Phase-Change Absorption of SO2 by N,N,N′,N′-Tetramethyl-p-phenylenediamine in Organic Solvents and Utilization of Absorption Product

As SO2 removal via traditional aqueous amine scrubbing requires large amounts of energy for absorbent regeneration, phase-change absorption was considered to be a promising alternative, as regeneration of only the SO2-rich phase is needed. The SO2-lean phase can be directly reused, thus greatly reducing energy requirements. We herein investigated the phase-change absorption behavior of N,N,N′,N′-tetramethyl-p-phenylenediamine (TPD) in organic solvents. In general, the TPD absorption rate in organic solvents followed the order: dimethylformamide > diethylene glycol dimethyl ether > propylene carbonate > butanol, which is related to their Henry’s constant. Our results indicated that TPD reacted with SO2 to form the charge-transfer complex TPD·SO2, which was further converted into TPD·2SO2 upon increasing the absorption time. Furthermore, the addition of H2O promoted the formation of TPD·2SO2, but it exhibited a negative effect on the absorption rate. Moreover, in the presence of O2 and H2O, TPD·SO2 in solution was converted slowly into [H2TPD][HSO4]2. TPD·SO2 decomposed into TPD and SO2 at ∼100 °C and exhibited a relatively stable recyclability for SO2 absorption. At last, TPD·SO2 was used as a surrogate of SO2 to synthesize sulfonamide; its activity was higher than that of a reported complex of triethylenediamine and SO2.