hi friends now we will start discussion on
the second part of the module energy production
from organic wastes through fermentation in
the first part of this module we have discussed
on the fundamentals of fermentation and methanol
fermentation reactions and different feed
stocks means waste which can be processed
through this biological routes for the production
of ethanol and we have started discussion
on the production of ethanol from lingo cellulosic
biomass and we have covered the pretreatment
of lingo cellulosic biomass and detoxifications
and hydrolysis and in this part of this module
we will discuss on the fermentation microorganisms
and product recovery ethanol production through
gasification route and butanol production
from lingo cellulosic biomass
so we have seen that in fermentation process
the organic waste is converted to ethanol
and if we use the starch based feed stocks
then we get the glucose as sugar or hexsose
like say ah mannose galactose etcetera so
only hexose sugar are present in this feed
stocks and so ethanol reaction takes place
through this reaction but in lingo cellulosic
biomass due to the presence of cellulose lignin
and hemi cellulose we get after lignin separation
cellulose and xylose this hexose and pentose
sugar so this pentose and hexose sugar in
in monosaccharide or maybe in terms of disaccharide
can be fermented so we have two four feed
socks mean sugar that is glucose xylose cellubiose
and xylobiose so cellubiose is the disaccharides
of the glucose and xylobiose is the disaccharide
of xylose or arabinose
so these are the reactions so from all those
sugar we get ethanol and carbon dioxide and
these are that structure of xylose arabinose
and glucose so six sugar six carbon sugar
and five carbon sugar now how can we find
out the ethanol yield so ethanol yield is
defined as ethanol indicated to c v by m where
c is the ethanol concentration in gram per
liter and v is the initial volume of liquid
medium in liter and m is the mass of the substrate
in kg then we will get ethanol yield that
is y e t o h is that is in gram per kg now
what is the ethanol productivity if we can
determine the ethanol yield then if we divide
it by time then we will get the ethanol productivity
the definition of ethanol productivity is
the amount of ethanol produced per unit of
substrate utilized per unit of time
so this can be written as q e t o h that is
the productivity of ethanol that is equal
to c v by m into t if it is gram per kg then
it is fine otherwise if it it can be expressed
in m g per kg then we have to multiply it
by one thousand so eternal productivity is
equal to one thousand into y e t o h by t
in when the unit is m g per k g hour now what
is the maximum yield so maximum ethanol yield
is defined as ethanol production in reactor
in gram divided by theoretically available
ethanol that is sugar initially available
in the reactor into zero point five one one
into hundred so where from we are getting
this expression so if we have this reaction
say c six h twelve o six this is reacting
and it is this sugar is converted to c two
h five h plus c o two
so c two h five o s plus c o two to two c
two h five plus two c o two so this is the
reaction here so glucose molecular weight
is equal to six into twelve plus twelve into
one plus six into sixteen so that is equal
to one eighty and here we are getting two
into twelve into two plus five into one plus
sixteen plus one so two into forty six so
that is equal to ninety two so if we divide
this ninety two divided by one eighty then
it is becoming point five one one so this
function which we have got that point five
one one that means maximum with hundred percent
conversion of this glucose takes place to
ethanol then we can get zero point five five
one one times of this
so that is why this expression is there the
ethanol production is reactor divided by initial
sugar in reactor in gram into zero point five
one one into hundred that is the maximum yield
of ethanol production now we will see the
microorganisms which are suitable for the
production of ethanol from the lingo cellulosic
biomass as we have discussed that in lingo
cellulosic biomass we have both pentose and
hexose sugar and yeast that is saccharomyces
cerevisioe which is every conventional microorganisms
for the production of ethanol from organic
sugar is also applicable here because hexose
sugar is present but these natural strain
cannot ferment on the pentose sugar but some
type of yeasts are there that is pichia stipitis
and candida species basically
so candida shechatoe and candida parapsilosis
so these two can be these two stain can work
on the pentose sugar and converted into ethanol
so these are the yeast not only yeast some
bacterial species are also available which
can work on this sugar and give the ethanol
as a product some examples are given here
that is your zymomonas mobilis so this is
one bacteria escherichia coli is another one
and this is one klebsiella oxytoca so these
are some bacteria which can also work on the
sugar for the production of ethanol now efforts
are on how to get more efficient strain those
can be equally applicable or suitable to convert
both pentose and hexose sugar and genetically
modified microorganisms are being developed
and experiments are going on to develop new
microorganisms genetic genetically modified
