- Email: [email protected]
Kinetic study of thermal and catalytic hydrocracking of asphaltene
Catalysis Today xxx (xxxx) xxx–xxx
Contents lists available at ScienceDirect
Catalysis Today journal homepage: www.elsevier.com/locate/cattod
Kinetic study of thermal and catalytic hydrocracking of asphaltene Hai Hung Phama,b, Ngoc Thuy Nguyenb, Kang Seok Goa,b, , Sunyoung Parkb, Nam Sun Nhoa,b, , Gyoo Tae Kimb, Chul Wee Leeb, Guillermo Felixc ⁎
⁎
a
Climate Change Research Division, Korea Institute of Energy Research, 152 Gajeong-ro, Yuseong-gu, Daejeon, 34129, Republic of Korea Center for Convergent Chemical Process, Korea Research Institute of Chemical Technology, 141 Gajeong-ro, Yuseong-gu, Daejeon, 34114, Republic of Korea Instituto Politécnico Nacional, Centro de Investigación en Ciencia Aplicada y Tecnología Avanzada, Unidad Legaria, Legaria 694, Col. Irrigación, Mexico City, 11500, Mexico
b c
ARTICLE INFO
ABSTRACT
Keywords: Asphaltene Thermal hydrocracking Catalytic hydrocracking Coke induction period Kinetics
In this study, a five-lump model was proposed for kinetic modeling of asphaltene placed in a batch reactor with a commercial slurry-phase catalyst (Mo-octoate). Asphaltene was separated from vacuum residue using normal pentane. The kinetic experiments were carried out at 380∼430℃ for 1∼20 h together with a 1000 ppm concentration of Molybdenum in thermal and catalytic hydrocracking reaction modes. The results showed that the coke induction period and maximum maltene yield are changed with reaction temperature and time at thermal and catalytic hydrocracking. In addition, a linear relationship between coke and liquid (maltene + asphaltene remains) yields was shown so that the critical gas amount could be found as a criterion for determining the end of the coke induction period. Significantly, the kinetic model fit the experimental data well and, moreover, was found to be able to predict the moment when coke begins to form as well as maximum maltene yields.
1. Introduction In order to meet the ever rising demands for light fuel oils, refiners have been increasingly looking for ways to maximize the upgrading of heavy crude [1–4]. In general, heavy crude contains a large amount of high molecular weight compounds such as asphaltene, which is the heaviest portion and contains a very complex mixture of constituents [5]. Asphaltene causes many problems in heavy oil upgrading, such as deactivation of catalysts and formation of sludge or sediment that clog filters, separators and pipe systems. Asphaltene is also known as one of the precursors of coke formation because it is prone to form coke during hydrocracking [6,7]. Therefore, finding ways to treat asphaltene is of prime importance for upgrading heavy oil technologies. Among the technologies currently used for highly converting asphaltene into high-value products with less coke formation, slurryphase hydrocracking is commonly considered to be one of the most efficient [1,5,8–11]. The dispersed catalyst plays an important role to prevent excessive cracking and coke formation, and minimize the risk of catalyst deactivation [10–12]. Nguyen et al. [13] conducted experiments at a temperature of 380 for 10 h in a catalytic hydrocracking reaction. In their research, coke yield was significantly reduced from 9.6% to 0.8% while a more liquid product yield was
produced. Coke formation is a complicated process that involves many reactions such as polymerization of free radicals, cyclization of alkyl chains, dehydrogenation and aromatization of naphthenic rings, elimination of side chains on aromatic rings, and condensation and pericondensation of aromatic rings [5,14,15]. Coke induction has been commonly observed by many previous studies in the thermal cracking process [16] as well as in the catalytic hydrocracking process [8,13,17]. The formation of coke is commonly associated with asphaltene and its stability in the oil system [5,18]. Consequently, it is essential to predict the exact moment when coke formation occurs as well as the amount of coke formed due to the type of feedstock, temperature and reaction time changes that occur during slurry-phase hydrocracking. A large number of studies have been made to develop the kinetic model of asphaltene undergoing different processes, including thermal cracking [16,19–21], thermal hydrocracking [9], and catalytic hydrocracking [8,9]. Martinez [19] presented a three-lump kinetic model including parallel cracking of asphaltene to oil plus gas and coke while Wang and Anthony [20] re-examined their data and offered a formula for estimating oil and gas yields as a function of asphaltene conversion. Yasar et al. [21] proposed a four-lump model, which included asphaltene, maltene, gas and coke, and Zhao et al. proposed a modified threelump model, which involved parallel reactions of asphaltene to liquid
⁎ Corresponding authors at: Climate Change Research Division, Korea Institute of Energy Research, 152 Gajeong-ro, Yuseong-gu, Daejeon, 34129, Republic of Korea. E-mail addresses: [email protected] (K.S. Go), [email protected] (N. Sun Nho).
https://doi.org/10.1016/j.cattod.2019.08.031 Received 9 April 2019; Received in revised form 21 August 2019; Accepted 27 August 2019 0920-5861/ © 2019 Elsevier B.V. All rights reserved.
Please cite this article as: Hai Hung Pham, et al., Catalysis Today, https://doi.org/10.1016/j.cattod.2019.08.031
Catalysis Today xxx (xxxx) xxx–xxx
H.H. Pham, et al.
Nomenclature
A A* Ai C Ea,i fobj G i ki M
yA y A* yM yG yC yGcrit yExp yCal R t T
C5-isolated asphaltene asphaltenecore pre-exponential parameter of the ith reaction, (h−1) coke activation energy of the ith reaction, (kJ/mol) objective function for optimization, (-) Gas reaction indicator. reaction rate constant of the ith reaction, (h−1) maltene
oil and gas plus coke, and a consecutive reaction of liquid oil to gas plus coke [9]. Recently, Sheng et al. [8] proposed a seven-lump kinetic model that induces detailed distribution in maltene during asphaltene conversion in a hydrogen donor process. Some studies have tried to find the coke induction period with respect to asphaltene conversion in thermal cracking reactions. For example, Wiehe [16] suggested a phase separation model which could represent the coke induction period. Rahmani et al. [17] modified the kinetic model proposed by Wiehe [16] to examine the kinetics of coke formation in different solvent environments in a closed reactor within a nitrogen atmosphere. However, those studies focused only on the thermal cracking reaction. Therefore, there is a need for a detailed study of asphaltene kinetics involving the coke induction period while undergoing a thermal and catalytic hydrocracking reaction. In this study, the reaction of C5-isolated asphaltene (Asphaltene) hydrocracking in the presence or absence of the slurry-phase Mo-catalyst precursor at 380, 410 and 430 °C was investigated. As a result of the experiment, a simple relation between coke and liquid yields was found that can be used to easily predict coke yield. The critical gas mas fraction was proposed as a criterion to determine the onset of the coke formation period. A new five-lump model, including the criterion and an intermediate product named the "asphaltene core" was proposed to represent the asphaltene conversion undergoing the thermal and catalytic hydrocracking reactions. A mechanism for inducing coke formation during the conversion of asphaltene was proposed. The kinetic model can help predict the onset point of coke formation and provide insights into the optimal utilization of asphaltene and the catalyst.
