Adsorption of Nonionic Surfactants on Quartz in the Presence of

Chapter 11

Adsorption of Nonionic Surfactants on Quartz in the Presence of Ethanol, HCl, or CaCl Downloaded by UNIV OF CINCINNATI on November 10, 2014 | http://pubs.acs.org Publication Date: July 20, 1988 | doi: 10.1021/bk-1988-0373.ch011

2

Its Effect on Wettability A. M . Travalloni Louvisse and Gaspar González Petrobrás/Cenpes, Cidade Universitária, Q-7, Rio de Janeiro-RJ, Brazil The effects of HCl, CaCl , and ethanol on the adsorption of Triton X-100 on s i l i c a , glass, and quartz have been investigated. Ethanol and HCl reduced the adsorption of surfactant by the solid; CaCl presented the opposite effect. The results have been attributed to changes in the solubility behavior of the surfactant in the presence of these compounds. Measurements of the cloud point and c r i t i c a l micelle concentration (CMC) of the surfactant solutions under similar conditions confirmed this view. The adsorption process resulted in a hydrophobization of the solid. Measurements of contact angles on glass and quartz indicate that this transition takes place at a very low surfactant concentration (Θ = 26° for C = 10 molar), and that ethanol and HCl reduce this value of contact angle. The reverse transi tion to zero contact angle was effective at concentra tions well below the c r i t i c a l micelle concentration, indicating that association of the surfactant at the solid-solution interface precedes the CMC. The results are discussed in terms of their relevance to some sur factant mediated (enhanced) o i l recovery processes. 2

2

-6

Nearly a l l of the treatment processes i n which f l u i d s are injected into o i l wells to increase or restore the levels of production make use of surface-active agents (surfactant) i n some of t h e i r various applications, e.g., surface tension reduction, formation and s t a b i l i z a t i o n of foam, anti-sludging, prevention of emulsification, and mobility control for gases or steam i n j e c t i o n . The question that sometimes arises i s whether the l e v e l of surfactant added to the i n j e c t i o n f l u i d s i s s u f f i c i e n t to ensure that enough surfactant reaches the region of treatment. Some of the mecha nisms which may reduce the surfactant concentration i n the f l u i d are p r e c i p i t a t i o n with other components of the f l u i d , thermally induced p a r t i t i o n into the various coexisting phases i n an o i l well treatment, and adsorption onto the reservoir walls or mineral 0097-6156/88/0373-0220$06.00/0 « 1988 American Chemical Society In Surfactant-Based Mobility Control; Smith, D.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

11.

LOUVISSE & GONZALEZ

Adsorption of Nonionic Surfactants on Quartz

p a r t i c l e s . Some of these processes may be predicted and prevented by an adequate formulation of the f l u i d s and a proper control of the additives. The e f f e c t of adsorption, however, i s d i f f i c u l t to evaluate due to the complexity of the rocks forming the o i l bearing geological formations. I t i s to this aspect of the rockf l u i d interaction that this work was directed. We studied the solution behavior of T r i t o n X-100, a nonionic surfactant of struc ture similar to those used i n completion and stimulation f l u i d s , i t s adsorption at the s i l i c a - s o l u t i o n interface, and the e f f e c t of these processes on the concentration of surfactant i n the f l u i d s injected i n porous media.

Downloaded by UNIV OF CINCINNATI on November 10, 2014 | http://pubs.acs.org Publication Date: July 20, 1988 | doi: 10.1021/bk-1988-0373.ch011

Experimental Materials -- The surfactant used i n this study was an o c t y l phenol exthoxylated with 9-10 oxyethylenic units. The product was manu factured by J . T. Baker Chemical Company, and marketed as T r i t o n X-100. Most of the surfactants used as additives for i n j e c t i o n f l u i d s present a structure similar to T r i t o n X-100. For the adsorption tests, a sample of s i l i c a (Merk) with a spe c i f i c surface area of 388 m g measured by the BET method was used. The s o l i d specimens used to measure the contact angles were microscope glass slides and pieces of quartz polished using a rotating plate covered with a polishing cloth impregnated with 10 μπι diamond polishing p a r t i c l e s . 2

_1

These solids were treated with concentrated acid, thoroughly rinsed with double d i s t i l l e d water, and ultrasonicated to remove p a r t i c l e s which may have remained deposited on the s o l i d surface. A l l the chemicals, including the ethanol, were Analar grade. water used was twice d i s t i l l e d from an all-Pyrex s t i l l .

