TW201906992A - Method for producing aromatic hydrocarbon - Google Patents

Abstract

Provided are: a method for producing a purified aromatic hydrocarbon, the method being capable of stably producing the purified aromatic hydrocarbon having a low sulfur content; and a purified aromatic hydrocarbon or the like having a low sulfur content. The method for producing a purified aromatic hydrocarbon is characterized by comprising at least: a hydrogenating step for hydrogenating an aromatic hydrocarbon raw material; and a heat-exchanging step for providing, to a heat-exchanger, the purified aromatic hydrocarbon which has been subjected to the hydrogenating step, and cooling the purified aromatic hydrocarbon, wherein the heat-exchanging step performs heat-exchange on said purified aromatic hydrocarbon under the condition that cyclohexanethiol (CHT) is not produced as a byproduct.

Description

   Method for producing aromatic hydrocarbon   

The present invention relates to a method for producing a petrochemical raw material using crude oil as a raw material, and more specifically to a method for producing an aromatic hydrocarbon with a low sulfur content.

In recent years, it is expected to reduce the sulfur concentration in petrochemicals. For example, when a sulfur-containing petrochemical is used as a fuel, there is a problem that sulfur oxides are easily released in the air and the exhaust treatment catalyst is polluted. To solve these problems, the aromatic hydrocarbons, which are often used as raw materials for petrochemicals, are hydrogenated when crude oil is refined. At this time, most of the sulfur in the crude oil will become hydrogen sulfide, which can then be separated through steps such as a distillation column and then subjected to adsorption treatment to reduce the sulfur concentration in the obtained petrochemicals.

    [Prior technical literature]         [Patent Literature]    

[Patent Document 1] International Publication No. 2004/009735

However, it was unexpectedly found that the final product also contained more sulfur. On the other hand, customer requirements for reducing residual sulfur are becoming more stringent.

In this case, for example, as described in Patent Document 1, desulfurization is performed by using a method such as nickel or a nickel-copper metal-based desulfurizer. However, although hydrorefining treatment has been performed, desulfurization treatment still needs to be performed by using a reforming catalyst, causing double troubles. In addition, although the sulfur content can usually be sufficiently reduced by hydrorefining treatment, the sulfur content is unexpectedly increased. Therefore, the modification catalyst is often used for the treatment, which is not good from the viewpoint of productivity or economy.

From the above, even if hydrorefining is performed to reduce the sulfur concentration in the petrochemical raw materials, the cause of the fluctuation in the sulfur concentration in the obtained petrochemical raw materials must be confirmed, and this situation should be prevented.

The present invention has been made in view of the above problems. That is, an object of the present invention is to provide a method for producing an aromatic hydrocarbon that can stably produce an aromatic hydrocarbon having a low sulfur content. Another object of the present invention is to provide an aromatic hydrocarbon having a low sulfur content.

The present inventors have conducted intensive studies in order to solve the above-mentioned problems, and as a result, found that the unexpected change in the sulfur content is generated after the hydrorefining treatment (hydrogenation step) and then the cooling by a heat exchanger (heat exchange step). More specifically, the sulfur content is cyclohexanethiol (hereinafter also referred to as "CHT"), and the cyclohexanethiol is based on metal sulfides, especially iron sulfides, which are present in the heat exchanger, as catalysts. It is generated in a specific temperature range, and the above-mentioned problem can be solved by suppressing the chemical reaction.

That is, the present invention provides various specific aspects shown below.

[1] A method for producing refined aromatic hydrocarbons, comprising at least: a hydrogenation step of hydrogenating an aromatic hydrocarbon raw material; and a heat exchange for supplying the refined aromatic hydrocarbons obtained by the above hydrogenation step to a heat exchanger for cooling Step; wherein, the above-mentioned heat exchange step is performed under the condition that cyclohexanethiol (CHT) is not by-produced, and the refined aromatic hydrocarbon is heat-exchanged.

[2] A method for producing refined aromatic hydrocarbons, comprising at least: a hydrogenation step of hydrogenating an aromatic hydrocarbon raw material; and heat exchange for supplying the refined aromatic hydrocarbons obtained by the above hydrogenation step to a heat exchanger for cooling Step; wherein, the above-mentioned heat exchange step is performed under the following conditions (1) and (2): (1) at least a part of the material of the refined aromatic hydrocarbon contacted in the heat exchange step is composed of Chromium and / or molybdenum iron alloys, and / or metal materials or alloys having a passive film formed on the surface; (2) The above heat exchanger is a shell and tube type heat exchanger, and The purified aromatic hydrocarbon flows through the tube side of the heat exchanger.

