Method for decomposing organic substances into smaller molecules

Abstract

The present invention provides a method for more efficiently decomposing and gasifying organic substances into smaller molecules, comprising the steps of: mixing a carbon monoxide-containing gas with water vapor in a number of molecules exceeding the number of carbon monoxide molecules to cause a shift reaction and obtaining a mixed gas containing hydrogen and carbon dioxide produced by the shift reaction and excess water vapor not consumed in the shift reaction; and introducing the organic substance and the mixed gas into a fluidized bed in which powder or granular material is flowing, and recovering low-molecular-weight products produced by the chemical reaction between the organic substance and the mixed gas, wherein superheated steam is further introduced into the fluidized bed.

Description

[Technical Field]

[0001] The present invention relates to a method for converting organic substances into low molecular weight substances, and in particular, to a method for modifying organic polymers such as plastics, rubber, and elastomers to convert them into low molecular weight products, and using the obtained low molecular weight products as gaseous fuels, etc., although not limited thereto. [Background technology]

[0002] Many industrial wastes containing organic polymers, such as waste plastics, oil-containing sludge, and waste rubber, are currently incinerated due to the lack of established chemical recycling technologies for converting them into other substances through chemical treatment. However, incineration of organic polymers generates CO2 and other environmentally harmful substances, and the high heat output can cause thermal damage to incinerators. Therefore, there is a need for the establishment of chemical recycling technologies for organic polymers. In particular, various technologies for converting organic polymers into low-molecular-weight products such as gaseous and liquid fuels have been investigated, focusing on waste plastics.

[0003] For example, the prior art disclosed in Patent Document 1 is a method of promoting thermal decomposition and hydrocracking of organic substances by reacting coke oven gas (hereinafter sometimes referred to as "COG"), which is produced in the final stage of the carbonization process using a coke oven and has a hydrogen concentration of 60 vol% or more and a temperature of 600°C or more, with organic substances such as waste plastics. By reacting COG containing a high concentration of hydrogen with organic substances, hydrocracking of the organic substances is promoted.

[0004] Furthermore, the prior art disclosed in Patent Document 2 is a method for reducing the molecular weight of organic substances by adding excess steam to exhaust gas containing carbon monoxide and carrying out a shift reaction to produce a mixed gas containing hydrogen and carbon dioxide produced in the shift reaction and excess steam not consumed in the shift reaction, and then contacting this mixed gas with an organic substance to reform the organic substance into lower molecular weight substances. Here, the "shift reaction" is a chemical reaction represented by the following chemical formula (1). In the shift reaction, carbon monoxide reacts with steam to produce hydrogen and carbon dioxide. This makes it possible to increase the concentration of hydrogen in the mixed gas. CO + H2O → H2 + CO2 (1)

[0005] Furthermore, Patent Document 3 discloses a method for reducing the molecular weight of organic substances, which is an improved version of the conventional technology disclosed in Patent Document 2, in which a mixed gas and organic substances are contacted in a fluidized bed containing powder or granular material containing at least one element selected from Fe, Ni, and Cr. This method uses a fluidized bed reactor as a reforming reactor, thereby preventing the adhesion of organic substances, which is a problem in flow-type fixed-bed reactors. Furthermore, the powder or granular material also functions as a catalyst, allowing the reaction for reducing the molecular weight of organic substances to proceed more efficiently. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-224206 [Patent Document 2] Japanese Patent Application Laid-Open No. 2012-188641 [Patent Document 3] Japanese Patent Application Laid-Open No. 2014-37524 Summary of the Invention [Problem to be solved by the invention]

[0007] The method disclosed in Patent Document 3, in which organic substances are decomposed into smaller molecules using a mixed gas in a fluidized bed, is a method that is excellent in terms of processing efficiency and cost. However, the conventional technology disclosed in Patent Document 3 has the following unresolved problems.

[0008] The inventors compared the progress of the decomposition reaction in the method for decomposing organic substances disclosed in Patent Document 3 between converter furnace dust generated in steelworks and silica sand. Converter furnace dust contains Fe, Ni, and Cr, which have catalytic properties, while silica sand does not. Therefore, it was expected that the decomposition reaction would proceed more easily with converter furnace dust than with silica sand. However, actual investigations revealed that the progress of the decomposition reaction did not differ significantly regardless of the type of powder. This is presumably because undecomposed organic substances adhere to the surface of the converter furnace dust, preventing contact between the organic substances and the converter furnace dust, thereby preventing the catalytic function of the Fe, Ni, and Cr contained in the converter furnace dust from working effectively.

[0009] Furthermore, although it is not entirely clear from the results of the comparative study, if components of undecomposed organic substances adhere to the surface of powder or granules, not only will their catalytic function be impaired, but the powder or granules may also agglomerate, making it difficult to maintain a fluid state. If the powder or granules lose their fluidity, their original functions of mixing reactants and conducting heat are impaired, hindering the progress of the chemical reaction. Agglomeration of powder or granules is particularly likely to occur when the low-molecular-weight products produced by the decomposition of organic substances contain highly viscous tar.

[0010] Therefore, an object of the present invention is to provide a method for reducing the molecular weight of organic substances, which comprises adding excess steam to a gas containing carbon monoxide to generate hydrogen gas and carbon dioxide gas through a shift reaction, producing a mixed gas containing the generated hydrogen gas and carbon dioxide gas and excess steam not consumed in the shift reaction, introducing the mixed gas and organic substances into a fluidized bed in which powder or granular material is flowing, and recovering low-molecular-weight products produced by a chemical reaction between the organic substances and the mixed gas, wherein the method prevents components of undecomposed organic substances from adhering to the surface of the powder or granular material inside the fluidized bed reactor, and enables efficient reduction of the molecular weight of the organic substances and gasification. [Means for solving the problem]

[0011] As a result of extensive research to solve the above problems, the inventors discovered that by directly introducing superheated steam into a fluidized bed in which powder and granular material is flowing, in addition to a mixed gas containing excess steam not consumed in the shift reaction, and separately from the mixed gas, the reaction of decomposing organic substances into smaller molecules in the fluidized bed can be promoted, resulting in more efficient gasification. Here, "superheated steam" refers to steam heated to a temperature higher than the boiling point of water. Superheated steam has a specific heat capacity approximately twice that of air and has extremely high hydrolysis ability. By directly introducing superheated steam into the fluidized bed, the decomposition of organic substances is promoted and the adhesion of undecomposed organic substance components to the powder and granular material can be prevented.

