Ashok Khanna

Genetic algorithm to estimate interaction parameters of multicomponent systems for liquid¿liquid equilibria

Abstract Genetic algorithm (GA) has been utilized to estimate the binary interaction parameters from multicomponent liquid–liquid equilibria data; and its applicability for NRTL and UNIQUAC thermodynamic models has been demonstrated. These models being highly non-convex can have several local extrema. GA leads to globally optimum values; it does not require any initial guess but only the upper and lower bounds of the interaction parameters. It has also been shown to perform better than inside variance estimation method (IVEM) and the techniques used in ASPEN, DECHEMA. The objective function and the root-mean-square deviation for these four techniques have been compared for methanol–diphenylamine–cyclohexane system using UNIQUAC. The applicability of GA to six ternary, two quaternary and two quinary systems has also been undertaken. Invariably the rmsd values for GA are better than reported in the literature.

Extraction of UO22+ into Ionic Liquid Using TTA and TBP as Extractants

Thenoyltrifluoroacetone and Tributyl-phosphate have been used for extraction of UO22+ into Ionic Liquid 1-Butyl-3-methylimidazoliumbis(trifluoromethylsulfonyl)imide. Increasing acidity of uranyl solution from 0.01 to 3 mol L−1 HNO3 for TTA in IL, the distribution ratio (DU) and extraction efficiency (%E) both decreased. Further increment in acidity shows reversal of trend. Similar behavior is observed for TBP. With increasing concentration of TTA, %E increases stabilizing at 0.5 mol L−1 TTA. Adding methanol to TTA increased the DU due to active enolic formation. The developed kinetic model estimates the overall mass transfer coefficient (Ka) as 3.6 x 10−2 s−1. Synergistic effect has been observed for combination of TTA + TBP resulting in enhanced DU.

Closure Equations in the Estimation of Binary Interaction Parameters

Binary interaction parameters used in the UNIQUAC activity coefficient model are found to be dependent on each other and related by a linear relation termed as the closure equation. For a ternary system, six binary interaction parameters are related by one closure equation. Similarly for quaternary systems, three independent closure equations are obtained for the twelve binary interaction parameters and for quinary systems there are six closure equations for twenty parameters. Each closure equation consists of six parameters. The binary interaction parameters that do not satisfy the closure equations may lead to a less accurate prediction of liquid-liquid equilibria. In this work the binary interaction parameters have been estimated with and without closure equations for few ternary and quaternary systems. Parameters that satisfy the closure equations exhibit better root mean square deviation than those that do not satisfy the closure equations in most of the cases. A similar behavior is observed for NRTL model also.

Mass Transfer Studies on Ternary Systems in a Bench-scale Liquid-Liquid Extraction (LLX) Column and a Comparison with Simulations

Mass transfer studies in a laboratory scale extraction column have been conducted for Toluene-Acetone-Water and MIBK-Acetic Acid-Water systems. From these experiments stage-wise solute (Acetone or Acetic-Acid) composition profiles have been obtained for both dispersed and continuous phase. These composition profiles have been compared with those obtained from ASPENPLUS, CHEMSEP and LLXSIM simulators. For liquid-liquid equilibrium calculations all these simulators use UNIFAC and UNIQUAC model. The binary interaction parameters for the UNIFAC are inbuilt in ASPENPLUS and CHEMSEP. UNIQUAC binary parameters were borrowed from DECHEMA. Error square analysis indicates that simulations based onnon-equilibrium option of LLXSIM matchclosely with experimental results. Temperature profiles and hydrodynamic features characterized by number of drops and static holdup on the stages have been compared between the LLXSIM simulated and the experimental results and these match well. However simulations on ASPENPLUS give sum of relative error-squares for all the experimental runs at leastten times higher, in spite of tuning the average stage efficiency.

Selection of Mass Transfer Correlations for Rate Based Liquid-Liquid Extraction Model

A rate-based model formass transfer in liquid-liquid extraction (LLX) has been developed usingthree distinct stages of drop formation, drop fall or rise and drop coalescence. Binary diffusivities in infinite dilution as well as for concentrated multicomponent mixtures were used to estimate the Maxwell-Stefan binary mass transfer coefficients for both the phases. The mass transfer resistances associated with these coefficients have been categorized in four configurations. Because of the very large number of computations associated with repeated calculations of mass transfer coefficients, alocal model has been incorporated. Acomparative study between rate-based and non-equilibrium simulator and our bench scale experiments (LLX of toluene-acetone-water system) has been done. The stage-wise composition profiles of acetone in water and toluene phase of the experimental and simulation runs have been compared by using the relative error square analysis. Based on this analysis, best mass transfer combination and mass transfer resistance model has been selected.

Nonuniform Arrangement of Emitter-Receiver Pairs Arrangement and Compact Ultrasonic Tomography Setup

Arrangements of emitter-receiver pairs with two possibilities: nonuniform and uniform locations, are studied. Ultrasonic computerized tomographic (UCT) setups are developed with these configurations for parallel and fan beam scanning modes. Optimization is used to determine the best nonuniform arrangement. The CT reconstructions with nonuniform emitter-receiver pair arrangements from the data acquired via computer generated pixel images and real world specimens show promising results compared with their uniform arrangement. A flow channel, e.g., a metal pipe with small ratio of pipe diameter to emitter/receiver aperture, imposes restriction on the number of emitter-receiver pairs. A practical application, for void-fraction estimation for water-air flow, is investigated with the best design. Reconstructed flow profiles and estimated air fractions match with 3-D numerical simulation obtained using FLUENT 14. Cost of a focused acoustic emitter/receiver pair and its noise response depends on its focal length. The optimized nonuniform design can be best suited for emitter/receiver pairs of small focal lengths and can aid in developing low budget and compact UCT scanners.

