Energy & Fuels 1995,9, 665-672
665
Hydrotreating of a Bitumen-Derived Coker HGO and Evaluation of Hydrotreated HGOs as Potential FCC Feeds Using Microactivity Test Unit Sok M. Yui* Research Center, Syncrude Canada Ltd. 9421 -1 7 Avenue, Edmonton, Alberta, Canada T6N l H 4
Siauw H.Ng Western Research Center, CANMET, 1 Oil Patch Drive, Devon, Alberta, Canada TOC 1EO Received November 18, 1994@
A coker heavy gas oil (HGO) derived from Athabasca bitumen was hydrotreated over a typical Ni/Mo catalyst in a downflow fixed bed pilot-scale reactor in order t o investigate HGO hydrotreating kinetics in a wide range of operating conditions and to provide feedstocks for evaluating the processibility of hydrotreated HGOs in fluid catalytic cracking (FCC) units. A microactivity test (MAT) reactor loaded with a typical commercial FCC catalyst was used for the latter purpose. Rates of hydrodenitrogenation (HDN), 343 "C+ conversion to lighter materials (mild hydrocracking or MHC), and density reduction of HGO during hydrotreating are adequately described by modified first-order kinetics, while the rate of hydrodesulfurization (HDS) can be described by 15th-order kinetics. MAT experiments show that bitumen-derived coker HGO can make a premium FCC feedstock if it is hydrotreated under appropriate conditions.
Introduction Syncrude Canada Ltd. operates a surface mining oil sands plant in northern Alberta and produces a light sweet crude oil from the extracted bitumen. Bitumen is currently upgraded in two fluid cokers and an ebullated-bed hydrocracker followed by hydrotreating of naphtha, light gas oil, and heavy gas oil streams in separate hydrotreaters. The hydrotreated products are combined and shipped to refineries by pipeline as a crude oil. Compared with conventional Western Canadian crudes, Syncrude's oil is very low in sulfur and essentially free of residuum and has a larger gas oil fraction. Refiners use HGO primarily as feed t o FCC units t o produce motor gasoline. Therefore, raw coker HGO must first be hydrotreated to lower its contents of aromatics and heteroatoms such as sulfur and nitrogen. We need to establish the relationship between the severity of hydrotreating and the performance of Syncrude's HGO in downstream FCC operation. The MAT ~ a unit is a useful tool for this p ~ r p o s e . l - Employing MAT unit, Fisher1 investigated the effect of hydrocarbon type, as determined by low-resolution mass spectrometry (MS), on catalytic cracking yields for nine vacuum gas oils (VGOs) derived from various Canadian crude oils. Sato et aL2 examined the effect of hydrotreating severity applied to atmospheric residue from Athabasca Abstract published in Advance ACS Abstracts, April 15, 1995. (1)Fisher, I. P. Effect of Feedstockvariability on Catalytic Cracking Yields. Appl. Catal. 1990, 65, 189-210.
(2) Sato, Y.; Yamamoto, Y, Kamo, T.; Miki, K.; Cyr, T. Fluid Catalytic Cracking ofAlberta Tar Sands Bitumen. Energy Fuels 1992, 6, 821-825. (3) Ng., S;Rahimi, P. Catalytic Cracking of Canadian Nonconventional Feedstocks. 1. Cracking Characteristics of Gas Oils Derived from Coprocessing Distillate and Shale Oil. Energy Fuels 1991,5, 595-601.
0887-0624/95/2509-0665$09.00/0
bitumen on cracking yields and product quality. Ng and Rahimi3 performed a similar study over three commercial FCC catalysts using two VGOs obtained from a shale oil and a coal-oil coprocessed distillate. In the present study, the coker HGO was hydrotreated t o a range of nitrogen contents t o allow useful conclusions to be drawn from hydroprocessing and the MAT evaluation. Four hydrotreated coker HGOs were selected for MAT runs along with an HGO from conventional crude which served as a reference. While the primary purpose of the present study was to evaluate the performance of hydrotreated coker HGOs in FCC units, preparation of the MAT feeds presented an opportunity t o extend HGO hydrotreating kinetics to a wider range of operating conditions than previously r e p ~ r t e d . ~
Experimental Section Hydrotreating of Coker HGO. The feedstock was a bitumen-derived HGO obtained from one of Syncrude's commercial fluid cokers. The Ni/Mo catalyst (120 mL or 86.5 g), same as catalyst " S used in a n earlier study,* was diluted with a n equal volume of 46 mesh silicon carbide. The downflow pilot-scale reactor and experimental procedure were likewise the same as reported p r e v i ~ u s l y . Experiments ~ were undertaken by varying reactor temperature (340-410 "C), pressure (7, 8.8, and 11 MPa) and LHSV (0.6-1.3 h-l) while keeping hydrogedoil ratio constant (600 S m3/m3). "he system was once-through. The hydrogen was of 100% purity and the measured pressure was the reactor total pressure. The total pressure was considered to be hydrogen partial pressure. (4)Yui, S. M.; Sanford, E. C. Mild Hydrocracking of BitumenDerived Coker and Hydrocracker Heavy Gas Oils: Kinetics, Product Yields, and Product Properties. Ind. Eng. Chem. Res. l969,28,12781284.
