A continuous closed-loop production process for preparing propionic acid esters from methanol or dimethyl ether as raw material
By employing a closed-loop process involving the hydrogenation of methyl acetate, etherification of mixed alcohols, and carbonylation of mixed ethers, the problems of strong catalyst corrosivity, high raw material costs, and limited product variety in propionate preparation have been solved. This process enables efficient co-production and continuous production, reduces production costs, and improves raw material utilization.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Filing Date
- 2026-05-13
- Publication Date
- 2026-07-10
Abstract
Description
Technical Field
[0001] This invention relates to the field of organic synthesis chemical technology, specifically to a continuous closed-loop production process for preparing propionate using methanol or dimethyl ether as raw materials. Background Technology
[0002] Propionates (including methyl propionate, ethyl propionate, etc.) are an important class of high-value-added organic chemical raw materials, widely used in food flavorings, pharmaceutical synthesis, coating solvents, plasticizers and other fields, and market demand continues to grow.
[0003] The mainstream preparation method for propionic esters is the direct esterification reaction of propionic acid with the corresponding alcohol. This process requires strong acids such as concentrated sulfuric acid as catalysts, which leads to serious equipment corrosion problems. This not only increases the cost of equipment selection and maintenance, but also easily triggers side reactions to generate impurities such as ethers and olefins, resulting in difficult product separation and purification and low product yield. At the same time, the raw material propionic acid has a high preparation cost, which further increases the total production cost of propionic esters and limits their large-scale application.
[0004] Methanol and dimethyl ether are widely available and inexpensive basic chemical raw materials that can be produced from various raw materials such as coal, natural gas, biomass, and coke oven gas via a syngas route. Existing technologies for the preparation of methyl acetate via methanol etherification and dimethyl ether carbonylation are relatively mature. However, current technologies are limited to the preparation of methyl acetate alone and have not yet achieved the conversion from methyl acetate to higher value-added propionate esters. Furthermore, existing ester preparation processes using methanol / dimethyl ether as raw materials generally suffer from low raw material utilization, lack of closed-loop recycling design, and limited product variety. They cannot achieve the co-production of propionate esters and other esters such as ethyl acetate, resulting in low resource utilization efficiency and low economic benefits.
[0005] In summary, there is an urgent need in this field to develop a continuous production process that uses methanol or dimethyl ether as raw materials, is free from strong acid corrosion, allows for the recycling of raw materials, and enables the efficient co-production of propionate esters. This process would address the many drawbacks of existing propionate ester preparation processes and meet the needs of industrial production. Summary of the Invention
[0006] To address the technical problems of existing propionate preparation processes, such as highly corrosive catalysts, high raw material costs, and limited product variety, as well as the lack of closed-loop design and low raw material utilization in methanol / dimethyl ether esterification processes, this invention provides a continuous closed-loop production process for propionate preparation using methanol or dimethyl ether as raw materials. This invention achieves efficient co-production of methyl propionate, ethyl propionate, and ethyl acetate by constructing a fully automated closed-loop process for methyl acetate, while significantly improving raw material utilization, reducing production costs, and providing mild reaction conditions with no equipment corrosion issues, enabling continuous industrial production.
[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: This invention provides a continuous closed-loop production process for preparing propionate from methanol or dimethyl ether, comprising the following steps: S1. Hydrogenation of methyl acetate: Methyl acetate undergoes a hydrogenation reaction with hydrogen gas under the action of a hydrogenation catalyst to produce a mixed alcohol of methanol and ethanol. S2. Etherification of Mixed Alcohols: The mixed alcohols obtained in step S1 are mixed with methanol feedstock, and an etherification reaction occurs under the action of an etherification catalyst to generate a mixed ether containing dimethyl ether, diethyl ether, and methyl ethyl ether. S3, Carbonylation of mixed ether: The mixed ether obtained in step S2 is mixed with fresh dimethyl ether raw material, and then mixed with carbon monoxide to carry out a carbonylation reaction to generate a mixed ester containing methyl acetate, ethyl acetate, methyl propionate and ethyl propionate. S4. Product separation: The mixed ester obtained in step S3 is separated by multi-tower continuous distillation, passing through a light-removal tower, a methyl acetate tower, an ethyl acetate tower, a methyl propionate tower, and an ethyl propionate tower in sequence to obtain ethyl acetate, methyl propionate, and ethyl propionate products, while methyl acetate is separated. S5. Closed-loop recycling: The methyl acetate separated in step S4 is returned to the methyl acetate hydrogenation step in step S1 to repeat the hydrogenation reaction, thereby achieving the directional closed-loop recycling of methyl acetate.
