JP2005232122A - Method for producing propylene - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing propylene from ethylene in high yield and efficiency and capable of remarkably varying the yield balance of ethylene and propylene in the production of olefins by the pyrolysis of naphtha to increase the propylene/ethylene ratio and reduce the steam cost in the pyrolysis of naphtha. <P>SOLUTION: Propylene is produced by reacting ethylene produced in an olefin-production apparatus by the pyrolysis of naphtha with a gas containing methanol and/or dimethyl ether in the presence of a catalyst and using the by-produced water as the steam-generation source for the pyrolysis of naphtha. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for producing propylene using ethylene and methanol or / and dimethyl ether as raw materials, and more particularly to a method for producing propylene incorporated into an olefin production facility by thermal decomposition of naphtha.

Conventionally, as a method for producing propylene from C1 and C2, a method for producing propylene from methanol or / and dimethyl ether is known (for example, see Patent Document 1 and Patent Document 2). Since one molecule of propylene is generated from three molecules of methanol, the yield of propylene based on the raw material methanol is theoretically only 33% even if it is assumed that the reaction is performed at a selectivity of 100%. A method for obtaining propylene from ethylene and methanol is also known (see Non-Patent Document 1), but even in this method, the yield of propylene based on the raw material methanol does not reach 40% and is still insufficient. On the other hand, the present inventors have first made methanol and / or dimethyl from ethylene and methanol or / and dimethyl ether. The method may be a 40% or more propylene yield relative to the ether, and patent applications as Japanese Patent Application No. 2003-415367.
JP 59-222429 A JP-A-4-217828 Appl. Catal. A 218 (2001). 241-250

  By the way, in the method of thermal decomposition of naphtha, which is commonly used as a method for producing olefins such as ethylene and propylene, there is a limit to changing the yield balance of both in accordance with the demand balance of ethylene and propylene. On the other hand, although various thermal decomposition methods have been studied, it has been difficult to change the yield balance significantly.

  The present invention has been made in view of the above-described prior art. Accordingly, the present invention can efficiently produce propylene from ethylene in a high yield, and can also produce olefins by thermal decomposition of naphtha. To provide a method for producing propylene capable of significantly changing the yield balance between ethylene and propylene in production, increasing the propylene / ethylene amount ratio, and reducing the steam cost in naphtha pyrolysis. With the goal.

  The present invention produces propylene by reacting ethylene obtained in an olefin production facility by thermal decomposition of naphtha with a gas containing methanol or / and dimethyl ether in the presence of a catalyst, and by-produced water. The main point is a method for producing propylene in which naphtha is used as a steam generation source in naphtha pyrolysis.

  According to the present invention, propylene can be produced from ethylene in a high yield and efficiently, and in the production of olefins by thermal decomposition of naphtha, the yield balance between ethylene and propylene can be significantly changed. Thus, it is possible to provide a propylene production method capable of increasing the propylene / ethylene amount ratio and reducing the steam cost in naphtha pyrolysis.

  In the method for producing propylene of the present invention, a method for producing propylene using ethylene and methanol or / and dimethyl ether as raw materials is incorporated in an olefin production facility by thermal decomposition of naphtha.

  As an olefin production facility by thermal decomposition of naphtha in the present invention, it is commonly used as a production facility for olefins such as ethylene and propylene, and a schematic flow of a typical tubular furnace process, so-called steam cracking method, is described. Then, in the front-end demethanization process as one method, naphtha is introduced into a thermal cracking furnace together with steam, and hydrocarbons obtained by thermal cracking at a temperature of about 760 to 900 ° C. are quenched, and then purified. It is led to a distillation column, tar is obtained from the bottom of the column, gas oil is obtained from the side of the column, and hydrocarbons are obtained from the top fraction. The hydrocarbons as the top fraction are quenched and separated into mainly hydrocarbons having 5 or less carbon atoms and a mixture of water derived from steam and mainly hydrocarbons having 6 or more carbon atoms. The mixture of water and mainly hydrocarbons having 6 or more carbon atoms is separated into water and hydrocarbons having mainly 6 or more carbon atoms. The water separated here is reused as steam to be introduced into the thermal cracking furnace through the steam generation tank. However, since the separated water contains nonvolatile hydrocarbons, the nonvolatile hydrocarbons are used. In order to remove the water, a part of the water is discarded, and fresh water is supplied for the discarded amount.

