Novel zeolite Na-X synthesized from fly ash as a heterogeneous catalyst in biodiesel production

Fly Ash-Based Na-X Zeolite Application in Separation Process of Bovine Serum Albumin from Aqueous Solution in the Presence of Organic Substances with Anionic Character

The main purpose of the investigations was to explore the protein adsorption on porous materials, as well as to identify the mechanisms of protein attachment without and with other common environmental contaminants, such as drugs, polymers or surfactants. This study applied the Na-X zeolite for the adsorption of bovine serum albumin (BSA) from solutions with various pH values. Electrophoretic mobility measurements and potentiometric titrations were conducted in systems containing both protein and/or PAA (poly(acrylic acid) polymer/DCF (diclofenac) drug/SDS (sodium dodecyl sulfate) surfactant to investigate the protein binding mechanisms in the complex adsorbate systems. In addition, aggregate size and stability measurements were performed in the investigated systems. Based on the research results, it was possible to conclude that the protein adsorbed most preferably on the zeolite surface at a pH value close to its isoelectric point (pI) (102.15 mg/g), and protein adsorption was the lowest in the solutions with strongly alkaline (29.61 mg/g) or acidic (77.45 mg/g) pH values. Thus, the examined zeolitic material can be considered an effective adsorbent for protein removal from an aqueous solution.

Advancements in Basic Zeolites for Biodiesel Production via Transesterification

The excessive utilization of petroleum diesel has led to the depletion of fossil resources and severe environmental pollution. Biodiesel produced from renewable triglycerides (TGs) or waste lipids is a low-emission fuel substitute for diesel. Biodiesel is mainly produced by transesterification reactions over homogeneous base catalysts with excellent activity and low cost. In comparison, solid base catalysts are more attractive due to their lower environmental impact and simpler production and purification processes. It remains a challenge to further improve the stability and activity of solid base catalysts. Because of the high surface area, superior stability, and tunable basicity, basic zeolites, especially two-dimensional zeolites, have emerged as promising solid basic catalysts for the transesterification of TGs. In this review, we present recent advancements in the synthesis, characterization, and catalytic performance of basic zeolites for the transesterification of TGs. Challenges and development prospects of basic zeolites for biodiesel production via transesterification are also pointed out. We expect that this review will inspire the more efficient and rational design of zeolites for sustainable fuel production.

Catalytic Characterization of Synthetic K+ and Na+ Sodalite Phases by Low Temperature Alkali Fusion of Kaolinite during the Transesterification of Spent Cooking Oil: Kinetic and Thermodynamic Properties

The mineral raw Egyptian kaolinite was used as a precursor in the synthesis of two sodalite phases (sodium sodalite (Na.SD) and potassium sodalite (K.SD)) according to the low alkali fusion technique. The synthesized Na.SD phase demonstrates enhanced total basicity (6.3 mmol OH/g), surface area (232.4 m2/g), and ion exchange capacity (126.4 meq/100 g) compared to the K.SD phase (217.6 m2/g (surface area), 96.8 meq/100 g (ion exchange capacity), 5.4 mmol OH/g (total basicity). The catalytic performance of the two sodalite phases validates the higher activity of the sodium phase (Na.SD) than the potassium phase (K.SD). The application of Na.SD resulted in biodiesel yields of 97.3% and 96.4% after 90 min and 60 min, respectively, while the maximum yield using K.SD (95.7%) was detected after 75 min. Robust base-catalyzed reactions using Na.SD and K.SD as catalysts were suggested as part of an operated transesterification mechanism. Moreover, these reactions exhibit pseudo-first order kinetics, and the rate constant values were estimated with consideration of the change in temperature. The estimated activation energies of Na.SD (27.9 kJ.mol−1) and K.SD (28.27 kJ.mol−1) reflected the suitability of these catalysts to be applied effectively under mild conditions. The essential thermodynamic functions, such as Gibb’s free energy (65.16 kJ.mol−1 (Na.SD) and 65.26 kJ.mol−1 (K.SD)), enthalpy (25.23 kJ.mol−1 (Na.SD) and 25.55 kJ.mol−1 (K.SD)), and entropy (−197.7 J.K−1.mol−1 (Na.SD) and −197.8 J.K−1.mol−1 (K.SD)), display the endothermic and spontaneous nature of the two transesterification systems.

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.

