Yeah, welcome to Massive Open Online Course
on Chemical Process Intensification. In this module, the mechanism of intensification
we will discuss in this lecture, the intensification by fluid flow process. In the previous lecture we have discussed
something about the strategic aspect of chemical process intensification. So, based on that strategy how intensification
in the chemical engineering processes can be carried out, that has already been discussed. So as an extension that we can here describe
something about what are the mechanism of that process intensification in multiphase
flow system? So, as you know that, in our different chemical
engineering processes the different phases are directly or indirectly taking part for
a particular process yield. So, in that case you have to know something
about that, the multiphase flow system. So multiphase flow system, how it can be defined? That the multiphase flow system can be defined
as the system where the materials with different states or phases like gas, liquid and solid
can be taking part for a particular process. So that is called multiphase flow system. And process is called multiphase flow process. The multiphase flow also defined in different
other way, like if there are two phases immiscible to each other in a particular flow then you
can say that those phases will be different in their chemical properties. So, materials with different chemical properties
but in the same state or phase can also be referred to as multiphase flow. In this case, remember that whenever we are
processing any chemical engineering system, in that case when multiphase are taking part
for that particular process, in that case one of the phases is continuous while the
others are dispersed within the continuous phase. Like if suppose gas is dispersed in a continuous
liquid phase then we can say that gas is a dispersed phase and liquid is a continuous
phase there. So, in this case gas-liquid process like absorption
process or some other reaction processes also, gas-liquid reaction, there also these two
phases would be taking part but if that two phases would be taking place in presence of
solid catalyst then you can see here there will be a three-phase flow. So, in that case, the two phases may be in
that case discrete like gas and solid particles will be discrete where as liquid will be in
a continuous phase. So, in any multiple or multi phase flow system,
you can say that one phase should be discrete and another phase should be continuous. So, we can divide this multiphase system into
two system like gas liquid system or two-phase system and then three phase system. But two-phase system, not only the gas liquid,
there should be other like liquid solid, even gas solid system also. So, the two-phase will be as like gas-solid,
liquid-solid, and gas-liquid. And three phase system gas-liquid-solid. So, gas or liquid acts as continuous phase
there somewhere in particular processes and gas or solid acts as discrete or dispersed
phases. Sometimes if liquid is spraying as a dispersed
phase of droplets in a gaseous medium then that case liquid droplets would be a discrete
phase and gas will be continuous phase. So, gas phase may be either in continuous
or discrete, both may be there as per particular application. And let us have some application of that different
multiphase flow systems first. So, what are those gas liquid flow systems? In this case gas is used as a dispersed phase
and liquid as continuous fluid. Like absorption of gas in liquid to remove
it from gaseous mixture, example mixture of COx, NOx or hydrogen sulphide et cetera from
polluted air in solvent. Like ozonation of arsenic to arsenate or removal
of ammonia or dye in water treatment there. So in that case gas liquid operation is most
important. And also, some other applications like gas
liquid chromatography for analysis of liquid petroleum fractions, in that case gas liquid
both are taking part in this particular analysis. Even gas liquid reaction process like industrial
gases like oxygen, oxygenation process, hydrogenation process, carbon monoxide and carbon dioxides
those are widely used for synthetic processes in the chemical industry to produce different
type of hydrocarbons. So in that case gas-liquid systems are important. Liquid gas systems, as an example here in
this case, liquid is used as discrete fluid and gas as continuous fluid like in spray
column, the liquid is sprayed in gaseous medium for absorption of gas where as spray towers
can be very effective in removing pollutants if the pollutants are highly soluble in the
liquids there. And also, in the production of superphosphate
used in manufacturing fertilizer they are also this liquid will be used as a discrete
phase, and also production of silicon tetraflouride and hydrogen flouride gases are vented from
various points in the process where this gas-liquid operations for the production of superphosphate
used in manufacturing fertilizer, silicon tetrafluouride and hydrogen flouride gases. And spray towers are also used for odour removal
in the bone metal and tallow manufacturing industries by scrubbing the exhaust gases
with the solution of potassium permanganate. So, these are some applications where liquid
and gas will be taking part. In that case liquid will be discrete and gas
will be continuous phase. The gas solid system you will see there are
several applications of this gas solid system, the chemical engineering process and the heart,
it can be said that the gas solid operation are the most important and diverse application
in chemical industry. In that case, there are two processes like
physical processes and even some reactive processes, gas solid reactions are there. In physical processes like drying of particles