[0008] Furthermore, the hydrogenation catalyst in step S1 is a supported metal catalyst, the support is one or more of alumina, silica or activated carbon, and the active component is one or more of Cu, Zn, Ni or Mo. The loading of the active component is 2% to 50 wt.% based on the mass of the catalyst.
[0009] Preferably, the active component loading of the hydrogenation catalyst is 5 to 20 wt.%.
[0010] Furthermore, the hydrogenation reaction conditions in step S1 are: reaction temperature 120–250 °C, reaction pressure 1.0–5.0 MPa, and liquid hourly space velocity 0.5–5 h⁻¹. -1 The molar ratio of hydrogen to methyl acetate is 2 to 20:1.
[0011] Furthermore, the etherification catalyst in step S2 is a solid acid catalyst, selected from one or more of sulfonic acid ion exchange resins, supported heteropoly acids, and modified molecular sieves; the modified molecular sieve is one or more of H-MOR, H-ZSM-5, and H-FER.
[0012] Furthermore, the etherification reaction conditions in step S2 are: reaction temperature 100–250 °C, reaction pressure 0.5–5.0 MPa, and liquid hourly space velocity 0.5–3 h⁻¹. -1 .
[0013] Furthermore, in step S2, the volume ratio of the mixed alcohol to the fresh methanol feedstock is 0.2 to 10:1.
[0014] Furthermore, the carbonylation reaction in step S3 uses a modified H-zeolite molecular sieve catalyst, wherein the modified H-zeolite molecular sieve is a zeolite molecular sieve containing eight-membered ring channels, selected from one or more of H-MOR molecular sieve, H-ZSM-35 molecular sieve, H-FER molecular sieve, and H-MFI molecular sieve.
[0015] Furthermore, the carbonylation reaction conditions in step S3 are as follows: reaction temperature 150–400 °C, reaction pressure 1.0–10.0 MPa, and gas space velocity of the mixed ether, dimethyl ether, and carbon monoxide mixture 500–5000 h⁻¹. -1 The volume ratio of carbon monoxide to mixed ether is 2 to 50:1.
[0016] Furthermore, when dimethyl ether is used as a raw material, the volume ratio of the mixed ether to dimethyl ether in step S3 is 2 to 10:1.
[0017] Further, in step S4, the operating pressure of the light component removal tower is 0.5–0.75 MPa, and the top temperature is 25–35°C; the operating pressure of the methyl acetate tower is 0.01–0.5 MPa, and the top temperature is 50–80°C; the operating pressure of the ethyl acetate tower is 0.01–0.11 MPa, and the top temperature is -17–-20°C; the operating pressure of the methyl propionate tower is 0.006–0.15 MPa, and the top temperature is 50–70°C; and the operating pressure of the ethyl propionate tower is 0.06–0.07 MPa, and the top temperature is 80–90°C.
[0018] The technical solution of this invention has the following advantages: A. This invention is the first to organically integrate the hydrogenation of methyl acetate, the etherification of mixed alcohols, the carbonylation of mixed ethers, and the product separation and recycling steps, forming a complete closed-loop production process. In particular, the mixed alcohol (methanol / ethanol) produced in the hydrogenation step is directly etherified without separation to generate a mixed ether containing diethyl ether and methyl ethyl ether, which is then recycled back to the carbonylation unit. This successfully utilizes the ethanol structural unit to prepare high-value-added ethyl propionate and ethyl acetate, significantly improving the utilization rate of carbon atoms.
[0019] B. The process of this invention allows for the flexible production of multiple products, such as ethyl acetate, methyl propionate, and ethyl propionate, on the same production line, resulting in strong market adaptability. Furthermore, a high-purity (>99%) single product is obtained through an efficient distillation sequence.
[0020] C. The main raw materials of this invention are methanol or dimethyl ether, both of which can be produced on a large scale from non-petroleum routes such as coal, natural gas or biomass. The raw material cost is low, which is in line with my country's resource characteristics of "rich in coal, poor in oil and scarce in gas".
[0021] D. This invention uses solid acids or supported metal catalysts throughout the entire process, avoiding the use of traditional liquid strong acids and reducing equipment corrosion and waste emissions. The reaction conditions in each step are mild (e.g., hydrogenation temperature 120-250℃, carbonylation temperature 150-400℃), making it easy to achieve continuous industrial production.