0 1995 American Chemical Society
666 Energy &Fuels, Vol. 9, No. 4, 1995
Yui and Ng
Table 1. Properties of Feed and Hydrotreated Products at Typical Operating Conditions feed 4a run no. 3a 8 9 11" 12 14" 17 temperature ("C) 350 370 371 370 390 350 370 390 8.8 8.8 7.0 pressure (MPa) 8.8 11.0 8.8 8.8 8.8 LHSV (vMv) 1.04 1.24 0.60 1.04 1.03 0.76 1.04 1.05 yield (carbon balance) (v/v) 1.033 1.025 1.035 1.031 1.030 1.033 1.075 1.047 1.0017 0.9322 0.9289 0.9107 0.9177 density at 20 "C (g/mL) 0.9380 0.9307 0.9324 0.9336 43320 4357 5790 sulfur (SI(wppm) 2888 1510 1670 3494 3841 3830 total nitrogen (TN) (wppm) 3783 1495 2009 1482 1445 1787 992 443 745 basic nitrogen (BN) (wppm) 1200 320 520 170 82 75 280 320 380 84.21 87.44 carbon (C) (wt %) 87.60 87.33 87.55 87.48 87.68 85.72 87.38 hydrogen (H) (wt %) 10.17 12.14 12.00 12.19 12.03 13.47 12.00 11.76 12.70 27 2 4 bromine number (g/lOO g) 2 4 4 4 4 2 aniline point ("C) 52.5 55.8 63.2 55.5 56.2 56.1 55.2 53.9 54.3 1761 viscosity at 20 "C (cSt) 156 194 117 124 107 viscosity at 40 "C (cSt) 253 43.8 50.7 32.9 36.3 2.94 0.02 0.01 microcarbon residue (wt %) simulated distillation ("C) IBP 242 143 146 101 117 111 102 70 86 266 242 5% 314 262 241 200 240 147 172 10% 298 336 294 284 281 253 282 285 23 1 385 352 30% 358 350 351 355 322 348 333 425 398 396 50% 371 392 40 1 394 394 379 443 70% 463 440 439 418 436 437 438 425 512 499 498 507 90% 496 482 497 485 498 524 529 95% 521 531 523 510 525 511 525 FBP 566 570 579 583 579 573 563 581 557 0.00 0.78 IBPi177 "C (wt %) 2.04 0.94 1.93 5.31 1.84 1.66 3.70 12.11 1771343 "C (wt %) 26.28 23.64 27.13 26.80 24.96 38.04 28.02 33.88 87.89 74.10 343 "C+ (wt %) 71.79 75.58 70.84 71.54 56.65 70.13 62.42 Products from runs 3, 4, 11, and 14 were used for MAT study Twenty-seven total liquid product (TLP) samples were collected and analyzed using the following methods: density, Anton-Parr density meter Model DMA-48; sulfur, ANTEK sulfur detection 714, oxidative microcoulometer; total nitrogen (TN), Dohrmann combustion analysis with chemiluminescent detection; basic nitrogen (BN), potentiometric titration (UOP 269-70); nonbasic nitrogen (NBN), balance of total and basic nitrogen; carbon and hydrogen, LECO Model CHNGOO, thermal conductivity after oxidation; bromine number, modified ASTM D1159; aniline point, Koehler instrument; microcarbon residue, ALCOR MCR Tester, ASTM D4530. TLP yields were determined by carbon balance. Catalytic Cracking Using a MAT Unit. Four TLPs from hydrotreating were selected for catalytic cracking based on their nitrogen contents. The more severely hydrotreated product was lower in nitrogen and was lighter due to hydrocracking. To eliminate the effect of lighter materials on cracking performance, the four TLPs were distilled by spinning band to remove the IBP/343 "C fraction. As a reference, VGO from a typical Western Canadian mixed crude was also tested. The MAT unit was a modified version of ASTM D3907 equipped with a downflow fured bed quarz reactor charged with a n equilibrium fluid catalyst, Akzo Chemicals KOB-627. General experimental procedure has been reported e1sewhe1-e.~ Prior to loading the catalyst into the reactor, coke was removed by combustion a t 600 "C for 3 h. Feed was delivered to the reactor by a syringe pump through a needle. Vaporization took place in a preheat zone, followed by cracking in the catalyst bed. Reactor effluent passed through two ice-cooled receivers in series where condensable product was collected. The amount of liquid product was determined by weighing the receivers before and after each run. Yields of gasoline (IBP/ 216 "C), light cycle oil (LCO, 216/343 "C), and heavy cycle oil (HCO, 343 "C+) were determined by simulated distillation (ASTM D2887). Gaseous product was collected and analyzed with a gas chromatograph. Coke deposited on the catalyst was determined by in-situ combustion and measurement of COz in the exhaust gas with a n on-line infrared analyzer. Since (5)Ng, S. H. Conversion of Polyethylene Blended with VGO to Transportation Fuels by Catalytic Cracking. Energy Fuels 1995, 9 ,
216-224.
