Preparation and Application of Nonionic Polypropylene Oxide-G-polyethylene Glycol Copolymer Surfactants as Demulsifier for Petroleum Crude Oil Emulsions

This article was downloaded by: [Ayman M. Atta]On: 22 October 2013, At: 10:21Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House,37-41 Mortimer Street, London W1T 3JH, UK

Journal of Dispersion Science and TechnologyPublication details, including instructions for authors and subscription information:http://www.tandfonline.com/loi/ldis20

Preparation and Application of Nonionic PolypropyleneOxide-graft-Polyethylene Glycol Copolymer Surfactantsas Demulsifier for Petroleum Crude Oil EmulsionsAyman M. Atta a b , H. S. Ismail b , A. M. Elsaeed b , R. R. Fouad c , A. A. Fada c & A. A.-H.Abdel-Rahman da Surfactant Research Chair, Chemistry Department , College of Science, King SaudUniversity , Riyadh , Saudi Arabiab Petroleum Application Department , Egyptian Petroleum Research Institute , Nasr City ,Cairo , Egyptc Department of Chemistry, Faculty of Science , Mansoura University , Mansoura , Egyptd Department of Chemistry, Faculty of Science , Menoufia University , Shebin El-koum ,EgyptPublished online: 30 Jan 2013.

To cite this article: Ayman M. Atta , H. S. Ismail , A. M. Elsaeed , R. R. Fouad , A. A. Fada & A. A.-H. Abdel-Rahman(2013) Preparation and Application of Nonionic Polypropylene Oxide-graft-Polyethylene Glycol Copolymer Surfactantsas Demulsifier for Petroleum Crude Oil Emulsions, Journal of Dispersion Science and Technology, 34:2, 161-172, DOI:10.1080/01932691.2012.657538

To link to this article: http://dx.doi.org/10.1080/01932691.2012.657538

PLEASE SCROLL DOWN FOR ARTICLE

Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) containedin the publications on our platform. However, Taylor & Francis, our agents, and our licensors make norepresentations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of theContent. Any opinions and views expressed in this publication are the opinions and views of the authors, andare not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon andshould be independently verified with primary sources of information. Taylor and Francis shall not be liable forany losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoeveror howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use ofthe Content.

This article may be used for research, teaching, and private study purposes. Any substantial or systematicreproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in anyform to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http://www.tandfonline.com/page/terms-and-conditions

Preparation and Application of Nonionic PolypropyleneOxide-graft-Polyethylene Glycol Copolymer Surfactantsas Demulsifier for Petroleum Crude Oil Emulsions

Ayman M. Atta,1,2 H. S. Ismail,2 A. M. Elsaeed,2 R. R. Fouad,3 A. A. Fada,3

and A. A.-H. Abdel-Rahman41Surfactant Research Chair, Chemistry Department, College of Science, King Saud University,Riyadh, Saudi Arabia2Petroleum Application Department, Egyptian Petroleum Research Institute, Nasr City, Cairo,Egypt3Department of Chemistry, Faculty of Science, Mansoura University, Mansoura, Egypt4Department of Chemistry, Faculty of Science, Menoufia University, Shebin El-koum, Egypt

GRAPHICAL ABSTRACT

This work aims to prepare new water soluble nonionic amphiphilic graft copolymers based onhydrophilic poly(ethylene glycol) (PEG) and hydrophobic poly(propylene oxide) (PPO) atambient temperature and normal atmospheric pressure. In this respect, poly(propylene oxide)were prepared and grafted with different molar ratios of maleic anhydride (MA) in the presenceof dibenzoyl peroxide as an radical grafting initiator to produce PPO-MA grafts. The producedgrafts were esterfied with different molecular weights of poly(ethylene glycol) momomethyl etherto produce PPO-MA-PEGME nonionic surfactants. The chemical composition and molecularweights of the prepared copolymers were determined from 1HNMR analyses. The surface proper-ties of the prepared surfactants were determined by measuring the surface tension at differenttemperatures. The prepared nonionic surfactants were evaluated as demulsifiers for waterin crude-oil emulsions that were pronounced at different ratios of crude oil: water at 60�C.The experimental results showed that the dehydration rate of the prepared demulsifiers reached100% based on demulsifier chemical compositions and concentrations.

Keywords Amphiphile, demulsifier, graft copolymer, polyethylene glycol, polypropyleneglycol, surface and interfacial tension, surfactant

1. INTRODUCTION

The demulsification process is of great importance inthe oil industry because the occurrence of emulsions is anatural phenomenon of oil extraction from reservoirscontaining systems of oil, water, and gas. It is necessaryto separate these components. The gas so recovered can

be attractive economically, and the water must be removedbecause it has a high salt content and forms emulsions withviscosities greater than that of the dehydrated oil. This beha-vior affects the sizing of the pumping system, the transfer andstorage of petroleum, and also generates problems of encrus-tation and corrosion in oil pipelines carrying the outflow.[1]

In the oil dehydration process, the use of demulsifying pro-ducts is essential to coalesce the emulsions formed in thefield. All agents that prevent or breakdown emulsions havesome tendency to be adsorbedat the interfaces.[2–6] Thechoice of a demulsifier is difficult because its performancecan be affected by various factors, including the type of oil,

Received 13 December 2011; accepted 6 January 2012.Address correspondence to Ayman M. Atta, Surfactant

Research Chair, Chemistry Department, College of Science, KingSaud University, Riyadh, Saudi Arabia. E-mail: [email protected]

Journal of Dispersion Science and Technology, 34:161–172, 2013

Copyright # Taylor & Francis Group, LLC

ISSN: 0193-2691 print=1532-2351 online

DOI: 10.1080/01932691.2012.657538

161

Dow

nloa

ded

by [

Aym

an M

. Atta

] at

10:

21 2

2 O

ctob

er 2

013

the presence and wettability of solids, the viscosity of the oil,and the size distribution of the dispersed water phase.[7]

Commercial demulsifiers are polymeric surfactants such ascopolymers of poly (ethylene oxide) (PEO) and poly(propyleneoxide) (PPO) or alkyl phenol=formaldehyde resins or blends ofdifferent surface active substances. The demulsifiers used in theprimary processing of petroleum are in most cases surfactantsbased on block copolymers of poly(ethylene oxide-propyleneoxide) (PEO–PPO) with different ethylene oxide (EO)=propy-lene oxide (PO) molar ratios. A surfactant’s efficiency ina determined application is intimately related to its chemicalstructure and physical–chemical properties in solution. Anevaluation of the solubility in aqueous nonionic surfactantsolutions is important because these surfactants can presentphase separation with increasing temperature.[8–10] Theobjective of this work was to evaluate the behavior of aqueousnonionic surfactant solutions based on PPO–PEO graft copo-lymers with respect to their properties in aqueous solutionsand their performance in destabilizing oil=water emulsions inthe oil industry. For this purpose, we used different types ofcopolymers with branched and linear structures.

