Concentration of sulfur dioxide from industrial waste-gases
by Robert A Damon
A Thesis Submitted to the Graduate Faculty in partial fulfillment of the requirements for the degree of
Master of Science in Chemical Engineering
Montana State University
© Copyright by Robert A Damon (1957)
Abstract:
Under the assumption that certain U. S. smelters expel enough waste SO2 to warrant its commercial
recovery, work was undertaken to discover a suitable process for recovering this SO2 and converting it
into elemental sulfur. The process' was considered to be twofold: that of concentrating the waste SO2
and that of reducing the concentrated SOg to elemental sulfur. This paper concerns the former.
The objective was to find an absorbent with a high capacity for absorbing SO2, with an ability to be
stripped of this SO2, with enough endurance to withstand repeated subjection to stripping temperatures
in the vicinity of 100°C without decomposition, and with a resistance to the formation of precipitates
during an absorption-desorption cycle.
Of the possible absorbents investigated to solve this problem, the sodium salts of citric, lactic, and
malic acids met the above absorbent requirements. The resulting indication of the investigations
conducted was that aqueous solutions of the alkali salts of alpha-hydroxy acids that do not yield a
precipitate of the acid upon contact with SOg in aqueous solution should serve as satisfactory
absorbents for the industrial concentration of SOg from waste gases containing approximately 5% SO2
by volume. CONCENTRATION OF SULFUR DIOXIDE FROM INDUSTRIAL WASTE-GASES
by
R o b e rt A. Damon
A T h e s is
S u b m itte d t o t h e G ra d u a te F a c u l ty
in
p a r t i a l f u l f i l l m e n t . o f t h e r e q u ir e m e n ts
f o r t h e d e g re e o f •
M a s te r o f S c ie n c e i n C h em ical E n g in e e rin g
at
M ontana S t a t e C o lle g e
A pproved;
H ead, M ajo r Deparb&a
ChaimSh^
.ning C om m ittee
D ean. G r id u a t
1Ov -'"'
Bozeman, M ontana
A p r i l 1957
%
-2 CONTENTS
A b s tr a c t
I .
II.
III.
IV .
V.
V I.
V II.
In tro d u c tio n
P r e v io u s Work
P la n o f I n v e s t i g a t i o n s
A b so rb e n ts I n v e s t i g a t e d U nder S te p s #1 and #2 o f t h e
P la n o f I n v e s t i g a t i o n s
A b s o rp tio n R eactio n -M ech an ism s
C o n tin u o u s Runs
E x p e rim e n ta l M ethods
SummaryN o m en clatu re
L i t e r a t u r e C ite d
12S7E9
-3 -
ABSTRAGT
U nder t h e a s s u m p tio n t h a t c e r t a i n U. S„ s m e lte r s e x p e l enough
w a s te SO^ t o w a r r a n t i t s co m m ercial r e c o v e r y j w ork was u n d e r ta k e n t o
d is c o v e r a s u i t a b l e p r o c e s s f o r r e c o v e r in g t h i s SOg and c o n v e r tin g i t
i n t o e le m e n ta l s u l f u r . The p r o c e s s ' was c o n s id e r e d t o be tw o fo ld :- t h a t
o f c o n c e n tr a ti n g th e w a s te SO2 an d t h a t o f re d u c in g t h e c o n c e n tr a te d
SO2 t o e le m e n ta l s u l f u r . T h is p a p e r c o n c e rn s t h e f o rm e r.
The o b j e c t i v e was t o f i n d an a b s o r b e n t w ith a h igh, c a p a c i t y f o r
ab so p b iB g SO2 , w ith an a b i l i t y t o b e s t r i p p e d o f t h i s SOp, w ith enough
e n d u ra n c e t o w ith s ta n d r e p e a te d s u b je c t io n t o s t r i p p i n g te m p e r a tu r e s
i n t h e v i c i n i t y , o f IOO0C. w ith o u t d e c o m p o s itio n , an d w ith a r e s i s t a n c e
t o t h e f o r m a tio n o f p r e c i p i t a t e s d u rin g an a b s o r p ti o n - d e s o r p t io n c y c le .
Of t h e p o s s i b l e a b s o r b e n ts i n v e s t i g a t e d t o s o lv e t h i s p ro b lem ,
t h e sodium s a l t s o f c i t r i c , l a c t i c , an d m a lic a c i d s m et t h e above
a b s o r b e n t r e q u ir e m e n ts . The r e s u l t i n g i n d i c a t i o n o f t h e i n v e s t i g a t i o n s
c o n d u c te d was t h a t aq u eo u s s o l u t i o n s o f t h e a l k a l i s a l t s o f a l p h a h y d ro x y a c i d s t h a t do n o t y i e l d a p r e c i p i t a t e o f th e a c i d upon c o n ta c t
w ith SO2 i n aq u eo u s s o l u t i o n s h o u ld s e r v e a s s a t i s f a c t o r y a b s o r b e n ts
f o r t h e i n d u s t r i a l c o n c e n tr a ti o n o f SO2 fro m w a s te g a s e s c o n ta in in g
a p p ro x im a te ly 5% SO2 b y v o lu m e.
-4 -
I.
In tro d u c tio n
S u b s t a n t i a l q u a n t i t i e s o f s u l f u r have been and a r e s t i l l b e in g
d i l u t e d i n t o t h e a tm o s p h e re , l a r g e l y i n t h e fo rm o f s u l f u r d io x i d e , a s
a d i r e c t r e s u l t o f t h e o x id a tio n o f v a r i o u s s u l f i d e o r e s .
T h is b y -p ro d u c t
o f s m e lte r o p e r a t io n s s h o u ld now b e , more th a n e v e r b e f o r e , r e g a r d e d a s a
p o t e n t i a l s o u rc e o f raw m a t e r i a l f o r t h e p r o d u c tio n o f e le m e n ta l s u l f u r .
The f o llo w in g f a c t s w i l l c l a r i f y t h e s i t u a t i o n a s i t now s ta n d s :
1.
U. S . i n d u s t r y a n n u a l ly consum es v a s t q u a n t i t i e s
of s u lfu r.
2.
S in c e U. S . i n d u s t r y i s e x p a n d in g , t h e a n n u a l demand
f o r s u lf u r w ill in c re a s e .
. 3«
D is c o v e ry o f new s u l f u r d e p o s i t s h a s n o t k e p t p ace ,
w ith i n c r e a s i n g U. S . i n d u s t r i a l e x p a n s io n .
N in e ty p e r c e n t o f t h e w o rld p r o d u c tio n o f e le m e n ta l s u l f u r comes
fro m t h e F r a s c h - p r o c e s s w e l l s a lo n g t h e G u lf C o ast ( l ) .
The 1935-39
a v e ra g e y e a r l y p r o d u c tio n o f F r a s c h s u l f u r was 2 . 2 m i l l i o n lo n g t o n s , an d ,
t h e 1951 p r o d u c tio n o f F r a s c h s u l f u r was 5»3 m i l l i o n lo n g t o n s .
G orjte-
sp e n d in g t o t h e s e p r o d u c tio n f i g u r e s a r e t h e co n su m p tio n f i g u r e s : 1 .4 and
4 . 8 m i l l i o n lo n g t o n s , r e s p e c t i v e l y .
T h ese f i g u r e s g iv e an i n d i c a t i o n
o f th e i n c r e a s i n g demands on e x i s t i n g s u l f u r r e s e r v e s ( 2 ) .
T h u s, t h e G u lf C o a st F r a s c h - w e lls , b e in g th e w o r ld 's l a r g e s t p ro ­
d u c e r s and h a v in g t h e lo w e s t p r o d u c tio n e x p e n se s p e r t o n , c o n t r o l t h e
w o rld s u l f u r m a r k e t.
H ow ever, i n 1 9 4 4 , t h e G u lf C o a st h ad o n ly 60 m i l l i o n
lo n g t o n s o f im m e d ia te ly a v a i l a b l e r e s e r v e s and 2 2 .2 m i l l i o n lo n g t o n s o f
fu tu re -a v a ila b le re se rv e s (3 ).
