Selective preparation of zeolite X and A from flyash and its use as catalyst for biodiesel production

Synthesis of high-crystallinity Zeolite A from rare earth tailings: Investigating adsorption performance on typical pollutants in rare earth mines

The ecological restoration of rare earth mines and the management of rare earth tailings have consistently posed global challenges, constraining the development of the rare earth industry. In this study, Zeolite A is efficiently prepared from the tailings of an ion-type rare earth mine in the southern Jiangxi Province of China. The resulting Zeolite A boasts exceptional qualities, including high crystallinity, a substantial specific surface area, and robust thermal stability. The optimum conditions for Zeolite synthesis are experimental determination and the adsorption properties of Zeolite A for typical pollutants (Cd2+, Cu2+, NH4+, PO43- and F-) in rare earth mines. The synthesised Zeolite A material is found to have strong adsorption properties. The adsorption mechanism is mainly cation exchange, and the priority of adsorption of pollutants is Cu2+> Cd2+ > NH4+ > PO43- > F-. Notably, the sodium Zeolite A material synthesized at room temperature can be effectively recycled multiple times. In summary, we propose a method to synthesise low cost and high adsorption zeolites using rare earth tailings. This will facilitate the reduction of rare earth tailings and the rehabilitation of rare earth mines. Our method has great potential as a rehabilitation technology for rare earth mines.

Fusion-Assisted Hydrothermal Synthesis and Post-Synthesis Modification of Mesoporous Hydroxy Sodalite Zeolite Prepared from Waste Coal Fly Ash for Biodiesel Production

Increases in biodiesel prices remains a challenge, mainly due to the high cost of conventional oil feedstocks used during biodiesel production and the challenges associated with using homogeneous catalysts in the process. This study investigated the conversion of waste-derived black soldier fly (BSF) maggot oil feedstock over hydroxy sodalite (HS) zeolite synthesized from waste coal fly ash (CFA) in biodiesel production. The zeolite product prepared after fusion of CFA followed by hydrothermal synthesis (F-HS) resulted in a highly crystalline, mesoporous F-HS zeolite with a considerable surface area of 45 m2/g. The impact of post-synthesis modification of the parent HS catalyst (F-HS) by ion exchange with an alkali source (KOH) on its performance in biodiesel production was investigated. The parent F-HS zeolite catalyst resulted in a high biodiesel yield of 84.10%, with a good quality of 65% fatty acid methyl ester (FAME) content and fuel characteristics compliant with standard biodiesel specifications. After ion exchange, the modified HS zeolite catalyst (K/F-HS) decreased in crystallinity, mesoporosity and total surface area. The K/F-HS catalyst resulted in sub-standard biodiesel of 51.50% FAME content. Hence, contrary to various studies, the ion exchange modified zeolite was unfavorable as a catalyst for biodiesel production. Interestingly, the F-HS zeolite derived from waste CFA showed a favorable performance as a heterogeneous catalyst compared to the conventional sodium hydroxide (NaOH) homogeneous catalyst. The zeolite catalyst resulted in a more profitable process using BSF maggot oil and was economically comparable with NaOH for every kilogram of biodiesel produced. Furthermore, this study showed the potential to address the overall biodiesel production cost challenge via the development of waste-derived catalysts and BSF maggot oil as low-cost feedstock alternatives.

Green method to synthesize magnetic zeolite/chitosan composites and adsorption of hexavalent chromium from aqueous solutions

This paper aims to synthesis a recyclable adsorbent from solid waste using a clean and environmentally friendly method to deal with Cr(VI) water pollution. Magnetic zeolite/chitosan composites (ZFA/MCS) were prepared by the neutralization method. The adsorption properties of ZFA/MCS, prepared by the neutralization method for Cr(VI) ions under different conditions especially cross-linking, were investigated in detail. The results showed that cross-linked ZFA/MCS generally showed higher adsorption capacity than uncross-linked ones. The uncross-linked ZFA/MCS and cross-linked ZFA/MCS showed a saturated adsorption capacity of 25.67 mg·g^-1 and 28.47 mg·g^-1 at pH = 3 and 30 °C, respectively. The experimental values were followed Langmuir adsorption equations and pseudo-second-order kinetic model, indicating that the adsorption was probably monolayer coverage and chemical adsorption, respectively. The effect of temperature proved that the adsorption was spontaneous and endothermic. Therefore, the adsorbent with excellent recyclability and adsorbability was successfully fabricated via a green synthetic strategy.