20 411 8.8 1.02 1.094 0.8990 567 286 16 84.91 13.48 2 51.0 -
-
38 133 187 293 349 398 465 495 551 8.95 47.58 43.47
;he feed contained very little metals t h a t might poison the :atalyst, MAT runs were performed repeatedly without changng catalyst. Specific conditions of the MAT runs were a s ?allows: reactor temperature = 510 "C; catalyst contact time t,) = 30 s (syringe pump drive time); catalyst'oil ratio = 2.5-8 :lg (catalyst weight constant at 4 g, feed weight varied).
Results and Discussion Hydrotreating of Coker HGO. Table 1lists prop2rties of the feed and hydrotreated products at typical iperating conditions. Compared with the coker HGO .wed in the previous s t ~ d ythe , ~ feed in this study was glightly heavier in terms of density (1.0017 vs 0.9983 g/mL a t 20 "C) and simulated distillation (531 vs 517 'C at 95 wt % off). It also contained more total nitrogen :TN, 3783 vs 3282 wppm) but less sulfur (4.33 vs 4.51 w t %). The TLPs from runs 4 (2009 wppm TN), 3 (1495 wppm TN), 11 (992 wppm TN), and 14 (443 wppm TN) were reserved to produce feeds for the MAT experinents. Kinetics of HDS, HDN, MHC, Density Reduction, and Z'LP Yield. Diluting catalyst with fine inert materials 3uch as silicon carbide in pilot-scale downflow reactors .s a normal practice to reduce axial dispersion and :hanneling. However, previous studies416showed that lilution does not improve catalyst wetting efficiency inder the operating conditions we typically employ. 4ccordingly, our modified plug flow model includes a ?ewer term (a)for space velocity. Use of a power term br LHSV was proposed by Henry and Gilbert7 based in a liquid holdup model and by M e a d based on a
I
( 6 )Yui, S. M. Hydrotreating of Bitumen-Derived Coker Gas Oil: (inetics of Hydrodesulfurization, Hydrodenitrogenation, and Mild -Iydrocracking,and Correlations to Predict Product Yields and Proper.ies. A O S T R A J . Res. 1989,5, 211-224. (7) Henry, H. C.; Gilbert, J. B. Scale Up of Pilot Plant Data for 2atalytic Hydroprocessing. Ind. Eng. Chem. Process Des. Dew. 1973,
' 2 , 328-334.
Energy & Fuels, Vol. 9, No. 4, 1995 667
Hydrotreating of a Bitumen-Derived Coker HGO
Table 2. Kinetic Parameters of HDS,HDN, MHC,Density Reduction, and TLP Yield HDN HDN HDN density HDS (BN) (TN) (NBN) MHC reduction kinetic order (n) no. of observations correlation coeff (r2) In K O E/R, K /3 for pressure a for LHSV
1.5 27 0.965 15.811" 11344 0.968 0.530
1
1
27 0.956 14.649 11239 1.465 0.719
27 0.978 11.448 9537 1.559 0.645
correlation coeff (r2)
0.960 18.609" 11344
0.945 17.835 11239
1
1 27 0.978 10.833 9346 1.640 0.620
27 0.962 10.568 8317 0.364 0.268
1 27 0.967 1.836 3160 0.223 0.166
0.959 11.361 8317
0.963 2.321 3160
TLP yield 1 23 0.858 0.275 177 0.016 0.013
Best Fit Equations in Figures 1 and 2 In ko
E/R; K
0.970 14.839 9537
0.969 14:400 9346
In ko for HDS (15.811 and 18.609) includes In 2 (0.693).
catalyst wetting model for an undiluted trickle-bed reactor. Various values (less than unity) for a have been rep~rted.~-~ In addition to the power term a for LHSV, the kinetic model also incorporates a power term p for hydrogen partial pressure. Based on previous ~ t u d i e swe ~ , ~assumed that HDS follows 13th-order kinetics and that HDN and MHC follow first-order kinetics. We also assumed that density reduction and TLP yield can be expressed by first-order kinetics. The model is summarized by the following equations:
HDS (15th-order):
1
0.1 I
0.011 I 1.44
1/Sp1'2- 1/S;I2 = kp~:/2LHsv ln(C{Cp) = kp,:?LHSVa
others (lst-order):
10
'
1.48
(1) (2)
$ in eq 1 represents sulfur (wppm) while C in eq 2 represents either nitrogen (wppm), density (g/mL) or 343 " C f material (wt %). The subscripts f and p on S and C refer t o feed and product. In eqs 1and 2 k is the rate constant, p~~is hydrogen partial pressure (MPa), and LHSV is liquid hourly space velocity defined as volume of feeWvolume of catalyst loaded. For TLP yield, C$Cp is expressed as volume of TLP/volume of feed. The rate constant is expressed using an Arrhenius equation
I
'
I I
I
1.52 1.3 1WOF, 1lK
I
'
1.6
1 I
1.64
Figure 1. Arrhenius plots of HDS, HDN for total nitrogen, MHC, and DEN (density reduction) at 8.8 MPa. n is reaction order. The units of y-axis are h-a for n = 1 and h-a ~ p p m - ~ . ~ for n = 1.5.
