Comb-like Polyoctadecylacrylate (POA) Wax inhibitor Triggers the

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Comb-like Polyoctadecylacrylate (POA) Wax inhibitor Triggers the Formation of Heterogeneous Waxy Oil Gel Deposit in a Cylindrical Couette Device Fei Yang, Liang Cheng, Hongye Liu, Bo Yao, Chuanxian Li, Guangyu Sun, and Yansong Zhao Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.7b03416 • Publication Date (Web): 08 Dec 2017 Downloaded from http://pubs.acs.org on December 29, 2017

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Energy & Fuels

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Comb-like

Polyoctadecylacrylate

(POA)

Wax

inhibitor

Triggers

the

2

Formation of Heterogeneous Waxy Oil Gel Deposit in a Cylindrical Couette

3

Device

4

Fei Yang1,2*, Liang Cheng1, Hongye Liu1, Bo Yao1,2, Chuanxian Li1,2, Guangyu Sun1,2 and Yansong

5

Zhao3

6

1

7

People’s Republic of China

8

2

9

Shandong 266580, People’s Republic of China

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

Shandong Provincial key laboratory of Oil & Gas Storage and Transportation Safety, Qingdao,

10

3

11

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

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*Corresponding Author: Fei Yang E-mail: [email protected] or [email protected]

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Abstract: In real crude oil pipelines, the formed wax deposits could be heterogeneous along the radial

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or axial direction. However, studies on this aspect are scarce. In this paper, the effect of the

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polyoctadecylacrylate (POA) wax inhibitor on the wax deposition of 10 wt% model waxy oil was

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investigated with the aid of an in-house wax deposition device, DSC test, HTGC/FT-IR analysis, and

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microscopic observation. The results showed that adding POA in the model waxy oil greatly modifies

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the morphology of precipitated wax crystals, thus greatly changing the wax deposition behavior of the

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oil. For oil sample 1 (without POA), the precipitated wax crystals (needle-like) are easier to form porous

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network structure, causing the formation of a thick and porous wax deposit with relatively low WAT,

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wax content and critical carbon number (CCN). With the increase of POA concentration (oil sample

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2~5), the precipitated wax crystals become more regular (spherical-like) and more compact, which

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favors the formation of thinner but more compact wax deposits with relatively high WAT, wax content

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

1 ACS Paragon Plus Environment

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and CCN. It was also found that adding a small amount of POA (50~200 ppm, oil sample 2~4) triggers

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the formation of heterogeneous wax deposits along the radial direction. When the POA concentration

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increases further (≥ 400 ppm, oil sample 5), however, the formed wax deposit structure turns back into

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homogeneous. Based on the fact that the POA molecules participate in wax precipitation and

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concentrate in the wax deposits, it is deduced that the continuous depletion of POA in bulk oil with

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deposition time triggers the formation of the heterogeneous wax deposits. The lower the original POA

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concentration is, the more obvious the depletion of POA in bulk oil is, resulting in the formation of a

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more explicit heterogeneous wax deposit structure. At the POA concentrations ≥ 400 ppm, however, the

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depletion of POA in bulk oil is so slow that it has little influence on the wax deposition process, thus

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turning back the wax deposit structure into homogeneous.

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1. Introduction

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Most of the crude oil contains a substantial amount of paraffin waxes, which are mainly composed by

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the n-alkanes with carbon number ≥ 18 [1]. When the temperature of the waxy crude oil is below its wax

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appearance temperature (WAT), paraffin waxes precipitate from the oil phase and then cause several

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problems in the pipelining process of the oil, such as aggravated rheological properties and wax

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deposition. Wax deposition in pipelines transporting waxy crude oil is a common phenomenon, which is

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resulted from the temperature differential between the flowing hot crude oil and the cold inner pipe wall

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(with the temperature < WAT) [2]. It has been verified that the wax deposits formed in crude oil pipelines

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are waxy oil gels with the precipitated wax crystals forming the network and the liquid oils entrapped in

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the network. The accumulation and aging of the waxy oil gel deposits on the inner pipe wall greatly

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decrease the efficiency and security of crude oil pipelines.

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In industry, pigging is often used to scrape off the wax deposit and then guarantee the efficiency and

46

security of crude oil pipelines. In order to set out a suitable pigging period, it is necessary to well


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understand the formation process of wax deposits in pipelines. During the last two decades, the wax

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deposition behavior has been widely studied through different testing systems including the cold fingers

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[3-6]

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oscillatory baffled tube system

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[16-18]

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oil composition [12-15,17,23] and deposition time [19,24,25] on the wax deposition behavior have been studied

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in detail. Several wax deposition mechanisms including molecular diffusion, heat transfer, Brownian

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diffusion, shear dispersion and gravity sedimentation have been put forward [2]. The molecular diffusion

55

approach was considered as the dominant mechanism for wax deposition, and many wax deposition

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models have been established based on the molecular diffusion approach and experimental data [26-28].

, flow loops

[6-9]

, cylindrical Couette devices [15]

[10-13]

, parallel plate deposition cell system

[14]

and

. The effects of the bulk oil temperature [16-18], pipe wall temperature

, temperature difference between the crude oil and the pipe wall (∆T) [16-19], flow rate

[20-22]

, crude

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Although peoples have gained many achievements on wax deposition in crude oil pipelines, most of

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the achievements considered that the formed wax deposits have a homogeneous structure, that is, the

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composition of the wax deposits at different points is the same. In real crude oil pipelines, however, the

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formed wax deposits could be heterogeneous, that is, the composition of the wax deposits changes along

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the radial or axial direction [29-31]. Recently, Yang et al [12,13] investigated the effect of asphaltenes on the

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formation of waxy oil gel deposits in an in-house cylindrical Couette device. They found that a small

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addition of the asphaltenes (≤ 3 wt%) in model waxy oil triggers the formation of a two-layer waxy oil

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gel deposit (along the radial direction), which is composed by a hard inner deposit layer and a loose

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outer deposit layer. The authors stated that (a) the asphaltenes disperse well in model waxy oil as small

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aggregates with an average size of 1.5 µm; (b) the asphaltene aggregates could take part in the

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crystallization process of wax molecules and then change the precipitated wax crystals’ morphology

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from needle-like to spherical-like; (c) both the molecular diffusion of wax molecules and the Brownian

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diffusion of asphaltenes result in the formation of the two-layer wax deposit, which is speculated to form


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through a four-step process. Up to now, studies on the formation process of the heterogeneous wax

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deposits are scarce. Detailed researches on the formation process of the heterogeneous wax deposits

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become urgent because it not only favors the development of wax deposition theory but also favors

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better guidance of the pigging operation.

