MXPA99010544A - Split-feed two-stage parallel aromatization for maximum para-xylene yield - Google Patents

Abstract

A full boiling hydrocarbon feed is reformed to enhance para-xylene and benzene yields. First, the hydrocarbon feed is separated into a C5- cut, a C6-C7 cut, and a C8+ cut. The C6-C7 cut has less than 5 lv.%of C8+ hydrocarbon, and the C8+ cut has less than 10 lv.%of C7- hydrocarbon. The C6-C7 cut is subjected to catalytic aromatization at elevated temperatures in a first reformer in the presence of hydrogen and using a non-acidic catalyst comprising at least one Group VIII metal and a non-acidic zeolite support to produce a first reformate stream;and the C8+ cut is subjected to catalytic aromatization at elevated temperatures in a second reformer in the presence of hydrogen and using an acidic catalyst comprising at least one Group VIII metal and a metallic oxide support to produce a second reformate stream. Less than 20 wt.%of the total amount of C8 aromatics produced in the first and second reformer is ethylbenzene, and more than 20 wt.%of the total amount of xylenes produced in thefirst and second reformer are para-xylenes.

Description

PARALLEL FLAME OF TWO STAGES OF FOOD SEPARATELY FOR M XIMO YIELD OF PARAXYLENE FIELD OF THE INVENTION The present invention relates to a process for reforming a hydrocarbon feed of maximum boiling range to improve the production of paraxylene and benzene.

BACKGROUND OF THE INVENTION The reformation of petroleum hydrocarbon streams is an important process for refining petroleum that is used to provide components that mix high octane hydrocarbon for gasoline. The process is usually practiced in a fraction of straight-run naphtha that has been hydrodesulfurized. The straight-run naphtha is typically highly paraffinic in nature, but may contain significant amounts of naphthene and minor amounts of aromatic or olefins. In a typical reforming process, reactions include dehydrogenation, isomerization, and hydrocracking. The REF .: 31530 dehydrogenation reactions will typically be the dehydroisomerization of alkylcyclopentanes to aromatics, the dehydrogenation of paraffins to olefins, the dehydrogenation of cyclohexanes to aromatics, and the dehydrocyclization of paraffins to aromatics. The aromatization of n-paraffins to aromatics is generally considered to be the most important cause of the high octane content of the resulting aromatic product compared to the low octane ratios for n-paraffins. Isomerization reactions include isomerization of n-paraffins to isoparaffins, and isomerization of substituted aromatics. Hydrocracking reactions include hydrocracking of paraffins and hydrodesulfurization of any sulfur that is remaining in the raw material. It is well known in the art that various catalysts are capable of reforming petroleum naphthas and hydrocarbons boiling in the boiling range of gasoline. Examples of known catalysts useful for reforming include platinum and optionally rhenium or iridium on an alumina support, platinum on zeolite X and Y zeolite, platinum or intermediate pore size zeolites as described in US Patent No. 4,347,394, and platinum on cation exchanged with zeolite L. US Patent No. 4,104,320 describes the dehydrocyclization of aliphatic hydrocarbons to aromatics by contact with a catalyst comprising a zeolite L containing alkali metal ions and a Group VIII metal such as platinum. The conventional reforming catalyst is a bifunctional catalyst that contains a metal hydrogenation-dehydrogenation component, which is usually dispersed on the surface of a porous inorganic oxide support, usually alumina. Platinum has been widely used commercially in the production of reforming catalysts, and platinum on alumina catalysts has been used commercially in refineries for some past decades. More recently, additional metallic components have been added to the platinum to further promote the activity or selectivity, or both. Examples of such metal components are iridium, rhenium, tin and the like. Some catalysts have superior activity, or selectivity, or both that contrast with other catalysts. Platinum-rhenium catalysts, for example, have high selectivity compared to platinum catalysts. Selectivity is generally defined as the ability of the catalyst to produce high yields of desirable products with low concurrent production of undesirable products, such as gaseous hydrocarbons.

