Department Of Chemical Engineering

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Electrochemical energy, being a safe and clean renewable energy source, is gaining considerable attention in recent years. The electrochemical energy technologies available are numerous and the choice of technology is usually guided by heuristics. The paper presents a critical review and comparison of three competing electrochemical energy technologies (secondary batteries, fuel cells and flow batteries) based on various characterization criteria like energy &amp; power densities, cost, weight, efficiency, controllability, reliability etc. A rational framework is proposed to characterize the technology best suited for a particular application to achieve the best energy utilization. The idea is posed as a constrained multi objective optimization of design, followed by choice based on gravimetric and volumetric cost comparison of the three systems under consideration. For various combinations of characterization criteria, optimal choice of technology for an extensive scope of power and energy is found using the proposed framework and presented as area plots for easy understanding. This framework is then used to examine the prospects and directions of improvement for emerging technologies. Discussions are presented using the example of Vanadium Redox Flow Battery (VRFB). © 2021 Elsevier Ltd

World University root node

Renewable and Sustainable Energy Reviews

A systems engineering perspective on electrochemical energy technologies and a framework for application driven choice of technology

Hypothesis: Albeit solid stabilized emulsions are studied for several decades, the surface of the emulsion drops most often are coated with densely packed and jammed monolayer of particles. However, a control over the area that the particles occupy on the drop surface is necessary, especially in applications involving controlled release of active compounds from emulsions. We hypothesize that it is possible to achieve precise control over the concentration of particles on the surface of emulsions by tailoring the adsorption of different species in a multi-component dispersion used for emulsification. Experiments: To this end, we carry out emulsification of oil and aqueous dispersions consisting of a combination of oppositely charged colloidal particles and polyelectrolyte. The droplet size distribution and storage stability of the oil-in-water emulsions, the microstructure, the percentage area of the drop surface occupied by the particles and the adsorption behavior of particle-polyelectrolyte binary dispersions are investigated. Findings: Our results demonstrate that the association between oppositely charged colloidal particles and polyelectrolyte can be exploited to obtain surface active species that aid in the formation of emulsions. Moreover, we found that the concentration of particle-polyelectrolyte complexes and polyelectrolyte in the dispersions used in emulsification greatly influence the mean diameter of the emulsions and their microstructure. Our findings provide a strategy to achieve control over surface coverage of particles on the emulsion droplets across a wide range – from a theoretically possible maximum, ≈90%, to as low as ≈5%. Interestingly, the emulsions formulated are found to possess excellent storage stability irrespective of the particle coverage on the drop surface. © 2021 Elsevier Inc.

Journal of Colloid and Interface Science

Controlling the microstructure of emulsions by exploiting particle-polyelectrolyte association

Electronic waste (e-waste) constitutes an important component of solid waste, and recovering valuable chemicals and resources from it holds a high priority in solid waste management. The various chemical functionalities present in the organic fraction of e-waste can be converted to valuable chemicals and fuel molecules by pyrolysis process. In this study, non-isothermal pyrolysis of waste printed circuit board (PCB), waste keyboard keys (KB), and their equal composition mixture is conducted in a thermogravimetric analyzer at different heating rates. The kinetic analysis was carried out using isoconversional method of Vyazovkin and the multi-Gaussian distributed activation energy model (DAEM). The average apparent activation energies of pyrolysis of PCB, PCB: KB, and KB, determined using the Vyazovkin method, were 188.4, 167.6, and 169 kJ mol-1, respectively. The apparent activation energy determined using the DAEM varied in a wide range owing to the decomposition of multiple pseudo-components. Analytical pyrolysis coupled with gas chromatograph/mass spectrometer (Py-GC/MS) was used to identify the pyrolysates from PCB, KB, and their mixtures at 500 °C. The major pyrolysate functional groups from PCB were phenolic derivatives (36%), oxygenates (26%), and phenyl phosphates (14.4%), while KB pyrolysis yielded aromatics (52%) containing styrene as the major compound. Pyrolysis of mixtures resulted in a net increase in the selectivity to aromatics with a concomitant decrease in oxygenates suggesting dehydration and decarboxylation to be the major reactions. A significant amount of nitriles was produced from the pyrolysis of mixtures owing to the decomposition of acrylonitrile-butadiene-styrene plastic that constitutes KB. © 2021 Elsevier Ltd.

