Indian Journal of Chemical Technology Vol. 6, May 1999, pp. 125-133

Low pressure equilibrium between H2S and alkanolamine revisited

M V Jagushte & V V Mahajani*

Department of Chemical Technology, University of Mumbai, Matunga, Mumbai 400019, Indi a

Received 4 September 1998; accepted 11 April 1999

A-bsorpti on of H2S in aqueous a1kanolamine solution is of considerable commercial importance. A simple method is presented to determine the equilibrium pressure having very low loading of H2S, with the help of 'sulfide' ion-selective e lectrode. By thi s method H2S-DEA and H2S-TEA VLE-data were obtained at different amine concentration and temperatures. A theoretical analysis of equilibrium between H2S and aqueous a1kanolamine solution has been reviewed. A semiempiri cal model with a correlation parameter, ~-factor, is introduced to predict the equilibrium between H2S and alkanolamines.

Absorption of H2S into aqueous alkanolamine solutions is of considerable industrial relevance particularly in natural gas, associated gas and biogas sweetening, Claus tail gas cleaning, refinery gas sweetening etc . Many times, process engineers are concerned wi th selective removal of H2S from the sour gas stream. Tertiary ami nes such as methyl diethanolamine (MDEA), and triethanolamine (TEA) are find ing popularity among gas processing engineers wh o would like to have selective removal of H2S.

The absorption of H2S in aqueous alkanolamine solution takes place with reversible chemical reaction.

... (I)

Due to reversible nature of the reaction there always ex ists finite equilibrium concentration of H2S. The H2S laden rich amine solution from the absorber is sent to regenerator or stripper where H2S is knocked off at higher tempe.ature, say 1 1O-12SoC and near atmospheric pressure. The regenerated solution is then returned back to the absorber. Thus absorber and regenerator are coupled together to remove H2S. The stripper overhead gas which is very rich in H2S is then processed suitably to convert it into elemental "Sul fur" . Purely, from economic consideration the amine solu tion has not been generated completely . Thus the degree of sulfidation defined as,

a = (moles of H2S)

(moles of amine)

*For correspondence

. .. (2)

a is finite and can be In the range 0.02 to 0.1 depending upon the local techno-economic considerations.

Due to reversible nature of the chemical reaction, the absorber is operated in counter current mode of operations. The driving f0rce , at the top of the column depends on the equilibrium pressure of H2S over regenerated amine solution. This is often called as back-pressure of H2S over the regenerated solution. The absorption of H2S is gas film controlled and at any point in an absorber, the rate is given by,

(3a)

I I I - - = --+-----KG a kG a (H )(kLa)(E)

. . . (3b)

Knowledge of both gas and liquid side mass transfer coefficients, namely. kG and kL and knowledge of effective interfacial area a is essential. The enhancement factor, E, can be computed based on theories of mass transfer with chemical reaction 1.2 .

From Eq. (3a), it is seen that at the top of the. absorber, partial pressure of H2S ( PH

2S) , in the bu lk

gas (sweetened gas) being very small , the driving

force (PH2S - P~2S ) depertds on the equilibrium partial

pressures of H2S, ( P~ 2S)' over the regenerated

solution . Thus the knowledge of P~2S becomes very

important to process design engineer because small

error in P~ 2S can make considerable error in driving

force, as ( PH2S) , itself will be very low.

126 INDIAN 1. CHEM. TECHNOL., MAY 1999

Experimental technique for measuring Vapour liquid equi librium data are such that accurate data is avai lab le in the middle range of loading and pressures.1· 5

• and very few equi librium' data are reported in the low loading region, encountered in commercial operations. A general method for obtaining VLE data at low loading is to sparge inert gas into an excess of known amine solution followed by analysis of the gas fo r H2S. However, this method had not provided the reliable VLE data at very low partial pressure of H2S. Recently , the increasing demand for sulfur free-fuel , the stricter air pollution control legi slation and the incentives for sulfur recovery have all resulted in removal pf H2S at very low level, which require the better experimental technique to understand the VLE'behaviour of H2S in the lean load ing region.

