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Waste Reduction: (1) Engineering problem - The manufacturing of a Silicone intermediate creates a flammable waste stream that must be disposed of at cost to QSI (0.48$/lb.). This stream contains two phases, which are mainly hexamethydisiloxane (HMDS) and aqueous ammonium hydroxide in roughly 50/50 ratio by volume. The HMDS phase (upper) is flammable and is thus hazardous. The clean aqueous phase (lower) can be discarded via the sewer at no cost if the flash point is above hazardous classification (60 °C). (2) Project deliverables - The Engineering solution must reduce the yearly volume of waste to under 13 tons/year and separate the mixture into two phases cleanly. Design and prototype a separation tank system that will allow the operator to safely decant the HMDS and dispose of the non-hazardous phase safely into the sewer. (3) Constraints - The system must prevent the operator from draining the flammable waste into the sewer before passing hazardous waste criteria while remaining intrinsically safe. The cost of the system must have a payback period of less than 5 years. (4) Approach - Develop analytical method to determine concentration and test initial flash point. Test salting concentrations then determine HMDS concentration change, add activated carbon in differing concentrations to determine absorption coefficient. (5) Results – 30 minute timed rough separation decanting top layer, adding 30% by mass salt pushing out more HMDS, passing the resulting mixture through a packed column of activated carbon. (6) Issues – Activated carbon has different absorption characteristics, finding the best carbon absorption characteristics while retaining low cost. Batch vs. Continuous carbon absorption, instrumentation to allow safe operating of system. (7) Impact – Packed Column allows the most absorption of HMDS but increases cost while keeping safety very high. If QSI decides to proceed with this Capital Project then they can reduce waste costs by $10,500/year.

Publication Date



Chemical and life science engineering, Waste Reduction, Two Phase Separation, Hexamethydisiloxane, Packed Column


Chemical Engineering | Engineering

Faculty Advisor/Mentor

Frank Gupton

Faculty Advisor/Mentor

Bryan Fry

VCU Capstone Design Expo Posters


© The Author(s)

Date of Submission

August 2016

Hazardous Waste Reduction: Hexamethyldisiloxane