[3] The method for producing a purified aromatic hydrocarbon according to claim 2, wherein the heat exchange step is performed by exchanging the purified aromatic hydrocarbons without producing by-produced cyclohexanethiol (CHT).

[4] The method for producing a refined aromatic hydrocarbon according to any one of [1] to [3], wherein the sulfur concentration contained in the aromatic hydrocarbon raw material is 10 to 1,000 ppm by weight.

[5] The method for producing a refined aromatic hydrocarbon according to [2] or [3], wherein at least a part of the tube is made of an iron alloy containing chromium and / or molybdenum and / or a passive film is formed on the surface Valve metal or its alloy.

[6] The method for producing a refined aromatic hydrocarbon according to any one of [1] to [5], wherein the heat exchanger is a shell-and-tube U-tube heat exchanger, and the hydrogenation step is performed according to the above. The obtained refined aromatic hydrocarbons circulate in the tubes of the U-tube heat exchanger.

[7] The method for producing a purified aromatic hydrocarbon according to any one of [1] to [6], wherein the purified aromatic hydrocarbon system contains a hydrocarbon having 5 to 10 carbon atoms.

[8] The method for producing a purified aromatic hydrocarbon according to any one of [1] to [7], wherein the purified aromatic hydrocarbon-based liquid hydrocarbon has a sulfur concentration of 1.5 ppm or less.

[9] A refined aromatic hydrocarbon obtained according to the production method described in any one of [1] to [8], and having a sulfur concentration of 1.5 ppm or less.

According to the present invention, a method for producing a refined aromatic hydrocarbon that can stably produce high-purity refined aromatic hydrocarbons with low sulfur content in particular can be realized. In addition, according to the production method of the present invention, refined aromatic hydrocarbons having a low sulfur content can be stably produced, and the sulfur concentration in petrochemical products can be stably reduced.

1, 7‧‧‧ tube side nozzle

2‧‧‧ partition

3‧‧‧ tube cap

4‧‧‧shell

5‧‧‧ tube

6, 9‧‧‧ shell side nozzle

8‧‧‧ deflector

10‧‧‧shell cover

11‧‧‧Fixed tube sheet

12‧‧‧ exhaust hole

13‧‧‧drain

FIG. 1 is an explanatory diagram showing an example of the structure of a shell and tube heat exchanger.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The following embodiment is an example (representative example) for explaining the present invention, but the present invention is not limited to these. In addition, in this specification, a positional relationship such as up, down, left, right, and the like is assumed to be based on a positional relationship shown in a drawing unless otherwise specified. The dimensional ratios in the drawings are not limited to the illustrated ratios. For example, the numerical range expression of "1 to 100" includes both the lower limit value "1" and the upper limit value "100". The same applies to other numerical ranges.

As described above, the present invention is based on the method for producing a refined aromatic hydrocarbon, and it was found that the CHT is generated after the hydrorefining treatment (hydrogenation step), and is then cooled by a heat exchanger (heat exchange step). It was found that the CHT is generated in a specific temperature range by using a metal sulfide, particularly iron sulfide present in a heat exchanger as a catalyst, and the present invention was completed by suppressing the chemical reaction.

That is, the method for producing a refined aromatic hydrocarbon of the present invention includes at least: a hydrogenation step of hydrogenating an aromatic hydrocarbon raw material; and a refined aromatic hydrocarbon obtained after the hydrogenation step, that is, obtained by the hydrogenation step. Aromatic hydrocarbons are provided to a heat exchanger for cooling and heat exchange steps; the above heat exchange step is to heat exchange the refined aromatic hydrocarbons without producing CHT as a by-product.

The "non-by-product" as used herein refers to the concentration of CHT contained in the refined aromatic hydrocarbons after the heat exchange step, and is substantially 1.5 ppm by weight or less. At this time, the concentration of CHT is the sulfur detected by (quantitative analysis of sulfur content) described in the examples, and is calculated based on all forms derived from CHT. Hereinafter, aspects of this embodiment will be described. The method for producing a refined aromatic hydrocarbon according to this embodiment includes at least: a step of hydrogenating an aromatic hydrocarbon raw material (hydrogenation step); and supplying the purified aromatic hydrocarbon obtained by the hydrogenation step to heat exchange. Cooling step (heat exchange step); and the above heat exchange step is performed under the following conditions (1) and (2): (1) the refined aromatic hydrocarbons contacted in the heat exchange step At least a part of the material is composed of an iron alloy containing chromium and / or molybdenum, and / or a metal material or an alloy with a passive film formed on the surface; (2) The heat exchanger is a shell and tube heat exchanger, and uses The purified aromatic hydrocarbon obtained in the hydrogenation step flows through the tube side of the heat exchanger.

