NMR Characterization of Asphaltene Derived from Residual Oils and

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NMR Characterization of Asphaltene Derived from Residual Oils and their Thermal Decomposition Faisal S AlHumaidan, Andre Hauser, Mohan S Rana, and Haitham M.S. Lababidi Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.6b03433 • Publication Date (Web): 06 Mar 2017 Downloaded from http://pubs.acs.org on March 7, 2017

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NMR Characterization of Asphaltene Derived from Residual Oils and their Thermal Decomposition

Faisal S. AlHumaidana, Andre Hauser a, Mohan S. Ranaa*, Haitham .M.S. Lababidib a

Petroleum Research Center, Kuwait Institute for Scientific Research, P. O. Box: 24885, Safat 13109 Kuwait b Chemical Engineering Department, College of Engineering & Petroleum, Kuwait University, P. O. Box: 5969 Safat, 13060 Kuwait

*Corresponding author Dr. Mohan S. Rana Petroleum Research Center Kuwait Institute for Scientific Research P.O. Box 24885, 13109-Safat Kuwait E-mail: [email protected]

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Abstract The main objective of this work is to determine the effect of thermal cracking on asphaltene molecular structure by using Nuclear Magnetic Resonance (NMR). The NMR is used to identify and quantify the structural parameters and the functional groups; which subsequently helped in deriving a hypothetical average structure for the asphaltene molecules. The NMR analysis revealed a number of valuable findings and developed better understanding about the nature of structural changes that asphaltene molecules undergo during the thermal cracking of vacuum residues (VRs). For instance, the polyaromatic structure of asphaltene in the parent VRs consists of peri-condensed cores interlinked through aliphatic bridges. This peri-condensed polyaromatic core converts to cata-condensed polyaromatic as the reaction severity increases. The NMR analysis confirmed that the observed reduction in the average molecular weight of asphaltene molecules, as reaction severity increases, is mainly due to cracking of the saturated parts of the asphaltenes molecules, loss of sulfur and nitrogen located in the saturated parts, and shrinking in the aromatic core. Another observation is the growth in the percentages of aromatic carbon and aromatic carbon bearing hydrogen with the increase in cracking severity.

Keywords: Asphaltene, thermal cracking, NMR characterization, vacuum residue,


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1. Introduction Asphaltene is commonly presumed to represent the most refractory fraction of crude oil and frequently associated with many problems in downstream processes. Understanding the behavior of asphaltene molecules in deep conversion processes will allow the refiners to determine the best upgrading scheme for the various heavy petroleum fractions. A number of research

groups

investigated

the

chemical

transformation

of

asphaltene

during

hydroprocessing1-17. Studies related to asphaltene behavior during the thermal cracking are limited and most of the earlier studies are related to coke formation and kinetic model development 18-21. NMR is a powerful analytical technique that can identify and quantify the aromatic and aliphatic carbons in asphaltene molecule to understand asphaltene structure at a molecular level. Various research groups utilized NMR in asphaltene characterization Ancheyta et al.

22

22-29

.

utilized the NMR to determine the most important structural parameters in

asphaltene and reported that solvent type influences asphaltene composition. According to them, the aromaticity of asphaltene that is precipitated using n-heptane is higher than that obtain through n-pentane. Merdrignac et al.

23

studied the evolution of asphaltene under

hydroconversion and showed that the increase in conversion reduces the size of asphaltene and increase the aromaticity, which was attributed to dealkylation. Similarly, Seki and Kumata

24

and Hauser et al.

25

reported an increase in aromaticity due to the shortening of

alkyl side chains. Ibrahim et al. 26 also used the NMR to characterize asphaltene derived from Kuwaiti crude oils and indicated that the molecules have between 5-9 polycondensed aromatic units that are attached by alkyl chains of 4-6 carbons. Hauser et al.

27

recently

utilized 1H and 13C NMR to obtain quantitative data (average structural parameters) about the structural composition of different vacuum residues and their thermally cracked products (i.e. cracked oil and pitch). They reported that the vacuum residues are mainly made of alkyl


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aromatics with more than three cata-condensed aromatic rings that decompose under thermal stress into saturated hydrocarbons and aromatics with less aliphatic carbon. Hauser et al.

