Correlation of Temperature-Programmed Oxidation with Microscopy

Jan 21, 2015 - Obviously, most of the optical textures of QDSHC are medium-grained mosaic textures, with an average grain size of 2.3 μm, as seen in ...
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Correlation of Temperature-Programmed Oxidation with Microscopy for Quantitative Morphological Characterization of Thermal Cokes Produced from Pilot and Commercial Delayed Cokers Zongxian Wang,* Peng Xue, Kun Chen, Aijun Guo,* Cunhui Lin, Dehui Kong, Zhengda Song, and Yawen Bo State Key Laboratory of Heavy Oil Processing and College of Chemical Engineering, China University of Petroleum (East China), 66 Changjiangxi Road, Qingdao Economic Development Zone, Qingdao, Shandong 266580, People’s Republic of China ABSTRACT: A wide series of thermal cokes obtained from commercial delayed cokers and a pilot coking plant have been investigated by polarized light microscopy observation, scanning electron microscopy (SEM), and temperature-programmed oxidation (TPO) technology. For discrimination of the characterization of the coke samples, the anisotropy degrees of the cokes are found to be considerably different. According to the series of runs in the pilot plant, the restricted mesophase development in thermal cokes could be ascribed to the increasing severity of coking conditions. A previous proposed signal analysis procedure was then applied to the TPO profiles of the cokes to quantitatively acquire parameters for further correlation. A fairly good linear dependency of optical texture index (OTI) upon the proportion of anisotropic carbon species from TPO (correlation coefficient of 0.984) was observed. All of the results obtained in this and our previous (Chen, K.; Xue, Z.; Liu, H.; Guo, A.; Wang, Z. A temperature-programmed oxidation method for quantitative characterization of the thermal cokes morphology. Fuel 2013, 113, 274−279) studies fall within a 95% confidence interval when the dependence of OTI upon the proportion from TPO is considered, therefore clearly demonstrating the validity and adaptability on the convenient determination of the proportion of anisotropic carbon species from TPO for the coke samples ranging from laboratory sources to pilot and even commercial origins. The distribution map of cokes established in this study could be used for quantitatively characterizing the morphology of various thermal cokes.

1. INTRODUCTION One important factor influencing the operation economy of delayed coking is the coke morphology (sponge coke versus shot coke),1 which is desired to be intentionally controlled to increase the process capacity of commercial plants2 and liquid yield,3 for instance, by the formation of so-called free-flowing shot coke. The effectively increased processing capacity because of the easier and faster removal of shot coke from the coker drums and higher liquid yield would offset the reduced economic value of shot coke for its low grindability from stiffness.1,4 Much attention has thus been focused on the formation mechanism of shot coke5,6 and the study of coke morphology controlling4,7,8 during coking. Therefore, the quantitative assessment of coke morphology is particularly and necessarily important in these studies for the understanding of the structural characterization of thermal coke and the research of factors affecting shot-coke-forming propensity. Typically, the assessments are implemented using polarized light optical microscopy observation with image analysis.9 It was claimed as a best method for identifying and characterizing the coke morphology.1 However, it is also suggested to be a time-consuming and laborious method for both coke sample preparation and image analysis. More convenient and suitable methods based on quantitative morphology characterization are therefore required. Preliminary studies of solid carbons10−12 provided useful clues for the solution, which demonstrated that various carbon species (e.g., isotropic carbon and anisotropic carbon) could be discriminated by relating the thermal reactivity of solid carbons © XXXX American Chemical Society

