......

THE EFFECT OF H2 S ON SURFACE PROPERTIES IN OIL-WATER SYSTEMS

by

G.G. Strathdee* and R.M. Given

A B S T R ACT

Hydrogen sulfide is a surface-active gas which readily adsorbs

at gaS-\vater or oil-wa·ter interfaces and lmlers surface or interfacial

tensions. Our surface property and phase composition measurements have

been employed to calculate spreading coefficients for pure- and surfactant­

modified-oils in the aqueous system. These results have been used to

evaluate the influence of H2 S on the performance of antifoam agents in

aqueous systems. The implications of this work for the Girdler-Sulfide

heavy water enrichment process are discusse4.

• 'r

Presented at the 27th Canadian Chemical Engineering Conference

Calgary, Alberta October 27, 1977

*Atomic Energy of Canada Limited Whiteshell Nuclear Research Establishment

Pinawa, Hanitoba, ROE lLO

- 1 ­

1 . INTRODUCT ION

Canada is the leading producer of heavy water in the world and

has adopted the Girdler-Sulfide (GS) heavy water process. It is based on

two important chemical factors (1) the rate of chemical exchange of deuter­

ium between H2S and H20 is extremely rapid in the aqueous phase, and (2)

the equilibrium constant for distribution of deuterium between gaseous H2S

and liquid water varies significantly with temperature (1) • To produce heavy

water on a commercial scale, large counter-current si~ve-tray gas-liquid

contactors are necessary, as shown in the photograph (Figure 1) of the Glace Bay

Heavy Water Plant that is owned and operated by AECL.

The interest of AECL in the effects of H2S on surface properties of

materials followed directly from our need to understand fully the chemistry

within these plants. The chemistry of H2S was of particular importance.

Specifically, severe operational problems which occurred several years ago,

and which were correlated to foaming transien~s within the H2S-H20 cold con­~~ ,

tactors, made it essential to establish if that two-component system was intrinsi­• ~ ( 3)

cally foamy. This paper describes some of our research on that topic 2, .

The objectives were (1) to determine the effect of H2S on the

equilibrium surface properties of multicomponent and multiphase systems, and

(2) to apply that new information to develop improved antifoam agents for the

GS process. The stud ies \l7hich are described below were complementary to the

work of N.H. Sagert on the dynamics of thin aqueous liquid-film stability in

pressurized H S(4,5).2

This paper is structured as follows. First, our published research

on the general effects of H2S on the surface tension (or surface free energy) of

water and aqueous solutions of surfactants will be reviewed. Second, the trends

in surface and interfacial tensions in the H2S-dodecane-water system will be

considered. Finally, the effects of H2S on the properties of aqueous and oil

solutions of commercial non-ionic surfactants of the type used to formulate antifoam

- 2 ­

fluids will be described. Since this report summarizes a considerable amount

of work, the experimental data will not be examined in detail. Instead, the

emphasis will be upon the important principles that underline each class of

experiment.

2. EXPERIMENTAL

We employed the pendant drop method for all surface and interfacial

tension measurements at elevated pressures and temperatures because it was

simple and contamination of freshly-formed surfaces was minimized (2) • A schematic

diagram of the equipment and the important principles of the techniques are

summarized in Figure 2. The profile dimensions of pendant H2S-saturated water or

oil droplets suspended in a second gas or liquid phase within the optical cell

were obtained from photographs of the static droplets taken at chemical equilibrium.

The droplets were produced with a syringe pump and valve system. Droplets equili­

brated rapidly in the gas phase but more slowly in interfacial tension experiments

" with two liquid phases, particularly if other surfactants were present with H2S,

The precision of the pendant drop-method was better than 0.1 percent (± 0.1 mN/m).

The materials purities were as follows. Water was triply distilled.

H2 S was CP grade or better. Dodecane was research grade and was percolated through

silica and stored under nitrogen prior to use. The normal alcohols were freshly

distilled. Commercial surfactants were used as received.

