Kristalisasi 4 Rev - 3 May 2012
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Transcript of Kristalisasi 4 Rev - 3 May 2012
3 May 2012 Jurusan Teknik Kimia UKWM 1
Nani Indraswati
PROSES PEMISAHAN 1CHE223
CRYSTALLIZATION(4)
3 May 2012 Jurusan Teknik Kimia UKWM 2
CRYSTALLIZATIONHeat balance
Heat removed to cool the feed solution from T1 (Tfeed) to T2 (Tcrystallization) without any solid phase precipitating out
+ heat liberated when crystals are formed (heat of crystallization) at T2
= heat lost through walls + latent heat of evaporation + heat removed by cooling
Using specific-heat and heat of crystallization data :
3 May 2012 Jurusan Teknik Kimia UKWM 3
Example 12.11-2
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ExampleHeat removal in crystallization cooling of lactose
Lactose syrup is concentrated to 8 g lactose per 10 g of water and then run into a crystallizing vat which contains 2500 kg of the syrup. In this vat, containing 2500 kg of syrup, it is cooled from 57°C to 10°C. Lactose crystallizes with one molecule of water of crystallization. The specific heat of the lactose solution is 3470 J/(kg)(°C). The heat of solution for lactose monohydrate is -15,500 kJ/ mol. The molecular weight of lactose monohydrate is 360 and the solubility of lactose at 10°C is 1.5 g / 10 g water. Assume that 1% of the water evaporates and that the heat loss through the vat walls is 4 x 104 kJ. Calculate the heat to be removed in the cooling process.
3 May 2012 Jurusan Teknik Kimia UKWM 5
ADIABATIC VACUUM CRYSTALLIZER
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CRYSTALLIZATION: Mass Balance
CrystallizerCrystals C kg/h
Mother liquor L kg/h(saturated solution)
Magma M kg/h
Feed F kg/h
H2OVaporV kg/h
Feed F = magma M + vapor VMagma M = crystals C + mother liquor L
CLMF CxLxMxFx balance Solid
V M V CLF
balance material Overall
3 May 2012 Jurusan Teknik Kimia UKWM 7
Adiabatic evaporator-vacuum crystallizer: Heat balance
Adiabatic operation : → Q = 0
F = rate of feed, kg/h L = rate of mother liquor , kg/h C = rate of crystals, kg/h M = rate of magma, kg/h V = rate of vapor (superheated), kg/h H, h = enthalpy, J/kg
VMF
VCLF
VHMhFh
or
VHChLhFh
3 May 2012 Jurusan Teknik Kimia UKWM 8xL xM xC
TCryst
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Enthalpy-concentration diagram
SystemMgSO4 - H2O
hF
xFxL xM xC
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qp
q
M
L
qp
p
M
Cba
b
F
Vba
a
F
M
a
bp
q
q
p
L
C
b
a
V
M
F = feedL = mother liquorC = crystalsM = magmaV =vapor
V
Feed F
Vapor V
Mother liquor L
Magma M
Crystals C
Adiabatic evaporator-vacuum crystallizer
F = M + VM = L + C
3 May 2012 Jurusan Teknik Kimia UKWM 11lb crystal/lb mother liquor
Example
L
CC = 10000 lb
3 May 2012 Jurusan Teknik Kimia UKWM 12
ExampleThe vapor leave the crystallizer at 86oF (superheated vapor → saturated at 84oF + BPR 2oF)
HV = Hsat + (Cpsuperheated vapor )( oC or oF superheat)
enthalpy of saturated vapor at TSat BPR
1.884 kJ/kg.oC
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Vapor V
Magma M
Feed F
Crystal C
mother liquor L
F = M + VM = C + L
xL xM xC
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vapor
magmafeed
crystals
mother liquor
isotherm 86oF
fd
fede
fe
0.2241
0.224
M
C1
0.224
L
C
ab
be
M
V
0.285 0.488
-62.4-43
1098
-149
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Enthalpy-concentration diagram
SystemMgSO4 - H2O
hF
xFxL xM xC
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point e
1 x 0.2850.322
d f
d f
ab
be
M
V
Basis: 1 lb mother liq L
lb 10000C1
0.224
L
C
VM
L
= F
M
M
F
V
LC
V =
3 May 2012 Jurusan Teknik Kimia UKWM 17
vapor
magmafeed
crystals
mother liquor
isotherm 86oF
fd
fede
fe
0.2241
0.224
M
C1
0.224
L
C
ab
be
M
V
0.285 0.488
-62.4-21
1098
3 May 2012 Jurusan Teknik Kimia UKWM 18
qp
q
M
L
qp
p
M
Cba
b
F
Vba
a
F
M
a
bp
q
q
p
L
C
b
