EP1666568A1 - Desulfurisation process of a hydrocarbon fraction using a simulated moving bed - Google Patents

Abstract

The invention describes a process for desulfurizing a hydrocarbon fraction of the gas oil type by adsorption making it possible to obtain a desulfurized effluent at less than 10 ppm by weight with a yield greater than 95% by weight. This method comprises a simulated moving bed adsorption stage of the sulfur compounds of the feed, a raffinate distillation step and a distillation step of the extract.

Description

The present invention relates to a process for desulphurizing a hydrocarbon fraction of distillate type by adsorption in a simulated moving bed. By "distillate type cut" is meant a cut resulting from the distillation of the crude or from a conversion unit such as catalytic cracking, and whose distillation range is between 150 ° C. and 450 ° C.

In the following text we will call this diesel cut, but this designation has no restrictive character. Any hydrocarbon fraction containing sulfur and distillation range similar to that of a diesel fuel cut may be concerned by the method object of the present invention.

The process according to the invention thus makes it possible to produce a desulfurized cut at contents of less than or equal to 10 ppm by weight of sulfur (S), or even 5 ppm by weight of sulfur, or even less than 1 ppm by weight of sulfur, and this starting from a charge to be treated whose sulfur content may be equal to a few tens of ppm by weight and may be up to 2, or even 3% by weight. The ppm weight notation means part per million by weight and is equivalent to 10 ^-6 kg / kg.

Moreover, the diesel yield of this process is significantly higher than that of a process operating in a fixed bed.

Future specifications on automotive fuels provide for a sharp decrease in the sulfur content in fuels, including diesel fuels. This reduction is intended to limit the content of sulfur oxide and nitrogen in automobile exhaust. European legislation specifies the diesel fuel specifications which have been 350 ppm by weight since 2000, and in 2005 will be 50 ppm by weight of sulfur, and in 2009 by 10 ppm by weight of sulfur.

The evolution of sulfur content specifications in fuels thus requires either the improvement of the existing hydrotreatment catalytic processes with consequent excessive hydrogen consumption and / or an increase in operating pressure, ie the development of new processes for the deep desulphurization of gas oils, a combination of both.

EXAMINATION OF THE PRIOR ART

Among the alternative routes of desulfurization of gas oils, the processes for the adsorption purification of sulfur compounds on a selective adsorbent present an interesting alternative to conventional hydrodesulfurization processes.

For example, US Pat. No. 4,337,156 (UOP 1982) recommends the use of a KX type zeolite, and a 1-octanol desorbent for separating polar compounds (sulfur, nitrogen, oxygenated) by Simulated Mobile Bed (LMS). of a naphtha cut (term of the skilled person designating a petrol cut of initial boiling point about 70 ° C and end boiling point about 220 ° C).

The sulfur compounds present in the naphtha section are of the thiophene type and not of the benzo or dibenzothiophene type which are the sulfur compounds the most difficult to eliminate in the case of a distillate, ie those which will be encountered in the context of the present invention.

US Pat. No. 5,454,933 describes a process for the desulphurisation of diesel fuel, which consists in linking a conventional hydrotreatment to eliminate sulfur compounds known as "easy sulfur" according to the English terminology (which can be translated as sulfur compounds which are easy to remove) with a process. adsorption of difficult sulfur compounds on activated carbon having a specific surface area of between 800 and 1200 m ² / gram and having a certain porous structure. These sulfur compounds difficult to eliminate (so-called "hard sulfur" according to the English terminology) correspond to beta-substituted dibenzothiophene type aromatics.

The adsorption process described in this patent is not designed to fully treat the diesel fuel feedstock, but necessarily requires prior hydrotreatment.

Patent FR 02/03314 proposes a process for desulfurizing a hydrocarbon feedstock on a complexing solid based on π electron acceptors. This process can be preceded by a fractionation column which allows to produce a light effluent to the specifications and a heavy effluent that must be desulphurized. In the case of fixed bed operation, the losses of the product to be desulphurized are not negligible because of the physical filling of the porous volume of the adsorbent. To remedy this, it is proposed in said patent to use different washing fluids with varying adsorption forces thus reducing hydrocarbon losses without, however, avoid them entirely.

SUMMARY DESCRIPTION OF THE FIGURES

Figure 1 shows a diagram of the method according to the invention in its most general design.

