The general theory of polarographic kinetic currents

A unified mathematical formulation of the transport problem to the dropping electrode, accounting for diffusion, chemical reactions in solution and electrode reactions, is given. The method for the reduction of the problem to a diffusion problem where the effect of chemical reactions is restricted to boundary conditions is described. Conditions are defined for appearance of a kinetic current and, on the contrary, of a diffusion current dependent on equilibrium constants of chemical reactions. The general results are exemplified by the case of a single chemical and a single electrode reaction.     

How graphical analysis helps interpreting optimal experimental designs for nonlinear enzyme kinetic models

Progress curve experiments combined with optimal experimental design (OED) are an efficient approach to determine enzyme kinetics. However, it is hardly possible to verify why specific experiments are suggested for nonlinear enzyme kinetic model identification. Therefore, we systematically investigated the surface and contour plots of the sensitivities and of the OED criteria which are based on sensitivities. The model reaction was an enzyme catalyzed self‐ligation of aldehydes to chiral 2‐hydroxyketones. The visualization improved the understanding of OED and allowed for deducing and confirming five suggestions for kinetic identification: (1) Avoid experiments vicinal to the reaction equilibrium, (2) Choose the design space as large as possible, (3) Prefer D(eterminant)‐ and E(igenvalue)‐criteria over the A(verage)‐criterion, (4) Apply enzyme concentrations such that the reaction does not complete too fast, and (5) Few optimal experiments result in significantly improved parameter estimations. The graphical analysis also provides information about selecting appropriate optimization algorithms. © 2017 American Institute of Chemical Engineers AIChE J, 2017     

A comparison of the indirect and direct quantification of glycidol ester by kinetic analysis

In a comparison of the German society's official indirect method and the direct LC‐MS method to determine the levels of glycidol fatty acid esters (GEs) in edible oils, the indirect method showed lower GE levels in cases of a high level of GEs and/or containing partial acylglycerols (PGs). The present study used kinetic analysis to compare the scope of both methods. A kinetic model combination of reversible decomposition of GEs and 3‐monochloro‐1,2‐propanediol forming substances (MCPD‐FS) generated from PGs accurately predicted a persistent level of underestimation of commercial vegetable oils when the indirect method was used. The results of the kinetic prediction showed that the underestimation in the indirect method was proportional to the PG and GE levels in oils. Although most conventional cooking oils are low in GEs and PGs, significant error may occur in oils such as palm oil, which are reported to have a higher content of GEs and DAGs. The direct method was affected by neither the GEs nor the PGs, and proved to be a truer and more accurate determinant of GE levels in a wide range of edible oil products.     

Reactor design from batch data by a direct graphical method

A graphical method for reactor design is presented which uses the plot of concentration vs. time. This method can be used to compare stirred tank, plug flow and recycle reactors as well as various reactor combinations. With Monod Kinetics the concept of wash-out can be illustrated. A brief comparison with other graphical methods is made.     

A graphical approach to causes and effects analysis of chemical processing systems

An original method developed for solving the problem of locating the origin of a system failure on the concept of a signed digraph has been extensively applied to the cause and effect analysis of chemical processing systems, whose mathematical models are expressed by differential equations. As an illustrative example, a propane vaporizer has been taken up to show the usefulness of the present approach.     

A graphical approach to cause and effect analysis of chemical processing systems

A method for cause and effect analysis of chemical processing systems has been developed on the concept of a signed directed graph. The signed directed graph, called a “model graph,” is used for representing cause and effect relationships among process variables in a system, and a “Pattern” on the graph is introduced to represent a state of the system, which is specified by “0” for normal state, “ + ” and “ ? ” for larger and smaller deviation from the normal state, respectively. For a given model graph and pattern on it, the cause of state changes and the manner of their propagation are easily found out by the present approach, which is mainly based on the depth-first search algorithm developed by Tarjan. As an illustrative example, a propane vaporizer has been taken to show the usefulness of the present approach.     