T h is i n d i c a t e s t h a t t h e 9 , 136 m i l l i o n lo n g
-5 -
)
to n s o f b y - p r o d u c t s u l f u r r e s e r v e s (3 ) ( p y r it e s * s m e lte r g a s e s , coke-­
oven g a s e s , e t c O
should* i n th e f u t u r e , be a b l e t o e f f e c t i v e l y com pete
w ith F r a s c h -p ro d u e ed s u l f u r and i t s i n e v i t a b l e p r i c e i n c r e a s e b ro u g h t
a b o u t b y d w in d lin g , h a r d e r - t o - g e t - a t r e s e r v e s .
A t 1944 o p e r a t io n r a t e s , U. S. s m e l te r s w ould h av e d is c h a r g e d 20
m i l l i o n lo n g to n s Of s u l f u r a s d i l u t e d SO^ i n t o t h e atm o sp h e re i n th e
n e x t 100 y e a r s ( 3 ) .
I f t h i s s u l f u r can be r e c o v e re d a t a c o s t p e r to n
t h a t w ould e n a b le i t t o , a t t h e p r e s e n t ti m e , e c o n o m ic a lly com pete W ith
F ra sc h s u lf u r , i t
s h o u ld , i n t h e f u t u r e , have a d e c id e d econom ic ad ­
v a n ta g e o v e r t h e l a t t e r .
A ls o , i t i s f o r s e e a b lO t h a t an y p r o c e s s f o r r e c o v e r in g s u l f u r from
.1
s m e l te r w a s te - g a s e s can b e a p p l ie d t o t h e r e c o v e r y o f s u l f u r fro m p y r i t e s
when i t becom es e c o n o m ic a lly a d v a n ta g e o u s t o do s o .
T h ere w ere 160 m il­
l i o n lo n g t o n s o f s u l f u r r e s e r v e s a s p y r i t e s i n t h e U. S . i n 1944 (3)*
W ith t h e s e f a c t s i n m in d , w ork was u n d e rta k e n t o d is c o v e r a p r o c e s s
f o r r e c o v e r in g s u l f u r fro m w a s te s m e l te r - g a s e s o f a p p r o x im a te ly $$ SO2
b y volum e.
I n d u s t r i a l l y , t h e r e c o v e r y o f s u l f u r can be d iv id e d i n t o two s t e p s :
1.
C o n c e n tr a tio n o f SOg i n t o a r e l a t i v e l y p u re s t a t e .
2.
R e d u c tio n o f th e c o n c e n tr a te d SOg i n t o e le m e n ta l s u l f u r .
T h is i n v e s t i g a t i o n was c o n c e rn e d w ith t h e f i r s t o f th o s e s t e p s .
The
o b j e c t i v e was t o f i n d an i n d u s t r i a l l y - f e a s i b l e m ethod w h ich w ould a c ­
c o m p lis h t h e c o n c e n tr a ti o n o f SOg fro m g a s e s c o n ta in in g d i l u t e SOg.
-6 —
Gas a b s o r p ti o n was ch o sen a s t h e p h y s i c a l o p e r a t io n f o r c o n c e n tr a ti n g
t h e SO2 , an d t h e a b s o r b e n t - o b j e c t i v e s i n i t i a l l y s e t f o r t h w ere a s f o l l o w s :
1»
F in d a l i q u i d a b s o r b e n t w ith a r e l a t i v e l y l a r g e c a p a c i t y
f o r a b s o r b in g SOg,
2.
The S O g -c o n c e n tra te d a b s o r b e n t m u st be c a p a b le o f b e in g
s t r i p p e d o f n e a r l y a l l i t s SOg c o n t e n t .
3.
The a b s o r b e n t m u st be c a p a b le o f b e in g r e c y c le d w ith
l i t t l e o r no l o s s o f a b s o r b e n t.
P r e v io u s Work
A s u rv e y o f t h e l i t e r a t u r e fro m 1910 th ro u g h 1954 r e v e a le d t h a t t h e
f o llo w in g a b s o r b e n ts h ad b een e i t h e r c o m m e rc ia lly o r s e m i-c o m m e rc ia lly
u s e d f o r t h e p u rp o s e o f a b s o rb in g ' SOg5 o r s u g g e s te d f o r t h a t p u rp o se s
2 -am ino cym ol
alum inum s u l f i t e
d i- m e th y l a n a l i n e
aluminum s u l f a t e
d i- e th y le n e tria m in e
c i t r a t e-p h o s p h a t e
t r i - e t h y l e n e te tr a m i n e
q u in o lin e
magnesium s u l f i t e o r
b i-s u lfite
sodium c a r b o n a te
te tra lin
ammonium s u l f i t e
p y r id in e '
ammonium th i o c y a n a t e
a n a lin e
s ilic a gel
x y lid in e
a l k a l i h y d ro x id e
a l k a l i fo rm a te
ammonium, h y d ro x id e
The m a jo r d i f f i c u l t y w ith p r o c e s s e s u s in g v a r io u s o f t h e a b o v e m e n tio n e d a b s o r b e n ts , was t h e l o s s o f a b s o r b e n t th ro u g h v a p o r i z a t i o n
o r th r o u g h f o r m a tio n o f b y - p r o d u c ts w h ich o c c u r a s p r e c i p i t a t e s .
- 7-
Some b y -p r o d u c ts su ch a s ammonium s u l f a t e , r e s u l t i n g when ammonia i s u se d
a s an a b s o r b e n t, a r e e a s i l y m a r k e ta b le , w h ile o t h e r s su ch a s c a lc iu m s u l ­
f a t e a r e 'n o t e a s i l y m a r k e ta b le .
e l im in a t e d , ite m
I n o r d e r t h a t th e s e h a n d ic a p s m ig h t be
o f t h e a fo re m e n tio n e d a b s o r b e n t—o b j e c t i v e s was
s tip u la te d .
Howat ( 4 ) , i n 1940> sum m arized th e w ork t h a t had b een done on SOg
a b s o rp tio n .
He s t a t e d t h a t t h e c a p a c it y o f a g iv e n s o l u t i o n f o r a b s o rb in g
SO2 i s i n v e r s e l y p r o p o r t i o n a l t o t h e s q u a re o f th e h y d ro g e n -io n c o n c e n tr a ­
tio n .
L a rg e q u a n t i t i e s o f SO^.may be d is s o lv e d i n a l k a l i n e s o l u t i o n s ,
b u t r e g e n e r a tio n o f t h e SOg b y h e a t in g th e n becom es a lm o s t im p o s s ib le .
H ow at1s c a l c u l a t i o n s r e v e a le d t h a t s o l u t i o n s w ith pH l e s s th a n 3 .$ w i l l
n o t d i s s o l v e s u f f i c i e n t SO2 and t h a t s o l u t i o n s w ith pH g r e a t e r th a n 3 .5
do n o t f a v o r e a s y r e g e n e r a tio n o f SO2 b y h e a t i n g .
III.
P la n o f I n v e s t i g a t i o n s
To p r e d i c t th e b e h a v io r o f an y a b s o r b e n t u n d e r o p e r a t in g c o n d i tio n s ,
e q u i lib r i u m d a t a f o r th e g a s - a b s o r b e n t s y ste m i s n e c e s s a r y .
D e te r­
m in a tio n o f o p e r a t in g c o n d i tio n s an d column d e s ig n a r e im p o s s ib le w ith ­
o u t t h i s in f o r m a tio n .
E q u ilib r iu m d a t a f o r t h e a b s o r b e n ts c o n s id e r e d d u r in g t h i s i n v e s t i ­
g a t i o n w ere n o t a v a i l a b l e i n t h e l i t e r a t u r e ; t h u s , a th r e e - p h a s e r e s e a r c h
p la n was i n s t i g a t e d :
1.
D eterm in e e q u ilib r iu m d a ta f o r a s e r i e s o f p o s s i b l e
a b s o r b e n ts .
2.
D eterm in e t h e e a s e and c o m p le te n e s s o f s t r i p p i n g SO2
-8 -
fro m t h e s e a b s o r b e n ts ,
3.
IV .
W ith t h e a i d o f t h e ab o v e i n f o r m a tio n , e l im i n a te t h e
u n d e s i r a b l e a b s o r b e n ts and s tu d y t h e d e s i r a b l e a b ­
s o r b e n ts u n d e r s im u la te d l a r g e - s c a l e o p e r a t in g c o n d i­
t i o n s on l a b o r a t o r y s c a l e i n a c o n tin u o u s - a b s o r p tio n
colum n.
