Effect of a Support on the Properties of Zinc Oxide Based Sorbents

We present the comparative analysis of three Zn-based sorbents for the process of sulphur removal from hot coal gas. The sorbents were prepared by a slurry impregnation of TiO2, SiO2 and Al2O3, resulting in complex, multiphase materials, with the dominant phases of Zn2TiO4, Zn2SiO4 and ZnAl2O4, respectively. We have analyzed the effect of supports on the phase composition, texture, reducibility and H2S sorption. We have found that the phase composition significantly influences the susceptibility of the investigated materials to reduction by hydrogen. Zn2TiO4 have been found to be the easiest to reduce which correlates with its ability to adsorb the largest amount of hydrogen sulphide—up to 4.2 gS/100 g—compared to the other sorbents, which absorb up to 2.2 gS/100 g. In the case of Zn2SiO4 and ZnAl2O4, this effect also correlates with reducibility—these sorbents have been found to be highly resistant to reduction by hydrogen and to absorb much less hydrogen sulphide. In addition, the capacity of ZnAl2O4 for H2S adsorption decreases in the subsequent work cycles—from 2.2 gS/100 g in the first cycle to 0.8 gS/100 g in the third one. Computational analysis on the DFT level has shown that these materials show different thermodynamic stability of sulphur sites within the unit cells of the sorbents. For Zn2TiO4 and Zn2SiO4, the adsorption is favorable in both the first and second layers of the former and only the top layer of the latter, while for zinc aluminate it is not favorable, which is consistent with the experimental findings.

Gas molecules (CH4, CO, H2O and H2S) adsorption on VC (001)surface: a first principles study

The first principle plane wave pseudo-potential method based on density functional theory system is used to calculate and simulate the geometric structure, density of states and optical properties of intrinsic VC materials. And we further studied the adsorption performance of small gas molecules (CH4, CO, H2O, H2S) on the surface of VC(001). The most stable adsorption geometry of CH4, CO, H2O and H2S on the intrinsic VC(001) was determined, and the electronic structure and differential charge were calculated by the first principle method. The results show that the adsorption stability of the same molecule on the surface is related to the interaction position between the molecule and the surface after adsorption. According to the analysis of the differential charge density and the charge layout number, the charge layout number of the central atom C, O, S of the gas molecule increases after adsorption, and the adsorption strength of the gas molecule on the surface is CO>H2S>H2O>CH4. The H2S adsorbed on VC surface has the strongest adsorption energy (-1.442 eV) and more transfer charge (-0.12 e). The calculated dielectric function results shows that the existence of gases molecules inhibited the photon adsorbed on VC(001) surface. Our research provide a theoretical basis for further research on the gas sensing properties of material.

H2O and H2S adsorption by assistance of a heterogeneous carbon-boron-nitrogen nanocage: Computational study

A model of heterogeneous carbon-boron-nitrogen (C-B-N) nanocage was investigated in this work for adsorbing H2O and H2S substances. To achieve this goal, quantum chemical calculations were performed to obtain optimized configurations of substances towards the surface of nanocage. The calculations yielded three possible configurations for relaxing each of substances towards the surface. Formation of acid-base interactions between vacant orbitals of boron atom and full orbitals of each of oxygen and sulfur atoms yielded the strongest complexes of substance-nanocage in comparison with orientation of substances through their hydrogen atoms towards the surface of nanocage. As a consequence, formations of interacting H2O@C-B-N and H2S@C-B-N complexes were achievable, in which mechanism of action showed different strengths for the obtained complexes. Variations of molecular orbital features and corresponding energy gap and Fermi energy for the models before/after adsorption could help for detection of adsorbed substance through a sensor function. And finally, such C-B-N nanocage showed benefit of providing activated surface for efficient adsorption of each of H2O and H2S substance with possibility of differential adsorption regarding the strength of complex formations.

Chitosan Biocomposites for the Adsorption and Release of H2S

The search for H2S donors has been increasing due to the multiple therapeutic effects of the gas. However, the use of nanoporous materials has not been investigated despite their potential. Zeolites and activated carbons are known as good gas adsorbents and their modification with chitosan may increase the material biocompatibility and simultaneously its release time in aqueous solution, thus making them good H2S donors. Herein, we modified with chitosan a series of A zeolites (3A, 4A and 5A) with different pore sizes and an activated carbon obtained from glycerin. The amount of H2S adsorbed was evaluated by a volumetric method and their release capacity in aqueous solution was measured. These studies aimed to verify which of the materials had appropriate H2S adsorption/release properties to be considered a potential H2S donor. Additionally, cytotoxicity assays using HeLa cells were performed. Considering the obtained results, the chitosan composite with the A zeolite with the larger pore opening was the most promising material to be used as a H2S donor so a further cytotoxicity assay using H2S loaded was conducted and no toxicity was observed.

