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Hydrotreating Characteristics Of Coked And Of Hydrocracked Gas Oils From Alberta Heavy Bituminous Oils With Commercial Ni-Mo Catalysts, And Prediction Of Some Product Properties
S. Kaliaguirie and A. Mahay (Editors), Cat atysis on the Energy Scene 19t5.,l Elsevier Science Publishers B.Y., Amsterdam -- Printed in The Netherlands
585
HYDROTREATING CHARACTERISTICS OF COKED AND OF HYDROCRACKED GAS OILS FROM ALBERTA HEAVY BITUMINOUS OILS WITH COMMERCIAL NI-MO CATALYSTS, AND PREDICTION OF SOME PRODUCT PROPERTIES E.C. SANFORD and S.M. YUI Research Department, Syncrude Canada Ltd., P. O. Box 5790, Edmonton, Alberta
ABSTRACT Pilot scale hydrotreating experiments have been conducted on three synthetic distillates using three commercial Ni-Mo catalysts. Kinetics of hydrodesulfurization (HDS), hydrodenitrogenation (HDN) and aromatics hydrogenation were studied, and catalyst activities were compared. Based on temperatures needed to attain target product quality while maintaining other operating conditions constant, all the catalysts were found to have essentially the same initial activities. Correlations were developed to predict the yield and some product properties, based on operating conditions used. The results show a good fit in all cases for the catalysts and feeds tested. INTRODUCTION Syncrude Canada Ltd. operates a surface mlnlng oil sand plant in Athabasca oil sands deposit and produces synthetic crude oil from extracted bitumen. This bitumen is currently upgraded by fluid coking followed by hydrotreating of the naphtha and gas oil. Syncrude is one of the world's largest individual users of hydrotreating catalysts. Product yields and operating cost are greatly affected by catalyst type. The Company is also interested in the hydrotreating charateristics of gas oils derived from northern Alberta bituminous feedstocks prepared by methods other than fluid coking, which may provide options for future plant capacity additions. For these reasons, screening studies of commercially available catalysts are regularly conducted. This report discusses results of a screening study on three commercial catalysts using coker gas oil from Athabasca bitumen and gas oils from the CANMET hydrocracking (ref. 1) of Cold Lake heavy oil vacuum residue. The latter is considered to be a difficult material to hydrotreat. EXPERIMENTAL The trickle bed hydrotreating pilot plant has three identical flow systems with three reactors set in a common fluidized sand bath which provides isothermal conditions. Each reactor is 1.66 cm i .d. and 90cm long, which meets the Mears criterion (ref. 2) for plug flow conditions. The system is once-through and the
586
treat gas is vented without recycling. Three feedstocks were used in this study: combined gas oil from the fluid coking of Athabasca bitumen (coker gas oil) from the Sync rude commercial plant, and light and heavy gas oils from the hydrocracking of Cold Lake heavy oil vacuum residue (hydrocracked LGO and HGO) from a CANMET hydrocracking pilot plant. The properties of these materials are summarized in Table 1. Since the gas oils from bitumen and heavy oil contain relatively high concentrations of nitrogen, denitrogenation becomes more important. Ni-Mo catalysts are considered to be superior for nitrogen removal. Catalysts from three different suppliers/ licensors were tested in this study. Prior to running the feedstocks, all catalysts were: • activated by sulfiding with hydrotreated kerosene with 1% sulfur equivalent I-butanethiol, and • precoked with coker gas oil to obtain a steady state activity. The variables selected are temperature(340--400 0C), pressure (7~11 MPa) and l). LHSV(0.5~1 hThe hydrogen rate was maintained at the same rate throughout the tests. TABLE 1 Properties of feedstock Density @ 200C, kg/m 3 Sulfur, wt% Nitrogen, wpprn Aromatics, % Simulated Distillation, IBP 10% 50% 90% FBP
Coker Gas Oil 967.6 4.12 2610
