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Abstract Nitration is one of the oldest and the most extensively
studied reactions. Nitration reactions, conducted using mixed acid,
are extremely exothermic, and tend to be explosive. Moreover, this
process has been the most acceptable and favoured route for the
manufacture of explosives and precursors for dyes and intermediates
and industrial solvents. Aromatic nitrations are performed using
“mixed acid” and involve two phases viz. the aromatic phase and the
mixed acid phase. It is an accepted proposition that the reaction
occurs exclusively in the acid phase in which aromatics are
sparingly soluble. The rate controlling step involves electrophilic
attack of nitronium ion on the aromatic ring. Reaction is known to
be irreversible and first order in concentration of the aromatic
species and nitric acid. A large amount of literature highlighting
the mechanistic, kinetic, optimization and safety aspects exists.
It is necessary to study the reaction kinetics in detail to
identify the window of operating parameters which offers safe
operation yet desired performance. During our studies on nitration
of nitroaromatics, the data suggests that nitroaromatics exist in
the form of microemulsion at ambient temperatures. The
microemulsion is found to play a major role in the kinetics of
polynitration. The reaction of nitro compound (nitrobenzene) and
nitric acid occurs at the interface between the organic microphase
and acid phase. Whenever nitration of nitroaromatics is conducted
at high concentrations of sulfuric acid (> 80% w/w), the system
begins to show anomalous behavior. Nitroaromatics have very high
solubility in concentrated sulfuric acid. Moreover, the solubility
rapidly increases with increase in the concentration of the acid.
Winsor III- phase behavior is observed at certain temperature and
composition of the system, indicating the existence of
microemulsion. The existence of microemulsion of nitroaroamtic
species in sulfuric acid is confirmed through the results of a
variety of experiments, which include the phase equilibrium data,
surface and interfacial tension, viscosity and electrical
conductivity of the system and extensive kinetic data, both in
batch and continuous (CSTR) modes. Kinetics has been modeled based
on the hypothesis of microemulsion. Keywords: Nitration,
Microemulsion, Winsor- III phases, Polynitration.
Aromatic Nitration Studies in Higher Strength of Sulfuric Acid
Ameya Diwan, Sanjay Mahajani & Vinay Juvekar* Department of
Chemical Engineering, Indian Institute of Technology Bombay,
Mumbai, -400076, India [email protected], [email protected] ,
[email protected]*
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Abstract
Cell cycle is the central process that regulates growth and
division. The series of phase specific events
(G1->S->G2->M) and phase transitions are governed mainly
by Cyclin dependent kinases and its positive and negative
regulators. In most of the cancer types the cell cycle regulation
is disturbed. Modeling studies can provide insights about the
mis-regulation or loss of control at molecular level since the key
cell cycle controllers and their interactions are conserved among
eukaryotes. We have developed a purely mechanism based model for
cell cycle regulation of fission yeast Schizosaccharomyces pombe.
The model describes the dynamic evolution of fifteen crucial
regulators, their active and inactive states. The molecular events
that characterizes the cell division cycle are driven by the
different stoichiometric and enzymatic modification that results
from the complex network architecture. The distinguishing features
of this model are, that this model does not use any condition based
phase transitions unlike the existing models, it does not use any
total protein concentration and Goldbeter switches to bring switch
like response for phase specific activation or inactivation of
regulators. For model simulation, parameters were chosen to
represent the reported dynamics of the regulators. Cell division
time of 150 minutes was observed for wild type cells which is
consistent with the experimental studies. In order to validate the
model, it was simulated and verified for various known mutants. An
input output response based analysis was developed to understand
the role of the individual regulators. Such a study would enhance
our understanding of control strategies, and biological design
principles evolved in cell division process.
Mechanism Based Model Development For Cell Cycle Regulation of
Schizosaccharomyces pombe Anbumathi. P1, Sharad Bhartiya1, K.V.
