Note: Descriptions are shown in the official language in which they were submitted.
~ 25~ 5
F-3046-L
VISBREAKING PROCESS
This invention relates to the processing of residual
petroleum charge stocks by visbreaking in the presence of certain
highly aromatic hydrogen-donor materials.
Visbreaking, or viscosity breaking, is a well-known
petroleum refining process in which reduced crudes are pyrolyzed, or
cracked, under comparatively mild conditions to provide products
having lower viscosities and pour points, thus reducing the amounts
of less-viscous and more valuab~e blending oils required to make the
residual stocks useful as fuel oils. The visbreaker feedstock
usually consists of a mixture of two or more refinery streams
derived from sources such as atmospheric residuum, vacuum residuum,
furfural-extract~ propane-deasphalted tar and catalytic cracker
bottoms. Most of these feedstock components, except the heavy
aromatic oils, behave independently in the visbreaking operation.
Consequently, the severeity of operation for a mixed feed is limited
greatly by the least desirable (highest coke forming) components.
In a typical visbreaking process, the crude or resid feed is passed
through a heater and heated to about 425 to about 525C and at about
450 to about 7000 kPa. Light gas-oil may be recycled to lower the
temperature of the effluent to about 260 to about 370C. Cracked
products from the reaction are flash distilled with the vapor
overhead being fractionated into a light distillate overhead
product, for example gasoline and light gas-oil bottoms, and the
liquid bottoms being vacuum fractionated into heavy gas-oil
distillate and residual tar. Examples of such visbreaking methods
are described in Beuther et al, "Thermal Visbreaking of Heavy
Residues," The Oil and Gas Journal, 57:46, November 9, 1959, pp.
151-157; Rhoe et al, "Yisbreaking: A Flexible Process,~ Hydrocarbon
Processing~ January 1979, pp. 131-136; and United States Patent
4,233,138.
Yarious visbreaking processes have been proposed in which
residual oils are added to the visbreaking stage with or without
added hydrogen or hydrogen-donors. For example, U.S. Patent
2~ S S
F-3046-L -- 2 --
3,691,058 describes the production of single ring aromatic
hydrocarbons (70-220C) by hydrocracking a heavy hydrocarbon feed
(565C-) and recycling 32-70C and 220C+ product fractions to
extinction. This is integrated with visbreaking of residua in the
presence of 1-28 weight % free radical acceptor at ~70 to 480C in
the presence or absence of hydrogen (to enhance residua
depolymerization). U.S. Patent 4,067,757 describes a process
comprising passing a resid up through a bed of inert solids (packed
bed reactor) in the presence or absence of 9-1800 Nm3 hydrogen per
m3 resid at 400 to 540C to enhance the production of middle
distillate (175-345C).
U.S. Patent 2,953,513 proposes the production of
hydroyen-donors by partial hydrogenation of certain distillate
thermal and catalytic tars, boiling above 370C, containing a
minimum of 40 weight ~ aromatics, to contain H/C ratios of 0.7-1.6.
The resid feed is then mixed with 9-83 volume % of hydrogen-donor
and thermally cracked at 427-482C to produce low boiling products.
U.S. Patent 4~090/947 describes a thermal cracking process
(425-540C) for converting resids into lighter products in the
presence of 10-500 volume % hydrogen-donor. The hydrogen-donor is
produced by hydrotreating premium coker gas oil (345-480C) alone or
blended with gas oil produced in the thermal cracker. U.S. Patent
4~292,168 proposes upgrading heavy hydrocarbon oils without
substantial fonnation of char by heating the oil with hydrogen and a
hydrogen transfer solvent without a catalyst at temperatures of
about 32û-500C and a pressure of ~200-18000 kPa for a time of about
3-30 minutes. Examples of hydrogen-donor transfer solvents include
pyrene, fluoranthene, anthracene and benzanthracene. U.SO Patent
4,292,686 describes a process for contacting a resid with a
hydrogen_donor at 350-50ûC and a pressure of 2-7 MPa with liquid
hourly space velocities ranging from 0.5-10.
