Macro- and micromixing in a novel sonochemical reactor using high frequency ultrasound

This paper deals with the influence of ultrasound on macro- and micromixing in a new developed sonochemical reactor. Unprecedented piezoelectric transducer arrangement with a high frequency of 1.7 MHz has been used in this novel reactor. Macromixing quality has been investigated visually and the Dushman reaction (iodide-iodate) coupled with a neutralization reaction have been examined in order to characterize micromixing quality. In addition, the effect of liquid viscosity on the segregation index has been studied. The results show that this new developed reactor can establish reasonable macro- and micromixing inside the reactor. Moreover, the performance of this reactor has been compared with a stirred tank reactor equipped with a Rushton turbine impeller. It is found that with the same input electrical power, the obtained segregation index for stirred tank reactor is approximately 10% more than proposed new ultrasound reactor, which means the sonoreactor works more efficiently.     

Using sonochemical reactor for degradation of LAS from effluent of wastewater treatment plant

Linear alkylbenzene sulfonates (LAS) are anionic surfactants, which are found in relatively high amounts in domestic and industrial wastewaters. The effectiveness of using sonochemical reactor for the degradation of LAS from effluent of wastewater treatment plant has been investigated. In this study, experiments of LAS solution were performed using methylene blue active substances (MBAS) method. The effectiveness of sonochemical reactor for LAS degradation is evaluated with emphasis on the effect of sonication time and initial LAS concentration. Experiments were carried out at initial concentrations of 0.2 mg/L, 0.5 mg/L, 0.8 mg/L and 1 mg/L, frequency of 130 kHz, acoustic power value of 400 W, temperature of 18-20 °C and pH value of 6.8-7. This study showed that LAS degradation was found to increase with increasing sonication time. In addition, as the concentration is increased, the LAS degradation rate decreases in the sonochemical reactor.     

Mechanistic optimization of a dual frequency sonochemical reactor

The present study addresses the problem of optimization of the dual frequency ultrasonic processor with a two-fold approach, viz. optimization of the resultant acoustic field in the processor, and assessment of production of radicals from cavitation bubbles. The resultant acoustic field in the processor has been optimized using two conditions, viz. highest total energy dissipation and most uniform energy dissipation in the processor. The optimization parameters are the frequency ratio (α) of and phase difference (φ) between the two ultrasound sources. Set of combinations of α and φ have been found corresponding to the two conditions mentioned above, and simulations of radial bubble motion have been carried out for these sets at three locations in the processor. Results of simulations indicate that the extent of radical production for the condition of most uniform energy dissipation is at least two fold higher than that for the highest total energy dissipation. Among the two optimization parameters, φ has been found to have greater influence on production of radicals. On the other hand, α has only a marginal impact on the sonochemical effect. A variation of 3-4 fold in α causes only marginal change in radical production. The effect of interference between two ultrasound waves on radical production has also been assessed. It is revealed that if the compression phase of the coupling frequency coincides with the transient collapse of the bubble initiated by the base frequency, the intensity of the collapse receives an additional boost resulting in greater production of radicals. Some recommendations for the design of the dual frequency processor based on the results of simulations have also been given.     

Hydrodynamics of a slurry airlift reactor at high solid concentrations

The hydrodynamics of a slurry airlift reactor at high solid concentrations were experimentally studied. The influences of the average solid concentration, superficial gas velocity and particle size on the radial and axial profiles of the solid holdup, average gas holdup and liquid circulation velocity were investigated. The local solid holdup was measured with an electrical conductivity probe. At low solid concentrations or high superficial gas velocities, the radial profile of the solid holdup was uniform. At high solid concentrations, the radial profile of the solid holdup was nonuniform, with higher values near the wall. This radial nonuniformity increased with decreased superficial gas velocity or increased average solid concentration. The axial profile of the cross-sectional average solid holdup was uniform at all conditions in this work, even at high solid concentrations. The average gas holdup and liquid circulation velocity increased with the superficial gas velocity but decreased with the average solid concentration. A mathematical model based on the balance of the transverse lift force and turbulent dispersion force was proposed to predict the radial profile of the solid holdup. Reasonable predictions were obtained from this model with an adjustable model parameter.     