[0022] E. The reaction intermediate methyl acetate of this invention is fully utilized through closed-loop recycling, avoiding waste of raw materials; by-products (such as mixed alcohols) are converted within the system, resulting in high overall atom utilization and significantly reducing production costs, thus possessing strong prospects for industrial application. Detailed Implementation
[0023] This invention can be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the inventive concept to those skilled in the art. All other embodiments derived by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention. Example 1
[0024] This embodiment provides a continuous closed-loop production process for preparing propionate, as detailed below: (1) Preparation of mixed ether carbonylation catalyst (for step S3): Hydrogen-form mordenite (H-MOR) powder with a silicon-to-aluminum ratio of 7:1 was calcined in air at 500°C for 4 hours. The calcined powder was then pressed into tablets, crushed, and sieved to obtain 20-40 mesh particles. 10 g of these particles were weighed and impregnated with methyl acetate as a modifier using an equal-volume impregnation method at room temperature for 12 hours. Subsequently, the particles were dried at 120°C for 4 hours and calcined in a nitrogen atmosphere at 500°C for 4 hours to obtain the modified carbonylation catalyst.
[0025] (2) Preparation of methyl acetate hydrogenation catalyst (for step S1): A Cu-Zn-Al₂O₃ catalyst was prepared by co-precipitation. Copper nitrate, zinc nitrate, and aluminum nitrate were dissolved in deionized water at a mass ratio of Cu:Zn:Al = 10:5:85 (total loading of active component Cu+Zn was 15 wt.%). The mixed salt solution and a 10 wt.% sodium carbonate solution were added concurrently to the precipitation tank at 70°C with vigorous stirring, maintaining the pH at 7.0 ± 0.2. After aging the precipitate for 2 hours, the solution was filtered, washed, dried at 110°C for 12 hours, calcined at 350°C for 4 hours, and then compressed into tablets.
[0026] (3) Continuous closed-loop process operation: S1. Hydrogenation of methyl acetate: 20 mL of the above hydrogenation catalyst was packed into a fixed-bed reactor. Hydrogen was introduced for reduction and activation at 180 °C and 2.0 MPa. Then, methyl acetate (recycled material) separated in step S4 was mixed with fresh hydrogen, controlling the hydrogen / methyl acetate molar ratio at 5:1 and the liquid hourly space velocity (LISH) at 1 h⁻¹. -1 The reaction was carried out at a temperature of 190℃ and a pressure of 2.0 MPa. After condensation, the reaction products yielded a mixed alcohol (mainly containing methanol and ethanol), with a methyl acetate conversion rate of 92.8% and an ethanol selectivity of 65.5%.
[0027] S2, Mixed Alcohol Etherification: 20 mL of commercially available sulfonic acid type ion exchange resin (such as Amberlyst-35) is packed into a fixed-bed reactor. The mixed alcohol from step S1 is mixed with fresh methanol at a volume ratio of 5:1, and then discharged at an LHSV of 1.5 h⁻¹. -1 The mixture was introduced into a reactor at a temperature of 150°C and a pressure of 1.5 MPa. In the etherification products, the total conversion rate of the mixed alcohol was 46.2%, and the selectivities for dimethyl ether, diethyl ether, and methyl ethyl ether were 28.5%, 47.2%, and 24.3%, respectively.
[0028] S3. Mixed Ether Carbonylation: 15 mL of the modified H-MOR catalyst prepared above was packed into a fixed-bed reactor. The mixed ether from step S2 was mixed with fresh dimethyl ether at a volume ratio of 3:1, and then mixed with carbon monoxide at a volume ratio of 1:20 (CO:total ether = 20:1). The total gas hourly space velocity was 4000 h⁻¹. -1 The reaction was carried out at a temperature of 230℃ and a pressure of 3.0 MPa. The reaction product was a mixed ester, in which the dimethyl ether conversion rate was 46.8%. The composition of the mixed ester was: methyl acetate 44.5%, ethyl acetate 26.2%, methyl propionate 16.1%, and ethyl propionate 13.2%.
