Photocatalytic oxidation of butyraldehyde over titania in air: By-product identification and reaction pathways

In this study, gas phase photocatalytic oxidation (PCO) of n-butyraldehyde was carried out in a packed-bed reactor (titania supported on an inert packing). An on-line system consisting of two collection columns (one glass bead and one activated carbon) and a GC/MS was used for by-product identification. Various temperature levels (50, 90, 115, 170, 270, 320°C) were used in the by-product desorption from the activated carbon column. The oxidation yielded carbon dioxide as the end product. The by-products revealed many reaction pathways of the photocatalytic process. The major by-products (propionaldehyde, 1-propanol, ethanol, and acetaldehyde) were believed to undergo a C-C bond cleavage followed by hydrolysis. Secondary by-products (propyl formate, di-n-propyl ether, and 3-heptene) were caused by esterification, dehydration, and reductive coupling. Aldol condensation of the vapor phase aldehydes on TiO 2 surfaces followed by cyclization may be partially responsible for the formation of some minor by-products such as ethylbenzene.     

A COMPARISON OF APPROXIMATE AND EXACT SOLUTIONS FOR HOMOGENEOUS IRREVERSIBLE CHEMICAL REACTION IN THE LAMINAR BOUNDARY LAYER

A comparison of approximate and exact solutions for homogeneous irreversible chemical reaction in the laminar boundary layer flow has been made. By using the Method of Weighted Residuals, approximate analytical expressions for the velocity and concentration profiles were developed for the case of a laminar boundary layer flow over a flat plate at zero incidence angle, where isothermal, homogeneous, nth order chemical reaction takes place. Both the Subdomain and Galerkin methods were employed to examine the influence of the choice of the weighting function on the predictions, and to provide a means for improving the solutions systematically. The problem was also solved numerically for the case of first order reaction by using a similarity solution for the hydrodynamic flow and a power series expansion method for the mass transfer. The analytical results were compared with the exact solutions in order to evaluate the accuracy of the approximate analytical solutions. The Method of Weighted Residuals provided approximate solutions that are qualitatively correct and, within limits, quantitatively accurate. The resulting approximate expressions can be used to give quick estimates for reactions investigated herein and to predict the results for higher order reactions when there are no exact solutions.     

化学外加剂抑制碱硅酸反应原理及进展

概述了化学外加剂抑制碱硅酸反应 (ASR)膨胀的原理及其几十年来国际上的研究进展 ,并讨论了应进一步研究的问题     

A GENERALIZED PERTURBATION APPROACH TO THE ANALYSIS OF MASS TRANSFER WITH CHEMICAL REACTION

A generalized perturbation approach is presented for the analysis of the simultaneous absorption of two gases in a liquid accompanied by a chemical reaction. The main objective is to derive approximate analytical solutions for the enhancement factors of the solute gases, for all reaction rates. The method consists of constructing a regular perturbation solution for slow reaction, whose convergence is accelerated by means of an Euler transformation, thereby extending its range of utility for larger reaction rates. Convergence is further improved by suppressing the leading singularity of the Euler-transformed series. The accelerated solution is found to predict the enhancement factors very accurately in the slow, intermediate and fast reaction regimes, and in particular, approach the boundary layer limit associated with fast reaction.     

DEVELOPMENT OF A NEW REACTOR FOR COMBINED COMMINUTION AND CHEMICAL REACTION

The combining of the two process steps comminution and chemical reaction is realized in a newly developed apparatus, the so-called reaction-mill. It is an up to 450°C heatable vibration-mill, that is resistant to pressures up to 2 MPa and that has a gas inlet and outlet for running heterogeneous chemical reactions during the process of comminution. The possible accelerations of the vibration-mill exceed up to 65 g and relative amplitudes of maximum 0.14 are adjustable. The advantage of the combination of the two process steps is the utilization of the effects of comminution exceeding the changes in the dispersity of the solid. The examined heterogeneous non-catalytic gas-solid reaction is the conversion of metallurgical grade (MG) silicon with gaseous hydrogen chloride to give trichlorosilane and silicontetrachloride. The examinations of the combined hydrochlorination and comminution have shown, that the induction periods in the starting phase of the reaction, carried out singularly, can be reduced to a minimum. Furthermore it could be noticed, that the lower temperature limit, which is necessary to start the reaction, could be lowered from 300°C to 100°C and that the selectivity of the reaction products is influenced by the mechanical energy. On one hand the effects are explained by the changes in the dispersity of the solid during comminution and on the other hand by a mechanical activation of the MG silicon.     