a
V
M
F = feedL = mother liquorC = crystalsM = magmaV =vapor
V
Feed
Vapor
Mother liquor
magma
crystals
Adiabatic evaporator-vacuum crystallizer
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Adiabatic evaporator-vacuum crystallizer
If TF is increased at the same P the point F(xF,hF) moves upward on a vertical line the point M move downward to the right ratio C/M will increase
If lower operating P is used at the same TF and xF lower operating temperature HV decreases → point V(y,H) will move downward the line LM will move downward point L will move to the left along curve A the point C moves down on the vertical line the point M shifts downward to the right ratio C/M will increase
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Problem Larutan MgSO4 30% berat pada suhu
220oF dialirkan ke suatu crystallizer dengan laju 3500 lb/jam. Suhu pada crystallizer 86oFLarutan jenuh MgSO4 mempunyai kenaikan titik didih sebesar 2oF.Hitung laju kristal yang dihasilkan
3 May 2012 Jurusan Teknik Kimia UKWM 21
Crystallization Mechanism
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CRYSTALLIZATIONCrystal growth
Rate of crystal growth: the distance moved per unit time in a direction perpendicular to the face
Solute molecules A reach the face by diffusion from the super-saturation bulk solution to the surface
surface the at A)solute of fraction (mole ionconcentrat solute y
solution bulk of A)solute of fraction (mole ionconcentrat ationsupersatur y
m area, surface A
A/skmol A.solute of rate tranfer mass N
tcoefficien transfer mass k
1-12.12 ...........................
'A
A
2
A
_
y
.
frac molmskmol/ , 2
)'A
yA
(yykA
_
AN
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CRYSTALLIZATIONCrystal growth
surface the at ionconcentrat solute C
solution bulk of ionconcentrat ationsupersatur C
area surface A
A/skmol A,solute of rate tranfer mass N
tcoefficien transfer mass k
'A
A
A
_
c
_
)'A
CA
(CckAA
N
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CRYSTALLIZATION Crystal growth
At the surface : integration reaction of the molecules into the space lattice
surface the at A of fraction) (mole ionconcentrat solute y
Aof fraction) (mole ionconcentrat saturation y
area surface A
kmol/s A,solute of rate tranfer mass
frac) )(molkmol/(s)(m t,coefficien reaction surface k
2-12.12 ...................
'A
Ae
A
2S
_
N
)Ae
y'A
(yS
kAA
N
3 May 2012 Jurusan Teknik Kimia UKWM 25
CRYSTALLIZATION Crystal growth
surface the at ionconcentrat solute C
ionconcentrat saturation C
area surface A
kmol/s A,solute of rate tranfer mass N
)/)(kmol/(s)(m t,coefficien reaction surface k
2-12.12 ...................
'A
Ae
A
2sc
3mmol
)Ae
C'A
(CsckAA
N
3 May 2012 Jurusan Teknik Kimia UKWM 26
CRYSTALLIZATION Crystal growth
Solution must be super-saturated for the diffusion (12.12-1) & interfacial (12.12-2) steps to proceed
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CRYSTALLIZATION Crystal growth
Combining eq. 12.12-1 & 12.12-2 :
ky predicted by methods for mass transfer to suspensions of small particles (sect. 7.4), mass transfer through fixed bed or fluidized bed
tcoefficien transfer overall K
3-12.12 .........).........yK(y.
k1
k1
)(y
A
NAeA
Sy
AeAA
_
y
3 May 2012 Jurusan Teknik Kimia UKWM 28
CRYSTALLIZATION Crystal growth
tcoefficien transfer overall K
)C(CK.
k1
k1
)C(C
A
N
c
AeAc
SCC
AeAA
_
kc predicted by methods for mass transfer to suspensions of small particles (sect. 7.4), mass transfer through fixed bed or fluidized bed
3 May 2012 Jurusan Teknik Kimia UKWM 29
CRYSTALLIZATION Crystal growth
Crystal growth is measured as the increase in length L (linear dimension of one crystal, mm)
In the same environmental conditions, L is independent of initial crystal size
t time at crystal of dimension linear D
constant rate growth G
ttGDDΔL 1212
3 May 2012 Jurusan Teknik Kimia UKWM 30