EP1427796A1

EP1427796A1 - Method for reducing sulphur compound content in a light fraction

Info

Publication number: EP1427796A1
Application number: EP02796295A
Authority: EP
Inventors: Pierre Crespin; Sébastien Decker; François HUTSCHKA; Emmanuelle Remy
Original assignee: TotalFinaElf France SA
Current assignee: Total Marketing Services SA
Priority date: 2001-08-31
Filing date: 2002-08-14
Publication date: 2004-06-16
Anticipated expiration: 2022-08-14
Also published as: DK1427796T3; FR2829144A1; FR2829144B1; DE60212660T2; WO2003018718A1; ATE331013T1; EP1427796B1; ES2266619T3; DE60212660D1

Abstract

The invention concerns a method comprising the following three successive phases: a) contacting the fraction with an adsorbent mass at a temperature ranging between 20 and 60 DEG C and under absolute pressure higher than 3.10<5> Pa, so that the fraction is in liquid state; b) contacting the adsorbent mass loaded with said sulphur compounds with a desorbing gas, at a temperature ranging between 20 and 150 DEG C, under absolute pressure less than 2.10<5> Pa; c) compressing the gas effluent comprising the sulphur compounds, at absolute pressure ranging between 2.10<5> Pa and 6.10<5> Pa; d) contacting the compressed gas effluent with an absorbent hydrocarbon in conditions suitable for absorption of the gaseous sulphur compounds with liquid hydrocarbon.

Description

PROCESS FOR REDUCING THE SULFUR CONTENT OF A LIGHT OIL CUT.

TECHNICAL AREA

The invention relates to the treatment of petroleum fractions to produce fuels with a very low content of sulfur compounds, in order to comply with the new environmental rules in force in many countries.

It finds its application in crude oil refineries.

STATE OF THE PRIOR ART

In many countries, environmental regulations impose increasingly severe sulfur content limits for gasolines. By 2005, the species should have a sulfur compound content of less than 10 ppm by weight.

Known methods for producing gasolines with very low sulfur compound contents consist in hydrotreating sulfur gasolines in the presence of one or more selective catalysts vis-à-vis the sulfur compounds in fixed bed reactors, the catalysts being chosen according to cutting points of the essences to be desulfurized.

Despite the selective nature of the catalysts used, hydrogenation reactions of the olefins contained in the treated gasolines still occur, which result in a loss of octane number.

To compensate for this loss, it is necessary to treat the desulfurized gasoline, for example in an isomerization unit.

In addition, conventional catalytic hydrodesulfurization processes lead to parasitic cracking reactions, which reduce the gasoline yield of this type of process.

The implementation of these methods requires expensive equipment because of the high pressures and temperatures at which they must operate. In addition, they consume hydrogen, which is an expensive product.

Species with very low sulfur content may be ^'produced using a known method for reducing the amount of sulfur in a petroleum fraction, described in International Patent Application No. WO 00/77124.

This process consists in performing the following operations: a) bringing the petroleum fraction comprising hydrocarbons and sulfur compounds into contact with a selective adsorbent mass for the adsorption of said sulfur compounds, under adsorption conditions such that adsorption is ensured sulfur compounds on the adsorbent mass, to obtain an effluent of desulphurized hydrocarbons, b) collecting said effluent of desulphurized hydrocarbons, c) desorbing the sulfur compounds fixed on the adsorbent mass, by putting the latter in contact with a desorbent, for obtaining a desorption effluent comprising said desorbent and the sulfur compounds, d) treating the desorption effluent to remove the sulfur compounds from said effluent and collecting a desulfurized desorbent.

This last operation generally consists in hydrσtreating the desorption effluent in a catalytic reactor either existing or to be created. In both cases, it is an expensive operation.

If the desorbent is a petroleum cut with very low sulfur content which has been obtained by hydrotreatment, this cut must be hydro treated a second time.

STATEMENT OF THE INVENTION

The object of the present invention is precisely to remedy these drawbacks and to provide an economical process for producing gasoline with a low sulfur content.

