Enhancement of CO2 Adsorption Containing Zinc-ion-exchanged Zeolite NaA Synthesized from Rice Husk Ash

The objectives of the research were to develop synthesis and estimation of each factor on carbon dioxide adsorption of advanced functional zeolite NaY material derived from bagasse ash and rice husk ash with different crystallization temperatures and weight percentages of zinc by the ion exchange method. The adsorbents were tested in a packed bed reactor at different temperatures and flow rates of carbon dioxide. The Minitab program was used to estimate the effects of each factor on carbon dioxide adsorption properties. The results showed that extracted silicon dioxide from bagasse ash and rice husk ash could be successfully used as raw material for zeolite NaY synthesis with a crystallization temperature of 298.15 K. The zeolite NaY crystalline structure was well-preserved after ion exchange. The highest capacity of carbon dioxide adsorption was at 10.33 mmol/g with zeolite 5B298-373-1. The results of the Minitab program showed that the carbon dioxide adsorption decreased with increasing crystallization temperature and carbon dioxide flow rate parameters. However, the increased weight percentage of zinc loading on zeolite NaY resulted in better carbon dioxide adsorption. The factors of the types of adsorbents and adsorption temperature showed interaction with each other.

Zeolite NaA was successfully prepared from nickel laterite residue for the first time via a fusion-hydrothermal procedure. The structure and morphology of the as-synthesized zeolite NaA were characterized with a range of experimental techniques, such as X-ray diffraction, scanning electronic microscopy, and infrared spectroscopy. It was revealed that the structures of the produced zeolites were dependent on the molar ratios of the reactants and hydrothermal reaction conditions, so the synthesis conditions were optimized to obtain pure zeolite NaA. Adsorption of nitrogen and carbon dioxide on the prepared zeolite NaA was also measured and analyzed. The results showed that zeolite NaA could be prepared with reasonable purity, it had physicochemical properties comparable with zeolite NaA made from other methods, and it had excellent gas adsorption properties, thus demonstrating that zeolite NaA could be prepared from nickel laterite residue.

In this study, both zeolites NaA and NaY were synthesized from rice husk ash (RHA) by a simple conventional hydrothermal route. Rice husk (RH) was used as a silicate source to produce various zeolites. The hydrothermal route was conducted via a seeding technique involving the preparation of two separate gels, i.e. colloidal seed and feedstock gel. The zeolite was first produced using commercially available chemicals and followed by the replacement of the commercial silicate sources with RHA derived silicate. The RHA silicate was obtained by combusting the RH at different temperatures and durations i.e. 450 °C for both 2 and 6 hours, as well as 750 °C for 6 hours. Zeolite NaY (faujasite) was successfully synthesized with commercial chemical seed and RHA derived feedstock gel. On the other hand, using RHA silicate in both colloidal seed and feedstock gel would give only zeolite NaA. Elemental, structural and morphological analyses of RHA and zeolites were carried out with X-ray fluorescence (XRF) spectrometer, X-ray diffractometer (XRD) and scanning electron microscopy (SEM).

The synthesis of zeolite NaA from Bangka kaolin was started by activation step with calcination at temperature 650°C for 2 hours. This activation produced metakaolin, an amorphous phase as assigned by XRD pattern. Based on the result by XRF technique, metakaolin produced from thermal treatment was mostly composed of silicon and aluminum with SiO2/Al2O3 ratio=1.63, and other minor metal elements. This metakaolin was suitable to use as a source for zeolite NaA synthesis which had Si/Al ratio close to one. For the synthesis of zeolite NaA, metakaolin was mixed with NaOH solution, followed by crystallization at 100°C for 24 hrs. The solid product, zeolite NaA was separated by filtration. The resulted filtrate was reused for next zeolite NaA synthesis by the addition of metakaolin. The synthesis was performed by varying initial NaOH concentrations of 2, 3, 4, 5, and 6 M at a constant crystallization temperature at 100°C and constant crystallization time of 24 hours. The synthesis products were characterized by FTIR spectroscopy, X-ray diffraction, and scanning electron microscopy technique. The optimum results with the highest degree of purity and structural order were obtained from initial NaOH concentration 3M. Synthesis with NaOH concentration higher than 3M produced hydroxisodalite as another phase. The reused of filtrate in the synthesis showed the good product of zeolite NaA up to two times reused. Further reused of filtrate resulted significant decrease of purity and structural order. Further investigation indicates that another factor such as aging time for three days before synthesis could produce zeolite NaA at lower crystallization temperatures. While the amount of metakaolin in the initial mixture did not give a significantly better product. The production of zeolite NaA from Bangka kaolin using reused filtrate as partial nutrients could be an excellent way to minimize environmental impacts and decrease processing costs.

