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Hydrocessing of an asphaltenic coal residue
Coal Science
J.A. Pajares and J.M.D. Tasc6n (Editors) 9 1995 Elsevier Science B.V. All rights reserved.
HYDROCESSING
1467
OF AN ASPHALTENIC COAL RESIDUE
Benito, A.M., Martinez, M.T. and Miranda, J.L. Instituto de Carboquimica. C.S.LC., P.O. Box 589. $0080-ZARAGOZA. SPAIN
A residue from deasphalting of coal liquids obtained by direct coal liquefaction of a subbituminous Spanish coal was processed by thermal and catalytic hydrotreatment under the conditions of hydrovisbreaking and hydrocracking respectively. The hydrotreatment reduced the viscosity of the starting material and the catalyst produced the inhibition of the coke formation.
1. INTRODUCTION A residue from coal liquefaction or pyrolysis, a petroleum residue or a residual oil is characterised by a high viscosity, high heteroatoms and asphaltene contents, high molecular weight, high mean boiling point and low H/C ratio. Then, the objectives in the processes of hydrogen addition to residua or to heavy oils will be mainly to increase the H/C atomic ratio, to remove the metals and to reduce the heteroatom content (reaching a good desulfurization is specially important) to improve the product quality and to make easier the subsequent treatments [ 1]. The hydroconversion processes can be thermal or catalytic or consist of several thermal and/or catalytic stages. The hydroprocessing conditions currently used are high temperature and pressure, high hydrogen/feedstock ratios and high activity catalysts. Among the processes of hydroconversion we focus our attention on hydrovisbreaking (thermal hydroprocessing) and hydrocracking (catalytic hydroprocessing). In the range of temperatures currently applied in hydroconversion processes, the driving force of the conversion reactions is essentially a thermal activation. The catalyst, the hydrogen pressure and the sophistication of the techniques basically limit and control the non-desirable side reactions of condensation [2]. These processes are very flexible and can be applied to a wide range of feedstocks from light naphthas to vacuum residues [3]. In this paper, a residue from deasphalting of coal liquids was processed by thermal and catalytic hydrotreatment under similar conditions to those used in hydrovisbreaking and hydrocracking processes respectively in petroleum industry. The aim of this work is to study the effect of the temperature and residence time during the hydroprocessing experiments by measuring the change produced in viscosity, coke content, elemental analysis and boiling point distribution.
1468 2. EXPERIMENTAL The material used in this work has been a residue from deasphalting of coal liquids obtained by direct liquefaction of a subbituminous Spanish coal. Operating conditions of the liquefaction and deasphalting processes have already been described in detail [4,5]. Experiments were conducted batchwise using 15 MPa of hydrogen pressure at the operating conditions. Temperature and residence time were the main variables modified during the processes. Experiments at 425, 450 and 475 *C of temperature and at 5, 10, 20, 30 y 40 minutes of residence time were carried out. A commercial catalyst, Harshaw HT-500E (NiMo) was used in the hydrocracking process in a catalyst to sample ratio of 1/5. The hydrovisbroken products obtained in each experiment were analysed for viscosity (measured at 65 ~ with Canon-Fenske viscometers (ASTM D445, -86, ASTM D-446, -85)), coke content (determined by ultrasonic extraction as the material insoluble in toluene with a solvent to product ratio of 5), boiling point distribution (determined by gas chromatography in a Varian 3400 chromatographer with capillary SE 50 column and FID detector in the conditions: Injector temperature: 250 ~ detector temperature: 250 ~ initial temperature: 50 ~ (5 minutes); final temperature: 300 ~ and temperature gradient: 5 ~ Calibrating was carried out with several pure compounds (naphthalene, phenanthrene, fluoranthene and chrysene) and n-decane as internal standard was used for quantification), elemental analysis (C, H, N and S elemental analysis was carried out in an elemental analyser CARLO ERBA CHNSO model EA1108)
3. RESULTS The feedstock used in these experiments has a heavy nature (only 23.63 % boils under 350 o C and from the rest 14.95 % is coke) and it is characterised by a high viscosity (4608 cSt, 65 ~ and high heteroatom content (C:81.78%; H:6.38%; N:1.55%; S:4.65%;O:5.64%). During the course of the reaction, the heavy fraction content (H) (b.p.< 350 ~ decreased with the time while the concentration of the light fraction (L) (b.p.>350 ~ gas (G) and coke (C) increased with the time (Figure 1). The cracking reaction to produce light distillates followed a first order kinetic for all the temperatures essayed and a lineal correlation between coke and distillates has been observed in the hydrovisbreaking experiments. Taking into account that there is an hydrogen excess all the time and that the hydrogen pressure effect is the same in all the experiments, it can be considered that hydrogen concentration remains constant. Kinetic study of both hydroprocessing treatments has been performed by proposing a first order mechanism. Two processes have been considered in this mechanism: 1)The cracking of the fraction with b.p.>350 ~ to produce lighter structures (liquid fraction with b.p.<350 ~ and Gases) and 2) the coke formation as a result of the condensation reactions produced in this
