FR3130834A1 - Process for treating a gasoline containing sulfur compounds - Google Patents

Abstract

Process for treating a gasoline containing sulfur compounds, olefins and diolefins, the process comprising at least the following steps: a) the gasoline, hydrogen and a catalyst are brought into contact in at least one reactor hydrodesulphurization comprising an oxide support and an active phase comprising a metal from group VIB and a metal from group VIII;b) the effluent resulting from stage a), hydrogen and a hydrodesulphurization catalyst comprising an oxide support and an active phase consisting of at least one group VIII metal;c) the effluent resulting from stage b) is sent to a separation drum operating at a pressure of between 1.0 and 2.0 MPa to obtain a gaseous fraction containing H2S and hydrogen and a liquid fraction containing the desulfurized gasoline and a fraction of dissolved H2S;d) said liquid fraction obtained in step c) in a stabilization column to obtain a stream comprising the residual H2S and C4- hydrocarbon compounds at the top and a stabilized gasoline at the bottom; e) the gaseous fraction is recycled at least in part obtained at the end of step c) towards at least one of steps a) and/or b).

Description

Process for treating gasoline containing sulfur compounds

Field of invention

The present invention relates to a method for producing gasoline with a low sulfur and mercaptan content.

State of the art

The production of gasolines meeting the new environmental standards requires a significant reduction in their sulfur content.

It is also known that conversion gasolines, and more particularly those originating from catalytic cracking, which can represent 30 to 50% of the gasoline pool, have high mono-olefin and sulfur contents.

The sulfur present in the gasolines is for this reason attributable, at nearly 90%, to the gasolines resulting from the processes of catalytic cracking, which will be called in the following gasolines of FCC (Fluid Catalytic Cracking according to the Anglo-Saxon terminology, that can be translated by catalytic cracking in a fluidized bed). FCC gasolines therefore constitute the preferred feedstock for the process of the present invention.

Among the possible ways to produce fuels with a low sulfur content, the one that has been very widely adopted consists in specifically treating sulfur-rich gasoline bases by catalytic hydrodesulphurization processes in the presence of hydrogen. Traditional processes desulfurize gasolines in a non-selective way by hydrogenating a large part of the mono-olefins, which generates a high loss in octane number and a high consumption of hydrogen. The most recent processes, such as the Prime G+ process (trademark), make it possible to desulphurize cracked gasolines rich in olefins, while limiting the hydrogenation of mono-olefins and consequently the loss of octane and the high consumption resulting hydrogen. Such processes are for example described in patent applications EP1077247 and EP1174485.

The residual sulfur compounds generally present in desulfurized gasoline can be separated into two distinct families: the unconverted refractory sulfur compounds present in the charge on the one hand, and the sulfur compounds formed in the reactor by so-called secondary recombination reactions. Among this last family of sulfur compounds, the majority compounds are the mercaptans resulting from the addition of the H2S formed in the reactor to the mono-olefins present in the charge.

Mercaptans, with the chemical formula R-SH, where R is an alkyl group, are also called recombinant mercaptans. Their formation or decomposition obeys the thermodynamic equilibrium of the reaction between mono-olefins and hydrogen sulphide to form recombinant mercaptans. An example is illustrated according to the following reaction:

The sulfur contained in the recombinant mercaptans generally represents between 20% and 80% by weight of the residual sulfur in the desulphurized gasolines.

The formation of recombination mercaptans is in particular described in patent US6231754 and patent application WO01/40409 which teach various combinations of operating conditions and of catalysts making it possible to limit the formation of recombination mercaptans.

Other solutions to the problem of the formation of recombination mercaptans are based on a treatment of partially desulfurized gasolines to extract said recombination mercaptans therefrom. Some of these solutions are described in patent applications WO02/28988 or WO01/79391.

Still other solutions are described in the literature for desulphurizing cracked gasolines using a combination of hydrodesulphurization and elimination of recombinant mercaptans by reaction to thioethers or disulphides (also called sweetening or “ sweetening ”) according to Anglo-Saxon terminology) (see for example US7799210, US6960291, US2007/114156, EP2861094).

Finally, patent application US2006/278567 discloses a process for the hydrodesulphurization of a cracked gasoline in two stages comprising intermediate separation stages making it possible in particular to limit the formation of mercaptans.

