WO2001096498A1

WO2001096498A1 - Method for desulphurizing a cracking or steam cracking effluent

Info

Publication number: WO2001096498A1
Application number: PCT/FR2001/001362
Authority: WO
Inventors: Patrick Briot; Blaise Didillon; Alain Forestiere; Eric Llido; Vincent Coupard
Original assignee: Institut Francais Du Petrole
Priority date: 2000-06-13
Filing date: 2001-05-04
Publication date: 2001-12-20

Abstract

The invention concerns a sequence of steps for desulphurizing gasoline for example from catalytic cracking comprising the elimination of thiophenic compounds by alkylating said compounds, Said method enables to cut out the step of eliminating nitrogenous compounds in gasoline to be alkylated.

Description

PROCESS FOR DESULFURIZING A CRACKING OR VAPOCRACKING EFFLUENT

The process which is the subject of the present application is a process for desulphurising hydrocarbon cuts containing at least 3% of olefins and sulfur in the form of ihiophenic or benzothiophenic compounds at contents ^" at least greater than 5 ppm and which can range up to 3% weight.

This process is characterized by the fact that the boiling points of this cup are less than JO or equal to 350 ° C. This cup may contain benzene. It is therefore gasoline coming either all or in part (at least 10% by weight), from any conversion process known to those skilled in the art.

Gasoline from catalytic cracking processes constitutes 40% of the L5 gasoline “pool” in France. They are very interesting because they have significant contents of unsaturated hydrocarbons of olefinic type. These olefins give these species high octane numbers. However, they sometimes have a high sulfur content of between 0.1 and 1%. In the European specifications, the sulfur content in gasolines for sale must reach 50 or even 10 ppm in the near future.

20

To achieve this objective, a conventional hydrodesulfurization process is most often used. This process, which is well known to those skilled in the art, consists in hydrogenating these products in order to remove the sulfur in gaseous or H2S form. The disadvantage of the various hydrodesulfurization processes currently used is that they also hydrogenate the olefins whatever the catalysts used. This hydrogenation of olefins results in a significant drop in the octane number, a very important property for the refiner.

The process claimed by the applicant consists in selectively weighing down the sulfur compounds contained in the gasolines, thus making it possible to separate them by distillation from the olefins.

J o 11 only remains to hydrogenate a cut containing no more than sulfur and completely devoid of olefins. The other cut, sulfur-free and containing olefins, does not undergo hydrogenation. The present invention makes it possible not to proceed with the elimination of the nitrogen compounds present

^" in the charges to be treated. The presence of such compounds required either to use a completely different type of sequence, or in the case where it is wished to eliminate the thiophene or the thiophenic compounds, to get rid of these nitrogenous compounds, generally basic, by acid washing or by using a guard bed.

Diagram No. 1 is provided to serve as an example and to explain the operating principle of the process claimed by the applicant.

The gasoline (or α) which may contain diolefins is injected via line 1 into a hydrogenation unit for diolefins A. This step A, as well as step C are optional if the charge is devoid of diolefins. The hydrogen is injected via line 2. The charge and the hydrogen are brought into contact with a hydrogenation catalyst. This diolefin hydrogenation step is known to those skilled in the art.

After the hydrogenation, the effluent is sent to a separation unit B which can be a vaporization flask, a splitter or a distillation column in order to separate the effluents into two sections:

- a so-called light cup (or β) with boiling points below 60 ° C. This temperature is given as an indication, it is in fact the maximum temperature in which the thiophene content is less than 5 ppm,

- a so-called heavy cut (or γ) with boiling points above 60 ° C.

The light cut is then injected into a liquid gas separation flask in order to separate the unconsumed hydrogen and the H2S, via line 5, olefins generally having from 5 to 7 carbon atoms, leaving through line 6 .