It is desirable to maximize the production of xylene and benzene and finally the production of paraxylene and benzene. The problem of how referring to this, has not been solved previously. The previous technique has dealt with the problem of maximizing only benzene production when processing a naphtha of 5 to 11 atoms It has not directed how to maximize the production of paraxylene and secondly the production of benzene. It is pointed out that maximizing benzene production could occur by degrading aromatics of 8 to 9 carbon atoms to benzene. This is especially important when paraxylene has historically commanded a previous benzene difficult to achieve. There are several processes for dividing naphtha feed streams into an upper boiling part and a lower boiling part and reforming these parts separately. The American Patent No. 2No. 867,576 describes the separation of straight-run naphtha in lower and upper boiling portions, in which the upper boiling portions are reformed with a hydrogenation-dehydrogenation catalyst with the liquid reforming produced which is sent to an aromatics separation process . The paraffinic fraction obtained from the separation process is mixed with the lower boiling naphtha fraction and the resulting mixture is reformed with a reforming catalyst, which may or may not be of the same type used in the reforming of the part or fraction high boiling point. U.S. Patent No. 2,944,959 discloses the fractionation of a straight-through gasoline in a light paraffinic fraction, from and 6 carbon atoms, which is hydroisomerized with hydrogen and a platinum-alumina catalyst, an intermediate fraction that is catalytically reformed with hydrogen and a platinum-alumina catalyst, and a heavy fraction that is catalytically reformed with an oxide catalyst of molybdenum and that recovers liquid products. US Patents Nos. 3,003,949, 3,018,244 and 3,776,949 also describe the fractionation of a feed in a fraction of 5 to 6 carbon atoms, which is isomerized, and a heavier fraction that is reformed. Other processes for dividing raw materials and treating them separately are included in: US Pat. Nos. 3,172,841 and 3,409,540 describe the separation of fractions of a hydrocarbon feedstock and catalytically reforming of various feedstock fractions; North American Patent No. 4,167, 72 describes the separation of the straight chain from hydrocarbons of 6 to 10 carbon atoms of non-straight chain- and converting aromatics separately; and US Patent No. 4,358,364 describes the catalytically reforming of a 6 carbon atom fraction and yielding additional benzene by hydrogasification of a C5_ fraction, a fraction with a boiling point greater than 149 ° C (300 ° F) and the gas stream produced from the catalytic reforming. U.S. Patent No. 3,753,891 describes the fractionation of a straight-run naphtha in a light naphtha fraction containing C6 and a substantial portion of 7-carbon hydrocarbons and a heavy naphtha fraction having boiling point from about 93 °. C at 204 ° C (200 ° to 400 ° F); then the reforming of the light fraction to convert naphthenes to aromatics onto a platinum-alumina catalyst or a bimetallic reformation catalyst; reforming separately from the heavy fraction, then improving the reforming effluent of the low-boiling fraction on a ZSM-5 type zeolite catalyst to divide the paraffins and recover an effluent with improved octane variation.

U.S. Patent No. 4,645,586 describes the parallel reforming of a hydrocarbon feed. In a stream, the hydrocarbons are reformed with an acid catalyst. In the second stream, the hydrocarbons are reformed with a non-acid catalyst. This patent is silent regarding the composition of each fraction. Preferably, the difunctional reforming catalyst is not presulphurized. U.S. Patent No. 4,897,177 discloses the use of a monofunctional catalyst for reforming a hydrocarbon fraction having less than 10% by volume of Cg + hydrocarbons. The fraction is either a fraction of C, C ?, C8, C6-C7, C7-C8, or Cß-Cs, with the most preferred being a fraction of Cß-C_. This fraction can contain up to 15% vol. of hydrocarbons outside the named range (col 3, line 44-49). A heavier fraction can be reformed using a bifunctional catalyst in an acid metal oxide. This bifunctional catalyst can be a Pt / Sn / alumina catalyst. U.S. Patent No. 33,323, Reprinted, describes the solvent extraction of a light fraction from a reformate. The goal or objective of this patent is to maximize only benzene production. A hydrocarbon feed is separated into a lighter fraction (a fraction of e containing 15-35% Iv of C7 +) and a heavier fraction (all the heavier components and C7 remaining). The lighter fraction is reformed in the presence of a non-acid catalyst to maximize benzene production. The heavier fraction is reformed in the presence of an acid catalyst. The reforming of the non-acidic catalyst is introduced into an extraction wherein a stream of aromatic extract and a non-aromatic refining stream are recovered. The refining stream can be recirculated to the feed. The document entitled 'New Options For Aro Atics Production' ('New Options for Aromatic Production') presented at the 20h Annual 1995 Dewitt Petrochemical Review (Houston, Texas, March 21-23, 1995) by D.J. Swift et al. refers to the recent improvements in the UOP process for the production of benzene and paraxylene. Case studies were presented to demonstrate the benefits of using such a process to increase total aromatics production from a fixed amount of naphtha. A configuration of this process involves a process of division feeding, but it is not clear that the composition of each feeding is.