in that case, fluidization operation is very important. Coating of surfaces, granulation, even you
know heat treatment and also you can say that filtration, blending and segregation or classification
of the solid particles in fluidized bed. So, these are actually gas solid operations. Also, in gas solid reactions like roasting
of ores, combustion of coal to produce different types of hydrocarbons, even for power plant
operation to produce the power there, of course, this coal is combusted and there different
types of gaseous products are coming out and separating those gaseous products, they have
been used for several purposes And also, those are used for unwanted gas
also sometimes producing the steam by, just by burning coal and that steam will be used
for, or is being used for the production of power and thereby just by rotating the turbine. So, in that case that gas solid operation
is important. And also, calcination and limestone phosphates,
even aluminum hydroxide, fluid coking etc for that, these gas solid operations are very
useful. And also, liquid-liquid system, there are
several applications for this liquid-liquid system. Liquids are used as both here, discrete as
well as continuous phase. Like use for flow of emulsion of oil, and
water in pipelines. Different types like contactors like packed
bed, packed columns, pulsed columns and stirred tank reactors in various applications where
liquid and liquid systems are important. Also, liquid-liquid extractions, solvent extractions,
to remove the contamination from the waste water, the extraction of that contaminants
by another liquid component or organic liquid that is also important. So liquid-liquid extraction is also important
just to remove some contaminants from the waste water or some other liquid medium where
it will not be useful. And liquid solid system where hydraulic conveying
of solid materials are there, so it is important. And in that case solid particle is dispersed
in liquid and slurry flow covers a wide spectrum of applications there. That ranges from transport of coals and ores
to the flow of mud. And also, in crystallization you will see
solids are suspended in liquid, and the flow of liquid through a solid is another example
of porous media flow. So, these are the operation for the liquid
solid system. In three phase systems you will see some gas
liquid solid system, if your combination of this separation of gas, liquid, solid you
will see in the mineral industry, the flotation is one of the important process by which that
metals will be separated from its ore. Valuable metals will be separated from the
ores. In that case also the flotation process important
and during that flotation this aeration is being done and during that aeration this gas
and liquid and solid both, three phases will be taking part. And also, sometimes some, you know fine particles
to be removed from the muddy water Or you can say that milk, water where solid
particles are suspended. To separate those fine particles this flotation
process also important. In that case surfactant, some you know that
products to be used so that, that as per froth flotation, that, these fine particles will
be separated by aeration. So, in that case gas and liquid and solids,
three phases are taking part. Other applications like fluid bed catalytic
cracking in presence of some catalyst particles, hydro cracking, hydroprocessing and biochemical
processes, those are involved in three phase systems. And very common flows of oil water natural
gas that is found in condensation or evaporation of immiscible liquid mixer. There also gas-liquid-liquid systems are important. And solid-liquid-liquid systems there you
will see in pipelines that sand is mixed with oil and water the three-phase flow is important
there. So, these are the various applications of
the three phase systems. And four phase systems also, one application
like in freeze desalination process, you will see that when butane liquid is added into
a saline water that will results a formation of icicles, and in this case, system is a
mixture of butane liquid, water, ice and the butane vapor. These four phase systems are there. That is why four phase systems are there it
is considered. So, we have then seen the different applications
of four phase systems. In our daily life whatever products, we are
getting, all processes by which these products are coming out are related to the multiphase
flow systems. Whether it is gas liquid, liquid solid, or
gas solid or gas liquid solid system even gas liquid solid and vapor system both are
directly or indirectly related to the particular processes. So, based on these multiphase flow processes,
whenever we are going to perform this processes in a particular unit, that process can be
intensified based on the development of the unit or equipment or based on the fundamental,
like that phenomena, even sometimes the fluid phenomena, based on the fluid phenomena, based
on the equipment size, based on the, you know that policy, so we can intensify the process
in different aspects. So, in this lecture we will discuss that based
on these multiphase flow systems what are the different mechanisms of the process intensification
which are being used in industry as per process intensification background. So, flow-based process unit for intensification
you can say that some important chemical engineering process unit for process intensifications
are like this, trickle bed reactor where liquid phase and gas phase are flowing through the
packed bed and there liquid phase will be flowing as a, you know laminar stream just
as called trickle phenomena so that is trickle bed reactor. So, in that case you will see that plug flow