massfraction of asphaltene, (-) massfraction of asphaltene core, (-) massfraction of maltene, (-) massfraction of gas, (-) massfraction of coke, (-) mass fraction of critical gas when coke begins to form, (-) massfraction of experimental data, (-) massfraction of calculated data, (-) universal gas constant, (kJ/mol K) reaction time, (h) temperature of reaction, (K)
for 24 h. then dried at 110 The hydrothermal and catalytic hydrothermal cracking experiments were carried out in a 100 ml Parr batch reactor filled with 20 g of feedstock. Hydrogen was injected into the reactor until 80 bar of pressure were registered at 80 . The warm-up time needed to reach the base temperature of 80 was approximately 20 min. At that point the temperature was raised systematically from 80 to target temperatures of 380, 410 and 430 while being stirred at 1500 rpm. When it reaches to the desired temperature, the experiments were carried out for 1∼20 h. At the desired temperature points, the pressures were 124.2, 124.1 and 125.3 bar for 380, 410 and 430 for thermal cracking, respectively. For catalytic cracking, the pressures were 102.2, 103.6 and 105.3 bar for 380, 410 and 430 , respectively. All experiments were done separately. The average material balances of the experiments were more than 95% and normalized to 100% for the estimation of kinetic model parameters. In total there are 40 experiments with 160 observed data points. 2.2. Product separation and analysis After the reaction finished, the internal temperature of the reactor was rapidly cooled to room temperature, and the resulting products (gas, coke, asphaltene deposits and maltene) were separated according to the procedure shown in Fig. 1 [13]. The gas was collected in a sample bag and its composition was analyzed using a chromatograph (Model 7890B, Agilent Technologies Co. Ltd.). The liquid product was separated by a Soxhlet extractor into coke, asphaltene deposits, and DAO as toluene insoluble, n-pentane insoluble, and n-pentane soluble fractions, respectively. The Soxhlet extraction was carried out at 80 and 120 °C for n-pentane and toluene, respectively. The coke, asphaltene deposits, maltene and gas yields were calculated based on various references [13,22,23].
2. Experiment 2.1. Experiment procedure For this experiment, asphaltene separated from vacuum residue (VR) was used as feedstock. The separation was done by following the procedure specified previously [13]. First, VR and n-pentane (nC5) with mass ratio of 1:40 was stirred for 4 h. The mixture was then separated by filtering to obtain the solid state asphaltene, the liquid mixture of deasphaltene oil (DAO) and n-pentane solvent. After that, the solid state asphaltene was mixed again with n-pentane and washed continuously in Soxhlet extractor for 24 h to remove the remained DAO. Finally, the solid obtained was dried at 80 °C for 20 h to remove the remaining solvent. Table 1 shows the properties of the VR and asphaltene. Molybdenum octoate (Shepherd Chemical) was used as an oil-soluble dispersed catalyst precursor. For solvents, n-pentane and toluene rated at 99.5% purity were purchased from Samchun Chemical. In order to disperse liquid phase Mo-octoate into solid phase asphaltene to create a catalytic hydrocracking feedstock, a mixture of asphaltene and 1000 ppm of Mo-octoate (based on the weight of the feedstock) was pre-mixed for one hour by adding toluene and stirring at a speed of 80 rpm. When finished, the toluene was then removed from the mixture using a rotary evaporator for 1 h. The remaining solid was
Table 1 Properties of vacuum residue (VR) and C5-isolated asphaltene feedstock [13,23]. Properties
VR
Asphaltene
C (wt.%) H (wt.%) N (wt.%) S (wt.%) Ni (wt.ppm) V (wt.ppm) MCR * (wt.%) C5 asphaltene (wt.%) Vacuum gas oil (343-524 °C) (wt.%) Residue (524 °C-FBP) (wt.%)
83.4 10.1 0.5 5.89 72.3 309.1 23.3 25.0 21.5 78.5
82.4 7.6 1.0 7.3 241.0 1070.0 52.4 – 11.5 88.5
* MCR: Micro carbon residue. 2
Catalysis Today xxx (xxxx) xxx–xxx
H.H. Pham, et al.
Fig. 1. Products separation procedure for analysis [13,23].
3. Results and discussion
(Fig. 2-b). The maximum coke yields were found to be up to approximately 40 wt.%. This was possible because the MCR in the feedstock was 52.4 wt.%. The mass fractional distribution of maltene and asphaltene remaining with each reaction time are plotted in Fig. 3. A sharp decrease of asphaltene remaining with the increase of maltene was observed at the begining period of asphaltene conversion. This phenomena occurs mainly because asphaltene decomposes quickly into maltene with a small amount of gas at a fast rate. After that, the remaining asphaltene continued to decrease due to condensation into coke. However, the existing maltene reached a maximum mass fraction and then decreased, indicating that the maltene could participate in the gas formation reaction. In the thermal hydrocracking reaction, the maximum maltene fraction was 0.45, 0.35 and 0.33 at temperatures of 380, 410 and 430 , respectively, while in the catalytic hydrocracking reaction it was 0.56, 0.52 and 0.49 at temperatures of 380, 410 and 430 , respectively. In conclusion, catalytic hydrocracking is a suitable method
3.1. Conversion of asphaltene undergoing thermal and catalytic hydrocracking Fig. 2 shows the formation of coke as a function of reaction time at different temperatures for the thermal hydrocracking and catalytic hydrocracking reactions. When comparing the two cases at any point on the reaction timeline it can be seen that catalytic hydrocracking resulted in a lower coke yield while thermal cracking resulted in a much higher yield. Coke induction periods are observed for both thermal and hydrocracking processes except for thermal hydrocracking at 430 °C. It should be noted that the coke induction period shortens as the temperature increases. In the thermal hydrocracking reaction, the coke induction period decreased from 4 h to almost no time as the temperature rose from 380 to 430 °C (Fig. 2-a). In the same manner, it decreased from 6 h to 15 min in the catalytic hydrocracking process
Fig. 2. Coke distribution with reaction time variations at different temperature (380, 410, 430 [Component: (○) 380 ℃, (□) 410 ℃, (Δ) 430 ℃]. 3
) for (a) thermal hydrocracking and (b) catalytic hydrocracking.
Catalysis Today xxx (xxxx) xxx–xxx
H.H. Pham, et al.
Fig. 3. Asphaltene remains and maltene distribution with reaction time variations at different temperature (380, 410, 430 ℃) for (a) thermal hydrocracking and (b) catalytic hydrocracking. [Asphaltene remain: (●) 380 ℃, (◼) 410 ℃, (▲) 430 ℃, Maltene: ( ) 380 ℃, ( ) 410 ℃, ( 430 ℃, Gas: (○) 380 ℃, (□) 410 ℃, (Δ) 430 ℃].
which can help increase maltene yield and suppress coke formation with a longer coke induction time.
alkyl-chain and a more aromatic core due to dealkylation [16,17]. It should be noted that the asphaltene and asphaltene core are lumped as asphaltene deposits. The equation for determining the rate of decomposition in this induction period can be written as follows:
3.2. Kinetic modeling
Asphaltene:
A common approach known as the "lump strategy" was adopted for describing asphaltene conversion [5,24,25]. The proposed kinetic model is shown in Fig. 4. This mechanism is based on the high molecular reactants cracked down to the low molecular products. The following assumptions were made for the model: (1) the change of hydrogen transfer was negligible, (2) there were no mass transport phenomena affecting the catalyst, (3) the volume of the reaction system was not changed, and (4) The catalyst deactivation was not considered in this kinetic modeling.