  The hydrocarbons mainly having 5 or less carbon atoms obtained by quenching the above-mentioned column top fraction are compressed by a compressor, then the sulfur compound is removed by an alkali washing section, and then decomposed and produced after passing through a drying section. The product is led to a demethanizer tower to collect methane and hydrogen as the top fraction, and the bottom fraction is led to the deethanizer, and acetylene in the ethane / ethylene mixture is hydrogenated as the top fraction. Ethane / ethylene is converted into ethane / ethylene in the reactor and sent to the ethylene fractionation column. The bottom fraction is led to the depropanizer, and methylacetylene and propadiene in the propane / propylene mixture as the top fraction are fed in the hydrogenation reactor. It is converted into propane / propylene and sent to the propylene fractionating column, and the bottom fraction is led to the debutane column. The ethylene fractionator collects product ethylene from the side of the tower and recycles ethane as the bottom fraction to the cracking furnace. The propylene fractionator collects product propylene from the side of the tower, Propane as the bottom fraction is recycled to the cracking furnace. Accordingly, high purity ethylene of about 99.95%, high purity propylene of about 99.0%, and the like are separated and recovered.

  Further, in the front-end depropanization process as an alternative method, the decomposition product after passing through the drying section as described above is led to a depropanizer tower, and ethane / ethylene, propane / propylene as a top fraction. The acetylene, methylacetylene, and propadiene in the mixture are converted into ethane / ethylene and propane / propylene in a hydrogenation reactor and led to the demethanizer tower, and the bottom fraction is led to the debutane tower. In the demethanizer tower, methane and hydrogen are recovered as the top fraction, and the bottom fraction is led to the deethanizer, and ethane / ethylene as the deethanizer overhead is sent to the ethylene fractionator. At the same time, the bottom fraction is led to the propylene fractionation tower. The ethylene fractionator collects product ethylene from the side of the tower and recycles ethane as the bottom fraction to the cracking furnace. The propylene fractionator collects product propylene from the side of the tower, Propane as the bottom fraction is recycled to the cracking furnace.

  As another variation of the front-end depropanization process, there is a method in which the top fraction of the depropanizer is led to the deethanizer instead of the demethanizer. The top fraction of the depropanizer tower contains acetylene and methylacetylene, but when it contains a lot of methylacetylene, it may be led to the deethanizer after passing through the hydrogenation reactor as described above. If the methylacetylene content is low, acetylene in the methane, hydrogen, and ethane / ethylene mixture, which is the top fraction of the deethanizer after being led to the deethanizer without going through the hydrogenation reactor May be passed through a hydrogenation reactor to ethane / ethylene. The top fraction of the deethanizer is sent to the demethanizer after passing through a hydrogenation reactor installed as necessary, and then to the demethanizer, and the bottom fraction is sent to the propylene fractionator. In the demethanizer tower, methane as the top fraction is recovered and ethane / ethylene as the bottom fraction is led to the ethylene fractionator. In the propylene fractionating tower, product propylene is recovered from the side of the tower, and propane as the bottom fraction is recycled to the cracking furnace. In the ethylene fractionator, product ethylene is recovered from the side of the tower, and ethane as the bottom fraction is recycled to the cracking furnace.

  As another method, there is a front-end deethanation process in which the decomposition product after passing through the drying section as described above is led to a deethanizer tower.

  The present invention produces propylene by reacting ethylene obtained in the olefin production facility by thermal decomposition of naphtha with a gas containing methanol or / and dimethyl ether, and by-produces water into steam in naphtha thermal decomposition. It is used as a generation source. As a result, in the production of olefins by naphtha pyrolysis, the yield balance between ethylene and propylene can be significantly changed to increase the propylene / ethylene ratio, and the steam cost in naphtha pyrolysis is reduced. be able to.

