Note: Descriptions are shown in the official language in which they were submitted.
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PROCESS FOR THE CONVERSION OF HEAVY HYDROCARBON FEED-
STOCKS TO DISTILLATES WITH THE SELF-PRODUCTION OF HYDRO-
GEN
The present invention relates to a high-productivity
process for the total conversion to distillates alone,
with no contextual production of fuel oil or coke, of
heavy feedstocks, among which heavy crude oils also with
a high metal content, distillation residues, heavy oils
coming from catalytic treatment, "visbreaker tars",
"thermal tars", bitumens from "oil sands" possibly ob-
tained from mining, liquids from different types of coal
and other high-boiling feedstocks of a hydrocarbon na-
ture, known as "black oils", also comprising hydrogenat-
ing treatment in which hydrogen, self produced in the
same process, is used.
The conversion of heavy feedstocks to liquid prod-
ucts can be substantially effected through two methods:
one of the thermal type, the other based on hydrogenating
treatment. The increasing demand for high-quality dis-
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tilled products and the parallel reduction in the demand
for by-products such as coke and fuel oil, make it neces-
sary to look for new integrated processes which allow the
complete conversion of heavy feedstocks.
Thermal processes, mainly coking and Visbreaking,
have certain advantages as they allow feedstocks having a
high polluting level to be fed. The high production of
coke and tar, however, is such that its validity is
greatly limited in some cases. In addition, the poor
quality of the distillates leads to the necessity of se-
vere hydrogenating treatment to favour the removal of
heteroatoms and bring the products to specification.
Visbreaking allows very low yields to distillates
to be obtained together with low-quality products, ob-
taming, on the contrary, high amounts of tar.
Coking, in addition to having higher investment
costs, also produces low-quality distillates and high
quantities of coke.
As far as hydrogenating processes are concerned,
these consist of treating the feedstock in the presence
of hydrogen and suitable catalysts, following various ob-
jectives:
= to demolish the high molecular weight asphaltene
structures, favouring the removal of Ni and V (hy-
drodemetallation, HDM) and, contemporaneously, reduce
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the content of asphaltenes in the feedstock
= to remove S and N through hydrogenation and hydro-
genolysis reactions (hydrodesulphurization, HDS and
hydrodenitrogenation HDN, respectively)
= to reduce CCR (Conradson Carbon Residue) by means of
Hydrocracking (HC) and Hydrodearomatization (HDA) re-
actions
= to transform high molecular weight molecules into
light molecules (distillates) through Hydrocracking
(HC) reactions.
The hydroconversion technologies currently used make
use of fixed bed or ebullated bed reactors and adopt
catalysts generally consisting of one or more transition
metals (Mo, W, Ni, Co, etc.) supported on silica and/or
alumina or another oxide support.
Fixed bed technologies, even in the most advanced
versions, have severe limitations both with respect to
the flexibility of the feedstock fed (as the presence of
high concentrations of metals and other pollutants would
imply excessively frequent regeneration cycles of the
catalyst) and also because they do not allow the conver-
sion of heavy feedstocks to levels higher than 30-40%. As
a result of said limitations, fixed bed hydroconversion
technologies prove to be completely inadequate for con-
figuring total conversion schemes of heavy feedstocks to
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distillates.
In order to at least partly overcome these limita-
tions, ebullated bed processes were developed, wherein
the catalytic bed, even if confined in a certain part of
the reactor, is moveable and can expand due to the effect
of the reagent flow in liquid and gaseous phase. This al-
lows the reactor to be equipped with mechanical appara-
tuses for removing the exhausted catalyst and feeding the
fresh catalyst in continuous, without interrupting the
running. As a result of this possibility of continuously
substituting the exhausted catalyst, ebullated bed tech-
nologies can process heavy feedstocks with a metal con-
tent of up to 1,200 ppm Ni + V. Even if the ebullated bed
technology benefits from the improvements provided by the
continuous regeneration of the catalyst, it allows con-
version levels to distillates of up to a maximum of 60%
to be obtained. It is possible to reach a conversion of
80% by operating under high severity conditions and recy-
cling an aliquot of the products, encountering however
problems of stability of the fuel oil produced by the
separation of the non-converted asphaltene phase, which,
in this case too, represents the heart of the problem.
