Low-steam-carbon-ratio methane reforming catalyst capable of retaining molten salt and preparation method of low-steam-carbon-ratio methane reforming catalyst

Abstract

The invention discloses a low-steam-carbon-ratio methane reforming catalyst capable of retaining molten salt and a preparation method of the low-steam-carbon-ratio methane reforming catalyst. The low-steam-carbon-ratio methane reforming catalyst comprises an active component, an auxiliary agent, an inorganic oxide skeleton and the molten salt, the active component accounts for 0.5-10.0% of the mass of the catalyst; the auxiliary agent accounts for 0.1-5.0% of the mass of the catalyst; the fused salt is mixed nitrate of sodium and potassium and accounts for 0.01-10% of the mass of the catalyst; and the balance of an inorganic oxide skeleton. The preparation method comprises the following steps: mechanically ball-milling and mixing metal salt and fused salt to prepare a catalyst precursor, and roasting at high temperature; and washing the roasted product by using a washing solvent, so that part of fused salt is reserved in the washed product, and finally drying to obtain the product. A proper amount of molten salt is reserved in the catalyst, and part of molten salt is reserved in a catalyst framework by controlling the washing frequency during preparation, so that the carbon deposition resistance of alkali metal is exerted, the salt concentration in a solvent is reduced, and the treatment difficulty and cost are further reduced.

Description

Technical Field

[0001] The invention relates to a methane reforming catalyst and a preparation method thereof, in particular to a low steam-to-carbon ratio methane reforming catalyst retaining molten salt and a preparation method thereof. Background Art

[0002] Steam methane reforming (SMR) can be used to produce synthesis gas. This technology has been industrialized as early as 1926. The gas produced can be further used for Fischer-Tropsch synthesis and methanol synthesis, and is the basis of the modern large-scale methanol industry. SMR is a typical endothermic reaction. Increasing the reaction temperature is conducive to the positive chemical equilibrium, and it needs to be carried out at high temperature (within 700-1000°C). The catalysts used are generally non-precious metal active components such as nickel, iron, and cobalt, and precious metal active components such as palladium, rhodium, and platinum. The latter is restricted to a certain extent due to its high cost due to its small natural reserves. Among them, nickel-based catalysts are widely recommended by the industry due to their high activity (equivalent to the activity of precious metals).

[0003] Since a large amount of carbon deposits will be generated on the surface of the nickel-based catalyst during the SMR reaction, the steam-to-carbon ratio is often increased during feeding to make the reaction equilibrium proceed in the forward direction, thereby inhibiting the occurrence of carbon deposits and extending the life of the catalyst. However, a high steam-to-carbon ratio will increase the consumption of water vapor and energy, and also derive a dilution effect on the gas production, so the use of low steam-to-carbon ratio conditions for SMR reactions has gradually become a trend, but severe catalyst carbon deposition is still the primary problem to be solved in low steam-to-carbon ratio SMR technology.

[0004] The preparation method of the catalyst determines various characteristics including structure, size, dispersion, etc., and the preparation method also directly affects the activity, selectivity and stability of the catalyst. Common catalyst preparation methods include mixing method, impregnation method, precipitation method, etc., but the above classic methods all have their own advantages and disadvantages, especially for SMR reaction under low steam-to-carbon ratio conditions, which requires high reaction activity and excellent anti-carbon deposition ability, and there is still a need for breakthroughs.

[0005] In recent years, the molten salt method has gradually attracted the attention of researchers in the synthesis of multi-component materials. This method uses one or more alkali metal salts with low melting points as a medium, mixes them with reactants in a certain proportion and then heats them, so that the reaction is carried out in the melt of the molten salt medium, and finally uses a solvent to wash the product. Therefore, it has the advantages of low temperature, simple operation and short synthesis time. However, the existing molten salt method needs to wash and remove the molten salt medium when preparing catalysts. Summary of the invention

[0006] Purpose of the invention: The purpose of the present invention is to provide a methane reforming catalyst with a low steam-to-carbon ratio that retains molten salt, a methane steam reforming catalyst that has anti-carbon deposition ability under low steam-to-carbon ratio conditions, and reduces the amount of solvent used and the cost of washing solvent treatment;

[0007] The second object of the present invention is to provide a method for preparing the above-mentioned low steam-to-carbon ratio methane reforming catalyst retaining molten salt.

