JP2006199508A - Method for removing carbon monoxide from reformed gas - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method capable of effectively removing carbon monoxide from a reformed gas while preventing the carbon dioxide in the reformed gas from undergoing a hydrogen consumption reaction. <P>SOLUTION: The method is one for removing carbon monoxide from a reformed gas by feeding a feedstock gas comprising hydrocarbons and steam into one end of a reformer comprising an externally heated cylinder, a reformation catalyst packed into the cylinder, and a membrane pipe buried in the reformation catalyst, reforming the fed feedstock gas with the reformation catalyst, and feeding the reformed gas having permeated the membrane pipe and containing hydrogen, a small amount of carbon monoxide, carbon dioxide, etc., into a CO methanator to methanate the carbon monoxide in the reformed gas, wherein the reformed gas is fed into the CO methanator at a space velocity of 2,000 to 4,000h<SP>-1</SP>and is methanated at 190 to 240°C. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an improvement in a method for removing carbon monoxide from a reformed gas that removes carbon monoxide from a reformed gas recovered in a reforming reactor, and more specifically, hydrogen of carbon dioxide in the reformed gas. The present invention relates to a method for removing carbon monoxide from a reformed gas that makes it possible to effectively remove carbon monoxide while suppressing consumption reaction and suppressing an increase in hydrogen consumption.

As is well known, fuel cells have recently attracted attention. As a reforming reactor for supplying hydrogen (H ₂ gas) as a fuel to a fuel cell, a reformed gas generated by steam reforming of hydrocarbons can be used. A membrane reactor that extracts hydrogen using a hydrogen permeable membrane is known. When hydrogen is allowed to permeate through the membrane tube by the hydrogen permeable membrane, a metal film such as a palladium alloy is thinned (for example, about 5 μm) in order to obtain a high permeation rate. It cannot be avoided. For this reason, carbon monoxide, carbon dioxide and methane other than hydrogen enter the membrane tube through the pinhole. Even in the case of an inorganic porous membrane, about 0.1% of carbon monoxide is mixed due to the separation factor.

  In a fuel cell, carbon monoxide becomes a catalyst poison of the catalyst electrode. Therefore, before supplying to the fuel cell, carbon monoxide in the reformed gas mainly composed of hydrogen discharged from the reforming reactor is constant. It is necessary to remove it below the concentration. Therefore, in order to remove carbon monoxide in the reformed gas, hydrogen gas discharged from the reforming reactor is the main component, and reformed gas containing carbon monoxide and carbon dioxide is introduced into the CO methanator. By reacting, carbon monoxide is converted to methane.

  Hereinafter, a typical method for removing carbon monoxide from a reformed gas according to a conventional example in which carbon monoxide is removed by introducing a reformed gas discharged from the reforming reactor into a CO methanator to cause a methanation reaction. A specific example will be described.

First, the carbon monoxide removal method according to Conventional Example 1 uses a ruthenium-based methanation catalyst. More specifically, three types of Ru—K / TiO ₂ (catalyst 1), Ru—K / Al ₂ O ₃ (catalyst 3), and Ru—K / TiO ₂ —Al ₂ O ₃ (catalyst 5) are individually provided. A reformed gas is introduced into each of the CO methanators used in the above so that the space velocity in the CO methanator becomes 10,000 h ^−1, and a methanation reaction is performed at 250 ° C. The composition of the reformed gas, CO; 0.6 volume%, _CO 2; 15 _volume%, H 2 O; 20 _volume%, H 2; 64.4 a% by volume, and CO methanation reaction selectivity (% ) Is calculated by the formula [inlet CO concentration (volume ppm) −outlet CO concentration (volume ppm)] / outlet CH ₄ concentration (volume ppm) × 100, and 83 to 86 are obtained (for example, Patent Document 1). reference).