  Here, the ethylene obtained in the olefin production facility by thermal decomposition of naphtha is obtained through the ethylene rectification tower in the front end demethanization process, front end depropane process, front end deethane process and the like. An ethane / ethylene mixture obtained by converting acetylene in the ethane / ethylene mixture as the top fraction of the deethanizer in the front-end demethanization process into ethane / ethylene in a hydrogenation reactor, Ethane / ethylene mixture as deethanizer overhead in the front end depropanization process, methane, hydrogen, and ethane as deethanizer overhead in other variations of the front end depropanization process / Acetylene in ethylene mixture as required Mixture in the mixture containing ethylene after being converted to ethane / ethylene in the hydrogenation reactor, and methane, hydrogen, and ethane / ethylene mixture as the top fraction of the deethanizer tower in the front end deethanation process This also includes a mixture containing ethylene after acetylene is converted to ethane / ethylene in a hydrogenation reactor. The other variations of the front-end depropanization process and the mixture containing ethylene in the front-end deethane process are obtained by separating at least a part of hydrogen and / or ethane contained in these mixtures as necessary. There may be.

  On the other hand, in the production of propylene by reacting ethylene with methanol or / and dimethyl ether in the presence of a catalyst, methanol and dimethyl ether are not particularly limited, but by hydrogenation reaction of a hydrogen / carbon monoxide mixed gas. It is preferable to use the obtained methanol and dimethyl ether.

  The mixed gas of ethylene and methanol or / and dimethyl ether includes helium, argon, nitrogen, carbon monoxide, carbon dioxide, hydrogen, water, paraffins in addition to gaseous ethylene and methanol and / or dimethyl ether. An inert gas such as hydrocarbons such as methane, aromatic compounds, and mixtures thereof is optionally present as a carrier in an amount of 1 mol% to 99 mol% as a concentration in the mixed gas, for example. Of these, it is preferable to coexist at least water (that is, water vapor). Therefore, when using the top fraction of the deethanizer in the front end demethanization process and the front end depropanization process, the ethane in the fraction of the top of the tower is used in addition to the front end depropanization process. When the top fraction of the deethanizer in the front-end deethanation process is used, ethane, methane, and hydrogen in the top fraction can each be given a function as a carrier. .

  In addition, if the mixed gas is mixed at the time of the reaction, the form of introduction into the reactor is not particularly limited, and ethylene and methanol and / or dimethyl ether, and other inerts used as necessary. Each of the gases may be supplied into the reaction apparatus, or may be supplied into the reaction apparatus after previously preparing a mixed gas thereof.

  The catalyst used in the reaction is not particularly limited as long as it is a solid having a Bronsted acid point, and conventionally known catalysts are used. Specifically, for example, clay minerals such as kaolin; clay Impregnated / supported acid such as sulfuric acid or phosphoric acid on a carrier such as mineral; acid ion exchange resin; aluminum phosphates; zeolites; mesoporous silica alumina such as Al-MCM41; layered zeolite such as ITQ-2, etc. Solid acid catalyst.

  As these solid acid catalysts, those having a molecular sieving effect are preferable, and those having a low acid strength are preferable. Among the solid acid catalysts, the structures of aluminum phosphates and zeolites having a molecular sieving effect are represented by codes defined by the International Zeolite Association (IZA), for example, AEI, AET, AEL, AFI, AFO, AFS, AST, ATN, BEA, CAN, CHA, EMT, ERI, EUO, FAU, FER, LEV, LTL, MAZ, MEL, MFI, MOR, MTT, MTW, MWW, OFF, PAU, RHO, STT, TON, etc. AEI, BEA, CHA, and MFI are preferable.

Further, the solid acid catalyst is more preferably a crystalline aluminum phosphate, a crystalline aluminosilicate having a SiO ₂ / Al ₂ O ₃ molar ratio of more than 10 and, in particular, a micropore having a pore diameter of 3 to 9 mm. Or metallosilicates.

