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Unformatted text preview: NAME m May 12, 2007 . Separations Processes
CHE 353 . FiNAL EXAM You may refer to a text of your choice (inciuding the Continuous Distillation Chapter 12
and Belter Drying and Crystallization printouts), but no class notes. Short answer (2 pts each)
‘1. Give the dimensions of the following in terms of length L, mass M, time fand temperature T
a. population density n (le de} ti? /L_4a
b. overall mass transfer coefficient based on a partial pressure driving force, A}; ‘ m  Ni NIL3‘4: MLl'tz
M akPAptvi /Lo_4; m glare) .._ _M , f g JC/L _ I tip ‘ Fm “ML/9+1
c. adsorbent concentration at saturation qo
M
A}
d. crystal nucleation rate 8
133‘:
/L.3t
e. diffusion coefficientD
L1
/t 2. Which separation technique is indicated for the following processes? Choose from:
absorption] stripping, adsorption, distiilation, membranes, extraction, leaching,
drying, crystallization.  a. Acid to recover copper from low—grade ore lucid“? («OIo//M @ Whammy)
b. Purifying black Hawaiian sea salt to sell for $9 a bag at Whole Foods 00’3in / Wﬁmufgﬁvﬁ c. Purifying bio—ethanol from a liquid cuiture of yeast (an aqueous “beer")
distillation d. Chasing a Drano cocktail with activated charcoal
Gal Sorp’h' 6% e. Aerating yourtropicai fish tank with a bubbler
aloSov P—l {m 3. In distillation, would a feed composed of saturated vapor or saturated liquid likely
require more stages and why? Which would require more energy? Problems: SHOW YOUR WORK 1. Mg(OH)2 can be made by continuously reacting MgClg and Ca(Oi—i)2 in a 1 L stirred
tank. The popuiation density vs orystai size for an average time of 300 seconds is
given below. ,3 f a. What is the growth rate? pts) ‘
b. What is the nucieation rate? (Mrs) 14, A
w
l <
E
U
V
3.
a:
In
E
U
'U
C
.2
4!
.‘E
‘3
D.
O
Q. I”) Vwm ngja‘ﬂ/‘i'w, 2. You want to scate up an adsorption process; your smallmscale laboratory cotumn (’1
cm diameter, 20 cm long) showed a breakthrough time of 40 min and an exhaustion
time of 52 minutes. Other experiments suggest that the unused bed length (LUB) is
about equal to an HTU and you expect mass transfer coefficients in this bed to vary
inverseiy with the square root of the ﬂow rate. In your new column, you need t0,000 times greater capacity using a bed 130 cm
long (to minimize the pressure drop). You ptan to increase the flow 17 times. a. What is the LUB for the smelt—scale column? (5 pts)
b. What is the LUB in small—scale column with the new ﬂow—rate? (5 pts)
0. For the large column, what bed diameter should be used? (10 pts) Awri' bounce +5 GHWVIMCQ+B 13—1—0} Waalqj a; Caiumn Mn +0 +5: = .3 M F 95b?)
[7 ~77: m4 $08483] "ii
. 4045i 0.5590  <9 LWﬁ = ifse) : ao ¢m({'0.3~7o) : 5342/ an 4 dudm t b LLH$2 H , G ‘ '
D I‘ Tu . M Kax if“;
“W” the our; CM a) I‘M!” MM"; <4”! “I3 «15‘ 196% ass/54’ awe"
__ SMALL
8'16 7‘ :le/dZ(/30"/°‘8)CM * lO‘q {({CM)2‘(.§20~3\6/)6m " SLGLQ/
afhﬁw = 33’._,1 CM
6 d “U— “(elm/8&1, 3. The attached chart gives the weight of damp Cheerios vs time in a graduated cylinder
3.67 cm in diameter. The weight changes because the cereal is slowly drying in air
(c:sat = 2 x 10'5 gromB; 40% humidity). a. What is the drying mechanism for the ﬁrst day? (Hint: use the data to sketch
weight vs time or rate vs time) (5 pts)
b. What is the mass transfer coefﬁcient out of the cylinder in cmi sector Day 1’? (10 pts) Time (hrs) Weight (g) W 15; 0 28 3 27 B 26 m age 9 25 not“ H“ 03:; ‘(0 12 24 18 22 24 20 36 18 3..
