EthyleneâVinyl Acetate Copolymer and Resin-Stabilized Asphaltenes

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Ethylene-Vinyl Acetate Copolymer (EVA) and Resinstabilized Asphaltenes Synergistically Improve the Flow Behavior of Model Waxy Oils: 2. Effect of Asphaltenes Content Bo Yao, Chuanxian Li, Fei Yang, Xiaoping Zhang, Zhonghua Mu, Guangyu Sun, Gang Liu, and Yansong Zhao Energy Fuels, Just Accepted Manuscript • Publication Date (Web): 30 Mar 2018 Downloaded from http://pubs.acs.org on March 30, 2018

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Energy & Fuels

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Ethylene-Vinyl Acetate Copolymer (EVA) and Resin-stabilized Asphaltenes

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Synergistically Improve the Flow Behavior of Model Waxy Oils: 2. Effect of

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Asphaltenes Content

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Bo Yao a, b, Chuanxian Li a, b, Fei Yang a, b, *, Xiaoping Zhang a, b, Zhonghua Mu

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Liu a, b and Yansong Zhao c

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a

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China

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b

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266580, PR China

a, b

, Guangyu Sun a, b, Gang

College of Pipeline and Civil Engineering, China University of Petroleum, Qingdao, Shandong 266580, PR

Shandong Provincial Key Laboratory of Oil & Gas Storage and Transportation Safety, Qingdao, Shandong

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c

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Science, Western Norway University of Applied Sciences, Inndalsveien 28, 5063 Bergen, Norway

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Abstract: In the previous article (Energy Fuels 2018, 32(2): 1567-1578), the synergistic effect of EVA PPD

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and rensin-stabilized asphaltenes on improving the flowability of synthetic waxy oil has been verified. This

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paper is a continuous work studying the effect of asphaltenes content (0.01~3wt%) on the synergistic effect

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between EVA PPD and resin-stabilized asphaltenes. The results showed that in the absence of EVA and with

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the increase of asphaltenes content, the precipitated wax crystals of the waxy oil tend to grow gradually from

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initial big needle-like to smaller and more regular (spherical-like) particles with larger amount, therefore,

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adding aphaltenes can only decrease the apparent viscosity of waxy oil at the temperature range slightly

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lower than the WPT (the precipitated wax crystal amount is low), and the temperature range is broadened by

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increasing the asphaltenes content; when the temperature is decreased far below the WPT of the oil, however,

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the apparent viscosity of oil rises up with increasing the aphaltenes content due to the large amount of wax

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crystals and asphaltenes. In addition, only a part of the asphaltenes participates in the wax precipitation

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process and the rest part of the asphaltenes disperses in the oil phase as asphaltene aggregates, which could

Department of Biomedical Laboratory Sciences and Chemical Engineering, Faculty of Engineering and

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adhere or adsorb on the existed wax crystal flocs, strengthening the interactions between wax flocs. After

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adding asphaltenes together with EVA, EVA molecules can adsorb onto the asphaltene aggregates to

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generate the formation of the EVA/asphaltenes composite particles, and the synergistic effect of the

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EVA/asphaltenes composite particles on the flowability of waxy oil improves first with the increase of

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asphaltenes content and then somewhat deteriorates at higher asphaltenes content (3 wt%). When the

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asphaltenes content is low, the wax crystal modification by the composite particles is insufficient and the

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formed large wax flocs have very loose structure, which favor the wax crystal structure building. When the

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asphaltenes content is too high (3 wt%), EVA/asphaltenes composite particles disperse the precipitated wax

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flocs into relatively small spherical-like wax flocs with larger amount. Although the structure of the wax

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flocs is compact, the large amounts of wax flocs and asphaltenes aggregates in oil phase lead to somewhat

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deterioration of the synergistic performance of EVA and asphaltenes. At the middle contents of asphaltenes

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(0.75~1.5 wt%), EVA/asphaltenes composite particles cause the formation of relatively large spherical-like

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wax flocs with compact structure and the asphaltenes content is moderate, both of which greatly promote the

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flow behavior improving of the oil.

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Keywords: EVA; asphaltene aggregates; waxy oil; flow behavior; synergistic effect

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1. Introduction

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Waxy crude oil is an important fossil fuel and often contains a substantial amount of paraffin waxes (≥ 10

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wt%). Paraffin waxes generally denote the n-alkanes with a carbon number range of C18~C40, which are

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dissolved in the crude oil at relatively high temperatures with a balanced state [1]. When the temperature falls

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below the wax precipitation temperature (WPT), however, paraffin waxes will continuously precipitate,

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crystallize, and form network structures with the decrease of oil temperature

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of waxy crude oil will deteriorate with the temperature drop, which results in huge challenges in oil

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exploitation and transportation, as well as cost control [4-6].

[1-3]

. Therefore, the flowability


2

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Energy & Fuels

In petroleum industry, treating the crude oil with small amounts of polymeric pour point depressants [7]

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(PPDs) is a common way to improve its flowability

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developed many types of polymeric PPDs, among which the linear copolymer PPDs like ethylene-vinyl

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acetate copolymer (EVA)

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have been widely used in the exploitation and pipeline transportation of waxy crude oil. These two types of

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polymeric PPDs are composed of both the nonpolar alkane chains and the polar groups, with the nonpolar

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parts affecting the crystallization process of paraffin waxes and the polar groups interfering in the growth of

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wax crystals

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in the outstanding improvement of the waxy crude oil flowability.

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. During the last three decades, peoples have

[8-10]

, and the comb-like copolymer[11-15] PPDs like polyoctadecylacrylates (POA),

[7]

. Therefore, the morphologies of the precipitated wax crystals are greatly changed, resulting

In order to improve the performance of polymeric PPDs, some types of inorganic nanoparticles, such as [16-20]

[21-25]

[26-28]

[29]

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silica

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matrix of polymeric PPDs to prepare the nano-composite PPDs. Yang et al

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investigated the effects of several nano-composite PPDs on the flow behavior of waxy crude oil and

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analyzed the action mechanism of the composite PPDs. They concluded that: (a) the composite PPDs

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disperse in oil phase as micro-sized particles, which can take effect as the heterogeneous nucleation for the

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precipitation of waxes and dramatically modify the wax crystals’ structure, facilitating the improving of

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waxy crude oil flow behavior; (b) compared with solvent blending method, the composite PPDs prepared by

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melt blending method give a better performance; (c) organic modification of inorganic nanoparticles is

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crucial to obtain the composite PPDs with high efficiency.