    <Aromatic hydrocarbon feedstock>    

In this embodiment, the aromatic hydrocarbon raw material (also referred to as "hydrocarbon (raw material)" or "raw material" in the present specification) that is subject to purification by hydrogenation is a liquid material containing aromatic hydrocarbons, and a representative example is crude oil. Crude oil generally varies in appearance depending on the region where it is produced, and in composition or nature. The classification system includes, for example, classification using physical properties and classification using chemical properties. This embodiment can be used regardless of whether it belongs to any classification. Crude oil can be separated into LP gas, naphtha, kerosene, light oil and other fractions before use. In this case, the aromatic hydrocarbon raw material suitable for use in this embodiment is a heavy hydrocarbon containing 5 or more carbon atoms. For example, naphtha, decomposed petroleum, etc. belong to this category. More preferably, they are heavy hydrocarbons containing aromatic hydrocarbons having 5 or more and 10 carbon atoms, and particularly preferred are hydrocarbons containing aromatic hydrocarbons having 6 or more and 8 carbon atoms. In addition, hydrocarbons containing 5 or more and 10 or less aromatic hydrocarbons are generally obtained in the form of C5 to C10 fractions refined from petroleum. In addition, hydrocarbons containing aromatic hydrocarbons having a carbon number of 6 or more and 8 or less are generally obtained as petroleum refined C6 to C8 fractions (benzene, toluene, xylene fractions). In this specification, the aromatic hydrocarbons having 5 to 10 carbon atoms refer to hydrocarbons having 5 carbon atoms and aromatic hydrocarbons having 6 to 10 carbon atoms.

The concentration of sulfur contained in the aromatic hydrocarbon raw material supplied to the hydrogenation step is not particularly limited, but it is preferably 10 ppm by weight to 1,000 ppm by weight. In order to prevent the reaction tube from being easily blocked by coke, etc., from the viewpoint of forming a protective film on the surface of the reaction tube required during the operation of the decomposition furnace, it is preferably 10 ppm by weight or more, and to suppress corrosion in the purification step after decomposition. From a viewpoint, it is preferably 1,000 ppm by weight or less. The sulfur concentration in the aromatic hydrocarbon raw material is more preferably 50 ppm by weight or more, 70 ppm by weight or more, 900 ppm by weight or less, and 850 ppm by weight or less. The sulfur concentration in the aromatic hydrocarbon feedstock is implemented in accordance with JIS K2541-6 "Crude oil and petroleum products-Test method for sulfur content-Part 6: Ultraviolet fluorescence method".

    <Hydrogenation step>    

The above-mentioned aromatic hydrocarbon raw material is first supplied to a hydrogenation step (hereinafter also referred to as "hydrogenation step"). This hydrogenation step is carried out for various purposes such as desulfurization, denitrification, deoxygenation, dehalogenation, olefin saturation, generation of naphthenes from aromatics, removal of metal compounds, and decomposition of hydrocarbons. The reaction conditions are not particularly limited depending on the composition or properties of the hydrocarbon (raw material) to be supplied to the hydrogenation step, and they can be appropriately selected from known conditions. Generally, the higher the boiling point and the larger the molecular weight of the raw materials, the higher the temperature, the higher the pressure, the larger the hydrogen circulation, the liquid space velocity (the feed rate of the raw material liquid (the liquid volume flow rate at 20 ° C)), or the The ratio of catalyst filling volume. It is expressed in terms of the supply rate of raw material liquid per hour, and the unit is h ^-1 . Use as the index of the degree of contact between the raw material and the catalyst.

The generally adopted conditions are a reaction temperature of 290 ° C to 420 ° C, a pressure of 1 MPa to 8 MPa, and a hydrogen cycle volume of 35 to 350 m ³ / KL. The catalyst used in the hydrogenation step may be, for example, various known catalysts, and is not particularly limited. Generally, a cobalt · molybdenum-based or nickel-molybdenum-based catalyst is preferably used.

    <Heat Exchange Procedure>    

Hydrocarbons subjected to hydrogenation by the above steps are then supplied to a heat exchange step. This step is carried out in order to reduce the temperature of the hydrocarbons that have been heated during the hydrogenation step. This heat exchange step takes into consideration energy saving or heat recovery, and most of them implement a heat energy recovery step to recover heat energy. In this specification, hydrocarbons that are hydrogenated by the hydrogenation step are also expressed as "refined aromatic hydrocarbons obtained by the hydrogenation step" or "refined aromatic hydrocarbons after the hydrogenation step".

