Process for the direct hydrogenation decomposition reduction of carbonates based on iron-containing solid waste

Abstract

The application provides a process for direct hydrogenolysis reduction of carbonates based on iron-containing solid waste. The iron-containing solid waste is mixed into the carbonate raw material, and then calcination and reduction are carried out under the condition of hydrogen molecule supply, so that metal oxides can be obtained at a relatively low temperature, and in-situ capture and conversion of CO2 can be realized, which has a significant potential for emission reduction and consumption reduction. The added solid waste can be directly used in the production process of cement, refractory and the like, and does not need to be separated and treated as a "catalyst". The new process realizes high-value utilization of solid waste, energy saving and consumption reduction of carbonate decomposition process and in-situ conversion and utilization of CO2, and has important practical significance and broad industrial application prospect.

Description

Technical Field

[0001] This invention belongs to the technical field of carbon reduction and efficiency improvement in the calcination and decomposition process of carbonates in industries such as cement, steel, and refractory materials, and also to the technical field of efficient and comprehensive utilization of iron-containing solid waste. Specifically, it relates to a new process for the direct hydrogenation reduction of carbonates catalytically derived from iron-containing solid waste. Background Technology

[0002] High-temperature thermal decomposition of carbonates is a core process in industries such as cement, steel, and refractory materials. This process consumes a large amount of fossil energy and emits a significant amount of CO2, thus necessitating the development of effective carbon reduction and efficiency-enhancing solutions. Although carbon capture, utilization, and storage (CCUS) technology can cool, separate, and capture industrial CO2 emissions before storage and utilization, this technology faces industrial challenges such as complex processes, high energy consumption, low efficiency, and high costs. Using H2 and CH4 as hydrogen donor molecules (reducing agents), coupled with the catalytic reduction of hydrogen donor molecules through the co-thermal decomposition of carbonates, in-situ CO2 conversion can be achieved, significantly reducing the energy consumption of carbonate decomposition reactions. This approach has excellent industrial application prospects and extremely high eco-economic value. Research on this coupling process, both domestically and internationally, is still in its early stages. Preliminary experimental results have verified the feasibility of introducing hydrogen donor molecules in reducing carbonate decomposition temperature and synergistically converting CO2, but the process still suffers from slow carbonate decomposition rates and low in-situ conversion efficiency between CO2 and hydrogen donor molecules. Introducing a suitable catalyst into this coupled reaction process is an effective means to improve the reaction kinetic rate and conversion efficiency. However, how to achieve efficient catalyst promotion of this "gas-solid-solid" three-phase reaction process, and ensure that the addition of the catalyst does not affect the quality of carbonate decomposition products (especially cement production processes for human settlements), while not adding excessive economic costs, is the challenge in selecting catalysts for this coupled process.

[0003] Bulk solid waste (hereinafter referred to as "solid waste") is abundant, widespread, has a significant environmental impact, and has broad utilization prospects, making it a core area of ​​comprehensive resource utilization. Promoting the comprehensive utilization of bulk solid waste is of great significance for improving resource utilization efficiency, enhancing environmental quality, and promoting the comprehensive green transformation of economic and social development. The comprehensive utilization of bulk iron-containing solid waste such as steel slag, fly ash, tailings, and smelting slag remains a challenge for the industry, with billions of tons of solid waste accumulating and urgently requiring a rational utilization method. Although special cements such as steel slag cement have been developed, the addition of steel slag in the cement clinker stage only achieves the purpose of disposing of solid waste and fails to utilize the high iron content to improve its economic efficiency. Moreover, numerous studies have shown that the free calcium oxide and magnesium oxide contained in steel slag have a significant negative impact on cement performance.

[0004] Considering these two realities, this application proposes a novel process for the co-thermal decomposition of carbonates under a reducing atmosphere, coupled with hydrogen-donating molecular catalytic reduction, using iron-containing solid waste as a catalyst. This process can synergistically achieve emission reduction and efficiency improvement in the carbonate refining process and the efficient utilization of bulk solid waste, demonstrating strong innovation and industrial application value. Summary of the Invention

[0005] The purpose of this invention is to provide a novel process for the catalytic decomposition of carbonates using iron-containing solid waste coupled with the catalytic reduction of hydrogen-donating molecules.

[0006] The technical solution adopted by the present invention to achieve this objective is as follows:

[0007] A process for the direct hydrogenation decomposition and reduction of carbonates based on iron-containing solid waste is disclosed. The iron-containing solid waste is used as a catalyst to catalyze the pyrolysis of carbonates coupled with the catalytic reduction of hydrogen molecules in a reactor, yielding a solid product containing metal oxides and a gaseous product containing carbon monoxide. The iron-containing solid waste is selected from one or more of red mud, steel slag, fly ash, and coal gangue.

