Method for synthesizing acetic acid by methanol low-pressure carbonyl with high catalyst stability

Abstract

The invention discloses a method with high catalyst stability for low-pressure carbonyl synthesis of acetic acid from methanol, and relates to the technical field of low-pressure carbonyl synthesis of acetic acid from methanol, and the method comprises the following steps: S1, reaction section: introducing methanol or a reactive derivative thereof and CO into a reactor, adding a group VIII metal catalyst, an iodomethane cocatalyst and inorganic iodide, and carrying out a reaction for 2-4 hours; the preparation method comprises the following steps: by taking a raw material as a raw material and an ionic liquid with a [NR1R2R3R4] < + > [CH3COO] <-> structure as a catalyst stabilizer, carrying out carbonyl synthesis reaction on the material in a reactor to obtain an acetic acid crude product, and in the formula, R1, R2, R3 and R4 are alkyl, aryl and acyl containing 4-9 carbons or a combination thereof; s2, carrying out gas-liquid separation; s3, evaporating and washing; s4, light component removal treatment; and S5, purification treatment, so that the VIII group metal catalyst can still keep stable when reactants are in a reaction system with low water content of 0.5-1.0%, the energy consumption of a rear-end dehydrating tower and a finished product tower is reduced, and the production cost is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of methanol low-pressure carbonylation to acetic acid, and in particular to a method for methanol low-pressure carbonylation to acetic acid with high catalyst stability. 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 methanol low-pressure carbonyl synthesis method for producing acetic acid can use coal as raw material, with high yield and low cost. It is an advanced technology for acetic acid production and is also a commonly used method for producing acetic acid.

[0003] In recent years, the company is still continuously researching existing technologies and optimizing and upgrading its processes, and is committed to making technological breakthroughs in product yield, product quality, reaction efficiency, production cost, equipment optimization, etc. On January 31, 2023, the company disclosed a patent document with application number "202211316195.1" and titled "A method for low-pressure carbonyl synthesis of acetic acid from methanol with high catalyst stability". In this scheme, the structure of the first-stage reactor is optimized to ensure that the temperature difference inside the reactor is small, making the product more stable; a two-stage reactor structure is added. The first-stage reactor is a fluid agitator with an external circulation heat exchanger, which is the main reactor, and the second-stage reactor is a plug flow reactor, which reduces logistics backmixing, maintains a more ideal reaction rate, and improves methanol. To improve the alcohol conversion rate, an inter-stage heat exchanger is set between the two-stage reactors to maintain the two-stage reactors at an optimal reaction temperature and improve the reaction rate; at the same time, it is proposed to use a washing device to wash the gas after flash evaporation, which can reduce the loss of catalyst caused by mist entrainment; a heat exchanger is set outside the flash evaporator to reduce the scaling loss of the catalyst on the heat exchanger through the forced flow of the fluid. In addition, an integrated flash evaporation washing tower is proposed, which has the functions of flash evaporation and gas washing at the same time, occupies a small area, and achieves the purpose of low-cost, continuous and stable production of acetic acid. However, the method of synthesizing acetic acid from methanol at low pressure carbonylation still has the problem of poor catalyst stability in a reaction system with low water content, which makes the separation energy consumption of the distillation system always at a high level. Summary of the invention

[0004] The object of the present invention is to provide a novel method for synthesizing acetic acid from methanol at low pressure carbonylation with high catalyst stability, so that the catalyst can remain stable under the condition of 0.5-14% water content of the reactants. That is, the catalyst can still remain stable in a reaction system with a low water content of 0.5-1.0%.

