Method for reducing reaction temperature for generating dimethyl ether through methanol dehydration

Abstract

The invention discloses a method for reducing reaction temperature for generating dimethyl ether by methanol dehydration, which comprises the following steps: performing methanol dehydration reaction in a fixed bed catalytic reactor, taking an H-ZSM-5 molecular sieve as a catalyst, and when a mixed solution of methanol and acetone replaces a methanol solution to serve as a reactant to be co-injected into a reaction system, the starting temperature of the reaction for generating dimethyl ether through methanol dehydration is reduced from 90 DEG C to 30 DEG C, and the conversion rate of methanol at the same temperature is greatly improved. The method is simple in treatment mode, can effectively reduce the reaction energy consumption for generating dimethyl ether through methanol dehydration, and has very high industrial application value.

Description

Technical Field

[0001] The invention relates to a method for reducing the reaction temperature of methanol dehydration to generate dimethyl ether, belonging to the field of catalysis. Background Art

[0002] Methanol and dimethyl ether (DME) are widely used in the production of olefins, aromatics and other key compounds, and gradually replace the decreasing fossil energy and become important raw materials in the chemical industry. Studies have shown that DME exhibits higher reactivity in many key reaction processes compared to methanol. The use of DME has significant advantages, especially in that it reduces the generation of water during the reaction, thereby greatly improving the stability of the catalyst. In addition, DME has a higher hydrogen / carbon ratio and lower biological toxicity, which makes it a more ideal and attractive initial reactant in industrial applications. At present, there are two main ways to produce DME: one is through the direct conversion of synthesis gas, and the other is through methanol dehydration reaction. Among them, the direct production of DME from synthesis gas is an extremely complex process, which usually requires high temperature (473-573K) and pressure (50-100bar) and expensive catalysts. In contrast, the methanol dehydration method is relatively mature and can be achieved by solid acid catalysts (such as cheap acidic molecular sieves), with significant catalytic activity and high DME yield. In industrial production, the reaction temperature of molecular sieve-catalyzed methanol dehydration to produce DME is usually higher than 423K. Although this temperature is lower than most catalytic reactions (for example, the methanol to olefins reaction requires more than 523K), it still consumes a lot of energy.

[0003] In order to improve the catalytic performance (such as activity, selectivity and stability) of molecular sieve catalysts and reduce additional energy consumption, the most commonly used strategy is to develop new catalysts. For example, a variety of new nano, metal-loaded, multi-level porous and other functionalized molecular sieve catalysts have shown excellent catalytic performance in a variety of small molecule conversion reactions. In addition to the catalyst itself, some additive molecules as co-reactants have also been found to improve catalytic activity. In addition, regulating the local microenvironment of the reactants is also one of the effective strategies to improve the activity of heterogeneous catalytic reactions. The most typical example is the "solvation effect", which can significantly affect the adsorption behavior and electronic structure of the reactant molecules. Although a lot of research has been done on improving the methanol conversion rate, these important catalytic processes still require higher operating temperatures, which are difficult to meet the current energy-saving needs. Achieving efficient conversion of methanol to DME under mild conditions has always been the goal pursued by industry and academia. Summary of the invention

[0004] In order to solve the technical problems of high reaction temperature and low methanol conversion rate in methanol dehydration to dimethyl ether, the purpose of the present invention is to provide a method for reducing the reaction temperature of methanol dehydration to dimethyl ether. The method innovatively uses a mixed solution of methanol and acetone to replace the traditional methanol solution as a reactant, so that the reaction start-up temperature of methanol dehydration is reduced from 90°C (conversion rate is 0.2%) to 30°C (conversion rate is 2.1%). And at a reaction temperature of 100°C, a methanol conversion rate of more than 90% can be achieved, and the dimethyl ether selectivity is 100%. When pure methanol is used as a reactant, the above catalytic effect can only be achieved at 150°C. This method can effectively reduce the reaction temperature of methanol dehydration to dimethyl ether.