Low-cost zeolitic carriers for delivery of hydroxychloroquine immunomodulatory agent with antiviral activity

The coronavirus pandemic prompted scientists to look for active pharmaceutical ingredients that could be effective in treating COVID-19. One of them was hydroxychloroquine, an antimalarial and immunomodulatory agent exhibiting antiviral activity. The anchoring of this drug on porous carriers enables control of its delivery to a specific place in the body, and thus increases bioavailability. In this work, we developed low-cost zeolitic platforms for hydroxychloroquine. The waste solution generated during zeolite production from fly ashes was used in the synthesis of Na-A and Na-X carriers at laboratory and technical scale. The materials were characterized by high purity and single mineral phase composition. The surface charge of zeolites varied from negative at pH 5.8, and 7.2, to positive at pH 1.2. All samples indicated good sorption ability towards hydroxychloroquine. The mechanism of drug adsorption was based on electrostatic interactions and followed the Freundlich model. Zeolitic carriers modified the hydroxychloroquine release profiles at conditions mimicking the pH of body fluids. The mode of drug liberation was affected by particle size distributions, morphological forms, and chemical compositions of zeolites. The most hydroxychloroquine controlled release at pH 5.8 for the Na-X material was noted, which indicates that it can enhance the drug therapeutic efficacy.

Managing the hazardous waste cooking oil by conversion into bioenergy through the application of waste-derived green catalysts: A review

Waste cooking oil (WCO) is a hazardous waste generated at staggering values globally. WCO disposal into various ecosystems, including soil and water, could result in severe environmental consequences. On the other hand, mismanagement of this hazardous waste could also be translated into the loss of resources given its energy content. Hence, finding cost-effective and eco-friendly alternative pathways for simultaneous management and valorization of WCO, such as conversion into biodiesel, has been widely sought. Due to its low toxicity, high biodegradability, renewability, and the possibility of direct use in diesel engines, biodiesel is a promising alternative to mineral diesel. However, the conventional homogeneous or heterogeneous catalysts used in the biodiesel production process, i.e., transesterification, are generally toxic and derived from non-renewable resources. Therefore, to boost the sustainability features of the process, the development of catalysts derived from renewable waste-oriented resources is of significant importance. In light of the above, the present work aims to review and critically discuss the hazardous WCO application for bioenergy production. Moreover, various waste-oriented catalysts used to valorize this waste are presented and discussed.

Sustainable biodiesel generation through catalytic transesterification of waste sources: a literature review and bibliometric survey

Sustainable renewable energy production is being intensely disputed worldwide because fossil fuel resources are declining gradually. One solution is biodiesel production via the transesterification process, which is environmentally feasible due to its low-emission diesel substitute. Significant issues arising with biodiesel production are the cost of the processes, which has stuck its sustainability and the applicability of different resources. In this article, the common biodiesel feedstock such as edible and non-edible vegetable oils, waste oil and animal fats and their advantages and disadvantages were reviewed according to the Web of Science (WOS) database over the timeframe of 1970–2020. The biodiesel feedstock has water or free fatty acid, but it will produce soap by reacting free fatty acids with an alkali catalyst when they present in high portion. This reaction is unfavourable and decreases the biodiesel product yield. This issue can be solved by designing multiple transesterification stages or by employing acidic catalysts to prevent saponification. The second solution is cheaper than the first one and even more applicable because of the abundant source of catalytic materials from a waste product such as rice husk ash, chicken eggshells, fly ash, red mud, steel slag, and coconut shell and lime mud. The overview of the advantages and disadvantages of different homogeneous and heterogeneous catalysts is summarized, and the catalyst promoters and prospects of biodiesel production are also suggested. This research provides beneficial ideas for catalyst synthesis from waste for the transesterification process economically, environmentally and industrially.

Sustainable renewable energy production is being intensely disputed worldwide because fossil fuel resources are declining gradually.

Fundamental features of mesoporous functional materials influencing the efficiency of removal of VOCs from aqueous systems: A review

