ES2281145T3 - DEHYDROCICLATION PROCESS WITH SEPARATION OF CURRENT DIMETHYLBUTANE BELOW. - Google Patents

Abstract

In the present invention, dimethylbutanes are removed from the raffinate component of the feed to a dehydrocyclization process. Thus, according to a preferred embodiment, a process is provided for producing aromatics by the following steps: (a) contacting fresh paraffins rich feed hydrocarbons, containing 0.1 to 20.0 wt.% dimethylbutanes with a highly selective dehydrocyclization catalyst in a reaction zone, under dehydrocyclization reaction conditions, to convert paraffins to aromatics and obtain an aromatics rich effluent; (b) separating aromatics from the effluent to obtain an aromatics lean raffinate; (c) removing dimethylbutanes from the raffinate to obtain a raffinate of reduced dimethylbutane content; and (d) recycling the raffinate of reduced dimethylbutane content to the reaction zone. Preferably, the dehydrocyclization catalyst used is a nonacidic, monofunctional catalyst. Platinum on L zeolite is a particularly preferred highly selective dehydrocyclization catalyst for use in the process.

Description

Dehydrocycling process with separation of dimethylbutane downstream.

Field of the Invention

The present invention relates to dehydrocycling using a very selective catalyst of dehydrocycling and, in particular, separation of dimethylbutanes from recycling to a catalytic dehydrocycling zone very selective

Background of the invention

In the process of the present invention, by dehydrocycling aromatic hydrocarbons from a hydrocarbon feed. In the reaction zone they may have place other reactions and the reaction stage can be called in general renovated. Thus, in the reaction stage of the process of present invention, in addition to the dehydrocycling reaction or aromatization, other reactions may occur, such as dehydrogenation, isomerization, hydroisomerization, cyclization and hydrocracking The main reaction is dehydrocycling for form aromatic hydrocarbons from paraffins.

United States Patent Number 4,104,320, granted on August 1, 1978, describes that it is possible  dehydrocycling paraffins to produce aromatic hydrocarbons with high selectivity using a non-acidic monofunctional catalyst. Preferably, the catalyst comprises a type L zeolite. The type L zeolites preferred in the patent process of the United States number 4,104,320 are those that have cations interchangeable, of which at least 90% are sodium, lithium, potassium, rubidium or cesium. The catalyst used in the patent of United States number 4,104,320 also contains at least one noble metal of group VIII (or tin or germanium). In particular, in 4,104,320 are claimed catalysts having platinum in a zeolite L, in which potassium has been exchanged of zeolite L replacing a portion of potassium with rubidium or cesium, to achieve exceptionally high selectivity in the conversion of n-hexane to benzene. As described in U.S. Patent No. 4,104,320, preferably the zeolite L used is synthesized in its form Potassium A portion can be exchanged, usually no larger that 80% of potassium cations so other cations, preferably rubidium or cesium, replace potassium interchangeable.

After the United States patent No. 4,104,320, an important step forward was described in U.S. Patents Nos. 4,434,311, 4,435,283, 4,447,316 and 4,517,306, all of which were granted in 1984 and 1985. These patents describe dehydrocycling catalysts comprising a large pore zeolite, exchanged with a alkaline earth metal (barium, strontium or calcium, preferably barium) and in which the catalyst contains one or more metals of the group VIII, most preferably platinum. An essential element The catalyst of these patents is the alkaline earth metal. Especially when the alkaline earth metal is barium and the zeolite of large pores is zeolite L, the catalysts of these patents provide selectivities greater than those of the catalyst corresponding zeolite L exchanged with an alkali metal described in U.S. Patent No. 4,104,320.

These platinum catalysts on zeolite L mentioned in the previous two paragraphs, both in potassium form as in the form of another alkali metal or in exchange form with a alkaline earth metal, are substantially "non-acidic". These non-acid catalysts have been called catalysts "monofunctional". Such monofunctional catalysts do not acids are very selective to form aromatic hydrocarbons by dehydrocycling of paraffins.

Having a very selective catalyst, the Marketing seemed simple. However, this was not the case.  It was found that the very selective zeolite L catalysts that contain a group VIII metal were unexpectedly susceptible to sulfur poisoning at extremely low levels of sulfur in food. United States Patent Number 4,456,527 describes this discovery. Specifically, it was found that the concentration of sulfur in the hydrocarbon feed should be reduced to extremely low levels, preferably to less than 50 parts per billion, for stability acceptable, that is, a long running time, of catalyst when used in the process of dehydrocycling.

With the advances of US Patent No. 4,456,527, more attention was paid to the provision of the process under which the global dehydrocycling process is performed to produce aromatic hydrocarbons
cos.

United States patents numbers 4,648,961 and 4,650,565 describe processes that use a catalyst very selective dehydrocycling in which a rich diet in paraffins it contacts the catalyst to form aromatic hydrocarbons and then aromatic hydrocarbons are separate from the effluent from the reaction zone by means of a stage extraction with a solvent or by sieve separation molecular, and a stream of refining rich in paraffins from extraction with a solvent or from the stage of separation with molecular sieves is recycled to the area of the dehydrocycling reaction.

