CaA Zeolite Research Articles

Study On the Adsorption Performance of Zeolite Molecular Sieve for CO2

In this paper, CO2 was used as the target adsorbate to study the adsorption capacity of three kinds of zeolite molecular sieves for CO2 and the selective adsorption of CO2/N2. The results show that the adsorption capacity of NaX zeolite molecular sieve for CO2 is significantly higher than that of NaA and CaA zeolite molecular sieves.

Differential entropy and thermokinetics of ammonia molecule adsorption on CaA zeolite (M-22)

Differential entropy and thermokinetics of ammonia molecule adsorption on CaA zeolite (M-22)

Zeolite-coated fin–coil heat exchanger for CO2 recovery from simulated dry flue gas via low-temperature-heat-driven TSA

Adsorbent-coated heat exchangers are expected to achieve not only high adsorption and desorption rates based on the rapid heat transfer in their adsorbent layers but also a low pressure drop owing to their structured adsorbent layers. In this study, a CaA-zeolite-coated adsorber was experimentally investigated to improve the CO2 capture performance of low-temperature-heat-driven temperature swing adsorption (TSA) from dry flue gas, a major source of greenhouse gas emissions. At a feed CO2 concentration of approximately 10 vol%, a flow rate of 1 L-STP/min, and a temperature swing range of 20 °C–80 °C, the performance of the coated adsorbent was first compared with that of a heat exchanger of a similar volume packed with CaA zeolite pellets. Due to the enhancement in heat transfer of the coated adsorbent, almost the same CO2 concentration and a higher CO2 recovery ratio as those of the packed adsorbent were obtained at an appropriate cycle time despite that the amount of coated adsorbent was only one-third that of the packed adsorbent. Therefore, the accelerated heat transfer in the adsorbent layer significantly affected the increased mass transfer rate in or around the coated adsorbent. Next, the effect of the space velocity (SV) was investigated using a coated heat exchanger that had a three-times-longer length in the gas flow direction and approximately the same thickness of the adsorbent coating layer as the above coated heat exchanger. Although a separate discussion on the larger adsorber size is necessary, the CO2 recovery concentration was over 50% and the recovery ratio exceeded 80% as the SV was reduced by one-third. Furthermore, the fin pitch of the heat exchanger was doubled and the thickness of the adsorbent coating was doubled while maintaining the same volume of the heat exchanger and the same amount of adsorbent coating. This was done to reduce the heat capacity of the heat exchanger, which is a factor in heat loss in TSA, by reducing the number of fins used. The doubled adsorbent coating layer thickness and halved contact area with the gas flow resulted in a decrease in CO2 capture. Thus, the effects of an increased adsorbent layer thickness and a reduced contact area should be determined to further increase the effectiveness of the adsorbent-coated heat exchangers.

Catalytic Hydrogenation of Anthracene on Binary (Bimetallic) Composite Catalysts

The catalytic activity of the binary composite catalysts of Fe2O3-CoO/CaA and Fe2O3-CoO/ZSM-5 was studied. They were obtained by impregnation of CaA and ZSM-5 zeolites with aqueous solutions of sulfates of iron (FeSO4·7H2O) and cobalt (CoSO4·7H2O). The total metal content was no more than 5%. Then, oxidizing burning at 720 °C for 60 min was performed to produce the metal oxides. It was found that the obtained Fe-Co/CaA catalyst contains iron and cobalt as CoFe2O4 compound, and the Fe-Co/ZSM-5 catalyst includes CoFe2O4 and CoFe. The phase composition of the obtained catalysts was detected by the X-ray diffraction analysis. The surface morphology was investigated by the electron microscopy. The elemental composition of the obtained catalysts was determined by energy dispersive spectroscopy with mapping and inductively coupled plasma atomic emission spectroscopy. The atomic absorption analysis by the IR-spectroscopy showed the shifts of absorption bands in the infrared spectra of the pure zeolites and with added Fe and Co. The catalytic hydrogenation of anthracene was performed to determine the catalytic properties of the obtained catalysts. It is one of the most common model compounds applied to investigate the efficiency of catalytic systems. The result of hydrogenation found that conversion of anthracene at 400 °C, initial pressure of 6 MPa and duration of 60 min using the Fe-Co/CaA catalytic system equaled to ~87%. However, hydrogenation products equaled to ~84%. Anthracene conversion using the Fe-Co/ZSM-5 catalytic system and the same conditions was ~91%; among them, hydrogenated derivatives were ~71%. The proposed method is characterized by its simple execution. The obtained catalysts are be slightly inferior to platinum and rhodium catalysts in the catalytic activity.

