JP2009101328A - Ethanol reforming catalyst and hydrogen manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ethanol reforming catalyst which can be easily manufactured and increase hydrogen yield at a lower temperature than by a conventional catalyst while inhibiting a coking process, and a hydrogen manufacturing method. <P>SOLUTION: This ethanol reforming catalyst has La<SB>2</SB>O<SB>3</SB>as a carrier, on which Co and K are supported. The molar ratio of K to Co, K/Co is 0.01 to 0.3. In addition, prior to the chemical reaction between ethanol and water vapor by the ethanol reforming catalyst, K-Co/La<SB>2</SB>O<SB>3</SB>of the ethanol reforming catalyst is subjected to hydrogen reduction at 400 to 600°C. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an ethanol reforming catalyst for producing hydrogen by reforming ethanol and a method for producing hydrogen.

  Conventionally, hydrogen (gas) has been used in large quantities as a basic material gas for petrochemicals, and in recent years, there has been great expectation as a clean energy source. Such hydrogen is mainly composed of hydrocarbons such as methane, butane and kerosene, and oxygen-containing hydrocarbons (hydrocarbons containing oxygen atoms) such as methanol, ethanol and dimethyl ether, and water (steam), carbon dioxide, oxygen Can be obtained from these source gases using chemical reactions such as reforming reaction, partial oxidation reaction, and decomposition reaction.

Among the main raw material gases, ethanol is expected as a carbon-neutral next-generation raw material derived from biomass, and steam reforming using ethanol as a raw material is represented by the following chemical formula.
C ₂ H ₅ OH + 3H ₂ O = 2CO ₂ + 6H ₂

The above reaction can proceed thermodynamically at about 400 ° C. However, in reforming catalysts such as Ni / Al ₂ O ₃ and Rh / Al ₂ O ₃ that are generally used in the past, methane is produced as a by-product, so that methane steam reforming is substantially achieved to obtain a sufficient reaction rate. Required a high temperature of 700-800 ° C. Therefore, in recent years, a catalyst for reforming ethanol at a low temperature (a catalyst that does not produce methane as a by-product) has been developed.

Patent Documents 1 and 2 propose ethanol steam reforming using a ruthenium-based catalyst (ZrO ₂ , CeO ₂ , ZrO ₂ -CeO ₂ support) and a cobalt-based catalyst (ZrO ₂ -CeO ₂ support), respectively. It is said that hydrogen can be produced at 250 to 500 ° C. in the former and 300 to 500 ° C. in the latter.

In Non-Patent Document 1, it is reported that a cobalt-based catalyst (ZnO, La ₂ O ₃ support) generates hydrogen at a high yield at 400 to 500 ° C.

JP 2005-131468 A JP 2005-131469 A Applied Catalysis A: General 243 (2003) 261-269

However, in these prior arts, the hydrogen yield (in the ethanol steam reforming, a maximum of 6 mol of hydrogen is generated per 1 mol of ethanol, the actual hydrogen ratio to the maximum value of 6 mol is expressed as hydrogen in this application. (E.g., defined as the yield) is low, and evaluation is performed under reaction conditions (raw gas is dilute or H ₂ O / EtOH is high) that seems to be effective for suppressing coking. Under the conditions, there is a problem that coking occurs in a short time and lacks durability.

Non-Patent Document 1 shows that Co / La ₂ O ₃ prepared using Co ₂ (CO) ₈ as a cobalt precursor has activity for ethanol steam reforming. When Co ₂ (CO) ₈ is used as a precursor, CO accompanying the cobalt is released by vacuum degassing, so that Co / La ₂ O ₃ is obtained without requiring firing in the atmosphere and reduction with hydrogen. There is an advantage that you can. However, Co ₂ (CO) ₈ has disadvantages that it is expensive and is a toxic substance.

  An object of the present invention is to provide an ethanol reforming catalyst and a hydrogen production method that are easy to produce and capable of improving the hydrogen yield at a lower temperature than before while suppressing coking.

The inventors of the present application can solve the above-mentioned problems by reacting ethanol and steam using La ₂ O ₃ as a carrier and an ethanol reforming catalyst in which Co and K are supported on the carrier. I found. That is, according to the present invention, the following ethanol reforming catalyst and hydrogen production method are provided.

[1] An ethanol reforming catalyst in which La ₂ O ₃ is used as a carrier and Co and K are supported on the carrier.

[2] The ethanol reforming catalyst according to the above [1], wherein the molar ratio K / Co of Co and K supported on La ₂ O ₃ is 0.01 to 0.3.