For the above reasons, the ebullated bed technology is
also unsuitable for total conversion processes to distil-
lates, as it is associated with a significant production
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of fuel oil.
Processes have been proposed which use catalysts ho-
mogeneously dispersed in the reaction medium (slurry), as
an alternative to hydroconversion processes based on the
use of catalysts supported on a fixed bed or ebullated
bed. These slurry processes are characterized by the
presence of catalyst particles with very small average
dimensions and uniformly dispersed in the hydrocarbon
phase. The catalytic activity is consequently scarcely
influenced by the presence of metals or carbonaceous
residues deriving from the degradation of asphaltenes.
With respect to thermal processes, hydroconversion
technologies of residues also have limitations due to the
high investment costs. They also require considerably
high hydrogen consumptions. This latter element repre-
sents a very critical factor, mainly in certain cases in
which there is a limited availability of natural gas. It
can therefore be important to produce hydrogen starting
from alternative sources, for example through the gasifi-
cation of by-products such as coke, residues, tar, as-
phaltenes, etc..
For the above reasons, the effecting of integrated
processes in which it is possible to use low-value by-
products for the production of hydrogen for internal use,
represents an advantageous solution from all points of
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view.
Deasphaltation, a liquid-liquid extraction treatment
based on the use of paraffins, allows a variable aliquot
of DAO, deasphalted oil, to be separated, which can have
qualitative characteristics (in terms of metal content,
carbonaceous residue, etc..) which are such as to favour
the subsequent conversion. This process has several ad-
vantages with respect to coking: significantly lower in-
vestment costs, the possibility of modulating the yield
and quality of DAO and asphaltenes according to neces-
sity, the production of a by-product (the same asphalte-
nes) which can be fed to the gasification process.
As is known, deasphalting does not produce distil-
lates: it is therefore necessary to subject the DAO to
subsequent cracking treatment.
In US.6274003 of Ormat Industries a process has been
recently claimed for the primary upgrading of heavy hy-
drocarbons, which combines distillation, solvent
deasphalting and thermal cracking to produce a synthetic
crude oil, partially upgraded, substantially without met-
als and asphaltenes. In the upgrading process, the feed-
stock is first distilled to produce a lighter fraction,
substantially with no asphaltenes, and a residue contain-
ing metals and asphaltenes.
An aliquot of the distilled fraction is sent to a hy-
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drotreating unit, whereas the residual fraction is
deasphalted to produce an oil (DAO) and an asphaltene
residue. DAO, and possibly an aliquot of the hydrotreat-
ing product (which acts as a diluent, hydrogen donor) are
joined and sent to thermal cracking: the cracking product
returns to the distillation column, from which the frac-
tions forming the partially upgraded syncrude, are col-
lected.
The process scheme is improved in subsequent patents
of the same owner (W003060042, US-6,702,936, US-
20040118745, EP1,465,967) claiming the use of a treatment
which also comprises the gasification of asphaltenes to
produce synthesis gas, the treatment of the synthesis gas
with the production of hydrogen and the hydroprocessing
of the distillates. In patent application IT-2004A002446
a conversion process of heavy feedstocks is claimed,
which allow the complete transformation of the same
("zero residue refinery"). In said patent application IT-
2004A002446 a process is described more specifically in-
cluding the use of the following units: solvent
deasphalting (SDA), DAO hydroconversion with slurry phase
catalysts, distillation. The residue from the hydrotreat-
ing stream, together with the catalyst in slurry phase
contained therein, is recycled to the hydrotreatment sec-
tion. The asphaltene stream can be sent to a gasification
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section (P0x) in order to obtain a mixture of H2 and CO.
