Scheme for Hydrotreatment of Fluid Catalytic Cracking Decant Oil with

Sep 20, 2016 - Earth and Mineral Sciences (EMS) Energy Institute and Department of Energy and Mineral Engineering, The Pennsylvania State University, ...
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Scheme for Hydrotreatment of Fluid Catalytic Cracking Decant Oil with Reduced Hydrogen Consumption and High Needle Coke Yield upon Carbonization Joseph P. Abrahamson, Ronald T. Wincek, and Semih Eser* Earth and Mineral Sciences (EMS) Energy Institute and Department of Energy and Mineral Engineering, The Pennsylvania State University, 114A Hosler Building, University Park, Pennsylvania 16802, United States ABSTRACT: Two decant oils with different sulfur contents and their vacuum distillation fractions were hydrotreated in a fixedbed flow reactor to produce a feed with sufficiently low sulfur content for needle coke production. Products from hydrotreatment were subsequently carbonized in a tubing bomb reactor to characterize the carbonaceous mesophase development seen in the resulting semicoke. Although the purpose of the hydrotreatment is to reduce sulfur content, hydrogenation of aromatic compounds also takes place during the treatment, thus increasing the hydrogen consumption. Modest hydrogenation of decant oil from the hydrotreatment improved the mesophase development but resulted in a significant decrease of the semicoke yield upon carbonization of the treated product. As a remedy to conserve hydrogen during hydrotreatment and achieve higher coke yields in the subsequent carbonization, only the middle fraction from vacuum distillation of the decant oil was hydrotreated and blended back with the vacuum bottoms to simulate the coker feed. This scheme was successful to attain the desirable sulfur reduction in the feedstock without the penalty of a reduced coke yield upon carbonization or useless hydrogen consumption.

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INTRODUCTION When decant oil (DO) from a fluid catalytic cracker (FCC) undergoes carbonization in a delayed coker, it produces a premium-grade coke known as needle coke. Needle coke is highly graphitizable and is the primary filler used in the production of graphite electrodes for electric-arc furnaces. When the sulfur content of needle coke is higher than a threshold level, an irreversible volume expansion (puffing) has been observed when cokes are subject to graphitization heat treatment. The volume expansion reduces the strength and conductivity of the graphite electrodes. Puffing in needle coke results from the explosive evolution of sulfur in the form of CS2 and H2S in a narrow temperature window during graphitization heat treatment.1,2 Puffing has typically been observed in needle cokes containing greater than 0.8 wt % sulfur.3 Therefore, the sulfur content in needle coke used for the production of graphite electrodes has historically been limited to less 0.8 wt %.4 More recently, needle coke producers have elected to attain a conservative limit of 0.5 wt % sulfur in coker feeds.5 Several techniques have been proposed to inhibit puffing, including the addition of metal oxides to cokes before the graphitization heat treatment. The metal provides a bonding site for evolving sulfur to form sulfides and, therefore, inhibits puffing because metal sulfides decompose more slowly at higher temperatures during the graphitization heat treatment. Posttreatment techniques, such as metal addition and hydrodesulfurization (HDS), of solid needle coke are costly options.6 A more reasonable approach is to start with sufficiently lowsulfur-content DO feed. However, the trend of processing heavy and sour crude oils has reduced the availability of lowsulfur DO from the operating refineries.5 The average sulfur weight percent and production of DO by the refineries in different regions of the U.S.A. are given in Table 1.5 © XXXX American Chemical Society

Table 1. U.S. FCC DO Sulfur Content and Production by Region region

production (%)

sulfur (wt %)

Gulf Coast Inland U.S. West Coast East Coast

49 25 14 12

2.1 2.2 1.1 2.0

Hydrogenation (HYD) is an unavoidable side reaction that occurs during HDS. There is a strong relationship between carbonaceous mesophase development and the aromatic/ aliphatic hydrocarbon ratio in delayed coking feedstocks.7 Therefore, HYD during HDS should be kept to a minimum to preserve the hydrogen aromaticity of FCC DOs and reduce hydrogen consumption. Recent publications have presented results from studies on a laboratory-scale hydrotreatment of two DO samples8 and catalyst preparation for the optimum hydrotreatment operation to selectively target the large sulfurcontaining compounds for sulfur removal.9 These studies have shown that it is possible to reduce the sulfur contents of FCC DO to the desired levels by hydrotreatment with correct selection of catalysts and the operation conditions. Both studies have also indicated that HYD of polyaromatic hydrocarbons (PAHs) as a side reaction during hydrotreatment reduces the coke yield from the hydrotreated product. The objective of this study is to investigate the development of a HDS scheme for needle coke feedstocks to achieve the desirable sulfur reduction without compromising coke quality or coke yield from the hydrotreated product. Received: June 14, 2016 Revised: August 24, 2016

