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Rheological Study of O/W Concentrated Model Emulsions for HeavyCrude Oil TransportationD. Gabrielea; M. Miglioria; F. R. Lupia; B. De Cindioa

a Department of Engineering Modelling, University of Calabria, Rende, Italy

Online publication date: 05 October 2010

To cite this Article Gabriele, D. , Migliori, M. , Lupi, F. R. and De Cindio, B.(2011) 'Rheological Study of O/WConcentrated Model Emulsions for Heavy Crude Oil Transportation', Energy Sources, Part A: Recovery, Utilization, andEnvironmental Effects, 33: 1, 72 — 79To link to this Article: DOI: 10.1080/15567030902937283URL: http://dx.doi.org/10.1080/15567030902937283

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Energy Sources, Part A, 33:72–79, 2011

Copyright © Taylor & Francis Group, LLC

ISSN: 1556-7036 print/1556-7230 online

DOI: 10.1080/15567030902937283

Rheological Study of O/W Concentrated Model

Emulsions for Heavy Crude Oil Transportation

D. GABRIELE,1 M. MIGLIORI,1 F. R. LUPI,1 and

B. DE CINDIO1

1University of Calabria, Department of Engineering Modelling, Rende, Italy

Abstract The oil-in-water emulsion is increasing in popularity as a cost-reducing

method for “heavy” crude oil transportation. In order to analyze the effect of oil-in-water ratio and emulsifier amount on the viscosity of the final emulsion, concentrated

model-emulsion of oil-in-water were rheologically characterized. Two emulsificationmethods were investigated: batch and “in-flow” in a lab scale plant. Comparison

revealed the effect of the emulsifier amount both on the viscosity decay during timeand on the final emulsion viscosity. Qualitative microscopy results revealed a rather

wide drop size distribution for systems exhibiting a lower viscosity value.

Keywords crude oil, emulsifier effect, flow emulsification, O/W emulsion viscosity,rheology

1. Introduction

The preparation of crude oil in water emulsion is one of the methods used to decrease

the fluid viscosity for crude oil transportation in pipelines (Saniere et al., 2004). Emulsi-

fication can decrease the viscosity of crude oil, reducing pressure drop in pipelines as a

consequence. Nevertheless, the study of formation and characterization of crude oil-water

emulsion is still an interesting topic to be exploited, in the view of industrial application.

Viscosity of heavy oils may widely range from 0.1 to 100 Pa � s�1 (Ahmed et al., 1999;

Quiñones-Cisneros et al., 2005), also showing shear thinning behavior, depending upon

type and amount of minor components (such as waxes, resins, asphaltenes, sand, or

eventually hydrates). In the view of a systemic approach of the rheology of heavy oil

O/W emulsion, it would be useful to set up a “model oily” phase, based on standard

oil and accounting for relevant viscosity effect (including waxes, asphaltenes, and solid

particles), to be used as a test material in a bench scale test. Packing degree, droplet size,

and distribution of disperse phase strongly affect the viscosity; thus, the control of the

rheological behavior of emulsions becomes rather crucial (Pal, 2000). In this concern,

this article shows results of oil-in-water (O/W) emulsion of a base oil having a Newtonian

viscosity comparable to that of heavy oil without any additive component. Viscosity data

of O/W emulsion, prepared using hydrophilic nonionic emulsifier (Yaghi and Al-Bemani,

2002), are obtained either from batch preparation or from an emulsifying loop, a lab scale

loop-plant aiming at reproducing flow emulsification process on a small scale. Different

emulsifier amounts and O/W ratios are investigated in terms of either emulsion viscosity

or “in-flow” emulsion formation.

Address correspondence to Massimo Migliori, University of Calabria, Department of Engi-neering Modelling, Via P. Bucci Cubo 39c, Rende 87036, Italy. E-mail: migliori@unical.it

72

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Rheology of Heavy Crude O/W Concentrated Emulsions 73

2. Materials and Methods

2.1. Materials

O/W emulsions are prepared using distilled water and commercial paraffin oil Finavestan

A360B (Total, France); hydrophilic nonionic emulsifier is Tween 60 (polyoxyethilene-

sorbitan monostereate, HLB 14.9, gives O/W emulsions) purchased from Sigma Aldrich

(Milan, Italy). The oil/water ratio and the emulsifier amount were varied and each

recipe was prepared following two different emulsification processes, batch and in-flow,

producing different samples, labeled as Bx and Ex respectively, as reported in Table 1.

2.2. Batch Emulsification

Water is heated up to 70ıC and the hydrophilic emulsifier is gently added in a cylindrical

beaker (volume 600 ml), stirring the solution for 5 min. The oil is slowly dropped and the

mixture is agitated for another 5 min. Homogenization of the emulsion is completed for

10 min using a commercial blender (Minipimer Braun MR 404 Plus, Frankfurt, Germany)

having a nominal power of 300 W. After homogenization, rheological characterization

was performed after 3 h of rest at room temperature (Samples B1–B3).