under an oxidation atmosphere to their structure. Altin and Eser13 analyzed the thermal carbons deposited on different tube surfaces with a temperature-programmed oxidation (TPO) technique and identified three distinctly characteristic coke species (i.e., hydrogen-rich chemisorbed constituent, amorphous carbon, and structurally ordered carbon). AlonsoMorales et al.14 deconvoluted TPO curves of thermal carbons and identified six different groups of carbon domains with the same oxidation reactivity. Sánchez et al.15 suggested that coke analysis by TPO with oxidation kinetics plus proper Gaussian deconvolution of TPO curves would favor the interpretation of coke morphology. Most recently, as suggested by Kok,16 Chen et al.17 further used a TPO technique with a calorimetric detection system [i.e., differential scanning calorimetry (DSC)] to investigate the general morphology of eight thermal cokes resulting from petroleum residues and fractions and presented a more rapid method than polarized light microscopy to quantitatively characterize the thermal coke morphology. However, the coke samples were merely obtained from small-scale coking experiments in the laboratory.17 Although the polarized light microscopic observation showed that these coke samples and cokes from a commercial delayed coker18 and pilot plant4 had rather high similarity in the coke texture, it was not indicated that the aforesaid method could be valid in the study of morphology characterization of thermal cokes from a Received: November 2, 2014 Revised: January 21, 2015

A

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Energy & Fuels commercial delayed coker and/or pilot plant. Our interest here thus lies in further investigating the adaptability of our method to thermal cokes from a commercial delayed coker and pilot coking plant. This research aims to conduct adaptability research for exploring a wider application possibility of the TPO technique in coke morphology characterization and, thus, could favor the research of the shot coke formation mechanism and the controlling of coke morphology. To test the method well, a systematic study is undertaken using a series of shot cokes plus a sponge coke and a needle coke from commercial delayed cokers as the experimental cokes. Meanwhile, thermal cokes resulting from a pilot coking plant under different coking operation conditions are also employed as a complement. The coke morphology is microscopically recorded by a photograph with image analysis and is then generally characterized by TPO with a deconvolution procedure, and the correlation between the coke morphology by both methods is explicitly presented.

Table 2. Coking Conditions for the Preparation of Thermal Cokes

2.1. Coking Feedstocks Used in the Pilot Plant and the Acquisition of Cokes from Commercial Delayed Cokers and Pilot Unit. One vacuum residue with a boiling range of 500 °C+ derived from a Venezuelan crude oil, i.e., VNVR, was used as a coking feedstock because VNVR is believed to have a high shot-coke-forming propensity during the coking.4 Three coker distillates (i.e., coking atmospheric gas oil, light coker gas oil, and heavy coker gas oil) regarded as circulation fractions were then acquired from the liquid product produced from the coking of VNVR in a pilot coking plant, which was previously reported and described in detail.19 The selected properties of VNVR and the three coker distillates are listed in Table 1. VNVR and one of coker distillates (used as recycle oils) were

Table 1. Selected Properties of VNVR and Three Coker Distillates −3

density at 20 °C (g/cm ) MCRd (wt %) S (wt %) N (wt %) group analysis saturates aromatics resins n7-asphaltenes

VNVR

CAGOa

CLVGOb

CHVGOc

1.0167 19.48 3.38 0.74

0.8850

0.9689 0.22 2.96 0.35

1.0042 2.60 2.99 0.37

20.43 37.62 30.43 11.47

2.47 0.16

46.23 42.01 11.76 0

temperature (°C)

pressure (MPa)

