Removal of hydrogen sulfide by clinoptilolite in a fixed bed adsorber

Fuel Processing Technology, 2015

Being a successful adsorbent for removal of hydrogen sulfide, zeolites should have good sulfur loading capacity, good regenerability and stable structure. These are natural zeolites having high adsorption capacity compared to other zeolites and synthetic zeolites. Zeolites can be modified by metals or metal oxides in order to increase their adsorption capacity. Removal of H 2 S is an essential process because it leads to corrosion in transport lines and poisoning of many catalysts even in low levels. Different types of adsorption methods such as fixed bed adsorption, pressure swing adsorption and sequential bed methods were experimentally used to investigate the removal of hydrogen sulfide. Computational methods (DFT) were also utilized theoretically. ETS-2 zeolite can be good choice to remove H 2 S due to its adsorbent properties. However this material has not been studied so much. Therefore more studies should be done experimentally and theoretically to examine the removal of hydrogen sulfide on excellent metal exchange forms of ETS-2. Consequently zeolites that have sulfur capacity increasing with modifications of metals or metal oxides are promising materials due to their high surface-volume ratio which is one of the most important factors in adsorption.

Chemical Engineering Journal, 2008

In this work Grand Canonical Monte Carlo (GCMC) simulations have been used to study hydrogen sulfide (H 2 S) removal from biogas streams by different zeolites such as FAU (Faujasite, NaX and NaY), LTA (zeolite A (Lynde division, Union Carbide)) and MFI (Zeolite Socony Mobil-five). Additionally, quantum mechanics (QM) molecular simulations have been performed to obtain structures and partial charges of some sorbates. The computational procedure adopted has been validated by comparison with experimental data available for H 2 S removal in atmospheric environment by zeolite NaY. In order to obtain a priority list in terms of both H 2 S isotherms and adsorption selectivity, adsorption simulations for pure H 2 S at low pressures and for a prototype biogas mixture (i.e., CO 2 , CH 4 , and H 2 S) have been performed and compared. The adsorption mechanisms and competition for accessible adsorption sites in terms of thermodynamic behavior have been also examined. Overall, the results obtained in this work could be routinely applied to different case studies, thus yielding deeper qualitative and quantitative insights into adsorption pollutant removal processes in environmental fields.

Chemical Engineering Journal, 2008

Coupled Grand Canonical-Canonical Monte Carlo and molecular dynamics (MD) simulation techniques have been used to investigate in details the adsorption of low-pressure hydrogen sulfide (H 2 S) in zeolites, and the selective adsorption behavior towards carbon dioxide and methane, the main biogas constituents. Results from Monte Carlo (MC) simulations indicated, among many others, zeolite NaY as the best option for H 2 S removal. Afterwards, deterministic simulations have been performed to investigate hydrogen sulfide pathway inside NaY, with respect to other adsorbed molecules (methane and carbon dioxide), as a function of zeolite loading and H 2 S partial pressure (i.e., biogas composition). Thermodynamic evaluations for 2D molecular dynamic simulations in terms of binding energy evolution vs. time confirm and reinforce the results obtained from Monte Carlo simulations, testifying the greater affinity for H 2 S to NaY zeolite framework. Results give also new quantitative insights in terms of pathways, binding energies, and equilibration time inside zeolite pores for stabilization.

Microporous and Mesoporous Materials, 2005

In this study, water vapor adsorption properties of the clinoptilolite rich zeolite tuff, from Bigadic (Turkey), and its modified forms were examined. The modified forms were obtained by treating the tuff with HCl solutions (0.032, 0.16, 0.32, 1.6 or 5 M) at 25, 40, 75 and 100°C for 3 h. Infrared spectroscopy and water vapor adsorption were used for the characterization of the zeolites. Langmuir, BET and Dubinin-Raduschevich methods were applied in the analysis of water vapor adsorption data. Applications of Dubinin Raduschevich equation to the water adsorption data displayed that the super-micropore volume was not very sensitive to acid treatment. It was found out that the Langmuir surface area and ultra-micropore volume depend on the degree of the removal of aluminum from the structure.

