Process for converting petroleum residuals

An improved process for hydrocracking petroleum residuals wherein total conversion and the yield of lower boiling range products are increased. The hydrocracking is accomplished in the presence of a hydrogen donor solvent and molecular hydrogen. The conversion is accomplished at a pressure within the range from about 1500 to about 2500 psig and at a temperature within the range from about 800.degree.to about 850.degree. F. Operation at these conditions is essential to achieving the increased conversion and the increased yield of lower boiling liquid products. While the present invention has been described and illustrated by reference to particular embodiments thereof, it will be appreciated by those of ordinary skill in the art that the same lends itself to variations not necessarily illustrated herein. For this reason, then, references should be made solely to the appended claims for purposes of determining the true scope of the present invention.

BACKGROUND OF THE INVENTION 
This invention relates to an improved process for converting petroleum 
residuals. More particularly, this invention relates to an improved 
process for hydrocracking petroleum residuals. 
Heretofore, several processes have been proposed for converting or 
demetalizing petroleum residuals. Such conversions and demetalizations may 
be accomplished over a relatively broad range of pressures and, generally, 
such conversions or demetalizations are accomplished at temperatures known 
to be effective in hydrocracking operations. It is known to effect such 
conversions or demetalizations in the presence of a solvent capable of 
donating hydrogen at the conditions employed to effect the conversion or 
demetalization and molecular hydrogen may or may not be present. The 
processes which have been proposed, heretofore, are used primarily for the 
purpose of upgrading the petroleum residuals such that the converted and 
demetalized product can satisfactorily be used as a feedstock to various 
petroleum processes such as catalytic cracking, hydrocracking and the 
like. As a result, however, the processes proposed heretofore have not 
resulted in significant conversion of the petroleum residual or in 
significant production of lighter boiling materials, particularly those in 
the naptha boiling range. The need, then, for an improved process for 
converting petroleum residuals to lighter products which may be used 
directly as a fuel is believed readily apparent. 
SUMMARY OF THE INVENTION 
It has now been discovered that the foregoing and other disadvantages of 
the prior art processes can be avoided with the method of the present 
invention and an improved process for converting petroleum residuals 
provided thereby. It is, therefore, an object of this invention to provide 
an improved process for the conversion of petroleum residuals. It is 
another object of this invention to provide such a conversion process 
wherein the total conversion of residuals is increased. It is still a 
further object of this invention to provide such an improved process 
wherein the relative yield of lighter boiling materials is increased. The 
foregoing and other objects and advantages will become apparent from the 
description set forth hereinafter and from the drawings appended thereto. 
In accordance with the present invention, the foregoing and other objects 
and advantages are accomplished by converting a petroleum residual in the 
presence of molecular hydrogen and a hydrogen donor solvent at an elevated 
pressure and temperature. As pointed out more fully hereinafter, the total 
conversion of petroleum residual to lower boiling materials is increased 
by controlling the pressure within a relatively narrow critical range and 
by effecting the conversion in the presence of a hydrogen donor solvent 
containing at least 0.8 weight percent donatable hydrogen. As also pointed 
out more fully hereinafter, continuous operation of the process can be 
maintained by controlling the concentration of aromatic and hydroaromatic 
materials in the solvent relative to the amount of paraffinic materials 
therein.

DETAILED DESCRIPTION OF THE INVENTION 
As indicated, supra, the present invention relates to an improved process 
for converting petroleum residuals to lower boiling materials wherein 
total conversion of the petroleum residual and the yield of lighter 
boiling materials is increased. As indicated more fully hereinafter, it is 
critical to the present invention that the liquefaction be accomplished in 
the presence of a solvent containing at least about 0.8 weight percent 
donatable hydrogen at the time the solvent is fed to the conversion step; 
that the ratio of paraffinic materials to aromatic and hydroaromatic 
materials in the solvent be controlled such that the ratio is within the 
range from about 0:1 to about 0.5:1; and that the conversion be 
accomplished in the presence of molecular hydrogen at a partial pressure 
within the range from about 1500 to about 2500 psia. 