A known heat exchanger can be used as a machine for heat exchange. Known heat exchangers are, for example, plate heat exchangers, or tube heat exchangers such as double-tube type, spiral type, and shell and tube type. Any of the heat exchanger systems used here can be used, but it is more difficult to stay inside because of its excellent heat exchange performance, less susceptibility to fluid retention, and iron-based sulfides that can act as catalysts for CHT formation. Jia series shell and tube heat exchanger.

The so-called "shell-and-tube heat exchanger" is a heat exchanger in which a plurality of tubes (heat transfer tubes) are housed in a shell (body portion), and a large heat transfer area can be obtained in a small space. Specifically, the heat transfer tube is composed of a plurality of heat transfer tubes and a tube body portion including the heat transfer tube. The heat transfer tubes are a first fluid flowing through the heat transfer tube and a heat transfer tube inside the tube body portion. The second fluid flowing outside performs heat exchange. There may be a plurality of barrier plates inside the tube body. In most cases, the baffle plate is configured to block a vertical cross-section or a nearly horizontal semi-circular portion relative to the longitudinal direction of the tube body. The plurality of baffle plates are spaced apart in the long-side direction of the tube body by blocking the semi-circular portion interactively. Appropriately spaced and fixed.

In addition, one type of heat exchanger used in the heat exchange step may be used alone, or one or more types may be used in any combination and connection method. For example, one type of heat exchanger may be connected in series and / or in parallel, or two or more types of heat exchanger may be connected in series and / or in parallel. Here, when a heat exchanger of a tubular heat exchanger is used, it is preferable that the hydrocarbons subjected to hydrogenation through the above-mentioned steps circulate on the tube side (inside the tube) of the tubular heat exchanger. The better reason will be described later.

The heating medium used in general heat exchangers uses water, but seawater or groundwater can also be used. However, in the event of damage to the heat exchanger, it is preferable to use a reclaimed water or the like in a factory to form a structure in which water used as a heating medium does not directly flow to the outside.

The present inventors have discovered that the hydrogen sulfide contained in the refined aromatic hydrocarbons provided to the heat exchange step uses iron-based sulfides as catalysts, and in the high temperature region, specifically in the temperature range of about 130 ° C to about 205 ° C Reacts with hydrocarbons and produces CHT as a by-product.

CHT has a boiling point of 158 ° C and will not be discharged outside the system at normal temperature. Therefore, CHT remains in the refined aromatic hydrocarbon, and as a result, the residual sulfur concentration increases. Therefore, in the present embodiment, two solutions (the first and second solutions) described in detail below are used to suppress the generation of CHT, and as a result, the sulfur concentration in the purified aromatic hydrocarbon is reduced.

    1. The first solution    

The first solution is implemented from the viewpoint of suppressing the generation of iron-based sulfides that serve as a by-product catalyst for CHT. According to the findings of the present inventors, in the presence of hydrocarbons and hydrogen sulfide, the CHT system uses iron-based sulfide as a catalyst, and is generated excessively at 130 ° C or higher. In addition, it is known that iron, which is a constituent element of iron-based sulfides, is mixed in when carbon steel, which is a common component of heat exchangers (plates, shells, tubes, pipes, etc.), is corroded. In addition, as described above, in a certain temperature range, iron-based sulfides have a significant catalyst effect. Therefore, after the hydrogenation step, in the heat exchange step, before cooling the refined aromatic hydrocarbons to 130 ° C, at least a part of the contacted material is made of an iron alloy containing chromium and / or molybdenum (also referred to as "iron alloy") By using a metal material or an alloy of which a passive film has been formed on the surface, it is possible to suppress the formation of iron-based sulfides that serve as a by-product catalyst for CHT. As a result, the amount of CHT produced can be significantly reduced.

The ferrous alloy containing chromium and / or molybdenum may be selected after taking into consideration factors such as corrosion resistance strength or cost, and is not particularly limited. The iron alloy preferably contains 50% by weight or more of iron. Moreover, it is preferable that it contains chromium 12 weight% or more and 26 weight% or less. The content of molybdenum in the iron alloy is preferably 1% by weight or more and 4% by weight or less. This special steel (alloy steel) containing chromium or molybdenum has particularly strong corrosion resistance, which can greatly reduce the outflow of iron components caused by corrosion and the like. Specific examples of the ferroalloy include chromium steel, chromium molybdenum steel, nickel chromium steel, nickel chromium molybdenum steel, manganese chromium steel, molybdenum-containing carbon steel, and stainless steel. The iron alloy is preferably a chromium-containing iron alloy, and more preferably a stainless steel. Specifically, for example, SUS304, such as Vosstian iron-based stainless steel, SUS400-type Asada loose iron-based or fat-grained iron-based stainless steel, etc. From the viewpoint of brittleness of hydrogen sulfide, SUS400-type Asada loose iron Series or fat iron series stainless steel. This ferroalloy particularly preferably forms a passive film on the surface.