°c 197 268 362 480 603
Hydrocracked LGO 879.4 2.31 2300 50.0
Hydrocracked HGO 967.0 2.50 5140
121 194 281 358 423
318 350 405 480 541
RESULTS AND DISCUSSION Rate of Reaction Assuming plug flow, the rate of reaction including temperature and pressure terms can be expressed as -dC/dt
=
k exp(-E/RT) pmC n o
(1 )
where C = concentration of reactant; t = reaction time; k = frequency factor; " . 0 E = ac t lvatlon energy; R = gas constant; T = absolute temperature; P = pressure; and m,n = reaction order. By integrating, Equation 1 results in
587
I/C pn-l - I/C f n-l = (n-l)k exp(-E/RT) Pm/LHSV o
at n
(2 )
at nt-I
(3)
where subscript f and p of C represent feed and product, respectively, and LHSV is defined as feed rate/reactor volume. Kinetic parameters (m, n, ko and E) were determined by analyzing the experimental results. Kinetics of HDS It was found that 1.5th order dependence with respect to sulfur content gave the best fit to the data for all catalysts and feedstocks employed in this study. Reaction order m was determined to be 0.7 for all catalysts using hydrocracked LGO and HGO. The number of data for coker gas oil with different pressures was not sufficient to determine m distinctly. To compare with the results of the hydrocracked LGO and HGO, 0.7th order dependence was assumed for coker gas oil. Arrhenius plots for catalyst B (Fig. 1) show that the HDS rate constant for coker gas oil is quite close to that of the hydrocracked HGO. Similar results were obtained for the other catalysts. Kinetics of HDN The HDN occurs simultaneously with the HDS, but the % HDN is lower than the corresponding % HDS. A first order dependence with respect to nitrogen content gave the best fit to the data for all catalysts and feedstocks. Reaction order m with respect to pressure was determined to be 0.9 for hydrocracked and coker LGOs and 1.2 for hydrocracked HGO. Arrhenius plots for catalyst A (Fig. 1) shows that the rate constant of coker gas oil lies between those for hydrocracked LGO and HGO. Similar results were obtained for the other catalysts. Kinetics of Aromatics Saturation High aromatics content in middle distillates is detrimental to fuel quality, adversely affecting, for instance, smoke point of jet fuel and cetane number of diesel fuel. It is well known that there is a maximum % aromatics saturation at a certain temperature and the % saturation decreases above this temperature due to thermodynamic equilibrium control (ref. 3,4,5). Fig. '2 shows % aromatics saturation vs. operating conditions for hydrocracked LGO. Aromatics content was measured by the combination of the fluorescence indicator analysis (1950C-) and high pressure liquid chromatography (195 0C+) methods, and the total aromatics content was then calculated. The results indicate that maximum % saturation shifts to the right (higher temperature) with increasing pressure. The data in Fig. 2 also shows that the kinetic control is predominant rather than a thermodynamic equilibrium control under the conditions
588
..
...s:
9" c Q.
::E ......
on
'?
..
;e
50..----------------------..., HDS CATALYST B
20
10
0
~
~
I-
z
2
~
en
z
0
U
0.5
LtJ
~
0::
0.2 L-_L-_..L.-_..L-_...l-_...L-_....L.-_...J...._--!..._.......L.--'=~
1.46
1.50
1.54
1.58
1.62
1.66
5r-----------------------, HDN 'CATALYST A
2
I-
z ~(f) z
8
0.5 0.2 0.1
0.05
1.50
1.54
I
I
1.58
1.62
IOOOlT , K-
1
Fig. 1. Arrhenius plots of rate constant (HDS and HDN)
1.66
589 o
z o
~
80,---------,
CATALYST
Z
lJ.J
(!)
o
a:::
o >J:
(/)
o ~
« ~ o a::: «
7.1 0.7
PRESSURE. MPa LHSV. h- I
•• 7.1 10
8.8 0.7
88 1.0
CATALYST 'C
CATALYST B
A
60
40~~ ---.
u..
/'
20
~
/
340
360
~
~~.
'0-
340
380
~-
360
~ /'
340
380
---
--..- ',_ - - - . . .:-J-
. - _ _,-J
360
380
TEMPERATURE. 'C
Fig. 2.
Aromatics hydrogenation (feed: hydrocracked LGO)
010....------------------------, 0.08
0.06
=-t------__~=-~
0.04
AROMATICS HYDROGENATION CATALYST C
HYOROC;;;C;;;;--Yl_ lGO eo
0.03
0.02 I
1.(52
1.(54
1.(56
1.(58
IOOO/T. K-
Fig. 3.
