1,720,964 research outputs found
Polyaniline doped ultrafiltration membranes: Mechanism of membrane formation and pH response characteristics
No full textInterplay of thermodynamic instability and kinetic effects during formation of polymeric membrane using polyaniline (PANI) as additive are studied along with the pH responsive characterization of the membranes. PANI membranes exhibit pH responsive permeability hysteresis having >30% variation between the two end points. Effect of pH on mechanical strength, contact angle, surface pore size and roughness, etc was studied in detail. It was observed that PANI molecules shrunk in acidic pH whereas, in alkaline pH, swelling occurred leading to increase in size of PANI molecule from 40 μm at pH 2–88 μm at pH 12. Mechanism of membrane pore constriction was proposed based on swelling of PANI in response to pH change and hydrogen bonding. Change in porosity with pH gets reflected by highest rejection of dextran at pH 12 (71%) followed by pH 7 (57%) and pH 2 (50%)
Transport model-based prediction of polymeric membrane filtration for water treatment
No full textModelling is an integral part of the design, development, and scale-up of membrane-based separation processes. Among the different modelling approaches, transport phenomena-based models are thorough and versatile. This chapter focuses on various methodologies of transport phenomena-based models to quantify the mass transfer through the membranes. Typically, there are two flow domains in which the modelling is carried out: inside the flow channel and inside the membrane. These two domains are interconnected by the interface boundary condition at the membrane surface. The mass transfer problem in the flow channel can be solved by using numerical methods or semianalytical techniques, such as the similarity solution or approximate integral method. The governing equation for the solute and solvent transport within the membrane phase can be tailor-made depending on the nature of the membrane and solute. The solvent flux through the membrane is generally dictated by the osmotic pressure model. The solute flux through the membrane is governed by (1) the solution-diffusion model for a dense reverse osmosis membrane, (2) the extended Nernst Planck equation for the transport of ions through the charged pores of the membrane, and (3) merely the definition of real retention in the case of ultrafiltration membrane in which the size exclusion is the primary concern. However, these generalities will be modified to account for the physical nature of the membrane fouling, that is, whether the filtration is purely osmotic pressure controlling or purely gel polarization governed. The modelling of mixed matrix membrane is rather complicated, owing to solute adsorption in the membrane matrix. All these issues influence the modelling pathways and are discussed extensively in this chapter. In a nutshell, this chapter is a complete guide to understand the modelling of the membrane separation process validated by using synthetic as well as real solutions that include brackish water and textile and tannery effluent streams
Arsenic removal from drinking water using treated laterite-based adsorbent
No full textAccess to safe drinking water is an essential element for sustainable life. Arsenic poisoning in groundwater has been a cause of concern since decades and is one of the most hazardous contaminants of potable groundwater. The major sources of contamination are geogenic, agricultural, and industrial as well. This chapter presents the development of a novel adsorbent using naturally occurring laterite soil that has proved to be an excellent material for the removal of arsenic from groundwater. Natural laterite has been acid-activated using acid alkali treatment process under optimized process conditions to prepare treated laterite (TL) having 40 times higher adsorption capacity compared to the untreated material. The enhanced adsorption capacity of 8 mg/g for As(III) and 24.1 mg/g for As(V) is the highest among all natural adsorbents or their derivatives reported so far and also has the advantage of a granular nature that rules out high-pressure drop during operation. The adsorbent also meets the safe disposal guidelines and can even be used for road laying purpose without any risk of leaching. The laboratory-scale column run experiments are carried out to study the effect of incoming concentration, flow rate, bed height, and the presence of co-ions. The adsorption equilibrium and kinetics using TL as an adsorbent are studied in detail, and a kinetic model has been established. The model parameters required for upscaling are determined by comparing with the experimental results. Different aspects of scale-up of the technology in the form of integrated filters designed for domestic applications (capacity 100 L/day) as well as community-scale filters (capacity 2 m3/h) are discussed in brief. A transport-based model to predict the permeate concentration and filter life is also presented in detail that can be of immense help at different stages of product life, including design, installation, and maintenance
