Mixing method and method for producing lower olefins

Abstract

To provide a naphtha mixing method which can produce lower olefin having low methanol production concentration when receiving a receiving naphtha in a tank having a remaining naphtha and mixing the naphtha.SOLUTION: There is provided a mixing method for receiving a receiving naphtha in a tank having a remaining naphtha and mixing the naphtha, wherein in the mixed naphtha in the tank, a content of ether having an asymmetric structure derived from the remaining naphtha and the receiving naphtha is equal to or less a predetermined threshold as a content of the oxygen atom derived from the ether.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a blending method for receiving and blending incoming naphtha into a tank with inventory naphtha. Furthermore, the present invention relates to a method for producing lower olefins, which comprises thermally cracking the naphtha obtained by the above-mentioned mixing method. [Background technology]

[0002] Naphtha transported in a Very Large Crude (Oil) Carrier (hereinafter referred to as "VLCC") is temporarily lifted into a naphtha tank before being supplied to an ethylene plant where petrochemical products such as ethylene and propylene are produced. Because the raw naphtha varies in composition and properties depending on its place of origin, in the above-mentioned petrochemical product production process, the transported naphtha is mixed with naphtha stored in advance in a tank at an appropriate ratio, or naphtha stored in one or more tanks is mixed at an appropriate ratio and supplied to the ethylene plant to produce various petrochemical products.

[0003] A typical method for producing lower olefins such as ethylene and propylene 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).

[0004] 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.

[0005] For this reason, the concentration of oxygen-containing compounds in naphtha is used as a criterion for judging the quality of naphtha, and usually, naphtha purchasers blend naphtha having a high oxygen-containing compound content with naphtha having a low oxygen-containing compound content to reduce the concentration of oxygen-containing compounds in the naphtha before using it for producing light olefins. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-40913 Summary of the Invention [Problem to be solved by the invention]

[0007] 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, no method has been known to accurately obtain high-quality naphtha with a low concentration of methanol produced.

[0008] An object of the present invention is to solve these problems. That is, an object of the present invention is to provide a mixing method for mixing transported naphtha with naphtha stored in advance in a tank at an appropriate mixing ratio, or for mixing naphtha stored in one or more tanks at an appropriate mixing ratio, so as to obtain naphtha that can produce lower olefins with a low methanol concentration. Another object of the present invention is to provide a method for producing lower olefins with a low methanol content using naphtha obtained by the mixing method. [Means for solving the problem]

[0009] 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.

[0010] That is, the present invention is summarized as follows.

[0011] A first aspect of the present invention relates to a method for receiving and mixing an incoming naphtha into a tank containing an inventory naphtha, the method comprising mixing the incoming naphtha and the inventory naphtha so that the contents of ethers having asymmetric structures derived from the inventory naphtha and the incoming naphtha in the mixed naphtha in the tank are equal to or less than a predetermined threshold value as the content of oxygen atoms derived from the ethers. The second gist of the present invention relates to a method for producing lower olefins, which comprises thermally cracking naphtha obtained by the above-mentioned mixing method, wherein 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, which are determined by density functional theory for two carbon atoms bonded to oxygen atoms constituting an ether bond of the ether, 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) Here, e means the elementary electron quantity, e = 1.602176634 × 10 -19 [Unit: C] [Effects of the Invention]

[0012] According to the present invention, by blending stock naphtha and incoming naphtha, naphtha that produces a low amount of methanol during thermal cracking can be more accurately obtained, and such naphtha can be used to produce lower olefins with a low methanol content. That is, by blending stock naphtha and incoming naphtha so that the content of oxygen atoms derived from specific ethers, specifically ethers having an asymmetric structure, in the naphtha is equal to or less than a predetermined threshold, a high-quality raw naphtha with a low methanol content can be accurately obtained.

[0013] Furthermore, according to the present invention, by controlling the content of oxygen atoms derived from specific ethers in a blended 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, it is possible to more accurately obtain a high-quality raw material naphtha with a low methanol production concentration. 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]

[0014] [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

[0015] The present invention will be described in detail below, but the present invention is not limited to the following description and can be practiced with any modifications within the scope of the gist of the present invention.

[0016] Unless otherwise specified, in this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​written before and after "to" as the lower and upper limits, and "A to B" means A or more and B or less.

[0017] 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.

[0018] [Mixing method] The mixing method of the present invention is a method of receiving incoming naphtha into a tank containing inventory naphtha and mixing the naphtha, and includes mixing the naphtha so that the content of ethers having an asymmetric structure derived from the inventory naphtha and the incoming naphtha (hereinafter, may be referred to as "asymmetric ethers") in the naphtha after mixing in the tank is equal to or less than a predetermined threshold value (hereinafter, may be simply referred to as "threshold value") as the content of oxygen atoms derived from the ethers (hereinafter, may be referred to as "ether oxygen atoms" or "asymmetric ether oxygen atoms"). Here, the embodiment of "receiving incoming naphtha into a tank having stock naphtha and mixing it" is not particularly limited, and examples include mixing transported naphtha with naphtha stored in advance in a tank at an appropriate mixing ratio, or mixing naphtha stored in one or more tanks at an appropriate mixing ratio.

