Removal of minor concentration of H2S on MDEA-modified SBA-15 for gas purification

A promising adsorbent for H₂S removal of minor concentration for gas purification was prepared by synthesizing and modifying the mesoporous molecular silica of SBA-15 with methyl-diethyl-amine (MDEA). Removal performance of minor concentration of H₂S on the adsorbent was experimentally studied in a dynamic setup. The adsorbents showed good performance in removing H₂S from gas steams. The loaded amines did not change the ordered structure of SBA-15, but enhanced its removing H₂S. The adsorbents were characterized by X-ray powder diffraction (XRD) and N₂ adsorption/desorption. Effect of the R (the loading ratio) of MDEA, effect of initial H₂S concentration and effect of moisture on removal performance of H₂S were studied respectively. With increase of the R of MDEA, the H₂S removal performance of the adsorbent was improved obviously. When R of MDEA was 0.6, the removal performance was optimum. Initial H₂S concentration had a large effect on the removal performance. Both breakthrough capacity and saturation capacity increased as the initial H₂S concentration increased. In the presence of moisture, the experimental results showed the improvement in the removal performance of H₂S. In addition, not only was the adsorbent regenerable by purging with the purified gas, but also the removal performance was stable in removal adsorption cycles.     

Amine modified mesocellular siliceous foam (MCF) as a sorbent for CO2

Adsorption is considered a promising method for carbon capture. CO₂ adsorbents take a variety of forms - but one approach is to fill mesoporous substrates with a polymeric CO₂ selective sorbent. SBA-15 and mesocellular siliceous foam (MCF) are high pore volume, high surface area ordered mesoporous materials for which modification with amine should result in high capacity, highly selective adsorbents. SBA-15 and MCF were separately loaded with approximately one pore volume equivalent of linear polyethyleneimine (PEI) (M_w = 2500) or branched PEI (M_n = 1200). CO₂ adsorption/desorption isotherms under dry CO₂ were obtained at 75, 105 and 115 °C. The CO₂ adsorption/desorption kinetics were improved with temperature, though the CO₂ capacities generally decreased. The adsorption capacity for MCF loaded with branched PEI at 105 and 115 °C were 151 and 133 mg/g adsorbent, respectively (in 50% CO₂/Ar, 20 min adsorption time). These are significantly higher than the adsorption capacity observed for SBA-15 loaded with branched PEI under same conditions, which were 107 and 83 mg/g adsorbent, respectively. Thus the results indicate that, on a unit mass basis, amine modified MCF's are potentially better adsorbents than amine modified SBA-15 for CO₂ capture at modestly elevated temperature in a vacuum swing adsorption process.     

混合胺改性SBA-15的二氧化碳吸附特性

为实现廉价高效的二氧化碳捕集，新型燃烧后CO₂捕集固体吸附材料的设计和开发具有重要的研究意义。为提高CO₂吸附量，胺功能化改性吸附剂的方法主要有湿浸渍和表面嫁接。基于此，提出了“混合胺”修饰的概念，把湿浸渍和表面嫁接两种改性技术结合起来。把3-氨丙基三甲氧基硅烷（APTS）嫁接到分子筛SBA-15孔道表面，再把聚乙烯亚胺（PEI）浸渍到载体孔道的间隙，制备出高密度胺功能化的CO₂吸附剂。主要考察了不同含量的PEI和APTS功能化SBA-15的结构性能、CO₂吸附量及胺吸附效率。CO₂吸附结果表明，混合胺功能化SBA-15吸附主要依赖于动力学扩散。其中，SBA-15-（APTS-0.5-PEI-50），SBA-15-（APTS-1.0-PEI-50）和SBA-15-（APTS-2.0-PEI-30）在75℃时具有很好的吸附潜力。混合胺功能化SBA-15的胺吸附效率介于单纯嫁接和单纯浸渍的胺功能化SBA-15之间。     

Adsorption of binary CO2/CH4 mixtures using carbon nanotubes: Effects of confinement and surface functionalization

Effect of confinement and surface functionalization in carbon nanotubes (CNTs) on the competitive adsorption of a binary CO₂/CH₄ mixture has been investigated by grand canonical Monte Carlo simulations. Adsorption using CNTs with different functionalization arrangements, different diameters, different functionalization degrees, and different functional groups, such as –COOH, –CO, –OH, –CH₃, is investigated. Effects of (a) the pore textural properties, such as pore size and accessible surface area, and (b) the gas–adsorbent interaction, especially the electrostatic interaction, are discussed. From these results, we discuss the impact that variables such as confinement and surface functionalization have on the performance for CO₂ separation.     

