MXPA98009777A - Procedure for the separation of a c5-c8 load or an intermediary load, in three respectively rich effluents in linear, monorramified and multi-graphic paraffines - Google Patents

Abstract

The present invention relates to a separation process that allows having three effluents respectively rich in linear paraffins, in monorbrated, di-branched, trirramified paraffins and optionally in naphthenic and / or aromatic and olphinic compounds. This procedure employs at least two separation units that function either by adsorption or by permeation. The process of the invention is particularly useful when coupled with a hydroisomerization process because it allows a selective recirculation of the real and mono-branched paraffins necessary for paraffins comprising at least 7 carbon atoms.

Description

PROCEDURE FOR SEPARATION OF A LOAD C5-C8 OR ONE ITERMEDIARY LOAD, IN THREE RESPECTIVELY RICH EFFLUENTS IN LINEAR, MONORRAMIFIED AND MULTIRRAMMED PARAFFINS FIELD OF THE INVENTION The invention relates to a separation process which makes it possible to obtain three effluents, respectively rich in linear paraffins, in monoframed paraffins and in diradified paraffins, trirramified and optionally in naphthenic and / or aromatic compounds, from C5-C8 cuts or intermediates (C5-C7, C6-C8, C7-C8, C6-C7, C7 or C8), which include paraffinic, naphthenic, aromatic and olefinic hydrocarbons. The separation process according to the invention implements at least two separation units that function either by absorption or by permeation. The procedure can also result from the combination of these two separation techniques. The process is adapted to operation in liquid phase or gas phase. In the case where the separation uses at least one adsorption unit, the separation can be carried out from adsorbents capable of preferentially adsorbing the linear paraffins, REF .: 028878 or from adsorbents capable of preferentially adsorbing monorbrated paraffins. In the case where the separation is effected by permeation, the separation of the isomerate can be carried out using a gas permeation or pervaporation technique. The separation process according to the invention is particularly useful when coupled with the hydroisomerization process as described in the patent application entitled "High octane gasoline, and its production by a procedure combining hydroisomerization and separation ", deposited on the same day by the Applicant, then allows a selective recirculation of the linear and monoframed paraffins, necessary for the paraffins comprising at least 7 carbon atoms.

BACKGROUND OF THE INVENTION In the case where the loading of the process comprises the cut C5, the isopentane left from this cut can be separated either by the process according to the invention with the monorbrated paraffins, or be removed from the flow through the process with the aid at least one deisopentanizer placed upwards and / or downwards of the different separation units. In the latter case, the isopentane can serve as an eluent or as a scanning or scanning gas, respectively in the separation units by adsorption or by permeation. The consideration of the increased environmental obligations produced by the elimination of the compounds of lead in gasolines, effective in the United States and Japan and in generalization in Europe. In a first period, the aromatic compounds, main constituents of reforming gasolines, isoparaffins produced by aliphatic alkylation or isomerization of light gasoline have compensated for the loss of octane number that results from the suppression of lead in gasolines. Accordingly, oxygenates such as Methyl Tertiary Butyl Ether (MTBE) or Ethyl Tertiary Butyl Ether (ETBE) have been introduced into fuels. Recently, the recognized toxicity of compounds such as aromatics, in particular benzene, olefins and sulfur compounds, as well as the intention to reduce the vapor pressure of gasoline, have caused the production of reformulated gasoline in the United States. . For example, the maximum amounts in olefins, total aromatics and benzene, in gasolines distributed in California in 1996 are respectively 6% vol., 25% vol., And 1% vol. In Europe, the specifications are more severe; nevertheless, the foreseeable trend is a similar reduction in the maximum amounts of benzene, in aromatic compounds and in olefins in the gasolines produced and sold. The "gasoline communities" comprise several components. The main components are reforming gasoline, which commonly comprises between 60 and 80% vol. of aromatic compounds, and catalytic cracking (FCC) essences, which typically contain 35 vol.%. of aromatics but provide most of the olefinic and sulfur compounds present in the essences. The other components may be the alkylates, without aromatic or olefinic compounds, light isomerized or non-isomerized gasolines, which do not contain unsaturated compounds, oxygenated compounds such as MTBE and butanes. To the extent that the maximum aromatic quantities are not reduced below 30 or 40% vol., The contribution of the reformed in the "gasoline communities" will still be important, typically 40% vol. An increased severity of the maximum allowable amount of aromatic compounds at 20 or 25% vol. It will lead to a decrease in the use of reforming, and consequently the need to valorize C7-C10 direct distillation cuts through other routes than the reformed one. Its valorization by hydroisomerization is one of the possible routes, as described in the patent application entitled "High octane gasoline, and its production by a process that combines hydroisomerization and separation", registered the same day by the Applicant The hydroisomerization process leads to the formation of multi-branched compounds from the compounds of low octane numbers. It can only be used in the condition of recirculation of linear and monoframed paraffins in C7-C10, since the hydroisomerization reaction is balanced and that these paraffins with low octane numbers can not be sent to the <; < petrol community ». In addition, different hydroisomerization conditions should be put into practice for these isomeric paraffins in order to avoid cracking, or reformation of the more branched paraffins. These two points justify the search for separation procedures that allow obtaining three different effluents, respectively an effluent rich in linear paraffins, an effluent rich in monoframed paraffins and an effluent rich in multi-branched paraffins and eventually in naphthenic and / or aromatic compounds.