3. RESULTS AND DISCUSSION

The experimental data for the surface tension (0) of H2S-saturated

water between 25 and 130°C and at total pressures up to 3.3 MPa are shown in Figure

3. These results show that at each temperature, the surface tension of an aqueous

H2 S solution decreases linearly with pressure, at least up to one half the saturation

3.1

- 3 ­

vapour pressure of H2S. Some curvature is evident above 2.0 MPa at the

lower temperatures.

The free energies of adsorption at the H2S gas-aqueous interface

at the zero-pressure limit were calculated from the slopes of the linear portions

of the curves shown in Figure 3 and the Henry's Law constants for H2S in water (7) ,

using equation 1*:

° ° t\G 2 - RT In (m2/11 ) [1]

RT In fd<oo-a) ~ . dP • da2 11 ° _

The thermodynamics of H2S adsorption have been reported and discussed elsewhere(2).

For the present purpose it will be valuable to consider the physical state of the

aqueous interface.

From a plot of our H2S-H20 surface tension data against the logarithm

of the dissolved H2S activity, the surface excess of H2S was calculated using the

Gibbs adsorption isotherm and the Gibbs convention (2) . Some adsorption isotherms

are shown in Figure 4. Our data suggest tQat at conditions characteristic of GS

process cold tower contactors (2. L MPa and 30°C), the aqueous interface has

adsorbed upon it about 3 monolayers of H2S.

This conclusion led· us to expect that the behaviour of other surfact­

ants co-adsorbed under the same conditions would be considerably modified com­

pared to the case with no H2 S present. The following section considers the effect

of H2S on the adsorption of three normal alcohols at the aqueous interface. These

surfactants were selected for study because their adsorption at aqueous interfaces

has been studied in detail(8,9).

* See list of symbols, section 7.

- 4 ­

3.2 H2 S - NO&'1AL ALCOHOL -fuO

The surface tensions of H2S - n alcohol - H20 solution at 30°C

are shown in FigureS as a function of H2S pressure. At zero H2S pressure,

the progressive depression of the surface tension of water by the dilute

n-alcohols is evident. As the H2S pressure was increased, 0 decreased, although

the limiting slope do/dP was dependent upon the aqueous n-alcohol concentration.

From this information we can calculate that at its zero-pressure limit, the free

energy of adsorption of H2S varies with the surface coverage of water by other

surfactants. This phenomenon is illustrated in Figure 6 as a plot of the free

energy of adsorption of H2S against ~-alcohol surface coverage.

Similarly, if the ~-propyl-. ~-butyl, or ~-pentyl alcohol is adsorbed

at the gas-liquid interface of aqueous H2S, the free energy of adsorption is

found to increase to more positive values as a function of increased surface cover­

age by H2S. This result is shown in Figure 7.

. hWe conc1ude f rom t hese experlments (3) t hat when ot er surf actants are

co-adsorbed with H2S at the aqueous interfa~e, each surfactant is less adsorbed

than it would be in the absence of the oth~~. In other words, one surfactant

attempts to displace the other from the surface region. Qualitatively, this a

highly important conclusion, since in principle the behaviour of surface active

materials for use in H2S service will differ to some extent from that found in

the presence of a less surface-active gas such as air.

3.3 B2S - DODECANE - H20 SYSTEM. OIL PHASE COMPOSITION, SURFACE TENSION, AND INTERFACIAL TENSION AGAINST H2S - SATURATED WATER AT 30°C

This three-component system was selected for study, because dodecane

was representative of oil contaminants found within the GS process. Hydrocarbon

oils may enter the process from oil-seals or as components in antifoam additives.

- 5 ­

The data are summarized in Figure 8. In panel A, the pressure

of HZS is shown to increase almost linearly with HzS mole fraction in dodecane.

The dodecane would contain about 90 mole percent H2S at GS process cold tower

conditions of 2.1 MPa and 30°C.

The change of surface tension of the dodecane phase with mole

fraction (XH2 S) is illustrated in panel C. The smooth change in 01 with XH2S

suggests that there was no significant adsorption of H2S at the gas-oil liquid

interface. This is in marked contrast to the behaviour of H2S in water under

comparable conditions. Note that liquid H2 S has an exceedingly low surface

tension at 30°C, 10.5 mN/m. This suggests that there is a lack of a strong

intermolecular hydrogen bond between H2S molecules and that cohesion is due

mainly to weak dipolar and dispersion forces. Because H2S is so highly soluble

in dodecane, the oil phase also has a much lower surface tension than a typical

hydrocarbon at GS process conditions. On the mole fraction scale, we are essen­

tially dealing with a dilute solution of dodecane in liquid H2 S.