All

Experimental Procedure -- The surface tensions of Triton X-100 solutions, with or without other additives, were measured using a du Nouy ring tensiometer (Fisher S c i e n t i f i c Company) at 25°C. The temperature at which a 1% surfactant solution became turbid ("cloud point") i n pure water or i n the presence of additives was determined by v i s u a l observation of the solution contained i n a test tube as the temperature was increased. For this purpose, the test tubes were placed i n a transparent water bath equipped with a control unit which permitted temperature increases at the rates of 3°/min and 0.2°/min. A dark background permitted a sharper estimation of cloud points. The amount of surfactant adsorbed by s i l i c a was determined by mea suring the difference between the i n i t i a l and f i n a l concentration of 25 ml of surfactant solution after 3 hours of contact with one gram of s i l i c a . The surfactant concentration was determined from the adsorbance at 281 nm i n 10 mm optical-path quartz c e l l s , using a double-beam Varian 634 spectrophotometer. An alternative proce dure used for some cases was based upon the fact that the γ-log C

In Surfactant-Based Mobility Control; Smith, D.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

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diagram i s roughly a straight l i n e i n the range 3.2 χ 10 to 2 χ 10 molar. The surfactant solutions were diluted to reach a value of surface tension corresponding to a solution of composi t i o n within this range. Hence, as the d i l u t i o n factor was known i t was possible to calculate the concentration of the o r i g i n a l solution. Both methods led to similar r e s u l t s . 4

The contact angles at the quartz- (or glass) water-air interface were measured using a modified captive-bubble apparatus (1).


Results and Discussion Solution Behavior of T r i t o n X-100 — Figures 1 and 2 show the sur face tension of aqueous solutions of T r i t o n X-100 and the e f f e c t of various additives at 25°C. The c r i t i c a l micelle concentration (CMC) for the surfactant i n water was 2.8 χ 10~ mol dm~ . This figure agrees with results reported by other authors. The graph shows a rather shallow minimum i n the CMC which i s usually i n t e r preted as evidence of some degree of p o l y d i s p e r s i t y (2). Curves b and c show the e f f e c t of ethanol at 10 and 25 v o l % . The reduction of surface tension for low-surfactant concentration corresponds to the e f f e c t of ethanol. For higher concentrations, the surfactant i s p r e f e r e n t i a l l y adsorbed at the l i q u i d surface, displacing the alcohol from the interface, However, as the slope of the y-log C curve i n the CMC region i s lower i n the presence of alcohol, i t seems that this displacement i s not complete. Nishikido studied t h i s e f f e c t for various oxyethylenic surfactants and concluded that the r a t i o between the maximum adsorption of surfactant i n the presence of alcohols and i t s corresponding value i n pure water decreased l i n e a r l y with the mole f r a c t i o n of the alcohol (3). The results of Figure 1 also indicate that ethanol does not modify to a great extent the CMC of T r i t o n X-100. According to the same author, two opposite effects are responsible for t h i s behavior; the solvency e f f e c t , which would increase the CMC, and a p a r t i a l penetration of the alcohol into the micelle structure, which would result i n a reduction of the CMC. Hydrocholoric acid increases the CMC of T r i t o n X-100, and calcium chloride reduces i t s value. The changes shown i n Figure 2 may be attributed to changes i n the surfactant s o l u b i l i t y i n e l e c t r o l y t e solutions. 4

3

Nonionic surfactants dissolve i n aqueous solutions through hydro gen bonding between the water molecules and the oxyethylenic por t i o n of the surfactant. These interactions are weak but enough i n number to maintain the molecule i n solution up to the cloud point temperature, at which the surfactant separates as a d i f f e r ent phase (4). Figure 3 shows that electrolytes l i k e calcium chloride, potassium chloride, or sodium chloride reduce the cloud point of T r i t o n X-100. Hydrochloric acid instead promoted a s a l t i n g - i n e f f e c t similar to that observed for ethanol. +

According to Schott, et a l . , H and a l l bivalent and t r i v a l e n t cations form complexes with the ether linkages of nonionic surfac tants, increasing t h e i r s o l u b i l i t y (5). Among the anions, only large, polarizable ions l i k e iodide and thiocyanate break the


LOTJVISSE & GONZALEZ



11.

