Fluid Catalytic Cracking Study of Coker Gas Oil ... - ACS Publications

Dec 17, 2013 - (3) It is mainly upgraded by hydrocracking and the fluid catalytic cracking (FCC) process. In China, because of the lack of hydrocracki...
0 downloads 0 Views 810KB Size
Download PDF
Article pubs.acs.org/EF

Fluid Catalytic Cracking Study of Coker Gas Oil: Effects of Processing Parameters on Sulfur and Nitrogen Distributions Jinhong Zhang, Honghong Shan,* Xiaobo Chen, Wenjing Liu, and Chaohe Yang* State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Qingdao, 266580, People’s Republic of China S Supporting Information *

ABSTRACT: To investigate the effects of operating conditions and the catalyst activity on the transfer regularity of sulfur and nitrogen during the cracking process of coker gas oil (CGO), the CGO was catalytically cracked in a pilot-scale riser fluid catalytic cracking (FCC) apparatus at different test environments. Then the cracked liquid products were analyzed for sulfur and nitrogen distributions with boiling point, from which the sulfur and nitrogen concentrations of gasoline, light cycle oil (LCO), and heavy cycle oil (HCO) fractions were determined. The sulfur and nitrogen compounds in each product cut, and their possible reaction pathways were reviewed and discussed. The results show that sulfur-containing species are easier to crack but more difficult to be removed from the liquid product, while nitrogen compounds are easier to form coke, then be removed from the liquid product. The sulfur distribution of CGO is different from that of conventional feedstocks. Different processing parameters can significantly affect the sulfur and nitrogen distribution yields and concentrations in liquid products. Increasing the reaction temperature and the catalyst-to-oil ratio as well as shortening the residence time cannot only increase the light oil yield but also improve the product quality and reduce the SOx and NOx emissions in the regenerator.

1. INTRODUCTION Delayed coking, as an important residue upgrading process, becomes more popular in the current refining scenario due to the deterioration of crude qualities, the lower price of heavy crudes, and the flexibility of the delayed coking process to handle different inferior feedstocks.1 Recently, the processing capacity of coking process sharply increased in China. In 2010, it had reached as high as 110 million tons.2 Coker gas oil (CGO) is a major product of the delayed coking process, which accounts for 20−30 wt % in the product distribution.3 It is mainly upgraded by hydrocracking and the fluid catalytic cracking (FCC) process. In China, because of the lack of hydrocracking units and its high operating costs, the more attractive way is using FCC units to upgrade CGO.4−7 However, directly blending CGO into conventional FCC feedstocks will cause four main problems. The first one is the inferior crackability of CGO, due to its low hydrogen content, high aromatic and nitrogen contents, especially basic nitrogen content. The poisoning effect of basic nitrogen compounds on cracking catalysts has been discovered for several decades,8−11 which led to the development of catalysts with higher nitrogen tolerance.12−15 Li et al.16 reported that the nonbasic nitrogen compounds and condensed aromatics in CGO also could be easily adsorbed on catalysts, leading to the pore blocking. Thus, the decrease of feed conversion and light oil yield as well as higher coke yield can be seen when cracking CGO at conventional FCC operating conditions. Increasing the reaction temperature and the catalyst-to-oil ratio, shortening the reaction time, as well as improving the catalyst activity could help to resolve this problem, which has been reported in our previous work.7 The nitrogen-containing compounds and condensed aromatics in CGO are easier to adsorb on the catalyst acid sites than other hydrocarbons in AGO or VGO, which will significantly © XXXX American Chemical Society

reduce the activity and selectivity of the catalyst. Thus, the blending of CGO would remarkably impede the cracking of other feedstocks, which is the second problem. To resolve this problem, the denitrified catalytic cracking (DNCC) process,17 the two-stage riser (TSR) FCC process,18 the divisional fluid catalytic cracking (DFCC) process,6 and the two-stage synergistic (TSS) FCC process7 have been proposed by adding a separate reaction zone for CGO cracking. The third problem is caused by the transfer of sulfur and nitrogen from the feed to products, leading to the poor product quality. Sulfur in transportation fuels is of particular concern to society mainly due to the air pollution caused by SOx and its poisoning effect on automotive catalytic converters.19 By contrast, nitrogen receives less environmental attention. However, nitrogen compounds can affect product stability. Moreover, the poisoning effect of nitrogen compounds on the hydrodesulfurization catalysts20,21 and FCC catalysts may pose challenges to further upgrade the gasoline, diesel, and heavy cycle oil (HCO) by hydrorefining or FCC processes. Thus, it is very important to study the sulfur and nitrogen levels in feeds and products during the FCC process22 and learn the effects of operating conditions and catalysts on distributions of sulfur and nitrogen in liquid products, especially for the catalytic cracking of CGO or other feedstocks which have higher sulfur and nitrogen contents. However, little work has been focused on it. Previous work showed that,23 in the FCC process, 35−45% of the feed sulfur is converted into H2S, and 50−60% appears in the liquid products, while only 2−5% forms coke. By contrast, about half of the feed nitrogen remains in the liquid products, and most of the rest presents in the coke, while less than 10% is converted Received: October 8, 2013 Revised: November 30, 2013

A

dx.doi.org/10.1021/ef401990s | Energy Fuels XXXX, XXX, XXX−XXX

Energy & Fuels

Article

catalysts can be found in the literature7 or Tables S1 and S2 in the Supporting Information. The proposed three enhancing schemes for CGO cracking were carried out in a pilot scale riser FCC apparatus which has been described previously.34 This unit can be operated continuously similar to the commercial units. Moreover, the experimental results are consistent with the industrial data, and it has afforded the design data for several commercial plants. In the study, the conversion was defined as the total yield of dry gas, liquefied petroleum gas (LPG), gasoline, light cycle oil (LCO), and coke. Schemes I, II, and III corresponding to the high reaction temperature and CTO with short residence time scheme (T, 500−580 °C; CTO, 6− 16 w/w; t, 0.8 s; catalyst A), the long residence time scheme (T, 500− 540 °C; CTO, 6−9 w/w; t, 3.0 s; catalyst A), and the high catalyst activity with short residence time scheme (T, 500−575 °C; CTO, 6−13 w/w; t, 0.8 s; catalyst B), respectively. The detailed reaction conditions and yield structures for each test have been described elsewhere.7 The product distribution of different processing schemes can also be found in Figure S1 in the Supporting Information. 2.2. Product Analysis. The total liquid product (TLP) collected were fractionated by the true boiling point distillation to separate the gasoline (GN, IBP−204 °C), light cycle oil (LCO, 204−350 °C), and heavy cycle oil (HCO, >350 °C) fractions (ASTM D2892 method). The sulfur and nitrogen concentrations of gasoline and LCO were determined on a Multi EA-3100 S/N micro analyzer, while that for HCO were measured by a VARIO EL-III CHNS/O element analyzer. The sulfur distribution yields in product cuts can be calculated by

