Hot-melt granulation of waste plastics emits fumes with unpleasant plastic-burning odor during the heating process. This study uses sodium hypochlorite (NaOCl) solution to scrub and oxidize the volatile organic compounds (VOCs) and the associated odors from polystyrene (PS) hot-melting exhaust. An alkaline hydrogen peroxide (H2O2) solution was followed to remove Cl2 emitted from the oxidative solution. 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 an available chlorine of 300–370 mg/L at an adjusted pH (6.5–7.0) for oxidation of the absorbed odorous compounds, and then through a solution with pH > 12.0 and 0.35% H2O2 for absorption and reduction of Cl2 (< 11.2 ppm) in the exhaust gas from the oxidation liquid, around 90% of the VOCs in the range of 3.2–55.5 ppm (expressed as methane equivalent) was removed.
Estimations indicate that it requires around 1.62, 0.0452, and 0.0827 kg NaOCl solution (12% available Cl2), H2O2 solution (35% H2O2), and sodium hydroxide solution (45% NaOH), respectively, for scrubbing 1,000 m3 of the exhaust gas with 10 ppm NMHC (expressed as methane equivalent). The chemicals cost a total of approximately USD 0.32.
The study has developed a new, effective and economic process for reducing odorous compounds in the hot-melted gas. When commercialized the process is hoped to decrease a lot of odorous complaints.