Lanthanum oxycarbonate similar to elm leaves as well as preparation method and application of lanthanum oxycarbonate

Abstract

The invention relates to the technical field of methane oxidative coupling, and discloses elm leaf-like lanthanum oxycarbonate as well as a preparation method and application thereof, the lanthanum oxycarbonate comprises elm leaf-like lanthanum oxycarbonate, and the average thickness of the elm leaf-like lanthanum oxycarbonate is 1-10nm. The method for preparing lanthanum oxycarbonate comprises the following steps: (1) aging a solution to be aged, the solution to be aged containing a lanthanum source, carbamide, alcohol and an alkali source; and (2) in the presence of gas containing carbon dioxide, roasting a solid product obtained by aging. When the lanthanum oxycarbonate disclosed by the invention is used for the oxidative coupling reaction of methane, a relatively high conversion rate and selectivity of two hydrocarbons and above can be obtained at a relatively low temperature.

Description

Technical Field

[0001] The invention relates to the technical field of methane oxidative coupling, and in particular to an elm leaf-shaped lanthanum oxycarbonate and a preparation method and application thereof. Background Art

[0002] Ethylene is a compound composed of two carbon atoms and four hydrogen atoms, with the two carbon atoms connected by a double bond.

[0003] Ethylene is a basic chemical raw material for synthetic fibers, synthetic rubber, synthetic plastics (polyethylene and polyvinyl chloride), and synthetic ethanol (alcohol). It is also used to manufacture vinyl chloride, styrene, ethylene oxide, acetic acid, acetaldehyde, ethanol, and explosives. It can also be used as a ripening agent for fruits and vegetables. It is a proven plant hormone.

[0004] Ethylene is one of the world's largest chemical products. The ethylene industry is the core of the petrochemical industry. Ethylene products account for more than 75% of petrochemical products and play an important role in the national economy. The world has taken ethylene production as one of the important indicators to measure the level of development of a country's petrochemical industry.

[0005] In recent years, the discovery and exploitation of shale gas has brought revolutionary impetus to the development and utilization of natural gas. Therefore, as the most direct, effective and economically competitive method of natural gas utilization, the oxidative coupling of methane to ethane and ethylene under the action of catalysts has also received more and more attention. Summary of the invention

[0006] The purpose of the present invention is to overcome the problem of low selectivity of C2 and above hydrocarbons in the existing lanthanum carbonate catalyst at low temperature, and to provide an elm leaf-shaped lanthanum carbonate and its preparation method and application.

[0007] In order to achieve the above-mentioned object, the first aspect of the present invention provides a lanthanum oxycarbonate, which includes elm leaf-shaped lanthanum oxycarbonate, wherein the average thickness of the elm leaf-shaped lanthanum oxycarbonate is 1-10nm.

[0008] A second aspect of the present invention provides a method for preparing lanthanum oxycarbonate, the method comprising the following steps:

[0009] (1) aging a solution to be aged, wherein the solution to be aged contains a lanthanum source, carbonamide, alcohol, and an alkali source;

[0010] (2) calcining the solid product obtained by aging in the presence of a gas containing carbon dioxide.

[0011] The third aspect of the present invention provides lanthanum oxycarbonate prepared by the method described above.

[0012] A fourth aspect of the present invention provides the use of the above-mentioned lanthanum carbonate in the oxidative coupling reaction of methane to produce C2 and higher hydrocarbons.

[0013] A fifth aspect of the present invention provides a method for preparing hydrocarbons having two or more carbon atoms from methane, the method comprising: in the presence of oxygen and under the conditions of a methane oxidative coupling reaction, contacting methane with the above-mentioned lanthanum oxycarbonate for reaction;

[0014] Alternatively, lanthanum oxycarbonate is prepared according to the method described above, and then methane is contacted with the obtained lanthanum oxycarbonate in the presence of oxygen and under the conditions of methane oxidative coupling reaction to react.

