect. From titration, wastewater was determined to be 3.3 ± 0.2 wt.% aqueous ammonia. This ammonia concentration was used to spike water samples prepared with variable HMDSO concentrations with the target of determining HMDSO concentrations in the treated water that would flash above 60°C. Without ammonia, 36 ppm HMDSO passed the flash point test. Adding ammonia expanded the tolerance to >50 ppm HMDSO. Waste was subjected to various treatment method combinations: adsorption on activated carbon, reaction with bleach, and semi-batch gas stripping with nitrogen in column packed with ceramic saddles. Flash point results are given below. The process very nearly satisfies the 60°C flash point goal, with some variation. To correctly quantify HMDSO, standard addition was used with GC. Consequently, the proposed treatment process is gravity phase separation, activated carbon packed bed treatment, and then semi-batch stripping with nitrogen. Recommendations for future work are to explore amendments to the proposed procedure, including time-dependent mass transfer analysis, counter-current gas stripping through a packed bed, and implementation of automated sample preparation and testing.
hexamethyldisiloxane, water treatment, packed column, gas stripping
Chemical Engineering | Engineering
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