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Al2O3 catalysts
Accepted Manuscript Title: Phenomenological Kinetics Modeling of Simultaneous HDS of Dibenzothiophene and Substituted Dibenzothiophene over CoMoP/Al2 O3 Catalysts Author: Ahmad H. Al-Rashidy Syed A. Ali Shakeel Ahmed Shaikh A. Razzak Mohammad M. Hossain PII: DOI: Reference:
S0263-8762(15)00375-5 http://dx.doi.org/doi:10.1016/j.cherd.2015.10.001 CHERD 2034
To appear in: Received date: Revised date: Accepted date:
9-7-2015 19-9-2015 1-10-2015
Please cite this article as: Al-Rashidy, A.H., Ali, S.A., Ahmed, S., Razzak, S.A., Hossain, M.M.,Phenomenological Kinetics Modeling of Simultaneous HDS of Dibenzothiophene and Substituted Dibenzothiophene over CoMoP/Al2 O3 Catalysts, Chemical Engineering Research and Design (2015), http://dx.doi.org/10.1016/j.cherd.2015.10.001 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
PHENOMENOLOGICAL KINETICS MODELING OF SIMULTANEOUS HDS OF DIBENZOTHIOPHENE AND SUBSTITUTED DIBENZOTHIOPHENE OVER COMOP/AL2O3 CATALYSTS
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Ahmad H. Al-Rashidy1, Syed A. Ali2, Shakeel Ahmed2, Shaikh A. Razzak1, Mohammad M. Hossain1,2* 1
Department of Chemcial Engineering, Center of Research Excellence in Petroleum Refining and Petrochemicals, King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia
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ABSTRACT
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A series of CoMo/γ-Al2O3 catalysts modified with P2O5 were prepared. The phosphorus concentration varied from 0.0 to 1.0 wt.% P2O5. The catalysts prepared were evaluated in a batch autoclave reactor to investigate the effect of P2O5 on the simultaneous MDBT).
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hydrodesulfurization (HDS) of dibenzothiophene (DBT) and 4-methyl dibenzothiophene (4The phenomenological based kinetics models are developed based on the
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experimental conversion and selectivity data. The analysis of the developed model suggests that a Langmuir-Hinshelwood mechanism fits the experimental data adequately. The rate
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constants for the formation of BP are 6-8 times higher than the rate constants for the formation of CHB. Similarly, the rate constants for the formation of MBP are 3-5 times
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higher than the rate constants of MCHB formation. These observations indicate that the HDS of the model compounds through the DDS route is several times faster than the HDS through the HYD route. Furthermore, the rate constant for the formation of BP and CHB is about two times higher than the respective rate constant for the formation of MBP and MCHB. The addition of P2O5 favored the DDS pathway over the HYD pathway for both DBT and 4MDBT.
Keywords: Kinetic modeling, CoMo/Al2O3, P2O5 promotion, HDS, DBT, 4-MDBT *Corresponding author: Tel: +966 13 860 1478; E-mail address: [email protected] (M. M. Hossain)
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1. INTRODUCTION Environmental regulations have been enacted in many countries to reduce the sulfur content
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in diesel fuel to ultra-low levels (10-15 ppm) to circumvent the harmful effects of exhaust emissions. Meeting such stringent sulfur specifications represents a major operational and
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economic challenge for the petroleum refining industry (Cooper and Knudsen, 2006; Babich
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and Moulijn, 2007). Factors that influence the ultra-deep desulfurization of diesel feed streams include activity of the HDS catalyst and the reactivities of different species of sulfur
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compounds (Stanislaus et al., 2010). Several studies have shown that the sulfur compounds that remain in the diesel fuel after conventional HDS are mainly dibenzothiophenes (DBTs),
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especially those with alkyl substituents at the 4 and 6 positions (Shafi and Hutchings, 2000; Bej et al., 2004). Removal of these refractive sulfur compounds is necessary to achieve the
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10-15 ppm sulfur content specifications of ultra-low sulfur diesel.
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Most conventional industrial HDS catalysts used contain molybdenum and cobalt or nickel
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supported on γ-Al2O3, which are modified by addition of promoters to improve their performance. Lewis et al. (1992) studied the effect of modifying Ni-Mo/Al2O3 catalysts with 0-7 wt% phosphorus and reported that 1 wt% of phosphorus loading was optimal. The promotional effect of phosphorus was attributed to the higher dispersion and lower reducibilty/sulfidibilty of molybdate. Studies by Liu and his coworkers reported that the interaction between the active component and the γ-Al2O3 is weakened by the addition of phosphorus causing an increase in the dispersion of the MoS2 particles through increasing the stacking number and decreasing the slab length (Zhaou et al, 2009; Yin et al., 2010). Nava et. al (2007; 2011) found that the presence of P2O5 favors the sulfidation degree of Co species and the creation of medium strength acid sites leading to the enhancement of the 4,6DMDBT HDS reaction via isomerization route. Although the role of phosphate on the 2
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deactivation is still controversial, high amount of P2O5 seems to favor deactivation by coke. Ali et al. (2012) studied simultaneous HDS of DBT and 4-MDBT as well as DBT and 4,6DMDBT over a series of phosphorus promoted CoMo/γ-Al2O3 catalysts. They found that
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addition of phosphorus strongly increased the HDS activity and the maximum enhancement was achieved with 1.0 wt.% P2O5.
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HDS of sulfur containing molecules occurs via two routes (Ho, 2004): (i) direct
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desulfurization (DDS) or hydrogenolysis by C-S bond cleavage; and (ii) hydrogenation of the aromatic ring (HYD) followed by C-S bond cleavage. The DDS route is favorable as it Ahmed et al. (2011) studied the influence of
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reduces the consumption of hydrogen.
[Co/(Co+Mo)] ratios in CoMo/Al2O3 catalysts on simultaneous HDS of BT and DBT and
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found that the [Co/(Co+Mo)] ratio has significant influence on the DDS pathway but almost no effect on the HYD pathway. They reported an optimum [Co/(Co+Mo)] ratio of 0.4 for
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overall HDS as well as for HDS by DDS pathway.
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The kinetic model used to describe the HDS of sulfur containing molecules is Langmuir-
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Hinshelwood mechanism (Vrinat, 1983; Jimenez et al., 2007; Garcia-Martinez et al., 2012). Through this kinetic model, the DDS and HYD routes should be accounted for adsorption of different species. Furthermore, there is a debate over the active sites that are aiding on HDS of DBT and alkyl-DBTs. Different kinetic models that consider occurence of DDS and HYD reactions on a single active site or dual active sites over the catalyst have been studied and experimentally confirmed (Froment, 1986; Borgna et al., 2004; Wang et al., 2004). It is generally accepted that DDS and HYD occur at separate catalytic sites. Furthermore, dual site mechanism for HDS requires adsorption of sulfur compound on one site and adsorption of hydrogen on another site of the catalyst (Vrinat, 1983).
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The present research is aimed at investigating phenomenological kinetics of simultaneous HDS of DBT and 4-MDBT over phosphorus modified CoMo/γ-Al2O3 catalysts. The kinetic model based on Langmuir-Hinshelwood approach that takes into account the reaction
reaction and adsorption are evaluated using non linear regression.
Materials
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2.1
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2. EXPERIMENTAL
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network was proposed for HDS of DBT and 4-MDBT. The kinetic parameters of the surface
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For the precursor of the active metals, ammonium heptamolybdate tetrahydrate (NH4)6Mo7O24.4H2O) (Sigma-Aldrich, 99.98% trace metals basis) and cobalt(II) nitrate
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hexaydrate (Co(NO3)2.6H2O) (Sigma-Aldrich, 99.999% trace metals basis) were used. Boehmite alumina (Alcoa) was used to form the γ-alumina support. DBT (Sigma-Aldrich,
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98%) and 4-MDBT (Sigma-Aldrich, 96%) were used are the model compounds. Decalin
Catalyst Preparation
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2.2
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(Merck Chemicals, >99%) was used as a solvent in the catalyst performance tests.
Boehmite alumina was calcinated at 873 K for 3 h to form γ-alumina which was utilized as the support for the catalyst. Modification of the support was carried out by adding of 0.5, 1.0 or 1.5 wt% of P2O5 before impregnation of the active metals. Impregnation of ammonium heptamolybedate tetrahydrate and cobalt nitrate heaxahydrate on calcined γ-alumina was done at room temperature to form the catalyst. The catalyst was dried at 100 oC for 12 h followed by calcination at 500 oC for 1 h. The total metal oxide (MoO3+CoO) content of the catalysts was kept constant at 19.0 wt% with a [Co/(Co+Mo)] ratio of 0.4. The catalysts were sulfided prior to their performance tests by light kerosene whose sulfur content was increased to 2.5 wt.% by addition of dimethyl disulfide. Catalyst presulfiding was carried out in a tubular reactor under flowing hydrogen (7.5 NL/h) at 6.2 MPa and 320 oC for 16 h. The 4
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catalysts were denoted as CMP(a), in which a represents P2O5 content in wt%. The composition of prepared catalysts is presented in Table 1. The nominal values of metal content in the prepared catalysts were confirmed by XRF and they were found to be in close
Catalyst Characterization
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agreement.
The pore volume, pore size distribution and the BET surface area of the catalysts in their
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oxide form were determined from nitrogen adsorption-desorption isotherms measured by BJH method at -196 oC using Quantachrome, NOVA-1200 unit.
