EP1702029B1 - Method for the catalytic purification of light hydrocarbons - Google Patents

Abstract

Purifying light hydrocarbons boiling between 20 and 250[deg]C comprises oxidatively polymerizing cyclic sulfur or nitrogen compounds in the presence of an oxidizing metal cation, removing the resulting polymers and the metal cation, and oxidizing the metal cation. Purifying light hydrocarbons boiling between 20 and 250[deg]C comprises oxidatively polymerizing cyclic sulfur or nitrogen compounds containing a group of formula (I) in a hydrocarbon ring of 5 or 6 atoms in the presence of an oxidizing metal cation, removing the resulting polymers and the metal cation, and oxidizing the metal cation. -X-CH= (I) X =S or N.

Description

The present invention relates to a process for purifying light hydrocarbons containing sulfur compounds and / or nitrogen compounds refractory to conventional catalytic hydrotreatments, such as thiophene compounds and pyrrole-type compounds, by oxidative polymerization of these compounds. It also relates to the regeneration and reactivation of the oxidizing agent used in this process. This process is intended more particularly for the treatment of gasolines, in particular gasoline from catalytic cracking, and hydrocarbons from steam cracking naphthas containing refractory compounds.

By compounds refractory to conventional catalytic hydrotreating is meant thiophene, benzothiophene and their alkyl derivatives, as well as pyrrole and its derivatives, benzopyrrole and carbazole, optionally alkylated.

Usually, significant quantities of these thiophene species are introduced into more desulfurized direct distillation gasolines, which are sold in service station networks, and it is, essentially, these thiopheneic compounds contained in the thiophene species that generate Sulfur dioxide to the exhaust of automobiles. The nitrogen compounds present in these products are known, for their adverse effect with regard to the activity and the life of the catalysts used.

Moreover, these refractory compounds are well known to industry for the difficulty of eliminating them. It is, however, increasingly necessary to eliminate these compounds from light hydrocarbons because, especially for refractory sulfur compounds, environmental restrictions, both in Europe, the USA and Japan, and even elsewhere, sulfur to the atmosphere, become more and more drastic. Currently, the maximum permissible limit in gasolines is 150 ppm in total sulfur. However, international organizations are calling for a limit of sulfur in gasoline to less than 50 ppm of total sulfur by 2005 and provide for a limitation of less than 10 ppm of total sulfur by 2009 for all productions. In thiophene hydrocarbons, for example gasolines or naphthas, these contents are much higher than 100 ppm and, in general, they are between 100 and 1000 ppm of total sulfur.

The formation of mixtures with desulfurized and denitrogenous gasolines is the only way to eliminate the stocks of gasoline from catalytic cracking in the fluid state or FCC or the pyrolysis gasolines.

In order to remove thiophene and its derivatives from thiophene species, it has been proposed in the patent U.S. Patent No. 6,338,788 extracting the thiophenic compounds from the charge by mixing it with an electrolyte and a solvent. The mixture thus formed is introduced into an electrochemical cell so as to oligomerize the thiophene compounds. These oligomers are subsequently removed from the charge. The recovered electrolyte / solvent mixture can be recycled to a new mixture with the feed to be treated. The preferred solvents are generally compounds capable of complexing aromatic compounds contained in hydrocarbons, such as alkylene carbonates, benzonitriles, sulfolanes or morpholine derivatives. As salts, tetraalkylammonium salts are used, such as fluoroborates, fluorophosphates or halides. In addition to the difficulty of implementing this technique with an electrochemical cell on an industrial scale, such a process becomes prohibitive for refiners, when it is necessary to obtain the necessary solvents and electrolytes, but also to recycle them for Environmental Protection.

