KR810000479B1 - Method for isomerization of hydrocarbon - Google Patents

Abstract

Isomerization of C8 alkyl arom. hydrocarbons by contacting the feedstock with an isomerization catalyst, e.g. PtSiO2 Al2O3, in the presence of H, sepg. the effluent from the previous step into a H-rich fraction, a 1st hydrocarbon-rich fraction contg. C6H6 and PhMe, and a 2nd fraction enriched in C8 alkyl arom. hydrocarbon, and recovering at least one C8 alkylarom. hydrocarbon from the 2nd fraction, was improved by recycling at least a portion of the 1st hydrocarbon-rich fraction to the isomerization zone.

Description

[Name of invention]

Isomerization method of hydrocarbon

Detailed description of the invention

The invention C ₈ relates to the isomerization (異性化) aromatic alkyl and more particularly, the present invention is the isomerization process of C ₈ aromatic alkyl that is produced by-product (副産物) having a C ₈ lower molecular weight (低分子量) than aromatic alkyl .

Processes for the preparation of various C ₈ alkyl isomers are of great importance in the petroleum and petrochemical industries, which have become industrially important due to the increasing demand for certain isomers, in particular paraxylene and orthoxylene.

C ₈ one or more separation steps or units from the mixed flow (混合流) of an aromatic alkyl, to remove the one or more of specific C ₈ aromatic alkyl isomers (e.g. crystallization, adsorption, second fractionation (超分別; aromatic alkyl such Superfractionation) The remaining C ₈ aromaticalkyl material is fed to the isomerization zone supplemented with the desired isomeric concentration, or the effluent or effluent from the isomerization zone. A portion of is fed to a separation unit to recover the desired isomers.

In particular, in the isomerization method of C ₈ aromatic alkyl, the isomerization reaction is generally carried out by contacting a bifunctional catalyst having hydrogenation and cracking activity and causing a desired isomerization reaction with a hydrocarbon mixed with hydrogen under isomerization conditions. Is performed. Contacting the C ₈ aromaticalkyl with the catalyst under isomerization conditions produces C ₈ naphthenes, toluene and C ₉ + aromatics in the byproducts.

Such C ₈ naphthenes are advantageously maintained in a stream of C ₈ aromatic alkyls and passed through the separation zone, and then recycled to the isomerization reaction to improve the yield of specific or desired C ₈ aromatic alkyl isomers. do. Recycling C ₈ naphthenes in a C ₈ aromaticalkyl isomerization reaction to obtain a beneficial effect is described in a number of patents, such as US Pat. Nos. 3, 538, 173 and 3, 553, 276.

Although methods for increasing the yield of specific or desired aromaticalkyl isomers have been shown in numerous prior art, the yield of C ₈ aromaticalkyl isomers can still be increased further.

The present invention is directed to promoting the isomerization of C ₈ alkyl benzene in the presence of hydrogen under isomerization conditions, where a feed containing C ₈ alkyl aromatic hydrocarbons can isomerize at least a portion of the C ₈ aromatic hydrocarbons in the isomerization zone. Contact with an effective catalyst to produce an effluent, which separates the effluent to form a hydrogen-rich stream, the first hydrocarbon containing toluene and having a lower average molecular weight than C ₈ aromaticalkyl Is separated into a higher fraction and a second fraction with enhanced C ₈ aromatic alkyl content compared to the effluent to recover at least one C ₈ aromaticalkyl product from the second fraction and the first hydrocarbon the method of isomerization of C ₈ alkyl aromatic hydrocarbon to a portion of the many ryubun back into contact by recirculation as isomerization The. This improved process increases the yield of certain or desired C ₈ aromaticalkyl hydrocarbon isomers and results in more efficient and complete isomerization of C ₈ aromaticalkyl.

In the isomerization zone of the process of the invention, C ₈ naphthenes and toluene are sometimes produced. These naphthenes are produced by hydrogenation of C ₈ aromaticalkyl and some naphthenes continue to isomerize. Toluene is produced by disproportionation of C ₈ aromatic alkyls and other cracking reactions.

