JP7806453B2 - Naphtha inspection method - Google Patents

Description

The present invention relates to a naphtha inspection method for determining whether naphtha is suitable as a raw material for use in producing lower olefins by cracking naphtha using a tubular heating method or a steam cracking method.

Naphtha transported in Very Large Crude (Oil) Carriers (hereinafter referred to as "VLCCs") is first pumped into naphtha tanks before being sent to ethylene plants where petrochemical products such as ethylene and propylene are produced. Because the components and properties of raw naphtha vary depending on its place of origin, in the above-mentioned petrochemical production process, the transported naphtha is sometimes supplied to the ethylene plant as is, or it 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.

A typical method for producing lower olefins such as ethylene and propylene involves 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.

For this reason, the concentration of oxygen-containing compounds in naphtha is used as a criterion for judging the quality of naphtha. Naphtha purchasers typically inspect the oxygen-containing compound content of the naphtha they purchase, and use naphtha with an oxygen-containing compound content below a specified value for the production of light olefins without blending it with other naphthas. Conversely, naphtha with a high oxygen-containing compound content is blended with naphtha with 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.

JP 2009-40913 A

As mentioned above, the relationship between the types of oxygen-containing compounds contained in naphtha and the amount of methanol produced from the thermal decomposition of those oxygen-containing compounds had not previously been clarified. Therefore, even if the quality of naphtha was determined based on the concentration of oxygen-containing compounds contained in the naphtha, the concentration of methanol produced when lower olefins were actually produced by thermal decomposition was not necessarily proportional to that concentration. In other words, no method had been known to accurately determine high-quality naphtha with a low concentration of methanol produced.

The objective of the present invention is to solve these problems. Specifically, the objective of the present invention is to provide a naphtha inspection method that accurately determines whether or not naphtha containing ethers is acceptable as a raw material for use in producing lower olefins when the naphtha is cracked using a tubular heating method or a steam cracking method to produce lower olefins.

As a result of extensive research aimed at solving the above-mentioned problems, the inventors discovered that, among oxygen-containing compounds, certain ethers that have an asymmetric structure with respect to the oxygen atom of the ether bond are prone to selective decomposition of specific bonds in the molecule during the naphtha thermal cracking process, and are particularly prone to producing methanol through decomposition. They also discovered that the quality of naphtha can be determined based on the content of oxygen atoms derived from such specific ethers with an asymmetric structure, more preferably specific ethers with an asymmetric structure, where the absolute value ΔE [unit: e] of the difference in the electric charges of the two carbon atoms bonded to the oxygen atom of the ether bond is a predetermined value or greater. Based on this discovery, the present invention was completed.

That is, the present invention provides:
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:
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.

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 identified, and such naphtha can be used to produce lower olefins with a low concentration of methanol. Specifically, when the content of oxygen atoms derived from specific ethers, specifically ethers with an asymmetric structure, in naphtha is below a predetermined value, it can be accurately identified as a high-quality raw material naphtha that produces a low concentration of methanol during the production of lower olefins.

Furthermore, according to the present invention, the suitability of naphtha as a lower olefin raw material 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 having a low content of oxygen atoms derived from ethers with 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 if naphtha has a high concentration of oxygen-containing compounds, if it has a low content of oxygen atoms derived from ethers with a ΔE of 0.05 (unit: e) or more, it can be used as the raw material naphtha as is without blending it with naphtha having a low concentration of oxygen-containing compounds.

1 is a graph showing the relationship between ΔE [unit: e] of various ethers and the methanol production ratio B.

The present invention is described in detail below, but the present invention is not limited to the following description and can be modified and implemented as desired without departing from the spirit of the present invention.

Unless otherwise specified, numerical ranges expressed using "~" in this specification mean a range that includes the numbers written before and after "~" as the lower and upper limits, and "A~B" means greater than or equal to A and less than or equal to B.

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

[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 by cracking the naphtha using a tubular heating method or a steam cracking method, 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.

