This art icle was downloaded by: [ Aym an M. At t a] On: 03 Sept em ber 2014, At : 04: 59 Publisher: Taylor & Francis I nform a Lt d Regist ered in England and Wales Regist ered Num ber: 1072954 Regist ered office: Mort im er House, 37- 41 Mort im er St reet , London W1T 3JH, UK Journal of Dispersion Science and Technology Publicat ion det ails, including inst ruct ions f or aut hors and subscript ion inf ormat ion: ht t p: / / www. t andf online. com/ loi/ ldis20 Demulsification of Crude Oil Emulsions Using Some New Water-Soluble Schiff Base Surfactant Blends Ayman M. At t a a , Adel A. -H. Abdel-Rahman & Nora A. Hamad b , Shymaa M. Elsaeed a , Saeed AbouElf ot ouh c b a Egypt ian Pet roleum Research Inst it ut e , Nasr Cit y, Cairo, Egypt b Facult y of Science, Depart ment of Chemist ry , Menouf ia Universit y , Shebin El-koum, Egypt c General Pet roleum Company , Cairo, Egypt Published online: 13 Apr 2009. To cite this article: Ayman M. At t a , Adel A. -H. Abdel-Rahman , Shymaa M. Elsaeed , Saeed AbouElf ot ouh & Nora A. Hamad (2009) Demulsif icat ion of Crude Oil Emulsions Using Some New Wat er-Soluble Schif f Base Surf act ant Blends, Journal of Dispersion Science and Technology, 30: 5, 725-736 To link to this article: ht t p: / / dx. doi. org/ 10. 1080/ 01932690802548403 PLEASE SCROLL DOWN FOR ARTI CLE Taylor & Francis m akes every effort t o ensure t he accuracy of all t he inform at ion ( t he “ Cont ent ” ) cont ained in t he publicat ions on our plat form . However, Taylor & Francis, our agent s, and our licensors m ake no represent at ions or warrant ies what soever as t o t he accuracy, com plet eness, or suit abilit y for any purpose of t he Cont ent . Any opinions and views expressed in t his publicat ion are t he opinions and views of t he aut hors, and are not t he views of or endorsed by Taylor & Francis. The accuracy of t he Cont ent should not be relied upon and should be independent ly verified wit h prim ary sources of inform at ion. Taylor and Francis shall not be liable for any losses, act ions, claim s, proceedings, dem ands, cost s, expenses, dam ages, and ot her liabilit ies what soever or howsoever caused arising direct ly or indirect ly in connect ion wit h, in relat ion t o or arising out of t he use of t he Cont ent . This art icle m ay be used for research, t eaching, and privat e st udy purposes. Any subst ant ial or syst em at ic reproduct ion, redist ribut ion, reselling, loan, sub- licensing, syst em at ic supply, or dist ribut ion in any form t o anyone is expressly forbidden. Term s & Condit ions of access and use can be found at ht t p: / / www.t andfonline.com / page/ t erm s- and- condit ions Journal of Dispersion Science and Technology, 30:725–736, 2009 Copyright # Taylor & Francis Group, LLC ISSN: 0193-2691 print=1532-2351 online DOI: 10.1080/01932690802548403 Demulsification of Crude Oil Emulsions Using Some New Water-Soluble Schiff Base Surfactant Blends Ayman M. Atta,1 Adel A.-H. Abdel-Rahman,2 Shymaa M. Elsaeed,1 Saeed AbouElfotouh,3 and Nora A. Hamad2 1 Egyptian Petroleum Research Institute, Nasr City, Cairo, Egypt Faculty of Science, Department of Chemistry, Menoufia University, Shebin El-koum, Egypt 3 General Petroleum Company, Cairo, Egypt Downloaded by [Ayman M. Atta] at 04:59 03 September 2014 2 Six new surfactant blends were prepared by mixing one Schiff base non ionic surfactant prepared by etherification of Schiff base monomer with b0,b-dichlorodiethylether and PEG 400 in presence of NaOH with six water soluble Schiff base non-ionic surfactants prepared in the same way but etherified with PEG 2000. The mixing process was based on the high dehydration rates given by the PEG 400 Schiff base surfactant compared to the other PEG 2000 surfactants. The experimental results of this study indicate that the demulsification rates of these blends are higher than those of the PEG 400 surfactant. Demulsification process was carried out on an emulsion of w/o ratio 50:50 and studied at 60 C at two different concentrations of the demulsifiers (200 and 240 ppm). The dehydration rates of the six prepared blends reached 100%. The total dehydration time varied from 50 minutes up to 2 hours. Keywords Crude oil emulsions, demulsifiers, Schiff base, surfactants 1. INTRODUCTION During oil production, crude oils are typically produced as water in crude oil (w=o) emulsions, which are often very stable. Among the indigenous natural surfactants contained in the crude oils, asphaltenes and resins are known to play an important role in the formation and stability of w=o emulsions.[1,2] The coproduction of water and crude oil in the form of an emulsion is highly undesirable, such emulsions introduce technical challenges so they must be resolved to provide the specified product quality.[3–5] In this respect, many studies have been carried on stability and demulsification of crude oil emulsions reported by many investigators.[6–11] Recently, there has been increasing interest in the synthesis and characteristics of polymeric surfactants because they probably offer greater opportunities in terms of flexibility, diversity and functionality.[12–14] Commercial demulsifiers are polymeric surfactants such as copolymers of polyoxyethylene and polypropylene or polyester or blends of different surfaceactive substances.[15,16] These blends of surfactants are generally used and they are formulated in solvents like short-chain alcohols, aromatics or heavy aromatic naphtha.[17,18] Attempts have Received 17 December 2007; accepted 27 December 2007. Address correspondence to Ayman M. Atta, Egyptian Petroleum Research Institute, Nasr City, Cairo 11727, Egypt. E-mail: khaled_00atta@yahoo.com been made to arrive at some correlation between demulsifier performance and properties like HLB, partition coefficient, interfacial viscosity, and interfacial tension.