EP0245124A1 - Combined process for hydroreforming and hydroisomerization - Google Patents

Abstract

1. A combined process for heavy naphtha hydroreforming and light naphtha hydroisomerization, wherein a first charge, consisting in major part of a heavy naphtha, is fed, through at least one heating zone, to at least two catalytic hydroforming zones arranged in series, the effluent from each hydroreforming zone, except the effluent from the last reforming zone wherethrough passes the charge, also circulating through at least one heating zone, the effluent from the last reforming zone being subjected to at least one fractionation so as to obtain a reformate and a hydrogen containing gas, a portion of said hydrogen being recycled to the hydroreforming zones, another portion of said hydrogen being admixed with a second charge consisting in major part of a light naphtha, the resultant mixture being preheated and then introduced into a catalytic hydroisomerization zone, the reformate and the effluent from the hydroisomerization zone being collected together and subjected to fractionation in the same stabilization column in order to obtain an improved isomerizate and reformate mixture, said process further comprising the use in the hydroisomerization zone of a catalyst containing at least one zeolite, the hydroisomerization being conducted without introduction of halogen or halogen compound into the hydroisomerization zone.

Description

In the catalytic reforming processes, the charge is generally a naphtha distilling for example between about 60 and 200 ° C; let us cite in particular the direct distillation naphthas. Light naphthas are most often eliminated by distillation because their interest in reforming is not very interesting since they cannot be transformed into aromatics and they are not very isomerized. These light naphthas are then either recovered as such for the petrol pool, or recovered by an isomerization process in a unit separate from the reforming unit.

The isomerization of normal low molecular weight paraffins is of considerable importance in the petroleum industry, given the particularly high octane number of isoparaffins.

It is interesting to be able to transform the n-paraffins C4-C7 and especially C5-C6 into isoparaffins in order to obtain a fuel with a high octane number. This process is advantageous for improving the light gasoline fractions and in particular, the direct distillation overhead fractions.

The naphthas which are generally known as heavy naphthas are then alone sent to the reforming unit (reforming).

In the process of the present invention, a reforming unit and an isomerization unit are used jointly to comply with the new regulations in the context of the manufacture of unleaded petrol, in particular in Europe and in the USA. It becomes essential to enhance the light naphtha cut, hence the idea of integrating the isomerization unit with that of reforming to minimize investments and used. Until relatively recently, isomerization reactions were carried out with the injection of chlorine. A support could be used as a catalyst in which a noble group VIII metal was incorporated, the support being impregnated for example with a hydrocarbylaluminum halide of formula:
Al X _y R _{(3 - y)}
where y is 1 or 2,
X is halogen
and R is a monovalent hydrocarbon radical

It is also possible to use catalysts of the Friedel and Crafts type, such as aluminum chloride. It is possible to use (USP 3903192), in addition to conventional catalysts of the platinum type on silica-alimine, halogenated alumina or other acid supports, alumina supports with introduction into alumina, halogen and at least one compound of metal of group VI or VIII of the periodic table of the elements in the presence of a mixture of chlorine and or hydrochloric acid. All these catalysts can be used for the isomerization in a hydrogen atmosphere of paraffins having 4 to 7 carbon atoms and preferably 5 and / or 6 carbon atoms, at a temperature between 50 and 250 ° C. The operation is preferably carried out under a pressure of 5 to 100 kg / cm 2 (5 to 100 bars) with a space velocity of 0.2 to 10 liters of feed per liter of catalyst per hour. A halogenated promoter, such as, for example, hydrochloric acid, carbon tetrachloride, an alkyl halide, such as, for example, ethyl chloride, isopropyl chloride, chloride, may be introduced continuously or periodically into the feed. tert-butyl or tert-butyl bromide.