0
k
= k, exp(-E/RT)
(3)
where ko is the frequency factor (h-a MPa-P ~ p p m - , . ~ for 1.5th-order and h-a MPa-P for first-order), E is activation energy (kJ/mol),R is the gas constant (8.314 kJ/moVK), and T is absolute temperature (K). Kinetic parameters and power terms were determined using multiple linear regression after combining eqs 1 and 2 with eq 3, respectively, and taking logarithms:
HDS (1.5th-order): ln(l/Sp1'2- 1/Sf1'2)= Ink, - (E/R)(l/T) /?In pH,- ln2 - a In LHSV (4)
+
2 0.1
1.44
1.52 1.56 lOOOF, 1lK
1.6
1.64
Figure 2. Arrhenius plots of first-order HDN (basic, nonbasic, and total nitrogen) at 8.8 MPa. The unit of y-axis is h-a.
The results so obtained are summarized in Table 2. Figure 1illustrates Arrhenius plots for HDS, HDN (total nitrogen), MHC, and DEN (density reduction). Figure 2 illustrates Arrhenius plots for removal of basic, nonbasic, and total nitrogen. In Figures 1and 2 , y-axis data (8.@k, rate constant a t 8.8 MPa) were obtained from the following equations: HDS:
(8)Mears, D.E. The Role of Liquid Holdup and Effective Wetting in the Performance of Trcikle-Bed Reactors. Chem. React. Eng.-IZ Adv. Chem. Ser. No. 133 1974,218-227. (9) Parakos, J. A,; Frayer, J. A,; Shah, Y. T. Effect of Holdup Incomplete Catalytic Wetting and Backmixing during Hydroprocessing in Tricke Bed Reactors. Ind. Eng. Chem. Process Des. Deu. 1976, 14, 315-322.
1.48
Others:
8.8pk = 2LHSV(1/Sp - 1/s,"2)(8.80~96s/p~z0~968) (6)
8.8% = L H S V ln(CdCp)(8.8p/p,$)
(7)
The best fit lines were obtained from an equation of the form
668 Energy & Fuels, Vol. 9, No. 4, 1995 1.08 1
I
I
I
I
I
Yui and Ng 2500
I
1.07
d PZ
1.05
8 z- 1.04 p$ 85 25
1.03 1.02
* 1.01 1.00 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 ~
I I I 330 340 350 360 370 380 390 400 410 420
04
Calculated Yield Based on Carbon Balance, vlv of Feed
Reactor Temperature, 'C
Figure 3. TLP yield predicted from first-order kinetics vs yield calculated from carbon balance. 100 a
ISulfurl
loa
r
ol"o
I
Figure 5. Total nitrogen vs reactor temperature at various pressures and constant LHSV (1 h-l). The points are actual test results and the lines are predictions based on eq 5 and kinetic parameters in Table 2.
I
85 80
s 75
'
70
E-
$ $
+
$ 60
30 20 10 J 20
65
I
30
I
I
I
I
1
40 50 60 70 80 90 Removal of Total Nitrogen,wt %
8
I
50
100
330 340
Figure 4. Total nitrogen removal vs 343 "C- yield and removals of sulfur and basic nitrogen.
rate constant = exp[ln KO - (E/R)(l/Z')I
55
(8)
where the values of the parameters are given in the lower part of Table 2. From the table and figures, the following are evident: 1. The kinetic approach and assumptions made in the present study with respect to reaction order and power terms for P H ~and LHSV are reasonable. 2. The power term (a)for LHSV is not unity (0.65 for HDN, 0.53 for HDS, 0.27 for MHC, 0.17 for density reduction and 0.01 for TLP yield). 3. HDN shows the largest effect of P H ~on rate constants (p = 1.561, followed by HDS (p = 0.97), MHC (p = 0.361, density reduction (p = 0.22), and TLP yield (p = 0.02). 4. Basic nitrogen is more easily removed than nonbasic nitrogen. Basic, nonbasic, and total nitrogen removal can all be described by modified first-order kinetics. 5. TLP yield can also be described by modified firstorder kinetics. The relatively low correlation coefficient (r2 = 0.858) is due probably to relatively inaccurate carbon data. TLP Yields and Properties. Figure 3 shows the yield of TLP predicted from first-order kinetics against TLP yield computed from carbon balance. Figure 4 illustrates that yield of 343 "C- material and removals of sulfur and basic nitrogen can be correlated with removal of total nitrogen. Figures 5-10 illustrate TLP properties (total nitrogen and 343 "Cf yield) as functions of reactor conditions (temperature, pressure, and LHSV). The results support the preceding discussion.
