How isoprene is produced?

Abstract

A method for producing isoprene, said method comprising: a first separation step for separating a C5 fraction, which is mainly composed of a hydrocarbon having 5 carbon atoms, from gasoline; a second separation step for separating isoamylene from the C5 fraction that has been obtained in the first separation step; an isomerization step for producing isoamylene by bringing the C5 fraction that has been obtained in the second separation step into contact with an isomerization catalyst; and a dehydrogenation step for producing isoprene by subjecting the isoamylene that has been separated in the second separation step and the isoamylene that has been produced in the isomerization step to a dehydrogenation reaction.

Description

[Technical field]

[0001] The present invention relates to a method for producing isoprene. This application claims priority based on Japanese Patent Application No. 2019-185966, filed in Japan on October 9, 2019, the contents of which are incorporated herein by reference. [Background technology]

[0002] Isoprene is in high demand as a main component of synthetic rubber and the like, and is widely used industrially. Isoprene can be obtained, for example, by recovering it by extractive distillation from a C5 fraction, which is a by-product of pyrolysis of naphtha to produce ethylene and is mainly composed of hydrocarbons having a carbon number of 5. Patent Document 1 also describes that isoprene is produced by recovering isoamylene from the residual oil of the extractive distillation and subjecting the isoamylene to a dehydrogenation reaction. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2015-151391 A Summary of the Invention [Problem to be solved by the invention]

[0004] In recent years, the demand for isoprene has been increasing. However, because there are only a few naphtha cracker facilities worldwide, there has been a limit to the amount of isoprene that can be produced using the C5 fraction, a by-product of naphtha cracking, as a raw material. On the other hand, gasoline has been produced in large quantities as a fuel for a wide range of applications. However, in recent years, in consideration of environmental issues, various clean energy alternatives to gasoline have been proposed. Therefore, it is expected that the demand for gasoline will decrease in the future, and there is a demand for gasoline to be used for purposes other than fuel. In addition, because the demand for gasoline as a fuel has traditionally been overwhelmingly high, the demand for by-products in the gasoline manufacturing process has been low and they have not been used effectively.

[0005] The present invention has been made in consideration of the above circumstances, and an object of the present invention is to provide a method for producing isoprene that is capable of producing isoprene in a high yield using gasoline as a raw material. [Means for solving the problem]

[0006] A first aspect of the present invention is a method for producing isoprene, comprising: a first separation step of separating a C5 fraction, mainly composed of hydrocarbons having a carbon number of 5, from gasoline; a second separation step of separating isoamylene from the C5 fraction obtained in the first separation step; an isomerization step of contacting the C5 fraction obtained in the second separation step with an isomerization catalyst to produce isoamylene; and a dehydrogenation step of subjecting the isoamylene separated in the second separation step and the isoamylene produced in the isomerization step to a dehydrogenation reaction to produce isoprene.

[0007] In one embodiment, the isomerization step may include contacting only a portion of the C5 fraction obtained in the second separation step with an isomerization catalyst to produce isoamylenes. In one embodiment, the isomerization step may include subjecting 50 mass% or more of the total amount of the C5 fraction obtained in the second separation step to an isomerization catalyst. In one embodiment, the second separation step may further include separating isopentane from the C5 fraction from which isoamylene has been separated. Effect of the Invention

[0008] According to the present invention, there is provided a method for producing isoprene, which is capable of producing isoprene from gasoline in a high yield. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] The method for producing isoprene according to this embodiment includes a first separation step of separating a C5 fraction, mainly composed of hydrocarbons having a carbon number of 5, from gasoline; a second separation step of separating isoamylene from the C5 fraction obtained in the first separation step; an isomerization step of contacting the C5 fraction obtained in the second separation step with an isomerization catalyst to produce isoamylene; and a dehydrogenation step of subjecting the isoamylene separated in the second separation step and the isoamylene produced in the isomerization step to a dehydrogenation reaction to produce isoprene. As the gasoline, for example, a gasoline fraction obtained from a fluid catalytic cracker (catalytic cracking gasoline) or a gasoline fraction obtained from a thermal cracker (thermal cracking gasoline) can be suitably used, but is not limited thereto.

[0010] According to the above production method, the C5 fraction contained in gasoline is efficiently converted into isoprene, making it possible to produce isoprene from gasoline at a high yield.

[0011] Each step of the manufacturing method according to this embodiment will be described in detail below.

[0012] <First separation process> In the first separation step, a C5 fraction, which is mainly composed of hydrocarbons with a carbon number of 5, is separated from gasoline. In this embodiment, the C5 fraction mainly composed of hydrocarbons having a carbon number of 5 contains 70 mass % or more, preferably 80 mass % or more, and more preferably 90 mass % or more of hydrocarbons having a carbon number of 5.