In panel B, the dependence of the dodecane-H20 liquid-liquid inter­

facial tension on the mole fraction of H2S in the oil is shown. As with

the oil phase surface tension, 01. there a slight positive deviation of 012

from ideal behaviour. We have been~unable to determine if the non-ideality

originates in the bulk phase or is localized within the surface region. The

magnitude of the decrease in 012 between 0 and 2.2 MPa at 30°C is somewhat less

than the depression of the surface tension of water by , and about twice the

decrease in 01'

Interfacial tension may be calculated from the separate surface

tensions of the H2S-saturated oil and aqueous phases because our data suggest

that the ~-ratio of Good and Elbing(lO) is constant up to 2.0 MPa H2S:

0.527 + 0.005 [2]

This expression has previously been found valuable for calculations of the inter­

facial tension between two pure, immiscible liquids. The magnitude of ~ has been

evaluated theoretically by considering the basic intermolecular interactions in

solution, but the treatment has not been extended to include. three-component systems

- 6 ­

of the present type where one component is highly surface active in one of the

two liquid phases. Although we cannot offer a quantitative explanation for

the applicability of equation 2 to the H2S-dodecane-water system, it is extremely

valuable to be able to estimate 012 in terms of 01 and 02' Experimental measure­

ments of 012 are difficult.

3.4 SURFACE AND INTERFACIAL TENSIONS FOR THE H2S-DODECANE-n BUTAl~OL­

H20 SYSTEM

This four-component system is not as complex as one might initially

expect, since the' principles which were described above for two- and three­

component precursors also may be transferred to this two-liquid phase mixture.

T:1e initial aqueous phase contained 7.32 g g-butanol per kg of water.

This lowered 02 from 71.5 for pure water to 54.5 mN/m (-17 mN/m). The bulk

aqueous phase was approximately ideal and only slightly affected by this solute.

Figure 9 illustrates the effect of H2S pressure on the surface tension i'

of the aqueous (02), oil (01) and, aqueoud-oil interfaces (012) with and without

the surfactant n-butanol present. we observed in the three-component system,

g-butanol depressed the surface tension of water and reduced the slope of 02 ­

against P. The surfactant had little effect on 01' but altered 012 in a manner

similar to 02"

Substitution of our experimental data for 01. 02 and 012 into equation

2 yielded values of 11 which decreased from 0.609 at zero H2S pressure to 0.520 at

2.0 }1Pa. Because 11 varied through this range of pressure, 012 could not be

calculated from 01 and 02 using a single value of~. That is, a simple additivity

rule did not hold. This is the usual finding for systems containing at least

one highly adsorbed component.

3.4

- 7 ­

The effects of H2S on surface and interfacial properties in other

oil-water systems should be similar to those results reported here. Firstly,

our correlation for the H2S-H20 phase will be directly transferable to other

cases. Secondly, the surface and interfacial tensions of the pure oils will

vary incrementally with the molecular weight, but the decrease upon saturation

with H2S should remain about the same. Since both 01 and 012 exhibit only

slight positive deviations from ideal mixing, an estimate of values for other

systems may be obtained graphically, assuming an ideal mixing rule to hold.

The error associated with those approximations would be 2-3 ruN/m for each

variable.

SPREADING COEFFICIENTS

One of the objectives of this work was to understand the behaviour

and improve the formulation of antifoam additives for the GS process. In this

section the effect of H2S on spreading coefficients, calculated from data reported

above for the dodecane-H20 system and additional data for the polydimethylsiloxane .~

(PDMS)-water system is considered. ..