into NH3. Ng et al.22 studied the influences of feedstocks (two kinds of hydrotreated oil and a VGO) and catalysts on the distributions of sulfur and nitrogen in cracked products. Their results showed that the order of sulfur or nitrogen concentrations in products corresponded to that in the feedstocks and the hydrogen transfer ability of the catalysts. Yuan et al.24 reported that the reaction conditions could significantly influence the nitrogen distribution in products. Research found that both thiophene, benzothiophene, and short chain alkylthiophenes are not very reactive under FCC conditions.19,25−27 However, CGO is the deep thermal cracking intermediate product of residues which usually contain a certain amount of thiophenic sulfur compounds. Thus, it can be inferred that the sulfur compounds in CGO are more likely to be benzothiophene/dibenzothiophene or alkylbenzothiophenes/alkyldibenzothiophenes with shorter chains, which are difficult to be cracked. Moreover, in the CGO cracking process, the higher amount of nitrogen compounds and condensed aromatics will compete for acid sites with thiophenic sulfur compounds. Therefore, measures should be taken to enhance the CGO cracking and study the cracking behavior of sulfur and nitrogen compounds in CGO under different operating conditions. It is well-known, in the FCC process, a certain amount of feed sulfur and nitrogen will deposit on the coke and be oxidated into SOx and NOx in the regenerator. The higher concentrations of sulfur and nitrogen, as well as the higher contents of thiophenic sulfur and basic nitrogen compounds in the feed, the higher the percentage of feed sulfur and nitrogen existing in the coke.28−30 Thus, when processing inferior feedstocks with higher sulfur and nitrogen contents, the FCC regenerator poses a challenge to the increasingly strict environmental regulations for controlling SOx and NOx emissions, which is the fourth problem. Research found that, in addition to the nature of the feed, the coking conditions, the design of the regenerator, and the amount of excess O2 or CO promoter added can significantly affect the concentrations of SOx and NOx in flue gases.23,28,31−33 Thus, choosing the appropriate operating conditions can help to reduce pollutants. In the previous work,7 on the basis of the industrial operation and operating convenience, we proposed three methods to enhance the catalytic conversion of CGO, which are increasing the reaction temperature and catalyst-to-oil ratio (CTO) while shortening the residence time, prolonging the residence time, and adding more fresh catalysts into the catalyst system to increase the catalyst activity. The results indicated that different processing schemes could significantly influence the reaction pathways and the product distribution. The present work covers the product quality with emphasis on the distributions of sulfur and nitrogen in liquid products and shows a better knowledge about the conversion chemistry of sulfur and nitrogen compounds in CGO under different processing schemes, in view of a possible improvement of the FCC process. Besides, the combustion behavior of sulfur and nitrogen in coke was studied by the temperature programmed oxidation-mass spectrometry (TPO-MS) technology.

SDY, i(%) =

Yi(%) × CS, i CS,feed

(1)

where SDY, i is the sulfur distribution yield in product cuts, i refers to gasoline, LCO, or HCO; Yi is the yield of product cuts; CS,i is the sulfur content of product cuts; CS, feed is the sulfur content of feedstock. The nitrogen distribution yields in product cuts can be calculated by

NDY, i(%) =

Yi(%) × C N, i C N,feed

(2)

where NDY, i is the nitrogen distribution yield in product cuts; CN,i is the nitrogen content of product cuts; CN, feed is the nitrogen content of feedstock. 2.3. Coke Oxidation Analysis. The TPO analysis of coked catalysts (10 mg) was carried out under flowing nitrogen (20 mL/min) and oxygen (10 mL/min) with a heating rate of 20 °C/min (35−800 °C) using a NETZSCH STA 449C thermoanalysis instrument. The coked catalysts were obtained from the spent catalyst standpipe (after stripping by the steam at 500 °C) of the pilot scale FCC units. Before testing, they were pretreated at 200 °C (24 h) in dry air.

3. RESULTS AND DISCUSSION 3.1. Sulfur and Nitrogen Distribution in TLPs. Figure 1 shows the correlations of feed sulfur and nitrogen distributed in TLPs and TLP yields with conversion. As the increase of feed conversion, the sulfur and nitrogen remaining in TLPs under different processing schemes all decreased linearly. It should be noted that the TLP yields significantly declined as well, which indicates that as the increase of feed conversion, the sulfur and nitrogen compounds would continually transfer into gases and coke. However, the reactivity of sulfur compounds seems much lower than that of nitrogen compounds, which need to be further studied. When the equilibrium catalyst was used (schemes I and II), the feed sulfur distributes in TLPs were all over 74%, much higher than the situations of cracking hydrotreated feeds or VGO that was reported in the literature.22,35 This may be because the CGO contains a large amount of polycyclic aromatic sulfur heterocycles, which are rather unreactive at FCC conditions. Moreover,

2. EXPERIMENTAL SECTION 2.1. Catalytic Cracking. The Qilu CGO (provided by the Qilu refinery) was chosen as the feedstock which contains 1.27% S, 0.66% N, and its basic nitrogen content is as high as 2178 μg/g. Catalyst A was a commercial Y-zeolite based equilibrium FCC catalyst supplied by Changqing refinery, and catalyst B is a mixture of catalyst A and the fresh one at the ratio of 9:1. The detail properties of the feedstock and B

dx.doi.org/10.1021/ef401990s | Energy Fuels XXXX, XXX, XXX−XXX

Energy & Fuels

Article

where SPD, TLP is the percentage decline of sulfur in TLP, SDY is the distribution yield of sulfur, SDY, base is the sulfur distribution yield of the base experiment (e.g., scheme I, the second test point, conversion = 75.35%, SPD, TLP (%) = {(80.34 − 75.97)/80.34} × 100 = 5.44). NPD,TLP(%) =

ΔNDY × 100 NDY,base

(4)

where NPD, TLP is the percentage decline of nitrogen in TLP, NDY is the distribution yield of nitrogen, NDY, base is the nitrogen distribution yield of the base experiment. YPD,TLP(%) =

Figure 1. Feed sulfur and nitrogen distribute in TLPs and TLP yields as a function of conversion.

ΔSDY × 100 SDY,base

(5)

where YPD, TLP is the percentage decline of TLP yield, YTLP is the TLP yield, YTLP, base is the TLP yield of the base experiment. It is clear, in all three processing schemes, the percentage declines of sulfur were much lower than that of the TLP yields, which indicates the sulfur compounds tend to concentrate in the TLPs. By contrast, the figures for nitrogen are about double of that for the TLP yields. Thus, as the increase of conversion, the nitrogen compounds tend to be removed from the liquid products. When at the same conversion, the declines of TLP yields under scheme I showed the lowest value; therefore, choosing scheme I to process CGO can obtain more liquid products. Because of the increase of catalyst acid sites, scheme III has the highest desulfurization and denitrogenation ability, compared to other schemes. When the equilibrium catalyst was used, scheme I has higher desulfurization ability, but lower denitrogenation ability, compared to scheme II. This is because in order to reach the same conversion at a shorter residence time, higher reaction temperature should be chosen, which is unfavorable for the adsorption and reaction of nitrogen compounds, especially for basic nitrogen compounds.8 3.2. Sulfur Distribution Yields and Concentrations in Product Cuts. 3.2.1. In Gasoline Fraction. The main sulfur components in FCC naphthas are thiols, sulfides, thiophene and alkylthiophenes, tetrahydrothiophene, thiophenols, and benzothiophene.19,28 There are four main factors that will influence the sulfur concentration and composition of gasoline. The most important one is the properties of feedstocks, such as sulfur and nitrogen contents and species. Ng et al.22 and Valla et al.36 reported that the order of sulfur concentration in each product cut corresponded to the order of the sulfur concentration in the feed. Yin and Xia37 found that residues generate gasoline products with higher thiophenic sulfur, which can be up to approximately 70% of the total sulfur in the RFCC gasoline, compared to that in the FCC gasoline with lower than 60%. In our previous work, the thiophenic sulfur even represents over 85% of the total sulfur in the gasoline from Hengyuan CGO catalytic cracking.38 Moreover, Vistisen and Zeuthen35 reported that nitrogen compounds, such as quinoline, could lower the reactivity of sulfur compounds. The second factor is the properties of catalysts, especially the hydrogen-transfer activity. Hydrogen transfer is an important elementary reaction step for thiophene and alkyl-thiophene species desulfurization via cracking.26 Besides adjusting the properties of catalysts, additives for sulfur removal from FCC gasoline have been developed and applied in commercial units.39−41 The third factor is the reaction conditions. The reaction temperature, catalyst-to-oil ratio, and residence time can

