Aminosilane-Modified Ordered Hierarchical Nanostructured Silica for Highly-Selective Carbon Dioxide Capture at Low Pressure

Abstract

Ordered hierarchical nanostructured silica (OHNS) adsorbents were prepared, and their surface was controllably modified by aminosilanization using two different aminosilanes, one bearing one primary amine unit per molecule (4-aminobutyltriethoxysilane, ABTS) and the other bearing both a primary and a secondary amine (N-(2-aminoethyl)-3-aminopropylmethyldiethoxysilane, AAMS). Following physicochemical, structural, morphological, and porosity characterization, the CO2 adsorption performance was evaluated at low pressures (up to 100 mbar) and at different temperatures (25, 45, and 60 °C), including determination of CO2 adsorption–desorption, kinetics, CO2/N2 selectivity, regeneration/cycling, heat of adsorption, and CO2 adsorption under humid conditions. The unique hierarchical silica framework together with the aminosilanization scheme applied resulted in enhanced kinetics and CO2 uptake, the latter being increased with temperature, thus revealing a dominant chemisorption mechanism, which was further evidenced by the increase in the enthalpy of adsorption of the modified materials compared to the pristine OHNS. Among the tested adsorbents, at 100 mbar and 25 °C, the OHNS modified by AAMS yielded the highest CO2 uptake under dry (1.3 mmol/g) and wet (1.9 mmol/g) conditions. Notably, at very low pressure (1 mbar), the CO2 capacity of OHNS-AAMS reached >40% of the material’s total uptake at 1 bar. Compared to the unmodified OHNS, the CO2 capacity of the OHNS-AAMS and OHNS-ABTS increased by approximately 21- and 16-fold, respectively, at 1 mbar and 25 °C. At even lower pressure (0.4 mbar), a capacity of 0.55 mmol/g was evidenced for OHNS-AAMS in dry CO2. A very high CO2/N2 selectivity of the AAMS-modified analogue at low pressure was also obtained, i.e., 13,854 at 50 mbar, confirming the significant increase in CO2-philicity via aminosilanization with aminosilanes bearing combined primary and secondary amine groups. Furthermore, the water affinity of the aminosilane-modified OHNS adsorbents was found to decrease, which is beneficial for capture from humid mixtures. Cyclic stability was confirmed by performing 10 thermal pressure swing adsorption (TPSA) cycles up to 100 mbar. The hierarchical nanostructured silica-based framework and the functionalization scheme presented here render these robust systems promising for selective CO2 capture at low pressures in industrial applications and direct air capture.

Ambient and sub-ambient temperature direct air CO2 capture (DAC) by novel supported in situ polymerized amines

“…Functionalized amine sorbents are widely recognized for their selectivity for CO 2 over N 2 and O 2 in numerous publications. 33,84,85…”

“…Functionalized amine sorbents are widely recognized for their selectivity for CO 2 over N 2 and O 2 in numerous publications. 33,84,85 While oxygen is a signicant component of the air, our equipment did not allow us to study the selectivity of the sorbents for oxygen. However, a study by Belmabkhout et al 59 demonstrated that the adsorption of oxygen onto aminefunctionalized silica was very similar to that of nitrogen.…”

A Systematic Approach to Understanding and Optimizing the CO2 Capture Performance of Triamine-Functionalized Mesoporous Silica with Amine Blends Using Molecular Simulations

“…According to different studies in the literature, ,,− there is strong evidence that most of the chemisorption of CO 2 on amines occurs at low pressures up to 5 kPa (50 mbar) for medium and high functionalization degrees. Reports simulating the chemisorption of CO 2 on amine-grafted materials have either assumed a 100% conversion rate where all amines are present as carbamate–ammonium pairs, ,, or have used experimental adsorption studies to estimate the conversion rate of the amine–CO 2 reaction into carbamate–ammonium pairs.…”

Nitrogen-Enriched Carbon Aerogels Derived from Polybenzoxazine Cross-Linked Graphene Oxide-Chitosan Hybrid Matrix with Superior CO2 Capture Performance

“…In addition, the CO 2 emission from fluid catalytic cracking (FCC) regenerators may contain a CO 2 concentration in the range of 20−35%. 3 Currently, natural gas (NG) is considered to be the primary source of world energy, and it is expected to grow in the future. However, the effluent streams from the well may include several impurities, which contain 4−50% CO 2 .…”

“…In particular, in the subject of CO 2 capture, the high CO 2 content gas effluents need significant CO 2 capture and storage (CCS) technologies to overcome the urgent power needs. 1,3 The development of efficient technologies and advanced materials for CO 2 capture and storage (CCS) has received tremendous attention during the last decides. Among the separation methods, absorption, adsorption, membrane separation, and cryogenic separation are commonly employed techniques for CO 2 removal from gas mixtures.…”