Preferred specific methods of the present invention are as follows. A hydrocarbon feed consisting of C ₈ aromaticalkyl hydrocarbons in a non-equilibrium mixture, ie, paraxylene, orthoxylene, methaxylene, ethylbenzene, etc., is contacted with the catalyst composition in the presence of hydrogen under isomerization conditions in at least one reaction zone. . The reaction zone effluent passes through a gas separator such as a flash drum, where hydrogen-rich gaseous stream is removed from the effluent.

At least a portion of this hydrogenous gas phase stream is recycled to the isomerization zone where isomerization takes place to replenish a portion of the hydrogen. The remainder of the effluent from the gas separator is sent to a second separator, such as a distillation column, where it is produced in the isomerization zone, where the first hydrocarbon containing toluene has a lower average molecular weight than C ₈ aromatic alkyl. The minutes are recovered. The remainder of the effluent, consisting of a second stream enriched with C ₈ aromatic alkyl content relative to the total isomerization zone reactor effluent, may be further sent to a separator, e.g. distillation, crystallization, adsorption, fractionation, etc., to at least one desired C ₈ aromatic. The alkyl isomer product is recovered. Preferably, for example, some of the C ₉ and heavy hydrocarbon materials produced in the isomerization zone are removed from the effluent. Part of the remaining C ₈ aromaticalkyl hydrocarbons after recovery of the desired isomer product is preferably recycled to the isomerization zone for further isomerization. Sending a large fraction of the first hydrocarbon portion of the portion to the isomerization reaction yields higher yields of specific or desired C ₈ aromaticalkyl hydrocarbon isomers and effectively completes the isomerization of C ₈ aromaticalkyl. Specifically, the first hydrocarbon-rich stream also contains C ₈ naphthenes.

Up to about 5% by weight of alkyl, more preferably up to about 1%.

The first hydrocarbon-rich stream further contains C ₁ to C ₈ paraffins and C ₅ , C ₆ , and C ₇ naphthenes and benzenes of various structures, such as methane, ethane, propane, butane, pentane, hexane, heptane and octane. It may contain. Preferred component concentrations of the first hydrocarbon-rich stream are as follows.

0 to about 40 weight percent C ₁ to C ₄ component

0 to about 40 weight percent C ₅ to C ₈ paraffins

About 1 to about 20% by weight of C ₅ to C ₇ naphthenes

0 to about 50 weight percent C ₈ naphthenes

About 1 to about 20 weight percent benzene and

From about 3 to about 70 weight percent of toluene.

Preferably, the first hydrocarbon-rich separator, e.g., a distillation column, is a substantial part of the toluene and C ₈ naphthenes produced in the feed to this separator, for example in the isomerization feed and in the isomerization reaction zone. It is best to design most of them to remain in the material that is sent to further processes, such as, for example, bottom products from a distillation column. Thus, given the specific description of the first hydrocarbon-rich stream, the remainder of the isomerization zone effluent from the gasparation zone has, for example, one or more columns and reboilers, condensers. It is supplied to a distillation column apparatus consisting of a cooler, a product collection stage, a pump, and the like, where the low boiling point material is concentrated into the column top product of the tower.

The overhead product of the tower can maintain the liquid phase as a whole or substantially by adjusting the operating pressure of the tower and the like. Preferably, however, the operation of the distillation column is controlled so that a portion of the column product remains in the system with gaseous material. At least a portion of the liquid column product of the tower is returned to the isomerization stage. Moreover, the first hydrocarbon-rich stream, partly delivered to the isomerization zone, can be obtained as a tributary product of this distillation column. In either case, the first hydrocarbon-rich stream can be obtained as a tributary product of this distillation column. In either case, the first hydrocarbon-rich stream contains tributane toluene, may contain C ₈ naphthenes, and has a lower average molecular weight than C ₈ aromaticalkyl. This first hydrocarbon-rich stream is substantially free of C ₈ aromaticalkyl hydrocarbons, for example the C ₈ aromatic toluene content is at least 10%, more preferably at least 20%, as part of the total toluene supplied to this separator. Preferably, the content of C ₈ naphthenes in the first hydrocarbon-rich stream is 90% or less, preferably 80% or less, as part of the total C ₈ naphthenes supplied to this separator. It is also preferred that at least 30% by weight, preferably 40% by weight and more preferably 50% by weight of the first hydrocarbon-rich fraction is returned to the isomerization zone. A portion of this material is preferably removed from the process to control the toluene and light component content in the reaction zone to economically advantageous levels. The first number of the first ryubun of hydrocarbons also is a C ₈ naphthyl C ₈ naphthenes is the first of the hydrocarbon-containing Tendo to and removed from the process by removing a portion of the number of components. The loss of C ₈ naphthenes in this first hydrocarbon-rich stream has a detrimental effect on the yield of certain desired C ₈ aromaticalkyl isomers and should be kept to a minimum, for example, as described above.

