Method for producing lower olefins, method for producing lower olefin compositions, method for producing propylene compositions, naphtha for producing lower olefins, lower olefin compositions, and polyolefin polymers

Abstract

To provide: a production method of a lower olefin or a lower olefin composition with little amount of methanol produced; naphtha for lower olefin production with little amount of methanol produced; and a lower olefin composition with little content of methanol.SOLUTION: Provided is a production method of a lower olefin comprising a step of decomposing naphtha containing an ether, where the ether has an asymmetric structure relative to an oxygen atom constituting the ether bond and a content of oxygen atom contained in the naphtha, the oxygen atom being derived from the ether, is 20,000 mass ppm or less. Also provided is naphtha for lower olefin production containing an ether, where the ether has an asymmetric structure relative to the oxygen atom constituting the ether bond and a content of the oxygen atom derived from the ether is 20,000 mass ppm or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing lower olefins from naphtha, and a method for producing a lower olefin composition or a propylene composition by the method for producing lower olefins. Furthermore, the present invention relates to naphtha for producing lower olefins, a lower olefin composition using the naphtha for producing lower olefins, and a polyolefin polymer. In the present invention, the term "lower olefin" refers to an unsaturated hydrocarbon having 2 to 4 carbon atoms and containing one or two unsaturated bonds in one molecule, and specific examples thereof include ethylene, propylene, 1-butene, 2-butene, isobutene, 1,2-butadiene, and 1,3-butadiene. [Background technology]

[0002] A typical method for producing lower olefins is the thermal cracking (steam cracking) of naphtha (a crude oil-derived hydrocarbon mixture with a boiling point range of approximately 30 to 230°C) in the presence of steam (see, for example, Patent Document 1). Naphtha contains oxygen-containing compounds, and when naphtha is thermally cracked to produce various lower olefins, methanol may be produced from the pyrolysis products of the oxygen-containing compounds. Although naphtha contains a variety of oxygen-containing compounds, the ratio of methanol produced from these oxygen-containing compounds is not constant, and the details have not been made clear. Methanol derived from the thermal decomposition products of oxygen-containing compounds has the problem that, when mixed with the product lower olefins such as propylene, it reduces the performance of the catalyst used in polymerizing the lower olefins such as propylene.

[0003] For this reason, the concentration of oxygen-containing compounds in naphtha is used as a criterion for judging the quality of naphtha, and usually, purchasers of naphtha check the concentrations of various oxygen-containing compounds present in the naphtha before purchasing it. Furthermore, the concentration of oxygen-containing compounds in naphtha is reflected in the price of naphtha, with naphtha with a high oxygen-containing compound concentration being sold at a low price and naphtha with a low oxygen-containing compound concentration being sold at a high price.

[0004] In view of the above-mentioned circumstances, a purchaser of naphtha usually blends naphtha having a low oxygen-containing compound content with naphtha having a high oxygen-containing compound content that it has purchased, thereby reducing the oxygen-containing compound content in the naphtha, and then uses the blended naphtha for the production of light olefins. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-40913 Summary of the Invention [Problem to be solved by the invention]

[0006] As described above, the relationship between the types of oxygen-containing compounds contained in naphtha and the amount of methanol produced by thermal decomposition of the oxygen-containing compounds has not been clarified in detail until now. Therefore, even if the quality of naphtha is determined based on the concentration of oxygen-containing compounds contained in the naphtha, the concentration of methanol produced when lower olefins are actually produced by thermal decomposition is not necessarily proportional to the concentration of oxygen-containing compounds. In other words, a method for accurately determining high-quality naphtha with a low concentration of methanol produced has not been known until now.

[0007] An object of the present invention is to solve these problems. That is, an object of the present invention is to provide a method for producing lower olefins with a low methanol concentration, a method for producing a lower olefin composition, a method for producing a propylene composition, and naphtha for producing lower olefins. Another object of the present invention is to provide a lower olefin composition with a low methanol content produced by the method for producing lower olefins and / or the naphtha for producing lower olefins, and a polyolefin polymer using this lower olefin composition. [Means for solving the problem]

[0008] As a result of extensive investigations to solve the above-mentioned problems, the present inventors have found that, among oxygen-containing compounds, specific ethers having an asymmetric structure with respect to the oxygen atom of the ether bond are prone to selective decomposition of specific bonds in the molecule in the naphtha thermal cracking process, and are particularly prone to producing methanol through decomposition, and that the quality of naphtha can be determined based on the content of oxygen atoms derived from the specific ether having an asymmetric structure, more preferably from ethers having an asymmetric structure where the absolute value ΔE [unit: e] of the difference in the values ​​of the charges of the two carbon atoms bonded to the oxygen atom of the ether bond is a predetermined value or more, and have completed the present invention based on this finding.

[0009] That is, the present invention is summarized as follows.

