Kinetic modeling of pyrolysis of scrap tires

The disposal of used tires is a major environmental problem. With increasing interest on recovery of wastes, pyrolysis is considered as an alternative process for recovering some of the value in scrap tires. An accurate kinetic model is required to predict product yields during thermal or catalytic pyrolysis of scrap tires. Pyrolysis products contain a variety of hydrocarbons over a wide boiling range. A common approach for kinetic modeling of such complex systems is lumping where each lump is defined by a boiling point range. Available experimental data for thermal and catalytic pyrolysis of scrap tires from the literature were used to evaluate two types of lumping models; discrete and continuous lumping models. The lumps were described in terms of the boiling point distribution of the reactant mixture. In the discrete model, the conversion of heavier to lighter lumps was described in terms of series and parallel first order reactions. In the continuous model, the normalized boiling point was used to describe the reactant mixture as a continuous mixture. An optimization procedure was implemented for estimation of the model parameters using experimental data reported in the literature. Model predictions with indicated that although the discrete model could reasonably predict the yields of different cuts in the products, predictions of the continuous model were very good, especially in thermal pyrolysis.     

A new kernel discriminant analysis framework for electronic nose recognition

Electronic nose (e-Nose) technology based on metal oxide semiconductor gas sensor array is widely studied for detection of gas components. This paper proposes a new discriminant analysis framework (NDA) for dimension reduction and e-Nose recognition. In a NDA, the between-class and the within-class Laplacian scatter matrix are designed from sample to sample, respectively, to characterize the between-class separability and the within-class compactness by seeking for discriminant matrix to simultaneously maximize the between-class Laplacian scatter and minimize the within-class Laplacian scatter. In terms of the linear separability in high dimensional kernel mapping space and the dimension reduction of principal component analysis (PCA), an effective kernel PCA plus NDA method (KNDA) is proposed for rapid detection of gas mixture components by an e-Nose. The NDA framework is derived in this paper as well as the specific implementations of the proposed KNDA method in training and recognition process. The KNDA is examined on the e-Nose datasets of six kinds of gas components, and compared with state of the art e-Nose classification methods. Experimental results demonstrate that the proposed KNDA method shows the best performance with average recognition rate and total recognition rate as 94.14% and 95.06% which leads to a promising feature extraction and multi-class recognition in e-Nose.     

Joule–Thomson inversion curves of mixtures by molecular simulation in comparison to advanced equations of state: Natural gas as an example

Molecular modelling and simulation as well as four equations of state (EOS) are applied to natural gas mixtures regarding Joule–Thomson (JT) inversion. JT inversion curves are determined by molecular simulation for six different natural gas mixtures consisting of methane, nitrogen, carbon dioxide and ethane. These components are also regarded as pure fluids, leading to a total of 10 studied systems. The results are compared to four advanced mixture EOS: DDMIX, SUPERTRAPP, BACKONE and the recent GERG-2004 Wide-Range Reference EOS. It is found that molecular simulation is competitive with state-of-the-art EOS in predicting JT inversion curves. The molecular based approaches (simulation and BACKONE) are superior to DDMIX and SUPERTRAPP.     

三通道气相色谱法测定炼厂气组成

炼厂气是炼油工艺产生的各种气体的混合物,采用四阀六柱将炼厂气分离分解为3部分,以双TCD+FID检测器3通道气相色谱法快速分析炼厂气.FID通道用于分析烃类,一个TCD通道分析永久性气体和硫化物,另一个TCD通道分析氢气,采用面积归一化法定量计算分析结果.用该法测定了3种标准气体,测定值与标准值基本一致,测定结果的相对标准偏差小于8％.该法适用于测定包括液化气、烟气、裂解气等组分相近的样品组成.     

