Sucrose-mediated sol–gel synthesis of nanosized pure and S-doped zirconia and its catalytic activity for the synthesis of acetyl salicylic acid

Nano-sized pure and S-doped zirconia was prepared by the sol–gel method in the presence of sucrose and zirconium(IV) acetylacetonate (Zr(acac)₄) as a gelation agent and Zr⁴⁺ source, respectively. Acid catalyst activity of samples was tested for the production of acetyl salicylic acid from salicylic acid and acetic anhydride as precursors, The yield (64.0%) of acetylsalicylic acid was obtained from 50 mg of S-doped zirconia calcined at 550 °C and after a 3 h reaction, was comparably higher than the yield of the reaction (13.3%) in the absence of a catalyst and under the same reaction condition.     

Effect of pre-oxidation on the porosity development in a heavy oil fly ash by CO2 activation

The effect of pre-oxidation on the porosity evolution in heavy-oil fly ash subjected to activation with CO₂ has been investigated. After preliminary acid leaching, used to reduce the mineral matter content, the leached fly ash has been oxidised in air at 250 °C for 36 h. Pyrolysis was conducted on the unoxidised and oxidised leached fly ash at 900 °C for 2 h and the resultant chars were activated with CO₂ at 900 °C for different times. The activated samples have been characterised as regards the surface area and the pore volume.The pre-oxidation enhances the porosity development mainly in terms of mesoporosity leading to obtain activated products with higher surface area (about 270 m²/g at a 40% burn-off).     

Effect of pre-oxidation on the porosity development in a heavy oil fly ash by CO2 activation

The effect of pre-oxidation on the porosity evolution in heavy oil fly ash subjected to activation with CO₂ has been investigated. After preliminary acid leaching, used to reduce the mineral matter content, the leached fly ash has been oxidised in air at 250 °C for 36 h. Pyrolysis was conducted on the unoxidised and oxidised leached fly ash at 900 °C for 2 h and the resultant chars were activated with CO₂ at 900 °C for different times. The activated samples have been characterised as regards the surface area and the pore volume.The pre-oxidation enhances the porosity development mainly in terms of mesoporosity leading to obtain activated products with higher surface area (about 270 m²/g at a 40% burn-off).     

Catalytic dehydration of lactic acid to acrylic acid over dibarium pyrophosphate

Barium phosphate catalysts were prepared by a precipitation method. The catalysts were calcined at 500 °C for 6 h in air atmosphere and characterized by SEM for morphological features, by XRD for crystal phases, by N₂ sorption for specific surface area, by TPD–NH₃ for acidity and by TG for thermal stability. The dibarium pyrophosphate catalyst was found to have the best catalytic performance, ascribing to weak acidity on the surface. Under the optimal reaction conditions, 99.7% of the lactic acid conversion and 76.0% of the selectivity to acrylic acid were achieved over the dibarium pyrophosphate catalyst.     

Recycling of harmful waste lead-zinc mine tailings and fly ash for preparation of inorganic porous ceramics

The porous ceramics were prepared by directly sintering of lead-zinc mine tailings and fly ash as the raw materials without any additional sintering and foaming agent. The effects of fly ash addition on the crystalline phases, pore structure, physical–chemical porosities and mechanical strength were investigated. The results showed that the bulk density decreased firstly and then increased while the porosity and water absorption presented the opposite tendency with the increase of fly ash content. Meanwhile, the chemical stability improved and the flexural strength had the same variation tendency of the bulk density. The phase evolution of sample with 60 wt% fly ash addition indicated that anorthite phase was formed at low temperature (1000 °C). The thermal behavior illustrated that the foaming process was initiated by the reaction of internal constituents in the lead-zinc mine tailings. Different pore structures indicated different foaming mechanisms that probably occurred at different temperatures. The porous ceramics with 60 wt% fly ash addition exhibited excellent properties, including bulk density of 0.93 g/cm³, porosity of 65.6%, and flexural strength of 11.9 MPa.     