recycle ratio

label

VNVR + CAGO VNVR + CLVGO VNVR + CHVGO VNVR VNVR VNVR VNVR VNVR VNVR

480 480 480 450 490 510 480 480 480

0.2 0.2 0.2 0.2 0.2 0.2 0.0 0.1 0.2

0.3 0.3 0.3 0 0 0 0 0 0

TCI TCII TCIII TCIV TCV TCVI TCVII TCVIII TCIX

(labeled as QDSPC) was acquired from Qingdao Refinery, and a needle coke (labeled as JZNC) was achieved from Jinzhou Refinery. 2.2. Polarized Light Optical Microscopy Observation. Polarized light optical microscopic samples were prepared by mounting the coke sample in a polyester resin, which were then polished according to a series of standard pretreatments suggested by Siskin et al.1 The fully exposed cross-section of each sample was ground and polished until the sample surface was free of scratches. Each sample was then examined under polarized light to reveal an optical texture. The sizes of anisotropic isochromatic units in the optical texture, varying from less than 0.5 μm to more than 60 μm, were defined in referenced literature.7 On the basis of the definitions, an optical texture index (OTI) for each sample was thus calculated using a referenced formula,17 as described in detail in the research by O̅ ya et al.12 and Wang and Eser,21 and was then used to quantitatively assess the general morphology of coke. As recommended by Siskin et al.1 and Chen et al.,17 each polarized light image was marked with a scale of 10 μm for a primary recognition of coke morphology. 2.3. TPO Analysis. TPO analyses were carried out in a Linseis STA PT1600 DSC analyzer. All of the 15 cokes were strictly ground to powder of 120−130 mesh, as suggested by Chen et al.17 The powder samples were heated from ambient temperature to 800 °C at a rate of 15 °C min−1 within 50 mL min−1 of oxygen diluted in 50 mL min−1 of high-purity nitrogen. The heat flow curves in the TPO profiles were deconvoluted into Gaussian peaks using the Origin Pro version 8.0 software (OriginLab, Northampton, MA). Results from repeated tests showed that the TPO profiles were reproducible, in agreement with our previous research.17

2. MATERIALS AND METHODS

property

feedstock

35.53 46.95 17.52 0

3. RESULTS AND DISCUSSION 3.1. General Observation of Cokes from Commercial Delayed Cokers and a Pilot Coking Plant. The photos of cokes from commercial delayed cokers are compiled in Figure 1. It can be observed that the three shot cokes, CXSHC, GQSHC, and SXSHC, although differing in sphere diameter, all present scattering, while QDSHC is a cluster type formed by aggregation and bonding of individual coke spheres. Typically, QDSHC could be classified as a secondary shot coke4 of table tennis ball size. It is worth while to note that, although QDSHC radically differs from QDSPC in macroscopical morphology (as seen in Figure 1), their feedstocks are the same. QDSHC is acquired from the commercial plant under severer coking conditions than that of QDSPC for the purpose of a higher liquid yield, while QDSPC (black, porous, and sponge-like) is produced on the premise of a long period running operation of a delayed coker. As a needle coke, JZNC shows typical silver gray metallic luster and evident fiber-like texture on the fracture surface (shown as position A in Figure 1). Figure 2 shows the cross-section and vertical section of a representative coke (TCVIII) acquired from a pilot coking plant. The coke, with a porous structure, generally shows a

Coking atmospheric gas oil distillate (180−350 °C). bLight coker gas oil distillate (350−420 °C). cHeavy coker gas oil distillate (420−500 °C). dMicrocarbon residue determined according to ASTM D453011.20 a

blended to obtain three other coking feedstocks, which would correspondingly result in three types of thermal cokes in the pilot delayed coker. They are labeled as TCI, TCII, and TCIII, respectively. The coking conditions are listed in Table 2. Six types of thermal cokes were subsequently prepared using VNVR as the coking feedstock and the aforementioned pilot delayed coker as the reactor. They are labeled as TCIV, TCV, TCVI, TCVII, TCVIII, and TCIX, and the corresponding coking conditions are also listed in Table 2. Four types of shot coke were acquired from Chenxi Refinery, Qingdao Refinery, Gaoqiao Refinery, and Shengxing Refinery. These shot cokes are labeled as CXSHC (Chenxi shot coke, around 5 mm in diameter), QDSHC (Qingdao shot coke, cluster type), GQSHC (Gaoqiao shot coke, less than 1.5 mm in diameter), and SXSHC (Shengxing shot coke, around 6.5 mm in diameter). A sponge coke B

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Figure 3. Photographs of cokes acquired from a pilot coking plant: (a) TCIV (450 °C and 0.2 MPa) and (b) TCVI (510 °C and 0.2 MPa).

cokes resulting from a pilot coking plant are sponge-like, except TCVI, which contains smooth spheres. Such spheres were previously defined as primary shot coke and reported in detail.4 All of the cokes have been examined by a scanning electron microscopy (SEM) technique to further reveal the morphological difference. The four commercial shot cokes, i.e., CXSHC, QDSHC, GQSHC, and SXSHC, all have the morphology of Figure 4a, for the QDSHC; that is, they are

Figure 1. Photographs of cokes (i.e., a sponge coke, a needle coke, and four shot cokes) acquired from commercial delayed cokers.