[0008] Technical solution: The low steam-to-carbon ratio methane reforming catalyst retaining molten salt described in the present invention comprises an active ingredient, an additive, an inorganic oxide skeleton and molten salt; the active ingredient accounts for 0.5-10.0% of the catalyst mass percentage; the additive accounts for 0.1-5.0% of the catalyst mass percentage; the molten salt is a mixed nitrate of sodium and potassium, accounting for 0.01-10% of the catalyst mass percentage; the remainder is an inorganic oxide skeleton.

[0009] The catalyst is prepared by a mechanical ball milling-assisted molten salt method, and all or part of the molten salt is retained in the catalyst.

[0010] Wherein, the active ingredient is nickel, the auxiliary agent is tin, and the inorganic oxide skeleton is aluminum oxide.

[0011] The method for preparing the low steam-to-carbon ratio methane reforming catalyst retaining molten salt comprises the following steps:

[0012] (1) mechanically ball-milling and mixing the metal salt and the molten salt to obtain a catalyst precursor;

[0013] (2) calcining the catalyst precursor at high temperature;

[0014] (3) The calcined product is washed with a washing solvent so that a portion of molten salt is retained in the washed product, and then dried to obtain a low steam-to-carbon ratio methane reforming catalyst retaining the molten salt.

[0015] Wherein, in step (1), the metal salt includes a nickel metal salt, a tin metal salt and an aluminum metal salt; the nickel metal salt is nickel acetate, the tin metal salt is tin oxalate, and the aluminum metal salt is aluminum nitrate.

[0016] Wherein, in step (1), the molten salt comprises sodium and potassium nitrates; the molar ratio of sodium nitrate to potassium nitrate in the molten salt is 0.1-10; and the molar ratio of the molten salt to the metal salt is 1.5-2.5.

[0017] Wherein, in step (1), the ball milling time is 20-60 min.

[0018] Wherein, in step (2), the calcination atmosphere is air; and the calcination temperature is 400-550°C.

[0019] Wherein, in step (3), the washing solvent is deionized water or ethanol; the volume ratio of the washing solvent to the calcined product is 10-20:1; and the number of washing times is 0-5 times.

[0020] Wherein, in step (3), the total content of sodium and potassium in the catalyst obtained after washing and drying is 0.01-10wt%. The content of molten salt retained in the calcined product after washing should be within a certain range. If the content of molten salt retained is too high, the active sites will be shielded, resulting in reduced catalytic performance. If it is too low, a large amount of washing solvent will be consumed while the catalytic activity is slightly affected, and the processing cost will be increased.

[0021] Wherein, in step (3), the nickel-tin-aluminum ternary methane steam reforming catalyst obtained contains 0.5-10.0wt% nickel and 0.1-5.0wt% tin.

[0022] Beneficial effects: Compared with the prior art, the present invention achieves the following significant effects: (1) When preparing catalysts by the traditional molten salt method, molten salt is regarded as an impurity and needs to be washed to be completely removed. However, an appropriate amount of molten salt is retained in the catalyst of the present invention. During preparation, part of the molten salt is retained in the catalyst skeleton by controlling the number of washings. On the one hand, the anti-carbon deposition effect of the alkali metal is exerted, and on the other hand, the salt concentration in the solvent is reduced, thereby reducing the difficulty and cost of processing; (2) The nickel-tin-aluminum ternary methane steam reforming catalyst of the present invention uses tin as a suitable additive for the nickel-based catalyst, which can form a nickel-tin alloy in the catalyst structure, thereby fully exposing the active sites of nickel and enhancing the reaction activity; (3) The present invention adopts a mechanical ball milling-assisted molten salt method to prepare the catalyst. The molten salt environment can make the nickel-tin alloy highly dispersed on the alumina skeleton, and the mechanical external force can fully anchor the nickel-tin alloy, thereby inhibiting the sintering of the active sites and enhancing the reaction stability. DETAILED DESCRIPTION

[0023] The present invention is described in further detail below.