the effect of nitrogen compounds on the sulfur conversion should not be neglected. Vistisen and Zeuthen35 found that quinoline or carbazole can significantly influence the conversion of dibenzothiophene. By contrast, the nitrogen compounds have higher reactivities because of their stronger proton affinity or larger molecular weight, which made them more easily adsorb on the catalyst surface and end up in the coke.9,10,16,29 The coking ratio of nitrogen compounds can be even higher than 60%.24 Compared to scheme II, the TLPs obtained from scheme I contain lower sulfur (when the conversion >72%) and higher nitrogen. This is because under scheme I, higher catalyst-to-oil ratio could enhance the conversion of sulfur and nitrogen compounds; however, the high temperature would restrain the adsorption and reaction of nitrogen compounds on the acid sites.8 When the fresh catalyst was added into the catalyst system (scheme III), the feed sulfur and nitrogen remaining in TLPs showed a significant drop as a result of the relieved competition effect and enhanced hydrogen transfer reactions.7 The first test was set as the base experiment, which reacted at 500 °C, 0.8 s, C/O = 6 and had the lowest conversion. The percentage declines of sulfur and nitrogen in TLPs and the TLP yields were calculated and shown in Figure 2. SPD,TLP(%) =

ΔYDY × 100 YDY,base

(3)

Figure 2. Percentage declines of sulfur and nitrogen distribute in TLPs and TLP yields as a function of conversion (SPD, TLP (%) = |Δ SDY/ SDY, base| × 100, NPD, TLP (%) = |Δ NDY/NDY, base| × 100, YPD, TLP (%) = |Δ YTLP/YTLP, base| × 100). C

dx.doi.org/10.1021/ef401990s | Energy Fuels XXXX, XXX, XXX−XXX

Energy & Fuels

Article

Figure 3. Sulfur distribution yields and concentrations in product cuts: (a) sulfur distribution yields in product cuts as a function of conversion; (b) sulfur concentration of gasoline and gasoline yield as a function of conversion; (c) sulfur concentration of LCO and LCO yield as a function of conversion; and (d) sulfur concentration of HCO and HCO yield as a function of conversion.

(mainly methyl-benzothiophenes) that out of the gasoline range.25,43,44 Figure 3a shows the sulfur distribution yields in product cuts as a function of conversion. It can be seen, with the increase of feed conversion, more sulfur remained in gasoline for all three processing schemes. This is because, under a higher operating severity, more heavy sulfur compounds cracked into thiophene, short chain alkyl-thiophenes, and benzothiophene, which are less reactive sulfur compounds, through protolytic cracking which is favored at higher temperatures,45 and accumulated in the gasoline fraction. Figure 3a shows that more sulfur is distributed in gasoline under scheme I as compared to scheme II. It may be due to the enhanced protolytic cracking caused by higher reaction temperatures in scheme I (in order to reach the same conversion as scheme II). Moreover, the longer residence time in scheme II would promote more sulfur compounds in gasoline to form heavier sulfur compounds belonging to the LCO fraction, which can be proved by the higher sulfur distribution yields of LCO. It is well-known, under FCC conditions, hydrogen transfer was the rate-limiting step of the decomposition of thiophene and short chain alkyl-thiophenes.19 Thus, theoretically, in scheme III, lower sulfur would remain in gasoline. However, it can only be observed under mild operating conditions. When under a higher operating severity, the sulfur in the gasoline from scheme III was higher than that from scheme I. This may be due to the further cracking of heavy sulfur compounds, and the increased H2S and olefin concentrations boosted the formation of thiophene and alkylthiophenes through the recombination of H2S with olefins or diolefins.25,27,35 Besides the influence of the sulfur input-output balance, the sulfur concentration of gasoline was also influenced by the gasoline yield. Specifically, it is determined by the relative

influence the relative ratio of catalytic cracking and hydrogen transfer reactions, leading to different yield structures, sulfur distributions, and sulfur concentrations in product cuts; however, little information can be obtained from the literature. In addition, the easiest operation to decrease the sulfur concentration of gasoline is setting a lower cut point for gasoline. When setting it at 200 °C, such as in China, most of the benzothiophene (boiling point 221−222 °C) and alkyl-benzothiophenes can be removed from the gasoline fraction, at the expense of some gasoline products. The sulfur distribution yield of gasoline is determined by the balance of sulfur input and output. Sulfur in gasoline is mainly formed by the cracking of heavy sulfur compounds in the feed.19,25,42 Research found that they also can be generated by the recombination of H2S with olefins or diolefins produced from the catalytic cracking of hydrocarbons followed by cyclization reactions.19,25,27,35 Nevertheless, according to the industrial investigation made by Stratiev et al.,42 it only accounts for a little part. In contrast, the sulfur compounds in gasoline can be removed by three pathways: cracking into H2S, converting to alkylbenzothiophenes through a cyclization reaction step and end up in the diesel range, or forming coke through condensation and dehydrogenation reactions.25,27,36 Thiophene is quite unreactive and mainly converted into coke.25,43 The reactivities of alkyl-thiophenes are determined by the chain length. Long chain alkylthiophenes are easier to be removed from gasoline range through cyclization and dehydrogenation reactions to form benzothiophene and alkylbenzothiophenes, while short chain alkylthiophenes undergo mainly dealkylation and isomerization reactions.25,36 Benzothiophene is also not very reactive under FCC conditions25 but more reactive than thiophene.43 It is mainly converted into coke or alkylated benzothiophenes D

dx.doi.org/10.1021/ef401990s | Energy Fuels XXXX, XXX, XXX−XXX

Energy & Fuels

Article

including the unreacted polycyclic aromatic sulfur heterocycles (PASHs) presented in the feed and the high-molecular-weight PASHs cracking products. Also, they can be generated from the alkylbenzothiophenes or alkyldibenzothiophenes in the LCO fraction. Because of the complexity, it is unrealistic to analyze individual sulfur compounds in heavy oils.48 They tend to be characterized by class, type, and carbon number distribution, using Fourier transform-ion cyclotron resonance mass spectrometry (FT-ICR MS).49−53 However, research found that different ionization methods show different results.48,51 Thus, it remains a challenge to characterize PASHs in heavy oil. However, it can be inferred that the PASHs remaining in HCO have shorter side chains and a higher condensation degree than that in the feedstocks. Hence, they are more likely to form coke in the end. Figure 3a indicates that the increased operating severity can enhance the further cracking of heavy sulfur compounds in HCOs. However, as the PASHs are less reactive than most other hydrocarbons in HCOs, the sulfur concentration of HCOs significantly increased for all three processing schemes, which can be seen in Figure 3d. With the first test set as the base experiment (T = 500 °C, t = 0.8 s, C/O = 6), the ratio of sulfur transferred from HCOs into gasoline and LCO fractions can be calculated.