A FLUID MECHANICAL APPROACH TO TURBULENT MIXING AND CHEMICAL REACTION PART III COMPUTATIONAL AND EXPERIMENTAL RESULTS FOR THE NEW MICROMIXING MODEL

The basic ideas for modelling micromixing, given in Part II, are applied to a pair of consecutive, competitive reactions conducted in semibatch as well as in continuous stirred tank reactors. The objections to earlier work, given in Part I, no longer apply, The principles of calculating the product distribution X for each reactor type are outlined and numerical results are given, using the parameters for the diazo coupling of 1-naphthol with diazotised sulphanilic acid. These showed the dependence of X on mode of reactor operation (SBR and CSTR), volume ratio of reagent solutions (V_A/V_B), Schmidt number (S_c) and mixing modulus (M = k₂c_B0δ_v²/DA). Under typical experimental conditions, the first reaction was instantaneous, whilst the second was fast (see Appendix), permitting a transformation of composition variables and an enormous saving of computer time.

Measured product distributions for the diazo couplings were available covering two tank sizes, three impeller types, three volume ratios, several initial concentrations of reagents, semibatch and continuous operating modes and several feed points. These points were grouped together as (a) suction side of impeller, (b) just below liquid surface, and (c) midway between impeller and wall. (The only major independent variable not covered here is fluid viscosity). In order to make a prediction with the new model, only the rate of energy dissipation (ε) in the reaction zone must still be known. This was expressed as a multiple (φ) of the average rate(ε = ε) and the values consistent with the product distributions measured for the three feed points were (a) 8, (b) 0.23, and (c) 1. These are in good agreement with flow visualisations as well as local ε-measurements using hot film and laser doppler anemometry. These and other results suggest that the new model represents a significant advance on previous methods     

A COMPILATION OF THE D-OPTIMAL DESIGNS IN CHEMICAL KINETICS

This paper links the chemical kinetic models that obey the framework of nonlinear statistical models with optimal design theory. We provide the appropriate optimal designs for them, so that the involved parameters can be estimated as well as possible. Therefore, the D-optimality criterion is adopted, under the optimal design approach, for a number of models used in chemical kinetic applications. In the tables, the collected results are presented for 15 models.     

动态（脉冲）—原位测试技术的发展及其在多相催化研究中的应用

介绍一种动态－原位红外技术,采用这一技术可以获取在催化剂表面上生成的中间化合物的特征光谱信息。根据特征峰出现的先后,峰的大小和消长以及形成的时间,可以直接地、更有论据地推断反应机理,比目前采用“黑箱”的方法优越。通过标定特征峰与表面浓度的关系,可以研究表面中间化合物生成的复杂反应网络,求出相应的动力学参数和最慢的速控步骤。利用上述技术还可以发展一种“化学捕获”法,直接证明催化剂表面存在的中间化合物。     

MASS TRANSFER WITH HETEROGENEOUS CHEMICAL REACTION OF THE FIRST ORDER IN FALKNER-SKAN FLOW OF A POWER-LAW FLUID

ABSTRACT

Mass transfer with a heterogeneous chemical reaction of the first order in a Falkner-Skan flow of non-Newtonian power-law fluid is investigated. This problem is solved by the method of Laplace transform following the approach suggested by Apelblat (1980 Apelblat , A. ( 1980 ). Chem. Eng. J. , 19 , 19 – 37 . [CSA] [CROSSREF]  [Google Scholar]). The solution is obtained in a closed analytical form.     

MASS TRANSFER WITH HETEROGENEOUS CHEMICAL REACTION OF THE FIRST ORDER IN FALKNER-SKAN FLOW OF A POWER-LAW FLUID

Mass transfer with a heterogeneous chemical reaction of the first order in a Falkner-Skan flow of non-Newtonian power-law fluid is investigated. This problem is solved by the method of Laplace transform following the approach suggested by Apelblat (1980). The solution is obtained in a closed analytical form.     

应用分子模拟求取流体化学势的新途径

提出了分子模拟中求取流体化学势的新途径——参考试验粒子方法、通过适当选择参考试验粒子,避免了试验粒子的插入操作和计算,同时解决了移出粒子方法在Metropolis取样构型中难以得到正确结果的缺陷.应用该方法对ρσ~3=0.5和 0.65的硬球流体以及kT/ε=1.2时ρσ~3=0.65、0.70、0.80、0.90的Lennard-Jones流体的研究结果表明,该方法具有收敛快、计算量小和精度高的优点.     

HEAT AND MASS TRANSFER IN STAGNATION-POINT FLOW OF A POLAR FLUID TOWARDS A STRETCHING SURFACE IN POROUS MEDIA IN THE PRESENCE OF SORET,DUFOUR AND CHEMICAL REACTION EFFECTS

This work is focused on the numerical solution of steady boundary-layer stagnation-point flow of a polar fluid towards a stretching surface embedded in porous media in the presence of the effects of Soret and Dufour numbers and first-order homogeneous chemical reaction. The governing boundary-layer equations of the problem are formulated and transformed into a self-similar form. The obtained equations are solved numerically by an efficient, iterative, tri-diagonal, implicit finite-difference method. Both assisting and opposing flow conditions are considered. Comparisons of the present numerical results with previously published work under limiting cases are performed and found to be in excellent agreement. Representative results for the fluid velocity, angular velocity, temperature, and solute concentration profiles as well as the local heat and mass transfer rates for various values of the physical parameters are displayed in both graphical and tabular forms.     