The samples were
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pretreated under nitrogen flow at 350 oC for 1 h. X-ray diffraction (XRD) analyses of the catalysts in their oxide form were performed with JEOL JDX-3530 diffractometer equipped
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with a scintillator detector and operated in 2-theta/theta geometry. Data were collected in the
2.4
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CuKα (λ=0.154178 nm) radiation.
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4 to 80° 2θ range, with step size 0.020° 2θ and 1.00 second/ step accumulation time using
Reaction System and Procedure
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To perform the catalyst performance experiments, a 100 ml autoclave was used as a stirredbatch reactor. An impeller with controllable speed, thermo-well, and product sampling system were equipped with the reactor. Specific amounts of the model compounds, 50 g of decalin, 0.5 g of freshly sulfided catalyst were loaded to the reactor. Experiments were performed with DBT and 4-MDBT. The initial concentration of each model compound is 500 ppm of sulfur resulting in a total sulfur content of 1,000 ppm. The experiments were conducted under 6.2 MPa pressure of hydrogen at temperatures of 300, 325 and 350 oC. Samples were taken through a specially-designed sampling tube after 15, 30, 45, 60, 90 and 120 minutes. It should be noted that, unlike the flow reactor, in the batch autoclave reactor
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the contact time to stabilize the catalyst is not enough. Hence initial activity of the catalyst
2.5
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was determined which is quite suitable for determining the reaction kinetics.
Product Analysis
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Gas chromatograph (GC, Agilent 7890A) equipped with sulfur chemiluminescence detector (SCD, Sievers 355) was used to quantitatively analyze sulfur species in the products. For the of hydrocarbons like biphenyls and cyclohexylbenzenes,
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identification
GC-Mass
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spectrometer (GC-MS, Agilent 6890 N with Mass Selective Detector 5973) was utilized. PIONA analyzer (Shimadzu GC 2010 with flame-ionization detector) was used to quantify
3. RESULTS AND DISCUSSION
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Physico-Chemical Characterisation
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3.1
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these hydrocarbons in the product samples.
Addition of phosphorus to the catalyst produced a decrease in the pore size, pore volume and
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surface area as shown in Table 1. Figure 1 presents the pore size distribution between the four types of catalyst prepared. Adsorption of phosphorus takes place on the walls of the pores blocking small pores first causing a higher decrease in pore volume (up to 35%) than surface area (up to 26%).
X-ray diffractograms for the catalysts are presented in Figure 2. The CoMoO4 phase in the catalyst caused the diffraction peak to occur at 2θ=26.2, as the phosphorus percentage in the catalyst increased the crystallinity of the CoMoO4 phase also increased. The peaks that occurred at 2θ=24 and 27 were due to MoO3 (Kim et al., 1997). Calcination of the catalyst at high temperature (500oC) caused the formation of the CoMoO4 phase and the addition of phosphorus facilatied the CoMoO4 phase formation. 6
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3.2
HDS of DBT and 4-MDBT
The distribution of the products resulting from the HDS of DBT and 4-MDBT at 350oC over CMP(0) and CMP(1) catalysts are presented in Figure 3. It can be observed that HDS of
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DBT and 4-MDBT proceeded predominantly via DDS pathway and 1wt.% P2O5 enhanced the HDS via both pathways. However, the enhancement on DDS pathway was significantly
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higher for HDS of 4-MDBT than DBT. These trends are in line with those reported by
Mechanism of HDS and its Pathways
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3.3
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Ergova and Prins (2004; 2006).
As mentioned earlier, the HDS of DBT and 4-MDBT occurs via two routes: DDS or HYD.
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DDS is the direct desulfurization or hydrogenolysis by C-S bond scission while the HYD involves hydrogenation of one the phenyl rings prior to C-S bond scission (Moon, 2003).
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HDS of DBT by DDS produces biphenyl (BP) and H2S while the HYD pathway yields
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transitional compounds like tetrahydro dibenzothiophene (THDBT) and hexahydro dibenzothiophene (HHDBT) which are quickly desulfurized to cyclohexyl benzene (CHB).
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Similarly, HDS of 4-MDBT by DDS produces methyl biphenyl (MBP) and HDS by HYD produces 3-methyl-1-cyclohexybenzene (MCHB) as the partial hydrogenated hydrocarbon product.
Figure 4(A) and Figure 4(B) show a simple scheme for the reaction pathways of the DBT and 4-MDBT, respectively. DDS consumes less hydrogen therefore it is the preferred pathway. The intermediates produced during the HDS of DBT and 4-MDBT through the HYD pathway were found to be very low in concentrations and the major products produced from the HYD pathway were CHB and MCHB. Taking into account what preceded, the flowing reaction scheme is suggested for the kinetic modeling.
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(1)
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(2)
3.4.
(4)
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(3)
Development of Kinetic Model for the Simultaneous HDS of DBT and 4-MDBT
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On the basis of above discussion, a kinetic model for simultaneous HDS of DBT and 4MDBT is proposed which include surface reactions controlled by Langmuir-Hinshelwood
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mechanism. The steps involved in the overall reaction mechanism are as follows:
(ii)
Adsorption of DBT:
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(i)
(iii)
(5)
Adsorption of hydrogen:
(6)
Adsorption of 4-MDBT:
(7)
(iv)
Surface reactions: 8
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(8)
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(9)
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Desorption of products:
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(v)
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(10)
(11)
(12)
(13)
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(14)
(15)
The reaction rates for the surface reactions [(8) to (11)] are as follows:
(16)
(17)
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(18)
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The fractional coverage for DBT, MDBT and H2 are expressed as:
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(19)
(20)
(21)
(22)
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It is important to note that hydrogen is in excess which makes it possible to have one as the
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numerator of the fractional coverage for hydrogen. Furthermore, the adsorption constant of
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hydrogen and all the gaseous intermdiat and final products are assumed to be negligible to simplify the model.
The relation between the reaction rates and the concentration of the involving species is described by the mole balance of the reactants and the products species during the HDS of DBT and 4-MDBT in the batch reactor. The mole balance was governed by certain assumptions and they are as follows: i.
The HDS reactions are irreversible.
ii.
Thermal cracking of the model compounds is neglected. This assumption was confirmed by conducting experimental runs in the absence of the catalyst. 10
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iii.
Isothermal conditions are assumed which is confirmed by negligible temperature fluctuation observed during the reaction runs.
mole balance of the various species present in the reaction medium.
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(i) Rate of formation of BP
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Considering the above assumptions, the following set of differential equations describes the
(24)
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(iii) Rate of disappearance of DBT
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(ii) Rate of formation of CHB
(23)
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(25)
(iv) Rate of formation of MBP
(26)
(v) Rate of formation of MCHB
(27)
(vi) Rate of disappearance of 4-M DBT
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(28)
3.5.
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where Ci is the molar concentration of species i at any time t. Parameter Estimation and Model Discrimination
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The parameters of the mole balance equations incorporated with the Langmuir Hinshelwood
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models were evaluated by the least-squares fitting of the experimental data for the HDS of DBT with 4-MDBT. Data points were collected at 15, 30, 45 and 60 mins at three different
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temperatures of 300, 325 and 350 oC. The differential equations were solved using RungeKutta method (Mathematica's ParametricNdsolve) and for the parameter estimation the
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Levenberg-Marquardt algorithm (Mathematica’s NonLinearModelFit) was used. The criteria used for optimization is that all the estimated parameters are positive.
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Coefffient of determination (R2), lowest sum of squares of the residuals (SSR), cross
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correlation matrix and minimum individual confidence intervals were used for the model
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discrimination of the estimated parameters. The cross correlation matrix for CMP(0) at 350°C is shown below:
(29)
The cross correlation matrix shows the dependence between the estimated parameters to each other. The small values of the matrix enteries suggest that the variables are independent of each other.
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The values of the estimated rate constants for the surface reactions [(8) to (11)] using catalysts CMP(0), CMP(0.5) and CMP(1) at 300, 310, 325, 335 and 350 oC are listed in Table 2 with a R2 value greater than 0.99. The rate constant for the formation of BP is 6-8
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times higher than the rate constant for the formation of CHB. Similarly the rate constant for the formation of MBP is 3-5 times higher than the rate constant of MCHB. These
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observations indicate that the HDS of the model compounds through the DDS route is several times faster than the HDS through the HYD route. Futhermore, the rate constant for the
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formation of BP and CHB is about two times higher than the respective rate constant for the
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formation of MBP and MCHB. These results are consistent with trends in pseudo-first order kinetics reported by Ali et al. (2012).
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The Arrhenius plot for the HDS of DBT by DDS route, shown in Figures 5, indicate that the influence of variation in catalyst composition on reaction rate was not significant. However,
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the Arrhenius plot for the HDS of 4-MDBT by DDS route, shown in Figures 6, indicate that
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catalyst containing 1 wt.% phoshphorus [CPM(1)] exhibited higher reaction rate compared to
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phosphorus-free catalyst [CPM(0)].
