Catalyst system for synthesizing acetic acid by means of methanol low-pressure carbonylation, and use thereof

Abstract

The present invention relates to the technical field of synthesis of acetic acid by means of methanol low-pressure carbonylation. Disclosed is a catalyst system for synthesizing acetic acid by means of methanol low-pressure carbonylation. The catalyst system comprises a group VIII metal main catalyst, an iodomethane cocatalyst, an inorganic iodide and an ionic liquid containing [NR1R2R3R4]+[CH3COO]- as a catalyst stabilizer, wherein R1, R2, R3 and R4 in the ionic liquid are an alkyl containing 4-9 carbons, an aryl and an acyl or a combination thereof. When the catalyst system is applied to a process for synthesizing acetic acid by means of methanol low-pressure carbonylation, a metal catalyst can be kept stable under the condition of a low water content, thereby reducing the separation energy consumption of a subsequent rectification system.

Description

A catalyst system for the low-pressure carbonyl synthesis of acetic acid from methanol and its application Technical Field

[0001] This invention relates to the technical field of low-pressure carbonyl synthesis of acetic acid from methanol, and to catalyst systems for acetic acid production, specifically to a catalyst system for low-pressure carbonyl synthesis of acetic acid from methanol and its application. Background Technology

[0002] Acetic acid is an important basic organic chemical raw material, used to produce vinyl acetate monomer (VCM), cellulose acetate, acetic anhydride, terephthalic acid, chloroacetic acid, polyvinyl alcohol, acetate esters, and metal acetates, etc. It has wide applications in dyes, pharmaceuticals, pesticides, adhesives, and organic solvents, and is one of the most rapidly developing and important organic chemical products in recent years. The methanol low-pressure carbonylation synthesis method for acetic acid production is an advanced technology and a commonly used industrial method for producing acetic acid.

[0003] The low-pressure carbonyl synthesis of acetic acid from methanol using a rhodium-based catalyst was developed by Monsanto in 1970. This process requires the materials to maintain catalyst stability at a water content of 14-15%. Celanese subsequently added inorganic iodides to this catalyst (see patent publication CN100341836C) to maintain stability even when the water content in the reaction system was reduced to 2%. Southwest Chemical Research and Design Institute Co., Ltd. further improved catalyst stability by adding morpholine compounds to the rhodium catalyst system (see patent publication CN100525910C) to maintain stability even when the water content in the reaction system was reduced to 5%. However, higher water content in the reaction system means higher energy consumption and a higher incidence of water-gas side reactions (CO + H₂O → CO₂ + H₂). Furthermore, as the water content decreases, the catalyst struggles to maintain its stability and is more likely to enter the downstream system with the products. Therefore, reducing the water content in the reaction system while maintaining catalyst stability at low water content has been a key direction for catalyst improvement.

[0004] For example, the invention patent with publication number "CN101716527A", entitled "A highly stable catalyst for the carbonylation process of acetic acid production and its application method", proposes a catalyst system with rhodium as the main catalyst, iodomethane or a mixture of iodomethane and lithium iodide as the co-catalyst, and 1,3-dialkylimidazolium phosphate as the ionic liquid as the stabilizer. This system is used for the low-pressure carbonylation process to produce acetic acid, ensuring that the rhodium catalyst maintains good stability even with extremely low water content (1-9% water content in the reaction system). Another example is the invention patent with publication number "CN102266795A", entitled "A catalyst for low-water acetic acid synthesis process and its preparation and application method", which proposes an H[RhM(CO)4(N)4] bimetallic complex. This complex utilizes the synergistic catalytic effect between the two metals to achieve high catalytic efficiency in the range of 0.1-15 wt% water concentration in the reactants.

[0005] Therefore, the catalyst system for the low-pressure carbonyl synthesis of acetic acid from methanol is still being continuously improved and optimized to ensure the stability of the catalyst under low water concentration conditions. Summary of the Invention

[0006] The purpose of this invention is to provide a catalyst system for the low-pressure carbonyl synthesis of acetic acid from methanol and its application. A new ionic liquid is proposed as a catalyst stabilizer in the catalyst system, which ensures that the catalyst system remains stable in a reaction system with a water content of 0.5-14%, thus ensuring stable reaction and reducing catalyst loss.

[0007] This invention is achieved through the following technical solution:

[0008] A catalyst system for the low-pressure carbonyl synthesis of acetic acid from methanol includes a Group VIII metal main catalyst, iodomethane co-catalyst, an inorganic iodide, and an ionic liquid with the structure of formula (I) as a catalyst stabilizer.

