Catalyst system for synthesizing acetic acid from methanol through low-pressure carbonyl and application of catalyst system

Abstract

The invention discloses a catalyst system for methanol low-pressure carbonyl synthesis of acetic acid, and relates to the technical field of methanol low-pressure carbonyl synthesis of acetic acid, the catalyst system comprises a group VIII metal main catalyst, an iodomethane cocatalyst, an inorganic iodide, and an ionic liquid with [NR1R2R3R4] < + > [CH3COO] <-> as a catalyst stabilizer, r1, R2, R3 and R4 in the ionic liquid are alkyl, aryl and acyl containing 4-9 carbons or a combination thereof, and when the catalyst system is applied to a process for synthesizing acetic acid by methanol low-pressure carbonyl, a metal catalyst can be kept stable under the condition of low water content, so that the separation energy consumption of a subsequent rectification system is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of low-pressure carbonylation of methanol to acetic acid, and relates to a catalyst system for acetic acid production, and in particular to a catalyst system for low-pressure carbonylation of methanol to acetic acid and application thereof. Background Art

[0002] Acetic acid is an important basic organic chemical raw material, which can be used to produce vinyl acetate monomer (VCM), acetate fiber, acetic anhydride, terephthalic acid, chloroacetic acid, polyvinyl alcohol, acetate esters and metal acetates, etc. It has a wide range of uses in dyes, medicines, pesticides, adhesives, organic solvents, etc. It is one of the important organic chemical products that has developed rapidly in recent years. The low-pressure carbonyl synthesis method of methanol to produce acetic acid is an advanced technology for acetic acid production and is also a commonly used method for industrial production of acetic acid.

[0003] The low-pressure carbonylation of methanol to acetic acid using rhodium-based catalysts was developed by Monsanto in 1970. In this process, the material needs to maintain the stability of the catalyst under the condition of 14-15% water content. Later, Celanese added inorganic iodide to the catalyst (reference patent document with publication number CN100341836C), which can maintain the stability of the catalyst system when the water content of the reaction system is reduced to 2%. Southwest Chemical Research and Design Institute Co., Ltd. added morpholine substances to the rhodium catalyst system (reference patent document with publication number CN100525910C), which can maintain the stability of the catalyst system when the water content of the reaction system is reduced to 5%. In the reaction system, a higher water content means higher energy consumption in the production process and a higher occurrence of water-gas side reactions (CO+H2O→CO2+H2). As the water content in the reaction decreases, it is difficult for the catalyst to maintain its stability and it is easy to enter the back-end system with the product. Therefore, reducing the water content in the reaction system and maintaining the stability of the catalyst at low water content have always been the direction of catalyst improvement.

[0004] For example, the invention patent with the publication number of "CN101716527A" and the name of "Highly stable catalyst for carbonylation process to produce acetic acid and its use method" proposes a catalyst system with rhodium as the main catalyst, methyl iodide or a mixture of methyl iodide and lithium iodide as the co-catalyst, and ionic liquid-1,3-dialkyl imidazole dialkyl phosphate as the stabilizer, and uses the low-pressure carbonylation method to produce acetic acid, so that the rhodium catalyst still maintains good stability under extremely low water content (water content in the reaction system is 1~9%). For another example, the invention patent with the publication number of "CN102266795A" and the name of "A catalyst for low-water acetic acid synthesis process and its preparation and use method" proposes a H[RhM(CO)4(N)4] bimetallic complex, which utilizes the synergistic catalytic effect between the two metals, so that the water concentration in the reactant has a high catalytic efficiency in the range of 0.1~15wt%.

[0005] Therefore, the catalyst system in the low-pressure carbonylation process of methanol to acetic acid is still being continuously improved and optimized so that the stability of the catalyst can be guaranteed under low water concentration conditions in the reaction system. Summary of the invention

[0006] The purpose of the present invention is to provide a catalyst system for low-pressure carbonylation of methanol to acetic acid and its application, and proposes a new ionic liquid as a catalyst stabilizer in the catalyst system, so that the catalyst system remains stable in a reaction system with a water content of 0.5-14%, thereby ensuring stable reaction and reducing catalyst loss.