[0005] The present invention is achieved through the following technical solutions: A method for synthesizing acetic acid from methanol at low pressure carbonylation with high catalyst stability comprises the following steps: S1, reaction section: methanol or its reactive derivative and CO are introduced into a reactor, and a Group VIII metal catalyst, methyl iodide co-catalyst, inorganic iodide, and an ionic liquid having a structure of formula (I) are added as a catalyst stabilizer to allow the materials to undergo carbonyl synthesis reaction in the reactor, and crude acetic acid is obtained. , Among them, R 1 , R 2 , R 3 , R 4 is an alkyl group, an aryl group, an acyl group or a combination thereof containing 4 to 9 carbon atoms; S2, gas-liquid separation: the crude acetic acid product generated in step S1 is transported to a gas-liquid separator for gas-liquid separation, the gas phase obtained after treatment in the gas-liquid separator is sent to a high-pressure absorption tower and washed with a liquid phase raw material, the liquid phase obtained after washing is sent back to the reactor, and the liquid phase obtained after treatment in the gas-liquid separator is transported to the next stage for treatment; S3, evaporation washing: the liquid phase obtained after separation in step S2 is passed into a flash evaporator for flash evaporation and evaporation treatment, and the gas phase obtained after flash evaporation and evaporation treatment is washed with the light phase dilute acetic acid of the rear-end light removal treatment section, and the carbonylation catalyst, co-catalyst, and ionic liquid catalyst stabilizer material obtained after the treatment are returned to the reactor, and the obtained gas phase logistics are transported to the next section for treatment; S4, light removal treatment The gas phase in step S3 is sent to a light-removing tower for separation treatment to separate a tower top stream rich in methyl iodide, a side stream rich in acetic acid, and a tower bottom stream rich in heavy components. The tower top stream is cooled by a heat exchanger to obtain a liquid phase that enters a separator to obtain a light phase rich in water and a heavy phase rich in methyl iodide. The heavy phase is returned to the reactor, and the light phase is sent to step S3 as a washing liquid; the gas phase obtained after cooling treatment is sent to a low-pressure absorption tower and washed with a liquid raw material, and the liquid phase obtained after washing is returned to the reactor; the tower bottom stream rich in heavy components separated by the light-removing tower is returned to the reactor; the side stream rich in acetic acid separated by the light-removing tower is sent to the next section for treatment; S5, purification treatment: the side product rich in acetic acid in step S4 is sent to a finished product tower for further separation and purification treatment to obtain finished acetic acid and a byproduct stream rich in propionic acid.

[0006] Furthermore, a dehydration treatment step is added between step S4 and step S5, and the acetic acid-rich side stream obtained after the treatment in step S4 is sent to a dehydration tower for treatment to obtain an acetic acid-rich stream and an aqueous dilute acetic acid stream, wherein a portion of the aqueous dilute acetic acid stream or / and a portion of the light phase obtained in step S4 is used to wash the gas phase stream obtained after flash evaporation and evaporation in step S3.

[0007] Furthermore, in step S1, the Group VIII metal catalyst is one of rhodium, iridium, and ruthenium, or a combination thereof; the inorganic iodide is one of lithium iodide, potassium iodide, and nickel iodide; The ionic liquid of formula (I) has R 1 , R 2 , R 3 , R 4 The groups are all the same groups, partly the same groups or completely different groups; the ionic liquid is a single compound or a mixture of multiple compounds of ionic liquids having the structure of formula (I).

[0008] Furthermore, the molar ratio of the ionic liquid to the Group VIII metal catalyst is 5-60:1.

[0009] Furthermore, in step S1, the reactor includes a first-stage reactor and a second-stage reactor, and a fluid stirring mechanism is provided in the first-stage reactor. After the reaction materials are added to the first-stage reactor, a carbonyl synthesis reaction occurs under the catalytic conditions of the catalyst system. The product outlet at the top of the first-stage reactor is connected to a second-stage reactor in which the fluid flows upward without backmixing and the fluid transitions from a mixed flow to a plug flow. The mixed material obtained after the first-stage reactor is continuously transported to the second-stage reactor for further reaction, so as to obtain a crude acetic acid product. The catalyst-containing material obtained after the treatment in step S3, the heavy phase obtained in step S4 and the bottom stream of the light-removal tower are all sent back to a first reactor of the reactor.

[0010] Furthermore, an inter-stage heat exchanger is provided between the first-stage reactor and the second-stage reactor, and the heat exchange medium in the inter-stage heat exchanger comes from boiler water.

[0011] Furthermore, in step S4, the gas phase logistics obtained after treatment in the light phase removal tower is first cooled by a heat exchanger, and then the cooled liquid phase is sent to a stratifier for stratification treatment, and the obtained heavy phase logistics is sent back to a first reactor for recycling, and the obtained light phase logistics part rich in water and acetaldehyde is sent to the aldehyde removal section.

