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Hydrogenation of residual oil using an ore derived water soluble ammonium molybdate catalyst
Hydrogenation of residual oil using an ore derived water soluble ammonium molybdate catalyst Abdul
R. Mohamed
Department of Chemical USA (Received 2 November
and Virendra Engineering, 1990; revised
K. Mathur
University 27 February
of New
Hampshire,
Durham,
NH 03824,
7997)
Hydrogenation of residual oil, though attractive, has been expensive due to hydrogen requirements, high pressure equipment, and high cost of a generally used cobalt-molybdenum supported catalyst. In this study, hydrogenation of atmospheric residual oil (260°C’) with API gravity of 16 (20°C) and viscosity of 252 x 10m3 Pa s (30°C) is carried out in an internally stirred autoclave in the presence of a dispersed water soluble unsupported ammonium molybdate catalyst prepared from a molybdenum ore. This provides an effective economic alternative to the use of expensive supported commercial catalysts for the hydrogenation of residual oil. The most suitable hydrogenation experimental conditions for the hydrogenation of residual oil were found to be 0.216% molybdenum based on residual oil, 13.8 MPa pressure, 405°C reactor temperature, and 30 min reaction time. Under these conditions, API gravity of the product oil increased to 23 with a decrease in viscosity to 16.6 x 1O-3 Pa s. An ASTM distillation of the hydrogenated residual product gave 34% liquid boiling below 235°C. (Keywords:
residual oil; hydrogenation;
ore catalyst)
In order to provide the industrialized world with sufficient inexpensive hydrocarbon fuels and chemical feedstocks, petroleum crude has to be utilized to its maximum. Hydrogenation of residual oil, obtained from a petroleum distillation unit, provides a product with an increased hydrogen content. However, to increase the hydrogen content of the product to the level necessary for transportation fuels or chemical feedstocks, catalysts which promote hydrogenation and hydrocracking must be employed. Catalytic reactions play an important role in residual oil hydrogenation yielding products of lower molecular weight with higher hydrogen to carbon ratioie5. The removal of sulphur, nitrogen and oxygen heteroatoms and hydrogenation of the residual oil molecule is usually accomplished by using commercial catalysts containing various combinations of cobalt, nickel, molybdenum and tungsten on A&O, or A1,03-SiO, support. Catalyst deactivation is a major problem in the catalytic residual oil hydrogenation process. Coke formation decreases catalyst activity by blocking catalyst active sites, primarily through blocking the pore mouths. Deposits of nickel and vanadium deactivate the catalyst permanently by restricting diffusion paths of the reactant molecules. Even regeneration of commercial catalysts may not restore the original hydrogenation activity. Therefore, commercial supported catalysts used in residual oil hydrogenation are difficult to regenerate and have a short life. The usage and loss of expensive commercial catalysts are one of the major critical problems in this area. The solution to these problems to some extent is to find an inexpensive catalyst that can be effective enough in hydrogenation activity to replace commercial ones. 001~2361/91/080983-05 N., 1991 ButterworthbHeinemann
Ltd.
LITERATURE
REVIEW
It has been reported that cobalt, which acts as a promoter, and molybdenum are eminently effective catalysts for hydrogenation and hydrodesulphurization of residual oil whereas nickel and molybdenum are good for hydrodenitrogenation6. The most inexpensive source of these metals is their ores in which they are present as sulphides or oxides. Several authors7-I3 have studied and listed the advantages of using a dispersed-phase water soluble catalyst over commercially used, supported catalysts for hydrogenation of coal, residual oil and coprocessing. The results from the hydrogenation of residual oil using a dispersed-phase catalyst show that the catalyst gives a high degree of desulphurization and demetalation (nickel and vanadium removal). The small particle size of the catalyst provides two advantages. First, the catalyst is highly active due to a large specific surface area, and second, the catalyst microcrystalline particles are sufficiently small to be readily dispersed in the residual oil allowing the oil to be easily pumped. It has been reported7 that the average particle diameter is 3-30 pm. It is also claimed that moderate or relatively large amounts of nickel and vanadium can be deposited on the catalyst surface without reducing its activity. Moreover, the recycled catalyst can accommodate as much as 70-85 wt% of nickel and vanadium without excessive loss of activity. Another advantage of the dispersed-phase catalyst over a supported one is that the former can be recovered and recycled. The spent catalyst can easily be separated from the reaction products by extracting the residue with a light hydrocarbon solvent such as propane, butane or FUEL,
1991,
Vol 70, August
983
Hydrogenation
of residual
oil: A. R. Mohamed
and V. K. Mathur