phenomena will observe. And then reaction efficiency or that, you
know that process performance will be higher than the conventional processes for that particular
process. Bubble column reactor, there also it is being
developed based on the increase of, or enhancement of the interfacial area between phases. Like in bubble column reactor if it is two
phases, gas liquid operations or the physical operations like carbon dioxide gas will be
absorbed in a sodium hydroxide solution there. In that case, gas phase is dispersed in that
column, as dispersed phase of bubbles in the continuous liquid medium there as a sodium
hydroxide solution. In that case whenever bubbles will be forming
there will be interface between the bubbles and liquid. So, you can get that interfacial area through
which there will be a mass transfer and based on that mass transfer you can say that absorption
of that carbon dioxide gas in the gas phase mixer, this will be absorbed in a liquid medium
through the interface. So, if you can increase the interfacial area
you can have the more efficiency of the absorption process. So that is why the process intensification
can be obtained based on this enhancement of this interfacial area. Fluidized bed reactor also there are several
applications of this fluidized bed operation, like you know the drying operation or roasting
operation, whatever. Suppose coffee, we are getting, that is dust
coffee we are getting in our coffee shop that is actually after several processes, initially
that coffee bean, the raw coffee bean is green coffee bean. And whenever it would be roasted, this being
done in a fluidized bed you will see at a certain temperature, 400 like 50 degree Fahrenheit,
that case you will see after roasting of that coffee bean in fluidized bed that here will
be, you know that mixing of that coffee bean with the gaseous, hot gaseous mixer and there
will be particle interactions and you will see heat transfer will be more important there. And based on that heat transfer that coffee
bean will be becoming that brown coffee bean and after that it will be becoming dust and
to serve you as coffee. So, in that case the coffee bean is roasted
in a fluidized bed. So there, why fluidized bed is there, why
not simply that in a, just in a bed, just we are heating it? Not like that. If you are heating that coffee bean or some
other any particles you can see in a fluidized bed there will be intensification of process
for better heat transfer, better interfacial heat transfer between the solid particles
and the gas. So that is why the fluidization operation
over there. Even for mass transfer also, in the fluidized
bed you will see for Fisher-Tropsch synthesis there, for better contact and better mass
transfer, you are just doing that fluidization operation. So fluidized bed is one also important intensified
process in chemical engineering. Rotating packed bed also to get the better
contact of the gas and liquid and solid particles, we are having this rotating packed bed. Spinning disk reactor also better mass transfer,
heat transfer, this spinning disk reactor important there also, the making a thin film
in this spinning disk reactor so that the mass transfer through the liquid film will
be intensified there. So that is why this spinning disk reactor
is important for this chemical engineering process where the intensification is being
done. Multiphase monolith reactor also is important
nowadays. There, you know that, some catalyst particles
in a particular fashion, in a particular, you know that structure; this catalyst particles
will be produced and arranged so that the interfacial area will be more and then reaction
will be better there. So, these are the various process equipments
for process intensifications which are being used in chemical engineering processes. And you will see flow-based process unit for
intensification like other heat integrated reactions for high temperature, millisecond
contact time and catalysts also important for this process intensification. Micro engineered reactors are being developed
nowadays for chemical engineering processes. Monoliths as biocatalytic reactors are developed
as a process intensification, membrane separations nowadays are widely used in chemical engineering
process for separation of the particles, even nanosized particles are being separated by
this membrane separation processes. So, this is also an important intensified
process. Two phase flow under magnetic field gradient
also important there, applications of ultrasound in membrane separation process nowadays are
in research stage to apply for chemical engineering process. Various mechanisms like yes, slurry bubble
column reactors, in that case for creating more interfacial area between phases to enhance
the mass and heat transfer. So, slurry bubble column reactor is one important
process intensified unit that based on the multiphase flow system. Fluidized bed reactor for better heat and
mass transfer operation of the gas liquid flow important, and also rotating disk packed
bed in that case, better mass transfer, well mixed liquid, you can see and gas phases,
high interfacial surface area, even you can operate it in counter current mode. So, these are some basic mechanism based on
which this multiphase flow system-based process intensified unit are developed for chemical
engineering processes. Even you will see compact heat exchanger like
in that case, the reducing channel size will give you the better power generation. Even by surface enhancement, by metal coated
polymer foam for micro power generation, foam heat exchangers are developed and based on
the increase in residence time and better phase mixing, downflow system or inverse flow