In general, the method of the present invention can be used to convert any 
petroleum residual material. For purposes of this invention, petroleum 
residual material shall mean the material remaining after a crude oil has 
been processed to separate lower boiling constitutents. In general, the 
petroleum residuals will have an initial boiling point within the range 
from about 650 to about 1050.degree. F. and will be normally solid at 
atmospheric conditions. The petroleum residuals will, however, be liquid 
at the conditions used to effect the conversion. The petroleum residuals 
may be derived or separated from essentially any crude including those 
generally classed as aromatic, napthenic and paraffinic. In general, the 
petroleum residuals useful in the method of this invention will be bottoms 
from a vacuum distillation column but the same could be any residual from 
a carbonaceous material having an initial boiling point within the range 
hereinbefore noted that is also liquid at the conditions used to effect 
the conversion. 
In the method of the present invention, the petroleum residual will be 
combined with a solvent or diluent capable of donating hydrogen at the 
conditions employed to effect the conversion and containing at least 0.8 
weight percent donatable hydrogen. The solvent may be a pure component but 
is preferably a mixture of components, some of which are capable of 
donating hydrogen and some of which are not. In a most preferred 
embodiment, at least a portion of the solvent will be a distillate 
fraction separated from the conversion liquid product and, depending on 
the particular petroleum residual subjected to conversion, this distillate 
fraction may be separately hydrotreated to produce components therein 
which are capable of donating hydrogen during conversion. In this regard, 
it should be noted that when the petroleum residual is highly aromatic, 
the distillate fraction will, generally, contain sufficient aromatic 
materials, that can be converted via hydrotreating to corresponding 
hydroaromatic materials to provide all of the donatable hydrogen required 
in the solvent. When the petroleum residuals are primarily napthenic or 
paraffinic, however, it will, generally, be necessary to add aromatic 
and/or hydroaromatic materials to the distillate fraction which has been 
separated from the conversion product for use as a solvent. Also, it may 
be necessary, particularly with paraffinic crudes, to remove at least a 
portion of the paraffinic material in the solvent fraction. When aromatics 
are added, separate hydrotreating will be necessary to convert at least a 
portion of the aromatics to corresponding hydroaromatics. When 
hydroaromatics are added directly, however, such separate hydrotreating 
will not be necessary. In this regard, it should be noted that an 
important feature of the present invention is the discovery that paraffins 
are the principal contributor to coke formation during conversion and that 
the presence of aromatics and hydroaromatics during such conversions 
either inhibit the formation of coke or solubilize the same to avoid 
plugging during conversion operations. Also, in a most preferred 
embodiment, use of a solvent having characteristics similar to the 
characteristics of the conversion product increases total conversion of 
the petroleum residuals. The use of a solvent which is a distillate 
fraction containing a relatively broad range of compounds is, therefore, 
particularly advantageous and when the petroleum residual is an aromatic, 
the solvent should contain aromatic materials, when the petroleum residual 
is napthenic, the solvent should contain napthenic materials and when the 
residual is paraffinic, the solvent should contain paraffins. 
Compounds which will donate hydrogen during liquefaction are believed 
well-known in the prior art and many are described in U.S. Pat. No. 
3,867,275. These include the indanes, the dihydronapthalenes, the C.sub.10 
-C.sub.12 tetrahydronapthalenes, the hexahydroflourines, the dihydro-, 
tetrahydro-, hexahydro- and octahydrophenanthrenes, the C.sub.12 -C.sub.13 
acid napthenes, the tetrohydro-, hexahydro-, and decahydropyrenes, the 
di-, tetra-, and octahydroanthracenes, and other derivatives of partially 
saturated aromatic compounds. Particularly effective mixed solvents for 
use in the present invention include mixtures comprising a distillate 
fraction separated from the conversion product which is separately 
hydrotreated to convert at least a portion of the aromatic materials 
contained therein to the corresponding hydroaromatic components, 
hydrogenated creosote oils and hydrogenated catalytic cracking cycle stock 
and mixtures of such mixtures. Particularly effective solvents include 
distillate fractions of such mixtures having an initial boiling point 
within the range from about 400.degree. to about 650.degree. F. and a 
final boiling point within the range from about 850.degree. to about 
1050.degree. F. which have been hydrogenated so as to contain at least 25 
weight percent of hydrogen donor species and preferably at least 50 weight 
percent of such species. 
