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Underground coal gasification (UCG) is a clean coal technology to utilize deep coal resources effectively. In-situ CO2-oxy coal gasification may eliminate the operational difficulty of the steam gasification process and utilize CO2 (greenhouse gas) effectively. Furthermore, it is necessary to convert the clean gasified energy from the UCG into clean combustion energy for an end-use. In order to achieve efficient clean power production, the present work investigates the thermodynamic feasibility of integration of CO2 based UCG with power generating systems operating in a chemical looping combustion (CLC) of product gas. The use of CO enriched syngas from O2/CO2 based UCG reduces the difficulty of the heat balance between a fuel reactor and an air reactor in a nickel oxygen-carrier based CLC system. Thermodynamic analyses have been made for various routes of power generation systems such as subcritical, supercritical and ultra-supercritical boiler based steam turbines and gas turbines for the UCG integrated system. It is shown, based on mass and energy balance analysis, that the integration of CO2 based UCG with the CLC system reduces the energy penalty of carbon capture and storage (CCS) significantly. A net thermal efficiency of 29.42% is estimated for the CCS incorporated system, which operates in a subcritical condition based steam turbine power plant. Furthermore, it is found that the efficiency of the proposed steam turbine system increases to 35.40% for an ultra-supercritical operating condition. The effect of operating temperature of the air reactor and the fuel reactor of the CLC system on the net thermal efficiency of combined cycle power plant is investigated. It is found that a net thermal efficiency of 42.53% can be obtained for the CCS incorporated combined cycle power system operating at an air reactor temperature of 1200°C. © 2014 Elsevier Ltd. Source


Pan S.C.,Indian Institute of Technology Guwahati
Beilstein Journal of Organic Chemistry | Year: 2012

Organocatalytic C-H activation reactions have recently been developed besides the traditional metal-catalysed C-H activation reactions. The recent non-asymmetric and asymmetric C-H activation reactions mediated by organocatalysts are discussed in this review. © 2012 Pan. Source


Malani R.S.,Indian Institute of Technology Guwahati
Journal of hazardous materials | Year: 2013

For degradation of biorefractory pollutants, enzymatic treatments and sonochemical treatments have shown high potential. A combined technique of sono-enzymatic treatment is of special interest as it has shown enhancement effect than the individual techniques. This work has attempted to give a mechanistic insight into the interaction of sonochemical and enzymatic treatments using immobilized horseradish peroxidase (HRP) enzyme on the decolourization of acid red dye (an azo dye). In order to segregate the effect of ultrasound and cavitation, experiments were conducted at elevated static pressure. The kinetic parameters of HRP, viz. Vmax and Km were marginally affected by immobilization. There was a minor change in pH optima and temperature optima for immobilized HRP (6.5, 25°C) from free HRP (7.0, 20-25°C). Though the specific activity of free enzyme (0.272U/mg) was found to be higher than the immobilized enzyme (0.104U/mg), immobilized enzyme exhibited higher stability (up to 3 cycles) and degradation potential than free enzyme in all experiments. The results revealed that the coupling of sonication and enzymatic treatment at high pressure in presence of polyethylene glycol (PEG) yielded the highest decolourization of acid red (61.2%). However, the total decolourization achieved with combined technique was lesser than the sum of individual techniques, indicating negative synergy between the sonochemical and enzymatic techniques. Copyright © 2013 Elsevier B.V. All rights reserved. Source


The diastereoselective self-assembly of five Cu(ii) heterochiral complexes containing a racemic Schiff base ligand LH (where LH = (R,S) 2-((1-(2-pyridyl)ethylimino)methyl)phenol in a chiral self-discriminating process is reported. Complexes 1-5 are synthesized using ligand LH, Cu(NO 3)2·3H2O, Cu(ClO4) 2·6H2O, and co-ligands such as N3 -, NCS-, NCO-, and are conclusively structurally characterized. Determination of the molecular structures of 1-5 confirmed the presence of a di-copper core with an inversion centre located directly between the two copper ions. In 1-5, each ligand in the di-copper core discriminates its own chirality and results in heterochiral dimerization in a chiral self-discriminating manner. The crystal packing pattern of compounds 1-5 are analyzed in terms of non-covalent C-H⋯O, C-H⋯N, C-H⋯π, and parallel displaced π⋯π interactions. In the crystal structure of compounds 1-4, there is a parallel displaced π⋯π interaction between the pyridine and benzene rings in the two adjacent heterochiral dimers, which act cooperatively with other different non-covalent interactions. In 2, the coordinated water molecule acts as a bifurcated H-bond donor to phenoxo-O and perchlorate-O in a diastereoselective and enantioselective manner, respectively. The results described here address new examples of the rarely occurring chiral self-discriminating process. This journal is © the Partner Organisations 2014. Source


Sarma A.K.,Indian Institute of Technology Guwahati
Journal of the Optical Society of America B: Optical Physics | Year: 2014

We carry out a modulation instability (MI) analysis in nonlinear complex parity-time (PT) symmetric periodic structures. All three regimes defined by the PT-symmetry breaking point or threshold, namely, below threshold, at threshold, and above threshold, are discussed. It is found that MI exists even beyond the PT-symmetry threshold, indicating the possible existence of solitons or solitary waves, in conformity with some recent reports. We find that MI does not exist at the PT-symmetry breaking point in the case of normal dispersion below a certain nonlinear threshold. However, in the case of the anomalous dispersion regime, MI does exist even at the PT-symmetry breaking point. © 2014 Optical Society of America. Source

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