Adsorption Science & Technology, 2011

The adsorption of SO 2 onto clinoptilolite-rich zeolite tuff from Gördes (Turkey) (natural-G) and its cation-exchanged (Na ϩ , K ϩ , Ca 2ϩ and Mg 2ϩ) forms was investigated up to 100 kPa pressure at two different temperatures (273 K and 293 K). The structural properties of the clinoptilolites were studied by X-ray diffraction (XRD) and Fourier-transform infrared (FT-IR) spectroscopy. Quantitative XRD analysis showed that the major component of the natural-G sample was clinoptilolite, together with minor amounts of feldspar, opal-CT, smectite, mica-illite and amorphous material (opal-A). It was established that the uptake of SO 2 onto the adsorbents increased in the order Ca-G Ͻ natural-G Ͻ Mg-G Ͻ K-G Ͻ NaG at both temperatures.

Hungarian Journal of Industry and Chemistry

Hydrogen sulphide removal from simple gas mixtures using a highly polar zeolite was studied by molecular simulation. The equilibrium adsorption properties of hydrogen sulphide, hydrogen, methane and their mixtures on dehydrated zeolite NaA were computed by Grand Canonical Monte Carlo simulations. Existing all-atom intermolecular potential models were optimized to reproduce the adsorption isotherms of the pure substances. The adsorption results of the mixture, also confirmed by IAST calculations, showed very high selectivities of hydrogen sulphide to the investigated non-polar gases, predicting an outstanding performance of zeolite NaA in technological applications that target hydrogen sulphide capture.

2004

The adsorption experiments were carried out under dynamic conditions for the removal of trace sulfur-dioxide (SO 2) in nitrogen by 5A zeolites. The experiments were conducted to characterize the breakthrough characteristics of SO 2 in a fixed bed under different operating conditions including temperature, pellet size, concentration levels, and gas flowrate. At a reaction temperature of 70 8C, the breakthrough time was found to be maximum. The adsorption isotherm was found to be linear over the gas concentration range from 1000 to 10 000 ppm. The exothermic heat of adsorption assuming Arrehenius type of temperature dependence of the equilibrium constant was determined to be 9.8 kc/mol. The mathematical model was developed to predict the breakthrough profiles of SO 2 during adsorption over the biporous zeolites (containing both macro and micro-pores). The model incorporates all resistances to mass transfer, namely: diffusion in the gas film around pellets in the bed, diffusion in the binder-phase of zeolites and within the crystals, and adsorption/desorption at the interface of binder-phase and crystals. The model was successfully validated with the observed experimental breakthrough data. The study showed potential application of 5A zeolites in controlling SO 2 emissions at trace levels.

Nanochemistry Research, 2016

Natural clinoptilolite zeolite (CLP) in its original or metal ion- exchanged form (Ni2+) is a weak adsorbent for relatively large thiophene derivative molecules like benzothiophene (BT) and di-benzothiophene (DBT), due to its rather restricted micro-channel structure. A novelty of this work is that upon desilication treatments, it is possible to enhance the adsorption behavior of Ni2+-exchanged CLP for such large sulfur- containing molecules. A natural CLP zeolite has been desilicated using NaOH solutions in a concentration range of 0.2-2.0 M. The resulting powders have been subjected to XRF, XRD, FTIR, nitrogen adsorption/desorption, TEM and TGA analyses. The adsorption isotherms for the removal of thiophene (TP), BT, DBT and iso-propyl mercaptan (IPM) have been obtained experimentally at 20 °C from simulated liquid fuels using iso-octane as solvent. The sample treated with 1.5 M NaOH solution showed the most significant enhancement in adsorptive properties. The selectivity order is IPM > TP > BT > DBT. Regenerability tests show a quasi constant adsorption capacity after the first cycle. The observed phenomena have been thoroughly discussed based on the physico-chemical analyses of the samples.

