Liquid-solid phase-change absorption of SO2 with tertiary diamines in long-chain alkane

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 SO 2 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 SO 2 molar absorption capacity of ~2.6 mol/mol. The SO 2 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 SO 2 loading indicated that the absorbed SO 2 would force diamines to be separated from liquid phase completely. TG analysis indicated that the initial decomposition temperature sequence of absorption products is C 10 H 26 N 2 S 2 O 5  > C 7 H 20 N 2 S 2 O 5  > C 6 H 16 N 2 S 2 O 5 ·H 2 O > C 6 H 18 N 2 S 2 O 5 .