Vinay A. Juvekar

Investigating the differences in acid separation behaviour on weak base ion exchange resins

Differences in acid separation behaviour on weak base ion exchange resins have been investigated in this work. Experimental data has been obtained on sorption equilibrium using various types of weak base resins and both inorganic and organic monobasic acids. A detailed analysis has been presented using the experimental data of present work and also that reported in the literature. Apart from acid concentration and type of acid, other factors such as resin type and basicity are also discussed. It was found that, resins with high basicity are most suitable for the acid removal applications. For resins with medium and weak basicity, large variation in the sorption capacity with concentration was observed. A new theoretical approach incorporating effect of resin basicity has been proposed and examined qualitatively and quantitatively using the sorption data. The results substantiate reversibility of sorption through lower values of protonation equilibrium constants and also indicate incomplete resin salt dissociation in some cases.

Gas absorption into slurries containing fine catalyst particles

Abstract A cell model has been proposed to predict the enhancement of gas absorption rates into slurries containing catalyst particles which are smaller than liquid diffusion flim thickness. The model accounts for interparticle and particle—film interactions. The finite-element technique has been used to solve the model equations. Simulations have been carried out to study the effect of catalyst loading, particle diameter, and homogeneous reaction rate constant on enhancements of the rate of gas absorption. The experimental data available in the literature have been used to verify the model. The agreement has been found to be fair, keeping in view the limitations of the experimental data. An analytical model has also been proposed to predict the upper limit of the enhancement factor.

Steady dynamic friction at elastomer–hard solid interface: A model based on population balance of bonds

We present a model for the steady dynamic friction of a block of an elastomer, sliding steadily on a hard surface. The model uses population balance of the bonds between the hard surface and the polymer chains of the elastomer to estimate the force of friction. Although the basic premises of the present model are the same as those of the Schallamach model for dynamic friction (1963), the present formulation is a clearer representation of the phenomena involved. Moreover, the model is not based on the ergodic hypothesis and is therefore more versatile. It also allows us to correct the error in the expression for the force of friction in the Schallamach model. The present model exhibits the same qualitative trends as the Schallamach model. However, there are significant quantitative differences between the two models. We also show that our expression for the force of friction is equivalent to that obtained by the Chernyak and Leonov (1986) model, which is based on the ergodic hypothesis. The model is further modified to account for both the non-Hookean extension of the bonded chains and the viscous retardation effect. The model is validated using the experimental data of Vorvolakos and Chaudhury (2003) on sliding of crosslinked PDMS solid on silane coated silicon wafer. From this analysis, scaling laws, which relate the model parameters to the molecular weight of the polymer chains and the temperature, are derived and justified.

Ion-Exchange Studies in the Removal of Polybasic Acids. Anomalous Sorption Behavior of Phosphoric Acid on Weak Base Resins

Abstract Sorption behavior of phosphoric acid on the weak base resins Amberlite IRA-93 and Dowex WGR-2 is reported. Studies on sorption equilibria and dynamics reveal anomalous sorption behavior as compared to sorption of strong and weak monobasic acids. A mathematical treatment is developed to correlate the experimental data on sorption dynamics. An alternative type of mechanism is also proposed based on the results obtained in this work to explain the anomalous sorption behavior of phosphoric acid on weak base resins.

Problem associated with the use of TBP for LEM extraction of U(VI) and attempt to overcome this problem using other ligands

Suitability of TBP for recovery of uranium(VI) from dilute HNO3 using LEM extraction is investigated. TBP co-extracts significant amount of HNO3 along with U(VI). Beyond a critical time, extraction of U(VI) ceases due to attainment of critical acid level when the strip phase is unable to break TBP–U(VI) complex. The observed critical time is in good agreement with that estimated from rate of acid extraction. Optimal conditions at which the relative extraction of HNO3 is minimal with respect to U(VI) is arrived at. The extraction efficiency of TBP is compared with other ligands viz., TiAP, TEHP, TOPO, TOA and D2EHPA.

