The effect of methanol group on absorption of SO2 by diamine compound was investigated via density functional theory. It was observed that the presence of methanol group increases the binding energy of absorption. According to the result of binding energy, the di-methanol-diamine (D-b) structure can be the best diamine for SO2 absorption and the results of Gibbs energy verified the most thermodynamically favorable structure. According to the weak energy analysis, the absorption interactions in D-b are both vdW and HB interactions. The result of second-order perturbation energy showed that the interaction of the donor atom of diamine with antibonding orbital of S-O (BD*S) in D-b is the highest which points to the most stable structure. According to molecular frontier orbital analysis, it can be concluded that the absorption of SO2 on the diamines is not very strong and desorption of SO2 would be easier than that the strong chemical absorption.

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