1360
Energy & Fuels 2003, 17, 1360-1366
Relating Feedstock Composition to Product Slate and Composition in Catalytic Cracking. 6. Feedstocks Derived from Merey, a Venezuelan Crude C. M. Sheppard,* S. S. Al-Alloush,† J. B. Green,‡ E. J. Zagula, L. L. Young,‡ and K. D. Wisecarver University of Tulsa, 600 South College, Tulsa, Oklahoma 74104-3189 Received April 4, 2003. Revised Manuscript Received July 10, 2003
The fluid catalytic cracking (FCC) behavior of compound types present in the >650 °F resid from Merey crude was investigated. Distillation and liquid chromatography were used to separate selected compound-type fractions from the resid; the resulting fractions were then cracked using a benchscale FCC unit. The FCC behavior for each compound type was defined in terms of the resulting product distribution (yields of gas, gasoline, etc.); sulfur, nitrogen, nickel, and vanadium partitioning; and, in selected cases, gasoline composition. Results obtained from the Merey fractions were compared to those obtained from earlier FCC studies of compound types from Lagomedio (Venezuelan), Wilmington (Californian), Maya (Mexican), and Brass River (Nigerian) >650 °F resids. Correlations using the five sets of data were developed for light gas, light cycle oil, and heavy cycle oil, as a function of five feed parameters (metals, microcarbon residue, sulfur, basic nitrogen, and hydrogen contents). The correlations are consistent with the data and have a standard error of 2 wt %.
Introduction This paper is the sixth paper that has resulted from a program whose purpose is to relate feedstock composition to product slate and composition from fluid catalytic cracking (FCC) processes. This information is being sought in an effort to improve the FCC processing of conventional feedstocks and to extend FCC to lowerquality feedstocks, such as atmospheric resids from heavy oils. The first three papers presented results from feedstocks that were derived from Wilmington (California), Brass River (Nigeria), and Maya (Mexico) crudes.1-3 The fourth paper involved a model for calculating nine product subclasses from mass spectral analysis of hydrocarbon and sulfur types in the feed.4 The fifth paper presented a revised gasoline correlation that included the atomic ratio of hydrogen to the sum of carbon plus sulfur, the feed fraction volatized at the cracking temperature, and the effective metals and nitrogen contents (both basic and amide type).5 This nitrogen type determination is particularly relevant to * Author to whom correspondence should be addressed. E-mail:
[email protected]. † Currently with Saudi Aramco, Dhahran. ‡ Currently with ConnocPhillips, Barttlesville, OK 74004. (1) Green, J. B.; Zagula, E. J.; Reynolds, J. W.; Wandke, H. H.; Young, L. L.; Chew, H. Energy Fuels 1994, 8, 856-867. (2) Green, J. B.; Zagula, E. J.; Reynolds, J. W.; Young, L. L.; Chew, H.; McWilliams, T. B.; Grigsby, R. D. Energy Fuels 1996, 10, 450462. (3) Green, J. B.; Zagula, E. J.; Reynolds, J. W.; Young, L. L.; McWilliams, T. B.; Green, J. A. Energy Fuels 1997, 11, 46-60. (4) Sheppard, C. M.; Green, J. B.; Vanderveen, J. W. Energy Fuels 1998, 12, 320-328. (5) Green, J. B.; Zagula, E. J.; Grigsby, R. D.; Reynolds, J. W.; Young, L. L.; McWilliams, T. B.; Green, J. A.; Chew, H. Energy Fuels 1999, 13, 655-666.
the current research on mechanisms for NOx formation in the regenerator.6 Several equations that describe simple feed gasoline and coke product correlations have been introduced in these earlier papers. For continuity, they are listed below. Maximum gasoline yield may be estimated from the proportions of neutral components (primarily hydrocarbons and sulfur compounds) in the feed (fN) multiplied by the anticipated gasoline yield from pure neutrals (GN):
Gcalcd ) GNfN
(1)
GN can be determined experimentally or estimated via the following relationship:
[
GN ) 10.25
]
[H] + log(fcT) + 30.2 [C] + [S]
(2)
where the [H]/([C] + [S]) term is the atomic ratio of those elements and fcT is the fraction of neutrals that boil below the cracking temperature. We use the term effective metals to refer to the weighted sum of nickel and vanadium, where vanadium has only a quarter of the impact of nickel (Meff ) [Ni] + [V]/4, given in units of µequiv/g).7 The basic nitrogen content is denoted as [NB], and the amide nitrogen content denoted as [NAm]; both terms are given in terms of weight percent. The measurement of amide nitrogen was discussed in the last paper.5 Qian and co-workers presented evidence for (6) Efthimiadis, E. A.; Iliopoulou, E. F.; Lappas, A. A.; Iatridis, D. K.; Vasalos, I. A. Ind. Eng. Chem. Res. 2002, 41, 5401-5409. (7) Green, J. B.; Green, J. A.; Young, L. L. Prepr.sAm. Chem. Soc., Div. Pet. Chem. 1998, 43, 623-627.