Elucidation of Band Structure of Charge Storage in Conducting Polymers Using a Redox Reaction

A novel technique to investigate charge storage characteristics of intrinsically conducting polymer films has been developed. A redox reaction is conducted on a polymer film on a rotating disk electrode under potentiostatic condition so that the rate of charging of the film equals the rate of removal of the charge by the reaction. The voltammogram obtained from the experiment on polyaniline film using Fe(2+)/Fe(3+) in HCl as the redox system shows five distinct linear segments (bands) with discontinuity in the slope at specific transition potentials. These bands are the same as those indicated by electron spin resonance (ESR)/Raman spectroscopy with comparable transition potentials. From the dependence of the slopes of the bands on concentration of ferrous and ferric ions, it was possible to estimate the energies of the charge carriers in different bands. The film behaves as a redox capacitor and does not offer resistance to charge transfer and electronic conduction.

On the Importance of Purification of Sodium Polystyrene Sulfonate

Ion exchange is commonly employed for purification of sodium polystyrene sulfonate (NaPSS), a molecule widely used as a model polyelectrolyte. However, the present work demonstrates that the ion exchange process itself may introduce some extraneous species into NaPSS samples by two possible mechanisms: (i) chemical transformation of polystyrene sulfonic acid (HPSS), a relatively unstable intermediate formed during ion exchange and (ii) release of small amount of “condensed” acid from cationic resins during the elution of NaPSS molecules. Based on these observations, it is proposed that simple dialysis is adopted as a standard protocol for the purification of primary NaPSS sample.

Co-Extraction of U(VI) and HNO3 Using TBP and its Higher Homologues TiAP and TEHP: Comparison of Equilibria, Kinetics, and Rate of Extraction

In this work, bulk-liquid membrane (BLM) system is used to compare tri-n-butyl phosphate (TBP), tri-isoamyl phosphate (TiAP), and tris(2-ethylhexyl) phosphate (TEHP) for their relative ability to co-extract U(VI) and nitric acid from aqueous nitric acid feed-phase into water strip-phase, through hydrocarbon membrane-phase. The kinetics of extraction is modelled and the model is validated through experiments. The quantity which determines the efficiency of liquid emulsion membrane (LEM) process is the relative rate of extraction of U(VI) to nitric acid. This is in the order TiAP>TEHP>TBP, indicating that TiAP is most suitable for extraction of U(VI) from nitric acid using LEM.

Stochastic simulation of polymer reactions

Abstract A procedure is developed for stochastic simulation of dynamics of polymer reactions in a homogeneous, batch or continuous flow reactor. The procedure is applicable to condensation-type reactions involving linear macromolecules, and yields the dynamic evolution of product microcomposition. A molecule is represented by an ordered set of group identifiers, group being segment of a molecule which is indivisible with respect to the reactions occurring in the system. Link is a reactive site between adjacent groups. The reactor space is a combination of vectors, representing the types of species in the reactor, their weights and the weights of the links associated with them. The occurrence of various events such as inflow, outflow, volatilisation and reactions, is regarded as random. A priori probabilities of occurrence of these events and magnitudes of the changes they bring about in the reactor space are related to their global rates. Deterministic bias and event scaling techniques are employed to improve accuracy of the simulation. The procedure is illustrated with a test example. The developed procedure is general in its applicability to stochastic modelling of any homogeneous, condensation-type polymerisation process.

Effect of conducting core on the dynamics of a compound drop in an AC electric field

Dynamics of 0.1M NaCl/castor oil/silicone oil compound drop in an alternating electric field of frequency 1 Hz was investigated experimentally in a parallel plate electrode cell. A novel yet simple method was used for producing the compound drop with different ratios of the core radius to shell radius. Deformation dynamics under both transient and cyclical steady states were recorded using high-speed imaging. We observed that with an increase in the radius ratio, deformation of the shell increases and that of the core decreases. The temporal deformation of the core always leads that of the shell. The phase lead between the core and the shell is independent of electric field strength and salt concentration in the core but strongly depends on the viscosity of the medium and radius ratio. At a small radius ratio, the breakup of the core is similar to the disintegration of the isolated drop in an infinite fluid; whereas the core attends a diamond-like shape at a high radius ratio before ejecting the small dro...