Chapter 5
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Interactions Between Acrylamide—Acrylic Acid Copolymers and Aluminum Ions in Aqueous Solutions Ramine Rahbari, Dominique Sarazin, and Jeanne François Institut Charles Sadron, CRM-EAHP, CNRS-ULP, 6 rue Boussingault, 67083 Strasbourg-Cedex, France
Phase separation, gelation and viscosity of acrylamide-acrylic acid copolymer solutions containing aluminium chloride have been studied as a function of pH, s a l i n i t y and composition of the polymer. In the range of polymer concentration investigated, the most common behavior is phase separation with loss of v i s c o s i t y and formation of large agregates. At pH 5 gelation phenomenon can occur due to the presence of polynuclear ions of aluminium and the conditions of gel formation are studied as a function of salinity. At pH 7, phase separation is due to f l o c c u l a t i o n of Al(OH) p a r t i c l e s by polymer bridges . These behaviors are discussed from A l NMR data giving the f r a c t i o n of A l ions bound on the polymer and from of a model of e l e c t r o s t a t i c interactions. 3
27
The strong interaction of polyvalent cations with polyions is well known to strongly a l t e r the rheological properties of hydrolyzed polyacrylamide used i n the t e r t i a i r y o i l recovery process (1-4). The influence of divalent cations have already been studied(5-7) but the role played by the presence of small quantities of aluminium ions has never been investigated. In a f i r s t part of this paper, we w i l l discuss results of a A1 NMR study of the binding of A l ions on acrylamide-acrylic acid copolymers as a function of pH, at the l i g h t of a simple e l e c t r o s t a t i c model. The second part deals with the phase diagrams , physical gelation and p r e c i p i t a t i o n phenomenon, for different copolymer compositions and under various conditions of concentrations , pH and s a l i n i t y . Experimental i n this study AD10,AD17,AD27 and AD37 (Rhone Poulenc Industries(8) of acrylate content r (mole %) equal to 1.5, 7, 17 and 27 , and 27
0097-6156/89/0396-0124$06.00/0 c 1989 American Chemical Society Borchardt and Yen; Oil-Field Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1989.
5. RAHBARI ET AL.
125
Copolymers and Aluminum Ions 6
of weight average molecular weight M approximately 5*10 . An other sample (PAMNH) (7=0.3% and M =10 ) has been prepared i n our laboratory by photopolymerization. The d e t a i l s concerning the experimental methods used i n this work can be found i n ref. 9 and 10. Solutions of Aluminium Chloride The pure A1C1 solutions neutralized by NaOH contain ions of general formula A l (OH) P , which can be mononuclear (Al , A1(0H) , Al(0H) and* AL(OH) ~) or polynuclear (Al (0H) * and A1 (0H) "P ) and also non ionic species (Al(0H) ). Their amounts depend on the neutralization r a t i o R ( R= (Na0H/AlCl ) according to six diferent equilibrium laws of constants K w
6
w
3
( 3 I -
) +
+ + +
++
+
2
( 3 9
A
2
2
) +
13
3
3
L
p
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+++
3i
(A1 )*K. *f. " > f. * (HV
+
P
(Al^OH) < "*> ) -
1 , P
(1)
where f. i s the a c t i v i t y coefficient of Al.(OH) "P which can be obtained from Debye-huckel expression (11-13). The s o l u b i l i t y of Al i s l i m i t e d by: ( 3 L
) +
+ + +
+++
3
(A1 )*(0H~) < K