[3] Using La ₂ O ₃ as a carrier and using K-Co / La ₂ O ₃ as an ethanol reforming catalyst in which Co and K are supported on the carrier, ethanol and water vapor are reacted to generate hydrogen. Hydrogen production method to produce.

[4] The hydrogen according to [3], wherein K-Co / La ₂ O ₃ of the ethanol reforming catalyst is hydrogen reduced at 400 to 600 ° C., and then hydrogen is produced by reacting ethanol and water vapor. Production method.

[5] The method for producing hydrogen according to [3] or [4], wherein ethanol and water vapor are reacted at a reaction temperature of 350 to 550 ° C.

By using an ethanol reforming catalyst in which La ₂ O ₃ is used as a support and Co and K are supported on the support, coking is suppressed and the hydrogen yield can be improved at a lower temperature than in the past.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. The present invention is not limited to the following embodiments, and changes, modifications, and improvements can be added without departing from the scope of the invention.

The ethanol reforming catalyst of the present invention comprises La ₂ O ₃ as a carrier, and Co and K are supported on the carrier. And the hydrogen manufacturing method of this invention manufactures hydrogen using this ethanol reforming catalyst.

Ethanol steam reforming is a reaction that generates hydrogen from ethanol and steam as shown in the following equation.
C ₂ H ₅ OH + H ₂ O → 2CO + 4H ₂

However, ethanol steam reforming involves multiple reaction processes (ethanol decomposition reaction, dehydrogenation reaction, ethylene polymerization reaction, acetaldehyde condensation, acetaldehyde reforming, shift reaction, CO disproportionation reaction, CO and CO ₂ methanation, etc.) It progresses simultaneously. For this reason, in order to improve the hydrogen yield, the C ₁ conversion rate (the ratio of carbon converted from ethanol to C ₁ components (CO, CO ₂ , CH ₄ )) is increased and the CH ₄ ratio (C ₁ component) It is necessary to lower the ratio of CH _{4 in} the inside.

The hydrogen production method of the present invention produces hydrogen by reacting ethanol and water vapor using an ethanol reforming catalyst in which La ₂ O ₃ is used as a carrier and Co and K are supported on the carrier. K-Co / _La 2 _{O 3} as ethanol reforming catalysts can be made to the _La 2 _{O 3} as a carrier Co, the impregnation method of impregnating an aqueous solution containing K. First, an aqueous cobalt nitrate solution in which a carrier of La ₂ O ₃ is immersed is stirred to evaporate to dryness, then dried and baked in the air, whereby Co / La ₂ in which Co is supported on La ₂ O _3. O ₃ is obtained. The amount of Co supported on the carrier is preferably 3 to 25% by mass, more preferably 10 to 20% by mass. Then, by immersing Co / La ₂ O ₃ in an aqueous potassium hydroxide solution, stirring and evaporating it to dryness, drying, and firing in the air, La ₂ O ₃ is used as a carrier, and on the carrier An ethanol reforming catalyst K-Co / La ₂ O ₃ in which K is supported as Co and a co-catalyst can be used. The molar ratio of K and Co is preferably K / Co = 0.01 to 0.3. Further, prior to reacting the ethanol and water vapor, it is preferable to hydrogen reduction a K-Co / _La 2 _{O 3} at 400 to 600 ° C.. Thus, increasing the C ₁ ratio, with a lower CH ₄ ratio, thereby improving the hydrogen yield. Unlike the non-patent document 1, the ethanol reforming catalyst of the present invention uses cobalt nitrate, which is inexpensive and commonly used, as a cobalt precursor, and has high K-Co / La activity for ethanol steam reforming. ₂ O ₃ can be obtained.

The above ethanol reforming catalyst promotes a shift reaction (CO + H ₂ O = CO ₂ + H ₂ ) that is considered to have an effect of suppressing CO disproportionation reaction (2CO = C + CO ₂ ) that causes coking. Hydrogen can be efficiently obtained at a low temperature while suppressing the above.

  Moreover, it is preferable to perform reaction of ethanol and water vapor | steam at 1-2 atm, and it is preferable to carry out at reaction temperature 350-550 degreeC. When the reaction pressure is 3 atm or more, the hydrogen yield decreases.

Next, a hydrogen production method for producing hydrogen by a reaction between ethanol and steam using the ethanol reforming catalyst of the present invention will be described. The hydrogen production equipment is a general equipment that is configured so that water and ethanol can be used as a raw material gas source, and water and ethanol can be vaporized and mixed by a vaporizer to be supplied to the reactor. Can be used. The catalyst layer of the reactor is equipped with the K-Co / La ₂ O ₃ ethanol reforming catalyst described above.

