Anionic surfactant adsorption on to asphalt-covered clays

Anionic clays

(Received

surfactant

22 May 1992: accepted

adsorption

9 August

on to asphalt-covered

1992)

b.bstract _ iiiitc ulays \v’ Asphalt :Idsorption from water-s;ltur:ltcd tolucnc on Na - kaolinitc. C;l’_ knnlinitc. N;t illile illlci Cu' invcstigatcd. it was found that the kaolinitc surfxc adsorbed more x:phalt [bon illilc Tw both the Na-- and !\I:: C;t” cschangcd rorms. Adsorption from aqueous solutions of sodium dodccylh~nzsncsulphoniltc (Sf?BS) and sodium dodzq! sulphatc (SDS) on various asphalt-covcrcd clays\V;ISalso studied. The hhnpc of the icothcrms dcpcndcd on the i\Sphi\Itclay substrate and showed ;I much lower adsorption of SDBS hcyond the CMC. Dcsorption of asphalt from vxiwls The pcrccntagc wcipht or asphalt dcsorhed clayswith SDBS and SDS surfxtants was mcnsurcd spcctrophotomctrically. with SDBS w;ts twofold higher than that dcsorbcd with SDS surfxtant.

Introduction In a petroleum reservoir, heavy oil or asphalt contains polar compounds which may be highly adsorbed on clay mineral surfaces, leading to oil cntrapmcnt within the rock ports. The extent of adsorption is rctatcd to the properties of ?hi: clay mineral, such as surf:ice area, cation exchange capacity, crystattinity and surface affinity for polar organic compcrunds. In turn, if adsorption dots : Iced occur, the clay properties could be significantly altered, the clay becoming hydrophobic and its cation exchange capacity being towered [t]. The polar compounds of asphalt known as asphattcnes and resins are complex mixtures of large potyaromatic hydrocarbons containing hcteroatoms such as N, S, 0 and polar functional groups. A variety of mechanisms for asphalt Corrc.spr~l~rlel~~(~IO: B. SilTcrt. Ccntrc dc Rcchcrchcs sur lo Physico-Chimie dcs Surfaces Solidcs, 2-l. ovcnuc du Prksidcnt Kcnncdy. 68200 Mulhousc. France. 0 166~6622/91/SO5.00

<’ 1997 -

Elscvicr

Scicncc

Publishers

adsorption on clay minerals, such as hydrogen charged bonding. cation 1:sc~~,~~qy with positively nitrogen groups present in the asphalt structure, n-electron interactions of aromatic rings with the clay exchange cations, has been reported by ;everat authors [Z-6]. are being Methods of oil and asphalt recovery investigated. s uch as the surfactant flooding process [7-t t]. However, the limiting factor in this process is the adsorption of the surfactrlnt at the sotidliquid interface. The magnitude of this adsorption can determine the utility of the process. The purpose of this study was to investigate asphalt adsorption on to clay surfaces in watersaturated totuene and the effect of surfactant structure on asphalt desorption from the clays. Materials The clays used were kaotinite (Ploemeur, France) and itiite (Brives-Charenzac, France). Each clay B.V. All rights

rcscrvcd.

46

was purified and exchanged with Na’ and Ca2+ ions by addition of the appropriate chloride salt, following the procedure of Robert and Tessier [I 21. The clay particles were suspended in distilled water and were fractionated to a size smaller than 2 pm according to Caill&c and Henin [13]. The purity of the clays was checked by elemental analysis and X-ray diffraction. The surface areas of each of the clays were measured by adsorption of mcthylene blue from aqueous solution using the procedure of Hang and Brindley [i4]. The surfactants used were sodium dodccyl sulphate (SDS) and sodium dodccylbcnzcncsulphonate (SDBS), purchased from Fluka and used with no further purification. Their CMC were 0.0045 mol drnm3 and 0.008 mol drn-j for SDBS and SDS respectively, as determined by electrical conductivity measurements at 23 C. The asphalt and the material used for titrating the surfactants have been described previously [ 15). Experimental