Investigation of isotherms of differential heat-entropy adsorption of carbonyl sulfide in CaA zeolite during gas purification

The task of this research cycle was to measure adsorption isotherms (а) in the temperature range from 273 to 373 K, based on isotherms measured at different temperatures, to calculate isosteric heats (Qd) and entropies (∆Sd) of adsorption in order to select an effective adsorbent for purifying natural gas and oil products from sulfur-containing compounds. This article presents the results of studies of the isotherms of COS adsorption on CaA, carried out at four temperatures: 273, 298, 303, and 373 K, and the corresponding thermodynamic functions of adsorption in CaA zeolite.

Insights into the adsorption performance and separation mechanisms for CO2 and CO on NaX and CaA zeolites by experiments and simulation

Adsorption and recovery of CO2 from industrial gases are of great environmental significance in the field of environmental protection with reducing greenhouse gas emissions and increasing CO concentration. A comprehensive investigation with thermodynamics and kinetics experiments of CO2 and CO on NaX and CaA zeolites were studied and the separation mechanism explained by molecular simulation methods. The experiments show that the NaX zeolites have significant differences on CO2 and CO adsorption amounts leading the high CO2/CO selectivity, while the CaA zeolites exhibit separation stability under various partial pressures of mixed gas, which is supported by the standard deviation results. The theoretical simulations verify the above-mentioned experimental phenomena and provide a visual mechanism explanation for adsorption selectivity from the aspect of systematic interaction between cations and gas molecules. Compared with NaX, the same number and homogeneous distributions of Ca2+ and Na+ in the CaA provide stable separation performance. The strong electrostatic interactions between divalent Ca2+ and gas molecules especially CO make differences in the order of adsorption capacity and adsorption heat. Deeper insights into the cations-gas adsorption complexes revealed that the significant differences in the types of adsorption complexes for CO and CO2 in NaX contribute to the improvement of the adsorption selectivity.

System Analysis and Simulation of the Process of Destructive Hydrogenization of Deasphaltisate of Heavy Oil

The article presents a systematic analysis and simulation of the process of destructive hydrogenation of deasphalted oil. The process of thermoregeneration of spent zeolite and the surface - acid properties of CaA zeolite catalysts are also studied. It has been established that such patterns that allow predicting their influence and to regulate the quality of the hydrogenation obtained on one or another form of the catalyst obtained from the studied factors and catalysts. In addition, the obtained data can be used in the search for the optimal process modes of the process under consideration on the specific form of the catalyst.

Research and application of natural zeolite in the processes of gas purification and drying

This article describes the adsorption capability of natural zeolites for the purification and dehydration of natural gases. Studies were carried out with natural clinoptilolite treated with various cadmium and titanium solutions. Zeolite-containing rocks were used as a natural adsorbent and experiments using a synthetic CaA zeolite were also carried for comparison. The experiments showed that zeolite from the Ai-Dag deposits possesses the highest activity in terms of sulfur compound. Its activity is closer to that of synthetic CaA zeolite. Studies showed that natural zeolites and adsorbents obtained on their basis allow the gas to be dehydrated to a dew point temperature of minus 40-45 °C. This is sufficient to prepare gas for transportation directly from the fields under any climatic conditions. Keywords: gas dehydration; zeolite; adsorbent; sulfur compounds.

CaA, NaX, NaY ve ZSM-5 Sentetik Zeolitleri Üzerine Adsorbe Edilen Polietilen Glikol (Mono- ve Di- Metil) Eterin Kırmızıaltı ve Raman Spektroskopileri ile Analizi

The adsorptions of polyethylene glycol monomethyl ether (PEGMME) and polyethylene glycol dimethyl ether (PEGDME) on CaA, NaX, NaY, and ZSM-5 zeolites have been analyzed by using experimental FT-IR and Raman spectroscopies. The vibration wavenumbers of polymers adsorbed on zeolites have been reported and the adsorption properties of zeolites with different molecular sizes and cations have been compared. Disappearing of some vibration modes of polymers or shifts to the higher and lower frequency region after the polymers have been adsorbed on zeolites; indicates an interaction between polymers and zeolites. By considering the obtained experimental spectral results we can suggest that the source of adsorption of polymers on zeolites can be based on the interactions between OH groups or oxygen atoms settled in polymer chains and the silanol hydroxyl groups on the surface of each zeolite.