light naptha. The amount of catalyst that may be recovered can be as high as 97%. The most abundant natural source of molybdenum which is commercially significant is molybdenite, MoS,. Molybdenite is first concentrated by hydroclassification to -90% of MoS, and then roasted to convert sulphide to oxide. The molybdenum trioxide (MOO,) thus formed is sublimed to produce a high purity compound or it can be leached with a dilute ammonia solution to give ammonium molybdate. Ammonium molybdate or MOO, is reduced to molybdenum powder by the action of hydrogen’ 4*1‘. Most commercial catalysts are prepared by depositing pure molybdenum on silica or alumina support to provide a large surface area. These are expensive catalysts. In many cases the supported catalysts are poisoned and may be difficult to regenerate. In previous studies16-’ ‘, it has been shown that some of the ore concentrates can be directly used for coal hydrogenation reactions. Based on this premise, efforts have been made to use sulphide or oxide concentrate as a catalyst or a starting point for the preparation of dispersed molybdenum catalysts for residual oil hydrogenation reactions. It is obvious that this procedure will result in cost reduction because of a significant saving in material and processing expenses. EXPERIMENTAL Materials
The major materials used in this study” consist of residual oil, hydrogen gas, catalysts and tetrahydrofuran (THF). The residual oil used in this study was Arabian Light atmospheric residual oil. Table I presents the analysis of the residual oil. Hydrogen gas of 99.99% purity was used for hydrogenation, and analytical grade THF was used as a solvent to filter residue and wash the equipment. The catalysts used were ammonium molybdate extracted from a MOO, ore concentrate, molybdenum sulphide ore concentrate and supported cobalt-molybdenum-alumina (0402T). The materials used as catalysts in this study and their compositions are listed in Table 2. Equipment
The hydrogenation reactions were carried out in a stainless steel liner placed in a high pressure internally stirred autoclave (1 1 capacity). The experiments were carried out at a stirrer speed of 1000 rev min-‘. The autoclave was provided with a cooling coil through which water could be passed to reduce the temperature of the
Table 1
Analysis
of residual
oil _ 16.4 252 x 1o-3 > 260°C
API gravity Viscosity at 30°C (Pa s) Boiling point (“C) Ultimate analysis Carbon (X) Hydrogen (%) Nitrogen (%) Sulphur (%) Oxygen (%) Nickel (ppm) Vanadium (ppm) Iron (ppm) Copper (ppm)
984
FUEL, 1991, Vol 70, August
85.51 11.34 0.14 2.94 0.67 7 21 7
._
I
Table 2 catalyst
Percentage
compositions
Ore concentrates Regular molybdenum concentrate
Molybdenum
of ore concentrates
and commercial
sulphide
MO Fe Si S
49.8 0.7 2.6 23.5
Ca Al K
0.6 0.4 0.3
oxide concentrate
MO
Mg Al S
47.0 2.8 3.5 0.6 0.6 0.4
Ca Cu Sn Zn K
0.4 0.5 0.4 0.2 0.2
Si co MO Al
2.1 1.9 8.6 37.4
:ie
Commercial catalyst Harshaw cobalt-molybdenum (0402T)
reaction if so desired, and had an electric furnace controlled by a proportional temperature controller. The temperature of the reaction mass was continuously monitored by a temperature recorder. A compressor was used to pressurize the autoclave with hydrogen. In addition, the autoclave was provided with a pressure gauge, a vent, a sampling valve, a safety rupture disc and a thermowell. Procedure
The detailed procedures for the preparation of the catalysts and for conducting the hydrogenation reactions are discussed in the following. Preparation of water soluble dispersed catalyst. The MOO, ore concentrate was used to prepare the ammonium molybdate catalyst. Ammonium hydroxide was then added to MOO, in excess. The mixture was stirred under constant heat and total reflux for several hours. Occasionally, ammonium hydroxide was added to keep it in excess. The solution was then filtered to ensure that it was free of foreign materials. The mother liquor was then transferred into a crucible and evaporated. A light green ammonium molybdate salt with a molybdenum concentration of 54.3% was obtained and stored in a desiccator. Hydrogenation of the residual oil. Residual oil (80 g) was first added to the liner. A predetermined amount of amonium molybdate dissolved in 10 ml of distilled water was then added to the liner. In the case of commercial catalyst or disposable ore catalyst (-200 mesh), the catalyst was added to the residual oil in the liner with 10 ml of distilled water. The stirrer assembly was fitted onto the autoclave and securely bolted. After testing for leakage, the autoclave was purged with hydrogen. Heating was initiated thereafter. It usually took 60-80 min to heat the reaction mixture from room temperature to the desired temperature and pressure. The reaction was allowed to proceed for a given period of time. As in most autoclave work for coal hydrogenation this time variation in the initial heating was assumed not to affect the results in any significant manner. The reaction was arrested by turning off the power to the furnace and cooling down the autoclave contents rapidly by passing cold water through the cooling coil. The
Hydrogenation
of residual oil: A. R. Mohamed
autoclave was then left overnight to cool to room temperature after which the product was removed and hot-filtered to remove solid residue and catalyst. The viscosity of the hydrogenated oil was determined at 30°C using a viscometer. The oil samples were then kept in a refrigerator to prevent possible polymerization until the ASTM distillation was carried out.