BRIEF DESCRIPTION OF THE INVENTION The present invention provides a process for reforming a hydrocarbon feed of maximum boiling point to improve the yields of paraxylene and benzene. - This invention is based on the realization that a non-acid catalyst had an adverse effect on the production of paraxylenes. It is thought that the catalyst really dealkylates those xylenes. Therefore, the C8 + fraction should not be subject to a non-acid catalyst if it is difficult to recover xylenes. In this process, the hydrocarbon feed is separated into a C5_ fraction, a C6-C7 fraction, and a C8 + fraction, where the C6-C7 fraction had less than 5% Iv of the C8 + hydrocarbon, and where the C8 + fraction had less than 10% of Iv. of hydrocarbon C7-. The Cg-C7 fraction is subjected to catalytic aromatization at elevated temperatures in a first reformer in the presence of hydrogen and using a non-acid catalyst comprising at least one Group VIII metal and a non-acidic zeolite support, preferably platinum in a support of non-acidic zeolite L, to produce a first reforming stream. The C8 + fraction is subjected to catalytic aromatization at elevated temperatures in a second reformer in the presence of hydrogen and. using an acid catalyst comprising at least one Group VIII metal and a metal oxide support, preferably a non-presulphurized acid catalyst comprising platinum and tin on an alumina support, to produce a secondary reforming stream. Less than 20% by weight of the total amount of C8 aromatics produced in the first and second reformer is ethylbenzene, and more than 20% by weight of the total amount- of xylenes produced in the first and second reformers are paraxylenes. Preferably, the first reforming stream and the second reforming stream combine to form a combined reforming stream, the combined reforming stream is separated into a light fraction and a heavy fraction, and at least part of the light fraction is recirculated already either to the hydrocarbon feed or to at least one of the reformers. From their experimental studies where the aromatization of a broad-boiling naphtha has been investigated on a non-acidic zeolite such as Pt / K-Ba L zeolite or Pt / KL zeolite with F and Cl, it has been found that Non-acid catalysts are more efficient than the standard bi-functional catalysts in aromatics of C6 and C7 to the corresponding aromatic. However, it has also been found that standard bi-functional reforming catalysts such as Pt / Sn / Cl in alumina are more efficient than non-acidic zeolites in C8 and Cg flavorings to the corresponding aromatic. For example, in paraffin conversions of C8 and naphtha or (P + N) of 92.9%, the selectivity to aromatics of C8 is approximately 50% with the non-acidic zeolite when processing a paraffinic naphtha of Cß-Cio- When the same naphtha is processed on a bi-functional aromatization catalyst such as Pt / Sn / Cl on alumina the aromatic selectivity of C8 is about 80% in C8 (P + N) conversions of 90% +. lower C8 aromatics with the non-acidic zeolite is due to the hydrodesalkylation of C8 aromatics to benzene and toluene, and when the C6-C? 0 naphtha is processed on a non-acidic zeolite, not only is the yield of lower C8 aromatics, 19% by weight against 24% by weight with a bi-functional catalyst, but also the aromatic stream of C8 is of very poor quality.The aromatic stream of C8 made with the non-acidic zeolite contains 30% by weight. % ethylbenzene compared to approximately 16% produced with the bi-functional catalyst. Thus, the produced xylene is lower, 13% by weight against 20% by weight with the bi-functional catalyst. In other words, the bi-functional catalyst makes 50% more xylenes. further, with the non-acidic zeolite, the concentration of paraxylene on a xylene base is low, 12% compared to 20% with the bifunctional catalyst. This later value is very close to the equilibrium value of 23% in the operating temperature of the aromatization stage. Accordingly, a C8 aromatization starting point, the bi-functional catalyst, had a high C8 aromatics production, a higher xylene production, and a lower production of ethylbenzene than the non-acidic zeolite. Also, the bifunctional catalyst forms a xylene stream with a higher concentration of para-xylene than the non-acid zeolite. All these are advantages for the para-xylene producer when they minimize the cost of operation and capital. An additional benefit of the bi-functional catalyst is that the conversion and selectivity of paraffins from C9 and naphthenes to the aromatics of C9 is much greater. Thus, the production of full Cg aromatics is about 10% by weight compared to about 4.0% by weight with the non-acidic zeolite. In addition, the C9 aromatics produced with the bi-functional catalyst contain about 55% tri ethylbenzenes, and about 35% methyl ethylbenzenes. This compares to about 20% trimethylbenzenes and about 46% methyl ethylbenzenes with the non-acidic zeolite. Cg aromatics are converted to xylenes and benzene by transalkylation with toluene. In this process, trimethylbenzenes are the preferred species, when they produce two moles of xylenes per mole of trimethylbenzenes and toluene, while methyl ethylbenzenes can produce one mole of xylenes and ethylbenzenes, which is undesirable, or alternatively one mole of benzene and an aromatic of Cío. In this way not only the bi-functional catalyst makes more Cg aromatics, but they are of a better quality from a point of view of production of xylenes and finally of paraxylene.

