ISSN 0104-6632
P in ed in B azil
www.abeq.o g.b /bjche
Vol. 30, No. 04, pp. 801 - 809, Oc obe - Decembe , 2013
*To whom co espondence should be add essed
B azilian Jou nal
o Chemical
Enginee ing
HYDRODYNAMIC AND ABSORPTION STUDIES
OF CARBON DIOXIDE ABSORPTION
IN AQUEOUS AMIDE SOLUTIONS USING
A BUBBLE COLUMN CONTACTOR
A. Blanco, A. Ga cía-Abuín, D. Gómez-Díaz* and J. M. Na aza
PF&PT esea ch eam, Depa men o Chemical Enginee ing, ETSE, Uni e si y o San iago de Compos ela,
Rúa Lope Gómez de Ma zoa, San iago de Compos ela, E-15782, Galicia, Spain.
E-mail: dieg[email p o ec ed]
(Submi ed: Augus 3, 2012 ; Re ised: No embe 27, 2012 ; Accep ed: Decembe 30, 2012)
Abs ac - The p esen wo k analyses he ca bon dioxide abso p ion p ocess in aqueous n-alkylpy olidones
solu ions, om he poin o iew o hyd odynamic s udies as well as mass ans e , using a bubble column
con ac o . An analysis o he in luence o solu e concen a ion and gas low- a e is complemen ed by he
s udy o he e ec caused by he alkyl g oup on he hyd odynamics and mass ans e . The p esence o his
kind o subs ance p oduces a dec ease in mass ans e a e, bu on he basis o in e acial a ea and mass
ans e coe icien alues, e hyl-2-py olidine (EP) shows sui able cha ac e is ics o eplace me hyl-2-
py olidine (MP) in gas sepa a ion p ocesses due o i s lowe sa e y p oblems.
Keywo ds: Abso p ion; Alkyl-py olidone; Bubble column; In e acial a ea; Mass ans e coe icien .
INTRODUCTION
In he las yea s, acidic gas sepa a ion in indus-
ial s eams has been commonly pe o med by gas-
liquid abso p ion using di e en ypes o con ac o s.
This kind o sepa a ion can be done using physical
sol en s such as wa e , me hanol (Rec isol p ocess)
o 1-me hyl-2-py olidone (Lu gi’s Pu isol p ocess),
o by a gas-liquid chemical eac ion ( eac i e abso p-
ion) o example: po assium ca bona e (Ben ield
p ocess), -monoe hanolamine (Gi bo ol p ocess),
Sul olan + diisop opanolamine (Shell’s Sul inol
p ocess) (Kohl and Nielsen, 1997) o amine blends
(Bonen an e al., 2007; Bishnoi and Rochelle, 2002).
Being mo e speci ic, he Pu isol p ocess, ha em-
ploys 1-me hyl-2-py olidone as sol en , was i s
applied o na u al gas swee ening; howe e , his p o-
cedu e has shown highe impo ance in o he p ocesses
such as in he hyd ogen pu i ica ion p ocess. These
p ocedu es a e based on physical abso p ion-deso p-
ion cycles o pollu an gases, di e ing om o he
p ocesses ha in ol e a he e ogeneous chemical
eac ion be ween he gas and liquid phases. The
Pu isol p ocess has been ca e ully analysed o i s
use in powe s a ions (Schü z e al., 1992), o desul-
phu iza ion and also o ca bon dioxide cap u e. The
egene a ion p ocess o he sol en can be pe o med
by means o p essu e changes o deso b he pollu an
gases. This a oids he he mal egene a ion neces-
sa y in chemical abso p ion, which p oduces liquid
phase deg ada ion (Supap e al., 2009) and inc eases
he ene ge ic cos s. Due o he use o aqueous 1-
me hyl-2-py olidone solu ions o he ca bon dioxide
abso p ion p ocess, we ha e ca e ully analysed in
his wo k he abso p ion o his gas in hese aqueous
solu ions. Besides, we ha e also used o he cyclic
amides, such as 2-py olidone and 1-e hyl-2-py oli-
done, o e alua e he di e ences be ween he e ec s
802 A. Blanco, A. Ga cía-Abuín, D. Gómez-Díaz and J. M. Na aza
B azilian Jou nal o Chemical Enginee ing
caused by hese sol en s on he abso p ion p ocess in
bubbling equipmen , analyzing he hyd odynamic
and he mass ans e p ocesses. 1-Me hyl-2-py oli-
done has e y nega i e haza d cha ac e is ics (i i a-
ion o skin, eyes and espi a o y ac and also may
damage he unbo n child) in compa ison wi h he
o he amides used in p esen esea ch wo k. Also,
1-me hyl-2-py olidone is a candida e included in
he Eu opean Chemical Agency (ECHA) lis o
Subs ances o Ve y High Conce n (SVHC). Cyclic
amides ha e shown in e es ing cha ac e is ics as high
densi y, high boiling poin and high pola i y
sol en s, which allow hei usabili y a an indus ial
le el (Noll e al., 1996). Also, hei high solubili y in
wa e allows he use o his kind o subs ance in a
wide ange o indus ial and labo a o y ope a ions.
