DE2521569A1 - PROCESS FOR ISOMERIZATION OF HYDROCARBONS - Google Patents

Description

PATENT ADVERTISER DR. HANS-GÜNTHER EGGERT ₁ DIPLOMA CHEMIST

5 COLOGNE 51, OBERLÄNDER UFER 90

Cologne, April 28, 1975 Fü / Ei / 54

UNION CARBIDE CORPORATION, 270 Park Avenue / New York NY 10017, USA .

Process for isomerizing hydrocarbons

The present invention relates to a process for isomerizing hydrocarbons, generally the Octane number of certain petroleum fractions and especially n-hydrocarbons continuously from branched-chain Hydrocarbons are separated and the n-fraction is isomerized and so branched-chain hydrocarbons higher octane number.

High octane gasoline has become scarce, and many Methods to improve this situation have been developed, using the petroleum available as effectively as possible converts. Historically, the reforming process was used in many individual process variants to convert gasoline fractions to convert low octane products, such as heavy naphthas, to higher octane gasoline products. It Another catalytic conversion process for hydrocarbons, isomerization, was also used. The emergence of processes for size- and shape-selective adsorptive separation by molecular sieves became Another process available for petroleum refining is the removal of the chain-like hydrocarbons a high octane product was obtained from the low octane gasoline range. At her The catalytic and the selective applications have individual applications

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Adsorption processes have had certain drawbacks either in yield or in conversion to high products Octane content or in the octane content of these products themselves. A number of procedures have been developed that include a combine a catalytic process with a selective adsorption process, but none achieved the successful one Combination of these methods to achieve effectiveness and simplicity, such as the new method according to the invention.

The invention relates to an isomerization process having three fixed adsorbent beds, each of which is essentially has the same adsorption capacity and void and contains particles that form a crystalline zeolitic Contain molecular sieves with an effective pore diameter of greater than 4 to less than 6 angstroms as an adsorbent, over which a mixture of normal and non-normal hydrocarbon compounds is passed, the normal Paraffin fraction contains n-pentane and η-hexane. From the starting material, the n-pentane and η-hexane are in the called fixed beds adsorbed by adding the starting material to one end of the beds and the non-adsorbed non-normal hydrocarbons decreases from the other end of each bed. The n-pentane and η-hexane is of each bed is desorbed by purging with hydrogen in countercurrent to the direction of flow of the feedstock. The mixture of hydrogen, n-pentane and η-hexane that escapes is then passed through under isomerizing conditions given a reactor containing a zeolitic molecular sieve isomerization catalyst. The inventive The method is characterized in that said three beds are desorbed in such a way that that never more than two beds are desorbed at a given time and the last stage of desorption in one of the three beds occurs simultaneously with the first stage of desorption in another of the three beds.

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The above-mentioned method makes it possible to solve a problem in a very satisfactory manner, which occurs in the separation of normal from non-normal hydrocarbons by selective adsorption of normal hydrocarbons in selective fixed-bed adsorbers and subsequent desorption of normal hydrocarbons with a flushing flow, in which the outflowing flow occurs directly is added to the catalytic isomerizer occurs. This difficulty arises from the fact that the adsorbed hydrocarbons are not desorbed in a uniform ratio and escape from the adsorption bed. There are a number of factors at play here; however, the overall effect is that the concentration of normal hydrocarbons in the effluent from the adsorber is markedly greater in the first section of the desorption than in the last sections. When the stream from the adsorber is fed directly to the catalytic isomerizer, the rate of the unit weight of normal hydrocarbons flowing through a given unit of space per hour (WHSV) through the isomerizer fluctuates over an undesirably wide range. Although the WHSV rate can vary over the wide range of about 1 to 10 (weight of hydrocarbon per hour per weight of catalyst compound) for a given isomerization unit, the optimum within this range will be determined by the other process conditions chosen. In practice, in the course of the isomerization process, it is not possible to continuously adapt and relate all process conditions to a constantly fluctuating WHSV value. Therefore, with fluctuating WHSV values, the overall process can never be carried out optimally, which causes losses in the yield and / or in the conversion rate.

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In the method according to the invention, this is reduced in sections Desorption from two beds so that the initial hydrocarbon rich stream of one bed is combined with the low hydrocarbon output streams of the other bed, the fluctuations of the WHSV value in the isomerizer and thus allows a greatly improved process management.

The process according to the invention also reduces a difficulty which normally occurs when the starting material to be catalytically isomerized contains a mixture of C 1-4 and Cg hydrocarbons. The difficulty relates to temperature control in the isomerizer and includes several factors. The optimum temperature for isomerizing η-hexane is partly dependent on the specific catalyst compound used, but in any case it requires a balance between the degree of conversion of η-hexane into the isomeric forms with a higher octane content and the degree of cracking of η-hexane to undesirable Products. A relatively low temperature favors the production of high yields of isomerizate with a low octane content per pass through the isomerizer. By raising the temperature slightly, you can get a product with a slightly higher octane content. but in a much lower yield. As the isomerization temperature continuously increases, the yield of the desired product, C ₅ , decreases rapidly because of excessive hydrocracking, even if the octane number of the desired product does not decrease significantly.