To this end, it proposes a process for reducing the content of sulfur compounds in an oil cut having a distillation point 95% below 150 ° C, characterized in that the following operations are carried out successively: a) bringing the petroleum fraction into contact with an adsorbent mass at a temperature between 20 and 60 ° C and under a higher absolute pressure at 3.10 ⁵ Pa, so that the petroleum fraction is in the liquid state, to selectively fix the sulfur compounds on the adsorbent mass and obtain a desulphurized petroleum fraction, b) bringing into contact the adsorbent mass loaded with sulfur compounds with a desorbent gas, at a temperature between 20 and 150 ° C, under an absolute pressure lower than 2.10 ⁵ Pa, so that the sulfur compounds are in the gaseous state, to desorb the sulfur compounds and obtain an effluent gaseous comprising the sulfur-containing compounds, c) compression of the gaseous effluent comprising the sulfur-containing compounds, at an absolute pressure between 2.10 ⁵ Pa and 6.10 ⁵ Pa, so as to bring e n part the sulfur compounds in the liquid state, d) bringing the compressed gaseous effluent into contact with a liquid absorbent hydrocarbon under conditions which allow the absorption of the gaseous sulfur compounds by the liquid hydrocarbon, in order to obtain on the one hand, a gas stream having a low content of sulfur compounds and, on the other hand, a liquid hydrocarbon rich in sulfur compounds.

The operations c) and d) can advantageously be carried out simultaneously.

In one form of implementation of the method of the invention, the absorbent liquid hydrocarbon is a gasoline resulting directly from the atmospheric distillation of a crude oil.

The desorbent gas can comprise at least one gas chosen from the group consisting of hydrogen, nitrogen, argon, carbon dioxide and a gaseous hydrocarbon containing 1 to 4 carbon atoms.

The method of the invention preferably comprises an additional operation e) of recycling the gas stream with a low sulfur compound content obtained by operation d) to carry out operation b). The process of the invention may also include an operation f) of bringing the adsorbent mass into contact with a liquid hydrocarbon very weakly charged with sulfur-containing compounds at an absolute pressure greater than 3.10 ⁵ Pa and at a temperature between 20 and 60 ° C, to improve the selectivity of adsorption of sulfur compounds with respect to hydrocarbons in particular olefinic.

The liquid hydrocarbon very weakly charged with sulfur compounds of operation f) is advantageously part of the desulphurized petroleum fraction obtained at the end of operation a). The liquid hydrocarbon used in operation f) is preferably a light hydrocarbon containing less than 1% of olefins and whose sulfur content is less than 5 ppm by weight.

The process of the invention can advantageously also include a preliminary operation of removing water and mercaptans from the petroleum fraction to be desulfurized.

The compression in step c) of the gaseous effluent comprising the sulfur-containing compounds can be carried out by means of at least one device of the ejector-separator type with liquid working fluid.

The working fluid of the device of the ejector-separator type can be a gasoline resulting directly from the atmospheric distillation of crude oil.

Preferably, the contacting of step d) of the compressed gaseous effluent with an absorbent liquid hydrocarbon is carried out in the device of the ejector-separator type which has just been mentioned. The operation of bringing the compressed gaseous effluent into contact with an absorbent liquid hydrocarbon can also be carried out in an absorption column dedicated to this operation.

Alternatively, this operation of bringing the compressed gaseous effluent into contact with an absorbent liquid hydrocarbon can be carried out, on the one hand, in the above-mentioned device of the ejector-separator type and, on the other hand, in an absorption column .

The subject of the invention is also the application of the process for reducing the content of sulfur compounds in the desulphurization of an petroleum fraction having an olefin content greater than 20% by weight. The process of the invention can be implemented with equipment which does not have to withstand high temperatures and pressures, therefore achievable at costs much lower than the costs of producing the devices for implementing the conventional hydrodesulfurization processes. catalytic.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood with the aid of the appended drawing, in which FIG. 1 diagrammatically represents a desulfurization unit for a light gasoline of catalytic cracker, which implements the process of the invention.

DETAILED DESCRIPTION OF THE INVENTION

In general, the process of the invention aims to reduce the amount of sulfur in a light petroleum cut with a very low octane loss and economically, since it consumes very little hydrogen and that it avoids losses in fuel efficiency.

FIG. 1 schematically represents a processing unit for a light gasoline of catalytic cracker having a 95% distillation point below 150 ° C., measured according to the ASTM D86 standard.

