A method for preparing corresponding alcohols by catalytic oxidation of low-carbon alkanes

Abstract

A method for preparing corresponding alcohols by catalytic oxidation of low-carbon alkanes relates to the field of selective oxidation of low-carbon alkanes. An intermittent reactor is used, and in the presence of a reducing gas, oxygen is used as an oxidant to directly catalytically oxidize low-carbon alkanes to corresponding alcohols in an aqueous medium in which a catalyst is dispersed. The low-carbon alkane is at least one of methane, ethane, and propane; the corresponding alcohol is methanol corresponding to methane, ethanol corresponding to ethane, and n-propanol / isopropanol corresponding to propane; the reducing agent is at least one of CO and H2; the catalyst used is a zeolite molecular sieve-supported Au nanoparticle catalyst, the mass percentage of Au in the catalyst is 0.05% to 10%, and the remainder is a zeolite molecular sieve carrier. The reaction temperature is 80 to 200°C, and the reaction time is 1 to 300 minutes. The method has the advantages of simple catalyst preparation, mild reaction conditions, good catalyst stability, and high selectivity of target products.

Description

Technical Field

[0001] The invention relates to the field of low-carbon alkane activation, and in particular to a method for preparing corresponding alcohols by catalytic oxidation of low-carbon alkanes. Background Art

[0002] In recent years, with the large-scale exploitation and utilization of natural gas, shale gas and other resources, the proportion of low-carbon alkanes such as methane, ethane, and propane in my country's energy structure and chemical raw materials is increasing year by year. The rational use of low-carbon alkanes is of great significance to my country's energy structure adjustment and environmental protection. It can not only be used as a fuel for direct combustion, but also as an important chemical raw material to produce downstream products with a wide range of uses. Low-carbon alcohols have a huge market demand. They can not only be used as a clean gasoline additive to partially replace crude oil, but also can be used to produce a large number of downstream products, playing an important role in the fields of national defense chemical industry, medical and health care, and food industry. At present, the preparation of low-carbon alcohols using natural gas or shale gas as raw materials is mainly based on synthesis gas as a platform molecule, which is indirectly converted. This indirect process has high energy consumption and high equipment cost. In contrast, the direct catalytic oxidation of low-carbon alkanes as raw materials to prepare the corresponding low-carbon alcohols has the advantages of simple process, low energy consumption, and mild reaction conditions, which is a more attractive path.

[0003] Since the CH bond energy in low-carbon alkane molecules is high, high energy is required to activate the CH bond. At the same time, target products such as low-carbon alcohols are easily over-oxidized, resulting in low selectivity for alcohols. Therefore, it is a huge challenge to achieve high activity conversion of low-carbon alkanes and high selectivity to obtain target products. In recent years, the selective oxidation reaction of methane using hydrogen peroxide (H2O2) as an oxidant has received a lot of attention. For example, using a molecular sieve-supported iron-based (Fe-HZSM-5) catalyst, methane can be oxidized to formic acid as the main product in the aqueous phase at a reaction temperature of 50°C (Angew. Chem. Int. Ed., 2012, 51, 5129-5133), but the selectivity of methanol in the total product is only 12%; using a titanium dioxide-supported gold palladium (AuPd / TiO2) catalyst, methane can be oxidized to a mixture of methanol and methanol peroxide (Angew. Chem. Int. Ed., 2013, 52, 1280-1284), but the selectivity of methanol in the total product does not exceed 50%. In the presence of reducing gas CO, methane can be oxidized to a mixture of methanol, formic acid and acetic acid using O2 as an oxidant (Nature, 2017, 551, 605-608; CN112390704B), in which the selectivity of methanol is relatively low. In order to obtain methanol with high selectivity, it is usually necessary to dope the catalyst with a second metal component, which inevitably leads to problems such as complex catalyst components, difficult to identify active centers, and high production costs. At the same time, the conversion rate of low-carbon activity also needs to be further improved. Therefore, developing a catalytic oxidation system with simple composition and low cost, while improving the conversion rate of low-carbon alkanes and improving the selectivity of target alcohols are still the key points and difficulties of the selective oxidation of low-carbon alkanes. Summary of the invention

[0004] The object of the present invention is to solve the above problems in the prior art and to provide a method for preparing corresponding alcohols by catalytic oxidation of low-carbon alkanes with high activity, high stability and high selectivity.

