A system and method for preparing acetic acid by low-pressure carbonylation of methanol

Abstract

The present invention relates to a system for producing acetic acid by low-pressure carbonylation of methanol. The system comprises a reactor, a flash evaporator, a catalyst recovery unit, a lightness removal column, a dual-effect thermally coupled heavy removal column, and a raw material and return material metal ion removal tank located between the return port at the top of the lightness removal column and the reactor feed port. Compared with the prior art, the present invention removes impure metal ions at the source by adding a metal ion removal tank with built-in ion exchange resin before the reactor, slowing the accumulation of non-catalyst metal ions in the reaction solution and reducing catalyst loss. The thermally coupled heavy removal column also achieves dual-effect distillation, effectively reducing energy consumption.

Description

Technical Field

[0001] The invention belongs to the technical field of organic synthesis and relates to a system and method for preparing acetic acid by low-pressure carbonylation of methanol. Background Art

[0002] As an important basic organic chemical raw material, acetic acid is widely used in a variety of fields, including fibers, plasticizers, paints, adhesives, and copolymer resins. It has been a chemical product that has seen rapid growth in production capacity in recent years. Currently, the main methods for producing acetic acid worldwide include acetaldehyde oxidation, butane and light oil oxidation, and methanol carbonylation. Methanol carbonylation accounts for over 70% of global acetic acid production.

[0003] During the production of acetic acid from methanol carbonylation, the zirconium, Hastelloy, and stainless steel used in the acetic acid production equipment contain metals such as iron, chromium, manganese, and nickel. The circulating stream in the reaction system will dissolve iron, chromium, nickel, and other metal ions from the pipeline and accumulate in the system. When these foreign metal ions reach a certain level, they will reduce the carbonylation reaction rate and the stability of the catalyst system. Furthermore, the removal of these foreign metal ions will cause the loss of active elements in the catalyst, increasing the consumption of active elements and increasing costs accordingly.

[0004] Traditional acetic acid plants use three distillation towers to first remove light products, then dehydrate (secondary light products removal), and finally remove heavy products. Acetic acid is extracted from the top of the tower. The process is long, requires many pieces of equipment, consumes a lot of energy, and has high acetic acid separation costs. Summary of the Invention

[0005] The present invention aims to provide a system and method for producing acetic acid by low-pressure carbonylation of methanol, aiming to address the high energy and catalyst consumption issues associated with the low-pressure carbonylation of methanol to produce acetic acid. To address these issues, the present invention utilizes iridium and a complex metal as the primary catalyst, utilizes the heat of reaction in the distillation reboiler, and utilizes both a first and a second weight removal column to achieve thermal coupling between the two columns, creating a dual-effect distillation technology.

[0006] The purpose of the present invention can be achieved by the following technical solutions:

[0007] A system for preparing acetic acid by low-pressure carbonylation of methanol, comprising:

[0008] A reactor for carrying out a low-pressure carbonylation reaction of methanol to obtain a reaction product liquid;

[0009] Flash evaporator, which flashes the reaction product liquid, returns the liquid phase to the reactor, and the gas phase enters the catalyst recovery device;

[0010] The light removal tower is used to remove light components, and the heavy components extracted from the bottom of the tower are sent to the first and second heavy removal towers set in parallel;

[0011] The first deweighting tower and the second deweighting tower are distilled to produce acetic acid products; the top of the second deweighting tower is cyclically connected to the bottom heat exchanger of the first deweighting tower, and heat exchange occurs between the first deweighting tower and the second deweighting tower through the bottom heat exchanger.

[0012] Furthermore, the system also includes a raw material and return material metal ion removal tank, which is located between the top discharge port of the light removal tower and the feed port of the reactor, has a built-in macroporous strong acid ion exchange resin, and is provided with a methanol raw material inlet on the tank body.

[0013] Furthermore, the macroporous strong acid ion exchange resin includes ion exchange resin WET, ion exchange resin S or ion exchange resin LYS.

[0014] Furthermore, there is at least one raw material and return material metal ion removal tank, preferably two tanks that are connected in parallel with each other.

[0015] Furthermore, the reactor is externally looped with a reaction liquid heat exchanger.

