Naphtha inspection method

Abstract

To provide a naphtha inspection method for accurately determining acceptance / rejection of naphtha as a raw material naphtha to be used for lower olefin production, in decomposing the naphtha containing ether to manufacture lower olefins, by applying a pipe-type heating method or steam cracking.SOLUTION: In a naphtha inspection method, naphtha is accepted as a raw material naphtha to be used for lower olefin production, if a content of ether with an asymmetric structure in the naphtha, being measured using gas chromatography, is 20,000 mass ppm or lower when converted to a content of oxygen atoms derived from the ether.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a naphtha inspection method for determining whether naphtha is acceptable as a raw material for use in producing lower olefins when naphtha is cracked by a tubular heating method or a steam cracking method to produce lower olefins. [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 components and properties depending on its place of production, in the above-mentioned petrochemical product production process, the transported naphtha is sometimes supplied to the ethylene plant as is, or the transported naphtha is mixed with naphtha stored in advance in a tank at an appropriate mixing ratio, or naphtha stored in one or more tanks is mixed at an appropriate mixing 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. Usually, naphtha purchasers inspect the oxygen-containing compound content of the naphtha they purchase, and sometimes use naphtha having an oxygen-containing compound content of a predetermined value or less for the production of light olefins without blending it with other naphthas. On the other hand, naphtha having a high oxygen-containing compound content is blended with naphtha having a low oxygen-containing compound concentration to reduce the oxygen-containing compound concentration in the naphtha before using it for the production of 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, a method for accurately determining high-quality naphtha with a low concentration of methanol produced has not been known until now.

[0008] The present invention aims to solve these problems. That is, an object of the present invention is to provide a method for inspecting naphtha to accurately determine whether the naphtha is acceptable as a raw material for producing lower olefins when the naphtha containing ethers is cracked by a tubular heating method or a steam cracking method to produce lower olefins. [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 provides: A naphtha inspection method for determining whether or not naphtha containing ethers is acceptable as a raw material naphtha for use in producing lower olefins by cracking the naphtha using a tube heating method or a steam cracking method, comprising: a naphtha inspection method, in which naphtha having a content of the ether having an asymmetric structure, measured by gas chromatography, converted into a content of oxygen atoms derived from the ether, of 20,000 mass ppm or less is deemed acceptable as a raw material naphtha to be used in the production of lower olefins; The summary is as follows. [Effects of the Invention]

[0011] According to the present invention, naphtha that produces a low amount of methanol during the production of lower olefins by thermal cracking can be more accurately determined, and lower olefins with a low methanol content can be produced using such naphtha. Specifically, when the content of oxygen atoms derived from a specific ether, specifically an ether having an asymmetric structure, in naphtha is equal to or less than a predetermined value, the naphtha can be accurately determined to be a high-quality raw material naphtha that produces a low methanol content during the production of lower olefins.

[0012] Furthermore, according to the present invention, the suitability of naphtha as a raw material for lower olefins can be more 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 0.05 (unit: e). [Brief explanation of the drawings]

[0013] [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

[0014] 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.

[0015] 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.

[0016] 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.

[0017] [Naphtha inspection method] The naphtha inspection method of the present invention is a naphtha inspection method for determining whether or not a naphtha containing ethers is acceptable as a raw material naphtha to be used in the production of lower olefins when the naphtha is cracked by a tubular heating method or a steam cracking method to produce lower olefins, and naphtha having a content of ethers having an asymmetric structure (hereinafter sometimes referred to as "asymmetric ethers") measured by gas chromatography, converted into a content of oxygen atoms derived from the ethers (hereinafter sometimes referred to as "ether oxygen atoms" or "asymmetric ether oxygen atoms") of 20,000 mass ppm or less, is deemed to be acceptable as a raw material naphtha to be used in the production of lower olefins.

[0018] In the present invention, as described above, the acceptability of naphtha as a raw material for lower olefin production may be determined based on the content of asymmetric ether oxygen atoms in the naphtha, and further based on the specific gravity of the naphtha and / or the contents of linear paraffins and branched paraffins in the naphtha to determine the acceptability of naphtha as a raw material for lower olefin production. Hereinafter, the judgment based on the content of asymmetric ether oxygen atoms will be referred to as "judgment criterion I," the judgment based on the specific gravity will be referred to as "judgment criterion II," and the judgment based on the contents of linear paraffins and branched paraffins will be referred to as "judgment criterion III."