[0010] A first gist of the present invention relates to a method for producing lower olefins, which includes a step of cracking naphtha containing an ether, wherein the ether has an asymmetric structure with respect to an oxygen atom constituting an ether bond, and the content of oxygen atoms derived from the ether contained in the naphtha is 20,000 ppm by mass or less. A second aspect of the present invention relates to a method for producing a lower olefin composition, which comprises producing a lower olefin composition containing a lower olefin and methanol by using the above-mentioned method for producing a lower olefin. A third aspect of the present invention relates to a method for producing a propylene composition, which comprises producing a propylene composition containing propylene and methanol by using the above-mentioned method for producing a lower olefin. A fourth aspect of the present invention relates to a naphtha for producing lower olefins, which contains an ether and is used for producing lower olefins, wherein the ether has an asymmetric structure with respect to an oxygen atom constituting an ether bond, and the content of oxygen atoms derived from the ether is 20,000 ppm by mass or less. The fifth aspect of the present invention relates to a lower olefin composition containing a lower olefin or a derivative thereof, which is a cracking product of the naphtha for producing lower olefins. The sixth aspect of the present invention relates to a polyolefin polymer containing repeating units derived from the lower olefin or a derivative thereof contained in the lower olefin composition. [Effects of the Invention]

[0011] According to the present invention, naphtha that produces a small amount of methanol during thermal cracking can be more accurately determined, and lower olefins with a low methanol content can be produced using such naphtha. According to the present invention, the suitability of naphtha as a raw material for lower olefins can be accurately determined from the content of oxygen atoms derived from specific ethers in naphtha, specifically, ethers in which the absolute value ΔE (ΔE = |E1 - E2|) of the difference between the charge E1 of one carbon atom and the charge E2 of the other carbon atom, determined by density functional theory, is 0.05 [unit: e] or more for two carbon atoms bonded to oxygen atoms constituting an ether bond. Therefore, for example, by selecting naphtha with a low content of oxygen atoms derived from ethers and a ΔE of 0.05 (unit: e) or more from among naphthas that are inexpensive due to their high concentration of oxygen-containing compounds, it is possible to produce high-purity lower olefins using inexpensive naphtha as a raw material while suppressing the concentration of methanol produced. Furthermore, even naphtha with a high concentration of oxygen-containing compounds can be used as is as a raw material naphtha without blending it with naphtha with a low concentration of oxygen-containing compounds, as long as it has a low content of oxygen atoms derived from ethers and a ΔE of 0.05e (unit: e). [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a graph showing the relationship between ΔE [unit: e] of various ethers and the methanol production ratio B. DETAILED DESCRIPTION OF THE INVENTION

[0013] The present invention will be described in detail below, but the present invention is not limited to the following description and can be practiced in any modified form without departing from the gist of the present invention.

[0014] Unless otherwise specified, in this specification, a numerical range expressed using "to" means a range including the numerical values ​​before and after "to" as the lower and upper limits, and "A to B" means It means greater than or equal to A and less than or equal to B.

[0015] In the present invention, the term "lower olefin" refers to an unsaturated hydrocarbon having 2 to 4 carbon atoms and containing one or two unsaturated bonds in one molecule, and specific examples thereof include ethylene, propylene, 1-butene, 2-butene, isobutene, 1,2-butadiene, and 1,3-butadiene.

[0016] <Production method of lower olefins> The method for producing lower olefins of the present invention is a method for producing lower olefins comprising a step of cracking naphtha containing an ether, wherein the ether has an asymmetric structure with respect to an oxygen atom constituting an ether bond (hereinafter, may be referred to as "ether oxygen atom"), and the content of oxygen atoms derived from the ether contained in the naphtha is 20,000 ppm by mass or less.

[0017] In the method for producing lower olefins of the present invention, the ether contained in the naphtha has an asymmetric structure with respect to the ether oxygen atom, and the content of oxygen atoms derived from the ether is set to 20,000 ppm by mass or less, whereby the content of methanol in the lower olefins obtained by thermal cracking the naphtha can be reduced for reasons described below.

[0018] Furthermore, in the method for producing lower olefins of the present invention, the ether has two carbon atoms bonded to ether oxygen atoms, and the absolute value ΔE (ΔE=|E1-E2|) of the difference between the charge E1 [unit: e] of one carbon atom and the charge E2 [unit: e] of the other carbon atom, as determined by density functional theory, is 0.05 [unit: e] or more. This makes it possible to more effectively reduce the methanol content in the lower olefins obtained by thermal cracking of naphtha for reasons described below. In this specification, "e" means the elementary electron quantity, and e = 1.602176634 × 10 -19 [Unit: C]

[0019] Furthermore, in the method for producing lower olefins of the present invention, when the ΔE [unit: e] and the methanol formation ratio B in the obtained lower olefins satisfy the following formulas (1) and (2), lower olefins with a reduced methanol content can be obtained by thermally cracking the naphtha. 0.05≦ΔE Formula (1) B≦1.25×ΔE+0.10 Formula (2)

[0020] As mentioned above, methanol has an adverse effect on the polymerization catalyst when polymerizing lower olefins. Lower olefins obtained by thermal cracking naphtha under the conditions satisfying the above formulas (1) and (2) have a reduced methanol content, and are therefore effective in producing lower olefins such as propylene.