350
360
370
380
390
400
410
420
Reactor Temperature, 'C
Figure 6. 343 "C+ yield vs reactor temperature at various pressures and constant LHSV (1h-l). The points are actual test results and the lines are predictions based on eq 5 and kinetic parameters in Table 2. 2500
1 g
500 I
I
0 6
7
8
9 10 Pressure, MPa
11
12
Figure 7. Total nitrogen vs pressure at various temperatures and constant LHSV (1 h-l). The points are actual test results
and the lines are predictions based on eq 5 and kinetic parameters in Table 2. Catalytic Cracking ofHydrotreated Coker HGOs. Four hydrotreated TLPs from runs 3,4,11, and 14 were selected as feeds for MAT experiments. As Table 1 shows, these TLPs contained different amounts of 343 "C- material. For example, TLP 4 contained 24.42 wt % whereas TLP 14 contained 43.35 wt %. To minimize the effect of lighter materials on extent of cracking, these TLPs were distilled by spinning band to remove the 343 "C- fractions. A typical FCC feed from conventional Western Canadian mixed crude was included in the MAT experiments as a reference. Table 3
Energy & Fuels, Vol. 9, No. 4, 1995 669
Hydrotreating of a Bitumen-Derived Coker HGO I
I
I
I
I
I
I
I
I
I
I
7
8
9
10
11
80
ae
-' d
75 70
8 65
2+ 60 4
55
6
12
Pressure, MPa
Figure 8. 343 "C+ yield vs pressure a t various temperatures and constant LHSV (1 h-l). The points are actual test results and the lines are predictions based on eq 5 and kinetic parameters in Table 2.
2. Total nitrogen in the 343 "Cf fraction of each hydrotreated HGO is 13-37% higher (25% on average) than in the undistilled TLP. This compares with 21% reported previ~usly.~ 3. Although nitrogen level could be significantly reduced by increasing hydrotreating severity (for N1 and N4: 2268 vs 608 wppm of total nitrogen; 570 vs 99 wppm for basic nitrogen), the hydrocarbon type by MS was not affected to the same degree (4.2 vs 5.8 wt % parafins; 35.1 vs 40.7 wt % naphthenes; 60.8 vs 53.5 wt % aromatics). Table 4 summarizes MAT results for each feed a t two catalysffoil ratios, the lowest ratio, and the ratio a t which the conversion is close to its maximum based on precursor concentrations given in Table 3. Conversion. Conversion is defined as
100 x (weight of feed weight of unconverted material)/weight of feed (9)
-
2
$
1.5
=
1
z"
' 410T
Prtasure :: 8.8 MPa
2.5 -
/'
t 0.5
0 0
0.2
0.4
0.8 1 1lLHSV"0.645
0.6
1.2
1.4
1.6
Figure 9. ln(TNflN,) vs 1/LHSV0.645 at various temperatures and constant pressure (8.8 MPa). The points are actual test results and the lines are predictions based on eq 5 and kinetic parameters in Table 2. 0.6
-a
I
I
I
I
I
I
I
I
0.5
2 0.4
e2 0.3 P
3 0.2 v
-
0.1
0 0
0.2
0.4
0.6 0.8 1 1ILHSW0.268
1.2
1,4
1.6
Figure 10. 1n[(343"C+)d(343 "C+),] vs 1/LHSV0.26sa t various temperatures and constant pressure (8.8 MPa). The points are actual test results and the lines are predictions based on eq 5 and kinetic parameters in Table 2.
summarizes the properties of the five 343 "C+ MAT feeds: the four hydrotreated coker HGOs (Nl, N2, N3, and N4) and the one conventional crude HGO (CON). Also included in Table 3 are hydrocarbon types as determined by low-resolution MS and precursors of conversion, LCO and HCO. The table shows the following: 1. Conventional crude HGO (CON), which was untreated, is characterized by high nitrogen (1225 wppm), sulfur (0.93 wt %), aniline point (89.4 "C), and microcarbon residue (0.90 wt %).