In the present invention, a first charge consisting mainly of a heavy naphtha is sent through at least one heating zone to at least two catalytic reforming zones arranged in series, the effluent from each reforming zone, except the effluent from the last reforming zone crossed by said first charge, also circulating through at least one heating zone, (the same heating zone already used can be used to heat the heavy naphtha before it enters the first zone of reforming) the effluent from the last reforming zone being subjected to at least one fractionation with a view to obtaining, on the one hand, a reformate and, on the other hand, a first stream of a gas containing in particular hydrogen, part at least this hydrogen being mixed with a second charge consisting mainly of a light naphtha, the mixture thus obtained being preheated before being introduced into a catalytic isomerization zone from which o n draw an isomerisate. This preheating can be carried out either by circulating the mixture thus obtained directly through the fumes of at least one of said heating zones defined above, either by indirect contact with steam, or by indirect contact with the effluent from the last reforming zone crossed by the heavy naphtha. The hydrogen produced in the reforming reaction covers the hydrogen requirements of the light naphtha isomerization unit (correct H2 / hydrocarbon ratio). Thus by operating in accordance with the invention, the integration of the two reactions, reforming and isomerization, makes it possible to process the light cut using the equipment existing in the reforming unit:
- the operating thermal level of the isomerization reactor is obtained with optimum effect, either by heat recovery from the smoke from the reforming furnaces or indirectly.
- the supply of H2 and the recycling of hydrogen are ensured by the compressor for the export of hydrogen (recontacting) of the reforming,
- the isomerization unit is operated without recycling hydrogen which further minimizes the consumption of utilities compared to an isomerization unit which would operate independently of the reforming unit (the purity of the gas is better ).
- The recovery of light hydrocarbons at the outlet of the reaction zone of the isomerization unit is improved by recontacting with the reformate.

However, according to the invention, for the isomerization zone to function properly, it is not possible to use the conventional isomerization catalysts described above because the use of such catalysts requires injecting a halogen or a halogenated compound, including chlorine. The process according to the invention can only be conceived with a new generation of particularly suitable catalysts, which can precisely function in the absence of injection of halogen or of a halogenated compound. According to the invention, they are catalysts based on a zeolite generally diluted in a generally amorphous matrix. The isomerization catalyst (hydroisomerization) may optionally contain at least one group VIII metal, and for example platinum, palladium or nickel. In the case of platinum and palladium, the content (by weight) is between 0.05 and 1% and preferably between 0.1 and 0.6%. In the case of nickel, the weight content is between 0.10 and 10% and preferably between 0.2 and 5%.

The catalysts which can be used, according to the present invention, for isomerization contain a zeolite which advantageously will be a mordenite, in acid form, with or without hydrogenation promoter (s). Preferably so-called large pore mordenites are used.

There are, in fact, two types of mordenite, which are distinguished by their adsorption properties: the large pore form, always synthetic, which adsorbs molecules such as benzene (kinetic diameter = 6.6 x 10⁻¹⁰m and the form with small pores, natural or synthetic, which only absorbs molecules with a kinetic diameter less than about 4.4 x 10⁻¹⁰m. These mordenites are also distinguished by morphological differences - needles for mordenite small pores, spherulites for large pore and structural morenite: presence or absence of defects. In all the literature, large pore mordenite is used, including USP 3190939, USP 3480539, USP 3551353.

Now, a mordenite which is particularly suitable for use in the present invention is a mordenite prepared from a small pore mordenite under conditions such that the mordenite used will have retained the morphology of the small pore mordenite while having the capacity to adsorb the benzene molecule (kinetic diameter: 6.6 x 10⁻¹⁰m) which is not the case for a small pore mordenite which has not undergone the special treatment. The use of this mordenite of particular morphology (needles), specially treated, leads to a significant gain in activity and selectivity for the isomerization reaction.

It is possible to "unclog" the channels of this particular zeolite by treatment in a strong mineral acid and / or by calcination in the presence of water vapor and to reach an adsorption capacity close to that of large pore mordenite. .

These synthetic small pore mordenites can be obtained by synthesis in particular under the following conditions: temperature between 200 and 300 ° C. approximately and crystallization time from 5 to 50 hours.