[0012] The inventors further discovered that when the organic matter in the treated material contains rubber or elastomer, the hydrocracking reaction is further accelerated, allowing for the efficient production of high-calorie low-molecular-weight products and also effectively suppressing the generation of tar, leading to the completion of the present invention.

[0013] The gist and configuration of the present invention are as follows.

[0014] [1] A step of mixing a gas containing carbon monoxide with water vapor in a number of molecules exceeding the number of carbon monoxide molecules to cause a shift reaction, and obtaining a mixed gas containing hydrogen and carbon dioxide produced by the shift reaction and excess water vapor not consumed in the shift reaction; a step of introducing an organic substance and the mixed gas into a fluidized bed in which powder or granular material is flowing, and recovering low molecular weight products produced by a chemical reaction between the organic substance and the mixed gas; A method for reducing the molecular weight of an organic substance comprising: A method for reducing the molecular weight of an organic substance, further comprising introducing superheated steam into the fluidized bed.

[0015] [2] The method for decomposing organic substances into smaller molecules according to the above [1], wherein the temperature of the superheated steam introduced into the fluidized bed is higher than the temperature of the mixed gas introduced into the fluidized bed.

[0016] [3] The method for breaking down organic substances into smaller molecules according to the above [1] or [2], wherein the powder or granule contains at least one selected from Fe, Ni, and Cr.

[0017] [4] The method for reducing the molecular weight of an organic substance according to any one of [1] to [3] above, wherein the organic substance includes a rubber or elastomer.

[0018] [5] The method for reducing the molecular weight of an organic substance according to [4] above, wherein the rubber / elastomer comprises a non-thermoplastic rubber. [Effects of the Invention]

[0019] According to the method for decomposing organic substances into smaller molecules of the present invention, it is possible to prevent the adhesion of undecomposed organic substance components to the surface of the powder or granules constituting the fluidized bed, thereby preventing the loss of the functionality of the fluidized bed midway and enabling the decomposition of organic substances into smaller molecules to be carried out efficiently and continuously. [Brief explanation of the drawings]

[0020] [Figure 1]1 is a schematic diagram showing an example of a fluidized bed reactor used in the method for decomposing organic substances into smaller molecules according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0021] In one embodiment, the present invention is a method for reducing organic substances to smaller molecules, comprising the steps of: mixing a gas containing carbon monoxide with water vapor in a number of molecules exceeding the number of carbon monoxide molecules to cause a shift reaction, thereby obtaining a mixed gas containing hydrogen and carbon dioxide produced by the shift reaction and excess water vapor not consumed in the shift reaction; and introducing an organic substance and the mixed gas into a fluidized bed in which powder or granular material is fluidized, and recovering low-molecular-weight products produced by a chemical reaction between the organic substance and the mixed gas, wherein superheated steam is further introduced into the fluidized bed. The following describes the features that define the present invention.

[0022] [Mixed gas] In this embodiment, organic substances are decomposed into smaller molecules using two types of gases: a mixed gas and superheated steam. Of these gases, the mixed gas contains hydrogen, carbon dioxide, and excess steam. The mixed gas is obtained by adding steam in an amount greater than the number of carbon monoxide molecules to a gas containing carbon monoxide, thereby causing a shift reaction. As described above, the "shift reaction" is a chemical reaction represented by the following chemical formula (1). By utilizing the shift reaction, a mixed gas containing a high concentration of hydrogen can be produced at a lower cost than when using commercially available hydrogen gas. The shift reaction for producing the mixed gas can be carried out by a known method, and there are no particular limitations. Of the two types of gases mentioned above, superheated steam will be described later. CO + H2O → H2 + CO2 (1)

[0023] The carbon monoxide-containing gas used in the shift reaction is preferably exhaust gas generated from a metallurgical furnace. A typical example of exhaust gas generated from a metallurgical furnace is converter gas generated from a converter in which the decarburization step of the steelmaking process is performed. In addition, exhaust gas generated from, for example, a hot metal pretreatment furnace, a smelting reduction furnace, a shaft furnace, etc. may also be used. Furthermore, a gas obtained by mixing one or more of these exhaust gases may also be used.

[0024] The typical composition of exhaust gas generated from a metallurgical furnace is 80-25 vol% carbon monoxide, 10-25 vol% carbon dioxide, 10-30 vol% nitrogen, and 0-20 vol% hydrogen. For exhaust gases with a relatively low carbon monoxide concentration and a high nitrogen concentration, such as blast furnace gas, at least a portion of the nitrogen may be removed to increase the carbon monoxide concentration before the shift reaction is carried out. The mixed gas may contain nitrogen and other components derived from the exhaust gas.

[0025] If the hydrogen concentration in the mixed gas is too low, CO2 tends to remain in the low-molecular-weight products when the organic substance reforming reaction is carried out at a relatively low temperature. Therefore, the hydrogen concentration is preferably 10 vol% or more, and more preferably 12 vol% or more. On the other hand, if the hydrogen concentration is too high, the organic substance decomposition rate cannot be maintained at a desirable level. Therefore, the hydrogen concentration is preferably 40 vol% or less, and more preferably 35 vol% or less.

[0026] If the concentration of carbon dioxide in the mixed gas is too low, hydrogen, a gas component with a lower calorie content than hydrocarbons and carbon monoxide, is likely to remain in the low-molecular-weight product. Therefore, the carbon dioxide concentration is preferably 10 vol% or higher, and more preferably 13 vol% or higher. On the other hand, if the carbon dioxide concentration is too high, the decomposition rate of organic substances cannot be maintained at a desirable level. Therefore, the carbon dioxide concentration is preferably 40 vol% or lower, and more preferably 35 vol% or lower.

[0027] The "excess steam" contained in the mixed gas refers to the steam that is mixed with the carbon monoxide-containing gas during the shift reaction and remains in the mixed gas without being consumed in the shift reaction. In order to leave excess steam in the mixed gas, it is sufficient to add steam in an amount that exceeds the number of carbon monoxide molecules to the carbon monoxide-containing gas. There are no particular limitations on the method for producing the steam used in the shift reaction.