[0021] It is more preferable that the condition of the formula (2) satisfies B≦1.25×ΔE+0.05.

[0022] The methanol production ratio B is an index showing the production rate of methanol produced during thermal decomposition of naphtha, and means the ratio of "the number of oxygen atoms in methanol contained in condensed water" to "the number of oxygen atoms in ether contained in naphtha." Specific measurements of the methanol production ratio B are described in the Experimental Examples section.

[0023] <Ether> Ethers are compounds contained in naphtha, which is a raw material for thermal cracking in the process for producing lower olefins of the present invention.

[0024] In the process for producing lower olefins of the present invention, the ether has an asymmetric structure with respect to the ether oxygen atom (hereinafter, such an ether may be referred to as an "asymmetric ether").

[0025] Furthermore, in the method for producing lower olefins of the present invention, the asymmetric ether has two carbon atoms bonded to ether oxygen atoms, and the absolute value ΔE (ΔE=|E1-E2|) of the difference between the charge E1 of one carbon atom and the charge E2 of the other carbon atom, as determined by density functional theory, is 0.05 (unit: e) or more. This makes it possible to more effectively reduce the methanol content in the lower olefins obtained by thermal cracking of naphtha for reasons described below. The charges of the two carbon atoms are calculated by density functional theory (DFT) calculations of the molecular structure of the ether. The DFT calculation conditions are def-TZVP as the basis set, the COSMO solvation model (Conductor-like Screening Model) for the solvent effect, and Mulliken's population analysis. The above ΔE can be calculated using quantum chemistry calculation software "TURBOMOLE" (manufactured by TURBOMOLE) and a graphical user interface for TURBOMOLE "TmoleX" (manufactured by TURBOMOLE).

[0026] In general, ethers with a large ΔE are asymmetric ethers having an asymmetric structure with respect to the ether oxygen atom. The present inventors have found that asymmetric ethers tend to be easily thermally decomposed to produce methanol under thermal decomposition conditions. Furthermore, the present inventors have found that the larger the ΔE of an ether, the more biased the charge is between the two carbon atoms bonded to the ether oxygen atom, and therefore, such an ether tends to be easily thermally decomposed to produce methanol under pyrolysis conditions.

[0027] Furthermore, the present inventors have found that by using an asymmetric ether as the ether, more preferably an asymmetric ether having the ΔE (unit: e) of 0.05 or more, and by setting the content of oxygen atoms derived from the asymmetric ether contained in the naphtha to 20,000 ppm by mass or less, it is possible to reduce the concentration of methanol contained in the lower olefins obtained by thermal cracking the naphtha.

[0028] For example, asymmetric ethers with asymmetric structures relative to the ether oxygen atom, 2-methoxybutane (CHCHCH(CH)-O-CH), methoxycyclopentane (C5H9-O-CH), and 1-methoxypropane (CHCHCH-O-CH) have ΔE (unit: e) of 0.181, 0.151, and 0.084, respectively. Because of their large ΔE and large charge imbalance, specific bonds in the molecules are likely to be selectively decomposed. As a result, in the thermal cracking process of naphtha containing these ethers, the ethers are likely to produce methanol.

[0029] On the other hand, ethers having a symmetric structure with respect to the ether oxygen atom (hereinafter referred to as "symmetric ethers"), such as dimethyl ether (CH3-O-CH3), diethyl ether (CH3-CH2-O-CH2-CH3), diisopropyl ether ((CH3)2CH-O-CH(CH3)2), and dipropyl ether (CH3-CH2-CH2-O-CH2-CH2-CH3), have ΔE (unit: e) of 0.004, 0.001, 0.010, and 0.000, respectively. Because ΔE is small and charge bias is small, selective decomposition of specific bonds in the molecule is unlikely to occur. As a result, in the thermal cracking process of naphtha containing these symmetric ethers, the symmetric ethers are unlikely to produce methanol.

[0030] In the method for producing lower olefins of the present invention, naphtha having an asymmetric ether content of a predetermined value or less is thermally cracked to produce lower olefins, so that the content of produced methanol in the obtained lower olefins can be reduced.

[0031] The asymmetric ether is preferably a monoether having only one ether oxygen atom in the molecule, since this can effectively reduce the content of produced methanol in the obtained lower olefin.

[0032] Furthermore, the asymmetric ether having a ΔE (unit: e) of 0.05 or more is one in which the ΔE value of at least one ether bond in the molecule is 0.05 or more. However, since there is a high correlation between the ΔE value and the amount of methanol produced, it is preferable that the asymmetric ether be a monoether having only one ether oxygen atom in the molecule, since this can effectively reduce the content of produced methanol in the obtained lower olefin.

