A method for producing methanol by partial oxidation of coalbed methane

Abstract

The present invention discloses a method for producing methanol by partial oxidation of coalbed methane. The reaction using coalbed methane comprises the following steps: pressurizing the coalbed methane and charging it into an autoclave filled with deionized water and a catalyst material. Carbon monoxide is then introduced at a certain pressure as an auxiliary reaction gas. The reaction system catalytically oxidizes methane in the coalbed methane under the action of a rhodium-based hydroxyapatite catalyst at a certain temperature to produce methanol. Compared to existing technologies, the present invention directly uses coalbed methane as the reaction gas, allowing methanol to be produced with high selectivity with only a small amount of carbon monoxide added. Furthermore, the reaction system, catalyzed by the rhodium-based hydroxyapatite, offers high yields and low energy consumption, making it a promising reaction system.

Description

Technical Field

[0001] The present invention belongs to the technical field of coalbed methane utilization, and more specifically, relates to a method for producing methanol by partial oxidation of coalbed methane. Background Art

[0002] Coal dominates China's fossil energy reserves, and its coal-based energy consumption structure is unlikely to change in the near future. Coal mining produces significant amounts of coalbed methane (CMM), primarily composed of methane, oxygen, carbon dioxide, and a small amount of carbon monoxide. Currently, CMM is typically released directly into the atmosphere through ventilation equipment during coal mine operations. Given that methane, the primary component of CMM, is chemically stable and has a greenhouse effect over twenty times greater than that of carbon dioxide, the safe and efficient utilization of CMM remains a hot topic of research within the scientific community.

[0003] Direct oxidation of methane to methanol is a "holy grail" reaction in chemistry, as it effectively circumvents the high energy consumption of the traditional coal gasification-Fischer-Tropsch synthesis process, offering advantages such as low energy consumption, a direct process, and high atomic efficiency. If methane from coalbed methane could be used as a reaction gas and selectively converted to methanol over a catalyst, it would provide a promising solution for coalbed methane utilization. However, due to the stable carbon-hydrogen bonds of methane molecules and the instability of methanol molecules, how to maintain a high methane conversion rate while improving methanol selectivity is a key technical challenge that must be addressed for the industrialization of this route. Summary of the Invention

[0004] In view of the above problems existing in the prior art, the present invention has developed a method for producing methanol by partial oxidation of coalbed methane. The reaction system of the method can obtain methanol with high yield and high selectivity under relatively mild reaction conditions.

[0005] The present invention provides a method for producing methanol by partial oxidation of coalbed methane, wherein coalbed methane is used as reaction gas and partially oxidized to produce methanol in the presence of carbon monoxide as an auxiliary and catalyst, wherein the catalyst is rhodium-based hydroxyapatite.

[0006] Specifically, the method includes the following steps:

[0007] The coalbed methane is pressurized and charged into a high-pressure reactor filled with deionized water and a catalyst. Subsequently, a certain pressure of carbon monoxide is charged as a reaction auxiliary gas. While stirring is maintained in the reactor, the reaction temperature is increased and the reaction is carried out for a period of time to obtain methanol.

[0008] Preferably, the pressure of the coalbed methane is 0.5-10.0 MPa.

[0009] Preferably, the pressure of the carbon monoxide is 0.1-2.0 MPa.

[0010] Preferably, the mass ratio of the deionized water to the catalyst is 500:1-2000:1.

[0011] Preferably, the stirring rate is 400-1000 rpm.

[0012] Preferably, the reaction temperature is 100-280° C.; and the reaction time is 0.5-24 h.

[0013] Preferably, the liquid product is taken out after the reaction and distilled to obtain the methanol produced by the reaction.

[0014] Preferably, the rhodium-based hydroxyapatite uses hydroxyapatite as a carrier, and the active component rhodium is dispersed on the surface of the hydroxyapatite.

[0015] Preferably, the rhodium loading in the rhodium-based hydroxyapatite is 0.1-5.0 wt%, preferably 0.25-1.0 wt%, and more preferably 0.5 wt%.

[0016] Preferably, the preparation method of rhodium-based hydroxyapatite comprises the following steps:

[0017] The rhodium source is introduced into the surface of hydroxyapatite by an impregnation method or a solid-state grinding method, and the product is calcined to obtain rhodium-based hydroxyapatite.

[0018] Preferably, the calcination temperature is 300-800°C, preferably 600°C.

