EP1182247A1 - Process for the production of high octane gasoline including hydroisomerisation and separation with a zeolitic adsorbent - Google Patents

Abstract

Production of high octane base petrol by hydroisomerization of 5 - 8C charge comprises sections of hydroisomerization and separation by adsorption. Separation section contains adsorbent with two types of channels, main channels having ring opening defined by at least 10 oxygen atoms (10MR) and secondary channels of at least 12 oxygen atoms(12MR), secondary channels being accessible to charge only by main channels.

Description

The present invention relates to the production of high octane gasoline by a process combining at least one hydroisomerization section and at least one separation section by adsorption in which the adsorbent is a microporous zeolitic solid having a mixed structure with channels of different sizes.

More specifically, the process of the invention makes it possible to obtain a petrol base with a high octane number which is used in the composition of a petrol pool.
The quality of a gasoline is partly dependent on its octane number. Thus, from the point of view of the octane number, it is preferable that the hydrocarbons constituting the gasoline are as branched as possible as shown by the values of the research octane numbers (RON) and engine octane number ( MON) of different hydrocarbon compounds (table below). paraffins CN8 nC7 mono C7 mono C6 di C6 di C5 sort C4 sort C5 RON <0 0 21-27 42-52 55-76 80-93 112 100-109 MY <0 0 23-39 23-39 56-82 84-95 101 96-100

To increase the octane number of a gasoline, several techniques have already been proposed. First, the aromatic compounds, main constituents of the essences of reforming, isoparaffins produced by aliphatic alkylation or isomerization of gasolines slight compensated for the loss of octane number resulting from the removal of lead in species, this removal being due to the taking into account of environmental constraints always more drastic. Subsequently, oxygenated compounds such as Methyl Tertiobutyl Ether (MTBE) or Ethyl Tertiobutyl Ether (ETBE) have been introduced into the fuels. More recently, the recognized toxicity of compounds such as aromatics, in particular benzene, olefins and sulfur compounds, as well as the desire to decrease the pressure of gasoline vapor, resulted in the production of reformulated gasolines. For example, since on January 1, 2000, the maximum levels of olefins, total aromatic compounds and benzene in the petrol distributed in France is 18% vol., 42% vol. and 1% vol.

Essence pools include several components. The majority components are reforming gasoline, which usually comprises between 60 and 80% vol. of compounds aromatic, and FCC essences which typically contain 35% vol. aromatic but provide the majority of the olefin and sulfur compounds present in the pools species. The other components can be alkylates, without aromatic compounds nor olefinic, light isomerized or non-isomerized gasolines, which do not contain unsaturated compounds, oxygenated compounds such as MTBE, and butanes. Insofar where the aromatic contents are not reduced below 35-40% vol., the contribution reformates in gasoline pools will remain significant, typically 40% vol. Conversely, increased severity of the maximum admissible content of aromatic compounds at 20-25% flight. will cause a reduction in the use of reforming, and consequently the need to enhance C7-C10 direct distillation cuts by other means than reforming.

In this perspective, the production of multibranched isomers from heptanes and octanes weakly branched contained in naphthas, instead of the production of toluene and xylenes from these same compounds, appears to be an extremely promising. This justifies the search for high-performance isomerization catalytic systems heptanes (also called hydro-isomerization when carried out in the presence hydrogen), octanes and more generally C5-C8 cuts and cuts intermediates as well as the research of processes allowing to selectively recycle isomerization (hydro-isomerization) the low octane compounds that are linear and monobranched paraffins.

In order to selectively recycle to hydroisomerization the linear and monobranched paraffins and to recover the multibranched paraffins, with high octane number, to introduce them into the composition of a gasoline pool, it is necessary to at least separate the multibranched paraffins. Thus a separation unit, producing at least two separate effluents, one with a high octane number and the other with a low octane number, and integrated into a process also comprising at least one hydroisomerization unit makes it possible to recycling the effluent with a low octane index to the hydroisomerization unit, which converts linear and monobranched paraffins of low octane to multibranched paraffins of high octane.
The main difficulty in implementing such a process, combining hydroisomerization and separation steps, is the separation of multibranched paraffins.

State of the art

Adsorption separation techniques, using selective molecular sieves thanks to the size of the accessible pores, are particularly suitable for the separation of linear, monobranched and multibranched paraffins. Separation processes by conventional adsorption can result from PSA (Pressure Swing) type implementations Adsorption), TSA (Temperature Swing Adsorption), chromatography (chromatography of elution or simulated counter-current for example). They can also result from a combination of these implementations. These processes all have in common the contacting of a mixture liquid or gaseous with a fixed bed of adsorbent to remove certain constituents from the mixture which can be adsorbed. Desorption can be carried out by various means. So the common feature of the PSA family is to perform bed regeneration by depressurization and in some cases by low pressure scanning. Type processes PSA are described in US-3-430 418 or in the more general work of Yang ("gas separation by adsorption processes ", Butterworth Publishers, US, 1987). In general, PSA type processes are operated sequentially and alternately using all adsorption beds. These PSAs have had many successes in the gas sector natural, separation of compounds from air, production of solvent and in different refining sectors.

The TSA processes that use temperature as the driving force for desorption are the first to have been developed in adsorption. The bed to be regenerated is heated by a circulation of preheated gas, in open or closed loop, in the opposite direction to that of the adsorption stage. Many variations of schemes ("gas separation by adsorption processes ”, Butterworth Publishers, US, 1987) are used depending on the constraints local conditions and the nature of the gas used. This implementation technique is generally used in purification processes (drying, desulfurization of gases and liquids, natural gas purification; US-4-770 676).

Gas or liquid chromatography is a separation technique very efficient thanks to the use of a very large number of theoretical stages (BE 891 522, Seko M., Miyake J., Inada K .; Ind. Eng. Chem. Prod. Res. Develop., 1979, 18, 263). She thus makes it possible to take advantage of relatively low adsorption selectivities and to produce difficult separations. These processes are highly competitive with the continuous processes at simulated moving bed or simulated counter current. The latter have experienced very strong development in the petroleum field (US-A-3,636,121, US-A-3,997,620 and US-A-6,069,289). The regeneration of the adsorbent uses the technique of displacement by a desorbent which may optionally be separated by distillation from the extract and the raffinate.

The separation by adsorption of linear, monobranched and multibranched paraffins can be performed by two different techniques well known to those skilled in the art: separation by difference in adsorption thermodynamics, and separation by difference in kinetics of adsorption of the species to be separated. Depending on the technique used, the adsorbent chosen will have different pore diameters. Zeolites, made up of channels, are adsorbents of choice for the separation of such paraffins.

The term pore diameter is conventional for those skilled in the art. It is used to functionally define the size of a pore in terms of the size of the molecule capable of entering this pore. It does not designate the real size of the pore because it is often difficult to determine since often of irregular shape (that is to say non-circular). DW Breck provides a discussion of effective pore diameter in his book Zeolite Molecular Sieves (John Wiley and Sons, New York, 1974) at pages 633-641. The sections of the channels of zeolites being rings of oxygen atoms , one can also define the pore size of zeolites by the number of oxygen atoms forming the annular section of the rings, designated by the term "member rings" or MR in English. It is for example indicated in the “Atlas of Zeolite Structure Types” (WM Meier and DH Olson, 4 ^th Edition, 1996) that zeolites of the FAU structural type have a network of crystal channels of 12 MR, that is to say of which the section consists of 12 oxygen atoms. This definition is well known to those skilled in the art and will be used later.

