Siddhartha Datta

Studies on transport mechanism of Cr(VI) extraction from an acidic solution using liquid surfactant membranes

Abstract A mathematical model for analysing the extraction of Cr(VI) from aqueous acidic solution by emulsion liquid membrane using Aliquat 336 as extractant and NaOH as stripping agent has been presented. The existing models developed so far do not account for the existence of different forms of Cr(VI) ions in the aqueous phase depending on pH conditions. Accordingly, in the present model, reaction equilibrium has been considered instead of distribution coefficient to represent realistically the transport mechanism for this type of system through liquid surfactant membrane. Unlike other models, liquid–liquid equilibrium of sodium hydroxide-chloride of Aliquat 336 has also been considered. The carrier thus exists in the membrane phase in hydroxide and chloride forms and extraction of hexavalent chromium from the external phase proceeds by the two carriers. The validity of the model has been checked from comparison of the simulated curves and experimental data using chemical reaction equilibrium constant and D eff / R 2 as fitting parameters.

Analysis of the performance of a continuous membrane bioreactor with cell recycling during ethanol fermentation

Abstract The effects of the introduction of cell recycling on ethanol productivity were examined for a continuous membrane fermentor-separator (CMFS) with continuous removal of ethanol by pervaporation. Modifications of the Ghose-Tyagi specific growth rate model and the Luedeking-Piret production model were used to formulate and simulate the CMFS model. The effects of pervaporation for systems with and without a cell separator were compared in terms of yeast cell density, substrate utilization, ethanol concentration in the fermentation broth and productivity. The results demonstrate that the elimination of cell wash-out allows the CMFS with cell separator unit to operate at a very high value of dilution rate and increases the productivity of ethanol at the same value of the pervaporation factor (PF) compared with a system without cell separator. An increase in the value of PF always results in an increase in ethanol productivity.

Treatment of leather industry wastewater by aerobic biological and Fenton oxidation process.

Degradation of leather industry wastewater by sole aerobic treatment incorporating Thiobacillus ferrooxidans, Fentons reagents, and combined treatment was investigated in this study. The sole treatment by Fentons oxidation involving the introduction of 6g FeSO(4) and 266 g H(2)O(2) in a liter of wastewater at pH of 3.5 and 30 degrees C for 30 min at batch conditions reduced COD, BOD(5), sulfide, total chromium and color up to 69%, 72%, 88%, 5%, 100% and T. ferrooxidans alone showed maximum reduction to an extent of 77, 80, 85, 52, 89, respectively, in 21 d treatment at pH 2.5, FeSO(4) 16 g/L and temperature of 30 degrees C. The combined treatment at batch conditions involving 30 min chemical treatment by Fentons oxidation followed by 72 h biochemical treatment by T. ferrooxidans at batch conditions gave rise up to 93%, 98%, 72%, 62% and 100% removal efficiencies of COD, BOD, sulfide, chromium and color at pH of 2.5 and 30 degrees C. Decrease in photo absorption of the Fentons reagent treated samples, as compared to the banks, at 280, 350 and 470 nm wave lengths was observed. This may be the key factor for stimulating the biodegradation by T. ferrooxidans.

Effect of drop size distribution on mass transfer analysis of the extraction of nickel(II) by emulsion liquid membrane

In the separation process using emulsion liquid membranes, the polydispersity affects mass transport of metal ions from the external phase because under steady operating conditions, drop size and size distribution are proportional to the interfacial area. The present study aims to assess the importance of polydisperse character of the emulsion globules. An advancing reaction front model considering emulsion globules of various sizes with same sauter mean diameter has been proposed for this purpose. In this paper, the important variables affecting sauter mean diameter of the emulsion drops, including injection method of emulsion, stirring speed, oil phase viscosity, composition of inner water phase and solute permeation rate are also systematically investigated.

Simulation of unstirred batch ultrafiltration process based on a reversible pore-plugging model

Abstract An unsteady state mass transfer model has been developed taking into account the effect of reversible pore plugging by the diffusing solute molecules. The osmotic pressure model has been used to predict the membrane surface concentration. The rate of available fractional area of the membrane that is blocked at any time due to pore plugging phenomenon has been assumed to be the function of dimensionless membrane surface concentration prevailing at that time. Experimental data generated in this study using cellulose acetate membrane of 5000 MWCO and polyethylene glycol (PEG)-6000 as solute in unstirred batch configuration has been used to find the appropriate nature of the above-mentioned function. Once the functional dependency between the rate of fractional area blocked and dimensionless membrane surface concentration has been found, it can be used to simulate flux and rejection behaviour during unstirred batch ultrafiltration (UF). The predicted results show very good agreement with the experimental data and the average deviations for all the cases are found to be well within ±10%.