I -6

1

-5

1 -4

1 -3

1

-2 l o g C ( moles

Figure 2.

3

dm )

Plots of the surfactant tension versus logarithm of the surfactant concentration for T r i t o n X-100 i n (a) pure water, (d) 1 mole dm HC1, (e) 1 mole dm HC1, 10% ethanol, and (f) 10 wt% C a C l . 3

2


223



224

Figure 3. Effect of different additives on the cloud point of Triton X-100 (1 wt%) solutions of ethanol, HC1, CaCl , KC1, and NaCl. 2


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structure of water to reduce the extent of hydrogen bonding between water molecules to favor the hydration of the ether l i n k ages v i a hydrogen bonding. Chloride has a very strong salting-out e f f e c t , which determines the reduction of the clouai point observed for C a C l i n spite of the s a l t i n g - i n e f f e c t of Ca 2

Adsorption Behavior of T r i t o n X-100 — The adsorption of T r i ton X-100 onto s i l i c a i s shown i n Figures 4 and 5. The results indicate that there are three well-defined regions i n the i s o therm. I n i t i a l l y , for low concentrations of surfactant, the adsorption i s rather low. Following this region there i s a sudden increment i n the adsorption, and f i n a l l y a saturation plateau i s reached for an equilibrium concentration of 6 χ 10 moles dm for the case of pure aqueous solutions. The amount adsorbed i n the plateau i s 1.3 μ moles m . This figure i s lower than the results reported by Doren, et a l . , f o r quarts, but compares well with results of Rouquerol and van den Boomgaard (6-8). This value of adsorption corresponds to a molecular cross section of 1.2 nm . The area per molecule i n a compact monolayer at the air-water interface, calculated from the results of Figure 1 i s 2.22 nm . These figures indicates that the adsorption plateau at the s o l i d solution interface i s attained when a b i l a y e r of surfactant i s formed on the s o l i d . This association process takes place at the interface before the formation of micelles i n solution. Scamehorn and Schechter, et a l . , have studied i n d e t a i l the adsorption of ionic surfactants on polar s o l i d s , and they denominated as "admi c e l l e s " this b i l a y e r structure to d i s t i n g u i s h i t from the "hemimic e l l e s " described by Gaudin (9,10). The results of Figure 4 indicate that the mechanism of adsorption for nonionics on s i l i c a follows a s i m i l a r o v e r a l l pattern.


4

3

2

2

2

Calcium chloride, hydrochloric acid, or ethanol at low concentra tions do not modify the adsorption plateau; nevertheless, the saturation i s attained at a d i f f e r e n t equilibrium concentration due to the changes i n the s o l u b i l i t y behavior of the surfactant i n the presence of these additives. When the concentration of ethanol i s 25% (6 molar), the adsorption maximum i s reduced to 0.8 μ moles m , indicating that for t h i s rather high concentra t i o n of ethanol, the surfactant does not completely dislocate the alcohol from the s o l i d surface. 2

The Contact Angle at the Quartz (Glass) - Solution Interface i n the Presence of T r i t o n X-100 — The values of receding contact angle as a function of the concentration of T r i t o n X-100 i n water (Curve a) or i n the presence of ethanol (Curves b and c) are shown i n Figure 6. The shape of the curves corresponds to a t y p i c a l wetting isotherm for polar, high-energy solids (11). In this case, the contact angle increases for low-surfactant concentra t i o n , r e f l e c t i n g the adsorption of single molecules onto the polar groups of the s o l i d . After reaching a maximum, the contact angle decreases as a consequence of the formation of a second layer of surfactant with t h e i r polar groups oriented toward the l i q u i d phase. The addition of ethanol reduces the recending angles, but the shapes of the wetting isotherms are s t i l l maintained.