Figure 2. Photographs of representative coke (TCVIII) acquired from a pilot coking plant under 480 °C and 0.1 MPa: (a) cross-section and (b) vertical section.

Figure 4. SEM micrographs of cokes: (a) QDSHC, (b) TCVI, (c) JZNC, and (d) QDSPC.

typical sponge-like surface morphology. A morphology of fibrous and rough pore (around 1 cm in diameter, seen as position A in Figure 2) is also observed from the fracture surface of the vertical section. The implications of the observation are that the fibrous pore is plastic and fluid subsequent to the formation and that volatiles were being released in finite quantities to create the so-called fiber-like macroporosity, which collapse or deform to some extent after the passage of the main relief of volatiles. Thermal coke resulting from a relatively low coking temperature (450 °C) has the morphology shown in Figure 3a; that is, it is sponge-like, with its structure being quite compact and its surface being rough. The appearance detected in Figure 3a could be attributable to the mild turbulence of volatiles and the high plasticity of the mesophase22 because of the relatively low coking severity. However, the coke from a high coking temperature (510 °C) is wave-like, with its structure being unconsolidated and its surface being rather smooth, which might be attributed to the significant relief of volatiles and the self-reforming of high viscous paste-like materials for the decrease of surface tension.18,23,24 All of the

almost spheres, with most of their surfaces being smooth. The surfaces are pitted with pores (100−150 μm in diameter), a typical phenomenon of shot coke previously reported in the literature.18 Figure 4c is of the JZNC. Evidently, streamlined lamellar carbon structures are observed. Figure 4d is of QDSPC. Rough surfaces with channels (around 1 mm) are observed. Figure 4b is of TCVI. As expected, the microscopic morphology shows some similarity to the image of QDSPC on the smoothing propensity of the surface probably because VNVR has a high shot-coke-forming propensity under a high temperature of 490 °C, as reported by Guo et al.,4 not to mention under the temperature of 510 °C in this study. The rest of the coke samples from the pilot plant show various similarities with QDSPC. Generally, the morphological features of cokes are found to be considerably different for discriminating characterization. 3.2. Morphological Characterization of Cokes from Commercial Delayed Cokers and a Pilot Coking Plant: Polarized Light Microscopy. The morphology of thermal cokes could be effectively modified through the control of operational parameters, such as coking temperature, pressure, C