[0016] Furthermore, a catalyst recovery device is provided between the gas phase outlet of the flash evaporator and the lightness removal tower, and the catalyst recovery device is used to recover the catalyst in the gas phase product of the flash evaporator; an ion remover is cyclically connected between the liquid phase outlet of the flash evaporator and the feed port.

[0017] Furthermore, the reactor is cyclically connected to a heat exchanger of the lightness removal tower, and heat exchange occurs between the reactor and the lightness removal tower through the heat exchanger.

[0018] In some preferred technical solutions, the reaction liquid directly exchanges heat with the lightness removal column, including direct heating of the column bottom liquid by the reaction liquid, or heating of the intermediate reboiler of the lightness removal column by the reaction liquid. Alternatively, steam produced as a by-product of the reaction liquid can be used to heat the lightness removal column bottom liquid or the intermediate reboiler of the lightness removal column.

[0019] To address the high energy consumption of low-pressure carbonylation of methanol to acetic acid, this invention utilizes iridium and a complex metal as the primary catalyst, utilizes the reaction heat in the distillation reboiler, and utilizes the first and second weight-removal columns as high-pressure and low-pressure columns, respectively. The high-pressure column is heated by steam, and the condenser at the top of the high-pressure column serves as the reboiler for the low-pressure column, thermally coupling the two columns and achieving dual-effect distillation technology. The first and second weight-removal columns are designed to separate heavy components such as propionic acid, potassium salts, and long-chain alkanes.

[0020] A method for preparing acetic acid by low-pressure carbonylation of methanol based on the above system comprises:

[0021] 1) After passing through the raw material and return material metal ion removal tank, the reaction raw materials enter the reactor and undergo a low-pressure carbonylation reaction of methanol under the action of a catalyst to obtain a reaction product liquid;

[0022] 2) passing the reaction product liquid into a flash evaporator for flash evaporation to obtain a liquid phase component and a gas phase component; the liquid phase component returns to the reactor, and the gas phase component enters a catalyst recovery device to recover the catalyst to obtain a purified gas phase component;

[0023] 3) The purified gas phase components are passed into a light removal tower for distillation to obtain light components from a dehydrogenation tower and heavy components from a dehydrogenation tower;

[0024] 4) The light components from the dehydrogenation tower are mixed with the raw materials methanol and CO in the raw material and return material demetallization tank to remove metal ions, and then circulated back to the reactor for reaction; the heavy components from the dehydrogenation tower enter the first deweighting tower and the second deweighting tower for distillation to produce acetic acid product.

[0025] Furthermore, the feed ratio of the first deweighting tower to the second deweighting tower is 1:1 to 2:8;

[0026] The operating pressure of the first deweighting tower is -100kPaG to 100kPaG, and the operating temperature is 70-150°C;

[0027] The operating pressure of the second deweighting tower is 0-100 kPaG, and the operating temperature is 130-200°C.

[0028] Furthermore, the operating pressure of the lightness removal tower is 100-200 kPaG, and the operating temperature is 90-160°C.

[0029] Furthermore, the operating pressure of the raw material and return material metal ion removal tank is 0 to 3.6 MPaG.

[0030] During the low-pressure carbonylation of methanol to acetic acid, impurity metals are introduced into the reaction liquid by the feed methanol, the absorption rich liquid, and the light components returned by distillation. Once the non-catalyst metals in the reaction liquid increase, the activity of the main catalyst will decrease, so regeneration is required. The regeneration cycle varies according to the impurity time of different feeds, and the shortest regeneration is about one month. Ion exchange resin is used for regeneration, which will cause catalyst loss while removing non-catalyst metals. Currently, precious metals such as iridium, ruthenium, osmium, and rhenium are mainly used as catalysts. The loss of catalyst will increase the cost of acetic acid preparation.

[0031] Therefore, to reduce catalyst consumption, it is necessary to remove it from the source and reduce the metal ion content of the feed. In the present invention, the methanol fed into the reactor, the absorbed rich liquid and the light components returned by distillation are mixed and then enter the metal ion removal tank to remove all metals. The metal ions after removal can reach below 50PPb, which can slow down the enrichment of non-catalyst metal ions in the reaction liquid, increase the regeneration cycle, and thus reduce the loss of catalyst.