Volatile organic compounds (VOCs) are harmful contaminants that are emitted into the environment as a result of various commercial, industrial, and domestic practices. Their presence in water leads to pollution and poses a huge threat to the ecological environment and human health. They are typically released into the environment through a spill or inappropriate disposal which allows the chemicals to get absorbed into the ground or enter the sewage system. Thus far, several treatment methods have been developed to remove VOCs from water, including steam stripping or air stripping, ion exchange, filtration, adsorption, and application of various types of sorbents. Due to their cost-effectiveness and efficiency, the use of mesoporous materials, especially those synthesized from coal fly ash (FA), is recognized as the most promising strategy for slowing down the impact of VOCs. This study is believed to be the first to assess the advances made in improving the adsorption of VOCs by different functional mesoporous materials (FA, zeolites, mesoporous silica, metal organic frameworks). The impact associated with the properties of these materials is carefully summarized in this paper, in regard to their solid-state characteristics, material synthesis method, and surface modification. In addition, their chemical and physical interactions in solution, the reaction kinetics, and the influence of temperature and pH are described in detail. The aim of this work was to compare the sorption properties of the materials synthesized from FA with more complex mesoporous materials. This overview provides a comprehensive understanding of VOC removal from water systems using various functional materials, as well as helps in identifying the materials that may play a key role in the future.

Electrolytic transesterification of waste frying oil using Na+/zeolite-chitosan biocomposite for biodiesel production

Given the economic and environmental advantages of using Waste Fried Oil (WFO) as a starting material, this investigation explores the conversion of WFO to Fatty Acid Methyl Ester (FAME) via electrolysis for use in waste. In electrolysis, hydroxyl ions are generated from water in close proximity to the cathode. When hydroxyl ions react with methanol, they produce a species of nucleophilic methoxide which is the main actor in converting WFO into FAME. This study specifically investigates the effects of voltage, catalyst concentration, co solvent amount, rotation speed, and molar ratio of methanol to WFO in electrolytic transesterification converting WFO into FAME using graphite electrodes in the presence of a heterogeneous, catalytic zeolite-chitosan composite. With an alcohol to WFO molar ratio of 8:1, 1 wt% zeolite-chitosan composite concentration at 40 V in the presence of 2 wt% H₂O of the whole solution at room temperature and stirrer rate of 400 rpm and reaction time of 30 min, a 96.5% yield of FAME was achieved. Characterization of physical and biodiesel fuel properties was performed using American Society for Testing and Materials (ASTM) methods. The biocomposite was characterized using Fourier Transform Infrared (FTIR), X-ray Diffraction (XRD), Transmission Electron Microscopy(TEM), Brunauer Emmett Teller(BET), Thermogravimetric analysis (TG), Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray spectrometry (EDX). Finally, the physical properties of FAME produced under optimal conditions were studied using Gas Chromatography-Mass Spectrometry (GC-MS), FTIR, surface tension, and viscosity.

Enhancing the Catalytic Performance of NiO during the Transesterification of Waste Cooking Oil Using a Diatomite Carrier and an Integrated Ni0 Metal: Response Surface Studies

Two types of NiO-based composites (NiO@diatomite and Ni/NiO@diatomite) were synthesized as modified products of enhanced catalytic performances during the transesterification reactions of waste cooking oil. The influence of the diatomite substrate and the integration of metallic Ni⁰ in inducing the catalytic activity were evaluated in a series of transesterification reactions. The experimental conditions were adjusted according to the response surface methodology and the central composite statistical design. Experimentally, the diatomite substrate and the Ni⁰ metal induced the efficiency of the reaction to achieve a yield of 73.4% (NiO@diatomite) and 91% (Ni/NiO@diatomite), respectively, as compared to 66% for the pure phase (NiO). This was obtained under experimental conditions of 80 °C temperature, 100 min time, 12:1 methanol/oil molar ratio, and 3.75 wt % loading. The theoretical optimization functions of the designs suggested enhancement to the experimental conditions to achieve a yield of 76.3% by NiO@diatomite and 93.2% by Ni/NiO@diatomite. This reflected the role of the diatomite substrate in enhancing the surface area, the adsorption of fatty acids, and the exposure of the catalytic sites in addition to the effect of the Ni⁰ metal in enhancing the catalytic reactivity of the final product. Finally, the biodiesel produced over Ni/NiO@diatomite as the best product was of acceptable properties according to the international standards.

From typical silicon-rich biomass to porous carbon-zeolite composite: A sustainable approach for efficient adsorption of CO2

Focusing on the high-valued utilization of the widespread silicon-rich waste biomass, a sustainable route by simultaneous utilization of carbon and silicon from silicon-rich rice husk was proposed in this work. Specifically, porous carbon-zeolite composite with hierarchical porous structure of micro/meso pores (carbon) and ultra-microporous pores (Na-X zeolite) was in situ prepared by a facile one-pot method. The obtained porous carbon-zeolite composite (PC₂-Z) had a higher yield of 67.66% compared to the porous carbon without silicon (PC₂) of 43.33%. Moreover, due to the high ultra-micropore volume of the PC₂-Z sample (up to 0.181 cm³/g), it exhibited high dynamic CO₂ adsorption capacity of 1.81 mmol/g and CO₂/N₂ selectivity of 9.80 (1 bar), which were higher than 1.67 mmol/g and 7.01 (1 bar) for PC₂, respectively. PC₂-Z also showed good regeneration efficiency above 99% after ten cycles. Furthermore, the economic and energy consumption assessment of this utilization route was conducted. Overall, a facile one-pot route was developed to prepare highly efficient composite absorbents from silicon-rich biomass, which can be widely used in different environmental applications.