[2.4: 1* 3L {,3 M.“ 48 17
WW 0U: w  69 LEM. M33 ’7’ gm Hw WW 4. You want to absorb 99% of the carbon dioxide in 4.2 kg/sec of nearly pure air by
washing it with water in two countercurrent stages. The water enters pure. The equilibrium Eine under these conditions is y" = 16 x. How much water is required?
(10 pts) 5. pawlpg i—e‘bu'WﬂS DC NTLL = You want to purify 99% trichllorosilane to produce a 99.999% distillate in a
differential distillation column with 9.6 transfer units. The equilibrium Eine under the
operating conditions of this column is y* = 0.65 + 0.35X. You plan to feed the column
at the bottom with a saturated vapor. The column has a total condenser but no reboiler. What is the highest purity trichlorosilane you canmake with this column?
(20 pts) ‘ ‘ Kym/x ((1,3) We 4%) I)“ #338 0 “ .55,
g ( $.35gﬂjj
xii—a .45 (f‘.‘?‘?)
, ‘i .62 5 , '
1T L‘X’A'ﬂ ? / 0.35 Ja’ aé§.(fﬂg.) : ' ﬂ ..
p36, JLWU “wit/12 amiga "X0 6. You need to estimate an overall mass transfer coefficient for Solute adsorption from
an aqueous solution of density 1.3 g/cm3 into hydrogel beads 0.03 cm in diameter.
The coefﬁcient Ky is defined by N1 = Kylyy") where Ni has units of gfcmzsec and
the y is in units of solute mass fraction in the water. The mass transfer coefficient
kS in the soiution is 10“3 cm/sec; that within the beads is given by kb 2 601d where d
is the particle diameter and D the diffusion coefﬁcient, equal here to 3 x 10“3 cm2/
sec. Because the beads are hydrogels, the partition coefficient is one. a. Write an expression for Ky in terms of ks and Rh (3 pts)
b. Estimate K3, in the units given (7 pts) ‘ Aqueous Solution N1 7 K3 131:3 2 KL £5 CL
With solute J, L
a : 0 Units Wilts
. 3 Flu“)! uticbﬁj l l “i 
a) K '5 a + 0 4w Fayvr‘rrlfak Cwﬁ‘C/UMS ~é/C 507% magma/m! assm ms % mic ﬂaw}, Ezi‘a‘s Jets] abwﬂwmawﬁdaam
i“ {3 5’ lily/(3] 41:“ assumes umf’j ) lam/c, CDWCCMVZM  ‘A...v, __.,_.. FINAL EXAM POSSIBLY USEFUL INFORMATIO N
Rate Processes dc1 NI = — Dm+Clvu {Fisk’s law}
dz . Fufgfliiz‘yg); A ::.:'.:f:::..‘::d_ 7. ._ ,. H , gag_p1mgg,.ﬁmss (trangfg}:)fi‘i'ff‘2.".ii".L1...
2 KJI )1  yr") (overall mass transfer)
=  31—3} {overaii mass transfer)
1 m
——+
k), c_r
. DH _
N! =1} = T AC1 (membrane separation)
1/ 2/3 h =11 2/3 ' _
k f)" = a “if = fit/2 ‘ (Chilton—Colbum anaiogy)
G . L L  . .
y 2 (ya  "G" x0} + E; x ‘ (operatmg hue)
' ~ ﬂ 5 ' L “ . .
H=(H0 —_LE1THEOZ'0)+ "5'3 THZG ‘ (opemtmg hm?)
'yo
6 z W?» “(QM (absorption)
Kya y. y n y
1: g
2 mg ﬁg; . (watercooliiig)
kya #6 H —H ' 
Stawed Unit Operatlons
I, _ L . .
)1” : (y!  5 x0) + g x” (operatmg 11116:)
“CD RD  . . . _ _ . .
3 f + RD + I + RD xn (chstillatmn. Lacﬂfymg sec’uonD ﬁAIHJ A 1 Au
YN+J E 1 _ A ) 3’1” ( (j 14 )) yo (linear‘iSotherm;A : L/mG)
N — inrm'rywj / I; {hm EM] (3116a; ssiheam}
yl "yo VN yr: J ...
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