Simple Functionalization of Asphaltene and Its Application for Efficient

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Simple functionalization of asphaltene and its application for efficient asphaltene removal Seonung Choi, Wonbum Pyeon, Jong-Duk Kim, and Nam-Sun Nho Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.6b01184 • Publication Date (Web): 23 Aug 2016 Downloaded from http://pubs.acs.org on August 26, 2016

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Energy & Fuels

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Simple functionalization of asphaltene and its

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application for efficient asphaltene removal

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Seonung Choi,a Wonbum Pyeon,a Jong-Duk Kim,a* Nam-sun Nhob

5

a

6

Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon 305-701, Republic of Korea

7

b

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(KIER), 152 Gajeong-ro, Yuseong-gu, Daejeon, 305-343, Republic of Korea

Department of Chemical and Biomolecular Engineering, Korea Advanced Institute of Science

High Efficiency and Clean Energy Research Division, Korea Institute of Energy Research

9 10

Abstract

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Asphaltene, the cheapest fraction of petroleum was modified to a novel additive in order to

12

facilitate the deasphalting process such as paraffinic froth treatment. Asphaltene powder was

13

oxidized by ozone, which is more powerful and less harmful on the environment than other

14

oxidants. The ozonized asphaltene was characterized, and the reaction kinetics of ozonation

15

were interpreted by the shrinking core model. Ozonized asphaltene was added to a water/n-

16

pentane/bitumen emulsion to enhance the precipitation of asphaltene. Control of the

17

properties of the precipitate was allowed by adjusting the ozonation degree and dosage of

18

ozonized asphaltene. The removal of asphaltene was enhanced from 40 % to a maximum of

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70 % by adding ozonized asphaltene under the same conditions. The boiling point

20

distribution of deasphaltened oil indicates that a large amount of residue was removed using

21

ozonized asphaltene. The dispersion behavior was checked by measuring the aggregate size

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in toluene and alkane solution. It was confirmed that asphaltene and ozonized asphaltene can

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interact with each other with high affinity.

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Keywords:

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Ozonation, Asphaltene, Shrinking core model, Paraffinic froth treatment

6 7

1. Introduction

8

Bitumen is one of the unconventional oils recovered from oil sands by steam assisted gravity

9

drainage (SAGD) or mining.1-4 When mined oil sands are mixed with water, bitumen froth was

10

generated and cleaned by the froth treatment process, a separation process that removes water

11

and sand particles from bitumen froth.5

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In general, two main froth treatment processes are in operation; naphthenic froth treatment

13

(NFT) and paraffinic froth treatment (PFT). In naphthenic froth treatment, naphtha is used as

14

a diluent to reduce viscosity and density, and can achieve a high yield of recovery (aproximately

15

99%), however, the produced bitumen contains water and solids. Conversely, paraffinic froth

16

treatment, which is a relatively new process, uses paraffin solvent as a diluent, and produces a

17

higher quality bitumen with low concentrations of water, solids, and asphaltene. Moreover, it

18

consumes less energy than naphthenic froth treatment. However, one drawback of paraffinic

19

froth treatment is the loss of hydrocarbons and a higher ratio of solvent/bitumen than seen with

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naphthenic froth treatment.6 In some cases, bitumen is required to be transported long distances,

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such as to Shell’s Albian Sands project, thus, it is necessary to remove asphaltene during

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paraffinic froth treatment.7 Often, partial deasphalting can be conducted by paraffinic froth

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treatment on-site at the mine to remove the majority of asphaltene from bitumen.8

24

Recent research has examined certain factors that have an effect on froth treatment. For

25

instance, a temperature change from 80 to 50 oC resulted in a great decrease in recovery and


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an increase in the optimum paraffin/bitumen ratio in paraffinic froth treatment, while the

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temperature decrease had little on naphthenic froth treatment. Additionally, paraffinic froth

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treatment has been shown to be more sensitive to the conditions of bitumen extraction.6, 9-12.

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Unlike conventional oil, bitumen contains a high amount of asphaltene, which is insoluble in

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n-pentane or n-heptane, but soluble in toluene.13 Moreover, asphaltene contains several

6

aromatic rings and heteroatoms (N, S, and O). Thus, asphaltene has surface activity and polarity

7

14-17

8

of the pipeline during refinement and transportation.18, 19 Asphaltene is dispersed by resin-like

9

surfactant in crude oil,20 which can interact with asphaltene via several intermolecular forces;

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Van der Waals force, π-π stacking, acid-base interaction, and hydrogen bonding, electrostatic

11

interaction.21, 22 The dispersion or aggregation can be controlled by adjusting the amount or

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species of surfactant, resin, or functional group in resin/asphaltene.23, 24 Based on this fact, in

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the present paper, we studied an innovative method to facilitate the aggregation of asphaltene

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during paraffinic froth treatment. It was assumed that oxidized asphaltene can encourage

