Preparation of Single Phase Na-X Zeolite from Oil Shale Ash by Melting Hydrothermal Method

A single phrase Na - X zeolite was synthesized from pretreated oil shale ash by alkaline fusion and hydrotherreal treatment. Eff3cts of the NaOH concentration, crystallization time ant temperature on the formation of Na-X zeolite were studied in detail. The single phase Na- X zeolite powders can. be prepared by alkaline fusion o.f pretreated oil shale ash at 600 ℃ .for 1 h, and crystalli-zation at 80 - 100 ℃ .for 8 - 10 h with NaOH concentration of 3 -3. 5 tool · L-1. Na - A zeolite appears when decreasing NaOH concentration, crystallization time or temperature, ant an unnamed zeolite emerges when prolonging crystallization time or raising crystalli-zation, temperature. SEM micrographs suggest that the aggregates of Na-X zeolite particles have perfect dispersity and uniform granular with about 1.5 μm in size, and most of the Na-X zeolite crystals display a regular octahedral structure with the size of about 500 nm. The specific surface area of the powders with single Na-X zeolite phase reaches the maximum value of 488. 163 2 m2· g -1, larger than that of multiple zeolite powders.

Nanocrystalline low-silica X zeolite as an efficient ion-exchanger enabling fast radioactive strontium capture

NaA zeolite(Si/Al=1.00)has been commercially applied for capturing radioactive 90Sr^(2+)because of its high surface charge density,effectively stabilizing the multivalent cation.However,owing to its narrow micropore opening(4.0Å),large micron-sized crystallites,and bulkiness of hydrated Sr^(2+),the Sr^(2+)exchange over NaA has been limited by very slow kinetics.In this study,we synthesized nanocrystalline low-silica X by minimizing a water content in a synthesis gel and utilizing a methyl cellulose hydrogel as a crystal growth inhibitor.The resulting zeolite exhibited high crystallinity and Al-rich framework(Si/Al of approximately 1.00)with the sole presence of tetrahedral Al sites,which are capable of high Sr^(2+)uptake and ion selectivity.Meanwhile,the zeolite with a FAU topology has a much larger micropore opening size(7.4Å)and a much smaller crystallite size(~340 nm)than NaA,which enable significantly enhanced ion-exchange kinetics.Compared to conventional NaA,the nanocrystalline low-silica X exhibited remarkably increased Sr^(2+)-exchange kinetics(>18-fold larger rate constant)in batch experiments.Although both the nanocrystalline low-silica X and NaA exhibited comparable Sr^(2+)capacities under equilibrated conditions,the former demonstrated a 5.5-fold larger breakthrough volume than NaA under dynamic conditions,attributed to its significantly faster Sr^(2+)-exchange kinetics.

Synthesis of zeolite A and zeolite X from electrolytic manganese residue,its characterization and performance for the removal of Cd^(2+)from wastewater

Electrolytic manganese residue(EMR)can cause serious environmental and biological hazards.In order to solve the problem,zeolite A(EMRZA)and zeolite X(EMRZX)were synthesized by EMR.The pure phase zeolites were synthesized by alkaline melting and hydrothermal two-step process,which had high crystallinity and excellent crystal control.And the optimum conditions for synthesis of zeolite were investigated:NaOH-EMR mass ratio=1.2,L/S=10,hydrothermal temperature=90℃,and hydrothermal time=6 h.Then,EMRZA and EMRZX showed excellent adsorption of Cd^(2+).When T=25℃,time=120min,pH=6,C0=518 mg·L^(-1),and quantity of absorbent=1.5 g·L^(-1),the adsorption capacities of EMRZA and EMRZX reached 314.2 and 289,5 mg·g^(-1),respectively,In addition,after three repeated adsorption-desorption cycles,EMRZA and EMRZX retained 80%and 74%of the initial zeolites removal rates,respectively.Moreover,adsorption results followed quasi-second-order kinetics and monolayer adsorption,which was regulated by a combination of chemisorption and intra-particle diffusion mechanisms.The adsorption mechanism was ions exchange between Cd^(2+)and Na+.In summary,it has been confirmed that EMRZA and EMRZX can be reused as highly efficient adsorbents to treat Cd^(2+)-contaminated wastewater.

