JP2006131691A - Method for producing hydrogen from biomass by partial oxidation in high temperature and high pressure water - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method capable of selectively synthesizing hydrogen at a low temperature under high pressure, without using a high-priced catalyst. <P>SOLUTION: In this method, biomass is partially oxidized at the low temperature, so as to make carbon monoxide (CO) selectively react, and the CO and water are converted into the hydrogen through water gas shift reaction. Thus, the hydrogen is selectively produced at one step by making the biomass, the water of the high pressure and a high temperature, oxygen, and a metal oxide, such as zinc oxide, coexist in a reaction tube and together reacting them for a prescribed time. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention relates to a method for producing hydrogen that can be processed at a low temperature and does not use an expensive catalyst.

  Conventionally, hydrogen production from woody biomass represented by cellulose has been performed by dry gasification without using water and wet gasification using water. In the case of dry gasification, in order to efficiently gasify, it is still performed at a high temperature of 600 ° C. or higher, whereas wet gasification is performed aiming at a more energy-saving process. In particular, the following methods have been proposed so far regarding gasification of high-temperature and high-pressure water using liquid-like high-temperature and high-pressure water while maintaining pressure.

  In Patent Document 1 (Japanese Patent Laid-Open No. 11-502891), biomass and organic waste are subjected to catalytic pyrolysis in supercritical water using a solid carbon-based catalyst without adding oxygen to produce a gas containing hydrogen and methane. It has gained. According to this, a gas containing methane and a large amount of hydrogen can be generated from wet biomass or the like.

  However, it is necessary to use a considerably larger amount of solid carbon-based catalyst such as coconut shell activated carbon than the amount of biomass to be treated, and the final treatment of the carbon-based catalyst after use is a problem. In addition, solid carbon catalysts such as activated carbon have a strong adsorption function and collect inorganic salts contained in biomass and the like, and thus easily lose their activity in a short time. For this reason, the lifetime of the solid carbon-based catalyst is not sufficient. Furthermore, there is a possibility that inorganic salts and carbon are deposited between the catalyst particles and the reactor is blocked.

  In Patent Document 2 (Japanese Patent Application Laid-Open No. 2004-131560) proposed as a gasification method that compensates for the drawbacks of Patent Document 1 (Japanese Patent Application Laid-Open No. 11-502891), an organic slurry in a supercritical water in the presence of oxygen or a Ni-based catalyst Catalytic cracking with Ru-based catalyst is performed to obtain gas containing methane and hydrogen as main components. At this time, it has been proposed that solid particles for collecting inorganic salts and carbon are mixed in an organic slurry to prevent catalyst deterioration. Although this method may reduce catalyst deterioration due to inorganic salts, etc., since the catalyst used for gasification is Ni or a noble metal, methanation also proceeds simultaneously. Hydrogen cannot be selectively synthesized when operating.

  Furthermore, the gasification of biomass in high-temperature water will be summarized. The following three methods have been proposed for this method.

  The first is a method using activated carbon above 500 ° C (activated carbon method) developed by a group of Prof. Antal at the University of Hawaii. This is the patent document 1 described above. As described above, this method has problems such as requiring a high temperature and depositing carbon on the activated carbon.

  The second is a method using an alkali catalyst at 400-600 ° C (alkaline method) proposed by Dr. Minowa of AIST and Dr. Kruse of Karlsruhe Institute in Germany. In this case as well, a relatively high temperature is required, and in the case of an organic compound containing no alkali, an alkali must be added, and there are problems of catalyst reuse and corrosion of the inner wall of the reaction due to the alkali.

The third is a method (noble metal method) proposed by Tohoku University / Professor Arai, AIST / Minowa, Dr. Elliott of the United States and Prof. Dumesic using a noble metal catalyst at 200-400 ° C. In this case, although depending on the temperature range, various biomass resources can be gasified, the problem is that expensive noble metals are used and the selectivity of hydrogen is low due to the byproduct of methane. is there. Prof. Fuyasu of Shinshu University has proposed a method using ruthenium oxide, but this method can be seen basically as the precious metal method.