[0033] Furthermore, the asymmetric ether, preferably the asymmetric ether having a ΔE of 0.05 or more, is preferably one in which one of the two carbon atoms bonded to an ether oxygen atom is a carbon atom of a methyl group, such as 2-methoxybutane, methoxycyclopentane, or 1-methoxypropane, because this can more effectively reduce the content of produced methanol in the obtained lower olefin.

[0034] When an ether molecule has two or more ether bonds, ΔE of each ether bond is calculated as the absolute value of the difference in electric charges between the two carbon atoms bonded to each ether oxygen atom, and the ΔE of the ether refers to the largest value among the two or more ΔE.

[0035] <Naphtha / Naphtha for light olefin production> In the process for producing lower olefins of the present invention, naphtha is used as a thermal cracking raw material for producing lower olefins. One embodiment of the naphtha is a naphtha for producing lower olefins that contains an ether, the ether having an asymmetric structure with respect to the ether oxygen atom, and the content of oxygen atoms derived from the ether being 20,000 ppm by mass or less. When the content of oxygen atoms derived from the ether contained in naphtha for producing lower olefins is 20,000 ppm by mass or less, the content of methanol produced in the lower olefins obtained by thermal cracking the naphtha can be reduced. The content of oxygen atoms derived from the ether is preferably 1,000 ppm by mass or less, more preferably 100 ppm by mass or less, and even more preferably 50 ppm by mass or less.

[0036] In the naphtha for producing lower olefins, the ether preferably has an absolute value ΔE (ΔE=|E1-E2|) of the difference between the charge E1 of one carbon atom and the charge E2 of the other carbon atom, determined by the density functional theory described above, of 0.05 or more for the reasons described above.

[0037] In the naphtha for producing lower olefins, the ether is preferably a monoether having only one ether oxygen atom in the molecule, since this can more effectively reduce the content of produced methanol in the lower olefins obtained.

[0038] In the naphtha for producing lower olefins, the ether is preferably an ether in which one of the two carbon atoms bonded to the ether oxygen atom is a carbon atom of a methyl group, such as 2-methoxybutane, methoxycyclopentane, or 1-methoxypropane, because this can more effectively reduce the content of produced methanol in the obtained lower olefins.

[0039] In the naphtha for producing lower olefins of the present invention, the upper limit of the content of oxygen atoms derived from the ether contained in the naphtha is 20,000 ppm by mass or less, preferably 1,000 ppm by mass or less, more preferably 100 ppm by mass or less, and even more preferably 50 ppm by mass or less, from the viewpoint of suppressing the amount of methanol produced in the lower olefins obtained by thermal cracking the naphtha.

[0040] On the other hand, the lower limit of the content of oxygen atoms derived from the ether contained in the naphtha is not particularly limited and is usually 0.1 ppm by mass or more from the lower limit of quantitation measured by GC and GC / MS, which are common analytical instruments, but is preferably 0.2 ppm by mass or more, more preferably 0.5 ppm by mass or more, even more preferably 1 ppm by mass or more, particularly preferably 10 ppm by mass or more, and most preferably 20 ppm by mass or more.

[0041] Such naphtha can be obtained, for example, by purchasing or obtaining naphtha having a content of oxygen atoms derived from the ether of 20,000 mass ppm or less. When the content of oxygen atoms derived from the ether in the purchased or obtained naphtha exceeds 20,000 mass ppm, the naphtha can be obtained by mixing it with naphtha or the like having a content of oxygen atoms derived from asymmetric ethers of less than 20,000 mass ppm to reduce the content.

[0042] <Naphtha decomposition method> In the method for producing lower olefins of the present invention, lower olefins can be produced in accordance with a conventional method, except that naphtha having a low content of asymmetric ether, preferably an asymmetric ether with a ΔE (unit: e) of 0.05 or more, is selected or prepared and used as described above.

[0043] That is, the asymmetric ether, preferably an asymmetric ether having a ΔE of 0.05 or more, is thermally cracked (steam cracked) in naphtha having an oxygen atom content of 20,000 mass ppm or less in the presence of steam at a temperature of 700 to 1000°C to obtain lower olefins.

[0044] Among the conditions for thermal cracking, the ratio of naphtha to steam is preferably 20 to 100 parts by mass, more preferably 30 to 70 parts by mass, and particularly preferably 35 to 60 parts by mass, of steam per 100 parts by mass of naphtha. If the amount of steam is less than 20 parts by mass, there is a tendency for a large amount of carbonaceous material to be deposited on the piping for carrying out the cracking reaction installed in the thermal cracking furnace. On the other hand, if the amount of steam exceeds 100 parts by mass, the amount of heat given to the steam increases, resulting in an excessive energy load on the device.

[0045] The reaction temperature for thermal cracking is usually 700 to 1000°C, preferably 750 to 950°C. If the reaction temperature is less than 700°C, the thermal cracking of naphtha does not proceed sufficiently, resulting in a decrease in the yield of the target lower olefins. On the other hand, if the reaction temperature exceeds 1000°C, the thermal cracking of naphtha becomes excessive, increasing the generation of undesirable by-products such as methane, and the yield of the target lower olefins tends to decrease.