Furthermore, instead of these iron alloys, a metal material or an alloy thereof having a passive film formed on the surface may be used instead. More preferably, it is composed of a valve metal or an alloy thereof having a passive film formed on the surface. The "valve metal" used herein refers to aluminum, zirconium, titanium, chromium, zinc, tantalum, niobium, hafnium, tungsten, bismuth, antimony, etc., and forms an oxide film on the surface of the metal to resist corrosion. By using a valve metal or an alloy thereof that has formed a passive film, the outflow of iron components due to corrosion and the like can be greatly reduced. Among these, from an industrial point of view, stainless steel that has been subjected to aluminum anodizing and passivation treatment is preferred.

These materials are preferably used in a portion that is touched before the refined aromatic hydrocarbon is cooled to 130 ° C. in the heat exchange step. Specifically, as long as the various structural members that belong to the heat exchanger: plates, shells, tubes, piping, etc., are made of these materials. As described later, when a shell-and-tube heat exchanger is used to circulate the purified aromatic hydrocarbons after the hydrogenation step on the tube side, the tube system may be composed of the above-mentioned various materials.

    2. The second solution    

The second solution is implemented from the viewpoint of suppressing the accumulation of iron-based sulfides serving as a catalyst for CHT by-products in the heat exchanger. As mentioned above, CHT is produced in a heat exchanger by reacting hydrogen sulfide contained in refined aromatic hydrocarbons with iron sulfides as a catalyst and reacting with hydrocarbons. Generally, in order to improve the heat exchange efficiency, the liquid to be reduced in temperature (the refined aromatic hydrocarbons after the hydrogenation step in this embodiment) is circulated in a curved flow path, and is sufficiently exposed to the outside of the flow path system. The medium is heated at a low temperature for heat recovery. For example, if it is a shell-and-tube heat exchanger, the temperature-reduced liquid is allowed to circulate on the shell side (for example, Table 4‧13 of the Chemical Engineering Fact Sheet Revised 7th Edition P261) Fuel oil, petroleum, heavy oil).

A general cross-sectional view of a general structure of a shell-and-tube heat exchanger shown in FIG. 1. Hereinafter, the second solution will be described in more detail using FIG. 1. This second solution means that the temperature-reduced liquid (refined aromatic hydrocarbons subjected to the hydrogenation step in the present embodiment) is circulated on the pipe side as opposed to usual. That is, the refined aromatic hydrocarbons after the hydrogenation step are introduced into the heat exchanger from the tube-side nozzle 1, pass through the upper side of the cap portion 3 divided by the partition plate 2, and then flow into the U-shaped tube arranged in the shell 4. The tube 5 is then discharged out of the heat exchanger from a tube-side nozzle 7 located below the tube cap portion 3 below. At this time, the purified aromatic hydrocarbons passing through the tube 5 are cooled by moving heat to a heating medium introduced into the case 4 from the case-side nozzle 9. On the other hand, after the heat-receiving heating medium is introduced from the shell-side nozzle 9, it is snaked in the shell 4 by the baffle plate 8, is heated by contact with the tube 5, and is discharged from the shell-side nozzle 6. Outside the heat exchanger. In this way, heat energy can be recovered.

As can be seen from the figure, the shell-side heat exchanger (the space outside the tube inside the shell) of the shell-and-tube heat exchanger is prone to cause a difference in flow velocity in the shell due to the curved portion of the deflector 8, so that the flow velocity will be relatively slow. The slow region (for example, the back side portion closest to the lower partition plate) has a structure in which solid matter and the like are easily retained in the low flow velocity region. Therefore, when the purified aromatic hydrocarbons after the hydrogenation step are introduced into the shell side, if the heat exchanger is continuously used, iron-based sulfides will gradually accumulate in the same area, and as a result, it is found that there is a tendency to gradually increase CHT by-products. Therefore, when a shell-and-tube heat exchanger is used, the refined aromatic hydrocarbons after the hydrogenation step are circulated on the tube side, and a heating medium such as water is circulated on the shell side, thereby suppressing the accumulation of iron-based sulfides, which can greatly reduce The CHT by-products in the heat exchanger increase.