The so-called heavy cut (or γ), that is to say the cut whose temperatures are above 60 ° C., is transported by line 7 in a distillation column D or any other separation process capable of separating this cut into two cuts:

- a cut (or η) whose boiling points for example are at least 60 ° C and at most 150 ° C or even 180 ° C. These temperatures as a benchmark correspond to boiling temperatures of chemical compounds. 60 ° C is the boiling point (eutectic) of thiophene and 180 ° C corresponds to the boiling point of aniline, - a heavier cut (or φ) with boiling points above 180 ° C or even at 150 ° C.

The heavy cut (or φ) whose boiling temperatures are above 150 ° C or even 180 ° C is sent to a conventional hydrodesulfurization unit G and known to those skilled in the art.

The light cut (or η) whose boiling points are between 60 ° C and 180 ° C (or even 150 ° C) is sent, after mixing with part of the olefins coming from line 10 in an alkylation unit E.

The thiophenic compounds and the benzene contained in the 60 ° C-180 ° C section will react in full with the olefins to form thiophene alkyls or benzene alkyls according to the following reaction for the thiophene:

These higher molecular weight compounds are mostly characterized by higher boiling temperatures than they had before alkylation. Thus the theoretical boiling temperature which is 80 ° C are shifted to 250 ° C for thiophene alkyls.

This alkylation step is carried out in the presence of an acid catalyst. This catalyst can be either a resin, a zeolite, a clay or any silico-aluminate having any acidity. The ratio of the volume of feed injected to the volume of catalyst is between 0J and 10 liters / liter / hour and preferably between 0.5 and 4 liters / liter / hour. More specifically, this alkylation step is carried out in the presence of at least one acid catalyst chosen from the group formed by silicoaluminates, titano silicates, mixed alumina titanium, clays, resins, mixed oxides obtained by grafting of at least one compound organometallic organosoluble or water-soluble (chosen from the group formed by alkys. and / or alkoxy. metals of at least one element such as titanium, silicon zirconium, germanium, tin, tantalum, niobium ...) on at least one oxide such as alumina (gamma, delta, eta forms, alone or as a mixture) silica, silica aluminas, titanium silicas, zirconia silicas or any other solid having any acidity. A particular embodiment of the invention may consist in implementing a physical mixture ^" of at least two of the above catalysts in proportions varying from 95/5 to 5/95, preferably 85/15 to 15/85 and very preferably. 70/30 to 30/70 ".

The temperature for this stage is between 30 and 350 ° C. depending on the type of catalyst or the strength of the acidity. Thus, for an acidic resin of ion exchange type, the temperature is between 50 and 150 ° C. preferably between 50 and 120 ° C.

The molar ratio of olefin to thiophene is between 0J and 1000 mole / mole, preferably between 0.5 and 500 mole / mole.

The pressure of this stage is such that the charge is in liquid form under the temperature and pressure conditions, ie at a pressure greater than 5 bars. In a first aspect of the invention, this heavy cut (or φ), after alkylation, is sent via line 11 to a distillation column F or to any other separation unit known to those skilled in the art to be separated into two fractions:

- a 60 ° C-180 ° C or K section this time devoid of any thiophenic compound, therefore of sulfur, which is collected by line 12,

- a cut or λ whose boiling temperatures are higher than 180 ° C which is optionally mixed by line 13 in part with the cut 180 ° C, or even 150 ° C + (or φ) and sent to a hydrotreating unit G.

The total gasoline, resulting from the mixture of adequate cuts, that is to say supplied by lines 6, 12 and 15, does not have sulfur (less than 10 ppm), no longer has benzene and has undergone a loss in olefins equal to 2 times the thiophene content. Our process makes it possible to treat the charges containing nitrogenous compounds unlike the prior art. Indeed, the light nitrogen compounds of the dimethyl, diethylamine type are hydrogenated during stage A (hydrogenation of diolefins). The resulting ammonia is then removed during step B, by line 5 of diagram 1.