The estimated adsorption equilibrium constants for the model are listed in Table 3. The mathimatica code failed to estimate these parameters with reasonable low confidence interval. However the adsorption constants follow the Van’t Hoff equation as presented in the Van’t Hoff plots for the HDS of DBT in Figure 7 and for the HDS of 4MDBT in Figure 8. From Table 3, it can be noticed that the adsorption equilibrium for DBT is significantly higher than the adsorption of 4-MDBT which indicate that the catalysts CMP(0), CMP(0.5) and CMP(1) are more selective for HDS of DBT than HDS of 4-MDBT. Activation energies are reported in Table 4. The values of the activation energy for the formation of BP when using the catalyst CMP(0) is 103 kJ/mol whereas the activation energy 13
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for the formation of CHB is slightly less at 102 kJ/mol. This observation shows that at low temperatures the catalyst is more selective towards the HYD route and at high temperatures the catalyst is more slelective towards the DDS route. Furthermore, the activation energy for
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the formation of BP when using the catalyst CMP(0.5) is 98.1 kJ/mol whereas it is 112.4 kJ/mol when using the catalyst CMP(1). Similarly the activation energy of formation of
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CHB for CMP(0.5) is 101.4 kJ/mol and for CMP(1) is 108.0 kJ/mol. Similar trends are observed with MBP and MCHB also. These results show that the activity of the catalyst
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increases up to phosphorus content of 0.5 wt% and further increase in phosphorus content is
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not helpful. This result is not consistent with the earlier report published by Ali et al. (2012). A comparison of the concentrations for DBT, BP, CHB, 4-MDBT, MBP and MCHB as
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predicted by the kinetic model and the experimentally determined concentrations (wt.%) at 350°C are presented as a parity plot on Figure 9. From the plot, it be observed that the
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excellent manner.
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predicted concentration by the kinetic model matches the experimental concentration in an
4. CONCLUSIONS
Phenomenological kinetics modeling of simultaneous HDS of dibenzothiophene and substituted dibenzothiophene over CoMo/P-Al2O3 has been carried out.
The following
conclusions are drawn from this study: 1. Addition of P2O5 to CoMo/γ-Al2O3 catalyst increased the HDS activity. 2. A comparison of the reaction rates constants for the formation of BP, CHB, MBP and MCHB and the activation energies show that the simultaneous HDS of DBT and 4-
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MDBT occur mostly by DDS route rather than HYD route – especially at high temperatures. 3. By comparing the activation energies for the formation of BP, CHB, MBP and MCH and
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the equilibrium adsorption rate constants it can be conculed that CoMo/P-Al2O3 catalysts
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are more selective towards the HDS of DBT over the HDS of 4-MDBT.
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ACKNOWLEDGEMENTS
The authors wish to acknowledge the support of King Fahd University of Petroleum and
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Minerals (KFUPM). Acknowledgement is due to the Ministry of Higher Education, Saudi
Petrochemicals (CoRE-PRP) at KFUPM.
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NOTATIONS
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Arabia for establishing the Center of Research Excellence in Petroleum Refining and
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Ci = Concentration of species i in the batch reactor Ei = apparent activation energy of the ith reaction (kJ/mol) ki = apparent rate constant for the ith reaction (min-1) Ki = adsorption constant for the ith component t = reaction time (min)
T = reaction temperature (K) X = catalyst free active site i-X = active site occupied by the i component 15
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= fraction coverage for the I component
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ABBREVIATIONS DBT = dibenzothiophene
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4-MDBT = 4-methyl dibenzothiophene
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BP = biphenyl
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CHB = cyclohexyl benzene
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HDS = hydrodesulfurization
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MCHB = 3-methyl-1-cyclohexylbenzene
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MBP = methyl biphenyl
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DDS = direct desulfurization route HYD = hydrogenation route
REFERENCES
Ahmed, K., Ali, S. A., Ahmed, S., Al-Saleh. M., 2011. Simultaneous hydrodesulfurization of benzothiophene and dibenzothiophene over CoMo/Al2O3 catalysts with different
[Co/(Co + Mo)] ratios, Reaction Kinetics, Mechanisms and Catalysis, 103, 133-123. Ali, S. A., Ahmed, S., Ahmed, K.W., Al-Saleh, M., 2012. Simultaneous hydrodesulfurization of dibenzotiophene and substituted dibenzothiophenes over phosphorus modified CoMo/Al2O3 catalysts, Fuel Proc. Tech., 98, 39-44.
16
Page 16 of 36
Babich, I.V., Moulijn, J.A., 2007. science and technology of novel processes for deep desulfurization of oil refinery streams: A review, Fuel, 82, 607-631. Bej, S.K., Maity, S.K., Taraga, U.T., 2004. Search for an efficient 4,6-DMDBT
ip t
hydrodesulfurization catalyst: A review of recent studies, Energy Fuels 18, 1227-
cr
1237.
Borgna, A., Hensen, E. J. M., van Veen, J. A. R., Niemantsverdriet, J. W., 2004. Intrinsic
us
kinetics of thiophene hydrodesulfurization on a sulfided NiMo/SiO2 planar model
an
catalyst. J. Catal., 221(2), 541-548.
Cooper, B.H., Knudsen K.G., 2006. Ultra deep desulfurization of diesel: How an
M
understanding of the underlying kinetics can reduce investment costs, Practical Advances in Petroleum Processing, 297.
d
Egorova M., Prins, R. 2006. The role of Ni and Co promoters in the simultaneous HDS of
Ac ce p
172.
te
dibenzothiophene and HDN of amines over Mo/γ-Al2O3 catalysts. J. Catal., 241, 162-
Egorova, M., Prins, R., 2006. The role of Ni and Co promoters in the simultaneous HDS of dibenzothiophene and HDN of amines over Mo/γ-Al2O3 catalysts, J. Catal., 241, 162-
172.
Froment, G.F., 1986. The kinetics of catalytic processes: importance in reactor simulation and design. Appl. Catal., 22, 3-20. García-Martínez, J.C., Castillo-Araiza, C. O. De los Reyes Heredia, J. A., Trejo, E., Montesinos, A. 2012. Kinetics of HDS and of the inhibitory effect of quinoline on
17
Page 17 of 36
HDS of 4,6-DMDBT over a Ni-Mo-P/Al2O3 catalyst: Part I. Chem. Eng. J., 210, 5362.
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Ho, T.C., 2004. Deep HDS of diesel fuel: Chemistry and catalysis, Catal. Today, 98, 3-18. Jiménez, F., Kafarov, V. Nuñez, M., 2007. Modeling of industrial reactor for hydrotreating of
cr
vacuum gas oils. Chem. Eng. J., 134(1-3), 200-208.
us
Lewis, J.M., Kydd, R. A., Boorman, P.M., Van Rhyn, P. H., 1992. Phosphorus promotion in nickel-molybdenum/alumina catalysts: model compound reactions and gas oil
an
hydroprocessing. Appl. Catal. A: Gen., 84(2), 103-121.
Nava, R., Infantes-Molina, A., Castano, P., Guil-Lopez, R., Pawelec, B. 2011. Inhibition of
M
CoMo/HMS catalyst deactivation in the HDS of 4,6-DMDBT by support modification
d
with phosphate. Fuel, 90, 2726-2737.
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Nava, R., Morales, J., Alonso, G., Ornelas, C., Pawelec, B., Fierro, J. L.G. 2007. Influence of the preparation method on the activity of phosphate-containing CoMo/HMS catalysts
Ac ce p
in deep hydrodesulphurization. Appl. Catal. A: Gen., 321, 58-70.
Shafi, R., Hutchings, G.J., 2000. Hydrodesulfurization of hindered dibenzothiophenes: an overview. Catal. Today, 59(3-4), 423-442.
Stanislaus, A., Marafi, A., Rana, M.S., 2010. Recent advances in the science and technology of ultra-low sulfur diesel. Catal. Today, 153, 1-68.
Vrinat, M.L., 1983. The kinetics of the hydrodesulfurization process. Appl. Catal., 6, 137156.
18
Page 18 of 36
Wang, Y., Sun, Z., Wang, A., Ruan, L., Lu, M., Ren, J., Li, X., Li, C., Hu, Y., Yao, P. 2004. Kinetics of hydrodesulfurization of dibenzothiophene catalyzed by sulfided Co-Mo/ MCM-41. Ind. Eng. Chem. Res., 43, 2324-2329.
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Yin, H., Zhou, T., Liu, Y., Chai, Y., Liu, C., 2010. Study on the structure of active phase in NiMoP impregnation solution using Laser Raman spectroscopy 1. Effect of
cr
phosphorous content, J. Fuel Chem. Technol., 38(6), 705-709.
Influences of different
us
Zhou, T. Yin, H., Han, S., Chai, Y., Liu, Y., Liu, C., 2009.
phosphorus contents on NiMoP/Al2O3 hydrotreating catalysts. J. Fuel Chem.
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Technol., 37(3), 330-334.
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Zhou, T., Yin, H., Liu, Y., Han, S., Chai, Y., Liu, C. 2010. Effect of phosphorus content on the active phase structure of NiMoP/Al2O3 catalyst. J. Fuel Chem. Technol., 38(1),
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69-74.
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LIST OF FIGURES Pore size distribution of CMP catalysts.
Figure 2.
Powder X-ray diffraction patterns of γ-Al2O3 and CMP catalysts.
Figure 3.
Product distribution during simultaneous HDS of DBT [A] and 4-MDBT [B]
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over CMP(0) and CMP(1) catalysts at 623 K.
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Figure 1.
Reaction pathways Scheme for (A) DBT and (B) 4-MDBT.
Figure 5.
Arrhenius plot for HDS of DBT by DDS route
Figure 6.
Arrhenius plot for HDS of 4-MDBT by DDS route.
Figure 7.
Van't Hoff plot for HDS of DBT.
Figure 8.
Van't Hoff plot for HDS of 4-MDBT
Figure 9.
Parity plot between experimental values of product composition (wt%) and the
Ac ce p
te
d
M
an
Figure 4.
values predicted by kinetic model.