reactors are nowadays coming to get more contact time, even for more residence time of the
phases in the reactor. Membrane distillation is one of the important,
you know that integrated system where transport mechanisms are Knudsen diffusion, PoiseuilleÃs
flow and molecular diffusion all these processes are simultaneously happened. And the thermal boundary layer is considered
to the mass transfer controlling factor here in this membrane distillation process. Even you will see liquid membrane system also
one of the important process where diffusion can be enhanced by liquids then in solids,
in that case transport rate several orders of magnitude higher than the solid membranes
because their diffusions is faster in the liquids compared to the solids. Reactive separation also nowadays important
because you know that in fluid system the reaction as well as separation both will be
combined in a particular unit and in that case chemical process industries, they are
using this, they are following this integrated system to have the favorable economics for
carrying out reaction and simultaneously with separation for certain classes of reacting
systems and many new processes called reactive separations are carried out. Like methyl acetate production, there you
will see both; you know that reaction as well as distillation is being happened in a particular
column. So, in that case here in this picture it is
shown that how methyl acetate is produced in a distillation column. Methanol is supplied and catalyst as sulphuric
acid in that case, the reaction is being carried out in a particular zone. After that whatever products are coming out,
those will be separated, that is the, what is that methyl acetate and the water to be
separated after that distillation also. And so here this reactive separation is one
of the important mechanisms of process intensification. In that case combination of separation and
the reaction inside the single unit happens. Like some of the fatty acid esterification
also, one of the important, this reactive separation process there so the reactive separation
is important as a process intensification. And the reactive separation units you will
see may also be treated as a kind of multifunctional reactor in which the functionalities of several
processes are combined to generate the new reactor concept. You will see in this diagram there if we are
considering that gas and liquid there may be reactive absorption between that gas and
liquid system. And reactive distillation also happens within
this gas and liquid system. Reactive absorption also happens, this gas
and liquid system. Even gas and solid system there you will see
that the reactive adsorption also important and liquid and solid system, there reactive
chromatography this process is important and also liquid-liquid system, there reaction
extraction is the example for that liquid-liquid system. So, this you can say that in multiphase process
systems how different chemical engineering process can be intensified for a particular
reaction based on that, you know that combination of unit operation like reactive separation,
reactive distillation, reactive extraction in that direction. And feasibility of the reactive separation,
that depends on various parameters like mechanical design, chemical reaction, event separation
performance also. So, in this diagram you will see some, at
a particular temperature and pressure you will see how chemical reactions are being
taking place for a particular process intensification. Even mechanical design, how it will be giving
you that process intensification for that particular operation. So, in this case we can say that any reactive
separation process that depends on mechanical design, even chemical reaction performance
and the separation performance. The most important examples of the reactive
separation processes are reactive distillation, reactive absorption and reactive extraction
processes. Common feature of that reactive absorption,
distillation and extraction are that these processes involve at least one liquid phase
and the properties of the liquid state become significant in that case. And they occur in moving systems. Thus, the process hydrodynamics play as an
important role there. Because all the process performance depends
on the mixing processes, even some other particle interactions like is there any gas solid particles,
if they are gas bubbles and solid particles, even solid and solid, then solid-solid interaction,
gas-gas, gas-particle interaction, even bubble-bubble interactions like bubble-bubble coalescence,
bubble breakups, if you are having more breakup of the bubbles you can produce more finer
bubbles so that you can get more interfacial area. Even if your process is more prone to coalescence,
bubble coalescence in that case performance will be less. So, you have to design a unit in such way
that some mechanical probition to be placed so that the breakage of the bubbles will be
there. Even uniformity of the bubble flow will be
there or interfacial phenomena will be created in such a way that the uniform mixing will
be there, even the distribution of that phases will be there so that that you can get the
better performance of the reaction and even processes. So the properties of the liquid state become
also significant there. In that case what we have to do that what
type of fluid are being used, that whether it is corrosive or not that also you have
to think about it so you have to synthesize a solvent which are not that much of hazardous
and not corrosive. So even if it is corrosive you have to design
the unit in such way that the wall surface of that unit should be non-corrosive. So, the process intensification should be
in that directions. So, the properties of the liquid state should