Experimental analysis and development of correlations for gas holdup in high pressure slurry co-current bubble columns

The effect of liquid and gas velocities, solid concentrations, and operating pressure has been studied experimentally in a 15 cm diameter air-water-glass beads bubble column. The superficial gas and liquid velocities varied from 1.0 to 40.00 cm/s and 0 to 16.04 cm/s, respectively, while the solid loading varied from 1 to 9%. The gas holdup in the column was reduced sharply as we switched from batch to co-current mode of operation. At low gas velocity, the effect of liquid velocity was insignificant; while at high gas velocity, increasing liquid velocity decreased the gas holdup. Drift flux approach was applied to quantify the combined effect of liquid and gas velocities over gas holdup. For co-current three phase flows, the gas holdup decreased with increase in solid loading for all pressures. But for batch operations, when solid loading was 5% or more, settling started leading to higher gas holdup. Increasing pressure from atmospheric conditions increased the gas holdup significantly, flattening asymptotically.

Efficient homogeneous and supported ionic liquid catalysts for production of linear alkylbenzenes

AlCl3 based homogeneous ionic liquids, such as 1-butyl 3-methyl-imidazolium chloroaluminate ([BMIm]+Al2Cl 7− ), 1-butyl 3-methyl-pyridinum chloroaluminate ([BMPy]+Al2Cl 7−), and triethylamine hydrochloride chloroaluminate (Et3NHCl-AlCl3), were prepared to study the benzene alkylation with 1-dodecene. All homogeneous ionic liquid catalysts have shown higher selectivity (∼40%) for desired 2-LAB (2-linear alkylbenzene) than the conventional AlCl3 catalyst (∼32%). Apart from the homogeneous catalysts, one supported ionic liquid catalyst (SG–N+(C2H5)3–Al2Cl 7−) was also synthesized. The supported ionic liquid catalyst showed further increased selectivity of the 2-LAB (∼45%). Moreover, the reusability of SG–N+(C2H5)3–Al2Cl 7− catalyst was much higher than the homogeneous ionic liquid catalysts. The supported ionic liquid catalyst was characterized by various techniques such as FT-IR, MAS-NMR and Scanning Electron Microscopy (SEM). Hammett acidity function (Ho) was used to determine the acidity of supported ionic liquid catalysts. The pyridine adsorbed FT-IR spectra of (SG–N+(C2H5)3–Al2Cl 7−) catalyst showed presence of common Brönsted (Brønsted)—Lewis acidic sites. The 27Al MAS-NMR of (SG-N+(C2H5)3-Al2Cl 7−) catalyst showed a band at ∼6.987 ppm, which is attributed to 6-coordinated Al species. A nonlinear optimization algorithm was developed in MATLAB 7.4.0 to determine the kinetic parameters of the benzene alkylation with 1-dodecene in presence of (SG–N+(C2H5)3–Al2Cl 7−) catalyst. The concentrations of the products predicted by model were found in good agreement with experiments (relative error ∼1.5%).

Estimation of LLX for PIONA families and its validation

Abstract In petroleum processing, the intermediate streams contain compounds of the five homologous families—n-paraffins, iso-paraffins, olefins, naphthenes and aromatics (PIONA). It is unwieldy to use all these true compounds in any rigorous simulator to get the actual picture of the plant operations. To attain a quantitative description of the phase equilibrium of such mixtures, a novel shortcut method, which is, based on only one reference component and the ratio of the adjacent distribution coefficients for homologous family has been developed. At a particular temperature the recursive ratios of the distribution coefficients in a homologous family indicate a fixed value on the main branch. The dependency of relative distribution coefficients on temperature and solvent to feed ratio has been estimated. For all the PIONA families, exponentially distributed feed has been used in the AspenPlus simulator to calculate the distribution coefficients K. The shortcut PIONA liquid–liquid extraction (LLX) simulation program has been trained using the above distribution coefficients to obtain the relative distribution parameter β. For testing PIONA LLX proposition, single stage liquid–liquid extraction experiments for gamma (continuous) and random (discrete) distributed feeds were done. n-Paraffin, naphthene and aromatic families were investigated independently. The single stage PIONA approach has been extended to the multistage extraction column. The multistage PIONA shortcut results have also been compared with rigorous simulation results and they match closely. It reduces the computational time by an order of magnitude.

Analytical solution of molecular-weight distribution in reversible step-growth polymerization in homogeneous continuous-flow stirred tank reactors following unequal reactivity

Abstract General unequal reactivity in reversible step-growth polymerization has been modelled by assuming that monomer reacts at different rates. The generation relation for the moment-generating function G has been derived for polymerization in homogeneous continuous-flow stirred tank reactors. It is a non-linear ordinary differential equation and has been solved analytically using the Frobenius method. Analytical solution of the molecular-weight distribution of the polymer is obtained from this in a natural way and is shown to be valid even when there is flashing of condensation product. Subsequently, the molecular-weight distribution at equilibrium has been derived.