Next, the carbon monoxide removal method according to Conventional Example 2 will be described with reference to FIG. 4 of the flowchart of the carbon monoxide removal method. That is, methanol and water vapor are introduced into a reformer (corresponding to a reforming reactor) 51 that is heated by exhaust gas sent from the combustor 54 to perform a reforming reaction of methanol. A reformed gas containing approximately 1% carbon monoxide, approximately 22% carbon dioxide, and approximately 10% steam from the reformer 51 is a Ni-based catalyst (the content of Ni is approximately 20% by weight). Is introduced into a carbon monoxide remover 52 (corresponding to a CO methanator) filled with. In this carbon monoxide remover 52, monoxide in the reformed gas is obtained by a methanation reaction while maintaining a reaction temperature range of 240 to 250 ° C. and a space velocity (SV value) of 300 to 500 h ^−1. Carbon is preferentially reacted to reduce the carbon monoxide concentration in the reformed gas to 10 ppm (see, for example, Patent Document 2).
JP 2002-68707 A Japanese Patent No. 2852320

First, in the case of the carbon monoxide removal method according to the conventional example 1, the reformed gas is introduced into the CO methanator so that the space velocity (SV value) is 10,000 h ^−1. Since the methanation reaction is performed at a reaction temperature of 250 ° C., a large amount of reformed gas can be treated. However, since the space velocity (SV value) is too large, a sufficient methanation reaction cannot be performed, and the concentration of carbon monoxide in the reformed gas containing hydrogen as a main component is set to the fuel cell. It is difficult to even make it possible to substantially supply 100 ppm, and there is a problem in the practicality of the carbon monoxide removal method according to Conventional Example 1.

Next, in the case of the carbon monoxide removal method according to Conventional Example 2, since the methanation reaction temperature is high, carbon dioxide also undergoes a methanation reaction (CO ₂ + 4H ₂ → 2H ₂ O + CH ₄ ). In addition to consuming a larger amount of hydrogen than in the case of carbon oxide methanation reaction (CO + 3H ₂ → H ₂ O + CH ₄ ), the space velocity (SV value) is small, so the problem is that the amount of reformed gas processed is small. There is.

  Accordingly, an object of the present invention is to remove carbon monoxide from the reformed gas, which makes it possible to effectively remove carbon monoxide while suppressing hydrogen consumption due to the methanation reaction of carbon dioxide in the reformed gas. Is to provide a method.

The present invention has been made in view of the above circumstances. Therefore, the gist of the carbon monoxide removal method from the reformed gas according to claim 1 of the present invention, which has been adopted in order to solve the above problems, is One end side of a reforming reactor comprising a cylindrical body heated from the side, a reforming catalyst filled in the cylindrical body, and a membrane tube disposed in a state embedded in the reforming catalyst A raw material gas composed of hydrocarbon and water vapor is introduced from the above, and the introduced raw material gas is reformed by the reforming catalyst into a reformed gas composed of hydrogen, carbon monoxide, and carbon dioxide, and hydrogen that has permeated through the membrane tube. In a method for removing carbon monoxide from a reformed gas, which introduces a reformed gas containing carbon monoxide and a small amount of carbon dioxide into a CO methanator, and converts the carbon monoxide in the introduced reformed gas into methane. , The CO methanator Space velocity in the CO methanator is introduced reformed gas so as to 2000~4000h ^-1, it is characterized in that to methanation reaction at 190 to 240 ° C..

Moreover, the gist of the carbon monoxide removal method from the reformed gas according to claim 2 of the present invention adopted in order to solve the above problems is a cylindrical body heated from the outside, and the cylindrical body is filled. A raw material gas composed of hydrocarbons and steam was introduced from one end of a reforming reactor composed of the reformed catalyst and a membrane tube disposed in a state embedded in the reformed catalyst. A reformed gas containing hydrogen, a small amount of carbon monoxide, carbon dioxide, etc., which has been reformed into a reformed gas composed of hydrogen, carbon monoxide and carbon dioxide by the reforming catalyst, and has passed through the membrane tube In the method for removing carbon monoxide from the reformed gas by converting carbon monoxide in the introduced reformed gas into methane, the space velocity in the CO methanator is 2000 to 2000. 3500 Introducing a reformed gas to be ^-1, it is characterized in that to methanation reaction at 200 to 230 ° C..

That is, when the methanation reaction temperature is high, the reaction of CO ₂ + 4H ₂ → 2H ₂ O + CH ₄ becomes active and the methane conversion amount of carbon dioxide increases, so that the consumption of hydrogen increases. In this case, methanation of carbon monoxide does not proceed. Further, when the space velocity (SV value) increases, even if the methanation reaction temperature is high, carbon monoxide does not fully react and hydrogen gas containing CO methanator is discharged. Therefore, the present invention has found a range of preferable space velocity of methanation reaction and a range of methanation reaction temperature which can effectively remove carbon monoxide while suppressing consumption of hydrogen with space velocity and reaction temperature as parameters. It is.

