In view of the promising applicability of adsorption to the capture of CO
2
from post-combustion gases, the use of mesoporous silica functionalized with 3-aminopropyltriethoxysilane (APTES) was ...studied as adsorbent in a fixed bed for CO
2
–N
2
separation under thermal swings. Characterization of the adsorbent performed before and after functionalization indicated that amine grafting was successful. Additionally, CO
2
adsorption on a magnetic suspension balance showed a significant increase in uptake of the APTES-functionalized sample over the support, mainly at low relative pressures. Relatively high values of adsorption enthalpy suggest the occurrence of chemical adsorption attributed to CO
2
bonding with the amines. Breakthrough curves were measured for pure CO
2
, N
2
and the CO
2
/N
2
(15/75% v/v) mixture, which showed good agreement with respect to the uptake of the individual gases, as determined from gravimetric tests. Full CO
2
desorption from the bed required a temperature rise, which suggests that these materials may be suitable for TSA cyclic processes. A temperature of 90 °C was enough for a complete regeneration of the adsorbent during the desorption phase under dynamic conditions. The material showed very stable behavior after 20 successive cycles.
We propose a pore size analysis methodology for carbonaceous materials that reduces complexity while maintaining the significant elements of the structure-property relationship. This method chooses a ...limited number of representative pores, which will constitute a simplified kernel to describe the pore size distribution (PSD) of an activated carbon. In this study we use the representative pore sizes of 7.0, 8.9, 18.5, and 27.9 Å and N
isotherms at 77.4 K to determine the PSD which is later applied to predict the adsorption equilibrium of other gases. In this study we demonstrate the ability to predict adsorption of different gas molecules on activated carbon from the PSD generated with representative pores (PSD
). The methodology allows quick solutions for large-scale calculations for carbonaceous materials screening, in addition to make accessible an easily understood and prompt evaluation of the structure-property relationship of activated carbons. In addition to the details of the methodology already tested in different fields of application of carbonaceous materials, we present a new application related to the removal of organic contaminants in dilute aqueous solutions.
Growing concern about climate change has been driving the search for solutions to mitigate greenhouse gas emissions. In this context, carbon capture and utilization (CCU) technologies have been ...proposed and developed as a way of giving CO
2
a sustainable and economically viable destination. An interesting approach is the conversion of CO
2
into valuable chemicals, such as methanol (MeOH) and dimethyl ether (DME), by means of catalytic hydrogenation on Cu-, Zn-, and Al-based catalysts. In this work, three catalysts were tested for the synthesis of MeOH and DME from CO
2
using a single fixed-bed reactor. The first one was a commercial CuO/γ-Al
2
O
3
; the second one was CuO-ZnO/γ-Al
2
O
3
, obtained
via
incipient wetness impregnation of the first catalyst with an aqueous solution of zinc acetate; and the third one was a CZA catalyst obtained by the coprecipitation method. The samples were characterized by XRD, XRF, and N
2
adsorption isotherms. The hydrogenation of CO
2
was performed at 25 bar, 230°C, with a H
2
:CO
2
ratio of 3 and space velocity of 1,200 ml (g cat · h)
−1
in order to assess the potential of these catalysts in the conversion of CO
2
to methanol and dimethyl ether. The catalyst activity was correlated to the adsorption isotherms of each reactant. The main results show that the highest CO
2
conversion and the best yield of methanol are obtained with the CZACP catalyst, very likely due to its higher adsorption capacity of H
2
. In addition, although the presence of zinc oxide reduces the textural properties of the porous catalyst, CZAWI showed higher CO
2
conversion than commercial catalyst CuO/γ-Al
2
O
3
.
An experimental investigation on the synthesis of zeolite A, based on the treatment of fly ash and controlled extraction of silica and alumina from coal fly ash, combined with the adjustment of the ...reaction mixtures aiming minimum amount of secondary phases, is presented herein. The precursor samples of fly ash and the obtained zeolites were widely characterized considering different techniques including powder X-ray diffraction, infrared vibrational spectroscopy, scanning electron microscopy, and thermogravimetric analysis. A new pore characterization technique that combines experimental CO₂ isotherms at 273 K and molecular simulation was specially developed for this system. The synthesized zeolites presented zeolite A as the major phase, with high crystallinity and low degree of defects in the supercages. The treated fly ashes affected the synthesis yield and the properties of the obtained zeolites, which proved to be efficient in decreasing the viscosity of the modified asphalt cement, during heating, contributing to improve its workability.
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•High-quality zeolite A is successfully obtained from fly ash.•Fly ash is subjected to different treatments prior to zeolite syntheses.•A novel pore characterization method based on CO₂ isotherms and molecular simulation is applied.•The obtained zeolite acts decreasing the work temperature of mix asphalt.
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•HMS were synthesized with different ethanol/water ratio (EWR).•Increasing EWR shifts the pore size distributions to narrow pore sizes.•The morphology of the samples evolves to a ...spherical arrangement as EWR increases.•The synthesized samples are more likely to be used as primary dryers.•The samples have characteristics suitable for atmospheric water harvesting.