Venkatesh1,2
1Department of Chemical Engineering and 2School of Biosciences
and Bioengineering, Indian Institute of Technology Bombay, Mumbai,
-400076, India [email protected]
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Abstract
Heavy tracer particles sinking in a flowing medium of light
particles of same size are studied by DEM simulations. Using an
effective medium argument for buoyant force, we show the existence
of an effective buoyancy volume Vbouyant that must be larger than
volume of the trace particle Vp. We find that the drag force on the
sphere sinking with velocity v in a granular medium of viscosity is
given as F=6adragv, where adrag is hydrodynamic radius of the
sinking sphere, establishing that Stokes’ law holds for powders as
well. This hydrodynamic radius is different from the one obtained
from effective buoyancy volume. Using the Stokes-Einstein relation,
we define an effective temperature Teff =6adragD, where D is the
diffusivity of the particle. Balancing the segregation and
diffusion fluxes, we propose a theory for segregation due to
density differences for a binary mixture of same size particles. It
is shown that density segregation is determined by effective
temperature profiles as predicted by the theory. By the means of
DEM simulations of binary granular mixtures flowing over an
inclined plane, we show that the theory accurately predicts
segregation for mixtures of different overall compositions at
various inclination angles of the plane. Trace particles of
different size however behave differently and with bigger particles
of density same as that of the base flow particles rising,
questioning the granular buoyancy mechanism of segregation
suggested earlier. By detailed analysis of different size and
density trace particles, we show that the granular buoyancy can be
an appropriate method of looking at the size segregation as
well.
Granular Buoyancy, Stokes’ Law and Segregation of Powders Anurag
Tripathi*, Devang V. Khakkar Department of Chemical Engineering,
Indian Institute of Technology Bombay, Mumbai, -400076, India
[email protected] *
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Abstract
The process of drying colloidal dispersions, namely, evaporation
of the solvent leading to the formation of continuous polymer/metal
oxide films is common to a range of important technologies, e.g.
forming polymer films from latex dispersions, casting magnetic
tapes, encapsulating vitamins in beads, manufacturing photographic
film etc. The thickness of the consolidated bed can vary from an
order of a micron (i.e. thin films) to an order of meters (i.e.
river beds). The particles often are polymer lattices or inorganic
oxides, e.g. silica, alumina, or zirconia, and the solvent is
normally water, but occasionally a low molecular weight organic
solvent. In this work we provide a general framework for studying
the consolidation of charged colloids and apply it to case of
drying of latex dispersion which contains sub-micron sized
particles dispersed in water. Since the final mechanical properties
of a colloidal film depend on the nature of the particle packing,
understanding the factors influencing consolidation becomes
important. Our experiments and simulation show that at lower
particle volume fraction surface charge of a particle does have an
effect on consolidation. The results of this work are not only
applicable to coatings and ceramic processes but also to diverse
industrial processes such as waste water treatment where
particulate matter is separated from the feed using gravity or
centrifugal action. Once the particles consolidate, the liquid
menisci results in large (negative) capillary pressures that
deforms the packed array of the particles resulting in a stress
field across the bed. Our experiments show that the consolidated
bed could crack under certain conditions. Hence, we looked at the
problem of stress distribution and nucleation of cracks of a thick
bed of colloidal particles. We carried out experiments and
simulation related to crack propagation and their dependence on
evaporation rate. We also have identified critical parameters
related to nucleation of crack.
Consolidation of Latex Dispersion Arijit Sarkar∗, Mahesh S.