The crystalline aluminum phosphates are preferably crystalline silicoaluminophosphates having a CHA-type structure such as SAPO34 and SAPO44, having an AEI structure such as SAPO18, having an AFI structure such as SAPO5, and SAPO41. And those having an AFO structure such as SAPO11, those having an AST structure such as SAPO16, those having a FAU structure such as SAPO37, those having an ERI structure such as SAPO17, etc. It has a CHA type structure, and SAPO34 is particularly preferable. These other various commercially available products may be used after synthesized by the known methods described in the IZA issued "Verified Syntheses Of Zeolitic Materials" ( 2 nd Revised Edition 2001 Elsevier) , and the like. The crystalline aluminum phosphate preferably has a BET specific surface area of 200 to 700 m ² / g and a pore volume of 0.1 to 0.5 g / cc.

  These aluminum phosphates may be those in which a part of Al atoms and P atoms constituting the aluminum phosphates are replaced by Si atoms or other metal atoms, and furthermore, they are of the H type. Also, an aluminophosphate obtained by salt exchange may be used. Examples of the metal atom other than the Si atom include a trivalent metal atom capable of isomorphous substitution; a divalent metal atom selected from Ni, Co, Sn, and an alkaline earth metal. Among these, preferably It is a trivalent metal atom that can be substituted with the same type, and more preferably B, Ga, Fe, Cr, Mn, Y, La, or Ce.

Further, the crystalline aluminosilicates preferably have an AFI structure such as SSZ-24, those having a BEA structure such as β, those having a CAN structure such as Cancrinite, and CHA structures such as Chabazite and SSZ-13. Having an EMT structure such as EMC-2, having an ERI structure such as erionite, having an EUO structure such as EU-1, having a FAU structure such as USY, ferrierite, ZSM35, etc. Those having a FER structure, those having a LEV structure such as Levine, those having an LTL structure such as L-type zeolite, those having a MAZ structure such as Mazzite, those having an MFI structure such as ZSM5, and MEL structures such as ZSM11 Having MOR structure such as mordenite Those having an MTT structure such as ZSM23, those having an MYW structure such as ZSM12, those having an MWW structure such as MCM22, those having an OFF structure such as offretite, those having a PAU structure such as ECR18, and RHO such as Rho One having a structure, one having an STT structure such as SSZ23, one having a TON structure such as ZSM22, preferably one having a BEA structure, or one having an MFI structure, particularly preferably ZSM5 or β It is. These other various commercially available products may be used after synthesized by the known methods described in the IZA issued "Verified Syntheses Of Zeolitic Materials" ( 2 nd Revised Edition 2001 Elsevier) , and the like. The crystalline aluminosilicates preferably have a BET specific surface area of 200 to 700 m ² / g and a pore volume of 0.1 to 0.5 g / cc.

Moreover, as these crystalline aluminosilicates, a part of Al atoms constituting the crystalline aluminosilicates may be substituted with other metal atoms similar to those mentioned in the aluminum phosphates. Moreover, a part of Al atoms constituting these aluminosilicates can be removed by steaming, acid treatment or the like to obtain a high silica alumina ratio. Of these, SiO ₂ / Al ₂ O can be used. The molar ratio of ₃ is preferably 80 or more, more preferably 100 or more, still more preferably 150 or more, and particularly preferably 200 or more. As the upper limit, the molar ratio of SiO ₂ / Al ₂ O ₃ is usually 1000 or less, more preferably 750 or less, and particularly preferably 500 or less. Zeolite such as ZSM5 can control the amount of Al contained by controlling the amount of Al during synthesis in addition to the above method.

  Further, as the metallosilicates, aluminosilicates, particularly preferably the above crystalline aluminosilicates, all of the Al atoms constituting the metallosilicates are replaced with other metal atoms similar to those mentioned in the aluminum phosphates. Can be mentioned.

  The catalyst may be used for the reaction as it is, or may be used for the reaction by granulating and molding it using a substance or a binder inert to the reaction. Examples of the substance and binder inert to the reaction include alumina, alumina sol, silica, silica gel, quartz, and a mixture thereof. Mixing with these substances is effective for reducing the cost of the entire catalyst and as a heat sink for assisting heat shielding during catalyst regeneration, and is also effective for increasing the density of the catalyst and increasing the catalyst strength.