[0012] Furthermore, the treatment method of the aldehyde removal section is as follows: the light phase stream obtained after the treatment by the separator is sent to the aldehyde concentration tower for treatment, and the obtained tower top stream rich in acetaldehyde and methyl iodide and tower bottom stream rich in water are sent, and the tower top stream rich in acetaldehyde and methyl iodide is sent to the extraction section, and the tower bottom stream rich in water is sent to the separator or the reaction section; The top stream rich in acetaldehyde and methyl iodide is sent to the extraction tower after heat exchange cooling treatment, and is extracted with desalted water in the extraction tower. The obtained formaldehyde-containing wastewater is sent to the wastewater treatment system for treatment, and the obtained raffinate is returned to the classifier or reaction section.

[0013] Furthermore, the gas phase obtained after treatment in the high-pressure absorption tower of step S2 and / or the gas phase obtained after treatment in the low-pressure absorption tower of step S4 is sent to a pressure swing adsorption tower for treatment, and the purified CO gas is sent to a first reactor as a raw material for carbonyl synthesis reaction.

[0014] Furthermore, in step S5, the obtained propionic acid-rich by-product stream is sent to a propionic acid concentration tower for treatment, and then sent to a propionic acid product tower for treatment to obtain a propionic acid product liquid.

[0015] Furthermore, in step S5, the obtained finished acetic acid is treated by a deiodination system to obtain low-iodine acetic acid with an iodine content lower than 10 ppb, and the deiodination system includes a two-stage deiodination tank.

[0016] Compared with the prior art, the present invention has the following advantages and beneficial effects: 1. In the present invention, a new method for synthesizing acetic acid from methanol at low pressure carbonyl group is proposed. In the method, a quaternary ammonium ionic liquid catalyst stabilizer is introduced into the reaction section of step S1, 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 be used 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 conducive to the stability of the catalyst. 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, making the system simpler and the post-processing more convenient.

[0017] 2. In the present invention, the novel method for synthesizing acetic acid from methanol at low pressure carbonylation has good stability in the process of synthesizing acetic acid from methanol at a water content of 0.5-14%. In particular, when flash distillation and / or evaporation process is performed at an ultra-low water content of less than 1%, the catalyst can still remain stable, so that the entire process of synthesizing acetic acid from methanol at low pressure carbonylation has lower energy consumption, less investment, and a wider process adjustment space, providing favorable conditions for improving production efficiency and product quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 A schematic diagram of the structure of the low-pressure carbonylation system for producing acetic acid from methanol in Example 1.

[0019] Figure 2 It is a structural diagram of another embodiment of a system for producing acetic acid by low-pressure carbonylation of methanol.

[0020] Figure 3 It is a structural diagram of another embodiment of a system for producing acetic acid by low-pressure carbonylation of methanol.

[0021] Figure 4 It is a schematic diagram of the structure of the experimental device for the low-pressure carbonylation of methanol to acetic acid.

[0022] Among them, 1. a first-stage reactor; 2. a methanol feed pipeline; 3. a CO feed pipeline; 4. a second-stage reactor; 5. an inter-stage heat exchanger; 6. a gas-liquid separator; 7. a flash evaporator; 8. an evaporative heat exchanger; 9. a light-removal tower; 10. a dehydration tower; 11. a finished product tower; 12. a high-pressure absorption tower; 13. a low-pressure absorption tower; 14. a classifier; 15. an aldehyde concentration tower; 16. an extraction tower; 17. a deiodine tank one; 18. a deiodine tank two; 19. a finished acetic acid pipeline; 20. a waste acid extraction pipeline; 21. an integrated flash evaporation washing tower; 22. a washing tower; 23. a pressure swing adsorption tower; 24. a propionic acid concentration tower; 25. a propionic acid product tower; 26. a reactor; 27. a pipeline I; 28. a mother liquor pipeline I; 29. ​​a mother liquor pipeline II; 30. a product discharge pipeline; 31. a recovery pipeline. DETAILED DESCRIPTION

[0023] The present invention is further described in detail below in conjunction with examples, but the embodiments of the present invention are not limited thereto.

[0024] Example 1 To facilitate the public to understand the present scheme, this embodiment takes a methanol low-pressure carbonyl synthesis acetic acid system currently in industrial operation as an example to further illustrate the present scheme.

[0025] A method for synthesizing acetic acid from methanol at low pressure carbonylation with high catalyst stability, reference Figure 1 , including the following steps: The first step, reaction section: Methanol or its reactive derivative and CO are introduced into the reactor through the methanol feed pipeline and the CO feed pipeline, respectively, and 800 ppm of rhodium, 3.2% of water, 8% of [N(C 5 H 11 ) 2 (C 8 H 17 ) 2 ] + [CH 3 COO]－ 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, wherein the molar ratio of ionic liquid to rhodium is 23:1, and crude acetic acid is obtained.