Infrared and Raman Spectroscopic Analyses of Poly(allylamine) Adsorbed on CaA, NaX, NaY, and ZSM-5 Synthetic Zeolites

The adsorptions of poly(allylamine) solution on CaA, NaX, NaY, and ZSM-5 zeolites have been investigated by using FT-IR and micro-Raman spectroscopies. Vibrational wavenumbers of poly(allylamine) adsorbed on the mentioned zeolites have been reported and the adsorption characteristics of zeolites with different cations and molecular sizes have been compared. The small shifts to the high or low-frequency regions in the position of vibration modes or the disappearance of the vibration bands show that there are interactions between poly(allylamine) and zeolites. By considering the obtained results, we can say that the adsorption source of polymer on the mentioned zeolites can withstand the interaction between the amine group of polymer and the silanol hydroxyl group on the surface of the zeolites.

Experimental Study of the Possibility of Using Composite Adsorption Materials for Compressed Air Dehumidification Plants

Experimental studies of composite adsorption materials (CAM) and initial adsorbents (active aluminum oxides and CaA zeolite) in the static mode by the desiccator method were carried out, and experimental sorption isotherms were constructed. The specific surface area of the studied adsorption materials was determined. The adsorption capacity of СAM samples based on active aluminum oxide and CaA zeolite is about 90% and 73% of the capacity of the source materials, respectively (due to the presence of a binder), while the bulk density of monoblocks is 15% higher than the bulk density of the initial adsorbent. It was found that an increase in the CAM samples molding pressure (at a constant binder content) slightly affects the adsorption capacity of CAM samples.

Freeze Granulated Zeolites X and A for Biogas Upgrading.

Biogas is a potential renewable energy resource that can reduce the current energy dependency on fossil fuels. The major limitation of utilizing biogas fully in the various applications is the presence of a significant volume fraction of carbon dioxide in biogas. Here, we used adsorption-driven CO2 separation using the most prominent adsorbents, NaX (faujasite) and CaA (Linde Type A) zeolites. The NaX and CaA zeolites were structured into hierarchically porous granules using a low-cost freeze granulation technique to achieve better mass transfer kinetics. The freeze granulation processing parameters and the rheological properties of suspensions were optimized to obtain homogenous granules of NaX and CaA zeolites 2–3 mm in diameter with macroporosity of 77.9% and 68.6%, respectively. The NaX and CaA granules kept their individual morphologies, crystallinities with a CO2 uptake of 5.8 mmol/g and 4 mmol/g, respectively. The CO2 separation performance and the kinetic behavior were estimated by breakthrough experiments, where the NaX zeolite showed a 16% higher CO2 uptake rate than CaA granules with a high mass transfer coefficient, 1.3 m/s, compared to commercial granules, suggesting that freeze-granulated zeolites could be used to improve adsorption kinetics and reduce cycle time for biogas upgrading in the adsorption swing technology.

SYNTHESIS OF TARGETED CATALYST FOR THE OXIDATIVE DEHYDRATION OF SEC-BUTANOL AND STUDY OF THE KINETICS AND MECHANISM OF THE PROCESS

The catalytic activity of CaA zeolite modified with metal cations (Cu, Zn, Pd) by means of ion exchange in the reaction of partial oxidation of sec-butanol to methyl ethyl ketone was studied at atmospheric pressure in the temperature range of 240-3500 C, space velocities 1500-4000 h-1 and partial pressures of butanol-2 PB−2 = 0.12-0.36 atm, oxygen O2 P = 0.12-0.24 atm. It found that the metal zeolite catalyst CuZnPdCaA containing 3.0 wt% Cu2+ , 2.0 wt% Zn2+ and 0.1 wt% Pd2+ exhibited the highest activity and selectivity in the reaction under consideration. Also, kinetic regularities of the reaction on the indicated catalyst were studied. On the basis of experimental data, a probable stepwise mechanism of the reaction was proposed and a theoretically substantiated kinetic model of the process developed.