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Polymeric wax inhibitors (PWIs) are frequently used in the recovery and transportation processes of [32]

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waxy crude oil to inhibit the wax deposition in wellbores and pipelines

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decrease the pour point, apparent viscosity and yield stress of waxy crude oil (Non-Newtonian fluids at

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temperatures < WAT), that is, the PWIs can also act as pour point depressants for waxy crude oil [32-34].

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Similar to the asphaltenes, the PWIs could participate in the wax precipitating process and greatly

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change the wax crystallization habits, thus inhibiting the wax deposition and improving the flow

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behavior of waxy crude oil

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EVA-type [33,37-41] and the comb-like type [35,36,42-46]. The effects of the PWIs’ molecular structure [38,45,47],

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wax composition and content

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evaluated, and the wax deposition rate is the main evaluation criteria. Meanwhile, several researches

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stated that the wax deposit structure changes after adding the PWIs

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become not only thinner but also significantly harder due to an increase in the wax content of the

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deposits. However, it is still unclear if the PWIs could trigger the formation of heterogeneous wax

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deposit structure (along the radial direction), just like the asphaltenes did.

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[35-37]

. Most of the PWIs can also

. Normally, the PWIs could be divided into two classifications, the

[48]

, asphaltenes

[49]

on the efficiency of the PWIs have been widely

[50,51]

: with PWIs the wax deposits

Polyoctadecylacrylate (POA) is a kind of comb-like PWIs and has been widely investigated as model [35,45,52-54]

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PWIs due to its explicit molecular structure

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deposition of 10 wt% model waxy oil has been studied with the aid of an in-house wax deposition

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device. We found that adding a small amount of POA (50~200 ppm) triggers the formation of

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heterogeneous wax deposits along the radial direction. The formation mechanism of the heterogeneous

. In this paper, the effect of the POA on the wax


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wax deposit structure was also well discussed here. 2. Experimental section 2.1 Materials As was shown in the former published papers

[12,13]

, the paraffin wax used here is composed mainly

by n-paraffins (around 95 wt%), with the remainders as the branched or cyclic paraffins. The carbon number distribution of the paraffin wax is C19~C38, with the peak carbon number around C24~C25. The diesel oil used here is composed mainly by n-alkane and isoalkane (56.3 wt%), cycloalkane (31.2 wt%) and aromatics (12.4 wt%), with the wax content and the WAT as 1.34 wt% and -10 °C (see Figure S1 in the support information file), respectively

[12,13]

. The comb-like POA PWI was prepared

through the solution free-radical polymerization of octadecylacrylate monomer under nitrogen atmosphere with AIBN as the initiator and toluene as the solvent. Detailed information of the POA could be seen in our previous work [52-54]. The model waxy oil used here was prepared by dissolving 10 wt% paraffin waxes into the diesel oil. During the experiments, the dosages of the POA in the waxy oil were fixed at zero, 50 ppm, 100 ppm, 200 ppm and 400 ppm, respectively, and the corresponding waxy oil samples were denoted as oil sample 1~5. As shown in Table 1, the WAT and pour point of the waxy oil without POA (oil sample 1) are 20 °C and 19 °C, respectively. Addition of POA slightly decreases the WAT and pour point of the oil samples. For oil sample 2 and 3, the WAT and pour point are suppressed to 19 °C and 17 °C, respectively. For oil sample 4 and 5, the WAT and pour point decreased further to 18 °C and 15 °C, respectively. The effect of the POA PWI on the viscosity/equilibrium viscosity of the model waxy oil is demonstrated in Figure S7 of the support information file. Obviously, adding POA greatly improve the flowability of the waxy oil samples at temperatures ≤ WAT, and the flow improving efficiency of POA enhances with increasing the POA dosage.


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2.2 Experiments 2.2.1 Wax deposition test An in-house cylindrical Couette device was used here to carry out the wax deposition test. As seen in Figure 1 of the previous work [12,13], the oil sample barrel containing model waxy oil can rotate with the aid of the conveyor, while the wax deposition barrel which could be lifted out of the device is stationary in the center of the oil sample barrel. Detailed information of the device could be found in the previous work

[12,13]

. The oil sample mass used for each test was fixed at 1.5 kg, and the rotation speed of the

sample barrel was fixed at 150 r/min. The hot bath was kept constant at WAT + 5 °C and was used to heat the oil samples contained in the wax deposition device, while the cold bath was kept constant at WAT - 5 °C and was used to cool the wax deposition barrel. The deposition time was fixed at 1 h, 3 h, 6 h, 12 h and 24 h. Right after each test, the wax deposition barrel was lifted out of the rotating sample barrel immediately. The wax deposits formed at different deposition times were carefully scraped off from the surface of wax deposition barrel and collected in different sealed bottles. The bottles containing wax deposits were weighted, and then the wax deposit mass were obtained. Compared with the oil sample mass (1.5 kg), the wax deposit mass at deposition time 24 h was very small (less than 50 g), indicating that wax deposition do not change the composition of bulk oil significantly. Meanwhile, a small amount of outermost-layer and innermost-layer wax deposits formed at different deposition times were carefully conserved for the following DSC, HTGC, FTIR tests and microscopic observation. By comparing the properties of the outermost-layer and innermost-layer wax deposits, we could evaluate the homogeneity/heterogeneity of the formed wax deposit. 2.2.2 DSC test of the wax deposit A DSC821e Differential Scanning Calorimeter (Mettler-Toledo Co., Switzerland) was applied to measure the exothermic curves of the outermost-layer and innermost-layer wax deposits formed at


