JP2000219508A - Production of co from off-gas in hydrogen pressure swing adsorption (psa) - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing carbon monoxide (CO) from an off-gas in hydrogen (H2)-pressure swing adsorption(PSA) by converting carbon dioxide (CO2) contained in the off-gas in the H2-PSA to CO to be recovered. SOLUTION: The method is the one for producing CO from the off-gas 8 containing CO2 and H2 discharged from H2-PSA process for separating and recovering H2 6 by introducing a reformed gas 4 produced by reforming a hydrocarbon 1 into a PSA device 7 and separating and recovering CO by using the PSA device after catalytically reducing CO2 contained in the off-gas 8 with H2 in the presence of a reverse CO shift catalyst at 500-850 deg.C to generate CO and steam (H2O) and cooling the generated gas to remove steam as condensed water.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing CO from hydrogen PSA off-gas, and more particularly to a method for producing CO from hydrogen PSA.
The present invention relates to a method for producing CO from an off-gas of hydrogen PSA, wherein the CO ₂ contained in the off-gas is shifted to CO and then separated.

[0002]

2. Description of the Related Art CO is useful as a raw material for plastics such as polycarbonate and polyurethane or acetic acid. If this CO can be produced from off-gas discharged from various processes, it is considered to be an effective technology for suppressing the generation of CO ₂ , which is a substance causing global warming.

[0003] Conventionally, H ₂ , CO, and C obtained by reforming hydrocarbons by steam reforming have been used.
A pressure swing adsorption (PSA) method is used as a method for separating and recovering hydrogen from a mixed gas containing O ₂ , methane (CH ₄ ), and the like. This process is based on hydrogen (H ₂ ) -PS
Called A. Offgas of such H _2-PSA has been conventionally incinerated as an auxiliary fuel such as a steam reformer.

[0004]

However, H_Two−
The PSA off-gas is generally H_TwoAnd CO_TwoWith the main component
And H_Two: 40% to 60%, CO_Two: 40-50%, C
O: 5% to 10%, CH _Four: Mixing consisting of 5% to 10%
Gas and H_TwoAnd CO_TwoIs usually 1 to 1.5
It is. Therefore, this off-gas as it is as fuel
Consumption is a waste of resources and the above-mentioned offgas is effective.
The development of the technology to be used was desired.

[0005] The object of the present invention is to meet the above-mentioned demand and to provide H _2-
Without performing significant modification of such existing steam reformer in PSA, by effectively utilizing the off-gas, the CO ₂ contained in the off-gas can be recovered by converting the CO, CO from the offgas of H _2-PSA It is to provide a manufacturing method.

[0006]

Means for Solving the Problems To solve the above problems, the present inventor has proposed that H ₂ and C _{2 in} the off gas of H ₂ -PSA be used.
Focusing on the mixing ratio with O ₂ , as a result of intensive research, H ₂ and C
The off-gas of H ₂ -PSA having a mixing ratio of O ₂ of about 1 to 1.5 is a convenient gas for generating CO by water gas denaturation (reverse CO shift reaction), and the CO ₂ contained in the off-gas is used. From 500 to 8 in the presence of a reverse CO shift catalyst
The mixture is heated to 50 ° C. and catalytically reduced by H ₂ contained in the off-gas to produce CO and water vapor (H ₂ O). The produced gas is cooled to separate water vapor as condensed water. It has been found that high-purity CO can be obtained by separating and recovering, and the present invention has been achieved.

That is, the invention claimed in the present application is as follows. (1) Pressure-reducing adsorption of reformed gas obtained by reforming hydrocarbons (P
SA) Separating and recovering hydrogen (H ₂ ) by introducing into the apparatus,
Carbon dioxide (CO2) emitted from the hydrogen PSA process
₂ ) producing carbon monoxide (CO) from an off-gas containing H ₂ , wherein CO ₂ contained in the off-gas is converted to H ₂ at 500 to 850 ° C. in the presence of a reverse CO shift catalyst.
To produce CO and water vapor (H ₂ O) in a catalytic manner, cool the produced gas to separate the water vapor as condensed water, and then separate and recover CO.
A method for producing CO from off-gas of hydrogen PSA.