On he o he hand, he excellen he mal and chemi-
cal s abili y a e o he in e es ing cha ac e is ics o
he use o his kind o subs ance as sol en .
In p esen wo k he gas-liquid con ac o was a
bubble column because his kind o equipmen
shows an e ec i e beha iou wi h a simple cons uc-
ion and ope a ion (S oyan e al., 2007). This de ice
gene ally has excellen hea and mass ans e cha ac-
e is ics, li le main enance and low ope a ing cos s
(Kan a ci e al., 2005). Impo an a iables mus be
aken in o accoun wo king wi h bubble columns:
gas hold-up, bubble cha ac e is ics (size, shape, ise
eloci y, con amina ion) (Lage, 1999), low egime,
mass ans e , e c (Ma ínez and Casas, 2012).
Di e en s udies (Da mana e al., 2005; Cen s e al.,
2004) indica e ha se e al phenomena in luence
hese a iables: chemical eac ion, mass ans e and
luid low. Thus, all o hese mus be aken in o
accoun o model, simula e and scale-up abso p ion
p ocesses in bubble columns.
MATERIALS AND METHODS
2-Py olidone, P (CAS numbe : 616-45-5), 1-me hyl-
2-py olidone, MP (CAS numbe : 872-50-4) and
1-e hyl-2-py olidone, EP (CAS numbe : 2687-91-4)
we e supplied by Fluka wi h a pu i y ≥ 99% o
2-py olidinone, and ≥98% o he o he alkyl-py -
olidones. Comme cial g ade ca bon dioxide o 99.998%
pu i y, supplied by Ca bu os Me álicos, was also used
as gas phase in his wo k.
The gas-liquid con ac o employed in he hyd o-
dynamics and gas abso p ion s udies pe o med
in he p esen wo k was a squa e bubble column
(6 cm×6 cm×110 cm) wi h a liquid olume o 3 li es
(see Figu e 1). The gas spa ge was a glass capilla y
wi h only one o i ice o p oduce a small numbe o
bubbles. The bubble diame e was measu ed using a
pho og aphic me hod based on images aken along
he bubble column using he expe imen al p ocedu e
desc ibed in a p e ious wo k (Gómez-Díaz e al.,
2008). Ca bon dioxide mass ans e om he gas
phase o he liquid one was s udied on he basis o
he di e ence be ween inle and ou le gas low- a e
in he bubble con ac o . The gas phase is pu in
con ac wi h pu e wa e o sa u a e he gas and o
emo e he esis ance o he mass ans e o wa e
om he liquid o he gas phase. The gas low- a e
ed o he bubble column was measu ed and con-
olled wi h wo mass low con olle s (Alica
Scien i ic). The mass low con olle s employed in
he p esen s udy o he gas low- a e and he p es-
su es we e calib a ed by he supplie o pu e ca bon
dioxide s eams. The ope a ion egime employed in
he abso p ion expe imen s was con inuous in ela ion
o he gas phase and ba ch ega ding he abso ben
liquid.