[0005] To achieve the above object, the present invention provides the following technical solution: a method for reducing the reaction temperature of methanol dehydration to generate dimethyl ether, comprising:

[0006] Mixing methanol and acetone in a molar ratio of 1 to 80:1 to prepare a reaction solution;

[0007] The reaction temperature is 30-150°C and the reaction pressure is normal pressure;

[0008] The catalyst is H-ZSM-5 molecular sieve, with a mass of 0.2 g and a particle size of 40 to 60 mesh, which is loaded into a fixed bed catalytic reactor;

[0009] Before the reaction started, the reactant injection channel was closed, and the catalyst was activated at a nitrogen flow rate of 30 mL / min and a temperature of 500 °C for 2 h;

[0010] When the catalyst temperature drops to room temperature, the nitrogen flow rate is adjusted to 4 mL / min, and the temperature of the reactant vaporizer is raised to 120°C;

[0011] Then the methanol and acetone mixed solution was heated for 0.2 to 0.8 h. -1 The mass space velocity is injected into the reactant vaporizer through a constant flow pump to evaporate into gas, and then mixed with the carrier gas into a fixed bed catalytic reactor to contact and react with the catalyst. The reaction products are detected by online chromatography.

[0012] Analysis of the catalytic results shows that the addition of acetone can significantly reduce the reaction temperature of methanol dehydration to form dimethyl ether, and at 100°C, the methanol conversion rate of mixed solutions of methanol and acetone in different proportions as reactants is much higher than that of pure methanol as a reactant.

[0013] Preferably, the carrier gas is an inert gas such as nitrogen or helium.

[0014] Compared with the prior art, the present invention does not require modification of the existing reaction device or the catalyst, and only requires the addition of acetone to the methanol solution to reduce the reaction temperature of methanol dehydration to generate dimethyl ether and promote methanol conversion. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 The adsorption of methanol and acetone in different proportions on each acid site of the catalyst 13 C MAS NMR spectrum.

[0016] Figure 2 It is the simultaneous adsorption of 2 methanol and 1 acetone on each acid site of the catalyst. 1 H- 1 H SQ MAS NMR spectrum. DETAILED DESCRIPTION

[0017] All embodiments are operated according to the operating steps of the technical solution of the above invention content.

[0018] The analysis method, methanol conversion rate and dimethyl ether selectivity in the embodiment are calculated as follows:

[0019] The products were automatically analyzed online using a GC-9790PLUS gas chromatograph equipped with a gas autosampler, a Plot-Q capillary column and a FID detector.

[0020] In some embodiments of the present invention, methanol conversion and dimethyl ether selectivity are calculated based on carbon moles:

[0021] Methanol conversion rate = [(methanol carbon moles in feed) - (methanol carbon moles in output)] ÷ (methanol carbon moles in feed) × (100%)

[0022] Dimethyl ether selectivity = (carbon moles of dimethyl ether in the output) ÷ (carbon moles of all products in the output) × (100%)

[0023] Example 1

[0024] A mixed solution of methanol and acetone with a molar ratio of 8:1 was used as the raw material. The reaction temperature was 30°C, the reaction pressure was normal pressure, and the mass space velocity of the mixed solution injection was 0.2h -1 Under the conditions of 0.2g of catalyst, the raw materials pass through the catalyst bed to undergo catalytic reaction to produce dimethyl ether.

[0025] The reaction results are shown in Table 1.

[0026] Example 2

[0027] The implementation process is the same as Example 1 except for the following differences:

[0028] The reaction temperature is 60°C

[0029] The reaction results are shown in Table 1.

[0030] Example 3

[0031] The implementation process is the same as Example 1 except for the following differences:

[0032] The reaction temperature is 70°C

[0033] The reaction results are shown in Table 1.

[0034] Example 4

[0035] The implementation process is the same as Example 1 except for the following differences: the reaction temperature is 80°C

[0036] The reaction results are shown in Table 1.

[0037] Example 5

[0038] The implementation process is the same as Example 1 except for the following differences: the reaction temperature is 90°C

[0039] The reaction results are shown in Table 1.

[0040] Example 6

[0041] The implementation process is the same as Example 1 except for the following differences: the reaction temperature is 100°C

[0042] The reaction results are shown in Table 1.

[0043] Example 7

[0044] The implementation process is the same as Example 1 except for the following differences: the reaction temperature is 110°C

[0045] The reaction results are shown in Table 1.