Lumping analysis for the prediction of long-time dynamics: from monomolecular reaction systems to inherent structure dynamics of glassy materials

In this work we develop, test, and implement a methodology that is able to perform, in an automated manner, "lumping" of a high-dimensional, discrete dynamical system onto a lower-dimensional space. Our aim is to develop an algorithm which, without any assumption about the nature of the system's slow dynamics, is able to reproduce accurately the long-time dynamics with minimal loss of information. Both the original and the lumped systems conform to master equations, related via the "lumping" analysis introduced by Wei and Kuo [Ind. Eng. Chem. Fundam. 8, 114 (1969)], and have the same limiting equilibrium probability distribution. The proposed method can be used in a variety of processes that can be modeled via a first order kinetic reaction scheme. Lumping affords great savings in the computational cost and reveals the characteristic times governing the slow dynamics of the system. Our goal is to approach the best lumping scheme with respect to three criteria, in order for the lumped system to be able to fully describe the long-time dynamics of the original system. The criteria used are: (a) the lumping error arising from the reduction process; (b) a measure of the magnitude of singular values associated with long-time evolution of the lumped system; and (c) the size of the lumped system. The search for the optimum lumping proceeds via Monte Carlo simulation based on the Wang-Landau scheme, which enables us to overcome entrapment in local minima in the above criteria and therefore increases the probability of encountering the global optimum. The developed algorithm is implemented to reproduce the long-time dynamics of a glassy binary Lennard-Jones mixture based on the idea of "inherent structures," where the rate constants for transitions between inherent structures have been evaluated via hazard plot analysis of a properly designed ensemble of molecular dynamics trajectories.     

Identification of Additives to Render Mixtures of Gasoline and the Ethanol-Water Azeotrope Hiscible

The economical production of gasohol, in terms of both energy and dollars, is dependent upon th e use of pure, water-free ethanol. Since a small amount of water will cause phase separation in the gasohol, the ethanol must be completely water free. Rather than using pure ethanol, it was proposed to use the ethanol-water azeotrope and some kind of modifier to remove the phase splitting that would occur from using the azeotrope, thus removing the burden of producing water-free ethanol.

A thermodynamic analysis of a set of mixtures containing the gasoline, ethanol azeotrope, and an additive was performed. Each system was evaluated using a computer algorithm which interfaced liquid-liquid equilibrium calculations with the UNIFAC ac tivity coefficient prediction model. The amount of each additive necessary to produce a single phase in the mixture was then determined.

Thirty six compounds were evaluated as possible additives and, of these, six were found to require less than 10% by volume added in order to produce complete miscibility in the gasoline-ethanol azeotrope mixture. All six of these additives were alcohols. Another six components were also found for which 10 to 20% by volume added was required to produce single phase behavior.     

Simulation and optimization of a supercritical extraction process for recovering provitamin A

In this work, a simulation procedure of a supercritical extraction process was developed through the use of the commercial simulator HYSYS^TM (Hyprotech Ltd.), adapting the existing units to the operating conditions typical of the supercritical extraction process. The objective is to recover provitamin A (β-carotene) from palm oil (esterified) using carbon dioxide/ethanol as the supercritical mixed solvent. This example characterizes the problem for recovering high added value product from natural sources, as the palm oil, which is desired by the market. Owing to the fact that esterified palm oil is a complex mixture, made by several components, in order to characterize this system in the simulator, it was necessary to create hypothetical components using the UNIFAC (universal function-group activity coefficients model) group contribution, because they are not present in a conventional database and, then, their physical properties must be estimated and/or predicted before the simulation. The optimization was carried out in each simulation for each equipment, in terms of operating conditions (temperature and pressure), in order to obtain the maximum recovery of carotenes. According to the results, it was possible to concentrate carotenes through two cycles of supercritical extraction with high yield. Furthermore, ethyl esters (biodiesel) were also obtained, as a byproduct of the proposed process, which can also be used as an alternative fuel, with the important characteristic that it is renewable.     

