JPH03437B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to the hydrotreatment of cracked gasoline, and more particularly, to a method for hydrotreating a fraction having a boiling point range of a gasoline fraction among by-product oils produced by thermal decomposition of hydrocarbons, etc. be. Cracking gasoline, especially pyrolysis gasoline that is produced as a by-product when producing olefins by steam cracking of hydrocarbons, contains pentene, hexene,
Contains large amounts of olefins such as heptene and styrene, and conjugated diolefins such as butadiene, isoprene, piperylene, and cyclopentadiene. It also often contains sulfur-containing compounds such as thiophene and methylthiophene, nitrogen-containing compounds such as pyridine and lutidine, and various oxygen-containing compounds. On the other hand, these pyrolysis gasoline fractions contain large amounts of valuable aromatic compounds such as benzene, toluene, and xylenes, and these aromatic compounds are being recovered from pyrolysis gasoline.
However, in order to recover these aromatic compounds with high purity, it is first necessary to hydrogenate cracked gasoline. Various processes have been proposed for hydrotreating methods, but their objectives are to convert diolefins contained in cracked gasoline as raw materials into monoolefins by hydrogenation, and to convert monoolefins into paraffins. These include hydrogenation, partial hydrogenation of polyaromatic to monoaromatic, and desulfurization, denitrification, and deoxygenation by hydrogenation treatment of sulfur-containing compounds, nitrogen-containing compounds, oxygen-containing compounds, etc. To achieve these objectives, hydroprocessing currently uses two reactors and achieves each objective through two-stage hydrogenation. That is, hydrogenation of diolefin is carried out in the first stage reactor, and hydrogenation of monoolefin and reactions of desulfurization, denitrification and deoxygenation are carried out in the second stage reactor. This two-stage hydrogenation has the advantage of being able to use an effective catalyst depending on the purpose of each reaction.
For example, in the first stage reactor, hydrogenation is carried out at a reaction temperature of 50 to 200°C using a palladium-based or nickel-based catalyst, or a reaction temperature of 150 to 300°C is employed using a cobalt-molybdenum-based catalyst.
Cobalt-molybdenum catalysts are mainly used in the post-stage reaction. In these hydrogenation reactions, in addition to a reduction in activity due to poisoning of the catalyst used, there is a problem in that the catalyst activity tends to decrease due to polymerization of the diolefin to be hydrogenated. , and cobalt-molybdenum catalysts where the hydrogenation reaction is carried out at high temperatures, diolefin polymerization is likely to occur. In the current process of recovering aromatic compounds from cracked gasoline, the cracked gasoline is first converted into a middle distillate, i.e., a C ₆ -C ₈ fraction or a C ₆ -C ₉ fraction, from which light and heavy substances are separated in a front distillation section. The fraction is fed to a pre-hydrogenation reactor. In order to elucidate the polymerization trouble of diolefin in the hydrogenation treatment of cracked gasoline, the present inventors conducted a detailed analysis of the above-mentioned middle distillate supplied to the front reactor.
It was found that most of the diolefins contained in this fraction were cyclopentadiene and methylcyclopentadiene. However, these cyclopentadienes are compounds that originally have a boiling point that should be separated in a light matter separation column in the front distillate. However, these compounds form stable dimers at temperatures below 150°C, and decomposition is small at temperatures around 135°C, which is the bottom temperature of the light separation column, and therefore they are not separated as light substances. It is sent as a dimer to the next heavy substance separation column without being separated. It was found that the bottom temperature of the heavy substance separation column is approximately 200℃, and the dimer is decomposed here, distilled from the top of the column together with the middle distillate, and supplied to the first stage reactor of the hydrotreating process. . That is, by repeating the Diels-Alder reaction and its reverse reaction in the distillation column, these compounds are not separated as light or heavy substances, but are ultimately converted into cyclopentadiene and methylcyclopentadiene. It has become clear that it is mixed in the form of monomers into the middle distillate that is fed to the first stage reactor of the hydrotreating process. By separating cyclopentadienes in the form of monomers, the present invention greatly reduces the diene content of the middle distillate supplied to the hydrotreating process, thereby reducing the burden on the hydrotreating process, especially on the pre-stage reactor. In some cases, it may even be possible to omit the pre-stage reactor. That is, the present invention provides a method for hydrotreating a middle distillate obtained by separating light substances and heavy substances from cracked gasoline, in which the bottom temperature of a light substance separation column is maintained at 150°C or higher under pressure. This is a method for hydrotreating cracked gasoline, which is characterized by subjecting the cracked gasoline to heat treatment, separating and removing cyclopentadiene, and subjecting the middle distillate with reduced cyclopentadiene content to hydrotreating. The flow of a conventionally commonly used hydrogenation process for pyrolyzed gasoline is shown in FIG. The raw material pyrolysis gasoline is supplied to the light separation column 2 through line 1, and is passed through line 3 from the top of the column.
A C ₅ fraction and lighter fractions are withdrawn.
Further, a heavy fraction of C ₆ or more is extracted from the bottom of the column through a line 4 and introduced into a heavy material separation column 5 .
In the heavy substance separation column 5, from the bottom of the column, a heavy fraction of C ₁₀ or higher, or in some cases a C ₉ fraction or higher, is extracted through a line 6. The top fraction of the heavy substance separation column 5 is extracted as a target C ₆ -C ₈ fraction or C ₆ -C ₉ fraction as a middle distillate. This middle distillate has the following two purposes: a part 12 of the outlet oil 11 of the first stage reactor of hydrotreating, or a part 12 of the outlet oil 11 of the second stage reactor.
A portion 19 of 7 is introduced via line 20 and mixed. The first purpose is that if there are many conjugated diolefins in the middle distillate 7 extracted from the top of the heavy material separation column 5, this will reduce the catalytic activity of the front reactor due to gum formation. The goal is to dilute the gas to suppress gum formation in the pre-stage reactor.
The second purpose is to reduce the temperature rise in the hydrogenation reaction of a large amount of diolefin by dilution, and to facilitate reaction temperature control. The mixed middle distillate is mixed with hydrogen from line 8 and supplied to the front reactor 10 from line 9. The first stage reactor 10 is a normal temperature type or adiabatic type reactor filled with a palladium-based, nickel-based, or cobalt-molybdenum-based catalyst, and the conjugated diolefin in the introduced middle distillate is mainly hydrogenated.