Another possible solution is that which has been disclosed in the patent U.S. 4,188,285 . It proposes to remove thiophenes from gasolines by contacting the gasoline from C ₅ to C ₇ with a catalyst consisting of a faujasite Y type zeolite exchanged with silver at a temperature of between 20 and 370.degree. ° C, and at a space velocity between 0.1 and 20. Here, the silver atom is exchanged on faujasite. In such an operation, the olefin content remains unchanged before and after treatment of gasoline. In this patent, it is a question of adsorbing the thiophene and its alkyl derivatives on the zeolite Y exchanged with the ions Ag ⁺ and Cu ²⁺ by using the complexation phenomena using the formation of π bonds, the copper being reduced in Cu ⁺ as described by Ralph T. Yang et al., In Science & Technology, vol.301, p.79 , and in Ind.Eng.Chem.Res. 2001, 40.6236-6239 , or again by A.Hernandez-Maldonado and collaborators, in Ind.Chem.Res. 2003, 42, 3103-3110 .

The Applicant has studied a process for the purification of light hydrocarbons containing sulfur compounds and / or nitrogen compounds refractory to catalytic hydrotreatments, which aims to increase the weight of these compounds by oxidative polymerization thereof, in order to extract them more easily from these hydrocarbons. . In this purification process, the Applicant aims at both the desulphurization and the denitrogenation, but also the regeneration of the activity of the oxidizing agent used, by combining the oxidation reaction with a regeneration and activation process. the oxidizing agent used.

1. (a) une étape de polymérisation oxydative des composés comprenant un groupement -X-CH= dans un cycle hydrocarboné de 5 ou 6 chaînons, où X représente un atome de soufre ou d'azote, en présence d'au moins un agent oxydant choisi parmi les cations métalliques,
2. (b) une étape de séparation des polymères formés et de l'agent oxydant d'avec les hydrocarbures légers, et
3. (c) une étape d'oxydation du cation métallique,

ces étapes étant réalisées dans cet ordre, chacune de ces étapes pouvant être combinée avec au moins l'étape suivante.The subject of the present invention is therefore a process for purifying light hydrocarbons having a cutting point of between 20 ° and 250 ° C., containing sulfur and / or nitrogen compounds which are refractory to conventional hydrotreatments, characterized in that it comprises

1. (a) a step of oxidative polymerization of compounds comprising a group -X-CH = in a hydrocarbon ring of 5 or 6 members, where X represents a sulfur or nitrogen atom, in the presence of at least one chosen oxidizing agent among the metal cations,
2. (b) a step of separating the formed polymers and the oxidizing agent from the light hydrocarbons, and
3. (c) a step of oxidation of the metal cation,

these steps being performed in this order, each of these steps can be combined with at least the next step.

In the context of the present invention, the compounds comprising a group -X-CH = in a 5- to 6-membered hydrocarbon ring are thiophene compounds, ranging from thiophene to its alkylated or arylalkyl derivatives, and pyrrole compounds, ranging from pyrrole its alkylated or arylalkylated derivatives, generally present in hydrocarbons and constituting products refractory to desulfurization and / or denitrogenation by conventional catalytic hydrogenation treatments.

To implement the invention, the metal cations are introduced in liquid form, dispersed or dissolved in an aqueous or organic liquid or supported on a solid. The process according to the invention is therefore a two or three-phase polyphasic process. phases, depending on whether or not the metal cations are deposited on a solid support before the start of the reaction carried out in this process, namely a polymerization of the sulfur and / or nitrogen compounds.

In the context of the present invention, when the metal cations are fixed on a solid support in a fixed or moving bed, the polymerization reaction is carried out at ambient temperature, under atmospheric pressure, at a space velocity (vvh) of less 0.1h ^-1 .

In general, for the metal cations to polymerize the sulfur and / or nitrogen compounds, the oxidizing metal cation must have a redox potential greater than that of the molecule to be oxidized / polymerized in the reaction medium.

In order to achieve such redox potentials for the polymerization of thiophene or pyrrole compounds, the metal cation is chosen from among the metal element cations of the group consisting of iron, copper, molybdenum, cerium, manganese and vanadium, each of these metals to be present in the reaction with a degree of oxidation of at least 2. These metal cations are used in the form of salts of the group consisting of halides, nitrates, citrates, carboxylates, phosphates, sulfates, persulfates, borates, perborates and bi- and polydentate complexes in linear or cyclic form, comprising nitrogen, sulfur and / or oxygen atoms as a coordination element. By bi- and polydentate complexes is meant, but not limited to, phthalocyanines, porphyrins, cyclams, bi-pyridines and salt complexes.