Thermal-catalytic degradation kinetics of polypropylene over BEA,ZSM-5 and MOR zeolites

In this study, thermal degradation of additive-free polypropylene powder over different type of zeolite catalysts was investigated. BEA, ZSM-5 and MOR with different surface areas, pore structures, acidities and Si/Al molar ratios were used as solid catalysts for degradation of polypropylene (PP). Degradation rate of the PP over zeolites was studied by thermogravimetric analysis (TGA) employing four different heating rates and apparent activation energies of the processes were determined by the Kissinger equation. The catalytic activity of zeolites decreases as BEA > ZSM-5a (Si/Al = 12.5) > ZSM-5b (Si/Al = 25) > MOR depending on pore size and acidity of the catalysts. On the other hand, initial degradation is relatively faster over MOR and BEA than that over both ZSM-5 catalysts depending on the apparent activation energy. It can be concluded that acidity of the catalyst is the most important parameter in determining the activity for polymer degradation process as well as other structural parameters, such as pore structure and size.     

Effects of fly ash on the properties of environmentally friendly dam concrete

The utilization of a solid waste – fly ash (FA) in the construction of concrete dams was investigated in this paper, which contained its effects on the strength, shrinkage and expansion strain of dam concrete with and without 8% of a novel MgO-bearing expansive agent. The results are shown a relationship between the content of fly ash replacing cement and the above properties of dam concrete.The compressive strengths of dam concrete with 50% fly ash in 90 d are higher than that of dam concrete with 30% fly ash or without fly ash slightly. Fly ash may decrease the deformation of dam concrete in that with 50% fly ash, and the shrinkage and expansive strain was reduced significantly – about 33% and 40% less than that of the specimens without fly ash respectively.     

Catalytic dehydration of glycerol to acrolein over sulfuric acid-activated montmorillonite catalysts

For the development of efficient solid acid catalysts for the catalytic dehydration of glycerol to acrolein, catalysts made from montmorillonitic clay activated by sulfuric acid were investigated. Montmorillonite was activated in diluted sulfuric acid in the concentration range of 5–40 wt.%. The effects of sulfuric acid treatment on the structure of the montmorillonite were characterized by X-ray diffraction, measurements of acidity, N₂ adsorption–desorption isotherms, and Fourier transform infrared spectroscopy. The catalytic behavior of sulfuric acid-activated montmorillonite catalysts in the gas-phase dehydration of glycerol were investigated under varying conditions, including the reaction temperature, the feed rate, and the concentration of glycerol. After montmorillonitic clay was activated by sulfuric acid, the layered structural features of montmorillonite remained nearly intact. Ca^2 +-montmorillonite was changed to H⁺-montmorillonite by ion exchange reaction during activation. The optimal catalytic glycerol dehydration reaction conditions were found to be: temperature at 320 °C, liquid hourly space velocity (LHSV) = 18.5 h^− 1, concentration of glycerol solution = 10 wt.%, and the flow rate of N₂ carrier gas = 10 mL/min. A conversion of 54.2% of glycerol and a yield of 44.9 wt.% acrolein were achieved over the montmorillonite catalyst activated by an aqueous 10 wt.% sulfuric acid solution. The H⁺ in the interlayer space of acid-activated montmorillonite catalysts played a critical role in the catalytic dehydration of glycerol. The temperature, the LHSV, and the concentration of glycerol affected the performance of the catalysts through their influence on the reaction mechanism, the contact time, and the reaction equilibrium.     

Dry pressed ceramic tiles based on fly ash–clay body: Influence of fly ash granulometry and pentasodium triphosphate addition

Fly ash from brown coal (70 wt.%) and stoneware clay (30 wt.%) were used for the dry pressed ceramic tiles (according to EN 14411) raw materials mixture. The effects of fly ash milling and pentasodium triphosphate addition as a deflocculant and fluxing agent on the properties of green body (flexural strength, bulk density) and fired body (EN ISO 10545—water absorption, bulk density, true density, apparent porosity, flexural strength, frost resistance) were studied and explained as a function of the firing temperature (1000–1150 °C). Fly ash milling (corresponding to 5 wt.% residue of fly ash grains on 0.063 mm sieve) increased the sintering abilities of the fly ash–clay body. A similar effect was achieved by 1.3 wt.% pentasodium triphosphate (PST) addition with an increase in green body flexural strength and a decrease in water content of the granulate. Fly ash–clay bodies can be frost resistant with water absorption above 10% due to positive pore size distribution, which were examined using the high-pressure mercury porosimetry method.     