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stronger interaction with asphaltene due to increased proportion of hydrophilic groups.25

In industrial process, asphaltene causes catalyst deactivation, coke formation, and plugging

16

Among the various oxidants, ozone is a great candidate for the oxidation of asphaltene, since

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the ozonation process is not only simple, but also leaves smaller number of byproduct than

18

other oxidants. In industrial process, ozone is usually used for the treatment of water,

19

intermediate preparation of plasticizer and lubricant synthesis, the food industry, and

20

pharmaceutical production. Further, ozone has been used to produce azelaic acid and

21

pelargonic acids from oleic acids by Emery Oleochemicals, Inc..26

22

The generally accepted mechanism of ozonation is the Criegee mechanism proposed by

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Rudolf Criegee,27-29 in which ozone attacks the C=C bond in alkenes, and forms primary

24

ozonide (-COOOC-). The primary ozonide then rapidly decomposes into Criegee intermediate

25

which is an unstable molecule and reacts to produce a more stable molecule. Following


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formation, Criegee intermediate undergoes unimolecular decomposition, rearrangement, or

2

bimolecular reaction. Ketones, ethers, and carboxyl acids, or various gases (H2O, SO2, or NO3)

3

are produced by reaction with trace gas. Even though the structure of asphaltene is ambiguous,

4

and the reaction kinetics of the ozonation of asphaltene are inscrutable, it is assumed to

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generally follow these mechanisms. The ozonation product of asphaltene has been reported to

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contain various molecules.30

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In the present research, the ozonation of asphaltene was conducted without solvent. As a result,

8

the reaction begins on the surface of the asphaltene particles and heterogeneous reactions

9

continue until all carbons has been exhausted. The shrinking core model can be applied to this

10

case because it is generally used for non-porous solid reactants that reacts with fluid.31

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In the present paper, the ozonation of asphaltene and the characteristic of ozonized asphaltene

12

were studied. Further, ozonized asphaltene was added to a water/n-pentane/bitumen emulsion

13

as a novel additive to enhance the efficiency of asphaltene precipitation. The effect of ozonized

14

asphaltene was investigated for pretreatment in the solvent deasphalting (SDA) process.

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2. Experimental Section

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2.1 Materials and Chemicals

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Bitumen from Athabasca, Alberta, Canada was used. Solvents used in the experiment (n-C5,

19

n-C6, n-C7, ethanol, methanol, toluene, 1 % phenolphthalein solution, sodium hydroxide, and

20

dichloromethane) were purchased from Sigma-Aldrich. Water was deionized before use.

21 22

2.2 Asphaltene preparation

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Asphaltene was extracted from bitumen with an excess amount of n-pentane solvent. 1 g

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bitumen was added to 100 ml n-pentane with stirring for 1 h at room temperature. After

25

blending, the solution was filtered with a 0.45 μm membrane filter and dried to remove residual


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Energy & Fuels

solvent. Completely dry asphaltene was ground and strained through a 100 μm mesh sieve.

2 3

2.3 Ozonation of asphaltene

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200 mg ground asphaltene was placed in an SUS316 reactor, and oxygen gas passing through

5

the ozone generator (1KNT-24, Enaly) was flowed into the reactor. The concentration of ozone

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in gas was 1.06 v/v%, and the flow rate was 1.5 L/min. The temperature and pressure were

7

maintained at 40 oC and 1 bar, respectively. The reactor volume was 276.6 cm3. The ozonized

8

asphaltene (OA) yield was measured immediately after the end of the reaction, and stored in a

9

desiccator until use, in order to prevent the absorption of water.

10 11

2.4 Characterization and evaluation of ozonized asphaltene

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2.4.1 Neutralization titration of oxidized asphaltene

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The acidity of oxidized asphaltene was measured using neutralization titration. 30 mg

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oxidized asphaltene was dispersed in 15 ml DI water for 30 min using bath sonication.

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Subsequently, 100 μl phenolphthalein (1% in ethanol) solution was added, followed by the

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repeated addition of 20 μl 0.1 N NaOH solution until the solution turned a red wine color. The

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total amount of added NaOH was then calculated.

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2.4.2 Estimation of ozonized asphaltene conversion

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Conversion of ozonized asphaltene was measured by dispersion in ethanol. Ozonized

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asphaltene was dissolved in ethanol at 1 g/L using bath sonication. The undissolved fraction

22

was filtered using a 0.45 μm PVDF syringe filter, the ethanol was evaporated, and the weight

23

of the ethanol soluble part was measured.

24 25

2.4.3 Precipitation enhancement with ozonized asphaltene


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10-50 mg ozonized asphaltene was dispersed in 5-15 ml DI water in a 125-ml Erlenmeyer

2

flask with sonication for 30 min. 3 g bitumen and 9-50 ml n-pentane was added. The bitumen

3

emulsion was stirred magnetically at 200 rpm and room temperature for 30 min. Following

4

agitation, the emulsion was filtered with filter paper (F2141 grade, CHMLAB GROUP, Spain).