2. EXPERIMENTAL

2.1. Materials

Poly ethylene glycol monomethyl ether having molecularweight (550 and 750 g=mol) designated as PEGME 550 andPEGME 750 were purchased from Aldrich Chemicals Co.(USA) and used as received. Acetic anhydride (Ac), maleicanhydride (MA), dibenzoyl peroxide (DBP), p-toluenesulfonic acid (PTSA), and propylene glycol (PG) were pur-chased from Merck (Germany) and used without purifi-cation. Distilled water used in surface tension measurements.

Baker crude oil (produced from General Petroleum Co.,Egypt) was used and its physical properties are representedin Table 1. On the other hand, the used sea water wasobtained from the Mediterranean Sea, Alexandria, Egypt.

2.2. Methods and Techniques

2.2.1. Preparation of PPO

Poly(propylene glycol), PPG, was prepared throughanionic polymerization of PG and propylene oxide (PO)in the presence of 20 (wt%) of KOH as a catalyst under

N2 atmosphere at the reaction temperature of 25�C. Thereaction mixture was agitated during the reaction time byadjusting the PO monomer feeding rate. The producedpolymer was treated with HCl to form neutral solution.

2.2.2. Grafting of MA onto PPO

The acetylation reaction of PPGwere carried out in a reac-tor fitted with a four-necked flask equipped with a condenser,mechanical stirrer, and thermometer and nitrogen inlet. PPG(1mol) and 2mol of acetic anhydride were refluxed in thereactor. The complete acetylation of PPO with acetic anhy-dride was carried out for 10 hours at 80�C to obtain thediacetate form of PPO. The graft reactions of PPO diacetate(PPO-Ac) with maleic anhydride (MA) were carried outusing MA initial concentrations of 5, 10, and 20wt%, withrespect to PPO-Ac. BP was used as initiator using 2.5mol%related to MA. Subsequently, the graft reactions werecarried out under nitrogen atmosphere by heating the reac-tion mixtures to 80�C for 10 hours. The unreacted MA andby-products of the initiator decomposition were removedby vacuum distillation (30 minutes at 90�C and 1 mbar).The reaction products were usually extracted five timesin hexane at room temperature. Since low-grafted chains ofPPO-Ac were soluble in hexane, whereas highly graftedPPO-Ac parts were insoluble, during this procedure highlygrafted parts of the reaction products could be isolated fromungrafted PPO-Ac chains. The percentage of MA graftingonto PPO-AC was calculated from relation: % of MA graft-ing (wt%)¼ [(weight of highly grafted PPO-MA)=(weight ofMAþweight of PPO-Ac)]� 100. Titrations of the sampleswere made by using an automatic Titrator Schott TR 250.Before titration, the reaction products were hydrolyzedin an acetone=water-mixture (2.5: 1 v=v) for 7 hours at theboiling point of the mixture. After this procedure thesolutions were titrated with aqueous 0.1M NaOH.

2.2.3. Esterification of PEGME onto PPO-MA Grafts

The esterification reaction of PPO-MA with PEGMEwas carried out in a reactor fitted with a Dean–Stark sep-arator, mechanical stirrer, and thermometer and nitrogeninlet. PEGME (1mol) having different molecular weightswas mixed with 1mol of PPO-MA in the presence ofo-xylene and 0.1wt% PTSA (based on total weight of reac-tants). The theoretical amount of water was removed at120�C. o-Xylene was distilled off from the reaction productby using arotary evaporator under reduced pressure. Theproduct was separated by salting out use saturated NaClsolution and extracted with isopropanol using separatingfunnel. The purified products were isolated after evapor-ation of is opropanol.

2.3. Measurements

Infrared spectra were determined with a Perkin-Elmermodel 1720 FTIR.

TABLE 1Specifications of Baker crude oil

Test Method Value

API gravity at 60�F Calculated 21.7Viscosity at 60�F(Cst) IP71 762.8Specific gravity at 60�F IP 160=87 0.843Asphaltene contents (wt%) IP 143=84 7.83

162 A. M. ATTA ET AL.

Dow

nloa

ded

by [

Aym

an M

. Atta

] at

10:

21 2

2 O

ctob

er 2

013

1HNMR spectra of the prepared polymers were recor-ded on a 400MHz Bruker Avance DRX-400 spectrometer(USA).

A model Waters 600E (USA) GPC was used to deter-mine the average molecular weights of the prepared poly-mers. It contains on-line degasser, a 600E multisolventdelivery system, a 410 differential refractometer, a coolheater module, a Millennium 2010 chromatographymanager and a waters fraction collector. Test portions of0.0500 g polystyrene standard and sample were dissolvedin 10ml of THF at room temperature. A 100 ml injectionsample loop was filled with polystyrene standard andsample. THF served as an eluent. The flow rate was setat 1.0ml=min.

Cloud points of 2% of the prepared surfactant aqueoussolutions were determined visually by testing the temperatureat which turbidity was observed. We also noted the tempera-ture at which turbidity disappeared on cooling. The averageof the three results was taken as the cloud point of the system.