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different deposition times. The temperature scanning range was -20~60 °C, the cooling rate was fixed at 10 °C/min. According to the exothermic curves, the WAT and wax content of the outermost-layer and innermost-layer wax deposits were obtained. 2.2.3 HTGC and FT-IR analysis of the wax deposit The n-alkane composition (≥ C18) of the outermost-layer and innermost-layer wax deposits formed at different deposition times was analyzed by a high temperature gas chromatograph (Varian Co., America). By comparing with the n-alkane composition of bulk oil, the concentration differential at different carbon number (∆wt%) and the critical carbon number (CCN) of the outermost-layer and innermost-layer wax deposits were ascertained. The POA concentration in the wax deposits formed by oil sample 5 at different deposition times were analyzed qualitatively through a FT-IR spectrometer (Thermol Fisher Scientific Co., America). 2.2.4 Microscopic observation of the wax deposit The wax crystals’ morphology in the waxy oils and in the outermost-layer/innermost-layer wax deposits formed at 24 h was observed by an Olympus BX51 polarized microscope fitted with a thermal stage (Motic China group Co., China). The thermal stage was first preheated at 15 °C. Subsequently, a glass slide was placed in the thermal stage and a small amount of deposit sample was coated on the slide. Finally, the wax crystals’ morphology in the waxy oils and in the outermost-layer/innermost-layer wax deposits was observed and recorded at 15 °C. 3. Results and discussion 3.1 Macroscopic observation of the wax deposits As shown in Figure 1a and 1b, for oil sample 1 (without POA), a thick wax deposit with light green color forms on the wax deposition barrel surface at 24 h. The outmost-layer and innermost-layer wax deposits show the same appearance and there is no obvious difference between them. Figure 1c


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demonstrates the DSC curves of the utmost-layer and innermost-layer wax deposits formed by oil sample 1 at 24 h, and Figure 1d shows the precipitated wax crystal amounts of the utmost-layer and innermost-layer wax deposits at different temperatures. It is clear that the two wax deposits have the similar WAT and wax content, indicating that the structure of the whole wax deposit formed by oil sample 1 is homogenous. The appearances of the wax deposits formed by oil sample 2~5 at 24 h are demonstrated in Figure 2~5. Obviously, the structure of the formed wax deposit is greatly influenced by POA addition. When the POA concentration is relatively small (≤ 200 ppm), the formed wax deposit becomes heterogeneous. As seen in Figure 2~4, the outmost-layer wax deposits show slight green color but the innermost-layer wax deposits show more white color. Meanwhile, the WAT and wax content of the outmost-layer wax deposit are greatly lower than those of the innermost-layer wax deposit. For example, for oil sample 3, the WAT and the wax content at -20 °C of the outmost-layer wax deposit are 41 °C and 39.8 wt%, while those of the innermost-layer wax deposit are 47 °C and 56.5 wt%. The states of the outmostlayer/innermost-layer wax deposits are also displayed in Figure S8b and 8c of the support information file, which shows clearly a liquid-like outermost-layer wax deposit and a solid-like innermost-layer wax deposit. Therefore, it could be concluded that the formed wax deposit becomes heterogeneous after a small dosage of POA (≤ 200 ppm). It should be noticed that no clear stratification boundary could be identified in the heterogeneous wax deposit, indicating that the wax deposit transits gradually from the strong innermost-layer structure to the weak outermost-layer structure. When the POA concentration is relatively high (≥ 400 ppm), however, the structure of the wax deposit turns back into homogeneous. As seen in Figure 5, there is no obvious difference between the outermost-layer and innermost-layer wax deposits, and the WAT and wax content of the outermost-layer wax deposit are similar to those of the


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Energy & Fuels

innermost-layer wax deposit, which verify the formation of a homogeneous wax deposit after adding 400 ppm POA. 3.2 Developments of the mass, WAT and wax content of wax deposits with deposition time As seen in Figure 6a, the wax deposit mass increases continuously with increasing deposition time. Compared to the wax deposits formed by oil sample 2~5 (with POA), the wax deposit formed by oil sample 1 (without POA) has the highest deposition rate, meaning that the POA inhibits wax deposition. Meanwhile, at a fixed deposition time, the total wax deposit mass decreases with increasing the POA concentration. As seen in Figure 6b, at a fixed deposition time 24 h, the wax deposit masses formed by oil sample 1~5 are 16.59 g/dm2, 10.82 g/dm2, 7.16 g/dm2, 6.07 g/dm2 and 4.88 g/dm2, respectively. Obviously, increasing the POA concentration enhances its wax inhibition efficiency, that is, increasing the POA concentration favors the formation of a thinner wax deposit. As seen in Table 2, the WATs of the wax deposits increasing continuously with increasing deposition time. For oil sample 1 (without POA), the wax deposit is homogeneous and its WAT is relatively low (22 °C at 1 h, 29 °C at 24 h). After the addition of POA in the waxy oil, the WATs of the formed wax deposits increase greatly with increasing the POA concentration. For example, at deposition time 1 h, the WATs of the outermost-layer wax deposits formed by oil sample 2~4 are 24 °C, 28 °C and 32 °C, respectively, while the WATs of the innermost-layer wax deposits are 36 °C, 37 °C and 39 °C, respectively. At deposition time 24 h, the WATs of the outermost-layer wax deposits formed by oil sample 2~4 are 38 °C, 41 °C and 44 °C, respectively, while the WATs of the innermost-layer wax deposits are 45 °C, 47 °C and 49 °C, respectively. The wax deposit formed by oil sample 5 turns back into homogenous and has the highest WAT (41 °C at 1 h and 50 °C at 24 h) due to the highest dosage of POA (400 ppm). As shown in Figure 7, the wax contents of all the wax deposits increase with the increase of


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deposition time. The wax content of the wax deposit formed by oil sample 1 (without POA, homogeneous structure) increases from 11.56 wt% at 1 h to 13.61 wt% at 6 h, then to 17.47 wt% at 24 h. The addition of POA increases the wax contents of the outermost-layer wax deposits formed by oil sample 2~4. For example, at a fixed deposition time 24 h, the wax contents of the outermost-layer wax deposits formed by oil sample-2~4 are 29.77 wt%, 39.77 wt% and 49.05 wt%, respectively. The wax content of the innermost-layer wax deposits formed by oil sample 2~4 also increases with increasing the POA concentration. For example, at a fixed deposition time 24 h, the wax contents of the innermostlayer wax deposits formed by oil sample-2~4 are 48.76 wt%, 56.48 wt% and 61.33 wt%, respectively. The wax content of the wax deposit formed by oil sample 5 (with 400 ppm POA, homogeneous structure) is the largest (67.15 wt% at 24 h) due to the highest POA dosage. The average wax content of the wax deposits formed by oil sample 1~5 is also demonstrated in Figure 7c, it is clear that increasing the POA concentration greatly increases the average wax content of the wax deposits. The results mentioned above corroborate the incipient gelation mechanism established by Singh and Fogler [55-58]. Obviously, increasing the POA concentration not only decreases the total wax deposit mass but also increases the WAT and wax content of the wax deposits, that is, increasing the POA concentration favors the formation of thinner and harder wax deposit structure. 3.3 Development of the n-alkane composition for the wax deposits with deposition time The development of the n-alkane composition in the wax deposit formed by oil sample-1 (without POA) with deposition time is shown in Figure 8a. The contents of the n-alkanes with carbon number ≤ C24 in the wax deposit are smaller than those in the bulk oil, and the concentration differential (∆wt%) becomes larger with increasing deposition time. For example, the ∆wt% of C18 decreases from -2.76 wt% at 1 h to -3.96 wt% at 24 h, and the ∆wt% of C24 decreases from -0.35 wt% at 1 h to -0.94 wt% at 24 h. On the contrary, the contents of the n-alkanes with carbon number > C24 in the wax deposit are