5

To completely eliminate n-pentane and water, the flask and filter were dried at 105 oC for 4 h.

6

The dried precipitate was weighed and dissolved in dichloromethane (DCM) to collect all the

7

precipitate. DCM was evaporated at 50 oC for further analysis of the precipitate. Moreover,

8

deasphaltened oil (DAO) was separated from n-pentane and water using a vacuum rotary

9

evaporator, and DAO was then evaporated in an oven at 120 oC for further analysis.

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2.4.4 Asphaltene aggregate size measurement

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The asphaltene/ozonized asphaltene mixtures in various proportions were dispersed in solvent

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at 0.5 g/L with ultrasonication for 30 min. Ozonized asphaltene, which was ozonized for 1 h,

14

was used for size measurement. The solvent was mixed with various ratios of toluene and

15

alkane (n-pentane, n-hexane, and n-heptane). Particle size distribution was measured using the

16

dynamic light scattering (DLS) method within 10 min of sonication.

17 18

2.5 Instrument and measurement

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Particle size distribution of ground asphaltene was measured using a laser scattering particle

20

size analyzer (HELOS), which can detect in the range of 0.1-8,750 μm. Element composition

21

(CHONS) was confirmed using the FlashEA 1112 (Thermo Finnigan, Italy) and FLASH 2000

22

series (Thermo Scientific). In addition, the chemical state data of each sample was obtained by

23

x-ray photoelectron spectroscopy (XPS) using MultiLab 2000. SARA (saturate, aromatic, resin,

24

and asphaltene) analysis results were obtained using a TLC/FID Analyzer (IATROSCAN MK-

25

6s Mitsubishi Kagaku Iatron, Japan). The thermostability of samples was studied using a


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thermogravimetry analyzer (TGA) (TG209 F3 NETZSCH, Germany). TGA was performed

2

under a nitrogen atmosphere (100 ml/min), and temperature was increased to 1,000 oC at a rate

3

of 10 oC/min. Simulated distillation (SIMDIS) analysis was performed to measure the boiling

4

point distribution of DAO using Agilent Technologies 6890N. Helium gas (99.999% purity)

5

was used as the carrier gas. Samples were diluted in carbon disulfide (CS2) to 10%. The boiling

6

point range was from 200 to 750 oC, and the analysis method was based on ASTM D7500-12.

7

The functional groups of the oxidized asphaltene were analyzed using Fourier transform

8

infrared (FT-IR) spectroscopy (Alpha-p, Germany). Dynamic light scattering (DLS)

9

measurement was conducted to determine size distribution in solvent using a Zetasizer Nano

10

ZSP (Malvern, UK) equipped with a laser diode.

11 12

3. Result and discussion

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3.1 Ozonation of asphaltene

14

Particle size distribution of ground asphaltene (sieved using a 100-μm mesh) was measured

15

by the laser diffraction method. For ground asphaltene particles, the x10, x50, and x90 were 1.45

16

μm, 3.75 μm, and 23.91 μm, respectively, where xn denotes the particle dimension

17

corresponding to n% of the cumulative undersize distribution.

18

Following ozonation of ground asphaltene, the product weight and element composition were

19

estimated as shown in Figure 1. In the first 15 min of the reaction, the oxygen content in

20

ozonized asphaltene was radically increased from 1% to 19% (Figure 1). However, after 15

21

min, the rate of the increase in oxygen content was conspicuously low, and the O/C atomic

22

ratio showed a similar trend. Moreover, the yield of ozonized asphaltene showed a rapid

23

increase in the early stage of the reaction, however, when the reaction time reached 2 h, the

24

yield converged to 120%, and the oxygen content increased. (Figure S1) This indicates that

25

loss of ozonized asphaltene occurs during ozonation. The total weight of oxygen and carbon in


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1

the ozonized asphaltene was also calculated, as shown in Figure S2. Initial weight of asphaltene,

2

carbon, and oxygen were 200 mg, 162 mg, and 2 mg, respectively. The weight of carbon

3

decreased by 14 mg in the first 15 min of the reaction, and oxygen increased by 41 mg.

4

Therefore, at the beginning of ozonation, the addition of oxygen is preferred while the removal

5

of carbon also occurs. As the ozonation reaction progressed, the rate of oxygen addition and

6

carbon removal decreased.