(2) As the reverse CO shift catalyst, a catalyst containing Fe and Cr as active components or activated alumina (A
( ₂ ) using a catalyst containing (L ₂ O ₃ ) as an active component.
How to manufacture. (3) CO is produced from hydrogen PSA offgas as described in (1) or (2) above, wherein the reaction of catalytically reducing CO ₂ with H ₂ is performed at a pressure of 1 atm to 20 atm. Method. (4) The method of separating and recovering CO from a product gas obtained by separating water vapor as condensed water is pressure fluctuation adsorption (PSA).
The method for producing CO from off-gas of hydrogen PSA according to any one of the above (1) to (3), which is a method.

In the present invention, H ₂ -PSA means hydrogen separated from a mixed gas containing H ₂ , CO, CO ₂ , CH _4, etc. obtained by reforming a hydrocarbon by a pressure swing adsorption (PSA) method. , A method or process of collecting. Examples of the hydrocarbon source include naphtha, raffinate, LPG,
Natural gas and the like are used, and as a hydrocarbon reforming method,
An example is steam reforming. Steam reforming is a process in which the hydrocarbon source is supplied to a reaction tube having a heating means and brought into contact with steam in the presence of a reforming catalyst to convert the hydrocarbon into H ₂ , CO, CO ₂ ,
It refers to reforming into a mixed gas containing CH _{4 and the} like.

In the pressure fluctuation adsorption (PSA) method, a mixed gas is introduced into a plurality of adsorption towers filled with an adsorbent such as activated carbon, and for example, an adsorption step, a pressure reduction step, a purge step, a pressure increase step, etc. are repeated according to a time sequence. A gas separation method that separates components that are easily adsorbed by an adsorbent from components that are hardly adsorbed in a mixed gas by pressure fluctuation adsorption (PS
A) Apparatus refers to an apparatus for performing the method.

In the present invention, the reverse CO shift catalyst is
A catalyst for promoting a reverse CO shift reaction represented by the following formula (1). _{CO 2 + H 2 → CO +} H 2 O ΔH 0 298K = 9.6kcal / mol ... (1) where, [Delta] H ⁰ _298K is the standard heat of formation at 25 ° C..

That is, the present invention provides a water-based gas represented by the following formula (2), wherein a water-containing gas or other CO-containing gas is reacted with water vapor to convert CO in the gas into H ₂ and CO _2. The reaction utilizes the denaturation, and promotes the reaction (reverse CO shift reaction) from the right side to the left side in the equation (2) to thereby reduce the CO ₂ contained in the H ₂ -PSA off-gas.
To CO, which is separated and recovered. In the present invention, the reaction from left to right in equation (2) is called a CO shift reaction, and the reaction from right to left is called an inverse CO shift reaction.

CO + H ₂ O = H ₂ + CO ₂ (2) The reverse CO shift reaction is an endothermic reaction, but the reaction heat is small, and the necessary endothermic amount is 1 compared to the steam reforming and the CO ₂ reforming reactions. / 3 to 1/4. Therefore, the reactor does not require a large heating furnace unlike a reformer, and a normal catalyst packed bed reactor can be used.

In the present invention, as the reverse CO shift catalyst, for example, a catalyst containing Fe and Cr as active components and a catalyst containing activated alumina (Al ₂ O ₃ ) as active components are used. The reverse CO shift catalyst is, for example, a fine powder of Fe ₂ O ₃
fines r ₂ O ₃ added and mixed 5 to 10 wt%, wet, for example, formed into 2 mm × 10 mm, was calcined for 6 hours at 800 ° C. or more, and the pellets.

When the reaction between CO ₂ and H ₂ in the off-gas is carried out in the presence of such a reverse CO shift catalyst, CO ₂
Is converted only into CO, CH ₄ does not generate almost.
Therefore, at a relatively low temperature of 500 ° C to 700 ° C, CO ₂
Can be converted to CO, and C
The burden on the O purification step is reduced.

In the present invention, formation of a reverse CO shift reaction
Unreacted CO from gas_TwoAnd CH _FourTo remove CO
As a method of separation and recovery, components with intermediate adsorption power
It is preferable to employ a PSA method for separation and concentration.