The use of adsorption separation processes to fractionate charges containing linear, monobranched and multibranched paraffins is well known and many patents refer to it. Different adsorbents are recommended in these patents.
In the case of so-called “thermodynamic” separation, the adsorbent has a pore diameter greater than the critical diameter of the molecules to be separated. Thus, some patents describe the separation of multibranched paraffins from linear and monobranched paraffins by thermodynamically selective adsorption. US Pat. No. 5,107,052 proposes to preferentially adsorb multibranched paraffins on zeolites SAPO-5, AIPO-5, SSZ-24, MgAPO-5 or MAPSO-5. US-A-3,706,813 proposes the same type of selectivity on X or Y zeolites exchanged with barium. US Pat. No. 6,069,289 proposes, on the contrary, to use zeolites having selectivities inversely proportional to the degree of branching of paraffins, such as beta, X or Y zeolites exchanged with alkaline or alkaline-earth cations, SAPO- 31, MAPO-31. All the zeolites mentioned above have pore diameters of 12 MR.

In the case of so-called “diffusional” separation, the separating power of the adsorbent is due to the difference in diffusion kinetics of the molecules to be separated in the pores of the zeolite. In the case of separation of multi-branched paraffins from paraffins monobranches and linear, we can thus use the fact that the higher the degree of connection important, the more the kinetic diameter of the molecule increases, and therefore the more the kinetics of diffusion is low. So that the adsorbent can have a separation power, the adsorbent must have a pore diameter close to that of the molecules to be separated, which corresponds to zeolites with a pore diameter of 10 MR. Many patents describe the separation of linear, monobranched and multibranched paraffins by selectivity diffusional. US-A-4,717,784, US-A-4,804,802, US-A-4,855,529 and US-A-4,982 048 use adsorbents of intermediate channel size between 8 and 10 MR, the adsorbent preferred being ferrierite. US-A-4,982,052 recommends the use of silicalite. The US-A-4,956,521, US-A-5,055,633 and US-A-5,055,634 describe the use of zeolites having pores of elliptical section with dimensions between 5.0 and 5.5 Å according to the minor axis and approximately 5.5 to 6.0 Å along the major axis, and in particular the ZSM-5 and its shape dealuminated, silicalite, or of dimensions between 4.5 and 5.0 Å, and in particular the ferrierite, ZSM-23 and ZSM-11.

Zeolite adsorbents proposed for the diffusional separation of paraffins multibranches have a homogeneous structure with regard to their channel size and are not composed of only small channels (8 to 10 MR), which considerably reduces their volume adsorption capacity. These materials which sin in particular by their low adsorption capacity do not allow optimal efficiency of the unit to be obtained separation. The performance of a process combining both hydroisomerization and separation by adsorption is therefore inevitably hindered.

Summary of the invention

The present invention is based on the new use of zeolitic adsorbents with a structure mixed, composed of two types of channels of different sizes, in a section of separation of multibranched paraffins included in a hydrocarbon feed consisting of a section between C5 and C8 and containing in particular paraffins linear, monobranched and multibranched, said separation section being integrated in a process also comprising at least one hydroisomerization section. So the process of the invention is such that it comprises at least one hydroisomerization section and at minus a separation section of multibranched paraffins functioning by adsorption and containing at least one zeolitic adsorbent of mixed structure with main channels whose opening is defined by a ring with 10 oxygen atoms (also called 10 MR) and secondary channels whose opening is defined by a ring with at least 12 atoms oxygen (12 MR), the channels with at least 12 MR being inaccessible to the load to be separated only through the channels at 10 MR.

The zeolitic adsorbents targeted by the invention are zeolites which advantageously belong to the structural types EUO, NES and MWW. The NU-85 and NU-86 zeolites are also particularly suitable for implementing the process of the invention.
In a first version of the process of the invention, the process comprises at least one hydroisomerization section and at least one separation section. The hydroisomerization section comprises at least one reactor. The separation section (composed of one or more units) produces two streams, a first stream rich in di- and tribranched paraffins, possibly in naphthenes and aromatics which constitutes the base gasoline with high octane number and which is sent to the pool gasoline, a second stream rich in linear and monobranched paraffins which is recycled at the entrance to the hydro-isomerization section.

In another version of the method of the invention, the overall method comprises at least two hydroisomerization sections and at least one separation section. The separation section (composed of one or more units) produces three streams, a first stream rich in paraffins di- and tribranchées, possibly in naphthenes and aromatic which constitutes a base high octane gasoline which is sent to the gasoline pool, a second stream rich in linear paraffins which is recycled to the inlet of the first hydroisomerization section and a third stream rich in monobranched paraffins which is recycled at the entrance to the second section. Two types of implementation of this version of the process are preferred: in the first the entire effluent from the first hydro-isomerization section crosses the second section, in the second the effluents from the hydro-isomerization sections are sent to the separation section (s).

The process according to the invention thus makes it possible to obtain a gasoline pool with a high octane number by incorporating into said pool a high octane petrol base from hydroisomerization of sections between C5 and C8, such as sections C5-C8, C5-C6, C5-C7, C6-C8, C6-C7, C7-C8, C7, C8 etc

Interest of the invention

The zeolitic adsorbents used in the separation section for the implementation of the process of the invention have clearly improved adsorbent properties by compared to the adsorbents of the prior art, in particular as regards the capacity adsorption itself. Indeed, it has been surprisingly discovered that the use of a zeolitic adsorbent having at least two types of channels of distinct sizes, main channels whose opening is defined by a ring with 10 oxygen atoms and secondary channels whose opening is defined by a ring with at least 12 atoms of oxygen, has a beneficial effect on the performance of a process for the separation of multibranched paraffins included in a hydrocarbon charge consisting of a cut between C5 and C8 and containing in particular linear, monobranched paraffins and multibranched. The zeolitic adsorbent used in the separation section of the the invention combines good selectivity with an optimal adsorption capacity, allowing in particular to ensure productivity gains compared to previous adsorbents. It results in a better profitability of the process of the invention compared to the other processes associating hydroisomerization and separation by adsorption with the previous adsorbents.

The process of the invention leads to an improvement of the separation process associated with the hydroisomerization process. The combination of these processes concerns the recovery of light cuts comprising paraffinic, naphthenic, aromatic and olefins having a number of carbon atoms between 5 and 8, by hydroisomerization and recycling of low octane paraffins, that is to say linear paraffins and monobranched while multibranched paraffin, high octane, separated linear and monobranched paraffins, constitute a gas base which is sent to the petrol pool. Said base increases the octane number of the gasoline pool.

The method according to the invention aims to modify the landscape of gasoline production by reducing the aromatic content while retaining a high octane number by sending a charge consisting of a C5-C8 cut (for example obtained by direct distillation) or any intermediate cut included between C5 and C8, no longer towards reforming and hydroisomerization units of C5-C6 paraffins, but towards at least one hydroisomerization section which converts linear paraffins (nCx , x = 5 to 8) in branched paraffins and optionally monobranched paraffins (monoC _(x-1) ) in di- and tribranched paraffins (diC _(x-2) or triC _(x-3) ).

Detailed description of the invention

The process for producing a high octane gasoline base according to the invention highlights operates at least one hydroisomerization section and at least one separation section operating by adsorption and containing at least one zeolitic adsorbent. The section separation integrated into the process of the invention is designed so as to separate the multibranched paraffins linear and monobranched paraffins, contained in a load consisting of a cut between C5 and C8. Said separation section of multibranched paraffins thus produces at least two effluents, a first index effluent high octane, rich in dibranched, tribranched paraffins and possibly in compounds naphthenic and / or aromatic, and a second effluent with a low octane number rich in linear and monobranched paraffins. According to the invention, the linear paraffins and monobranches are recycled to the hydroisomerization section so as to convert them into compounds having a better octane number. Generally, the section hydroisomerization converts linear paraffins into monobranched paraffins and monobranched paraffins into multibranched paraffins.