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."

<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.

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 charge values of the two carbon atoms are calculated by performing density functional theory (DFT) calculations on the molecular structure of the ether. The DFT calculation conditions include using def-TZVP as the basis set, the COSMO solvation model (Conductor-like Screening Model) as the solvent effect, and Mulliken's population analysis.
The ΔE can be calculated using quantum chemistry calculation software "TURBOMOLE" (manufactured by TURBOMOLE) and a graphical user interface for TURBOMOLE, "TmoleX" (manufactured by TURBOMOLE).

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.

Furthermore, the inventors have discovered that if the naphtha contains asymmetric ethers, more preferably asymmetric ethers with a ΔE (unit: e) of 0.05 or more, and the content of oxygen atoms derived from these is 20,000 mass ppm or less, the methanol concentration in the lower olefins obtained by thermal cracking this naphtha can be more significantly reduced.

For example, asymmetric ethers having an asymmetric structure with respect to the ether oxygen atom, 2-methoxybutane ( _{CH3CH2CH ( CH3} )-O- _CH3 ), methoxycyclopentane ( _C5H9 - _O - _CH3 ), and 1-methoxypropane ( _{CH3CH2CH2 -} O- _CH3 ) have ΔE [unit: e] of 0.181, 0.151, and _0.084 , respectively. Because ΔE is large and the charge is highly biased, specific bonds in the molecule 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.

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 imbalance 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.

In the naphtha inspection method of the present invention, naphtha with an asymmetric ether oxygen atom content of 20,000 ppm by mass or less is determined to be acceptable as a naphtha feedstock for the production of light olefins. By using such naphtha as a feedstock for the production of light olefins, it is possible to reduce the amount of methanol produced and produce light olefins with high commercial value.

<Judgment Criteria I>
In Criterion I, the content of asymmetric ether in naphtha is measured by gas chromatography, and naphtha having a converted value of 20,000 mass ppm or less asymmetric ether oxygen atom content 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 passing 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.

On the other hand, there is no particular lower limit for the asymmetric ether oxygen atom content value that is evaluated as passing. It 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 0.2 ppm by mass or more is preferable, 0.5 ppm by mass or more is more preferable, 1 ppm by mass or more is even more preferable, 10 ppm by mass or more is particularly preferable, and 20 ppm by mass or more is most preferable.

In addition, in Criterion I, it is preferable that the asymmetric ether to be evaluated 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, calculated by density functional theory, for the two carbon atoms bonded to the ether oxygen atom, of 0.05 (unit: e) or more, from the perspective of more effectively reducing the methanol content in the lower olefins obtained by thermal cracking naphtha that has been determined to be acceptable according to the present invention.

Asymmetric ethers according to the present invention include, but are not limited to, 2-methoxybutane (CH ₃ CH ₂ CH(CH ₃ )—O—CH ₃ ), methoxycyclopentane (C ₅ H ₉ —O—CH ₃ ), 1-methoxypropane (CH ₃ CH ₂ CH ₂ —O—CH ₃ ), and the like.

The asymmetric ether is preferably a monoether having only one ether oxygen atom in the molecule, since this can effectively reduce the content of methanol produced in the lower olefins obtained by thermal cracking naphtha that has been determined to be acceptable according to the present invention.

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

Furthermore, the asymmetric ether, preferably an asymmetric ether with a ΔE of 0.05 or greater, is preferably one in which one of the two carbon atoms bonded to the ether oxygen atom is a carbon atom of a methyl group, such as in 2-methoxybutane, methoxycyclopentane, and 1-methoxypropane, since this more effectively reduces the content of produced methanol in the resulting lower olefin.

When an ether has two or more ether bonds in one molecule, the ΔE of each ether bond is calculated as the absolute value of the difference in charge between the two carbon atoms bonded to each ether oxygen atom, and the ΔE of the ether is the largest value among the two or more ΔEs.