[0007] The present invention is achieved through the following technical solutions: A catalyst system for low-pressure carbonylation of methanol to acetic acid comprises a Group VIII metal main catalyst, a methyl iodide co-catalyst, an inorganic iodide, and an ionic liquid having a structure of formula (I) as a catalyst stabilizer. , Among them, R1, R2, R3, and R4 are alkyl, aryl, acyl, or a combination thereof containing 4 to 9 carbon atoms.

[0008] Furthermore, the Group VIII metal catalyst is one of rhodium, iridium, and ruthenium, or a combination thereof.

[0009] Furthermore, the inorganic iodide is one of lithium iodide, potassium iodide and nickel iodide.

[0010] Furthermore, the groups R1, R2, R3 and R4 in the structure of formula (I) of the ionic liquid are all the same groups, partially the same groups or completely different groups.

[0011] Furthermore, the ionic liquid is a single compound or a mixture of multiple compounds of ionic liquids having the structure of formula (I).

[0012] Furthermore, the molar ratio of the ionic liquid to the Group VIII metal catalyst is 5-60:1.

[0013] Furthermore, the molar ratio of the ionic liquid to the Group VIII metal catalyst is 10-50:1.

[0014] For example, the aforementioned catalyst system is used in the low-pressure carbonylation process for acetic acid synthesis from methanol with a water content of 0.5 to 14%.

[0015] Furthermore, in the process of low-pressure carbonylation of methanol to acetic acid, when separating the product liquid and the catalyst, if the flash evaporation method is adopted, the flash evaporation pressure is controlled to be 0.10~0.30MPa; if the flash evaporation method is adopted, the flash evaporation temperature is controlled to be 135~143℃ and the pressure is 0.10~0.30MPa.

[0016] Compared with the prior art, the present invention has the following advantages and beneficial effects: 1. In the present invention, a quaternary ammonium ionic liquid is proposed as a stabilizer in the catalyst system for low-pressure carbonyl synthesis of acetic acid from methanol. The quaternary ammonium ionic liquid is a new catalyst stabilizer. The acetate anions in the new ionic liquid stabilizer form acetic acid or acetate with the cations in the acetic acid production system without introducing other impurity ions, thereby simplifying the system and making post-processing more convenient.

[0017] 2. In the present invention, a quaternary ammonium ionic liquid catalyst stabilizer is used, and quaternary ammonium cations can be used to form ionic compounds with active diiodide dicarbonyl 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 maintaining the stability of the catalyst.

[0018] 3. In the present invention, the new catalyst system for low-pressure carbonylation of methanol to acetic acid has good stability in the process of low-pressure carbonylation of methanol to acetic acid at a water content of 0.5-14%. In particular, when the flash and / or evaporation process is carried out at an ultra-low water content of less than 1%, the catalyst can still remain stable, so that the entire low-pressure carbonylation of methanol to acetic acid process has a wider process adjustment space, and provides more favorable conditions for equipment optimization, thereby providing favorable conditions for improving production efficiency and product quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a partial structural schematic diagram of the production system of methanol low-pressure carbonylation to acetic acid.

[0020] Figure 2 It is a partial structural schematic diagram of a production system for synthesizing acetic acid from methanol at low pressure carbonylation according to another embodiment.

[0021] Among them, 1. Reactor; 2. Flash evaporator; 3. Evaporation heat exchanger; 4. Methanol feed pipeline; 5. CO feed pipeline; 6. Pipeline I; 7. Mother liquor pipeline I; 8. Mother liquor pipeline II; 9. Product discharge pipeline; 10. Recovery pipeline; 2.1. Feed inlet. DETAILED DESCRIPTION

[0022] The present invention is further described in detail below in conjunction with examples, but the embodiments of the present invention are not limited thereto.

[0023] Example 1 To facilitate the public to understand the present scheme, this embodiment uses the catalyst system of low-pressure carbonylation of methanol to acetic acid in the process of low-pressure carbonylation of methanol to acetic acid as an example to further illustrate the present scheme.