Environmentally benign solid catalysts for sustainable biodiesel production: A critical review

Versatile bio-derived catalysts have been under dynamic investigation as potential substitutes to conventional chemical catalysts for sustainable biodiesel production. This is because of their unique, low-cost benefits and production processes that are environmentally and economically acceptable. This critical review aspires to present a viable approach to the synthesis of environmentally benign and cost-effective heterogeneous solid-base catalysts from a wide range of biological and industrial waste materials for sustainable biodiesel production. Most of these waste materials include an abundance of metallic minerals like potassium and calcium. The different approaches proposed by researchers to derive highly active catalysts from large-scale waste materials of a re-usable nature are described briefly. Finally, this report extends to present an overview of techno-economic feasibility of biodiesel production, its environmental impacts, commercial aspects of community-based biodiesel production and potential for large-scale expansion.

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.

Biomass waste-derived recyclable heterogeneous catalyst for aqueous aldol reaction and depolymerization of PET waste

Eco-friendly biomass waste-derived recyclable heterogeneous catalyst for aldol reaction in water and for methanolysis of PET waste.

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.

Microwave Irradiation-Assisted Synthesis of Zeolites from Coal Fly Ash: An Optimization Study for a Sustainable and Efficient Production Process

Class F South African coal fly ash was used as a precursor for the synthesis of zeolite A via complete microwave irradiation. To attain optimal conditions for the synthesis of zeolite A with minimum impurities, the microwave synthesis time, irradiation power, and Si/Al ratio were varied. Sodalite with fly ash phases were obtained when the Si/Al ratio in the coal fly ash was not adjusted and when the microwave irradiated coal fly ash slurry was used instead of the extract solution. Increased microwave irradiation time power and time favored the crystallization of zeolite A phase due to sufficient energy needed to ensure the dissolution of Al and Si from coal fly ash. A Brunauer-Emmett-Teller surface area of 29.54 m2/g and a cation exchange capacity of 3.10 mequiv/g were achieved for zeolite A, suggesting its potential application as an adsorbent and cation exchange material for environmental remediation. Complete microwave irradiation offers a greener approach toward zeolite synthesis from coal fly ash compared to conventional hydrothermal and fusion methods that consume a lot of energy and require longer reaction times.

Development of biocatalysts immobilized on coal ash-derived Ni-zeolite for facilitating 4-chlorophenol degradation

A new type of biocatalyst was developed to facilitate the biochemical decomposition of 4-chlorophenol (4-CP) in this study. Oxydoreductases that catalyze the initial steps of 4-CP biodegradation were immobilized on a synthetic inorganic enzyme support. Type-X zeolite, a high-surface area support, was synthesized from coal fly ash, on which nickel ions were plated by impregnation (Ni-zeolite), followed by the effective immobilization (77.5% immobilization yield) of recombinant monooxygenase (CphC-I), dioxygenase (CphA-I), and flavin reductase (Fre) isolated from Pseudarthrobacter chlorophenolicus A6 and Escherichia coli K-12, respectively. The retained catalytic activity of the enzymes immobilized on Ni-zeolite was as high as 64% of the value for the corresponding free enzymes. The Michaelis-Menten kinetic parameters v_max and K_M of the immobilized enzymes were determined to be 0.20 mM·min^-1 and 0.44 mM, respectively. These results are expected to provide useful information with respect to the development of novel enzymatic treatments for phenolic hydrocarbon contaminants.

