JPH0732859B2 - Method for producing mixed gas for synthesis - Google Patents

Description

Detailed Description of the Invention a. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a mixed gas for synthesis consisting of H ₂ and CO from a steam reforming gas of a hydrocarbon, in particular, a mixed gas for synthesis to be subjected to an oxo reaction.

Conventional technology The steam reforming method uses hydrocarbons such as natural gas (main component: methane), LPG, and naphtha as raw materials to react with steam on a nickel catalyst to make H _{2 the} main component, and other CO, CO ₂ It is a method of changing to gas consisting of.

In the case of butane as an example, the reaction formula is C ₄ H ₁₀ ＋ 4H ₂ O → 4CO ＋ 9H ₂ (1) In this case, the following reactions also occur and C ₄ H ₁₀ ＋ 8H ₂ O → 4CO ₂ ＋ 13H ₂ (2) CO + H ₂ OCO ₂ + H ₂ (3) CO + 3H ₂ CH ₄ + H ₂ O (4) CO ₂ + 4H ₂ CH ₄ + 2H ₂ O (5) CO ₂ and methane are also by-produced.

Therefore, in order to obtain a mixed gas for synthesis consisting only of CO and H ₂ , the reforming reaction temperature is raised (4), the reaction of (5) proceeds to the left to reduce methane, and then CO ₂ is removed. Must.

In order to adjust the H ₂ / CO ratio, CO ₂ in the reformed gas is conventionally absorbed and removed by an absorbing solution, and the CO ₂ generated during regeneration of the absorbing solution is recycled to the reforming reactor. .

For example, in the mixed gas manufacturing process for oxo synthesis, an alkaline absorption liquid such as monoethanolamine is used to absorb CO ₂ , but this method requires a large amount of heat energy to regenerate the absorption liquid, and the absorption liquid is circulated. There are problems that the amount is large, the apparatus is expensive, and there are many corrosion troubles.

Further, in order to allow the reactions of the above formulas (4) and (5) to proceed to the left and reduce the amount of methane, the ratio of steam to hydrocarbon in the steam reforming reaction must be made larger than the stoichiometric ratio and at a high temperature.

An object of the present invention is to provide a method for producing a mixed gas for synthesis that solves the above problems.

B. Means for Solving the Problems A method for producing a mixed gas for synthesis according to the present invention is a mixed gas for synthesis comprising H ₂ and CO by removing CO ₂ from the reformed gas after steam reforming a hydrocarbon. a method of obtaining a steam reformed gas pressurized with CO ₂ adsorption to the adsorbent the filled with CO ₂ passed through the adsorption tower is adsorbed on the adsorbent H ₂ and CO leaked was synthesized gas mixture The adsorption tower is switched before CO ₂ leaks from the adsorption tower or when a small amount leaks, and the adsorption of CO ₂ is continued in a different adsorption tower and the pressure of the used adsorption tower is reduced to hydrogen gas or hydrogen-CO. It is characterized in that a mixed gas is introduced to regenerate the adsorbent, and CO ₂ is supplied from the outside of the system to the steam reforming reactor together with the gas flowing out during the pressure reduction and regeneration.

As the raw material hydrocarbons used in the steam reforming process, hydrocarbons such as natural gas (mainly composed of methane), LPG and naphtha are used.

The present invention will be described in detail below with reference to the attached FIG. 1, but the embodiment of the present invention is not limited to FIG.

After the hydrocarbon raw material 1 and hydrogen 2 are mixed and heated in the heating furnace 3, the sulfur compound in the raw material is hydrocracked in the hydrodesulfurization tower 4, and the produced hydrogen sulfide is adsorbed and desulfurized. The desulfurized raw material is introduced into the high temperature steam reforming reactor 5 together with the steam from the steam generator 15 to carry out the steam reforming reaction as represented by the above formulas (1) to (5).

The produced gas is cooled by a cooler 6 to separate condensed water,
Adsorption tower 8A packed with an adsorbent for adsorbing CO _2, 8B, and introduced into one of 8C, the CO ₂ was drained of H ₂ and CO from the top of the adsorption tower is adsorbed on the adsorbent, the buffer tank 9 After that, a mixed gas for synthesis 10 is obtained. The gas flowing out in the adsorption process becomes hydrogen at first and then becomes a mixture of hydrogen and CO, and the composition fluctuates.
To provide.

Regarding the operating conditions such as the type and temperature of the steam reforming catalyst, pressure, steam / carbon ratio, etc., the conditions used in the prior art,
That is, the temperature is 750 ° C to 850 ° C, the pressure is 30 Kg / cm ₂ G, water vapor /
Conditions such as a carbon ratio of 2.0 to 4.5 mol / atom and a CO ₂ / C ratio of 0 to 4.5 mol / atom may be used, but when the raw material is LPG or naphtha, low temperature steam reforming is performed before the high temperature steam reforming reactor. A reactor is installed, and the raw materials are preliminarily CH ₄ and H 2 in the low temperature steam reforming reactor.
₂ , when CO, CO ₂ and then CO ₂ is added for high temperature reforming, low temperature reforming reaction conditions are 400 ℃ ~ 500 ℃, pressure ~ 30 Kg / c
m ² G, steam / carbon ratio 1.5 to 2.5 mol / atom, high temperature reforming steam / carbon ratio 2.4 to 4.5 mol / atom, CO ₂ /
It is also possible to operate with a C ratio of 2.0 to 4.5 mol / atom.