[19–22] The main purpose of this work is to study the preparation of some new surfactant blends based on a comparison between using Schiff base surfactants and using blends of these surfactants as demulsifiers for crude oil emulsions. 2. EXPERIMENTAL 2.1. Used Chemicals Salicyadehyde (Fluka, Switzerland), o-phenylenediamine, p-phenylenediamine Ethylenediamine (Aldrich, USA), 1,4-Diaminobutane, 1,8-Diaminooctane (Merck, Germany), 1,3,5-trioxane (Aldrich, USA), glacial acetic acid, absolute ethanol, DMF, methanol, HCl, NaOH, NaCl (El Nasr Pharmaceutical Chemicals Co., Egypt), b0,b- Dichlorodiethylether, PEG 2000 and PEG 400. Table 1 presents details of the Baker crude oil (produced from General Petroleum Co., Egypt) and its origin. On the other hand, the used sea water was obtained from Mediterranean Sea, Alexandria, Egypt. 2.2. Methods and Techniques 2.2.1. Synthesis of Schiff Base of Monomers (SBM) In a three-nicked flask equipped with a condenser, magnetic stirrer, thermometer, dropping funnel and nitrogen atmosphere inlet, an aromatic or aliphatic diamine (0.25 725 726 A. M. ATTA ET AL. TABLE 1 Specifications of bakr crude oil Test Downloaded by [Ayman M. Atta] at 04:59 03 September 2014 API gravity at 60 F Viscosity at 6 F (Cst) Specific gravity at 60 F Asphaltene contents (wt%) Method Value Calculated IP71 IP 160=87 IP 143=84 21.7 762.8 0.843 7.83 mole) in (200 ml) absolute ethanol was added with stirring at 60jC for about 15 minutes, then salicylaldehyde (0.5 mole) in (200 ml) absolute ethanol was added dropwise to the above mixture within 1 hour with stirring under nitrogen. The temperature was raised gradually up to reflux temperature, and then the reaction mixture was refluxed for about 3 hours.[23] After that it was cooled, filtered to get the prepared Schiff base monomers as crystalline precipitates. Condensation of salicylaldehyde with o-phenylenediamine, p-phenylenediamine, ethylenediamine, 1,4-diaminobutane and 1,8-diaminooctane produced bis(N, N-disalicylidene)o-pheylenediamine (DOPD), bis(N,N-disalicylidene)p-pheylenediamine (DPPD), bis(N,N-disalicylidene)ethylenediamine (DED), bis(N,N-disalicylidene)1, 4-butylenediamine (DBD) and bis(N,N-disalicylidene)1,8octylenediamine (DOD), respectively. 2.2.2. Synthesis of Schiff Base (5,5-Methylene-bissalicyaldehyde) Saliclaldehyde (80 g, 0.65 mol), glacial acetic acid (50 ml) and trioxane (7 g) were added with stirring at 50–60jC for about 15 minutes. A mixture of (0.5 ml) conc. H2SO4 and (2.5 ml) of glacial acetic acid was added slowly using dropping funnel. The reaction temperature was raised to 90– 95jC under nitrogen. The reaction mixture was refluxed for 22 hours, then it was cooled at room temperature after that it was poured into 3 L of ice-water and allowed to stand overnight. The solid product was filtered and washed with petroleum ether. The isolated solid was dried and recrystallized from acetone. 2.2.3. Synthesis of Polymer of Schiff Base In 500 ml three-necked flask 5,50 -Methylene bissalicylaldehyde (15 g), absolute ethanol (50 ml) and glacial acetic acid (200 ml) were added together with stirring at 50–60jC under nitrogen. Then a solution of o-phenylendiamine (6.6 g) in glacial acetic acid (200 ml) was added slowly using dropping funnel. After few minutes a bright yellow precipitate was formed. Methanol (50 ml) was added with stirring. The reaction mixture was refluxed for 6 hours. The solid product was isolated by filteration and washed with methanol to give Schiff base polymer SP1. 2.2.4. Etherification of Schiff Base Monomers and Polymer In 250 ml three-necked flask fitted with condenser, mechanical stirrer, and thermometer the Schiff-base monomer (0.1 mole), b0,b-DichloroDiethylEther (0.2 mole), PEG 2000 (0.2 mole), NaOH (0.4 mole), and DMF (100 ml) were added together with stirring. The reactants were agitated and slowly heated to a temperature of 170jC. The reaction mixture was maintained at this temperature for 5 hours. The progress of the reaction was evaluated by determine the NaCl content that increases gradually to reach a constant value at the end of the reaction. The product was treated with an equal volume of saturated NaCl solution and neutralized with dilute HCl. Then the reaction mixture was filtered to get ride of the solid NaCl, then the product was dried from DMF under vacuum. During the evaporization of DMF, a ppt. of NaCl formed again, so by the end of drying process the product was separated from NaCl by filtration on an oil pump to give the corresponding Schiff base polymers. The etherified products of DOPD, DPPD, DED, DBD, and DOD with PEG 2000 can be designed as D1, D2, D3, D5, and D5, respectively, while the etherification of Schiff base polymer SP1 gives ESP1. 2.2.5. Preparation of Surfactant Blends The surfactant blends were prepared by mixing water soluble Schiff base surfactants of PEG 2000 (D1-D5) and ESP1 with another Schiff base surfactant (EDOD) prepared from PEG 400 in previous work. The mixing percentage of PEG 400 to PEG 2000 surfactants was 90:10, respectively. The surfactant blends of (EDOD) with (D1D5) are (B1-B5), respectively, while that of (EDOD) with (ESP1) is (BP1). Mixture of isopropanol: toluene (50: 50 vol%) was used as solvent for surfactant blends at concentration 50 wt%. 2.2.6. Preparation of Water Crude-Oil Emulsions (w=o) The emulsions were prepared by mixing water and crude oil using a Silverstone homogenizer. In the prepared emulsions, the water=oil ratio was 1:1. The speed was ca.1500 rpm for 1 hour. In 500 ml beaker, the crude oil was stirred at 25 C while sea water was added gradually to the crude oil until the two phases become completely homogenous. Demulsification was studied at 60 C and at two concentrations of the demulsifiers (200 and 240 ppm). Water separation was recorded after various intervals of time for 2 hours. 