ADVANCED CHEMICAL OXIDATION OF 2,4,6 TRICHLOROPHENOL IN AQUEOUS PHASE BY FENTON'S REAGENT-PART I: EFFECTS OF THE AMOUNTS OF OXIDANT AND CATALYST ON THE TREATMENT REACTION

Fenton's Reagent is a strong oxidant for 2,4,6 Trichlorophenol (TCP) in aqueous phase. This reaction can be effectively utilized to treat an industrial wastewater containing TCP, and reduce the toxicity of the discharge. This paper reports the effects of the amounts of the oxidant (hydrogen peroxide) and the catalyst (ferrous ions), relative to TCP, on the rates and extents of reaction. The progress of each reaction has been monitored in terms of TCP removal, chloride ions release from the organic structure, change in pH, and the reductions in COD and TOC. This information is important in order to maximize the level of treatment with minimum application of chemicals. A set of optimum molar ratios of oxidant to substrate, and catalyst to oxidant were determined.     

EFFECTS OF HALL CURRENT AND CHEMICAL REACTION ON OSCILLATORY MIXED CONVECTION-RADIATION OF A MICROPOLAR FLUID IN A ROTATING SYSTEM

This article is concerned with the analysis of the effects of thermal radiation on oscillatory mixed convection flow of a micropolar fluid in a rotating frame of reference in the presence of transverse magnetic field and Hall current. The influence of a first-order homogeneous chemical reaction and heat source effects is also analyzed. The governing partial differential equations with the appropriate boundary conditions are reduced to a set of ordinary differential equations using similarity transformations. The dimensionless governing equations for this investigation are solved analytically after using small perturbation approximation. The effects of various parameters on the velocity, temperature, and concentration fields as well as on skin-friction coefficient, Nusselt number, and Sherwood number with their amplitude and phase are discussed in detail. Numerical results are discussed with the help of graphs and tables. Present results are also compared with previously published work.     

湖南界牌土的化学组成和颗粒组成与干燥强度间定量关系的数学模型

本工作,选用湖南界牌土作原料,对所选原料进行颗粒分级和量化处理,依据最优化的基本理论,经二次回归正交试验设计,测量其干燥强度,最后应用回归技术建立了原料的干燥强度与其化学组成和颗粒组成之间的定量关系的数学模型,并用数学方法和工艺原理对其影响因素进行了分析讨论,结果表明界牌土的化学组成和颗粒组成对其干燥强度有着重大的影响。     

SIMILARITY SOLUTION FOR UNSTEADY HEAT AND MASS TRANSFER FROM A STRETCHING SURFACE EMBEDDED IN A POROUS MEDIUM WITH SUCTION/INJECTION AND CHEMICAL REACTION EFFECTS

An analysis is presented to investigate the effects of chemical reaction on unsteady free convective heat and mass transfer on a stretching surface in a porous medium. The governing partial differential equations have been transformed by a similarity transformation into a system of ordinary differential equations, which are solved numerically using an efficient tri-diagonal implicit finite-difference method. The results obtained show that the flow field is influenced appreciably by the presence of unsteadiness parameter, chemical reaction parameter, permeability parameter, and suction/injection parameter.     

AN INTEGRAL-SPECTRAL FORMULATION FOR CONVECTIVE-DIFFUSIVE TRANSPORT IN A PACKED-BED WITH ADSORPTION AT THE WALL AND BULK REACTION

A solution for a convective-diffusive transport problem coupled with bulk reaction and adsorption at the wall in packed-bed reactor has been obtained. Such solution has been derived in terms of a particular solution that satisfies the non-homogeneous boundary conditions, at the wall, and the solution to the differential model with homogeneous boundary conditions. The latter is given in terms of integral equations whose kernel is the Green function of the parabolic differential operator of the transport problem. The Green function is expanded in terms of the eigenvalues and the eigenfunctions of the radial diffusion operator of the differential problems. This methodology allows a decoupling of the linear aspects of the problem (i.e., transport part) of the nonlinear source (i.e., kinetic of the reaction) and facilitates the convergence of the Fourier series involved in the spectral expansion in the case of a need for numerical solutions. Details about the solution methodology and the identification and solution of the eigenvalue problem, are given.     

ON THE MINLP APPROACH FOR OPTIMAL DESIGN OF CHEMICAL ENGINEERING SYSTEMS (I) A GLOBAL OPTIMIZATION METHOD FOR NONCONVEX MINLP PROBLEMS

An algorithm for global optimization of a class of nonconvex MINLP problems is devel-oped and presented in this paper.By partitioning the variables,dual representation of the primal ofsubproblems and outer-approximation strategy are used to develop a representative relaxed iterativeproblem.Then the original MINLP problem is replaced by a series of subproblems and relaxediterative problems.By exploiting the particular form of the nonconvex MINLP problem,the feasibleregion of this problem is explicitly included in the representative problem,thus the inconvenienceencountered with the GBD method can be avoided.The proposed method is illustrated andinterpreted geometrically with an example problem.