Article

Application of natural zeolites in the purification and separation of gases

Authors:
To read the full-text of this research, you can request a copy directly from the authors.

Abstract

There are many natural zeolites of which a small number including clinoptilolite, chabazite, mordenite, erionite, ferrierite and phillipsite offer the greatest promise for gas separation. Patents and other literature have been surveyed to identify the bulk separation and purification processes for which these zeolites have potential. The abundance and low raw material cost of natural zeolites have rarely offset such disadvantages as variable composition, low purity and often poorer separation performance compared to the more-favored synthetic zeolites. The results of the present study indicate that these natural zeolites are particularly well suited for trace-gas removal. In contrast, they are less likely to provide competitive performance in bulk separations. Clinoptilolite and chabazite are judged the most versatile, while also offering unique adsorption characteristics. Effective and efficient methods for screening all types of adsorbents are presented for various gas separations. Natural zeolites must demonstrate unique or superior performance to be serious contenders in commercial separations. Use of these methods should enhance such opportunities. The importance of including relevant process considerations in the analyses is demonstrated through application to processes for a bulk separation (O2 production from air) and purification (removal of trace levels of N2O from air). The results are not encouraging for the use of natural zeolites in air separation. Conversely, clinoptilolite and chabazite outperform commercially available synthetics in N2O removal from air.

No full-text available

Request Full-text Paper PDF

To read the full-text of this research,
you can request a copy directly from the authors.

... [26] . 沸石相比, 其存在化学组成不一致、纯度低等不足 [28] . [46] . ...
... (LTA)、P型沸石(GIS)和X型沸石(FAU) [47] . [29] Si/Al [28] 骨架 类型 [30] 晶格类型/ 空间群 [30] 主要孔道环数及 孔径(Å×Å) [30] 孔隙度 (%) [31] CEC (meq g −1 ) [ [48,49] . 利用沸石的大比表面积和高稳定性, 以沸石 作为基质负载nZVI构筑的Z-nZVI可以有效克服nZVI 稳定性差、易团聚的缺点 [50] ; 除此之外, 沸石与nZVI的 复合还可以进一步弥补沸石对阴离子的亲和能力不足 等弱点. ...
Article
Soil contamination has become a global environmental crisis due to the development of the industry. Exploring costeffective and long-term active soil remediation materials is the key to tackle the soil contamination problem. Based on excellent absorption and cation exchange capacity (CEC), zeolite molecular sieve materials have been widely used in soil remediation. Herein, we summarize the available works in the literature on conventional zeolite materials which have been applied in soil remediation. Especially, focusing on composition and structure features of zeolite materials, we elaborate on their structure-activity relationship down to details. Besides, the microscopic interaction between zeolites and soil contaminants have elucidated. The research process of zeolite used in soil remediation has been reviewed. As discussed in this review, for the conventional zeolite materials used for soil remediation can be classified into pure zeolite materials and zeolite-based composite materials. Pure zeolite materials can be divided into natural zeolites and synthetic zeolites. Natural zeolites are cheap but with multiple elements inside the structure and composition, which is of low purity, and small pore volumes. Ion exchange, acid/alkali washing, and heat treatment are standard methods that have been used to improve the sorption capacity of natural zeolites. Compared to natural zeolites, synthetic zeolites are with tunable compositions and frameworks with high purity. But the cost for synthetic zeolites is higher, which hinders their large-scale application. In recent years, zeolite-based composite materials have been frequently employed as a composite material mixed with other kinds of materials, including nanoscale zero-valent iron or biochar, or humic acid, etc., for soil remediation. The obtained composite materials can be nanoscale zero-valent iron/zeolite composite materials (Z-nZVI), humic acids/zeolite composite materials (HZ), and biochar/zeolite composite materials (BZ). Usually, the soil remediation effect of zeolite-based composite materials is better than pure zeolite materials due to the synergy between the components. Targeting different types of pollutants in the soil requires the dedicated zeolite materials for the treatment, and the microscopic interaction mechanism between zeolite materials and pollutants are also various. For cationic contaminants, such as heavy metal ions, zeolite with low Si/Al ratio and large pore size are effective amendments, because the soil remediation effect directly correlated to the CEC in the used materials. As most of the zeolites have a net negative structural charge, which typically results in little or no affinity for anionic species. Therefore, pure zeolite materials are rarely used for anionic pollutants remediation. While combining zeolite with other materials, such as nZVI, both the cationic and anionic pollutants in the soil can be effectively removed. Moreover, organic pollutants can also be removed by zeolite as the organic pollutants can be physically adsorbed within the zeolite channels through Van der Waals forces or hydrogen bonding. The adsorption capacity of zeolite materials on the organic matter is heavily dependent on the zeolites' pore sizes and hydrophobic properties. Usually, zeolites with a high Si/Al ratio and large pore size can be used to immobilize organic pollutants more effectively. We concluded this review with some perspectives. We think that elucidating the remediation mechanism down to the atomic-scale and optimizing the green chemistry synthesis process for zeolites are two urgent approaches that need to be considered seriously soon.
... Natural zeolites are, indeed, largely available in different regions in the composition of different types of rocks. 89,90 Therefore, their variable composition that may change even in a single deposit, low purity, and likely inferior separation performance compared to the more performant synthetic zeolites are somehow counterbalanced by their Process conditions (P CO 2 and T) are also provided for a better comparison. P CO 2 , CO 2 partial pressure; T, temperature; FAU, faujasite; LTA, Linde type A zeolite; and BEA, β zeolite. ...
... Review abundance and low or null price. 89 In this framework, natural zeolites have been promisingly tested for both CO 2 capture from flue gas 33 and biogas purification. 91,92 2.1.3. ...
... There are several SCMs that each have specific properties and therefore play a different role in enhancing the mechanical properties of concrete, for example, Silica fume shows a However, the variation of the mechanical properties of concrete containing ZE [28,29] and reduction in workability of the mixture [30][31][32][33] are the main drawbacks of widespread utilization of this SCM. Prior research related to the use of ZE in ternary systems is scarce and the knowledge of their performance is limited. ...
Article
Full-text available
Several advantages of supplementary cementitious materials (SCMs) have led to widespread use in the concrete industry. Many various SCMs with different characteristics are used to produce sustainable concrete. Each of these materials has its specific properties and therefore plays a different role in enhancing the mechanical properties of concrete. Multiple and often conflicting demands of concrete properties can be addressed by using combinations of two or more SCMs. Thus, understanding the effect of each SCM, as well as their combination in concrete, may pave the way for further utilization. This study aims to develop a robust and time-saving method based on Machine Learning (ML) to predict the compressive strength of concrete containing binary SCMs at various ages. To do so, a database containing a mixture of design, physical, and chemical properties of pozzolan and age of specimens have been collected from literature. A total of 21 mix design containing binary mixes of fly ash, metakaolin, and zeolite were prepared and experimentally tests to fill the possible gap in the literature and to increase the efficiency and accuracy of the ML-based model. The accuracy of the proposed model was shown to be accurate and ML-based model is able to predict the compressive strength of concrete containing any arbitrary SCMs at ay ages precisely. By using the model, the optimum replacement level of any combination of SCMs, as well as the behavior of binary cementitious systems containing two different SCMs, can be determined.
... A potential application of the proposed MS model in future studies is in the design of air pre-purification processes (Ackley et al., 2003) by evaluating the mixture adsorption of CO, CO 2 , N 2 and NO on clinoptilolite, which has not been addressed so far, even though some aspects of singlecomponent adsorption are available in the literature (Triebe and Tezel, 1995). ...
Article
Clinoptilolite is a low-cost and abundant natural zeolite with a high CO2 selectivity, which is abundant in many regions around the world, but with limited industrial use. By combining experimental and theoretical (molecular simulation) approaches, the present work aims at contributing with fundamental data to assist the design of adsorption processes based on this zeolite. A sample of naturally occurring (raw) clinoptilolite was characterized by TGA, XRD, XRF, N2 adsorption isotherms at -196 °C and CO2 at 0 °C. Single-component (CO2, N2, CH4 and O2) and binary (CO2/CH4 and CO2/N2) equilibrium isotherms were measured gravimetrically. Column dynamics experimental data were obtained in order to validate a fixed-bed model, which was then used to evaluate the performance of separation processes. Molecular simulation (MS) was used to build a predictive zeolite model validated with experimental data for CO2, N2, CH4 and O2 able to investigate adsorption of mixtures and gas diffusion. TGA results demonstrated structural stability up to 600 °C with the X-ray diffraction pattern revealing clinoptilolite as the main phase, together with cristobalite and other silicon phases as contaminants. The textural properties obtained from N2 adsorption isotherms at -196 °C of the studied sample were comparable to those reported in the literature, though inaccurate for the actual clinoptilolite structure, which poses significant diffusional resistance for N2 at such temperature. IAST combined with Sips model was used to predict the behavior of mixtures. The proposed clinoptilolite MS model was used to verify the suitability of IAST in predicting mixture equilibrium on clinoptilolite and to predict the selectivity of CO2 over O2. The MS model was able to assess the equilibrium effects in the adsorption of the CH4-N2 mixture and to confirm the relationship between the diffusivity of gases and the positioning and nature of cations in the structure. The fixed-bed model highlighted the different performances of the raw and exchanged clinoptilolite samples, including the theoretical Na-clinoptilolite crystal predicted by the MS model. Together with experimental data, the MS model can be used to aid the design of separation processes of such gas stream with multiple components using clinoptilolite.
... Many industrial molecule separation applications strongly rely on the selective hosting capabilities of zeolites [130][131][132][133][134][135]. For example, xylene molecules diffusing along the zeolite pores can undergo isomerization, disproportionation and 1 5 transalkylation reactions [136][137][138][139]. Before molecules can be transformed inside a zeolite, the molecules have to be adsorbed and then diffuse to the active sites [140,141]. ...
... Zeolites and zeotypes have emerged as some of the most significant crystalline microporous materials. Owing to their structural variability and widespread industrial applications, they have been extensively studied [1][2][3]. The silicoalumino-phosphate zeolite SAPO-34 with a CHA framework is an important microporous crystal with uniform and intricate channels, high specific surface area, adsorption capacity, and high thermal and hydrothermal stabilities, which have been widely used in catalysis [4,5], adsorption, ion-exchange, separation [6], etc. ...
Article
Full-text available
A triclinic SAPO-34 molecular sieve was synthesized ionothermally. The as-synthesized products were characterized by powder X-ray diffraction (XRD), scanning electron microscope (SEM), nuclear magnetic resonance (NMR), fourier infrared spectrometer (FT-IR) and thermogravimetric (TG) analyses. The formation mechanism of the hierarchical porous triclinic SAPO-34 zeolites and the factors affecting the morphology of the SAPO-34 molecular sieve were investigated. The results show that the formation mechanism of the hierarchical pores is in accordance with Ostwald ripening theory, and the accumulation of grains constitutes the existence of mesopores and macropores. The crystallization temperature, ionic liquid type, and organic amines can effectively change the morphology and crystallinity of the SAPO-34 molecular sieve. The crystallization temperature, ionic liquid and template have great influence on the (111) crystal plane, thus affecting the morphology of the molecular sieve. Moreover, it can be proven through NMR and TG analyses that ionic liquids and organic amines can be used as structure directing agents together.
... Therefore, an effective method is needed to decompose this dye. 6 Photolysis is one possible method that TiO2 / zeolite and ZnO / zeolite are effective catalysts of the related azo dye congo red 4,7 . Zeolite is a naturally occurring, an underutilized mineral found in Java and Sumatra in Indonesia. ...