United States Patent Number 4,594,145 and reissued patent 33,323 describe a process that uses  a very selective dehydrocycling catalyst in which a paraffin-rich food contacts the catalyst to form aromatic hydrocarbons and then the aromatic hydrocarbons are separated from the effluent from the zone of reaction and the remaining paraffins are recycled to the area of reaction.

United States patents numbers 4,568,656 and 4,595,668 describe the use of a very catalyst selective dehydrocycling in which the metal component of the group VIII of the catalyst is very dispersed on a support of zeolite L. These two patents specify (see column 16, line 38, of patent 4,595,668): "as the catalyst is monofunctional and does not promote isomerization without cyclization, compounds of food like dimethylbutans are not effective. "

Another process-oriented patent that uses a very selective dehydrocycling catalyst is European Patent 335,540. This patent describes a process in which (a) a hydrocarbon feed is separated into a first fraction comprising C 5 - and dimethylbutanes hydrocarbons and into a second fraction comprising C 5 + hydrocarbons; (b) the second fraction is separated into (i) a light fraction comprising no more than 10% by volume of dimethylbutanes, the light fraction being selected from a C6 fraction, a C7 to C8 fraction , a C 7 -C 8 fraction, a C 6 -C 8 fraction and a fraction consisting essentially of C 6 and C 8 hydrocarbons, and (ii) a heavy fraction; and (c) the light fraction is dehydrocycled under dehydrocycling conditions in the presence of a monofunctional catalyst. Thus, according to the process of European Patent 335,540, dimethylbutanes are separated from the new hydrocarbon feed before dehydrocycling of the new feed to form hydrocarbons
aromatic

Summary of the Invention

In accordance with the present invention, provides a dehydrocycling process, a process that understands:

(to)

contact a food new hydrocarbon rich in paraffins and containing 0.1 to 20.0% by weight of dimethylbutanes with a very selective catalyst of dehydrocycling in a reaction zone under conditions of dehydrocycling reaction, to convert paraffins into aromatic hydrocarbons and get an effluent rich in aromatic hydrocarbons,

(b)

separate hydrocarbons from the effluent aromatic to obtain a refined low in hydrocarbons aromatic,

(C)

separate dimethylbutanes, in which the cited separation of dimethylbutanes consists in separating from effluent rich in aromatic hydrocarbons from step (a) or separate of the refined aromatic hydrocarbons poor from step (b), Y

(d)

recycle to the reaction zone a refined with a reduced content of dimethylbutanes,

in which said catalyst very selective dehydrocycling is a catalyst that, in the conversion of n-hexane into aromatic hydrocarbons under dehydrocycling reaction conditions, it causes a selectivity with respect to aromatic hydrocarbons corresponding to a conversion of n-hexane in aromatic hydrocarbons of at least 40% by weight per pass, excluding conversion of recycling.

Preferably the very selective catalyst of Dehydrocycling is a non-acid catalyst.

The catalyst preferably includes a group VIII metal, most preferably platinum, and preferably includes a one-dimensional crystalline aluminosilicate. The term "one-dimensional" means that the pores or channels of the crystals are oriented substantially only in one direction along the length or axis c of the
crystals.

Preferred aluminosilicates are zeolite L, Zeolite?, ZSM-10 and mordenite.

Most preferably the aluminosilicate is zeolite L. The zeolite L is one-dimensional.

In the process of the present invention, a centrally important feature is the separation of a main portion of dimethylbutanes downstream from the area of dehydrocycling reaction. So, dimethylbutanes don't They separate mainly from the new feed to the process. In its instead, in the present invention, dimethylbutanes are separated mainly from the effluent of the dehydrocycling reaction. The downstream dimethylbutane separation can be performed after having separated from the effluent from the reaction of dehydrocycling aromatic hydrocarbons or before separation of aromatic hydrocarbons but, in any case, downstream of the dehydrocycling reaction zone.

The separation of aromatic hydrocarbons from effluent from the reaction stage is preferably made by solvent extraction, distillation or sieve extraction molecular. Most preferably the hydrocarbon separation Aromatic is made by extraction with a solvent. This stage of separation of aromatic hydrocarbons causes a current of product rich in aromatic hydrocarbons and a stream of refined rich in paraffins.

In the process of the present invention, the dimethylbutanes are preferably separated from the stream of refined. Then the refining is recycled to the stage of reaction.

Among other factors, the present invention is based on the concept of separating dimethylbutanes primarily downstream of the dehydrocycling reaction stage in instead of separating dimethylbutanes from the new feed to the reaction zone In addition, the present invention is based on the discovery that this unusual point of separation from dimethylbutanes causes surprising advantages when performance and operating cost of the dehydrocycling process very selective

As described above, agree with an embodiment of the present invention, the separation of downstream dimethylbutanes is performed after having separated of the effluent of the hydrocarbon dehydrocycling stage aromatic

In accordance with another embodiment of the present invention, dimethylbutanes are separated downstream from the zone dehydrocycling reaction but before the treatment of effluent from the reaction zone to separate paraffins from aromatic hydrocarbons. Thus, according to this embodiment, provides a process for hydrocarbon dehydrocycling which includes:

(to)

contact a food new hydrocarbon rich in paraffins and containing 0.1 to 20.0% by weight of dimethylbutanes with a very selective catalyst of dehydrocycling in a reaction zone under conditions of dehydrocycling reaction, to convert paraffins into aromatic hydrocarbons and get an effluent rich in aromatic hydrocarbons,

(b)

separate from the effluent rich in aromatic hydrocarbons dimethylbutanes, to obtain a mixture  of aromatic paraffins-hydrocarbons with a reduced content of dimethylbutanes,

(C)

separate from the mixture of paraffins-aromatic hydrocarbons hydrocarbons aromatic to obtain a refined low in hydrocarbons aromatic, and

(d)

recycle the refined to the area of reaction.

