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A semi-continuous flow reactor technique for coal liquefaction studies
Fuel Processing Technology, 11 (1985) 127--132
127
Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands
A SEMI-CONTINUOUS FLOW R E A C T O R TECHNIQUE F O R COAL L I Q U E F A C T I O N STUDIES
J O R G E L A I N E and O M A R
BECERRA
Centro de Quirnica, Instituto Venezolano de lnvestigaciones Cientificas, Apartado 182 7, Caracas 1010-A (Venezuela) (Accepted March 4th, 1985)
ABSTRACT A novel semicontinuous tubular reactor flow technique was used to study liquefaction of a typical Venezuelan coal. The technique allows a simple procedure to calculate coal liquefaction conversion. This was found to be increased by various catalysts only if the appropriate amount with the proper particle size was employed. Nickel--molybdate and cobalt--molybdate catalysts were found to be better catalysts than copper--chromite for desulfurizing the coal; however, the latter catalyst produced the largest liquefachon conversion. INTRODUCTION
Small laboratory scale studies of coal liquefaction have been carried out for the most part in batch reactors (see e.g. Refs. [1--4] ). These generally involve tedious post-reaction procedures for obtaining data necessary to calculate the coal conversion. In this communication a simple semicontinuous tubular reactor flow technique is introduced in which coal conversion can be easily obtained. The technique has been e m p l o y e d to study the effect of catalysts in the liquefaction of a typical Venezuelan coal. APPARATUS
AND PROCEDURE
A sketch of the apparatus is shown in Fig. 1. The sample of coal (5 g, 30--60 mesh) was mixed with 5 g of silica (35--70 mesh). The silica was used to avoid coal agglomeration during liquefaction. When catalysts (0.5 or 1 g) were used, the a m o u n t of silica was adjusted to give a weight of 5 g of silica plus catalyst. The properties of the coal and catalysts used are given in Tables 1 and 2. The mixture o f coal, silica and catalyst was placed in a stainless steel tubular reactor of 1.27 cm (1/2") O.D., 0.93 cm I.D. and 35 cm length, which was previously filled with an appropriate a m o u n t of glass spheres {about 2 mm diameter) so that the coal bed was located at the middle of the
0378-3820/85/$03.30
© 1985 Elsevier Science Publishers B.V.
128
? M
V1
H2
N2
V -7 I
f
[ I
IF I I
L
I I
R
I I I I I I I I J
)v Fig. 1. Schematic of the semicontinuous flow system for coal liquefaction. V: valves, P: liquid pump, R: reactor, F: furnace, B: coal bed, G: glass spheres, C: condenser, L: liquid receiver, M: manometer, T: liquid N 2 trap, R: rotameter. TABLE1 "Lobatera" coal characteristics
Proximate analysis (wt. % air dried basis) Moisture Ash Volatile matter
1.4 9.4 48.5
Ultimate analysis (wt. % daf basis) C H S
76.3 5.7 2.1
Petrographic components (vol. %) Vitrir~ite Exinite Inertinite
83 9 2
tube. A thermocouple was soldered to the external reactor wall to control the temperature. Both ends of the reactor tube were connected through swagelock reducing
129 TABLE 2 C h a r a c t e r i s t i c s o f c a t a l y s t s used Catalyst
Composition (wt. %)
Surface area (m2/g)
Aero a UOP a Harshaw
3%NiO--15%MoO 3 3%CoO--12%MoO 3 17%Cr203- 81%CuO
180 130 8
aSupported on alumina.