[0015] Through the above technical solution, the present invention achieves the following beneficial effects:

[0016] The invention prepares elm leaf-shaped lanthanum carbonate by aging and roasting a solution containing a lanthanum source, carbonamide, alcohol and an alkali source. When the lanthanum carbonate is used in a methane oxidative coupling reaction, a higher conversion rate and a selectivity of carbon dihydrocarbons and above can be obtained at a lower temperature.

[0017] The preparation method of the catalyst of the present invention is simple and the calcination temperature is low, which can reduce the energy consumption in the catalyst preparation process. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a scanning electron microscope image of the lanthanum carbonate prepared in Example 1.

[0019] Figure 2 This is a partial magnified image of the lanthanum oxycarbonate prepared in Example 1 taken through a scanning electron microscope. DETAILED DESCRIPTION

[0020] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0021] A first aspect of the present invention provides a lanthanum oxycarbonate, which includes elm leaf-like lanthanum oxycarbonate, wherein the average thickness of the elm leaf-like lanthanum oxycarbonate is 1-10 nm.

[0022] In the present invention, the average thickness of the elm leaf-like lanthanum carbonate oxide can be 1nm, 2nm, 3nm, 4nm, 5nm, 6nm, 7nm, 8nm, 9nm, 10nm, and a range consisting of any two of the above points. Preferably, the average thickness of the elm leaf-like lanthanum carbonate oxide is 1-5nm, more preferably 1-2.3nm.

[0023] According to the present invention, preferably, the average length of the elm leaf-like lanthanum carbonate oxide is 5-10 μm. The average length of the elm leaf-like lanthanum carbonate oxide can be 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 10 μm, and a range consisting of any two of the above points. More preferably, the average length of the elm leaf-like lanthanum carbonate oxide is 5-6 μm.

[0024] According to the present invention, preferably, the average width of the elm leaf-like lanthanum carbonate oxide is 1-10 μm. The average width of the elm leaf-like lanthanum carbonate oxide can be 1 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, and a range consisting of any two of the above points. More preferably, the average width of the elm leaf-like lanthanum carbonate oxide is 2-3.5 μm.

[0025] The lanthanum carbonate oxide of the present invention contains not only elm leaf-like lanthanum carbonate oxide, but also spherical lanthanum carbonate oxide. Preferably, the lanthanum carbonate oxide also includes spherical lanthanum carbonate oxide co-grown on the elm leaf-like lanthanum carbonate oxide.

[0026] According to the present invention, preferably, the average diameter of the spherical lanthanum carbonate oxide is 50-1000nm. The average diameter of the spherical lanthanum carbonate oxide can be 50nm, 100nm, 200nm, 300nm, 400nm, 500nm, 600nm, 700nm, 800nm, 900nm, 1000nm, and a range consisting of any two of the above points. More preferably, the average diameter of the spherical lanthanum carbonate oxide is 500-1000nm.

[0027] The shape of lanthanum carbonate is determined by scanning electron microscopy. The test method for the size of elm leaf-shaped lanthanum carbonate is as follows: 5-10 elm leaf-shaped samples are selected in the field of view, and the thickness, length and width are measured using the measuring instrument provided by the scanning electron microscope, and then the average thickness, average length and average width of the 5-10 samples in the field of view are calculated. The test method for the size of the average diameter of spherical lanthanum carbonate is as follows: 5-10 spherical lanthanum carbonate samples are selected in the field of view, and the diameter is measured using the measuring instrument provided by the scanning electron microscope, and then the average diameter of the 5-10 samples in the field of view is calculated.

[0028] A second aspect of the present invention provides a method for preparing lanthanum oxycarbonate, the method comprising the following steps:

[0029] (1) aging a solution to be aged, wherein the solution to be aged contains a lanthanum source, carbonamide, alcohol, and an alkali source;

[0030] (2) calcining the solid product obtained by aging in the presence of a gas containing carbon dioxide.

[0031] In the present invention, carbonamide is also called urea.