A b s o rb e n ts I n v e s t i g a t e d U nder S te p s I an d 2 o f th e
P la n of. .I n v e s t i g a t i o n s
E ach a b s o r b e n t was a llo w e d t o r e a c h a s t a t e o f e q u ilib r iu m w ith a
s e r i e s o f S O g -a ir m ix tu r e s i n t h e a b s o r p tio n a p p a r a tu s p i c t u r e d i n F ig u r e
10.
The q u a n t i t y o f SOg i n a n y g iv e n a b s o r b e n t was d e te rm in e d by
titra tio n .
When p o i n t s r e p r e s e n t i n g SOg c o n c e n tr a ti o n i n an a b s o r b e n t
v s . SOg c o n c e n tr a ti o n o f t h e S O g -a ir m ix tu r e i n e q u ilib r iu m w ith t h e
a b s o r b e n t, w ere p l o t t e d , an. e q u ilib r iu m c u rv e f o r t h a t p a r t i c u l a r a b s o r ­
ben t re s u lte d .
The a b i l i t y o f an a b s o r b e n t t o be s t r i p p e d o f i t s SOg c o n te n t was
d e te rm in e d b y m a in ta in in g t h e a b s o r b e n t a t 90°C an d p e r i o d i c a l l y t i t r a ­
t i n g sam ples o f t h e a b s o r b e n t u n t i l t h e SOg c o n te n t had a t t a i n e d a
minimum v a l u e .
D u rin g t h e a b s o r p ti o n and d e s o r p tio n d e t e r m in a tio n s , p a r t i c u l a r
a t t e n t i o n was d i r e c t e d to w a rd t h e f o r m a tio n o f an y b y - p r o d u c ts o r de­
c o m p o s itio n p r o d u c ts f ' I f e i t h e r o f t h e s e a p p e a r e d , t h e y w ere a n a ly z e d
an d t h e i r s i g n i f i c a n c e e v a lu a te d .
E q u ilib r iu m d a t a an d c u rv e s f o r t h e f o llo w in g a b s o r b e n ts a p p e a r
a t t h e end o f t h i s s e c t i o n .
-9 -
A6
Sodium F o rm ate
A r e c e n t J a p a n e s e p a t e n t had been s e c u re d on th e u s e
o f a l k a l i fo rm a te a s an a b s o r b e n t f o r SOg, b u t no e q u i l i ­
b riu m d a t a was a v a i l a b l e .
I t was d e c id e d t o d e te rm in e
e q u i lib r i u m d a t a f o r aq u eo u s sodium f o r m a te s o l u t i o n s o f
in c re a s in g c o n c e n tra tio n .
T h is w ould show th e n a t u r e o f
e q u i lib r i u m f o r a s u c c e s s f u l a b s o r b e n t an d a l s o show t h e
b e h a v io r o f e q u i lib r i u m a s th e c o n c e n tr a ti o n o f th e
a b s o r b e n t was i n c r e a s e d .
D ata was o b ta in e d f o r s o l u t i o n s o f 1 0 , 2 0 ^ and 30
gram s o f sodium fo rm a te p e r 100 gram s o f w a te r .
A b so rp -
'
t i o n was s u c c e s s f u l and was fo u n d t o be more e f f e c t i v e a s
t h e c o n c e n tr a ti o n o f sodium fo rm a te was in c r e a s e d .
The
20 pbw s o l u t i o n was I i 15 tim e s a s e f f e c t i v e a s t h e 10 pbw
s o l u t i o n , an d t h e 30 pbw s o l u t i o n was 1 .5 tim e s a s e f f e c ­
t i v e a s t h e 10 pbw s o l u t i o n .
T h is i n c r e a s e i n e f f e c t i v e -
n e s s i s , o f c o u r s e , l i m i t e d b y t h e maximum s o l u b i l i t y o f
a g iv e n s a l t i n w a te r .
H ence, i t was d e c id e d t o u s e a
50 pbw s o l u t i o n (an a v e ra g e w i t h i n t h e l i m i t s o f maximum
s o l u b i l i t y f o r t h e s a l t s o f m ost o r g a n ic a c id s ) ' when
s tu d y in g o t h e r p o s s i b l e a b s o r b e n ts .
A lth o u g h sodium fo rm a te p ro v e d a good a b s o r b e n t f o r
SOg, i t d id n o t s a t i s f a c t o r i l y m eet t h e a b s o r b e n t r e q u i r e ­
m e n ts s e t f o r t h i n i t i a l l y .
Upon h e a t in g t o s e t f r e e th e
.
-1 0 a b s o rb e d SOg, a c o l l o i d a l p r e c i p i t a t e a p p e a r e d .
T h is
o c c u r r e n c e h e ld t r u e f o r each pbw s o l u t i o n s t u d i e d .
The
p r e c i p i t a t e was s o lu b le i n ca rb o n d i s u l f i d e , a n d , upon
e v a p o r a tio n o f t h e carb o n d i s u l f i d e , y e llo w c r y s t a l s ,
i d e n t i f i a b l e a s s u lf u r , ap p e a re d .
The m echanism f o r t h i s
r e a c t i o n was p ro p o s e d a s f o llo w s ( r e a c t i o n m echanism s a r e
d is c u s s e d m ore f u l l y i n a l a t e r s e c t i o n ) :
B.
------ >>
1.
SO2 + H2O
2.
HCOONa
3.
H+ + HCOO-
4.
2Na+ + SO3 =
5.
2HC00H + Na2 SO3
2H+ + SO3 =
------ HCOO- + Na+
------ - )
------- )
HCOOH
Na2SO3
->
2NaHC03 + S
v
+
H2O
Sodium C h lo r id e
Sodium c h l o r i d e , a lo n e n o t s a t i s f a c t o r y f o r a b ­
s o r b in g an d r e c o v e r in g SO2 , was b u f f e r e d t o a pH 3*5
w ith c o n c e n tr a te d HCl i n o r d e r t o im prove t h e d e s o r p tio n
c h a r a c t e r i s t i c s o f th e s o l u t i o n .
E q u ilib r iu m d a t a was
o b ta in e d f o r a 35 pbw aq u eo u s NaCl s o l u t i o n b u f f e r e d t o
pH 3 . 5 .
I t p ro v e d t o be a v e r y p o o r a b s o r b e n t f o r SO2 , ab ­
s o r b in g a p p r o x im a te ly 0 .0 0 1 m o ls S02/m o l a b s o r b e n t, f o r
a 5$ SO2 i n l e t g a s .
D e s o rp tio n c h a r a c t e r i s t i c s w ere such
t h a t t h e r e c o u ld be no p o s s i b l e r e c o v e ry o f SO2 b y d e­
-1 1 -
s o r p tio n u n l e s s an i n l e t g a s c o n ta in in g g r e a t e r th a n I ? „5$
SO^ b y volum e w ere u s e d .
C.
G ly c in e
A 20 pbw aq u eo u s s o l u t i o n o f g ly c in e was u s e d a s an
a b s o r b e n t.
A b s o rp tio n c a p a c i t y f o r a 5$ SO^ i n l e t g a s
•was Oo007 Hiols S 02/m ol a b s o r b e n t.
F o r r e c o v e r y o f OOg by
d e s o r p t i o n , ho w ev er, an i n l e t g a s o f g r e a t e r th a n 9$ SOg
w ould be r e q u i r e d .
D.
Sodium C i t r a t e
A 50 pbw aq u eo u s sodium c i t r a t e s o l u t i o n was s tu d ie d .
E q u ilib r iu m w ith 5% SOg i n l e t g a s was 0 .0 4 3 5 m p ls SOg/mol
a b s o r b e n t.
A f t e r d e s o r p ti o n , t h e s o l u t i o n c o n ta in e d 0 .0 1 3 6
m o ls SOg/mol a b s o r b e n t.
No p r e c i p i t a t e s o r u n d e s ir a b l e
b y - p r o d u c ts o c c u r r e d d u r in g a b s o r p ti o n o r d e s o r p ti o n .
E.
Sodium B en zo ate
A 50 pbw aq u eo u s sodium b e n z o a te s o l u t i o n was s t u d i e d .
• H owever, a v e r y heavy, p r e c i p i t a t e o f b e n z o ic a c i d c r y s t a l s
o c c u r r e d d u r in g t h e A b s o rp tio n , t h u s r e n d e r in g sodium b en ­
z o a te an u n d e s ir a b l e a b s o r b e n t.