20
Page 20 of 36
ip t
LIST OF TABLES Composition and characteristics of CMP catalysts.
Table 2.
Estimated rate constants for HDS of DBT and 4-MDBT via DDS and HYD pathways.
cr
Table 1.
Estimated equlibrium adsorption constants.
Table 4.
Estimated activation energies for HDS of DBT and 4-MDBT via DDS and
us
Table 3.
Ac ce p
te
d
M
an
HYD pathways.
21
Page 21 of 36
ip t cr us an M
Ac ce p
te
d
Figure 1: Pore size distribution of CMP catalysts.
22
Page 22 of 36
ip t cr us an M d
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Powder X-ray diffraction patterns of γ-Al2O3 and CMP catalysts.
Ac ce p
Figure 2:
23
Page 23 of 36
100
DBT-CMP(1) BP-CMP(1) CHB-CMP(1)
ip t
80 60
cr
40 20 0 0
10
20
30
40
50
60
M
an
Time (min)
us
Transformation of DBT(%)
DBT-CMP(0) BP-CMP(0) CHB-CMP(0)
Ac ce p
te
d
[A]
Figure 3.
Product distribution during simultaneous HDS of DBT [A] and 4-MDBT [B] [B] over CMP(0) and CMP(1) catalysts at 623 K.
24
Page 24 of 36
BP
DBT
ip t
DDS
cr
HYD CHB
TH-DBT
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HYD
(A)
MBP DDS
CH3
CH3
M
HYD
an
4-MDBT
4-MTHBT
MCHB
d
HYD
te
CH3
CH3
(B)
Ac ce p
Figure 4: Reaction pathways Scheme for (A) DBT and (B) 4-MDBT.
25
Page 25 of 36
ip t cr us an M
Arrhenius plot for HDS of DBT by DDS route
Ac ce p
te
d
Figure 5.
26
Page 26 of 36
ip t cr us an M
Arrhenius plot for HDS of 4-MDBT by DDS route.
Ac ce p
te
d
Figure 6.
27
Page 27 of 36
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Van't Hoff plot for HDS of DBT.
Ac ce p
te
Figure 7.
28
Page 28 of 36
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Van't Hoff plot for HDS of 4-MDBT
Ac ce p
te
d
Figure 8.
29
Page 29 of 36
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Parity plot between experimental values of product composition (wt%) and the values predicted by kinetic model.
Ac ce p
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d
Figure 9.
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Composition and characteristics of CMP catalysts.
MoO
CoO
P2O5
Surface Area (m2/g)
CMP(0)
15.0
4.0
0.0
155.0
CMP(0.5)
15.0
4.0
0.5
135.0
CMP(1)
15.0
4.0
1.0
130.0
Pore Volume (cm3/g)
Average pore size (nm)
0.6
14.2
ip t
Composition (wt%)
0.5
14.2
0.4
12.9
us
Catalyst
cr
Table 1.
Ac ce p
te
d
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an
Note: The catalysts were denoted as CMP(a), in which a represents P2O5 content in wt%.
31
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ip t cr
Catalyst
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Estimated rate constants for HDS of DBT and 4-MDBT via DDS and HYD pathways CMP(0)
Temperature Sulfur HDS (oC) Compound Route
CMP(0.5)
k × 100 (min-1)
Confidence Interval
CMP(1)
k × 100 (min-1)
Confidence Interval
k × 100 (min-1)
Confidence Interval
{0.202, 0.394} {0.006, 0.070} {0.05, 0.147} {0.004, 0.066}
0.35 0.06 0.14 0.04
{0.304, 0.397} {0.029, 0.096} {0.101, 0.178} {0.005, 0.068}
0.32 0.05 0.17 0.03
{0.204, 0.429} {0.015, 0.092} {0.100, 0.233} {0.000, 0.068}
{0.382, 0.388} {0.049, 0.050} {0.138, 0.141} {0.045, 0.046}
0.47 0.07 0.20 0.04
{0.350, 0.593} {0.055, 0.095} {0.151, 0.264} {0.028, 0.052}
0.40 0.07 0.21 0.04
{0.389, 0.412} {0.071,0.088} {0.204, 0.226} {0.035, 0.521}
0.49 0.06 0.20 0.06
{0.381, 0.606} {0.009, 0.119} {0.121, 0.272} {0.006, 0.112}
0.52 0.07 0.25 0.04
{0.334, 0.701} {0.011, 0.131} {0.163, 0.329} {0.000, 0.095}
0.59 0.08 0.30 0.05
{0.508, 0.675} {0.009, 0.160} {0.218, 0.379} {0.000, 0.122}
M an
Table 2.
DDS HYD DDS HYD
k1 k2 k3 k4
0.30 0.04 0.10 0.04
310
DBT DBT 4MDBT 4MDBT
DDS HYD DDS HYD
k1 k2 k3 k4
0.38 0.04 0.13 0.04
325
DBT DBT 4MDBT 4MDBT
DDS HYD DDS HYD
k1 k2 k3 k4
335
DBT DBT 4MDBT 4MDBT
DDS HYD DDS HYD
k1 k2 k3 k4
0.92 0.11 0.36 0.11
{0.926, 0.930} {0.115, 0.117} {0.365, 0.367} {0.114, 0.117}
1.02 0.14 0.45 0.09
{1.027, 1.030} {0.140, 0.141} {0.450, 0.453} {0.097, 0.098}
1.08 0.16 0.55 0.09
{1.043, 1.125} {0.154, 0.167} {0.528, 0.574} {0.091, 0.100}
350
DBT DBT 4MDBT 4MDBT
DDS HYD DDS HYD
k1 k2 k3 k4
1.71 0.22 0.70 0.21
{1.545, 1.878} {0.133, 0.299} {0.630, 0.770} {0.150, 0.279}
1.92 0.25 0.82 0.19
{1.719, 2.117} {0.145, 0.347} {0.737, 0.904} {0.116, 0.268}
2.08 0.31 1.03 0.19
{1.866, 2.286} {0.208, 0.416} {0.942, 1.117} {0.112, 0.265}
Ac
ce pt
ed
300
DBT DBT 4MDBT 4MDBT
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ip t cr us
Estimated equlibrium adsorption constants.
Table 3.
CMP(0)
CMP(0.5)
M an
Catalyst
CMP(1)
K × 103 (l/mol) K × 103 (l/mol) K × 103 (l/mol) 300 oC
945.8
124.6
48.5
28.1
53.1
4.9
K1
912.3
82.2
6.2
K2
1.5
11.2
4.1
K1
840.5
7.0
3.1
K2
0.1
3.1
0.1
K1
781.7
6.0
2.9
K2
0.1
0.3
0.1
K1
732.7
4.6
2.5
K2
0.0
0.0
0.0
K1
ed
K2 310 oC
ce pt
325 oC
Ac
335 oC
350 oC
33
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Table 4.
Estimated activation energies for HDS of DBT and 4-MDBT via DDS and HYD pathways
Confidence Interval
CMP(0.5)
Confidence Interval
CMP(1)
Confidence Interval
ip t
Activation Energy CMP(0) (kJ/mol) 103.0
{57.6,148.6}
98.1
{41.5,154.7}
112.4
{71.6,153.2}
E2
102.4
{58.8,145.3}
78.4
{12.4,144.5}
99.1
{43.9,154.3}
E3
114.0
{75.1,152.7}
101.4
{58.7,144}
108.0
{67.0,149.1}
E4
106.7
{59.7,154.5}
98.7
{22.1,175.4}
99.5
{48.6,150.4}
Ac ce p
te
d
M
an
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cr
E1
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PHENOMENOLOGICAL KINETICS MODELING OF SIMULTANEOUS HDS OF DIBENZOTHIOPHENE AND SUBSTITUTED DIBENZOTHIOPHENE OVER COMOP/AL2O3 CATALYSTS
Shaikh A. Razzak1, Mohammad M. Hossain1,2* 1
Department of Chemcial Engineering,
Center of Research Excellence in Petroleum Refining and Petrochemicals,
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2
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Ahmad H. Al-Rashidy1, Syed A. Ali2, Shakeel Ahmed2,
an
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King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia
Ac ce p
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Graphical Abstract
Figure : Parity plot between model predicted and experimental data.
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PHENOMENOLOGICAL KINETICS MODELING OF SIMULTANEOUS HDS OF DIBENZOTHIOPHENE AND SUBSTITUTED DIBENZOTHIOPHENE OVER COMOP/AL2O3 CATALYSTS Ahmad H. Al-Rashidy1, Syed A. Ali2, Shakeel Ahmed2, Shaikh A. Razzak1, Mohammad M. Hossain1,2*
2
Department of Chemcial Engineering,
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1
Center of Research Excellence in Petroleum Refining and Petrochemicals,
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King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia
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HIGHLIGHTS
Synthesized P2O5 promoted CoMo/γ-Al2O3 catalysts for HDS of heavy oil.
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Investigated the effects of P2O5 on the simultaneous HDS of DBT and 4-MDBT.
P2O5 favors the DDS pathway over the HYD pathway for both DBT and 4-MDBT.
Ac ce p
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Langmuir-Hinshelwood mechanism fits the experimental data adequately.
