Method for preparing synthesis gas through ultrasonic enhanced carbonate hydrogenation

Abstract

The invention provides a method for preparing synthesis gas through ultrasonic-enhanced carbonate hydrogenation, which comprises the following steps: step 1, ultrasonic pretreatment: placing carbonate in an ultrasonic field for pretreatment, and weakening the bonding strength of metal-oxygen polar bonds in the carbonate through ultrasonic action; 2, hydrogenation coupling pyrolysis: placing the carbonate subjected to ultrasonic pretreatment in a reaction device, and collecting solid-phase carbonate; and placing the solid-phase carbonate in a reaction device, introducing reducing gas as reaction gas, and carrying out a coupling pyrolytic reaction under a normal pressure condition, so that carbon dioxide generated by carbonate decomposition is subjected to in-situ reduction by the reducing gas, and the synthesis gas with carbon monoxide as a main carbon-containing component is prepared. According to the method, a catalyst is not needed, the problem of high energy consumption of a traditional process is solved, and the reaction selectivity is improved through the ultrasonic-enhanced directional catalysis effect.

Description

Technical Field

[0001] This invention relates to the field of carbonate pyrolysis technology, and in particular to a method for ultrasonically enhanced hydrogenation of carbonates to produce syngas. Background Technology

[0002] Carbonates (such as calcium carbonate and dolomite) are among the most abundant inorganic carbon resources on Earth, widely found in raw materials and byproducts of industrial production in cement, steel, and metallurgy. In traditional processes, the high-temperature pyrolysis of carbonates (e.g., calcium carbonate requires temperatures above 900℃) generates large amounts of CO2, becoming a major source of carbon emissions in the industrial sector. The carbonate decomposition emissions from cement production alone account for 5%-7% of global anthropogenic carbon emissions. Driven by the dual carbon goals (carbon reduction and high-value utilization), achieving low-carbon treatment and high-value utilization of carbonates has become a key issue in overcoming the bottleneck of high-carbon emission industrial development.

[0003] The emergence of carbonate hydrogenation to syngas technology offers an innovative solution to this challenge. This technology introduces hydrogen and low-carbon alkanes as hydrogen donor molecules, directly converting carbonaceous species in carbonates into syngas—a core "platform molecule" in the chemical industry—based on CO and H2. This syngas can then be further processed through processes such as Fischer-Tropsch synthesis to produce high-value-added products such as hydrocarbons and oxygen-containing organic compounds. Compared to traditional pyrolysis processes, this technology offers two advantages: firstly, the hydrogen atmosphere lowers the carbonate pyrolysis temperature by more than 150°C, significantly reducing energy consumption; secondly, it converts the original CO2 emissions into high-value resources, achieving a synergistic effect of "emission reduction and efficiency improvement," and is considered a disruptive technological strategy for high-carbon emission industries to achieve "carbon neutrality."

[0004] As early as 1968, scholars such as Giardini and Reller reported in *Science* and *Nature* the feasibility of hydrogenating carbonates to form carbon-containing compounds under high temperature and pressure, laying the technological foundation. In recent years, with the advancement of catalytic material research and development and reaction system optimization, this technology has gradually transitioned from theoretical exploration to industrial-scale testing, and related patent technologies have emerged continuously. However, the core technological bottlenecks have not yet been overcome, limiting its large-scale application.

[0005] Currently, patent research and development on carbonate hydrogenation to syngas technology mainly focuses on reaction system construction, catalyst design and process integration. However, existing technologies generally suffer from problems such as low conversion efficiency, high energy consumption and rapid catalyst deactivation, which are significantly different from the needs of industrial-scale applications.

[0006] (a) Hydrogenation technology using hydrogen as a hydrogen source

[0007] This type of technology couples carbonate pyrolysis with a reverse water-gas shift reaction, using hydrogen as a reducing agent to achieve carbon species conversion. For example, CN113582208A discloses a method for the co-production of syngas from carbonate hydrogenation for carbon dioxide emission reduction, clarifying the industrial application path of carbonate hydrogenation to syngas. By optimizing reaction temperature and pressure parameters, the directional conversion of carbonate to syngas is achieved. However, the mass transfer efficiency of this reaction system is low, the contact between hydrogen and solid carbonate is insufficient, and the pyrolysis temperature of carbonate is as high as 800℃ or more, resulting in a CO2 conversion efficiency of only 60%-70%, far below industrial requirements.

