Modeling the ultrasonic cavitation‐enhanced removal of nitrogen oxide in a bubble column reactor

A model study of the sonochemical removal of nitric oxide (NO) in a bubble column reactor is presented. The detailed model is developed to investigate the actual cavitation phenomena taking place during the absorption of NO. The expansion and subsequent collapse of cavitation bubble according to the theory of cavity collapse—initially developed by Lord Rayleigh and then improved on by coupling the energy balance equation of the bubble and the chemical reactions taking place inside the cavity to calculate the composition of different species formed during the collapse—are modeled. The model takes into consideration (1) cavitation bubble dynamics, (2) generation and transfer of oxidizing species from bubble collapse through reaction kinetics, (3) transfer of NO from gas to liquid, and (4) chemical reactions of oxidizing species with dissolved NO. The results of the simulations surprisingly indicate that the chemistry induced by ultrasonic cavitation cannot explain the absorption of NO beyond about 30% of the inlet concentration if the mass transfer is assumed to be the same as that in the bubble column without ultrasound. When experimental values of mass‐transfer coefficients, calculated in the studies by other researchers (which are in the range of about five times the physical mass‐transfer coefficient in a bubble column), are used, absorption up to 80% are calculated in the simulations consistent with experimental results obtained from the sonochemical bubble column reactor. The present model provides a framework on which more robust and rigorous models can be developed for the complex gas‐liquid sonochemical systems and reactors. © 2011 American Institute of Chemical Engineers AIChE J, 58: 2397–2411, 2012     

Noncatalytic Hydrolysis of Iminodiacetonitrile in Near‐Critical Water – A Green Process for the Manufacture of Iminodiacetic Acid

The hydrolysis of iminodiacetonitrile (IDAN) in near‐critical water, without added catalysts, has been successfully conducted with temperature and residence time ranges of 200–260 °C and 10–60 min, respectively. The effects of temperature, pressure, and initial reactant/water ratio on the reaction rate and yield have been investigated. The final reaction products primarily included iminodiacetic acid (IDA) and ammonia associated with other by‐products; gas formation was negligible. The maximum yield of IDA was 92.3 mol.‐% at 210 °C and 10 MPa, with a conversion of almost 100 %.The apparent activation energy and ln A of IDAN hydrolysis were evaluated as 45.77 ± 5.26 kJ/mol and 8.6 ± 0.1 min^–1, respectively, based on the assumption of first‐order reaction. The reaction mechanism and scheme were similar to those of base‐catalyzed reactions of nitriles examined in less severe conditions.     

Effect of preparation parameters on the morphologically induced photocatalytic activities of hierarchical zinc oxide nanostructures

Hierarchical zinc oxide nanostructures were successfully synthesized by facile hydrothermal and sonochemical routes using citrate and PEG as structure directing agents. The effect of precursor concentration and preparation methods on the formation of typical morphology was systematically studied under hydrothermal and sonochemical conditions. Different concentrations of zinc acetate, sodium citrate and NaOH under hydrothermal and sonochemical methods generate different hierarchical structures such as flower-like, cabbage-like, and ellipsoidal ball-like morphologies, depending on the preparation conditions. The as-prepared ZnO samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission election microscopy (TEM), photoluminescence (PL) spectroscopy, Fourier transform infrared spectroscopy (FTIR) and particle size distribution (PSD) analysis. Catalytic activities of the as-prepared samples were studied by photodegradation of Methylene blue.     

Copper‐Catalyzed Three‐Component Coupling of Terminal Alkyne,Dihalomethane and Amine to Propargylic Amines

The direct C H and C halogen activation for C C bond formation is one of the most interesting reactions in organic chemistry. C C bond formation using alkynes as a carbon nucleophilic source is a very useful method in synthesis. Herein, a copper(I) chloride catalyzed three‐component coupling reaction of alkynes, dihalomethanes and amines through C H and C halogen activation to form propargylic amines under mild conditions has been established. The reaction can be conducted in water, in neat or in common organic solvents and it was applicable to both aromatic and aliphatic alkynes with good functional groups tolerance. It represents an excellent example of multi‐component reactions (MCRs), provides an elegant method for the synthesis of propargylic amines which are frequent skeletal components and synthetically versatile key intermediates for the preparation of many nitrogen‐containing biologically active compounds. From the mechanism point of view, this chemistry offers not only a new approach to propargylic amines with new C C and C N bonds formation through C H and C halogen activation, but also provides valuable mechanistic insight into the novel multi‐component reactions.     