The zeolite preferably used in the catalyst of the present invention is produced from a small pore mordenite whose sodium content is generally between 4 and 6.5 percent (by weight) relative to the weight of dry mordenite, the Si / Al atomic ratio is generally between 4.5 and 6.5 and the mesh volume generally between 2.80 and 2.77 nm³. This mordenite only adsorbs molecules with a kinetic diameter of less than about 4.4 x 10⁻¹⁰m. After treatments, mordenitis is characterized by different specifications: an Si / Al atomic ratio of between 5 and 50 and preferably between 5.5 and 30, a sodium content of less than 0.2% by weight and preferably less than 0.1% relative to the weight of dry zeolite, a mesh volume, V, of the elementary mesh between 2.78 and 2.73 nm³ and preferably between 2.77 and 2.74 nm³, a benzene adsorption capacity greater than 5% and preferably at 8% relative to the weight of dry solid (zeolite), a particular morphology, namely that it is mainly in the form of needles preferably of average length 5 microns (5 x 10⁻⁶m) of which the hexagonal faces have a length of approximately 1 micron, (1 x 10⁻⁶m) and a "height" of approximately 0.3 microns (0.3 x 10⁻⁶m).

The mordenite thus prepared and intended to be used in hydroisomerization reactions is then mixed with a generally amorphous matrix, the hydroisomerization catalyst also preferably containing at least one group VIII metal, in particular platinum, palladium and nickel with possibly a group IV metal: tin, germanium or lead. The matrix can be alumina, silica-alumina, a natural clay (kaoline or bentonite for example), alumina-boron oxide. The content of mordenite in the catalyst is advantageously greater than 40% (preferably 60%) by weight.

This catalyst constitutes an excellent hydroisomerization catalyst for sections rich in normal paraffins with 4 or 7 carbon atoms and preferably with 5 or 6 carbon atoms per molecule, having an enhanced selectivity and activity compared to conventional hydroisomerization catalysts. .

As indicated above, the heavy naphtha is subjected to catalytic reforming in the presence of hydrogen in at least two reaction zones.

The general conditions for hydroreforming or catalytic hydroreforming reactions are as follows: in each reaction zone, the average temperature is between, approximately 480 and 600 ° C., the pressure is between, approximately 5 and 20 kg / cm² (5 and 20 bars), the hourly speed is between 0.5 and 10 volumes of liquid naphtha per volume of catalyst and the recycling rate is between 1 and 10 moles of hydrogen per mole of feed.

The catalyst may contain for example at least one metal of the platinum family, that is to say a noble metal such as platinum, palladium, iridium, rhodium, ruthenium, osmium, deposited on an alumina or an equivalent compound (examples: platinum-alumina-halogen or platinum-iridium halogen). The total content of noble metals is from 0.1% to 2% by weight relative to the catalyst and the halogen content, preferably chlorine or fluorine, from 0.1 to 10%. The alumina-halogen combination can be replaced by other supports, for example silica-alumina. The catalyst may contain at least one other metallic promoter chosen from the most diverse groups of the periodic table.

There are many ways to operate:

First, one can operate in a fixed bed using several reactors. The charge passes successively through each of the reactors; the catalyst remains in service for long periods before being regenerated.

• a) la régénération fréquente est utilisée lorsque l'on utilise plusieurs réacteurs qui renferment le catalyseur en lit fixe. L'un de ces réacteurs est en régénération (ou en attente), pendant que les autres réacteurs sont en service;
• b) la catalyseur s'écoule de haut en bas de chaque réacteur (lit mobile) et la régénération se fait, par exemple, en continu, dans un réacteur principal de manière à ne pas interrompre la réaction. Le catalyseur peut s'écouler progressivement et successivement à travers chaque zone de réaction.

According to another process, called "regenerative", the catalyst is regenerated either frequently or continuously:

• a) frequent regeneration is used when several reactors are used which contain the catalyst in a fixed bed. One of these reactors is in regeneration (or on standby), while the other reactors are in service;
• b) the catalyst flows from top to bottom of each reactor (moving bed) and the regeneration takes place, for example, continuously, in a main reactor so as not to interrupt the reaction. The catalyst can flow gradually and successively through each reaction zone.