[0028] If the concentration of excess steam in the mixed gas generated by the shift reaction is too low, the decomposition rate of organic substances decreases and the amount of heavy components produced increases, which can reduce the fluidity of powder and granular materials. Therefore, the concentration of excess steam is preferably 20 vol% or more, and more preferably 25 vol% or more. On the other hand, if the concentration of excess steam is too high, carbon dioxide tends to remain in the low-molecular-weight products and the lower heat of combustion (LHV) tends to decrease. Therefore, the concentration of excess steam is preferably 70 vol% or less, and more preferably 65 vol% or less.

[0029] In the method for depolymerizing organic substances according to this embodiment, the temperature and pressure of the mixed gas when introduced into the fluidized bed are not particularly limited. Because the shift reaction used to generate the mixed gas is an exothermic reaction, if the reaction temperature is too high, the shift reaction will not proceed smoothly. For this reason, it is preferable that the reaction temperature of the shift reaction does not greatly exceed 400°C. Furthermore, in order to avoid imposing excessive pressure resistance on the reaction vessel in which the shift reaction occurs, it is preferable that the shift reaction be carried out at atmospheric pressure. Therefore, when the mixed gas obtained by the shift reaction is used as is, it is preferable that the temperature of the mixed gas does not greatly exceed 400°C and that the pressure does not differ significantly from atmospheric pressure. Here, "atmospheric pressure" refers to the pressure of air at sea level.

[0030] Although it is unclear why the mixed gas used in this embodiment is effective in breaking down organic substances into smaller molecules, it is believed that the following reason is likely. When hydrogen is present during high-temperature pyrolysis of organic substances, hydrogenation and hydrocracking of hydrocarbon species proceed, which is effective in suppressing the formation of heavier compounds and breaking down organic substances into smaller molecules. However, hydrocracking requires high temperatures and consumes a large amount of hydrogen, which is problematic. Meanwhile, oxygen atoms contained in excess steam and carbon dioxide gas have the ability to oxidize hydrocarbons, and these processes are sometimes called steam reforming and carbon dioxide reforming, respectively. Steam reforming and carbon dioxide reforming are characterized by the fact that the reaction temperature decreases as the carbon chain of the organic substance being reformed increases. Therefore, by using a mixed gas containing excess steam and carbon dioxide gas in addition to hydrogen gas, the four reactions of hydrogenation, hydrocracking, steam reforming, and carbon dioxide reforming proceed simultaneously, which is thought to efficiently promote the breakdown of organic substances into smaller molecules even at relatively low reaction temperatures.

[0031] [Organic substances] In this embodiment, low-molecular-weight products generated by a chemical reaction between an organic substance and a mixed gas are recovered. The "organic substance" to be reduced in molecular weight in this embodiment is preferably a polymer compound such as synthetic resins, such as polyethylene and polypropylene, or synthetic rubber materials. Specific examples include waste plastics, oil-containing sludge, waste oil, and biomass, and one or more of these may be used. Organic substances with four or fewer carbon atoms, such as methane and ethanol, may be included in the organic substance in this embodiment, but are not the primary target of reduction in molecular weight.

[0032] The type of waste plastic, which is one of the targets of low molecular weight conversion in this embodiment, is not particularly limited, but examples thereof include industrial waste plastics, waste plastics subject to the Containers and Packaging Recycling Law, etc. More specifically, examples thereof include polyolefins such as polyethylene and polypropylene, thermoplastic polyesters such as polyamide and polyethylene terephthalate, elastomers such as polystyrene, thermosetting resins, synthetic rubbers, and polystyrene foam.

[0033] "Oil-containing sludge," one of the targets of low-molecular-weight reduction in this embodiment, refers to a sludge-like mixture generated in an oil-containing wastewater treatment process, and generally contains approximately 30% to 70% by mass of water. Examples of oils contained in oil-containing sludge include, but are not limited to, various mineral oils, natural and / or synthetic oils and fats, and various fatty acid esters. From the perspective of improving the handleability of the oil-containing sludge, it is preferable to reduce the water content of the oil-containing sludge to approximately 50% by mass or less in advance using a method such as centrifugation.

[0034] Examples of waste oils that are targets for low-molecular-weight reduction in this embodiment include, but are not limited to, various used mineral oils, natural and / or synthetic oils and fats, and various fatty acid esters. A mixture of two or more of these types of waste oils may also be used. When targeting waste oil generated in the rolling process of a steel mill, it generally contains more than 80% by mass of water. It is preferable to reduce this water content in advance by a method such as gravity separation in terms of ease of handling.

[0035] Examples of biomass, which is one of the targets for reduction to smaller molecules in this embodiment, include, but are not limited to, sewage sludge, paper, construction waste wood, packaging and transportation waste wood, wood such as thinned wood, and processed biomass such as refuse-derived fuel (RDF). Biomass usually contains a large amount of moisture, so it is preferable to dry it beforehand from the viewpoint of energy efficiency.

[0036] The moisture contained in the organic material vaporizes into water vapor during the chemical reaction with the mixed gas. The generated water vapor is contained in the mixed gas in the fluidized bed, increasing the concentration of water vapor in the mixed gas. Therefore, when adjusting the concentration of excess water vapor contained in the mixed gas generated by the shift reaction, it is preferable to determine the amount of water vapor to be added during the shift reaction, taking into account the amount of water vapor generated from the moisture contained in the organic material.

[0037] [Fluidized bed] In this embodiment, a chemical reaction between the organic substance and the mixed gas is caused by introducing an organic substance and a mixed gas into a fluidized bed in which powder or granular material is flowing. Here, the term "fluidized bed" refers to a type of gas-phase reaction apparatus in which powder or granular material is suspended and fluidized in a gas flow blown up from below, and reacts, dries, absorbs, and the like with the reactants. As described above, by using a fluidized bed reactor as a reforming reactor that breaks down organic substances into smaller molecules, it is possible to prevent the adhesion of organic substances, which is a problem in flow-type fixed-bed reactors. This is thought to be because the temperature within the fluidized bed is nearly uniform and heat is exchanged very quickly. The structure of the fluidized bed reactor will be described in detail later.