This light essence rich in olefins, which constitutes the charge of the processing unit, arrives via line 1 in the adsorber 3, through the open valve 2d, then passes through this adsorber which contains an adsorbent mass 4 made up of grains alumina or silica, the valves 2a and 2c being kept closed.

During its passage through the adsorber 3, the light gasoline is brought into contact with the alumina or silica grains at a temperature between 20 and 60 ° C. and under an absolute pressure greater than 3.10 ⁵ Pa, by example 4.5.10 ⁵ Pa. By a phenomenon of selective adsorption, the sulfur compounds contained in gasoline are fixed at least partially on the surface of the alumina or silica grains. At the outlet of the adsorber 3, a light gasoline with a very low sulfur content is obtained, which is evacuated by the line 8 through the open valve 7a, the valves 7b and 7d being closed.

When the adsorbent mass 4 is saturated with the sulfur compounds which it has fixed, the charge to be desulphurized is directed by action on the valves 2a to 2d and 7a to 7d towards the adsorber 5, which also contains an adsorbent mass 6 under the form of alumina or silica grains.

When the adsorbent mass 6 is saturated, the charge to be desulfurized is again oriented towards the adsorber 3.

While one of the adsorbers is crossed by the charge to be desulfurized, the other operates in desorption.

The number of adsorbers indicated in Figure 1 is only indicative and, depending on the nature of the charge treated and the sulfur content sought at the outlet of the unit, it is possible to envisage having more than two adsorbers or sets adsorbers operating alternately in adsorption and desorption.

To desorb the adsorbent mass 6 contained in the adsorber

5, hydrogen arriving via line 12 is heated by passage through the heat exchanger 11, then introduced into the adsorber 5 through the open valve 7c, the valves 7b and 7d being closed. This heated hydrogen passes through the adsorber 5.

During this crossing, it is brought into contact with the adsorbent mass 6 loaded with sulfur compounds, at a temperature between 20 and 150 ° C. and under an absolute pressure less than 2.10 ⁵ Pa.

Under these conditions, the partial pressure of the sulfur-containing hydrocarbons adsorbed is high enough for vaporization to occur and consequently the desorption of these sulfur-containing compounds. This desorption phenomenon is accentuated by the stream of hydrogen which passes through the adsorber 5.

The hot hydrogen in contact with the alumina or silica grains is charged with sulfur compounds to form a sulfurous gaseous effluent, which leaves the adsorber 5 by the line 13 through the open valve 2b, the valves 2c and 2a being closed. The low pressure in the adsorber 5 is obtained by means of an ejector 14 with liquid feed connected by line 19 to a feed pump 20 and a separator flask 15.

The driving liquid of the ejector 14 is a gasoline, sulfur or not, which has absorption properties of the sulfur compounds under the operating conditions of the ejector 14 and of the separator 15, for example gasoline obtained directly from distillation of crude oil or naphtha.

The gaseous effluent loaded with sulfur compounds leaving the adsorber 5 is sucked by the ejector 14 through the line 13, then brought into contact, in the upstream part of the ejector 14, with the motor liquid with which it to mix. The gaseous effluent loaded with sulfur compounds is thus compressed and partially liquefied in the downstream part of the ejector 14, then separated in the separator 15 into a gas phase and a liquid phase.

The ejector 14 and the separator 15 make it possible to obtain an absolute pressure of less than 2.10 ⁵ Pa in the adsorber 5, and an absolute pressure of the mixture constituted by the driving liquid and the gaseous effluent charged with sulfur compounds, of between 2.10 ⁵ Pa and 6.10 ⁵ Pa in the downstream part of the ejector 14 and in the separator

15.

Under these pressure and temperature conditions, the sulfur compounds contained in the sulfur gaseous effluent from the adsorber 5 are absorbed at least in part by the driving liquid to form a gasoline loaded with sulfur, which is partially withdrawn at the bottom of the separator 15 by line 16.

This portion of gasoline withdrawn is cooled by passage through the exchanger 17, then recycled to the suction of the pump 20. The excess gasoline at the bottom of the separator 15 is withdrawn by the line 28.

