JP2013151384A - Hydrogen production method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hydrogen production method for producing hydrogen gas using an inorganic/organic mixed waste material containing an inorganic component capable of serving as a sulfur supply source, while inhibiting or suppressing the generation of hydrogen sulfide gas.SOLUTION: Hydrogen is generated under anaerobic conditions while inhibiting or suppressing the generation of hydrogen sulfide by putting zinc oxide in an environment in which (1) a treatment object containing at least a sulfur source, an organic component and water and (2) an anaerobic microorganism capable of generating hydrogen sulfide under anaerobic conditions exist at the same time. The zinc oxide is preferably provided in the form of dissolved dust. The treatment object is preferably a waste gypsum board, effluent sludge, sewage sludge or livestock excreta.

Description

The present invention relates to a hydrogen generation method for generating hydrogen gas (H ₂ ) while preventing or suppressing generation of hydrogen sulfide (H ₂ S) gas.

  A method of generating hydrogen gas by causing microorganisms to act on organic resources such as biomass is known. For example, in Patent Document 1 (Japanese Patent Laid-Open No. 11-130402), a harvested plant cut to an appropriate size is placed in a container and left as it is or immersed in water and kept under dark or light conditions for a predetermined time. Discloses a method for producing hydrogen by the action of hydrogen-producing bacteria attached to the plant. Patent Document 2 (Japanese Patent Laid-Open No. 2007-159534) uses waste biomass such as food residue as a raw material, and heats the raw material under anaerobic conditions at a temperature of about 75 ° C. in the presence of a complex anaerobic microorganism group. Thus, a method for producing hydrogen using hydrogen fermentation is disclosed.

  However, any of the hydrogen generation methods described above utilize resources (or waste organic resources) mainly composed of organic substances, and are not intended to use inorganic / organic mixed wastes mainly composed of inorganic components.

On the other hand, recycling of inorganic / organic mixed waste with a high content of inorganic components is desired. For example, waste gypsum board (waste gypsum board) is an inorganic / organic mixed waste in which a piece of gypsum mainly composed of calcium sulfate (CaSO ₄ ) is bonded with starch paste, but waste gypsum dumped in a landfill site It has been pointed out that toxic hydrogen sulfide may be generated from the board. Although there are various theories about the mechanism of hydrogen sulfide generation from waste gypsum board, according to one theory, when anaerobic microorganisms decompose starch paste (which is a nutrient source for microorganisms) on waste gypsum board, it is the calcium sulfate (a source of sulfur) ) To produce hydrogen sulfide. Therefore, it is sought to use such a mixed inorganic / organic waste to extract a more useful resource (for example, hydrogen gas) instead of a toxic gas such as hydrogen sulfide.

In addition, two patent documents that may have doubts about the relevance with the present application will be explained (explained) in advance. First, Patent Document 3 (Japanese Patent Application Laid-Open No. 2002-282893) discloses an air purifying agent (more specifically, desulfurization) obtained by solidifying and dissolving molten dust discharged and recovered from a cast iron melting furnace with cement. It can be used as a hydrogenation agent. However, the technique of Document 3 is intended to purify or desulfurize malodorous components (that is, H ₂ S molecules) already present in the gas phase system to be treated. Hydrogen sulfide from a solid sulfur source It is not a technique for suppressing the generation (or release) of gas itself. Next, Patent Document 4 (Japanese Patent Application Laid-Open No. 2004-41998) discloses “a method for removing and suppressing hydrogen sulfide using a hydrogen sulfide removing agent for surely removing hydrogen sulfide from an object to be processed and preventing generation thereof”. The purpose is to provide a device (see Summary / Problem column of Reference 4). However, the hydrogen sulfide removing agent used in Document 4 is merely one containing iron oxide or a metal oxide containing iron oxide as a main component, and is different from the present invention.

Japanese Patent Laid-Open No. 11-130402 JP 2007-159534 A JP 2002-282893 A Japanese Patent Laid-Open No. 2004-041998

  An object of the present invention is to provide a hydrogen generation method for generating hydrogen gas while preventing or suppressing generation of hydrogen sulfide gas by using an inorganic / organic mixed waste containing an inorganic component that can be a supply source of sulfur. It is in.

The hydrogen generation method of the present invention comprises:
(A) A processing object comprising at least a sulfur source, an organic component and moisture, and
(B) By introducing zinc oxide into an environment where anaerobic microorganisms capable of generating hydrogen sulfide under anaerobic conditions coexist, while preventing or suppressing the generation of hydrogen sulfide under anaerobic conditions It is characterized by generating hydrogen.