The same considerations apply to the isomerization of n-pentane. However, this is the optimal temperature for isolation not the same for n-pentane as for η-hexane, and when mixtures of n-pentane and η-hexane are isomerized should, the relative proportion of the two compounds that is fed to the isomerizer determines the optimum Temperature of the isomerization process.

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For this as well as other reasons it is important / that large fluctuations in the concentration of both n-pentane and η-hexane in the feedstock for the isomerizer can also be avoided. Such fluctuations arise in and of themselves by direct abandonment of a single adsorption bed, which is used for the selective adsorption of n-pentane and η-hexane a mixture with isopentanes and isohexanes was used, fractions flowing out to the isomerizer. Corresponding the fact that η-hexane is more strongly adsorbed than n-pentane by zeolitic molecular sieves, this enriches itself η-hexane at the inlet end and the n-pentane at the outlet end of the adsorption bed. Therefore, when rinsing the Bed for desorption, in which the feedstock for the isomerizer is obtained, highly fluctuating compositions of the outflowing desorbate. Previously, the uniformity of this feed was achieved in that large storage tanks were used in which all of the desorbate was collected from the adsorption bed and placed on the Isomerizer was mixed. This collection time and the expensive facilities required fall with the invention Proceeding. To be determined by the coordinated and section-wise desorption of two adsorption beds together Times so that the η-hexane-rich outflowing fraction of the last section of an adsorber in the pipeline to the Isomerizer with the outflowing fraction rich in n-pentane from the first section of another adsorber is mixed, an optimal isomerization temperature can be selected, which is constantly used for the conversion of the feedstock into a high octane end product.

The starting material, which according to the invention is to be improved in terms of its octane number, consists mainly of the various isomeric forms of saturated hydrocarbons containing 5 to 6 carbon atoms. Preferably the starting material consists of at least 40 mol% Cj-. and C, - saturated hydrocarbons, where n-pentane and η-hexane each at least 10% of the total starting

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- Make 6 materials.

As explained in more detail below / determines the composition of the available starting material, the preferred use in certain embodiments of the method. This means that the raw feedstock is first sent to the isomerizer or to the selective adsorption unit or both are given. The determination of the particular drop point depends on one or the other point of view the composition of the starting material.

In the embodiment of the process in which the starting material is fed to the plant through the adsorption unit, the starting material consists mainly of the various isomeric forms of saturated hydrocarbons having 5 to 6 carbon atoms. The starting material can contain larger amounts of iSO-C ₇ molecules, but should be relatively free of nC and higher hydrocarbons. The presence of iso-C_ in the starting material for the process according to the invention is acceptable, since the starting material first goes through the process section of molecular sieve separation, from where the iso-C_ is better directed to a collecting vessel for processed product than to the catalytic conversion stage, where it is would crack and increase coke formation. Polefinically unsaturated hydrocarbons must practically not be present in the starting material, since they consume hydrogen during the isomerization process and form residues in the adsorption bed. The saturated C ₅ and C _g hydrocarbon isomers advantageously form at least 40 mol% of the starting material, at least 10 mol% being normal pentane and / or normal hexane. The starting material often contains naphthene, sometimes up to 20%. A typical composition for the starting material is the following:

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Components % by weight

16.6 23.2 21.2 22.2 16.7

i-C 5 n-C 5 i-C 6th n-C 6th i-C 7th n-C 7th

In the embodiment of the process according to the invention, in which the starting material is introduced into the system by means of the isomerizer, the starting material is mainly composed of the various isomeric forms of saturated hydrocarbons with 5 Ls 6 carbon atoms. Such Ausgangsmater.al is usually the product of Desti Hationsverfahrer in the refining and therefore small amounts of C ₇ uid also contain higher hydrocarbons, but d ^ ise are often, if at all, only in trace amounts vorhandei. For the reasons given above, it is advantageous if the amount of olefinic hydrocarbons present in the starting material is less than about 4 mol%. Aromat ^ jche and Cyclopar äff inMolekoleküle have a relatively high octane beam, but are cracked to a large extent in the isomerizer and / or converted into molecules with a significantly lower octane number. Accordingly, the starting material should not contain more than about 15 mol% of aromatic and cycloparaffinic hydrocarbons together. _{The C 5} - and Cg-acyclic paraffins advantageously make up at least 85 mol% of the starting material, at least 10 mol% being n-petane and / or η-hexane. A starting material of the following composition is typical:

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Existing text Wt% XC ₅ 12.5 nC ₅ 29.5 ic ₆ 32.0 HC ₆ 24.6 X-C- 1.4

n-C_

In the preceding description of the starting material suitable for the process according to the invention, the The term "the various isomeric forms of pentane and hexane" includes all straight-chain and branched forms of these Designate connections. The prefix "iso" or "i" should also generally include all branched forms of the so-called Include connection.

