2324
Ind. Eng. Chem. Res. 1990,29, 2324-2327
KINETICS AND CATALYSIS Suppression of Sludge Formation by Two-Stage Hydrocracking of Vacuum Residue at High Conversion Isao Mochida,* Xing-zhe Zhao, and Kinya Sakanishi Institute of Advanced Material Study, Kyushu University, Kasuga, Fukuoka 816, Japan
Hydrocracked products from Arabian light vacuum residue at high conversion into distillate (>50%) were analyzed in order to reveal how sludge formation was suppressed in the two-stage reaction. Althugh the asphaltene in the starting residue was highly soluble in the starting maltene in spite of its largest molecular weight, single-stage hydrocracking a t a higher temperature of 420 "C increased the aromaticity of the asphaltene through extensive dealkylation and dehydrogenation, leading to sludge formation. In contrast, two-stage hydrocracking a t 390" C-3 h/420 "C-1 h accomplished effective depolymerization of the asphaltene, high conversion being achieved without sludge. The carbon aromaticity (fa) of the produced asphaltene was maintained rather low, although its amount in the product was much the same regardless of the reaction conditions. The heptane-soluble maltenes in the hydrocracked oils exhibited variable dissolving abilities against the asphaltene according to the content and aromaticity of its aromatic fraction, also influencing sludge formation. Hydrocracking produced paraffins through the hydrogenative dealkylation of long-chain alkylbenzenes, decreasing fa and the dissolving ability of the hydrocracked maltene. Introduction Refineries (processing residues) want to attain high conversions of vacuum residue into distillate (bp 550 "C) of Arabian light crude was hydrocracked by single- and two-stage reactions under hydrogen pressure (15 MPa), using two commercial Ni-Mo catalysts (KF-842 and KFR-10; both from Japan Ketjen
Co.) in a batch autoclave of 100-mL capacity. The catalysts were presulfided under 5 % H,S/H, flow at 360 "C for 6 h. After the residue (20 g) and the catalyst (2 g) were charged into an autoclave without any solvent, the autoclave was purged with nitrogen gas and then pressurized with hydrogen gas until it reached 15 MPa at the reaction temperature. The standard conditions were 390 "C-3 h or 420 "C-4 h for the single-stage reaction and 390 "C-3 h (first stage) and 420 "C-1 or 3 h (second stage) for the two-stage reaction, respectively. The heating rate of the autoclave was ca. 7 "C/min. The reaction time was counted when the reactor was heated to the prescribed temperature. After filtration of the catalyst, the product was observed at room temperature under an optical microscope to judge semiquantitatively the amount of sludge in the product oil, because the amount is so small (less than 0.5 wt % ) in the laboratory-size reaction. The product was distilled under vacuum (5 mmHg) at 355 "C to obtain the distillate (565- "C fraction) yield. The vacuum residue (ALVR) and whole products were fractionated by extraction with n-heptane into heptanesoluble (maltene: Ma) and -insoluble (asphaltene: As) fractions. Maltene was further fractionated by column chromatography using active alumina into hexane-eluted (saturate: Sa), benzene-eluted (aromatics: Ar), and chloroform-eluted (resin: Re) fractions as illustrated in Figure 1. All these fractions were analyzed with 'H and I3C NMR spectroscopies and GPC. Results Fractional Change after Hydrotreatment. Table I summarizes the distillate yields and the fractional compositions of ALVR before and after hydrotreatment. Hydrotreatment decreased asphaltene, aromatics, and resin, the extents of reduction depending very much upon
0 1990 American Chemical Society 08~~-5885/90/2629-2324~02.50/0
Ind. Eng. Chem. Res., Vol. 29, No. 12, 1990 2325 Table 111. 'H NMR Analyses of Resin before a n d after Hydrotreatment H composition, %
Heptane soluble
sample" ALVR-OR KF-842 [390-3/420-1] KFR-10 [420-41 KFR-10 [390-31 KFR-10 [390-3/420-1] KFR-10 [390-3/420-31
Heptane insoluble (Aspha1tene:As)
[Column chrbmatography 1
Ha 9 9 11
10 9 9
H a
H,
H,
fa
11
53 54 54 51 56 57
27 21 22 24 22 19
0.44 0.41 0.43 0.47 0.42 0.42
15 13 15 14 15
" See Table I. Table IV. 'H NMR Analyses of Aromatics before a n d after Hvdrotreatment H composition, %
Figure 1. Fractionation flow sheet of ALVR.
sample" A'LVR-OR KF-842 [390-3/420-1] KFR-10 [420-41 KFR-10 [390-31 KFR-10 [390-3/420-1] KFR-10 [390-3/420-3]
Table I. Fractional Compositions of ALVR before and after Hydrotreatment samplea ALVR-OR KF-842 [390-3/420-I] KFR-10 [420-41 KFR-10 [390-31 KFR-10 [390-3/420-11 KFR-10 [ 390-3/420-31
composition,b wt % Sa Ar Re 11 48 34 6 6 80 13 1
As
DY,' wt %
ASd
82
much much trace
8 6 7
71 60 68
18 30 21
2 3 4
83 49 79
vt
5
74
18
2
82
trace
Ha 14 18 26 15 19 19
H a
H,
H,
fa
17 24 27 22 20 24
47 42 31 46 42 42
22 16 16 17 20 14
0.50 0.54 0.62 0.51 0.56 0.56
" See Table I. Molecular weight
4
a ALVR-OR: Arabian light vacuum residue. KF-842 (
