R Ravi

The non-edible oils of mahua and jatropha were transesterified using methanol and 1 wt % KOH as the catalyst. The effect of co-solvent and the kinetic study of the transesterification of mahua oil is being reported here for the first time. Kinetics, modeled as a single-step reaction, revealed that the order of the reaction is 2 with respect to the triglyceride concentration and 1 with respect to the methanol concentration in both oils. In the presence of co-solvent, tetrahydrofuran (THF), methanolysis of mahua oil resulted in the increase of the rate constants from 0.08 to 1.17 L2 mol-2 min-1 at 28 °C and from 0.43 to 3.18 L2 mol -2 min-1 at 45 °C. The corresponding values for jatropha oil were found to be 0.50 and 2.76 L2 mol-2 min-1 at 28 °C and 1.26 and 4.56 L2 mol-2 min-1 at 45 °C. © 2011 American Chemical Society.

Coulson and Richardson’s Chemical Engineering: Volume 3A: Chemical and Biochemical Reactors and Reaction Engineering, Fourth Edition, covers reactor design, flow modelling, gas-liquid and gas-solid reactions and reactors.

The kinetics of transesterification of Pongamia oil using methanol at 60°C were studied. The forward as well as the reverse rate constants of all three steps involved in the transesterification of Pongamia oil are reported for the first time. Among the forward rate constants, the one governing the conversion of TG to DG was the highest and the one for DG to MG was the lowest. A distinct feature of the present work is the direct estimation of the equilibrium constants of all three steps by measuring the concentrations of TG, DG, and MG at very long reaction times. This reduced the number of parameters to be determined from the kinetic data by one-half, thereby leading to more accurate estimation of the rate constants. The equilibrium constant of the final step involving the conversion of MG to methyl ester and glycerol was at least an order of magnitude greater than that of the first two reaction steps. A detailed comparison was made with kinetic parameters reported in literature. The trend in the relative magnitudes of the rate constants appears to be unique to Pongamia oil. Copyright © 2006 by AOCS Press.

A four-parameter equation of state proposed by Serrin is investigated for its ability to predict accurately the saturation pressures of pure substances. The area rule or the generalized Maxwell’s rule is used for the calculation. An algorithm has been proposed by Serrin for implementing the calculations. The algorithm as it appears in print is found to yield results which are vastly different from those presented in Serrin’s article. As a result, a corrected algorithm has been derived and presented in the present article. Although the structure of the algorithm remains intact, the various coefficients and equations in the algorithm are found to differ from what appears in print. Saturation pressure predictions of the corrected algorithm are found to match very closely the predictions of an independent MATLAB-based algorithm developed in this work thereby providing validation of the corrections to Serrin’s algorithm proposed in this article. The corrected algorithm predicts saturation pressures that are close to the experimental values (error within 10%) for water when the parameters of the equation state as predicted by the critical point criteria are used. The sensitivity of the predictions to the specific heat model is also discussed.

A new method is proposed for obtaining the transformations that enable the application of the McCabe-Thiele method to the case when the saturated liquid and vapor enthalpy curves are straight but non-parallel lines. A rigorous framework which has a sound physical and mathematical basis and which brings into greater focus the central importance of the parallel enthalpy lines assumption to the McCabe-Thiele method is developed. Explicit expressions for the transformations of not only the composition and flow rate but also enthalpy are obtained. A detailed comparison of the methods adopted in this work with those in the literature is made. The specializing conditions under which the transformations in the literature emerge from a more general set are found. Extension to multi-component mixtures is demonstrated. It is shown that the framework presented here provides a rational basis for the prescriptions obtained from the "fictitious molecular weight" concept. Further, contrary to claims in the literature, the applicability of that concept to multi-component mixtures is demonstrated. Finally, the fresh perspective gained from the framework is used to widen the scope of its applicability and generalization to other separation processes such as extraction, adsorption and leaching is undertaken. © 2008 Elsevier Ltd. All rights reserved.

The concept of frequency response for linear time-invariant systems is clarified, demonstrating its validity for unstable systems as well. Some pitfalls in the use of the Nyquist criterion and the ways to avoid them are highlighted.

A study of the applicability of CST towards predicting transport coefficients in liquid metals has been undertaken with particular emphasis on alkali metals. Characteristic parameters were obtained from six different first principles calculations of inter-ionic potentials of simple metals reported in the literature. A wide variation was observed in the characteristic parameters as reported by various authors. Among these, the potential parameters of Shyu et al. provided the best correlation of experimental diffusivity and viscosity data for alkali metals over moderate temperature ranges. However, use of the Goldschmidt diameter as the characteristic distance parameter and k BTm, where Tm is the melting temperature, as the characteristic energy parameter gave as good, if not better, results for alkali metals. This parameter set was not found to be satisfactory when non-alkali metals were also included. Chapman's characteristic parameters, obtained from a fit to the viscosity data, provided a reasonable correlation of the diffusivity data to most, but not all metals studied. Fundamental issues associated with attempting to group all liquid metals under a single corresponding states theory as well with the conventional use of the potential well-depth and the distance at which the potential becomes zero as characteristic parameters for liquid metals have been pointed out. A preliminary statistical analysis has been performed to assess the reliability of our predictions in view of the experimental uncertainties in viscosity and diffusivity data. © 2004 Elsevier B.V. All rights reserved.

The importance of specifying the state of the inlet streams in determining the degrees of freedom (DOF) of a process is highlighted in the context of a single-stage separation unit. It is shown that, for the separation of a C-component mixture, the commonly accepted value of 2C + 6 as the DOE of an equilibrium single stage holds only if neither of the inlet streams lie on the phase envelope. The implications of this feature for the DOF of multistage processes is explored. The importance of a precise interpretation of the phase rule in arriving at the above results is emphasized. © 2005 American Chemical Society.

The ideas used by Gibbs in defining the ideal gas mixture are brought to light in view of their fundamental significance and the fact that they have not received due attention in the literature. Specifically, the central role played by the well-known Gibbs-Duhem equation in this regard is explained. The concept of a fundamental equation and its importance in the definition of an ideal gas as well as an ideal gas mixture is elucidated. The manner in which these ideas enabled Gibbs to give a very general interpretation of Daltons law is examined in detail. © 2011 American Chemical Society.