Brief description of the drawing

The drawing is a simplified schematic flow chart of the process illustrating a preferred embodiment of the present invention, in which dimethylbutanes are separated downstream from the dehydrogen reaction zone.
cyclization

Detailed description of the invention

Making more detailed reference to the drawing simplified, new feed is introduced to the reaction zone of dehydrocycling by pipes 1 and 2. Feeds suitable are non-aromatic organic compounds, preferably feeds with boiling points in the range of naphtha, such as C6 {C} {C10} paraffins, more preferably C 6 -C 8. As the dehydrocycling is the key reaction in reaction zone 3, the feed is preferably composed of organic compounds non-aromatic C 6 or higher. Component Examples C6 {C} {8} paraffinic feed include n-hexane, n-heptane and n-octane.

The type of gasoline can be fed get directly from crude oil by distillation or you can obtain indirectly from a feed of fractions of oil by separating a stream with a boiling point in the range of gasoline from the effluent of a process of hydrocracking, coking or catalytic cracking. The adequate feeds of the type of naphtha can boil between approximately 60 and 220 ° C. Preferably, the feeding of the type of gasoline is predominantly composed (more than half in weight) of paraffins and, most preferably, paraffins C_ {6} -C_ {8}. Feeds particularly Preferred are C6 paraffins, especially n-hexane and also methylpentanes.

As indicated below in more detail, these feeds almost invariably contain dimethylbutans because dimethylbutanes boil at a temperature close to the point boiling hexanes. The following table 1 lists the boiling points of hydrocarbons in the range of C5 {C} {7} paraffins.

TABLE 1 Boiling points of hydrocarbons C_ {5} -C_ {7} selected

100

As you can see in table 1, the dimethylbutanes boil at a temperature close to the point of boiling of n-hexane and also of the methylpentanes, which are preferred feeds to the area of dehydrocycling reaction.

The new net food to the process of The present invention will contain dimethylbutanes, typically 0.1 to 20%, preferably 0.3 to 18%, more preferably 0.5 to 18% and most preferably 1.0 to 15% by weight of dimethylbutanes, based on the net or new hydrocarbon feed weight at process.

As dimethylbutanes are not desired in the area of dehydrocycling reaction 3, the prior art describes separate dimethylbutanes from the new feed. The separation of dimethylbutanes from the new feed can be done by distillation, as described in European Patent 335,540 before cited

However, in the process of the present invention dimethylbutanes are not primarily separated from the new feed to reaction zone 3. In the present invention dimethylbutanes are separated mainly downstream in the process, after aromatic hydrocarbons have formed in the dehydrocycling reaction zone. This separation of Dimethylbutanes downstream is described below.

Here, the term "new feed" means net feed of hydrocarbons to the process that has not passed through the area of dehydrocycling.

In the present invention, reaction zone 3 uses a dehydrocycling catalyst that has high selectivity to form aromatic hydrocarbons. In the present invention, the term "selectivity" is defined as percent moles of acyclic hydrocarbons converted into aromatic compared to moles converted into aromatic hydrocarbons and products cracked Thus, the percentage of selectivity can be defined by the following formula:

Selectivity = (A / B) x 100

in the that

A = moles of converted acyclic hydrocarbons in aromatics, and

B = moles of converted acyclic hydrocarbons in aromatic hydrocarbons and cracked products.

In the determination of selectivity it is not consider the isomerization of paraffins or the interconversion of paraffins and alkylcyclopentanes having the same number of atoms of carbon per molecule.

The selectivity to convert hydrocarbons acyclic in aromatic is a measure of the effectiveness of the stage of dehydrocycling reaction to convert into the reaction zone dehydrocycling, acyclic hydrocarbons in desired products and valuable (aromatic hydrocarbons and hydrogen) as opposed to Less desirable by-products, such as hydrocracking products.

Very selective catalysts produce more hydrogen than less selective catalysts because it is produced hydrogen when acyclic hydrocarbons are converted into aromatic while hydrogen is consumed when they become acyclic hydrocarbons in cracked products. By increasing the process selectivity increases the amount of hydrogen produced (more aromatization) while decreasing the amount of hydrogen consumed (less cracking).