The diagrams given as examples illustrate the invention.

In FIG. 1, a heavy naphtha is introduced into the unit via line 1, passed through through line 2, the heat exchanger 3 and through line 4 passes through an oven 5. At the outlet of the oven, heavy naphtha traveling along line 4 is introduced into a first reforming reactor 6 here enclosing a fixed bed of catalyst. The effluent from the reactor 6 is withdrawn through line 7 and passes through the furnace 5 before being directed into a second reactor (8) also enclosing in the figure a fixed bed of catalyst. The effluent from this second reactor, via line 9 is also sent through the furnace 5 and is then introduced into a third reactor 10, containing a fixed bed of catalyst. The effluent from the reactor 10, drawn off through the pipe 11, passes through the exchanger 3 and through the pipe 12, the coolings 13 and 15, the lines 14 and 16, reaches a separator flask 17 from which one recovers, in the background, a reformate, via line 18.

At the head of the separator flask 17, a gas essentially based on hydrogen is drawn off via line 21. At least part of this gas can be returned (recycling hydrogen) via line 22, compressor 23 and line 24, to the reforming unit, after having been mixed in line 2 with the charge of heavy naphtha. At least another part of the hydrogen from line 21 is mixed after passage through line 25, at least one compression stage 26 and line 27, with the charge of light naphtha introduced into the unit through line 28 ( a variant would consist here of taking hydrogen from line 25 and not at the outlet of the balloon 17, that is to say in line 21 but at the outlet of compressor 23, therefore in line 24 so as to gain, in line 25, the pressure differential of compressor 23). The mixture of light naphtha and hydrogen coming from the reforming zone, crosses, via line 29, the exchanger 30, travels through line 31 and is heated in FIG. 1 at 32, in the upper part of the oven. 5, therefore by the fumes from the reforming furnace. Another method for heating the mixture of line 31 would consist of contacting this mixture indirectly with water vapor produced in the flue gases in order to carry out a heat exchange. Another method (see FIG. 1A) would consist in separating the effluent from the last hydroreforming reactor into two parts; a part of this effluent circulates as in FIG. 1 through the exchanger 3 then towards the line 12. Another part supplying (via the line 11.a) calories to an exchanger 32.a into which the said mixture of line 31, the said mixture then flowing through line 33 to the hydroisomerization zone 34. Then, this mixture traveling in line 33, reaches the hydroisomerization reactor 34, which here contains a fixed bed of catalyst (this could be a moving bed). The effluent from the isomerization zone, discharged through line 35, passes through the exchanger 30, flows through line 36 through cooling 37, and through line 38 is introduced into a separator flask 39. Via line 41, at the head of this separator flask, a gas rich in hydrogen is recovered. At the bottom of the separator flask 39, an isomerisate is recovered via line 40. It is possible, in the present invention, to treat conventionally and separately the reformate of line 18 and the isomerisate of line 40: each of these effluents can thus be sent to a stabilization column, the different fractions coming from the reformate of 'on the one hand and from isomerisate on the other hand being collected for their usual uses in refining. However, in the context of the present invention, the device used makes it possible to eliminate the stabilization column from the isomerization unit and to treat the isomerisate and the reformate in a single column. In this case, the reformate withdrawn from the separator flask 17 through the pipe 18 is sent, by means of the pump 19, through the pipe 20 and is then mixed in line 46 with at least part of the hydrogen-rich gas withdrawn by the pipe 41 of the separator flask 39, this gas having previously passed through the compress 42, the pipes 43 and 45 and the cooler 44. This reformate-gas mixture is sent to the separator flask 47 from which the head is recovered a gas with a high hydrogen content (line 48) and at the bottom of the flask a reformate (line 49) which is mixed with the isomerisate of line 40, the mixture obtained being sent via line 50 to the stabilization column 52. At the bottom of the column, via line 52, a mixture of isomerisate and reformate of excellent quality is recovered. At the top of the column, light gases, cooled at 54, and treated in the separator flask 56 are recovered via line 53. A few light vapors are thus collected in line 57 and light distillates are collected in lines 58 and 60, a portion of these distillates are recycled via line 59 at the head of the stabilization column 51. It may be advantageous to have on line 27 a chlorine guard pot, not shown in FIG. 1.