reaction rate of sulfur compounds and sulfur-free hydrocarbons. If the growth rate of gasoline yield is higher than that of sulfur, the sulfur concentration can be reduced. Figure 3b illustrates that, under schemes I and II, the gasoline sulfur concentration declined as the increase of conversion due to the dilution effect by the additional formed sulfur-free gasoline hydrocarbons, which was also observed by Dupain.46 As the reactivity of thiophene and alkylthiophenes are lower than most other hydrocarbons in gasoline, prolonging the residence time would lead to the decrease of gasoline yields and the enrichment of sulfur in gasoline. Thus, the scheme I provided gasolines with lower sulfur concentrations, compared to scheme II. By contrast, the sulfur concentration of gasoline under scheme III showed an upward trend due to the increased cracking of heavy sulfur compounds and the generation of sulfur compounds from H2S and olefins. 3.2.2. In LCO Fraction. Hua et al.47 used the comprehensive two-dimensional gas chromatography to determine the sulfur species in diesel oils and found that in FCC diesel oils, benzothiophene, alkyl-benzothiophenes, dibenzothiophene, and alkyl-dibenzothiophenes account for 90% of the total sulfur, and in RFCC diesel oils the ratio can be up to 95%. They are mainly generated from the cracking of heavy sulfur compounds in the feed 46 and also can be formed from the long chain alkylthiophenes by alkylation and hydride transfer reactions.25 Valla et al.44 studied the reaction behaviors of heavy sulfur compounds by adding model compounds into a gas oil and found that benzothiophene was mainly converted into C1-benzothiophenes, C2-benzothiophenes, and coke. 2-Methyl-benzothiophene was particularly stable, which mainly isomerized to other C1-benzothiophenes. Dibenzothiophene was mainly converted to C1-dibenzothiophenes, C2-dibenzothiophenes and heavier sulfur compounds belonged to the HCO range. The main reaction of 4,6-dimethyl-dibenzothiophene are isomerization for the production of other C2-dibenzothiophenes and condensation reaction for the production of coke. All these compounds are more difficult to crack than the feedstock, and their impacts on the sulfur content in gasoline are small. Thus, the sulfur compounds in the LCO can be removed mainly through polymerization and condensation reactions to form heavier sulfur compounds or end up in the coke. Figure 3a shows that the sulfur distribution yields of LCO rose linearly with the conversion. It indicates that under a higher operating severity, the cracking of heavier sulfur compounds in heavy oil is easier than the conversion of sulfur compounds in LCO, thus the feed sulfur accumulated in the LCO fraction. LCOs from scheme II showed the highest sulfur distribution yield, because the prolonged reaction time enhanced the transfer of sulfur both from the HCO and gasoline into the LCO fraction. By contrast, scheme III produced LCOs with the lowest sulfur distribution yield due to the increased hydrogen transfer reactions. It can be seen from Figure 3c, with the increase of conversion, the LCO yields showed a downward trend for all the processing schemes, while the sulfur concentration of LCO increased linearly, mainly due to the concentration effect. The LCOs from scheme I had lower sulfur concentrations because of the lower sulfur distribution yields and higher LCO yields. Although fewer sulfur distributed in LCO under scheme III, the dramatic decline of the LCO yield led to the sharply increased sulfur content in the LCO fraction. 3.2.3. In HCO Fraction. The sulfur heterocycles in HCO are composed of two parts. The major part is derived from the feed,

R GN(%) =

ΔSDY,GN ΔSDY,HCO

× 100 (6)

where RGN is the ratio of sulfur transferred from HCO into gasoline, SDY,GN is the sulfur distribution yield of gasoline, and SDY, HCO is the sulfur distribution yield of HCO. RLCO(%) =

ΔSDY,LCO ΔSDY,HCO

× 100 (7)

where RLCO is the ratio of sulfur transferred from HCO into LCO, and SDY, LCO is the sulfur distribution yield of LCO. The calculated results were presented in Figure 4. It can be seen, RGN showed an upward trend, while RLCO saw an opposite

Figure 4. Ratios of sulfur transferred from HCOs into gasoline and LCO fractions (RGN (%) = |ΔSDY, GN/ΔSDY, HCO| × 100, RLCO (%) = |ΔSDY, LCO/ΔSDY, HCO| × 100).

trend, which indicates some sulfur compounds in HCO can crack into LCO fractions and further transfer into gasoline fractions. The total ratio for scheme I was approximately 55%, which meant another 45% would form H2S or end up in the coke. When prolonging the residence time from 0.8 to 3.2 s, the RGN showed a negative value, which is because the sulfur compounds in the gasoline formed heavier sulfur compounds belonging to the LCO E

dx.doi.org/10.1021/ef401990s | Energy Fuels XXXX, XXX, XXX−XXX

Energy & Fuels

Article

Figure 5. Nitrogen distribution yields and concentrations in product cuts: (a) nitrogen distribution yields in product cuts as a function of conversion; (b) nitrogen concentration of gasoline and gasoline yield as a function of conversion; (c) nitrogen concentration of LCO and LCO yield as a function of conversion; (d) nitrogen concentration of HCO and HCO yield as a function of conversion.

nitrogen distribution yields of gasoline and LCO under scheme II are lower than that under scheme I. As the increase of the reaction temperature and CTO, more acid sites are available; therefore, prolonging the residence time could also increase the cracking of heavy nitrogen compounds. Hence, higher nitrogen distribution yields of gasoline and LCO (under scheme II) can be seen in Figure 5a. Moreover, research found that anilines and indoles could also be generated from NH3 and olefins through condensation and dehydrogenation reactions.35 The possible reaction pathways can be seen in Figure 6. Because of the dilution effect, the nitrogen concentration of gasoline all decreased with conversion, which can be seen from Figure 5b. Scheme I showed the biggest drops due to the decline of nitrogen distribution yields and the increase of gasoline yields. When the conversion was higher than 80%, the nitrogen

fraction. As the increase of feed conversion, the crackability of sulfur compounds in HCO would reduce; however, the total ratio for schemes II and III showed an upward trend. Thus, the results might be influenced by the sulfur compounds generated from the recombination of H2S with olefins. It indicates that long residence time, high catalyst activity, or high concentration of H2S (under a high conversion) would enhance the recombination reactions of H2S with olefins. 3.3. Nitrogen Distribution Yields and Concentrations in Product Cuts. 3.3.1. In Gasoline Fraction. Most of the nitrogen compounds presented in the FCC gasoline are anilines and indoles.35 In China, because the final boiling point (FBP) of the gasoline is about or lower than 200 °C, most of the indoles (BP > 253 °C) were removed into the LCO fraction. Figure 5a indicates that only a small part of the feed nitrogen (less than 1.1%) remained in the gasoline fraction during the FCC process, which is consistent with the previous studies.22,24,35 Scheme III produced TLPs with the lowest nitrogen distribution yield, which indicates the conversion of nitrogen compounds is catalyzed by the acid sites. Moreover, hydrogen transfer reactions are beneficial for the cracking of nitrogen compounds. The decrease of the nitrogen distribution yield of gasoline under scheme I is because of the enhanced protolytic cracking under higher reaction temperatures, which is beneficial to the cracking of anilines into NH3 and hydrocarbons. However, under the long residence time scheme (scheme II), an opposite trend can be seen, which may be due to the further cracking of heavy nitrogen compounds. When reacted at 500 °C, due to the low catalyst-to-oil ratio and the poisoning effect of nitrogen compounds, the catalyst deactivated seriously. The heavy nitrogen compounds are difficult to crack but the light nitrogen compounds, such as anilines, still can be cracked. Thus, the