Radiation-induced grafting onto wool. A kinetic analysis

The radiation-induced graft copolymerization of styrene onto wool in aqueous methanol was studied over a temperature range of 0°C to 45°C and a radiation dose-rate range of 0.05 to 2.0 Mrad/hr. The rate of grafting was found to obey the classical polymerization equation. Chain transfer to wool was found to play an important role in the grafting process, and the molecular weight of the resulting graft copolymer was found to be independent of the irradiation dose. The activation energy of the graft process changed from a value of 4.7 kcal/mole below 19°C to a value of 18.7 kcal/mole above this temperature. This phenomenon is ascribed to the formation of hydrogen-bonded systems between the protic solvent molecules and the protein chain in the wool.     

Moment analysis of nonlinear systems: A kinetic study

The moment method has been used extensively to evaluate parameters of chemical reactions, adsorption or reactor design, but only for linear systems. Moment analysis of nonlinear systems is studied in the present work. A general complicated reaction system involving nonlinear terms in a batch slurry reactor is chosen to demonstrate the method. The first and second improved solutions in Laplace domain and moment expressions are obtained. The improved solution can converge to the exact solution if the iterative procedures are repeated several times.     

用于反应精馏过程可行性分析的立体图解法

开发了一种用于反应精馏可行性分析和概念设计研究的新方法—立体图解法,该方法创新之处在于温度参数的加入,解决了传统判断方法中无法考虑温度因素的难题.立体图解法依据研究体系的气液相平衡方程和反应平衡方程得到泡点曲面和反应平衡曲面,进而得到精馏边界及反应精馏曲线.依据目标产物的质量分数在立体图中画出反应精馏路径,分析体系反应精馏过程的可行性,同时得到初步概念设计的相关信息,如反应精馏是否需要精馏段和提馏段、反应精馏过程可行的进料组成范围、进料位置等.以假定的通式化三元反应体系阐述立体图解法的应用方法及普适性.通过与传统平面图解法的对比,得出该立体图解法能够更加准确地计算反应精馏过程可行的进料组成范围.     

A kinetic analysis of the thermal-oxidative decomposition of expandable polystyrene

The kinetics of the thermal-oxidative decomposition of expandable polystyrene (EPS) was studied by a conventional thermogravimetric technique in various concentrations of oxygen from 0 to 21%. A kinetic model that accounts for the effects of oxygen concentration was proposed to describe the thermal-oxidative decomposition of EPS. The thermogravimetric analysis curve and its derivative have been analyzed by using differential and integral methods with modification of the Friedman and Coats-Redfern methods. The activation energy, the pre-exponential factor, and the reaction order for unreacted material and oxygen concentration have been determined. When oxygen was present, the activation energy was reduced significantly.     

A direct volumetric method for the analysis of soap

Summary Glycol, or preferably its mixture with a solvent for hydrocarbons, such as isopropyl alcohol or chloroform, possesses high solvent power for soaps, which may be directly titrated with strong acids, either potentiometrically or with the use of methyl red or methyl orange. The ionization of the organic acid is suppressed so that salts of weak acids can be directly titrated by this method. The colors of the indicators are brighter and the end-point sharper than those in alcohol or water. Presented at the 19th Annual Fall Meeting of The American Oil Chemists’ Society, Nov. 7–9, 1945, in Chicago. Bristol-Myers Company post-doctorate fellow in chemistry.     

Supplementary graphical analysis for the multi-density expansion of associating fluids

We present a detailed analysis of Wertheim’s multi-density formulation for the thermodynamic properties of associating fluids with a single attraction site. Graphical expressions are explicitly illustrated for the partition function, multi-densities and direct correlation functions, and they are compared with those from the classical single-density formulation of simple fluids. The steric incompatibility among three monomers greatly simplifies cluster integrals of associating fluids, which allows dimerizing association only. Graphical expressions for the pressure and the Helmholtz energy are derived by using functional derivatives, which provide a theoretical base for TPT and SAFT equations of state.     

Measurement and differential kinetic analysis of wall temperatures in monolith converters—I kinetic analysis

It is possible to measure axial wall temperature profiles in adiabatic monolith converters under actual reaction conditions. By applying a differential method of kinetic analysis, axial profiles of concentrations at the wall as well as of reaction rates can be derived with proper computation methods. The data thus obtained may serve for further kinetic evaluation, that is for model building and parameter estimation by proven and well-known methods. The whole procedure looks also promising for performing activity tests on fresh and partly deactivated monolith converters. The slightly greater effort of measuring wall temperatures compared with the usual method only to record inlet and outlet temperatures and integral conversions might more than pay off. In the present first part of the paper the differential method of kinetic analysis is developed and tested by some simulation studies. The second part will deal with actual experiments.     