where unconverted material is the liquid product with a boiling point above 216 "C. Therefore, by definition, the converted materials are gases, gasoline, and coke. LCO is considered unconverted material even though its boiling range (2161343 "C) is lower than that of the feed (343 "C+). Figure 11 illustrates conversion vs catalysffoil ratio for the five feeds. Conversion increases with increasing catalysffoil ratio and tends to level off at ratios higher than 7. The results also show higher conversions, at equal catalyst/oil ratio, for the more severely hydrotreated feedstocks. This is due to both saturation of uncrackable benzene rings to naphthenic rings and reduction of nitrogen level during hydrotreating. The conversion data were analyzed using the following second-order rate expression: conversiod(100 - conversion) = b/WHSV = (b/l20)(catalyst/oil ratio) (10) where b is a constant and WHSV is weight hourly space velocity (g/h/g) defined as (3600, s/h)/[(catalyst/oil ratio, g/g)(t,, s)]. The catalyst contact time, tc,was 30 s in the present study. Equation 10 is commonly used in the petroleum industry1°-12 and the left-hand side of this equation is often referred to as second-order conversion or crackability.11J2 Table 5 summarizes the values for b obtained by linear regression. Figure 12 illustrates the fit of the second-order conversion. It is noted from Table 5 and Figures 11 and 12 that two hydrotreated coker HGOs (N3 and N4) can achieve the same level of conversion as conventional crude HGO (CON). The highest obtainable conversions from experiments and the conversion limits defined by precursor concentrations in Table 3 are compared. This is shown in Table 6. The agreement between the two is generally good. Gasoline Yield. Gasoline is the most desirable product from FCC operation. Figure 13 shows gasoline yield vs catalysffoil ratio. Yields increase with increasing catalysffoil ratio. For N3, N4, and CON the gasoline yields level off or decline due t o overcracking at a ratio (10) Blanding, F. H. Reaction Rates in Catalytic Cracking of Petroleum. Ind. Erg. Chem. 1963,45, 1186-1197. (11)Mott, R. W. New Concept Measures Catalyst Performance. Oil Gas J. 1987,Jan. 26, 73-77. (12) Chin, A. A,; Child, J. E.; Hall, G.; Altman, L. J.; Schipper, P. H.; Sapre, A. V. FCC Cracking of Coker Gas Oils. Paper 91'2, 1989 AIChE Fall National Meeting.
670 Energy & Fuels, Vol. 9, No. 4,1995
Yui and Ng
Table 3. Characterization of 343 "C+ MAT Feeds ~
feed name run no. (refer to Table 1) temperature ("C) pressure (MPa) LHSV (v/h/v) total nitrogen in TLP (wppm) 343 "C+ by spinning band (wt %) density a t 20 "C (g/mL) total nitrogen (TN) (wppm) basic nitrogen (BN) (wppm) sulfur ( S ) (wppm) carbon (C) (wt %) hydrogen (H) (wt %) bromine number (g/lOO g) aniline point ("C) microcarbon residue (wt %) simulated distillation ("C) IBP 5% 10% 30% 50% 70% 90% 95% FBP 343 "C- (wt %) hydrogen type by MS (wt %) paraffins cycloparaffins (naphthenes) monoditritetrapentahexaaromatics monoditritetrapentaaromatic sulfur benozthiophenes (2-rings) dibenzothiophenes (3-rings) benzonaphthothiophenes polars total conversion precursorsa LCO precursorsb HCO precursorsc
N2
CON
4 350 8.8 1.04 2009 79.7 0.9492 2268 570 6515 86.98 11.52 6 61.0 0.44
3 350 8.8 0.60 1495 77.0 0.9459 1836 370 4919 86.94 11.65 5 64.4 0.34
370 11.0 1.05 992 74.5 0.9412 1276 210 3431 86.98 11.86 4 65.6 0.30
318 342 354 389 422 457 508 531 580 5.4
320 344 355 389 421 455 507 529 575 4.7
320 343 354 387 419 453 506 529 580 5.0
317 339 349 381 412 446 499 523 573 6.8
319 343 355 391 429 470 527 549 607 4.9
4.20 35.05 7.65 7.89 8.93 7.09 2.78 0.71 60.75 26.77 16.33 6.34 1.17 2.46 3.51 1.21 2.13
5.03 37.05 8.92 8.79 7.17 8.03 3.27 0.87 57.92 25.90 14.97 5.42 0.99 2.20 4.42 1.12 3.04 0.26 4.02 100.00 67.98 19.13 12.89
6.18 41.43 10.12 10.22 8.09 8.76 3.38 0.86 52.39 24.07 13.84 4.63 1.02 2.05 4.02 1.12 2.78 0.12 2.76 100.00 71.68 17.74 10.58
5.79 40.72 11.25 10.58 7.45 7.59 3.07 0.78 53.49 20.20 16.54 6.04 2.75 1.97 3.88 1.23 2.63 0.02 2.11 100.00 66.71 20.40 12.89
21.59 36.26 13.33 9.42 6.08 4.57 1.64 1.22 42.15 14.28 11.43 5.50 1.88 1.06 3.09 1.17 1.90 0.02 4.91 100.00 72.13 14.50 13.37
0.16
4.17 100.00 66.02 19.67 14.31
+
a Conversion precursors = parafins naphthenes + monoaromatics. HCO precursors = 100 - conversion precursors - LCO precursors.