F.
Sodium S a l i c y l a t e
The 50 pbw aq u eo u s s o l u t i o n o f sodium s a l i c y l a t e
s t u d i e d p ro v e d t o hav e a low a b s o r p tio n c a p a c i t y f o r SOg:
f
-1 2 -
0 .0 0 4 4 m ols SOg/mol a b s o r b e n t w ith a
SOg i n l e t g a s .
A f t e r d e s o r p t i o n , h ow ever, th e s o l u t i o n c o n ta in e d o n ly
0 .0 0 1 8 3 m ols SOg/mol a b s o r b e n t .
T h u s, a s m a ll am ount o f
r e c o v e r y i s p o s s i b l e from a % SO2 i n l e t g a s .
A s m a ll
am ount o f s a l i c y l i c a c i d was p r e c i p i t a t e d d u r in g a b s o r p ­
t i o n , b u t t h i s r e d i s s o l v e d d u r in g d e s o r p ti o n .
0.
n - B u ty l and n -H exyI Amines
A p r e li m i n a r y t e s t by O r s a t a n a l y s i s on aq u eo u s s o lu ­
t i o n s o f th e above am in es r e v e a le d t h a t t h e i r a b s o r p tio n
c a p a c i t y f o r SOg was e x c e e d in g ly s m a ll.
A b s o rp tio n e q u i l i b r i a w ere n o t fo u n d f o r th e am in es
b e c a u se a s u c c e s s f u l t i t r a t i o n c o u ld n o t be c a r r i e d o u t
i n o r d e r t o a n a ly z e th e am ines f o r SOg c o n te n t:
a b s o r p ti o n :
RNH2
R N H g.SOL
p ro p o s e d t i t r a t i o n :
RNH2 + RNH2 . SOg
HA
——— ^ , RNHg
HA + RNHg
a c tu a l t i t r a t i o n r e s u lts :
RNH2 + RNH2 . SO2
H.
ZRNH2 . HA + SO2
C y c lo - p e n ta d ie n e
C y c lo - p e n ta d iene was t r i e d a s an a b s o r b e n t.
The
su p p o sed r e a c t i o n was t h a t SOg w ould add t o t h e ey eI o -
-1 3 -
p e n ta d ie n e m o le c u le b y 1 -4 a d d i t i o n .
S o lv e n t l o s s ,
h o w ev er, was so g r e a t t h a t c y c lo - p e n ta d ie n e was Abandoned
a s u n fe a s ib le .
I .
Sodium T a r t r a t e
E q u ilib r iu m d a t a was o b ta in e d f o r a 50 pbw aq u eo u s
s o l u t i o n o f sodium t a r t r a t e .
T h is s o l u t i o n had a good
a b s o r p ti o n c a p a c i t y f o r SOg; 0 .0 1 9 5 0 m o ls S02 /m o l a b ­
s o r b e n t f o r a 5% SOg i n l e t g a s .
The SOg c o n te n t a f t e r •
d e s o r p ti o n was 0 .0 0 3 0 8 m o ls SOg/mol a b s o r b e n t.
A m o d e ra te
am ount o f t a r t a r i c a c i d was p r e c i p i t a t e d d u r in g a b s o r p ti o n ,
b u t i t r e d i s s o l v e d d u r in g d e s o r p ti o n .
K.
Sodium ,M a la te
Sodium m a la te a l s o e x h i b i t e d a good a b s o r p tio n cap a­
c i t y f o r SOg.
A 50 pbw aq u eo u s s o l u t i o n o f sodium m a la te
i n e q u ilib r iu m w ith 5% SOg i n l e t g a s h e l d 0 .0 1 9 2 m o ls SOg
/m o l a b s o r b e n t.
A f t e r d e s o r p t i o n , th e SOg c o n te n t was
Oe00643 m o ls SOg/mol a b s o r b e n t.
No p r e c i p i t a t e was ob­
s e r v e d d u r in g a b s o r p tio n o r d e s o r p t i o n i
Vi
A b s o rp tio n R eac tio n -M ech a n ism s
T h e -fo llo w in g f a c t s l e d t o t h e p ro p o s e d m echanism f o r t h e r e ­
a c t i o n o f t h e sodium s a l t o f an o r g a n ic a c i d w ith SOg i n ' aq u eo u s
s o lu ti o n s
—14~
1.
H ydrogen io n s w ere form ed and t h e o r g a n ic a c i d , o r i g i n a l l y
p r e s e n t a s i t s sodium s a l t , was a p r o d u c t.
2.
S m all am ounts o f SOg i n t h e p r e s e n c e o f e x c e s s sodium s a l t - o f - t h e - a c i d r e n d e r e d t h e a b s o r p tio n k i n e t i c s e x tre m e ly
s e n s i t i v e t o even a s m a ll v a r i a t i o n i n th e am ount o f SOg
a v a i l a b l e f o r a b s o r p ti o n .
3.
The a c i d p r o d u c ts w ere v a s t l y more s o lu b le i n w a te r a t 90°C
th a n i n w a te r a t 2 5 ° C .
The p ro p o s e d m echanism w as:
2H+ + SO3 =
1.
H2O + SOg £ - - - >
2.
ANa
3•
A
4.
ZNa+ + SO3 = ^------ ^ NagSO3
A" + Na+
+ H+ ^ A
H
Sodium s u l f i t e i s n e a r l y tw ic e a s s o lu b le i n w a te r a t 9 0°C a s i n w a te r
a t 2 5 ° C , and th e a c i d s i n v e s t i g a t e d w ere i n s o l u b l e o r s l i g h t l y s o lu b le
a t 2 5 °C and v e r y s o lu b le a t 9 0 ° C .
T h is w ould te n d t o a i d a r e v e r s a l
o f th e above m echanism d u r in g d e s o r p t i o n .
The r e v e r s a l o f r e a c t i o n #1
i s a l s o f a v o r e d b y in c r e a s e d te m p e r a tu r e .
The sodium s a l t s o f c i t r i c , t a r t a r i c , l a c t i c , and m a lic a c id s w ere
fo u n d t o be e x c e p t i o n a l l y good a b s o r b e n t m edia f o r SOg.
a c i d s a r e a lp h a h y d ro x y .
A l l o f th e s e
The in f l u e n c e o f t h i s a lp h a h y d ro x y l group
seemed t o be e x e c u te d i n su ch a m anner t h a t th e d i s s o c i a t i o n c o n s ta n t
o f th e a c i d was n e a r 10
~3 «5
* a s s u g g e s te d by Howat ( 4 ) .
I n o th e r w o rd s,
t h e sodium s a l t s o f a lp h a h y d ro x y a c i d s a r e c a p a b le o f a b s o r b in g s u f ­
-1 5 -
f i c i e n t q u a n t i t i e s o f SOg and y e t a r e c a p a b le o f e a s i l y r e l e a s i n g t h i s
SOg upon h e a t i n g .
F o r th e kby r e a c t i o n :
SOg + HgO , ---- SO3
+ 2H+
K
was c a l c u l a t e d fro m d e lta - H an d d e l t a - ? o f t h e r e a c t i o n ,
eq
273°K:
Keq - 8 .7 x 1 0 -9
298°K:
Keq , 1 .9 x ID "9
323°K:
K
= 4 .9 x 1 0 "10
eq
T h u s, t h e r e a c t i o n i s f a v o r e d b y d e c r e a s in g te m p e r a t u r e i
V a lu e s o f
where:
w ere c a l c u l a t e d f o r t h i s r e a c t i o n a t v a r io u s p r e s s u r e s .
L ,
tllH2O)
(mSO. - )
_
^ ________
tllSO2 )
"
Kr ' p ^ n
N = mol f r a c t i o n
The c a l c u l a t e d r e s u l t s f o r
I atm :
K
a t 298°K an d v a r io u s p r e s s u r e s w e re :
= 1 .6 $ x IO "?
. 50 atm,:
Kn = 5 .1 2 x 10-1 1
100 atm :
= 5 .4 8 x 10” 14
T h u s, in c r e a s e d p r e s s u r e d o es n o t f a v o r an in c r e a s e d c o n c e n tr a ti o n o f
SO3 - and H+ i o n s .