Preparation of platinum-ruthenium alloys supported on carbon by a sonochemical method

Pt and Pt-Ru alloys with several Pt/Ru ratios supported on carbon (Vulcan) were prepared using high-intensity ultrasound by reduction of H₂PtCl₆ and RuCl₃ precursors in an aqueous solution. This method of catalyst preparation was performed in absence of any surfactant or organic addictive. The particles formed were characterized by X-ray diffraction (XRD), energy dispersive X-ray (EDX) and transmission electron microscopy (TEM). From the XRD studies, a decrease of metal particle size and of the lattice parameters was observed with the increase of the Ru content. The electroactivities were tested for the methanol oxidation reaction in acid electrolyte, and it was found that Pt-Ru catalysts were more activity than pure Pt.     

新型外循环厌氧反应器污泥沉降的数值模拟

结合EGSB及其它厌氧高效反应器的结构特征而开发的新型外循环厌氧反应器,在高上升流速下能有效控制污泥的流失,处理城市污水时获得了良好的效果。为了对新型外循环反应器的污泥沉降性能进行准确模拟和有效控制,利用质量平衡方程与颗粒污泥自由沉降理论,考虑沉降速率与浓度的关系,确定污泥沉降速率,从而建立了该反应器污泥沉降的弥散模型。对不同上升流速下的污泥浓度分布情况进行了模拟,其模拟结果与实测值吻合良好。然后纳入三相分离器分离效率（SE）的概念,实现了对出水SS的模拟,模拟数据的标准偏差小于6%。在确定污泥相对浓度的前提下,利用二次插值预测污泥层高度,结果表明不同上升流速的污泥层高度基本一致,但是同一高度不同上升流速的污泥浓度各不相同。     

Pollutant destruction in a reverse-flow chromatographic reactor

A reverse-flow chromatographic reactor (RFCR) is a packed reactor in which the flow direction is reversed periodically and in which one of the reactants is strongly adsorbed on the catalyst. We study the performance of a RFCR used to destruct a pollutant A by a reaction with a reactant B, the emission level of which is subject to even stricter restrictions. Due to safety considerations, this reactant B is introduced in the center of the reactor. The RFCR operation enables a reduction of the regulated effluent products well below the minimum attainable under a steady-state operation of the same packed-bed reactor. Moreover, it can respond effectively to any perturbations in the pollutant feed rate and/or concentration. When the environmental regulations on the emission of B are stricter than those of A, it is often advantageous to feed slightly less B than the amount needed for complete conversion of A. We present a methodology for finding the operating conditions that lead to the minimal level of weighted emission of both A and B. A continuous feed of the reactant B is superior to operation in which the same amount of B is fed during each semi-cycle but in a non-continuous fashion.     

The sonochemical preparation of a mesoporous NiO/yttria stabilized zirconia composite

A sonochemical process for the fabrication of the mesoporous composite NiO/yttria stabilized zirconia (YSZ) is described. Its surface area after the extraction of the surfactant is 193 m²/g for a sample containing 40 atom-% Ni. The main advantages of the sonochemical method, as compared with previous works, are the short reaction time (6 h) and that there is no requirement for the glycolation of the nickel, yttrium, and zirconium ions. The reduction of NiO/YSZ to the corresponding Ni/YSZ is also reported.     

A comparative study of a fluidised bed reactor and a gas lift loop reactor for the ibe process: Part III. Reactor performances and scale Up

Continuous fermentations using Clostridium spp. DSM 2152 immobilised in calcium alginate beads to produce butanol and isopropanol from glucose were carried out in a fluidised bed reactor with liquid recycle (FBR, 10.9 dm³ working volume, 41 % solids) and in a gas lift loop reactor (GLR, 11.4 dm³ working volume, 32% solids). In the FBR in-situ produced non-coalescing gas bubbles had a negligible influence on the fluidisation pattern and the steady state results of the fermentation were in accordance with those predicted by a reactor model. The FBR was operated reliably for 5 weeks without decrease of activity. The GLR behaved as a three phase reactor because of the recycled fermentation gas. The steady state fermentation results were as predicted by the GLR model. Scale up to a 50 m³ FBR and a 65 m³ GLR led to development of a plug flow with recycle model for the FBR and a stirred tank model for the GLR. On the basis of overall reactor performance and ease of integration with a simultaneous product recovery the FBR is preferred to the GLR for application in a large scale butanol/isopropanol process using immobilised Clostridia spp.     