BRIEF DESCRIPTION OF THE DRAWINGS To assist in the understanding of this invention, reference will now be made to the accompanying drawings. The drawings are only examples, and should not be construed as limiting the invention.

Figure 1 shows a flow chart of an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION In its broadest aspect, the present invention involves a process for reforming a hydrocarbon feed of maximum boiling point to improve yields of paraxylene and benzene. In this process the hydrocarbon feed is separated into a fraction of Cs-, a fraction of C6-C7, and a fraction of Cg +. The C6-C7 fraction had less than 5% Iv. of C8 + hydrocarbon, and the C8 + fraction had less than 10% Iv. of hydrocarbon of C7-. The C6-C7 fraction is subjected to catalytic aromatization at elevated temperatures in a first reformer in the presence of hydrogen and using a non-acid catalyst comprising at least one group VIII metal and a non-acidic zeolite support to produce a first stream of reformed. The C8 + fraction is subjected to catalytic aromatization at elevated temperatures in a second reformer in the presence of hydrogen and using an acid catalyst comprising at least one Group VIII metal and a metal oxide support to produce a second reforming stream. Less than 20% by weight of the total amount of C8 aromatics produced in the first and second reformer is ethylbenzene, and more than 20% by weight of the total amount of xylenes produced in the first and second reformers are para-xylenes. To minimize capital investment and maximize the production of aromatics, both the reformers operate at a common operating pressure that allows the linking of the two reformers and where the possible common equipment can be used such as recirculated gas compressor, impeller compressor of net gas, separator and depentanizer. So, essentially you have an aromatization plant. This processing scheme solves the problem of how to maximize benzene and particularly the production of paraxylene at a low cost of capital.

NON-ACID CATALYSTS One of the catalysts used should be a non-acid catalyst having a non-acidic zeolite support changed with one or more dehydrogenation constituents. Among the zeolites useful in the practice of the present invention are zeolite L, zeolite X, and zeolite Y. These zeolites have evident pore sizes in the order of 7 to 9 Angstroms. Zeolite L is a synthetic crystalline zeolitic molecular sieve which can be written as: (0.9-1.3) M2 / nO: Al2? 3 (5.2-6.9) Si02: yH20 where M designates a cation, n represents the valence of M, and y can be any value from 0 to about 9. The zeolite L, its X-ray diffraction pattern, its properties, and method for its preparation are described in detail in The patent North American No. 3,216,789. U.S. Patent No. 3,216,789 is incorporated herein by reference - to show the preferred zeolite of the present invention. The actual formula can vary without changing the crystalline structure, for example, the molar ratio of silicon to aluminum (Si / Al) can vary from 1.0 to 3.5. Zeolite X is a synthetic crystalline zeolitic molecular sieve which can be represented by the formula: (0 .7-1. 1) M2 n0: A1203: 2. 0-3. 0) Si02: and H20 where. M represents a metal, particularly alkali and alkaline earth metals, n is the valence of M, e and can have any value up to about 8 depending on the identity of M and the degree of hydration of the crystalline zeolite. Zeolite X, its configuration by X-ray diffraction, its properties, and method for its preparation are described in detail in U.S. Patent No. 2,882,244. U.S. Patent No. 2,882,244 is incorporated herein by reference to show a zeolite useful in the present invention. Y zeolite is a synthetic crystalline zeolitic molecular sieve which can be written as: (0.7-1.1) Na20: A1203: xSi02: yH20 wherein X is a value greater than 3 to about 6 e and can be a value of up to about 9. Zeolite Y has a characteristic X-ray powder diffraction pattern which can be employed with the above formula for identification. Y zeolite is described in more detail in U.S. Patent No. 3,130,007. U.S. Patent No. 3,130,007 is incorporated herein by reference to show a zeolite useful in the present invention.