This C ₈ naphthene is 1, 1, 3-trimethylcyclopentane, 1, 1, 2-trimethylcyclopentane, 1, 2, 4-trimethylcyclopentane, 1, 2, 3-trimethylcyclopentane, 1, 1- Various alkylcyclopentanes and alkylcyclohexanes such as dimethylcyclohexane, 1,4-dimethylcyclohexane, methyl-ethyl-cyclopentane and the like. Recycling a portion of the naphthene hydrocarbons present in the effluent of the isomerization zone to the isomerization reactor is advantageous because it minimizes the loss of aromatic hydrocarbons caused by the presence of naphthenes in equilibrium with C ₈ aromaticalkyl.

At least one isomerization catalyst composition is used in the process of the present invention. Such catalysts include at least one hydrogenation-dehydrogen component, preferably selected from Group VI metals, Group VIII metals, Group VIII metals, and mixtures thereof. These metallic components may be formed by a carrier such as at least one acidic inorganic oxide, such as alumina, silica-alumina, faujsites, mordenite, or a combination thereof by a method such as impregnation. ), Preferably from about 0.05 to 30% by weight of the catalyst composition is used as the carrier, calculated on an elemental basis. Moreover, the catalyst may contain a small amount of halogen, such as about 0.1 to 5.0% by weight of the catalyst, such as chlorine and fluorine, thereby enhancing the catalytic effect of the catalyst and the halogen being The isomerization zone may continue to pass in the form of a mixture with hydrogen and / or hydrocarbon feed.

Preferred catalytic materials used in the present invention include natural or synthetic crystalline aluminosilicates, which have a regular internal structure. These materials have a large surface area per gram and are microporous. Due to the nature of the regular internal structure it has a certain size of pores. Several forms are industrially useful. For example, a 5A material refers to a material having an A structure and having a pore diameter of about 5 mm 3 and a 13X material having a kind of X-positive site structure and having a pore diameter of 10 to 13 mm 3. In addition, a substance having a Y-positive site structure and the like is also known. Many of these materials can be converted to H or acid form, where hydrogen occupies the cation site. For example, this conversion can be accomplished by ion exchange of this material with ammonium ions, heating to remove NH ₃ or by acid leaching. In general, H type is more stable because it has a high Si / A1 ratio of about 2. 5/1 or more. The concentration of aluminosilicate is in the range of about 1 to 75% by weight, preferably about 5 to 50% by weight, based on the total isomerization catalyst composition.

Indeed, the material having C ₈ aromaticalkyl isomerization catalysis is H mordenite. Mordenite is naturally produced with sodium hydroxide corresponding to the following structural formula.

Na ₈ (A ₁ O ₂ ) ₉ (Si ₂ ) ₄₀ . 24H ₂ 0

This mordenite material can be leached to H or acidic form with dilute hydrochloric acid. Preferably the mordenite material useful in the present invention contains at least 50% acidic form.

Another isomerization catalyst with high activity is prepared using conventional 13X molecular sieves such as those described in US Pat. No. 2, 882, 244. This material contains rare earth chlorides at about 180 to 200 ° F (82 to 93 ° C.) to remove sodium ions from aluminosilicate complexes and to replace some of them with chemical equivalents of rare earth ions. ) solution (containing 4% of REC1 _3. 6H ₂ O) as a base exchange (鹽基交換) of the can. Washing and drying the free soluble material results in REX aluminosilicates containing about 1.0 to 1.5 weight percent sodium and about 20 to 30 weight percent rare earth ions, calculated as RE ₂ O ₃ .

Materials with both metal base exchange and ammonia base exchange can be obtained by treatment and heating simultaneously or sequentially with metal salts and ammonia to obtain the metal-hydrogen form of crystalline aluminosilicates.