[0038] The powder or granular material constituting the fluidized bed used in this embodiment is preferably a material that has excellent fluidity and thermal conductivity and is stable against reactions that decompose organic substances into smaller molecules. Specifically, for example, iron-containing dust, mill scale, reduced iron powder, atomized iron powder, alumina powder, silica sand, and the like generated in the steelmaking process can be used, but the types of powder or granular material are not limited to these. Furthermore, a mixture of multiple types of powder or granular material can be used.

[0039] If the particle size of the powder or granules constituting the fluidized bed is too small, the ventilation of the mixed gas and the superheated steam described below in the fluidized bed may be hindered. Therefore, the particle size of the powder or granules is preferably 0.01 mm or more in D50, and more preferably 0.1 mm or more. On the other hand, if the particle size of the powder or granules constituting the fluidized bed is too large, smooth stirring of the organic substances in the fluidized bed may be hindered. Therefore, the particle size of the powder or granules is preferably 5 mm or less in D50, and more preferably 1 mm or less. The D50 of the powder or granules can be measured by a sieving method or the like.

[0040] If the true density of the powder and granules that make up the fluidized bed is too low, the density difference between them and the ash of the organic matter is small, making it difficult to separate and collect them from the ash of the organic matter, and separation of the powder and ash tends to be insufficient. 3 On the other hand, if the true density of the powder or granule is too high, the difference in specific gravity with the organic substance being treated becomes large, making it difficult to sufficiently mix the organic substance and the powder or granule and make them flow. Therefore, the true density of the powder or granule should be 8.0 g / cm or more. 3 When a plurality of types of powder or granular materials are mixed and used, the true density of the powder or granular material can be the volume average value of the true densities of the individual powder or granular materials.

[0041] In a preferred embodiment, the powder or granule contains at least one element selected from Fe, Ni, and Cr. Fe, Ni, and Cr are all active in the reaction of decomposing organic substances into smaller molecules, and the powder or granule also functions as a catalyst, allowing the reaction of decomposing organic substances to proceed with high efficiency. The Fe, Ni, and Cr contained in the powder or granule may be present in any form, such as metal or oxide.

[0042] In this preferred embodiment, if the total content of Fe, Ni, and Cr in the powder or granules is too low, the true density of the powder or granules will be low, making it difficult to separate the powder or granules dispersed in the gas discharged from the fluidized bed reactor from the ash of the organic matter. Therefore, the total content of Fe, Ni, and Cr in the powder or granules is preferably 20% by mass or more, and more preferably 30% by mass or more. On the other hand, if the total content of Fe, Ni, and Cr in the powder or granules is too high, the true density will be too high and the fluidity will be reduced. Therefore, the total content of Fe, Ni, and Cr in the powder or granules is preferably 90% by mass or less, and more preferably 80% by mass or less.

[0043] [Degradation of organic substances] In this embodiment, organic substances and a mixed gas are introduced into a fluidized bed, and a chemical reaction between the organic substances and the mixed gas occurs within the fluidized bed, thereby reducing the molecular weight of the organic substances, and the resulting low-molecular-weight products are recovered. As described above, in the method for reducing molecular weight according to the present invention, four reactions, namely, hydrogenation reaction, hydrocracking reaction, steam reforming, and carbon dioxide reforming, proceed simultaneously, thereby enabling highly efficient reduction of the molecular weight of organic substances. In reality, it is clear that a thermal decomposition reaction also proceeds in addition to these reactions. Of these reactions, the hydrocracking reaction, steam reforming, carbon dioxide reforming, and thermal decomposition are endothermic reactions, while the hydrogenation reaction is exothermic. Therefore, the overall reduction reaction of organic substances is an endothermic reaction, and reaction heat must be supplied from an external source to continue the reaction.

[0044] The excess water vapor contained in the mixed gas has a very large thermal conductivity and an extremely high calorific value, and therefore plays an important role in maintaining a high temperature inside the fluidized bed. Furthermore, in the present invention, by causing the low-molecular-weight reaction inside the fluidized bed, where the heat transfer rate is high, the reaction heat supplied from the outside can be used efficiently to low-molecular-weight the organic substances. This prevents problems such as clogging due to fusion of the organic substances inside the fluidized bed.

[0045] [Superheated steam] In this embodiment, superheated steam is further introduced into the fluidized bed. In the present invention, organic substances are decomposed into smaller molecules using two types of gases: a mixed gas and superheated steam. As described above, "superheated steam" refers to steam heated to a temperature higher than the boiling point of water. The boiling point of water is, for example, 100°C under atmospheric pressure. As described above, the shift reaction used to generate the mixed gas is an exothermic reaction, and therefore, if the reaction temperature is too high, the shift reaction does not proceed easily. For this reason, it is preferable that the reaction temperature of the shift reaction does not greatly exceed 400°C. In contrast, the temperature of superheated steam is not restricted by the shift reaction and can be heated to any temperature. By using superheated steam in combination, organic substances are decomposed into smaller molecules more efficiently than when only a mixed gas containing excess steam is used.

[0046] In this embodiment, the reason why the introduction of superheated steam into the fluidized bed further accelerates the depolymerization of organic substances is unclear, but it is believed to be due to the following reasons. As is well known, liquid water has a very high specific heat, and therefore steam also exhibits very high thermal conductivity. Heat conduction through steam is usually convective, and at high temperatures, radiative heat transfer is also involved. However, in the case of superheated steam, a type of heat transfer called condensation heat transfer is also involved. Here, "condensation heat transfer" refers to heat transfer that occurs when superheated steam imparts latent heat when it adheres to the surface of an object as condensed water. This heat transfer has a heating capacity five to ten times greater than that of heated air. Furthermore, because superheated steam is made up of water molecules themselves, it also has a very high hydrolysis capacity in an oxygen-free atmosphere. The heating and hydrolysis capacity of superheated steam, due to its excellent thermal conductivity, is thought to enable highly efficient depolymerization of organic substances even at low temperatures and in a short time.