[0009] ,

[0010] R1, R2, R3, and R4 are alkyl, aryl, acyl, or combinations thereof containing 4 to 9 carbon atoms.

[0011] Furthermore, the Group VIII metal catalyst is one or a combination of rhodium, iridium, and ruthenium.

[0012] Furthermore, the inorganic iodide is one of lithium iodide, potassium iodide, and nickel iodide.

[0013] Furthermore, in the ionic liquid, R1, R2, R3, and R4 of formula (I) are groups that are all the same, partially the same, or completely different.

[0014] Furthermore, the ionic liquid is a single compound or a mixture of multiple compounds having the structure of formula (I).

[0015] Furthermore, the molar ratio of the ionic liquid to the group VIII metal catalyst is 5 to 60:1.

[0016] Furthermore, the molar ratio of the ionic liquid to the group VIII metal catalyst is 10 to 50:1.

[0017] The aforementioned catalyst system is used in the low-pressure carbonyl synthesis of acetic acid from methanol with a water content of 0.5-14%.

[0018] Furthermore, in the methanol low-pressure carbonyl synthesis of acetic acid process, when separating the product liquid and the catalyst, if flash evaporation is used, the flash evaporation pressure is controlled at 0.10~0.30MPa; if flash evaporation is used, the flash evaporation temperature is controlled at 135~143℃ and the pressure is 0.10~0.30MPa.

[0019] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0020] I. In this invention, a quaternary ammonium ionic liquid is proposed as a stabilizer in the catalyst system for the low-pressure carbonyl synthesis of acetic acid from methanol. This is a new type of catalyst stabilizer. In this new ionic liquid stabilizer, the acetate anion reacts with the cations in the acetic acid production system to form acetic acid or acetate salts, without introducing other impurity ions, thus simplifying the system and making post-processing more convenient.

[0021] II. In this invention, a quaternary ammonium ionic liquid catalyst stabilizer is used. The quaternary ammonium cation can form an ionic compound with the active diiododicarbonyl rhodium. The added ionic liquid with a specific structural formula (Ⅰ) can provide cations for the active component rhodium and other Group VIII metal catalysts, and can also serve as a solvent for the catalyst. According to the principle of like dissolves like, the ionic liquid has good solubility in the catalyst system, which is beneficial to the stability of the catalyst.

[0022] Third, the novel catalyst system for the low-pressure carbonyl synthesis of acetic acid from methanol in this invention exhibits good stability in the process of low-pressure carbonyl synthesis of acetic acid from methanol with a water content of 0.5-14%. In particular, the catalyst remains stable even when flash evaporation and / or evaporation processes are carried out at ultra-low water content below 1%, which provides a wider range of process adjustment space for the entire low-pressure carbonyl synthesis of acetic acid from methanol and provides more favorable conditions for equipment optimization, thus providing favorable conditions for improving production efficiency and product quality. Attached Figure Description

[0023] Figure 1 is a partial structural schematic diagram of the production system for the low-pressure carbonyl synthesis of acetic acid from methanol.

[0024] Figure 2 is a partial structural schematic diagram of a production system for the low-pressure carbonyl synthesis of acetic acid from methanol, according to another embodiment.

[0025] Among them, 1. Reactor; 2. Flash evaporator; 3. Evaporation heat exchanger; 4. Methanol feed line; 5. CO feed line; 6. Line I; 7. Mother liquor line I; 8. Mother liquor line II; 9. Product discharge line; 10. Recovery line; 2.1. Feed inlet. Embodiments of the present invention

[0026] The present invention will be further described in detail below with reference to embodiments, but the implementation of the present invention is not limited thereto.

[0027] Example 1

[0028] To facilitate public understanding of this scheme, this embodiment uses the catalyst system for the low-pressure carbonyl synthesis of acetic acid from methanol as an example to further illustrate this scheme.

[0029] In this embodiment, the methanol low-pressure carbonyl synthesis of acetic acid process uses the production system shown in Figure 1 to synthesize acetic acid. The production system includes a reactor 1, a flash evaporator 2, and an evaporation heat exchanger 3. The reactor 1 is connected to a methanol feed line 4 and a CO feed line 5. The reactor 1 is connected to the feed inlet 2.1 of the flash evaporator 2 through a line I 6. The flash evaporator 2 is connected to the reactor 1 through a mother liquor line I 7 and to the evaporation heat exchanger 3 through a mother liquor line II 8. The top of the flash evaporator 2 is connected to a product discharge line 9. The crude product evaporated in the flash evaporator is sent to the distillation process for further processing through the product discharge line 9. The reactor 1 is also connected to a recovery line 10.