Maltene: Gas:
dyA = dt
(k1 + k2 + k3 ) yA
dyM = k3 yA dt
k4 yM
dyG = k2 yA + k4 yM dt
Asphaltene core:
dy A* dt
(1) (2) (3)
= k1 yA
(4)
The coke induction period ends when yG < yGCrit . The reaction rates are given by the following equations:
3.2.1. Model description The model consists of five lumped pseudo-components including asphaltene (A), asphaltene core (A*), maltene (M), coke (C), and gas (G). The overall conversion of asphaltene decomposition has been found to follow first-order reaction [8,16] or second-order reaction [9,19]. In this study, the reaction order of asphaltene decomposition was found to be first-order since it best fit the data (Table 2). As discussed in section 3.1, determining the coke induction period is important for finding the reaction characteristics of coke formation with heavy feedstocks. In this respect, there were some efforts to predict the coke induction period with thermodynamic properties. A solubility limit, SL , can be used as a criterion for determining when phase separation occurred [16,17]. However, the criterion is based on the common features of asphaltene conversion undergoing a thermal cracking process. Asphaltene precipitation or aggregation could also be related to the amount of hydrocarbon gases in the system under high pressure [26–28]. This phenomena could be attributed to the interaction between asphaltene molecules and the gases [28]. Therefore, it could be possible that the formation of gas in the batch reactor could deteriorate the hydrogenation, which then resulted in asphaltene precipitation. Interestingly, it was found that coke yield had a linear relationship with liquid yield (the summation of both remaining asphaltene and maltene as shown in Fig. 5). This relationship is not dependent on temperature under the given conditions, so it can be used to predict coke yield based on this linear relationship without measuring it. As suggested by the effect of the amount of gas on asphaltene precipitation [26–28], coke formation could be triggered by the extent of gas formation. As a result, the conversion of asphaltene core into coke progressed via condensation [17]. Here the critical gas amount, yGCrit , is proposed as a criterion for determining the onset of coke formation. As can be seen, yGCrit for thermal hydrocracking is 0.053 and for the catalytic hydrocracking process it is 0.079. When the gas mass fraction is greater than the critical gas mass fraction, yGCrit , coke begins to form. During the coke induction period, asphaltene can only be decomposed to lower molecular weight products, such as maltene, asphaltene core and gases. The asphaltene core is known to be asphaltene with a shorter
Asphaltene:
Maltene: Gas:
dyA = dt
(k1 + k2 + k3 ) yA
dyM = k3 yA dt
k4 yM
dyG = k2 yA + k4 yM dt
Fig. 4. Asphaltene kinetic model. 4
(5) (6) (7)
Catalysis Today xxx (xxxx) xxx–xxx
H.H. Pham, et al.
be seen that for thermal hydrocracking the asphaltene converted completely into asphaltene core in 30 min whereas for catalytic hydrocracking the time required was 3 h. As mentioned earlier, the dependence of the critical gas yield on the type of hydrocracking reaction indicates that a catalyst can enhance hydrogenation reaction and prevent gas formation in the system. The rate constants for each lump in both reactions are shown in Table 3. As can be seen, the rate constant for the overall conversion of asphaltene was much lower for catalytic hydrocracking than for it was 7.25 h−1 for catalytic hydrothermal hydrocracking. At 430 −1 cracking and 84.77 h for thermal hydrocracking. The asphaltene reaction to produce maltene and asphaltene core is the main reaction with the largest rate constant. The rate constant of the reaction for asphaltene core formation (k1) is higher than that of the reaction for maltene formation (k3) at all temperatures. The ratio between k1/ k3 (380 : 0.75, 410 : 0.86 and 430 : 1.02) in catalytic hydrocracking was lower than that of thermal hydrocracking (380 : 1.03, 410 : 1.64 and 430 : 1.98) indicating high selectivity towards maltene from asphaltene with the presence of a catalyst. For gas formation, the rate constant of gas formation from maltene is weaker than the one from asphaltene. For coke formation, the conversion of asphaltene core to coke was much lower for catalytic hydrocracking. At 430 , the rate constant of coke formation from asphaltene core was 1.2893 and 0.2775 h−1 for thermal hydrocracking and catalytic hydrocracking, respectively, suggesting that the presence of a catalyst suppressed the formation of coke from the aggregation of the asphaltene core. According to the Arrhenius equation, the activation energies were calculated as shown in Table 3, where it can be seen that the activation energies of all the reactions in catalytic hydrocracking were lower than those of thermal hydrocracking. In catalytic hydrocracking, the activation energies needed to form asphaltene core, maltene and gas were 188, 162, and 165 kJ/mol, while in thermal hydrocracking they were 400, 352 and 350 kJ/mol. This indicates that thermal hydrocracking is more temperature-sensitive. In addition, this also suggests asphaltene is prone to form an asphaltene core at high temperature. The activation energy of coke formation reaction was 306 kJ/mol in thermal hydrocracking and 163 kJ/mol in catalytic hydrocracking. However, unlike the activation energy of gas formation from asphaltene, the one from maltene during thermal hydrocracking (370 kJ/mol) was similar to that of catalytic hydrocracking (355 kJ/mol). Considering the rate constants for gas formation from maltene together, it suggests that this reaction is not influenced much by the catalytic reaction. Based on the reaction kinetics information, the proposed reaction condition can be selected to enhance the liquid product and avoid the coke formation.
Table 2 Sum of square errors versus reaction. Overall asphaltene reaction order
SSE
1 4/3 5/3 2
0.048 0.05 0.054 0.06
SSE: sum of square errors.
Asphaltene core: Coke:
dy A* dt
dyC = k5 y A* dt
= k1 yA
k5 y A*
(8) (9)
3.2.2. Estimation of kinetic parameters For this kinetic model no fewer than seven constants were estimated at each temperature. The kinetic parameters were calculated according to the following procedure [5,29,30]. (i) The initial values of the reaction rate constants were determined by a Monte Carlo algorithm [30]. (ii) The objective function was established as shown in Eq. 10.
Fobj =
(ycal
yexp )2
(10)
(iii) The set of differential equations were solved using the RungeKutta method, and the values of reaction rate coefficient were re-examined using an optimization algorithm based on the LevenbergMarquardt method. (iv) After that, a sensitivity analysis was conducted to evaluate the obtained parameters. If optimal parameters do not give a global minimum, step (iii) is carried out again until the global minimum is satisfied. (v) Once the reaction rate coefficients were found to give a global minimum, the frequency factors and apparent activation energies were calculated by using the Arrhenius equation.
ki = Ai e
Eai RT
(11)
3.2.3. Comparison of predicted vs. experimental values Fig. 6 shows the parity chart of the predicted yields of products and experimental data from the kinetic model. The comparison shows that the kinetic model anticipated quite well the experimental data for both thermal and catalytic reactions in the operating range. The predicted yields and experimental data of each lump at varying reaction times at 380, 410, and 430 for the thermal and catalytic processes are presented in Fig. 7. Again, the model agreed well with the experimental data. Moreover, the coke induction periods can also be predicted. It can
4. Conclusions The reaction characteristics of asphaltene (separated from VR) undergoing thermal and catalytic hydrocracking were investigated. Two
Fig. 5. Relation of coke yield with a summation of asphaltene remains and maltene yield for (a) thermal hydrocracking and (b) catalytic hydrocracking. The equation is the results of linear regression for all data and R2 is the square of the relation coefficient. [Temperature, °C: (○) 380, ( ) 410, ( ) 430]. 5
Catalysis Today xxx (xxxx) xxx–xxx
H.H. Pham, et al.
Fig. 6. Parity plots for predicted and experimental value for (a) thermal hydrocracking and (b) catalytic hydrocracking. [Component: (○) Asphaltenes, (◼) Maltene, (△) Gas, ( ) Coke].
Fig. 7. Comparison of predictions of products yields with experimental data reaction time variations at different (380, 410, 430 °C) for (a) thermal hydrocracking and (b) catalytic hydrocracking. Curves were calculated from the kinetic model. Symbols represent experimental data. [Component: (○) Remained asphaltene, (◼) Maltene, (△) Gas, ( ) Coke. Curves: (–) Asphaltenes remain, (—) Maltene, ( ) Asphaltenes core, (-.-) Gas, ( ) Coke]. Table 3 Kinetic parameters of the kinetic model. Thermal hydrocracking Parameters
Reaction path
Rate constant value (h−1)
k1 k2 k3 (k1 + k2 + k3) k4 k5
Asp → Asp* Asp → Gas Asp → Mal Overall Asp Mal → Gas Asp* → Coke
380 0.2589 0.0382 0.2503 0.5474 0.0036 0.0290
410 4.0918 0.1230 2.5015 6.7163 0.2481 1.2283
Catalytic hydrocracking
430 51.9050 5.1316 26.7320 84.7686 0.3709 1.2893
Activation energy
R2
Rate constant value (h−1)
EA (kJ/mol) 400 352 350 – 370 306
0.99 0.83 0.98 – 0.90 0.86
380 0.2949 0.0554 0.3939 0.7442 0.0012 0.0293
common features of asphaltene conversion during both reactions, especially the coke induction period and maximum maltene fraction, were observed and noted. In addition, a simple relation between coke and liquid yield (asphaltene deposits and maltene) was found. Based on this relationship, a critical gas amount was proposed as a criterion for
410 1.5323 0.1135 1.7779 3.4237 0.0635 0.0540
430 3.4006 0.5152 3.3342 7.2500 0.1053 0.2775
Activation energy
R2
EA (kJ/mol) 188 162 165 – 355 163
1.00 0.89 0.99 – 0.92 0.85
determining the point at which the coke induction period ends. A fivelumped kinetic model, including the critical gas amount, was developed to understand the conversion of asphaltene undergoing either thermal or catalytic hydrocracking. The kinetic model can be used to predict both the reaction behavior 6
Catalysis Today xxx (xxxx) xxx–xxx
H.H. Pham, et al.