  According to the hydrogen generation method of the present invention, hydrogen gas can be generated while preventing or suppressing the generation of hydrogen sulfide gas by using an inorganic / organic mixed waste containing an inorganic component that can be a sulfur supply source. .

The figure which shows the outline of the apparatus and procedure of hydrogen gas generation | occurrence | production experiment. The experimental result of Examples 1-6 and Comparative Examples 5 and 6 is shown, (a) is a graph of zinc oxide addition amount, (b) is a graph of hydrogen sulfide generation amount, (c) is a graph of hydrogen generation amount. The experimental result of Comparative Examples 1-4 is shown, (a) is a graph of hydrogen sulfide generation amount, (b) is a graph of hydrogen generation amount. The figure which shows the outline of the apparatus and procedure for a sulfide measurement experiment. Graph of measured sulfide content.

Hereinafter, preferred modes for carrying out the present invention will be described.
The hydrogen generation method of the present invention comprises:
(A) A processing object comprising at least a sulfur source, an organic component and moisture, and
(B) It is carried out under anaerobic conditions by introducing zinc oxide into an environment where anaerobic microorganisms capable of generating hydrogen sulfide under anaerobic conditions coexist.

Here, the “treatment object comprising at least a sulfur source, an organic component and moisture” in (a) is any one selected from the group consisting of waste gypsum board, wastewater sludge, sewage sludge, and livestock manure, for example. One type, typically inorganic / organic mixed waste. In particular, (waste) gypsum board wraps plastered gypsum pieces mainly made of calcium sulfate (CaSO ₄ ) with special paperboard (called “gypsum board base paper”) and paste (eg starch paste) It is made by bonding. Therefore, in (waste) gypsum board, gypsum is a source of sulfur and glue is a source of organic components. In addition, when exposed to the outdoors as a waste material, it absorbs rainwater and the like and has moisture. Examples of organic components contained in starch paste include starch, cellulose, paraffin, and wax. It goes without saying that “drainage sludge”, “sewage sludge” and “livestock manure” similarly contain sulfur sources, organic components and moisture.

  (B) “Anaerobic microorganisms capable of generating hydrogen sulfide under anaerobic conditions” are, for example, sulfate-reducing bacteria (also referred to as sulfate-reducing bacteria), which are microorganisms that inhabit the natural world. For example, by leaving the treatment object in a wet state, it can be propagated in the treatment object.

  Zinc oxide is introduced into the environment in which the above (a) and (b) coexist. As this zinc oxide, high-purity zinc oxide (ZnO) marketed as an industrial product can be used, but the zinc oxide used is in the form of dissolved dust discharged from a melting furnace for cast iron such as a foundry. May be provided in Such dissolved dust is a mixture of various metal oxides and is generally regarded as waste. However, since it contains not a few zinc oxides, in the present invention, the oxidation involved in hydrogen generation by anaerobic microorganisms. It can be used as a source of zinc.

  The amount of zinc oxide used is preferably 0.03 parts by mass or more (more preferably 0.05 parts by mass or more) of zinc oxide with respect to 50 parts by mass of the object to be processed. By making the amount of zinc oxide used 0.03 parts by mass or more, the generation of hydrogen sulfide can be suppressed to a low level, and by making the amount of zinc oxide used 0.05 parts by mass or more, the generation of hydrogen sulfide can be suppressed. Almost can be prevented. There is no particular upper limit on the amount of zinc oxide used, but from the viewpoint of cost effectiveness, it is appropriate that the upper limit is 2.0 parts by mass of zinc oxide with respect to 50 parts by mass of the object to be treated.

  According to the present invention, even in an anaerobic environment where hydrogen sulfide may be generated by the action of microorganisms in the presence of moisture, generation of hydrogen sulfide is prevented or suppressed by simply introducing zinc oxide therein. Hydrogen can be produced. In the present invention, there is an advantage that there is no need to prepare conditions in particular except that zinc oxide is introduced into the environment, and there is little effort and the implementation cost is low.

  In addition, it is not certain about the reason or mechanism that hydrogen can be generated while suppressing the generation of hydrogen sulfide by adding zinc oxide. Even when the inventors of the present application have repeated experiments and considerations, it is not likely that hydrogen sulfide once generated simply reacts with zinc oxide and is converted into another compound (in the reference experiment described later, metal Sulfur formation was not observed, and when the amount of zinc was compared with the amount of suppressed hydrogen sulfide, it was not stoichiometrically correct assuming the formation of another compound). Rather, it is considered that zinc oxide suppresses the generation of hydrogen sulfide itself and is involved in the generation of hydrogen gas instead of hydrogen sulfide.