  The reaction mode in the method for producing propylene of the present invention is not particularly limited as long as the feedstock is in a gas phase in the reaction zone, and a known gas using a fluidized bed reactor, a moving bed reactor, or a fixed bed reactor is used. A phase reaction process can be applied. Further, it can be carried out in a batch, semi-continuous or continuous form, but is preferably carried out continuously, and the method may be a method using a single reactor, in series, or A method using a plurality of reactors arranged in parallel may be used.

  In the method for producing propylene of the present invention, the amount of ethylene used is preferably an excess amount relative to methanol or / and dimethyl ether as a whole reaction system. Specifically, the number of moles of ethylene is The number of moles of methanol, 1/2 of the number of moles of dimethyl ether, or the total number of moles of both is preferably more than 1, more preferably 1.8 or more, and particularly preferably 3 or more. In addition, if ethylene is excessive, it tends to cause problems in terms of cost, production of by-products, and operational complexity, so the upper limit is preferably 20 or less. The number is preferably 10 or less, particularly preferably 6 or less.

  Here, when a large amount of unreacted methanol or / and dimethyl ether is present in the effluent component from the reaction system, the utilization rate of methanol or / and dimethyl ether is reduced, and not only the cost merit is lost, but also the target product with propylene. The load on the separation and propylene purification process increases, and this reaction is an exothermic reaction. When a large amount of methanol reacts at once, temperature control becomes difficult due to the reaction heat generated, and the yield of the target product is also increased. It is preferable to supply methanol or / and dimethyl ether in a divided manner because of adverse effects such as reduction or shortening of catalyst life.

  The method of split supply differs depending on the design of the reaction system, such as using a single reactor, arranging a plurality of reactors in series, or arranging them in parallel. Examples include a method in which a plurality of methanol or / and dimethyl ether inlets are provided in a reactor and divided supply, a method in which each of a plurality of reactors is provided with a methanol or / and dimethyl ether inlet and supplied in a divided manner. In the case of divided supply here, it is preferable to supply additional methanol or / and dimethyl ether after 90% or more of the previously introduced methanol or / and dimethyl ether has been consumed.

  In the method for producing propylene of the present invention, the reaction pressure is preferably less than 2 MPa, more preferably 1 MPa or less, and particularly preferably 0.7 MPa or less. The lower limit is not particularly limited, but is preferably 0.1 kPa or more, more preferably 7 kPa or more, and particularly preferably 50 kPa or more.

  The reaction temperature is usually about 200 ° C. or higher, preferably about 250 ° C. or higher, more preferably about 300 ° C. or higher, depending on the type of catalyst used. The upper limit is usually about 700 ° C. C. or lower, preferably about 600 ° C. or lower, more preferably about 500 ° C. or lower. If the reaction temperature is too low, the reaction rate is low, the formation rate of the target product is remarkably slow, and a large amount of unreacted raw material remains. On the other hand, if the reaction temperature is too high, the yield of the target product tends to decrease. .

The weight space velocity (WHSV) is usually about 50 hours ^-1 or less, preferably about 20 hours ^-1 or less, more preferably about 10 hours ^-1 or less. The lower limit, since it tends to yield fall separation of the desired product becomes difficult due to an increase in by-products and WHSV is too small, typically about 0.01 hours ^-1, preferably from about 0.05 hours ^{- 1} or more, more preferably about 0.1 hour- ¹ or more.

  In the production method of the present invention, as the reaction is continued, the catalyst causes coking in the reactor and the reaction activity decreases. In this case, the catalyst can be removed from the reactor and, for example, the coke accumulated in the oxygen-containing atmosphere can be oxidized to remove all or a part of the catalyst, thereby regenerating the catalyst. The regenerated catalyst is reintroduced into the reactor again. From the viewpoint of extracting and reintroducing the catalyst, a moving bed reactor or a fluidized bed reactor is used from the fixed bed. The process is simpler to operate.