The hydrogen stream, which is used as a purge gas when desorbing the adsorption bed and as a hydrogenation material in the Isomerization reactor is used need not be pure and generally consists of one or of the Combination of two or more refining hydrogen streams like reforming hydrogen and something like that. In this Containing impurities should be relatively unadsorbable and inert towards the zeolitic adsorber, the zeolitic catalyst and the hydrocarbon in the system. It should be noted that light hydrocarbons with 1 to 4 carbon atoms in the recycled hydrogen occur in the course of the implementation of the process, since these low-boiling substances in the catalytic unit getting produced. The recycled hydrogen stream preferably consists of at least 60 mol% hydrogen.

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The zeolitic molecular sieve used in the adsorption bed must select the normal paraffins of the starting material can adsorb, with the molecular size and configuration being the decisive selection criteria. Such a molecular sieve must therefore have an apparent pore diameter of less than about 6 angstroms and greater than about 4 angstroms. A particularly suitable zeolite of this type is zeolite A, described in US Pat. No. 2,883,243, which is disclosed in various divalent exchanged forms, especially in the calcium cation form, have an apparent pore diameter of about 5 angstroms and has a very large capacity for the adsorption of normal paraffins. Other suitable Molecular sieves are, for example, Zeolite R, US Pat. No. 3,030,181, Zeolite T, US Pat. No. 2,95O,952 and the naturally occurring ones zeolitic molecular sieves chabazite and erionite. The term "apparent pore diameter" as used herein can can be defined as the largest critical dimension or as the type of molecule that is produced by the adsorbent under normal conditions is adsorbed. The critical dimension is defined as the diameter of the smallest cylinder that makes up a model of the molecule using the available values of bond lengths, bond angles and Van der Waals radii was set up. The apparent pore diameter is always larger than the structural pore diameter, the can be defined as the free diameter of the corresponding silica ring in the structure of the adsorbent.

The zeolitic catalyst used in the isomerization reactor can be any of the catalyst compositions based on molecular sieves known to the person skilled in the art, which under the operating conditions of the present process shows selective and, above all, isomerization activity. As a general class, such catalysts include the crystalline zeolitic molecular sieves with an apparent pore diameter large enough to adsorb neopentane, a molar ratio of SiO ₂ / Al ₂ O ₃ greater than 3, with less than 60, preferably less than 15 val percent

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Alkali metal cations and in which the AlO. "- tetrahedra that are not associated with alkali metal cations are either associated with no metal cation or with a divalent or other polyvalent metal cation, the zeolitic constituent being associated with a hydrogenation catalyst, preferably a noble metal of Group VIII of the Periodic Table The catalyst compound can be used alone or together with a porous inorganic oxide diluent as a binder. The carrier for the hydrogenating agent is the zeolitic constituent and / or the binder. A large variety of inorganic oxidic diluents are known to those skilled in the art, of which some themselves have hydrogenation activity. Therefore, the term "an inorganic diluent with a hydrogenation agent" as used herein includes both diluents which themselves have no hydrogenation effect and carry a separate hydrogenation agent and those diluents which per se are hydrogenating agents are catalysts. Oxides which are suitable as diluents and which themselves have a hydrogenating effect are the oxides of the metals of Group VI of the Periodic Table. Examples of these metals are chromium, molybdenum and tungsten. However, the diluent preferably has no pronounced catalytic activity, in particular no cracking activity. In any event, the diluent must not have a quantitatively greater degree of cracking activity than the zeolitic component of the entire isomerization catalyst. Suitable oxides of this latter type are the aluminum oxides, silicon oxides, oxides of metals of groups III, IV-A and IV-B of the periodic table and cogels of SiO ₂ and oxides of metals of groups III, IV-A and IV-B, in particular aluminum oxide , Zirconium oxide, titanium oxide, thorium oxide and mixtures thereof. Aluminosilicate clays such as kaolin, attapulgite, sepiolite, polygarskite, bentonite, montmorillonite, etc. are also suitable thinners if they are converted into a pliable, plastic-like form by thorough mixing with water, especially if these clays are not used to remove larger Al ₃ O. , -Mengeη are acid-washed. Excellent isomerization catalysts are used in the

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individually in U.S. Patents 3,236,761 and 3,236,762. A particularly preferred catalyst is made from zeolite Y (US _{Pat. No. 3,130,007), which has a molar ratio of SiO 2} / Al ₂ O ₃ of about 5, in which the content of sodium cations is reduced to less than about 15 VaI by ammonium ion exchange then about 35 to 50 Val-% rare earth cations are introduced through ion exchangers and then the zeolite is calcined to remove the substantial proportion of ammonium ions. As the hydrogenation component, platinum or palladium can be deposited on the zeolite in an amount of about 0.1 to 1% by weight by any conventional method.

Depending on the particular catalyst compound used, the operating temperature of the isomerizer will generally be in the range from 240 to 390 C and the pressure in the range from 12.25 to 42 Ata. Although the entire adsorption, separation and Isomerization process is preferably carried out under essentially isobaric and isothermal conditions the effective working conditions with the adsorption beds in a wider range than with the isomerizer. Prints over the atmospheric pressure in conjunction with temperatures in the range of 240 to 39O ° C, which the starting material in gaseous Maintain condition are suitable for the process in the adsorbers.