[0026] Step 2: Gas-liquid separation: The crude acetic acid generated in step S1 is transported to a gas-liquid separator for gas-liquid separation. The gas phase obtained after treatment by the gas-liquid separator is sent to a high-pressure absorption tower and washed with a liquid phase raw material. The liquid phase obtained after washing is returned to the reactor. The liquid phase obtained after treatment by the gas-liquid separator is transported to the next stage for treatment.

[0027] Step 3: Evaporation washing: The liquid phase obtained after separation in step 2 is passed into an integrated flash evaporation washing tower for flash evaporation and evaporation treatment, and the gas phase obtained after flash evaporation and evaporation treatment is washed with the light phase dilute acetic acid of the rear-end light removal treatment section, and the carbonylation catalyst, co-catalyst, and ionic liquid catalyst stabilizer material obtained after the treatment are returned to the reactor, and the obtained gas phase logistics are transported to the next section for treatment.

[0028] Step 4: Lightweight treatment: The gas phase in step three is sent to a light-removing tower for separation treatment to separate a tower top stream rich in methyl iodide, a side stream rich in acetic acid, and a tower bottom stream rich in heavy components. The liquid phase obtained after cooling the tower top stream by a heat exchanger enters a classifier to obtain a light phase rich in water and a heavy phase rich in methyl iodide. The heavy phase is returned to the reactor, and the light phase is sent to step three as a washing liquid; the gas phase obtained after cooling treatment is sent to a low-pressure absorption tower and washed with a liquid raw material, and the liquid phase obtained after washing is returned to the reactor; the tower bottom stream rich in heavy components separated by the light-removing tower is returned to the reactor; the side stream rich in acetic acid separated by the light-removing tower is sent to the next section for treatment.

[0029] In this embodiment, the gas phase logistics obtained after treatment in the light phase removal tower is first cooled by a heat exchanger, and then the cooled liquid phase is sent to a stratifier for stratification treatment, and the obtained heavy phase logistics is sent back to a first reactor for recycling, and the obtained light phase logistics rich in water and acetaldehyde is sent to the aldehyde removal section.

[0030] Furthermore, the treatment method of the aldehyde removal section is as follows: the light phase stream obtained after the treatment by the separator is sent to the aldehyde concentration tower for treatment, and the obtained tower top stream rich in acetaldehyde and methyl iodide and tower bottom stream rich in water are sent, and the tower top stream rich in acetaldehyde and methyl iodide is sent to the extraction section, and the tower bottom stream rich in water is sent to the separator or the reaction section; The top stream rich in acetaldehyde and methyl iodide is sent to the extraction tower after heat exchange cooling treatment, and is extracted with desalted water in the extraction tower. The obtained formaldehyde-containing wastewater is sent to the wastewater treatment system for treatment, and the obtained raffinate is returned to the classifier or reaction section.

[0031] Step 5: Dehydration: The acetic acid-rich side stream obtained after the treatment in step 4 is sent to a dehydration tower for treatment to obtain an acetic acid-rich stream and an aqueous dilute acetic acid stream, wherein a portion of the aqueous dilute acetic acid stream or / and a portion of the light phase obtained in step 4 are used to wash the gas phase stream obtained after flash evaporation and evaporation in step 3.

[0032] Step 6: Purification: The acetic acid-rich side product in step five is sent to a finished product tower for further separation and purification to obtain finished acetic acid and a propionic acid-rich byproduct stream.

[0033] Furthermore, the obtained propionic acid-rich by-product stream is sent to a propionic acid concentration tower for treatment, and then sent to a propionic acid product tower for treatment to obtain a propionic acid product liquid.

[0034] In this embodiment, the gas phase obtained after treatment in the high-pressure absorption tower in step 2 and / or the gas phase obtained after treatment in the low-pressure absorption tower in step 4 is sent to a pressure swing adsorption tower for treatment, and the purified CO gas is sent to a first reactor as a raw material for carbonyl synthesis reaction.

[0035] In this embodiment, the final product acetic acid is treated by a deiodination system to obtain low-iodine acetic acid with an iodine content lower than 10 ppb. The deiodination system includes two-stage deiodination tanks, namely, a first deiodination tank and a second deiodination tank.