and onset of coke formation. It was also found that the main reaction for forming coke are the aggregation of the asphaltene core. In addition, it was observed that maltene yield increased more than that of the asphaltene core for the catalytic reaction. The information from the kinetic model is important for providing some solutions for optimizing utilization of asphaltene in hydrocracking processes as well as the catalyst. Although the kinetic model is in a good agreement with experimental results, the criterion of critical gas yield was a hypothesis from the observation in this study. It is suggested that these results should be confirmed by further experiments in the future.
[11] [12] [13] [14] [15] [16]
Acknowledgments
[17]
This work was supported by the National Research Council of Science and Technology (NST) grant by the Korea government (MSIT) (No. CRC-14-1-KRICT).
[18] [19] [20]
References
[21]
[1] K.S. Go, S.H. Lim, Y.K. Kim, E.H. Kwon, N.S. Nho, Characteristics of slurry-phase hydrocracking for vacuum residue with reaction temperature and concentrations of MoS2 dispersed catalysts, Catal. Today 305 (2018) 92–101. [2] S.H. Lim, K.S. Go, N.S. Nho, J.G. Lee, Effect of reaction temperature and time on the products and asphaltene dispersion stability in slurry-phase hydrocracking of vacuum residue, Fuel 234 (2018) 305–311. [3] K. Aleklett, M. Höök, K. Jakobsson, M. Lardelli, S. Snowden, B. Söderbergh, The peak of the oil age - analyzing the world oil production reference scenario in world energy outlook 2008, Energy Policy 38 (2010) 1398–1414. [4] M.S. Rana, V. Sámano, J. Ancheyta, J.A.I. Diaz, A review of recent advances on process technologies for upgrading of heavy oils and residua, Fuel 86 (2007) 1216–1231. [5] J. Ancheyta, F. Trejo, M.S. Rana, Asphaltenes Chemical Transformation During Hydroprocessing of Heavy Oils, CPC Press, 2009. [6] F. Trejo, M.S. Rana, J. Ancheyta, Thermogravimetric determination of coke from asphaltenes, resins and sediments and coking kinetics of heavy crude asphaltenes, Catal. Today 150 (2010) 272–278. [7] J. Ancheyta, G. Centeno, F. Trejo, J.G. Speight, Asphaltene characterization as function of time on-stream during hydroprocessing of Maya crude, Catal. Today 109 (2005) 162–166. [8] Q. Sheng, G. Wang, Q. Zhang, C. Gao, A. Ren, M. Duan, J. Gao, Seven-lump kinetic model for non-catalytic hydrogenation of asphaltene, Energy Fuels 31 (2017) 5037–5045. [9] Y. Zhao, Y. Yu, Kinetics of asphaltene thermal cracking and catalytic hydrocracking, Fuel Process. Technol. 92 (2011) 977–982. [10] M.J. Angeles, C. Leyva, J. Ancheyta, S. Ramírez, A review of experimental
[22] [23] [24] [25] [26] [27] [28] [29] [30]
7
procedures for heavy oil hydrocracking with dispersed catalyst, Catal. Today 220–222 (2014) 274–294. S.M. Elahi, C.E. Scott, Z. Chen, P. Pereira-Almao, In-situ upgrading and enhanced recovery of heavy oil from carbonate reservoirs using nano-catalysts: upgrading reactions analysis, Fuel 252 (2019) 262–271. M.T. Nguyen, N.T. Nguyen, J. Cho, C. Park, S. Park, J. Jung, C.W. Lee, A review on the oil-soluble dispersed catalyst for slurry-phase hydrocracking of heavy oil, J. Ind. Eng. Chem. 43 (2016) 1–12. N.T. Nguyen, K.H. Kang, C.W. Lee, G.T. Kim, S. Park, Y.K. Park, Structure comparison of asphaltene aggregates from hydrothermal and catalytic hydrothermal cracking of C5-isolated asphaltene, Fuel 235 (2019) 677–686. Y. Zhao, M.R. Gray, K.H. Chung, Molar kinetics and selectivity in cracking of Athabasca asphaltenes, Energy Fuels 15 (2001) 751–755. T.F. Yen, G.V. Chilingarian, Asphaltenes and Asphaltes, 2, Elsevier Science, 2000. I.A. Wiehe, A phase-separation kinetic model for coke formation, Ind. Eng. Chem. Res. 32 (1993) 2447–2454. S. Rahmani, W. McCaffrey, M.R. Gray, Kinetics of solvent interactions with asphaltenes during coke formation, Energy Fuels 16 (2002) 148–154. L.L. Zhang, G.H. Yang, G.H. Que, The conglomerating characteristics of asphaltenes from residue during thermal reaction, Fuel 84 (2005) 1023–1026. M.T. Martínez, A.M. Benito, M.A. Callejas, Thermal cracking of coal residues: kinetics of asphaltene decomposition, Fuel 76 (1997) 871–877. J. Wang, E.J. Anthony, A study of thermal-cracking behavior of asphaltenes, Chem. Eng. Sci. 58 (2003) 157–162. M. Yasar, D.M. Trauth, M.T. Klein, Asphaltene and resid pyrolysis. 2. The effect of reaction environment on pathways and selectivities, Energy Fuels 15 (2001) 504–509. N.T. Nguyen, S. Park, J. Jung, J. Cho, C.W. Lee, Y.K. Park, Comparative reactivity between thermal and catalytic hydrocracking of vacuum residue: effect of asphaltenes, J. Ind. Eng. Chem. 61 (2018) 32–38. H. Ortiz-Moreno, J. Ramírez, R. Cuevas, G. Marroquín, J. Ancheyta, Heavy oil upgrading at moderate pressure using dispersed catalysts: effects of temperature, pressure and catalytic precursor, Fuel 100 (2012) 186–192. G. Félix, J. Ancheyta, Comparison of hydrocracking kinetic models based on SARA fractions obtained in slurry-phase reactor, Fuel 241 (2019) 495–505. J. Ancheyta, S. Sánchez, M.A. Rodríguez, Kinetic modeling of hydrocracking of heavy oil fractions: a review, Catal. Today 109 (2005) 76–92. B. Journal, S. Moradi, M. Dabiri, B. Dabir, D. Rashtchian, M.A. Emadi, Investigation of asphaltene precipitation in miscible gas injection processes: experimental study and modeling, Braz. J. Chem. Eng. 29 (2012) 665–676. Y. Kazemzadeh, R. Parsaei, M. Riazi, Experimental study of asphaltene precipitation prediction during gas injection to oil reservoirs by interfacial tension measurement, Colloids Surf. A Physicochem. Eng. Asp. 466 (2015) 138–146. P. Zanganeh, H. Dashti, S. Ayatollahi, Comparing the effects of CH4, CO2, and N2injection on asphaltene precipitation and deposition at reservoir condition: a visual and modeling study, Fuel 217 (2018) 633–641. G. Félix, J. Ancheyta, F. Trejo, Sensitivity analysis of kinetic parameters for heavy oil hydrocracking, Fuel 241 (2019) 836–844. H. Hassanzadeh, J. Abedi, Modelling and parameter estimation of ultra-dispersed in situ catalytic upgrading experiments in a batch reactor, Fuel 89 (2010) 2822–2828.