[0005] In order to achieve the above object, the present invention adopts the following technical scheme:

[0006] A method for preparing corresponding alcohols by catalytic oxidation of low-carbon alkanes, using an intermittent reactor, in the presence of a reducing gas, using oxygen as an oxidant, and directly catalytically oxidizing low-carbon alkanes to corresponding alcohols in a water medium in which a catalyst is dispersed. The reducing gas is at least one of CO or H2; the low-carbon alkane is one of methane, ethane, and propane; the corresponding alcohols are methanol for methane, ethanol for ethane, and n-propanol / isopropanol for propane; the catalyst used is a supported Au nanoparticle catalyst, wherein the carrier is a zeolite molecular sieve, the mass percentage of Au in the catalyst is 0.05% to 10%, and the remainder is the carrier.

[0007] The zeolite molecular sieve can be selected from at least one of MOR, ZSM-5, SSZ-13, Beta, ZMS-35, and Y-type molecular sieves; the zeolite molecular sieve is a hydrogen-type molecular sieve.

[0008] The Au is uniformly dispersed on the surface of the zeolite molecular sieve in the form of nanoparticles with a size of 2 to 10 nm.

[0009] In the present invention, the preparation of the zeolite molecular sieve supported Au nanoparticle catalyst comprises the following steps: firstly, dissolving a soluble Au precursor in pure water to obtain a corresponding solution; then mixing a hydrogen-type zeolite molecular sieve carrier with the above solution; then evaporating the solvent, drying, and reducing to obtain the zeolite molecular sieve supported Au nanoparticle catalyst.

[0010] The drying temperature is 60-120° C., the drying time is 4-24 hours, and the drying atmosphere is one of vacuum / inert gas / air; the reduction temperature is 300-800° C., the reduction time is 1-4 hours, and the reduction gas is a hydrogen-argon or hydrogen-nitrogen mixed gas with a hydrogen content of not less than 5%.

[0011] The catalytic oxidation reaction steps are as follows: dispersing the catalyst in an aqueous medium, loading it into an intermittent reactor, and then filling the reactor with O2, reducing gas and low-carbon alkane gas in sequence; then heating the intermittent reactor to a reaction temperature and reacting for a period of time to catalytically oxidize the low-carbon alkanes into corresponding alcohols.

[0012] In an intermittent reactor, the aqueous medium accounts for 20% of the total volume of the reactor, and the mass ratio of the catalyst to the aqueous medium is 1:1000 to 1:100; the partial pressure of O2 is 0.5 to 5 bar, the partial pressure of reducing gases such as CO or H2 is 0.5 to 5 bar, and the partial pressure of low-carbon alkanes such as methane, ethane or propane is 1 to 20 bar; the reaction temperature is 80 to 200°C; and the reaction time is 1 to 300 min.

[0013] Compared with the existing technology of catalytic oxidation of low-carbon alkanes to prepare corresponding alcohols, the beneficial effects of the present invention are embodied in the following aspects:

[0014] (1) The present invention shows excellent catalytic activity for direct oxidation of low-carbon alkanes to corresponding alcohols, mild reaction conditions, high product selectivity, and good catalyst stability. At a reaction temperature of 80 to 200° C., the selectivity of methanol prepared by catalytic oxidation of methane, ethanol prepared by catalytic oxidation of ethane, or n-propanol / isopropanol prepared by catalytic oxidation of propane in liquid products all reaches more than 90%.

[0015] (2) The catalyst used in the present invention is a zeolite molecular sieve-loaded Au nanoparticle catalyst. Compared with the traditional low-carbon alkane oxidation catalyst, it avoids the doping of the second metal component; the catalyst composition is simple; the preparation process is simple and controllable, and mass production can be carried out.

[0016] (3) The catalyst used in the present invention has a weak adsorption capacity for target products such as methanol, ethanol, and n-propanol / isopropanol, which is conducive to the desorption of the products and avoids excessive oxidation of the products.

[0017] (4) The catalyst used in the present invention has good stability and its reaction performance remains unchanged after repeated use. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is the TEM image of the 0.5 wt% Au / HMOR catalyst prepared in Example 1.

[0019] Figure 2 for Figure 1 Particle size distribution of 0.5wt% Au / HMOR catalyst.