[0032] According to the present invention, preferably, the molar ratio of the lanthanum source, carbon amide, and alcohol in the solution to be aged is 1:30-50:110-150, wherein the lanthanum source is calculated as lanthanum element. More preferably, the molar ratio of the lanthanum source, carbon amide, and alcohol in the solution to be aged is 1:30-40:110-130.

[0033] According to the present invention, the lanthanum source can be a conventional substance containing lanthanum element; preferably, the lanthanum source is a water-soluble salt of lanthanum, more preferably at least one of lanthanum nitrate, lanthanum chloride and lanthanum acetate.

[0034] According to the present invention, preferably, the alcohol is a C1-C4 monohydric alcohol and / or a C1-C4 dihydric alcohol, preferably at least one of methanol, ethanol and propylene glycol.

[0035] According to the present invention, preferably, the solution to be aged is obtained by mixing a lanthanum source and an aqueous solution of carbonamide and alcohol to obtain a mixed solution, and then mixing an alkali source with the mixed solution to obtain the solution to be aged.

[0036] According to the present invention, preferably, in the aqueous solution of alcohol, the weight ratio of alcohol to water is 1:0.5-3; 1:1-2. In the present invention, unless otherwise specified, water generally refers to deionized water. In the aqueous solution of alcohol, the weight ratio of alcohol to water can be 1:0.5, 1:1, 1:1.5, 1:1.8, 1:2, 1:2.5, 1:3, and a range consisting of any two of the above points.

[0037] According to the present invention, preferably, the amount of the alkali source used is such that the pH of the solution to be aged is 8-9.5.

[0038] According to the present invention, preferably, the alkali source is ammonia, more preferably aqueous ammonia. The mass percentage of aqueous ammonia can be 20-36wt%.

[0039] According to the present invention, preferably, the aging conditions include: a temperature of 80-100°C, a time of 2-8h, preferably 2-3h. It should be noted that aging refers to a certain time of reaction at a reaction temperature, and the reaction process can be carried out under stirring or not. Usually, in order to increase the reaction rate, aging is carried out under stirring. The stirring rate is not particularly limited, for example, it can be 200-500r / min.

[0040] According to the present invention, preferably, the reaction is carried out in a water bath, that is, the aging of the present invention is usually carried out under normal pressure.

[0041] According to the present invention, preferably, the method further comprises, after the aging reaction is completed, allowing the reaction solution obtained by aging to stand. More preferably, the standing temperature is 15-40°C and the time is 12-24h.

[0042] According to the present invention, preferably, the method further comprises: drying the solid product before roasting, and the drying conditions include: temperature of 80-120° C. and time of 10-50 h.

[0043] According to the present invention, preferably, the method further comprises: performing solid-liquid separation on the aged solution to obtain a solid product, then washing the solid product with water and alcohol (ethanol) in sequence, and then drying. The number of water washings may be 2-4 times, and the number of alcohol washings may be 1-2 times.

[0044] According to the present invention, preferably, the concentration of carbon dioxide in the carbon dioxide-containing gas is 0.01-10% by volume; more preferably, the carbon dioxide-containing gas is air.

[0045] According to the present invention, preferably, the flow rate of the carbon dioxide-containing gas is 10-50 ml / min.

[0046] According to the present invention, preferably, the calcination conditions include: temperature of 450-550°C, time of 2-10h. More preferably, the calcination conditions include: heating to 450-550°C at a heating rate of 2-10°C / min, and maintaining at this temperature for 2-10h.

[0047] In the present invention, XRD characterization of the calcined product shows that the calcined product mainly contains lanthanum oxycarbonate, and the lanthanum oxycarbonate is monoclinic lanthanum oxycarbonate.

[0048] According to the present invention, preferably, oxalates (such as sodium oxalate, potassium oxalate and lithium oxalate) are not used in the preparation of lanthanum oxycarbonate.

[0049] According to the present invention, preferably, polyvinyl pyrrolidone, polyacrylic acid, sodium polyacrylate and maleic acid-acrylic acid copolymer are not used in the preparation of lanthanum oxycarbonate.