Objects of the invention

The subject of the present invention is a method for treating a gasoline containing sulfur compounds, olefins and diolefins, the method comprising at least the following steps:

a) gasoline, hydrogen and a hydrodesulphurization catalyst comprising an oxide support and an active phase comprising a group VIB metal and a group VIII metal are brought into contact in at least one reactor, a temperature of between 210 and 320°C, at a pressure of between 1.5 and 3 MPa, with a space velocity of between 1 and 10 h ^-1 and a ratio between the hydrogen flow rate expressed in normal m ³ per hour and the feed rate to be treated expressed in m ³ per hour under standard conditions of between 100 and 600 Nm ³ /m ³ , so as to convert at least some of the sulfur compounds into H ₂ S;

b) in at least one reactor, the effluent from step a) without removal of the H ₂ S formed, is brought into contact with hydrogen and a hydrodesulphurization catalyst comprising an oxide support and a active phase consisting of at least one group VIII metal, at a temperature between 280 and 400°C, at a pressure between 1.0 and 3 MPa, with a space velocity between 1 and 10 h ^-1 and a ratio between the hydrogen flow rate expressed in normal m ³ per hour and the feed flow rate to be treated expressed in m ³ per hour at standard conditions of between 100 and 600 Nm ³ /m ³ ;

c) the effluent from step b) is sent to at least one separation drum operating at a pressure of between 1.0 and 2.0 MPa to obtain a gaseous fraction containing H ₂ S and hydrogen and a liquid fraction containing desulfurized gasoline and a fraction of dissolved H ₂ S;

d) said liquid fraction obtained in step c) is sent to a stabilization column to obtain at the top a stream comprising the residual H ₂ S and C4- hydrocarbon compounds and at the bottom a stabilized gasoline;

e) the gaseous fraction obtained at the end of step c) is recycled at least in part to at least one of steps a) and/or b).

The Applicant has identified, surprisingly, that in order to maintain a mercaptan and sulfur content in the hydrodesulfurized gasoline below 10 ppm by weight while limiting the loss of octane, the pressure in the hydrodesulfurization section (step a) of the process ) should be between 1.5 and 3 MPa, and the pressure of the separation vessel should be within a specific range between 1.0 and 2.0 MPa. Indeed, if the pressure of the separation drum is less than 1.0 MPa, the purity of the hydrogen contained in the recycle gas fraction will decrease, thus leading to a decrease in the ratio between the hydrogen flow rate and the flow rate of load to be processed. Thus, to maintain a content of mercaptans and sulfur of 10 ppm by weight, it is necessary to increase the temperature of the hydrodesulphurization stages, which has the effect of increasing the hydrogenation of the olefins of the gasoline cut, which will have has the effect of increasing octane loss. Furthermore, if the pressure of the separation drum is greater than 2.0 MPa, the purity of the hydrogen contained in the recycle gaseous fraction will certainly increase, but this leads to an increase in the pressure at the inlet of the reactors of hydrodesulfurization, and therefore, in addition to an overconsumption of hydrogen, will lead to an increase in the mercaptan content in the hydrodesulfurized gasoline and an increase in the loss of octane.

According to one or more embodiments, the pressure of the separation drum of step c) is between 1.2 and 1.8 MPa.

According to one or more embodiments, the catalyst of step a) comprises a group VIII metal content of between 0.1 and 10% by weight of group VIII metal oxide relative to the total weight of the catalyst, and a group VIB metal content of between 1 and 20% by weight of group VIB metal oxide relative to the total weight of the catalyst.

According to one or more embodiments, the catalyst of stage a) comprises a molar ratio of metal from group VIII to metal from group VIB of the catalyst of between 0.1 and 0.8.

According to one or more embodiments, the catalyst of step a) comprises a specific surface of between 5 and 400 m²/g.

According to one or more embodiments, the catalyst of step a) comprises alumina and an active phase comprising cobalt, molybdenum and optionally phosphorus, said catalyst containing a content by weight relative to the total weight of catalyst cobalt oxide, in CoO form, between 0.1 and 10%, a content by weight relative to the total weight of molybdenum oxide catalyst, in MoO ₃ form, between 1 and 20%, a ratio molar cobalt/molybdenum of between 0.1 and 0.8, a content by weight relative to the total weight of catalyst of phosphorus oxide in the P ₂ O ₅ form of between 0.3 and 10% when the phosphorus is present, said catalyst having a specific surface between 50 and 250 m²/g.

According to one or more embodiments, the catalyst of step b) comprises a group VIII metal content of between 1 and 60% by weight of group VIII metal oxide relative to the total weight of the catalyst.

According to one or more embodiments, the catalyst of step b) comprises a specific surface of between 5 and 400 m²/g.

According to one or more embodiments, the catalyst of step b) consists of alumina and nickel, said catalyst containing a content by weight relative to the total weight of catalyst of nickel oxide, in NiO form, comprised between 5 and 20%, said catalyst having a specific surface between 30 and 180 m²/g.

According to one or more embodiments, the temperature of step b) is higher than the temperature of step a).

According to one or more embodiments, the temperature of step b) is higher by at least 5° C. than the temperature of step a).

According to one or more embodiments, before step a), a gasoline distillation step is carried out so as to split said gasoline into at least two light and heavy gasoline cuts and the heavy gasoline cut is treated in steps a ), b), c), d) and e).

According to one or more embodiments, before step a) and before any possible distillation step, the gasoline is brought into contact with hydrogen and a selective hydrogenation catalyst to selectively hydrogenate the diolefins contained in said l gasoline into olefins.