Table 3
RESULTS AND DISCUSSION
3
The objective of this investigation was to study the hydrogenation of Arabian Light atmospheric residual oil for the production of light distillates using a dispersed water soluble ammonium molybdate catalyst. The experimental variables held constant during the study were water content for dissolving the catalyst, the amount of residual oil used for each experimental run and the stirrer speed. The viscosity of the hydrogenated residual oil was determined and used as a measure of the degree of hydrogenation reaction. The results of this study have been divided into the effect of catalyst loading on residual oil hydrogenation, the performance of the dispersed catalyst compared to a commercial cobaltmolybdenum catalyst, and the results of the effect of pressure, temperature and reaction time on residual oil hydrogenation. The results from the ASTM distillation of the hydrogenation oil obtained at the most suitable conditions of catalyst loading, pressure, temperature and reaction time are also presented. .Effect
qf dispersed
catalyst on residual oil hydrogenation
The effect of the catalyst on the residual oil hydrogenation was studied based on molybdenum per cent loading with respect to the residual oil. In all experiments, the reactor pressure was maintained at 17.2 MPa, the reactor temperature between 400°C and 410°C and the reaction time was 30 min. In each run, the amount of residual oil used was 80 g. A predetermined amount of ammonium molybdate was dissolved in 10 ml of water and used as a catalyst. The effect of catalyst loading is shown in Figure 1. The amount of ammonium molybdate salt was varied from 0.0 to 0.443 g with a molybdenum loading of O&0.3% based on the residual oil. The viscosity of the hydrogenated residual oil decreased from 94.6 x 10m3
Serial number I 2
Hydrogenation
of residual
and V. K. Mathur
oil with various
Name of catalyst Cobalt-molybdenum Harshaw 0402T Ammonium molybdate salt solution Molybdenum sulphide ore
catalysts
Molybdenum loading W)
(Pa s)
0.215
20.5
0.216
14.5
0.222
26.1
Viscosity (x 10-S)
Pa s at 0.0% molybdenum loading to w 14.5 x 10m3 Pa s at 0.216%. After 0.216% molybdenum loading, the viscosity of the hydrogenated residual oil did not alter much with increase in the amount of catalyst. In order to study the catalytic effect of molybdenum in various forms in hydrogenating the residual oil, several experiments using other catalysts were also performed. The results are shown in Table 3. A commercial cobaltmolybdenum hydrotreating catalyst (- 200 mesh) was used at the same operating conditions of 17.2 MPa reactor pressure, 40&41O”C reactor temperature, and 30 min reaction time. The amount of the commercial cobalt-molybdenum catalyst used was -2.0 g with a molybdenum loading of 0.215% based on the residual oil. The viscosity of the hydrogenated residual oil was found to be 20.5 x low3 Pa s which was higher than that of the hydrogenated product obtained using dispersed ammonium molybdatq salt solution as a catalyst. An experiment was also conducted using molybdenum sulphide concentrate ore (Molybdenite) as a catalyst. As mentioned earlier, MOO, is prepared commercially by roasting MoS,. Therefore, it would be more economical if molybdenum sulphide ore concentrate could be used directly as a catalyst. Molybdenum sulphide (-0.35 g) with 0.222% of molybdenum was used in the experimental run at the same operating conditions. The viscosity of the hydrogenated residual oil was measured to be 26.1 x 1O-3 Pa s at 30°C. The result shows it is better to use dispersed ammonium molybdate salt as a catalyst than molybdenum sulphide ore concentrate as a slurry. The viscosity of the hydrogenated residual oil using dispersed ammonium molybdate salt as a catalyst was 44.4% lower than when molybdenum sulphide was used as a catalyst. An attempt was also made to extract ammonium molybdate by reacting ammonium hydroxide with molybdenum suphide ore concentrate with no success. Results from this experiment justify the use of MOO, ore concentrate as a starting material for the preparation of ammonium molybdate salt. The results from the above study validate the use of a dispersed solution of ammonium molybdate for the hydrogenation of residual oil. _EfSectof pressure
0
I
0
0.1 % molybdenum
Figure 1
Reaction
I
0.2
I
0.3
0.4
loading (based on oil loading)
Effect of molybdenum loading on hydrogenated conditions: 405”C, 17.2 MPa, 30 min
oil viscosity.
The effect of pressure on the residual oil hydrogenation was studied in the pressure range of 6.9-17.2 MPa. The temperature and the time of the reaction were kept constant at 4OWlO”C and 30 min, respectively. The effect of pressure on the residual oil hydrogenation is shown in Figure 2. It was found that the viscosity of the hydrogenated oil decreased steadily from 32.5 x 10e3 Pa s at 6.9 MPa to 16.6 x lop3 Pa s at 13.8 MPa. There
FUEL,
1991,
Vol
70,
August
985
Hydrogenation
of residual
oil: A. R. Mohamed
and V. K. Mathur
50
ASTM
40 z 0 g (3 s
q
30
.r’ 8 20 .> 10
0
I
I
I
1000
2000 Reactor
pressure
I
3000
(p.s.i.g.)
Figure 2 Effect of reactor pressure on hydrogenated oil viscosity. Reaction conditions: 405”C, 30 min, 0.216% molybdenum loading (I psig=6.895 kPa)
distillation
of hydrogenated
residual
oil
The hydrogenated oil sample for ASTM distillation was collected from two experimental runs operating the autoclave at 13.8 MPa pressure, 405°C temperature, and 30 min reaction time. The amount of catalyst used for each run was 0.216% of molybdenum loading based on the residual oil. The viscosity of the sample was found to be 16.5 x 10m3 Pas. The sample was then subjected to the ASTM D86-78 standard method for distillation of petroleum products. The ASTM distillation of the hydrogenated residual oil gave a total 34% liquid boiling below 235°C (cracking started above this temperature). The API gravity of this distillate was found to be 43. About 25% of the total distillate was found to be in the gasoline boiling range (32-204°C). There was - 14% of distillate in the kerosine boiling range (165-282°C). The sulphur content of the distillate was found to be 0.02 wt%. CONCLUSIONS
was only a slight decrease in the hydrogenated oil viscosity to 14.5 x 10m3 Pas when the pressure was further increased to 17.2 MPa. This viscosity reduction is small and probably within the experimental error. A reactor pressure of 13.8 MPa was chosen to be used for determining the effect of temperature and time. EfSect of temperature
The effect of temperature on the residual oil hydrogenation was studied in the temperature range 350430°C. The pressure was maintained at 13.8 MPa and the reaction time used was 30 min. The amount of ammonium molybdate salt catalyst used was -0.32 g (0.216% of molybdenum loading) as it was found earlier to be the most suitable loading. The effect of temperature on the residual oil hydrogenation is shown in Figure 3. The temperature was varied from 350 to 430°C. The viscosity of the hydrogenated residual oil decreased steadily from 101.4x 10m3 Pas at 350°C to -10.4x 10m3 Pas at 430°C. There was a substantial carbon residue formation at 430°C which caused a loss in the amount of hydrogenated residual oil. The viscosity of hydrogenated residual oil at a reaction temperature of 405°C was found to be 16.6 x 10e3 Pa s. The temperature of 405°C and reactor pressure of 13.8 MPa were used subsequently to study the effect of reaction time. Ef/‘ect of reaction
“Oh 320
360
400
Reactor
440
temperature
(“C)
Figure 3 Effect of reactor temperature on hydrogenated oil viscosity. Reaction conditions: 13.8 MPa, 30 min, 0.216% molybdenum loading
80
,
time
The effect of time on the residual oil hydrogenation was studied in the range of 15-45 min. The temperature and pressure were maintained at 405°C and 13.8 MPa, respectively, and all other conditions were the same as in earlier experiments. The effect of time on the hydrogenation of residual oil is shown in Figure 4. It can be seen that the viscosity of the hydrogenated oil decreased sharply from 62.6 cp (62.6 x 10m3 Pa s) at 15 min to - 16.6 cp (- 16.6 x lop3 Pa s) at 30 min. A further increase in time up to 45 min showed no significant reduction in the viscosity of the hydrogenated oil. The most suitable time of reaction was thus found to be 30 min for which the viscosity of the hydrogenated oil was found to be - 16.6 x 10m3 Pa s.