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, montmorillonite

, grapheme oxide

, and attapulgite

have been introduced into the [20,22-24]

To further improve the organic modifying degree of the inorganic particles, Yang et al

systematically

[30,31]

prepared

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polymethylsilsesquioxane (PMSQ) microspheres through sol-gel method. They found that: (a) the PMSQ

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microspheres disperse well in oil phase as a single sphere; (b) the neat PMSQ microsphere cannot participate

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in wax precipitation process and change the morphology of precipitated wax crystals, but can impede the ACS Paragon Plus Environment

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interactions of the precipitated wax crystals through spacial hindrance effect, which inhibits the development

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of wax crystal network structure and then improves the flow behavior of waxy oil; (c) the flow improving

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efficiency of the PMSQ microsphere is far below that of the traditional polymeric PPDs. Therefore, Yang et

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al

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dosage of PMSQ microsphere (around 2.5 ppm) can significantly improve the performance of the EVA PPD

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(50 ppm). The EVA molecules could adsorb and concentrate onto the PMSQ microsphere, resulting in the

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forming of EVA/PMSQ composite PPDs. The formed composite particles could take effect as nucleation

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templates during the wax precipitation process, generating larger and more compact microstructure of wax

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crystal and further enhancing the flowability of the oil. To further promote the adsorption of EVA PPD on

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the microsphere and enhance the efficiency of the composite PPDs, the amino-functionalized PMSQ

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microspheres with different amino molar ratios (PAMSQ) were synthesized and added into waxy crude oil

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[33]

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adsorbing and concentrating on the PAMSQ microsphere; (b) the formed EVA/PAMSQ composite particles

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provide stronger nucleation effect for the wax precipitation, resulting in larger and more compact wax

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microstructures and then further improving the flow behavior of the oil; (c) the best performance is found at

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adding 50 ppm EVA+2.5 ppm PAMSQ-2 (with amino molar ratios at 15 %).

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[32]

added the EVA PPD together with PMSQ microsphere into waxy crude oil and found that a small

. Results showed that: (a) a certain degree of amino-functionalization facilitates more EVA molecules

Asphaltenes are the most polar component of crude oil and can disperse as associated aggregates in oil [34-36]

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phase, which are often recognized as the natural PPDs

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synergistic effect with polymeric PPDs on improving the flowability of waxy crude oil? The relevant works,

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however, are scarce. Recently, Yang et al

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resin-stabilized asphaltenes in ameliorating the flowability of model waxy oils. They found that (a) the

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asphaltenes could disperse in the xylene/mineral oil mixed phase well as micro-sized aggregates (the

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average size is 550 nm); (b) the flowability improving performance of the neat EVA or asphaltenes is limited,

[37]

. As the natural PPDs, could asphaltenes take

investigated the synergistic performance of EVA PPD and


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while EVA together with asphaltenes could greatly suppress the pour point, G′, G″ values, gelation point and

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apparent viscosity at low temperatures of waxy oils; (c) according to the asphaltenes precipitation test, the

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EVA molecules can adsorb on the asphaltenes aggregates and act as the dispersant, coming into being the

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EVA/asphaltenes composite particles and inhibiting the asphaltenes precipitation; (d) the EVA/asphaltenes

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composite particles could take effect as the micro-sized templates for the precipitation of waxes and modify

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wax crystals into large spherical-like wax flocs with compact structure, thus sharply enhancing the

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flowability of waxy oil. Meanwhile, they also investigated the synergistic effect of POA together

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resin-stabilized asphaltenes in improving the flowability of synthetic oils and arrived at the similar

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conclusions

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PPDs, but also contribute a novel way to the investigation of nano/micro composite PPDs.

[38]

. These two papers not only help to further understand the action mechanism of polymeric

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This work is a continuous study of the former published paper [37]. In this work, the effect of asphaltenes

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content (0.01~3 wt%) on the synergistic effect of EVA (100 ppm) and asphaltenes was studied in detail.

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Firstly, the effect of asphaltenes content on the rheological characteristics of synthetic waxy oil

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undoped/doped with 100 ppm EVA was investigated by testing the pour point, static and dynamic cooling

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rheological properties. Then, the effect of asphaltenes content on the crystallization exothermic

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characteristics and microstructures of the oils undoped/doped with 100 ppm EVA was tested and analyzed.

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Finally, the influencing mechanism of asphaltenes content on the synergistic performance between

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polymeric PPDs and asphaltenes was discussed here.

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2. Experimental

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2.1 Materials

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The mineral oil, n-pentane, xylene and EVA copolymer used here were all obtained from Sigma-Aldrich

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Co., Ltd. As shown in Figure S1 of the support information file, the mineral oil mainly contains isoalkanes

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of C16 to C26 but few macro-paraffin waxes. The solid wax in the model waxy oil is composed of two ACS Paragon Plus Environment

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macro-paraffin waxes, the melting point ranges and carbon number distribution of which could be seen in a

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former published paper

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distribution of the solid wax is wide (C19~C50), similar to that in the real crude oil. The vinyl acetate group

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content of EVA are 28 wt%. The melt index of the EVA is 6, and accordingly, its average molecular weight

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is ~20000 [37]. The dosage of EVA in the subsequent model waxy oils was fixed at 100 ppm.

[37]

. As seen in Figure S2 of the support information file, the carbon number

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A settled amount of solid wax was dissolved in the xylene/mineral oil solvent to prepare the model waxy

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oil, in which the solid wax and xylene concentration was 10 and 20 wt%, respectively and the rest part was

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mineral oil. To guarantee the initial dispersing state of asphaltenes in crude oil, a certain amount of Tahe

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heavy oil was directly added into the waxy oils. According to Figure S3 and Table 1 of the support

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information file, there are few paraffin waxes and large amounts of asphaltenes (29.8 wt%, C5-asphaltenes)

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and resins (5.1 wt%). The dosage of asphaltenes in the model waxy oil was set at zero, 0.01 wt%, 0.05 wt%,

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0.1 wt%, 0.3 wt%, 0.75 wt%, 1.5 wt% and 3 wt%, respectively, and the corresponding dosage of heavy oil

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should be zero, 0.03 wt%, 0.17 wt%, 0.33 wt%, 1 wt%, 2.5 wt%, 5 wt% and 10 wt%, respectively.

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2.2 Methods

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2.2.1 Pour point tests

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The pour point of each undoped/doped waxy oil sample was tested based on the method of the Chinese

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Standard SY/T 0541-2009 [32].