  Hereinafter, the present invention will be described more specifically by Examples 1 to 6 and Comparative Examples 1 to 6. In addition, “processing object”, “anaerobic bacteria”, “dissolved dust” and other materials used in each example were prepared as follows.

Processing object:
Using a commercially available gypsum board, the waste material (waste gypsum board) is pulverized with a machine, and the crushed waste gypsum board is passed through a sieve with a mesh opening of 2 mm. Used as. By the way, gypsum board is obtained by wrapping platy gypsum pieces mainly made of calcium sulfate with special paperboard (called “gypsum board base paper”) and glued with starch paste.

Anaerobic bacteria:
As anaerobic bacteria, microorganisms naturally attached to waste gypsum board were used. More specifically, the waste gypsum board piece is immersed in pure water in an airtight container, and the gypsum paper (gypsum board base paper) in the waste gypsum is left in the water-containing state. Then, sulfate-reducing bacteria (also called sulfate-reducing bacteria) propagate on the gypsum paper, and hydrogen sulfide gas is generated as evidence. When hydrogen sulfide gas is generated, the aqueous solution in the container is used as a seed. The seed was added to another aqueous solution and cultured for 1 to 2 weeks as an “anaerobic bacteria-containing aqueous solution”.

Dissolved dust:
Iron raw materials such as steel, pig iron and / or return iron, etc. are loaded into a melting furnace (cupola or electric induction furnace) and melted at a temperature of 1500 to 1600 ° C., and dust generated at that time (metal gas is caused by air “Oxidized powder formed by oxidation” is recovered by a dust collector attached to a melting furnace, which is “dissolved dust”. In Examples 1 to 4 and Comparative Examples 5 and 6 below, “Dissolved Dust 1” to “Dissolved Dust 6” are used, but these 6 types of dissolved dust have different melting furnaces or contain raw materials at the time of melting It is the melted dust which becomes a lot different from each other by having different. Therefore, the ZnO component ratio differs between these six types of dissolved dust (see Table 1 below). Incidentally, the component composition of the dissolved dust is a value converted to an oxide based on the result of the fluorescent X-ray measurement. Note that the dissolved dust also contains a composite metal oxide that can be expressed by the (Fe, Zn, Mn) _x O _{y characteristic} formula, and the value of the fluorescent X-ray measurement becomes the amount of zinc oxide as it is. However, when compared with the results of X-ray diffraction separately measured, the order (order) of the zinc oxide content ratio could be equated with the results of fluorescent X-ray measurement, so in Examples 1 to 4 and Comparative Examples 5 and 6 The measurement result of fluorescent X-ray was treated as the amount of zinc oxide.

Additives other than dissolved dust:
In Examples 1 to 4 and Comparative Examples 5 and 6, dissolved dust was used as an additive, while in Examples 5 and 6 and Comparative Examples 1, 2 and 3, those other than dissolved dust were used as additives. That is, in Examples 5 and 6, commercially available zinc oxide (ZnO) was used as an additive (see Table 1). In Comparative Example 1, Fe ₃ O ₄ was used as an additive, in Comparative Example 2 Fe ₂ O ₃ was used as an additive, and in Comparative Example 3 pure iron powder (Fe) was used as an additive (see Table 2).

[Examples 1 to 4 and Comparative Examples 5 and 6]
A hydrogen generation experiment was conducted according to the procedure shown in FIG. Specifically, in a 500 mL (milliliter) Duran bottle, 50 g of a processing object (crushed waste gypsum board), 0.1 g of dissolved dust, 200 mL of pure water, and 1 mL of an anaerobic bacteria-containing aqueous solution And put it in. Table 1 shows the additive formulation of each example. Thereafter, high-purity nitrogen gas was blown into the bottle to substantially replace the air in the bottle with nitrogen gas (setting an anaerobic atmosphere). The upper end opening of the bottle was sealed with a silicon stopper, and this was stored in a static state at 35 ° C. for 25 days. After 25 days, gas was extracted from the head space (gas phase) of each bottle with a syringe, and the components of this gas were measured by gas chromatography. The measurement results are shown in the graph of FIG.

[Examples 5 and 6]
As in Examples 1 to 4, a hydrogen generation experiment was performed according to the procedure shown in FIG. However, in Examples 5 and 6, zinc oxide (ZnO) was used as an additive instead of dissolved dust, in Example 5, the ZnO addition amount was 0.03 g, and in Example 6, the ZnO addition amount was 0.05 g. It was. The addition formulation of each example is shown in Table 1, and the measurement result of gas chromatography is shown in the graph of FIG.