Similar combinations having isomerization catalytic activity include various crystalline aluminosilicates, such as Y porssite, gmelinite, chabazite and the like. The nature and methods of making aluminosilicates are described in US Pat. Nos. 3, 033, 778 and 3, 013, 989.

Preferred aluminosilicate containing catalysts can be widely modified depending on the aluminosilicate used, the nature and concentration of the cation, the additives introduced by precipitation, ion exchange, adsorption and the like. Of particular importance is the ratio of silica to alumina, pore diameter and space arrangement of cations. The cation may be a proton (acid) derived by base exchange with a solution of an acid or ammonium salt, and proton is released when the ammonium ion is pyrolyzed. The polyvalent metal is supplied as a cation, which acts as a spacing or stabilizer for the stabilization of acidic alumino-silicates. In addition to the circuit metals mentioned above, suitable cations for exchange in aluminosilicates are magnesium, calcium, manganese, cobalt, zinc, silver and nickel.

Preferred crystalline aluminosilicates include hydrogen and / or polyvalent metal-formed possites and mordenites, in particular mordenites having a diameter of 6 mm 3 and a silica to alumina ratio of about 6 to 15, with the most preferred being It is a small mordenite. Particularly preferred crystalline aluminosilicates are acid extracted mordenites with a SiO ₂ / A 1 ₂ O ₃ ratio of about 10. As a method of preparing this material, mordenite in the conventional form having a ratio of SiO _{2 /} A1 ₂ O ₃ of about 9 to 10 is subjected to hydrochloric acid, sulfuric acid, fluoride under conditions in which a part of aluminum can be removed or extracted from the mordenite. There is a method of reacting a strong acid such as hydrogen acid. Typically this method can be used to obtain mordenite having an SiO ₂ / A ₁₀ O ₃ ratio of 11 or greater.

The grade of crystalline aluminosilicates useful in the present invention is that hydrogen, polyvalent metals, and mixtures thereof occupy at least 50% and more preferably occupy at least 90% of the cation sites of the aluminosilicate structure.

The isomerization catalyst composition useful in the present invention preferably contains at least one platinum group metal component.

Moreover, some diesel oils contain a rhenium component but tend to contain platinum group metals such as platinum, palladium, ruthedium, iridium, rhodium and osmium. Platinum group metal components such as platinum and palladium are present in the final catalyst composition in the form of compounds such as oxides, sulfides and halides or as elemental metals. Generally, the white metal metal components in the final catalyst composition are present in small amounts relative to the other components to which they are bound. In practice, the platinum metal component in the final catalyst composition is calculated to be about 0.02 to 3. 0% by weight on an elemental basis and excellent catalyst compositions containing about 0.2 to 1.0% by weight of the platinum group metal are excellent. You can get the result.

The catalytic metal component, that is, the platinum group metal component, may be co-precipitated or cogelled with the carrier material before, during and after the introduction of aluminosilicate into the carrier material and before and after calcination (calcination) of the carrier material, The catalyst composition can be mixed with a suitable method such as ion exchange or impregnation with a carrier material. A preferred method of introducing and mixing the platinum group metal component is to use a water-soluble platinum group compound bonded to the carrier material by impregnation. Thus, the platinum group metal can be added to the carrier material by co-mingling the carrier material with an aqueous solution of chloro platinic acid. Other water soluble platinum compounds can be used as the impregnation solution, such as ammonium platinum chloride, platinum chloride and dinitro diamino platinum. Preferably, the platinum group metal is mixed with the carrier material by immersion before adding the aluminosilicate. It is also preferred that the platinum group metal be free of crystalline aluminosilicate components of the final catalyst in practice. The carrier material is preferably impregnated after calcination to prevent the valuable platinum group metals from being washed away. In some cases, however, it is advantageous to impregnate the carrier or support when it is in the gel state. The impregnated support obtained after impregnation is dried. Crystalline aluminosilicate is mixed into the impregnated carrier material using conventional methods. Catalysts useful in the present invention are granulated by conventional methods such as extrusion, tableting, sphericalization, and the like. The catalyst is preferably hot calcined at about 600 ° to 1500 ° F. (316 to 816 ° C.) for at least about 0.5 to 20 hours.

