Olefin and methanol co-production plant and olefin and methanol co-production method

An olefin and methanol co-production plant for co-production of an olefin and methanol from a source gas containing methane includes: an olefin production unit for producing the olefin; and a methanol production unit for producing methanol from a carbon oxide gas in the olefin production unit. The olefin production unit includes a partial oxidative coupling device for producing the olefin by partial oxidative coupling reaction of methane contained in the source gas. The methanol production unit includes a reforming device for producing hydrogen by reforming reaction of methane, and a methanol production device for producing methanol by reaction with hydrogen produced by the reforming device. At least one of the reforming device or the methanol production device is configured to perform reaction using the carbon oxide gas in the olefin production unit.

This application is a national stage application claiming priority to PCT/JP2017/044831, now WO/2019/116484, filed on Dec. 14, 2017.

TECHNICAL FIELD

The present invention relates to an olefin and methanol co-production plant and an olefin and methanol co-production method.

BACKGROUND

As a method for producing olefins such as ethylene and propylene, the MTO (Methanol To Olefin) method is known. In the MTO method, methanol is produced from a source gas (e.g., natural gas) containing methane, and further, olefins are produced from methanol. However, in the MTO method, since olefins are produced via methanol, which is an intermediate product, the total energy consumed for producing olefins is large. Therefore, as a new method for producing olefins, partial oxidative coupling reaction of methane (hereinafter simply referred to as OCM reaction) has been attracting attention.

As a technique for producing olefins using the OCM reaction, a technique disclosed in Patent Document 1 is known. Patent Document 1 describes that olefins are produced from methane using the OCM reaction.

CITATION LIST

Patent Literature

Patent Document 1: US Patent Application Publication No. 2016/0200643 (especially see abstract and claim 1)

SUMMARY

Problems to be Solved

In the OCM reaction, besides olefins, carbon dioxide is produced as a by-product. Since carbon dioxide is a stable compound, it is usually difficult to make good use of the by-produced carbon dioxide. Accordingly, in practice, the by-produced carbon dioxide is discharged outside as it is. However, the emission of carbon dioxide causes global warming. Therefore, it is desired to reduce the emission amount of carbon dioxide.

Further, in the OCM reaction, carbon monoxide is also produced as a by-product. Carbon monoxide is not a greenhouse gas, as it does not absorb much infrared radiation from the earth surface, unlike carbon dioxide. However, when carbon monoxide is irradiated with ultraviolet rays, ozone is generated, and the ozone in the troposphere (tropospheric ozone) causes global warming. Therefore, it is also desired to reduce the emission amount of carbon monoxide.

Under such circumstances, the present inventors have conducted studies and found that a carbon oxide gas, such as carbon monoxide and carbon dioxide, can be used as the source of production of methanol. Therefore, it is conceivable to use a carbon oxide gas which is a by-product of the OCM reaction to produce methanol in order to reduce the emission amount of the carbon oxide gas.

In view of the above, an object of at least one embodiment of the present invention is to provide an olefin and methanol co-production plant and an olefin and methanol co-production method whereby it is possible to produce olefins by the OCM reaction, and simultaneously, it is possible to produce methanol using a carbon oxide gas produced as a by-product of the OCM reaction.

Solution to the Problems

(1) An olefin and methanol co-production plant according to some embodiments of the present invention for co-production of an olefin and methanol comprises: an olefin production unit for producing the olefin; and a methanol production unit for producing methanol from a carbon oxide gas in the olefin production unit. The olefin production unit includes a partial oxidative coupling device for producing the olefin by partial oxidative coupling reaction of methane contained in the source gas. The methanol production unit includes a reforming device for producing hydrogen by reforming reaction of methane, and a methanol production device for producing methanol by reaction with hydrogen produced by the reforming device. At least one of the reforming device or the methanol production device is configured to perform reaction using the carbon oxide gas in the olefin production unit.

