Department of Chemical Engineering

Indian Institute of Technology Hyderabad (IITH) is a premier institute of science and technology established in 2008. IITH has been consistently ranked in the&nbsp;<a href="https://iith.ac.in/reports/" rel="noopener noreferrer">top 10 institutes</a>&nbsp;in India for Engineering&nbsp;<a href="https://www.nirfindia.org/2021/EngineeringRanking.html" rel="noopener noreferrer" target="_blank">according to NIRF</a>&nbsp;making it one of the most coveted schools for science and technology in the country.

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IIT Hyderabad

Nano-sized, high surface area TiO2, synthesized by a solution combustion method, was employed for the photodegradation of poly(bisphenol-A- carbonate) in solution. The products formed during degradation were detected using UV-Vis spectroscopy, FT-IR and GC/MS. The mechanism of breakage during photocatalytic degradation can be attributed to concerted rearrangement (Photo-Fries) and non-concerted cage recombination (oxidation). The degradation was followed by determining the molecular weight distribution using gel permeation chromatography (GPC) and modeled with continuous distribution kinetics. The mode of breakage was purely by random chain scission and showed the presence of weak and strong photodegradable links. The presence of combustion-synthesized TiO2 catalyst did not alter the degradation mechanism but increased the degradation rates by an order of magnitude compared to the photodegradation rate. However, the presence of commercial Degussa P-25 catalyst did not cause a significant increase in degradation rates compared to the photodegradation rate. The higher photoactivity of combustion-synthesized TiO2 compared to that of Degussa P-25 for the photodegradation of polycarbonate may be due to reduced band-gap, higher hydroxyl content, higher surface area, nano-size and crystallinity of the combustion-synthesized TiO 2. © 2004 Elsevier B.V. All rights reserved.

World University root node

Applied Catalysis A: General

Photocatalytic degradation of poly(bisphenol-A-carbonate) in solution over combustion-synthesized TiO2: Mechanism and kinetics

Reactive mixing in liquids can be quantitatively described by combining chemical kinetics and hydrodynamics so that dispersed reactants interact at evolving fluid-element interfaces. For the batch reactor we postulate that the dispersed fluid elements are fragmented in a cascade of increasingly smaller sizes and larger interfacial area. The reversible fragmentation-coalescence is described by a population dynamics equation that has an exact self-similar solution for the size distribution as a function of time. Two types of competitive reaction kinetics incorporating a diffusion-limited fast reaction satisfy nonlinear differential equations, written in terms of moments of the time-dependent dispersed-fluid size distribution. Applying a compressed time variable to transform to a simple system of differential equations readily solves the nonlinear equations. The straightforward solutions display realistic effects of dispersed fluid volume fraction, rate parameters, and initial concentrations. Final fractional conversions, occurring when the limiting reactant is depleted, are functions of a Damkohler number, volume fraction of dispersed reactant, and scaled initial conditions. © 2004 American Institute of Chemical Engineers.

AIChE Journal

Kinetics and Reactive Mixing: Fragmentation and Coalescence in Turbulent Fluids

Background: The phenomenon of switch-like response to graded input signal is the theme involved in various signaling pathways in living systems. Positive feedback loops or double negative feedback loops embedded with nonlinearity exhibit these switch-like bistable responses. Such feedback regulations exist in insulin signaling pathway as well. Methods: In the current manuscript, a steady state analysis of the metabolic insulin-signaling pathway is presented. The threshold concentration of insulin required for glucose transporter GLUT4 translocation was studied with variation in system parameters and component concentrations. The dose response curves of GLUT4 translocation at various concentration of insulin obtained by steady state analysis were quantified in-terms of half saturation constant. Results: We show that, insulin-stimulated GLUT4 translocation can operate as a bistable switch, which ensures that GLUT4 settles between two discrete, but mutually exclusive stable steady states. The threshold concentration of insulin required for GLUT4 translocation changes with variation in system parameters and component concentrations, thus providing insights into possible pathological conditions. Conclusion: A steady state analysis indicates that negative feedback regulation of phosphatase PTP1B by Akt elicits bistability in insulin-stimulated GLUT4 translocation. The threshold concentration of insulin required for GLUT4 translocation and the corresponding bistable response at different system parameters and component concentrations was compared with reported experimental observations on specific defects in regulation of the system. © 2004 Giri et al; licensee BioMed Central Ltd.

