Zeolite 4A Research Articles

Removal of Toxic Phenolic Compounds from Wastewater Using Zeolite (4A) Prepared from Local Clays Taken from the Slopes of the Tigris River

The massive scale of industrial development has resulted in environmental pollution in general and water contamination in particular. It is important at the present time to treat water for the purpose of eliminating or reducing pollutants, especially toxic pollutants, such as phenol compounds. In this study, zeolite (4A) was prepared firstly from the available and cheap materials using an inclined rotary disk. Then, physical, mechanical, and chemical properties were also studied. Experiments were conducted to determine these properties using local clay and the following results were obtained: Zeolite (4A) 70% and clay 30%, the time of calcination 3 h at a temperature of 850��C, breakage resistance of 17 Ib pounds, surface area 530-590 m2/g, grinding value 14% and moisture absorption ratio 30%. The prepared zeolite (4A) was used in the process of removing phenolic compounds (chlorophenol, nitrophenol) by the adsorption method. Different amounts of prepared zeolite (5g/l and 10g/L) will be used in the treatment process and different concentrations (2mg/L, 5 mg/L and 10 mg/L) of the pollutants Nitrophenol and Chlorophenol were used in the contaminated water tested. The removal process was carried out with a mixing speed of 200 rpm and pH (7.5-8.5). From the results of this study, we note that the highest percentage of Nitrophenol removal is (84.8%) when using an amount of zeolite (5g) and highest percentage of Nitrophenol removal is (95.5%) when using an amount of zeolite (10g) while that the highest percentage of Chlorophenol removal is (78.3%) when using an amount of zeolite (5g) and highest percentage of Chlorophenol removal is (0.894) when using an amount of zeolite (10g) it could be deduced that the percentage of the removal of nitrophenol was higher than that of chlorophenol because its solubility of chlorophenol in water is higher than the solubility of Nitrophenol.

Application of Catalytic Ozonation Process Using a Novel Fe3O4/Mg(OH)2/4A-Zeolite Catalyst for Swift Treatment of Dairy Effluent

The present study investigated the feasibility of employing a catalytic ozonation process by a novel Fe3O4/Mg(OH)2/4A zeolite catalyst to facilitate the treatment of real dairy effluent. The Fe3O4/Mg(OH)2 magnetic nanoparticles supported onto 4A zeolite (Fe3O4/Mg(OH)2/4AZ) were synthesized and characterized by extensive techniques (XRD, FE-SEM, TEM, EDS, VSM, and BET). Reaction rate, operating conditions, mechanism, and thermodynamics of the dairy effluent treatment by the Fe3O4/Mg(OH)2/4AZ-catalyzed ozonation process were investigated. Catalytic ozonation experiments indicated that synchronous use of Fe3O4/Mg(OH)2/4AZ and O3 considerably accelerated the rate of COD reduction, compared to sole ozonation. Results of the designed experiments by response surface methodology (RSM) revealed that approximately 80% of COD was reduced within 30 min at natural pH of solution (≈ 7) when the catalyst and ozone dosages were 5 g L−1 and 9 mg min−1, respectively. Exploration of the mechanism disclosed that the process mainly followed a hydroxyl radical reaction pathway. Thermodynamics studies demonstrated that the process was endothermic and temperature sensitive, so that it was spontaneous at the temperature of 313 K. Overall, this study supplies a bold and quick manner as well as environmental friendliness (no secondary pollution) to eradicate refractory substances and wastewater treatment.

Experimental study on heat release characteristics of thermochemical heat storage considering various operating parameters

Thermochemical heat storage is a promising energy storage method and has received much attention in recent years. To improve the design and application of such systems, a better understanding of the characteristics of thermochemical heat storage is required. In this study, we analyze the heat release characteristics of thermochemical heat storage considering various operating parameters, such as charging temperature, humidity, and material. Three different thermochemical materials are considered herein, namely, zeolite 13X, zeolite 5A, and silica gel. The temperature profile at the inlet and outlet of the storage chamber, and that inside the chamber packed with thermochemical material, were measured. The pressure drop across the chamber was measured as well. The results indicate that the heat release characteristics change with position and time. Furthermore, the temporal curves of released heat are significantly affected by charging temperature and humidity. Zeolite 13X rapidly released a large amount of heat within a short period of time, whereas silica gel gradually released a small amount of heat, over a longer duration of time. The pressure drop across the chamber was found to vary with the bead size of the thermochemical material. Thus, the operating parameters including charging temperature, humidity, and material, have a significant effect on the characteristics of heat release. The data obtained herein can serve as a reference for the design of thermochemical storage systems.