To compensate for this last draw-off, a top-up of engine liquid is carried out upstream of the pump 20 by the line 21, which connects the suction of the pump 20 to the gasoline supply line 22, itself connected to a tank. petrol, not shown. The gaseous phase which leaves the separator 15 via the line 18 enters the absorber 23, in which it is brought into contact with an absorbent liquid, which is the same essence as that used as the driving liquid of the ejector 14. For this , a sprinkler 25 placed at the upper part of the absorber 23 is connected by line 24 to the line 22 for fuel.

The sulfur compounds contained in the gas phase coming from the separator 15 are absorbed by the gasoline injected at the upper part of the absorber 23.

A gas stream with a very low content of sulfur compounds is extracted at the top of the absorber 23 and recycled by line 27 as a desorbent upstream of the exchanger 11.

The gasoline loaded with absorbed sulfur compounds is drawn off through line 26 at the bottom of the absorber 23 and mixed with the gasoline drawn off through line 28 at the bottom of the separator 15, to form a stream of liquid hydrocarbons comprising the sulfur compounds desorbed from the adsorbent mass 6.

This flow of liquid hydrocarbons is then treated in a conventional manner in a hydrotreatment unit not shown in FIG. 1.

When the desorption is complete, the adsorber 5 becomes available to operate in adsorption replacing the adsorber 3, which can then operate in desorption. The transition from one operation to the other takes place by switching valves 2a to 2d and 7a to 7d.

Before entering desorption mode, the saturated adsorber is emptied of its liquid content and depressurized beforehand.

Conversely, before entering adsorption mode, the regenerated adsorber is previously repressurized by means of an available gas network, for example a hydrogen network.

To complete the desorption, before operating the adsorber 5 in adsorption, it is advantageous to bring the adsorbent mass 6 into contact with a light liquid hydrocarbon. containing less than 1% olefins and having a sulfur content of less than 5 ppm by weight.

To improve the adsorption selectivity of the sulfur-containing compounds by the adsorbent mass relative to hydrocarbons and in particular to olefins, it is also possible to bring the adsorbent mass 6 into contact with the desulphurized petroleum fraction obtained during operation a) of the process. of the invention, under pressure and temperature conditions ensuring that this cut is in the liquid state, for example at the temperature of 30 ° C. and under an absolute pressure of 3.5 × 10 ⁵ Pa.

These additional operations are carried out with means known to those skilled in the art of the invention, not shown in FIG. 1.

With the method of the invention, it is possible to reduce the sulfur content of petroleum light cutting compounds to a very low value, without using a hydrocarbon containing no ^• sulfur. Its implementation therefore does not require costly additional processing facilities.

Another advantage of the process of the invention stems from the fact that there is no hydrogenation of the olefins contained in the treated petroleum fraction and therefore no loss of octane, as with the known tri-desulfurization processes.

The process of the invention also has the advantage of being a low energy consumer and of using available streams in petroleum refineries, which makes its exploitation economical.

It will be noted that the contacting of the compressed gaseous effluent from the adsorber 5 with an absorbent liquid hydrocarbon is carried out, on the one hand, in the ejector 14 and the separator 15 and, on the other hand, in the 'absorber 23. Depending on the higher or lower desulfurization rate sought for the light gasoline treated, the alumina or silica must be more or less well regenerated. If a low desulfurization rate is sought, hydrogen with a relatively high content of sulfur compounds can be used to regenerate alumina or silica. In this case, the contact between the gaseous effluent loaded with sulfur compounds leaving the adsorber 5 and the absorbent hydrocarbon also used as the driving liquid in the ejector-separator device is sufficient, the passage of the gaseous effluent through the absorber 23 then not being necessary, which makes the process of the invention even more economical.

To increase the contact of the compressed gaseous effluent from the adsorber 5 with the absorbent liquid hydrocarbon, it is possible to mount several ejector-separator devices in series.

The Examples which follow and which are not limiting in nature illustrate applications of the process according to the invention to various petroleum fractions.

EXAMPLE 1 1.1 Characteristics of the petroleum cut treated:

1.2 Operating conditions for adsorption:

- Adsorbent mass:

• Nature: alumina activated at 450 ° C under a stream of hydrogen,

• specific surface: 220 m ² / g,

• type CK-300, manufactured by the Ketjen Company.