The interfacial tension (IFT) of emulsions or betweencrude oil emulsions and chemical solutions at 45�C wasdetermined by Du Nouy ring method using a Kruss K-12tensiometer. It reached equilibrium about 60 minutes atwhich time (IFT) values were measured. The surface ten-sion measurements of the prepared surfactants were carriedout at different molar concentrations and different tempe-ratures (25, 35, 45, and 55�C) by using platinum tensiometer.

2.4. Preparation of Water in Crude-Oil Emulsions

All emulsions were prepared with a total volume of100mL. The ratio between crude oil and the aqueous phase(sea water) was varied from 10 to 50% (vol%). Theemulsions were prepared by mixing using a Silverstonehomogenizer. The speed was ca.1500 rpm for 1 hour. Inthis respect, in 500ml beaker, the crude oil was stirredat 35�C (1500 rpm) while sea water was added graduallyto the crude oil until the two phases become completelyhomogenous. The emulsion was pronounced at differentratios of crude oil: water (90:10, 80:20, 70:30, and 50:50).

2.5. Demulsification of the Prepared Emulsions

The bottle test is used to estimate the capability of theprepared demulsifiers in breaking of water in oil emulsions.Demulsification was studied at 45�C and 60�C using grad-uated cone-shaped centrifuge tube. The prepared demulsi-fiers were diluted to 70% (wt%) using xylene: ethanolmixture (1:1). The concentrations of the demulsifiers were50, 100, 250, and 500 ppm was injected into the emulsionusing a micropipette. After the contents in the tube hadbeen shaken for 1 minute, the tube was placed in a waterbath at 45�C or 60�C to allow the emulsion to separate.The phase separation was recorded as a function of time.During the settling, the interface between the emulsionand separated water phase can be easily observed. The

reason for working at elevated temperatures is to meltthe content of wax in the oil and thereby prevent influ-ence from the wax on the emulsion stability. The elevatedtemperature is also more closely related to the real workingtemperature used in the processes onshore.

3. RESULTS AND DISCUSSION

Surfactants derived from maleic acid have a veryimportant additional advantage: they are not able tohomopolymerize. In addition, maleates seem to be ratherreactive, with a high level of conversion during thecopolymerization process. This makes reactive maleatespromising as surfactants for the improvement of surfacecharacteristics of polymer latexes. This work aims to pre-pare poly (oxyethylene)-co-poly (oxypropylene) graft copo-lymers to use them as demulsifiers. It is well known thatPEO-PPO-PEO copolymers were prepared by anionicpolymerization and they required pressure reactor to com-plete polymerization. The present work aims to preparethis copolymer in the normal condition. Evaluation ofthe prepared surfactants as demulsifiers for crude oil emul-sions is the main goal of the present study. The grafting ofPPO with PEGME was completed throught two steps. Thefirst step of the present work aimed to produce nonionicpolymeric surfactants from reaction of modified PPO withMA followed by reaction with PEG having different mol-ecular weights to produce PPO block PEG copolymers.In the present section PPO-MA grafts were reacted withPEGME to form PPO-g-PPG graft copolymers throughformation of PPO-MA grafts followed by esterificationwith PEGME.

3.1. Grafting of PPO with PEGME

Poly(propy1ene oxide) is a widely applied type of ali-phatic polyether, used for the preparation of surfactants.For the development of advanced water soluble surfac-tants, a well-defined polar modification and functionaliza-tion of PPO could be important. The polymerization ofpropylene glycol and propylene oxide using KOH as acatalyst was used to produce poly (propylene glycol),PPG, at the reaction temperature 25�C. The number-average molar mass (Mn�), weight-average molar mass(Mw�) and polydispersity (PD) for prepared PPG weredetermined using gel permeation chromatography (GPC)as 3149, 5215 g=mol and 1.65, respectively. The retentiontime of PPG was determined at 28.36 minute. Frentzelet al.[11] and O’Connor et al.[12] carried out the graftingof PPO with maleic acid and fumaric acid. Gaylord[13,14]

proposed the formation of poly(maleic anhydride) sidechains by the grafting of MA onto polyethylene whereasRussell and Kelusky[15] described the formation of mono-substituted succinic anhydride units by graft reactions ofMA onto eicosane. A defined structure modification of

POLYPROPYLENE OXIDE-g-POLYETHYLENE GLYCOL DEMULSIFIERS 163

Dow

nloa

ded

by [

Aym

an M

. Atta

] at

10:

21 2

2 O

ctob

er 2

013

the aliphatic polyether poly (tetrahydrofuran) via graftingwith MA has been described.[16] This work deals with thefunctionalization and polar modification of PPO by

the radical-initiated grafting with MA. To prevent side-reactions of MA with hydroxyl end groups, PPO was com-pletely acetylated to obtain the diacetate form of PPO(PPO-Ac) prior to the graft reaction as described inScheme 1. Figure 1a shows the carbonyl region of theFTIR spectrum of PPO-Ac. The vibration of acetateend-groups appears at 1738 cm�1. The graft reactions withMA initial concentrations of 5 and 10wt% related toPPO-Ac occurred in homogeneous phase. In contrast, byan MA initial concentration of 20wt% a phase separationwith the precipitation of a solid phase took place during thereaction. FTIR spectroscopy is a suitable method to inves-tigate grafted products of MA and po1yolefins.[17] Acharacteristic shift of the carbonyl valence vibrations ofcyclic anhydrides to higher wave numbers was observeddue to the graft reactions. Figure 1b depicts the carbonylregion of a reaction product of PPO-Ac and 10wt% MArelated to PPO-Ac after vacuum distillation. Since unreacted MA was removed completely during this distil-lation procedure[16] the detected anhydride carbonylvalence vibrations are due to grafted anhydrides. Com-pared to MA, the asymmetric carbonyl valence vibrationof the reaction products is shifted from 1781 to1783.5 cm�1 and the symmetric vibration is shifted from1856 to 1862 cm�1.[18] This finding indicates the formationof a saturated cyclic anhydride structure.[17] The small shiftof the carbonyl vibration of acetoxy end groups to a lowerwave number (1734.5 cm�1) is probably caused by thepresence of some hydrolyzed anhydride groups of graftunits. Vibrations of free carboxyl groups appear below1730 cm�1. For a further structure characterization, highlygrafted parts of the reaction products were isolated byextracting five times in hexane at room temperature. In thisway, three different samples of highly grafted PPO-Acparts were isolated from the reaction products synthesizedusing MA initial concentrations of 5, 10, and 20wt% rela-ted to PPO-Ac. The solid phase precipitated during thereaction with an initial concentration of 20wt% was takenas fourth sample Table 2. The reaction products as well asthe samples of the highly grafted parts were titrated todetermine the amount of grafted anhydrides. The conver-sion of all reaction products was approximately 75% ofthe initial MA concentration. For example, the productsynthesized using an MA initial concentration of 10wt%related to PPO-Ac showed a conversion of 78%. The valuesof the percentage of grafting were approximately similarfor all isolated samples, as depicted in Table 2. This indi-cates that a certain concentration of graft units ontoPPO-Ac chains is necessary (approximately 20wt%) toachieve an insolubility of the appropriate chains in hexane.Considering free radical graft reactions of polyolefins, it isknown that the reaction of macro radicals causes a cross-linking at polyethylene but a chain scission at poly-propylene. However, compared to the GPC curve of