Preferred catalysts for use in the area reaction 3 are very selective dehydrocycling catalysts,  particularly catalysts comprising a group metal VIII dispersed in a one-dimensional crystalline aluminosilicate. He very selective dehydrocycling catalyst is preferably a non-acid catalyst and preferably is a catalyst monofunctional

Preferably the catalyst used in the zone reaction 3 contains one or more metals of group VIII, for example, nickel, iridium, rhodium, platinum, rhenium or platinum. The most preferred group VIII metals for use in the catalyst of dehydrocycling are iridium, palladium and platinum, the most preferably platinum. The amount of Group VIII metal in the catalyst is preferably between 0.1 and 5% by weight, plus preferably 0.3 to 2% by weight, based on the catalyst total.

The metal or metals of group VIII can be introduce into the catalyst, that is, into the zeolitic component of the catalyst, by synthesis, impregnation or ion exchange made in aqueous solution of an appropriate salt. When desired introduce two metals of group VIII into the zeolitic component of catalyst, the operation can be performed simultaneously or sequentially

As an example, platinum can be introduced impregnating the zeolite with an aqueous nitrate solution of tetraamminplatin (II), chloroplatinic acid, chloroplatinous acid or diamminplatin or tetraamminplatin (II) chlorite. In a ion exchange process, platinum can be introduced using cationic platinum complexes, such as tetraamminplatin nitrate (II).

Preferably an inorganic oxide is used as a support to bind the zeolite containing the group VIII metal and provide greater strength and integrity to the particulate catalyst. The support can be a natural or synthetic inorganic oxide or a combination of inorganic oxides. Typical inorganic oxides that can be used as supports include kaolin, alumina and silica in which the acid sites have preferably been exchanged for cations that do not impart strong acidity (such as sodium, potassium, rubidium, cesium, calcium, strontium or
barium).

Preferred one-dimensional aluminosilicates for use in the dehydrocycling catalyst are zeolite L, Zeolite?, ZSM-10, cancrinite and mordenite. As the catalyst used in reaction zone 3, it is preferred especially zeolite L.

The zeolites L are synthetic zeolites. A theoretical formula is M_9 / n [(AlO2) 9 (SiO2) 27],  in which M is a cation that has valence n.

The actual formula may vary without changing the crystal structure For example, the silicon molar ratio to Aluminum (Si / Al) can vary from 1.0 to 3.5.

Although there are a number of cations that may be present in the zeolite L, in one embodiment it is preferred to synthesize the potassium form of the zeolite, that is, the way in which all interchangeable cations present are substantially potassium ions. The reactants consequently used can be easily obtained and are generally soluble in water. The exchangeable cations present in the zeolite can be conveniently replaced by other exchangeable cations, as will be indicated below, thus giving isomorphic forms of
zeolite L.

In a method of obtaining zeolite L, the Potassium form of zeolite L by heating a mixture properly aqueous of a metallic aluminosilicate whose composition, expressed as molar ratios of oxides, it falls within the following intervals:

K 2 O / (K 2 O + Na 2 O)

From about 0.33 to about 1

(K 2 O + Na 2 O) / SiO 2

Approximately 0.35 to about 0.5

SiO_ {2} / Al_ {2} O_ {3}

From about 10 to about 28

H 2 O / (K 2 O + Na 2 O)

From about 15 to approximately 41

Thus the exempt desired product crystallizes relatively of zeolite of different crystalline structure.

In another method, you can also prepare the Potassium form of zeolite L together with other zeolitic compounds using a reaction mixture whose composition, expressed as molar ratios of oxides, falls within the following intervals:

K 2 O / (K 2 O + Na 2 O)

From about 0.26 to about 1

(K 2 O + Na 2 O) / SiO 2

Approximately 0.34 to about 0.5

SiO_ {2} / Al_ {2} O_ {3}

From about 15 to about 28

H 2 O / (K 2 O + Na 2 O)

From about 15 to approximately 51

It should be noted that the presence of sodium in the reaction mixture is not critical to the present invention.

When the zeolite is prepared from mixtures reaction reactions containing sodium, in general they are also included sodium ions in the product as part of the cations interchangeable together with potassium ions. The product obtained from from the aforementioned intervals it has a composition, expressed as moles of oxides, which corresponds to the formula

0.9 - 1.3 [(1-x) K 2 O, x N 2 O]: Al 2 O 3: 5.2-6.9 SiO2: H2O

in which "x" can take Any value from 0 to about 0.75 and "y" can take any value from 0 to approximately 9.

To prepare zeolite L, reactants Representative as alumina origin are activated alumina, alumina  γ, alumina trihydrate and sodium aluminate. It can be obtained silica from sodium or potassium silicate, silica gels, silicic acid, soles of aqueous colloidal silica and solid silicas reactive amorphous In United States patents numbers 3,574,902 and 2,597,872 describe the preparation of silica soles typical that are suitable for use in the process of the present invention. Typical of the group of reactive amorphous solid silicas which preferably have a final size less than 1 micrometer they are materials such as fumes condensed silica and silicas chemically precipitated. Sodium and potassium hydroxides can provide the metal cation and help control the pH.

To prepare zeolite L, the usual method it comprises dissolving sodium or potassium aluminate and an alkali, by example, sodium or potassium hydroxide, in water. This solution is mixture with an aqueous solution of sodium silicate or preferably with a mixture of silicate-derived water, at least in part, from a sol of aqueous colloidal silica. The mixture of resulting reaction is placed in a container made, for example, of metal or glass. The container must be closed to avoid loss of water. The reaction mixture is then stirred to ensure its homogeneity.