When the metal cation is introduced in the dispersed state or in solution in water, the polymerization reaction is biphasic liquid / liquid (organic / aqueous), and the polymers formed and the oxidizing cations can be removed by decantation of separate phases. , by filtration and / or extraction according to techniques known per se to those skilled in the art.

In another embodiment of the invention, the process is carried out in the presence of a solid selected from the group consisting of coal, clays, zeolites, molecular sieves, amorphous silica aluminas, alkali silicates , borate silicas, magnesium silicas, and aluminophosphates. This solid can withstand the salts of the metal cations necessary for the invention, whether or not there is ionic interaction between these cations and these solids.

In a preferred embodiment, the protons initially present on the support have been exchanged for the metal cations, and then these metal cations have been oxidized before use, which makes it possible to obtain an oxidation state of these higher or lower metals. equal to two. This oxidation state is essential for the polymerization reaction to occur in hydrocarbons, as already observed by Mr Bein for less complex media than the hydrocarbons derived from the distillation of petroleum, in his article. Studies in Surface Science and Catalysis, vol. 102, 1996, pp. 295-319 .

The advantage of a process using the metal cation in the form of counter-ion of a solid support is to be able to carry out the polymerization reaction under usual refining conditions, that is to say with a catalytic bed. of the type used in refining. Another advantage is to be able to envisage the regeneration in situ or ex situ of the metal cations used as oxidizing agent.

As support for these metal cations, it is possible to choose crystalline or amorphous solids, cation exchangers, containing at least one metal of the group of elements constituted by silicon, aluminum, zirconium, titanium, germanium, gallium and boron, taken alone or in combination, and having a specific surface area of at least 10 cm ² / g.

Preferably, these supports are chosen from clays, including bentonites, and zeolites, including Sapo, Alpo and Beta, and mesoporous, for example of the MCM 41 type, molecular sieves, amorphous silica aluminas, alkali silicates , borate silicas, magnesium silicas, these solids having a pore size of between 1.5 nm and 200 nm.

To obtain such supported cations, it is necessary to contact the solid with metal cation salts in the form of an aqueous or organic solution, the salts being chosen from nitrates, carboxylates, sulphates, persulfates, citrates, phosphates, borates, perborates and halides of metals, including iron, copper, molybdenum, manganese, vanadium and cerium. Preferred salts are selected from ferric chloride, cuprous chloride, molybdenum chloride, vanadium oxychloride and cerium chloride.

Preferably, the amount of metal cation present on the support can vary from 0.1% to 30% by weight of the metal corresponding to said cation.

Such supported cations can act in a fixed bed, moving bed, fluidized bed or liquid suspension process.

During the polymerization of sulfur and / or nitrogen compounds, the polymers formed are suspended in the hydrocarbon or deposited on the solid. They can be extracted, decanted, filtered or even distilled, in order to be eliminated from the hydrocarbon thus purified. When the polymers formed are deposited on the solid, the elimination step consists in extracting the polymers deposited on the support by washing with the solvent, in particular by the filler, by desorption by a stream of inert gas chosen from helium, nitrogen, carbon dioxide and water vapor, at a temperature above 100 ° C, and / or by combustion by injection of air or oxygen, preferably after removal of the light hydrocarbons still present on the particles of support.

To reduce or maintain the supported cation in an oxidation state sufficient for the polymerization reaction to proceed normally, the metal cation is oxidized. This step of oxidation of the metal cation, supported or not, consists of returning the metal cations in an oxidation state of at least 2, by oxidation, by injecting air or liquids containing peroxides or other more oxidizing metal cations, possibly simultaneously increasing the temperature of the oxidizing agent.