SCH. 1. Preparation of PPG-PEG Graft copolymers.

FIG. 1. FTIR spectra of a) PPO-Ac and b) PPO-MA10.

164 A. M. ATTA ET AL.

Dow

nloa

ded

by [

Aym

an M

. Atta

] at

10:

21 2

2 O

ctob

er 2

013

PPOAc, the peak of one of the grafted products shows nosignificant difference of the elution time (Figure 2). Eventhe chromatogram of the highly grafted parts of the pro-duct shows only a slight shift to higher elutiontimes (Figure 2). This can be explained by a higher molecu-lar mass due to the relative high concentration of graftunits. However, the depicted chromatograms indicate thatneither a chain scission nor a cross linking takes place dur-ing the grafting reaction of MA onto PPO. This finding issimilar to the grafting of MA onto poly(tetrahydrofuran)and dioxane.[16,19–24] A nearly complete conversion of MAwas obtained by grafting of poly (tetrahydrofuran) whileunder comparable conditions the conversion by graftingonto PPO-Ac was significantly lower (approximately 75%).The grafting occurs onto both methylene and methine car-bons at the PPO chain. At graft reactions carried out withlow MA initial concentrations up to 10wt%, monosubsti-tuted succinic anhydrides are formed as graft units. How-ever, at higher MA initial concentrations (20wt%) besidesingle units a small amount of oligo (maleic anhydride)units are found. The degree of conversion was approxi-mately 75% of the initial MA. However, by extraction withhexane highly grafted PPO chains could be isolated easilyfrom the reaction products. The percentage of grafting ofthe isolated products was up to 24.3wt%. The synthesizedhighly functionalized PPOs are of potential interest as com-ponents for cross linked elastomers. Furthermore, the

formed anhydride graft units may be used to carry outfurther reactions such as esterification with PEG to formnew surfactant molecules with new interesting properties.

The second part of preparation describes the esterifi-cation of PPO-MA with PEGME to produce nonionic sur-factants having different hydrophile-lipophile balance(HLB) and to study the effect of surfactant structure onits properties. In this respect, the PPO-MA was subjectedto react with PEGME having different molecular weights400 and 600 at 180�C. The produced surfactants are solublein water, toluene, xylene, and CHCl3. Besides that, pro-ducts with high ester yield can be obtained either by usingcatalysts or by adding one of the reacting components inlarge excess or even by removal of water. In view of this,the reaction took place at relatively high temperature inorder to remove any water from the reaction medium toshift the reaction to complete esterification. Addition ofPTSA significantly increased the reaction rate. The schemeof reaction with PEGME as model component is given inScheme 1. However, basic knowledge of the relationbetween the structure of the surfactants and their perfor-mances is still lacking. The chemical structures of PPO-MA-PEG were confirmed by 1HNMR analysis. 1HNMRspectra of PPO-MA5-PEG550, PPO-MA10-PEG550, andPPO-MA20-PEG550 are illustrated in Figure 3 as rep-resentative samples. Careful interpretation to these spectraindicated the appearance of peak at the chemical shift atd¼ 3.6 ppm for protons of oxyethylene units, the chemicalshift at 4.3 ppm which represented COO-(CH2CH2O).These peaks were observed in all spectra of the preparedsurfactants. There are some other characteristic peaks suchas the chemical shift of methyl groups of PPO andPEGME, which appeared at d¼ 0.92 and 3.2 ppm, respect-ively. Also, the -OH signal that usually appears at 10.3 ppmin spectrum of MA and assigned for -COOH groupappeared in all spectra of PPO-MA-PEGME surfactants.This observation certainly indicates that only one carbo-xylic group of MA was esterified with PEGME. Moreover,the integration area of terminal COOH signal appeared at10.3 ppm was compared to the integration area of either–OCH3 signal, 3.2 ppm, or with the chemical shift at4.3 ppm which represented COO-(CH2)-to determine thedegree of esterification of PPO-MA with PEGME and tocalculate the theoretical molecular weight of the prepared

TABLE 2Reaction conditions of PPO grafts with MA

Sample MA concentration related to PPO-Ac Treatment Percentage of grafting (wt%)

PPO-MA5 5 Isolated highly grafted parts 22.5PPO-MA10 10 Isolated highly grafted parts 20.4PPO-MA20 20 Isolated highly grafted parts 20.5PPO-MA20P 20 Precipitated during the reaction 24.5

FIG. 2. GPC curves (refractive signal curves) of PPO-Ac, PPO-MA10

and isolated highly grafted parts of the reaction products of PPO-MA10.