FIG. 2 illustrates a variant of the invention. Here, the reformate is also mixed with the isomerization effluent but this effluent does not pass through the separator flask 39 of FIG. 1. Here this flask is deleted. A heavy naphtha is introduced into the unit through line 1, passes through line 2, the heat exchanger 3 and through line 4 passes through an oven 5. At the outlet of the oven, heavy naphtha, traveling through the line 4 is introduced into a first reforming reactor 6 here enclosing a fixed bed of catalyst. The reactor effluent 6 is withdrawn through line 7 and passes through the furnace 5 before being directed into a second reactor 8 also containing in the figure a fixed bed of catalyst. The effluent from this second reactor, via line 9 is also sent through the furnace 5 and is then introduced into a third reactor 10, containing a fixed bed of catalyst. The effluent from the reactor 10, drawn off through the pipe 11, passes through the exchanger 3 and through the pipe 12, the coolings 13 and 15, the lines 14 and 16, reaches a separator flask 17 from which one recovers, in the background, a reformate, via line 18.

At the head of the separator flask 17, a gas essentially based on hydrogen is drawn off via line 21. At least part of this gas can optionally (recycling hydrogen) be returned via line 22, compressor 23 and line 24, to the reforming unit, after having been mixed in line 2 with the charge of heavy naphtha . At least another part of the hydrogen from line 21 is mixed after passage through line 25, at least one compressor 26 and line 27 (line on which a chlorine guard pot is optionally placed), with the charge of light naphtha introduced into the unit via line 28. Note that, as explained with reference to FIG. 1, the content of line 25 can come from line 24, therefore being passed through the compressor 23. The mixture of light naphtha and the hydrogen coming from the reforming zone, crosses, via the line 29, the exchanger 30, travels through the pipe 31 and is heated at 32, in the upper part of the furnace 5, therefore by the fumes from the reforming furnace . But, as in FIG. 1, it is possible to carry out an indirect heating by production of water vapor and exchange or else (as indicated in FIG. 1A) to carry out a heating with at least part of the effluent from the last reactor. reforming.

Then, this mixture traveling in line 33, reaches the hydroisomerization reactor 34, which here contains a fixed bed of catalyst (it could be a moving bed). The effluent from the isomerization zone, discharged through line 35, passes through the exchanger 30, circulates through line 36 through the cooling 37, and through line 38, is introduced into a separator tank 40, then is mixed. , (after having circulated in line 36, the cooling zone 37 and the line 38) in line 39 with the reformate withdrawn from the separator flask 17 by line 18 and sent by means of the pump 19 in line 20. By line 41, at the head of this separator flask 40, a gas rich in hydrogen is recovered. At the bottom of the separator flask 40, a mixture of isomerisate and reformate is recovered via line 42. The mixture obtained is sent to the stabilization column 43. At the bottom of the column, via line 44, a mixture of isomerisate and reformate of excellent quality is recovered. Light gases, cooled at 46, and treated in the separator flask 48, are recovered at the head of the line 45. Light gas in the vapor phase is thus collected in the line 49 and light distillates are in the liquid phase in the lines. 50 and 52; some of these distillates are recycled via line 51 at the head of the stabilization column 43.

Example:

For example, in the pipe 1, a heavy naphtha charge of 21,500 BPSD (about 140 m³ / hour) was used, the composition of which is as follows:

In line 28, a charge of light naphtha of 6,800 BPSD (approximately 45 m³ / hour) was used, the composition of which is as follows: (% by weight):

In the case of FIG. 1, a gas rich in hydrogen of the following composition is recovered in line 48:

In the case of FIG. 2, a gas rich in hydrogen of the following composition is recovered in line 41:

The product, a mixture of isomerisate and reformat of 25,175 BPSD (approximately 166m³ / hour) is recovered in line 52 in the case of Figure 1, (44 in the case of Figure 2).