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lower viscosity and stronger recoalescence tendency of a partial mesophase during volatile release,18,25 which has been rationalized by the relatively lower coking severity than that for the production of QDSHC. The size data of the anisotropic isochromatic spherules of TCIV derived from VNVR at a rather low coking temperature (i.e., 450 °C) are scattered in the range of 10−30 μm, which means that the optical texture of TCIV is dominated by medium flow. As the coking temperature increases, the texture of coke evidently becomes more mosaic-like, and then, as seen in panels d−f of Figure 5, the sizes of the anisotropic isochromatic areas decrease progressively with the increasing temperature. The optical texture development of TCVI (finegrained mosaics) combined with the wave-like and smooth macroporosity indicates that a higher coking temperature than 490 °C can sharply promote shot-coke formation. A reasonable explanation for the behavior has been reported by Rahimi et al.,26 who stated that free radicals, reacting drastically at a high temperature, would not be stabilized by active hydrogen and, thus, accelerate condensation. In this way, the coking reaction system could only have a quite narrow time window for the lowest viscosity,27 leading to the hindered growth of the mesophase. As observed in panels g−i of Figure 5, the impact of the coking pressure on the coke texture is shown. The average sizes of the mesophase increase as pressure rises from 0 to 0.2 MPa. When the pressure is 0 MPa, the average size of the optical texture is 3.5 μm (seen in Figure 5g), which is in evident contrast to the average size of 4.9 μm at a coking pressure of 0.2 MPa (seen in Figure 5i). It is indicated that the rise in the coking pressure would favor the development of the mesophase, which has been reported by Elliott23 and Guo et al.4 It is probably attributable to the reduction of volatiles with small molecular weight under a relatively high pressure, which could enrich the liquid and lower the viscosity. Panels j−l of Figure 5 show the polarized light micrographs of three cokes derived from blends for VNVR mixed with CAGO, CLVGO, and CHVGO, respectively. The substantially different optical texture sizes seen in panels j−l of Figure 5 indicate that the blending of circulation fractions could modify the optical texture of the cokes to a certain degree, which has been rationalized by the much lower viscosities of these fractions than VNVR and probably by the hydrogen donation abilities being beneficial for the mesophase development through growth and fusion of mesophase spherules.28 For instance, the average grain size of the texture is considerably promoted by 9.4 μm as CHVGO was used as the blending fraction. To summarize, the general morphological performances, e.g., anisotropic degree, of cokes, resulting from different coking conditions and species origins (e.g., shot coke, sponge coke, and needle coke), are quite different for discriminating characterization, which has been proven by the OTI (seen in Table 3) calculated for quantitative description of coke morphology and sequent parameter study using the procedure reported previously.17

and feed blending, the effects of which on the general morphology and the average anisotropic sizes of optical textures are investigated using the pilot unit in this study. The polarized light micrographs of cokes are compiled in Figure 5. Despite differing in macrospherical size, all four shot

Figure 5. Optical polarized light micrographs of cokes obtained from commercial cokers and a pilot plant: (a) QDSHC, (b) QDSPC, (c) JZNC, (d) TCIV, (e) TCV, (f) TCVI, (g) TCVII, (h) TCVIII, (i) TCIX, (j) TCI, (k) TCII, and (l) TCIII.

cokes have a good similarity in terms of the anisotropic degrees and isochromatic spherule distribution. Therefore, the polarized light micrograph of QDSHC is chosen as the representative of the four commercial shot cokes for comparison to micro-optical textures of other cokes and further discussion. It can be observed that cokes have different optical textures depending upon the coke species (i.e., QDSHC, QDSHC, and JZNC) and pilot experiment conditions (i.e., TCIV, TCV, TCVI, TCVII, TCVIII, TCIX, TCI, TCII, and TCIII). Some of the micrographs show mosaic texture (i.e., QDSHC, QDSPC, TCV, TCVI, TCVII, TCVIII, and TCI), and others have flow (i.e., QDSPC, TCIV, TCIX, TCII, and TCIII) or even predominant domain texture (i.e., JZNC). Obviously, most of the optical textures of QDSHC are medium-grained mosaic textures, with an average grain size of 2.3 μm, as seen in Figure 5a and Table 3, while the JZNC consists predominantly of domains (over 60 μm, Figure 5c). It should be noted that the mixture of two considerably different optical textures (mosaic versus flow) in QDSPC could be attributed to the relatively

Table 3. OTI of Cokes from Commercial Cokers and a Pilot Plant Plus Average Grain Sizes property

GQSHC

CXSHC

OTI average grain size (μm)

9.04 1.4

12.25 2.0

QDSHC SXSHC 11.63 2.3

11.13 1.9

QDSPC

JZNC

TCI

TCII

TCIII

TCIV

TCV

TCVI

TCVII

TCVIII

TCIX

13.01 2.9

28.75 35

14.77 3.6

18.21 7.2

21.45 13

24.45 15

12.87 3.5

8.49 1.2

13.29 3.5

15.08 4.2

17.61 4.9

D

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Figure 6. TPO profiles of all 15 cokes in this study: T, coking temperature; P, coking pressure; and R, recycled ratio and circulation fraction. The oxidation temperature range shown is 50−800 °C.