[0008] Furthermore, the iron-containing solid waste and carbonates are fed in powder form and react in a fluidized state in the reactor under the action of a gas containing hydrogen molecules.

[0009] Furthermore, the carbonate raw material and iron-containing solid waste can be premixed and fed simultaneously, or they can be fed separately. The mass ratio of iron-containing solid waste to carbonate is 1:(2-10), for example, 3:10 or 1:5.

[0010] Furthermore, the iron-containing solid waste is selected from red mud or steel slag powder with high iron content.

[0011] Furthermore, the particle size of the carbonate is 200-400 mesh; the particle size range of the iron-containing solid waste catalyst is 200-400 mesh.

[0012] Furthermore, the catalytic carbonate pyrolysis coupled with hydrogen molecule catalytic reduction reaction can be continuous or intermittent. For continuous reactions, solid and gaseous feedstocks are fed simultaneously and continuously, with the flow rate ratio controlled so that the powdered feedstock particles can be decomposed in suspension within the furnace; preferably, the feed flow rate ratio of solid powder to gas is 10000–60000 ml / g. cat -1 h -1 For example, 30000ml g cat -1 h -1 50000ml g cat -1 h -1For intermittent reactions, solid raw materials can be added to the reactor first, and gaseous materials can be introduced under closed conditions so that the solid powder is dispersed in a suspended state under the action of the gaseous materials; preferably, the gas flow rate is 0.5-2 m / s.

[0013] Furthermore, the operating temperature of the reactor is 600-850℃.

[0014] Furthermore, the carbonate is selected from one or more combinations of calcium carbonate, magnesium carbonate, and ferrous carbonate, or from one or more combinations of limestone, dolomite, marble, calcite, magnesite, and siderite.

[0015] Furthermore, the hydrogen-donating molecule is selected from one or more combinations of hydrogen, methane, ethane, and propane.

[0016] Furthermore, the gas containing hydrogen donor molecules includes hydrogen donor molecules and an inert gas, wherein the volume of the inert gas accounts for 50-90% of the total volume of the gas containing hydrogen donor molecules.

[0017] Furthermore, the reactor is a fluidized bed reactor or a conventional carbonate decomposition furnace reactor.

[0018] Furthermore, the reactor includes a reactor body, which is provided with a solid raw material inlet, a tail gas outlet, a gaseous raw material inlet, and a solid material outlet from top to bottom.

[0019] Compared with existing technologies, the method for catalytic co-thermal decomposition of iron-containing solid waste into carbonate coupled with hydrogen molecule reduction provided by this invention has the following advantages:

[0020] (1) By coupling the thermal decomposition reaction of carbonates with the catalytic reduction reaction of hydrogen-donating molecules, CO2 can be captured and converted in situ, thereby achieving the goal of reducing CO2 emissions at the source. At the same time, the pyrolysis process of carbonates is promoted after coupling, which reduces the energy consumption of the carbonate decomposition process.

[0021] (2) Iron-containing solid waste acts as a catalyst to promote the kinetic rate of the coupled reaction, and there is no need to consider the separation of the "catalyst". The calcined iron-containing solid waste can be directly used for subsequent cement clinker production, which significantly improves the utilization value of iron-containing solid waste and reduces production costs.

[0022] (3) Adding iron-containing solid waste during the carbonate calcination and decomposition stage can promote the reaction between hydrogen-donating molecules and carbonates through the catalytic function of iron-containing solid waste. At the same time, the active free calcium oxide in the solid waste can be calcined at high temperature, which can solve the problem of poor mechanical properties of traditional steel slag cement. Attached Figure Description

[0023] Figure 1The attached diagram is a schematic diagram of a reactor structure for realizing a new process of direct hydrogenation reduction of iron-containing solid waste catalytic carbonates according to an embodiment of the present invention; the figures are labeled as follows: 1, reactor body; 2, solid raw material inlet; 3, solid material outlet; 4, gaseous raw material inlet; 5, tail gas outlet.

[0024] Figure 2 The figures show the pyrolysis results of Examples 1 and 2, and Comparative Examples 1 and 2; the left figure shows the change in CO2 content in the exhaust gas, and the right figure shows the change in CO content in the exhaust gas.

[0025] Figure 3 The thermogravimetric results are for the products of Examples 1 and 2 and Comparative Examples 1 and 2 of the present invention; the left figure shows the decomposition rate of calcium carbonate, and the right figure shows the in-situ utilization rate of carbon dioxide.

[0026] Figure 4 The differences in the performance of different iron-based catalysts for the catalytic decomposition of carbonates in Example 1 and Comparative Example 1 of this invention are shown; (a) shows the gaseous products of the catalytic hydrogenation decomposition of calcium carbonate; (b) shows the XRD patterns of 10Fe / SBA-15 and steel slag powder (GZF).