A

DOI: 10.1021/acs.energyfuels.6b01443 Energy Fuels XXXX, XXX, XXX−XXX

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of the process scheme used in this study to conserve hydrogen and maximize the semicoke yield is displayed in Figure 1.

EXPERIMENTAL SECTION

Needle Coke Feedstocks. Two FCC DOs, DO-HS-P and DOLS-P, representing high (HS, 2.5 wt %) and low (LS, 0.9 wt %) sulfur content DOs, respectively, were selected for this study, where the P in DO-HS-P and DO-LS-P is used to identify these oils as the parent oils. In addition to the DOs, their vacuum distillation fractions were also evaluated. DOs were separated into fractions using a simple vacuum distillation setup with accordance to ASTM D1160-03 (Standard Test Method for Distillation of Petroleum Products at Reduced Pressure). To avoid unwanted thermal cracking, temperatures were kept well below the cracking temperature of 350 °C. The vacuum was maintained at 5 mmHg. Atmospheric equivalent cut points of 385 and 490 °C were chosen to separate the light fraction, comprised mainly of two−three-member PAHs, from the middle fraction and the vacuum bottoms (VBs). The middle fractions believed to consist of mainly of four−five-member PAHs11 were hydrotreated and used as needle coke feedstock for experimental purposes. VBs were not hydrotreated to conserve the desired properties of the VBs that result in an increase in the coke yield.11 The light fraction is comprised of compounds with boiling points below 385 °C; the middle fraction contains compounds with boiling points between 385 and 490 °C; and the VBs are compounds with boiling points in excess of 490 °C. The VBs were ground down and blended with treated middle fractions at a ratio of 1 part VBs to 4 parts treated middle fraction comprising the coker feed. The 1:4 ratio was selected from a material balance and results from gas chromatography simulated distillation (GC Sim Dis) with reference to ASTM D2887-14 (Standard Test Method for Boiling Range Distribution of Petroleum Fractions by Gas Chromatography). Distillation yields from a material balance and GC Sim Dis results are given in Table 2.

Figure 1. Flow diagram displaying the scheme used to maximize the coke yield while reducing hydrogen consumption. This scheme takes advantage of the relatively high desulfurization activity of the middle fractions. The middle fractions are far more active toward desulfurization than the parent oils as previously reported.9 This may be because the polyaromatic sulfur compounds in the middle fraction, such as four-member benzonaphthothiophenes and five-member condensed thiophenes, are readily desulfurized, while the di- and trimethyldibenzothiophenes found in the light fraction are more refractory. Additionally, hydrotreating the light fraction is an inefficient way to reduce the resulting needle coke sulfur content, considering that the large sulfur compounds found in DO are incorporated into coke in larger proportions than smaller sulfur compounds upon carbonization. Therefore, removing sulfur from larger ring systems in DOs is the most effective way of reducing the needle coke sulfur content. However, the VBs, containing the heaviest sulfur compounds, were not hydrotreated to conserve the desired properties of the VBs that result in an increase in the coke yield.12 The desired sulfur limit of the coker feed can be meet without treating the VBs because they are blended at a ratio of 1:4 with treated middles that are readily desulfurized. 1 H NMR. The extent of HYD of the DO compounds during hydrotreatment was measured by analyzing the hydrogen functionality with 1H NMR. 1H NMR data for parent oils, fractionated oils, and HDS products were collected on a Bruker DRX 400 spectrometer. Peak assignments are given in Table 4.

