Method for preparing CO through molten salt thermocatalysis of CO2

Abstract

The invention relates to the technical field of carbon dioxide conversion, in particular to a method for preparing CO through molten salt thermocatalysis of CO2, CO2 and H2 are introduced into carbonate-containing molten salt, a thermocatalytic reduction reaction is carried out, and CO is prepared. The method has the advantages of low energy consumption, green and pollution-free catalytic system, simple process, low cost, easy amplification production, high CO selectivity and yield, and more types of molten salts suitable for the technology, and provides more choices for the conversion of CO2 from the molten salt through thermocatalysis.

Description

Technical Field

[0001] The present invention relates to the technical field of carbon dioxide conversion, and in particular to a method for preparing CO by molten salt thermal catalysis of CO2. Background Art

[0002] The resource utilization of CO2 is an important technical means to ensure the high-quality completion of the dual carbon goals. Converting CO2 to CO is a more feasible approach, and the synthesis gas (CO+H2) obtained by mixing CO with H2 can be used to manufacture bulk chemicals and energy high-value chemicals such as liquid fuels and aromatics. Using CO2 as a carbon source to prepare CO not only realizes the recycling of carbon resources, but also has important significance for alleviating the energy crisis and achieving the goal of carbon neutrality. Hydrogenation reduction of CO2 to CO through the reverse water-gas shift reaction (RWGS) is one of the common methods for preparing CO. Since the RWGS reaction is an endothermic reaction, the traditional way to prepare CO is to use a high-temperature fixed bed reactor, fix the nanometal catalyst layer in the reactor, and introduce CO2 and H2 into the catalyst bed at the same time to prepare CO. This method is highly dependent on the use of catalysts. Not only does it require a large amount of catalyst to be used, but it also has high requirements for the catalytic activity of the catalyst. At the same time, there are problems such as easy carbon deposition and deactivation of the catalyst, low CO selectivity and yield, which is not conducive to large-scale industrial production. Therefore, how to provide a technology for efficiently converting CO2 into CO by molten salt thermal catalysis has become a technical problem that needs to be solved urgently in this field. Summary of the invention

[0003] The object of the present invention is to provide a method for preparing CO by thermally catalyzing CO2 with molten salt, which has low energy consumption, green process, simple flow, low cost and is easy to scale up for production.

[0004] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0005] The present invention provides a method for preparing CO by thermally catalyzing CO2 using molten salt, comprising the following steps:

[0006] CO2 and H2 are introduced into a molten salt containing carbonate to carry out a thermal catalytic reduction reaction to produce CO.

[0007] Optionally, the carbonate-containing molten salt is an alkali metal carbonate.

[0008] Optionally, the carbonate-containing molten salt includes alkali metal carbonates and alkaline earth metal carbonates.

[0009] Optionally, the carbonate-containing molten salt includes carbonate and halide salt, the carbonate includes at least one of alkali metal carbonate and alkaline earth metal carbonate, and the halide salt includes at least one of alkali metal halide salt and alkaline earth metal halide salt.

[0010] Optionally, the alkali metal carbonate comprises one or more of Li2CO3, Na2CO3 and K2CO3.

[0011] Optionally, the alkaline earth metal carbonate comprises one or more of CaCO3, MgCO3, BaCO3 and SrCO3.

[0012] Optionally, the alkali metal halide salt comprises one or more of LiCl, NaCl, KCl, LiF, NaF and KF;

[0013] The alkaline earth metal halide salt comprises one or more of CaCl2, BaCl2, MgCl2, CaF2, BaF2 and MgF2.

[0014] Optionally, the molar ratio of CO2 to H2 is 1:1-10.

[0015] Optionally, the CO2 and H2 are introduced into the molten salt in the form of a mixed gas; the introduction rate of the CO2 and H2 is 10mL / min to 50L / min.

[0016] Optionally, the temperature of the thermal catalytic reduction reaction is 200-900°C.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] The present invention provides a method for preparing CO by thermally catalytically converting CO2 with molten salt. CO2 and H2 are introduced into a molten salt containing carbonate to carry out a thermal catalytic reduction reaction to prepare CO. The method has low energy consumption, a green and pollution-free catalytic system, a simple process, low cost and easy scale-up production, high selectivity and yield of CO, and the technology is applicable to a wide variety of molten salts, providing more options for thermally catalytically converting CO2 with molten salt. DETAILED DESCRIPTION

[0019] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0020] It should be understood that the terms described in the present invention are only for describing special embodiments and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. Each smaller range between the intermediate value in any stated value or stated range and any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0021] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0022] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention description without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention description will be apparent to those skilled in the art. The present application description and examples are exemplary only.