We have surprisingly found that, by subjecting the
DAO obtained from the deasphalting of the distillation
residue of the heavy feedstock to hydrocracking in the
presence of low concentrations of dispersed catalyst,
high yields to distillate can be obtained with an optimum
control on the formation of coke and gases. In this way,
it is not necessary to recycle the non-converted residue
to the hydrocracking section. This residue can be di-
rectly recycled to the initial fractionation column or to
the deasphalting zone, from which, in addition to the as-
phaltenes present in the feedstock, the side-products
possibly formed in the hydrocracking phase can be re-
moved, said by-products thus being used, at the same time
self-producing the hydrogen necessary for the hydrogenat-
ing treatment envisaged, by sending the asphaltene stream
to a gasification section. By comparing this solution
with that comprising a thermal cracking step for the DA0
conversion, it is possible to optimize the process selec-
tivity, maximizing the yield to distillates and minimiz-
ing the production of coke and gas. With respect to the
solution claimed in patent application IT-2004A002446,
which includes the use of high catalyst concentrations
and the recycling of the same together with the distilla-
tion residue from the hydrotreatment, the new solution
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proposed herein allows the use of minimum concentrations
of catalyst, which can be used only once, greatly simpli-
fying the scheme; even at low catalyst concentrations,
its formulation allows an optimal hydrogenation of the
feedstock, preventing or minimizing the formation of
coke. The sending of the hydrotreatment residue to the
deasphalting section allows the possible recovery of fur-
ther quantities of DA0 to be converted and, at the same
time, to send the most concentrated fraction of pollut-
ants (metals deriving from the feedstock, together with
traces of catalyst) to gasification.
The process, object of the present invention, for the
conversion of heavy feedstocks, comprises the following
steps:
= sending the heavy feedstock to a first distillation
zone (D1) having one or more atmospheric and/or vac-
uum distillation steps whereby one or more light
fractions are separated from the distillation resi-
due;
= sending the fraction consisting of the distillation
residue of the first distillation zone (D1) to a
deasphalting zone (SDA) in the presence of solvents,
obtaining two streams, one consisting of deasphalted
oil (DAO), the other containing asphaltenes;
= sending the stream containing asphaltenes to a gasi-
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fication zone (PDX) in order to obtain a mixture of
H2 and CO;
= mixing the stream consisting of deasphalted oil (DAO)
with a suitable hydrogenation catalyst and sending
the mixture thus obtained to a hydrocracking zone
(HCK) in which hydrogen is introduced self-produced
in the gasification area (PDX) after separation in a
gas separation (GS) zone from the mixture containing
CO;
= sending the effluent stream from the hydrocracking
zone to a second distillation zone (D2), consisting
of one or more flash steps, and/or one or more atmos-
pheric distillation steps, whereby the different
fractions coming from the hydrocracking reaction are
separated from the distillation residue, which is re-
cycled to the first distillation zone (D1) and/or to
the deasphalting zone (SDA).
The heavy feedstocks treated can be of different
kinds: they can be selected from heavy feedstocks, dis-
tillation residues, "heavy oils" from catalytic treat-
ments, for example "unconverted oils" from hydrotreatment
with fixed or ebullated beds, "heavy cycle oils" from
catalytic cracking treatment, "thermal tars" (coming, for
example, from visbreaking or similar thermal processes),
bitumens from "oil sands", different kinds of coals and
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any high-boiling feedstock of a hydrocarbon origin, generally known in the art
as
"black oils".
More particularly, there is provided a process for the conversion to
distillates
of heavy feedstocks selected from heavy and extra-heavy crude oils,
distillation
residues from crude oil or from catalytic treatment, visbreaking tars, thermal
tars,
bitumens from oil sands liquids from coals of different origins and other high
boiling
feedstocks of a hydrocarbon origin, known as black oils, comprising the
following
steps:
= sending the heavy feedstock to a first distillation zone (D1) having one
or more
atmospheric and/or vacuum distillation steps, whereby one or more light
fractions
are separated from the distillation residue;
= sending the fraction consisting of the distillation residue of the first
distillation zone
(D1) to a deasphalting zone (DSA) in the presence of solvents, obtaining two
streams, one consisting of deasphalted oil (DAO), the other containing
asphaltenes;
= sending the stream containing asphaltenes to a gasification zone (POO in
order to
obtain a mixture of H2 and CO;
= mixing the stream consisting of deasphalted oil (DAO) with a suitable
hydrogenation catalyst and sending the mixture obtained to a hydrocracking
(HCK) zone into which hydrogen self-produced in the gasification area (POO is
introduced, after separation from the mixture containing CO in a gas
separation
area (GS);
= sending the stream coming from the hydrocracking area to a second
distillation
area (D2) consisting of one or more flash steps and/or one or more atmospheric
distillation steps whereby the different fractions coming from the
hydrocracking
reaction are separated from the distillation residue, which is recycled to the
first
distillation area (D1) and/or to the deasphalting area (SDA).
