In situ FCC gasoline sulfur reduction using spinel based additives

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In situ FCC gasoline sulfur reduction using spinel based additives A.V. Karthikeyani a,*, N. Anantharaman b, K.M. Prabhu a, L. Kumaresan a, C. Alex Pulikottil a, S.S.V. Ramakumar a a b

Research and Development Centre, Indian Oil Corporation Limited, Faridabad, India Department of Chemical Engineering, National Institute of Technology, Tiruchirappalli, India

article info

abstract

Article history:

ZnAl2O4, MgAl2O4, and CuAl2O4 based additives were prepared, characterized, and evalu-

Received 30 March 2017

ated in micro activity test unit using heavy combined hydrocarbon feedstock at the fluid

Received in revised form

catalytic cracking (FCC) unit conditions to study the gasoline sulfur reduction. These ad-

1 August 2017

ditives were prepared at identical conditions and characterized by X-Ray Diffraction, NH3-

Accepted 3 August 2017

TPD & N2 sorption analysis to establish the spinel formation, acidity measurement and

Available online xxx

pore-size distribution respectively. The performance of these additives was studied along with base FCC catalyst at 10 weight percent concentration. Hydrogen transfer reaction,

Keywords:

aromatization and alkylation functionalities were established to rank the prepared addi-

FCC

tives for their activity, selectivity, and gasoline sulfur removal efficiency. The sulfur

Gasoline

shifting in other liquid products such as heavy naphtha, light cycle oil and clarified oil were

Sulfur

also studied. While studying the gasoline sulfur removal efficiency of these additives, the

Spinel

research octane number (RON) of gasoline property has taken into consideration as the FCC gasoline contains lot of olefins (20e40 wt%), which involves in the sulfur removal reactions. © 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Introduction Environmentally driven regulations throughout the world demand dramatic improvements in the quality of transportation fuels gasoline and diesel. The exhaust gases from motor vehicles contribute to a large extent to air pollution through their NOx and SOx content [1]. Sulfur in gasoline and diesel fuels not only contribute directly to SOx emission but also poison catalytic converter in automobiles. Therefore, the refining industry is under constant environmental pressure to achieve more rigorous standards on sulfur content in fuel used in transportation sector. In India, the new gasoline specification requires sulfur, aromatics and research octane

number (RON) content to be 10 ppm (maximum), 35 vol% and 91 (minimum) respectively, by 2017 [2]. In the refinery, commercial gasoline blend stocks/pool is made up of different fractions coming from reforming, isomerization and fluid catalytic cracking (FCC). It is a well-known fact that gasoline from FCC makes up about 30e35 vol% of gasoline blend stocks/pool, and at the same time accounts for over 90% of the sulfur (90e98%) and olefins in the entire gasoline pool. Therefore, desulfurization of FCC gasoline without sacrificing research octane number (RON) is very important to make it acceptable for various applications. Various approaches are available to reduce sulfur content in FCC gasoline, which includes (i) reducing the end point of

* Corresponding author. E-mail addresses: [email protected], [email protected] (A.V. Karthikeyani). http://dx.doi.org/10.1016/j.ijhydene.2017.08.006 0360-3199/© 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved. Please cite this article in press as: Karthikeyani AV, et al., In situ FCC gasoline sulfur reduction using spinel based additives, International Journal of Hydrogen Energy (2017), http://dx.doi.org/10.1016/j.ijhydene.2017.08.006

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the gasoline stream, but this will add sulfur in the light cycle oil (LCO) stream and can be removed by LCO hydrotreater, (ii) pre-treating the FCC feed to remove sulfur through catalytic feed hydrotreater (CFHT), but the disadvantage of FCC feed hydrotreatment is its high operating and capital costs, (iii) post-treatment of the gasoline product leads to a significant loss of octane number and yield. The other disadvantages of post treating process are its high hydrogen consumption, investment and operating costs, (iv) processing of relatively light and low-sulfur crude oil, which can force the refiner into purchasing more expensive feeds and (v) use of FCC catalyst additives [3]. Sulfur reduction by use of additive along with base catalyst inside the FCC unit offers economic advantages over the pretreatment and post-treatment processes. It is evident that in the gasoline post-treatment processes, the reduction of sulfur from the high sulfur content gasoline feed leads to a big loss of RON. Therefore, the acceptable sulfur content in the feed (with and without recycle gasoline) for the post treatment processes that come from FCC unit should not cross the range of 60e300 ppm [4], which can be achieved by the use of gasoline sulfur reduction additives in FCC unit, as it does not require additional process and capital cost. Spinels MAl2O4 (M2þ metal ion) are widely used as catalysts or catalyst supports for different applications due to their high acidity, good chemical stability, melting points and mechanical strength [5,6]. In the FCC field, these additives have been used for reducing SOx emission during regeneration of FCC catalyst and reducing the sulfur level of cracked products such as gasoline fuel. The mechanism by which the Lewis acid containing spinel based additive removes the sulfur components normally present in cracked hydrocarbon products (hydrogen sulfide, thiols, disulfide, thiophenes and alkyl thiophenes derivatives, and benzothiophene) is not precisely understood. It is believed the Lewis base (basic) sulfur species produced in the cracking of sulfur containing hydrocarbons such as gas oil, interact with Lewis acid on spinel based additive by adsorption or chemical reaction [7]. Other additives tested to assess their effectiveness in reducing sulfur species in gasoline include Zn/alumina, Ti/alumina and Ga/alumina [8], Ni, Cu, Zn, and Ag aluminates [9e12], V/alumina [13,14] and ZneMg spinels [15], were studied by different authors. Effects of operating conditions, feed composition and catalyst type on sulfur in gasoline were studied by Valla et al., Stratiev et al. and Gatte et al. [16e18]. Yaoshun et al. [7] indicated that the desulfurization activity and product distribution should be both taken into consideration during the cracking desulfurization process. Effects of USY/ZnO/Al2O3 additive were studied in a confined fluidized bed unit for catalytic cracking experiments with vacuum gas oil (VGO) as feed by Yi et al. [19]. The literature information also indicated that the commercial industry data by using gasoline sulfur reduction (GSR) additive demonstrated that the degree of sulfur reduction is limited, not more than 20e30 wt% [7]. While studying sulfur removal efficiency of GSR additives, the octane number of gasoline property should be taken into consideration, as the FCC gasoline contains lot of olefins (20e40 wt %), which provides it with a fairly good octane number. Therefore, the challenge is to eliminate maximum amount of sulfur impurities with a minimum olefin saturation

to maintain RON [1]. However, most of the available literature does not discuss collectively about the sulfur reduction capability along with gasoline RON interaction using different spinel based additive and their preferential sulfur removal in different product cut by using real FCC feed. Hence, the present work discusses in detail about the in-situ sulfur reduction, olefin saturation and consequent implication on RON of gasoline produced from FCC unit by using spinel based additives along with base catalyst by employing combined feed stock at the identical reaction condition.

