RESEARCH EXPERIENCE
Design of Multiphase reactors
Multiphase Reactors, such as mechanically agitated contactors, bubble columns, modified bubble columns and fluidised beds have been studied. The flow patterns and interphase relationships have been established. Mixing, heat and mass transfer for seemingly different multiphase contactors have been presented under a unified theme. Two new impeller designs namely convex bladed mixed flow impeller (CBMF) and flinging blade impeller have also been developed and characterized.
Mixing time studies have been carried in a 0.3 m diameter and 1 m tall vessel equipped with three impellers in the absence and presence of the gas. The dependency of the mixing time on the tracer properties (tracer density and tracer volume) for two impeller combinations at different impeller rotational speeds has been established and the different flow regimes for gas-liquid operation have also been identified. The compartmental model with single compartment per impeller has been used to predict the observed conductivity response. The experimental and the predicted conductivity responses are compared and the liquid exchange flow rate between adjacent compartments has been calculated, which is subsequently used to predict the mixing time.
Fundamentals of bubble break-up processes in large scale fermenters with liquids, simulating biological liquids have been studied. Correlations have been developed for a priori prediction of the bubble size distribution.
Development of novel strategies for the control of foam in bioreactors.
Engineering Science of slurry treatment
A reaction engineering approach was adapted to study pig slurry aeration. The parameters such as slurry properties and the type of equipments have been studied. A new high efficiency impeller (international patent) and a novel pump stirred aerator has been developed. These have been used commercially with tremendous success.
Cavitation damage in orifice flow and acoustic technique for the measurement of bubble size distribution
The effect of the compressible fluid media surroundings, on the damage due to cavitation flow has been studied. A new technique for the measurement of bubble size distribution in opaque liquids have been developed, which has also been used for the identification of the gas pocket and its characteristics in mechanically agitated gas liquid contactors.
Studies in pulsatile flow
Effect of fluid pulsations on mass transfer behavior of bubble columns have been studied.
Hydrodynamics of thin films
Drainage rates, break-up mechanisms and drop formation during the rupture of thin liquid films have been studied. Pressure drop of moving single and multiple soap films have been measured and theoretically predicted.
Studies in hydrodynamic cavitation for the microbial cell disruption
Hydrodynamic cavitation has been successfully used to carry out microbial cell disruption and for disinfection of water to make it potable. It has been shown, that under optimized conditions, cell disruption and water disinfection can be carried out using only a fraction of the energy required otherwise. These techniques are simpler and can be also used to assess the cell morphology. A global scale technology is being developed in collaboration with CSIR laboratory for ballast water disinfection.
Optimization of impeller design for large mechanically agitated contactors
The effect of tracer volume and its properties such as viscosity and density on mixing time has been studied. Optimum impeller configuration and design correlations have been developed to carry out mixing operation most efficiently. Impeller configurations have been suggested to obtain high gas hold-up and mass transfer coefficients in multiple impeller bioreactors.
Development of radioactive tracer technique for the measurement of gas hold-up profiles
Radiotracer based residence time distribution studies and gamma ray attenuation techniques have been developed to optimize the performance of visbreaker. Industrial columns have been scanned and the strategies have been suggested for enhanced performance based on sound theoretical analysis and the interpretation of this data. The developments are being patented internationally.
Performance assessment (theoretical) of various static mixer designs
A sound theoretical analysis has been done to asses the efficacy of various static mixer designs for specific operations. It has been shown that a unified approach can explain almost all the performance parameters of these devices successfully.
Studies in Incineration of Distillery waste
In an attempt to exploit the heat of combustion of the various dissolved organic compounds which are responsible for the high COD and BOD, the distillery waste was concentrated to different solid concentration levels viz. 20, 30, 40, 50, 60% and the viscosities and other physico‑chemical properties have been determined to design an efficient incinerator. The incineration properties of the waste containing 50% solid has been studied alone as well as in a mixture with sugar cane bagass. Based on these studies the combustion as well as thermal properties of the waste have been estimated. A suitable combination of bagass and 50% Waste has been found out to reduce the severe fouling problem faced in the incinerator otherwise.