[0017]

Next, the present invention will be described in more detail by way of examples. FIG. 1 shows the H ₂ -PSA according to the present invention.
FIG. 2 is a system diagram of a two-column PSA device used as the PSA device 12 in FIG.

In FIG. 1, the device is a hydrocarbon source.
For example, a naphtha 1 is brought into contact with and reacts with steam 2.
And a reforming furnace (steam reformer) 3 for reforming by steam.
CO in reformed gas 4 generated by team reformer 3
And H_TwoO to H_TwoAnd CO_TwoShift reaction to shift to
From the mixed gas at the outlet of the CO shift reactor 5 _Two
To separate and recover H_TwoH having a PSA device 7_Two−
A PSA process and the H_Two-Discharged from the PSA device 7
A heater 9 for heating the off-gas 8 to be heated,
CO in step 8_TwoTo H_TwoReverse to reduce to CO with
CO shift reactor 10 and the reverse CO shift reactor 10
Outlet product gas and H_Two-Off gas at the outlet of PSA device 7
Heat exchanger 11 for exchanging heat with the heat exchanger 8 and gas generated after the heat exchange
PSA device 12 for separating and recovering CO from water
Mainly from the CO-PSA device 13 for purifying CO
It is configured.

In FIG. 2, the PSA device 12 comprises:
It is mainly composed of adsorption towers A and B, buffer tanks 31 and 32 for storing various component gases, vacuum pump 29, piping groups 22 to 28 connecting these, and valve groups provided in these pipings. . In FIG. 1, 6 is H ₂ , 14 is CO, 15
Is the off-gas of the PSA device 12, 16 is the hot gas, 1
7 is steam (H ₂ O).

In such a configuration, the naphtha 1, which is a hydrocarbon source, is introduced into the steam reformer 3 together with the steam 2, and is supplied to a reforming catalyst such as alumina based on N 2.
In the presence of a catalyst supporting i, for example, the reaction is carried out at 860 ° C. to form a reformed gas 4 comprising a mixture of H ₂ , CO ₂ , CO, CH _{4 and the} like. The reformed gas 4 flows into a CO shift reactor 5 where a CO shift catalyst, such as C
u and Zn catalysts at 280 ° C. and 18 atm.
₂ O is transformed into H ₂ and CO ₂ . Mixed gas containing the produced H ₂ flows into H _2-PSA device 7 on the downstream, high purity, for example, with a purity of 99.999% H ₂ separation, is recovered, the off-gas 8 is discharged. Off gas 8
For example, at 30 ° C., the reverse CO shift reactor 10
After exchanging heat with the outlet gas and elevating the temperature to, for example, 350 ° C., it flows into, for example, a heat exchanger 9 installed in a convection heat transfer section of a steam reformer, where the high-temperature gas 16 is heated to, for example, 840 ° C. The temperature is raised. Heated off-gas 8
Flows into a reverse CO shift reactor 10 filled with a reverse CO shift catalyst containing, for example, Fe and Cr as a main component, where CO ₂ contained in the off-gas 8 is reduced by H ₂ to form CO and H ₂ O. Is generated. The generated gas containing the generated CO, for example, at 700 ° C., flows into the heat exchanger 11, where it exchanges heat with the off-gas of the H ₂ -PSA device 7 to be rapidly cooled to, for example, 30 ° C. After separation, P filled with an adsorbent, for example, an activated carbon-based adsorbent
It flows into the SA device 12, where the unreacted CO ₂ and CH _{4 and the} like are removed by the PSA method including the adsorption step, the pressure reduction step, the purge step, and the pressure increase step to recover high-concentration CO. The obtained CO gas is CO-P for downstream CO purification.
It flows into the SA device 13, where it is purified, for example, with a purity of 9
CO becomes 9% or more.