... Zeolitites (rocks with more than 50 % in zeolite content) have been used since ancient times (in construction, as lightweight dimension stone and for the production of pozzolanic cements and concrete); other uses are in the field of soil amendment and water regulation output in agriculture, while most of them have been extensively developed in the last half century: hydroponic agronomy and horticulture; water and wastewater treatment, soil decontamination from heavy metals and radioactive elements, adsorption and catalysis, aquaculture and animal feeding, pet litter and animalwaste treatment, purification and separation of gases, etc. (Ackley et al., 2003;Wang and Peng, 2010;R. de Gennaro et al., 2009, and references therein;B. ...
Article
Full-text available
This paper focuses on the authigenic mineralization processes acting on “Tufo Rosso a Scorie Nere” (TRS), i.e. one of the main pyroclastic units of the Vico stratovolcano (Latium, Italy). The pyroclastic deposits appear in general massive and made of “black vitreous vesiculated juvenile scoriae”, immersed in an ashy matrix lithified after zeolitization processes. The main minerals are chabazite and phillipsite, and the zeolitic content is locally variable, reaching 68 % wt. Zeolites grow replacing both amorphous fraction and pre-existing phases, occurring inside both matrix and scoriae. Concerning scoriae, zeolitization moves from the rim to the core of the scoriaceous fragment as a function of (a) temperature of the fluids and (b) permeability (primary or secondary). Composition of parental fresh glass and that of zeolitized rocks is compatible with trachyte chemistry, lightly undersaturated in SiO2, and the alteration processes modified the parental rock chemical features. Zeolites genesis is ascribed to a “geoautoclave-like system”, and zeolites display a Si/Al ratio similar to that of the parental glasses. TRS presents promising mineralogical characteristics as supplementary cementitious material in the production of mixed cements.
... Natural CHAs, found in sedimentary or other geological environments, typically do not have this low SAR and are only preferred over synthetic zeolites in specific gas separations. 1 The CHA structure consists of the secondary building units double-six rings (D-6Rs) and the tilted four-ring (4R) linking the D-6Rs into a three-dimensional crystal. The cation-free window of CHA is 3.8 Å, which makes Al-rich CHA ideal for tailoring the pore size with different cations to selectively adsorb one gas over another on a kinetic basis. ...
... These range from industrial gas separation, environmental monitoring and remediation, basic geochemistry, geomaterial characterization, and nuclear power byproduct cleanup and storage, among others. Whereas many of these systems utilize synthetic materials for separations or catalytic processes, others occur in geologic systems, where the materials are naturally more heterogeneous (Ackley et al. 2003). Many techniques have been developed to characterize relatively small porous media samples (e.g., BET, MIP, quartz microbalance, small-angle neutron scattering, X-ray computed tomography (Anovitz and Cole 2015)). ...
Article
Full-text available
Uptake of noble gases into heterogeneous geologic core samples was measured using a piezometric methodology. In addition to measuring accessible porosity—as with gas pycnometry—by monitoring the rate of pressure decay, this method can also be used to estimate the gas effective diffusivity in the sample. In contrast to previous applications of this method, where milligram quantities of fractured grains are characterized, here approximately kilogram core samples were left intact when tested. In doing so, a more representative sample of the heterogeneous field geology is provided. Additionally, alteration of the pore structure and connectivity during sample preparation is avoided. To scale the piezometric method from milligrams to kilograms, the system was designed to operate at medium vacuum (1 to 100 Pa) to restrict transport in pores less than approximately 60 µm to large Knudsen numbers. To test the system performance, two samples of interest were selected: a rhyolitic welded tuff from Blue Canyon Dome at the Energetic Materials Research and Testing Center and a zeolitized non-welded rhyolitic tuff from the Nevada National Security Site. Three noble gases were utilized in this test series; Argon and xenon as they are of direct interest to nuclear monitoring efforts and helium as it is a weakly adsorbing reference standard. Additionally, mercury intrusion porosimetry measurements were made on subsamples of the core to compare the observed porosity by the two methods and to discuss gas transport rates in the context of the measured pore distribution. Article Highlights The piezometric method was extended to measure transport in intact geologic core samples between 800 and 1400 g. Transport in the pores spaces was restricted to Knudsen flow using medium vacuum, enabling a closed-form solution. Argon and xenon in a zeolitized tuff core exhibited significant adsorption and enhanced transport relative to helium.
... The optimal replacement percentage suggested by various authors are 10% and 15% of cement weight [22][23][24][25]. Although some problems associated with the inclusion of zeolites are the properties of zeolite added cement composite that greatly depends upon the source of zeolite [26,27]. In some cases, it can reduce the strength of the composite, especially at the early age of the hydration process [4,28]. ...
Article
To lower the carbon footprint and alleviate global warming, it is essential to reduce cement consumption in concrete. In an endeavour to mitigate the problem, use of virgin cement can be curtailed by adopting pozzolanic materials as a partial substitution to cement. To address the constraint, present study investigated the properties of cement pastes blended with natural zeolite powder of size up to 50 μm as a partial replacement to cement. Owing to the presence of a greater quantity of reactive silica and alumina, zeolite has interesting aspects that relate to its pozzolanic behavior. This study presents the strength and durability behavior of zeolite blended concrete with up to 30% replacement to cement, in addition cement-hardened pastes were examined for microstructural properties. The progress of hydration of cement and consumption of portlandite was determined quantitatively by a thermal analysis test after 48 days of hardening. The results showed that use of zeolite powder delayed the hydration leading to a decrease in compressive strength up to 28 days. As a pozzolan material, zeolite needs a longer hydration time and it gains strength and dense structure at later curing ages, perhaps samples can lower the porosity with curing time. Interestingly, zeolite was very effective in absorbing heavy metals, zeolite added cement paste shows significantly lower leached heavy metals than the control specimen owing to its high absorption capacity.
... It have several advantages compared with other CO 2 adsorbents [10]. For example, the presence of H 2 O enhances the CO 2 adsorption capacity [13], while in Zeolitic materials the presence of water vapor dramatically decreases its adsorption efficiency, which requires high energy to be regenerated [14]. LDH materials are low-cost adsorbents compared to other adsorbents such as metal organic framework (MOF) materials. ...
Article
Full-text available
In this study, layered double hydroxide [MII-Al LDH (MII = Mg/Zn)] were used as selective CO2 adsorbents from methane stream. It prepared by microwave (MW) assisted homogenous precipitations via urea hydrolysis. The LDH structures and the type of intercalated anions were confirmed by the X-ray diffraction (XRD), Fourier transform infrared (FTIR), thermal analysis (DSC and TGA), and elemental analysis, and scanning and transmission electron microscopes (SEM and TEM) imaging. The results indicated that; the LDH morphology and the intercalated anions (carbonate and urea species) were dependent on MW power, time, and MII type. The predominant urea species were carbamate and isocyanate for Mg-Al LDH and Zn-Al LDH, respectively. The efficiencies of the LDH were tested towards CO2 capture from methane stream using dynamic flow system under atmospheric pressure. Effect of temperature and adsorption/desorption cycles were studied. The best CO2 adsorption capacities obtained at (30C) were 3.25, and 2.47 mmol g�1 for Mg-Al-LDH and Zn-Al LDH, respectively. Whereas, those for the calcined LDH (at 550C) were 2.96 and 2.29 mmol g-1 for Mg-Al-LDO and Zn-Al LDO, respectively. The results revealed the role of the intercalated urea derived anions type in enhancing the LDH adsorption properties to selectively capture CO2 from methane stream.
... Many materials, such as CO 2 sorbents, are tested. These include, among others, synthetic or natural zeolites [17][18][19][20][21] and activated carbon [22]. However, each material requires different methods of modification or activation in order to obtain better CO 2 sorption properties. ...
Article
Full-text available
One of the solid waste produced during the combustion of coal are fly ashes. Disposal challenges and environmental consequences are the results of significant process yield and atmospheric emission of fly ashes. The exact chemical composition of FA depends mainly on the type of utilised fuel and combustion conditions. It consists mainly of chemically stable metal oxides, such as Al2O3, Fe2O3, SiO2, CaO, MgO, K2O, Na2O and TiO2, but its toxicity is related to the possible presence of some trace elements, such as As, Hg, Cd, Se and Cr. The chemical and physical properties of fly ash (e.g., particle size distribution, porosity, and surface area) make it suitable as an adsorbent to remove various impurities from process flows such as flue gas stream. Its suitability for capturing mercury from flue gas was experimentally confirmed due to its abundant supply, particle size, bulk density, porosity, chemical composition and low cost. Hence, the use of fly ash as adsorbents and precursors for the production of heavy metal adsorbents is of great practical importance, as it reduces the cost of mercury capture and alleviates the problems associated with the disposal of solid waste. Studies showed that the chemical components present in fly ash additives could stimulate catalytic oxidative capacity, which increases the adsorption of Hg0 oxidation and adsorption of both Hg and CO2. The presented study analysed fly ashes from different zones of the electrostatic precipitator and verified their suitability for removing impurities from flue gases, i.e., mercury and carbon dioxide. The results outlined modified fly ash as having good Hg and CO2 removal capabilities. The adsorption efficiency of Hg reached 92% for Hg and 66% for CO2, while untreated fly ash reached 67% for Hg and 59% for CO2.
... However, because of the structure instability and low CH 4 /N 2 selectivity, these solids are still far from commercially competitive. In addition, although zeolite-based adsorbents with high structural stability and tunable sorption sites have also been studied for CH 4 /N 2 separation [13,14], their industrial use in CH 4 / N 2 separation is not considered satisfactory, owing to the recycling issue and low CH 4 uptake [13]. Among the cage-based, small-pore zeolites that have been applied to light hydrocarbon and CH 4 /N 2 separations, on the other hand, ZK-5 (framework type KFI) has received much interest, because there is still room for improvement towards industrial applications [9,15,16]. ...
Article
Decreasing crystal size and introducing more electronegative extraframework metal cations to small-pore zeolites provide clear-cut advantages for small gas adsorption and separations. Here, nanocrystalline (∼100 nm) silver-exchanged ZK-5 (Ag-ZK-5) has been prepared and studied as an adsorbent for CH4/N2 separation. Nanocrystalline Ag-ZK-5 was found to show a CH4 uptake of 1.6 mmol g⁻¹ at 298 K and 1.0 bar and an IAST CH4/N2 selectivity of 11.8 in vacuum-swing adsorption mode, which are the highest values ever reported for zeolite-based adsorbents for CH4/N2 separation. This zeolite is also characterized by fast adsorption kinetics and excellent regenerability, revealing its high potential for practical applications. It appears that nanocrystalline Ag-ZK-5 may have a more homogenous Ag⁺ distribution than the microcrystalline one, providing the former zeolite with a better CH4/N2 separation performance.
... Zeoliitteja on jo kauan pidetty erinomaisina vaihtoehtoina kaasujen puhdistuksessa ja erotuksessa (Ackley, Rege & Saxena, 2003 Zeoliitit muodostuvat kahdesta tetraedrin muotoisista rakenneosista, joissa neljä negatiivistesti varautunutta happiatomia ympyröivät keskusatomeja, joita voivat olla alumiini-ioni/atomi ja pii-ioni/atomi (kuva 2). Rakenteessa tetraedrimuodot jakavat yhdessä vuorotellen yhden happiionin, jolloin syntyy paikallisia varauseroja (Bhatia, 1989). ...