Studies in Foam stability
Control of excessive foam formation in the case of fermenter and the role of ultrasonic method in controlling the foam is being investigated. Preliminary work has been carried out in a glass column of 50 mm ID and 600 mm height with ultrasonic bath as well as ultrasonic horn, which involve measurement of foam height/time relationship under the influence of acoustic field. It has been found that under ultrasonic vibration the foam collapse rate was greater compared to the foam collapse rate in the absence of vibrations. Also, the location of foam column with respect to the ultrasonic bath had an effect on the rate of foam collapse. Simple mathematical models for the drainage of the liquid from a form bed, under the influence of ultrasound have been developed and experimentally validated.
Studies in cavitation phenomena, development of a novel sonic reactors
Theoretical front has been explored to gain fundamental understanding of the cavitation Phenomena generated in a variety of equipments and for assessing its efficacy to bring about the desired level of chemical and physical transformations. Studies have resulted into optimization of the equipment as well as liquid medium physicochemical properties for maximizing the cavitational effects. Fundamental studies are being carried for the prediction of the actual cavity size depending on the operating conditions, its inception, collapse and the generation of the reactive species. Experimental work involved a variety of equipments such as Ultrasonic Horn, bath, flow cell, High pressure and high speed homogenizer, Pilot plant orifice set-up. These transformations have been carried out on different scales ranging from 2 gms to 50 kgs. The chemical transformations involved emulsification process, oxidation of alkyl arenes, synthesis of TATB, Benzonitrile, alkaline hydrolysis of methyl benzoate, destruction of various effluents such as phenol, trichlorophenol, formic acid etc. Biological applications such as microbial cell disruption have been carried out to recover intracellular proteins and used for the disinfection of water to make it potable.
Development of Cavity Dynamics Simulator:
The main physical phenomenon responsible for the production of local extremes of pressure and temperature in cavitation is the radial motion of the bubble driven by the varying pressure in the flow. Cavity dynamic equations are quiet complex to solve thus a user friendly graphical interface ‘Cavity Dynamic Simulator’ (CDS) was developed in ‘Microsoft Visual Basic’. CDS is a tool which solves the complex cavity/bubble dynamics equation and gives the final cavity collapse conditions, in the form of final collapse pressure pulse and maximum temperature attained, under the given cavitating conditions. This tool is useful for the Chemist and Engineers, working in the area of ‘Cavitation and its Applications’, who do not want to be bothered about mathematically solving the complex cavity dynamic equations, but still want to interpret their experimental results in the light of cavity dynamics. CDS can be used to get 'apriori' information about the expected cavitational effects that can be utilized for designing of the cavitational or sonochemical equipments and planning out the operating conditions.
Application of the ultrasound in heterogeneous systems
The application of the ultrasound in the homogeneous system has been extensively explored. In comparison, the ultrasound application in heterogeneous system is not much explored. Heterogeneous liquid-liquid systems hold an important place in the domain of the chemical engineering. The success of the above systems that may be reacting or non-reacting, depends on the ability to generate high interfacial area by an equipment economically. Ultrasound assisted cavitation generating equipment is a better solution when fine emulsions are required. The quality of emulsion generated by sonication is far more superior to that of conventional processes. The important advantage is that the generation of an emulsion does not require addition of surfactant. In this work, ultrasonic emulsification of oil and water has been carried out. Experiments were performed, using oil of different physicochemical properties. The parameters, which varied, are the height of ultrasonic horn from the interface, power of the ultrasonic source and the ultrasound irradiation time. The effect of the variation of these parameters on the stability, volume fraction of one phase into other and droplet diameter of dispersed phase has to be studied. Droplet diameter of the dispersed phase has been calculated by Coulter Particle Size Analyzer. Measurement of liquid circulation velocity and bubble size in sonochemical reactors. The exact quantification of the liquid velocities as well as the bubble size is a must for the design of sonochemical reactors. Laser Doppler Anemometers were used for the quantification of the mean and the turbulent liquid velocity at a specific location in the reactor with a capacity of 2 L, diameter of 13.5 cm and irradiated using a 20 kHz immersion transducer. The effect of different operating parameters such as the diameter of the transducer, power dissipation into the system, liquid holding capacity etc. on the local velocities (radial and axial) has been established. The work regarding the optimization of these operating parameters and the measurements of bubble size using granulo-velocimeter is the first and only of its kind in this area.