1.62
1.60
1.64
1.66
I
Arrhenius plots of rate constant (aromatics hydrogenation)
used, particularly at the higher pressure (8.8 MPa). Kinetics for aromatics saturation are usually based on reversible reactions. To obtain the kinetic parameters, the equilibrium aromatics content must be determined (ref. 3) or a nonlinear regression technique employed using a large number of data points (ref. 4). However, since the data in this study indicates that kinetic control is predominant, an irreversible reaction has been assumed as a first approximation. Applying a similar method used for HDS/HDN kinetics, a first order dependence with respect to both aromatics content and pressure was found. Arrhenius plots of rate constant with catalyst C are shown in Fig. 3. The comparatively low correlation coefficients observed for aromatics saturation (r2 = 0.8 vs 0.9 for HDS/HDN) are probably due to the fact that analytical data for aromatics content are less accurate and that the aromatics are partially in equilibrium at the lower pressure (7.1 MPa).
590
Comparison of Catalyst Activity Regarding HDS, catalyst A is marginally more active (1 or 2 °c lower) than the other two catalysts at typical operating conditions. Regarding HDN, for coker gas oil and hydrocracked LGO, catalysts A and B have higher activity than catalyst C, but for hydrocracked HGO all three catalysts have essentially the same activity. Regarding aromatics saturation, catalyst A is marginally more active (1 or 2% lower in aromatics content at the same severity) than the other two catalysts. Product Density According to a block pricing scheme provided by Alberta Petroleum Marketing Commission, a crude oil gravity premium is awarded to the synthetic oil producer for the lighter crude oil group (ref. 6). Therefore, product density is important from an economic view point, although it is an incidental result of the hydrotreating reaction. Fig. 4 shows the density changes for the hydrocracked HGO at the severities. Similar results were obtained for the other two feedstocks. It is interesting to note that: • all three catalysts show a similar result; there is no trend that would favor one catalyst over another • the product density decreases as the temperature, pressure or residence time (I/LHSV) increases. 7.1 MPo
0.97~FEED
0.96~1
11\
11\
II \ ~ II \ \\
, 1\ ,
0.95
o o o
N
I
>-
0.94~
11\
III I I' 1\'
\\'
\.>"
11,
0.92
-
11\
\, \ "" " \ " ~ " ,'
\"
\ \
-,
", ' '~
0.93
\\
-
360"C
w o
0.90
,
o
"
I
I
I
1.0
1.5
2.0
- - - . . 360·C
"-
380.C
~400~
400"C
0.5
0.89~-""""---J~-""""-"""'"
-
'I. ~
' - " ' " 38O"C
0.91
z
,,
III
,, '
\,
t
(f)
~I
.CATALYST A .CATALYST B .CATALYST C
\\ \ \
8.8 MFa
t. FEED
0
0.5
1.0
1.5
-
2.0
I/LH5V. h
Fig. 4.
Product density at various operating conditions (feed: hydrocracked HGO)
591
Based on this information, a correlation to predict the density was determined for hydrocracked HGO as follows: SV O.018 (4) r 2 = 0.976 0.9617 1 0.124 0.022 p 360 8 where d = product density at 20 °c (kg/m3); df = feed density at 20 °c (kg/m3); p 0 0 1360 = reduced temperature ( C/360 C); P8 = reduced pressure (MPa/8 MPa); SV = LHSV without dimension. Similar results, but different constants, were obtained for the other two feedstocks. Liquid Product Yield Like the density and kinetic results, no significant differences of the yields among the catalysts have been noticed. Assuming a similar correlation as Equation 4, the following equation was obtained for coker gas oil with combined catalysts: Yield (%)
104.93
1 0.205 P 0.015 360 8 , SvO.001
r2
0.832
(5)
Aniline Point Aniline point is a diesel fuel property that has been used for many years to predict cetane number. No significant differences of aniline point among the catalysts have been noticed. Assuming a similar correlation as Equation 5, the following equation was obtained for hydrocracked LGO: AP
~
AP f
1 0.599 P 0.102 360 8 SvO. 056
= 1.2353
r2
= 0.865
(6)
where AP p and AP f are aniline point of product and feed (47.3 °C) in °C. Cetane Number Cetane number (CN) of hydrotreated CANME1 hydrocracked LGO was measured for the topped product (1950C+). Depending on operating severities, the CN ranges from 43 to 47 whereas that of diesel fuel originated from coker gas oil is about 34 (ref. 7). An excellent agreement was obtained between observed CN and cetane index by Steere and Nunn (ref. 7): Cetane Index where AP
=
13.072 + 0.4710 AP + 0.0007685 Ap 2
= aniline
point in °C.
