Fuel 87 (2008) 2943–2950

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Studies on the influence of long chain acrylic esters polymerswith polar monomers as crude oil flow improver additives

Ana Erceg Kuzmic *, Marko Radoševic, Grozdana Bogdanic, Vlasta Srica, Radivoje Vukovic 1

INA-INDUSTRIJA NAFTE, d.d., Research and Development Sector, 10002 Zagreb, Lovinciceva bb, Box 555, Croatia

a r t i c l e i n f o a b s t r a c t

Article history:Received 29 October 2007Received in revised form 14 April 2008Accepted 15 April 2008Available online 8 May 2008

Keywords:Crude oilPolymer additivesFlow improver

0016-2361/$ - see front matter � 2008 Elsevier Ltd. Adoi:10.1016/j.fuel.2008.04.006

* Corresponding author. Tel.: +385 1 238 15 73; faxE-mail address: ana.erceg-kuzmic@ina.hr (A. Erceg

1 Dr. Vukovic has passed away in the midst of wmanuscript. Our very sad duty was to complete what wmind all our discussions, debates, and shared plans. Wewill not be able to see this paper published.

This study investigated the efficiency of 22 polymer additives of defined and controlled structural char-acteristics in improving the flow properties of crude oil. The additives were synthesized by the solutionpolymerization of alkyl acrylates of various alkyl chain lengths with styrene, acrylic acid and 1-vinyl-2-pyrrolidone as copolymers or terpolymers. Polymerization was performed by tert-butylperoxy-2-ethylhexanoate as initiator in xylene at 92 �C, up to high conversion. The influence of polymerizationconditions on additive composition and properties, and their effect on the pour point and rheologicalproperties of crude oil samples from the fields of Števkovica, Obod and Ðeletovci located in the northernCroatia were studied. Additive efficiency was dominantly influenced by the alkyl acrylate chain length.The influence of component with carboxyl functional group or heterocyclic-nitrogen compound onadditive quality was less obvious. Additive efficiency significantly depended on the properties of crudeoil, and n-paraffin content and distribution. The main advantage of the process is that additives can bedirectly used without purification.

� 2008 Elsevier Ltd. All rights reserved.

1. Introduction

Crude oil contains a wide range of hydrocarbon componentswith extremely differing physical properties. The major constituentof these hydrocarbon streams is generally described as paraffinwax. Depending on the field of production, crude oil may containconsiderable amounts of wax (long chain normal alkanes) [1–4].These paraffins are relatively insoluble and they precipitate whencrude oil is cooled down below certain temperature [3,5,6]. Thecoherence of separated wax crystals in special structures impartscertain stiffness to oil. At sufficiently low temperature, oil may evensolidify completely. The presence of crystallized wax impairs theflow of crude oil. The higher the wax content is, the greater the flowproblems are [7]. However, there is no correlation between pourpoint and wax content, because other constituents in crude oil suchas asphaltene, resin, lighter distillates, and polar aromatics also af-fect its flow properties [8]. Highly waxy crude oils are characterizedby a high pour point, viscosity, and yield stress, and exhibit non-Newtonian flow behaviour below pour point temperature [9–12].The flow properties of crude oil play a great role in its production,

ll rights reserved.

: +385 1 238 12 28.Kuzmic).riting the main part of thise started together, bearing in

deeply regret that Dr. Vukovic

storage, transport, and refining [1,5,11,13]. Therefore, it is veryimportant to minimize the adverse effects of wax on the flow prop-erties of oil. Several options are available including stream heating,blending with lighter cutter stocks, mechanical scraping, and use ofchemical additives [3,13–15]. The preferred option is the use ofchemical additives referred to as wax crystal modifiers, also knownas pour point depressants (PPDs), flow improvers (FIs), and paraffininhibitors. PPDs modify the size and shape of crystals and inhibitformation of large wax crystal lattices [1,4,15–18]. They typicallyhave a wax-like paraffinic part that cocrystallizes with wax, form-ing components of oil and a polar component limiting the degreeof cocrystallization. Polymers with these properties are homo-and copolymers of alpha olefins [19], ethylene–vinyl acetatecopolymers [20,21], polyalkyl acrylates and methacrylates [22–26], alkyl esters of styrene–maleic anhydride copolymers [27–30],and alkyl fumarate–vinyl acetate copolymers [7]. Flow improversare very selective, that is, not all additives are sufficiently effectivefor every crude oil [10]. For example, some additives that consider-ably reduce viscosity and gel strength are poor PPDs.