Study of the pilot-scale pan granulation of zeolite-based molecular sieves

This work describes a systematic study of the granulation process of a 5A zeolite into molecular sieves. Initially, a 5A zeolite was synthesized at the pilot scale and subsequently granulated in a core–shell structure using a rotary tilted pan. The effect of water content of the paste, pan rotating velocity and inclination, proportion of zeolite in the core and shell, shell thickness, the type of binding clay, and the calcination temperature were studied. The effect of these variables on the shape, size, water adsorption capacity, and crush resistance of the agglomerates was assessed. According to the results, suitable bead shape and size were obtained at high rotation velocity (59 rpm), low pan inclination (60°) and with 30 wt. % of added water. High content of zeolite in the core and shell provided suitable adsorption capacity, but lower crush resistance. Actigel 208® exhibited better binding performance and the recommended calcination temperature was 873 K.

Ultrafine tuning of the pore size in zeolite A for efficient propyne removal from propylene

Abstract The removal of trace propyne (C3H4) from propyne/propylene (C3H4/C3H6) mixtures is a technical and challenging task during the production of polymer-grade propylene in view of their very similar size and physical properties. While some progress has been made, it is still very challenging to use some highly stable and commercially available porous materials via an energy-efficient adsorptive separation process. Herein, we report the ultrafine tuning of the pore apertures in type-A zeolites for the highly efficient removal of trace amounts of C3H4 from C3H4/C3H6 mixtures. The resulting ion-exchanged zeolite 5A exhibits a large C3H4 adsorption capacity (2.3 mmol g−1 under 10−4 MPa) and high C3H4/C3H6 selectivity at room temperature, which were mainly attributed to the ultrafine-tuned pore size that selectively blocks C3H6 molecules, while maintaining the strong adsorption of C3H4 at low pressure region. High purity of C3H6 (>99.9999%) can be directly obtained on this material under ambient conditions, as demonstrated by the experimental breakthrough curves obtained for both 1/99 and 0.1/99.9 (V/V) C3H4/C3H6 mixtures.

Efficient separation of strontium radionuclides from high-salinity wastewater by zeolite 4A synthesized from Bayer process liquids

The efficient, selective, and economical sorbents for the removal of Sr radionuclides are largely needed for the decontamination of effluents with high salinity. In this study, the removal of Sr was investigated using the zeolite produced from the Bayer process liquids. Based on the XRD, SEM/EDS analysis, the product was pure and highly crystalline zeolite 4A (Z4A). Removal of Sr was fast (5 min for 100% removal at 8.80 mg/L), with high maximum sorption capacity (252.5 mg/L), and independent on the initial pH in the range 3.5–9.0. Specific sorption of Sr by protonated groups on the Z4A surface was operating in addition to ion-exchange with Na ions. The selectivity of Z4A decreased in the order Sr > Ca > K > Mg > Na. 84% of Sr was separated from seawater within 5 min, at the Z4A dose of 5 g/L, while efficiency increased to 99% using the dose of 20 g/L. Desorption of radioisotope 89Sr from seawater/Z4A solid residue was very low in deionized water (0.1–0.2%) and groundwater (0.7%) during 60 days of leaching. Z4A is a cost-effective, selective, and high-capacity medium for Sr removal, which provides high stability of retained radionuclides.