[0008] (ii) Patent defects in reforming hydrogenation technology using low-carbon alkanes as hydrogen sources This type of technology couples carbonate pyrolysis with alkane reforming reactions, using methane and other similar molecules as hydrogen donors. For example... CN114735956B discloses a low-carbon production method and system for cement clinker. This patent innovatively uses a conversion furnace instead of a traditional decomposition furnace, allowing methane to be used as both fuel and reactant gas, achieving the synergistic conversion of CO2 from carbonate decomposition and CO2 from fuel. However, the main drawbacks of this technology are: firstly, the large gas volume in the conversion furnace leads to a CO concentration in the syngas below 30%, increasing subsequent purification costs; secondly, the heat absorbed by the methane dry reforming reaction is twice that of the in-situ hydrogen reduction, requiring additional heat sources and significantly increasing energy costs. The carbonate methane dry reforming (CADRM) technology route can achieve a 95% CaO yield and a 90% CH4 conversion rate at 700℃, but there are significant thermodynamic and kinetic contradictions. Although high temperatures can promote the forward reforming reaction, the direct pyrolysis rate of carbonates increases sharply above 800℃, causing the CO2 conversion efficiency to drop below 75%; simultaneously, catalyst carbonation is severe at high temperatures, resulting in insufficient lifespan for Ni-based catalysts, far below the industrial catalyst requirement of over 1000 hours.

[0009] A comprehensive analysis of relevant studies shows that the defects of the existing carbonate hydrogenation to syngas technology can be summarized into four aspects: (1) Low mass transfer efficiency: In the gas-solid two-phase reaction system, hydrogen and methane molecules do not have sufficient contact with solid carbonate, resulting in low reaction rate and insufficient conversion efficiency, which is the primary bottleneck restricting the technology's production capacity; (2) Catalyst performance degradation: Under high temperature reaction conditions, catalysts are prone to carbon deposition, metal sintering and adhesion to metal oxides, resulting in decreased activity and shortened lifespan, increasing equipment maintenance and operating costs; (3) High reaction energy consumption: Both the strong endothermic characteristics of methane dry reforming and the high temperature requirements of traditional pyrolysis result in high process energy consumption, weakening the economic feasibility of the technology; (4) Uneven product quality: The CO concentration in the syngas fluctuates greatly and the impurity content is high, and the subsequent purification process is complex, further raising the threshold for industrial application.

[0010] Therefore, overcoming the existing technical barriers to the production of syngas from carbonate hydrogenation is a pressing technical problem that needs to be solved. Summary of the Invention

[0011] To address the problems of existing technologies, this invention provides an ultrasound-enhanced method for the hydrogenation of carbonates to produce syngas. This method eliminates the need for a catalyst and includes ultrasonic pretreatment and hydrogenation coupled with pyrolysis, thus solving the problem of high energy consumption in traditional processes. Furthermore, the ultrasonic-enhanced directional catalysis improves the selectivity of the reaction.

[0012] The technical solution of the present invention is as follows: Step 1: Ultrasonic pretreatment: Carbonates are pretreated in an ultrasonic field to weaken the bonding strength of metal-oxygen polar bonds in the carbonates through ultrasonic action. Step 2: Hydrogen-coupled pyrolysis: The carbonate pretreated by ultrasound is placed in a reaction apparatus, and a reducing gas is introduced as the reaction gas. The coupled pyrolysis reaction is carried out under normal pressure, so that the carbon dioxide produced by the decomposition of carbonate is reduced in situ by the reducing gas, and syngas with carbon monoxide as the main carbon component is prepared.

[0013] Further, in step 1, the carbonate is a metal carbonate, which is selected from one or more of calcium carbonate, magnesium carbonate, barium carbonate, and strontium carbonate, and the particle size of the carbonate raw material is 10μm-500μm.

[0014] Furthermore, in step 1, the ultrasonic frequency of the ultrasonic pretreatment is 15kHz-80kHz, and the ultrasonic power is 100W-1500W.