This paper describes the preparation and evaluation of flowimprover additives for crude oil and could be regarded as a con-tinuation of a recently developed and published procedure [31].Additives were synthesized by free radical solution polymerizationusing tert-butylperoxy-2-ethylhexanoate as the initiator. Fourtypes of additives of different composition and molar weight wereprepared by copolymerization and terpolymerization of acrylesters of different alkyl chain length with styrene, acrylic acid

2944 A. Erceg Kuzmic et al. / Fuel 87 (2008) 2943–2950

and 1-vinyl-2-pyrrolidone. The quality of the prepared additives aspour point depressants and rheology improvers was tested oncrude oil samples from INA oil fields of Števkovica, Obod, andÐeletovci, Croatia.

2. Experimental

2.1. Materials

Monomers: Acrylate R�av 20.74 (acrylate C18-22, Arkema, Paris);acrylate Rav 19.24 (octadecyl acrylate, 97%, Aldrich); acrylate Rav

17.15 (hexadecyl acrylate, 95%, ABCR); acrylate Rav 13.02 (dodecylacrylate, 90%, Fluka); acrylic acid (AA) >99%, Fluka; styrene (St),99.5%, Fluka; 1-vinyl-2-pyrrolidone (1V2P), 99%, Aldrich.

Solvents: Xylene, isomers mixture, Fluka.Precipitating agent (nonsolvent): Methanol, 99%, Fluka.

Table 1Physical characteristics of crude oil samples

Property Method Crude oil sample

Štv 40 Ob 41 Ðt 22

Specific gravity, d154 , kg/m3 ASTM D 5002 844.4 846.3 876.1

API degree DMA 4500 36.07 35.69 29.34Pour point, �C ASTM D 97 25 23 22Dynamic viscosity, 30 �C, mm2/s ASTM D 445 8.53 8.58 7.36Paraffins, wt% UOP 46 9.69 8.20 6.60Water, wt% ASTM 4006e1 Traces Traces 0Sulphur, wt% Leco S 132 0.23 0.24 0.29

ASTM distillation ASTM D 86/93 Temperature, �CIBP 63 53 5910 vol.% 143 140 16820 vol.% 200 142 24230 vol.% 263 250 29540 vol.% 312 300 34150 vol.% 355 341 37560 vol.% 382 380 38665 vol.% 388

Fig. 1. Distribution of n-paraffin fractions in crude oi

Initiator: tert-butylperoxy-2-ethylhexanoate, Trigonox 21 C 70,Akzo Chemie.

The materials were used as received.Crude oil samples were taken from INA-INDUSTRIJA NAFTE d.d.,

Zagreb, Croatia (INA) oil fields Števkovica (Štv 40), Obod (Ob 41),and Ðeletovci (Ðt 22). Their properties and n-paraffin distributionare shown in Table 1 and Fig. 1.

*Rav = average alkyl chain length.

2.2. Measurements

The average number of carbon atoms in acrylic ester chain andadditive composition were determined in CDCl3 at room tempera-ture using a FT NMR Bruker Avance 300 with TMS as the internalstandard. Elemental analysis data were obtained using a LECOCHNS-932 automatic analyzer. Molar weights, based on calibrationwith monodispersed polystyrene standards (Polymer Laborato-ries), were determined by GPC (Varian HPLC, Model 8500 withPLgel Mixed gel C columns) at room temperature, using THF as sol-vent. Paraffin distribution in crude oil samples was analyzed usinga modified SIM DIS analysis and GC Varian Star 3400 cx apparatus.Pour point was determined using the Linetronic Oil Lab apparatus(ASTM D 97 method). Viscosity and flow curves (rheograms) weremeasured using a Haake RV 20/CV 100 rotating viscometer. Acrylicacid content was determined using the standard method for acidity(ASTM D 3242-05).

