Hydrotreating vacuum gas oils with catalyst and added organic fluorine compound

The method of converting at least 20% by weight of a vacuum gas oil fraction boiling above 650.degree. F. into products having a boiling point less than about 650.degree. F., which comprises hydrotreating a vacuum gas oil with a hydrodesulfurization catalyst comprising a Group VIB and Group VIII metal wherein an organic fluorine compound is added to the vacuum gas oil during hydrotreating and the vacuum gas oil is hydrotreated under hydrogen at a temperature of at least 740.degree. F.

This invention relates to hydrotreating vacuum gas oils containing at least 
0.5% by weight sulfur with a hydrodesulfurization catalyst wherein an 
organo-fluorine compound is added on stream to the vacuum gas oil feed and 
the vacuum gas oil is hydrotreated under hydrogen at a temperature of at 
least 740.degree. F. 
In the last few years, it has become necessary to process oils containing 
higher and higher levels of sulfur. At the same time, environmental rules 
have placed more stringent limitations on the amount of sulfur that can be 
emitted into the air. In many refineries, low sulfur vacuum gas oils are 
hydrodesulfurized to a relatively low sulfur content and conveyed to a 
cracking unit, such as a fluidized catalytic cracker. When a low sulfur 
vacuum gas oil is employed, a relatively high percentage of the sulfur is 
removed from the vacuum gas oil before the hydrotreated product is 
cracked. Even in these cases, an undesirable level of SO.sub.x can be 
emitted from the cracking units. This has led to numerous schemes and 
additives for converting the SO.sub.x to H.sub.2 S which can be handled 
readily in sulfur recovery units attached to hydrotreating units and 
cracking units. As the level of sulfur in the vacuum gas oil increases, 
there is less complete conversion of sulfur to H.sub.2 S in the 
hydrotreating units and a commensurately higher load of SO.sub.x produced 
in the cracking units. For example, it is not unusual when processing a 
vacuum gas oil containing 3% sulfur in conventional hydrotreating units to 
remove only 90% of the sulfur. However, this is not satisfactory today. 
Since some refineries lack cracking facilities or have insufficient 
cracking capacity for processing all the hydrodesulfurized vaccum gas oil 
produced, substantially complete removal of sulfur from gas oils during 
hydrodesulfurization is even more important. Accordingly, there is a need 
for more efficient methods of reducing the level of sulfur in vacuum gas 
oils. 
As indicated above, some refineries do not have adequate cracking 
facilities for treating all hydrodesulfurized gas oil. Accordingly, the 
product slate produced by hydrodesulfurization is critical to the economic 
viability of the refinery. It is important that these refineries have 
means of converting the hydrodesulfurized gas oils into large volume 
products boiling below 650.degree. F., such as, gasoline or middle 
distillates. Unfortunately, hydrodesulfurization produces very little 
gasoline or middle distillates since there is less than 10% conversion of 
the 650+.degree. F. fraction. Therefore, there is a need for 
hydrodesulfurization processes that produce substantially higher levels of 
gasoline and middle distillates, preferably middle distillates boiling 
below 650.degree. F. High volumes of middle distillates are desirable 
since they can be utilized for diesel fuel. 
It is well known that hydrodesulfurization catalysts have optimum 
temperature ranges to accomplish the desired result. For example, the 
conventional cobalt-molybdenum and nickel-molybdenum hydrodesulfurization 
catalysts are generally employed at a temperature of around 700.degree. F. 
If one carries out hydrodesulfurization with these molybdenum catalysts at 
higher temperatures, such as 740.degree. F., the catalysts deactivate 
rapidly. Accordingly, it is not possible to obtain greater conversion of 
the 650+.degree. F. by raising the treating temperature of the vacuum gas 
oil. 
Numerous patents describe the use of halogen promoters for the treatment of 
petroleum streams. Some of these patents describe the treatment of various 
hydroprocessing catalysts with halogens such as a chlorine and fluorine. 
In other cases, organic halogen compounds, preferably carbon 
tetrachloride, have been added to the hydrocarbon stream being treated. In 
most cases the patentees desire to avoid the conversion of the hydrocarbon 
stream into low-boiling gaseous materials. 