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S0263-8762(15)00375-5 http://dx.doi.org/doi:10.1016/j.cherd.2015.10.001 CHERD 2034
To appear in: Received date: Revised date: Accepted date:
9-7-2015 19-9-2015 1-10-2015
Please cite this article as: Al-Rashidy, A.H., Ali, S.A., Ahmed, S., Razzak, S.A., Hossain, M.M.,Phenomenological Kinetics Modeling of Simultaneous HDS of Dibenzothiophene and Substituted Dibenzothiophene over CoMoP/Al2 O3 Catalysts, Chemical Engineering Research and Design (2015), http://dx.doi.org/10.1016/j.cherd.2015.10.001 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
PHENOMENOLOGICAL KINETICS MODELING OF SIMULTANEOUS HDS OF DIBENZOTHIOPHENE AND SUBSTITUTED DIBENZOTHIOPHENE OVER COMOP/AL2O3 CATALYSTS
ip t
Ahmad H. Al-Rashidy1, Syed A. Ali2, Shakeel Ahmed2, Shaikh A. Razzak1, Mohammad M. Hossain1,2* 1
Department of Chemcial Engineering, Center of Research Excellence in Petroleum Refining and Petrochemicals, King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia
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2
ABSTRACT
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A series of CoMo/γ-Al2O3 catalysts modified with P2O5 were prepared. The phosphorus concentration varied from 0.0 to 1.0 wt.% P2O5. The catalysts prepared were evaluated in a batch autoclave reactor to investigate the effect of P2O5 on the simultaneous MDBT).
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hydrodesulfurization (HDS) of dibenzothiophene (DBT) and 4-methyl dibenzothiophene (4The phenomenological based kinetics models are developed based on the
d
experimental conversion and selectivity data. The analysis of the developed model suggests that a Langmuir-Hinshelwood mechanism fits the experimental data adequately. The rate
te
constants for the formation of BP are 6-8 times higher than the rate constants for the formation of CHB. Similarly, the rate constants for the formation of MBP are 3-5 times
Ac ce p
higher than the rate constants of MCHB formation. These observations indicate that the HDS of the model compounds through the DDS route is several times faster than the HDS through the HYD route. Furthermore, the rate constant for the formation of BP and CHB is about two times higher than the respective rate constant for the formation of MBP and MCHB. The addition of P2O5 favored the DDS pathway over the HYD pathway for both DBT and 4MDBT.
Keywords: Kinetic modeling, CoMo/Al2O3, P2O5 promotion, HDS, DBT, 4-MDBT *Corresponding author: Tel: +966 13 860 1478; E-mail address: [email protected] (M. M. Hossain)
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1. INTRODUCTION Environmental regulations have been enacted in many countries to reduce the sulfur content
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in diesel fuel to ultra-low levels (10-15 ppm) to circumvent the harmful effects of exhaust emissions. Meeting such stringent sulfur specifications represents a major operational and
cr
economic challenge for the petroleum refining industry (Cooper and Knudsen, 2006; Babich
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and Moulijn, 2007). Factors that influence the ultra-deep desulfurization of diesel feed streams include activity of the HDS catalyst and the reactivities of different species of sulfur
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compounds (Stanislaus et al., 2010). Several studies have shown that the sulfur compounds that remain in the diesel fuel after conventional HDS are mainly dibenzothiophenes (DBTs),
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especially those with alkyl substituents at the 4 and 6 positions (Shafi and Hutchings, 2000; Bej et al., 2004). Removal of these refractive sulfur compounds is necessary to achieve the
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10-15 ppm sulfur content specifications of ultra-low sulfur diesel.
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Most conventional industrial HDS catalysts used contain molybdenum and cobalt or nickel
Ac ce p
supported on γ-Al2O3, which are modified by addition of promoters to improve their performance. Lewis et al. (1992) studied the effect of modifying Ni-Mo/Al2O3 catalysts with 0-7 wt% phosphorus and reported that 1 wt% of phosphorus loading was optimal. The promotional effect of phosphorus was attributed to the higher dispersion and lower reducibilty/sulfidibilty of molybdate. Studies by Liu and his coworkers reported that the interaction between the active component and the γ-Al2O3 is weakened by the addition of phosphorus causing an increase in the dispersion of the MoS2 particles through increasing the stacking number and decreasing the slab length (Zhaou et al, 2009; Yin et al., 2010). Nava et. al (2007; 2011) found that the presence of P2O5 favors the sulfidation degree of Co species and the creation of medium strength acid sites leading to the enhancement of the 4,6DMDBT HDS reaction via isomerization route. Although the role of phosphate on the 2
Page 2 of 36
deactivation is still controversial, high amount of P2O5 seems to favor deactivation by coke. Ali et al. (2012) studied simultaneous HDS of DBT and 4-MDBT as well as DBT and 4,6DMDBT over a series of phosphorus promoted CoMo/γ-Al2O3 catalysts. They found that
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addition of phosphorus strongly increased the HDS activity and the maximum enhancement was achieved with 1.0 wt.% P2O5.
cr
HDS of sulfur containing molecules occurs via two routes (Ho, 2004): (i) direct
us
desulfurization (DDS) or hydrogenolysis by C-S bond cleavage; and (ii) hydrogenation of the aromatic ring (HYD) followed by C-S bond cleavage. The DDS route is favorable as it Ahmed et al. (2011) studied the influence of
an
reduces the consumption of hydrogen.
[Co/(Co+Mo)] ratios in CoMo/Al2O3 catalysts on simultaneous HDS of BT and DBT and
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found that the [Co/(Co+Mo)] ratio has significant influence on the DDS pathway but almost no effect on the HYD pathway. They reported an optimum [Co/(Co+Mo)] ratio of 0.4 for
d
overall HDS as well as for HDS by DDS pathway.
te
The kinetic model used to describe the HDS of sulfur containing molecules is Langmuir-
Ac ce p
Hinshelwood mechanism (Vrinat, 1983; Jimenez et al., 2007; Garcia-Martinez et al., 2012). Through this kinetic model, the DDS and HYD routes should be accounted for adsorption of different species. Furthermore, there is a debate over the active sites that are aiding on HDS of DBT and alkyl-DBTs. Different kinetic models that consider occurence of DDS and HYD reactions on a single active site or dual active sites over the catalyst have been studied and experimentally confirmed (Froment, 1986; Borgna et al., 2004; Wang et al., 2004). It is generally accepted that DDS and HYD occur at separate catalytic sites. Furthermore, dual site mechanism for HDS requires adsorption of sulfur compound on one site and adsorption of hydrogen on another site of the catalyst (Vrinat, 1983).
3
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The present research is aimed at investigating phenomenological kinetics of simultaneous HDS of DBT and 4-MDBT over phosphorus modified CoMo/γ-Al2O3 catalysts. The kinetic model based on Langmuir-Hinshelwood approach that takes into account the reaction
reaction and adsorption are evaluated using non linear regression.
Materials
us
2.1
cr
2. EXPERIMENTAL
ip t
network was proposed for HDS of DBT and 4-MDBT. The kinetic parameters of the surface
an
For the precursor of the active metals, ammonium heptamolybdate tetrahydrate (NH4)6Mo7O24.4H2O) (Sigma-Aldrich, 99.98% trace metals basis) and cobalt(II) nitrate
M
hexaydrate (Co(NO3)2.6H2O) (Sigma-Aldrich, 99.999% trace metals basis) were used. Boehmite alumina (Alcoa) was used to form the γ-alumina support. DBT (Sigma-Aldrich,
d
98%) and 4-MDBT (Sigma-Aldrich, 96%) were used are the model compounds. Decalin
Catalyst Preparation
Ac ce p
2.2
te
(Merck Chemicals, >99%) was used as a solvent in the catalyst performance tests.
Boehmite alumina was calcinated at 873 K for 3 h to form γ-alumina which was utilized as the support for the catalyst. Modification of the support was carried out by adding of 0.5, 1.0 or 1.5 wt% of P2O5 before impregnation of the active metals. Impregnation of ammonium heptamolybedate tetrahydrate and cobalt nitrate heaxahydrate on calcined γ-alumina was done at room temperature to form the catalyst. The catalyst was dried at 100 oC for 12 h followed by calcination at 500 oC for 1 h. The total metal oxide (MoO3+CoO) content of the catalysts was kept constant at 19.0 wt% with a [Co/(Co+Mo)] ratio of 0.4. The catalysts were sulfided prior to their performance tests by light kerosene whose sulfur content was increased to 2.5 wt.% by addition of dimethyl disulfide. Catalyst presulfiding was carried out in a tubular reactor under flowing hydrogen (7.5 NL/h) at 6.2 MPa and 320 oC for 16 h. The 4
Page 4 of 36
catalysts were denoted as CMP(a), in which a represents P2O5 content in wt%. The composition of prepared catalysts is presented in Table 1. The nominal values of metal content in the prepared catalysts were confirmed by XRF and they were found to be in close
Catalyst Characterization
cr
2.3
ip t
agreement.
The pore volume, pore size distribution and the BET surface area of the catalysts in their
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oxide form were determined from nitrogen adsorption-desorption isotherms measured by BJH method at -196 oC using Quantachrome, NOVA-1200 unit.
The samples were
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pretreated under nitrogen flow at 350 oC for 1 h. X-ray diffraction (XRD) analyses of the catalysts in their oxide form were performed with JEOL JDX-3530 diffractometer equipped
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with a scintillator detector and operated in 2-theta/theta geometry. Data were collected in the
2.4
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CuKα (λ=0.154178 nm) radiation.