In the present process the molar ratio of hydrogen to hydrocarbons is 5 to 6 carbon atoms at least 2, preferably at least 3, and up to about 30 in the feedstock added to the isomerizer. If the hydrogen content of the fraction flowing out of the adsorption unit is passed on to the isomerizer falls below the minimum of this molar ratio at any time, additional hydrogen can enter the Feed stream to the isomerizer may be added from any suitable source. It is preferable to set a share of the recirculated hydrogen stream from the same

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Procedural system too.

In the context of this invention, the term "bed void" is intended to denote any void in the bed that does not go through Solid material is ingested, with the exception of the intracrystalline cavities of the zeolite crystals. Against it the pores within a binder that can be used to form zeolite crystal agglomerates are voids in this sense.

With regard to the desorption step that each of the three Is subjected to adsorption beds as a result of purging with hydrogen in countercurrent flow, the term "first" is intended Section "not a special fraction of the entire desorption period, but only the first part of the Desorption period containing the highest concentration of n-pentane in the fraction flowing out of the bed, describe. In no case is the term "first segment" used to refer to more than the first 50% of the desorption period. It can also be just the first 5% or less of the desorption period, depending on factors such as concentration of normal hydrocarbons in the starting material to be treated and the relative ratio of n-pentane concentration to n-hexane concentration. The name is similar The term "last section" means a final portion of the desorption period which has the highest concentration of η-hexane in the contains the fraction flowing out of the bed and its duration is exactly as long as the said "first Section".

FIG. 1 is a schematic flow diagram showing the embodiment of the present invention in which the Starting material initially on the adsorption separation unit is added and the fraction flowing out of the isomerizer is returned to the separation unit.

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«13 -

Figure 2 is a schematic flow diagram illustrating the embodiment in which the starting material is initially applied to the Isomerizer is given and the product flowing out therefrom is returned to the adsorption separation unit.

The invention is illustrated by the following examples:

example 1

A starting material having the following composition was made according to a preferred embodiment of the present invention Isomerized process:

Starting material mole percent of the total

Component of the starting material

Isopentane 18.2

n-pentane 25.6

Cyclopentane 3.2

2,2-dimethylbutane 0.73

2,3-dimethylbutane 1.95

2-methylpentane 13.4

3-methylpentane 8.5

n-hexane 19.5

Benzene 1.17

Cyclohexane .4 5

Methylcyclopentane 7.3

When describing the cyclic process, it must be taken into account that the system has been in operation for a long enough time to reach a state of equilibrium, while using essentially the same starting material as above. According to Figure 1, fresh starting material is used abandoned through the pipe 10 on the system and with the condensate fraction of the brought up through pipe 11 out the isomerizer outflowing product in the barrel for the starting material 12, in which the temperature is about 32 ° C and the Pressure 11.55 ata, mixed. The mixed feedstock is from the drum 12 through the line 13 and the

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Pump 14 on heat exchanger 15, furnace 16, and then given through line 17 and valve 18 to the adsorber. When the feedstock enters the adsorber, it has a temperature of 371 C, a pressure of 16.73 Ata and the following composition:

Starting material mole percent of the total

Part of the starting material

Hydrogen 0.43

Methane O, 37

Ethan O, 25

Propane O.54

i-butane O. 43

η-butane O.19

iso-pentane 26.41

n-pentane 24.14

Cyclopentane 1.94

2,2-dimethylbutane 2.8O

2,3-dimethylbutane 2.36

2-methylpentane 12.62

3-methylpentane 8.O4

n-hexane 14.16

Benzene .65

Cyclohexane .27

Methylcyclopentane 4.39

Adsorber 19 contains just like the adsorber 2O and 21 a Fixed bed with pellets (1.6 mm diameter) of zeolitic molecular sieve type 5A, the effective pore openings of about Angstrom owns. By opening the valve 18 and Letting the compressed heated hydrocarbon gas pass becomes the adsorption fill step of the process initiated, at which point the adsorber essentially contains hydrogen gas of 37l ° C and 16.73 Ata. If that Starting product of gaseous hydrocarbons enters the adsorber, hydrogen gas leaves at the other end the adsorber through valve 22 into the manifold