Figure 6. Formation of anilines and indoles from NH3 and olefins. F

dx.doi.org/10.1021/ef401990s | Energy Fuels XXXX, XXX, XXX−XXX

Energy & Fuels

Article

molecule) with a double bond equivalence (DBE) value of 4− 16. These compounds may be quinoline, indol, and carbazole derivatives. The characterization of nitrogen compounds in the HCO after CGO cracking has never been reported and will be presented in our subsequent papers. Figure 5a shows that, as the increase of operating severity, the nitrogen distribution yields of HCO for different processing schemes all showed a downward trend, which indicates the higher reaction temperature and CTO are beneficial for the conversion of high-molecular-weight nitrogen compounds. Although they were mainly converted into coke, some nitrogen species could crack into ammonia, anilines, indoles, and crabazoles. Because high temperature and short residence time would inhibit the adsorption of nitrogen compounds on the acid sites, more nitrogen compounds remained in HCO under scheme I. In contrast, prolonging the residence time would boost the adsorption of nitrogen compounds on the catalyst surface, leading to a higher coke yield. Adding fresh catalysts into the catalyst system could increase the density of acid sites, enhancing the hydrogen transfer reaction, which is beneficial to the cracking and condensation of nitrogen compounds. Therefore, the lowest nitrogen distribution yields of HCO can be obtained from scheme III. Because nitrogen-free hydrocarbons in HCO have higher reactivities than nitrogen compounds, as the increase of feed conversion, more nitrogen compounds are enriched in the HCO fraction. Figure 5d shows that the nitrogen concentrations of HCO from different schemes ranked in the same order as that of nitrogen distribution yields but showed an opposite trend. 3.4. Sulfur and Nitrogen Balances. Figures 8 and 9 show the schematic of the sulfur and nitrogen balances of coker gas oil

concentration of gasoline under scheme I declined to the lowest position. 3.3.2. In LCO Fraction. Dorbon and Bernasconi54 selectively extracted basic and nonbasic nitrogen compounds from different LCOs and analyzed them by gas chromatography (GC) and mass spectrometry (MS). Research found that the basic compounds are aniline and C1- to C4-alkylanilines, and the nonbasic compounds are indole, C1- to C4-alkylindoles, carbazole, and C1- to C3-alkylcarbazoles. Laredo et al.55 used the GC−MS technique to quantitatively analyze the nitrogen compounds in LCO and found that the ratio of anilines, indoles, and carbazoles was 1/2.3/12.2, and no quinolines were detected. However, Cheng et al.56 discovered quinolines in the RFCC diesel. A recent study showed that in the RFCC diesel, quinolines with side chains ranging from C0 to C6 accounted for 23% of total basic nitrogen-containing compounds (about half of the quantity of anilines).57 According to the study of Vistisen and Zeuthen,35 carbazoles are difficult to crack into anilines or indoles under FCC conditions but mainly convert into alkylcarbazoles. Therefore, the cracking of alkylanilines and indoles would be the main reason that caused the generation of anilines in gasoline. Yu et al.58 found that quinoline can also convert into aniline with tetrahydroquinoline as the intermediate. The possible reaction pathways for the generation of aniline can be seen in Figure 7.

Figure 7. Possible reaction pathways for the generation of anilines from alkylanilines, alkylindoles, and quinolines. Figure 8. Schematic of the sulfur balance of coker gas oil catalytic cracking (conversion, 63−91%; dotted lines mean less important pathways).

It can be seen from Figure 5a, the nitrogen distribution yield of LCO decreased with feed conversion (except scheme II). The nitrogen compounds in LCO can be removed through cracking (form anilines and NH3), alkylation (form alkylcarbazoles in the HCO fraction), or condensation (form coke) reactions. Although, the lowest nitrogen distribution yield can be obtained from scheme III, due to the sharp decrease of LCO yields, the nitrogen content in LCO showed an upward trend (see Figure 5c). Because of the decreased nitrogen distribution yields, the nitrogen concentration of LCO under scheme I significantly decreased with conversion and could finally reach the lowest position. 3.3.3. In HCO Fraction. Shi et al.59,60 used the FT-ICR MS to characterize the nitrogen compounds in coker gas oil by class, type, and carbon number. They found that the majority of nitrogen-containing compound classes are N1, N2, N1O1, N1O2, N1S1, and N2O1, while the dominant compounds are N1-class species (the compounds with one nitrogen atom in the

Figure 9. Schematic of the nitrogen balance of coker gas oil catalytic cracking (conversion, 63−91%; dotted lines mean less important pathways).

G

dx.doi.org/10.1021/ef401990s | Energy Fuels XXXX, XXX, XXX−XXX

Energy & Fuels

Article

Figure 10. Emissions of SOx and NOx during the TPO analysis of coked catalysts.

technology was used to study the combustion behavior of sulfur and nitrogen in coke. Research found that, although there is only 2−5% of the feed sulfur appears in the coke, they are all burned to SOx.28 By contrast, about 90% of nitrogen in coke is converted to N2, rather than NOx.32 Figure 10 shows the analysis of SO2, SO3, NO, and NO2 emissions during the TPO of two spent catalysts (from schemes I and III) at the close feed conversion. It can be seen from Figure 10a, the spent catalyst from scheme I emitted less amounts of SOx. Moreover, the emission temperatures were shifted to a narrower range under scheme I [300−675 °C (scheme III) vs 350−625 °C (scheme I)]. Figure 10b shows that remarkably lower amounts of NO and NO2 were formed during the oxidization of spent catalyst from scheme I, which further proved that higher reaction temperatures can inhibit the deposition of nitrogen on the catalyst. It also can be seen that the emission temperatures of NO2 were shifted to a narrower range under scheme I. The signals of NO2+ disappeared before that of NO+, which indicates NO is difficult to be further oxidized into NO2 under higher temperatures and even enriched air (33% O2). Why the high reaction temperature scheme (scheme I) significantly changed the emission temperatures of SO2, SO3, and NO2 but has no influence on that of NO and CO2 (not shown), which need to be further studied for an accurate answer.