The spreading coefficients given by the expressions

51 01 - 02 - 012

are useful measures of potential antifoam effectiveness. Experience has shown

that for an antifoam formulation to function well, the fluid should spontaneously

disperse in, and spread upon, the foamy substrate. The spreading coefficients

give a quantitative measure of the free energy change associated with these proces­

ses. If 51 is positive, then the oil-pIus-surfactant mixture will spontaneously

emulsify in the aqueous phase to yield a thermodynamically stable, highly dis­

persed oil-in-water (O/W) microemulsion. If 52 is positive. the antifoam fluid

(the oil phase 1) will spontaneously spread on the surface of the aqueous sub­

strate with which there may be a foaming problem. It is one objective of antifoam

suppliers to modify their products with surfactants to cause both 51 and 52 to be

positive. Two empirically determined criteria may thus be satisfied: (1) that the

- 8 ­

antifoam fluid must readily disperse in water and (2) that the antifoam must

spread on the foamy substrate to promote bubble breaking.

Data for the dodecane-water system are presented in Figure 10 and

those for the PDM8-water system in Fig~re 11. In the former case, 81 increased

with HzS pressure with and without ~-butanol present, but always remained

negative. Oil-phase droplets would therefore not be stabilized in the aqueous

phase by surface forces alone. In addition, 8Z was found to be negative under

all conditions, therefore no spontaneous spreading of the oil phase would occur

upon the aqueous phase.

Data for the H28-PDM8-HzO system were more limited for experimental

reasons. The density of the PDM8 was close to that of water so that little

gravitational distortion of oil-phase pendant droplets in water was obtained.

Interfacial tensions were exceedingly difficult to measure llnder those conditions.

Nevertheless, an interesting transition in spreadability of the PDM8-phase upon

water was found as Hz8 pressure was increased. Below about 1.8 MPa Hz8, PDMS

theoretically spread on water, but above 1.8 MPa the negative values of S2 suggest

spreading would not occur. As in the H2S-dqdecane-H20 case, coefficient 82 was

negative under all conditions.

PDMS is a critical component of many antifoam formulations for

aqueous systems because of its capability to spread spontaneously on water. It

was therefore surprizing to find that S2 was negative at high H2S pressure as

found within the GS process. The effect of surfactants in PDMS on this phenomenon

could not be assessed as no additive soluble in PDMS was found. If surfactants

in the aqueous phase affect this system in the same way as the dodecane-water

system, the reduction of S2 upon increase of H2S pressure should be enhanced. The

inversion of sign of S2 may therefore occur at lower H28 pressure.

- 9 ­

3.5 SURFACTANTS

Commercial antifoam agents generally contain mixtures of high

molecular weight surfactants which permit ready dispersion of the oil phase

in the foamy system. In practice, suppliers formulate their products to

allow easy handling in the plant, but at the same time directly or indirectly

achieve objectives such as ensuring that spreading coefficients are positive.

In contrast to the dilute surfactant solutions employed in the studies reported

above, commercialantifoam agents contain high proportions of surfactants to

enable ready dispersion and emulsification of the active foam-breaking phase.

He therefore attempted to determine if H2S altered the properties of solutions

of commercial surfactants.

In particular, the effect of H2 S on the Hydrophile Lipophile Balance

index (HLB number) of nonionic surfactants of the IGEPAL, MYRJ and SPAN series

were of interest (c. f. Figure 12). The former twc.' water-soluble surfactants are

mixtures of condensation products obtained by reacting an alkylphenol or a fatty

acid with a polydisperse poly 0xyethylene)(POE) fraction (11). Depending upon the

average molecular weight of the POE, the distribution coefficient between oil and

water and the related HLB number of the product are altered. Tile oil-soluble SPAN

surfactants are mono- or polyesters formed between the fatty acids and sorbitol.

The length of the fatty acid chain, and the number of ester linkages per molecule,

c~ntrols the HLB number in this case (11) .

Po (oxyethylene) SUT'factants In Water

We have studied a series of poly(oxyethylene) water-soluble surfactants

with HLB numbers between 12.6 ar.d 16.9 (Myrj 52, Atlas Chemical Industries,

Brantford) and have found that the cloud points of 1 weight percent solutions

decrease with H2S pressure as shown in Figure DA. The cloud points were determined

visually in our high-pressure optical cell by recording the pressure at which the

first stable haze, or cloud, appeared as the pressure was increased. The cell

temperatures were constant and H2S pressure was the variable. Note that at zero

H2S pressure, the intercept temperatures decrease with HLB number. The general

- 10 ­

effect of On these is thus to decrease water-solubility of

these poly(oxyethylene) ives. This may be interpreted to mean that

the effective HLB number of a given surfactant in water is reduced at high

H2S pressure.