The green synthesis method of fly ash-based NaA zeolite was explored to reduce the synthesis cost and environmental hazards. For the prepared NaA samples, the effects of crystallization time, solid-liquid ratio, and Si/Al ratio were systematically studied. CO2 adsorption isotherm is used for adsorption model fitting analysis and adsorption selectivity determination. According to the experimental results, the optimized NaA zeolite synthesis conditions are as follows: the Si/Al ratio of NaA zeolite is 1.4, the solid-liquid ratio is 10, and the crystallization time is 6 h. The green synthesis method reported in this study can successfully prepare NaA zeolite and exhibit excellent CO2 adsorption performance, reaching 4.34 mmol/g, with high CO2 selective adsorption ability, reaching 89.2 for N2, 257.1 for O2, and 45.8 for CH4. The adsorbed CO2 can be released for further utilization, and NaA zeolite also has strong adsorption and regeneration performance, with a ten cycle adsorption capacity only decreasing by 1.17%. In addition, the use of cheap raw materials synthesis methods will promote the large-scale industry application of green synthesis technology in the future.

Synthesis of Na-A zeolite from coal gangue with the in-situ crystallization technique

In this work, zeolite NaA (RA) and NaX (RX) have been successfully synthesized using rice husk ash and it is a low cost synthesis process and it does not produce environmental hazards. Sodium silicate (SS) is extracted from rice husk ash which is an alternative silica source for zeolite synthesis. The zeolites are prepared by using a SS silica source extracted from the rice husk ash, and it has been used as an adsorbent for the CO2 adsorption process which may help in controlling the global warming problems. The zeolites are synthesized by a hydrothermal method without using any organic templating agent. FESEM and TEM micrographs revealed that the synthesized zeolites RA and RX have “Ice cube” and octahedral morphology respectively. From the N2 sorption studies, the BET surface area of the synthesized zeolites have been found and are 106.25 m2 g−1 and 512.79 m2 g−1 respectively. The maximum CO2 adsorption capacities of zeolite RA and RX are 2.22 and 2.45 mmol g−1, respectively at a temperature of 297.15 K. The recorded data are fitted by using non-linear adsorption isotherm models of Langmuir, Freundlich and Toth isotherm models. The fitted isotherm models are observed to be a type I adsorption isotherm according to the IUPAC classification criterion.

In this research, NaA zeolite samples were synthesized from aluminosilicate solution through hydrothermal method. The effects of different parameters such as the SiO2/Al2O3, OH-/Si and H2O/Na2O molar ratios of the initial gel solution, crystallization time and temperature on the crystallinity and morphology of the synthesized zeolites were investigated. The final products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and laser particle size analyzer. The experiment results indicated that the SiO2/Al2O3 molar ratio had influence on morphology and size of the synthesized zeolites, the optimum range of SiO2/Al2O3 molar ratio for synthesizing NaA zeolite was 1.5-2. Alkalinity (OH-/Si and H2O/Na2O molar ratio) had a significant effect on particle sizes of the synthesized zeolites, the higher the alkalinity, the smaller the crystal particle size. In addition, it was found that crystallization temperature during hydrothermal treatment played an important role in reducing the over all reaction time. The crystallization time had effect on the crystallinity of the synthesized zeolites. Finally, the optimum synthesis parameters can be proposed in order to synthesize NaA zeolite with desirable particle size, crystallinity and morphology.