European Patent Application 133,774, published March
6, 1985, describes a process for the production of fuel oil
products in which the formation of coke or filtration sedi-
ment is suppressed by visbreaking heavy petroleum
~2S~55
F-3046-L __ 3 __
residua under liquid phase, non-catalytic conditions in the presence
of certain hydrogen-donor materials and in the absence of added free
hydrogen. By means of the invention described in that application,
heavy petroleum oil feed stocks containing deleterious contaminants
such as sulfur and nitrogen compounds, asphaltenes and metals, can
be visbroken at high severities to provide lower molecular weight
fuel oil products of improved viscosity and pour point
characteristics. The process of that invention offers the potential
of substantially eliminating and/or reducing the need for cutter
stock to meet fuel oil product viscosity specifications.
The present invention represents an improvement in the
visbreaking process described in that application and involves
introducing an organic sulfur compound into the heavy petroleum
residual oil before it is subjected to visbreaking in the presence
of a hyrogen donor material.
According to the invention, therefore, there is provided a
process for visbreaking a heavy petroleum resdual oil comprising:
(a) adding to the residual oil an organic sulfur compound
having an active thiol component; and
(b) visbreaking the residual oil in the presence of a
highly aromatic hydrogen donor material having a
content of HAr and Ha hydrogen each of at least 20
percent of the total hydrogen-donor hydrogen content,
and recovering a fuel oil product having a viscosity
lower than that of the starting residual oil.
The hydrogen-dnnor material used in the process of the
invention is a thermally stable, polycyclic aromatic or
hydroaromatic distillate mixture which results from one or more
petroleum refining operations. The hydrogen-donor preferably has an
average boiling poiont in the range of 230 to 510C and an A.P.I.
gravity below 20C.
Examples of suitable hydrogen-donors are highly aromatic
petroleum refinery streams, such as fluidized catalytic cracker
(FCC) "main column~ bottoms, FCC ~'light cycle oil," and thermofor
- ~s~s~
F-3046-L -- 4 --
cata~ytic cracker (TCC) "syntower" bottoms, all of which contain a
substantial proportion of polycyclic aromatic hydrocarbon
constituents such as naphthalene, dimethylnaphthalene, anthracene,
phenanthrene, fluorene, chrysene, pyrene, perylene, diphenyl,
benzothiophene, tetralin and dihydronaphthalene, for example. Such
refractory petroleum materials are resistant to conversion into
higher (lower molecular weight) products by conventional
non-hydrogenative procedures. Typically, these petroleum refinery
residual and recycle fractions are hydrocarbonaceous mixtures having
an average carbon to hydrogen ratio above about l:l, and an average
boiling point above 230C.
An FCC main column bottoms refinery fraction is a highly
preferred donor for use in the process of the invention. A typical
FCC main column bottoms (or FCC clarified slurry oil (CS0)) contains
a mixture of constituents as represented in the following mass
spectrometric analysis:
- ` ~LZ5~:1L5~
F-3046-L -- 5 --
Naphthenic/
Compounds Aromatics Aromatics Labile H
Alkyl-Benzene 0.4 - 0.00
Naphthene_Benzenes - l.O 0.03
Dinapthene-Benzenes - 3.7 0.16
Naphthalenes 0.1 - n . oo
Acenaphthenes (biphenyls) - 7.4 0.08
Fluorenes - lO.l 0.11
Phenanthrenes 13.1
Naphthene_phenanthrenes - 11.0 0.18
Pyrenes, fluoranthenes20.5 - O
Chrysenes 10.4 - O
Benzofluoranthenes 6.9 - O
Perylenes 5.2 - O
Benzothiophenes 2.4
Dibenzothiophenes 2.4
Naphthobenzothiophenes - 2.4
TOTAL 64.4 35.6 0.60
A typical FCC main column bottoms or clarified slurry oil
has the following analysis and properties:
Elemental Analysis, wt. %
C 89~93
H 7.35
0 0.99
N 0.44
S 1.09
TOTAL 99.80
~.2S~l55
F-3046-L -- 6 --
Pour Point, C: 10
COR, %: 9.96
Distillation:
IBP, C : 254
5%, C : 338
95%, C : 485
Another preferred hydrogen-donor material is a light cycle
oil (LCO) taken from the main tower fractionator in a FCC operation
of the riser type in which the LCO results from a distillation cut
point not substantially above about 370C.