The preferred non-acid catalyst is an L-type zeolite loaded with one or more dehydrogenated cituents. The zeolitic catalysts according to the invention are charged with one or more metals of the Group VIII, for example, nickel, ruthenium, rhodium, palladium, iridium or platinum. Preferred Group VIII metals are iridium and particularly platinum, which are more selective with respect to dehydrogenation and are also more stable under the dehydrocyclization reaction conditithan other Group VIII metals. The preferred percentage of platinum in the dehydrocyclization catalyst is between 0.1% and 5%, the lower limit corresponding to the minimum catalyst activity and the upper limit to maximize the activity. This infers that the high price of platinum, which is not justified by using a higher amount of the metal since the result is only a slight improvement in catalytic activity. Group VIII metals are introduced into the large pore zeolite by synthesis, impregnation or exchange in an appropriate aqueous salt solution. When it is desired to introduce two Group VIII metals into the zeolite, the operation can be performed simultaneously or sequentially. As an example, platinum can be introduced by impregnation of the zeolite with an aqueous solution of tetraminplatinum (II) nitrate, tetraminplatinum (II) hydroxide, dinitrodiamino-platinum or tetraminplatinum (II) chloride. In an ion exchange process, platinum can be introduced using cationic platinum complexes such as tetraminplatinum (II) nitrate. A preferred but not essential element of the present invention is the presence of an alkaline earth metal in the dehydrocyclization catalyst. This alkaline earth metal can be barium, strontium or calcium. Preferably the alkaline earth metal is barium. The alkaline earth metal can be incorporated into the zeolite by synthesis, impregnation or ion exchange. Barium is preferred for the other alkaline earths because the resulting catalyst had high activity, high selectivity and high stability. An inorganic oxide can be used as a carrier to join the large pore zeolite containing the Group VIII metal. The carrier can be a synthetically produced or natural inorganic oxide, or combination of inorganic oxides. Typical inorganic oxide supports which can be used include clays, alumina, and silica, in which the acid sites are preferably exchanged for catithat do not impart strong acidity. The non-acid catalyst can be used in any of the conventional types of equipment known in the art. They can be used in the form of pills, pellets, granules, broken fragments, or several special shapes, arranged as a fixed bed within a reaction zone, and the loading pile can be passed through all the liquid, vapor, or mixed phase, and in countercurrent or descending flow. Alternatively, it can be prepared in a manner suitable for use in beds of motion, or in solid-fluidized processes, in which the loading pile is passed upwards through a turbulent bed of finely divided catalyst.

ACID CATALYSTS An acid catalyst is used in conjunction with the non-acid catalyst. The acid catalyst may comprise a metal oxide support having a Group VIII metal disposed therein. Suitable metal oxide supports include alumina and silica. Preferably, the acid catalyst comprises a metal oxide support having a Group VIII metal (preferably platinum) metal and a Group VIII metal promoter, such as rhenium, tin, germanium, cobalt, nickel, iridium, disposed therein in intimate admixture. , rhodium, ruthenium and combinations thereof. More preferably, the acid catalyst comprises a support of alumina, platinum, and rhenium. A preferred acid catalyst comprises platinum and tin in an alumina support. Preferably, the acid catalyst has not been presulphurized before use. This is important to avoid sulfur contamination of the non-acid catalyst by recirculation of part of the reforming produced by the acid catalyst. On the one hand, if one can ensure the non-sulfur contamination of the non-acid catalyst from the reforming produced by the acid catalyst, then it may be able to use a presulphurized catalyst, such as Pt / Re on alumina.

