Research On Mass Transfer Of SO₂ Capture In Flue Gas By Room Temperature Ionic Liquid

Room temperature ionic liquids(ILs) has gained tremendous interest for SO₂ capture due to their unique physico-chemical properties. Conventional flue gas desulfurization have many disadvantages, therefore, development of environment friendly desulfurization sorbents that characterized by recyclable, highly efficient, pollution-free is not only the requirements for sustainable development, but also the key for flue gas desulfurization to achieve transformation from traditional treatment model with additional pollution to the circular economy mode with the advantages of lower consumption, lower pollution, and high-efficiency.Two basic ionic liquids were selected to investigate the behaviors of SO₂ absorption and desorption. It was found that both of the two basic ionic liquids have excellent absorption ability and great potential as alternative solvents for the recovery of SO₂ from SO₂-containing gases such as flue gas in industrial process.Firstly, the absorption performance of SO₂ in 1-Butyl-3-methylimidazolium Hydroxide ([BMIM][OH]) was studied. The results showed that [BMIM]OH could absorb large amounts of SO₂ at low temperature. With the increase of the temperature, the absorption amounts and absorption rate for SO₂ decreased sharply. Most notably was that the SO₂ absorbed could be desorbed mostly at high temperature and the IL can be recycled several times for consecutive absorption/desorption cycles with the average yield of recovery was over 94.7%. Under a typical operation condition, about 0.59 gram SO₂ per gram of [BMIM]OH can be separated in one cycle at 25℃and 0.1MPa.(i.e. 1.45mol SO₂/mol IL). To enhance the absorption rate and reduce the viscosity of ionic liquid, [BMIM]OH was immobilized on porous SiO₂, and the formed supported ionic liquid also showed pronounced SO₂ absorption ability with the yield of recovery was above 90% during five times of absorption and desorption cycles. In one cycle, about 0.1 gram SO₂ per gram [BMIM]OH could be recovered.In order to seek ionic liquid having even higher absorption ability, another ionic liquid, 1-allyl-3-methylimidazolium chloride (AMIMCl), was investigated. It was found that up to 3.27 moles of SO₂ could be absorbed per mole of [AMIM]Cl at 25℃and 0.1MPa. With the absorption of SO₂, the physicochemical properties of the solution changed greatly, the viscosity and pH decreased, and the conductivity and density increased. The absorption process was exothermic. The phenomenon indicated that there were interactions between the gas and IL. [AMIM]Cl has been repeatedly recycled for SO₂ absorption and 1.03 gram SO₂ per gram of [AMIM]Cl could be separated in one cycle at 25℃and 0.1MPa( i.e. 2.55 mole SO₂/mol IL). Supported ionic liquid also showed higher SO₂ gas absorption ability. The supported [AMIM]Cl could be reused, about 0.58 gram SO₂ per gram [AMIM]Cl could be removed.In addition, the experimental results were explained in terms of a thermodynamic model by calculation of enthalpy and entropy. The calculated enthalpy and entropy of SO₂ in two ionic liquid showed a certain degree of agreement with their absorption amount for SO₂, the magnitude and sign of enthalpy and entropy could yield the strength of interactions between the gas and ILs. A fifth-order polynomial was proposed to correlate the solubility data of mole fraction and temperature in order to attain a better understanding of the relationship between temperature and solubility.With a characteristics of simple preparation, higher absorption capacity and reusable ability, the two ionic liquids were environmentally benign desulfurization sorbent and show promising potential for industrial application.