A typical FCC light cycle oil (LCO) has the following
analysis and properties:
FCC LCO
Boiling Point Distribution, wt. %
215C 4.8
215 - 343C 87.9
343 - 427C 7-3
427 - 538C __
538C~ __
H, wt. % 10.64
S, wt. % 1.01
N, wt. % 0.24
Ni + V, PRM --
COR, wt. % __
Paraffins, wt. % 12.7
Mononaphthenes 11.7
Polynaphthenes 12.8
Monoaromatics 24.7
Diaromatics 21.7
Polyaromatics 14.3
Aromatic sulfur type 2.1
Total hydrogen, wt. % ~.0-9.5
~5~S~
F-3046-L -- 7 --
FCC main tower bottoms and light cycle oils are obtained by
the catalytic cracking of gas oil in the presence of a solid porous
catalyst. More complete descriptions of the production of these
petroleum fractions can be found in U.S. Patents 3,725,240 and
4,302,323, for example.
Catalytically cracked stocks such as clarified slurry oils
and light cycle oils are preferred hydrogen-donor materials because
of their unique physical properties and chemical constituents. A
critical aspect of the hydrogen-donor material is the particular
proportions of aromatic naphthenic and paraffinic moieties and the
type and content of aromatic and naphthenic structures together with
a high content of alpha (~ ) hydrogen provides a superior
hydrogen-donor material.
The hydrogen transfer ability of a donor material can be
expressed in terms of specific types of hydrogen content as
determined by proton nuclear magnetic resonance spectral analysis.
Nuclear magnetic resonace characterization of heavy hydrocarbon oils
is well developed. The spectra 60 (c/sec) are divided into four
bands (H~ , H ~ , Hr and HAr) according to the following
frequencies in Hertz (Hz) and chemical shift (~ ):
H~ H ~ Hr H ~r
Hz 0-60 60-100 120-200 360-560
0-1.0 1.0-1.8 2.0-3.3 6.0-9.2
The HAr protons are attached to aromatic rings and are a
measure of aromaticity of a material. H ~ protons are attached to
non-aromatic carbon atoms themselves attached directly to an
aromatic ring structure, e.g~, alkyl groups and naphthenic ring
structures. H~ protons are attached to carbon atoms which are in a
second position away from an aromatic ring, and H r protons are
attached to carbon atoms which are in a third position or more away
~L25~55
F-3046-L -- 8 --
from an aromatic ring structure. This can be illustrated by the
following:
CH2-C82-CH3 ~Ar~28
~Ar HAr~2
HAr ~2
(3)
~ CH2 ~3
(4)
~3- C~2 _C:12 ~3
(S~ ~2/~
~2. ~2
H2 H2 H2
(8) ~ B Y
~ CH2-- CH2 C~3
~2~LSS
F-3046-L - 9 --
The HAr protons are important because of their strong
solvency power. A high content of H ~ protons is particularly
significant because H ~ protons are labile and are potential
hydrogen-donors.
It is particularly preferred that the hydrogen-donor
material used in the process of the invention has a hydrogen content
distribution in which the HAr proton content is from 20 to 50
percent and the H ~ proton content is at least 20 percent,
prefereably from 20 to 50 percent. For example, in H-donor streams
containing 9.5 weight % total hydrogen, the ~ -hydrogen content
should be at least l.9 wt. % (20% of total hydrogen content). The
balance of the hydrogen is non- ~ hydrogen.
Hydrogen-donors possessing the desired hydrogen content
distribution can be obtained as a bottoms fraction from the
catalytic cracking or hydrocracking of gas oil stocks in the moving
bed or fluidized bed reactor processes. In general, depending upon
such conditions as temperature, pressure, catalyst-to-oil ratio,
space velocity and catalyst nature, a high severity cracking process
results in a petroleum residuum solvent having an increased content
of HAr and H u protons and a decreased content of the less
desirable non- ~ hydrogen.
The proton distribution in examples of various highly
aromatic hydrocarbon by-product streams is shown below.