Sze U.S. Pat. No. 4,181,601 discloses a process of producing light olefins, 
benzene, toluene and xylenes wherein a halogenated bimetallic catalyst is 
employed to hydrotreat gas oils without excessive hydrocracking and gas 
production at a temperature of about 640.degree. F. to 950.degree. F. 
followed by thermal cracking. The patentee indicates that there are 
increased yields of light olefins, benzene, toluene and xylene ensuing 
from the use of the halogenated catalyst in the first step of the two step 
process. While the patentee indicates that either chlorine or fluorine 
substituted organic compounds can be employed to halogenate the catalyst 
on stream, all of the examples in the patent utilize organic chlorine 
compounds. Further, while the patentee indicates that the hydrogenation 
can be carried out at 640.degree. F. to 950.degree. F., preferably 
650.degree. F. to 750.degree. F., all of the examples employ a temperature 
in the range of about 690.degree. F. to 700.degree. F. The patentee fails 
to appreciate the fact that the use of an organic fluorine compound plus a 
higher temperature in the range of about 740.degree. F. to 800.degree. F. 
results in advantageous hydrocracking of the fraction of the gas oils 
boiling at more than 650.degree. F. without the formation of undesirable 
gaseous products. 
Michelson U.S. Pat. No. 4,220,557 discloses the fluoriding of 
hydrodesulfurization catalysts with fluorosilicates. While the patentee 
indicates that these catalysts can be advantageously used for the 
hydrogenation and cracking of organic sulfur and nitrogen compounds in 
hydrocarbon feedstocks, including light and heavy gas oils, at a 
temperature of 450.degree. F. to 900.degree. F., preferably 550.degree. F. 
to 800.degree. F., the patentee's sole example is directed to 
hydrodesulfurization of a light diesel fuel boiling between 400.degree. F. 
and 650.degree. F. with the hydrodesulfurization being carried out at 
700.degree. F. However, the patentee fails to recognize that it is 
possible to convert a substantial portion of the 650+.degree. F. fraction 
of vacuum gas oils to middle distillates by treatment at approximately 
740.degree. F. to 780.degree. F. with on stream fluoriding of the 
catalyst. 
The general object of this invention is to provide a process of 
hydrotreating relatively high sulfur vacuum gas oils under conditions 
wherein substantially all of the sulfur contained in the vacuum gas oil is 
converted to H.sub.2 S and wherein approximately 20 to 50% by weight or 
more of the vacuum gas oil fraction boiling above 650.degree. F. is 
converted into products having a boiling point less than about 650.degree. 
F. without the formation of excessive quantities of low molecular weight 
gaseous hydrocarbons, such as ethane, propane, etc. Other objects appear 
hereinafter. 
We have now found that the objects of this invention can be attained by 
hydrotreating vacuum gas oils containing at least 0.5% sulfur, preferably 
at least 1% sulfur, with a hydrodesulfurization catalyst wherein an 
organic fluoride compound is added to the vacuum gas oil feed during 
hydrotreating and the vacuum gas oil is hydrotreated under hydrogen at a 
temperature of at least 740.degree. F. Our studies have shown that there 
is relatively little hydrocracking of the vacuum gas oil unless the vacuum 
gas oil is heated to at least 740.degree. F. with cobalt-molybdenum 
catalyst. Further, hydrocracking does not start until such time as 
substantially all of the sulfur in the feedstock capable of being removed 
at 740.degree. F. has been removed. When prior art processes are carried 
out at about 700.degree. F. without on stream fluoriding using a vacuum 
gas oil containing 3% by weight sulfur (1) only about 90% of the sulfur is 
removed and (2) there is less than 10% conversion of the fraction boiling 
at above 650.degree. F. Other things being equal when the process of this 
invention is employed there is 99% removal of sulfur and over 20% 
conversion of the fraction boiling at above 650.degree. F. into desirable 
non-gaseous products. 
Although the organo-fluorine compound can be added continuously to the 
hydrocarbon stream, it is generally preferable to add a sufficient 
concentration of organo-fluorine compound to the hydrocarbon stream to 
raise the level of fluorine on the catalyst to about 0.5 to 6% by weight 
and then operate the hydrocracker for several weeks without replenishment 
of the organo-fluorine compound. The instant process has the additional 
advantage that it is possible to operate the unit as a hydrotreater 
without any substantial hydrocracking by allowing the fluorine to 
dissipate during use. The unit can be operated as a hydrocracker again by 
replenishing the organo-fluorine compound from time to time. 
