The Development Of Water-lean Absorbents For High-efficiency CO₂ Capture By Alkoxy-functionalization

Nowadays,carbon dioxide（CO₂）emission from industrial flue gas is the main source of greenhouse gases that causing climate change worldwide.Aqueous alkanolamine-based processes represent the most mature and widely used CO₂ capture technology.However,high energy consumption,solvent volatility and equipment corrosion are their inevitable disadvantages due to the large amount of water which is essentially required as diluent to reduce system viscosity.Therefore,the development of water-lean CO₂capture technology,which could reduce desorption energy consumption by decreasing the specific heat capacity and absorption enthalpy has increasingly become an important research direction in both industry and academia.Hence,great progress has been made in design and operation of non-aqueous absorbents,but their industrial application still face the dilemma of exponentially increasing viscosity during absoption and excessive cost of synthesis,which would lead to low efficiency and difficult pipeline transportation.In this work,aiming at reducing working viscosity of water-lean systems,a class of non-aqueous CO₂absorbents with high capacity and flowability were developed by introducing alkoxy functionalization,while the corresponding structure-property relationship were interpreted at the molecular level.The main contents are as follows:（1）A series of alkoxy-functionalized methylamines have been devised as single-component post-combustion CO₂ absorbents under water-lean condition.These nonaqueous amines have low viscosities（48-114 c P at 25 ^oC,27-63 c P at 40 ^oC）at their maximal gravimetric CO₂ capacities（15-21wt%at 25 ^oC,13-20wt%at 40 ^oC）.Comprehensive mechanistic studies by means of in situ FTIR spectroscopy,density functional theory（DFT）calculations as well as control experiments revealed that the stabilization of sequestered CO₂ by intramolecular hydrogen bonding between in situ formed carbamic acid and the flexible alkoxy side chain of the designed amines should play the key role to enhance both capacity and flowability as well as the mechanism of viscosity reduction of absorbent was further explained.Meanwhile,thermal desorption of the captured CO₂ could be easily carried out at feasible temperature（no more than 75 ^oC）under ambient pressure,and the CO₂-saturated absorbents would sustain intact at 80 ^oC for two days within closed system.Furthermore,these novel absorbents would exhibit significant physisorption by operating at high pressures（20 and 30 bar）,owing to the CO₂-philic nature of alkoxy functionality.Hence,the integration of high capacity,low operating viscosity and easy reversibility makes such alkoxy-functionalized amine type absorbent a compelling candidate for practical application.（2）A series of diamine based dual-component solvents for high-efficiency CO₂capture under water-lean condition have been devised,which poccess excellent capture ability（15-21wt%）with no significant temperature dependence,and could maintain low operational viscosity（below 150 c P at 25 ^oC and below 60 c P at 40 ^oC）.The easy desorption of these absorbents has been revealed by DSC from three indexes:reversal temperature,regeneration enthalpy and evaporation temperature.In situ FTIR was used to further monitor entire CO₂ capture-release process,rendering total reversibility.CO₂-saturated absorbents remained intact for 48 h at 80 ^oC within closed autoclave and underwent ten cycles of absorption-desorption with almost no change in capacity.The wide applicability of dual-component absorbents under different pressures（less than 1 MPa）has been revealed by vapor-liquid equilibrium（VLE）experiments.Meanwhile,they have also shown excellent tolerance and capture performance under high operating pressures（20 and 30 bar）.The present study on diamine based dual-component solvents for high-efficiency CO₂ capture under water-lean condition could provide a new strategic direction for absorbent design as well as process optimization.