Next, referring to FIG.
A method of separating and recovering CO will be described. Reverse C of FIG.
The product gas flowing out of the O-shift reactor 10 contains moisture.
After being separated, the PSA device 12
It flows into the adsorption tower A, and the adsorbent in the tower, for example, activated carbon-based adsorption
CO, CH_Four, CO_TwoAnd H_TwoO adsorbs and H _Two
Flows out through the pipe 22 and is collected in the buffer tank 31.
(Adsorption step). Next, the outflowing CO and H_TwoBlend of
The joint gas is sent to the CO-PSA via lines 22 and 23,
Purified to high purity CO. Next, the vacuum pump 29 is started.
And mainly CO_Two, CH_FourGas containing a large amount of
It is discharged from 4. This mixed gas passes through line 25
It is recycled to 21 raw material feed gases. Next, suck
H recovered in the loading process_TwoA part of the gas is
Is supplied through the pipe 26 in the direction opposite to the row,
CO adsorbed on_Two, CH_FourAnd residual H_TwoO is a tube
Desorbed and removed via paths 24 and 27, for example, with fuel gas
(Purge step). Next, the purging step
After the completion, the inside of the adsorption tower A is recovered by a predetermined valve operation.
H_TwoThe pressure is increased by a part of the gas (pressure increase step). adsorption
The same operation is performed in the column B, and in the latter half of the adsorption step,
50-70% of CO separated and recovered by
O-purified CO-PSA unit 13 (Fig. 1)
In a manner as described above, for example, to obtain CO having a purity of 99.0%.
You.

In the present embodiment, high purity (purity: 99.999%) H ₂ was reduced to 1000 by steam reforming.
When manufactured at 0 Nm ² / Hr, the flow rate of the off gas 8 of the H ₂ -PSA 7 is 6704 Nm ³ / Hr, and the flow rate of the generated gas at the outlet of the reverse CO shift reactor 10 is 6034 Nm ³ / H.
r, the CO flow rate at the exit of the product CO-PSA device 13 is:
1420 Nm ² / Hr (purity 99%), PSA device 12
Was 4614 Nm ³ / Hr.

Table 1 shows the gas balance in this embodiment.

[Table 1] Table 1 shows that according to this example, high-concentration CO having a purity of 99% can be efficiently produced. According to the present embodiment, about half of the CO ₂ conventionally released into the atmosphere is reduced to C
It can be recovered as O.

In this embodiment, the heat source of the heat exchanger 9 includes the off-gas 15 of the PSA device 12 for recovering CO,
Reformer combustion gases or hot process gases can be used. Exhaust gas from a large boiler or exhaust gas from a heating furnace in another process can also be used. PSA device 1
2 is a mixed gas of CO ₂ and H ₂ ,
It is also possible to recycle and use it as a part of the raw material gas.

In this embodiment, P is obtained by separating condensed water.
The gas composition of the gas at the inlet of the SA device 12 is H ₂ : 30.4
%, CO ₂ : 24.5%, CO: 32.5%, CH ₄ :
This was 12.6%, and 46% of the CO ₂ supplied to the reverse CO shift reactor 10 was converted to CO.

In the present embodiment, the CO-PSA apparatus is an apparatus for purifying CO recovered by the PSA apparatus 12, and each component is separated according to the PSA apparatus 12. The off-gas of the CO-PSA device 13 is mainly composed of H ₂ , and can be used as, for example, a purge gas of the PSA device 12, or can be recovered together with CO ₂ and recycled as a raw material.

In this embodiment, the CO-PSA device 13 for CO purification is provided downstream of the PSA device 12, but depending on the target CO concentration, the CO-PSA device for CO purification may be used.
The device may be omitted. Example 2 In the apparatus of FIG. 1, the heating furnace of the steam reformer 3 was modified and nine reaction tubes were added near the wall of the furnace (28 before modification) to form a heater 9 and a reverse CO shift reactor 10 When CO was produced from H ₂ -PSA off-gas in the same manner as in Example 1 except that the reaction tube of the heater 9 was filled with activated alumina as a reverse CO shift catalyst instead of % CO is 2365 Nm ² / Hr
Was obtained.

At this time, the temperature at the outlet of the reaction tube is 800 ° C.
The generated gas flow rate was 7085 Nm ² / Hr, the gas composition was H ₂ : 40.7%, CO ₂ : 13.5%, CO: 42.
4%, CH ₄ : 3.4%, and 62% of CO ₂ contained in the off-gas 8 was converted to CO.