3.3. Morphological Characterization of Cokes from Commercial Delayed Cokers and a Pilot Coking Plant: TPO Analysis with Deconvolution. The TPO profiles of all of the cokes from commercial delayed cokers and a pilot coking plant in this study are compiled in Figure 6. It is believed that the reactivity of thermal cokes toward oxidizing gas (i.e., O2) is strongly dependent upon the structure and composition of coke.14 A more detailed discussion of the TPO profiles of cokes with respect to the species origins and coking conditions in various series of cokes is presented as follows. All coke burnoff profiles, except that of TCIV, show one predominant peak observed around 600 °C, which normally corresponds to less-active coke species or anisotropic carbon deposit.29 The immobility of the predominant peak listed in the first column of Figure 6 indicates that shot cokes might have a similar coke structure, despite them being from different commercial delayed cokers. The average grain sizes (as seen in Table 3) of the shot cokes imply that the coke micromorphological performances of the shot cokes indeed fit for the aforementioned speculation to some extent. SEM images (as seen in Figure 7) show that all of these shot cokes have an evident twisting and buckling lamellar structure, which has been rationalized by the medium-grained mosaic isochromatic textures (as seen in Figure 5 and Table 3), resulted from the hindered development of the mesophase30−32 in the coking process. In other words, the fusion and growth of the carbonaceous mesophase spherules during shot coke formation is hindered. As observed from top to bottom in the second column of Figure 6, an apparent shift of the major peak to the relatively higher temperature reveals that more highly ordered carbon structures are presented in the corresponding cokes that follow. As it turns out, SEM micrographs show that JZNC is dominantly composed of an evident streamline-like lamellar carbon structure, while QDSHC is mainly composed of twisting lamellar structures with more oxidation reactive sites. In the case of QDSPC, the microstructural performance lies between that of QDSHC and that of JZNC. It appears that lowering the coking severity could considerably spare the coke morphology from mosaic textures and consequent from the massive formation of shot coke.1 When we run our eyes down

Figure 7. SEM micrographs of cokes obtained from commercial delayed cokers.

the third, fourth, and fifth columns of Figure 6, apparent shifts to higher temperatures are also observed, which indicates that reducing the coking temperature, raising the coking pressure, and blending the circulation fraction with a considerable hydrogen-donating ability are effective means for producing cokes with more highly ordered carbon structures, which is substantially favorable for the quality improvement of petroleum coke from cokers. All profiles show a broad band that seems to consist of several overlapping peaks. Specially, some of the profiles have apparently separable peaks (e.g., TCVI). It can be deduced that thermal coke labeled as TCVI has a more heterogeneous morphology, which can be proven by the coexistence of flow E

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fractions, asphaltenes are the most likely to be responsible for the formation of shot coke.33 The OTI of TCVI, which is even a little lower than those of the commercial shot cokes, strongly suggests that, in all probability, largely, the coking at a very high coking temperature (510 °C) would produce shot coke if a commercial delayed coker was involved. Both the macroscopical morphology (as seen in Figure 3b) and the SEM image (as seen in Figure 4b) of TCVI are convincing illustrations for the speculated point. Needle coke is located in section C in Figure 8. Beyond that, most cokes are categorized to sponge/ sponge-like coke scattered in section B. The closer the coke is to section A, the worse the mesophase development, which quantitatively means higher propensity to be shot coke and vice versa. It seems that the distribution map of cokes (Figure 8) could be used to quantitatively characterize the morphology of cokes acquired from commercial cokers and pilot units in the laboratory as we expected.