An analytical consistent pseudo-component delumping procedure for equations of state with non-zero binary interaction parameters

For mixtures with many components, some or most of the components are grouped into pseudo-components in order to reduce the dimensionality of the problem for phase equilibrium calculations, and therefore the computational effort. However, knowing the detailed fluid phase split may be important for a variety of applications. The detailed phase compositions resulting from a flash calculation performed on a lumped mixture can be predicted using a delumping (inverse lumping) procedure [C.F. Leibovici, E.H. Stenby, K. Knudsen, Fluid Phase Equilibr. 117 (1997) 225–232].If the mixture parameters of an equation of state (EoS) can be expressed as a linear combination of pure component parameters and the phase mole fractions, then the component fugacity coefficients can also be expressed as a linear combination of pure component parameters with coefficients only depending on mixture properties. As a result, the equilibrium coefficients are related only to component properties and EoS coefficients, independently on phase compositions.In this work, we show using a reduction method how to effectively obtain such an expression of the equilibrium constants even for non-zero binary interaction parameters (BIPs) in the EoS, and based on these results, we propose a totally consistent analytical procedure for the estimation of equilibrium constants of detailed mixtures from lumped information, which is an extension of Leibovici's delumping method.For several examples with non-zero BIPs between hydrocarbon components and classical contaminants, phase mole fractions and the vapor mole fraction of the delumped mixture are in excellent agreement with the exact values obtained by flashing the original mixture. The delumping procedure has multiple applications, mainly for reservoir simulation and distillation problems.     

Tertiary recycling of commingled polymer waste over commercial FCC equilibrium catalysts for producing hydrocarbons

A mixture of post-consumer polymer waste (PE/PP/PS) was pyrolysed over cracking catalysts using a fluidising reaction system similar to the FCC process operating isothermally at ambient pressure. Greater product selectivity was observed with a commercial FCC equilibrium catalyst (FCC-E1) with about 53 wt% olefin products in the C₃-C₆ range. Experiments carried out with various catalysts gave good yields of valuable hydrocarbons with differing selectivity in the final products dependent on reaction conditions. A kinetic model based on a lumping reaction scheme for the observed products and catalyst coking behaviours has been investigated. The model gave a good representation of experiment results. This model provides the benefits of lumping product selectivity, in each reaction step, in relation to the performance of the catalyst used and particle size selected as well as the effect of operation conditions, such as rate of fluidising gas and reaction temperature. It is demonstrated that under appropriate reaction temperatures and suitable catalysts can have the ability to control both the product yield and product distribution from polymer degradation, and can potentially lead to a cheaper process with more valuable products.     

Chromatographic behavior of a polyclonal antibody mixture on a strong cation exchanger column. Part I: Adsorption characterization

In this work, the adsorption of a polyclonal antibody (IgG) on a preparative strong cation exchanger is described in detail. In a first stage, the polyclonal mixture is characterized using both chromatographic and non-chromatography methods. This analysis suggested that the mixture can be simplified by lumping the different components of the IgG into two "macro-components", referred to as pseudo-variants in the following. An analytical method for the determination of the concentrations of the two pseudo-variants is developed. Based on this, the mass transport and the adsorption isotherm parameters are determined experimentally using only well known sort-cut methods. This analysis is evidencing the complexity of the characterization when operating in the presence of slow diffusing mixtures of components. Even in the presence of strong competition, mass transport plays a major role in determining the peak shape. In frontal analysis, competition is still operative after full saturation of the column.     

Mutual peak matching in a series of HPLC–DAD mixture analyses

One of the largest challenges in high performance liquid chromatography (HPLC) method development is the necessity for tracking the movement of peaks as separation conditions are changed. Peak increments are then used to build a mathematical model capable of minimizing the number of experiments in an optimization circuit. Method optimization for an unknown mixture is, moreover, complicated by the absence of any a priori information on component properties and retention times when direct signal assignment is not possible. On the contrary, achievement of the maximum separation becomes an important factor for successful identification or quantitation. In this case, the optimization may be based on assigning peaks of the same component chosen from different experiments to each other. In other words, mutual peak matching between the HPLC runs is required.

