Entrance effect on mass transfer in a parallel plate electrochemical reactor

The influence of different fluid inlet types, slits or tubes, on mass transfer in a rectangular reactor was studied. Measurements of mass transfer coefficients were made using the limiting diffusion current technique based on ferricyanide ion reduction at a large nickel electrode located downstream of abrupt expansions. The overall mass transfer coefficients obtained were 3 to 13 times greater than those obtained in fully developed flows. Overall mass transfer coefficients were correlated for Reynolds numbers ranging from 400 to 3500 by a unique equation by introducing a nondimensional expansion factor defined by the ratio of the fluid inlet cross-section to that of the reactor. The correlation equation obtained was compared with literature data.     

The Role of Electrochemistry in Future Dynamic Bio‐Refineries: A Focus on (Non‐)Kolbe Electrolysis

The vision of a circular economy with closed carbon dioxide cycles is inevitably connected to a change of raw materials. Non‐edible biomass is an attractive carbon source for chemical industry. Brought together with renewable energy, the electrocatalytic transformation of biomass‐based feedstocks enables to directly integrate renewable electrical energy into chemical value chains. Considering the major role of natural carboxylic acids, the well‐known Kolbe and non‐Kolbe electrolysis attract increasing interest as versatile tools to valorize renewable feedstocks providing access to both biofuels and bulk or fine chemicals. They allow via decarboxylation access either to the corresponding dimerization product or the terminal alkene. Here, the electrochemical valorization of biomass is discussed with special emphasis on the possible role of (non‐)Kolbe electrolysis in a future electrified biorefinery.     

Laminar and turbulent mass transfer simulations in a parallel plate reactor

Laminar and turbulent mass transfer in a parallel plate reactor at high Schmidt number obtained from numerical simulation is compared with literature data. In a first step, the fluid flow is determined numerically in the reactor by solving the Navier–Stokes equations. For turbulent flow, a low Reynolds number k— model is used to calculate the turbulent viscosity. Using the obtained flow field and turbulent viscosity, the current density distribution is calculated for different flow velocities by solving the equations describing the transport of multiple ions due to diffusion, convection and migration. For the laminar case, a very good agreement with literature data is obtained. For turbulent flow, different numerical models for turbulent mass transfer are proposed in the literature. A detailed study of the behaviour close to the wall of these different turbulence models is presented, together with a comparison of the calculated results with literature correlations. This allows identification of the benefits and disadvantages of each of the turbulence models for the numerical calculation of mass transfer at high Schmidt numbers in a parallel plate reactor.     