Fly ash-supported cerium triflate as an active recyclable solid acid catalyst for Friedel–Crafts acylation reaction

An efficient solid Lewis acid, has been synthesized by loading cerium triflate (7 wt%) on the acid activated fly ash with high silica content (81%). The physico-chemical properties of synthesized fly ash-supported cerium triflate catalyst (CFT) were monitored by XRD, FT-IR spectroscopy, FT-IR spectroscopy of the ammonia adsorbed catalyst, SEM-EDAX, TEM, Flame Atomic Absorption Spectrophotometer and TG-DTA study. The increased concentration of silica surface hydroxyl groups on activated fly ash have a major influence on the loading of cerium triflate. The catalytic activity of the catalyst CFT was tested in the acylation of veratrole using acetic anhydride as the acylating agent. The proposed model structure of CFT shows that the triflate species withdraws the electron density from the surface cerium making it electron deficit and generate Lewis acidity on the surface of fly ash as confirmed by NH₃ adsorbed FT-IR spectrum. The activity data indicate that this heterogeneous catalyst is very active, corresponding to high conversion (88%) of veratrole to 3,4-dimethoxyacetophenone. The catalyst could be easily recovered and reused giving similar conversion up to three reaction cycles indicating its stability under experimental conditions. Thus fly ash-supported cerium triflate is a novel and efficient catalyst and is a promising way of bulk utilization of waste fly ash by developing cost effective catalyst system for industrially important Friedel–Crafts acylation reactions.     

Catalytic performance and characterization of Ni-doped HZSM-5 catalysts for selective trimerization of n-butene

A series of Ni-doped HZSM-5 catalysts were prepared and the catalytic performance of these catalysts in n-butene trimerization was investigated. The Ni-loading, the Si/Al ratio of HZSM-5 and the reaction conditions (temperature, pressure and WHSV) played great influences on the catalytic performance of these catalysts in the reaction. 77.5 wt.% conversion of n-butene and 50.5 wt.% selectivity of trimers as well as 19.6 × 10^? 2 g_trimers/(g_cat h) yield of trimers were obtained on 1NiHZSM-5(320) catalyst up to 148 h at 420 °C, WHSV = 2 h^? 1 and 1.0 MPa. In addition, the physicochemical properties of these catalysts were comparatively characterized by powder X-ray diffraction (XRD), N₂ isothermal adsorption–desorption, infrared red spectroscopy (IR) and pyridine adsorbed infrared red spectroscopy (Py-IR) techniques. The doping of Ni into HZSM-5(320) modified the specific surface area and the acidity of these catalysts, which in turn affected the catalytic performance of these catalysts in n-butene trimerization. The acidic amount and the ratio of Lewis/Brönsted acid sites (L/B) on the external surface of these catalysts were close relative to the catalytic performance of these catalysts. 1NiHZSM-5(320) catalyst showed the highest catalytic performance in n-butene trimersization among the investigated catalysts because it had the proper acidic amount and the proper L/B ratio on its external surface.     

Production of acrolein from glycerol over silica-supported heteropoly acids

Dehydration of glycerol to produce acrolein was performed over several solid acids. Supported heteropoly acids were effective as a catalyst for the dehydration of glycerol. The catalytic activity depended on the types of heteropoly acid and on the size of the mesopores in the silica support. Silicotungstic acid supported on silica with mesopores of 10 nm showed the highest catalytic activity with the acrolein selectivity of >85 mol% at an ambient pressure and 275 °C.     

Effect of Temperature on Phase and Alumina Extraction Efficiency of the Product from Sintering Coal Fly Ash with Ammonium Sulfate

A new developed technology for extracting alumina from coal fly ash was studied in this paper. In this technology, coal fly ash is first sintered with ammonium sulfate, forming ammonium aluminum sulfate in the resultant product, where alumina can be easily leached without using any strong acid or alkali. The products obtained under different sintering conditions were characterized by X-ray diffractometry. Alumina extraction efficiency of these products was also investigated. The results show that the sintering temperature and time substantially influence the phase composition and alumina extraction efficiency of sintered products, while the heating rate has little influence. The optimal sintering condition is 400 °C for 3 h in air with a heating rate of 6 °C·min^− 1. Under the optimal sintering condition, the alumina extraction efficiency from as-sintered coal fly ash can reach 85% or more.     