Similarly to the present invention, a hydrogen production method utilizing partial oxidation in water includes methane and methanol reforming and hydrogen production methods. The reaction temperature in this method is about 250 ° C., which is the same as this method. However, since the pressure is normal pressure, this method cannot be applied to substances other than those that become gas under these conditions.
Japanese Patent Laid-Open No. 11-502891 Japanese Patent Laid-Open No. 2004-131560

  Organizing and consolidating the information in the above patents and non-patent literature, high temperature reaction method (activated carbon and alkali method) is easy to gasify and hydrogen selectively, but requires high energy of high temperature and carbon deposition. And the point of corrosion of the reactor is cited as a problem. The low temperature reaction method (noble metal method) is problematic in that expensive noble metals are used and methane is by-produced. In addition, since steam reforming and hydrogen production from methane and methanol are steam conditions, the biomass is not dissolved and cannot be applied to hydrogen production from biomass. To solve these problems, we propose a method that can selectively synthesize hydrogen at low temperature and high pressure without using expensive catalysts.

ADVANTAGE OF THE INVENTION According to this invention, the hydrogen production method from biomass characterized by using a metal oxide catalyst and an oxidizing agent in the gasification reaction of biomass in high temperature / high pressure water can be obtained. According to the present invention, the oxidizing agent may be a partial oxidation catalytic ability metal oxide having a high performance of partially oxidizing organic substances to generate CO, or a water gas shift reaction metal oxide that effectively proceeds a water gas shift reaction of CO, It is possible to obtain a method for producing hydrogen from biomass characterized by being one or both of the above.

According to the present invention, the partial oxidation catalytic ability metal oxide is Ce oxide, Cu oxide, Cr oxide, Mn oxide, Mo oxide, Ni oxide, Zn oxide, Zr oxide, W oxidation. It is possible to obtain a method for producing hydrogen from biomass, which is characterized in that it is one of the products or a combination thereof.
According to the present invention, the water gas shift reaction metal oxide is one or a combination of Cu oxide, Cr oxide, Fe oxide, Ni oxide, Zn oxide, and Zr oxide. A method for producing hydrogen from biomass can be obtained.

  According to the present invention, it is possible to obtain a method for producing hydrogen from biomass, characterized in that the high temperature is 200 ° C. to 500 ° C. and the high pressure is 10 to 30 atm.

  The present invention selectively reacts with CO by partially oxidizing biomass at a low temperature by actively presenting an oxidizing agent such as oxygen or hydrogen peroxide, which has been avoided in the gasification reaction of biomass as much as possible. The CO is converted to hydrogen through water and water gas shift reaction. Advantageous Effects of Invention According to the present invention, hydrogen can be selectively produced in one step by reacting a reaction tube at a predetermined time with an organic substance such as glucose, high-temperature and high-pressure water, and oxygen and a metal oxide such as zinc oxide in a reaction tube. Is obtained.

  The advantage of this method is that CO is first produced at a low temperature by partial oxidation with an oxidant, and then hydrogen gas is produced by water gas shift. Therefore, in this gasification reaction, methane is hardly produced and highly selective. This is a new hydrogen production method.

  The second merit is that almost no carbon deposition occurs on the catalyst because it is gasification by oxidation reaction with an oxidizing agent.

  Third, unlike hydrogen reforming of methane or methanol in atmospheric steam, this method uses high-temperature and high-pressure water (a high-density aqueous solvent environment) as a reaction field, so there are various types of biomass and organic waste. It can be mentioned that it can be applied to gasification of organic substances and hydrogen production.

  Fourthly, the catalyst used in this method can use an inexpensive metal oxide such as zinc oxide. The performance required for this catalyst is two points: high performance of partially oxidizing organic substances with an oxidizing agent to generate CO, and effective progression of CO water gas shift reaction. Therefore, metal oxides (Ce oxide, Cu oxide, Cr oxide, Mn oxide, Mo oxide, Ni oxide, Zn oxide, Zr oxide, W oxide, etc.) with high partial oxidation catalytic ability Each metal oxide (Cu oxide, Cr oxide, Fe oxide, Ni oxide, Zn oxide, Zr oxide, etc.) effective for the water gas shift reaction or a composite thereof is effective for this method.