28

also used NMR spectroscopy to analyze the SARA fractions (i.e. saturates, aromatics, resins, and asphaltenes) of the vacuum residue (VR), cracked oil, and pitch (the by-products of VR thermal cracking). They reported that VR and pitch consist mainly of aromatic hydrocarbons (VR: 94 wt%, pitch: 99 wt%) while cracked oil contains around 42 wt% saturated hydrocarbon. In an earlier study, Weinberg and Yen 29 also utilized solid state 13C NMR and 1

H NMR to obtain the hypothetical average molecular structures of two coal liquid

asphaltenes. In previous studies, we have utilized X-Ray Diffraction (XRD) and FourierTransform Infrared (FTIR) to reveal the impact of thermal treatment on asphaltene macrostructure and the functional groups that exist in asphaltene 30,31. The XRD study 30 indicated a decrease in cluster diameter as the severity of cracking increases, which was mainly attributed to the loss of aliphatic carbon in the side chains and the decrease in the number of aromatic sheet per stack. AlHumaidan et al. 30 also reported possible reaction routes and their thermal treatment impact on the layer distance between the aromatic sheet, the distance between the aliphatic chains (or naphthenic sheet), and the average diameter of the aromatic sheet. The FTIR investigation, on the other hand, revealed obvious differences between asphaltenes exposed to thermal cracking and their parent asphaltenes from the vacuum residues 31. The conclusions suggest that thermal treatment mainly affect the paraffinic side chains in asphaltene structure while changes in aromatic core appear to be very limited. In an earlier study, Lababidi et al.

32

studied the changes and transformation in asphaltene

molecules during the thermal cracking. They reported that thermal cracking conditions influence the structure and the properties of asphaltene, where an increase in cracking severity results in a significant decrease in asphaltene molecular weight, a notable increase in


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aromatcity, and a reduction in H/S ratio. Lababidi et al.

32

also indicated that the increase in

cracking severity concentrates the metals (Ni and V) in the core aromatic ring of the asphaltene molecule. Asphaltene characterization provides a very powerful tool for understanding the likely changes that asphaltene might undergo during refining processes. The analytical data can be utilized in improving the design of existing processes to make them more compatible with heavier feedstock, which normally has higher asphaltene content. This study mainly determines the effect of thermal cracking on asphaltene molecular structure using NMR. The objective is to derive and compare the hypothetical average structure for asphaltene before and after thermal treatment. The parent asphaltene samples (before treatment) were extracted from vacuum residues (VRs) of three crude oils while the thermally treated asphaltene were obtained from residual pitch, the by-products of VR thermal cracking.

2. Experimental 2.1 Thermal cracking experiments The thermal cracking experiments were performed in a pilot plant emulating the Eureka process, a commercially proven thermal cracking process that produces cracked oil and aromatic petroleum pitch from vacuum residues

33-35

. The vacuum residues (VRs) were

obtained from atmospheric and vacuum distillation of three Kuwaiti crude oils: RatawiBurgan (RB), Lower-Fars (LF), and Eocene (EC). The properties of the vacuum residues are shown in Table 1. The thermal cracking experiments of the vacuum residues were performed in a 2 L semi-batch pilot-scale reactor. A schematic diagram of the thermal cracking facility is reported in AlHumaidan et al.

33

. The reactor is equipped with a mixer and a nitrogen

injector. An uniform reaction temperature was maintained by using continuous magnetic


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agitation (300 rpm) and preheated nitrogen gas flow (1 Nl/min). The continuous stripping by nitrogen prevents over-cracking of products and reduces the hydrocarbon partial pressure within the reactor, which shifts the reaction equilibrium toward product formation. For each experimental run, the reactor is initially loaded with 500 g of VR. The thermal cracking tests were carried out at three cracking temperatures (400, 415, and 430°C) and three reaction times (30, 50, and 60 min). Each experimental run resulted in three products: cracked oil, offgases, and pitch. Our previous effort 27,28,30-34 indicated that asphaltene tends to concentrate in the pitch by-product, while the thermally cracked oils, at all given operating conditions, contain negligible amount of asphaltene. More details about the thermal cracking experiments are given in AlHumaidan et al. 34.

2.2 Precipitation of Asphaltene Samples Asphaltenes were separated from the VRs and the pitch samples by using normal paraffin (i.e., n-heptane) as precipitating agent. The precipitation methodology was based on the IP 143/90 (ASTM 6560). Initially, the residue samples (liquid) were heated to a temperature around 80°C and mixed well, while Pitch (solid) samples were grounded to fine powder. The samples were weight to the nearest 10 gram and then placed in round-bottom conical flasks. n-heptane was added to the flasks at a ratio of 30 ml per 1 gram of sample. The mixture was heated to 70-80°C and stirred for 30 min on a magnetic-stirrer hot plate to distribute the sample in the solvent. Then, the flasks containing the samples and solvent were cooled and stored in a dark place for 12 hours to precipitate the asphaltenes. The solid-liquid separation was subsequently performed in a funnel filtration assembly using a 0.22 µm filter paper. The precipitates in the filter papers were washed with excess warm n-heptane and left to dry. The precipitated asphaltenes were then dissolved by washing with 100 ml of toluene to extract the resin. Toluene was then evaporated by placing the mixture in a fume hood. The remaining


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fractions in the flasks were the asphaltene samples. Details about asphaltene extractions are also given in AlHumaidan et al. 30 and Lababidi et al. 32.