10.1021/ef030077j CCC: $25.00 © 2003 American Chemical Society Published on Web 08/12/2003
Feedstocks Derived from Merey
Energy & Fuels, Vol. 17, No. 5, 2003 1361
Figure 1. Gasoline model yield versus experimental yield (eq 4).
strong interaction of both basic and amide nitrogen compounds with active catalyst sites in their FCC coke studies.8 The gasoline yield from non-neutral types (i.e., acidic or basic) may be compared to that of the neutrals by means of the neutral equivalent gasoline yield (NEGY) parameter, which is defined in eq 3:
NEGY )
Gmeasd - Gcalcd GNfA/B
(3)
where Gmeasd is the actual gasoline yield and fA/B is the weight fraction of acids/bases in the feed. The optimized correlation for total gasoline yield (see Figure 1) is given as
G ) 10.25
{
}
[H] + log(fcT) - 1.5Meff [C] + [S] 29([NB] + [NAm]) + 30.2 (4)
An earlier correlation for the total coke yield, CΣ (given in terms of weight percent), was based on feed microcarbon residue (MCR, ASTM D 4530), the catalytic coke formed from a nitrogen-free feedstock (C0, given in terms of weight percent), the feed nitrogen content ([N], given in terms of weight percent), and the fraction of feed nitrogen incorporated into the coke (χcN):
CΣ ) MCR + C0(1 + [N]χcN)
(5)
A later and improved correlation was developed based on the content of MCR, hydrogen ([Hw], given in terms of weight percent), basic nitrogen ([NB], given in terms of weight percent), effective metals (Meff, given in units of µequiv/g), and sulfur ([Sw], given in terms of weight percent) in the feed (see Figure 2). (8) Qian, K.; Tomczak, D. C.; Rakiewicz, E. F.; Harding, R. H.; Yaluris, G.; Cheng, W.-C.; Zhao, X.; Peters, A. W. Energy Fuels 1997, 11, 596-601.
Figure 2. Coke model yield versus experimental yield (eq 6).
CT ) MCR + 0.66[Hw] exp(-[NB]) + Meff + [NB] 25[NB] exp (6) [NB] + 0.437[Sw]
(
)
Considering the Qian et al. work, which shows both basic and amide nitrogen in the catalyst coke, an amide nitrogen term can be added to the coke correlation.8 This paper presents data from the fifth feedstock, Merey (Venezuelan crude), as well as correlations for yield of gas, light cycle oil (LCO), and heavy cycle oil (HCO) products. Merey is a Venezuelan Orinoco Belt heavy crude that contains 2.2 wt % sulfur, 68.16 vol % 650 F+ resid, and 75 ppm nickel/302 ppm vanadium in the resid, according to published assays.9 Its maturity is intermediate, compared to other Venezuelan heavy oils, and its vacuum residue exhibits intermediate difficulty in regard to typical upgrading processes.10 In a study that compared coke (carbon residue) formation to the composition of vacuum residues, data for Merey fit correlations that had been derived for it and the other resids in the study, thereby implying that Merey exhibits typical behavior for its compositional characteristics.11 It is a significantly lower-quality crude, compared to Lagomedio, which is the Venezuelan crude that was used to derive feedstocks for the most recent paper in this series.5 The high degree of interaction between heteroatomic species and catalyst surfaces has been previously borne out by the analysis of spent catalysts,8 studies with pure compounds,12-16 as well as experiments that involve (9) Oil and Gas Journal Databook; PennWell Publishers: Tulsa, OK, 1995; p 296. (10) Izquierdo, A.; Carbognani, L.; Leon, V.; Parisi, A. Fuel Sci. Technol. Int. 1989, 7, 561-570. (11) Green, J. B.; Shay, J. Y.; Reynolds, J. W.; Green, J. A.; Young, L. L.; White, M. E. Energy Fuels 1992, 6, 836-844. (12) Hughes, R.; Hutchings, G. J.; Koon, C. L.; McGhee, B.; Snape, C. E.; Yu, D. Prepr.sAm. Chem. Soc., Div. Pet. Chem. 1995, 40, 413417. (13) Hughes, R.; Hutchings, G. J.; Koon, C. L.; McGhee, B.; Snape, C. E. Prepr.sAm. Chem. Soc., Div. Pet. Chem. 1994, 39, 379-383. (14) Corma, A.; Fornes, V.; Monton, J. B.; Orchilles, A. V. Ind. Eng. Chem. Res. 1987, 26, 882-886. (15) Ho, T. C.; Katritzky, A. R.; Cato, S. J. Ind. Eng. Chem. Res. 1992, 31, 1589-1597. (16) Fu, C.-M.; Schaffer, A. M. Ind. Eng. Chem. Prod. Res. Dev. 1985, 24, 68-75.