Studies on basicity of alkali metal catron exchanged β and X zeolites by pyrrole-IR spectroscopy

The strength of basic sites has been measured by pyrrole-IR on alkali metal cation exchanged β and X zeolites, as well as NaOH loaded Naβ. The influence of cation type and the structure of zeolites on their basicity has been studied. The acidic and basic properties of the samples were investigated by NH3-TPD and isopropanol reaction. It was shown that the strength of basic sites on samples could be characterized by the shift of vNH band in the pyrrole-IR spectra. The framework oxygen charges were calculated from the Sanderson electronegativity. The changes in basic properties with various alkali metal cation are consistent with the changes of local oxygen charges of the zeolite framework.

Stellerite-seeded facile synthesis of zeolite X with excellent aqueous Cd^(2+)and Ni^(2+)adsorption performance

Zeolite X was synthesized by a two-step hydrothermal method using natural stellerite zeolite as the silicon seed,and its adsorption performance for Cd^(2+)and Ni^(2+)ions was experimentally and comprehensively investigated.The effects of p H,zeolite X dosage,contact time,and temperature on adsorption performance for Cd^(2+)and Ni^(2+)ions over were studied.The adsorption process was endothermic and spontaneous,and followed the pseudo-second-order kinetic and the Langmuir isotherm models.The maximum adsorption capacitiesfor Cd^(2+)and Ni^(2+)ions at 298 K were 173.553 and 75.897 mg.g-1,respectively.Ion exchange and precipitation were the principal mechanisms for the removal of Cd^(2+)ions from aqueous solutions by zeolite X,followed by electrostatic adsorption.Ion exchange was the principal mechanisms for the removal of Ni^(2+)ions from aqueous solutions by zeolite X,followed by electrostatic adsorption and precipitation.The zeolite X converted from stellerite zeolite has a low n(Si/Al),abundant hydroxyl groups,and high crystallinity and purity,imparting a good adsorption performance for Cd^(2+)and Ni^(2+)ions.This study suggests that zeolite X converted from stellerite zeolite could be a useful environmentally-friendly and effective tool for the removal of Cd^(2+)and Ni^(2+)ions from aqueous solutions.

Synthesis of Zeolite X from Locally Sourced Kaolin Clay from Kono-Boue and Chokocho, Rivers State, Nigeria

This work describes the development of a process to produce zeolite X from mined kaolin clay from Kono-Boue and Chokocho, Rivers State, Nigeria. The procedures involved the beneficiation of the raw kaolin and calcinations at 850°C, to transform the kaolin to a more reactive metakaolin. Afterwards, the extremely reactive metakaolin was purge with sulphuric acid to obtain the much needed silica-alumina ratio for zeolite X synthesis. An alkaline fusion stage was then carried out to transform the metakaolin into zeolite by mixing with aqueous NaOH to form gel then allowed to stay for a duration of seven days at room temperature. The samples were then charged into a propylene container and placed in an oven at a temperature of 100°C for the reaction to take place for 6 h. Identification of the crystalline phases by X-ray Diffraction (XRD), chemical/elemental compositions by X-ray Fluorescence (XRF)/Energy Dispersive Spectroscopic analyses (EDS), surface morphology by Scanning Electron Microscopy (SEM) and molecular vibration of units by Fourier Transform Infrared Spectrophotometry (FT-IR) were done. The results showed that the zeolite synthesized from Chokocho kaolin (CK) was more crystalline/larger with sharper peaks on both XRD and FTIR than that from Kono-Boue. This was also supported by slightly rougher surface morphology of CK over KK on SEM. XRF Si:Al ratios of 10.73 and 14.36 were obtained for KK and CK respectively. EDS results supported the XRF ratios. Sharper zeolitic characteristic O-H stretching bands at 3488 and 3755 cm-1 were recorded for CK than KK. However, both results showed that zeolite X have been produced from both Kono-Boue and Chokocho kaolin clays respectively.

Role of ball milling during Cs/X catalyst preparation and effects on catalytic performance in side-chain alkylation of toluene with methanol

Ball milling modification was performed on Cs/X catalysts before or after cesium ion exchange.Multiple characterization results(such as pyridine-FTIR,XPS,and solid-state NMR)demonstrated that ball milling played a distinct role in these two different preparation procedures of the catalyst.Ball milling performed after the cesium modification has a strong influence on the Cs/X structure and acid-base properties,which results in the enhancement of the catalytic performance for side-chain methylation of toluene with methanol.Detailed studies revealed that ball milling intensified the interactions between oxides and molecular sieves,which not only increased the dispersion of the Cs species but also generated some weaker basic centers.It is proposed that the new basic centers could be Si-O-Cs and Al-O-Cs,which are produced by breaking of the Si-O-Al bonds of the zeolite framework under the synergetic effect of ball milling and alkali treatment.These new active sites may help to promote the side-chain methylation reaction.However,excessive ball milling will lead to the vanishing of zeolite micropores,thus deactivating side-chain methylation activity,which indicates that microporosity plays a key role in side-chain methylation and individual basic centers cannot catalyze this reaction.