1
3
4
6
8
5
2
7
2
1
3
4
6
8
5
2
7
2
1
3
4
6
8
5
2
7
2
1. Ca bon dioxide cylinde ;
2. Alica Scien i ic mass lowme e /con olle ;
3. Humidi ie and he mos a ic ba h;
4. P essu e gauge;
5. Bubble column con ac o ;
6. Tempe a u e gauge;
7. Flow da a eco de ;
8. Se up o in e acial a ea de e mina ion.
Figu e 1: Expe imen al se -up employed in he ca bon dioxide abso p ion expe imen s.
Hyd odynamic and Abso p ion S udies o Ca bon Dioxide Abso p ion in Aqueous Amide Solu ions Using a Bubble Column Con ac o 803
B azilian Jou nal o Chemical Enginee ing Vol. 30, No. 04, pp. 801 - 809, Oc obe - Decembe , 2013
RESULTS AND DISCUSSION
Gas-Liquid In e acial A ea
An example o he pho og aphs used o ob ain he
abo emen ioned bubble size dis ibu ion is shown
in Figu e 2. We can also obse e in his igu e he
in luence caused by he p esence o one solu e
(me hyl-2-py olidone, MP) on he bubble size. Pho-
og aphs indica e ha , o aqueous solu ions o MP,
an inc ease o solu e concen a ion in he liquid
phase could p oduce a dec ease in he bubble size
because an inc ease in he numbe o bubbles is
clea ly obse ed. This beha iou is inconsis en wi h
he ac ha an inc ease in he alue o MP concen-
a ion p oduces an inc ease in he liquid phase
iscosi y (Geo ge and Sas y, 2004). The inc ease in
his physical p ope y usually p oduces an inc ease
in he bubble size (Gómez-Díaz e al., 2009a), bu
he concen a ion ange used in his wo k did no
p oduce la ge changes in liquid phase iscosi y. On
he o he hand, he p esence o his kind o subs ance
also p oduces impo an changes in o he physical
p ope ies ha could cause an impo an in luence on
he bubbles size p oduced in he con ac o . Fo his
kind o subs ance, he e ec caused by small con-
cen a ions on he su ace ension alue (Ga cía-
Abuín e al., 2008) indica es a beha iou simila o
aqueous su ac an solu ions (Gómez-Díaz e al.,
2007). This beha iou comp ises a d ama ic dec ease
in he su ace ension alue wi h he addi ion o e y
low solu e quan i ies, caused by he accumula ion o
his kind o molecule a he gas-liquid in e ace.
When su ac an s a e p esen in he liquid phase,
he e is a di e ence wi h he p esen expe imen al
sys ems because he su ac an concen a ion ange
does no in luence he liquid iscosi y (Gómez-Díaz
e al., 2007). In ela ion o he p e iously analysed
e ec o su ace ension on he bubble diame e
(Sa deing e al., 2006), a dec ease in his physical
p ope y p oduces a dec ease in he bubbles size, in
ag eemen wi h he beha iou shown in Figu e 2.
The bubble images p ocessing (pho og aphs shown
in Figu e 2, o ins ance) p o ides he bubble size
dis ibu ion unde he di e en expe imen al condi-
ions. An example o he esul s ob ained o bubble
size dis ibu ion p oduced in he bubble con ac o is
shown in Figu e 3. This igu e shows ha , unde ce ain
ope a ional condi ions, he use o aqueous solu ions
o P p oduces mo e bubbles o all he diame e
anges han in he case o aqueous solu ions o MP
and EP. In ela ion o gas hold-up, a simila be-
ha iou was ound o di e en solu es, he mos
impo an pa ame e being bubble diame e .
C
MP
= 0.1 M C
MP
= 0.3 M C
MP
= 0.5 MC
MP
= 0.1 M C
MP
= 0.3 M C
MP
= 0.5 M
Figu e 2: Bubble con ac o pho og aphs using aqueous
MP solu ions. Ug = 0.0014 m·s-1.
Figu e 3: In luence o alkyl-py olidone ype on he
bubble size dis ibu ion. Ug = 0.0014 m·s-1. CP = 0.5
mol·L-1. ({) P; (z) MP; () EP.