(7)
592
CONCLUSIONS • Assuming plug flow, the reaction rate for HDS and HDN can be expressed as a function of reactant concentration, flow rate, temperature, and pressure as shown in Equation 1. The kinetic parameters were experimentally determined. • The HDS rate for coker gas oil from Athabasca bitumen is quite close to that of CANMET hydrocracked HGO from Cold Lake heavy oil vacuum residue whereas the sulfur content in coker gas oil is higher. The HDN rate for coker gas oil lies between those of hydrocracked LGO and HGO. • Under the operating conditions employed; aromatics saturation, which occurs simultaneously with HDS and HDN, was expressed by an irreversible first order reaction with respect to both pressure and concentration. • Based on the kinetic results, the activities of all catalysts are essentially the same for all feedstocks considering the experimental error. • The liquid product yield, density and aniline point can be estimated by the power form of operating severities. There is no trend that would favor one catalyst over another. • The diesel fraction from hydrocracked distillates is superior to a similar fraction from coker products. A published cetane index with aniline point terms gives excellent agreement with observed cetane number. ACKNOWLEDGMENT This work was assisted by the following Syncrude personnel, i.e., B. Andrichuk, T. Bulmer, J. Cooley, E. Fukuda, A. Maskwa and K. Nastiuk. The assistance of R. Logie of EMR and A. Silva and co-workers of Petro Canada, in procuring the CANMET hydrocracking distillates and providing useful input into the design of the experiments and analyses of the data, is also acknowledged. REFERENCES ~
2 3 4 5 6 7
M.A. Menzies, A. Silva, J. Hepton and R. Logie, 1981 NPRA Annual Meeting, San Antonio, Texas, Paper No. AM-81-34. D.E. Mears, Chern. Eng. Sci. 26 (1971) 1361-1366. M.F. Wilson and J.F. Kriz, Fuel, 63 (1984) 190-196. R.H. Heck and T.R. Stein, Am. Chern. Soc. Div. Petrol. Chem. Reprints, 22 (1977) 3, 948-961. D.C. McCulloch, Oil and Gas J. 73 (1975) 29, 53-58. Oilweek, 32 (1982) Jan. pp. 10 and 43. D.E. Steere and T.J. Nunn, SAE Technical Paper 790922 (1979) 1-12.
585
HYDROTREATING CHARACTERISTICS OF COKED AND OF HYDROCRACKED GAS OILS FROM ALBERTA HEAVY BITUMINOUS OILS WITH COMMERCIAL NI-MO CATALYSTS, AND PREDICTION OF SOME PRODUCT PROPERTIES E.C. SANFORD and S.M. YUI Research Department, Syncrude Canada Ltd., P. O. Box 5790, Edmonton, Alberta
ABSTRACT Pilot scale hydrotreating experiments have been conducted on three synthetic distillates using three commercial Ni-Mo catalysts. Kinetics of hydrodesulfurization (HDS), hydrodenitrogenation (HDN) and aromatics hydrogenation were studied, and catalyst activities were compared. Based on temperatures needed to attain target product quality while maintaining other operating conditions constant, all the catalysts were found to have essentially the same initial activities. Correlations were developed to predict the yield and some product properties, based on operating conditions used. The results show a good fit in all cases for the catalysts and feeds tested. INTRODUCTION Syncrude Canada Ltd. operates a surface mlnlng oil sand plant in Athabasca oil sands deposit and produces synthetic crude oil from extracted bitumen. This bitumen is currently upgraded by fluid coking followed by hydrotreating of the naphtha and gas oil. Syncrude is one of the world's largest individual users of hydrotreating catalysts. Product yields and operating cost are greatly affected by catalyst type. The Company is also interested in the hydrotreating charateristics of gas oils derived from northern Alberta bituminous feedstocks prepared by methods other than fluid coking, which may provide options for future plant capacity additions. For these reasons, screening studies of commercially available catalysts are regularly conducted. This report discusses results of a screening study on three commercial catalysts using coker gas oil from Athabasca bitumen and gas oils from the CANMET hydrocracking (ref. 1) of Cold Lake heavy oil vacuum residue. The latter is considered to be a difficult material to hydrotreat. EXPERIMENTAL The trickle bed hydrotreating pilot plant has three identical flow systems with three reactors set in a common fluidized sand bath which provides isothermal conditions. Each reactor is 1.66 cm i .d. and 90cm long, which meets the Mears criterion (ref. 2) for plug flow conditions. The system is once-through and the