- Pressure and temperature conditions:

• Pressure: 5.10 ⁵ Pa absolute, • Ambient temperature (around 20 ° C).

- Spatial velocity in the adsorber: • pph = approximately lrr ¹ , • wh ≈ approximately 1 h ^-1 . pph represents the weight of light gasoline which is brought into contact with a certain weight of adsorbent mass and per unit of time. wh represents the volume of light gasoline which is brought into contact with the adsorbent mass of the adsorber per unit volume of this adsorbent mass.

- Contact time: 100 minutes.

This time represents the time during which the gasoline treated with the adsorbent mass of the adsorber ensures a residual content of sulfur compounds of less than 110 ppm by weight.

- Retention capacity of sulfur compounds measured over an adsorption period of 6 hours: 1.35 g of sulfur compounds per kg of adsorbent mass.

1.3 Characteristics of the desulphurized petrol produced:

• Content of sulfur compounds: 110 ppm by weight,

• Olefin content: around 61% by weight.

1.4 Desorption conditions:

Current of hydrogen for 2 hours, at a temperature of 60 ° C, under an absolute pressure of 0.1.10 ⁵ Pa.

1.5 Ejector driving liquid and absorbing liquid: Gasoline obtained directly from the distillation of crude oil. EXAMPLE 2 1.1 Characteristics of the treated petroleum cut

1.2 Adsorption operating conditions

- Adsorbent mass:

• Nature: alumina activated at 450 ° C under a stream of hydrogen,

• specific surface: 220 m ² / g

• type CK-300, manufactured by the Ketjen Company

Pressure and temperature conditions:

• Pressure: 5.10 ⁵ Pa absolute,

• Ambient temperature (around 20 ° C).

- Spatial velocity in the adsorber:

• pph = about llr ¹ ,

• wh = approximately 1 h " ^1. Pph represents the weight of light gasoline which is brought into contact with a certain weight of adsorbent mass and per unit of time. Wh represents the volume of light gasoline which is brought into contact with the adsorbent mass per unit volume of this adsorbent mass.

Contact time: 100 minutes. This time represents the time during which the gasoline treated with the adsorbent mass of the adsorber ensures a residual content of sulfur compounds of less than 30 ppm by weight.

- Retention capacity of sulfur compounds measured over an adsorption period of 6 hours: 0.15 g of sulfur compounds per kg of adsorbent mass.

1.3 Characteristics of the desulphurized petrol produced:

• Content of sulfur compounds: 30 ppm by weight,

• Olefin content: around 61% by weight.

1.4 Desorption conditions:

1.5 Ejector driving liquid and absorbing liquid: Gasoline obtained directly from the distillation of crude oil.

EXAMPLE 3

1.1 Characteristics of the treated petroleum cut:

1.2 Operating conditions for adsorption:

- Adsorbent mass:

• Nature: silica activated at 150 ° C under a stream of hydrogen,

• specific surface: 600 m ² / g.

- Pressure and temperature conditions:

• Pressure: 5.10 ⁵ Pa absolute,

• Temperature: ambient about 20 ° C.

- Spatial velocity in the adsorber:

• pph ≈ about llr ¹ , • wh ≈ about 1 h- ¹ . pph represents the weight of light gasoline which is brought into contact with a certain weight of adsorbent mass and per unit of time. wh represents the volume of light gasoline which is brought into contact with the adsorbent mass per unit volume of this adsorbent mass.

- Contact time: 100 minutes.

This time represents the time during which the gasoline treated with the adsorbent mass of the adsorber ensures a residual content of sulfur compounds of less than 20 ppm by weight.

- Retention capacity of sulfur compounds measured over an adsorption period of 6 hours: 0.25 g of sulfur compounds per kg of adsorbent mass.

1.3 Characteristics of the desulphurized petrol produced:

• Content of sulfur compounds: 20 ppm by weight, • Olefin content: around 55% by weight.

1.4 Desorption conditions:

SUMMARY TABLES

Content of sulfur compounds (ppm by weight)

Light gasoline to Desulfurized gasoline produced

Example 1 448 110

Example 2 184 30

Example 3,184 20

The results recorded in these summary tables clearly show the effectiveness of the process of the invention in reducing the content of sulfur compounds in a light gasoline, without significantly reducing the content of olefins and therefore with a low loss in octane number. .