Briefly, this invention comprises hydrotreating vacuum gas oils containing 
at least 0.5% by weight sulfur, preferably at least 1% by weight sulfur, 
with a hydrodesulfurization catalyst comprising a Group VIB metal and 
Group VIII metal wherein an organic fluoride compound is added to the 
vacuum gas oil feed during hydrotreating and the vacuum gas oil is 
hydrotreated under hydrogen at a temperature of at least 740.degree. F. 
As indicated above, vacuum gas oils useful in this invention contain at 
least 0.5% by weight sulfur, preferably at least 1% by weight sulfur. 
While substantially any vacuum gas oil can be used in this invention, the 
process is particularly useful for hydrodesulfurization of vacuum gas oils 
having a substantial quantity of sulfur. For example, the process of this 
invention can be utilized to remove approximately 99% by weight of the 
sulfur contained in a vacuum gas oil having 3% by weight sulfur. 
The catalyst useful in this invention is a bimetallic catalyst comprising 
at least one metal from Group VIB and at least one metal from Group VIII 
of the periodic table. The Group VIB metal is generally molybdenum and the 
Group VIII metal is generally nickel and/or cobalt. The active form of the 
catalyst is the sulfided form and such sulfiding can be effected prior to 
the use of the catalyst, or in situ, since the gas oil feed contains 
sulfur. The catalyst can be supported on any of the supports normally used 
in this art, such as, alumina; alumina-silica; alumina-silica containing 
zeolites; alumina-magnesia, etc. The various Group VIB and Group VIII 
metals can be used in the concentrations normally employed in this art. 
The organic fluorine compounds include carbon tetrafluoride; 
difluoroethane, fluorobenzene, etc. As indicated above, the fluorine 
component apparently reacts with the support to provide hydrocracking 
activity to the catalyst. Further, the fluorine component acts as a 
stabilizer for the catalyst in the sense that it permits the catalyst to 
be utilized at a higher temperature without deactivation of the catalyst. 
For example, whereas typical molybdenum/Group VIII catalysts deactivate at 
a temperature of about 740.degree. F. and higher, the fluorided catalysts 
utilized in this invention function effectively as hydrocracking catalysts 
at a temperature range of about 740.degree. F. to 800.degree. F. without 
deactivation. The catalysts can be pretreated with any fluorine containing 
compound, such as organo-fluorine compounds or inorganic fluorine 
compounds prior to use. However, the preferred procedure is to treat the 
catalyst in situ with a fluoro-substituted hydrocarbon in the vacuum gas 
oil feedstock. Irrespective of the fluoriding method, sufficient fluorine 
containing compound should be reacted with the catalyst to increase its 
weight by 0.5 to 6%. Further, it is essential for the purpose of this 
invention that organo-fluorine compound be supplied to the catalyst from 
time to time to maintain hydrocracking activity and stabilizing effect on 
the catalyst. Under these circumstances, the fluorine containing compound 
is supplied as an organo-compound which decomposes on contact with the 
catalyst. The orgao-fluorine containing compounds have the advantage that 
there is less of a tendency for degradation of the reactor walls due to 
the formation of hydrofluoric acid. 
Hydrogenation is effected at a temperature of at least 740.degree. F., e.g. 
740.degree.-800.degree. F. Other things being equal, the higher the 
reaction temperature, the greater the conversion of the 650+.degree. F. 
fraction of the gas oil into 650-.degree. F. material. For example, at 
about 740.degree. F., there is at least 20% conversion of the 650+.degree. 
F. fraction, whereas at about 780.degree. F., there is approximately 50% 
conversion of the 650+.degree. F. fraction. The maximum temperature is 
dependent on the metallurgical limits of the reactor. The 
hydrodesulfurization reaction is carried out under hydrogen using a 
sufficient concentration of hydrogen to effect efficient hydrotreating and 
hydrocracking of the vacuum gas oil. In general, hydrogen can be employed 
in a concentration of 1,000 to 15,000 SCF per barrel. The liquid hourly 
space velocity can range from about 0.5 to 3.40.

EXAMPLE I 
A Kuwait heavy vacuum gas oil having a gravity of 22.8.degree. API, 3.01 
percent by weight sulfur, 0.09 percent nitrogen, 4.9 percent by weight 
fraction boiling between 360.degree. to 650.degree. F. and 95.1 percent by 
weight fraction boiling at 650+.degree. F. was hydrotreated in an 
isothermal bench-scale, trickle-bed reactor using once-through hydrogen. 