Tirumkudulu Department of Chemical Engineering, Indian Institute of
Technology Bombay, Mumbai, -400076, India
[email protected]*
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Abstract
E.coli has survived for ages, which is credited to their ability
to move away from repellents and move towards attractants. This
strategy of movement is well known as chemotaxis. This is done with
the help of flagella. E.coli has a sequence of smooth swimming
‘runs’ punctuated by intermittent ‘tumble’. ‘Run’ is for longer
time, where the flagella moves counter clock wise (CCW). In
‘tumble’ flagella moves clockwise (CW) which is for fraction of
seconds, this helps in effectively randomize the direction of next
run. Duration of ‘run’ can last from few fractions of seconds to
several minutes depending on the chemo stimulus (attractant or
repellent). E.coli cannot measure the gradients and behave as point
sensors which posses a kind of memory ( 3 second) that allow them
to compare past chemical environment to the current. So the
probability of a smooth ‘run’ depends on its immediate surrounding
being compared to their chemistry of the previous surrounding which
it encountered earlier. Frequency of ‘tumble’ increases as the
attractant depletes or repellent concentration increases. But as
soon as it detects the condition is improving ‘running’ increases
and ‘tumbling is suppressed. This whole phenomenon is molecularly
controlled by signal transduction. The movement of bacteria is
measured by capillary assay or ring formation on semisolid agar
plate. In our study we have investigated E.coli’s movement in
presence of chemo attractant (Tryptone, Luria-Bertani broth (LB),
Serine, Aspartate, and Glycerol) and chemo repellent (Cobalt
Chloride (CoCl2), Nickel Chloride (NiCl2) & Sodium Acetate) in
semisolid agar plate by observing the ring formation.
Chemotaxis of E.coli Rajesh Jesudasan*, Mahesh S. Tirumkudulu
Department of Chemical Engineering, Indian Institute of Technology
Bombay, Mumbai, -400076, India [email protected]*
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Abstract
In the vicinity of the surface of a charged body/electrode in
contact with an aqueous solution, a thin region of counterions,
called electric double layer, exists. The thickness of the
electrical double layer is in the range of 1 nm to 1 m .
Practically all of the electric field generated by the electrode is
screened by the electrical double layer and field is practically
zero outside the double layer. The electrical double layer, thus,
acts as a barrier against penetration of the field to a longer
distance from the electrode surface. The double layer can be
completely eliminated by alternating the potential of the electrode
at a sufficiently high frequency. The aim of the present work is to
understand the dynamics of the double layer subjected to an AC
field with variety of waveforms. Idea behind this exercise is not
only to eliminate the double layer, but also to make the ions of
the same charge to assemble, at high concentration, in the region
far away from the electrode so that a very high electric field is
generated at that point. With these objectives in mind, a setup has
been developed consisting of a signal generator, followed by a high
voltage amplifier and a cell with parallel plate electrodes. The
potential and the current are measured using a picoscope. Here, we
measure the current density and phase lead of the current with
respect to potential as functions of the frequency and waveform of
the electrode potential. When a sinusoidal potential is applied,
the current density and phase lead profile show three distinct
regions. In the low frequency region, the current density increases
and phase lead decreases with increase in the frequency. It is due
to the diminishing of the electrical double layer with frequency.
The frequency at which phase lead becomes almost zero called as
threshold frequency. At this frequency, the double layer is
completely eliminated. Beyond this frequency, the current density
and phase lead nearly remains constant with further increase in the
frequency over a certain range of frequency. In this region, the
system is purely resistive. Beyond this range, the current density
and phase lead begins to increase with increase in the frequency.
At sufficiently high frequency, the system again starts behaving as
pure dielectric. The current density increases linearly with
frequency. The phase lead value approaches to the 90 degree. In
this region, the ions are in immobilized state, the current density
is due to the rotation of the dipoles of water. The theoretical
model is also developed to understand in detail about the dynamics
of the electrical double layer. The results obtained by simulation
are compared to experimental and they are in quite good
agreement.
Dynamics of the Electrical Double Layer R. S. Patil*, V. A.