The use of separation processes by adsorption or permeation to effect the separation of linear, monoframed and multi-branched paraffins has already been the subject of several patents (for example US-A-4 717 784, 4 956 521 and 5 233 120, BE-A-891 522, FR-A-2 688 213, US-A-5 055 633, 4 367 364 and 4 517 402). However, these patents do not apply, on the one hand, to the light fraction C5-C6, and refer only to the separation of these distillation cuts into two effluents, one with a low octane number and the other with high octane number. Also, US-A-4 210 771 and 4 709 116 describe the separation of linear paraffins from a C5-C6 naphtha cut using an ascorbent known in the industry under the name of zeolite 5A in calcium. Likewise, US-A-4 367 364 discloses this same separation effected with the aid of silicalite (US-A-4 061 724). The separation processes described in these patents are frequently coupled to an isomerization process of linear paraffins since they have a low octane number. In the same way, certain patents (such as US-A-4 717 784 and 5 055 633) describe the procedures they allow to perform; the separation of linear paraffins and monorbrated paraffins from a C5-C6 cut. These linear and monoframed paraffins constitute the community of low octane index, when the multi-branched paraffins constitute the community of high octane index. In this case, these patents emphasize the interest of using adsorbents such as ferrierite (US-A-4 804 802 and 4 717 784), zeolites ZSM-5 (US-A-3 702 886), ZSM-11 (US-A-4 108 881), ZSM-23 (US-A-4 076 842) and ZSM-35 (US-A-4 016 245) and silicalite (US-A-5 055 633), since these adsorbents adsorb both the linear paraffins and the monorbrated paraffins of the C5-C6 cuts or fractions and exclude the paraffins of higher branching grades. During the operation of such adsorbers, the isopentane is separated from the charge and is produced in the community of low octane number, with the linear and monoframed paraffins, when this compound has a strong octane number. The patent US-A-5 055 633 therefore emphasizes the interest of an implementation that allows to produce the isopentane with the flux rich in multirrified compounds, naphthenic and / or aromatic compounds from a C5-C6 filler. It contains at least 10 mol% isopentane, as well as the C7 + compounds in amounts less than 10 mol%. Such a procedure leads to a secondary stream rich in linear and monoframed paraffins that can be sent to an isomerization reactor. These patents do not contemplate effecting the fractionation in three effluents of cuts C5-C6 within the framework of its isomerization for two reasons: on the one hand, the octane number of monorbrated paraffins in C5-C6 is often considered sufficient for these compounds to be sent to the gasoline community, in which case these paraffins are separated with the multi-branched paraffins. On the other hand, when linear paraffins and monoframed paraffins are recirculated towards isomerization, it is not useful to separate them, since these compounds can be isomerized under the same operating conditions, contrary to the harder cuts or fractions such as those related by the present invention. US-A-5 055 634 is the only one to describe a process that can lead to three flows respectively rich in linear paraffins, mono-branched and multi-branched from a light cut C5-C6, but are the main interest, as that of the US-A-5 055 633 patent process, resides in the possibility of separating and producing isopentane with the flow rich in multirrified paraffins. The loading of such a process contains at least 10% isopentane. It is centered on C5-C6 and can sometimes contain small amounts of paraffins comprising seven carbon atoms or more. In consecuense, the process described in the patent is applied for the amounts of these C7 + compounds below 10% nolar. This method comprises putting into practice two units arranged in series. The charge arrives in the first unit which contains an adsorbent capable of selectively retaining the linear paraffins. The effluent of this unit is constituted as a consequence of mono and multirrified paraffins. This abnormal effluent is then introduced into the second unit filled with an adsorbent capable of preferably retaining the monorbrated paraffins with the exception of the isopentane, which is produced with the multirrified paraffins. This patent indicates that the regeneration of two units is carried out with the help of a non-adsorbable gas such as hydrogen, for example. This runs through the second unit first and allows desorbing the monoframed paraffins. At least a part of this flow is then sent to the first unit and allows to desorb the linear paraffins that are contained. The regeneration thus effected leads to mixing a part of the monorbrated paraffins to the linear paraffins previously separated with the exception of the isopentane, which is recovered with the compounds of high or high octane numbers in the production flow. In a preferred version of this method, the desorption flow assembly or assembly that leaves the second unit runs through the first in order to minimize the amount of non-adsorbable gas needed to regenerate the assembly or assembly of two units. In the latter case, the process produces no more than two streams, the first rich in multirrurated paraffins, naphthenic, aromatic and isopentane compounds, ^ 1 second rich in linear and monoframed paraffins. Such separation can then be effected with the aid of a single adsorber containing two types of adsorbents according to the example given in this patent. The techniques of separation by adsorption used by these different patents in order to enhance the cuts or fragments C5-C6, are those known to the person skilled in the art. Thus, the adsorption separation process may be of the PSA type (Pressure S ing Adsorption (Pressure Swing Adsorption)), TSA (Temperature Swing Adsorption (Temperature Swing Adsorption)), chromatographic (simulated elution or countercurrent chromatography, for example) or result from a combination of these techniques. These processes have in common to contact a liquid or gaseous mixture with a fixed bed of adsorbent in order to remove certain constituents of the mixture that can be adsorbed. The desorption can be done by different means. Thus, the common characteristic of the PSA family is to effect the regeneration of the bed by depressurization and in certain cases by low pressure sweeping. Procedures of the PSA type are described in US-A-3 430 418 or in the more general work of Yang ("Gas Separation by Adsorption Processes," Butterworth Publishers, US, 1987"). Cycles based on the use of Different bed arrangements are, in particular, described in detail.In general, PSA-type procedures are operated sequentially and using all adsorption beds alternately.These PSAs have achieved numerous events in the field of natural gas, Separation of the compounds from the air, the production of solvent and in different sectors of the refining.The TSA procedures, which use temperature as the driving force of desorption, are the first to have been developed in adsorption. The bed to regenerate is to ensure by a preheated gas circulation, in a ring or open or closed circuit, in the opposite direction of that of the adsorption stage. is of schemes (see also: "Gas Separation by Adsorption Processes", Butterworth Publishers, US, 1987) are used depending on local tensions or obligations and on the nature of the gas used. This technique put into practice is generally used in purification procedures (drying, desulfurization of gas and liquids, purification of natural gas (US-A-4 770 6"c)). Chromatography, gas phase or liquid phase is a very effective separation technique thanks to the implementation of a large number of theoretical stages, thus allowing to take advantage of relatively weak adsorption selectivities and perform difficult separations The N-ISELF® procedures of Elf Aquitaine (BE-A-891 522) for the separation of n / isoparaffins and ASAHI (Seko M., Miyake J., Inada K., Ind. Eng. Chem. Prod. Res. Develop., 1979, 18, 263) for the separation of paraxylene and ethylbenzene from an aromatic C8 cut or fraction, present this type of operation. These procedures are strongly concurrent or used by the continuous simulated or countercurrent moving bed procedures. The latter have known a very strong development in the oil field (US-A-3 636 121 and 3 997 620). The regeneration of the absorbent refers to the displacement technique by a desorbent, which can be separated by distillation of the extract and refining.

Permeation separation techniques have the advantage in relation to adsorption separations, of being continuous and consequently of being relatively simple to function. In addition, they are recognized for their modulation and compactness or tenacity. They have found their place in the vicinity of adsorption techniques in gas separation for about ten years, for example to recover hydrogen from refinery gas, decarbonize natural gas, produce inertial nitrogen («Handbook of Industrial Membranes », Elsevier Science Publishers, UK, 1995). Its use to separate the isomeric hydrocarbons becomes possible thanks to the recent advances of the techniques of synthesis of inorganic materials that allow to grow the crystals of zeolite in the form of continuous thin layer supported or self-supported. The international application WO-A-96/01 687 describes a method of synthesis of supported zeolite membrane and its applications mainly in view of the separation of a normal mixture and isopentane. Another method of supported zeolitic membrane synthesis adapted in particular to the separation of linear alkanes from a mixture of more branched hydrocarbons is described in the international application O-A-93/19 840.

Linear and branched hydrocarbon permeability measurements in zeolite films that are either self-supported or placed in supports of different natures have been reported in the literature. For example, Tsikoyiannis J.G. et Haag W. 0., Zeolithe 1992, 12 126-30, observe in a self-supporting film of ZSM-5, with respect to the permeability of 17.2 for nC6 in relation to iC6. T he measurements of permeabilities in pure gas in a membrane composed of silicalite crystals on a porous steel support show that the flow of nC4 is higher than that of iC4 (Geus ER, Van Bekkum H., Bakker WJ., Moulijn JA, Microporous Mater., 1993, 1, 1311-47). For these same gases, the ratio of permeabilities (nC4 / iC4) is 18, at 30 ° C, and 31, at 185 ° C, with a ZSM-5 zeolite membrane on a porous aluminum support. As regards the nC6 / 2,2 dimethylbutane separation, a selectivity of 122 could be measured with the silicalite membranes on the porous glass support (Meriaudeau P., Thangaraj A. and Naccache C, Micro porous Mater. , 1995, 4, 213-219).

