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Ind. Eng. C h e m . Res. 1990, 29, 334-337
Catalytic Two-Stage Hydrocracking of Arabian Vacuum Residue at a High Conversion Level without Sludge Formation Isao Mochida,* Xing-Zhe Zhao, and Kinya Sakanishi Institute of Advanced Material Study, Kyushu University, Kasuga, Fukuoka 816, Japan
Catalytic two-stage hydrocracking of Arabian vacuum residue was studied using commercial Ni-Mo catalysts in a batch autoclave to achieve a higher conversion above 50% to 540 "C- distillate without producing "dry sludge", which is defined as insoluble substances in the product oil matrix. The hydrogenation a t 390 "C of the first stage was found to be very effective in suppressing sludge formation in the second stage at higher temperatures, 430-450 "C, where the cracking to produce the distillate dominantly proceeded. The larger pore size catalyst (KFR-10) was suitable for these purposes, while the smaller pore size catalyst (KF-842) failed to suppress the sludge formation. The shorter contact time of the second stage at a relatively higher temperature appears favorable to increase the conversion without producing the sludge. The mechanism of sludge formation and the storage stability of the hydrocracked product are preliminarily examined. Demand for clean distillate from the bottom of the barrel leads to severe hydrocracking of petroleum residues at higher temperatures (Saito and Shimizu, 1985). These severe conditions cause problems of coke deposition on the catalyst and sludge formation in the product oil (Symoniak and Frost, 1971). Such troublemakers of both carbonaceous materials, of which formation may be intimately related, shorten the life of the catalyst, plug the transfer line, and deteriorate the quality of the products (Mckenna et al., 1964). The dry sludge is believed to be produced when the conversion to the distillate is beyond a certain level (ca. 50%) regardless of the catalyst and feedstocks (Saito and Shimizu, 1985). Its structure, properties, and formation mechanisms are not fully understood yet (Haensel and Addison, 1967). In a previous paper, the solubility, fusibility, and reactivity of the dry sludge produced in a hydrocracked oil were studied to propose a mechanism of sludge formation in the hydrocracking process (Mochida et al., 1989). The dry sludge is soluble in aromatic solvents such as 1methylnaphthalene and miscible with the matrix of the hydrocracked product at elevated temperatures, and hence, hydrogenation can convert it miscible at room temperature, suggesting procedures of hydrocracking without its formation. In the present study, catalytic two-stage hydrocracking was proposed to achieve a higher conversion into a 540 "Cdistillate above 50% with a minimum amount of dry sludge in the product. The idea is based on the mechanism previously proposed: the deep hydrogenation of the aromatic fraction in the residue by the first stage at lower temperature may accelerate the cracking and solubility of the heaviest aromatic portion in the second stage at higher temperature, where major hydrocracking takes place, leaving no highly condensed aromatic component of the dry sludge in the hydrocracked product. The storage stability of the hydrocracked product was briefly studied. The sufficient hydrogenation of the product is expected to improve the stability.
Experimental Section A vacuum residue (bp > 550 "C) of Arabian light oil (10 g), the properties of which are shown in Table I, was hydrocracked by single- and two-stage reactions under hydrogen pressure (- 15 MPa at the reaction temperature), using one of the Ni-Mo catalysts (1 g) in a batch autoclave of 100-mL capacity. The catalysts, the properties of which are summarized in Table 11, were presulfided under 5 % H,S/H2 flow at 360 "C for 6 h before the reaction.
Table I. Solubility" of Arabian Light Vacuum Residue (ALVR) Wt
ALVR
HS 91
90
HI-BS 9
BI 0
HS, hexane soluble: HI-BS, hexane soluble-benzene insoluble; BI, bezene insoluble.
Table 11. Some Properties of the Catalysts* wt lo catalyst KF-842 KFR-10 a
support alumina alumina
NiO 3.1 1.0
MOO, 15 5.0
surface area, m2/g 273 147
pore vol, mL/g 0.52 0.71
mean pore diameter, 8,