Converted to monoolefin. The product liquid from the front reactor 10 is withdrawn to the line 11, and if necessary, a part of it is mixed with the middle distillate 7, which is the raw material to be fed to the reactor, through the line 12 and the line 20, and the rest is passed through the line 11. From 13, the temperature is raised in a heating furnace 14, and supplied to a downstream reactor 16 through a line 15. The latter stage reactor 16 is generally an adiabatic reactor, and is filled with a cobalt-molybdenum-based catalyst or a cobalt-molybdenum-nickel-based catalyst. Here, monoolefin is mainly subjected to hydrogenation, desulfurization, denitrification, and deoxygenation reactions, and is converted into paraffin, H ₂ S, NH ₃ , and H ₂ O, respectively. The product liquid from the second stage reactor 16 is transferred to the line 17.
If necessary, part of it is extracted from line 1.
9 and 20 to be mixed with the middle distillate in line 7, and the remainder is recovered as a stabilized product through several steps. In the method of the present invention, in order to separate cyclopentadienes in the form of monomers, the middle distillate supplied to the light separation column is heat-treated at a temperature of 150°C or higher, thereby converting the dimers of cyclopentadienes into monomers. It is decomposed into monomers and separated by distillation. To do this, it is necessary to heat the bottom fraction of the light separation column, where the dimer mainly exists, to 150℃ or higher. Specifically, the bottom temperature of the light separation column must be 150℃ or higher. Generally, the dimer is decomposed by increasing the operating pressure of the distillation column so that the decomposed monomer is distilled out as a light product. The method of heating the bottom fraction to 150℃ or higher is as follows:
Alternatively, the bottom temperature can be raised by adding a high boiling point fraction to the light separation column, or the bottom fraction of the light separation column can be extracted and heated to 150℃ or higher in another distillation column. It is also possible to separate the decomposed monomers by returning them to the light separation column. Hereinafter, the present invention will be specifically explained with reference to FIG. 2 showing an embodiment thereof. Pyrolyzed gasoline 1 is supplied to a light separation column 2 . The light separation column 2 is operated under pressure. The degree of pressurization is the pressure necessary to raise the bottom temperature of the light material separation column 2 to 150°C or higher, which is a temperature sufficient to decompose the dimer of cyclopentadiene, and is usually 5 kg/cm ² A pressure of G or more is applied. As a result, dimers of cyclopentadienes, which have conventionally been produced at the top of the light separation column, especially the column, are decomposed into monomers at the bottom of the column, and the monomers are extracted as the top fraction 3. Therefore, the amount of cyclopentadiene contained in the form of dimers in the bottom fraction 4 extracted from the bottom of the light separation column 2 is greatly reduced compared to the amount in the original pyrolysis gasoline 1. Cyclopentadiene in the middle distillate 7 obtained through the heavy material separation column 5 is also reduced compared to the conventional method, and the diene number is extremely small. As a result, in some cases, the pre-stage reactor 10 in the hydrotreating process becomes unnecessary, and even if it is necessary, the diene number is small, so there is no need to recirculate the oil at the outlet of the hydrogenation reactor as in the past. . Conventionally, most troubles in the hydroprocessing of cracked gasoline have occurred in the first stage reactor 10 of the hydroprocessing, and the method of the present invention greatly reduces the diene number of the middle distillate supplied to the hydroprocessing. This enables extremely stable hydrogenation treatment. The heating furnace 14 and below are processed in the same manner as in the conventional method. FIG. 3 shows a flow sheet in the case where the bottom temperature of the light material separation column is raised to 150° C. or higher by adding the heavy material 21 together with the pyrolysis gasoline 1 to the light material separation column 2. In this case, the light substance separation column does not require pressurization, but pressurization is effective when the boiling point of the heavy substance 21 to be added is relatively low. As the heavy substance to be added, any oil can be used as long as it is miscible with pyrolysis gasoline, but heavy oil 6 from the bottom of the heavy substance separation column 5 can also be used. Figure 4 shows that the bottom fraction 4 of the light separation column 2 is introduced into another distillation column 22, where it is heat-treated at 150°C or higher to remove cyclopentadienes produced in the light separation column 2. The dimer is decomposed, and the decomposed monomer is returned to the light material separation column as an overhead fraction 23, and the bottom fraction 24 is supplied to the heavy material separation column. The bottom temperature of the distillation column 22 is maintained at 150° C. or higher by pressurization or addition of heavy oil. The present inventors also investigated the reactivity of cyclopentadiene dimer in the hydrogenation process. As a result, one of the double bonds in the cyclopentadiene dimer is more reactive than the double bonds in common monoolefins, such as pentene and hexene, and is used in the front reactor to react with a palladium-based or nickel-based catalyst. It has been found that hydrogenation treatment in the latter stage reactor can be carried out easily and stably by carrying out hydrogenation using. That is, as shown in Fig. 7, the cyclopentadiene still remaining in the middle distillate before being fed to the hydrotreating is dimerized in advance and then fed to the first stage reactor, thereby allowing the hydrotreating to be carried out. It can be made more stable. Therefore, in the method of the present invention, the middle distillate 7 whose cyclopentadiene content has been reduced according to each of the above embodiments (Figs. 2 to 4) is fed to the hydrotreating step as shown in Fig. 5. Before, dimerization tank 29
It is advantageous to carry out a heat treatment in order to dimerize any remaining cyclopentadienes. The dimerization process in this dimerization tank 29 converts the middle distillate into 60
It is carried out by treatment for 1 to 12 hours at a temperature of ~120°C. At this time, pressurization is applied if necessary to keep the middle distillate in the liquid phase. For example, by treating at 100°C for 4 hours under a pressure of 8 kg/cm ² G, the dimerization rate of the cyclopentadienes contained is 70
It was ~80%. Comparative Example In accordance with the flow sheet shown in FIG. 1, a middle distillate for hydrotreating pyrolysis gasoline, which is a by-product during ethylene production by naphtha steam cracking, was separated. Light separation separates light substances below _C5 fraction,
As for heavy substances, _C9 fraction and above were separated. The operating conditions of the light material separation tower and the heavy material separation tower are as follows.

