Amine Efficiency Research Articles

Oxidatively-Stable Linear Poly(propylenimine)-Containing Adsorbents for CO2 Capture from Ultradilute Streams.

Aminopolymer-based solid sorbents have been widely investigated for the capture of CO2 from dilute streams such as flue gas or ambient air. However, the oxidative stability of the widely studied aminopolymer, poly(ethylenimine) (PEI), is limited, causing it to lose its CO2 capture capacity after exposure to oxygen at elevated temperatures. Here, we demonstrate the use of linear poly(propylenimine) (PPI), synthesized through a simple cationic ring-opening polymerization, as a more oxidatively stable alternative to PEI with high CO2 capacity and amine efficiency. The performance of linear PPI/SBA-15 composites was investigated over a range of CO2 capture conditions (CO2 partial pressure, adsorption temperature) to examine the tradeoff between adsorption capacity and sorption-site accessibility, which was expected to be more limited in linear polymers relative to the prototypical hyperbranched PEI. Linear PPI/SBA-15 composites were more efficient at CO2 capture and retained 65-83 % of their CO2 capacity after exposure to a harsh oxidative treatment, compared to 20-40 % retention for linear PEI. Additionally, we demonstrated long-term stability of linear PPI sorbents over 50 adsorption/desorption cycles with no loss in performance. Combined with other strategies for improving the oxidative stability and adsorption kinetics, linear PPI may play a role as a component of stable solid adsorbents in commercial applications for CO2 capture.

Structural parameters to consider in selecting silica supports for polyethylenimine based CO2 solid adsorbents. Importance of pore size

Hybrid solid CO2 adsorbents prepared from commercially available silica and polyethylenimine (PEI) are potential candidate for large scale carbon capture applications. In this study, the effect of the silica support structure and morphology on the CO2 adsorption capacity of the adsorbent was investigated. Two series of silica supports with distinct morphology, i.e. granular and microspherical, available from PQ-Corp., and well defined surface area, pore diameter, and pore volume were loaded with branched PEI. The CO2 adsorption characteristics of these adsorbents were measured using thermogravimetric analysis (TGA). The increase in PEI loading on the porous silica caused a significant decrease in surface area and pore volume. At a certain loading level, the pores were completely filled with PEI, and the CO2 diffusion was hindered resulting in lower adsorption capacity and amine efficiency. With granular silicas, supports having an average pore diameter greater than about 240 Å performed best. However, once this threshold in pore diameter was passed, the adsorption capacity did not improve much further. For microspherical silica supports this threshold was around 300 Å. For supports with a same pore volume, the ones with a larger pore diameter had higher CO2 adsorption capacity, even if their surface area was lower. This difference was mainly due to the easier diffusion of CO2 into the pores, because the phenomenon was more pronounced at a low adsorption temperature (25 °C), where diffusion control was most significant.

Role of Amine Structure on Hydrogen Sulfide Capture from Dilute Gas Streams Using Solid Adsorbents

The hydrogen sulfide composition in biogas ranges from 0 to 5% depending on the feed source to the biogas digester. To meet renewable natural gas specifications of 0–4 ppm of H2S content, technologies that remove H2S from raw biogas feeds are needed. This contribution assesses three adsorbents with similar textural and physical properties but with different amines grafted to the surface. Specifically, materials containing primary, secondary, and tertiary amines at the end of a propyl surface linker grafted on a silica support are explored. H2S adsorption isotherms and cyclic studies are presented for these materials, and it is shown that secondary amines have the best amine efficiency while tertiary amines are the most stable for H2S capture, of the materials studied. The results suggest the consideration of secondary and tertiary amines for the design of amine adsorbents suitable for H2S removal in dilute gas streams over multiple cycles.