1362 Energy & Fuels, Vol. 17, No. 5, 2003
heteroatom-rich petroleum-based feeds.17-23 With the high concentration of heteroatoms in the feed, their effect on the product yields is expected to be significant. The correlations in this paper were developed by multiple linear regression analysis, using the data from five crude feedstocks. Five different feedstock parameters were used in correlations for predicting the gas, LCO, and HCO yields.24 These five feed parameters were microcarbon residue (MCR), feed metal content, feed sulfur content, feed basic nitrogen content, and feed atomic hydrogen content. The form of the equation for these three products (gas, LCO, and HCO yields) is
product ) aMCR + bMeff + c[Sw] + d[NB] + e[H] + f (7) Experimental Section The scheme and methodology for crude fractionation and blending of the fractions to obtain FCC feedstocks were the same as those used earlier.1 Briefly, the 650-930 °F and >930 °F boiling ranges of the crude were fractionated into nine fractions, using liquid chromatography (LC). These fractions were used singly or in combination as feedstocks to a benchscale fluidized unit. Feedstocks were cracked at 521 °C (970 °F), using a Davison XP-series equilibrium catalyst at a cat./ oil ratio of (8.5 ( 0.5)/1. The FCC unit, catalyst, and procedures for conducting cracking experiments were unchanged from the prior work, except for refinements that were added later.1,2 The feedstocks were charged to the unit over a time period of 30 s. The sweep gas (N2) velocity was set such that the catalyst volume was displaced approximately every 20 s. Good correlation of results obtained using this methodology with those from commercial-scale FCC units has been reported.l The amide nitrogen content was determined by IR spectrometry.5 The basic nitrogen content was determined via nonaqueous titration, as described previously;7 the concentrations of basic and amide forms of nitrogen, as well as that of nickel and vanadium, were used to predict gasoline yields, as discussed below. The procedure for determining the amount of nickel and vanadium in feeds and products was described in the third paper of this series.3
Results Feedstock Composition. Table 1 lists the distributions of compound types, as determined from LC separation of the 650-930 °F and >950 °F boiling ranges of Merey crude. Those data were used, in turn, to calculate the distribution of compound types for the >650 °F resid, which is indicated in the table. The 950 °F cut point cited for the two boiling ranges was the crossover point for their gas chromatography-simulated distillation profiles. In fact, there was considerable overlap in their distillation curves. As noted in the table, the relative proportion of 650-950 °F material in the >650 (17) Cimbalo, R. N.; Foster, R. L.; Wachtel, S. J. Oil Gas J. 1972, 70, (20), 112-122. (18) Scherzer, J.; McArthur, D. P. Ind. Eng. Chem. Res. 1988, 27, 1571-1576. (19) Ng, S. H.; Rahimi, P. M. Energy Fuels 1991, 5, 595-601. (20) Harding, R. H.; Zhao, X.; Qian, K.; Rajagopalan, K.; Cheng, W.C. Ind. Eng. Chem. Res. 1996, 35, 2561-2569. (21) Larocca, M.; Farag, H.; Ng, S. H.; deLasa, H. Ind. Eng. Chem. Res. 1990, 29, 2181-2191. (22) Green, J. B.; McWilliams, T. B.; Sturm, G. P., Jr. Prepr.sAm. Chem. Soc., Div. Pet. Chem. 1995, 40, 681-684. (23) Green, J. B.; Zagula, E. J.; Young, L. L.; Sturm, G. P., Jr. Prepr.sAm. Chem. Soc., Div. Pet. Chem. 1995, 40, 691-694. (24) Al-Alloush, S. S. Master’s Thesis, University of Tulsa, Tulsa, OK, December 2002.