[0024] In this embodiment, the methanol low-pressure carbonyl synthesis of acetic acid process uses Figure 1 The invention discloses a production system for synthesizing acetic acid, which comprises a reactor 1, a flash evaporator 2 and an evaporation heat exchanger 3. The reactor 1 is connected with a methanol feed pipeline 4 and a CO feed pipeline 5. The reactor 1 is connected with a feed port 2.1 of the flash evaporator 2 via a pipeline Ⅰ6. The flash evaporator 2 is connected with the reactor 1 via a mother liquor pipeline Ⅰ7; the mother liquor pipeline Ⅱ8 is connected with the evaporation heat exchanger 3. The top of the flash evaporator 2 is connected with a product discharge pipeline 9. The crude product evaporated in the flash evaporator is sent to a distillation process via the product discharge pipeline 9 for further treatment. The reactor 1 is also connected with a recovery pipeline 10.

[0025] The reactant raw material methanol is transported to the reactor 1 through the methanol feed pipeline 4, and the reactant raw material carbon monoxide is transported to the reactor 1 through the CO feed pipeline 5, and 800 ppm of rhodium, 3.2% of water, 8% of [N(C5H 11 )2(C8H 17 )2] + [CH3COO] －A homogeneous mixture of ionic liquid, appropriate amount of methyl iodide and lithium iodide, the total amount of catalyst (including main catalyst, co-catalyst, ionic liquid) accounts for 35% of the total amount of materials. After the reaction in reactor 1 is completed, the material is transported to flash evaporator 2 through pipeline Ⅰ6, and flash evaporator 2 cooperates with evaporation heat exchanger 3 to flash evaporate the material to achieve separation of product and catalyst. The material containing catalyst and ionic liquid is sent back to reactor 1 through mother liquor pipeline Ⅰ7 to achieve the recycling of catalyst. The gas phase (product gas) obtained after flash evaporator 2 is sent to the distillation system through product discharge pipeline 9 for further treatment. The light components (including water, methyl iodide, methyl acetate and other components) obtained after treatment by the distillation system are returned to reactor 1 through recovery pipeline 10. Evaporation heat exchanger 3 assists in accelerating the flash evaporator to separate materials. After one week of stable operation, the rhodium content in the reaction system is detected.

[0026] In this embodiment, in the process of low-pressure carbonylation of methanol to acetic acid, when separating the product liquid and the catalyst, the flash evaporation temperature is controlled to 138° C., the pressure is controlled to 0.10 MPa, the rhodium content before feeding is 800 ppm, and after one week of operation, the rhodium content in the reaction system is measured to be 784 ppm, and the loss rate of the rhodium catalyst is 2.00%.

[0027] In actual production, taking into account factors such as reaction rate, product quality, product yield and production cost, the temperature of flash evaporation is controlled to be 135~143℃ and the pressure is preferably in the range of 0.10~0.30MPa.

[0028] After sampling in multiple batches, it was found that under this process condition, the loss rate of rhodium catalyst was stable at about 2.00%, with very small differences. It can be seen that when the catalyst system is added to the methanol low-pressure carbonylation process for acetic acid, the catalyst can still remain stable under the condition of a low water content of 3.2%. In the methanol low-pressure carbonylation process for acetic acid, low water content can reduce the separation energy consumption of the distillation system.

[0029] Example 2 The difference between this embodiment and embodiment 1 is that only the flash evaporator 2 is used to flash the product liquid, replacing the structure of the flash evaporator 2 + the evaporation heat exchanger 3 in embodiment 1.