Optimization of biodiesel synthesis from Jatropha curcas oil using kaolin derived zeolite Na–X as a catalyst

Biodiesel is an alternative renewable green fuel obtainable from the reaction of plant or animal oil with a low molecular weight alcohol in the presence of a catalyst. However, the cost of its production remains high due to costly feedstock, the majority of which is competitively also used as food, and the use of homogeneous catalysts, which pose difficulties in product purification and resulting environmental pollution. The aim of this study was to explore the production of biodiesel through transesterification of non-edible and cheap Jatropha curcas (JC) oil using a zeolite Na–X catalyst obtained from naturally occurring kaolin clay. The transesterification parameters, namely reaction temperature, reaction time, catalyst loading and methanol to oil molar ratio were optimized using the L₁₆(4⁴) Taguchi orthogonal array approach. The catalyst loading was found to be the most influential parameter at 93.79%. The optimum conditions for the conversion of JC oil, with a biodiesel yield of up to 93.94%, were found to be a methanol to oil molar ratio of 10 : 1, catalyst loading of 8%, reaction temperature of 70 °C and reaction time of 5 h. Fuel characterization parameters were within the European Norm (EN) 14214:2019 biodiesel specifications. Our findings offer insights into the ideal parametric conditions for the cost-effective synthesis of biodiesel from JC oil via zeolite-catalyzed esterification.

Zeolite Na–X derived from inexpensive kaolin clay is an effective catalyst (up to 94% yield) for Jatropha curcas oil conversion to biodiesel; Taguchi optimization shows methanol/oil ratio of 10, with 8% catalyst loading at 70 °C for 5 h as optimum.

NaOH-Catalyzed Methanolysis Optimization of Biodiesel Synthesis from Desert Date Seed Kernel Oil

Biodiesel synthesis from non-edible vegetable oil via catalytic transesterification is one of the effective ways to replace petroleum-based fuels in the area of renewable energy development and is beneficial to environmental security. Therefore, this research investigates the optimization of process parameters (temperature, methanol to oil ratio, and NaOH catalyst dose) for the conversion of biodiesel from non-edible desert date (Balanites Aegyptiaca) seed kernel oil using the Box-Behnken experimental design of response surface methodology statistical analysis. Accordingly, the optimum values of reaction conditions, namely, a temperature of 60.5 °C, methanol to oil ratio of 6.7:1, and catalyst dose of 0.79 %wt, yielded 93.16% biodiesel. Fourier transform infrared spectroscopy analysis confirmed the cracking of a single glycerol backbone from the triglycerides and the substitution by methoxyl in the presence of a NaOH catalyst. The physicochemical properties of the biodiesel were investigated and compared with standards in terms of its density, viscosity, higher heating value, acid value, saponification value, cetane number, cloud point, pour point, and flash point, and the values are within the recommended standard limits of American Standard for Testing Material (ASTM D6751) and European Committee for Standardization (EN14214). Thus, the results revealed that homogeneous base catalysis of non-edible oil under optimum reaction conditions provides high yield of biodiesel.

Study on the correlation between pore morphology of porous calcium silicate and high-capacity formaldehyde adsorption

A novel porous calcium silicate (PCS) material with unique pore structure prepared from coal fly ash (CFA) was reported. The microstructure was investigated through X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, nuclear magnetic resonance cryoporometry, and Brunauer-Emmett-Teller method. Model describing the nanostructure of the prepared PCS was proposed in this work. Results show that the prepared PCS has open pores, a high specific surface area, and multi-peak pore size distributions (macro-, meso-, and micropores). The unique conical pore structure and interconnected micro-, meso-, and macropores are favourable to the reduction of the diffusion resistance of gas molecules. Benefiting from such a valuable structure, PCS exhibits excellent gas adsorption properties. Used in formaldehyde (HCHO) adsorption experiment, PCS shows excellent properties, including high storage capacity and endurance. The saturated adsorption capacity of the prepared PCS is 2.056 mg/g, which is enhanced by fourfold compared with that of active carbon commercially used for formaldehyde adsorption. This work provides a new, efficient, and rational way to utilize CFA. The prepared material can be used as an efficient and cost-effective adsorbent of HCHO under ambient conditions. Furthermore, the microstructure and the correlation between pore morphology and gas adsorption properties of the prepared PCS are revealed.