586
treat gas is vented without recycling. Three feedstocks were used in this study: combined gas oil from the fluid coking of Athabasca bitumen (coker gas oil) from the Sync rude commercial plant, and light and heavy gas oils from the hydrocracking of Cold Lake heavy oil vacuum residue (hydrocracked LGO and HGO) from a CANMET hydrocracking pilot plant. The properties of these materials are summarized in Table 1. Since the gas oils from bitumen and heavy oil contain relatively high concentrations of nitrogen, denitrogenation becomes more important. Ni-Mo catalysts are considered to be superior for nitrogen removal. Catalysts from three different suppliers/ licensors were tested in this study. Prior to running the feedstocks, all catalysts were: • activated by sulfiding with hydrotreated kerosene with 1% sulfur equivalent I-butanethiol, and • precoked with coker gas oil to obtain a steady state activity. The variables selected are temperature(340--400 0C), pressure (7~11 MPa) and l). LHSV(0.5~1 hThe hydrogen rate was maintained at the same rate throughout the tests. TABLE 1 Properties of feedstock Density @ 200C, kg/m 3 Sulfur, wt% Nitrogen, wpprn Aromatics, % Simulated Distillation, IBP 10% 50% 90% FBP
Coker Gas Oil 967.6 4.12 2610
°c 197 268 362 480 603
Hydrocracked LGO 879.4 2.31 2300 50.0
Hydrocracked HGO 967.0 2.50 5140
121 194 281 358 423
318 350 405 480 541
RESULTS AND DISCUSSION Rate of Reaction Assuming plug flow, the rate of reaction including temperature and pressure terms can be expressed as -dC/dt
=
k exp(-E/RT) pmC n o
(1 )
where C = concentration of reactant; t = reaction time; k = frequency factor; " . 0 E = ac t lvatlon energy; R = gas constant; T = absolute temperature; P = pressure; and m,n = reaction order. By integrating, Equation 1 results in
587
I/C pn-l - I/C f n-l = (n-l)k exp(-E/RT) Pm/LHSV o
at n
(2 )
at nt-I
(3)
where subscript f and p of C represent feed and product, respectively, and LHSV is defined as feed rate/reactor volume. Kinetic parameters (m, n, ko and E) were determined by analyzing the experimental results. Kinetics of HDS It was found that 1.5th order dependence with respect to sulfur content gave the best fit to the data for all catalysts and feedstocks employed in this study. Reaction order m was determined to be 0.7 for all catalysts using hydrocracked LGO and HGO. The number of data for coker gas oil with different pressures was not sufficient to determine m distinctly. To compare with the results of the hydrocracked LGO and HGO, 0.7th order dependence was assumed for coker gas oil. Arrhenius plots for catalyst B (Fig. 1) show that the HDS rate constant for coker gas oil is quite close to that of the hydrocracked HGO. Similar results were obtained for the other catalysts. Kinetics of HDN The HDN occurs simultaneously with the HDS, but the % HDN is lower than the corresponding % HDS. A first order dependence with respect to nitrogen content gave the best fit to the data for all catalysts and feedstocks. Reaction order m with respect to pressure was determined to be 0.9 for hydrocracked and coker LGOs and 1.2 for hydrocracked HGO. Arrhenius plots for catalyst A (Fig. 1) shows that the rate constant of coker gas oil lies between those for hydrocracked LGO and HGO. Similar results were obtained for the other catalysts. Kinetics of Aromatics Saturation High aromatics content in middle distillates is detrimental to fuel quality, adversely affecting, for instance, smoke point of jet fuel and cetane number of diesel fuel. It is well known that there is a maximum % aromatics saturation at a certain temperature and the % saturation decreases above this temperature due to thermodynamic equilibrium control (ref. 3,4,5). Fig. '2 shows % aromatics saturation vs. operating conditions for hydrocracked LGO. Aromatics content was measured by the combination of the fluorescence indicator analysis (1950C-) and high pressure liquid chromatography (195 0C+) methods, and the total aromatics content was then calculated. The results indicate that maximum % saturation shifts to the right (higher temperature) with increasing pressure. The data in Fig. 2 also shows that the kinetic control is predominant rather than a thermodynamic equilibrium control under the conditions
588
..