Reaction mechanism and gasoline sulfur species In FCC unit, typically ~35e45% of the feed sulfur is converted to H2S, 2e5% is found in coke, 2e10% in gasoline and the rest ends up in the light cycle oil (LCO) and bottoms [20,21]. Fig. 1 illustrates percentage distribution of sulfur components in FCC products. The reactivity of feed sulfur compounds and the mechanism by which they end up in gasoline is a subject of ongoing study. The literature [21] indicates that there are three mechanisms for the reduction of sulfur in gasoline. The primary ‘dilution' mechanism is most effective at lower conversions. The gasoline forming reaction follows the second order equation pattern at FCCU conditions. At a particular temperature, while increasing the conversion in the FCC unit, the yield of gasoline starts increasing and reaches the optimum level. Further increase of conversion reduces the gasoline yield and it starts to crack into lighter components like LPG and dry gas. If the catalyst/oil has to be increased further to achieve the same conversion after the addition of an additive to the base catalyst, and then it indicates the dilution effect of additives due to lower cracking activity. However, the sulfur concentration ending up in the liquid gasoline product remains the same. Therefore, increasing the gasoline yield decreases the overall percentage of sulfur levels in the gasoline. The net effect is a reduction of sulfur concentration in gasoline due to the increase of gasoline yield with the low sulfur material. The second mechanism is the ‘inhibition of sulfur species formation'. Most of the sulfur species found in the product gasoline are formed during cracking; they are not present initially in the feed. Primarily the sulfur containing feed hydrocarbon molecules catalytically crack to more valuable products and less difficult sulfur compounds due to the presence of Y-zeolite and selective matrix components. A secondary effect is due to the active alumina sites of FCC catalyst, which allow cracking of sulfur compounds themselves, which are originally present in the fresh feed or products. Therefore, the sulfur species formation can be altered based on the amount of active alumina sites present in catalyst system. The third mechanism is the ‘cracking of sulfur species'. In this mechanism, the sulfur species are cracked after they are formed. The sulfur removed is released as H2S along with dry gas. The ability to catalytically reduce sulfur content in FCC gasoline is limited by the molecular species that are present. The typical full range of FCC gasoline has sulfur in the form of

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Feed Sulfur FCC H2S +LPG (35-45%) Gasoline

Light Cycle Oil

Heavy Cycle Oil

Coke

(2-10%)

(10-25%)

(5-35%)

(2-5%)

Fig. 1 e Distribution of sulfur components in FCC products.

mercaptans, sulfides, disulfides, thiophene and its alkyl derivatives. Some of these are easier to remove than others. The mercaptans, sulfides, and disulfides are primarily present in the lighter fraction of the gasoline stream and can be cracked very easily on active catalyst sites. The sulfur is mostly liberated as H2S. The heavier fractions of FCC gasoline (in the boiling range of about 220  C) containing sulfur molecules (thiophenes and its alkyl derivatives) are very stable molecules and cannot be cracked easily and the quality of fractionation can have a big impact on their concentration. Hence, enhancing the conversion of thiophenes and its alkyl derivatives is also the key target for in-situ sulfur removal through the FCC process.

Experimental Feed In this study, heavy hydrocarbon feedstock containing unconverted oil (UCO): vacuum gas oil (VGO): low sulfur vacuum residue (LS-VR): straight run naphtha (SRN) with the

Table 1 e Feed properties of combined heavy feedstock. Property

Value 

Density, gm/cc @ 15 C Viscosity, CST @ 100  C Total Nitrogen, ppmw Sulfur, ppmw CCR, wt% Distillation, D-1160 Vol % IBP 10 30 50 70 80 90 100

0.8824 7.72 2200 5521 2.9 Boiling Point,  C 187 381 434 463 514 573 590 (82%) e

composition in weight % respectively as 26.2, 54, 16, and 3.8 is used and its major properties are given in Table 1.

Base catalyst and additive preparation The commercial fresh catalyst is used as the base catalyst. The GSR additives were prepared from zinc (Zn), magnesium (Mg) and copper (Cu) based spinel support. Stoichiometrically zinc, magnesium, and copper aluminate spinel (ZnAl2O4, MgAl2O4, and CuAl2O4) were prepared by a co-precipitation method [22e25] using aqueous solutions of the following metal nitrates: Mg(NO3)2$6H2O, Cu(NO3)2$H2O and Zn(NO3)2$6H2O. A solution of sodium aluminate was used as base material and precipitating agent. The solutions of nitrates and aluminate were simultaneously added with vigorous stirring. During the precipitation, the pH is maintained at 10.0. The slurry obtained was stirred for 30 min at 40  C, then filtered and washed with distilled water. The prepared materials were dried and calcined in air at 850  C for 2 h to produce the spinel structure from the double hydroxide. The spinel precursor slurry (25 wt%) was then mixed with binder alumina matrix (25 wt%) and clay (50 wt%) to prepare an additive. The prepared slurry was mixed uniformly by using over head stirrer for 1 h at room temperature. Temperature was maintained by using the recirculating water bath. The final slurry was then spray dried in a conventional spray dryer (ACMEFIL Model supplied by M/s. ACMEFIL Engineering Pvt Ltd) fitted with two fluid nozzles in counter current mode. The spray dried products were calcined and characterized for physicoechemical properties.