Widely used catalysts in biodiesel production: a review

An ever-increasing energy demand and environmental problems associated with exhaustible fossil fuels have led to the search for an alternative renewable source of energy. In this context, biodiesel has attracted attention worldwide as an eco-friendly alternative to fossil fuel for being renewable, non-toxic, biodegradable, and carbon-neutral. Although the homogeneous catalyst has its own merits, much attention is currently paid toward the chemical synthesis of heterogeneous catalysts for biodiesel production as it can be tuned as per specific requirement and easily recovered, thus enhancing reusability. Recently, biomass-derived heterogeneous catalysts have risen to the forefront of biodiesel productions because of their sustainable, economical and eco-friendly nature. Furthermore, nano and bifunctional catalysts have emerged as a powerful catalyst largely due to their high surface area, and potential to convert free fatty acids and triglycerides to biodiesel, respectively. This review highlights the latest synthesis routes of various types of catalysts (including acidic, basic, bifunctional and nanocatalysts) derived from different chemicals, as well as biomass. In addition, the impacts of different methods of preparation of catalysts on the yield of biodiesel are also discussed in details.

An ever-increasing energy demand and environmental problems associated with exhaustible fossil fuels have led to the search for an alternative energy. In this context, biodiesel has attracted attention worldwide as an alternative to fossil fuel.

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

Nitrate reduction on surface of Pd/Sn catalysts supported by coal fly ash-derived zeolites

In this study, we synthesized four zeolites (i.e., Zeolite-X&A9, -X&A&HS12, -X&HS15, -X&HS18) from coal fly ash (CFA), and evaluated their potential for use as support materials to fabricate novel Pd-Sn bimetallic catalysts for reactive and selective reduction of NO₃^- to N₂. The successive transformation of zeolite (Na-A and Na-X to hydroxy sodalite (HS)) was observed with increasing crystallization time from 9 to 18 h, which resulted in different degrees of crystallinity, morphology, BET surface area, and pore volume. Compared to other monometallic and bimetallic catalysts, Pd-Sn/Zeolite-X&HS15 (crystallization time = 15 h) showed remarkable nitrate removal (100%) with the highest kinetic rate constant (k = 0.055 min^-1, K' = 0.219 min^-1 g_cat^-1, K'' = 2.922 L min^-1 g_Pd^-1) and N₂ selectivity (88.1%). These results can be attributed to high surface area and stability of each of the zeolite phases (i.e., Na-X and HS). The reaction mechanism was elucidated by Energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy analyses, demonstrating the presence of Pd°, Sn°, and Sn²⁺ and the uniform distribution of proximate Pd-Sn ensembles on the surface. These results suggest new promising strategies for applying industrial solid waste-derived zeolites to the synthesis of novel bimetallic catalysts to ensure efficient and economical denitrification of wastewater.

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.

Fly Ash-Based Geopolymers as Sustainable Bifunctional Heterogeneous Catalysts and Their Reactivity in Friedel-Crafts Acylation Reactions

This study presents the synthesis, characteristics and catalytic reactivity of sustainable bifunctional heterogeneous catalysts derived from coal fly ash-based geopolymer, particularly those with a high Ca content (C-class) fly ash. The developed catalysts were synthesized at room temperature and pressure in a simple ecologically-benign procedure and their reactivity was evaluated in the Friedel-Crafts acylation of various arenes. These catalysts can be produced with multilevel porous architecture, and a combination of acidic and redox active sites allowing their use as bifunctional catalysts. The acidic sites (Lewis and Brønsted acidic sites) were generated within the catalyst framework by ion-exchange followed by thermal treatment, and redox sites that originated from the catalytically reactive fly ash components. The developed catalysts demonstrated higher reactivity than other commonly used solid catalysts such as Metal-zeolite and Metal-mesoporous silicate, heteropolyacids and zeolite imidazole frameworks (ZIF).

Characterizations and mechanisms for synthesis of chitosan-coated Na-X zeolite from fly ash and As(V) adsorption study

Solid waste fly ash with low aluminum of Yunnan Province in China was used as pristine material to prepared chitosan-coated Na-X zeolite, and the obtained composite material was employed as As(V) adsorbent. Then, the prepared materials were characterized by XRD, FT-IR, and XPS. And the results suggested that the low aluminum fly ash was successfully convert into Na-X zeolite, and the mineralization between Si-OH of the obtained Na-X zeolite and C-OH of chitosan was the dominated mechanism for coated chitosan over the surface of Na-X zeolite. From the batch experiments of As(V) removal, it has been found that the coated chitosan could significantly improve As(V) performance of Na-X zeolite. The optimal working pH for removal As(V) by chitosan-coated Na-X zeolite was attained at pH 2.1 ± 0.1, and the maximum adsorption capacity was 63.23 mg/g. And the adsorption data at different interval time was excellent fitted by pseudo-second-order kinetic model. From the analyze of XPS, the results suggested that As(V) uptake over adsorbent by the bond of As-N and As-O and the surface hydroxyl group of Al-OH and -NH₂ were involved in uptake As(V) from acid wastewater.

