Somenath Ganguly

Prediction of VLE data using radial basis function network

Artificial neural network with radial basis function (RBF) was explored for prediction of the vapor liquid equilibrium (VLE) data. Four typical binary systems, representing different deviations from ideality (in mixing) were considered. For each type of binary system, a set of experimental VLE data from Dechema series was used to train the network. The rest of the available experimental data was used for testing the predictive capability of the network. VLE data for two ternary systems were predicted utilizing a similar network. Three sets of binary data include all the binary combinations possible with three components of the ternary system. These three sets were used to train the network for each ternary system. UNIQUAC model stores the VLE data through regression of the model parameters. The same set of VLE data can be reproduced utilizing thermodynamic models. The accuracy of such reproduction (as reported in Dechema series) is compared with the accuracy of prediction of the same set of data by RBF network. The comparison is presented here for all the four binary systems and the ternary system. The computational (storage) requirements for the networks were also evaluated.

First electrosynthesis of transition metal peroxo complexes. Synthesis, characterization and reactivity of molybdenum and tungsten heteroligand peroxo complexes

Abstract Molecular peroxo complexes of molybdenum and tungsten, viz. [MO(O2)2L] (M = Mo or W; L = 2,2′-bipyridine, 1,10-phenanthroline or 2,2′-bipyridine-N,N′-dioxide), in the presence of hydrogen peroxide and then precipitating with the corresponding heteroligands. These complexes have also been prepared by the dissolution of metal powders in hydrogen peroxide. They have been characterized by elemental analysis and vibrational spectra. The complexes oxidize triphenylphosphine and triphenylarsine to triphenylphosphine oxide and triphenylarsine oxide, respectively.

First electrosynthesis of transition metal peroxofluoro complexes. Synthesis, characterization and reactivity of some peroxofluoro complexes

Abstract Peroxofluoro complexes of the transition metals, viz. V, Nb, Ta, Mo and W, have been synthesized electrochemically using the sacrificial metal anodes in the presence of hydrogen peroxide (15%) and hydrofluoric acid (10%). These complexes have also been prepared by the dissolution of the metal powders in a mixture of hydrogen peroxide and hydrofluoric acid. While the monoperoxo complexes are formed at lower pH, higher pH is conducive to the formation of diperoxo complexes. The compounds have been characterized by elemental analysis and vibrational spectral studies. K2[MoO(O2)F4]·H2O and K2[WO(O2)F4]·H2O can oxidize triphenylphosphine to triphenylphosphine oxide in high yield.

Diffusion of Moisture from Hydrogel Scaffold with Induced Porosity from Self-Assembled Bubbles

Hydrogel scaffolds find use in the regulated release of biological agents, and as three-dimensional supports for the formation of a tissue matrix. This article addresses the diffusion of moisture from the alginate and chitosan scaffolds under vacuum, and the resulting evolution of pore structure. A fluidic arrangement was used to induce a self-aligned monolayer of bubbles in the aqueous film prior to crosslinking. The regular alignment of bubbles remained unchanged as the film underwent crosslinking and subsequent shrinkage due to the release of moisture. A mathematical model was utilized to derive an effective diffusivity of the scaffold as a function of the moisture content. The gradient in this profile and the limiting value at zero moisture content were analyzed for scaffolds of different thicknesses in the presence or absence of bubbles. The desaturation behavior of the bubble zone, the surface of the scaffold, and the gel matrix were studied. The moisture profile within the scaffold was also simulated using the mathematical model.

Rupture of Polyacrylamide Gel in a Tube in Response to Aqueous Pressure Gradients

Hydro‐gel and the evolution of its strength as the gel matures from the state of aqueous fluid to the state of viscoelastic solid provides opportunity to employ hydro‐gel in certain critical applications, such as sealing of fractures or high permeability streaks in a hydrocarbon reservoir. The mature gel, inside the channel, helps in diverting the injected water into an un‐swept oil bearing zone. For the gel treatment to be effective, the gel layer inside the channel has to resist failure under water pressure. This article describes evaluation of the strength of Cr(III)–partially hydrolyzed polyacrylamide gel, formed in transparent tubes. A pressure gradient was imposed on the gel by injecting water on one end of the tube, leaving the other end open to atmosphere. Pressure gradient that increased with time caused shear deformation, and bulging of gel at the outlet end of the tube. At a threshold pressure, the deformation culminated to a rupture at the center of the gel, and subsequent burst of water through the outlet. Rupture was visualized using colored water that fingered through the center of the gel, leaving the rest of the gel intact. Rupture pressure, similar to the ultimate strength of a material, is defined for the gel layer. The rupture pressure was found to increase with the length, and decrease with the width of aperture. A theoretical model in support of this trend is presented here. When the pressure was built up fast, the rupture took place at a much smaller pressure. In case of pressure build‐up over a long period of time, rupture pressure became independent of the duration of build‐up. The effect of the rate of pressure build‐up is analyzed using the concept of viscoelasticity. Also, the rupture model is extended to the situations where the porous media hinder the free movement of gel at the outlet, and allow partial movement of gel laterally through the surrounding wall.

Diffusion in and around alginate and chitosan films with embedded sub-millimeter voids.