Thesis
Full-text available
Online ja in-situ mittareita voidaan käyttää laboratoriossa nopeiden, halpojen ja luotettavien jatkuvatoimisten mittausten tuottamisessa. Typen olomuotojen tutkimiseen on kehitetty tällaisia analysointimittareita, jotka tunnistavat kaasuvirrasta typpiyhdisteiden pitoisuuksia. Tällaisia mittareita voidaan yhdistää laboratorioon rakennetuissa analyysilaitteistoissa antamaan helposti nopeita tuloksia sopivalla tarkkuudella. Tässä työssä oli tavoitteena suunnitella ja rakentaa laboratorio-olosuhteisiin kaasuanalyysilaitteisto, jolla pystytään tutkimaan kaasuvirtaa puhdistavia materiaaleja seuraamalla kaasun pitoisuuksia jatkuvatoimisella mittarilla. Rakennetulla laitteistolla suoritettiin koeajoja, joilla seurattiin kaasuvirran käyttäytymistä laitteistossa, sekä suoritettiin mittauksia kolmella erilaisella tutkittavalla puhdistusmateriaalilla. Työssä rakennettiin saatavilla olevista laboratoriotarvikkeista suunniteltu, jolla kyettiin suorittamaan sekä koeajoja, että mittauksia. Laitteistossa käytetty mittari ei kuitenkaan tuottanut tarpeeksi luotettavia tuloksia tarkempia analyysejä varten. Kehitys- ja jatkotutkimusehdotuksia on esitettynä työn lopussa. Työ on osa Suomen Akatemian tutkimusta, jossa tutkitaan mm. erilaisia orgaanisia ja mineraalipitoisia adsorbentteja, joilla pyritään typen talteenottoon ja sen saattamiseen takaisin kiertoon.
... Natural zeolites possess serious drawbacks, such as variable composition. They may also contain impurities and may exhibit poor performance in separation and adsorption [31]. For instance, according to Ramezani et al. natural zeolites were only able to adsorb 15.2 milligrams of methylene blue per gram of zeolite [32]. ...
Article
Poly-anionic Xanthan gum-based hydrogels were synthesized and used as potent adsorbents for the removal of dye pollutants from waste water effluents. The adsorbents were synthesized by esterification of Xanthan gum with maleic anhydride, followed by thiol-ene cross-linking chemistry with 2,2′-(ethylenedioxy)diethanethiol. Methylene blue was used as model cationic dye to mimic dye polluted water. The adsorption kinetics of methylene blue by the Xanthan gum-based hydrogels was modeled by pseudo-first-order, pseudo-second-order and intraparticle diffusion models. The experimental adsorption data at 25°C was modeled by the Langmuir isotherm. The effects of adsorption operation parameters such as the initial dye concentration, pH, ionic strength, and adsorbent dose were also investigated. The pseudo-second-order and Langmuir models were found to be the most appropriate models for the description of the adsorption kinetics and isotherm data, respectively. The Xanthan gum-based hydrogel exhibited a high adsorption capacity of up to qmax=435 mg/g (1.35 mmol/g) towards methylene blue. The incorporation of carboxylic acid groups in the Xanthan gum backbone afforded appreciable charge density at pH > 5, which can effectively facilitate the binding of cationic dye molecules. Consequently, the uptake mechanism of methylene blue by the polyanionic Xanthan hydrogel is attributed mainly to the electrostatic interactions. The Xanthan gum-based hydrogel had a remarkable selectivity for the cationic dye in binary and ternary mixtures of methylene blue with methyl orange or sunset yellow FCF. Finally, the hydrogel showed a potential to be re-used for at least for twenty times after regeneration and maintaining over 95% efficiency dye removal as well as recovery.
... Zeolites with both natural and synthetic origins are metallosilicate materials possessing unique physicochemical properties such as crystallinity, acidity, hydrothermal stability, ion-exchange ability and shape selectivity [1,2]. Due to these prominent features, zeolites are applicable in different commercial fields such as catalysis, adsorption and separation processes [3][4][5]. On the other hand, their synthesis is a challenging task that requires the tuning of several parameters in order to obtain the desired product at the end of the process. For instance, chemical compositions of precursors, type of mineralizers, temperature, aging time as well as the type and concentration of structure-directing agents (SDAs) are needed to be optimized smartly during the synthesis of zeolites [6,7]. ...
Article
Full-text available
The study on the synthesis of zeolites, including both the development of novel techniques of synthesis and the discovery of new zeolitic frameworks, has a background of several decades. In this context, the application of organic structure-directing agents (SDAs) is one of the key factors having an important role in the formation of porous zeolitic networks as well as the crystallization process of zeolites. There are various elements that are needed to be explored for elucidating the effects of organic SDAs on the final physicochemical properties of zeolites. Although SDAs were firstly used as pore generators in the synthesis of high-silica zeolites, further studies proved their multiple roles during the synthesis of zeolites, such as their influences on the crystallization evolution of zeolite, the size of the crystal and the chemical composition, which is beyond their porogen properties. The aim of this mini review is to present and briefly summarize these features as well as the advances in the synthesis of new SDAs during the last decades.
... 8 Zeolites widely used in gas separation have several positive features such as high temperature and pressure stability and low energy consumption in regeneration. 9 The adsorption and separation of the zeolites are determined by many elements such as their microstructure, the nature and number of balanced cations, the silicon-to-aluminum (Si/Al) ratio, and so on. 10−12 There are more cations in the framework in the case of the lower Si/Al ratio, which are preferred adsorption sites and would enhance the electrostatic field. ...
Article
Full-text available
Efficient adsorbents are critical to the purification of liquefied natural gas (LNG) by the adsorption method. In this study, the physiochemical properties of JLOX-500 and 13X were examined. JLOX-500 with more Al content had a more compact unit cell, a larger surface area and pore volume, a smaller average pore size, and more microchannels on the surface than 13X. The separation performance of the two adsorbents was evaluated by the adsorption experiment. The CO2 adsorption capacity of JLOX-500 was higher than that of 13X, while the equilibrium and ideal selectivity and separation factor of CO2/CH4 were also larger for JLOX-500. Especially in dynamic adsorption, the CO2 adsorption capacities at 50 ppm of the gas mixture at the outlet were 3.46 and 1.64 mmol/g for JLOX-500 and 13X, respectively. The adsorption heats of CO2 and CH4 on JLOX-500 were 40.50 and 18.77 kJ/mol, whereas these values were 31.49 and 18.50 kJ/mol for 13X, respectively. A better separation performance for JLOX-500 was observed because of fewer binders and a lower Si/Al ratio (1.34). The Toth adsorption isotherm model described best the experimental data. According to the results of this study, JLOX-500 was a more efficient adsorbent used in purification for LNG production at high pressure with low CO2 concentration.
... For these samples, the −qst values assume the following order: −qst CO 2 > −qst CH 4 > −qst H 2 and this is largely due to the magnitudes of the quadrupolar moments of the adsorptive molecules (Table 1) with the cations of structure of chabazite zeolites. Sorption data of CO 2 on some other adsorbents were previously studied [31]. The −qst values related to the CHA zeolites correspond to the following decreasing sequence: −qst (CO 2 ): Na: 1 > 3 > 2; Ca: 1> 3 > 2; Ca: 2 > 3 > 1 and Mg: 3 > 1 > 2 −qst (CH 4 ): Mg: 1 > 2 > 3; Ca: 2 > 1 > 3; Na: 1 > 2 > 3, while for −qst (H 2 ): Mg: 1 > 2 > 3, Ca: 2 > 3 > 1, and Na: 2 > 3 > 1. ...
Article
Full-text available
This paper describes the isosteric enthalpy through narrow pores at low levels of coverage through adsorption of CO2, CH4, and H2 on pores in natural chabazite exchanged with aqueous solutions of Na+, Mg2+, and Ca2+ salts at different concentrations, and with variable time and temperature of treatment. Experimental data of CO2, CH4, and H2 adsorption were treated by the Freundlich and Langmuir equations. Complementarily, the degree of interaction of these gases with these zeolites was evaluated by the evolution of isosteric enthalpy of adsorption. The exchange with Mg2+ and Na+ favors an increase in the adsorption capacity for CO2. while that of Ca2+ and Mg2+ favor adsorption through to H2 and CH4. These cations occupy sites in strategic positions S4 and S4’, which are located in the channels and nanocavities of these zeolites. The presence of Ca2+ and Mg2+ at S4 and S4′ sites causes increased adsorption into the nanocavities and on the external area of the ion-exchanged zeolites. Depending on the conditions of the exchange treatment, Ca2+ and Mg2+, and Na+ were found to be most favorable, well distributed, and accessible for CO2, CH4, and H2 adsorption.
Article
Currently, due to economic importance and environmental characteristics, biopolymeric matrices containing metal-organic frameworks (MOFs) are being extraordinarily considered in high-tech and commercial applications. In these materials, MOFs are usually incorporated into polymer chains and highly effective and multi-functional organic-inorganic composites are fabricated with high electrical, optical, mechanical, and thermal features. The excellent porous structure, flexibility, and organic-inorganic nature of MOFs are interesting properties for their examination in the fabrication of biopolymeric composites. Here, we provide a complete and vital review of MOF/biopolymeric composites in recent years and discuss their importance and features. Additionally, since bio-nanocomposite materials based on biodegradable polymers and MOFs have presented great potential in the past decade, in this review, we have critically concentrated on the most significant and interesting applications of MOF/biopolymeric composites and their advantages in modern technology. © 2021 The Royal Society of Chemistry and the Centre National de la Recherche Scientifique.
Article
Hydrothermal synthesis of SSZ-13 zeolite from precursors comprises many unanswered fundamental questions, in which understanding the effects of alkali metal cations on the structural rearrangement during the crystallizing period is an active and expanding area of research. Experimental results showed that the continuous crystallization process of SSZ-13 crystals can be easily hindered by the amorphous gel during the synthesis process. Accordingly, we carefully explored and repeated the crystallization period of SSZ-13 zeolite with different K⁺ mole ratios, which demonstrated significant effects on their crystallization behaviors with the easy breaking of amorphous gel state. The crystallization time was obviously shortened to 18 h. Theoretical calculation results also demonstrated that K⁺ cation in the precursor solution is more inclined to control the successive deprotonation process due to the higher activation energies for Si–O–Al bonds formation. Accordingly, the SSZ-13 zeolite sample tend to realize fast synthesis and transform into scattered crystals without aggregation by addition of K⁺ cation.
Article
The Li⁺, K⁺, Mg²⁺ and Ca²⁺-exchanged X zeolites were prepared using ion exchange method for producing efficient adsorbents that could be used in the purification of liquefied natural gas (LNG). The adsorption, separation and regeneration characteristics of the samples were systematically explored and discussed using static adsorption of pure gases, dynamic adsorption of a binary gas mixture (3%CO2 and 97%CH4) and regeneration experiments. The results showed that Li13X had the largest surface area of 520 m²/g, whereas Ca13X possessed the highest micropore volume of 0.25 m³/g with the smaller pore size observed from the pore size distribution. The adsorption capacity of Li13X for CO2 (4.10 mmol/g) was almost the same as that of Ca13X (4.12 mmol/g), which were larger than all the other samples at 120 kPa and 30 °C. However, K13X had the highest static CO2/CH4 separation factor 46, which was due to the increased basicity of the framework. For the dynamic adsorption, Ca13X possessed the highest CO2/CH4 separation factor 93, and showed the smallest CH4 adsorption capacity of 1.22 mmol/g. As for the regeneration of the proposed adsorbent, the heat requirement for CO2 in dynamic was not only affected by the isosteric heat, but was also dependent on the competition between CH4 and CO2. Moreover, the static and dynamic vacuum regenerations had the same tendency and mainly depended on the pore size distribution.
Article
The main contaminants in biogas namely carbon dioxide, hydrogen sulfide, and siloxanes limit its application especially in engines by reducing energy density and causing corrosion on machine parts. Furthermore, the carbon dioxide in biogas contributes highly to global warming. Therefore, biogas should be upgraded to increase its safe application. Most commercial methods of biogas cleaning are expensive for small and medium scale digesters. There is no review documentation detailing the usage of natural materials in the purification of biogas. The aim of the current study was to systematically and critically review recent developments in the applications of natural materials in the purification and upgrade of biogas. Documented literature indicate that the low-cost natural adsorbents have potential in purification of biogas. The adsorption capacity of biogas contaminants for most materials can be enhanced by physical and chemical activation. The two mechanisms through which these material eliminate carbon dioxide in biogas namely surface adsorption and wet carbonation process have been discussed. In addition, the study looked at the factors that affect the removal of carbon dioxide from biogas using natural materials. The adsorption capacity of biogas contaminants for different natural and modified materials were reviewed. Furthermore, a summary of the merits and demerits of different natural adsorbents for biogas purification is presented. Future studies should investigate the methane loss during upgrading process using low-cost adsorbents. Comparative investigations of the process cost-effectiveness of using natural materials to upgrade biogas should be carried out to determine their suitability against the commercial processes.