2.2.7. Demulsification of the Prepared Emulsions The bottle test is used to estimate the capability of the prepared demulsifiers in breaking of water in oil emulsions. Demulsification was studied at 60 C using gravitational settling using graduated cone-shaped centrifuge tube. The prepared PEG 2000 Schiff base surfactants and the PEG DEMULSIFICATION OF CRUDE OIL EMULSIONS Downloaded by [Ayman M. Atta] at 04:59 03 September 2014 400 Surfactant were diluted to 50% (wt%) using toluene: ethanol mixture (1:1). Then six surfactant blends were prepared by mixing the prepared solution of EDOD with the six solutions of (D1-D5) and (ESP1), the six blends are B1–B5 and BESP1, respectively. Two concentrations of the demulsifiers (200 and 240 ppm) were injected into the emulsion using a micropipette. After the contents in the tube had been shaken in an oscillating shaker for 1 minute, the tube was placed in a water bath at 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 emulsion and separated water phase can be easily observed. 2.2.8. Measurements The nitrogen content was measured with a Tecator Kjeltech auto analyzer. A Tecator 1007 digester was used for the initial digestion of the samples. Infrared spectra were determined with a Perkin-Elmer model 1720 FTIR (KBR). While, 1H-NMR spectra of the prepared Schiff base monomers and polymers were recorded on a 400 MHz Bruker Avance DRX-400 spectrometer. 3. RESULTS AND DISCUSSION 3.1. Synthesis of Schiff Base Surfactants The prepared Schiff base surfactants were prepared from the etherification of Schiff base monomers and the polymer of Schiff base 5,50 -Methylene bis-salicylaldehyde as reported in experimental section. The physicochemical characteristics of the prepared Schiff base monomers were listed in Table 2. The purity of the prepared Schiff base monomers is very important because they act as starting materials to produce water soluble Schiff base polymeric surfactants. Elemental analysis indicates good agreements between the experimental and theoretical values. This reveals that the method of synthesis and purification were performed successfully. The chemical structure of some TABLE 2 Physicochemical characteristics of the prepared Schiff base monomers Monomers DOPD DPPD DED DBD DOD P1 Color m.p.
C Yield (%) Dark orange powder Pale orange powder Pale green crystals Pale green crystals Pale green powder Dark pink crystals 165–167 217–219 128–130 90–92 80–82 146–148 89.0 76.7 52.5 85.0 78.0 47.0 727 Schiff base monomers was discussed briefly using IR and 1 HNMR analyses in previous work.[23] In this respect, IR and 1HNMR spectra were not recorded here for brevity. The formation of azomethine nitrogen in all compounds was concluded due to the appearance of strong band at 1600 cm1. This band indicates the formation of condensed products between salicylaldehyde and aromatic or aliphatic diamine derivatives. The IR spectra of all derivatives show a strong broad band in the region 3420– 3200 cm1 assigned to inter and intramolecular hydrogen band phenolic OH stretching vibrations. The bands at 1580 and 1555 cm1 correspond to aromatic cC¼C stretching vibrations. The medium intense band at 1257 cm1 may be assigned to cC–O phenolic stretching. The disappearance of strong bands of aldehyde groups at 2750 and 1700 cm1 which assigned for CH and C¼O stretching of aldehyde groups indicates the formation Schiff base monomer with high purity grade. The 1HNMR spectra of Schiff base monomers show a complicated aromatic proton multiplet (7.8-6 ppm) and an imino proton singlet at 8.3 ppm downfield from the usual aromatic proton region. The strong band of chemical shift (d) 11.9 ppm is assigned to OH aromatic of Schiff bases. The triplet beaks, observed in spectra of DBD and DOD, at 4.2 ppm can be assigned to (CH)2 groups attached to azomethine group. While, multiple peak at 2.1 ppm (spectra of DBD and DOD) can be attributed to (CH2)n groups. The structure of the prepared Schiff base 5,50 -Methylene bis-salicylaldehyde was also illustrated by 1HNMR spectra which show a singlet beak of chemical shift (d) 3.8 ppm can be assigned to CH2 group, two doublet and one singlet beak of chemical shifts (d) 6.9, 7.3, and 7.5 ppm, respectively, represent the six aromatic protons, two strong singlet beaks of chemical shifts (d) 10.2 and 10.5 ppm can be assigned to OH aromatic and OH of the aldehyde groups of the Schiff base monomer.[23] The prepared Schiff base polymer of 5,50 -Methylene bis-salicylaldehyde was illustrated by IR spectra which shows a strong broad band in the region 3420–3200 cm1 assigned to ph-O stretching vibrations. A strong band at 1615 cm1 is assigned for cC¼N stretching vibrations. The two strong bands at 850 and 805 cm1 may be attributed to out of plan bending of aromatic rings and indicates the formation of 1,2,4trisubstituted rings. The appearance of the bands at 2950 cm1 and 2875 cm1, characteristic for cC–H aliphatic, confirms the formation of CH2 aliphatic. While the appearance of band at 2650 cm1 and 1700 cm1 indicates the formation of aldehyde end group. The physicochemical characteristics of the prepared Schiff base surfactants were listed in Table 3. IR and 1H-NMR spectra were used to illustrate the structure of the prepared surfactants. In this respect it was observed that IR spectra of all ethoxylated Schiff base derivatives are nearly identical. Downloaded by [Ayman M. Atta] at 04:59 03 September 2014 728 A. M. ATTA ET AL. 3.2. Solubility Properties of the Prepared Surfactants It is well known that the modification of Schiff base monomers yields different hydrophobicity, chain flexibility and solubility due to the difference of inter- and intramolecular interactions. This difference in solubility is due to the difference in hydrophil-lipophil balance (HLB) of the surfactants. The HLB values were calculated by using the general formula for nonionic surfactants.