In what follows, multibranched paraffins are understood to mean paraffins having at least two branches. According to the invention, multibranched paraffins therefore include dibranched paraffins.
The process of the invention is characterized in that said adsorbent, in the separation section, has a mixed structure with main channels, the opening of which is defined by a ring with 10 oxygen atoms (also called 10 MR) and secondary channels whose opening is defined by a ring with at least 12 oxygen atoms (12 MR), the channels with at least 12 MR being accessible only through the channels with 10 MR. It is recalled that the channels at 10 MR, respectively at 12 MR, can schematically be represented by a continuous succession of rings, each ring being made up of 10, respectively 12, oxygen atoms. The invention is in no way limited to the use of a zeolitic adsorbent having channels having a specific number of rings. In particular, it is not departing from the scope of the invention if the method of separation of multibranched paraffins is implemented with an adsorbent having 10 MR channels restricted to a single ring. These zeolitic adsorbents can have a mono-, bi- or three-dimensional structure.

According to the invention, the zeolitic adsorbent preferentially adsorbs linear paraffins, to a lesser extent monobranched paraffins and finally in a minority multibranched paraffins, naphthenic and aromatic compounds.

In a context of reduction of the aromatic content of essences, the charge treated in the process according to the invention consists of a section between C5 and C8 such that cuts C5-C8, C5-C6, C5-C7, C6-C8, C6-C7, C7-C8, C7, C8 etc from the atmospheric distillation of crude oil, a reforming unit (light reformate) or a conversion unit (hydrocracking naphtha for example). In the rest of the text, this set of possible loads will be designated by the terms "C5-C8 cuts and cuts intermediaries ”. It is mainly composed of linear, monobranched and multibranches, naphthenic compounds such as dimethylcyclopentanes, compounds aromatics such as benzene or toluene and optionally olefinic compounds.

The feed introduced into the process according to the invention comprises at least one alkane which will be isomerized to form at least one product of greater degree of branching. The filler may in particular contain normal pentane, 2-methylbutane, neopentane, normal hexane, 2-methylpentane, 3-methylpentane, 2,2-dimethylbutane, 2,3 dimethylbutane, normal heptane, 2-methylhexane, 3-methylhexane, 2,2-dimethylpentane, 3,3-dimethylpentane, 2,3-dimethylpentane, 2,4-dimethylpentane, 2,2,3-trimethylbutane, normal octane, 2-methylheptane, 3-methylheptane, 4-methylheptane, 2,2-dimethylhexane, 3,3-dimethylhexane 2,3-dimethylhexane, 3,4-dimethylhexane, 2,4-dimethylhexane, 2,5-dimethylhexane, 2,2,3-trimethylpentane, 2,3,3-trimethylpentane, 2,3,4-trimethylpentane. To the extent that the charge comes from C5-C8 cuts and / or intermediate cuts obtained after distillation atmospheric, it can also contain cyclic alkanes, such as dimethylcyclopentanes, aromatic hydrocarbons (such as benzene, toluene, xylenes) as well as other C9 + hydrocarbons (i.e. hydrocarbons containing at least 9 carbon atoms) in less quantity. The charges made up of sections C5-C8 and intermediate cuts of reformate origin may also contain hydrocarbons olefinic, in particular when the reforming units are operated at low pressure.

The paraffin content (P) essentially depends on the origin of the charge, i.e. its paraffinic or naphthenic and aromatic character, sometimes measured by the parameter N + A (sum of the naphthenes content (N) and the aromatics content (A)), as well as its initial point of distillation, i.e. the content of C5 and C6 in the feed. In the hydrocracking naphthas, rich in naphthenic compounds, or light reformates, rich in aromatics, the paraffin content in the feed will generally be low, from around 30% by weight. In C5-C8 cuts and intermediate cuts (like for example C5-C6, C5-C7, C6-C8, C6-C7, C7-C8 ...) direct distillation, the paraffin content varies between 30 and 80% by weight, with an average value of 55-60% by weight. In accordance with invention, the gain in octane is all the more important as the paraffin content of the load is higher.

In the case of a C5-C8 load or a load composed of intermediate cuts from atmospheric distillation, obtained for example at the top of naphtha splitter, the fraction heavy corresponding naphtha can feed a catalytic reforming section. In in this case, the installation of a hydro-isomerization section of these sections will cause reduction in the load rate of the reforming section, which can continue to process the C8 + heavy fraction of naphtha.

The effluent from the hydro-isomerization section can contain the same types of hydrocarbons than those described above, but their respective proportions in the mixture leads to higher octane numbers RON and MON than those of the filler.

The filler introduced into the process of the invention and containing paraffins comprising 5 to 8 carbon atoms is generally of low octane number. The method according to the invention consists in particular in increasing the octane number of said charge without increasing its content in aromatics using at least one hydro-isomerization section and at least a separation section operating by adsorption.

The octane number of the effluent of the process of the invention varies depending on the nature of the load introduced, and in particular depending on the nature of the cut. For a C5-C6 cut from the distillation of crude oil, typical values of the base RON and MON gasoline at the output of the process of the invention are of the order of 93 and 89 respectively. petrol base comprising in its composition such a petrol base therefore has a high octane number.

According to the invention, the separation section contains one or more adsorbents, at least one of the adsorbents being a zeolitic solid having a mixed structure including the microporous network has both main channels, the opening of which is defined by a ring at 10 oxygen atoms (also called 10 MR) and secondary channels whose opening is defined by a ring with at least 12 oxygen atoms (12 MR), said main channels and secondary channels being arranged in such a way that access to secondary channels of at least 12 MR is only possible via the main channels at 10 MR.

These different adsorbents have channel sizes such that each of the isomers of the C5-C8 sections or intermediate sections can be adsorbed. The diffusion kinetics of these isomers in the channels at 10 MR is however different enough to be put to profit.

According to the invention, optimal diffusive selectivity is obtained by slowing the entry of multibranched molecules via the channels at 10 MR and an optimal adsorption capacity is obtained by the presence of the channels at least 12 MR.
It goes without saying that the separation section integrated into the process of the invention is based on the difference in kinetics of adsorption of the species to be separated and thus exploits the characteristics of the so-called "diffusional" separation.

Channels at least 12 MR can be either simple side pockets (or called by those skilled in the art “side pockets”) (cf. FIG. 3) or form porous segments perpendicular to the channels at 10 MR, such that these segments are only accessible by the 10 MR channels (see Figure 4).

The adsorbents used in the separation section for implementing the process according to the invention advantageously contain silicon and at least one element T chosen from the group formed by aluminum, iron, gallium and boron, preferably aluminum and boron. The silica content of these adsorbents can be variable. The most suitable adsorbents for this type of separation are those with high silica contents. The molar ratio If / T is preferably at least equal to 10.

Said microporous adsorbents can be in acid form, that is to say containing hydrogen atoms, or preferably exchanged with alkaline or alkaline-earth cations.

It is advantageous to mix zeolites with structural type zeolites LTA, such as those described in patent US-A-2 882 243, preferably zeolite A. In most of their exchanged cationic forms, in particular in the calcium form, these zeolites have a pore diameter of the order of 5Å and have strong capacities to adsorb linear paraffins. Mixed with zeolitic adsorbents having a structure as defined above, they can make it possible to accentuate the separation of the elution fronts and therefore make it possible to obtain better purity in each of the enriched feeds obtained.

Advantageously, the zeolitic adsorbents used in the process of the invention are structural type EUO, NES and MWW zeolites. Examples of zeolites included in these families are the zeolites EU-1 (EP-A-42 226), ZSM-50 (US-A-4 640 829), TPZ-3 (US-A-4 695 667), NU-87 (EP-A-378 916), SSZ-37 (US-A-5 254 514), MCM-22, ERB-1 (EP-A-293 032), ITQ-1 (US-A-004 941), PSH-3 (US-A-4 439 409), and SSZ-25 (EP-A-231 860). The NU-85 zeolites (US-A-5,385,718 and EP-A-462,745) and NU-86 (EP-A-463,768), which have no specific structural type, are also advantageously used in the method of the invention.