A new method for mutual peak matching in a series of HPLC with diode array detector (HPLC–DAD) analyses of the same unknown mixture acquired at varying separation conditions has been developed. This approach, called mutual automated peak matching (MAP), does not require any prior knowledge of the mixture composition. Applying abstract factor analysis (AFA) and iterative key set factor analysis (IKSFA) on the augmented data matrix, the algorithm detects the number of mixture components and calculates the retention times of every individual compound in each of the input chromatograms. Every candidate component is then validated by target testing for presence in each HPLC run to provide quantitative criteria for the detection of “missing” peaks and non-analyte components as well as confirming successful matches. The matching algorithm by itself does not perform full curve resolution. However, its output may serve as a good initial estimate for further modeling. A common set of UV-Vis spectra of pure components can be obtained, as well as their corresponding concentration profiles in separate runs, by means of alternating least-square multivariate curve resolution (ALS MCR), resulting in reconstruction of overlapped peaks.

The algorithms were programmed in MATLAB^® and tested on a number of sets of simulated data. Possible ways to improve the stability of results, reduce calculation time, and minimize operator interaction are discussed. The technique can be used to optimize HPLC analysis of a complex mixture without preliminary identification of its components.     

CALCULATION METHOD OF EFFECTIVENESS FACTOR FOR NON-LINEAR COMPLEX REACTION SYSTEM

A calculation procedure of the effectiveness factor for very complex multiple reaction system is developed by using the concept of continuous lumping. The calculation procedure proposed in this paper enables not only the reaction-diffusion equations to be solved as an initial value problem, but also the number of the nonlinear algebraic equation which have to be solved in each iterative step to be reduced considerably.     

Influence of mixture design on multivariate prediction of PAHs in mixture spectra

This work describes a simulation study aimed at establishing the impact of mixture design on the prediction ability of PLS regression models. Data sets are formed by multiplying UV absorbance spectra of 12 PAHs by their concentration profiles. In these case studies, either all possible mixtures of 1-12 components are used or randomly chosen selections of the mixtures. The effects of the number of samples and the number of concentration levels in the mixture designs on the results of the calibration are assessed. Comparisons are made between models formed using orthogonal fractional factorial mixture designs and those based on random designs. The applicability limits of the orthogonal designs are analysed in terms of actual concentration ranges of individual components in the mixtures.     

Gas phase SMB for propane/propylene separation using enhanced 13X zeolite beads

A gas phase simulated moving bed technology using improved 13X zeolite beads and isobutane as desorbent is assessed for the separation of propane/propylene. Adsorption equilibrium (via gravimetric method) and dynamics (via breakthrough curves) were determined in order to validate the mathematical model used to describe the adsorption process. Simulation results have shown that it is possible to separate propylene from a mixture with propane using gas phase SMB technology. The results indicate that high purity propylene (99.99 % desorbent free basis) can be recovered up to 99.96 % with a productivity of 17.6 mol kg^?1 h^?1, with propane being also recovered at high levels (99.98 %) and high purity (99.89 % desorbent free basis). Comparing the SMB simulation results obtained for this new 13X zeolite beads with those obtained with a commercial 13X zeolite characterized elsewhere, it was found that the productivity of the process was raised by 25 %, with half desorbent consumption.     

What is a Perfect Gas Mixture?

The definition of a perfect gas mixture varies substantially within the chemistry textbook literature. A recent International Union of Pure and Applied Chemistry (IUPAC) definition is here criticised as being insufficient to cover properties traditionally associated with such mixtures. Possible supplements to the definition to rectify the deficiency are considered. An alternative definition in molecular terms is shown to be comprehensive. The paper should serve as a summary of the properties of a perfect gas mixture and of essential components of its definition. This revised version was published online in July 2006 with corrections to the Cover Date.     