With the above configuration (1), olefins can be produced directly from methane contained in natural gas by the OCM reaction (partial oxidative coupling), not via methanol as an intermediate product. Thus, it is possible to reduce energy consumed for producing olefins. Further, since methanol can be produced from a carbon oxide gas in the olefin production unit, it is possible to reduce the emission amount of the carbon oxide gas such as carbon monoxide and carbon dioxide. Further, since methanol can be produced from carbon derived from the source gas used for producing olefins, it is unnecessary to separately prepare the source for methanol production from outside. Thus, it is possible to reduce the production cost of methanol.

(2) In some embodiments, in the above configuration (1), the reforming device is configured to produce hydrogen by reforming of methane in the olefin production unit.

With the above configuration (2), hydrogen for methanol production can be produced using methane in the olefin production unit, in addition to the carbon oxide gas. Thus, methanol can be produced using compounds present in the olefin and methanol co-production plant. This eliminates the need to separately supply methane for methanol production, and reduces the amount of the source gas to be used. Thus, it is possible to save the production cost.

(3) In some embodiments, in the above configuration (2), the olefin production unit includes a methane separation device for separating at least methane from a gas in the olefin production unit, and the reforming device is configured to produce hydrogen from methane separated by the methane separation device.

With the above configuration (3), since methane purified through separation by the methane separation device is used, the amount of methane supplied to the reforming device is increased. Thus, it is possible to enhance the reforming reaction, and it is possible to increase the production amount of hydrogen.

(4) In some embodiments, in any one of the above configurations (1) to (3), the olefin production unit includes a methanation device for producing methane from the carbon oxide gas in the olefin production unit, and the reforming device is configured to produce hydrogen from methane produced by the methanation device.

With the above configuration (4), the concentration of methane is increased by the methanation device, and the amount of methane supplied to the reforming device is increased. Thus, it is possible to enhance the reforming reaction, and it is possible to increase the production amount of hydrogen. Further, since the production amount of hydrogen is increased, it is possible to increase the production amount of methanol.

(5) In some embodiments, in any one of the above configurations (1) to (4), the olefin production unit includes a methanation device for producing methane from the carbon oxide gas in the olefin production unit, and the partial oxidative coupling device is configured to produce the olefin from methane produced by the methanation device.

With the above configuration (5), the concentration of methane is increased by the methanation device, and the amount of methane supplied to the partial oxidative coupling device is increased. Thus, it is possible to enhance the OCM reaction using methane, and it is possible to increase the production amount of olefins.

(6) In some embodiments, in any one of the above configurations (1) to (5), the reforming device is configured to produce hydrogen by reforming the source gas.

With the above configuration (6), since hydrogen can be obtained directly from the source gas by the reforming device, it is possible to easily obtain hydrogen.

(7) In some embodiments, in any one of the above configurations (1) to (6), the methanol production unit includes a combustion device for combusting a fuel to generate heat used for the reforming in the reforming device, and at least one of the reforming device or the methanol production device is configured to perform reaction using a carbon oxide gas produced by the combusting device.

With the above configuration (7), at least one of the methane reforming or the methanol production can be performed using the carbon oxide gas produced by the combustion device while using heat generated by the combustion device in the reforming device. Further, the amount of the carbon oxide gas supplied from the olefin production unit to the methanol production unit can be reduced. As a result, even if the production amount of the carbon oxide gas is reduced to increase the yield of olefins in the olefin production unit, it is possible to cover the amount of the carbon oxide gas required by the methanol production unit.

(8) An olefin and methanol co-production method according to some embodiments of the present invention for co-production of an olefin and methanol comprises: a partial oxidative coupling step of producing the olefin by partial oxidative coupling reaction of methane contained in the source gas; a reforming step of producing hydrogen by reforming reaction of methane; and a methanol production step of producing methanol by reaction with hydrogen produced in the reforming step. At least one of the reforming step or the methanol production step includes reaction using a carbon oxide gas produced in the partial oxidative coupling step.