EUO structural type zeolites (EU-1, ZSM-50, TPZ-3) have a one-dimensional porous network. The main channels have openings of 10 MR, and they are provided with side pockets corresponding to an opening of 12 MR. The configuration of these zeolites of structural type EUO is that presented in FIG. 3.

NES structural type zeolites (NU-87 and SSZ-37) have an interconnected two-dimensional network. They have 10 MR channels in one direction, interconnected by porous 12 MR segments, perpendicular to the 10 MR channels. The 12 MR channels are therefore only accessible by the 10 MR channels. The configuration of these NES structural type zeolites is that presented in FIG. 4.
It should be noted that the NU-85 zeolite is an intergrowth of the NU-87 and EU-1 zeolites: each crystal of NU-85 comprises discrete bands of NU-87 and EU-1, said bands having practically a continuity between them of the crystal lattice.

The NU-86 zeolite has a three-dimensional porous network. In one of the dimensions are channels with 11 oxygen atoms (11 MR). In the other two dimensions are channels with 12 oxygen atoms with restrictions at 10. Channels with 12 MR are only accessible only by the channels at 10 MR. The configuration of the NU-86 zeolite is that shown in Figure 3.

MWW structural type zeolites (MCM-22, ERB-1, ITQ-1, PSH-3, SSZ-25) have a network two-dimensional non-interconnected. One of the porous networks consists of channels of 10 MR, and the second of 12 MR channels linked together by 10 MR channels, in such a way that access to the 12 MR channels can only take place through the 10 MR channels. The configuration of these MWW structural type zeolites is that presented in FIG. 3.

Any other zeolitic adsorbent having main channels whose opening is defined by a ring with 10 oxygen atoms and secondary channels whose opening is defined by a ring with more than 12 oxygen atoms, the secondary channels being accessible to the load to be separated only by the main channels, suitable for implementation of the method of the invention.

Several versions and embodiments of the process are possible depending on the number and the arrangement of the different hydro-isomerization or separation sections and of the different recycles.

For all the versions and embodiments of the method according to the invention, the separation section or sections by adsorption using one or more adsorbents separate the multibranched paraffins from the normal and monobranched paraffins, the normal and monobranched paraffins then being recycled. According to the process variants, the separation section can be arranged upstream or downstream of the hydro-isomerization section.
The separation section integrated into the process of the present invention can use the adsorption separation techniques well known to those skilled in the art such as PSA (Pressure Swing Adsorption), TSA (Temperature Swing Adsorption), and methods chromatography (elution chromatography or simulated counter-current for example) or result from a combination of these techniques. The separation section can operate both in the liquid phase and in the gas phase. In addition, generally several separation units (from two to fifteen) are used in parallel and alternately to lead to a section operating continuously while by its nature it is discontinuous.

The operating conditions of the separation section depend on the adsorbent (s) considered, as well as the degree of purity in each of the desired flows. They are included between 50 ° C and 450 ° C for the temperature and from 0.01 to 7 MPa for the pressure. More specifically, if the separation is carried out in the liquid phase, the separation conditions are: 50 ° C to 250 ° C for temperature and 0.1 to 7 MPa, preferably 0.5 to 5 MPa, for pressure. If said separation is carried out in the gas phase, these conditions are: 150 ° C. at 450 ° C for temperature and 0.01 to 7 MPa, preferably 0.1 to 5 MPa, for pressure.

In a first preferred version of the process (FIGS. 1A and 1B for variants 1a and 1b), the hydro-isomerization section 2 comprises at least one reactor. The separation section 4 operating by adsorption, consisting of at least one unit, produces two streams, a first stream, with a high octane number, rich in di- and tribranched paraffins, possibly in naphthenes and aromatics (stream 8 for the variant 1a and 18 for variant 1b), which constitutes a petroleum base with a high octane number and can be sent to the petrol pool, a second stream rich in linear and monobranched paraffins which is recycled (7 for variant 1a and 9 for the variant 1b) at the entrance to the hydro-isomerization section 2. By “recycled” is meant both the first introduction and the reintroduction into the hydro-isomerization section of linear and monobranched paraffins, as explained below below that said separation section is arranged upstream or downstream of the hydroisomerization section.
In variant 1a, the hydro-isomerization section 2 precedes the separation section 4 whereas it is the reverse in variant 1b. Consequently in variant 1a, only the linear and monobranched paraffins are recycled to the hydro-isomerization section (stream 7). In variant 1b, all of the effluent 10 from the hydro-isomerization section 2 is recycled to the separation section 4. Said effluent therefore contains linear, monobranched and multibranched paraffins. The operating conditions of this variant of the process are in particular chosen to minimize the cracking of di- and tribranched paraffins containing more than 7 carbon atoms. In addition, in the case where the process charge includes the C5 cut, the process for recycling linear and monobranched paraffins can optionally comprise a deisopentanizer, disposed upstream or downstream of the hydro-isomerization and / or separation sections. It can in particular be placed on the load 1, between the separation and hydro-isomerization sections (flow 6 and 9) or on the recycled flows 7 and 10. Preferably, the isopentane can indeed be eliminated insofar as it does not is not isomerized to a higher degree of connection under the operating conditions of the hydro-isomerization section.

It may therefore be advantageous to add a depentaniser or the combination of a depentanizer and a deisopentanizer on at least any one of streams 1, 6, 9, 7 or 10. Isopentane, pentane or the mixture of these two bodies thus removed from the charge, can advantageously serve as an eluent for the separation section. Isopentane can also possibly be sent directly to the petrol pool due to its good index octane.

Similarly, when the cut does not contain C5 but contains C6, a deisohexanizer can optionally be placed on at least any one of streams 1, 6, 7, 9 or 10 (Figures 1A and 1B). The isohexane thus recovered can serve as an eluent for the section separation by adsorption. Preferably, isohexane is not sent to the petrol pool due to its too low octane number and must therefore be separated from streams 8 or 18 high octane number.

In general, it may be advantageous to prepare, by distillation of the charge, one or more several light fractions, which can serve as eluent for the separation section. This use of part of the load in the separation section is a very good integration of said separation section. However, this section can also use other compounds. In particular, light paraffins such as butane and isobutane can be advantageously used because they are easily separable from paraffins more heavy by distillation.

Finally, when the separation section is arranged upstream of the hydro-isomerization section (variant 1b), the quantity of naphthenic and aromatic compounds crossing the section hydroisomerization is less than in the reverse configuration (variant 1a). This limits the saturation of the aromatic compounds contained in sections C5 to C8 resulting in a lower consumption of hydrogen in the hydro-isomerization section. In addition, in the variant 1b, the volumes of the flows passing through the hydro-isomerization section are reduced by compared to variant 1a, which allows a reduction in the size of this section, and a minimization of the amount of catalyst required.

In a second preferred version of the process (Figures 2.1A, 2.1B, 2.2A, 2.2B, 2.2C, 2.2D embodiments 2.1 and 2.2; variants 2.1a and b; 2.2 a, b, c and d), the hydro-isomerization reaction is carried out in at least two separate sections, each comprising at minus one reactor (sections 2 and 3). The load is divided into three flows in at least one separation section operating by adsorption (sections 4 and possibly 5), comprising at least one unit, to lead to the production of a first stream rich in di- and tribranched, possibly in naphthenes and aromatics, of a second stream rich in linear paraffins and a third stream rich in monobranched paraffins. The rich effluent in linear paraffins is recycled to the hydro-isomerization section 2 and the effluent rich in monobranched paraffins is recycled to the hydro-isomerization section 3.

In a first embodiment (2.1) of the second version of the method, all of the effluent leaving the first hydro-isomerization section 2 is sent to the second hydroisomerization section 3. This embodiment has two variants in which the separation section, made up of one or possibly several units, is located downstream (variant 2.1a) or upstream (variant 2.1b) of the hydro-isomerization section.