The choice of sending the recycling of the distillation residue of the second
distillation zone to the first distillation zone (D1) and/or the deasphalting
zone (SDA)
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is influenced by how the second distillation zone is effected: it is in fact
preferable to
send this residue completely, or at least partially, to the deasphalting area
(SDA) if
said second area consists of one or more atmospheric distillation steps.
The first distillation zone (D1) preferably consists of one or more
atmospheric
distillation steps or one or more distillation steps and one vacuum step.
The heavier fraction of the light fractions separated in the first
distillation zone,
can possibly be at least partially sent to the hydrocracking zone (HCK).
The gasification can be effected by feeding the stream containing asphaltenes
to the gasifier, together with oxygen and vapour which react under exothermic
conditions at a temperature of over 1,300 C and a pressure ranging from 30 to
80
bar, to produce mainly H2 and CO.
The separation of H2 from the mixture of H2 and CO obtained from the
gasification is preferably effected by means of molecular sieves.
A portion of the syngas stream, i.e. a mixture of H
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and CO, obtained from the gasification, can be further
upgraded as fuel for the generation of vapour or by com-
bustion with combined cycles (IGCC) or it can be trans-
formed into paraffin hydrocarbons through Fischer-Tropsch
synthesis or it can be converted to methanol, dimethyl-
ether, formaldehyde and, more generally, into the series
of products deriving from Cl chemistry.
The distillation steps are preferably carried out at
a reduced pressure ranging from 0.001 to 0.5 MPa, pref-
erably between 0.1 and 0.3 MPa.
The deasphalting step (SDA), effected by means of ex-
traction with a hydrocarbon or non-hydrocarbon solvent is
generally carried out at temperatures ranging from 40 to
200 C and pressures of between 0.1 and 7 MPa.
Furthermore, the same can be composed of one or more
sections operating with the same solvent or different
solvents; the recovery of the solvent can be carried out
under sub-critical or super-critical conditions, with
several steps, thus allowing a further fractionation be-
tween deasphalted oil and resins.
It is advisable for the solvent of this deasphalting
step to be selected from light paraffins having from 3 to
6 carbon atoms, preferably from 4 to 5 carbon atoms, or a
mixture of the same.
The hydrocracking (HCK) step is carried out in the
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presence of catalysts in slurry phase, preferably at tem-
peratures ranging from 380 to 4800C, more preferably from
420 to 470 C, at a pressure ranging from 2 to 20 MPa,
more preferably from 10 to 18 MPa.
Hydrogen is fed to the hydrocracking reactor which
can operate both in the down-flow and, preferably, up-
flow mode. This gas can be fed to different sections of
the reactor.
The catalyst precursors used can be selected from
those obtainable from easily decomposable oil-soluble
precursors (metal naphthenates, metal derivatives of
phosphonic acids, metal-carbonyls, etc..) or from pre-
formed compounds based on one or more transition metals
such as Ni, Co, Ru, W and Mo: the latter is preferred
thanks to its higher catalytic activity.
The concentration of the catalyst, defined according
to the concentration of the metal or metals present in
the hydrocracking reactor, ranges from 50 to 5,000 ppm,
preferably from 50 to 900 ppm.
The process claimed therein allows the production of
a completely deasphalted and demetallized "light syn-
crude" (atmospheric and vacuum distillates) and also up-
graded in terms of density, viscosity, CCR sulphur con-
tent.
An embodiment of the present invention is now pro-
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vided with the help of the enclosed figure 1, which should not be considered
as
limiting the scope of the invention itself.
In Fig. 1, the heavy feedstock (1) is fractionated in a first distillation
zone
(D1) from which the light fractions are separated (2) and (3) from the
distillation
residue (4).
The first distillation residue (4) is sent to a deasphalting unit (SDA), said
operation being effected by means of solvent extraction (8).
Two streams are obtained from the deasphalting unit (SDA): one (9)
consisting of deasphalted oil (DAO), the other containing asphaltenes (10).
Once the stream consisting of deasphalted oil (9) has been freed from the
solvent used for the extraction, it is sent to a hydrocracking zone (HCK).