[0015] Furthermore, in step 1, the temperature of the ultrasonic pretreatment is an ice-water bath, and the pretreatment time is 0.2h-1.9h; when the pretreatment time is 0.5h-1.5h, the bond energy of the metal-oxygen bond in the carbonate is reduced by 20%-40%.

[0016] Furthermore, in step 2, the reducing gas is hydrogen, and the volume fraction of the hydrogen is 50%-100%; when the hydrogen volume fraction is ≥80%, the carbon monoxide selectivity is ≥85%.

[0017] Furthermore, in step 2, the flow rate of the reaction gas is 30 mL / min to 200 mL / min, preferably 100 mL / min, and the flow rate is adjusted by precise control using a mass flow controller.

[0018] Furthermore, in step 2, the heating rate of the coupled pyrolysis reaction is 1℃ / min-50℃ / min, preferably 10℃ / min.

[0019] Furthermore, in step 2, the reaction temperature of the coupled pyrolysis reaction is 500℃-700℃, preferably 600-650℃.

[0020] Furthermore, in step 2, the reaction time of the coupled pyrolysis reaction is 1 min to 100 min.

[0021] Furthermore, in step 2, when the reaction temperature of the coupled pyrolysis reaction is 600-650℃ and the heating rate is 5℃ / min-20℃ / min, the carbonate conversion rate is ≥85%.

[0022] Furthermore, in step 2, the reaction device is a fixed-bed reactor, a fluidized-bed reactor, or a moving-bed reactor; a gas distributor is provided inside the reaction device, which is a perforated plate type, a nozzle type, or a spiral type to ensure uniform contact between the reaction gas and the solid carbonate.

[0023] Further, in step 2, the selectivity of carbon monoxide in the synthesis gas is 85%-95%, and the carbon monoxide selectivity is defined as the ratio of the number of moles of carbon monoxide to the total number of moles of all gaseous components (including carbon monoxide, carbon dioxide, unreacted hydrogen, etc.) in the reaction products.

[0024] Furthermore, in step 2, the solid product generated by the coupled pyrolysis reaction is a metal oxide, which is selected from one or more of calcium oxide, magnesium oxide, barium oxide, and strontium oxide.

[0025] Furthermore, in step 2, after the tail gas from the coupled pyrolysis reaction is condensed and dehydrated, and the unreacted reducing gas is recycled back to the reaction device for reuse, with a recycling rate of ≥80%.

[0026] The beneficial effects of this invention are as follows: 1. This invention provides a method for ultrasonically enhanced hydrogenation of carbonates to produce syngas. By treating carbonate raw materials with ultrasound and then carrying out coupled pyrolysis reaction, the decomposition temperature of carbonates can be reduced and the reaction process accelerated without the use of catalysts. At the same time, the carbon in carbonates can be converted into carbon monoxide chemicals with higher added value.

[0027] 2. In view of the common defects of the existing technology, the present invention breaks down the gas-solid two-phase contact barrier by using the cavitation effect and stirring effect of the ultrasonic field, increases the contact area between hydrogen molecules and carbonate particles, solves the problem of insufficient conversion efficiency and reaction rate caused by low mass transfer efficiency, and achieves a carbon monoxide selectivity of 80%-95% and a CO reaction rate of 0.4-2.0 mmol / g / min in the synthesis gas.

[0028] 3. This invention utilizes the dispersing effect of ultrasound to inhibit catalyst particle agglomeration, and at the same time removes carbon deposits on the catalyst surface through ultrasonic vibration, thus solving the performance degradation problems caused by catalyst adhesion, sintering, and carbon buildup.

[0029] 4. This invention utilizes the local thermal effect of the ultrasonic field to assist the reaction, thereby reducing the overall temperature requirement of the reaction system and solving the problem of high energy consumption in traditional processes.

[0030] 5. This invention improves the selectivity of the reaction and stabilizes the ratio of CO to H2 in the syngas through ultrasonic-enhanced directional catalysis, thus solving the problem of excessively high subsequent purification costs caused by uneven product quality.