[0050] The third aspect of the present invention provides lanthanum oxycarbonate prepared by the method described above.

[0051] A fourth aspect of the present invention provides the use of the above-mentioned lanthanum carbonate in the oxidative coupling reaction of methane to produce C2 and higher hydrocarbons.

[0052] A fifth aspect of the present invention provides a method for preparing hydrocarbons having two or more carbon atoms from methane, the method comprising: in the presence of oxygen and under the conditions of a methane oxidative coupling reaction, contacting methane with the above-mentioned lanthanum oxycarbonate for reaction;

[0053] Alternatively, lanthanum oxycarbonate is prepared according to the method described above, and then methane is contacted with the obtained lanthanum oxycarbonate in the presence of oxygen and under the conditions of methane oxidative coupling reaction to react.

[0054] According to the present invention, preferably, the molar ratio of the methane to the oxygen (hereinafter referred to as the alkoxygen ratio) is 1-10:1.

[0055] According to the present invention, preferably, the temperature of the contact reaction is 500-700°C, preferably 500-650°C.

[0056] According to the present invention, preferably, the methane is 5000-150000 mL / (g·h).

[0057] According to a particularly preferred embodiment of the present invention, the method for preparing lanthanum carbonate comprises: (1) mixing lanthanum nitrate hexahydrate, carbonamide, and ethanol aqueous solution and stirring them to completely dissolve them, and then adding ammonia water to adjust the pH of the solution to 8.9-9 to obtain a solution to be aged. The solution to be aged is transferred to a water bath at 80-85°C and stirred for 2-2.5 hours, wherein the stirring speed is 250-300r / min, and then left to stand overnight at room temperature (about 12-14 hours), and the obtained solid-liquid mixture is centrifuged to obtain a solid product, and the solid product is washed with water and ethanol, and then dried at 110-120°C for 11-12 hours. The molar ratio of lanthanum nitrate hexahydrate, carbonamide, and ethanol is 1:30-32:120-125; in the ethanol aqueous solution, the weight ratio of ethanol to water is 1:1.5-1.8.

[0058] (2) transferring the dried solid product to a muffle furnace, heating the temperature to 540-550° C. at a heating rate of 2-3° C. / min, and maintaining the temperature for 2-3 h to obtain a calcined product; wherein the calcination process is carried out under air purge, and the air flow rate is set to 10-15 ml / min.

[0059] The present invention will be described in detail below by way of examples. In the following examples,

[0060] The room temperature is about 25℃.

[0061] The concentration of the ammonia water was 36 wt %.

[0062] The calculation method of methane conversion rate is as follows:

[0063] Methane conversion rate = amount of methane consumed in the reaction / initial amount of methane × 100%.

[0064] The ethylene selectivity is calculated as follows:

[0065] Ethylene selectivity = amount of methane consumed by produced ethylene / total methane consumption x 100%.

[0066] The ethane selectivity is calculated as follows:

[0067] Ethane selectivity = amount of methane consumed by produced ethane / total methane consumption x 100%.

[0068] The selectivity of C2 and above hydrocarbons includes the sum of ethylene, ethane, propylene, propane and higher carbon hydrocarbons.

[0069] Example 1

[0070] (1) Lanthanum nitrate hexahydrate, carbonamide, and ethanol aqueous solution are mixed and stirred to completely dissolve, and then ammonia water is added to adjust the solution pH to 8.9 to obtain a solution to be aged. The solution to be aged is transferred to a water bath at 80°C and stirred for 2 hours, wherein the stirring speed is 300r / min, and then allowed to stand overnight at room temperature (about 12 hours). The obtained solid-liquid mixture is centrifuged to obtain a solid product, which is washed three times with water and once with ethanol, and then placed in an oven and dried at 120°C for 12 hours. The molar ratio of lanthanum nitrate hexahydrate, carbonamide, and ethanol is 1:30:120; in the ethanol aqueous solution, the weight ratio of ethanol to water is 1:2.