That is, in the carbon monoxide removing method from the reformed gas according to claim 1 or 2 of the present invention, the space velocity in the CO methanator is 4000h ^-1 or 3500H ^-1 below, and 240 ° C. or 230 ° C. The following reaction The reformed gas is methanated at temperature. Therefore, carbon monoxide can be effectively removed while suppressing an increase in hydrogen consumption by suppressing the progress rate of the methanation reaction of carbon dioxide in the reformed gas.

  Hereinafter, a reformer for carrying out the method for removing carbon monoxide from the reformed gas of the present invention will be described with reference to FIG. Reference numeral 1 shown in FIG. 1 is a reformer having a lateral configuration for carrying out the method for removing carbon monoxide from the reformed gas according to the present invention. The reformer 1 is a fuel mainly composed of hydrocarbon and steam. A reforming reactor 2 for reforming the gas, and a reformed gas obtained by methanating carbon monoxide in the reformed gas introduced from the reforming reactor 2 and removing the carbon monoxide to a fuel cell (not shown) It is comprised from the CO methanator 7 to supply.

  More specifically, the reforming reactor 2 includes a cylindrical body 3 that is heated to, for example, 650 ° C. by a heating means (not shown) provided on the lower side in FIG. A raw material gas inlet 3a into which a raw material gas composed of hydrocarbons and water vapor is introduced from an evaporator (not shown) is provided at one end on the left side of the cylindrical body 3 in the figure. Further, an outer wall portion of the cylindrical body 3 in the vicinity of the right side in the figure protrudes outward and is off gas (the off gas contains hydrogen and carbon monoxide, and is usually supplied as auxiliary fuel to the heating means. Off gas discharge port 3b is provided.

  Inside the cylindrical body 3, a membrane tube 4 sharing the central axis in the radial direction with the cylindrical body 3 is provided. The membrane tube 4 is closed at one end on the left side in the figure, and has a reformed gas discharge port (not shown) for discharging the reformed gas permeated into the other end on the right side in the figure. A porous ceramic tube (consisting of alumina, silica, silica-alumina, mullite, cordierite, zirconia, etc.) and electroless plating on the outer surface of the porous ceramic tube, for example, palladium having a thickness of 5 μm It is comprised from the alloy (Pd-Ag) film 4a. In the case of the reforming reactor 2, the membrane tube 4 is composed of a porous ceramic tube. However, for example, carbon or porous glass may be used instead.

  The cylindrical body 3 is filled with a reforming catalyst 5 described later in a state in which the membrane tube 4 is buried. By this reforming catalyst 5, a raw material gas composed of hydrocarbon gas and water vapor is converted into hydrogen, carbon monoxide, and carbon dioxide with water gas reaction and shift reaction (hereinafter, these reactions are collectively referred to as reforming reaction). .) The reforming catalyst 5 is made of known ruthenium (Ru) supported on granular porous alumina, and the particle size of the reforming catalyst 5 is about 1.5 mm at the maximum. .

  A heat exchanger 6a is connected between the reformed gas discharge port of the reforming reactor 2 and a CO methanator 7 configured as described later by a reformed gas introduction pipe 6 to control the temperature of the reformed gas. It is intervened. The CO methanator 7 is composed of a cylindrical casing and a methanation reaction catalyst made of a ruthenium metal filled in the casing. Then, the reformed gas after the methanation reaction (hydrogen + carbon dioxide + methane + volume ppm unit of carbon monoxide is included) is supplied from the CO methanator 7 to a fuel cell (not shown). It is like that. The space velocity (SV value) of the reformed gas introduced from the reforming reactor 2 into the CO methanator 7 is determined by the membrane permeation rate from the reaction conditions (temperature, pressure, raw material supply amount) of the reactor.

Hereinafter, using the reformer 1, monoxide in the reformed gas discharged from the reforming reactor while suppressing the progress of the methanation reaction of carbon dioxide (CO ₂ + 4H ₂ → 2H ₂ O + CH ₄ ). An example of a carbon monoxide removal test in which the range of methanation reaction temperature and the range of space velocity (SV value) that enable efficient methanation of carbon is determined will be described with reference to the accompanying drawings. FIG. 2 is an explanatory diagram of the relationship between the carbon monoxide concentration (ppm) and the carbon dioxide concentration (ppm) with respect to the methanation reaction temperature (° C.), and FIG. 3 is an explanatory diagram of the relationship between the carbon monoxide concentration with respect to the space velocity (SV value). FIG.