[24] HLB values of the prepared nonionic surfactants were calculated and listed in Table 3. The solubility of non-ionic surfactants in water increases with increasing their HLB values. It is noticed that the HLB values of the prepared surfactants ranges from 16.7–17.3, this indicates the high water solubility of these surfactants. Due to the high values of HLB the prepared surfactants will be less soluble in non-polar solvents.[25] But as mentioned before due to the little difference in HLB values of the prepared surfactants the effect of HLB on their efficiency is not completely clear. Because HLB is difficult to determine experimentally, we instead used cloud point to represent the hydrophile– lipophile balance. The cloud point is the temperature below which a single phase of molecular or micellar solution exists; above the cloud point the surfactant loses sufficient water solubility and a cloudy dispersion results.[26] Above this temperature, the surfactant also ceases to perform some or all of its normal functions. So cloud point can be used to limit the choice of nonionic surfactants for application in certain processes. A suggestion was made to regard the cloud point in solution of nonionic surfactant as a pseudo phase inversion. For polyoxyethylene-type surfactant, the cloud point and the phase inversion temperature (PIT) are directly correlated when surfactant alone is dispersed in water. PIT is defined as the temperature at which the hydrophile–lipophile property of surfactant just balances at the interface.[27] So for the polyoxyethylenetype surfactants, cloud point is related to the hydrophile– lipophile balance. A study on the effect of structural changes in the surfactant molecule on its cloud point.[28] indicates that, at constant oxyethylene content the cloud point is lowered due to decreased molecular weight of the surfactant and increasing length of the hydrophobic group. 3.3. Surface Activity of the Prepared Surfactants The surface activity of surfactants can be determined by measuring surface or interfacial tensions versus time for a freshly formed surface.[29] The micellization and adsorption of surfactants are based on the critical micelle concentrations (CMC), which was determined by the surface balance method. The CMC values of the prepared polymeric surfactants were determined at 298, 308, 318, and 328 K from the change in the slope of the plotted data of surface tension (c) versus the natural logarithm of the solute concentration. Some representative plots Figure 1 are illustrated here for brevity. The presented plots and all other plots are used for estimating surface activity and confirming the purity of the studied surfactants. It is of interest to mention that all obtained isotherms showed one phase, which is considered as an indication on the purity of the prepared surfactants. TABLE 3 The physicochemical characterization of the prepared PEG 2000 surfactants Surfactants D1 D2 D3 D4 D5 Molecular weight HLB Cloud point
C 2360 2360 2312 2340 2396 16.9 16.9 17.3 17.1 16.7 68 80 75 73 70 FIG. 1. Adsorption isotherms of (a) D1, (b) D3, and (c) D5 at different temperatures. DEMULSIFICATION OF CRUDE OIL EMULSIONS Downloaded by [Ayman M. Atta] at 04:59 03 September 2014 The direct determination of the amount of surfactant adsorbed per unit area of liquid-gas or liquid-liquid interface, although possible, is not generally under taken because of the difficulty of isolating the interfacial region from the bulk phase for purpose of analysis when the interfacial region is small, and of measuring the interfacial area when it is large. Instead, the amount of material adsorbed per unit area of interface is calculated indirectly from surface or interfacial tension measurements. As a result, a plot of surface (or interfacial) tension as a function of equilibrium, concentration of surfactant in one of the liquid phases, rather than an adsorption isotherm, is generally used to describe adsorption of this interface can readily be calculated as surface excess concentration Cmax. The surface excess concentration of surfactant at the interface may therefore be calculated from surface or interfacial tension data by using Equation (1): Cmax   1 @c ¼ RT @ ln c T ½1   where @@c ln c T is the slope of the plot of c versus ln c at a constant temperature (T), and R is the gas constant in J mol1 K1. The surface excess concentration at surface saturation is a useful measure of the effectiveness of adsorption of surfactant at the liquid-gas or liquid-liquid interface, since it is the maximum value which adsorption can attain. The Cmax values were used for calculating the minimum area Amin at the aqueous-air interface. The area per molecule at the interface provides information on the degree of the packing and the orientation of the adsorbed surfactant molecules, when compared with the dimensions of the molecule as obtained by use of models. From the surface excess concentration, the area per molecule at interface is calculated using Equation (2). Amin ¼ 1016 NCmax ½2 where N is Avogadro’s number. The surface tension values at CMC were used to calculate values of surface pressure (effectiveness). The effectiveness of surface tension reduction, PCMC ¼ co  cCMC, where co is the surface tension of water and cCMC is the surface tension of solution at CMC,[30] was determined at different temperatures. The values of PCMC show that, the most efficient one is that which gives the greater lowering in surface tension at the critical micelle concentration. The effectiveness increases with increasing the length of carbon chain in the hydrophobic moiety. Efficiency PC20 is determined by the concentration (mol=L) capable to suppress the surface tension by 20 dyne=cm. The efficiency of the prepared surfactants, listed in Table 4, increases with 729 increasing the length of carbon chain and with increasing temperature. Careful inspection of data indicates that, Amin at the surface decreased with increasing the temperature and this is due to increased dehydration of the hydrophilic group at higher temperature. The effectiveness of surface tension reduction, PCMC, in these compounds shows a steady increase with increase in the length of aliphatic diamine units. The effectiveness of adsorption, however, may increase, decrease or show no change with increase in the length of the hydrophobic group depending on the orientation of the surfactant at interface. If surfactant is perpendicular to the surface in a close-packed arrangement, an increase in the length of the straight-chain hydrophobic group appears to cause no significant change in the number of moles of surfactant adsorbed per unit area of surface at surface saturation.