The heavier nitrogen compounds (aromatic), the lightest of which is aniline, boils at a temperature above 184 ° C. They are therefore removed by distillation (step D, line 8). They fall to the bottom of the column and are sent directly to hydro-treatment.

The charge which is then sent to the alkylation (60 ° C-180 ° C or 60 ° C-150 ° C) is then freed, almost entirely, of the basic nitrogen compounds, without it having been necessary to do call for an acid wash or a guard bed.

Our process has a definite advantage compared to that of the prior art: - nitrogen problem, - diolefin problem, olefin problem.

Thus, in patent 6,048,451 the section is sent directly by alkylation on an acid catalyst. However, everyone knows that diolefins have the annoying tendency to polymerize and make gums thus clogging the reactors and the exchangers. This is not the case in our present process since these diolefins are selectively hydrogenated before alkylation.

Similarly, in patent 6,048,451, the entire petroleum cut is sent in alkylation, so the light olefins will dimerize. This dimerization will be reflected in the effluent by a reduction in the octane number. However in our case, before the alkylation, we separate the PI-60 ° C cut which consists almost exclusively of olefins. So we don't have that kind of problem. The olefins remaining in the 60 ° C-180 ° C section have longer chain lengths, therefore lower dimerization rates and a lower impact on octane. The present process makes it possible to obtain lower octane losses than those of patent 6,048,451. With regard to recycling, the process according to the invention proposes two schemes 1 and 2. In scheme 1, the effluent after alkylation is sent to a distillation column which is different from the first. However, in scheme 2, the effluent is recycled in the same distillation column. In this case, what has been written previously concerning nitrogen compounds, diolefins and olefins is still valid.

In another aspect of the invention, the alkylation products are not directed to the separation or distillation column, but are sent, at least in part, directly into the heavy cut.

In a third aspect of the invention, the alkylation products are at least partly sent to the distillation column and at least partly sent to the heavy fraction.

In the example below, two different methods have been compared to iso-performance in hydrodesulfurization:

- the classic hydrodesulphurization method using cobalt and molybdenum sulphide based catalysts deposited on alumina,

- the method claimed by the applicant where hydrodesulfurization is represented by step G.

The treated cut is a gasoline from catalytic cracking with boiling points below 160 ° C.

The load and effluent analyzes from the pilot tests are presented in the following table:

This comparison makes it possible to show that the process claimed by the applicant while being as efficient as a hydrodesulfurization at the level of sulfur removal makes it possible to obtain products retaining a high content of olefins and therefore a very good octane number. .

One can imagine variants of the process of the invention and in particular that represented by FIG. 2.

D0

According to this other diagram, the three separation units B, D and F of FIG. 1 are advantageously replaced by a distillation column. The operating principle is identical to that of Figure 1.

The total gasoline containing diolefins can be as previously sent by a line 1 in a unit A of conventional hydrogenation of diolefins with hydrogen, line 2. This stage as well as stage C is optional if the charge is devoid of of diolefins. The liquid and gaseous effluents are then sent to a distillation column where several sections are separated:

20 - at the head, cut PI-60 ° C by line 4. Then, a separator flask makes it possible to separate the gases (H2S and hydrogen not consumed by line 5), olefins with boiling points below 60 ° C, transported by line 6, - the cut 60 ° C-180 ° C is drawn off through line 9 and is sent to the alkylation unit D. This cut is mixed with part of the said light olefins coming from line 7. In this unit, the olefins are added, as before, on thiophenic compounds and on benzene to transform them into alkyls with higher boiling points. The effluents are then injected into the column, by line 10,

- in the column, these alkyls fall to the bottom and are then eliminated by line 11. They are then sent with hydrogen to a hydrotreating unit.

- Line 9 takes out the 60 ° C-150 ° C section which is itself free of sulfur compounds.

J O

By operating according to this FIG. 1, here again, the nitrogen compounds have no undesirable effect on the whole process.