2.3 Asphaltene Characterization by NMR The 1H and

13

C NMR were carried out on a Bruker Avance600 spectrometer

operating at 14.095T. CDCl3 (99.8%) and TMS, both from MERCK, were used as solvent and as internal standard for the 1H NMR measurements. The 13C chemical shift values were referred to the central signal of the CDCl3 at 77.7 ppm. For 1H NMR, the sample concentration was approximately 15 wt% in 0.5 ml CDCl3. The solution was filled into a 5 mm tube and a drop of TMS (tetramethylsilane) was added. To obtain quantitative 13C NMR spectra, the solution was concentrated up to about 200mg/0.5ml (21 wt%). 1H NMR spectra were acquired with a spectral width of 12.3 kHz, a pulse angle of 90° (10.5 µs), and a delay time of 1 s. The settings for the quantitative

13

C NMR measurements were pulse program:

inverse gated decoupling, spectral width: 35 kHz, pulse angle: 30° (2.2 µs) and delay time: 180 s.

3. Results and Discussion To understand the nature of structural changes that take place during thermal cracking, one needs first to develop a good understanding of the molecular structures of the asphaltene samples extracted from the three parent VRs. To acquire this understanding, it is important to note that all petroleum fractions, including the asphaltene, are made of common building blocks. For instance, CHx groups (with 0 ≤ x ≤ 3) show characteristic signals in 1H (Figure 1 and Table 2) and 13C NMR (Figure 2 and Table 3). Complex hydrocarbon mixtures like asphaltenes are made of such groups. A number of average structural parameters (ASP) 36

can be quantified for these hydrocarbon groups using elemental analysis results, together


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with 1H and 13C NMR, from which structural characteristics of the hydrocarbon mixture can be deduced (Table 4). The ASPs indicate how much carbon or hydrogen out of the total is located in specific building blocks that hydrocarbon mixtures consist of. The following paragraphs refer to these as ASPs, which carry the unit number of atoms per average molecular structure (AMS). It is obvious from the typical 1H NMR spectrum of the parent asphaltenes, as shown in Figure 1, that all hydrogen building blocks listed in Table 2, except olefinic entities (no signal between 4.5-6.5 ppm), are present in the analyzed asphaltenes. Likewise, the 13C NMR spectrum, shown in Figure 2, demonstrates the characteristic signals of carbon building blocks listed in Table 3. The average structural parameters (ASPs) of the parent asphaltenes have been evaluated from the NMR spectra in conjunction with GPC and elemental analysis results, which are respectively reported in Tables 5 and 6. Thus, the ASPs of the parent asphaltenes are obtained as indicated in Table 7. Based on the data compiled in Table 7, an average molecular structure (AMS) has been tentatively constructed as shown in Figure 3. The proposed AMS matches the analytical results and represents a typical asphaltene molecule of the parent RB-VR (the "Formula" column in Table 7). Despite the fact that analyses results of asphaltene samples from different feeds (see Tables 5-7) differ somewhat from each other, it is acceptable, within the range of the experimental error, to consider the AMS suggested in Figure 3 as a common molecular structure for all three parent asphaltenes. Although asphaltenes consist of hundreds or even thousands of different molecules, the common structural characteristics of all these molecules can be tentatively depicted by the same AMS (Figure 3), which indicates that the parent asphaltenes are significantly rich in aromatic carbon. The proposed AMS consists of an archipelagoes structure where the peri8 ACS Paragon Plus Environment

