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TABLE OF CONTENT PAGE ABSTRACT
1
INTRODUCTION
2
AIMS
2
THEORY
3-5
APPARATUS
6
PROCEDURE RESULTS CALCULATIONS
7-8
9-15
16-19
DISCUSSIONS
20
CONCLUSION
21
RECOMMENDATIONS
22
REFERENCE
22
APPENDIX
23
ABSTRACT
This experiment is conducted to measure the value of volumetric mass transfer coefficient ( !a" of a stirred tan reactor #ith $u$$le aeration% &efore the experiment can $e'in the reactor must first $e cali$rated $ pur'in' ox'en in the vessel usin' nitro'en to o$tain 0) dissolved ox'en readin' and then allo#in' air to enter the vessel to o$tain a 100) dissolved ox'en readin'% The parameters manipulated in this experiment are* aeration rate* stirrin' rate and temperature% The aeration rates used in this experiment are 0%5 !+min - 2%5 !+min* the stirrin' rates are 200 rpm - 1000 rpm and the temperatures are 30, - 50,% The results of the experiment are for 200 rpm* -1
-1
.00 rpm* 600 rpm* 800 rpm and 1000 rpm the value of !a is 0%0205 s * 0%03.0 s * -1
-1
-1
0%0516 s * 0%0707 s and 0%0820 s respectivel #hile for varin' temperatures of -1
-1
30,* 35,* .0,* .5, and 50, the value of !a is 0%00.0 s * 0%0761 s * 0%0.09 s 1
-1
-1
* 0%0387 s and 0%0.23 s respectivel and for varin' aeration rates of 0%5 !+min* -1
-1
1%0 !+min* 1%5 !+min and 2%0 !+min the value of !a is 0%0210 s * 0%0200 s * 0%036.s 1
-
-1
-
and 0%0.92 s respectivel% /n conclusion* an increase in these parameters #ill affect
the value of volumetric mass transfer coefficient ( !a"%
1
INTRODUCTION
icroor'anisms are used as $iolo'ical catalsts to snthesie various* mechanicall /mportant products in a variet of different $ioprocess confi'urations% or example* easts and molds are essential to the production of man foods* includin' $read* cheese* $eer* #ine* and so sauce% /n the pharmaceutical industries* east* $acteria* and mammalian cells are modified to produce therapeutic proteins and other $ioactive compounds% inall* $acteria and easts are also used to convert li'nin* cellulose* and su'ars into alcohol $iofuels% 4 pre-reuisite to each of the a$ove f unctions is the a$ilit to promote and preserve the health and phsiolo'ical state of the cells(if ou dont eep the catalst happ *it cant+#ont do its o$ effectivel"% Thus* re'ardless of the specific application* the operation an $ioprocess first reuires an understandin' of ho# to optimie the 'ro#th of cells and enhance their a$ilit to produce the compounds of interest%
1
&ioreactors are vessels or tans in #hich #hole cells or cell-free enmes
transform ra# materials into $iochemical products and+or less undesira$le $-products and is desi'ned to provide the environment for product formation selected $ the scientist* $aer* or #inemaer #hich is the heart of man $iotechnolo'ical sstems that are used for a'ricultural* environmental* industrial* and medical applications% 1
/ndustrial $ioreactors ma $e operated as $atch reactors or continuousl* aero$icall
or anaero$icall* and #ith pure or mixed cultures #here$ in man $ioreactors* three phases ('as* liuid* and solid" are present and mass transfer is an important consideration% 2
The process of mass transfer across an interface* or across a surface in the $ul
of a phase (liuid* 'as or solid"* is the result of a chemical potential drivin' force #hich is usuall expressed in terms of concentrations of a species in liuid phase* or partial pressures in the case of 'as phases% /n the case of ox'en transfer in a 3
$ioreactor* the measurements of the volumetric mass-transfer coefficient* !a provide important information a$out a $ioprocess or $ioreactor and these determinations ensure that processin' conditions are such it supplies enou'h ox'en for the 'ro#th of cells%
3
The !a value can also $e used to optimie control varia$les (product ield*
po#er consumption or processin' time" over the life ccle of a $ioprocess #hich #ould $e $ased on the ox'en demand at various points in the process and 'ro#th phase of the cells%
AIMS
This experiment #as conducted to measure the volumetric mass transfer coefficient ( !a" of a stirred tan reactor #ith $u$$le aeration%
To investi'ate the effect of temperature* a'itation and aeration rate on ox'en mass transfer coefficient in a cell-free sstem
2
THEORY 3
issolved ox'en (:" is often the limitin' su$strate in fermentation and cell-
culture sstems in the case of $acteria and east cultures* the critical ox'en concentration is usuall 10;50) of air saturation and if the critical level is exceeded* the ox'en concentration no lon'er limits 'ro#th%
3
for optimum 'ro#th* it
is therefore important to maintain : levels a$ove the critical value $ spar'in' ($u$$lin' 'as throu'h" the $ioreactor #ith air or pure ox'en% :f course* to $e effective* the mass transfer rate of ox'en to the liuid $roth must eual or exceed the rate at #hich 'ro#in' cells tae up that ox'en% .
