Investigation of low concentration SO2 adsorption performance on different amine-modified Merrifield resins

Three amine-modified Merrifield resins (AMMRs) were synthesized with ethane diamine, methylamine and dimethylamine to assess the impact of amine group on SO2 adsorption under low SO2 concentration. The dimethylamine-modified Merrifield resin (DMAMR) grafting with tertiary amine groups showed the greatest SO2 adsorption compared with ethane diamine-modified Merrifield resin (EDAMR) and methylamine-modified Merrifield resin (MAMR). Different amine groups had different reaction mechanisms with SO2. It was much easier for SO2 to form noncovalent charge transfer complex with tertiary amine group than the zwitterion and ion/counterion products with primary and secondary amine groups under dry condition. The noncovalent charge transfer complex had a relatively weaker thermostability than the zwitterion and ion/counterion products. As the temperature increased from 25 °C to 75 °C, the SO2 adsorption capacity on DMAMR decreased by 78.92%, which was much higher than that of EDAMR and MAMR (63.77% and 63.41% respectively). As SO2 concentration increased from 40 ppm to 100 ppm, significant increase (∼100%) in SO2 adsorption capacity was observed. Lower SO2 flow rate led to a more sufficient reaction between SO2 and amine groups, resulting the increase in SO2 adsorption capacities. Water vapor enhanced the SO2 adsorption performance of AMMRs significantly due to the formation of salt. However, it was more difficult for tertiary amine group to react with SO2 in the presence of water due to its relatively weaker basicity. DMAMR showed a greater regeneration performance than EDAMR and MAMR under dry and humid condition.