[0032] Compared with the prior art, the present invention has the following characteristics:

[0033] 1) The present invention adds a raw material and return material metal ion removal tank with built-in ion exchange resin before the reactor to remove impurity metal ions from the source, slowing the enrichment of non-catalyst metal ions in the reaction solution and increasing the regeneration cycle, thereby reducing catalyst loss;

[0034] 2) The present invention can adopt a double demetallization tank and use different adsorbents to remove impurity metals at different stages, thereby improving the carbonylation reaction rate and the stability of the catalyst system;

[0035] 3) The present invention uses the reboiler of the first deweighting tower as the condenser of the second deweighting tower, realizing thermal coupling of the deweighting towers, effectively improving the utilization rate of the system heat, and reducing energy consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is a schematic structural diagram of a system for preparing acetic acid by low-pressure carbonylation of methanol in Example 1;

[0037] Figure 2 This is a schematic structural diagram of a system for preparing acetic acid by low-pressure carbonylation of methanol in Example 2;

[0038] Description of the marks in the figure:

[0039] 1-reactor, 2-flash evaporator, 3-catalyst recovery device, 4-light removal tower, 5-raw material and return material metal ion removal tank, 6-reaction liquid heat exchanger, 7-ion remover, 8-first heavy removal tower, 9-second heavy removal tower. DETAILED DESCRIPTION

[0040] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0041] like Figure 1The system shown is a low-pressure carbonylation system for producing acetic acid by methanol, comprising a reactor 1, a flash evaporator 2, a catalyst recovery device 3, a light-removal column 4, a coupled heavy-removal column, and a raw material and return material metal ion removal tank 5 located between the top discharge port of the light-removal column 4 and the feed port of the reactor 1, which are connected in sequence along the material flow direction.

[0042] The raw material and return material metal ion removal tank 5 is provided with a methanol raw material inlet and a macroporous strong acid ion exchange resin inside to remove impurity metal ions from the feed liquid entering the reactor 1. Preferably, the operating pressure of the raw material and return material metal ion removal tank 5 is 0 to 3.6 MPaG.

[0043] Macroporous strong acid ion exchange resin can be selected from ion exchange resin WET, ion exchange resin S or ion exchange resin LYS. This type of ion exchange resin is used to remove corrosive metal ions (Fe 2+ Cr 2+ 、Mn 2+ 、Ni 2+ , Ca 2+ and Mg 2+ At the same time, it ensures that the catalyst metal ions and auxiliary metal ions do not produce a large amount of loss.

[0044] In some preferred embodiments, reactor 1 is a non-stirred reactor, and the catalyst used is an iridium / ruthenium-based catalyst for catalyzing the low-pressure carbonylation reaction of methanol with CO. Reactor 1 is provided with a feed inlet at the bottom, and product outlets at the top and middle, respectively. The discharged reaction product liquid is collected and fed into a flash evaporator 2. Reactor 1 also has a reaction liquid circulation inlet and a reaction liquid circulation outlet at the top and middle, respectively. A reaction liquid circulation pump and a reaction liquid heat exchanger 6 are circulated between the two. Reactor 1 uses external heat exchange to control the temperature of the reaction system.

[0045] After flash evaporation, the reaction liquid returns to the reactor 1, and the gas phase enters the catalyst recovery device 3 to recover the catalyst. The acetic acid gas phase after the catalyst is recovered enters the light component removal tower 4 to separate the light components. The crude acetic acid is taken out from the bottom of the tower and sent to the first and second weight removal towers 8 and 9 arranged in parallel for refining to obtain the product acetic acid.

[0046] In some preferred embodiments, an ion remover 7 is cyclically connected between the liquid phase outlet and the feed inlet of the flash evaporator 2. The discharge from the bottom of the flash evaporator 2 is divided into two streams, one of which enters the ion remover 7, removes non-catalyst metal ions, and then returns to the flash evaporator.

[0047] In some preferred embodiments, the reactor of the lightness removal column 4 has two reboilers: one is a conventional steam-heated reboiler, and the other reboiler is in cyclic communication with the reactor 1, using the reaction liquid for direct heating or indirectly using the steam produced as a by-product of the reaction liquid for heating, thereby fully recovering the heat produced by the reaction within the device and reducing energy consumption. Preferably, the operating pressure of the lightness removal column 4 is 100-200 kPaG and the operating temperature is 90-160°C.