Analysis of polarized layer resistance during ultrafiltration of PEG-6000: an approach based on filtration theory

A mathematical model based on filtration theory, coupled with resistance in series model and gel polarization/film model has been developed in the present study. Unlike the cake filtration equipment where cake deposition continues until the wash cycle comes, in case of continuous stirred ultrafiltration the deposited solutes are allowed to build up over the membrane indefinitely, along with continuous back transport of deposited solutes into bulk by the turbulence created by stirring action. To account for this back transport, a coefficient called back transport coefficient has been defined which is found to be independent of any operating variables. Variation of polarized layer resistance was also studied with different operating variables like bulk concentration, stirrer speed and pressure differential. A correlation was also developed relating polarized layer resistance with those operating variables. A comparative study has been made between experimentally found polarized layer resistance value, using ultrafiltration data of Bhattacharjee and Bhattacharya, with those found from correlation and this developed model based on filtration theory. The model has been found to predict the polarized layer resistance reasonably well once the three parameters describing the model viz. permeability coefficient, back transport coefficient and membrane hydraulic resistance are known along with the operating condition. Using the above-mentioned parameters, it is also possible to predict flux and/or total permeate volume at any time under a given operating condition.

A new model of batch-extraction in emulsion liquid membrane: Simulation of globule-globule interaction and leakage

Abstract The present paper seeks to provide an understanding of the possible effect of interaction between emulsion globules, on batch extraction, utilising emulsion liquid membranes. The conventional reversible model of Bunge and Noble (1984) considers an isolated globule, for explaining type-1, reaction-facilitated transport. Their basic approach has been extended here through Monte Carlo simulation of a system of emulsion globules, interacting via coalescence-redispersion. Collision of such an interacting pair results in internal circulation in membrane phase of globules and causes mixing of solute existing therein. This translates into faster solute penetration inside the globule. Hence, solute depletion rate in the external phase is enhanced, over and above that of a diffusion-limited reaction. In experiments, at high stirring speeds involving extraction of weakly basic amines with a strong internal phase acid ( Baird et al., 1987 ), this trend has been observed during the initial period. A further shortcoming of the reversible model is that it overpredicts the maximum extraction achieved in these experiments, which is corrected by introducing leakage of internal drops during redispersion.

Chapter 4 – Emulsion Liquid Membranes: Definitions and Classification, Theories, Module Design, Applications, New Directions and Perspectives

Publisher Summary The objective of this chapter is to provide comprehensive knowledge-based information by critical analysis, classification, model description, and applications of a variety of emulsion liquid membrane (ELM) separation processes. It also discusses new perspectives and directions of development in these fields. Liquid membrane separations have been extensively examined for potential application in many fields such as metal recovery, gas separation, organic compound removal, pollutant removal, and bioseparations. The difficulties in the application of these processes did not consist in sophisticated equipment or installation but in the adequate choice of reagent to allow the selective extraction of solute in required quantity. The widespread use of the ELM process has been limited due to the instability of emulsion globules against fluid shear. Numerous studies have attempted to enhance the stability of ELMs. Examples include adding more surfactants into the membrane phase and increasing the membrane viscosity. However, in most reported attempts increased stability has been unfortunately accompanied by loss in extraction efficiency and rate. A unique contacting device, a Taylor-Couette column, provides a relatively low and uniform fluid shear that helps maintain the stability of emulsion without compromising the extraction efficiency of a target compound. Current research has also been directed to minimizing membrane leakage or rupture through the use of bifunctional surfactants, which act as both emulsifier and extractant, and on additives (e.g., polymer) to impact elasticity of membrane.

Study of the Stability of W/O/W-Type Emulsion During the Extraction of Nickel via Emulsion Liquid Membrane

ABSTRACT Considerable effort has been directed toward describing the analysis of mass-transfer resistance for solute diffusion and reaction in an emulsion liquid membrane (ELM) system but very little attention has been paid to the loss of extraction efficiency often encountered in these systems due to rupture of the emulsion globules. In the present work, batch extraction of nickel(II) with ELM from a dilute sulfate solution by using di-(2-ethylhexyl) phosphoric acid (D2EHPA) as an extractant and hydrochloric acid as a stripping agent is reported. However, separation efficiency significantly decreases with breakage of the liquid membrane. Important variables affecting the stability of the emulsion, such as pH of the feed phase, speed of agitation, emulsion drops size per unit specific interfacial area, surfactant concentration, pH in inner aqueous phase, and the presence of different tracers, are systematically investigated during the extraction of nickel(II) ions.

A mass transfer model for the prediction of rejection and flux during ultrafiltration of PEG-6000

Abstract A mass transfer model in case of ultrafiltration is proposed in the present study which is capable of predicting the permeate volumetric flux and rejection at different pressure, concentration and stirrer speed. The model is based on the steady state mass balance over the boundary layer, coupled with the results from irreversible thermodynamics. It first predicts the membrane surface and permeate concentrations — which are then utilized to calculate rejection. Permeate flux is then predicted using the result obtained from filtration theory. The model utilizes four parameters, namely, solvent permeability, solute permeability, reflection coefficient and specific cake resistance. These parameters along with the known values of the operating conditions and solution properties enable one to predict the flux as a function of time and rejection. The computed results are found to be in good agreement with the previously published data of Bhattacharjee and Bhattacharya during ultrafiltration of PEG-6000 by cellulose acetate membrane.