[0024] Example 1

[0025] Weigh 2.12g Ni(CH 3 COO 2 ·4H 2 O, 0.35gSnC 2 O 4 and 67.23gAl(NO 3 ) 3 9H 2 O, and weigh a certain amount of NaNO 3 and KNO 3Molten salt, (Ni+Sn+Al) / (Na+K) molar ratio is 1:1.5, the above metal salts are mixed and put into a ball mill, and the ball mill is performed at a rate of 300r / min for 40min. The catalyst precursor that is evenly ball-milled is taken out and placed in a muffle furnace for constant temperature roasting at 450°C in an air atmosphere for 4h, and then the roasted product is washed once with 500mL of deionized water, and after drying, a nickel-tin-aluminum ternary methane steam reforming catalyst containing 5.0wt% nickel and 2.0wt% tin is obtained; wherein the total content of sodium and potassium in the catalyst obtained after drying is 3.45wt%.

[0026] Example 2

[0027] Weigh 2.12g Ni(CH 3 COO 2 ·4H 2 O, 0.35gSnC 2 O 4 and 67.23gAl(NO 3 ) 3 9H 2 O, and weigh a certain amount of NaNO 3 and KNO 3 Molten salt, (Ni+Sn+Al) / (Na+K) molar ratio is 1:1.5, the above metal salts are mixed and put into a ball mill, and the ball mill is performed at a rate of 300r / min for 60min. The catalyst precursor that is evenly ball-milled is taken out and placed in a muffle furnace for constant temperature roasting at 500°C in an air atmosphere for 3h, and then the roasted product is washed with 500mL of ethanol each time, for a total of 3 times, and after drying, a nickel-tin-aluminum ternary methane steam reforming catalyst containing 5.0wt% nickel and 2.0wt% tin is obtained; wherein the total content of sodium and potassium in the catalyst obtained after drying is 0.46wt%.

[0028] Example 3

[0029] Weigh 2.12g Ni(CH 3 COO 2 ·4H 2 O, 0.35gSnC 2 O 4 and 67.23gAl(NO 3 ) 3 9H 2 O, and weigh a certain amount of NaNO 3 and KNO 3Molten salt, (Ni+Sn+Al) / (Na+K) molar ratio is 1:1.5, the above metal salts are mixed and put into a ball mill, and the mixture is ball milled alternately at a rate of 300r / min for 50min, and the catalyst precursor uniformly ball milled is taken out, and placed in a muffle furnace and calcined at a constant temperature of 475°C in an air atmosphere for 3h, and then the calcined product is washed with 500mL of deionized water each time, for a total of 5 times, and dried to obtain a nickel-tin-aluminum ternary methane steam reforming catalyst containing 5.0wt% nickel and 2.0wt% tin; wherein the total content of sodium and potassium in the catalyst obtained after drying is 0.08wt%.

[0030] Example 4

[0031] Weigh 2.12g Ni(CH 3 COO 2 ·4H 2 O, 0.35gSnC 2 O 4 and 67.23gAl(NO 3 ) 3 9H 2 O, and weigh a certain amount of NaNO 3 and KNO 3 Molten salt, (Ni+Sn+Al) / (Na+K) molar ratio is 1:1.5, the above metal salts are mixed and put into a ball mill, and the ball mill is performed at a rate of 300r / min for 60min. The catalyst precursor that is evenly ball-milled is taken out, and placed in a muffle furnace and calcined at a constant temperature of 500°C in an air atmosphere for 4h. 500mL of deionized water is used for washing 0 times to obtain a nickel-tin-aluminum ternary methane steam reforming catalyst containing 5.0wt% nickel and 2.0wt% tin; wherein the total content of sodium and potassium in the catalyst obtained after drying is 8.53wt%.