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2.2.2 Rheological tests

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An AR-G2 Rheometer (TA instrument Co., USA) with a coaxial cylinder system was used to carry out the

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rheological tests. The DIN Rotor with a diameter of 28 mm was applied and the gap was 1 mm. A well-fitted

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cover was used to minimize the evaporation of the solution. Before each rheological test, the each

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undoped/doped waxy oil sample was sealed in a glass bottle and then preheated at 60 °C for 20 min for the

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heat treatment. The cooling rate during the cooling process of rheological tests was 0.5 °C/min. Each ACS Paragon Plus Environment

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Energy & Fuels

measurement was repeated 2-3 times for the reproducibility of the results.

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Structural development of the waxy oils under static cooling. An oscillation process during cooling (from

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60 °C to 15 °C) was conducted, where the elastic modulus G′, viscous modulus G″ and loss angle δ were

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recorded. The gelation point was determined at the temperature where the G′=G″ or δ=45°. The oscillatory

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amplitude (0.0005) was so small that the oscillation would not disturb the waxy oil gel structure (that is,

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static cooling condition) [31,32]. The oscillatory frequency was 1 Hz.

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Structural development of the waxy oils under dynamic cooling. A continuous shearing process during

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cooling (60 °C~15 °C) was conducted, where the oil viscosity/apparent viscosity was measured with the

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decrease of temperature. The shear rate was kept at 10 s-1.

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2.2.3 Crystallization exothermic characteristics tests

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The crystallization exothermic properties of the oils were evaluated with the aid of a DSC 821e

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calorimeter (Mettler-Toledo Co., Switzerland). A cooling process (85~-20°C) with a constant cooling rate

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(10 °C/min) was conducted, where the heat flow alteration with the temperature drop and the WPT of each oil

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sample were recorded. The DSC test for each sample was repeated three times to guarantee the accuracy of the

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result.

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2.2.4 Microstructure observation tests

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The microstructure observation of the waxy oil were performed on a BX51 microscope (Olympus Co.,

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Japan) under the polarized optical conditions. The temperature was precisely controlled by an automatic

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thermal stage. The heat-treated waxy oil was added onto the glass slide as a one droplet and then covered by

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the coverslip. Subsequently, the oil was statically cooled (60 °C~20 °C) in the thermal stage from with a

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constant cooling rate (0.5 °C/min). The wax crystal morphology was carefully photographed at 20 °C, and

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each test was repeated 3 times.

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3. Results and discussions ACS Paragon Plus Environment

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3.1 Effect of asphaltenes content on the crystallization exothermic characteristics of undoped/doped waxy

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oils

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The crystallization exothermic characteristics of the undoped/doped waxy oil are measured and the WPT

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of each oil sample is illustrated in Figure 1. The addition of 100 ppm EVA could slightly reduce the WPT

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from 34.9 °C to 33.8 °C. Based on the polymeric PPD theory, EVA PPD can co-crystallize with paraffin

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waxes during cooling, enhancing the effective solubility of paraffin waxes. In addition, the polar group (VA

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moieties) brought by EVA PPD can increase the solid-liquid interfacial tension, increasing the size of critical

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nucleation radius and the nucleation potential barrier of wax crystals. Both of these two sides inhibit the

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precipitation of wax molecules at a certain temperature[9, 10, 32]. Adding asphaltenes also decreases the WPT

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of waxy oil, and the higher asphaltenes content results in the lower WPT of the oil. In general, asphaltenes

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can provide the wax molecules with large amounts of nucleation sites for precipitation (see Figure 6~8),

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which should have increased the WPT of waxy oil. The resin-stabilized asphaltenes used here, however,

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often contain a certain amount of aliphatic side chains. These aliphatic chains are able to co-crystallize with

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wax molecules during cooling, thus decreasing the WPT of the oil. It is considered that the co-crystallization

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efficiency of asphaltene dominates over its nucleation efficiency, thus leading to the WPT reduction of the

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oil doped with asphatlenes. It is a very interesting phenomenon that adding EVA/asphaltenes cannot

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suppress the WPT of the waxy oils further, but compared to the identical asphaltenes, adding

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EVA/asphaltenes slightly increases the WPT of the waxy oils.

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The accumulated amount of the precipitated wax crystal of the oils with the decrease of temperature could [30,31,37]

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be calculated based on the DSC curves

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precipitated wax crystal at 20 °C and -20 °C is shown in Table 1. Apparently, the increase of asphaltenes

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content slightly decreases the precipitated wax crystal amount at a fixed temperature because of the dilution

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effect due to the addition of heavy oil, which should have a positive impact on the flow improvement of the

, and the effect of asphaltenes content on the amount of the


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Energy & Fuels

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waxy oil. However, when the asphaltenes content is too high (1.5~3 wt%), the flowability of the oil adding

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asphaltenes is deteriorated (see Figure 4). Therefore, we consider the dilution effect of heavy oil is limited

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and the asphaltenes content dominates the flowability of the oil.

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Based on the discussions mentioned above, the conclusion can be drawn that the co-crystallization effect

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between the additives (EVA or asphaltene) and wax molecules is predominant, which finally leads to the

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WPT decreasing, while the addition of additives exerts no apparent impact on the precipitated wax crystals

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amount at low temperatures.

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3.2 Effect of asphaltenes content on the pour point of undoped/doped waxy oils

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The effect of asphaltenes content on the pour point of waxy oils is shown in Table 2. The pour point of the

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pure waxy oil is 36 °C, and addition of 100 ppm EVA depresses it to 31 °C. In the absence of EVA, the pour

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points of waxy oils adding neat asphaltenes decreases slowly with the increase of asphaltenes content. For

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example, when the asphaltenes content increases from 0 to 0.1 wt%, the pour point of waxy oil adding neat

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asphaltenes only decreases by 1 °C; when the asphaltenes content finally rises to 3 wt%, decrease of pour

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point is 7 °C. Adding asphaltenes together with EVA dramatically reduces the pour point of the oil. Adding

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0.01 wt% and 0.05 wt% asphaltenes together with EVA suppresses the pour point to 25 °C and 20 °C,

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respectively. After the asphaltenes content increases to 0.1 wt% and 0.3 wt%, the pour point of waxy oil

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decreases sharply to 7 °C and -5 °C, respectively. The pour point of waxy oil falls to lower than -10 °C after

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the addition of 0.75 wt% and 1.5 wt% asphaltenes together with EVA, respectively. When the asphaltenes

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content is too high (3 wt%), the pour point of waxy oil doped with both EVA and asphaltenes recovers to

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-8 °C. It is clear that EVA together with different contents of resin-stabilized asphaltenes can synergistically

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suppress the pour point of waxy oils, and the synergistic efficiency is first enhanced with the increase of

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asphaltenes content and then somewhat deteriorated when the asphaltenes content is too high.