[0019] <Mechanism> Ethers are compounds found in naphtha. In the present invention, an asymmetric ether has an asymmetric structure with respect to the ether oxygen atom.

[0020] Among the asymmetric ethers, those for which 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, for the two carbon atoms bonded to the ether oxygen atom, is 0.05 [unit: e] or more, can be mixed based on the threshold value, thereby making it possible to more effectively reduce the methanol content in the lower olefins obtained by thermal cracking the naphtha after mixing. In this specification, "e" means the elementary electron quantity, and e = 1.602176634 × 10 -19 [Unit: C] 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).

[0021] 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.

[0022] 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 mixing the mixture so that the content of asymmetric ether oxygen atoms in the naphtha after mixing is a predetermined value or less, preferably 20,000 mass ppm or less, the methanol concentration in the lower olefins obtained by thermal cracking the naphtha after mixing can be reduced.

[0023] 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.

[0024] 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.

[0025] In the blending method of the present invention, inventory naphtha and incoming naphtha are blended so that the content of asymmetric ether oxygen atoms in the blended naphtha is a predetermined value or less. This suppresses the production of methanol in the process for producing lower olefins obtained by thermal cracking the blended naphtha, and makes it possible to produce lower olefins with a low methanol content and high product value.

[0026] <Mixing of stock naphtha and incoming naphtha> According to the present invention, specific methods for mixing naphtha so that the content of asymmetric ether oxygen atoms in the mixed naphtha is equal to or less than the threshold value include the following methods. (1) When the asymmetric ether oxygen atom content of the stock naphtha exceeds the threshold, the stock naphtha is mixed with incoming naphtha having an asymmetric ether oxygen atom content less than the threshold, so that the asymmetric ether oxygen atom content of the mixed naphtha is equal to or less than the threshold. (2) When the asymmetric ether oxygen atom content of the stock naphtha is equal to or less than the threshold, the stock naphtha is mixed with incoming naphtha having an asymmetric ether oxygen atom content equal to or less than the threshold, so that the asymmetric ether oxygen atom content of the mixed naphtha is equal to or less than the threshold. (3) When the asymmetric ether oxygen atom content of the stock naphtha is equal to or less than the threshold value, the incoming naphtha having an asymmetric ether oxygen atom content exceeding the threshold value is blended in an amount such that the asymmetric ether oxygen atom content of the resulting blended naphtha is equal to or less than the threshold value.

[0027] The asymmetric ether oxygen atom content of naphtha can be determined based on the asymmetric ether contained in the naphtha using general analytical equipment such as GC and GC / MS measurement.

[0028] Therefore, by providing a measuring means for measuring the asymmetric ether oxygen atom content of each of the stock naphtha and the received naphtha, and a control device for calculating and adjusting the selection of the stock naphtha and the received naphtha to be mixed and the mixing ratio thereof based on these measured values ​​so that the asymmetric ether oxygen atom content of the naphtha after mixing is equal to or less than a threshold value, it is also possible to automatically mix the stock naphtha and the received naphtha.

[0029] For example, when there are multiple storage tanks for stock naphtha, the storage tank into which the received naphtha is charged can be selected based on the asymmetric ether oxygen atom content of the received naphtha so that the received naphtha is mixed by any one of the above methods (1) to (3), and the amount charged can be controlled so that the asymmetric ether oxygen atom content of the naphtha after mixing is equal to or less than a threshold value. Furthermore, when there are multiple naphthas to be received, it is also possible to select stock naphthas to be mixed based on the asymmetric ether oxygen atom content of each of the received naphthas and switch the storage tanks into which each naphtha is to be fed.

[0030] <threshold> In the present invention, the threshold value of the asymmetric ether oxygen atom content in the naphtha after mixing is preferably 20,000 ppm by mass or less, more preferably 1,000 ppm by mass or less, further preferably 100 ppm by mass or less, and particularly 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 after mixing.

[0031] On the other hand, the lower limit of this threshold is not particularly limited and is usually 0.1 ppm by mass or more from the lower limit of quantitation by GC and GC / MS measurement using common analytical equipment, 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.

[0032] <Asymmetric ether> As described above, the asymmetric ether according to the present invention is preferably such that 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, for two carbon atoms bonding to ether oxygen atoms, from the viewpoint of more effectively reducing the methanol content in the lower olefins obtained by thermal cracking the naphtha after blending according to the present invention.

[0033] Asymmetric ethers according to the present invention include, but are not limited to, 2-methoxybutane (CH3CH2CH(CH3)-O-CH3), methoxycyclopentane (C5H9-O-CH3), 1-methoxypropane (CH3CH2CH2-O-CH3), and the like.

[0034] 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 lower olefins obtained by thermal cracking the naphtha after mixing according to the present invention.

[0035] 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.

[0036] 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 lower olefins obtained by thermal cracking the naphtha after mixing according to the present invention.

