pluronic × tetronic polyols: study of their properties and performance in the destabilization of...

9
Journal of Colloid and Interface Science 271 (2004) 232–240 www.elsevier.com/locate/jcis PLURONIC × TETRONIC polyols: study of their properties and performance in the destabilization of emulsions formed in the petroleum industry Claudia R.E. Mansur, a,Sheila P. Barboza, a Gaspar González, b and Elizabete F. Lucas a a Instituto de Macromoléculas, Universidade Federal do Rio de Janeiro (IMA/UFRJ), C.T., Bloco J, P.O. Box 68525, 21945-970, Rio de Janeiro, RJ, Brazil b Petrobras Research Center (CENPES/PETROBRAS), Ilha do Fundão, Q.7, 21949-900 Rio de Janeiro, RJ, Brazil Received 14 May 2003; accepted 13 November 2003 Abstract In this work, a new family of branched poly(ethylene oxide–propylene oxide) (PEO–PPO) block copolymers designed as TETRONIC polyols is evaluated and compared to linear PEO–PPO block copolymers designed as PLURONIC polyols. Additives have been employed as well in order to improve solubility of these materials in aqueous solution. Such additives include the sodium p-toluene sulfonate (NaPTS) hydrotrope and concentrated hydrochloric acid. Solubility tests and aqueous solution surface tension data showed consistent results: the structure of the block PEO–PPO copolymers exerts a huge influence on their solubility in water. The solubility of such copolymers is increased by the presence of the sodium toluene sulfonate (NaPTS) hydrotrope. The presence of HCl caused increased solubility for the copolymer TETRONIC polyol only, the effect being less than that observed for the hydrotrope. It is concluded that as regards emulsion stabilization, TETRONIC copolymer polyols perform better. Correlation between structure and properties leads to the optimization of block PEO–PPO copolymer selection aiming at using these materials for the separation of petroleum industry emulsions. 2003 Elsevier Inc. All rights reserved. Keywords: Hydrotropy; Solubility; Nonionic surface agents; Polyoxides; Demulsifying agent 1. Introduction Surface agents may be used in the petroleum industry, in tertiary petroleum recovery as well as in other processes, such as, for example, the preparation of drilling well fluids and the separation of water–oil emulsions [1]. Processes for water–oil emulsion breaking are very relevant since emul- sions occur naturally during petroleum production conse- quent to the prevalence of the oil, water, and gas system in a reservoir. Phase separation is made necessary since gas is of eco- nomical interest for the industry. As regards water, it should be withdrawn in view of its high salt content and its tendency to form emulsions having viscosities higher than those of the dehydrated oil. This behavior influences the dimensioning of * Corresponding author. E-mail addresses: [email protected] (C.R.E. Mansur), [email protected] (G. González). the pumping and transfer system and oil tanking and causes scale and corrosion drawbacks in the oil export lines [2]. The efficacy of a surface agent in a particular use is intimately linked to its chemical structure as well as its physical–chemical solution properties. Data on solubility as a function of concentration, temperature, aggregation, and adsorption are of paramount importance to the understand- ing of the surfactant behavior. The evaluation of solubility in aqueous solution of non- ionic surface agents is important in view of the fact that such surface agents may show phase separation as a result of in- creased temperature. Before a phase separation is observed, such surface agents may be soluble in the aqueous solution not as monomers but rather as molecular aggregates, known as micelles [3,4]. Our research group is involved with various studies us- ing nonionic surface agents based on poly(ethylene oxide– propylene oxide) (PEO–PPO) block copolymers of different structures, the behavior of such compounds being evaluated in aqueous solution, using different physical–chemical char- 0021-9797/$ – see front matter 2003 Elsevier Inc. All rights reserved. doi:10.1016/j.jcis.2003.11.034

Upload: claudia-re-mansur

Post on 26-Jun-2016

218 views

Category:

Documents


0 download

TRANSCRIPT

Page 1: PLURONIC × TETRONIC polyols: study of their properties and performance in the destabilization of emulsions formed in the petroleum industry

TRONICemployed)results: theymers isility for theemulsionof block

Journal of Colloid and Interface Science 271 (2004) 232–240www.elsevier.com/locate/jcis

PLURONIC× TETRONIC polyols: study of their propertiesand performance in the destabilization of emulsions formed

in the petroleum industry

Claudia R.E. Mansur,a,∗ Sheila P. Barboza,a Gaspar González,b and Elizabete F. Lucasa

a Instituto de Macromoléculas, Universidade Federal do Rio de Janeiro (IMA/UFRJ), C.T., Bloco J, P.O. Box 68525, 21945-970,Rio de Janeiro, RJ, Brazil

b Petrobras Research Center (CENPES/PETROBRAS), Ilha do Fundão, Q.7, 21949-900 Rio de Janeiro, RJ, Brazil

Received 14 May 2003; accepted 13 November 2003

Abstract

In this work, a new family of branched poly(ethylene oxide–propylene oxide) (PEO–PPO) block copolymers designed as TEpolyols is evaluated and compared to linear PEO–PPO block copolymers designed as PLURONIC polyols. Additives have beenas well in order to improve solubility of these materials in aqueous solution. Such additives include the sodiump-toluene sulfonate (NaPTShydrotrope and concentrated hydrochloric acid. Solubility tests and aqueous solution surface tension data showed consistentstructure of the block PEO–PPO copolymers exerts a huge influence on their solubility in water. The solubility of such copolincreased by the presence of the sodium toluene sulfonate (NaPTS) hydrotrope. The presence of HCl caused increased solubcopolymer TETRONIC polyol only, the effect being less than that observed for the hydrotrope. It is concluded that as regardsstabilization, TETRONIC copolymer polyols perform better. Correlation between structure and properties leads to the optimizationPEO–PPO copolymer selection aiming at using these materials for the separation of petroleum industry emulsions. 2003 Elsevier Inc. All rights reserved.