  In the reaction system, water is by-produced with the progress of the reaction. However, it is preferable to add water to the reaction raw material so that moisture (that is, water vapor) coexists from the beginning of the reaction. The presence of water in the system has the effect of suppressing coke formation that causes catalyst deactivation and the effect of extending the life of the catalyst, and also suppresses the formation of paraffins and oligomerization of the generated olefins. There are effects such as increasing propylene selectivity. As the amount of water coexisting in the reaction system, although it depends on the type of solid acid catalyst used and other reaction conditions, it is usually preferably 0.025 or more in terms of the molar ratio to the number of moles of raw material ethylene, More preferably, it is 0.1 or more, Most preferably, it is 0.5 or more. As the upper limit, if the amount of water is too large, the reaction rate decreases, and the yield of the target product tends to decrease or the catalyst itself tends to react with water and change in quality. Preferably it is 10 or less, more preferably 5 or less.

  In the present invention, the reaction product mixture obtained by the above reaction contains propylene as a main component, and also contains ethylene as an unreacted raw material and components of C4 or higher, but C4 or higher paraffins, The amount of by-products such as olefins and aromatic hydrocarbons is preferably 30% or less, more preferably 15% or less as the molar concentration in the reactor outlet hydrocarbon component, and at least the raw material methanol. It contains propylene in a yield of preferably 0.40 or more, and more preferably 0.50 or more, in terms of the molar ratio to the number of moles or 1/2 of the number of moles of dimethyl ether, or the total number of moles of both.

  In order to isolate the target propylene from the reaction product mixture, for example, it is introduced into a separation / purification facility such as a deethanizer or a depropanizer as in the naphtha pyrolysis process, and depending on each component. , Collection, purification, recycling, discharge, etc.

  Furthermore, in the present invention, water produced as a by-product when propylene is produced by reacting ethylene and a gas containing methanol or / and dimethyl ether in the presence of a catalyst is used as a steam generation source in naphtha pyrolysis. . As described above, the pyrolysis furnace in the naphtha pyrolysis process uses water as a dilution gas of naphtha, but it is necessary to discard a part of the recovered water when reused, and the operating conditions of the pyrolysis furnace In some cases, water may be deficient, while when propylene is produced from ethylene and methanol or / and dimethyl ether, 1 mole of water is produced as a by-product per mole of ethylene. The lack of water at the steam source can be compensated.

  In addition, for example, a part of water by-produced in producing propylene is used as a diluent for a gas containing ethylene and methanol or / and dimethyl ether in the reaction for producing propylene, and the remaining water is decomposed by naphtha. May be used such as supplying to a steam generator, and a part of the water recovered from the steam used in the thermal decomposition of naphtha may be used in the reaction between ethylene and methanol or / and dimethyl ether. Alternatively, and / or as a diluent for a gas containing dimethyl ether.

  According to the present invention, propylene can be produced from ethylene in a high yield and efficiently, and in the production of olefins by thermal decomposition of naphtha, the yield balance between ethylene and propylene can be significantly changed. Propylene / ethylene content ratio can be increased, and a method for producing propylene that can reduce the steam cost in naphtha pyrolysis can be provided. Production of olefins corresponding to the demand for an increase in the propylene / ethylene amount ratio can be made possible.

Claims (6)

Propylene is produced by reacting ethylene and methanol or / and dimethyl ether-containing gas obtained from an olefin production facility by naphtha pyrolysis in the presence of a catalyst, and by-product water is steamed in naphtha pyrolysis. A method for producing propylene, which is used as a generation source. The method for producing propylene according to claim 1, wherein a part of water recovered from steam used in the thermal decomposition of naphtha is used as a diluent for a gas containing ethylene and methanol or / and dimethyl ether. The number of moles of ethylene is more than one mole relative to the number of moles of methanol, or the number of moles of dimethyl ether, or the total number of moles of both, and the number of moles of methanol or the number of moles of dimethyl ether Or the manufacturing method of the propylene of Claim 1 or 2 which obtains a propylene with the yield of 0.40 or more by the molar ratio with respect to the total mole number of both. The method for producing propylene according to any one of claims 1 to 3, wherein the catalyst is a solid acid catalyst. The solid acid catalyst is any one selected from the group consisting of crystalline aluminum phosphates, crystalline aluminosilicates having a SiO ₂ / Al ₂ O ₃ molar ratio of more than 10, and metallosilicates. Propylene production method. The method for producing propylene according to any one of claims 1 to 5, wherein water of 0.025 or more is present in the reaction system in a molar ratio with respect to the number of moles of ethylene.