Protein/Enzyme Synthesis and Usage:
Surface modified supports have been prepared by way of grafting of a functional polymer on the support in order to increase the selectivity of the substrate. Optimization of pH and temperature of the system with Non‑ionic AMBERLITE XAD‑16 (polymeric PS‑DVB macro‑reticular resin) as a support and (α‑glucosidase {EC 3.2.1.20} from the bakers yeast Saccharomyces cerevisae, as the target enzyme has been carried out for maximum selectivity and activity of the enzyme. Reusability and storage stability of the enzyme immobilized on native and polymeric grafted form of the resin has been examined. Various operational parameters such as the time of the fermentation, pH of the medium, speed of the shaker and surface area of the medium for the production of the lipase enzyme have been optimized. Optimum conditions of pH and temperature for the hydrolysis of castor oil using Lipase as a catalyst has been found out. The pH and temperature optima were found to be 7.0 and 55 0C respectively. The major parameters influencing the rate of the reaction were found to be oil‑water interfacial area, solvent addition, enzyme concentration and product inhibition. About 90% conversion could be achieved by formulating a strategy for enzyme addition during the course of the reaction. Work has also been carried out towards preparation of immobilized lipase for the hydrolysis of castor oil using a reversible‑soluble polymer, which is being patented.
Mixing time studies in multiple impeller agitated gas-liquid contactors
Mixing time studies have been carried in a 0.3 m diameter and 1 m tall vessel equipped with three impellers in the absence and presence of the gas. The dependency of the mixing time on the tracer properties (tracer density and tracer volume) for two impeller combinations at different impeller rotational speeds has been established and the different flow regimes for gas-liquid operation have also been identified. The compartmental model with single compartment per impeller has been used to predict the observed conductivity response. The experimental and the predicted conductivity responses are compared and the liquid exchange flow rate between adjacent compartments has been calculated, which is subsequently used to predict the mixing time successfully. CFD simulations of this gas-liquid system have been carried out, which successfully captures the variation in the mixing time under a variety of operating conditions.
Optimization of microbial cell disruption process for release of enzymes/proteins
The energy efficiency of the cell disruption process for the recovery of intracellular proteins depends on the physical strength of the cell wall of the microorganism and on the intracellular location of the target enzymes. The translocation provides an external means to reduce the severity of the cell disruption process and the reduction in the energy requirements for the same. The heat stress was found to induce the translocation of the target enzyme (b-galactosidase) and also to promote the aggregates formations of the total insoluble proteins after their translocation. The purity and selectivity of the target enzyme could be substantially improved along with the reduction in the energy requirement for their disruption by introducing the cells to the heat stress. The kinetics of translocation has been reported on the basis of the variation in Location factor (LF) and could be used to optimize the heat treatment protocol for maximum enzyme recovery with almost 75% reduction in overall energy costs.
Waste management and recovery of valuable products
Various food industries like Dairy, Canning, distilleries, fisheries etc. generate a large amount of waste material with very high BOD and COD causing a problem in disposal of wastes. Studies were aimed at recovery of lactose/proteins from these waste streams of the dairy industry. Heat treatment and few combination treatments to separate protein from whey have been investigated with an aim of optimizing the operating conditions, which would in turn simplify the process of lactose separation. The maximum protein separation for paneer and shrikhand whey has been achieved. Subsequent to this, almost 80 to 85% of the Lactose has been recovered from the Shrikhand & Paneer whey, which is being drained and wasted currently.
Distillery wastewater treatment
Distillery wastewater, generally known as stillage, slops, dunder or Spent wash is amongst the worst pollutants produced by these industries, both in magnitude and strength. In the present work we have tried to explore the possibilities of treating the distillery spent wash with the recent advanced techniques in the treatment of wastewater (Combination of Acoustic Cavitation, Enzyme treatment and Ozonation with the conventional biological oxidation). Combination of ozonation, ultrasound followed by enzyme yielded best results in terms of extent and rate of biological oxidation than that obtained when these techniques were studied as stand-alone. A plausible treatment scheme for the treating distillery spent wash has also been presented.