The main objective of the present study was to synthesize nanozeolite Na–A by a hydrothermal method with extracted silica from rice husk ash as source in order to reduce the mean particle size of zeolite Na–A as well as crystallization conditions by keeping the economic interactive in mind. High-grade amorphous silica was extracted from rice husk ash by an appropriate alkali solution. Amorphous extracted silica powder was composed of 88% wt of SiO2. The effects of Na2O/SiO2 ratio in the initial system, the crystallization condition, crystallization time, crystallization temperature and shaking conditions (static, stirring and shaking) on the properties of final products were investigated. Various techniques including X-ray diffraction, scanning electron microscope, energy dispersive X-ray, N2 adsorption/desorption and Fourier transform infrared were then applied for characterization of the synthesized products. The results showed that the crystallization condition and alkalinity have a significant effect on the structural properties of the synthesized nanozeolite Na–A. Without adding any organic additives, nanocrystals of Na–A ranging from 40 to 120 nm in size were synthesized at 40°C and with 18 h aging, whereby crystals with a specific surface area of 36.9 m2 g−1 and an average pore diameter of 10.6 nm (using BJH method) were obtained. Na–X nanocrystals with crystallite size ranging from 70 to 260 nm were obtained from a sodium aluminosilicate solution at 60°C after 2 days in static crystallization condition, whereby crystals with a specific surface area of 89.9 m2 g−1 and an average pore diameter of 9.2 nm (using BJH method) were obtained.

The zeolite NaA was successfully synthesized by hydrothermal method using kaolin as a raw material. In order to study the crystallization mechanism, the products and intermediates of different crystallization stages were systematically characterized using x-ray diffraction (XRD), Fourier transform infrared (FTIR), and scanning electron microscopy (SEM)-energy-dispersive spectrometry (EDS). The results show that the metakaolin is completely dissolved during the first hour of the crystallization process, forming a rich crystal nucleus. As the crystallization time increases, the nucleus grows rapidly to form zeolite NaA crystals. When the crystallization time reaches 3 h, the percentage crystallinity of zeolite NaA reaches a maximum. Therefore, it can be concluded that the optimum crystallization time of zeolite NaA is 3 h. Meanwhile, we can come to the conclusion that the synthesis of zeolite NaA from kaolin is a liquid phase transition mechanism. The microstructure of zeolite NaA synthesized at 3 h of crystallization was further investigated by transmission electron microscopy (TEM) technique. The SAED patterns indicate the polycrystallinity of the zeolite NaA structure. The electron diffraction pattern indicates that the crystal structure type of the zeolite NaA belongs to the body center cube (BCC). The textural properties of the zeolite NaA synthesized at 3 h of crystallization were studied by nitrogen adsorption technique. It can be concluded that the BET surface area of the zeolite NaA obtained by the BET method is 21.106 m2·g−1. Meanwhile, from the BJH method, it is found that the microporous surface area and micropore volume of the zeolite NaA are 13.929 m2·g−1 and 0.052 cm3·g−1, respectively.

Rice husk has become global concern due to the environmental problem since it has been dumped and open burned that contributed to the emissions of carbon dioxide to the atmosphere. Therefore, utilization of rice husk to other useable product such as silica aerogel for adsorption has been study recently due to the silica content in rice husk is about 60% and this material is sustainable and cost effective. Silica aerogel was prepared from rice husk ash and dried by using ambient pressure drying method with addition of tetraethyl orthosilicate (TEOS) due to its capability to prevent the gel from crack and increase the porosity of gel to increase the capacity of adsorption process. The silica aerogel was further characterized by using Fourier Transform Infrared spectroscopy (FTIR), Elemental Anaylzer (EA) and Scanning Electron Microscopic (SEM). The results show that the silica aerogel was successfully synthesized using rice husk ash. The FTIR studies reveal that silica aerogel produced consist of amorphous silica with Si-O-Si bonding and stretching’s. From EA analysis, the carbon in the rice husk decreasing when turn into silica aerogel due to the burning of carbon content in the preparation of silica. The SEM studies confirm that the silica aerogel has a porous structure and has ability to for the application adsorption process such as carbon dioxide adsorption, methylene blue adsorption and others application.