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condensed polyaromatic rings (Figure 4) are connected to each other through aliphatic hydrocarbon bridges. The structure shows high percentage of carbon in bridge head position (Cal,b2=19%, Cal,b3=10%). The carbon is nearly equally distributed between aliphatic and aromatic building blocks and the average chain length of n-paraffinic substituent is n = 11.5. The procedure described above was followed in deriving the analytical data needed to study the structural changes in asphaltenes separated from the pitch samples, when subjecting the VRs to thermal cracking (see the supplementary data in the Appendix). For in depth analyses, two analytical data sets were selected for asphaltene samples resulted from the thermal cracking of the three VRs at the mildest (T=400 °C, t=30 min) and the most sever (T=430 °C, t=60 min) conditions and their respective analytical data are compiled in Tables 5 and 8 to 10. Figures 5 and 6 display the AMS of the RB-VR asphaltenes cracked at 400ºC for 30 min and 430ºC for 60 min, respectively. ASP results listed in Table 9 and the respective AMS displayed in Figure 5 indicate that under mild reaction conditions, the structure of the parent asphaltenes from RB-VR does not change much. The degree of condensation (Car,b/C) is the same (28%) and the percentage of aliphatic carbon (Cal/C) decreases slightly (parent:47%, cracked: 43%). The percentage of aromatic carbon that bears a hydrogen (Car;H/C) increases slightly (parent:11%, cracked: 14%). Under the most sever cracking conditions (i.e. 430ºC for 60 min), besides the fact that the average molecular weight (AMW) has reduced to half of the parent VRs, their AMS have changed drastically. The aromatic core of the asphaltenes have changed from peri- to more cata- condensation (Figure 6), and they have lost most of their aliphatic carbons, which were present in the parent asphaltenes (parent:47%, cracked: 18%). To illustrate the effect of gradual changes in reaction conditions on the ASP of the cracked asphaltenes from RB-VR, consider the histograms shown in Figures 7 and 8 that plot, for selected parameters (the data are normalized to total carbon equals 100 % to make them comparable), the trend versus the cracking conditions. As anticipated from the two AMS in 9 ACS Paragon Plus Environment

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Figure 5 and 6, the percentage of total aliphatic carbon as well the carbon in n-parafinic (Cal;n-alkyl), iso-parafinic and naphthenic groups (Cal;ip+naphth) consistently decrease with increasing thermal cracking severity (Figure 8a), indicating that the cracking reactions are mainly taking place in the saturated part of the asphaltene molecules. On the contrary, the percentage of aromatic carbon parameters (Car, Car;alk) increase with increasing severity (Figure 8b). It is evidently shown also in Figure 8(b) that thermal cracking changes the aromatic core of asphaltene molecules from peri- (high content of triple bridged aromatic carbon Car;b3) to cata-condensation (high content of double bridged aromatic carbon Car;b2). Moreover, the trends shown in Figure 8(c) illustrate that the removal of hetero atoms (N and S) enhances with increasing cracking severity. In fact, sulfur and nitrogen atoms are mainly removed from saturate parts of the asphaltene molecules. Results reported for thermal cracking of asphaltenes from RB-VR are similar to those observed for the asphaltenes from LF-VR and EC-VR as illustrated in Figures 9 and 10. Impact of thermal cracking on the aromatic nature of asphaltene molecules is illustrated further in Figure 11 in terms of aromaticity (fa) and aliphatic to aromatic carbon ratio (Cal/Car). The trends indicate clearly that asphaltene molecules become more aromatic in nature (i.e. more refractory) with increasing cracking severity. This is mainly attributed to cracking of paraffinic side chains of the asphaltene molecules. The significant reductions in the Cal/Car ratio indicate the extent of changes introduced to the aliphatic part of asphaltene molecule by thermal cracking. The relatively larger drop in Cal/Car ratio for LF asphaltene at short residence time (i.e. 30 min), as shown in Figure 11, suggests that LF asphaltene molecule has lower stability in structure compared to asphaltenes from RB and EC. This observation is in agreement with observations reported in a previous study in which FTIR was used in studying the effect of thermal cracking on asphaltenes

31

. Figure 11 also

illustrates limited variations in the aromaticity of LF and EC asphaltenes at the highest 10 ACS Paragon Plus Environment

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residence time (i.e. 60 min), which might be attributed to the fact that at high cracking severity, the aliphatic hydrocarbon chain is abolished and the asphaltene molecule becomes more refractory in nature (aromatic core of asphaltene is difficult to crack).

4. Conclusions The NMR analysis in this study has developed better understanding of the structural changes that asphaltene molecules undergo during the thermal cracking of vacuum residues. Conclusions drawn from the NMR study can be summarized as follows: •

Carbons in asphaltenes separated from the "parent" VRs are to some extent equally distributed between aliphatic and aromatic building blocks (Cal/Car=0.79).

•

Aliphatic carbons are equally distributed between n-paraffinic substituents and iso-paraffinic and naphthenic substituents.

•

The polyaromatic structure of asphaltenes from the parent VRs consists of peri-condensed cores interlinked through aliphatic bridges. Such pericondensed cores are converted to cata-condensed polyaromatic cores as the reaction severity increases.