There are very few techniques reported in the literature, which measure VLE data at very low loading of H2S. Amongst , Rogers et al.6 has used FfIR spectroscopy to measure VLE data at low

. 7 partial pressure of H2S. Rochelle et al. have developed electrode method for the measurement of VLE using pH-silver sulfide electrode. These in vesti gators related partial pressure of H2S with e lectrode potential difference between the pH and sulfide e lectrode by the equation ,

I log H,S=Constant+ (E

H, - Es= )

- 0 .0296

But the va lue of constant in the above equation was calculated based on the assumption of Kent & Eisenberg model8 as stated by Rochelle et al.' Naturally, this might introduce some deviation in the measurement as in this model (Kent & Eisenberg), the values of equilibrium constants (K, & K2) were determined by forcing computational fit on the reported data available in the literature.

In the present paper, a simple method to determine

eq uiHbrium partial pressure of H2S, (P~ 2S) over

alkanolamine solution, having very low a values, with the he lp of 'su lfide' ion-selective electrode has been presented . This experimental technique will aid to generate the valuable equilibrium data at very low loading of H2S in aqueous alkanolamine solutions. A theoretical tulalysis of equilibrium between H2S and

alkanolamine solution has been reviewed and a simpler semi-empirical model is presented to aid the process design engineer.

TO CONDUCTIVITY ME1~R ,--+

H TIC)

5 1-11. - {)

U f-

3 ~ '-- 7

2 f-:.-:-:-1 '.

~h--~ . ,

, . . ~L. , .

' D-Lo M ' . \.. , ' ': , ..,' ..........

II////A I~ :~: 6"'1 1111117m

Fi g. ! - Expcrimenlal sel-up fo r Vapour Liquid Equi lihrium measurement

Experimental Procedure Materials-Diethanolamine (DEA), triethanolamine

(TEA) and sodium sulfide used were of analytical grade with 99.5% purity and obtained from S.D. Fine Chem. Ind ., Mumbai, (India). H2S gas was generated in Kipp' s apparatus. Sulfuric acid was used to -generate H2S from iron sulfide so that contamination due to HCI and water is avoided. Also sufficient quantity of gas is generated and purged out so that air contamination in H2S is eliminated.

Experimental set-up-The experimental set-up consisted of a gas bubbler with magnetic stirrer to enhance equilibri um process . The equilibrium cell is fitted with conductivity probe. The exi t of the cell is connected to a glass reservoir. The gas-circulating blower takes gas from reservoi r and passes into the equilibrium cell. The pressure maintained in this system is practically near atmosphere. The enti re assembly is placed into a constant temperature bath except gas circulating blower. Since temperatures are not widely different from ambient 300C, the heat loss from the blower to surrounding can safely be neglected. Fig.l shows a schematic experimental diagram for the entire set-up.

Experimental Proced'1re-A known quantity of alkanolamine solution was taken in an equilibrium cell . H2S gas was injected into reservoir to get desi red partial pressure. The gas-circulating blower was then started. Some H2S would get adsorbed into alkanolamine solution . To compensate this, additional quantity of H2S was injected so that the system is near atmospheric pressure. The approach to equilibrium is monitored with the he lp of a conductivity probe.

JA GUSHTE & MAHAJANI: LOW PRESSURE EQUILIBRIUM BETWEEN HzS ALKANOLAMfNE 127

Since the reaction of H2S with aqueous alkanolamine solution is ionic in nature, the concentration of ionic species remains constant after reaching equilibrium. The constant reading of conductivity probe over a few hours indicates that the equilibrium was achieved. At this stage, the gas composition was identica l in the cell as well as in the reservoir. The reservoir was then isolated from the system with the help of valves. A known quantity of caustic , which is far excess than required, is added to the reservoir with the help of liquid syringe. It was then well mixed by shaking and left for about 48 h so that entire amount of H2S gas is absorbed into aqueous NaOH solution. A sample was taken from amine solutioh with the help of a gas-tight

syringe and introduced into caustic solution to convert it into Na2S. With the he lp of sulfide ion-selective elec trode, both samples were analyzed for sulfide content and hence H2S content was back calculated both in the gas phase and in the liquid phase.

The sul fide ion selective e lectrode (ORION , USA make) was cali brated before the reading with the help of st .. ndard aqueous solutions of Na2S. It was ensured that all readings were obtained in linear behaviour of the electrode.

Results and Discussion During absorpti on of H2S in an aqueous solution of

alkanolamine fo llowing reactions take place and equilibria are establi shed,

Dissociation of HzS

· .. (4a)

· .. (4b)

also, we have

.. . (Sa)

... (5b)

Reaction of amine with H2S

· . . (6a)

K _ (AmH/ ) (HS- ) SAm - (H

2S) (AmH)

... (6b)

0 .6 -.---- ---------------,

as Il.