Hydrogel scaffolds from biopolymers have potential use in the controlled release of drugs, and as 3-D structure for the formation of tissue matrix. This article describes the solute release behavior of alginate and chitosan films with embedded voids of sub-millimeter dimensions. Nitrogen gas was bubbled in a fluidic arrangement to generate bubbles, prior to the crosslinking. The crosslinked gel was dried in a vacuum oven, and subsequently, soaked in Vitamin B-12 solution. The dimensions of the voids immediately after the cross-linking of gel, and also after complete drying were obtained using a digital microscope and scanning electron microscope respectively. The porosity of the gel was measured gravimetrically. The release of Vitamin B-12 in PBS buffer on a shaker was studied. The release experiments were repeated at an elevated temperature of 37°C in the presence of lysozyme. The diffusion coefficient within the gel layer and the mass transfer coefficient at the interface with the bulk-liquid were estimated using a mathematical model. For comparison, the experiment was repeated with a film that does not have any embedded void. The enhancement in diffusion coefficient due to the presence of voids is discussed in this article.

In Situ Combustion of Light Oil: Stoichiometric, Kinetic, and Thermodynamic Analyses from the Flow Experiments

In situ combustion of light oil (37°API) was studied here through combustion tube experiment and mathematical modeling. The flue gas at the effluent provided a reaction stoichiometry, and indicated an aggregate molecular entity similar to bitumen as the burning fraction of the crude oil. A mathematical model based on 1D heat and mass transport with three phases in porous media effectively simulated the sustenance and progression of the combustion front, observed experimentally. The sensitivity of these aspects to the perturbations in rate constants, activation energy, and heat of reaction is discussed here. The extent of accumulation of oil and water at the downstream side of the combustion front was evaluated. The simulation results concerning cumulative collection of oil at the effluent was verified with experimental data. The width of the combustion zone, evident from the concentration profile of oxygen, is discussed in this article.

Enhancement of solute release from alginate scaffold with embedded sub-millimeter voids.

Alginate scaffold has potential use in the controlled release of drugs, and as 3-D structure for the formation of tissue matrix. This article describes the solute release behavior of alginate scaffold that bears embedded voids of sub-millimeter dimensions. Nitrogen gas was bubbled in a fluidic arrangement to generate uniform and self-aligned bubbles in alginate, prior to the cross-linking by CaCl2. The cross-linked gel was dried in a vacuum oven, and subsequently, soaked in Vitamin B12 solution. The dimensions of the voids immediately after the cross-linking of gel, and also after complete drying were obtained using a digital microscope and the scanning electron microscope, respectively. The porosity of the gel was measured gravimetrically. The release of Vitamin B12 in water on a shaker was studied. For comparison, the experiment was repeated with a scaffold that did not have any embedded void. The enhancements in uptake and release of Vitamin B12 due to the presence of voids are estimated in this article.

Enhancement of Solute Release From Chitosan Scaffold With Embedded Submillimeter Voids

Chitosan scaffold has potential use in the controlled release of drugs, and as 3-D structure for the formation of tissue matrix. This article describes the solute release behavior of chitosan scaffold that bears embedded voids of submillimeter dimensions. Formaldehyde and glyoxal were considered as crosslinkers, and alcohol ethoxylate was used as the surfactant. Nitrogen gas was bubbled in a fluidic arrangement to generate an ensemble of self-aligned bubbles in chitosan, prior to the crosslinking. The crosslinked gel was dried in a vacuum oven, and subsequently, the absorption capacity of the scaffold in PBS buffer was estimated. The type of crosslinker significantly affected the absorption capacity of the scaffold. The dimensions of the voids immediately after the cross-linking of gel, and also after complete drying were obtained using a digital microscope and a scanning electron microscope respectively. Two levels of porosity are evident from these images. The smaller pores were intrinsically provided by the gel matrix. The larger ones were induced by the fluidic arrangement. The porosity of the gel was measured gravimetrically. The uptake of Vitamin B-12 was found significantly higher when formaldehyde was used as crosslinker instead of glyoxal. The release of Vitamin B-12 in PBS buffer on a shaker was studied. For comparison, the experiment was repeated with a scaffold that did not have any embedded void. The enhancements in the release of Vitamin B-12 due to the presence of voids are estimated in this article. The bubbles, placed in more than one layer, enhanced the porosity and the ability to absorb Vitamin B-12 further. GRAPHICAL ABSTRACT

Charge transport in carbon electrodes made by electrospray of precursor sol and subsequent carbonization in situ

As an alternative to binder-based overlay of carbon powder on the current collector, the precursor sol may be carbonized directly on the current collector for the purpose of making supercapacitor electrodes. The disintegration of precursor sol into fine droplets prior to the deposition and subsequent removal of solvent from the deposited gel through lyophilization may enhance the internal surface area and the pore connectivity. This article presents the impedance spectroscopy analysis of such electrodes and reports the resistance to transport of electrolyte ions in such pore network through meaningful equivalent circuits. Neutral, alkaline, and acidic electrolytes were considered in this study. Multiple levels of hierarchy in the pore network are considered here to ascertain the extent of heterogeneity and branching in the pore structure. The electrodes from the binder-based overlay of carbon powder are studied here for comparison. The method of spray coating, followed by in situ carbonization seems to have produced a pore structure, which is less branched. The resistance to access the internal surface is more uniform over the entire domain for such electrodes. The equivalent series resistance was found significantly smaller for these electrodes.