[Comparative Examples 1-4]
As in Examples 1 to 4, a hydrogen generation experiment was performed according to the procedure shown in FIG. However,
In Comparative Example 1, 1 g of Fe ₃ O ₄ was used instead of 0.1 g of dissolved dust.
In Comparative Example 2, instead of 0.1 g of dissolved dust, 1 g of Fe ₂ O ₃
In Comparative Example 3, 0.1 g of pure iron powder (Fe) was used as an additive in place of 0.1 g of dissolved dust. Comparative Example 4 is an example without additives. The addition formulation of each example is shown in Table 2, and the measurement result of gas chromatography is shown in the graph of FIG.

  As can be seen from Table 2 and FIG. 3, in Comparative Examples 1 to 4 in which no zinc oxide was used as an additive, almost no hydrogen was generated. In addition, a large amount of hydrogen sulfide was generated in Comparative Example 4 without an additive, and generation of hydrogen sulfide was also observed in Comparative Examples 1 and 2 employing iron oxide as an additive. On the other hand, as can be seen from Table 1 and FIG. 2, a positive correlation was observed between the amount of zinc oxide added and the amount of hydrogen gas generated, and on the contrary, the amount of zinc oxide added and hydrogen sulfide A negative correlation was observed between the amount of occurrence and From the comparison of the four examples of Example 4, Comparative Examples 5, 6, and Example 5, the generation of hydrogen sulfide is reduced to a low level by using 0.03 g or more of zinc oxide (ZnO) with respect to 50 g of the object to be treated. While suppressing, hydrogen gas generation can be promoted. In particular, when looking at the trends of Examples 1 to 4 and 6, by using 0.05 g or more of zinc oxide (ZnO) with respect to 50 g of the object to be treated, hydrogen gas is almost completely prevented from being generated while hydrogen gas is generated. Generation can be promoted.

[Reference experiment and speculative consideration]
In the present invention, a reference experiment is conducted to find out the reason why hydrogen gas can be generated while suppressing the generation of hydrogen sulfide.

  As a reason why hydrogen sulfide is not observed, the assumption (hypothesis) that hydrogen sulfide once generated reacts with zinc oxide to become sulfide and is fixed inside or on the surface of the solid (object to be treated) holds. In order to confirm whether or not this guess is correct, the following experiments were performed using the Duran bottles of Examples 2 and 6 and Comparative Examples 3 and 4 using an apparatus as shown in FIG. This experiment corresponds to a partial modification of the sulfide measurement method of JIS K0102.

  That is, as shown in FIG. 4, the duran bottle after being left at 35 ° C. for 25 days was placed on a machine. However, since hydrogen sulfide gas is generated only in Comparative Example 4, 5 mL of an aqueous solution of zinc acetate (concentration 200 g / L) is added to the Duran bottle of Comparative Example 4 to absorb the hydrogen sulfide in the bottle into the aqueous solution. After that, the Duran bottle of Comparative Example 4 was placed on a machine. Then, the Duran bottle on the machine was connected to a nitrogen gas cylinder through an upstream pipe, and was connected in series with two absorption bottles installed on a magnetic stirrer via a downstream pipe. Each absorption bottle contained an aqueous zinc acetate solution (hydrogen sulfide absorption solution). Thereafter, a band heater was wound around a Duran bottle and heated to 70 ° C., and the contents were stirred by a rotary shaker so that the contents always flowed. In addition, in the two absorption bottles, in order to increase the gas flow rate, two straight pipe impingers were connected in series, and in order to increase gas absorption efficiency, a stirrer was placed in each impinger and stirred with a magnetic stirrer ( (Stirring speed 1500 rpm).

  When the piping and heating to 70 ° C are complete, 10 mL of sulfuric acid is added to the Duran bottle, and sulfur fixed as a sulfide to the sample in the bottle (when it is possible) is volatile. Was released as hydrogen sulfide gas. The liberated hydrogen sulfide was recovered in an aqueous zinc acetate solution in an absorption bottle disposed on the downstream side of the Duran bottle. After collecting the entire amount of free hydrogen sulfide, an aqueous zinc acetate solution in an absorption bottle was collected, and an excessive amount of iodine solution was added thereto, followed by titration with a sodium thiosulfate solution. Based on the titration results, the amount of sulfide (mgS / kg, the amount converted to sulfur per kg of the sample) fixed to the sample in the Duran bottle was calculated. The graph of FIG. 5 shows the calculation results of the sulfide amounts for Examples 2 and 6 and Comparative Examples 3 and 4.