Effects of different structure-directing agents (SDA) in MCM-41 on the adsorption of CO2

CO₂ capturing technologies have attracted significant attention in order to limit emissions and reduce their negative effect on the environment. Mesoporous silica materials (MCM-41) are easily recyclable, affordable, and thermally and mechanically stable, providing added benefits in CO₂ capture. However, further studies are necessary to characterize the effects of MCM-41 pore size, adsorption temperature and surface silylation on CO₂ adsorption efficiency. In this work, mesoporous silica is synthesized using alkyltrimethylammonium bromide with different chain lengths (C_nH_2n + 1 N(CH₃)₃Br, n = 14, 16 and 18) as structure-directing agents, and the adsorption capacity of CO₂ on TTMCM-41 (C₁₇H₃₈NBr), CTMCM-41 (C₁₉H₄₂NBr), DTMCM-41(C₂₁H₄₆NBr) samples was measured gravimetrically at room temperature and pressure up to 40 bar. The silica structures were characterized by X-ray diffraction (XRD), nitrogen adsorption/desorption, Fourier transform infrared spectroscopy, thermogravimetric analysis, scanning electron microscopy and transmission electron microscopy (TEM). The XRD, N₂ adsorption–desorption and TEM measurements indicated the presence of a well-ordered hexagonal array with uniform mesostructures. The mesoporous silica obtained, denoted as TTMCM-41, CTMCM-41 and DTMCM-41, had distinct physical properties, such as BET surface area, hexagonal unit cell, pore volume, pore diameter and pore wall thickness. CTMCM-41 exhibited an adsorption capacity (0.58 g CO₂/g adsorbent) of more than DTMCM-41 (0.48 g CO₂/g adsorbent) and TTMCM-41 (0.42 g CO₂/g adsorbent). The results suggest that CTMCM-41 can be a better mesoporous adsorbent for CO₂ adsorption .     

Adsorption of Eu(III), Th(IV), and U(VI) by mesoporous solid materials bearing sulfonic acid and sulfamic acid functionalities

ABSTRACT

SBA-15 mesoporous materials modified by sulfonic acid and sulfamic acid functionalities, abbreviated as SBA-15/SO₃H and SBA-15/NHSO₃H, were synthesized and applied for the removal–separation of Eu(III), Th(IV), and U(VI). SBA-15/NHSO₃H showed an excellent selectivity toward U(VI), while SBA-15/SO₃H was more efficient adsorbent for Eu(III) and Th(IV). It was found that in the presence of KNO₃ (1 mol L^?1), the separation of Eu(III)/Th(IV) from their mixtures is possible. The results of the sorption behavior indicated a high adsorption capacity toward U(VI) and Th(IV) ions (140.5 and 106.7 mg g^?1, respectively) and ultrafast kinetics (15 min) in Eu(III) adsorption.     

Removing H2S from Biogas Using Sorbents for Solid Oxide Fuel Cell Applications

Desulfurization of biogas is essential for its application in solid oxide fuel cells. The influence of CH₄, CO₂, H₂, and O₂ as well as the effect of moisture onto desulfurization performance of an activated carbon, an adsorbent based on a CuO‐MnO mixture, and a zeolite adsorbent were analyzed. The use of moisturized gas had no negative influence on the H₂S adsorption performance of activated carbon. The CuO‐MnO sorbent showed the best performance, but the presence of moisture had a negative influence. The performance of zeolite dropped for three gas mixtures, while for two other mixtures moisture had little to no influence on H₂S adsorption performance.     