With the above configuration (8), olefins can be produced directly from methane contained in natural gas by the OCM reaction (partial oxidative coupling), not via methanol as an intermediate product. Thus, it is possible to reduce energy consumed for producing olefins. Further, since methanol can be produced from a carbon oxide gas obtained in the partial oxidative coupling step, it is possible to reduce the emission amount of the carbon oxide gas such as carbon monoxide and carbon dioxide. Further, since methanol can be produced from carbon derived from natural gas used for producing olefins, it is unnecessary to separately prepare the source for methanol production from outside. Thus, it is possible to reduce the production cost of methanol.

Advantageous Effects

According to at least one embodiment of the present invention, there is provided an olefin and methanol co-production plant and an olefin and methanol co-production method whereby it is possible to produce olefins by the OCM reaction, and simultaneously, it is possible to produce methanol using a carbon oxide gas produced as a by-product of the OCM reaction.

DETAILED DESCRIPTION

Embodiments of the present invention will now be described in detail with reference to the accompanying drawings. However, the following embodiments and the drawings are illustrative only, and various modifications may be applied as long as they do not depart from the object of the present invention. Further, two or more embodiments may be optionally combined in any manner.

It is intended, however, that unless particularly specified, dimensions, materials, shapes, relative positions and the like of components described in the embodiments shall be interpreted as illustrative only and not intended to limit the scope of the present invention.

FIG. 1is a system diagram of an olefin and methanol co-production plant100according to a first embodiment of the present invention. The co-production plant100is configured to simultaneously produce an olefin and methanol from natural gas (source gas containing methane). The co-production plant100includes an olefin production unit10for producing an olefin (ethylene, propylene, butylene, etc.) and a methanol production unit20for producing methanol from a carbon oxide gas (at least one of carbon monoxide or carbon dioxide, the same shall apply hereinafter) in the olefin production unit10.

The olefin production unit10includes a desulfurization device1, a carbon dioxide recovery device2, a dehumidification device3, a separation device4, a methanation device5, and an OCM reaction device6.

The desulfurization device1is configured to remove sulfur components contained in natural gas. Illustrative examples of the sulfur components include hydrogen sulfide. As a specific configuration of the desulfurization device1, there may be mentioned an adsorbent for adsorbing sulfur components in natural gas.

The carbon dioxide recovery device2is configured to separate and recover carbon dioxide in the olefin production unit10(specifically, carbon dioxide contained in natural gas and carbon dioxide (carbon oxide gas) produced by the OCM reaction device6described later) from a circulating gas. The circulating gas in this context means a gas that flows through a passage running from the carbon dioxide recovery device2, passing through the dehumidification device3, the separation device4, the methanation device5, and the OCM reaction device6, and returned to the carbon dioxide recovery device2. By recovering carbon dioxide with the carbon dioxide recovery device2, it is possible to prevent solidification of carbon dioxide (i.e., production of dry ice) in freezing in the separation device4described later.

The recovery of carbon dioxide with the carbon dioxide recovery device2can be performed by, for instance, bringing an alkaline aqueous solution into contact with the gas. The recovered carbon dioxide is separated from the alkaline aqueous solution by, for instance, heating of the alkaline aqueous solution, and is then supplied to a reforming device21, which will be described later, and the methanation device5.

The dehumidification device3is configured to remove water in the olefin production unit10(specifically, steam contained in natural gas and water produced by the OCM reaction device6described later, etc.) from the circulating gas. By dehumidification with the dehumidification device3, it is possible to prevent solidification of water (i.e., production of ice) in freezing in the separation device4described later. The recovery of water in the dehumidification device3can be performed by, for instance, bringing the gas into contact with a desiccant.

The separation device4may be, for example, a distillation tower, which is configured to separate and recover methane, hydrogen, and carbon monoxide from the gas using a difference in boiling point, by cooling and then supplying the gas to the distillation tower. The hydrogen and carbon monoxide separated and recovered here include hydrogen and carbon monoxide produced by the OCM reaction device6described later.