POLYPROPYLENE OXIDE-g-POLYETHYLENE GLYCOL DEMULSIFIERS 165

Dow

nloa

ded

by [

Aym

an M

. Atta

] at

10:

21 2

2 O

ctob

er 2

013

surfactants. The acid value (mg KOH=g) and esterificationpercentages of the prepared surfactants were determinedand listed in Table 3. Theoretical molecular weight (Mn�)can be determined from relation: Mn�¼ [MA%�PEGMEMw�PEGME%=100]þ [PPOMw]. The data indicated thatthe percentage of esterification of PEGME was increased

with increasing molecular weights of PEGME from 400to 600 g=mol and with increasing of MA content from 5to 20wt%. This can be attributed to the higher solubility ofPPO-MA20 in toluene than PPO-MA5 that enhances theprobability for reaction of PPO-MA with PEGME.[25]

3.2. Surface Activity of the Prepared Surfactants

It is well known that the modification of polymer back-bone yields different hydrophobicity, chain flexibility andsolubility due to the difference of inter- and intramolecularinteractions. This difference in solubility is due to the dif-ference in HLB of the surfactants. The HLB values werecalculated by using the general formula fornonionic surfac-tants, HLB¼ [MH=(MHþML)]� 20, where MH is the mol-ecular weight of the hydrophilic portion of the surfactantmolecule and ML is the formula weight of the hydrophobicportion. HLB values of nonionic surfactants based onPPO-MA-PEGME graft copolymers were calculated andlisted in Table 4. The data indicated that the HLB valuesof the prepared surfactants varied from 13.7 to 17.1, whichindicates that the prepared surfactant have different deg-rees of solubility in water. It is well known that the aqueoussolutions of polyoxyethylenated nonionics having oxyethyl-ene content below about 80wt% become turbid on beingheated at a temperature known as the cloud point, abovewhich there is a separation of the solution into twophases.[26] This phase separation occurs in a narrow tem-perature range (fairly constant) for surfactant concentra-tions below a few weight percent. The temperature atwhich clouding occurs depends on the structure of the poly-oxyethylenated nonionic surfactant. The cloud temperatureswere measured and listed in Table 4. A study of the effect ofstructural changes in the surfactant molecule on its cloudpoint[26] indicates that, at constant oxyethylene content,the cloud point is lowered for the following reasons:

. branching of the hydrophobic group;

. more central positions of the polyoxyethylenehydrophilic group in the surfactant molecule; and

FIG. 3. 1HNMR spectra of a) f PPO-MA10-PEGME550, b)

PPO-MA10-PEGME750, and c) PPO-MA5-PEGME550.

TABLE 3Grafting percentages and theoretical molecular weights of PPO-MA-PEGME grafts

Sample

Grafting percentage (Determined from1HNMR analyses)

Theoretical average molecular weights(Mn�)g=mol

MA (%) PEGME (%) PEGME PPO PPO-MA-PEGME

PPO-MA5-PEGME550 70 20 6151 3149 9300PPO-MA5-PEGME750 70 25 10451 3149 13600PPO-MA10-PEGME550 75 33 9851 3149 13000PPO-MA10-PEGME750 75 38 17051 3149 20200PPO-MA20-PEGME550 78 45 14051 3149 17200PPO-MA20-PEGME750 78 50 23401 3149 26550

166 A. M. ATTA ET AL.

Dow

nloa

ded

by [

Aym

an M

. Atta

] at

10:

21 2

2 O

ctob

er 2

013

. replacement of the ether linkage between the hydro-philic and hydrophobic group by an ester linkage.

The data of cloud temperature of PPO-MA-PEGMEsurfactants, listed in Table 4, in dicated that the cloudtemperatures were reduced with increasing of MA contentswhich produced branching of PPO and more centralposition of PEGME.

The micellization and adsorption of surfactants arebased on the critical micelle concentrations, cmc, whichwas determined by the surface balance method. The cmcvalues of the prepared polymeric surfactants were deter-mined at 25, 35, 45, and 55�C from the change in the slopeof the plotted data of surface tension (c) versus naturallogarithm of the solute concentration (� ln C). Somerepresentative plots of the relation between surface tension(c) and -ln C of the prepared surfactants are illustratedin Figure 4. This kind of plot is used for estimating thesurface activity and confirming the purity of the studiedsurfactants. It is of interest to mention that all isothermsshowed one phase, which is considered as an indicationof the purity of the prepared surfactants. The valuesobtained of (cmc) for nonionic surfactants at different tem-peratures were listed in Table 5, together with values forthe surface tension at cmc (ccmc). In the present system, itwas found that the ccmc values show an increase withincreasing of PEGME contents in the PPO-MA-PEGMEmolecule. This can be attributed to the hydrophobic inter-action between maleate and oxypropylene groups whichincreases coiling of PEGME located at the end of the mole-cules. So, the solubility of the surfactants in water is con-trolled by the structure of hydrophobic groups. It is ofinterest to mention that the cmc for the prepared surfactantdecreases with increasing temperature. This may be attrib-uted to the increase in the radius of gyration of themolecule as a result of increasing the temperature.[27]

The amount of material adsorbed per unit area ofinterface is calculated indirectly from the surface orinterfacial tension measurements. The concentration ofsurfactants at the water–air interface can be calculatedas surface excess concentration Umax. The surface excessconcentration of surfactant at the interface may therefore

be calculated from surface or interfacial tension data usingthe following equation: Umax¼ 1=RT� (�@c=@ ln c)T,where (�@c=@ ln c)T is the slope of the plot of c versus

TABLE 4Calculated HLB Values of the prepared PPO-MA-PEGME surfactants

Surfactants Number-average molar mass (g=mol) HLB Cloud point �C

PPO-MA5-PEGME550 9300 13.2 80–83PPO-MA5-PEGME750 13600 14.7 75–77PPO-MA10-PEGME550 13000 15.1 78–80PPO-MA10-PEGME750 20200 16.8 73–75PPO-MA20-PEGME550 17200 16.3 70–72PPO-MA20-PEGME750 26550 17.1 65–67

FIG. 4. Adsorption isotherms of a) PPO-MA5-PEGME400 and b)

PPO-MA5-PEGME600 at 25, 35, 45, and 55�C. (Figure available in color

online.)