catalytic cracking. It can be seen, most of the feed sulfur and nitrogen remained in the HCO, followed by the LCO and the gasoline. However, the sulfur balance is different from the nitrogen balance. More heavy sulfur compounds in the feedstock can crack into gasoline and LCO fractions, while more nitrogen compounds will end up in the gases and coke. The nitrogen distribution yields of gasoline are only around 1%, which indicates the opening of nitrogen heterocycles in the FCC process is really difficult. Thus, the generation of NH3 is limited, and most of the feed nitrogen will end up in the coke finally. Also, it can be inferred, the high-molecular-weight sulfur compounds in the feedstock are more likely thiophenes or benzothiophenes combined with polycyclic aromatics by single bonds, thus they are more easily cracked into thiophenes or benzothiophenes in the gasoline or LCO range. By contrast, the heavy nitrogen compounds are more likely polycyclic aromatic nitrogen heterocycles, which tend to form coke through condensation and dehydrogenation reactions. Comparing Figure 3a with Figure 5a, the sulfur distribution yields of gasoline and LCO under scheme I increased with feed conversion; on the other hand, the nitrogen distribution yields saw an opposite trend. This is because higher temperatures and CTOs could promote the cracking of some high-molecularweight sulfur compounds. However, the increased protolytic cracking would reduce the side chain length of alkylthiophenes and alkylbenzothiophenes, lowering their reactivities. Thus, more sulfur compounds are retained in the gasoline and LCO fractions. By contrast, the heavy nitrogen compounds have a higher condensation degree and are difficult to be cracked even under higher operating severity. However, the increased operating severity could enhance the cracking of anilines into aromatics and ammonia by protolytic cracking as well as promote the coking of indoles and carbazoles through dehydrogenation and condensation reactions. 3.5. Combustion of Sulfur and Nitrogen in Coke. The amounts of sulfur and nitrogen in coke are difficult to determine due to the restriction of the analytical instrument for small amount samples (the S or N content in the coked catalyst is usually lower than 0.05%). Moreover, the adsorption of air (N2) on catalyst pores will influence the test results. Barth et al.61 used the HF solution (40%) to extract the coke from the catalyst; however, Caeiro et al.11 found the dissolution process is not completely effective, because some of the catalyst components are not completely destroyed by the HF treatment. Indeed, researchers care more about the SOx and NOx emissions during the regeneration of coked catalyst. Thus, the TPO-MS

4. CONCLUSIONS In the catalytic cracking process of coker gas oil, both sulfur and nitrogen distributed in HCO, LCO, and gasoline ranked in a descending order but showed different distribution yields. Compared to nitrogen compounds, the heavy sulfur compounds are easier to crack into lighter ones but more difficult to be removed from liquid products. As the increase of feed conversion, feed sulfur and nitrogen remained in TLPs decreased linearly. The sulfur compounds tend to concentrate in the TLPs, while the nitrogen compounds tend to form coke and be removed from the TLPs. Different processing parameters can significantly affect the sulfur and nitrogen distribution yields and concentrations in liquid products. The high reaction temperature and CTO with short residence time scheme can produce gasoline and LCO with lower sulfur and nitrogen contents. It can inhibit the coking of heavy nitrogen compounds as well. Thus, more nitrogen compounds remained in HCO, and the poisoning effect can be relieved. Prolonging the residence time, a certain amount of sulfur in HCO and gasoline would transfer into the LCO fraction, H

dx.doi.org/10.1021/ef401990s | Energy Fuels XXXX, XXX, XXX−XXX

Energy & Fuels

Article

(6) Li, Z. K.; Wang, G.; Liu, Y. D.; Wang, H.; Liang, Y. M.; Xu, C. M.; Gao, J. S. Catalytic cracking constraints analysis and divisional fluid catalytic cracking process for coker gas oil. Energy Fuels 2012, 26 (4), 2281−2291. (7) Zhang, J. H.; Shan, H. H.; Liu, W. J.; Chen, X. B.; Li, C. Y.; Yang, C. H. Synergistic Process for Coker Gas Oil Catalytic Cracking and Gasoline Reformation. Energy Fuels 2013, 27 (2), 654−665. (8) Mills, G. A.; Boedeker, E. R.; Oblad, A. G. Chemical characterization of catalysts. I. Poisoning of cracking catalysts by nitrogen compounds and potassium ion. J. Am. Chem. Soc. 1950, 72 (4), 1554−1560. (9) Fu, C. M.; Schaffer, A. M. Effect of nitrogen compounds on cracking catalysts. Ind. Eng. Chem. Prod. Res. Dev. 1985, 24 (1), 68−75. (10) Ho, T. C.; Katritzky, A. R.; Cato, S. J. Effect of nitrogen compounds on cracking catalysts. Ind. Eng. Chem. Res. 1992, 31 (7), 1589−1597. (11) Caeiro, G.; Costa, A. F.; Cerqueira, H. S.; Magnoux, P.; Lopes, J. M.; Matias, P.; Ribeiro, F. R. Nitrogen poisoning effect on the catalytic cracking of gasoil. Appl. Catal., A 2007, 320, 8−15. (12) Young, G. W. Fluid catalytic cracker catalyst design for nitrogen tolerance. J. Phys. Chem. 1986, 90 (20), 4894−4900. (13) Corma, A.; Fornes, V.; Monton, J. B.; Orchilles, A. V. Catalytic cracking of alkanes on large pore, high SiO2/Al2O3 zeolites in the presence of basic nitrogen compounds. Influence of catalyst structure and composition in the activity and selectivity. Ind. Eng. Chem. Res. 1987, 26 (5), 882−886. (14) Scherzer, J.; McArthur, D. P. Catalytic cracking of high-nitrogen petroleum feedstocks: effect of catalyst composition and properties. Ind. Eng. Chem. Res. 1988, 27 (9), 1571−1576. (15) Corma, A.; Mocholí, F. A. New silica-alumina-magnesia FCC active matrix and its possibilities as a basic nitrogen passivating compound. Appl. Catal., A 1992, 84 (1), 31−46. (16) Li, Z. K.; Gao, J. S.; Wang, G.; Shi, Q.; Xu, C. M. Influence of nonbasic nitrogen compounds and condensed aromatics on coker gas oil catalytic cracking and their characterization. Ind. Eng. Chem. Res. 2011, 50 (15), 9415−9424. (17) Zhang, R. C.; Shi, W. Y. Denitrified Catalytic Cracking (DNCC) Technology for Coker Gas Oil Processing. Pet. Process. Petrochem. 1998, 29, 22−27. (18) Yuan, Q. M.; Wang, Y. L.; Li, C. Y.; Yang, C. H.; Shan, H. H. Study on conversion of coker gas oil by two-stage riser fluid catalytic cracking. J. China Univ. Pet. (Ed. Nat. Sci.) 2007, 31 (1), 122−126. (19) Brunet, S.; Mey, D.; Pérot, G.; Bouchy, C.; Diehl, F. On the hydrodesulfurization of FCC gasoline: a review. Appl. Catal., A 2005, 278 (2), 143−172. (20) La Vopa, V.; Satterfield, C. N. Poisoning of thiophene hydrodesulfurization by nitrogen compounds. J. Catal. 1988, 110 (2), 375−387. (21) Laredo S, G. C.; De los Reyes H, J. A.; Luis Cano D, J.; Jesús Castillo M, J. Inhibition effects of nitrogen compounds on the hydrodesulfurization of dibenzothiophene. Appl. Catal., A 2001, 207 (1−2), 103−112. (22) Ng, S.; Zhu, Y.; Humphries, A.; Zheng, L.; Ding, F.; Yang, L.; Yui, S. FCC Study of Canadian Oil-Sands Derived Vacuum Gas Oils. 2. Effects of Feedstocks and Catalysts on Distributions of Sulfur and Nitrogen in Liquid Products. Energy Fuels 2002, 16 (5), 1209−1221. (23) Zhao, X.; Peters, A. W.; Weatherbee, G. W. Nitrogen Chemistry and NOx Control in a Fluid Catalytic Cracking Regenerator. Ind. Eng. Chem. Res. 1997, 36 (11), 4535−4542. (24) Yuan, Q. M.; Wang, Y. L.; Li, C. Y.; Yang, C. H.; Shan, H. H. Studies on nitrogen distribution in products during catalytic cracking of coker gas oil. J. Fuel Chem. Technol. 2007, 35 (3), 375−379. (25) Corma, A.; Martínez, C.; Ketley, G.; Blair, G. On the mechanism of sulfur removal during catalytic cracking. Appl. Catal., A 2001, 208 (1− 2), 135−152. (26) Shan, H. H.; Li, C. Y.; Yang, C. H.; Zhao, H.; Zhao, B. Y.; Zhang, J. F. Mechanistic studies on thiophene species cracking over USY zeolite. Catal. Today 2002, 77 (1−2), 117−126.