986
1. Results of hydrogenation of residual oil showed that dispersed water soluble ammonium molybdate catalyst was an effective catalyst and compared
FUEL, 1991, Vol 70, August
20 Reaction
40
60
time (min)
Figure 4 Effect of reaction time on hydrogenated oil viscosity. Reaction conditions: 405”C, 17.2 MPa, 0.216% molybdenum loading
Hydrogenation
favourably with the commercially available, supported cobalt-molybdenum Harshaw catalyst. It is most significant that the dispersed catalyst could be prepared directly from inexpensive MOO, ore concentrate. The experimental conditions for the hydrogenation of residual oil were found to be 0.216% molybdenum based on residual oil, 13.8 MPa pressure, 405°C reactor temperature, and 30 min reaction time. Under these conditions, the product API gravity increased to 23 with a decrease in viscosity to 16.6 x 10m3 Pa s. An ASTM distillation of the hydrogenated product gave 34% liquid boiling below 235°C. The API gravity of this distillate was found to be 43 with a sulphur content of 0.02 wt%. _ . The use of ammonium molybdate prepared from MOO, ore concentrate was a cheaper alternative to the use of analytical grade ammonium molybdate compound as a catalyst.
1 2 3 4 5 6 7 8 9 IO II
13
Authors thank Dr M. K. Sood, Mobil Corporation, Princeton, NJ for supplying the atmospheric residual oil. Thanks are also due to the Harshaw Chemical Co., Cleveland, OH, Molycorp Inc., Washington, PA and Climax Molybdenum Co., Langeloth, PA for supplying catalyst and ore samples. One of the authors (A.R.M.) thanks the Malaysian government for its financial support during the course of this study.
oil: A. R. Mohamed
and V. K. Mathur
REFERENCES
12
ACKNOWLEDGEMENTS
of residual
14
15
Gary, J. H. and Handwerk, G. E. ‘Petroleum Refining, Technology and Economics’, Marcel Dekker, New York, 1975 Speight, J. G. ‘The Desulfurization of Heavy Oil and Residua’, Marcel Dekker, New York, 1981 Baldassari, M. C. and Hamilton, G. L. Paper presented at the AIChE Meeting, Houston, April 1989 Beret, S. and Reynolds, J. G. Am. C&m. Sot. Dir. Fuel Chem. Prepr. 1985, 30(3), 397 Sy, 0.. Desmarais, L., Bode, D. rr (11. Paper presented at the AIChE Meeting, Houston, April, 1989 Kellett, T. F., Trevino, C. A. and Sartor, A. F. Oil Gas J. 1980, 78( 18). 244 Lopez. J.. McKinney, J. D. and Pasek. E. A. US Par. 4557821, 1985 Cugini. A. V., Ruether, J. A.. Cillo. D. L. ct crl. Am. Ckw. SK. Dir. Fuel Chem. Prqr. 1988, 33( 1 ), 6 Ha. B. C., Ruether. J. A., Smith, D. N. et ul. Am. Chem. Sot. Dir. Fuel Chrm. Prepi-. 1988, 33(3), 343 Snape. C. E., Bolton, C., Dosch, R. G. et d. Am. Chem. SW. Div. Fuel Chum. Prcpr. 1988, 33(3). 351 Hirschon, A. S. and Wilson, R. B. Am. Chem. SM. Dia. Fuel Chem. Prepr. 1989, 34(3), 881 Utz, B. R.. Cugini. A. V. and Frommell. E. A. Am. Chem. SK. Die. Fuel Chcm. Prepr. 1989, 34(4), 1423 Krastman. D., Utz, B. R., Cugini, A. V. and Lett, R. G. Am. Chem SW. Dir. Fud Chem. Prepr. 1990, 35(2), 570 Killeffer, D. H. and Linz, A. ‘Molybdenum Compounds, Their Chemistrv and Technoloav’. -, Interscience Publishers, New York, 1952 . Mark. H. F., Othmer, D. F., Overburger, C. G. et cd. ‘Concise Encylopedia of Chemical Technology’, John Wiley and Sons. New York, 1985. nn. . 774-775 Mathur, V. K. and Venkataramanan, V. .4nr. Cliem. Sot. Div. Furl Chem. Prrpr. 1982. 27(2), 1 Mathur, V. K.. Fakoukakis, E. P. and Ruether. J. A. Fuel 1984, 63. 1700 Mathur, V. K. and Reddy Karri, S. B. Fuel 1986, 65, 790 Mohamed. A. R. MS Thesis University of New Hampshire, 1989 L
16 17 18 19
FUEL, 1991, Vol 70, August
987
R. Mohamed
Department of Chemical USA (Received 2 November
and Virendra Engineering, 1990; revised
K. Mathur
University 27 February
of New
Hampshire,
Durham,
NH 03824,
7997)
Hydrogenation of residual oil, though attractive, has been expensive due to hydrogen requirements, high pressure equipment, and high cost of a generally used cobalt-molybdenum supported catalyst. In this study, hydrogenation of atmospheric residual oil (260°C’) with API gravity of 16 (20°C) and viscosity of 252 x 10m3 Pa s (30°C) is carried out in an internally stirred autoclave in the presence of a dispersed water soluble unsupported ammonium molybdate catalyst prepared from a molybdenum ore. This provides an effective economic alternative to the use of expensive supported commercial catalysts for the hydrogenation of residual oil. The most suitable hydrogenation experimental conditions for the hydrogenation of residual oil were found to be 0.216% molybdenum based on residual oil, 13.8 MPa pressure, 405°C reactor temperature, and 30 min reaction time. Under these conditions, API gravity of the product oil increased to 23 with a decrease in viscosity to 16.6 x 1O-3 Pa s. An ASTM distillation of the hydrogenated residual product gave 34% liquid boiling below 235°C. (Keywords:
residual oil; hydrogenation;
ore catalyst)
In order to provide the industrialized world with sufficient inexpensive hydrocarbon fuels and chemical feedstocks, petroleum crude has to be utilized to its maximum. Hydrogenation of residual oil, obtained from a petroleum distillation unit, provides a product with an increased hydrogen content. However, to increase the hydrogen content of the product to the level necessary for transportation fuels or chemical feedstocks, catalysts which promote hydrogenation and hydrocracking must be employed. Catalytic reactions play an important role in residual oil hydrogenation yielding products of lower molecular weight with higher hydrogen to carbon ratioie5. The removal of sulphur, nitrogen and oxygen heteroatoms and hydrogenation of the residual oil molecule is usually accomplished by using commercial catalysts containing various combinations of cobalt, nickel, molybdenum and tungsten on A&O, or A1,03-SiO, support. Catalyst deactivation is a major problem in the catalytic residual oil hydrogenation process. Coke formation decreases catalyst activity by blocking catalyst active sites, primarily through blocking the pore mouths. Deposits of nickel and vanadium deactivate the catalyst permanently by restricting diffusion paths of the reactant molecules. Even regeneration of commercial catalysts may not restore the original hydrogenation activity. Therefore, commercial supported catalysts used in residual oil hydrogenation are difficult to regenerate and have a short life. The usage and loss of expensive commercial catalysts are one of the major critical problems in this area. The solution to these problems to some extent is to find an inexpensive catalyst that can be effective enough in hydrogenation activity to replace commercial ones. 001~2361/91/080983-05 N., 1991 ButterworthbHeinemann
Ltd.
LITERATURE
REVIEW
It has been reported that cobalt, which acts as a promoter, and molybdenum are eminently effective catalysts for hydrogenation and hydrodesulphurization of residual oil whereas nickel and molybdenum are good for hydrodenitrogenation6. The most inexpensive source of these metals is their ores in which they are present as sulphides or oxides. Several authors7-I3 have studied and listed the advantages of using a dispersed-phase water soluble catalyst over commercially used, supported catalysts for hydrogenation of coal, residual oil and coprocessing. The results from the hydrogenation of residual oil using a dispersed-phase catalyst show that the catalyst gives a high degree of desulphurization and demetalation (nickel and vanadium removal). The small particle size of the catalyst provides two advantages. First, the catalyst is highly active due to a large specific surface area, and second, the catalyst microcrystalline particles are sufficiently small to be readily dispersed in the residual oil allowing the oil to be easily pumped. It has been reported7 that the average particle diameter is 3-30 pm. It is also claimed that moderate or relatively large amounts of nickel and vanadium can be deposited on the catalyst surface without reducing its activity. Moreover, the recycled catalyst can accommodate as much as 70-85 wt% of nickel and vanadium without excessive loss of activity. Another advantage of the dispersed-phase catalyst over a supported one is that the former can be recovered and recycled. The spent catalyst can easily be separated from the reaction products by extracting the residue with a light hydrocarbon solvent such as propane, butane or FUEL,
1991,
Vol 70, August
983
Hydrogenation
of residual
oil: A. R. Mohamed
and V. K. Mathur
light naptha. The amount of catalyst that may be recovered can be as high as 97%. The most abundant natural source of molybdenum which is commercially significant is molybdenite, MoS,. Molybdenite is first concentrated by hydroclassification to -90% of MoS, and then roasted to convert sulphide to oxide. The molybdenum trioxide (MOO,) thus formed is sublimed to produce a high purity compound or it can be leached with a dilute ammonia solution to give ammonium molybdate. Ammonium molybdate or MOO, is reduced to molybdenum powder by the action of hydrogen’ 4*1‘. Most commercial catalysts are prepared by depositing pure molybdenum on silica or alumina support to provide a large surface area. These are expensive catalysts. In many cases the supported catalysts are poisoned and may be difficult to regenerate. In previous studies16-’ ‘, it has been shown that some of the ore concentrates can be directly used for coal hydrogenation reactions. Based on this premise, efforts have been made to use sulphide or oxide concentrate as a catalyst or a starting point for the preparation of dispersed molybdenum catalysts for residual oil hydrogenation reactions. It is obvious that this procedure will result in cost reduction because of a significant saving in material and processing expenses. EXPERIMENTAL Materials