In variant 2.1a (fig 2.1A), the fresh charge (flow 1) containing linear paraffins, monobranches and multibranches, as well as naphthenic and aromatic compounds, is mixed with the recycling of linear paraffins from separation section 4 (flow 30). The resulting mixture 33 is sent to the first hydro-isomerization section 2 which converts part of the linear paraffins into monobranched paraffins and part of the monobranched paraffins into multibranched paraffins. The effluent (flow 6) leaving the hydro-isomerization section 2 is mixed with recycling 39, rich in paraffins monobranched and coming from the separation section 4, then the mixture is sent to the hydro-isomerization section 3. The effluent 37 of section 3 is sent to the section of separation 4. In this section 4, a separation process in three streams is implemented to lead to the production of three effluents rich either in linear paraffins (30) or in monobranched paraffins (39), or multibranched paraffins, naphthenic compounds and aromatic (8). The effluent (8) rich in multibranched paraffins as well as in compounds naphthenic and aromatic has a high octane number, it constitutes a petrol base with a high octane number and can be sent to the petrol pool. The process of the invention leads the production of a gasoline rich in multibranched paraffins with a high octane number.

In variant 2.1b (fig. 2.1B), the fresh charge (stream 1) containing linear, monobranched and multibranched paraffins, naphthenes and aromatic compounds is mixed with stream 14 from the hydro-isomerization section 3, then the resulting mixture 23 is sent to the separation section 4 in which the charge is divided into three streams leading to the production of three effluents rich in either linear paraffins (11), monobranched paraffins (12), or multibranched paraffins, naphthenic and aromatic compounds (18). The effluent (11) rich in linear paraffins is sent to the hydroisomerization section 2. The effluent (18) rich in multibranched paraffins as well as in naphthenic and aromatic compounds has a high octane number. Said effluent (18) therefore constitutes a gasoline base with a high octane number and can be sent to the gasoline pool.
The hydroisomerization section 2 converts part of the linear paraffins into monobranched paraffins and into multibranched paraffins. To the effluent (13) from section 2, the stream rich in monobranched paraffins (12) from the separation section 4 is added. The whole is sent to the second hydroisomerization section 3 (fig. 2.1 B).

The advantages of the configurations of variants 2.1a and 2.1b are manifold. These configurations allow, in fact, to operate the two hydro-isomerization sections 2 and 3 at different temperatures and different VVH so as to minimize cracking dibranched and tribranched paraffins, which is particularly important for cuts considered. They also make it possible to minimize the amount of catalyst in the section 2 by recycling only linear paraffins to this section, which also allows to work at a higher temperature. Section 3, mainly supplied with paraffins monobranched, operates on the other hand at a lower temperature which improves the yield in di- and tribranched paraffins due to the more favorable thermodynamic balance in these conditions, while limiting the cracking of multi-branched paraffins, disadvantaged at low temperatures.

When the separation section, made up of one or more units, is arranged upstream of the hydro-isomerization section (variant 2.1b), the quantity of naphthenic compounds and aromatics crossing the hydro-isomerization section is less than in the configuration reverse (variant 2.1a). This limits the saturation of the aromatic compounds contained in the C5-C8 cut or in intermediate cuts, resulting in lower consumption of hydrogen in the process.

In the case where the charge comprises section C5, the method according to the invention in its mode of implementation 2.1 (variants 2.1a and 2.1b) may possibly include a deisopentanizer disposed upstream or downstream of the hydro-isomerization and / or separation. In particular, this deisopentanizer can be placed on flow 1 (load), between the two hydro-isomerization sections (flow 6 for variant 2.1a and flow 13 for variant 2.1b), after the hydro-isomerization section (flow 37 or 14), after the separation section on the stream rich in monobranched paraffins (stream 39 or 12). Preferably, isopentane can possibly here again be eliminated as long as it is not isomerized to a degree of higher connection under the operating conditions of the hydro-isomerization section. Isopentane can optionally serve as an eluent for the separation section. he can also be sent directly to the petrol pool because of its voucher octane number. It may be advantageous to place a depentaniser on at minus any of flows 1, 6, 37, 30 (fig. 2.1A) or 1, 11, 13 and 14 (fig. 2.1B). The combination of a deisopentanizer and a depentanizer is also optionally possible. The pentane or the mixture of pentane and isopentane thus separated can optionally serve as an eluent for the adsorption separation section. In this last case, pentane cannot be sent to the petrol pool due to its low octane number. he must therefore be separated from streams 8 and 18 of high octane.

Similarly, when the cut does not contain C5 but contains C6, a deisohexanizer can optionally be placed on at least one of the flows 1, 6, 37, 39 for the variant 2.1a (fig. 2.1A) and 1, 13, 14 and 12 for variant 2.1b (fig. 2.1B). Isohexane as well recovered can be used as eluent for the adsorption separation section. Isohexane cannot however not be sent to the petrol pool due to its too low octane number and must therefore be separated from streams 8 and 18 (fig. 2.1A and 2.1B) of high octane number.

In general, it may be advantageous to prepare one or more light fractions by distillation of the feed, which can serve as an eluent for the separation section.
These uses of part of the load in the separation section constitute a very good integration of said separation section. However, this section can also use other compounds. In particular, light paraffins such as butane and isobutane are advantageous since they are easily separable from heavier paraffins by distillation.

A second embodiment (2.2) of version 2 of the method of the invention is such that the effluents from hydro-isomerization sections 2 and 3 are sent to the section (s) separation 4 and 5. This embodiment can be divided into four variants 2.2a, 2.2b, 2.2c and 2.2d. Variants 2.2a and 2.2b (fig. 2.2A and 2.2B) correspond to the case where the process includes at least two separation sections to perform two types of separation that is to say to separate the linear paraffins and the monobranched paraffins in two separate sections. In variants 2.2c and 2.2d (fig. 2.2C and 2.2D), the section separation can consist of one or more units. Variants 2.2a, 2.2b, 2.2c and 2.2d present an optimization in the assembly of the separation and hydro-isomerization sections since they make it possible in particular to avoid the mixing of flows with high indices octane with the low index charge.

Variant 2.2a has the following steps:

The fresh charge (flow 1, FIG. 2.2A) containing linear paraffins, monobranched and multibranches, naphthenes and aromatic compounds is mixed with the effluent (36) rich in linear paraffins from separation section 4, then the resulting mixture 33 is sent to the hydroisomerization section 2 which converts part of the linear paraffins to monobranched paraffins and part of the monobranched paraffins in paraffins multi-branched. The assembly leaving the hydro-isomerization section 2 is sent to the separation section 4. Said separation section 4 leads to the production of two effluents respectively rich in linear paraffins (36) and in monobranched paraffins, multibranches, naphthenic and aromatic compounds (35). The effluent (35) is mixed with stream (12) rich in monobranched paraffins originating from the separation section 5, then sent to the hydroisomerization section 3. The hydroisomerization section 3 converts part of the monobranched paraffins into multibranched paraffins. The assembly (flow 31) leaving the hydro-isomerization section 3 is sent to the separation section 5. In said section, a process of separation into two streams is implemented to lead to the production of two effluents, one rich in monobranched paraffins (12), the other rich in multi-branched paraffins (8). Effluent 8 (fig. 2.2A) rich in di- and tribranched paraffins as in naphthenic and aromatic compounds has a high octane number, it constitutes a petroleum base with high octane number and can be sent to the petrol pool.

Variant 2.2b differs from variant 2.2a in that the separation sections 4 and 5 (fig. 2.2B) are placed before the hydroisomerization sections 2 and 3. In this configuration, the charge 1 is mixed with the effluent (17) from the hydro-isomerization section 2, then the resulting mixture (23) is sent to separation section 4. Said section produces two fluxes respectively rich in linear paraffins (16) and in monobranched paraffins and multi-branch (32).