Table 2. Distillation Fraction Percent Yields DO-HS-P light fraction middle fraction VBs

DO-LS-P

distillation

Sim Dis

distillation

Sim Dis

32 53 15

35 54 11

23 58 19

20 62 18

As seen in Table 2, the material balance and GC Sim Dis data are in accordance. These data confirm that vacuum distillation achieved good separation of the molecular constituents. Sulfur weight percent and hydrogen aromatic content as measured by proton nuclear magnetic resonance (1H NMR) are given in Table 3 for both parent oils and their vacuum distillation fractions. Process Scheme. As the trend of processing sour crude oils continues, needle coke produced from DO will require processing to lower the sulfur content to avoid unwanted puffing of the graphite electrode during graphitization. Although the purpose of the hydrotreatment is to reduce the sulfur content, HYD of aromatic compounds also takes place during the treatment, thus increasing the hydrogen consumption. Modest HYD of DO from hydrotreatment improves mesophase development but results in a significant decrease of the semicoke yield upon carbonization of the treated product. As a remedy to conserve hydrogen during hydrotreatment and achieve higher coke yields in the subsequent carbonization, only the middle fraction from vacuum distillation of the DO was hydrotreated and blended back with the VBs to simulate the coker feed. A flow diagram

Table 4. 1H NMR Peak Assignments chemical shift (ppm)

functional group

0 0.5−1.1 1.1−1.7 1.7−2.0 2.0−2.4 2.4−3.5 3.5−4.5 4.5−6.0 6.0−9.3

tetramethlysilane CH3 γ to the ring or further or paraffinic CH2 β and CH3 β to the ring hydroaromatic CH3 α to the ring CH and CH2 α to the ring CH2 α to two rings (bridge) olefinic aromatic

Table 3. Sulfur and Aromatic Contents of Oils and Distillation Fractions LS sulfur (wt %, ±0.07) 1 H NMR aromatic signal (%)

HS

parent

light fraction

middle fraction

VBs

parent

light fraction

middle fraction

VBs

0.94 23.2

1.06 22.8

0.87 22.3

1.05 23.7

2.51 29.0

2.19 28.9

2.85 28.1

1.98 29.3

B

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Energy & Fuels Peak assignments were adapted from Rodriguez et al.10 Data were processed using Bruker Topinspin 2.1 software. Gas Chromatography−Mass Spectrometry (GC−MS). The samples were analyzed using a Shimadzu GC-17A gas chromatograph and a QP-5000 mass spectrometer with reference to United States Environmental Protection Agency (U.S. EPA) method 8270C. Additional details have been previously reported.8 Hydrotreatment. Oils were hydrotreated in a fixed-bed flow reactor. The experimental matrix included two temperatures (350 and 400 °C) and two hydrogen pressures (3.45 and 6.89 MPa) and were maintained at a liquid hour space velocity of 1.0 h−1. Additional details and experimental procedures have previously been reported.8,9 Total Sulfur Analysis. The total sulfur contents for parent oils, fractioned oil products, and HDS products were analyzed for the total sulfur content. A model SC 144-DR sulfur−carbon analyzer manufactured by Leco Corporation was used to determine the sulfur content. Carbonization of Needle Coke Feedstocks. Semicoke production permits the evaluation of the feedstocks relative propensity to yield anisotropic domains during carbonization. Tubing bomb reactors were filled with 4 g of feedstock and purged of oxygen with a nitrogen manifold prior to being plunged into a preheated fluidized sand bath. Carbonization experiments were carried out at 500 °C for a duration of 5 h. After carbonization, semicoke bars were extracted and washed with dichloromethane to remove any liquid product. The carbonization experiments and sample extraction were adapted from Eser and Wang.11 Optical Texture Index (OTI) Evaluation. Semicoke bars were mounted in epoxy longitudinally and polished in preparation for polarized reflected light microscopy. Evaluation was performed using a Nikon Microphot-FXAII microscope. An overall OTI was calculated on the basis of the abundance of four different optical textures as previous reported.8 The OTIs were developed specifically for the evaluation of needle cokes because needle cokes contain a larger proportion of anisotropy in the form of flow domains and domains compared to metallurgical cokes.7 Higher OTIs are assigned to flow domain and domain designations to emphasize the significance of the microstructural anisotropy of needle cokes.

