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   Welcome to Prof. Ajay K. Ray's Research Group on       "Engineering of Chemical Reactions & Processes"

• Process modelling, simulation and multi-objective optimization
• Simulated Moving Bed (SMB) systems for difficult or impossible separations
• Band-engineered semiconductor photocatalysis
• Integrated reactor-separator
• Oscillatory reactor

Engineering of Chemical Reactions and Processes

Research Interests and Program

My indulgence in research is to pursue practical chemical engineering issues in order to leave behind positive changes for society and industry. My research thrust is aimed at synthesis of new environmentally-friendly materials, development of innovative reactor and new process design with emphasis on analysis of the interactions between the transport processes and chemical reactions, inventing novel approaches to improve process performance and process intensification, optimal operation of such process systems and its application to relevant problems in the chemical, biochemical, environmental and related industries. Novel processes are the key in finding new ways to produce useful products and energy sources with improved efficiency, reactor simplicity, and lower costs. The motivation is to obtain a deep understanding required to develop the next generation of technologies for applications in energy, environment, food, health and water, the humanity's most important challenges for next few decades, and garner significant fundamental expertise in a wide range of areas such as reaction engineering, reactor design, fluid mechanics, separation processes, nanotechnology, modeling, simulation, and multi-objective optimization.

 Many of my research problems deals with the mathematical modeling of various complicated engineering systems with interactions between the transport processes and chemical reactions. The design, development, simulation, optimization and analysis of chemical reactors and processes provide an ideal habitat to explore such problems. The objectives of the research are to gain fundamental understanding of the complex behavior of the nonlinear systems and use this understanding to practical advantage. All my research projects exhibit a good blend of fundamental theory and practice in terms of developing theoretical and computational tools addressing design and operational issues of complex systems followed by systematic experimental verification. Research approaches include analytical, experimental and numerical techniques.

 I have made significant contributions particularly to three areas: semiconductor photocatalysis and photocatalytic reactor design, Simulated Moving Bed (SMB) systems, and process modeling, simulation and multi-objective optimization of (bio)chemical processes. The most notable contributions of my work on photocatalysis among others are few designs of novel photocatalytic reactor, effect of mass transfer and catalyst layer thickness on degradation of pollutants, reaction kinetics and mechanism of organics as well as removal of toxic metal ions. In Simulated Moving Bed (SMB), my noteworthy contributions include incorporation of reactions to SMB separation, multi-component separation, distributed feed and solvent, non-synchronous switching (Varicol operation), and hybrid SMB-crystallization. I am the first one to apply the concept of multi-objective optimization in the innovative design of SMB systems. In multi-objective optimization, I have optimized several important industrial chemical reactors and processes, such as hydrogen plant, hydrocracking process, ethylene and styrene manufacturing processes, and several polymer reactors such as Nylon 6, PMMA, Polyester and polyethylene. Recently, I have optimized oxidative coupling of methane (OCM) reaction in membrane and SMB reactors, ethylene oxide in catalytic membrane reactor, protein purification in circulating fluidized bed reactor and penicillin bio-reactor. Many of my articles on photocatalysis, SMB and optimization are highly cited and some of them are cited in recent books.

My several past and present projects are associated with various reacting systems, such as simulated moving bed chromatographic reactors, photocatalytic reactors, oscillatory reactors, and polymer reactors. My research covers a broad range of topics in engineering of chemical reactions and processes, which can be categorized in the following areas to give a better overview:

(a) Simulated Moving Bed Systems and Integrated Reactor-Separator

Simulated Moving Bed (SMB) systems are used for separations that are either impossible or difficult using traditional separation techniques. SMB has become one of the most popular techniques finding its application in petrochemical and sugar industries, and of late, there has been an increased interest in pharmaceutical industry for enantio-separations. SMB systems can also be integrated to include reactions, which can provide economic benefit for equilibrium limited reversible reactions, such as many hydrogenation, isomerization, and esterification reactions. These are continuous flow reactors in which chemical reactions are carried out in the presence of solid adsorbents so that both separation and chemical reaction are integrated into a single process unit. In-situ separation of the products facilitates the reversible reaction to completion beyond thermodynamic equilibrium and at the same time obtaining products of high purity. Furthermore, the integration of reactor and separator can lead to considerable savings in capital and operating costs. The unique aspect of our research is to apply the concept of multi-objective optimization in innovative design of SMB systems.

The present investigations endeavor to determine to what extent the moving bed reactor advantages of high product purity and favorable equilibrium shifts are retained for various important chemical reactions. Our research addresses (a) experimental determination of adsorption and/or kinetic parameters, (b) modeling, experimentation and application of multi-objective optimization in the design of SMB systems, and (c) modeling, experimentation and multi-objective optimization of Varicol (based on non-synchronous switching) process, which is a new modification of more rigid traditional SMB systems. Systems studied and being studied based on SMB technology are:

 • Chiral drug separation (enantio-separation),

 • hybrid simulated moving bed (SMB) and crystallization process

• Production of High Fructose Syrup by inversion of sucrose and isomerization of glucose,

• Separation of xylene isomers - industrial Parex process,

• Hydrogenation of mesitylene to tri-methyl cyclohexane,

• Synthesis of ethers and esters such as MTBE and Methyl acetate,

 • Oxidative coupling of methane (OCM) to ethane and ethylene,

• Process intensification in biodiesel production from microalgae grown on waste  resources

 • Trans-esterification of oil or animal fats with alcohol to produce biodiesel

 • Intensified purification and refolding of inclusion body proteins

(b) Band-Engineered Photocatalysis … for Water Purification, Production of Clean Hydrogen Fuel and Self-cleaning of Building Surfaces