The flow (16) is sent to the hydro-isomerization section 2 to produce the effluent (17). The effluent (32) is mixed with the stream (15) from the hydro-isomerization section 3, then the mixture is sent to separation section 5. Said section produces two effluents, one rich in monobranched paraffins (34), which is sent to the hydro-isomerization section 3, the other rich in multibranched paraffins, naphthenic and aromatic compounds (18), which has a high octane number and constitutes a petroleum base with a high octane number. The effluent (18) can therefore be sent to the petrol pool.

In variant 2.2c (fig. 2.2C) the separation section 4 consists of one or more several units, and is located between two hydro-isomerization sections (2 and 3). In this configuration, the charge 1 is mixed with the effluent rich in linear paraffins from the separation section 4, and the resulting mixture 33 is sent to the hydro-isomerization section 2. This produces an effluent (19) of higher octane rating than that of the charge. This effluent (19) is mixed with the effluent (22) from the hydro-isomerization section 3, then the assembly is sent to the separation section 4. This section produces three streams (20, 21 and 28). The stream (21) rich in monobranched paraffins is sent to the hydro-isomerization section 3 which converts these paraffins into higher degrees of branching. The flow (28), rich in multibranched paraffins, naphthenic and aromatic compounds, presents a high octane number and constitutes a petroleum base with high octane number. The effluent (28, fig. 2.2C)) can therefore be sent to the petrol pool.

In variant 2.2d (fig. 2.2D), the separation section which consists of one or more several units, is placed upstream of the two hydro-isomerization sections. In this configuration, the load 1 is mixed with the recycled flows (25) and (27) from hydro-isomerization sections 2 and 3 respectively. The resulting stream (23) is sent to the separation section 4. This produces three effluents (24), (26) and (38). The flow (24), rich in linear paraffins, is sent to the hydro-isomerization section 2 which converts these paraffins in higher degrees of branching. Flux (26), rich in paraffins monobranched is sent to the hydro-isomerization section 3 which also converts these paraffins in higher degrees of branching. The stream (38) rich in paraffins multibranches, aromatic and naphthenic compounds, has a high octane number and constitutes a petroleum base with a high octane number. The effluent (38, fig. 2.2D) can therefore be sent to the petrol pool.

The advantages of the implementation mode 2.2 are multiple. It allows, as for the mode of implementation 2.1, to operate the reactors of the hydro-isomerization sections at different temperatures and different VVH so as to minimize the cracking of di- and tribranched paraffins. It also leads to minimizing the amount of catalyst by recycling to the hydroisomerization section 2 only the linear paraffins, which allows to work at higher temperature and therefore to minimize the amount of catalyst in this section. The hydroisomerization section 3, mainly supplied with monobranched paraffins for 2.2b, c and d and in mono and multibranched paraffins for 2.2a, operates at a lower temperature, which improves the yield of di- and tribranchées because of the more favorable thermodynamic equilibrium under these conditions, while limiting the cracking of multi-branched paraffins, disadvantaged at low temperatures. This configuration (with the exception of variant 2.2d) also makes it possible to avoid mixing the flows with high octane numbers with low index fluxes. Thus, the recycling flows (36, fig. 2.2A) and (20, fig. 2.2C) rich in linear paraffins are mixed with the filler 1. The flow 12 rich in monobranched paraffins is mixed with the stream (35) rich in paraffins monobranches and multibranches. Finally, the flows (15) and (22) from the hydro-isomerization sections 3 are respectively mixed with the streams (32) and (19) of higher octane number to that of the load.

In variants 2.2b and 2.2d (fig. 2.2B and 2.2D), the arrangement of the separation sections 4 and optionally 5 with respect to the hydro-isomerization sections 2 and 3 is such that the quantity of naphthenic and aromatic compounds crossing the hydro-isomerization section is less than in configuration 2.2a. This limits the saturation of aromatic compounds contained in section C5-C8 or in intermediate sections where consumption less hydrogen in the process. Similarly, in variant 2.2c, the arrangement of the separation section 4 relative to the hydro-isomerization section 3 makes it possible to reduce the hydrogen consumption in the latter.

As in the case of embodiment 2.1, when the load comprises a section C5, the method according to embodiment 2.2 may optionally include a deisopentanizer located upstream or downstream of the separation and hydroisomerization sections. In particular, this deisopentanizer can be placed on the feed stream 1, on any of the feeds 1, 6, 35, 40, 31, 12 (fig. 2.2A), on any of the flows 1, 32, 34, 15, 17 (fig. 2.2B), on one any of flows 19, 21, 22 (fig 2.2C) and on any of flows 23, 25, 26 and 27 (fig 2.2D). It may also be possible to place a depentaniser on one any of flows 1, 6 and 36 (variant 2.2a) or 1, 16 and 17 (variant 2.2b), 1, 19 and 20 (variant 2.2c) or 1, 23, 24, 25 (variant 2.2d). The combination of a deisopentanizer and a depentaniser is also possible. Isopentane, pentane or mixture of pentane and isopentane thus separated can optionally serve as eluent for the separation section by adsorption. In the latter case, preferably the pentane is not sent to the pool gasoline due to its low octane number. It is therefore preferably separated from streams 8, 18, 28 and 38 (fig. 2.1A and 2.1B) of high octane numbers. Isopentane, on the contrary, is preferably sent to the petrol pool with flows 8, 18, 28 and 38 due to its good octane number.

As for the implementation mode 2.1, when the section does not contain C5 but contains C6, a deisohexanizer can optionally be placed on any of the flow 1, 6, 35, 40, 31 and 12 (fig. 2.2A) or 1, 32, 34, 15 and 17 (fig. 2.2B) or 19, 21, 22 (fig. 2.2C) or 23, 25, 26 and 27 (fig. 2.2D). The isohexane thus recovered can serve as an eluent for the section separation by adsorption. Preferably, isohexane is not sent to the pool gasoline due to its too low octane number. It is preferably separated from flows 8, 18, 28 and 38 (fig. 2.2A, 2.2B, 2.2C, 2.2D) of high octane numbers. This use of a part of the load in the separation section constitutes a very good integration of the process. However, this section can also use other compounds as eluent for the adsorption separations. In particular, light paraffins such as butane and isobutane are interesting since they are easily separable from heavier paraffins by distillation.

It will be recalled that each separation section integrated into the process of the invention can be composed of several units, at least one of which contains a zeolitic adsorbent having the characteristics defined above, namely at least the presence of at least two types channels, main channels whose opening is defined by a ring with 10 atoms oxygen (10 MR) and secondary channels whose opening is defined by a ring at at least 12 oxygen atoms (at least 12 MR), said secondary channels being accessible to the load to be separated only by said main channels. When said section separation is made up of several units and at least one of these units contains a zeolitic adsorbent having the characteristics defined above, the other (s) unit (s) may (may) contain a different adsorbent such as silicalite. It is not no more excluded from mixing in the same unit a zeolitic adsorbent having the characteristics defined previously with another adsorbent such as those used in prior art.