As was men ioned in he expe imen al sec ion,
he calcula ed Sau e mean diame e as well as he
gas hold-up da a ha e been used o calcula e he gas-
liquid in e acial a ea. Figu e 4 shows he alues o
he gas-liquid in e acial a ea de e mined by his
me hodology. We can obse e in his igu e he
in luence o he gas low- a e (supe icial gas
eloci y) ed o he bubble con ac o and also he
in luence o MP concen a ion on in e acial a ea. In
ela ion o he i s ope a ional a iable (gas low-
a e), an inc ease in his a iable p oduces an
inc ease in he in e acial a ea, ending o a cons an
alue a high supe icial gas eloci y. This beha iou
has been commonly obse ed in he li e a u e (Yang
e al., 2001; K ishn and an Ba en, 2003), since an
inc ease in his a iable p oduces an inc ease in he
gas hold-up (wi h posi i e in luence on he in e a-
804 A. Blanco, A. Ga cía-Abuín, D. Gómez-Díaz and J. M. Na aza
B azilian Jou nal o Chemical Enginee ing
cial a ea). A he same ime, an inc ease in supe icial
gas eloci y p oduces an inc ease in he bubble size,
bu his ac has a nega i e in luence on he gas-
liquid in e acial a ea. Taking in o accoun he da a
shown in Figu e 4, he in luence o gas hold-up is
highe o low supe icial gas eloci ies, and an
impo an inc ease in he in e acial a ea is obse ed
om 18 o 30 L·h-1; howe e , when highe alues o
his a iable a e ed in o he bubble column, he
nega i e in luence o he bubble size compensa es
he posi i e e ec om gas hold-up.
U
g
/ m·s
-1
0.001 0.002 0.003
a / cm
-1
0
0.04
0.08
0.12
0.16
Figu e 4: In luence o supe icial gas eloci y on
he gas-liquid speci ic in e acial a ea. Aqueous
solu ions o MP: ({) CMP = 0 M; (z) CMP = 0.1 M;
() CMP = 0.3 M; () CMP = 0.5 M.
On he o he hand, in ela ion o he in luence o
he liquid phase composi ion (MP concen a ion in
Figu e 4), he obse ed beha iou was an inc ease in
he alue o he gas-liquid in e acial a ea when MP
concen a ion inc eases in he liquid phase. This be-
ha iou is ela ed o he p e ious discussion abou
he pho og aphs shown in Figu e 2, and he in luence
o physical p ope ies on he bubble size. The
conclusion eached in Figu e 2 indica es ha an
inc ease in he MP concen a ion p oduces a dec ease
in he bubble diame e . This ac is in ag eemen wi h
he da a calcula ed o he gas-liquid in e acial a ea,
shown in Figu e 4. This beha iou is due o he
impo an dec ease in he su ace ension alue when
he MP concen a ion inc eases in he liquid phase
(Ga cía-Abuín e al., 2008). This phenomenon p o-
duces a dec ease in bubble size ha has been
con i med in di e en s udies (Gómez-Díaz e al.,
2008; Painmanakul e al., 2005). The e ec caused
by he su ace ension is highe han he possible
in luence o iscosi y (inc ease in bubble diame e )
due o he concen a ion anges, because he com-
posi ion used in his wo k has a highe in luence on
su ace ension han on iscosi y (Geo ge and Sas y,
2004; Ga cía-Abuín e al., 2008).
In ela ion o he in luence o gas- low- a e on he
in e acial a ea alue, he beha iou obse ed is
simila o ha in Figu e 4. Bu he in luence o solu e
concen a ion on he in e acial a ea indica es signi i-
can di e ences, as shown in Figu e 5. Thus, o
aqueous solu ions o MP and EP, an inc ease in he
alue o he gas-liquid in e acial a ea is obse ed
when he MP and EP concen a ion inc eases in he
liquid phase, due o he educ ion in bubble diame e
caused by he dec ease in su ace ension. Fo aque-
ous P solu ions, he beha iou consis s o he absence
o an in luence o solu e concen a ion, ob aining a
cons an alue o gas-liquid in e acial a ea. This be-
ha iou could be due o he ac ha he p esence o
P causes a smalle dec ease in su ace ension alue
han ha caused by he o he alkyl-py olidones
(Ga cía-Abuín e al., 2008). The in luence o iscos-
i y could hen inhibi he e ec caused by su ace
ension o aqueous P solu ions. The expe imen al
da a co esponding o he in e acial a ea indica e
ha he alkyl-subs i u ed py olidones show a simila
beha iou in ela ion o he hyd odynamic pa ame-
e s analysed in his s udy, wi h clea di e ences o
aqueous P solu ions ha could a ec he global mass
ans e p ocess. Taking in o accoun he expe imen-
al esul s co esponding o in e acial a ea, aqueous
solu ions o P do no show good cha ac e is ics as a
MP subs i u e. On he o he hand, aqueous EP solu-
ions show a beha iou simila o aqueous MP solu-
ions and, o his eason, he be e sa e y cha ac-
e is ics make EP a sui able subs i u e.