Contents lists available at ScienceDirect
Catalysis Today journal homepage: www.elsevier.com/locate/cattod
Kinetic study of thermal and catalytic hydrocracking of asphaltene Hai Hung Phama,b, Ngoc Thuy Nguyenb, Kang Seok Goa,b, , Sunyoung Parkb, Nam Sun Nhoa,b, , Gyoo Tae Kimb, Chul Wee Leeb, Guillermo Felixc ⁎
⁎
a
Climate Change Research Division, Korea Institute of Energy Research, 152 Gajeong-ro, Yuseong-gu, Daejeon, 34129, Republic of Korea Center for Convergent Chemical Process, Korea Research Institute of Chemical Technology, 141 Gajeong-ro, Yuseong-gu, Daejeon, 34114, Republic of Korea Instituto Politécnico Nacional, Centro de Investigación en Ciencia Aplicada y Tecnología Avanzada, Unidad Legaria, Legaria 694, Col. Irrigación, Mexico City, 11500, Mexico
b c
ARTICLE INFO
ABSTRACT
Keywords: Asphaltene Thermal hydrocracking Catalytic hydrocracking Coke induction period Kinetics
In this study, a five-lump model was proposed for kinetic modeling of asphaltene placed in a batch reactor with a commercial slurry-phase catalyst (Mo-octoate). Asphaltene was separated from vacuum residue using normal pentane. The kinetic experiments were carried out at 380∼430℃ for 1∼20 h together with a 1000 ppm concentration of Molybdenum in thermal and catalytic hydrocracking reaction modes. The results showed that the coke induction period and maximum maltene yield are changed with reaction temperature and time at thermal and catalytic hydrocracking. In addition, a linear relationship between coke and liquid (maltene + asphaltene remains) yields was shown so that the critical gas amount could be found as a criterion for determining the end of the coke induction period. Significantly, the kinetic model fit the experimental data well and, moreover, was found to be able to predict the moment when coke begins to form as well as maximum maltene yields.
1. Introduction In order to meet the ever rising demands for light fuel oils, refiners have been increasingly looking for ways to maximize the upgrading of heavy crude [1–4]. In general, heavy crude contains a large amount of high molecular weight compounds such as asphaltene, which is the heaviest portion and contains a very complex mixture of constituents [5]. Asphaltene causes many problems in heavy oil upgrading, such as deactivation of catalysts and formation of sludge or sediment that clog filters, separators and pipe systems. Asphaltene is also known as one of the precursors of coke formation because it is prone to form coke during hydrocracking [6,7]. Therefore, finding ways to treat asphaltene is of prime importance for upgrading heavy oil technologies. Among the technologies currently used for highly converting asphaltene into high-value products with less coke formation, slurryphase hydrocracking is commonly considered to be one of the most efficient [1,5,8–11]. The dispersed catalyst plays an important role to prevent excessive cracking and coke formation, and minimize the risk of catalyst deactivation [10–12]. Nguyen et al. [13] conducted experiments at a temperature of 380 for 10 h in a catalytic hydrocracking reaction. In their research, coke yield was significantly reduced from 9.6% to 0.8% while a more liquid product yield was
produced. Coke formation is a complicated process that involves many reactions such as polymerization of free radicals, cyclization of alkyl chains, dehydrogenation and aromatization of naphthenic rings, elimination of side chains on aromatic rings, and condensation and pericondensation of aromatic rings [5,14,15]. Coke induction has been commonly observed by many previous studies in the thermal cracking process [16] as well as in the catalytic hydrocracking process [8,13,17]. The formation of coke is commonly associated with asphaltene and its stability in the oil system [5,18]. Consequently, it is essential to predict the exact moment when coke formation occurs as well as the amount of coke formed due to the type of feedstock, temperature and reaction time changes that occur during slurry-phase hydrocracking. A large number of studies have been made to develop the kinetic model of asphaltene undergoing different processes, including thermal cracking [16,19–21], thermal hydrocracking [9], and catalytic hydrocracking [8,9]. Martinez [19] presented a three-lump kinetic model including parallel cracking of asphaltene to oil plus gas and coke while Wang and Anthony [20] re-examined their data and offered a formula for estimating oil and gas yields as a function of asphaltene conversion. Yasar et al. [21] proposed a four-lump model, which included asphaltene, maltene, gas and coke, and Zhao et al. proposed a modified threelump model, which involved parallel reactions of asphaltene to liquid
⁎ Corresponding authors at: Climate Change Research Division, Korea Institute of Energy Research, 152 Gajeong-ro, Yuseong-gu, Daejeon, 34129, Republic of Korea. E-mail addresses: [email protected] (K.S. Go), [email protected] (N. Sun Nho).
https://doi.org/10.1016/j.cattod.2019.08.031 Received 9 April 2019; Received in revised form 21 August 2019; Accepted 27 August 2019 0920-5861/ © 2019 Elsevier B.V. All rights reserved.
Please cite this article as: Hai Hung Pham, et al., Catalysis Today, https://doi.org/10.1016/j.cattod.2019.08.031
Catalysis Today xxx (xxxx) xxx–xxx
H.H. Pham, et al.
Nomenclature
A A* Ai C Ea,i fobj G i ki M
yA y A* yM yG yC yGcrit yExp yCal R t T
C5-isolated asphaltene asphaltenecore pre-exponential parameter of the ith reaction, (h−1) coke activation energy of the ith reaction, (kJ/mol) objective function for optimization, (-) Gas reaction indicator. reaction rate constant of the ith reaction, (h−1) maltene
oil and gas plus coke, and a consecutive reaction of liquid oil to gas plus coke [9]. Recently, Sheng et al. [8] proposed a seven-lump kinetic model that induces detailed distribution in maltene during asphaltene conversion in a hydrogen donor process. Some studies have tried to find the coke induction period with respect to asphaltene conversion in thermal cracking reactions. For example, Wiehe [16] suggested a phase separation model which could represent the coke induction period. Rahmani et al. [17] modified the kinetic model proposed by Wiehe [16] to examine the kinetics of coke formation in different solvent environments in a closed reactor within a nitrogen atmosphere. However, those studies focused only on the thermal cracking reaction. Therefore, there is a need for a detailed study of asphaltene kinetics involving the coke induction period while undergoing a thermal and catalytic hydrocracking reaction. In this study, the reaction of C5-isolated asphaltene (Asphaltene) hydrocracking in the presence or absence of the slurry-phase Mo-catalyst precursor at 380, 410 and 430 °C was investigated. As a result of the experiment, a simple relation between coke and liquid yields was found that can be used to easily predict coke yield. The critical gas mas fraction was proposed as a criterion to determine the onset of the coke formation period. A new five-lump model, including the criterion and an intermediate product named the "asphaltene core" was proposed to represent the asphaltene conversion undergoing the thermal and catalytic hydrocracking reactions. A mechanism for inducing coke formation during the conversion of asphaltene was proposed. The kinetic model can help predict the onset point of coke formation and provide insights into the optimal utilization of asphaltene and the catalyst.
massfraction of asphaltene, (-) massfraction of asphaltene core, (-) massfraction of maltene, (-) massfraction of gas, (-) massfraction of coke, (-) mass fraction of critical gas when coke begins to form, (-) massfraction of experimental data, (-) massfraction of calculated data, (-) universal gas constant, (kJ/mol K) reaction time, (h) temperature of reaction, (K)
for 24 h. then dried at 110 The hydrothermal and catalytic hydrothermal cracking experiments were carried out in a 100 ml Parr batch reactor filled with 20 g of feedstock. Hydrogen was injected into the reactor until 80 bar of pressure were registered at 80 . The warm-up time needed to reach the base temperature of 80 was approximately 20 min. At that point the temperature was raised systematically from 80 to target temperatures of 380, 410 and 430 while being stirred at 1500 rpm. When it reaches to the desired temperature, the experiments were carried out for 1∼20 h. At the desired temperature points, the pressures were 124.2, 124.1 and 125.3 bar for 380, 410 and 430 for thermal cracking, respectively. For catalytic cracking, the pressures were 102.2, 103.6 and 105.3 bar for 380, 410 and 430 , respectively. All experiments were done separately. The average material balances of the experiments were more than 95% and normalized to 100% for the estimation of kinetic model parameters. In total there are 40 experiments with 160 observed data points. 2.2. Product separation and analysis After the reaction finished, the internal temperature of the reactor was rapidly cooled to room temperature, and the resulting products (gas, coke, asphaltene deposits and maltene) were separated according to the procedure shown in Fig. 1 [13]. The gas was collected in a sample bag and its composition was analyzed using a chromatograph (Model 7890B, Agilent Technologies Co. Ltd.). The liquid product was separated by a Soxhlet extractor into coke, asphaltene deposits, and DAO as toluene insoluble, n-pentane insoluble, and n-pentane soluble fractions, respectively. The Soxhlet extraction was carried out at 80 and 120 °C for n-pentane and toluene, respectively. The coke, asphaltene deposits, maltene and gas yields were calculated based on various references [13,22,23].