...s:
9" c Q.
::E ......
on
'?
..
;e
50..----------------------..., HDS CATALYST B
20
10
0
~
~
I-
z
2
~
en
z
0
U
0.5
LtJ
~
0::
0.2 L-_L-_..L.-_..L-_...l-_...L-_....L.-_...J...._--!..._.......L.--'=~
1.46
1.50
1.54
1.58
1.62
1.66
5r-----------------------, HDN 'CATALYST A
2
I-
z ~(f) z
8
0.5 0.2 0.1
0.05
1.50
1.54
I
I
1.58
1.62
IOOOlT , K-
1
Fig. 1. Arrhenius plots of rate constant (HDS and HDN)
1.66
589 o
z o
~
80,---------,
CATALYST
Z
lJ.J
(!)
o
a:::
o >J:
(/)
o ~
« ~ o a::: «
7.1 0.7
PRESSURE. MPa LHSV. h- I
•• 7.1 10
8.8 0.7
88 1.0
CATALYST 'C
CATALYST B
A
60
40~~ ---.
u..
/'
20
~
/
340
360
~
~~.
'0-
340
380
~-
360
~ /'
340
380
---
--..- ',_ - - - . . .:-J-
. - _ _,-J
360
380
TEMPERATURE. 'C
Fig. 2.
Aromatics hydrogenation (feed: hydrocracked LGO)
010....------------------------, 0.08
0.06
=-t------__~=-~
0.04
AROMATICS HYDROGENATION CATALYST C
HYOROC;;;C;;;;--Yl_ lGO eo
0.03
0.02 I
1.(52
1.(54
1.(56
1.(58
IOOO/T. K-
Fig. 3.
1.62
1.60
1.64
1.66
I
Arrhenius plots of rate constant (aromatics hydrogenation)
used, particularly at the higher pressure (8.8 MPa). Kinetics for aromatics saturation are usually based on reversible reactions. To obtain the kinetic parameters, the equilibrium aromatics content must be determined (ref. 3) or a nonlinear regression technique employed using a large number of data points (ref. 4). However, since the data in this study indicates that kinetic control is predominant, an irreversible reaction has been assumed as a first approximation. Applying a similar method used for HDS/HDN kinetics, a first order dependence with respect to both aromatics content and pressure was found. Arrhenius plots of rate constant with catalyst C are shown in Fig. 3. The comparatively low correlation coefficients observed for aromatics saturation (r2 = 0.8 vs 0.9 for HDS/HDN) are probably due to the fact that analytical data for aromatics content are less accurate and that the aromatics are partially in equilibrium at the lower pressure (7.1 MPa).
590
Comparison of Catalyst Activity Regarding HDS, catalyst A is marginally more active (1 or 2 °c lower) than the other two catalysts at typical operating conditions. Regarding HDN, for coker gas oil and hydrocracked LGO, catalysts A and B have higher activity than catalyst C, but for hydrocracked HGO all three catalysts have essentially the same activity. Regarding aromatics saturation, catalyst A is marginally more active (1 or 2% lower in aromatics content at the same severity) than the other two catalysts. Product Density According to a block pricing scheme provided by Alberta Petroleum Marketing Commission, a crude oil gravity premium is awarded to the synthetic oil producer for the lighter crude oil group (ref. 6). Therefore, product density is important from an economic view point, although it is an incidental result of the hydrotreating reaction. Fig. 4 shows the density changes for the hydrocracked HGO at the severities. Similar results were obtained for the other two feedstocks. It is interesting to note that: • all three catalysts show a similar result; there is no trend that would favor one catalyst over another • the product density decreases as the temperature, pressure or residence time (I/LHSV) increases. 7.1 MPo
0.97~FEED
0.96~1
11\
11\
II \ ~ II \ \\
, 1\ ,
0.95
o o o
N
I
>-
0.94~
11\
III I I' 1\'
\\'
\.>"
11,
0.92
-
11\
\, \ "" " \ " ~ " ,'
\"
\ \
-,
", ' '~
0.93
\\
-
360"C
w o
0.90
,
o
"
I
I
I
1.0
1.5
2.0
- - - . . 360·C
"-
380.C
~400~
400"C
0.5
0.89~-""""---J~-""""-"""'"
-
'I. ~
' - " ' " 38O"C
0.91
z
,,
III
,, '
\,
t
(f)
~I
.CATALYST A .CATALYST B .CATALYST C
\\ \ \
8.8 MFa
t. FEED
0
0.5
1.0
1.5
-
2.0
I/LH5V. h
Fig. 4.