In the separation device4, the gas is cooled to about −90° C. to −120° C. When the gas is cooled to this temperature range, methane, hydrogen, and carbon monoxide in the gas are separated and recovered in the form of gas. The recovered mixed gas of methane, hydrogen, and carbon monoxide is supplied to the later-described methanation device5and to the reforming device21.

On the other hand, the separation device4is supplied with natural gas, which is fed from outside, and with reaction gas produced in the OCM reaction device6via the carbon dioxide recovery device2and the dehumidification device3. Accordingly, the separation device4is supplied with ethane and olefins such as ethylene, propylene, and butylene manufactured (produced) by the OCM reaction device6. Therefore, when the gas is cooled to the above temperature range in the separation device4, the other components (e.g., olefins, ethane) in the gas are also liquefied. This allows separation and recovery of the other components. The recovered other components are further separated by a separation tower (not shown) individually. As a result, substances such as olefins are obtained as final products.

As the separation device4, for example, a freezer using both ethylene refrigerant and propylene refrigerant can be used.

The methanation device5is configured to produce methane from a carbon oxide gas (at least one of carbon monoxide or carbon dioxide) in the olefin production unit10. More specifically, the methanation device5converts a part of carbon dioxide recovered by the carbon dioxide recovery device2and carbon monoxide produced by the OCM reaction device6(described later) and separated and recovered by the separation device4into methane.

A catalyst (methanation catalyst) for the methanation reaction may be any methanation catalyst. Examples of the methanation catalyst include nickel catalysts. Reaction conditions may be, for example, 220° C. to 510° C. and 0 MPa to 3.0 Mpa approximately at the outlet of a catalytic layer placed in the methanation device5.

In this reaction, as described above, the methanation device5is supplied with a part of carbon dioxide recovered by the carbon dioxide recovery device2. The amount of carbon dioxide supplied to the methanation device5may be constant at all times or may vary as appropriate. For instance, when the amount of carbon dioxide supplied to the methanation device5is constant, the amount of carbon dioxide supplied to the methanol production unit20is, for example, 0.1 or more and 2.0 or less, preferably 0.5 or more and 1.5 or less, more preferably 0.8 or more and 1.2 or less, particularly preferably about 1, in terms of a value obtained by dividing the amount of substance of carbon dioxide by the amount of substance of methane.

When the amount of carbon dioxide supplied to the methanation device5varies as appropriate, the following may be applied: In the co-production plant100, as described later in detail, the reforming device21is supplied with carbon dioxide, and the reforming device21produces carbon monoxide and hydrogen from methane and carbon dioxide. Further, the methanol production device22disposed downstream of the reforming device21produces methanol from carbon monoxide and carbon dioxide. Therefore, by measuring the amount of methane supplied to the reforming device21and calculating the amount of carbon dioxide used in the reforming device21, the excess of carbon dioxide can be supplied to the methanation device5. Thus, it is possible to produce olefins using excess carbon dioxide while increasing the production amount of methanol.

On the other hand, thorough investigation by the inventors has shown that as the mole ratio of oxygen to methane increases in the OCM reaction device6downstream of the methanation device5, more carbon dioxide is produced as a by-product in the OCM reaction device6. Therefore, it is preferable to increase methane in order to reduce the mole ratio of oxygen to methane (specifically, for example, 0.5 or less in terms of mole ratio obtained by dividing the amount of substance of oxygen by the amount of substance of methane). In view of this, the methanation device5may be supplied with carbon dioxide so as to increase the amount of methane supplied to the OCM reaction device6(such that the mole ratio is 0.5 or less in the OCM reaction device6, for example). More specifically, for example, the concentration of oxygen may be measured, and the methanation device5may be supplied with carbon dioxide in an amount such that the above mole ratio is about 0.2 to 0.4, and the remainder may be supplied to the reforming device21. Thus, it is possible to suppress by-production of carbon dioxide and increase the production amount of olefins.