The s m a ll f l u c t u a t i o n o f p r e s s u r e (640+5 mm Hg)
d u r in g t h e c o l l e c t i o n o f e q u ilib r iu m d a ta s h o u ld n o t h av e had an y a d ­
v e r s e e f f e c t on th e a c c u r a c y o f th e e q u ilib r iu m d e t e r m in a tio n s .
-1 6 -
V I.
C o n tin u o u s Runs
Those a b s o r b e n ts t h a t gave s a t i s f a c t o r y r e s u l t s f o r p h a s e s #1
an d #2 o f t h e p la n o f i n v e s t i g a t i o n s w ere s u b je c te d t o a 2 0 -h o u r t e s t
ru n i n t h e c o n tin u o u s - a b s o r p tio n s e tu p p i c t u r e d i n F ig u r e 11„
The
sodium s a l t s o f c i t r i c , t a r t a r i c , m a lic , l a c t i c , an d s a l i c y l i c a c i d s
w ere c o n s id e r e d f o r s u b j e c t i o n t o c o n tin u o u s ru n a n a l y s i s , b u t th e
n e t a b s o r p ti o n c a p a c i t y o f sodium s a l i c y l a t e was re g a r d e d a s to o sm a ll
f o r sodium s a l i c y l a t e t o b e in c lu d e d i n t h e a c t u a l t e s t r u n s .
The p u rp o s e o f t h e t e s t ru n s was tw o f o ld ;
1.
To se e i f t h e a b s o r b e n t u n d e r c o n s id e r a tio n w ould
m a in ta in i t s a b s o r p ti o n - d e s o r p t io n c h a r a c t e r i s t i c s
o v e r a 2 0 -h o u r p e r io d ( r e g a r d e d by t h e a u th o r a s a
s u f f i c i e n t e n d u ra n c e t e s t ) w ith o u t a n y d e c o m p o sitio n
o r f o r m a tio n o f p r e c i p i t a t e d b y - p r o d u c ts o c c u r r i n g .
2.
To ch eck t h e a c c u r a c y o f t h e e q u ilib r iu m c u r v e s ( th e
o p e r a t in g l i n e , d e te rm in e d fro m t h e s lo p e o f t h e
e q u ilib r iu m c u rv e w i l l n o t y i e l d p r e d i c t e d r e s u l t s
i f t h e e q u i lib r i u m cu rv e i s m ore th a n m o d e ra te ly i n
e r r o r ) .■
Sodium l a c t a t e> sodium c i t r a t e , an d sodium m a la te w ere fo u n d
s a t i s f a c t o r y f o r p o s s i b l e i n d u s t r i a l u s e a s a b s o r b e n ts f o r SO^ r e ­
c o v e ry .
Sodium t a r t r a t e , h o w ev er, c o u ld n o t be f u l l y t e s t e d i n t h e
c o n tin u o u s - a b s o r p tio n a p p a r a t u s .
p r e c i p i t a t e d d u r in g t h e t e s t ru n .
L a rg e am ounts o f t a r t a r i c a c i d w ere
T h is c a u se d c lo g g in g o f t h e pumps ■
a n d colum n, m aking f u r t h e r t e s t i n g im p o s s ib le .
The t e s t s i n d i c a t e d t h a t l a c t a t e , c i t r a t e , and m a la te sh o u ld
w ith s ta n d i n d u s t r i a l u s e a t d e s o r p tio n te m p e r a tu r e s o f IOO0C and
a b s o r p ti o n te m p e r a tu r e s o f 25°C .
-1 7 -
The t e s t r e s u l t s a l s o gave e v id e n c e t h a t th e a b s o r p ti o n c u rv e s
w ere r e a s o n a b ly a c c u r a t e .
H owever, f o r a c c u r a te i n d u s t r i a l c a l c u l a t i o n s
t h e a u t h o r s u g g e s ts t h a t t h e r e g io n o f th e c u rv e s fro m y=0 t o y= 0 i0 6 b e
m ore a c c u r a t e l y d e te rm in e d b y u s in g f lo w m e te r s w ith g r e a t e r s e n s i t i v i t y
a t low f lo w r a t e s th a n w ere a t th e d i s p o s a l o f t h e a u t h o r .
T hese a b s o r b e n ts r e c o v e r e d a p p r o x im a te ly 96# o f th e SOg i n th e
g a s p a s s e d th ro u g h th e a b s o r p ti o n colum n.
As f a r a s low pumping c o s t s .
a r e c o n c e rn e d ; th e a b s o r b e n ts sh o u ld be ra n k e d i n t h e o r d e r c i t r a t e
^ la c ta te
/ m a la te , t h e o r d e r b e in g d e te rm in e d by t h e e q u i lib r i u m -
c u rv e s l o p e s .
The a c c u r a c y o f t h e e q u ilib r iu m c u rv e s was d e te rm in e d i n t h e
f o llo w in g m a n n erJ
The lo w e r t e r m i n a l o f t h e o p e r a t in g l i n e f o r each a b s o r b e n t was
p ic k e d t o n e a r l y c o in c id e w ith th e e q u i lib r i u m c u rv e a t a g a s o u t l e t c o m p o sitio n o f yg = 0 .0 0 2 .
The o p e r a t in g c o n d itio n s w ere th e n S et so
t h a t t h e o p e r a t in g l i n e c l o s e l y p a r a l l e l e d t h e e q u ilib r iu m c u r v e .
v a lu e was p r e d i c t e d f t i r
A
a s d e te rm in e d by th e i n t e r s e c t i o n o f th e
o p e r a t in g l i n e w ith y ^ = 0 .0 5 , t h e i n l e t g a s - c o m p o s itio n .
I f t h e ex­
p e r im e n ta l y ^ - v a lu e was r a d i c a l l y g r e a t e r th a n y = 0 .0 0 2 , t h e im p lic a ­
t i o n w ould be t h a t t h e c u rv e c r o s s e d t h e o p e r a tin g l i n e a t a y - v a lu e
o f l e s s th a n t h e i n l e t g a s - c o m p o s itio n o r , i n o th e r w o rd s, t h e s lo p e o f
t h e e q u i lib r i u m c u rv e was g r e a t e r th a n th o u g h t t o b e .
I f t h e v a lu e
p r e d i c t e d f o r x ^ ch ec k ed c l o s e l y w ith t h e e x p e r im e n ta l r e s u l t s , th e
s lo p e o f t h e e q u i lib r i u m cu rv e was e i t h e r l e s s th a n th o u g h t t o be o r a s
-1 8 -
o r i g i n a l l y d e te rm in e d .
The e q u ilib r iu m - c U r v e s lo p e s u s e d f o r d e te rm in in g t h e o p e r a tin g
l i n e s w ere p ic k e d a s s te e p a s p o s s i b l e , w ith i n t h e l i m i t s o f r e a s o n ­
a b le e x tr a p o la tio n .
I f t h e e x p e r im e n ta l e v id e n c e d id n o t show t h a t
t h e e q u i lib r i u m c u rv e c r o s s e d o v e r t h e o p e r a t in g l i n e , t h e c u rv e was
th e n th o u g h t t o be s a t i s f a c t o r y .
S m all v a lu e s f o r th e s lo p e o f th e
e q u i lib r i u m c u rv e a r e d e s i r a b l e , f d r $ a s t h e s lo p e a p p ro a c h e s a 0 v a l u e ,
t h e a b s o lu t io n c a p a c it y a p p ro a c h e s t h e i n f i n i t e and t h e l i q u o r - t o - g a s
r a t i o a p p ro a c h e s a v a lu e o f CL
V ila
E x p e rim e n ta l M ethods
A.
D e te rm in a tio n o f E q u lib riu m C u rv es
As s t a t e d i n t h e p la n o f i n v e s t i g a t i o n s , t h e f i r s t s te p was
t o d e te rm in e e q u i lib r i u m d a ta f o r a s e r i e s o f p o s s i b l e a b s o r b e n tSd
F ig u r e 10 i s a d ia g ra m o f t h e a p p a r a tu s an d a c c e s s o r i e s u s e d t o
o b ta in t h i s in f o r m a tio n .
A ir and SOg w ere m e te re d b y means o f m anom eters th ro u g h a
s e r i e s o f m ix in g o r i f i c e s i n t o a m ix in g f l a s k .