SUMMARY OF THE INVENTION The invention relates to a separation process that makes it possible to obtain three effluents, respectively rich in linear paraffins, in monoframed paraffins and n-paraffins, dihydrified and optionally in naphthenic and / or aromatic compounds, from light cuts C5-C8 or intermediate cuts. , such as C5-C7, C6-C8, C7-C8, C6-C7, C7 or C8, which comprises the paraffinic and optionally naphthenic, aromatic and / or olefinic hydrocarbons. The separation process according to the invention can implement at least two separate units "arranged in series operating either by adsorption _) by permeation (using one or more membranes) .The process can also result from the combination of These separation techniques The process according to the invention is adapted to a liquid phase or gas phase operation, Such a separation process is particularly useful when coupled with a hydroisomerization process as described in the patent application. has the title: "Gasoline with a high octane number and its production by a process that combines hydroisomerization and separation", registered the same day by the Applicant. In fact, the described procedure needs to recirculate both the linear paraffins (nCx, x = 5 to 8) and the monoframed paraffins (monC <);? - u), since linear paraffins and mono-branched C7-C8 have low octane numbers (see Table 1 below). In addition, different hydroisomerization conditions should be put into practice for these two types of isomers to avoid cracking or reforming the more branched paraffins. These two points justify the search for the separation procedure that allows us to obtain three different effluents, respectively rich in nCx linear paraffins, in mono-branched paraffins monoC (? - i) and in multi-branched paraffins (diC (x-.2) or triC (x- 3) )), naphthenic and / or aromatic compounds.

Table 1 In a first version of the process, a first separation unit makes it possible to separate the linear paraffins from the branched paraffins. This unit produces a denormalized or abnormal charge which is sent to a second separation unit, which allows to separate, on the one hand, the monoframed paraffins and on the other hand, the multirrified paraffins and the naphthenic and / or aromatic compounds.

In a second version of the process, the first unit makes it possible to separate the multi-branched paraffins and the naphthenic and / or aromatic compounds from the linear and mon-branched paraffins. The latter are sent to the second separation unit which effeces the separation into two effluents, one rich in monoframed paraffins, the other rich in linear paraffins. The regenerations of the units, when they use one or several adsorbents, are always independent in the sense or they do not contribute to mix the different isomers thus separated. In the case where the process load comprises the cut or fraction C5, the isopentane exited from this cut can either be separated by the process with the monorbrated paraffins, or be removed from the flow through the process with the help of a deisopentanizer placed upstream or downstream of the different separation units. In the latter case, the isopentane can serve as an eluent or as a scanning or scanning gas, respectively, for the processes of separation by adsorption or by permeation.

DETAILED DESCRIPTION OF THE INVENTION The charge treated in the process according to the invention comes from the cut or fraction C5-C8 or from all intermediate cuts (such as C5-C7, C6-C8, C6-C7, C7-C8) , C7 or C8) from the atmospheric distillation, from a reforming unit (light reforming) or from a conversion unit (hydrocracking naphtha, for example). In the continuation of the text, this possible load set will be designated by the terms "cut C5-C8 and intermediate cuts". It is composed mainly of linear, monoframed and multiracerated paraffins, of naphthenic compounds, such as dimethylcyclopentanes, of aromatic compounds such as benzene or toluene and optionally of olefinic compounds. It will be grouped under the term multi-branched paraffins, all paraffins whose degree of branching is equal to or greater than two. The charge may mainly 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 load comes from the cuts C5-C8 or intermediate cuts (such as C5-C7, C6-C8, C6-C7, C7-C8, C7, C8) obtained after atmospheric distillation, moreover it may contain the cyclic alkanes, such as the dimethylcyclopentanes, the aromatic hydrocarbons (such as benzene, toluene, xylenes) as well as other C9 + hydrocarbons (ie, hydrocarbons containing at least 9 carbon atoms) in smaller amounts. The C5-C8 fillers or those composed of intermediate cutting of reforming origin can also contain olefinic hydrocarbons, in particular when the reforming units are operated at low pressure. The amount of paraffin (P) depends mainly on the origin of the load, that is, on its paraffinic or naphthenic and aromatic character, sometimes measured by the parameter N + A (sum of the amount in naphteños (N) and the quantity in aromatics (A)), as well as its initial distillation point, that is, the quantity in C5 and C6 in the load. In hydrocracking naphthas, rich in naphthenic compounds, or light reformers, rich in aromatic compounds, the amount or proportion of paraffins in the filler will be generally reduced, of the order of 30% by mass. In the C5-C8 cuts or in the intermediate cuts (such as C5-C7, C6-C8, C6-C7, C7-C8, C7, C8) of direct distillation, the amount of paraffins varies between 30 and 80% in mass, with an average value of 55-60% by mass. The paraffin-rich filler comprising between 5 and 8 carbon atoms is generally of low octane number and the process according to the invention consists of fractionating it into three different effluents of motor octane numbers and looking for growths, respectively rich in paraffins linear, in monoframed paraffins and in dirramified paraffins, trirramified and eventually in naphthenic and / or aromatic compounds. For this fact, at least two separation units are to be considered. Several versions of the procedure are possible following the arrangement of different units. For each of the versions of the process of this invention, the separations can be carried out in liquid or gaseous phase by means of processes employing adsorbents or membranes. The adsorption separation methods used can be of the PSA type (Pressure Swing Adsorption), TSA (Temperature Swing Adsorption), chromatographic (elution or countercurrent chromatography, for example) or result from a combination of these implementations. The separation units can use one or several molecular sieves. In addition, generally several separation units (from two to ten) are used in parallel and alternatively to lead to a process that operates continuously when by nature the adsorption processes are discontinuous. In the case where the separation is carried out by permeation, the separation of the isomerate can be carried out using a gas permeation or pervaporation technique. Version 1 of the procedure is illustrated by the Figure. The recent charge (flow 1) containing the linear, monorbrated and multi-branched paraffins, naphthenic and / or aromatic compounds reaches the separation unit 2. Normal paraffins (flow 4) from the C5-C8 cuts or intermediate cuts (C5-C7, C6-C8, C6-C7, C7-C8, C7, C8) are separated from the charge in this unit 2. The characteristics that include the adsorbents and the membranes capable of effecting such separation are given in the continuation of the text. The unit 2 supplies the unit 3 with an abnormal load 5. The monoframed paraffins (flow 6) of this charge are separated from the abnormal load 5 in unit 3. The characteristics that include the adsorbents and the membranes capable of effecting such separation are give in the continuation of the text. Unit 3 produces two effluents, one rich in multi-branched paraffins, naphthenic and / or aromatic compounds (flow 7), another rich in monoframed paraffins (flow 6). This procedure allows to divide in three effluents 4, 6 and 7 of increasing octane and motor indices, a C5-C8 load or all intermediate loads. Version 2 of the procedure is illustrated by Figure 2. The new or recent load (flow 1) containing the linear, monorbrated and di-branched paraffins, naphthenes and aromatics arrive at the separation unit 3. The multirrified paraffins, the naphthenic compounds and / or • aromatics (flow 17) from cuts C5-C8 or intermediate cuts (C5-C7, C6-C8, C6-C7, C7-C8, C7, C8) are separated from the load in this unit 3. The characteristics that include the adsorbents and the membranes capable of effecting such separation are given in the continuation of the text. Unit 3 provides in Unit 2 a low octane index load 15 containing mainly linear and monoframed paraffins. The mono-branched paraffins (flow 16) of this charge will be separated from the load 15 in unit 2. The characteristics that include the adsorbents and the membranes capable of effecting such separation are given in the continuation of the text. Unit 2 produces two effluents, one rich in linear paraffins (flow 14), another rich in monoframed paraffins (flow 16). This procedure allows to divide in three effluents 14, 16 and 17 of increasing octane and motor indices, a C5-C8 load or all intermediate loads. For each of these two versions, when the load 1 contains the cut C5, the isopentane that comes from this cut can be either separated by the process according to the invention with the monorbrated paraffins, or be removed from the flow through the process with the aid of at least one deisopentanizer positioned upwards and / or downwards of the different separation units. In the latter case, the isopentane can serve as eluent or scavenging gas respectively in the separation units by adsorption or by permeation. The process comprises at least two units that can each work with the aid of adsorbent or membrane. The process can result from the association of at least one unit operating by adsorption in order to carry out one of the separations and at least one membrane unit allowing another separation to be carried out in accordance with the invention.