It is necessary to recall two facts about these surfactant

solutions to understand what is One percent concentrations are well

above the critical micelle concentration (CMC) of these solutes (typically 0.1

~eight percent). The room solutions appear clear or slightly hazy

since the micelle dimensions are less than the wavelengths of light in the visible

region. Hhen the temperature is increased, desolvation of the poly(oxyethylene)

water-soluble segment of the surfactants occurs, the micelles grow in size, and

light is scattered thereby causing an opaque or cloudy dispersion to form. Above

the cloud point temperature, a surfactant-rich second liquid phase will separate.

Hithin this context, isothermal addition of H2S has the same

phenomenological effect as raising the temperature does in air. On the molecular

scale there are two possible explanations: (1) RZS may decrease solubility

by reducing the stability of the (CH2CHzO) ~hain in water by displacement of watern,"

of solvation from the ether link, qr,.- (2) H2S may dissolve in and

swell the surfactant micelles to cause light There are examples of

each of these cases in the literature for other systems. Spectroscopic studies , sugge£t Sf) may be the dominant factor.

Span 60 In Dodecane

"Cloud point" results for Span 60 in research-grade dodecane are

presented in Figure l3B. Note that for the case of Span 60 (the multi-component

condensation product of sorbitol plus stearic acid) the cloud point is more ana­

logous to precipitation than to "clouding" in the aqueous phase. Flocculation

was observed in some experiments. At a given temperature, raising S pressure

caused dissolution of Span 60, that is H2S made the surfactant more soluble in

dodecane. Simplistically, that could be interpreted to mean that the effective

IDJB number of Span 60 was decreased (i.e., made more oil soluble) by HzS. That

- 11 ­

is not surprising because we have found that liquid H2 S is a good solvent for

Span 60 and for Myrj 52.

Span 60 In Polydimethylsiloxane

We have examined the effect of H2 S on Span 60 in a 3.5 cm2/s VlH()<;

Dow-Corning PDMS. Span 60, with HLB of 4.7, was insoluble in the PDMS. Above

its melting point of about 55°C, two liquid phases were present. Addition of

H2S had no detectable effect on Span 60 solubility. Ready coalescence of the

molten Span 60 globules was observed at pressures up to 2.2 MPa. Evidently,

PDMS or S-PDMS solvent systems do not dissolve Span 60. This is

consistent with the slightly higher "required HLB number" of 11 for PDMS compared

to 10 for dodecane in which Span 60 was soluble. The results suggest that a more

water-soluble Span-series surfactant is needed to dissolve in PDMS. However,

neither Span 20 (sorbitan monolaurate, fILB 8.6) or Span 40 (sorbitan monopalmitate,

HLB 6.7) was soluble.

dAt '·p 77 .:y-,an .n 1".) oam ,oY'mU&at1"ons

Combination of the results on cloud point depression of poly­

(oxyethylene)-type surfactants in water and the cloud/precipitation point de­

pression of Span 60 in dodecane by H2S indicates that the net result is reduction

of the effective HLB number for binary surfactant mixtures. He concluded that

antifoam fluids which are designed to yield stable oil-in-water emulsions in air

will be significantly less stable in H2S-saturated water. The only factor we have

in our favour in the C.S. process is the 106_fold dilution in the feedwater. Oil

droplet coalescence rates will be lowered orders of magnitude because of the

reduction in droplet collision frequency. vJithout information on oil-water inter­

facial tensions, it is difficult to predict the on spreading coefficients

and antifoam potential.