Catalysts useful in the present invention also contain a rhenium component. These components are present as elemental metals, as compounds such as oxides, sulfides, halides, or as physical or chemical bonds with other components of the carrier and / or catalyst. In general, the rhenium component is calculated as elemental metal and an amount sufficient to contain about 0.02 to 1.0% by weight of rhenium in the final catalyst composition is used. The preferred method of mixing the rhenium component is to impregnate the carrier before, during or after adding the other components mentioned above. In some cases, the impregnating solution uses an aqueous solution of a suitable rhenium salt, such as ammonium perrhenate, sodium perhenate, or potassium perhenate. Moreover, if necessary, an aqueous solution of rhenium halides such as chloride is used, but an aqueous solution of perrenic acid is preferable as the impregnation solution. The rhenium component is impregnated before, after and simultaneously with the addition of the platinum group metal component to the carrier. However, the best results can be obtained by impregnating the rhenium component with the platinum group metal component.

Typical reaction conditions used in this process are about 50 ° F (10 ° C.) to 1200 ° F (649 ° C.), preferably 400 ° F (204 ° C.) to 1000 ° F (538 ° C.) Weight of hydrocarbons per hour, per weight of catalyst) is from about 0.1 to 40, preferably about 0.5 to 8 and the reaction pressure is from atmospheric to about 100 atmospheres or more, preferably from about 5 to 50 atmospheres The proportion of C ₈ aromaticalkyl hydrocarbons is at least about 0.5: 1 to 25: 1, preferably about 3: 1 to 15: 1 and the reactants in the isomerization zone are substantially gaseous:

The method for recovering the C ₈ isomer product from the reactor effluent depends on the desired isomer. For example, if 0-xylene is desired, it is separated from other isomers by fractional distillation, ie, hyperfractionation, which can be easily separated by conventional distillation because the boiling point of 0-xylene is significantly higher than that of other C ₈ aromaticalkyl hydrocarbons. Can be. The remaining isomer is recycled back to the isomerization reactor and isomerized again. However, the m- and p-isomers are not easily separated from each other by distillation because of the boiling point. They can be separated from one another by known chemical separation methods such as sulfate sulfonation, all-kylation-dealkyIation techniques, and the like. Furthermore, ρ-xylene can be recovered by physical separation methods such as crystallization and adsorption-desorption.

C ₈ alkyl aromatic hydrocarbon-containing feed supplied to the process of the present invention is such as pure C ₈ alkyl benzene isomers, mixtures of the C ₈ C ₈ alkyl benzene isomer or a number of hydrocarbon ryubun alkylbenzene isomer. For example, the source of C ₈ alkylbenzene isomers may be C ₈ aromatics recovered from catalytic reformates, pyrolysis naphtha, coal tar, etc., remaining C ₈ alkyl after all or part of the separation and recovery of the given isomers from these sources. Benzene fraction is a feed containing C ₈ aromaticalkyl suitable for the process of the present invention. Therefore, P-xylene, which is becoming increasingly important, can be recovered from the C ₈ contact reformate by low temperature crystallization. The mother liquor resulting from this low temperature crystallization has insufficient P-xylene due to the thermodynamic equilibrium concentration of the C ₈ alkylbenzene isomer, which is a good C ₈ aromaticalkyl containing feed for the process of the invention.

As is well known, the catalyst used in the process of the present invention may be used in any suitable manner, including batch or continuous. In the preferred method of the present invention, continuous operation is effective. Thus, a particularly preferred method of fixedbed operation is to continuously feed non-equilibrium alkyl aromatic hydrocarbons to a reaction bed having a fixed bed containing the desired catalyst and supply the bands to suitable operating conditions at such temperatures and pressures. Keep it. The reaction zone consists of an unfilled vessel or coil or is lined with adsorbent filler.

The following examples are presented to illustrate the advantageous advantages and effects of the present invention. However, this example is not intended to limit the scope of the present invention but to describe in more detail.

[Examples I and II]

This example describes the advantages of the method.

The C ₈ aromaticalkyl isomerization system is operated to recover 0-xylene and p-xylene. The catalyst used in this isomerization zone is an industrially useful catalyst, containing about 0.4% by weight of platinum, supported on a silica-alumina support as calculated by elemental metal. This catalyst is placed in a fixed-bed reaction system.