According to one or more embodiments, the gasoline is a catalytic cracked gasoline.

List of Figures

There is a schematic representation of an embodiment according to the invention.

There is a schematic representation of a method not in accordance with the invention.

Claims (14)

Process for treating a gasoline containing sulfur compounds, olefins and diolefins, the process comprising at least the following steps:
a) gasoline, hydrogen and a hydrodesulphurization catalyst comprising an oxide support and an active phase comprising a group VIB metal and a group VIII metal are brought into contact in at least one reactor, a temperature of between 210 and 320°C, at a pressure of between 1.5 and 3 MPa, with a space velocity of between 1 and 10 h ^-1 and a ratio between the hydrogen flow rate expressed in normal m ³ per hour and the feed rate to be treated expressed in m ³ per hour under standard conditions of between 100 and 600 Nm ³ /m ³ , so as to convert at least some of the sulfur compounds into H ₂ S;
b) in at least one reactor, the effluent resulting from stage a) without elimination of the H ₂ S formed, is brought into contact with hydrogen, and a hydrodesulphurization catalyst comprising an oxide support and an active phase consisting of at least one group VIII metal, at a temperature of between 280 and 400°C, at a pressure of between 1.0 and 3 MPa, with a space velocity of between 1 and 10 h ^-1 and a ratio between the hydrogen flow rate expressed in normal m ³ per hour and the feed flow rate to be treated expressed in m ³ per hour at standard conditions of between 100 and 600 Nm ³ /m ³ ;
c) the effluent from step b) is sent to at least one separation drum operating at a pressure of between 1.0 and 2.0 MPa to obtain a gaseous fraction containing H ₂ S and hydrogen and a liquid fraction containing desulfurized gasoline and a fraction of residual H ₂ S;
d) said liquid fraction obtained in step c) is sent to a stabilization column to obtain at the top a stream comprising the residual H ₂ S and C4- hydrocarbon compounds and at the bottom a stabilized gasoline;
e) the gaseous fraction obtained at the end of step c) is recycled at least in part to at least one of steps a) and/or b). Process according to Claim 1, in which the pressure of the separation vessel of step c) is between 1.2 and 1.8 MPa. Process according to either of Claims 1 and 2, in which the catalyst of stage a) comprises a group VIII metal content of between 0.1 and 10% by weight of oxide of the group VIII metal with respect to the total weight of the catalyst, and a group VIB metal content of between 1 and 20% by weight of group VIB metal oxide relative to the total weight of the catalyst. Process according to any one of claims 1 to 3, in which the catalyst of step a) comprises a Group VIII metal to Group VIB metal molar ratio of the catalyst of between 0.1 and 0.8. Process according to any one of Claims 1 to 4, in which the catalyst of step a) comprises a specific surface of between 5 and 400 m²/g. Process according to any one of Claims 1 to 5, in which the catalyst of step a) comprises alumina and an active phase comprising cobalt, molybdenum and optionally phosphorus, said catalyst containing a content by weight per relative to the total weight of cobalt oxide catalyst, in CoO form, of between 0.1 and 10%, a content by weight relative to the total weight of molybdenum oxide catalyst, in MoO ₃ form, of between 1 and 20%, a cobalt/molybdenum molar ratio of between 0.1 and 0.8, a content by weight relative to the total weight of catalyst of phosphorus oxide in the P ₂ O ₅ form of between 0.3 and 10% when phosphorus is present, said catalyst having a specific surface between 50 and 250 m²/g. Process according to any one of claims 1 to 6, in which the catalyst of step b) comprises a group VIII metal content of between 1 and 60% by weight of oxide of the group VIII metal relative to the total weight of the catalyst. Process according to any one of Claims 1 to 7, in which the catalyst of stage b) comprises a specific surface comprised between 5 and 400 m²/g. Process according to any one of Claims 1 to 8, in which the catalyst of step b) consists of alumina and nickel, said catalyst containing a content by weight relative to the total weight of catalyst of nickel oxide , in NiO form, between 5 and 20%, said catalyst having a specific surface between 30 and 180 m²/g. Process according to any one of claims 1 to 9, in which the temperature of step b) is higher than the temperature of step a). Process according to Claim 10, in which the temperature of step b) is at least 5°C higher than the temperature of step a). Process according to any one of Claims 1 to 11, in which, before step a), a gasoline distillation step is carried out so as to split the said gasoline into at least two light and heavy gasoline cuts and the cut is treated heavy gasoline in steps a), b), c), d) and e). Process according to any one of Claims 1 to 12, in which before stage a) and before any optional distillation stage, the gasoline is brought into contact with hydrogen and a selective hydrogenation catalyst in order to selectively hydrogenate the diolefins contained in said gasoline into olefins. Process according to any one of claims 1 to 13, in which the gasoline is a catalytic cracked gasoline.