Characterization of base catalyst and additives The prepared GSR additives (additive A (ZnAl2O4), additive B (MgAl2O4), and additive C (CuAl2O4)) were tested for physical e chemical properties such as surface area, pore volume, average particle size, pore size distribution, apparent bulk density, XRD, chemical composition and total acidity. The surface area, pore volume, average particle size and pore size distribution of additives were measured by sorption analyzer (Model: TriStar II 3020) of Micromeritics using

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nitrogen as sorbent at 77 K. Prior to analysis, the samples were degassed for 3 h at 400  C under vacuum (105 bar) in the degassing port of the adsorption analyzer. Apparent Bulk Density (ABD) was measured by Density Meter (Model-IH-2000) of Seishin. The X-ray diffraction (XRD) patterns of additive support were recorded with a 18 kW X-ray diffractometer (Model: DMax-25500/PC) of Rigaku, using CuK radiation as the X-ray source. The high angle diffractograms were recorded in the 2q range of 5e80 in steps of 0.02 with a count time of 20 s at each point. Rare earth (lanthanum and cerium) content of the base catalyst was measured using 4-kW wavelength dispersive Xray fluorescence (Model: ZSX Primus) using Rh as the X-ray source. The dispersed X-rays were measured by scintillation counter and flow proportional detector. A temperature programmed desorption (TPD) experiment was conducted for additive samples by employing ammonia as probe molecule in a temperature range of 100e500  C with a linear heating rate of 10  C min1. Thermal conductivity detector (TCD) was used to obtain desorption profile to measure the catalyst total surface acidity (Micromeritics AutoChem II 2920 analyzer). 0.3 g of sample weighed in a quartz container, degassed for 1 h at 550  C at a temperature rate of 10  C/min. After degassing, the sample was cooled down to 120  C for conducting adsorption experiment. NH3/He gas mixture (10% ammonia, 90% helium) was used to saturate the catalyst sites. Ammonia adsorption was carried out for 1 h at 120  C to assess the acidity of active sites. In order to remove physisorbed ammonia, the ammonia flow was switched off and replaced by an inert purge gas (He) at a rate of 50 mL/min for 1 h at 120  C. Then, the temperature was raised at a rate of 10  C/min and NH3-TPD chromatograms were recorded by TCD.

Performance evaluation of additives Pretreatment of fresh FCC/RFCC catalyst and GSR additives The metal free base catalyst/additive deactivation was accomplished by steam treatment at elevated temperature to simulate the hydrothermal deactivation, which occurs in a commercial regenerator. The base catalyst and additives were deactivated at a temperature of 810  C for 5 h with 100% steam.

Simulated micro activity test (MAT) The activity measurement for base catalyst and additive samples (10 wt% concentration) was done using advanced cracking evaluation resid (ACE Rþ) MAT unit supplied by M/s. Kayser technologies, USA. The experiments were carried out at the catalyst/oil ratio of 4.5, 6.0 and 7.5 by varying the amount of catalyst loading (with and without additive) at a constant feed rate and feed injection time. The feed injection time was such; it minimized the effect of time averaging on yields because of catalyst deactivation due to the formation of coke. Reactor operating temperature was maintained close to the riser outlet temperature in the commercial plant (i.e. 510  C). After the completion of the reaction, the catalyst was stripped with nitrogen to remove adsorbed reaction products. Coke on the catalyst was determined by in-situ regeneration at about 650  C by fluidizing with air. The gaseous sample was analyzed, online, by M/s. Agilent micro

gas chromatography analyzer. The H2, C1, C2, C3, C4, and C5 lump were determined quantitatively. The liquid products were diluted in the CS2 solvent and analyzed in a simulated distillation analyzer (Make and Model e Perkin Elmer Clarus 500 gas chromatography). The percentage of the liquid products boiling in the range of gasoline (C5-150  C), heavy naphtha (C150-216  C), light cycle oil (C-216 -370  C) and clarified oil (370  Cþ) were calculated. Carbon content of the catalyst was determined by online IR analyzer (Make and Model e Servomex 1440). The collected product samples were analyzed for the presence of sulfur in Analytical Control's high-temperature carbon e nitrogen e sulfur simulated distillation (HT CNS SIMDIST) analyzer with Agilent 7890B gas chromatography. The paraffin, olefins, naphthenes, and aromatics (PONA) analysis and RON of the product samples were analyzed in Analytical Control's built-in custom paraffin, iso-paraffins, olefins, naphthenes and aromatics (PIONA) pre-fractionator M3 reformulyzer analyzer with Agilent's 7890 gas chromatography.

Results and discussions Physicalechemical properties characterization To give an insight into the textural properties of additives, surface area and pore volume were measured and the results are shown in Table 2. The N2 adsorption-desorption isotherms were measured and the result is shown in Fig. 2. Additive A exhibited high surface area and total pore volume (108 m2/g and 0.26 cc/g) when compared to additive B (98 m2/g and 0.21 cc/g) and additive C (91 m2/g and 0.22 cc/g) respectively. The high pore volume of additive A is due to actual mesopores and does not represent intra-crystalline void volume. The result is well supported by the observation cited earlier [26]. This is evident from the broad hysteresis effect in desorption curve at the P/P0 range of 0.7e1.0 for additive A as illustrated in Fig. 2. The N2 adsorption isotherm for additive B and additive C showed a gradual rise at the relative pressures (P/P0) of 0.5e1.0 and 0.6e1.0 respectively. All these three samples have indicated that there is no adsorbent e adsorbate interactions when P/P0 is below of 0.5, which means, there is no micro pore present. Further N2 adsorption-desorption isotherms also indicated that all the additives have type IV isotherms with pronounced H2 hysteresis loops, which are the characteristics of many mesoporous materials [26]. The pore size distribution (PSD) was measured and the result is shown in Fig. 3. The BJH pore-size distribution demonstrated that all samples have different pore size distribution. Additive A has the highest <40  A size (16.9%) and 40e80  A size (33%) when compared to additive B < 40  A size (8.2%) and 40e80  A size (26.5%) and additive C < 40  A size (8.5%) and 40e80  A size (32%). As depicted in Fig. 3, the additive C possesses highest average pore diameter of 94.2  A. It is confirmed that the pore size distribution of all additives showed bimodel distribution patterns. A narrow peak in the range of 30e40  A in PSD curve depicts inter particle pore structure of