In a preferred embodiment of the invention, it is possible that steps taken alone or in combination combine in a continuous or batch process. Thus, at the end of the metal oxidation step, the oxidized metal cation is directly reused for a new oxidative polymerization step. In addition, it is not beyond the scope of the invention to implement simultaneously certain process steps, such as, for example, the first oxidative polymerization step and the second step of removing the polymers obtained, which are present in the process. liquid phase and / or on the support, when a support is used. It is even if the step of removing the polymers obtained and the third oxidation step of the metal cation are combined. Also within the scope of the present invention is a form of implementation of the method simultaneously combining the third and the first step, or even the three steps depending on the type of fixed or mobile bed that can be implemented.

Another object of the invention is the application of this process to the finishing treatment of industrial streams containing sulfur and / or nitrogen-containing refractory compounds. More particularly, this process can be used for the desulfurization / denitrogenation of gasolines produced by catalytic cracking and steam cracker effluents, especially pyrolysis gasolines. This process can also be applied as a finishing treatment of aromatic effluents of benzene, toluene and xylene type.

The example given below, is intended to illustrate the invention without, however, limiting its scope.

EXAMPLE

The present example describes several embodiments of the process of the invention, using various oxidizing cations, and their efficiency vis-à-vis the desulphurization and / or denitrogenation.

Trial I:

FeCl ₃ powder is suspended in a catalytic cracking gasoline or LCCS by mixing at a temperature of 25 ° C. The Fe / S ratio (total sulfur in LCCS) is 16 Fe atoms per sulfur atom (16 atoms / atom).

Trial II:

Anhydrous FeCl ₃ is deposited on silica: the supported cation thus formed is mixed with LCCS at 40 ° C. The Fe / S ratio is 13 atoms / atom.

Trial III:

Anhydrous FeCl ₃ is deposited on activated charcoal: the supported cation thus formed is mixed with LCCS at 40 ° C. The Fe / S ratio is 13 atoms / atom.

Trial IV:

A sodium zeolite β, in the form of particles of 0.15 to 0.5 mm, exchanged with copper acetate, is charged to a reactor tubular, and circulates LCCS at a space velocity of 1.2h ^-1 hour and at a temperature of about 25 ° C at atmospheric pressure. Sulfur and / or nitrogen analyzes on the effluent are carried out after 3 hours of circulation and after 15 hours.

Test V:

A sodium zeolite β is charged in the form of particles of 0.15 to 0.5 mm, exchanged with copper acetate, in a tubular reactor, and LCCS is circulated at a space velocity of 1, 2 h ^-1 and at a temperature of about 150 ° C under atmospheric pressure. Sulfur and / or nitrogen analyzes on the effluent are carried out after 1h30 of circulation and after 14 hours.

Trial VI:

Test V is repeated four times, each test lasting 7 hours. The supported cation is reactivated according to steps 2 and 3 described above, these steps being simultaneous and carried out under air circulation, for 5 hours, at 350 ° C.

The zeolite β is charged to the copper II-exchanged sodium thus reactivated in a tubular reactor and the LCCS is again circulated at a space velocity of 1.2 h ^-1 and at a temperature of about 150 ° C., under pressure. atmospheric. Sulfur and / or nitrogen analyzes on the effluent are carried out after 1h30 of circulation and after 3.5 hours.

Trial VII:

A zeolite β initially in protonated form, with a particle size varying from 0.15 to 0.5 mm, is exchanged with copper acetate, then is mixed with LCCS at a temperature of approximately 40 ° C., under atmospheric pressure. The Cu / S ratio is 0.96 atom / atom. Sulfur and / or nitrogen analyzes on the effluent are carried out after 7 hours.

TEST VIII:

A sodium zeolite β is mixed in the form of particles of 0.15 to 0.5 mm, exchanged with copper acetate, with LCCS at 40 ° C. The Cu / S ratio is 10.3 atoms / atom. Sulfur and / or nitrogen analyzes on the effluent are carried out after 6 hours.

TEST IX:

A sodium zeolite β, in the form of particles of 0.15 to 0.5 mm, exchanged with copper acetate, is mixed with LCCS. 40 ° C. The Cu / S ratio is 30.8 atoms / atom. Sulfur and / or nitrogen analyzes on the effluent are carried out after 5 hours 30 minutes.