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higher than those in the bulk oil. With the increase of deposition time, the ∆wt% also becomes larger. For example, the ∆wt% of C25 increases from 0.63 wt% at 1 h to 1.14 wt% at 24 h, and the ∆wt% of C28 increases from 3.79 wt% at 1 h to 4.69 wt% at 24 h. It can be induced that the CNN of the wax deposit formed by oil sample-1 is C24: the n-alkanes with carbon number > C24 continuously diffuse from the bulk oil into the wax deposit with time, while the n-alkanes with carbon number ≤ C24 continuously counter-diffuse from the wax deposit into the bulk oil with time. Figure 8b and c demonstrates the development of the n-alkane composition in the outermostlayer/innermost-layer wax deposits formed by oil sample 3 (with 100 ppm POA) with deposition time. The CNN of the two wax deposits increase to C25 and the ∆wt% values of the two wax deposits become much larger: at a fixed deposition time 24 h, the ∆wt% values of C18 become -5.71 wt% for the outermost-layer wax deposit and -6.90 wt% for the innermost-layer wax deposit, while the ∆wt% values of C28 become 9.83 wt% for the outermost-layer wax deposit and 11.42 wt% for the innermost-layer wax deposit. As seen in Figure 8d, the CNN of the wax deposit formed by oil sample 5 (with 400 ppm POA) is also C25. However, the ∆wt% values of the wax deposit become the largest due to the highest POA concentration: at a fixed deposition time 24 h, the ∆wt% values of C18 become -7.46 wt%, while the ∆wt% values of C28 become 12.07 wt%. It is obvious that the addition of POA favors the richness of the n-alkanes with higher carbon number in the wax deposit, which results in the high WAT and wax content of the wax deposits (see Table 2 and Figure 7). 3.4 FT-IR analysis of the wax deposits with deposition time The POA PWI contains ester group (C=O-O-) in its molecular structure, and the specific absorption peak of the ester group is around 1735 cm-1. Therefore, FT-IR analysis was carried out on the wax deposits formed by oil sample 1~5 to make sure if the POA molecules take part in the formation of the wax deposit. However, the wax deposits formed by oil sample 1~4 exhibits no apparent peak at 1735


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cm-1 due to the relatively small dosage of POA (≤ 200 ppm). Figure 9 shows the FT-IR curves of the wax deposit formed by oil sample 5 at different deposition time. At deposition time 0 h, there is no peak around 1735 cm-1 (see Figure 9a), meaning that the original 400 ppm POA in the oil sample is not enough to show a clear peak around 1735 cm-1. When the deposition time is ≥ 1 h, the formed wax deposits show clear absorption peak around 1735 cm-1 (see Figure 9b~9d), indicating that the POA concentration in the wax deposits is much higher than the original 400 ppm and is enough to show a clear peak around 1735 cm-1. Although we cannot quantify the POA concentration in the wax deposits, the FT-IR results verify that the POA molecules take part in the wax deposition process and concentrate in the wax deposits, which will result in the concentration depletion of POA in the bulk oil with deposition time. 3.5 Microstructure of the waxy oils and wax deposits The microscopic structures of oil sample 1~5 are shown in Figure 10. The precipitated wax crystals in oil sample 1 (without POA) are all needle-like and are easy to build up network structures. Addition of the POA in waxy oil greatly changes the morphology of the precipitated wax crystals. With the increase of POA concentration, the morphology of precipitated wax crystals transits gradually from needle-like to spherical-like, and the structure of precipitated wax crystals becomes more compact. The spherical-like and compact wax crystals are difficult to build up a continuous network structure, thus improving the flow behavior of the oils. The microscopic structures of the outermost-layer and innermost-layer wax deposits formed by oil sample-1~5 are displayed in Figure 11 and 12, respectively. Compared to the original oil samples, the amounts of precipitated wax crystals in the wax deposits are greatly increased, indicating that the wax molecules continuously diffuse from the oil phase into the wax deposits. For the oil sample-1 (Figure 11a and 12a), the microstructures of the outermost-layer and innermost-layer wax deposits are the same


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Energy & Fuels

(the precipitated wax crystals are needle-like with large size), verifying that the wax deposit formed by oil sample 1 (without POA) is homogeneous. After the addition of POA, the amounts of precipitated wax crystals in the microscopic images increase greatly with the increase of POA concentration. Meanwhile, the morphology of the precipitated wax crystals changes from feather-like to spherical-like flocs with the increase of POA concentration. For oil sample 2~4 (50~200 ppm POA), the microstructures of the outermost-layer and innermost-layer wax deposits are different, with the innermost-layer wax deposits containing larger amount of wax crystals. This verifies that the wax deposits formed by oil sample 2~4 are heterogeneous, with the wax content gradually decreasing from the innermost-layer to the outermost-layer. For oil sample 5 (400 ppm POA), the microstructures of the outermost-layer and innermost-layer wax deposits have the same wax crystal amount and morphology, verifying that the wax deposit formed by oil sample 5 turns back into homogeneous again. 3.6 Formation mechanism of the heterogeneous wax deposits induced by POA PWI According to the wax deposition tests (section 4.1~4.4) and the microstructures of the waxy oils/wax deposits (section 4.5), it could be concluded that the wax crystals’ morphology controlled by the POA concentration dominates the wax deposition behavior. For oil sample 1 (without POA), the precipitated waxy crystals are needle-like and are easier to form porous network structures. Therefore, the wax deposit formed by oil sample 1 are thick and porous waxy oil gel with large amounts of liquid oil enveloped in the network structure. Meanwhile, the network structure impedes the further diffusion of wax molecules from the bulk oil into the wax deposit, thus greatly retarding the increment of the WAT and wax content of the wax deposit with deposition time (see Table 2 and Figure 7). For oil sample 2~5, the addition of POA greatly changes the precipitated wax crystals’ morphology: with the increase of POA concentration, the wax crystal morphology becomes more regular (spherical-like) and more compact. The regular and compact wax crystals are adverse for the buildup of a continuous network and