[0048] In some preferred embodiments, a reboiler is provided at the bottom or in the middle of the light removal tower 4, and the reaction liquid exchanges heat with the tower bottom or the intermediate reboiler, or the steam produced as a by-product of the reaction liquid exchanges heat with the tower bottom or the intermediate reboiler.

[0049] In some preferred embodiments, the reaction liquid heat exchanger 6 and the reboiler of the second deweighting tower 9 are both steam heaters.

[0050] In some preferred embodiments, the methanol-containing liquid product condensed from the top of lightness removal column 4 is returned to the feed and return material metal ion removal tank 5, mixed with methanol and other feed materials, and then removed from impurity metal ions before being recycled back to the reactor for carbonylation. The crude acetic acid produced in the bottom of lightness removal column 4 is split into two streams, entering the first and second weight removal columns 8 and 9, respectively. The feed mass flow ratio between the two weight removal columns is 1:1 to 2:8, preferably 5:5, 4:6, 3:7, or 2:8. The first weight removal column 8 is a low-pressure column, and the second weight removal column 9 is a pressurized column. Preferably, the operating pressure of the first weight removal column 8 is between -100 kPaG and 0 kPaG, or between 0 kPaG and 100 kPaG, and the operating temperature is between 70 and 150°C; the operating pressure of the second weight removal column 9 is between 0 and 100 kPaG, and the operating temperature is between 130 and 200°C. The acetic acid vapor from the top of the second deweighting tower 9 is used to heat the kettle of the first deweighting tower 8. The kettle of the first deweighting tower 8 does not use steam. Both deweighting towers extract acetic acid products by side lines, saving steam for one deweighting tower. Compared with conventional three-tower ordinary distillation or two-tower ordinary distillation, steam is saved by 30-50%, and circulating water is saved by about 30%.

[0051] Specifically, by using the reboiler in the bottom of the first de-weighting tower 8 as the top condenser for the second de-weighting tower 9, the acetic acid vapor at the top of the second de-weighting tower 9 is used to heat the bottom of the first de-weighting tower 8, achieving thermal coupling. The two de-weighting towers are then used to separate heavy components such as propionic acid, potassium salts, and long-chain alkanes.

[0052] The method of the present invention specifically comprises:

[0053] S1: The reaction raw materials methanol, absorption liquid (rich methanol, rich acetic acid) and light components recovered by distillation (methyl iodide, methyl ester, water, acetic acid) first enter the raw material and return material demetallization tank 5 for metal ion removal, and then enter the reactor 1; in the presence of a catalyst, methanol and CO undergo a low-pressure methanol carbonylation reaction to obtain a reaction product liquid;

[0054] S2: The reaction product liquid is passed into the flash evaporator 2 for flash evaporation to obtain a liquid phase component and a gas phase component; the liquid phase component returns to the reactor 1, and the gas phase component enters the catalyst recovery device 3 to recover the catalyst to obtain a purified gas phase component;

[0055] S3: The purified gas phase components are passed into the light removal tower 4 for distillation to obtain light components from the dehydrogenation tower and heavy components from the dehydrogenation tower;

[0056] S4: The light components from the dehydrogenation tower are mixed with the raw materials methanol and CO in the raw material and return material metal ion removal tank 5 to remove metal ions, and then circulated back to the reactor 1 for reaction; the heavy components from the dehydrogenation tower enter the first deheaving tower 8 and the second deheaving tower 9 arranged in parallel, and are distilled to produce acetic acid products.

[0057] Example 1:

[0058] The reaction raw materials methanol, absorption liquid (rich methanol, rich acetic acid) and light components recovered by distillation (methyl iodide, methyl ester, water, acetic acid) enter the raw material and return material demetallization tank 5 for metal ion removal, and then enter the reactor 1; under the action of the catalyst, methanol and CO undergo a low-pressure methanol carbonylation reaction to obtain a reaction product liquid; the reaction product liquid is passed into a flash evaporator 2 for flash evaporation to obtain a liquid phase component and a gas phase component; the liquid phase component returns to the reactor 1, and the gas phase component enters a catalyst recovery device 3 to recover the catalyst to obtain a purified gas phase component; the purified gas phase component is passed into a light phase removal tower 4 and distilled to obtain a dehydrogenation tower light component and a dehydrogenation tower heavy component; the dehydrogenation tower light component is mixed with the raw materials methanol and CO in the raw material and return material demetallization tank 5 to remove metal ions, and then circulated back to the reactor 1 for reaction; the dehydrogenation tower heavy component enters a first heavy phase removal tower 8 and a second heavy phase removal tower 9 arranged in parallel, and is distilled to produce an acetic acid product.