[0046] The reaction time for thermal cracking is preferably 0.01 to 1 second, more preferably 0.04 to 0.7 seconds. If the reaction time is less than 0.01 second, the thermal cracking of naphtha does not proceed sufficiently, and the yield of the target lower olefins tends to decrease. On the other hand, if the reaction time exceeds 1 second, the thermal cracking of naphtha becomes excessive, and the generation of undesirable by-products such as methane increases, and the yield of the target lower olefins tends to decrease.

[0047] The reaction pressure for the thermal decomposition is preferably 0.01 to 1.5 MPa (gauge pressure), more preferably 0.05 to 0.5 MPa (gauge pressure), and even more preferably 0.07 to 0.2 MPa (gauge pressure).

[0048] The reaction product that has left the pyrolysis reaction zone can be rapidly cooled to prevent excessive decomposition. The cooling temperature is not particularly limited, but for example, when carried out on an industrial scale, it can be preferably 200 to 700°C, more preferably 250 to 650°C, and when carried out on a small scale such as in a pilot plant or laboratory, it can be preferably 0 to 100°C, more preferably 3 to 40°C.

[0049] The reaction product containing lower olefins thus obtained can be purified, fractionated, and the like according to conventional methods. As a result, lower olefins such as ethylene, propylene, butene, and butadiene, aromatic hydrocarbons, and other hydrocarbons are obtained, respectively. Saturated hydrocarbons such as ethane and propane can be recovered and subjected to thermal cracking again. Among the lower olefins, butene and butadiene are usually obtained as a mixture with butane. Therefore, it is preferable to isolate butadiene by solvent extraction in a separate process, and to utilize and fractionate the mixture of butene and butane remaining after extraction by polymerization, rectification, and the like in a separate process.

[0050] <Method for producing lower olefin composition and method for producing propylene composition> By using the method for producing a lower olefin of the present invention, a lower olefin composition containing a lower olefin and methanol can be produced. More specifically, by using the process for producing lower olefins of the present invention, it is possible to produce a lower olefin composition which contains lower olefins and in which the production of methanol is suppressed, i.e., which has a low methanol content.

[0051] Furthermore, by using the process for producing lower olefins of the present invention, a propylene composition containing propylene and methanol can be produced. More specifically, by using the process for producing lower olefins of the present invention, it is possible to produce a propylene composition which contains propylene and in which the production of methanol is suppressed, i.e., a propylene composition with a low methanol content.

[0052] In the process for producing a lower olefin composition of the present invention or the process for producing a propylene composition of the present invention, the ether is preferably a monoether having only one ether oxygen atom in the molecule for the reasons mentioned above.

[0053] Furthermore, in the method for producing a lower olefin composition of the present invention or the method for producing a propylene composition of the present invention, the ether is preferably an ether in which one of the two carbon atoms bonded to the ether oxygen atom is a carbon atom of a methyl group, for the reasons described above.

[0054] As mentioned above, methanol has an adverse effect on the polymerization catalyst when polymerizing lower olefins or propylene, and therefore the production method of the present invention is effective when producing lower olefins such as propylene.

[0055] <Lower olefin composition> The lower olefin composition of the present invention is a composition containing a lower olefin or a derivative thereof, which is a cracking product of the naphtha for producing lower olefins of the present invention.

[0056] The "lower olefin" can be an unsaturated hydrocarbon having 2 to 4 carbon atoms and containing one or two unsaturated bonds per molecule. Specific examples include ethylene, propylene, 1-butene, 2-butene, isobutene, 1,2-butadiene, and 1,3-butadiene. Of these, at least one selected from the group consisting of ethylene, propylene, 1-butene, and 2-butene is preferred.

[0057] The "derivative thereof", i.e., the "derivative of a lower olefin" may be a compound produced during cracking of the naphtha for producing lower olefins of the present invention, or may be a compound obtained using a lower olefin that is a cracking product of the naphtha for producing lower olefins of the present invention. The "derivative of a lower olefin" is not particularly limited, but examples thereof include the following ethylene derivatives, propylene derivatives, and butene derivatives.

[0058] a) Ethylene derivatives: Examples include ethylene oxide, ethylene glycol, ethanolamine, glycol ether, etc., obtained by the oxidation reaction of ethylene, vinyl chloride monomer obtained by chlorination, 1,1,1-trichloroethane, vinylidene chloride, polyvinyl chloride, etc. Also included are α-olefins obtained by polymerization of ethylene, and higher alcohols obtained by the oxo reaction and subsequent hydrogenation reaction using α-olefins as raw materials. Also included are low-density and high-density polyethylenes obtained by polymerization of ethylene. Also included are vinyl acetate obtained by the reaction of ethylene with acetic acid. Also included are acetaldehyde obtained by the Wacker reaction of ethylene and its derivative, ethyl acetate, etc.