The reactor had a nominal inside diameter of 0.546", a thermowell with a 
nominal outside diameter of 0.125" which passed axially through the 
catalyst bed. Eurotherm temperature controls were used to maintain an 
isothermal (.+-.3.degree. F.) reactor bed temperature by means of 
electrical heaters around the top, middle and bottom sections of the 
reactor. The 33.5 cc catalyst bed was 9.2" in length and was loaded into 
the middle heating zone with the oil delivered to the reactor by a Ruska 
pump together with hydrogen. The 2-phase reactant mixture (oil and 
hydrogen) passed vertically downward through the catalyst bed comprising a 
sulfided commercial 1/16" cobalt-molybdenum on alumina extrudate. The 
products were then passed into a separator with the flow of liquid product 
being controlled by a level control valve. The conditions of reaction over 
a 27 day period are set forth below in Table I. The catalyst was fluorided 
over the period of days 8 to 9 and again at day 21 by adding 
difluoroethane in liquid naphtha from a second Ruska pump to the gas oil. 
Fluoridation at days 8 and 9 was continued until the catalyst had a weight 
gain of approximately 3 percent by weight fluoride. Fluoridation at day 21 
was continued until the fluoride level was approximately 3 percent by 
weight. Table I also indicates the sulfur content of the treated gas oil 
and the extent of conversion of the 650+.degree. F. fraction of the vacuum 
gas oil. 
TABLE I 
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Wt. % 
Days 650 + .degree.F. 
Wt. % 
on Tempera- LHSV Wt. % Conver- Desulfur- 
Oil ture .degree.F. 
Vo/Hr/Vc Sulfur 
sion ization 
______________________________________ 
1 650 1.68 1.62 3.07 47.04 
2 650 1.68 1.63 2.35 46.91 
3 650 1.68 1.61 4.28 47.31 
4 700 1.68 0.96 6.97 68.73 
5 700 1.68 0.85 6.70 72.34 
6 700 1.68 0.87 6.58 71.66 
7 700 1.68 0.90 6.72 70.72 
8 650 1.80 1.30 4.83 57.50 
9 650 1.80 1.48 3.97 51.67 
10 700 1.68 0.90 5.08 70.74 
11 700 1.68 0.74 5.43 75.95 
12 700 1.68 0.80 5.60 74.01 
13 700 1.68 0.74 6.09 75.99 
14 700 1.68 0.70 5.61 77.21 
15 739 1.68 0.33 10.03 89.36 
16 740 1.68 0.29 12.45 90.64 
17 740 1.68 0.30 13.31 90.31 
18 741 0.45 0.02 29.24 99.37 
19 741 0.45 0.09 24.78 97.14 
20 740 0.45 0.02 26.71 99.26 
21 650 0.45 0.28 11.51 90.91 
22 740 0.45 0.05 27.96 98.40 
23 740 0.45 0.02 30.22 99.39 
24 740 0.45 0.02 30.85 99.37 
25 740 0.45 0.01 29.48 99.58 
26 740 0.45 0.01 31.26 99.65 
27 740 0.45 0.01 29.84 99.61 
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The above Table clearly shows that there is no substantial conversion of 
650+.degree. F. material until the catalyst is fluorided and the reaction 
temperature is raised to about 740.degree. F. Further, the above data 
clearly shows it is possible to remove in excess of 99% by weight of the 
sulfur contained in the vacuum gas oil. In days 18 through 27 when the 
process was operated at about 740.degree. F. using a fluorided catalyst, 
there was in excess of 20% by weight conversion of the 650+.degree. F. 
fraction of the vacuum gas oil. 
EXAMPLE II 
When the process described in Example I was carried out at approximately 
760.degree. F. for a ten day period after fluoriding, the average degree 
of conversion of the 650+.degree. F. fraction of the vacuum gas oil was 
approximately 35% and desulfurization was at least 99.4%. 
EXAMPLE III 
When the process described in Example I was repeated at a temperature of 
about 780.degree. F. for a period of ten days after fluoriding, the 
average degree of conversion of the 650+.degree. F. fraction of the vacuum 
gas oil was about 48% and desulfurization was at least 99.5% by weight.