The major materials used in this study” consist of residual oil, hydrogen gas, catalysts and tetrahydrofuran (THF). The residual oil used in this study was Arabian Light atmospheric residual oil. Table I presents the analysis of the residual oil. Hydrogen gas of 99.99% purity was used for hydrogenation, and analytical grade THF was used as a solvent to filter residue and wash the equipment. The catalysts used were ammonium molybdate extracted from a MOO, ore concentrate, molybdenum sulphide ore concentrate and supported cobalt-molybdenum-alumina (0402T). The materials used as catalysts in this study and their compositions are listed in Table 2. Equipment
The hydrogenation reactions were carried out in a stainless steel liner placed in a high pressure internally stirred autoclave (1 1 capacity). The experiments were carried out at a stirrer speed of 1000 rev min-‘. The autoclave was provided with a cooling coil through which water could be passed to reduce the temperature of the
Table 1
Analysis
of residual
oil _ 16.4 252 x 1o-3 > 260°C
API gravity Viscosity at 30°C (Pa s) Boiling point (“C) Ultimate analysis Carbon (X) Hydrogen (%) Nitrogen (%) Sulphur (%) Oxygen (%) Nickel (ppm) Vanadium (ppm) Iron (ppm) Copper (ppm)
984
FUEL, 1991, Vol 70, August
85.51 11.34 0.14 2.94 0.67 7 21 7
._
I
Table 2 catalyst
Percentage
compositions
Ore concentrates Regular molybdenum concentrate
Molybdenum
of ore concentrates
and commercial
sulphide
MO Fe Si S
49.8 0.7 2.6 23.5
Ca Al K
0.6 0.4 0.3
oxide concentrate
MO
Mg Al S
47.0 2.8 3.5 0.6 0.6 0.4
Ca Cu Sn Zn K
0.4 0.5 0.4 0.2 0.2
Si co MO Al
2.1 1.9 8.6 37.4
:ie
Commercial catalyst Harshaw cobalt-molybdenum (0402T)
reaction if so desired, and had an electric furnace controlled by a proportional temperature controller. The temperature of the reaction mass was continuously monitored by a temperature recorder. A compressor was used to pressurize the autoclave with hydrogen. In addition, the autoclave was provided with a pressure gauge, a vent, a sampling valve, a safety rupture disc and a thermowell. Procedure
The detailed procedures for the preparation of the catalysts and for conducting the hydrogenation reactions are discussed in the following. Preparation of water soluble dispersed catalyst. The MOO, ore concentrate was used to prepare the ammonium molybdate catalyst. Ammonium hydroxide was then added to MOO, in excess. The mixture was stirred under constant heat and total reflux for several hours. Occasionally, ammonium hydroxide was added to keep it in excess. The solution was then filtered to ensure that it was free of foreign materials. The mother liquor was then transferred into a crucible and evaporated. A light green ammonium molybdate salt with a molybdenum concentration of 54.3% was obtained and stored in a desiccator. Hydrogenation of the residual oil. Residual oil (80 g) was first added to the liner. A predetermined amount of amonium molybdate dissolved in 10 ml of distilled water was then added to the liner. In the case of commercial catalyst or disposable ore catalyst (-200 mesh), the catalyst was added to the residual oil in the liner with 10 ml of distilled water. The stirrer assembly was fitted onto the autoclave and securely bolted. After testing for leakage, the autoclave was purged with hydrogen. Heating was initiated thereafter. It usually took 60-80 min to heat the reaction mixture from room temperature to the desired temperature and pressure. The reaction was allowed to proceed for a given period of time. As in most autoclave work for coal hydrogenation this time variation in the initial heating was assumed not to affect the results in any significant manner. The reaction was arrested by turning off the power to the furnace and cooling down the autoclave contents rapidly by passing cold water through the cooling coil. The
Hydrogenation
of residual oil: A. R. Mohamed
autoclave was then left overnight to cool to room temperature after which the product was removed and hot-filtered to remove solid residue and catalyst. The viscosity of the hydrogenated oil was determined at 30°C using a viscometer. The oil samples were then kept in a refrigerator to prevent possible polymerization until the ASTM distillation was carried out.