Keywords:Hydrotropy; Solubility; Nonionic surface agents; Polyoxides; Demulsifying agent

stry,ses,idss forul-se-in a

f eculd

ncytheg of

uses

isitsasandand-

n-uchof in-erved,lutionnown

us-ide–entated

har-

1. Introduction

Surface agents may be used in the petroleum induin tertiary petroleum recovery as well as in other processuch as, for example, the preparation of drilling well fluand the separation of water–oil emulsions [1]. Processewater–oil emulsion breaking are very relevant since emsions occur naturally during petroleum production conquent to the prevalence of the oil, water, and gas systemreservoir.

Phase separation is made necessary since gas is onomical interest for the industry. As regards water, it shobe withdrawn in view of its high salt content and its tendeto form emulsions having viscosities higher than those ofdehydrated oil. This behavior influences the dimensionin

* Corresponding author.E-mail addresses:[email protected] (C.R.E. Mansur),

[email protected] (G. González).

0021-9797/$ – see front matter 2003 Elsevier Inc. All rights reserved.doi:10.1016/j.jcis.2003.11.034

o-

the pumping and transfer system and oil tanking and cascale and corrosion drawbacks in the oil export lines [2].

The efficacy of a surface agent in a particular useintimately linked to its chemical structure as well asphysical–chemical solution properties. Data on solubilitya function of concentration, temperature, aggregation,adsorption are of paramount importance to the understing of the surfactant behavior.

The evaluation of solubility in aqueous solution of noionic surface agents is important in view of the fact that ssurface agents may show phase separation as a resultcreased temperature. Before a phase separation is obssuch surface agents may be soluble in the aqueous sonot as monomers but rather as molecular aggregates, kas micelles [3,4].

Our research group is involved with various studiesing nonionic surface agents based on poly(ethylene oxpropylene oxide) (PEO–PPO) block copolymers of differstructures, the behavior of such compounds being evaluin aqueous solution, using different physical–chemical c

Page 2: PLURONIC × TETRONIC polyols: study of their properties and performance in the destabilization of emulsions formed in the petroleum industry

C.R.E. Mansur et al. / Journal of Colloid and Interface Science 271 (2004) 232–240 233

PPOion-the

re-of

era-eense,

r hyeasblepic

saltssuridsthis

ly-oly-m-as

hel as

ithofad-)

T-O)ur-

asioncidna-

ersog-nu-

POte-t ofolu-PO

re as

ly-ad-

ghtsS-t, atben-

siondexenel-

ar-ssi-

asnanceel

om-orm

er-thetedar-the

O

testy ade-

aredso-

eenwasared.

EO–olu-lu-

acterization techniques. The results show that for PEO–block copolymers, structure vs properties vs use relatships are coherent and very useful in the prediction ofperformance of emulsion-breaking additives [5–9].

One of the strategies envisaged for minimizing theduced solubility that is observed for aqueous solutionsnonionic surface agents resulting from increased temptures is the use of additives. The literature [10–12] has breporting the use of some kinds of additives for this purposuch as a class of compounds known as hydrotropes odrotropic agents. Such substances have the ability to incrthe solubility of organic compounds that are slightly soluin water. However, the molecular mechanism of hydrotrosolubilization is not yet well known.

Other additives are also evaluated, among which areand acids. Some salts may reduce the hydration of theface agent molecules, reducing its solubility, while acmay form a complex with a surface agent ether group,complex being more soluble in aqueous solution.

In this work, the aqueous solutions of branched po(ethylene oxide–propyleneoxide) (PEO–PPO) block copmers, known as TETRONIC polyols, is evaluated and copared to linear (PEO–PPO) block copolymers, knownPLURONIC polyols. This study aimed at evaluating tinfluence of the structure of such copolymers, as welobtaining data on their properties in aqueous solution wand without the presence of additives, on the efficacythe copolymers as emulsion-destabilizing agents. Theditives used were the sodiump-toluene sulfonate (NaPTShydrotrope and concentrated hydrochloric acid.

2. Experimental

2.1. Materials

Bifunctional (PLURONIC) polyols and branched (TERONIC) polyols were employed in this work as (PEO–PPblock copolymers. These industrial copolymers were pchased from BASF.

The sodiump-toluene sulfonate (NaPTS) hydrotrope wpurchased from COEMA S.A. do Brasil in aqueous solutat a concentration of 2.10 M. Concentrated hydrochloric awas purchased from Vetec Química Fina Ltda. Brasil, alytical grade. It was also employed as an additive.

The structural characterization of PEO–PPO copolymwas carried out with the aid of size exclusion chromatraphy (SEC), vapor pressure osmometry, and hydrogenclear magnetic resonance (1H NMR).