When at least one of the units works by adsorption, it is filled with a natural or synthetic adsorbent capable of separating the linear paraffins from the mono-branched, multirrified, naphthenic and / or aromatic paraffins (version 1 unit 2), or these same linear paraffins of monoframed paraffins (version 2 unit 2), or multi-branched paraffins, naphthenic and / or aromatic compounds of monoframed paraffins (version 1 unit 3), or these same compounds of monoframed and linear paraffins (version 2 unit) 3). The separation with the help of such adsorbents is carried out on the basis of the differences between the geometrical, diffusion or thermodynamic properties of the adsorbents for the adsorbents considered. There is a large number of adsorbent materials that allow this type of separation to be carried out. These include carbon molecular sieves, active clays, silica gel, activated alumina and crystalline molecular sieves. The latter have a uniform pore size and for this reason they are particularly suited to two types of separation. These molecular sieves mainly include the different forms of silico aluminophosphates and aluminophosphates described in US-A-4 444 871, 4 310 440 and 4 567 027 as well as the zeolitic molecular sieves. Those in their calcined form can be represented by the chemical formula: M2 / n 0: A1203: x Si02: and H20 where M is a cation, x is between 2 and infinity, and has a value between 2 and 10 and n is the valence of the cation. Within the framework of the separation of the linear paraffins (flow 4) of the charge 1 (unit 2, version 1), or of these same linear paraffins (flow 14) of the monorrated paraffins (flow 16) (unit 2, version 2) ), adsorbents are used whose pore size is sufficient to allow the adsorption of the linear paraffins and excludes the most important molecules such as the monorbrated, multirrified paraffins and the naphthenic and / or aromatic compounds. Particularly suitable zeolites are the type A zeolites described in US-A-2 882 243 which, in most of their cationic forms exchanged mainly in the form of calcium, have a pore diameter of the order of 5A and possess strong capacities to adsorb linear paraffins. The term "pore diameter" is conventional for the person skilled in the art. It is used to define in functional form the size of a pore in terms of the size of the molecule capable of entering this pore. It does not designate the actual dimension of the pore because it is often difficult to determine since most of the time it is irregular (that is, not circular). D. Breck provides a discussion on effective pore diameter in his book entitled "Zeolite Molecular Sieves" (John Wiley and Sons, New York, 1974) at pages 633 to 641. Other molecular sieves include, for example, the R zeolite. { US-A-3 030 181), zeolite T (US-A-2 950 952), silicoaluminophosphates and aluminophosphates (US-A-4 440 871, 4 310 440 and 4 567 027), as well as natural zeolites, such as clinoptilolite, chabazite and erionite are suitable for carrying out the separations implemented in unit 2 of versions 1 and 2. Finally, the use of sieves such as ferrierite (US-A-4 804 802 and 4 717 784), zeolites ZSM-5 (US-A-3 702 886), ZSM-11 (US-A-4 108 881), ZSM-23 (US-A-4 076 842) and ZSM-35 (US- A-4016245) and silicalite (US-A-5 055 633) is also perfectly adapted to the separations carried out in unit 2 of versions 1 and 2, since diffusional or diffusion properties different from the isomers at its center they can be exploited. The details of the adsorption of the linear paraffins in each of these sieves is known to the person skilled in the art and will not be the subject of further details.