of about 6. However, for N1 and N2, the yields still increase beyond the ratio of 6. This is probably attributable t o catalyst poisoning by the higher nitrogen contents of the feeds. Figure 14 shows gasoline yield vs conversion. Refiners are more interested in the yield-conversion relationship than yield-catalysUoi1 ratio relationship because in commercial FCC operation, the catalyst/oil ratio cannot be fured as it is not an independent variable. In FCC operation, the independent variables are reactor temperature, feed rate, feed preheat temperature, catalysUoi1 contact time, and reactor pressure; the dependent variables are catalyst circulation rate (and hence catalysUoi1 ratio), regenerator temperature, and conversion.13 Although conversion is a dependent variable, it is one of the targets set in commercial operation for a given feedstock. In MAT (13)Venuto, P. V.; Habib, E. T. Jr. Fluid Catalytic Cracking with Zeolite Catalysts. Chemical Industries Series, Vol. I ; Marcel Dekker, Inc: New York, 1979.
N3
~~
N4 14 390 8.8 0.76 445 66.5 0.9334 608 99 2600 86.88 11.76 5 67.6 0.32
N1
11
-
0.9078 1225 232 9294 86.24 12.62 5 89.4 0.90
LCO precursors = diaromatics + aromatic sulfur (2- and 3-rings).
runs, varying catalysUoi1 ratio is just one way of achieving certain conversions. In Figure 14 the gasoline yield appears to reach a maximum at a certain conversion depending on the feedstock. From Figures 13 and 14, gasoline yields of N3 and N4 could be higher than that of CON. LCO Yield. With high level of aromatics, the cetane number of light cycle oil is very low. Thus, it is usually blended with good quality components in the diesel pool. All feeds contain 5-7 wt % of 216/343 "C fraction which is in the boiling range of LCO. Figure 15 shows LCO yield vs conversion. As the conversion increases, the LCO yield also increases, reaches a maximum, and then declines, approaching its lower limit based on the precursor concentration. At the same conversion, the LCO yields from hydrotreated coker HGOs (Nl-N4) are about 5 wt % higher than conventional crude HGO (CON) and the effect of hydrotreating severities on the LCO yield is not markedly observed in this study. Table
Hydrotreating of a Bitumen-Derived Coker HGO
Energy & Fuels, Vol. 9,No. 4, 1995 671
Table 4. Microactivity Test Results at High and Low CatalystJOil Ratios (Catalyst KOB-627,SO s Contact Time, 510 "C) Feed catalysb'oil ratio (g/g) wHsva(gmlg) product yield (wt %) H2 H2S
c1 c2
C2= total dry gas c3
C3= i-C4 n-C4 C4= total LPG total gas Cs+ gasoline LCO HCO coke total conversion (gas
+ gasoline + coke)
N1 3.02 39.74 0.07 0.12 0.35 0.26 0.27 1.07 0.34 1.58 1.66 0.28 2.17 6.02 7.09 30.17 20.54 39.73 2.47 100.00 39.73
N1 7.91 15.17
N2 2.63 45.61
N2 7.69 15.61
N3 2.44 49.26
0.13 0.20 0.89 0.69 0.86 2.77 0.90 2.98 3.76 0.62 2.63 10.89 13.66 45.70 20.19 14.14 6.31 100.00 65.67
0.08 0.09 0.33 0.28 0.26 1.05 0.33 1.24 1.31 0.21 1.52 4.61 5.65 30.47 19.96 41.63 2.29 100.00 38.41
0.10 0.13 0.84 0.68 0.87 2.62 0.95 2.94 4.20 0.71 2.59 11.39 14.01 50.28 19.09 11.06 5.56 100.00 69.84
0.04 0.09 0.05 0.03 0.26 0.83 0.20 0.63 0.24 0.78 0.79 2.36 0.29 1.00 1.50 2.95 1.68 4.16 0.22 0.65 1.76 -2.59 5.45 11.35 6.24 13.71 33.26 49.93 19.38 20.21 39.36 10.96 1.75 5.19 100.00 100.00 41.25 68.83
WHSV (gmlg) = (3600, s/h)/[(catalysffoil ratio, g/g) I
I
I
I
I
I
x
N3 6.84 17.55
N4 2.51 47.82
N4 6.61 18.15
CON 2.39 50.23
CON 7.69 15.60
0.04 0.09 0.23 0.17 0.23 0.76 0.30 1.59 2.03 0.25 1.90 6.07 6.83 36.70 22.05 32.52 1.90 100.00 45.43
0.08 0.12 0.62 0.44 0.63 1.89 0.81 3.04 4.18 0.60 2.61 11.24 13.14 52.27 19.97 10.06 4.55 100.00 69.96
0.05 0.33 0.41 0.30 0.25 1.34 0.45 1.54 1.73 0.29 2.08 6.09 7.43 33.71 16.01 40.33 2.52 100.00 43.66
0.06 0.55 0.92 0.62 0.83 2.98 1.06 4.06 5.57 0.82 4.35 15.87 18.84 47.06 16.04 12.04 6.01 100.00 71.91
(catalyst contact time, 30 s)].