leading to a higher sulfur concentration of LCO. However, the sulfur content of gasoline also increased, due to the decrease of gasoline yield. Increasing the catalyst activity can enhance the conversion of sulfur and nitrogen compounds. However, only under mild operating conditions, it can help to reduce the sulfur and nitrogen concentrations of light oil. Long residence time, high catalyst activity, and high concentration of H2S under high feed conversion would enhance the recombination reactions of H2S with olefins. Choosing the high reaction temperature and CTO with short residence time parameters to process CGO cannot only increase the light oil yield but also reduce the sulfur and nitrogen contents of light oil as well as decrease the SOx and NOx emissions in the regenerator, which can also be used to process other high nitrogen-content feedstocks. Considering the low reactivity of sulfur compounds in CGO, it is better to pretreat this kind of feeds by hydrodesulfurization. The data presented in the work can also be used to estimate the sulfur and nitrogen distributions influenced by the blending of CGO in the conventional feedstock.

■

ASSOCIATED CONTENT

S Supporting Information *

Properties of the feedstock, catalysts, and product distribution of different processing schemes. This material is available free of charge via the Internet at http://pubs.acs.org.

■

AUTHOR INFORMATION

Corresponding Authors

*Phone: +86-532-86981718. Fax: +86-532-86981718. E-mail: [email protected]. *E-mail: [email protected]. Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS The authors acknowledge the financial support provided by the National Basic Research Program of China (Grant 2012CB215006), the Fundamental Research Funds for the Central Universities (Grant 13CX05002A), the research fund of Key Laboratory for Advanced Technology in Environmental Protection of Jiangsu Province (Grant AE201303), and the Graduate Student Innovation Project of China University of Petroleum (Grant CX2013029). We gratefully thank Dr. Yongming Chai for help with the TPO-MS analysis. We also thank the reviewers for some valuable comments that led to a better manuscript.

■

REFERENCES

(1) Sawarkar, A. N.; Pandit, A. B.; Samant, S. D.; Joshi, J. B. Petroleum residue upgrading via delayed coking: A review. Can. J. Chem. Eng. 2007, 85 (1), 1−24. (2) Qu, G. H. Hot points and hard points in processing of heavy oil. Technol. Econ. Petrochem. 2013, 29 (2), 10−16. (3) Xu, C. M.; Yang, C. H. Petroleum Refining Engineering. 4th ed.; Petroleum Industry Press: Beijing, China, 2009. (4) Wang, G.; Liu, Y. D.; Wang, X. Q.; Xu, C. M.; Gao, J. S. Studies on the catalytic cracking performance of coker gas oil. Energy Fuels 2009, 23 (4), 1942−1949. (5) Wang, G.; Li, Z. K.; Huang, H.; Lan, X. Y.; Xu, C. M.; Gao, J. S. Synergistic process for coker gas oil and heavy cycle oil conversion for maximum light production. Ind. Eng. Chem. Res. 2010, 49 (22), 11260− 11268. I