[0046] Example 8

[0047] The implementation process is the same as Example 1 except for the following differences: the reaction temperature is 120°C

[0048] The reaction results are shown in Table 1.

[0049] Example 9

[0050] The implementation process is the same as Example 1 except for the following differences: the reaction temperature is 130°C

[0051] The reaction results are shown in Table 1.

[0052] Example 10

[0053] The implementation process is the same as Example 1 except for the following differences: the reaction temperature is 140°C

[0054] The reaction results are shown in Table 1.

[0055] Embodiment 11

[0056] The implementation process is the same as Example 1 except for the following differences: the reaction temperature is 150°C

[0057] The reaction results are shown in Table 1.

[0058] Example 12

[0059] A mixed solution of methanol and acetone in a molar ratio of 1:1 was used as the raw material. The reaction temperature was 100°C, the reaction pressure was normal pressure, the catalyst mass was 0.2 g, and the mass space velocity of the mixed solution injection was 0.2 h -1 Under the conditions of , the raw materials pass through the catalyst bed to undergo catalytic reaction to produce dimethyl ether.

[0060] The reaction results are shown in Table 1.

[0061] Example 13

[0062] The implementation process is the same as Example 12 except for the following differences:

[0063] A mixed solution of methanol and acetone with a molar ratio of 2:1 was used as the raw material

[0064] The reaction results are shown in Table 1.

[0065] Embodiment 14

[0066] The implementation process is the same as Example 12 except for the following differences:

[0067] A mixed solution of methanol and acetone with a molar ratio of 4:1 was used as the raw material

[0068] The reaction results are shown in Table 1.

[0069] Embodiment 15

[0070] The implementation process is the same as Example 12 except for the following differences:

[0071] A mixed solution of methanol and acetone with a molar ratio of 16:1 was used as the raw material

[0072] The reaction results are shown in Table 1.

[0073] Example 16

[0074] The implementation process is the same as Example 12 except for the following differences:

[0075] A mixed solution of methanol and acetone with a molar ratio of 40:1 was used as the raw material

[0076] The reaction results are shown in Table 1.

[0077] Embodiment 17

[0078] The implementation process is the same as Example 12 except for the following differences:

[0079] A mixed solution of methanol and acetone with a molar ratio of 80:1 was used as the raw material

[0080] The reaction results are shown in Table 1.

[0081] Embodiment 18

[0082] A mixed solution of methanol and acetone with a molar ratio of 8:1 was used as the raw material. The reaction temperature was 100°C, the reaction pressure was atmospheric pressure, the catalyst mass was 0.2g, and the mass space velocity of the mixed solution injection was 0.4h -1 Under the conditions of , the raw materials pass through the catalyst bed to undergo catalytic reaction to produce dimethyl ether.

[0083] The reaction results are shown in Table 1.

[0084] Embodiment 19

[0085] A mixed solution of methanol and acetone with a molar ratio of 8:1 was used as the raw material. The reaction temperature was 100°C, the reaction pressure was normal pressure, the catalyst mass was 0.2g, and the mass space velocity of the mixed solution injection was 0.8h -1 Under the conditions of , the raw materials pass through the catalyst bed to undergo catalytic reaction to produce dimethyl ether.

[0086] The reaction results are shown in Table 1.

[0087] Comparative Example 1

[0088] Using pure methanol solution as raw material, the reaction temperature is 30°C, the reaction pressure is normal pressure, the catalyst mass is 0.2g, and the methanol injection mass space velocity is 0.2h -1 Under the conditions of , the raw materials pass through the catalyst bed to undergo catalytic reaction to produce dimethyl ether.

[0089] The reaction results are shown in Table 2.

[0090] Comparative Example 2

[0091] The implementation process is the same as that of Comparative Example 1 except for the following differences:

[0092] The reaction temperature is 60°C

[0093] The reaction results are shown in Table 2.

[0094] Comparative Example 3

[0095] The implementation process is the same as that of Comparative Example 1 except for the following differences:

[0096] The reaction temperature is 70°C

[0097] The reaction results are shown in Table 2.

[0098] Comparative Example 4

[0099] The implementation process is the same as that of Comparative Example 1 except for the following differences:

[0100] The reaction temperature is 80°C

[0101] The reaction results are shown in Table 2.