Juvekar, Rochish T. and V. M. Naik
Department of Chemical Engineering, Indian Institute of
Technology Bombay, Mumbai, -400076, India
[email protected]*
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Abstract Underground coal gasification (UCG) is a technique
which permits access to coal which either lies too deep
underground, or is otherwise too costly to exploit using
conventional mining techniques. At the same time, it eliminates
many of the health, safety and environmental problems of deep
mining of coal. UCG product gas may be used as a chemical feedstock
or as fuel for power generation. The UCG cavity is a result of the
complete interaction of fluid flow, heat transfer, mass transfer,
chemical reactions, water influx, thermo mechanical properties of
coal, spalling phenomenon and other geological aspects. The shape
and rate of growth of this cavity will strongly impact the
important phenomena, such as reactant gas flow patterns, kinetics,
temperature profiles, and ultimately determines the quality of the
product gas. There is a need for experimental data to characterize
the cavity evolution in the UCG process. The goal of our work is to
establish a relationship between cavity evolution and various
parameters. A systematic methodology is proposed for laboratory
scale experiments to mimic the UCG process and empirical
correlations are developed to relate cavity volume and three
dimensional shapes to various design and operating parameters. In
addition to the experimental studies, it is necessary to reduce the
computational efforts to get the product gas composition through a
complete process model. Computational Fluid Dynamics has been used
as a tool to characterize the non-ideal flow patterns by performing
residence time distribution (RTD) studies in actual size UCG
cavities and the results validated against lab-scale experiments.
The new approach of compartment modeling that reduces the
computational burden on UCG process simulation has been explored
here. The compartment model is developed based on the CFD
simulation results and it is validated by comparing the homogeneous
water gas shift reaction-enabled steady state CFD simulation
results with that of obtained from the steady state flow simulator
(i.e. Aspen Plus). Finally, a detailed parametric study on heat and
mass transfer coefficients for actual size UCG cavities has been
undertaken and the obtained trends validated against well-designed
lab-scale experiments. Overall, this research is expected to
contribute significantly to the comprehension, optimization and
process modeling of the complex UCG process.
Studies on Underground Coal Gasification Daggupati Sateesh*,
Preeti Aghalayam, Sanjay M Mahajani Department of Chemical
Engineering, Indian Institute of Technology Bombay, Mumbai,
-400076, India [email protected]*
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Abstract
Metal nanoclusters (1 – 100 nm) are of significance because they
exhibit unique physico-chemical properties, very different from
those in the bulk. They are used as building blocks for
hierarchical materials. These materials can be achieved if the
properties of the nanoclusters can be manipulated on all scales
(molecular, micro and meso) to incorporate desired characteristics
for applications in varied fields ranging from opti-electronic
devices, magnetic storage devices, catalysts to medical implants
and drug delivery. Wet chemical synthesis is gaining popularity
because it provides the flexibility to control nanocluster
properties like size, shape and morphology by manipulating the
stabilizer parameters like molecular weight, functional groups and
concentration. We are interested in understanding the self-assembly
process for bulk-synthesis of nanoclusters. In literature,
considerable amount of work has been done on how these parameters
influence nanocluster properties – however, the stabilization
mechanism is not yet fully understood. The processes occurring
simultaneously in the system are decomposition, nucleation, growth
& aggregation, stabilization and breakage / fragmentation. To
get a better understanding of this mechanism we have attempted for
the first time, to the best of authors' knowledge, to capture the
nucleation and growth pattern using extensive transmission electron
microscopy and, more importantly, study how polymers and
surfactants influence these. The model system chosen for this
purpose was the thermal decomposition of an organo-metallic
precursor, octa-carbonyl di-cobalt in an inert atmosphere in the
presence of polystyrene/AOT as stabilizer, both dissolved in a
common solvent, toluene. The octa-carbonyl di-cobalt decomposes to
give highly active nascent cobalt atoms. FTIR was used to monitor
the progress of the reaction. TEM images were taken at different
stages of the decomposition reaction. These micrographs captured
the size and shape of nanoclusters spanning over the growth period.
Interesting observations were made which helped us conclude that
polymers are definitely involved in the nucleation and growth
process of nanoclusters in a complex manner. Chain length plays a
critical role in the rate at which nanocluster size decreases.