[0027] Figure 5 Examples 9 and 10 of the present invention and Comparative Examples 4 and 5 show the complete pyrolysis results; wherein (a) is the change in CO2 content in the exhaust gas, (b) is the change in CO content in the exhaust gas, (c) is the decomposition rate of calcium carbonate, and (d) is the in-situ utilization rate of carbon dioxide. Detailed Implementation

[0028] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0029] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0030] Figure 1 This is a schematic diagram of the reactor structure for a novel process of direct hydrogenation reduction of iron-containing solid waste into carbonates, provided by an embodiment of the present invention.

[0031] like Figure 1As shown, the reactor includes: a reactor body 1, a solid feed inlet 2, a tail gas outlet 5, a gas feed inlet 4, and a solid material outlet 3. The solid feed is a mixture of carbonate powder F1 and iron-containing solid waste powder F2, which enters the reactor body 1 from the solid feed inlet 2 at the top of the reactor. Hydrogen-donating gas F4 enters the reactor from the gas feed inlet 4 at the bottom side and participates in the gas-solid reaction within the reactor. The solid powder flow and the flue gas flow are in opposite directions, with the solid powder remaining suspended in the air. The decomposition solid product F3 gradually descends to the bottom solid material outlet 3 under gravity and exits the reactor, while the reaction product gas F5 is discharged from the tail gas outlet 5 at the top side.

[0032] The above-mentioned process couples the carbonate decomposition process and the hydrogen molecule reduction and conversion process using iron-containing solid waste, enabling the coupled process to be carried out continuously in the same reactor. This effectively reduces the carbonate decomposition temperature and achieves in-situ conversion and utilization of CO2 during the carbonate decomposition process. It has significant advantages such as reducing process energy consumption, reducing CO2 emissions, and improving overall process efficiency. In addition, the active iron component in the iron-containing solid waste can effectively catalyze the coupling reaction, improve reaction kinetics, and supplement raw materials, thus achieving efficient and comprehensive utilization of bulk solid waste.

[0033] The present invention will be further described below with reference to specific embodiments, but these are not intended to limit the scope of the invention.

[0034] Example 1:

[0035] 100 mg of calcium carbonate powder and 10 mg of steel slag powder were mixed and added to a reactor body made of glass tube. A hydrogen-donating gas of 20% H₂-80% Ar was introduced from below at a rate of 50 ml / min, causing the mixed powder in the reactor to remain in a suspended state under the influence of the gas. The temperature was controlled at 700℃. After running for 6 minutes, the solids were collected for thermogravimetric analysis to determine the carbonate content, while the exhaust gas was analyzed by mass spectrometry for gas composition and concentration. Based on this, two process evaluation indicators could be obtained: the decomposition rate of calcium carbonate within 6 minutes; and the in-situ conversion rate of CO₂.

[0036] The main parameters involved in the various embodiments of the present invention are shown in Table 1 below. Table 2 provides reference compositions for several different types of iron-containing solid waste.

[0037] Table 1. Parameters and process evaluation indicators for Examples 1-10

[0038]

[0039]

[0040] Table 2. Composition Reference of Different Types of Iron-Containing Solid Waste

[0041]

[0042] Comparative Example 1

[0043] The same process as in Example 1 was used, except that no catalyst was added.

[0044] Comparative Example 2

[0045] The same process as in Example 1 was used, except that no catalyst was added and the hydrogen donor molecules H2 were replaced with air.

[0046] Comparative Example 3

[0047] The same process as in Example 1 was used, except that mesoporous SiO2 loaded with 20 wt% Fe was used as the catalyst (Fe@SBA-15). This catalyst was prepared by a solid-phase impregnation method. Specifically, SBA-15 was first prepared using a soft template method, with the P123 template agent remaining inside the pores without being removed by calcination. A certain amount of Fe(NO3)3·9H2O was weighed and mixed with the prepared SBA-15, and mechanically ground for 30 minutes to obtain a solid mixture powder. This powder was then placed in a muffle furnace and calcined at 700°C for 3 hours. The resulting sample was pre-reduced in pure H2 in a tube furnace for 1 hour before use.

[0048] The amount of Fe@SBA-15 catalyst used should be such that its Fe content is consistent with the Fe content in the steel slag powder in Example 1.

[0049] Comparative Example 4

[0050] The same process as in Example 9 was used, except that no catalyst was added.

[0051] Comparative Example 5

[0052] The same process as in Example 10 was used, except that no catalyst was added and the hydrogen donor H2 was replaced with air.