[31] This is because the cross-sectional area occupied by the chain oriented perpendicular to the interface does not change with increase in the number of units in the chain. When the area of hydrophilic group is greater than that of the hydrophobic chain, the larger the hydrophilic group, the smaller the amount adsorbed at surface saturation. If the arrangement is predominantly perpendicular but not close-packed, there may be some increase in the effectiveness of adsorption with increase length of hydrophobic group, resulting from greater Van der Waals attraction and consequent closer packing of longer chains.[32] Finally we can concluded that, the increasing in length of hydrophobic saturated alkyl chain increases the surface excess of molecule and consequently, decreases Amin of molecule at air=water interface. This behavior can be attributed to increment of hydrophobic interaction at interface, which increase with increasing length of hydrophobic moieties, which reflects on increasing of surfactant concentration and consequently decreases area per molecule. It is evident that, the minimum area per molecule at air=water interface can contribute to the molecular area. Accordingly, the adsorption of the surfactant molecules at air=water interface increase with increasing length of alkyl chain diamine in the prepared surfactants. 3.4. Thermodynamic Parameters of the Prepared Schiff Base Surfactants The formation of micelles in aqueous solutions is generally viewed as a compromise between the tendency for alkyl chains to avoid energetically unfavorable contacts with water and the desire for the polar parts to maintain contact with the aqueous environment. There are two principally different models for micelle structure. A mean density model[33] is the most appropriate one for micelles consisting of a large core and a relatively thin corona, and star model[34] is the most appropriate for those having a small core from which long chains protrude to form a large 730 A. M. ATTA ET AL. TABLE 4 Surface properties of the prepared Schiff base surfactants at different temperatures Temperature (K) Designation D1 Downloaded by [Ayman M. Atta] at 04:59 03 September 2014 D2 D3 D4 D5 EPDPD Surface property 298 Cmax  1010 (mol cm2) Amin (nm2=molecule) Pcmc (mNm1) CMCx 104 (g=mol) c cmc (mN=m) pC20 Cmax  1010 (mol cm2) Amin (nm2=molecule) Pcmc (mNm1) CMC  104 (g=mol) c cmc (mN=m) pC20 Cmax  1010 (mol cm2) Amin (nm2=molecule) Pcmc (mNm1) CMCx 104 (g=mol) c cmc (mN=m) pC20 Cmax  1010 (mol cm2) Amin (nm2=molecule) Pcmc (mNm1) CMC  104 (g=mol) c cmc (mN=m) pC20 Cmax  1010 (mol cm2) Amin (nm2=molecule) Pcmc (mNm1) CMC  104 (g=mol) c cmc (mN=m) pC20 Cmax  1010 (mol cm2) Amin (nm2=molecule) Pcmc (mNm1) CMC  104 (g=mol) c cmc (mN=m) pC20 1.26 0.13 30.5 2.2 41.5 4.88 1.3 0.13 32.7 3.7 39.3 4.91 1.34 0.12 32 3.7 40 5.6 1.12 0.14 36.5 3.7 35.5 5.96 1.34 0.12 29.6 3 45.1 4.37 0.91 0.18 18 3.4 54 3.34 308 318 328 1.13 0.15 30 1.1 41 5.37 1.13 0.14 32.5 3 38.5 5.21 1.34 0.12 31.9 3.4 39.1 5.8 1.09 0.15 35.9 3 35.1 6.52 1.27 0.13 27 1.36 44 4.94 0.71 0.23 17.8 3 53.2 3.85 0.83 0.19 29.5 0.91 40.5 5.97 1.04 0.15 32.1 2.2 37.9 5.49 1.13 0.14 31.5 3.1 38.5 5.9 1.06 0.17 35.5 2.7 34.5 6.76 1.24 0.13 26.5 1.2 26.5 5.11 0.65 0.25 17.5 2.7 52.5 3.91 0.73 0.23 29 0.83 40 6.43 1.01 0.16 31.9 1.8 37.1 5.82 0.98 0.16 30.9 2.7 38.1 6.11 0.96 0.17 35.2 2.2 33.8 6.86 1.2 0.14 26.1 1.01 26.1 5.21 0.71 0.23 17.2 2.2 51.8 4.1 corona. The ability for micellization processes depends on thermodynamic parameters, (enthalpy DH, entropy DS, and free energy DG) of micellization. Thermodynamic parameters of micilization of the prepared non-ionic surfactants were calculated and listed in Table 5. The thermodynamic parameters of micellization are the standard free energies DGmic, enthalpies DHmic, and entropies DSmic, of micellization for nonionic surfactants. Values of DSmic were obtained from the following equation by invoking the values of DGmic at 298, 308, 318, and 328 K. DGmic ¼ RT ln CMC DHmic ¼ DGmic þ TDSmic ½3 @DGmic ¼ DSmic ½4 @T In addition, DHmic, was calculated from DGmic and DSmic by applying Equation (5). ½5 731 DEMULSIFICATION OF CRUDE OIL EMULSIONS TABLE 5 Thermodynamic parameters of micellization for the prepared surfactants Thermodynamic parameters at different temperatures 25
C Surfactants Downloaded by [Ayman M. Atta] at 04:59 03 September 2014 D1 D2 D3 D4 D5 ESP1 35
C 45
C DGmic DHmic DGmic DHmic DGmic DHmic DGmic DHmic DSmic 20.8 19.6 19.6 19.5 20.1 19.8 26.9 19.1 8.4 13.3 27.6 10.0 23.3 20.7 20.4 20.7 22.8 20.7 25.9 19.3 8.6 13.1 26.5 10.1 24.5 22.2 21.4 21.7 23.7 21.6 26.5 19.1 8.5 13.2 27.2 10.2 25.6 23.5 22.4 22.9 25.1 22.9 26.9 19.1 8.4 13.1 27.4 9.9 0.16 0.13 0.094 0.11 0.16 0.1 The thermodynamic parameters values of adsorption, DGad, DHad, and DSad were calculated via Equations (6), (7), and (8), respectively,[35] and listed in Table 6. DGad ¼ RT ln CMC  0:6023PCMC Amin ½6 @DGad ¼ DSad @T ½7 DHad ¼ DGad þ TDSad ½8 Analyzing the thermodynamic parameters of micellization leads to the fact that micellization process is spontaneous (DGmic < 0). The data show that DGmic values are less negative with increasing the number of methylene group. This indicates that the increase of hydrophobic groups decreases the micellization process. This can be explained on the basis of steric bulk structure leads to steric inhibition of micellization.[36] On the other hand, the data reveal that – DGmic increases with increasing temperature from 298 to 328 K. The data listed in Table 5 show that DSmic values are all positive, indicating increased randomness in the system upon transformation of the nonionic surfactant molecules into micelles or increasing freedom TABLE 6 Thermodynamic parameters of adsorption for the prepared surfactants IFT (mN=m) Surfactant B1 B2 B3 B4 B5 ESP1 55
