CATEGORY: HEAVY CRUDE
PATENT
Method for the valorization of heavy charges by
bubbling-bed deasphalting and hydrocracking (IFP Energies Nouvelles)
Publication number US8636896 B2
Application number US 12/900,987
Publication date Jan 28, 2014
Also published as CA2464796A1, 5 More »
Inventors
Christophe Gueret, Stéphane Kressmann, Jan Verstraete
Original Assignee
IFP Energies Nouvelles
Abstract
The invention relates to a method for treating a
hydrocarbons charge comprising the following stages, in which: •a) the charge
is brought into contact with a solvent in order to obtain a deasphalted effluent having a content of asphaltenes below
3000 ppm by weight,
•b) the deasphalted effluent is cracked in the
presence of hydrogen and a hydrocracking catalyst, in a bubbling-bed reactor,
so as to convert at least 50 wt. % of the fraction of the deasphalted effluent
boiling above 500° C. to compounds having a boiling point below 500° C.,
•c) the effluent from stage b) is fractionated to recover gasolines, kerosene,
gas oils and a first residue, and
•d) at least a portion of this first residue is cracked so as to obtain an
effluent comprising gasolines, kerosene, gas oils and a second residue.
The field of the present invention is the refining of petroleum fractions. It
relates in particular to the field of processes for treatment of heavy charges
such as residues from atmospheric distillation or from vacuum distillation.
In view of the increasing demand for fuels, gasolines and diesel fuel, and the
decline in consumption of heavy fuel oils, it is becoming more and more
important to be able to convert the bottom of the barrel to a very high level.
This is particularly true for certain countries where the local oil output
consists essentially of so-called heavy crudes for example Athabasca crude in
Canada, Morichal in Venezuela, containing very few, light distillates. In fact,
these heavy crudes contain about 80 wt. % of vacuum residue. These crudes are
also characterized by a low API density, below 12.
Moreover, the heavy charges such as atmospheric residues and vacuum residues
contain large amounts of metals, sediments and asphaltenes. When these charges
are used in thermal conversion processes, such as a visbreaking, the impurities
in these charges quickly lead to coking and the clogging of capacities by
flocculation and sedimentation. When these same charges are used in fixed-bed
catalytic conversion processes, the presence of impurities' makes it necessary
to use a guard bed to protect the refining catalysts and avoid too rapid a
deactivation, thus increasing the volume of the reactors in these units.
Furthermore, in fixed-bed conversion units, the conversion of the charge is limited
by thermal levels that are lower than in bubbling-bed conversion units. When
these charges are used as they are in bubbling-bed catalytic conversion
processes, the presence of these impurities leads to an increase in the rate of
catalyst replacement.
French patent FR 2 803 596 describes a method for the conversion of distillates
comprising a bubbling-bed hydroconversion stage, a separation stage in which a
light fraction and a heavy fraction are obtained, and a stage of catalytic
cracking of the heavy fraction. Such a process can lead to high conversion
rates, but its employment is generally envisaged only for charges having a
final boiling point below 600° C. Moreover, the Method described in this patent
is not suitable, a priori, for the treatment of an atmospheric residue or of a
vacuum residue originating from a heavy crude.
A method has been found that makes it possible to overcome the aforementioned
drawbacks and also obtain high yields of gasolines, kerosene and gas oils,
starting from residues originating from an atmospheric distillation or from a
vacuum distillation of a heavy crude. This method also makes it possible to
obtain products of good quality that do not require post-treatment or require
only moderate post-treatments.
The present invention therefore relates to a method of treatment of a
hydrocarbon charge of which at least 95 wt. % consists of compounds having a
boiling point of at least 340° C., characterized in that it comprises the
following stages, in which:
• ◦a) the charge is brought into contact with a solvent in order to obtain a
deasphalted effluent having a content of asphaltenes (insoluble in n-heptane
according to standard NF-T-60-115) below 3000 ppm by weight,
◦b) the deasphalted effluent is cracked in the presence of hydrogen and a
hydrocracking catalyst, in a bubbling-bed reactor, so as to convert at least 50
wt. % of the fraction of the deasphalted effluent boiling above 500° C. to
compounds having a boiling point below 500° C.,
◦c) the effluent from stage b) is fractionated to recover gasolines, kerosene,
gas oils and a first residue, and
◦d) at least a portion of this first residue is cracked catalytically so as to
obtain an effluent comprising gasolines, kerosene, gas oils and a second
residue.
An advantage of the invention is that it provides a method that makes it
possible to obtain a better valorization of heavy charges such as atmospheric
residues, vacuum residues obtained from any crude oils, in particular from
heavy crudes. These heavy crudes generally have an API density below 12.
