A physico-chemical method to calculate time-dependent reaction mixtures

A method is proposed to calculate multicomponent chemical reaction mixtures as a series of sequential, time-dependent thermochemical states. The procedure is based on the two general principles of physical chemistry, viz., decreasing Gibbs-energy for a natural process and the exponential Arrhenius rate law for the overall reaction kinetics. The calculation is performed in repeated sequences for a closed system element with known heat transfer to its surroundings. The temperature of each sequential reactor element is determined by a Gibbs-energy minimization routine (SOLGASMIX) connected to the closed system enthalpy balance iteration. The extent of overall reaction is limited by the Arrhenius kinetics, while the possible side reactions may reach equilibrium. The mass balance relations forming the subsidiary constraints of the Lagrange method are modified to facilitate the Gibbs-energy minimization for the intermediate “reactor states”. The well-known reaction of titanium (IV) chloride oxidation to titanium dioxide with such side reactions as chlorine dissociation and oxychloride formation is given as a calculational example.     

A new method for fast isolation of insect antifeedant compounds from complex mixtures

Bioassay-guided isolation of bioactive natural substances requires monitoring of all fractionation and purification steps using a bioassay system. This is often a long and tedious process, especially with insect feeding bioassays. We report here a new method, based on the principle of bioautography, for a quick isolation of insect antifeedant compounds. TLC plates, after development, are coated with a thin layer of artificial diet and fed toSpodoptera litura larvae. The location of uneaten areas is then compared with theR _fvalues of the TLC spots, in order to determine rapidly the active fractions. This methods allows for a very fast determination of the most active antifeedant compounds in a complex mixture and considerably speeds up the isolation process. This new method was successfully applied in the study of antifeedant activity of several plant samples, and results are presented here for a model plant,Skimmia japonica (Rutaceae). Using this new method, the compounds responsible for the feeding-deterrent activity, three furanocoumarins (bergapten, xanthotoxin, and oxypeucedanin), were quickly and efficiently identified.     

复杂反应的代数分析建模方法

反应器的设计通常只能以实验室实验数据或者经验规则作为标准,特别是对于复杂的化学反应。由于缺少一个合适的模型进行模拟、预测,很难确定该反应系统的最优条件,导致生产成本增高或者理想产物产量降低。为实现反应系统的优化,需要建立一个能够准确模拟、预测反应系统的模型。介绍了一种确定可行反应网络的代数分析建模方法,从原子层面出发探究复杂反应中所涉及的物质之间的关系,基于原子矩阵的转换寻找所有可行的反应步骤,建立可行的反应网络。通过Aspen Plus建立反应模型,模拟分析选择最适合的复杂反应系统的模型。分析结果与模型指导下的实验相结合,可达到对复杂反应系统进行优化设计、模拟预测乃至控制反应进行方向的目的。根据该建模方法对煤汽化反应系统进行了优化。     

A systematic method for reaction invariants and mole balances for complex chemistries

Reaction invariants are quantities that take the same values before, during and after a reaction. We identify a set of reaction invariants that are linear transformations of the species mole numbers. The material balances for chemically reacting mixtures correspond exactly to equating these reaction invariants before and after reaction has taken place. We present a systematic method for determining these reaction invariants from any postulated set of chemical reactions. The strategy presented not only helps in checking the consistency of experimental data, and the reaction chemistry but also greatly simplifies the task of writing material balances for complex reaction chemistries. For examples where the reaction chemistry is not known, we employ Aris and Mah's (Ind. Eng. Chem. Fundam. 2 (1963) 90) classic method to determine a candidate set of chemical equations. Application of reaction invariants in validating proposed reaction chemistry is discussed. One of the important applications of this method is the automation of mole balances in the conceptual design of chemical processes.     

Hydroxyl group determination in high molecular weight alcohols and complex organic mixtures

Acetylation of complex organic mixtures and high mol wt alcohols is inconsistent by existing procedures because of sample insolubility. By choosing a suitable mixed paraffin-ethyl acetate solvent to bring about nearly instantaneous solu-tion, and utilizing the known catalysis property of perchloric acid, acetylation is quantitative in 10 min or less at room temp. The effect of per-chloric acid concn on these high mol wt systems was studied, and from 0.05-0.45M consistent results were obtained without difficulty. Acetylation of polyethylene oxide (P.E.O.) ad-ducts of straight chain monohydric alcohols pro-ceeds normally and without degradation by the prescribed procedure. Extended reaction time re-sults in partial degradation of the polyether link-ages and amounts to nearly 8% after 30 min.     