In the framework of the adsorption of monoframed paraffins from the flow 5 rich in mono- and multirrafied paraffins, naphthenic and / or aromatic compounds (unit 3, version 1), either monorbrated and linear paraffins from the loading 1 (unit 3, version 2), microporous molecular sieves having an effective pore diameter slightly greater than 5 Á will be preferred for the application of the invention. Among them are those that have pores of elliptical section with dimensions between 5.0 and 5.5 Á following the small axis and approximately 5.5 to 6.0 Á following the large axis. An adsorbent having these characteristics and thus particularly adapted to the present invention is silicalite. The term silicalite includes both the silicopolymorphs described in US-A-4 061 724 and also the silicalite F described in patent US-A-4 073 865. Other adsorbents having these same characteristics and consequently particularly adapted to the present application are ZSM-5, ZSM-11, ZSM-35 (US-A-4 016 245), ZSM-48 as well as numerous other analogous crystalline aluminosilicates. ZSM-5 and ZSM-11 are described in US-A-3 702 886, Re 29 948 and US-A-3 709 979. The silica content of these adsorbents can be variable. The adsorbents most adapted for this type of separation are those that present high amounts in silica. The Si / Al molar ratio should preferably be at least equal to 10 and preferably greater than 100. Another type of adsorbent particularly adapted to the application of the invention has pores of elliptical cross section with dimensions comprised between 4.5 and 5.5 Á. This type of adsorbent has for example been characterized in US-A-4 717 748 as being a tectosilicate having pores of intermediate size between these pores of the calcium sieve 5A and those pores of the ZSM-5. Preferred adsorbents of this family include the ZSM-23 described in US-A-4 076 872 and the ferrierite described in US-A-4 016 425 and 4 251 499. These different adsorbents have pore sizes such that each one of the isomers of the cuts or fractions C5-C8 or of the intermediate cuts can be adsorbed. The diffusion kinetics of these isomers, however, is sufficiently different to be exploited. In certain operating conditions, these molecular sieves will allow each of the corresponding separations to be carried out in units 2 or 3 of versions 1 and 2 of the present invention. In the case where one of the separation units operates with the help of a permeation technique, the membrane used may take the form of hollow fibers, bundles of tubes, or a stack of plates. These configurations are known to the person skilled in the art, and make it possible to ensure the homogeneous distribution of the fluid to be separated over the entire surface of the membrane, to maintain a pressure difference on one side and on the other of the membrane, to recover separately the fluid which it has permeated (the permeate) and that which has not permeated (the retained). The selective layer may be made by means of one of the above-described adsorbent materials provided, which may constitute a uniform surface delimiting an area in which at least a part of the load can circulate, and an area in which it circulates to the minus a part of the fluid that has permeated. The selective layer can be deposited on a permeable support that ensures the mechanical strength of the membrane thus constituted, as described for example in international applications WO-A-96/01 687 and 93/19 840. Preferably, the selective layer is made by growth of zeolite crystals from a microporous support, such as described in the patent applications EP-A-778 075 and 778 076. According to a preferred mode of the invention, the membrane is constituted by a continuous layer of silicalite crystals approximately 40 microns thick, joined to a support in alpha alumina that has a porosity of 200 nm. The operating conditions will be chosen to maintain a difference in the chemical potential of the constituent (s) to be separated in order to favor their transfer across the membrane. The pressures on the one hand and on the other of the membrane should allow to perform the average deviations of transmembrane partial pressures of the constituents to be separated from 0.05 to 1.0 MPa. To reduce the partial pressure of the constituents it is possible to use a sweeping or scanning gas or maintain the vacuum by a vacuum pump at a pressure which, according to the constituents, can vary from 100 to 104Pa and from condensing the vapors to very low temperature, typically towards -40 ° C. According to the hydrocarbons used, the temperatures should not exceed 200 to 400 ° C, in order to limit the reactions of cracking or reforming and / or coking of the olefinic and / or aromatic hydrocarbons to the contact of the membrane. Preferably, the circulation speed of the load must be such that its flow takes place in a turbulent regime. The operating conditions of two separation factors depending on their implementation, the adsorbent or the membrane considered, as well as the separation to be carried out. They are between 50 ° C and 450 ° C for the temperature and 0.01 to 7 MPa for the pressure. More precisely, if the separation is carried out in liquid phase, the separation conditions are: 50 ° C to 200 ° C for the temperature and 0.1 to 7 MPa for the pressure. If the separation is carried out in the gas phase, these conditions are: 150 ° C to 450 ° C for the temperature and 0.01 to 7 MPa for the pressure. The version 1 of the procedure leads to minimize, in relation to version 2 of the procedure, the amount of adsorbent or membrane surface necessary for separation in unit 3. In effect, in version 2, the implementation of the unit 3 causes, depending on the separation technique used, either the adsorption of the sets of linear and monoframed paraffins, or their passage through the membrane. In version 1, the operation of unit 3 drags the adsorption alone of the monorbrated compounds or the passage through the membrane of these isomers alone (the permeate is made up only of one branch). In the case where the process load comprises the cut or fraction C5, the isopentane exited from this cut may either be separated by the process with the monorbrated paraffins, or be removed from the flow through the process with the aid of a deisopentanizer This can be arranged either on load 1, or on flows 5 or 6 for version 1 or on flows 1, 15 and 16 for version 2. Such implementation makes it possible to optimize the flow management of this procedure that the isopentane thus separated can serve as eluent or scavenging gas respectively for the processes of separation by adsorption or by permeation. The arrangement of the deisopentanizer respectively in flow 6 on the one hand (version 1) and flows 15 or 16 on the other hand (version 2) show that the isopentane is preferably separated under the operating conditions of the separation sections with the monorbrated compounds and not with the multi-branched compounds. The invention including the deisopentanization is clearly distinguished from those related to US-A-5 055 633 and 5 055 634. It may also be advantageous to have a depentanizer in flows 1 and / or 4 for version 1 and in flows 1 and / or 15 and / or 14 for version 2. If the depentanizer is located in flows 1, for version 1 or in flows 1 and 15 for version 2, it can be followed by a deisopentantizer with the object of disposing within the framework of the process either a mixture of isopentane / pentane or each of these pure bodies independently. These pure bodies or this mixture can also serve as eluent or scavenging gas respectively for the processes of separation by adsorption or by permeation. By last, in the same way, in the case of cuts or fractions that do not contain C5 but contain C6, the process may comprise a deisohexanizer located in flows 1, 5 or 6 for version 1 or in flows 1, 15 and 16 for version 2. Such implementation makes it possible to optimize the management of the fluxes of this process, since the C6 monorbrated compounds thus separated can serve as eluent or scavenging gas respectively for the separation processes by adsorption or by permeation EXAMPLES: Example 1: Separation procedure in three effluents with the help of two units operating by gas phase adsorption To illustrate the invention in its version 1, an example is given below in which the two separations are carried out by adsorption in gas phase according to the PSA technique, from a C5-C8 direct distillation fraction or fraction comprising paraffinic, naphthenic, aromatic and olefinic hydrocarbons. The new or recent loading of the process has the composition indicated in Table 2 and consequently a sought octane number of 73.1 and a motor or motor octane number of 70.33.

Table 2 Components% of mass ic4 0.01 nC4 0.46 nC5 9.10 iC5 6.10 cyclopentane 0.61 nC6 6.38 monorbranches in C6 6.43 di-branched in C6 1.31 cyclohexane 3.87 methylcyclopentane 3.01 nC7 6.23 monorbranded in C7 4.18 di-branched in C7 2.43 trirrified in C7 0.46 dimethylcyclo C5 4.24 methylcyclo C6 20.10 nC8 2.91 C8 2.18 monopramified (Continued Table 2) Component% by weight di-branched C8 1.31 trirramifed C8 0. 64 trimethylcyclo C5 6. 00 ethylbenzene 0. 92 toluene 10 .00 benzene 1. 16 The new or recent cargo arrives on line 1 with a yield of 26.29 kg / h. This charge becomes deisopentanized in a first deisopentantizer. The light fraction recovered in the upper part of this first deisopentantizer No. 1 has the composition indicated in Table 3, a wanted octane number of 92.4 and a yield of 1.73 kg / h. This fraction is subsequently used as the scanning gas or scanning of the PSA process of the separation unit 2.

Table 3 The deisopentanized charge, previously reheated to 250 ° C and at a pressure of 1.4 MPa, arrives in separation unit 2. This unit comprises 4 adsorbers, which are cylinders of 0.053 m internal diameter and 4. 77 m high, each containing 8.05 kg of 5A molecular sieve (or 5A zeolite), placed in the form of 1.2 mm diameter balls. The charge and the desorbent feed the separation unit under the performance control and the effluents are recovered under pressure control.