[0059] b) Propylene derivatives: Examples include acrylonitrile obtained by ammoxidation of propylene, acrolein, acrylic acid and acrylic acid esters obtained by selective oxidation of propylene, normal butyraldehyde obtained by the oxo reaction of propylene, and oxo alcohols such as 2-ethylhexanol. Also included are polypropylene obtained by polymerization of propylene. Other examples include propylene oxide and propylene glycol obtained by selective oxidation of propylene, and isopropyl alcohol obtained by hydration of propylene. Other examples include acetone obtained by the Wacker reaction of propylene, methyl isobutyl ketone and acetone cyanohydrin obtained from acetone, and methyl methacrylate obtained from acetone cyanohydrin.

[0060] c) Butene derivatives: Examples include butadiene obtained by oxidative dehydrogenation of butene. Also included are 1,4-butanediol obtained through acetoxylation, hydrogenation, and hydrolysis of butadiene, and pyrrolidones such as γ-butyl lactone and N-methylpyrrolidone obtained from butadiene as raw materials. Furthermore, examples include tetrahydrofuran and polytetramethylene glycol obtained by dehydration of pyrrolidones. Also included are various synthetic rubbers obtained using butadiene.

[0061] By using the naphtha for producing lower olefins of the present invention, for the reasons described above, it is possible to produce a lower olefin composition which contains lower olefins and in which the production of methanol is suppressed, i.e., which has a low methanol content.

[0062] In the lower olefin composition of the present invention, the ether contained in the naphtha for producing lower olefins is an asymmetric ether having an asymmetric structure with respect to the ether oxygen atom.

[0063] In the lower olefin composition of the present invention, the ether contained in the naphtha for producing lower olefins is preferably a monoether having only one ether oxygen atom in the molecule, since this can more effectively reduce the content of produced methanol in the obtained lower olefins.

[0064] In the lower olefin composition of the present invention, the ether contained in the naphtha for producing lower olefins is preferably an ether in which one of the two carbon atoms bonded to the ether oxygen atom is a carbon atom of a methyl group, such as 2-methoxybutane, methoxycyclopentane, or 1-methoxypropane, because this can more effectively reduce the content of produced methanol in the obtained lower olefins.

[0065] Furthermore, when the ether is an ether in which one of the two carbon atoms bonded to the ether oxygen atom is a carbon atom of a methyl group, the lower olefin composition of the present invention contains methanol.

[0066] The content of the lower olefin in the lower olefin composition is not particularly limited, but is preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, particularly preferably 95% by mass or more, and particularly preferably 98% by mass or more, relative to 100% by mass of the total mass of the lower olefin composition. The content of the lower olefin in the lower olefin composition may be 100% by mass.

[0067] The content of methanol in the lower olefin composition is not particularly limited, but is preferably 10,000 ppm by mass or less, more preferably 1,000 ppm by mass or less, even more preferably 100 ppm by mass or less, particularly preferably 10 ppm by mass or less, particularly preferably 5 ppm by mass or less, and most preferably 1 ppm by mass or less, relative to the total mass of the lower olefin composition.

[0068] Such a lower olefin composition or, as described above, an asymmetric ether can be obtained by selecting naphtha containing 20,000 mass ppm or less of oxygen atoms of the asymmetric ether and cracking the naphtha.

[0069] <Polyolefin polymer> The polyolefin polymer of the present invention is a polyolefin polymer obtained by polymerizing the lower olefin or a derivative thereof contained in the lower olefin composition of the present invention using a known polymerization method. The polyolefin polymer of the present invention is a polyolefin polymer containing repeating units derived from an olefin (hereinafter referred to as "lower olefin units") or repeating units derived from a derivative thereof (hereinafter referred to as "lower olefin derivative units"). That is, the polyolefin polymer of the present invention may be a polymer containing only lower olefin units, a polymer containing lower olefin units and lower olefin derivative units, or a polymer containing only lower olefin derivative units. The "repeating unit" means a unit formed directly by the polymerization reaction of a lower olefin or a derivative thereof, and may be a unit in which a part of the unit is converted into a different structure by treating the polymer.

[0070] The polyolefin polymer of the present invention may be a polyolefin polymer obtained by polymerizing a lower olefin composition of the present invention from which methanol has been removed by a known methanol separation method such as distillation. Alternatively, the polyolefin polymer of the present invention may be a polyolefin polymer obtained by polymerizing the lower olefin composition of the present invention as it is. In this case, since the methanol content in the lower olefin composition is low for the reasons described above, the performance of the catalyst used in polymerizing the lower olefin is not substantially impaired by methanol, and the obtained polyolefin polymer is excellent in quality from the viewpoints of molecular weight distribution, impurities, etc. [Example]

[0071] The present invention will be explained in more detail below by way of experimental examples and comparative experimental examples that serve as substitutes for the working examples.