Sonochemical synthesis of ZnO‐ZnS core‐shell nanorods for enhanced photoelectrochemical water oxidation

The ultrasonic‐assisted synthesis method provides a fast, simple, and large‐scale route for synthesizing desired materials under ambient conditions. In this work, we report on the facile preparation of ZnO‐ZnS core‐shell nanorods on a fluorine‐doped tin oxide (FTO) substrate. The core‐shell nanorods were synthesized by sequential nanoscale reactions involving the preparation of ZnO nanorods and conversion of the ZnO surface into a ZnS shell on the FTO substrate, using an in situ sonochemical method. The ZnO‐ZnS core‐shell nanorods showed improved photocurrents compared with ZnO nanorods for the water oxidation reaction. During the water oxidation reaction, the ZnS shell passivates the surface‐defects of the ZnO, which results in enhanced charge separation in the ZnO nanorods and higher performance.     

Synthesis of formaldehyde and methanol from methane and water in an electrical discharge two-phase reactor

The synthesis of formaldehyde and methanol from methane and water vapour initiated by a d.c. discharge has been carried out in a two-phase gas-liquid reactor in which liquid water was present as a pool covering one electrode. Decomposition reactions, responsible for the low energy efficiency, are limited by a shorter residence time of the soluble products in the gas phase. The experimental results, when compared with those obtained in the absence of water, show a considerable increase in the energy yield.     

Heterogeneous Asymmetric Reactions 20. Effect of Ultrasonic Variables on the Enantiodifferentiation in Cinchona-Modified Platinum-Catalyzed Sonochemical Hydrogenations

The effect of sonochemical variables on a cinchona alkaloid modified Pt/Al₂O₃ catalyst system and its application in -ketoester hydrogenation are described. The sonochemical pretreatment of these commercial Pt/Al₂O₃-cinchonidine catalysts resulted in excellent ee values (up to 92-98% ee) under mild experimental conditions. To gain more insight into the nature of the ultrasonic effect the reactions were screened under widely varied conditions (ultrasound source, frequency, insonation time). Besides investigating the reactions, the catalyst-modifier system was also studied. The changes in metal particle size were determined by transmission electron microscopy, while the alteration of modifier concentration in the solvent upon sonication was followed by UV-vis spectroscopy. The transformation of the modifier during the pretreatment was detected by GC-MS and verified by NMR. Summarizing the results, the major effects of the sonochemical activation on the cinchona-modified supported Pt catalyst system can be described. The ultrasonic pretreatment increased the quantity of adsorbed cinchona and blocked its hydrogenation to provide more and highly stable chiral active sites for enantioselection.     

Influence of synthesis parameters on the physical properties of Cu3Se2 nanostructures using the sonochemical method

Copper selenide (Cu₃Se₂) nanostructures were grown by reaction of copper acetate and sodium selenide in a solvent of distilled water and ethanol at a temperature of 80 °C using the sonochemical method. In this study, the change of molarity, time, and power of ultrasonication waves was investigated on the physical properties of Cu₃Se₂ nanostructures. Cu₃Se₂ nanostructures were characterized by X-ray diffraction (XRD) patterns, field emission scanning electron microscopy (FESEM), Energy-dispersive X-ray spectroscopy (EDX), photoluminescence (PL), and UV–Vis spectroscopies. In this study the optimized conditions were selected as 30 min, 200 W, 1:2 for time, ultrasonic power, and molar ratio of Cu:Se, respectively. The XRD patterns and EDX results represent the formation of tetragonal Cu₃Se₂ phase and the presence of Cu and Se elements in the samples. FESEM images showed nanostructures in the form of spherical agglomerated particles. The results of the PL showed the effect of time, power, and molarity parameters on the appearance of different emission peaks. In all samples, the relative absorption ratio corresponded to the energy band gap such that with the increase in the time and power of ultrasound and the relative change in molarity, the relative absorption, and energy band gap were changed.     

