JPS61141602A - Steam reforming of hydrocarbon - Google Patents

Abstract

PURPOSE:To enable the reduction of the necessary amount of steam in the steam reforming of hydrocarbon using plural reforming reaction zones connected in series, by inserting methanation reaction zone between each reaction zone. CONSTITUTION:The steam supplied from the line 1 and the hydrocarbon supplied from the line 2 are preheated with the heating furnace 4, and transferred to the first reforming reactor 5 to convert the hydrocarbon to reformed gas by the contact with a catalyst. The reformed gas is cooled with the heat-exchanger 6 and methanized in the methanation reactor 7. The gas discharged from the reactor 7 is cooled with the heat-exchanger 8, mixed with the remaining part of the fed hydrocarbon branched from the line 2 to the line 9, and introduced to the second reforming reactor 10. The unreacted steam in the reformed gas discharged from the first reactor 5 and the steam by-produced in the methanation reactor 7 are used as the steam necessary for the second reactor 10.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a hydrocarbon steam reforming method, and more specifically, in a hydrocarbon steam reforming method using a plurality of reforming reaction zones in series, each reaction This invention relates to a hydrocarbon steam reforming method that makes it possible to reduce the amount of steam required by inserting a methanation reaction zone between the zones.

Raw material hydrocarbons such as LPG and naphtha from 300℃ to 550℃
When steam reforming is carried out at a low temperature of about 0.degree. C., it is generally considered necessary to use an excess amount of steam with respect to the raw material hydrocarbon in order to prevent carbon deposition on the reforming catalyst. However, using an excessive amount of steam is undesirable from the economic point of view of the process. In order to improve this inconvenience, a multi-stage steam reforming method is proposed in Japanese Patent Publication No. 44-22413. This multi-stage process typically uses two steam reforming reaction zones, with a portion of the feed hydrocarbon and steam first being fed to a first reaction zone for steam reforming;
Next, the reformed gas flowing out from the first reaction zone is supplied to the second reaction zone together with the remainder of the raw material hydrocarbon for steam reforming, and according to this method, the raw material hydrocarbon is By dividing the supply into the second reaction zone, the overall steam requirement can be reduced compared to a single stage steam reforming method. Also, special public service No. 51-3440
Publication No. 3 describes an alternative method to the multi-stage method, in which a raw material hydrocarbon with a small average molecular weight is supplied together with steam to a first reaction zone, and the reformed gas flowing out from this reaction zone is used as a raw material with a large average molecular weight. A method is taught in which the hydrocarbon and a small amount of steam are fed into the second reaction zone, which also makes it possible to reduce the amount of steam required.

However, in the conventional multi-stage method described above, in the second reaction zone, C in the reformed gas sent from the first reaction zone is
The methanation reaction of O, Co, and the reforming reaction of the newly added raw material hydrocarbon occur simultaneously, and the methanation reaction of 00% CO7 has a large calorific value, so the temperature rises due to these two exothermic reactions. In order to suppress carbon deposition on the reforming catalyst, start from the first reaction zone! l! The amount of unreacted water vapor supplied to the reaction zone 2 must be maintained within a range that can suppress carbon deposition on the reforming catalyst. This means that there is a limit to how much water vapor can be reduced by using the conventional multi-stage method.

The present invention provides a multi-stage steam reforming method for hydrocarbons that can significantly reduce the amount of steam required compared to conventional multi-stage methods. A part of the raw material hydrocarbon and steam are supplied to the first reaction zone of the reforming reaction zone for reforming, and each subsequent reaction zone is supplied with the reformed gas flowing out from the previous reaction zone, and the raw material In the hydrocarbon steam reforming method in which the remainder of the hydrocarbon is divided and supplied, a methanation reaction zone is inserted between each reforming reaction zone, and the reformed gas flowing out from the previous reforming reaction zone is , is characterized in that it is subjected to a methanation reaction in the methanation reaction zone before being supplied to the subsequent reforming zone.