[0013] The C5 fraction separated in the first separation step and mainly composed of hydrocarbons having a carbon number of 5 (hereinafter sometimes referred to as the "(C5-1) fraction") contains at least n-pentene, isopentane, n-pentane, and isoamylene as hydrocarbons having a carbon number of 5. The (C5-1) fraction may further contain isoprene, cyclopentene, cyclopentadiene, piperylene, etc. as hydrocarbons having a carbon number of 5.

[0014] The content of n-pentene in the (C5-1) fraction is preferably 10% by mass or more, more preferably 15% by mass or more, and even more preferably 20% by mass or more. With such a content, the above-mentioned effects of the invention are more significantly exhibited. The content of n-pentene in the (C5-1) fraction may be, for example, 70% by mass or less, or 60% by mass or less.

[0015] The content of isopentane in the (C5-1) fraction is, for example, 10% by mass or more, preferably 15% by mass or more, and more preferably 20% by mass or more. At such a content, the above-mentioned effects of the invention are more pronounced. The content of isopentane in the (C5-1) fraction may be, for example, 70% by mass or less, preferably 60% by mass or less, and more preferably 50% by mass or less.

[0016] The content of n-pentane in the (C5-1) fraction is, for example, 1% by mass or more, preferably 3% by mass or more, and more preferably 5% by mass or more. At such a content, the above-mentioned effects of the invention are more pronounced. The content of n-pentane in the (C5-1) fraction may be, for example, 30% by mass or less, or 20% by mass or less.

[0017] The content of isoamylene in the (C5-1) fraction is, for example, 10% by mass or more, preferably 15% by mass or more, and more preferably 20% by mass or more. The content of isoamylene in the (C5-1) fraction may be, for example, 70% by mass or less, preferably 60% by mass or less, and more preferably 50% by mass or less.

[0018] When the (C5-1) fraction contains components other than n-pentene, isopentane, n-pentane and isoamylene, the content of the other components is preferably 30 mass % or less, more preferably 20 mass % or less.

[0019] In the first separation step, the method for separating the C5 fraction is not particularly limited, and can be performed by a conventionally known method. In the first separation step, isopentane, a C6 fraction, a gasoline fraction, and the like in the remaining fraction after separation of the (C5-1) fraction may be separately separated and recovered.

[0020] <Second separation process> In the second separation step, isoamylene is separated from the C5 fraction ((C5-1) fraction) obtained in the first separation step. The method for separating isoamylene from the (C5-1) fraction is not particularly limited, and can be performed by a known method. For example, it can be performed by an extraction separation method using sulfuric acid or the like as an extractant. The isoamylene separation device used for separating isoamylene from the (C5-1) fraction is not particularly limited.

[0021] In the second separation step, it is preferable to further separate isopentane from the C5 fraction from which isoamylene has been separated (hereinafter, sometimes referred to as "(C5-2) fraction"). By further separating isopentane from the (C5-2) fraction, it is possible to suppress accumulation of mainly isopentane in the stream fed to the process. As a result, for example, when recycle operation is performed in the isoamylene separation device in the second separation step and the isomerization device in the isomerization step described below, the inlet flow rate of each device can be reduced, and the isoamylene yield in the isoamylene separation device and the isomerization device can be further improved. In addition, it is desirable to separate isopentane after isoamylene separation from the viewpoint of improving the efficiency of the production process.

[0022] In the second separation step, the method of further separating isopentane from the (C5-2) fraction is not particularly limited, and may be a known method, for example, distillation. In addition, the apparatus for separating isopentane from the (C5-2) fraction is not particularly limited. Hereinafter, the C5 fraction obtained by further separating isopentane from the (C5-2) fraction may be referred to as the (C5-3) fraction.

[0023] In the second separation step, a part of the (C5-2) fraction may be purged and removed, and the remainder may be fed to the isomerization step described below. This makes it possible to prevent the accumulation of hydrocarbons having a carbon number of 5 other than isoamylene (including isopentane) in the stream fed to the isomerization step. This step of purging the (C5-2) fraction may be carried out alone, or may be carried out together with the step of separating isopentane from the (C5-2) fraction. In the latter case, the step of purging the (C5-2) fraction is preferably carried out before separating isopentane. The proportion of this (C5-2) fraction purged is preferably 50 mass% or less.