A model for the Kolbe reaction of acetate in a parallel-plate reactor

A mathematical model is developed for the study of the Kolbe oxidative dimerization of acetate to ethane and carbon dioxide in a parallel-plate reactor operating at a fixed cell potential, with hydrogen evolution being the cathode reaction. The volume of gas evolved into the interelectrode gap is tracked by constructing a hypothetical gas layer which increases in thickness with the streamwise direction in a manner determined by solution to the model equations; concurrently, the liquid flows in a hypothetical layer which decreases in thickness. The three-component gas phase is assumed to be ideal, and the liquid phase is an aqueous mixture of five species: acetate, proton, sodium and hydroxyl ions and acetic acid. The model predicts the concentration profiles and the streamwise variation of the gas-void fraction, reaction current density and liquid and gas velocities. Gas evolution causes a decreasing current density in the streamwise direction and an increasing gas and liquid velocity. The concentrations of acetic acid and proton decrease in the streamwise direction, while hydroxyl concentration increases; the decrease in acetate concentration, however, is not significant until the local base-to-acid ratio is near unity because of the buffering effect from undissociated acetic acid. The average current density increases with inlet solution velocity and cell potential and asymptotically approaches the secondary current limit. There exists an optimal interelectrode separation where the cell resistance is minimum. The average current density exhibits a shallow maximum with the baseto-acid ratio of the feed, but decreases precipitously when the ratio is near unity due to the rapid decrease in the proton concentration.Nomenclature b _a anodic Tafel constant of the Kolbe reaction of acetate (V) - b _c cathodic Tafel constant of hydrogen evolution reaction (V) - c ₁ acetate concentration, mol cm^–3 - c ₁, ref reference concentration of acetate (mol cm^–3) - c ₂ acetic acid concentration (mol cm^–3) - c ₃ proton concentration (mol cm^–3) - c ₃, ref reference concentration of proton (mol cm^–3) - c ₄ hydroxyl concentration (mol cm^–3) - C _A stoichiometric concentration of acetic acid in the feed stream (mol cm^–3) - C _B stoichiometric concentration of sodium hydroxide in the feed stream (mol cm^–3) - c _B/A C _B/C _A, base-to-acid ratio in the feed stream (sodium hydroxide to acetic acid) - c _i(0) concentration of species i at cell inlet (mol cm^–3) - c _i ^* c _i/c _A - E _d decomposition potential (V) - E _neq,a ^o standard open-circuit potential of the Kolbe reaction of acetate (V) - E _eq,a ^o open-circuit potential of the Kolbe reaction of acetate (V) - E _eq ^c standard open-circuit potential of hydrogen evolution reaction (V) - E _eq,e open-circuit potential of hydrogen evolution reaction (V) - F Faraday constant (96 487 C equiv.^–1) - f gas-void fraction - h cell height (cm) - IR ohmic-voltage drop in the electrolyte (V) - i current density (A cm^–2) - i _a,ref exchange current density of acetate Kolbe reaction at reference concentration (A cm^–2) - i _c,ref exchange current density of hydrogen evolution reaction at a reference concentration (A cm^–2) - i _avg average current density (A cm^–2) - i(0) current density at the inlet of the cell (A cm^–2) - i ^* i/i(00) - Ka ionization constant of acetic acid (mol cm^–3) - K _a ^* K _a/c _A     

A computational multi-reaction model of a Cu electrolysis cell

A computational model for quantitatively describing the behavior of four simultaneous chemical reactions taking place on two copper electrodes in a Cu–Cu electrolysis cell is formulated. The individual reaction rates, corresponding current densities and total cell current and voltage are obtained as direct model output. The model parameters are found based on cyclic voltammetry experiments done in a Cu–Cu electrolysis cell with CuSO₄ (aq) concentrations between 0.1 M and 1 M. The model is fit against the data of one experiment and compared against a series of other measurements. A full set of model parameters is given and the effect of selected parameters on the simulated current–time response is analyzed.     

A110-5Q 型氨合成催化剂在双层并流合成塔中的使用

介绍了A 11025Q 型氨合成催化剂的装填、升温还原及使用情况。装填该催化剂后, 在合成塔有缺陷的情况下仍创出了合成氨产量记录, 表明该催化剂性能优良、活性好、生产强度大,在双层并流合成塔的应用是成功的。     

A comparative computational study of diesel steam reforming in a catalytic plate heat‐exchange reactor

A two‐dimensional steady‐state model of a catalytic plate reactor for diesel steam reforming is developed. Heat is provided indirectly to endothermic reforming sites by flue gas from a SOFC tail‐gas burner. Two experimentally validated kinetic models on diesel reforming on platinum (Pt) catalyst were implemented for a comparative study; the model of Parmar et al., Fuel. 2010;89(6):1212–1220 for a Pt/Al₂O₃ and the model of Shi et al., International Journal of Hydrogen Energy. 2009;34(18):7666–7675 for a Pt/Gd‐CeO₂ (GDC). The kinetic models were compared for: species concentration, approach to equilibrium, gas hourly space velocity and effectiveness factor. Cocurrent flow arrangement between the reforming and the flue gas channels showed better heat transfer compared to counter‐current flow arrangement. The comparison between the two kinetic models showed that different supports play significant role in the final design of a reactor. The study also determined that initial 20% of the plate reactor has high diffusion limitation suggesting to use graded catalyst to optimize the plate reactor performance. © 2016 American Institute of Chemical Engineers AIChE J, 63: 1102–1113, 2017     