225


226


Figure 4.

Adsorption isotherms for T r i t o n X-100 on s i l i c a (a) pure water, (b) 10% ethanol, and (c) 25% ethanol.

(e)

(0)

jA mol J

m

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D

1,0

•Γ 0,8

i

)

0,6

J

0,4

0,2

-7

-6

-5

•j Δ

-4

-3 log C ( mol d m ) 3

Figure 5.

Adsorption isotherms for Triton X-100 on s i l i c a (a) pure water, (d) 1 mol dm~ HC1, (e) 1 mol dm HC1, 10% ethanol, and ( f ) 10 wt% C a C l . 3

2


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LOUVISSE & GONZALEZ

C a p i l l a r y Pressure of Fluids Containing Ethanol and T r i ton X-100 -- The c a p i l l a r y pressure, P, of a f l u i d i n a porous medium i s defined by the r e l a t i o n (12) ΔΡ =

&

(1) r e

LV where γ represents the surface tension of the f l u i d , Θ i s the contact angle, and ^ y i e f f e c t i v e radius of the porous medium. The term 2y cos0 represents the product between the c a p i l l a r y pressure and the e f f e c t i v e radius of the porous medium^ From Figures 1 and 6 i t i s possible to calculate the product 2y cos0 as a function of the concentration of Triton; the results are shown i n Figure 7. It seems clear that the addition of ethanol reduces the c a p i l l a r y pressure for low concentrations of surfac tant, and this e f f e c t substantiates the use of alcohols i n work over f l u i d s when i t i s necessary to remove aqueous f l u i d s trapped i n the formation by c a p i l l a r y forces. Recent f i e l d tests indicate that water blockages may be e f f e c t i v e l y removed by the use of perfluorocarbonate surfactants i n connection with ethanol and hydro c h l o r i c acid (13).


r

s

t n e

The E f f e c t of Adsorption on the Levels of Surfactant i n Injection Fluids -- From the results of Figures 4 and 5 i t i s possible to assess the changes i n the concentration of surfactant as a conse quence of i t s adsorption on the minerals forming the reservoir. The results reported i n this paper are for quartz, s i l i c a , or glass; nevertheless, these solids probably represent the worst cases, because the adsorption of nonionics on alumina (and by extension onto alumino s i l i c a t e s ) and on calcareous minerals i s lower than the adsorption onto quartziferous materials (G. Gonzalez, A. T r a v a l l o n i , i n progress). To calculate the reduction i n the concentration of surfactant i n the f l u i d by adsorption i t i s necessary to have an estimation of the inner surface area of the reservoir. This parameter i s related to the porosity of the medium and to i t s permeability. Attempts have been made to correlate these two quantities; but the results have been unsuccessful, because there are parameters c h a r a c t e r i s t i c of each p a r t i c u l a r porous medium involved i n the description of the problem (14). For our analysis we adopted the approach of Kozeny and Carman (15). These authors defined a parameter called the "equivalent hydraulic radius of the porous medium" which represents the surface area exposed to the f l u i d per unit volume of rock. They obtained the following relationship between the permeability, k, and the porosity, Θ: 3


227


228


log C(moles dm )

Figure 6.

Receding contact angle at the quartz-aqueous solutiona i r interface versus logarithm of the surfactant concentration i n (a) pure water, (b) 10% ethanol, (c) 25% ethanol, and (d) 1 mol dm" HC1. 3

log

Figure 7.

C(moles dm )

Calculated c a p i l l a r y pressures for aqueous solutions of T r i t o n X-100 i n a quartziferous porous media versus logarithm of the surfactant concentration i n (a) pure water, (b) 10% ethanol, and (c) 25% ethanol.