The zeolite can be prepared successfully at temperatures of approximately 90 to 200 ° C, the pressure being the atmospheric or at least that corresponding to the vapor pressure of water in equilibrium with the mixture of reactants to the higher temperature Any suitable device of heating, for example, an oven, sand bath, oil bath or jacketed autoclave. The heating is continued until it is form the desired crystalline zeolite. Then the crystals of zeolite are filtered and washed to separate them from the mother liquor of reactants The zeolite crystals should be washed, preferably with distilled water, until the wash water effluent, in equilibrium with the product, have a pH between approximately 9 and 12. When the zeolite crystals are washed, It is believed that the exchangeable cation of the zeolite may be partially separated and replaced by hydrogen cations. Whether interrupts the wash when the pH of the effluent wash water is between about 10 and 11, the molar ratio (K 2 O + Na 2 O) / Al 2 O 3 of the crystalline product will be about 1.0. Then, the zeolite crystals can be Dry, conveniently on a stove with vent.

Zeolite L has been characterized by Donald W. Breck in "Zeolite Molecular Sieves", John Wiley & Sons, 1974, having a main structure comprising 18 units cancrinite tetrahedral units joined by 6 double rings in columns and crosslinked by simple oxygen bridges forming 12-member flat rings. These 12 member rings produce wide channels parallel to the c axis without failures of stacking Unlike erionite and cancrinite, the cancrinite cages are placed symmetrically through the 6 double ring units. There are four types of positions of cations: A in the 6 double rings, B in the cages of the type of the cancrinite, C between the cages of the cancrinite type and D in the channel wall. It seems that the cations in position D are the only interchangeable cations at room temperature. During dehydration, the cations of position D probably come out from the walls of the channels to a fifth position, position E, located between positions A. The absorption pores of hydrocarbons have a diameter of approximately 0.7 to 0.8 nm.

A more complete description of these zeolites it is given, for example, in United States patent number 3,216,789 which, more particularly, gives a conventional description of these zeolites. United States Patent Number 3,216,789 shows a zeolite L useful in the present invention.

Zeolite L differs from other pore zeolites large in a variety of ways, in addition to the diagram of X-ray diffraction.

One of the most pronounced differences is the Zeolite L channel system. Zeolite L has a system of one-dimensional channels parallel to the c axis while the most other zeolites have channel systems two-dimensional or three-dimensional. Zeolites A, X and Y have three-dimensional channel systems. The mordenite (of pores large) has a system of main channels parallel to the c axis and another system of very restricted channels parallel to axis b. The zeolita \ omega (mazzita) has a channel system One-dimensional

Another pronounced difference is in the structure Main of the various zeolites. Zeolite L has cages of type of the cancrinite joined by six double rings in columns and crosslinked by oxygen bridges forming 12 flat rings. The zeolite A has a cubic arrangement of β-cages in the form of truncated octahedra joined by units of four double rings. Zeolites X and Y have β-cages in the form of octahedra truncated tetrahedrally joined by six double rings with an arrangement similar to that of carbon atoms in the Diamond.

The mordenite has complex chains of five rings crosslinked by four ring chains.

The zeolite \ omega has polyhedra of the type of the gmelinite joined by oxygen bridges in columns parallel to the axis c.

The zeolite ZSM-10 is built by columns of alternate cages of the cancrinite type and six double rings. In the ZSM-10 zeolite there are two 12-ring oriented pore systems parallel to axis c. A 12-ring channel is apparently identical to the undulating channel of the main structure of the zeolite L and the other is apparently identical to the 12-ring channel of the main structure of the offer. Thus, it is believed that the ZSM-10 zeolite has two different systems of 12 channel parallel channels.

ZSM-10 zeolite is described in "ZSM-10: Synthesis and Tetrahedral Framework Structure", Zeolites , 16, 4, 236-244 (April 1996). The synthesis of zeolite ZSM-10 is also described in U.S. Patent No. 3,692,470.

Various factors affect the diagram of X-ray diffraction of a zeolite. These factors include the temperature, pressure, crystal size, impurities and type of cations present. For example, when the size of the crystals of zeolite L are smaller, the ray diffraction diagram X is wider and less precise. Thus, the term "zeolite L" includes zeolites made from cancrinite cages that have a X-ray diffraction diagram substantially similar to X-ray diffraction diagrams shown in the patent of the United States number 3,216,789.

Conventionally the zeolites L are synthesized mainly in its potassium form, that is, in the theoretical formula given above most of the M cations are potassium. The M cations are interchangeable so a zeolite can be used L given, for example, a zeolite L in potassium form, to obtain zeolites L containing other cations subjecting zeolite L to an ion exchange treatment in an aqueous solution of appropriate salts. However, it is difficult to exchange all original cations, for example, potassium, since some interchangeable zeolite cations are at sites that are difficult to reach by reagents.

As it mentioned above, preferably the catalyst used in reaction zone 3 is not acid. Absence of acidity can be achieved using metals alkaline or alkaline earth metals in the zeolitic component as it is described, for example, in United States patents 4,104,320 and 4,435,311.