Energy & Fuels 1 2 3 299 4 5 6 300 7 8 301 9 10302 11 12 303 13 14 15304 16 17305 18 19 306 20 21 22307 23 24308 25 26309 27 28 29310 30 31311 32 33312 34 35 313 36 37 38314 39 40315 41 42 316 43 44 45317 46 47318 48 49319 50 51 52320 53 54321 55 56 57 58 59 60

Page 14 of 33

favor the continuous diffusion of wax molecules from the bulk oil into the wax deposit. Therefore, the wax deposits become thinner but more compact (with high WAT and wax content) with the increase of POA concentration. According to Figure 9, the POA molecules concentrate in the wax deposits formed by oil sample 2~5, meaning that the POA concentration in the wax deposits is much higher than that in the bulk oil. This leads to the depletion of POA in bulk oil with deposition time, that is, the POA concentration in bulk oil decreases gradually with deposition time. The continuous depletion of POA in bulk oil causes the gradual morphological change of the precipitated wax crystals (becomes more irregular and loose) with deposition time, and then causes the gradual composition and structure change of the newly-formed wax deposit (contains less paraffin wax and becomes more weak) with deposition time. We consider that the continuous depletion of POA in bulk oil with deposition time triggers the formation of the heterogeneous wax deposits: (a) for oil sample 2, the depletion of POA should be more obvious due to the relatively low original POA concentration (50 ppm) in bulk oil, thus the wax deposit formed by oil sample 2 showing the most explicit heterogeneous structure; (b) for oil sample 3 and 4, the heterogeneity of the formed wax deposit structure weakens due to the relatively high original POA concentration in bulk oil (100~200 ppm), which slows down the depletion of POA; (c) when the original POA concentration in bulk oil is ≥ 400 ppm (oil sample 5), the depletion of POA is so slow that it has little influence on the wax deposition process. Therefore, the wax deposit structure formed by oil sample 5 turns back into homogeneous. In addition, it could also be imagined that the depletion of POA molecules could take place axially along the length of the real pipeline, resulting in the formation of heterogeneous wax deposit structure alone the axial direction. 4. Conclusions This work investigated the effect of the POA PWI on the wax deposition of 10 wt% model waxy oil.


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Energy & Fuels

It was found that the wax inhibiting efficiency of POA increases with the increase of POA concentration. The formed wax deposit structure without POA is homogeneous but becomes heterogeneous after a small addition of the POA. At the POA concentrations ≥ 400 ppm, the formed wax deposit structure turns back into homogeneous. The following conclusions are put forward: (1) The wax deposit structure formed by oil sample 1 (without POA) is homogenous. The formed wax deposit becomes heterogeneous with no clear stratification boundary after a small dosage of POA (≤ 200 ppm, oil sample 2~4). When the POA concentration is relatively high (≥ 400 ppm, oil sample 5), however, the structure of the wax deposit turns back into homogeneous again. (2) Increasing the POA concentration not only decreases the total wax deposit mass but also increases the WAT and wax content of the wax deposits, that is, increasing the POA concentration favors the formation of thinner and harder wax deposit structure. (3) HTGC results show that the addition of POA favors the richness of the n-alkanes with higher carbon number in the wax deposit (high value of CCN). Although the POA concentration in the wax deposits cannot be quantified, the FT-IR results verify that the POA molecules take part in the wax crystallization process and concentrate in the wax deposits, which results in the concentration depletion of POA in the bulk oil with deposition time. (4) The precipitated waxy crystals of oil sample 1 (without POA) are needle-like and are easier to form porous network structures, impeding the further diffusion of wax molecules from the bulk oil into the wax deposit, thus greatly retarding the increment of the WAT and wax content of the wax deposit with deposition time. Increasing the POA concentration greatly changes the precipitated wax crystals into more regular (spherical-like) and more compact morphologies, which are adverse for the buildup of a continuous network and favor the continuous diffusion of wax molecules from the bulk oil into the


Energy & Fuels 1 2 3 344 4 5 6 345 7 8 346 9 10347 11 12 348 13 14 15349 16 17350 18 19 351 20 21 22352 23 24353 25 26354 27 28 29355 30 31356 32 33357 34 35 358 36 37 38359 39 40360 41 42361 43 44362 45 46363 47 48364 49 50365 51 52366 53 54367 55 56368 57 58 59 60

Page 16 of 33

wax deposit. Therefore, the wax deposits become thinner but more compact (with high WAT and wax content) with the increase of POA concentration. (5) The continuous depletion of POA in bulk oil with deposition time triggering the formation of the heterogeneous wax deposits. When the POA concentration is relatively low (oil sample 2), the depletion of POA should be more obvious, thus the wax deposit showing the most explicit heterogeneous structure. When the POA concentration is relatively high (oil sample 3 and 4), the depletion of POA slows down, which weakens the heterogeneity of the formed wax deposit structure. When the POA concentration is too high (oil sample 5), the depletion of POA is so slow that it has little influence on the wax deposition process, resulting in that the wax deposit structure turns back into homogeneous. Acknowledgement The authors thank the financial support from the National Natural Science Foundation of China (51774311),

Shandong

Provincial

Natural

Science

Foundation

of

China

(ZR2016EEM22,

ZR2017MEE022), and Shandong Provincial Key Research and Development Program of China (2017GSF216003). References (1) Yang, F.; Li, C.; Li, C.; Wang, D. Energy Fuels 2013, 27, 3718–24. (2) Aiyejina, A.; Chakrabarti, D. P.; Pilgrim, A.; Sastry, M. K. S. Int. J. Multiph. Flow 2011, 37, 671–694. (3) Paso, K. G.; Fogler, H. S. AIChE J. 2003, 49, 3241–52. (4) Jennings, D. W.; Weispfennig, K. Energy Fuels 2005, 19, 1376–86. (5) Kasumu, A. S.; Mehrotra, A. K. Energy Fuels 2015, 29, 501–511. (6) Chi, Y.; Daraboina, N.; Sarica, C. Energy Fuels 2017, 31, 4915–24. (7) Singh, A.; Panacharoensawad, E.; Sarica, C. Energy Fuels 2017, 31, 2457–78. (8) Zheng, S.; Zhang, F.; Huang, Z.; Fogler, H. S. Energy Fuels 2013, 27, 7379–88. (9) Wang, W.; Huang, Q.; Wang, C.; Li, S.; Qu, W.; Zhao, J.; He, M. J. Therm. Anal. Calorim. 2015, 119, 471–485. (10) Zougari, M.; Jacobs, S.; Ratulowski, J.; Hammami, A.; Broze, G.; Flannery, M.; Stankiewicz, A.; Karan, K.