In the PSA of four adsorbers, each of the adsorption beds suffers cyclically the following steps: 1. Pressurization: the charge of desisopentanizado (24.66 kg / h) enters the bed which contains the desorption gas at low pressure. In the future and as this charge is introduced, the pressure rises in the adsorber until the 1.4 MPa adsorption pressure is achieved. 2. Adsorption: the charge is sent to the co-current of the pressurization stage in the bed and the linear paraffins are selectively adsorbed in the zeolite 5A, when the mono and multirrified paraffins and the aromatic and naphthenic compounds are produced as effluent of this High pressure adsorber. 3. Depressurization: when the adsorbent is sufficiently loaded with linear paraffins, a depressurization stage at 0.3 MPa is carried out at the co-current of the pressurization and adsorption stages. During this stage, a large part of mono- and multirrafinated paraffins contained in the dead or lower volumes of the adsorber are produced. Sweeping gas removal: the light fraction produced by the deisopentanizers n ° l and 2, is used as a sweeping gas to desorb most of the linear paraffins of the 5A sieve.

The operation described above is that of one of the adsorbers. The four adsorbers forming the separation unit 2 function in the same manner but in an out-of-phase manner in order to lead to the continuous production of two effluents. The removal flow containing linear paraffins and isopentane is produced with a yield of 18.95 kg / h and a desired octane number of 69.47. This flow is also sent to the deisopentanizer No. 2 in order to obtain, on the one hand, the isopentane, which is recirculated as a scavenging gas to the separation unit 2., with a yield of 12.3 kg / h and, on the other hand, the desired linear paraffins (flow 4) with a yield of 6.65 kg / Y and a desired octane number of 27 (composition given in Table 4). This stream 4 contains traces of monorbrated paraffins in an amount of 5%. The production flow 5 rich in mono- and multirrifined paraffins, and in naphthenic and / or aromatic compounds, is produced with a yield of 16.64 kg / h and an octane number of 89.9. This flow contains 9% isopentane and 0.25% linear paraffins. The flow 5 is also sent to the separation unit 3. This unit also operates following the PSA separation technique. It comprises 4 adsorbers, which are cylinders of 0.04 m in internal diameter and 5.7 m in height, each containing 5.47 kg of silicalite, placed in the form of 1.2 mm diameter balls. Each of the adsorption beds of this unit 3 suffers cyclically the same steps as those described in the separation frame carried out in unit 2. During the pressurization and adsorption stages, the adsorbers are fed by a flow rich in paraffins mono-, multi-branched, naphthenic and / or aromatic compounds (flow 5). Under the conditions of implementation of the separation, the monorbrated paraffins are preferably adsorbed on the silicalite by displacing the adsorbed isopentane present in the adsorber followed by the removal step. Under the operating conditions of the adsorber, the multi-branched paraffins, the aromatic and naphthenic compounds are not adsorbed and are produced as an effluent from the adsorber at high pressure (1.4 MPa). The depressurization stage at 0.3 MPa to co-current allows to produce a large part of the non-adsorbed compounds contained in the dead volumes of the adsorber. Finally, a fraction of the isopentane from deisopentanizer No. 3 is then used as a scavenging gas to desorb most of the monorbrated paraffins of silicalite. The isopentane makes it possible, on the one hand, to reduce the partial pressure of the monorbrated compounds adsorbed and also allows these compounds to be displaced, on account of their own adsorption by silicalite. The four adsorbers forming the separation unit 3 function in the same manner but in an out-of-phase manner in order to lead to the continuous production of two effluents. The sweep flow containing the monomerized paraffins and isopentane is produced with a yield of 10.58 kg / h. The 'or contains 5.48% of dirramified paraffins and has an octane number of 82.9. This flow is then sent to the deisopentantizer No. 3 to obtain, on the one hand, the isopentane, which is recirculated as a desorption gas to the separation unit 3 and, on the other hand, the desired monoframed paraffins (flow 6: yield 3.6 Kg / h, octane rating 65.3, composition given in Table 4). The production flow 7, rich in multi-branched paraffins and in naphthenic and / or aromatic compounds, is produced with a yield of 15.17 kg / h. This flow also comprises 5.9% isopentane, 0.4% monorbrated paraffins. Its composition is given in Table 4 and its octane number is 92.8. This procedure requires the recirculation in closed ring of a certain amount of isopentane between the deisopentanizers n ° 2 and n ° 3 and the separation units 2 and 3. The performance of this desorption gas can be adjusted according to the specifications of the units from separation. A portion of this ring circulating or closed loop desorption gas can be recovered in streams 4, 6, 7 and preferably in stream 7 containing the dirramified paraffins, naphthenic and / or aromatic compounds. • in the light fractions of the deisopentanizers n ° 2 and n ° 3.

This amount of desorption gas thus taken as a sample corresponds to the amount of the light fraction taken as a sample by the deisopentanizer n ° 1 of the new charge whose composition is given in Table 3. In the case of example 1, 52% of the Isopentane introduced into the charge is in flow 7, the gasoline of the remaining quantity is taken upwards from deisopentantizer No. 3.

Table 4 Overall, the process according to the invention leads to the production of three effluents respectively rich in linear paraffins, in monoframed paraffins and in multirrified paraffins, naphthenic and / or aromatic compounds, from a C5-C8 direct distillation fraction or fraction comprising paraffinic, naphthenic and / or aromatic hydrocarbons.

Example 2: Separation procedure in three effluents with the help of two reactors, one operating by adsorption in liquid phase and the other by gaseous permeation To illustrate the invention in its version 2, an example is given below in which the first separation step is carried out by adsorption in liquid phase in accordance with the counter-current simulated technique, from a direct distillation cut C5- C8 comprising paraffinic, naphthenic, aromatic and olefinic hydrocarbons. The new loading of the procedure has the composition indicated in Table 5 and consequently a sought octar.o index of 65.06 and a motor or principal octane number of 63.53.

Table 5 Components% by mass ic4 0.02 nC4 0.91 nC5 15.23 iC5 9.50 cyclopentane 0.73 nC6 15.80 monorramificados in C6 12.61 (Continuation Table 5) Components% by mass dirramified in C6 -5.30 cyclohexane 2.34 methylcyclopentane 3.27 nC7 7.45 monorramificados in C7 3.95 dirramificados in C7 1.06 trirramificados in C7 1.20 dimetiliciclo C5 4.58 methylciclo C6 3.79 nC8 1.12 monorramificados C8 0.93 dirramificados C8 0.77 trirramificados C8 0.28 trimetilciclo C5 4.03 ethylbenzene 0.99 toluene 3.73 benzene 0.41 New or recent cargo arrives on line 1 with a yield of 25.75 kg / h. This charge becomes deisopentanized in a first deisopentantizer. The light fraction recovered in the upper part of this first deisopentanizer (No. 1) has the composition indicated in Table 6, a wanted octane number of 92.4 and a yield of 2.68 kg / h. This fraction is subsequently used as a scavenging gas in the gaseous permeation unit (separation unit 2).