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4 to 80° 2θ range, with step size 0.020° 2θ and 1.00 second/ step accumulation time using
Reaction System and Procedure
Ac ce p
To perform the catalyst performance experiments, a 100 ml autoclave was used as a stirredbatch reactor. An impeller with controllable speed, thermo-well, and product sampling system were equipped with the reactor. Specific amounts of the model compounds, 50 g of decalin, 0.5 g of freshly sulfided catalyst were loaded to the reactor. Experiments were performed with DBT and 4-MDBT. The initial concentration of each model compound is 500 ppm of sulfur resulting in a total sulfur content of 1,000 ppm. The experiments were conducted under 6.2 MPa pressure of hydrogen at temperatures of 300, 325 and 350 oC. Samples were taken through a specially-designed sampling tube after 15, 30, 45, 60, 90 and 120 minutes. It should be noted that, unlike the flow reactor, in the batch autoclave reactor
5
Page 5 of 36
the contact time to stabilize the catalyst is not enough. Hence initial activity of the catalyst
2.5
ip t
was determined which is quite suitable for determining the reaction kinetics.
Product Analysis
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Gas chromatograph (GC, Agilent 7890A) equipped with sulfur chemiluminescence detector (SCD, Sievers 355) was used to quantitatively analyze sulfur species in the products. For the of hydrocarbons like biphenyls and cyclohexylbenzenes,
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identification
GC-Mass
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spectrometer (GC-MS, Agilent 6890 N with Mass Selective Detector 5973) was utilized. PIONA analyzer (Shimadzu GC 2010 with flame-ionization detector) was used to quantify
3. RESULTS AND DISCUSSION
d
Physico-Chemical Characterisation
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3.1
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these hydrocarbons in the product samples.
Addition of phosphorus to the catalyst produced a decrease in the pore size, pore volume and
Ac ce p
surface area as shown in Table 1. Figure 1 presents the pore size distribution between the four types of catalyst prepared. Adsorption of phosphorus takes place on the walls of the pores blocking small pores first causing a higher decrease in pore volume (up to 35%) than surface area (up to 26%).
X-ray diffractograms for the catalysts are presented in Figure 2. The CoMoO4 phase in the catalyst caused the diffraction peak to occur at 2θ=26.2, as the phosphorus percentage in the catalyst increased the crystallinity of the CoMoO4 phase also increased. The peaks that occurred at 2θ=24 and 27 were due to MoO3 (Kim et al., 1997). Calcination of the catalyst at high temperature (500oC) caused the formation of the CoMoO4 phase and the addition of phosphorus facilatied the CoMoO4 phase formation. 6
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3.2
HDS of DBT and 4-MDBT
The distribution of the products resulting from the HDS of DBT and 4-MDBT at 350oC over CMP(0) and CMP(1) catalysts are presented in Figure 3. It can be observed that HDS of
ip t
DBT and 4-MDBT proceeded predominantly via DDS pathway and 1wt.% P2O5 enhanced the HDS via both pathways. However, the enhancement on DDS pathway was significantly
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higher for HDS of 4-MDBT than DBT. These trends are in line with those reported by
Mechanism of HDS and its Pathways
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3.3
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Ergova and Prins (2004; 2006).
As mentioned earlier, the HDS of DBT and 4-MDBT occurs via two routes: DDS or HYD.
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DDS is the direct desulfurization or hydrogenolysis by C-S bond scission while the HYD involves hydrogenation of one the phenyl rings prior to C-S bond scission (Moon, 2003).
d
HDS of DBT by DDS produces biphenyl (BP) and H2S while the HYD pathway yields
te
transitional compounds like tetrahydro dibenzothiophene (THDBT) and hexahydro dibenzothiophene (HHDBT) which are quickly desulfurized to cyclohexyl benzene (CHB).
Ac ce p
Similarly, HDS of 4-MDBT by DDS produces methyl biphenyl (MBP) and HDS by HYD produces 3-methyl-1-cyclohexybenzene (MCHB) as the partial hydrogenated hydrocarbon product.
Figure 4(A) and Figure 4(B) show a simple scheme for the reaction pathways of the DBT and 4-MDBT, respectively. DDS consumes less hydrogen therefore it is the preferred pathway. The intermediates produced during the HDS of DBT and 4-MDBT through the HYD pathway were found to be very low in concentrations and the major products produced from the HYD pathway were CHB and MCHB. Taking into account what preceded, the flowing reaction scheme is suggested for the kinetic modeling.
7
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(1)
ip t
(2)
3.4.
(4)
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(3)
Development of Kinetic Model for the Simultaneous HDS of DBT and 4-MDBT
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On the basis of above discussion, a kinetic model for simultaneous HDS of DBT and 4MDBT is proposed which include surface reactions controlled by Langmuir-Hinshelwood
te
d
mechanism. The steps involved in the overall reaction mechanism are as follows:
(ii)
Adsorption of DBT:
Ac ce p
(i)
(iii)
(5)
Adsorption of hydrogen:
(6)
Adsorption of 4-MDBT:
(7)
(iv)
Surface reactions: 8
Page 8 of 36
(8)
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(9)
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Desorption of products:
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(v)
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cr
(10)
(11)
(12)
(13)
Ac ce p
(14)
(15)
The reaction rates for the surface reactions [(8) to (11)] are as follows:
(16)
(17)
9
Page 9 of 36
(18)
M
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The fractional coverage for DBT, MDBT and H2 are expressed as:
ip t
(19)
(20)
(21)
(22)
d
It is important to note that hydrogen is in excess which makes it possible to have one as the
te
numerator of the fractional coverage for hydrogen. Furthermore, the adsorption constant of
Ac ce p
hydrogen and all the gaseous intermdiat and final products are assumed to be negligible to simplify the model.
The relation between the reaction rates and the concentration of the involving species is described by the mole balance of the reactants and the products species during the HDS of DBT and 4-MDBT in the batch reactor. The mole balance was governed by certain assumptions and they are as follows: i.
The HDS reactions are irreversible.
ii.
Thermal cracking of the model compounds is neglected. This assumption was confirmed by conducting experimental runs in the absence of the catalyst. 10
Page 10 of 36
iii.
Isothermal conditions are assumed which is confirmed by negligible temperature fluctuation observed during the reaction runs.
mole balance of the various species present in the reaction medium.
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(i) Rate of formation of BP
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Considering the above assumptions, the following set of differential equations describes the
(24)
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d
(iii) Rate of disappearance of DBT
M
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(ii) Rate of formation of CHB
(23)
Ac ce p
(25)
(iv) Rate of formation of MBP
(26)
(v) Rate of formation of MCHB
(27)
(vi) Rate of disappearance of 4-M DBT
11
Page 11 of 36
(28)
3.5.
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where Ci is the molar concentration of species i at any time t. Parameter Estimation and Model Discrimination
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The parameters of the mole balance equations incorporated with the Langmuir Hinshelwood
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models were evaluated by the least-squares fitting of the experimental data for the HDS of DBT with 4-MDBT. Data points were collected at 15, 30, 45 and 60 mins at three different
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temperatures of 300, 325 and 350 oC. The differential equations were solved using RungeKutta method (Mathematica's ParametricNdsolve) and for the parameter estimation the
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Levenberg-Marquardt algorithm (Mathematica’s NonLinearModelFit) was used. The criteria used for optimization is that all the estimated parameters are positive.
d
Coefffient of determination (R2), lowest sum of squares of the residuals (SSR), cross
te
correlation matrix and minimum individual confidence intervals were used for the model
Ac ce p
discrimination of the estimated parameters. The cross correlation matrix for CMP(0) at 350°C is shown below:
(29)
The cross correlation matrix shows the dependence between the estimated parameters to each other. The small values of the matrix enteries suggest that the variables are independent of each other.
12
Page 12 of 36
The values of the estimated rate constants for the surface reactions [(8) to (11)] using catalysts CMP(0), CMP(0.5) and CMP(1) at 300, 310, 325, 335 and 350 oC are listed in Table 2 with a R2 value greater than 0.99. The rate constant for the formation of BP is 6-8
ip t
times higher than the rate constant for the formation of CHB. Similarly the rate constant for the formation of MBP is 3-5 times higher than the rate constant of MCHB. These
cr
observations indicate that the HDS of the model compounds through the DDS route is several times faster than the HDS through the HYD route. Futhermore, the rate constant for the
us
formation of BP and CHB is about two times higher than the respective rate constant for the
an
formation of MBP and MCHB. These results are consistent with trends in pseudo-first order kinetics reported by Ali et al. (2012).
M
The Arrhenius plot for the HDS of DBT by DDS route, shown in Figures 5, indicate that the influence of variation in catalyst composition on reaction rate was not significant. However,
d
the Arrhenius plot for the HDS of 4-MDBT by DDS route, shown in Figures 6, indicate that
te
catalyst containing 1 wt.% phoshphorus [CPM(1)] exhibited higher reaction rate compared to
Ac ce p
phosphorus-free catalyst [CPM(0)].
