Note: Descriptions are shown in the official language in which they were submitted.
2~ 7~
CONVERSION INCREASE OF V~CUUM RESIDUUMS
(D#79,023 ~F~
BACKGROUND OF THE INVENTION
This invention relates to a process for the con-
version of vacuum residua in a hydrocracking operation.
More particularly, it relates to the treatment of uncon-
verted vacuum residua to remove the most undesired asphal-
tenic materials therefrom in order to increase the conver-
sion of the vacuum residue vir~in feed.
In converting heavy vacuum residua, e.g., in a
hydrocracking operation, a problem with obtaining a good or
better conversion is the amount of asphaltenes or asphalte-
nic materials which ar~ deficient in hydrogen and have a
high trace metals content. In selectively removing a major
portion of the more hydrogen deficient asphaltenes from the
unconverted 1000F plus material, the effective conYersion
of the remaining 1000F material, as well as the original
vacuum residum chargestock, may be significantly enhanced.
Thus, it is àn ob~ect~of the present invention to
provide a means of treating the unconverted vacuum bottoms
to obtain the optimum conversion of virgin vacuum residuum.
:~
DISCLOSURE STATEMENT
U.S. Patent Rs. 32,265 discloses a hydrogenation
process using at least one fluidized catalytic stage and a
recycle material o~ heavy~hydrogenated effluent. The heavy
effluent materlal is cooled to a temperature within
7~4
350-600F to separate toluene and heptane insoluble coke
precursors prior to recycle. This separation may be en-
hanced by the use of centrifugation, filtration or a bed of
particulate matarial, e.y., calcined coke.
U.S. Patent 4,411,7~8 discloses a higher conver-
sion in a process for upgrading high boiling hydrocarbon
materials to valuable lower boiling hydrocarbon materials in
an ebullated catalytic bed wherein rscycle is recovered from
the upgraded product and at least 25 percent by volume of
the recycle is comprised of the 950~F plus components of the
product. The liquid recycle is cooled to a temperature of
350F to 700F to separate coke precursors from the liquid
recycle on a bed of particulate solids prior to recycling it
back to the hydrogenation zone.
U.S. Patent 4,305,~14 discloses discloses an
energy efficient process for separating a hydrocarbonaceous
material into various fractions employing solvents at ele-
vated temperatures and pressures. The solvent compositioncomprises at least one member sslected from the group of
paraffinic hydrocarbons containing from 3 through 9 carbon
atoms, mono-olfin hydrocarbons containing from 4 through 8
carbon atoms, aromatic hydrocarbons having a normal boiling
point temperature below about 350F and alcohols containing
from 3 through 9 carbon atoms. The particular amount of
asphaltenes or sediment that should be removed to obtain a
deasphalted oil that has excellent recycle properties is not
disclosed.
U.S. Patent 4,502,944 discloses a method oE sepa-
rating a process material comprising oils, resins and as-
phaltenes into at least three fractions. Method employs
light organic solvents (paraffinic hydrocarbons preferably
having between 3 and 8 carbon atoms in a solvent/process
PR\VAM121 - 2 -
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material ratio of at least about 3:1) under elevated temper-
ature and pressure conditions. As in U.S. Patent 4,305,814,
the particular amount of asphaltenes or sediment that should
be removed to obtain a d0asphalted oil that has excellent
recycle properties is not disclosed.
U.~. Patent 3,412,010 discloses that the conv~r-
sion of a vacuum residuum in a hydrocracker is improved by
recycling the 680-975F cut and the 975 plus residue back
to the reactor. No mention of removing coke precursors or
asphaltenes in the recycle streams is provided.
U.S. Patent 3,905,892 discloses a process for
hydrocrackiny vacuum residuum wherein the g75F plus product
may be recycled after removing the asphaltenes. The latter
is partially oxidized to yield hydrogen for providing make-
up hydrogen for the hydrocracking reactor. Tha effect of
deasphalting conditions on product yields when the deasphal-
ted oil is recycled is not disclosed.