be considered for that particular process intensification. And how to control that hydrodynamic cons
are there. So if there is heterogeneous mixture, to make
it homogenous, to get better performance you have to make a provision like sometimes you
know that, to reduce the back mixing you have to use some waffle. Or you have to design that unit like two dimensional
or even microstructure system so that, that back mixing will be reduced. So, to get that reduced back mixing you can
intensify the process intensifications just by allowing it as a plug flow reactor because
plug flow phenomena will give you the better performance of the reactions and also other
physical operations there. These processes are based on the contact of
at least two phases also where these reactive separations or you know that absorption, distillation,
or extraction are there. So for mass transfer through the interfacial
area there of course two phases should be involved and therefore the interfacial transport
phenomena have to be considered for process intensification. And also, further multicomponent interactions
of the mixture components, a tricky interplay of mass transport and chemical reactions and
complex processes chemistry and thermodynamics issues should be considered. So those are involved in those particular
process intensifications. Now let us consider that reactive distillation,
some features of that. In that case complex interactions between
chemical reaction and operation and also if it is there, separations of course will be
there, based on that complex interactions of the phases and the performance is influenced
by the size and location of the reactive and non-reactive column and also you know that
reflux ratio is one of the important parameters. Feed location and throughput by which you
can change the hydrodynamics in the column for that reactive distillation system. Like esterification and hydrolysis reactions
which are catalyzed by acidic ion exchange resins like Amberlite 15, one of the important,
you know that resins in which that, you know that reactive distillation as well as separation
is being happened in a particular unit. And you will see that reactive distillations
where the reactants to be transferred into the reactor and heat integration is important
phenomena and after that integration you will see whenever products are coming out, some
unwanted or unreacted products, unreacted reactants to be recycled and then final products
should be separated based on the separation principles. And this successive, you know sequential operation
of these reactive distillation can be organized here in the figure as shown in b. Here that reactant is supplied and in a particular
zone that reaction as well as distillation, both will be happened and at the top and bottom
sections that as far as you know that density difference and boiling point differences that
products should be coming out or separated and from the top that product A will be coming
out and from the bottom B that heavy products will be coming out. So, in that particular unit the sequential
you can say the, you know in some zone the distillation and reaction both will be happen
in that and after that the distillation process will happen in that particular unit. So, to intensify the process we can say that
there is also a need to improve the catalyst and column internals for the reactive distillation
applications. And also, reaction and distillation takes
place within the same zone of the distillation column. Reactants are converted to products with simultaneous
separation of products and recycling of unused reactants and among suitable reactive distillation
processes like etherifications, nitrations, esterifications, trans-esterifications and
condensations and alkylations are the most common applications in reactive distillation
process. These operation provide, you can say promising
processes, alternatives to traditional sequential operations for this particular operation. Now what are those, actually advantages for
which that reactive distillations are being carried out in a single unit? In this case it is a new, you can say less
expensive products, even avoiding some hotspots, saving due to smaller equipment you can say,
less environmental pollution, higher efficiency because of overcoming the thermodynamic and
kinetic limitations, better selectivity to suppressing of undesired reactions. So, these are the some, you know that potential
advantages of reactive distillation system. In case of reactive absorption, you will see
some example here. Carbon dioxide absorption in liquid here,
suppose air and carbon dioxide mixtures are being supplied from the bottom of the packed
bed reactor, in that case water and sodium hydroxide solutions to be used for liquid
and through that liquid in a packed bed this air plus carbon dioxide mixture will be supplied. And you will see parallelly that reaction
as well as absorption will happen. When reactions will happen in the packed bed
there will be product like water and what is that, sodium carbonate and water and along
with air, air will be coming out from the, you know that top of the packed bed as a clean
air. So, during that operation you will see if
we use the sodium hydroxide for absorption of carbon dioxide there the reaction as well
as absorption both will happen. Here reaction will be sodium hydroxide and
carbon dioxide will react and it will give you the sodium carbonate solution and that
sodium carbonate will be used for other application. So, in this case the scrubbing of this carbon
dioxide is happened from this air carbon dioxide mixture and clean air will be coming out from
the top of the column. Even absorption of stack gases like sulphur
