Experimental study and kinetic modeling of kerosene thermal cracking

Thermal cracking of kerosene for producing ethylene and propylene has been studied in an experimental setup. A set of experiments were designed using Response Surface Design (Box Behnken) method. In these experiments, the coil outlet temperature (COT), residence time and steam ratio varied from 795 °C, 0.13 s and 0.6 to 838 °C, 0.27 s and 1.0, respectively. Obtained maximum ethylene and propylene yield in these experiments were 32 and 16.9 wt.%, respectively. In next step of studies, we tried to develop an applicable kinetic model to predict yield distribution of products of the kerosene thermal cracking. Therefore, a reaction mechanism is generated on the basis of major reactions classes in the pyrolysis and feed compounds using some simplification assumptions in the model. This semi-mechanistic kinetic model contains 172 reactions, 22 molecular and 29 radical species. A sensitivity analysis was done on kinetic model and controlling reactions identified. An objective function was defined and used to tune the model with experimental data. Finally, the calculated model results were compared with the experimental data. Scatter diagrams showed good agreement between model and experimental data.     

Recommendations for reporting thermal analysis data

Recommendations for reporting of thermal analysis data relating to differential thermal analysis, differential scanning calorimetry, thermogravimetry and thermomechanical analysis were developed some two decades ago. Since that time there have been significant changes in the techniques, as well as a greater understanding of the effect of experimental variables on the results obtained from thermonalytical experiments. This paper reports on a preliminary review of the Recommendations by the Task Group established by the ICTAC Committee on Standardization to undertake their revision. Particular attention has been paid to the properties of the sample; control of the instrument variables; and the data acquisition and manipulation by computers.     

The generalized potential energy function for diatomic molecules

A new generalized potential energy function is suggested for diatomic molecules. The Dunham, Simons—Parr—Finlan, Thakkar and Ogilvie potentials are shown to be particular cases of the generalized potential energy function. It is also shown that the function suggested may reproduce the path of the potential curve with sufficient accuracy even for the cases of small expansion length.     

Toward a modeling study of thermal conductivity of nanofluids using LSSVM strategy

Journal of Thermal Analysis and Calorimetry - In the present study, a comprehensive model based on least square support vector machine algorithm (LSSVM) was developed to estimate thermal...     

Raman correlation function for generalized M-diffusion model

A generalized version of Gordon's M-diffusion model for reorientation of molecules in dense phase was proposed by Duttagupta and Sood. They calculated the IR correlation function and compared it with a few experimental data. We calculate the Raman correlation function for this model and compare it with experimental data for OCS, N₂O in CCl₄, and CH₃I. We find that at short times, the agreement with the experimental data is much better than that for Gordon's M-diffusion model. We have also shown that, at long times the correlation function decays as an inverse power of time. However, the experimental correlation function at long times decays much faster.     

Profile function modeling for fitting powder diffraction peaks

Powder diffraction patterns can be modeled using profile distributions determined from experimental data. This reduces the number of spectrum model parameters and hence enhances the reliability of the mathematical and physical interpretation. The present paper describes the cubic-spline approximation of the profile function. The calculations of Si and α-Al₂O₃ powder diffraction patterns give better residuals than those obtained by the ML and Pearson type VII approximations, which are widely used in the Rietveld method. M. V. Lomonosov Moscow State University. Translated fromZhurmal Strukturnoi Khimii, Vol. 36, No. 1, pp. 138–143, January–February, 1995. Translated by I. Izvekova     

Multi-way modeling of hydro-chemical data of an alluvial river system--a case study

A large data set pertaining to water quality of an alluvial river was analyzed using multi-way data analysis methods with a view to extract the hidden information, spatial and temporal variation trends in the river water quality. Four-way data (8 monitoring sites × 22 water quality variables × 10 monitoring years × 12 sampling months) analysis was performed using PARAFAC and Tucker3 models. A two component PARAFAC model, although explained 35.1% of the data variance, could not fit to the data set. Tucker3 model of optimum complexity (2,3,1,3) explaining 39.7% of the data variance, allowed interpretation of the data information in four modes. The model explained spatial and temporal variation trends in terms of water quality variables during the study period and revealed that sampling sites in mid-stretch of the river were dominated mainly by the variables of anthropogenic origin. The results delineated the mid stretch of the river as critical from pollution point of view and also identified summer months as having high influence on river water quality in this stretch. The information regarding spatial and temporal variations in water quality generated by the four-way modeling of data would be useful in developing long-term water resources management strategies in the river basin.     

Thermodynamical modeling of silicon carbide synthesis in thermal plasma

The synthesis process of solid SiC in thermal plasma was investigated theoretically by computing the equilibrium composition of the gas mixtures involving silicon and carbon in the presence of argon and hydrogen at various silicon/carbon amounts and at two different total pressures in the system, in the temperature range between 1000 and 6000 K. Use is made of the fact that a thermal plasma, by definition, is a plasma in (local) thermodynamical equilibrium, which makes possible the theoretical determination of its equilibrium composition at definite temperature by employing Gibbs free energy data for the compounds present in the system. From the calculated compositions of the investigated gas systems the temperature-composition phase diagrams were obtained. Using these data the temperature zones with saturated and/or oversaturated vapour of SiC as well as of Si and C were determined and the possibility of the formation of SiC in the solid state via different reaction routes was analyzed This revised version was published online in July 2006 with corrections to the Cover Date.     