It has the following characteristics:

The operating conditions were as follows:

Claims (10)

1. Combined process for hydroreforming a heavy naphtha and hydroisomerizing a light naphtha in which a first charge consisting mainly of a heavy naphtha is sent through at least one heating zone to at least two zones of catalytic hydroreforming arranged in series, the effluent from each hydroreforming zone, except the effluent from the last reforming zone crossed by said first charge, also flowing through at least one heating zone, the effluent from the last reforming zone being subjected to at least one fractionation with a view to obtaining on the one hand a reformate and on the other hand a gas containing in particular hydrogen, at least part of this hydrogen being mixed with a second charge consisting mainly of a light naphtha, the mixture thus obtained being preheated and then introduced into a catalytic hydroisomerization zone, a process in which, in addition, the catalyst used in the hydroisomerization zone re contains at least one zeolite, the hydroisomerization process being carried out in the absence of injection of a halogen or of a halogen compound in the hydroisomerization zone. 2) The method of claim 1 wherein the reformate and the effluent from the isomerization zone are collected together and are subjected to fractionation in the same stabilization column in order to obtain an improved mixture of an isomerisate and d 'a reformate (figure 2). 3) Process according to claim 1 wherein the hydroisomerization effluent is subjected to at least one fractionation with a view to obtaining on the one hand a second stream of a gas containing in particular hydrogen and on the other hand a isomerisate, and in which the second stream of a gas containing hydrogen, is first treated with at least part of the said reformate, then the reformate is mixed with at least part of the isomerisate, the whole reformate-isomerisate thus obtained being subjected to fractionation in the same stabilization column in order to obtain an improved mixture of an isomerisate and a reformate (FIG. 1). 4) Method according to one of claims 1 to 3 wherein the catalyst used in the hydroisomerization zone contains at least a mixture of a mordenite and a matrix. 5) Method according to one of claims 1 to 4 wherein the catalyst further contains at least one metal from group VIII of the periodic table of the elements. 6) Method according to one of claims 1 to 5 wherein, in the hydroisomerization zone, using a catalyst based on a large pore mordenite, adsorbing molecules with a kinetic diameter greater than about 6.6 x 10 ⁻¹⁰m, having an Si / Al atomic ratio of between approximately 5 and 50, a sodium content of less than 0.2% by weight, relative to the totality of the dry zeolite, a volume of mesh V, of elementary mesh , between 2.78 and 2.73 nm³, a benzene adsorption capacity greater than 5% by weight relative to the weight of dry zeolite, the zeolite being, for the most part, in the form of needles. 7) Process according to claim 6, in which a catalyst based on a large pore mordenite is used, adsorbing molecules with a kinetic diameter greater than about 6.6 × 10⁻¹⁰m, an Si / Al atomic ratio of between 5, 5 and 30, a sodium content of less than 0.1% by weight relative to the totality of dry zeolite, a volume of the elementary mesh between 2.77 and 2.74 nm³, a higher benzene adsorption capacity at 8% relative to the weight of dry zeolite, the zeolite being mainly in the form of needles of average length 5 x 10⁻⁶m whose faces, mainly hexagonal, have a length of approximately 1 x 10⁻ ⁶m and a height of about 0.3 x 10⁻⁶m. 8) Method according to one of claims 1 to 7 wherein another part of the hydrogen obtained after the fractionation of the reformate is recycled to the hydroreforming zones. 9) Method according to one of claims 1 to 8 wherein the light naphtha and the effluents from each reforming zone (except the effluent from the last reforming zone) are heated in the same heating zone. 10) The method of claim 9 wherein the mixture of light naphtha and said portion of hydrogen obtained after fractionation of the reformate, is preheated directly through the fumes of the heating zone.

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