Water Enhancement in CO2 Capture by Amines: An Insight into CO2–H2O Interactions on Amine Films and Sorbents

Water, a component in flue gas, plays a significant role in CO2 capture through a complex interaction between water molecules and adsorbed CO2 on amine sorbents. To determine how the H2O–CO2–amine interactions affect amine efficiency and the binding energy of adsorbed CO2, we used in situ infrared spectroscopy (IR) to determine the structure of adsorbed CO2 and H2O as well as their relations to adsorption/desorption kinetics and CO2 capture capacity on tetraethylenepentamine (TEPA) films and Class I amine (i.e., impregnated) sorbents. H2O enhanced amine efficiency of TEPA films and sorbents by increasing the accessibility of secondary amine sites to CO2 and promoting the formation of hydronium carbamate and carbamic acid. CO2 adsorbed on the surface of the TEPA film as a weakly adsorbed CO2 in the form of hydronium and ammonium–carbamate with a low IR intensity of hydrogen bonding (−OH···–OOC or −NH···–OOC) between hydronium/ammonium ions and carbamate ions. CO2 adsorbed on the middle layers (i.e., 0.2–0....

Tuning the textural properties of HMS mesoporous silica. Functionalization towards CO2 adsorption

HMS mesoporous silica materials were prepared using different amines as structure directing agents. Textural properties showed a clear dependence on the molecule used, with too long and too short amines yielding significantly distorted structures.CO2 adsorbents were obtained by loading additional amino groups on supports before (as made) or after removing the structure directing agent (extracted and calcined). Organic loading was performed by grafting with diethylenetriamine-trimethoxysilane (DT) and by impregnation with polyethyleneimine (PEI). CO2 adsorption analyses showed a higher CO2 uptake and amine efficiency (defined as the molar ratio CO2/N) for uniformly-structured adsorbents. Besides, as-made materials showed the best CO2 adsorption properties due to a synergistic effect between loaded amines and those already present in the support.The influence of adsorption temperature, operation cycles and CO2 concentration was also studied. A maximum CO2 uptake of 4.19 mmol CO2/g (184 mg CO2/g) was registered in pure CO2 (90 °C, 1 bar), while a value of 1.80 mmol CO2/g was found in direct air capture conditions (400 ppm CO2, 45 °C, 1 bar).

Comparative Study of Molecular Basket Sorbents Consisting of Polyallylamine and Polyethylenimine Functionalized SBA-15 for CO2 Capture from Flue Gas.

Polyallylamine (PAA)-based molecular basket sorbents (MBS) have been studied for CO2 capture in comparison with polyethylenimine (PEI)-based MBS. The characterizations including N2 physisorption, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), and thermogravimetric analysis (TGA) showed that PAA (Mn =15 000) is more rigid and has more steric hindrance inside SBA-15 pores than PEI owing mainly to its different polymer structure. The effects of temperature and PAA loading on the CO2 sorption capacity of PAA-based MBS have been examined by TGA by using 100 % CO2 gas stream and compared with PEI/SBA-15. It was found that the capacity of the PAA/SBA-15 sorbent increased with increasing temperature. The optimum capacity of 88 mgCO2 gsorb-1 was obtained at 140 °C for PAA(50)/SBA-15 whereas the optimum sorption temperature was 75 and 90 °C for PEI-I(50)/SBA-15 (PEI-I, Mn =423) and PEI-II(50)/SBA-15 (PEI-II, Mn =25 000), respectively. The capacity initially increased with the increase of PAA loading and then dropped at high amine contents, owing to the increased diffusion barrier. The highest CO2 capacity of 109 mgCO2 gsorb-1 was obtained at a PAA loading of 65 wt %, whereas the PAA(50)/SBA-15 sorbent gave the best amine efficiency of 0.23 molCO2 molN-1 . The effect of moisture was examined in a fixed-bed flow system with simulated flue gas containing 15 % CO2 and 4.5 % O2 in N2 . It was found that the presence of moisture significantly enhanced CO2 sorption over PAA(50)/SBA-15 and greatly improved its cyclic stability and regenerability. Compared with PEI/SBA-15, PAA/SBA-15 possesses a better thermal stability and higher resistance to oxidative degradation. However, the CO2 sorption rate over the PAA(50)/SBA-15 sorbent was much slower.