0.5

0 .4

.lo: 0.3

.= ::t

Il. 0 .2

0 .1

c:x::xx:o present work ~ Mather etai.[5]

o

0 .0 -rrrnrrT-rrT"T'T"T"T"rnrrT'T'T'"rT"T"T"T"T"T'T"T"T"rnrrT-rrrri

0.0 10.0 20.0 30.0 40 .0 at 2/ ( l-CI\ ) J( l()'

Fig. 2- Plot of a~ / ( I - a) versus PH2S of H2S-OEA (2M) system

at 313 K .

The reac ti on between amine and H2S IS

in stantaneous as compared to rate of diffusion.

Protonatiol1 n.famine

K" = (H+)(An: H)

(A mH 2 )

Dissociation of water

H20 ~ ~ H+ + OH-

Kw = (H+) (OH- )

Amine dissociation in water

(ArnH) + H2O OIl • (ArnH/) + OH-

K _ (AmH2 +) (OH- ) b- (AmH)

and then from Eqs (7b) & (8b),

K _ Kw b--

Ka

.. . (7a)

· .. (7b)

(8a)

(8b)

· .. (9a)

· .. (9b)

· .. (9c)

1-28 INDIAN 1. CHEM. TECHNOL., MAY 1999

. . . (10)

The solubility is assumed to be established instantaneously at gas-liquid interface.

Also there exist a possibility of reaction of H2S with air as given below due to the pres~nce of air ions in liquid phase (Eqs 8a & 9a)

Thus it is seen that during absorption of H2S in aqueous alkanolamine solutions, the entire absorption process can be attributed to . reaction of H2S with amine provided concentration of (OH- ) is sufficiently small so that the Eq. ( 11") can be practically ignored. Further, the dissociation of HS- to S= via Eqs (5a & 5b) be very small so that only reaction can be considered by Eqs (4a) and (4b) . The above aspects

have been dealt in details by da Silva and Danckwerts9

• For the sake of clarity it shall be reviewed here also.

For selective absorption of H2S the use of tertiary amine such as triethanolamine, (TEA), methyl­diethanolamine (MDEA) is recommended. Mahajani and Joshi 10 have reviewed the kinetics of reactions between CO2 and alkanolamines (primary, secondary and tertiary alkanolamine). MDEA is very popular tertiary. amine for H2S removal. However MDEA reacts with CO2 also. Authors recommended, the use of TEA for selective removal of H2S. The kinetic selectivity for H2S would be more in the case of TEA because CO2 reacts very slowly with TEA as compared to MDEA. Equilibrium with respect to all types of amines, namely, primary, secondary and tertiary shall be discussed. The experimental results would be compared with those published in case of diethanolamine system and data would be presented for triethanolamine system.

The condition underwhich, there will be negligible fo rmation of s= as compared to HS-

From Eq. (5b),

(s=) ( K 2S ) --=--(HS-) (H+)

.. , (1 2)

Also from Eq. (7b),

(H+)= ( Ka) (AmH/) (AmH)

· . . (13)

for the sake of argument, the reaction wherein S=· is formed is considered,

(14)

It is being assuming that all amine can form S=

where 0:. = sulfidation ratio

_ (mole of H2S)

(moles of amine)

Eq. ( 13), gives

(H+)= (K,) (20:. ) (AmH)o (1- 2a) (AmH)o

=3:0:. ( K,) (I - 20:.)

Therefore,

(1 5)

· . . (16)

· . . ( 17)

· .. (18)

However, in maJonty of cases fi rst dissociation IS

dominating as given in Eq. (4a)

(AmH) = (1 -0:. ) (AmH)o · . . (19)

(S=) (K2S)(I - 0:.) --=-=---(HS-) (Ka) 0:.

· .. (20)

From Eqs ( 18) and (20) one can see that the ratio of K2S I Ka is more important than sulfjdation ratio. By and large the loading of H2S in the absorber will not exceed 0.3, (i .e. 0:. = moles of H2S per moles of amine). Under such a situation the multiplier of K2S I Ka in Eq. ( \8) will be 0.67 and that from Eq (20) will be 2.33. In the regenerated solution (lean solution) loading , a , could be as low as 0.02 and therefore the multiplier of K2S I Ka could be 24 in Eqs ( 18) and 49 in Eq (20). Thus a condition can arise where,