The OCM reaction device6(partial oxidative coupling device) is configured to produce olefins by OCM reaction of methane contained in natural gas. More specifically, the OCM reaction device6produces olefins from methane (including methane in natural gas) separated and recovered by the separation device4and methane produced by the methanation device5. In the OCM reaction device6, in addition to olefins such as ethylene, propylene, and butylene, a carbon oxide gas such as carbon monoxide and carbon dioxide and ethane are also produced. The produced olefins, carbon oxide gas, ethane, etc. are supplied to the carbon dioxide recovery device2.

In the OCM reaction device6, first, methyl radicals are produced from methane and oxygen. The produced methyl radicals react with each other and produce ethane. Then, two hydrogen atoms are removed from ethane, so that ethylene and hydrogen (molecules) are produced. In addition, methyl radicals produced in the middle of reaction react with ethylene to produce propylene. Furthermore, methyl radicals produced in the middle of reaction react with propylene to produce butylene. In addition to these, as the oxidation further proceeds, a carbon oxide gas such as carbon monoxide and carbon dioxide is produced.

By using methane produced by the methanation device5for the OCM reaction in the OCM reaction device6, since the concentration of methane is increased by the methanation device5, the amount of methane supplied to the OCM reaction device6is increased. Thus, it is possible to enhance the OCM reaction using methane, and it is possible to increase the production amount of olefins.

A catalyst (OCM reaction catalyst) for the OCM reaction may be any OCM reaction catalyst. As the OCM reaction catalyst, a catalyst disclosed in the U.S. Pat. No. 8,962,517 may be used. Reaction conditions may be, for example, 450° C. to 600° C. approximately at the inlet of a catalytic layer placed in the OCM reaction device6.

The methanol production unit20includes a reforming device21, a methanol production device22, and a separation device23.

The reforming device21is configured to produce hydrogen by reforming reaction of methane. More specifically, the reforming device21produces hydrogen by reforming methane separated and recovered by the separation device4. By reforming methane in the olefin production unit10to produce hydrogen, hydrogen for methanol production can be produced using methane in the olefin production unit10, in addition to carbon dioxide. Thus, methanol can be produced using compounds present in the co-production plant100. This eliminates the need to separately supply methane for methanol production and reduces the amount of natural gas to be used. Thus, it is possible to save the production cost.

In particular, in the co-production plant100, a part of the gas circulating in the olefin production unit10is extracted and used in the reforming device21. Accordingly, the amount of the gas circulating in the olefin production unit10is reduced. Thus, it is possible to reduce drive energy of a compressor (not shown) for circulating the olefin production unit10.

The olefin production unit10includes the separation device4(methane separation device) for separating methane from the gas in the olefin production unit10. The reforming device21produces hydrogen from methane separated by the separation device4. In this way, since methane purified through separation by the separation device4is used, the amount of methane supplied to the reforming device21is increased. Thus, it is possible to enhance the reforming reaction, and it is possible to increase the production amount of hydrogen.

The reforming device21is supplied with carbon dioxide recovered by the carbon dioxide recovery device2(i.e., carbon dioxide in the olefin production unit10). Since the reforming is performed in the presence of carbon dioxide, carbon potential is increased, and the following reaction equation (1) proceeds.
3CH4+CO2+2H2O→4CO+8H2reaction equation (1)

As shown by the reaction equation (1), 3 mol of methane produces 4 mol of carbon monoxide. Accordingly, in the subsequent methanol production device22, 4 mol of carbon monoxide produces 4 mol of methanol.

Although described in detail later, in the methanol production device22downstream of the reforming device21, 2 mol of hydrogen is used per 1 mol of carbon monoxide to produce methanol. Therefore, in the reforming device21, when the mole ratio of the produced carbon monoxide to hydrogen is 1:2 as shown in the reaction equation (1), the composition of the source gas for methanol production approximates the theoretical ratio.