Recycling of Waste Solution after Hydrothermal Conversion of Fly Ash on a Semi-Technical Scale for Zeolite Synthesis

Nowadays, using fly ash for zeolites production has become a well-known strategy aimed on sustainable development. During zeolite synthesis in a hydrothermal conversion large amount of post-reaction solution is generated. In this work, the solution was used as a substrate for Na-A and Na-X zeolites synthesis at laboratory and technical scale. Obtained materials were characterized using particle size analysis, X-ray diffraction (XRD), X-ray fluorescence spectroscopy (XRF), transmission electron microscopy (TEM), Fourier transformed infrared spectroscopy (FTIR), and nitrogen adsorption/desorption isotherm. Produced zeolites revealed high purity (>98%) and monomineral zeolitic phase composition. The SiO₂ content was in the range 39–42% and 40–38%, whereas Al₂O₃ content was 23–22% and 25–26% for Na-X and Na-A, respectively. TEM and BET analyses revealed Na-X zeolite pores were almost identical to commercial 13X with S_BET in the range 671–734 m²/g. FTIR indicated slight differences between materials obtained at laboratory and technical scale in Si-O-(Si/Al) bridges of the zeolitic skeleton. The results showed good replicability of the laboratory process in the larger scale. The proposed method allows for waste solution reusability with a view to highly pure zeolites production in line with circular economy assumptions.

Development of Heterogeneous Alkali Methoxide Catalyst from Fly Ash and Limestone

This study is aimed to use fly ash and limestone as raw materials for preparing alkali methoxide heterogeneous catalysts for transesterification of palm oil into biodiesel. The heterogeneous catalyst was synthesized from fly ash and limestone through wet and dry methods and calcined within 1073–1273 K. X-ray diffraction and scanning electron microscopy analyses indicated the well-dispersed presence of the Ca(OCH3)2 crystal over the fly ash and limestone framework, which was mixed using wet method and calcined at 1073 K (W-800). Results showed that W-800 exhibited larger surface area and more uniform active sites than the other catalysts. About 88.6 % of biodiesel was produced from commercial palm oil with W-800 as the catalyst. The product possesses physicochemical characteristics, such as density, kinematic viscosity and free fatty acid content, which satisfy the international biodiesel standard. The catalyst was used for biodiesel production for four cycles, and the biodiesel yield was maintained up to 91.87 % from the initial value.

Progress in the Utilization of Coal Fly Ash by Conversion to Zeolites with Green Energy Applications

Fly ash (FA) from lignite coal combusted in different Thermal Power Plants (TPPs) was used for the synthesis of zeolites (FAZs) of the Na-X type by alkaline activation via three laboratory procedures. FAZs were characterized with respect to their morphology, phase composition and surface properties, which predetermine their suitability for applications as catalysts and adsorbents. FAZs were subsequently modified with metal oxides (CuO) to improve their catalytic properties. The catalytic activity of non-modified and CuO-modified FAZs in the total oxidation of volatile organic compounds was investigated. FAZs were studied for their potential to retain CO₂, as their favorable surface characteristics and the presence of iron oxides make them suitable for carbon capture technologies. Thin films of FAZs were deposited by in situ crystallization, and investigated for their morphology and optical sensitivity when exposed to pollutants in the gas phase, e.g., acetone. This study contributes to the development of novel technological solutions for the smart and valuable utilization of FA in the context of the circular economy and green energy production.

Effect of the Formation of Diglycerides/Monoglycerides on the Kinetic Curve in Oil Transesterification with Methanol Catalyzed by Calcium Oxide

Many researchers reported that a sigmoid kinetic curve was obtained in oil transesterification with methanol catalyzed by CaO and gave different explanations for this formation. In this paper, heterogeneously catalyzed transesterification of soybean oil with methanol using CaO has been investigated. The solid catalyst and the liquid reaction mixture under different reaction time periods were characterized by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, and high-performance liquid chromatography (HPLC) to reveal the formation of an S-shape kinetic curve. The appearance of calcium hydroxide, calcium methoxide, calcium glyceroxide, fatty acid calcium, diglycerides, and monoglycerides and their contributions to the kinetic curve have been discussed. The low reaction rate in the induction period can be attributed to mass transfer in this three-phase system. However, the formation of surfactants, diglycerides and monoglycerides, promotes the emulsification of the reaction mixture and numerous emulsion reactors are generated. These emulsion reactors can improve the contact of the solid catalyst with the reactants and thus accelerate the reaction.