FIG. 2 represents a variant of the process diagram according to the invention.

SUMMARY DESCRIPTION OF THE INVENTION

• une étape d'adsorption des composés soufrés de la charge à traiter réalisée dans au moins une première colonne d'adsorption fonctionnant en lit mobile simulé (LMS) et contenant une pluralité de lits constitués d'un solide adsorbant ayant une sélectivité différente pour les hydrocarbures soufrés et les hydrocarbures non soufrés, ladite colonne comprenant au moins quatre zones de fonctionnement;
  une première zone comprise entre le point d'introduction du désorbant et le point de soutirage de l'extrait , une seconde zone comprise entre le point de soutirage de l'extrait et le point d'introduction de la charge, une troisième zone comprise entre le point d'introduction de la charge et le point de soutirage du raffinat, et une quatrième zone comprise entre le point de soutirage du raffinat et le point d'introduction du désorbant.
• une étape de distillation du raffinat réalisée dans au moins une colonne de distillation, de laquelle on soutire d'une part un effluent gazole et d'autre part, un flux de désorbant que l'on recycle au moins en partie dans la première colonne d'adsorption.
• une étape de distillation de l'extrait réalisée dans au moins une colonne de distillation, de laquelle on soutire d'une part un effluent contenant les impuretés soufrées, et d'autre part un flux de désorbant pratiquement pur que l'on recycle en partie au moins dans la première colonne d'adsorption.

The invention can be defined as a process for the deep desulphurization of a hydrocarbon feedstock, a distillation range of between 150 ° C. and 450 ° C., and which may contain up to 3% sulfur, method comprising successively the following steps:

• a step of adsorbing the sulfur compounds of the feedstock to be treated carried out in at least a first adsorption column operating in a simulated moving bed (LMS) and containing a plurality of beds consisting of an adsorbent solid having a different selectivity for hydrocarbons sulfur and non-sulfur-containing hydrocarbons, said column comprising at least four operating zones;
  a first zone between the point of introduction of the desorbent and the extraction point of the extract, a second zone between the extracting point of the extract and the point of introduction of the charge, a third zone between the point of feed introduction and the raffinate draw point, and a fourth zone between the raffinate draw point and the desorbent feed point.
• a step of distillation of the raffinate carried out in at least one distillation column, from which a diesel effluent is withdrawn on the one hand and a stream of desorbent which is recycled at least partly in the first column of 'adsorption.
• a distillation step of the extract carried out in at least one distillation column, from which an effluent containing the sulfur-containing impurities is removed on the one hand and a stream of substantially pure desorbent which is partially recycled at least in the first adsorption column.

The sulfur content of the gas oil obtained will generally be less than 10 ppm by weight, preferably less than 5 ppm by weight, and even more preferably less than 1 ppm by weight, with a weight yield relative to the incoming charge generally greater than 97% and preferably greater than at 99%.

According to a variant of the process, the feedstock to be treated may be previously sent to a distillation column located upstream of the simulated moving bed adsorption unit, from which a head stream is extracted which is used at least partly as a feedstock. desorbent, and a bottom stream that is introduced as a charge of the simulated moving bed adsorption unit.

DETAILED DESCRIPTION OF THE INVENTION

The invention will be better understood by following the process diagram shown in FIG.

The feedstock (1) enters the adsorption desulfurization unit operating in a simulated moving bed (2). This adsorption desulphurization unit consists of at least one adsorption column containing a plurality of adsorbent beds, interconnected with one another and having a selectivity in favor of the sulfur-containing compounds with respect to the chemical families of the charge (alkanes and aromatics). ) that one wishes to purify.

Said adsorption column comprises at least four zones delimited on the one hand by the injections of the mixture (1) constituting the adsorption charge and the desorbent (9b), on the other hand by the withdrawals of a raffinate (3) containing the desulphurized gas oil mixed with desorbent, and an extract (4) containing predominantly sulfur compounds removed in mixture with desorbent.

The desorption zone 1 of the sulfur compounds is between the injection of the desorbent (9b) and the extraction of the extract (4).

Zone 2 desorption of alkanes and aromatics is between the withdrawal of the extract (4) and the injection of the adsorption charge (1).