JAG USHTE & MAHAJANI : LOW PRESSURE EQUILIBRJUM BETWEEN H2S ALKANOLAMrNE 129

Table \-Various equilibria as a function of temperature

I . MEA (monoethanolamine) pK, = 3.791 exp (276.567 / 1) ,

2. DEA (diethanolamine) pK, = 18.082 - 561 .2 - 0.024 T ,

3. TEA ( tri ethanolamine) pK, = 2.524 + 1563 / T ,

4. MDEA (methyldiethanolamine) pK, = 2.56 + 1809.056/ T ,

5. First dissociation constant for H2S in water pK ls = - 106.67 + 6045 .2 / T + 37.744 log T,

6. Second di ssociation constant for H2S in water pK2S= 4.7 + 2739 / T ,

7. Solubility of H2S in water

10g HH S = 65 1.2 / T - 8.206, 2

8. Di ssociation constant of water In (Kw) = -13445 .9 / T - 22.4773 In T + 140.932 ,

K Table 2-Values of 2S for different alkanolami nes at 303 . 3 13

and 323 K

Amine

MEA

DEA

MDEA

TEA

Ka

Temperature, (K )

303

3 13

323

303

3 13

323

303

3 13

323

303

3 13

323

(for K2S and K, refer to Table I)

(s=) = (50)* (K2S ) «50x I0-4 (HS ) ( Ka)

(K 2S) --xI06

( Ka)

50.587

52.7 12

55 .63 1

10.143

12.797

15.366

6. 177

7.744

9.570

0.876

1.166

1.524

. .. (2 Ia)

. .. (2 Ib)

so that contribution of S= can be neglected without sacrificing engineering accuracy.

Reference

Ka == (kmol. m-3 )

[Perrin 12]

Ka == (kmol. m-3)

[Perrin 12]

Ka == (kmol. m-3)

[Perrin 12]

Ka == (kmol. m-3)

[Little 13 j

KJ S == (kmol. m-3 )

'[Bosch l4]

K2S == (kmol. m-3)

[Bosch l4]

H H S == (kmol. m-3 Pa- I)

[Bosch l4] 2

Kw= (gmoI.Kg- 1)2 [Edward 15]

Various equilibria used to illustrate above condititms as well as in formulating the model at later stage, have been presented in Table I . Table 2 presents such computations of K2S / Ka for ' monoethanolamine (MEA) (primary alkanolamine); diethanolamine (DEA) (secondary alkanolamine); trie thanolamine (TEA) (tertiary alkanolamine) and methyl diethanolamine (MDEA) (tertiary alkanolamine) at three different temperatures . Thus it is seen that, the above inequality (2Ib) is easily sati sfi ed and hence formation of S= can be neglected without sacri ficing engineering accuracy.

The condition under which there will be no significant reaction between OH - and H2S

While formul ating a mathematical model fo r va pour-liquid equilibrium. It is essential that one has to consider reacti on between H2S (solute gas) and OW as given by Eq ( II ). However, if there are in significant quantity of hydroxyl ions (OW) as compared to free alkanolamine (AmH) present in soluti on, then the reaction between H2S and OH- can be safe ly neglec ted without sacrific ing engineering accuracy.

Therefore, if (OW ) / (Am H) < 10- 2 contribution due to (OH-) can be neglected . Thus,

.. , (22)

130 INDIAN J. CHEM. TECHNOL., MAY 1999

(K w) < (AmH)xlO-4 (Ka)

... (23)

For MEA, DEA, TEA and MDEA, Table 3 exhibits this ratio .

It is thus seen that between temperature 303 to 323 K the lowest value of Kw I Ka is 0.686 X 10-6 in the case of TEA. Therefore under real operating conditions where concentration of free amine could be more than 0.1 M , it is seen that inequality of Eq. (23) is easily satisfied. At the top of the countercurrently operated absorber free amine concentration being higher, say > 2 M, in case of MEA, also this inequality holds true. As absorbent goes down the column, free amine concentration goes down and in case of MEA, the inequality may not hold true at the bottom part of the absorber. However at the bottom portion of the absorber, the effect of equilibrium partial pressure of H2S in the gas phase is not

K Table 3-- Yalues of ~of different alkanolamines at 303, 313

Amine

MEA

DEA

MDEA

TEA

Ka and 323 K

( :: ) x IO'(k~lIm') Temperature, K

303 313

39.583 37.500

7.934 9.107

4.834 5.509

0.686 0.830

323

43.830

12.106

7.540

1.201

worrying. As seen from Table 3, as temperature increases, Kw 1Ka also increases. Nonetheless, under real operating conditions it is seen that inequality of Eq. (23) is easily satisfied.