A low cost,low energy,environmentally friendly process for producing high-purity boron carbide

Boron carbide with purity levels higher than that achievable by traditional manufacturing processes using an electric arc furnace (EAF) was produced by a novel low cost, low energy, environmentally friendly process of carbothermic reduction of boric acid (H₃BO₃) with carbon using a self-designed temperature-controllable electric resistance furnace (ERF). The process is divided into three stages: the pelleting stage, the low-temperature pre-dehydration stage, and the high-temperature reduction stage. The optimal conditions are determined as a pelleting pressure of 20?MPa, pre-dehydration temperature of 400?°C, H₃BO₃/C ratio of 3.38, and reduction temperature of 1900–2300?°C. The formation of boron carbide changes from liquid-solid reactions to gas-solid reactions with increasing temperature. Furthermore, the decreasing CO partial pressure is verified to be beneficial for the synthesis of boron carbide. The proposed process circumvents the disadvantages caused by the evaporation of large quantities of water steam and unstable reduction temperature and B/C ratios exhibited by the traditional EAF process. Moreover, it provides a more stable and controllable reduction temperature for producing high-purity boron carbide that leads to improved energy consumption, product quality, and cost efficiency and reduces air pollution mainly caused by volatilization and condensation of boron oxides.     

Possible Impact of Heterogeneous Photocatalysis on the Global Chemistry of the Earth's Atmosphere

Photochemistry is recognized to be important for various physicochemical processes in the atmosphere, such as formation of the ozone layer and smogs, degradation of waste substances, etc. [1]. However, up to the present the emphasis in atmospheric photochemistry has been mainly on the study of photochemical reactions that occur with molecules directly excited by absorption of light quanta. However, the major components and impurities of the earth's atmosphere (such as nitrogen, oxygen, water, carbon dioxide, methane, methane halides, etc.) are totally transparent to most solar radiation. Electronically excited states of these molecules are formed only upon absorption of vacuum ultraviolet light quanta with energy hv ≥ 5 eV (i.e., with wavelength λ ≤ 200 nm). Only a small portion of the energy of solar light is found in this spectral region. In other words, most of the energy of the solar flux cannot participate in such direct photochemical reactions.     

Possible Impact of Heterogeneous Photocatalysis on the Global Chemistry of the Earth's Atmosphere

Photochemistry is recognized to be important for various physicochemical processes in the atmosphere, such as formation of the ozone layer and smogs, degradation of waste substances, etc. [1]. However, up to the present the emphasis in atmospheric photochemistry has been mainly on the study of photochemical reactions that occur with molecules directly excited by absorption of light quanta. However, the major components and impurities of the earth's atmosphere (such as nitrogen, oxygen, water, carbon dioxide, methane, methane halides, etc.) are totally transparent to most solar radiation. Electronically excited states of these molecules are formed only upon absorption of vacuum ultraviolet light quanta with energy hv ≥ 5 eV (i.e., with wavelength λ ≤ 200 nm). Only a small portion of the energy of solar light is found in this spectral region. In other words, most of the energy of the solar flux cannot participate in such direct photochemical reactions.     