•

The AMW may be reduced by up to 66% at the most severe thermal cracking conditions (i.e. T = 430ºC, t = 60 min.). Such reduction is due to cracking of the saturated parts of the asphaltene molecules, loss of sulfur and nitrogen located in saturated parts, and shrinking of the aromatic core.

•

Percentage of aromatic carbon as well as aromatic carbon bearing hydrogen increases with increasing severity.


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Acknowledgement

The authors acknowledge the financial support of Kuwait Institute for Scientific Research (KISR) and they gratefully recognize Kuwait University help in conducting the NMR analysis in (GS01/03) core facility.

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[26] Ibrahim, Y.A.; Abdelhameed, M. A.; Al-Sahhaf, T. A.; Fahim, M.A., Structural characterization of different asphaltenes of Kuwaiti origin. Petroleum Science & Technology 2003, 21 (5-6), 825-837. [27] Hauser, A.; AlHumaidan, F.; Al-Rabiah, H., NMR investigations on products from thermal decomposition of Kuwaiti vacuum residues. Fuel 2013, 113, (0), 506-515. [28] Hauser, A.; AlHumaidan, F.; Al-Rabiah, H.; Absi-Halabi M., Study on thermal cracking of Kuwait heavy oil (vacuum residue) and its SARA fractions by NMR spectroscopy. Energy & Fuels 2014, 28, 4321-4332. [29] Weinberg, V. A.; Yen, T. F., Hypothetical average structures of two coal liquid asphaltenes from solid state 13C nuclear magnetic resonance and 1H nuclear magnetic resonance data. Carbon 1983, 21, 149-156. [30] AlHumaidan, F.; Hauser, A.; Rana, M.S.; Lababidi, H.; Behbehani, M., Changes in asphaltene structure during thermal cracking of residual oils: XRD study. Fuel 2015; 150: 558-564 [31] AlHumaidan, F.; Hauser, A.; Rana, M.S.; Lababidi, H., Impact of thermal treatment on asphaltene functional groups. Energy & Fuels 2016, 30 (4): 2892-2903. [32] Lababidi, H. M. S.; Sabti, H. M.; AlHumaidan, F. S., Changes in asphaltenes during thermal cracking of residual oils. Fuel 2014, 117, 59-67. [33] AlHumaidan, F.; Al-Rabiah, H.; Lababidi, H., Thermal cracking kinetics of Kuwaiti vacuum residues in Eureka process. Fuel 2013, 103, 923-931. [34] AlHumaidan, F.; Hauser, A.; Al-Rabiah, H.; Lababidi, H.; Bouresli, R., Studies on thermal cracking behavior of vacuum residues in Eureka process. Fuel 2013, 109, 635-646. [35] Takatsuka, T.; Watari, R., Renewed attention to the eureka process: Thermal crackingprocess and related technologies for residual oil upgrading. Studies in Surface Science and Catalysis1996, 100, 293-301. [36] Petrakis, L. ; Allen, D., NMR of fossil fuels, Elsevier. Oxford, New York, Tokyo, 1987. [37] Knight, S. A., Analysis of aromatic petroleum fractions by means of absorption mode carbon-13 NMR spectroscopy. Chem. Ind. 1967, 1920-1923. [38] Gillet, S. ; Gubini, P.; Delduech, J. J.; Escalier, J. C.; Valentin, P., Quantitative carbon13 and proton nuclear magnetic resonance spectroscopy of crude oil and petroleum products: 1. Some rules for obtaining a set of reliable structural parameters. Fuel 1981, 60 (3), 221-225. [39] Gillet, S.; Gubini, P.; Delduech, J .J.; Escalier, J. C.; Valentin, P., Quantitative carbon13 and proton nuclear magnetic resonance spectroscopy of crude oil and petroleum products: 2. Average structure parameters of representative samples. Fuel 1981, 60, 226-230.


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[40] Dickinson, E. M., Structural comparison of Petroleum fractions using proton and 13C NMR spectroscopy. Fuel 1980, 59 (5), 290-294. [41] O’Donnell, D. J.; Sigli, S. O.; Berlin, K. D.; Sturm, G. P.; Vogh, J. W., Characterization of high-boiling petroleum distillate fractions by proton and 13C nuclear magnetic resonance spectrometry. Fuel 1980, 59, 166-174. [42] Netzel, D. A.; McKay, D. R.; Heppner, R. A.; Gaffey, F. D.; Cooke, S. D.; Varie, D. L.; Linn, D. E., 1H and 13C NMR studies on naphtha and light distillate saturate hydrocarbon fractions obtained from in-situ shale oil. Fuel 1981, 60 (4), 307-320. [43]

Seshadri, K. S.; Albaugh, E. W. ; Backa J. D., Characterization of needle coke feedstocks by magnetic resonance spectroscopy. Fuel 1982, 61 (4), 336-340.