Page 17 of 33 1 2 3 369 4 5 370 6 7 371 8 9 372 10 11373 12 13374 14 15375 16 17376 18 19377 20 21378 22 23379 24 25380 26 27381 28 29382 30 31383 32 33384 34 35 385 36 37 386 38 39 387 40 41 388 42 43 389 44 45 390 46 47 391 48 49 392 50 51 393 52 53 394 54 55 395 56 57 58 59 60

Energy & Fuels

Energy Fuels 2006, 20, 1656–63. (11) Akbarzadeh, K.; Zougari, M. Ind. Eng. Chem. Res. 2008, 47, 953–963. (12) Li, C.; Cai, J.; Yang, F.; Zhang, Y.; Bai, F.; Ma,Y.; Yao, B. J. Pet. Sci. Eng. 2016, 140, 73–84. (13) Yang, F.; Cheng, L.; Cai, J.; Li, C.; Ji, Z.; Yao, B.; Zhao, Y.; Zhang, G. Energy Fuels 2016, 30, 9922–32. (14) Tinsley, J. F.; Prud’homme, R. K. J. Pet. Sci. Eng. 2010, 72, 166–174. (15) Ismail, L.; Westacott, R. E.; Ni, X. Chem. Eng. J. 2008, 137, 205–213. (16) Mehrotra, A. K.; Bhat, N. V. Energy Fuels 2010, 24, 2240–48. (17) Arumugam, S.; Kasumu, A. S.; Mehrotra, A. K. Energy Fuels 2013, 27, 6477–90. (18) Paso, K. G.; Fogler, H. S. Energy fuels, 2004, 18, 1005-1013. (19) Lashkarbolooki, M.; Seyfaee, A.; Esmaeilzadeh, F.; Mowla, D. Energy Fuels 2010, 24, 1234–41. (20) Singh, P.; Venkatesan, R.; Fogler, H. S.; Nagarajan, N. R. AIChE J. 2001, 47, 6–18. (21) Wu, C. H.; Wang, K. S.; Shuler, P. J.; Tang, Y.; Creek, J. L.; Carlson, R. M.; Cheung, S. AIChE J. 2002, 48, 2107–10. (22) Fong, N.; Mehrotra, A. K. Energy Fuels 2007, 21, 1263–76. (23) Lei, Y; Han, S.; Zhang, J. Fuel Process. Technol. 2016, 146, 20–28. (24) Bhat, N. V.; Mehrotra, A. K. Ind. Eng. Chem. Res. 2006, 45, 8728–37. (25) Parthasarathi, P.; Mehrotra, A. K. Energy Fuels 2005, 19, 1387–1398. (26) Ramirez-Jaramillo, E.; Lira-Galeana, C.; Manero, O. Petrol. Sci. Technol. 2004, 22, 821–861. (27) Edmonds, B.; Moorwood, T.; Szczepanski, R.; Zhang, X. Energy Fuels 2008, 22, 729–741. (28) Huang, Z.; Lee, H. S.; Senra, M.; Fogler, H. S. AIChE J. 2011, 57, 2955–2964. (29) Yang, X. Design and Management of Pipelines Transporting oils, 1st ed. China University of Petroleum Press, Dongying, pp. 225–226 (in Chinese), 2006. (30) Toma, P.; Ivory, J.; Korpany, G. J. Energ. Resour. -ASME 2006, 128, 49–60. (31) Bi, Q.; Huang, Q.; Fan K. Oil & Gas Storage and Transportation 2016, 35, 952–57. (Chinese Journal) (32) Yang, F.; Zhao, Y.; Sjöblom, J.; Li, C.; Paso, K. J. Dispersion Sci. Technol. 2015, 36, 213–25. (33) Machado, A.L.C.; Lucas, E.F.; González, G. J. Pet. Sci. Eng. 2001, 32, 159–165. (34) Taraneh, J.B.; Rahmatollah, G.; Hassan, A.; Alireza, D. Fuel Process. Technol. 2008, 89, 973–77.


Energy & Fuels 1 2 3 396 4 5 397 6 7 398 8 9 399 10 11400 12 13401 14 15402 16 17403 18 19404 20 21405 22 23406 24 25407 26 27408 28 29409 30 31410 32 33411 34 35 412 36 37 413 38 39 414 40 41 415 42 43 416 44 45 417 46 47 418 48 49 419 50 51 420 52 53 421 54 55 422 56 57 58 59 60