dx.doi.org/10.1021/ef401990s | Energy Fuels XXXX, XXX, XXX−XXX

Energy & Fuels

Article

(27) Leflaive, P.; Lemberton, J. L.; Pérot, G.; Mirgain, C.; Carriat, J. Y.; Colin, J. M. On the origin of sulfur impurities in fluid catalytic cracking gasolineReactivity of thiophene derivatives and of their possible precursors under FCC conditions. Appl. Catal., A 2002, 227 (1−2), 201−215. (28) Cheng, W. C.; Kim, G.; Peters, A. W.; Zhao, X.; Rajagopalan, K.; Ziebarth, M. S.; Pereira, C. J. Environmental Fluid Catalytic Cracking Technology. Catal. Rev. 1998, 40 (1−2), 39−79. (29) Li, Z. K.; Wang, G.; Shi, Q.; Xu, C. M.; Gao, J. S. Retardation effect of basic nitrogen compounds on hydrocarbons catalytic cracking in coker gas oil and their structural identification. Ind. Eng. Chem. Res. 2011, 50 (7), 4123−4132. (30) Chen, J. W.; Cao, H. C. Catalytic Cracking Technology and Engineering, 2nd ed.; SINOPEC Press: Beijing, China, 2005; p 1260. (31) Barth, J. O.; Jentys, A.; Lercher, J. A. Elementary Reactions and Intermediate Species Formed during the Oxidative Regeneration of Spent Fluid Catalytic Cracking Catalysts. Ind. Eng. Chem. Res. 2004, 43 (12), 3097−3104. (32) Dishman, K. L.; Doolin, P. K.; Tullock, L. D. NOx Emissions in Fluid Catalytic Cracking Catalyst Regeneration. Ind. Eng. Chem. Res. 1998, 37 (12), 4631−4636. (33) Li, J.; Luo, G.; Wei, F. A multistage NOx reduction process for a FCC regenerator. Chem. Eng. J. 2011, 173 (2), 296−302. (34) Zhang, J.; Shan, H.; Chen, X.; Li, C.; Yang, C. In Situ Upgrading of Light Fluid Catalytic Cracking Naphtha for Minimum Loss. Ind. Eng. Chem. Res. 2013, 52 (19), 6366−6376. (35) Vistisen, P. Ø.; Zeuthen, P. Reactions of Organic Sulfur and Nitrogen Compounds in the FCC Pretreater and the FCC Unit. Ind. Eng. Chem. Res. 2008, 47 (21), 8471−8477. (36) Valla, J. A.; Lappas, A. A.; Vasalos, I. A.; Kuehler, C. W.; Gudde, N. J. Feed and process effects on the in situ reduction of sulfur in FCC gasoline. Appl. Catal., A 2004, 276 (1−2), 75−87. (37) Yin, C.; Xia, D. A study of the distribution of sulfur compounds in gasoline produced in China. Part 3. Identification of individual sulfides and thiophenes. Fuel 2004, 83 (4−5), 433−441. (38) Zhang, J. H.; Shan, H. H.; Chen, X. B.; Li, C. Y.; Yang, C. H. Multifunctional Two-Stage Riser Catalytic Cracking of Heavy Oil. Ind. Eng. Chem. Res. 2013, 52 (2), 658−668. (39) Andersson, P. O. F.; Pirjamali, M.; Järås, S. G.; Boutonnet-Kizling, M. Cracking catalyst additives for sulfur removal from FCC gasoline. Catal. Today 1999, 53 (4), 565−573. (40) Myrstad, T.; Engan, H.; Seljestokken, B.; Rytter, E. Sulphur reduction of fluid catalytic cracking (FCC) naphtha by an in situ Zn/ Mg(Al)O FCC additive. Appl. Catal., A 1999, 187 (2), 207−212. (41) Siddiqui, M. A. B.; Ahmed, S.; Aitani, A. M.; Dean, C. F. Sulfur reduction in FCC gasoline using catalyst additives. Appl. Catal., A 2006, 303 (1), 116−120. (42) Stratiev, D. S.; Shishkova, I.; Tzingov, T.; Zeuthen, P. Industrial Investigation on the Origin of Sulfur in Fluid Catalytic Cracking Gasoline. Ind. Eng. Chem. Res. 2009, 48 (23), 10253−10261. (43) Valla, J. A.; Lappas, A. A.; Vasalos, I. A. Catalytic cracking of thiophene and benzothiophene: Mechanism and kinetics. Appl. Catal., A 2006, 297 (1), 90−101. (44) Valla, J. A.; Mouriki, E.; Lappas, A. A.; Vasalos, I. A. The effect of heavy aromatic sulfur compounds on sulfur in cracked naphtha. Catal. Today 2007, 127 (1−4), 92−98. (45) Haag, W. O.; Dessau, R. M. In Duality of Mechanism in Acid Catalyzed Paraffin Cracking; The Eighth International Congress on Catalysis, Berlin, Germany, 1984; Verlag Chemie: Berlin, Germany, 1984; pp 305−315. (46) Dupain, X.; Rogier, L. J.; Gamas, E. D.; Makkee, M.; Moulijn, J. A. Cracking behavior of organic sulfur compounds under realistic FCC conditions in a microriser reactor. Appl. Catal., A 2003, 238 (2), 223− 238. (47) Hua, R.; Li, Y.; Liu, W.; Zheng, J.; Wei, H.; Wang, J.; Lu, X.; Kong, H.; Xu, G. Determination of sulfur-containing compounds in diesel oils by comprehensive two-dimensional gas chromatography with a sulfur chemiluminescence detector. J. Chromatogr., A 2003, 1019 (1−2), 101− 109.

(48) Panda, S. K.; Andersson, J. T.; Schrader, W. Characterization of Supercomplex Crude Oil Mixtures: What Is Really in There? Angew. Chem. 2009, 121 (10), 1820−1823. (49) Müller, H.; Andersson, J. T.; Schrader, W. Characterization of High-Molecular-Weight Sulfur-Containing Aromatics in Vacuum Residues Using Fourier Transform Ion Cyclotron Resonance Mass Spectrometry. Anal. Chem. 2005, 77 (8), 2536−2543. (50) Panda, S. K.; Schrader, W.; al-Hajji, A.; Andersson, J. T. Distribution of Polycyclic Aromatic Sulfur Heterocycles in Three Saudi Arabian Crude Oils as Determined by Fourier Transform Ion Cyclotron Resonance Mass Spectrometry. Energy Fuels 2007, 21 (2), 1071−1077. (51) Purcell, J. M.; Juyal, P.; Kim, D.-G.; Rodgers, R. P.; Hendrickson, C. L.; Marshall, A. G. Sulfur Speciation in Petroleum: Atmospheric Pressure Photoionization or Chemical Derivatization and Electrospray Ionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry. Energy Fuels 2007, 21 (5), 2869−2874. (52) Shi, Q.; Pan, N.; Liu, P.; Chung, K. H.; Zhao, S.; Zhang, Y.; Xu, C. Characterization of Sulfur Compounds in Oilsands Bitumen by Methylation Followed by Positive-Ion Electrospray Ionization and Fourier Transform Ion Cyclotron Resonance Mass Spectrometry. Energy Fuels 2010, 24 (5), 3014−3019. (53) Liu, P.; Shi, Q.; Pan, N.; Zhang, Y.; Chung, K. H.; Zhao, S.; Xu, C. Distribution of Sulfides and Thiophenic Compounds in VGO Subfractions: Characterized by Positive-Ion Electrospray Fourier Transform Ion Cyclotron Resonance Mass Spectrometry. Energy Fuels 2011, 25 (7), 3014−3020. (54) Dorbon, M.; Bernasconi, C. Nitrogen compounds in light cycle oils: identification and consequences of ageing. Fuel 1989, 68 (8), 1067−1074. (55) Laredo, G. C.; Leyva, S.; Alvarez, R.; Mares, M. T.; Castillo, J.; Cano, J. L. Nitrogen compounds characterization in atmospheric gas oil and light cycle oil from a blend of Mexican crudes. Fuel 2002, 81 (10), 1341−1350. (56) Cheng, X.; Zhao, T.; Fu, X.; Hu, Z. Identification of nitrogen compounds in RFCC diesel oil by mass spectrometry. Fuel Process. Technol. 2004, 85 (13), 1463−1472. (57) Shi, Q.; Xu, C.; Zhao, S.; Chung, K. H. Characterization of Heteroatoms in Residue Fluid Catalytic Cracking (RFCC) Diesel by Gas Chromatography and Mass Spectrometry. Energy Fuels 2009, 23 (12), 6062−6069. (58) Yu, D. Y.; Xu, H.; Que, G. H.; Wang, Z. X. Study on conversion of basic nirogen compound quinoline in FCC. J. Fuel Chem. Technol. 2004, 32 (1), 43−47. (59) Shi, Q.; Xu, C.; Zhao, S.; Chung, K. H.; Zhang, Y.; Gao, W. Characterization of Basic Nitrogen Species in Coker Gas Oils by Positive-Ion Electrospray Ionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry. Energy Fuels 2010, 24 (1), 563−569. (60) Zhu, X.; Shi, Q.; Zhang, Y.; Pan, N.; Xu, C.; Chung, K. H.; Zhao, S. Characterization of Nitrogen Compounds in Coker Heavy Gas Oil and Its Subfractions by Liquid Chromatographic Separation Followed by Fourier Transform Ion Cyclotron Resonance Mass Spectrometry. Energy Fuels 2011, 25 (1), 281−287. (61) Barth, J. O.; Jentys, A.; Lercher, J. A. On the Nature of NitrogenContaining Carbonaceous Deposits on Coked Fluid Catalytic Cracking Catalysts. Ind. Eng. Chem. Res. 2004, 43 (10), 2368−2375.

J

dx.doi.org/10.1021/ef401990s | Energy Fuels XXXX, XXX, XXX−XXX