-` ~2~ L5S
F-3046-L -- 10 --
Example H ~Non- ~ Hydrogen H H Total
-Ar --
(weight %) (weight %) (weight %) ~weight %)
FCC/LCO
~1 22.2 (2.07) 57.8 20.0 9.34
#2 34.1 (3.18) 36.8 29.1 9.32
~3 34.3 (3.19) 35.5 30.2 9.30
(Note the values in ( ) are absolute percentage amounts and all
three LCO streams are effective H-donors.)
FCC/Clarified Slurry Oil
#1 34.0 (2.43) 33.0 33.0 7.15
~t2 30.0 (2.15) 35.0 35.0 7.17
~3 19.4 (1.39) 65.0 5.0 7.16
FCC/Main Column Bottoms
~1 36.0 (2.65) 32.0 32.0
~2 36.4 (2.68) 18.8 44.8
~3 18.5 (1.36) 64.3 17.2
#4 18.1 (1.33) 67.7 14.2
TCC/Syntower
Bottoms
#1 29.8 (2.78) 28.8 41.4
1~2 18.2 (1.70) 58.8 23.0
~3 16.3 (1.52) 68.1 15.6
SRC Recycle
Oil 27.1 21.6 46.3
TCC Distillate
i~l 21.5 (2.39) 58.4 20.1
#2 20 (2.07) 58 22
~3 6.g (0.89) 85.1 8
~25~5~
F-3046-L -- ll --
All of the values reported above are for non-hydrotreated
materials.
From the data given above, it will be seen that
hydrocarbons having the same general process derivation may or may
not have the desired proton distribution. For example, FCC/~CB #l
and #2 and FCC/CS0 #l and #2 have the desired proton distribution
while FCC/MCB #3 and #4 and FCC/CS0 #~ do not. Furthermore,
although it is preferred that the highly aromatic hydrogen donor
component is derived from petroleum, it will be noted that the SRC
recycle solvent closely resembles FCC/MCB #l and ~2.
The organic sulfur compound which is introduced into the
residuum to be subjected to visbreaking is preferably one in which
there is present an active thiol (-SH) group. Suitable compounds in
this respect include thiophenol, dodecanethiol and benzothiophene.
Dibenzothiophene, on the basis of present knowledge, is not a
suitable sulfur compound.
In addition, refinery streams obtained from the extraction
of paraffinic oils to remove aromatics, for example with furfural,
and other refinery streams can contain sufficient sulfur compounds
having sufficient thiol functionality and can be added to the
residuum, directly or indirectly.
Another method of introducing the organic sulfur compound
into the heavy residuum is to sulfonate the aromatic extract derived
from extracting a paraffinic oil with phenol or furfural, for
example to remove aromatic compounds; the sulfonated aromatics are
then mildly hydrogenated to form the organic sulfur compound
suitable for addition to heavy residua for visbreaking. Techniques
for aromatic extraction, sulfonation, and hydrogenation are well
known in the art.
Still another source of thiol compounds is the extract
obtained by contacting a hydrocarbon stream containing thiophenols
with an alkaline solution3 such as sodium hydroxide in water or
alcohol, decanting the alkaline phase, and then acidifying the
solution to release the thiol compounds. The thiol compounds can be
~LZ5~55
F-3046-L -- 12 --
separated and mixed with the heavy residua. This technique provides
a means for removing sulfur from one portion of a refinery stream
and utilizing the sulfur in another part of the refinery process.
Hydrocarbon streams that can be used in the manner include aromatic
(furfural) extracts from lube oil stock and cycle oil stock.
The process of the invention is advantageously carried out
in refinery facilities of the type shown diagrammatically in the
accompanying drawing. Referring to the drawing, a viscous
hydrocarbon oil feed, typified by a 496C+ Arab Heavy resid, is
supplied by line 4 to visbreaking heater 8. The feed is blended
with hydrogen donor materials supplied through line 6 in an amount
from 0.1 to 50 weight percent, preferably from 0.1 to 20 weight
percent based on the resid charge (a weight ratio of hydrogen-donor
to resid of 0.001 to 0.5, preferably 0.001 to 0.2). Organic sulfur
compounds are added through line 2 to provide an amount equivalent
to 0.05 to 10 percent by weight of sulfur in the stream flowing in
line 2. Preferably the amount added is equivalent to from 0.5 to 5
percent sulfur. Mild thermal cracking of the resid under
visbreaking conditions occurs in visbreaker 8 and produces a
visbreaker effluent stream carried by line 10. This stream is
cooled by admixture with a quench stream from line 147 and the
visbreaker effluent continues through line 12 to distillation column
- 22 where it is fractionated to obtain C5-gases (C3, C4 and
lower) and a C5-135C naphtha fraction from the top through line
24. A 220C+ fraction is taken off as a bottoms stream through line
16 where portions may be recycled as a quench stream through line
14, recovered as heavy fuel oil through line 18 or, via line 20,
blended with cutter stock to meet fuel oil product specifications.