Concentration of both polymer and surfactant has an impact on the
formation mechanism.
Capturing the Nucleation and Growth Patterns of
Stabilizer-Induced Metal Nanocluster Formation by Thermal
Decomposition of Organometallic Precursors Sonia Tikku*, Late
Kartic C Khilar, Jayesh Bellare, and Rajdip Bandyopadhyaya
Department of Chemical Engineering, Indian Institute of Technology
Bombay, Mumbai, -400076, India. [email protected]*
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Abstract
The galactose uptake mechanism in yeast is a well studied
regulatory network. The regulatory players in the galactose
regulatory mechanism (GAL system) are conserved in Saccharomyces
cerevisiae and Kluyveromyces lactis but the molecular mechanisms
that occur due to the interactions between them are different. The
key differences in the GAL system of K. lactis as compared with S.
cerevisiae are, (i) autoregulation of transcriptional activator
KlGal4p (ii) dual role of KlGal1p as a metabolizing enzyme as well
as a galactose sensing protein (iii) shuttling of KlGal1p between
nucleus and cytoplasm (iv) nuclear confinement of KlGal80p (v)
KlGAL4 is the only gene in GAL system with one binding site, while
remaining genes having two binding sites. A steady-state model was
used to elucidate the roles of these molecular mechanisms in the
transcriptional response of the GAL system. The steady state
results were experimentally validated with measurements for
β-galactosidase to represent the expression for genes having two
binding sites. Subsequently, the steady state model was extended to
determine the dynamic profile of fractional protein expression and
was compared with experimental results. The results show that the
autoregulation of the activator protein KlGal4p is responsible for
the leaky expression of the GAL genes even at high glucose
concentrations. Further, the GAL gene expression in K. lactis shows
a maximum expression level of only about 35% at high galactose
concentration. The low expression levels are due to the fact that
the bifunctional protein KlGal1p is limiting in its function
towards the induction process in order to cope with the need for
metabolizing lactose/galactose. The steady-state model of the GAL
system of K. lactis provided an opportunity to compare with the
design prevailing in S. cerevisiae. The comparison indicates that
existence of a protein, Gal3p, dedicated for sensing of galactose
in S. cerevisiae due to genome duplication has resulted in a system
which metabolizes galactose efficiently. While presence of glucose,
the absence of Gal4p autoregulation help S. cerevisiae completely
switch off the GAL system.
Systems Biology of GAL Regulon in Saccharomyces cerevisiae and
Kluyveromyces lactis Venkatraman Prabhu, K.V. Venkatesh* Department
of Chemical Engineering, Indian Institute of Technology Bombay,
Mumbai, -400076, India [email protected]*
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Abstract
Reactive Distillation (RD) combines reaction and distillation in
a single unit to offer enhancement in the overall performance of
the process. It leads to enhancement in conversion for reversible
reactions and selectivity improvement in multiple reaction schemes.
The main underlying principle in application of RD for selectivity
engineering is to facilitate the separation of selected components
and favorably manipulate the composition profiles in the reactive
zone to expedite the desired reaction. In the present work, a
geometric approach of attainable region (AR), which is already
developed for conventional reactor network, is extended further to
include representative RD configurations. AR is the set of all
compositions that are achievable by a reactor network which may
consists of ideal reactors and few representative RD units such as
reactive rectification and reactive stripping. A model reaction
with van de Vusse scheme (A B C and 2A D) was studied and an
algorithm is developed to obtain AR for the given kinetics, feed
composition and relative volatilities. AR should be convex with
newly defined RD composition vectors on the boundaries should
always point inward. The RD vectors emphasize on the need of RD
model networking to enlarge the set of attainable compositions
until no further enlargement is seen. As an illustration purpose,
van de Vusse reaction scheme with unity rate constants and
increasing relative volatilities order (αA>αB>αC>αD) is
examined. The regions defined by basic RD models viz, reactive
rectification and reactive stripping overlap only over a certain
conversion range, which implies insufficiency of a single type of
RD unit for maximum selectivity towards desired product ‘B’ over
the entire conversion range. This invites the necessity of
networking of RD models among themselves and possibly with
conventional reactors. The AR for corresponding RD network thus
obtained for representative case is shown in Fig.A. The dark line
represents attainable region, whereas dotted lines correspond to
the profiles of reactive stripping and rectification units with
varying number of reactive stages.