【table】

[Table] Diene number of the top fraction of the heavy material separation tower (sample oil
The number of grams of iodine corresponding to the number of equivalents of maleic anhydride reacting with 100 grams was 13.0. Example 1 The heavy substance separation column was operated under the same conditions as in the comparative example with the same flow, but the light substance separation column carried out pressurized distillation under the following conditions. Number of distillation column plates: 30 Feed plates: 16 Reflux ratio: 1.5 Column top temperature: 107℃ Column top pressure: 7Kg/cm ² G Column bottom temperature: 177℃ Column bottom pressure: 7Kg/cm ² G The diene number of the top fraction of the heavy material separation column is 8.0 It was hot. Example 2 The top fraction (diene number 8.0) of the heavy material separation column obtained by the operation of Example 1 was heated at 110° C. for 3 hours and then supplied to the first reactor. The processing conditions in the first stage reactor are as follows. Reaction temperature 100℃ Reaction pressure 50Kg/cm ² G LHSV 0.5hr ^-1 H ₂ /oil 2mol/mol Catalyst 0.3wt%Pd/Al ₂ O _3The diene value of the middle distillate supplied to the first reactor is
3.0, but the diene number of the product hydrotreated under the above conditions was 0.8.

[Brief explanation of the drawing]

FIG. 1 is a flow sheet of a conventional method for hydrotreating pyrolysis gasoline, and FIGS. 2 to 5 are flow sheets showing various embodiments of the method of the present invention. The correspondence between the main parts illustrated and the symbols is as follows. 1...Pyrolysis gasoline, 2...Light matter separation column,
5...Heavy substance separation column, 8...Hydrogen, 10...Pre-stage reactor, 14...Heating furnace, 18...Hydride, 2
1...High boiling point fraction, 22... Distillation column, 29... Dimerization tank.

Claims (1)

[Claims] 1. In a method for hydrotreating a middle distillate obtained by separating light and heavy substances from cracked gasoline, the bottom temperature of a light substance separation column is adjusted to 150°C under pressure.
1. A method for hydrotreating cracked gasoline, which comprises performing a heat treatment while maintaining the above temperature, separating and removing cyclopentadiene, and subjecting a middle distillate with a reduced cyclopentadiene content to a hydrotreating process. 2. In a method of hydrotreating the middle distillate obtained by separating light and heavy substances from cracked gasoline, the bottom temperature of the light substance separation column is increased to 150°C under pressure.
cyclopentadiene is separated and removed to obtain a middle distillate with a reduced cyclopentadiene content. 1. A method for hydrotreating cracked gasoline, which comprises treating it for 1 to 12 hours and then subjecting it to hydrotreating.