Optimal operation of a membrane reactor network

In this contribution, the operation of a membrane reactor network (MRN) for the oxidative coupling of methane is optimized. Therefore, three reactors, a fixed bed reactor (FBR) and two packed bed‐membrane reactors, are modeled. For the (CPBMR), a two‐dimensional (2‐D) model is presented. This model incorporates radial diffusion and thermal conduction. In addition, two 10 cm long cooling segments for the CPBMR are implemented based on the idea of a fixed cooling temperature positioned outside the reactor shell. The model is discretized using a newly developed 2‐D orthogonal collocation on finite elements with a combination of Hermite for the radial and Lagrangian polynomials for the axial coordinate. Membrane thickness, feed compositions, temperatures at the inlet and for the cooling, diameters, and the amount of inert packing in the reactors are considered as decision variables. The optimization results in C₂ yields of up to 40% with a selectivity in C₂ products of more than 60%. The MRN consisting of an additional packed‐bed membrane reactor with an alternative feeding policy and a FBR shows a lower yield than the individual CPBMR. © 2013 American Institute of Chemical Engineers AIChE J, 60: 170–180, 2014     

Synthesis and characterization of BaMoO4 nanostructures prepared via a simple sonochemical method and their degradation ability of methylene blue

Rod-like and sphere-like barium molybdate (BaMoO₄) nanostructures have been synthesized by a large scale and simple sonochemical method by using Ba(Sal)₂ (Sal=salicylidene) and Na₂MoO₄·2H₂O for the first time. The effects of sonochemical irradiation time, sonochemical power, temperature, solvent, surfactant and barium source were considered to obtain a controlled shape. It was established that morphology, particle size and phase composition of the final products could be greatly affected by these parameters. The photocatalytic activity of the synthesized products has been compared for the photodegradation activity of methylene blue (MB).     

Experimental study and simulation of the polymerization of methyl methacrylate at high temperature in a continuous reactor

The bulk polymerization of MMA at high temperature (120–180°C) in a continuous pilot‐plant reactor has been studied. The polymerization is initiated by diterbutyle peroxide and the chain transfer agent is 1‐butanethiol. A simulation program has been developed to predict the steady state behavior of the reactor. The particular features of the kinetic at above‐T_g temperature are included in the model, especially the thermal initiation of the reation and the attenuation of the autoacceleration effect. For the flow and mixing model, the actual vessel cannot be approximated to a single ideal reactor because of its design and of the moderate agitation imposed by the high viscosity of the reacting fluid. A tanks in series model with a recycle stream between tanks is proposed to evaluate the backmixing caused by the special design of the agitator. The parameters of the model are determined with the help of the experimental residence time distribution measured on the reactor. The data collected on the actual reactor, i.e., operation, conversion, molecular weight, temperature, are compared to the calculated one. The agreement is satisfactory but the tendencies are slightly underestimated. The program is a tool to evaluate the effect of modifications of the design of the reactor or changes on the operation parameters like input rate, temperature, and agitation on its behavior. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 2038–2051, 2001     

Design and characterisation of a close-concentric annular reactor for kinetic studies at high temperatures

A novel annular reactor for kinetic studies at high temperature and flow conditions has been designed to keep eccentricity tolerances below 10%. In a previous work, we have shown that it is very important to keep such low eccentricity values in order to collect reliable kinetic data from this type of reactors. As proposed in this study, a modified reactor with the use of a spacer could guarantee an annular duct with low levels of eccentricity. Manufacturing tolerances or deformation effects giving rise to eccentricity can be significantly minimised when using this apparatus. The reactor has been both experimentally and theoretically characterised. Carbon monoxide oxidation was used as a model reaction under mass-transfer limited conditions revealing an eccentricity of ∼5%. With such small eccentricity levels, a concentric annular form can be assumed in the reactor analysis. Simple 1D or 2D models can therefore be inexpensively used in the evaluation of the kinetic data. Also, prior to the design of the annular reactor, a numerical investigation was carried out to clarify the effects of eccentricity, physical properties of the carrier gas and the annular aspect ratio on mass-transfer limitations. Contrary to expectations, a considerable increase in the fuel mass-diffusivity by carrier gas substitution did not change the mass-transfer rates for cases when eccentricity and aspect ratios were high.     