Optimization of a hydrodynamic cavitation reactor using salicylic acid dosimetry

In the present work, optimization of a hydrodynamic cavitation reactor, for maximizing the extent of hydroxyl radical generation, has been investigated using salicylic acid as a dosimeter. The effect of different operating parameters such as inlet pressure into the reactor, shape of the orifice, and concentration of salicylic acid employed was investigated where the extent of hydroxyl radical generation was quantified in terms of concentration of the hydroxylated products 2,5- and 2,3-dihydroxybenzoic acid. With an upstream pressure of <100 psi no hydroxyl radicals were produced but excellent results were obtained with a small circular nozzle at 4000 psi and a salicylate concentration of 750 ppm. The use of a combination of ultrasound along with hydrodynamic cavitation is also reported for the first time and results in a 15% improvement in the hydroxyl radical generation when the distance between the orifice and transducer is 5–10 mm.     

Characteristics of coal fly ash and adsorption application

Several fly ash samples were collected and their physico-chemical properties were characterised using N₂ adsorption, XRD, SEM, and pH titration. These fly ash samples were applied as low-cost adsorbents for removal of methylene blue and humic acid from aqueous solution. It is found that the adsorption has a close relationship with surface area and pore volume. Higher surface area and pore volume of fly ash will result in higher adsorption of methylene blue (MB) and humic acid (HA). The adsorption of MB and HA on various fly ash samples can reach 7 and 10 mg/g, respectively. Solution pH will also influence humic acid adsorption on fly ash and higher pH will result in lower adsorption. Ionic strength will also influence HA adsorption.     

Adsorption of heavy metal ions from aqueous solution by fly ash

The removal characteristics of lead and copper ions from aqueous solution by fly ash were investigated under various conditions of contact time, pH and temperature. The influence of pH of the metal ion solutions on the uptake levels of the metal ions by fly ash were carried out between pH 4 and 12. The level of uptake of Pb²⁺ and Cu²⁺ ions by the fly ash generally increased, but not in a progressive manner, at higher pH values. The effect of temperature on the uptake of Pb²⁺ and Cu²⁺ ions was investigated between 30 °C and 60 °C, the adsorption of being enhanced at the lowest temperature. Rate constants were evaluated in terms of a first-order kinetics. The rate constant, k for uptake of Pb²⁺ and Cu²⁺ ions were 1.77 × 10⁻² s⁻¹ and 2.11 × 10⁻² s⁻¹, respectively. The experimental results underline the potential of coal fly ash for the recovery of metal ions from waste water. The main mechanisms involved in the removal of heavy metal ions from solution were adsorption at the surface of the fly ash and precipitation.     

The effect of alkalinity of Class F PC fly ash on metal release

Thirty-five samples of Class F fly ash from pulverized coal (PC) combustion boilers were leached with deionized water, acetic acid, and sulfuric acid. The release of metal ions from fly ash was related to the pH of the leachant solution and to the alkalinity of the ash. The maximum soluble concentration of the metallic elements was measured when the pH of the leachate was less than 5. Twenty-three of the samples were strongly alkaline and buffered the leachate until the ash was neutralized. The leachate from the other 13 samples became acidic with the addition of less than 1 L of 0.1 N acid. The alkalinity of the ash and the volume of acid required to neutralize it were a function of the Ca concentration.     

Improvements in acidity for TiO2 and SnO2 via impregnation with MoO3 for the esterification of fatty acids

The impregnation of TiO₂ or SnO₂ with MoO₃ forms solid materials exhibiting high acidity (MoO₃/TiO₂ and MoO₃/SnO₂) that might be applied as catalysts for the esterification of fatty acids. TiO₂ and SnO₂ oxide matrixes were prepared using a metal-chitosan complex method, and the acidity of these materials was modified via impregnation with MoO₃. These catalytic systems were characterized by FTIR, N₂ adsorption/desorption isotherms, thermogravimetric analysis, and NH₃ temperature programmed desorption (NH₃-TPD) and tested in the esterification of fatty acids in the presence of methanol. The esterification reactions were carried out at three different temperatures (120 °C, 140 °C and 160 °C) with a 400:100 molar ratio of alcohol:fatty acid and 1% (mass) catalyst loading. Both TiO₂ and SnO₂ only exhibited catalytic activity after their acidity was improved via impregnation with MoO₃, and yields of 80% and 90%, respectively, were achieved at 6 h and 160 ºC.