[0024] <Isomerization process> In the isomerization step, the C5 fraction (the (C5-2) fraction and / or the (C5-3) fraction) obtained in the second separation step is contacted with an isomerization catalyst to produce isoamylene. More specifically, in the isomerization step, n-pentene contained mainly in the (C5-2) fraction and / or the (C5-3) fraction is subjected to an olefin isomerization reaction to produce isoamylene. In the isomerization step, it is preferable to supply only a portion of the C5 fraction obtained in the second separation step to the isomerization catalyst, and it is more preferable to supply 50 mass% or more of the total amount of the C5 fraction obtained in the second separation step to the isomerization catalyst.

[0025] The isomerization catalyst may be, for example, a zeolite catalyst. The zeolite used is preferably at least partially in the hydrogen form, for example, but not limited to, MFI, FER, or AEL zeolites. The zeolite may be incorporated in another material, called a matrix or binder.

[0026] The conditions for the isomerization reaction are not particularly limited, and for example, the reaction temperature may be 50 to 500° C., 100 to 400° C., or 200 to 300° C. If the reaction temperature is 350° C. or higher, the amount of light hydrocarbons produced tends to be greater. The reaction pressure, i.e., the atmospheric pressure inside the reactor, may be 0.01 to 20 MPa, 0.1 to 10 MPa, or 0.5 to 5 MPa.

[0027] The reaction apparatus for carrying out the isomerization reaction is not particularly limited. When the isomerization reaction is carried out in a continuous reaction apparatus in which the raw material gas is continuously supplied, the weight hourly space velocity (hereinafter referred to as "WHSV") is 0.1 to 500 h -1 may be 0.1 to 400h -1 May be 5 to 100 hours -1 Here, WHSV is the ratio (F / W) of the feed rate (feed amount / time) F of the raw material gas to the mass W of the dehydrogenation catalyst in a continuous reaction apparatus. The amounts of the raw material gas and catalyst used may be appropriately selected from more preferable ranges depending on the reaction conditions, the activity of the catalyst, etc., and the WHSV is not limited to the above range.

[0028] In addition, the (C5-2) fraction and / or the (C5-3) fraction may contain a small amount of n-pentane. In such a case, the n-pentane contained in the (C5-2) fraction and / or the (C5-3) fraction can be subjected to the paraffin isomerization reaction. In the isomerization step, by providing the ability to isomerize both n-pentene and n-pentane, accumulation of n-pentane in the stream fed to the process can be suppressed, and as a result, for example, the recycle ratio of the isoamylene separation unit and isopentane separation unit in the second separation step, and the isomerization unit in the isomerization step can be reduced. The method for the paraffin isomerization reaction is not particularly limited, and can be a conventionally known method.

[0029] From the viewpoint of improving the efficiency of the production process, a part or all of the isoamylene produced in the isomerization step is combined with the isoamylene separated in the second separation step. In this case, the stream containing isoamylene produced in the isomerization step may be combined with the isoamylene separated from the (C5-1) fraction in the second separation step, or may be recycled to the second separation step (isoamylene separation device).

[0030] <Dehydrogenation process> In the dehydrogenation step, the isoamylene separated in the second separation step and the isoamylene produced in the isomerization step are subjected to a dehydrogenation reaction to produce isoprene. In this embodiment, not only the isoamylene separated in the second separation step, but also the isoamylene produced in the isomerization step is subjected to a dehydrogenation reaction, thereby making it possible to improve the yield of isoprene.

[0031] The conditions for the dehydrogenation reaction in the dehydrogenation step are not particularly limited, and any catalyst and conditions can be used without particular limitation as long as they are capable of converting isoamylene to isoprene.

[0032] The dehydrogenation catalyst may be, for example, a catalyst in which an active metal is supported on an inorganic oxide carrier. The active metal source may be at least one selected from the group consisting of platinum, tin, chromium, iron, bismuth, molybdenum, manganese, cobalt, cerium, ruthenium, and iridium.

[0033] The conditions for the dehydrogenation reaction are not particularly limited, and for example, the reaction temperature may be 300 to 800° C., or 500 to 700° C. The reaction pressure, i.e., the atmospheric pressure inside the reactor, may be 0.01 to 1 MPa, or 0.05 to 0.8 MPa, or 0.1 to 0.5 MPa. When the reaction pressure is within the above range, the dehydrogenation reaction proceeds more easily, and there is a tendency that even better reaction efficiency can be obtained.