[0036] In this embodiment, the reactor temperature is 192° C. and the pressure is controlled to be 2.90 MPa. After one month of operation, the rhodium content is 790 ppm when sampled at the reactor and the loss rate of the rhodium catalyst is 1.25%.

[0037] After sampling multiple batches, it was found that under this process condition, the loss rate of rhodium catalyst was stable at about 1.2%, with very small differences. It can be seen that when this catalyst system is added to the methanol low-pressure carbonyl synthesis acetic acid process, the catalyst can remain stable under the condition of a low water content of 3.2%. Compared with the previous process, the energy consumption of the dehydration tower and the finished product tower was reduced by about 10% each.

[0038] Example 2 The difference between this embodiment and embodiment 1 is that: In step 1, the reactor is a preferred embodiment, specifically including a first-stage reactor and a second-stage reactor. Figure 2The first stage reactor is provided with a fluid stirring mechanism. After the reaction materials are added to the first stage reactor, a carbonyl synthesis reaction occurs under the catalytic conditions of the catalyst system. The product outlet at the top of the first stage reactor is connected to a second stage reactor in which the fluid flows upward without back mixing and the fluid transitions from a mixed flow to a plug flow. The mixed material obtained after the first stage reactor is continuously transported to the second stage reactor for further reaction, thereby obtaining a crude acetic acid product. The catalyst-containing material obtained after treatment in step 3, the heavy phase obtained in step 4 and the bottom stream of the light-removal tower are all sent back to a first reactor of the reactor.

[0039] In addition, an inter-stage heat exchanger is provided between the first-stage reactor and the second-stage reactor, and the heat exchange medium in the inter-stage heat exchanger comes from boiler water.

[0040] In this embodiment, the reactor temperature is 192° C. and the pressure is controlled at 2.90 MPa. After one month of operation, the rhodium content detected by sampling at the reactor is 790 ppm, and the loss rate of the rhodium catalyst is 1.25%.

[0041] After sampling multiple batches, it was found that under this process condition, the loss rate of rhodium catalyst was stable at about 1.2%, with very small differences. It can be seen that when the catalyst system is added to the methanol low-pressure carbonyl synthesis of acetic acid process, the catalyst can remain stable under the condition of low water content of 3.2%, reducing the energy consumption of the dehydration tower and the finished product tower by about 10% each.

[0042] Compared with Example 1, this embodiment adopts a more optimal reaction equipment structure to replace the original ordinary reactor. It is found through investigation that the present invention includes [N(C 5 H 11 ) 2 (C 8 H 17 ) 2 ] + [CH 3 COO] － The ionic liquid catalyst system can keep the rhodium catalyst (Group VIII metal catalyst) stable in different methanol low-pressure carbonylation acetic acid synthesis systems under the condition of low water content of 3.2%, and the loss rate of the rhodium catalyst is consistent with that in Example 1. At the same time, the introduction of the new methanol low-pressure carbonylation acetic acid synthesis system can put the reactants under more ideal reaction conditions and increase the reaction rate.

[0043] Example 3 The difference between this embodiment and embodiment 2 is that: In step 1, the water content is 0.5%. Acetic acid is used to make up for the reduced water mass. The process conditions are controlled according to the following requirements. After one month of operation, the rhodium content of the catalyst is tested.

[0044] 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 month 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%.

[0045] 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 carbonyl synthesis acetic acid process, the catalyst can remain stable under the condition of low water content of 0.5%, reducing the energy consumption of the dehydration tower and the finished product tower by about 17% each.

[0046] Example 4 The present embodiment is different from the embodiment 2 only in that the water content is 8%, 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 month of operation.

[0047] 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 month 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%.

[0048] In industrial production, the higher the water content in the reactor, the easier it is to ensure the stability of the Group VIII metal catalyst, but as the water content in the reactor increases, the energy consumption of the dehydration tower and the finished product tower at the rear end will gradually increase. In addition, in industrial production, the water content is generally controlled below 9%. Therefore, this example takes the condition of 8% water content as an example to examine the energy consumption of the dehydration tower and the finished product tower under this process condition.

[0049] In this embodiment, the unit energy consumption of the dehydration tower and the finished product tower is 1.0 t. The energy saving value of the dehydration tower and the finished product tower in other embodiments is based on this embodiment as the benchmark value.