One-pot sol–gel synthesis of amine hybrid titania/silsesquioxane composite aerogel for CO2 capture

Amine hybrid titania/silsesquioxane composite aerogel (AHTSA) was prepared by an one-pot sol–gel process without any catalyst. The sol-gel reaction mechanism of AHTSA was proposed. The use of 3-aminopropyltriethoxysilane (APTES) plays as an “internal catalyst” and promotes the formation of gel during sol–gel process. The morphology, microstructure, pore structure and CO2 capture performances of AHTSA were investigated. AHTSA exhibits microstructure of the typical silica aerogels with colloidal structure. Moreover, AHTSA has a large number of macropores which favor the CO2 adsorption. Thermogravimetric analysis reveals that AHTSA has a high CO2/N2 selectivity in CO2/N2 mixture gas. CO2 adsorption capacity with dry and humid 1 vol% CO2 is as high as 4.19 and 5.04 mmol/g, respectively. Correspondingly, amine efficiency under dry and humid conditions is 0.37 and 0.44, respectively. AHTSA has very short adsorption halftime below 4 min, and its CO2 adsorption capacity do not show obvious attenuation after 30 adsorption-regeneration cycles, indicating AHTSA is a dynamic and regenerable sorbent.

CO2 capture over molecular basket sorbents: Effects of SiO2 supports and PEG additive

The objective of this work is to study the influences of silica supports and PEG additive on the sorption performance of molecular basket sorbent (MBS) for CO2 capture consisting of polyethylenimine and one of the following supports: SBA-15 (2-D structure), TUD-1 (3-D sponge-like structure) and fumed silica HS-5 (3-D disordered structure). Effects of the supports regarding pore structures and pore properties, the PEI loading amount as well as the sorption temperature were examined. Furthermore, polyethylene glycol (PEG) was introduced as an additive into the sorbents and its effect was investigated at different PEI loadings and sorption temperatures. The results suggest that the pore properties of MBS (after PEI loading) play a more important role in the CO2 sorption capacity, rather than those of the supports alone. MBS with 3D pore structure exhibits higher CO2 sorption capacity and amine efficiency than those with 2D-structured support. Among the sorbents studied, fumed silica (HS-5) based MBS showed the highest CO2 sorption capacity in the temperature range of 30–95 °C, probably due to its unique interstitial pores formed by the aggregation of polymer-loaded SiO2 particles. It was found that the temperature dependence is directly related to the PEI surface coverage layers. The more PEI surface coverage layers, the higher diffusion barrier for CO2 and the stronger temperature dependence of CO2 capacity. 3D MBS exceeds 2D MBS at the same PEI coverage layers due to lower diffusion barrier. Adding PEG can significantly enhance the CO2 sorption capacity and improve amine efficiency of all MBS, most likely by alleviating the diffusion barrier within PEI bulk layers through the inter-molecular interaction between PEI and PEG.

A Study on Grafting Efficiency of Amine and CO2 Sorption Behavior Inside Amorphous Silica

The effect of the physical properties of support materials on the performance of CO2 adsorbents was evaluated. Amine functional group was grafted covalently inside nanopore of silica having different surface area, pore diameter and pore structure. The prepared CO2 adsorbents were evaluated for its CO2 sorption capacity and their kinetics. In addition, the adsorbents were characterized by elemental analysis, BET, SEM and FT-IR. The 2NS/NPS-1 adsorbent showed the highest CO2 sorption capacity of 7 wt% and the highest grafting efficiency because of the large surface area and 3D pore structure of the NPS-1 support. CO2 sorption rate of 2NS/NPS-2 was observed to be higher than NPS-1 and n-silica because of more effective internal diffusion of CO2 inside larger pores.

The Role of Water in CO2 Capture by Amine

An in situ IR study unraveled that adsorption of CO2 on 20 μm TEPA film at 50 °C followed a zwitterion-intermediate pathway: zwitterion → ammonium carbamate. H2O in the mixed TEPA/H2O (5:1) film decreased the rate of CO2 adsorption but increased the amine efficiency. CO2 preferentially adsorbs on primary amine sites and H2O on secondary amine sites. The presence of H2O promotes the formation of carbamic acid and produces a broad IR band centered at 2535 cm–1, which can be assigned to the ν(O–H) of hydronium carbamate, −NCOO–···H–OH2+. The broadness of this 2535 cm–1 band ranging from 2100 to 2800 cm–1 persists at 120 °C. These broad components of the band can be ascribed to ν(N–H) in hydrogen-bonded ammonium carbamate, a R–NH3+/R1R2–NH2+···–NCOO– moiety. The binding strength of adsorbed species on the TEPA film increases in the order adsorbed H2O < carbamic acid < ammonium carbamate < hydrogen-bonded water/ammonium carbamate.