Hollow microspheres of silica were synthesized with different ethanol/water ratios (0.4, 1.0, 2.0 and 6.0) to assess the influence of this parameter on the morphology/porosity of the samples and thus on their water adsorption capacity. The samples were characterized by N2 at 77 K and CO2 at 273 K adsorption isotherms, scanning electron microscopy, transmission electron microscopy and water vapor isotherms at 298, 313 and 328 K. The textural properties of the samples were slightly different: as the ethanol/water ratio increases, the pore volume and specific surface area decrease and the structure of the samples evolves into a well-defined spherical arrangement. In addition, water adsorption capacity of the samples was similar to that of commercial adsorbents used for gas drying at high relative pressures, but significantly lower at low relative pressures. Moreover, varying of the ethanol/water ratio did not lead to a noticeable improvement in the water adsorption capacity at low relative pressures and hence these samples are not suitable for deep gas drying. On the other hand, as they require less energy to be regenerated, HMS are alternatives to be considered in less demanding situations, such as coarse drying and water harvesting from air.
•A film of chitosan and natural zeolite has been evaluated for ethylene release control.•Ethylene equilibrium of adsorption was measured gravimetrically.•Ethylene adsorption capacity was affected by ...zeolite amount and film drying process.•Chitosan/zeolite film chose for ethylene is based on the product to be packed.
Ethylene is the hormone responsible for the development and ripening of fruits and vegetables. Thus, in order to extend the postharvest shelf life, its accumulation should be avoided. Films, dense and porous, composed of chitosan/zeolite (CZ), were obtained using chitosan as support for clinoptilolite zeolites. These films were characterized by nitrogen and carbon dioxide adsorption isotherms, water vapor permeability and ethylene adsorption capacity. Zeolites distribution and the development of the pores were observed by scanning electron microscopy. Films were dried (partially or totally) by a convective process, followed or not by lyophilization. Lyophilized-CZ (with 93 % zeolite (CZ93 L) showed adsorption capacity similar to that of pure zeolite regenerated at 90 °C (ZR90) and higher than CZ93. Dense-chitosan films (DCF), porous-chitosan films (PCF) and CZ33 (33 % zeolite) exhibited small amounts of adsorbed ethylene when compared to the other materials. Based on these results, the chitosan/zeolite films may be viable for packaging applications.
•Ultramicropores exert a strong influence on the adsorption capacity of the materials.•A method to block ultramicropores has been proposed based on molecular simulation.•The ultramicropore blockage ...causes a drastic drop in H2S retention.•The ultramicropore blockage affects not only physisorption, but also chemisorption.•Ultramicropores immobilize and then redistribute molecules to the pore network.
The pore distribution in activated carbon is crucial for its performance on adsorption processes. In desulfurization applications, the literature highlights the importance of pores from 5 to 10 Å. However, little is known and reported about the range of ultramicropores smaller than 4 Å, which has been found in commercial samples used for H2S retention. In order to clarify the influence of this fraction of pores on the H2S retention of typical biogas mixtures, measurements of multicomponent adsorption of hydrogen sulfide in the presence of carbon dioxide for activated carbon samples further impregnated with potassium hydroxide have been performed in column dynamics. Molecular simulation, XRF analysis and textural characterization were applied to aid the study. Results have shown that the H2S retention capacity in the presence of CO2 decreased significantly mainly in the impregnated samples. The degree of reduction in H2S retention indicates that ultramicropores can be of substantial importance through a synergistic immobilizing effect of H2S molecules. The better understanding of such an effect could improve the development of more efficient adsorbents for chemical industries.
Coprecipitation is one of the most practical methods used to synthesize ferrite nanoparticles. Fine characteristics of these materials can be improved by means of a series of modifications in the ...synthesis method. In this paper we present a study of influence of glycerol as structure directing and stabilizing agent in the synthesis of zinc ferrite nanoparticle, exploring its chelating capacity and oxidation. The studied materials include two series of zinc ferrite samples and its precursors obtained with or without glycerol throughout different stages during the synthesis process. The structural and morphological characteristics were evaluated by means of different techniques such as X-ray diffraction, Fourier transformed infrared spectroscopy, scanning and transmission electron microscopy and thermal analysis. The oxidation of glycerol was determined by high-performance liquid chromatograph. The obtained results demonstrate that zinc ferrite crystals synthesized in the presence of glycerol are initially bigger than those synthesized in absence of it, but according to the oxidation process they tend to decrease giving rise to intermediate phases. Interestingly, these samples grow back during more advanced stages and become structurally better organized, compared to the series of samples produced in absence of glycerol. These results indicate that glycerol is capable to modify the synthesis route of zinc ferrite nanoparticles via coprecipitation, acting directly over the size and morphology of the crystals.
Microporous activated carbon samples were prepared from coconut shells (low-cost lignocellulose waste), using chemical activation with zinc chloride followed by physical activation. Textural ...characterization was performed using nitrogen adsorption at 77
K. The sample that presented the best characterization results was then evaluated for methane adsorption at pressures between 0.1
MPa and 7
MPa and temperatures in the range 283–333
K. At 298
K and 40
bar, a capacity of ca. 122
mg of methane/g of carbon (80
v/v) was observed, just short of the target established in Brazil for ANG in remote sites transportation (100
v/v). These results suggest that activated carbons prepared from coconut shells, using chemical activation followed by physical activation, may be further developed as potential adsorbents for natural gas storage applications.
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