As described above, the use of the first and second solutions can suppress the generation of CHT, and as a result, the sulfur concentration in the refined aromatic hydrocarbon can be reduced. The following solutions can be used alone or in combination with the first and second solutions.

    3. Other solutions    

Other solutions are implemented from the viewpoint of controlling the reaction of CHT formation. As mentioned above, in the presence of hydrocarbons and hydrogen sulfide, the CHT system uses iron-based sulfide as a catalyst, and is generated excessively at 130 ° C or higher. Therefore, for example, even if iron-based sulfide is present, if the temperature in the reaction system (heat exchange step) is less than 130 ° C, the reaction rate of CHT formation is slow, so there is no need to worry too much about CHT formation. When the temperature in the reaction system exceeds 205 ° C, since CHT has an equilibrium composition with a low concentration of less than 1 ppm by weight in terms of sulfur content, there is no need to worry too much about the amount of CHT generated by this amount. From these phenomena, if the cooling of the purified aromatic hydrocarbon in the temperature range of 130 ° C. or higher and 205 ° C. or lower in the heat exchange step, problems due to CHT generation become apparent.

Therefore, if the refined aromatic hydrocarbon is cooled in a temperature range of 130 ° C. to 205 ° C., the processing time is shortened, in other words, the aromatic hydrocarbon is quenched and purified in the temperature range, which is particularly effective for suppressing the generation of CHT. .

Specifically, after the hydrogenation step, before the refined aromatic hydrocarbon is cooled from 205 ° C to 130 ° C, it is preferable to set the time of the purified aromatic hydrocarbon in the system to suppress CHT generation, for example, in 60 seconds. The following is adopted. More preferably, it is 40 seconds or less, and particularly good is 35 seconds or less. The transit time in this system can be appropriately set according to the heat exchanger used. For example, by measuring the CHT concentration on the inlet and outlet sides of the heat exchanger, the transit time in the heat exchanger can be set.

In a preferred embodiment, the temperature at which the refined aromatic hydrocarbons after the hydrogenation step circulates in the heat exchanger is 205 ° C or higher, and the temperature at which the refined aromatic hydrocarbons are discharged from at least one heat exchanger is 130 ° C or lower, The passage time from circulation to discharge is 60 seconds or less. The passage time in the system is preferably 40 seconds or less, and more preferably 35 seconds or less.

The temperature at which the refined aromatic hydrocarbons circulate through the heat exchanger is 180 ° C or higher, preferably 190 ° C or higher, more preferably 200 ° C or higher, and particularly preferably 205 ° C or higher, and the temperature when discharged from the heat exchanger. The temperature is 150 ° C or lower, preferably 145 ° C or lower, more preferably 140 ° C or lower, and particularly preferably 130 ° C or lower.

In this specification, the "intra-system transit time" refers to a value obtained by dividing the volume of the flow path of the machine including the heat exchanger by the volume flow rate per unit time.

According to the other solutions described above, by passing the temperature range in which CHT is excessively generated for a short time, the amount of CHT generation can be sufficiently reduced. In addition, for example, by using the first and second solutions in combination to suppress the accumulation of iron-based sulfides that act as catalysts, the amount of CHT production can be more reliably reduced.

    <Other steps>    

In addition, when producing a high-purity purified aromatic hydrocarbon, various known steps such as a distillation step and a washing step may be combined after the heat exchange step.

    <Refined aromatic hydrocarbons>    

The obtained refined aromatic hydrocarbon preferably contains a hydrocarbon having 5 or more and 10 carbons, and more preferably contains an aromatic hydrocarbon having 5 or more and 10 carbons. The refined aromatic hydrocarbon thus obtained preferably contains hydrocarbons having a carbon number of 5 or more as a main component, and more preferably contains hydrocarbons having a carbon number of 6 or more and 10 or less as a main component. The “main component” herein refers to a component that contains 50% by weight or more, and preferably 70% by weight or more, relative to the total amount of aromatic hydrocarbons. When producing aromatic hydrocarbons having 6 or more and 10 or less carbon atoms, since CHT is easily generated in the heat exchange step, the application value of the present embodiment is obvious. In particular, the effect of the present invention is exerted when the obtained refined aromatic hydrocarbon is a mixed fraction (benzene-toluene-xylene mixed fraction) of benzene, toluene, and xylene. The benzene-toluene-xylene mixed fraction is an aromatic hydrocarbon mixture having a benzene ring or a structure in which a methyl group as a substituent is introduced, and a cyclic olefin which is a raw material for CHT formation is easily generated in the hydrogenation step. The cyclic olefin reacts with hydrogen sulfide to generate CHT particularly easily, and thus the effect of the present invention can be particularly obviously obtained.