Table 3
RESULTS AND DISCUSSION
3
The objective of this investigation was to study the hydrogenation of Arabian Light atmospheric residual oil for the production of light distillates using a dispersed water soluble ammonium molybdate catalyst. The experimental variables held constant during the study were water content for dissolving the catalyst, the amount of residual oil used for each experimental run and the stirrer speed. The viscosity of the hydrogenated residual oil was determined and used as a measure of the degree of hydrogenation reaction. The results of this study have been divided into the effect of catalyst loading on residual oil hydrogenation, the performance of the dispersed catalyst compared to a commercial cobaltmolybdenum catalyst, and the results of the effect of pressure, temperature and reaction time on residual oil hydrogenation. The results from the ASTM distillation of the hydrogenation oil obtained at the most suitable conditions of catalyst loading, pressure, temperature and reaction time are also presented. .Effect
qf dispersed
catalyst on residual oil hydrogenation
The effect of the catalyst on the residual oil hydrogenation was studied based on molybdenum per cent loading with respect to the residual oil. In all experiments, the reactor pressure was maintained at 17.2 MPa, the reactor temperature between 400°C and 410°C and the reaction time was 30 min. In each run, the amount of residual oil used was 80 g. A predetermined amount of ammonium molybdate was dissolved in 10 ml of water and used as a catalyst. The effect of catalyst loading is shown in Figure 1. The amount of ammonium molybdate salt was varied from 0.0 to 0.443 g with a molybdenum loading of O&0.3% based on the residual oil. The viscosity of the hydrogenated residual oil decreased from 94.6 x 10m3
Serial number I 2
Hydrogenation
of residual
and V. K. Mathur
oil with various
Name of catalyst Cobalt-molybdenum Harshaw 0402T Ammonium molybdate salt solution Molybdenum sulphide ore
catalysts
Molybdenum loading W)
(Pa s)
0.215
20.5
0.216
14.5
0.222
26.1
Viscosity (x 10-S)
Pa s at 0.0% molybdenum loading to w 14.5 x 10m3 Pa s at 0.216%. After 0.216% molybdenum loading, the viscosity of the hydrogenated residual oil did not alter much with increase in the amount of catalyst. In order to study the catalytic effect of molybdenum in various forms in hydrogenating the residual oil, several experiments using other catalysts were also performed. The results are shown in Table 3. A commercial cobaltmolybdenum hydrotreating catalyst (- 200 mesh) was used at the same operating conditions of 17.2 MPa reactor pressure, 40&41O”C reactor temperature, and 30 min reaction time. The amount of the commercial cobalt-molybdenum catalyst used was -2.0 g with a molybdenum loading of 0.215% based on the residual oil. The viscosity of the hydrogenated residual oil was found to be 20.5 x low3 Pa s which was higher than that of the hydrogenated product obtained using dispersed ammonium molybdatq salt solution as a catalyst. An experiment was also conducted using molybdenum sulphide concentrate ore (Molybdenite) as a catalyst. As mentioned earlier, MOO, is prepared commercially by roasting MoS,. Therefore, it would be more economical if molybdenum sulphide ore concentrate could be used directly as a catalyst. Molybdenum sulphide (-0.35 g) with 0.222% of molybdenum was used in the experimental run at the same operating conditions. The viscosity of the hydrogenated residual oil was measured to be 26.1 x 1O-3 Pa s at 30°C. The result shows it is better to use dispersed ammonium molybdate salt as a catalyst than molybdenum sulphide ore concentrate as a slurry. The viscosity of the hydrogenated residual oil using dispersed ammonium molybdate salt as a catalyst was 44.4% lower than when molybdenum sulphide was used as a catalyst. An attempt was also made to extract ammonium molybdate by reacting ammonium hydroxide with molybdenum suphide ore concentrate with no success. Results from this experiment justify the use of MOO, ore concentrate as a starting material for the preparation of ammonium molybdate salt. The results from the above study validate the use of a dispersed solution of ammonium molybdate for the hydrogenation of residual oil. _EfSectof pressure
0
I
0
0.1 % molybdenum
Figure 1
Reaction
I
0.2
I
0.3
0.4
loading (based on oil loading)
Effect of molybdenum loading on hydrogenated conditions: 405”C, 17.2 MPa, 30 min
oil viscosity.
The effect of pressure on the residual oil hydrogenation was studied in the pressure range of 6.9-17.2 MPa. The temperature and the time of the reaction were kept constant at 4OWlO”C and 30 min, respectively. The effect of pressure on the residual oil hydrogenation is shown in Figure 2. It was found that the viscosity of the hydrogenated oil decreased steadily from 32.5 x 10e3 Pa s at 6.9 MPa to 16.6 x lop3 Pa s at 13.8 MPa. There
FUEL,
1991,
Vol
70,
August
985
Hydrogenation
of residual
oil: A. R. Mohamed
and V. K. Mathur
50
ASTM
40 z 0 g (3 s
q
30
.r’ 8 20 .> 10
0
I
I
I
1000
2000 Reactor
pressure
I
3000
(p.s.i.g.)
Figure 2 Effect of reactor pressure on hydrogenated oil viscosity. Reaction conditions: 405”C, 30 min, 0.216% molybdenum loading (I psig=6.895 kPa)
distillation
of hydrogenated
residual
oil
The hydrogenated oil sample for ASTM distillation was collected from two experimental runs operating the autoclave at 13.8 MPa pressure, 405°C temperature, and 30 min reaction time. The amount of catalyst used for each run was 0.216% of molybdenum loading based on the residual oil. The viscosity of the sample was found to be 16.5 x 10m3 Pas. The sample was then subjected to the ASTM D86-78 standard method for distillation of petroleum products. The ASTM distillation of the hydrogenated residual oil gave a total 34% liquid boiling below 235°C (cracking started above this temperature). The API gravity of this distillate was found to be 43. About 25% of the total distillate was found to be in the gasoline boiling range (32-204°C). There was - 14% of distillate in the kerosine boiling range (165-282°C). The sulphur content of the distillate was found to be 0.02 wt%. CONCLUSIONS
was only a slight decrease in the hydrogenated oil viscosity to 14.5 x 10m3 Pas when the pressure was further increased to 17.2 MPa. This viscosity reduction is small and probably within the experimental error. A reactor pressure of 13.8 MPa was chosen to be used for determining the effect of temperature and time. EfSect of temperature
The effect of temperature on the residual oil hydrogenation was studied in the temperature range 350430°C. The pressure was maintained at 13.8 MPa and the reaction time used was 30 min. The amount of ammonium molybdate salt catalyst used was -0.32 g (0.216% of molybdenum loading) as it was found earlier to be the most suitable loading. The effect of temperature on the residual oil hydrogenation is shown in Figure 3. The temperature was varied from 350 to 430°C. The viscosity of the hydrogenated residual oil decreased steadily from 101.4x 10m3 Pas at 350°C to -10.4x 10m3 Pas at 430°C. There was a substantial carbon residue formation at 430°C which caused a loss in the amount of hydrogenated residual oil. The viscosity of hydrogenated residual oil at a reaction temperature of 405°C was found to be 16.6 x 10e3 Pa s. The temperature of 405°C and reactor pressure of 13.8 MPa were used subsequently to study the effect of reaction time. Ef/‘ect of reaction
“Oh 320
360
400
Reactor
440
temperature
(“C)
Figure 3 Effect of reactor temperature on hydrogenated oil viscosity. Reaction conditions: 13.8 MPa, 30 min, 0.216% molybdenum loading
80
,
time
The effect of time on the residual oil hydrogenation was studied in the range of 15-45 min. The temperature and pressure were maintained at 405°C and 13.8 MPa, respectively, and all other conditions were the same as in earlier experiments. The effect of time on the hydrogenation of residual oil is shown in Figure 4. It can be seen that the viscosity of the hydrogenated oil decreased sharply from 62.6 cp (62.6 x 10m3 Pa s) at 15 min to - 16.6 cp (- 16.6 x lop3 Pa s) at 30 min. A further increase in time up to 45 min showed no significant reduction in the viscosity of the hydrogenated oil. The most suitable time of reaction was thus found to be 30 min for which the viscosity of the hydrogenated oil was found to be - 16.6 x 10m3 Pa s.