  The graph of FIG. 5 shows how much sulfur (S) was fixed as sulfide per kg of waste gypsum boat (the sulfur was detected as free as hydrogen sulfide). As shown in FIG. 5, since the amount of sulfide in Comparative Examples 3 and 4 is about 1400 mgS / kg, sulfide equivalent to about 70 mgS was fixed in the 50 g waste gypsum boat. Here, in consideration of the fact that Comparative Example 4 is an example without additives and that almost no sulfide was detected in Examples 2 and 6, in Examples 2 and 6, the amount corresponding thereto was It can be understood that the generation of hydrogen sulfide was suppressed. More specifically, the amount of sulfur in Comparative Example 4 (without additives) is about 70 mg, the amount of ZnO added in Example 2 is 0.056 g, and the amount of ZnO added in Example 6 is From the fact that it is 0.05 g, in Example 2, 1330 mg of hydrogen sulfide is generated per 1000 mg of ZnO, and in Example 6, generation of 1490 mg of hydrogen sulfide is suppressed per 1000 mg of ZnO.

As a sulfide formed by the reaction of zinc (Zn) and sulfur (S), ZnS and ZnSO ₄ can be considered. In either case, the stoichiometric ratio (molar ratio) is Zn: S = 1: 1. When this is converted into mass based on the atomic weight, Zn: S = 65: 32 = about 2: 1. In consideration of this point, when the amount of suppression of hydrogen sulfide generation in Examples 2 and 6 (that is, suppression of generation of 1330 mg of hydrogen sulfide per 1000 mg of ZnO) is evaluated from a stoichiometric viewpoint, Examples 2 and 6 In this case, it is unlikely that sulfides such as ZnS and ZnSO ₄ are generated.

According to the above reference experiment and speculative consideration, the theory that sulfur (S) is sulfide (ZnS, ZnSO ₄ ) does not hold as the reason why hydrogen sulfide is not observed. Then, in the present invention, it is presumed that zinc oxide promotes hydrogen production while suppressing the generation of hydrogen sulfide in the first place. And what can be considered as a mechanism for suppressing hydrogen sulfide generation is a generally known hydrogen sulfide removal reaction by zinc oxide, that is,
It is not ZnO + H ₂ S → ZnS + H ₂ O, but it must be considered as a completely different mechanism. Since at least the generation of hydrogen sulfide is suppressed more than expected from the generally known reaction formula, it is considered that the reaction mechanism in the present invention is based on a novel reaction system that is not well known. .

  Since the present invention relates to a microbial reaction under anaerobic conditions when there is a sulfur source, waste treatment plants such as waste gypsum board, wastewater treatment plants that produce inorganic and organic wastewater sludge in companies, It can be used for waste recycling processes at sewage treatment plants that produce sewage sludge, biogas generation facilities that handle livestock manure, and the like. In particular, the present invention can be utilized as a method that does not increase the environmental load because new raw materials are not required by using dissolved dust. According to the present invention, there is a possibility that the desulfurization equipment can be abolished in a biogas generation facility or the like.

Furthermore, the present invention is expected to improve the activity of hydrogen-utilizing microorganisms as hydrogen is produced in the reaction system, and there is a possibility that the microbial reaction is promoted. In addition, with the generation of hydrogen, a reduction action of heavy metal ions present in the reaction system is expected. For example, there is a possibility of promoting detoxification of the reaction system by reducing hexavalent chromium to trivalent chromium.
Therefore, the present invention is not limited to a closed system that stores and utilizes hydrogen generated in a biogas generation facility or the like, for example, in an open system such as a building pit, a sludge deposition site, and a waste deposition site. Is expected to act effectively in the reaction system.

  In the graphs of FIGS. 2, 3 and 5, “actual” means an example, and “ratio” means a comparative example.

Claims (3)

(A) A processing object comprising at least a sulfur source, an organic component and moisture, and
(B) By introducing zinc oxide into an environment where anaerobic microorganisms capable of generating hydrogen sulfide under anaerobic conditions coexist, while preventing or suppressing the generation of hydrogen sulfide under anaerobic conditions A method for producing hydrogen, comprising generating hydrogen.   The method for generating hydrogen according to claim 1, wherein the zinc oxide is provided in the form of dissolved dust.   The method for generating hydrogen according to claim 1 or 2, wherein the object to be treated is any one selected from the group consisting of waste gypsum board, wastewater sludge, sewage sludge, and livestock manure.

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