:x'en has comparativel small solu$ilit in aueous solutions= in distilled
#ater at standard conditions* the solu$ilit of ox'en is 8ppm% /n order for ox'en to transfer into a cell* it must 'o throu'h a series of resistances as sho#n $elo#>
Figure 1 shows he
!"#
o$%ge& r'&s(er hrough ' series o( resis'&)es*
.
4t point (1" the diffusion initiall occurs from the $ul 'as to the 'as-liuid
interface then at point (2" it moves throu'h the 'as-liuid interface #hile at point (3" the ox'en diffuses throu'h to the adacent $ul liuid re'ion%
.
4t point (."* the
ox'en travels throu'h the $ul liuid to the cells outer most surface then at point (5" it diffuses throu'h the cells mucous laer and at point (6" it diffuses into the cellular mcelia or soil particle and finall at point (7" and (8" the transport occurs across the cell envelope and into the intracellular reaction site%
3
/n a $ioreator it is important to understand the factors affectin' ox'en uptae and .
ox'en transfer rates in cell cultures%
:x'en uptae in cell cultures* (:?@" is
affected $ the concentration of cells and the rate of ox'en consumption per cell #hile the ox'en transfer rates* (:T@" are affected $ $u$$le sie* aeration rate* a'itation rate* presence of cells and temperature% The euations representin' :?@ and :T@ can $e represented $ the follo#in' euations> :?@> :T@>
.
.
QO qO X 2
2
k L a C BO
2
C l O
2
.
Ahere*
Q
=
ox'en uptae rate per volume ('mol+!%s"
=
specific ox'en uptae rate ('mol+'%s"
=
cell concentration ('+!"
=
volumetric mass transfer coefficient
C BO
=
maximum ox'en concentration ('+!"
C l O
=
critical ox'en concentration ('+!"
O2
q O2
X
k L a 2
2
.
4t stead state* there is no accumulation of ox'en an#here in the $ioreactor%
Therefore* the rate of ox'en transfer from the $u$$les must $e eual to the rate of ox'en consumption $ the cells* :T@ C :?@
[4]
/n short* an
B
k La C O 2
C l O
2
qO X 2
.
increase in a'itation and aeration rates #ill result in an increase
value of !a $ecause* an increase in aeration rate causes more $u$$les to enter the vessel #hich increases the surface area in contact #ith the contents of the vessel #hile increased a'itation causes tur$ulent shear #hich reduces the thicness of liuid film in the vessel% or temperature ho#ever* an
.
increase #ill cause an increase in the value
of !a $ut once the temperature 'oes $eond .0, the solu$ilit of ox'en drops #hich results in a lo#er value of !a%
4
The value of volumetric mass transfer coefficient can $e determined usin' a fe# methods* namel static 'assin' out* dnamic 'assin' out* ox'en $alance method and sulphite oxidation method%
.
Dtatic 'assin' out method is used in the a$sence of
respirin' or'anism (:?@ C 0" #here$ ox'en concentration in the solution is lo#ered $ 'assin' it out #ith nitro'en% The de-ox'enated liuid is then aerated and a'itated #hile the increase in dissolved ox'en (:" is measured usin' a pro$e% The euations represented in this method are as follo#s> :T@>
.
& inte'ration*
dC L dt
.
B
k L a C O
B
ln C O
2
l
C O 2
2
l
C O 2
k La t
.
namic 'assin' out on the other hand involves the presence of respirin'
or'anisms% /nitiall* at time* t C 0 the air suppl to the vessel is s#itched off and the reduction in : is measured $et#een t C 0 and t C 1% 4t time* t C 1 the sir suppl is s#itched on and the rise in : is monitored% The euation represented in this method is as follo#s> [4]
i'ure 2 sho#s the
dC L dt
k La C O
.