[0019] <Mechanism> Ethers are compounds found in naphtha, a raw material used in the production of lower olefins. The asymmetric ethers to be measured in the present invention have an asymmetric structure with respect to the ether oxygen atom.

[0020] Among the asymmetric ethers to be measured, 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, is 0.05 [unit: e] or more, can be used to measure the methanol content in the lower olefins obtained by thermal cracking of the raw naphtha, thereby making it possible to more effectively reduce the methanol content in the lower olefins obtained by thermal cracking of the raw naphtha. 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 when naphtha contains asymmetric ethers, more preferably naphtha containing oxygen atoms derived from asymmetric ethers having a ΔE (unit: e) of 0.05 or more, in an amount of 20,000 mass ppm or less, the methanol concentration in lower olefins obtained by thermal cracking the naphtha can be more significantly 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 naphtha inspection method of the present invention, naphtha having an asymmetric ether oxygen atom content of 20,000 ppm by mass or less is judged to be acceptable as a raw material naphtha for producing light olefins, and by using such naphtha as a raw material for producing light olefins, it is possible to produce light olefins with high commercial value while suppressing the amount of methanol produced.

[0026] <Judgment Criteria I> In Criterion I, the content of asymmetric ether in naphtha is measured by gas chromatography, and naphtha whose converted value as the content of asymmetric ether oxygen atoms is 20,000 mass ppm or less is judged to be acceptable. If the content of asymmetric ether oxygen atoms in naphtha is 20,000 ppm by mass or less, the content of methanol produced in lower olefins obtained by thermal cracking of this naphtha can be reduced. The value of the asymmetric ether oxygen atom content evaluated as acceptable 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.

[0027] On the other hand, the lower limit of the asymmetric ether oxygen atom content that is evaluated as passing 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.

[0028] In the judgment criterion I, the asymmetric ether to be evaluated is preferably one 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, as determined by density functional theory, for two carbon atoms bonding to an ether oxygen atom, is 0.05 [unit: e] or more, from the viewpoint of being able to more effectively reduce the methanol content in the lower olefins obtained by thermal cracking of naphtha judged to be acceptable according to the present invention.

[0029] 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.

[0030] 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 naphtha that has been determined to be acceptable according to the present invention.

[0031] 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, the content of produced methanol in the obtained lower olefin can be effectively reduced. Therefore, it is preferable that the asymmetric ether be a monoether having only one ether oxygen atom in the molecule.

[0032] 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 resulting lower olefin.

[0033] 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 ΔEs.

[0034] <Criteria II> In Criterion II, the specific gravity of naphtha is measured, and naphtha having a specific gravity of 0.60 g / ml or more and 0.80 g / ml or less is judged to be acceptable as raw naphtha for use in the production of lower olefins. It is known that there is a correlation between naphtha density and naphtha composition, and from the viewpoint of being able to produce the lower olefins of the present invention, i.e., unsaturated hydrocarbons having 2 to 4 carbon atoms and containing one or two unsaturated bonds per molecule, in a high yield while suppressing the production of by-products, the specific gravity of naphtha is preferably 0.60 g / ml or more and 0.8 g / ml or less, and more preferably 0.66 g / ml or more and 0.71 g / ml or less. The specific gravity of naphtha can be measured using JIS K2249-1:2011.

[0035] <Criterion III> In Criterion III, the linear paraffin content and branched paraffin content of naphtha are measured, and naphtha having a linear paraffin content P1 of 20% by mass to 70% by mass and a branched paraffin content P2 of 20% by mass to 70% by mass is deemed acceptable as a raw naphtha for use in the production of lower olefins. If the linear paraffin and branched paraffin contents are within the above ranges, the lower olefins of the present invention, i.e., unsaturated hydrocarbons having 2 to 4 carbon atoms and containing one or two unsaturated bonds per molecule, can be produced in high yield while suppressing the generation of by-products. The linear paraffin and branched paraffin contents are more preferably 25% by mass to 65% by mass, respectively.

[0036] Furthermore, in Criterion III, the ratio (P1 / P2) of the linear paraffin content P1 to the branched paraffin content P2 is calculated, and naphtha having this P1 / P2 ratio of 0.3 to 3.5 is determined as a suitable feedstock naphtha for use in the production of lower olefins. If P1 / P2 is within the above range, the lower olefins of the present invention, i.e., unsaturated hydrocarbons having 2 to 4 carbon atoms and containing one or two unsaturated bonds per molecule, can be produced in high yield while suppressing the production of by-products. P1 / P2 is more preferably 0.5 to 2.5.

