Search

In this paper, the sorption of NH3, H2O, SO2 and CO2 was tested for several selected inorganic materials. The tests were performed on samples belonging to two topologies of materials, faujasite (FAU) and framework-type MFI, the structures of which differ in pore size and connectivity. All sorbates are important in terms of reducing their emissions to the environment. They have different chemical nature: basic, alkaline, and acidic. They are all polar in structure and composition and two of them (ammonia and water vapor) can form hydrogen bonds. These differences result in different interactions with the surface of the adsorbents. This paper presents experimental data and proposes a mathematical description of the sorption process. The best fit of the experimental data was obtained for the Toth and GAB models. The studies showed that among the selected samples, faujasite has the best sorption capacity for ammonia and water vapor, while the best sorbent for sulfur dioxide is the MFI framework type. These materials behave like molecular sieves and can be used for quite selective adsorption of relevant gases. In addition, modification of the faujasite with organic silane resulted in a drastic reduction in the surface area of the sorbent, resulting in significantly lower sorption capacities for gases. [ABSTRACT FROM AUTHOR]

Abstract: CVD (chemical vapor deposition) procedures were investigated by using a counter diffusion CVD method. The effects of silica precursors on the hydrogen permeation properties of the silica membranes were discussed. 5 types of silica alkoxides (tetramethylorthosilicate (TMOS), methyltrimethoxysilane (MTMOS), propyltrimethoxysilane (PTMOS), dimethyldimethoxysilane (DMDMOS), and trimethylmethoxysilane (TMMOS)) were employed as the silica precursors; they have different numbers of methyl groups. Hydrogen permeance through the DMDMOS membrane prepared at 500°C was 9.0 × 10–7 mol m–2 s–1 Pa–1, and H2/N2 selectivity was 920. Activation energy of H2 permeation through the silica membrane prepared from TMOS was 10.5kJ mol-1 that was the maximum among the 5 types of the silica precursor. This indicates dense silica layer can be obtained from TMOS. Thus, TMOS was employed for the further Li4SiO4 preparation. High temperature CO2 permselective membranes were successfully prepared by using Li4SiO4 as a CO2 selective layer. Pinholes of the Li4SiO4 layer was filled by the CVD post treatment at 600°C. CO2/N2 permselectivity was 1.2 at the 600°C permeation test. The CO2 permeance ratio is higher than the Knudsen diffusion difference. Thus, this selectivity was explained by the CO2 selective adsorption on the Li4SiO4 layer. [Copyright &y& Elsevier]

Abstract: High temperature CO2 separation is effective for the efficient CO2 reduction. Li4SiO4 is one of the high temperature CO2 adsorbents. In this study, a Li4SiO4 thin membrane was developed by using a novel solid state conversion method. Li4SiO4 membranes were successfully prepared on a porous alumina substrate at 600°C conversion from mesoporous silica as silica source. Mesoporous silica was better silica source to obtain Li4SiO4 at the low temperature conversion method compared with MFI zeolite, fumed silica and colloidal silica. CO2/N2 permselectivity was 0.85 at 600°C that is higher than the Knudsen diffusion difference. Thus, Li4SiO4 layer showed CO2 permselectivity at 600°C. It was important to use the mixtures of Li2CO3 and K2CO3 to fill the pinholes of the Li4SiO4 membrane. N2 permeance through the Li4SiO4 membrane decreased to 1.8 x 10-9 mol m-2 s-1 Pa-1 from 3.9 x 10-7 mol m-2 s-1 Pa-1 by the addition of the mixtures of Li2CO3 and K2CO3. [Copyright &y& Elsevier]

Thin pure-silica chabazite (Si-CHA) membranes have been synthesized by using a secondary growth method on a porous silica substrate. A CO2 permeance of 2.62 × 10−6 mol m−2 s−1 Pa−1 with a CO2/CH4 permeance ratio of 62 was obtained through a Si-CHA membrane crystallized for 8 h using a parent gel of H2O/SiO2 ratio of 4.6. The CO2 permeance through the Si-CHA membrane on a porous silica substrate was twice as high as that through the membrane synthesized on a porous alumina substrate, which displayed a similar zeolite layer thickness. [ABSTRACT FROM AUTHOR]