The isomerization process flow for the standard operation is as follows: C ₈ aromatic alkyl Non-equilibrium mixture of fresh feed with the recycle described below and hydrogen to C ₈ alkyl in the feed (raw material) sent to the reaction zone. Mix with hydrogen so that the molar ratio of aromatic hydrocarbon is 8. 8 and send it to the reactor. The effluent from the reaction zone is sent to a flssh drum to remove hydrogen-containing gas phase material from the effluent. This hydrogen-containing stream is partially recycled to the reactor. The remainder of the effluent is sent to a first distillation column to remove light flakes having a light molecular weight from the effluent. The first distillation column is operated at an appropriate temperature and pressure to produce liquid phase overhead product and gas phase overhead product.

In a conventional isomerization system, the liquid and gaseous products of this first distillation column are removed from the process. The bottom product of the first distillation column is sent to the next process to distill again to remove C ₉ + material from the reactor effluent, recover the 0-xylene product per fruit and recover the P-xylene product by crystallization. The remaining material after crystallization is recycled to the isomerization zone and mixed with the original fresh feed.

The reaction conditions in the isomerization zone are as follows.

Molar ratio of hydrogen to C ₈ alkylaromatic hydrocarbons 8. 8

Reactor Pressure (psig) 203

Reactor Outlet Temperature (° F) 815

The result of passage of the isomerization zone in a conventional operation as described above is as follows.

(1) The total feed to the isomerization reactor is an unbalanced mixture of C ₈ aromaticalkyl. Isomerization in the reaction zone tends to produce an equilibrium mixture of C ₈ aromaticalkyl. Thus, the closer to equilibrium, that is, the higher the percentage approaching equilibrium, the more fully or effectively isomerized in the reaction zone. Equilibrium values are used to calculate access to equilibrium.

According to the improved process of the present invention, a portion of the liquid overhead, or 65% by weight, of the first distillation column is mixed with other feed streams entering the reactor described above and circulated to the reactor. This circulating portion sent to the reactor is about 60% by weight of the total gas and liquid product from this first distillation column. The reaction conditions are as described above.

_Top column liquid of the first distillation column is about 22% C 5 _파라 paraffin, about 10% C ₆ + naphthene, about 6% C ₅ and naphthene, about 4% C ₆ naphthene, And about 11 weight percent benzene and about 41 weight percent toluene. The recirculation of the column top liquid in the first distillation column is about 1.8% of the total hydrocarbons passed through the operated isomerization reactor.

The result of having passed through the isomerization reactor operated based on this invention is as follows.

(1) The total feed fed to the isomerization reactor contains an unbalanced mixture of C ₈ aromaticalkyl. Isomerization in the reaction zone tends to produce an equilibrium mixture of C ₈ aromaticalkyl. Thus, the closer to equilibrium, that is, the higher the percentage approaching equilibrium, the more fully or effectively isomerized in the reaction zone. The equilibrium value is used to calculate the approach to equilibrium.

The results show that the yield of valuable C ₈ alkylbenzene isomers is increased by circulating a portion of the column top liquid from the first distillation column in accordance with the present invention in an isomerization reaction. For example, the revised operation of the present invention not only increases the C ₈ ring preservation (as compared to normal operation) but also substantially increases the access to the equilibrium of the unexpected C ₈ dimethyl benzene isomer. In other words, compared to the normal operation, the concentration of P-xylene and 0-xylene in the effluent from the reaction zone based on the total alkylbenzene content is increased by circulating the column top liquid from the first distillation column to the isomerization reactor. Therefore, according to the present invention, the yield of 0-xylene and P-xylene is improved.

Claims (1)

A catalyst having the effect of promoting isomerization of C ₈ alkylbenzene in the presence of hydrogen under isomerization conditions in which feed containing C ₈ alkyl aromatic hydrocarbons isomerized to C ₈ aromatic hydrocarbons in one or more isomerization zones. In contact with the effluent to produce This effluent is separated to form a hydrogen-rich stream, the first hydrocarbon-rich fraction containing toluene and having a lower average molecular weight than C ₈ aromatic alkyls, compared with the effluent. To separate the second stream having the enhanced C ₈ aromatic alkyl content, recovering at least one C ₈ aromatic alkyl product from the second stream, and recovering a portion of the first hydrocarbon-rich stream again. Isomerizing the C ₈ alkyl aromatic hydrocarbon, characterized in that it has a step of circulating and contacting the isomerization reactor.