2. Experiment 2.1. Experiment procedure For this experiment, asphaltene separated from vacuum residue (VR) was used as feedstock. The separation was done by following the procedure specified previously [13]. First, VR and n-pentane (nC5) with mass ratio of 1:40 was stirred for 4 h. The mixture was then separated by filtering to obtain the solid state asphaltene, the liquid mixture of deasphaltene oil (DAO) and n-pentane solvent. After that, the solid state asphaltene was mixed again with n-pentane and washed continuously in Soxhlet extractor for 24 h to remove the remained DAO. Finally, the solid obtained was dried at 80 °C for 20 h to remove the remaining solvent. Table 1 shows the properties of the VR and asphaltene. Molybdenum octoate (Shepherd Chemical) was used as an oil-soluble dispersed catalyst precursor. For solvents, n-pentane and toluene rated at 99.5% purity were purchased from Samchun Chemical. In order to disperse liquid phase Mo-octoate into solid phase asphaltene to create a catalytic hydrocracking feedstock, a mixture of asphaltene and 1000 ppm of Mo-octoate (based on the weight of the feedstock) was pre-mixed for one hour by adding toluene and stirring at a speed of 80 rpm. When finished, the toluene was then removed from the mixture using a rotary evaporator for 1 h. The remaining solid was
Table 1 Properties of vacuum residue (VR) and C5-isolated asphaltene feedstock [13,23]. Properties
VR
Asphaltene
C (wt.%) H (wt.%) N (wt.%) S (wt.%) Ni (wt.ppm) V (wt.ppm) MCR * (wt.%) C5 asphaltene (wt.%) Vacuum gas oil (343-524 °C) (wt.%) Residue (524 °C-FBP) (wt.%)
83.4 10.1 0.5 5.89 72.3 309.1 23.3 25.0 21.5 78.5
82.4 7.6 1.0 7.3 241.0 1070.0 52.4 – 11.5 88.5
* MCR: Micro carbon residue. 2
Catalysis Today xxx (xxxx) xxx–xxx
H.H. Pham, et al.
Fig. 1. Products separation procedure for analysis [13,23].
3. Results and discussion
(Fig. 2-b). The maximum coke yields were found to be up to approximately 40 wt.%. This was possible because the MCR in the feedstock was 52.4 wt.%. The mass fractional distribution of maltene and asphaltene remaining with each reaction time are plotted in Fig. 3. A sharp decrease of asphaltene remaining with the increase of maltene was observed at the begining period of asphaltene conversion. This phenomena occurs mainly because asphaltene decomposes quickly into maltene with a small amount of gas at a fast rate. After that, the remaining asphaltene continued to decrease due to condensation into coke. However, the existing maltene reached a maximum mass fraction and then decreased, indicating that the maltene could participate in the gas formation reaction. In the thermal hydrocracking reaction, the maximum maltene fraction was 0.45, 0.35 and 0.33 at temperatures of 380, 410 and 430 , respectively, while in the catalytic hydrocracking reaction it was 0.56, 0.52 and 0.49 at temperatures of 380, 410 and 430 , respectively. In conclusion, catalytic hydrocracking is a suitable method
3.1. Conversion of asphaltene undergoing thermal and catalytic hydrocracking Fig. 2 shows the formation of coke as a function of reaction time at different temperatures for the thermal hydrocracking and catalytic hydrocracking reactions. When comparing the two cases at any point on the reaction timeline it can be seen that catalytic hydrocracking resulted in a lower coke yield while thermal cracking resulted in a much higher yield. Coke induction periods are observed for both thermal and hydrocracking processes except for thermal hydrocracking at 430 °C. It should be noted that the coke induction period shortens as the temperature increases. In the thermal hydrocracking reaction, the coke induction period decreased from 4 h to almost no time as the temperature rose from 380 to 430 °C (Fig. 2-a). In the same manner, it decreased from 6 h to 15 min in the catalytic hydrocracking process
Fig. 2. Coke distribution with reaction time variations at different temperature (380, 410, 430 [Component: (○) 380 ℃, (□) 410 ℃, (Δ) 430 ℃]. 3
) for (a) thermal hydrocracking and (b) catalytic hydrocracking.
Catalysis Today xxx (xxxx) xxx–xxx
H.H. Pham, et al.
Fig. 3. Asphaltene remains and maltene distribution with reaction time variations at different temperature (380, 410, 430 ℃) for (a) thermal hydrocracking and (b) catalytic hydrocracking. [Asphaltene remain: (●) 380 ℃, (◼) 410 ℃, (▲) 430 ℃, Maltene: ( ) 380 ℃, ( ) 410 ℃, ( 430 ℃, Gas: (○) 380 ℃, (□) 410 ℃, (Δ) 430 ℃].
which can help increase maltene yield and suppress coke formation with a longer coke induction time.
alkyl-chain and a more aromatic core due to dealkylation [16,17]. It should be noted that the asphaltene and asphaltene core are lumped as asphaltene deposits. The equation for determining the rate of decomposition in this induction period can be written as follows:
3.2. Kinetic modeling
Asphaltene:
A common approach known as the "lump strategy" was adopted for describing asphaltene conversion [5,24,25]. The proposed kinetic model is shown in Fig. 4. This mechanism is based on the high molecular reactants cracked down to the low molecular products. The following assumptions were made for the model: (1) the change of hydrogen transfer was negligible, (2) there were no mass transport phenomena affecting the catalyst, (3) the volume of the reaction system was not changed, and (4) The catalyst deactivation was not considered in this kinetic modeling.