From t h i s f l a s k ,
t h e g a s m ix tu r e p a s s e d th r o u g h a g l a s s t u b e , ti p p e d w ith S in te r e d
g l a s s an d im m ersed i n t h e a b s o r b e n t b e in g i n v e s t i g a t e d .
The g a s
m ix tu re em erged fro m t h e s i n t e f e d - g l a s s t i p i n t h e fo rm o f m in u te
b u b b le s .
The b u b b le s , r i s i n g up t h e n a rro w s e c t i o n o f th e a b s o rp ­
t i o n f ia s k > c r e a t e d t u r b u l e n t m ix in g o f th e g a s m ix tu r e and ab ­
s o r b e n t, an d th u s p ro v id e d e f f i c i e n t c o n t a c ti n g o f t h e tw o .
-1 9 -
The c o n d e n s e r, th r o u g h w h ich t h e e x h a u s t g a s - m ix tu r e p a s s e d ,
p r o v id e d a m eans f o r rem oving e n t r a i n e d a b s o r b e n t.
The a b s o rb e n t
te m p e r a tu r e was m a in ta in e d a t 25 0G w ith a w a te r b a t h .
was t h a t o f th e a tm o s p h e re , b e in g an a v e ra g e 64 O mm Hg.
P ressu re
P ressu re
d o e s n o t e x e r t a g r e a t amount o f in f l u e n c e on th e a b s o r p tio n o f
SOg i n aq u eo u s s o l u t i o n s .
' F o r a g a s m ix tu r e w ith a g iv e n SOg c o m p o s itio n , t h e a b s o r b e n t
was t i t r a t e d p e r i o d i c a l l y u n t i l a c o n s ta n t t i t r a t i o n v a lu e was
a tta in e d .
The amount o f SOg i n t h e a b s o r b e n t a t c o n s ta n t t i t r a ­
t i o n was t h e amount i n e q u ilib r iu m w ith t h e s p e c i f i e d g a s -m ix tu re
i n c o n t a c t w ith t h e a b s o r b e n t.
The g a s m ix tu r e was a n a ly z e d by
m eans o f an O r s a t .
The above p ro c e d u re was r e p e a te d f o r v a r io u s s p e c i f i e d g a s m ix tu r e s t o g iv e e q u ilib r iu m p o i n t s r e p r e s e n t i n g an e q u ilib r iu m
c u rv e .
B.
C o n tin u o u s Buns
Those a b s o r b e n ts t h a t w ere p r e d i c t e d s u i t a b l e f o r a b s o r p tio n
o f SOg w ere s t u d i e d i n th e c o n tin u o u s a b s o r p ti o n - d e s o r p t io n ap ­
p a r a t u s p i c t u r e d i n F ig u r e 1 1 .
Tw-O 3 6 " x I " g l a s s colum ns p ack e d w ith g l a s s r i n g s w ere
u s e d , one f o r a b s o r p ti o n and t h e o t h e r f o r d e s o r p ti o n .
A b s o rb e n t, S tr ip p e d o f i t s SOg c o n te n t and a t 25 °C , was
pumped i n t o t h e to p o f t h e a b s o r p ti o n column and a llo w e d t o t r i c k l e
-2 0 -
dovm t h e column a t a p r e d e te r m in e d P a t e i
An a ir-S O ^ m ix tu r e
(5% SOg) was f e d i n t o t h e b o tto m o f t h e column^ c o u n t e r - c u r r e n t
t o th e a b s o r b e n t f lo w .
The g a s m ix tu r e > b e ih g r e l i e v e d o f i t s
SOg c o n te n t d u r in g i t s t r a v e r s e o f t h e colum n, was p a s s e d th ro u g h
a c o n d e n s e r t o rem ove a n y e n t r a in e d a b s o r b e n t an d th e n a n a ly z e d
f o r SO2 b y th e O rs a t m ethod.
The S O g -c o n c e n tra te d a b s o r b e n t d is c h a r g e d from t h e a b s o r p tio n
column was c o l l e c t e d and f e d i n t o a d e s o r p tio n column w hich was
m a in ta in e d a t IOO0C.
I n t h i s colum n, SOg was s t r i p p e d fro m th e
a b s o r b e n t and p a s s e d th ro u g h a c o n d e n s e r.
c o n d e n s e r was c o n c e n tr a te d SOg.
The g a s le a v in g th e
The s t r i p p e d a b s o r b e n t was th e n
pumped th r o u g h a h e a t e x c h a n g e r and b ack t o th e a b s o r p ti o n colum n.
A n a ly s is o f t h e c o n c e n tr a te d an d s t r i p p e d a b s o r b e n ts was accomp­
lis h e d by t i t r a t i o n .
C.
M ethod o f T i t r a t i o n
A known am ount o f a b s o r b e n t was p la c e d i n an O rs a t p i p e t t e
and c a u se d t o a b s o rb a g iv e n volum e o f SOg, a s m e a su re d by th e
O rs a t.
T h is s o l u t i o n was th e n t i t r a t e d w ith a s ta n d a r d iz e d NaOH
s o l u t i o n t o g iv e a t i t r a t i o n c o n s ta n t ;
Itt i t r
m l NaOH
m ol SOg
Ih e n an a b s o r b e n t c o n ta in in g an unknown amount o f SOg was t i t r a t e d :
t i t r a t i o n v a lu e = m l NaOH/ml a b s o r b e n t
th e n :
-2 1 -
m o ls SOg
m l a b so rb e n t
=
m o ls SOg
t i t r a t i o n v alu e/K j.
=
t i t r a t i o n v a lu e
m o ls a b s o r b e n t
The
x
^ titr
m l ab so rb e n t
m ol a b s o r b e n t
^ o r e a c ^ a b s o r b e n t was ch eck ed and v e r i f i e d i n
o r d e r t o o b ta in a v a lu e w ith l i t t l e o r no d e v i a tio n o v e r th e ra n g e
o f SOg c o n c e n tr a ti o n t h a t a p p l ie d t o each a b s o r b e n t„
D.
D is c u s s io n o f E x p e rim e n ta l E r r o r s
O r s a t g a s - a n a l y s i s i s a c c u r a te t o + 0 ,0 0 1 f o r y - v a lu e s i f
1 0 0 -c c g a s -s a m p le s a t room te m p e r a tu r e a r e u s e d .
R e p e a te d a n a ly s e s
o f a g iv e n g a s -s a m p le w ere d u p lic a b le , w ith in th e s e v a l u e s .
B ecause o f t h e c a r e ta k e n t o v e r i f y t h e t i t r a t i o n c o n s ta n t ,
t h e e r r o r i n SOg-c o n c e n tr a ti o n v a l u e s d e te rm in e d b y t i t r a t i o n
s h o u ld have b een o n ly t h a t e r r o r g o v e rn e d by t h e r e a d in g a c c u ra c y
o f t h e 50-m l b u r e t t e s u se d f o r t i t r a t i n g .
The a u th o r was n o t a b le t o o b ta in r e p r o d u c ib le p o i n t s on th e
e q u ilib r iu m c u r v e s i n th e r e g io n fro m y = 0 t o y = 0 .0 6 .
However,
p o i n t s r e p r e s e n t i n g y - v a lu e s above t h i s r e g io n w ere r e p r o d u c i b l e .
The u n r e p r o d u c ib le r e g io n , b e in g o n ly a s m a ll p a r t o f t h e t o t a l
c u r v e , was e x t r a p o l a t e d t o t h e o r i g i n a s d e te rm in e d b y t h e c h a ra c ­
t e r i s t i c s o f t h e known c u r v e .
T h a t t h e e x t r a p o l a t i o n s w ere s u f ­
f i c i e n t l y a c c u r a te was c o r r o b o r a te d b y t h e r e s u l t s o f th e ,c o n t in u o u s
ru n s.
The r e a s o n s f o r la c k o f r e p r o d u c i b le r e s u l t s i n th e r e g io n
-2 2 -
s t a t e d above w ere b e l ie v e d t o b e :
1.
S in c e t h e a b s o r p tio n Was p re d o m in a n tly c h e m ic a l
and n o t p h y s i c a l , t h e g r e a t e r c o n c e n tr a tio n o f
a b s o r b e n t com pared t o SOg c o n c e n tr a tio n i n t h i s
r e g io n , w ould hav e made SOg c o n c e n tr a tio n t h e
c o n tro llin g f a c to r .