B 2
l
C O 2
qO2 X
'raph of : versus time in dnamic 'assin' out method
5
APPARATUS
Exit Gas Tube
Entering Gas Tube
Heang Jacket pO2 Probe Filter
Flo !egulator Glass "essel
#ontrol Panel
$igital $ispla%
i'ure 3 sho#s the $ioreator model /E/:@
&
PROCEDURE
Re')or )'+i,r'io&
1% The reactor displa #as adusted to displa p:2 (dissolved ox'en readin'" $efore cali$ratin' the reactor% 2% 4ll ox'en in the reactor #as first pur'ed #ith pure nitro'en $ connectin' the air inlet to the nitro'en tu$e% 4ll the ox'en #ould have $een full pur'ed #hen the displa reads 0) then the value #as confirmed on the control panel% 3% The nitro'en #as then disconnected from the reactor% Eext* air #as pumped into the reactor $ connectin' its inlet to an air pump% .% :nce the displa reads 100) the value #as confirmed on the control panel and the air flo# into the reactor #as stopped and the cali$ration #as completed%
E((e)s o( sirri&g r'e o& o$%ge& r'&s(er
1% 4ll ox'en in the reactor #as first pur'ed #ith pure nitro'en $ connectin' the air inlet to the nitro'en tu$e% 4ll the ox'en #ould have $een full pur'ed #hen the displa reads 0)% 2% The nitro'en #as then disconnected from the reactor% The stirrer #as then set to 200 rpm* the temperature #as set to 30, and the aeration rate #as set to 2 !+min Eext* air #as pumped into the reactor $ connectin' its inlet to an air pump% 3% The p:2 displaed on the di'ital displa #as taen ever 5 seconds until the displa reads 100)% The air flo# into the pump #as then stopped% .% Dteps 1-3 #ere repeated for .00 rpm* 600 rpm* 800 rpm and 1000 rpm #ith constant temperature and aeration rate%
'
E((e)s o( sirri&g r'e o& o$%ge& r'&s(er
1%4ll ox'en in the reactor #as first pur'ed #ith pure nitro'en $ connectin' the air inlet to the nitro'en tu$e% 4ll the ox'en #ould have $een full pur'ed #hen the displa reads 0)% 2% The nitro'en #as then disconnected from the reactor% The stirrer #as then set to .00 rpm* the temperature #as set to 30, and the aeration rate #as set to 2 !+min Eext* air #as pumped into the reactor $ connectin' its inlet to an air pump% 3% The p:2 displaed on the di'ital displa #as taen ever 5 seconds until the displa reads 100)% The air flo# into the pump #as then stopped% .% Dtep 1 #as repeated $efore the vessel #as heated to 35,% 5% Dteps 2-. #ere repeated for temperatures of .0,* .5, and 50, #ith constant stirrin' and aeration rate%
E((e)s o( sirri&g r'e o& o$%ge& r'&s(er
1% 4ll ox'en in the reactor #as first pur'ed #ith pure nitro'en $ connectin' the air inlet to the nitro'en tu$e% 4ll the ox'en #ould have $een full pur'ed #hen the displa reads 0)% 2% The nitro'en #as then disconnected from the reactor% The stirrer #as then set to 200 rpm* the temperature #as set to 30, and the aeration rate #as set to 0%5 !+min Eext* air #as pumped into the reactor $ connectin' its inlet to an air pump% 3% The p:2 displaed on the di'ital displa #as taen ever 5 seconds until the displa reads 100)% .% The air flo# into the pump #as then stopped% Dteps 1-3 #ere repeated for aeration rate of 1%0 !+min* 1%5 !+min and 2%5 !+min #ith constant temperature and stirrin' rate%
(
RESULTS Ta$le 1 sho#s the dissolved ox'en (:)" readin' for various stirrin' rate (@F" RPM
-..
"..
/..
Tie
DO 2
DO 2
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1*5
3*1
4*+
1)
4*3
(*)
15
+*+
2)
0..
1...
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DO 2
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1*'
5*1
2*'
14*'
1&*)
1)*'
13*3
23*(
2+*(
25*4
11*+
1+*'
32*)
43*'
41*4
25
15*4
2&*4
41*1
53*(
5&*+
3)
1+*3
32*&
5)*4
&+*(
&&*2
35
23*+
3(*&
5'*+
'2*(
''*3
4)
2'*+
45*(
&4*(
'+*3
(3*5
45
31*(
5)*+
')*5
(4*1
((*'
5)
35*(
55*(
'5*'
((*4
+2*)
55
3+*5
&)*&
()*5
+1*4
+4*(
&)
42*'
&5*2
(4*)
+4*)
+'*)
&5
4&*2
&+*2
(&*(
+5*'
+(*)
')
4+*+
'3*)
(+*4
+'*)
++*)
'5
53*)
'&*2
+1*&
+(*3
++*(
()
55*(
'+*2
+3*5
++*1
(5
5(*'
(1*&
+5*1
++*(
+)
&1*4
(3*+
+&*4
+5
&3*+
(5*+
+'*4
1))
&&*5
('*&
+(*3
1)5
&(*'
(+*2
+(*+
11)
')*&
+)*5
++*5
115
'2*'
+1*(
++*+
12)
'4*5
+3*)
1))*)
125
'&*3
+4*1
13)
''*+
+5*1
135
'+*4
+5*+
14)
()*'
+&*&
145
(1*+
+'*2
15)
(3*1
+'*(
155
(4*4
+(*3
1&)
(5*5
+(*&
1&5
(&*&
++*1
1')
('*5
++*4
1'5
((*4
++*'
(+*2
1))*)
1() 1(5
+)*2
+
1))*)
1))*)
1+)
+)*+
1+5
+1*&
2))
+2*2
2)5
+2*+
21)
+3*5
215
+4*)
22)
+4*&
225
+5*)
23)
+5*4
235
+5*(
24)
+&*3
245
+&*'
25)
+'*)
255
+'*3
2&)
+'*&
2&5
+'*+
2')
+(*1
2'5
+(*4
2()
+(*&
2(5
+(*'
2+)
+(*+
2+5
++*1
3))
++*3
3)5
++*4
31)
++*&
315
++*(
32)
++*+
325
1))*)
1)
Ta$le 2 sho#s the dissolved ox'en (:)" readin' for various temperatures% -