The reforming in the reforming device21is steam reforming. Accordingly, in the reforming device21, hydrogen is produced by reaction of steam and methane at high temperature and high pressure. Reforming conditions may be, for example, 900° C. to 1000° C. and 0 MPa to 3.5 Mpa approximately at the outlet of a catalytic layer placed in the reforming device21. The reforming can be performed with any reforming catalyst. As the reforming catalyst, an oxide of transition metal such as nickel and platinum can be used.

The methanol production device22is configured to produce methanol by reaction with hydrogen produced by the reforming device21. In the methanol production device22, methanol is produced from hydrogen produced by the reforming device21and carbon monoxide and carbon dioxide discharged from the reforming device21. More specifically, 2 mol of hydrogen and 1 mol of carbon monoxide produce 1 mol of methanol. Further, 3 mol of hydrogen and 1 mol of carbon dioxide produce 1 mol of methanol.

Here, carbon monoxide and carbon dioxide discharged from the reforming device21and supplied to the methanol production device22include unreacted carbon monoxide and carbon dioxide. The unreacted carbon monoxide discharged from the reforming device21includes carbon monoxide separated and recovered together with methane by the separation device4. Further, the unreacted carbon dioxide discharged from the reforming device21includes carbon dioxide separated and recovered by the carbon dioxide recovery device2.

Accordingly, in the methanol production device22, methanol is produced from carbon monoxide separated and recovered by the separation device4and carbon monoxide produced by the reforming device21(see the reaction equation (1)). Further, in the methanol production device22, methanol is directly produced from unreacted carbon dioxide in the reforming device21. Thus, by using both carbon monoxide and carbon dioxide, it is possible to increase the production amount of methanol.

In the reforming device21upstream of the methanol production device22, as shown by the reaction equation (1), carbon dioxide is consumed to produce carbon monoxide. As a result, the gas supplied to the methanol production device22contains a relatively high amount of carbon monoxide and a relatively low amount of carbon dioxide. Accordingly, in the methanol production device22, mainly, methanol is produced from carbon monoxide.

Regarding methanol production conditions, for example, a mixed gas of hydrogen, carbon monoxide, and carbon dioxide may be caused to react at 200° C. to 350° C. at 5 MPa to 25 MPa approximately, using any catalyst. Examples of the catalyst include a composite catalyst of copper, zinc oxide, and aluminum oxide.

The separation device23is configured to separate and recover methanol from the reaction liquid (containing methanol) discharged from the methanol production device22. As the separation device23, for example, a distillation tower using difference in boiling point can be used. Thereby, methanol is obtained as final products.

Operation control of the co-production plant100is performed by a control device not depicted. The control device includes a central processing unit (CPU), a random access memory (RAM), a read only memory (ROM), a hard disk drive (HDD), and a control circuit, not depicted, and is realized by executing a predetermined control program stored in the ROM by the CPU.

With the co-production plant100having the above configuration, olefins can be produced directly from methane contained in natural gas by the OCM reaction, not via methanol as an intermediate product. Thus, it is possible to reduce energy consumed for producing olefins. Further, since methanol can be produced from a carbon oxide gas in the olefin production unit10, it is possible to reduce the emission amount of the carbon oxide gas such as carbon monoxide and carbon dioxide. Further, since methanol can be produced from carbon derived from natural gas used for producing olefins, it is unnecessary to separately prepare the source for methanol production from outside. Thus, it is possible to reduce the production cost of methanol.

Although in the above example, the reforming device21is configured to perform the reforming using hydrogen in the olefin production unit10, the reforming device21may be configured to produce hydrogen by reforming natural gas (source gas). In other words, although not depicted, a pipe connecting a supply system of natural gas and the reforming device21may be provided, and the reforming may be performed using natural gas supplied through the pipe. Thus, since hydrogen can be obtained directly from the source gas by the reforming device21, it is possible to easily obtain hydrogen.