For each of these variants and these implementations, the hydro-isomerization of the light sections can be carried out in the gas, liquid or mixed liquid-gas phase in one or more reactors where the catalyst is used in a fixed bed. For example, it is possible to use a catalyst from the family of bifunctional catalysts, such as catalysts based on platinum or of sulphide phase on an acid support (chlorinated alumina, zeolite such as mordenite, SAPO, zeolite Y, zeolite beta) or of the family of acid monofunctional catalysts, such as chlorinated alumina, sulfated zirconia with or without platinum and promoter, heteropolyacids based on phosphorus and tungsten, oxycarbons and molybdenum oxynitrides which are usually classified among monofunctional catalysts of metallic character. They operate in a temperature range between 25 ° C, for the most acidic of them (heteropolyanions, supported acids) and 450 ° C, for bifunctional catalysts or molybdenum oxycarbons. The chlorinated aluminas are preferably used between 80 and 110 ° C and the platinum-based catalysts on a support containing a zeolite between 260 and 350 ° C. The operating pressure is between 0.01 and 0.7 MPa, and depends on the concentration of C5-C6 in the feed, the operating temperature and the H ₂ / HC molar ratio. The space velocity, measured in kg of feed per kg of catalyst and per hour, is between 0.5 and 2. The molar ratio H ₂ / hydrocarbons is generally between 0.01 and 50, depending on the type of catalyst used. work and its resistance to coking at operating temperatures. In the case of low H ₂ / HC ratios, for example H ₂ / HC = 0.06, it is not necessary to provide for recycling of the hydrogen, which makes it possible to save a separator flask and a hydrogen recycling compressor.

The hydro-isomerization section may include one or more reactors arranged in series or in parallel which may contain for example one or more of the catalysts mentioned above. For example, in the case of variants 1a and 1b, the hydro-isomerization section 2 includes at least one reactor, but may include two or more reactors arranged in series or in parallel. In the case of variants 2.1a and b, and 2.2 a, b, c and d, the sections hydro-isomerization 2 and 3 can optionally each comprise, for example, two reactors possibly containing two different catalysts. Sections 2 and 3 can optionally also each comprising several reactors in series and / or in parallel, with different catalysts depending on the reactors.

Similarly, each separation section can consist of one or more units allowing overall separation into two or three effluents rich in linear paraffins, monobranches and multibranches, naphthenic compounds and aromatics. Thus, each of the separations 4 and / or 5 of any of the variants 2.1a or b, 2.2 a, b, c or d, includes at least one separation unit which may be substituted by two or more separation units, arranged in series or in parallel.

The process according to the invention leads to the production of a gasoline pool with a high octane number thanks to the incorporation in its composition of a high octane gasoline base obtained according to the method of the invention.

Downstream of the hydro-isomerization section, it will generally be advantageous to have a load stabilization column in order to limit the voltage of the load to an acceptable value isomerate vapor. This control of the vapor pressure will be obtained by eliminating a certain amount of volatile compounds, such as C1-C4, following good techniques known to those skilled in the art. In the absence of hydrogen recycling, the hydrogen may be separated from the load in the stabilization column. In case the correct operation of one of the isomerization catalysts used upstream requires the addition in the feed of a chlorinated agent upstream of the hydro-isomerization section, the column of separation will also allow the elimination of the hydrogen chloride formed. In this case, it it is advantageous to mount a gas washer from the stabilization in order to limit the releases of acid gases to the atmosphere.

• un volume moindre de la section d'hydro-isomérisation
• les aromatiques présents dans la charge ne sont pas saturés, d'où une moindre consommation d'hydrogène dans le procédé et une réduction moins importante de l'indice d'octane de l'effluent.

As described above, the separation section can be arranged upstream (Figures 1B, 2.1B, 2.2B, 2.2D) or downstream (Figures 1A, 2.1A, 2.2A, 2.2C) from the section of hydroisomerization. In the first case, most of the naphthenic and aromatic compounds avoid the hydro-isomerization section, which has at least two important consequences:

• less volume of the hydro-isomerization section
• the aromatics present in the feed are not saturated, hence a lower consumption of hydrogen in the process and a less significant reduction in the octane number of the effluent.

In the second case (Figures 1A, 2.1A, 2.2A and 2.2C), the aromatic compounds and Naphthenics cross all or at least part of the hydro-isomerization section. It may then be necessary to add, immediately upstream of the isomerization section (if there is only one) or from the first isomerization section (if there is more than one), a reactor saturation of aromatic compounds. The criterion used for the addition of a saturation could be, for example, an aromatic content in the feed greater than 5% weight.

As illustrated in Figures 2.1A; 2.1B; 2.2A, 2.2B, 2.2C and 2.2D, there may also be have at least two hydro-isomerization sections 2 and 3 with recycling, at the top of the section 2, a stream rich in linear paraffins and recycling at the top of section 3, a stream rich in monobranched paraffins. Such an arrangement makes it possible to operate the second section at a lower temperature than the first, which reduces the cracking of mono- and paraffins multibranches formed in the first section, in particular the cracking of paraffins tribranched such as 2,2,4 trimethylpentane which gives isobutane very easily by acid cracking.

The examples which follow in no way limit the scope of the invention.

EXAMPLES

The diffusional selectivity tests (examples 1b and 2b) are carried out with a mixture of a feedstock coming from a hydroisomerization reactor and containing normal hexane (nC6), 2-methylpentane (2MP) and 2, 2-dimethylbutane (2,2DMB). The RON and MON of these compounds are given in the table below: paraffin nC6 2MP 2,2DMB RON 24.8 73.4 91.1 MY 26 74.2 93.4

EXAMPLE 1 (according to the invention)

The zeolitic adsorbents studied are the EU-1 zeolites (one-dimensional structure with side pockets) and NU-87 (two-dimensional structure). These zeolites are in their Na ⁺ exchanged form, that is to say that each of the crude synthesis zeolites, once calcined, has undergone three successive ionic exchanges in a 1N NaCl solution, at ambient temperature. The EU-1 zeolite has an Si / B ratio equal to 24 and the NU-87 zeolite has a Si / Al ratio equal to 16.

a) adsorption capacity:

The adsorption capacities of EU-1 and NU-87 were measured by gravimetry at different temperatures (100 and 200 ° C) for a partial pressure of 200 mbar of isopentane (iC5) using a SETARAM TAG 24 symmetrical thermobalance. Before each adsorption measurement, the solids are regenerated for 4 hours at 380 ° C. The results are found in Table 1 below: adsorption capacity of EU-1 and NU-87 zeolites Temperature (° C) Mass of iC5 adsorbed (mg.g ^-1 ) with a partial pressure of iC5 of 200 mbar EU-1 NU-87 100 80.3 92.9 200 49.6 58.8

b) diffusion selectivity:

The diffusional selectivities of normal hexane (nC6), 2-methylpentane (2MP) and 2,2-dimethylbutane (2,2DMB) were experimentally determined by reverse chromatography. To do this, the response of a fixed zeolite bed to a concentration disturbance of the "impulse" type was measured. A 10 cm column filled with 1.4 g of zeolite, maintained at a constant temperature of 200 ° C., is crossed by a nitrogen flow at 1 nl / h. The pressure in the column is 1 bar and the operation is carried out in the gas phase. The responses of the column to the injections of the various hydrocarbons were measured. The results obtained are summarized in Table 2, in the form of the first moment (µ ₁ ) or average exit time and the second moment (µ c / 2) or variance of the curves. The so-called “moments” analysis (cf. p. 246 in the work of D. Ruthven “Principles of Adsorption and Adsorption Processes”, John Wiley and Sons, New York, 1984) teaches us that overall resistance to the transfer of subject noted R can be calculated using the equation below: R = μ vs 2 2 · μ 2 1 · The v where L is the length of the bed and v the pore velocity in the bed.
This resistance is also noted in Table 2. zeolite Temperature (° C) Hydrocarbon µ ₁ (min) µ c / 2 (min ² ) R (min) EU-1 200 nC6 54.3 2074.1 5.1 2 MP 20.6 330.1 5.6 2.2 DMB 0 0 ∞ Nu-87 200 nC6 59.3 1220.5 2.5 2 MP 40.1 1068.3 4.8 2.2 DMB 13.1 546.1 22.9