unions ( 1 / 2 " - - 1 / 8 " ) with stainless steel filter discs (5 pm, 1/2" diameter). Another filter disc of diameter equal to the reactor inside diameter was placed at the b o t t o m of the coal bed. The liquefaction procedure was the following: the temperature of the reactor was first increased to 150°C under a flow of nitrogen at atmospheric pressure for 1/2 h. The system was then pressurized with hydrogen to 6.9 MPa (1000 psi) adjusting the flow of hydrogen to 300 ml/min ($TP) by means of a needle valve V1. Then, the solvent (3 ml/min of n-heptane or tetralin) was p u m p e d using a high pressure Milton R o y duplex pump. At the m o m e n t the liquid flow started, the temperature was increased from 150 ° to 450°C in 10 min. The reaction was allowed to continue at 450°C for 50 min longer. After stopping the liquid flow, the system was depressurized and then a flow of nitrogen was circulated for 1 h, maintaining the temperature at 450°C. The reactor was then cooled and disconnected through the t w o 1/8" nuts of the 1 / 2 " - - 1 / 8 " reducing unions. Each experiment was repeated at least twice in order to verify the reProducibility. The fraction of coal converted (X) to liquid and gases is defined as: %X = (1 - m/mo) × 100 where m and m0 are the ash- and moist-free weights of coal after and before the test respectively. The value of m was estimated by extracting the reactor content and carefully separating the glass spheres from the coal bed left. The conversion could also be estimated by comparing the reactor weight before and after the test. Both values of conversion were within a range of error less than 5%. The liquid collected in container L (Fig. 1) was distilled to separate the coal liquids from the solvent (heptane or tetralin). The selectivity to liquids is defined as %SL =
(mL/mo) X 1 0 0 / X
130
where mL is the weight of coal liquid after distillation. The gas selectivity is then %S G = 100 - %S L
The gas selectivity also includes liquids with boiling points equal to or smaller than that of the solvent. EXPERIMENTAL RESULTS AND DISCUSSION
Experiments were designed to test the reaction system in the measurement of conversion and selectivity as a function of parameters such as the presence of catalyst; type, a m o u n t and particle size of catalysts; type of solvent (H2 donor: tetralin, non-donor: heptane). The hydrodesulfurization ability of the catalysts was also estimated. As expected, tetralin produced larger conversions (more than twice as large) than heptane (Tables 3 and 4). The results shown in Tables 3 and 4 also indicate that the introduction of the catalysts is beneficial only if appropriate amounts of material with the proper particle sizes are employed. For example, the coal conversion is decreased in the cases where the amount of catalysts and/or the catalyst particle size are the largest (i.e., 1 g and 60-120 mesh). This may be the result of a variation in the flow mode which impairs the hydrogen transfer to the coal. In fact, transport phenomena theory indicates that an increase in the particle size may diminish mass transfer in a fixed bed reactor [ 5 ] . Hence the use of the smallest possible particle size is a c o m m o n practice in coal liquefaction processes, to the limit of using coal impregnation with catalyst solutions [6]. TABLE 3 Coal liquefaction with n-heptane (1000 psi, 450oc) Catalyst a
A m o u n t of catalyst (gig coal)
Conversion (%)
Selectivity (%) SL
SG
No catalyst
-
32
79
21
Aero
0.1 O.2
33 32
86 81
14 19
UOP
0.1 0.2
34 30
86 80
14 20
Harshaw
0.1 0.2
34 36
84 91
16 9
aCatalyst size: 60--120 mesh, except the Harshaw catalyst: 200--400 mesh.
131 TABLE 4 Coal liquefaction with tetralin (1000 psi, 450°C) Catalyst
No catalyst
Conversion
Catalyst sizea (ASTM mesh)
(%)
Selectivity (%) SL
$6
--
83
96
4
Aero
60--120 2O0-400
83 84
98 98
2 2
UOP
60--120 200--400
82 87
99 98
1 2
Harshaw
60--120 200--400
94 97
99 99
1 1
a A m o u n t of catalyst: 0.2 g/g coal; 60--120:0.25--0.125 mm diameter; 200--400: 0.074--0.037 mm diameter.
It can also be seen in Tables 3 and 4 that the use of catalysts increases the selectivity towards liquids, which is mostly desired in coal liquefaction processes. Table 5 shows that catalysts also diminish the sulfur content in the liquid product. Chromium, nickel--molybdenum, and cobalt--molybdenum formulations are recognized as efficient catalysts for hydrodesulfurization of petroleum [7]. The data show that t h e y are also efficient for coal desulfurization. A higher a m o u n t of desulfurization was observed using nickel--molybd e n u m and cobalt--molybdenum catalysts when compared with copper-chromite (Table 5). However, the latter catalyst produced the largest coal conversion (Table 4). This matter is presently under further investigation. Finally, it can be concluded that the present experimental system allows an easy calculation of coal conversion in a coal liquefaction test, and offers TABLE5 Sulfur contents in liquid products Catalyst a
No catalyst Aero UOP Harshaw
Sulfur (wt. %) Distillate
Residue
0.48 0.01 0.01 0.10
0.50 0.02 0.02 0.11
aWeight of catalyst: 1 g, size: 200--400 mesh. Solvent: tetralin.