Photo-stimulated catalysis offers an attractive tool for applications in producing clean fuel and in degrading toxic organic pollutants (as well as removing toxic metal ions) for environmental cleanup. However, a specific problem associated with commonly used photo-catalysts is the large band-gap energy, which requires artificial light. Because of the ubiquity of sunlight the success of this technology depends on engineering of electronic bands of the catalyst for paradigm-shift to solar-based photocatalysis that could produce very large economic and social benefits. Two approaches address this issue in the on-going research. The first involves reducing the band-gap through addition of dopants, thereby permitting light absorption in the visible part of the spectrum. The second strategy involves dye-sensitization. The quintessence of dye-sensitization is the electron injection from the excited dye to the conduction band (CB) of TiO₂ and the subsequent interfacial electron transfer. Successful synthesis of chemically modified photocatalyst through molecular band engineering will enable use of sunlight for splitting water into clean hydrogen fuel, sun-powered remediation of environmental pollutants (particularly use TiO2 tablets to get potable water), and creation of solar-driven self-cleaning and antifogging building materials. A transparent liquid form of the photocatalyst when sprayed onto building panels, glass surfaces, painted walls and (kitchen or bathroom) tiles will offer substantial self-cleaning and cost savings in maintenance.

Another thrust aims at developing a technical solution to the design of a commercial (large-scale) photocatalytic reactor that provides a high ratio of activated immobilized catalyst surface area per unit reactor volume thereby allowing for much higher specific reactor capacity. All experiments involve novel reactor configurations and catalysts to achieve high selectivity. Modeling involves simulation of the processes and description of reaction mechanisms using detailed surface reaction steps. This research involves the interplay between surface and solution chemistry, catalysis and reaction engineering, and mass transfer effects. Main contributions on photocatalysis are (a) fundamental kinetic studies for photocatalytic degradation of organics to determine true kinetic rate parameters in slurry as well as fixed catalyst systems. (b) systematic thermodynamic analysis and kinetic study for removal of toxic metal ions such as Hg(II), Cr(VI) and As(III) from wastewater, and (c) design and development of novel large-scale photocatalytic reactors for water purification such as multiple tube reactor, tube light reactor, rotating tube reactor, pulsating reactor and Taylor vortex reactor. The design specifically addressed critical issues of increasing illuminated catalyst density, uniform distribution of light and mixing of fluids. Experiments were done to show the effectiveness and efficiency of these reactors. Detailed computer simulation of photocatalytic reactors using Fluent® has also been carried out.

(c) Modeling, Simulation and Multi-objective Optimization

Our research group is pioneer to apply the concept of multi-objective optimization in the design and operation of chemical reactors and processes. Chemical reactors are often the important equipment in many process industries. Multi-objective optimizations of industrial reactors are carried out to identify the optimal conditions for producing valuable products economically using different adaptations of genetic algorithm, which usually result in an optimal Pareto set. Detailed simulation models are first developed for industrial systems. These models are verified (sometimes tuned) using industrial data. Additional control variables, important objective functions, constraints of significance, accurate kinetic schemes and practical aspects of various physical processes are considered. All these make the optimization problem more complex but the ultimate results are far more meaningful. Better (optimal) operating conditions are computed using powerful and recently developed techniques like NSGA and Simulated Annealing. These studies help optimize several objectives while simultaneously satisfying several real-life constraints present in industry. Significant cost savings and enhanced productivity are achieved. In addition to application of the multi-objective optimization to different industrial applications, we are also involved on improving the optimization methodologies. Industrial process studied and being studied are (a) hydrogen production by steam reforming of hydrocarbons based on natural gas or higher hydrocarbon feed using side or top fired steam reformer, (b) industrial polymerization reactors for the production of Nylons, Polyesters, Perspex, polyethylene, polystyrene, etc., (c) beer dialysis using hollow fiber membranes, (d) industrial Styrene manufacturing process, (e) industrial Ethylene reactor, (f) catalytic membrane reactor for production of ethylene oxide and formaldehyde and oxidative coupling of methane reaction, and (g) multi-functional reactors such as SMBR and Varicol based on Simulated Moving Bed technology. These are continuous flow reactors in which chemical reactions are carried out in the presence of solid adsorbents so that both separation by adsorption and chemical reaction are integrated into a single process unit. Carrying out separation during chemical reaction helps to overcome reactant conversion limitation because of chemical equilibrium. Moreover, the integration of reactor and separator lead to considerable savings in capital and operating costs. Systems optimized are SMB and Varicol units for separation of chiral drugs, mixtures of C8 hydrocarbons, glucose-fructose mixture, and reactive systems such as synthesis of methyl acetate ester, MTBE, trimethyl cyclohexane, production of concentrated high fructose syrup by inversion of sucrose and isomerization of glucose, and production of ethylene by oxidative coupling of methane. Current projects involve hybrid SMB-Crystallization, biodiesel production, Process intensification in biodiesel production from microalgae grown on waste resources, and Intensified purification and refolding of inclusion body proteins.

(d) Performance Improvement of Chemical Reactors by Natural       Oscillations

The dynamic behavior of two coupled continuous stirred-tank reactors in sequence was studied when the first reactor is operated under limit cycle regimes producing self-sustained natural oscillations. This new concept of coupling free and forced oscillation does not require any additional external energy but at times the overall performance of the system can be greatly enhanced. Systems studied are (a) wastewater treatment by activated sludge process, (b) synthesis of ethanol from glucose, (c) oxo reaction for production of aldehydes from olefins and synthesis gas, etc.

KEYWORDS:

Reaction Engineering, Photocatalysis, Simulated Moving Bed Systems, Modeling, Simulation and Multi-objective Optimization, Process Systems and Engineering, Integrated Reactor-Separator, Separation and Purification of Chiral Drugs, Chemical Process Development.

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