Sonochemical surface functionalization of exfoliated LDH: Effect on textural properties, CO2 adsorption, cyclic regeneration capacities and subsequent gas uptake for simultaneous methanol synthesis

To improve CO2 adsorption, amine modified Layered double hydroxide (LDH) were prepared via a two stage process, SDS/APTS intercalation was supported by ultrasonic irradiation and then followed by MEA extraction. The prepared samples were characterised using Scanning electron microscope-Energy dispersive X-ray spectroscopy (SEM-EDX), X-ray Photoelectron Spectroscopy (XPS), X-ray diffraction (XRD), Temperature Programmed Desorption (TPD), Brunauer-Emmett-Teller (BET), and Thermogravimetric analysis (TGA), respectively. The characterisation results were compared with those obtained using the conventional preparation method with consideration to the effect of sonochemical functionalization on textural properties, adsorption capacity, regeneration and lifetime of the LDH adsorbent. It is found that LDHs prepared by sonochemical modification had improved pore structure and CO2 adsorption capacity, depending on sonic intensity. This is attributed to the enhanced deprotonation of activated amino functional groups via the sonochemical process. Subsequently, this improved the amine loading and effective amine efficiency by 60% of the conventional. In addition, the sonochemical process improved the thermal stability of the adsorbent and also, reduced the irreversible CO2 uptake, CUirrev, from 0.18mmol/g to 0.03mmol/g. Subsequently, improving the lifetime and ease of regenerating the adsorbent respectively. This is authenticated by subjecting the prepared adsorbents to series of thermal swing adsorption (TSA) cycles until its adsorption capacity goes below 60% of the original CO2 uptake. While the conventional adsorbent underwent a 10 TSA cycles before breaking down, the sonochemically functionalized LDH went further than 30 TSA cycles.

Synthesis and CO2 adsorption behavior of amine‐functionalized porous polystyrene adsorbent

ABSTRACTA solid amine adsorbent was prepared by modifying a porous polystyrene resin (XAD‐4) with chloroacetyl chloride through a Friedel–Crafts acylation reaction, followed by aminating with tetraethylenepentamine (TEPA). The adsorption behavior of CO2 from a simulated flue gas on the solid amine adsorbent was evaluated. Factors that could determine the CO2 adsorption performance of the adsorbents such as amine species, adsorption temperature, and moisture were investigated. The experimental results showed that the solid amine adsorbent modified with TEPA (XAD‐4‐TEPA), which had a longer chain, showed an amine efficiency superior to the other two amine species with shorter chains. The CO2 adsorption capacity decreased obviously as the temperature increased because the reaction between CO2 and amine groups was an exothermic reaction, and its adsorption amount reached 1.7 mmol/g at 10 °C in dry conditions. The existence of water could significantly increase the CO2 adsorption amount of the adsorbent by promoting the chemical adsorption of CO2 on XAD‐4‐TEPA. The adsorbent kept almost the same adsorption amount after 10 cycles of adsorption–desorption. All of these results indicated that amine‐functionalized XAD‐4 resin was a promising CO2 adsorbent. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45046.

Effect of pore size, aminosilane density and aminosilane molecular length on CO2 adsorption performance in aminosilane modified mesoporous silica

Mesoporous silicas with different pore size were modified by aminosilanes with different molecular length. CO2 adsorption capacity was improved by all aminosilane modification, and the CO2 adsorption capacity was further improved with increasing the aminosilane density. However, CO2 adsorption capacity and the amine efficiency of (3-trimethoxysilylpropyl)diethylentriamine (TA) modified mesoporous silicas with small pores such as MCM-41(2.9 or 3.1 nm) and SBA-15(6.2 or 7.1 nm) were significantly decreased at high aminosilane density. In contrast, TA modified SBA-15 with a large pore (10.6 nm) exhibited further improvement of CO2 adsorption capacity and amine efficiency. N2 adsorption desorption measurements suggested that the pore plugging occurred at high aminosilane density in TA modified mesoporous silicas with small pores. In situ FT-IR spectra and the half-value period of CO2 equilibrium adsorption capacity clearly shows the CO2 adsorption kinetics in these adsorbents with small pores were significantly lower than that in the adsorbent with large pores. To develop the CO2 adsorbents with high adsorption performance, the correlation between aminosilane molecular length, pore size of mesoporous silica and aminosilane density should be considered.