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and valve 24 to the adsorber 20, in which the Desorption step of the process is performed. Valve 35 is open and adsorber 21 is simultaneously in Direction of flow flushed. It should be noted here that simultaneously with the adsorption-filling step in adsorber in the adsorber 21 the step of purging takes place in the direction of flow and in adsorber 20 the desorption takes place Rinsing is carried out in countercurrent and that each of the adsorbers successively the process stages: adsorption filling, Rinsing in the direction of flow and desorption by rinsing in countercurrent. While the Adsorption cycle in adsorber 19, during which one Bed volume of hydrogen is expelled from the adsorber, the outflowing gas flow is through valve 22 through the Distributor line 23 and valve 24 passed to the adsorber 2O. If the product is made from non-normal paraffins, which displaces the hydrogen from the adsorber 19, reaches the outlet end of the adsorber 19, becomes valve 22 closed and the product of non-normal hydrocarbons passed through valve 25 into the manifold 26 and withdrawn from the system after the greater proportion of the hydrogen contained therein in the cooling unit 27 was removed. The adsorption cycle in adsorber 19, whereby the product is obtained from non-normal ones, is interrupted, before the content of normal paraffins of the starting material in the bed cavity in the adsorber is unused Exceeds the sorption capacity of the bed for the feedstock of normal hydrocarbons. Definitely the adsorption cycle is ended before the normals break through the mass transfer zone. Assuming a time period of twelve equal units for a complete cycle for adsorption, purging in the direction of flow and desorption for each of the adsorber beds 19,2O and FIG. 21 the following diagram shows the time relationship of the three steps for each adsorber in this example:

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Adsorber
19th
20th
21

- 16 -

Time unit

12 3 4 ⁵ I ⁶ 7 I 8 I 9 I Io I 11 I 12 adsorption Wash
i.Str. Desorption adsorption Wash
i.Str. Desorption Desorption adsorption Desorption Wash
i.Str.

Accordingly, during the period from the beginning of the adsorption stroke in bed 19 until valve 22 closes, the is off Adsorber 19 outflowing hydrogen is used to desorb the adsorber 20 while purging. To avoid the desorption of Adsorber 20 at the same time as the end of the adsorption cycle in adsorber 19. contains the hydrogen recycled from the cooling unit 44 and, if necessary, additional hydrogen flowing through Line 28 is applied to the system through line 29, fan 47, heat exchanger 30, furnace 31, line 32 to Manifold 23 and then passed through valve 24. Simultaneously with the beginning of the adsorption cycle in the adsorber 19 makes the desorption of the adsorber 20 is progressing well and the effluent consists of a mixture of hydrogen purge gas and desorbed normal hydrocarbons. At the same time in the adsorber 21 was just a The adsorption cycle has ended, and there is sufficient unused adsorption capacity there, all of which are normal Can adsorb hydrocarbons of the starting material contained in the bed cavity. At this point will the product flowing out of the adsorber 20 is passed through valve 48 into distributor 33 and through valve 34, where it is in Adsorber 21 flushed through in the direction of flow. The scavenging of the adsorber 21 in the direction of flow is carried out as long as like the leaking non-normal hydrocarbons that leave the bed through valve 35, have the desired purity. This percentage of the product in non-normal hydrocarbons is passed through manifold 26 and in the cooler

5 0 '} -; / ♦ 7/1 1 8 0

collected. After completion of the purging cycle in the adsorber 21 in the direction of flow, valve 35 is closed and a hydrogen stream for purging-desorption is passed through valve 36 from distributor 23 and the desorbed normal hydrocarbons and hydrogen purging gas through valve 34, distributor 33, heat exchanger 15, line 37 passed to the catalytic isomerizer 39. Since the purging of the adsorber 21 in the flow direction was carried out using the mixture of hydrogen and normal hydrocarbons from the distributor, the bed cavity of the adsorber 21 contains a higher concentration of normal hydrocarbons than would be the case at the beginning of the purge-desorption cycle in adsorber 21 if essentially pure hydrogen were used for the flushing step in the direction of flow. Furthermore, the use of essentially pure hydrogen as the purge gas would cause a certain discharge of the normal hydrocarbon adsorbate from the inlet end of the adsorber in the direction of flow. Therefore, after the start of the countercurrent desorption cycle in adsorber 21, the first fraction flowing out therefrom, which is passed directly to the isomerizer 39, would be relatively poor in hydrocarbons. Since fluctuations in the hydrocarbon content of the feed to the isomerizer 39 are undesirable, this type of operating procedure is advantageously avoided. The method according to the invention considerably reduces these undesirable fluctuations by the special flushing step in the flow direction, which has been described above and in which adsorbed hydrocarbons are not discharged from the inlet end of the adsorber during the flushing in the flow direction. Therefore, the fraction initially flowing out of the adsorber 21 during the purge-desorption cycle is not excessively poor in hydrocarbons. The catalyst in the isomerizer 39 is a zeolite Y-palladium composition, in which the zeolite has a molar SiO ₂ / Al ₂ O ₃ ratio of 5, a sodium cation occupancy of about 10 eq% and an occupancy with rare earth cations of about 43 Val-% and the remaining cation sites are in the state that after calcining the for two hours

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Zeolite at 550 C / with the mentioned places with ammonium cations were occupied. The composition contains 0/5% by weight of finely divided palladium.

With reference to the timing diagram given above, it should be noted that the end portion of the desorption cycle in adsorber 20 is simultaneous with the first section of the desorption takes place in adsorber 21 and that a similar overlap of the desorption cycles of adsorber 21 with adsorber 19 and adsorber 19 with adsorber 20 occurs. Since the outflow from adsorber 20 Fractions in the last desorption section are relatively poor in desorbed hydrocarbons and those from adsorber 21 The effluent fraction is relatively rich in hydrocarbons during its first leg, is the stream of desorbates from the adsorbers 20 and 21 in the distributor 33 at all times with regard to the hydrocarbon concentration is much more uniform, than would otherwise be the case.