In general, the petroleum residual and the solvent will be combined in a 
solvent-to-residual weight ratio within the range from about 0.5:1 to 
about 2:1. The combination may be effected in accordance with any 
procedure obvious to one of ordinary skill in the art which will be 
effective in uniformly distributing the petroleum residual throughout the 
solvent. Best results are generally, however, obtained at elevated 
temperatures within the range from about 100.degree. to about 350.degree. 
F. in suitable mixing equipment. 
After the mixture of petroleum residual and solvent is prepared, the same 
is then subjected to conversion at a temperature within the range from 
about 800.degree. to about 850.degree. F. in the presence of molecular 
hydrogen. Generally, molecular hydrogen will be present at a concentration 
within the range from about 4 to about 8 weight percent based on petroleum 
residual and the partial pressure of molecular hydrogen will be within the 
range from about 1500 to about 2500. The mixture will be held at these 
conditions for nominal holding time within the range from about 30 to 
about 120 minutes. 
Another important feature of the present invention is the discovery that 
when a properly selected solvent is used the nominal holding time in 
either a batch or continuous operation can be extended when the hydrogen 
partial pressure is maintained within the critical range heretofore noted 
without a reduction in total conversion of the petroleum residual which 
has been experienced in processes heretofore proposed. In this regard, it 
should be noted that total conversion as used herein means the percentage 
of the petroleum residual which is converted to materials having boiling 
points less than the initial boiling point of the petroleum residual 
subjected to conversion. This discovery is illustrated in FIG. 1. 
Referring then to FIG. 1, curve 1 is a plot of conversion vs. contacting 
time when a heavy Arab resid was treated in the presence of a non-donor 
solvent at 840.degree. F. at a solvent-to-residual ratio of 1.5:1 and at a 
hydrogen partial pressure of 2000 psia. Curve 2 is a plot of conversion 
vs. holding time at the same conditions except that a solvent capable of 
donating hydrogen during conversion was employed. In the runs used to 
generate curve 2, hydrogenated creosote oil was used as a solvent at a 
solvent-to-residual ratio of 1.5:1. As will be apparent from FIG. 1, 
significantly increased conversions can be achieved when operating in 
accordance with the method of the present invention. 
While the inventors do not wish to be bound by any particular theory, it is 
believed that when the hydrogen partial pressure is increased during 
conversion of a petroleum residual to a value within the critical range 
heretofore specified in the presence of a solvent capable of donating 
hydrogen at the conditions of the conversion, free radicals which have 
formed at the more severe conditions associated with increased holding 
time in processes proposed heretofore are scavenged by reaction with 
hydrogen contributed either by the donor solvent or from the molecular 
hydrogen. Surprisingly, however, a reduction in total conversion has been 
experienced when the hydrogen partial pressure is increased above about 
2500 psia. 
While also not wishing to be bound by any particular theory, it is believed 
that the solvent must contain a sufficient amount of donatable hydrogen to 
provide at least 0.4 weight percent of such hydrogen based on petroleum 
resid in the initial mixture of petroleum resid and solvent. It is also 
believed necessary that the solvent contain at least 50 weight percent 
aromatic plus hydroaromatic components to prevent plugging as the result 
of coke formation during conversion. 
During the conversion, at least a portion of the petroleum residual will be 
converted to a normally gaseous product and at least a portion will be 
converted to a normally liquid product. Generally, the liquid product will 
have an initial boiling point at or near the atmospheric temperature and a 
final boiling point equal to the initial boiling point of the petroleum 
residual and within the range from about 650.degree. to about 1050.degree. 
F. The liquid product may then be fractionated into any desired fractions 
for further upgrading or direct use as an end product. Unconverted 
material; i.e., material having a boiling point equal to or greater than 
the initial boiling point of the petroleum residual subjected to 
conversion may either be recycled to the conversion step, burned directly 
as a fuel or discarded. 