That is, in the method of the present invention, a methanation reaction zone for converting CO1co and '6 methanation in the reformed gas in the previous stage is provided between each reforming reaction zone. By allowing the CO1CO, methanation reaction of the pre-formed reformed gas and the reforming reaction of the raw material hydrocarbon, which were occurring simultaneously in the reformed reaction zone, to occur separately in their own dedicated reaction zones, both reactions can be performed in the same reaction zone. This suppresses the rise in reaction temperature resulting from the simultaneous occurrence of these reactions, making it possible to reduce the amount of steam required for the entire process.

The accompanying drawing is a flow sheet for steam reforming feedstock hydrocarbons using two reforming reaction zones and one methanation reaction zone as one embodiment of the present invention. In the drawing, the steam supplied into the system from line 1 and the feedstock hydrocarbon supplied into the system from line 2 and diverted to line 3 have a steam ratio of approximately 1.0 to 2.0 ( It is defined as the number of moles of water vapor per carbon atom of the feedstock hydrocarbon, and is 8 /
Expressed in C (mol/atom). same as below)
The mixture is mixed and supplied to the heating furnace 4. In the heating furnace 4,
The raw material hydrocarbon and steam preheated to a temperature of about 300 to about 550°C are fed to the first reforming reactor 5, which is typically filled with a nickel-based catalyst, and upon contact with the catalyst, methane, It is converted into a reformed gas consisting of carbon dioxide, -carbon oxide, hydrogen and unreacted water vapor.

The reformed gas flowing out from the reforming reactor 5 is heat-removed by a heat exchanger 6, and then supplied to a methanation reactor 7 filled with a nickel-based catalyst, where it is reformed by contact with the methanation catalyst. co, co in gas.

is CO,+4H,→CH,+2H,0,CO+3)1
．． →CH.

It is methanated like +H20. Then, the gas flowing out from the methanation reactor 7 is heat-removed by a heat exchanger 8, and then mixed with the remainder of the raw material hydrocarbon that is diverted from line 2 to line 9, and is supplied to the 8g2 reforming reactor lO. Ru. Note that the raw material hydrocarbon may be mixed into the methanation reactor effluent on the upstream side of the heat exchanger 8, as shown by the chain line in the drawing.

Like the first reforming reactor 5, the second reforming reactor IO is typically filled with a nickel-based catalyst, and by contacting this catalyst, the raw material supplied from the line 9 is carbonized. Hydrogen is steam reformed and converted into reformed gas. In the second reactor 10, a methanation reaction of the reformed gas generated in the reactor also occurs, but since the reformed gas in the first reforming reactor has already been methanized in the methanation reactor, it generates heat. is relatively minor. The reformed gas flowing out of the second reactor 10 is taken out to the line 11 as a product gas. Second reactor 1
Unreacted water vapor in the reformed gas flowing out from the first reactor 5 and water vapor by-produced in the methanation reactor 7 can be used to produce the water vapor necessary for Needless to say, the amount is sufficient to suppress carbon deposition on the catalyst.

In the illustrated embodiment, the gas flowing out from the first reforming reactor 5 is cooled by the heat exchanger 6, but it is also possible to cool the flowing gas by water injection instead. When this method is adopted, there is an advantage that the steam ratio of the log gas entering the second reforming reactor can be increased. In the illustrated embodiment, the entire amount of steam supplied into the system from line 1 is introduced into the first reforming reactor 5, but a portion of it is introduced into the second reforming reactor 10 as needed. It can also be supplied in parts.

As described above, in the method of the present invention, the reformed gas flowing out from the previous reforming reaction zone is treated in the methanation reaction zone inserted between each reforming reaction zone, and then the reformed gas is used for the subsequent reforming reaction zone. Since it is supplied to the reaction zone, it is possible to suppress the heat generation due to methanation in the subsequent reforming reaction zone. In addition, in the methanation reaction zone of the present invention, there is no need to reform the feedstock hydrocarbon, so the inlet temperature can be lowered to around 250°C, and the outlet temperature can be lowered by that amount. . In the present invention, in order to cause the steam reforming reaction to occur adiabatically, the temperature at the inlet of the reforming reaction zone must be a temperature sufficient to cause the steam reforming reaction to occur adiabatically, and this condition is complied with. In fact, the lower the reforming reaction zone inlet temperature, the lower the risk of carbon deposition on the reforming catalyst. Therefore, being able to lower the methanation reaction zone outlet temperature is preferable in that the steam ratio can be reduced without worrying about carbon deposition on the reforming catalyst. Furthermore, the method of the present invention has the advantage that steam can be produced as a by-product in the methanation reaction zone, and this can contribute to the steam reforming reaction.

