Yan-Ping Sun

Approximate solution for the nonlinear model of diffusion and reaction in porous catalysts by the decomposition method

The problem of diffusion and reaction in catalyst pellets is considered for the case of nth order reactions. The Adomian decomposition method is used to solve the nonlinear model of diffusion and reaction and to obtain approximate solutions. The variation of reactant concentration in the catalyst pellet and the effectiveness factors are determined for second-, half- and first order reaction. The approximate analytical solutions obtained are compared with solutions obtained with a finite difference numerical method. In general, the Adomian polynomial method with three terms gives solutions comparable to the numerical procedure for Thiele modulus approximately up to 4.0.

Approximate Analytical Solutions for Models of Three-Dimensional Electrodes by Adomian's Decomposition Method

Three dimensional electrode structures are used in several applications, where high current densities are required at relatively low electrode and cell polarisations, e.g. water electrolysis and fuel cells. In these applications it is desirable to fully utilize all of the available electrode area in supporting high current densities at low polarisation. However conductivity limitations of threedimensional electrodes generally cause current and overpotential to be non-uniform in the structure. In addition the reaction rate distribution may also be non-uniform due to the influence of mass transfer. In this chapter generalized mathematical models of three dimensional electrodes are developed. The models describe the coupled potential and concentration distributions in porous or packed bed electrodes. Four dimensionless variables that characterize the systems have been derived from modeling; a dimensionless conduction modulus , a dimensionless diffusion (or lateral dispersion) modulus s, a dimensionless transfer coefficient and a dimensionless limiting current density . The first three are

A study of the electrochemical reduction of nitrobenzene to p-aminophenol in a packed bed electrode reactor

Abstract A reaction engineering model and an electrochemical reactor model are developed for the reduction of nitrobenzene to p-aminophenol in a packed bed electrode reactor. The reactor model is based on a simplification of the two-dimensional Poisson equation for the potential distribution. The predictions of the model are in reasonable agreement with the experimental results. The process can be operated at a superficial current density greater than 1500 A m −2 , with an average selectivity greater than 80%, and a current efficiency > 75% for p-aminophenol in the experimental packed electrode reactor.

A study of the performance of a sparged packed bed electrode reactor for the direct electrochemical oxidation of propylene

A non-linear model for the direct electrochemical oxidation of propylene in a new type of reactor — a sparged packed bed electrode reactor (SPBER) is developed. The model consists of a set of second-order ordinary differential equations, which includes a one-dimensional Poisson equation, describing the effect of the electric field on this system, and material balance equations for reactants and products. The model accounts for gas–liquid mass transport, liquid–solid mass transport at the electrode, heterogeneous electrochemical reaction and homogeneous reaction in the bulk solution. The reactant, propylene, undergoes direct oxidation to the epoxide, which undergoes further chemical reaction (saponification), in solution, to the glycol. Numerical solution of this model is used to determine lateral distributions of overpotential, current density and concentrations of products in a SPBER, and to simulate the effects of important operating parameters, such as gas sparging rate and applied overpotential, on these distributions.

Simulation and reaction engineering of electrochemical gas/liquid reactions

Abstract A mathematical model of an electrochemical reactor is developed in which the reaction is initially between a gaseous, organic species and an inorganic oxidant which is generated electrochemically. In the electrolyte solution several chemical reactions occur, leading to several organic and inorganic compounds. The model accounts for the mass transfer processes occurring at the electrode/electrolyte interface, where chemical reactions also occur, and at the gas/liquid interface, ie the absorption and desorption processes. The model is used to simulate the behaviour of a single stage cell and a multi-stage cell. The reaction between anodically generated chlorine and ethylene gas is used to illustrate the system behaviour.

Transient Response and Steady-State Analysis of the Anode of Direct Methanol Fuel Cells Based on Dual-Site Kinetics

An intrinsic time-dependent one-dimensional (1D) model and a macro two-dimensional (2D) model for the anode of the direct methanol fuel cell (DMFC) are presented. The two models are based on the dual-site mechanism, which includes the coverage of intermediate species of methanol, OH, and CO (θM, θOH,Ru, and θCO,Pt) on the surface of Pt and Ru. The intrinsic 1D model focused on the analysis of the effects of operating temperature, methanol concentration, and overpotential on the transient response. The macro 2D model emphasises the dimensionless distributions of methanol concentration, overpotential and current density in the catalyst layer which were affected by physical parameters such as thickness, specific area, and operating conditions such as temperature, bulk methanol concentration, and overpotential. The models were developed and solved in the PDEs module of COMSOL Multiphysics, giving good agreement with experimental data. The dimensionless distributions of methanol concentration, overpotential, and current density and the efficiency factor were calculated quantitatively. The models can be used to give accurate simulations for the polarisations of methanol fuel cell.

Approximate solution for nonlinear model of the second and half order reactions in porous catalyst by decomposition method

Abstract The problem of the process of coupled diffusion and reaction in catalyst pellets is considered for the case of second and half order reactions. The Adomian decomposition method is used to solve the non-linear model. For the second, half and first order reactions, analytical approximate solutions are obtained. The variation of reactant concentration in the catalyst pellet and the effectiveness factors at ϕ<10 are determined and compared with those by the BANDs finite difference numerical method developed by Newman. At lower values of ϕ, the decomposition solution with 3 terms gives satisfactory agreement with the numerical solution, at higher values of ϕ, as the term number in the decomposition method is increased, an acceptable agreement between the two methods is achieved. In general, the solution with 6 terms gives a satisfactory agreement.