  The fifth merit is that this method has a low temperature of around 300 ° C. in the biomass gasification method, which is advantageous in terms of energy. Sixthly, the reaction time for biological gasification reaction with microorganisms such as biomass gasification at around 200 ° C to 300 ° C or at normal temperature and normal pressure is required from several hours to several days, whereas in this method, it takes from several seconds. Biomass can be gasified on the order of several minutes.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. First, the contents of an experiment for demonstrating the present invention will be described.

In the experiment, D-Glucose (purity 98 +%) manufactured by Wako Pure Chemical Industries, Ltd. was used. Distilled water treated using an ultrapure water production apparatus was used as water. The catalysts used in the experiment were H ₂ SO ₄ and NaOH as homogeneous catalysts, and the concentrations were both 1 mM. In addition, MoO3, Ag2O, TiO2, MnO2, ZrO2, Fe2O3, Cr2O3, CuO, NiO, ZnO, and RuO2 were used as metal oxides, and all commercially available products purchased from Wako Pure Chemicals were used as they were. Ni and Ru were also used as metal catalysts. These were also purchased from Wako Pure Chemical.

The experiment was conducted using a batch reactor shown in FIG. The internal volume is 6
cc. In addition, a high-pressure stop valve was installed for gas charging and recovery. Although the reaction temperature was changed from 200 to 500 ° C, it was mainly 300 ° C. Other experimental conditions were 1.0 g of water, 0.1 g of glucose, and 0.1 g of various solid catalysts. In the experiment in which oxygen was added, about 0.05 to 0.1 g of oxygen of about 10 to 30 atmospheres or 30% hydrogen peroxide was charged. The reaction time was 60 to 300 seconds. During the experiment at a reaction temperature of 200 ° C., the reaction was carried out for up to about 60 minutes.

A predetermined amount of sample, distilled water, catalyst, and the like were charged into the reaction tube, and the air in the reaction tube was replaced with 2.5 MPa Ar gas or a predetermined amount of oxygen was introduced. The reaction was started by putting the reaction tube into a fluidized sand bath set at a predetermined temperature. In order to raise the temperature rapidly, the charged reaction tube was shaken in a sand bath. After a predetermined period of time, the reaction tube was removed from the sand bath and immersed in a cold water bath to stop the reaction. As a result of measuring the temperature change in the reaction tube with a sheath type K-type thermocouple attached to the reaction tube, it was almost 90 regardless of the temperature of the sample or the fluidized sand bath.
The temperature was raised to the temperature of the sand bath in sec and cooled to room temperature in 10 sec.

A stop valve was connected to a volumetric syringe to collect the generated gas and measure the volume. Thereafter, the gas products (H ₂ , CO, CO ₂ ) were quantified using two GC-TCDs. A calibration curve was prepared using the peak area of the standard gas.

After gas recovery, the inside of the reaction tube was washed with ultrapure water, and the entire contents were recovered in a beaker. This is a membrane filter (pore size 0.2
(μm) and filtered with suction to separate a water-soluble component and a water-insoluble component. The water-insoluble matter was weighed after drying at 60 ° C. for 24 hours. For water-soluble matter, the total organic carbon content was measured by TOC, and qualitative and quantitative analysis was performed using HPLC-UV / RI. A calibration curve was prepared using the peak area of a sample with a known concentration.

The carbon (or hydrogen) yield of the product was evaluated on a glucose basis.
Next, the experimental results will be described.
Here, the results will be described focusing on the gasification reaction, particularly the generation of hydrogen.
FIG. 2 shows the carbon yield and hydrogen yield of the gaseous product. The conversion was almost 100% for all the catalysts, and mainly H ₂ and CO ₂ were obtained as gaseous products.

When no oxidizing agent such as hydrogen peroxide is charged (the experiment with only the catalyst name shown in Fig. 2 is the experimental result when no oxidizing agent is charged), the gasification progress is MoO3, Ag2O, CuO, ZnO. , RuO ₂ , and Ru / C. RuO ₂ , which is known to be effective for gasification of supercritical water (374 ° C, 22.1 MPa or more), has a high CO ₂ yield (32.9%) under this experimental condition, but hardly generates H _2. (0.6%). MoO3, Ag2O, and Ru / C also had high CO2 yields (almost 20%), but almost no hydrogen was produced, as was RuO2. On the other hand, ZnO and CuO used in methanol steam reforming catalysts showed high H ₂ yields (ZnO: 4.7%, CuO: 2.3%), but CuO also had high CO ₂ yields (31.6%). ).