11. LOUVISSE & GONZALEZ


I

I

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co

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^

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229

230


From Equation 2 i t i s possible to calculate the inner s.urface area of the porous medium, S . Hence, from the adsorption data of F i g ure 4 i t i s possible to calculate the volume of rock necessary to adsorb a l l of the surfactant and the t o t a l volume of rock attained by the f l u i d . Assuming a r a d i a l penetration, these two volumes may be transformed into the radius of penetration of the f l u i d as a whole, r and the radius necessary to consume the surfactant, r · The ratio r / r ! w i l l be higher than one i f the surfactant i s s t i l l available when the f l u i d reaches i t s programmed penetration distance. Figure 8 shows the ratio r / r x as a function of the permeability for three d i f f e r e n t p o r o s i t i e s and four d i f f e r e n t concentrations of surfactant. For low-porosity solids i t i s almost certain that the surfactant w i l l be present i n a l l the f l u i d penetration distances, and i n this case the use of 0.2, 0.1, or 0.05 v o l % surfactant solution does not result i n important differences. The l e v e l of surfactant becomes important for porous media of high porosity and low permeability. In these cases, due to the t o r t u o s i t y of the porous medium, the surfactant w i l l be depleted unless i t s concentration i n the f l u i d i s rather high. 1 ?

2

2


2

The addition of ethanol increases the penetration distance of the surfactant; this i s shown for various p o r o s i t i e s i n Figure 9 where the r a t i o r / r ! i s plotted as a function of the permeability for a 2

0

100

200

300

400

K/milidorcy

Figure 9. Ratio between the radius of penetration of the surfactant and the radius of penetration of the fluid as a function of the permeability (k) and concentration of surfactant (indicated in eachfigure)in water ( ) and in 25% ethanol (») under the conditions Ο = 25%, treatment volume = 150 L, and maximum adsorption as in Figure 1.


11. LOUVISSE & GONZÀLEZ


porosity of 25% and a solution containing 25% ethanol. It seems reasonable to conclude that for fluids containing alcohols i t may be possible, under certain circumstances, to reduce the concentrat i o n of surfactant without reducing i t s penetration distance i n porous media. This behavior i s related to the cosolvency effect of ethanol and to the reduction of the maximum adsorption shown i n Figure 4.


Literature Cited 1.

Adamson, A.W. Physical Chemistry of Surfaces. York, J. Wiley and Sons, 1976.

3rd ed., New

2.

Crook, E.M.; Fordyce, D.B.; Tregzi, G.F. J. Phys. Chem., 1963, 67, 1987.

3.

Nishikido, N. J. Colloid Interface S c i . , 1986, 112(1), 87.

4.

Shinoda, K.; Saito, H. J. Colloid Interface S c i . , 1968, 26, 70.

5.

Schott, H . ; Royce, A . E . ; Suck, K.H. J. Colloid Interface Sci., 1984, 98(1), 196.

6.

Doren, Α.; Vargas, D.; Goldfarb, J. Trans. IMM, 1975, 84, C33.

7.

Requerol, J.; Partyka, S.; Requerol, F. In Adsorption at the Gas-Solid and Liquid-Solid Interface. J. Requerol; K.S.W. Sing, Eds., Elsevier Sci. Pub. Co.: Amsterdam, 1982, p. 69.

8.

Van den Boomgaard, Th.; Tadros, Th.F.; Kyklema, J. J. Colloid Interface S c i . , 1987, 116(1), 8.

9.

Scamehorn, J.F.; Schechter, R.S.; Wade, W.H. J. Colloid Interface S c i . , 1982, 85(2), 463.

10.

Gaudin, A.M.; Fuerstenau, D.W. Trans. AIME, 1955, 202, 958.

11.

Wolfram, E. Adhesion at Solid-Liquid Interface. Lecture Course at University of Bristol, England, 1977/1978.

12.

Defay, R.; Prigogine, I. Tension Superficielle et Adsorption. Liege: Desoer, 1951, pp. 6-9.

13.

González, G.; Dubai, A. Redutores de tensão superficial para fluidos de injecão, Relatório Técnico CENPES, 1987.

14.

Kinghorn, R.R.F. An Introduction to the Physics and Chemistry of Petroleum. J. Wiley and Sons: New York, 1983.

15.

Scheidegger, A.E. The Physics of Flow through Porous Media. University of Toronto Press: Toronto, 1973, p. 141.

Received March 3, 1988


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Adsorption of Nonionic Surfactants on Quartz in the Presence of

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