The estimated adsorption equilibrium constants for the model are listed in Table 3. The mathimatica code failed to estimate these parameters with reasonable low confidence interval. However the adsorption constants follow the Van’t Hoff equation as presented in the Van’t Hoff plots for the HDS of DBT in Figure 7 and for the HDS of 4MDBT in Figure 8. From Table 3, it can be noticed that the adsorption equilibrium for DBT is significantly higher than the adsorption of 4-MDBT which indicate that the catalysts CMP(0), CMP(0.5) and CMP(1) are more selective for HDS of DBT than HDS of 4-MDBT. Activation energies are reported in Table 4. The values of the activation energy for the formation of BP when using the catalyst CMP(0) is 103 kJ/mol whereas the activation energy 13
Page 13 of 36
for the formation of CHB is slightly less at 102 kJ/mol. This observation shows that at low temperatures the catalyst is more selective towards the HYD route and at high temperatures the catalyst is more slelective towards the DDS route. Furthermore, the activation energy for
ip t
the formation of BP when using the catalyst CMP(0.5) is 98.1 kJ/mol whereas it is 112.4 kJ/mol when using the catalyst CMP(1). Similarly the activation energy of formation of
cr
CHB for CMP(0.5) is 101.4 kJ/mol and for CMP(1) is 108.0 kJ/mol. Similar trends are observed with MBP and MCHB also. These results show that the activity of the catalyst
us
increases up to phosphorus content of 0.5 wt% and further increase in phosphorus content is
an
not helpful. This result is not consistent with the earlier report published by Ali et al. (2012). A comparison of the concentrations for DBT, BP, CHB, 4-MDBT, MBP and MCHB as
M
predicted by the kinetic model and the experimentally determined concentrations (wt.%) at 350°C are presented as a parity plot on Figure 9. From the plot, it be observed that the
te
Ac ce p
excellent manner.
d
predicted concentration by the kinetic model matches the experimental concentration in an
4. CONCLUSIONS
Phenomenological kinetics modeling of simultaneous HDS of dibenzothiophene and substituted dibenzothiophene over CoMo/P-Al2O3 has been carried out.
The following
conclusions are drawn from this study: 1. Addition of P2O5 to CoMo/γ-Al2O3 catalyst increased the HDS activity. 2. A comparison of the reaction rates constants for the formation of BP, CHB, MBP and MCHB and the activation energies show that the simultaneous HDS of DBT and 4-
14
Page 14 of 36
MDBT occur mostly by DDS route rather than HYD route – especially at high temperatures. 3. By comparing the activation energies for the formation of BP, CHB, MBP and MCH and
ip t
the equilibrium adsorption rate constants it can be conculed that CoMo/P-Al2O3 catalysts
cr
are more selective towards the HDS of DBT over the HDS of 4-MDBT.
us
ACKNOWLEDGEMENTS
The authors wish to acknowledge the support of King Fahd University of Petroleum and
an
Minerals (KFUPM). Acknowledgement is due to the Ministry of Higher Education, Saudi
Petrochemicals (CoRE-PRP) at KFUPM.
te
d
NOTATIONS
M
Arabia for establishing the Center of Research Excellence in Petroleum Refining and
Ac ce p
Ci = Concentration of species i in the batch reactor Ei = apparent activation energy of the ith reaction (kJ/mol) ki = apparent rate constant for the ith reaction (min-1) Ki = adsorption constant for the ith component t = reaction time (min)
T = reaction temperature (K) X = catalyst free active site i-X = active site occupied by the i component 15
Page 15 of 36
= fraction coverage for the I component
ip t
ABBREVIATIONS DBT = dibenzothiophene
cr
4-MDBT = 4-methyl dibenzothiophene
us
BP = biphenyl
an
CHB = cyclohexyl benzene
te
HDS = hydrodesulfurization
d
MCHB = 3-methyl-1-cyclohexylbenzene
M
MBP = methyl biphenyl
Ac ce p
DDS = direct desulfurization route HYD = hydrogenation route
REFERENCES
Ahmed, K., Ali, S. A., Ahmed, S., Al-Saleh. M., 2011. Simultaneous hydrodesulfurization of benzothiophene and dibenzothiophene over CoMo/Al2O3 catalysts with different
[Co/(Co + Mo)] ratios, Reaction Kinetics, Mechanisms and Catalysis, 103, 133-123. Ali, S. A., Ahmed, S., Ahmed, K.W., Al-Saleh, M., 2012. Simultaneous hydrodesulfurization of dibenzotiophene and substituted dibenzothiophenes over phosphorus modified CoMo/Al2O3 catalysts, Fuel Proc. Tech., 98, 39-44.
16
Page 16 of 36
Babich, I.V., Moulijn, J.A., 2007. science and technology of novel processes for deep desulfurization of oil refinery streams: A review, Fuel, 82, 607-631. Bej, S.K., Maity, S.K., Taraga, U.T., 2004. Search for an efficient 4,6-DMDBT
ip t
hydrodesulfurization catalyst: A review of recent studies, Energy Fuels 18, 1227-
cr
1237.
Borgna, A., Hensen, E. J. M., van Veen, J. A. R., Niemantsverdriet, J. W., 2004. Intrinsic
us
kinetics of thiophene hydrodesulfurization on a sulfided NiMo/SiO2 planar model
an
catalyst. J. Catal., 221(2), 541-548.
Cooper, B.H., Knudsen K.G., 2006. Ultra deep desulfurization of diesel: How an
M
understanding of the underlying kinetics can reduce investment costs, Practical Advances in Petroleum Processing, 297.
d
Egorova M., Prins, R. 2006. The role of Ni and Co promoters in the simultaneous HDS of
Ac ce p
172.
te
dibenzothiophene and HDN of amines over Mo/γ-Al2O3 catalysts. J. Catal., 241, 162-
Egorova, M., Prins, R., 2006. The role of Ni and Co promoters in the simultaneous HDS of dibenzothiophene and HDN of amines over Mo/γ-Al2O3 catalysts, J. Catal., 241, 162-
172.
Froment, G.F., 1986. The kinetics of catalytic processes: importance in reactor simulation and design. Appl. Catal., 22, 3-20. García-Martínez, J.C., Castillo-Araiza, C. O. De los Reyes Heredia, J. A., Trejo, E., Montesinos, A. 2012. Kinetics of HDS and of the inhibitory effect of quinoline on
17
Page 17 of 36
HDS of 4,6-DMDBT over a Ni-Mo-P/Al2O3 catalyst: Part I. Chem. Eng. J., 210, 5362.
ip t
Ho, T.C., 2004. Deep HDS of diesel fuel: Chemistry and catalysis, Catal. Today, 98, 3-18. Jiménez, F., Kafarov, V. Nuñez, M., 2007. Modeling of industrial reactor for hydrotreating of
cr
vacuum gas oils. Chem. Eng. J., 134(1-3), 200-208.
us
Lewis, J.M., Kydd, R. A., Boorman, P.M., Van Rhyn, P. H., 1992. Phosphorus promotion in nickel-molybdenum/alumina catalysts: model compound reactions and gas oil
an
hydroprocessing. Appl. Catal. A: Gen., 84(2), 103-121.
Nava, R., Infantes-Molina, A., Castano, P., Guil-Lopez, R., Pawelec, B. 2011. Inhibition of
M
CoMo/HMS catalyst deactivation in the HDS of 4,6-DMDBT by support modification
d
with phosphate. Fuel, 90, 2726-2737.
te
Nava, R., Morales, J., Alonso, G., Ornelas, C., Pawelec, B., Fierro, J. L.G. 2007. Influence of the preparation method on the activity of phosphate-containing CoMo/HMS catalysts
Ac ce p
in deep hydrodesulphurization. Appl. Catal. A: Gen., 321, 58-70.
Shafi, R., Hutchings, G.J., 2000. Hydrodesulfurization of hindered dibenzothiophenes: an overview. Catal. Today, 59(3-4), 423-442.
Stanislaus, A., Marafi, A., Rana, M.S., 2010. Recent advances in the science and technology of ultra-low sulfur diesel. Catal. Today, 153, 1-68.
Vrinat, M.L., 1983. The kinetics of the hydrodesulfurization process. Appl. Catal., 6, 137156.
18
Page 18 of 36
Wang, Y., Sun, Z., Wang, A., Ruan, L., Lu, M., Ren, J., Li, X., Li, C., Hu, Y., Yao, P. 2004. Kinetics of hydrodesulfurization of dibenzothiophene catalyzed by sulfided Co-Mo/ MCM-41. Ind. Eng. Chem. Res., 43, 2324-2329.
ip t
Yin, H., Zhou, T., Liu, Y., Chai, Y., Liu, C., 2010. Study on the structure of active phase in NiMoP impregnation solution using Laser Raman spectroscopy 1. Effect of
cr
phosphorous content, J. Fuel Chem. Technol., 38(6), 705-709.
Influences of different
us
Zhou, T. Yin, H., Han, S., Chai, Y., Liu, Y., Liu, C., 2009.
phosphorus contents on NiMoP/Al2O3 hydrotreating catalysts. J. Fuel Chem.
an
Technol., 37(3), 330-334.
M
Zhou, T., Yin, H., Liu, Y., Han, S., Chai, Y., Liu, C. 2010. Effect of phosphorus content on the active phase structure of NiMoP/Al2O3 catalyst. J. Fuel Chem. Technol., 38(1),
Ac ce p
te
d
69-74.
19
Page 19 of 36
LIST OF FIGURES Pore size distribution of CMP catalysts.
Figure 2.
Powder X-ray diffraction patterns of γ-Al2O3 and CMP catalysts.
Figure 3.
Product distribution during simultaneous HDS of DBT [A] and 4-MDBT [B]
us
over CMP(0) and CMP(1) catalysts at 623 K.
cr
ip t
Figure 1.
Reaction pathways Scheme for (A) DBT and (B) 4-MDBT.
Figure 5.
Arrhenius plot for HDS of DBT by DDS route
Figure 6.
Arrhenius plot for HDS of 4-MDBT by DDS route.
Figure 7.
Van't Hoff plot for HDS of DBT.
Figure 8.
Van't Hoff plot for HDS of 4-MDBT
Figure 9.
Parity plot between experimental values of product composition (wt%) and the
Ac ce p
te
d
M
an
Figure 4.
values predicted by kinetic model.