A stock solution was prepared by dissolving 1g of asphalt in 1 dm3 of water-saturated toluenc. The purpose of using water-saturated toluene solutions was to hydrate the clays. thus preventing agglomeration of the clay particles in water-free toluene. The dispersion mechanism is not well understood, but it seems that water provides a higher surface charge for the particles and therefore a better dispersion [ 161. The water content was analysed by Karl Fischer Titration and the average value obtained was 0.48 mg I-I20 per 1 ml of toluene. Aliquots of the stock solution were pipetted into 100 ml volumetric flasks. One gram of dried clay was added to each flask, which was then filled with solvent to give the desired concentration of asphalt. The mixture was shaken for 48 h, sedimented for 3 days and the asphalt remaining in the supernatant (equilibrium asphalt concentration) was determined with a LERES S30 WV/ViS spectrophotometer at

525 nm. This wavclcngth was chosen because it gave a linear fit of the calibration curve. The amount of asphalt adsorbed on clay was then calculated from the difference between the initial and the equilibrium asphalt concentrations. The sediment obtained at the adsorption isotherm plateau (maximum asphalt adsorption) was dried at 11O’C and was then used as the substrate for the surfactant adsorption experiments.

Adsorption studies were performed by mixing the dried sediment with aqueous surfactant solution in 20 ml centrifuge tubes. The initial surfactant concentrations wcrc varied from IO-’ to IO- ’ mol dm -’ and the asphalt/clay ratio for each clay was held constant. The mixture was shaken for 24 h and centrifuged. The final concentration of the surfactant remaining in the supernatant was determined by the two-phases titration method [17]. The procedure consists of the preparation of a stock solution of 0.5 g of Disulphine Blue-0.25 g of dimidium bromide dissolved in 50 ml of 10% ethanol, then heated, diluted with water and acidified with sulphuric acid. An aliquot of aqueous surfactant solution of zzkcnwn molarity was added to a small quantity of the stock solution. Extractions of the salt formed between the surfactant and dimidium bromide were carried out with chloroform, leading to a pink coloration of the organic phase. Aqueous Hyamine 1622 solution was then added dropwisz to the extracted organic phase and the end point was Teached when a bluegrey coloration was obtained. In order to complete the transfer of surfactant from the aqueous to the chloroform phase, two or more further extractions were needed until a colourless organic phase was obtained. A surfaciant solution of known molarity was used for the standardization of Hyamine. The amount of surfactant adsorbed (F) on the asphalt-clay substrate was then calculated from the diflerence between the initial and the final surfactant concentrations (C,).

E. S@w

cr a/.iCn//oid.s

TABLE

Swfi~ces 69 (1992) 45-5 I

47

1

Composition

and spccilic

Clay

surf&c

areas of the clays

Composition

Knolinitc

(Plocmeur)

Illitc (Brivcs)

(mg g- *)

sio 2

A120,

WO

Fc,O,

TiOr

cao

Na,O

K20

Hz0

45.67 SO.80

39.6 I X.58

0.23 4.16

0.56 7.46

0.08 0.82

0.4 0.65

0.14 0.23

0.85 6.86

IX2 6.44

Mixtures of dried asphalt-clay substrate and aqueous surfactant solution were prepared and equilibrated using the same procedure as for the surfactant adsorption measurements. The amount of asphalt desorbed from the clay by the surfactant was measured spectrophotometrically using a calibration curve obtained at 525 nm with known concentrations of asphalt in toluene. At this wavelength, no absorbance was observed for the aqueous SDBS and SDS surfactant solutions. Results

Composiiions and specific surface areas of the clays are given in Table 1. Adsorption isotherms of asphalt on Na+ kaolinite, Ca’+ kaolinite, Na+ illite and Cal+ illite expressed in milligrams per gram and milligrams per square metre are shown Figs 1 and 2 respectively, and are typical

“Wi

04 0.0

I 0.2

0.4

Equilibrium concentration

0.6

of

asphalt,

0.0

g/l

Fig. I. Adsorption isotherms of asphalt on the various clays (cxprcssed in milligrams per gram of clay): N;1- illitc (3); Na’ kaolinitc (a): Ca’ * illite (A): Ca” kaolinitc (0).

-010

0:2 Equaibkm

0:4 oxenaatan

123”

10.5”

0.6 of

specific surracc area (m’ g-‘)

as@ak

.