Studies on non-modified and copper-modified coal ash zeolites as heterogeneous catalysts for VOCs oxidation

The present study is aimed at investigations on the catalytic activity for total oxidation of volatile organic compounds (VOCs), such as toluene, acetone, n-hexane and dichlorobenzene onto zeolite-like materials synthesized from coal fly ash (FA) directed to development of an economically efficient approach for degradation of VOCs. Fly ash zeolites (FAZ) were prepared by alkaline conversion of FA collected from Thermal Power Plants supplied with lignite coal from "Maritza-East" basin in Bulgaria. Different synthesis procedures double stage fusion-hydrothermal activation, fusion-atmospheric crystallization and atmospheric aging were applied. The synthesis products were identified by X-ray diffraction, and were assigned to zeolite Na-X. Scanning electron microscopy images reveal submicron dimensions of the composing crystallites. Nitrogen adsorption/desorption measurements reveal a mixed micro-mesoporous structure and specific surface area between 116 and 396 m²/g for the obtained FAZ. Relationships between surface properties, iron content and the catalytic activity of FAZ were investigated and discussed. Copper-modified fly ash zeolites (Cu-FAZ) were prepared by incipient wetness impregnation technique with copper acetylacetonate. The loading of 5 wt. % copper on the zeolite samples was achieved. The catalytic activity of FAZ and Cu-FAZ in the total oxidation of model VOCs mixture containing n-hexane, acetone, toluene, 1,2 dichlorobenzene was evaluated.

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.

The activity and stability of CeO2@CaO catalysts for the production of biodiesel

A novel CeO₂@CaO catalyst was prepared via a hydrothermal method. The physicochemical properties and morphologies of the prepared CeO₂@CaO catalysts were characterized by X-ray diffraction, N₂ physisorption, CO₂ temperature-programmed desorption, X-ray photoelectron spectroscopy, transmission electron microscopy and energy dispersive X-ray analysis. It was found that the prepared CeO₂@CaO catalyst had a distinct core–shell structure. The catalytic activity of the CeO₂@CaO sample as a heterogeneous catalyst for the transesterification of soybean oil to produce biodiesel has been studied. The results showed that the optimum yield of biodiesel can reach 98% over the CeO₂@CaO-60 catalyst under the reaction conditions of 3 wt% catalyst, methanol to oil molar ratio of 6 : 1, reaction temperature of 70 °C and reaction time of 6 h. Stability tests indicated that the biodiesel yield can reach more than 80% even after 9 reaction cycles due to the strong synergic interaction between CaO and CeO₂.

The stability test results for the CaO, CeO₂@CaO-60 and CeO₂–CaO-60 catalysts for biodiesel production.

Heterogeneous basic catalysts for biodiesel production

We review the recent advances in the synthesis and utilization of heterogeneous basic catalysts for biodiesel production.

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

This work discusses the utilization of flyash for synthesis of heterogeneous catalyst for transesterification. Different types of zeolites were synthesized from alkali fusion followed by hydrothermal treatment of coal flyash as source material. The synthesis conditions were optimized to obtain highly crystalline zeolite based on degree of crystallinity and cation exchange capacity (CEC). The effect of CEC, acid treatment, Si/Al ratio and calcination temperature (800, 900 and 1000 °C) on zeolite formation was also studied. Pure, single phase and highly crystalline zeolite was obtained at flyash/NaOH ratio (1:1.2), fusion temperature (550 °C), fusion time (1 h), hydrothermal temperature (110 °C) and hydrothermal time (12h). The synthesized zeolite was ion-exchanged with potassium and was used as catalyst for transesterification of mustard oil to obtain a maximum conversion of 84.6% with 5 wt% catalyst concentration, 12:1 methanol to oil molar ratio, reaction time of 7 h at 65 °C. The catalyst was reused for 3 times with marginal reduction in activity.

Design and fabrication of mesoporous heterogeneous basic catalysts

Recent advances in mesoporous solid bases were reviewed, and fundamental principles of how to fabricate efficient basic catalysts were highlighted.

Synthesis of biodiesel from soybean oil using zinc layered hydroxide salts as heterogeneous catalysts

In this work, the transesterification of soybean oil with methanol using layered heterogeneous catalysts to produce biodiesel was studied.