7

Ozone would react immediately after contact with the surface of asphaltene particles, since

8

ozone is very reactive and can oxidize asphaltene. Thus, the ozonation of asphaltene can be

9

thought of as occurring at the surface of asphaltene particles. Once the entire surface of the

10

ground asphaltene is oxidized by ozone, ozone will penetrate into the core of unoxidized

11

asphaltene. The unoxidized asphaltene core will then diminish gradually, and the oxidized

12

asphaltene shell will thicken. This concept is called the ‘shrinking core model’, and can be

13

applied to heterogeneous reactions. Here, ground asphaltene particles were assumed to be

14

spherical. Figure 2 shows the conception of ozonation on a spherical asphaltene particle, and

15

the effect of grinding during ozonation. While the coverage on the surface of asphaltene

16

particles by ozonized asphaltene is very fast, the infiltration of ozone into the unoxidized

17

asphaltene core is slow. Prior to the surface being completely covered by ozonized asphaltene,

18

the total reaction is mainly controlled by the reaction on the surface. However, when ozone

19

infiltrates towards the core, the reaction at the core zone is limited by the internal diffusion of

20

ozone into the unoxidized core.

21 22 23 24

Based on the shrinking core model on spherical particles,31, 32 the relationship between time and conversion can be expressed as: 1

t = 𝜏𝜏𝑟𝑟 (1 − (1 − 𝑋𝑋)3 )

2

t = 𝜏𝜏𝑑𝑑 (1 − 3(1 − 𝑋𝑋)3 + 2(1 − 𝑋𝑋))


(1) (2)

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where X is the conversion, t is the reaction time, and τ is the characteristic time. Here, τr and τd

2

denote the characteristic time for the surface reaction dominant case and the internal diffusion-

3

limited case, respectively. These characteristic times indicate the time required to complete the

4

reaction. Moreover, τr and τd can be obtained from the following equations:

5 6

𝜌𝜌𝜌𝜌

(3)

𝜌𝜌𝑅𝑅 2

(4)

𝜏𝜏𝑟𝑟 = 𝑘𝑘𝑘𝑘

𝜏𝜏𝑑𝑑 = 6𝐷𝐷𝐷𝐷

7

where ρ is the density of solid particle, R is the radius of particle, C is the concentration of

8

fluid, k is the reaction rate constant, and D is diffusion coefficient.

9

To investigate the conversion kinetics of ozonized asphaltene, the ethanol soluble proportion

10

was measured. We assumed that all ozonized asphaltene was soluble in ethanol, and that

11

asphaltene was insoluble. As ozonation proceeded, the ethanol soluble fraction increased, but

12

the conversion rate decreased (Figure 3). The solid line indicates ideal kinetics of shrinking

13

core model for surface reaction dominant and internal diffusion dominant. In particular, there

14

was an upsurge in conversion during the early stage of the reaction, similar to the results seen

15

with oxygen content. The difference in conversion with the fitting model after 8 h can be

16

considered as a loss by the reaction of ozonized asphaltene, and this is consistent with the

17

convergence of yield. In particular, there was an upsurge in conversion during the early stage

18

of the reaction, similar to the results seen with oxygen content. The difference in conversion

19

with the fitting model after 8 h can be considered as a loss by the reaction of ozonized

20

asphaltene, and this is consistent with the convergence of yield. D (5.22×10-10 m2/h) and k

21

(4.82×10-2 m/h) were calculated by fitting to the model. The diffusion coefficient of ozone to

22

asphaltene is about one-sixth-fold of the diffusion coefficient of free ozone in air.33 Furthermore,

23

this k value is relatively large for the oxidation of pyrite (k=3.07×10-6 m/h) with air, which can

24

be considered as a slower reaction.34 This is reasonable in view of the fact that ozone is very


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reactive.

2

Asphaltene is insoluble in n-pentane or n-heptane, but soluble in toluene, however, the

3

solubility of asphaltene can be altered by ozonation. To visualize the hydrophilicity of ozonized

4

asphaltene, asphaltene and asphaltene ozonized for various time were dispersed in a

5

water/toluene emulsion (Figure 4). After 30 min ozonation, the portion of ozonized asphaltene

6

could be dispersed in water, while the oxygen content increased slightly relative to the sample

7

that was ozonized for 15 min. On the other hand, no visible change could be observed thereafter,

8

even though the oxygen proportion in ozonized asphaltene was highly increased after 15 min.

9

We suppose that some of the ozonized asphaltene coheres to asphaltene when dispersed in

10

toluene. Excessive ozonized asphaltene may then be dissolved in water, when the proportion

11

of ozonized asphaltene exceeds the coherence with asphaltene. A detailed argument will be

12

discussed in Section 3.3. As the ozonation time increased, a larger fraction of the sample was

13

dissolved in water, indicating higher hydrophilicity. In particular, after 18 h ozonation, the

14

toluene solution of ozonized asphaltene became almost transparent.