A Procedure for the Development of a Low-Cost Treatment Technology of Raw Biogas for Application in a Gas Engine. A Case of Sizing a Carbon Dioxide Removal Unit

A test laboratory (lab) for carbon dioxide (CO₂) adsorption from raw biogas onto a novel adsorbent was used to size a CO₂ removal unit in the development of a low-cost biogas treatment technology. The novel adsorbent was made out of clay and burnt maize cob particles, impregnated with hot natural alkaline solution of pH 10 ± 0.5, degassed, and then activated at a temperature of 250°C, thereby making it low cost. The activated absorbents were spherical balls of average diameter 17 mm, density 410 kg/m³, and surface area 128 m²/g, and contained exchangeable ions due to the presence of clay and increased pore sizes due to impregnation, degassing, and activation. The effect of pressure drops on CO₂ removal, the breakthrough curve, and the absorption isotherm were studied. As a result, reduced pressure drops enhanced CO₂ removal and 102 Pa/m was the suitable pressure drop; pressure drops less than 102 Pa/m were impractical because the biogas did not exit. The breakthrough curve was in typical s-shape and thus satisfied its use for determining the adsorption rate constant (k₁) to be 0.001952 l/mg s and the maximum percent of CO₂ removal to be 87.8% at 102 Pa/m pressure drop and temperatures ranging from 20 to 28°C. The isotherm was found to closely conform to the definition of the Freundlich equation with the Freundlich coefficient of 0.01809 (l/g)ⁿ, where n = 1.37 at the same temperature range. Therefore, the determined k₁ and fitted Freundlich isotherm can be used to size the CO₂ adsorption unit under these conditions.     

Promoting the CO2 adsorption in the amine-containing SBA-15 by hydroxyl group

Novel CO₂ capturer with a high efficiency is fabricated through dispersing the amine mixture of tetraethylenepentamine (TEPA) and diethanolamine (DEA) or glycerol within the as-synthesized mesoporous silica SBA-15, and the resulting sample is characterized by low angle X-ray diffraction and N₂ adsorption to evaluate the distribution of the guest. The influence of hydroxyl group on the CO₂ adsorption capacity of the composite is investigated by using CO₂-TPD and TG–MS techniques. The hydroxyl group of the P123 ((EO)₂₀(PO)₇₀(EO)₂₀, template preserved in as-synthesized SBA-15) and the guest could promote the capture of CO₂ by the amine through changing the interaction mechanism. In addition, the presence of hydroxyl group promotes the formation of the intermediate between CO₂ and the amine with a lower thermal stability hence the CO₂ trapped by the composite is easier to be desorbed and thus the regeneration of adsorbent is facilitated. Therefore, using this mixed amine (TEPA and DEA) modified as-synthesized SBA-15 as CO₂ capturer not only saves the energy for removal of template, but also cut down the cost in the preparation and regeneration of CO₂ capturer, which is critical in CO₂ separation and capture.     

Bulk Separation and Purification of CH4/CO2 Mixtures on 4A/13X Molecular Sieves by Using Pressure Swing Adsorption

Abstract

Results of bulk gas separation and purification of a CH₄/CO₂ mixture by pressure swing adsorption (PSA) are reported. Bulk gas separation and purification of CH₄/CO₂ mixture have direct application in landfill gases and tertiary oil recovery and effluent separations. ZMS-13X/4A with calculated kinetic selectivities equal to 0.604 and 0.601, respectively, were used as sorbents. The step times corresponding to various flow rates and compositions were chosen to allow sorption of CO₂ but preclude penetration of CH₄ into the micropores. By using a simulated biogas mixture (66% CH₄ and 34% CO₂) as a feed, the results for bulk gas separation for a PSA cycle between 1.2–36.0 P_H/P_L ratios over ZMS-13X adsorbent was 95% or more CH₄ in the raffinate, whereas with a 10/90 CH₄/CO₂ feed, purification over ZMS-4A at P_H/P_L ratios of 10–304 gave 85–90% CH₄ at 900 and 1800 mL/min flow rates.     