From the forgoing discussions, it is seen that there will be negligible formation of S= and under normal conditions, the contribution of OR- to absorption of H2S could be neglected.

H2S - aqueous alkanolamine equilibrium With the help of above assumption, H2S­

alkanol amine equilibrium can now be presented Eq. (6b) gives,

K _ (AmH/) (HS- ) SAm - (H

2S) (AmH)

and Eq. (4b), gives,

Therefore,

(H2S) = (H+) (HS- )

(KHS )

Eq. (7b), gives

(H+) = (Ka) (AmH/) (AmH)

... (24)

.. . (25)

Table 4-H2S-aqueous alkanolamine equilibrium data

System Partial Pressure of H2S (KPa) Sulfidation Ratio (a) Partial Pressure of H2S (Kpa) Sulfidation Ratio (a)

Temperature = 313 K Temperature = 323 K

0.04 0.045 0.03 0.020

0.22 0.089 0.08 0.043

0.24 Q.loo 0.12 0.093

0.40 0.148 0.24 0.125

0.50 0.169 0.33 0.147

Concentration = 2 M Concentration = 4 M

0.09 0.009 0.30 0.018

0.59 0.049 0.54 0.036

'"1.88 0.058 1.10 0.050

1.04 0.060 4.33 0.072

1.55 0.071 6.32 0.085

J>,

JAGUSHTE & MAHAJANI: LOW PRESSURE EQUILIBRIUM BETWEEN H2S ALKANOLAMINE 131

Table 5-Variation of ~-factor with respect to temperature and amine concentration for H2S- DEA and H2S-TEA systems

Amine Concentration Temperature ~-factor kmol / m3 K

DEA 2 313 0.316

DEA 2 323 0.167

TEA 2 313 0.500

TEA 4 313 0.704

0.40....-------------------,

0.30

~

CIS c.. ~0.20

C

0.10

0.00 0 .0 5.0 10.0 15.0 20 .0 25.0 30.0

';/(1-0:.) x 10'

Fig. 3-Plot of a2 / ( I -a) versus PH ZS of H2S-DEA (2M) system

at 323 K.

Substituting the above value of (H+) in Eq. (22)

(HzS) = (Ka) (AmH/) (HS- ) (Kls ) (AmH)

relation obtained is,

a= (moles of HzS)

(moles of amine)

... (26)

If (AmH)o is the original concentration of amine, then Eqs (6a) & (26) gives,

(HzS) = (Ka) ~ (AmH)o (Kls ) (I-a)

.. . (27)

Concentration of (HzS) is also correlated with

2.0....------------------,

III c.. ,.\II 1.0

.S ::t

c..

0 .5

o

o. 0 *,"TTT"rTTTTTT1"TTT"rrrrTTnrrTTTTT1"TTT"rTTTTTT1rrTTTTT1"TTT"rTTT~ 0.0 1.0 2.0 3.0 4.0 5.0 8.0

c<2/(1-0'.) x 10'

Fig. 4-Plot of a2 / ( I -a) versus PH S of H2S-TEA (2M) system

2

at 3 13 K.

pressure through Eq . ( 10). Thus equilibrium pressure of H2S over amine solution is given by

. . . (28)

If a graph of PH2S against aZ

/ ( I-a) is plotted, for

the given concentration of amine (AmH)o, it would be straight line through the origin. Using the equilibrium data tabulated in Table. 4, Fig. 2 to Fig. 5 exhibit such plots for H2S-DEA and H2S-TEA system at different

conditions. For H2S-DEA system, the comparison with dat" publi shed by Mather et al. 11 is presented in Fig. 2. The data fit in the model quite well .

At any given time in an absorber there exists many ionic species as given by Eqs (1 )-( 11) and therefore the adsorbent becomes a non-ideal solution .

Atwood et al .4 have shown that even for ionic ,s trength of 0 .075, the mean activity coefficient for MEA, DEA and TEA reduces to approximately 0.75 from unity . In order to account for non-ideality , the factor ~ has been introduced which takes into account deviation of the system parameters from ideal situation . Thus,

... (29)

132 INDIAN 1. CHEM. TECHNOL., MAY 1999

'T 6 . 0 .

.

.; Q..

2.0

0 . 0~~~rnnn"~nnnn"TTrrrnno~,,rrnnrl 0 . 0 2.0 4 . 0 6. 0

c:J.2j( 1-0() J: 10" B.0

Fi g. 5- Plot of a ' / ( I - a ) versus PH2S of H1S-TEA (4M) system

at 3 13 K.