[0102] Comparative Example 5

[0103] The implementation process is the same as that of Comparative Example 1 except for the following differences:

[0104] The reaction temperature is 90°C

[0105] The reaction results are shown in Table 2.

[0106] Comparative Example 6

[0107] The implementation process is the same as that of Comparative Example 1 except for the following differences:

[0108] Reaction temperature: 100°C

[0109] The reaction results are shown in Table 3.

[0110] Comparative Example 7

[0111] The implementation process is the same as that of Comparative Example 1 except for the following differences:

[0112] The reaction temperature is 110°C

[0113] The reaction results are shown in Table 2.

[0114] Comparative Example 8

[0115] The implementation process is the same as that of Comparative Example 1 except for the following differences:

[0116] The reaction temperature is 120°C

[0117] The reaction results are shown in Table 2.

[0118] Comparative Example 9

[0119] The implementation process is the same as that of Comparative Example 1 except for the following differences:

[0120] The reaction temperature is 130°C

[0121] The reaction results are shown in Table 2.

[0122] Comparative Example 10

[0123] The implementation process is the same as that of Comparative Example 1 except for the following differences:

[0124] The reaction temperature is 140°C

[0125] The reaction results are shown in Table 2.

[0126] Comparative Example 11

[0127] The implementation process is the same as that of Comparative Example 1 except for the following differences:

[0128] Reaction temperature: 150℃

[0129] The reaction results are shown in Table 2.

[0130] Comparative Example 12

[0131] Using pure methanol solution as raw material, the reaction temperature is 100℃, the reaction pressure is normal pressure, the catalyst mass is 0.2g, and the methanol injection mass space velocity is 0.4h -1 Under the conditions of , the raw materials pass through the catalyst bed to undergo catalytic reaction to produce dimethyl ether.

[0132] The reaction results are shown in Table 2.

[0133] Comparative Example 13

[0134] Using pure methanol solution as raw material, the reaction temperature is 100℃, the reaction pressure is normal pressure, the catalyst mass is 0.2g, and the methanol injection mass space velocity is 0.8h -1 Under the conditions of , the raw material passes through the catalyst bed to undergo a catalytic reaction to generate dimethyl ether. The reaction results are shown in Table 2.

[0135] Table 1 Reaction evaluation results

[0136]

[0137] Table 2 Reaction evaluation results

[0138]

[0139] From the evaluation of the reaction results of Examples 1 to 11, it can be seen that when the reactant is a mixed solution with a molar ratio of methanol to acetone of 8:1 and the reaction temperature is 30°C, methanol has begun to undergo a dehydration reaction to produce dimethyl ether, and the methanol conversion rate is 2.1%. As the reaction temperature increases, the methanol conversion rate reaches 91.1% at 100°C, and the dimethyl ether selectivity is 100%. When the temperature continues to rise to 130°C, the selectivity of dimethyl ether decreases due to further reactions to produce olefins, alkanes and other products. In Comparative Examples 1 to 11, the starting temperature of the methanol dehydration reaction is 90°C, and the conversion rate is only 0.2%. It is not until 150°C that the methanol conversion rate reaches 92.5%. The above results show that the mixed solution of methanol and acetone as a reactant can greatly reduce the reaction temperature of methanol dehydration to produce dimethyl ether. From the reaction evaluation results of Examples 12 to 17, it can be seen that changing the molar ratio of methanol to acetone can still promote the conversion of methanol. Even when the molar ratio of methanol to acetone is as high as 80:1, the methanol conversion rate (36.5%) at 100°C is still 6 times that of pure methanol as a reactant (5.6%). From Examples 6, 18, 19 and Comparative Examples 6, 12, and 13, it can be seen that even if the mass space velocity of the reactants is changed, the methanol conversion rate of the mixed solution of methanol and acetone as a reactant is still significantly higher than the methanol conversion rate of the pure methanol solution as a reactant. From the results of the above embodiments, it can be seen that the present invention uses H-ZSM-5 molecular sieve as a catalyst and a mixed solution of methanol and acetone as a reactant, which can significantly reduce the reaction temperature of methanol dehydration to generate dimethyl ether, and has high selectivity and good stability.