15

As mentioned earlier, ozonation can give asphaltene an acidic fraction. The total amount of

16

acidic fraction in ozonized asphaltene can be quantified using neutralization titration. As shown

17

in Figure 5, an increasing trend in acidity presented a similar change in the shape of the O/C

18

atomic ratio by ozonation. Moreover, the linear relationship between acidity and the O/C

19

atomic ratio was confirmed by plotting (O/C atomic ratio) vs. (acidity). Thus, it can be said

20

that the ozonation of asphaltene causes the acidification of asphaltene, which can be controlled

21

by reaction time.

22

The increase in hydrophilic groups by ozonation was also identified using FT-IR spectroscopy,

23

as seen in Figure 6. There was a remarkable increase in the peak of O-H stretching (3,400 cm-

24

1

25

hand, the intensity of the aromatic C-H peak (2,850–2,950 cm-1), a pair of aromatic C=C peaks

), C=O stretching (1,625-1,800 cm-1), and C-O stretching (1,000-1,260 cm-1). On the other


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(1,475 and 1,600 cm-1), and the –CH2/-CH3 asymmetric deformation peak (1,456 cm-1) were

2

abated by ozonation.35 In summary, the hydrophilic parts such as carboxyl, alcohol, ketone, and

3

aldehyde groups in asphaltene were increased by ozonation, while the hydrophobic parts were

4

decreased.

5

Based on the shrinking core model, the chemical state of the surface of asphaltene particles

6

should be unchanged following consumption of all molecules that can react with ozone. Using

7

XPS analysis, the chemical state of carbon (C 1s) on the surface was measured (Figure 7). The

8

spectra were deconvoluted to 4 main peaks. The binding energy of unoxidized carbon was

9

calibrated to 284.7 eV. C-O (ether, hydroxyl), C=O (ketone), and O-C=O (ester, carboxyl) were

10

fitted to 286.0, 287.1, and 288.9 eV, respectively.36 The majority of the carbon (90%) in

11

asphaltene (n-pentane insoluble) was unoxidized, while the amounts of C-O, C=O, and O-C=O

12

were small. Following 1 h ozonation, however, the proportion of carbon in the oxidized part

13

remarkably increased to almost 60%, and the proportions of C-O, C=O, and O-C=O were

14

highly increased to 10-15%. Nevertheless, there was no significant change in the spectrum

15

when the ozonation time was longer than 1 h. While the oxygen content, acidity, and

16

hydrophilicity increased continuously, the yield, conversion, and proportion of bonding

17

between C and O converged. This supports the notion that ozonation of asphaltene follows the

18

shrinking core model, and that some ozonized asphaltene can be lost by ozone flow during

19

excessive reaction. That is, excessive ozonation causes loss of ozonized asphaltene surface and

20

new ozonized asphaltene surface is exposed to ozone, resulting in the maintenance of the

21

surface properties of ozonized asphaltene.

22 23

3.2 Precipitation enhancing with ozonized asphaltene

24

SARA (saturate, aromatic, resin, and asphaltene) analysis of the precipitate was performed to

25

evaluate the precipitation ability of ozonized asphaltene. By measuring the SARA ratio of the


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1

precipitate, the efficiency of elimination from bitumen was calculated using the following

2

equations:

3 4 5 6 7

𝐴𝐴𝐴𝐴𝐴𝐴ℎ𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎 𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒 % =

�𝑚𝑚𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝 ×𝐴𝐴𝐴𝐴𝐴𝐴ℎ𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎 %� −𝑚𝑚𝑂𝑂𝑂𝑂 (𝑚𝑚𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏 ×𝐴𝐴𝐴𝐴𝐴𝐴ℎ𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎 %)

(5)

𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆, 𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴, 𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅 𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒 % =

× 100%

�𝑚𝑚𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝 × 𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶 %� (𝑚𝑚𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏 × 𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶 %)

× 100%. (6)

Here, OA denotes the ozonized asphaltene, and m is the weight of each material. We assumed that all the ozonized asphaltene was included in the precipitate.

8

Figure 8 shows the precipitation efficiency without ozonized asphaltene in a water/n-

9

C5/bitumen emulsion. C and W denote the volume of n-pentane and water, respectively. Since

10

asphaltene is insoluble in n-pentane, the amount of precipitate increased when a larger volume

11

of n-pentane was used. For instance, in the case of (C25 W15) and (C50 W15), the elimination

12

efficiency of asphaltene increased to 45% and 60%, respectively. The removal efficiency of

13

asphaltene was mainly influenced by the amount of n-pentane solvent. When 15 ml n-pentane

14

was used, approximately 40% asphaltene and 20% resin were filtered. At the same time, little

15

saturates or aromatics were involved in the precipitate. The increased amount of water from 5

16

to 15 ml caused little increase in asphaltene precipitation. When the amount of n-alkane solvent

17

used is low, the presence of emulsified water increases the asphaltene precipitation. Asphaltene

18

absorbs the interface of the water droplet and is removed with water at a yield below

19

precipitation onset.37

20

Ozonized asphaltene was added to enhance the precipitation of asphaltene, as shown in Figure

21

9. The effects of the amount, degree of oxidation, and solvent of ozonized asphaltene on

22

precipitation were investigated. When ozonized asphaltene O19% (oxygen content: 19 wt%)

23

was added, the effect on precipitation was not significant, even when 50 mg (1.7% to bitumen)

24

ozonized asphaltene was added. For ozonized asphaltene O24%, the addition of ozonized


Page 13 of 31

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Energy & Fuels

1

asphaltene resulted in a gradual increase in asphaltene removal efficiency. However, the higher

2

the amount of ozonized asphaltene added, the more saturates and aromatics were removed.