Article
The aim of this research was to show the better use of internal resources and increased capability of utilizing and optimizing minerals. Also, in this research we tried to present a new way of petrochemical wastewater treatment. In this sample of bentonite, after the production process in microwave through digestion method with Nano Precision, a long chain of detergents was processed and optimized with an organic material (dimethyl octadecyl ammonium chloride). In the beginning of tests, a statistical method was drawn by MINITAB software and Taguchi method. Sampling was made in different times and testing started by a standard method. Among measuring factors, 5 factors of turbidity, TSS, TDS, pH, and COD were evaluated and their changes were investigated in different times based on the amount and type of materials. The effluent COD and BOD are very important. The petrochemical wastewater was measured and it was90ppm(COD) and 3 ppm(BOD). Also, the highestlevel of turbidity for material A (modified bentonite) was 1.2 NTU with 10mg/L of sludge. Considering that the country needed a better wastewater treatment through environment protection, modification of bentonite's structure, and nano application process in this industry along with various available methods, we aimed to take a step towards the development of the country.
Thesis
Dans le cadre du Traité d’Interdiction Complète des Essais nucléaires, le Commissariat à l’Energie Atomique et aux Energies Alternatives (CEA) développe des systèmes de détection des essais nucléaires en se basant sur la mesure des isotopes radioactifs du xénon, tels que le Système de Prélèvement d’Air en Ligne avec l’Analyse des radioXénons. L’adsorption est un procédé adapté pour ce type d’applications mais nécessite l’utilisation de matériaux adsorbants très performants pour piéger et séparer les gaz rares d’intérêt présents dans l’air à l’état de traces. Ce travail doctoral a tout d’abord permis de poser un cadre méthodologique permettant de comparer les matériaux adsorbants disponibles pour séparer le xénon aux faibles pressions partielles et de sélectionner la zéolithe Ag@ZSM-5. De nombreuses techniques ont été employées dont la microscopie électronique à transmission et la simulation ab initio afin d’étudier le vieillissement de ce matériau en conditions procédés, lié aux étapes d’élution en température et aux conditions environnementales, et d’approfondir la connaissance de cet adsorbant. L’influence du support zéolithique sur la formation et la stabilité des particules métalliques, ainsi que l’interaction entre les nanoparticules et le xénon ont en effet été investigués. Finalement la zéolithe Ag@ZSM-5 a été mise en application dans un pilote de laboratoire automatisé. Ce procédé compact de séparation des gaz rares basé uniquement sur des étapes d’adsorption présente des performances encourageantes et permet d’envisager l’utilisation de ce matériau dans des applications variées, de la dépollution de l’air en radon jusqu’à la production industrielle de xénon
Article
Full-text available
Zeolite-clay was successfully employed in as resistance type humidity sensor. Zeolite-clay humidity sensor was synthesized by crushing into powder and soaked into 6% H 2 SO 4 while stirred for two hours using a magnetic stirrer. The solution was filtered, washed using aquadest and dried at 100°C for 5 hours with the mixture process of zeolite and clay were varied into 10%:0%, 9.5%:0.5%, 9%:1%, 8.5%:1.5%, and 8%:2%. The result pressed with a size of 3x3x1 cm ³ using a hydraulic under 3 tons pressure for 10 minutes and heated at temperatures of 800°C.Zeolite-clay was placed in a testing chamber equipped with the electrode that connected to an electrical supply of 3 Volt. The electrical resistance was recorded using Multimeter Hydra Series III Fluke when exposed with humidity in range of 18.5-99% RH. Zeolite 8%-clay 2% sensor exhibits the highest sensitivity properties, which indicate saturated resistance value at 99% RH.Meanwhile, Zeolite 8.5 gr-clay 1.5 gr revealed the highest response value at 54.3 Mega Ohm. Based on SEM and EDX characterization, the ratio of Si/Al and microstructure surface have an effect towards humidity detection process. The results indicate enhancement than previous research on zeolite as a sensor, and therefore Zeolite-Clay has proved the capability to detect humidity.
Article
Computational high-throughput screening using molecular simulations is a powerful tool for identifying top-performing metal-organic frameworks (MOFs) for gas storage and separation applications. Accurate partial atomic charges are often required to model the electrostatic interactions between the MOF and the adsorbate, especially when the adsorption involves molecules with dipole or quadrupole moments such as water and CO2. Although ab initio methods can be used to calculate accurate partial atomic charges, these methods are impractical for screening large material databases because of the high computational cost. We developed a random forest machine learning model to predict the partial atomic charges in MOFs using a small yet meaningful set of features that represent both the elemental properties and the local environment of each atom. The model was trained and tested on a collection of about 320 000 density-derived electrostatic and chemical (DDEC) atomic charges calculated on a subset of the Computation-Ready Experimental Metal-Organic Framework (CoRE MOF-2019) database and separately on charge model 5 (CM5) charges. The model predicts accurate atomic charges for MOFs at a fraction of the computational cost of periodic density functional theory (DFT) and is found to be transferable to other porous molecular crystals and zeolites. A strong correlation is observed between the partial atomic charge and the average electronegativity difference between the central atom and its bonded neighbors.
Article
Aluminosilicate/silicate and carbonate materials (pure and industrial) interacted with natural Acid Mine Drainage (AMD) under ambient conditions for different time periods in order to elucidate the chemical processes at the aluminosilicate and carbonate mineral-AMD interface. More precisely, powdered materials were subjected to macroscopic neutralization experiments (using on-line pH-measurements, Inductively Coupled Plasma Optical Emission Spectroscopy, Powder X-ray Diffraction and Scanning Electron Microscopy with Energy Dispersive Spectroscopy), whereas interacted mm-sized single crystals were examined by means of nanoscale microscopic (in-situ Atomic Force Microscopy) and surface & bulk spectroscopic techniques (X-ray Photoelectron Spectroscopy, ¹²C-Rutherford Backscattering Spectroscopy, Solid-State ²⁹Si and ²⁷Al Solid-State Magic-Angle-Spinning Nuclear Magnetic Resonance). The carbonates were proven to be more effective for neutralization of AMD, related to adequate removal of metals from the contaminated aqueous medium, but they are readily dissolved. The application of aluminosilicate/silicates showed that the removal of metals is considerably lower, and the pH stabilized at lower values, but they are more resistant. The investigation of interacted zeolite and calcite crystals revealed changes to the macrotopography, microtopography and nanotopography of surfaces. It was indicated that coupled dissolution and sorption (surface precipitation/co-precipitation, nucleation/crystal growth, adsorption or even absorption-including solid-state diffusion) phenomena occur simultaneously. Based on the experimental results, two generalized models -in nano(molecular)-scale- can be suggested regarding interaction of AMD with aluminosilicate and carbonate mineral surfaces.
Article
Density functional theory was used to study carbon monoxide adsorption on several graphene-based surfaces. The surfaces were based on oxygen ions adsorbed (and without oxygen adsorption) on double- and triple-vacancy graphene and on a particular N-doped graphene surface. Magnetic transition, the largest adsorption energy (-6.5 eV) and CO reduction, occur in a proposed and more sensitive stationary point of the triple-vacancy graphene surface after CO adsorption. Oxygen adsorption on the former triple-vacancy graphene surface produces magnetic transition, chemisorption (-2.4 eV) forming an ester and CO oxidizes all after CO adsorption. The magnetic transition observed in both systems is correlated with charge transfer. Following the results of molecular dynamics the magnetic order prevails even at room temperature (T=300 K) in the former two systems. The results presented in this work could be useful for the development of magnetic CO sensors.
Article
Cadmium (Cd) contamination in soils is a global ecological threat. Conventional powdered biochar added to soil can temporarily immobilize Cd but is difficult to separate from soil, leading to secondary release of Cd and posing potential ecological and human health risks. The blocky biochar is also difficult to separate from the soil due to its fragile nature. One of the keys to overcome the difficulties in separating biochar from soil is to improve its mechanical strength. Blocky zeolite-biochar composites (ZBC) that have good mechanical strength were obtained after pyrolyzing the mixture of 50% feedstock and 50% zeolite powder at 400°C. ZBC and NaOH-activated ZBC (ZBCa) were applied to remove Cd from soil. After sieving Cd-loaded ZBC and ZBCa from soil, the bioavailable Cd content in the soil decreased by 59.70% and 68.54%, respectively. Zeolite contributed to improving both adsorption performance and mechanical properties of the composites. After repeating the process of “remediation-sieving-desorption-regeneration” three times, the recoveries of ZBC and ZBCa were above 97.00%, and regeneration rates were 48.70% to 83.26%, respectively. Under simulated mechanical sieving conditions, ZBC and ZBCa lost only 4.06% and 5.40% of their mass and retained their integrity. Remediation of Cd-contaminated soil with blocky zeolite-biochar composite is sustainable and safe because the removal of bioavailable Cd from soil is permanent rather than a temporary decrease of bioavailability. This study provides a reference for the preparation of separable and recyclable adsorbents for the removal of contaminants from soil.
Article
This review provides a fundamental assessment of the potential of zeolite particles incorporated into polymeric membranes in view of improving the performance of these membranes. Zeolites are of interest as extensive potential in separation processes due to their unique frameworks and properties. Significant investigations were carried out to improve conventional membrane properties by the inclusion of zeolites. Zeolite membranes can be classified into three categories: (i) self‐supported zeolite membranes, (ii) inorganic supported zeolite membranes and (iii) zeolites mixed into the polymeric membrane matrix or top layer. The focus of this review is on nano‐sized zeolite particles incorporated into the polymeric structure of the membranes, with specific attention to the polyamide layer used in pressure‐driven membrane processes such as reverse osmosis (RO). The incorporation of inorganic zeolite particles in the polymer matrix enhances the permeability without decreasing the selectivity, and increases the mechanical strength in a harsh environment, fouling and chlorine resistance of the membranes. Agglomeration of nano‐sized zeolites and defect formation are highlighted as the main obstacles to the fabrication of large‐scale high‐performance zeolite membranes in order to identify strategies to solve these issues. Among the different strategies, adding a cross‐linking agent to the interfacial polymerization process might be a promising method to fabricate homogeneous zeolite‐polymer composite membranes with excellent performance. This paper provides a better understanding of the knowledge acquired in the development of polymer‐based zeolite nanocomposite membranes and gives perspectives for future research. This article is protected by copyright. All rights reserved.
Article
Barium exchanged ETS-4 is the promising size-selective and thermally stable adsorbent in nitrogen separation from methane. The halogen contained Ba-ETS-4, named Ba-RPZ, by upgrading the steric effect has superior performance in this separation process. In this work, the Na-ETS-4 was synthesized in two ways, chlorine halogen contained and halogen free medium, and the synthesized adsorbents (i.e., RPZ and HFZ, respectively) were ion exchanged with Ba²⁺. Equilibria and kinetic adsorption properties of nitrogen and methane were investigated on two types of Ba-ETS-4 adsorbents, i.e., Ba-RPZ and Ba-HFZ. The adsorption experimental data were measured at 30 ◦C and 0-100 kPa pressure range by the static volume adsorption method. The experimental equilibrium data were correlated with the Toth isotherm. Also, the uptake rates of nitrogen and methane were correlated with Crank’s method and diffusion time constant parameter was predicted for both gases at the aforementioned conditions above. A temperature range of 250 – 400 ◦C was selected to study the impact of heat treatment on the Ba-ETS-4 adsorptive performance. Also, equilibrium and kinetic selectivities of Ba-HFZ were calculated for the first time. An acceptable equilibrium (i.e., 3.79) and kinetic (i.e., 67) nitrogen/methane selectivity have been obtained for Ba-HFZ at 375 ◦C activation temperature. Moreover, chlorine halogen by creating an extra molecular exclusion property in Ba-RPZ framework leads to an improved nitrogen/methane equilibrium (i.e., 3.9) and kinetic selectivities (i.e., 290) at 375 ◦C activation temperature.