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Table 2 e Physicoechemical characterization of base catalyst and additives. Properties

Base catalyst

Additive-A Zinc Aluminate

Additive-B Magnesium Aluminate

Additive-C Copper Aluminate

220 0.32 76 0.89 52.62 3.5

108 0.26 72 0.88 87.3 e

98 0.21 77 0.76 81.6 e

91 0.22 68 0.84 94.2 e

Surface area, m2/g Pore Volume, cc/g APS, micron Apparent Bulk Density, g/cc Average Pore Diameter  A Re2O3

Quanty Adsorbed (cm3/gm STP)

metal oxide and a broad distribution curve in the range of 50e100  A shows pore structure of matrix interaction in additives. The XRD pattern of spinel support was taken to confirm the formation of spinel structure and the result is shown in Fig. 4. XRD phase analysis result confirmed the formation of spinel structure (MAl2O4). Distinctive reflections at 31, 37, 45, 49, 55, 58, 65 and 74 (2q) correspond to the formation of spinel phases of different support, which are used in the preparation of additive A, additive B and additive C. The result is well supported by the observation in literature [27e29]. As compared to other spinel supports the two peaks at 35.5 and 38.6 (2q) in additive C indicates the formation of monoclinic phase of CuO present. The result is very well correlated with the earlier studies [30e32]. The calcination temperature of 850  C could have been sufficient for converting other materials such as zinc and magnesium to convert to spinel phase, but not sufficient for copper [33]. The literature findings match well with the

current findings for additive A; i.e. a narrow peak in the range of 30e40  A in PSD curve (Fig. 3), which indicates that the particle pore structure of zinc metal oxide is lesser. The XRD data for additive samples were not done due to the interference of amorphous nature of matrix alumina and clay. The total surface acidity was measured by temperature programmed desorption of ammonia (NH3-TPD) method for both base catalyst and spinel based additives (ZnAl2O4, MgAl2O4, and CuAl2O4) and is shown in Fig. 5. The NH3-TPD profiles for the base catalyst and additives were drawn with the amount of ammonia desorbed as a function of temperature. The area of the peaks correspond to a number of acid sites in that temperature region. Base catalyst, additive A, additive B and additive C exhibited total acidity of 0.163, 0.195, 0.211 and 0.432 mmol/g respectively. The ammonia desorbed in the temperature range of 100e950  C is divided into three different temperature regions ( C) such as 100e300, 301e600 and 601e950 and assigned as weak, medium and strong acid sites respectively. However, the

250 240 230 220 210 200 190 180 170 160 150 140 130 120 110 100 90 80 70 60 50 40 30 20 10 0 0.0

0.1

0.2

0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 Relave Pressure (P/Po) Base Catalyst Addive A ZnAl₂O₄ Addive B MgAl₂O₄ Addive C CuAl₂O₄

Fig. 2 e Adsorption e Desorption isotherm.

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Fig. 3 e Pore size distribution.

quantification of Bronsted and Lewis acid sites could not be established due to the limitation in the NH3-TPD techniques [34]. Table 3 presents data illustrating the distribution of acid sites based on TPD of ammonia from the base catalyst and additives. Additive C has shown a higher area under the curve in the range of 100e300  C, 301e600  C and 601e950  C as compared

to additive A, additive B, and base catalyst. Next, to additive C, the base catalyst has shown the larger area under the curve in the range of 100e300  C, which indicates the presence of weak acid sites. The influence of profile area at 100e300  C of base catalyst indicates the presence of zeolite (Re-Y). Next, to additive C, additive B has shown the larger area under the curve range of 300e600  C, which indicates the presence of medium

Fig. 4 e XRD patterns of ZnAl2O4 support, MgAl2O4 support and CuAl2O4 support. Please cite this article in press as: Karthikeyani AV, et al., In situ FCC gasoline sulfur reduction using spinel based additives, International Journal of Hydrogen Energy (2017), http://dx.doi.org/10.1016/j.ijhydene.2017.08.006

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Fig. 5 e NH3-TPD profiles of different samples.

Table 3 e Distribution of acid sites. Acid sites, mmol/gm Weak acid sites (0e300)  C Medium acid sites (301e600)  C Strong acid sites (601e950)  C Total acid sites

Base catalyst

Additive-A Zinc Aluminate

Additive-B Magnesium Aluminate

Additive-C Copper Aluminate

0.079 0.079 0.006 0.163

0.076 0.102 0.017 0.195

0.019 0.177 0.016 0.211

0.095 0.273 0.064 0.432

Fig. 6 e Feed sulfur-boiling point distribution. Please cite this article in press as: Karthikeyani AV, et al., In situ FCC gasoline sulfur reduction using spinel based additives, International Journal of Hydrogen Energy (2017), http://dx.doi.org/10.1016/j.ijhydene.2017.08.006

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Fig. 7 e Product sulfur boiling point distribution at catalyst/oil ratio of 5.5.

acid sites. However, additive A and additive B has shown the almost similar area under the curve range of 600e900  C.

Feed and product sulfur boiling point distribution The total sulfur content in the feedstock is 5521 ppm. Fig. 6 illustrates the distribution of sulfur, in ppm, with respect to the boiling point of the feedstock. After cracking reaction, the distribution of sulfur species in product gasoline for the feed containing 5521 ppm sulfur is shown in Fig. 7. The results correspond to a constant feed conversion of 76.37 wt% obtained for base catalyst and its blend with additives. Most of the sulfur present in FCC liquid product is produced through the cracking of heavy sulfur containing molecules, which are present in the feedstock. The feed sulfur is also converted into H2S so that the addition of H2S to the olefins or the diolefins produced through hydrocarbon cracking followed by a cyclization into tetrahydrothiophene compounds, which in turn, dehydrogenate into thiophene compounds [1]. Fig. 7 indicates that there is an increasing trend of sulfur content with boiling range. However, the distribution is quite irregular with respect to the specific sulfur species involved. Fig. 7 is divided into four boiling point range i.e., (35e150)  C, (150e216)  C, (216e370)  C and beyond 370  Cþ for better understanding. Therefore, cracking of carbon-sulfur bond in thiophene ring is an important reaction step in gasoline sulfur reduction under FCC conditions. Saturating some of these thiophene compounds is an important step in order to crack them to H2S. The use of high hydrogen transfer systems helps to reduce the recombination of H2S and olefins to reform mercaptans. The sulfur species in product light cycle oil between 216 and 370  C represent the presence of benzothiophene and di-

benzothiophene, which account for 58e60% of total sulfur contents. The sulfur species in unconverted clarified oil above 370  C represent the presence of heavy sulfur components and this accounts for 28e30%. The total liquid sulfur after cracking reaction in base catalyst, additive A, additive B, and additive C are 5248 ppm, 4304 ppm, 4495 ppm, and 4230 ppm respectively with respect to the feed sulfur of 5521 ppm.