3

Furthermore, the use of ozonized asphaltene O32% showed a notable effect on asphaltene

4

removal. For instance, the addition of 20 mg ozonized asphaltene caused the maximum

5

improvement of 25% on precipitation efficiency. This result indicates that precipitation can be

6

controlled by adjusting the amount and oxidation degree of ozonized asphaltene. However,

7

when the added O32% ozonized asphaltene was 50 mg, the eliminated saturates and aromatics

8

were approximately 60% and 7%, respectively, which is an unwanted increase. It seems that

9

saturates and aromatics are entangled in asphaltene aggregates due to an excessive quantity of

10

ozonized asphaltene. Thus, an appropriate amount of ozonized asphaltene should be added to

11

achieve effective precipitation. The volume of water and n-pentane were changed to observe

12

their effect on precipitation. Changing the water volume to 5 ml (C15 W5 O24%) hardly

13

affected precipitation with the other conditions fixed. As discussed earlier, a larger volume of

14

n-pentane (C25 W15 O24%) generally resulted in a greater amount of asphaltene removal than

15

seen with the sample (C15 W15 O24%). The increase in precipitation efficiency by a higher

16

oxidation degree (C15 W15 O32%) exceeded the increase seen with the addition of n-pentane

17

(C25 W15 O24%) under the same conditions. This indicates that the degree of ozonation is as

18

influential a factor as the quantity of alkane solvent, thus, it would be possible to contrive an

19

efficient process of froth treatment with ozonized asphaltene.

20

Oil can be cut based on the boiling point; naphtha (540 oC).38 For evaluation of DAO, the distribution of

22

boiling points was analyzed using a simulated distillation method (SIMDIS). SIMDIS is a

23

standardized chromatographic method that simulates the distillation curve of hydrocarbons,

24

and translates the retention time to a boiling point. The proportion of oxygen in the ozonized

25

asphaltene was 32%, when 10, 20, and 30 mg (0.33, 0.67, 1.00 wt% bitumen 3 g, respectively)


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

1

ozonized asphaltene was added. As shown in Figure 10 (a), the addition of ozonized asphaltene

2

to a bitumen/n-pentane/water emulsion resulted in a left-shift, which means a decrease in the

3

overall boiling point of DAO. In particular, the highest boiling point in DAO decreased from

4

740oC to 640oC by the addition of 1.00 wt% ozonized asphaltene. Moreover, the proportion

5

of residue decreased, while the proportion of vacuum gas oil (VGO) and gas oil in DAO

6

increased (Figure 10 (b)). Thus, a finer quality of deasphaltened oil was obtained by the

7

successful facilitation of precipitation using ozonized asphaltene.

Page 14 of 31

8 9

3.3 Asphaltene/ozonized asphaltene aggregate

10

Asphaltene has a critical concentration at which it starts to form a nanoaggregate structure

11

similar to the critical micelle concentration (CMC) of surfactants, which is called the critical

12

nanoaggregate concentration (CNC or CNAC).39 Even though the characteristics of crude oil

13

are varying depending on the production site, and there is some controversy regarding the value

14

of CNC, the CNC of asphaltene in the literature is 0.164 g/L in toluene.40 Thus, the asphaltene

15

concentration selected in this study was 0.5 g/L, which is low enough, but higher than 0.164

16

g/L, to form nanoaggregates. At a dilute concentration, the radius of gyration of asphaltene

17

aggregates in toluene was measured as 1-10 nm by several methods such as DLS and SANS.41-

18

43

19

(Figure 11 (a)) with unimodal distribution.

Moreover, the aggregate size of asphaltene in the present study was measured as 7.372 nm

20

A DLS spectrum of ozonized asphaltene in toluene was also obtained. Ozonized asphaltene

21

in toluene tended to hide hydrophilic groups inside and form a much larger particle size (891.2

22

nm), as shown in Figure 11 (b). In addition, asphaltene and ozonized asphaltene were dispersed

23

in toluene together at various ratios (asphaltene: ozonized asphaltene = 20:1, 10:1, 5:1, and 1:1

24

by weight). By measuring particle sizes, three types of peak were confirmed; nano sized cluster

25

(0.1-10 nm), submicron cluster (0.1-1 μm), and micron sized aggregate (1-10 μm). While


Page 15 of 31

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Energy & Fuels

1

asphaltene and ozonized asphaltene had an unimodal distribution, the mixture of asphaltene

2

and ozonized asphaltene in toluene showed a bimodal distribution. If there were no interaction

3

between asphaltene and ozonized asphaltene, the spectra of (c)-(f) would be bimodal, which is

4

just the total spectrum of asphaltene and ozonized asphaltene; nano sized and submicron sized

5

particles. The existence of micron sized particles indicates that there is an interaction between

6

asphaltene and ozonized asphaltene. Thus, ozonized asphaltene would play the role of enhancer

7

to condense asphaltene with high affinity to asphaltene.