2.3. Polymerization of additives

All additive samples were prepared by free radical solutionpolymerization in xylene using Trigonox 21 C 70 as the initiator.Polymerization was performed in a reaction flask equipped witha condenser, mechanical stirrer, and temperature controller. Poly-merization reaction was carried out in nitrogen atmosphere at92 �C for 5 h, under continuous stirring. During that time, morethan 95% of monomer was polymerized. The resulting homoge-neous product was then cooled down to room temperature andused as additive without any further treatment.

l samples Štv 40, Ob 41, Ðt 22, SIM DIS analysis.

A. Erceg Kuzmic et al. / Fuel 87 (2008) 2943–2950 2945

To determine monomer-to-polymer conversion and additivecomposition, we isolated the ultimate polymer by repeated precip-itation with methanol, filtering, and dissolving in xylene. The finalproduct was vacuum dried at 60 �C. The 1H NMR spectra indicatedthe absence of unreacted monomer in the isolated polymer. Theconversion of monomers was determined gravimetrically. Polymercomposition was obtained from 1H NMR, elemental analysis (fromnitrogen content), and acrylic acid content (alkalimetric titrationusing potassium hydroxide as titrant).

Table 3Characteristics of additives (property and method)

Samplecode

Density (15 �C), kg/m3

ASTM D4052/91Pour point, �CASTM D 97/93

Flash pHR EN

1 889.4 15 272 884.8 9 283 889.3 6 28.54 893.5 �18 285 890.4 15 306 883.3 9 29.57 886.2 6 29.58 892.4 �45 289 885.7 21 27

10 889.7 21 2411 889.7 21 2812 890.7 21 2613 890.8 21 2814 883.6 15 2715 883.4 9 28.516 876.9 0 28.517 893.5 �45 2718 896.7 24 2719 884.5 15 2720 883.4 6 29.521 876.4 �6 29.522 893.0 �48 27EVATANa 869.3 3 27

a Evatan, ICI, commercial sample, ethylene-co-vinylacetate: 0.864:0.136 mole ratios; 1

Table 2The influence of polymerization conditions on additive composition

Sample code Monomer composition in feed and in polymer (), mole fractio

Rav, acrylate St AA

1 20.74, 0.78 (0.84) – 0.22 (2 19.24, 0.78 (0.84) – 0.22 (3 17.15, 0.78 (0.82) – 0.22 (4 13.02, 0.78 (0.81) – 0.22 (5 20.74, 0.78 (0.82) 0.05 (0.04) 0.17 (6 19.24, 0.78 (0.81) 0.05 (0.06) 0.17 (7 17.15, 0.78 (0.81) 0.05 (0.04) 0.17 (8 13.02, 0.78 (0.80) 0.05 (0.04) 0.17 (9a 20.74, 0.78 (0.82) 0.05 (0.04) 0.17 (10a 20.74, 0.78 (0.82) 0.05 (0.05) 0.17 (11a 20.74, 0.78 (0.81) 0.05 (0.04) 0.17 (12a 20.74, 0.78 (0.79) 0.05 (0.05) 0.17 (13a 20.74, 0.78 (0.82) 0.05 (0.04) 0.17 (14 20.74, 0.78 (0.78) – 0.17 (15 19.24, 0.78 (0.80) – 0.17 (16 17.15, 0.78 (0.78) – 0.17 (17 13.02, 0.78 (0.80) – 0.17 (18a 20.74, 0.78 (0.81) – 0.11 (19 20.74, 0.78 (0.82) 0.05 (0.06) –20 19.24, 0.78 (0.83) 0.05 (0.07) –21 17.15, 0.78 (0.82) 0.05 (0.05) –22 13.02, 0.78 (0.83) 0.05 (0.06) –

Polymerization temperature 92 �C; polymerization time 5 h; solvent–monomer ratio.a 60:40; in other samples is 70:30; additive composition (1H NMR).* Titration method.** Based on nitrogen content.