[0031] 6. This invention innovatively couples ultrasonic technology with the carbonate hydrogenation reaction system, specifically addressing the aforementioned technical bottlenecks and providing an industrially feasible technical solution for the low-carbon, high-value utilization of carbonates. Attached Figure Description

[0032] Figure 1 XRD patterns of solid products of calcium carbonate after ultrasonic pretreatment for different times.

[0033] Figure 2 This is a scanning electron microscope image of calcium carbonate from Comparative Example 1.

[0034] Figure 3 This is a scanning electron microscope image of calcium carbonate after ultrasonic pretreatment in Example 1.

[0035] Figure 4 The thermogravimetric diagrams of calcium carbonate in Comparative Example 1 at different temperatures are shown.

[0036] Figure 5 Thermogravimetric analysis (TGA) of calcium carbonate after ultrasonic pretreatment in Example 7 at different temperatures.

[0037] Figure 6 The reaction rate of calcium carbonate hydrogenation to syngas at different temperatures is given. Detailed Implementation

[0038] Preferred embodiments of the invention will now be described in more detail. While preferred embodiments of the invention are described below, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that the invention will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0039] Example 1 Step 1: Ultrasonic pretreatment: Calcium carbonate was pretreated in an ultrasonic field for 0.5 h to weaken the binding strength of the metal-oxygen polar bonds in the carbonate through ultrasonic action. The ultrasonic pretreatment was performed at a frequency of 40kHz and a power of 600W. The temperature for ultrasonic pretreatment is an ice-water bath; Step 2: Hydrogen-coupled pyrolysis: Weigh 2g of calcium carbonate after ultrasonic pretreatment, compress it into tablets, and granulate it using a 40-mesh granule. 200 mg of granulated calcium carbonate was placed in a fixed-bed reactor under atmospheric pressure and fixed with quartz wool. Pure hydrogen was introduced as the reaction gas at a flow rate of 100 mL / min. A coupled pyrolysis reaction was carried out under atmospheric pressure at a reaction temperature of 600 °C and a heating rate of 10 °C / min until the calcium carbonate was completely decomposed. The reaction tail gas was collected in a gas bag and then subjected to qualitative and quantitative analysis of the gaseous products by gas chromatography.

[0040] At 600℃, the CO reaction rate of CaCO3 (abbreviated as U-CaCO3(0.5h)) pretreated with ultrasound for 0.5h was 0.45 mmol / (g). The CO selectivity was 85% (min).

[0041] Example 2 Step 1: Ultrasonic pretreatment: Calcium carbonate was pretreated in an ultrasonic field for 0.5 h to weaken the binding strength of the metal-oxygen polar bonds in the carbonate through ultrasonic action. The ultrasonic pretreatment was performed at a frequency of 40kHz and a power of 600W. The temperature for ultrasonic pretreatment is an ice-water bath; Step 2: Hydrogen-coupled pyrolysis: Weigh 2g of calcium carbonate after ultrasonic pretreatment, compress it into tablets, and granulate it using a 40-mesh granule. 200 mg of granulated calcium carbonate was placed in a fixed-bed reactor under atmospheric pressure and fixed with quartz wool. Pure hydrogen was introduced as the reaction gas at a flow rate of 100 mL / min. A coupled pyrolysis reaction was carried out under atmospheric pressure at a reaction temperature of 650 °C and a heating rate of 10 °C / min until the calcium carbonate was completely decomposed. The reaction tail gas was collected in a gas bag and then subjected to qualitative and quantitative analysis of the gaseous products by gas chromatography.

[0042] At 650℃, the CO reaction rate of CaCO3 (abbreviated as U-CaCO3(0.5h)) pretreated with ultrasound for 0.5h was 1.46 mmol / (g). (min), CO selectivity was 88%.