The physical–chemical characterization of PEO–Pblock copolymers was carried out using the following staof-the-art techniques: (i) assessment of the cloud pointhe PEO–PPO block-copolymer-containing aqueous stions; (ii) surface tension measurements of the PEO–Pblock copolymer aqueous solutions at a fixed temperatua function of the concentration.

-e

-

Finally, the performance of the PEO–PPO block copomers as emulsion destabilization agents with or withoutditives was evaluated.

2.2. Structural characterization of the PEO–PPOblock copolymers

2.2.1. Vapor pressure osmometry (VPO)Measurements of number average molecular wei

( �Mn) of PEO–PPO copolymers were obtained in a WECAN vapor pressure osmometer, with toluene as solven60◦C. The apparatus standard was toluene-solubilizedzyl.

2.2.2. Size exclusion chromatography (SEC)PEO–PPO copolymers were analyzed in a size exclu

chromatograph, Model Waters 600E, with a refractive indetector and columns made up of styrene–divinylbenzcopolymer (104–103–500–100 Å). THF was used as sovent. A calibration curve was obtained from low-moleculweight polystyrene standards. This technique made it poble to obtain the polydispersion (�Mw/ �Mn) of the materials.

2.2.3. Hydrogen nuclear magnetic resonance (1H NMR)The composition of the PEO–PPO block copolymers w

assessed by means of hydrogen nuclear magnetic reso(1H NMR). Spectra were obtained from a Varian ModVXR-300 300-MHz nuclear magnetic resonance spectreter. All samples were analyzed in deuterated chlorofsolutions at 30◦C.

The composition of the block copolymers was detmined by a conventional calculation method based onclassical principle that the peak area is directly correlato the number of hydrogen nuclei in that region. Peakeas were calculated with the aid of software supplied bymanufacturer.

2.3. Physical–chemical characterization of the PEO–PPblock copolymers

2.3.1. Shaping a temperature vs concentrationphase diagram

Cloud point measurements were obtained using atube immersed in a water-containing beaker heated bheating plate. A thermometer placed inside the test tubetermined temperatures. Duplicate solutions were prepfor each point and two measurements were run for eachlution. Cloud point was determined by the average betwthe measurements where evidence of the first cloudinessobserved and the temperature where cloudiness disappe

Temperature vs concentration phase diagrams for PPPO block copolymers were drafted using aqueous stions, sodiump-toluene sulfonate-containing aqueous sotions, and HCl-containing aqueous solutions.

Page 3: PLURONIC × TETRONIC polyols: study of their properties and performance in the destabilization of emulsions formed in the petroleum industry

234 C.R.E. Mansur et al. / Journal of Colloid and Interface Science 271 (2004) 232–240

K10

r/airous

nsio%

sateul-zil)tion

atedsts,

theolledasin.

ereol-

tson-

r the

withdeofandhe

on-uctca-entsm toicaldi-

esl and

ba

enttec-Ctionple

nksride

urewithon-

tru-ideheoilyeffi-

EC,

theowlec-n ofper-

n

opo-rvesfor

or theis

ersasturefor

t atare

larU-s

2.3.2. Surface tension studiesSurface tension measurements were run in a Model

Krüss digital tensiometer at 30◦C.Surface tension measurements were run for the wate

interface, the copolymers being dissolved in the aquephase. For each copolymer a plot of average surface te(in mM/m) against the logarithm of the concentration (inw/v) was drafted.

2.4. Performance evaluation of the PEO–PPOblock copolymers

2.4.1. Preparation of synthetic water–oil (W/O) emulsionThe performance of some surface agents was evalu

in the laboratory from a synthetic (50/50 by volume) emsion obtained from a Campos Basin (Rio de Janeiro, Brapetroleum oil and a NaCl aqueous solution of concentra70 g/l.

2.4.2. Water–oil (W/O) emulsion separation testsThe performance of PEO–PPO copolymers was evalu

using water–oil gravitational separation tests or Bottle Teusing the as-prepared emulsion.

Tests were run by placing the test tube containingemulsion and the surface agent in a temperature-contrbath at 60◦C after vigorous agitation. Water separation wobserved at time intervals of 3, 6, 9, 12, 15, 18, and 21 mIn view of the high viscosity of the surface agents they wpreviously diluted in a xylene–ethanol solution (1:1 by vume).

2.4.3. Surface agents’ performance as flocculating agenAqueous solutions of nonionic surface agents at a c

centration of 0.1% were tested as flocculating agents foW/O emulsion (oily water) in a Jar Test.

Synthetic oily water used in the tests was preparedthe aid of a Turrax PT 3100 mixer. Oily water was maup of brine, which mimicked the marine environment55,000 ppm salt concentration (having sodium chloridecalcium chloride in the amounts of 10:1) and oil from tCampos Basin, Rio de Janeiro, Brazil.

2.4.4. The Jar TestThe Jar Test, a system for evaluating coagulation, c

sists in agitating the oily water test sample with the prodfor particle agglomeration and therefore for water clarifition. Tests were first run at 350 rpm and then surface agwere added at concentrations of 0, 10, 50, and 100 ppeach beaker. After 1-min homogenization of the chemin oily water, rotation was reduced to 40 ppm for an adtional 14 min for flock formation. After 20 min the samplwere collected for assessment of the total recoverable oigrease (TOG).

n

d

2.4.5. Assessment of the oil content in water using Horioil concentration monitoring analyzers (OCMA-350)

The principle of the technique for determining the contof oil and grease in emulsions is based on infrared detion by the OCMA-350 instrument of the amplitude of C–and C–H bonds present in a sample, making a correlawith the amount of solvent used and providing the samoil concentration in ppm.