Table 6. Semicoke Percent Yields from Carbonization at 500 °C for 5 h

RESULTS AND DISCUSSION Semicoke Yields. In the manufacture of needle coke from DOs, a large coke yield is desired. As observed from carbonization of parent oils and their middle distillates, semicoke yields between parent oils and middle fractions were nearly the same, with yields typically between 44 and 50 wt % of the carbonization feedstock. The VBs, as expected, as a result of their high molecular weight and low volatility, produce the largest semicoke yield, converting 64 wt % of the carbonization feedstock to semicoke. The yields from parent oils, middle fractions, and VBs are given in Table 5. Table 5. Semicoke Percent Yields from Carbonization at 500 °C for 5 h parent oils (±3.0)

middle fractions (±3.0)

VBs (±3.0)

LS HS

49.1 44.5

49.8 44.3

64.7 63.8

treated middles (±3.0)

treated middles blended with VBs (±3.0)

LS-A-350-3.45 LS-B-350-3.45 LS-A-400-3.45 LS-B-400-3.45 LS-A-350-6.89 LS-B-350-6.89 LS-A-400-6.89 LS-B-400-6.89

43.6 45.3 43.9 44.8 36.3 38.7 37.4 39.8

49.4 53.6 47.2 47.9 46.1 48.5 41.3 42.9

catalysts supported on γ-alumina. Catalyst B has an average pore diameter nearly twice that of catalyst A, with 86% of the internal pore diameters between 12 and 16 nm, whereas 81% of pore diameters in catalyst A range between 5 and 10 nm. Additional details regarding catalyst properties and activity have been previously reported.9 The second column in Table 6 represents the semicoke yield from hyrotreated middle fractions, and the last column is the semicoke yield from hydrotreated middles blended back with VBs at a ratio of 4:1. The coke yield from the blends is greater than the linear combination of the treated oils and VBs. Therefore, the incorporation of the large VB compounds must react with the lighter compounds from the treated oils that may have escaped mesophase and ended up in the liquid product without VB addition. It was demonstrated by Eser and Wang11 that VBs have a high rate of carbonization and produced a welldeveloped mesophase. Therefore, it is presumed that, by adding in VBs, the rate of mesogen formation is increased and lighter compounds are incorporated into the resulting mesophase before evaporating out of the reaction medium. The extent of HYD of DOs during hydrotreatment was determined by the 1H NMR signal reduction from the aromatic hydrogen region (6−9.3 ppm). This approach assumes that the observed decrease in the aromatic hydrogen content comes solely from HYD of the aromatic rings, ignoring any possible catalytic cracking and coke deposition onto the catalyst. It was observed that the decrease in the aromatic signal is largely accounted for by the increase in the hydroaromatic signal (1.7− 2.0 ppm). Around 90% of the hydrogenated aromatics end up in the hydroaromatic region. The remaining hydrogenated product is in the form of naphthenic structures and observed by the small signal increase between 1.1 and 1.6 ppm. There was no recognizable increase in signal between 0.5 and 1.1 ppm (aliphatic CH3 or CH2 attached γ or further to the ring and paraffinic compounds). It can, therefore, be inferred that hydrocracking was not prevalent during the hydrotreatment of samples. This trend is illustrated by 1H NMR spectra in Figure 2 for both untreated and hydrotreated DO-HS-P, where the peak at 1.59 ppm is from water that was found in the deuterated chloroform solvent. HYD increased most drastically with an increasing hydrogen pressure, whereas an increasing reaction temperature slightly suppressed HYD, because HYD is less favorable thermodynamically during high-temperature HDS as a result of aromatic stability.13 An increase in HYD directly results in a decreased semicoke yield, as displayed in Figure 3, where HYD as displayed was measured by the aromatic signal decrease from 1 H NMR spectra.