The zone 3 for adsorption of the sulfur compounds is between the injection of the feedstock (1) and the withdrawal of the raffinate (3).

Zone 4 is between the raffinate withdrawal (3) and the injection of the desorbent (9b) and allows to adsorb the alkanes and aromatics.

The step of separating the streams (3) and (4) is carried out by means of two distillation columns (5) and (6) fed respectively by the raffinate (3) and the extract (4) which make it possible to eliminate substantially all the desorbent at the bottom of the column, for example.

At the top of the column (5) is withdrawn a stream (8) of desulphurized gas oil at less than 10 ppm by weight of sulfur, preferably less than 5 ppm by weight of sulfur, and more preferably less than 1 ppm by weight of sulfur, and a mixture (10) of sulfur and nitrogen compounds is withdrawn at the top of the column (6).

This mixture can itself be advantageously mixed with a flow from the refinery whose sulfur specifications allow it, and whose boiling temperatures are compatible with those of the product mixture, such as for example fuel oil.

This mixture can also be recycled to a conventional hydrotreating unit which will make it possible to eliminate the recycled sulfur compounds by an effect of increasing the sulfur content of the feedstock, since the catalytic activity of the hydrodesulfurization process is directly linked. at the sulfur input concentration to be treated.

The desorbents (9) and (11) are recovered at the bottom of the columns (5) and (6) to form the stream (9a) which is returned to the simulated moving bed desulfurization unit (LMS) (2) with a possible addition of desorbent (12) corresponding to the possible losses of desorbent undergone in the distillation columns (5) and (6).

The different streams (9), (11) and (12) form the addition of desorbent (9b) which is introduced into the simulated moving bed column (2).
the flow (7) constitutes the recirculation flow necessary for the operation of a simulated moving bed column. It consists of regeneration solvent and diesel in varying proportions over time.

FIG. 2 describes a variant of the invention in which a distillation step corresponding to the unit (1c) is placed upstream of the diagram described in FIG.

This distillation step consists of sending the feedstock (1) into a distillation tower (1e) which produces a sulfur-containing heavy hydrocarbon fraction (1b) which is sent to the LMS adsorption unit (2) as described. in FIG. 1, and a light hydrocarbon fraction (1a) whose sulfur content is less than or equal to the required specifications.

This desulphurized section (1a) can also be used as a desorbing agent in the LMS adsorption unit (2), in which case once the permanent pseudo regime is reached, the portion (1d) of the stream (1a) will be used. as a desorbent booster and mixed with the stream (9a) to form the desorbent stream (9b) of the adsorption column (2). The remaining part (1c) of light desulphurized hydrocarbons is already to the required specifications and can therefore be used as a base in commercial diesel.

In another variant of the process, it is possible to treat a gas oil which has already been desulphurized in a conventional unit known as catalytic hydrodesulphurization well known to those skilled in the art.

The diesel produced by this unit will have a variable sulfur content depending on the operating conditions of the hydrotreatment. Diesel fuel thus produced, the sulfur content of which may vary between 10 ppm by weight and 1000 ppm by weight, can be treated with one or other of the variants of the method according to the invention corresponding to Figures 1 and 2.

The adsorbent used in the LMS adsorption unit is generally chosen from the following families of conventional adsorbents: activated carbon, zeolites, silicas, aluminas, silica-aluminas, spent catalysts, resins, clays, bridged clays, reduced metals or oxides and any possible mixture between these different families of adsorbents.

According to a characteristic of the process, the adsorbent used in the LMS adsorption unit in the active carbon family will be chosen, since these solids have a sufficient selectivity between the sulfur-containing molecules and the remainder of the diesel fuel matrix. Among the different types of activated carbons, preference will be given to those having a specific surface area greater than 1200 m ² / gram, and a total pore volume greater than 0.5 cm ³ / gram, the precursor being which type, and the type of activation used to create porosity can be either physical or chemical, or a combination of both.

Whatever the adsorbent solid retained in the process, the total pore volume is preferably greater than or equal to 0.5 cm ³ / gram, and the pore volume fraction included in the microporosity of said adsorbent solid is preferably greater than or equal to 0.2 cm ³ / gram.

Microporosity is defined as the category of pores whose diameter is less than 20 angstroms (2 nanometers, ie 2 10 ^-9 meters).