Based on the fact that its structure bears only C–Cl lithat are not detected by the instrument, carbon tetrachlowas chosen as solvent for the extraction process.

At first, the instrument is adjusted to zero value with pcarbon tetrachloride and immediately afterward gaugeda standard oil solution in carbon tetrachloride at a fixed ccentration.

TOG measurement of a sample in the OCMA-350 insment was run by first extracting it in carbon tetrachlor(to withdraw oil from the oily water) and then making treading and correlating it with the blank (extracted purewater). This procedure makes it possible to obtain thecacy of a product as flocculating agent.

3. Results and discussion

Table 1 shows results of analyses obtained through SVPO, and1H NMR techniques.

Molecular weights and structures of copolymers ofPLURONIC and TETRONIC polyols were selected to allcomparison between the families. The objective of this setion was to evaluate the influence of structure/compositiothe PEO–PPO copolymers on the physical–chemical proties of their solutions.

3.1. Physical–chemical characterization of PEO–PPOcopolymers in aqueous solution

3.1.1. Temperature vs concentration in aqueous solutiophase diagrams

Phase diagrams in aqueous solution for PEO–PPO clymers are illustrated in Fig. 1. It can be seen that the culimit the phase separation of each copolymer solution:temperatures above each curve there are two phases fcorresponding copolymer solution, while below it, thereonly one phase.

Upon reviewing the results collected for the copolymof the PLURONIC polyol type it may be observed thattheir concentration in solution is increased, the temperavalues corresponding to cloud points are reduced. Ascopolymers of the TETRONIC polyol type, data show thareduced concentrations, cloud points for this copolymerreduced and that at higher concentrations (above 3 g/dl), thepoints remain practically constant.

As expected, in view of similar features (molecuweight and EO/PO ratio—Table 1), data obtained for PLRONIC copolymer polyols show similar solubility. A

Page 4: PLURONIC × TETRONIC polyols: study of their properties and performance in the destabilization of emulsions formed in the petroleum industry

C.R.E. Mansur et al. / Journal of Colloid and Interface Science 271 (2004) 232–240 235

Table 1Characterization of PEO–PPO block copolymers by SEC, VPO, and1H NMR

Copolymer �Mw/ �Mna �Mn

b EO/PO ratioc Copolymer structure

PLURONIC 1 1.30 4720 2.80 HO–(PO)m–(EO)n–(PO)m–OHPLURONIC 2 1.20 4180 2.10 HO–(PO)m–(EO)n–(PO)m–OHPLURONIC 3 1.60 8000 6.20 HO–(EO)n–(PO)m–(EO)n–OH

TETRONIC 1 1.70 4250 1.30

HO–(PO)m–(EO)n (EO)n–(PO)m–OH

N–(CH2)–(CH2)–N

HO–(PO)m–(EO)n (EO)n–(PO)m–OH

TETRONIC 2 1.50 6050 0.30

HO–(PO)m–(EO)n (EO)n–(PO)m–OH

N–(CH2)–(CH2)–N

HO–(PO)m–(EO)n (EO)n–(PO)m–OH

TETRONIC 3 1.60 8250 3.40

HO–(EO)n–(PO)m (PO)m–(EO)n–OH

N–(CH2)–(CH2)–N

HO–(EO)n–(PO)m (PO)m–(EO)n–OH

TETRONIC 4 1.65 9080 3.65

HO–(EO)n–(PO)m (PO)m–(EO)n–OH

N–(CH2)–(CH2)–N

HO–(EO)n–(PO)m (PO)m–(EO)n–OH

a By SEC.b By VPO.c By 1H NMR.

solu-

fheof

be-IC

12

ndey-1

heiorNIClyololy-

ddi-retedlu-

4t the

s be-thehy-

usea-ech-

y-con-sol-inTheon of

tionsnderith

ons.1,-

Fig. 1. Phase diagrams of PEO–PPO block copolymers in aqueoustions.

for the TETRONIC copolymer polyols, the solubility othe TETRONIC 2 copolymer is lower than that of tTETRONIC 1 copolymer, this being expected in viewthe lower EO/PO ratio of this latter.

Based on data from Table 1, from a comparisontween the families of the PLURONIC and TETRONpolyol copolymers it was expected that the TETRONICcopolymer would be more insoluble than the PLURONICcopolymer in view of the higher molecular weight alower EO/PO ratio of the former, these features conving a more hydrophobic character to the TETRONICcopolymer. However, according to the plot of Fig. 1, tTETRONIC 1 copolymer is more soluble. This behavseems related to the chemical structure of the TETROseries of polyols: these copolymers contain nitrogen. Poamines such as these typically behave differently from p

ols such as PLURONIC because the amines impart ational hydrophilicity. Moreover, the TETRONIC polyols abranched and bears (hydrophilic) EO moieties distributhroughout its chains, this possibly making its water sobility easier.

Data for PLURONIC 3, TETRONIC 3, and TETRONICare not shown since these have been soluble throughouwhole concentration range and temperature studied. Thihavior has been attributed to the high EO/PO ratio ofcopolymers (Table 1), which conveys to them a strongdrophilic character.