,

B

s/r

Fig. 2. Adsorption isotherms of asphalt on the \va;ious clays (expressed in milligrams per squaw metrc or clay): Na’ illitc (II): Na- kaolinite(0): Ca’- illitc( A); Ca” kaolinite (I).

Langmuir isotherms. The initial slopes shown in Fig. 1 increase in the order Na+ illite > CaZf illite > Na+ kaolinite > Ca2+ kaolinite. A differc I order appears in Fig. 2. The maximum amounts of asphalt adsorbed (adsorption plateaux) are indicated in Table 2 and range from 26 mg g-t for Ca’+ kaolinite to 48.5 mg g- i for Naf illite or from 0.4 mg m-’ for Ca2+ and Na+ illite to 4.3 mg mm2 for Na+ kaolinite. Surfactant adsorption isotllerms on asphaltcovered Na+ kaolinitelillite, and Cat+ kao!inite/ illite are reported in Figs 3 and 4 respectively. The SDS adsorption isotherms on asphalt-covered Na+ kaolinite and Naf illite are Langmuir type I isotherms. Complex isotherms showing a maximu’n with a decrease beyond the CMC are obtained for SDBS adsorption on the four asphaltclay substrates. Another important feature of Figs 3 and 4 is the amount of SDBS adsorbed above

N;I _ I;;wlinitc

lh.7

C:I? * holinitc

2h.O

2.9

Na - illitc

-1H.5

0.4

0’ ~-~

45.3

0..37

- iilitc

Ce Fig

3. Adsorption

isotherms

cI;Ly subslr~ttcs. N:I _ kaolinitc

(A).

N;I _ kaolinitc

( .‘_1.

1.3

(mmol/l)

of

SDKGasphlt

111~ CMC; it is smaI1 compared to that of SDS. This dilkcnce in adsorption may be due to the difference in molecular interactions which occur bctwcen the hydrophobic part of the surfact:mt and the asphalt polyaromatic component. Hou+ever. the SDS adsorption isotherms on asphaltcovered Ca’ l l:ao!initc and Ca’+ illitc shown in Fig. 4 suggest that an cxchangc of the ciay’s calcium ion with the surfactant sodium ion occurs. Hence 111~ surfzzctant uptake at ihc CMC by asphaltca’+ -clay substrates increases whatever the !ype of surfactant. As explained in the discussion. the dccrcasc in surfactant uptake above the maxima :iriscs from two diffcrcnt mcch;ir3Y Fiwrcs 5 and 6 show the cl?’ J surfa&!nt = 1-kaolinite structure on asphalt dcsorptil desorbed and Nu 7 iltitc respectively.

aurfxtant thy

SDS-:~sphalt-clay

on

systems:

;tsphxlt--Na :J;I *

systems:

Na

.

*-

illitc

(W):

illitc

I _I): Equilibrium Fig. 5.

isotiicrms

of

of ;isphitlt

surfactant

from

(mmol/l)

Nit - kaolinitc

by

(.’ i and SDS (A).

SDBS 30

Dcsorption

concentration

_____~__

,

,O

0 0

Fig. 1.

Adsorption

clay

substrxtcs.

Ca’-

kilolinitc

Co’ r kxolinitc

~sothcrnis

of silrbtct:lnt

SDBS-asph:llt-cl~Iv

(_S_ ). SDS-;lSpll;iit-clay (A).

systems:

on

asphalt-Ca2 Ca’

’

illitc

!

0

40

20

90

60

100

-Equilibrium

(LI):

S\:l
Fig. 6. SDBS

Dcsorption

(Id)

and

concentration

isotherms SDS

(Kl.1).

of

of ;tl;ph:dt

suriactant from

Nn-

(mmol/l) illite

by

is enhanced when micelles are formed and levels off with increasing surfactant concentration. The percentage weights of asphalt removed from the clays by SDS and SDBS are reported in Table 3. The increase in asphalt desorption in the order Na+ illite > Cal+ illitc > Ca”’ kaolinite > Na+ knolinitc indicates a high degree of irreversible adsorption of asphalt on kaolinitc relative to illite. 0.0

Discussion

Fig. 7. Adsorption on Na- ksolinitc.