Automatic analysis of mixed spectra : Generalised spectral subtraction applied to electron spin resonance spectroscopy

A new technique is described for estimating the pure component spectra from a set of linearly independent spectra. The process is one of generalised spectral subtraction in which an iterative combination of multivariate linear least-squares analysis and matrix transformation is applied to the input data to give estimates of the number of independent components in the original mixed spectra. This technique is applicable to bipolar data (e.g. from e.p.r. spectra) as well as absorption spectra determined by any spectroscopic technique, provided that the spectra may be reasonably assumed to be an additive mixture of unknown pure components. Numerical model examples are given together with an experimental application to electron spin resonance.     

Calculating the separation coefficients in argon, krypton and xenon gas mixture separation by gas hydrate crystallization

The separation of gas mixtures based on noble gases by means of gas hydrate crystallization is considered for various schemes of the process. The separation coefficient and the separation factor of the basic mixture components at 273 K and at different pressures and compositions of the gas mixture are calculated. It is shown that xenon can be almost completely separated from a mixture in two stages of gas hydrate crystallization even without the use of booster gases. Directional crystallization allows us to separate xenon more completely and crystallization at constant pressure enables us to obtain a more highly purified product.     

Simulation of concentration changes in complex volatile mixtures during evaporation by using gas chromatography

Summary A method is proposed for the simulation of weathering and aging of mixtures of organic components of similar polarity, e.g. gasolines. Semi-empirical equations are derived and tested which correlate the composition of samples after evaporation with the composition of the original material. In this way, changes in composition during partial evaporation of the liquid mixture can be predicted. In the context of forensic investigations this procedure can be helpful for tracing back the composition of the liquid remaining to that of the original unweathered liquid. To perform this simulation, the relative volatilities of the individual components in the mixture have to be known. These are determined by gas chromatographic retention data simultaneously with the concentrations of the volatile components. The paper evaluates the semi-empirical equations employed and discusses the influence of the simplifying assumptions introduced on the accuracy of the simulation.     

Application of vapour phase chromatography in the gas-analytical field

Of the various, types of gas chromatography developed in the past few years gas-liquid partition chromatography has been found to be the best method for the analysis of hydrocarbon gases.By a suitable choice of the liquid phase and the other conditions it is possible to separate each individual hydrocarbon in the C₁–C₅ range from the other components. The influence of size of column nature of carrier material, concentration of liquid phase on carrier, and gas velocity, has been discussed.For the quantitative determination of the components two methods were used, viz.: (a) Continuous measurement of the thermal conductivity of the gas mixture leaving the column. This method is preferred for the analysis of gas mixtures consisting of a limited number of components and for the determination of a single component in a complex mixture. (b) Measurement of the pressure increments obtained by collecting the components in an evacuated vessel after the CO₂ stripper gas has been removed by absorption in a caustic solution. This method is particularly suitable for the analysis of gas mixtures consisting of many components with widely different boiling points.     

Ethanoled gasoline bubble pressure determination: Experimental and Monte Carlo modeling

In this work, we present some experimental and modeling studies of ethanoled gasoline bubble pressures (ethanol + gasoline blends) at various temperatures and ethanol contents. Modelings are carried out using Monte Carlo simulations in a specific bubble-point pseudo ensemble and using the AUA4 force field. This method is first validated on the prediction of binary mixture bubble pressures (ethanol + n-hexane, ethanol + propylene, ethanol + toluene, ethanol + isooctane). It is shown that a good accuracy is reached without introducing empirical binary interaction parameter, demonstrating the predictivity of the approach. Then, simulations of ethanoled gasolines have been performed. The molecular representation of the gasoline is obtained using a lumping scheme from the detailed composition of a commercial gasoline. Simulation results are compared to experimental bubble pressures measured in this work on this commercial gasoline in which various proportions of ethanol have been added. From a qualitative point of view, the azeotropic behavior of such fuels is observed both experimentally and by simulations. From a quantitative point of view, an average deviation of 15% between experimental and simulation data is found. Such results show that Monte Carlo simulation using an accurate force field is an efficient method to predict phase equilibrium of complex mixtures such as oxygenated gasolines. This methodology can thus be seen as an efficient tool that can be used by engineers for fuel formulation or for equation of state or process model calibration.