The temperature in reactor 39 is kept at about 26O C and the internal pressure is about 15.4 Ata. Normally, in the process described here, a molar ratio of Maintain hydrogen to hydrocarbons in the reactor above 2; but if due to any changes in the system if this ratio in the gas flowing into the reactor becomes less than 2, additional hydrogen will be of the recycled hydrogen from line 29 through valve 41, line 42 and valve 38 added. That from reactor 39 through Line 40 and heat exchanger 30 outflowing product has the following composition:

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Ingredient mol%

Hydrogen 68.45

Methane 8.75

Ethane 1.49

Propane 1.3O

iso-butane .47

n-butane .16

iso-pentane 8.52

n-pentane 4.65

Cyclopentane .0O

2,2-dimethylbutane 1.13

2,3-dimethylbutane .55

2-methylpentane 2.O8

3-methylpentane 1.33

n-hexane 1.11

and after flowing through the valve 43 and the recycle separator 44, in which most of the hydrogen and the light hydrocarbons, mainly those with 1 to 4 carbon atoms, it is deposited through valve 45 and line 11 to the adsorption unit returned.

In carrying out the embodiment of the method described above, it is not critical that the Hydrogen before passing through the adsorption unit with beds 19, 20 and 21 from the product coming from the isomerizer flows out, in the cooling unit 44 is removed. If desired, the cooling unit 44 can with the aid of the valve 43, the line 51 and the valve 45 are bypassed and all of the product flowing out of the isomerizer 39 through Line 11 are returned. In this case the system is kept at a much higher working pressure than in the embodiment described above, so that the partial pressure the hydrocarbon constituents of the feedstock for the adsorber beds on one for effective operation the adsorber is at a sufficient level. Impression of

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about 49 Ata in the adsorber is well suited for this purpose; however, it is not a critical value. With this "high pressure" variant of the process, hydrogen is used to desorb the adsorption bed through line 50 from cooling unit 27, in which non-normal products are removed from the system. With the help of the suction device 49 is off a fraction of the hydrogen flow from the cooling unit to the system 49 withdrawn, since this stream also contains a smaller proportion of light hydrocarbons that are caused by the Cooling unit 27 have not been removed and which would otherwise accumulate undesirably. A balancing amount of hydrogen is applied to the system through line 28.

Example 2

According to another preferred embodiment of the invention In the process, starting material of the following composition is isomerized:

Starting material mole percent of the total

Component of the starting material

Isopentane 18.23

n-pentane 25.56

Cyclopentane 3.21

2,2-dimethylbutane. 7 3

2,3-dimethylbutane 1.95

2-methylpentane 13.41

3-methylpentane 8.50

n-hexane 19.56

Benzene 1.08

Cyclohexane .45

Methylcyclopentane 7.32

The description of the cycle assumes that the system has been running for a long enough time to reach a state of equilibrium su using essentially the same starting material me described above.

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According to FIG. 2, fresh starting material is fed into the system through a line and flows through the heat exchanger 53, lines 54 and 55 into the isomerizer. The temperature in the isomerizer is about 260 ° C. and a pressure of about 15.4 Ata is used. Via the distributor 57, normal hydrocarbons desorbed by the selective absorption unit and hydrogen, which was used in the flow desorption, are mixed with the fresh starting material for the reactor. The catalyst for the isomerizer 56 is a zeolite Y-palladium composition, in which the zeolite has a molar SiO ₂ / Al ₂ O_ ratio of 5, a sodium cation occupancy of about 10 eq% and an occupancy of rare earth cations of about yal ~ * hak and where the other cation sites are in the state that results after calcining the zeolite, in which the sites are occupied with ammonium cations, for two hours at 55O ° C. The composition contains 0.5% by weight of finely divided palladium. The mixed feed to isomerizer 14 has the following composition:

Starting material mole percent of the total

Components of the starting material

Hydrogen 59.88

Methane 11.4

Ethane 2.17

Propane 1.53

i-butane .71

n-butane .12

iso-pentane 4.70

n-pentane 8.49

Cyclopentane .55

2,2-dimethylbutane .11

2,3-dimethylbutane .35

2-methylpentane 2.3O

3-methylpentane 1.44

n-hexane 4.86

Benzene .17

Cyclohexane .07

Methylcyclopentane 1.19

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The fractions flowing out of the reactor flow through Line 58, heat exchanger 53 and valve 59 to separator 60, where the largest proportion of hydrogen and light hydrocarbons, especially those with 1 to 4 carbon atoms, can be removed through line 61, and the rest of the effluent Fraction is then through valve 62, heater 63, line 64 to the pump 65 through valve 66 on the Adsorption bed 67 passed. Adsorber 67, like adsorbers 68 and 69, contains a fixed bed with pellets (1.6 mm diameter) of zeolitic molecular sieve type 5A with effective pore openings of about 5 angstroms. By opening the Valve 66 through which the compressed heated hydrocarbon gases are admitted, the adsorption-filling step of the process begins with the adsorber essentially Contains hydrogen gas at 371 ° C and 16.73 Ata. When the gaseous Hydrocarbons flowing into the adsorber as starting material escape at the other end of the adsorber Hydrogen gas from the bed cavity through valve 70 into manifold 71 and valve 72 to adsorber 68 where simultaneously the desorption step of the process is in progress. Valve 73 is open and adsorber 69 is simultaneously in the direction of flow flushed. It should be emphasized here that when the adsorption-filling step takes place in adsorber 67, it takes place simultaneously in adsorber 69 the purging takes place in the direction of flow and desorption takes place in the adsorber 68 by purging in countercurrent and that each of the adsorbers goes through the following steps one after the other: adsorption-filling, flushing in the direction of flow and desorption by countercurrent purging. During the course of the adsorption cycle in the adsorber 67, the one Bed volume of hydrogen is driven off from the adsorber, the outflowing fraction flows through valve 7O through the distributor and valve 72 in adsorber 68. If the non-normal paraffins product containing hydrogen from the Adsorber 67 drives out, reaches the outflow end of this adsorber, valve 70 is closed and that from abnormal Product containing hydrocarbons is passed through valve 74 into collection manifold 75 and removed from the system,

509847/1180

after most of the hydrogen contained therein has been removed in the cooling unit 76. The adsorption cycle in the adsorber 67 with recovery of the product of abnormal is interrupted before the content of abnormal Paraffin of the feed product contained in the bed cavity in the adsorber reduces the unused sorption capacity of the bed for normal hydrocarbon feedstocks. In any case, the adsorption cycle is ended before the material transfer zone of the normal hydrocarbons breaks through.

If one takes a period of twelve equal units for a full cycle of adsorption, purging in Assumes the flow direction and desorption for each of the adsorbent beds 67, 68 and 69, the following table shows the relationship of the three steps for each adsorber in this example:

Time unit

Adsorber r-l 2 3 4th adsorption 5 6th 7th 8th 9 Io 11 I 12 adsorption Wash
i.Str. Desorption 67 Desorption Wash
i.Str. Desorption Desorption adsorption 68 Wash
i.Str. 69

Accordingly, during the period from the beginning of the adsorption stroke in bed 67 until valve 7O closes the hydrogen flowing out of the adsorber 67 for flushing-desorbing of the adsorber 68 is used. In order to complete the desorption of adsorber 68 at the same time as the end of the adsorption cycle in adsorber 67, hydrogen purge gas, with hydrogen returned from the cooling unit 60 via line 61 and, if necessary, additional hydrogen, which is applied to the system through line 67, through line 78, pump 79, furnace 80, line 81 to the manifold and then passed through valve 72. Simultaneously with the beginning of the

5 0 9 8 4 7/1180

adsorptions takte ^ ini Adsorbs ι 537 sac ^ c flis »se sorption of the Ädsorfasrs 6 £ well ·, -; Fi> rtsG ^ rit / ts nnü dia outflowing Frakti consists of a,:; G ^ inissli? Oa i ^ oxygen-Splii ^ as aod

t-jöiT'üs in Adsorber 69 straads 3i2 ^ z ^ äsojrjptiomstak-c ibseüdet iiRd Adsorber 69 liat. : .i £ r: '? - anri "STiii!". 3i ".'/;Ädsoep" c.lOEisk. £ pasItIIt ₄ - the Susi üd3--3j. ". biaren lar gesc ^ rc ^ ;: nersalZioliISiAyasseirctoffei. the Ib de £ Si t'ui iSa-tfclicIilrn'nnL "bsfiiitlli ^ IdB :; ^ .TascjaiigsEiatsrial "" / o ^ lisgen _D £ usrelcli "te 2 ^: 'diass ^ 26: Ltp": ;; J; t "visifl -ilJ.-s' 7OEi Msoirfcsr 68 aas =

sowis £ ΐΐΓΰΙΐ "/ ¹ SJi ^- C.". I 32 Cj "a% s: lt - 2 '* ^ ΐ / ο siü as flushing gas in StsöaauEaijsriCiitysr for ild'scrb-SÄ: öS ulsn ^ o the flushing of the adsorber 69 in z ^r ~ v, z'c-iaun ~ zj - j.oircv.ri <y ^ jlza continued as long as dis from η1 &: -> = 22ΰί; 3? Β1 <= Ώ "Jhl-s' i ^ asiS'SZ'st.offeK bsst agisstsöEasBae IFza.iitxon, äi:?: d ^.? ^ Yssitil 73 the bed ^