Fulltext

Theoretical Biology and Medical Modelling

A steady state analysis indicates that negative feedback regulation of PTP1B by Akt elicits bistability in insulin-stimulated GLUT4 translocation

The epoxy-polymerization process can be better understood by investigating the underlying optimization problem involving a number of conflicting objectives and more than 20 decision parameters. A combination of minimization or maximization of objectives, such as the number average molecular weight, polydispersity index and reaction time, are considered in this paper. The first two objectives are related to the properties of a polymer, whereas the third objective is related to productivity of the polymerization process. The decision variables are addition quantities of various reactants, e.g. the amount of addition for bisphenol-A (a monomer), sodium hydroxide and epichlorohydrin at different time steps (modeled in a semi-batch operation), whereas the satisfaction of all species balance equations is treated as constraints. A multi-objective evolutionary algorithm (the elitist non-dominated sorting genetic algorithm or NSGA-II) is used to obtain a set of non-dominated solutions in a single simulation run. The results show a substantial improvement (with about 300% more productivity) over the benchmark condition (reported by performing a one-time addition of reactants in the beginning in a batch process). Importantly, this study brings out a salient aspect of using an evolutionary approach to multi-objective problem solving. The availability of multiple optimal trade-off solutions allows a process engineer to have salient information about the polymerization process. Changes in the distribution of various polymer species in the course of polymerization process as observed among various. Pareto-optimal solutions are identified and explained for this purpose. Such information provide important information about optimal operating conditions corresponding to different trade-offs among objectives, which are otherwise difficult to obtain. The systematic approach of starting from the two-objective problems to capture the essential features of interesting optimal operating conditions to finally solving the three-objective problem associated with the epoxy-polymerization problem in discovering the optimal trade-off interactions should motivate further such studies on other chemical process optimization problems. Overall, this paper demonstrates how fundamental optimization principles can be used systematically and reliably to find optimum operating conditions for complex chemical process operations. © 2004 Elsevier Ltd. All rights reserved.

Chemical Engineering Science

Towards a better understanding of the epoxy-polymerization process using multi-objective evolutionary computation

Separation of organic-organic mixtures using membrane separation techniques is being investigated extensively owing to its great importance in chemical and petrochemical industries. Pervaporation is today considered as a basic unit operation for separation of organic-organic liquid mixtures because of its efficiency in separating azeotropic and close-boiling mixtures, isomers and heat-sensitive compounds. Membranes used for separating the four major categories of organic-organic mixtures viz., polar/non-polar mixtures, aromatic/alicyclic mixtures, aromatic/aliphatic mixtures, aromatic isomers are made of materials that are organic as well as inorganic in nature. A considerable amount of background information related to the developments in the field, and the current trends of industrial pervaporation are dealt with. This review seeks to define the current scientific, and technological factors that govern the field of application of membranes for separation of organic mixtures. Potential membrane materials for further research in this area are also discussed. © 2004 Elsevier B.V. All rights reserved.

Journal of Membrane Science

Separation of organic-organic mixtures by pervaporation - A review

The interaction between surface components on the invading pathogen and host cells such as platelets plays a key role in the regulation of endovascular infections. However, the mechanisms mediating Staphylococcus aureus binding to platelets under shear remain largely unknown. This study was designed to investigate the kinetics and molecular requirements of platelet-S. aureus interactions in bulk suspensions subjected to a uniform shear field. Hydrodynamic shear-induced collisions augment platelet-S. aureus binding, which is further potentiated by platelet activation with stromal derived factor-1β. Peak adhesion efficiency occurs at low shear (100 s -1) and decreases with increasing shear. The molecular interaction of platelet αIIbβ3 with bacterial clumping factor A through fibrinogen bridging is necessary for stable bacterial binding to activated platelets under shear. Although this pathway is sufficient at low shear (≤5400 s-1), the involvement of platelet gpIb and staphylococcal protein A through von Willebrand factor bridging is essential for optimal recruitment of S. aureus cells by platelets in the high shear regime. IgG plays an inhibitory role in the adhesion process, presumably by interfering with the binding of von Willebrand factor to staphylococcal protein A. This study demonstrates that platelet activation and a fluid-mechanical environment representative of the vasculature affect platelet-S. aureus cell-adhesive interactions pertinent to the process of S. aureus-induced bloodstream infections.