Comparative simulation study of methanol production by CO2 hydrogenation with 3A, 4A and 5A zeolites as adsorbents in a PSA reactor

In this work, the performance of 3A, 4A and 5A zeolites in a PSA reactor to obtain methanol by CO2 hydrogenation has been compared by numerical simulation. Henry's constants of adsorption and the reciprocal diffusion time constants of water and methanol in these adsorbents have been measured in the reaction temperature range (200–350 °C) to simulate their performance using a zeolite/Cu-ZnO-Al2O3 catalyst mixture. A new cycle has been proposed for PSA reactors including a complete recirculation of heavy product, without using a purge. The best performance is obtained with 3A zeolite, having the lower water and methanol affinities facilitating bed regeneration. With the proposed process, methanol can be produced from CO2 hydrogenation at 250 °C and 50 bar with a conversion of 99.6% in one step, a selectivity of 83–96%, and productivities of 0.023–0.13 mol m3 s−1. The process has minimal loss of H2 in the form of water (1 mol H2O/mole converted CO2).

Adsorption Study of Main Gas Products from Water Radiolysis on 4A Zeolite by Numerical Simulations

This work is motivated by the results obtained during a study on the tritiated water adsorbed in zeolite [L. Frances et al., J. Phys. Chem. C, 119, 28462 (2015)]. The decomposition of water by radiolysis leads to the production of dioxygen and dihydrogen as main stable products. By studying the evolution of their quantities of matter, one can note an increase in a first stage, followed by a decrease after a few hundred days of storage until complete disappearance. This interesting process depends on the water loading ratios, expressed in mass percentage, lying between 4%, and 19%; such a phenomenon is not observed in saturated zeolite. Our goal is to determine, through numerical simulations, how this disappearance, which is associated with the recombination of the radiolysis products, occurs by making a microscopic study on the adsorption of H2O, H2, and O2 molecules on 4A zeolite (Z4A). Computational physics is useful to understand the effects of molecule adsorption on its structure and also to closely examine the molecule-zeolite and molecule-molecule interactions. Indeed, different simulation methods are used from static to dynamic studies employing both quantum and classical tools with the periodical structure of Z4A. To summarize, the adsorption of molecules from the radiolysis of water are studied according to different points of view (quantum and classical) using various numerical simulation tools, such as density functional theory for ab initio structural optimization and energy calculation, Monte Carlo to study the distribution of the adsorbed molecules in the zeolite, and molecular dynamics to follow the evolution of the system (molecule + zeolite) over time depending on the temperature, in order to extract as much information as possible (structurally, statistically, energy, electronically) to understand the main problematic of this work: How do stable molecules issued from radiolysis recombine in Z4A?

Advanced pore characterization and adsorption of light gases over aerogel-derived activated carbon

Abstract Activated carbon produced by etching with CO2 is an attractive adsorbent material because of its ultrahigh surface area above 1000 m2/g and substantial pore volume. This being stated, because etched carbon was only reported recently, many of its properties, such as its textural properties, high-pressure adsorption capacities towards CO2, N2, H2, CO, and CH4, and dynamic performance, have never been thoroughly investigated. Accordingly, this study explored these characteristics for the first time. The textural and adsorptive properties were also assessed for zeolite 5A, a metal-organic framework (Ni MOF-74), and activated carbon provided by Ingevity corporation to allow for comparison to established benchmarks. The textural properties were assessed by a combination of N2 physisorption at 77 K and CO2 adsorption at 273 K using a combination of t-plot, Dubinin–Radushkevich, 2D-NLDFT, and Horvath–Kawazoe models. Therein, it was determined that the etched carbon had a hierarchical porosity, with pores appearing in both the ultramicro- and meso-porous ranges. From the adsorption isotherms at 298 K and 0–20 bar, the etched carbon exhibited adsorption capacities of 20, 9, 5, 4.5, and 1 mmol g−1 for CO2, CH4, CO, N2, and H2 respectively, indicating that the samples high (i.e., 95%) pore volume made it selective towards multiple species at high pressure. Having said this, when the material was examined for dynamic CO2 adsorption from N2, H2, and CH4 mixtures at 25 °C and 1 bar, it achieved CO2/CH4, CO2/H2, and CO2/N2 selectivities of 2.4, 15.4, and 6.6 mol/mol, respectively, meaning that it can be used for kinetic separations. The high dynamic selectivity was retained for CO2/H2 at 20 bar, however, the CO2/CH4 breakthrough fronts were much broader compared to the low-pressure experiments, meaning that the two species' diffusivities were competitive. As such, EC-RF was concluded to be effective for low-pressure CO2 separations as well as for high pressure CO2/H2 separations. More importantly, this study provides an in-depth characterization and better understanding of EC-RF's properties, which is imperative to its use as an adsorbent material.