which will be suitable for both type of sugar
for the ethanol fermentation
now once the ethanol is produced we have to
separate it as we have discussed in the first
part of this module that when ethanol is produced
in the fermenter the concentration is around
say eight to ten percent and then we have
to increase this concentration so we had used
some distillation unit so do after dissolution
it gives ninety five point five percent ethanol
so ninety five point five percent ethanol
after distillation and then we had dehydration
dehydration unit so these are the steps we
have discussed in the first part of this module
so this is these are on the thermal route
so for the recovery of the ethanol from the
solid residue as well as the waste water in
the fermenter we have two types of operations
or two types of routes one is thermal route
another is membrane based route
so low temperature route that is membrane
and molecular sieve these two processes are
being used in recent years and conventionally
this thermal route is available for the separations
of ethanol from the fermenting media or the
fermenter so from the fermenter we the steam
stripper then distillation and distillation
to vapor phase drying so a distillation if
we think than this by distillation we can
get ninety five point five percent of ethanol
then how can we get ninety nine percent pure
ninety nine point nine percent pure ethanol
preliminary at the initial stage the attempt
was like this azeotropic distillation was
utilized as well as ex extractive distillation
was utilized so azeotropic distillation one
third component was was added in this mixture
that is azeotropic mixture of ethanol and
water so we see here the ethanol boiling point
is seventy point four degree centigrade water
is hundred degree centigrade but when it is
a mixture azeotropic mixture the boiling point
is seventy eight point one degree centigrade
so if we can add one external agent in it
or external chemical in it which can lower
the boiling point further with respect to
water and that particular compound as as for
example we have cyclohexane and benzene anyone
can be used so cyclohexane boi boiling point
is eighty point seven degree centigrade water
is hundred degree centigrade but when it is
a mixture azeotropic mixture its temperature
is sixty nine point eight degree centigrade
so when this cyclohexane is added and use
in the distillation so cyclohexane and water
will goes off whereas ethanol will be remaining
in the bottom of the distillation column
so that way we can separate the ethanol and
that was the primitive approach then extractive
distillation in this case another external
component was added in this ethanol water
azeotro which increases the relative volatility
of the ethanol so as a as a result ethanol
comes with the solvent or it is in the vapor
phase and the water remains in the distillation
column so ethylene glycol is an example of
that extractive distillation so apart from
these some other methods like salt distillation
pressure swing distillations and pervaporations
are used for the separations of ethanol from
the media now we will discuss some other routes
which are applicable for the production of
ethanol so here two routes have been shown
one is by the gasification the waste material
can be converted to syngas and that syngas
can further we converted to ethanol through
catalytic reaction we have discussed in previous
modules that once syngas is produced that
can be converted to ethanol or methanol or
any other higher alcohol
so in case of methanol production koperoxide
best catalyst is used high pressure and temperatures
reaction is applied and ethanol also other
catalyst are used but this is not commercially
produced as on today and another route that
is biological route from syngas to ethanol
that is also being tested in laboratory but
not it is applied in commercial scale some
microorganisms have been developed which can
convert syngas that is c o c o two and hydrogen
the microorganism consumed is and ethanol
is produced so these are the other routes
but these routes are not commercial route
now we are coming on butanol production so
butanol can be produced through the fermentation
but here the process will be slight different
the separations of the butanol from the media
will also be slightly different from that
of ethanol production
let us see here the clostridium species the
bacteria that is clostridium acetobit butylicum
and clostridium beijerinckii are the two bacteria
which have been found to suitable for the
production of butanol from the sugar now when
butanol is produced not only butanol is produced
in the media other two components that is
acetone and ethanol are also produced that
is called a b e fermentation acetone butanol
and ethanol fermentation and in this fermentation
the product is a is to b is to e that is acetone
is to butanol is to ethanol is equal to three
is to six is to one so this is a typical ratio
of these three components in this methanol
for a butanol fermentation route or a b route
now a b e fermise a b e fermentation is if
by phasic fermentation that is acidogenic
phase and solventogenesis phase
so acid acidogenesis and solventogenesis two
phases are there unlike ethanol fermentation
so acidogenic phase involves the production
of acids like say acetic acid butyric acid