The eco-friendly synthesis of nanozeolite need to be developed in order to minimize the consumption of unwanted excess extracted solutions or solvents and maximize the utilization of beneficial wastes as its raw materials. Thus, the synthesis of nanozeolite NaA from rice husk ash (RHA) without extraction of silica from RHA and without organic template has been successfully achieved. Nanozeolite NaA was synthesized from rice husk ash (RHA) via this main step: aging the aluminosilicate suspension (3.190 Na2O: Al2O3: 1.4SiO2:235.07H2O) for 3 days at room temperature with agitation rate of 150 rpm followed by heating at 55 °C for 18 hours. The nanozeolite NaA was confirmed by XRD, FTIR, FESEM and particle size distribution analysis where the highest particle size was in the range of 100 to 400 nm. Its efficiency in removing ammonium ions in aqueous solution was found to be better than that of microsized zeolite NaA thus proved that the lower particle sizes of zeolite NaA (nanosize) tended to have higher adsorption sites and higher exchange capacity.

A number of investigations have demonstrated that zeolite NaA could be synthesized using Si, extracted from rice husk ash; however, experiments on direct extraction of Si from rice husk (RH) are scarce. The main objective of the present study was to explore the possibility to synthesize high-quality zeolite NaA from RH and waste aluminium cans (as a source of Al), applying different procedures for the preparation of initial hydrogel and a unified procedure for crystallization of zeolite NaA. Products were characterized by SEM–EDX and XRD analyses. The investigation demonstrated that Si could be extracted directly from RH, avoiding the process of RH burning. Practically complete dissolution of Si from RH was achieved by alkali treatment (with 10 % NaOH for 7 h) at boiling temperature and atmospheric pressure, i.e. using refluxing system instead of autoclave for the preparation of Si-gel. Zeolite NaA samples synthesized from such Si-gels were pure, highly crystalline and white. Furthermore, it was found that the direct dissolution of Al in Si-gel did not affect the quality of the final product. Although this investigation was not focused on the mechanism of zeolite NaA crystallization, the results obtained indicated clearly that the history of Si-gel preparation played an important role in the nucleation and growth of zeolite NaA crystals and influenced their yield, size, and shape. Therefore, the optimization of Si-gel preparation procedure has to be considered as essential not only for the economy of the synthesis of NaA from RH, but also for the quality of the final product.

Carbon dioxide adsorption kinetics in the presence of light paraffins on NaA and CaA zeolites

Concrete, a fundamental construction material, consists of aggregates, water, cement, and additives. Unfortunately, the large-scale production of cement is a major contributor to carbon dioxide (CO2) emissions, primarily from the manufacturing process and the consumption of fossil fuels. This not only incurs environmental costs associated with global warming but also depletes vital limestone deposits. To mitigate these issues, this study aims to explore the optimal utilization of Guinea Corn Husk Ash (GCHA) and Rice Husk Ash (RHA) in concrete. This research investigated the chemical properties of GCHA and RHA, and their impact on the compressive and split-tensile strengths of concrete when integrated in various proportions. The study reveals that both GCHA and RHA meet the minimum oxide content requirement of 70% set by ASTM C618, with silicon dioxide (SiO2) as the predominant oxide. Increasing the content of RHA and GCHA from 5% to 10% improves the concrete's compressive and split-tensile strengths after curing for 56 days. Optimization results indicate that the ideal mix consists of 10% GCHA, 8.5% RHA, and 82.5% cement, yielding a compressive and split tensile strength of 31.34 N/mm² and 3.07 N/mm² respectively. This study thus offers a promising solution for sustainable concrete production by reducing the environmental footprint of cement while enhancing material properties and promoting an eco-friendlier approach to construction. Keywords: Concrete, Guinea Corn Husk Ash, Rice Husk Ash, Compressive Strength, Split-Tensile Strength