In this embodiment of the carbon monoxide removal test, a method of measuring each of the inlet composition and outlet composition of the reformed gas CO methanator 7 by a chromatograph is adopted, but the reformed gas inlet composition is constant. The methanation reaction temperature and the SV value were changed while maintaining the temperature. Regarding the influence of the methanation reaction temperature, reformed gas was used, and the inlet composition was hydrogen (H ₂ ); 97.04%, carbon monoxide (CO); 0.23%, methane (CH ₄ ); 1.60%, carbon dioxide _(CO 2); which is 1.12%. In the measurement of the influence of the SV value, a reformed gas simulation gas was used, and the inlet composition was hydrogen (H ₂ ); 96.19%, carbon monoxide (CO); 0.32%, methane (CH ₄ ); 0.19%, carbon dioxide _(CO 2); 1.14% nitrogen _(N 2); 2.17%.

First, the space velocity (SV value) of the reformed gas in the CO methanator 7 is maintained at 2700 h ^−1, and methanation reaction temperatures of 200 ° C., 210 ° C., 220 ° C., 230 ° C., 240 ° C., and 250 ° C. The stage was changed by 10 ° C. Then, CO concentration of the outlet compositions of the reformed gas to each of the methanation reaction temperature (ppm), CH ₄ concentration (% by volume), and CO ₂ concentrations were determined (ppm). The results are as shown in Table 1 below, and the relationship between the carbon monoxide concentration (ppm) and the carbon dioxide concentration (ppm) in the reformed gas with respect to the methanation reaction temperature (° C.) is as shown in FIG. is there.

According to Table 1 and FIG. 2, CO ₂ in the reformed gas having the above inlet composition introduced into the CO methanator 7 at 250 ° C. is about 70% (CO ₂ is reduced from 1.14% to 0.36%). And 0.78% is consumed.) Is methanated. Then, _{H 2} is consumed approximately 3% because it is four times the amount of decrease in CO ₂ from the methanation reaction formula _{CO 2 + 4H 2 → 2H 2} O + CH 4. In contrast to this, only about 8% of CO ₂ in the reformed gas having the above inlet composition introduced into the CO methanator 7 at 220 ° C. is methanated, so that only about 0.4% of H ₂ is consumed. Absent.

That is, when the space velocity (SV value) of the reformed gas is 2700 h ⁻¹ , the curve estimated from the plot of CO concentration against the methanation reaction temperature in FIG. It can be seen that the CO concentration becomes 10 ppm or more when the temperature is lower than 190 ° C. In other words, if the methanation reaction temperature is 190 ° C. or higher, the CO concentration can be 10 ppm or lower. In addition, when the methanation reaction temperature is 240 ° C. or less, the amount of CO ₂ consumed by the methanation reaction is small and the amount of H ₂ consumed is small, so that a larger amount of H ₂ can be obtained. That is, the methanation reaction temperature is 190 to 240 ° C, preferably 200 to 240 ° C, more preferably 210 to 230 ° C.

By the way, it is desirable to change the space velocity (SV value) of the reformed gas stepwise and to perform the same test as above for space velocity (SV value) other than 2700h- ¹ . However, as described above, from the fact that the CO concentration decreases as the space velocity (SV value) of the reformed gas decreases and the result of the carbon monoxide removal test, the space velocity (SV value) of the reformed gas. Test is not necessary (if the CO concentration is 10 ppm or less, it is sufficient), and if the space velocity (SV value) is about 4000 h ⁻¹ , the result is reasonable. Because of the prospects, the same test as above was not performed for space velocities (SV values) other than 2700h- ¹ .

Next, a methanation reaction temperature of the reforming gas maintained at 240 ℃, 4050h space velocity (SV value) ^-1, 2700H ^-1, varied in three steps of 2025H ^-1, modified for each space velocity Changes in the outlet composition (H ₂ , CO, CH ₄ , CO ₂ , and N ₂ ) of the gas were determined. The results are as shown in Table 2 below, and the relationship of the carbon monoxide concentration (ppm) to the space velocity (SV value) is as shown in FIG.