[0023] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0024] The raw materials used in the present invention are all commercially available.

[0025] The present invention provides a method for preparing CO by thermally catalyzing CO2 using molten salt, comprising the following steps:

[0026] CO2 and H2 are introduced into a molten salt containing carbonate to carry out a thermal catalytic reduction reaction to produce CO.

[0027] In the present invention, a molten salt system containing carbonates is used as a catalytic and heating medium. H2 can react with carbonates to generate CO and hydroxides (i.e., metal hydroxides). Hydroxides can react with CO2 to generate carbonates. This process is equivalent to carbonates acting as catalysts in the process of preparing CO by the reaction of CO2 and H2, thereby promoting the generation of CO.

[0028] In the present invention, the liquid molten salt used as a catalyst is widely available and inexpensive, and the molten salt can directly absorb solar energy and convert it into thermal energy, providing the heat required for the reverse water-gas change reaction. The synthesis process of traditional solid-phase catalysts is complex, energy-intensive, and requires an external heating device to provide the heat required for the reaction. Therefore, the process of preparing CO from CO using molten salt thermal catalysis of CO2 has the advantages of low energy consumption and low cost.

[0029] In the present invention, the carbonate-containing molten salt may be any carbonate-containing salt that is in liquid phase at the melting temperature. In an embodiment of the present invention, the carbonate-containing molten salt may be an alkali metal carbonate; the carbonate-containing molten salt may also be a mixture of alkali metal carbonate and alkaline earth metal carbonate; the carbonate-containing molten salt may also be a mixture of carbonate and halide salt, wherein the carbonate includes at least one of alkali metal carbonate and alkaline earth metal carbonate, the halide salt includes at least one of alkali metal halide and alkaline earth metal halide, and the content of the carbonate is preferably 1 to 100% (excluding 100%), such as 5%, 10%, 15%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, etc.

[0030] In some embodiments of the present invention, the alkali metal carbonate comprises one or more of Li2CO3, Na2CO3 and K2CO3.

[0031] In some embodiments of the present invention, the carbonate of the alkaline earth metal comprises one or more of CaCO3, MgCO3, BaCO3 and SrCO3.

[0032] In some embodiments of the present invention, the alkali metal halide salt comprises one or more of LiCl, NaCl, KCl, LiF, NaF and KF.

[0033] In some embodiments of the present invention, the alkaline earth metal halide salt comprises one or more of CaCl2, BaCl2, MgCl2, CaF2, BaF2 and MgF2.

[0034] In the present invention, when the carbonate-containing molten salt is a mixture, there is no particular limitation on the ratio between the salt mixtures, which may vary according to different raw materials, as long as it can ensure that the carbonate-containing molten salt remains in a liquid state at the reduction temperature; and the carbonate content can be adjusted by those skilled in the art according to the required reaction rate, for example, the greater the carbonate content, the faster the reaction rate.

[0035] In the present invention, there is no special restriction on the pipeline for introducing CO2 and H2 into the molten salt, as long as CO2 and H2 can be introduced into the molten salt. In the embodiment of the present invention, CO2 and H2 are introduced into the molten salt through an aeration head.

[0036] In the present invention, there is no special limitation on the material of the aeration head, as long as it can ensure that the gas is passed into the molten salt. In an embodiment of the present invention, the material of the aeration head is stainless steel, Fe, Co, Ni, Cu, Mo, W or Ti, preferably stainless steel, Fe, Co, Ni or Ti, more preferably stainless steel, Fe, Ni or Ti, and even more preferably stainless steel or Fe.

[0037] In the present invention, the smaller the aperture of the aeration head, the larger the contact area between the gas and the molten salt. In the embodiment of the present invention, the aperture of the aeration head is 1 to 100 μm, preferably 10 to 90 μm, more preferably 20 to 80 μm, and more preferably 50 to 60 μm. Those skilled in the art can also adjust the aperture or choose other methods to pass the gas into the molten salt according to the specific conditions of the reaction.