In summary, the present invention relates to a process for desulfurization of a filler containing thiophene or thiophenic compounds making it possible to work on a filler containing nitrogenous compounds and which consists in: a) optionally eliminating the diolefins which it contains, b ) fractionating the feed in a distillation zone into a heavy fraction which will then be desulfurized and into a lighter fraction containing thiophene and / or compounds

Thiophenics, c) alkylating the thiophene and / or the thiophenic compounds with at least one olefin.

Preferably, the process for desulfurization of a charge containing thiophene or thiophenic compounds consists in: a) optionally eliminating the diolefins which it contains, b) in fractioning the charge in a distillation zone into a heavy fraction which will be then desulphurized and in a lighter fraction containing thiophene and / or thiophenic compounds, c) to alkylate the thiophene and / or thiophenic compounds with at least one olefin, d) to recycle, at least in part, the alkylated products thus obtained in said distillation zone so as to pass them through the so-called heavy fraction. More particularly, the process for desulfurization of a charge containing thiophene or thiophenic compounds consists in: a) optionally eliminating the diolefins which it contains, b) in fractioning the charge in a distillation zone into a heavy fraction which will then be desulfurized and in a lighter fraction containing thiophene and / or thiophenic compounds, c) to alkylate the thiophene and / or thiophenic compounds with at least one olefin, d) to send at least partially the alkylated products thus obtained directly in the so-called heavy fraction.

According to a variant, the process for desulfurization of a charge containing thiophene or thiophenic compounds consists in: a) optionally removing the diolefins which it contains, b) in fractioning the charge in a distillation zone into a heavy fraction which will be then desulfurized and in a lighter fraction containing thiophene and / or thiophenic compounds, c) to alkylate the thiophene and / or thiophenic compounds with at least one olefin, d) to recycle at least partially the alkylated products thus obtained in said distillation zone so as to pass them through the so-called heavy fraction, and to send these alkylated products, at least in part directly into the so-called heavy fraction.

According to preferred conditions, said olefin used is at least partly present on at least one of the plates of said distillation zone.

The feedstock is generally chosen from the group consisting of catalytic cracking, steam cracking or coking effluents.

Preferably, the alkylation catalyst is chosen from the group consisting of zeolites, silica-aluminas and ion exchange resins.

It is also preferable to desulfurize hydrocarbon cuts with boiling points below 350 ° C. and containing both olefins, at least 3% by weight and at most 90% by weight, and sulfur, at least 5 ppm and at most 3 % weight, with the sequence of the following stages: at least one distillation, ^at least an alkylation unit, at least one hydrotreatment unit.

More preferably, the distillation is carried out before the alkylation, but also the distillation can be carried out at the same time as the alkylation, either using a side-reactor (reactor in parallel) or in a catalytic column.

The hydrotreating unit can be located after at least one distillation step.

More preferably, the sulfur compounds are alkylated on an acid catalyst in the presence of olefins having at least 2 carbon atoms and at most 10 carbon atoms; the olefin to sulfur molar ratio being between OJ to 1000 moles per mole and preferably 0.5 to 500 moles / mole, the pressure of the alkylation unit being more particularly at least 5 bars.

Claims

A process for desulfurization of a charge containing thiophene or thiophenic compounds and which consists of: d) optionally eliminating the diolefins which it contains, e) fractionating the charge in a distillation zone into a heavy fraction which will then be desulfurized and in a lighter fraction containing thiophene and / or thiophenic compounds, f) alkylating the thiophene and / or thiophenic compounds with at least one olefin.

2 - Process according to claim 1 for desulfurization of a charge containing thiophene or thiophenic compounds and which consists: e) optionally eliminating the diolefins it contains, f) fractionating the charge in a distillation zone into a fraction heavy which will then be desulfurized and in a lighter fraction containing thiophene and / or thiophenic compounds, g) to alkylate the thiophene and / or thiophenic compounds with at least one olefin, h) to recycle, at least in part, the alkylated products thus obtained in said distillation zone so as to pass them through the so-called heavy fraction.