[0043] Example 3 Step 1: Ultrasonic pretreatment: Calcium carbonate was pretreated in an ultrasonic field for 0.5 h to weaken the binding strength of the metal-oxygen polar bonds in the carbonate through ultrasonic action. The ultrasonic pretreatment was performed at a frequency of 40kHz and a power of 600W. The temperature for ultrasonic pretreatment is an ice-water bath; Step 2: Hydrogen-coupled pyrolysis: Weigh 2g of calcium carbonate after ultrasonic pretreatment, compress it into tablets, and granulate it using a 40-mesh granule. 200 mg of granulated calcium carbonate was placed in a fixed-bed reactor under atmospheric pressure and fixed with quartz wool. Pure hydrogen was introduced as the reaction gas at a flow rate of 100 mL / min. A coupled pyrolysis reaction was carried out under atmospheric pressure at a reaction temperature of 690 °C and a heating rate of 10 °C / min until the calcium carbonate was completely decomposed. The reaction tail gas was collected in a gas bag and then subjected to qualitative and quantitative analysis of the gaseous products by gas chromatography.

[0044] At 690℃, the CO reaction rate of CaCO3 (abbreviated as U-CaCO3(0.5h)) pretreated with ultrasound for 0.5h was 1.79 mmol / (g). (min), CO selectivity is 90%.

[0045] Example 4 Step 1: Ultrasonic pretreatment: Pretreatment of calcium carbonate in an ultrasonic field for 1 hour weakens the binding strength of metal-oxygen polar bonds in carbonates through ultrasonic action. The ultrasonic pretreatment was performed at a frequency of 40kHz and a power of 600W. The temperature for ultrasonic pretreatment is an ice-water bath; Step 2: Hydrogen-coupled pyrolysis: Weigh 2g of calcium carbonate after ultrasonic pretreatment, compress it into tablets, and granulate it using a 40-mesh granule. 200 mg of granulated calcium carbonate was placed in a fixed-bed reactor under atmospheric pressure and fixed with quartz wool. Pure hydrogen was introduced as the reaction gas at a flow rate of 100 mL / min. A coupled pyrolysis reaction was carried out under atmospheric pressure at a reaction temperature of 600 °C and a heating rate of 10 °C / min until the calcium carbonate was completely decomposed. The reaction tail gas was collected in a gas bag and then subjected to qualitative and quantitative analysis of the gaseous products by gas chromatography.

[0046] At 600℃, the CO reaction rate of CaCO3 (abbreviated as U-CaCO3(1h)) pretreated with ultrasound for 1 h was 0.48 mmol / (g). (min), CO selectivity was 86%.

[0047] Example 5 Step 1: Ultrasonic pretreatment: Pretreatment of calcium carbonate in an ultrasonic field for 1 hour weakens the binding strength of metal-oxygen polar bonds in carbonates through ultrasonic action. The ultrasonic pretreatment was performed at a frequency of 40kHz and a power of 600W. The temperature for ultrasonic pretreatment is an ice-water bath; Step 2: Hydrogen-coupled pyrolysis: Weigh 2g of calcium carbonate after ultrasonic pretreatment, compress it into tablets, and granulate it using a 40-mesh granule. 200 mg of granulated calcium carbonate was placed in a fixed-bed reactor under atmospheric pressure and fixed with quartz wool. Pure hydrogen was introduced as the reaction gas at a flow rate of 100 mL / min. A coupled pyrolysis reaction was carried out under atmospheric pressure at a reaction temperature of 650 °C and a heating rate of 10 °C / min until the calcium carbonate was completely decomposed. The reaction tail gas was collected in a gas bag and then subjected to qualitative and quantitative analysis of the gaseous products by gas chromatography.

[0048] At 650℃, the CO reaction rate of CaCO3 pretreated with ultrasound for 1 h (abbreviated as U-CaCO3(1h)) was 1.47 mmol / (g) (min), CO selectivity was 88%.

[0049] Example 6 Step 1: Ultrasonic pretreatment: Pretreatment of calcium carbonate in an ultrasonic field for 1 hour weakens the binding strength of metal-oxygen polar bonds in carbonates through ultrasonic action. The ultrasonic pretreatment was performed at a frequency of 40kHz and a power of 600W. The temperature for ultrasonic pretreatment is an ice-water bath; Step 2: Hydrogen-coupled pyrolysis: Weigh 2g of calcium carbonate after ultrasonic pretreatment, compress it into tablets, and granulate it using a 40-mesh granule. 200 mg of granulated calcium carbonate was placed in a fixed-bed reactor under atmospheric pressure and fixed with quartz wool. Pure hydrogen was introduced as the reaction gas at a flow rate of 100 mL / min. A coupled pyrolysis reaction was carried out under atmospheric pressure at a reaction temperature of 690 °C and a heating rate of 10 °C / min until the calcium carbonate was completely decomposed. The reaction tail gas was collected in a gas bag and then subjected to qualitative and quantitative analysis of the gaseous products by gas chromatography.