C / mol·L-1
0 0.2 0.4 0.6
a / cm-1
0
0.05
0.1
0.15
Figu e 5: In luence o alkyl-py olidone ype and
concen a ion on he speci ic in e acial a ea. Ug =
0.0031 m·s-1. ({) P; (z) MP; () EP.
Hyd odynamic and Abso p ion S udies o Ca bon Dioxide Abso p ion in Aqueous Amide Solu ions Using a Bubble Column Con ac o 805
B azilian Jou nal o Chemical Enginee ing Vol. 30, No. 04, pp. 801 - 809, Oc obe - Decembe , 2013
Mass T ans e Coe icien
The p esen wo k also includes s udies o he
p ocess o ca bon dioxide mass ans e o aqueous
solu ions o alkyl-py olidones. Bo h pa ame e s a e
impo an o unde s and he abso p ion p ocess o
his gas in hese aqueous solu ions. As a p elimina y
s ep, di e en s udies ha e been ca ied ou in o de
o de e mine he kind o abso p ion (physical o
chemical) ha akes place in he sys ems analysed in
his wo k. This p e ious s udy is necessa y since, in
esea ch wo ks de eloped by ou esea ch eam, he
eac ion be ween ca bon dioxide and py olidine
(Ga cía-Abuín e al. 2011) was de ec ed. Due o he
simila chemical s uc u e and he p esence o an
amino g oup, i was necessa y con i m he abso p-
ion ype o each sys em. These s udies we e
de eloped using an expe imen al p ocedu e p e i-
ously desc ibed (Ga cía-Abuín e al. 2011). The ex-
pe imen al esul s showed ha all he alkyl-py oli-
done aqueous solu ions p oduce physical abso p ion,
wi h he inhibi ion o he chemical eac ion by he
p esence o he ke one g oup, ha educes he elec-
on densi y on he amino g oup. This ac a oids he
eac ion be ween ca bon dioxide and he amino g oup.
Figu e 6: Expe imen al da a i ing using Equa ion (1).
Ug = 0.0014 m·s-1. () CP = 0 (wa e ), () CP = 0.1 M.
Physical abso p ion expe imen s we e pe o med
using he same bubbling con ac o used in he
p e ious sec ion (hyd odynamic s udies) o pu bo h
phases in con ac , unde he di e en expe imen al
condi ions ( ype o solu e, concen a ion o solu e
and gas low- a e), and he olume ic mass ans e
coe icien (kL·a) was calcula ed using he in eg a ed
o m o Equa ion (1). Figu e 6 shows ha he slope
o he plo is highe o he expe imen in he absence
o P, in compa ison wi h he p esence.
L
dC Ka(C*C)
d
=
⋅⋅ − (1)
Figu e 7 shows ha an inc ease in solu e con-
cen a ion always p oduces a dec ease in he alue o
he olume ic mass ans e coe icien . Howe e ,
his dec ease is mo e impo an o aqueous solu ions
o P, mainly a low solu e concen a ion in he liquid
phase. This beha iou is in ag eemen wi h he p e i-
ous s udies pe o med in his wo k, since a lowe
alue was p e iously obse ed o he speci ic gas-
liquid in e acial a ea (pa ame e included in he
olume ic mass ans e coe icien ) o aqueous
solu ions o P han o solu ions o MP and EP.
Taking in o accoun he obse ed beha iou o
sys ems wi h MP and EP in he p e ious sec ion: an
inc ease in he concen a ion o hese subs ances in
he liquid phase p oduces an inc ease in he in e a-
cial a ea alue, bu Figu e 6 shows a dec ease in he
alue o he olume ic mass ans e coe icien ( he
opposi e beha iou o in e acial a ea). This beha iou
implies ha he e ec caused by he p esence o his
kind o subs ance on he mass ans e coe icien
(kL) is mo e impo an han he co esponding in lu-
ence on he gas-liquid in e acial a ea.