[0020] Figure 3 The NMR spectrum of the product obtained in Example 2 is shown in FIG. DETAILED DESCRIPTION

[0021] The catalyst preparation process and the method for preparing corresponding alcohols by catalytic oxidation of low-carbon alkanes provided by the present invention are described in further detail below, but the present invention is not limited thereto.

[0022] Example 1

[0023] The supported Au metal catalyst was prepared by the equal volume impregnation method. Taking 0.5wt% Au / HMOR as an example, the specific preparation process is as follows: First, hydrated tetrachloroauric acid is dissolved in pure water to prepare an Au precursor solution with a mass concentration of 0.05g / mL; then, 1g HMOR molecular sieve is mixed with 100μL of the above Au precursor solution; then, the solvent is evaporated, dried at 80℃ overnight, and then reduced with 5% hydrogen at 400℃ for 2h to obtain an Au / HMOR catalyst with a loading of 0.5wt%. The loading amount of Au can be controlled by changing the amount of Au precursor solution used. The process for preparing Au nanoparticle catalysts with different carriers is the same as above, except that HMOR needs to be replaced with other molecular sieves. See Figures 1-2 The particle size of the 0.5wt% Au / HMOR prepared in this example is 2-10nm and is uniformly loaded on the HMOR.

[0024] Example 2

[0025] 100 mg Au / HMOR (Au mass percentage is 0.5%) catalyst was weighed and dispersed into 20 g water and loaded into a batch reactor; 5 bar O2, 5 bar CO and 20 bar methane were then charged into the reactor in sequence; the reactor was then placed in an oil bath, heated to 150°C, reacted for 60 min, and then cooled rapidly. Finally, the product was analyzed by a 500 MHz nuclear magnetic resonance spectrometer, see Figure 3 The catalytic reaction performance is shown in Table 1.

[0026] Example 3

[0027] 100 mg Au / HMOR (Au mass percentage is 0.1%) catalyst was weighed and dispersed into 20 g water and loaded into a batch reactor; then 5 bar O2, 5 bar CO and 20 bar methane were sequentially charged into the reactor; then the reactor was placed in an oil bath, heated to 150°C, reacted for 60 minutes and then cooled rapidly, and finally the product was analyzed by a 500 MHz nuclear magnetic resonance spectrometer. The catalytic reaction performance is shown in Table 1.

[0028] Example 4

[0029] 100 mg Au / HMOR (Au mass percentage is 1.0%) catalyst was weighed and dispersed into 20 g water and loaded into a batch reactor; then 5 bar O2, 5 bar CO and 20 bar methane were sequentially charged into the reactor; then the reactor was placed in an oil bath, heated to 150°C, reacted for 60 minutes and then cooled rapidly, and finally the product was analyzed by a 500 MHz nuclear magnetic resonance spectrometer. The catalytic reaction performance is shown in Table 1.

[0030] Example 5

[0031] 100 mg Au / HMOR (Au mass percentage is 0.5%) catalyst was weighed and dispersed into 20 g water and loaded into a batch reactor; then 5 bar O2, 5 bar CO and 10 bar methane were sequentially charged into the reactor; then the reactor was placed in an oil bath, heated to 150°C, reacted for 60 minutes and then cooled rapidly, and finally the product was analyzed by a 500 MHz nuclear magnetic resonance spectrometer. The catalytic reaction performance is shown in Table 1.

[0032] Example 6

[0033] 100 mg Au / HMOR (Au mass percentage is 0.5%) catalyst was weighed and dispersed into 20 g water and loaded into a batch reactor; then 3 bar O2, 5 bar CO and 20 bar methane were sequentially charged into the reactor; then the reactor was placed in an oil bath, heated to 150°C, reacted for 60 minutes and then cooled rapidly, and finally the product was analyzed by a 500 MHz nuclear magnetic resonance spectrometer. The catalytic reaction performance is shown in Table 1.

[0034] Example 7

[0035] 100 mg Au / HMOR (Au mass percentage is 0.5%) catalyst was weighed and dispersed into 20 g water and loaded into a batch reactor; then 5 bar O2, 1 bar CO and 20 bar methane were sequentially charged into the reactor; then the reactor was placed in an oil bath, heated to 150°C, reacted for 60 minutes and then cooled rapidly, and finally the product was analyzed by a 500 MHz nuclear magnetic resonance spectrometer. The catalytic reaction performance is shown in Table 1.