[0050] At 690℃, the CO reaction rate of CaCO3 (abbreviated as U-CaCO3(1h)) pretreated with ultrasound for 1 h was 1.81 mmol / (g). (min), CO selectivity was 91%.

[0051] Example 7 Step 1: Ultrasonic pretreatment: Calcium carbonate was pretreated in an ultrasonic field for 1.5 hours to weaken the metal-oxygen polar bond strength in the carbonate through ultrasonic action. The ultrasonic pretreatment was performed at a frequency of 40kHz and a power of 600W. The temperature for ultrasonic pretreatment is an ice-water bath; Step 2: Hydrogen-coupled pyrolysis: Weigh 2g of calcium carbonate after ultrasonic pretreatment, compress it into tablets, and granulate it using a 40-mesh granule. 200 mg of granulated calcium carbonate was placed in a fixed-bed reactor under atmospheric pressure and fixed with quartz wool. Pure hydrogen was introduced as the reaction gas at a flow rate of 100 mL / min. A coupled pyrolysis reaction was carried out under atmospheric pressure at a reaction temperature of 600 °C and a heating rate of 10 °C / min until the calcium carbonate was completely decomposed. The reaction tail gas was collected in a gas bag and then subjected to qualitative and quantitative analysis of the gaseous products by gas chromatography.

[0052] At 600℃, the CO reaction rate of CaCO3 (abbreviated as U-CaCO3(1.5h)) pretreated with ultrasound for 1.5h was 0.50 mmol / (g). (min), CO selectivity was 86%.

[0053] Example 8 Step 1: Ultrasonic pretreatment: Calcium carbonate was pretreated in an ultrasonic field for 1.5 hours to weaken the metal-oxygen polar bond strength in the carbonate through ultrasonic action. The ultrasonic pretreatment was performed at a frequency of 40kHz and a power of 600W. The temperature for ultrasonic pretreatment is an ice-water bath; Step 2: Hydrogen-coupled pyrolysis: Weigh 2g of calcium carbonate after ultrasonic pretreatment, compress it into tablets, and granulate it using a 40-mesh granule. 200 mg of granulated calcium carbonate was placed in a fixed-bed reactor under atmospheric pressure and fixed with quartz wool. Pure hydrogen was introduced as the reaction gas at a flow rate of 100 mL / min. A coupled pyrolysis reaction was carried out under atmospheric pressure at a reaction temperature of 650 °C and a heating rate of 10 °C / min until the calcium carbonate was completely decomposed. The reaction tail gas was collected in a gas bag and then subjected to qualitative and quantitative analysis of the gaseous products by gas chromatography.

[0054] At 650℃, the CO reaction rate of CaCO3 (abbreviated as U-CaCO3(1.5h)) pretreated with ultrasound for 1.5h was 1.50 mmol / (g). (min), CO selectivity was 89%.

[0055] Example 9 Step 1: Ultrasonic pretreatment: Calcium carbonate was pretreated in an ultrasonic field for 1.5 hours to weaken the metal-oxygen polar bond strength in the carbonate through ultrasonic action. The ultrasonic pretreatment was performed at a frequency of 40kHz and a power of 600W. The temperature for ultrasonic pretreatment is an ice-water bath; Step 2: Hydrogen-coupled pyrolysis: Weigh 2g of calcium carbonate after ultrasonic pretreatment, compress it into tablets, and granulate it using a 40-mesh granule. 200 mg of granulated calcium carbonate was placed in a fixed-bed reactor under atmospheric pressure and fixed with quartz wool. Pure hydrogen was introduced as the reaction gas at a flow rate of 100 mL / min. A coupled pyrolysis reaction was carried out under atmospheric pressure at a reaction temperature of 690 °C and a heating rate of 10 °C / min until the calcium carbonate was completely decomposed. The reaction tail gas was collected in a gas bag and then subjected to qualitative and quantitative analysis of the gaseous products by gas chromatography.