In general, at least a portion of the liquid product will be separated and 
recycled to provide at least a portion of the solvent required to effect 
the conversion. When the separated fraction contains sufficient aromatics 
and/or hydroaromatics, it will not be necessary to combine this fraction 
with any extraneous solvent fractions. To the extent that the separated 
fraction contains primarily aromatics, this fraction may be subjected to 
hydrotreating to convert at least a portion of the aromatics to a 
corresponding hydroaromatic material. When this fraction does not, 
however, contain sufficient aromatic or hydroaromatic materials, it will 
be necessary to combine the same with an extraneous solvent fraction to 
produce a solvent having an aromatic/hydroaromatic concentration within 
the ranges heretofore specified. A catalytic cracking recycle oil is a 
particularly preferred extraneous fraction to employ since this oil is 
particularly high in aromatic materials. Creosote oils may also be used as 
an extraneous solvent fraction since these oils, too, generally, contain 
significant concentrations of aromatic materials. 
PREFERRED EMBODIMENT 
In a preferred embodiment of the present invention, the petroleum residual 
will be converted at a temperature within the range from about 820.degree. 
to about 845.degree. F. in the presence of a solvent capable of donating 
at least about 1.0 weight percent hydrogen, based on petroleum resid in 
the initial mixture of petroleum resid and solvent, and in the presence of 
molecular hydrogen at a hydrogen partial pressure within the range from 
about 1700 to about 2200 psia. In the preferred embodiment, the petroleum 
residual will be maintained at these conditions for a nominal holding time 
within the range from about 60 to about 90 minutes. Also in the preferred 
embodiment, the solvent will contain at least 60 weight percent aromatic 
and hydroaromatic components and the ratio of paraffinic materials to 
aromatic and hydroaromatic materials will be within the range from about 
0:1 to about 0.25. In a preferred embodiment, the aromatic and 
hydroaromatic materials may be contained in a distillate fraction of the 
conversion liquid product or obtained by hydrotreating such a fraction 
containing aromatic materials or the same may be obtained from alternate 
sources such as a catalytic cracking cycle oil or a creosote oil. In a 
most preferred embodiment, however, a petroleum residual containing 
sufficient aromatic materials will be subjected to liquefaction and a 
sufficient concentration of aromatic materials will be present in a 
distillate fraction separated from the conversion liquid product and the 
required hydroaromatic concentration will be provided by hydrotreating 
this fraction to convert at least a portion of the aromatic materials to 
corresponding hydroaromatic materials. Any suitable catalyst may be used 
during the hydrotreating. 
It is believed that the invention will be even better understood by 
reference to attached FIG. 2 which illustrates a particularly preferred 
embodiment. Referring then to FIG. 2, a petroleum resid, a suitable 
solvent and molecular hydrogen are fed into mixing manifold 201 through 
lines 202, 203 and 204, respectively. The petroleum resid will be 
introduced at a temperature above the temperature at which the same is 
liquid and pumpable, generally at a temperature within the range from 
about 100.degree. to about 350.degree. F. In general, any suitable solvent 
may be introduced through line 203 to effect "start up" of a commercial 
operation but at steady state recycle solvent will be introduced through 
line 205 and only makeup or extraneous solvent will be introduced through 
line 203. Extraneous solvent will, of course, be introduced when the 
recycle solvent introduced through line 205 is deficient in aromatic 
and/or hydroaromatic content. To the extent that hydroaromatic materials 
are introduced through line 203, the solvent will, preferably, be a 
hydrogenated creosote oil or a hydrogenated catalytic cracking cycle 
stock. In general, the solvent and molecular hydrogen will be preheated to 
a temperature within the range from about 800.degree. to about 850.degree. 