(2)
s
By using a set of K and f values found i n l i t e r a t u r e , we have calculated the compositions of A1C1 solutions (without polymer) at two different concentrations (see figure 1). If one considers the pH range of major interest i n application (4.5 < pH < 8) , i t appears: -around pH = 5, for the low A1C1 concentrations only mononuclear species are present while at higher concentrations ,polynuclear ions and non ionic species are preponderant. The time i s also an important parameter since polyions (Al ) progressively disappear and after 6 months aging ,only non ionic species are i n equilibrium with monovalent ions A l ( 0 H ) . 15 days aged solutions have been used i n this study ; The composition of the solutions given in Figure 1 have been confirmed by NMR and correspond to this aging time ( 9,11-12). - around pH = 7, Al(0H) is present at more than 90% and i t has been shown that the size of aggregates depend on concentration and aging time. We have recently shown (14) by electrophoresis measurements that the Al(0H) p a r t i c l e s are p o s i t i v e l y charged and become neutral only after a long time ( 6 months ) of heating at 8 0 ° C . E l a s t i c and q u a s i - e l a s t i c l i g h t scattering measurements have revealed that their size scales as C : at 1 ppm of A l (or 3*10" M/l) , the radius of gyration R is 500 A while at 12 ppm R =15000 A. Moreover these p a r t i c l e s have a form of plaquets as already described(15,16) Model of e l e c t r o s t a t i c interactions It i s well known that the concentration of ionized groups COO" on the polymer chain obeys the c l a s s i c a l law: L
3
3 +
1 3
+
2
3
3
1 , s
5
a
+
p K = (C00")*(H ) / a
where C
i p
(C. - COO") p
(3)
is the molar concentration of carboxylic groups.
Borchardt and Yen; Oil-Field Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1989.
OIL-FIELD CHEMISTRY
Downloaded by UNIV OF ALABAMA on September 15, 2016 | http://pubs.acs.org Publication Date: July 10, 1989 | doi: 10.1021/bk-1989-0396.ch005
126
Figure 1 : A1C1 solutions :Calculated fractions of A l A1(0H) ( ),A1(0H) ( -), A l ( O i l ) / Al (OH) ( ) and Al(OH) ( ) 3
+
2+
+
2
2
+ + +
( (tuv)
3+
13
27
3
Borchardt and Yen; Oil-Field Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1989.
),
5. RAHBARI ET AL.
111
Copolymers and Aluminum Ions
In order to obtain a rough evaluation of the f r a c t i o n of aluminium bound on polymer, we have assumed i n a f i r s t approach: i) the polyelectrolyte effects due to the polymer are n e g l i g i b l e and the d i s t r i b u t i o n of ionic species i n the bulk can be considered as uniform. Such an assumption can be considered as correct i f the polymer concentration c i s higher than c , the c r i t i c a l concentration of chain overlapping. ii) among the different possible interactions between polymer and aluminium species, the most important are the electrostatic interactions between carboxylate groups COO" and the A l t r i v a l e n t ions which are oppositively charged. Then we have taken into account the equations corresponding to the following e q u i l i b r i a , with constants K and K : p
Downloaded by UNIV OF ALABAMA on September 15, 2016 | http://pubs.acs.org Publication Date: July 10, 1989 | doi: 10.1021/bk-1989-0396.ch005
±
(Al (Al
+++
) + 3
+ + + 1 3
Q
(COO")
) + 3 ----(COO")
~
C00 A1
K.