[0056] At 690℃, the CO reaction rate of CaCO3 pretreated with ultrasound for 1.5 h (abbreviated as U-CaCO3(1.5h)) was 1.84 mmol / (g). The CO selectivity was 92% (min).

[0057] Comparative Example 1 The preparation method is as follows: Weigh 2g of calcium carbonate without ultrasonic pretreatment, compress it into tablets, and granulate it using a 40-mesh granule. 200 mg of granulated calcium carbonate was placed in a fixed-bed reactor under atmospheric pressure and fixed with quartz wool. Pure hydrogen was introduced as the reaction gas at a flow rate of 100 mL / min. A coupled pyrolysis reaction was carried out under atmospheric pressure at a reaction temperature of 600 °C and a heating rate of 10 °C / min until the calcium carbonate was completely decomposed. The reaction tail gas was collected in a gas bag and then subjected to qualitative and quantitative analysis of the gaseous products by gas chromatography.

[0058] At 600℃, the CO reaction rate of CaCO3 without ultrasonic pretreatment was 0.29 mmol / (g). (min), CO selectivity was 84%.

[0059] Comparative Example 2 The preparation method is as follows: Weigh 2g of calcium carbonate without ultrasonic pretreatment, compress it into tablets, and granulate it using a 40-mesh granule. 200 mg of granulated calcium carbonate was placed in a fixed-bed reactor under atmospheric pressure and fixed with quartz wool. Pure hydrogen was introduced as the reaction gas at a flow rate of 100 mL / min. A coupled pyrolysis reaction was carried out under atmospheric pressure at a reaction temperature of 650 °C and a heating rate of 10 °C / min until the calcium carbonate was completely decomposed. The reaction tail gas was collected in a gas bag and then subjected to qualitative and quantitative analysis of the gaseous products by gas chromatography.

[0060] At 650℃, the CO reaction rate of CaCO3 without ultrasonic pretreatment was 1.23 mmol / (g). (min), CO selectivity was 86%.

[0061] Comparative Example 3 The preparation method is as follows: Weigh 2g of calcium carbonate without ultrasonic pretreatment, compress it into tablets, and granulate it using a 40-mesh granule. 200 mg of granulated calcium carbonate was placed in a fixed-bed reactor under atmospheric pressure and fixed with quartz wool. Pure hydrogen was introduced as the reaction gas at a flow rate of 100 mL / min. A coupled pyrolysis reaction was carried out under atmospheric pressure at a reaction temperature of 690 °C and a heating rate of 10 °C / min until the calcium carbonate was completely decomposed. The reaction tail gas was collected in a gas bag and then subjected to qualitative and quantitative analysis of the gaseous products by gas chromatography.

[0062] At 690℃, the CO reaction rate of CaCO3 without ultrasonic pretreatment was 1.50 mmol / (g). (min), CO selectivity is 90%.

[0063] Figure 1 XRD patterns of solid products of calcium carbonate after ultrasonic pretreatment for different times.

[0064] Figure 1 It can be observed that the diffraction peaks belong to the characteristic diffraction peaks of the (012), (104), (006), (110), (113), (202), (018), and (116) crystal planes of calcite (PDF#47-1743), indicating that CaCO3 remains calcite-type after ultrasonic pretreatment. After ultrasonic pretreatment, the peak intensity of U-CaCO3 in the XRD pattern decreased, and structural disorder is the main reason for the peak weakening. Furthermore, the diffraction peaks belonging to the (104) crystal plane of CaCO3 shifted to higher diffraction angles, and the interplanar spacing increased, which suggests that the Ca-O bond length increased and the lattice expanded.

[0065] Figure 2 and Figure 3 The comparison shows that the calcium carbonate raw material after ultrasonic pretreatment has a rougher surface, higher active sites, and is more likely to combine with hydrogen.

[0066] Figure 4 The thermogravimetric diagram of calcium carbonate in Comparative Example 1 under programmed temperature rise is shown. Figure 5 Thermogravimetric analysis (TGA) of calcium carbonate after ultrasonic pretreatment under programmed temperature rise in Example 7. Figure 4 and Figure 5 As can be seen from the comparison, in Comparative Example 1, the initial decomposition temperature of CaCO3 without ultrasound during hydrogen-coupled pyrolysis was 540°C; in Example 7, the initial decomposition temperature of CaCO3 after ultrasonic pretreatment during hydrogen-coupled pyrolysis was 490°C.