Activated alumina (dehumidification) as the adsorbent used in the adsorption tower
And it is better to use activated carbon (CO ₂ removal).

When adsorption operation is performed, CO ₂ leaks from the top of the adsorption tower, but the adsorption tower is switched immediately before or when a small amount leaks, and CO ₂ adsorption is continued in a different adsorption tower to continue mixing for synthesis. When gas is obtained, the pressure of the used adsorption tower is reduced and hydrogen gas or hydrogen / CO mixed gas is introduced to regenerate the adsorbent.

The hydrogen gas or hydrogen-CO mixed gas for regeneration is introduced into the adsorption tower from above the adsorption tower, and the gas (H ₂ , CO, CO ₂ ) flowing out from below the adsorption tower is the buffer tank 12 and the compressor 13. And is recycled to the high temperature steam reforming furnace 5. Since the composition and amount of the gas flowing out at the time of regeneration and regeneration of the pressure in the adsorption tower also vary, the buffer tank 12 is provided to average the composition and amount of the recycled gas.

Hydrogen for regenerating the adsorbent may be introduced from outside the system, but a portion of the purified high-purity hydrogen in the early stage of the adsorption process may be transferred to the high-purity hydrogen tank 11.
It is good to store it in and use it.

Adsorption of three or more adsorption towers, adsorption (transfer pressure), depressurization, regeneration,
(Transfer pressure) and boosting should be performed in sequence.

The CO ₂ was absorbed, the operating conditions of the adsorption tower suitable to leakage of H ₂ and CO, depending on the kind of the adsorbent, pressure 5-30
Kg / cm ² G is suitable.

The steam used in the high temperature steam reforming reactor 5 may also be introduced from outside the system, but as shown in FIG. 1, the water in the boiler 15 is heated by the residual heat of the heating furnace 14 of the high temperature steam reforming reactor 5. Then
High temperature steam reforming reactor 5 by further heating the generated steam
It is most effective in terms of heat economy.

CO _{2 in} the gas recycled to the high temperature steam reforming reactor
Is (1), (2), together with steam and raw hydrocarbons.
H ₂ is produced by the reactions of (3), (4), (5) and (6) below.
Becomes CO.

C ₄ H ₁₀ ＋ 4CO ₂ → 8CO ＋ 5H ₂ (6) In this way, CO ₂ is not released to the outside of the system, but all can be converted to CO.

The H ₂ / CO ratio in the obtained mixed gas for synthesis is governed by the H / C ratio in the raw material hydrocarbon.

When the raw material hydrocarbon is represented by CH _X, it becomes CH _X + H ₂ O → CO + (1 + 1/2 _X ) H ₂ , and the H ₂ / CO ratio is (1 + 1/2 _X ), which is always greater than 1.

The value of H ₂ / CO is 3.0 when the raw material is methane and 2.
5, 2.33 for propane and 2.25 for butane.

Therefore, when the ratio of H ₂ / CO is set to a smaller value, for example, when producing a mixed gas for oxo synthesis with a H ₂ / CO value of around 1.0, the amount of the steam reforming reactor required outside the system When CO _{2 is} introduced, the reaction of CH _X + CO ₂ → 2CO + 1/2 _X H ₂ , for example, in the case of butane, the reaction of C ₄ H ₁₀ + 4CO ₂ → 8CO + 5H ₂ (6) (H ₂ / CO ratio = 5/8 ) With the reaction of formula (1). In this way, a mixture gas for synthesis having an arbitrary H ₂ / CO ratio is obtained by adjusting the ratio of steam introduced into the steam reforming reactor and CO ₂ introduced from outside the system according to the type of raw material. be able to.

C. EFFECTS OF THE INVENTION Compared with the conventional method of absorbing and removing CO ₂ in the reformed gas with an absorbing liquid, there are the following advantages.

No heat energy is required to regenerate the absorbing liquid.

There is no need for a pump and kinetic energy for circulating the absorbent.

There is no corrosion trouble due to the alkaline absorbent.

Since no absorbent is used, there are no operational management problems such as loading, flooding and forming.

[Brief description of drawings]

FIG. 1 is a process chart for specifically explaining an embodiment of the present invention.

Claims (3)

[Claims] 1. From a reformed gas after steam reforming a hydrocarbon
In the method of removing CO ₂ to obtain a mixed gas for synthesis consisting of H ₂ and CO, the steam-reformed gas is subjected to CO ₂ under pressure.
CO ₂ is adsorbed through an adsorption tower filled with an adsorbent that adsorbs H ₂ and CO is leaked to obtain a mixed gas for synthesis, and before the CO ₂ leaks from the adsorption tower or when a small amount leaks. Switch the adsorption tower with, continue adsorbing CO _{2 in} a different adsorption tower, depressurize the used adsorption tower and introduce hydrogen gas or hydrogen-CO mixed gas to regenerate the adsorbent. A method for producing a mixed gas for synthesis, characterized in that CO ₂ is supplied to the steam reforming reactor from the outside together with the gas flowing out. 2. The method for producing a mixed gas for synthesis according to claim 1, which is carried out by sequentially switching three or more adsorption towers. 3. The synthesis according to claim 1, wherein the high-purity hydrogen gas or hydrogen-CO mixed gas in the initial stage of the adsorption step is used as it is or after being temporarily stored and then used as a regeneration gas for a used adsorption tower. Method for mixed gas production.