C Efficiency Time % (minute) HLB 200 ppm 240 ppm 100 100 100 100 100 100 120 60 50 100 45 95 10.7 10.7 10.8 10.8 10.7 10.7 0.56 0.13 0.05 0.34 0.03 0.24 0.13 0.08 0.004 0.13 0.001 0.11 of the hydrophobic chain in the nonpolar interior of the micelles compared to aqueous environment. The decrement of positive DSmic values with increasing the chain length units in the surfactant molecule has been observed and can be attributed to increase m.wt. hydrophobic group leads to decreasing the hydrogen bonds between water and PEG, which increase freedom motion of surfactants. The dissolution of the oxyethylene units has been stated to be the major contributing factor to the positive entropy of micellization in polyoxyethylenated nonionics. An alternative explanation is that there is less restriction on the motion of the surfactant molecule when it is in the essentially water-free environment of the micelle than in the aqueous phase. This extends to both the hydrophobic chain, which is in a hydrocarbon-like environment in the interior of the micelle, and the adjacent part of the hydrophilic polyoxyethylene chain, which is freed, on the only partially solvated micelle surface, from some of the restrictions placed upon it by hydrogen bonding to water molecules. This explanation, which assigns the change in entropy to the solute rather than to the solvent, is consistent with the re-evaluation of the concept[37] of entropy of solution. All DGad values are more negative than DGmic, indicating that adsorption at the interface is associated with a decrease in the free energy of the system. This may be attributed to the effect of steric factor on inhibition of micellization more than its effect on adsorption. The values of DSad are all positive and have greater values than DSmic for nonionic surfactants. This may reflect the greater freedom of motion of the hydrophobic chains at the planar air-aqueous solution interface compared to that in the relatively cramped interior beneath of the convex surface of the micelle. This indicates that the steric factor inhibits micellization more than do adsorption for nonionic surfactants. On the other hand, the positive values of DHad are much greater than the corresponding values of DHmic. This indicates that the dehydration-breaking of hydrogen bonds- at micellization is easier than at adsorption. Downloaded by [Ayman M. Atta] at 04:59 03 September 2014 732 A. M. ATTA ET AL. 3.5. Demulsification Performance Previous work[38] studied the effect of solvent on the demulsification efficiencies of crude oil emulsions. This study revealed that, the xylene and alcohol mixtures possess better demulsification efficiencies. In the present work, we investigate the effect of the solvent used to dissolute the prepared surfactants with respect to its ability to break up water-in-oil emulsions. The solubility of the prepared surfactants based on etherified products of Schiff base monomers with PEG 400 have partial solubility in water. Accordingly, xylene=isopropanol mixture (50=50) is selected as solvent for the present surfactants. This mixture is the best solvent and can be explained in terms of their being much more efficient in solubilizing polar and nonpolar moieties in the demulsifier molecule. The polar moiety represented by PEG units are stabilized by isopropanol, while the nonpolar moiety (hydrocarbon moiety) is solubilized by xylene. This enhanced solubilization is reflected in a better dispersion in crude oil-water emulsion and, consequently, in a better demulsification performance. It was found that the demulsification performance of a demulsifier is based on the interaction between dissolute surfactants and water droplet through diffusion and adsorption, which permits faster transport of demulsifier molecules to the water droplet interface. Moreover, dissolute demulsifiers give a better separation of the phases (water and crude oil phases) than an undiluted demulsifier does. Demulsification is the breaking of a crude-oil emulsion into oil and water phases. Demulsifiers are a class of surfactants used to destabilize emulsions. This destabilization is achieved by reducing the interfacial tension at the emulsion interface, often by neutralizing the effect of other naturally occurring surfactants which are stabilizing the emulsion. Produced oilfield emulsions posses a degree of kinetic stability arises from the formation of interfacial films encapsulating the water droplets. Therefore, destabilizing or breaking emulsions is linked very intimately to the removal of these interfacial films. Demulsification by use of chemicals or demulsifiers is a very complex phenomenon. Demulsifiers displace the natural stabilizers (emulsifiers) present in the interfacial film around the water droplets. This displacement is brought about by the adsorption of the demulsifier at the interface. This displacement occurring at the oil=water interface, influence the coalescence of water droplets through enhanced film drainage. The efficiency of the demulsifier is dependent on its adsorption at the oil=water, or droplet surface.[39] The preparation of the six surfactant blends was based on EDOD Schiff base surfactant due to its high dehydration rates. Figure 2 shows the dehydration rate of EDOD with different Crude Oil: Water Emulsions at 60