Table 6 Component% in mass nC4 8.75 iC4 0.15 iC5 91.1 The deisopentanized charge, previously reheated to 100 ° C and at a pressure of 1.8 MPa, feeds the separation unit 3, which consists of an adsorption unit operating in simulated countercurrent (CCS). This unit comprises several columns in series consisting of cylinders of 0.1 m internal diameter. The complete unit of a length of 15 m and containing 95 kg of silicalite, placed in the form of 0.7 mm diameter balls. The charge and the desorbent (coming from the deisopentanizers n ° 2 and n ° 3 that will be described further away) feed the separation unit 3 that works under yield control (respectively 23.07 kg / h and 57.65 kg / h) and the effluents they are recovered under pressure control. In the CCS unit, the deisopentanized charge (23.07 kg / h) enters the bed. The linear and mono-branched paraffins are then adsorbed by silicalite by displacing the adsorbed isopentane. Under start-up conditions, multi-branched paraffins, aromatic and naphthenic compounds are not adsorbed. The injection points of the load, the refining and the extract are continuously displaced. This procedure makes it possible to produce a flow rich in dirramified paraffins, naphthenic and / or aromatic compounds and isopentane with a yield of 29.26 kg / h and an octane number of 94.16. This flow is deisopentanized in the deisopentantizer No. 2 so that the isopentane is recirculated to the separation unit 3. The isopentane recovered in liquid phase in the condenser upstream of the deisopentanizer column No. 2 is sent on the one hand, in reflux of the column and, on the other hand, to the recirculation of the eluent of the separation unit 3. This recirculation has a yield of 20.9 kg / h. At the bottom of this second deisopentanizer, a flow 17 rich in dirrmified, naphthenic and / or aromatic paraffins is recovered whose simplified composition is given in Table 7. The flow from the separation unit 3 containing the paraffins linear, monorramified and a part of the desorbent, is produced with a yield of 51.45 kg / h and a sought octane number of 78.47. It contains 71% by mass of isopentane.

This flow is then sent to a third deisopentanizer in order to obtain: • on the one hand, at the top of the column, the isopentane, which is partly recirculated as an eluent to the separation unit 3, with a yield of 36.75. kg / h and on the other hand, at the bottom of the column, the desired linear and monoframed paraffins (flow 15) with a yield of 14.7 kg / h and a desired octane number of 42.9. This flow contains traces of multi-branched paraffins at an amount of 5% by mass.

This flow is stopped at a pressure of 0.2 MPa and 100 ° C in order to feed the separation unit 2 consisting of a gaseous permeation unit. This unit consists of a bundle of tubes in alumina whose internal surface is covered with a layer of silicalite 20 microns thick. The total useful surface of the membrane is 5 m2. The gaseous charge is distributed inside the tubes, the sweeping gas coming from the first deisopentanizer and the fourth deisopentanizer (described below) is introduced after expanding to atmospheric pressure and reheating at 100 ° C in the calender of the permeator and it recovers in another extremity on the linear paraffins. The introduction and transfer or pouring of a sweeping gas on the one hand and on the other hand of the calender of the permeator are carried out in such a way that the permeate loading fluids circulate countercurrently. The flow velocities of the fluids are chosen in such a way that they maintain their flow in a turbulent regime. The paraffins 1 'of adsorbents preferentially in the cavities of the zeolite (silicalite), and diffuse under the effect of their gradient of chemical potential maintained on the one hand and on the other hand of the membrane by the above-mentioned operating conditions. The impoverished load in linear paraffins recovered at the outlet of the permeator (flow 16: yield of 4.39 kg / h) contains 7.8% by mass of linear paraffins and 6.8% by mass of isopentane. The composition of flow 16 is reported in Table 7. The sweeping gas, during its circulation in the permeator, is loaded with linear paraffins and a small amount of monorbrated paraffins that have also been permeated through the membrane. It leaves the permeator with a yield of 15.54 kg / h, with a proportion of 31.2% by mass of isopentane. This flow is sent to the deisopentanizer No. 4, where the isopentane is taken as a sample at the top. A part of this isopentane is sent to the reflux of the deisopentanizer No. 4; another part (2.3 kg / h) in the form of steam is reheated and, together with the flow of the top of the deisopentanizer No. 1, introduced as a scavenging gas in the permeator, under a yield of 5 kg / h. On the other hand, a purge of the upper part of this deisopentanizer allows to extract a flow of 2.4 kg / h. The bottom of the deisopentanizer No. 4 produces, under a yield of 10.61 kg / h, a flow 14 rich in linear paraffins, whose composition is given in Table 7 below.

Table 7 The amount of the isopentane recirculation circulating in a closed circuit or ring between the permeator and the deisopentanizer is a variable of the procedure. For the same installed membrane surface, it is possible to operate with the sweep gas performance ratios in the load between 0 and 3. When this ratio increases, the amount of linear paraffins that permeate through the membrane increases, the increase occurs to the detriment of the purity of the linear paraffins extracted. Overall, the process according to the invention leads to the production of three effluents respectively rich in linear paraffins, in monoframed paraffins and in multirrified paraffins, naphthenic and / or aromatic compounds, from a direct distillation cut C5-C8 comprising hydrocarbons paraffinic, naphthenic and / or aromatic.

Example 3: Separation procedure: in three effluents with the aid of two units operating by gas phase adsorption To illustrate the invention in its version 2, an example is given below in which the two separations are carried out by adsorption in gas phase according to the PSA technique, from a direct distillation cut C5-C8 comprising paraffinic hydrocarbons , naphthenics, aromatics and olefins. The recent loading of the process has the composition indicated in Table 8 and consequently a sought octane number of 73.1 and an engine octane number of 70.33.

Table 8 (Continuation Table 8) Fresh or recent cargo arrives on line 1 with a yield of 26.29 kg / h. This charge becomes deisopentanized in a first deisopentantizer. The light fraction recovered in the upper part of this first deisopentantizer No. 1 has the composition indicated in Table 9, a wanted octane number of 92.4 and a yield of 2.44 kg / h. This fraction is then used as the scavenging gas or scanning of the PSA process of the separation unit 2.

Table 9 The deisopentanized charge, previously heated to 250 ° C and a pressure of 1.4 MPa, arrives in the separation unit 2. This unit comprises 4 adsorbers, which are cylinders of 0.3 m internal diameter and 2.2 m high, which contain each one 108 kg of silicalite, placed in the form of 1.2 mm diameter balls., The charge and the desorbent feed the separation unit under the yield control and the effluents are recovered under pressure control. In the PSA of four adsorbers, each of the adsorption beds suffers cyclically the following steps: 1 - Pressurization: the deisopentanized load (23.86 kg / h) enters the bed which contains the desorption gas at low pressure. In the future and as this charge is introduced, the pressure rises e- the adsorber until the 1.4 MPa adsorption pressure is reached. 2 - Adsorption: the charge is sent to the co-current of the pressurization stage in the bed and the linear paraffins are selectively adsorbed in the silicalite when the multirrified paraffins and the aromatic and naphthenic compounds are produced as an effluent of this adsorber at high pressure 3 - Depressurization: when the adsorbent is sufficiently charged with linear and monofrained paraffins, a depressurization stage at 0.3 MPa is carried out at co-current of the pressurization and adsorption stages. During this stage, a large part of multi-branched paraffins contained in the dead or lower volumes of the adsorber are produced. - 'Removal by sweeping gas: the light fraction produced by the deisopentanizers n ° l and 2, is used as a sweeping gas to desorb most of the linear and monoframed paraffins.