[0059] Among them, 78.8t / h of crude acetic acid in the bottom of the light-removing tower 4 is divided into two streams: 39.4t / h and 39.4t / h enter the first weight-removing tower 8 and the second weight-removing tower 9 respectively. The operating pressure of the first weight-removing tower 8 is -60kPaG, and a 70-layer plate tower is adopted. In other embodiments, a plate tower and a packed tower composite tower internal can also be used. The pressure difference of the tower is 50kPa, the reflux rate is 80t / h, and the side line is extracted from the 5th layer. The production volume is 37.5t / h. The steam consumption of the second weight-removing tower 9 is 15.4t. The second weight-removing tower 9 does not use circulating water, and the first weight-removing tower 8 does not use steam. The circulating water consumption of the first weight-removing tower 8 is 960t.

[0060] The reaction liquid was extracted from the middle of reactor 1 for 400m 3 / h, goes to the reboiler of the light removal tower 4, the temperature before entering the reboiler is 200℃, the temperature out of the reboiler is 180℃, and after cooling, the reaction returns to the middle and upper part of the reactor 1.

[0061] The raw methanol, the absorption rich liquid and the light substances (water, acetic acid, methyl acetate, methyl iodide, etc.) separated by the distillation light removal tower 4 first enter the demetallization ion adsorption tank. After passing through the cation exchange resin, the metal ions in the feed (containing ~100ppm of impurity metals) are exchanged onto the ion resin, and the total metal ion content in the discharge is ≤50ppb.

[0062] The concentration of metal ions other than the catalyst in the reaction liquid is ≥200PPM, and the reaction liquid is subjected to a metal ion removal operation. The reaction liquid enters the ion remover 7, and is selectively adsorbed by the ion exchange resin to remove the metal ions other than the catalyst ruthenium and iridium to below 50ppm.

[0063] Under the same conditions, without using raw material pretreatment resin and return liquid demetallization resin tank, the iridium consumption is about 0.14g and ruthenium is about 0.18g. After using it, it is reduced to about 0.09g of iridium and about 0.12g of ruthenium.

[0064] The finished product tower saves 50% of steam, reducing acetic acid consumption from 0.8 tons of steam per ton of acetic acid to approximately 0.5 tons of steam per ton of acetic acid. Taking a 500,000-ton / year acetic acid plant as an example, with an annual operating time of 8,000 hours, the hourly acetic acid output is approximately 62.5 tons. Using a single de-weighting tower process, the steam consumption of the lightness removal tower is approximately 28 tons / hour, and the steam consumption of the de-weighting tower is 28 tons / hour, for a total steam consumption of approximately 0.848 tons / ton of acetic acid. The present invention uses two double-effect thermally coupled de-weighting towers, reducing the steam consumption of the lightness removal tower to 15.5 tons / hour. The total steam consumption after double-effect heat exchange of the two de-weighting towers is 24 tons / hour, for a total steam consumption of approximately 0.44 tons / ton of acetic acid. This shows that the present invention effectively improves the utilization rate of system heat and reduces system energy consumption.

[0065] Example 2:

[0066] like Figure 2 The system for preparing acetic acid by low-pressure carbonylation of methanol shown in the figure differs from that in Example 1 only in that:

[0067] The system comprises two raw material and return material metal ion removal tanks 5 which are arranged in parallel and used alternately and have the same specifications. The rest of the system is the same as that of Example 1.

[0068] The above description of the embodiments is intended to facilitate understanding and use of the invention by those skilled in the art. It will be apparent that those skilled in the art can readily make various modifications to these embodiments and apply the general principles described herein to other embodiments without requiring inventive effort. Therefore, the present invention is not limited to the above-described embodiments. Improvements and modifications made by those skilled in the art based on the disclosure of the present invention, without departing from the scope of the present invention, should be within the scope of protection of the present invention.