Amino-modified pillared adsorbent from water-treatment solid wastes applied to CO2/N2 separation

In this work, solid wastes from the flocculation step of a drinking water treatment plant were used as starting material to obtain CO2 adsorbents upon thermal treatment and a pillaring strategy. Thermally treated solid waste and pillared materials were characterized by XRD, FTIR, TGA, N2 adsorption–desorption isotherms at 77 K, XPS and elemental analysis. From the characterization results, it was found that the introduction of silica pillars was successful, leading to heterostructured materials with higher specific surface area and pore volume. In order to improve the CO2 adsorption capacity, pillared materials were functionalized by grafting with (3-aminopropyl)triethoxysilane (APTES)and impregnation with polyethylenimine (PEI). Pillared materials could be loaded with up to 50 wt% PEI. PEI-impregnated pillared adsorbents were tested for CO2 adsorption at 298 and 348 K and CO2/N2 adsorption at 348 K using a Magnetic Suspension Balance equipped with a mixture gas dosing (Rubotherm, Germany). Langmuir and Sips models were used to fit monocomponent and mixture experimental data, considering two different sites for CO2 adsorption. At 1 bar, 50PEI-SiFe (loaded with 50 wt% PEI) adsorbed 2.5 and 3.6 mmol CO2 g−1 at 298 and 348 K, respectively and exhibited an extremely high CO2/N2 selectivity (above 150 mol CO2/mol N2 at 348 K). Nevertheless, PEI loaded adsorbents still exhibit a lower amine efficiency as compared to APTES-grafted counterparts, due to diffusion restrictions caused by the high viscosity of the impregnated polymer.

Using Robust-DEA optimization approach to analyze performance and efficiency of a mine in north of Iran

Using Robust-DEA optimization approach to analyze performance and efficiency of a mine in north of Iran

Effect of Amine Structure on CO2 Adsorption of Modified Poly(ethyleneimine)-Impregnated Mesostructured Silica Sorbents

Abstract Poly(ethyleneimine) (PEI) was modified to study the effect of amine type and introduced hydroxy groups on its ability to capture carbon dioxide. Amines were impregnated in as-synthesized mesostructured silica (MSU-F) to fabricate solid amines, and the resulting samples were characterized via 13C nuclear magnetic resonance spectroscopy and diffuse reflectance infrared Fourier transform spectroscopy. Nitrogen contents, structural properties, adsorption capacity, and sorbent durability during CO2 adsorption/desorption processes were measured to study the CO2 sorption performances of the sorbents. Reaction between PEI and propylene oxide (PO) altered the ratio of primary, secondary, and tertiary amines and also produced hydroxy groups on amine molecules. With a specific reactant ratio, a modified amine-impregnated sorbent (M-EP10) showed a CO2 adsorption capacity and amine efficiency of 13.90 wt % and 0.37, respectively, which were higher than that of the pristine PEI-impregnated sorbent. The new adsorbents also showed excellent stability in cyclic adsorption–desorption operations, even under pure CO2 desorption conditions in which commercial PEI adsorbents are known to lose CO2 adsorption capacity owing to urea formation.

Effect of amine double-functionalization on CO2 adsorption behaviors of silica gel-supported adsorbents

Amine double-functionalized adsorbents were fabricated using silica gel as supports and their capabilities for CO2 capture were examined. Aminopropyltrimethoxysilane (1N-APS), and N1-(3-trimethoxysilylpropyl)diethylenetriamine (3N-APS) were used as grafted amine compounds, and tetraethylenepentamine and polyethyleneimine were used as impregnated species. The influence of double-functionalization method on the CO2 adsorption performance and textural properties of adsorbents was investigated. The adsorption capacity, the amine efficiency, and the thermal stability of double-functionalized sorbents depend strongly upon molecular variables associated with two different functional states (i.e., chemically grafted and physically impregnated amines). The temperature dependence of adsorption isotherms reveals that the CO2 adsorption behavior in the double-functionalized adsorbents follow the diffusion limitation model proposed by Xu et al. (Energy Fuels 16:1463–1469, 2002) where the CO2 adsorption is helped by the diffusion of impregnated amines. It is also found that the adsorption isotherm in the double-functionalized sorbent system with a proper choice for grafted and impregnated amines is nearly independent of temperature, which may offer a novel means to fabricate practically useful sorbents that can be used in a wide range of temperature without loss of CO2 adsorption capacity.