[0038] In some embodiments of the present invention, the molar ratio of CO2 to H2 is 1:1-10, preferably 1:2-8, more preferably 1:3-6, and even more preferably 1:4-5.

[0039] In the present invention, the CO2 and H2 can be introduced into the molten salt through different pipelines respectively, or can be mixed in advance and introduced into the molten salt in the form of a mixed gas, as long as it can be ensured that the two gases can contact in the molten salt. In an embodiment of the present invention, the CO2 and H2 are introduced into the molten salt in the form of a mixed gas.

[0040] In some embodiments of the present invention, when the CO2 and H2 are introduced into the molten salt in the form of a mixed gas, the introduction rate of the CO2 and H2 is 10 mL / min to 50 L / min, preferably 100 mL / min to 5 L / min. In the present invention, when CO2 and H2 are introduced into the molten salt separately, the sum of the introduction rates of CO2 and H2 is preferably within the above range.

[0041] In some embodiments of the present invention, the temperature of the thermal catalytic reduction reaction is 200 to 900°C, preferably 300 to 850°C, more preferably 450 to 750°C, and even more preferably 600 to 650°C;

[0042] In the present invention, the higher the height from the position where CO2 and H2 begin to contact the molten salt to the liquid level of the solution, the longer the time for CO2 and H2 to contact the catalyst, and the higher the yield of CO. In some embodiments of the present invention, the height from the position where CO2 and H2 begin to contact the molten salt to the liquid level of the solution is 10 cm to 10 m, preferably 20 cm to 5 m. When industrial applications are carried out, the height from the position where CO2 and H2 begin to contact the molten salt to the liquid level of the solution can be proportionally enlarged or adaptively adjusted according to the height in the embodiment, or those skilled in the art can refer to the height in the embodiment for adjustment.

[0043] The technical solutions provided by the present invention are described in detail below in conjunction with the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0044] Example 1

[0045] Li2CO3-Na2CO3-K2CO3 molten salt with a molar ratio of 43.5:31.5:25 was used as a catalytic medium, and then a mixed gas of CO2 and H2 with a molar ratio of 1:1 was continuously introduced into the molten salt catalytic medium at a rate of 200 mL / min through a stainless steel aeration head with a pore size of 10 μm, and thermal reduction was performed at 650°C to obtain CO, wherein the height from the stainless steel aeration head to the liquid level of the molten salt was 10 cm. The concentration of CO was detected at the outlet.

[0046] The selectivity and yield of CO at the outlet were detected by gas chromatography.

[0047] According to the test, the selectivity of CO at the gas outlet of Example 1 is 100%, and the yield of CO is 85%.

[0048] Example 2

[0049] The only difference from Example 1 is that a molten salt of LiCl-KCl with a molar ratio of 59:41 and containing 5 mol % Li2CO3 is used as the catalytic medium.

[0050] According to the test, the selectivity of CO at the gas outlet of Example 2 is 100%, and the yield of CO is 65%.

[0051] Example 3

[0052] The only difference from Example 1 is that a molten salt of NaF-KF with a molar ratio of 50:50 containing 10% MgCO3 is used as the catalytic medium.

[0053] According to the test, the selectivity of CO at the gas outlet of Example 3 is 100%, and the yield of CO is 73%.

[0054] The gas products of Example 1, Example 2 and Example 3 all contain high concentration of CO.

[0055] Example 4

[0056] A molten salt of Li2CO3-K2CO3 with a molar ratio of 50:50 was used as a catalytic medium. A mixed gas of CO2 and H2 with a molar ratio of 1:2 was continuously introduced into the molten salt at a rate of 500 mL / min through an Fe aeration head with a pore size of 10 μm. Thermal reduction was performed at 750°C to obtain CO, wherein the height from the Fe aeration head to the liquid level of the molten salt was 15 cm. The concentration of CO was detected at the gas outlet.

[0057] After testing, the selectivity of CO at the gas outlet of Example 4 was 100%, and the yield of CO was 98%.

[0058] Example 5

[0059] The only difference from Example 4 is that a Ni aeration head is selected and the aperture of the aeration head is 50 μm.

[0060] According to the test, the selectivity of CO at the gas outlet of Example 4 is 100%, and the yield of CO is 90%.