[0030] refer to Figure 2The production system includes a reactor 1 and a flash evaporator 2. The reactor 1 is connected to a methanol feed pipeline 4 and a CO feed pipeline 5. The reactor 1 is connected to a feed port 2.1 of the flash evaporator 2 through a pipeline Ⅰ6. The flash evaporator 2 is connected to the reactor 1 through a mother liquor pipeline Ⅰ7. The top of the flash evaporator 2 is connected to a product discharge pipeline 9. The crude product evaporated in the flash evaporator 2 is sent to the distillation process through the product discharge pipeline 9 for further treatment. After the reaction in the reactor 1 is completed, the material is transported to the flash evaporator 2 through the pipeline Ⅰ6 to separate the product from the catalyst. The material containing the catalyst and the ionic liquid is sent back to the reactor 1 through the mother liquor pipeline Ⅰ7 to realize the recycling of the catalyst. The gas phase (product gas) obtained after the flash evaporator 2 is sent to the distillation system through the product discharge pipeline 9 for further treatment. The light components (including water, methyl iodide, methyl acetate and other components) obtained after the distillation system treatment are returned to the reactor 1 through the recovery pipeline 10.

[0031] The reaction conditions were controlled according to the following requirements. After one week of stable operation, the rhodium content in the reaction system was detected.

[0032] In the low-pressure carbonylation process of methanol to acetic acid, when separating the product liquid and the catalyst, the flash evaporation temperature was controlled at 137°C and the pressure was controlled at 0.10MPa. The rhodium content before feeding was 800 ppm. After one week of operation, the rhodium content in the reaction system was measured to be 786 ppm, and the loss rate of the rhodium catalyst was 1.75%.

[0033] After sampling multiple batches, it was found that under this process condition, the loss rate of rhodium catalyst was stable at about 1.75%, with little difference. It can be seen that when this catalyst system is added to the methanol low-pressure carbonyl synthesis of acetic acid process, under the condition of low water content of 3.2%, whether using flash distillation or flash evaporation process, the catalyst can remain stable.

[0034] Example 3 The present embodiment is different from the embodiment 1 only in that the water content is 0.5%, acetic acid is used to supplement the reduced water mass, the process conditions are controlled according to the following requirements, and the rhodium content of the catalyst is detected after one week of operation.

[0035] In this embodiment, in the process of low-pressure carbonylation of methanol to acetic acid, when separating the product liquid and the catalyst, the flash evaporation temperature is controlled to 138° C., the pressure is controlled to 0.10 MPa, the rhodium content before feeding is 800 ppm, and after one week of operation, the rhodium content in the reaction system is measured to be 782 ppm, and the loss rate of the rhodium catalyst is 2.25%.

[0036] After sampling multiple batches, it was found that under this process condition, the loss rate of rhodium catalyst was stable at about 2.25%, with little difference. It can be seen that when the catalyst system is added to the methanol low-pressure carbonylation process for acetic acid, the catalyst can still remain stable under the condition of low water content of 0.5%, which is a major breakthrough compared with the existing technology. In the methanol low-pressure carbonylation process for acetic acid, low water content can reduce the separation energy consumption of the distillation system.

[0037] Example 4 The present embodiment is different from the embodiment 1 only in 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 running for one week.

[0038] In this embodiment, in the process of low-pressure carbonylation of methanol to acetic acid, when separating the product liquid and the catalyst, the flash evaporation temperature is controlled to 138° C., the pressure is controlled to 0.10 MPa, the rhodium content before feeding is 800 ppm, and after one week of operation, the rhodium content in the reaction system is measured to be 790 ppm, and the loss rate of the rhodium catalyst is 1.25%.

[0039] After sampling from multiple batches, it was found that under the process conditions, the loss rate of rhodium catalyst was stable at around 1.25%, with very small differences.

[0040] Example 5 The present embodiment is different from the embodiment 1 only in 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 running for one week.

[0041] In this embodiment, in the process of low-pressure carbonylation of methanol to acetic acid, when separating the product liquid and the catalyst, the flash evaporation temperature is controlled to 137° C., the pressure is controlled to 0.12 MPa, the rhodium content before feeding is 800 ppm, and after one week of operation, the rhodium content in the reaction system is measured to be 790 ppm, and the loss rate of the rhodium catalyst is 1.25%.

[0042] It can be seen from the above experiments that when the catalyst system of this scheme is added, the catalyst can remain stable under the condition of 0.5~14% water content, but under the condition of high water content, it will cause an increase in energy consumption.