Journal of Environmental Chemical Engineering

Pyrolysis of electronic waste and their mixtures: Kinetic and pyrolysate composition studies

The current work is focused to investigate the synergetic interactions between biomass (groundnut shell, bagasse, rice husk, Prosopis juliflora, mixed wood sawdust) and hydro-rich plastics (Low-density polyethylene (LDPE) and Polyisoprene (PIP)) in microwave co-pyrolysis. The heating value of co-pyrolysis oil (38–42 MJ kg−1) was enhanced dramatically compared to biomass pyrolysis oil (20–28 MJ kg−1). Among biomasses studied, the energy yield of bio-oil obtained from rice husk with LDPE mixture is higher (42%). Whereas bio-oil from polyisoprene and groundnut shell mixture has the highest energy yield (78%). Each gram of co-pyrolysis feedstock consumed 12–18 kJ of incident microwave energy. An increase in overall energy efficiency in co-pyrolysis (62–70%) is observed compared to that of biomass pyrolysis (46–57%). Actual mass yield (31–47 wt%) of co-pyrolysis bio-crude is lower than its predicted value (42–57 wt%) due to the formation of lighter gases. In the combinations of and hydrogen-rich plastics considered in this study, it was found that co-pyrolysis of LDPE: bagasse has produced bio-crude with the highest yield of aliphatic hydrocarbons (25.78%), and co-pyrolysis of LDPE: rice husk has produced bio-crude with high selectivity of aromatics (11.7%). The extent of de-oxygenation was promoted in the co-pyrolysis due to synergy. © 2021 Elsevier Ltd

Renewable Energy

Biomass waste conversion into value-added products via microwave-assisted Co-Pyrolysis platform

This study is focused on evaluating the apparent kinetics of fast pyrolysis of different lignocellulosic biomass viz, rice straw, pine wood and empty fruit bunch. The goal of the study is to investigate the effect of biomass composition on kinetics, time evolution of pyrolysis vapors and the production of major bio-oil components during the fast pyrolysis of biomass. The isothermal mass loss data were generated at different pyrolysis times between two and sixty seconds in the temperature range of 400–700 °C. The data generated were then analyzed using various reaction models, viz., first-order model, diffusion models, contracting cylinder model and Avrami-Erofeev model to determine the rate constants and the rate parameters. Kinetic compensation effect was established using a large number of kinetic data reported in the literature to validate the results. The time evolution of major functional groups in the pyrolysates was analyzed using in-situ analytical pyrolyzer coupled with Fourier transform infrared spectrometer (Py-FTIR), and evolution of the volatiles was observed in time range of 5–60 s. Increase in pyrolysis temperature led to faster evolution of volatiles as evidenced by the shifting of maximum rate of vapor evolution to shorter time periods. © 2021 The Authors

Fulltext

Energy Conversion and Management: X

Fast pyrolysis kinetics of lignocellulosic biomass of varying compositions

BACKGROUND: Different formulae have been developed globally to estimate gestational age (GA) by ultrasonography in the first trimester of pregnancy. In this study, we develop an Indian population-specific dating formula and compare its performance with published formulae. Finally, we evaluate the implications of the choice of dating method on preterm birth (PTB) rate. This study's data was from GARBH-Ini, an ongoing pregnancy cohort of North Indian women to study PTB. METHODS: Comparisons between ultrasonography-Hadlock and last menstrual period (LMP) based dating methods were made by studying the distribution of their differences by Bland-Altman analysis. Using data-driven approaches, we removed data outliers more efficiently than by applying clinical parameters. We applied advanced machine learning algorithms to identify relevant features for GA estimation and developed an Indian population-specific formula (Garbhini-GA1) for the first trimester. PTB rates of Garbhini-GA1 and other formulae were compared by estimating sensitivity and accuracy. RESULTS: Performance of Garbhini-GA1 formula, a non-linear function of crown-rump length (CRL), was equivalent to published formulae for estimation of first trimester GA (LoA, - 0.46,0.96 weeks). We found that CRL was the most crucial parameter in estimating GA and no other clinical or socioeconomic covariates contributed to GA estimation. The estimated PTB rate across all the formulae including LMP ranged 11.27-16.50% with Garbhini-GA1 estimating the least rate with highest sensitivity and accuracy. While the LMP-based method overestimated GA by 3 days compared to USG-Hadlock formula; at an individual level, these methods had less than 50% agreement in the classification of PTB. CONCLUSIONS: An accurate estimation of GA is crucial for the management of PTB. Garbhini-GA1, the first such formula developed in an Indian setting, estimates PTB rates with higher accuracy, especially when compared to commonly used Hadlock formula. Our results reinforce the need to develop population-specific gestational age formulae.