Figu e 7: In luence o alkyl-py olidone ype and
concen a ion on he olume ic mass ans e coe i-
cien . Ug = 0.0014 m·s-1. ({) P; (z) MP; () EP.
The dec ease in he alue o he olume ic mass
ans e coe icien p e iously desc ibed ( o P aque-
ous solu ions) was obse ed o all he expe imen al
sys ems, as well as o all he gas low- a es em-
ployed in his wo k in he bubble con ac o (see
Figu e 8). The e ec caused by P concen a ion is
simila in all cases, bu he supe icial gas eloci y
p oduces an inc ease in he alue o he olume ic

806 A. Blanco, A. Ga cía-Abuín, D. Gómez-Díaz and J. M. Na aza
B azilian Jou nal o Chemical Enginee ing
mass ans e coe icien caused by he inc ease in
he gas-liquid in e acial a ea, due o he supe icial
gas eloci y (see p e ious sec ion and Figu e 4). The
inc ease in he supe icial gas eloci y could also
p oduce an inc ease in he alue o he mass ans e
coe icien (Hashemia e al. 2009), bu ce ain
s udies ha e shown a lack o in luence o his
a iable on his pa ame e (Gómez-Díaz e al., 2006;
Vasconcelos e al., 2003).
C
p
/ mol·L
-1
00.20.40.6
k
L
·a · 10
-3
/ s
-1
0
0.5
1
1.5
2
2.5
Figu e 8: In luence o supe icial gas eloci y and
P concen a ion on he olume ic mass ans e
coe icien . ({) Ug = 0.0014 m·s-1; (z) Ug = 0.0023
m·s-1; () Ug = 0.0031 m·s-1.
Taking in o accoun ha he olume ic mass
ans e coe icien and he gas-liquid in e acial a ea
we e de e mined in he p esen wo k unde di e en
ope a ional condi ions, he mass ans e coe icien
could be calcula ed as he quo ien be ween he
olume ic mass ans e coe icien and he speci ic
in e acial a ea. Le us hen analyse he e ec o
expe imen al a iables ( ype o solu e and concen a-
ion, and supe icial gas eloci y) on mass ans e ,
emo ing he in luence caused by he in e acial
a ea. Figu e 9 shows an example o he calcula ed
esul s o he mass ans e coe icien . These esul s
indica e once again a di e ence be ween he be-
ha iou o aqueous solu ions o P in ela ion o ha
o MP and EP aqueous solu ions. In all cases, a
simila beha iou , p e iously commen ed o he
olume ic coe icien , is obse ed: a dec ease in he
mass ans e coe icien o all sys ems when he
solu e concen a ion inc eases, bu wi h a highe de-
c ease in his coe icien a low P concen a ion. Fo
his sys em (aqueous solu ions o P), a cons an alue
o he mass ans e coe icien is eached; howe e ,
o aqueous solu ions o MP and EP, a con inuous
dec ease is obse ed in all he composi ion ange.
The same beha iou was obse ed o he o he gas
low- a es employed in he p esen wo k (see Figu e
10). A low amide concen a ion, P aqueous solu-
ions ake alues o he mass ans e coe icien
lowe han o MP and EP solu ions. This ac is due
o a be e bubbling dis ibu ion in hese las sys ems
because i p oduces a be e u bulence in he liquid
phase, inc easing he mass ans e a e.
C / mol·L
-1
0 0.2 0.4 0.6
k
L
· 10
-2
/ cm· s
-1
0
1
2
3
4
Figu e 9: In luence o alkyl-py olidone ype and
concen a ion on he mass ans e coe icien . Ug =
0.0014 m·s-1. ({) P; (z) MP; () EP.
C
p
/ mol·L
-1
00.20.40.6
k
L
· 10
-2
/ cm· s
-1
0
1
2
3
4
Figu e 10: In luence o alkyl-py olidone ype and
concen a ion on he mass ans e coe icien . Ug =
0.0031 m·s-1. ({) P; (z) MP; () EP.