2.3. Flow Emulsification

Flow emulsification on laboratory scale was performed using the experimental home-

made system. During the start-up, oil and water were mixed using a module M (Figure 1)

consisting of an external cylindrical poly(methyl methacrylate) (PMMA) vessel (IDV

64 mm, ODV 70 mm) with an internal coaxial copper pipe (IDP 20 mm, ODP 22 mm).

Oil was pumped by a peristaltic pump (Watson Marlow 323Du, Wilmington, MA)

running at 400 rpm, equipped with a series of four pumping heads (type 313-X), while

water was fed using a centrifugal pump having a nominal power of 0.5 hp (Tecno

05/4M, Brescia, Italy). At the end of the start-up phase, when both the pure fluid

reservoirs were empty, the loop was full of oil-water mixture to be emulsified re-

circulating the fluid from the reservoir S (volume 20 l) to the module M. The reser-

voir S was equipped with a shaft agitator (Heidolph, Kelheim, Germany) to prevent

potential spontaneous de-emulsification and temperature control of the reservoir was

Table 1

Samples identification and composition

Sample

ID

Paraffin oil,

% [v/v]

Water,

% [v/v]

Emulsifier,

% [w/w]

Emulsification

method

E1 50 50 2 Flow

E2 60 40 2 Flow

E3 50 50 1 Flow

B1 50 50 2 Batch

B2 60 40 2 Batch

B3 50 50 1 Batch

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74 D. Gabriele et al.

Figure 1. Plant flowsheet.

guaranteed by cold water (15ıC) flowing in a coil from a thermostatic bath TC (Neslab,

Newington, NH). PP1 and PP2 pipelines (length 3.73 m and 1.75 m, respectively), were

made of Rilsan® (ID 10 mm). The sampling for rheological test was performed from

the reservoir S at different times (measured from start-up end on) as reported in Table 2

(Px samples), and for contrast phase microscopy tests (Leica DHIL, Solms, Germany) as

reported in Table 3 (Mx samples).

2.4. Rheological Characterization

Flow curves were obtained using a controlled strain rheometer ARES-RFS (TA Instru-

ment, New Castle, DE) equipped with a Couette cylinder geometry (internal bob diameter

32 mm, gap 1 mm). The shear rate range was 0.1–100 s�1 except when higher shear

rates (at least 1 s�1) were required to measure torque values within the instrument limits

(from 2 � 10�7 N � m to 0.1 N � m). Temperature was set at 25ıC using a thermostatic

bath (Julabo, San Diego, CA). Preliminary “step shear rate” test at 0.1 s�1 or 1 s�1, was

Table 2

Sampling time (min) for rheological

measurement (P) and for microscopy test (M)

during in-flow emulsification test

Sampling

label E1 E2 E3

P1 2 5 3

P2 15 19 16

P3 80 34 29

P4 180 185 100

M1 15 19 16

M2 80 46 29

M3 180 185 100

Start up time 5 4 5

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Rheology of Heavy Crude O/W Concentrated Emulsions 75

Table 3

Plateau viscosity of different in-flow

emulsification test

Sample

Viscosity,

Pa � s

Std. Dev.,

Pa � s

E1 (P4) 0.0083 0.0004

B1 0.0119 0.0005

E2 (P4) 0.0144 0.0002

B2 0.03055 0.0005

E3 (P4) 0.0107 0.0009

B3 0.0106 0.0003

performed to evaluate the time needed to reach the steady state before measurement. For

all samples, a time of 20 s was found to be sufficient to reach the time independent

viscosity value and steady shear viscosity was averaged over 10 s sampling time.

3. Results and Discussion

3.1. Rheological Test

The flow curves of batch preparation and of the samples collected during the in-flow

emulsification test are shown in Figures 2–4. Each plot also includes the constant viscosity

of pure paraffin oil (measured value 0.1570 ˙ 0.0002 Pa � s). Batch emulsions Bx

exhibited a constant viscosity in the investigated shear rate range. When the oil/water

Figure 2. Flow curve for test E1 compared to pure oil and batch emulsion.

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76 D. Gabriele et al.

Figure 3. Flow curve for test E2 compared to pure oil and batch emulsion.

ratio is considered (sample B1 and B2), a nonlinear increase in viscosity was observed

when increasing the oil fraction. As for the emulsifier effect (samples B1 and B3), a

decrease in viscosity was found when decreasing the emulsifier amount (Yaghi and Al-

Bemani, 2002). Indeed, it is known that a lower amount of emulsifier leads to bigger

droplets (with a lower surface to volume ratio) (Barnes, 2000) and, therefore, to lower

viscosity values as confirmed by some open literature finding (Ford et al., 1997). Referring

to the loop test, a marked time-dependence of the viscosity for early samples was found.

Figure 4. Flow curves for test E3 compared to paraffin oil and batch test.