Implementation of Ion Exchange Processes for Carbon Dioxide Mineralization Using Industrial Waste Streams

Sequestration of CO2 within stable mineral carbonates (e.g., CaCO3) represents an attractive emission reduction strategy because it offers a leakage-free alternative to geological storage of CO2 in an environmentally benign form. However, the pH of aqueous streams equilibrated with gaseous streams containing CO2 (pH < 4) are typically lower than that which is required for carbonate precipitation (pH > 8). Traditionally, alkalinity is provided by a stoichiometric reagent (e.g., NaOH) which renders these processes environmentally hazardous and economically unfeasible. This work investigates the use of regenerable ion-exchange materials to induce alkalinity in CO2-saturated aqueous solutions such that the pH shift required for mineralization occurs without the need for stoichiometric reagents. Na+-H+ exchange isotherms (at [H+] = 10−8–10−1 M) and rates were measured for 13X and 4A zeolites and TP-207 and TP-260 organic exchange resins in batch equilibrium and fixed-bed exchange experiments, respectively. At solutions equilibrated with CO2 at 1.0 atm (pH = 3.9), H+ exchange capacities for the materials were similar (1.7–2.4 mmol H+/g material) and resulted in pH increases from 3.9 to greater than 8.0. Multi-component mixtures using Ca2+ and Mg2+ cations (at 10−3–10−1 M) in CO2-saturated water were used to probe competitive ion exchange. The presence of divalent cations in solution inhibited H+ exchange, reducing capacities to as low as 0.2 mmol H+/g for both resins and zeolites. Dynamic H+ exchange capacities in fixed-bed ion exchange columns were similar to equilibrium values for resins (∼1.5 mmol/g) and zeolites (∼0.8 mmol/g) using inlet solutions that were equilibrated with gaseous streams of CO2 at 1.0 atm. However, exchange kinetics were limited by intraparticle diffusion as indicated by the increased rate parameters with increasing inlet flow rates (20–160 cm3 min−1). Experimental calcite precipitation from mixing the alkaline CO32−-rich water solution obtained from the ion-exchange column with a simulated liquid waste stream solution achieved thermodynamic maximum yields. The results from these studies indicate that ion exchange processes can be used as an alternative to the addition of stoichiometric bases to induce alkalinity for the precipitation of CaCO3, thereby opening a pathway toward sustainable and economic mineralization processes.

Optimization of pressure swing adsorption for hydrogen purification based on Box-Behnken design method

Pressure swing adsorption (PSA) is an important technology for mixture gas separation and purification. In this work, a dynamic model for a layered adsorption bed packed with activated carbon and zeolite 5A was developed and validated to study the PSA process. The model was validated by calculating breakthrough curves of a five-component gas mixture (H2/CH4/CO/N2/CO2 = 56.4/26.6/8.4/5.5/3.1 mol%) and comparing the results with available experimental data. The purification performance of six-step layered bed PSA cycle was studied using the model. In order to optimize the cycle, the Box-Behnken design (BBD) method was used, as implemented in Design Expert™. The parametric study showed that, for adsorption step durations ranging from 160 to 200 s, as the adsorption time increased, the purity decreased, whereas the recovery and productivity increased. During the pressure equalization step, the purity increased as the pressure equalization time increased, but the recovery and productivity decreased for step durations ranging from 10 to 30 s. As the P/F ratio (hydrogen used in purge step to hydrogen fed in adsorption step) increased from 0.05 to 0.125, the purity increased, whereas the recovery and productivity decreased. The optimization of the layered bed PSA process by the BBD method was then performed. In addition to the adsorption time, the pressure equalization time and the P/F ratio were considered as independent optimization parameters. Quadratic regression equations were then obtained for three responses of the system, namely purity, recovery, and productivity. When purity is set as the main performance indicator, the following values were obtained for the optimization parameters: an adsorption time of 168 s, a pressure equalization time of 14 s, and a P/F ratio of 0.11. Under those conditions, the system achieved a purity of 99.99%, a recovery of 57.76%, and a productivity of 6.41 mol/(kg·h).