Claims

1. A system for preparing acetic acid by low-pressure carbonylation of methanol, characterized in that: Including connected in sequence along the direction of material flow A reactor (1) is used for performing a low-pressure carbonylation reaction of methanol to obtain a reaction product liquid; The flash evaporator (2) flashes the reaction product liquid, the liquid phase returns to the reactor (1), and the gas phase enters the light removal tower (4); The light removal tower (4) is used to remove light components, and the heavy components extracted from the bottom of the tower are fed into the first heavy removal tower (8) and the second heavy removal tower (9) arranged in parallel; The first de-weighting tower (8) and the second de-weighting tower (9) are distilled to produce acetic acid products; the top of the second de-weighting tower (9) is cyclically connected to the bottom heat exchanger of the first de-weighting tower (8), and heat exchange occurs between the first de-weighting tower (8) and the second de-weighting tower (9) through the bottom heat exchanger; The system further comprises a raw material and return material demetallization tank (5), which is arranged between the top discharge port of the delight tower (4) and the feed port of the reactor (1); a macroporous strong acid type ion exchange resin is arranged in the raw material and return material demetallization tank (5); and a methanol raw material inlet is arranged on the raw material and return material demetallization tank (5); The reactor (1) is cyclically connected to the heat exchanger of the light removal tower (4), and the reaction liquid extracted from the reactor (1) is heat-exchanged with the liquid in the light removal tower (4) through the heat exchanger.

2. The system for preparing acetic acid by low-pressure carbonylation of methanol according to claim 1, characterized in that: The macroporous strong acid ion exchange resin includes ion exchange resin WET, ion exchange resin S or ion exchange resin LYS.

3. The system for preparing acetic acid by low-pressure carbonylation of methanol according to claim 1, characterized in that: The heat exchanger of the light removal tower (4) is arranged at the bottom or middle of the light removal tower (4).

4. The system for preparing acetic acid by low-pressure carbonylation of methanol according to claim 1, characterized in that: A catalyst recovery device (3) is further provided between the gas phase outlet of the flash evaporator (2) and the lightness removal tower (4); and an ion remover (7) is cyclically connected between the liquid phase outlet of the flash evaporator (2) and the feed port.

5. A method for preparing acetic acid by low-pressure carbonylation of methanol based on the system according to any one of claims 1 to 4, characterized in that: include: 1) After the reaction raw materials pass through the raw material and return material metal ion removal tank (5), they enter the reactor (1) and undergo a low-pressure carbonylation reaction of methanol under the action of a catalyst to obtain a reaction product liquid; 2) passing the reaction product liquid into the flash evaporator (2) for flash evaporation to obtain a liquid phase component and a gas phase component; The liquid phase components are returned to the reactor (1); 3) The gaseous components are passed into a light fraction removal tower (4) and distilled to obtain light fractions from a dehydrogenation tower and heavy fractions from a dehydrogenation tower; 4) The light components from the dehydrogenation tower are mixed with the raw material methanol and CO in the raw material and return material demetallization tank (5) to remove metal ions, and then circulated back to the reactor (1) for reaction; the heavy components from the dehydrogenation tower enter the first dehydrogenation tower (8) and the second dehydrogenation tower (9) for distillation to produce acetic acid product.

6. The method for preparing acetic acid by low-pressure carbonylation of methanol according to claim 5, characterized in that: The feed ratio of the first deweighting tower (8) to the second deweighting tower (9) is 1:1 to 2:8; The operating pressure of the first deweighting tower (8) is -100 kPaG to 100 kPaG, and the operating temperature is 70-150°C; The operating pressure of the second deweighting tower (9) is 0~100 kPaG, and the operating temperature is 130~200℃.

7. The method for preparing acetic acid by low-pressure carbonylation of methanol according to claim 5, characterized in that: The operating pressure of the lightness removal tower (4) is 100-200 kPaG, and the operating temperature is 90-160°C.

8. The method for preparing acetic acid by low-pressure carbonylation of methanol according to claim 5, characterized in that: The operating pressure of the raw material and return material metal ion removal tank (5) is 0~3.6MPaG.

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