Article
Full-text available
Hierarchical zeolites containing both micro- (<2 nm) and mesopores (2–50 nm) have gained increasing attention in recent years because they combine the intrinsic properties of conventional zeolites with enhanced mass transport rates due to the presence of mesopores. The structure of the hierarchical self-pillared pentasil (SPP) zeolite is of interest because all-silica SPP consists of orthogonally intergrown single-unit-cell MFI nanosheets and contains hydrophilic surface silanol groups on the mesopore surface while its micropores are nominally hydrophobic. Therefore, the distribution of adsorbed polar molecules, like water and ethanol, in the meso- and micropores is of fundamental interest. Here, molecular simulation and experiment are used to investigate the adsorption of water and ethanol on SPP. Vapor-phase single-component adsorption shows that water occupies preferentially the mesopore corner and surface regions of the SPP material at lower pressures (P/P0 < 0.5) while loading in the mesopore interior dominates adsorption at higher pressures. In contrast, ethanol does not exhibit a marked preference for micro- or mesopores at low pressures. Liquid-phase adsorption from binary water–ethanol mixtures demonstrates a 2 orders of magnitude lower ethanol/water selectivity for the SPP material compared to bulk MFI. For very dilute aqueous solutions of ethanol, the ethanol molecules are mostly adsorbed inside the SPP micropore region due to stronger dispersion interactions and the competition from water for the surface silanols. At high ethanol concentrations (CEtOH > 700 g L–1), the SPP material becomes selective for water over ethanol.
Article
Gaseous and volatile active compounds are versatile to enhance safety and preserve quality of agri-food products during storage and distribution. However, the use of these compounds is limited by their high vapor pressure and/or chemical instability, especially in active packaging (AP) applications. Various approaches for stabilizing and controlling the release of active gaseous/volatile compounds have been developed, including encapsulation (e.g., into supramolecular matrices, polymer-based films, electrospun nonwovens) and triggered release systems involving precursor technology, thereby allowing their safe and effective use in AP applications. In this review, encapsulation technologies of gases (e.g., CO2, ClO2, SO2, ethylene, 1-methylcyclopropene) and volatiles (e.g., ethanol, ethyl formate, essential oils and their constituents) into different solid matrices, polymeric films, and electrospun nonwovens are reviewed, especially with regard to encapsulation mechanisms and controlled release properties. Recent developments on utilizing precursor compounds of bioactive gases/volatiles to enhance their storage stability and better control their release profiles are discussed. The potential applications of these controlled release systems in AP of agri-food products are presented as well.
Article
On the basis of the density functional theory (DFT) calculations, the successive isomorphic substitution of one to six tetrahedrally coordinated Si cations by trivalent Al was systematically studied. As a result of exploring a significant number of configurations, without using a priori assumptions, it was found that the Al atoms are accommodated according to the ground state sequence in the tetrahedral sites TI − TIII − TIII − TI − TIII − TIII. The results in the general show: a) Al cations preferentially occupy TIII positions, b) the distribution of cations in the framework does not violate Löwenstein’s rule, c) the distribution of cations in the framework does not satisfy Dempsey’s rule, and d) only one Al cation is found per ζ-cage.
Article
Zeolite-based porous ceramics were developed using inexpensive natural zeolite powder with B2O3, Bi2O3, and SiO2 additives and sintered at low temperatures (500–600 °C) compared to those in previous studies (800–1300 °C). The effects of sintering temperature on the porosity, microstructure, flexural strength, thermal conductivity, and water absorption capacity were investigated. As the sintering temperature increased from 500 to 600 °C, the porosity of the zeolite-based porous ceramics decreased from 49.6 to 45.7%, which is attributed to improved densification at high temperature via viscous flow of the glass phase. The flexural strength and thermal conductivity increased from 5.4 to 11.9 MPa and from 0.19 to 0.30 W/mK, respectively, with increasing sintering temperature. The samples sintered at 550 and 600 °C were highly stable in water, with high absorption capacities of 37.6 and 34.1 wt%, respectively. The typical flexural strength, thermal conductivity, and water absorption capacity of the zeolite-based porous ceramic sintered at 550 °C (~ 46% porosity) were 8.4 MPa, 0.24 W/mK, and 37.6%, respectively.
Article
This paper describes the synthesis of FER zeolite using commercially available 4-(aminomethyl)pyridine as organic structure-directing agent(OSDA). FER zeolites were prepared in mixtures with SiO2/Al2O3 molar ratios in a narrow range and the resultant products possessed a typical flake-shaped morphology. The crystallization of FER zeolite was tracked in order to better understand the formation mechanism and the products obtained at different crystallization time were systematically characterized using multiple techniques. It showed that a majority of Si atoms and nearly all the Al atoms transformed into the solid phase during the hydrothermal synthesis. The rearrangement of inorganic species gave rise to zeolitic 5-membered rings(5-MRs) and 6-membered rings(6-MRs). Consequently, FER zeolite crystals were formed by the consumption of amorphous bulky gel/solid matrix. Tracking the synthesis process of FER can help.
Article
Full-text available
The traditional hydrothermal synthesis methods are mainly performed under batch operation, which generally takes few days to weeks to yield a zeolite with the desired properties and structure. The zeolites are the backbone of the petrochemical and wastewater industries due to their importance. The commercial methods for zeolite synthesis are e xpensive, laborious and energy intensive. Among waste products, incense sticks ash is a compound of aluminosilicates and could act as a potential candidate for the synthesis of zeolites for daily needs in these industries. Incense sticks ash is the byproduct of religious places and houses and is rich in Ca, Mg, Al and Si. As a result, incense sticks ash can be proven to be a potential candidate for the formation of calcium-rich zeolites. The formation of zeolites from incense sticks ash is an economical, reliable and eco-friendly method. The application of incense sticks ash for zeolite synthesis can also minimize the problem related to its disposal in the water bodies, which will also minimize the solid waste in countries where it is considered sacred and generated in tons every day.
Article
Full-text available
The abatement of nitrogen monoxide (NO) from the polluted air is a very significant challenge in the industries. In the present work, molecular simulation was carried out to study the ability of pure silica CHA- and DDR-type zeolite membranes in separation of NO molecules from a gas mixture including NO/N2/O2 under temperature ranges (298, 323, and 348 K) and applied pressure up to 1000 kPa. The simulation results showed the N2 and O2 molecules transferring through Si-CHA and Si-DDR membranes, while NO molecules could not pass through them. In this regard, high removal of NO molecules from NO/N2/O2 gas mixture through the studied membranes was obtained, which makes them promising in separation of NO molecules from polluted air at industrial relevant compositions. Besides, the potential of mean force (PMF) profile was calculated for gas molecules along the z-direction through the studied membrane, which confirmed the simulation results for molecules permeation. The PMF indicated that the NO molecules face the highest energy level difference as an energy barrier, and cannot pass through the membranes under studied conditions. It is hoped that this research will be helpful for the design and development of membranes in order to remove contaminants from gas mixtures.
Article
For air separation, the separation method relying on adsorbents has attracted wide attention as a low energy consumption process, and the development of O2-selective adsorbents is of great significance. Metal-organic frameworks with coordinatively unsaturated transition metal sites have great potential in O2-selective adsorption, but most of them cannot be completely regenerated at ambient temperature or can only be effective at very low temperatures. Herein, we report two mixed-ligand metal–organic framework adsorbents [M(AIP)(BPY)0.5·H2O]n·2nH2O with coordinatively unsaturated cobalt(II) and nickel(II) sites, which can preferentially adsorb O2 versus N2, and their IAST O2/N2 selectivities are both significantly greater than 1 at 25 °C. These materials exhibited excellent stability and had no loss of adsorption capacities even after immersion in water for 7 days. More importantly, O2 adsorption–desorption cycle experiments showed that these adsorbents can be completely regenerated at ambient temperature after adsorbing O2, and the breakthrough experiments further confirmed their dynamic O2/N2 separation potential and regeneration ability. The results of theoretical calculations suggested that the interactions between adsorbents and O2 are stronger than those of N2, and they have relatively obvious differences in the N2 and O2 interaction energies. This work provides inspirations for searching for metal–organic frameworks that can selectively adsorb O2 at ambient temperature.
Chapter
Palm oil mill effluent (POME) is characterized by high biological oxygen demand (BOD) and chemical oxygen demand (COD) content. Anaerobic digestion pond is a very sustainable form of processing because it does not release methane gas into the air, potent greenhouse gas. Proper pretreatment strategies are necessary to handle recalcitrant materials. Nutritional addition methods and digester configurations have been developed to produce and capture as much methane gas as possible to reduce impurities. Organic loading rate (OLR) is one of the key parameters that must be maintained high to ensure the biogas production's continuity and stability. Various operating conditions, especially the feed and pond temperatures, affect the OLR and removal of organics. Biogas purification is aimed to remove hydrogen sulfide and carbon dioxide, hence, increasing the methane concentration.
Article
A progressive machine learning methodology was utilised to not only identify the relationship between zeolite synthesis descriptors but also evaluate the potential for machine learning to predict the quantitative output of synthesis routes. The hypothesis was if statistics and machine learning principles are applied, then it may enable pre-evaluation and result in potential increases to zeolite yield and performance. Various machine learning algorithms were applied to zeolite LTA synthesis data; including linear regression, ridge regression, regression tree, random forest, XGBoost and artificial neural network models. Major findings included the use of input synthesis variables and the product yield for model training. Additionally, the use of both quantitative and qualitative X-ray diffraction (XRD) data was required to accurately determine product composition (“hybrid XRD” approach). Models, including linear regression, ridge regression and regression trees, returned R2 values less than 0.5 indicating the complexity inherent with the problem. Embedded tree-based models, including random forest and XGBoost, resulted in testing accuracies equal to R2=0.620 and R2=0.700, respectively. An ANN model achieved the highest accuracy among all machine learning algorithms of R² = 0.84. Notably, this model was the most accurate because it exploited non-linear and complex relationships within a multidimensional and intercorrelated dataset such as that obtained from zeolite synthesis. Despite reaching an accuracy greater than 80%, the ANN model accuracy continued to increase by increasing the network size, indicating that advanced deep learning models should be considered as part of future work.
Article
In spaceflight applications, molecular contamination control has become one of the most challenging issues. Porous zeolites are a potent molecular adsorbent with advantages of efficient adsorption at low pressure and/or high temperature, high interaction with adsorbates, and superior durability in extreme environments. Herein, zeolite 13X pellets were selected for adsorption of stearyl alcohol (C18H37OH) as a target molecular contaminant. Considering the excellent hydrophilicity of the zeolite 13X which limits the adsorption of most hydrophobic organic molecules, modification of the zeolite 13X by deposition of TiO2 via atomic layer deposition (ALD) technology was performed. Results show that ALD-grown TiO2 not only improves hydrophobicity but also renders high activity, whilst retains the hierarchical pores of the zeolites. As a result, the as-prepared zeolite [email protected]2 exhibits efficient adsorption toward trace stearyl alcohol under low pressure through the synergistic contribution of physisorption and chemisorption. Monte Carlo (MC) simulation, molecular dynamic (MD) and Density Functional Theory (DFT) calculations further discover that pore wall surfaces are primary adsorption sites for the physisorption while ALD-grown TiO2 provides active sites for the chemisorption.