    <Sulfur concentration>    

The sulfur-converted weight concentration of the purified aromatic hydrocarbon thus obtained, that is, the sulfur concentration is preferably 1.5 weight ppm or less, more preferably 1.0 weight ppm or less, particularly preferably 0.8 weight ppm or less, and most preferably 0.6 weight ppm or less. The method for measuring the sulfur concentration is implemented in accordance with JIS K2541-6 "Crude oil and petroleum products-Test method for sulfur content-Part 6: Ultraviolet fluorescence method". The concentration of CHT can be obtained from the sulfur concentration in the aromatic hydrocarbon.

    <CHT concentration>    

The CHT concentration of the purified aromatic hydrocarbon thus obtained was substantially 1.5 ppm by weight or less. The concentration of CHT is calculated by considering all sulfur detected by quantitative analysis of sulfur content in aromatic hydrocarbons as derived from CHT. In addition, as described in the examples, the gas chromatography can also be implemented.

    [Example]    

Hereinafter, the present invention will be described in more detail by using examples. However, the present invention is not limited to the following examples unless it exceeds the gist thereof.

In Examples and Comparative Examples, the aromatic hydrocarbon feedstock was subjected to a hydrogenation step and a heat exchange step using decomposed petroleum. The quantitative analysis of sulfur and the quantitative analysis of CHT in the obtained refined aromatic hydrocarbons were carried out in accordance with the methods described below.

    (Quantitative sulfur analysis)    

Quantitative sulfur analysis is performed in accordance with JIS K2541-6 "Crude oil and petroleum products-Test method for sulfur content-Part 6: Ultraviolet fluorescence method".

The measurement device used a trace sulfur analyzer (TS-100 type) [manufactured by Mitsubishi Chemical Analytech Co., Ltd.], and an automatic sample changer for liquid (ASC-150L) [manufactured by Mitsubishi Chemical Analytech company]. As the reagent system, a dimethyl disulfide standard solution was used. The gas system required for the measurement uses a gas having an oxygen content of 99.5% or more as specified in JIS K1101 and a gas having an argon gas content of 99.99% or more as specified in JIS K1105.

The measurement method is as follows. Using argon as a carrier gas, 40 μL of the sample was poured into a reaction tube maintained at 800 to 1000 ° C. The argon flow rate at this time was 400 ml / min. The sulfur compounds in the sample were thermally decomposed and then oxidized with oxygen. The oxygen flow rate at this time is 300ml / min for both the main and the auxiliary. Then, the moisture in the sulfur dioxide gas generated by the oxidation was removed, and then ultraviolet light was measured.

Sulfur dioxide absorbs energy from ultraviolet light and converts it to sulfur dioxide in an excited state. The photoluminescence is used to detect the fluorescence emitted when the excited sulfur dioxide returns to the base state sulfur dioxide, and the sulfur amount is calculated from the fluorescence amount. At the time of measurement, a sample measurement was performed from a calibration curve prepared using a dimethyl disulfide standard solution (500 μg / ml, 5 μg / ml, 2 μg / ml).

    (CHT quantitative analysis)    

The quantitative analysis of CHT was carried out using a gas chromatography layer analyzer (apparatus: Shimadzu Corporation, model GC-2014, column DB-1), and the CHT amount was calculated using the absolute calibration line method. In this case, a flame photometric detector using an interference filter for sulfur compounds was used as a detector.

    [Examples 1 to 10]    

As shown in Table 1, the aromatic hydrocarbon feedstocks to be refined are decomposed petroleum (hydrocarbons) with sulfur content of 70.0 to 816.6 ppm by weight, and the hydrogenation reaction is performed using a hydrogenation reactor. Circulated in machines and piping made of chromium-containing stainless steel and molybdenum-containing carbon steel. It is cooled by circulating through the tube side of the shell-and-tube heat exchanger designated by TEMA (American Heat Exchanger Industry Association) It is higher than 205 ° C and lower than 130 ° C. At this time, the system transit time (residence time) in the temperature range of 205 ° C to 130 ° C is 19.0 seconds to 36.1 seconds. In addition, the sulfur content contained in the processed refined aromatic hydrocarbons (liquid hydrocarbons) was all 0.2 ppm by weight or less (see Table 1). The CHT concentration contained in the processed refined aromatic hydrocarbons is 0.5 ppm or less when converted from sulfur concentration. The processed refined aromatic hydrocarbons include benzene, toluene, xylene, and the like.

