Volume 3, Issue 2 - Papers from CITICCOMS 2007

Coimbatore Institute of Technology, India, organized an International Conference on Modeling and Simulation (CITICOMS 2007) during August 27–29, 2007. The conference covered research works on modeling & simulation in a large number of diverse disciplines viz., biotechnology, chemical engineering, mechanical engineering, civil engineering, mathematics and nanotechnology, electrical engineering, electronic engineering and computer engineering.This special issue presents a set of nine selected research papers, which have undergone the peer-review process of the journal of Chemical Product and Process Modeling. Although these papers do not cover the entire gamut of modeling and simulation activities, they certainly present interesting and useful topics. In particular these topics include the black box modeling approach for identification of nonlinear systems, kinetic modeling of the adsorptive removal of toxic and hazardous pollutants from wastewaters, analysis and modeling of homogeneous tubular reactors, monolithic catalytic converters, and a constitutive model equation for the rheological behaviour of three phase polymer blends or so called double emulsions.

Presence of phenol and phenolic compounds in various wastewaters and its harmful effects has led to the use of different treatment methods. Work on biological methods shows the use of different microorganisms and different bioreactors so as to improve the removal efficiency economically. The present work deals with the use of N. hydrocarbonoxydans (NCIM 2386), an actinomycetes, for the degradation of phenol. N. hydrocarbonoxydans was immobilized on GAC and used in a spouted bed contactor for effective contact of microorganisms and the substrate. The contactor performance was studied by varying flow rates, influent concentrations and the solids loading in the contactor. The effect of these variables on phenol degradation was investigated and modeling study was carried out using the artificial neural network (ANN). A feed forward neural network with back propagation was used for the model development. The experiments were planned as per the face centered cube design (FCCD) and used for training of the model, whereas data from four other experimental runs were used for testing and validation of the model. The network was optimized for the number of neurons based on the mean square error. The ANN model with three layers with three input neurons, eight neurons in hidden layers and one output neuron was found to predict effectively the effluent concentration for the given operating conditions in the spouted bed contactor. The mean square error was found to be 9.318e-12 for this ANN model. Also the experimental data was used to develop second order nonlinear empirical model obtained using multiple regression (MR) and the results compared with ANN using correlation coefficient (R2), average absolute error (AAE) and root mean square error (RMSE). Results show that R2, AAE and RMSE values of MR model were 0.9363, 2.085 % and 2.338 % respectively, while in case of ANN model these values were 0.9995, 0.59 % and 1.263 % respectively. This shows that ANN model prediction is better than multiple regression model prediction.

A compact and efficient model that is capable of approximating both the linear and nonlinear components of the process is in high demand. In this paper, a novel black-box modeling technique viz. Wiener type Laguerre-Wavelet model is proposed. The Laguerre-Wavelet model has the capability to approximate a function with moderate/reasonable number of data with appreciable approximation accuracy. The Laguerre filter is used to approximate the linear dynamic components of the process, whereas wavelet structure is used for the static nonlinear components. The ability of wavelets to approximate any square-integrable function to any arbitrary precision by input-output mappings is utilised for the nonlinear approximation following a modified single scaling method. The performance efficiency of the proposed Wiener type model structure, Laguerre-Wavelet model, is demonstrated using simulation case study on a continuous bioreactor.

Distillation exhibits highly nonlinear dynamic behavior and the development of suitable nonlinear model to distillation pose a challenging problem to current process industry. In the absence of a reasonably accurate nonlinear model, distillation column is difficult to control using advanced model based control strategies. In this paper, a novel sigmoidnet based nonlinear auto-regressive with exogenous inputs (NARX) model is developed for high purity distillation column and verified using the experimentally validated first principle model. The model validation and regressor analysis proved that the developed NARX model was capable of capturing the nonlinear dynamics of a distillation column.

Sorption capacity of two different parts of Eichhornia crassipes such as Lamina and Petiole on a Basic dye (Basic Aurophine-O), Acidic dye (Acid Fast Red-A) and Reactive dye (Brill Red-5B) was studied in a batch system. The maximum equilibrium uptake capacity of petiole was 25.5 mg/g for Basic Aurophine-O, 23.1 mg/g for Acid Fast Red-A and 0.18 mg/g for Brill Red-5B. The equilibrium uptake capacity of petiole was found to be more in Basic Aurophine-O dye when compared to all other dyes studied. The maximum equilibrium uptake capacity of lamina was 27.0 mg/g for Basic Aurophine-O, 25.2 mg/g for Acid Fast Red-A and 4.2 mg/g for Brill Red-5B. The equilibrium uptake capacity of lamina was found to be more in Basic Aurophine-O when compared to Brill Red-5B and Acid Fast Red-A dyes studied in the present investigation. From the result, it was observed that the uptake capacity of dyes using E. crassipes part Lamina was found to be more when compared to the other E. crassipes part of Petiole used in the present study. Sorption results were found to be fitted very well with the Pseudo-second order kinetic model when compared to Pseudo-first order kinetic model. The intra particle diffusion coefficient (Ki) and diffusion coefficient (Di) obtained for the removal of dyes studied using Lamina was found to be more when compared to the other part of Petiole. The polynomial equations are developed and can be used as a ready reckoner equation to find out the percentage color removal of dyes studied in the present investigation at different period of time intervals.