CONDITIONS OF REFORM The reforming in both reformers is carried out in the presence of hydrogen at a pressure adjusted to favor the thermodynamically dehydrocyclization reaction and to limit undesirable hydrocracking reactions. The pressures used preferably range from 1 atmosphere to 35,155 kg / cm 2 (500 psi), more preferably from 3,515 to 21,093 kg / cm 2 (50 to 300 psi) the molar ratio of hydrogen to hydrocarbons is preferably 1. : 1 to 10: 1, more preferably from 2: 1 to 6: 1. In the temperature range that varies from 400 ° C to 600 ° C, the dehydrocyclization reaction occurs with acceptable speed and selectivity. If the operating temperature is lower than 400 ° C, the reaction speed is insufficient and consequently the efficiency is too low for industrial purposes. When the dehydrocyclization operating temperature is higher than 600 ° C, secondary reactions such as hydrocracking interfere and conversion to coke occurs, and production is substantially reduced. Therefore, it is not convenient to exceed the temperature of 600 ° C. The preferred temperature range (430 ° C to 550 ° C) of dehydrocyclization is that in which the process is optimal with respect to the activity, selectivity and stability of the catalyst. The space velocity for each liquid hour of the hydrocarbons in the dehydrocyclization reaction is preferably between 0.3 and 5.

EXAMPLES The invention will be illustrated by the following examples, which describe particularly advantageous method modalities. While the Examples are provided to illustrate the present invention, they are not intended to limit it.

EXAMPLE 1 Referring to Figure 1, in one embodiment, a hydrocarbon feed of maximum boiling point 1 is fed to a depentanizer 10 to produce a C5-2 fraction stream and a C6 + 3 stream. The C6 + 3 stream is fed to the separator 15 to produce a larger fraction or division of C6-C7 with no C8 +, and a lower C8 + fraction with all the C8 + material. Note that the material without Cg + is in the upper C6-C7 fraction. The lower C8 + fraction 5 contains less than 10% Iv of C7_ hydrocarbon. The amount of feed to the top and bottom, as well as the composition of each part or fraction, is shown in Table I.

Table I Upper Lower% in% by weight% in% in% by weight weight of weight of a to file. food comp. food comp. n-paraffin c5 1.21 1.21 1.21 2.43 c6 13.49 13.49 27.06 c7 8.99 8.99 18.03 0.47 0.93 c8 10.60 _ 10.60 21.13 C9 3.69 _ 3.69 7.36 i-paraffin c5 0.21 0.21 0.42 c6 10.06 10.06 20.17 c7 5.76 5.76 11.55 c8 11.28 _ 11.28 22.50 C9 6.12 _ 6.12 12.21 Cío 0.42 0.42 0.84 Olefins 0.64 0.64 1.28 Naphthene C5 0.40 0.40 0.80 c6 3.28 3.28 6.58 c7 5.19 4.93 9.89 0.26 0.52 c8 6.01 6.01 11.99 c9 2.80 - 2.80 5.58 C6 aromatics 0. 89 0.89 1.79 c7 2 .28 2 .28 4. 35 c8 5. 88 5. 88 11-73 c9 + 0. 33 0 .33 0. 66 The upper Ce-C7 fraction 4 is passed through a sulfur absorber 20 to protect against sulfur / H2S contamination, and is processed on a first reformer 22 which contains a non-acidic zeolite, such as zeolite L Pt / K-Ba, or zeolite L of Pt / K with and without fluorine and / or chlorine. The operating conditions of the first reformer are 5.2732 kg / cm2 (75 lb / in2), 1.0 LHSV_hr_I, a hydrogen / hydrocarbon (H2 / HC) ratio of 5/1 mol / mol and a Cß + C- target? normal and conversion of isoparaffin (n + i) 90-93% paraffin. The Nafteños of Ce and C7 as cyclohexanes are completely converted while the cyclopentanes are not fully converted. The conversion of paraffin, isoparaffin and naphthene, individually, by carbon number in the first reformer is shown in Table II with the selectivity associated with the corresponding aromatic. The first reforming stream 24, from the first reformer 22, had a yield or benzene production of 21.0% by weight of the separator feed and a toluene yield of 14.8% by weight of the separator feed. The lower C8 + fraction is passed through a sulfur sorber 30 to protect against sulfur / H2S contamination, and is processed on a second reformer 32 which contains a bifunctional acid aromatization catalyst which is not required to be sulfided, such as Pt / Sn / Cl on alumina. The operating conditions of the second reformer are 5.2732 kg / cm2 (75 lb / in2). 1.0 LHSV ~ hr-1, a molar ratio of H2 / HC of 5/1 and a conversion of paraffin (n + i) C8 + C9 of 95-100%. The Nafteños of C8 and Cg are also totally converted. The paraffin and naphtha or conversion and selectivity used are shown in Table II.