3. Results and discussion

Flow improver additives of defined and controlled structuralcharacteristics were prepared by solution polymerization of acrylicesters of different alkyl chain length (acrylate, Rav) with styrene (St),acrylic acid (AA) and 1-vinyl-2-pyrrolidone (1V2P). We studied theinfluence of polymerization conditions on additive composition andproperties, and consequently the effects of additives on the pourpoint and rheological behaviour of various crude oil samples.

oint, �C2719

Viscosity (40 �C), mm2/sASTM D446/95

Molar weight,g/mol � 10�3

Mw Mn

6.79 37.6 18.44.67 20.4 10.76.20 19.6 10.77.08 22.7 11.68.51 22.6 11.75.03 22.0 12.85.15 20.0 11.46.23 22.6 11.3

11.2 40.2 22.118.1 32.1 15.722.6 30.4 15.118.8 28.6 14.221.47 24.7 12.1

4.91 22.1 13.85.25 20.3 12.11.53 13.2 9.35.62 18.6 9.57.14 36.3 15.78.32 29.8 17.48.27 27.4 15.91.53 10.9 7.58.92 27.3 13.63.48 66.5 24.3

H NMR.

n Conc. init., wt% Conv., %

1V2P

0.16)* – 0.4 970.16)* – 0.4 960.18)* – 0.4 980.19)* – 0.4 96.50.14) – 0.4 970.13) – 0.4 96.50.15) – 0.4 970.16) – 0.4 980.14) – 0.2 96.50.13) – 0.35 970.15) – 0.5 970.16) – 0.6 980.14) – 0.9 98.40.19)* 0.05 (0.03)** 0.5 97.50.18)* 0.05 (0.02)** 0.5 980.18)* 0.05 (0.04)** 0.5 980.16)* 0.05 (0.04)** 0.5 96.50.13)* 0.11 (0.06)** 0.5 97.5

0.17 (0.12) 0.5 960.17 (0.10) 0.5 96.50.17 (0.13) 0.5 970.17 (0.11) 0.5 98

2946 A. Erceg Kuzmic et al. / Fuel 87 (2008) 2943–2950

3.1. Polymerization conditions and additive composition

Copolymer samples of alkyl acrylates of average alkyl chainlength (acrylate) of 13.02, 17.15, 19.24, 20.74 carbon atoms withAA, poly(acrylate-co-AA), were prepared. For comparison, we alsoprepared acrylate additives of the same alkyl chain length withSt and AA, poly(acrylate-St-AA), with AA and 1V2P, poly(acrylate-AA-1V2P), and with St and 1V2P, poly(acrylate-St-1V2P). Experi-mental conditions and additive composition are given in Table 2.

Table 4The influence of additive compositions and molar weights on the pour point of crude oil

Sample code Additive composition, mole fraction

Rav, Acrylate St AA 1V2P

1 20.74, 0.84 – 0.16 –2 19.24, 0.84 – 0.16 –3 17.15, 0.82 – 0.18 –4 13.02, 0.81 – 0.19 –5 20.74, 0.82 0.04 0.14 –6 19.24, 0.81 0.06 0.13 –7 17.15, 0.81 0.04 0.15 –8 13.02, 0.80 0.04 0.16 –9 20.74, 0.82 0.04 0.14 –