[44] Suzuki, T.; Itoh, M.; Takegami, Y.; Watanabe, Y., chemical structure of tar-sand bitumens by 13C and 1H NMR spectroscopic method. Fuel 1982, 61, 402-410. [45] Hasan, M. U.; Ali, M. F.; Bukhari, A., Structural characterization of Saudi Arabian heavy crude oil by NMR spectroscopy. Fuel 1983, 62 (5), 518-523.


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Page 16 of 36

Table 1: Properties of RB, LF, and EC vacuum residues Property

Method

RB-VR

EC-VR

LF-VR

TBP Cut Range, °C

550

550

550

Yield on Crude, wt%

31.2

40.2

36.3

Yield on Crude, vol %

26.6

40.8

32.4

Density at 15°C, g/cc

D 5002

1.0497

1.0583

1.0659

Gravity, °API

D 1250

3.2

2.1

1.2

1174

1256.1

1045.3

Molecular weight, g/mol Asphaltene, wt.%

D6560

14.6

22.3

14.7

CCR, wt.%

D 4530

25.98

29.17

31.76

RB-VR: Ratawi-Burgan vacuum residue; LF-VR: Lower-Fars vacuum residue; EC-VR: Eocene vacuum residue.


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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

Table 2. 1H NMR Chemical Shift Ranges of Building Blocks 37-45 Chem. Shift Abbreviation

Building Block Ranges (ppm)

Hal

total aliphatic hydrogen

0.5 - 4.5

Hal;γ

aliphatic hydrogen in γ–position and further to aromatic ring

0.5 - 1.0

Hal;β

aliphatic hydrogen in β–position to aromatic ring

1.0 – 1.9

Hal;α

aliphatic hydrogen in α–position to aromatic ring

1.9 - 4.5

Hol

hydrogen attached to olefinic carbon

4.5 - 6.5

Har

aromatic hydrogen

6.5 - 9.0


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Page 18 of 36

Table 3. 13C NMR Chemical Shift Ranges of Building Blocks [37-45] Chem. Shift Abbreviation

Building Block

Ranges (ppm)

Cal

total aliphatic carbon

10 -70

Cal;CH3

aliphatic carbon in CH3-groups of n-paraffinic straight chains

Cal;CH3(total) aliphatic carbon in CH3-groups

14.1 10 – 22.7 29.7

Cal;CH2

aliphatic carbon in CH2-groups further than γ-position of n-paraffinic straight chains

Col

Carbon in olefinic groups

106 - 145

Car

total aromatic carbon

100 - 178

Car;H,b3

aromatic carbon bearing a hydrogen and aromatic carbon in triple bridge position

Car;alk

aromatic carbon attached to alkyl side chains (without CH3)

138 - 150

Car;X

aromatic carbon attached to heteroatom

150 - 178


118 – 128.5

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Energy & Fuels

Table 4. Description of Average Structural Parameters (ASP) Abbreviation Cal Cal;n-alkyl Cal;ip+naph Cal;CH3 Car Car;H Car;q Car;alk Car;sub Car;X Car;nb Car;b Car;b2 Car;b3 Hal Hal;α Har n* n σ total γ σ alk

Remarks total aliphatic carbon aliphatic carbon in n-alkyl with n>6 (Cal;n-alkyl=Cal;CH2+5* Cal;CH3, Cal;CH2: signal at 29. 5ppm, Cal;CH3: signal at 14.1ppm) aliphatic carbon in branched-alkyl and naphthens (Cal;ip+naph=Cal-Cal;n-alkyl) aliphatic carbon in CH3-groups total aromatic carbon aromatic carbon bearing a hydrogen (Car;H=%H*{Har/(Hal+Har)}*12 aromatic carbon attached to carbon or heteroatom (Car;q=Car-Car;H) aromatic carbon attached to alkyl side chains (without CH3) aromatic carbon attached to acyclic or cyclic alkylsubstituent (Car;sub=Cal/n*) aromatic carbon attached to heteroatom nonbridged aromatic carbon (Car;nb=Car;H+Car;sub+Car:X) total aromatic carbon in bridge head position (Car;b=Car-Car;nb) aromatic carbon in bridge head position of two aromatic rings (Car;b2=Car;b-Car;b3) aromatic carbon in bridge head position of three aromatic rings (Car;b3= Car;H,b3Car;H) aliphatic hydrogen aliphatic hydrogen in α–position to aromatic ring aromatic hydrogen average number of carbons in alkyl substituent (n*=Hal/Hal;α) average number of carbons in n-alkyl with n>6 (n= Cal;CH2/Cal;CH3+5) Car;sub/(Car;sub + Car,H) (Degree of Substitution) Car;b/Car (Degree of Condensation) Car;alk/(Car;H + Car;alk) (Degree of Paraffinic Substitution without CH3)