The overhead fraction removed from the distillation column
in line 24 is passed through a cooler separator 26 which is operated
under conditions effective to separate the incoming liquid into a
C5-off-gas stream 28, mainly C3 or C4 and lower, and a C5-
135C naphtha fraction which is taken off via line 30. 8ecause of
the quality of the hydrogen-donor, it can be removed in admixture
with the heavy oil fraction and used directly as heavy fuel oil,
thus avoiding the need for separation.
~25~55
F-3046-L -- 13 --
The process of the invention is suitable for upgrading a
wide variety of heavy liquid hydrocarbon oils in which mixtures of
at least 75 weight percent of the components boil over 370C.
Included in this class of materials are residual fractions obtained
by catalytic cracking of gas oils, solvent extracts obtained during
the processing of lube oil stocks, asphalt precipitates obtained
from deasphalting operations, high boiling bottoms or resids
obtained during vacuum distillation of petroleum oils and tar sand
bitumen feedstocks.
Visbreaking process conditions can vary widely bsaed on the
nature of the heavy oil material, the hydrogen-donor material and
other factors. In general, the process is carried out at
temperatures ranging from 350 to 485C, preferably 425 to 455~C, at
residence times ranging from 1 to 60 minutes, preferably 7 to 20
minutes. The pressures employed will be sufficient to maintain
liquid phase conditions usually 1480 to 7000 kPa.
An important aspect of the invention is the improvement of
visbreaker performance by optimizing operation severity for heavy
oil feedstocks. In general, as severity is increased, increased
yields of distillate and gaseous hydrocarbons are obtained with a
reduction in the amount of cutter oil required for blending to
obtain specification-viscosity residual fuel oil. At high
severities, however, ther is an increased tendency to form coke
deposits which result in plugged heater tubes and/or the production
of unstable fuel oils as measured by sediment formation. By means
of the process of-the invention, the use of certain hydrogen-donors
in combination with certain organic sulfur compounds has been found
to suppress the formation of sedimentation species and thus permit
visbreaking at a higher severity consistent with the production of
stable fuel oil. As an example, the visbreaking of a heavy
petroleum feed stock conventionally carried out at, say, 427C with
a residence time of 500 seconds may be carried out at 427C with a
residence time of 800 seconds under the conditions of the invention
to obtain a fuel oil product ~ree of sedimenting species. At such
higher severities, the cutter stock requirement is substantially
reduced and this represents a considerable financial savings.
- ~ ~25~55
F-3046-L -- 14 --
EXAMPLE
The effectiveness of thiophenolic compounds in increasing
the hydrogen donor capacity of a hydrogen donor solvent was
demonstrated by the follo~ing tests.
Four tests were made utilizing heavy-wall glass tubes into
which the materials shown in Column 2 of the following Table were
added in the amounts shown in Column 3. The tubes were blanketed in
nitrogen, sealed and heated at 440C for 1 hour. The mixtures were
then analyzed using vapor pressure chromatography and the
hydrogen-donor capacity of each mixture was calculated.
TABLE
1 2 3 4 5
Run No. Compounds ~ei~ht,~ms Weisht % Sulfur H-donor Capacity
1 Durban Clarified
Slurry Oil 0.2311 4.83 0.893
benzophenone 0.2007
2 Clarified
Slurry oil 0.2093 0.95 1.16
benzophenone 0.2026
3 Clarified
Slurry oil 0.2110 0.95 4.81
thiophenol 0.0431 3.88
benzophenone 0.2011 --
4 Clarified
Slurry oil 0.2069 0.95 0.876
dibenzothiophene 0.0770 3.88
benzophenone 0.2019 --