Effect of catalyst/oil ratio on conversion The conversion data for feedstock was obtained with base catalyst and base catalyst along with additive by varying the catalyst/oil ratio 4e8 and the results are shown in Fig. 8. The conversion is defined as the ratio of the weight of products having components boiling below 216  C (i.e. Dry gas, LPG, gasoline, heavy naphtha, and coke) produced to the weight of the feedstock. Fig. 8 indicates that conversion increases with increasing catalyst/oil ratio. Additive C produces 1.3 wt% higher conversion than the base catalyst at catalyst/oil ratio of 5.5. Additive A and additive B produce low conversion as compared to the base catalyst. The results indicate that the activity of copper aluminate based additive C is better than the other additives based on zinc aluminate and magnesium aluminate. The XRD data of additive C indicates that the amorphous raw product did not transform into a pure aluminate phase. Rather an intermediate CuO phase became evident, which could have diminished with increasing the calcination temperature beyond 850  C while forming the spinel structure. This tendency of phase separation was observed only during the processing of copper aluminate precursor. This was possible because of the reduction of Cu2þ to the Cu1þ state, which after phase separation is again oxidized to a 2þ state after complete removal of carbonaceous

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Fig. 8 e Effect of catalyst/oil ratio on conversion.

matter. Therefore, the more conversion associated with additive C could be attributed to the strong acidity and hydrogen transfer function. The total yield of products i.e. dry gas, LPG, gasoline, heavy naphtha, light cycle oil, clarified oil and coke were estimated from Figs. 9e15 at the conversion of 76.37 (weight %) and the results are shown in Table 4. Table 4 indicates that the dry gas

selectivity is good for base catalyst with additive C when compared to additive A and additive B. All the additives have produced more LPG and less gasoline than the base catalyst. Additive B and additive C have produced more heavy naphtha than the base catalyst. Additive A and additive B have produced more light cycle oil than the base catalyst and less clarified oil. Additive A and additive C have produced more coke than that from the use of base catalyst. Fig. 16 illustrates the variation in yield of coke with varying catalyst/oil, and this indicates the coke making tendency of

Fig. 9 e Conversion Vs. dry gas yield.

Fig. 10 e Conversion Vs. LPG yield.

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Fig. 11 e Conversion Vs. gasoline yield. Fig. 13 e Conversion Vs. light cycle oil yield.

various additives. Coke yield from base catalyst with additive A and additive C is more than that from the pure base catalyst. However, the base catalyst with additive B has produced less coke yield at all the catalyst/oil ratio. Further, from Table

4, it can be seen that the gasoline and heavy naphtha yield achieved for the ZnAl2O4 case is 1.374 wt% and 0.165 wt% less when compared to the base catalyst. The coke yield of ZnAl2O4 (1.135 wt %) is higher than the base catalyst due to low

Fig. 12 e Conversion Vs. heavy naphtha yield.

Fig. 14 e Conversion Vs. clarified oil yield.

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Fig. 16 e Catalyst/Oil Vs. coke yield. Fig. 15 e Conversion Vs. coke yield.

hydrogen transfer activity. The other reason for increase in coke yield of ZnAl2O4 is the highest reduction in clarified oil range sulfur molecules [Table 5], which are the precursor for coke formation [8].

Sulfur reduction The amount of sulfur present in gasoline, heavy naphtha, light cycle oil, and clarified oil were measured and the sulfur obtained with different products with respect to conversion is shown in Figs. 17e20. The property of catalyst and additives influence the feed sulfur for their performance in the liquid products. The effect of acid-base properties of the additive is essential, however the Lewis base compounds present in the feedstock is also important, which can be strongly adsorbed on Lewis acids of the additives [35]. The additive having more mesopores is also important for the diffusion of substances, which enhances the synergy between acid types and increases the sulfur removal efficiency [28].

Further, the hydrogen transfer function also to be considered for evaluating the additives performance with respect to sulfur removal from the cracked products. The hydrogen transfer factor (HTF) is proposed to quantitatively analyze the degree of hydrogen transfer reaction of the additives, which is defined as the ratio of the weight percentages between paraffin and olefin in LPG and is shown in Fig. 21. All the additives have produced less gasoline sulfur than the base catalyst (402 ppm). Gasoline sulfur reduction is high for the additive C (339 ppm) followed by additive A (345 ppm) and additive B (357 ppm), which correspond to 15.5%, 14.11%, and 11.02% reduction respectively. The results correlate well with the acidity data, where additive C, additive A, and additive B possess larger area under the curve (0e300  C), which indicates the presence of weak acid sites. The presence of high total acid sites in additive C helped to increase the dehydrogenation reactions (low HTF), which converts the intermediate hydrogenated thiophene derivatives in the gasoline range molecule into hydrogen sulfide. Additionally, the high average pore diameter also helped to reduce the sulfur in gasoline of CuAl2O4 based additive C.