The operation described above is that of one of the adsorbers. The four adsorbers forming the separation unit 2 function in the manner but in the form of phase shift in order to lead to the continuous production of two effluents. The production flow, rich in multi-branched paraffins and in naphtha and / or aromatic compounds, is produced with a yield of 14.2 kg / h and an octane number of 86.1. This flow contains 4.4% isopentane and 6.3% linear and moncrranified paraffins. The removal flow containing linear and monoframed paraffins and isopentane is produced with a yield of 11.8 kg / h. This flow is then sent to the deisopentantizer No. 2 in order to obtain, on the one hand, the isopentane, which is recirculated as a scavenging gas to the separation unit 2, with a yield of 1.5 kg / h, on the other hand , the desired linear and monolized paraffins (flow 4) with a yield of 10.3 kg / h and a desired octane number of 42.75 (composition given in Table 10). This stream 4 contains traces of multi-branched paraffins, aromatic and naphthenic compounds at an amount of 14%. The flow 4 is then sent to the separation unit 3. This unit also operates following the PSA separation technique. It includes 4 adsorbers that are cylinders of 0.25 m in internal diameter and 2 m in height, each containing 70 kg of molecular sieve 5A (zeolite 5A), placed in the form of 1.2 mm diameter balls. Each of the adsorption beds of this unit 3 suffers cyclically the same steps as those described in the separation frame carried out in unit 2. During the pressurization and adsorption stages, the adsorbers are fed by a flow rich in paraffins linear and monoframed (flow 4). The linear paraffins are preferably adsorbed on the zeolite 5A by displacing the adsorbed isopentane present in the adsorber followed by the removal step. Under the operating conditions of the adsorber, monorbrated paraffins are not adsorbed and are produced as high pressure adsorber effluent (1.4 MPa). The depressurization stage at 0.3 MPa at co-current allows to produce a large part of non-adsorbed compounds contained in the dead volumes of the adsorber. Finally, a fraction of the isopentane released from the ncl, n ° 2 or n ° 3 deisopentanizers is then used as the scavenging gas to desorb most of the linear paraffins of zeolite 5A. The four adsorbers forming the separation unit 3 function in the same manner but in an out-of-phase manner in order to lead to the continuous production of two effluents. The sweep flow containing the linear paraffins and isopentane is produced with a yield of 5.75 kg / h. Contains 13.66% of multi-branched paraffins, aromatic and naphthenic compounds. This flow is then sent to the deisopentantizer No. 3 in order to obtain, on the one hand, the isopentane, which is recirculated as a desorption gas towards the separation units 2 and 3 and, on the other hand, the desired linear paraffins ( flow 6: yield of 5.2 kg / h, octane number 22.4, composition given in Table 10). Production flow 7, rich in monoframed paraffins, is produced with a yield of 7 kg / h. This flow comprises more than 26.85% isopenta:; Its composition is given in Table 10 and its octane number is 72.6.

This procedure requires the recirculation in closed circuit of a certain amount of isopentane between the deisopentanizers n ° 1, n ° 2 and n ° 3 and the separation units 2 and 3. The yield of this desorption gas can be adjusted depending on the specifications of separation units. A part of this desorption gas circulating in the closed circuit can be recovered. • in flows 5, 6 or 7 • in the light fractions of deisopentanizers n ° 2 and n ° 3. »This amount of desorption gas thus taken corresponds to the amount of the light fraction coined by the deisopentantizer No. 1 of the fresh or new charge whose composition is given in Table 9. Table 10 Overall, the process according to the invention leads to the production of three effluents respectively rich in linear paraffins, in monoframed paraffins, and in multi-branched paraffins, naphthic compounds, cos and / or aromatics, from a direct distillation cut C5. -C8 comprising paraffinic, naphthenic and / or aromatic hydrocarbons.

It is noted that in relation to this date, the best method known by the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention. Having described the invention as above, the content of the following is claimed as property

Claims (14)

1. A method of separating light cuts C5-C8 or intermediate cuts such as C5-C7, C6-C8, C7-C8, C6-C7, C7 or C8, comprising paraffinic, and eventually naphthenic, aromatic and / or olefinic hydrocarbons , characterized in that it implements at least two separation units placed in series, to obtain three effluents, respectively a effluent rich in pa. : linear fines, an effluent rich in monoframed paraffins and an effluent rich in dirramified paraffins, trirramified and eventually in naphthenic and / or aromatic compounds.

2. The method according to claim 1, characterized in that the charge is sent in a first separation unit, where the linear paraffins are separated from the branched paraffins, the unit that produces an abnormal load, which is sent to the second unit of separation, where on the one hand monoframed paraffins and on the other hand multiracerated paraffins, and eventually naphthenic and / or aromatic compounds are separated.

3. The process according to claim 1, characterized in that the charge is sent in a first separation unit, where on the one hand, the multirrurated paraffins and, optionally, the naphthenic and / or aromatic compounds and on the other hand the linear and monorramificados, which are sent to the second separation unit where two effluents are separated, one rich in monoframed paraffins, the other rich in linear paraffins.

4. The process according to one of claims 1 to 3, characterized in that the charge comprises the cut C5 and the isopentane leaving this cut is separated with the monorbrated paraffins.

5. The process according to one of claims 1 to 3, characterized in that the charge comprises the cut C5 and the isopentane exited from this cut is removed from the flow through the process with the help of a deisopentanizer placed upwards of one (or of) separation unit (s).

6. The process according to one of claims 1 to 3, characterized in that the load comprises the cut C5 and the isopentane exited from this cut is removed from the flows that pass through the process with the help of a desisopentanizer placed in descending order of the units from separation.

7. The method according to one of claims 1 to 6, characterized in that it implements at least two separation units operating by adsorption.

8. The process according to one of claims 1 to 6, characterized in that at least one separation unit operating by adsorption and at least one permeation separation unit using one or more membranes is operated.

9. The process according to one of claims 7 and 8, characterized in that the isopentane removed serves as an eluent for the regeneration of the separation unit (s) by adsorption.

10. The process according to one of claims 1 to 6, characterized in that it implements at least two permeation separation units using one or several membranes.

11. The process according to claim 10, characterized in that the isopentane removed serves as the scavenging gas for the regeneration of the permeation separation unit (s).

12. The process according to one of claims 1 to 11, characterized in that the charge escapes from atmospheric distillation.

13. The method according to one of claims 1 to 11, characterized in that the load is exited from a reforming unit, such as a light reforming.

14. The process according to one of claims 1 to 11, characterized in that the charge is released from a conversion unit, such as a hydrocracking or cracking naphtha or catalytic reforming under a hydrogen atmosphere.