[0067] Depend on Figure 6 It can be seen that ultrasonic pretreatment of calcium carbonate can simultaneously increase the CO reaction rate.

[0068] (1) CO reaction rate: 600℃ (low temperature range): ultrasound for 0.5h (0.45), 1h (0.48), 1.5h (0.50), the rate increased by 55%-72% compared with no ultrasound (0.29), but the rate of increase slowed down after 1h (0.48→0.50, only 4.2% increase); 650℃ (medium temperature range): ultrasound for 0.5h (1.46), 1h (1.47), and 1.5h (1.50) showed an increase of 18.7%-22% compared to no ultrasound (1.23), with the growth rate further decreasing after 1h; 690℃ (high temperature range): The ultrasound group showed an increase of 19.3%-22.7% compared to the non-ultrasound group (1.50), and the growth rate slowed down after 1 hour.

[0069] This indicates that the rate of hydrogen-coupled pyrolysis reaction increases with the increase of ultrasonic pretreatment time; the rate-enhancing effect of ultrasonic pretreatment is more significant in the medium and low temperature range, with the optimal pretreatment time being about 1 hour.

[0070] (2) CO selectivity: The CO selectivity of the ultrasound group was consistently slightly higher than that of the non-ultrasound group (600℃: 85%-86% vs 84%; 650℃: 88%-89% vs 86%), but the selectivity difference between different pretreatment times was small (e.g., 690℃: 90%-92%), indicating that ultrasound pretreatment has a limited effect on improving selectivity, but can stably maintain a high directional conversion efficiency.

[0071] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for producing syngas by ultrasonically enhanced hydrogenation of carbonates, characterized in that, Includes the following steps: Step 1: Ultrasonic pretreatment: Carbonates are pretreated in an ultrasonic field to weaken the bonding strength of metal-oxygen polar bonds in the carbonates through ultrasonic action. Step 2: Hydrogen-coupled pyrolysis: The carbonate pretreated by ultrasound is placed in a reaction apparatus, and a reducing gas is introduced as the reaction gas. The coupled pyrolysis reaction is carried out under normal pressure, so that the carbon dioxide produced by the decomposition of carbonate is reduced in situ by the reducing gas, and syngas with carbon monoxide as the main carbon component is prepared.

2. The method according to claim 1, characterized in that, In step 1, the carbonate is a metal carbonate, which is selected from one or more of calcium carbonate, magnesium carbonate, barium carbonate, and strontium carbonate, and the particle size of the carbonate raw material is 10μm-500μm.

3. The method according to claim 1 or 2, characterized in that, In step 1, the ultrasonic frequency of the ultrasonic pretreatment is 15kHz-80kHz, and the ultrasonic power is 100W-1500W.

4. The method according to claim 1 or 2, characterized in that, In step 1, the temperature of the ultrasonic pretreatment is an ice-water bath, and the pretreatment time is 0.2h-1.9h.

5. The method according to claim 1 or 2, characterized in that, In step 2, the reducing gas is hydrogen, and the volume fraction of the hydrogen is 50%-100%.

6. The method according to claim 1 or 2, characterized in that, In step 2, the flow rate of the reaction gas is 30 mL / min to 200 mL / min.

7. The method according to claim 1 or 2, characterized in that, In step 2, the heating rate of the coupled pyrolysis reaction is 1℃ / min-50℃ / min.

8. The method according to claim 1 or 2, characterized in that, In step 2, the reaction temperature of the coupled pyrolysis reaction is 500℃-700℃, preferably 600-650℃.

9. The method according to claim 1 or 2, characterized in that, In step 2, the reaction time of the coupled pyrolysis reaction is 1 min to 100 min.

10. The method according to claim 1 or 2, characterized in that, In step 2, when the reaction temperature of the coupled pyrolysis reaction is 600-650℃ and the heating rate is 5℃ / min-20℃ / min, the carbonate conversion rate is ≥85%.

Images