(4)
K
(5)
3
=
C00 A1 3
13
Q
By using the expressions (1) to ( 5 ) , i t is possible to calculate the concentrations of the different ionic (Al.(OH) "P and C00) and non ionic (Al(OH) , COOH, C00 A1 and COO^f^) species i n the mixed A1C1 - polymer solutions as a function of pH and composition. As shown i n Figures 2 and 3, we have found two maxima i n the amount of the "bound" monomeric ions or more precisely the difference between the t o t a l monomeric ions concentration i n absence and presence of polymer ( NMR experiments give this quantity): for pH = 4 and pH — 4.6. Comparison with figure 1 indicates that these maxima correspond to the formation of C00 A1 and C00 A1 respectively. For very aged or very d i l u t e A1C1 solutions where polynuclear ionic species are absent, only one maximum is found, around pH = 4.5. A1 NMR Bottero et A l . (11,12) have shown that A1 NMR allows to distinguish the mononuclear from the polynuclear species of Aluminium ions i n A1C1 solutions. We have performed the same type of studies by adding different amounts of copolymers and we have measured the decrease of monomeric A l ions concentration by increasing the polymer content. Figures 2 and 3 give some examples of results; "Al bound" as measured by NMR is plotted as a function of pH, for two different systems and can be compared with the values calculated for K.-10 * and K =10 . As expected from the model, we observe: i ) Two reproducible maxima at pH s l i g h t l y shifted with respect to predictions , i i ) the amount of A l ions bound onto polymer increases by increasiong r and the same couple of K and K values gives a rather good account of experimental results for 1.5% < r < 30%. This result shows that is reasonable to neglect other type of interactions between aluminium ions and the polymer: for instance coordination binding with amide groups. This f i r s t study is very Important: the good agreement between c a l c u l a t i o n and experiments j u s t i f i e s the previous ( 3 I
3
) +
3
3
3
3
27
27
3
1
16
0
Q
Borchardt and Yen; Oil-Field Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1989.
3
13
128
OIL-FIELD CHEMISTRY
AL "BOUND" / AL TOTAL
0.4h
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0.3-
Figure 2 : Interactions polymer-aluminium : concentration of bound aluminium ions for A l C l (27 ppm ) and AD27 (0.25 g/1 ) F u l l line : Calculated curve ; Dotted l i n e :NMR results 3
Figure 3: Interactions polymer-aluminium : concentration of bound aluminium ions for A1C1 (27 ppm ) and AD37 (0.25 g/1) F u l l l i n e : calculated curve; dotted l i n e :NMR results
Borchardt and Yen; Oil-Field Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1989.
5. RAHBARI ET AL.
Copolymers and Aluminum Ions
hypothesis. Moreover i t c l e a r l y demonstrates that polynuclear ions of A l strongly interact with polymers and w i l l play an important role i n their s t a b i l i t y . p a r t i c u l a r l y around pH 5. However, we must point out that, by hypothesis, the interactions between non i o n i c species of aluminium (A1(0H) are not taken into account i n our c a l c u l a t i o n and i n NMR studies these A l species do not give any s i g n a l . Thus , our model is rather good for pH6. Phase diagrams and v i s c o s i t y This part deals with the s t a b i l i t y of the polymer i n the presence of the different species of aluminium. For strongly charged polyelectrolytes such as polyphosphate or sodium polyacrylate i n the presence of divalent cations ( C a , B a . . . . ) , i t has been shown that p r e c i p i t a t i o n occurs when a given f r a c t i o n of charged groups i s "neutralized" by the binding of the cations and t h i s situation i s r e a l i z e d for a molar concentration of cations of the same order of magnitude than that of charged groups(17,18). In the case of acrylamide-acrylic acid copolymers, the problem becomes more complex since the distance between the charged groups is much higher depending on T. Truong(5,7) has recently shown that the r e l a t i v e p r o b a b i l i t y to form i n t r a or inter molecular bridges must be taken into account. I f intramolecular f i x a t i o n i s preponderant, precipitation can be expected while i n the case where the intermolecular bridgings are favoured physical gelation should occur with or without syneresis effects. From these q u a l i t a t i v e considerations and taking into account only e l e c t r o s t a t i c interactions according to our model, we could expect the following features for the behavior of acrylamidea c r y l i c acid copolymer i n the presence of aluminium: - no interaction with unhydrolyzed polymer (PAMNH) since only e l e c t r o s t a t i c interactions are considered i n the model -for T > 0 , the maximum of i n s t a b i l i t y should be observed at the pH values where the interaction with ionic A l species has found to be maximum i n NMR experiments and no effect i s expected at pH 7 i f r e a l l y only uncharged species of Aluminum are present. Moreover, the high valency and great size of A l ions could lead to gelation. We w i l l summarize the results of a systematical study of these systems by phase t i t r a t i o n , turbidimetry and viscosimetry. The concentration ranges were 0