10 20.74, 0.82 0.05 0.13 –11 20.74, 0.81 0.04 0.15 –12 20.74,0.79 0.05 0.16 –13 20.74, 0.82 0.04 0.14 –14 20.74, 0.78 – 0.19 0.0315 19.24, 0.80 – 0.18 0.0216 17.15, 0.78 – 0.18 0.0417 13.02, 0.80 – 0.16 0.0418 20.74, 0.81 – 0.13 0.0619 20.74, 0.82 0.06 – 0.1220 19.24, 0.83 0.07 – 0.1021 17.15, 0.82 0.05 – 0.1322 13.02, 0.83 0.06 – 0.11Evatan, ICI, ethylene-co-vinylacetate:0.864:0.136 mole ratioUntreated crude oil samples

Fig. 2. Structural representation of: (a) copolymer of acrylate-AA; (b) terpolymer ofacrylate-St-AA; (c) terpolymer of acrylate-AA-1V2P; (d) terpolymer of acrylate-St-1V2P.

Polymer additives of various molar weights of acrylate Rav 20.74(molar fraction 0.78) with St (molar fraction 0.05) and AA (molarfraction 0.17), poly(acrylate-St-AA), were prepared with 0.2, 0.35,0.5, 0.6, and 0.9 wt% of initiator Trigonox 21 C 70.

Additive properties are presented in Table 3. The chemicalstructure of the synthesized compounds is shown in Fig. 2.

The results in Table 2 show that the conversion yield is morethan 95%. It is also evident that molar fractions of alkyl esters inthe additives closely correspond to those in the comonomer mix-ture regardless of the alkyl chain length. This can be attributed tosimilar structure and electron environment around the doublebond [32]. Acrylate reactivity can be exploited in polymerizationwith AA and St, based on the earlier results [33] obtained by thepolymerization of octadecyl acrylate (C18) with St and AA. Mono-mer reactivity ratios of St (r1) and C18 acrylate (r2) were 0.78 and0.31, respectively. The reactivity ratios of C18 acrylate (r1) with AA(r2) were 3.0 and 0.5, respectively [34]. These data show that acry-late units are incorporated into the additive preferably to AA units.In contrast, St units are incorporated preferably to acrylate. In thecopolymerization of St (r1) and AA (r2), the reactivity ratios are 0.25and 0.15 [35]. Recently, the reactivity ratios for 1V2P(r1)-co-AA(r2)were determined as 0.1 and 1.1, respectively [36], showing that AAunits are incorporated into the polymer preferably to 1V2P. Fur-thermore, additive samples prepared with 1V2P in these experi-ment were as homogeneous as all other samples, which meansthat 1V2P was not homopolymerized [poly(1V2P) is insoluble inaromatic solvents and precipitates from solution] [37].

The most remarkable conclusion drawn from Table 3 is thatpolymer additive compositions (Table 2) exhibit almost the sameeffect on additive properties. An exception is the effect on the pourpoint temperature; the pour point decreases with decreasing acry-late chain length of the additive. For example, polymeric additiveprepared by the polymerization of acrylate Rav 20.74 with AA and1V2P exhibited pour point at 15 �C. Terpolymer of acrylate Rav

13.02, with the same monomers of the same molar ratios of com-ponents exhibited pour point at �45 �C.

In order to estimate the influence of molar weight, terpolymersof acrylate with St and AA were prepared by adding the initiator to

samples Štv 40, Ob 41, Ðt 22; additive concentration 1000 ppm

Molar weight, g/mol � 10�3 Pour point, �C

Crude oil sample

Mw Mn Štv 40 Ob 41 Ðt 22

37.6 18.4 10 4 920.4 10.7 8 18 2119.6 10.7 27 21 2325.3 16.3 27 25 2422.6 11.7 3 0 �622.0 12.8 6 20 2120.0 11.4 26 22 2322.6 11.3 26 24 2140.2 22.1 21 6 �1032.1 15.7 19 2 �1030.4 15.1 21 4 �1028.6 14.2 24 5 �1024.7 12.1 22 15 �1022.1 13.8 23 1 �1020.3 12.1 1 17 1713.2 9.3 27 23 2318.6 9.5 25 22 2436.3 15.7 1 2 �529.8 17.4 5 5 �827.4 15.9 7 22 1410.9 7.5 23 22 2327.3 13.6 27 24 2466.5 24.3 11 5 3

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A. Erceg Kuzmic et al. / Fuel 87 (2008) 2943–2950 2947

the polymerization mixture in the following concentrations: 0.35;0.5; 0.6; 0.9 wt%. The results are presented in Table 3, too.