Non-oxidative thermal degradation of amines: GCMS/FTIR spectra analysis and molecular modeling

Aqueous amino solvents, such as monoethanolamine (ETA/MEA), methyl diethanolamine (MDEA) or amine blends, are the most widely used solvents in commercial CO₂ or acid gas separation applications. These commercial solvents have various disadvantages, such as the possibilities of the solvent to be degraded. This research examines the impact of non-oxidative thermal degradations on the performance of the CO₂ absorption and the degradation mechanism of amine solvents. The impact of degradation was conducted by measuring the CO₂ solubility of solvent that had been heated to 120°C for 2 h. Although the performance of CO₂ absorption was not significantly reduced, the degradation of amines was found. Supported by Fourier Transform Infrared (FTIR) and Gas Chromatography/Mass Spectrometer result, the suspected products of non-oxidative thermal degradation of MDEA were MEA and acetone.     

Separation of CO2 and CH4 on CaX zeolite for use in Landfill gas separation

In this study, adsorption separation of main components of landfill gas, methane (CH₄) and carbon dioxide (CO₂) was carried out. Henry's law constants, limiting heat of adsorption values, pure and binary isotherms for CO₂ and CH₄ were determined for CaX zeolite adsorbent. Pure isotherm data were compared to those for NaX zeolite from previous studies. The CO₂ adsorption capacity of CaX was greater than that of NaX; however, NaX's separation factor was higher. The heat of adsorption for CO₂ for CaX was higher than those for NaX. © 2013 Canadian Society for Chemical Engineering     

Computational screening of porous carbons,zeolites, and metal organic frameworks for desulfurization and decarburization of biogas,natural gas,and flue gas

Eighteen kinds of porous materials from carbons, zeolites, and metal organic frameworks (MOFs) have been extensively investigated for desulfurization and decarburization of the biogas, natural gas, and flue gas by using a molecular modeling approach. By considering not only the selectivity but also capacity, Na‐5A, zeolite‐like MOF (zMOF), and Na‐13X, MIL‐47 are screened as the most promising candidates for removal of sulfide in the CH₄? CO₂? H₂S and N₂? CO₂? SO₂ systems, respectively. However, for simultaneous removal of sulfide and CO₂, the best candidates are zMOF for the natural gas and biogas (i.e., CH₄? CO₂? H₂S system) and MOF‐74‐Zn for the flue gas (i.e., N₂? CO₂? SO₂ system). Moreover, the regeneration ability of the recommended adsorbents is further assessed by studying the effect of temperature on adsorption. It is found that compared to the zMOF and MIL‐47 MOFs, the Na‐5A and Na‐13X zeolites are not easily regenerated due to the difficulty in desorption of sulfide at high temperature, which results from the stronger adsorbent–adsorbate interactions in zeolites. The effect of sulfide concentration on the adsorption properties of the recommended adsorbents is also explored. We observe that the zMOF and MIL‐47 are also superior to the Na‐5A and Na‐13X for desulfurization of gas mixtures containing high sulfide concentration. This is because MOFs with larger pore volume lead to a greater sulfide uptake. The effects of porosity, framework density, pore volume, and accessible surface area on the separation performance are analyzed. The optimum porosity is about 0.5–0.6, to meet the requirements of both high selectivity and uptake. It is expected this work provides a useful guidance for the practical applications of desulfurization and decarburization. © 2013 American Institute of Chemical Engineers AIChE J, 59: 2928–2942, 2013     

Carbon Di-Oxide Removal with Mesoporous Adsorbents in a Single Column Pressure Swing Adsorber

Abstract

A five-step PSA cycle was studied for CO₂ separation from CO₂-N₂ gas mixture in a single column at elevated temperatures using Poly-ethyleneimine (PEI) impregnated mesoporous silica SBA-15 as adsorbent. The PSA cycle study included a strong adsorptive rinse step in which the strongly adsorbed component, i.e., CO₂ was used for rinsing the adsorbent bed in order to increase the purity of CO₂ product. The study indicates that the adsorbent is regenerable under typical PSA conditions. The productivity of the adsorbent studied for CO₂ separation was found to be comparable with commercial zeolite adsorbents as reported in literature.     