[0043] Example 6 Compared with Example 1, the only difference between this embodiment and Example 1 is that Based on the total mass of the solution, 5% [N(C6H 13 )3(C6H5)] + [CH3COO] － , 10% [N(C4H9)2(C9H 19 )(C3H7CO)]+ [CH3COO] － The ionic liquid mixture had a water content of 2% and 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 detected to be 788 ppm, and the loss rate of the rhodium catalyst was 1.50%.

[0044] It can be seen that whether adding a single ionic liquid or adding multiple mixed ionic liquids, the stability of the catalyst can be maintained.

[0045] Example 7 Compared with Example 6, the only difference is that the rhodium content is increased to 1600 ppm, and the other components remain unchanged. After running for one week, the rhodium content of the catalyst is detected to be 1589 ppm.

[0046] It can be seen that after adding ionic liquid, the stability of the catalyst can be maintained even at high catalyst concentrations.

[0047] Example 8 This example examines the effect of ionic liquid catalyst stabilizers on different Group VIII metal main catalysts when the catalyst system is applied to the low-pressure carbonylation process of methanol to acetic acid.

[0048] In this embodiment, the production system in Example 1 was used, and the reaction conditions were controlled according to Table 1. The ionic liquid in the catalyst system was a single [N(C5H 11 )2(C8H 17 )2] + [CH3COO] － After one week of stable operation, the content of metal catalyst in the reaction system was detected. The test results are shown in Table 1.

[0049] Table 1 As can be seen from Table 1, in the catalyst system for the low-pressure carbonylation of methanol to acetic acid, 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 remain stable, and can even remain stable under ultra-low water content conditions of 0.5%.

[0050] Comparative Example 1 The difference between this comparative example and the embodiment 1 is that No [N(C5H 11 )2(C8H 17 )2] + [CH3COO] － The mass of ionic liquid was supplemented with acetic acid. After one week of operation, the rhodium content of the catalyst was detected to be 396 ppm, and the catalyst loss rate was 50.5%.

[0051] Comparative Example 2 Compared with the solution of Example 2, the only difference between this comparative example and Example 2 is that No [N(C5H 11 )2(C8H 17 )2] + [CH3COO] － The mass of the ionic liquid was supplemented with acetic acid. After one week of operation, the rhodium content of the catalyst was detected to be 465ppm, and the catalyst loss rate was 41.875%.

[0052] Comparative Example 3 This comparative example is different from the solution in Example 3 in that [N(C5H 11 )2(C8H 17 )2] + [CH3COO] － The mass of ionic liquid was supplemented with acetic acid, and the mass of water was supplemented with acetic acid. After one week of operation, the rhodium content of the catalyst was detected to be 205 ppm. It can be seen that under this reaction system, the loss rate of catalyst-rhodium increased significantly, and the stability of the catalyst system decreased significantly.

[0053] It can be seen from the above examples that, without adding the ionic liquid catalyst stabilizer in the present solution, especially under low water content conditions, the catalyst loss is obvious.

[0054] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any simple modification or equivalent change made to the above embodiment 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 low-pressure carbonylation of methanol to acetic acid, characterized in that: The catalyst comprises a Group VIII metal main catalyst, a methyl iodide co-catalyst, an inorganic iodide, and an ionic liquid having a structure of formula (I) as a catalyst stabilizer. （Ⅰ）， Among them, R1, R2, R3, and R4 are alkyl, aryl, acyl, or a combination thereof containing 4 to 9 carbon atoms.

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

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

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

6. The catalyst system for low-pressure carbonylation of methanol to acetic acid 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 carbonylation of methanol to acetic acid 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. Use of the catalyst system according to any one of claims 1 to 7 in a process for low-pressure carbonylation of methanol to acetic acid with a water content of 0.5 to 14%.

9. The use according to claim 8, characterized in that: In the process of low-pressure carbonylation of methanol to acetic acid, when separating the product liquid and the catalyst, if the flash evaporation method is adopted, the flash evaporation pressure is controlled to be 0.10~0.30MPa; if the flash evaporation method is adopted, the flash evaporation temperature is controlled to be 135~143℃ and the pressure is 0.10~0.30MPa.

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