Industrial & Engineering Chemistry Research, 2005

Five carbonaceous adsorbents were studied as media for H 2 S removal from the gas phase. Materials were characterized using nitrogen adsorption, thermal analysis, XRF, and other standard methods. Hydrogen sulfide removal capacities were measured using the ASTM test. Then the species adsorbed/formed on the carbon surfaces were identified. The results showed that surface chemical features have a significant effect on the performance of materials as H 2 S adsorbents. To be adsorbed, hydrogen sulfide has to be oxidized to either elemental sulfur or sulfuric acid. The amount adsorbed and the extent of oxidation are governed by the surface pH and the dispersion of catalytic centers. Such centers can be nitrogen-containing basic groups and metals (iron and alkali and alkaline earth metals). A high volume of small micropores is also important. Contributing to a high dispersion of catalyst and providing adsorption centers for storage of oxidation products, these pores form specific oxidation microreactors.

Adsorption Science & Technology, 2003

The carbon dioxide and water vapour adsorption properties of local clinoptilolite-rich material, both as the original and as lead-, barium- and hydrogen-rich forms, were examined. The lead- and barium-rich forms were prepared by treatment of the original clinoptilolite with Pb(NO3)2 and BaCl2 respectively, while the hydrogen-rich form was prepared by NH4Cl and heat treatment. Water and CO2 adsorption experiments were conducted in a volumetric system under static conditions, with low-pressure adsorption data being used for the characterization of the natural, Pb-rich, Ba-rich and H-rich clinoptilolite samples. Although the existence of barium-exchange was not noted, an appreciable decrease in CO2 adsorption was observed with the Pb-rich and H-rich forms due to a decrease in the electrostatic interaction between the surface and the adsorbate. Application of the Dubinin–Astakhov equation to the water adsorption data established the existence of micropores of different sizes that exhibi...

Asian Journal of Applied Sciences

Hydrogen sulfide adsorption performance of sonicated natural zeolite in the Ferric chloride hexahydrate solution has been studied. In this research natural zeolite exposed with high intensity ultrasonic waves for 40 minutes, 80 minutes and 120 minutes. Qualitative analysis and characterization of modified zeolite carry out with X-ray diffraction, Infrared spectroscopy, BET adsorption desorption, LAS particle size analysis and scanning electron microscopy prior and after H2S adsorption. Natural zeolite phase are clipnotilolite and mordenite phase with 0.99%wt and 0.512 x 10-3 %wt respectively. By adding 5gr FeCl3.6H2O and ultrasonic exposure, zeolite chemical and physical properties such as chemical composition, particle size, surface area and pore radius are improved. Hydrogen sulfide %wt adsorption effectiveness showing that modified zeolite higher 70-117% comparing with unmodified zeolite.

Adsorption Science & Technology, 2003

The adsorption kinetics of pure CO2, N2 and CH4 on a natural clinoptilolite (ZSL) sample from Villa de Reyes (San Luis Potosí, México) were measured at different temperatures using a glass, high-vacuum volumetric system. The ability of the natural zeolite to adsorb these gases depended on the gas–adsorbent contact time, t. For short values of t, the gas adsorption uptakes decreased in the order CO2 >> N2 > CH4. However, for long t values, the adsorption uptakes decreased in the sequence CO2 > CH4 > N2. It was established that the activation energies (kJ/mol) for the adsorption process increased in the following order CO2 (15) < N2 (18) < CH4 (40), correlating fairly well with the increasing order of kinetic diameter (Å) of the molecules: CO2 (3.3) < N2 (3.64) < CH4 (3.8). In comparison to the ZSL sample, the rate of adsorption of N2 and CH4 on H-ZSL increased and the total adsorption capacity decreased. The ZSL sample may be recommended as an effective ads...