3.1.2. Phase diagrams for aqueous solutions ofhydrotrope-containing copolymers

The use of additives, known as hydrotropes, may caimproved solubility for block PEO–PPO copolymers in wter. The evaluation of these solutions could assess the manisms possibly involved in this phenomenon.

From the literature [13,14] it could be seen that hdrotropes may form structures associated with a certaincentration and temperature, their action in increasingubility of organic compounds that are slightly solublewater depending on the formation of such structures.NaPTS aggregation point was observed at a concentrati0.5 M [5].

Phase diagrams of NaPTS-containing aqueous soluof PEO–PPO block copolymers for the PLURONIC aTETRONIC polyols are shown in Fig. 2. The copolymconcentration was constant and equal to 1 (% w/v), wthe NaPTS concentration being varied in these solutiSuch diagrams could be obtained with the PLURONICPLURONIC 2, TETRONIC 1, and TETRONIC 2 copoly

Page 5: PLURONIC × TETRONIC polyols: study of their properties and performance in the destabilization of emulsions formed in the petroleum industry

236 C.R.E. Mansur et al. / Journal of Colloid and Interface Science 271 (2004) 232–240

utions

studallin-r, in

ue-flu-bovse-inoly-ag-

hasnginheirfectlva-

ag-thatr isg-ares, it

in-er

ercid

nsonsuseax-

tionility.t in

utions

tedin-

velsto-

1ed an-

o17].in-

thathatthe

andfec-

O

erses,ctionataur-0rsoly-

ondoint.oturveere

Fig. 2. Phase diagrams of PEO–PPO block copolymers in aqueous sol(1 wt%), as a function of NaPTS concentration.

mers only, these having shown phase separation in theied concentration range. It may be observed that forcopolymer solutions, the cloud point increases with thecrease in NaPTS concentration. Curve profiles are similaspite of the different solubility of these copolymers in aqous solution (Fig. 2). Besides, such copolymers are inenced by the NaPTS presence only at concentrations a0.5 M. Behavior observed in the literature [15], where aries of PLURONIC polyol-like copolymers was studiedthe presence of NaPTS and the solubility of these copmers was more thoroughly increased, was similar to thegregation concentration of this hydrotrope. This worksuggested that the NaPTS aggregates should be arrathemselves around the EO units, in order to prevent tdehydration at high temperatures, or alternatively, to afsomehow the EO–water interaction, thus increasing sotion ability.

In another study [9] and with the aid of the nuclear mnetic resonance technique (NMR) it could be shownthe interaction of aggregated NaPTS with the copolymelower in the micelle form than in the monomer form, sugesting that free copolymer molecules in solution onlyable to penetrate the organized NaPTS network. Thuseems that aggregated NaPTS is performing better tocrease the solubility before the formation of the copolymmicelles.

3.1.3. Phase diagrams of aqueous solutions ofacid-containing copolymers

Fig. 3 shows the variation in cloud points for copolymsolutions (at 1% w/v) as a function of the hydrochloric a(HCl) concentration.

Obtained data indicate that the TETRONIC solutioshow increased solubility even at low HCl concentratiand that the increase in acid concentration does not cacontinuous solubility increase; it seems that there is a mimum hydration value above which the acid concentraincrease does not strongly influence the solution solubThis behavior can be attributed to the nitrogen presen

-

e

g

a

Fig. 3. Phase diagrams of PEO–PPO block copolymers in aqueous sol(1 wt%), as a function of HCl concentration.

the TETRONIC chains. This amine part can be protonato add a positive charge to the polymer, which greatlycreases water solubility. The protonation of the amine leoff when complete (all equivalents of amine are fully pronated).

On the other hand, curves obtained for PLURONICand 2 copolymers show that the presence of HCl causslight reduction in their solubility when low acid concetrations were used. In this case, it seems that the Cl− ionis exerting a stronger influence than the H+ ion. Literaturedata indicate that the Cl− ion causes lower solubility due tthe lower hydration of the surface agent molecules [16,For higher HCl concentrations, a slight solution solubilitycrease could be observed, more discrete, however, thanobserved for TETRONIC solutions. It may be possible tthe branched structure of the TETRONIC family makesether group hydration easier.

Upon comparison of the effects caused by NaPTSHCl, it may be observed that NaPTS is much more eftive than HCl in increasing the solubility of the PEO–PPcopolymer solutions.

3.1.4. Surface tension studies of PEO–PPO copolymeraqueous solutions

In order to study the activities of PEO–PPO copolymat the water/air interface and determine CMC [18,19] valusurface tension measurements were carried out as a funof the copolymer concentration in aqueous solution. Dare illustrated in Fig. 4. For all copolymers the water sface tension is reduced from 72 mN/m to values around 3to 40 mN/m. TETRONIC 2 and PLURONIC 1 copolymewere not analyzed using this technique: for the first copmer the temperature used for the tests (30◦C) was aboveits cloud point at 1% w/v in aqueous solution; for the seccopolymer, the temperature was very close to its cloud p

The CMC value for the TETRONIC 1 copolymer was ncalculated, since its surface tension vs concentration c(Fig. 4) does not show an inflection point. CMC data wopposite to the expected.