Article
Hydrogen can be released from ammonia (NH3) by cracking, but the residual ammonia is harmful to polymer exchange membrane fuel cells and should be less than 0.1 ppm (μmol/mol). In this paper, the adsorption of NH3 by commercial faujasite (FAU) zeolites to below 0.1 ppm have been investigated. The results show that the Si/Al ratio of zeolite is inversely proportional to the adsorption capacity, and the strength of ammonia adsorption by cation Li⁺ is more than that of Na⁺, thus the ammonia adsorption capacity of LiLSX zeolite is greater than that of 13X–HP zeolite. However, the small granule size of crystalline microspheres and the rough surface of 13X–HP zeolite were the factors that lead to the dynamic NH3 adsorption capacity of 13X–HP zeolite close to LiLSX zeolite. In the dynamic 1700 ppm NH3 adsorption, with a breakthrough point of 0.1 ppm, the adsorption capacity is 9.27 wt% for LiLSX zeolite and 8.73 wt% for 13X–HP zeolite.
Article
Structural properties of Pb-exchanged zeolites are of interest because of their applications in environmental remediation and in industrial processes. In this study, we report on a Pb-exchanged stellerite (Pb-STI), with particular focus on the cationic species, which form inside the zeolitic pores as a result of the exchange experiments. The produced zeolite had chemical composition Pb13.4(OH)10Al17.4Si54.6O144 ∙38H2O, indicating that Pb was uptaken in form of [Pb(OH)x](2-x) species. The STI framework maintained the Fmmm space group characteristic of the type material. However, the extraframework occupants, Pb²⁺, H2O and OH⁻, were characterized by a strong positional-disorder. The latter was resolved and interpreted combining Extended X-ray Absorption Fine Structure (EXAFS) analysis with Molecular Dynamics (MD) simulations. On average, Pb²⁺ ions are coordinated by 2 OH⁻ and 1H2O at distances <2.5 Å, whereas bonds to framework oxygen-atoms were found only at longer distances (>2.8 Å). Pb²⁺ adopts mainly a sided distorted coordination, indicating a stereochemical activity of the lone pair electrons. The obtained results were compared with those of other mono-cationic forms of STI zeolites. Based on the analysis of the framework distortion experienced after the incorporation of different metal ions, considerations are drawn on the potential effect of Pb²⁺ on the thermal stability of STI framework type zeolites.
Article
Full-text available
Samples of clinoptilolite enriched with Na+, K+, Cs+, NH4+, Ca2+, Mg2+, and Ba2+ cations were prepared by ion-exchange. The degree of exchange for the different samples is discussed in terms of location and diffusivity of the cations. The thermal stability of natural clinoptilolite and of the enriched forms, as determined by XRD, is related to the nature and location of the major countercation in the zeolite framework. The specific retention volumes of O2, N2, CO and CH4 on each sample and the adsorption enthalpies of these gases were measured by a chromatographic method in the range of 298–393 K. The results are explained on the basis of the strength of the interaction molecule-adsorption sites of the zeolite, taking into account the diffusivity of gas molecules through the zeolite channels, and their accessibility to the adsorption sites, according to the more probable location of the cation in the lattice.
Article
Full-text available
Interest in mordenite as an inhalation hazard arose when it was discovered that the mineral exists in the subsurface of Yucca Mountain, NV, the site of a federally proposed nuclear waste repository. During preliminary geologic investigations at Yucca Mountain, workers performing air coring (dry-drilling) operations were potentially exposed to aerosols of mordenite. Mordenite is also increasingly used in industrial applications, such as cation exchange, molecular absorbency, and reversible dehydration. Concern that the fibrous nature of mordenite may present an inhalation hazard is supported by the ''Stanton Hypothesis," which states that the carcinogenicity of any fiber type depends upon dimension and durability rather than physicochemical properties. To date, little scientific literature is available on the inhalation health hazards of mordenite. This study initiates research in this area. Mordenite specimens collected from different geologic localities were analyzed macroscopically and microscopically. Mineral verification was performed using energy dispersive x-ray and x-ray diffraction analysis. Fibrous aerosols were generated to simulate aerosols created during air coring operations. Anderson cascade impactors were used to obtain aerosol mass median aerodynamic diameters. Electron microscopy of nucleopore filters allowed for individual aerosol fibers to be morphologically sized and applied to the Stanton Hypothesis for mesothelioma induction. Physical fiber dimensions were used to calculate aerodynamic diameters and to estimate pulmonary deposition. Results obtained from this study indicate that under similar conditions of aerosolization, using similar mordenite materials, inhalation of mordenite fibers could produce substantial deep-lung deposition.
Article
Uses, prices, and applications in gas purification and wastewater treatment are discussed.
Article
The adsorption behaviors of O//2 and N//2 in pressure-swing adsorption (PSA) at low temperature on various American natural zeolites and synthetic zeolites having different pore structures were studied. The adsorption properties were largely dependent on whether the dimension of the pore-structure connection is one or three. Molecular sieves MS-5 A and MS-4 A, which have a large amount of adsorption and a large difference in adsorption capacity for N//2 and O//2, were preferable to air separation by the PSA method. The applicability to the air separation at low temperature was also investigated by using MS-4 A and MS-5 A as the adsorbents. Highly concentrated N//2 was obtained by MS-5 A in the elution period and by MS-4 A in the adsorption period. Furthermore, the applicability to air separation at room temperature was examined by using MS-4 A as the adsorbent, and separation was confirmed under this condition.
Article
The most significant advances in adsorption over the last 20 to 25 years has been the development and utilization of microporous molecular sieve absorbents. These are based upon the well-known crystalline aluminosilicate zeolites, primarily the synthetic types. Activated carbon, alumina, and silica gel have been used for a long time in adsorption, but these materials lack one characteristic; they do not exhibit the uniform pore size shown by zeolites, particulary in the pore diameter range of 3 to 10 angstroms. This paper reveals experimental data which show the effectiveness of natural and synthetic zeolites in hydrocarbon separation. Limitations of zeolite adsorbents are also included. The future research and applications are indicated.
Article
Water Sorption isotherms on natural chabazitc modified with an organic binder are reported As expected, samples showed type I IUPAC isotherms. The applicability of potential theory and the Dubinin equation was examined. A temperature-independent characteristic curve was obtained by introducing the reduced adsorption potential. This successful correlation gives the possibility of predicting adsorption isotherm points at any temperature and pressure. Kinetic tests were made to establish the temperature and pressure dependence of the diffusivity parameter.
Article
Here is a look at modern design for gas recovery and air prepurification alike.
Article
A sample collected from the Aurangabad District, Maharashtra, India was characterized by XRD, IR, TG and DTA methods, and by chemical analysis, as a calcium-rich clinoptilolite. Two different methods involving exchange with KOH or NH 4 Cl led to the formation of K-clinoptilolite (K-Clino) and H/NH 4 -clinoptilolite (H/NH 4 -Clino). Water sorption studies were carried out on the parent clinoptilolite (P-Clino), K-Clino and H/NH 4 -Clino at five different temperatures in the range 303–423 K. Different adsorption models were applied to the data obtained from such sorption studies. Thermodynamic parameters such as the chemical potential were also computed from the sorption data and their significance is discussed.
Article
An overview is presented of gas phase 'adiabatic' sorption processes utilized in applications such as petrochemical intermediates production, hydrogen upgrading and industrial air separation. The growth of these processes during the last twenty-five years is discussed with particular emphasis on recent trends and developments. Typcial operating conditions are presented along with a discussion of various adsorbents used.
Article
The zeolites not only provide an outstanding example of geometrical patterns among the framework silicates, but also in their permanently porous and rigid nature are of great commercial interest. This book collates the current knowledge ragarding zeolite synthesis, isomorphous substitution and chemical transformation. The principal features of hydrothermal systems and reactions are outlined, and the extension of zeolite synthesis to compositions unknown in nature and with unusual topologies is described.-R.A.H.
Article
Itaya natural zeolite and its cation-treated zeolite were characterized by X-ray diffraction, thermo-gravimetric analysis, adsorption and chemical analysis. No change of X-ray diffraction pattern was found for Itaya zeolites treated with 1mol·dm-3 hydrochloric acid but a slight change of SiO2/Al2O3 ratio was found.The surface of Itaya zeolite seem to contain both meso- or macropores, but its heterogeneous surface became homogeneous with hydrochloric acid treatment, being predominantly composed of micropores. The monolayer adsorption capacity of zeolite for nitrogen gas decreased as the amount of cations in the Itaya zeolite increased. The cation (Na+, K+, NH+4, Ca2+) exchanged Itaya zeolite samples had less nitrogen adsorbing power than the hydrochloric acid-treated zeolite.The gas separation behaviour of Itaya zeolite was compared with that of the cation-treated zeolite. Separation of hydrogen, oxygen, nitrogen, methane and carbon monoxide from the surface of zeolites was investigated at 30-100°C by using Itaya zeolite and its cation-treated zeolite as column packings. Hydrogen, oxygen, nitrogen, carbon monoxide and methane were found to be separatable completely from the mixture gases by using Itaya zeolite, hydrochloric acid treated zeolite and its K+ exchange zeolites. A methane-oxygen mixture could not be separated by Na+, NH+4 and Ca2+ exchanged Itaya zeolites.
Article
Zeolite clinoptilolite is a natural mineral with ionexchange and gas-adsorption properties. Ammonium- and ammonia-adsorption processes were studied in the zeolite clinoptilolite and zeolite-like sepiolite minerals. Maximum adsorption capacities of both ammonium and ammonia were determined by fitting the experimental results of the adsoption isotherm to Langmuir and first-order models. Ammonium-adsorption capacities of the zeolites were from 8·149 to 15·169 mg N g−1; up to 10·3 times higher than that of sepiolite. Ammonium-adsorption capacity increased with the surface charge density of the material, due to the readily available exchange sites in the surface.Ammonia-adsorption capacities of the zeolites were between 6·255 and 14·155 mg N g−1. Because of its large surface area, sepiolite had a capacity of ammonia adsorption three times higher than that of the ammonium ion. The complexity of the ammonia-adsorption process meant that no individual characteristics of the materials influenced directly the adsorption capacity. However, ammonia adsorption was enhanced on the ammonium adsorption in zeolites with relatively low surface charge density.
Article
This paper describes the preparation and testing of various ionic forms of clinoptilolite, a natural zeolite, and a study of their properties for the removal of water vapour from air. The calcium form of the zeolite showed the highest uptake of 0.127 g of water per gram of zeolite and the potassium form was the worst with a capacity of half this value. The sorption data were correlated by a ‘Langmuir’ isotherm. The size of the cation sorbed had a direct effect on the water sorption data. The results are compared with the properties of other desiccants. The zeolite uptake of water is less than that of silica gel.
Article
Numerous sedimentary deposits of appreciable size are known to occur in the Western United States of the zeolites chabazite, erionite, mordenite, phillipsite and clinoptilolite. Experimental studies of the sorption characteristics of several samples reveal a uniqueness of erionite both in its low enthalpy of water sorption, and in its appreciable, selective, and rapid sorption of n-paraffins as heavy as n-tetradecane. Erionite was further found to contain the most easily exchangeable cations. n-Tetradecane was also sorbed by the chabazite and to a lesser degree by the mordenite samples, as was nitrogen in the more restrictive channels of those of phillipsite and clinoptilolite.
Article
Nitrogen adsorption isotherms were measured for four samples of chabazite, collected from different geographical locations, and for a Linde 5A synthetic zeolite. All isotherms were Type I and obeyed the Langmuir adsorption model. Surface areas and pore diameters were calculated from the adsorption data. The MP method was used to determine the pore volume distribution for each sample. Results indicated that the chabazite samples had nearly identical properties, and these properties were very similar to those of the Linde 5A synthetic zeolite.