Table II% Conversion% Selectivity ler Reformer n paraffins Ce 91.0 92.9 n paraffins C7 98.0 84.0 Demethylbutane C_ 40.0 methylpentane C6 91.0 92.9 isoparaffins C7 98.0 84.0 naphthenes Ce 89.1 92.9 naphthenes C7 100.0 84.0 2nd reformer paraffins (n + i) C7 88. 0 74.0 paraffin (n + i) C8 100. 0 81.0 paraffin (n + i) Cg 100. 0 92.0 naphthenes C7 100. 0 74.0 naphthenes C8 100. 0 81.0 naphthenes C9 100. 0 92.0 The first reforming stream 24 of the first reformer 22 is combined with the second reforming stream 34 of second reformer 32 and sends to a common gas-liquid separator 40 where the produced H2 is recovered along gas C1-C3 and it is recirculated to each reformer via a common recirculation compressor 42. The excess H2 and O.-C3 leave the system via line 44 for the subsequent recovery of pure H2, and O.-C3 as fuel gas. One of the benefits of a common separator is that it allows a common recirculating compressor that operates on gas released from the separator. Alternatively, you could also have two separate recirculation compressors (one for each reformer) to maintain flexibility in the operation. A benefit of a common separator is that it reduces the capital cost, which is further reduced if a common recirculating compressor is used. An additional benefit is that the gas produced in the non-acid reformer will have a hydrogen purity greater than the gas produced in the acid reformer. By combining these exhaust gases the acid reformer will be provided with a gas having a higher hydrogen purity. This can be taken advantage of by reducing the contaminated ratio or decreasing the operation and capital cost of the recirculating compressor. The liquid 46 of the separator 40 can be sent to a depentanizer to recover an upper fraction of C4-C5 and a lower fraction of C6 +, and the components of the current of C & + can be processed to separate the current in component streams.

While the present invention has been described with reference to specific embodiments, it is intended that this application cover several changes and substitutions that can be made by those skilled in the art without departing from the spirit and scope of the appended claims.

It is noted that in relation to this date, the best method known to the applicant to carry. the practice of said 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 (1)

1. CLAIMS 1. A process for reforming a hydrocarbon feed of maximum boiling point to improve yields or productions of para-xylene and benzene, characterized in that it comprises: (a) separating the hydrocarbon feed into a C5- fraction, a C6-C7 fraction , and a C8 + fraction, where the C6-C7 fraction had less than 5% Iv. of C8 + hydrocarbon, and where the fraction of. C8 + had less than 10% Iv of C7- hydrocarbon; (b) subjecting the C6-C7 fraction to catalytic aromatization at elevated temperatures in a first reformer in the presence of hydrogen and using a non-acid catalyst comprising at least one Group VIII metal and a non-acidic zeolite support to produce a first stream of reforming; and (c) subjecting the C8 + fraction to catalytic aromatization at elevated temperatures in a second reformer in the presence of hydrogen and using an acid catalyst comprising at least one metal of Group VIII acid catalyst comprises platinum and tin on an alumina support. 5. A process for the reforming according to claim 3, characterized in that the process further comprises the steps of: (d) combining the first reforming stream and the second reforming stream to form a combined reforming stream; (e) separating the combined reforming stream into a light fraction and a heavy fraction; (f) recirculate at least part of the light fraction either to the hydrocarbon feed or to at least one of the reformers.