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Page 20 of 36

Table 5: Average molecular weight (Da) using GPC analysis for parent and cracked asphaltenes Sample

VR1)

400/302)

430/603)

RB

1456

1110

572

LF

1580

1089

494

EC

1487

1176

445

1)

Vacuum residue (VR) (Ref. 32)

2)

Reaction conditions: T=400oC, t=30 min.

3)

Reaction conditions: T=430oC, t=60 min.


Page 21 of 36

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

Table 6. Elemental Analysis Data of Parent Asphaltenes [32] Parameter, wt%

VRs RB

LF

EC

C

81.61

80.10

81.70

H

7.62

7.33

7.32

N

2.04

1.94

1.84

S

8.73

10.61

9.15

H/C, mol/mol

1.120

1.098

1.075


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Page 22 of 36

Table 7. Average Structural Parameters (ASP) of Parent Asphaltenes (number of atoms) ASP

Asphaltenes RB-VR

LF-VR

EC-VR

Formula in Fig. 3

Abs. Diff.1)

C

99

105

101

102

3

Cal

47

46

42

46

1

Cal;n-alkyle

23

21

20

23

0

Cal;ip+naphth

24

25

21

23

1

Cal;CH3 (total)

9

10

9

9

0

Car

53

59

60

56

3

Car;H

11

11

12

13

2

Car;q

42

48

48

43

1

Car;alk

11

13

14

11

0

Car;sub

12

12

10

13

1

Car;X

2

2

1

2

0

Car;nb

25

25

23

28

3

Car;b

28

34

36

27

1

Car;b3

10

11

11

10

0

Car;b2

19

23

25

17

2

H

111

116

109

112

1

Hal

100

105

97

99

1

Hal; α

26

28

24

29

3

Har

11

11

12

13

2

n

11.5

10.3

10.1

11.5

0

n*

3.9

3.8

4.0

3.4

0.5

S

4

5

4

4

0

N

2

2

2

2

0

AV2) 1) 2)

1.10

Abs Diff.= Absolute([RB-VR value] – [Formula value]) AV= Average


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Energy & Fuels

Table 8. Elemental Analysis Data of Cracked Asphaltenes (AS). Cracked AS from Parameter, wt%

RB-VR 1)

LF-VR 2)

400/30

430/60

C

81.90

82.84

80.80

80.40

83.00

82.60

H

6.90

5.89

6.58

6.56

6.53

6.31

N

2.27

1.94

1.70

1.79

1.79

2.05

S

8.93

9.34

10.87

11.21

8.73

9.03

H/C, mol/mol

1.012

0.854

0.978

0.945

0.918

1) 2)

400/30

EC-VR 430/60

0.980

400/30

Reaction conditions: T=400oC, t=30 min. Reaction conditions: T=430oC, t=60 min.


430/60

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Page 24 of 36

Table 9. Average Structural Parameters (ASP) of Asphaltenes (AS) Cracked at 400oC for 30 min. Cracked AS from ASP

RB-VR

LF-VR

EC-VR

Formula in Fig. 5

Abs. Diff.1)

C

76

73

81

76

0

Cal

33

29

29

31

2

Cal;n-alkyle

12

14

13

11

1

Cal;ip+naphth

21

14

16

20

1

Cal;CH3 (total)

7

6

6

6

1

Car

43

45

52

45

2

Car;H

11

12

11

13

2

Car;q

32

32

41

32

0

Car;alk

8

8

9

9

1

Car;sub

9

8

8

11

2

Car;X

2

1

1

1

1

Car;nb

21

21

20

25

4

Car;b

21

24

33

20

1

Car;b3

8

7

12

7

1

Car;b2

14

16

21

13

1

H

77

72

77

77

0

Hal

66

59

65

64

2

Hal; α

17

16

17

22

5

Har

11

12

11

13

2

n

9.6

8.6

10.2

11

1.4

n*

3.9

3.7

3.8

S

3

4

N

2

1

2.9

1

3

2

1

2

2

0

AV2) 1) 2)