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3.3 Effect of asphaltenes content on the structural development of undoped/doped waxy oils ACS Paragon Plus Environment

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3.3.1 Structural development of waxy oils under static cooling condition

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Figure 2 shows the viscoelastic development with temperature drop of waxy oils doped with different

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content of asphaltenes in the absence of EVA. For the original waxy oil (Figure 2a), at temperatures higher

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than or around the WPT, few wax molecules precipitates from the liquid phase where G′ and G″ values are

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small, and G″ (around 10-2 Pa) is one order of magnitude larger than G′ (around 10-3 Pa) with δ approaching

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90°, verifying the viscous fluid nature of the oil. Oil temperature continuing to fall, both G′ and G″ start to

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rise up because of the continuous precipitation of wax crystals, and the increase of G′ dominates over that of

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G″, leading to a crossover of the G′ and G″ value at the gelation point of the oil (37.0 °C). With the further

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decrease of oil temperature, G′ and G″ go on increasing and the value of G′ is always higher than G″,

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meaning that the oil mainly exhibits the gel properties. Adding 0.01 wt% asphaltenes slightly decreases the

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gelation point to 36.4 °C, and also decreases the G′/G″ value at 15 °C from 194400 Pa/11215 Pa to 125630

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Pa/6903 Pa, indicating that a small dosage of asphaltenes can slightly retard the waxy oil gelation process.

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Increasing the asphaltenes content can suppress both the gelation point and the G′/G″ values at low

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temperatures of waxy oil. For example, when the asphaltenes content increases to 0.05 wt%, 0.1 wt%, 0.3

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wt% and 0.75 wt%, the gelation point of doped waxy oil decreases to 33.9 °C, 33.4 °C, 33.0 °C and 30.9 °C,

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respectively. After adding relatively high content of asphaltenes (1.5 wt% and 3 wt%), at high temperature

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ranges, the value of G′ has increased a lot (over 10-2 Pa), meaning that the high content of asphaltenes, as a

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dispersant, contributes a lot to the elastic response of the oil. However, the gelation points of the oils doped

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with 1.5 wt% and 3 wt% asphaltenes are further suppressed to 29.4 °C and 27.6 °C, respectively, and the

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G′/G″ value at 15 °C decreases to 5192 Pa/946.4 Pa and 939.5 Pa/165.0 Pa, respectively, which are the

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lowest in all the doped samples, meaning that the higher content of asphaltenes favors gelation inhibition

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and the viscoelasticity improvement of waxy oil at low temperatures.

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As illustrated in Figure 3, associated with 100 ppm EVA, the gelation point and the G′/G″ values at low ACS Paragon Plus Environment

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temperatures of waxy oil doped with different content of asphaltenes decrease further. The gelation point of

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waxy oil decreases to 25.8 °C after adding 100 ppm neat EVA, then to 20.7 °C, 18.2 °C and 16.2 °C after

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adding EVA/0.01 wt%, EVA/0.05 wt% and EVA/0.1 wt% asphaltenes, respectively. The G′/G″ value of the

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oil doped with EVA/0.01 wt%, EVA/0.05 wt% and EVA/0.1 wt% asphaltenes at 15 °C are only 3256

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Pa/617.4 Pa, 633 Pa/159.5 Pa and 119.7 Pa/35.9 Pa, respectively. For the waxy oil doped with EVA together

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with asphaltens ≥ 0.3 wt%, the oils display no gelation point under experimental condition. However, the

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G′/G″ value of the oil first decreases from 3.49 Pa/6.68 Pa at EVA/0.3 wt% asphaltenes to 0.0022 Pa/0.064

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Pa at EVA/0.75 wt% asphaltenes, then increases from 0.088 Pa/0.166 Pa at EVA/1.5 wt% asphaltenes to

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0.255 Pa/0.376 Pa at EVA/3 wt% asphaltenes.

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It is obvious that adding EVA together with different contents of resin-stabilized asphaltenes in waxy oil

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can synergistically benefit the viscoelasticity improvement of the oil during the static cooling process, and

242

the synergistic efficiency first increases (< 1.5 wt%) and then somewhat decreases (≥ 1.5 wt%) with

243

increasing the asphaltenes content.

244

3.3.2 Structural development of waxy oils under dynamic cooling condition

245

The apparent viscosity changes with decreasing temperature of the undoped/doped waxy oils is displayed

246

in Figure 4. For the pure waxy oil, the apparent viscosity first exhibits a gradual increase with the decrease

247

of temperatures above WPT, and then increases quickly when the temperature drops to lower than WPT and

248

the increasing amplitude is sharp; after that, the viscosity of the pure waxy oil exhibits the gradual increase

249

again with a larger slope. At temperatures above the WPT, adding 100 ppm EVA shows no apparent effect

250

on the viscosity of waxy oil; at temperatures lower than the WPT, the apparent viscosity developing is a

251

slowly and gradually increasing trend. Above 16 °C, EVA can effectively reduce the apparent viscosity of

252

the oil, while below 16 °C, the apparent viscosity of the oil adding EVA rises up over that of the pure waxy

253

oil. For example, at 15 °C, the apparent viscosity of pure waxy oil is 394 mPa·s, while the apparent viscosity ACS Paragon Plus Environment

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254

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of the waxy oil adding 100 ppm EVA is 450 mPa·s.

