Studies On Properties And Mechanism For Sulfur Dioxide Absorption

The output and consumption of coal in China are the strongest all over world. In recentyears, coal consumption has been growing with the rapid economic development, so theemission of SO₂has been increasing, which threatens the environment and human health.At the same time, the sulfur resources are shortage in China, so it is necessary to removeSO₂from flue gases and save it.Our research group has paid great attention to the Ethylene Glycol （EG） system toremove SO₂for several years. In this work, N,N-dimethylformamide （DMF） was addedinto EG to improve the absorption capacity of SO₂which can reduce the energyrequirements for SO₂absorption processes. The isothermal gas liquid equilibrium （GLE）data of dilute SO₂in DMF+EG mixtures were determined as a function of composition atT=308.15K and p=122.66kPa. The results indicate that the solubility of SO₂increaseswith the increasing DMF concentration and the absorption of dilute SO₂in DMF+EGmixtures obey Henry’s law at low pressure. Meanwhile, the densities and viscosities for thebinary mixtures of DMF+EG were measured over the whole concentration range at T=（298.15,303.15,308.15,313.15and318.15） K. The experimental results were comparedwith reported data in literatures. From the experimental density and viscosity data, theexcess molar volumes （VmE） were calculated, and the values of VmEare shown to benegative at all experimental temperatures and compositions. From the viscosity data,viscosity deviations（Δν）, Gibbs energies of activation of viscous flow （ΔG*）, enthalpy ofactivation for viscous flow （ΔH*） and entropy of activation for the viscous flow （ΔS*）were also calculated.The interaction mechanism of SO₂with EG+DMG was mainly studied by modernspectroscopic technologies such as UV-vis, FTIR, and1H-NMR. The results show thatinteraction between unlike molecules takes place by hydrogen bond as-C=O···H-O-, andthe sulfur atom of SO₂can interact with carbonyl oxygen atom of DMF.Amine loss is a serious problem in amine desulfurization. In this work, we present datafor the use of magnesium tetraphenyl porphyrin （MgTPP） as an amine-fixing agent for SO₂capture. The amines initially form adducts with MgTPP. When SO₂is introduced, it competes with MgTPP for the amines, which eventually leads to the release of MgTPP.The amines can form adducts with the regenerated MgTPP when separated from SO₂,which may reduce amine losses. Meanwhile, the coordination reaction between MgTPPwith amine by fluorescence titration, and the binding constant （K）, the enthalpy （H）,entropy （S）, and free energy （G） of the binding process are calculated according to thefluorescence data.