TEST X:

A sodium zeolite β, in the form of particles of 0.15 to 0.5 mm, exchanged with copper acetate, is mixed at 40 ° C. with a model fluid containing, in% by weight, 0.5% by weight. thiophene, 0.5% dodecane and 99% toluene. The Cu / S ratio is 1.5 atoms / atom. The thiophene and mercaptan analyzes on the effluent are carried out after 6 hours 30 minutes.

TEST XI:

202 g of organic solution containing, in% by weight, 99% of toluene, 0.5% of pyrrole and 0.5% of n-decane, are emulsified at ambient temperature with 112 g of aqueous FeCl ₃ to 6 solution. , 4% by weight. The Fe / N ratio is 2.94 atoms / atom. The total nitrogen analyzes are made after 5 hours.

TEST XII:

200 g of organic solution containing, in% by weight, 99% of toluene, 0.5% of pyrrole and 0.5% of n-decane, are emulsified at ambient temperature with an aqueous solution of Ce (SO ₄ ) ₂ to 30% by weight. The Ce / N ratio is 4.7 atoms / atom. Total nitrogen analyzes are done after 40 minutes.

TEST XIII:

4.3 g of anhydrous FeCl ₃ in powder form are dispersed in 183 g of a solution containing, in% by weight, 99.25% toluene, 0.5% thiophene and 0.25% dodecane, at 30 ° C. vs. The Fe / S ratio is 2.45 atoms / atom. The total sulfur analyzes are made after 2 hours.

TEST XIV:

A zeolite β, initially in protonated form, in powder, is exchanged with copper acetate, then is mixed with 200 g of a solution containing, in% by weight, 99.25% toluene, 0.5% thiophene and 0.25% dodecane at a temperature of about 40 ° C and at atmospheric pressure. The Cu / S ratio is 0.8 atom / atom. The total sulfur analyzes are made after 4 hours.

The desulphurization and denitrogenation results are given in the Table below, where the sulfur and nitrogen contents are expressed in ppm. <U> Table </ u> Trial S _(total) S _(thiophene) S (2 + 3méthylthiophène) N _(total) (Entrance) (exit) (Entrance) (exit) (Entrance) (exit) (Entrance) (exit) I 121 94 60 54 50 35 - - II 121 80 60 49 50 35 - - III 121 97 60 46 50 46 - - IV 113 70 53 28 50 36 - - 113 93 53 44 50 36 - - V 121 31 57 23 53 6 - - 121 76 57 35 53 37 - - VI 105 46 - - - - - - 105 70 - - - - 17 1.7 VII 215 166 39 26 122 117 - - VIII 121 84 60 40 50 36 - - IX 121 93 57 36 53 49 - - X - - 2074 1064 - - - - XI - - - - - 1050 597 XII - - - - - - 1050 177 XIII - - 1900 733 - - - - XIV - - 1900 488

Claims (21)

1. A process for purifying light hydrocarbons with a cut point of between 20 and 250°C, containing sulfur and/or nitrogen compounds resistant to conventional hydrotreatments, characterised in that it comprises

   (a) an oxidative polymerisation stage for the compounds comprising an -X-CH= group in a 5- or 6-membered hydrocarbon ring, where X represents a sulfur or nitrogen atom, in the presence of at least one oxidising agent selected from among metallic cations,

   (b) a separation stage separating the polymers formed and the oxidising agent from the light hydrocarbons, and