This fac t o r-~ can be function of original amine concentration and degree of sulfidation and

te mpe rature. Thus values of Ka , Kts H H,S reported

at infinite diluti on can be considered and then correction may be introduced through factor-~ .

Vapour liqui d equilibrium data of H2S-DEA and H2S-TEA system have been correlated with the help of Eqs (2R) and (29). Table 5 shows ~-factor for typical sys tem involving aqueous solu tions of DEA, and TEA-systems. It can be seen that for DEA­

system, the va ri ation in the va lue of ~-factor was more (nearl y one hal f) for change in temperature of 10K as compared to TEA-sys te m, where the amine concentrati on was varied from 2M to 4M. It may imply that the temperature rather than amine . concen trati on has the pronounced effect on the

parameters wh ich govern the ~-fac tor.

Conclusion An experimental tec hnique has been developed for

the measurement of vapour-liquid equilibrium between H2S and aqueous a lkanolamine solution using ion-selective electrode at low partial pressure of H2S. Usi ng this technique, VLE-data for DEA-H2S and TEA-l-hS systems were measured by varying the te mpe rature and amine concentrat ion. By considering a ll the equilibria in the system, a sem iempirical model is presented . A correlation parameter, ~ -fac tor,

is introduced to predict the equilibrium between H2S and alkanolamine.

Acknowledgement

One of the authors (MV J) wishes to thank the G P Kane Trust for awarding research fellowship to enable this investigation.

Nomenclature

(A mH)

(A mH)"

K 2S

Ka · ( pKa)

~h ' (pKh)

KG

= concentration of amine, (kmol.m-3 )

= o ri ginal concentration of amine, (kmol.m-3 )

= interfacial area, (m1.m-3)

= enhancement Factor = so lubility of H2S, (kmol. m-·1.Pa- l

)

= equil ibrium constant for dIssociation of H2S in Eq. 4a, (kmol.m-3 )

= equilibrium constant in Eq. (5b), (kmol.m-3 )

= equilibri um constant in E . (7b) , (kmol.m-.l )

=equilibrium constant in Eq. (9b) , (kmol.m-3 )

= overall mass transfer coefficient , (kmol.m-2 .Pa- I. s- I )

= gas side mass transfer coefficient, (kmol m-2.Pa- l .s-1 )

= liquid side mass trans fer coefficient, ( m.s- I ) = equilibrium constant fo r reaction of amine

wi th H"S in Eq. (6b), (kmol.m-3)

= equi li brium constant in Eq. (8b) in Table I, (gmoI.Kg- 1 )2

= parti al pressure of H2S in !he bulk o f gas phase. (Pa)

=predi cted equilibrium parti al pressure of H2S in the bul k of gas phase, (Pa)

=eq ui librium parti al pressu re of H2S. (pa)

R., =rate of absorpt ion, (kmol.rn-3 . sec- I) a =suilldation ratio, Eq . (2) f3 =correctioll factor. Eq. (29) All {,K ' s are defIned in Ta ble I.

References

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2 Danek werts P V, Gas-Liquid Reactions (McGraw Hil l Book Co) 1970.

3 Lcibush A G & Shneerson A L, } Appl Chem (U 5 5 R ), 23 ( 1950) 149.

4 At wood M R, Arnold R C & Kindrick. Ind Eng eire"" 49 (1957) 1439.

5 Muhlbauer H G & Monaghan P R, Oil Gas J, 55 ( 1957) 139. 6 Rogers E A, A I eh E J, 43 ( 1997) 3223. 7 Rochelle G T , Tseng P C , Ho W S & Savage D W, Ind Eng

e ire", Res, 27 ( 1988) 195 .

''1'

JAGUSHTE & MAHAJANI: LOW PRESSURE EQUILlBRlUM BETWEEN H,S ALKANOLAMINE 133

8 Kent R L & Eisenberg B, Hydrocarbon Processing, 55 (1976) 87.

9 da Silva T A & Danckwerts P V, I Chem Eng Symposium Ser, 28 (1968) 48.

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1 I Mather . A E, Otto F D & La! D, Can 1 Chem Eng, 63 (1968)

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13 Little R J, Bos M & Knoop G J, 1 Chem Eng Data, 35 (1990), 276.

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15 Edwards T J. Maurer G J, Newman J & P,ausnitz M, A I Ch E 1, 24 (1978) 966.