In ela ion o he ac ha he p esence o his
kind o subs ance p oduces a dec ease in he alue o
he mass ans e coe icien , his beha iou is
p oduced due o he end o his kind o solu e o
Hyd odynamic and Abso p ion S udies o Ca bon Dioxide Abso p ion in Aqueous Amide Solu ions Using a Bubble Column Con ac o 807
B azilian Jou nal o Chemical Enginee ing Vol. 30, No. 04, pp. 801 - 809, Oc obe - Decembe , 2013
accumula e molecules a he gas-liquid in e ace,
as can be obse ed in he su ace ension alues
(Ga cía-Abuín e al., 2008). The p esence o mole-
cules in he gas-liquid in e ace gene ally causes a
dec ease in he mass ans e a e due o an inc ease
in anspo esis ance because he gas di usi i y
nea o he in e ace is educed (Jamnongwong e al.
2010). The accumula ion o a compound a a gas-
liquid in e ace can be analysed on he basis o
adso p ion iso he ms (Sa deing e al., 2006). P e i-
ous s udies ha analysed his kind o sys em in gas-
liquid abso p ion ha e employed he Langmui
iso he m o e alua e he accumula ion o molecules
a he gas-liquid in e ace (Sa deing e al., 2006).
Figu e 11: Su ace co e age a io o P aqueous
solu ions. Full ci cles show he co e age o he gas-
liquid su ace a he composi ions employed in
p esen wo k.
The accumula ion o P molecules a he in e ace
is shown in Figu e 10, ha indica es he deg ee o
accumula ion on he basis o he Se pa ame e (su -
ace co e age a io), whe e Se = 1 indica es he maxi-
mum accumula ion and Se = 0 indica es a ee gas-
liquid su ace (Heb a d e al. 2009). The solu e con-
cen a ions employed in he p esen wo k p oduce
accumula ion deg ees nea o sa u a ion (see Figu e
11) and hence an impo an numbe o molecules a e
loca ed a he gas-liquid in e ace. The p ocedu e o
accumula ion a he gas-liquid in e ace commonly
p oduces a educ ion in he alue o he mass ans e
coe icien (Vasconcelos e al., 2003; Heb a d e al.,
2009; Gómez-Díaz e al., 2009b). Di e en s udies
ha use su ac an s (compounds ha end o accumu-
la e a he in e ace), ha e concluded ha he accu-
mula ion o molecules a he gas-liquid in e ace also
educe he liquid enewal a he in e ace, and hen
p oduces a dec ease in he mass ans e a e. A he
same ime, o he sys ems employed in his wo k
(aqueous solu ions o alkyl-py olidones), he inc ease
in he solu e concen a ion nea he in e ace p oduces
an inc ease in he iscosi y alue (Geo ge and Sas y,
2004; Blanco e al., 2010). An inc ease in iscosi y
p oduces a dec ease in he gas di usi i y in he
liquid phase, and his e ec causes a dec ease in he
mass ans e a e. Thus, he accumula ion o hese
subs ances a he gas-liquid in e ace is esponsible
o he educ ion in he alue o he mass ans e
coe icien because i inc eases he esis ance o mass
ans e .
Gi en he di e ence in he beha iou o aqueous
solu ions o MP and EP compa ed wi h he end
ob ained o aqueous solu ions o P, i is necessa y o
ake in o accoun he p e ious discussion abou he
bubble size; mo e speci ically, he in luence o com-
posi ion on he bubble diame e . A di e en in lu-
ence o solu e concen a ion on he bubbles diame e
o aqueous solu ions o MP and EP in compa ison
wi h solu ions o P was obse ed in he p e ious
sec ion. This is due o he ac ha he i s wo
p oduce a dec ease in he bubble diame e when he
MP o EP concen a ion inc eases in he liquid phase,
while a lack o in luence o P concen a ion on he
bubble size was obse ed. Taking in o accoun his
beha iou and he p e ious s udies (Sa deing e al.