Design of Multiphase reactors
Multiphase Reactors, such as mechanically agitated contactors, bubble columns, modified bubble columns and fluidised beds have been studied. The flow patterns and interphase relationships have been established. Mixing, heat and mass transfer for seemingly different multiphase contactors have been presented under a unified theme. Two new impeller designs namely convex bladed mixed flow impeller (CBMF) and flinging blade impeller have also been developed and characterized.
Mixing time studies have been carried in a 0.3 m diameter and 1 m tall vessel equipped with three impellers in the absence and presence of the gas. The dependency of the mixing time on the tracer properties (tracer density and tracer volume) for two impeller combinations at different impeller rotational speeds has been established and the different flow regimes for gas-liquid operation have also been identified. The compartmental model with single compartment per impeller has been used to predict the observed conductivity response. The experimental and the predicted conductivity responses are compared and the liquid exchange flow rate between adjacent compartments has been calculated, which is subsequently used to predict the mixing time.
Fundamentals of bubble break-up processes in large scale fermenters with liquids, simulating biological liquids have been studied. Correlations have been developed for a priori prediction of the bubble size distribution.
Development of novel strategies for the control of foam in bioreactors.
Engineering Science of slurry treatment
A reaction engineering approach was adapted to study pig slurry aeration. The parameters such as slurry properties and the type of equipments have been studied. A new high efficiency impeller (international patent) and a novel pump stirred aerator has been developed. These have been used commercially with tremendous success.
Cavitation damage in orifice flow and acoustic technique for the measurement of bubble size distribution
The effect of the compressible fluid media surroundings, on the damage due to cavitation flow has been studied. A new technique for the measurement of bubble size distribution in opaque liquids have been developed, which has also been used for the identification of the gas pocket and its characteristics in mechanically agitated gas liquid contactors.
Studies in pulsatile flow
Effect of fluid pulsations on mass transfer behavior of bubble columns have been studied.
Hydrodynamics of thin films
Drainage rates, break-up mechanisms and drop formation during the rupture of thin liquid films have been studied. Pressure drop of moving single and multiple soap films have been measured and theoretically predicted.
Studies in hydrodynamic cavitation for the microbial cell disruption
Hydrodynamic cavitation has been successfully used to carry out microbial cell disruption and for disinfection of water to make it potable. It has been shown, that under optimized conditions, cell disruption and water disinfection can be carried out using only a fraction of the energy required otherwise. These techniques are simpler and can be also used to assess the cell morphology. A global scale technology is being developed in collaboration with CSIR laboratory for ballast water disinfection.
Optimization of impeller design for large mechanically agitated contactors
The effect of tracer volume and its properties such as viscosity and density on mixing time has been studied. Optimum impeller configuration and design correlations have been developed to carry out mixing operation most efficiently. Impeller configurations have been suggested to obtain high gas hold-up and mass transfer coefficients in multiple impeller bioreactors.
Development of radioactive tracer technique for the measurement of gas hold-up profiles
Radiotracer based residence time distribution studies and gamma ray attenuation techniques have been developed to optimize the performance of visbreaker. Industrial columns have been scanned and the strategies have been suggested for enhanced performance based on sound theoretical analysis and the interpretation of this data. The developments are being patented internationally.
Performance assessment (theoretical) of various static mixer designs
A sound theoretical analysis has been done to asses the efficacy of various static mixer designs for specific operations. It has been shown that a unified approach can explain almost all the performance parameters of these devices successfully.
Studies in Incineration of Distillery waste
In an attempt to exploit the heat of combustion of the various dissolved organic compounds which are responsible for the high COD and BOD, the distillery waste was concentrated to different solid concentration levels viz. 20, 30, 40, 50, 60% and the viscosities and other physico‑chemical properties have been determined to design an efficient incinerator. The incineration properties of the waste containing 50% solid has been studied alone as well as in a mixture with sugar cane bagass. Based on these studies the combustion as well as thermal properties of the waste have been estimated. A suitable combination of bagass and 50% Waste has been found out to reduce the severe fouling problem faced in the incinerator otherwise.