C and concentrations 200 and 240 ppm. Figure 3 shows a comparison between the dehydration rates of EDOD and the prepared PEG 2000 Schiff FIG. 2. Effect of demulsifiers on dehydration rate of 50:50 oil: water emulsion at 60
C. base surfactants D1, D2, D3, D4, D5 and ESP1 respectively with W=O emulsion 50:50 at 60
C. It is noticed that there is a wide range between the dehydration rate of EDOD and those of the other six surfactants. In this respect, the idea of using EDOD to make blends appeared with an expectation to improve the low dehydration rates of the other Schiff base surfactants. The experimental results showed that the dehydration rates of the prepared FIG. 3. Effect of dehydration rate of EDOD demulsifier compared with (a) D1, D2, and D3 (b) D4, D5, and ESP1 demulsifiers at 60
C and concentration of 240 ppm. DEMULSIFICATION OF CRUDE OIL EMULSIONS FIG. 4. Effect of five blends (B1, B2, B3, B4, and B5) on the dehydra- 733 possessing high HLB migrate faster to the interface than those having low HLB. As a result of such enhanced migration toward the interface, the surfactant forms a continuous hydrophilic pathway between the dispersed water droplets. This leads to a rapture of the interfacial oil film surrounding the water droplets. . Another point of view regarding the enhanced demulsification efficiency of the more hydrophilic surfactants is based on the stability of emulsions containing asphaltene. The higher HLB surfactants reveals higher demulsification efficiency. Downloaded by [Ayman M. Atta] at 04:59 03 September 2014 tion rate at 60
C. blends are higher than that given by EDOD as shown in Figure 4 the dehydration rates of surfactant blends (B1-B5) is in the order B5>B3>B2>B4>B1. Figure 5. shows the dehydration rate of BP1 at 200 and 240 ppm. From the given results it was obtained that the dehydration rates reached 100% for all surfactants indicating the high efficiency of them for treating crude oil emulsions. The present work deals with a water-in-oil emulsion and hence it is clear that the higher the HLB the higher the demulsification efficiency. From the given data it was shown that the maximum dehydration rate of these surfactants for 50:50 w=o emulsion at 60
C is 20% which is very low comparing with the other PEG 400 surfactants which gave dehydration rates of 100% for nearly all types of emulsions. The data reveal that the amount of water separated after 24 hours expressed as a percentage coalescence increases with increase in the HLB. This finding may be explained by the following speculations: . The increase in the HLB value increases the solu- bility of the surfactant in the aqueous phase (dispersed phase). When the demulsifier is initially introduced to the water-in-oil emulsion, it will be thermodynamically stable at the interface of the water droplets. Accordingly, the surfactants FIG. 5. 60
C. Effect of concentration on the dehydration rate of BP1 at HLB is determined using theoretical equations that relate the length of the water-soluble portion of the surfactant to the oil-soluble portion of the surfactant. A surfactant having HLB between 1 and 8 promotes the formation of water-in-oil emulsions and one with an HLB between 12 and 20 promotes the formation of oil-in-water emulsions. A surfactant having HLB between 8 and 12 may promote either type of demulsifiers. In the present study, it was observed that the surfactants have HLB (10–12.2) show good demulsification efficiencies. While surfactants having HLB above 13.8 show low demulsification efficiencies. Careful inspection of demulsification efficiency data reveal that surfactant having HLB equal 10 show maximum demulsification efficiency. This behavior reflects the dependence of the demulsification power on the presence of surfactant molecules in the soluble form rather than micelles.[36] This can be attributed to the solubilization of crude oil into the hydrophobic interior core of micelle.[40] The decrease in demulsification power at surfactant concentration far above CMC may be refereed to the saturation of bulk phase by micelles which leads to a reduction in the availability of crude oil to soluble into surfactant micelles. The high demulsification power of surfactants based on PEG 400 reflects the hydration of long hydrophilic groups into bulk phase which prevents the crude oil to penetrate the exterior region of micelle to arrive to their interior core and solublize there.[36] In the same time, the long hydrophilic chain reduces the hydrophobicity of the surfactant molecule, hence, the solubilization efficiency is reduced.[40] This behavior can be correlated with the ability of surfactants to reduce surface tension at CMC (cCMC), Tables 3 and 4, which indicate that the ability of surfactants based on PEG 400 to reduce cCMC is more than that for those based on PEG 2000. A typical demulsifier formulation consists of a pair of non-ionic surfactants in proportions to yield an average HLB of 10–11. Hydrophilic-lipophilic balance, HLB and the chemical structure of the surfactants exert a large influence on the rate of coalescence of emulsions containing blends of non-ionic surfactants. The best stability was obtained by mixing surfactants varied in HLB values. In order to estimate the validity of this observation with Downloaded by [Ayman M. Atta] at 04:59 03 September 2014 734 A. M. ATTA ET AL. asphaltenic crude oil dispersions, blends of the prepared nonionic surfactants were prepared. It is readily apparent that both HLB and chemical sconstitution of the demulsifiers exert a large influence on the percentage of demulsification. In all cases the surfactant were blended in different weight percentage. HLB values of the surfactant blends were calculated as, HLB blends ¼ HLBa Xa þHLBb where X is mole fraction of surfactant a, and b. The composition of the blends, their designation and HLB values were recorded in Table 7 for the prepared surfactant blends. It can be seen that, from Table 7, HLB values of blends EQUALS 10.7. The preparation of the six surfactant blends was based on EDOD Schiff base surfactant due to its high dehydration rates. The mixing process was based on the high dehydration rates given by the PEG 400 Schiff base surfactant EDOD compared to the other PEG 2000 surfactants. In this respect it was expected to improve the dehydration rates by making these blends. The experimental results of this study indicated the expected ones but the demulsification rates of these blends are higher than those of EDOD surfactant. Demulsification process was carried out on an emulsion of w=o ratio 50:50 and studied at 60