An amorphous silica membrane with an excellent hydrogen/nitrogen (H2/N2) permselectivity of >10 000 and a He/H2 permselectivity of 11 was successfully synthesized on a γ-alumina (γ-Al2O3)-coated α-alumina (α-Al2O3) porous support by counter diffusion chemical vapor deposition using tetramethylorthosilicate and oxygen at 873 K. An amorphous silica membrane possessed a high H2 permeance of >1.0 × 10−7 mol·(m2·s·Pa)−1 at ≥773 K. The dominant permeation mechanism for He and H2 at 373–873 K was activated diffusion. On the other hand, that for CO2, Ar, and N2 at 373–673 K was a viscous flow. At ≥673 K, that for CO2, Ar, and N2 was activated diffusion. H2 permselectivity was markedly affected by the permeation temperature, thickness, and pore size of a γ-Al2O3 mesoporous intermediate layer. [ABSTRACT FROM AUTHOR]

We report here on our thermal and hydrothermal investigations comparing mesoporous γ-Al2O3 membrane with single and double dopant membranes prepared by the sol–gel method. Improvements in the hydrothermal stability of mesoporous γ-Al2O3 by transition (Ga3+) or rare-earth (La3+) cations are discussed, along with the effectiveness of double dopant (Ga3+–La3+). The amounts of Ga2O3 oxide used varied between 0.0 and 30 mol% and those of La2O3 between 6 and 15 mol%. The thermal and hydrothermal (up to 75% steam) stability of nine types of membranes fabricated on an asymmetric porous α-Al2O3 support by means of a dip-coating process was characterized by H2 gas permeation at 500°C. By conducting tests with wide variations in dopant concentrations, material characterizations, and gas permeance performance, we have been able to optimize the key parameters for hydrothermally stable systems. [ABSTRACT FROM AUTHOR]

The development of acid separation membranes is important. Silica-based reverse osmosis (RO) membranes for sulfuric acid (H2SO4) solution separation were developed by using a counter diffusion chemical vapor deposition (CVD) method. Diphenyldimethoxysilane (DPhDMOS) was used as a silica precursor. The deposited membrane showed the H2SO4 rejection of 81% with a total flux of 5.8 kg m−2 h−1 from the 10−3 mol L−1 of H2SO4. The γ-alumina substrate was damaged by the permeation of the H2SO4 solution. In order to improve acid stability, the silica substrates were developed. The acid stability was checked by the gas permeation tests after immersing in 1 mol L−1 of the H2SO4 solution for 24 h. The N2 permeance decreased by 11% with the acid treatment through the silica substrate, while the permeance decreased to 94% through the γ-alumina substrate. The flux and the rejection through the DPhDMOS-derived membrane on the silica substrate were stable in the 70 wt % H2SO4 solution. [ABSTRACT FROM AUTHOR]

Hydrogen (H 2 ) has become one of the promising alternative clean energy resources. Membrane technology is a potential method for hydrogen separation or production. This study aims to develop a new carbon membrane for hydrogen separation or production. Moreover, the permeation behavior of H 2 , CO 2 , and CH 4 through a hollow fiber composite carbon membrane derived from P84 co-polyimide and with incorporation of zeolite composite carbon (ZCC) was also examined. ZCC was synthesized via the impregnation method of sucrose into zeolite-Y pores, followed by carbonization at 800 °C. Thus, this filler has a high surface area, high microporosity, ordered pore structure, and low hydrophilicity. The presence of zeolites in ZCC is predicted to increase certain gases' affinity for the membrane. Various heating rates (1-5 °C/min) were applied during pyrolysis to understand the effect of the heating rate on the pore structure and H 2 /CO 2 and H 2 /CH 4 gas separation performance. Moreover, gas permeation was evaluated at various temperatures (298-373 K) to study the thermodynamic aspect of the process. A characteristic graphite peak was detected at 2θ ∼ 44° in all carbon samples. Scanning electron microscopy (SEM) observations revealed the void-free surface and the asymmetric structure of the carbon membranes. During the permeation test, it was found that gas permeation through the membrane was significantly affected by the temperature of the separation process. The highest permeability of H 2 , CO 2 , and CH 4 was detected on the composite carbon membrane at a 3 °C/min heating rate with a permeation temperature of 373 K. The thermodynamic study shows that CO 2 and H 2 have lower activation energies compared to CH 4 . The transport mechanism of the membrane involved adsorption and activated surface diffusion. The permeation temperature has a large impact on the transport of small penetrants in the carbon matrix., Competing Interests: The authors declare no competing financial interest., (© 2021 The Authors. Published by American Chemical Society.)