[0030] The reactant raw material, methanol, is fed into reactor 1 via methanol feed line 4. The reactant raw material, carbon monoxide, is fed into reactor 1 via CO feed line 5. Reactor 1 is also supplemented with 800 ppm rhodium, 3.2% water, and 8% [N(C5H)]... 11 )2(C8H 17 )2] + [CH3COO] －A homogeneous mixture of ionic liquid, appropriate amount of iodomethane, and lithium iodide is used. The total amount of catalyst (including main catalyst, co-catalyst, and ionic liquid) accounts for 35% of the total material. After the reaction in reactor 1 is completed, the material is transported to flash evaporator 2 through pipeline I6. Flash evaporator 2, in conjunction with evaporation heat exchanger 3, performs flash evaporation of the material to separate the product from the catalyst. The material containing catalyst and ionic liquid is returned to reactor 1 through mother liquor pipeline I7 to achieve catalyst recycling. The gas phase (product gas) obtained after flash evaporation 2 is sent to the distillation system for further processing through product discharge pipeline 9. The light components (including water, iodomethane, methyl acetate, etc.) obtained after distillation are returned to reactor 1 through recovery pipeline 10. Evaporation heat exchanger 3 assists in accelerating the separation of materials by flash evaporator. After one week of stable operation, the rhodium content in the reaction system is measured.

[0031] In this embodiment, during the methanol low-pressure carbonyl synthesis of acetic acid process, the flash evaporation temperature was controlled at 138°C and the pressure was controlled at 0.10 MPa when separating the product liquid and the catalyst. The rhodium content before feeding was 800 ppm. After running for one week, the rhodium content in the reaction system was measured to be 784 ppm, and the loss rate of the rhodium catalyst was 2.00%.

[0032] In actual production, considering factors such as reaction rate, product quality, product yield, and production cost, the temperature of flash evaporation should be controlled within the range of 135~143℃ and the pressure within the range of 0.10~0.30MPa.

[0033] Multiple batches of sampling revealed that under these process conditions, the loss rate of the rhodium catalyst remained stable at around 2.00%, with very little variation. This indicates that adding this catalyst system to the methanol-to-acetic acid low-pressure carbonylation process maintains stability even with a low water content of 3.2%. Furthermore, the low water content in the methanol-to-acetic acid low-pressure carbonylation process reduces the energy consumption of the distillation system.

[0034] Example 2

[0035] The only difference between this embodiment and embodiment 1 is that flash evaporator 2 is used to flash the product liquid, replacing the structure of flash evaporator 2 + evaporation heat exchanger 3 in embodiment 1.

[0036] Referring to Figure 2, the production system includes reactor 1 and flash evaporator 2. Reactor 1 is connected to methanol feed line 4 and CO feed line 5. Reactor 1 is connected to the feed inlet 2.1 of flash evaporator 2 via line I6. Flash evaporator 2 is connected to reactor 1 via mother liquor line I7. The top of flash evaporator 2 is connected to product discharge line 9. The crude product evaporated in flash evaporator 2 is sent to the distillation process for further processing via product discharge line 9. After the reaction in reactor 1 is completed, the material is transported to flash evaporator 2 via line I6 to separate the product from the catalyst. The material containing the catalyst and ionic liquid is returned to reactor 1 via mother liquor line I7 to achieve catalyst recycling. The gas phase (product gas) obtained after flash evaporator 2 is sent to the distillation system for further processing via product discharge line 9. The light components (including water, methyl iodide, methyl acetate, etc.) obtained after distillation are returned to reactor 1 via recovery line 10.

[0037] Control the reaction conditions as follows, and after one week of stable operation, test the rhodium content in the reaction system.

[0038] In the methanol low-pressure carbonyl synthesis of acetic acid process, the flash evaporation temperature is controlled at 137℃ and the pressure is controlled at 0.10MPa when separating the product liquid and the catalyst. The rhodium content before feeding is 800ppm. After running for one week, the rhodium content in the reaction system is measured to be 786ppm, and the loss rate of rhodium catalyst is 1.75%.