I
I
3 ,
70
z
65
s 6o g 55
'1
50
6 45 0 35 -
CON 0
1
2
3
4
5
6
7
8
9
CatalystIOil Ratio, g/g
Figure 12. Second-order conversion vs catalystJoi1 ratio. The lines are predictions based on eq 1 0 and parameters in Table 5. no. of observations 8 7 11 5 5 correlation coeff (r2) 0.964 0.974 0.888 0.994 0.961 b 29.12 33.78 39.46 42.44 41.67
6 shows a comparison between the lowest LCO yields obtained from experiments and the calculated yield limits based on LCO precursor concentrations in Table 3. Good agreement between the two is generally obtained. HCO Yield. By definition of conversion (eq 91, the yields of HCO and LCO have the following relationship:
HCO yield = (100 - conversion) - LCO yield (11) Figure 16 shows that as conversion increases HCO yield monotonically decreases. At the same conversion, the HCO yields from hydrotreated coker HGOs are about 5 wt % lower than CON and the effect of hydrotreating severities is not markedly observed. Table 6 indicates the good agreement between the lowest experimental HCO yields and the calculated limits based on precursor concentrations. Gas and Coke Yields. Figures 17 and 18 show that gas and coke yields increase with increasing conversion. More severely hydrotreated coker HGOs (N3 and N4)
Table 6. Comparison of the Highest Conversions and Lowest LCO and HCO Yields Obtained from MAT Experiments with Precursor Concentrations feed
N1
catalysffoil ratio (gig) 7.91 highest conversion from 65.7 experiments (wt %) precursor concentrations from 66.0 Table 3 (wt %) lowest LCO yield from 20.2 experiments (wt %) precursor concentrations from 19.7 Table 3 (wt %) lowest HCO yield from 14.1 experiments (wt %) precursor concentrations from 14.3 Table 3 (wt %)
N2
N3
N4
CON
7.69 6.84 6.61 7.69 69.8 68.8 70.0 71.9 68.0
71.7
66.7
72.1
19.1 20.2
20.0
15.5
19.1
17.7
20.4
14.5
11.1 11.0
10.1
12.0
12.9
12.9
13.4
10.6
produce less gas and coke than conventional crude HGO at equal conversion.
Conclusions With respect to hydrotreating of coker HGO derived from Athabasca bitumen, HDS, HDN, MHC, density reduction, and TLP yield can be adequately described by modified power-form kinetic equations that include
Yui and Ng
672 Energy & Fuels, Vol. 9, No. 4, 1995 55
* N1
0
50
dr
ae
s 45
s
2-
35 30
5 40
.-%!
8 20
135
I
0 30
-1
15 10
1
I
1
2
3
I
4
1
4 5 6 Catalyst /Oil Ratio, glg
7
8
9
Figure 13. Gasoline yield vs catalysffoil ratio. 55
,
I
I
1
1
I
I
I
50
ae 'j 45
-
Q0
F 40
Q1
.-
f
35
0 30 CON
25 35
40
45
50 55 60 Conversion, wt %
65
70
75
Figure 14. Gasoline yield vs conversion.
41 35
I
I
40
45
ae
I +
Nl
0
N2
N3
X
0
N4
-
I
I
I
I
I
I
I
I
I
65
70
I 75
I
I
I
Figure 17. Total gas yield vs conversion.
28
26
I
50 55 60 Conversion, wt %
I
CON
I
I
7
I
24 22
35 20
8 18
16
2 35
1
I
40
45
I
I
I
50 55 60 Conversion, wt %
I
I
I
65
70
75
11 35
! 40
I 45
I I I 50 55 60 Conversion, wt %
1
I
1
65
70
75
Figure 15. LCO yield vs conversion.
Figure 18. Coke yield vs conversion.
power terms for LHSV and hydrogen partial pressure. As hydrotreating seventy is increased, more heteroatoms are removed from coker HGO and more naphtha and middle distillates are produced due t o mild hydrocracking. Higher hydrotreating severity produces a coker HGO with improved quality in terms of conversion and gasoline yield in FCC operation. By reducing nitrogen to the same level as that of HGO from conventional Western Canadian crude, coker HGO can produce more gasoline than conventional crude HGO at the same FCC severity.
Acknowledgment. Hydrotreating of coker HGO was performed at Syncrude Research while MAT runs were carried out at CANMET. The authors thank Dave Famulak for operating the hydrotreating pilot plant, technologists at Syncrude Research for analytical services, John Stone at Syncrude Research for reviewing this manuscript, Tony Mankowski at Syncrude Technical for support this program, and Syncrude Canada Ltd. for permission to publish. EF940210V