Page 6: PLURONIC × TETRONIC polyols: study of their properties and performance in the destabilization of emulsions formed in the petroleum industry

C.R.E. Mansur et al. / Journal of Colloid and Interface Science 271 (2004) 232–240 237

con-

that

tionntraondponettion

en-greeby

avethef thence,on-ntrarves

--Oadthend

func-

uc-ters,ps

eyers

O–facetion

be-g. 4.tantoint.aftergenting

sts itationmerasthe

theag-t, foriony beer,les

ingame5);

Fig. 4. Surface tension as a function of aqueous copolymer solutionscentrations, at 30◦C.

Copolymer surface tension curves obtained indicateat low concentrations, up to values close to 10−3%, thosecurves show a discontinuity. Beyond that value, the solusurface tension keeps decreasing until it attains a concetion where the surface tension variation is minimal (secdiscontinuity). This behavior has been observed mainly uanalyzing PLURONIC copolymer curves. Alexandridisal. [20] have studied the surface tension curves as a funcof the PLURONIC 3 copolymer aqueous solution conctration obtained at two temperatures. Results obtained awith those of the present work and are also confirmedother experimental methods. A few authors [21,22] hattributed the occurrence of the first discontinuity insurface tension curves to the conformational change ocopolymer chains in the aqueous solution surface. Siafter CMC, the solution surface tension should be kept cstant, the CMC values have been attributed to the concetion where the second discontinuity observed in these cuoccurred.

CMC values for TETRONIC copolymer polyols (TETRONIC 3 and TETRONIC 4) were similar those of PLURONIC 3 copolymer in spite of the fact that their EO/Pratios were lower (Table 1). This behavior confirms what halready been suggested for the solubility study (Fig. 1):TETRONIC polyols own the amine groups in the chains a

-

-

Fig. 5. Surface tension of aqueous copolymer solutions (1 wt%) as ation of NaPTS concentrations, at 30◦C.

present higher hydrophilicity due to their branched strture. In TETRONIC copolymer polyols there is a betdistribution of the hydrophilic moieties along their chainwhich may improve solubility. Besides, the amine grouof TETRONIC polyols cause higher hydrophilicity and thmay be responsible for a looping structure of the copolymforming the micelle.

3.1.5. Surface tension study of aqueous solutions ofhydrotrope-containing PEO–PPO block copolymers

In order to study the influence of the presence of PEPPO copolymers in the NaPTS aqueous solution, surtension curves as a function of the NaPTS concentracontaining 1% w/v copolymer were drafted (Fig. 5). Thehavior suggested by such curves is opposite to that of FiWith increasing NaPTS, surface tension remains consand starts to increase after the hydrotrope aggregation pThis occurs because the solubility increase is strongerthe molecular aggregation that displaces the surface afrom the surface toward the center of the solution, causa surface tension increase [7,8]. From the conducted temay be observed that the NaPTS aggregation concentrdepends on the structure and composition of the copolyadded to the solution [6,7]. PLURONIC 2 copolymer hshown a stronger influence on the NaPTS solution thanTETRONIC 1 copolymer. The presence of micelles ofTETRONIC copolymer polyol does not alter the NaPTSgregation concentration in aqueous solutions. In contrasthe PLURONIC copolymer polyol the NaPTS aggregatoccurs at a higher concentration (1 M). This behavior maassociated with micelle formation by the latter copolymwhich would entail a larger number of free water molecuto solubilize NaPTS.

3.1.6. Surface tension studies of acid-containingPEO–PPO copolymer aqueous solutions

Fig. 6 shows curves of HCl aqueous solutions containPEO–PPO copolymers. Such curves have shown the sbehavior observed with the presence of NaPTS (Fig.

Page 7: PLURONIC × TETRONIC polyols: study of their properties and performance in the destabilization of emulsions formed in the petroleum industry

238 C.R.E. Mansur et al. / Journal of Colloid and Interface Science 271 (2004) 232–240

func-

ig. 3the

Clsoluse,rvedof

ers

erstleoccustsing

abi-s ae ar

on-acy

d toed.etro-des

hatsur-stereoi-ientsur-nd,on-re-rfor-o ofion.was

oftiond thee off these-sing

a-r-e

om-d at

thatv-that

Fig. 6. Surface tension of aqueous copolymer solutions (1 wt%) as ation of HCl concentrations, at 30◦C.

however, as already observed in the phase diagrams of Fthe presence of this additive was more effective forTETRONIC 1 copolymer.

Besides, it may be observed that it is only at higher Hconcentrations that surface tension figures of aqueoustions of PLURONIC 2 copolymers show a slight increaconfirming at the same time the behavior already obsein the solubility study of this copolymer in the presenceHCl.

3.2. Performance evaluation of the PEO–PPO copolym

A performance evaluation of the PEO–PPO copolymin water–oil emulsions was run with the aid of the BotTest. Besides, surface tension agents were tested as fllant in oil in water emulsions by means of flocculation tein the Jar Test equipment, followed by TOG analysis usOCMA-350.

3.2.1. Water-in-oil emulsions (W/O)Usually, the selection of a commercial emulsion-dest

lizing agent starts with the laboratory Bottle Test. This imethod used to assess the emulsion stability and therdifferent procedures.

,

-

-

e

Performance evaluation tests in the field for emulsidestabilizing products have been showing that the efficof the gravitational separation process is intimately linkethe efficacy of the emulsion-destabilizing product employBesides, it has also been observed that for each kind of pleum oil there is a certain commercial product that provithe best desired result for the oil and water separation.