986
1. Results of hydrogenation of residual oil showed that dispersed water soluble ammonium molybdate catalyst was an effective catalyst and compared
FUEL, 1991, Vol 70, August
20 Reaction
40
60
time (min)
Figure 4 Effect of reaction time on hydrogenated oil viscosity. Reaction conditions: 405”C, 17.2 MPa, 0.216% molybdenum loading
Hydrogenation
favourably with the commercially available, supported cobalt-molybdenum Harshaw catalyst. It is most significant that the dispersed catalyst could be prepared directly from inexpensive MOO, ore concentrate. The experimental conditions for the hydrogenation of residual oil were found to be 0.216% molybdenum based on residual oil, 13.8 MPa pressure, 405°C reactor temperature, and 30 min reaction time. Under these conditions, the product API gravity increased to 23 with a decrease in viscosity to 16.6 x 10m3 Pa s. An ASTM distillation of the hydrogenated product gave 34% liquid boiling below 235°C. The API gravity of this distillate was found to be 43 with a sulphur content of 0.02 wt%. _ . The use of ammonium molybdate prepared from MOO, ore concentrate was a cheaper alternative to the use of analytical grade ammonium molybdate compound as a catalyst.
1 2 3 4 5 6 7 8 9 IO II
13
Authors thank Dr M. K. Sood, Mobil Corporation, Princeton, NJ for supplying the atmospheric residual oil. Thanks are also due to the Harshaw Chemical Co., Cleveland, OH, Molycorp Inc., Washington, PA and Climax Molybdenum Co., Langeloth, PA for supplying catalyst and ore samples. One of the authors (A.R.M.) thanks the Malaysian government for its financial support during the course of this study.
oil: A. R. Mohamed
and V. K. Mathur
REFERENCES
12
ACKNOWLEDGEMENTS
of residual
14
15
Gary, J. H. and Handwerk, G. E. ‘Petroleum Refining, Technology and Economics’, Marcel Dekker, New York, 1975 Speight, J. G. ‘The Desulfurization of Heavy Oil and Residua’, Marcel Dekker, New York, 1981 Baldassari, M. C. and Hamilton, G. L. Paper presented at the AIChE Meeting, Houston, April 1989 Beret, S. and Reynolds, J. G. Am. C&m. Sot. Dir. Fuel Chem. Prepr. 1985, 30(3), 397 Sy, 0.. Desmarais, L., Bode, D. rr (11. Paper presented at the AIChE Meeting, Houston, April, 1989 Kellett, T. F., Trevino, C. A. and Sartor, A. F. Oil Gas J. 1980, 78( 18). 244 Lopez. J.. McKinney, J. D. and Pasek. E. A. US Par. 4557821, 1985 Cugini. A. V., Ruether, J. A.. Cillo. D. L. ct crl. Am. Ckw. SK. Dir. Fuel Chem. Prqr. 1988, 33( 1 ), 6 Ha. B. C., Ruether. J. A., Smith, D. N. et ul. Am. Chem. Sot. Dir. Fuel Chrm. Prepi-. 1988, 33(3), 343 Snape. C. E., Bolton, C., Dosch, R. G. et d. Am. Chem. SW. Div. Fuel Chum. Prcpr. 1988, 33(3). 351 Hirschon, A. S. and Wilson, R. B. Am. Chem. SM. Dia. Fuel Chem. Prepr. 1989, 34(3), 881 Utz, B. R.. Cugini. A. V. and Frommell. E. A. Am. Chem. SK. Die. Fuel Chcm. Prepr. 1989, 34(4), 1423 Krastman. D., Utz, B. R., Cugini, A. V. and Lett, R. G. Am. Chem SW. Dir. Fud Chem. Prepr. 1990, 35(2), 570 Killeffer, D. H. and Linz, A. ‘Molybdenum Compounds, Their Chemistrv and Technoloav’. -, Interscience Publishers, New York, 1952 . Mark. H. F., Othmer, D. F., Overburger, C. G. et cd. ‘Concise Encylopedia of Chemical Technology’, John Wiley and Sons. New York, 1985. nn. . 774-775 Mathur, V. K. and Venkataramanan, V. .4nr. Cliem. Sot. Div. Furl Chem. Prrpr. 1982. 27(2), 1 Mathur, V. K.. Fakoukakis, E. P. and Ruether. J. A. Fuel 1984, 63. 1700 Mathur, V. K. and Reddy Karri, S. B. Fuel 1986, 65, 790 Mohamed. A. R. MS Thesis University of New Hampshire, 1989 L
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987