Binderless zeolite monoliths production with sacrificial biopolymers

3D printing has emerged as an attractive way of formulating structured adsorbents, as it imparts lower manufacturing costs compared to hydraulic extrusion while also allowing for unprecedented geometric control. However, binderless structures have not been fabricated by 3D printing, as ink formulation has previously required clay binders which cannot be easily removed. In this study, we report the development of a facile approach to shape engineer binderless zeolites. 3D-printed inks comprised of 13X, 5A, ZSM-5, and experimental South African zeolites were prepared using gelatin and pectin as binding agents along with dropwise addition of various solvents. After printing, the dried monoliths were calcined to remove the biopolymers and form 100% pure zeolite structures. From N2 physisorption and CO2 adsorption measurements at 0 °C, all monoliths showed narrowing below 1 nm from their powders, which was attributed to pore malformation caused by intraparticle bridging during calcination. The various adsorption isotherms indicated that this narrowing led to varying degrees of enhanced adsorption capacities for all three gases, as the slightly smaller pores increased electrostatic binding between the sorbent walls and captured species. Analysis of CO2 adsorption performance revealed comparable diffusivities and adsorption capacities to the commercial bead analogues, implying that biopolymer/zeolite printing can produce contactors which are competitive to commercial benchmarks. The binderless monoliths also exhibited faster diffusivities compared to zeolite monoliths produced by conventional direct ink writing – on account of an enhancement in macroporosity – highlighting that this new method enhances the kinetic properties of 3D-printed scaffolds. As such, the sacrificial biopolymer technique is an effective and versatile approach for 3D printing binderless zeolite structures.

Mixed-Matrix Membranes Comprising of Polysulfone and Porous UiO-66, Zeolite 4A, and Their Combination: Preparation, Removal of Humic Acid, and Antifouling Properties.

High-performance Mixed-Matrix Membranes (MMMs) comprising of two kinds of porous fillers UiO-66 and Zeolite 4Aand their combination were fabricated with polysulfone (PSf) polymer matrix. For the very first time, UiO-66 and Zeolite 4A were jointly used as nanofillers in MMMs with the objective of complimenting synergistic effects. The individual and complimentary effects of nanofillers were investigated on membrane morphology and performance, pure water flux, humic acid rejection, static humic acid adsorption, and antifouling properties of membranes. Scanning Electron Microscopy (SEM) analysis of membranes confirmed that all MMMs possessed wider macrovoids with higher nanofiller loadings than neat PSf membranes and the MMMs (PSf/UiO-66 and PSf/Zeolite 4A-UiO-66) showed tendency of agglomeration with high nanofiller loadings (1 wt% and 2 wt%). All MMMs exhibited better hydrophilicity and lower static humic acid adsorption than neat PSf membranes. Pure water flux of MMMs was higher than neat PSf membranes but the tradeoff between permeability and selectivity was witnessed in the MMMs with single nanofiller. However, MMMs with combined nanofillers (PSf/Zeolite 4A-UiO-66) showed no such tradeoff, and an increase in both permeability and selectivity was achieved. All MMMs with lower nanofiller loadings (0.5 wt% and 1 wt%) showed improved flux recovery. PSf/Zeolite 4A-UiO-66 (0.5 wt%) membranes showed the superior antifouling properties without sacrificing permeability and selectivity.

Integral Mass Balance (IMB) Method for Measuring Multicomponent Gas Adsorption Equilibria in Nanoporous Materials

To assess the performance of an adsorbent for a particular gas separation, and for process design, it is necessary to determine multicomponent gas adsorption equilibria, either experimentally or from predictions based on models or theory. The experimental techniques commonly used for this purpose, however, are time-consuming and typically require large samples. In this article, we describe a new approach, called the Integral Mass Balance (IMB) method, which combines the controlled flow of a gas mixture with in situ gravimetric measurement and gas composition analysis using quadrupole mass spectrometry. The IMB method allows very rapid equilibrium multicomponent gas adsorption measurements to be performed on samples weighing only a few grams. The method is demonstrated and validated by performing binary O2/N2 adsorption measurements on a commercial 5A zeolite, at ambient temperature and a total pressure of 0.915 MPa. Excellent agreement with previously published data was found, using a 3.5 g sample, with a measurement time of only 4 h for a 20 point isotherm. In contrast, other techniques of equivalent accuracy would require around 20 days of experimental effort to collect a comparable amount of data. Selectivities were also calculated and shown to agree with previously published results. In principle, the technique could readily be extended to measure gas adsorption from ternary or higher mixtures.