[0019] Beneficial effects:

[0020] The reaction system of the present invention directly uses coalbed methane as the reaction gas, partially oxidizing the methane in the coalbed methane to produce methanol with the aid of only a small amount of carbon monoxide and as a catalyst. Compared to existing technologies, this method directly uses coalbed methane as the reaction gas, allowing for highly selective methanol production with only a small amount of carbon monoxide added. Furthermore, this reaction system, catalyzed by rhodium-based hydroxyapatite, offers high yields and low energy consumption, making it a promising reaction system. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Exemplary embodiments of the present invention will be described in more detail with reference to the accompanying drawings.

[0022] Figure 1 is a transmission electron micrograph of the rhodium-based hydroxyapatite obtained in Example 1 of the present invention;

[0023] Figure 2 This is a scanning transmission electron microscope image of the rhodium-based hydroxyapatite obtained in Example 1 of the present invention.

[0024] Figure 3 The liquid product of Example 1 of the present invention 1 H NMR spectrum. DETAILED DESCRIPTION

[0025] The following is a detailed description of the specific embodiments of the present invention. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention and are not intended to limit the present invention.

[0026] The present invention provides a method for producing methanol by partial oxidation of coalbed methane, wherein coalbed methane is used as reaction gas and partially oxidized to produce methanol in the presence of carbon monoxide as an auxiliary and catalyst, wherein the catalyst is rhodium-based hydroxyapatite.

[0027] Specifically, the method includes the following steps:

[0028] The coalbed methane is pressurized and charged into a high-pressure reactor (liquid phase reactor) filled with deionized water and a catalyst. Subsequently, a certain pressure of carbon monoxide is charged as a reaction auxiliary gas. While stirring is maintained in the reactor, the reaction temperature is increased and the reaction is carried out for a period of time. The liquid product is taken out and distilled to obtain methanol.

[0029] In some embodiments, the volume concentration of methane in the coalbed methane is 5-30%.

[0030] "Partial oxidation" refers to the oxidation of methane to methanol, while complete oxidation produces carbon dioxide and water.

[0031] In the present invention, oxygen molecules, with the assistance of carbon monoxide, activate the active sites in the rhodium-based hydroxyapatite catalyst to Rh-O. Subsequently, the methane molecules in the coalbed methane are activated to methyl groups (-CH3) at the Rh-O sites and then combine with the hydroxyl (-OH) groups obtained after activation with deionized water to generate methanol (CH3OH).

[0032] The pressure of the selected coalbed methane is preferably 0.5-10.0 MPa, such as 1, 2, 3, 4, 5, 6, 7, 8, 9 MPa, more preferably 1.0-3.0 MPa, and most preferably 2.0 MPa;

[0033] The pressure of the carbon monoxide is preferably 0.1-2.0 MPa, such as 0.1, 0.2, 0.5, 1.0 MPa, more preferably 0.1-1.0 MPa, and most preferably 0.5 MPa.

[0034] The mass ratio of the deionized water to the catalyst is preferably 500:1-2000:1, such as 600:1, 700:1, 800:1, 900:1, 1200:1, 1500:1, 1800:1, more preferably 1000:1;

[0035] The stirring rate is preferably 400-1000 rpm, more preferably 800 rpm;

[0036] The reaction temperature is preferably 100-280°C, for example, 120, 150, 160, 180, 200, 220, 240, 250, 260°C, more preferably 240°C; the reaction time is preferably 0.5-24h, for example, 1, 2, 4, 6, 8, 10, 12, 15, 16, 18, 20, 22h, more preferably 1.0-4.0h, most preferably 1.0h.

[0037] Rhodium-based hydroxyapatite uses hydroxyapatite as a carrier, and the active component rhodium is dispersed on the surface of hydroxyapatite.

[0038] The loading amount of rhodium in the rhodium-based hydroxyapatite is 0.1-5.0 wt %, preferably 0.25-1.0 wt %, and more preferably 0.5 wt %.

[0039] The preparation method of the rhodium-based hydroxyapatite comprises the following steps:

[0040] The rhodium source is introduced into the surface of hydroxyapatite by an impregnation method or a solid-state grinding method, and the product is calcined to obtain rhodium-based hydroxyapatite.

[0041] According to a specific embodiment of the present invention, the preparation method of rhodium-based hydroxyapatite comprises the following steps:

[0042] The rhodium source is dissolved in deionized water, and hydroxyapatite is added and stirred for impregnation. After the impregnation is completed, the temperature is increased to evaporate the solvent, and the mixture is calcined to obtain rhodium-based hydroxyapatite.

[0043] Preferably, the calcination temperature is 300-800°C, preferably 600°C.