[0072] The names of the compounds used in the experimental examples and comparative experimental examples are as follows: 2-Methoxybutane (Tokyo Chemical Industry Co., Ltd.) Methoxycyclopentane (Tokyo Chemical Industry Co., Ltd.) 1-Methoxypropane (Tokyo Chemical Industry Co., Ltd.) Dimethyl ether (Koike Chemical Co., Ltd.) Diethyl ether (Tokyo Chemical Industry Co., Ltd.) Diisopropyl ether (Tokyo Chemical Industry Co., Ltd.) Dipropyl ether (Tokyo Chemical Industry Co., Ltd.)

[0073] <Evaluation method> (1) Calculation method of ΔE For the ethers used in the Experimental Examples and Comparative Experimental Examples, the absolute value ΔE (unit: e) of the difference in charge between the two carbon atoms bonded to the ether oxygen atom in the ether was calculated according to the following procedure. The molecular structure of the ether was subjected to density functional theory (DFT) calculations to calculate the charges of the two carbon atoms. The DFT calculation conditions used def-TZVP as the basis set, the COSMO solvation model (Conductor-like Screening Model) for the solvent effect, and Mulliken's population analysis method. Next, for the two carbon atoms bonded to the oxygen atom of the ether bond in the ether, the absolute value ΔE (ΔE = |E1 - E2|) (unit: e) of the difference between the charge E1 of one carbon atom and the charge E2 of the other carbon atom was calculated. Here, "e" means the elementary charge of an electron, and e = 1.602176634×10 -19 [unit: C]. For example, when ΔE is 0.05 [unit: e], expressing this in SI units, ΔE = 0.05×1.602176634×10 -19 [unit: C]. For the calculation of the above ΔE, the quantum chemistry calculation software "TURBOMOLE ver7.2" (manufactured by TURBOMOLE) and the graphical user interface "TmoleX ver4.4.1" for TURBOMOLE (manufactured by TURBOMOLE) were used.

[0074] (2) Calculation of methanol production ratio B Methanol generated from the thermal decomposition of naphtha is substantially contained in the condensed water obtained in the experimental examples and comparative experimental examples and is not contained in the gas components and oil components. Therefore, the methanol production ratio B of the condensed water obtained in the experimental examples and comparative experimental examples was measured under the following conditions using a gas chromatography-mass spectrometry measurement device (GC / MS device) (device name: GCMS-QP2010Ultra, manufactured by Shimadzu Corporation). It was previously confirmed that no methanol is generated from the blank naphtha used in the experimental examples and comparative experimental examples. <GC / MS measurement conditions> Carrier gas: Helium, linear velocity 40 cm / sec Column: SUPELCOWAX-10 (manufactured by Supelco, inner diameter 0.32 mm × length 60 m × film thickness 0.25 μm) Temperature (temperature rising condition): 50°C (holding time 5 minutes) → rising temperature at 20°C / min → 200°C (holding time 2.5 minutes) [[ID=2​​​​​​​Split ratio: 1:5 Measurement mode: SIM (m / z=31)

[0075] The amount of methanol produced as a thermal decomposition product from the condensed water obtained in the Experimental Example and Comparative Experimental Example was quantified, and the methanol production ratio B relative to the added ether was calculated using the following formula based on a calibration curve prepared in advance using standard solutions of methanol with known concentrations.

[0076] [Methanol production ratio B] = [Number of oxygen atoms in methanol in condensed water] ÷ [Number of oxygen atoms in ether added to blank naphtha]

[0077] In other words, when the methanol production ratio B is 1.00, it means that all of the added ether was quantified as methanol. Note that the number of oxygen atoms contained in the added ether is one oxygen atom per molecule of the ether compound.

[0078] [Experimental Example 1] 2-Methoxybutane was added to blank naphtha used as a raw material so that the content of ether-derived oxygen atoms was 50 ppm by mass, and then thermally decomposed in the presence of steam using a thermal decomposition furnace under the following thermal decomposition conditions. The resulting thermal decomposition product was quenched at 5°C and subjected to gas-liquid separation using a gas-liquid separator at 0.1 MPa (gauge pressure) and 5°C to obtain gas components and a separated liquid. The separated liquid was then subjected to oil-water separation using a separatory funnel at atmospheric pressure and room temperature to separate the oil and condensed water.

[0079] <Pyrolysis conditions> Naphtha flow rate: 83.1g / hr Steam / naphtha mass ratio: 0.4 Residence time: 0.6 seconds Thermal decomposition temperature: 810℃ Thermal decomposition pressure: 0.1 MPa (gauge pressure)

[0080] The methanol production ratio B of the condensed water was measured by the above-mentioned method and is shown together with the value of ΔE in Table 1. The relationship between ΔE and the methanol production ratio B is also shown in FIG.