Asymmetric logistic peak as a suitable function for the resolution of highly asymmetric voltammograms in non-bilinear systems

The asymmetric logistic peak is tested as a new function for the parametric signal fitting (PSF) of highly asymmetric electrochemical signals in non-bilinear datasets, such as those obtained in linear sweep voltammetry (LSV) or in the presence of irreversible electrochemical processes. This new multivariate curve resolution strategy (PSF-ALPA) is successfully applied to LS voltammograms measured for the Cd(II)-glutathione system with a hanging mercury drop electrode, where Cd(II) is reversibly reduced, and to differential pulse voltammograms (DPV) measured at a glassy carbon electrode, where Cd(II) reduction becomes irreversible. Matrix augmentation by using LS voltammograms measured at different scan rates provides good results and encourages the development of ALPA methodology for third order data.     

Molecular modeling study on surface,thermal, mechanical and gas diffusion properties of chitosan

The motivation of this work is to provide reliable and accurate modeling studies of the physical (surface, thermal, mechanical and gas diffusion) properties of chitosan (CS) polymer. Our computational efforts have been devoted to make a comparison of the structural bulk properties of CS with similar type of polymers such as chitin and cellulose through cohesive energy density, solubility parameter, hydrogen bonding, and free volume distribution calculations. Atomistic modeling on CS polymer using molecular mechanics (MM) and molecular dynamics (MD) simulations has been carried out in three dimensionally periodic and effective two dimensionally periodic condensed phases. From the equilibrated structures, surface energies were computed. The equilibrium structure of the films shows an interior region of mass density close to the value in the bulk state. Various components of energetic interactions have been examined in detail to acquire a better insight into the interactions between bulk structure and the film surface. MD simulation (NPT ensemble) has also been used to obtain polymer specific volume as a function of temperature. It is demonstrated that these V–T curves can be used to locate the volumetric glass transition temperature (T_g) reliably. The mechanical properties of CS have been obtained using the strain deformation method. Diffusion coefficients of O₂, N₂, and CO₂ gas molecules at 300 K in CS have been estimated. The calculated properties of CS are comparable with the experimental values reported in the literature. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1260–1270, 2007     

Automatic comparison of thermodynamic data for species in detailed chemical kinetic modeling

This article describes the performance of an automatic comparator of thermochemical databases and demonstrates the use of a hypertext preprocessor to link chemical names with a three‐dimensional molecular viewer thus providing an unambiguous identification of species in a facile manner over the Internet. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 341–345, 2005     

Prediction of thermal explosion parameters for energetic materials on the basis of thermal analysis data

Results obtained in calculations of thermal ignition delay periods in a wide temperature range are in good agreement with published data for octogene samples in the form of a sphere 12.7 mm in diameter and cylindrical NEPE propellant samples with diameters of 20 to 80 mm. The kinetic parameters of the thermal decomposition of materials, used in the calculations, were obtained by the DSC method with the use of hermetically sealed crucibles and crucibles with perforated covers under a nitrogen pressure of 10 MPa at heating rates of 0.1 to 1.0 deg min^–1.     

A study of coupled logistic maps and their usefulness for modelling physico-chemical processes

Computations have been performed with the aid of coupled logistic maps. Regions of chaos and quasiperiodicity have been delineated in the relevant parameter space. The largest Lyapunov exponent has been calculated and corroborates the results obtained. The relevance and use of such maps is discussed.     

Esterification of butyric acid with n-butanol: Kinetic study using experimental data and modeling

Present study involves the investigation of the esterification kinetics between butyric acid and n-butanol. This reaction was conducted in a batch reactor, utilizing homogeneous methanesulfonic acid (MSA) catalyst. Response surface methodology (RSM) was conducted prior to the kinetic study using “Design Expert; version-11.0” for finding the causal factors influencing the conversion of butyric acid. Most important factors identified with their limits against conversions (during optimization of the process using RSM) were taken up to critically analyze the effect of them on butyric acid conversion. Concentration and activity-based model of the process were proposed assuming second order reversible reaction scheme using homogeneous MSA catalyst. During the study of non-ideal behavior of the system, UNIFAC model was adapted for assessing the activity coefficients of species present in equilibrated liquid phase. Experimental data were used to evaluate kinetic and thermodynamic parameters such as rate constants, activation energy, enthalpy, and entropy of the system. The endothermic nature of esterification was confirmed by positive value of enthalpy obtained. The effect of various levels of causal variables like temperature (60–90°C), catalyst concentration (0.5–1.5 wt.%), and molar ratio of n-butanol to butyric acid (1–3) on conversion kinetics of butyric acid was investigated during transient and equilibrium phase of the reaction. It has been observed that molar ratio of butanol to butyric acid has the highest influence on the conversion. The rate equation derived offered a kinetic and thermodynamic framework to the generated data. It also exhibits a notable degree of conformity of predicted data to the experimental ones and effectively characterizes the system across different reaction temperatures, reactant molar ratio, and catalyst concentration.     

Numerical modeling of titanium carbide synthesis in thermal plasma reactors

Titanium carbide powders synthesized in thermal plasma reactors are virtually always contaminated by soot. Equilibrium modeling predicts a viable process window without soot formation; however, this has not been achieved in practice. A numerical model incorporating chemical kinetics, nucleation and growth, and soot formation mechanisms has been developed to investigate this process. The chemical kinetic scheme teas based on ethylene pyrolysis and methane combustion with additional reactions to account for titanium-based molecules and the free carbon species found at plasma temperatures. Nucleation and .soot formation were based on simple kinetic models. The governing equations were integrated through time using typical temperature-time histories found by computational fluid dynamic (CFD) modeling of a radio frequency plasma torch. The results indicate that the synthesis is governed by interactions between several parallel processes and that there is a delicate balance between reactant stoichiometry, system pressure, cooling rate, product formation, and soot formation. This balance may be a limiting feature of ceramic carbide production in thermal plasma reactors.