and then solventogenesis converts these to
solvents like acetone butanol ethanol etcetera
the a b e producing bacteria can utilize both
starchy and lingo cellulosic biomass all type
of biomass or waste can be used for the production
of this a b e now one important factor here
that butonal which is produced in the media
that is toxic to the microorganisms and it
has been found that if its concentration is
more than say two percent so the microorganisms
suffer their growth hampers so that is the
main disadvantage of this process
so efforts are going on to develop new strains
which are suitable to resist the concentration
of butonal in the media and application of
molecular techniques to the solventogenesis
clostridia has resulted in the development
of hyper butanol producing strains such as
clostridium beijerinckii p two sixty and c
beijerinckii b a one zero one so these two
strains have recently been reported that is
modified genetically modified bacteria which
are having more butanol production capacity
and we have discuss this process is not a
very similar to that of ethanol process because
the mechanism the microorganisms are different
and the concentration of butanol present in
the media is also very less with respect to
ethanol only two percent so we have to remove
this butanol from the media so the methods
will also be slightly different from that
of ethanol separation process
so now we will see how the butanol can be
recovered the main problem for the recovery
of the butanol from the media is that's it
is partial solubility with the water and its
boiling point is also high that is one one
seven around one seventeen degree centigrade
boiling point that is why for the separations
is requires higher heat with respect to ethanol
production through distillation that is why
to separate the butanol in the a b process
some in situ separation techniques are being
developed so out of those the some important
are adsorption liquid liquid extractions pervaporation
gas stripping and supercritical fluid extraction
however one important thing is that all those
techniques are in infancy stage there is no
any commercials plant and not here developed
but conceptually these are available and people
are trying to develop these techniques
so now you will see the how the adsorption
process or adsorption column can be used to
separate butanol from the media there is a
ferment fermenter so from the fermenter that
is around two percent of butanol it is passed
through the first column the absorption column
so two percent butanol will be at adsorbed
selectively on this adsorbent base bed and
this adsorbent bed will be taken out another
bed new bed will be put here then this old
adsorbent bed will be regenerated by heating
so butanol will be coming out or desorbed
from the media or from the adsorbent and product
butanol we can get so this is the mechanism
of the separation of the butanol from the
fermenter media now the materials which has
been used here so for that is activated carbon
zeolite and polymeric resins silicalite adsorbent
resims amberlite polyvinyl pyridine
so these are the adsorbents which have been
tested by many researchers for the recovery
of the butanol from the fermented broth next
we will discuss on pervaporation process so
pervaporation process this is one one membrane
is required this membrane is not porous or
molecularly porous that means size selective
all molecules will not be able to pass through
it some selective size of the molecules will
be able to pass through it so one side we
will send the broth and through this membrane
the butanol will pass through why it will
pass through because this is selective to
butanol and this is hydrophobic in nature
butanol is hydrophobic in nature so butanol
will come out through this membrane into the
this chamber so when it is coming in this
chamber this chamber is under vacuum or some
gas part is there so the produce the product
which is coming in this side of this of the
membrane that will be in vapor phase
so this is the mechanism of the separation
of the butanol from the media using pervaporation
process and from the vapor we will collect
the butanol next we will discuss on the supercritical
fluid extraction to supercri critical fluid
if we have some fluid if we increase the pressure
and temperature so it will reach its super
critical stage so beyond the critical point
it will be supercritical fluid and supercritical
fluid are having some unique characteristics
it is a very good solvent it can ah ah it
can resolve organic molecules in it so we
can have option for water supercritical water
supercritical carbon dioxide etcetera so if
we want to use the supercritical water the
condition is that the temperature and pressure
is like this temperature is greater than three
seventy four degree centigrade and pressure
is also more than two twenty atmospheric pressure
so there is for water so similarly if we use
the carbon dioxide the temperature must be
more than thirty point nine five degree centigrade
and pressure will be more than seventy three
or seventy four atmospheric pressure so under
these conditions the water and carbon dioxide
will be behaving as a supercritical fluid
and if these fluids are used here when the
feed is entering in this same extraction column
in this extraction column feed we are giving