The stream containing asphaltenes (10) is sent to a gasification section (P0x)
in order to obtain syngas, i.e. a gaseous mixture of H2 and CO (11) which is
sent to a
separation area (GS), whereby a stream essentially consisting of CO (12) is
separated and a stream essentially consisting of H2 (13) which is sent to the
hydrocracking step, thus providing the necessary quantity of hydrogen.
The stream (16) leaving the hydrocracking step (HCK)
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is sent to a second distillation zone (D2).
In the second distillation zone (D2), consisting of a
distillation column, possibly preceded by a flash, the
lighter fractions (D21, D"2, D23, ...D2n) are separated
from the heavier fraction (19) at the bottom, which is
recycled (20) to the first distillation zone (D1) and/or
(21) to the deasphalting zone (SDA).
At least part (22) of the heavier light fraction (3),
separated in the first distillation zone (D1), can possi-
bly be sent to the hydrocracking (HCK) zone.
Some examples are provided hereunder for a better il-
lustration of the invention, it being understood that the
same should not be considered as being limited thereto or
thereby.
Example 1: Preparation of a deasphalted oil
Feedstock: 250 g of atmospheric residue
Deasphalting agent: about 2.5 1 of n-pentane
Temperature: 180 C
Pressure: 16 atm.
The residue and a volume of n-pentane equal to 8-10
times the residue volume are charged into an autoclave.
The mixture of feedstock and solvent is heated to a tem-
perature of 180 C, with stirring (800 rpm) by means of a
mechanical stirrer for a period of 30 minutes. At the end
of this operation, the two phases are decanted and sepa-
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rated, the asphaltene phase which is deposited on the
bottom of the autoclave and the deasphalted oil phase di-
luted in the solvent. The decanting lasts for about two
hours. The DAO-solvent phase is then transferred to a
second tank, by means of a suitable recovery system. The
DAO-pentane phase is subsequently recovered, and the sol-
vent is then eliminated by evaporation.
The yield obtained using the procedure described
above is equal to 89.8 by weight of deasphalted oil with
respect to the starting residue.
Example 2: Hydrocracking of the deasphalted oil with
n-pentane.
The test was effected making use of a stirred micro-
autoclave of 30 cm3, according to the following general
operative procedure:
- about 10 g of the feedstock are charged into the reac-
tor, and the catalyst precursor is added;
- the system is pressurized with hydrogen and brought to
temperature by means of an electrically heated oven;
- during the reaction the system is kept under stirring
by a swinging capillary system operating at a rotation
rate of 900 rpm; furthermore, the total pressure is
kept constant by means of an automatic reintegration
system of the hydrogen consumed;
- at the end of the test, quenching of the reaction is
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effected; the autoclave is then depressurized and the
gases collected in a sampling bag; the gaseous samples
are then sent for gas chromatographic analysis;
- the solids are separated from the products present in
the reactor by filtration; the liquid products are
analyzed in order to determine: the yields to distil-
lates, sulphur content, nitrogen content, carbonaceous
residue and metal content.
The reaction was carried out by feeding the feedstock
produced in example 1, under the same operative condi-
tions indicated in Table 1. The distribution data ob-
tained are shown in Table 2.
Example 3: Thermal cracking of the deasphalted oil
with n-pentane.
The test was effected according to the operative
procedure described in Example 2, without the addition of
catalyst and by substituting hydrogen with nitrogen. The
reaction was carried out by feeding the feedstock pro-
duced in example 1, under the operative conditions indi-
cated in Table 1. The product distribution data are shown
in Table 2.
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Table 1: Operative conditions
Operative conditions Test A ¨ Example 2 Test B ¨
Example 3
Temperature 460 C 460 C
Residence time 2 hours 2 hours
Pressure 160 bar H2 160 bar
N2
Molybdenum 100 ---
Table 2: Product distribution
Product distribution Test A ¨ Example 2 Test B ¨
Example 3
(w%)
Gas C1-C4 8.4 15.6
C5 ¨ 160 C 26.7 18.1
160-220 C 16.9 10.5
220-365 C 27.3 15.8
365-500 C 12.5 5.7
500 C + 4.3 2.0
Solids 3.9 32.3
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