[0050] Example 5 Compared with Example 2, the difference is: Eliminate step 5, that is, eliminate the dehydration tower. Since the water content of the reaction system is reduced, the dehydration tower can be eliminated without affecting the normal operation of the system. Eliminating the dehydration tower saves the investment cost of the device.

[0051] Example 6 Compared with Example 2, the difference is: In step 3, the traditional flash evaporator + evaporation heat exchanger + scrubber is used to replace the integrated flash evaporation scrubber. Figure 3The liquid phase obtained after separation in step 2 is passed to a flash evaporator, and flashes and evaporates the material in cooperation with an evaporative heat exchanger, and the gas phase obtained after flash and evaporation is washed with the light phase dilute acetic acid from the rear-end light removal treatment section through a washing tower.

[0052] In this embodiment, the reactor temperature is 192°C, the pressure is controlled to be 2.90MPa, and after one month of operation, the rhodium content detected by sampling at the reactor is 790ppm, and the loss rate of the rhodium catalyst is 1.25%. The loss rate of the metal catalyst is the same as that in Example 2, and the process can also be applied to the production system of the traditional flash evaporator + evaporation heat exchanger + washing tower, and the stability of the catalyst can also be ensured.

[0053] Example 7 In order to further investigate the method for synthesizing acetic acid from methanol at low pressure carbonylation according to the present invention, this example uses a laboratory test apparatus to investigate the influence of process conditions on the Group VIII metal catalyst.

[0054] refer to Figure 4 In this embodiment, the methanol low-pressure carbonylation process for acetic acid is as follows Figure 4 The invention discloses a production system for synthesizing acetic acid, wherein the production system comprises a reactor 26, a flash evaporator 7 and an evaporation heat exchanger 8. The reactor 26 is connected with a methanol feed pipeline 2 and a CO feed pipeline 3. The reactor 26 is connected with a feed port of the flash evaporator 7 via a pipeline I 27. The flash evaporator 7 is connected with the reactor 26 via a mother liquor pipeline I 28; the mother liquor pipeline II 29 is connected with the evaporation heat exchanger 8. The top of the flash evaporator 7 is connected with a product discharge pipeline 30. The crude product evaporated from the flash evaporator 7 is sent to a distillation process via the product discharge pipeline 30 for further treatment. The reactor 26 is also connected with a recovery pipeline 32.

[0055] The reactant raw material methanol is transported to the reactor 26 through the methanol feed pipeline 2, and the reactant raw material carbon monoxide is transported to the reactor 26 through the CO feed pipeline 3, and 800 ppm of rhodium, 3.2% of water, 8% of [N(C 5 H 11 ) 2 (C 8 H 17 ) 2 ] + [CH 3 COO] －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 the reactor 26 is completed, the material is transported to the flash evaporator 7 through pipeline I27, and the flash evaporator 7 cooperates with the evaporation heat exchanger 8 to flash evaporate the material to achieve separation of the product and the catalyst. The material containing the catalyst and the ionic liquid is sent back to the reactor 26 through the mother liquid pipeline I28 to achieve the recycling of the catalyst. The gas phase (product gas) obtained after the flash evaporator 7 is sent to the distillation system through the product discharge pipeline 30 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 26 through the recovery pipeline 32. The evaporation heat exchanger 8 assists in accelerating the flash evaporator 7 to separate the material. After one week of stable operation, the rhodium content in the reaction system is detected.

[0056] 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%.

[0057] 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.

[0058] 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.

[0059] From the above, it can be seen that compared with the industrial operation device, the loss of metal catalyst is more obvious when using the laboratory device, but it can still remain stable. This is related to the production system involved in the industrial production of acetic acid by low-pressure carbonylation of methanol.

[0060] Example 8 The difference between this embodiment and embodiment 7 is that: In step 1, based on the total mass of the solution, 5% [N(C 6 H 13 ) 3 (C 6 H 5 )] + [CH 3 COO] －, 10% [N(C 4 H 9 ) 2 (C 9 H 19 ) (C 3 H 7 CO)] + [CH 3 COO] － 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%.

[0061] 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.

[0062] Example 9 The only difference between this embodiment and embodiment 7 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 1591 ppm.

[0063] It can be seen that after adding ionic liquid, the stability of the catalyst can be maintained even at high catalyst concentrations.