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Rheology of Heavy Crude O/W Concentrated Emulsions 77

Moreover, as a result of the progressive emulsification process, the viscosity data showed

a less pronounced shear rate dependence when the emulsification time was increased

(i.e., residence time into the loop). It is noteworthy that within the investigated O/W

ratio range, emulsions show an apparent Newtonian behavior when samples are fully

emulsified (Pal, 2000; Romero et al., 2002). On the contrary, at the same O/W ratio, during

emulsification process, a shear rate-dependent behavior indicates a partial emulsification,

leading to an “apparent” time dependent behavior due to flow instability. Therefore,

referring to “in-flow” tests, samples showing shear rate-dependence of viscosity cannot be

quantitatively analyzed (samples P1–P3) and our analysis refers only to fully emulsified

material (samples P4) in comparison to batch samples (Table 3).

From Figure 2 it can be seen that for Sample E1 the “in-flow” test viscosity

value under-crossed the batch test value B1. This evidence can be explained because

viscosity is very sensitive to drop size distribution (Ford et al., 1997) and the average

drop size distribution in the “in-flow” test can be less narrow than that of the batch-

emulsification one. Drops of different dimensions allow a better dispersed phase packing

and, therefore, viscosity decreases below the batch sample value (Barnes, 2000), and

the observed viscosity decrease could be ascribed to the increased drop dimension (Ford

et al., 1997) due to coalescence phenomena induced by the shear effect during “in-flow”

test (Al-Mulla and Gupta, 2000). The analysis of E2 (oil-water ratio higher than E1) in

Figure 3 confirms this trend, with a final viscosity value greater than sample E1. On

the contrary, when the E3 sample is considered (lower emulsifier content than E1) in

Figure 4, an opposite behavior is observed: the plateau value of the viscosity (P4 after

100 min) did not significantly drop down to that of the batch sample, showing that with

the decrease of the emulsifiers amount, no significant effects are observed when changing

the emulsification method. A different explanation may support this evidence: if the role

of the emulsifier is considered, a smaller amount (E3) accelerates the emulsification

process but, with the increase of emulsification time, any drop in the viscosity of the

emulsion E3 is observed. It is attributed to the fact that lower emulsification availability

does not allow any further change of the drop size distribution. Still, comparing of the

plateau viscosity during loop test (P4) and batch (Table 3), it can be observed that for

sample E1 batch viscosity is higher than that of the in-flow because of the effect of the

higher emulsifier content. Higher emulsifier content promotes oil dispersion, decreases

average diameter, and increases the apparent viscosity, also for low emulsification times,

such as in the batch preparation. On the contrary, when “in-flow” process is considered,

a shear-induced coalescence is promoted by the higher number of (small) droplets, and

widening of the drop size distribution causes the decrease of the emulsion apparent

viscosity. Moreover, emulsions prepared with a very high shear rate seem to be bimodal

(Hénaut et al., 2009).

3.2. Microscopy Data

The viscosity data and the trend can be confirmed by the qualitative analysis made by

contrast phase microscopy. Samples have been analyzed after their dilution in water

in a volumetric proportion equal to 1:10 to improve a better visualization of droplets.

Data are reported in Figure 5, where label M1-M3 refers to the sampling time reported

in Table 2. It can be seen that sample E1-M1 and E3-M1 showed more pronounced

aggregates of disperses phase; on the contrary, sample E2-M1 shows small oil droplets,

and E2 viscosity data are less shear rate-dependent also for early loop residence time

(sample E2-P1), if compared to samples E1 and E3 having higher W/O ratio. In addition,

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78 D. Gabriele et al.

Figure 5. Droplets distribution from contrast phase microscopy for different sampling time.

Control bar is 100 �m.

when the effect of the emulsifier is considered (E1-P4 vs. E3-P4), it has been found that

the plateau viscosity is higher when the emulsifier amount (Table 1) is reduced. This can

be explained (Figure 5), because of the coarse grain of emulsion E1-P4, as shown by the

microscopy sample E1-M3, if compared to E3-M3: the lower the emulsion average drop

diameter, the higher the apparent Newtonian viscosity is (Ford et al., 1997).

4. Conclusions

In this article, a rheological approach to the study of concentrated O/W emulsion for

heavy crude oil transportation in pipelines is shown, comparing results of a lab scale

“loop emulsification” process to batch preparation ones. A constant viscosity, as shear

rate function, was found for all batch samples and for “in-flow” emulsions at long times,

while during emulsification in the loop plant a shear thinning behavior was observed

and this effect was mainly ascribed to the wideness of the drop size distribution curve.

A comparison of flow test results, including flow curves and microscopy, for samples

at a different percentage of emulsifier or oil/water ratio, shows that larger amounts of

emulsifier during prolonged emulsification could lead to a broader drop size distribution

and a lower viscosity as a consequence in comparison to the same O/W ratio sample but

with half the emulsifier amount. Therefore, lower plateau viscosity values are obtained

when increasing the amount of emulsifier, enhancing the effect of a wider drop size

distribution.

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Rheology of Heavy Crude O/W Concentrated Emulsions 79

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