[0053] Figure 2 The pyrolysis results of Examples 1 and 2 and Comparative Examples 1 and 2 of this invention are presented. The changes in CO2 content in the exhaust gas show that a hydrogen-containing atmosphere significantly promotes CO2 release, i.e., the decomposition of calcium carbonate. After adding iron-containing solid waste as a catalyst, CO2 levels decrease slightly, but CO release increases significantly. The total emissions of both represent the amount of carbonate decomposition. Therefore, adding iron-containing solid waste can further promote calcium carbonate decomposition based on hydrogen reduction. Furthermore, comparing low-iron-content steel slag powder (GZF) and high-iron-content red mud (CN), it can be concluded that iron, as an active species, is more conducive to carbonate decomposition and in-situ conversion of CO2 to CO. Combined with excess H2, industrial syngas feedstock gas can be obtained.

[0054] Figure 3 The thermogravimetric results of the products of Examples 1 and 2 of the present invention and Comparative Examples 1 and 2 were compared. The decomposition rate was calculated by dividing the weight loss by the theoretical maximum weight loss (because the theoretical maximum weight loss corresponds to a theoretical decomposition rate of 100%). The results showed that the decomposition rate of calcium carbonate under H2 conditions (26.5%) was much higher than that under air conditions (19.8%). Furthermore, the decomposition rate was further improved after adding the iron-containing solid waste catalyst, from about 26.5% to about 36.6%-39.3%. In addition, the in-situ utilization rate of carbon dioxide within 6 minutes was calculated. It was found that 50% of the carbon dioxide from the decomposition of carbonate after adding the iron-containing solid waste could be converted into CO in situ. These results confirmed the catalytic effect of the iron-containing solid waste.

[0055] Figure 4 The differences in the performance of Example 1 and Comparative Example 1 using different iron-based catalysts for the catalytic decomposition of carbonate hydrogenation are shown. The results indicate that the purified Fe@SBA-15 exhibits weaker catalytic performance than steel slag powder (GZF) with similar iron content, essentially showing no activity towards the RWGS reaction. XRD analysis revealed further differences. Figure 4 b) It can be found that Fe@SBA-15 has good dispersion of Fe active sites, but it still does not show similar activity to steel slag powder. The possible reason is that the third element in steel slag powder, such as manganese, aluminum, titanium, etc., produces a catalytic synergistic effect with iron active substances, thereby promoting the in-situ hydrogenation conversion of CO2.

[0056] Figure 5 The results show that the iron-containing solid waste catalyst of this application can achieve a carbonate decomposition rate of over 98% in 6 minutes at a decomposition temperature of 800℃, while the complete decomposition of carbonates in existing industries generally requires temperatures of 900℃ or higher. Compared with the system without catalyst, the carbonate decomposition and CO2 conversion rates are faster, especially in the system using red mud as catalyst, where CO2 is converted to CO at a higher reaction rate.

[0057] The above are merely preferred embodiments of the present invention and are not intended to limit the implementation methods and protection scope of the present invention. Those skilled in the art should recognize that any equivalent substitutions and obvious changes made based on the content of this specification should be included within the protection scope of the present invention.

Claims

1. A process for the direct hydrogenation decomposition and reduction of iron-containing solid waste into carbonates, characterized in that, Iron-containing solid waste is used as a catalyst to catalyze the pyrolysis of carbonate coupled with the catalytic reduction of hydrogen-donating molecules in a reactor, yielding a solid product containing metal oxides and a gaseous product containing carbon monoxide. The iron-containing solid waste is selected from one or more combinations of red mud, steel slag, fly ash, and coal gangue. Both the iron-containing solid waste and carbonates are fed in powder form and react in a fluidized state in the reactor under the action of a gas containing hydrogen-donating molecules. The hydrogen-donating molecules are selected from one or more combinations of hydrogen, methane, ethane, and propane. The operating temperature of the reactor is 700-850℃.

2. The process according to claim 1, characterized in that, The mass ratio of iron-containing solid waste to carbonates is 1:10 to 1:

2.

3. The process according to claim 1, characterized in that, The carbonate is selected from one or more of calcium carbonate, magnesium carbonate, and ferrous carbonate, or from one or more of limestone, dolomite, marble, calcite, magnesite, and siderite.

4. The process according to claim 1, characterized in that, The gas containing hydrogen donor molecules includes hydrogen donor molecules and inert gas, wherein the volume of inert gas accounts for 50-90% of the total volume of the gas containing hydrogen donor molecules.

5. The process according to claim 1, characterized in that, The carbonate has a particle size of 200-400 mesh; the iron-containing solid waste catalyst has a particle size range of 200-400 mesh.

6. The process according to claim 1, characterized in that, The reactor is a fluidized bed reactor.

7. The process according to claim 1, characterized in that, The reactor includes a reactor body, which is provided with a solid raw material inlet, a tail gas outlet, a gaseous raw material inlet, and a solid material outlet from top to bottom.

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