The structure of polymeric additives was determined by record-ing the 1H NMR spectra. The peak assignments for the polymersare as follows: (a) octadecyl acrylate polymer, d: 3.9 ppm,–OCH2– groups; 2.18 ppm, –CH–COO– groups; 1.2 ppm, –CH2–groups of the side chain; 0.98 ppm, end –CH3 groups of the sidechain; (b) styrene polymer, d: 6.9–7.2 ppm, –C6H5 groups; 1.1–2.4 ppm, –CH2–CH– groups; (c) acrylic acid polymer, d: 2.5–2.3 ppm, –CH–COO– groups; 1.5–2.1 ppm, –CH2– groups and (d)

1-vinyl-2-pyrrolidone polymer, d: 3.96 ppm, –CH-N– | and –CH2-N–

| groups; 3.3 ppm, –CH2-N-C=O

| groups; 2.2 ppm, –CH2– groups.

3.2. Influence of additive composition and molar weight on the pourpoint of crude oil samples Štv 40, Ob 41, and Ðt 22

Generally it is assumed that the compounds belong to the classof pour point depressants capable of decreasing the pour point byat least 6 �C for a rate of utilization not exceeding 0.2% by weight ofthe polymeric additive [24].

Table 4 compares pour point measurements of crude oil sam-ples containing 1000 ppm of the prepared additives and those con-taining commercial additive Evatan, ICI.

The experiment shows that additive composition and crude oilproperties (predominantly n-paraffin content and its distribution)highly influence the pour point of crude oil. The effect of acrylicacid copolymers with acrylates of various alkyl chain lengths isalso presented in Table 4. The results suggest that the acrylatechain length has a considerable effect on additive efficiency. Onthe other hand, the influence of the polar AA comonomer on pourpoint temperature depression is not evident.

Terpolymers of acrylate of various alkyl chain lengths and polar-ity were also evaluated as pour point depressants for crude oil sam-ples (Table 4). The results show that the effect of the preparedadditives depended on their composition and crude oil properties.Terpolymers of acrylate Rav 20.74 with St and polar AA were themost efficient for Ob 41 and Ðt 22 crude oils. Moreover, for Ðt 22they proved much better than the commercial additive Evatan,ICI. Terpolymers containing 1V2P failed to exhibit the expected effi-ciency. This suggests that copolymers and terpolymers of acrylateRav 20.74 are the best pour point depressants for treated crude oils,regardless of other additive components and their molar fraction.

Additives of molar weight bellow 20,000 g/mol were not effi-cient at all (Table 4).

3.3. Influence of additive concentration on crude oil pour point

The influence of additive concentration on pour point of crudeoil samples Štv 40, Ob 41, and Ðt 22 was studied in the range from500 to 2000 ppm (Table 5). The additives were prepared by poly-merizing acrylate Rav 20.74 with St and AA; acrylate Rav 20.74 withAA and 1V2P, and acrylate Rav 20.74 with St and 1V2P (Tables 2 and3; samples 5, 14, 19). Table 5 also shows the evaluation of thecommercial additive sample Evatan, ICI. Additive concentrationsefficiently decreasing the pour point of crude oil samples wereP1000 ppm for Ðt 22 and Ob 41 and 2000 ppm for Štv 40. Thecommercial additive had a satisfactory efficiency at 1000 ppm,except for crude oil Štv 40 which required the concentration of1500 ppm for a proper effect.