anisotropic texture (as seen in position A of Figure 5d) and mosaic texture (as seen in position B of Figure 5d) most likely originated from heavy components, i.e., asphaltenes,5,33 more exactly, asphaltenes with heterocyclic aromatic nitrogen and sulfur.5 Therefore, the wide oxidation temperature range of TPO profiles is quite indicative of heterogeneity of carbon natures in cokes, which is also confirmed by the similar finding from Alonso-Morales et al.14 As pointed out by Alonso-Morales et al.14 and discussed before, the variation of the coke structure because of the variation of coking conditions and feedstock compositions has a strong and direct influence on its reactivity toward oxygen (i.e., TPO profiles). According to the analysis procedure of TPO profiles,29 all TPO profiles are deconvoluted and analyzed on the basis of the corresponding principle described in previous literature in detail.17 The calculations of proportion calculation of the anisotropic texture based on the TPO deconvolution and OTI would allow for a possible quantitative correlation between the parameters from TPO analysis and polarized light optical observation, as suggested by Chen et al.17 Figure 8 shows overall OTI of all of the cokes from commercial cokers and a pilot coking plant versus the proportion data from TPO profiles.

4. CONCLUSION A range of typical thermal cokes produced from both commercial and pilot delayed cokers has been systematically studied using polarized light microscopy observation, SEM, and TPO technology. The anisotropy degrees of coke samples are found to be greatly different for discriminating characterization. The restricted mesophase development in thermal cokes from a pilot plant could be ascribed to the increasing severity of coking conditions. A previous proposed signal analysis procedure was then applied to the TPO profiles to acquire quantitative parameters for further correlation. There exists a fairly good linear dependency of OTI upon the proportion from TPO (correlation coefficient of 0.984). All of the results obtained in the study and from Chen et al.17 fall within a 95% confidence interval when the dependence upon the proportion from TPO is considered, therefore clearly confirming the validity of the experimental results acquired in the study and our previous study. The method has good adaptability in the morphology discrimination of cokes from commercial delayed cokers and a pilot plant. Furthermore, it seems that the distribution map of cokes could be used to quantitatively characterize the morphology of cokes acquired from commercial cokers and pilot units in the laboratory as we expected.

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Figure 8. Overall OTI of cokes from commercial delayed cokers and a pilot coking unit as a function of the proportion from TPO. The results from Chen et al.17 are shown for comparison (● and ▼).

AUTHOR INFORMATION

Corresponding Authors

*Telephone: +86-532-8698-1851. Fax: +86-532-8698-1787. Email: [email protected]. *Telephone: +86-532-8698-4615. Fax: +86-532-8698-1787. Email: [email protected].

Seven other thermal cokes and a carbon black from the research by Chen et al.17 have also been added to Figure 8 for comparison. As shown in Figure 8, there is a fairly good linear dependency of OTI upon the proportion from TPO (correlation coefficient of 0.984). The correlation coefficient is a little bit lower than that from Chen et al.17 Nevertheless, as shown in Figure 8, all of the results obtained in the study and from Chen et al.17 fall within a 95% confidence interval when the dependence upon the proportion from TPO is collectively considered, therefore clearly confirming the validity of the experimental results acquired in the study and our previous study. In Figure 8, the four commercial shot cokes lie in section A with the OTI range of 10−12.25. A thermal coke derived from asphaltenes is also located in this area, which indicates that, of all of the saturates, aromatics, resins, and asphaltenes (SARA)

Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China (Grant U1362101), the Fundamental Research Funds for the Central Universities, the China National Petroleum Corporation (CNPC) Foundation under the Grant “Research and Development for Commercial Application of Novel Technologies in Processing Inferior Heavy Oil” (PRIKY15002, and PRIKY15009), and the Natural Science Foundation of Shandong Province, China (ZR2014BQ030). The anonymous reviewers are also gratefully acknowledged for the effort and help in the reviewing process. F

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DOI: 10.1021/ef502452r Energy Fuels XXXX, XXX, XXX−XXX