1469 formation, has an activation energy much higher than the cracking reaction. Consequently, the coke formation was more important as the temperature increased. Thermodynamic control-like was observed in which as the temperature increased the tendency was to form the more stable product, in this case was the coke fraction that is a final product, because L and G fractions actually can condense to produce H. At the lowest temperature essayed (425 o C) the coke content hardly was modified with the time, but as the temperature went up an increase of C with the time was observed. The maximum coke percentage was reached at the more severe conditions used (475 ~ and 40 minutes) in which a light decrease in L was observed (Figure 1). Then at 425 ~ a kinetic control seems to conduct the reaction. That is, the process with lower activation energy (cracking reaction) was more favourable and the reaction with higher activation energy (condensation reaction) remained almost completely inhibited. In the catalytic hydroprocessing, the activation energy for the cracking reaction was found to be lower than on the hydrovisbreaking process and a total inhibition of the formation of coke was observed. Then, the effect of the utilised catalyst was reducing the activation energy for the cracking reaction making this process more favourable than the condensation reaction. The maximum conversion to L obtained during the hydrovisbreaking experiments was 2 1 % and at these conditions (450 ~ 40 minutes) the conversion to coke was 9 % and to gases 5%. During the catalytic process, the maximum conversion to L was 28 % and the conversion to gases was 7 %. Then, the catalyst has allowed a higher conversion to light products and the production of gases was lower. The main effect observed in these experiments has been the inhibition of the condensation reaction to produce coke, as compared with previous studies of thermal treatment of the same residue done in our laboratory. A total inhibition of the coke formation has been observed when a catalyst was used. In both processes, a sharp decrease of the viscosity with time and temperature was produced, going from 4600 cSt (at 65 *C) in the starting residue to 147 cSt in the hydrovisbreaking process and to 79 cSt in the hydrocracking experiments. Table 1.- Kinetic parameters obtained in the hydroprocessing experiments Hydrovisbreaking Temperature (~ 425 450 475 Ea(kJ/mol)
Hydrocracking
*kl(S"1)
*k2(s"1)
*kl(S "1)
3.10.10 -5 7.50.10 -5 9.59.10 -5 97
1.67.10 "5 3.71 -10 -5 8.89.10 -5 145
4.98 -10 -5 6.16.10 -5 12.60.10 -5 80
*kl kinetic constant for the cracking reaction k2 kinetic constant for the coke formation
1470 60.
~.---------
H
o•"50. 425 0C
..........................
v
t- 40. O
.m
9 L
,. ........... . ........................ ,, ........................ ,~ ........................
30. cO
0 to
20. ~
.....
~
....................
~" ........................
.
.........
C
(.) 10.
_
O, 0
~
,
~
10
O
............ : ........... ; . . . . . . . . . . . . . . . . . . . . . . . .
20
30
4C)
T i m e (min)
~'
r o
5o
450 oC
............... ~ ........................
"----------~
H
40
L
".1~
~
........................
t-
~ ~ e"
20.
C _~
~
"
lb
0 ,--"-'-
o
.............. i, ........................ 1,........................ 9
........................ I-,........................ . I-,........................ . z G
2o
3o
4b
T i m e (min)
6o
H
50
............................................................. . .......iii:::::::"......'
u f-
_
~
O
__
9
10 9
Or
0
~. . . . . . . .
,
10
9
i
Time
. . . . . . . . . . . . . . . .|
-
20
30
G
40
(min)
Figure 1.- Evolution of the heavy (H), light (L), gas (G) and coke (C) fractions during the hydroprocessing experiments (the solid lines represent the hydrovisbreaking experiments and the dot lines represent the hydrocracking experiments). REFERENCES
1. Teichmann, D.P. Hydrocarbon Processing, 1982, 61(5), 105. 2. Sikoma, J.G., Hydrocarb. Proc., 1980, 59(6), 73. 3. Mavity, V.T., Ward, J.W. and Whitebread, K.E. Hydrocarbon processing, 1978, 57(11),157. 4 Benito, A.M., Brower, L., Martinez, M.T., Severin, D. and Fernandez, I. Accepted for publication in Fuel Science and Technology International (17-2-94). 5. Martinez, M.T., Fem~.ndez, I., Benito, A.M., Cebolla, V., Miranda, J.L. and Oelert, H.H., Fuel Processing Technology, 1993, 33, 159.