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sample

sample

Hydrotreating DO results in a decreased coke yield and is dependent upon the extent of HYD, as displayed in Table 6 for the LS feedstock. Yields from the HS feedstock, not shown in Table 6, are similar and follow the same trend. The first column in Table 6 designates the feed and conditions used during hydrotreatment, where A and B are different catalysts followed by the temperature in degrees Celsius and hydrogen pressure in megapascals. Both catalysts A and B are CoMo-active metal C

DOI: 10.1021/acs.energyfuels.6b01443 Energy Fuels XXXX, XXX, XXX−XXX

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HYD measured by integrating 1H NMR curves is semiquantitative in nature. To combat the decreased yield, the hydrotreated middle fraction was blended with VBs. VBs were not hydrotreated to conserve the desired properties of the VBs that result in an increase in the coke yield.11 The VBs were ground down and blended with treated middle fractions at a ratio of 1 part VBs to 4 parts treated middle fraction comprising the coker feed. This scheme greatly increased yields from the hyrotreated oils, as displayed in Table 6. Therefore, one could efficiently achieve sufficiently high semicoke yields from feeds that require hydrotreating to reduce the sulfur content for use as needle coke feestocks while maintaining the desired sulfur levels. Semicoke Quality as Measured by OTI. Samples that underwent a higher degree of mesophase development will have higher textural anisotropy as measured under a polarized light microscope. The low-sulfur DO produced semicokes with higher OTIs than those derived from the high-sulfur DO, given in Table 7. Comparing the bulk characteristic of the DOs or their distillate fractions, such as hydrogen functionality, is not the most informative way to deduce carbonization reactivity and the resulting mesophase development. It is the individual molecular species and concentrations that govern the extent of mesophase development.14 Chromatographic methods have been previously employed by several researchers to identify relationships between molecular constitution of feedstocks and the resulting mesophase development. The common finding is that feeds with an abundance of pyrene and methyl-substituted pyrenes produce premium-quality needle cokes.15,16 Pyrenes function as hydrogen shuttlers during carbonization and act as good solvents to extend the fluidity of the reaction medium. Although the GC-amenable fraction of the oils is rather small, the two−four-member PAHs are well-resolved, and the concentrations of the resolved compounds are displayed in Figure 4.

Figure 2. 1H NMR spectra from both hydrotreated and untreated DO.

Figure 3. Semicoke yield as a function of HYD.

Table 7. Coker Feedstock Treatment Conditions, Properties, and Resulting Semicoke Yield and Quality feedstock HS-P HS-M HS-VB HS-M HS-M HS-M HS-M HS-B HS-B HS-B HS-B LS-P LS-M LS-VB LS-M LS-M LS-M LS-M LS-B LS-B LS-B LS-B

HDS reactor temperature (°C)

HDS reactor pressure (MPa)

hydrogen aromatic reduction (%)

350 400 350 400 350 400 350 400

3.45 3.45 6.89 6.89 3.45 3.45 6.89 6.89

14.8 14.1 33.7 28.8

350 400 350 400 350 400 350 400

3.45 3.45 6.89 6.89 3.45 3.45 6.89 6.89

15.0 14.5 29.7 27.4

D

coker feed sulfur (wt %, ±0.07)

coke yield (%, ±3.0)

OTI (±2.0)

2.51 2.85 1.98 0.44 0.13 0.43 0.11 0.75 0.50 0.74 0.48 0.94 0.87 1.05 0.39 0.07 0.38 0.04 0.52 0.27 0.51 0.24

44.5 44.3 63.8 40.0 40.3 29.1 30.3 53.1 50.3 43.5 44.4 49.1 49.8 64.7 45.3 44.8 38.7 39.8 53.6 47.9 48.5 44.1

76.9 80.1 84.7 88.9 87.1 85.0 85.0 87.8 91.2 87.6 87.7 88.0 88.7 84.4 90.8 89.8 86.5 87.3 88.6 88.0 87.0 91.0

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captured in a polarized light micrograph are displayed in Figure 6.

Figure 4. Two−four-member PAH concentrations from parent DOs.