According to Table 2 and FIG. 3, the CO ₂ concentration in the reformed gas having the inlet composition introduced into the CO methanator 7 at a space velocity (SV value) of 4050 h ⁻¹ is 1.14% to 0.93. The consumption of H ₂ is very small because about 2% of CO ₂ is methanated. From the above, the consumption of H ₂ corresponds to the case where the space velocity (SV value) of the reformed gas is 2700 h ⁻¹ and the methanation reaction temperature is 240 ° C. Can think. Further, according to Table 2, the CO concentration is quite high. However, if the space velocity (SV value) is 4000 h ⁻¹ , the CO concentration is 69 ppm, which is a sufficiently practical concentration. It can be seen that the space velocity (SV value) should be 3500 h ⁻¹ or less in order to obtain a preferable CO concentration of 10 ppm or less.

  Even in the case of this space velocity (SV value) test, it is preferable to perform a test in which the space velocity (SV value) of the reformed gas is changed at several methanation reaction temperatures other than 240 ° C. However, for example, from the value of CO concentration with respect to the methanation reaction temperature shown in Table 1 above, there is a point that about 240 ° C. is not much different from the case where the reformation gas methanation reaction temperature is kept constant at 240 ° C. In addition, the test of changing the space velocity (SV value) with respect to the methanation reaction temperature other than 240 ° C. was omitted.

From the above, at a space velocity of 2000~4000h ^-1 (SV value), then methanation reaction at 190 to 240 ° C., at a space velocity of preferably 2000~3500h ^-1 (SV value), at 200 to 230 ° C. It can be seen that a methanation reaction should be performed. And this makes it possible to continue supplying a larger amount of hydrogen containing a lower concentration of CO to the fuel cell while suppressing the consumption of hydrogen due to the methanation reaction of CO _2. In Examples 1 and 2, an excellent effect that cannot be obtained at all can be obtained.

It is typical structure explanatory drawing of the reformer which implements the carbon monoxide removal method from the reformed gas of this invention. It is a relationship explanatory view of carbon monoxide concentration (ppm) and carbon dioxide concentration (ppm) to methanation reaction temperature (° C.). It is explanatory drawing of the relationship of the carbon monoxide density | concentration with respect to space velocity (SV value). It is a flowchart of the carbon monoxide removal method which concerns on the prior art example 2.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Reformer, 2 ... Reforming reactor, 3 ... Cylindrical body, 3a ... Raw material gas inlet, 3b ... Off-gas outlet, 4 ... Membrane tube, 4a ... Palladium alloy coating, 5 ... Reforming catalyst, 6 ... reformed gas introduction pipe, 6a ... heat exchanger, 7 ... CO methanator.

Claims (2)

One end of a reforming reactor comprising a cylindrical body heated from the outside, a reforming catalyst filled in the cylindrical body, and a membrane tube disposed in a state embedded in the reforming catalyst A raw material gas consisting of hydrocarbon and water vapor was introduced from the side, and the introduced raw material gas was reformed into a reformed gas consisting of hydrogen, carbon monoxide and carbon dioxide by the reforming catalyst, and passed through the membrane tube. A method for removing carbon monoxide from a reformed gas by introducing reformed gas containing hydrogen, a small amount of carbon monoxide, carbon dioxide, etc. into a CO methanator, and converting carbon monoxide in the introduced reformed gas into methane. in, the CO methanator, a reformed gas space velocity in the CO methanator is introduced reformed gas so as to 2000～4000H ^-1, characterized thereby methanation reaction at 190 to 240 ° C. Carbon monoxide method of removing et al. One end of a reforming reactor comprising a cylindrical body heated from the outside, a reforming catalyst filled in the cylindrical body, and a membrane tube disposed in a state embedded in the reforming catalyst A raw material gas consisting of hydrocarbon and water vapor was introduced from the side, and the introduced raw material gas was reformed into a reformed gas consisting of hydrogen, carbon monoxide and carbon dioxide by the reforming catalyst, and passed through the membrane tube. A method for removing carbon monoxide from a reformed gas by introducing reformed gas containing hydrogen, a small amount of carbon monoxide, carbon dioxide, etc. into a CO methanator, and converting carbon monoxide in the introduced reformed gas into methane. in, the CO methanator, a reformed gas space velocity in the CO methanator is introduced reformed gas so as to 2000～3500H ^-1, characterized thereby methanation reaction at 200 to 230 ° C. Carbon monoxide method of removing et al.

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