Maltene: Gas:
dyA = dt
(k1 + k2 + k3 ) yA
dyM = k3 yA dt
k4 yM
dyG = k2 yA + k4 yM dt
Asphaltene core:
dy A* dt
(1) (2) (3)
= k1 yA
(4)
The coke induction period ends when yG < yGCrit . The reaction rates are given by the following equations:
3.2.1. Model description The model consists of five lumped pseudo-components including asphaltene (A), asphaltene core (A*), maltene (M), coke (C), and gas (G). The overall conversion of asphaltene decomposition has been found to follow first-order reaction [8,16] or second-order reaction [9,19]. In this study, the reaction order of asphaltene decomposition was found to be first-order since it best fit the data (Table 2). As discussed in section 3.1, determining the coke induction period is important for finding the reaction characteristics of coke formation with heavy feedstocks. In this respect, there were some efforts to predict the coke induction period with thermodynamic properties. A solubility limit, SL , can be used as a criterion for determining when phase separation occurred [16,17]. However, the criterion is based on the common features of asphaltene conversion undergoing a thermal cracking process. Asphaltene precipitation or aggregation could also be related to the amount of hydrocarbon gases in the system under high pressure [26–28]. This phenomena could be attributed to the interaction between asphaltene molecules and the gases [28]. Therefore, it could be possible that the formation of gas in the batch reactor could deteriorate the hydrogenation, which then resulted in asphaltene precipitation. Interestingly, it was found that coke yield had a linear relationship with liquid yield (the summation of both remaining asphaltene and maltene as shown in Fig. 5). This relationship is not dependent on temperature under the given conditions, so it can be used to predict coke yield based on this linear relationship without measuring it. As suggested by the effect of the amount of gas on asphaltene precipitation [26–28], coke formation could be triggered by the extent of gas formation. As a result, the conversion of asphaltene core into coke progressed via condensation [17]. Here the critical gas amount, yGCrit , is proposed as a criterion for determining the onset of coke formation. As can be seen, yGCrit for thermal hydrocracking is 0.053 and for the catalytic hydrocracking process it is 0.079. When the gas mass fraction is greater than the critical gas mass fraction, yGCrit , coke begins to form. During the coke induction period, asphaltene can only be decomposed to lower molecular weight products, such as maltene, asphaltene core and gases. The asphaltene core is known to be asphaltene with a shorter
Asphaltene:
Maltene: Gas:
dyA = dt
(k1 + k2 + k3 ) yA
dyM = k3 yA dt
k4 yM
dyG = k2 yA + k4 yM dt
Fig. 4. Asphaltene kinetic model. 4
(5) (6) (7)
Catalysis Today xxx (xxxx) xxx–xxx
H.H. Pham, et al.
be seen that for thermal hydrocracking the asphaltene converted completely into asphaltene core in 30 min whereas for catalytic hydrocracking the time required was 3 h. As mentioned earlier, the dependence of the critical gas yield on the type of hydrocracking reaction indicates that a catalyst can enhance hydrogenation reaction and prevent gas formation in the system. The rate constants for each lump in both reactions are shown in Table 3. As can be seen, the rate constant for the overall conversion of asphaltene was much lower for catalytic hydrocracking than for it was 7.25 h−1 for catalytic hydrothermal hydrocracking. At 430 −1 cracking and 84.77 h for thermal hydrocracking. The asphaltene reaction to produce maltene and asphaltene core is the main reaction with the largest rate constant. The rate constant of the reaction for asphaltene core formation (k1) is higher than that of the reaction for maltene formation (k3) at all temperatures. The ratio between k1/ k3 (380 : 0.75, 410 : 0.86 and 430 : 1.02) in catalytic hydrocracking was lower than that of thermal hydrocracking (380 : 1.03, 410 : 1.64 and 430 : 1.98) indicating high selectivity towards maltene from asphaltene with the presence of a catalyst. For gas formation, the rate constant of gas formation from maltene is weaker than the one from asphaltene. For coke formation, the conversion of asphaltene core to coke was much lower for catalytic hydrocracking. At 430 , the rate constant of coke formation from asphaltene core was 1.2893 and 0.2775 h−1 for thermal hydrocracking and catalytic hydrocracking, respectively, suggesting that the presence of a catalyst suppressed the formation of coke from the aggregation of the asphaltene core. According to the Arrhenius equation, the activation energies were calculated as shown in Table 3, where it can be seen that the activation energies of all the reactions in catalytic hydrocracking were lower than those of thermal hydrocracking. In catalytic hydrocracking, the activation energies needed to form asphaltene core, maltene and gas were 188, 162, and 165 kJ/mol, while in thermal hydrocracking they were 400, 352 and 350 kJ/mol. This indicates that thermal hydrocracking is more temperature-sensitive. In addition, this also suggests asphaltene is prone to form an asphaltene core at high temperature. The activation energy of coke formation reaction was 306 kJ/mol in thermal hydrocracking and 163 kJ/mol in catalytic hydrocracking. However, unlike the activation energy of gas formation from asphaltene, the one from maltene during thermal hydrocracking (370 kJ/mol) was similar to that of catalytic hydrocracking (355 kJ/mol). Considering the rate constants for gas formation from maltene together, it suggests that this reaction is not influenced much by the catalytic reaction. Based on the reaction kinetics information, the proposed reaction condition can be selected to enhance the liquid product and avoid the coke formation.
Table 2 Sum of square errors versus reaction. Overall asphaltene reaction order
SSE
1 4/3 5/3 2
0.048 0.05 0.054 0.06
SSE: sum of square errors.
Asphaltene core: Coke:
dy A* dt
dyC = k5 y A* dt
= k1 yA
k5 y A*
(8) (9)
3.2.2. Estimation of kinetic parameters For this kinetic model no fewer than seven constants were estimated at each temperature. The kinetic parameters were calculated according to the following procedure [5,29,30]. (i) The initial values of the reaction rate constants were determined by a Monte Carlo algorithm [30]. (ii) The objective function was established as shown in Eq. 10.
Fobj =
(ycal
yexp )2
(10)
(iii) The set of differential equations were solved using the RungeKutta method, and the values of reaction rate coefficient were re-examined using an optimization algorithm based on the LevenbergMarquardt method. (iv) After that, a sensitivity analysis was conducted to evaluate the obtained parameters. If optimal parameters do not give a global minimum, step (iii) is carried out again until the global minimum is satisfied. (v) Once the reaction rate coefficients were found to give a global minimum, the frequency factors and apparent activation energies were calculated by using the Arrhenius equation.
ki = Ai e
Eai RT
(11)
3.2.3. Comparison of predicted vs. experimental values Fig. 6 shows the parity chart of the predicted yields of products and experimental data from the kinetic model. The comparison shows that the kinetic model anticipated quite well the experimental data for both thermal and catalytic reactions in the operating range. The predicted yields and experimental data of each lump at varying reaction times at 380, 410, and 430 for the thermal and catalytic processes are presented in Fig. 7. Again, the model agreed well with the experimental data. Moreover, the coke induction periods can also be predicted. It can
4. Conclusions The reaction characteristics of asphaltene (separated from VR) undergoing thermal and catalytic hydrocracking were investigated. Two
Fig. 5. Relation of coke yield with a summation of asphaltene remains and maltene yield for (a) thermal hydrocracking and (b) catalytic hydrocracking. The equation is the results of linear regression for all data and R2 is the square of the relation coefficient. [Temperature, °C: (○) 380, ( ) 410, ( ) 430]. 5
Catalysis Today xxx (xxxx) xxx–xxx
H.H. Pham, et al.
Fig. 6. Parity plots for predicted and experimental value for (a) thermal hydrocracking and (b) catalytic hydrocracking. [Component: (○) Asphaltenes, (◼) Maltene, (△) Gas, ( ) Coke].
Fig. 7. Comparison of predictions of products yields with experimental data reaction time variations at different (380, 410, 430 °C) for (a) thermal hydrocracking and (b) catalytic hydrocracking. Curves were calculated from the kinetic model. Symbols represent experimental data. [Component: (○) Remained asphaltene, (◼) Maltene, (△) Gas, ( ) Coke. Curves: (–) Asphaltenes remain, (—) Maltene, ( ) Asphaltenes core, (-.-) Gas, ( ) Coke]. Table 3 Kinetic parameters of the kinetic model. Thermal hydrocracking Parameters
Reaction path
Rate constant value (h−1)
k1 k2 k3 (k1 + k2 + k3) k4 k5
Asp → Asp* Asp → Gas Asp → Mal Overall Asp Mal → Gas Asp* → Coke
380 0.2589 0.0382 0.2503 0.5474 0.0036 0.0290
410 4.0918 0.1230 2.5015 6.7163 0.2481 1.2283
Catalytic hydrocracking
430 51.9050 5.1316 26.7320 84.7686 0.3709 1.2893
Activation energy
R2
Rate constant value (h−1)
EA (kJ/mol) 400 352 350 – 370 306
0.99 0.83 0.98 – 0.90 0.86
380 0.2949 0.0554 0.3939 0.7442 0.0012 0.0293
common features of asphaltene conversion during both reactions, especially the coke induction period and maximum maltene fraction, were observed and noted. In addition, a simple relation between coke and liquid yield (asphaltene deposits and maltene) was found. Based on this relationship, a critical gas amount was proposed as a criterion for
410 1.5323 0.1135 1.7779 3.4237 0.0635 0.0540
430 3.4006 0.5152 3.3342 7.2500 0.1053 0.2775
Activation energy
R2
EA (kJ/mol) 188 162 165 – 355 163
1.00 0.89 0.99 – 0.92 0.85
determining the point at which the coke induction period ends. A fivelumped kinetic model, including the critical gas amount, was developed to understand the conversion of asphaltene undergoing either thermal or catalytic hydrocracking. The kinetic model can be used to predict both the reaction behavior 6
Catalysis Today xxx (xxxx) xxx–xxx
H.H. Pham, et al.