NOx废气吸收的板式塔模型

化学工业中产生的NOx废气是一种大气污染源,对人类和生态环境具有极大的危害,用水或稀硝酸溶液吸收氮氧化物可以回收硝酸,是化学工业中应用较为广泛的氮氧化物废气治理方法之一。文章通过对氮氧化物气体吸收过程中的气液相反应平衡和传质机理进行研究,结合板式塔吸收的特点,建立了水或稀硝酸在板式塔内吸收NOx废气的数学模型,并进行了实验验证,模拟结果和实验结果吻合良好。模型计算分析结果表明,氮氧化物的吸收效果随着温度的升高而降低,随着压力的增加而增加,而且压力对氮氧化物吸收效果的影响比温度对氮氧化物吸收效果的影响显著,随着停留时间的延长,起初氮氧化物的吸收效果迅速增强,当停留时间达到10 s时,氮氧化物的吸收效果的增强不再明显。     

Characterization and testing of sol-gel catalysts prepared as thin layers in a plate reactor

Catalytic plate reactors offer many advantages over conventional reactors, including a major reduction in size and much better temperature control. This study examines the characteristics of thin catalyst coats prepared by the sol-gel method and calcined at different conditions. Employing the catalyst as a thin layer (< 100 μm) on the surface of plate reactors reduces mass and heat transfer limitations compared with pellet catalysts and can improve the effectiveness factor. A sol-gel of Ni/Al₂O₃ catalyst, with good rheological properties and good adherence onto stainless steel substrate, was prepared and characterized. The effects of calcination temperature, nickel content and calcination environment on the catalyst properties were investigated. The results revealed that the highest catalyst surface area was obtained at 400 °C for all calcined coatings. The presence of nitrogen gas during drying and calcining seemed to increase the catalyst surface areas and improve its adherence properties. Rheological evaluation of the prepared coats proved to be an effective tool in characterizing the thin coatings. The Ni/Al₂O₃ catalyst exhibited high activity and achieved more than 80% conversion for steam reforming of methane. The reactions were not diffusion limited based on the values of activation energy.     

Effects of baffle length on mass transfer in a parallel plate rectangular electrochemical cell

Global mass transfer measurements in unbaffled and baffled configurations using different baffle lengths and Reynolds numbers have been made in a parallel plate cell of rectangular geometry. The entry jet arrangement and the repeated 180° changes in direction of the flow, followed by the exit, produces extremely complex hydrodynamics in the cell. A plot of mass transfer coefficient against baffle length shows an increase in mass transfer with baffle length. Comparison of data for the present work with those of other workers for similar devices showed higher mass transfer due to the modifications incorporated in the present cell.     

Optimization and kinetic modeling of waste lard methanolysis in a continuous reciprocating plate reactor

Continuous biodiesel production from a waste pig-roasting lard, methanol and KOH was carried out in a reciprocating plate reactor (RPR) using a factorial design containing three process factors, namely methanol/lard molar ratio, catalyst loading, and normalized height of the reactor. The main goals were to optimize the influential process factors with respect to biodiesel purity using the response surface methodology and to model the kinetics of the transesterification reaction in order to describe the change of triacylglycerols (TAG) and fatty acid methyl esters (FAME) concentrations along the RPR height. The first-order rate law was proved for both the reaction and the mass transfer. The model of the changing reaction mechanism and mass transfer of TAG was also applicable. Both kinetic models agreed with the experimental concentrations of TAG and FAME determined along the RPR height.     

A new method for the synthesis of disilylalkanes by Kolbe anodic oxidation of α-silylcarboxylic acids

A new method has been developed for the synthesis of disilylalkanes by Kolbe anodic oxidation of α-silylcarboxylic acids. Preparative electrolysis was carried out by constant current technique. The effect of various parameters (electricity consumption, current density, temperature, solvent, base and concentration of substrate) on the outcome of electrolytic process has been studied and evaluated. On the basis of optimal conditions found, the synthesis of three dimeric products Ph₂(Me)SiCH₂CH₂Si(Me)Ph₂, Ph(Me)₂SiCH₂CH₂Si(Me)₂Ph and Me₃SiCH₂CH₂SiMe₃ was achieved in good yields by anodic decarboxylation of the corresponding acids Ph₂(Me)SiCH₂CO₂H, Ph(Me)₂SiCH₂CO₂H and Me₃SiCH₂CO₂H.     