Table 4 e Yields at conversion e 76.37 weight%. Yields, Wt% Dry gas LPG Gasoline Heavy naphtha Light cycle oil Clarified oil Coke

BASE Yield, Wt%

Base þ 10% Additive A (ZnAl2O4)

Base þ 10% Additive B (MgAl2O4)

Base þ 10% Additive C (CuAl2O4)

1.63 16.61 42.51 10.96 16.33 7.30 4.67

1.98 16.66 41.13 10.80 16.44 7.18 5.80

1.70 16.82 41.94 11.32 16.73 6.89 4.60

1.40 17.37 41.54 11.30 15.97 7.65 4.76

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Table 5 e Liquid product sulfur distribution. Sulfur Component

Product Sulfur, PPM Base

Gasoline (C5-150  C)

Heavy naphtha (150e216  C)

Light cycle oil (216e370  C) Clarified oil (370  Cþ) Total Liquid ‘S’ PPM Feed ‘S’ PPM Sulfur in Gas and Coke, PPM % Liquid ‘S’ Reduction w.r.t Feed ‘S’

Additive A ZnAl2O4

Additive B MgAl2O4

Additive C CuAl2O4

Mercaptans Thiophene C1 e Thiophene Tetrahydrothiophene C2 e Thiophene C3 e Thiophene/Thiophenol C4 e Thiophene/C1 Thiophenol Benzothiophene Heavy sulfur component Heavy sulfur component e

402

345

357

339

177

212

142

149

3104 1608 5248

2539 1209 4304

2696 1300 4495

2491 1252 4230

e e e

5521 229 4.2

1217 22.04

1026 18.57

1290 23.36

As compared to heavy naphtha sulfur (177 ppm) from the use of a base catalyst, additive B has shown high heavy naphtha sulfur reduction of 20% (142 ppm) followed by additive C, which has shown 18% reduction (149 ppm). From Fig. 21 it can be seen that the HTF of additive A is high when compared to additive B and additive C, which indicates that additive A has low dehydrogenation function. Therefore, additive A (212 ppm) has given high sulfur when compared to sulfur from the use of a base catalyst (177 ppm). Further, the 100% spinel phase of ZnAl2O4 based additive A catalyzes cyclization reaction, which converts thiophene into bicyclic compounds such as alkyl benzothiophenes [16].

The current case is also matching with the literature finding, i.e., it reduces sulfur (thiophenes) in the gasoline and increases sulfur (benzothiophenes and alkyl benzothiophenes) in heavy naphtha and increases coke yield. In addition, the alkylation reactions must also be taken into consideration, if long chain alkyl benzothiophenes are present in the feed, they can easily transform either through dealkylation or cracking of the side chain into benzothiophene and short chain alkyl thiophenes which will end up in the gasoline range. ZnAl2O4 based additive has given high heavy naphtha sulfur as compared to the base catalyst due to the low hydrogen-transfer activity and the alkylation of thiophene to C1, C3, and C4 thiophene derivatives, which is also supported

Fig. 17 e Conversion Vs. gasoline sulfur.

Fig. 18 e Conversion Vs. heavy naphtha sulfur.

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i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y x x x ( 2 0 1 7 ) 1 e1 6

Fig. 19 e Conversion Vs. light cycle oil sulfur.

by the product sulfur distribution curve (Fig. 7) at the temperatures of 110  C, 170  C and 190  C [36]. Literature [13,37] findings also indicate that the additive with 50% ZnO/Al2O3 has the acid intensity and acid density that are appropriate for sulfur removal. It indicates that the large surface area with low ZnO content (10%) in ZnAl2O4 based additive doesn't

Fig. 20 e Conversion Vs. clarified oil sulfur.

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exhibit the best sulfur removal effect, which implies that ZnO content must be high enough; otherwise, sulfur removal effect will decrease. Therefore, the sulfur reduction in gasoline and heavy naphtha products of additive A is inferior when compared to other additives. Though the MgAl2O4 system does not show much sulfur reduction in the gasoline range, it has shown the better sulfur reduction in the heavy naphtha range. The heavy naphtha range sulfur molecule (for example dimethyl dibenzothiophene) is shifted to LCN range sulfur due to preferential dealkylation reaction for the MgAl2O4 additive. Further, this correlates very well with the literature findings [32] that the MgAl2O4 spinel phase at the Mg/Al molar ratio of 0.5 possesses the lowest amount of Lewis acid sites because of the good atomic compatibility. The light cycle oil sulfur reductions are in the order of 19.75%, 18.23% and 13.5% for additive C, additive A, and additive B respectively. The MgAl2O4 based additive B converts the heavy naphtha range sulfur molecules to light cycle oil and clarified oil range sulfur molecules through alkylation of light thiophenes compounds by olefins produced by cracking of hydrocarbons during FCC reaction process. The clarified oil sulfur reduction is high for additive A (24.86%) as compared to additive B and additive C, which has a sulfur reduction of 19.18% and 22.17% respectively. The result indicated a possible total liquid sulfur reduction by using additive A, additive B, and additive C as 22.04%, 18.57%, and 23.37% respectively. The long chain thiophenes can be formed in-situ through alkylation of light thiophene compounds by olefins produced by cracking of hydrocarbons, which is an important source for the formation of benzothiophene derivatives and coke during the FCC process.

Sulfur reduction vs research octane number Gasoline samples obtained from MAT experiment by using base catalyst and base catalyst along with additives were analyzed in PIONA analyzer for the determination of PONA distribution carbon number wise and to calculate RON. Fig. 22 depicts gasoline yield and RON with respect to conversion. The PONA analysis is calculated at 76.37 wt% and the results are given in Table 6. From Fig. 22 it can be seen that in all the ranges of conversion, the gasoline yield is high and RON is low with the pure base catalyst as compared to a base catalyst with additives. Gasoline yield with additive A, additive B, and additive C is less in comparison with gasoline yield from the use of a pure base catalyst; however, RON is better for all the additives as compared to base catalyst (Table 6). Rare earth metals in base catalyst control activity, coke selectivity, olefin selectivity of zeolite portion. The density of acid site can also be controlled with the amount of rare earth metal present in the base catalyst. Base catalyst with the low amount of rare earth metal show low density of acid site and thus prevent the hydrogen transfer reaction. However, the decrease of the rare earth metal causes a decrease of cracking activity, since the rare earth metal stabilizes the structure of USY zeolite which maintains the acid site [16]. In the current case, the base catalyst possesses a high rare earth content of 3.5 wt% (Table 2), which indicates the presence of high acid site density and also increased hydrogen transfer reaction.

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Fig. 21 e Hydrogen transfer reaction obtained from MAT LPG data.