Modeling of cross flow hollow fiber ultrafiltration for treatment of effluent from Railway Workshop
No full textIndustrial oily water containing oil, grease and dust has been treated using stage-wise filtration, first by sand bed followed by cross-flow ultrafiltration hollow fiber membrane. The sand bed removes majority of suspended particles and reduces the turbidity from 13.6 NTU to 2.6 NTU. Effects of transmembrane pressure drop and cross flow rate on ultrafiltration performance were investigated. A transport phenomena based model under the framework of boundary layer theory was developed to quantify the flux decline and oil transport through the membrane during cross flow filtration in hollow fiber. The model results matched remarkably well with the experimental data. The mechanism of filtration was analyzed and found to be governed by cake formation. Formation of cake-layer was supported by scanning electron micrography of fresh and fouled membranes and Fourier Transform Infrared spectroscopy. The modeling of separation mechanism and estimates system parameters will aid in scaling up of the filtration set-up to industrial scale for treatment of industrial effluent containing oil
Permeability hysteresis of polypyrrole-polysulfone blend ultrafiltration membranes: study of phase separation thermodynamics and pH responsive membrane properties
No full textPolypyrrole (PPy) is a promising conducting polymer with tunable redox properties that were exploited to prepare pH sensitive smart membranes. These membranes exhibited permeability hysteresis having >75% variation between the two extreme pH values. The morphological changes were studied using field emission scanning electron microscopy and atomic force microscopy. Membrane zeta potential also changed from −10 mV at pH 3 to −25 mV at pH 9. The synergistic effect of pore constriction along with electrostatic interaction due to high negative membrane zeta potential resulted into increase in bovine serum albumin rejection from 68% at pH 3 to 98% at pH 12. The mechanism of pore shrinking was proposed based on structural changes of PPy and confirmed using Fourier transform infra red spectroscopy. Thermodynamic modeling was carried out using Flory-Huggins theory of polymer solution to obtain ternary phase diagram of PPy-polysulfone membrane systems. Solubility parameter of PPy, required for modeling, was determined by group contribution method. Binodal curves at varying PPy concentration were used to quantify thermodynamic hindrance. Trade-off between thermodynamic hindrance and kinetic enhancement of phase inversion was used to predict membrane morphology and permeation characteristics. Model based predictions were validated using morphology and permeability trends available in literature
Modeling aspects of membrane-based industrial wastewater treatment
No full textMembrane-based separation processes have been widely used for the treatment of industrial effluent streams, considering their wide range of applicability and easy scale-up. The effluent streams usually consist of a mixture of interacting as well as noninteracting components. The physical and transport properties of these constituents, viz., the diffusivity properties of the cake layer deposited over the membrane surface, etc., are very important for modeling and cannot be determined experimentally. Lab scale filtration data can be utilized to determine these parameters for specific contaminants. The modeling of membrane performance has been carried out extensively focusing mainly on predicting the permeate flux. However, prediction of the quality of the filtrate is also very important considering the stringent requirement of the quality of the treated effluent. This chapter mainly focuses on various aspects of modeling of membrane-based separation process used for the industrial applications. This will be useful in predicting the efficiency and throughput of the filtration system and hence aiding in the scaling up
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Modeling of solution thermodynamics: A method for tuning the properties of blend polymeric membranes
No full textThermodynamics of polymer blends are modeled and ternary phase diagrams are plotted for various blend compositions using Flory-Huggins theory for polymer solutions. Equations of spinodal curve and plait point for the quaternary systems are derived based on solution thermodynamics. Binodal curves are calculated by minimizing Gibb's free energy for blend system, poly(acrylonitrile) and poly(urethane). Effects of polymer molecular weight and interaction parameters on the phase diagram are quantified. The published data of membrane transport characteristics are correlated with the modeled phase diagram and validated using FESEM and pore-diameter analysis. The reason for increase in the permeability of blend membranes is established with structural changes with the possible formation of hydrogen bond and justified by the infrared spectra analysis of the blend membranes
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