[0037] When the asymmetric ether has two or more ether bonds in one molecule, 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.

[0038] [Production method of lower olefins] The method for producing lower olefins of the present invention comprises thermally cracking naphtha obtained by the mixing method of the present invention, and the ΔE [unit: e] and the methanol formation ratio B in the obtained lower olefins satisfy the following formulas (1) and (2), and this method makes it possible to obtain lower olefins with a reduced methanol content. 0.05≦ΔE Formula (1) B≦1.25×ΔE+0.10 Formula (2)

[0039] As described above, methanol adversely affects the polymerization catalyst when polymerizing lower olefins. The lower olefins obtained by thermal cracking the mixed naphtha according to the present invention 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.

[0040] It is more preferable that the condition of the formula (2) satisfies B≦1.25×ΔE+0.05.

[0041] 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.

[0042] The process for producing lower olefins of the present invention can be carried out in a conventional manner using the mixed naphtha having a low content of asymmetric ether oxygen atoms obtained by the mixing method of the present invention.

[0043] That is, naphtha mixed with the asymmetric ether, preferably an asymmetric ether having a ΔE of 0.05 or more, in an amount of 20,000 mass ppm or less in terms of oxygen atom content is thermally cracked (steam cracked) 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] According to the process for producing lower olefins of the present invention, the production of methanol during the production of lower olefins is suppressed, and lower olefins with a low methanol content can be produced. For example, by using the process for producing lower olefins of the present invention, the production of methanol during propylene production can be suppressed, and propylene with a low methanol content can be produced.

[0051] As mentioned above, methanol has an adverse effect on the polymerization catalyst when polymerizing lower olefins such as propylene, and therefore the production method of the present invention is effective when producing lower olefins such as propylene.

[0052] The content of methanol in lower olefins such as propylene produced by the method for producing lower olefins of the present invention 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, especially preferably 5 ppm by mass or less, and most preferably 1 ppm by mass or less, relative to the total mass of the lower olefins. [Example]

[0053] 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.

[0054] 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.)

[0055] <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" represents 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.

[0056] (2) Calculation of methanol production ratio B Since the 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 not contained in the gas components and oil components, 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 increase condition): 50°C (holding time 5 minutes) → temperature increase at 20°C / min → 200°C (holding time 2.5 minutes) Inlet temperature: 200°C MS interface temperature: 200°C Ion source temperature: 200°C Sample amount: 0.5 μL Split ratio: 1:5 Measurement mode: SIM (m / z=31)

[0057] 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.

[0058] [Methanol production ratio B] = [Number of oxygen atoms in methanol in condensed water] ÷ [Number of oxygen atoms in ether added to blank naphtha]

[0059] 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.

[0060] [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.

[0061] <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)

[0062] 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.

[0063] [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.

[0064] [Table 1]

[0065] 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.

[0066] 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. Therefore, when stock naphtha and received naphtha are mixed as raw material naphtha for producing lower olefins, by mixing them so that the content concentration of ethers having an asymmetric structure with respect to the ether oxygen atom is equal to or less than a predetermined value, it is possible to produce lower olefins with high product value, in which methanol production is suppressed, using this mixed naphtha.

Claims

1. 1. A method for receiving and blending incoming naphtha into a tank with inventory naphtha, comprising: mixing the naphtha after mixing in the tank so that the contents of ethers having an asymmetric structure derived from the inventory naphtha and the received naphtha are 20,000 mass ppm or less in terms of the content of oxygen atoms derived from the ethers, the ether is a monoether, A mixing method in which one of the two carbon atoms bonded to the oxygen atom constituting the ether bond of the ether is a carbon atom derived from a methyl group.

2. 2. The mixing method according to claim 1, wherein the ether is mixed so that the content of oxygen atoms derived from the ether in the naphtha after the mixing is 0.1 ppm by mass or more.

3. A mixing method as described in claim 1 or 2, wherein the mixing is carried out so that the content of oxygen atoms derived from the ether in the naphtha after the mixing is 100 mass ppm or less.

4. A mixing method as described in claim 1 or 2, wherein the mixing is carried out so that the content of oxygen atoms derived from the ether in the naphtha after the mixing is 50 mass ppm or less.

5. The method for mixing according to any one of claims 1 to 4, 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. where e represents the elementary electron quantity, e = 1.602176634 × 10 －１９ [Unit: C].

6. A method for producing lower olefins, comprising obtaining naphtha by the mixing method according to any one of claims 1 to 5, and then thermally cracking the naphtha, The method for producing lower olefins is characterized in that 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, which are determined by density functional theory for two carbon atoms bonded to oxygen atoms constituting an ether bond of the ether, and the methanol formation ratio B in the obtained lower olefin satisfy the following formulas (1) and (2): 0.05≦ΔE Formula (1) B≦1.25×ΔE+0.10 Formula (2) where e represents the elementary electron quantity, e = 1.602176634 × 10 －１９ [Unit: C].

7. The method for producing lower olefins according to claim 6, wherein the lower olefin is propylene.

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