The number of adsorbent beds constituting the simulated moving bed adsorption unit is generally less than 24, and preferably less than 15.

The desorbent may be selected from the following chemical families: nitrogen compounds, alcohols, ethers, aromatics, light desulfurized cut, or any other refinery stream and their mixture. For example, the aromatics may be chosen.

The volume ratio of the desorbent on charge in the simulated moving bed separation unit is generally between 0.5 and 2.5, and preferably between 0.7 and 2.0.

The working temperature may be between ambient temperature and the final boiling temperature of the hydrocarbon fraction to be treated, knowing that it is necessary to ensure operation in the liquid phase. It will generally work between 50 ° C and 350 ° C, and more preferably between 50 ° C and 250 ° C.

The working pressure will be between the bubble point of the lightest compound and 15 bars absolute (1.5 MPa), so as to guarantee the existence of a liquid phase throughout the LMS adsorption unit, knowing that the performance of the process depends little on this parameter. However, it can affect the cost of fitting.

EXAMPLES ACCORDING TO THE INVENTION

• alcanes
• aromatiques : mono, di puis tri
• "easy sulfur" (composés soufrés faciles à éliminer)
• "hard sulfur" (composés soufrés difficiles à éliminer)
• composés azotés

An active carbon with a specific surface area of 1440 m ² / g is considered, the total pore volume of which is equal to 1.7 cm ³ / g, with a pore volume fraction included in the microporosity equal to 0.35 cm ³ / gram and as the order of elution of the different families of the distillate is as follows:

• alkanes
• aromatic: mono, di then sorting
• "easy sulfur" (sulfur compounds easy to eliminate)
• "hard sulfur" (sulfur compounds difficult to eliminate)
• nitrogen compounds

Example of treatment of a low sulfur diesel (50ppm wt of sulfur)

The purification of a gas oil containing 50 ppm by weight of sulfur is carried out in simulated moving bed, on a pilot unit comprising 15 beds of 609.6 cm ³ each divided into 4 zones in the following configuration: zone 1: 3 beds, zone 2 : 5 beds, zone 3: 5 beds and zone 4: 2 beds.

• Température : 210°C
• Pression : telle qu'on soit liquide en tout point de la boucle, soit 3 bars absolus (0,3 MPa).
• Débits d'injection, de soutirage et de recyclage aux conditions opératoires :
  • Charge : 200,0 cm³.mn^-1
  • Solvant : 147,0 cm³.mn^-1 de toluène
  • Extrait : 57,0 cm³.mn^-1
  • Raffinat : 290,0 cm³.mn^-1
  • Débit de recyclage (en zone 1) : 193 cm³.mn^-1

The operating conditions are as follows:

• Temperature: 210 ° C
• Pressure: such that it is liquid at any point of the loop, ie 3 bars absolute (0.3 MPa).
• Injection, withdrawal and recycling rates under operating conditions:
  • Charge: 200,0 cm ³ .mn ^-1
  • Solvent: 147.0 cm ³ .mn ^-1 toluene
  • Extract: 57.0 cm ³ .mn ^-1
  • Raffinate: 290.0 cm ³ .mn ^-1
  • Recycling rate (in zone 1): 193 cm ³ .mn ^-1

The permutation time of the valves (or period) is 152.0 seconds.

After distillation of the toluene, the raffinate obtained delivers a gas oil at a content of 1.5 ppm by weight of pure sulfur with a yield of 99.5%. The productivity of the unit expressed as the volume of gas oil produced per volume of adsorbent and per time unit is equal to 1.31 m ³ / (m ³ h).

Example of treatment of a gas oil with a high sulfur content (1.5% sulfur)

The purification of diesel fuel containing 1.5% sulfur (by mass) is carried out in simulated moving bed, on a pilot unit comprising 15 beds of 609.6 cm ³ each, divided into 4 zones according to the following configuration: zone 1: 3 beds , zone 2: 5 beds, zone 3: 5 beds and zone 4: 2 beds.