[0047] In this embodiment, the temperature of the superheated steam is not particularly limited as long as it is higher than the boiling point of water. As will be described later, the higher the temperature of the superheated steam, the greater the thermal conductivity and hydrolysis ability of the superheated steam. For this reason, the temperature of the superheated steam is preferably 200°C or higher, more preferably 400°C or higher, and even more preferably 600°C or higher. On the other hand, although there is no particular upper limit to the temperature of the superheated steam, since a great deal of energy is required to heat the superheated steam to a temperature above 1000°C, the temperature of the superheated steam is preferably substantially 1000°C or lower.

[0048] In a preferred embodiment, the temperature of the superheated steam introduced into the fluidized bed is higher than the temperature of the mixed gas introduced into the fluidized bed. The higher the temperature of the superheated steam, the greater the thermal conductivity and hydrolysis ability of the superheated steam. As mentioned above, the temperature of the superheated steam is not restricted by the shift reaction, and therefore the superheated steam can be heated to any temperature. In particular, when the temperature of the superheated steam is made higher than the temperature of the mixed gas containing excess steam, the high-temperature superheated steam introduced into the fluidized bed further promotes the reaction of depolymerizing the organic substances. The temperature of the superheated steam introduced into the fluidized bed is preferably at least 100°C higher, and more preferably at least 200°C higher, than the temperature of the mixed gas introduced into the fluidized bed.

[0049] The pressure of the superheated steam is not particularly limited. As in the case of a mixed gas, the pressure of the superheated steam is preferably not significantly different from atmospheric pressure in order to avoid imposing excessive pressure resistance on the equipment for heating the superheated steam and the fluidized bed reactor.

[0050] In this embodiment, the superheated steam is preferably introduced into the fluidized bed via a route different from that of the excess steam introduced into the fluidized bed as part of the mixed gas. This prevents a decrease in the temperature of the superheated steam before it is introduced into the fluidized bed. In this embodiment, the steam used in the shift reaction and the superheated steam may be supplied from the same supply source. In this case, the superheated steam may be branched, for example, into a pipe different from that of the steam used in the shift reaction, and additional heating may be performed after branching.

[0051] [Low molecule products] The low molecular weight products produced by the method for reducing organic substances to low molecular weight according to this embodiment typically contain light hydrocarbons with carbon numbers of about 1 to 4 and carbon monoxide. These gases can be suitably used as gaseous fuels. In addition, a portion of the low molecular weight products can be condensed to produce liquid fuel. The lower heat of combustion (LHV) of the low molecular weight products obtained by this invention is approximately 6 Mcal / Nm 3 More than 10 Mcal / Nm 3 The calorific value is comparable to that of natural gas, for example, and the high carbon monoxide concentration makes it more combustible than natural gas. Because of these characteristics, the low molecular weight product obtained by the present invention can be used, for example, as a fuel gas to replace city gas, which is the heat source for metallurgical furnaces used in steelworks.

[0052] Furthermore, the low molecular weight product obtained in this embodiment can be used as a reducing agent in a blast furnace, rather than as a fuel. As described above, this low molecular weight product contains light hydrocarbons and carbon monoxide, which are components of natural gas, and both light hydrocarbons and carbon monoxide are effective as reducing agents for iron ore. Therefore, in the operation of a blast furnace, by injecting the low molecular weight product obtained in this embodiment into the tuyere of the blast furnace, the amount of coke used as another reducing agent can be reduced. This reduces the amount of carbon dioxide emitted from the blast furnace, which is also effective in reducing steelmaking costs.

[0053] [Rubber and elastomers] In a preferred embodiment, the organic substance includes a rubber elastomer. Rubber elastomer is a general term for polymeric materials that have elasticity. This embodiment makes it possible to reduce the molecular weight of non-thermoplastic rubber, which has been particularly difficult to reduce the molecular weight of using conventional technology.

[0054] The production volume of rubber and elastomers is increasing every year. Consequently, the amount of rubber and elastomer waste generated during production and discarded by consumers is also increasing. Rubber and elastomers are broadly divided into non-thermoplastic rubbers and thermoplastic elastomers (TPEs), which are thermoplastic in the strict sense. Thermoplastic elastomer waste can be recycled and is not a major social problem. Rubber molecules, on the other hand, are formed by crosslinking through vulcanization, resulting in a three-dimensional structure. To recycle rubber, a regenerating agent must be added to restore its plasticity, plasticizing the crosslinked structure, severing sulfur crosslinks, and depolymerizing the molecular backbone. However, since it is difficult for recycled rubber to maintain its pre-recycled performance, it is often processed through thermal recycling. Meanwhile, the low-molecular-weight products obtained from rubber pyrolysis have a higher calorie content than waste plastics, potentially enabling more effective chemical recycling.

[0055] However, when attempting to depolymerize rubber using conventional techniques, heavy components and carbonaceous materials such as tar tend to be mixed into the low-molecular-weight product. Heavy components are unsuitable for use as fuel gas. Furthermore, carbonaceous materials adhere to the interior of the fluidized-bed reactor, piping, and the surface of the powder and granular material, reducing the exhaust capacity of the piping and reducing the fluidity and catalytic performance of the powder and granular material.

[0056] When the method for decomposing organic substances according to this embodiment is applied to rubber, the strong hydrolysis ability of the superheated steam introduced into the fluidized bed in addition to the mixed gas accelerates the decomposition reaction of the rubber. This suppresses the generation of heavy components and carbonaceous materials such as tar. Furthermore, since the superheated steam also decomposes carbonaceous materials adhering to the surface of powder or granules, the surface properties of the powder or granules are maintained, thereby maintaining fluidity and a high catalytic effect.

[0057] As described above, the method for depolymerizing organic substances according to this embodiment is particularly effective in depolymerizing non-thermoplastic rubbers. However, in this embodiment, the rubber / elastomer contained in the organic substance may also contain a thermoplastic elastomer. In this preferred embodiment, the content of the rubber / elastomer in the organic substance is not particularly limited, as long as it is greater than zero, and the entire organic substance may be rubber / elastomer. The form of the rubber / elastomer is not particularly limited, but from the perspective of shortening the reaction time inside the fluidized bed, it is preferable to introduce it into the reactor in a crushed state of approximately 2.5 cm or less.