dioxide, gas plus sulphur dioxide mixture, if they are to remove that sulphur dioxide,
if we use that calcium carbonate in a solid medium then you will see that calcium carbonate
will react to sulphur dioxide. It will give you the calcium sulphate and
that calcium sulphate will be, you know precipitated and remaining, you know solutions will be
reused and then carbon dioxide without sulphur dioxide will be coming out as a gaseous medium. So, in that case you can purify that gaseous
mixture for the sulphur dioxide or stack gases by this reactive absorption. In this reactive absorption you will see that
reaction occurs simultaneously with the component transport and absorptive separation in the
same column zone and it is used for the production of basic chemicals like sulphuric acid, nitric
acid and for the removal of components from the gas and liquid streams. And also, absorbers or scrubbers where this
reactive absorption are being carried out are often considered gas liquid reactors and
this can either be the cleanup of all process gas and streams or removal of toxic or harmful
substances in flue gases. So, the reactive absorptions are actually
considered both to actually perform like reaction and absorption. And it can be realized in a variety of equipment
types here in film absorbers, plate columns, packed units and bubble columns. And this process is characterized by independent
flow of both phases which is different from distillation and this will permit both cocurrent
like downflow and upflow and also counter current operations. So this reactive absorption you can intensify
either by absorber reactors or by designing some other different types of columns like
plate columns, packed columns, bubble columns, even intensification of bubble columns in
two dimensions, three dimensions, even bubble columns, downflow bubble columns, even bubble
columns with waffles, even some, you know that use of spargers, even producing more
finer bubbles by using different types of spargers, in that direction you can intensify
the bubble columns also. And this process can be characterized by;
you know that different mode of operation. In that case you can use the downflow system
to increase the mixing as well as increase the residence time of the phases and upflow
systems where the first reaction is being carried out, in that case upflow operations
is important where counter current operations also important where you will see that physical
separation or you can say that some mass transfer operations for mineral processing in that
case this counter current operation is also important. Reactive absorption represents the process
in which selective solution of gaseous species by a liquid solvent phase which is combined
with the chemical reactions and as compared to the purely physical absorptions, reactive
absorptions does not necessarily require the elevated pressure and high solubility of the
absorbed components because that chemical reaction in that case the equilibrium state
can be shifted favorably resulting in enhanced solution capacity there. So, we can say that most of the reactive absorption
processes involves their reactions in the liquid phase only and in some of the cases
both liquid and gas both will be taking places in the, as a medium so the medium also, the
mode of operations and discretizing the system, discretizing the medium also sometimes way
of the intensification of the process. Now in reactive extraction, in that case,
reaction as well as extraction both will happen and this reactive extraction uses liquid ion
exchangers that promote a selective reaction or separation. And the solutes are very often ionic species
like metal ions or some organic or inorganic species or you can say some intermediates
like furfural phenols etc. This can be used for separation and purification
or you can say that enhancement of the conversion of units, for the conversion of salts in the
units there. Like for biodiesel processes their combination
of extraction of oils using a solvent with the esterification reaction that will give
you yield of fatty esters, it is called biodiesel. So, the reactive extraction is the process
intensification by which you can produce the biodiesel there. And liquid-liquid extraction is sometimes
based on the partial miscibility of the liquid so you have to derive some liquids where that
immiscibility will be there but separability, capability of that liquids will be enhanced
there. So, both the way you can increase. So, immiscibility as well as that, you know
that, you know that absorbance of the contaminants in that particular liquid should be increased. In the simplest extraction system two compounds
have to be separated there and this can be done by extracting with a carefully selected
solvent in which one compound that is called solute easily dissolves where as the other
does not. Like as an example you can say that like propionic
acid to be actually separated from the liquid water or you can say waste water in a, you
know that paraffin or like octanol or Decanol like organic compounds. In that case Decanol and this water is immiscible
and propionic acid is miscible with water. So, from the water, this mixed propionic acid
to be separated by that Decanol and so this Decanol and water should be immiscible. And also, there should be selectivity based
on the boiling point also. You have to use the organic compounds which
have the boiling points which are higher difference with the, you know that propionic acid so
that after, you know that extraction of that propionic acid in a Decanol as an example
here which is to be separated by just distillation So, in that case, you have to select the organic