POLYPROPYLENE OXIDE-g-POLYETHYLENE GLYCOL DEMULSIFIERS 167

Dow

nloa

ded

by [

Aym

an M

. Atta

] at

10:

21 2

2 O

ctob

er 2

013

ln c at constant temperature (T) and R is the gas constant(in J mol�1K�1). The surface excess concentration at sur-face saturation is a useful measure of the effectiveness ofadsorption of surfactant at the liquid–gas or liquid–liquidinterface, since it is the maximum value that adsorptioncan attain. The Umax values were used for calculating theminimum area Amin at the aqueous–air interface. The areaper molecule at the interface provides information on thedegree of packing and the orientation of the adsorbedsurfactant molecules, when compared with the dimensionsof the molecule as obtained from models. From the surfaceexcess concentration, the area per molecule at the interfaceis calculated using the equation: Amin¼ 1016=N Umax, whereN is Avogadro’s number. The effectiveness of surface ten-sion reduction, Pcmc¼ co– ccmc (where co is the surface ten-sion of water and ccmc is the surface tension of solution atcmc), was determined at different temperatures. The Umax

max, Amin and Pcmc values were calculated and are listedin Table 5. The values of Pcmc (listed in Table 5) show thatthe most efficient one is that give the greater lowering insurface tension at the critical micelle concentration. Theeffectiveness increases with decreasing the PEGME chainand MA contents onto the PPO hydrophobic moiety.

The effectiveness of surface tension reduction, Pcmc, inthese compounds shows a steady decrease with an increasein the contents of oxyethylene units. In polyoxyethyly-enated nonionics, an increase in the number of oxyethyleneunits in the hydrophilic group above six units, in contrastto its large effect in decreasing the effectiveness of adsorp-tion, seems to cause only a small decrease in the efficiencyof adsorption. This appears to indicate a very small changein the free energy of transfer of the molecule frombulk phase interior to the interface with a change in thenumber of PEGME units above six in the hydrophilichead. The effectiveness of adsorption, however, mayincrease, decrease or show no change with an increase inthe length of the hydrophobic group depending on theorientation of the surfactant at the interface. If the surfac-tant is perpendicular to the surface in a close-packedarrangement, an increase in the length of the straight-chainhydrophobic group appears to cause no significant changein the number of moles of surfactant adsorbed per unitarea of surface at surface saturation.[28] This is becausethe cross-sectional area occupied by the chain oriented per-pendicular to the interface does not change with an increasein the number of units in the chain. When the area of the

TABLE 5Surface properties of the prepared PEG-PPO-PEG graft copolymers

DesignationTemp.(�C) cmc� 10�6 mMol=L ccmc mN=m Pcmc mN=m Cmax� 10 10mol=cm2

Amin nm2=molecule

PPO-MA5-PEG550 25 4.363 36.6 35.5 1.57 0.10635 2.182 35 36.1 1.59 0.10445 1.091 34 36.1 1.58 0.10555 1.091 33 36.1 1.53 0.109

PPO-MA5-PEG750 25 3.23 44.2 27.9 1.29 0.12935 1.62 43.3 27.8 1.27 0.13145 1.62 42.2 27.9 1.24 0.13555 1.62 41.1 28 1.21 0.137

PPO-MA10-PEG550 25 4.36 44 28.1 1.30 0.12735 4.36 42.9 28.2 1.25 0.13345 4.36 40.8 29.3 1.26 0.13255 4.36 39.9 29.2 1.22 0.136

PPO-MA10-PEG750 25 3.23 46.4 25.7 1.37 0.12235 1.617 45.3 25.8 1.39 0.12045 1.617 44.4 25.7 1.33 0.12555 1.234 43.5 25.6 1.32 0.126

PPO-MA20-PEG550 25 4.36 45 27.1 1.35 0.12335 4.36 44 27.1 1.32 0.12645 2.18 43 27.1 1.28 0.13055 2.18 42 27.1 1.23 0.135

PPO-MA20-PEG750 25 3.23 48.1 24 1.54 0.10835 3.23 47 24.1 1.53 0.10845 3.23 46 24.1 1.51 0.11055 1.617 45 24.1 1.45 0.115

168 A. M. ATTA ET AL.

Dow

nloa

ded

by [

Aym

an M

. Atta

] at

10:

21 2

2 O

ctob

er 2

013

hydrophilic group is greater than that of the hydrophobicchain, the larger the hydrophilic group, the smaller theamount adsorbed at surface saturation. If the arrangementis predominantly perpendicular but not close-packed, theremay be some increase in the effectiveness of adsorption withan increase in length of hydrophobic group, resulting fromgreater van der Waals attraction, and consequently yieldingcloser packing of longer chains.[29] Nonionic surfactants withshort and low PEGME chain contents show a decrease in bothefficiency and effectiveness with an increase in the length ofthe PEG.[30]

The Amin and Umax data indicate the dependence of theeffectiveness of adsorption at the aqueous solution–airinterfaces on the structure of surfactants. The nature of thehydrophilic group has a major effect on the effectiveness ofadsorption. In general, Amin appears to be determined by thecross-sectional area of the hydrated hydrophilic group atthe interface. Careful inspection of data, indicates that, Amin

of the surfactants have two opposite relations with thetemperature. The Amin may be increased or decreased withincreasing the temperature. In polyoxyethylenated nonionicsthe lack of significant temperature effect may be resultedfrom two compensating effects[31]:

. decrease in Amin at the surface due to increaseddehydration of the hydrophilic group at highertemperature; and

. increase in Amin as a result of enhanced molecularmotion at higher temperature.

It can be concluded that the adsorption of PPO-MA-PEGME at interface decreased with increasing ofboth MA and PEGME contents. This can be attributedto the hydrophobic interaction between maleate and oxy-propylene groups which increases coiling of PEGMElocated at the end of the molecules. Consequently, thiscoiling affected the adsorption of PPO-MA-PEGMEsurfactants at water=air interface.

