Effect of Different Acid Initiators on Branched Poly(propylenimine) Synthesis and CO₂ Sorption Performance

Abstract

Branched poly­(propylenimine) (PPI) provides an alternative to the prototypical amine polymer, commercially available branched poly­(ethylen­imine) (PEI), in composite adsorbents for CO2 capture. Herein, we investigate the synthesis of PPI via cationic ring opening polymerization of azetidine using various acid initiators (HBr, HClO4, HCl, CH3SO3H) and polymerization times, impacting the molecular weight and CO2 sorption behavior. The polymerization kinetics and the amine distribution (i.e., primary:​secondary:​tertiary ratios) are monitored with 1H NMR during polymerization, and a basic ion-exchange resin is used to neutralize charged amine centers and to remove unreacted acid. The polymers are impregnated into the model porous oxide support, mesoporous silica SBA-15, and the CO2 capacities under both simulated ambient air and flue gas conditions are elucidated. In parallel, the oxidative stability of the PPI-based sorbents is assessed and compared with the prototypical PEI sorbents. Sorbents with 30 wt % polymers synthesized using HBr and HClO4 exhibit higher CO2 capacities than those made with HCl or CH3SO3H. Sorbents from HBr polymers only lost 24% of their CO2 capacity after 12 h of oxidation in air at 383 K. Even trace amounts of residual ClO4 – anions in HClO4 initiated polymers, though, accelerated oxidation (decreased CO2 capacity by 64%). Extended resin treatments were needed to leave undetectable Cl content in these polymers, which resulted in sorbents that are much more oxidatively stable.

A Comparative Study of Different Sorbents in the Context of Direct Air Capture (DAC): Evaluation of Key Performance Indicators and Comparisons

“…Generally, research in this field has explored and optimized adsorption capacities, kinetics and regenerability for amine-functionalized sorbents individually [31][32][33][34][35][36] and this is also the case for MOFs [37][38][39][40][41].…”

“…Brilman and Veneman [43] considered a mixture of tetraethylenepentamine (TEPA) and PEI, obtaining a CO 2 uptake of 2.5 molCO 2 /kg, using temperature swing adsorption for regeneration. Other amines which have been investigated are: poly(propylenimine) (PPI) [33,44] and poly(allylamine) (PAA) [45].…”

Effect of Extended Aging and Oxidation on Linear Poly(propylenimine)-Mesoporous Silica Composites for CO2 Capture from Simulated Air and Flue Gas Streams

“…Building on studies by Bali et al showing that poly­(allylamine) (PAA) is a polymer with improved resistance to oxidation when compared to PEI, several variants of poly­(propyleneimine) (PPI) have been recently described as oxidation-resistant polymers for CO 2 capture from dilute and ultradilute gas streams . These include branched, small-molecule PPI, branched oligomeric PPI prepared via ring opening of azetidine, , and linear poly­(propylenimine) (LPPI) synthesized by cationic ring-opening polymerization of 2-methyl-5,6-dihydro-4 H -1,3-oxazine . The number-average molecular weight ( M n ) of the synthesized LPPI materials ranged from 700 to 36 000 Da.…”

Facile access to template-shape-replicated nitrogen-rich mesoporous carbon nanospheres for highly efficient CO2 capture and contaminant removal

“…[7][8][9] Various porous materials have been investigated to develop new CO 2 capture materials, such as zeolites, [10][11][12][13] carbons, [14][15][16][17][18][19][20][21] covalent organic frameworks, 22 metal organic frameworks, 23,24 polymers 25 and silica/polymer hybrids. [26][27][28][29][30] Porous carbon nanomaterials possessing controlled pore geometry and morphology are used in applications in energy storage, catalysis, and air purification. Porous carbons are also employed as CO 2 capture materials.…”