Fig. 22 e Conversion Vs. gasoline yield and research octane number. Please cite this article in press as: Karthikeyani AV, et al., In situ FCC gasoline sulfur reduction using spinel based additives, International Journal of Hydrogen Energy (2017), http://dx.doi.org/10.1016/j.ijhydene.2017.08.006

i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y x x x ( 2 0 1 7 ) 1 e1 6

Table 6 e RON of Gasoline sample calculated at 76.37 wt%. RON

Paraffin Olefin Naphthene Aromatics RON

Base

Additive A ZnAl2O4

Additive B MgAl2O4

Additive C CuAl2O4

26.02 26.58 8.37 39.03 88.46

25.44 26.52 8.11 39.93 91.7

26.05 26.12 7.81 39.48 92.61

26 30.38 8.89 34.73 94

The increase in weight of alumina with the larger pore in the spinel based additive will help to solve these problems i.e. reduction of hydrogen transfer reaction. In the current case, though the CuAl2O4 based additive C has the same alumina content of additive A and additive B, but it has the highest average pore diameter of 94.2  A (Table 2), which helps to retain the olefin content and produce high octane number gasoline of value 94. For understanding octane loss or gain, the sulfur concentrations should also be taken into consideration, as it depends both on thermodynamics (intermediates resulting from the addition of H2S to olefins or diolefins) and on kinetics (products resulting from consecutive steps) [35]. The recombination rate of CuAl2O4 based additive A is low i.e., the recombination of formed H2S from the decomposition of the sulfur compounds present in the feed to the olefins and diolefins formed from the cracking reaction, significantly lower the olefin saturation and octane loss. Secondly, the additive with transition metal ions exhibit high dehydrogenation activity (low HTF) and can promote the formation of light alkenes in the FCC process. Therefore, the presence of CuO in additive C maximized light alkenes yield (propylene, butylenes, and gasoline olefins) without increasing coke formation. Compounds with 100% spinel structure facilitate the aromatization of olefin type hydrocarbons formed during catalytic cracking. Aromatization leads to the release of additional amounts of hydrogen, which can result in the formation of hydrogenated sulfur derivatives [1]. In the current case, where ZnAl2O4 based additive A and MgAl2O4 based additive B follows the said mechanism, which can be correlated with the gasoline sulfur amount (Table 5), olefin content (Table 6) and hydrogen transfer reaction shown in Fig. 21.

Conclusions The current study has shown that the CuAl2O4 based additive produces 1.3 wt% higher conversion than the base catalyst due to the presence of high total acidity of additive. Gasoline range sulfur reduction is high for CuAl2O4 based additive (15.5%) when compared to ZnAl2O4 and MgAl2O4 based additives (14.11% and 11.02%) due to the formation of high acidity, which is mainly due to the presence of mixed metal oxide and spinel phase. The other reason is that the CuAl2O4 based additive has more mesopores, which is also an important feature for the diffusion of substances to enhance the synergy between acid types and thereby increase the sulfur removal efficiency. ZnAl2O4 based additive has given high heavy

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naphtha sulfur as compared to the base catalyst due to the low hydrogen-transfer activity and the alkylation of thiophene to C1, C3, and C4 thiophene derivatives. The Light Cycle Oil sulfur reduction is high for CuAl2O4 based additive as compared to ZnAl2O4 and MgAl2O4 based Additive. The Clarified Oil sulfur reduction is high for ZnAl2O4 based additive as compared to MgAl2O4 and CuAl2O4 based additive. However, ZnAl2O4 based additive has increased the coke yield, as the heavy sulfur molecules are the precursors for coke formation. The recombination of formed H2S from the decomposition of the sulfur compounds present in the feed to the olefins and diolefins formed from the cracking reaction is lower for CuAl2O4 based additive, which helped to increase the olefin content (30.38 wt %) and its RON (94). The 100% spinel phase formation in the ZnAl2O4 and MgAl2O4 based additives assists the aromatization of olefin type hydrocarbons formed during catalytic cracking and release of additional amounts of hydrogen and thus produces hydrogenated sulfur derivatives and almost maintains the similar PONA analysis.

Acknowledgement The authors acknowledge the characterization support provided by Dr. J. Christopher and evaluation support provided by Mr. B. Swamy of IOCL R&D Centre.

references

[1] Brunet Sylvette, Mey Damien, Perot Guy, Bouchy Christophe, Diehl Fabrice. On the hydrodesulphurization of FCC gasoline: a review. Appl Catal A General 2004;278:143e72. [2] International council on clean transportation. WWW. THEICCT.ORG; 2016. [3] Song Chunshan. New approaches to deep desulfurization for ultra clean gasoline and diesel fuels: an overview. Fuel Chem Div Prepr 2002;47:438e44. [4] Largeteau D, Ross J, labored M, Wisdom L. Challenges and opportunities of 10 ppm sulfur gasoline: Part 1. 2012. www. digitalrefining.com/article/1000547. PTQ Q3. [5] Yang M, Men Y, Li S, Chen G. Hydrogen production by steam reforming of dimethyl ether over ZnO-Al2O3 bi-functional catalyst. Int J Hydrogen Energy 2012;37:8360e9. [6] Francisco FS, Helvio SAS, Alcemira CO, Manoel CCJ, Alejandro PA, Eduardo BB, et al. Nanostructured Nicontaining spinel oxides for the dry reforming of methane: effect of the presence of cobalt and nickel on the deactivation behaviour of catalysts. Int J Hydrogen Energy 2012;37:3201e12. [7] Wen Yaoshun, Wang Gang, Xu Chunming, Gao Jinsen. Study on in situ sulfur removal from gasoline in fluid catalytic cracking process. Energy fuels 2012;26:3201e11. [8] Bari Siddiqui MA, Shakeel A, Aitani AM, Dean CF. Sulfur reduction in FCC gasoline using catalyst additives. Appl Catal A General 2006;303:116e20. [9] Richard FW, Gwan K. Sulfur reduction in FCC gasoline. US Patent No 5,525,210 1996. [10] Michael SZ, Michael DA, Robert HH, Richard FW. Compositions for use in catalytic cracking to make reduced sulfur content gasoline. US Patent No 6,036,847 2000. [11] Mystad T, Boe B, Rytter E, Engan H, Corma A, Rey F. Reduction of sulfur content in FCC naphtha. US Patent No 6,497,811 2002.