3.4. Influence of additive on the rheology of crude oil samples

Pour point does not completely describe crude oil flow proper-ties. Viscosity and gel strength should also be considered. Complexrheological relationships are usually characterized by a shear

Fig. 3. Viscosity versus shear rate for crude oil sample Štv 40, untreated and treatedwith 1000 ppm of additives at 10 �C.

2948 A. Erceg Kuzmic et al. / Fuel 87 (2008) 2943–2950

rate/shear stress rheogram. Rheological measurements can providea direct account of additive performance in the production, trans-

Fig. 4. Shear stress versus shear rate for crude oil sample Štv 40, untreated andtreated with 1000 ppm of additives at 10 �C.

portation, and storage of oil. This in particular refers to viscosity,which controls the pressure necessary to restart a pipeline or awell and corresponds to the minimum shear stress (yield value,yield point). Yield value is obtained by extrapolating the shearstress to zero shear rate on a linear plot. In this study, rheologicalbehaviour of untreated and additive treated crude oil was deter-mined by measuring viscosity and shear stress. The rotating vis-cometry method was used in stationary conditions. Additivepoly(acrylate20.74-AA-1V2P), sample 18, Table 2, and poly(acry-late20.74-St-1V2P), sample 19, Table 2, were evaluated for crudeoil samples Štv 40, Ob 41, and Ðt 22 because they exhibited satis-factory influence on the pour point of all crude oils. Figs. 3 and 4show viscosity versus shear rate, and shear rate versus shear stressfor untreated and additive treated crude oil Štv 40.

Figs. 5 and 6 show the influence of these additives on the viscos-ity/shear rate and shear rate/shear stress diagrams of the crude oilOb 41.

The results obtained for crude oil Ðt 22 are presented in Figs. 7and 8.

Table 1 shows that the examined crude oils possess unfavour-able rheological properties. Furthermore, flow curves of the un-treated crude oil samples suggest non-Newtonian fluid properties(Figs. 4, 6 and 8). The addition of two structurally different addi-tives 18 and 19 reduced the viscosity of Ob 41 and Ðt 22 crudeoil samples (Figs. 5 and 7). Additive 19 was not applicable for Štv40 (Fig. 3). The yield values (s0) of the untreated crude oil sampleswere much higher than in samples treated with additives 18 and19, which exhibited a favourable influence on the flow properties

Fig. 5. Viscosity versus shear rate for crude oil sample Ob 41, untreated and treatedwith 1000 ppm of additives at 10 �C.

Fig. 7. Viscosity versus shear rate for crude oil sample Ðt 22, untreated and treatedwith 1000 ppm of additives at 10 �C.

Fig. 8. Shear stress versus shear rate for crude oil sample Ðt 22, untreated andtreated with 1000 ppm of additives at 10 �C.

Fig. 6. Shear stress versus shear rate for crude oil sample Ob 41, untreated andtreated with 1000 ppm of additives 10 �C.

A. Erceg Kuzmic et al. / Fuel 87 (2008) 2943–2950 2949

of crude oils Ob 41 and Ðt 22 (Figs. 6 and 8). Again, additive 19 wasnot efficient for Štv 40 (Fig. 4). The efficiency of additive 18 inimproving the rheological properties of crude oil could be attrib-uted to its higher polarity owed to the presence of the AAcomonomer.

4. Conclusions

Our study has shown that additive efficiency (pour pointdepression and rheological properties) depends on its composition,polarity, as well as on crude oil properties, its n-paraffin contentand distribution. Additives prepared for this experiment exhibiteda satisfactory effect as flow improvers of crude oil. Copolymers andterpolymers of acrylate Rav 20.74 are the best pour point depres-sants for treated crude oils regardless of other additive compo-nents and their molar fraction. They also reduced the viscosity ofcrude oil samples. The yield values in untreated crude oil sampleswere much higher than in additive treated samples. In other words,additive treated crude oil could be transported with minimumenergy consumption and therefore minimum pressure in thepipeline.

Acknowledgement

The authors gratefully acknowledge the support of the Ministryof Science, Education and Sports of the Republic of Croatia.

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