Large‐scale sonochemical reactors for process intensification: design and experimental validation

Acoustic cavitation results in substantial enhancement in the rates of various chemical reactions but the existing knowledge about the application of reactors based on acoustic cavitation is limited to very small capacities (of the order of few millilitres). In the present work, an overview of the application of acoustic cavitation for the intensification of chemical reactions has been presented briefly, discussing the causes for the observed enhancement and highlighting some of the typical examples. A novel reactor has been developed operating at a capacity of 7 dm³ and tested with two reactions, ie liberation of iodine from aqueous potassium iodide and degradation of formic acid. The energy efficiency of the reactor has been calculated and compared with the conventional sonochemical reactors. The effect of frequency of irradiation on the percentage conversion of the reactants has been studied. Due to quite low conversions in the case of formic acid degradation, further intensification was attempted using aeration, addition of hydrogen peroxide, and the presence of solid particles (TiO₂). Compared with conventional reactors the novel reactor gives excellent results and it can be said that the future of using acoustic cavitation for process intensification lies in the development of large‐scale multiple frequency multiple transducer reactors. Copyright © 2003 Society of Chemical Industry     

Preparation of uniform 2D ZnO nanostructures by the ionic liquid-assisted sonochemical method and their optical properties

Uniform 2D ZnO nanostructures were successfully synthesized by a sonochemical method, using 1,4-diazabicyclo[2.2.2]octane (DABCO) and imidazolium-based ionic liquids in water as the solvent after 30 min. The effects of ionic liquids as template on the morphology and size of nanostructures were investigated. The structural and optical properties of ZnO nanostructures were studied by using XRD, SEM and UV–visible. The characteristic results revealed that using ionic liquids in water not only prevents a drastic increase in the crystallite size of the zinc oxide species but also provides suitable conditions for the oriented growth of primary nanoparticles with nanosheet morphology. SEM revealed that using the longer alkyl chain at position-1 of DABCO or dicationic ionic liquids causes a uniform nanosheet and nanoleaf. A possible mechanism was proposed to explain the formation of ZnO nanostructures with nanosheet morphology. Also band gap variation with particle size was investigated.     

Sono-synthesis of MnWO4 ceramic nanomaterials as highly efficient photocatalysts for the decomposition of toxic pollutants

As the subject of energy deficiency and environmental contamination has become a widespread concern, introducing green and quick procedure for synthesizing compounds with a catalyst role in solving environmental problems is followed with great interest. Herein, we offer a controllable sonochemical approach for photocatalyst synthesis. The nanostructured MnWO₄ is created via a sonochemical process utilizing a green capping agent, phenylalanine. It was observed that various quantities of precursors, different sonication times, and diverse types of capping agents could modify the shape, photocatalytic yield, and scale of MnWO₄ samples. The features of nanostructured MnWO₄ were examined with different kinds of analyses. The activity of various MnWO₄ structures as photocatalytic substances to eliminate organic contamination in water by visible radiation was also studied. Although all the various structures of manganese tungsten oxide were able to eliminate the organic contamination in the water, the photocatalytic performance of MnWO₄ nanostructure was created utilizing phenylalanine via sonochemistry was superior to that of the samples made under other conditions. The optimal sample manifested remarkable yield since the removal rates of Acid Yellow 23, eosin Y, and crystal violet in 50 min under visible radiation were 98.86, 99.15, and 97.56 %, respectively. The manganese tungsten oxide nanostructure is of the paramagnetic kind. Besides, the optimal MnWO₄ sample was reused as a photocatalytic substance. It manifested appropriate stability over 13 cycles, denoting its capability as a highly efficient photocatalytic substance to remedy the environment.     

Conversion of brown coals in aqueous and toluene-containing media under supercritical conditions in the presence of catalysts

The conversion of brown coals from the Borodino and Kangalas deposits in an aqueous medium and in a mixture of toluene with water was studied under supercritical conditions over the temperature range of 375–550°C and at pressures from 22 to 40 MPa. It was found that the methanation, hydrolysis, and oxidation reactions of brown coals with the predominant formation of gaseous products (methane, carbon dioxide, and hydrogen) prevailed in an aqueous medium. Liquid substances were formed in an insignificant amount. In the toluene solvent under supercritical conditions at 440°C, the addition of a small water amount (15%) stimulated the degradation of coals with the predominant formation of liquid products and moderate gas formation. The use of calcium oxide and sodium hydroxide as catalysts increased the yields of liquid products. It was noted that the reactivity of Kangalas coal in this process was higher than that of Borodino coal.     