Sheppard et al. Table 1. Compound-Type Distributiona in Merey, as a Function of Boiling Rangeb 650-950 °F
>950 °F
>650 °F
4.9 ( 0.1d
17.2 ( 0.6 8.8 ( 0.7 26.0 ( 0.9
10.2c 5.2c 17.4e
bases content, wt % strong weak total content, wt %
1.9 ( 0.1
13.0 ( 0.1 11.2 ( 0.7 24.2 ( 0.7
7.7c 6.6c 15.1e
neutrals content, wt % polar-neutral sulfide nonsulfide total
93.6 ( 2.1 0.6 ( 0.1 8.0 ( 0.2 82.9 ( 0.5 91.5 ( 0.6
50.1 ( 0.6 4.6 ( 0.6 13.9 ( 1.8 29.3 ( 2.6 47.8 ( 3.2
67.8 3.0 11.5 51.1 65.6
overall total content, wt %
100.4 ( 2.2
100.3 ( 1.3
acids content, wt % strong weak total
a
100.3 b
Distributions determined from LC mass balances. The following samples were used to demonstrate the boiling ranges: No. 3295, for 650-950 °F; No. 3063, for >950 °F; and Nos. 3295/3063, for >650 °F, which was calculated from data for the 650-950 °F and >950 °F boiling ranges (40.74 wt % was 650-950 °F material and 59.26 wt % was >950 °F material). c Includes >950 °F portion only. d Uncertainties given are average deviations over 2-3 separations. e Total >650 °F acids or bases content.
°F resid was 40.74 wt %. By comparison, the proportion of 650-950 °F material in >650 °F Lagomedio was 36.2 wt %.3 These are within the range of the other feedstocks studied, with Brass River being 93.0 wt % and Maya being 22.3 wt %.2,3 The distribution of compound types in the Merey crude was similar to that of the Lagomedio crude.5 The largest difference in the compound-type distributions between the two >650 °F resids was the greater proportion of strong acids in the Merey crude (4.9 wt %), compared to that in the Lagomedio crude (3.5 wt %). However, when making comparisons of distributions of relatively crude fractions, such as those listed in Table 1, it should be remembered that each classification, e.g., strong acids, actually includes a wide range of potential subtypes and homologues. For example, Maya versus Wilmington strong acids were, in fact, observed to be quite dissimilar in composition.3 Table 2 shows elemental and MCR data for each LC fraction and whole distillate/resid. As expected, the basic nitrogen concentration is greater in the basic fractions than in the acid fractions. The amide nitrogen content was measured for the whole resid fractions and the acid fractions. Also, as expected, acid/base fractions were substantially enriched in MCR precursors and all heteroatoms, except sulfur, compared to the respective whole material. The extremely refractory nature of the >950 °F strong acid and strong base fractions, in particular, is evident from their high heteroatom content, high MCR content, and low hydrogen content. Table 3 presents high-resolution mass spectrometric (MS) hydrocarbon-type results for Merey distillate neutrals. The MS method used is applicable only to neutral types tha boil at temperatures below ∼1050 °F.25 The results are similar to those for the Lagomedio crude, except that the Merey crude has less noncyclic paraffins and more multiple-ring paraffins. Table 4 shows properties of feedstocks that have been prepared by blending fractions listed in Tables 1 and 2. (25) Teeter, R. M. Mass Spectrom. Rev. 1985, 4, 123-143.