[0058] In a more preferred embodiment, the organic substance includes a non-thermoplastic rubber. Examples of non-thermoplastic rubbers that do not have thermoplastic properties include all so-called rubber materials. Specific examples of rubber materials include diene rubbers such as natural rubber, isoprene rubber, styrene-butadiene rubber, butadiene rubber, nitrile-butadiene rubber, chloroprene rubber, and butyl rubber; rubbers containing methylene groups such as ethylene-propylene rubber, ethylene-vinyl acetate copolymer, chlorinated polyethylene, chlorosulfonated polyethylene, and acrylic rubber; and specialty rubbers such as hydrin rubber, urethane rubber, polysulfide rubber, silicone rubber, and fluororubber, but are not limited to these.

[0059] Specific examples of rubber products made from the above-mentioned rubber materials include automobile rubber tires, which are discarded in large quantities every year. Also included are waste conveyor belts used to transport ore and coal at steel mills and thermal power plants. Tires and conveyor belts often contain steel cord or steel wire to improve their strength. These steels remain intact during thermal decomposition in the fluidized bed, allowing them to be naturally separated by weight during processing and recovered at the bottom of the fluidized bed.

[0060] [Fluidized bed reactor] In this embodiment, it is preferable to use a fluidized bed reactor as the reforming reactor. Fig. 1 is a schematic diagram showing an example of a fluidized bed reactor used in the method for reducing the molecular weight of an organic substance according to this embodiment. In this fluidized bed reactor 1, powder and granular material are loaded above a gas dispersion plate 1b provided at the bottom of a cylindrical container. A shift reactor 2 is supplied with a carbon monoxide-containing gas 3 and water vapor 4 having a molecular number exceeding that of carbon monoxide to cause a shift reaction, thereby producing a mixed gas 5 containing hydrogen, carbon dioxide, and excess water vapor.

[0061] By supplying mixed gas 5 through mixed gas inlet 1d provided at the bottom of fluidized bed reactor 1, the powder and granules are suspended and then fall toward the bottom under their own weight, repeating this process. This forms a fluidized bed 1a of powder and granules inside fluidized bed reactor 1. By introducing organic substance 6 into fluidized bed 1a through organic substance inlet 1c provided at the top of fluidized bed reactor 1, a chemical reaction occurs between organic substance 6 and mixed gas 5 inside fluidized bed 1a. Low molecular weight products 7 produced by the chemical reaction are discharged to the outside through low molecular weight product outlet 1e provided at the top of fluidized bed reactor 1 and collected. Fluidized bed reactor 1 may be equipped with a heating mechanism (not shown) that can heat the vessel from the outside.

[0062] In this fluidized-bed reactor 1, in addition to the mixed gas 5 supplied from the bottom, superheated steam 8 is also introduced into the fluidized bed 1a. This promotes the reaction of depolymerizing the organic substances 6 in the fluidized bed 1a, thereby achieving more efficient depolymerization. It is preferable that the superheated steam 8 be introduced into the fluidized-bed reactor 1 not through the gas dispersion plate 1b at the bottom, but through a superheated steam inlet 1f provided at the position where the fluidized bed 1a is located, as shown in FIG. 1 . In this case, the temperature of the superheated steam 8 is not lowered by mixing with the mixed gas, and the superheated steam 8 can be introduced into the fluidized bed 1a while maintaining its temperature at a high level.

[0063] The flow velocity of the mixed gas 5 blown from the gas dispersion plate 1b toward the fluidized bed 1a is preferably adjusted within a range that maintains a good dispersion state of the powder and granules. If the flow velocity of the mixed gas 5 is too low, the fluidity of the fluidized bed 1a decreases, hindering the progress of the low-molecular-weight reaction. Therefore, the flow velocity of the mixed gas 5 is preferably 0.05 m / s or higher. On the other hand, if the flow velocity of the mixed gas 5 is too high, the fluidity of the fluidized bed 1a is not affected, but the flow velocities of the low-molecular-weight products 7 and excess mixed gas 5 discharged from the fluidized-bed reactor 1 increase, resulting in an increase in the amount of powder and granules scattered to the outside through the low-molecular-weight product outlet 1e. Furthermore, as described below, when the organic substance 6 is supplied from the top of the fluidized-bed reactor 1, the particle size of the organic substance 6 must also be increased, which reduces the reaction efficiency of the low-molecular-weight reaction. Therefore, the flow velocity of the mixed gas 5 is preferably 2.0 m / s or lower.

[0064] It should be noted that in this embodiment, organic substance 6 such as plastic is broken down into low molecular weight substances, and the number of molecules increases by about two times, so the flow velocity of the gas containing low molecular weight products 7 discharged from fluidized bed reactor 1 is about twice that of mixed gas 5. For example, if the flow velocity of mixed gas 5 is 0.05 m / s, the flow velocity of the gas containing low molecular weight products 7 will be about 0.1 m / s. Furthermore, if the flow velocity of mixed gas 5 is 2.0 m / s, the flow velocity of the gas containing low molecular weight products 7 will be about 4.0 m / s.

[0065] The organic substance 6 can be supplied to the fluidized-bed reactor 1 by spraying liquid organic substances such as oil-containing sludge and waste oil using a spray nozzle or the like, and can be supplied to any position within the fluidized-bed reactor 1. Solid organic substances 6, such as waste plastics, biomass, and rubber / elastomers, are typically supplied from the top of the fluidized-bed reactor 1, but can also be supplied to the top of the gas distribution plate 1b by pneumatic transport. When supplying solid organic substances 6 from the top of the fluidized-bed reactor 1, it is convenient to allow the organic substance 6 to fall by gravity. However, in this case, it is preferable to mold the solid organic substance 6 to have a particle size and density that prevents scattering while also selecting a particle size that does not reduce reaction efficiency. Furthermore, when transporting organic substances 6 by pneumatic transport, it is preferable to use a mixed gas or exhaust gas containing carbon monoxide rather than air, because pneumatic transport can cause combustion within the reactor due to the oxygen contained in the air.

[0066] When the solid organic material 6 is supplied from the top of the fluidized bed reactor 1 and allowed to fall, the particle size of the supplied solid organic material 6 that does not scatter varies depending on the density of the organic material 6 and the flow rate of the gas containing the low-molecular-weight product 7. For example, if the true density of the solid organic material 6 is 1 g / cm 3 Therefore, when the flow velocity of the gas containing the low-molecular-weight product 7 is about 0.1 m / s, the particle size of the molded solid organic material 6 is preferably about 2.0 mm or more and 6.0 mm or less. Also, when the flow velocity of the gas containing the low-molecular-weight product 7 is about 4.0 m / s, the particle size of the molded solid organic material 6 is preferably about 15 mm or more and 20 mm or less.