[0029] S4. Product Separation: The mixed esters enter a multi-tower series distillation system. The light component removal tower (pressure 0.6 MPa, top temperature 27°C) removes the light components; the methyl acetate tower (pressure 0.1 MPa, top temperature 56°C) recovers unreacted methyl acetate (purity 99.5%); the ethyl acetate tower (pressure 0.11 MPa, top temperature -17°C) yields ethyl acetate (purity 99.2%); the methyl propionate tower (pressure 0.006 MPa, top temperature 59°C) yields methyl propionate (purity 99.1%); and the ethyl propionate tower (pressure 0.06 MPa, top temperature 85.5°C) yields ethyl propionate (purity 99.3%).
[0030] S5. Closed-loop circulation: The methyl acetate recovered from the top of the methyl acetate tower is recycled to the inlet of the hydrogenation reactor in step S1 for use as a feedstock. The system operated continuously and stably for 500 hours, with no significant decrease in the activity of the catalysts, and the product purity remained above 99%. Example 2
[0031] This embodiment provides a continuous closed-loop production process for preparing propionate, as detailed below: (1) Dimethyl ether carbonylation step (used in step S3): A supported metal carbonylation catalyst was used, with H-MOR molecular sieve as the support. The active components were Cu and La, with a Cu content of 5 g / L and a La content of 10 g / L. The catalyst was prepared by weighing Cu(NO3)2 containing 0.5 g of Cu. • Dissolve 3H₂O in water to prepare 30g of solution I; weigh out La(NO₃)₃ containing 1.0g of La. • 6H2O was dissolved in water to prepare 30g of solution II; solution I and solution II were mixed evenly and then impregnated onto H-MOR molecular sieve, impregnated at room temperature for 6h, dried at 120℃ for 12h, and calcined at 550℃ for 4h to obtain carbonylation catalyst.
[0032] The above catalyst was packed into a fixed-bed reactor, and the reaction temperature was 180℃, the reaction pressure was 4.5MPa, and a feed gas (volume ratio: carbon monoxide: dimethyl ether = 6.5:1) was introduced at a feed gas space velocity of 3500 h⁻¹. -1 The reaction results showed that the dimethyl ether conversion rate was 62.8%, and the methyl acetate selectivity was 95.8%.
[0033] (2) Continuous closed-loop process operation: S1, hydrogenation of methyl acetate: A supported Ni hydrogenation catalyst with a Ni content of 25 wt.% and activated carbon as the support was used. The reaction was carried out at a temperature of 200℃ and a pressure of 3.0 MPa, with a liquid hourly space velocity (LHSV) of 2 h⁻¹. -1 The molar ratio of hydrogen to methyl acetate was 8:1. The reaction results showed that the conversion rate of methyl acetate was 95.2%, the selectivity for ethanol was 68.5%, and the selectivity for methanol was 31.2%.
[0034] S2, Mixed alcohol etherification: A supported phosphotungstic acid catalyst was used, with a phosphotungstic acid loading of 20 wt.%, and the support was SBA-15 mesoporous molecular sieve. Under reaction conditions of 180℃ and 2.0 MPa, a mixed alcohol (a mixture of methanol and ethanol from step S1) was introduced at a liquid hourly space velocity (LISH) of 3 h⁻¹. -1The reaction results showed that the conversion rate of the mixed alcohol was 52.5%, the selectivity of dimethyl ether was 28.5%, the selectivity of diethyl ether was 48.2%, and the selectivity of methyl ethyl ether was 23.3%.
[0035] S3, Mixed ether cyclic carbonylation: The mixed ether obtained in step S2 above is mixed with fresh dimethyl ether (prepared by separate etherification of fresh methanol) at a volume ratio of 10:1, and then mixed with carbon monoxide at a volume ratio of 50:1 (CO:total ether = 50:1). The mixture is then introduced into a carbonylation reactor at a reaction temperature of 250°C, a reaction pressure of 4.5 MPa, and a feed gas space velocity of 3500 h⁻¹. -1 The reaction results showed that the conversion rate of the mixed ether was 48.5%, the selectivity of methyl acetate was 42.5%, the selectivity of ethyl acetate was 28.5%, the selectivity of methyl propionate was 16.5%, and the selectivity of ethyl propionate was 12.5%.