solvent in such way that where this compound or contaminant in the liquid can be easily,
you know that, transferred to the liquid medium which will be immiscible in the, you know
that continuous phases. So based on which this immiscibility, these
two liquids will be, or organic liquids will be produced as a droplet form so that you
can get the more interfacial area through that mass transfer or here in this case, as
an example, that propionic acid to be transferred through the interface of this liquid-liquid
to the, you know that Decanol or paraffin, some other organic liquid. So, this is the mechanism by which that liquid-liquid
extraction being happened, and in that case most important that you have to select the
suitable solvent where that you can produce the droplet and you can easily separate those
compounds after, you know that extraction of that contaminant. And also, it is related to the droplet phenomena
that I told that if you produce that droplet, if you are producing more finer droplets you
can get more interfacial area so that, you know that your extraction will be more and
process efficiency will be more. More mass transfer will be there. So that is why this reactive extraction process
that depends on your, you know that design and how it can be designed, how to produce
that more finer droplet, how to select that solvent, so for that, to produce the more
finer droplet there, you have to design some unit like mixer settler systems. You have to use some mechanical provision
so that, that more turbulence will be there, more interfacial area to be produced by producing
droplet. Column extractions to get the more interfacial
area between the liquid and liquid so that you can have more extraction. Even sometimes centrifugal extractors also
are being developed for process intensification for this extraction. In that case, centrifugal action, centrifugal
force will be applied to separate those liquid contaminants into another liquid by just action
of gyration, and also making a thin film of that liquid, immiscible liquid so that through
that thin film that mass transfer will be more efficient. Counter current column extractors can be further
subdivided into, you know that non-agitated, non-proprietary columns and agitated proprietary
extractors. In that case you will see sometimes that counter
current operations are being used there to actually design economically so that, that
without making a droplet how you can increase the, you know that efficiency of the extraction. So, in that case you can save some energy
and also, you know that easier to handle those operations. That is why counter current column extractors
are also one of the important intensifications of this extraction process. So, the extraction process you can say that,
various forms of energy inputs are required like rotation of propellers, impellers, disk
propulsion and also that pulsation process, even you know vibration and ultrasonic devices
and centrifugal devices. So, to run those equipments for this process
intensification of extraction you need various forms of energy. And agitating the liquid-liquid system that
breaks into droplets, to use this energy you can increase the droplets, you can increase
the interfacial area so that you can get the better mass transfer of extraction. And also, if you increase the droplets by
this energy you can increase the interfacial area to improve the mass transfer and column
efficiency. Other important intensification processes
of multiphase systems are development of, you know the microreactor, microchannel based
heat exchanger. In the case of microreactor, multiphase based
micro reactor, in that case they have some potential for the rapid heat and mass transfer. The enhancement of this transport processes
is related to the, you know that decrease of diffusion paths on the micro scale phenomena. For first multiphase reactions, these are
very important and the rate and selectivity of the chemical process, that can be greatly
influenced by the transport of this reagents within the, you know that phases. And here as shown in figure, some microchannel
based reactor where you know the porous catalysts are being used and the microstructure packing,
in that case, through that packing there will be reactions as well as mass transfer and
heat transfer will be there. So to increase that interfacial area, these
microstructure reactors are being developed and which, you know that enhancement of the
transport processes are taking place. And variety of different purposes also are,
you know that fulfilled based on this, you know the application and requirement of high
heat and mass transfer coefficients in the microreactors and also in the microreactors
we are getting that well-defined flow patterns and because you know that heterogeneous flow
patterns sometimes, there back mixing are being used or actually seen in the column
reactors. There to avoid those back mixing, so microchannel
based, you know slag flow pattern or plug flow patterns are, you know that devices. So that mechanisms are being used for process
intensification. The spectrum of the applications includes
gas and liquid flow as well as gas liquid or liquid-liquid multiphase flow systems in
this microreactor system. So why this intensification from macro to
micro reactor? So, when comparing the process in microreactors
with those in conventional systems, a few general differences can be identified. Like flow in microstructure is usually laminar
in contrast to the turbulent flow patterns on the macro scale and the diffusion paths
for heat and mass transfer are very small making microreactors ideal. And you can say that for heat and mass transfer
limited reactions which are very, you know convenient in these particular microreactors. The surface to volume ratios ofcourse in this