[0032] Comparative Example 1

[0033] Weigh 2.12g Ni(CH 3 COO 2 ·4H 2 O and 68.88gAl(NO 3 ) 3 9H 2 O, and weigh a certain amount of NaNO 3 and KNO 3Molten salt, (Ni+Al) / (Na+K) molar ratio is 1:1.5, the above metal salts are mixed and put into a ball mill, and the ball mill is performed at a rate of 300r / min for 60min. The catalyst precursor that is evenly ball-milled is taken out and placed in a muffle furnace for constant temperature roasting at 500°C in an air atmosphere for 3h, and then the roasted product is washed with 500mL of ethanol each time, for a total of 3 times, and after drying, a nickel-aluminum dimethyl methane steam reforming catalyst containing 5.0wt% of nickel is obtained; wherein the total content of sodium and potassium in the catalyst obtained after drying is 0.43wt%.

[0034] Comparative Example 2

[0035] Weigh 2.12g Ni(CH 3 COO 2 ·4H 2 O, 0.35gSnC 2 O 4 and 67.23gAl(NO 3 ) 3 9H 2 O, and weigh a certain amount of NaNO 3 and KNO 3 Molten salt, (Ni+Sn+Al) / (Na+K) molar ratio is 1:1.5, the above metal salts are mixed and put into a ball mill, and the mixture is ball milled alternately at a rate of 300r / min for 50min, and the catalyst precursor evenly ball milled is taken out, and placed in a muffle furnace and calcined at a constant temperature of 475°C in an air atmosphere for 3h, and then the calcined product is washed with 500mL of deionized water each time, for a total of 8 times, and dried to obtain a nickel-tin-aluminum ternary methane steam reforming catalyst containing 5.0wt% nickel and 2.0wt% tin; wherein the total content of sodium and potassium in the catalyst obtained after drying is 0.0014wt%.

[0036] The methane steam reforming catalyst prepared in Examples 1-4 and Comparative Examples 1-2 were respectively slowly heated to 450°C at a heating rate of 3-5°C / min under a nitrogen atmosphere, and the gas was switched to a reducing atmosphere of a mixture of nitrogen and hydrogen with a hydrogen concentration of 15-25% of the total gas volume, and the reduction was carried out at a constant temperature for 2-4 hours.

[0037] The reduced catalyst was further applied to the low steam-to-carbon ratio methane steam reforming reaction. The catalyst loading volume was 40 ml, the reaction conditions were normal pressure, temperature 800 °C, feed dry gas volume space velocity 2000 h -1 , feed dry gas CH 4 40% of the total volume, N 2 The amount of water vapor added to the dry gas is 60% of the total volume. 4 The molar flow ratio was 0.5-1.0. The results are shown in Table 1.

[0038] Table 1 Catalytic effect of samples on methane steam reforming

[0039]

[0040] By comparing Examples 1-4, it can be seen that different washing times, i.e. corresponding to different molten salt retention amounts, have different effects on the catalytic effects of catalysts with the same metal composition. Example 1 and Example 4 have a higher content of retained molten salt due to fewer washing times, resulting in a shielding effect of active sites, and thus a lower methane steam reforming activity; the washing times of Example 2 and Example 3 are further increased, the retained molten salt content is greatly reduced, and the methane conversion rate is significantly enhanced under all low steam-to-carbon ratio conditions, indicating that the nickel-tin-aluminum ternary catalysts of Example 2 and Example 3 have better catalytic performance than the nickel-tin-aluminum ternary catalysts in Example 1 and Example 4 because they retain an appropriate amount of molten salt.

[0041] By comparing Example 2 and Comparative Example 1, it can be found that the nickel-tin-aluminum ternary catalyst with similar retained molten salt content obtained by the same preparation method has higher reaction activity than the nickel-aluminum binary catalyst, indicating the advantage of adding tin additive to the catalyst.

[0042] By comparing Example 3 and Comparative Example 2, it can be found that although the number of washing times increased from 5 times to 8 times and the retained molten salt content decreased from 0.08wt% to 0.0014wt%, the methane conversion rate increased only slightly under various low steam-to-carbon ratio conditions, indicating that when the molten salt is removed to a certain extent by washing, increasing the number of washing times will not significantly enhance the catalytic effect of the nickel-tin-aluminum ternary catalyst.