Journal of Immunology

Fluid shear regulates the kinetics and receptor specificity of Staphylococcus aureus binding to activated platelets

The solar photocatalytic degradation of various dyes such as methylene blue (MB), remazol brill blue R (RBBR) and orange G (OG) has been studied over combustion synthesized nano TiO2 and the activity was compared with that of commercial Degussa P-25 TiO2 under similar conditions. The effect of catalyst loading, initial concentrations of the dyes and the deactivation studies of the catalysts were also investigated. The catalyst was characterized by techniques like X-ray diffraction (XRD), BET, gravimetric-differential thermal analysis (TG-DTA), IR and UV absorption. The initial degradation rates with combustion synthesized nano TiO2 was 20 times higher for RBBR, 4 times higher for MB and 1.6 times higher for OG, compared to Degussa P-25 TiO2. The enhanced photocatalytic activity of combustion synthesized catalyst is attributed to the crystallinity, nano-size, large amount of surface hydroxyl species and reduced band-gap. © 2003 Elsevier B.V. All rights reserved.

Applied Catalysis B: Environmental

Solar photocatalytic degradation of dyes: High activity of combustion synthesized nano TiO2

The ultrasonic degradation of poly(bisphenol A carbonate), poly(ε-caprolactone), and poly(vinyl acetate) was investigated with various solvents such as benzene, monochlorobenzene, and dichlorobenzene. The time evolution of molecular weight was determined using gel permeation chromatography. A limiting molecular weight was observed for all the systems and was a function of solvent properties. The degradation rates increased with increase in viscosity and decrease in vapor pressure. The polydispersity reached a maximum before reaching a constant value at longer times. The experimental data indicate that the breakage of the polymer is around midpoint, with a distribution rather than an ideal midpoint scission. A continuous distribution model with a stoichiometric kernel based on Lorentzian probability distribution function was developed to satisfactorily model the experimental data. © 2004 American Institute of Chemical Engineers.

Distributed midpoint chain scission in ultrasonic degradation of polymers

The thermal degradation of various vinyl polyperoxides (poly(styrene peroxide) [PSP], poly(methyl methacrylate peroxide) [PMMAP], poly(α-methyl styrene peroxide) [PAMSP]) and their binary copolyperoxides (PSP-PAMSP [SA], PSP-PMMAP [SM], PAMSP-PMMAP [AM]) were studied in a Thermogravimetric Analyzer (TGA). The thermal stability of the polyperoxides is in the order of PMMAP>SM>AM>SA>PSP>PAMSP. The addition of PAMSP to PSP showed a synergistic effect with higher thermal stability of the copolymer while the addition of PAMSP or PSP to PMMAP did not affect the thermal degradation of the copolymers. A method based on regression was proposed to determine the degradation parameters. The activation energies of degradation for the homopolyperoxides and copolyperoxides were determined by various methods and found in agreement with each other. © 2004 Elsevier Ltd. All rights reserved.

Polymer Degradation and Stability

Thermal degradation kinetics of vinyl polyperoxide copolymers

The esterification of palmitic acid with ethanol was investigated at various temperatures (35-70°C) in the presence of three lipases (Novozym 435, Lipolase 100T, and hog pancreas lipase) in supercritical carbon dioxide (SCCO2) and under solvent-free conditions. All enzymes showed an optimum temperature of 55°C under both conditions. The effect of water and ethanol addition on the esterification of acid was also investigated. The conversion obtained in SCCO2 and under solvent-free conditions with Novozym at optimal conditions was 74 and 97%, respectively. Although a higher apparent yield was obtained under the solvent-free conditions due to higher substrate and enzyme concentrations, the reaction in supercritical carbon dioxide is better because of lower enzyme loading, higher reaction rates and easier downstream processing.