2.
The m anom eters u s e d f o r m e te r in g th e S O g -a ir
m ix tu r e w ere n o t c a p a b le o f m a in ta in in g a
c o n s ta n t SOg c o n c e n tr a ti o n i n t h i s r e g i o n .
T h u s, s in c e t h e SOg c o n c e n tr a ti o n i s more d i r e c t l y c o n t r o l l i n g
i n t h i s r e g io n th a n i n an y o t h e r , an d s in c e t h e m anom eters co u ld
n o t h o ld t h e SOg c o n c e n tr a tio n s u f f i c i e n t l y c o n s ta n t i n t h i s
r e g io n , th e r e s u l t s w ere n o t r e p r o d u c i b l e .
f i c u l t y had l i t t l e
H owever, t h i s dif^-
e f f e c t on t h e n e t e x p e r im e n ta l r e s u l t s .
Summary
Sodium f o r m a te ^ sodium c h l o r i d e b u f f e r e d t o pH 3<*5* g l y c i n e , sodium
c i t r a t e , sodium b e n z o a te , sodium s a l i c y l a t e , n - b u t y l a m in e, n - h e x y l
a m in e, c y c lo p e h ta d ie n e , sodium t a r t r a t e , sodium l a c t a t e , and sodium
m a la te w ere i n v e s t i g a t e d a s p o s s i b l e i n d u s t r i a l a b s o r b e n ts f o r concen­
t r a t i n g SOg from w a s te g a s e s o f a p p r o x im a te ly 5% SOg by volum e.
T h e ir a b s o r p t i o n - d e s o r p t i o n c h a r a c t e r i s t i c s w ere s t u d i e d , and e q u i­
li b r iu m d a ta a t 25°C Was d e te rm in e d f o r th o s e a b s o r b e n ts w here t h i s
was p o s s i b l e .
Those w hich gave e v id e n c e o f b e in g i n d u s t r i a l l y f e a s i b l e
a s a b s o r b e n ts f o r SOg w ere s u b je c te d t o s tu d y i n a c o n tin u o u s a b s o r p ti o n d e s o r p ti o n a p p a r a tu s a t te m p e r a tu r e s o f 25 and IOO0G, r e s p e c t i v e l y .
” 23“
The sodium s a l t s o f c i t r i c , l a c t i c , an d m a lic a c i d s w ere th e onlymembers o f t h e ab o v e g ro u p o f a b s o r b e n ts i n v e s t i g a t e d t h a t p ro v e d *
e n tir e ly s a tis fa c to ry .
N o m en clatu re
L = l i q u i d flo w r a t e
G = g a s f lo w r a t e
M = s lo p e o f e q u i lib r i u m cu rv e
L/G = s lo p e o f o p e r a t in g l i n e
= a b s o r p ti o n te m p e r a tu r e
Tq = d e s o r p tio n te m p e r a tu r e
X = m o ls SOg/mol a b s o r b e n t
= a b s o r p tio n colum n l i q u i d - o u t l e t c o m p o s itio n ,
m o ls SOg/mol a b s o r b e n t
X^ = a b s o r p tio n column l i q u i d - i n l e t c o m p o s itio n ,
m ols SOg/mol a b s o r b e n t
Y = m o ls SOg/mol g a s
Y j = a b s o r p tio n column g a s - i n l e t c o m p o s itio n ,
m o ls SOg/mol g a s
Yg = a b s o r p ti o n colum n g a s - o u t l e t c o m p o s itio n ,
m o ls SOg/mol g as
-
TABLE I
EQUILIBRIUM DATA
A.
A b s o rb e n t: a 10 pbw aq u eo u s Sodium F o rm ate s o lu ti o n
G as: a ir-S O g m ix tu r e
-Z 0,0231
0.0253
0,0275
0,0284
0 ,0 6
0.132
0*249
0.390
D e s o r p tio n : a b s o r b e n t decom posed
B.
A b so rb e n t: a 20 pbw aq u eo u s Sodium F o rm ate s o l u t i o n
G as: a ir-S O g m ix tu re
X
0.0268
0.0288
0*0311
0.0322
-JL,
0*06
0,132
0.249
0*390
D e s o r p tio n : a b s o r b e n t decom posed
G„
A b s o rb e n t: a 30 pbw aq u eo u s Sodium F o rm ate s o lu ti o n
GaS: a ir-S O g m ix tu re
-2L.
_z_
0,0361
0.0376
0.0406
0.0410
0.06
0.132
0.249
0*390
D e s o r p tio n : a b s o r b e n t decom posed
-2 5 TABLE I - c o n tin u e d
EQUILIBRIUM DATA
Ds
A b so rb e n t: a 35 pbw aq u eo u s Sodium C h lo r id e s o l u t i o n , b u f f e r e d w ith
HCl t o an i n i t i a l pH a t 3 , 5 ,
G asi a ir-S O g m ix tu r e
.x
_X_
0 ,0 0 1 2 0
0 ,0 0 2 6 9
0 .0 6
0 ,1 3 2
0 .2 4 9
0 ,3 9 0
0.00582
0 ,0 0 9 9 0
D e s o r p tio n : x = 0 ,0 0 4
E,
A b s o rb e n t: a 20 pbw aq u eo u s G ljta in e s o l u t i o n
G as: a ir-S O g m ix tu r e
_z_
0 ,0 0 8 0
0,0132
0 .0 1 7 4
0 ,0 2 0 5
_Z_
0 ,0 6
0,132
0 .2 4 9
0 .3 9 0
/
D e s o r p tio n : X = 0 ,0 1 0 7 5
F,
A b s o rb e n t: a 50 pbw aq u eo u s Sodium C i t r a t e s o lu ti o n
G as: a ir-S O g m ix tu r e
-JL
0 ,0 4 7 0
0 ,0 5 1 7
0 ,0 5 6 1
0 .0 6 2 2
D e s o r p tio n : x = O i013 6
.
0 ,0 7 6
0 .1 3 2
0 ,2 4 9
0 .3 9 0
—26 -
TABLE I - c o n tin u e d
EQUILIBRIUM DATA
U.
A b s o rb e n t: a $0 pbw aq u eo u s Sodium S a l i c y l a t e s o l u t i o n
G as: a ir-S O g m ix tu r e
X
_Z_
0.00521
0.00544
0.00574
0 .0 0 5 8 2
0 ,0 7 6
0 .1 3 2
0 .2 4 9
0 .3 9 0
D e s o r p tio n : x = 0 .0 0 1 8 3
A b s o r b e n t: a 50 pbw aq u eo u s Sodium T a r t r a t e s o l u t i o n
G as: a ir-S O g m ix tu r e
X
0 .0 2 3 5 5
0 .0 2 5 0
0 .0 2 7 5
0 .0 3 0 9
_Z_
0 .0 9 8 3
0 .1 3 2
0 .2 4 9
0 .3 9 0
D e s o r p tio n : x = 00308
I.
A b so rb e n t: a $0 pbw aq u eo u s Sodium L a c ta t e s o l u t i o n
G as: a ir-S C >2 m ix tu r e
X
0 .0 2 2 4
0 .0 2 5 3
0 ,0 2 5 7
0.0266
D e s o r p tio n : x = 0 .0 0 9 4 6
-JZ_
0 .0 9 4
0 .1 4 2
0 .2 4 2
0 .3 8 0
-2 7 -
TABLE I - c o n tin u e d
EQUILIBRIUM DATA
J o A b s o rb e n t; ; L 50 pbw aq u eo u s Sodium M a la te s o l u t i o n
G as; a ir-S O g m ix tu r e
-JL
_Z_
0 .0 1 6 9 5
0 .0 3 6 8
0 .0 6 8
0 .1 4 2
0 .2 5 0
0 .3 8 0
0.0381
0 .0 4 4 2
D e s o r p t i o n ; x = 0 .0 0 6 4 3
-
28 -
TABLE' I I - CONTINUOUS RUN DATA FOR SODIUM LACTATE
S3
A v erag e o f
H o u rly R e a d in g s
Y
1
*2
*2
1st 4 hr
0.05
0 .0 0 1
0 .0 0 5 2
0.0 1 3 2
100
23
2nd 4 h r
0 .0 4 8
0 .0 0 2
0 .0 0 6 2 0
0 .0 1 3 5
100
23
3 rd 4 h r
0 .0 4 8
0 .0 0 2
0 .0 0 5 3 6
0 .0 1 3 4
100
24
4 th 4 h r
0 .0 4 6
0 .0 0 2
0 .0 0 5 8 ?