255

For the waxy oils with the addition of different contents of asphaltenes, when the asphaltenes content is

256

low (< 0.3 wt%), the doped asphaltenes increase the oil viscosities a bit at temperatures above WPT and has

257

no dramatic impact on the oil viscosities at temperatures just below WPT. When the temperature decreases

258

far below WPT, the asphaltenes slightly increase the viscosities of the oil. For example, at 15 °C, the

259

apparent viscosities of the waxy oil doped with 0.01 wt%, 0.05 wt% and 0.1 wt% asphaltenes are 424 mPa·s,

260

432 mPa·s and 459 mPa·s, respectively. When the asphaltenes content is ≥ 0.3 wt%, at temperatures above

261

WPT, the higher content of asphaltenes favors the viscosities increase; but at temperatures just below WPT,

262

the doped asphaltenes can reduce the apparent viscosity of the oil and the higher content of asphaltenes

263

broaden the apparent viscosity reducing temperature range. The viscosity-increasing trend of the oil adding

264

neat asphaltenes, however, is extremely quick, and at low temperatures, the apparent viscosity exceeds that

265

of the undoped. For example, at 15 °C, the apparent viscosity of the waxy oil doped with 0.3 wt%, 0.75 wt%,

266

1.5 wt% and 3 wt% asphaltenes is 534 mPa·s, 948 mPa·s, 1150 mPa·s and 2097 mPa·s, respectively. In

267

general, the effect of asphaltenes content on the viscosity/apparent viscosity of waxy oil is complicated: (a)

268

at temperatures above the WPT, adding asphaltenes leads to the increase of oil viscosity and the oil viscosity

269

increases with increasing asphaltenes content; (b) adding asphaltenes only decreases the apparent viscosity

270

of the oil at a temperature range slightly below the WPT, and the temperature range is broadened with

271

increasing asphaltenes content; (c) at temperatures far below the WPT, adding asphaltenes increases the oil

272

apparent viscosity, which increases with increasing asphaltenes contents.

273

For the waxy oil adding both EVA PPD and asphaltenes, EVA together with 0.01 wt% asphaltenes

274

exhibits a much greater viscosity reducing efficiency at temperatures below WPT than the neat EVA or

275

asphaltenes, but the apparent viscosity increases sharply with the decrease of temperatures and grows over

276

that of the pure waxy oil. At 15 °C, the apparent viscosity of waxy oil doped with EVA/0.01 wt% ACS Paragon Plus Environment

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asphaltenes is 452 mPa·s, slightly larger than that of the pure waxy oil. With the increase of asphaltenes

278

content, the viscosity reducing efficiency of EVA together with asphaltenes is greatly enhanced. For example,

279

the apparent viscosity at 15 °C of waxy oil doped with EVA/0.05 wt% asphaltenes and EVA/0.1 wt%

280

asphaltenes is 36.2 mPa·s and 16.2 mPa·s. When the asphaltenes content increases above 0.3 wt%, the waxy

281

oil adding EVA/asphaltenes presents no quick viscosity-increasing in the whole cooling pierod (60~15 °C).

282

The apparent viscosity of the oil at 15 °C is only 7.93, 7.42 and 8.87 mPa·s at 0.3 wt%, 0.75 wt% and 1.5

283

wt% asphaltenes content, respectively. In addition, adding EVA and 3 wt% asphaltenes still exhibits good

284

viscosity reducing performance, but the apparent viscosity at 15 °C slightly increases to 12.5 mPa·s.

285

Obviously, adding EVA together with different contents of asphaltenes can synergistically reduce the

286

apparent viscosity of waxy oils below WPT under dynamic cooling, and the synergistic effect is first

287

improved and then somewhat deteriorated with the increase of asphaltenes content.

288

3.4 Effect of asphaltenes content on the microstructures of waxy oils

289

For the undoped waxy oil (Figure 5a and 6a), the precipitated wax crystals at 20 °C are long needle-like

290

with high aspect ratios and in large amount. The wax crystal with this kind of morphology is easier to

291

overlap and form a continuous network structure, occluding the flowable liquid phase and thus causing the

292

highest pour point/gelation point of the oil. As shown in Figure 5b and 6b, after adding 0.05 wt%

293

asphaltenes, both the length and thickness of the precipitated wax crystals have been largely inhibited, but

294

the precipitated wax crystals are still needle-like. Therefore, a small dosage of asphaltenes does not clearly

295

improve the flowability of waxy oil (Figure 3). When the asphaltenes content increases to 0.3 wt% (Figure

296

5c and 6c), the length and thickness of the precipitated wax crystals get shorter and thinner, and some

297

spherical wax crystals with small sizes exist in the oil. After the addition of 3 wt% asphaltenes (Figure 5d

298

and 6d), there are no needle-like wax crystals existing but spherical-like wax crystals with smaller sizes. It is

299

clear that with the increase of asphaltenes content, the precipitated wax crystals of the waxy oil tend to grow ACS Paragon Plus Environment

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300

Page 14 of 29

into smaller and more regular spherical-like particles with larger amount.

301

As seen in Figure 7a and 8a, after adding 100 ppm EVA, the morphology of single wax crystal in waxy oil

302

is still needle-like but much shorter in length. In addition, the precipitated needle-like crystals aggregate into

303

loose radical pattern wax flocs, and the radical pattern wax flocs are in relative large amount. When adding

304

EVA together with 0.05 wt% asphaltenes (Figure 7b and 8b), the precipitated wax crystals aggregate into

305

large and spherical-like wax flocs with a much smaller amount, but the surrounding of the wax flocs still

306

presents radical pattern, meaning that the flocs structure is loose. When the asphaltenes content increases to

307

0.3 wt% asphaltenes (Figure 7c and 8c), adding EVA together with asphaltenes makes the precipitated wax

308

crystal flocs smaller, but more regular and compact. With the further increase of asphaltenes content to 3

309

wt% (Figure 7d and 8d), the sizes of precipitated wax flocs continue to decrease, and the number of wax

310

flocs significantly increases.

311

According to the microscopic images taken under bright background condition (Figure 6 and 8), the

312

dispersion state of asphaltenes can be observed more clearly. First of all, the mean size of the asphaltene

313

aggregates dispersed in waxy oil increases continuously with the increase of asphaltenes content. Secondly,

314

as seen in Figure 6 and 8, many asphaltene aggregates disperse independently in the oil phase, meaning that

315

only a part of the asphaltenes can participate in the wax crystallization process, and the rest part of the

316

asphaltenes disperses in oil phase as aggregates, which could adhere or adsorb onto the precipitated wax

317

flocs (see Figure 8d). What’s more, by comparing Figure 6 to 8, the size of asphaltenes aggregates is

318

enlarged after the addition of EVA, which further confirms that the EVA molecules adsorb on the

319

asphaltenes and then modify the dispersion state of asphaltenes in oil phase.

320

3.5 Influencing mechanism of asphaltenes content on the synergistic effect between EVA PPD and

321

asphaltenes

322

For the pure waxy oil, the formed wax crystals are long needle-like with high aspect ratios and in large ACS Paragon Plus Environment

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Energy & Fuels

323

amount. This kind of wax crystals is not only highly nonpolar, constraining thick nonpolar solvent layers,

324

but also easy to interact with each other to generate a continuous network, causing the highest pour

325

point/gelation point of the oil and the worst flowability of the oil at low temperatures.