Feedstocks Derived from Merey
Energy & Fuels, Vol. 17, No. 5, 2003 1363
Table 2. Microcarbon Residue (MCR) and Elemental Data for Merey Fractions fraction
C
H
whole distillate acids bases neutrals polar/sulfide-free neutrals
84.8 78.5 80.6 85.2 86.5
11.94 8.96 9.72 12.06 12.10
whole resid strong acids weak acids strong bases weak bases neutrals polar/sulfide-free neutrals
84.8 83.3 82.3 82.5 84.3 85.0 86.4
10.10 7.86 8.92 8.02 9.42 11.06 11.28
Content, wt % NAM NT
total
MCR content, wt %
Boiling Range ) 650-950 °F 0.023 0.20 2.21 0.31 0.46 2.12 0.96 1.91 3.02 1.95 0.036 2.20 0.026 1.45
99.2 90.5 95.3 99.5 100.1
0.42 8.6 3.6 0.11 0.16
Boiling Range > 950 °F 0.083 0.81 3.70 0.33 1.58 3.91 0.59 1.32 3.97 1.90 3.82 1.37 3.90 0.24 3.20 0.12 2.33
99.4 96.6 96.5 96.2 99.0 99.5 100.1
NB
0.14 0.09 0.63 0.39
paraffins monocycloparaffins dicycloparaffins tricycloparaffins tetracycloparaffins pentacycloparaffins total saturates
content, wt %a
formula Saturates CnH2n+2 CnH2n CnH2n-2 CnH2n-4 CnH2n-6 CnH2n-8
4.8 14.1 12.3 8.5 4.2 0.1 44.0
Aromatics aromatics alkylbenzenes CnH2n-6 benzocycloparaffins CnH2n-8 benzodicycloparaffins CnH2n-10 naphthalenes CnH2n-12 naphthocycloparaffins/ CnH2n-14 biphenyls naphthodicycloparaffins/ CnH2n-16 fluorenes triaromatics CnH2n-18 CnH2n-22 tetraromatics CnH2n-24 CnH2n-28 thiophenes thiophenes CnH2n-4S benzothiophenes CnH2n-10S dibenzothiphenes CnH2n-16S total aromatics
4.5 3.5 3.7 3.1 4.5 6.0 4.7 4.8 2.6 2.2 1.0 8.0 7.4 56.0
overall total
28.1 52.1 35.4 48.5 34.7 11.3 8.7
Content, ppm (w/w) Ni V 0.2 1.0 8 650 °F >650 °F P/S >650 °F residue neutrals neutrals neutrals 100 100 100 85.0
>650 °F neutrals 85.0
N+DA >650 °F neutrals 87.0
N+SB
N+WB
>650 °F neutrals 85.0
>650 °F neutrals 85.1
N+DB >650 °F neutrals 87.0
>950 °F >950 °F 650-950 °F >950 °F >950 °F 650-950 °F strong acid weak acid acids strong base weak base bases 15.0 15.0 13.0 15.0 14.9 13.0 84.8 10.85 0.131 0.059 0.56 3.09 99.3 17.3
85.1 11.62 0.010
86.5 11.77 0.005
84.7 11.21 0.022 0.088 0.31 2.84 99.1 9.9
84.3 11.27 0.049 0.060 0.39 2.42 98.4 5.8
84.7 11.08 0.103
85.0 11.29 0.067
84.5 11.37 0.257
0.064 1.80 100.1 3.3
84.9 11.06 0.030 0.050 0.35 2.83 99.1 12.4
0.13 2.64 99.5 5.4
0.40 2.82 99.0 11.9
0.32 2.83 99.4 9.8
0.51 2.55 98.9 5.2
89 353
19 90
10 4
58 245
34 177
17 79
62 257
43 191
18 79
1364 Energy & Fuels, Vol. 17, No. 5, 2003
Sheppard et al.
Table 5A. Overall Product Distributions from Merey Feedstocks Obtained at 521(1 °C (970°F) and a Cat./Oil Ratio of 8.5 ( 0.5: Feed Content, Nitrogen/Sulfur Partioning, and HCO Metal Contenta Partitioning Nitrogenb
Feed Content, wt % feedd 1. WR 2. N 3. N-P/S 4. N+SA 5.N+WA 6. N+DA 7. N+SB 8. N+WB 9. N+DB
HCO Metal Content, wt %
Sulfurc
gase gasolinef LCOg HCOh coke total conversioni gasoline efficiencyj liquid coke gas liquid coke total 15.9 17.7 16.6 17.0 16.7 15.1 16.2 17.6 14.3
31.4 41.7 42.0 35.6 35.2 39.0 35.3 36.5 37.7
11.7 13.6 13.6 12.5 12.0 14.4 12.7 11.5 14.6
10.6 12.2 14.5 12.4 14.3 17.6 14.8 14.1 17.8
29.6 99.2 14.4 99.6 12.0 98.7 23.1 100.6 21.2 99.4 14.9 101.0 21.4 100.4 20.9 99.7 14.9 99.3
76.8 73.8 70.6 75.8 73.1 69.1 72.8 74.0 67.0
40.8 56.5 59.5 47.0 48.2 56.5 48.5 49.3 56.3
5.7 7.8 13.1 3.5 8.2 25.6 3.5 6.5 14.6
94.3 92.2 86.9 96.5 91.8 74.4 96.5 93.5 85.4
57.3 63.1 44.1 64.7 63.9 64.8 60.0 58.6 63.3
15.5 26.6 49.6 20.0 24.9 26.0 23.3 25.7 27.4
26.5 9.8 6.6 17.0 12.3 7.9 14.6 15.7 9.3
99.3 99.5 100.3 101.7 101.1 98.7 97.9 100.0 100.8
Ni
Va
3.2 0.8