Preparation of Core-Shell SAPO-34 Adsorbent on Ceramic Particles; Improvement of CO2 Separation from Natural Gas

Fine crystals of SAPO-34 were synthesized by preparation of sol-gel precursor and hydrothermal process. The produced crystalline phase and the crystal shapes were analyzed by XRD patterns and SEM images. The core-shell adsorbent was prepared by the formation of the fine layer of SAPO-34 on the surface of the inert ceramic particles using the same synthesis parameters and hydrothermal conditions by in situ crystallization. The prepared core-shell SAPO particles were tested in dynamic adsorption experiments of a mixture of 5% CO₂ and 95% CH₄ at 298 K and 0.1 MPa, and their performance was compared with pure powders of SAPO-34 in the same adsorption operational conditions. The longer breakthrough time, sharper breakthrough curves, and higher CO₂ adsorbed amount were observed using core-shell SAPO-34 particles as adsorbent rather than using pure particles of SAPO-34. It is concluded that the production of a thin layer of SAPO-34 on cheap and inert porous ceramic particles is preferred rather than using higher amounts of SAPO-34 powders pelleted or binded with inert material in dynamic adsorption processes for the separation of CO₂ from natural gas.     

A high CO2 permselective mesoporous silica/carbon composite membrane for CO2 separation

Ordered mesoporous silica/carbon composite membranes with a high CO₂ permeability and selectivity were designed and prepared by incorporating SBA-15 or MCM-48 particles into polymeric precursors followed by heat treatment. The as-made composite membranes were characterized by high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD) and N₂ adsorption, of which the gas separation performance in terms of gas permeability and selectivity were evaluated using the single gas (CO₂, N₂, CH₄) and gas mixtures (CO₂/N₂ and CO₂/CH₄, 50/50 mol.%). In comparison to the pure carbon membranes and microporous zeolite/C composite membranes, the as-made mesoporous silica/C composite membranes, and the MCM-48/C composite membrane in particular, exhibit an outstanding CO₂ gas permeability and selectivity for the separation of CO₂/CH₄ and CO₂/N₂ gas pairs owing to the smaller gas diffusive resistance through the membrane and additional gas permeation channels created by the incorporation of mesoporous silicas in carbon membrane matrix. The channel shape and dimension of mesoporous silicas are key parameters for governing the gas permeability of the as-made composite membranes. The gas separation mechanism and the functions of porous materials incorporated inside the composite membranes are addressed.     

Sorption studies of CO<Subscript>2</Subscript>, CH<Subscript>4</Subscript>, N<Subscript>2</Subscript>, CO,O<Subscript>2</Subscript> and Ar on nanoporous aluminum terephthalate [MIL-53(Al)]

Aluminum terephthalate, MIL-53(Al), metal–organic framework synthesized hydrothermally and purified by solvent extraction method was used as an adsorbent for gas adsorption studies. The synthesized MIL-53(Al) was characterized by powder X-Ray diffraction analysis, surface area measurement using N₂ adsorption–desorption at 77 K, FTIR spectroscopy and thermo gravimetric analysis. Adsorption isotherms of CO₂, CH₄, CO, N₂, O₂ and Ar were measured at 288 and 303 K. The absolute adsorption capacity was found in the order CO₂>CH₄>CO>N₂>Ar>O₂. Henry’s constants, heat of adsorption in the low pressure region and adsorption selectivities for the adsorbate gases were calculated from their adsorption isotherms. The high selectivity and low heat of adsorption for CO₂ suggests that MIL-53(Al) is a potential adsorbent material for the separation of CO₂ from gas mixtures. The high selectivity for CH₄ over O₂ and its low heat of adsorption suggests that MIL-53(Al) could also be a compatible adsorbent for the separation of methane from methane–oxygen gas mixtures.     

