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Ph.D. (Texas A&M University)
Professor & Associate Faculty of the unit
Solid State and Structural Chemistry Unit
Indian Institute of Science
Bangalore – 560012, India
E-mail: giridhar@chemeng.iisc.ernet.in
giridharmadras@gmail.com
Web: http://chemeng.iisc.ernet.in/giridhar/
Tel.: +91 (0)80 22932321
Fax: +91 (0)80 23608121

Our research group focuses on reaction kinetics, as applied to various systems and processes:

Reactions with macromolecules.
The study of thermolytic degradation of polymers is of considerably importance both from practical and theoretical standpoints. Among the various applications, degradation has been extensively used to recycle waste plastics, convert plastics into useful end products. Degradation of plastics in solution is a new process and we are studying the kinetics and degradation rate of various polymers in solution. Due to high heat transfer rates, the degradation temperature is much lower than the degradation temperature of the polymer in pyrolysis. This process is of considerable interest since we are able to convert plastic waste to useful end products like fuel oil. We have recently extended our investigations to the degradation of polymers in supercritical fluids. We have shown that the mechanism of polymer degradation is considerably different and unique in these cases. We have developed continuous distribution kinetic models to determine the rate parameters and the activation energies for polymer degradation from the time evolution of the molecular weight distributions.
The conventional technique for polymerizations and depolymerizations has been the use of thermal energy. We have investigated the use of ultrasound, acids, microwaves and UV light as a means for polymerization and degradation. Based on the current studies, it has been determined the rates are considerably enhanced by the use of these non-conventional techniques. The kinetics of the reactions are investigated and radical mechanisms are proposed to satisfactorily explain the experimental data.
The future of the plastic industry depends on its ability to synthesize biodegradable polymers of the required strength and durability. We have developed new methods to synthesize these biodegradable polymers.

Catalytic reactions:
Our approach is to develop several new materials that are used as catalysts for known reactions. We also propose new reaction pathways/ mechanisms providing us with a method to develop new materials with superior properties. In this regard, we have synthesized new materials that work as photocatalysts for the degradation of a wide variety of dyes and organics that are common pollutants in waste water. We have also developed new catalysts for the three way catalysis for the NO+CO reaction and CO and hydrocarbon oxidation and proposed new mechanisms governing these reactions.

Reactions and separations in supercritical fluids:
A fluid heated to above the critical temperature and compressed to above the critical pressure is known as a supercritical fluid. Supercritical fluids have proven useful for the processing of biological materials and may provide an attractive alternative solvent for enzymatic catalysis. We have developed an indigenous high pressure reaction system to carry out the enzymatic reactions in supercritical fluids. We are studying the use of lipases for transesterfication, esterification and hydrolysis reactions, which result in products that are used in the pharmaceutical and food industries. These reactions are diffusion limited and are usually carried out in non-aqueous media. We have shown that cheap enzymes may be effectively used to achieve much higher conversions in supercritical carbon dioxide than that obtained in non-aqueous organic media like hexane.
For the efficient design of an extractor, a thorough knowledge of the adsorption isotherms, desorption profiles and the solubility limits of the solute is required. The experimental apparatus was set up indigenously and used to determine the fundamental parameters. We have developed models that predict the complex adsorption phenomena and the phase equilibria in supercritical fluids. These models take into account the unusual phenomena of high negative partial molar enthalpies that accompany the adsorption and control the desorption rates.

Representative Publications

  1. Hegde MS, Madras G, Patil KC. Noble metal ionic catalysts. Acc Chem Res. 2009;42(6):704-12.
  2. Roy S, Hegde MS, Madras G. Catalysis for NOx abatement. Appl Energy. 2009;86(11):2283-97.
  3. Paul AK, Madras G, Natarajan S. The illustrative use of thiosulfate in the formation of new three-dimensional hybrid structures. CrystEngComm. 2009;11(1):55-7.
  4. Sahoo PP, Sumithra S, Madras G, Guru Row TN. Synthesis, characterization, and photocatalytic properties of ZrMo 2O8. J Phys Chem C. 2009;113(24):10661-6.
  5. Mahanta D, Madras G, Radhakrishnan S, Patil S. Adsorption and desorption kinetics of anionic dyes on doped polyaniline. J Phys Chem B. 2009;113(8):2293-9.
  6. Vinu R, Madras G. Photocatalytic activity of ag-substituted and impregnated nano-TiO2. Appl. Catal. A: Gen. 2009;366(1):130-40.
  7. Garlapati C, Madras G. Solubilities of solids in supercritical fluids using dimensionally consistent modified solvate complex models. Fluid Phase Equilib. 2009;283(1-2):97-101.
  8. Varma MN, Madras G. Effect of chain length of alcohol on the lipase-catalyzed esterification of propionic acid in supercritical carbon dioxide. Appl Biochem Biotechnol. 2009:1-13.
  9. Konaganti VK, Madras G. Photocatalytic and thermal degradation of poly(methyl methacrylate), poly(butyl acrylate), and their copolymers. Indust. Eng. Chem. Res. 2009;48(4):1712-8.
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