Article
C1 to n-C4 paraffins are reversibly sorbed at a number of temperatures within the hydrogen forms of chabazite and of zeolite L. Thermodynamic equilibrium constants have been determined for the distribution of the paraffins at each temperature between crystal and gas phases, together with activity coefficients of sorbed hydrocarbons and standard heats, entropies and free energies of sorption. Isosteric and integral heats of sorption, and differential and integral entropies of the sorbed paraffins were determined as functions of amount taken up. There appear to be considerable differences between initial values of isosteric heats in hydrogen and in Ca-rich chabazites; but not in hydrogen and potassium forms of zeolite L. Near saturation of the zeolite crystals integral entropies of each intracrystalline hydrocarbon were intermediate between those of the same hydrocarbon in its bulk liquid and crystalline phases, but were nearer the liquid values. Diffusion coefficients of C3, n-C4 and n-C5 paraffins have been measured in hydrogen chabazite as functions of temperature and amount sorbed.
Article
Earlier and newer results of investigations on sedimentary zeolites in Hungary have been reviewed; some typical samples are characterized. Determination of the zeolite content with CO2 adsorption is described and the adsorption of N2, O2, H2O, CO2, SO2 and NH3 after different pretreatments of the zeolitic rock is also discussed. Catalytic properties of clinoptilolite and mordenite derivatives without separation from the parent rock have been examined for xylene and n-butene isomerization, as well as for methanol dehydration and acetylene hydration.
Article
There are three processes for adsorptive generation of oxygen from air using molecular sieve zeolites, namely pressure swing adsorption (PSA), vacuum swing adsorption (VSA) and pressure vacuum swing adsorption (PVSA). Two new variations have recently come onto the market: low-temperature VSA (LT VSA) and two-bed VSA (PVSA). Because of their reliability and long service life, swing adsorption systems have been producing good results for more than ten years, which is why the market share of these systems in the overall oxygen market is constantly rising. Capacity limits with adsorption processes stem at present from the design of the valves and vacuum pumps.
Article
Dimensionless Henry constants, sorption energies and separation factors are reported for the atmospheric gases (N2, O2 and Ar) on several different zeolites. The extent to which the pattern of selectivity can be understood in terms of differences in the basic molecular properties of the three sorbates is briefly considered.
Article
Recent advances have been made in research on carbon molecular sieve and zeolite adsorbents used in the non-cryogenic production of nitrogen and oxygen. Preparation methods that allow stringent control of porosity, density, and surface properties have resulted in carbon molecular sieve adsorbents with higher capacity and selectivity for nitrogen production. Recently, a new generation of mixed-cation zeolite adsorbents with high N2/O2 selectivity and improved stability has been developed for oxygen production.
Article
The characteristics of CO gas adsorption on chemically treated natural zeolite from the Kampo area of Korea were investigated. Acid treatment was more effective in liquid adsorption than alkali treatment because the exchanged H+ ion attributed to the enlargement of pore size. However, in gas adsorption, a different tendency was observed. In HCl treated zeolite, 80% of the pore area, which was derived from a higher portion of micropores around 10 Å, led to hindrance of the gas diffusion rate. Though the pore and surface area decreased in NaOH treatment, an increase in the gas adsorption amount was found, and it could be supposed that the exchanged Na+ ion located on the surface served as an adsorption site. The NaOH treated natural zeolite showed a higher value and 0.017 g of the adsorption amount at 5 N NaOH compared with 0.011 g at 5 N HCl.
Article
Adsorbent and cycle developments for the last 25 years have resulted in the advancement of vacuum swing adsorption processes for the production of oxygen from air, and in this review are traced and critically examined. The key criteria in the past developments and for future improvements are identified.
Article
Ion-exchange and dehydration in clinoptilolite are simulated revealing a novel feature, a hydration-controlled nano-valve, which explains hitherto anomalous behaviour of this important zeolite system.
Article
Various ion-exchange forms of phillipsite (Phi) were prepared. Anomalous dependences of the extent of rehydration and heats of immersionQ i on the temperature of thermovacuum treatment were revealed for the initial Na, K- and K-forms made by ion exchange. The curves pass through a minimum between 100 and 180°C, indicating structural changes accompanied by considerable contraction of the zeolite framework. No structural changes were observed when the ammonium form of phillipsite was evacuated at elevated temperatures; the curveQ i =F(T) passes through a maximum at 250°C. It was calculated that NH4-Phi is thermally much less stable than Na, K-Phi or K-Phi.
Article
Air fed to air separation units such as cryogenic distillation columns needs to be prepurified; that is, the concentration levels of air-borne impurities such as water vapor, CO2, and light hydrocarbons need to be brought down below the tolerable limits. This process is commonly carried out by using adsorptive methods such as pressure swing adsorption (PSA) or temperature swing adsorption (TSA). This work deals with the study of adsorption characteristics of two conventional microporous adsorbents, namely 13X zeolite molecular sieves, and activated γ-Al2O3, and three non-conventional adsorbents, namely a natural zeolite (clinoptilolite), and its K+- and Ca2+-ion exchanged forms. A noteworthy feature of this work is the measurement of adsorption isotherms at very low partial pressures of the adsorbate gas (to a few ppm). The relative merits of these adsorbents for the removal of trace amounts of water vapor, CO2, and hydrocarbons such as CH4, C2H4, and C2H6 are discussed. The isotherm data for 13X zeolite and γ-Al2O3 has been fit to the Langmuir–Freundlich, Tòth, and Dubinin–Astakhov (DA, or potential theory) isotherm models. It has been found that the potential theory model is the most suitable one for description of low pressure or concentration data. The origin of the better fit by potential theory is that its corresponding energy distribution function follows a quasi-Gaussian distribution with a broadening at high adsorption energies, and the high-energy sites are important for adsorption at low pressures or concentrations. Finally, the possibility of using H2O adsorption isotherm to evaluate the pore size distribution by the Horvàth–Kawazoe approach is discussed.
Article
The occlusion of argon and of nitrogen has been investigated in a variety of ion-exchanged, synthetic, faujasite-type crystals, over the temperature range 173 to 273 degrees K and for amounts sorbed between 0 and 0\cdot 3 of saturation (A in Li-, Na-, K- Ca-, Sr- and Ba-zeolite) and between 0 and 0\cdot 5 of saturation (N2 in Li-, Na-, and K-zeolite). The behaviour observed depends both on the cation present in the crystal and upon the serbate. In all cationic forms the affinities and heats of intercalation for nitrogen are considerably above those for argon. The crystals behave as energetically homogeneous sorbents for A in Na-, K- and Ba-forms and for N2 in the K-form. The heat of occlusion depends upon amount sorbed, to a greater or lesser degree, for A in Li-, Ca- and Sr-faujasites and for N2 in the Li- and Na-forms. Where energetic heterogeneity arises it is more noticeable in the case of nitrogen sorption. The isosteric heats of sorption of nitrogen are also distinguished from those of argon by showing considerable temperature coefficients. The data for both sorbates have been analyzed in terms of dispersion, repulsion, polarization and quadrupole interactions, and the different behaviour of each sorbate interpreted.
Article
Design and development of a pilot scale chromatographic process for separation of trace amounts of krypton from a nitrogen atmosphere is described. The system uses a large column (1.20 m × 0.055 m i.d.) packed with H-mordenite adsorbent and operated under overload conditions. A preliminary economic evaluation suggests that this process is competitive with the conventional cryogenic distillation process. On décrit la conception et la mise au point d'un procédé chromatographique à l'échelle pilote pour la séparation de quantités à l'état de trace de krypton à partir d'une atmosphère azotée. Le système utilise une grande colonne (1,20 m × 0,055 m de diamètre intérieur) garnie d'adsorbant au H-mordenite et fonctionnant dans des conditions de surcharge. Une évaluation économique préliminaire suggère que ce procédé est compétitif avec le procédé de distillation cryogénique traditionnel.
Article
H2S and SO2 adsorption isotherms of Bigadiç clinoptilolite and its Na−, K−, Ca−, and H−enriched forms were determined in the 0 to 100 kPa range at 25°C by using a constant volume adsorption system. Langmuir, Freundlich, Dubinin-Radushkevich (D-R), and Dubinin-Astakhov (D-A) models were applied to the isotherm data. Higher adsorption capacities and a larger increase in the amount adsorbed at higher pressures were observed for SO2, in agreement with its higher permanent dipole moment, resulting in stronger ion-dipole and dipole-dipole interactions for this molecule. The Ca-form exhibited a molecular sieving behavior for both gases, originating from the channel blockage caused by the cation locations in the sample. The highest capacities for both gases were obtained with the sample in its H-form, followed by the Na− and K-forms for SO2, parallel to the decrease in the electronegativity and ionic potential and the increase in the polarizability of the cation. In the case of H2S, the H-form was followed by the K-form, but the Na-form yielded very low adsorption capacities. Initial dissociative adsorption of H2S on certain Na sites to yield SH and OH species is thought to contribute to a more effective blocking of the channels, which were already partially blocked in this sample. Of the isotherm models tested, the D-A model explained the variations in the data better than either the Freundlich or D-R models. For the cation-gas combinations with a lower extent of channel blockage though, the Langmuir model was somewhat more representative. Lower E and n values were obtained from the D-A model for H2S on the Na-form, which may be related to the lower extent of micropore adsorption and to the presence of blocked, almost dead-end shorter channel segments in the sample. Pore volumes close to the theoretical value were estimated from the D-A parameters for SO2 adsorption.
Article
A chromatographic study of the adsorption kinetics and equilibrium of CH4, CO and N2 gases on molecular sieves zeolite 4A, zeolite 5A, H-mordenite and chabazite has been made. The objective of this study was to determine the adsorption characteristics of these zeolites and look at the viability of separation of the gases mentioned. Adsorption equilibrium constants, selectivities and nitrogen zeolitic diffusivities have been determined in the Henry law region. The results indicate that the synthetic zeolites (H-mordenite, zeolites 4A and 5A) have a higher capacity for the adsorption of all three gases compared with naturally occurring chabazite. Also, adsorption equilibrium constants are higher for all the gases with the larger-pore zeolites H-mordenite and zeolite 5A. Among the gas-zeolite systems studied, CO-CH4 and CO-N2 were the easiest pairs to separate on the basis of adsorption equilibrium selectivities. Intra-crystalline diffusional resistance was the major contributing factor to mass transfer for nitrogen in both H-mordenite and zeolite 4A.
Article
Clinoptilolite, the most abundant natural zeolite, has been modified by ion exchange to fully exchanged forms of the monovalent cations K+, Na+, and H+ and highly exchanged forms of the bivalent cations Ca2+ (89%) and Mg2+ (72%). The Dubinin-Astakhov volume filling model was applied to the supercritical isotherm data to predict pore volume at the normal boiling temperatures of N2 and CH4 - temperatures too low for practical isotherm measurement due to the slow diffusion of these gases. Adsorption isotherms and energetic heterogeneity have been discussed in terms of the various cations and their locations in the clinoptilolite channels. Adsorption characteristics have been greatly altered through cation manipulation to produce a range of CH4:N2 selectivity ratios exceeding 1 order of magnitude. In view of the difficulty of the CH4/N2 separation, these results suggest excellent potential for tailoring clinoptilolite for separation of other specific gas mixtures.