3.3. Demulsification of Crude Oil Emulsions

Crude oil emulsions are stabilized by high-molecularweight surfactants, viz., asphaltenes and resins. They donot develop high surface pressures, and, therefore, stericstabilization of water-in-crude-oil emulsions is the mostplausible mechanism of stabilization of such emulsions.Demulsifier molecules and natural surfactants competewith each other for adsorption onto the water-drop film.In this respect, the dehydration (water separation) rate ofcrude oil emulsions having the water cut from 10 to 50%were measured in the absence and the presence of theprepared surfactants at different temperature 60�C. Thedehydration curves using different concentrations of theprepared surfactants at temperature of 60�C for crude oilemulsion having different water cuts were selected andrepresented in Figures 5 and 6. The prepared surfactants

showed good efficiency as dehydrating agents for waterin crude oil emulsions at 60�C. The testing results showedthat there was no constant concentration for all surfactantsat which the best dehydration was given; some surfactants

FIG. 5. Water separation curves of oil:water (50:50) emulsions of a)

PPO-MA5-PEGME550, b) PPO-MA10-PEGME550, and a) PPO-MA20-

PEGME550 graft copolymer surfactants at 60�C.

POLYPROPYLENE OXIDE-g-POLYETHYLENE GLYCOL DEMULSIFIERS 169

Dow

nloa

ded

by [

Aym

an M

. Atta

] at

10:

21 2

2 O

ctob

er 2

013

reached the best dehydration rate at 500ppm and the othersat 250ppm or even 100ppm. It was found that the demulsifi-cation times for crude oil emulsion having water cut 10% and30% were increased with decreasing the surfactant concentra-tions from 500ppm to 100ppm. This behavior can correlatedto surface activity, solubility and HLB values of the preparedsurfactants which listed in Table 4 and discussed in the pre-vious section. The data indicated that the best HLB valuesfor dehydration of the crude oil emulsion are 13.2 ofPPO-MA5-PEGME550, listed in Table 3, which reflect ongood solubility of the prepared surfactants in both oil andwater phases at these HLB values. This data indicated thatPPO-MA5-PEGME550 surfactant has good adsorption atoil water interface. This indicates the partial solubility of most

of these surfactants in water. The low HLB values of the pre-pared surfactants will be more soluble in non polar sol-vents.[32] The prepared emulsions can be considered as waterin oil emulsions, in other words the oil percent in these emul-sions is more than water since the prepared surfactants aremore soluble in oil than water, so it will be expected to givegood dehydration rates with such emulsions. These resultsagree with the data reported on adsorption parameters andIFT measurements shown in Figure 7, which indicate thatPEG600-PPG1-PEG600 surfactant has best adsorptionperformance and high reduction in IFT.

In general, Figures 5 and 6 showed that there are in a steadystate at which the dehydration rates have constant values forsome time, and then it started to increase again till reachingthe final percent of dehydration for each surfactant. To under-stand this behavior, the mechanism of demulsification shouldbe discussed. The proposed mechanism for water separationof crude oil based on PPO-MA-PEGME demulsifiers can beillustrated in Figure 8. In this respect, crude oil emulsionsare stabilized by surfactants, viz., asphaltenes and resins. They

FIG. 7. The effect of PPO-MA-PEGME demulsifier concentrations

oninterfacial tensionof crude oil=water interfaces at 25�C.

FIG. 8. Physical model of water drops caught by PPO-MA-PEGME

copolymer: a) displacement and b) coalescence. (Figure available in color

online.)

FIG. 6. Water separation curves of oil:water (50:50) emulsions of a)

PPO-MA5-PEGME750, b) PPO-MA10-PEGME750, and a) PPO-MA20-

PEGME750 graft copolymer surfactants at 60�C.

170 A. M. ATTA ET AL.

Dow

nloa

ded

by [

Aym

an M

. Atta

] at

10:

21 2

2 O

ctob

er 2

013

do not develop high surface pressures, and therefore stericstabilization of water-in-crude-oil emulsions is themost plaus-iblemechanismof stabilization of such emulsions.Demulsifiermolecules and natural surfactants competewith eachother foradsorption onto the water-drop film.When demulsifier mole-cules, which lower interfacial tension much more than thenatural surfactants, are adsorbed at the interface, the filmbecomes unstable in the direction of coalescence of waterdrops. Emulsions formed in the petroleum industry are predo-minantly water-in-oil or regular emulsions, in which the oil isthe continuous or external phase and the dispersed water dro-plets, form the dispersed or internal phase. The water dropletsbecome biggerwith time after demulsifier is added. The role ofthe demulsifier is to change the interfacial properties and todestabilize the surfactant-stabilized emulsion film in thedemulsification process. In the beginning, small and uniformdrops flocculate and some large drops begin to form at 30minutes. Then two or more large drops continue to form asingle larger drop: coalescence happens. The droplet sizegrows fast and the droplet number reduces after demulsifieris added. It can be concluded that coalescence of water dro-plets destroyed emulsions. Three terms related to stabilitycommonly encountered in crude oil emulsion are flocculation,coalescence, and breaking. Although they are sometimes usedalmost interchangeably, those terms are in fact quite distinctinmeaning as far as the condition of an emulsion is concerned.Flocculation refers to the mutual attachment of individualemulsion drops to form flocks or loose assemblies. Floccu-lation can be, in many cases, a reversible process, overcomeby the input of much less energy thanwas required in the orig-inal emulsification process. Coalescence refers to the joining oftwo or more drops to form a single drop of greater volume,but smaller interfacial area. Although coalescence will resultin significant microscopic changes in the condition of thedispersed phase, it may not immediately result in a macrosco-pically apparent alteration of the system. The breaking of anemulsion refers to a process in which gross separation of thetwo phases occurs. In such an event, the identity of individualdrops is lost, along with the physical and chemical propertiesof the emulsion. Such a process obviously represents a trueloss of stability in the emulsion. It has been established thatthe kinetics of chemical demulsification is complicated bythe interaction of three main effects. These are the displace-ment of the asphaltene film from the oil water interfaceby the demulsifier; flocculation and coalescence of waterdrops.[33]

4. CONCLUSIONS

The following conclusions can be withdrawn from theabove mentioned results in the following points:

1. New water soluble poly (propylene glycol)–maleicanhydride–poly(ethylene glycol) graft copolymers, PPO-MM-PEGME, were prepared in the normal condition.