Studies in Foam stability
Control of excessive foam formation in the case of fermenter and the role of ultrasonic method in controlling the foam is being investigated. Preliminary work has been carried out in a glass column of 50 mm ID and 600 mm height with ultrasonic bath as well as ultrasonic horn, which involve measurement of foam height/time relationship under the influence of acoustic field. It has been found that under ultrasonic vibration the foam collapse rate was greater compared to the foam collapse rate in the absence of vibrations. Also, the location of foam column with respect to the ultrasonic bath had an effect on the rate of foam collapse. Simple mathematical models for the drainage of the liquid from a form bed, under the influence of ultrasound have been developed and experimentally validated.
Studies in cavitation phenomena, development of a novel sonic reactors
Theoretical front has been explored to gain fundamental understanding of the cavitation Phenomena generated in a variety of equipments and for assessing its efficacy to bring about the desired level of chemical and physical transformations. Studies have resulted into optimization of the equipment as well as liquid medium physicochemical properties for maximizing the cavitational effects. Fundamental studies are being carried for the prediction of the actual cavity size depending on the operating conditions, its inception, collapse and the generation of the reactive species. Experimental work involved a variety of equipments such as Ultrasonic Horn, bath, flow cell, High pressure and high speed homogenizer, Pilot plant orifice set-up. These transformations have been carried out on different scales ranging from 2 gms to 50 kgs. The chemical transformations involved emulsification process, oxidation of alkyl arenes, synthesis of TATB, Benzonitrile, alkaline hydrolysis of methyl benzoate, destruction of various effluents such as phenol, trichlorophenol, formic acid etc. Biological applications such as microbial cell disruption have been carried out to recover intracellular proteins and used for the disinfection of water to make it potable.
Development of Cavity Dynamics Simulator:
The main physical phenomenon responsible for the production of local extremes of pressure and temperature in cavitation is the radial motion of the bubble driven by the varying pressure in the flow. Cavity dynamic equations are quiet complex to solve thus a user friendly graphical interface ‘Cavity Dynamic Simulator’ (CDS) was developed in ‘Microsoft Visual Basic’. CDS is a tool which solves the complex cavity/bubble dynamics equation and gives the final cavity collapse conditions, in the form of final collapse pressure pulse and maximum temperature attained, under the given cavitating conditions. This tool is useful for the Chemist and Engineers, working in the area of ‘Cavitation and its Applications’, who do not want to be bothered about mathematically solving the complex cavity dynamic equations, but still want to interpret their experimental results in the light of cavity dynamics. CDS can be used to get 'apriori' information about the expected cavitational effects that can be utilized for designing of the cavitational or sonochemical equipments and planning out the operating conditions.
Application of the ultrasound in heterogeneous systems
The application of the ultrasound in the homogeneous system has been extensively explored. In comparison, the ultrasound application in heterogeneous system is not much explored. Heterogeneous liquid-liquid systems hold an important place in the domain of the chemical engineering. The success of the above systems that may be reacting or non-reacting, depends on the ability to generate high interfacial area by an equipment economically. Ultrasound assisted cavitation generating equipment is a better solution when fine emulsions are required. The quality of emulsion generated by sonication is far more superior to that of conventional processes. The important advantage is that the generation of an emulsion does not require addition of surfactant. In this work, ultrasonic emulsification of oil and water has been carried out. Experiments were performed, using oil of different physicochemical properties. The parameters, which varied, are the height of ultrasonic horn from the interface, power of the ultrasonic source and the ultrasound irradiation time. The effect of the variation of these parameters on the stability, volume fraction of one phase into other and droplet diameter of dispersed phase has to be studied. Droplet diameter of the dispersed phase has been calculated by Coulter Particle Size Analyzer. Measurement of liquid circulation velocity and bubble size in sonochemical reactors. The exact quantification of the liquid velocities as well as the bubble size is a must for the design of sonochemical reactors. Laser Doppler Anemometers were used for the quantification of the mean and the turbulent liquid velocity at a specific location in the reactor with a capacity of 2 L, diameter of 13.5 cm and irradiated using a 20 kHz immersion transducer. The effect of different operating parameters such as the diameter of the transducer, power dissipation into the system, liquid holding capacity etc. on the local velocities (radial and axial) has been established. The work regarding the optimization of these operating parameters and the measurements of bubble size using granulo-velocimeter is the first and only of its kind in this area.
