Relationship Between CO₂ Adsorption/Desorption Properties In Confined Space And Solid Amine Structure

Characteristics of CO2 in confined spaces including submarine,manned spacecraft and space station are low concentration,small adsorption force,and coexist with a certain amount of water vapor.The removal difficulty is much higher than in flue gas.The solid amine adsorbent combines the advantages of the adsorption and absorption method,and has attracted extensive attention due to its large adsorption capacity,strong selectivity,low regeneration energy consumption,and easy operation.Therefore,design and synthesis of a solid amine adsorbent which is highly efficient and suitable for low-concentration CO2 removal in confined space is the key to ensuring the normal operation of a confined space.In this dissertation,through the design and regulation of different supports and amines,the adsorption and desorption behavior of resin-based solid amine adsorbents and carbon-based solid amine adsorbents on low concentration CO2 is systematically studied,and the life prediction model of adsorbents is established.Meanwhile,the relationship between CO2 adsorption/desorption properties and amine structure is further discussed,with the design,optimization and expansion of organic amine structures carried out.Aiming at the problem that the real service life of the adsorbent is difficult to measure,the resin-based solid amine adsorbent is subjected to adsorption and desorption cycle test for 1 year under the actual operating conditions and still exhibits good adsorption and desorption performance.In order to reduce the experimental time,the thermal degradation and O2-induced deactivation kinetics of amines in adsorbent are studied under intensified temperature conditions.The activation energies of the thermal degradation and O2-induced deactivation are calculated to be 80.98 and 74.47 kJ/mol,respectively.A reasonable prediction model of adsorbent service life is established.The time required for the CO2 adsorption capacity of the solid amine adsorbent to decrease by 30%is used as the service life which is shortened with temperature increasing.The service life of adsorbent which adsorbed at 20℃ and desorbed at 30℃ is about 5.5 years,then it decreased to 1.4 years when the desorption temperature rises to 50℃.Carbon xerogels with adjustable pore structure are prepared by sol-gel method,and they are impregnated with amine to synthesis solid amine adsorbent.Different pore structures of supports affect the impregnation,thus affect the CO2 adsorption capacity of the adsorbent.CX1500 is a macroporous material with little physical adsorption interference,which is suitable for the impregnation of large amount of amine,therefore it can be used as support to analyze the effect of different amine structures on CO2 absorption/desorption.The desorption rate increases with temperature or current.In the initial stage of the desorption process,the desorption rate of electrothermal desorption is greater than that of thermal desorption,and electrothermal desorption is faster to reach the maximum desorption rate,which meets the requirement of rapid and efficient.Cerium-doped adsorbent is a promising CO2 adsorbent which behaves fast absorption/desorption rate,large amount of absorption/desorption capacity,and least energy consumption during the electrothermal desorption process.In order to investigate the relationship between CO2 adsorption/desorption properties and amine structure,four different amines are selected as research objects.The results show that N,N’-diethylethylenediamine-loaded adsorbent has the best CO2 adsorption and desorption properties simultaneously.This phenomenon may be caused by the "switching" effect of CO2 on amine molecular structure during the adsorption and desorption process.Before adsorption,a non-classical chemical bond:intramolecular hydrogen bond formed,and the electron effect is favorable for the CO2 adsorption.The molecular structure of the adsorbent is dominated by classical chemical bonds after adsorption,and the space effect replaces electron effect to be the main influencing factor,so the larger substituent helps to desorb.N,N’-diethyl-1,3-propanediamine/carbon xerogel adsorbent is prepared to verify the structure-activity relationship,and the adsorbent also exhibits excellent performance on CO2 adsorption and desorption process.