[0140] Furthermore, the present invention also performs solid nuclear magnetic resonance in-situ characterization on the H-ZSM-5 molecular sieve catalyst that adsorbs methanol and acetone molecules. The experimental steps include: 1. dehydrating and activating the H-ZSM-5 molecular sieve at 400°C; 2. accurately controlling 13 The adsorption amount of methanol or acetone enriched by C is such that each acid site adsorbs 1 acetone and 1 to 4 methanol molecules; 3. The adsorbed molecular sieve is transferred to a solid nuclear magnetic rotor for sampling and analysis. Figure 1 of 13 As shown in the C MAS NMR spectrum, the adsorption ratio of methanol and acetone at each acid site is changed. 13 The chemical shift of the acetone (C enriched) was significantly changed, indicating that acetone and methanol were competitively adsorbed on the active sites. The samples with 2 methanol and 1 acetone adsorbed on each acid site were subjected to two-dimensional 1 H- 1 H SQ MAS NMR sampling analysis, such as Figure 2 As shown in the figure, the peaks at (3.7, 2.5) and (2.5, 3.7) ppm appear in the spectrum, which can be attributed to the methyl H (δ 1 H=3.7ppm) and acetone methyl H (δ 1H=2.5ppm), indicating that the two molecules of methanol and acetone have spatial proximity. Through density functional theory (DFT) calculations, it was found that the single component methanol molecules would form a stable hydrogen bond network around the active site, and the hydrogen bond network must be destroyed before the dehydration reaction. When the acetone molecule is introduced, its alkaline carbonyl group can effectively destroy the methanol hydrogen bond network. This result explains the catalytic experimental phenomenon that the mixed solution of methanol and acetone as a reactant reduces the temperature of the methanol dehydration reaction from the reaction mechanism.

[0141] The above description is only a specific implementation of the present invention, and the protection scope of the present invention is not limited thereto. Any person familiar with the technology can understand and think of any changes or substitutions within the technical scope disclosed by the present invention, which should be included in the scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A method for reducing the reaction temperature of methanol dehydration to produce dimethyl ether, characterized in that: The method comprises: Methanol and acetone are mixed to prepare a reaction liquid, which is injected into a fixed bed catalytic reactor equipped with a solid catalyst in a gas phase to carry out a methanol dehydration reaction, and dimethyl ether is prepared after heating and reaction.

2. The method for reducing the reaction temperature of methanol dehydration to produce dimethyl ether according to claim 1, characterized in that: The molar ratio of the methanol to the acetone is 1 to 80:

1.

3. The method for reducing the reaction temperature of methanol dehydration to produce dimethyl ether according to claim 1, characterized in that: The reaction liquid injection mass space velocity is 0.2 to 0.8 h -1 .

4. The method for reducing the reaction temperature of methanol dehydration to produce dimethyl ether according to claim 1, characterized in that: The heating reaction temperature is 30-150°C.

5. The method for reducing the reaction temperature of methanol dehydration to produce dimethyl ether according to claim 1, characterized in that: The reaction system pressure is normal pressure.

6. The method for reducing the reaction temperature of methanol dehydration to produce dimethyl ether according to claim 1, characterized in that: The solid catalyst is H-ZSM-5 molecular sieve, with a mass of 0.2 g and a particle size of 40 to 60 meshes.

7. The method for reducing the reaction temperature of methanol dehydration to produce dimethyl ether according to claim 6, characterized in that: The molecular sieve catalyst H-ZSM-5 needs to be activated before use, and the activation condition is to maintain 500° C. for 2 h at a nitrogen flow rate of 30 mL / min.

8. The method for reducing the reaction temperature of methanol dehydration to produce dimethyl ether according to claim 1, characterized in that: The reaction liquid is evaporated into gas in a vaporizer and mixed with a carrier gas before entering the fixed bed catalytic reactor.

9. The method for reducing the reaction temperature of methanol dehydration to produce dimethyl ether according to claim 8, characterized in that: The temperature of the vaporizer was 120°C.

10. The method for reducing the reaction temperature of methanol dehydration to produce dimethyl ether according to claim 8, characterized in that: The carrier gas is an inert gas such as nitrogen or helium.

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