Department Of Biotechnology

BMC pregnancy and childbirth

Comparison of first trimester dating methods for gestational age estimation and their implication on preterm birth classification in a North Indian cohort

Oppositely charged bipolar colloids or colloids decorated with complementary deoxyribonucleic acid (DNA) on their surfaces are special kinds of patchy particles where only patch and non-patch parts are attractive. These are classified as inverse patchy colloids (IPCs). In this work, equilibrium self-assembly of IPC in two-dimensions is reported using Monte Carlo simulations. Square (SCs) and triangular crystals (TCs) are found to be stable at 0.5 patch coverage. Upon decreasing the patch coverage to 0.33, the regular SC is destabilized; instead rhombic and TCs are found to be stable. At low patch coverages such as 0.22 and 0.12, only TC is stabilized at high density. Particles of all the patch coverages show kinetically stable cluster phases of different shapes and sizes at low densities, and the average cluster size depends on the patch coverage and particle density. State-diagrams showing all the stable phases for each patch coverage are presented. Ordered phases are characterized by bond order parameters ψ 4, ψ 6 and radial distribution function. The effect of polydispersity in patch coverage on the polarization of the stable structures are also studied. The study demonstrates that IPCs can stabilize various ordered two-dimensional structures by tuning the size of the patch, density and interaction strengths. © 2021 IOP Publishing Ltd.

Journal of Physics: Condensed Matter

Stabilizing ordered structures with single patch inverse patchy colloids in two dimensions

In this study, microwave-assisted co-pyrolysis of blends of Indonesian coal (IC) with Indian medium ash coal (MAC), Indian high ash coal (HAC) and coking coal (CC) was performed to evaluate the product yield and quality of the pyrolysis tar, and to understand the interactions during co-pyrolysis. The tar yields from pyrolysis of individual coals, viz., IC, HAC, MAC and CC were 26 ± 3 wt%, 14 ± 2 wt%, 12 ± 2 wt% and 11 ± 2 wt%, respectively. In co-pyrolysis, tar yields decreased with decrease in IC fraction in the mixture. Importantly, the experimental yields of products were similar to that calculated using the mixture rule. However, interactions were evident in the gas and char yields from pyrolysis of IC-rich mixtures, and the deviation from calculated values was in the range of 3–5 wt%. Pyrolysis tar from IC predominantly contained phenols, whereas tars from HAC, MAC, and CC contained aromatic hydrocarbons, phenols and aliphatic hydrocarbons. The interactions were evidenced in the form of enhanced selectivity to naphthalene derivatives and polyaromatic hydrocarbons with a concomitant reduction in the selectivity to simple phenols in the coal tar. Interactions were predominant in equal composition and IC-rich mixtures of IC:HAC, IC:MAC and IC:CC, which is due to the early formation of char via decomposition of IC. Hydrogen and methane constituted a major fraction of pyrolysis gases from MAC, HAC and CC and their blends, while the pyrolysis gas from IC was rich in H2 and CO2. Higher heating values of coal chars varied in the range of 21–27 MJ kg−1. © 2020 Energy Institute

Journal of the Energy Institute

Evidence of interactions in microwave-assisted co-pyrolysis of different varieties of coals

Power generation from coupled devices employing combustion in microreactors is generating interest for portable or decentralized energy demands. We develop a model framework to predict the performance of an integrated catalytic microreactor-thermoelectric generator (TEG) device, using CFD. A strategy for modeling a standalone TEG module is proposed and validated first, followed by thermally integrating it with a microreactor. The concepts of 1D global energy conservation with lumped treatment of the electrical properties are used to develop the TEG model. Multiple thermocouples, consisting of p- and n-type semiconductors connected in series, are modeled as a single block. The properties of the Seebeck coefficient, internal resistance, and thermal conductance are aggregated for the entire block and estimated as polynomial functions of temperature. These parameters can be estimated from manufacturer data. The source terms for Seebeck, Peltier, Thomson, and Joule’s effects are incorporated into the energy conservation equation to model the TEG at steady state. The TEG model is validated with experiments in the literature. The catalytic combustion of hydrogen in a microreactor is validated independently and is subsequently used for modeling a catalytic microreactor integrated with a TEG module for power generation. The power extracted by various load resistances from the coupled device, at multiple values of inlet flow rates, is calculated and shows a good comparison with experimental data in the literature. © 2021 American Chemical Society.

Energy and Fuels

Modeling of thermal integration of a catalytic microcombustor with a thermoelectric for power generation applications

Desiccation cracks in colloidal deposits occur to release the excess strain energy arising from the competition between the drying induced shrinkage of the deposit and its adhesion to the substrate. Here we report remarkably different morphology of desiccation cracks in the dried patterns formed by the evaporation of sessile drops containing colloids on elastomer (soft) or glass (stiff) substrates. The change in the crack pattern, i.e., from radial cracks on stiff substrates to circular cracks on soft substrates, is shown to arise solely due to the variation in elasticity of the underlying substrates. Our experiments and calculations reveal an intricate correlation between the desiccation crack patterns and the substrate's elasticity. The mismatch in modulus of elasticity between the substrate and that of the particulate deposit significantly alters the energy release rate during the nucleation and propagation of cracks. The stark variation in crack morphology is attributed to the tensile or compressive nature of the drying-induced in-plane stresses. © 2021 American Physical Society.