<Judgment 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 a raw material naphtha used 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.

<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 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 deemed acceptable as a raw naphtha for use in the production of lower olefins. If the linear paraffin and branched paraffin contents are each 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 production of by-products. The linear paraffin and branched paraffin contents are more preferably 25% by mass or more and 65% by mass or less, respectively.

In addition, Criterion III may also be performed in combination with the determination of the ratio (P1/P2) of the linear paraffin content P1 to the branched paraffin content P2, and determining that naphtha with a P1/P2 ratio of 0.3 to 3.5 is acceptable as a feedstock naphtha for use in lower olefin production. If P1/P2 is within the above range, the lower olefins of the present invention, i.e., unsaturated hydrocarbons with 2 to 4 carbon atoms containing one or two unsaturated bonds per molecule, can be produced in high yield while suppressing the generation of by-products. P1/P2 is more preferably 0.5 to 2.5.

The content of linear paraffins and branched paraffins in naphtha can be measured by gas chromatography.

<Determination procedure>
When the above-mentioned Criterion I and Criterion II and/or Criterion III are adopted, these judgments may be made in any order, but it is preferable to perform them in the following procedures (1) to (3).
(1) Those that pass the Judgment Criterion I are judged according to the Judgment Criterion II, and those that pass are 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) Those that pass the Judgment Criterion I are judged according to the Judgment Criterion III, and those that pass are used as raw naphtha for the production of lower olefins.

<Raw material naphtha>
The naphtha raw material for producing lower olefins that is the subject of inspection in the present invention may be naphtha stored in a tank (inventory naphtha), may be incoming naphtha that is transported from outside the system and mixed with this inventory naphtha, or may be a blended naphtha in which inventory naphtha and incoming naphtha are mixed 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.

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.

<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 tube heating method or a steam cracking method.

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

Among the conditions for thermal cracking, the ratio of naphtha to steam is preferably 20 to 100 parts by mass of steam per 100 parts by mass of naphtha, more preferably 30 to 70 parts by mass, and particularly preferably 35 to 60 parts by mass. If the amount of steam is less than 20 parts by mass, there is a tendency for carbonaceous material to deposit in large amounts on the piping used for 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 equipment.

The reaction temperature for thermal cracking is typically 700 to 1000°C, preferably 750 to 950°C. If the reaction temperature is below 700°C, the thermal cracking of naphtha will not proceed sufficiently, resulting in a lower yield of the desired lower olefins. On the other hand, if the reaction temperature exceeds 1000°C, the thermal cracking of naphtha will be excessive, resulting in increased production of undesirable by-products such as methane, and a lower yield of the desired lower olefins.

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 will not proceed sufficiently, and the yield of the desired lower olefins will tend to decrease. On the other hand, if the reaction time exceeds 1 second, the thermal cracking of naphtha will be excessive, increasing the generation of undesirable by-products such as methane, and the yield of the desired lower olefins will tend to decrease.

The reaction pressure for pyrolysis 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).

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 is preferably 200 to 700°C, more preferably 250 to 650°C. When carried out on a small scale, such as in a pilot or laboratory, it is preferably 0 to 100°C, more preferably 3 to 40°C.

The reaction products containing lower olefins obtained in this manner can be purified, fractionated, and so on, according to conventional methods. This yields lower olefins such as ethylene, propylene, butene, and butadiene, aromatic hydrocarbons, and other hydrocarbons. 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 then utilize or fractionate the remaining butene and butane mixture in a separate process, such as polymerization or rectification.

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

As mentioned above, methanol has a detrimental effect on the polymerization catalyst used to polymerize lower olefins such as propylene. Therefore, determining which naphtha feedstocks produce less methanol according to the present invention is effective when producing lower olefins such as propylene.

The methanol content in lower olefins produced using 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, 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. Here, the methanol content in the lower olefins can be measured by gas chromatography.

The present invention will be explained in more detail below using experimental examples and comparative experimental examples that serve as alternatives to the working examples.