Biosorption of Reactive Red 2 dye, from an aqueous solution was evaluated using Tamarindus indica fruit hulls in a batch system. The influence of pH (1-6), temperature (20-30°C) and initial dye concentration (20 to 120 mg/L) on the biosorption process was studied. Maximum biosorption was observed at initial pH of 2.0, temperature of 30°C and at the initial dye concentration of 120 mg/L. Equilibrium data were analysed for Langmuir, Freundlich and generalized isotherm model. The equilibrium data were found to fit very well with Freundlich isotherm model when compared to all other isotherm models studied in the present investigation. Batch biosorption kinetics was studied with different initial dye concentrations and rate of biosorption was determined using pseudo first and pseudo second order rate equations. From the result it was observed that pseudo second order rate expression fit the experimental data well for Reactive Red 2 when compared to a pseudo first order kinetic model.

Biosorption of Reactive Orange 4 dye, from an aqueous solution was evaluated by Eichhornia crassipes in a batch system. The influence of pH (1-6), temperature (20-30°C) and initial dye concentration (20 to 120 mg/L) on the biosorption process was studied. Maximum biosorption was observed at initial pH of 2.0, temperature of 30°C and at the initial dye concentration of 120 mg/L. Batch biosorption kinetics was studied with different initial dye concentrations and rate of biosorption was determined using the pseudo first and pseudo second order rate equations. From the result it was observed that pseudo second order rate expression fit the experimental data well for Reactive Orange 4 when compared to pseudo first order kinetic model. The intra particle diffusion coefficient (Ki) and effective diffusion coefficient (Di) values obtained for the sorption of Reactive Orange 4 using E. crassipes was found to be increased with increase in initial dye concentrations.

Three-phase polymer blends with ``multiple droplet" morphology are important industrially. They are referred to as ``double emulsions" as the droplets of these blends themselves contain a number of smaller droplets inside. In this work, the dynamic viscoelastic behavior of double emulsions composed of three immiscible polymeric liquids is modeled. Simulations show that such double emulsions exhibit three relaxation domains due to relaxation of two different interfaces (internal and external) and the matrix polymer. The factors affecting the dynamic viscoelastic behavior of double emulsions composed of three immiscible polymeric liquids are discussed.

Interaction between transport and reaction generates a variety of complex spatio-temporal patterns in chemical reactors. These patterned states, which are typically initiated by autocatalytic effects and sustained by differences in diffusion/local mixing rates, often cause undesired effects in the reactor. In this work, we analyze the dynamic evolution of mixing-limited spatial pattern formation in fast, homogeneous autocatalytic reactions occurring in isothermal tubular reactors using two-dimensional (2-D) convection-diffusion-reaction (CDR) models that are obtained through rigorous spatial averaging of the three-dimensional (3-D) CDR model using Liapunov-Schmidt technique of bifurcation theory. We use the spatially-averaged 2-D CDR model (and its "regularized" form) to perform steady-state bifurcation analysis that captures the region of multiple solutions, and we analyze the stability of these multiple steady states to transverse perturbations using linear stability analysis. Parametric analyses of the steady-state bifurcation diagrams and stability boundaries show that when transverse mixing is significantly slower than the rate of autocatalytic reaction, mixing-limited patterns emerge from the unstable middle branch that connects the ignition and extinction points of an S-shaped bifurcation curve. Our dynamic simulations show the emergence of three different types of spatial patterns namely, Band, Anti-phase and Target, depending on the nature of transverse perturbation. The temporal evolution of these patterns consists of rapid intensification of the concentration-segregation process (especially when transverse mixing is much slower than reaction) followed by slow diffusion-mediated return to symmetry that occurs at time scales much larger than the reactor residence time. Our parametric analysis of the dynamics reveals that while larger Péclet numbers (both axial and transverse) increase the stability and decay time of the patterned states, larger Damköhler numbers lead to faster ignition resulting in the opposite effect.

In order to meet the strict future emission standards monolithic catalytic converters play a very important role. Although they have been extensively studied, still there are some areas that need to be further explored like the warm up period, during which the hydrocarbon emissions are relatively high. A single channel one-dimensional model can help evaluate the physicochemical processes occurring in the converter. In this study a decrease in the level of hydrocarbon emissions for propylene and propane during cold start are analysed taking into consideration the effect of both catalytic and homogenous reactions. The model proposed accounts for the combined effect of heat transfer, mass transfer and exothermic chemical reactions which are all strongly coupled.