U.S. Patent 4,457,830 discloses the use of inor-
ganic acids for precipitating and decomposing preasphaltenes
and coprecipitating solids. The effect of deasphalting
conditions on product yields when the deasphalted oil is
recycled is not disclosed.
SUMMARY OF THE INVENTION
The present invention provides an improvement in a
method for conversion of a vacuum residuum feed ir. a hydro-
cracking operation which comp~ises upgrading the vacuum
residuum feed, recovering and separating distillates from
the remaining vacuum residuum feed and recycling unconverted
vacuum residuum bottoms to the upgrading zone. The improve-
ment comprises deasphalting the unconverted asphaltene-
PR\VAM121 - 3 -
2~ 7'~
containing unconverted vacuum residuum bottoms in the re-
cycle stream by treating said unconverted vacuum residuum
bottoms in an extraction zone with a cosolvent under ambient
conditions to a related temperature (and sufficient pressure
wherein the recycle stream and cosolvent are maintained in a
liquid state), whereby the most undesirable hydrogen defici-
ent asphaltenes are selectively removed from the unconverted
vacuum residuum bottoms to increase the overall conversion
of the vacuum residuum feed.
DETAILED DESCRIPTION OF INVENTION
The present invention for improving the conversion
of a virgin vacuum residuum into a useful product suggests
the treatment of the unconverted vacuum bottoms after
separating it from the cracked reaction distillate product
in the reactor affluent. Then the treated vacuum bottoms,
less the most undesirable hydrogen deficient asphaltenes and
a majority of the trace metals, is recycled back to the
reaction æone to be converted to additional quantities of
the desired distillate products, i.e. naphtha, diesel fuel
and vacuum gas oil. The lattar stream is used to make addi-
tional naphtha and diesel fuel by using it as a charge stock
component for a fluidized catalytic cracking unit.
In khe overall process of converting a vacuum
residuum feed into the desired distillates, the improvement
provided by the present invention i5 the treatment o~ the
unconverted vacuum bottoms with a cosolvent to selectively
remove most of the undesirable hydrogen deficient asphal-
tenes from the vacuum bottoms prior to their being recycled
to the reactor, i.e., reaction zone, for further hydro-
cracking.
PR\VAM121 - 4 -
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As a result of the cosolvent treatment, the amount
of the most undesirable hydrogen deficient asphal~enes to be
selectively removed ranges ~rom about 10 percent to about 20
percent.
In treating the unconverted vacuum bottoms with a
cosolvent, the amount of cosolvent used is defined as the
volume ratio of cosolvent to unconverted vacuum bottoms and
ranges from about 1:1 to about 40:1.
The cosolvents that may be used according to the
present invention include individual solvents such as
n-pentane or n-heptane or (C5-C7) paraffines or a mixture of
(C5-C6) naphthenes and (C~-C7) aromatics. The aromatics
being benzene and toluene.
To illustrate the advantage o~ deasphalting with
n-heptane, a sample of the untreated unconverted vacuum
bottoms and various deasphalted oils from the same
unconverted vacuum bottoms sample were processed in a
continuous stirred tank reactor (CSTR) at a catalyst space
velocity of 0.13 bbl/lb/day at successive temperatures of
795, 805 and 815F over an Mo/A1203 catalyst that mimics the
steady-state activity of a commercial NiMo/A1203. The CSTR
25 pressure was held at 2,250 psig with hydrogen and an H2
treatment rate o~ 7,000 SCF/bbl. Processing the untreated
and unconverted vacuum bottoms and samples o~ the same
unconverted vacuum bottoms individually deasphalted with
toluene, cyclohexane and n-heptane gave the following
results:
PR\VAM121 - 5 -
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The above results show that the n-heptane deasphalted vacuum
bottoms sample provides a much improved recycle stream for a
residuum hydrocracking process designed to upgrade 1000F
and above boiling point components. Not only is the allow-
able conversion increased at a given temperature but, essen-
tially, no sediment is foxmed. The latter is very important
for reducing catalyst poisoning and minimizing plugging
problems on account of sediment formation and deposition in
flow control valves, heat exchangers and separation vessels
lQ downstream from the reaction zone. In addition,
deasphalting the vacuum bottoms recycle stream with n-hep-
tane versus the other solvents allows the reactor tempera-
ture to be increased by at least 10F to further improve
hydrocracking conversion without causing additional
sediment.