132
advantages relative to current batch autoclave techniques. However, the cost of the proposed system may be higher than an autoclave system, due primarily to the need of a high pressure liquid pump. ACKNOWLEDGEMENTS
The authors would like to express their thanks to Angelica Delgado (Universidad SimSn Bolivar) for the analysis and samples of coal, to Orlando Abraham (Universidad Central de Venezuela) for the sulfur analysis, and to Amir Attar (University of North Carolina) and Alfredo Viloria (Instituto TecnolSgico Venezolano del PetrSleo) for their comments. REFERENCES 1 Yan, T.Y. and Espencheid, W.F., 1983. Liquefaction of coal in petroleum fraction under mild conditions. Fuel Processing Technology, 7 : 121. 2 Curtis, C.W., Guin, J.A., Ray Tarrer, A. and Huan, W.J., 1983. Two-stage coal liquefaction using sequential mineral and hydrotreating catalysts. Fuel Processing Technology, 7: 277. 3 AndrOs, M., Charcosset, H., Chiche, P., Davignon, L., Djeda, G., Joly, J.P. and Pr~germain, S., 1983. Catalysis of coal hydroliquefaction by synthetic iron catalyst. Fuel, 62: 69. 4 Derbyshire, F., Varghese, P. and Whitehurst, D.D., 1983. Two-stage liquefaction of a subbituminous coal.. Fuel, 62: 491. 5 Satterfield, C.N., 1975. Trickle-bed Reactors. AIChE J., 21: 209. 6 Cusumano, J.A., Dalla Betta, R.A. and Levy, R.B., 1978. Catalysis in Coal Conversion. Academic Press, New York, N.Y., 272 pp. 7 Schuit, G.C.A. and Gates, B.C., 1973. Chemistry and engineering of catalytic hydrodesulfurization. AIChE J., 19: 417.
127
Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands
A SEMI-CONTINUOUS FLOW R E A C T O R TECHNIQUE F O R COAL L I Q U E F A C T I O N STUDIES
J O R G E L A I N E and O M A R
BECERRA
Centro de Quirnica, Instituto Venezolano de lnvestigaciones Cientificas, Apartado 182 7, Caracas 1010-A (Venezuela) (Accepted March 4th, 1985)
ABSTRACT A novel semicontinuous tubular reactor flow technique was used to study liquefaction of a typical Venezuelan coal. The technique allows a simple procedure to calculate coal liquefaction conversion. This was found to be increased by various catalysts only if the appropriate amount with the proper particle size was employed. Nickel--molybdate and cobalt--molybdate catalysts were found to be better catalysts than copper--chromite for desulfurizing the coal; however, the latter catalyst produced the largest liquefachon conversion. INTRODUCTION
Small laboratory scale studies of coal liquefaction have been carried out for the most part in batch reactors (see e.g. Refs. [1--4] ). These generally involve tedious post-reaction procedures for obtaining data necessary to calculate the coal conversion. In this communication a simple semicontinuous tubular reactor flow technique is introduced in which coal conversion can be easily obtained. The technique has been e m p l o y e d to study the effect of catalysts in the liquefaction of a typical Venezuelan coal. APPARATUS
AND PROCEDURE
A sketch of the apparatus is shown in Fig. 1. The sample of coal (5 g, 30--60 mesh) was mixed with 5 g of silica (35--70 mesh). The silica was used to avoid coal agglomeration during liquefaction. When catalysts (0.5 or 1 g) were used, the a m o u n t of silica was adjusted to give a weight of 5 g of silica plus catalyst. The properties of the coal and catalysts used are given in Tables 1 and 2. The mixture o f coal, silica and catalyst was placed in a stainless steel tubular reactor of 1.27 cm (1/2") O.D., 0.93 cm I.D. and 35 cm length, which was previously filled with an appropriate a m o u n t of glass spheres {about 2 mm diameter) so that the coal bed was located at the middle of the
0378-3820/85/$03.30
© 1985 Elsevier Science Publishers B.V.