Park and Tomiyasu relate to the catalytic reaction of RuO ₂ at about 400 ° C when Ru ⁴⁺ is reduced to Ru ²⁺ by organic oxidation as shown in Fig. 3, and when H ₂ is produced by reduction of H ₂ O, Ru ⁴ Proposes a mechanism to return to ⁺ . According to this reaction mechanism, the experimental results at 300 ° C. suggest that RuO ₂ oxidizes organic matter to CO ₂ and H ₂ O, but H ₂ production was low due to the slow reaction of reducing H ₂ O. In addition, Cu was easily reduced from +2 to +1, suggesting that the oxidation reaction of organic substances similar to RuO ₂ may proceed in CuO.

This is the same reaction on MoO3, Ag2O, and Ru / C, that is, the oxidation-reduction reaction of metal or metal oxide and organic matter / water promotes gasification. I think that the reaction to reduce does not progress easily. On the other hand, ZnO had a low CO ₂ yield and a high H ₂ yield. Considering the fact that ZnO catalyze the water gas shift (WGS) reaction, the WGS after decomposed into CuO or RuO ₂ with different glucose is first CO with H ₂ was produced. Therefore, by using the ZnO, organic matter prevents full oxidation to CO ₂ and H ₂ O, considered of H ₂ can be efficiently produced.

Next, in order to examine the catalytic activity of ZnO in more detail, the time course of the gas product was examined at 200 ° C and 300 ° C. FIG. 4 shows changes with time in the yield of gas products at 200 ° C. and 300 ° C. CO and CH ₄ yield are not shown for low and less than 0.4% in any case. The conversion rate was 80% at 200 ° C for 5 minutes, and almost 100% for the others. According to the examination results at 200 ° C., almost no gas was generated during the heating process. This indicates that the gasification reaction proceeds slowly below 200 ° C. The H ₂ yield gradually increased from 2% in 15 minutes to 3.1% in 60 minutes, and the CO 2 yield also increased from 7% (15 minutes) to 14% (60 minutes) with time. At 300 ° C, the gasification reaction proceeds very rapidly during the temperature increase process, but when the reaction time is changed from 15 minutes to 30 minutes, the H ₂ yield hardly increases, whereas the CO ₂ yield gradually increases. Increased.

Thus, at any temperature, the H ₂ production reaction proceeded at the beginning of the reaction, but the production rate slowed with time, while the CO ₂ yield continued to increase. The following reasons are conceivable. In other words, (1) If the production of CO ₂ indicates the progress of the WGS reaction, the reaction that consumes the generated H ₂ is proceeding. (2) Glucose undergoes isomerization, dehydration, reverse aldol condensation, etc. After that, it is converted to aldehyde and carboxylic acid, but CO ₂ is generated because the generated carboxylic acid is decomposed by decarboxylation, etc. (3) In ZnO, oxidation reaction similar to RuO ₂ and CuO proceeds gradually. And so on.

  As described above, it has been clarified that ZnO is effective for hydrogen production, but the yield of hydrogen was low only with ZnO / water / glucose. If ZnO is a catalyst for the water gas shift reaction, it is only necessary to promote the production of CO. To that end, an oxidation catalyst such as CuO or an oxidizing agent such as oxygen or hydrogen peroxide is added to promote the oxidation reaction. And increase the CO yield.

  Therefore, an experiment was conducted in which 0.055 g and 0.1 g of 30% hydrogen peroxide (H2O2) were added to the ZnO / water / glucose system. The results are shown in FIG. 2 (in the figure, items with ZnO + 30% H2O2 (0.055 g) and ZnO + 30% H2O2 (0.1 g)). As shown in the figure, by adding 0.055 g of hydrogen peroxide, the hydrogen yield increased to about 10%, which is twice as much as when hydrogen peroxide was not added. An additional 0.1 g of hydrogen could produce about 25% hydrogen.

  In order to compare this hydrogen production with other gasification reactions, experiments were conducted using RuO2 catalyst at 400 ° C for 5 minutes and at 500 ° C for 1 minute. The results are also shown in FIG. At 400 ° C for 5 minutes, about 12% of hydrogen was produced, and about 30% of methane was produced at the same time. At 500 ° C for 1 minute, about 20% of hydrogen was produced, and about 25% of methane was produced.