326

In the absence of EVA and with the increase of asphaltenes content, the precipitated wax crystals of the

327

waxy oil tend to grow into smaller and more regular (spherical-like) particles with larger amount. It is hard

328

for the wax crystals with this kind of morphology to form a network structure to occlude the flowable liquid

329

phase at low wax crystals precipitation amount, which helps to the rheological improvement of the oil.

330

Therefore, at the temperature range slightly below WPT, the viscosity reducing and pour point depressing

331

performance of the neat asphaltenes are observed and the improving efficiency is enhanced with increasing

332

asphaltenes content. When the temperature is decreased far below the WPT of the oil, on the one hand, the

333

largely increased amount of the spherical-like wax crystals enlarges the solid-liquid interfacial area a lot,

334

which causes the increase of both the liquid oil amount entrapped in the solvation layer and the solid-liquid

335

interfacial energy. Therefore, the interactions between wax crystals is strengthened a lot and the apparent

336

viscosity of the oil is significantly increased; on the other hand, the doped asphaltenes serve as the dispersed

337

phase to increase the concentration of dispersed phase. Both of the two aspects significantly increase the

338

apparent viscosity of the oil. In addition, it should be noticed that although the large amount of spherical-like

339

wax crystals greatly increases the oil apparent viscosity at low temperature, the viscoelastic parameters is

340

improved with increasing the asphlatenes content because that the spherical-like wax crystals are difficult to

341

build up network structures.

342

As reported in the previous work

[37,38]

, EVA molecules can adsorb onto the asphaltene aggregates to

343

generate the formation of the EVA/asphaltenes composite particles. Similar to the nano/micro composite

344

PPDs, the EVA/asphaltenes composite particles can take effect as the heterogeneous nucleation templates for

345

the wax precipitation, greatly changing the wax crystal morphology and improving the flowability of waxy ACS Paragon Plus Environment

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Page 16 of 29

346

oil. (a) When the asphaltenes content is low, the heterogonous nucleation effect of EVA/asphaltenes

347

composite particles is not enough, the wax crystal modification is insufficient and the formed large wax

348

flocs have very loose structure, which favor the wax crystal structure building. (b) When the asphaltenes

349

content is too high (3 wt%), EVA/asphaltenes composite particles disperse the precipitated wax flocs into

350

relatively small spherical-like wax flocs with larger amount. Although the structure of the wax flocs is

351

compact, which is adverse for the network structure building, the large amount of the wax flocs and

352

asphaltenes aggregates in oil phase generates large solid-liquid interfacial area, impeding the synergistic

353

performance. Meanwhile, according to Figure 8c, only part of the asphaltenes participates in the wax

354

precipitation process, the rest part of the asphaltenes disperses in the oil phase as asphaltene aggregates,

355

which could adhere or adsorb on the existed wax crystal flocs [40]. This part of asphaltenes acts as the binders

356

between the precipitated wax flocs to strengthen the interactions of dispersed phase and thus somewhat

357

increase the pour point, G′/G″ values, and apparent viscosity of the oil. (c) At the middle contents of

358

asphaltenes (0.75~1.5 wt%), EVA/asphaltenes composite particles causes the formation of large

359

spherical-like wax flocs with compact structure and the asphaltenes content is moderate, both of which favor

360

the flow improvement of waxy oil. Therefore, the synergistic effect of EVA PPD and asphaltenes on the

361

flowability of waxy oil improves first with the increase of asphaltenes content, and then somewhat

362

deteriorates at higher asphaltenes content (3 wt%).

363

4. Conclusions

364

In this paper, the effect of asphaltenes content (0.01~3wt%) on the synergistic effect between EVA and

365

resin-stabilized asphaltenes was studied by using rheological test, DSC analysis and microscopic

366

observation. The following conclusions are drawn: (a) the co-crystallization effect between the additives

367

(EVA or asphaltene) and wax molecules is dominant and finally leads to the decrease of WPT, while the

368

additives exert no apparent impact on the precipitated wax crystals amount at low temperatures. (b) In the ACS Paragon Plus Environment

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Energy & Fuels

369

absence of EVA, the low content of asphaltenes (< 0.3wt%) has no dramatic impact on the wax crystal

370

morphologies and thus do not apparently influence the flow behavior of the waxy oil; the further increase of

371

asphaltenes content favors the wax crystal morphology growing into smaller and more regular spherical-like

372

particles with larger amount, which helps to the flow improvement at relatively low wax crystals

373

precipitation amount, but when the temperature is decreased far below the WPT of the oil, the dispersed

374

spherical-like wax crystals with large amount largely increase the solid-liquid interfacial area, thus

375

somewhat deteriorating the flowability of oil. (c) EVA together with different contents of asphaltenes can

376

synergistically enhance the flowability of waxy oils by forming the EVA/asphaltenes composite particles.

377

The synergistic performance of EVA PPD and asphaltenes on the flowability of waxy oil improves first with

378

the increase of asphaltenes content, and then somewhat deteriorates at higher asphaltenes content. When the

379

asphaltenes content is low, the wax crystal growth modification is insufficient and the formed large wax

380

flocs have very loose structure, favoring the wax crystal structure building. When the asphaltenes content is

381

too high, the precipitated wax flocs are dispersed into relatively small spherical-like wax flocs with larger

382

amount, which increase the solid-liquid interface area a lot and some of the asphaltenes serve as binders

383

between the precipitated wax crystals to strengthen the interactions of dispersed phase and thus deteriorates

384

the flow behavior of the oil. At the middle contents of asphaltenes (0.75~1.5 wt%), EVA/asphaltenes

385

composite particles generate the formation of large spherical-like wax flocs with compact structure and the

386

asphaltenes content is moderate, both of which greatly promote the flow behavior improving of the oil.

387

Acknowledgement

388

This research was funded by National Natural Science Foundation of China (51774311), Natural Science

389

Foundation of Shandong Province of China (ZR2017MEE022), and Key Research Project of Shandong

390

Province of China (2017GSF216003).