Synthesize and characterize of Fe3O4/zeolite 4A magnetic nanocomposite

In order to solve the problem that separating zeolite 4A from solutions, we have synthesized Fe3O4/zeolite 4A magnetic nanocomposite by hydrothermal method. It is characterized by Transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR), Vibrating Sample Magnetometer (VSM), scanning electron microscope (SEM) and Brunner-Emmet-teller (BET). The XRD result shows that Fe3O4/zeolite 4A magnetic nanocomposite has a good crystal structure. It also shows that Fe3O4/zeolite 4A magnetic nanocomposite contains two phases of zeolite 4A and Fe3O4 MNP. The optimal sample (Z-2) was judged by the calculation of crystallinity. The successful combination of zeolite 4A and Fe3O4 MNP was visually observed through SEM technology. The functional groups of Fe3O4/zeolite 4A magnetic nanocomposite were characterized by FTIR technology. The TEM result shows that some Fe3O4 MNPs enter zeolite 4A, which further clarifies the microstructure of Fe3O4/zeolite 4A magnetic nanocomposite. N2 adsorption-desorption technique confirms that Fe3O4/zeolite 4A magnetic nanocomposite SBET is 55.3374 m2/g and Dave is 9.7128 nm. VSM result shows that Fe3O4/zeolite 4A magnetic nanocomposite magnetization is 18.4534 emu/g. Simulation experiment shows that Fe3O4/zeolite 4A magnetic nanocomposite exhibit a fast response to an external magnetic field.

Radium in groundwater hosted in porous aquifers: estimation of retardation factor and recoil rate constant by using NAPLs

A new method for estimating retardation factor and recoil constant of radium isotopes in groundwater hosted in porous aquifers is described. The method is based on the evidence that alpha-recoiled radium ions, supplied by thorium parent atoms which occur in phases immersed in NAPL (Non-Aqueous Phase Liquids), are not adsorbed on solid phases. Experimental evidence is given that manganese dioxide, zeolite 4A, natural clay, monazite and weathered volcanic rock, all phases normally adsorbing radium from aqueous solutions, when immersed in NAPL adsorb negligible amounts of radium. This allows using experimental data on rock samples, representative of porous aquifers, for estimating Ra retardation factor and its alpha recoil constant in groundwater, without using Rn data as a comparison term. Unlike estimation of retardation factor between the “NAPL method” and the method based on comparison with radon depends on the different process of entry from aquifer rock into groundwater for radon and radium. Precise estimates of retardation factor and recoil constants of radium allow to apply equations ruling the temporal evolution of radium isotopes in groundwater and to determine its age. Implications, useful for measuring the contamination age of soils by NAPL fluids, are described as well.

Active packaging for Salmon stored at refrigerator with Polypropylene nanocomposites containing 4A zeolite, ZnO nanoparticles, and green tea extract.

In this study, three types of Polypropylene‐based (PP) films (two active nanocomposites and one control film) containing zinc oxide nanoparticles (ZnO NPs), 4A zeolite (4A Z), and green tea extract (GTE) were studied as modern active packaging's that can adjust the release of antimicrobial agents. The influence of PP nanocomposite with 3% (w/w) ZnO NPs/4A Z/GTE (treatment 1) and 6% (w/w) ZnO NPs/4A Z/GTE (treatment 2) on controlling microbial growth and preserving the sensory and chemical qualities of Salmon over nine days of storage at 4 ± 1°C was evaluated. The disk diffusion test revealed inhibition zones in the range of 10.98 ± 0.03 to 13.42 ± 0.01 m for treatments 1 and 2, respectively; the nanocomposite film with 6% ZnO NPs/4A Z/GTE had the highest antimicrobial effect against Gram‐negative bacteria (p < .05). Chemical analysis revealed that the initial peroxide value of Salmon was 0.68 ± 0.0 mEq/kg, which increased by day 9 to 12.3 ± 0.03 mEq/kg in the control sample, but rising only to 9.9 ± 0.01 and 7.3 ± 0.02 mEq/kg in treatments 1 and 2, respectively (p < .05). The shelf life of Salmon given treatment 2 increased significantly to nine days relative to the control. Accordingly, these nanocomposite films are promising as new active packaging for preventing microbial growth and preserving the quality of salmon.