  Compared to the results of ZnO with hydrogen peroxide, the same amount of hydrogen was recovered as when gasified at 500 ° C using RuO2 despite the low temperature of 300 ° C. ZnO produces very little methane, so hydrogen selectivity is extremely high.

  In order to examine in detail gasification with ZnO when an oxidizing agent is added, an experiment was performed in which the amount of oxygen added was changed. The oxidizing agent is hydrogen peroxide or oxygen. The results are shown in FIG. Gasification progresses by increasing oxygen with respect to carbon, and about 25% hydrogen can be produced up to about 1 O / C. On the other hand, even if oxygen was increased further, the hydrogen yield was about 17-18%, which was almost constant regardless of the amount of oxygen. The amount of CO2 produced was almost constant at about 80%. This suggested that there may be an optimum value for the oxygen / carbon ratio.

  Furthermore, in order to further elucidate the mechanism of the gasification reaction, the O / C was fixed at about 2, and the change with time was examined. The results are shown in FIG. Methane was not shown here because the yield was 0 in all cases. Although there were variations in experimental points, CO2, CO, and H2 were gradually generated as oxygen was consumed. Although it can be seen that hydrogen is gradually increasing, the reaction time was already about 20% from 60 seconds, and no significant increase was observed. As a result, gas generation in this system, particularly hydrogen generation, proceeds in a very short time, and then hydrogen is increased to stop the hydrogen consumption reaction or CO generation reaction as in the case where oxygen is not added. I couldn't.

  In conventional hydrogen production methods, high-temperature reaction methods (activated carbon and alkali methods) are easy to gasify and selectively produce hydrogen, but they require high energy at high temperatures and carbon deposition and corrosion of reactors. It is mentioned as a point. The low temperature reaction method (noble metal method) is problematic in that expensive noble metals are used and methane is by-produced.

  According to the present invention, CO can be selectively reacted by partially oxidizing biomass at a low temperature, and the CO can be converted to hydrogen through water and water gas shift reaction. The present invention is an inexpensive hydrogen production method using biomass and free from harmful byproducts.

Batch reactor used in the experiment Effect of catalyst and hydrogen peroxide on glucose gasification reaction Reaction temperature: 300 ° C., reaction time: 90 seconds, water: 1.0 g, glucose 0.1 g, catalyst 0.1 g, H ₂ SO ₄ : 1 mM, NaOH: 1 mM. However, in the RuO ₂ experiment, experiments at 400 ° C. and 500 ° C. were also conducted. The reaction time at this time was 5 minutes at 400 ° C. and 1 minute at 500 ° C. Gasification mechanism in RuO2. Reaction time dependence of gasification reaction using ZnO Effect of oxygen / carbon ratio on gasification (300 ° C, 90 seconds) Temporal change of gasification reaction in ZnO / O2 / glucose / water system at O / C = 2 (300 ℃) Continuous biomass conversion hydrogen production system Continuous biomass conversion hydrogen production system

Claims (5)

A method for producing hydrogen from biomass, comprising using a metal oxide catalyst and an oxidizing agent in a gasification reaction of biomass in high-temperature and high-pressure water. The oxidizing agent may be one of a partial oxidation catalytic ability metal oxide having a high performance for partially oxidizing an organic substance to generate CO, or a water gas shift reaction metal oxide for effectively promoting a water gas shift reaction of CO, or The method for producing hydrogen from biomass according to claim 1, characterized in that it is both of them. The partial oxidation catalytic ability metal oxide is one of Ce oxide, Cu oxide, Cr oxide, Mn oxide, Mo oxide, Ni oxide, Zn oxide, Zr oxide, and W oxide. Or it is the combination, The hydrogen production method from biomass of Claim 2 characterized by the above-mentioned. 3. The water gas shift reaction metal oxide is one or a combination of Cu oxide, Cr oxide, Fe oxide, Ni oxide, Zn oxide, and Zr oxide. Of hydrogen production from the biomass. The method for producing hydrogen from biomass according to claim 1, wherein the high temperature is 200 ° C. to 500 ° C., and the high pressure is 10 to 30 atm.