- 12 ­

3.6 EFFECT OF H2S ON PARTITION COEFFICIENTS

The conclusion drawn above for surfactant solutions of concentrations

above the CMC must be qualified. We have determined mole fraction partition

coefficients for four normal alcohols between dodecane and water as a function

I of H2S pressure. Our results have been summarized in Figure 14, and show that

H2S does not have a major effect on the partition coefficients. That is, the

partition coefficient changes by less than two orders of magnitude up to 2.0 MPa

of H2S,

The results suggest that the relative solubility of the dilute n-alcohol

solutes were unchanged upon equilibration of the two-phase systems with H2S. Since

HLB numbers for surfactants are in principle directly related to the logarithm of

the distribution coefficient(12) (based on concentration, not mole fraction), we

conclude that H2S does not alter the effective HLB number of a dissolved surfact­

ant if its concentration is below its CMC.

The effect of H2S on surfactants is thus highly dependent upon the

phenomenon under investigation.

4. CONCLUS IONS

H2S is highly adsorbed at the gas-water and oil-water interfaces but

not at the gas-oil interface.

H2S causes desorption of nonionic surfactants from the gas-water and

oil-water interfaces compared to the equilibria established in air. H28 affects

spreading coefficients in the following way: Sl increases with pressure for both

hydrocarbon-, and polydimethylsiloxane-water systems. 82 is unaffected, or is

slightly reduced if surfactants are present.

H2 S may significantly affect nonionic surfactant phenomena if the

surfactant concentration is above the CMC.

- 13 ­

6. REFERENCES

(1) r.B. Lumb. J. British Nuclear Energy Society 12, 35 (1976).

(2) G.G. &trafudee and R.M. Given, J. Phys. Chem. ~, 1714 (1976).

(3) G.G. Strathdee and R.M. Given, J. Phys. Chem. 81, 327 (1977).

(4) N.H. Sagert and I1.J. Quinn, Can. J. Chem. Eng. 54, 392 (1976)

(5) N.H. Sagert and M.J. Quinn, J. Colloid. Interace Science 61, 279

(1977) .

(6) S. Ross and E.S. Chen in "Chemistry and Physics of Interfaces", American

Chemical Society, Washington, D.C., 1965, p. 44.

(7) H.J. Neuberg and L.G. Walker,Internal report, Atomic Energy of Canada >i. 'V--.

Limited. Equilibria of the Hydrogen Sulphide-Water System in the

G.S. Process ion Range" HWP-GS-R9l, December 1976. Unpublished internal

report of Chalk River Nuclear Laboratories of Atomic Energy of Canada Limited.

(8) J.H. Clint, 3.M. Corkill, J.F. Goodman and J.R. Tate, J. Colloid Interface

Science~, 522 (1968).

(9) R. Aveyard and R. W. Hitchell , Trans. Faraday Soc .• 2645, (1969).

(10) R.J. Good and E. Elb in "Chemistry and Physics of Interfaces",

American Chemical Society, l.Jashington, D.C. 1965, p. 72.

(11) M.J. Schick, Non-Ionic Surfactants, Volume 1, Marcel Dekker, New York, 1966.

(12) J.T. Davies and E.K. Rideal, Interfacial Phenomena, Academic Press,

New York, 1963. p.371.

- 14 -

7. LIST OF SYMBOLS

a. ).

activity of solute i

m. 1

slope = da/da*, mN/m1

P pressure, Pa

R gas constant, J/mol.K

spreading coefficient defined by equation [3]

spreading coefficient defined by equation [4]

T temperature, K

H2S mole fraction

o 'IT standard state surface pressure = 0.338 mN/m

surface tension of oil phase, mN/m

crz surface tension of aqueous phase., mN/m

oil-aqueous phase interfacial tension, mN/m

o

cr. 1

surface tension of pure liquid i, roN/m

ratio defined by equation 2.

- 15

- 16 ­

-5;

1

o = g(p, - P2)d~2iH· I/H = t(ds/de)

FIGURE 2: SCHEMATIC DIAGRAM OF EQUIPMENT USED TO MEASURE SURFACE TENSIONS

AT HIGH PRESSURE BY THE PENDANT DROP TECHNIQUE. COMPONENTS ARE:

1. MANUALLY OPERATED SYRINGE PUMP'. 2. HIGH PRESSURE OPTICAL

CELL. 3. LIGHT SOURCE. 4. POLAROID CAMERA.