[0036] Example 8

[0037] 100 mg Au / HMOR (Au mass percentage is 0.5%) catalyst was weighed and dispersed into 20 g water and loaded into a batch reactor; then 5 bar O2, 5 bar H2 and 20 bar methane were sequentially charged into the reactor; then the reactor was placed in an oil bath, heated to 120°C, reacted for 60 minutes and then cooled rapidly, and finally the product was analyzed by a 500 MHz nuclear magnetic resonance spectrometer. The catalytic reaction performance is shown in Table 1.

[0038] Example 9

[0039] 100 mg Au / HZSM-5 (Au mass percentage is 0.5%) catalyst was weighed and dispersed into 20 g water and loaded into a batch reactor; then 5 bar O2, 5 bar CO and 20 bar methane were sequentially charged into the reactor; then the reactor was placed in an oil bath, heated to 150°C, reacted for 60 minutes and then cooled rapidly, and finally the product was analyzed by a 500 MHz nuclear magnetic resonance spectrometer. The catalytic reaction performance is shown in Table 1.

[0040] Example 10

[0041] 100 mg Au / HSSZ-13 (Au mass percentage is 0.5%) catalyst was weighed and dispersed into 20 g water and loaded into a batch reactor; then 5 bar O2, 5 bar CO and 20 bar methane were sequentially charged into the reactor; then the reactor was placed in an oil bath, heated to 150°C, reacted for 60 minutes and then cooled rapidly, and finally the product was analyzed by a 500 MHz nuclear magnetic resonance spectrometer. The catalytic reaction performance is shown in Table 1.

[0042] Table 1

[0043] Embodiment 11

[0044] 100 mg Au / HMOR (Au mass percentage is 0.5%) catalyst was weighed and dispersed into 20 g water and loaded into a batch reactor; then 5 bar O2, 5 bar CO and 3 bar ethane were sequentially charged into the reactor; then the reactor was placed in an oil bath, heated to 80°C, reacted for 300 min and then cooled rapidly, and finally the product was analyzed by a 500 MHz nuclear magnetic resonance spectrometer. The catalytic reaction performance is shown in Table 2.

[0045] Table 2

[0046]

[0047] Example 12

[0048] 100 mg Au / HMOR (Au mass percentage is 0.5%) catalyst was weighed and dispersed into 20 g water and loaded into a batch reactor; then 5 bar O2, 5 bar CO and 3 bar propane were sequentially charged into the reactor; then the reactor was placed in an oil bath, heated to 80°C, reacted for 300 min and then cooled rapidly, and finally the product was analyzed by a 500 MHz nuclear magnetic resonance spectrometer. The catalytic reaction performance is shown in Table 3.

[0049] Table 3

[0050]

[0051] Comparative Example 1

[0052] The preparation method of HMOR-loaded metal Rh catalyst (Rh / HMOR) is the same as that in Example 1, except that the hydrated tetrachloroauric acid solution is replaced with a rhodium chloride solution. 100 mg of Rh / HMOR (Rh mass percentage is 0.5%) catalyst is weighed and dispersed into 20 g of water and loaded into a batch reactor; then 5 bar O2, 5 bar CO and 20 bar methane are sequentially charged into the reactor; then the reactor is placed in an oil bath, heated to 150°C, reacted for 60 minutes, and then cooled rapidly, and finally the product is analyzed by a 500 MHz nuclear magnetic resonance spectrometer. The catalytic reaction performance is shown in Table 1.

[0053] Comparative Example 2

[0054] The preparation method of HMOR-loaded metal Pd catalyst (Pd / HMOR) is the same as that in Example 1, except that the hydrated tetrachloroauric acid solution is replaced with palladium chloride solution. 100 mg of Pd / HMOR (Pd mass percentage is 0.5%) catalyst is weighed and dispersed into 20 g of water and loaded into a batch reactor; then 5 bar O2, 5 bar CO and 20 bar methane are sequentially charged into the reactor; then the reactor is placed in an oil bath, heated to 150°C, reacted for 60 minutes, and then cooled rapidly, and finally the product is analyzed by a 500 MHz nuclear magnetic resonance spectrometer. The catalytic reaction performance is shown in Table 1.