In the literature there is an empirical observation tmakes the basis for the choice of emulsion breakers, theface agent hydrophilic–lipophilic balance (HLB). For moof the nonionic surface agents, the HLB number is a mindication of the weight percentage of the hydrophilic mety of the molecule. It is also stated that the more efficoil-in-water emulsion breakers (flocculating agents) areface agents of low HLB (less hydrophilic); on the other hathe more efficient water-in-oil emulsion breakers (emulsidestabilizing agents) are those of higher HLB [23]. Thefore, the selection of surface agents designed for pemance tests was directed to products the EO/PO ratiwhich (Table 1) would be suitable to the desired applicat

The performance of block PEO–PPO copolymersevaluated for the concentrations of 36.5 and 162.5 ppmactive matter in the product. The 36.5 ppm concentrawas used since it favors the gravitational separation, an162.5 ppm was set to try to maximize the performancthe tested copolymers. Table 2 shows the performance ogravitational separation of a synthetic emulsion by thelected copolymers. Such performance was calculated uthe equation

(1)EFWO = (VWS/VWT) × 100,

where EFWO = efficacy of water–oil gravitational separtion, % by volume; VWS = volume of water separated duing the test, ml; VWT = volume of total water present insidthe tube, ml.

For the sake of comparison, the performance of a cmercial product A of ascertained efficacy was evaluatethe concentration of 36.5 ppm of active matter.

Based on data listed in Table 1 it may be observedonly the TETRONIC 1 copolymer led to water–oil graitational separation, but at a lower performance thanobserved for commercial product A.

in

Table 2Performance of the gravitational separation of a synthetic A/O emulsion by PEO–PPO block copolymers

Product Concentration EFAO (% v/v)

(ppm) 3 min 6 min 9 min 12 min 15 min 18 min 21 m

Aa 36.5 5.0 51.4 92.0 99.4 100.0 100.0 100.0PLURONIC 2 36.5 0 0 0 0 0 0 0

162.5 0 0 0 0 0 0 0PLURONIC 3 36.5 0 0 0 0 0 0 0

162.5 0 0 0 0 0 0 0TETRONIC 1 36.5 0 0.1 0.2 0.3 4.0 12.0 24.0

162.5 0.1 0.3 2.0 14.0 26.0 34.0 44.0TETRONIC 3 36.5 0 0 0 0 0 0 0

162.5 0 0 0 0 0 0 0

a Commercial product.

Page 8: PLURONIC × TETRONIC polyols: study of their properties and performance in the destabilization of emulsions formed in the petroleum industry

C.R.E. Mansur et al. / Journal of Colloid and Interface Science 271 (2004) 232–240 239

ob-on-theets.ci-upsper-

. 1theT-it

the2)s ofups ofhatidingin-lets

Theer

test

/oiltheof

hilices-e itsr).gerts),

sierm,hy-ers

oly-the

hat,in-the

uldthebe

tedp-c

nts,

nt

ateran-

d for

ly-ithef-

ntsval

y-ericalinshedtiessed

Otheof

ning, asncely-hile

ell

ov-ork,

ford,

er,

ac-

Data obtained from the remaining copolymers are prably associated with the low specificity to act as emulsidestabilizing agents, that is, to the difficulty in displacingnatural emulsifiers from the interface of the water droplThe efficacy of the TETRONIC copolymer may be assoated with its star-like structure, where the EO and PO groare better distributed in its chains, making easier their dission between the phases of the water/oil emulsion.

Besides, it may be observed that TETRONIC 1 (Figsand 4) is not the most water soluble copolymer; inTETRONIC family, the most soluble ones were TERONIC 3 and TETRONIC 4 copolymers. In this caseis possible that the structure is exerting its influence:chain ends of the TETRONIC R (TETRONIC 1 andcopolymers are made up of PO groups; the chain endTETRONIC (TETRONIC 3 and 4) copolymers are madeof EO groups (Table 1). The larger number of PO groupthe TETRONIC 1 copolymer, associated with the fact tthese groups are placed at the chain ends, may be provbetter mobility in the dispersing medium, thus improvingteraction with a larger number of dispersed water drop(from the hydrophilic moieties distributed in its chains).

3.2.2. Oil-in-water (O/W) emulsionsFlocculation tests were run in the Jar Test equipment.

tests have shown that only with TETRONIC 3 copolymthere has been a clarification of the oily water after theas well as the formation of a small number of flocks.

Analogously to what was observed in the wateremulsion-destabilizing tests, the star-like structure ofTETRONIC copolymers seems to make the flocculationoil/water systems easier. In this case, the more hydropstructure of the TETRONIC 3 copolymer as well as the prence of EO groups in its chain ends seems to increasmobility in the dispersing medium (which is now wateThis makes easier the copolymer interaction with a larnumber of dispersed droplets in the system (oil droplefrom the hydrophobic groups distributed in its chains.

In order to obtain better water solubility and make eathe copolymer molecule mobility in the dispersing mediuthe Jar Test experiments were also run using NaTPSdrotrope in the aqueous solutions of the tested copolymContrary to what was expected, the efficacy of the copmers was worsened in the presence of said additive inaqueous solutions. This behavior is due to the fact tas previously observed in Fig. 5, the hydrotrope, uponcreasing the solubility in the aqueous solution, displacescopolymer from the interfaces of such solution. This wocause a lower efficacy in the flocculation process, sincenumber of copolymers in the oil–water interfaces wouldreduced.