F. In general, the solvent will contain sufficient donatable hydrogen to 
provide at least 0.4 weight percent donatable hydrogen based on petroleum 
resid in the initial mixture and the combined aromatic/hydroaromatic 
concentration in the solvent will be at least 50 weight percent. The 
solvent will be combined with a petroleum resid in a ratio within the 
range from about 0.5:1 to about 2:1, preferably from about 1:1 to about 
1.5:1 and hydrogen will be added at a rate within the range from about 4 
to about 8 weight percent based on petroleum residual in the initial 
mixture. 
After mixing in mixing manifold 201, the petroleum resid, solvent and 
molecular hydrogen mixture is fed to conversion reactor 206. In the 
conversion reactor, the mixture is heated to a temperature within the 
range from about 800.degree. to about 850.degree. F. at a hydrogen partial 
pressure within the range from about 1500 to about 2500 psia and at a 
total pressure within the range from about 1800 to about 2800 psia. The 
nominal holding time in conversion reactor 206 will range from about 30 to 
about 120 minutes. In the conversion reactor, at least a portion of the 
petroleum resid will be converted to a normally gaseous product and at 
least a portion will be converted to a normally liquid product. Generally, 
at least a portion of the petroleum resid will remain unconverted. 
In the embodiment illustrated, the entire conversion product is withdrawn 
through line 207 and passed to a first separator 208. In the first 
separator, a product containing the normally gaseous product and all of 
the liquid product which is to be recycled as solvent is separated 
overhead through line 209 and a bottoms product is separated through line 
210. 
In those embodiments where the recycle solvent will contain aromatics, the 
fraction withdrawn overhead through line 209 is passed to hydrotreater 
211. In the hydrotreater, at least a portion of the aromatic materials are 
converted to corresponding hydroaromatic materials. Such conversion is 
believed to be well known in the prior art. Normally, such hydrotreatment 
will be accomplished at a temperature within the range from about 
600.degree. F. to about 950.degree. F., preferably at a temperature within 
the range from about 650.degree. F. to about 800.degree. F. and at a 
pressure within the range from about 650 to about 2000 psia, preferably 
1000 to about 1500 psia. The hydrogen treat rate during such hydrotreating 
generally will be within the range from about 1000 to about 10,000 
scf/bbl. Any of the known hydrogenation catalyst may be employed, but a 
"nickel moly" catalyst is most preferred. 
In the embodiment illustrated, then, the hydrotreated fraction is withdrawn 
through line 212 and recombined with the bottoms fraction from separator 
208 in line 213. The recombined fractions are then passed to a second 
separator 214. 
In the second separator 214, products boiling below the initial boiling 
point of the solvent fraction, including normally gaseous materials, are 
separated overhead through line 215, a fraction, at least a portion of 
which is intended for use as recycle solvent, is withdrawn through line 
216, a fraction having an initial boiling point equal to the higher 
boiling point of the solvent fraction is withdrawn through line 217 and a 
bottoms product generally having an initial boiling point equal to the 
initial boiling point of the petroleum resid subjected to conversion is 
withdrawn through line 218. In general, the fraction intended to be 
recycled as solvent will have an initial boiling point within the range 
from about 400.degree. to about 650.degree. F. and preferably an initial 
boiling point within the range from about 500.degree. to about 650.degree. 
F. and, generally, a final boiling point within the range from about 
850.degree. to about 1050.degree. F. and preferably a final boiling point 
within the range from about 950.degree. to about 1050.degree. F. To the 
extent that this fraction exceeds the amount of solvent required, a 
portion thereof may be withdrawn as product through line 219 and the 
remainder recycled as solvent through line 205. 
It will be appreciated that while hydrotreating has been illustrated on a 
relatively broad boiling range product and between a first and second 
separator, the hydrotreating could be accomplished after the solvent 
fraction has been separated from the second separator through line 216. As 
is well known in the prior art, however, hydrogenation does alter the 
boiling range of the solvent and further separation after hydrogenation 
affords better control over the boiling range of the solvent fraction. As 
a result, operation in the manner illustrated in the Figure is preferred. 