Polyethylenimine Functionalized As-Synthesized KIT-6 Adsorbent for Highly CO2/N2 Selective Separation

The present study targeted the synthesis of CO2 adsorbent by impregnation of DETA, TEPA, PEHA, and polyethylenimine in KIT-6 with a confiscated structure directing agent in minimum time and energy. The adsorbents were characterized and revealed the influence of polyethylenimine with CO2 at a wide range of temperatures. An examination by TGA confirmed that PluronicP123 present in adsorbent enhances its thermal stability and acts as a carrier for CO2 to the inner layer of polyethylenimine during adsorption. CO2 sorption capacity of the adsorbent was found to be dependent on the polyethylenimine loading, temperature, pressure, and the surfactant PluronicP123. At higher temperatures, adsorbents showed a positive impact for CO2 adsorption; however, a negative effect was exhibited in amine efficiency. The sorption capacity decreased with increasing the molecular weight of polyethylenimine following the order PEI-25K (66 mg CO2/g) < PEI-800 (114 mg CO2/g) < TEPA (124 mg CO2/g) < PEHA (139 mg CO2/g) at 75 °C. How...

Reuse and recycling of amine-functionalized silica materials for CO 2 adsorption

Abstract The reuse and recycling of amine-silica materials as CO2 adsorbents were investigated for understanding their industrial viability. CO2 adsorbents were obtained by grafting of diethylenetriamine (DT) or impregnation of polyethyleneimine (PEI) onto SBA-15 silica. CO2 desorption conditions were evaluated, optimizing the time and temperature to reduce energy costs. In all cases, conditions as mild as 90 °C and 90 min were enough to completely remove all CO2 adsorbed. After that, a number of adsorption-desorption cycles at 110 °C for DT (60 min) and PEI (75 min) samples were carried out in order to study their cyclability. The recycling of CO2 adsorbents after their lifespan was studied by analysing the physicochemical properties and CO2 uptake of recycled samples obtained by calcination and subsequent re-functionalization with DT or PEI. Materials obtained after grafting the calcined samples exhibited progressively thicker silica walls and lower silanol surface concentration, yielding a smaller amine efficiency during CO2 capture. On the contrary, materials obtained after impregnating the calcined samples maintained their CO2 adsorption properties even after 6 cycles, without significant changes in their silica structure or amine efficiency for CO2 adsorption.

Amine tethered pore-expanded MCM-41: A promising adsorbent for CO 2 capture

The current work investigates the influence of pore size as well as pore volume of MCM-41 supports on amine tethering. Initially, monoamine tethering on MCM-41-3 as well as MCM-41-30 is carried out under dry conditions to screen the best support. The CO2 adsorption capacity and amine efficiency results revealed the beneficial effect of utilizing MCM-41-30, which is a pore-expanded support fabricated by our research group in a cost-effective manner for amino silane tethering. In order to increase the amine loading and further enhance the CO2 uptake in the important low pressure regime (0.1–0.2 bar), wet grafting process is followed for amino silane tethering on MCM-41-30 support. The present work also elucidates the performance of amine tethered MCM-41-30 in terms of post combustion CO2 capture metrics such as (i) CO2 adsorption capacity (ii) amine efficiency (iii) operating window (iv) CO2 adsorption kinetics (v) selectivity (vi) cyclic adsorption-desorption studies and (vii) cost. Comparative analysis of the same with other adsorbents such as activated carbon, zeolites, metal organic frameworks, amine impregnated and amine tethered mesoporous silica is highlighted to rank the performance for post combustion CO2 capture application. The mono and triamine tethered MCM-41 adsorbents developed in the current work, exhibited a maximum adsorption capacity of ∼1.2 and ∼2.1 mmol/g (75 °C, 0.2 bar) respectively. This in turn, indicated that MCM-41-30 support developed herein serves as a promising support for amine tethering application and demonstrates effective CO2 capture characteristics.