Adsorption of H2S from Thermal Water Using Clinoptilolite

The goal was to study and develop the composite adsorbents to uptake H2S from thermal water on the base of natural zeolite clinoptilolite (CL) from deposit of Georgia and activated carbon (AC). Cation-modified forms of CL have been prepared by wet-milling method. The crystalline structure and content of prepared adsorbents have been studied by X-ray diffraction (XRD) technique, IR-and AAS methods. Adsorption experiments carried out varying the ratio zeolite: AC, composite: solution, duration of contact, granulation degree. The results obtained showed that modification of CL by ion-exchanging method with metal ions (Zn2+, Fe3+, Mn2, Cu2+) has improved the adsorption capacity. Adsorption equilibrium reached in seven-fifteen minutes, and adsorption activity grows in a row: DeCL < CL < CuDeCL < MnDeCL < FeDeCL < ZnDeCL < AC/CL. The sorption capacity ranged from 0.68 mg/g to 28.17 mg/g. pH of thermal water before sorption was 8.97 and in filtrates changed in very wide ranges – from 10.44 until 3.55 depending on type of modification. Presence of multivalent cations of metals in the zeolite confirmed to be an essential factor determined the adsorption activity in relation to H2S, adsorption occurs via both physical sorption and chemisorption. Most active was composite AC/CL with ratio AC:CL, equal 3:2. The difference for H2S between decationated and cation-exchanged forms of CL may be explained by the change of surface potential. Polarity of zeolites depends on Si/Al ratio, which by-turn depends on conditions of acid treatment.

Shrinking-Core Model Integrating to the Fluid-Dynamic Analysis of Fixed-Bed Adsorption Towers for H2S Removal from Natural Gas

Natural gas sweetening is an essential process within hydrocarbon processing operations, enabling compliance with product quality specifications, avoiding corrosion problems, and enabling environmental care. This process aims to remove hydrogen sulfide (H2S), carbon dioxide, or both contaminants. It can be carried out in fixed-bed adsorption towers, where iron oxide-based solid sorbent reacts with the H2S to produce iron sulfides. This study is set out to develop a fluid-dynamic model that allows calculating the pressure drop in the H2S adsorption towers with the novelty to integrate reactivity aspects, through an iron sulfide layer formation on the solid particles’ external skin. As a result of the layer formation, changes in the particle diameter and the bed void fraction of the solid sorbent tend to increase the pressure drop. The shrinking-core model and the H2S adsorption front variation in time support the model development. Experimental data on pressure drop at the laboratory scale and industrial scale allowed validating the proposed model. Moreover, the model estimates the bed replacement frequency, i.e., the time required to saturate the fixed bed, requiring its replacement or regeneration. The model can be used to design and formulate new solid sorbents, analyze adsorption towers already installed, and help maintenance-planning operations.

One-Pot Synthesis of Nano CuO-ZnO Modified Hydrochar Derived from Chitosan and Starch for the H2S Conversion

A novel kind of hydrochar adsorbent, modified by CuO-ZnO and derived from chitosan or starch, was synthesized for H2S adsorption. The prepared adsorbent was characterized by BET, XRD, EDX, SEM, and XPS. The results showed that the modified hydrochar contained many amino groups as functional groups, and the nanometer metal oxide particles had good dispersion on the surface of the hydrochar. The maximum sulfur capacity reached 28.06 mg/g-adsorbent under the optimized conditions. The amine group significantly reduced the activation energy between H2S and CuO-ZnO conducive to the rapid diffusion of H2S among the lattices. Simultaneously, cationic polyacrylamide as a steric stabilizer could change the formation process of CuO and ZnO nanoparticles, which made the particle size smaller, enabling them to react with H2S sufficiently easily. This modified hydrochar derived from both chitosan and starch could be a promising adsorbent for H2S removal.

Influences of Work Function Changes in NO2 and H2S Adsorption on Pd-Doped ZnGa2O4(111) Thin Films: First-Principles Studies

The work function variations of NO2 and H2S molecules on Pd-adsorbed ZnGa2O4(111) were calculated using first-principle calculations. For the bonding of a nitrogen atom from a single NO2 molecule to a Pd atom, the maximum work function change was +1.37 eV, and for the bonding of two NO2 molecules to a Pd atom, the maximum work function change was +2.37 eV. For H2S adsorption, the maximum work function change was reduced from −0.90 eV to −1.82 eV for bonding sulfur atoms from a single and two H2S molecules to a Pd atom, respectively. Thus, for both NO2 and H2S, the work function change increased with an increase in gas concentration, showing that Pd-decorated ZnGa2O4(111) is a suitable material in NO2/H2S gas detectors.