The term "non acidic" is used in opposition to dual function acid catalysts, such as platinum on alumina halurada or platino-rhenium on alumina halurada or platinum on a zeolite exchanged for ammonium (and then calcined). See examples of these double acid catalysts. function for reforming / dehydrocycling in the patents of United States numbers 3,006,841, 3,415,737 and 3,783,123 (as in the Example 16 relating to a zeolite support exchanged for ammonium).

Although halides have been used in the past, in particular chlorides, to achieve a measure of the acidity of dual-function platinum-alumina catalysts for reforming or dehydrocycling, it should be indicated that they can be involve halides in the preparation of non-acidic catalysts very selective dehydrocycling, particularly when the support is an aluminosilicate, such as zeolite L. In the United States patents United numbers 4,681,865, 5,073,652, 5,196,631 and 5,294,579 are given examples of recent catalysts that involve the use of halides to prepare non-acid catalysts of the group metal type VIII-zeolite L. All these patents lately cited give examples of monofunctional non-acid catalysts of dehydrocycling that have selectivity to convert paraffins in aromatic hydrocarbons.

Referring again to the drawing, in the reaction zone 3 the feed contacts the catalyst very selective dehydrocycling under reaction conditions of dehydrocycling turning paraffins into hydrocarbons aromatic Here the term "catalyst very selective dehydrocycling "refers to catalysts that, in the conversion of n-hexane into hydrocarbons aromatic under the dehydrocycling reaction conditions described, originate a selectivity with respect to hydrocarbons aromatics corresponding to a conversion of n-hexane in aromatic hydrocarbons of at least 40% by weight, preferably at least 50%, more preferably at least 70% and most preferably by at least 80% per pass (excluding recycling conversion).

Preferably, in the present invention the very selective dehydrocycling catalyst is used under reaction conditions, such as those described herein, effective to achieve a conversion of paraffins in aromatic hydrocarbons and other hydrocarbons of at least 50% by weight, more preferably at least 60% and most preferably at least 70%, per pass. The performance of desired aromatic products, by pass, is the conversion by past multiplied by selectivity.

Suitable reaction conditions include a temperature between 400 and 600 ° C so that the reaction very selective dehydrocycling occurs with speed and selectivity acceptable.

Preferably dehydrocycling is performed. in the presence of hydrogen at a pressure set to favor thermodynamically the reaction and limit undesirable reactions of hydrocracking by kinetic means. The pressures used vary from 0.1 to 3.5 MPa, more preferably 0.45 to 1.5 MPa. The reaction molar of hydrogen to hydrocarbons is preferably 1: 1 to 10: 1, more preferably from 2: 1 to 6: 1.

The liquid hourly space velocity of hydrocarbons through the catalyst bed in the area of reaction 3 is preferably between 0.3 and 5, more preferably between 0.5 and 2.0.

How the dehydrocycling reaction is endothermic, the new food combined with recycled e Recycled hydrogen is heated in one or more ovens before its introduction to the catalytic reaction zone. In the diagram of Simplified flows are not shown as ovens feature separated. Also, the reaction zone shown in the diagram simplified is not divided into a series of reforming reactors or dehydrocycling although preferably the reaction of Dehydrocycling is performed in a series of reactors. In addition, the simplified diagram does not show exchange stages of hot.

The effluent from reaction zone 3 is passed to the separation zone 5, which can comprise a series of stages from separation. Hydrogen is recycled through pipe 6 from the zone of separation 5 to the reaction zone 3.

From the separation zone 5 it is removed by the pipe 7 material rich in aromatic products that passes to the area of separation 8. In the separation zone 8 hydrocarbons are separated aromatics that are removed as a product through the pipe 10. By the Pipe 9 non-aromatic hydrocarbons are removed. The separation of aromatic hydrocarbons of non-aromatics in zone 8 are can be done by extraction with a solvent, by distillation or using molecular sieves. In any of these methods of separation, for convenience, the term "refined" is used to refer to the paraffin-rich stream separated from the product consisting of aromatic hydrocarbons.

The term "paraffin rich" means more than 50% by weight of paraffins. Preferably refining Contains more than 80% by weight of paraffins.

The use of molecular sieves to separate aromatic products of paraffin-rich refining can be made passing aromatic hydrocarbons and paraffins through a bed of molecular sieves. Molecular sieves absorb the normal paraffins and some of the isoparaffins present but not aromatic hydrocarbons. To cause such separation, the molecular sieve must have an effective pore diameter of 0.45 to 0.55 nm. Examples of these molecular sieves are silicalite, zeolite L, zeolite A, zeolite X, zeolite Y, offertite and zeolite ZSM-10, with cations properly used for design the size of the openings of the zeolites and accommodate them to the desired separation

Alternatively, the separation in zone 8 is can be performed by distillation to separate from the aromatic product a stream of "refined" rich in paraffins.