Synthesis of Hydroxy Sodalite from Coal Fly Ash for Biodiesel Production from Waste-Derived Maggot Oil

Zeolites are aluminosilicate crystalline materials known for their unique characteristics, and have been prominent for nearly half a century due to their wide and important industrial applications. The production of zeolites, however, remains a challenge due to the high cost of commercial reagents conventionally used as feedstocks. In the current study, hydroxy sodalite (HS) zeolite samples were synthesised from coal fly ash feedstock by a direct hydrothermal synthesis method. The effects of hydrothermal crystallisation synthesis time on phase crystallinity, crystal size, and morphology of the formed HS were investigated. The prepared samples were characterised using XRD, SEM, EDS and FT-IR techniques. The XRD results of the samples prepared with varying synthesis times confirmed the formation of HS from low to high phase purity and crystallinity from 11 to over 98%. The SEM results reflected gradual variation in crystal morphology, of which highly crystalline HS samples were associated with hexagonal-cubic and cubic-platelet crystals. The FTIR, depicting zeolite characteristics of T–O and T–O–T stretching vibrations in the molecular framework, further confirmed the formation of HS zeolites for samples obtained above the 24-h synthesis time. These zeolite samples were then evaluated for their catalytic activities in the conversion of maggot oil to biodiesel. The application of the various hydroxy sodalite samples for the transesterification of maggot oil yielded up to 84.10% biodiesel (FAME) with physicochemical properties that were in compliance with the biodiesel specification standards. This study investigated the novel use of a coal fly ash-derived, heterogeneous HS catalyst in biodiesel production from maggot oil, and indicates its potential to enhance biodiesel yield and quality upon process optimisation tests.

Composite coal fly ash solid acid catalyst in synergy with chloride for biphasic preparation of furfural from corn stover hydrolysate

A solid acid catalyst SO₄^2-/SnO₂-Al₂O₃-CFA was synthesized based on industrial waste coal fly ash (CFA) as carrier and applied in the conversion of oxalic acid pretreated corn stover hydrolysate to produce furfural. Physical properties of the solid acid catalyst were characterized by SEM, FTIR, XRD, BET, EDAX, and NH₃-TPD. Highly wrinkled structure of SO₄^2-/SnO₂-Al₂O₃-CFA could provide more specific surface area for the covalent linkage between SiO₂ and SnO₂. Factors influencing the efficacy of SO₄^2-/SnO₂-Al₂O₃-CFA were systematically explored. The highest furfural yield of 84.7% was reached in NH₄Cl-toluene biphasic system at 180 °C for 30 min. The recyclability of SO₄^2-/SnO₂-Al₂O₃-CFA and toluene could be achieved for five batches with stable performance in transformation of xylose-rich corn stover hydrolysate. This study provided a novel solid acid catalyst with promising potential in the synthesis of furfural from corn stover.

Zeolite-Based Catalysts: A Valuable Approach toward Ester Bond Formation

Zeolite-based catalysts are versatile catalytic systems for a wide range of laboratory studies and industrial scale processes. The chemical composition, ion exchange, and pore size structure attributes of zeolites are responsible for their extensive catalytic applications. Esterification is one of the most important and routinely processes in diverse fields of organic synthesis. It has a long history in both industrial processes and laboratory work due to its versatility. This review intends to give a detailed insight into the significance of zeolite-based catalysts for ester bond formation

Progressive utilisation prospects of coal fly ash: A review

The rapid surge in global energy needs has paved way for the development of various alternatives to natural resources every now and then. However, dependence on coal-based energy has not reduced greatly. Thus, massive quantities of coal fly ash (CFA) are generated worldwide, which is a serious threat to ecology owing to constraints associated with its storage and disposal. There exists a pressing and ongoing need to develop new, and green product streams from CFA to reduce the threat to the environment. The present review begins with an emphasis on the generation, physicochemical properties, and potential dangers of CFA. Then, it focuses on impending applications such as synthesis of geopolymers (alternative to cement), silica aerogels (insulating materials), carbon nanotubes (carbon allotropes) for electronic devices, and the separation of radioactive isotopes as well as rare earth elements from CFA. Furthermore, the review analyses factors restraining the motive for effective management strategies that drives utilisation of CFA (either in raw and processed state) for new product streams. Finally, the review elucidates the role of CFA as an emerging input in delivering eco-friendly amenities and future derivatives.

Preparation and characterization of animal bone powder impregnated fly ash catalyst for transesterification

The present work reconnoitres the feasibility of utilizing class F fly ash and calcined animal bone powder (CABP) as raw material for the synthesis of heterogeneous solid base catalyst with varying ratios (CABP of 10, 20, and 30 mass%), that is subsequently used for transesterification of mustard oil. Physicochemical characterization of CABP revealed crystalline behavior, signifying one of the components as hydroxyapatite (HAP); when calcined at 900 °C transforms to β-tricalcium phosphate having a specific surface area of 100 m² g^-1. The synthesized catalyst showed improved catalytic activity when compared to the parental species and the optimal value to achieve the highest conversion of 90.4% would be at CABP loading of 10 mass%, 5.5:1 methanol to oil molar ratio, and 10 mass% catalyst concentration for 6 h. The prepared biodiesel had a calorific value of 36.2 MJ kg^-1 with ash content < 0.01 mass%. The catalyst could be reused five times with no loss in its activity. Results indicated that calcium enriched waste materials when impregnated in fly ash might be a potential source of catalyst in biodiesel production.

