Energy Fuels 2011, 25, 269–272 Published on Web 12/16/2010
: DOI:10.1021/ef1012598
Characterization of the Reaction Performance for Residue Hydrotreating Feedstocks Yu-dong Sun,*,†,‡ Chao-he Yang,‡ Hong-hong Shan,‡ and Ben-xian Shen† †
East China University of Science and Technology, Shanghai 200237, People’s Republic of China, and ‡State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Qingdao, Shandong 266555, People’s Republic of China Received September 17, 2010. Revised Manuscript Received November 28, 2010
The properties and compositions of feedstocks have great impact on reaction performances in residue hydrotreating. It has been found that the widely accepted parameter (e.g., Watson K) for characterizing crude oil and distillate was inaccurate in describing residue hydrotreating properties. In this work, a new characterization index, the key parameter for residue hydrotreating (KRH), was put forward through analysis of a large amount of experimental data on residue feedstocks with different sources and properties. KRH can be expressed in terms of H/C, density, aromatic-carbon molar ratio, and average molecular weight of the feedstock. It correlates well with the sulfur removal rate, nitrogen removal rate, residue conversion, and coke yield for residue hydrotreating and, thus, can be used as a satisfactory index to predict the reaction performance and guide residue hydrotreating operation.
useful in determining appropriate process conditions for industrial residue hydrotreating.
1. Introduction With extensive exploitation of petroleum, worldwide crude oil is becoming heavier and declining in quality. For some heavy crude, about 50 wt % was still left as vacuum residue after atmospheric and vacuum distillation. Because of the requirement for light fuels, much research has been performed upon converting the residue to clean light fuels efficiently and economically. Nowadays, there are many residue upgrading processes. Among them, the residue hydrotreating process attracts more attention because of its high liquid product yields, good product quality, high production flexibility, and good environmental protection.1 The influencing factors on the residue hydrotreating reaction are temperature, pressure, liquid hourly space velocity (LHSV), hydrogen/oil ratio (H/O), catalyst, feedstock properties, etc. A lot of work on the first five influencing factors has been performed, and similar results have been obtained.3,4 For example, the reaction rate increases with temperature, and conversion increases with pressure, LHSV-1, and H/O. However, no recognized index has hitherto been developed for the characterization of the hydrotreating reaction performance for residue feedstocks, probably because of the complicated chemical structures and compositions of these feedstocks. Residue feedstocks are usually composed of thousands of hydrocarbons and non-hydrocarbons, and the exact composition is always difficult to obtain under the current technical level.2 The main purpose of the present work is to propose a characteristic index that can be expressed in terms of easily obtained physical properties. The index could be used as the evaluation basis and can assess the reaction performance for residue hydrotreating feedstocks. Therefore, this index is
2. Proposing the Key Parameter of Residue Hydrotreating The characteristic factor K (Watson K or UOP K)2 is an important and widely accepted parameter to characterize chemical compositions of light oil. Watson K is also a criterion for classifying crude oil. It is an important parameter in oil processing, crude oil evaluation, and physical property correlation. Watson K is obtained through summarizing physical properties of hydrocarbon and then extending to light oil. It could be calculated by the mean average boiling point and specific gravity or through consulting graphs using other physical properties of oil. Because of the large average molecular weight and complicated composition, the mean average boiling points of residues are always hard to obtain and the calculation of Watson K for residues is difficult and inaccurate. Shi et al.5 observed that Watson K increased with an increasing boiling range of the supercritical fluid extraction fractionation (SFEF) fraction. It means that the properties of residue SFEF fractions should be better if the density is quite large, which is in contrast to the actual situation. Consequently, Watson K is mainly used to characterize composition of light oil and not residue. Another characterization index, KH,5 which is proposed by the State Key Laboratory of Heavy Oil Processing of China University of Petroleum, can be used to evaluate the secondary processing performance of residue satisfactorily. However, when KH is used to evaluate hydrotreating of residue feedstocks, the deviation is relatively large.6 The characteristic factor of residue hydrotreating, H, proposed by Chang,7,8 has good relevance with various rate constants in residue hydrotreating. Although the expression of H seems simple, eight physical properties of residue are needed to obtain H. The more physical properties needed in calculation, the heavier the analyzing workload and the larger the error introduced by the experiment. Therefore, there is a
*To whom correspondence should be addressed. Telephone: þ86532-86984702. Fax: þ86-532-86981787. E-mail:
[email protected]. (1) Zhang, D. Y. Processing Technology of Sour Crude; Petrochemical Press of China: Beijing, China, 2003; p 408. (2) Lin, S. X. Petroleum Refining Engineering, 3rd ed.; Petroleum Industry Press: Beijing, China, 2000; p 74. (3) Marafi, A.; Fukase, S.; Al-Marri, M.; Stanislaus, A. Energy Fuels 2003, 17, 661–668. (4) Shyamal, K. B.; Ajay, K. D.; John, A. Energy Fuels 2001, 15, 1103– 1109. r 2010 American Chemical Society
(5) Shi, T. P.; Hu, Y. X.; Xu, Zh. M.; Su, T.; Wang, R. A. Acta Pet. Sin. 1997, 13 (2), 1–7. (6) Yang, C. H. Characteristics and Kinetics of Heavy Oil Hydroconversion; University of Petroleum: Beijing, China, 1997. (7) Chang, J. Kinetics and Deactivation Model of Residue Hydrotreating; Research Institute of Petroleum Processing of China: Beijing, China, 1997. (8) Li, D. D. Processes and Engineering of Residue Hydrogenation; China Petrochemical Press: Beijing, China: 2004; p 141.