    [Comparative Examples 1 to 5]    

As shown in Table 1, the aromatic hydrocarbon feedstocks to be purified were decomposed petroleum (hydrocarbons) with sulfur content of 50.0 to 70.0 ppm by weight, and hydrogenated using a hydrogenation reactor under the same conditions as in the examples. The reactor outlet fluid circulates in the machine and piping made of carbon steel, and is circulated through the tube side of the shell-and-tube heat exchanger designated by TEMA, and is cooled to over 205 ° C and below 130 ° C, respectively. At this time, the system transit time (residence time) in the temperature range of 205 ° C to 130 ° C is 37.6 seconds to 49.2 seconds. Moreover, the CHT (converted value from sulfur concentration) contained in the processed refined aromatic hydrocarbons (liquid hydrocarbons) is 5.8 to 8.0 weight ppm, and the sulfur content is 1.6 to 2.2 weight ppm, compared with Example 1 Below ~ 6, although the decomposed petroleum with a lower sulfur concentration is used as a raw material, the sulfur concentration is still higher.

In addition, the CHT (measured value measured by a gas chromatography device) contained in the treated aromatic hydrocarbons (liquid hydrocarbons) of Comparative Examples 1 to 5 is 5.8 to 7.5 ppm by weight, and the "from sulfur concentration of CHT The "converted value" is the same as the "measured value".

The CHT concentration of the refined aromatic hydrocarbons obtained in Examples 1 to 10 is low. When used as a fuel, it is difficult to release sulfur oxides into the air, and it is not easy to cause damage to the exhaust treatment catalyst. In addition, it is not necessary to perform desulfurization treatment again after the hydrorefining treatment, and it is preferable from the viewpoint of productivity or economy.

Claims (9)

    A method for producing a refined aromatic hydrocarbon, at least comprising: a hydrogenation step of hydrogenating an aromatic hydrocarbon raw material; and a heat exchange step of supplying the refined aromatic hydrocarbon obtained by the hydrogenation step to a heat exchanger for cooling; The heat exchange step is performed under the condition that cyclohexanethiol (CHT) is not by-produced, and the refined aromatic hydrocarbon is heat exchanged.         A method for producing a refined aromatic hydrocarbon, at least comprising: a hydrogenation step of hydrogenating an aromatic hydrocarbon raw material; and a heat exchange step of supplying the refined aromatic hydrocarbon obtained by the hydrogenation step to a heat exchanger for cooling; , The above heat exchange step is performed under the following conditions (1) and (2): (1) at least a part of the material contacted by the refined aromatic hydrocarbon in the heat exchange step is composed of chromium and / Or an iron alloy of molybdenum, and / or a metal material or an alloy thereof having a passive film formed on the surface; (2) the heat exchanger is a shell and tube heat exchanger, and the refined aromatic hydrocarbon is based on Tube side circulation.         According to the method for producing a refined aromatic hydrocarbon according to claim 2, wherein the heat exchange step is performed under the condition that cyclohexanethiol (CHT) is not by-produced, the refined aromatic hydrocarbon is subjected to heat exchange.         The method for producing a purified aromatic hydrocarbon according to any one of claims 1 to 3, wherein the sulfur concentration contained in the aromatic hydrocarbon raw material is 10 to 1,000 ppm by weight.         The method for producing a refined aromatic hydrocarbon according to claim 2 or 3, wherein at least a part of the tube is composed of an iron alloy containing chromium and / or molybdenum, and / or a valve metal or an alloy thereof having a passive film formed on the surface.         The method for producing a refined aromatic hydrocarbon according to any one of claims 1 to 3, wherein the heat exchanger is a shell-and-tube U-tube heat exchanger, and the refined aromatic hydrocarbon obtained according to the hydrogenation step. It circulates in the tubes of the U-tube heat exchanger.         The method for producing a purified aromatic hydrocarbon according to any one of claims 1 to 3, wherein the purified aromatic hydrocarbon system contains a hydrocarbon having 5 or more and 10 or less carbon atoms.         The method for producing a purified aromatic hydrocarbon according to any one of claims 1 to 3, wherein the purified aromatic hydrocarbon-based liquid hydrocarbon has a sulfur concentration of 1.5 ppm or less.         A refined aromatic hydrocarbon obtained by the production method according to any one of claims 1 to 8 and having a sulfur concentration of 1.5 ppm or less.