Deasphalting vacuum bottoms with toluene shows a negligible
improvement in the overall conversion of the 1000F plus
boiling point components compared with the untreated vacuum
bottoms and essentially no improvement in reducing sediment
formation as measured by Soxhlet extractions with toluene.
The cyclohexane deasphalted vacuum bottoms, on the other
hand, provides an intermediate valued recycle stream in that
the conversion is significantly improved over the untreated
or toluene deasphalted vacuum bottoms but sediment begins to
form in the reactor effluent as the reactor temperature is
raised to provide a better overall conversion of the compo-
nents boiling above 1000F.
It is of interest to note the relative amounts of sediment
removed from the particular vacuum bottoms sample (VB) with
solvents selected from each of the three basic hydrocarbon
types at solvent/VB dosages of 20/1 at ambient conditions:
PR\VAM121 - 7 -
2~077a~
Sediment, wt.%
Toluene < 0.5
Cyclohexane6 - 7
n-Heptane 15 - 16
It is well known in the art that the lighter the n-para~fin
used for deasphalting the more sediment (comprising asphal-
tenes, other carbonaceous material and trace metals) will be
removed from vacuum or atmospheric residuum. For instance,
deasphalting the same vacuum bottoms sample with n-pentane
removed 20-22 wt.~ sediment. The object is to remove as
little sediment as possible and still improve the overall
conversion of lOOo~F plus material while producing no more
sediment.
Certainly if the n~heptane deasphalted vacuum bottoms
improves conversion without causing any additional sediment,
the n-pentane deasphalted vacuum bottoms would do as well
but there would be the additional amount of asphaltenes to
be disposed of. Consequently, it is proposed that deasphal-
ting with n-heptane provides a standard for determining how
much of the asphaltene phase should be removed for a given
vacuum bottoms stream i~ a mixed solvent comprising paraf-
fins and naphthen2s with some aromatics is being used.
Another reason for not removing more of the sediment than
necessary is to avoid removing the lighter asphaltenes
containing a higher proportion of hydrogen and less carbon
since the number of condensed aromatics is less. The light-
er asphaltenes crack more easily and thereby help to improvethe overall conversion of the lOoo F plus boiling point
components. Some of the key analytical indicators for the
deasphalted vacuum bottom (VB) samples are summarized in
Table II:
PR\VAM121 - 8 -
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TABLE II
Micro Carbon Hydrogen/Carbon Trace Metal
Test, wt.% Weiqht Ratio Anal~ses. ~m
Nickel Vanadium
Untreated VB 22.5 0.1140 28 38
Toluene DAVB 22.3 0.1156 29 28
Cyclohexane DAvs 18.1 0.1211 13 14
n-Heptane DAVB 12.3 0.1341 < 5 2.4
n-Pentane DAVB 10.4 - < 5 2
In Table III below, samples of untreated and n-heptane deasphalt-
ed vacuum bottoms were blended with virgin vacuum residue and
processed in a CSTR, as described in ~he first illustration, to
better stimulate a commercial application. The blends were made
up of one part untreated VB (or n-hep~ane DAV~3 and two parts by
weight of virgin vacuum residue. The results show that as the
hydrocracking reactor severity was increased by raising the
temperature to 815F ~he n-heptane DAVB allowed the conversion of
1000F plus material to be increased without producing any
additional sediment. Moréover, by deasphalting the same vacuum
bottoms sample with n-heptane the reactor temperature could be
raised at least another 10F to obtain additional conversion
without producing any additional sediment formation.
TABLE III
Calculated Overall
Conversion of 1000F
Plus Boiling Point Presence
Sample TemPerature F Material (wt.%) of Sediment
Untreated 795 52 none
VB with 805 55 yes
Virgin VR 815 65 yes
n-Heptane Deasph. 795 51 none
VB recycle 805 55 none
with Virgin VR 815 66 none
825 70 none
PR\VAM121 - 9 -