集总方法在复杂反应动力学模型中的应用

介绍了集总方法在反应动力学建模中的应用进展,并结合建立大庆重石脑油蒸汽裂解集总动力学模型的经验,对用集总方法建立复杂反应体系动力学模型提出了几点经验和建议。     

Comparison of methods for characterization of complex mixtures

Comparative calculations of several methods of characterization for three multicomponent mixtures that include paraffin, naphthene, and aromatic fractions are shown. Each method requires different experimental information about the mixtures but all use the numerical Gauss-Legendre quadrature. The results show that characterization making direct use of the TPB distillation curve is the most suitable approach for characterizing complex multicomponent mixtures.     

The spectroscopic quinoidal ion method for the analysis of carbonyl compounds

The spectroscopic quinoidal ion method for carbonyl compound analysis has been evaluated. Conjugated aldehydes and saturated ketones are rather stable after an initial time period. Saturated aldehydes are unstable and decompose rapidly with time. The stability of aldehydes is directly related to the size of the alkyl group attached to the aldehyde function. The larger the group, the slower it decomposes.     

A development of the molybdate complexing method for the analysis of silicate mixtures

Analysis of molybdate complexing results from binary and ternary mixtures of silicic acids was refined by the use of an iterative least squares computation. The analysis gave reliable estimated proportions of silicates in mixtures of monosilicate, disilicate and polysilicate with a degree of condensation exceeding four. The rate constant for the complexing of the polysilicate could also be reliably estimated. With a given polysilicate the proportion of polysilicate was proportional to the concentration of silica unreacted after 300 seconds of complexing.     

The antioxidant capacity of complex mixtures by kinetic analysis of crocin bleaching inhibition

The capability of a compound or of a mixture of compounds to quench peroxyl radicals was measured by analyzing the kinetics of the competition of a parallel reaction where peroxyl radicals bleach the carotenoid crocin. This kinetic approach, originally described for the analysis of antioxidants reacting with hydroxyl radicals in water, was modified by both decreasing the polarity of the solvent, thus allowing the analysis of lipophilic compounds, and by substituting a source of peroxyl radicals for the hydroxyl radical generating system. Single compounds as well as complex mixtures were analyzed by kinetic data processing. Overall antioxidant capacity, relative to that of α-tocopherol or of its soluble analog Trolox C, was calculated. As examples of the use of this test, the antioxidant capacities of a crude rosemary extract, Maillard reaction products, and virgin olive oils were measured.     

Asymptotic analysis of a complex reaction scheme in solid-liquid system

Asymptotic analysis of a complex reaction, Claisen condensation, is discussed. Under certain assumptions related to experimental observations the kinetics scheme of the reaction can be considerably reduced. Additional complications in the problem arise due to the fact that one of the substances is present in a sparingly soluble solid phase. We show how reductions for increasingly complex systems with kinetics, mass transfer and feed can be systematically handled by employing the methodology of asymptotic analysis. Generalizations of the reduction approach for the case of an arbitrary number of fast intermediate reactions are also considered.The identification of model parameters is considered with aid of the reduced systems. Questions of parameter estimation and optimal design of experiments are discussed using the MCMC methods.     

Molecular reconstruction of complex hydrocarbon mixtures: An application of principal component analysis