Stability of Pt/γ-Al2O3 Catalysts in Model Biomass Solutions

The stability of a Pt/??-Al₂O₃ catalyst in liquid water and aqueous solutions of 5?wt% glycerol or sorbitol at 225?°C is examined using a variety of physicochemical methods. It is demonstrated that the presence of glycerol and sorbitol significantly reduces the hydration of ??-Al₂O₃ to form boehmite as compared to treatment in pure water. The stability against hydration increases with increasing carbon chain length. Treatment with polyol solutions also results in reduced agglomeration of supported metal particles. The prevention of boehmite formation and agglomeration of metal particles are attributed to the formation of carbonaceous species on the surface. In addition to these effects, the deposits block a considerable portion of active metal surface area. IR spectroscopic analysis indicates that dehydration reactions play an important role in the formation of the carbonaceous deposits. The present results illustrate that water and dissolved biomass compounds can strongly affect the stability of heterogeneous catalysts under reaction conditions.     

Particle formation mechanism in radical polymerization in miniemulsion based on in situ surfactant formation without high energy homogenization

Conventional radical polymerization of styrene at 70 °C in aqueous miniemulsion generated using the in situ surfactant technique, without use of high energy mixing, has been investigated in detail. The surfactant potassium oleate was formed in situ by reaction between oleic acid and potassium hydroxide at the styrene/water interface. The particle formation mechanism was investigated by use of pyrene as a probe, revealing that under suitable conditions with an oil-phase initiator, particle formation occurs primarily via monomer droplet nucleation. The droplet/particle stability is however inferior to that in a typical miniemulsion generated employing ultrasonication, as manifested by a marked increase in droplet/particle size with conversion and a bimodal droplet/particle size distribution by weight. The droplet/particle stability increases with increasing amount of oleic acid, hexadecane, water, and the ratio potassium hydroxide:oleic acid, respectively.     

An in situ synchrotron energy-dispersive diffraction study of the hydration of oilwell cement systems under high temperature/autoclave conditions up to 130 °C

The technique of synchrotron energy dispersive diffraction has been developed for in situ studies of cement hydration under autoclave conditions. This has been applied to oilwell cements hydrating at typical oilwell temperatures up to 130 °C. The results show clearly the detailed interplay between 11 detectable phases, from which a phase transformation scheme has been derived; this illustrates the progression of hydration up to 130 °C for two extreme cases, with and without conservation of water content and autoclave pressure. The monosulphate hydrate phases are found to exhibit different stability bounds, with a surprising sequence of the 14-water, 10-water then 12-water monosulphate as temperature/time increases; the latter form is particularly associated with conditions of water/pressure loss. The effect of retarders on C₃S dissolution and CH formation is negligible above 70 °C, whereas the effect on the calcium sulphoaluminate hydrates is more complex, and possible reasons for this are discussed.     

The reactions of formation of selected gas products during coal pyrolysis

Pyrolysis examinations conducted under non-isothermal conditions as well at low heating rate can show that the processes of hydrogen and methane formation are the result of several constituent reactions. In the presented paper a number of these reactions has been determined separately for each of the above mentioned gaseous products. The kinetic parameters of the reactions as well as the yields of products have also been calculated. It has been found that, during coal pyrolysis, methane is formed as a result of six constituent reactions and hydrogen is produced as a result of five constituent reactions. The values of activation energy and frequency factor for the reactions in question were determined. These values fall within the range, which is typical of chemical reactions.     

天然橡胶超声硫化

成功地利用超声波对天然橡胶进行了硫化,所得试件展示了与传统硫化方法制得的试件相同的性能,但该工艺表现出许多传统硫化方法所不具备的优点.用滞后能量损失理论及声化学作用,解释了超声硫化的机理.用温频转换法,得到了天然橡胶混炼胶在高频条件下的动态力学性能,由此得到硫化开始阶段的温升曲线,该曲线与实验结果吻合.