20
Page 20 of 36
ip t
LIST OF TABLES Composition and characteristics of CMP catalysts.
Table 2.
Estimated rate constants for HDS of DBT and 4-MDBT via DDS and HYD pathways.
cr
Table 1.
Estimated equlibrium adsorption constants.
Table 4.
Estimated activation energies for HDS of DBT and 4-MDBT via DDS and
us
Table 3.
Ac ce p
te
d
M
an
HYD pathways.
21
Page 21 of 36
ip t cr us an M
Ac ce p
te
d
Figure 1: Pore size distribution of CMP catalysts.
22
Page 22 of 36
ip t cr us an M d
te
Powder X-ray diffraction patterns of γ-Al2O3 and CMP catalysts.
Ac ce p
Figure 2:
23
Page 23 of 36
100
DBT-CMP(1) BP-CMP(1) CHB-CMP(1)
ip t
80 60
cr
40 20 0 0
10
20
30
40
50
60
M
an
Time (min)
us
Transformation of DBT(%)
DBT-CMP(0) BP-CMP(0) CHB-CMP(0)
Ac ce p
te
d
[A]
Figure 3.
Product distribution during simultaneous HDS of DBT [A] and 4-MDBT [B] [B] over CMP(0) and CMP(1) catalysts at 623 K.
24
Page 24 of 36
BP
DBT
ip t
DDS
cr
HYD CHB
TH-DBT
us
HYD
(A)
MBP DDS
CH3
CH3
M
HYD
an
4-MDBT
4-MTHBT
MCHB
d
HYD
te
CH3
CH3
(B)
Ac ce p
Figure 4: Reaction pathways Scheme for (A) DBT and (B) 4-MDBT.
25
Page 25 of 36
ip t cr us an M
Arrhenius plot for HDS of DBT by DDS route
Ac ce p
te
d
Figure 5.
26
Page 26 of 36
ip t cr us an M
Arrhenius plot for HDS of 4-MDBT by DDS route.
Ac ce p
te
d
Figure 6.
27
Page 27 of 36
ip t cr us an M d
Van't Hoff plot for HDS of DBT.
Ac ce p
te
Figure 7.
28
Page 28 of 36
ip t cr us an M
Van't Hoff plot for HDS of 4-MDBT
Ac ce p
te
d
Figure 8.
29
Page 29 of 36
ip t cr us an M
Parity plot between experimental values of product composition (wt%) and the values predicted by kinetic model.
Ac ce p
te
d
Figure 9.
30
Page 30 of 36
Composition and characteristics of CMP catalysts.
MoO
CoO
P2O5
Surface Area (m2/g)
CMP(0)
15.0
4.0
0.0
155.0
CMP(0.5)
15.0
4.0
0.5
135.0
CMP(1)
15.0
4.0
1.0
130.0
Pore Volume (cm3/g)
Average pore size (nm)
0.6
14.2
ip t
Composition (wt%)
0.5
14.2
0.4
12.9
us
Catalyst
cr
Table 1.
Ac ce p
te
d
M
an
Note: The catalysts were denoted as CMP(a), in which a represents P2O5 content in wt%.
31
Page 31 of 36
ip t cr
Catalyst
us
Estimated rate constants for HDS of DBT and 4-MDBT via DDS and HYD pathways CMP(0)
Temperature Sulfur HDS (oC) Compound Route
CMP(0.5)
k × 100 (min-1)
Confidence Interval
CMP(1)
k × 100 (min-1)
Confidence Interval
k × 100 (min-1)
Confidence Interval
{0.202, 0.394} {0.006, 0.070} {0.05, 0.147} {0.004, 0.066}
0.35 0.06 0.14 0.04
{0.304, 0.397} {0.029, 0.096} {0.101, 0.178} {0.005, 0.068}
0.32 0.05 0.17 0.03
{0.204, 0.429} {0.015, 0.092} {0.100, 0.233} {0.000, 0.068}
{0.382, 0.388} {0.049, 0.050} {0.138, 0.141} {0.045, 0.046}
0.47 0.07 0.20 0.04
{0.350, 0.593} {0.055, 0.095} {0.151, 0.264} {0.028, 0.052}
0.40 0.07 0.21 0.04
{0.389, 0.412} {0.071,0.088} {0.204, 0.226} {0.035, 0.521}
0.49 0.06 0.20 0.06
{0.381, 0.606} {0.009, 0.119} {0.121, 0.272} {0.006, 0.112}
0.52 0.07 0.25 0.04
{0.334, 0.701} {0.011, 0.131} {0.163, 0.329} {0.000, 0.095}
0.59 0.08 0.30 0.05
{0.508, 0.675} {0.009, 0.160} {0.218, 0.379} {0.000, 0.122}
M an
Table 2.
DDS HYD DDS HYD
k1 k2 k3 k4
0.30 0.04 0.10 0.04
310
DBT DBT 4MDBT 4MDBT
DDS HYD DDS HYD
k1 k2 k3 k4
0.38 0.04 0.13 0.04
325
DBT DBT 4MDBT 4MDBT
DDS HYD DDS HYD
k1 k2 k3 k4
335
DBT DBT 4MDBT 4MDBT
DDS HYD DDS HYD
k1 k2 k3 k4
0.92 0.11 0.36 0.11
{0.926, 0.930} {0.115, 0.117} {0.365, 0.367} {0.114, 0.117}
1.02 0.14 0.45 0.09
{1.027, 1.030} {0.140, 0.141} {0.450, 0.453} {0.097, 0.098}
1.08 0.16 0.55 0.09
{1.043, 1.125} {0.154, 0.167} {0.528, 0.574} {0.091, 0.100}
350
DBT DBT 4MDBT 4MDBT
DDS HYD DDS HYD
k1 k2 k3 k4
1.71 0.22 0.70 0.21
{1.545, 1.878} {0.133, 0.299} {0.630, 0.770} {0.150, 0.279}
1.92 0.25 0.82 0.19
{1.719, 2.117} {0.145, 0.347} {0.737, 0.904} {0.116, 0.268}
2.08 0.31 1.03 0.19
{1.866, 2.286} {0.208, 0.416} {0.942, 1.117} {0.112, 0.265}
Ac
ce pt
ed
300
DBT DBT 4MDBT 4MDBT
32
Page 32 of 36
ip t cr us
Estimated equlibrium adsorption constants.
Table 3.
CMP(0)
CMP(0.5)
M an
Catalyst
CMP(1)
K × 103 (l/mol) K × 103 (l/mol) K × 103 (l/mol) 300 oC
945.8
124.6
48.5
28.1
53.1
4.9
K1
912.3
82.2
6.2
K2
1.5
11.2
4.1
K1
840.5
7.0
3.1
K2
0.1
3.1
0.1
K1
781.7
6.0
2.9
K2
0.1
0.3
0.1
K1
732.7
4.6
2.5
K2
0.0
0.0
0.0
K1
ed
K2 310 oC
ce pt
325 oC
Ac
335 oC
350 oC
33
Page 33 of 36
Table 4.
Estimated activation energies for HDS of DBT and 4-MDBT via DDS and HYD pathways
Confidence Interval
CMP(0.5)
Confidence Interval
CMP(1)
Confidence Interval
ip t
Activation Energy CMP(0) (kJ/mol) 103.0
{57.6,148.6}
98.1
{41.5,154.7}
112.4
{71.6,153.2}
E2
102.4
{58.8,145.3}
78.4
{12.4,144.5}
99.1
{43.9,154.3}
E3
114.0
{75.1,152.7}
101.4
{58.7,144}
108.0
{67.0,149.1}
E4
106.7
{59.7,154.5}
98.7
{22.1,175.4}
99.5
{48.6,150.4}
Ac ce p
te
d
M
an
us
cr
E1
34
Page 34 of 36
PHENOMENOLOGICAL KINETICS MODELING OF SIMULTANEOUS HDS OF DIBENZOTHIOPHENE AND SUBSTITUTED DIBENZOTHIOPHENE OVER COMOP/AL2O3 CATALYSTS
Shaikh A. Razzak1, Mohammad M. Hossain1,2* 1
Department of Chemcial Engineering,
Center of Research Excellence in Petroleum Refining and Petrochemicals,
cr
2
ip t
Ahmad H. Al-Rashidy1, Syed A. Ali2, Shakeel Ahmed2,
an
us
King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia
Ac ce p
te
d
M
Graphical Abstract
Figure : Parity plot between model predicted and experimental data.
35
Page 35 of 36
PHENOMENOLOGICAL KINETICS MODELING OF SIMULTANEOUS HDS OF DIBENZOTHIOPHENE AND SUBSTITUTED DIBENZOTHIOPHENE OVER COMOP/AL2O3 CATALYSTS Ahmad H. Al-Rashidy1, Syed A. Ali2, Shakeel Ahmed2, Shaikh A. Razzak1, Mohammad M. Hossain1,2*
2
Department of Chemcial Engineering,
ip t
1
Center of Research Excellence in Petroleum Refining and Petrochemicals,
cr
King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia
us
HIGHLIGHTS
Synthesized P2O5 promoted CoMo/γ-Al2O3 catalysts for HDS of heavy oil.
an
Investigated the effects of P2O5 on the simultaneous HDS of DBT and 4-MDBT.
P2O5 favors the DDS pathway over the HYD pathway for both DBT and 4-MDBT.
Ac ce p
te
d
M
Langmuir-Hinshelwood mechanism fits the experimental data adequately.
37
Page 36 of 36