Absorption of SO2 with recyclable melamine slurry

SO2 emissions have caused severe acid rain and smog. For coping with this terrible problem, melamine (MN) was used in this study as an absorbent for SO2 removal from simulated flue gas. To better understand the desulfurization process, its possible products, melamine sulfite (MN-H2SO3) and melamine sulfate (MN-H2SO4), were first synthesized and then characterized by XRD, FTIR, SEM, Raman spectrum and TG-MS. The results showed that MN-H2SO4 cannot be regenerated, so its formation should be prevented during absorption. Furthermore, the effects of various process factors, such as the concentration of MN slurry, reaction temperature and SO2 concentration, were systematically investigated. The optimal parameters were determined as 4 wt% MN slurry at 40 degrees C with a liquid to gas volume ratio of 1:10. In those conditions, the duration for efficient desulfurization reached 140 min with a breakthrough sulfur capacity of 0.3 g/g. Unfortunately, the desulfurization products were a mixture of MN-H2SO3 and MN-H2SO4, reducing the regeneration efficiency. To prevent the oxidation of MN-H2SO3, various antioxidants were compared. Among them, 0.1 wt% hydroquinone exhibited the best antioxidative performance, with only 7% of MN-H2SO3 being oxidized to MN-H2SO4; MN can thus be recycled. Compared with liquid organic amine, the presented solid melamine can avoid volatilization and reduce energy consumption during regeneration, indicating promise in industrial applications.