Further, although in the above example, the reforming device21is supplied with carbon dioxide in the olefin production unit10, in addition to or instead of the reforming device21, the methanol production device22may be directly supplied with carbon dioxide in the olefin production unit10. In this case, the methanol production device22produces methanol from hydrogen produced by the reforming device21and carbon dioxide recovered by the carbon dioxide recovery device2. Further, in the reforming device21, 1 mol of carbon monoxide and 3 mol of hydrogen are produced from 1 mol of methane and 1 mol of water.

Further, although in the above example, the reforming device21is supplied with carbon monoxide in the olefin production unit10, if the reforming device21is separately supplied with methane, in addition to or instead of the reforming device21, the methanol production device22may be directly supplied with carbon monoxide in the olefin production unit10.

FIG. 2is a flowchart of an olefin and methanol co-production method according to an embodiment of the present invention (hereinafter, also simply referred to as “co-production method according to an embodiment”). Since this flowchart is performed in the co-production plant100,FIG. 2will be described with reference toFIG. 1as appropriate. Also, this flowchart is performed with the above control device.

The co-production method according to this embodiment includes an OCM reaction step S1(partial oxidative coupling step), a reforming step S2, and a methanol production step S3. However, other steps such as a methanation step and a separation step may also be included, if necessary.

In the OCM reaction step S1, an olefin is produced by OCM reaction (partial oxidative coupling reaction) of methane contained in natural gas (source gas). The OCM reaction step S1is performed in the OCM reaction device6. The olefin produced in the OCM reaction step S1is taken out of the co-production plant100.

Methane used in the OCM reaction step S1includes methane contained in natural gas and methane produced by the methanation device5. Further, methane used in the OCM reaction device6includes methane that is first supplied to the OCM reaction device6, but does not react and is discharged from the OCM reaction device6and returned through the carbon dioxide recovery device2, the dehumidification device3, the separation device4, and the methanation device5. Thus, in the OCM reaction step S1, the OCM reaction is performed using methane in the olefin production unit10.

OCM reaction conditions may be the reaction conditions described above regarding the OCM reaction device6.

In the reforming step S2, hydrogen is produced by reforming reaction of methane. The reforming step S2is performed in the reforming device21. In the reforming step S2, steam reforming of methane is performed using a gas (containing methane, hydrogen, carbon monoxide, etc.) discharged from the separation device4and carbon dioxide recovered by the carbon dioxide recovery device2. The reforming produces a gas containing hydrogen, carbon monoxide, and carbon dioxide. Specific reaction mechanism and reaction conditions are the same as those described above regarding the reforming device21.

In the methanol production step S3, methanol is produced from hydrogen produced in the reforming step S2and carbon monoxide and carbon dioxide (including unreacted carbon monoxide and carbon dioxide) produced in the reforming step S2. Specific reaction conditions are the same as those described above regarding the reforming device21. The methanol produced in the methanol production step S3is taken out of the co-production plant100.

According to the co-production method described above, olefins can be produced directly from methane contained in natural gas by the OCM reaction (partial oxidative coupling), not via methanol as an intermediate product. Thus, it is possible to reduce energy consumed for producing olefins. Further, since methanol can be produced from a carbon oxide gas in the OCM reaction step S1, it is possible to reduce the emission amount of the carbon oxide gas such as carbon monoxide and carbon dioxide. Further, since methanol can be produced from carbon derived from the source gas used for producing olefins, it is unnecessary to separately prepare the source for methanol production from outside. Thus, it is possible to reduce the production cost of methanol.

Although in the above example, the carbon oxide gas in the OCM reaction step S1is used for reaction in the reforming step S2, the carbon oxide gas in the OCM reaction step S1may be used for the reaction in the methanol production step S3. Thus, in the methanol production step S3, methanol can be produced from hydrogen obtained in the reforming step S2and the carbon oxide gas in the OCM reaction step S1. In addition, the carbon oxide gas in the OCM reaction process S1can be used for both reactions in the reforming step S2and the methanol production step S3.