1.38



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Energy & Fuels

Table 10. Average Structural Parameters (ASP) of Asphaltenes (AS) Cracked at 430oC for 60 min. Cracked AS from ASP

C

RB-VR

LF-VR

EC-VR

Formula in Fig. 6

Abs. Diff.1)

39

33

31

40

1

Cal

7

9

8

9

2

Cal;n-alkyle

3

5

4

3

0

-Cal;ip+naphth

4

5

5

6

2

Cal;CH3 (total)

4

3

2

3

1

Car

32

24

22

31

1

Car;H

10

9

7

10

0

Car;q

22

15

15

21

1

Car;alk

6

4

4

4

2

Car;sub

4

4

4

5

1

Car;X

1

0

0

0

1

Car;nb

15

13

11

15

0

Car;b

17

11

11

15

2

Car;b3

2

2

3

2

0

Car;b2

15

9

8

13

2

H

34

32

28

31

3

Hal

23

24

21

21

2

Hal; α

12

10

9

12

0

Har

10

9

7

8

2

n

7.5

7.0

8.0

4

3.5

n*

1.9

2.4

2.3

1.8

0.1

S

2

2

1

2

0

1

1

1

1

0

N 2)

AV 1) 2)

1.18



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Aromatic Hydrogen (Har)

Page 26 of 36

Aliphatic Hydrogen (Hal)

Hal;α Olefinic Hydrogen (Hol)

Figure 1. 1H NMR spectrum of parent asphaltene (RB-VR).


Page 27 of 36

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

Aliphatic Carbon (Cal)

Aromatic Carbon (Car)

Figure 2. 13C NMR spectrum of parent asphaltene (RB-VR).


Energy & Fuels

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Page 28 of 36

N

C12H25*

N

S

C11H23* S

S

S

*

n-Paraffin

C102H112N2S4; AMW=1492; H/C=1.10

Figure 3. Average molecular structure of parent asphaltenes from RB-VR.


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Energy & Fuels

Peri-condensed Polyaromates

Cata-condensed Polyaromates

Figure 4. Types of polyaromates.


Energy & Fuels

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Page 30 of 36

C11H23*

N

S N

S *

n-Paraffin

C76H77N2S2; AMW=1081; H/C=1.01

Figure 5. Average molecular structure of RB-VR asphaltenes cracked at 400oC for 30 min.


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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

N S

*

S

n-Paraffin

C40H31N1S2; AMW=589; H/C=0.78

Figure 6. Average molecular structure of RB-VR asphaltenes cracked at 430oC for 60 min.


Energy & Fuels

60 2.5

RB-VR

2.0

50

LF-VR

1.5

EOC-VR

1.0

40

0.5

30

Car;X

σstotal total

Car;alk

0.0

Car;b2

% Carbon

gγ

fa

σsalk alk

20

10

σ salk alk

fa

γg

σ stotal total

Car;X

{H/C}al

n*

Car;b3

n

Car;sub

Car;b

Car;nb

Car;q

Car;t

Car

Cal;CH3 (Arom)

Cal;ip+naphth

Cal;n-alkyle

0

Cal

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 32 of 36

Nature of carbon (functional group)

Figure 7. NMR analysis: Average structural parameters for the parent asphaltene from RBVR, LF-VR, and EC-VR.


Page 33 of 36

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Energy & Fuels

Figure 8. Effect of thermal cracking conditions (temperature/time) on selected ASP of asphaltenes from RB-VR.


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

Figure 9. Effect of thermal cracking conditions (temperature/time) on selected ASP of asphaltenes from LF-VR.


Page 34 of 36

Page 35 of 36

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Energy & Fuels

Figure 10. Effect of thermal cracking conditions (temperature/time) on selected ASP of asphaltenes from EC-VR.


Energy & Fuels

1 Aromaticity (fa) Aromaticity & Cal/Car ratio

Cal/Car ratio 0.8

0.6

0.4

0.2

30 min

50 min

60 min

30 min

RB

50 min

60 min

LF

400 415 430 400 415 430 400 415 430

400 415 430 400 415 430 400 415 430

0 400 415 430 400 415 430 400 415 430

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 36 of 36

30 min

50 min

60 min

EOC

Process condition

Figure 11. Overall nature of asphaltene carbon and its variation as a function of feedstock (RB, LF and EOC), reaction time (30, 50 & 60 min) and temperature (400, 415 and 430 °C).


NMR Characterization of Asphaltene Derived from Residual Oils and

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