Novel synthesis of nanoscale zerovalent iron from coal fly ash and its application in oxidative degradation of methyl orange by Fenton reaction

We firstly developed a novel synthesis method of nanoscale zerovalent iron (NZVI) using Fe sources in coal fly ash (CFA) for the oxidative degradation of methyl orange by Fenton reaction. Hydrochloric acid (HCl) and methyl isobutyl ketone (MIBK) were used for Fe dissolution from CFA and selective Fe(III) chelation, respectively. Among varied HCl concentrations, 7 N HCl showed the best performance for the oxidation of aqueous Fe(II) to Fe(III) and efficient chelation of Fe(III) with MIBK. The NZVI-CFA was synthesized by adding NaBH₄ to a solution of Fe(III)-chelated MIBK, yielding NZVI transformation >95% from Fe(III) in HCl. Various surface analyses were performed to characterize the NZVI-CFA, which was almost identical to typical NZVI-Bare. HCl and MIBK could be reused several times, indicating potential reusability of chemicals used in the synthesis. Remarkable >96% decolorization of methyl orange was obtained by the NZVI-CFA-induced Fenton reaction at pH 3, with a ∼22% decrease in total organic carbon in 7 min. The heterogeneous Fenton reaction initiated by NZVI-CFA with H₂O₂ showed reactivity similar to that of the homogeneous Fenton reaction (i.e., aqueous Fe(II) with H₂O₂), indicating the importance of homogeneous reaction for the oxidative degradation of methyl orange.

One-Step Hydrothermal Synthesis of Zeolite X Powder from Natural Low-Grade Diatomite

Zeolite X powder was synthesized using natural low-grade diatomite as the main source of Si but only as a partial source of Al via a simple and green hydrothermal method. The microstructure and surface properties of the obtained samples were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), wavelength dispersive X-ray fluorescence (XRF), calcium ion exchange capacity (CEC), thermogravimetric-differential thermal (TG-DTA) analysis, and N₂ adsorption-desorption technique. The influence of various synthesis factors, including aging time and temperature, crystallization time and temperature, Na₂O/SiO₂ and H₂O/Na₂O ratio on the CEC of zeolite, were systematically investigated. The as-synthesized zeolite X with binary meso-microporous structure possessed remarkable thermal stability, high calcium ion exchange capacity of 248 mg/g and large surface area of 453 m²/g. In addition, the calcium ion exchange capacity of zeolite X was found to be mainly determined by the crystallization degree. In conclusion, the synthesized zeolite X using diatomite as a cost-effective raw material in this study has great potential for industrial application such as catalyst support and adsorbent.

Optimization of crystal growth of sub-micron ZSM-5 zeolite prepared by using Al(OH)3 extracted from fly ash as an aluminum source

A novel approach was proposed to prepare ZSM-5 zeolite via hydrothermal synthesis by using Al(OH)₃, which was extracted from fly ash by a staged treatment, as an aluminum source. The synthesis parameters and crystal growth of ZSM-5 were optimized. The optimization of crystal growth for ZSM-5 was investigated under the effect of organic steric-hindrance agents. The crystal phase and morphology of the ZSM-5 were characterized by X-ray diffractometry and scanning electron microscopy, and the particle size distribution was measured by laser particle-size analyzer. The crystal growth of ZSM-5 under different hydrothermal conditions obeyed the "S" regulation. According to the analysis, the formation of ZSM-5 crystal occurred via four steps: (1) the formation of amorphous aluminosilicate by the condensation of silicate ions and aluminate ions; (2) the particle growth and aggregation of the amorphous aluminosilicate; (3) crystallization and crystal growth of ZSM-5; (4) Gentle growth after the zeolite crystal reaches a certain size. The addition of organic steric hindrance agents resulted in a decrease in grain size and crystal-particle formation with a narrow size distribution. Single-grain dispersion resulted and the micropore volume, mesopore volume, and specific surface areas were improved by the presence of organic steric agents.

Mg-modified ultra-stable Y type zeolite for the rapid catalytic co-pyrolysis of low-rank coal and biomass

To improve the quality of oil derived from the fast co-pyrolysis of low-rank coal with biomass, various metal-modified ultra-stable Y type (USY) zeolites are mixed with the samples for the co-pyrolysis process.