Three methods for reconstruction of the detailed molecular composition of complex hydrocarbon mixtures, based on their global properties, are compared: a method based on the Shannon entropy criterion, an artificial neural network and a multiple linear regression model. In spite of the broad range of naphthas included in the training set, the application range of the last two methods proved to be limited. Principal component analysis allowed to identify their three‐dimensional ellipsoidal application range. In this subspace, the artificial neural network is more accurate than the multiple linear regression model and the Shannon entropy method. However, outside its application range, the performance of the neural network, as well as the regression model, decreases drastically. In contrast, the performance of the Shannon entropy method is not influenced by the characteristics of the considered naphtha, but rather depends on the number of available commercial indices. The Shannon entropy method yields comparable results to the artificial neural network, provided that a sufficient amount of distillation data is available to supply information on the carbon number distribution. Combining the reconstruction methods with a fundamental simulation model illustrates the necessity of having accurate feedstock reconstruction methods since they allow to capture the full power of fundamental simulation models for the simulation of industrial processes. © 2010 American Institute of Chemical Engineers AIChE J, 2010     

Rediscovering the lattice-fluid theory for phase equilibria of complex mixtures

Various lattice statistical-thermodynamic theories after E. A. Guggenheim [Guggenheim, 1952] have been proposed with different assumptions on nonrandomness, the explicitness of the solution, and the model parameters. During the last decade, the present authors proposed a general approximation tool to the quasichemical solution of the nonrandom lattice-fluid combinatory and formulated a new rigorous EOS and the improved versions including the unified group contribution extensions and systems with strong association. In this study, developments of those EOSs are discussed with emphasis on the practical utility of each model.     

Controllability analysis of alternate schemes to complex column arrangements with thermal coupling for the separation of ternary mixtures

Thermally coupled distillation systems (TCDS) have been proposed to perform distillation separation tasks with the incentive of achieving lower energy consumption levels with respect to conventional distillation sequences. In particular, the presence of recycle streams for TCDS schemes has influenced the notion that control problems might be expected during the operation of those systems with respect to the rather well-known behavior of conventional distillation sequences. That has been one of the main reasons for the lack of industrial implementation of thermally coupled distillation schemes. Recently, some alternatives to thermally coupled distillation arrangements that might provide better operational properties than the complex columns have been proposed. In this work, we analyze the control properties of two alternatives to the coupled systems. The results indicate that a reduction in the number of interconnections in alternate configurations does not necessarily provide an improvement of controllability properties.     

Unified equation of state based on the lattice fluid theory for phase equilibria of complex mixtures part II. Application to complex mixtures

In part I of the present article [Yoo et al., 1995], new rigorous and simplified lattice-fluid equations of state (EOS) were derived and their characteristic features of the molecular thermodynamic foundation were discussed by applying to pure fluids. In this part II, both EOSs were extended to various phase equilibrium properties of mixtures. Comparison of the models with experimental mixture data ranges from density, to equilibria of vaporliquid, vapor-solid and liquid-liquid phases for nonpolar/nonpolar, nonpolar/polar, polar/polar mixtures. Both models were also applied to supercritical fluid phase equilibria and activities of solvents in polymer solutions. With two temperature dependent parameters for pure compounds and one temperature-independent binary interaction energy parameter for a binary mixtures, results obtained to date illustrated that both EOSs are quantitatively applicable to versatile phase equilibria of mixtures over a wide range of temperatures, pressures and compositions.     

Computation of enamel mixtures with complex composition

A computer software for computing complex charge compositions is described. It is shown that when using waste oxide catalysts of petroleum organic synthesis as a raw material, the fraction of oxides introduced by them into the composition of the enamel can reach 95 wt. % at admissible deviations of the computed composition from the specified one.     

A method for the quantitative analysis of molecular species of alkylacylglycerol and diacylglycerol

We describe a method for the quantitative analysis of molecular species of diacylglycerol and alkylacylglycerol as their diradylglycerobenzoate derivatives. Synthetic internal standards were used to provide quantitative determinations of the low levels of diacylglycerol and alkyl-acylglycerol and their individual molecular species in cultured cells. Diradylglycerols were isolated by thin-layer chromatography (TLC), converted to their benzoate derivatives and separated into subclasses by TLC. The molecular species of each subclass were analyzed by reversed-phase high performance liquid chromatography. Thirty-six species of diglyceride-type molecules were identified in Madin-Darby canine kidney cells. These cells were shown to contain 7.88 nmoles of diacylglycerol and 3.97 nmoles of alkylacylglycerol per μmole of phospholipid. Both subclasses contain predominantly monoenoic and saturated species. This technique should be valuable for studies examining the origin and metabolism of these important intracellular mediators.