[0039] Multiple batches of sampling revealed that under these process conditions, the loss rate of the rhodium catalyst remained stable at around 1.75%, with minimal variation. This indicates that when this catalyst system is added to the methanol-to-acetic acid low-pressure carbonylation process, it remains stable under low water content (3.2%), regardless of whether flash evaporation or flash distillation is used.

[0040] Example 3

[0041] The only difference between this embodiment and Example 1 is that the water content is 0.5%, the reduced water mass is replenished with acetic acid, the process conditions are controlled according to the following requirements, and the rhodium content of the catalyst is detected after one week of operation.

[0042] In this embodiment, during the methanol low-pressure carbonyl synthesis of acetic acid process, the flash evaporation temperature was controlled at 138°C and the pressure was controlled at 0.10 MPa when separating the product liquid and the catalyst. The rhodium content before feeding was 800 ppm. After running for one week, the rhodium content in the reaction system was measured to be 782 ppm, and the loss rate of the rhodium catalyst was 2.25%.

[0043] Multiple batches of sampling revealed that under these process conditions, the loss rate of the rhodium catalyst remained stable at around 2.25%, with minimal variation. This demonstrates that adding this catalyst system to the methanol-to-acetic acid low-pressure carbonylation process maintains catalyst stability even with a low water content of 0.5%, representing a significant breakthrough compared to existing technologies. Furthermore, the low water content in the methanol-to-acetic acid low-pressure carbonylation process reduces the energy consumption of the distillation system.

[0044] Example 4

[0045] The only difference between this embodiment and Example 1 is that the water content is 7.5%, the amount of acetic acid is reduced accordingly, the other components remain unchanged, the process conditions are controlled according to the following requirements, and the rhodium content of the catalyst is detected after one week of operation.

[0046] In this embodiment, during the methanol low-pressure carbonyl synthesis of acetic acid process, the flash evaporation temperature was controlled at 138°C and the pressure was controlled at 0.10 MPa when separating the product liquid and the catalyst. The rhodium content before feeding was 800 ppm. After running for one week, the rhodium content in the reaction system was measured to be 790 ppm, and the loss rate of the rhodium catalyst was 1.25%.

[0047] Multiple batches of sampling revealed that under these process conditions, the loss rate of the rhodium catalyst remained stable at around 1.25%, with very little variation.

[0048] Example 5

[0049] The only difference between this embodiment and Example 1 is that the water content is 14%, the amount of acetic acid is reduced accordingly, the other components remain unchanged, the process conditions are controlled according to the following requirements, and the rhodium content of the catalyst is detected after one week of operation.

[0050] In this embodiment, during the methanol low-pressure carbonyl synthesis of acetic acid process, the flash evaporation temperature was controlled at 137°C and the pressure was controlled at 0.12 MPa when separating the product liquid and the catalyst. The rhodium content before feeding was 800 ppm. After running for one week, the rhodium content in the reaction system was measured to be 790 ppm, and the loss rate of the rhodium catalyst was 1.25%.

[0051] The above experiments show that when the catalyst system of this scheme is added, the catalyst can remain stable under the condition of 0.5-14% water content. However, under the condition of high water content, energy consumption will increase.

[0052] Example 6

[0053] The only difference between this embodiment and Embodiment 1 is that...

[0054] Add 5% [N(C6H)] based on the total mass of the solution. 13 )3(C6H5)] + [CH3COO]－ 10% of [N(C4H9)2(C9H 19 (C3H7CO) + [CH3COO] － An ionic liquid mixture with 2% water content was used. The amount of acetic acid was reduced accordingly, while the other components remained unchanged. After one week of operation, the rhodium content of the catalyst was measured to be 788 ppm, and the loss rate of the rhodium catalyst was 1.50%.

[0055] It is evident that the stability of the catalyst can be maintained regardless of whether a single ionic liquid or a mixture of multiple ionic liquids is added.

[0056] Example 7

[0057] Compared with Example 6, the only difference is that the rhodium content is increased to 1600 ppm, while the other components remain unchanged. After one week of operation, the rhodium content of the catalyst was measured to be 1589 ppm.

[0058] It is evident that the addition of ionic liquids can maintain the stability of the catalyst even at high catalyst concentrations.

[0059] Example 8

[0060] This embodiment examines the effect of ionic liquid catalyst stabilizers on different Group VIII metal main catalysts when the catalyst system is applied to the methanol-to-acetic acid low-pressure carbonyl synthesis process.