J.A. Pajares and J.M.D. Tasc6n (Editors) 9 1995 Elsevier Science B.V. All rights reserved.
HYDROCESSING
1467
OF AN ASPHALTENIC COAL RESIDUE
Benito, A.M., Martinez, M.T. and Miranda, J.L. Instituto de Carboquimica. C.S.LC., P.O. Box 589. $0080-ZARAGOZA. SPAIN
A residue from deasphalting of coal liquids obtained by direct coal liquefaction of a subbituminous Spanish coal was processed by thermal and catalytic hydrotreatment under the conditions of hydrovisbreaking and hydrocracking respectively. The hydrotreatment reduced the viscosity of the starting material and the catalyst produced the inhibition of the coke formation.
1. INTRODUCTION A residue from coal liquefaction or pyrolysis, a petroleum residue or a residual oil is characterised by a high viscosity, high heteroatoms and asphaltene contents, high molecular weight, high mean boiling point and low H/C ratio. Then, the objectives in the processes of hydrogen addition to residua or to heavy oils will be mainly to increase the H/C atomic ratio, to remove the metals and to reduce the heteroatom content (reaching a good desulfurization is specially important) to improve the product quality and to make easier the subsequent treatments [ 1]. The hydroconversion processes can be thermal or catalytic or consist of several thermal and/or catalytic stages. The hydroprocessing conditions currently used are high temperature and pressure, high hydrogen/feedstock ratios and high activity catalysts. Among the processes of hydroconversion we focus our attention on hydrovisbreaking (thermal hydroprocessing) and hydrocracking (catalytic hydroprocessing). In the range of temperatures currently applied in hydroconversion processes, the driving force of the conversion reactions is essentially a thermal activation. The catalyst, the hydrogen pressure and the sophistication of the techniques basically limit and control the non-desirable side reactions of condensation [2]. These processes are very flexible and can be applied to a wide range of feedstocks from light naphthas to vacuum residues [3]. In this paper, a residue from deasphalting of coal liquids was processed by thermal and catalytic hydrotreatment under similar conditions to those used in hydrovisbreaking and hydrocracking processes respectively in petroleum industry. The aim of this work is to study the effect of the temperature and residence time during the hydroprocessing experiments by measuring the change produced in viscosity, coke content, elemental analysis and boiling point distribution.
1468 2. EXPERIMENTAL The material used in this work has been a residue from deasphalting of coal liquids obtained by direct liquefaction of a subbituminous Spanish coal. Operating conditions of the liquefaction and deasphalting processes have already been described in detail [4,5]. Experiments were conducted batchwise using 15 MPa of hydrogen pressure at the operating conditions. Temperature and residence time were the main variables modified during the processes. Experiments at 425, 450 and 475 *C of temperature and at 5, 10, 20, 30 y 40 minutes of residence time were carried out. A commercial catalyst, Harshaw HT-500E (NiMo) was used in the hydrocracking process in a catalyst to sample ratio of 1/5. The hydrovisbroken products obtained in each experiment were analysed for viscosity (measured at 65 ~ with Canon-Fenske viscometers (ASTM D445, -86, ASTM D-446, -85)), coke content (determined by ultrasonic extraction as the material insoluble in toluene with a solvent to product ratio of 5), boiling point distribution (determined by gas chromatography in a Varian 3400 chromatographer with capillary SE 50 column and FID detector in the conditions: Injector temperature: 250 ~ detector temperature: 250 ~ initial temperature: 50 ~ (5 minutes); final temperature: 300 ~ and temperature gradient: 5 ~ Calibrating was carried out with several pure compounds (naphthalene, phenanthrene, fluoranthene and chrysene) and n-decane as internal standard was used for quantification), elemental analysis (C, H, N and S elemental analysis was carried out in an elemental analyser CARLO ERBA CHNSO model EA1108)
3. RESULTS The feedstock used in these experiments has a heavy nature (only 23.63 % boils under 350 o C and from the rest 14.95 % is coke) and it is characterised by a high viscosity (4608 cSt, 65 ~ and high heteroatom content (C:81.78%; H:6.38%; N:1.55%; S:4.65%;O:5.64%). During the course of the reaction, the heavy fraction content (H) (b.p.< 350 ~ decreased with the time while the concentration of the light fraction (L) (b.p.>350 ~ gas (G) and coke (C) increased with the time (Figure 1). The cracking reaction to produce light distillates followed a first order kinetic for all the temperatures essayed and a lineal correlation between coke and distillates has been observed in the hydrovisbreaking experiments. Taking into account that there is an hydrogen excess all the time and that the hydrogen pressure effect is the same in all the experiments, it can be considered that hydrogen concentration remains constant. Kinetic study of both hydroprocessing treatments has been performed by proposing a first order mechanism. Two processes have been considered in this mechanism: 1)The cracking of the fraction with b.p.>350 ~ to produce lighter structures (liquid fraction with b.p.<350 ~ and Gases) and 2) the coke formation as a result of the condensation reactions produced in this