[0034] The reaction apparatus for carrying out the dehydrogenation reaction is not particularly limited. When the dehydrogenation reaction is carried out in a continuous reaction apparatus in which the raw material gas is continuously supplied, the weight hourly space velocity (hereinafter referred to as "WHSV") is 0.1 h -1 It may be 1.0h or more. -1 It may be more than 100h -1 may be less than 30h -1 or less. Here, WHSV is the ratio (F / W) of the feed rate (feed amount / time) F of the raw material gas to the mass W of the dehydrogenation catalyst in a continuous reaction apparatus. Note that the amounts of the raw material gas and catalyst used may be appropriately selected within more preferable ranges depending on the reaction conditions, catalyst activity, etc., and WHSV is not limited to the above range.

[0035] The type of reactor for the dehydrogenation reaction may be, for example, a fixed bed type, a moving bed type or a fluidized bed type. Among these, the fixed bed type is preferred from the viewpoint of equipment costs. EXAMPLES

[0036] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0037] (Gasoline feedstock) In Example 1 and Comparative Example 1, gasoline having the C5 composition shown in Table 1 below was used as the feedstock.

[0038] [Table 1]

[0039] [Example 1] <First separation process> Gasoline having the C5 composition shown in Table 1 (first stream, relative flow rate: 100) was fed into a distillation tower, and a C5 fraction mainly composed of hydrocarbons with a carbon number of 5 was separated by distillation (second stream, relative flow rate: 35).

[0040] <Second separation process> The C5 fraction ((C5-1) fraction) obtained in the first separation step was fed to an isoamylene separation apparatus to separate isoamylene. The C5 fraction from which isoamylene had been separated (C5-2 fraction) (third stream; relative flow rate: 57) was supplied to an isopentane distillation apparatus to separate isopentene.

[0041] <Isomerization process> The C5 fraction ((C5-3) fraction) (fourth stream; relative flow rate: 41) obtained in the second separation step was fed to an olefin isomerization apparatus to produce isoamylene. The isoamylene obtained in the isomerization step (fifth stream, relative flow rate: 41) was mixed with the isoamylene separation device.

[0042] <Dehydrogenation process> The isoamylene separated in the second separation step and the isoamylene produced in the isomerization step (sixth stream; relative flow rate: 19) were fed to a dehydrogenation reactor to produce isoprene. The isoprene produced in the dehydrogenation process was separated and recovered (seventh stream; relative flow rate: 16).

[0043] The compositions of the first to seventh streams in Example 1 are shown in Table 2.

[0044] [Table 2]

[0045] [Comparative Example 1] <First separation process> Gasoline having the C5 composition shown in Table 1 (first stream, relative flow rate: 100) was fed into a distillation tower, and a C5 fraction mainly composed of hydrocarbons with a carbon number of 5 was separated by distillation (second stream, relative flow rate: 35).

[0046] <Second separation process> The C5 fraction ((C5-1) fraction) obtained in the first separation step was fed to an isoamylene separation device, where isoamylene was separated from the C5 fraction excluding isoamylene (third stream; relative flow rate: 26) (fourth stream; relative flow rate: 8).

[0047] <Dehydrogenation process> The isoamylene separated in the second separation step was fed to a dehydrogenation reactor to produce isoprene. The isoprene produced in the dehydrogenation process was separated and recovered (fifth stream; relative flow rate: 7).

[0048] The compositions of the first to fifth streams in Comparative Example 1 are shown in Table 3.

[0049] [Table 3]

[0050] From the results shown in Tables 2 and 3, it was confirmed that the yield of isoprene was higher in Example 1, in which the isomerization step was carried out, than in Comparative Example 1.

Claims

1. A first separation step of feeding gasoline into a distillation tower and separating a C5 fraction from the gasoline, the C5 fraction being mainly composed of hydrocarbons having a carbon number of 5; a second separation step in which, immediately after the first separation step, the C5 fraction obtained in the first separation step is supplied to an isoamylene separation apparatus to separate isoamylene from the C5 fraction obtained in the first separation step, and isopentane is further separated from the C5 fraction from which isoamylene has been separated; an isomerization step of supplying the C5 fraction obtained in the second separation step to an isomerization apparatus after the second separation step and contacting the C5 fraction obtained in the second separation step with an isomerization catalyst to produce isoamylene; a dehydrogenation step in which the isoamylene separated in the second separation step and the isoamylene produced in the isomerization step are subjected to a dehydrogenation reaction to produce isoprene; A method for producing isoprene, comprising:

2. 2. The method for producing isoprene according to claim 1, wherein the isomerization step comprises contacting only a portion of the C5 fraction obtained in the second separation step with an isomerization catalyst to produce isoamylene.

3. 3. The method for producing isoprene according to claim 1 or 2, wherein the isomerization step comprises subjecting 50 mass% or more of the total amount of the C5 fraction obtained in the second separation step to an isomerization catalyst.

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