[0043] The catalytic stability of Example 2, Example 3 and Comparative Example 2 was evaluated for 30 hours, the catalyst loading volume was 40 ml, and the reduction step was the same as above; the reaction conditions for the stability evaluation were normal pressure, temperature 800°C, feed dry gas volume space velocity 2000h -1 , feed dry gas CH 4 40% of the total volume, N 2 The amount of water vapor added to the dry gas is 60% of the total volume. 4 The molar flow ratio was fixed at 0.8 and the results are shown in Table 2.

[0044] Table 2 Stability effect of samples in catalytic methane wet reforming

[0045]

[0046] From the above stability test results, it is found that the carbon deposits of Example 2 and Example 3, which retain a certain amount of molten salt, are less than those of Comparative Example 2, which has been washed more times and only has a trace amount of molten salt remaining, indicating that retaining molten salt improves the catalyst's ability to resist carbon deposition. In summary, the molten salt content retained in the calcined product after washing must be within a certain range. If the retained molten salt content is too high, the active sites will be shielded, resulting in reduced catalytic performance. If it is too low, a large amount of washing solvent will be consumed and the processing cost will be increased while the catalytic activity is minimally affected.

[0047] In summary, the nickel-tin-aluminum ternary catalyst with molten salt retained prepared by the present invention has excellent performance in low steam-to-carbon ratio methane reforming reaction, and the catalyst has strong anti-carbon deposition ability.

Claims

1. A low steam-to-carbon ratio methane reforming catalyst retaining molten salt, characterized in that: The catalyst comprises active ingredients, additives, an inorganic oxide skeleton and molten salt; the active ingredients account for 0.5-10.0% of the catalyst by mass; the additives account for 0.1-5.0% of the catalyst by mass; the molten salt is a mixed nitrate of sodium and potassium, accounting for 0.01-10% of the catalyst by mass; the remainder is the inorganic oxide skeleton.

2. The low steam-to-carbon ratio methane reforming catalyst retaining molten salt according to claim 1, characterized in that: The catalyst is prepared by a mechanical ball milling-assisted molten salt method, and all or part of the molten salt is retained in the catalyst.

3. The low steam-to-carbon ratio methane reforming catalyst retaining molten salt according to claim 1, characterized in that: The active ingredient is nickel, the auxiliary agent is tin, and the inorganic oxide skeleton is aluminum oxide.

4. A method for preparing a low steam-to-carbon ratio methane reforming catalyst retaining molten salt according to claim 1, characterized in that: The following steps are involved: (1) mechanically ball-milling and mixing the metal salt and the molten salt to obtain a catalyst precursor; (2) calcining the catalyst precursor at high temperature; (3) The calcined product is washed with a washing solvent so that a portion of molten salt is retained in the washed product, and then dried to obtain a low steam-to-carbon ratio methane reforming catalyst retaining the molten salt.

5. The method for preparing a low steam-to-carbon ratio methane reforming catalyst retaining molten salt according to claim 4, characterized in that: In step (3), the total content of sodium and potassium in the catalyst obtained after washing and drying is 0.01-10wt%.

6. The method for preparing a low steam-to-carbon ratio methane reforming catalyst retaining molten salt according to claim 4, characterized in that: In step (3), the volume ratio of the washing solvent to the calcined product is 10-20:

1.

7. The method for preparing a low steam-to-carbon ratio methane reforming catalyst retaining molten salt according to claim 4, characterized in that: In step (3), the washing solvent is deionized water or ethanol; and the washing times are 0-5 times.

8. The method for preparing a low steam-to-carbon ratio methane reforming catalyst retaining molten salt according to claim 4, characterized in that: In step (1), the molten salt comprises sodium and potassium nitrates; and the molar ratio of sodium nitrate to potassium nitrate in the molten salt is 0.1-10.

9. The method for preparing a low steam-to-carbon ratio methane reforming catalyst retaining molten salt according to claim 3, characterized in that: In step (2), the calcination atmosphere is air; and the calcination temperature is 400-550°C.

10. The method for preparing a low steam-to-carbon ratio methane reforming catalyst retaining molten salt according to claim 4, characterized in that: In step (1), the metal salt includes a metal salt of nickel, a metal salt of tin and a metal salt of aluminum; and the molar ratio of the molten salt to the metal salt is 1.5-2.5.

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