Amine-based Adsorbents

Some organic substances or polymers containing ammonium ions can chemically combine with acidic CO2 molecules at lower reaction temperatures and can therefore be used for CO2 adsorption capture. They have the advantages of high capacity at low CO2 partial pressures (10%-15%), low regeneration temperatures (<100 °C) and less equipment corrosion. The adsorption characteristics of amine-based adsorbents are related to factors such as amine loading, amine type, amine site density, amine molecular size on the solid support, and CO2 partial pressure. Since the adsorption performance of rich amine adsorbents is mainly based on chemical adsorption, their poor thermal regeneration ability remains a major disadvantage. A combined strategy was used to develop an ultra-stable amine-containing solid adsorbent that only lost 8.5% of its adsorption capacity even after aging for 30 days in O2-containing flue gas at 110 °C.

Polyethyleneimine (PEI) was impregnated into porous SiO2 to prepare an amine-containing adsorbent. The PEI on the outer surface of the adsorbent was selectively alkylated with epoxide to synthesize an amine-based CO2 adsorbent with high SO2 resistance. The adsorption capacity of CO2 under simulated flue gas conditions (60 ℃, 15% CO2, 10% H2O, 2% Ar, and balance gas N2) reached 139.48 mg/g. Under the condition of 50 ppm SO2 concentration, the adsorption capacity only lost 8.52% after 1000 cycles, showing good stability. HBS was grafted with amines under anhydrous and aqueous conditions. Under dry conditions at 25 ℃, using ambient air containing 415 ppm CO2, the dynamic adsorption capacity reached 1.04 mmol/g. The performance of amine-based adsorbents is affected by the type, loading amount, and molecular weight of the amine. Li et al. impregnated PEI into nano-SiO2 to produce a PEI-SiO2 adsorbent with high thermal stability.

The study found that branched PEI had a higher adsorption capacity of 202 mg/g than linear PEI. The effects of loading and molecular weight were studied. Too high or too low amine loading was not conducive to the increase of adsorption capacity. PEI-SiO2 adsorbents with lower PEI loading and molecular weight showed excellent adsorption kinetics. The structure and composition of the carrier material also affect the adsorption process. Many studies have focused on improving the adsorption performance of amine-based adsorbents by modifying SiO2. The CO2 adsorption rate was enhanced by changing the structure, and mesoporous SiO2 nanospheres with an inverted cone pore structure were synthesized. The adsorption capacity of the material increased by 50%, and the adsorption and desorption energy was also reduced. This means that the adsorbent has a better dynamic structure. Large surface pores are more conducive to the entry and exit of gas molecules, and large pore volume provides more space for diffusion.

Using single template and double template routes to synthesize bimodal and trimodal SiO2 as carrier materials, the adsorption capacity of bimodal SiO2 can reach 350 mg/g, while the adsorption capacity of trimodal SiO2 can reach 215 mg/g. Li et al. used metal nitrates to modify amorphous nano-SiO2. The study found that the solid amine adsorbent modified by Al, Zn, and Mg has better stability. After 50 adsorption cycles, only 2.6% to 28.8% of the original CO2 adsorption capacity was lost, while the original solid amine adsorbent lost 42.9%.