[0061] In this embodiment, the production system as described in Example 1 is used, and the reaction conditions are controlled according to Table 1. The ionic liquid in the catalyst system is a single [N(C5H)] ion. 11 )2(C8H 17 )2] + [CH3COO] － After running stably for one week, the content of metal catalyst in the reaction system was tested, and the test results are shown in Table 1.

[0062] Table 1

[0063]

[0064] As shown in Table 1, in the catalyst system for the low-pressure carbonyl synthesis of acetic acid from methanol, the Group VIII metal catalyst can be selected from one or a combination of rhodium, iridium, and ruthenium. Under low water content conditions, the metal catalyst can maintain stability, and it can even remain stable under ultra-low water content conditions of 0.5%.

[0065] Comparative Example 1

[0066] The only difference between this comparative example and Example 1 is that...

[0067] No [N(C5H)] is added to the reaction system.11 )2(C8H 17 )2] + [CH3COO] － The ionic liquid was replenished with acetic acid to maintain its mass. After one week of operation, the rhodium content of the catalyst was measured to be 396 ppm, and the catalyst loss rate was 50.5%.

[0068] Comparative Example 2

[0069] The only difference between this comparative example and Example 2 is that...

[0070] No [N(C5H)] is added to the reaction system. 11 )2(C8H 17 )2] + [CH3COO] － The ionic liquid was replenished with acetic acid to maintain its mass. After one week of operation, the rhodium content of the catalyst was measured to be 465 ppm, and the catalyst loss rate was 41.875%.

[0071] Comparative Example 3

[0072] The only difference between this comparative example and Example 3 is that [N(C5H] is not added. 11 )2(C8H 17 )2] + [CH3COO] － The ionic liquid was replenished by acetic acid to compensate for its mass, and the reduced water mass was also replenished by acetic acid. After one week of operation, the rhodium content of the catalyst was measured to be 205 ppm. This indicates that under this reaction system, the loss rate of the catalyst-rhodium ratio is significantly increased, and the stability of the catalyst system is significantly reduced.

[0073] As can be seen from the above examples, without the addition of the ionic liquid catalyst stabilizer in this scheme, especially under low water content conditions, the catalyst loss is significant.

[0074] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications or equivalent changes made to the above embodiments based on the technical essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A catalyst system for the low-pressure carbonyl synthesis of acetic acid from methanol, characterized in that: The catalysts include Group VIII metal main catalysts, iodomethane co-catalysts, inorganic iodides, and ionic liquids with the structure of formula (I) as catalyst stabilizers. （Ⅰ）， R1, R2, R3, and R4 are alkyl, aryl, acyl, or combinations thereof containing 4 to 9 carbon atoms.

2. The catalyst system for low-pressure carbonyl synthesis of acetic acid from methanol according to claim 1, characterized in that: The Group VIII metal catalyst is one or a combination of rhodium, iridium, and ruthenium.

3. The catalyst system for low-pressure carbonyl synthesis of acetic acid from methanol according to claim 1, characterized in that: The inorganic iodide is one of lithium iodide, potassium iodide, and nickel iodide.

4. The catalyst system for low-pressure carbonyl synthesis of acetic acid from methanol according to claim 1, characterized in that: The R1, R2, R3, and R4 groups of the ionic liquid in formula (I) are either all the same groups, partially the same groups, or completely different groups.

5. The catalyst system for low-pressure carbonyl synthesis of acetic acid from methanol according to claim 4, characterized in that: The ionic liquid is a single compound or a mixture of multiple compounds having the structure of formula (I).

6. The catalyst system for low-pressure carbonyl synthesis of acetic acid from methanol according to claim 1, characterized in that: The molar ratio of the ionic liquid to the group VIII metal catalyst is 5~60:

1.

7. The catalyst system for low-pressure carbonyl synthesis of acetic acid from methanol according to claim 6, characterized in that: The molar ratio of the ionic liquid to the group VIII metal catalyst is 10~50:

1.

8. The application of the catalyst system according to any one of claims 1 to 7 in the low-pressure carbonyl synthesis of acetic acid from methanol with a water content of 0.5 to 14%.

9. The application according to claim 8, characterized in that: In the methanol-to-acetic acid low-pressure carbonyl synthesis process, when separating the product liquid and the catalyst, if flash evaporation is used, the flash evaporation pressure is controlled at 0.10~0.30 MPa; if flash evaporation is used, the flash evaporation temperature is controlled at 135~143℃ and the pressure is 0.10~0.30 MPa.

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