Both Filley and Eser15 and Wang and Eser16 report that OTI increases with increasing pyrene/phenanthrene ratios. The pyrene/phenanthrene ratios of DO-LS-P and DO-HS-P are 0.83 and 0.46, respectively. The middle distillation fractions produced a higher extent of mesophase development than the parent oils. The increase is more noticeable in the high-sulfur oil as expected because the phenanthrene reduction from parent oil to middle fraction is greater for this oil. Increasing the molecular weight of the coker feed from middle fractions to VBs further increases the OTI in the high-sulfur oil. However, the VBs have a lower OTI than the middle fraction from the LS DO. The OTIs are the same for VBs from both oils. It is possible that the structures contained in these high-boilingpoint fractions are more uniform than that of the lowmolecular-weight compounds attributing to the similar OTI. Mesophase and OTI have a steady increase (although slight) with HYD, up until HYD exceeds a 20% hydrogen aromatic reduction. OTI begins to drop off beyond 20% HYD, as displayed in Figure 5. The initial increase in OTI with HYD can be explained by the presence of additional hydrogen. Additional hydrogen will slow the carbonization rate and allow for further mesophase development.17,18 The slower reaction rate of the treated feedstock is evident by the presence of mesophase spheres and isotropic pitch in the semicoke samples. Mesophase spheres

Figure 6. Polarized light micrograph of mesophase spheres from carbonization of DO-HS-P-A-400-3.45 for 5 h at 500 °C.

The OTI reduction as a result of excessive HYD can be attributed to the formation of hydroaromatics and naphthenic compounds that lack planarity desired for mesophase development. Additionally, the removal of sulfur from condensed thiophenes creates free rotation about a single bond. The carbonization of PAHs exhibiting free rotation, such as biphenyls, results in a poorly developed mesophase.19,20 The flexible σ bonds created by HYD may result in cross-linking between mesogens during mesophase development as a result of their high carbonization reactivity.21 Such cross-liking between sheets will reduce the fluidity and the resulting OTI. OTIs are given in Table 7, where feedstock nomenclature in Table 7 uses P for parent oil designation, M for middle fractions, VB for vacuum bottoms, and B to represent the 4:1 blend of treated middles and VBs. Semicokes produced from hydrotreated oils in Table 7 were processed over catalyst B,9 at varying temperatures (350 or 400 °C) and hydrogen pressures (3.45 or 6.89 MPa) as given in the table. The extent of HYD as measured by the 1H NMR aromatic signal reduction is also listed in Table 7 for treated feeds. The blended feed 1H NMR aromatic signal reduction is not listed because the VBs used in the blend are untreated and blended with the treated middles already documented in the table. The addition of VBs, which are known to have a high rate of carbonization, in the blended feeds have less quantity of isotropic pitch and mesophase spheres. Figures 7 and 8 display a few polarized light micrographs used to assign the OTIs in Table 7, HS-P and HS-B-400-3.45, respectively, where the light purple regions around the pores (black areas) in Figure 7 is

Figure 7. Polarized light micrographs of semicoke produced from HSP.

Figure 5. OTI plotted against the HYD extent. E

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and second, it uses the desired properties of the VBs that result in an increase in the coke yield and quality. The sulfur content of the blend should be below 0.5 wt % to meet the low-sulfur standards of the needle coke industry, and the middle fraction is readily desulfurized in comparison to the parent oils. Therefore, one could efficiently achieve a high yield of semicoke with good texture quality and meet the limit on sulfur content while reducing hydrogen consumption.

Figure 8. Polarized light micrographs of semicoke produced from HSB-400-3.45.