391

References

392

[1] H.P. Rønningsen, B. Bjoerndal, A.B. Hansen, W.B. Pedersen, Wax precipitation from North Sea crude oils: 1. ACS Paragon Plus Environment

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with nanocomposite pour point depressant, Fuel 184 (2016) 544-554. [23] B. Yao, C. Li, F. Yang, J. Sjöblom, J. Norrman, K. Paso, Z. Xiao, Organically modified nano-clay facilitates pour point depressing activity of polyoctadecylacrylate, Fuel 166 (2016) 96-105. [24] F. Yang, Y. Zhang, C. Li, B. Yao, K. Tian, Z. Xiao,. Effects of pour point depressant of EVA/nano MMT composites on Changqing crude oil. CIESC J. 11 (2015) 043. [25] A.M. Al-Sabagh, M.A. Betiha, D.I. Osman, A.I. Hashim, M.M. El-Sukkary, T. Mahmoud, A new covalent strategy for functionalized montmorillonite–poly (methyl methacrylate) for improving the flowability of crude oil. RSC Adv. 6 (2016) 109460-109472. [26] A.M. Al-Sabagh, M.A. Betiha, D.I. Osman, A.I. Hashim, M.M. El-Sukkary, T. Mahmoud, Preparation and evaluation of poly (methyl methacrylate)-graphene oxide nanohybrid polymers as pour point depressants and flow improvers for waxy crude oil, Energy Fuels 30 (2016) 7610-7621. [27] A. Kumar, B. Behera, G.D. Thakre, S.S. Ray, Covalently Grafted Graphene Oxide/Poly (C n-acrylate) Nanocomposites by Surface-Initiated ATRP: An Efficient Antifriction, Antiwear, and Pour-Point-Depressant Lubricating Additive in Oil Media, Ind. Eng. Chem. Res. 55 (2016) 8491-8500. [28] Z. Zhao, S. Yan, J. Lian, W. Chang, Y. Xue, Z. He, D. Bai, S. Han, A new kind of nanohybrid poly (tetradecyl methyl-acrylate)-graphene oxide as pour point depressant to evaluate the cold flow properties and exhaust gas emissions of diesel fuels, Fuel 216 (2018) 818-825. [29] Z. Tu, G. Jing, Z. Sun, Z. Zhen, W. Li, Effect of nanocomposite of attapulgite/EVA on flow behavior and wax crystallization of model oil. J. Dispersion Sci. Technol. (2017) 1-5. [30] F. Yang, B. Yao, C. Li, G. Sun, X. Ma, Oil dispersible polymethylsilsesquioxane (PMSQ) microspheres improve the flow behavior of waxy crude oil through spacial hindrance effect, Fuel 199 (2017) 4-13. [31] B. Yao, C. Li, F. Yang, Z. Mu, X. Zhang, G. Sun, Effect of oil dispersible polymethylsilsesquioxane microspheres on the formation and breakage of model waxy oil gels, Fuel 209 (2017) 424-433. [32] F. Yang, B. Yao, C. Li, X. Shi, G. Sun, X. Ma, Performance improvement of the ethylene-vinyl acetate copolymer (EVA) pour point depressant by small dosages of the polymethylsilsesquioxane (PMSQ) microsphere: An experimental study, Fuel 207 (2017) 204-213. [33] B. Yao, C. Li, X. Zhang, F. Yang, G. Sun, Y. Zhao, Performance Improvement of the Ethylene-Vinyl Acetate Copolymer (EVA) Pour Point Depressant by Small Dosage of the Amino-functionalized Polymethylsilsesquioxane (PAMSQ) Microsphere, Fuel 220 (2018) 167-176. [34] Y. Li, S. Han, Y. Lu, J. Zhang. Influence of Asphaltene Polarity on Crystallization and Gelation of Waxy Oils. Energy Fuels (2017) doi: 10.1021/acs.energyfuels.7b03553. [35] F. Yang, J. Cai, L. Cheng, C. Li, Z. Ji, B. Yao, Y. Zhao, G. Zhang, Development of Asphaltenes-Triggered Two-Layer Waxy Oil Gel Deposit under Laminar Flow: An Experimental Study, Energy Fuels 30 (2016) 9922-9932. [36] Y. Lei, S. Han, J. Zhang, Y. Bao, Z. Yao, Y. N. Xu. Study on the effect of dispersed and aggregated asphaltene on wax crystallization, gelation, and flow behavior of crude oil. Energy Fuels 28 (2014) 2314-2321. [37] B. Yao, C. Li, F. Yang, X. Zhang, Z. Mu, G. Sun, Y. Zhao, Ethylene-Vinyl Acetate Copolymer (EVA) and Resin-stabilized Asphaltenes Synergistically Improve the Flow Behavior of Model Waxy Oils: 1. Effect of Wax Content and the Synergistic Mechanism, Energy Fuels 32 (2018) 1567-1578. [38] B. Yao, C. Li, F. Yang, X. Zhang, Z. Mu, G. Sun, Polyoctadecylacrylate (POA) and Resin-Stabilized Asphaltene Synergistically

Improve

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of

Model

Waxy

Oils.

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19

Energy & Fuels

486

Figures

487 488 35.0

34.9

34.5

without EVA with 100 ppm EVA

34.0 33.8

WPT / °C

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

Page 20 of 29

33.5 33.0

33.7

33.6 33.4

33.4

33.3 33.1

33 32.8

32.6

32.5

32.7 32.5 32.1

32.0

31.6

31.5 0

489 490

Figure 1

0.01 0.05 0.1 0.3 0.75 1.5 Asphaltene content / wt%

3

Effect of asphaltenes content on the WPT of the waxy oils undoped/doped with EVA.

491


20

Page 21 of 29

492 493 5

10

5

10

4

80

4

10

3

10

3

60

2

10% undoped waxy oil

1

10

GP: 37.0 °C

40

G' G'' δ

0

10

-1

10

1

10

0

10

doped with 0.01 wt% asphaltenes

40

GP: 36.4 °C

-1

10

20

20

-2

10

-2

10

-3

10

0

-3

10

0

-4

10

20

30 40 Temperature / °C

494


(a)

5

50 (b)

5

10

80

4

80

4

10

10

3

3

60

10

1

10

40 G' G'' δ

GP: 33.9 °C

0

10

20

-1

10

60

2

10

1


0

GP: 33.4 °C

10 10

40

G' G'' δ

-1

δ/°


10 δ/°

2

G ' G'' / Pa

10

20

10

-2

-2

10

10

0

-3

10

20


495

0

-3

10

50

20

5

80

10

3

10

60

GP: 33.0 °C

G' G'' / Pa

40

G' G'' δ

10

1

G' G'' δ

0

10

-1

-1

10

20

10

40

-2

10

-3

-3

10

20

10

-2

60

10

δ/°

10


δ/°

0

80 doped with 0.75 wt% asphaltenes GP: 30.9 °C

2

2 1

(d)

3

10

10

50

4

4

10

10


(c)

10

G' G'' / Pa

20

50

10

20

496


50

10

0

20 (e)

80


50

(f)

3

10

3

10

60 2

2

10

10

0

GP: 29.4 °C

40

10

1

10

doped with 3 wt% asphaltenes G' G'' δ

GP: 27.6 °C

0

10

-1

10

20

40

δ/°

10


G' G'' / Pa

60 G' G'' δ

1

δ/°

G' G'' / Pa

60 δ/°

G' G'' / Pa

10

G' G'' δ

2

10

G' G'' / Pa

10

G ' G '' / Pa

80

10

δ/°

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

Energy & Fuels

20

-1

10

-2

10

-2

10 20

497 498

Figure 2


50

(g)

20


50 (h)

Effect of asphaltenes content on the viscoelasticity development of the waxy oil undoped with

499

EVA during static cooling.