FIG. 3is a system diagram of an olefin and methanol co-production plant101according to a second embodiment of the present invention. In the following description, points different from the co-production plant100shown inFIG. 1will be mainly described, and points common to the co-production plant100will not be described for simplification of description.

In the co-production plant101, the methanol production unit20includes a combustion device24for combusting natural gas (fuel) to generate heat used for reforming in the reforming device21. The methanol production device22is configured to produce methanol from a carbon oxide gas produced by the combustion device24. The carbon oxide gas in this context includes carbon dioxide produced by full combustion, and carbon monoxide produced by incomplete combustion.

With the combustion device24, at least one of the methane reforming or the methanol production can be performed using the carbon oxide gas produced by the combustion device24while using heat generated by the combustion device24in the reforming device21. Further, the amount of the carbon oxide gas supplied from the olefin production unit10to the methanol production unit20can be reduced. As a result, even if the production amount of the carbon oxide gas is reduced to increase the yield of olefins in the olefin production unit10, it is possible to cover the amount of the carbon oxide gas including carbon dioxide required by the methanol production unit20.

In the example shown inFIG. 3, as with the co-production plant100, the methanol production device22can produce methanol by reaction with carbon dioxide in the olefin production unit10. In addition, both the reforming device21and the methanol production device22can perform reaction with carbon dioxide in the olefin production unit10.

FIG. 4is a system diagram of an olefin and methanol co-production plant102according to a third embodiment of the present invention. In the following description, points different from the co-production plant100shown inFIG. 1will be mainly described, and points common to the co-production plant100will not be described for simplification of description.

In the co-production plant102, the entire amount of carbon dioxide recovered by the carbon dioxide recovery device2is supplied to the reforming device21. In other words, in the co-production plant102, unlike the co-production plant100, carbon dioxide recovered by the carbon dioxide recovery device2is not supplied to the methanation device5.

Thus, the entire amount of carbon dioxide in the olefin production unit10is supplied to the reforming device21, so that the production amount of carbon monoxide and hydrogen according to the above equation (1) can be increased. Consequently, it is possible to increase the production amount of methanol in the methanol production device22, and it is possible to increase the production amount of methanol in the co-production plant102.

In the example shown inFIG. 4, as with the co-production plant100, the methanol production device22can produce methanol by reaction with carbon dioxide in the olefin production unit10. In addition, both the reforming device21and the methanol production device22can perform reaction with carbon dioxide in the olefin production unit10.

FIG. 5is a system diagram of an olefin and methanol co-production plant103according to a fourth embodiment of the present invention. In the following description, points different from the co-production plant100shown inFIG. 1will be mainly described, and points common to the co-production plant100will not be described for simplification of description.

In the co-production plant103, a gas between the methanation device5and the OCM reaction device6is supplied to the reforming device21. In other words, although in the co-production plant100, the gas before methanation by the methanation device5is supplied to the reforming device21, in the co-production plant103shown inFIG. 5, the gas after methanation is supplied to the reforming device21. Thus, the reforming device21is configured to produce hydrogen from methane produced by the methanation device5.

Accordingly, the concentration of methane is increased by the methanation device5, and the amount of methane supplied to the reforming device21is increased. Thus, it is possible to enhance the reforming reaction, and it is possible to increase the production amount of hydrogen. Further, since the production amount of hydrogen is increased, it is possible to increase the production amount of methanol. Moreover, by methanizing carbon monoxide, which is a carbon oxide gas that does not contribute to production of olefin, it is possible to reduce the emission of carbon monoxide, and to make effective use of carbon monoxide. Furthermore, by methanizing carbon dioxide of the carbon oxide gas, even if there is carbon dioxide in an amount that cannot be used in the methanol production unit20, carbon dioxide can be converted to methane and used for reforming.

In the example shown inFIG. 5, as with the co-production plant100, the methanol production device22can produce methanol by reaction with carbon dioxide in the olefin production unit10. In addition, both the reforming device21and the methanol production device22can perform reaction with carbon dioxide in the olefin production unit10.

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