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representative of liquid pitch. No appreciable pitch is present in the semicoke in Figure 8 that was produced from a blend of treated middles and VBs. The addition of VBs to treated feedstock typically results in an increased OTI. As previously mentioned, the low-sulfur DO produced semicokes with higher OTIs than those from the high-sulfur DO; however, this trend is less noticeable from the middle and treated middle fraction. Furthermore, upon comparison of semicoke quality produced from treated middles blended with VBs, the quality is nearly the same between the low- and high-sulfur DOs. Therefore, by employing the process scheme illustrated in Figure 1 to needle coke feedstocks that require HDS, one can increase both quality and yield while conserving hydrogen consumption. Operating Conditions. As displayed in Table 7, an increase in the temperature from 350 to 400 °C (with everything else being the same) results in a greater sulfur reduction and suppression of HYD in all cases. The observed reduction of HYD with an increased temperature is not surprising considering that the reaction is exothermic and restricted by thermodynamic equilibrium and resonance stabilization of the PAHs under high temperatures. Farag et al.13 reported similar findings that there is little formation of hydrogenated compounds from HDS of 4,6-dimethyldibenzothiophene over CoMo supported on Al2O3 when temperatures are in excess of 380 °C. The effect of increasing hydrogen pressure from 3.45 to 6.89 MPa also increases HDS activity, albeit small in comparison to the effect of an increasing temperature, and is accompanied by a substantial increase in HYD. Any added sulfur reduction brought about by an increase in hydrogen pressure is quite small, and it would appear that pressures above 3.45 MPa are not needed for desulfurization of DO. Additionally, an increasing hydrogen pressure results in a sharp increase in HYD. Therefore, a high reaction temperature (400 °C) and low hydrogen pressure (3.45 MPa) are the preferred operating conditions to limit the undesirable HYD of aromatic ring systems. Using the preferred HDS conditions in the process scheme highlighted will increase the available DOs that can be used as low-sulfur feedstock for needle coke production. The success of this scheme is best shown by the bolded result in Table 7, where the HS middle fraction was hydrotreated with high-temperature and low-hydrogen-pressure conditions prior to being blended with untreated VBs and carbonized. The semicoke product was produced in yields greater than 50%. The high yield semicoke product possesses superior quality as gleaned by polarized light microscopy and reported by the OTI in Table 7. The coker feed used to produce the high-yielding high-quality semicoke meets the lowsulfur requirement for needle coke production.

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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REFERENCES

(1) Noda, T.; Kamiya, K.; Inagaki, M. Bull. Chem. Soc. Jpn. 1968, 41, 485. (2) Fujimoto, K.; Mochida, I.; Todo, Y.; Oyama, T.; Yamashita, R.; Marsh, H. Carbon 1989, 27, 909. (3) Brandtzaeg, S.; Oye, H. Carbon 1988, 26, 163. (4) Swain, E. Oil Gas J. 1991, 89, 49. (5) Guercio, V. Oil Gas J. 2010, 108, 96. (6) Mochida, I.; Nakamo, S.; Oyama, T.; Nesumi, Y.; Todo, Y. Carbon 1988, 26, 751. (7) Eser, S.; Jenkins, R. G. Carbon 1989, 27, 889. (8) Wincek, R. T.; Abrahamson, J. P.; Eser, S. Energy Fuels 2016, 30, 6281. (9) Abrahamson, J. P.; Wincek, R. T.; Eser, S. Energy Fuels 2016, 30, 7173. (10) Rodriguez, J.; Tierney, J. W.; Wender, I. Fuel 1994, 73, 1870. (11) Eser, S.; Wang, G. Energy Fuels 2007, 21, 3573. (12) Gilbert, W. R. Fuel 2014, 121, 65. (13) Farag, H.; Whitehurst, D.; Sakanishi, K.; Mochida, I. Catal. Today 1999, 50, 9. (14) Liu, Y.; Eser, S.; Hatcher, P. G. Prepr. Pap.Am. Chem. Soc., Div. Fuel Chem. 1992, 37, 1227. (15) Filley, R.; Eser, S. Energy Fuels 1997, 11, 623. (16) Wang, G.; Eser, S. Energy Fuels 2007, 21, 3563. (17) Eser, S.; Jenkins, R. G. Carbon 1989, 27, 877. (18) Yang, J.; Stansberry, P. G.; Zondlo, J. W.; Stiller, A. H. Fuel Process. Technol. 2002, 79, 207. (19) Walker, P. L., Jr Carbon 1990, 28, 261. (20) Eser, S. Carbonaceous mesophase formation and molecular composition of petroleum feedstocks. In Supercarbon: Synthesis, Properties and Applications; Yoshimura, S., Chang, R., Eds.; SpringerVerlag: Berlin, Germany, 1998; Vol. 33, p 147, DOI: 10.1007/978-3662-03569-6_12. (21) Mochida, I.; Korai, Y.; Oyama, T.; Nesumi, Y.; Todo, Y. Carbon 1989, 27, 359.

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CONCLUSION The scheme of hydrotreating only the middle fractions and then blending the treated middle fractions back with VBs serves two purposes: first, the process conserves valuable hydrogen, F

DOI: 10.1021/acs.energyfuels.6b01443 Energy Fuels XXXX, XXX, XXX−XXX