Design and experiment of high-productivity two-stage vacuum pressure swing adsorption process for carbon capturing from dry flue gas

A two-stage vacuum pressure swing adsorption(VPSA)process that coupled kinetically controlled and equilibrium controlled separation process with reflux has been investigated for capturing carbon dioxide from dry flue gas(85%N_(2)/15%CO_(2)).In the first enriching stage,carbon molecular sieve(CMS),which shows kinetic selectivity for CO_(2)/N_(2),is adopted as the adsorbent to remove most N_(2)in feed gas,thereby upgrading CO_(2)and significantly reducing the amount for further refinement.The second stage loads zeolite 13X as adsorbent to purify the CO_(2)-rich flow from the first stage for meeting the requirements of National Energy Technology Laboratory.Series of experiments have been conducted for adsorption isotherms measuring and lab-scale experimental validation as well as analysis.The effect of feed composition on the separation performance of the PSA system was studied experimentally and theoretically here.The optimal results achieved 95.1%purity and 92.9%recovery with a high CO_(2)productivity(1.89 mol CO_(2)·h^(-1)·kg^(-1))and an appropriate energy consumption of 1.07 MJ·(kg CO_(2))^(-1).Further analysis has been carried out by simulation for explicating the temperature,pressure,and concentration distribution at cyclic steady state.

Guidelines for rational design of high-performance absorbents:A case study of zeolite adsorbents for emerging pollutants in water

Rational design is important to achieve high-performance sorbents used to remove the contaminants of emerging concern(CECs) from water.However, it is hard to propose effective design guidelines due to the lack of a clear understanding of the interaction mechanisms. By means of systematic quantum chemical computations, as a case study, we investigated the interactions between zeolite X/M^(n+)-zeolite X(Si/Al=1,M^(n+)=Cu^(2+) and Ni^(2+)) and three commonly used CECs(namely salicylic acid, carbamazepine and ciprofloxacin) in water to clarify the adsorption mechanisms. Our computations found that anionic salicylic acid cannot be adsorbed by neither zeolite X nor M^(n+)-zeolite X in neutral water due to the high electrostatic repulsion. In comparison, carbamazepine and ciprofloxacin have favorable binding energies with both zeolite X and M^(n+)-zeolite X, and their interactions with M^(n+)-zeolite X are stronger due to the joint effects of H-bond, metal complexation and electrostatic interaction. The adsorption loading of ciprofloxacin, which has a large molecular size, on M^(n+)-zeolite X is limited due to the steric hindrance. In general, steric hindrance, electrostatic interaction, H-bond and metal complexation are dominant factors for the examined systems in this study. Thus, for the design of high-performance absorbing materials, we should fully consider the molecular properties of pollutants(molecular size, surface electrostatic potential and atomic type, etc.), and properly enhance the favorable effects and avoid the unfavorable factors as much as possible under the guidance of the interaction mechanisms.

Synthesis of Zeolite ZSM-2 Using Zeolite NaX as Seeds

A method is presented for the synthesis of zeolite ZSM-2 by adding zeolite X as seeds in the synthetic mixture containing both lithium and sodium. At the presence of zeolite X seeds, highly crystalline zeolite ZSM-2 with com-position of (0.3—0.7)Li2O·(0.7—0.3)Na2O·Al2O3·(2.5—4.0)SiO2·nH2O can be obtained in a wide range of SiO2/Al2O3 ratios from 2.5 to 16, and the optimum Li2O/(Li2O+Na2O) fraction is between 0.3 and 0.7. The ZSM-2 products were characterized by XRD, SEM, IR, 29Si MAS NMR and DTA/TG analysis etc. By 29Si MAS NMR spectroscopy, it was found that ZSM-2 contained nearly equal FAU and EMT phase, and the Si/Al ratios in FAU were slightly lower than those in EMT domains in most cases. The lithium form zeolite ZSM-2 has comparable N2 adsorption capacity with LiX.