"7OE2 dsr% ^r öwüassh '' _: 5n Sslsheit isto rdss-sr portion of the from aicliit = in, '3L;ZBal'in Echi-ifiv-ja-s ^' Si ^ 'tOiifsin fcsatelieiiäea Produlsts becomes di" rcfi d ^ ^ i Veör-AeSi-i sr 75 ^ i ^ iJhzr "; ^ nd i" i 2CSSiler 7 ¹ S gesaMSEeltc i'j'Snii ds ^ -pciiii "de ?; S'JÜlt'itcj: Ui StJr ⁱ 5nMiii9 ⁱ s "? Ichti2jii'y ia ÄdsGriber S aseiidet is«: - ~ ird ¥ sntil 72 fjssÄlosssn and a hydrogen = - stroa sks;. Splvlsr—Desorb.ie ^ £ i: d '; ^ - 3fe textile 84 from the ¥ s2r = part sir 71 ei ^' al ^ itefc is ^ d -jls dss-oribisrten MoriiialkGhleawasserstoffs iind ifasssrstviff-SpCIi'piK diareih Tsntil 83 mod distributor for the catalytic converter: IscmesriPisz) sgi ! ± _o et Ds of the adsorber la StrG3iiingp; i * icfic ig "i iinis: · 'J'sE'wsiidurag' sines mixture of hydrogen" ind ■ lorisalkoIils ^ wasSsrst.Qffea was flushed from deia distribution as a purge gas _e eiithält the bed wag! space of the adsorber 69 zn beginning of SjpüIHDssssptions-Takfcs in adsorber higher Could anfcr ation of norKialkoblenwasser material _s? would be as is the case when * would Substantially pure hydrogen for Spülscliritt in StroiTiurigsriclitHfig vejn-yendet _o ver Jenn also in wesentlichst pure hydrogen as a purge gas in Ströiiungsriehtung:? -rsndet word'sn 5 are, this would have a certain amount of discharge Noreialkohlsahydrogen ^ -Ädsorbat worn Siagangs' -. Risstei des Ädsorfc-22:; € • rvül consequence = accordingly, after the beginning of the iJec-eastrciiW ^^ orptioinstaktes in adsorber the dsr £, ^ 5e :: usv: _ cfesside sr ^ ts Fra.'stio ^ j the direct to the

bO3 '^ 47. 1130

Isomer! 56 is passed, a relatively small proportion of hydrocarbons. Because fluctuations in the concentration of hydrocarbons in the feed to the isomerizer 56 are undesirable, it is advantageous to avoid this procedure. The inventive method eliminates these undesirable Fluctuations in the direction of flow due to the special flushing step described above, in which adsorbed hydrocarbons are not discharged from the inlet end of the adsorber during purging in the direction of flow, which is very important down. Therefore, the first fraction flowing out of the adsorber 69 is not excessive during the purge desorption step low in hydrocarbons. When carrying out the embodiment of the invention described above Process, it is not essential that the hydrogen before being passed through to the adsorption unit with the beds 67, 68 and 69 is removed from the product flowing out of the isomerizer in the cooling unit 60. If desired, the Cooling unit 60 via the valve 59, the line 85 and the valve 62 are bypassed and all flow from the Isomerizer 56 can be recycled through heater 63, line 64 and blower 65. When working like this the system is kept at a much higher working pressure than in the embodiment described above, so the partial pressure of the hydrocarbon constituents in the feed product for the adsorber beds is sufficient for one effective working of the adsorber possesses. A pressure of about 49 Ata in the adsorber is well suited for this purpose, it is but not a critical value. With this "high pressure" variant of the process, hydrogen is used to desorb the adsorption bed from the cooling unit 76, in which from Non-normal hydrocarbon product removed from the system is recycled through line 86. To the distance a portion of the hydrogen electricity from the system, namely the cooling unit 76, an extraction device is provided, since this stream at the same time has a smaller proportion lighter contains hydrocarbons which have not been removed by the cooling unit 76 and which are otherwise undesirable

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Dimensions would accumulate. A corresponding amount of hydrogen is fed to the system via line 77.

509847/1180

Claims (1)

Patent.an .spr uch A process for isomerizing hydrocarbons in a plant which has three fixed adsorption beds, each having essentially the same absorption capacity and the same bed cavity and containing particles with an adsorbent based on crystalline zeolite molecular sieve having an effective pore diameter of greater than 4 to less than 6 angstroms owns / using a mixture of normal and non-normal hydrocarbon compounds, the proportion of normal paraffins containing n-pentane and η-hexane. , as a feedstock for adsorption, wherein n-pentane and n-hexane are adsorbed from the feedstock in the fixed adsorption beds by introducing the feedstock into one end of each bed and withdrawing the non-adsorbed abnormal hydrocarbon compounds from the other end of each bed, n -Pentane and η-hexane is desorbed from each bed by flushing with hydrogen in countercurrent to the direction of flow of the starting material and the outflowing mixture of hydrogen, n-pentane and η-hexane is passed under isomerization conditions through a reactor with a zeolitic molecular sieve as isomerization catalyst, thereby marked, that one desorbs the three beds in such a way that no more than two beds desorb at any one time and the last desorption section in one of the three beds at the same time as the first desorption section in another of the three beds. 6 0 j ii U 7/1 1 B 0