that is fermenter broth and here we have solvent
we are giving supercritical solvent so due
to the very good solvent property of this
supercritical fluid the organic molecules
like butanol will be dissolved in it maybe
other other organic compounds like say acetone
ethanol etcetera will also be coming and hear
it will be coming and after condensation we
will get the product so this by one stage
we will not get the high purity of the butanol
but successive steps can give the improvement
in the percentage of the butanol
so this is the mechanism of the separation
of the butanol using supercritical solvent
extraction method now we will discuss on the
gas stripping so gas stripping if we pass
some gas hot gas through this media so if
this is a fermenter so they are everything
is there solid material is there butanol acetone
everything all the other compounds also microorganisms
so when we will pass the gas the gas will
take the volatiles compound butanol acetone
etcetera or it will goes up ah after condensation
it will give us the product so hot gas is
going the volatiles are going out with the
hot gas and it is condensed and products have
been separated so this is the mechanism for
the separation of the butanol using gas stripping
and when condensation takes place then the
gas is again recycled
so this is the mechanism but one important
precaution is that the gas which we are sending
that that must be free from oxygen because
the whole reaction takes place in anaerobic
condition so oxygen will hamper the rate of
reaction and there will be no fermentation
so these has some beneficial this ah this
method has some benefit that is it is simple
and cost-effective and non toxicity and no
fouling or clogging due to presence of biomass
or cells next liquid liquid extractions so
fermnter broth can be contacted with some
liquid which will be having some specific
butanol capturing capacity and this works
on this the difference between the distribution
coefficients
so if you use to one solvents the distribution
coefficient of butanol will be more than the
broth butanol will come here so when it will
be going out the fluid that is extractant
so it will be regenerate[d] so we will get
the product butanol so this regeneration can
take place either by extraction using other
solvent or it can also be done through distillation
so after regeneration again solvent can be
used so this is the mechanism for the liquid
liquid extractions and different type of solvents
which has been used for these applications
or for this purpose are presented here some
examples are say ah corn oil polyaxyallkylene
ethers vegetable oil hexanol aromatic hydrocarbons
ketones alkanes esters dibutyl phthalate decanol
and oleyl alcohol crude palm oil and biodiesel
so all those things has been used for the
separation of the butanol from the neutron
broth
then distillation distillation is also one
process just like azetopic distillations as
discussed for ethanol separations so also
be applicable here but here we see the boiling
point is one one seven point eight degree
centigrade for butanol and water hundred degree
so heterogeneous mixture is ninety two point
four degree centigrade when the butanol concentration
is fifty five percent so fifty five percent
butanol can be recovered but it's high concentration
is not possible we have to go for another
we have that for other another molecules and
extractive distillations and azetopic distillations
may be followed here we will see the advantage
and limitations of these different techniques
for the recovery of the butanol from the fermentation
broth
so adsorption distillation and gas stripping
liquid liquid extraction and pervaporations
supercritical fluid extractions so all those
things we have presented in this ah table
so here advantage and disadvantage are provided
as well as energy requirement is also given
so adsorption is easy operations and less
energy intensive but it has low selectivity
and high material cost etcetera and distillations
is a traditional one and it is high operational
cost that is high energy intensive process
gas stripping it is having very high efficiency
non toxic it's a and easy operations no fouling
but low selectivity and low efficiency this
is the power requirement energy requirement
liquid liquid extractions also less energy
intensive high selectivity but high operational
cost also and toxicity of the extract and
that is most important point for this the
negative point that is toxicity of the extraction
and pervaporations and supercritical supercritical
fluid extraction is a good option but it is
not so matured so it needs more research so
these are the salient features and advantage
and disadvantages of these different methods
for the recovery of the butanol from the fermentation
broth now this slide gives us some example
of bacteria and different types of feed stocks
which have been used for the production of
butanol through this fermentation route so
here clostridium acetobutylicum p two six
two clostridium beijerinckii p two six zero
clostridium beijerinckii b a one zero one
clostridium beijerinckii b five nine two and
some acetobutylicum this nine twenty one so
some strains have been reported in recent
years for the production of butanol from the
biomass thank you very much so up to this
in this module
thank you very much for your patience