microstructure reactors are very high and thus surface effects are likely to dominate
over the volumetric effects. The share of solid wall material is typically
much higher in macroscopic equipment, thus the solid heat transfer plays an important
role and has to be accounted for, when designing that microreactors. And using, like silicon micro fabrication
it is possible to construct packed bed microreactors that provide a hundred-fold or more improvement
in mass transfer for gas liquid heterogeneously catalyzed processes such as hydrogenation
of unsaturated hydrocarbons, that is actually reported by Losey et al in 2007. They have done this, you know hydrogenation
of unsaturated hydrocarbons in multiscale, multichannel, you know microreactor. And in these devices, standard catalyst particles,
50 to 75 picometer diameters are retained in silicon channels by an integrated microfabricated
filter unit, a specially designed gas liquid inlet section with narrow channels provides
that rapid contact of the gas and liquid reagents. And now in order to achieve those uniform
flow in that microreactors you will see that pressure drop in the inlet gas and liquid
sections that will be higher than those in the individual reactor channels. So, though it has the higher pressures, still
it has some advantages to get the more efficient reactions. The small particles provide the high surface
area for improved gas liquid mixing but they also represent a challenge in terms of pressure
drop and fluid distribution among the parallel channels. And the pressure drop can be reduced by replacing
catalyst bed by a microfabricated support structures there. And uniformity of the structured packing arrangement
also important in that case, you can control over the fluid flow, that is by this structure
packing arrangement and that will give you the enhanced relative to the micropacked beds
condition and the activity is greatly enhanced if the catalytic component which is supported
upon a porous layer and formed by making the silicon posts porous. And in that case, direct flourination as an
example, that can be served as an inspiration for development of flow distribution allowing
controlled scaling of gas liquid reactions from a few channels to a large number of channels
like 100 micro channels with uniform flow distribution at a flow regime of plug or liquid
segments. Another important intensification by changing
the geometry of the channel, in some cases for example when large residence times are
desired, in that case you will see the comparatively long microchannels are, you know have to be
integrated in such way that it will be make a curve-shaped and it will be made curve channels. And in addition to this, straight channels
are often not suited for connecting a, you know microflow domain to the external world
so that you are making that curved flow and also whenever you are making a curved flow
there will be a creation of secondary flow that is called Dean flow due to the curve
perpendicular to the main flow direction which will be induced by the inertial forces which
is the main factor for the process intensification. And the typical secondary flow pattern in
curved channel is given by two counter rotating vertices separated by the plane of curvature. The strength of these vertices increases with
increasing Dean number. For that this factor K, that is Dean number
will be represented by the Reynolds number into root over of D h by R where D h is the
hydraulic diameter of the curved channel and R is the mean radius of the curvature of the
channel. So, some other intensified unit like microheat
exchanger development, in that case you will see that the design of microheat exchanger
where the goal is often to increase the heat flux while limiting the pressure drop and
also for that, you know for some pumping power or pressure drop, a considerably higher heat
flux is achieved in the curved channel. So, in that direction, the curved microchannel
based heat exchanger are developed. And other intensifications like ultrasound
cavitation, application of ultrasound processing and synthesis are widespread and offer unusual
and beneficial operating conditions. Two major principles are used in sonochemistry
like; you know mechanical effects of mixing and disintegration, high energy process for,
you know radial reactions. Most effective process like in that case,
sound pressure sometimes developed to produce that cavitation to get the more interfacial
area. So, in that direction this ultrasound cavitation
has produced to get more interfacial area and more mass transfer there. So, we can classify that range of applications
of ultrasound process based on different multiphase systems like chemical and physical effects
of ultrasound, here homogenous systems, liquid and gas systems, sewage treatments, sonolysis,
nanoparticles, even novel materials, liquid-liquid systems like emulsification, extraction, sewage
sludge even phase transfer catalysis, mixing etc, liquid solid like cleaning, crystallization,
extraction, dissolution reactions etc. So, in this lecture then we have gone through
what actually that, what are the different mechanism of different process intensification
of the chemical process which are being intensified for particular process systems and different
mechanisms which are involved in this process. So, I think it will be helpful for, you know
further understanding of the process intensification in chemical engineering processes. So, I would suggest you go further reading
with this, you know that suggested books for this further understanding of process intensification
mechanism for various application in chemical engineering process, thank you.