1469 formation, has an activation energy much higher than the cracking reaction. Consequently, the coke formation was more important as the temperature increased. Thermodynamic control-like was observed in which as the temperature increased the tendency was to form the more stable product, in this case was the coke fraction that is a final product, because L and G fractions actually can condense to produce H. At the lowest temperature essayed (425 o C) the coke content hardly was modified with the time, but as the temperature went up an increase of C with the time was observed. The maximum coke percentage was reached at the more severe conditions used (475 ~ and 40 minutes) in which a light decrease in L was observed (Figure 1). Then at 425 ~ a kinetic control seems to conduct the reaction. That is, the process with lower activation energy (cracking reaction) was more favourable and the reaction with higher activation energy (condensation reaction) remained almost completely inhibited. In the catalytic hydroprocessing, the activation energy for the cracking reaction was found to be lower than on the hydrovisbreaking process and a total inhibition of the formation of coke was observed. Then, the effect of the utilised catalyst was reducing the activation energy for the cracking reaction making this process more favourable than the condensation reaction. The maximum conversion to L obtained during the hydrovisbreaking experiments was 2 1 % and at these conditions (450 ~ 40 minutes) the conversion to coke was 9 % and to gases 5%. During the catalytic process, the maximum conversion to L was 28 % and the conversion to gases was 7 %. Then, the catalyst has allowed a higher conversion to light products and the production of gases was lower. The main effect observed in these experiments has been the inhibition of the condensation reaction to produce coke, as compared with previous studies of thermal treatment of the same residue done in our laboratory. A total inhibition of the coke formation has been observed when a catalyst was used. In both processes, a sharp decrease of the viscosity with time and temperature was produced, going from 4600 cSt (at 65 *C) in the starting residue to 147 cSt in the hydrovisbreaking process and to 79 cSt in the hydrocracking experiments. Table 1.- Kinetic parameters obtained in the hydroprocessing experiments Hydrovisbreaking Temperature (~ 425 450 475 Ea(kJ/mol)
Hydrocracking
*kl(S"1)
*k2(s"1)
*kl(S "1)
3.10.10 -5 7.50.10 -5 9.59.10 -5 97
1.67.10 "5 3.71 -10 -5 8.89.10 -5 145
4.98 -10 -5 6.16.10 -5 12.60.10 -5 80
*kl kinetic constant for the cracking reaction k2 kinetic constant for the coke formation
1470 60.
~.---------
H
o•"50. 425 0C
..........................
v
t- 40. O
.m
9 L
,. ........... . ........................ ,, ........................ ,~ ........................
30. cO
0 to
20. ~
.....
~
....................
~" ........................
.
.........
C
(.) 10.
_
O, 0
~
,
~
10
O
............ : ........... ; . . . . . . . . . . . . . . . . . . . . . . . .
20
30
4C)
T i m e (min)
~'
r o
5o
450 oC
............... ~ ........................
"----------~
H
40
L
".1~
~
........................
t-
~ ~ e"
20.
C _~
~
"
lb
0 ,--"-'-
o
.............. i, ........................ 1,........................ 9
........................ I-,........................ . I-,........................ . z G
2o
3o
4b
T i m e (min)
6o
H
50
............................................................. . .......iii:::::::"......'
u f-
_
~
O
__
9
10 9
Or
0
~. . . . . . . .
,
10
9
i
Time
. . . . . . . . . . . . . . . .|
-
20
30
G
40
(min)
Figure 1.- Evolution of the heavy (H), light (L), gas (G) and coke (C) fractions during the hydroprocessing experiments (the solid lines represent the hydrovisbreaking experiments and the dot lines represent the hydrocracking experiments). REFERENCES
1. Teichmann, D.P. Hydrocarbon Processing, 1982, 61(5), 105. 2. Sikoma, J.G., Hydrocarb. Proc., 1980, 59(6), 73. 3. Mavity, V.T., Ward, J.W. and Whitebread, K.E. Hydrocarbon processing, 1978, 57(11),157. 4 Benito, A.M., Brower, L., Martinez, M.T., Severin, D. and Fernandez, I. Accepted for publication in Fuel Science and Technology International (17-2-94). 5. Martinez, M.T., Fem~.ndez, I., Benito, A.M., Cebolla, V., Miranda, J.L. and Oelert, H.H., Fuel Processing Technology, 1993, 33, 159.