Controlling Odorous Fumes Produced by Melting Recycled Polypropylene

Abstract

Abstract

Hot-melt granulation of waste plastics as a renewable raw material emits fumes with unpleasant plastic-burning odors during the heating (160°C–200°C) process. This study uses sodium hypochlorite (NaOCl) solution in series with alkaline hydrogen peroxide (H₂O₂) solution in a two-stage scrubbing process to remove volatile organic compounds (VOCs) and the associated odors from polypropylene hot-melting exhaust gas. Laboratory scrubbing bottles with a liquid volume of 600 mL were used with the hot-melt gas injected into the system at a rate of 1 L/min at 25°C. Results indicate that by purging the test gas through a solution with available chlorine (Cl₂) of 15–50 mg/L at an unadjusted pH (9.3–10) for oxidation of the absorbed odorous compounds, and then through a solution with pH in the range of 12.0–12.5 and 0.35% H₂O₂ for absorption and reduction of Cl₂ (<3.8 ppm) in the exhaust gas from the oxidation liquid, ∼90% of the VOCs in the range of 45–204 ppm (expressed as methane equivalent) were removed. Estimations indicate that it requires around 1.38, 0.0173, and 0.0318 kg of NaOCl solution (12% available Cl₂), H₂O₂ solution (35% H₂O₂), and sodium hydroxide solution (45% NaOH), respectively, for scrubbing 1000 normal cubic meters (Nm³) of the exhaust gas. Chemical costs totalled approximately US $0.25. This study has developed a new, effective, and economic process for reducing odorous compounds in hot-melt gas.