2006; Calde nak and Moo-Young, 1961; Higbie,
1935) ha ha e concluded a clea in luence o he
bubble size on he mass ans e a e (small bubbles -
igid bubbles- show a lowe mass ans e a e han
la ge bubbles -mobile ones-), he ends shown in
Figu es 9 and 10 can be explained. When he MP
and EP concen a ion inc eases in he liquid phase, a
dec ease in he bubble size is p oduced and i causes
a dec ease in he mass ans e a e and, he e o e, o
he mass ans e coe icien (caused by he accumu-
la ion o molecules and o he bubble size dec ease).
On he o he hand, o aqueous P solu ions, he bub-
ble diame e emains p ac ically cons an and he
mass ans e coe icien eaches a cons an alue
a e he i s dec ease (a low concen a ions) caused
by he accumula ion o P molecules a he gas-liquid
in e ace, which p oduces a dec ease in gas di usi i y.
An inc ease in P concen a ion abo e 0.1 mol·L-1
does no p oduce a dec ease in he mass ans e
coe icien because he su ace co e age does no
inc ease signi ican ly. In he same way as p e iously
commen ed o he gas-liquid in e acial a ea, aque-
ous EP solu ions show a simila beha iou o
aqueous MP solu ions. Fo his eason EP can be a
sui able subs i u e in abso p ion p ocesses o gas
808 A. Blanco, A. Ga cía-Abuín, D. Gómez-Díaz and J. M. Na aza
B azilian Jou nal o Chemical Enginee ing
pu i ica ion ha use MP, aking in o accoun he ac
ha EP shows lowe isk cha ac e is ics han MP.
CONCLUSIONS
The use o py olidones in aqueous solu ion in
abso p ion p oduces impo an changes in he gas-
liquid in e acial a ea in he majo i y o cases caused
by he in luence o his kind o subs ance on bubble
size. Mo e speci ically, he use o MP and EP in
aqueous solu ions p oduces an impo an dec ease in
he bubble diame e , p oducing an enhancemen o
in e acial a ea be ween he gas and liquid phases.
On he o he hand, P does no p oduce his kind o
change because he dec ease caused by py olidones
in su ace ension is lowe o P. Also, he p esence
o P p oduces a highe inc ease in he liquid phase
iscosi y han MP and EP.
In ela ion o mass ans e , he p esence o all
amides used in he p esen wo k p oduces a dec ease
in he mass ans e coe icien wi h a la ge e ec
caused by P. The dec ease in he mass ans e
coe icien is due o he end o hese subs ances o
accumula e a he gas-liquid in e ace, inc easing he
iscosi y nea o he in e ace, which p oduces an
inc ease in he esis ance o mass ans e . This e ec
is highe o aqueous solu ions o P due o he
impo an e ec o his solu e on iscosi y.
On he basis o he p esen esul s, EP is a
sui able subs i u e o MP in sepa a ion p ocesses
since aqueous solu ions o EP show a simila abso p-
ion a e bu do no ha e he haza dous cha ac e is-
ics o aqueous MP solu ions.
Though he p esence o MP in he p esen s udy
p oduces a dec ease in he mass ans e a e, i is
used as an indus ial scale p ocess o gas pu i ica-
ion. The bubble column used in he p esen wo k, as
well as he concen a ion ange, p oduced a dec ease
in he alue o he mass ans e coe icien in
compa ison wi h pu e wa e . O e all, he expe imen-
al esul s show a simila beha iou o MP and EP
aqueous solu ions and o his eason EP is a sui able
subs i u e o MP.
ACKNOWLEDGEMENT
The au ho s hank he Conselle ía de Economía e
Indus ia o Galicia egional go e nmen (Xun a de
Galicia) o unding he esea ch h ough he
esea ch p ojec 10MDS265021PR. Diego Gómez-
Díaz g a e ully acknowledges he Minis e io de
Inno ación y Ciencia o Spain o he suppo unde
a “Ramón y Cajal” posi ion.
NOMENCLATURE
a speci ic in e acial a ea m2·m-3
C CO2 concen a ion mol·L-1
C* CO2 concen a ion a
equilib ium
mol·L-1
CP,CMP,
CEP
py olidone concen a ion mol·L-1
d equi alen sphe e diame e m
m
kL liquid mass ans e
coe icien
cm·s-1
kL·a olume ic liquid mass
ans e coe icien
s-1
Ug Supe icial gas eloci y L·h-1
Se su ace co e age a io (-)
ope a ion ime s
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