[0081] [Experimental Examples 2-3, Comparative Experimental Examples 4-7] Gas components, oil content, and condensed water were obtained and evaluated under the same conditions as in Experimental Example 1, except that the type of ether and the content of oxygen atoms derived from the ether were changed as shown in Table 1. The evaluation results are shown in Table 1 and Figure 1. Note that Experimental Example 1 refers to Experimental Examples 1-1 to 1-3 listed in Table 1. Experimental Example 2 refers to Experimental Examples 2-1 to 2-3 listed in Table 1. Experimental Example 3 refers to Experimental Examples 3-1 to 3-3 listed in Table 1. Experimental Examples 1-1, 2-1, 3-1, and Comparative Experimental Examples 4 to 7 are plotted in Figure 1.

[0082] [Table 1]

[0083] A comparison of Experimental Examples 1 to 3 and Comparative Experimental Examples 4 to 7 reveals that there is a correlation between the ΔE value of the ether and the methanol production ratio B, and that ethers having an asymmetric structure with respect to the ether oxygen atom have a high methanol production ratio B and are more likely to produce methanol. Furthermore, it is clear that ethers with a ΔE of 0.05 or more tend to produce more methanol as the ΔE value increases.

[0084] Furthermore, Experimental Examples 1 to 3 in Table 1 show that, for ethers having an asymmetric structure with respect to the oxygen atom constituting the ether bond, when the ether oxygen atom concentration was 20,000 ppm by mass or less, the methanol production ratio was approximately the same when the ether oxygen atom concentration was 50 ppm by mass, 500 ppm by mass, and 5,000 ppm by mass. This is presumably because ethers having an asymmetric structure have a large ΔE, which results in a large imbalance in the charge between the two carbon atoms bonded to the ether oxygen atom, making them more susceptible to thermal decomposition under the thermal decomposition conditions to produce methanol.

[0085] Therefore, it is clear that by using naphtha in which the content concentration of ethers having an asymmetric structure with respect to the ether oxygen atom is set to a predetermined value or less, it is possible to suppress the concentration of methanol produced and produce lower olefins with high commercial value.

Claims

1. A method for producing lower olefins, comprising a step of cracking naphtha containing ethers, the ether has an asymmetric structure with respect to the oxygen atom constituting the ether bond, the ether is 2-methoxybutane, methoxycyclopentane, or 1-methoxypropane; The naphtha has a content of oxygen atoms derived from the ether of 20,000 ppm by mass or less.

2. 2. The method for producing lower olefins according to claim 1, wherein the naphtha contains 0.1 ppm by mass or more of oxygen atoms derived from the ether.

3. 3. The method for producing lower olefins according to claim 1, wherein the naphtha contains 100 ppm or less of oxygen atoms derived from the ether.

4. 4. The method for producing lower olefins according to claim 1, wherein the ether has an absolute value ΔE (ΔE=|E1-E2|) of the difference between the charge E1 of one carbon atom and the charge E2 of the other carbon atom, determined by density functional theory, for two carbon atoms bonded to oxygen atoms constituting an ether bond, of 0.05 (unit: e) or more. Here, e means the elementary electron quantity, and e = 1.602176634 × 10 －１９ [Unit: C].

5. 5. The method for producing lower olefins according to claim 4, wherein the ΔE [unit: e] and the methanol formation ratio B in the obtained lower olefins satisfy the following formulas (1) and (2): 0.05≦ΔE Formula (1) B≦1.25×ΔE+0.10 Formula (2)

6. The method for producing a lower olefin according to any one of claims 1 to 5, wherein the lower olefin is propylene.

7. A method for producing a lower olefin composition, comprising producing a lower olefin composition containing a lower olefin and methanol using the method for producing a lower olefin according to any one of claims 1 to 6.

8. A method for producing a propylene composition, comprising producing a propylene composition containing propylene and methanol by using the method for producing a lower olefin according to claim 6.

9. A naphtha for producing lower olefins containing ether, the ether has an asymmetric structure with respect to the oxygen atom constituting the ether bond, the ether is 2-methoxybutane, methoxycyclopentane, or 1-methoxypropane; The naphtha for producing lower olefins has a content of oxygen atoms derived from the ether of 20,000 mass ppm or less.

10. The naphtha for producing lower olefins according to claim 9, wherein the content of oxygen atoms derived from the ether is 0.1 ppm by mass or more.

11. The naphtha for producing lower olefins according to claim 9 or 10, wherein the content of oxygen atoms derived from the ether is 100 ppm by mass or less.

12. The naphtha for producing lower olefins according to any one of claims 9 to 11, wherein the ether has an absolute value ΔE (ΔE = |E1 - E2|) of the difference between the charge E1 of one carbon atom and the charge E2 of the other carbon atom, determined by density functional theory, for two carbon atoms bonded to oxygen atoms constituting the ether bond, of 0.05 [unit: e] or more. Here, e means the elementary electron quantity, and e = 1.602176634 × 10 －１９ [Unit: C].

13. The naphtha for producing lower olefins according to any one of claims 9 to 12, wherein the lower olefin is propylene.

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