Experimental investigation of fast-mode liquid modulation in a trickle-bed reactor

Unsteady-state operation of trickle-bed reactors (TBRs) is a promising technique to improve reactor performances especially when mass transfer phenomena are rate controlling. Among the different techniques, fast-mode modulation of the liquid flow rate seems to be one of the most successful. In fact cycling the liquid flow rate at very low frequencies can induce the reactor to work at the high-interaction regime where mass and heat transfer phenomena are strongly enhanced. Fast-mode periodic operation, then, can be considered an extension of the natural high-interaction regime at a mean range of gas and liquid flow rate normally associated with trickling regime in steady-state conditions.Experimental tests have been performed in a TBR employing α-methyl styrene hydrogenation on Pd/C catalyst in unsteady-state conditions by “on-off” fast-mode liquid modulation. Results have been compared with the steady-state experiments at the corresponding average liquid flow rate, revealing a conversion rate improvement up to 60%. All experiments have been performed in isothermal conditions, so conversion improvement can be ascribed only to mass transfer increase and not to thermal effects. The variation of gas and liquid flow rates and liquid cycle parameters presented several important implications about the optimal working conditions.     

大型甲醇合成反应器的制造

从材料的选择、简体和封头制造、大型管板加工、部件组对、主要焊缝焊接工艺以及热处理等方面论述了200kt／a甲醇合成反应器制造的控制点，以确保其成功制造，为今后同类设备的制造提供借鉴与参考。     

光催化反应器的研究进展

目前,我国光催化领域的研究工作更多的集中在基础和应用基础研究方面,而在光催化技术的工程应用,尤其是光催化反应器工程方面的基础研究和中式工作开展的很少。这一环节的缺失,成为制约我国光催化技术从实验室走向工程应用的短板。综述了近些年来光催化反应器在国际、国内的研究进展,阐明了传统光催化反应器难以批量处理反应液等一系列缺点,指出了光催化反应器以后的研究方向,并进一步阐明了提高光吸收能力的手段和方法,为新型光催化反应器的制备及其向工业化实际应用奠定了基础。     

Hydrodynamics of a novel multi-stage external loop airlift reactor

In the present investigation a novel multi-stage external loop airlift reactor with hydro-dynamically induced continuous bubble generation, breakup and regeneration has been proposed. The system has been designed to operate with relatively large sized bubbles, so that interfacial circulation can be induced in the liquid-bubble interfaces and faster transfer of components can take place by turbulent diffusion through the interface of the bubbles and also due to the physical rupture and reformation of the bubbles. The system was also designed to operate in three stages operating in series so that in each stage completely deaerated liquid could be brought in contact with freshly generated bubbles. Detailed studies on the gas holdup and liquid circulation velocity have been carried out with respect to various values of superficial gas as well as liquid velocities. The gas holdup of the proposed multi-stage system is 45% higher than the single stage system, which results in better mass transfer characteristics. Empirical correlations describing the performance of the proposed reactor have been presented in this paper.     

Development of a three-phase fluidized bed reactor with enhanced oxygen transfer

A three-phase fluidized bed reactor (TFBR) was developed in this study with the objective to achieve high rates of oxygen transfer from the gas to the liquid phase in the presence of fluidized solid particles. With 2.9 m height, 0.605 m diameter, and a short residence time of 8 h, the TFBR is particularly suitable for industrial applications such as aerobic biodegradation of high-strength wastewaters including refractory compounds. Experiments with tap water and air show that the TFBR enables complete fluidization. With the water and air superficial velocities in the respective ranges of 0.005–0.203 and 0.8–2.0 cm/s, the volumetric oxygen transfer coefficient is 2.3 × 10⁻² s⁻¹, which is higher than that obtained in similar experimental studies on oxygen transfer carried out in the past. These results suggest that the developed TFBR could be very effective in industrial applications where short hydraulic time and high gas-to-liquid mass transfer rates are desirable.     

泰勒反应器中瞬态波状涡流场的CFD数值模拟

泰勒反应器中的波状涡流因存在周向波和涡间传质而受到广泛关注。本文针对泰勒反应器（半径比为0.83,纵横比为46.07）中的波状涡流进行了数值模拟研究,采用计算流体力学（CFD）软件研究了无轴向流动和有轴向流动时的两种流场。结果表明,数值模拟与文献中的PIV实验结果具有较好的一致性。在波状涡流场中,周向波动的存在消除了涡的轴对称性,导致涡随周向位置的周期性变化,包括涡的形状、位置以及涡量等,这也引起了速度的瞬态行为。轴流的引入降低了涡的周期性变化程度,改变了速度的瞬时特性,也稳定了流场。同时还发现轴向流动也影响着切向速度随时间的变化,切向速度随漩涡通过频率及其高次谐波而振荡。