[0044] The present invention will be further described below with reference to the examples, but the scope of the present invention is not limited to these examples.

[0045] The coalbed methane used in the following examples was from coal mines in Anhui Province, with a volume concentration of 5% to 30% methane, a small amount of CO gas, and the remainder being air. The other gases and reagents were commercially available.

[0046] Example 1

[0047] The preparation of the catalyst material includes the following steps: 100mg of rhodium trichloride is dissolved in 100mL of deionized water, and then 10.2mL of the prepared solution is placed in a beaker. 1.0g of commercially available hydroxyapatite material is placed in the taken solution and impregnated for 4 hours at a speed of 600rpm under magnetic stirring. After the impregnation is completed, the stirring temperature is set to 90°C and the solvent in the mixture is waited for to evaporate. After the solvent is completely evaporated, the obtained material is taken out and placed in a muffle furnace, and calcined at a temperature of 600°C in an air atmosphere for 4 hours to obtain a rhodium-based hydroxyapatite material (rhodium loading is 0.5wt.%).

[0048] The rhodium-based hydroxyapatite obtained in Example 1 was analyzed using a transmission electron microscope to obtain a transmission electron microscope scanning image thereof, as shown in FIG. Figure 1 As shown; the scanning transmission electron microscope is used to obtain the scanning transmission electron microscope, as shown Figure 2 As shown. Figure 1 and Figure 2 It can be seen that the active component rhodium exists in a highly dispersed form on its surface.

[0049] 2.0 MPa of coalbed methane was introduced into an autoclave containing 20 mL of deionized water and 20 mg of rhodium-based hydroxyapatite, followed by 0.5 MPa of carbon monoxide. The reactor was stirred at 800 rpm and maintained at 240°C for 1.0 hour. The liquid product was then removed and distilled to obtain methanol.

[0050] The yield and selectivity of methanol were determined by 1 H NMR analysis was performed using 3-(trimethylsilyl)propanesulfonic acid sodium salt as the internal standard.

[0051] Calculation method:

[0052] Methanol yield (μmol g cat -1 h -1 )=(C 甲醇 ×V)M cat -1 T -1 ;

[0053] Among them, C 甲醇 for 1 The concentration of methanol in the liquid product measured by H NMR (μmol / L); V is the volume of the liquid product (L); M cat is the mass of the catalyst (g); T is the reaction time of coalbed methane oxidation (h).

[0054] Methanol selectivity (%) = C 甲醇 / C 氧化产物 ×100%;

[0055] Among them, C 甲醇 for 1 The concentration of methanol in the liquid product measured by H NMR (μmol / L); C 氧化产物 for 1 The concentration of CBM oxidation products in the liquid products measured by H NMR (μmol / L).

[0056] Activity tests showed that when the reaction was carried out under the conditions described in Example 1, rhodium-based hydroxyapatite could partially oxidize coalbed methane and convert it into methanol at a temperature of 240°C, with a methanol yield of 3439.9 μmol g cat -1 h -1 , the selectivity of methanol is 100%.

[0057] See also Figure 3 and Table 1, Figure 3 The liquid product 1 H NMR spectroscopy revealed that, in addition to methanol, the product contained no other oxygen-containing products, such as formic acid and acetic acid, and the selectivity for methanol in the liquid product was 100%. Row 1 of Table 1 lists the yields of methanol from coalbed methane under the conditions and catalysts described in Example 1. It can be seen that the rhodium-based hydroxyapatite prepared by the above preparation method exhibits excellent methanol yields.

[0058] Example 2

[0059] The method of Example 1 was followed, but the amount of rhodium trichloride used was changed to 5.1 mL. The activity evaluation method of the catalyst was the same as that of Example 1. The activity test showed that the methanol yield of the rhodium-based hydroxyapatite material prepared by this method with a rhodium loading of 0.25 wt.% at 240°C was 3897.6 μmol g cat -1 h -1 , the selectivity of methanol is 100%.

[0060] Example 3

[0061] The method of Example 1 was followed, but the amount of rhodium trichloride used was changed to 20.4 mL. The activity evaluation method of the catalyst was the same as that of Example 1. The activity test showed that the methanol yield of the rhodium-based hydroxyapatite material prepared by this method with a rhodium loading of 1.0 wt.% at 240°C was 3823.8 μmol g cat -1 h -1 , the selectivity of methanol is 100%.