Synthesis of polyaniline/mesoporous carbon nanocomposites and their application for CO<Subscript>2</Subscript> sorption

Ordered mesoporous carbons (OMC), were synthesized by nanocasting using ordered mesoporous silica as hard templates. Ordered mesoporous carbons CMK-1 and CMK-3 were prepared from MCM-48 and SBA-15 materials with pore diameters of 3.4 nm and 4.2 nm, respectively. Mesoporous carbons can be effectively modified for CO₂ adsorption with amine functional groups due to their high affinity for CO₂. Polyaniline (PANI)/mesoporous carbon nanocomposites were synthesized from in-situ polymerization by dissolving OMC in aniline monomer. The polymerization of aniline molecules inside the mesochannels of mesoporous carbons has been performed by ammonium persulfate. The nanocomposition, morphology, and structure of the nanocomposite were investigated by nitrogen adsorption-desorption isotherms, Fourier Transform Infrared (FT–IR), X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and thermo gravimetric analysis (TGA). CO₂ uptake capacity of the mesoporous carbon materials was obtained by a gravimetric adsorption apparatus for the pressure range from 1 to 5 bar and in the temperature range of 298 to 348 K. CMK-3/PANI exhibited higher CO₂ capture capacity than CMK-1/PANI owing to its larger pore size that accommodates more amine groups inside the pore structure, and the mesoporosity also can facilitate dispersion of PANI molecules inside the pore channels. Moreover, the mechanism of CO₂ adsorption involving amine groups is investigated. The results show that at elevated temperature, PANI/mesoporous carbon nanocomposites have a negligible CO₂ adsorption capacity due to weak chemical interactions with the carbon nanocomposite surface.     

Greenhouse Gas Adsorptivity of Horn-Shaped Carbon Nanotubes over Nitrogen: Equilibrium Study

The synthesis of horn-shaped carbon nanotubes using carbon tetrachloride as carbon source was carried out by solvothermal method at 200°C for 2 h. The scanning and transmission electron microscopic characterization of the obtained product showed the formation of horn-shaped carbon nanotubes with irregular wall structure having inner diameter of ～105 nm and length of ～1 µm. The equilibrium gas adsorption properties of horn-shaped carbon nanotubes derived from carbon tetrachloride were successfully investigated for CO₂, CH₄, and N₂ at 288, 303, and 318 K. Horn-shaped carbon nanotubes possess better CO₂ adsorption capacity (2.53 mmol/g) with high capacity selectivity (14.7) and equilibrium selectivity (59.1) over N₂ at 288 K. The detailed adsorption study with estimation of physical parameters such as Henry's constant and heat of adsorption identifies the horn-shaped carbon nanotubes as a potential adsorbent material in the field of CO₂ storage and separation.     

Preparation of amine-modified SiO<Subscript>2</Subscript> aerogel from rice husk ash for CO<Subscript>2</Subscript> adsorption

Amine-modified SiO₂ aerogel was prepared using 3-(aminopropyl)triethoxysilane (APTES) as the modification agent and rice husk ash as silicon source, its CO₂ adsorption performance was investigated. The amine-modified SiO₂ aerogel remains porous, the specific surface area is 654.24 m²/g, the pore volume is 2.72 cm³/g and the pore diameter is 12.38 nm. The amine-modified aerogel, whose N content is up to 3.02 mmol/g, can stay stable below the temperature of 300 °C. In the static adsorption experiment, amine-modified SiO₂ aerogel (AMSA) showed the highest CO₂ adsorption capacity of 52.40 cm³/g. A simulation was promoted to distinguish the adsorption between the physical process and chemical process. It is observed that the chemical adsorption mainly occurs at the beginning, while the physical adsorption affects the entire adsorption process. Meanwhile, AMSA also exhibits excellent CO₂ adsorption–desorption performance. The CO₂ adsorption capacity dropped less than 10 % after ten times of adsorption–desorption cycles. As a result, AMSA with rice husk ash as raw material is a promising CO₂ sorbent with high adsorption capacity and stable recycle performance and will have a broad application prospect for exhaust emission in higher temperature.