Carbon dioxide (CO 2) adsorption is an important adsorbent characterization method and a significant industrial process. In separation and recovery technology, the adsorption of the CO 2 is important to reduce the concentration of this gas considered as one of the greenhouse gases. Natural zeolites, particularly clinoptilolite, are widely applied as adsorbents. In this regard, in the present research, the structure, composition and morphology of modified with hexafluorosilicate (HFSi) and orthophosphoric acid (H 3 PO 4) clinoptilolites were investigated by characterizations and measurements made with, X-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscopy-energy dispersive X-ray analysis (SEM-EDAX) and gravimetric adsorption. Additionally, the surface Chemistry of the modified clinoptilolites was analyzed by applying diffuse reflectance fourier transform infrared spectrometry (DRIFTS). Further, the interaction of CO 2 within the adsorption space of these modified clinoptilolites and a synthetic ZSM-5 zeolite was studied with the help of adsorption measurements. After all, an appropriate theoretical methodology for the analysis of the XRD and adsorption data was applied. The calculated cell parameters of the tested are similar to those reported for a typical clinoptilolite of: a = 17.662 Ǻ, b = 17.911 Ǻ, c = 7.407 Ǻ and β = 116.40 The resolution of the TGA derivative profiles indicated the presence of two steps for water release, one of them represents the loss of majority of the water present in the micropores. This was evidenced as a broad peak centered at about 50 0 C for the CSW-HFSi-0.1, but at 100 °C for the samples CSW-HFSi-0.4. The SEM micrographs corresponding to the modified clinoptilolites, was evidenced that the CSW zeolite shows secondary particles exhibiting diameters from 3 to 40 μm, formed by primary clinoptilolite crystallites showing a crystallite size, Φ = 40 nm. The EDAX elemental analysis it can be demonstrated that the exchange process replaced about 85% of the charge compensating ions. The DRIFT spectra of the modified clinoptilolites, specifically, CSW-HFSi-0.1, show a narrow band at about: 3,740 cm-l corresponding to terminal silanol groups (Si-OH) and a band 3,600-3,650 cm-1 resulting from extra-framework Al-OH. With the precision of the measured micropore volumes related to the excellent fitting of the adsorption data by the D-R isotherm equation, it can be affirm that carbon adsorption took only place in the micropore region. The isosteric heat of adsorption calculated for the modified clinoptilolites was greater than those values reported of ZSM-5 zeolite, particle packing silica, dealuminated Y zeolite (DAY) Cd, Zn and Ni-nitroprussides and Cu-nitroprusside and a Ni-MOF. With the obtained result it can be concluded that the modified clinoptilolites with HFSi showed a quality as adsorbent comparable to commercial synthetic zeolites.

Annali di chimica, 2007

The chromium, cobalt and lead removal from aqueous solution by natural and modified zeolites was examined by using a batch-type method. Clinoptilolite samples used in this study were supplied from Bigadiç, Turkey. All samples were modified with HNO3 or NaOH to improve the adsorption capacity for heavy metals. The removal efficiencies and kinetics of heavy metals such as chromium, cobalt and lead on natural and modified zeolites were determined. The effects of the initial metal concentration on the removal percentage of heavy metal ions were studied. Freundlich and Langmuir isotherm constants and correlation coefficients were found and the equilibrium process was described by the Freundlich isotherm. The adsorption kinetic was tested and then it indicates the process to be diffusion controlled.

Industrial & Engineering Chemistry Research, 2001

Sewage-sludge-derived fertilizer, Terrene, was used as a precursor of adsorbents tested for removal of hydrogen sulfide from moist air. The adsorbents were obtained by pyrolysis of zinc chloride-impregnated granular fertilizer at 400, 600, 800, and 950°C in a nitrogen atmosphere. Subsamples of the materials obtained were washed with hydrochloric acid to remove the excess zinc chloride and other soluble chlorides. This treatment results in a significant increase in the sample porosity. The highest H 2 S removal capacity was obtained for the sample carbonized at 600°C. This results from release of zinc chloride vapor during heat treatment, which acts to form micropores in the carbonaceous deposit. When inorganic oxides and salts are present in sufficient quantities, hydrogen sulfide undergoes surface reactions and is left on the surface in the form of nonvolatile sulfides and sulfates. The pores are gradually filled as the surface reaction proceeds. If catalytic metal oxides are removed, hydrogen sulfide is oxidized predominantly to sulfuric acid through the catalytic effect of the adsorption sites in the small micropores of the carbonaceous deposit. The removal of H 2 S occurs until all pore entrances are blocked with the oxidation product.