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Energy Fuels 2011, 25, 269–272
: DOI:10.1021/ef1012598
Sun et al.
simple, to reduce the experimental workload and decrease errors introduced through basic data. (2) KRH should reflect the hydrotreating performance of different residues and should be similar for different residues having similar reaction performance in hydrotreating. KRH should increase with the increase of hydrotreating activity and be consistent with the traditional understanding in oil processing. (3) KRH should have sound relevance with key evaluation indexes, e.g., conversion, impurity removal rate, coke yield, etc., in residue hydrotreating. In addition, those indexes should change monotonically with KRH. Residue is the most complex mixture comprising thousands of complicated organic compounds. High boiling point, large molecular weight, low H/C, and high content of asphaltene, heteroatom, and solid impurities are primary characteristics of residue. Many physical properties can be used to evaluate the chemical composition of residue. It has been found that the easily obtained H/C, relative density, aromatic-carbon molar ratio, and average molecular weight of residue have a significant effect on the hydrotreating reaction; therefore, they are chosen as the correlation parameters for KRH in this work. According to the traditional opinion, the property and secondary processing performance of residue was better when it has a higher H/C and lower density and molecular weight. Therefore, KRH should increase with an increasing H/C and decreasing density and molecular weight. Three typical residues and their SFEF fractions were selected for hydrotreating experiments in an autoclave in the presence of hydrogen. When different forms of KRH are compared and regressed with experimental data, final KRH was obtained as follows:
need to introduce a new parameter that can easily correlate the conversion characteristics with physical properties of residue oil. This parameter will be derived from the massive experimental data in the laboratory. The residue oil can be divided into different categories for the hydrotreating reaction by the value of this new parameter. The key parameter of residue hydrotreating (KRH) should satisfy the following conditions: (1) The basic data used in the correlation of KRH can be obtained easily, and the calculation of KRH should be Table 1. Primary Physical Properties of the Feedstocks feedstock
DGAR
AMVR
ALVR
SFEF 1 SFEF 2 SFEF 3 SFEF 4 SFEF 5 SFEF 6 SFEF 7 SFEF 8 endcut AR SFEF 1 SFEF 2 SFEF 3 SFEF 4 SFEF 5 SFEF 6 SFEF 7 endcut SFEF 2 SFEF 4 SFEF 6 SFEF 8 VR
d20 4
M
H/C
fa
KRH
0.8721 0.8793 0.8855 0.8905 0.8960 0.9027 0.9103 0.9267 1.0616 0.9143 0.9369 0.9484 0.9610 0.9740 0.9937 1.0056 1.0320 1.1405 0.9559 0.9714 0.9947 1.0606 1.0173
353 379 407 420 443 467 505 582 1473 461 498 611 657 711 802 826 1079 3394 610 653 744 1128 816
1.81 1.80 1.78 1.77 1.75 1.73 1.71 1.66 1.39 1.78 1.69 1.66 1.64 1.63 1.56 1.51 1.47 1.19 1.62 1.63 1.55 1.38 1.43
0.081 0.082 0.101 0.107 0.115 0.130 0.142 0.179 0.367 0.097 0.156 0.179 0.190 0.195 0.248 0.284 0.313 0.525 0.202 0.199 0.254 0.379 0.289
34.61 29.66 20.72 17.89 14.49 11.11 8.55 4.70 0.21 15.69 6.19 3.87 2.98 2.42 1.25 0.86 0.47 0.03 2.93 2.60 1.25 0.24 0.63
KRH ¼
e2:9012H=C d 6:5757 CA 0:9326 M 0:8439
where H/C is the atomic ratio of hydrogen to carbon of residue, d is the relative density of feedstocks at 20 °C, CA is the aromatic-carbon
Figure 1. Relationship between KRH and reaction performance: (a) effect of KRH on the sulfur removal rate, (b) effect of KRH on the nitrogen removal rate, (c) effect of KRH on the