装配水平筛板的气升式反应器中气液传质特性的数值模拟

利用Turbulent–Lehr组合模型对装配水平筛板的气升式反应器进行了计算流体力学(CFD)模拟,研究水平筛板对气含率、气泡直径、体积传质系数(kLa)和气液流速的影响。结果表明,筛板对气相的囤积作用和对液相的阻碍作用增加了反应器的整体气含率。筛板对气相的二次均布作用减弱了筛板和液面之间区域的气泡聚并过程,筛板筛孔对气泡的破碎作用产生了大量小于初始直径的气泡,增加了气泡比表面积(a);筛板对液相的阻碍作用提高了筛板附近的气–液相流动速度差,从而提高了该区域的液膜传质系数(kL),强化了反应器内的气液传质效果。     

Electrochemical destruction of thiourea dioxide in an undivided parallel plate electrodes batch reactor

The paper presents the results of a study on the electrochemical destruction of pollutants present in a spent reducing bath of a textile factory. The investigations comprised the electro-oxidation of thiourea dioxide (TUD) (the main component of the reducing bath), sulphites and urea, which are formed during oxidation of TUD. The study performed in an undivided cell parallel plate electrodes reactor, using eight different anode materials under various hydrodynamic conditions, proved that electro-oxidation can be successfully applied for treatment of spent reducing baths. The best results of TUD and SO₃²⁻ electro-oxidation were obtained with a Ti/Pt electrode, which showed electrocatalytic effect for both the compounds, indicating a possibility of their direct electro-oxidation on the anode. Destruction of TUD and SO₃²⁻ proceeded also via indirect electro-oxidation, mediated by chlorine evolved on the anode. The process kinetics was mass transport controlled till Re=5000. No electrocatalytic effects were observed for urea with any of the tested anode materials. The elimination of urea resulted to proceed only by indirect electro-oxidation, mediated by chlorine. For elimination of urea a Ti/Pt–Ir electrode proved to be the best anode, probably due to its high efficiency in electro-oxidation of chlorides into chlorine.     

2-氧代-4-苯基丁酸乙酯不对称加氢滴流床反应器模型

研究了滴流床反应器中2-氧代-4-苯基丁酸乙酯在10,11-二氢辛可尼定修饰的Pt/A l2O3作用下不对称催化加氢反应特征,实验在4个不同催化床层中进行。考虑催化剂部分润湿和静、动持液量,结合复杂的传质和反应过程,建立了不对称催化加氢滴流床反应器模型。在本征动力学研究的基础上,用模型模拟了滴流床中反应物和产物沿反应器轴向的浓度分布,并对不同操作条件下不对称加氢反应的转化率和光学收率进行了预测,与实验数据比较一致,表明此反应器模型对非均相不对称催化反应的工程化有重要的指导意义。     

A mathematical model for a biological fluidized bed reactor

A physical model is given in the present report for representing a three-phase biological fluidized bed reaction system which consists of microorganism-coated particles, waste water and air. The system is assumed to be well fluidized. The physical model can be represented by two differential equations describing, respectively, the substrate axial dispersion and diffusion/reaction. Numerical values of the physical parameters are selected from the literature or estimated from semi-empirical equations. The governing system equations are solved by an iterative finite-difference scheme. The theoretical predictions are compared with several experimental measurements and the agreement between them found to be very good, validating the physical model reported here.     

圆盘反应器的流动模型

剖析了圆盘反应器的流型及其影响因素,指出圆盘反应器的虚拟级数N应为盘数;讨论了反应器中熔体流动过程中存在多次的动量、能量的传递;由于反应器结构上存在死角和短路,其F(t),E(t)并非理想状态。对反应器气相流动作了简述。     

CFB提升管等效反应器网络模型

对气固循环流化床（CFB）提升管内的非均相流动行为进行了计算流体力学（CFD）模拟。基于CFD时均流场数据与信息,搭建了用于描述提升管内非理想流动过程的等效反应器网络（ERN）模型。在ERN模型建立过程中提出了反应器网络的6个拓扑结构参数和一个等效判据,并系统地分析了等效反应器网络结构六参数的性质与确定方法,从而形成了一套CFB提升管流动模型建模方法。