[0064] Example 10 This example uses the laboratory test device of Example 7, and controls the reaction conditions according to Table 1. The ionic liquid in the catalyst system is a single [N(C 5 H 11 ) 2 (C 8 H 17 ) 2 ] + [CH 3 COO] － The remaining process conditions were the same as those in Example 7. After one week of stable operation, the content of the metal catalyst in the reaction system was detected. The detection results are shown in Table 1.

[0065] 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%.

[0066] Comparative Example 1 This comparative example is different from the embodiment 7 in that: No [N(C 5 H11 ) 2 (C 8 H 17 ) 2 ] + [CH 3 COO] － 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%.

[0067] Comparative Example 2 This comparative example is different from the embodiment 8 in that [N(C 6 H 13 ) 3 (C 6 H 5 )] + [CH 3 COO] － ,[N(C 4 H 9 ) 2 (C 9 H 19 ) (C 3 H 7 CO)] + [CH 3 COO] － The ionic liquid mixture was supplemented with acetic acid to replace the mass of the ionic liquid and the mass of the reduced water. After one week of operation, the catalyst rhodium content was detected to be 358ppm and the catalyst loss rate was 55.2%. It can be seen that under this reaction system, the catalyst-rhodium loss rate increased significantly and the stability of the catalyst system decreased significantly.

[0068] It can be seen from the above examples that, without adding the ionic liquid catalyst stabilizer in the present scheme, especially under low water content conditions, the catalyst loss is obvious.

[0069] 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 method for synthesizing acetic acid from methanol at low pressure carbonylation with high catalyst stability, characterized in that: The following steps are involved: S1, reaction section: methanol or its reactive derivative and CO are introduced into a reactor, and a Group VIII metal catalyst, methyl iodide co-catalyst, inorganic iodide, and an ionic liquid having a structure of formula (I) are added as a catalyst stabilizer to allow the materials to undergo carbonyl synthesis reaction in the reactor, and crude acetic acid is obtained. ， Wherein, R1, R2, R3, and R4 are alkyl, aryl, acyl, or a combination thereof containing 4 to 9 carbon atoms; S2, gas-liquid separation: the crude acetic acid product generated in step S1 is transported to a gas-liquid separator for gas-liquid separation, the gas phase obtained after treatment in the gas-liquid separator is sent to a high-pressure absorption tower and washed with a liquid phase raw material, the liquid phase obtained after washing is sent back to the reactor, and the liquid phase obtained after treatment in the gas-liquid separator is transported to the next stage for treatment; S3, evaporation washing: the liquid phase obtained after separation in step S2 is passed into a flash evaporator for flash evaporation and evaporation treatment, and the gas phase obtained after flash evaporation and evaporation treatment is washed with the light phase dilute acetic acid of the rear-end light removal treatment section, and the carbonylation catalyst, co-catalyst, and ionic liquid catalyst stabilizer material obtained after the treatment are returned to the reactor, and the obtained gas phase logistics are transported to the next section for treatment; S4, light removal treatment The gas phase in step S3 is sent to a light-removing tower for separation treatment to separate a tower top stream rich in methyl iodide, a side stream rich in acetic acid, and a tower bottom stream rich in heavy components. The tower top stream is cooled by a heat exchanger to obtain a liquid phase that enters a separator to obtain a light phase rich in water and a heavy phase rich in methyl iodide. The heavy phase is returned to the reactor, and the light phase is sent to step S3 as a washing liquid; the gas phase obtained after cooling treatment is sent to a low-pressure absorption tower and washed with a liquid raw material, and the liquid phase obtained after washing is returned to the reactor; the tower bottom stream rich in heavy components separated by the light-removing tower is returned to the reactor; the side stream rich in acetic acid separated by the light-removing tower is sent to the next section for treatment; S5, purification treatment: the side product rich in acetic acid in step S4 is sent to a finished product tower for further separation and purification treatment to obtain finished acetic acid and a byproduct stream rich in propionic acid.

2. The method for synthesizing acetic acid from methanol at low pressure with high catalyst stability according to claim 1, characterized in that: A dehydration step is further provided between step S4 and step S5. The acetic acid-rich side stream obtained after the treatment in step S4 is sent to a dehydration tower for treatment to obtain an acetic acid-rich stream and a water-containing dilute acetic acid stream. Part of the water-containing dilute acetic acid stream or / and part of the light phase obtained in step S4 are used to wash the gas phase stream obtained after flash evaporation and evaporation in step S3.