Another advantage of the invention is that it provides a method that makes it
possible to aim at a high overall yield of gasolines, kerosene and gas oils.
Another advantage of the invention is that it provides a method that makes it
possible to obtain gasolines, kerosene and gas oils having excellent qualities
and to limit the number or the severity of post-treatments.
For better understanding, two non-limiting embodiments of the method of the
invention are illustrated by drawings.
FIG. 1 shows, as an example, an embodiment of the method according to the
invention comprising the following in succession: a deasphalting stage, a
bubbling-bed hydroconversion stage, a stage of fractionation by atmospheric
distillation and a stage of catalytic cracking of the FCC type.
FIG. 2 shows, as an example, a flow diagram similar to that of FIG. 1, but in
which the fractionation stage comprises an atmospheric distillation and a
vacuum distillation, the vacuum distillate being sent to a hydrocracking stage.
The charges that can be treated by the method of the invention are hydrocarbons
of which at least 95 wt. % consists of compounds having a boiling point of at
least 340° C. and which can reach 700° C. or more, for example between 500° C.
and 700° C.
The hydrocarbon charge has a final boiling point, preferably above 600° C.,
more preferably above 650° C., and even more preferably above 700° C.
These charges can be atmospheric residues and vacuum residues. For example,
these charges can be residues from direct distillations or from conversion
processes such as coking, fixed-bed hydroconversion processes such as the
HYVAHL process or bubbling-bed processes such as the H-Oil process. The charges
can be formed by mixing these fractions in any proportion or by dilution in
petroleum fractions with a boiling point below 360° C.
The invention proves particularly beneficial for certain residues of heavy
crudes, i.e. crudes containing few distillates. Typically Athabasca and
Morichal crudes contain 80% of vacuum residues. Their API density is generally
close to 10. These heavy crudes contain, compared with other crudes, many more
impurities such as, for example, metals (nickel, vanadium, silicon, etc.), a
high Conradson carbon residue, asphaltenes, sulphur and nitrogen.
Thus, according to a preferred embodiment, the hydrocarbon charge consists
essentially of atmospheric residues, of which at least 95 wt. % consists of
compounds having a boiling point of at least 600° C., and vacuum residues from
heavy crudes, of which at least 95 wt. % consists of compounds having a boiling
point of at least 650° C.
During stage a) of the method of the invention, the charge is brought into
contact with a solvent in order to obtain a deasphalted effluent. This
operation is often described as solvent deasphalting. It makes it possible to
extract a high proportion of the asphaltenes and to reduce the metals content.
During this deasphalting, the latter elements become concentrated in an
effluent called asphalt. The deasphalted effluent, often called deasphalted
oil, has a reduced content of asphaltenes and metals.
One of the aims of the deasphalting stage is, on the one hand, to maximize the
amount of deasphalted oil and, on the other hand, to maintain, or even
minimize, the content of asphaltenes. The said content of asphaltenes is
generally determined in terms of content of asphaltenes insoluble in heptane,
i.e. measured in accordance with a method described in standard NF-T-60-115 of
January 2002.
According to the invention, the asphaltenes content of the deasphalted effluent
is less than 3000 ppm by weight.
Preferably, the asphaltenes content of the deasphalted effluent is less than
1000 ppm by weight, and more preferably less than 500 ppm by weight.
Below an asphaltenes content of 500 ppm by weight, the method of standard NF-T
60-115 is no longer adequate for measuring the said content. The applicant has
developed an analytical method, covering the quantitative analysis of
asphaltenes in products of direct distillation and in heavy products obtained
from deasphalting of residues. This method can be used for asphaltene
concentrations below 3000 ppm by weight and above 20 ppm by weight. The method
in question consists of comparing the absorbance at 750 nm of a sample in
solution in toluene with that of a sample in solution in heptane after
filtration. The difference between the two measured values is correlated to the
concentration of heptane-insoluble asphaltenes using a calibration equation.
This method supplements AFNOR method T60-115 and the standard method IP143
which are used for higher concentrations.
The solvent used in the deasphalting stage a) is advantageously a paraffinic
solvent, a gasoline fraction or condensates containing paraffins.
Preferably, the solvent used in stage a) contains at least 50 wt. % of
hydrocarbon compounds having between 3 and 7 carbon atoms, more preferably
between 5 and 7 carbon atoms, even more preferably 5 carbon atoms.
The yield of deasphalted oil and the quality of the said oil can vary,
depending on the solvent used. For example, on changing from a solvent with
3-carbon atoms to a solvent with 7 carbon atoms, the yield of oil increases,
but against this there is also an increase in the levels of impurities
(asphaltenes, metals, Conradson carbon residue, sulphur, nitrogen, etc.).
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