8

In sample (c)-1:1 and (d)-5:1, micron and submicron sized particles were observed. It can be

9

thought that all the asphaltene was consumed to form micron sized aggregates, while the

10

residual ozonized asphaltene formed the submicron size clusters. The intensity of the micron

11

sized aggregates became greater as asphaltene was added. Eventually, the only micron sized

12

peak was detected in sample (e)-10:1. In other words, it can be said that 1 hr-ozonized

13

asphaltene can interact with 10-fold asphaltene by weight. On the other hand, when more

14

asphaltene was added to (f)-20:1, the micron and submicron sized aggregates suddenly almost

15

disappeared, which indicates nano sized dispersion of ozonized asphaltene. On the basis of this

16

result, we can infer that toluene permeates into asphaltene/ozonized asphaltene aggregates and

17

collapses them into nano sized clusters when more than 10-fold asphaltene is added. In addition,

18

the sudden change in solubility in water at 30 min ozonized asphaltene, as shown in Figure 4,

19

can be attributed to the fact that the ratio of asphaltene and ozonized asphaltene exceeded a

20

specific value to create residual ozonized asphaltene. Furthermore, it can be conjectured that

21

the interaction between asphaltene and ozonized asphaltene is higher than the toluene-

22

asphaltene interaction. Asphaltene and ozonized asphaltene interact not only via π-π stacking,

23

but also via acid-base and dipole interactions 22. Even though asphaltene molecules can have

24

inter-molecular acid-base and dipole interactions, they will happen more frequently in ozonized

25

asphaltene due to the abundance of acidic parts. When asphaltene and ozonized asphaltene are


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

1

dissolved in toluene, ozonized asphaltene will be hindered by asphaltene with acid-base

2

interactions, and this phenomenon induces the formation of large aggregates.

Page 16 of 31

3

Toluene is a good solvent for asphaltene, while n-alkane is a poor solvent, resulting in the

4

aggregation of asphaltene. The asphaltene cluster sizes at various ratios of n-heptane in toluene

5

have been studied.24, 44-46 In the present paper, the aggregate size increased with the addition of

6

n-alkane, and showed a similar trend (Figure 12). The aggregates started to grow when 30% n-

7

heptane was added, and suddenly increased near to 60% n-heptane content. The aggregate size

8

at more than 80% n-heptane in solution was unmeasurable due to the instability of asphaltene.

9

Following the addition of ozonized asphaltene (1 h, Asp:OA=10:1), large aggregates also

10

formed and showed growth with an increase in alkane proportion. It can be thought that the

11

aggregate profile was left-shifted by ozonized asphaltene. As the number of carbons in n-alkane

12

decreases, the solvency of alkanes also decreases, which causes more aggregation of asphaltene.

13

This fact also affected the growth of asphaltene/ozonized asphaltene aggregates with n-alkane

14

solvent addition. However, the size of asphaltene/ozonized asphaltene aggregates with a high

15

proportion of n-alkane were not measured, since the size of large aggregates was out of the

16

detectable range.

17 18

4. Conclusion

19

The precipitation of asphaltene was facilitated by ozonized asphaltene as an additive for

20

paraffinic froth treatment. Asphaltene was oxidized to give higher hydrophilicity using a simple

21

method with ozone. Since the majority of asphaltene, which is generated from froth treatment,

22

is buried in tailing ponds and causes environmental problems, the modification and application

23

of asphaltene have a great value with respect to cost and the environment. Ground asphaltene

24

was oxidized by ozone to achieve reaction kinetics and economical benefits. The ozonation of

25

asphaltene interpreted by the shrinking core model, and the product, were characterized by FT-


Page 17 of 31

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Energy & Fuels

1

IR, XPS, element analysis, and solubility.

2

The increase in hydrophilic parts of ozonized asphaltene strengthened the interaction with

3

asphaltene. The stronger interaction with asphaltene resulted in an aggregation of asphaltene.

4

As a result, the micron sized aggregation was detected, even in toluene solvent at a low

5

concentration of asphaltene, due to ozonized asphaltene. Moreover, the ozonized asphaltene

6

showed a significant effect on the agglomeration of asphaltene in water/n-pentane/bitumen,

7

and a significantly larger amount of precipitate was obtained. Thus, it can be said that

8

separating the unit load or alkane volume of paraffinic froth treatment can be reduced with

9

ozonized asphaltene.