and onset of coke formation. It was also found that the main reaction for forming coke are the aggregation of the asphaltene core. In addition, it was observed that maltene yield increased more than that of the asphaltene core for the catalytic reaction. The information from the kinetic model is important for providing some solutions for optimizing utilization of asphaltene in hydrocracking processes as well as the catalyst. Although the kinetic model is in a good agreement with experimental results, the criterion of critical gas yield was a hypothesis from the observation in this study. It is suggested that these results should be confirmed by further experiments in the future.
[11] [12] [13] [14] [15] [16]
Acknowledgments
[17]
This work was supported by the National Research Council of Science and Technology (NST) grant by the Korea government (MSIT) (No. CRC-14-1-KRICT).
[18] [19] [20]
References
[21]
[1] K.S. Go, S.H. Lim, Y.K. Kim, E.H. Kwon, N.S. Nho, Characteristics of slurry-phase hydrocracking for vacuum residue with reaction temperature and concentrations of MoS2 dispersed catalysts, Catal. Today 305 (2018) 92–101. [2] S.H. Lim, K.S. Go, N.S. Nho, J.G. Lee, Effect of reaction temperature and time on the products and asphaltene dispersion stability in slurry-phase hydrocracking of vacuum residue, Fuel 234 (2018) 305–311. [3] K. Aleklett, M. Höök, K. Jakobsson, M. Lardelli, S. Snowden, B. Söderbergh, The peak of the oil age - analyzing the world oil production reference scenario in world energy outlook 2008, Energy Policy 38 (2010) 1398–1414. [4] M.S. Rana, V. Sámano, J. Ancheyta, J.A.I. Diaz, A review of recent advances on process technologies for upgrading of heavy oils and residua, Fuel 86 (2007) 1216–1231. [5] J. Ancheyta, F. Trejo, M.S. Rana, Asphaltenes Chemical Transformation During Hydroprocessing of Heavy Oils, CPC Press, 2009. [6] F. Trejo, M.S. Rana, J. Ancheyta, Thermogravimetric determination of coke from asphaltenes, resins and sediments and coking kinetics of heavy crude asphaltenes, Catal. Today 150 (2010) 272–278. [7] J. Ancheyta, G. Centeno, F. Trejo, J.G. Speight, Asphaltene characterization as function of time on-stream during hydroprocessing of Maya crude, Catal. Today 109 (2005) 162–166. [8] Q. Sheng, G. Wang, Q. Zhang, C. Gao, A. Ren, M. Duan, J. Gao, Seven-lump kinetic model for non-catalytic hydrogenation of asphaltene, Energy Fuels 31 (2017) 5037–5045. [9] Y. Zhao, Y. Yu, Kinetics of asphaltene thermal cracking and catalytic hydrocracking, Fuel Process. Technol. 92 (2011) 977–982. [10] M.J. Angeles, C. Leyva, J. Ancheyta, S. Ramírez, A review of experimental
[22] [23] [24] [25] [26] [27] [28] [29] [30]
7
procedures for heavy oil hydrocracking with dispersed catalyst, Catal. Today 220–222 (2014) 274–294. S.M. Elahi, C.E. Scott, Z. Chen, P. Pereira-Almao, In-situ upgrading and enhanced recovery of heavy oil from carbonate reservoirs using nano-catalysts: upgrading reactions analysis, Fuel 252 (2019) 262–271. M.T. Nguyen, N.T. Nguyen, J. Cho, C. Park, S. Park, J. Jung, C.W. Lee, A review on the oil-soluble dispersed catalyst for slurry-phase hydrocracking of heavy oil, J. Ind. Eng. Chem. 43 (2016) 1–12. N.T. Nguyen, K.H. Kang, C.W. Lee, G.T. Kim, S. Park, Y.K. Park, Structure comparison of asphaltene aggregates from hydrothermal and catalytic hydrothermal cracking of C5-isolated asphaltene, Fuel 235 (2019) 677–686. Y. Zhao, M.R. Gray, K.H. Chung, Molar kinetics and selectivity in cracking of Athabasca asphaltenes, Energy Fuels 15 (2001) 751–755. T.F. Yen, G.V. Chilingarian, Asphaltenes and Asphaltes, 2, Elsevier Science, 2000. I.A. Wiehe, A phase-separation kinetic model for coke formation, Ind. Eng. Chem. Res. 32 (1993) 2447–2454. S. Rahmani, W. McCaffrey, M.R. Gray, Kinetics of solvent interactions with asphaltenes during coke formation, Energy Fuels 16 (2002) 148–154. L.L. Zhang, G.H. Yang, G.H. Que, The conglomerating characteristics of asphaltenes from residue during thermal reaction, Fuel 84 (2005) 1023–1026. M.T. Martínez, A.M. Benito, M.A. Callejas, Thermal cracking of coal residues: kinetics of asphaltene decomposition, Fuel 76 (1997) 871–877. J. Wang, E.J. Anthony, A study of thermal-cracking behavior of asphaltenes, Chem. Eng. Sci. 58 (2003) 157–162. M. Yasar, D.M. Trauth, M.T. Klein, Asphaltene and resid pyrolysis. 2. The effect of reaction environment on pathways and selectivities, Energy Fuels 15 (2001) 504–509. N.T. Nguyen, S. Park, J. Jung, J. Cho, C.W. Lee, Y.K. Park, Comparative reactivity between thermal and catalytic hydrocracking of vacuum residue: effect of asphaltenes, J. Ind. Eng. Chem. 61 (2018) 32–38. H. Ortiz-Moreno, J. Ramírez, R. Cuevas, G. Marroquín, J. Ancheyta, Heavy oil upgrading at moderate pressure using dispersed catalysts: effects of temperature, pressure and catalytic precursor, Fuel 100 (2012) 186–192. G. Félix, J. Ancheyta, Comparison of hydrocracking kinetic models based on SARA fractions obtained in slurry-phase reactor, Fuel 241 (2019) 495–505. J. Ancheyta, S. Sánchez, M.A. Rodríguez, Kinetic modeling of hydrocracking of heavy oil fractions: a review, Catal. Today 109 (2005) 76–92. B. Journal, S. Moradi, M. Dabiri, B. Dabir, D. Rashtchian, M.A. Emadi, Investigation of asphaltene precipitation in miscible gas injection processes: experimental study and modeling, Braz. J. Chem. Eng. 29 (2012) 665–676. Y. Kazemzadeh, R. Parsaei, M. Riazi, Experimental study of asphaltene precipitation prediction during gas injection to oil reservoirs by interfacial tension measurement, Colloids Surf. A Physicochem. Eng. Asp. 466 (2015) 138–146. P. Zanganeh, H. Dashti, S. Ayatollahi, Comparing the effects of CH4, CO2, and N2injection on asphaltene precipitation and deposition at reservoir condition: a visual and modeling study, Fuel 217 (2018) 633–641. G. Félix, J. Ancheyta, F. Trejo, Sensitivity analysis of kinetic parameters for heavy oil hydrocracking, Fuel 241 (2019) 836–844. H. Hassanzadeh, J. Abedi, Modelling and parameter estimation of ultra-dispersed in situ catalytic upgrading experiments in a batch reactor, Fuel 89 (2010) 2822–2828.