[0062] Example 4

[0063] The method of Example 1 was followed, but the amount of rhodium trichloride used was changed to 40.8 mL. The activity evaluation method of the catalyst was the same as that of Example 1. The activity test showed that the methanol yield of the rhodium-based hydroxyapatite material prepared by this method with a rhodium loading of 2.0 wt.% at 240°C was 2313.0 μmol g cat -1 h -1 , the selectivity of methanol is 100%.

[0064] Comparative Example 1

[0065] To compare the reaction system of the present invention with a conventional gas-phase system, a selective oxidation reaction was conducted in a fixed-bed reactor using the catalyst prepared in Example 1 and coalbed methane as the reaction gas in a gas-phase system. The temperature was also set at 240°C. The catalyst was evaluated using the same method as in Example 1. Activity tests showed that the yield of the catalyst in Example 1 in this reaction system was only 2.3 μmol g cat -1 h -1 , the selectivity of methanol is 28.6%.

[0066] Comparative Example 2

[0067] In order to compare the catalytic performance of the samples, a rhodium-based molecular sieve material with a rhodium loading of 0.5 wt.% was prepared using ZSM-5 molecular sieve as the carrier material. The subsequent steps were the same as in Example 1. The catalyst evaluation method was the same as in Example 1. The activity test showed that the methanol yield of the molecular sieve-supported rhodium catalyst with a rhodium loading of 0.5 wt.% prepared by this method was 542.7 μmol g at 240 °C. cat -1 h -1 , the selectivity of methanol is 42.7%.

[0068] The catalytic performances of the rhodium-based hydroxyapatite obtained in Examples 1 to 4 and the catalyst obtained in Comparative Example 1 are shown in Table 1.

[0069] Table 1 Catalytic activity test results of catalysts

[0070]

[0071] The above-mentioned data on the catalytic activity of methane in coalbed methane show that the reaction conditions and catalyst materials described in the present invention can efficiently partially oxidize the methane in coalbed methane into methanol. At the same time, compared with the rhodium-based catalyst prepared using molecular sieve materials as carriers, the rhodium-based hydroxyapatite prepared by the method of the present invention has a higher methanol yield in the reaction of partial oxidation of coalbed methane to produce methanol.

[0072] While various embodiments of the present invention have been described above, the above description is intended to be illustrative, not exhaustive, and not limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

[0073] The endpoints of the ranges and any values ​​disclosed herein 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 endpoints of each range, the endpoints of each range and 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 to be specifically disclosed herein.

Claims

1. A method for producing methanol by partial oxidation of coalbed methane, characterized in that: After pressurizing the coalbed methane, it is charged into a high-pressure reactor filled with deionized water and a rhodium-based hydroxyapatite catalyst, and then carbon monoxide is charged as a reaction auxiliary gas. The reaction temperature is increased while stirring is maintained in the reactor to react and obtain methanol, wherein the pressure of the coalbed methane is 0.5-10.0 MPa, the pressure of the carbon monoxide is 0.1-2.0 MPa, the reaction temperature is 100-280°C; the reaction time is 0.5-24h, the catalyst is rhodium-based hydroxyapatite, the rhodium-based hydroxyapatite uses hydroxyapatite as a carrier, and the active component rhodium is dispersed on the surface of hydroxyapatite.

2. The method according to claim 1, characterized in that The mass ratio of the deionized water to the catalyst rhodium-based hydroxyapatite is 500:1-2000:

1.

3. The method according to claim 1, characterized in that The rhodium loading amount in the rhodium-based hydroxyapatite is 0.1-5.0 wt %.

4. The method according to claim 3, characterized in that The rhodium loading amount in the rhodium-based hydroxyapatite is 0.25-1.0 wt %.

5. The method according to claim 4, characterized in that The loading amount of rhodium in the rhodium-based hydroxyapatite is 0.5 wt %.

6. The method according to claim 1, characterized in that The preparation method of the rhodium-based hydroxyapatite comprises the following steps: The rhodium source is introduced into the surface of hydroxyapatite by an impregnation method or a solid-state grinding method, and the product is calcined to obtain rhodium-based hydroxyapatite.

7. The method according to claim 6, characterized in that The preparation method of the rhodium-based hydroxyapatite comprises the following steps: The rhodium source is dissolved in deionized water, and hydroxyapatite is added and stirred for impregnation. After the impregnation is completed, the temperature is increased to evaporate the solvent, and the mixture is calcined to obtain rhodium-based hydroxyapatite.

8. The method according to claim 7, characterized in that The calcination temperature is 300-800°C.

9. The method according to claim 8, characterized in that The calcination temperature is 600°C.

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