- 17 ­

TEMPERATURE "C .. 2S

• !IO • "0 • !IOX 60

• 70o 80 .. go + 110 x 130

PRESSURE Mp.,

FIGURE 3: EFFECT OF PRESSURE AND TEMPERATURE ON THE SURFACE TENSION OF AQUEOUS H2 S. SOME DATA POINTS HAVE BEEN OMITTED FOR CLARITy(2).

FIGURE 4: DEPENDENCE OF THE SURFACI("1XCESS OF H2 S (r 2 (1» ON TOTAL PRESSURE AND TEMPERATURE ?- •

- 18 ­

80 CS" H2S - Des HllOH - li20

60"[~ltt~ .' 40 •

... 'eo-­

20 o 0.5 1.0 1.5 2.0

Total Pressure/MPa

FIGURE 5: THE EFFECT OF H2S PRESSURE ON THE SURFACE TENSION OF AQUEOUS n-ALKYL ALCOHOL SOLUTIONS. THE FILLED CIRCLES IN PANEL B AND THE DASHED LINES IN PANELS A AND C ARE FOR H2S-H20 WITHOUT n-ALKYL ALCOHOL. THE OTHER CURVES WITH DECREASING SURFACE TENSION INTERCEPTS IN EACH PANEL CORRESPOND TO THE SOLUTIONS OF INCREASING n-ALKYL ALCOHOL MOLE FRACTION (X104)

AS FOLLOWS, A: 8.7, 18.7; B: 4.3, 7.2, 29.8, 60.5; C: 1.1, 2.4(3).

-18,---.-----,-----,.--r---,

-21~-~--~---L--~--~ 345

rJ11/1018 Molecules rn-2

FIGURE 6: THE DEPENDENCE OF THE FREE ENERGY OF ADSORPTION OF HZS AT ITS ZERO-COVERAGE LIMIT ON THE SURFACE EXCESS OF n-PROPYL, n-BUTYL, AND n-PENTYL ALCOHOL}3).

-22

-24

-25. '0 E ~ -26 /Iti ~'" It",,' <l -27

-30~~_~_~_~_~_~~_~

-28

o 2 4 6 8 10 12 14 16

FIGURE 7: THE DEPENDENCE OF THE FREE ENERGY OF ADSORPTION OF n-PROPYL, n-BUTYL, AND n-PENTYL ALCOHOL, AT THEIR RESPECTIVE ZERO­COVERAGE LIMITS, ON THE SURFACE EXCESS OF HZS(3).

- 20 ­

ca 0. :IE ""'- 2.0LLI a:: ::;) en en LIJ 1.0a:: 0.

en N

:c 0

60

MOLE FRACTION H2S

FIGURE 8: DATA FOR THE H2S-DODECANE-H20 SYSTEM. EFFECT OF H2S MOLE FRACTION

ON TOTAL SYSTEM PRESSURE, A~~ OIL-WATER INTERFACIAL TENSION OIL­

PHASE SURFACE TENSION AT 30°C.

- -

- 21

'7E z E

.........

J'I

'7E z E

.........

60

40

20

60

40

20

0

20

0

OL-----~----~----~----~----~

I I I I ... .... &20 .. - .. ­

.& ........ 0 I I I I

1.0 2.0

H2S PRESSURE/MPa

FIGURE 9: THE EFFECT OF n-BUTANOL ON THE SURFACE AND INTERFACIAL TENSIONS OF

THE H2S - DODECANE - WATER SYSTEM AT 30°C.

• DATA FOR THE 3-COMPONENT SYSTEM

• DATA FOR THE 4-COMPONENT SYSTEM WITH 7.32 g

n-BUTANOL PER kg WATER (INITIAL)

• •

- 22 ­

o----------------~--------------,-------~

-20

E ......... -40z E 51 I ­Z UJ -60-(.) LI.­LI. UJ 0 -80 (.)

C!J Z-Q -100<LLI a::: 0a... rn 52 = 02 - 01 - 012

•52 -5

• -IO~------------~------~---------------

FIGURE 10:

1.0 2.0

H25 PRE55URE/MPa

SPREADING COEFFICIENTS FOR THE H2S-DODECANE-WATER SYSTEMS AT 30°C.