[0037] The contents of linear paraffins and branched paraffins in naphtha can be measured by gas chromatography.

[0038] <Determination procedure> When the above-mentioned criteria I, II and / or III are adopted, the judgments may be made in any order, but are preferably made in the following order (1) to (3). (1) Products that pass the Judgment Criterion I will be judged according to the Judgment Criterion II, and those that pass will be used as raw naphtha for the production of lower olefins. (2) Those that pass the Judgment Criterion I are judged according to the Judgment Criterion II, and those that pass are further judged according to the Judgment Criterion III, and those that pass are used as raw naphtha for the production of lower olefins. (3) Products that pass the Judgment Criterion I will be judged according to the Judgment Criterion III, and those that pass will be used as raw naphtha for the production of lower olefins.

[0039] <Raw naphtha> The naphtha used as a raw material for producing lower olefins to be inspected in the present invention may be naphtha stored in a tank (inventory naphtha), incoming naphtha transported from outside the system and mixed with the inventory naphtha, or a blended naphtha obtained by mixing inventory naphtha and incoming naphtha in a tank. The present invention is particularly suitable for inspecting a blended naphtha after incoming naphtha is received into a tank containing inventory naphtha and mixed therewith.

[0040] Naphtha that has been determined to pass the naphtha inspection method of the present invention is fed to the process for producing lower olefins as a raw naphtha for producing lower olefins. On the other hand, naphtha determined to be unacceptable (i.e., not satisfying the above-mentioned criteria) by the naphtha inspection method of the present invention can be adjusted to satisfy the criteria by, for example, mixing with another naphtha, and then fed to a lower olefin production process as a raw naphtha for the production of lower olefins. That is, for example, if naphtha is determined to be unacceptable because it does not satisfy the judgment criterion I, it can be mixed with naphtha having a low asymmetric ether oxygen atom content as measured by gas chromatography so as to satisfy the judgment criterion I, and then the resulting mixture can be fed to a production process of lower olefins as a raw material naphtha for the production of lower olefins.

[0041] <Naphtha cracking> Naphtha that has been determined to pass the naphtha inspection method of the present invention can be used to produce lower olefins by a tubular heating method or a steam cracking method.

[0042] For example, naphtha that has been judged to be acceptable is thermally cracked (steam cracked) in the presence of steam at temperatures of 700 to 1000°C to obtain lower olefins.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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).

[0047] 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.

[0048] 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.

[0049] By using naphtha that has been determined to pass the naphtha inspection method of the present invention, it is possible to suppress the production of methanol during the production of lower olefins, and to produce lower olefins with a low methanol content, particularly propylene with a low methanol content.

[0050] As described above, methanol adversely affects a polymerization catalyst when polymerizing lower olefins such as propylene. Therefore, determining a feedstock naphtha that produces a small amount of methanol according to the present invention is effective when producing lower olefins such as propylene.

[0051] The content of methanol in lower olefins produced using a feed naphtha judged to be acceptable according to 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, still 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 olefins. Here, the content of methanol in the lower olefins can be measured by gas chromatography. [Example]

[0052] 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.

[0053] 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.)

[0054] <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. Note that "e" represents the elementary electron quantity, e = 1.602176634 × 10 -19 [Unit: C]. For example, if ΔE is 0.05 [unit: e], this can be expressed in SI units as ΔE = 0.05 × 1.602176634 × 10 -19 [Unit: C] The ΔE was calculated using quantum chemistry calculation software "TURBOMOLE ver. 7.2" (manufactured by TURBOMOLE) and a graphical user interface for TURBOMOLE "TmoleX ver. 4.4.1" (manufactured by TURBOMOLE).

[0055] (2) Calculation of methanol production ratio B Methanol produced by the thermal decomposition of naphtha is substantially contained in the condensed water obtained in the Experimental Examples and Comparative Experimental Examples, but 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 measuring device (GC / MS device) (device name: GCMS-QP2010Ultra, manufactured by Shimadzu Corporation). It was previously confirmed that methanol is not 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) 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)

[0056] The amount of methanol, which is a thermal decomposition product, generated from the condensed water obtained in the experimental examples and comparative experimental examples was quantified, and based on the calibration curve prepared in advance using a standard solution of methanol with a known concentration, the methanol production ratio B with respect to the added ether was determined from the following formula.