500


21

Energy & Fuels 5

4

10

10

4

3

10

10

80

3

1

10

G' G'' δ

0

10

-1

40

G' G'' / Pa

60

doped with 100ppm EVA GP: 25.8 °C

10

-1

10 10

-2

10

60

GP: 20.7 °C

0

-2

20

doped with 100ppm EVA+ 0.01 wt% asphaltenes

1

10

δ/°

G' G'' / Pa

10

2

10

10

40

G' G'' δ

20

-3

10 0

-3

10

20

501


-4

10

50

20

(a)

3

10


0

50

(b)

2

10

80

2

10

80

1

1


0

-1

40

10


0

10

G' G'' δ

GP: 16.2 °C

-1

60 δ/°

GP: 18.2 °C

60 δ/°

10

G' G'' δ

G' G'' / Pa

10

10 G' G'' / Pa

80

2

10

δ/°

10

40 -2

10 -2

10

20

-3

20

10

-3

10

-4

10

20


502

50

2

80

10

1

GP: N/A

-1

10

-2

10

40

G' G'' / Pa


0

20

G' G'' δ

50 (d)

80

0

10

60

10



G' G'' δ

-1

10

GP: N/A

40

-2

10

20

-3

10

0

0 20


503

20

50

60 δ/°

G' G'' / Pa

10

20

(c)

δ/°


(e)

50 (f)

1

10

80

80 0

-1

10

-2

40

60

0

10

20

G' G'' δ

10

60 G' G'' / Pa

doped with 100ppm EVA+ 1.5 wt% asphaltenes GP: N/A

doped with 100ppm EVA+ 3 wt% asphaltenes GP: N/A

G' G'' δ

40

δ/°

G' G'' / Pa

10

δ/°

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

Page 22 of 29

-1

10

20 0

0 -2

10

20

504 505 506

Figure 3


50

(g)

20


50

(h)

Effect of asphaltenes content on the viscoelasticity development of the waxy oil doped with 100ppm EVA during static cooling.

507 ACS Paragon Plus Environment

22

-2

10

20

Apparent viscosity / Pa·s

508

30


undoped waxy oil doped with 100 ppm EVA doped with 0.1wt% asphaltenes doped with EVA+0.1wt% asphaltenes

-1

10

-2

10

20

509

30 40 50 Temperature / °C

-2

10


-1

10

-2

10



10

50

60 (d)


-1

10

-2

10

60 (e)

20


50

60 (f)

undoped waxy oil doped with 100 ppm EVA doped with 3wt% asphaltenes doped with EVA+3wt% asphaltenes

-1

10

-2

10

10

513

60 (b)


20


-1

10

0

Figure 4


0

10

512

-2

10

60 (c)


20

511

-1

10

20

0

10

510


60 (a)


-1



10


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

Energy & Fuels


Page 23 of 29

20


50

60

(g)

Effect of asphaltenes content on the apparent viscosity-temperature curves of the waxy oils undoped/doped with 100 ppm EVA during dynamic cooling. ACS Paragon Plus Environment

514

23

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

Page 24 of 29

515 516 517 518

(a)

(b)

519

(c)

(d)

520 521 522

Figure 5

Microstructure of the waxy oil undoped (a)/doped with 0.05 wt% asphaltenes (b), 0.3 wt%

asphaltenes (c) and 3 wt% asphaltenes (d) under the black background condition at 20 °C.

523


24

Page 25 of 29 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

Energy & Fuels

524 525

(a)

(b)

(c)

(d)

526

527 528 529

Figure 6

Microstructure of the waxy oil undoped (a)/doped with 0.05 wt% asphaltenes (b), 0.3 wt%

asphaltenes (c) and 3 wt% asphaltenes (d) under the bright background condition at 20 °C.

530


25

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

Page 26 of 29

531 532

(a)

(b)

(c)

(d)

533

534 535

Figure 7

Microstructure of the waxy oil doped with 100 ppm EVA (a), EVA/0.05 wt% asphaltenes (b),

536

EVA/0.3 wt% asphaltenes (c) and EVA/3 wt% asphaltenes (d) under the black background condition at

537

20 °C.

538


26

Page 27 of 29 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

Energy & Fuels

539 540 541

(a)

(b)

(c)

(d)

542

543 544

Figure 8

Microstructure of the waxy oil doped with 100 ppm EVA (a), EVA/0.05 wt% asphaltenes (b),

545

EVA/0.3 wt% asphaltenes (c) and EVA/3 wt% asphaltenes (d) under the bright background condition at

546

20 °C.

547


27

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

Page 28 of 29

548 549

Tables

550 551 552 553 554

Table 1

Effect of asphaltenes content on the amount of the precipitated wax crystal (wt%) of the

555

undoped/doped waxy oils at 20 °C and -20 °C. Asphaltenes concentration (wt%) Temperature

Dosage 0

0.01

0.05

0.1

0.3

0.75

1.5

3

Without EVA

3.61

3.60

3.61

3.59

3.58

3.54

3.47

3.31

With EVA

3.58

3.59

3.57

3.57

3.54

3.49

3.42

3.25

Without EVA

9.98

9.97

9.97

9.95

9.90

9.78

9.59

9.13

With EVA

10.02

9.97

9.98

9.97

9.91

9.78

9.57

9.11

At 20 °C

At -20 °C

556 557


28

Page 29 of 29 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

Energy & Fuels

558 559 560 561 562

Table 2

Effect of asphaltenes content on the pour points (°C) of the waxy oils undoped/doped with EVA. Asphaltenes 0

0.01

0.05

0.1

0.3

0.75

1.5

3

Without EVA

36

36

35

35

34

32

30

29

With EVA

31

25

20

7

-5

EthyleneâVinyl Acetate Copolymer and Resin-Stabilized Asphaltenes

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