• Température : 210°C
• Pression : telle qu'on soit liquide en tout point de la boucle
• Débits d'injection, de soutirage et de recyclage aux conditions opératoires :
  • Charge : 105,0 cm³.mn^-1
  • Solvant : 147,0 cm³.mn^-1 de toluène
  • Extrait : 82,0 cm³.mn^-1
  • Raffinat : 170,0 cm³.mn^-1
  • Débit de recyclage (en zone 1) : 193 cm³.mn^-1

The operating conditions are as follows:

• Temperature: 210 ° C
• Pressure: as one is liquid at any point of the loop
• Injection, withdrawal and recycling rates under operating conditions:
  • Charge: 105,0 cm ³ .mn ^-1
  • Solvent: 147.0 cm ³ .mn ^-1 toluene
  • Excerpt: 82.0 cm ³ .mn ^-1
  • Raffinate: 170.0 cm ³ .mn ^-1
  • Recycling rate (in zone 1): 193 cm ³ .mn ^-1

The permutation time of the valves (or period) is 152.0 seconds.

After distillation of toluene, the raffinate obtained delivers a gas oil at a content of 3.5 ppm by weight of sulfur of purity with a yield of 99.5%. The productivity of the unit expressed as a volume of diesel fuel produced per volume of adsorbent and per time unit is equal to 0.67 m ³ / (m ³ h).

Claims (10)

A process for the deep desulphurization of a hydrocarbon feedstock of distillation range of between 150 ° C and 450 ° C, containing up to 3% sulfur, the process comprising successively the following steps: a step of adsorbing the sulfur compounds of the feedstock (1) carried out in at least a first adsorption column (2) operating in a simulated moving bed and containing a plurality of beds of an adsorbent having a different selectivity for hydrocarbons sulfur and non-sulfur-containing hydrocarbons, said column comprising at least four operating zones; a first zone between the point of introduction of the desorbent (9b) and the extraction point of the extract (4), a second zone between the withdrawal point of the extract (4) and the point of introduction charge (1), a third zone between the point of introduction of the charge (1) and the raffinate offtake point (3), and a fourth zone between the raffinate offtake point (3) and the point of introduction of the desorbent (9b), the volume ratio desorbent charge is between 0.5 and 2.5 a step of distillation of the raffinate (3) carried out in at least one distillation column (5), from which a desulphurized diesel fuel (8) is withdrawn on the one hand and a desorbent stream (9) on the other hand; at least partly recycled in the first adsorption column (2). a step of distillation of the extract (4) carried out in at least one distillation column (6), from which an effluent containing the sulfur-containing impurities (10) is withdrawn, and on the other hand a flow of substantially pure desorbent (11) which is recycled at least in part in the first adsorption column. A method of high desulfurization according to claim 1 wherein the sulfur content of the desulphurized gas oil (8) is less than 10 ppm by weight, preferably less than 5 ppm by weight, and more preferably less than 1 ppm by weight, with a yield weight reported at the incoming charge greater than 97%, and preferably greater than 99%. A method of high desulfurization according to one of claims 1 or 2 wherein the adsorbent solid used in the adsorption unit is an active carbon with a specific surface area greater than 1200 m ² / g, and a total pore volume greater than 0, 5 cm ³ / gram A method of high desulfurization according to one of claims 1 or 2 wherein the fraction of pore volume included in the microporosity of said adsorbent is greater than 0.2 cm ³ / gram. A method of high desulfurization according to any one of claims 1 to 4 wherein the operating temperature of the adsorption unit is between 50 ° C and 350 ° C, and preferably between 50 ° C and 250 ° C. A method of high desulfurization according to any one of claims 1 to 5 wherein the simulated moving bed adsorption unit comprises at most 24 beds, and preferably at most 15 beds. A method of high desulfurization according to any one of claims 1 to 6 wherein the simulated moving bed adsorption unit has a desorbent charge to volume ratio of between 0.7 and 2.0. A high desulfurization process according to any one of claims 1 to 7 wherein the charge
to be treated is first sent to a distillation column located upstream of the adsorption unit in bed
simulated mobile, from which a head stream (1a) is extracted which is used at least partly as a desorbent,
and a bottom stream (1b) which is introduced as a charge of the simulated moving bed adsorption unit (2). A method of advanced desulfurization according to any one of claims 1 to 8 wherein the flow of
sulfur compounds (10) is mixed in a fuel oil (fuel) section. A method of high desulfurization according to any one of claims 1 to 9 wherein the stream of sulfur compounds (10) is recycled to a hydrodesulfurization unit

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