Claims

1- A process for reducing the content of sulfur compounds in an oil cut having a 95% distillation point below 150 ° C, characterized in that the following operations are carried out successively: a) bringing the oil cut into contact with an adsorbent mass at a temperature between 20 and 60 ° C and under an absolute pressure greater than 3.10 ⁵ Pa, so that the petroleum fraction is in the liquid state, to selectively fix the sulfur-containing compounds on the adsorbent mass and obtain a desulfurized petroleum fraction, b) bringing the adsorbent mass loaded with sulfur-containing compounds into contact with a desorbing gas, at a temperature between 20 and 150 ° C., under an absolute pressure lower than 2.10 ⁵ Pa, so that the sulfur compounds are in the gaseous state, to desorb the sulfur compounds and obtain a gaseous effluent comprising the sulfur compounds, c) compression of the gaseous effluent comprises enant sulfur compounds, at an absolute pressure between 2.10 ⁵ Pa and 6.10 ⁵ Pa, so as to bring partially the sulfur compounds in the liquid state, d) contacting the compressed gaseous effluent with an absorbent liquid hydrocarbon under conditions which allow the absorption of gaseous sulfur compounds by the liquid hydrocarbon and obtain, on the one hand, a gas flow having a low content of sulfur compounds and, on the other hand, a liquid hydrocarbon rich in sulfur compounds.

2- Method according to claim 1, characterized in that operations c) and d) are carried out simultaneously. 3- Method according to claim 1 or 2, characterized in that the absorbent liquid hydrocarbon is a gasoline resulting directly from the atmospheric distillation of a crude oil.

4- A method according to any one of claims 1 to 3 characterized in that the desorbent gas comprises at least one gas selected from the group consisting of hydrogen, nitrogen, argon, carbon dioxide and a gaseous hydrocarbon having 1 to 4 carbon atoms.

5- A method according to any one of claims 1 to 4, characterized in that it further comprises an operation e) of recycling the gas stream with a low content of sulfur compounds obtained by operation d) to carry out the operation b).

6- A method according to any one of claims 1 to 5, characterized in that it further comprises an operation f) of bringing the adsorbent mass into contact with a liquid hydrocarbon very weakly charged with sulfur compounds, at an absolute pressure higher than 3.10 ⁵ Pa and a temperature between 20 and 60 ° C, to improve the adsorption selectivity of sulfur compounds compared to hydrocarbons in particular olefinic.

7- A method according to claim 6, characterized in that the liquid hydrocarbon very weakly charged with sulfur compounds is a part of the desulfurized petroleum fraction obtained at the end of operation a).

8- A method according to any one of claims 6 and 7, characterized in that the liquid hydrocarbon used in operation f) is a light hydrocarbon containing less than 1% of olefins and whose sulfur content is less than 5 ppm by weight, to perfect the desorption carried out during operation b).

9- A method according to any one of claims 1 to 8, characterized in that it comprises a preliminary operation of removing water and mercaptans from the petroleum cut to be desulfurized.

10- Method according to any one of claims 1 to 9, characterized in that, in step c), the compression of the gaseous effluent comprising the sulfur compounds is carried out by means of at least one device of the ejector type - liquid motor fluid separator.

11- A method according to claim 10, characterized in that the working fluid of the device of the ejector-separator type is a gasoline resulting directly from the atmospheric distillation of crude oil. 12- A method according to claim 10 or 11, characterized in that the operation of step d) of bringing the compressed gaseous effluent into contact with an absorbent liquid hydrocarbon is carried out in the device of the ejector-separator type. 13- Method according to any one of claims 1 to 9, characterized in that the operation of step d) of bringing the compressed gaseous effluent into contact with an absorbent liquid hydrocarbon is carried out in an absorption column dedicated to this operation.

14- Method according to any one of claims 10 or 11, characterized in that the operation of step d) of bringing the compressed gaseous effluent into contact with an absorbent liquid hydrocarbon is carried out, on the one hand, in the device of the ejector-separator type and, on the other hand, in an absorption column.

15- Application of the method according to any one of claims 1 to 14 to the desulfurization of an oil cut having an olefin content greater than 20% by weight.