Product density at various operating conditions (feed: hydrocracked HGO)
591
Based on this information, a correlation to predict the density was determined for hydrocracked HGO as follows: SV O.018 (4) r 2 = 0.976 0.9617 1 0.124 0.022 p 360 8 where d = product density at 20 °c (kg/m3); df = feed density at 20 °c (kg/m3); p 0 0 1360 = reduced temperature ( C/360 C); P8 = reduced pressure (MPa/8 MPa); SV = LHSV without dimension. Similar results, but different constants, were obtained for the other two feedstocks. Liquid Product Yield Like the density and kinetic results, no significant differences of the yields among the catalysts have been noticed. Assuming a similar correlation as Equation 4, the following equation was obtained for coker gas oil with combined catalysts: Yield (%)
104.93
1 0.205 P 0.015 360 8 , SvO.001
r2
0.832
(5)
Aniline Point Aniline point is a diesel fuel property that has been used for many years to predict cetane number. No significant differences of aniline point among the catalysts have been noticed. Assuming a similar correlation as Equation 5, the following equation was obtained for hydrocracked LGO: AP
~
AP f
1 0.599 P 0.102 360 8 SvO. 056
= 1.2353
r2
= 0.865
(6)
where AP p and AP f are aniline point of product and feed (47.3 °C) in °C. Cetane Number Cetane number (CN) of hydrotreated CANME1 hydrocracked LGO was measured for the topped product (1950C+). Depending on operating severities, the CN ranges from 43 to 47 whereas that of diesel fuel originated from coker gas oil is about 34 (ref. 7). An excellent agreement was obtained between observed CN and cetane index by Steere and Nunn (ref. 7): Cetane Index where AP
=
13.072 + 0.4710 AP + 0.0007685 Ap 2
= aniline
point in °C.
(7)
592
CONCLUSIONS • Assuming plug flow, the reaction rate for HDS and HDN can be expressed as a function of reactant concentration, flow rate, temperature, and pressure as shown in Equation 1. The kinetic parameters were experimentally determined. • The HDS rate for coker gas oil from Athabasca bitumen is quite close to that of CANMET hydrocracked HGO from Cold Lake heavy oil vacuum residue whereas the sulfur content in coker gas oil is higher. The HDN rate for coker gas oil lies between those of hydrocracked LGO and HGO. • Under the operating conditions employed; aromatics saturation, which occurs simultaneously with HDS and HDN, was expressed by an irreversible first order reaction with respect to both pressure and concentration. • Based on the kinetic results, the activities of all catalysts are essentially the same for all feedstocks considering the experimental error. • The liquid product yield, density and aniline point can be estimated by the power form of operating severities. There is no trend that would favor one catalyst over another. • The diesel fraction from hydrocracked distillates is superior to a similar fraction from coker products. A published cetane index with aniline point terms gives excellent agreement with observed cetane number. ACKNOWLEDGMENT This work was assisted by the following Syncrude personnel, i.e., B. Andrichuk, T. Bulmer, J. Cooley, E. Fukuda, A. Maskwa and K. Nastiuk. The assistance of R. Logie of EMR and A. Silva and co-workers of Petro Canada, in procuring the CANMET hydrocracking distillates and providing useful input into the design of the experiments and analyses of the data, is also acknowledged. REFERENCES ~
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M.A. Menzies, A. Silva, J. Hepton and R. Logie, 1981 NPRA Annual Meeting, San Antonio, Texas, Paper No. AM-81-34. D.E. Mears, Chern. Eng. Sci. 26 (1971) 1361-1366. M.F. Wilson and J.F. Kriz, Fuel, 63 (1984) 190-196. R.H. Heck and T.R. Stein, Am. Chern. Soc. Div. Petrol. Chem. Reprints, 22 (1977) 3, 948-961. D.C. McCulloch, Oil and Gas J. 73 (1975) 29, 53-58. Oilweek, 32 (1982) Jan. pp. 10 and 43. D.E. Steere and T.J. Nunn, SAE Technical Paper 790922 (1979) 1-12.