[0055] Comparative Example 3

[0056] The preparation method of HMOR-loaded metal Ir catalyst (Ir / HMOR) is the same as that in Example 1, except that the hydrated tetrachloroauric acid solution is replaced with an iridium chloride solution. Weigh 100 mg of Ir / HMOR (Ir mass percentage is 0.5%) catalyst, disperse it into 20 g of water, and load it into a batch reactor; then fill the reactor with 5 bar O2, 5 bar CO and 20 bar methane in sequence; then place the reactor in an oil bath, heat it to 150°C, react for 60 minutes, and then cool it down quickly, and finally analyze the product by a 500 MHz nuclear magnetic resonance spectrometer. The catalytic reaction performance is shown in Table 1.

[0057] As can be seen from the results in Table 1, the present invention shows excellent catalytic activity for direct oxidation of low-carbon alkanes to corresponding alcohols, mild reaction conditions, high product selectivity, and good catalyst stability. At a reaction temperature of 80-200°C, the selectivity of methanol prepared by catalytic oxidation of methane, ethanol prepared by catalytic oxidation of ethane, or n-propanol / isopropanol prepared by catalytic oxidation of propane in liquid products all reaches more than 90%.

Claims

1. A method for preparing corresponding alcohols by catalytic oxidation of light alkanes, characterized in that: An intermittent reactor is used, and in the presence of a reducing gas, oxygen is used as an oxidant to directly catalytically oxidize low-carbon alkanes into corresponding alcohols in an aqueous medium dispersed with a catalyst; wherein the reducing gas is at least one of CO or H2; the low-carbon alkane is one of methane, ethane, and propane; the corresponding alcohols are methanol for methane, ethanol for ethane, and n-propanol / isopropanol for propane; the catalyst used is an Au nanoparticle catalyst supported by a hydrogen-type zeolite molecular sieve, the mass percentage of Au in the catalyst is 0.05% to 10%, and the remainder is a carrier; The average particle size of the Au nanoparticles is 5.9±1.9 nm; The preparation of the Au nanoparticle catalyst supported by the hydrogen-type zeolite molecular sieve comprises the following steps: firstly, dissolving a soluble Au precursor in pure water to obtain a corresponding solution; then mixing the hydrogen-type zeolite molecular sieve carrier with the above solution; subsequently, evaporating the solvent, drying, and reducing to obtain the Au nanoparticle catalyst supported by the hydrogen-type zeolite molecular sieve; the reducing gas is a hydrogen-argon or hydrogen-nitrogen mixed gas with a hydrogen content of not less than 5%.

2. The method for preparing corresponding alcohols by catalytic oxidation of light alkanes according to claim 1, characterized in that: The hydrogen-type zeolite molecular sieve is at least one selected from MOR, ZSM-5, SSZ-13, Beta, ZMS-35, and Y-type molecular sieves.

3. The method for preparing corresponding alcohols by catalytic oxidation of light alkanes according to claim 1, characterized in that: The reduction temperature is 300-800°C, and the reduction time is 1-4h.

4. The method for preparing corresponding alcohols by catalytic oxidation of light alkanes according to claim 1, characterized in that: The steps of catalytic oxidation are as follows: dispersing the catalyst in an aqueous medium, loading it into an intermittent reactor, and then sequentially filling the intermittent reactor with O2, reducing gas and low-carbon alkanes; then heating the intermittent reactor to a reaction temperature and reacting for a period of time to catalytically oxidize the low-carbon alkanes into corresponding alcohols.

5. A method for preparing corresponding alcohols by catalytic oxidation of light alkanes as claimed in claim 1 or 4, characterized in that: In the intermittent reactor, the mass ratio of the catalyst to the aqueous medium is 1:1000 to 1:

100.

6. A method for preparing corresponding alcohols by catalytic oxidation of light alkanes as claimed in claim 1 or 4, characterized in that: The partial pressure of O2 is 0.5 to 5 bar, the partial pressure of reducing gas is 0.5 to 5 bar, and the partial pressure of low-carbon alkanes is 1 to 20 bar.

7. The method for preparing corresponding alcohols by catalytic oxidation of light alkanes as claimed in claim 4, characterized in that: The reaction temperature is 80-200°C, and the reaction time is 1-300 minutes.

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