Modeling and Optimization of Cyclic Adsorption Enrichment of Gas Mixtures with Hydrogen

A mathematical model of the dynamics of pressure swing adsorption was developed. The adsorption, aimed at separating multicomponent gas mixtures for hydrogen concentration, is performed in a four-adsorber unit with a CaA zeolite adsorbent. An original description of the mass transfer of the adsorbate (H2, CO2, CO) from the gas phase to the solid adsorbent for the mixed-diffusion region depending on the gas flow rate in the adsorbent bed was proposed. A computational treatment of the effects of the raw materials load and control variables on the dynamics of the cyclic adsorption process of gas mixture enrichment with hydrogen was performed. The problem of adaptive optimization of process variables was formulated and studied by modeling.

EVALUATION OF MODIFIED FLY ASH BASED NAA-ZEOLITE: EFFECT OF CRYSTALLINITY ON CO2 ADSORPTION CAPACITY

NaA zeolite was successfully synthesised from fly ash through hydrothermal process. The synthesised NaA zeolite was modified with Li+, Ca2+ and Mg2+ through ion exchange at a temperature of 60 C and contact times of 1 h and 4 h. In this study the crystallinity of the synthesised NaA as well as its modified (LiA, CaA and MgA) was evaluated towards CO2 adsorption capacity using temperature programmed desorption (TPD) process at low temperature (40-150 C) and high temperature (150-700 C). The mineral phase and structural characteristics of zeolites were examined using XRD and FT-IR. The results from XRD and FT-IR spectra revealed unique structural alterations influenced by the intrinsic characteristic of individual cation incorporated in NaA zeolite. Monovalent cations displayed highest crystallinity compared to divalent cations (downward order: NaA > LiA > MgA > CaA). Low and high temperature CO2-TPD profiles were independent of the degree of crystallinity of the zeolites and a significant amounts of CO2 desorption occur at low temperature indicating that physisorption is the most prominent adsorption mode in NaA, LiA, CaA and MgA zeolite.

A variable temperature infrared spectroscopy study of CaA zeolite dehydration and carbonate formation.

Variable temperature diffuse reflection infrared spectroscopy is used to monitor the dehydration of calcium enriched Linde type A zeolite (CaA). Infrared spectrum changes indicate that the energy imparted to the zeolite by heating causes water desorption and also facilitates reactions between water and zeolite framework, yielding SiOHAl acid sites. Water also reacts with ambient carbon dioxide producing carbonic acid, which readily dissociates to form carbonate. Three types of carbonate species are reported. The most thermally stable carbonate is coordinated to Ca2+ as a monodentate ligand. A second carbonate-containing species may be simultaneously interacting with Ca2+ and the zeolite framework. The third type of carbonate is characterized by infrared absorption consistent with a highly symmetric configuration, suggesting weak interactions with the local environment. Temperature-dependent infrared spectrum variations suggest that protons from carbonic acid dissociations react with framework and Ca(OH)+ moieties, altering internal CaA pore structure configurations.

Dynamic adsorption of nitrogen dioxide on zeolites

The dynamic adsorption of nitrogen dioxide on Zeolon 900H, Zeolon 900K, Zeolon 900Na, Zeolon 200H, Zeolon 500H, H/ZSM-5, Na/ZSM-5, and CaA zeolites is studied. Breakthrough curves C/C0 = σ(t) (C 0 is the initial concentration of NO2 at the adsorption column inlet and C is the breakthrough concentration at the column outlet) is measured over a temperature range of 290–430 K. It has been shown that the time dependence of C/C 0 is described by the Wheeler–Jonas equation. The parameters of this equation, the adsorption constant rate k v and dynamic adsorption capacity (DAC) are determined by fitting the theoretical curves to the experimental data for the aforementioned zeolites at 290–430 K. The Hertz–Knudsen equation is used to obtain theoretical temperature dependence of k v. For this dependence, the curve fitting method is also used to determine the adsorption activation energy E ad. It is found that the activation energy ranges within 300–500 cal/mol, which shows that the adsorption of NO2 on these zeolites is a physical process, with the electronic structure of the molecules being perturbed only slightly during the adsorption process. A theoretical formula for calculating the time of protective action of the sorbent is derived. It is shown that the DAC and the corresponding protective action time for the studied sorbents depend on the temperature and increase in the series Zeolon 900Na < Na/ZSM-5 < Zeolon 900K < H/ZSM-5 < Zeolon 500H < Zeolon 200H < Zeolon 900H for gas mask filters at room temperature (293 K), and increase in the series CaA < H/ZSM-5 < Zeolon 900H < Zeolon 500H < Na/ZSM-5 < Zeolon 200H < Zeolon 900K < Zeolon 900Na for systems of purification of flue gases from thermal power plants at 350 K.