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.)

<Evaluation method>
(1) Method for Calculating 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.
Density functional theory (DFT) calculations were performed on the molecular structure of the ether to calculate the charge values of the two carbon atoms. The DFT calculation conditions used def-TZVP as the basis set, the COSMO solvation model (Conductor-like Screening Model) as 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" means the elementary electron quantity, and e = 1.602176634 × 10 ^-19 [unit: C]. For example, when ΔE is 0.05 [unit: e], this can be expressed in SI units as ΔE = 0.05 × 1.602176634 × 10 ^-19 [unit: C].
The calculation of ΔE was carried out 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).

(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 content. 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 confirmed in advance that no methanol was produced 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: SUPELCO WAX-10 (Supelco, inner diameter 0.32 mm)
Length 60m x film thickness 0.25μm)
Temperature (heating conditions): 50°C (holding time 5 minutes) → Heating at 20°C/minute → 200°C (holding time 2.5 minutes)
Inlet temperature: 200℃
MS interface temperature: 200°C
Ion source temperature: 200°C
Sample volume: 0.5 μL
Split ratio: 1:5
Measurement mode: SIM (m / z = 31)

The amount of methanol produced as a thermal decomposition product from the condensed water obtained in the experimental and comparative experimental examples was quantified, and the methanol production ratio B relative to the added ether was calculated using the following formula based on a calibration curve previously prepared using a standard solution of methanol of known concentration.

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

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 ether compound.

[Experimental Example 1]
2-Methoxybutane was added to blank naphtha (specific gravity 0.66 g/ml, linear paraffin content P1: 45 mass%, branched paraffin content P2: 40 mass%, P1/P2: 1.1) 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 water vapor using a thermal cracking 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 under conditions of 0.1 MPa (gauge pressure) and 5°C to obtain gas components and separated liquid. The separated liquid was then subjected to oil-water separation into oil and condensed water using a separatory funnel under atmospheric pressure and room temperature.

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

The methanol production ratio B of the condensed water was measured using the method described above, and is shown in Table 1 along with the ΔE value. The relationship between ΔE and the methanol production ratio B is also shown in Figure 1.

[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.

A comparison of Experimental Examples 1-3 and Comparative Experimental Examples 4-7 reveals that there is a correlation between the ether's ΔE value and the methanol production ratio B, and that ethers with an asymmetric structure relative 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 greater tend to produce more methanol as the ΔE value increases.

Furthermore, Experimental Examples 1 to 3 in Table 1 show that ethers having an asymmetric structure with respect to the oxygen atoms constituting the ether bond had approximately the same methanol production ratio when the ether oxygen atom concentration was 50 ppm by mass, 500 ppm by mass, and 5,000 ppm by mass, under conditions where the ether oxygen atom concentration was 20,000 ppm by mass or less. This is presumably because ethers having an asymmetric structure have a large ΔE, resulting 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 thermal decomposition conditions to produce methanol.

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 (12)

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. 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. The 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 deemed to be acceptable as a raw material naphtha used in the production of lower olefins. 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 represents the elementary electron quantity, and e=1.602176634×10 ⁻¹⁹ [unit: C]. The naphtha inspection method according to any one of claims 1 to 4, wherein the ether is any one of 2-methoxybutane, methoxycyclopentane, and 1-methoxypropane. 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. 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 naphtha to be used in the production of lower olefins. 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. 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 stock naphtha and mixing the incoming naphtha. The naphtha inspection method according to any one of claims 1 to 9 , which is a method for inspecting naphtha to determine whether the naphtha is acceptable as a raw material naphtha for producing lower olefins, the naphtha having a content of the ether-derived alcohol of 10,000 mass ppm or less as measured by gas chromatography. The naphtha inspection method according to claim 10 , wherein the alcohol is methanol. The naphtha inspection method according to any one of claims 1 to 11, wherein the lower olefin is propylene.