Experimental Investigation Of The Functionalized Deep Eutectic Solvents For Capturing SO₂

China is a fossil fuels consumption giant.SO₂ produced from burning of fossil fuels is one of the main reasons for the formation of acid rain and smog,which has caused serious harm to environment for survival.The application of gypsum/grit slurry to remove SO₂ in industry has the advantages of fast absorption rate and high capture efficiency,but it will produce massive solid waste of calcium sulfate.Deep eutectic solvents?DESs?are ionic liquid?ILs?analogues,which are composed of hydrogen bond donor?HBD?and hydrogen bond acceptor?HBA?.These DESs have many excellent properties similar to ILs.At the same time,they are usually cheap and available from raw materials.DESs provide new method for SO₂ capture,with the key of how to improve absorption capacity.Therefore,a variety of functional DESs are prepared and used as absorbents for SO₂ in present work.The absorption mechanism is proposed on the basis of spectrum analysis.In this work,three kinds of DES were prepared by pairing guaiacol?GC?with quaternary ammonium salts[Chlorine Choline?CC?,Acetylcholine Chloride?ACC?,Diethylamine Hydrochloride?DH?].The physical properties and solubility of SO₂ at303.15-333.15 K and 0-1.2 bar were measured,and the Henry constant H_m,the standard Gibbs free energy,enthalpy,and entropy were obtained by correlating experimental data.The results show that GC-CC?3:1?has the highest absorption capacity and SO₂/CO₂ selectivity.The negative enthalpies mean that the absorption processes are exotherci reactions.In order to increase the absorption capacity of SO₂ under low pressure,imidazole and triazole were introduced as functional HBDs and paired with acetylcholine chloride to construct a series of functionalized azole-based DESs.Their physical properties and perforamces for SO₂ capture were systematically studied.The results showed that the azole-based DES had low viscosity and good thermal stability.The absorption capacities of ACC-Im?1:2?were 0.381 g SO₂/g DES and 0.116 g SO₂/g DES at 313.15 K,0.1bar and 3300 ppm SO₂ concentrations,respectively.The azole-based HBD is a functional component for SO₂ absorption.Spectroscopic analysis shows that the main absorptiom comes from the reaction between SO₂ and the N atom in azole ring.The basicity of imidazole is stronger than that of triazole,which results in the higher absorption capacity of SO₂ in imidazole-based DES than triazole-based DES.The selectivity of ACC-Im?1:2?SO₂/CO₂ reached 198.38.The azole-based DESs have satisfactory recycling performance.On abovementioned basis,the cheaper choline chloride?CC?was used to replace ACC for preparation of CC-Im DES.However,they appeared as solid at room temperature.Thus,a serials of ternary functionalized DESs were prepared by adding environmentally friendly PEG200,ethylene glycol?EG?and glycerol?Gly?as diluents,and applied for SO₂ absoption.The results showed that the diluent of solvent had a significant influence on gravimetric absorption capacity of ternary DES.At 1%SO₂,313.15K,the absorption?expressed as g SO₂/g DES?were 0.294,0.258,and0.157 for CC-EG-Im?1:2:3?,CC-Gly-Im?1:2:3?,and CC-PEG200-Im?1:2:3?,respectively.The absorption capacity and SO₂/CO₂ selectivity increase with increasing content of Im in the DESs.Finally,ACC-Im?1:2?is selected as a flue gas desulfurization absorbent after comprehensive consideration of viscosity,absorption and SO₂/CO₂ selectivity.A process for SO₂ removing was simulated by using ASPEN plus with the absorbent of ACC-Im?1:2?.The results showed that decrease the SO₂ volume fraction in flue gas from 4000 ppm to 35 ppm and the corresponding removal rate reached 98.6%with the absorbent at 20°C and dosage was 42 m³·h^-1,when an initial condition of wet flue gas was at 80?and 6248 m³·h^-1.