   (c) an oxidising stage for the metallic cation,

   these stages being performed in this order, each of said stages being capable of being combined with at least the following stage.
2. A process according to claim 1, characterised in that the metallic cations are introduced in liquid form, in dispersed or dissolved form in an aqueous or organic liquid, or indeed supported on a solid.
3. A process according to one of claims 1 and 2, characterised in that the oxidising metallic cation has a redox potential greater than that of the molecule to be polymerised in the reaction medium.
4. A process according to one of claims 1 and 2, characterised in that the metallic cation is a cation of a metallic element from the group comprising iron, copper, molybdenum, manganese, cerium and vanadium, with a degree of oxidation of at least 2.
5. A process according to one of claims 1 to 4, characterised in that the metallic cation is used in the form of a halide, of nitrate, citrate, carboxylate, phosphate, sulfate, persulfate, borate, perborate, or of bi- and polydentate complex in linear or ring form, comprising nitrogen, sulfur and/or oxygen atoms as coordinating element.
6. A process according to one of claims 1 to 5, characterised in that, when the metallic cation is introduced in disperse form or in solution in the water, the polymerisation reaction is biphasic, and the polymers formed and the oxidising cations are removed by settling, filtration and/or extraction.
7. A process according to claim 6, characterised in that the polymerisation reaction is effected in the presence of a solid selected from the group comprising carbon, clays, zeolites, molecular sieves, amorphous aluminosilicas, alkali metal silicates, borosilicas, magnesiosilicas, and aluminophosphates.
8. A process according to one of claims 1 to 7, characterised in that the metallic cation is supported on a crystalline or amorphous, cation-exchanging solid containing at least one metal from the group of elements comprising silicon, aluminium, zirconium, titanium, germanium, gallium and boron, alone or in combination, and whose specific surface area is at least 10 cm²/g.
9. A process according to claim 8, characterised in that the solid is selected from among clays, including bentonites, zeolites, including SAPO, AlPO and Beta and mesoporous materials, molecular sieves, amorphous aluminosilicas, alkali metal silicates, borosilicas, magnesiosilicas, this solid having a pore size varying between 1.5 nm and 200 nm.
10. A process according to claims 8 and 9, characterised in that the supported metallic cation is obtained by bringing the solid into contact with metallic cation salts in the form of an aqueous or organic solution, the salts being selected from among nitrates, carboxylates, sulfates, persulfates, borates, perborates, citrates, phosphates and halides of metals, including iron, copper, molybdenum, manganese, vanadium and cerium.
11. A process according to claim 10, characterised in that the metallic salt is selected from among ferric chloride, cuprous chloride, molybdenum chloride, vanadium oxychloride and cerium chloride.
12. A process according to one of claims 8 to 11, characterised in that the supported metallic cation contains 0.1 to 30 % by weight of the metal corresponding to said cation.
13. A process according to one of claims 8 to 12, characterised in that the supported cation is used in a fixed bed, a mobile bed, a fluidised bed or in suspension in a liquid.
14. A process according to one of claims 8 to 13, characterised in that the stage of removing the polymers deposited on the solid supporting the cation consists in extracting said polymers by solvent washing, in particular by charging, by desorption by a stream of inert gas selected from among helium, nitrogen, carbon dioxide and steam, at a temperature of above 100°C, and/or by combustion by injection of air or oxygen, preferably after removing the light hydrocarbons still present on the solid support.
15. A process according to claims 8 to 14, characterised in that the polymerisation stage for the resistant compounds is followed by removal of the polymers formed and present in the treated hydrocarbon, either by settling, or by filtration, or by solvent extraction or indeed by distillation.
16. A process according to one of claims 1 to 15, characterised in that the oxidation stage for the metallic cation, whether supported or unsupported, consists in restoring the metallic cations to a degree of oxidation of at least 2 by oxidation, by injecting air or liquids containing peroxides or other more highly oxidising metallic cations, optionally by simultaneously increasing the temperature of the oxidising agent.
17. A process according to one of claims 1 to 16, characterised in that the stages of the process, taken alone or in combination, are combined into a continuous or discontinuous process.
18. A process according to one of claims 1 to 17, characterised in that the metallic cation, whether supported or unsupported, is reused in the first stage of the process.
19. Application of the process according to one of claims 1 to 18 as finishing treatment for industrial streams containing resistant sulfur and/or nitrogen compounds.
20. Application according to claim 19 to FCC gasolines and steam cracking effluents, in particular pyrolysis gasolines.
21. Application according to claim 19 as finishing treatment for aromatic effluents of the benzene, toluene and xylene type.