[0061] Example 6

[0062] The only difference from Example 4 is that a Ti aeration head is selected and the pore size of the aeration head is 20 μm.

[0063] According to the test, the selectivity of CO at the gas outlet of Example 6 is 100%, and the yield of CO is 93%.

[0064] Example 7

[0065] A mixed molten salt of Na2CO3-K2CO3 with a molar ratio of 55:45 was used as a catalytic medium. A mixed gas of CO2 and H2 with a molar ratio of 1:3 was continuously introduced into the molten salt at a rate of 50 mL / min through a stainless steel aeration head with a pore size of 10 μm. Thermal reduction was performed at 750°C to obtain CO, wherein the height from the stainless steel aeration head to the liquid level of the molten salt was 20 cm. The concentration of CO was detected at the gas outlet.

[0066] According to the test, the selectivity of CO at the gas outlet of Example 7 is 100%, and the yield of CO is 78%.

[0067] Example 8

[0068] The only difference from Example 7 is that the molar ratio of CO2 and H2 is 1:1.

[0069] According to the test, the selectivity of CO at the gas outlet of Example 8 is 100%, and the yield of CO is 64%.

[0070] Example 9

[0071] The only difference from Example 7 is that the molar ratio of CO2 to H2 is 1:4.

[0072] According to the test, the selectivity of CO at the gas outlet of Example 9 is 100%, and the yield of CO is 86%.

[0073] Example 10

[0074] A mixed molten salt of Li2CO3-Na2CO3-K2CO3 with a molar ratio of 43.5:31.5:25 was used as a catalytic medium. A mixed gas of CO2 and H2 with a molar ratio of 1:2 was continuously introduced into the molten salt at a rate of 100 mL / min through a stainless steel aeration head with a pore size of 10 μm. Thermal reduction was performed at 450°C to obtain CO, wherein the height from the stainless steel aeration head to the liquid level of the molten salt was 12 cm. The concentration of CO was detected at the outlet.

[0075] According to the test, the selectivity of CO at the gas outlet of Example 10 is 94%, and the yield of CO is 54%.

[0076] Embodiment 11

[0077] The only difference from Example 10 is that the thermal reduction is carried out at 600°C.

[0078] After testing, the selectivity of CO at the gas outlet of Example 11 was 100%, and the yield of CO was 89%.

[0079] Example 12

[0080] The only difference from Example 10 is that the thermal reduction was carried out at 850°C.

[0081] After testing, the selectivity of CO at the outlet of Example 12 was 100%, and the yield of CO was 100%.

[0082] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing CO by thermal catalysis of CO2 using molten salt, characterized in that: The following steps are involved: CO2 and H2 are introduced into a molten salt containing carbonate to carry out a thermal catalytic reduction reaction to produce CO.

2. The method according to claim 1, characterized in that: The carbonate-containing molten salt is an alkali metal carbonate.

3. The method according to claim 1, characterized in that The carbonate-containing molten salt includes alkali metal carbonates and alkaline earth metal carbonates.

4. The method according to claim 1, characterized in that: The carbonate-containing molten salt includes carbonate and halide salt, wherein the carbonate includes at least one of alkali metal carbonate and alkaline earth metal carbonate, and the halide salt includes at least one of alkali metal halide and alkaline earth metal halide.

5. The method according to any one of claims 1 to 4, characterized in that: The alkali metal carbonate includes one or more of Li2CO3, Na2CO3 and K2CO3.

6. The method according to claim 3 or 4, characterized in that: The alkaline earth metal carbonate comprises one or more of CaCO3, MgCO3, BaCO3 and SrCO3.

7. The method according to claim 6, characterized in that The alkali metal halide salt comprises one or more of LiCl, NaCl, KCl, LiF, NaF and KF; The alkaline earth metal halide salt comprises one or more of CaCl2, BaCl2, MgCl2, CaF2, BaF2 and MgF2.

8. The method according to claim 1, characterized in that The molar ratio of CO2 to H2 is 1:1-10.

9. The method according to claim 8, characterized in that The CO2 and H2 are introduced into the molten salt in the form of a mixed gas; the introduction rate of the CO2 and H2 is 10mL / min to 50L / min.

10. The method according to claim 1 or 9, characterized in that: The temperature of the thermal catalytic reduction reaction is 200-900°C.