Study of catalyst bed composition for the direct synthesis of dimethyl ether from CO2-rich syngas

In this work, we study the direct synthesis of DME using CO2-rich syngas, with a CO2/CO ratio similar to that obtained from the gasification of biomass, i.e., 1.9. We used catalytic beds consisting of physical mixtures of the benchmark catalysts used for the synthesis of methanol from syngas and for methanol dehydration to DME, namely Cu/ZnO/Al2O3 and γ-Al2O3, respectively. Our results show that the ratio between each catalytic phase determines the productivity and selectivity to DME, as well CO and CO2 conversions. Thus, higher total carbon conversions were obtained with the catalytic bed with the highest content of the Cu/Zn/Al2O3 phase. The presence of γ-Al2O3 allows to exceed the equilibrium conversion of CO for the syngas to methanol synthesis. The highest DME productivity is obtained with the catalytic bed containing equal amounts of both catalytic phases. In addition, we also show that other reaction variables such as temperature, pressure, and contact time also play an important role in terms of DME productivity. The presence of a high fraction of CO2 in the syngas results in a high production of H2O, which after long times on stream result in the deactivation of the Cu/ZnO/Al2O3 catalytic phase due to the sintering of the copper particles. The in situ removal of H2O via the addition of an H2O sorbent, zeolite 3A, into the catalytic bed, results in a significant enhancement of both carbon conversion and DME productivity.

One pot fusion route for the synthesis of zeolite 4A using kaolin

A new process route for obtaining zeolite 4A from kaolin was realized by subjecting all raw materials needed for hydrothermal synthesis to thermal activation in one pot method. For that purpose, different routes of activation steps for kaolin, which are metakaolinization, alkali fusion and one pot fusion were investigated for a wide range of kaolin sources in order to obtain zeolite 4A product with highest crystallinity. The influence of Si/Al ratio in addition to the chemical composition of raw kaolin, i.e. quartz and iron impurity content, on the product 4A was investigated following all three activation routes. It was found that alkali fusion process allows incorporation of quartz as silicon source during the hydrothermal synthesis of zeolite 4A, which may result in a variety of products such as zeolite P and zeolite 13X. In this study, a novel approach was developed by thermal activation of a mixture of kaolin, alkali and alumina sources at once in one pot route, which was followed by hydrothermal synthesis. The current study indicates the possibility of adjusting Si/Al ratio adding Al(OH)3 during the activation step in one pot fusion process, which resulted in synthetic zeolite 4A of higher than 90% crystallinity using low quality kaolin.

Value added utilization of ferronickel slags as raw materials of 4A zeolite for CO2 reduction

The scale of smelting ferronickel by RKEF (Rotary kiln—electric furnace) process is increasing these years, these untreated ferronickel slags will occupy a large area as accumulation and cause ecological damage. On the other hand, the CO2 emission and global warming are urgent problems to be solved as they have resulted in severe climate change. Carbon Capture and Storage (CCS) technology is considered as a feasible solution to the problem of excessive CO2 emissions, and the key of the CCS is the exploration for adsorbents which are low-cost, efficient and energy saving. We found that it is viable to use ferronickel slag as raw material to synthesize 4A zeolite. Further improvement for the purities of 4A zeolite was also accomplished by optimizing the synthesis conditions via single factor experiments. The as-synthesized sample was characterized in terms of structural morphology, chemical composition and surface properties. The adsorption and adsorption kinetics properties were investigated by thermal gravimetric analyzer and four models, respectively. The results indicated that 4A zeolite has a great performance in the adsorption and separation of CO2/N2 with the high value-added utilization of ferronickel slags which conducts.