A Geometric Approach to Reactive Distillation: the attainable
region and optimization in concentration space Vinay Amte*, Sanjay
M. Mahajani, Ranjan K. Malik Department of Chemical Engineering,
Indian Institute of Technology Bombay, Mumbai, -400076, India
[email protected]*
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Fig. A: Attainable region for the van de Vusse reaction (A B C
and 2A D). (relative volatilities: [5 3 1 1], rate constants: [1 1
1], Damkohler number: 0.005)
The results obtained through the algorithm developed above are
verified with independent simulation that maximizes selectivity. In
almost all different cases of kinetic regime and relative
volatilities, RD models perform better than conventional
reactors.
Keywords: reactive distillation, attainable region, van de Vusse
reaction, composition vector
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Abstract
First principles models offer better insight into evolution of
the plant states and have better prediction capabilities over a
wide operating range. Accurate estimation of the states is
important for applications like predictive control,
fault-diagnosis, etc. In presence of various unmeasured
disturbances and noise, the model may not be able to accurately
predict the states. The model, therefore, needs to be augmented
with an unmeasured disturbance model to generate better estimates,
and, in turn, better predictions of the states. In practice, the
structure and the parameters of the unmeasured disturbance model
are unknown. Moreover, the disturbances could be correlated in
time. In this work, given a reliable mechanistic model, a
systematic approach is proposed to construct an unmeasured
disturbance model using operating input-output data. A chosen
subset of unmeasured disturbances, which enter the system dynamics
as inputs are modeled as state realizations of a time series model.
The disturbance state space model is then combined with the
mechanistic model to construct a grey-box state observer. The
unknown parameters of the unmeasured disturbance model are
identified using prediction error method. The application on a
benchmark distillation column indicates the ability of the proposed
gray box model to capture the effect of unknown disturbances and
noise effectively.
Development of Gray Box Observer for a Distillation Column Vinay
A. Bavdekar and Sachin C. Patwardhan* Department of Chemical
Engineering, Indian Institute of Technology Bombay, Mumbai,
-400076, India [email protected], [email protected]*
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Abstract Flow cytometry employs hydrodynamic focusing of
concentric streams to measure the scattering and fluorescence
properties of cells and particles as they pass through laser beams.
This work illustrates the applicability of flow cytometry in fields
as diverse as cellular analysis and vesicle structure. The first
part of the work focuses on cellular assays which include
internalization of nanoparticles by NIH 3T3 cells and estimation of
intracellular reactive species (2’,7’-dichlorodihydrofluorescein
staining) and cell viability (propidium iodide staining) in HL-60
cells treated by retinoic acid-loaded copolymer nanoparticles. In
the second part, flow cytometry is used to analyze surfactant
micro-vesicle structures. Results indicate successful estimation of
nanoparticle internalization by flow cytometry and quantitative
assessment of the iROS and cell viability. Further, the technique
has been used to distinguish several types of micro-veiscle
structures like versosomes, multi-lamellar and uni-lamellar
vesicles. Characteristic signatures associated with these
structures have been identified and based on these the different
populations have been sorted and confirmed by microscopy. The
method can thus be used as a probe in a wide variety of areas.
Keywords: Flow cytometry, nanoparticles, cell viability,
micro-vesicles
Flow Cytometry: One Tool, Diverse Applications Manu Tiwari,
Jayesh Bellare* & Sameer Jadhav Department of Chemical
Engineering, Indian Institute of Technology Bombay, Mumbai-400076,
India [email protected] *