A kinetic analysis of the thermochemical conversion of solid fuels (A review)

The overview is focused on methods for the processing of kinetic curves (with and without models). The paper demonstrates that the kinetics of thermochemical conversion of solid fuels can be described by a great number of kinetic processing methods, which lead to inconsistent estimates of kinetic coefficients. They give a rather simple approximation of experimental thermogravimetric curves. However, the kinetic triplet to be determined (activation energy, order of reaction, and preexponential factor) depends on the conditions of thermoanalytical studies and (to a greater extent) on the reactivity of the test fuels.     

A direct method for regiospecific analysis of TAG using alpha-MAG

An analytical procedure was developed for regiodistribution analysis of TAG using α-MAG prepared by an ethyl magnesium bromide deacylation. In the present communication, the deacylation procedure is shown to lead to representative α-MAG, allowing the composition of the native TAG in the α-position to be determined directly. The composition in the β-position can then be estimated from the composition of the α-MAG and TAG according to the formula, 3×TAG-2×α-MAG. The estimates are superior to those obtained using the α,β-DAG and Brockerhoff calculations as they come closer to the theoretical value and have smaller SD. The present procedure, first demonstrated on a synthetic TAG, was then successfully applied to the analysis of borage oil, milkfat, and tuna oil.     

基于图形化剧情对象模型的安全评价及其应用

HAZOP分析的信息包括内容信息与结构信息两方面。采用基于知识本体的剧情对象模型,能够全面地表达安全评价信息的内容和结构,解决了传统HAZOP方法存在的信息隐含、信息缺失等问题。在此基础上开发的图形化剧情对象模型,有效地实现了计算机辅助自动安全评价和安全信息的传递、复查和共享。通过对实际案例的分析表明,图形化的剧情对象模型为安全评价信息的标准化奠定了基础,同时也为提高安全评价的质量和效率提供了强有力的手段。     

A simple kinetic analysis to determine the intrinsic reactivity of coal chars

The intrinsic oxidation reactivity in air of an activated carbon char derived from bituminous coal was investigated using a new thermogravimetric analysis (TGA) method. Applying the new method, values of the Arrhenius activation energy E and pre-exponential factor A were estimated from TGA data obtained via heating samples at different constant rates. A novel statistical criterion was subsequently used to determine the heating rate at which optimum values of E and A were obtained. This is a valuable development, for in conventional non-isothermal TGA, while it is accepted that Arrhenius parameters vary with heating rate, there is no formal method for selecting one rate (and hence one set of values of E and A) over another. Using this new method, the following optimum values were obtained for the carbon at a heating rate of 25 °C min⁻¹: E=129.4 kJ mol⁻¹ and ln(A/s⁻¹)=10.4. These results are very similar to those calculated for the same material using more time consuming and less accurate isothermal TGA methods. It is therefore proposed that this new analysis method might be an improvement on conventional techniques to determine the intrinsic oxidation reactivity in air of coal chars.     

Separation of surface and bulk phase diffusivities: A kinetic theory analysis

A kinetic model for the effective (e.g. surface plus bulk) diffusivity in a porous bed composed of rectangular channels is presented. The merit of this approach is that no distinction is made between the bulk and adsorbed phase and the effective axial flux can therefore be compared directly with experimental measurements. We utilize the elements of the BGK kinetic equation and express D_eff as an explicit function of the surface potential and collision frequency. Details concerning gas-gas collision dynamics and gas-solid interactions are contained in the relaxation time, τ, and the external force, F_s, respectively. For definiteness, the analysis is limited to hard sphere gas-gas collisions, although no special significance is implied by this choice. The assumption of a discontinuous gas-solid interaction potential results in a separation of the form D_eff = D_g + K_eqD_s, with interactive modification of both D_g and D_s. Preliminary calculations indicate that only when K_eq, is large will surface diffusion become a significant mode of transport.