Synthesis of 4A Zeolite and Characterization of Calcium- and Silver-Exchanged Forms

Calcium exchanged A type zeolite is extensively used as an adsorbent in petroleum and gas purification application. The precursor of calcium and silver-exchanged zeolite was prepared in a hydrothermal process, followed by an exchange process. In this study, LTA zeolite was synthesized. Calcium-ex- changed and silver-exchanged molecular sieves were prepared and characterized by a series of techniques, such as scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, etc. Physical properties of Ca- and Ag-exchanged zeolite A, such as surface structure, crystal structure, cation exchange capacity, and the ion-exchange properties were measured. Water adsorption studies using thermogravimetric method indicated that water molecules are more strongly bound in the Ca-A zeolite compared to Ag-A zeolite. XPS studies confirmed the presence of highly dispersed cationic silver species at exchange sites. The results of this study indicated that sodium was successfully exchanged with the calcium and silver in both Ca- and Ag-ex- changed zeolite frameworks. High cation exchange capacity, tailored aperture size, high porosity and specific surface area, as well as high thermal stability make cation-exchanged A type zeolite a successful candidate for adsorption, ion exchange, and catalysis applications.

A Hierarchically Micro-Meso-Macroporous Zeolite CaA for Methanol Conversion to Dimethyl Ether

A hierarchical zeolite CaA with microporous, mesoporous and macroporous structure was hydrothermally synthesized by a ”Bond-Blocking” method using organo-functionalized mesoporous silica (MS) as a silica source. The characterization by XRD, SEM/TEM and N2 adsorption/desorption techniques showed that the prepared material had well-crystalline zeolite Linde Type A (LTA) topological structure, microspherical particle morphologies, and hierarchically intracrystalline micro-meso-macropores structure. With the Bond-Blocking principle, the external surface area and macro-mesoporosity of the hierarchical zeolite CaA can be adjusted by varying the organo-functionalized degree of the mesoporous silica surface. Similarly, the distribution of the micro-meso-macroporous structure in the zeolite CaA can be controlled purposely. Compared with the conventional microporous zeolite CaA, the hierarchical zeolite CaA as a catalyst in the conversion of methanol to dimethyl ether (DME), exhibited complete DME selectivity and stable catalytic activity with high methanol conversion. The catalytic performances of the hierarchical zeolite CaA results clearly from the micro-meso-macroporous structure, improving diffusion properties, favoring the access to the active surface and avoiding secondary reactions (no hydrocarbon products were detected after 3 h of reaction).

Amine-Appended Hierarchical Ca-A Zeolite for Enhancing CO2 /CH4 Selectivity of Mixed-Matrix Membranes.

An amine-appended hierarchical Ca-A zeolite that can selectively capture CO2 was synthesized and incorporated into inexpensive membrane polymers, in particular polyethylene oxide and Matrimid, to design mixed-matrix membranes with high CO2 /CH4 selectivities. Binary mixture permeation testing reveals that amine-appended mesoporous Ca-A is highly effective in improving CO2 /CH4 selectivity of polymeric membranes. In particular, the CO2 /CH4 selectivity of the polyethylene oxide membrane increases from 15 to 23 by incorporating 20 wt % amine-appended Ca-A zeolite. Furthermore, the formation of filler/polymer interfacial defects, which is typically found in glassy polymer-zeolite pairs, is inhibited owing to the interaction between the amine groups on the external surface of zeolites and polymer chains. Our results suggest that the amine-appended hierarchial Ca-A, which was utilized in membrane fabrication for the first time, is a good filler material for fabricating a CO2 -selective mixed-matrix membrane with defect-free morphology.