A New Concept of Desulfurization: The Electrochemically Driven and Green Conversion of SO₂ to NaHSO₄ in Aqueous Solution

Abstract

A new concept of desulfurization was developed by designing a series of electrochemical reactions to drive an SO2 absorption-and-conversion process in aqueous solution, hence the SO2 in gas was eventually converted to a valuable chemical of NaHSO4. A model experiment of chemically substantiating this concept includes two steps: (I) absorption of SO2 gas by aqueous solution and oxidation of the absorbed SO2 to SO4(2-) by air and (II) transformation of the SO4(2-) to NaHSO4. The experiment demonstrated that in Step I, the cathodic reduction of 02 from ambient air scavenged the H+ released due to the SO2 absorption and its further oxidation, which thereby were accelerated. Meanwhile H2O2 as a cathodic product further enhanced the SO2 oxidation. In Step II, the anodic oxidation of H2O supplied H+ and allowed the NaHSO4 formation through balances of electrons and mass. Thereafter, a pH range of 5.0-6.0 for the SO2 oxidation was optimized, and an electrochemically driven process for the SO2 conversion to NaHSO4 was proposed. Sustainability evaluation indicated that this concept complies with the principles of green chemistry and potentially enables the SO2 conversion from flue gas to NaHSO4 as a value-added process.

Green SO2 conversion from flue gas by pH variation

“…, SO 4 2-, and OH -in cathodic chamber. Moreover, the final pH of cathodic chamber was 5.1-5.8 as shown in Table 1, which complied with Wang's result of 5.0-6.0 (Wang et al 2008).…”

“…In addition, a desulfurization concept (Wang et al 2008) has been developed by designing a series of electrochemical reactions to drive an SO 2 absorption and conversion process in aqueous solution. The overall reaction could be expressed as follows:…”

Experimental study on SO2 recovery using a sodium–zinc sorbent based flue gas desulfurization technology

“…Previous studies showed that these aqueous solutions work well in absorbing SO 2 in the flue gas [32,33]. Compared with CaO and ZnO suspensions, Na 2 CO 3 and Na 2 SO 3 solutions can avoid the clogging problem since they are clear liquids, and more cost-effective than ZnO ones.…”

Microwave intensified synthesis of regular shaped sodium bisulfate crystal

“…Conductive heating and electrolysis, two conventional but with low-efficiency methods [8][9][10], are applied to prepare NaHSO 4 crystal. However, few researches reported the NaHSO 4 crystal in regular shape by using such methods.…”