Abstract
Phase-change absorption was considered to be a new promising strategy for capture of acid gas since only the rich-phase needed to be disposed and the lean-phase could be reused directly. In the present work, liquid-solid phase-change absorption of SO2 with a series of tertiary diamines as absorbent was investigated. Long-chain alkane was found to be the best one among the tested solvents. Among the investigated diamines, tetramethylhexanediamine has the highest SO2 molar absorption capacity of ~2.6 mol/mol. The SO2 absorption products of diamines were demonstrated to be pyrosulfites based on the FTIR and elemental analysis. Among them, the single crystal of dimethylpiperazine pyrosulfite was obtained through recrystallization. These results indicated that the absorption mechanism of tertiary diamines is different from that of primary and secondary diamines. The effect of absorption conditions such as concentration of absorbent, temperature and partial pressure on the capacity was also investigated. The variation tendency of diamines in liquid along with SO2 loading indicated that the absorbed SO2 would force diamines to be separated from liquid phase completely. TG analysis indicated that the initial decomposition temperature sequence of absorption products is C10H26N2S2O5 > C7H20N2S2O5 > C6H16N2S2O5·H2O > C6H18N2S2O5.
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