hpparcr,tly the asphalt does not exhibit as great an afhini ,r the Na + illite sites as it does for Na+ kaolinite. In order to check which of the species, asphaltencs or resins, arc the active substances for adsorption, preliminary experiments were performed with asphaltenes. They were precipita;ed from asphalt in jr-hcptane, dissolved in water-s;tturated tolucne, and were brought into contact with the clays. isotherm was then A compIetc adsorption obtained as shown in Fig. 7 for Na+ kaolinitc. This isotherm is similar to that obtained with asphalt. Therefore it can bc concluded that asphaltcncs arc the active spt&cs. Hence, if we assume that these molecules have a disk-like shape and are adsorbed with their disk faces in contact with the surfaces of the clay particles [IS], and if a value of asphaltcnc density equal to 1.6 g cmU3 is used, as suggested by Parkash ct al. [ 193. it becomes possible to calculate TABLE Weight SDS

3 per cent of asphalt

Suhstratc

N:rL kaolinitc Ca’- kaolinitc Na- illitc Ca’- illitc

dcsorbcd

from clays by SDBS and

/,r..+.‘!~ rl.*c,,rbcd ( \+q”;) SDS

SDBS

2.1 3.4 ‘0.0 72.0

4.5 6.5 38.0 36.4 -.-

0.1

0.2 Equilibrium

isothums

0.3

olasphalt

I

0.4

concentration

5

. g/l

(+) and asphaltenc

(Ll)

the thickness of the adsorbed layers. With these assumptions. values equal to 3 nm. 1.7 nm, 0.27 nm and 0.25 nm were obtained for Na+ kaolinite, Ca’+ kaolinite, Na + iilite and Ca’+ illite respectiveIy. Within the accuracy of the data. the values obtained for the kaolinite mineral arc similar to those in the reported ranges 1.8-2.3 nm and X4-3.0 nm (see Ref. [Z]). However. the values for illitc are very small; this means that the clay surface is not entirely covered and it seems that only the edge surface of the itlitc crystals is covered by asphaltenes. Now the decrease in asphalt thickness for the same clay mineral with Ca’+ is probably due to an increase in hydration enthalpy of the exchangeable cation, so leading to a decrease in the oleophilicity of the Ca”+ minerals.

Surfactant adsorption on asphalt-covered clays (Figs 3 and 4) depends on the nature of the clay’s exchangeable cation and the asphaIt/clay ratio. Thus at surfactant concentrations near the CMC, is higher than the adsorption on Ca’+ substrates on Na+ substrates. A part of this adsorption is due to the precipitation of the ca!cium sa!t ST the surfactant, Ca(DBS)? or Ca(DS),. resulting from the exchange of surfactant sodium ions with the clay’s calciutn ions, as has been described in detail previously [20]. In fact, Ca(DBS)2 or Ca(DS), formed by ion exchange is sedimented with the

50

clay. When higher surfactant concentrations are used. mixed Na/Ca micelles allow any calcium form of the surfactant to bc solubilized (micelle with mixed counter-ions) and therefore not susceptible to sedimentation. It seems that a higher micelle concentration is necessary with sulphate surfacrani to dissoive Ihe calcium salt since its solubilily product is much lower than ihat of (SDBj2Ca. This dlssoiution of calcium salt lends to reduce the level of surfactant adsorption [2l] and enhances the amount of aspha!t desorbed due to solubilization of asphalt in the hydrophobic core of the micclle. In the presence of Na+ s:lbstratcs (Fig. 3) and at surfactant conccntralions above the CMC, the adsorption on the kzolinitc substrate is higher than on illite owing to the lower asphalt adsorption on iIlite. Another important feature of Figs 3 and 4 is that adsorption of SDBS molecules is generally much lower than that of SDS molecules, and SDBS miccllization is preferred rather than adsorption. Asphalt desorption isotherms from clays by SDBS and SDS are shown in Figs 5 and 6. It can be seen that the amount of asphalt desorbcd Icvcls off with SDS at the CMC and continues to increase with SDBS. The percentage weights of asphalt desorbed with SDBS are twofold higher than with SDS, as given in Table 3. This difference in behaviour of the two surfactants was expected, since the presence of an aromatic ring in the hydrophobic part of the SDBS molecule, as compared with SDS, leads to an increase in interaction with asphalt, thus reducing SDBS adsorption and increasing asphalt desorption from clay. Conclusion In the present study we showed that asphalt adsorption from water-saturated toluene on illite was much lower than that on kaolinite. Cal+ clays, compared with Naf clays, display a slight decrease in asphalt adsorption. This decrease is due to the higher hydration of Ca”+ cations. Adsorption isotherms of anionic surfactants such