3. The method for synthesizing acetic acid from methanol at low pressure with high catalyst stability according to claim 1, characterized in that: In step S1, the Group VIII metal catalyst is one of rhodium, iridium, and ruthenium, or a combination thereof; the inorganic iodide is one of lithium iodide, potassium iodide, and nickel iodide; The R1, R2, R3 and R4 groups of the ionic liquid structure of formula (I) are all identical groups, partially identical groups or completely different groups; the ionic liquid is a single compound or a mixture of multiple compounds of ionic liquids having the structure of formula (I).

4. The method for synthesizing acetic acid from methanol at low pressure with high catalyst stability according to claim 1, characterized in that: The molar ratio of the ionic liquid to the Group VIII metal catalyst is 5-60:

1.

5. The method for synthesizing acetic acid from methanol at low pressure with high catalyst stability according to claim 1, characterized in that: In step S1, the reactor includes a first-stage reactor and a second-stage reactor, and a fluid stirring mechanism is provided in the first-stage reactor. After the reaction materials are added to the first-stage reactor, a carbonyl synthesis reaction occurs under the catalytic conditions of the catalyst system. The product outlet at the top of the first-stage reactor is connected to a second-stage reactor in which the fluid flows upward without backmixing and the fluid transitions from a mixed flow to a plug flow. The mixed material obtained after the first-stage reactor is continuously transported to the second-stage reactor for further reaction, so as to obtain a crude acetic acid product; The catalyst-containing material obtained after the treatment in step S3, the heavy phase obtained in step S4 and the bottom stream of the light-removal tower are all sent back to a first reactor of the reactor.

6. The method for synthesizing acetic acid from methanol at low pressure with high catalyst stability according to claim 5, characterized in that: An inter-stage heat exchanger is provided between the first-stage reactor and the second-stage reactor, and the heat exchange medium in the inter-stage heat exchanger comes from boiler water.

7. The method for synthesizing acetic acid from methanol at low pressure with high catalyst stability according to claim 5, characterized in that: In step S4, the gas phase logistics obtained after treatment in the light phase removal tower is first cooled by a heat exchanger, and then the cooled liquid phase is sent to a stratifier for stratification treatment, and the obtained heavy phase logistics is sent back to a first reactor for recycling, and the obtained light phase logistics part rich in water and acetaldehyde is sent to the aldehyde removal section.

8. The method for synthesizing acetic acid from methanol at low pressure carbonylation with high catalyst stability according to claim 7, characterized in that: The treatment method of the aldehyde removal section is as follows: the light phase stream obtained after the treatment by the separator is sent to the aldehyde concentration tower for treatment, and the tower top stream rich in acetaldehyde and methyl iodide and the tower bottom stream rich in water are obtained, and the tower top stream rich in acetaldehyde and methyl iodide is sent to the extraction section, and the tower bottom stream rich in water is sent to the separator or the reaction section; The top stream rich in acetaldehyde and methyl iodide is sent to the extraction tower after heat exchange cooling treatment, and is extracted with desalted water in the extraction tower. The obtained formaldehyde-containing wastewater is sent to the wastewater treatment system for treatment, and the obtained raffinate is returned to the classifier or reaction section.

9. The method for synthesizing acetic acid from methanol at low pressure with high catalyst stability according to claim 7, characterized in that: The gas phase obtained after treatment in the high-pressure absorption tower of step S2 and / or the gas phase obtained after treatment in the low-pressure absorption tower of step S4 is sent to a pressure swing adsorption tower for treatment, and the purified CO gas is sent to a first reactor as a raw material for carbonyl synthesis reaction.

10. The method for synthesizing acetic acid from methanol at low pressure with high catalyst stability according to claim 1, characterized in that: In step S5, the obtained propionic acid-rich byproduct stream is sent to a propionic acid concentration tower for treatment, and then sent to a propionic acid product tower for treatment to obtain a propionic acid product liquid.

11. The method for synthesizing acetic acid from methanol at low pressure with high catalyst stability according to claim 10, characterized in that: In step S5, the obtained finished acetic acid is treated by a deiodination system to obtain low-iodine acetic acid with an iodine content lower than 10 ppb, and the deiodination system includes a two-stage deiodination tank.

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