[0057] [Methanol production ratio B] = [Number of oxygen atoms in methanol in condensed water] ÷ [Number of oxygen atoms in ether added to blank naphtha]

[0058] That is, when the methanol production ratio B is 1.00, it means that all of the added ether was quantified as methanol. Here, the number of oxygen atoms contained in the added ether is one oxygen atom per molecule of ether compound.

[0059] [Experimental Example 1] 2-Methoxybutane was added to blank naphtha (specific gravity 0.66 g / ml, linear paraffin content P1: 45% by mass, branched paraffin content P2: 40% by mass, P1 / P2 ratio 1.1) used as the raw material so that the content of ether-derived oxygen atoms was 50 ppm by mass. The mixture was then thermally decomposed in the presence of steam using a thermal cracking furnace under the following thermal decomposition conditions. The resulting pyrolysis 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 obtain oil and condensed water.

[0060] <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)

[0061] 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.

[0062] [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.

[0063] [Table 1]

[0064] 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.

[0065] 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.

[0066] Therefore, naphtha having a content concentration of ethers having an asymmetric structure with respect to the ether oxygen atom of not more than a predetermined value is judged to be acceptable as a raw material naphtha for producing light olefins, and it is found that by using such naphtha for producing light olefins, it is possible to suppress the concentration of methanol produced and produce light olefins with high commercial value.

Claims

1. A naphtha inspection method for determining whether or not a naphtha containing ether is acceptable as a raw material naphtha to be used in the production of lower olefins by cracking the naphtha using a tubular heating method or a steam cracking method, comprising: the ether is a monoether having an asymmetric structure, 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, The naphtha inspection method includes determining that naphtha having an ether content of 20,000 mass ppm or less, calculated as a content of oxygen atoms derived from the ether, as measured by gas chromatography, is acceptable as a raw material naphtha to be used in the production of lower olefins.

2. The naphtha inspection method according to claim 1, wherein naphtha having a content of oxygen atoms derived from the ether of 0.1 mass ppm or more is qualified as a raw material naphtha to be used in the production of lower olefins.

3. A naphtha inspection method according to claim 1 or 2, wherein naphtha having a content of oxygen atoms derived from the ether of 100 mass ppm or less is qualified as a raw material naphtha to be used in the production of lower olefins.

4. The naphtha inspection method according to any one of claims 1 to 3, wherein the ether has an absolute value ΔE (ΔE = |E1 - E2|) of a difference between an electric charge E1 of one carbon atom and an electric charge E2 of the other carbon atom, which is determined by a density functional theory method, of 0.05 [unit: e] or more. Here, e means the elementary electron quantity, and e = 1.602176634 × 10 －１９ [Unit: C].

5. The naphtha inspection method according to claim 1, wherein the ether is 2-methoxybutane, methoxycyclopentane, or 1-methoxypropane.

6. The naphtha inspection method according to any one of claims 1 to 5, further comprising: determining that naphtha having a specific gravity of 0.60 g / ml or more and 0.80 g / ml or less is acceptable as a raw material naphtha to be used in the production of lower olefins.

7. The naphtha inspection method according to any one of claims 1 to 6, further comprising: determining that naphtha having a linear paraffin content P1 of 20% by mass or more and 70% by mass or less and a branched paraffin content P2 of 20% by mass or more and 70% by mass or less is acceptable as a raw material naphtha to be used in the production of lower olefins.

8. The naphtha inspection method according to claim 7, further comprising the step of: determining that naphtha having a ratio of P1 to P2 (P1 / P2) of 0.3 to 3.5 is acceptable as a raw material naphtha to be used in the production of lower olefins.

9. The naphtha inspection method according to any one of claims 1 to 8, wherein the naphtha is a mixed naphtha obtained by receiving incoming naphtha into a tank containing inventory naphtha and mixing the incoming naphtha.

10. The naphtha inspection method according to any one of claims 1 to 9, which is a naphtha inspection method for determining whether or not a naphtha is acceptable as a raw material naphtha for producing lower olefins, the naphtha having a content of the ether-derived alcohol measured by gas chromatography being 10,000 ppm by mass or less.

11. The naphtha inspection method according to claim 10, wherein the alcohol is methanol.

12. The naphtha inspection method according to any one of claims 1 to 11, wherein the lower olefin is propylene.

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