Publications

Abstract A three-layer feed-forward neural network was constructed and tested to analyze the kinetic dye uptake of a batch activated carbon adsorption process. The operating variables studied are the contact time, initial dye concentration, agitation speed, temperature, initial solution pH, activated carbon mass, and volume of the dye solution treated. The studied operating variables were used as the input to the constructed neural network to predict the dye uptake at any time as the output or the target. The constructed network was found to be precise in modeling the rate of dye uptake for the operating conditions studied. The constructed neural network was found to be highly precise in predicting the dye uptake rate for the new input data, which are kept unaware of the trained neural network showing its applicability to determine the reaction rate for any operating conditions.

Abstract The present work reports the values of the gaseous standard (p degrees = 0.1 MPa) molar enthalpy of formation of three pyridine derivatives substituted with one, two, and three tert-butyl groups, in positions para, ortho-ortho and ortho-para-ortho to the nitrogen, respectively. The standard molar energies of combustion of each compound, determined by static bomb calorimetry, yielded their standard molar enthalpies of formation in the condensed phase at T = 298.15 K, which together with the values of the standard molar enthalpies of vaporization or sublimation, measured by Calvet microcalorimetry, allowed the calculation of the standard gas phase molar enthalpy of formation of each compound studied. The enthalpies of combustion for 4-tert-butylpyridine (1), 2,6-di-tert-butylpyridine (1) and 2,4,6-tri-tert-butylpyridine (cr) were found to be, respectively, -(5 370.1 +/- 3.4) kJ mol(-1), -(7954.2 +/- 4.0) kJ mol(-1), and -(10 542.9 +/- 4.9) kJ mol(-1). The molar enthalpies of vaporization were measured as (54.4 +/- 1.3) kJ mol(-1) for 4-tert-butylpyridine, (56.6 +/- 1.2) kJ mol(-1) for 2,6-di-tert-butylpyridine, whereas the enthalpy of sublimation of 2,4,6-tri-tert-butylpyridine was found to be (78.3 +/- 1.7) kJ mol(-1).

Abstract A comparison of linear and non-linear regression method in selecting the optimum isotherm was made to the experimental equilibrium data of basic red 9 sorption by activated carbon. The r(2) was used to select the best fit linear theoretical isotherm. In the case of non-linear regression method, six error functions namely coefficient of determination (r(2)), hybrid fractional error function (HYBRID), Marquardt's percent standard deviation (MPSD), the average relative error (ARE), sum of the errors squared (ERRSQ) and sum of the absolute errors (EABS) were used to predict the parameters involved in the two and three parameter isotherms and also to predict the optimum isotherm. Non-linear regression was found to be a better way to obtain the parameters involved in the isotherms and also the optimum isotherm. For two parameter isotherm, MPSD was found to be the best error function in minimizing the error distribution between the experimental equilibrium data and predicted isotherms. In the case of three parameter isotherm, r2 was found to be the best error function to minimize the error distribution structure between experimental equilibrium data and theoretical isotherms. The present study showed that the size of the error function alone is not a deciding factor to choose the optimum isotherm. In addition to the size of error function, the theory behind the predicted isotherm should be verified with the help of experimental data while selecting the optimum isotherm. A coefficient of non-determination, K-2 was explained and was found to be very useful in identifying the best error function while selecting the optimum isotherm.

Abstract The present study reports that it is impossible and inappropriate to approximate the Langmuir-Hinshelwood kinetics to zero order kinetics.

Abstract The standard (p degrees = 0.1 MPa) molar enthalpies of formation, at T = 298.15 K, of 4-chloro-3-nitroaniline and 5-chloro-2-nitroaniline, in the condensed phase, were derived from their standard molar energies of combustion, in oxygen, to yield CO2(g), N-2(g), and HCl center dot 600-H2O(1), measured by rotating bomb combustion calorimetry. From the temperature dependence of the vapour pressures of these compounds, measured by the Knudsen effusion technique, their standard molar enthalpies of sublimation, at T = 298.15 K, were derived by means of the Clausius-Clapeyron equation. The Calvet microcalorimetry was also used to measure the standard molar enthalpies of sublimation of these compounds, at T = 298.15 K. The combination of the standard molar enthalpies of formation in the condensed phases and the standard molar enthalpies of sublimation yielded the standard molar enthalpies of formation in the gaseous phase at T = 298.15 K for each isomer. Further, the standard (p degrees = 0.1 MPa) molar enthalpies, entropies and Gibbs free energies of sublimation, at T = 298.15 K, were also derived. The standard molar enthalpies of formation, in the gaseous phase of all the chloronitroaniline isomers were also estimated by the Cox scheme and by the use of computational thermochemistry and compared with the available experimental values.

Abstract The present manuscript reports the first application of molecular modelling to the design of molecularly imprinted polymers (MIPs) prepared by alkoxysilane sol-gel polymerization. The major goal was to determine the requisite level of theory for the selection of suitable alkoxysilane functional monomers. A comparative study, applied to the design of a MIP for beta-damascenone, involving different levels of theory, basis set superposition error (BSSE) correct ion and basis set augmentation and also semi-empirical methods, was performed. The computations results suggest that the use of the 3-21G basis set concomitantly with a method for BSSE correction represents a good compromise between theory level and computation time for the successful screening of functional monomers. Additionally, a few selected MIPs and their corresponding non-imprinted congeners (NIPs) were prepared and tested in the role of solid-phase extraction (SPE) sorbents. The confrontation of the computational results with the observed performance and morphological characteristics of the prepared MIPs suggest that besides the strength and type of interactions existing between template and functional monomers other concomitant features, related with the sol-gel process, must also be accounted for so that effective molecular imprinting is achieved in an alkoxysilane xerogel. Nevertheless, since an optimal ternplate-functional monomer interaction is a necessary condition for successful imprinting, the choice of the best monomers is still of the greatest importance and the proposed computational method may constitute an expeditious and reliable screening tool.

Abstract The formation mechanisms and properties of arc-induced gratings are intrinsically related to the temperature attained by the fiber during arc exposure. In this work, we present further results oil the estimation of the fiber temperature based oil the use of electrically insulated thermocouples. Computer simulations show that under typical arc discharge conditions, the fiber reaches steady-state thermal equilibrium in less than half a second, having a peak temperature of about 1350 degrees C (C) 2008 Wiley Periodicals, Inc.

Abstract The standard (p degrees = 0.1 MPa) molar enthalpies of formation in the crystalline state of phenylacetic acid and ortho-, meta- and para-chlorophenylacetic acids were derived from the standard molar energies of combustion in oxygen at T = 298.15 K, measured by combustion calorimetry. The Knudsen mass-loss effusion technique was used to measure the dependence of the vapour pressure of the solid isomers of chlorophenylacetic acid with the temperature from which the standard molar enthalpies of sublimation were derived using the Clausius-Clapeyron equation. [GRAPHICS] From these values the standard molar enthalpies in the gaseous phase, at T = 298.15 K, were derived, compared with the same parameters estimated from the Cox scheme and interpreted in terms of molecular structure. The standard (p degrees = 0.1 MPa) molar enthalpies, entropies, and Gibbs energies of sublimation, at T = 298.15 K, were derived for the three monochlorophenylacetic acids, using estimated values for the heat capacity differences between the gas and the crystal phases. Moreover, the enthalpies and the temperatures of fusion for the crystalline isomers of chlorophenylacetic acid were measured by differential scanning calorimetry.