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(35) Duffy, D.M.; Rodger, P.M. Phys. Chem. Chem. Phys. 2002, 4, 328–34. (36) Jang, Y.H.; Blanco, M.; Creek, J.; Tang, Y.; Goddard, W.A. J. Phys. Chem. B 2007, 111, 13173–9. (37) Zhang, J.; Zhang, M.; Wan, J.; Li, W. J. Phys. Chem. B 2008, 112, 36–43. (38) Machado, A.L.C.; Lucas, E.F. Petrol. Sci. Technol. 1999, 17, 1029–41. (39) Lashkarbolooki, M.; Esmaeilzadeh, F.; Mowla, D. J. Dispersion Sci. Technol. 2011, 32, 975–85. (40) Ansaroudi, H.R.J.; Vafaie-Sefti, M.; Masoudi, Sh.; Behbahani, T.J.; Jafari, H. Petrol. Sci. Technol. 2013, 31, 643–51. (41) Ashbaugh, H. S.; Guo, X.; Schwahn, D; Prud'homme, R. K.; Richter, D.; Fetters, L. J. Energy fuels, 2005, 19, 138-144. (42) Li, L.; Xu, J.; Tinsley, J.; Adamson, D. H; Pethica, B. A.; Huang, J. S.; Prud'homme, R. K.; Guo, X. AIChE J. 2012, 58, 2254-2261. (43) Li, L.; Guo, X.; Adamson, D. H.; Pethica, B. A.; Huang, J. S.; Prud’homme, R. K. Ind. Eng. Chem. Res. 2010, 50, 316-321. (44) Xu, J.; Jiang, H.; Li, T.; Wei, X.; Wang, T.; Huang, J.; Wang, W.; Smith, A. L.; Wang, J.; Zhang, R.; Xu, Y.; Li, L.; Prud’homme, R. K.;Guo, X. Ind. Eng. Chem. Res. 2015, 54, 5204-5212. (45) Wang, K.-S.; Wu, C.-H.; Creek, J.L.; Shuler, P.J.; Tang, Y. Petrol. Sci. Technol. 2003, 21, 359–68. (46) Adeyanju, O.A.; Oyekunle, L.O. SPE Nigeria Annual International Conference and Exhibition, Society of Petroleum Engineers, 2014. (47) Chi, Y.; Daraboina, N.; Sarica, C. AIChE J. 2016, 62, 4131–39. (48) García, M.C.; Carbognani, L.; Orea, M.; Urbina, A. J. Pet. Sci. Eng. 2000, 25, 99–105. (49) García, M.C.; Carbognani, L. Energy Fuels 2001, 15, 1021–27. (50) Masoudi, Sh.; Sefti, M.V.; Jafari, H.; Modares, H. Petrol. Sci. Technol. 2010, 28, 1598–1610. (51) Hoffmann, R.; Amundsen, L. J. Pet. Sci. Eng. 2013, 107, 12–17. (52) Yang, F.; Paso, K.; Norrman, J.; Li, C.; Oschmann, H.; Sjöblom, J. Energy Fuels 2015, 29, 1368–1374. (53) Yao, B.; Li, C.; Yang, F.; Sjöblom, J.; Zhang, Y.; Norrman, J.; Paso, K.; Xiao, Z. Fuel 2016, 166, 96–105. (54) Yao, B.; Li, C.; Yang, F.; Zhang, Y.; Xiao, Z.; Sun, G. Fuel 2016, 184, 544–554. (55) Singh, P.; Venkatesan, R.; Fogler, H. S.; Nagarajan, N. AIChE J. 2000, 46(5), 1059-1074.


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(56) Singh, P.; Fogler, H. S.; Nagarajan, N. J. Rheo. 1999, 43, 1437-1459. (57) Singh, P.; Venkatesan, R.; Fogler, H. S.; Nagarajan, N. R. AIChE J. 2001, 47, 6-18. (58) Singh, P.; Youyen, A.; Fogler, H. S. AIChE J. 2001, 47, 2111-2124


Energy & Fuels

Figures:

outermost wax deposit layer innermost wax deposit layer

Heat Flow / W·g

-1

0.9 0.8 0.7 0.6 0.5 (a)

Precipitated wax amount / wt%

1 2 3 4 427 5 6 7 428 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 429 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44430 45 46431 47 432 48 49433 50 51434 52 53435 54436 55 56 57 58 59 60

Page 20 of 33

(b)

-20

0 20 40 Temperature / ℃

60 (c)

16 12 8 outermost wax deposit layer innermost wax deposit layer

4 0 -20

-10

0

10

Temperature / ℃

20

30 (d)

Figure 1. Macroscopic appearances of the outermost layer (a)/innermost layer (b) wax deposits formed by oil sample 1, and the exothermic characteristics (c) and precipitated wax amount (d) of the outermost layer/innermost layer wax deposits at different temperatures.


Page 21 of 33

Heat Flow / W·g

-1

2.0


1.6 1.2 0.8 0.4 -20

(a)

0

20

40

60 (c)

Temperature / ℃


1 2 3 437 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 438 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 439 42 43 440 44 45441 46 47442 48 49443 50 444 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

50 40 30 20 10 0


-30 -20 -10 (b)

0

10

20

30

40

Temperature / ℃

50 (b)

Figure. 2. Macroscopic appearances of the outermost layer (a)/innermost layer (b) wax deposits formed by oil sample 2, and the exothermic characteristics (c) and precipitated wax amount (d) of the outermost layer/innermost layer wax deposits at different temperatures.


Energy & Fuels

Heat Flow / W·g

-1

2.5


2.0 1.5 1.0 0.5 0.0

-20

(a)


1 2 3 445 4 5 6 7 446 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25447 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44448 45 46449 47 48450 49 451 50 51452 52 53453 54 55 56 57 58 59 60

Page 22 of 33

(b)

0 20 40 Temperature / ℃

60 (c)

60

40

20 outermost wax deposit layer innermost wax deposit layer

0 -30 -20 -10

0

10

20

30

40

Temperature / ℃

50 (d)

Figure 3. Macroscopic appearances of the outermost layer (a)/innermost layer (b) wax deposits formed by oil sample 3, and the exothermic characteristics (c) and precipitated wax amount (d) of the outermost layer/innermost layer wax deposits at different temperatures.


Page 23 of 33

Heat Flow / W·g

-1

2.5


2.0 1.5 1.0 0.5 -20

0

(a)

40

60 (c)

60 40 20 outermost wax deposit layer innermost wax deposit layer

0 -30 -20 -10

(b)

20

Temperature / ℃


1 2 3 454 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23455 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42456 43 44457 45 46458 47 459 48 49460 50 51 52 461 53 54462 55 56 57 58 59 60

Energy & Fuels

0

10

20

30

40

Temperature / ℃

50 (d)

Figure. 4. Macroscopic appearances of the outermost layer (a)/innermost layer (b) wax deposits formed by oil sample 4, and the exothermic characteristics (c) and precipitated wax amount (d) of the outermost layer/innermost layer wax deposits at different temperatures.


Energy & Fuels

Heat Flow / W·g

-1

3.0


2.5 2.0 1.5 1.0 0.5 -20

(a)

0

20

40

60

Temperature / ℃ Precipitated wax amount / wt%

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20463 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39464 40465 41 42466 43 467 44 45468 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 33

(b)

(c)

60 40


20 0 -30 -20 -10 0

10 20 30 40 50 60

Temperature / ℃

(d)

Figure 5. Macroscopic appearances of the outermost layer (a)/innermost layer (b) wax deposits formed by oil sample 5, and the exothermic characteristics (c) and precipitated wax amount (d) of the outermost layer /innermost layer wax deposits at different temperatures.