Next, the effects of the present invention will be explained in more detail with reference to Examples.

Example 1 Specific gravity 0.58 OL PG (Cs, esHs, am
) Do steam reforming according to the flow shown in the attached drawing. For comparison, the methanation reactor 7 was removed and the
The same amount of LPG was steam-reformed using a flow in which the raw material hydrocarbon was mixed with the effluent from the reforming reactor 5, cooled, and then supplied to the second reforming reactor 10.

The catalyst used in both Examples and Comparative Examples was JP-A-57-24641.
A catalyst prepared by the method of No. 1 was used. Result t-1st
Shown in the table.

(Left below) Comparative Example 1 The conditions of the second reactor were an inlet temperature of 340°C,
After operating for 100 hours at a steam ratio S/C = 0.57 mol/atom, carbon deposition was observed on the catalyst.

Comparative Example 2 The conditions of the second reactor were an inlet temperature of 300°C,
When the reactor was operated for 100 hours at a steam ratio of 8/C w 0.57 mel/atom, no carbon was deposited, but the activity was significantly degraded due to the low temperature.

Example 1 A methanation reactor tube was installed before the second reactor, the reformed gas in the first reactor was first methanated, and the second reactor was operated for 100 hours at an inlet temperature of 340"C. It could be used without carbon deposition.

Example 2 Raw material hydrocarbon was converted into light naphtha (Ce-1) with a specific gravity of 0.71.
aHI! ,. Steam reforming was carried out in exactly the same manner as in Example 1, except that , ) were replaced. The results are shown in Table 2.

(Left below) Comparative Example 3 The conditions of the second reactor were an inlet temperature of 430°C,
When the reactor was operated for 100 hours at a steam ratio of 8/C sw 1.24 mol/atom, carbon deposition was observed on the catalyst.

Comparative Example 4 The conditions of the second reactor were an inlet temperature of 390°C,
When the reactor was operated for 100 hours at a steam ratio of 8/C m 1.24 mo 1/a tom, no carbon was deposited, but the activity was significantly degraded due to the low temperature.

Example 2 A methanation reactor was installed before the second reactor, the reformed gas in the first reactor was first methanated, and the second reactor was operated at an inlet temperature of 430°C for 100 hours. It could be used without precipitation.

As is clear from Tables 1 and 2, when a methanation reactor is provided, water vapor is produced as a by-product. Therefore, the steam ratio of the second reactor is 8/C.
The increase will be 9% in the case of Naphtha and 4% in the case of Naphtha. Therefore, S
/Ct- If maintained at the same level, the feedstock hydrocarbon supply amount can be increased accordingly, and in the method of the present invention, the total steam ratio 8/C is 0.48 in the case of LPG and 0.48 in the case of naphtha. 0.83, 8/C meeting L than the conventional method
It can be reduced by 4% in the case of PG and 1% in the case of naphtha.

[Brief explanation of the drawing]

The drawing shows an example of a flow sheet for carrying out the method of the present invention.

Claims (1)

[Claims] 1. A portion of the raw material hydrocarbon and steam are supplied to the first reaction zone of a plurality of steam reforming reaction zones connected in series for reforming, and each subsequent reaction zone is supplied with the previous reaction zone. In the hydrocarbon steam reforming method, in which the reformed gas flowing out from the gas is supplied and the remainder of the raw material hydrocarbon is divided and supplied, a methanation reaction zone is inserted between each reaction zone. 1. A method for steam reforming hydrocarbons, characterized in that gas flowing out from a first-stage reaction zone is methanated in the methanation reaction zone before being supplied to a second-stage reaction zone.