10 11 12

Supporting Information Figure S1-S5.

13

(1) Reaction yield at various ozonation time, (2) Total weight of carbon and oxygen of

14

ozonized asphaltene, (3) Conversion X vs. (1 − (1 − 𝑋𝑋)3 ) and regression curve, (4)

15 16

1

2

Conversion X vs. (1 − 3(1 − 𝑋𝑋)3 + 2(1 − 𝑋𝑋))and regression curve, (5) XPS spectrum of ozonized asphaltene at various ozonation time

17 18

Author Information

19

Corresponding Author

20

* Corresponding author. Tel.: +82 42 350 3921; fax: +82 42 350 3910; e-mail: [email protected]

21 22

Acknowledgement

23

We would like to acknowledge the financial support from BK21 plus program through the

24

National Research Foundation (NRF) funded by the Ministry of Education of Korea and the


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

1

R&D Convergence Program of MSIP (Ministry of Science, ICT and Future Planning) and

2

ISTK (Korea Research Council for Industrial Science and Technology) of Republic of Korea

3

(B551179-12-07-00).

Page 18 of 31

4 5

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2007; pp 439-468.

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46.

Wilt, B. K.; Welch, W. T.; Rankin, J. G., Determination of asphaltenes in petroleum crude oils Abdallah, W. A.; Taylor, S. D., Study of asphaltenes adsorption on metallic surface using XPS Tharanivasan, A. K.; Yarranton, H. W.; Taylor, S. D., Asphaltene precipitation from crude oils

Andreatta, G.; Bostrom, N.; Mullins, O. C., High-Q ultrasonic determination of the critical

Yarranton, H.; Ortiz, D.; Barrera, D.; Baydak, E.; Barre, L.; Frot, D.; Eyssautier, J.; Zeng, H.; Xu,

Fenistein, D.; Barre, L., Experimental measurement of the mass distribution of petroleum

Espinat, D.; Fenistein, D.; Barre, L.; Frot, D.; Briolant, Y., Effects of temperature and pressure

Ramalho, J. B. V.; Lechuga, F. C.; Lucas, E. F., Effect of the structure of commercial poly

Yudin, I. K.; Anisimov, M. A., Dynamic light scattering monitoring of asphaltene aggregation

Rajagopal, K.; Silva, S., An experimental study of asphaltene particle sizes in n-heptane-


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toluene mixtures by light scattering. Brazilian Journal of Chemical Engineering 2004, 21, (4), 601-

2

609.

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Energy & Fuels

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1

Figure 1. Oxygen content and O/C ratio of ozonized asphaltene at various ozonation time

2 3 4

Figure 2. Schematic design of ozonation on asphaltene powder particle based on the shrinking core model

5


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Figure 3. Conversion of reaction time and its curve fitting on the shrinking core model (ideal

2

surface reaction curve and ideal internal diffusion curve)

3 4

5 6


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Figure 4. Dispersion of ozonized asphaltene in a toluene/water emulsion

2

3

Asp

15min

30min

1hr

2hr

4hr


8hr

12hr

18hr

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Figure 5. Acidity change in ozonized asphaltene measured by neutralization titration and the

2

relationship between O/C ratio and acidity (inset)

3 4


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Figure 6. FT-IR spectrum of asphaltene and ozonized asphaltene

2 3

Figure 7. Chemical state of carbon (C 1s) on the surface of ozonized asphaltene measured by

4

XPS

5


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Figure 8. Removal efficiency of SARA without ozonized asphaltene at various water and n-

2

pentane volume

3 4


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Figure 9. Removal efficiency using ozonized asphaltene (a) C15 W15 O19%, (b) C15 W15

2

O24%, (c) C15 W15 O32%, (d) C15 W5 O32%, and (e) C25 W15 O24%

3

(a)

(b)

(c)

(d)

(e)

4


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Figure 10. (a) Effect of ozonized asphaltene (O32%) on the boiling point distribution of

2

deasphaltened oil (b) Change in the composition proportion based on boiling point cut

3 4

(a)

5 6

(b)

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1

Figure 11. Size distribution of asphaltene aggregate; (a) asphaltene (Asp), (b) O24% ozonized

2

asphaltene (OA), (c) Asp:OA = 1:1, (d) Asp:OA = 5:1, (e) Asp:OA = 10:1, and (f) Asp:OA =

3

20:1

4

(a)

(b)

(c)

(d)

(e)

(f)

5 6


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Figure 12. Change in asphaltene/ozonized asphaltene aggregate size in toluene by the addition

2

of alkane (n-C5, n-C6, and n-C7) and reference data24, 44, 45

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Simple Functionalization of Asphaltene and Its Application for Efficient

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