[0067] The gas containing low molecular weight products 7 discharged from the fluidized bed reactor 1 is contaminated with some of the powder and granular materials constituting the fluidized bed 1a, as well as ash produced by the decomposition of organic materials 6 such as waste plastics, rubber, and elastomers. These contaminants can be collected by a dust collector (not shown) installed downstream of the fluidized bed reactor 1. The powder and granular materials used in the present invention have a true density of 3.0 g / cm, which is higher than that of powder and granular materials commonly used in fluidized beds. 3When powders of this size are used, the powders and granules can be collected in a state where they are separated from the ash of the organic matter 6 in the dust collector. This makes it easy to return the separated powders and granules to the fluidized bed 1a through the powder inlet 1h shown in Figure 1, preventing the powders and granules from being diluted by ash that is inactive in the low-molecular-weight reaction. On the other hand, if the true density of the powders and granules is too high, as mentioned above, the flowability of the powders and granules will decrease, or the difference in specific gravity with the waste plastics, rubber, and elastomers will become too large, making it difficult to perform fluidization and stirring. Therefore, the true density of the powders and granules should be 8.0 g / cm. 3 It is preferable that:

[0068] In this embodiment, the action of the fluidized bed 1a and superheated steam 8 prevents the generation of heavy components of the undecomposed organic matter 6, such as tar and other carbonaceous materials. Even so, prolonged operation may result in the generation of small amounts of these components, which may remain inside the fluidized bed 1a or adhere to the surface of the powder or granular material. Furthermore, when waste tires or waste conveyor belts are used as rubber or elastomers, metals such as steel cords and steel wires may remain inside the fluidized bed 1a without being decomposed. Because of their high specific gravity, these heavy components, carbonaceous materials such as tar, and metals are not discharged from the low-molecular-weight product discharge port 1e along with the low-molecular-weight product 7 but remain inside the fluidized bed 1a. Furthermore, some of the ash remaining from the low-molecular-weight conversion reaction may remain inside the fluidized bed 1a. These residues can be discharged together with the powder or granular material from the residue discharge port 1g shown in FIG. 1 during the low-molecular-weight conversion reaction or when operation is stopped. Residues are separated from the discharged matter, and if the remaining powder or granules can be reused, they can be returned to the fluidized bed 1a again through the powder or granule inlet 1h. [Example]

[0069] The embodiments of the present invention will be described in more detail using examples, but the scope of the present invention is not limited to the scope of the following examples.

[0070] [Example 1] Converter furnace gas with an average composition of 12 vol% H2, 54 vol% CO, 17 vol% CO2, 1 vol% H2O, and 16 vol% N2 was used as the carbon monoxide-containing gas. A branch pipe for laboratory testing was installed on the gas outlet pipe of the gas holder, which temporarily stores the converter furnace gas, so that a small flow rate of converter furnace gas could be extracted through this branch pipe. Downstream of this branch pipe, a flow control valve, a steam mixer, a preheater for preheating the mixture of converter furnace gas and steam, a shift reactor for causing the shift reaction, and a fluidized bed reactor were arranged in this order. Of these, the shift reactor was packed with an Fe-Cr-based high-temperature shift catalyst.

[0071] The fluidized bed reactor had an inner diameter of 66 mm and was capable of being heated externally. A pipe was connected to the bottom of the fluidized bed reactor so that the entire amount of gas generated in the shift reactor could be supplied to the fluidized bed reactor. A gas distribution plate was installed at the bottom of the fluidized bed reactor, and a powder mixture of converter dust, mainly composed of Fe generated in the decarburization blowing, and silica sand was mixed in a mass ratio of 1:2 above the gas distribution plate, with a true density of 3.0 g / cm. 3 The powder and granules were loaded so that the D50 of the powder and granules was adjusted to 600°C by external heating, regardless of whether or not superheated steam was introduced. A circle feeder-type constant-volume feeder was installed at the top of the fluidized-bed reactor so that the organic substances could be introduced into the fluidized bed by dropping them. A superheated steam inlet was installed at a position one-third of the height from the bottom of the fluidized-bed reactor, allowing superheated steam to be introduced into the fluidized bed alone, separate from the mixed gas used in the shift reaction.

[0072] Next, the converter gas extracted through the branch pipe was supplied to the steam mixer at a flow rate of 1.3 NL / min, and the pressure was 10 kg / cm 2The converter gas was mixed with steam at a flow rate of 1.7 NL / min. The converter gas and steam mixture was then heated to 300°C in a preheater and introduced into the shift reactor. The composition of the mixed gas obtained by the shift reaction was 26 vol% H2, 2 vol% CO, 28 vol% CO2, 37 vol% H2O (excess steam), and 7 vol% N2. The temperature of the mixed gas at the outlet of the shift reactor was 400°C. This mixed gas was introduced into the bottom of the fluidized bed reactor through a gas dispersion plate at a flow rate of 3.0 NL / min. The pressure of the mixed gas was 10 kg / cm2, the same as that of the steam used in the shift reaction. 2 The steam from G was heated to 600°C using an electric heater to become superheated steam, and was introduced into the fluidized bed inside the fluidized bed reactor at a flow rate of 0.6 NL / min through a port, which is a route different from the gas dispersion plate, which is the route for the mixed gas.

[0073] Next, waste plastics with particle sizes of 8 mm and a rubber conveyor belt cut into cubes with sides of approximately 10 mm were fed into the fluidized-bed reactor at a feed rate of 5.0 g / min using a quantitative feeder. The depolymerization was continued for one hour. The feed was then stopped, the heating of the fluidized-bed reactor was stopped, and the powder and granules were cooled. During this time, the low-molecular-weight products recovered from the top of the fluidized-bed reactor and cooled by the gas cooler were analyzed to determine their composition, production rate, and lower heat of combustion (LHV). The liquid product collected using a liquid fuel collector installed below the gas cooler was also analyzed to determine its type and production rate, as well as the low-molecular-weight products. Furthermore, the solid product separated and recovered from the cooled powder and granules was also analyzed. These analytical results are summarized in Table 1.