128
? M
V1
H2
N2
V -7 I
f
[ I
IF I I
L
I I
R
I I I I I I I I J
)v Fig. 1. Schematic of the semicontinuous flow system for coal liquefaction. V: valves, P: liquid pump, R: reactor, F: furnace, B: coal bed, G: glass spheres, C: condenser, L: liquid receiver, M: manometer, T: liquid N 2 trap, R: rotameter. TABLE1 "Lobatera" coal characteristics
Proximate analysis (wt. % air dried basis) Moisture Ash Volatile matter
1.4 9.4 48.5
Ultimate analysis (wt. % daf basis) C H S
76.3 5.7 2.1
Petrographic components (vol. %) Vitrir~ite Exinite Inertinite
83 9 2
tube. A thermocouple was soldered to the external reactor wall to control the temperature. Both ends of the reactor tube were connected through swagelock reducing
129 TABLE 2 C h a r a c t e r i s t i c s o f c a t a l y s t s used Catalyst
Composition (wt. %)
Surface area (m2/g)
Aero a UOP a Harshaw
3%NiO--15%MoO 3 3%CoO--12%MoO 3 17%Cr203- 81%CuO
180 130 8
aSupported on alumina.
unions ( 1 / 2 " - - 1 / 8 " ) with stainless steel filter discs (5 pm, 1/2" diameter). Another filter disc of diameter equal to the reactor inside diameter was placed at the b o t t o m of the coal bed. The liquefaction procedure was the following: the temperature of the reactor was first increased to 150°C under a flow of nitrogen at atmospheric pressure for 1/2 h. The system was then pressurized with hydrogen to 6.9 MPa (1000 psi) adjusting the flow of hydrogen to 300 ml/min ($TP) by means of a needle valve V1. Then, the solvent (3 ml/min of n-heptane or tetralin) was p u m p e d using a high pressure Milton R o y duplex pump. At the m o m e n t the liquid flow started, the temperature was increased from 150 ° to 450°C in 10 min. The reaction was allowed to continue at 450°C for 50 min longer. After stopping the liquid flow, the system was depressurized and then a flow of nitrogen was circulated for 1 h, maintaining the temperature at 450°C. The reactor was then cooled and disconnected through the t w o 1/8" nuts of the 1 / 2 " - - 1 / 8 " reducing unions. Each experiment was repeated at least twice in order to verify the reProducibility. The fraction of coal converted (X) to liquid and gases is defined as: %X = (1 - m/mo) × 100 where m and m0 are the ash- and moist-free weights of coal after and before the test respectively. The value of m was estimated by extracting the reactor content and carefully separating the glass spheres from the coal bed left. The conversion could also be estimated by comparing the reactor weight before and after the test. Both values of conversion were within a range of error less than 5%. The liquid collected in container L (Fig. 1) was distilled to separate the coal liquids from the solvent (heptane or tetralin). The selectivity to liquids is defined as %SL =
(mL/mo) X 1 0 0 / X
130
where mL is the weight of coal liquid after distillation. The gas selectivity is then %S G = 100 - %S L
The gas selectivity also includes liquids with boiling points equal to or smaller than that of the solvent. EXPERIMENTAL RESULTS AND DISCUSSION
Experiments were designed to test the reaction system in the measurement of conversion and selectivity as a function of parameters such as the presence of catalyst; type, a m o u n t and particle size of catalysts; type of solvent (H2 donor: tetralin, non-donor: heptane). The hydrodesulfurization ability of the catalysts was also estimated. As expected, tetralin produced larger conversions (more than twice as large) than heptane (Tables 3 and 4). The results shown in Tables 3 and 4 also indicate that the introduction of the catalysts is beneficial only if appropriate amounts of material with the proper particle sizes are employed. For example, the coal conversion is decreased in the cases where the amount of catalysts and/or the catalyst particle size are the largest (i.e., 1 g and 60-120 mesh). This may be the result of a variation in the flow mode which impairs the hydrogen transfer to the coal. In fact, transport phenomena theory indicates that an increase in the particle size may diminish mass transfer in a fixed bed reactor [ 5 ] . Hence the use of the smallest possible particle size is a c o m m o n practice in coal liquefaction processes, to the limit of using coal impregnation with catalyst solutions [6]. TABLE 3 Coal liquefaction with n-heptane (1000 psi, 450oc) Catalyst a
A m o u n t of catalyst (gig coal)
Conversion (%)
Selectivity (%) SL
SG
No catalyst
-
32
79
21
Aero
0.1 O.2
33 32
86 81
14 19
UOP
0.1 0.2
34 30
86 80
14 20
Harshaw
0.1 0.2
34 36
84 91
16 9
aCatalyst size: 60--120 mesh, except the Harshaw catalyst: 200--400 mesh.