Most preferably the paraffins are separated of aromatic hydrocarbons in zone 8 by extraction with a solvent, that is, aromatic hydrocarbons are absorbed in a solvent and, therefore, extracted from the stream of paraffins-aromatic hydrocarbons leaving the reaction zone The aromatic hydrocarbons extracted can be separate from the solvent by distillation. The solvents that are can use in this extraction method include phenol, sulfolane and N-formylmorpholine. In the patent of the States United number 5.401365 describes preferred methods of solvent extraction useful for the present process, including in particular extractive distillation.

After the separation stage of aromatic hydrocarbons, the amount of dimethylbutanes remaining in the paraffin-rich stream it can vary from 5 to 50% by weight, preferably from 10 to 40% by weight, more preferably from 15 to 35% by weight and most preferably 20 to 30% by weight, based on the total weight of the refining stream (stream rich in paraffins)

In accordance with this preferred embodiment of the present invention, before recycling the paraffinic refining to the reaction zone 3, dimethylbutanes are separated from refining. Preferably the dimethylbutanes are distilled off. Be has found that the global dehydrocycling process is surprisingly efficient when dimethylbutanes separate mainly downstream instead of separating most of the dimethylbutanes upstream of the reaction zone of dehydrocycling. The dimethylbutanes are separated from the zone of separation 11 by the pipe 12.

After separation of dimethylbutanes of the paraffin-rich stream described above, the amount of remaining dimethylbutanes is preferably 0.01 to 15% by weight, plus preferably 0.1 to 10% and most preferably 1 to 10% by weight of the stream rich in paraffins.

Preferably the separation of dimethylbutanes downstream of this embodiment is performed to separate from the paraffin-rich stream 70 to 99.8% of dimethylbutanes, plus preferably 75 to 99% and most preferably 80 to 95% of the dimethylbutanes, based on the total weight of the stream rich in paraffins

The drawing shows the separation of dimethylbutanes downstream after having separated from recycled paraffins aromatic hydrocarbons.

According to another preferred embodiment of the In the present invention, dimethylbutanes are separated downstream from the dehydrocycling reaction zone but before treatment of the effluent from the reaction zone to separate from the paraffins aromatic hydrocarbons. So, according to this embodiment, a process for dehydrocycling of hydrocarbons comprising:

(to)

contact a food new hydrocarbon rich in paraffins and containing 0.1 to 20.0% by weight of dimethylbutanes with a very selective catalyst of dehydrocycling in a reaction zone under conditions of dehydrocycling reaction, to convert paraffins into aromatic hydrocarbons and get an effluent rich in aromatic hydrocarbons,

(b)

separate from the effluent rich in aromatic hydrocarbons dimethylbutanes, to obtain a mixture  of aromatic paraffins-hydrocarbons with a reduced content of dimethylbutanes,

(C)

separate from the mixture of paraffins-aromatic hydrocarbons hydrocarbons aromatic, to obtain a refined low in hydrocarbons aromatic, and

(d)

recycle to the reaction zone the refined.

In this preferred embodiment, the amount of dimethylbutanes in the aromatic paraffin-hydrocarbon mixture prior to separation of the dimethylbutanes downstream can vary from 0.1 to 20% by weight, preferably from 0.5 to 15%, more preferably from 1 to 12% and most preferably 2 to 10%, based on the weight of the
mixture.

The amount of dimethylbutanes remaining in the mixture of paraffin-aromatic hydrocarbons after the separation of dimethylbutanes can vary from 0.01 to 8%, preferably from 0.05 to 6%, more preferably from 0.1 to 4% and the more preferably 0.2 to 1%, based on the weight of the mixture.

Preferably, the separation of dimethylbutanes Downstream is done by distillation. Distillation stage it can be done in one or more distillation columns using conventional distillation techniques performed in accordance with the requirements for the separation of dimethylbutanes from the present invention. In the embodiment in which the separation of downstream dimethylbutanes is performed before separation of aromatic hydrocarbons, the preferred stage of separation by distillation separates from the effluent rich in aromatic hydrocarbons 60-99% of dimethylbutanes, more preferably 70-99% and most preferably 80-90% of the dimethylbutanes present in the effluent rich in aromatic hydrocarbons. It can be indicated that the separation cited in this paragraph is based on feeding the separation stage of dimethylbutanes downstream and not in the new feed The percentage of separation over the New food is the basis of the following two paragraphs.

In the present invention, in any of the embodiments, dimethylbutanes are separated mainly downstream of the very selective dehydrocycling stage. He term "mainly" means at least 50% based on the total content of dimethylbutanes in the new feed, excluding the portion of the dimethylbutanes that separate effectively of the system due to cracking or other reactions of conversion of dimethylbutanes in the reaction stage of dehydrocycling. Usual amounts of separation of dimethylbutanes by conversion in the reaction zone of dehydrocycling are 10 to 50%, more typically 15 to 45%, based on the content of dimethylbutanes in the new food.

Preferably, at least 50% of the dimethylbutanes that are separated by distillation or other separation physical (as opposed to reactive conversion separation in other materials in the reaction zone) are separated by separation downstream, more preferably at least 60% of the dimethylbutanes are separated from the feed at the stage of dehydrocyclization by downstream separation. This percentage relatively high separation is contrary to the portion of dimethylbutanes that can be separated upstream, for example, of the new feeding when this, alone or with paraffins of the recycled, it is preferred to separate C 5 - and hydrocarbons other hydrocarbons Downstream separation refers to separation downstream of the reaction zone. The percentage of separation of dimethylbutanes, unless otherwise indicated, based on the weight of dimethylbutanes present in the diet new.