[0074] According to Table 1, the composition of the recovered low molecular weight products ranged from 1 to 4 carbon atoms, and carbon atoms of 5 or more were below the analytical detection limit. The lower heat of combustion (LHV) of the low molecular weight products was 5.9 kcal / Nm 3The recovered product liquid was an oil with a calorific value of 10,373 kcal / kg, and the ash and moisture content and kinematic viscosity were all equivalent to those of heavy oil No. 1. The flash point of this oil was slightly low at 49°C, equivalent to that of diesel. The recovered solid was completely carbonized carbon black, with a production rate of 1.5 g / min. This carbon black is thought to have originated from the waste conveyor belt.

[0075] [Example 2] The test was conducted under the same conditions as in Example 1, except that the organic material fed into the fluidized bed reactor was a rubber conveyor belt cut into cubes with sides of approximately 10 mm, and the feed rate was 10 g / min. The amount of low molecular weight products obtained was reduced compared to Example 1, but the lower heat of combustion (LHV) was 6.3 kcal / Nm 3 This resulted in a gas with an even higher calorie content than that of Invention Example 1. On the other hand, the amount of oil, which is the produced liquid, and carbon black, which is the produced solid, was almost twice that of Invention Example 1.

[0076] [Example 3] The test was carried out under the same conditions as in Example 1, except that the organic material fed into the fluidized bed reactor was only waste plastics with a particle size of 8 mm, and the feed rate was 10 g / min. The amount of low molecular weight products obtained was increased compared to Example 1. In addition, hydrocarbons with a carbon content of 5 or more were included, and their lower heat of combustion (LHV) was 4.9 kcal / Nm 3 The resulting gas had a slightly lower calorie content than that of Example 1. The liquid produced was mainly tar, but no adhesion of tar to the piping or powder was observed.

[0077] [Comparative Example 1] The test was carried out under the same conditions as in Example 1, except that the supply of superheated steam through the port into the fluidized bed reactor was stopped. The composition of the obtained low molecular weight product showed an increase in the amount of hydrocarbons with a carbon number of 5 or more compared to Examples 1, 2, and 3, and the lower heat of combustion (LHV) was 2.5 kcal / Nm 3The resulting gas had an even lower calorie content than Example 3. Tar was observed adhering to the inner wall of the pipe leading to the liquid fuel collector installed below the gas cooler. Tar was also observed adhering to the surface of the powder and granules. The recovered solid product was carbon black, and the production rate was 1.7 g / min.

[0078] Comparative Example 2 The test was carried out under the same conditions as in Example 3, except that the supply of superheated steam through the port into the fluidized bed reactor was stopped. In Comparative Example 2, in which superheated steam was not used and the organic substance supplied did not contain rubber or elastomer, the low-molecular-weight reaction did not proceed, and the lower heat of combustion (LHV) of the low-molecular-weight product was 3.2 kcal / Nm 3 In addition, tar was found adhering to the inner wall of the pipe.

[0079] Comparative Example 3 The test was conducted under the same conditions as Comparative Example 2, except that silica sand alone was used as the powder charged into the fluidized bed, rather than a mixture of converter dust and silica sand. In Comparative Example 3, which did not use superheated steam and used powder containing no Fe, Ni, or Cr, the catalytic effect of the powder did not promote the decomposition reaction. In addition, the proportion of hydrocarbons with a carbon number of 4 or less in the low-molecular-weight products and the lower heat of combustion (LHV) of the low-molecular-weight products were the lowest among the Examples. Tar adhesion to the inside of the piping was also observed.

[0080] [Table 1]

[0081] The test results shown in Table 1 show that when superheated steam is introduced into a fluidized bed according to the method for reducing the molecular weight of organic substances of the present invention, the reaction for reducing the molecular weight of organic substances is promoted compared to conventional techniques that do not use superheated steam. It is also clear that a high lower heat of combustion (LHV) is obtained for the low molecular weight products, and tar does not adhere to the piping or powder. Furthermore, in the preferred embodiments shown in Invention Examples 1 and 2, in which the organic substance to be introduced contains rubber / elastomer, the carbon reduction reaction is further promoted, tar production is suppressed, and the carbon reduction reaction is reduced to 5.0 kcal / Nm 3 It can be seen that low molecular weight products with high lower heat of combustion (LHV) exceeding 1000 kJ / L are obtained. [Explanation of symbols]

[0082] 1. Fluidized bed reactor 1a Fluidized bed 1b Gas distribution plate 1c Organic substance inlet 1d Mixed gas inlet 1e Low molecular product outlet 1f Superheated steam inlet 1g residue outlet 1h Powder inlet 2. Shift reactor 3. Gases containing carbon monoxide 4. Water vapor 5. Mixed Gases 6 Organic substances 7 Low molecule products 8 Superheated steam

Claims

1. a step of mixing a gas containing carbon monoxide with water vapor in a number of molecules exceeding the number of carbon monoxide molecules to cause a shift reaction, and obtaining a mixed gas containing hydrogen and carbon dioxide produced by the shift reaction and excess water vapor not consumed in the shift reaction; a step of introducing an organic substance and the mixed gas into a fluidized bed in which powder or granular material is flowing, and recovering low molecular weight products produced by a chemical reaction between the organic substance and the mixed gas; A method for reducing the molecular weight of an organic substance comprising: A method for reducing the molecular weight of an organic substance, further comprising introducing superheated steam into the fluidized bed.

2. 2. The method for decomposing organic substances into smaller molecules according to claim 1, wherein the temperature of the superheated steam introduced into the fluidized bed is higher than the temperature of the mixed gas introduced into the fluidized bed.

3. 3. The method for breaking down organic substances into smaller molecules according to claim 1, wherein the powder contains at least one element selected from the group consisting of Fe, Ni, and Cr.

4. 3. The method for breaking down an organic substance into smaller molecules according to claim 1, wherein the organic substance includes a rubber elastomer.

5. 5. The method for breaking down organic substances into smaller molecules according to claim 4, wherein the rubber elastomer comprises a non-thermoplastic rubber.

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