First, before hydrogen production, K-Co / La ₂ O ₃ as an ethanol reforming catalyst is hydrogen reduced, for example, at 400 to 600 ° C. for 0.5 to 3 hours. Thereafter, vaporized H ₂ O (steam) and ethanol are introduced into the reactor of the hydrogen production apparatus and brought into contact with the ethanol reforming catalyst at 350 to 550 ° C., preferably 400 to 500 ° C. Preferably, ethanol and H ₂ O are reacted at about 450 ° C. At this time, ethanol and H ₂ O may be reacted at 1 to ₂ atm, more preferably at 1 atm. The molar ratio of water vapor (H ₂ O) to ethanol (C ₂ H ₅ OH) of the raw material gas is 1.5 to 5, more preferably 2 to 3.5. In addition, the ethanol reforming catalyst is reacted at 0.1 to 10 g, more preferably 0.5 to 5 g with respect to 100 cc / min of the raw material gas.

  The reaction may be carried out by selectively separating the carbon dioxide and hydrogen of the product with a selectively permeable membrane reactor or the like by combining a separation membrane and an adsorbent. When separating hydrogen, a palladium alloy membrane or a porous ceramic membrane such as silica or zeolite can be used as the membrane, or a carbon membrane and a hydrogen storage alloy containing nickel, manganese, vanadium, etc. can be used as the adsorbent. . As the carbon dioxide removing means, a carbon dioxide adsorbent, a carbon dioxide separation membrane, or the like can be suitably used. As the adsorbent, for example, an inorganic compound such as calcium oxide or lithium silicate, an alkali solution, an ionic solution, or an inorganic porous material such as alumina or silica carrying an alkali solution or an ionic solution is preferably used. Can do. As the carbon dioxide separation membrane, for example, a polymer membrane or a zeolite membrane can be suitably used.

  According to the above hydrogen production method, it is possible to efficiently produce hydrogen at 350 to 550 ° C., which is lower than conventional, while suppressing coking. For this reason, manufacturing cost can be reduced more than before.

  EXAMPLES Hereinafter, although this invention is demonstrated further in detail based on an Example, this invention is not limited to these Examples.

(Experiment 1)
Two types of catalysts, Co / La ₂ O ₃ and Co / Al ₂ O ₃ , were prepared. A method for manufacturing Co / La ₂ O ₃ will be described. Co / La ₂ O ₃ was produced by an impregnation method in which La ₂ O _{3 serving} as a carrier was immersed in an aqueous cobalt nitrate solution and impregnated into the carrier. While stirring the aqueous cobalt nitrate solution in which the La ₂ O ₃ carrier was immersed, the solution was evaporated to dryness at 90 ° C. Furthermore, it was dried overnight at 80 ° C. and baked in the air at 600 ° C. for 4 hours. In addition, the mass ratio with respect to the support | carrier of cobalt was 16 mass%. In use, the particle size was adjusted to 0.5 to 1 mm.

Co / Al ₂ O ₃ was prepared in the same manner by immersing Al ₂ O ₃ as a carrier in a cobalt nitrate aqueous solution.

(Evaluation device and evaluation method)
Each of the above catalysts was evaluated. The hydrogen production apparatus can supply ethanol and water vaporized by heating to a reactor filled with a catalyst. A flow meter for measuring the amount of product gas and a gas chromatograph for quantifying gas components are connected downstream of the reactor. A liquid trap set at about 5 ° C. is provided on the upstream side of the flow meter to collect liquid components such as water.

The reaction was carried out by appropriately setting the raw material gas flow rate, the reaction temperature, and the reaction pressure to desired values with the respective regulators. The hydrogen yield was determined from the outlet gas flow rate and its composition (concentrations of H ₂ , CH ₄ , CO, and CO ₂ ).
Hydrogen yield [%] = 100 × outlet gas flow rate × outlet gas H ₂ concentration / (inlet ethanol flow rate × 6)

Further, the C ₁ conversion rate and the CH ₄ ratio were determined.
C ₁ conversion rate [%] = 100 × (Outlet gas CH ₄ concentration + Outlet gas CO concentration + Outlet gas CO ₂ concentration) × Outlet gas flow rate / (2 × Inlet ethanol flow rate)
CH ₄ ratio [%] = 100 × Outlet gas CH ₄ concentration / (Outlet gas CH ₄ concentration + Outlet gas CO concentration + Outlet gas CO ₂ concentration)

  For each catalyst, the catalyst was hydrogen reduced at 400 ° C. for 2 hours before hydrogen production. Then, ethanol and water vapor were reacted at reaction temperatures of 400 ° C., 450 ° C., 500 ° C. and a reaction pressure of 1 atm to produce hydrogen. In addition, hydrogen yield etc. are the average after becoming steady (about 15 minutes to about 1 to 2 hours after reaction start).