The overhead product withdrawn through line 215 may be further separated 
into a normally gaseous product and a liquid product boiling, generally, 
in the naptha range. The gas may be scrubbed to remove impurities and used 
as a pipeline gas or as a process fuel. The naptha fraction may be further 
upgraded in accordance with well-known procedures to yield a high quality 
gasoline. The material withdrawn through line 219 boils, generally, within 
the known fuel oil ranges and may be used as such or further upgraded and 
used either as a diesel fuel or as a fuel oil. The material withdrawn 
through line 217 boils, generally, within the vacuum gas oil range and may 
be used as such or further upgraded or converted to different boiling 
range materials. The bottoms product withdrawn through line 218 may be at 
least partially recycled to the conversion reactor, burned for fuel value 
or discarded. 
Having thus broadly described the present invention and a preferred 
embodiment thereof, it is believed that the same will become more apparent 
by reference to the following examples. It will be appreciated, however, 
that the examples are presented solely for purposes of illustration and 
should not be construed as limiting the invention. 
EXAMPLE 1 
In this example, four runs were completed in an autoclave using a vacuum 
resid from a heavy Arab crude oil having an initial boiling point of 
1000.degree. F. to determine the effect of hydrogen partial pressure on 
conversion. In each run, a raw creosote oil was used. The solvent was used 
at a ratio of 1.5:1 based on petroleum residual in the initial blend. The 
solvent was, then, capable of donating 2.4 weight percent hydrogen based 
on petroleum resid in the initial mixture. The solvent contained 
essentially no paraffinic materials and, therefore, the ratio of paraffins 
to total aromatics plus hydroaromatics was 0. The hydrogen partial 
pressure was varied between about 1300 and about 2500 psig. After 90 
minutes at 820.degree. F. the total conversion, based on petroleum resid 
was determined. For convenience, the pressures employed and the total 
conversions obtained are tabulated below and for purposes of easy 
comparison, the total conversion as a function of pressure is plotted in 
FIG. 3 for RCO solvent. 
______________________________________ 
Approximate 
Total Conversion 
Run Number Pressure, psig 
Wt. % on Resid 
______________________________________ 
1 1300 54 
2 1500 58 
3 2000 68 
4 2500 64 
______________________________________ 
EXAMPLE 2 
In this example, a series of runs were completed using the same vacuum 
resid used in Example 1 at a hydrogen partial pressure of 2000 psig at a 
temperature of 840.degree. F. and at a nominal holding time of 60 minutes. 
The composition of the solvent was, however, varied in each run to 
determine the effect of solvent composition on the amount of coke make. At 
completion of experiment, the amount of coke actually prepared or 
generated was determined. The critical parameters relating to the 
composition of each solvent and the amount of coke generated is summarized 
and plotted in FIG. 4. 
EXAMPLE 3 
In this example, a heavy Arab vacuum resid was converted in a continuous 
unit using a hydrogenated creosote oil. The hydrogenated creosote oil 
contained 1.6 weight percent donatable hydrogen and was used in a solvent 
to resid ratio of 1.5:1. At this ratio, the solvent was capable of 
donating 2.4 weight percent hydrogen based on resid. The run was completed 
at 2000 psig at a space velocity of 0.75 v/hour/v and at a hydrogen treat 
rate of 4500 scf/bbl. The runs were completed at two different 
temperatures; viz., 840.degree. and 845.degree. F. The total conversion 
and product yields are tabulated in the table below. 
______________________________________ 
Reactor Temperature .degree.F. 
840 845 
______________________________________ 
Yields, Wt % 
C.sub.1 -C.sub.3 10 12 
C.sub.4 -350.degree. F. 
23 25 
350-650.degree. F. 25 29 
650-1000.degree. F. 19 12 
CONVERSION OF 77 78 
1000.degree. F..sup.+, WT % 
______________________________________ 
As will be apparent from the foregoing, particularly when viewed in light 
of FIG. 1, relatively high total conversions of a petroleum residual can 
be achieved when operating in accordance with the method of the present 
invention. As will also be apparent, the yield of lighter boiling range 
materials is significantly higher than has been achieved with processes 
heretofore proposed. The method of the present invention, then, offers an 
improved process for converting petroleum residuals to in-use products.