Table 2 shows the gas balance in Example 2.

[Table 2] Table 2 shows that high-concentration CO having a purity of 99% was efficiently produced also in this example.

[0030]

According to the first aspect of the present invention, CO ₂ in off-gas discharged from a hydrogen PSA process is reduced with H ₂ in the presence of a reverse CO shift catalyst, thereby reducing CO ₂ at a relatively low temperature. , CH ₄ can be converted to CO ₂ without producing CH ₄ , so that high-purity CO can be efficiently produced using the off-gas of the H ₂ -PSA process. Also, since the amount of heat required for the reverse CO shift reaction is relatively small, the reaction can proceed with the heat of the reactants themselves, so a simple gas heat exchanger and a reactor filled with catalyst can be used without reformer modification. CO can be produced from off-gas of H ₂ -PSA.

According to the invention described in claim 2 of the present application, the inverse C
C with Fe and Cr as active components as O shift catalyst
By using an O shift catalyst or a CO shift catalyst containing activated alumina (Al ₂ O ₃ ) as an active component, in addition to the effects of the present invention, the efficiency of CO ₂ conversion into CO is improved, and
O can be produced more efficiently.

According to the invention of claim 3 of the present application, the reaction pressure is set to 1 atm to 20 atm, so that C
Separation and recovery of O are facilitated, and CO can be produced more efficiently.

According to the invention of claim 4, wherein the separation of CO from the product gas, a method of recovering, by which a pressure swing adsorption (PSA) process, in addition to the effect of the invention, excess H ₂ And CO can be efficiently separated and recovered.

[Brief description of the drawings]

FIG. 1 is a system diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing a system of the PSA device of FIG.

[Explanation of symbols]

1 ... naphtha, 2 ... steam, 3 ... steam reformer, 4 ... reformed gas, 5 ... CO shift reactor, 6 ... H _2,
7 ... H _2-PSA unit, 8 ... offgas, 9 ... heater, 1
0: reverse CO shift reactor, 11: heat exchanger, 12: PS
A device, 13 ... CO-PSA device, 14 ... CO, 15:
Off, 16 ... hot gas, 17 ... H ₂ O, 21 to 28
... pipe, 29 ... vacuum pump, 31, 32 ... buffer tank.

Continued on the front page (72) Inventor Susumu Shishikura No. 1 Yawata Kaigandori, Ichihara City, Chiba Prefecture Mitsui Engineering & Shipbuilding Co., Ltd. F-term (reference) 4D012 CA20 CB16 CD07 CG01 CH05 CJ02 CK01 4G046 JA04 JB12 JB14 JC05 4G069 BA01A BC49A BC58A CC29

Claims (4)

[Claims] 1. A reformed gas obtained by reforming a hydrocarbon is introduced into a pressure fluctuation adsorption (PSA) device to separate and recover hydrogen (H ₂ ), and carbon dioxide (CO ₂₎ discharged from a hydrogen PSA process is used. ) And H ₂ from off-gas containing carbon monoxide (C
O), wherein CO ₂ contained in the off-gas is converted to 500 ° C. to 850 in the presence of a reverse CO shift catalyst.
℃ in contact reducible by H ₂ CO and water vapor (H
A method for producing CO from off-gas of hydrogen PSA, comprising producing ₂ O), cooling the produced gas and separating the water vapor as condensed water, and then separating and recovering CO. 2. A catalyst containing Fe and Cr as active components or activated alumina (Al ₂
The method for producing CO from off-gas of hydrogen PSA according to claim 1, wherein a catalyst containing O ₃ ) as an active component is used. 3. The method for producing CO from off-gas of hydrogen PSA according to claim 1, wherein the reaction for catalytically reducing CO ₂ with H ₂ is performed at a pressure of 1 atm to 20 atm. . 4. The method according to claim 1, wherein the method of separating and recovering CO from a product gas obtained by separating water vapor as condensed water is a pressure swing adsorption (PSA) method. For producing CO from off-gas of hydrogen PSA.