FIG. 1 shows the hydrogen yield, and FIG. 2 shows the C ₁ conversion rate. Co / La ₂ O ₃ had a higher hydrogen yield and C ₁ conversion rate at each temperature than Co / Al ₂ O ₃ . Moreover, the hydrogen yield and the C ₁ conversion rate could be further increased by setting the reaction temperature to 450 to 500 ° C. rather than 400 ° C.

The reaction temperature is preferably a low temperature from the viewpoint of suppressing hydrogen production cost and preventing deterioration of the separation membrane when combined with a separation membrane (for example, Pd membrane), but Co / La ₂ O ₃ is 400 When it was set to ° C., the hydrogen yield and the C ₁ conversion rate would be lower than 450 to 500 ° C., so an attempt was made to improve this point.

(Experiment 2)
Next, K—Co / La ₂ O _{3 in} which K was supported on the Co / La ₂ O ₃ produced in Experiment 1 as a promoter was produced. While immersing Co / La ₂ O ₃ in an aqueous potassium hydroxide solution and stirring it, it was evaporated to dryness at 90 ° C., further dried overnight at 80 ° C., and 600 ° C., 4 ° C. in air. Obtained by baking for a period of time. The molar ratio of K and Co was K / Co = 0.035. Moreover, the reduction temperature of the hydrogen reduction of the catalyst performed before hydrogen production was changed. Specifically, after reducing K-Co / La ₂ O ₃ at reduction temperatures of 400 ° C., 500 ° C., and 600 ° C. for 2 hours, ethanol and water vapor are reacted at 400 ° C. and a reaction pressure of 1 atm to generate hydrogen. Manufactured. In use, the particle size was adjusted to 0.5 to 1 mm.

FIG. 3 shows the hydrogen yield, the C ₁ conversion rate, and the CH ₄ ratio with respect to the reduction temperature. K-Co / La ₂ O ₃ can greatly improve the C ₁ conversion rate and reduce the CH ₄ ratio at the same reduction temperature of 400 ° C. and reaction temperature of 400 ° C. compared to Co / La ₂ O _3. It was. The reduction temperature is preferably 400 to 600 ° C, but 400 ° C is sufficient.

(Experiment 3)
Furthermore, the reaction pressure between ethanol and water vapor was changed, and the reaction was performed at a reaction temperature of 400 ° C. When the reaction pressure was increased to 3 atm or more, the C ₁ conversion rate and the hydrogen yield were drastically decreased. Therefore, the reaction pressure between ethanol and water vapor is preferably 1 to 2 atm.

From the above, K-Co / La ₂ O ₃ can have a higher hydrogen yield and C ₁ conversion rate than Co / La ₂ O ₃ even when the reaction temperature is 400 ° C. Moreover, even if the reaction temperature was 400 ° C., the hydrogen yield and the C ₁ conversion rate could be further increased by setting the reduction temperature of the hydrogen reduction of the catalyst before the reaction to 500 to 600 ° C.

  The catalyst of the present invention can be used as an ethanol reforming catalyst for reforming ethanol to produce hydrogen. In addition, the production method of the present invention can be used as a hydrogen production method that is more efficient at a lower temperature than in the past.

It is a graph which shows the hydrogen yield by reaction temperature. It is a graph showing a C ₁ rate by the reaction temperature. Hydrogen yield by reduction temperature is a graph showing _{C 1} ratio, and the CH ₄ ratio.

Claims (5)

An ethanol reforming catalyst comprising La ₂ O ₃ as a carrier and Co and K supported on the carrier. Ethanol reforming catalyst according to claim 1 mole ratio K / Co of supported Co and K in la ₂ O ₃ is 0.01 to 0.3. Hydrogen that uses La ₂ O ₃ as a carrier and reacts ethanol and water vapor to produce hydrogen using K-Co / La ₂ O ₃ which is an ethanol reforming catalyst in which Co and K are supported on the carrier. Production method. The hydrogen production method according to claim 3, wherein K-Co / La ₂ O ₃ of the ethanol reforming catalyst is subjected to hydrogen reduction at 400 to 600 ° C. and then reacted with ethanol and steam to produce hydrogen.   The method for producing hydrogen according to claim 3 or 4, wherein ethanol and water vapor are reacted at a reaction temperature of 350 to 550 ° C.

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