[0071] (2) The dried solid product was transferred to a muffle furnace, heated to 550°C at a heating rate of 2°C / min, and maintained at this temperature for 2 hours to obtain a calcined product; wherein the calcination process was carried out under air purge, and the air flow rate was set to 10 ml / min. The obtained lanthanum carbonate was recorded as cat1.

[0072] The scanning electron microscope image of lanthanum carbonate is as follows Figure 1-2 As shown by Figure 1 It can be seen that the lanthanum carbonate is elm-leaf-shaped as a whole, and there are a large number of small particles on the surface of the elm-leaf-shaped flakes. Figure 2 It can be seen that the small particles on the elm leaf-like surface are spherical.

[0073] Example 2

[0074] (1) Lanthanum nitrate hexahydrate, carbonamide, and ethanol aqueous solution are mixed and stirred to completely dissolve, and then ammonia water is added to adjust the solution pH to 8.5 to obtain a solution to be aged. The solution to be aged is transferred to a water bath at 90°C and stirred for 2 hours, wherein the stirring speed is 400r / min, and then allowed to stand overnight at room temperature (about 12 hours). The obtained solid-liquid mixture is centrifuged to obtain a solid product, which is washed three times with water and once with ethanol, and then placed in an oven and dried at 80°C for 12 hours. The molar ratio of lanthanum nitrate hexahydrate, carbonamide, and ethanol is 1:35:130; in the ethanol aqueous solution, the weight ratio of ethanol to water is 1:1.5.

[0075] (2) The dried solid product was transferred to a muffle furnace, heated to 500°C at a heating rate of 5°C / min, and maintained at this temperature for 2 hours to obtain a calcined product; wherein the calcination process was carried out under air purge, and the air flow rate was set to 20 ml / min. The obtained lanthanum carbonate was recorded as cat2.

[0076] Example 3

[0077] The method of Example 1 is followed, except that the molar ratio of lanthanum nitrate hexahydrate, carbonamide and ethanol is 1:40:150.

[0078] Example 4

[0079] The method of Example 1 is followed, except that in the ethanol aqueous solution, the weight ratio of ethanol to water is 1:1.

[0080] Example 5

[0081] The method of Example 1 was followed, except that ethanol was replaced with an equal molar amount of propylene glycol.

[0082] Comparative Example 1

[0083] The method of Example 1 was followed, except that carbonamide was replaced with an equal molar amount of ammonium bicarbonate.

[0084] The lanthanum oxycarbonate prepared in Comparative Example 1 was observed under a scanning electron microscope, and no elm leaf-like and spherical lanthanum oxycarbonate was found.

[0085] Comparative Example 2

[0086] The method of Example 1 was followed, except that ethanol was substituted for an equal mole of carbonamide.

[0087] The lanthanum oxycarbonate prepared in Comparative Example 2 was observed under a scanning electron microscope, and no elm leaf-like and spherical lanthanum oxycarbonate was found.

[0088] Test Example 1

[0089] The morphology of the lanthanum oxycarbonate prepared in the example was tested by scanning electron microscopy, and the average thickness, average length and average width of the elm leaf-shaped lanthanum oxycarbonate and the average diameter of the spherical lanthanum oxycarbonate were characterized. The test results are shown in Table 1.

[0090] The testing method for the size of elm leaf-shaped lanthanum oxycarbonate is: select 5-10 elm leaf-shaped samples in the field of view, measure the thickness, length and width with the measuring instrument provided by the scanning electron microscope, and then calculate the average thickness, average length and average width of the 5-10 samples in the field of view.

[0091] The testing method for the average diameter of spherical lanthanum oxycarbonate is as follows: 5-10 spherical lanthanum oxycarbonate samples are selected in the field of view, the diameters are measured using a measuring instrument provided with a scanning electron microscope, and then the average diameter of the 5-10 samples in the field of view is calculated.

[0092] The XRD characterization of the calcined product of the above embodiment shows that the calcined product mainly contains lanthanum oxycarbonate, and the lanthanum oxycarbonate is monoclinic lanthanum oxycarbonate.