The efficacy calculation for the flocculating agents tesin oil removal was run with the aid of the OCMA-350 aparatus. Initial TOG (TOGinitial) contained in the synthetiemulsion was related to final TOG (TOGfinal) obtained afteraddition of the flocculating agent.

.

Table 3Estimate of the efficacy of TETRONIC 3 copolymer as flocculating ageat different concentrations

Copolymer Concentration Flocculating age(ppm) efficacy (%)

TETRONIC 3 0 –10 2950 37

100 51

After the gauging of the OCMA-350 apparatus withfixed oil concentration, each extraction of the oily wasamples (collected after the Jar Test experiment) wasalyzed and the readings from the apparatus were usecalculating TOG in ppm (mg/l),

(2)TOG (mg/l) = apparatus reading(mg/l) × 100 ml

collected sample volume (ml).

Table 3 lists the results for the TETRONIC 3 copomer. The efficacy in oil removal gradually increased wthe increase in copolymer concentration. However, itsficacy was still low when compared to flocculating agenormally used for this purpose, that attain 100% oil remoat lower concentrations.

4. Conclusions

For similar EO/PO ratios, TETRONIC copolymer polols were more water-soluble than PLURONIC copolympolyols. This behavior has been attributed to the chemstructure: the TETRONIC own the amine groups in its chaand present the more hydrophilicity. Moreover, the brancstructure of these copolymers bears EO hydrophilic moiedistributed throughout the chain, making easier the increasolubility of this material.

In spite of the low efficacy of the tested PEO–PPcopolymers, in the emulsion-destabilizing process ofwater/oil system as well as in the flocculation processoil/water systems, the tests have been useful for obtaia correlation between copolymer structure and efficacywell as to confirm the influence of the hydrotrope presein the polymer aqueous solution. TETRONIC R copomers seem to be better emulsion-destabilizing agents wTETRONIC copolymers seem to be better flocculants.

References

[1] G.R. Gray, H.C.H. Darley, Composition and Properties of Oil WDrilling Fluids, Gulf Publishing Company, Houston, 1981.

[2] K. Lissant, in: D.O. Shah, R.S. Schechter (Eds.), Improved Oil Recery by Surfactant and Polymer Flooding, Academic Press, New Y1977.

[3] R.J. Hunter, Foundations of Colloid Science, Clarendon Press, Ox1986.

[4] B. Chu, Z. Zhou, in: M.J. Schick (Ed.), Nonionic Surfactants, DekkNew York, 1987.

[5] I.R. Schmolka, in: M.J. Schick, F.M. Fowkes (Eds.), Nonionic Surftants, Dekker, New York, 1966.

Page 9: PLURONIC × TETRONIC polyols: study of their properties and performance in the destabilization of emulsions formed in the petroleum industry

240 C.R.E. Mansur et al. / Journal of Colloid and Interface Science 271 (2004) 232–240

ppl.

u-

ids

uím.

(7)

hys.

Sci.

n-

89)

NJ,

27

eil-

r 10

ns,

[6] C.R.E. Mansur, C.M.F. Oliveira, G. González, E.F. Lucas, J. APolym. Sci. 66 (1997) 1767.

[7] C.R.E. Mansur, L.S. Spinelli, C.M.F. Oliveira, G. González, E.F. Lcas, J. Appl. Polym. Sci. 69 (1998) 2459.

[8] C.R.E. Mansur, C.M.F. Oliveira, G. González, E.F. Lucas, ColloSurf. A Physicochem. Eng. Aspects 149 (1999) 291.

[9] C.R.E. Mansur, C.R.N. Pacheco, G. González, E.F. Lucas, Rev. QNova 24 (1) (2001) 47.

[10] C.R.E. Mansur, M.R. Benzi, E.F.J. Lucas, Appl. Polym. Sci. 82(2001) 1668.

[11] D. Balasubramanian, V. Srinivas, V.G. Gaikar, M.M. Sharma, J. PChem. 93 (1989) 3865.

[12] H. Schott, J. Colloid Interface Sci. 205 (1998) 496.[13] G. González, E.J. Nassar, M.E.D. Zaniquelli, J. Colloid Interface

230 (2000) 223.[14] H. Schott, J. Colloid Interface Sci. 173 (1995) 265.

[15] R.C. Silva, W. Loh, J. Colloid Interface Sci. 202 (1998) 385.[16] V. Srinivas, G.A. Rodley, K. Ravikumar, W.T. Robinson, M.M. Tur

bull, D. Balasubramanian, Langmuir 13 (1997) 3235.[17] V.P. Iranova, I.N. Topchiyeva, Polym. Sci. U.S.S.R. 31 (19

2594.[18] J. Óscik, Adsorption, Wiley, New York, 1982.[19] W.J. Moore, Physical Chemistry, Prentice–Hall, Englewood Cliffs,

1972.[20] P. Alexandridis, J.F. Holzwarth, T.A. Hatton, Macromolecules

(1994) 2414.[21] K.N. Prasad, T.T. Luong, A.T. Florence, J. Paris, C. Vaution, M. S

ler, F. Puisieux, J. Colloid Interface Sci. 69 (1979) 225.[22] P. Alexandridis, V. Athanassiou, S. Fukuda, T.A. Hatton, Langmui

(1994) 2604.[23] K. Tsujii, Surface Activity. Principles, Phenomena and Applicatio

Academic Press, New York, 1998.