The ratio □ is calculated between the overall resistances of 2MP and 2.2DMB and between the overall resistances of 2MP and nC6 to assess the diffusive selectivity of the EU-1 and NU-87 zeolites in the separation of these three hydrocarbons. The values for □ have been calculated at 200 ° C for EU-1 and NU-87. These values are noted in Table 3. zeolite Temperature (° C) □ (2MP / 22DMB) □ (2MP / nC6) EU-1 200 ∞ 1.1 NU-87 200 4.76 1.9

Example 2 (comparative):

The same tests are repeated as those given in Example 1 and under the same operating conditions using as zeolitic adsorbent the silicalite zeolite with three-dimensional structure. Silicalite belongs to the structural type MFI and has only 10 MR channels. It is in its Na ⁺ exchanged form and has an Si / Al ratio of 250.

a) adsorption capacity:

Temperature (° C) Mass of iC5 adsorbed (mg.g ^-1 ) with a partial pressure of iC5 of 200 mbar 100 47.0 200 24.0

From the results presented in Tables 1 and 4, it can be seen that the capacities adsorption of EU-1 and NU-87 zeolites are higher than the adsorption capacities of silicalite at the temperatures studied. The adsorption capacity in iC5 is approximately 1.9 times higher than that of silicalite for EU-1 and 2.2 times for NU-87.

b) diffusion selectivity:

zeolite Temperature (° C) Hydrocarbon µ ₁ (min) µ c / 2 (min ² ) R (min) silicalite 200 nC6 28.7 321.5 2.8 2 MP 16.3 388.5 3.2 2.2 DMB 7.5 183.0 13.3 zeolite Temperature (° C) □ (2.2DMB / 2MP) □ (2MP / nC6) silicalite 200 4.17 1.2

From the results presented in Tables 3 and 6, it can be seen that the EU-1 and Nu-87 have very interesting diffusional selectivities for the separation of hydrocarbons at different degrees of connections. In particular, the 2,2DMB does not penetrate at all in the pores of the EU-1 zeolite (Table 2) under the experimental conditions data above, and the selectivity of this zeolite for the separation of 2,2DMB and 2MP is therefore infinite, therefore much greater than that of silicalite. The NU-87 zeolite presents at 200 ° C a better selectivity for the separation of 2.2DMB and 2MP than silicalite, and it also has better selectivity than silicalite for the separation of 2MP and of nC6.

In conclusion, the NU-87 and EU-1 zeolites have better adsorption capacity than silicalite and a generally better diffusive selectivity making it possible to guarantee a gain in productivity compared to a separation section of multi-branched paraffins using silicalite and therefore better profitability of the process of the invention combining hydroisomerization and separation by adsorption than another process also combining hydroisomerization and separation by adsorption but with an adsorbent not having the same characteristics as those defined in the invention.

Claims (22)

Process for the production of a gasoline base with a high octane number by hydroisomerization of a charge consisting of a cut between C5 and C8, comprising at least one hydroisomerization section and at least one separation section operating by adsorption, characterized in that said separation section contains at least one adsorbent having at least two types of channels, main channels whose opening is defined by a ring with 10 oxygen atoms (10 MR) and secondary channels whose opening is defined by a ring with at least 12 oxygen atoms (at least 12 MR), said secondary channels being accessible to the charge to be separated only by said main channels. Process according to Claim 1, characterized in that the said adsorbent in the separation section contains silicon and at least one element T chosen from the group formed by aluminum, iron, gallium and boron, the molar ratio Si / T being at least equal to 10. Process according to Claim 1 or 2, characterized in that the said zeolitic adsorbent in the separation section is a zeolite of structural type EUO. Process according to Claim 1 or 2, characterized in that the said zeolitic adsorbent in the separation section is a zeolite of the NES structural type. Process according to Claim 1 or 2, characterized in that the said zeolitic adsorbent is a zeolite of the MWW structural type. Process according to Claim 1 or 2, characterized in that the said zeolitic adsorbent in the separation section is the zeolite NU-85. Process according to Claim 1 or 2, characterized in that the said zeolitic adsorbent in the separation section is the zeolite NU-86. Method according to one of claims 1 to 7 characterized in that said zeolitic adsorbent is mixed with a zeolite of structural type LTA. Process according to one of Claims 1 to 8, characterized in that it comprises at least one hydro-isomerization section (2) and at least one separation section (4) by adsorption, in which the hydro-isomerization section (2 ) comprises at least one reactor, the separation section (4) comprises at least one unit and produces at least two streams, a first stream (8, 18) rich in di- and tribranched paraffins, optionally in naphthenes and aromatics which is sent to the gasoline pool, a second stream (7, 9) rich in linear and monobranched paraffins which is recycled at the entrance to the hydro-isomerization section (2). Process according to one of Claims 1 to 8, characterized in that it comprises at least two hydroisomerization sections (2, 3) and at least one separation section (4), in which the separation section produces three flows, a first stream (8, 18, 28, 38) rich in di- and tribranched paraffins, possibly in naphthenes and aromatics which is sent to the petrol pool, a second stream (11, 16, 20, 24, 30, 36) rich in linear paraffins which is recycled at the entrance to the first hydroisomerization section and a third stream (12, 21, 26, 34, 35, 39) rich in monobranched paraffins which is recycled at the entrance to the second hydroisomerization section ( 3). Method according to claim 10, characterized in that all of the effluent from the first hydroisomerization section (2) passes through the second section (3). Method according to claim 11, characterized in that the separation section (4) is located downstream of the hydroisomerization sections (2, 3), the charge (1) is mixed with the recycling of paraffins (30) from the section separation (4), the resulting mixture (33) is sent to the first hydroisomerization section (2), the effluent leaving the first hydroisomerization section is mixed with the stream rich in monobranched paraffins (39) from the separation section (4), then the mixture is sent to the second hydroisomerization section (3) and the effluent (37) from this last section is sent to the separation section (4). Method according to claim 11, characterized in that the separation section (4) is located upstream of the hydroisomerization sections (2, 3), the charge (1) is mixed with the stream (14) from the second section of hydroisomerization (3), then the resulting mixture (23) is sent to the separation section (4), the effluent rich in linear paraffins (11) is sent to the first hydroisomerization section (2), the flow is added rich in monobranched paraffins (12) coming from the separation section (4) with the effluent (13) coming from the first hydroisomerization section (2), and the whole is sent to the second hydro- isomerization (3). Process according to claim 10, characterized in that the effluents from the hydroisomerization sections are sent to at least one separation section. Process according to any one of Claims 1 to 14, characterized in that at least one light fraction is separated by distillation upstream or downstream from the hydroisomerization (2, 3) and / or separation (4, 5) sections ). Process according to any one of Claims 1 to 14, characterized in that the charge contains the section C5 and at least one deisopentanizer and / or at least one depentanizer are arranged upstream or downstream of the hydro-isomerization sections (2 , 3) and / or separation (4, 5). Process according to any one of Claims 1 to 14, characterized in that the charge contains the cut C6 but does not contain C5, and at least one deisohexanizer is placed upstream or downstream of the hydro-isomerization sections (2 , 3) and / or separation (4, 5). Process according to any one of Claims 15 to 17, characterized in that the light fraction, or isopentane and / or pentane and / or the mixture of these two bodies, or hexane, serve as eluent for the adsorption separation section. Process according to any one of Claims 1 to 18, characterized in that butane and / or isobutane is used as eluent for the separation section by adsorption. Method according to claim 16, characterized in that the isopentane is sent to the petrol pool. Process according to any one of Claims 1 to 20, characterized in that the hydro-isomerization is carried out at temperatures between 25 ° C and 450 ° C, at a pressure between 0.01 and 0.7 MPa, at a space speed, measured in kg of feed per kg of catalyst and per hour, of between 0.5 and 2, and with a H2 / hydrocarbon molar ratio of between 0.01 and 50. Process according to any one of Claims 1 to 21, characterized in that the separation is carried out at temperatures between 50 ° C and 450 ° C and at a pressure between 0.01 and 7 MPa.

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