[0093] Table 1

[0094]

[0095] Test Example 2

[0096] After the lanthanum carbonate tablets prepared in the above examples and comparative examples were sieved through 40-60 mesh, 100 mg was weighed and loaded into a quartz tube fixed bed reactor with an inner diameter of 4 mm, and methane and oxygen were introduced, with a methane space velocity of 140000 mL / (g·h), an alkoxy ratio of 7, and a reaction temperature of 550° C. The product composition was detected online by an Agilent gas chromatograph, and the methane conversion rate and the selectivity of C2 and above hydrocarbons were calculated based on the product composition, and the results are shown in Table 2.

[0097] Table 2

[0098] Methane conversion rate (%) Selectivity of C2 and above hydrocarbons (%) Example 1 20 70.2 Example 2 20.1 69.8 Example 3 19.5 67.3 Example 4 18.9 69.4 Example 5 18.8 68.3 Comparative Example 1 16.8 63.5 Comparative Example 2 17.2 62.3

[0099] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A lanthanum oxycarbonate, characterized in that The lanthanum oxycarbonate includes elm leaf-like lanthanum oxycarbonate, wherein the average thickness of the elm leaf-like lanthanum oxycarbonate is 1-10 nm.

2. The lanthanum oxycarbonate according to claim 1, wherein The elm leaf-shaped lanthanum carbonate oxide has an average length of 5-10 μm and an average width of 1-10 μm; And / or, the lanthanum oxycarbonate also includes spherical lanthanum oxycarbonate co-grows on the elm leaf-shaped lanthanum oxycarbonate.

3. The lanthanum oxycarbonate according to claim 1, wherein The average diameter of the spherical lanthanum oxycarbonate is 50-1000 nm.

4. A method for preparing lanthanum oxycarbonate, characterized in that: The method comprises the following steps: (1) aging a solution to be aged, wherein the solution to be aged contains a lanthanum source, carbonamide, alcohol, and an alkali source; (2) The solid product obtained by aging is calcined in the presence of a gas containing carbon dioxide.

5. The method according to claim 4, wherein: The molar ratio of the lanthanum source, carbonamide and alcohol in the solution to be aged is 1:30-50:110-150, wherein the lanthanum source is calculated as lanthanum element; and / or, the amount of the alkaline source is such that the pH of the solution to be aged is 8-9.5; and / or, the lanthanum source is a water-soluble salt of lanthanum, preferably lanthanum nitrate; and / or, the alcohol is a C1-C4 monohydric alcohol and / or a C1-C4 dihydric alcohol, preferably at least one of methanol, ethanol and propylene glycol; And / or, the solution to be aged is obtained by mixing a lanthanum source and an aqueous solution of carbonamide and alcohol to obtain a mixed solution, and then mixing an alkali source with the mixed solution to obtain the solution to be aged.

6. The method according to claim 4, wherein: The aging conditions include: temperature of 80-100° C. and time of 2-8 hours.

7. The method according to claim 4, wherein: The concentration of carbon dioxide in the carbon dioxide-containing gas is 0.01-10% by volume; And / or, the calcination conditions include: temperature of 450-550° C. and time of 2-10 h.

8. Lanthanum oxycarbonate prepared by the method described in any one of claims 4 to 7.

9. Use of the lanthanum oxycarbonate described in any one of claims 1-3 and 8 in the oxidative coupling reaction of methane to produce C2 or higher hydrocarbons.

10. A method for preparing hydrocarbons with carbon content of two or more carbon atoms from methane, characterized in that: The method comprises: in the presence of oxygen and under the conditions of methane oxidative coupling reaction, contacting methane with the lanthanum carbonate described in any one of claims 1 to 3 and 7 for reaction; Alternatively, lanthanum oxycarbonate is prepared according to the method described in any one of claims 3 to 7, and then methane is contacted with the obtained lanthanum oxycarbonate to react in the presence of oxygen and under the conditions of methane oxidative coupling reaction.

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