131 TABLE 4 Coal liquefaction with tetralin (1000 psi, 450°C) Catalyst
No catalyst
Conversion
Catalyst sizea (ASTM mesh)
(%)
Selectivity (%) SL
$6
--
83
96
4
Aero
60--120 2O0-400
83 84
98 98
2 2
UOP
60--120 200--400
82 87
99 98
1 2
Harshaw
60--120 200--400
94 97
99 99
1 1
a A m o u n t of catalyst: 0.2 g/g coal; 60--120:0.25--0.125 mm diameter; 200--400: 0.074--0.037 mm diameter.
It can also be seen in Tables 3 and 4 that the use of catalysts increases the selectivity towards liquids, which is mostly desired in coal liquefaction processes. Table 5 shows that catalysts also diminish the sulfur content in the liquid product. Chromium, nickel--molybdenum, and cobalt--molybdenum formulations are recognized as efficient catalysts for hydrodesulfurization of petroleum [7]. The data show that t h e y are also efficient for coal desulfurization. A higher a m o u n t of desulfurization was observed using nickel--molybd e n u m and cobalt--molybdenum catalysts when compared with copper-chromite (Table 5). However, the latter catalyst produced the largest coal conversion (Table 4). This matter is presently under further investigation. Finally, it can be concluded that the present experimental system allows an easy calculation of coal conversion in a coal liquefaction test, and offers TABLE5 Sulfur contents in liquid products Catalyst a
No catalyst Aero UOP Harshaw
Sulfur (wt. %) Distillate
Residue
0.48 0.01 0.01 0.10
0.50 0.02 0.02 0.11
aWeight of catalyst: 1 g, size: 200--400 mesh. Solvent: tetralin.
132
advantages relative to current batch autoclave techniques. However, the cost of the proposed system may be higher than an autoclave system, due primarily to the need of a high pressure liquid pump. ACKNOWLEDGEMENTS
The authors would like to express their thanks to Angelica Delgado (Universidad SimSn Bolivar) for the analysis and samples of coal, to Orlando Abraham (Universidad Central de Venezuela) for the sulfur analysis, and to Amir Attar (University of North Carolina) and Alfredo Viloria (Instituto TecnolSgico Venezolano del PetrSleo) for their comments. REFERENCES 1 Yan, T.Y. and Espencheid, W.F., 1983. Liquefaction of coal in petroleum fraction under mild conditions. Fuel Processing Technology, 7 : 121. 2 Curtis, C.W., Guin, J.A., Ray Tarrer, A. and Huan, W.J., 1983. Two-stage coal liquefaction using sequential mineral and hydrotreating catalysts. Fuel Processing Technology, 7: 277. 3 AndrOs, M., Charcosset, H., Chiche, P., Davignon, L., Djeda, G., Joly, J.P. and Pr~germain, S., 1983. Catalysis of coal hydroliquefaction by synthetic iron catalyst. Fuel, 62: 69. 4 Derbyshire, F., Varghese, P. and Whitehurst, D.D., 1983. Two-stage liquefaction of a subbituminous coal.. Fuel, 62: 491. 5 Satterfield, C.N., 1975. Trickle-bed Reactors. AIChE J., 21: 209. 6 Cusumano, J.A., Dalla Betta, R.A. and Levy, R.B., 1978. Catalysis in Coal Conversion. Academic Press, New York, N.Y., 272 pp. 7 Schuit, G.C.A. and Gates, B.C., 1973. Chemistry and engineering of catalytic hydrodesulfurization. AIChE J., 19: 417.