2. The percentage of MA grafting onto PPO was 24.3wt%.Furthermore, the formed anhydride graft units may beused to carry out further reactions such as esterificationwith PEGME to form new surfactant molecules withnew interesting properties.

3. The adsorption of PPO-MA-PEGME at interfacedecreased with increasing of both MA and PEGME con-tents. This can be attributed to the hydrophobic interactionbetween maleate and oxypropylene groups which increasescoiling of PEGME located at the end of the molecules.Consequently, this coiling affected the adsorption ofPPO-MA-PEGME surfactants at water=air interface.

4. The prepared PPO-MA5-PEGME550 surfactant redu-ced both surface and interfacial tension of water andwater=oil interface.

5. The time of maximum demulsification efficiency wasvaried from 10 minute up to 180 minutes. The data indi-cated that the best HLB values for dehydration of thecrude oil emulsion are ranged from 13.2 to 17.1.

REFERENCES

[1] Lissant, K. (1977) In Improved Oil Recovery by Surfactantand Polymer Flooding, edited by D.O. Shah, and D.O.

Schechter; New York: Academic Press; p. 93.[2] Gray, G.R. and Darley, H.C.H. (1981) Composition and

Properties of Oil Well Drilling Fluids; Houston, TX:Gulf.

[3] Gogarty, W.B. (1977) In Improved Oil Recovery by Surfac-tant and Polymer Flooding, edited by D.O. Shah, and D.O.Schechter; New York: Academic Press; p. 27.

[4] Atta, A.M., Abdel-Rahman, A.A.-H., Elsaeed, S.M., AbouElfotouh, S., and Hamad, N.A. (2008) J. Dispersion Sci.Technol., 29: 1484.

[5] Atta, A.M., Abdel-Rahman, A.A.-H., and Hamad, N.A.(2008) J. Dispersion Sci. Technol., 29: 1222.

[6] Atta, A.M., Fadda, A.A., Abdel-Rahman, A.H., Ismail,H.S., and Fouad, R. (2012) J. Dispersion Sci. Technol., 33:775–785.

[7] Mikula, R.J. and Munoz, V.A. (2000) In Surfactants: Funda-mentals and Applications in the PetroleumIndustry, edited by

L.L. Schramm; Cambridge, UK: University of Cambridge:Cambridge; p. 51.

[8] Hunter, R.J. (1986) Foundations of Colloid Science; Oxford,

UK: Clarendon.[9] Mansur, C.R.E., Barboza, S.P., Gonzalez, G., and Lucas,

E.F. (2003) J Colloid Interface Sci., 271: 232.[10] Claudia, R.E., Mansur, F.C., Lechuga, A.C., Mauro, G.,

and Elizabete, F.L. (2007) J. Appl. Polym. Sci., 106: 2947.[11] Frentzel, R.L., Rua, L., and Pacheco, A.L. (1984) US Pat.

No. 4460738. Chem. Abstr 101, 131: 354 (1987).

[12] O’Connor, J.M. and Frentzel, R.L. (1986) US Pat. No.4590255.

[13] Gaylord, N.G., Metha, M., and Kumar, V. (1982) Org. Coat.Appl. Polym. Sci. Proc., 46: 87.

[14] Gaylord, N.G. and Metha, M. (1982) J. Polym. Sci., Polym.Lett. Ed., 20: 481.

POLYPROPYLENE OXIDE-g-POLYETHYLENE GLYCOL DEMULSIFIERS 171

Dow

nloa

ded

by [

Aym

an M

. Atta

] at

10:

21 2

2 O

ctob

er 2

013

[15] Russell, K.E. and Kelusky, E.C. (1988) J. Polym. Sci. A, 26:2273.

[16] Rische, T., Zschoche, S., and Komber, H. (1996) Macromol.Chem. Phys., 197: 981.

[17] Kozel, T.H. and Kazmierczak, R.T. (1991) Ann. Tech. Conf,Soc. Plast. Eng., Tech. Pap., 37: 1570.

[18] Merck-Bibliothek, Bibliotheks und Suchsoftware, Opus=Search (V l.O), Bruker AnalytischeMeRtechnik GmbH, 1991.

[19] Regel, W. and Schneider, Ch. (1981) Makromol. Chem., 182:237.

[20] Kellou, M.S. and Jenner, G. (1976) Eur. Polym. J., 12: 883.[21] Nakayama, Y., Hayashi, K., and Okamura, S. (1974) J. Appl.

Polym. Sci., 18: 3633.[22] Jacobs, R.L. and Ecke, G.G. (1963) J. Org. Chem., 28: 3036.[23] Malatesta, V. and Caiano, J.C. (1982) J. Org. Chem., 47: 1455.[24] Malatesta, V. and Ingold, K.U. (1981) J. Am. Chem. Soc.,

103: 609.

[25] Atta, A.M., Elsayed, A.M. and Husein, I.S. (2008) J. Appl.Polym. Sci., 108: 1706.

[26] Nakagawa, T. and Shinoda, K. (1963) In New Aspects inColloidal Surfactants, edited by K. Shinoda, T. Nakagawa, B.

Tamamuushi, and T. Esemura; New York: Academic; p. 129.[27] Atta, A.M. (2007) Polym. Int., 56: 984.[28] Tamaki, K. (1967) Bull. Chem Soc., 40: 38.[29] Connor, P. and Ottewill, R.H. (1971) J. Colloid Interface

Sci., 37: 642.[30] Atta, A.M., Abdel-Raouf, M.E., Abdul-Rahiem, A.M., and

Abdel-azim, A.A. (2005) J. Polym. Res., 13: 39.[31] Crook, E.H., Trebbi, G.F., and Fordyce, D.B. (1964) J. Phys.

Chem., 68: 3592.[32] Anton, R.E. and Salager, J.L. (1986) J. Colloid Interface Sci.,

110: 54.[33] Xia, L., Lu, S., and Cao, G. (2004) J. Colloid Interface Sci.,

271: 504.

172 A. M. ATTA ET AL.

Dow

nloa

ded

by [

Aym

an M

. Atta

] at

10:

21 2

2 O

ctob

er 2

013