Article
Calcium chabazite used as a gas chromatographic packing provides a practical means for analyzing trace levels of a variety of permanent gases including oxygen and argon. An outstanding feature of properly activated calcium chabazite is its ability to resolve argon and oxygen at temperatures above 343 K. The level of dehydration achieved for this adsorbent has a direct influence on its efficiency and ability to resolve Ar and O2. In addition, we found that treating the chabazite at elevated temperature in an oxidizing atmosphere improves the resolution and lowers the detectability limits for determining oxygen. Part-per-billion levels of Ne, Ar, O2, N2, CH4, and CO could be measured by using a calcium chabazite column, in combination with a helium ionization detector. The column efficiency and resolution of this adsorbent were measured as a function of corrected flow rate and column temperature for Ar-O2 mixtures. Trace Ar and O2 were base-line-resolved in under 2 min by using a 6-ft column of this adsorbent at 343 K. Thus, calcium chabazite provides a practical adsorbent for analyzing a wide variety of gases with conventional instrumentation.
Article
Results of a chromatographic study of the adsorption of N2 and Kr on several molecular sieve adsorbents are reported. The objective was to find a suitable adsorbent for the removal of traces of radioactive Kr from the off-gas from nuclear fuel reprocessing facilities. Of the adsorbents examined, de-aluminated H-mordenite shows the highest selectivity for Kr relative to N2 and appears to be a promising adsorbent for this separation. The presence of traces of NO2, a likely impurity in the off-gas, was found to suppress the adsorption of N2 more than that of Kr, thereby increasing the separation factor (α ∼ 12). In most of the adsorbents investigated, intracrystalline diffusion was too fast to measure but for N2 in H-mordenite, intracrystalline resistance was found to be significant and strongly dependent on the initial dehydration temperature. On présente les résultats d'une étude chromatographique de l'adsorption de N2 et Kr sur plusieurs tamis moléculaires. Le but du travail était de trouver un adsorbant capable d'enlever les traces de Kr radioactif des gaz de sortie des installations de régénération du combustible nucléaire. De tous les adsorbants examinés, la H-mordenite désaluminée présente la sélectivité la plus élevée pour Kr par rapport à N2, et semble un adsorbant prometteur pour la séparation en question. On a constaté que la présence de traces de NO2, une impureté probable des gaz de sortie diminue l'adsorption de N2 plus que celle de Kr et augmente, par conséquent, le facteur de séparation (α ∼ 12). Dans la plupart des adsorbants étudiés, la diffusion intracristalline était trop rapide pour étre mesurée; mais pour le N2 dans la H-mordenite, la résistance intracristalline s'est avérée importante et fortement dépendante de la température initiale de déshydratation.
Article
Adsorption of N2 and CO has been studied on a natural Turkish clinoptilolite at near ambient conditions. Pure isotherms up to 101.3 kPa pressure, and binary isotherms at 101.3 kPa total pressure were determined chromatog-raphically at 303 K. Pure isotherms were modelled using the Langmuir model and the Wilson and Flory - Huggins forms of the Vacancy Solution Theory. Binary isotherms were predicted using both forms of the Vacancy Solution Theory, the Extended Langmuir model, and the Ideal Adsorbed Solution Theory. These predictions were compared to experimentally determined binary isotherms. Clinoptilolite is shown to be a particulahly promising sorbent for the separation of CO and N2. The Wilson form of the Vacancy Solution Theory was the only model flexible enough to provide a reasonable prediction of the binary isotherms. On a étudié l'adsorption du N2 et du CO sur une clinoptilolite de Turquie naturelle près des conditions ambiantes. Les isothermes des composants purs à une pression allant jusqu'à 101,3 kPa et les isothermes binaires à une pression totale de 101,3 kPa ont été déterminés par chromatographic à 303 K. Les isothermes des composants purs one été modélisés à l'aide du modèle de Langmuir et des formes de Wilson et Flory Huggins de la théorie des “Vacancy Solution”. Les isothermes binaires ont été prédits à l'aide des deux formes de cette théorie, du modèle de Langmuir étendu et de la théorie des solutions adsorbées idéales. Ces prédictions ont été comparées à des isothermes binaires déterminés expérimentalement. On montre que la clinoptilolite est un sorbant particulièrement prometteur pour la séparation du CO et du N2. La forme de Wilson de la théorie des solutions vacantes est le seul modèle suffisamment souple pour fournir une prédiction raisonnable des isothermes binaires.
Article
Gas chromatographic techniques were used to measure the diffusion coefficients and the isosteric heats of adsorption of CO2, NO, NO2, and SO2 on 5A and 13X molecular sieves, natural mordenites, and synthetic Na- and H-mordenites in the temperature range of 133 to 325°C. Diffusional resistances for all gases studied decrease in the following order: natural mordenites > Na-mordenites > H-mordenites > (13X, 5A) indicating the increased ease of flow in the 3-dimensional network. Isosteric heats of adsorption (range from 3 kcal/mole to 12 kcal/mole) and activation energies (range from 3 kcal/mole to 19 kcal/mole) decrease in the same order. The variations of diffusion coefficients, heats of adsorption, and activation energies are discussed in terms of the interaction between the surface and gas molecules as well as the openings of the pores relative to the size of the diffusing molecules.
Article
The two-dimensional channel structure of clinoptilolite has been altered systematically by ion exchange to study the effects of cation type, size, location, and distribution on the diffusion of N2 and CH4 probe molecules. Concentration-dependent diffusion time constants (D/L2) were determined from gravimetric uptake measurements for fully-exchanged K+, Na+, and H+ clinoptilolites, and highly-exchanged Ca2+ (89%) and Mg2+ (72%) clinoptilolites. Both plane sheet and parallel channel diffusion models were developed from the one-dimensional plane sheet diffusion equation and fit to the uptake data. Resulting values of D/L2 varied by a factor of more than 1,000 for both N2 and CH4, while kinetic selectivity spanned nearly two orders of magnitude for this group of modified clinoptilolites. Achieving this range in performance for the difficult N2/CH4 separation demonstrates the excellent potential for tailoring clinoptilolite by cation manipulation for the kinetic separation of other gas mixtures.
Article
Although asbestos and erionite are proven human carcinogens, most studies have concluded that these fibres are not mutagenic to mammalian cells in vitro. We have studied the potential of these fibres and chrysotile fibres to induce mutations in human peripheral lymphocytes, using a mutation assay that measures mutation at the autosomal HLA-A locus. Exposure of lymphocytes in culture to 400 μg/ml of crocidolite or erionite for 72 hr did not result in a statistically significant increase in the mutation frequency (MF) in the HLA-A assay, although a trend towards increased MF was observed. Exposure to 400 μg/ml chrysotile resulted in no increase in MF; however a significant increase was observed at 50 μg/ml. Mutations in somatic cells can be classified according to their molecular basis. Molecular analysis of mutants obtained following exposure of lymphocytes to crocidolite and erionite demonstrated a statistically significant increase in the class of mutations arising from loss-of-heterozygosity (LOH) events involving the selection locus (HLA-A) and more distal loci. Mutations following exposure to crocidolite and erionite showed a greater frequency of LOH than did spontaneous mutants (p < 0.02 and p < 0.005 respectively). Mutants following exposure to chrysotile did not display a significant difference in LOH when compared with spontaneous mutants. Thus, although an increase in overall mutation frequency following fibre exposure did not achieve statistical significance, the modest increase seen following exposure to erionite and crocidolite is translated into a highly significant change in those components of the spectrum of mutations which result in LOH. © 1994 Wiley-Liss, Inc.
Article
Adsorption of N2, CO, CO2 and NO has been studied on various molecular sieves using the gas chromatographic method to determine the potential for separation of these common atmospheric contaminants from air. The molecular sieves studied include H-Mordenite, 4A and 5A zeolite, a natural clinoptilolite and an activated carbon. Henry's law constants have been determined over a variety of temperature ranges from 243 to 473 K. Van't Hoff plots are presented for CO on all materials and for NO on all but 4A zeolite. Adsorption of CO2 on the clinoptilolite was too strong to produce an interpretable response peak. Results of CO adsorption on 4A and 5A zeolites have been compared to and are supported by data available in the literature. Heats of adsorption for CO, NO and N2 were determined. For CO the heats of adsorption decrease in the order of clinoptilolite > 5A zeolite > 4A zeolite > H-Mordenite > activated carbon. For adsorption of NO the heats of adsorption decrease in the order of clinoptilolite > 5A zeolite > activated carbon. Separation factors are presented for the CO/N2 and NO/N2 systems. The natural clinoptilolite shows most promise for the separation of CO and NO from N2 at the temperature range 273–398 K. Diffusion coefficients for CO and N2 on clinoptilolite between 348 and 423 K were also determined. Micropore diffusion proved to be the dominant mass transfer mechanism for both CO and N2 in clinoptilolite under the conditions examined.
Article
Air fed to air separation units such as cryogenic distillation columns needs to be prepurified; that is, the concentration levels of air-borne impurities such as water vapor, CO2, and light hydrocarbons need to be brought down below the tolerable limits which are in the ppm or sub-ppm levels. This process is commonly carried out by using adsorptive methods such as pressure swing adsorption (PSA) or temperature swing adsorption (TSA). In this work, the adsorption characteristics of a natural zeolite (chabazite) for the trace removal of water vapor, CO2, and a hydrocarbon (CH4) were studied and compared with those of two conventional microporous adsorbents, namely 13X (NaX) zeolite molecular sieves, and activated alumina (γ-Al2O3). The low pressure isotherm data was fit to the Dubinin–Astakhov (DA, or potential theory) isotherm model and was extended to multicomponent mixtures using the maximum available micropore volume model of Doong and Yang (Ind. Eng. Chem. Res. 27(4) (1988) 630). An equilibrium based non-isothermal model was used to simulate the performance of the above sorbents for a typical four-step Skarstrom-type PSA cycle for the simultaneous removal of H2O and CO2 from feed N2. Two types of bed configurations were considered: single beds containing only one type of sorbent, and layered beds with contiguous layers of two different sorbents (alumina/13X zeolite). The relative amounts of sorbents required for the layered bed were optimized for particular bed operating conditions.
Article
A review of the literature regarding the structure, composition, and ion exchange of clinoptilolite, as well as adsorption and diffusion in this natural zeolite, is summarized. Recently, adsorption and diffusion in modified clinoptilolites have been related to the location of exchangeable cations and the corresponding effects of these cations upon channel blockage. These results suggest a much greater potential for separation of gas mixtures by this natural zeolite than previously recognized. The kinetic separation of has been examined in terms of the equilibrium and rate properties of the modified clinoptilolites, and a pressure swing adsorption model has been applied to predict process performance.
Article
Zeolite scientists, whether they are working in synthesis, catalysis, characterization or application development, use theAtlas of Zeolite Framework Typesas a reference. It describes the main features of all of the confirmed zeolite framework structures, and gives references to the relevant primary structural literature. Since the last edition 34 more framwork types have been approved and are described in this new edition. A further new feature will be that characteristic building units will be listed for each of the framework types. Zeolites and their analogs are used as desiccants, as water softeners, as shape-selective acid catalysts, as molecular sieves, as concentrators of radioactive isotopes, as blood clotting agents, and even as additives to animal feeds. Recently, their suitability as hosts for nanometer spacing of atomic clusters has also been demonstrated. These diverse applications are a reflection of the fascinating structures of these microporous materials. Each time a new zeolite framework structure is reported, it is examined by the Structure Commission of the International Zeolite Association (IZA-SC), and if it is found to be unique and to conform to the IZA-SC's definition of a zeolite, it is assigned a 3-letter framework type code. This code is part of the official IUPAC nomenclature for microporous materials. The Atlas of Zeolite Framework Types is essentially a compilation of data for each of these confirmed framework types. These data include a stereo drawing showing the framework connectivity, features that characterize the idealized framework structure, a list of materials with this framework type, information on the type material that was used to establish the framework type, and stereo drawings of the pore openings of the type material. * Clear stereo drawings of each of the framework types * Description of the features of the framework type, allowing readers to quickly see if the framework type is suitable to their needs * References to isotypic materials, readers can quickly identify related materials and consult the appropriate reference.