Study Of CO₂ Capture By Using Functionalized Quaternary Phosphonium Ionic Liquid

The CO₂ discharge from the combustion of the fossil fuels plays a key role in climate change.CO₂ capture and storage?CCS?has become a widespread concern in the research areas.The chemical absorption is currently believed to be the most suitable ones for post-combustion CO₂ capture.This process has inherent drawbacks,including equipment corrosion,high energy consumption for regenration and secondary pollution.Therefore,it is an urgency to develop new green CO₂ capture absorbents to solve this problem.Ionic liquids have been applied to CO₂ capture since their unique properties including low volatility,high thermal stability,the tunable cations and anions.However,the reported functionalized ionic liquids have many drawbacks,such as high viscosity and low absorption capability.To overcome the above problems,three kinds of quaternary phosphonium ionic liquids have been synthesized,and then the CO₂ capture performance was investigated.In addition,in order to reduce the cost of ionic liquids and overcome the poor mass transfer performance caused by high viscosity,ionic liquids are immobilized on Al₂O₃ or MCM-41 by impregnation-evaporation method,the CO₂ capture performance of immobilized ionic liquids with different loading ratios are also studied.Meanwhile,the effects of temperature,CO₂concentration and components of flue gas,such as H₂O and O₂,on the absorption/adsorption performance are systematically studied.In situ diffuse reflectance infrared is applied to study the interaction between ionic liquids and CO₂.The main contents and results of this work are as following:?1?The CO₂ absorption performance ofthree kinds of quaternary phosphonium ionic liquids[aP₄₄₄₃][AA].Fourier transform infrared spectroscopy?FTIR?and Thermogravimetry?TGA?show that three kinds of ionic liquids have good thermal stability and desirable structural characteristics.[aP₄₄₄₃][Triz],[aP₄₄₄₃][2-Op]and[aP₄₄₄₃][2-Np]show good absorption performance at 30 ^oC,1atm and the saturated absorption capacity of pure CO₂ was 1.38 mol CO₂/mol IL,1.57 mol CO₂/mol IL and 1.88 mol CO₂/mol IL,respectively.The CO₂ capture capacity reduced with the temperature increased and CO₂ concentration decreased.Other components of flue gas,such as H₂O is not conducive to the CO₂ absorption.?2?The CO₂ capture capacity of immobilized ionic liquids.FTIR,BET and TGA show that ionic liquids are loaded well on the carriers,and the thermal stability of the immobilized ionic liquids is close to that of the free ionic liquids.The adsorbent with 30 wt%loading has good adsorption performance,the saturation adsorption for 15%CO₂/N₂ of[aP₄₄₄₃][2-Np]-Al₂O₃-30 wt%and[aP₄₄₄₃][2-Np]-MCM-41-30 wt%are 2.42 mmol/g and 3.19 mmol/g,respectively,at 30 ^oC,1 atm.The capture capacity remains 97.5%and 94.9%of the original CO₂ sorption capacity after six cycles regenerated at 110 ^oC under N₂ atmosphere.Elevated temperatures and reduced CO₂ concentrations are detrimental to CO₂adsorption.Other components of flue gas can reduce the CO₂ adsorption capacity.?3?Diffuse reflectance infrared fourier transform?DRIFT?is used to study the interaction between three ionic liquids and CO₂,and the mechanism is the amino group in the cation reacts with CO₂ in 2:1 mechanism;the electronegative nitrogen interacting site in the 1,2,4-Triazole anion reacts with CO₂ in 1:1mechanism;the electronegative oxygen and nitrogen cooperate with N atoms in the 2-hydroxypyridine and 2-aminopyridine anion react with CO₂ in higher than1:1.