To achieve a relatively high percentage of separation of dimethylbutanes downstream from the zone of reaction, as required by the present invention, the percentage of separation of dimethylbutanes from the feed to the process of downstream dimethylbutanes separation should be high. So, as indicated above, preferably the percentage of separation of dimethylbutanes based on the paraffins present in feeding to the current dimethylbutane separation stage below is at least 70% and more preferably at least 80%

Referring back to the drawing, before the dehydrocycling stage, the feed can be distilled new, or the new feed combined with paraffins from recycled, such as the refining indicated by pipe 13, to separate C 5 - hydrocarbons. C5 hydrocarbons - are not adequate feeding to the reaction stage of dehydrocycling. The drawing does not show the stage of prefracking, which is a preferred step to separate C5 hydrocarbons -. Feed pre-operation new or combined new and refined feed stream recycled can separate dimethylbutans together with hydrocarbons C5 - and other hydrocarbons. However, according to the present invention, as indicated above, the amount of dimethylbutanes separated by said pre-fractionation or Upstream distillation is less than 50% of dimethylbutanes total, based on new feed, preferably less than 40% of dimethylbutanes separated by distillation or other physical separation

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Examples

The first configuration of this example is a in which a refining from an extraction unit of aromatic hydrocarbons after a reaction step of highly selective dehydrocycling reform is combined with new feed and then distilled to separate hydrocarbons C5 - and a smaller portion of the dimethylbutanes. After the distilled and refined new feed are fed to the stage dehydrocycling. This is called the "base case."

In a second case, according to the invention, a refining from the hydrocarbon extraction unit aromatics are distilled to separate a main portion of the dimethylbutanes and then distillate refining, along with Fresh food, combine and move on to the stage of dehydrocycling.

In both cases, the new feed is composed of the following components: C 5 hydrocarbons -, dimethylbutanes (DMB), 2-methylpentanes, 3-methylpentanes, methylcyclopentane, n-hexane and cyclohexane. In this example, the portion of dimethylbutanes in the feed contained 18% of 2,2-dimethylbutane and 82% of 2,3-dimethylbutane. The following are the relative compositions of the feed in both cases, expressed as a percentage by volume of the liquid (in food of this type, the percentages in weight are very similar to those volume percentages of the liquid).

one

The conversion is indicated below by passed in the very selective dehydrocycling stage of this example, expressed as a percentage by weight of each component of the feeding. The catalyst used was non-acidic platinum-zeolite L.

Dimethylbutanes 29.8 2-methylpentane 80.8 3-Methylpentane 84.9 Methylcyclopentane 90.5 n-Hexane 95.0 Cyclohexane 98.6

The performance of benzene in both processes, expressed in kilograms of benzene per kilogram of feed to the reaction zone:

Base case 0.65 Invention 0.68

Benzene yield (referred to the feed) in the case of the invention was 3% higher than that of the base case This is a substantial economic advantage of the case. preferred because the cost of food is a portion important of the total cost of manufacturing aromatic products. Distillation costs were also surprisingly advantageous in the case of the invention compared to the case base.

Claims (7)

1. A process for dehydrocycling hydrocarbons comprising:

(to)

contact a feed of hydrocarbons rich in new paraffins and containing 0.1 to 20.0% by weight of dimethylbutanes with a very selective catalyst of dehydrocycling in a reaction zone under conditions of dehydrocycling reaction, to convert paraffins into aromatic hydrocarbons and get an effluent rich in aromatic hydrocarbons,

(b)

separate hydrocarbons from the effluent aromatic to obtain a refined low in hydrocarbons aromatic,

(C)

separate dimethylbutanes, in which the cited separation of dimethylbutanes consists in separating from effluent rich in aromatic hydrocarbons from step (a) or separate of the refined aromatic hydrocarbons poor from step (b), Y

(d)

recycle to the reaction zone a refined with a reduced content of dimethylbutanes,

in which said catalyst very selective dehydrocycling is a catalyst that, in the conversion of n-hexane into aromatic hydrocarbons under dehydrocycling reaction conditions, it causes a selectivity with respect to aromatic hydrocarbons corresponding to a conversion of n-hexane in aromatic hydrocarbons of at least 40% by weight, excluding conversion of recycling. 2. A process according to claim 1, in which the very selective dehydrocycling catalyst is a non-acid catalyst. 3. A process according to claim 2, wherein the catalyst comprises a group VIII metal on a one-dimensional crystalline aluminosilicate. 4. A process according to claim 3, in which the aluminosilicate is zeolite L, zeolite? Or mordenite 5. A process according to claim 4, in which the aluminosilicate is zeolite L and the group metal VIII is platinum. 6. A process according to claim 1, in which aromatic hydrocarbons are separated by extraction with a solvent, distillation or sieve extraction molecular. 7. A process according to claim 6, in which the aromatic hydrocarbons are separated by extraction with a solvent