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16

i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y x x x ( 2 0 1 7 ) 1 e1 6

[12] Richard FW, Gwan K. Sulfur reduction in FCC gasoline. US Patent No 5,376,608 1994. [13] Roberie TG, Ranjit K, Michael SZ, Wu CC, Xinjin Z Nazeer B. Gasoline sulfur reduction in FCC. US Patent No 6,482,315 2002. [14] Chester AW, Timken HKC, Ziebarth MS, Roberie TG. Gasoline sulfur reduction in FCC. US Patent No 6,852,214 2005. [15] Vargas-Tah AA, Garcia RC, Archila LFP, Solis JR, Lopez AJG. A study on sulfur reduction in FCC gasoline using ZneMgeAl spinels. Catal Today 2005:107e8. 713718. [16] Valla JA, Lappas AA, Vasalos IA, Kuehler CW, Gudde NJ. Feed and process effects on the in situ reduction of sulfur in FCC gasoline. Appl Catal A 2004;276:75e87. [17] Stratiev DS, Shishkova I, Tzingov T, Zeuthen P. Industrial investigation on the origin of sulfur in FCC gasoline. Ind Eng Chem Res 2009;48:10253e61. [18] Gatte RR, Harding RH, Albro TG, Chin DS, Wormsbecher RF. Influence of catalyst on sulfur distribution in FCC gasoline. Symposium on impact of environmental constraints on fuel composition. ACS Spring (SAN FRANCISCO) 1992;37(1):33e40. [19] Yi LC, Feng D, Min YQ, Hong SH, He YC, Fang ZJ. Evaluation of sulfur removal additive for FCC gasoline in a recycling fluidized bed apparatus. Prepr Pap Am Chem Soc Div Fuel Chem 2003;48(2):708e9. [20] Kirk-Othmer Encyclopedia of chemical technology. FCC catalysts and additives, vol. 1. Copyright John Wiley & Sons Inc. Retrieved from www.knovel.com. [21] Brown M, Evans M. FCC gasoline sulfur reduction using catalyst additives mechanisms and commercial experiences. In: 23rd annual Saudi-Japan symposium on “catalysts in petroleum refining and petrochemicals”, December 2e3, 2013 at KFUPM-research Institute, Dhahran, Saudi Arabia. [22] Movasati A, Alavi SM, Mazloom G. CO2 reforming of methane over Ni/ZnAl2O4 catalysts: influence of Ce addition on activity and stability. Int J Hydrogen Energy 2017;42:16436e48. [23] Katheria S, Gupta A, Deo G, Kunzru D. Effect of calcinations temperature on stability and activity of Ni/Al2O4 catalyst for steam reforming of methane at high pressure condition. Int J Hydrogen Energy 2016;41:14123e32. [24] Gonzalez CJ, Boukha Z, de Rivas B, Velasco JRG, Ortiz JIG, Fonseca RL. Behaviour of nickel e alumina spinel (NiAl2O4) catalysts for isooctane steam reforming. Int J Hydrogen Energy 2015;40:5281e8. [25] Bae JW, Kang SH, Dhar GM, Jum KW. Effect of Al2O3 content on the adsorptive properties of Cu/ZnO/Al2O3 for removal of odorant sulfur compounds. Int J Hydrogen Energy 2009;34:8733e40.

[26] Dhak D, Pramanik P. Particle size comparison of softchemically prepared transition metal (Co, Ni, Cu, Zn) aluminate spinels. J Am Ceram Soc 2006;89:1014e21. [27] Magdalena J, Chmielarz L, We˛grzyn A, Guzik K, Piwowarska Z, Witkowski S, et al. Thermal transformations of CueMg (Zn)eAl (Fe) hydrotalcite-like materials into metal oxide systems and their catalytic activity in selective oxidation of ammonia to dinitrogen. J Therm Anal Calorim 2013;114:731e47. [28] Yanyan J, Jinggang L, Xiaotao S, Guiling N, Chengyu W, Xiumei G. CuAl2O4 powder synthesis by sol-gel method and its photo degradation property under visible light irradiation. J Sol-Gel Sci Technol 2007;42:41e5. [29] Gholami T, Niasari MS. Green facile thermal decomposition synthesis, characterization and electrochemical hydrogen storage characteristics of ZnAl2O4 nanostructure. Int J Hydrogen Energy 2017;42:17167e77. [30] Niasari MS, Davar F, Farhad M. Synthesis and characterization of spinel-type CuAl2O4 nanocrystalline by modified solegel method. J Sol-Gel Sci Technol 2009;51(1):48e52. [31] Keyson D, Volanti DP, Cavalcante LS, Simoes AZ, Varela JA, Longo E. Synthesis of a complex nanostructure of CuO via a coupled chemical route. Mater Express Res 2008;43:771e5. [32] Feng R, Megren HA, Li X, Al-Kinany MC, Qiao K, Liu X. The effects of magnesium of Zn-Mg-Al additives on catalytic cracking of VGO and in-situ reduction of sulfur in gasoline. Appl Petrochem Res 2014;4:329e36. [33] Kiss E, Ratkovic S, Vujicic D, Boskovic G. Accelerated polymorphous transformations of alumina induced by copper ions impede spinel formation. Indian J Chem Sect A 2012;51:1669e76. [34] Shimoda N, Faungnawakij K, Kikuchi R, Eguchi K. A study of various zeolites and CuFe2O4 spinel composite catalysts in steam reforming and hydrolysis of dimethyl ether. Int J Hydrogen Energy 2011;36:1433e41. [35] Potapenko OV, Doronin VP, Sorokina TP, Gulyaeva TI, Drozdov VA. Effect of the acid e base properties of additives for a cracking catalyst on the sulfur content in liquid products. Catal Ind 2011;3:51e156. [36] Li C, Shan H, Yuan Q, Yang C, Zhang J. Effect of ZnO content on sulfur removal additives for FCC gasoline. Prepr Pap Am Chem Soc Div Pet Chem 2002;47(4):402e3. [37] Myrstad T, Engan H, Seljestokken B, Rytter E. Sulfur reduction of fluid catalytic cracking (FCC) naphtha by an in situ Zn/Mg (Al) O FCC additive. Appl Catal A 1999;187:207e12.

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