Page 25 of 33

Wax deposit mass / g·dm

-2

18 15 12

oil sample 1 oil sample 2 oil sample 3 oil sample 4 oil sample 5

9 6 3 0 0

5

10

15

20

Deposition time / h

25 (a)

-2

18 Wax deposit mass / g·dm

1 2 3 469 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26470 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47471 48 49472 50473 51 52474 53 54 55 56 57 58 59 60

Energy & Fuels

15 12 9 6 0

100

200

300

POA concentrition / ppm

400 (b)

Figure 6. Development of the wax deposit mass: (a) with deposition time; (b) with POA concentration at 24h.


Energy & Fuels

70 60

70


60 Wax content / wt%

80 Wax content / wt%

50 40 30 20 10

0

5 10 15 20 Deposition time / h

50

30 20 10

25 (a)


40

0

5

10 15 20 Deposition time / h

25

30 (b)

70 60 Wax content / wt%

1 2 3 475 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21476 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39477 40 41478 42 479 43 44480 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 26 of 33

50 40


30 20 10

0

5

10 15 20 25 30 Deposition time / h (c)

Figure 7. Development of the wax content of the wax deposits with deposition time: (a) outermostlayer wax deposits; (b) innermost-layer wax deposits; (c) average wax content.


Page 27 of 33

1h 3h 6h 12h 24h

9 6 ∆wt%

2 ∆wt%

12

1h 3h 6h 12h 24h

4

0 -2

3 0 -3 -6

-4

18 20 22 24 26 28 30 32 34 36 38 40

18 20 22 24 26 28 30 32 34 36 38 40 (a) Carbon number

12

Carbon number

1h 3h 6h 12h 24h

9 6 3

12 9 6 ∆wt%

∆wt%

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17481 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34482 35 36483 37 484 38 39485 40 41486 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

0

(b)

1h 3h 6h 12h 24h

3 0 -3

-3

-6

-6 18 20 22 24 26 28 30 32 34 36 38 40 Carbon number

(c)

-9 18 20 22 24 26 28 30 32 34 36 38 (d) Carbon number

Figure 8. Development of the n-alkane composition of the wax deposits with deposition time: (a) wax deposit of oil sample 1; outermost-layer (b) and innermost-layer (c) wax deposits of oil sample 3; (d) wax deposit of oil sample 5.


Energy & Fuels

100 Transmittance / %

Transmittance / %

100

80 1000

1500 Wave number / cm-1

1000

1000

2000 (a)


2000 (b)


80

80 1735 cm-1


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19487 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38488 39489 40 41490 42 43491 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 28 of 33

1735 cm-1


2000 (c)

80 1000

1735 cm-1


2000 (d)

Figure 9. Infrared spectrum analysis of the wax deposits formed by oil sample 5 with deposition time: (a) 0 h; (b) 1 h; (c) 6 h ; (d) 24 h.


Page 29 of 33 1 2 3 492 4 5 493 6 7 8 9 10 11 12 13 14 15 16 17 18494 19 20 21 22 23 24 25 26 27 28 29 30 31495 32 33 34 35 36 37 38 39 40 41 42 43 44496 45 46497 47 498 48 49499 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

(a)

(b)

(c)

(d)

(e)

Figure 10. Microscopic images of the model waxy oils: (a) oil sample 1; (b) oil sample 2; (c) oil sample 3; (d) oil sample 4; (e) oil sample 5.


Energy & Fuels 1 2 3 500 4 5 501 6 7 502 8 9 10 11 12 13 14 15 16 17 18 19 20503 21 22 23 24 25 26 27 28 29 30 31 32 33504 34 35 36 37 38 39 40 41 42 43 44 45 505 46 47506 48 49507 50 508 51 52 53 54 55 56 57 58 59 60

Page 30 of 33

(a)

(b)

(c)

(d)

(e)

Figure 11. Microscopic images of the outermost-layer wax deposits formed by oil sample 1~5 at 24 h: (a) oil sample 1 ; (b) oil sample 2 ; (c) oil sample 3 ; (d) oil sample 4 ; (e) oil sample 5.


Page 31 of 33 1 2 3 509 4 5 510 6 7 8 9 10 11 12 13 14 15 16 17 18511 19 20 21 22 23 24 25 26 27 28 29 30 31512 32 33 34 35 36 37 38 39 40 41 42 43 44513 45514 46 47515 48 49516 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

(a)

(b)

(c)

(d)

(e)

Figure 12. Microscopic images of the innermost-layer wax deposits formed by oil sample 1~5 at 24 h: (a) oil sample 1 ; (b) oil sample 2 ; (c) oil sample 3 ; (d) oil sample 4 ; (e) oil sample 5.


Energy & Fuels 1 2 3 4 517 5 6 7 518 8 9 519 10 11520 12 13 521 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 522 39 40523 41 42524 43525 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 32 of 33

Tables:

Table 1. Types of the model waxy oils. POA Types of waxy oils

Paraffin wax

Total wax

content / wt%

content / wt%

concentration

WAT

Pour point

/ °C

/ °C

/ ppm

Oil sample 1

10.0

11.32

0

20

19

Oil sample 2

10.0

11.34

50

19

17

Oil sample 3

10.0

11.36

100

19

17

Oil sample 4

10.0

11.32

200

18

15

Oil sample 5

10.0

11.33

400

18

15

Note: the total wax content and WAT are obtained from DSC curves (see Figure S2~S6 in the support information file).


Page 33 of 33 1 2 3 526 4 5 527 6 7 528 8 529 9 10530 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32531 33 34532 35 36533 37 534 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

Table 2. Development of the WAT of the outermost-layer/innermost-layer wax deposits with deposition time. Deposition time / h

Oil sample 1 / ºC

Oil sample 2

Oil sample 3

Oil sample 4

/ ºC

/ ºC

/ ºC

Oil sample 5 / ºC

1

22

24/36

28/37

32/39

41

3

23

26/37

30/38

35/42

44

6

25

31/39

35/42

41/47

48

12

28

35/42

39/45

43/48

49

24

29

38/45

41/47

44/49

50


Comb-like Polyoctadecylacrylate (POA) Wax inhibitor Triggers the

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