Protein/Enzyme Synthesis and Usage:
Surface modified supports have been prepared by way of grafting of a functional polymer on the support in order to increase the selectivity of the substrate. Optimization of pH and temperature of the system with Non‑ionic AMBERLITE XAD‑16 (polymeric PS‑DVB macro‑reticular resin) as a support and (α‑glucosidase {EC 3.2.1.20} from the bakers yeast Saccharomyces cerevisae, as the target enzyme has been carried out for maximum selectivity and activity of the enzyme. Reusability and storage stability of the enzyme immobilized on native and polymeric grafted form of the resin has been examined. Various operational parameters such as the time of the fermentation, pH of the medium, speed of the shaker and surface area of the medium for the production of the lipase enzyme have been optimized. Optimum conditions of pH and temperature for the hydrolysis of castor oil using Lipase as a catalyst has been found out. The pH and temperature optima were found to be 7.0 and 55 0C respectively. The major parameters influencing the rate of the reaction were found to be oil‑water interfacial area, solvent addition, enzyme concentration and product inhibition. About 90% conversion could be achieved by formulating a strategy for enzyme addition during the course of the reaction. Work has also been carried out towards preparation of immobilized lipase for the hydrolysis of castor oil using a reversible‑soluble polymer, which is being patented.
Mixing time studies in multiple impeller agitated gas-liquid contactors
Mixing time studies have been carried in a 0.3 m diameter and 1 m tall vessel equipped with three impellers in the absence and presence of the gas. The dependency of the mixing time on the tracer properties (tracer density and tracer volume) for two impeller combinations at different impeller rotational speeds has been established and the different flow regimes for gas-liquid operation have also been identified. The compartmental model with single compartment per impeller has been used to predict the observed conductivity response. The experimental and the predicted conductivity responses are compared and the liquid exchange flow rate between adjacent compartments has been calculated, which is subsequently used to predict the mixing time successfully. CFD simulations of this gas-liquid system have been carried out, which successfully captures the variation in the mixing time under a variety of operating conditions.
Optimization of microbial cell disruption process for release of enzymes/proteins
The energy efficiency of the cell disruption process for the recovery of intracellular proteins depends on the physical strength of the cell wall of the microorganism and on the intracellular location of the target enzymes. The translocation provides an external means to reduce the severity of the cell disruption process and the reduction in the energy requirements for the same. The heat stress was found to induce the translocation of the target enzyme (b-galactosidase) and also to promote the aggregates formations of the total insoluble proteins after their translocation. The purity and selectivity of the target enzyme could be substantially improved along with the reduction in the energy requirement for their disruption by introducing the cells to the heat stress. The kinetics of translocation has been reported on the basis of the variation in Location factor (LF) and could be used to optimize the heat treatment protocol for maximum enzyme recovery with almost 75% reduction in overall energy costs.
Waste management and recovery of valuable products
Various food industries like Dairy, Canning, distilleries, fisheries etc. generate a large amount of waste material with very high BOD and COD causing a problem in disposal of wastes. Studies were aimed at recovery of lactose/proteins from these waste streams of the dairy industry. Heat treatment and few combination treatments to separate protein from whey have been investigated with an aim of optimizing the operating conditions, which would in turn simplify the process of lactose separation. The maximum protein separation for paneer and shrikhand whey has been achieved. Subsequent to this, almost 80 to 85% of the Lactose has been recovered from the Shrikhand & Paneer whey, which is being drained and wasted currently.
Distillery wastewater treatment
Distillery wastewater, generally known as stillage, slops, dunder or Spent wash is amongst the worst pollutants produced by these industries, both in magnitude and strength. In the present work we have tried to explore the possibilities of treating the distillery spent wash with the recent advanced techniques in the treatment of wastewater (Combination of Acoustic Cavitation, Enzyme treatment and Ozonation with the conventional biological oxidation). Combination of ozonation, ultrasound followed by enzyme yielded best results in terms of extent and rate of biological oxidation than that obtained when these techniques were studied as stand-alone. A plausible treatment scheme for the treating distillery spent wash has also been presented.