0 .0 1 3 8
100
25
5 th 4 h r
0 .0 4 4
0 .0 0 2
0 .0 0 6 2 0
0 .0 1 3 6
100
28.
xL
TD ° G
A b so rb e n t: 50 pbw aq u eo u s s o l u t i o n o f Sodium L a c t a t e .
O p e ra tin g C o n d itio n s :
M = 2 .8 6
(a v g . fro m 7 = 0 t o y =
L/G = 4 .0 8
G ( a i r ) = 0 .1 6 5 3 S td ,,
CU,»
ft./m in .
G (SO2 ) = 0.008? S t d «.
CU, »
f t./m in .
L = 20 m i/m in . = 0 . 9 gm. m o ls/m in .
R e s u lts :
% SOg r e c o v e r y : 96„3%
- V '- .
2 1 .7 gm. SO^ r e c o v e r e d / l i t e r a b s o r b e n t c i r c u l a t e d .
iil... ••'
No d e c o m p o sitio n o f a b s o r b e n t o v e r 2 0 - h r . r u n .
-2 9 -
1I
X2
Y2
■
1L
o°
A v erag e o f
H o u rly R ead in g s
St**"3
TABLE I I I - CONTINUOUS RUN DATA FOR SODIUM MALATE
1st 4 hr
0.045
0 .0 0 2
0 .0 1 4 5
0.0215
100
25
2nd 4 h r
0.045
0 .0 0 2
0.0152
0 .0 2 2 7
100
25
3 rd 4 h r
0 .0 4 8
0 .0 0 2
0 .0 1 3 5
0 .0 2 1 1
100
2 3 .3
4 th 4 h r
0 .0 4 8
0 .0 0 2
0 .0 1 2 7
0 .0 2 0 3
101
23
5 th 4 h r
0 .0 4 6
0 .0 0 2 .
0 .0 1 0 4
0 .0 2 0 5
102
2 7 .8
A b s o rb e n t: a 50 pbw aq u eo u s s o l u t i o n o f Sodium M a la te .
O p e ra tin g C o n d itio n s :
M = 3 -3 4
(a v g . fro m y = 0 t o y = 0 .0 6 )
L/G = 4 -7 7
G ( a i r ) = 0 .1 2 9 2 S t d . c u . f t . / m i n .
G (SO2 ) = 0 .0 0 6 8 S td . c u . f t . / m i n .
L = 20 m l/m in . = 0 .8 1 2 g m -m ols/m in.
R e s u lts :
%■ SO2 r e c o v e r y :
95,7% •
2 0 .6 gm SO2 r e c o v e r e d / l i t e r a b s o r b e n t c i r c u l a t e d .
No d e c o m p o sitio n o f a b s o r b e n t o v e r 2 0 - h r . ru n —
l i g h t p p t . o f M a lic a c i d t h a t r e d i s s o l v e d d u r in g
d e s o r p ti o n .
-3 0 -
A v erag e o f
H o u rly R ead in g s
*2
xL
Td 0C
I
L
I c?
TABLE IV - CONTINUOUS RUN DATA FOR SODIUM CITRATE
1s t 4 h r
0 .0 4 4
0 .0 0 1 5
0 .0 1 5 4
0.0262
100
25
2n d 4 h r
0 .0 4 6
0 .0 0 1 5
0 .0 1 6 4
0.0 2 9 6
99
28
3rd 4 h r
0 .0 4 8
0.002
0.0172
0.0308
99
28.5
4t h 4 h r
0 .0 4 5
0 .002
0 .0 1 6 5
0.0296
100
28
5t h 4 . h r
'0 .0 4 9
0.002
0 .0 1 5 1
0.0286
100
26
A b s o rb e n t t . a 50 pbw aq u eo u s s o l u t i o n o f Sodium C i t r a t e .
O p e ra tin g C o n d itio n s ;
M = 2 .5 1 5
(a v g . fro m y = 0 t o 7 = 0 .0 6 )
L/G = 3 .5 9
G ( a i r ) = 0 .1 5 0 6 S td . c u e f t . / m i n .
G (SO2 ) = 0 .0 0 7 9 2 S td . c u . f t . / m i n .
L = 15 m l/m in . = 0 .7 1 7 g m -m ols/m in.
R e s u lt s ;
% SO2 r e c o v e r y ;
95 . 8#
3 8 .6 gm„ SO2 r e c o v e r e d / l i t e r a b s o r b e n t c i r c u l a t e d .
-No d e c o m p o sitio n o f a b s o r b e n t o v e r 2 0 - h r . r u n .
-3 1 -
REFERENCES:
(1 )
S h re v e jl C h em ical P r o c e s s I n d u s t r i e s . M cG raw -H ill^
195$, P . 354.
............\
(2 )
1951 M in e r a ls Y earbook, U. S„ B u reau o f M in es.
(3 )
M in e r a l R e s o u rc e s o f t h e U. S . , P u b lic A f f a i r s P r e s s ,
W ash in g to n , D. C .
(4 )
Howat, The C h em ical A ge, 4 2 , 249-75 (1 9 4 0 ).
C
—32—
O ------ /0 %
o ------ ZO %
HCOONa S o lu tio n
"
••
© ------- "
^ OJ
O
0.0/
MoJes SOz
F ig u r e I .
0.0Z
0.03
0.04-
0.05
P e r M ole HCOONa + Hz O
E q u ilib r iu m c u r v e s o f sodium f o r m a te .
/
/
-3 3 -
mm
S)
OJ
0.002
0. 004-
0.006
0.006
Mo/es SOz Per Mole NaC/ +Hz O
F ig u r e 2 .
E q u ilib r iu m c u rv e o f sodium c h l o r i d e .
-3 4 —
Moles SO9 Per Mole NaCI + H9O
0. 0!
0.006
a b s o r b e n t c o n d itio n
0.004-
tre a tm e n t
A b so rb e n t p H
F ig u r e 3 .
C om parison o f pH w ith SOg-conc e n tr a t i o n i n - t h e - a b s o r b e n t f o r sodium c h l o r i d e .
Moles SCL Per Mole Inlet Sas
-3 5 -
Z5°C $ 6 4 0 mmHq _
equilibrium after
desorption
Moles SOz Per Mole Glycine
F i g u r e Z*..
Y-
Wafer
E q u ilib riu m c u rv e o f g ly c in e .
“9 C-
o .o z
0 .0 4 -
0 .0 5
Moles SOz P e r Mole. N o - C l f r a f e f l/ V o f e r
F ig u r e
E q u ilib r iu m
sodium c i t r a t e
0 .0 6
Mo/es SOp P e r Mo/e I n le t G os
desorption
O
0 .0 0 Z
0 .0 0 4 -
0006
0 .0 0 6
M oles SOz P er Mo/e No-SaIicyIote -t W ater
F ig u re 6 .
E q u i li b r i u m c u r v e o f sodium s a l i c y l a t e
M oles SOz P erM o Ie I n l e t O as
-3 8 -
0 .0 2
0 .0 4
M o/es SOz Per Mote N a -T o r fr a te + W ater
F ig u re 7 .
E q u i li b r i u m c u r v e o f sodium t a r t r a t e .
-3 9 -
d e so rp Hon
0.03
M oles SO2 P e r M o/e N a - L o c f a f e + W a / e r
0 .0 ^
F ig u r e 8 .
.
E q u ilib r iu m c u rv e o f sodium l a c t a t e .
12P
129759
3
Moles S 0£ Per Mo/e In Ie tG a s
-4 0 -
D e s o r p +ion
0.04-
Mole S SO2 P e r M ole N a-M alofe 4 W a t e r
Figure 9 .
E q u i l i b r i u m c u r v e o f sodium m a l a t e .
A bsorption F lask
A b s o r b in g S o lu tio n
C o n s t a n t Tem p.
F ig u r e 10.
Apparatus for Equilibrium
Curve D eterm in ation s
—42—
SOz -Cone. SoIuHon
SO~Free. Solution
F ig u r e 11
Con+inuous- Flow Apparaius
Dia cjram
3
7 6 2 1001 3 3 9 0 7
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