3 - Process according to claim 1 for desulfurization of a charge containing thiophene or thiophenic compounds and which consists of: e) optionally eliminating the diolefins which it contains, f) fractionating the charge in a distillation zone into a fraction heavy which will then be desulfurized and in a lighter fraction containing thiophene and / or thiophenic compounds, g) to alkylate the thiophene and / or thiophenic compounds with at least one olefin, h) to send at least partially the alkylated products thus obtained directly in the so-called heavy fraction.

4 - Process according to claim 1 for desulfurization of a charge containing thiophene or thiophenic compounds and which consists of: e) optionally eliminating the diolefins which it contains, 1) to be fractionated in a distillation zone charging into a heavy fraction that will then ^{'desulfurized} and into a lighter fraction containing thiophene and / or thiophenic compounds, g) alkylating the thiophene and / or thiophenic compounds by the at least one olefin, 5 li) at least partly recycling the alkylated products thus obtained in said distillation zone so as to pass them through the so-called heavy fraction, and sending these alkylated products, at least partly directly into the fraction said to be heavy.

5 - Method according to one of claims 1 to 4 wherein said olefin used was at least () partially present on at least one of the plates of said distillation zone.

6 - Method according to one of claims 1 to 5 wherein the charge is selected from the group consisting of catalytic cracking effluents, steam cracking.

7 - Method according to one of claims 1 to 6 wherein the alkylation catalyst is selected from the group consisting of zeolites, silica-aluminas and ion exchange resins.

8 - Process according to one of claims 1 to 7 for desulfurization of hydrocarbon fractions with 0 boiling points below 350 ° C and containing both olefins, at least 3% by weight and at most 90% by weight, and sulfur, at least 5 ppm and at most 3% by weight, characterized by the sequence of the following stages: at least one distillation, at least one alkylation unit, at least one hydrotreating unit.

9 - Method according to one of claims 1 to 8 wherein the distillation is carried out before the alkylation.

0 10 - Process according to one of claims 1 to 8 wherein the distillation is carried out at the same time as the alkylation, either using a side-reactor (reactor in parallel) or in a catalytic column. 1 1 - Method according to one of claims 1 to 10 wherein the hydrotreating unit is located after at least one distillation step.

12 - Method according to one of claims 1 to 11 for which the sulfur compounds are alkylated on an acid catalyst in the presence of olefins having at least 2 carbon atoms and at most 10 carbon atoms; the olefin to sulfur molar ratio being between 0.1 to 1000 moles per mole and preferably 0.5 to 500 moles / mole

13 - Method according to one of claims 1 to 12 for which the pressure of the alkylation unit is at least 5 bars.

14 - Method according to one of claims 1 to 13 for desulfurization of a charge containing thiophene or thiophenic compounds and which consists of: a) optionally eliminating the diolefins it contains, b) to be fractionated in a distillation zone the charge into a heavy fraction which will then be desulphurised and into a lighter fraction containing thiophene and / or thiophenic compounds, c) to alkylate the thiophene and / or thiophenic compounds with at least one olefin, the process being characterized in that that the charge entering the alkylation zone is previously rid of at least in part the generally basic nitrogen compounds which it contains.

! 5 - Process according to claim 14 wherein to remove at least partially said nitrogenous compounds, one operates in an acid medium.

16 - Process according to claim 14 or 15 wherein the elimination of at least part of said nitrogenous compounds is carried out downstream or upstream of said distillation zone.

17 - Method according to one of claims 14 to 16 wherein said olefin used was at least partially present on at least one of the plates of said distillation zone.

1 8 - Process according to one of claims 14 to 17 wherein the effluent containing the nitrogen compounds thus eliminated is returned at least partially to the distillation zone.