as

SDS and SDBS on asphalt-clay substrates exhibited generally complex adsorption phenomena with maxima near the CMC, followed by a decrease. by SDBS was The amount of asphalt desorbed t:lv~oftild higher ihan that dcsorbed by SDS. Nil+ clays, as compared to Ca”+ clays, show a siight by the two in asphalt desorption decrease surfactants. All thcsc results show the high olcophilic character of kaolinite minerals as compared to illite clays. They also emphasize the influence of the molecular structure of the surfactant in the oil recovery process.

Achowledgements This work was initiated with support from the Centre National de la Recherche Scientifque and Association de Recherche des Techniques d’Etucie du PCtrole, under the CNRS-ARTEP agreement “Additifs Chimiques pour la R&uperation Assist& des Hydrocarbures”. The authors are indebted to the Soci@tCs Nationales ELF-Aquitaine, C.F.P. TOTAL and I.F.P.

References D.ivi. Clcmcntz. Clays Clay iviincr.. 24 (1970) 312-319; J. Pet. Tcchnol.. 29 (1977) IOhl-1066. J.P. Dickic. M.N. Halicr and T.F. Yen. J. Coiioid Intcrlucc Sci.. 29 (1969) 475-484. S.H. Collins and J.C. Mclrosc. Paper SPE I IX00 prcscntcd at Symp. on Oiifieid and Gcothcrmai Chemistry. Sot. Pet. Eng.. Denver, CO, i-3 June 1983. 3 E. Czornccka and J.E. Giiiott. Clays Clay Miner.. 28 (1980) 197-203. 5 S.T. Dubeg and M.H. Waxman, Paper SPE 18462 prcsentcd at Symp. on Oillicld Chemistry. Sot. Pet. Eng., Houston. TX, 8-10 February 1989. 6 G. Fritschy and E. Pnpirer, Fuel. 57 (1978) 701-704. 7 M. Prats and W.C. Miilcr. J. Pet. Tcchnoi., 3.5 (1973) i3611367. 8 G.P. Ahcarn. J. Am. Oil Chcm. 2x., 46 (1969) 540A-544A. 9 J.J. Novosad. E.B. Maini and A. Hunng, J. Can. Pet. Tcchnoi.. 25 (1986) 42. and J.J. Novosad, Rev. Inst. Fr. Pet.. 43 10 K. Mannhardt (1988) 659. K. Mannhard:. L.L. Schramm and J.J. Novosnd, Preprint, II

B. .Sifl~w ~‘1c~i./Colltrids Swfiwes

69 (1992) 45-51

SPE paper 20463, 65th Annu. Technol. Conf. SPE, New Orleans, LA, 23-26 September 1990. 12 M. Robert and D. Tessicr, Ann. Apron.. 25 (1974) 559-882. 13 S. CaiKre and S. Hcnin (Eds), MinCralogic dcs Argiles, Masson, Paris, 1963. !4 D-r a... Hang and C-.?I?. Brindlcy, Clays Clay Miner.. IX (1970) 203-212. I5 B. Siffcrt. A. Jada and F. Diyani, Appl. C!ay Sci., in press, and Ref. [6] cited thcrcin. 16 M.E. Labib, Colloids Surfaces, 29 (1988) 293-304.

51 17 18 19 20 21

V.W. Ried, G.F. Longmann and B. Hcinerthe. Tcnside, 4 (1967) 292-304; 5 (1968) 90-96. T.F. Yen, J.G. Erdman and S.S. Pollack, Anal. Chum., 33 (1961) 1587-1594. S. Parkash, S. Moschopcdis and J. Speight, Fuel, 58 (1979) 877-882. B. Siffcrt and J.P. Zundcl, Clay Miner.. 20 [ 1985) 189-208. J.P. Zundel and B. Silfcrt. in J.M. Cases (Ed.). Interactions Solid+Liquidc Dans Its Milicux Poreux, Technip Nancy, February 1984. pp. 447-463.