C at two concentrations of the demulsifiers (200 and 240 ppm). The dehydration rates of the six prepared blends reached 100% as listed in Table 7. The total dehydration time varied from 50 minutes up to 2 hours. Figures 4 and 5 shows a comparison between the dehydration rates of EDOD and the prepared PEG 2000 Schiff base surfactants D1, D2, D3, D4, D5, and ESP1 respectively with W=O emulsion 50:50 at 60
C. It is noticed that there is a wide range between the dehydration rate of EDOD and those of the other six surfactants. In this respect, the idea of using EDOD to make blends appeared with an expectation to improve the low dehydration rates of the other Schiff base surfactants. The experimental results showed that the dehydration rates of the prepared blends are higher than that given by EDOD as shown in Figures 4 and 5 the dehydration rates of surfactant blends (B1–B5) is in the order B5>B3>B2>B4>B1. From the given results it was obtained that the dehydration rates reached 100% for all surfactants indicating the high efficiency of them for treating crude oil emulsions. The relations between HLB of blends and their IFT values at 240 ppm were represented in Table 7. The oil-water interfacial tension (IFT) falls as the surfactant concentration increases and then attains a constant value at and above the concentration where surfactant aggregation occurs (CMC). The aggregation may occur either in the oil phase or in the aqueous phase, depending on conditions. This work will concern the dependence of IFT on the chain length of the hydrophobic moiety of the surfactant molecule and upon the number of EO units in the hydrophilic moiety. It is known[41] that minimum IFT results for the condition where phase inversion occurs, that is, where the coarse emulsion formed by agitation of the oil and aqueous phases changes from an oil-inwater (O=W) emulsion to a water-in-oil (W=O) emulsion, or vice versa. In cases where an O=W emulsion is given, surfactant is found to reside mainly in the aqueous phase, which is a swollen micellar solution (or O=W micro emulsion). The equilibrium oil phase in a coarse W=O emulsion, where all of the aggregated surfactant is present in the oil, is a W=O micro emulsion. The way in which the shape, size and curvature of the surfactant aggregates change as phase–inversion conditions are approached has been discussed in some detailed in terms of surfactant molecular geometry by Mitchell and Ninham[42] and in terms of a statistical mechanical model by Mukherjee et al.[43] It has been proposed in this work to study the changes in IFT with respect to the number of EO units and the methylene groups in the hydrophilic and hydrophobic portions in the surfactant molecule. Under these conditions the interfacial tension is generally quite low and the surface viscosity is high since these long chains add rigidity to the interface and making it more gel like. The lowering of IFT and the improved stability of O=W emulsions combining surfactants with high and low HLB have been explained through TABLE 7 Effect of HLB on the demulsification efficiency of surfactant blends for 50:50 O=W emulsion Thermodynamic parameters at different temperatures 25
C Surfactants D1 D2 D3 D4 D5 ESP1 35
C 45
C 55
C DGad DHad DGad DHad DGad DHad DGad DHad DSad 21.2 22.1 21.9 22.7 22.2 21.1 17.5 19.6 10.8 165 25.5 8.7 22.3 23.5 22.8 23.9 24.9 22.1 17.7 19.6 11.1 170.1 24.4 8.7 23.7 25.1 24.1 25.3 25.9 23.0 17.6 19.4 10.9 175 24.9 8.8 25.3 26.5 25.3 43.4 27.3 24.4 17.3 19.4 10.7 163.3 25.2 8.4 0.13 0.14 0.11 0.63 0.16 0.1 Downloaded by [Ayman M. Atta] at 04:59 03 September 2014 DEMULSIFICATION OF CRUDE OIL EMULSIONS some specific molecular association of surfactants at the interfaces[44] The minimum interfacial tensions of asphaltenic crude oil in presence of blends, Table 7, were obtained at HLB range from 10 to 12. It was also observed that the lower IFT values were determined for B5 (which has HLB ¼ 10.7). This may give indirect evidence that the HLB and interfacial tension are linked in the same way by the demulsification capability. In this respect, the interfacial tension of the mixed surfactants is less than of individual surfactant. On the other hand, increasing the demulsification capability could be attributed to the intermolecular interaction between the two polymeric molecules.[45] The relation between demulsification efficiency of the selected blends, which have lower IFT values were presented in Table 7. The interactions between components of B5 are favorable for interface stabilization and give a quite good demulsification, Figures 4 and 5, since the repulsion between phenyl rings is minimized and the concentration of surfactants at interface is increased by their proximity. The most effective nonionic surfactant blend, Figures 4 and 5, appears to be good with an HLB 10.7, having long hydrophobic chains. 4. CONCLUSIONS The following conclusions can be withdrawn from the previous results in the following points: 1. New water soluble Schiff base surfactants derived from etherified condensed products of salicylaldehyde and aromatic or aliphatic diamines with PEG 2000. 2. 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