• DATA FOR THE 3-COMPONENT SYSTEM

.. DATA FOR THE 4-COMPONENT SYSTEM WITH 7.32 mg n-BUTANOL PER

GRAM OF WATER (INITIAL)

-- ----

- 21 ­

60"i' E z E 40

20

60"i'E z E 40

..........

20

0

20

0

20

0

OL---~----~----~----~--~

I , , I .. .. ... ..~ ... .... - -

I I I I

1.0 2.0

H2S PRESSURE/MPa

FIGURE 9: THE EFFECT OF n-BUTANOL ON THE SURFACE AND INTERFACIAL TENSIONS OF

THE HZS - DODECANE - WATER SYSTEM AT 30DC.

• DATA FOR THE 3-COMPONENT SYSTEM

• DATA FOR THE 4-COMPONENT SYSTEM WITH 7.32 g

n-BUTANOL PER kg WATER (INITIAL)

- 22 ­

o----------------~------~------~------~

-20

E "- -40z E S1 I ­Z LI.I -60-(.)

.....­..... LI.I 0 -80 (.)

CJ

-Z Q -100c u.I a:: 00... U)

S2 = 02 - °1 -°12 •• •S2 -5

• -IO~----~------~----------------------

FIGURE 10:

1.0 2.0

H2S PRESSURE/MPa

SPREADING COEFFICIENTS FOR THE H2S-DODECANE-WATER SYSTEMS AT 30°C.

• DATA FOR THE 3-COMPONENT SYSTEM

.~ DATA FOR THE 4-COMPONENT SYSTEM WITH 7.32 mg n-BUTANOL PER

GRAM OF WATER (INITIAL)

- 23 ­

I I I I

-40 '­ -

E -60 ' ­, zE Sl

-

to-z L&.I-(,)-..... ..... L&.I 0 (,)

-80 -..

-100 I I I I

-

f!

... 'r­" -Z 10C <LLI S2a:: Q. en 5

o

1.0 2.0

H2S PRESSURE/MPa

FIGURE 11: SPREADING COEFFICIENTS FOR THE H2S - POLYDIMETHYLSILOXANE-WATER

SYSTEM AT 30°C.

- 24 ­

! - CaH17

Polyoxyethylene !~octylphenol (IGEPAL SERIES)

Anhydrohexitol Esters (SPAN SERIES)

FIGURE 12: CHEMICAL FOMULAE FOR IGEPAL AI'll SPk'l'-SERIES NONIONIC SURFACTANTS.

- 25

(.) o

" ... Z IGEPAL 630 720(5 Q.

C ::::> 9 (.)

B H2S - SPAN 60 ..~ DODECAN E40

20

o 1.0 2.0

TOTAL PRESSURE/MPa

FIGURE l3i1.: THE EFFECT OF H2S ON THE CLOUD POINTS IN AQUEOUS SOLUTION OF

THREE NON-IONIC POLY(OXYETHYLENE)-TYPE SURFACTANTS. SYMBOLS: 0 '1YRJ 52 (HLB 16.9) • IGEPAL 720 (HLB 14.4) OIGEPAL 720

PERCOLATED THROUGH SILICA GEL COLUMN ~ IGEPAL 630 (HLB 12.6)

FIGURE 13B: THE EFFECT OF H2S ON THE CLOUD POINTS (PRECIPITATION POINT) OF

SPAN 60 (HLB 4.7) IN DODECANE. ... 1 wt % 0 5 wt )~

,... z L&J """" 0...... Il.i.. LI.. UJ 0 u z 0 ~ ::> 00

IX: ...... €'.I) ...... c z 0...... lo-U <c:::: IU..

UJ ...J 0 :E

- 26 ­

6

4

2

10·0 8 6

4

2 j<

< ' ­1·0 8 6

C5

C4

4 C3­-e_•

2

0·10 o 1.0 2.0 H2S PRESSURE/MPa

FIGURE 14: THE EFFECT OF H2 S ON THE MOLE FRACTION DISTRIBUTION COEFFICIENT

FOR FOUR NORMAL ALCOHOLS BETWEEN DODECANE AND WATER.