[0036] S4. Product separation: The separation was performed using the same distillation system as in Example 1, i.e., sequentially passing the product through a light component removal column, a methyl acetate column, an ethyl acetate column, a methyl propionate column, and an ethyl propionate column. The light component removal column was operated at a pressure of 0.5 MPa and a top temperature of 25°C to remove light components; the methyl acetate column was operated at a pressure of 0.01 MPa and a top temperature of 50°C to recover unreacted methyl acetate (99.5% purity); the ethyl acetate column was operated at a pressure of 0.11 MPa and a top temperature of -20°C to obtain ethyl acetate (99.2% purity); the methyl propionate column was operated at a pressure of 0.006 MPa and a top temperature of 50°C to obtain methyl propionate (99.1% purity); and the ethyl propionate column was operated at a pressure of 0.06 MPa and a top temperature of 80°C to obtain ethyl propionate (99.3% purity).
[0037] S5, Loop: The methyl acetate obtained from the distillation separation is returned to the S1 hydrogenation reactor, where it is mixed with hydrogen and recycled for hydrogenation. The system operated continuously for 300 hours with stable performance and consistent catalyst performance. Example 3
[0038] This embodiment provides a continuous closed-loop production process for preparing propionate using methanol and dimethyl ether as raw materials, as detailed below: (1) Catalyst preparation: Carbonylation catalyst (used in step S3): Hydrogen-form ZSM-35 molecular sieve (H-ZSM-35, silicon-to-aluminum ratio 15:1) was used. Commercially available Na-ZSM-35 was subjected to two ammonium ion exchanges (1 mol / L NH4NO3 solution, 90℃ for 2 hours), filtered, washed, and dried, then calcined in air at 550℃ for 4 hours to obtain H-ZSM-35. 10 g of H-ZSM-35 was impregnated with an equal volume of 0.5 mol / L magnesium nitrate solution for modification, allowed to stand at room temperature for 12 hours, dried overnight at 120℃, and calcined at 500℃ for 3 hours to obtain the Mg-modified H-ZSM-35 carbonylation catalyst.
[0039] Hydrogenation catalyst (used in step S1): A Cu-Zn / SiO2 catalyst was prepared using an equal-volume impregnation method. Copper nitrate and zinc nitrate were dissolved in deionized water at a molar ratio of Cu:Zn = 3:1, and SiO2 support was added. The mixture was impregnated at room temperature for 8 hours, dried at 110°C for 12 hours, and reduced in a hydrogen atmosphere at 400°C for 4 hours to obtain the Cu-Zn / SiO2 catalyst with a Cu loading of 15 wt.% and a Zn loading of 5 wt.%.
[0040] Etherification catalyst (used in step S2): Hydrogen-form ZSM-5 molecular sieve (H-ZSM-5, silicon-to-aluminum ratio 25:1) is used. Na-ZSM-5 is obtained by ammonium exchange and calcination, and is directly used as the etherification catalyst.
[0041] (2) Continuous closed-loop process operation: S1. Methyl acetate hydrogenation: 30 mL of the above hydrogenation catalyst was packed into a fixed-bed reactor. Hydrogen was introduced for reduction at 240℃ and 3.5 MPa. Then, methyl acetate (recycled material + fresh feed) and hydrogen were introduced, controlling the H2 / methyl acetate molar ratio at 20:1 and the liquid hourly space velocity (LHSV) at 0.5 h⁻¹. -1 The reaction was carried out at a temperature of 250℃ and a pressure of 5.0 MPa. Product analysis: methyl acetate conversion rate 89.6%, ethanol selectivity 62.3%, and methanol selectivity 37.7%.
[0042] S2, Mixed Alcohol Etherification: 30 mL of H-ZSM-5 etherification catalyst was packed into a fixed-bed reactor. The mixed alcohol from step S1 was mixed with fresh methanol at a volume ratio of 10:1, with an LHSV of 2.0 h⁻¹. -1 The mixture was introduced into the reactor at a temperature of 250℃ and a pressure of 0.5 MPa. The reaction results showed a total conversion rate of 51.3% for the mixed alcohol, and selectivities for dimethyl ether, diethyl ether, and methyl ethyl ether were 32.1%, 44.5%, and 23.4%, respectively.
[0043] S3, Mixed Ether Carbonylation: 20 mL of the above Mg / H-ZSM-35 catalyst was packed into a fixed-bed reactor. The mixed ether from step S2 was mixed with fresh dimethyl ether at a volume ratio of 6:1, and then mixed with carbon monoxide (CO:total ether = 40:1, volume ratio), with a total gas hourly space velocity of 500 h⁻¹. -1 The reaction temperature was 400℃ and the pressure was 1MPa. Product analysis: The total conversion rate of the mixed ethers was 41.2%. The composition of the mixed esters was: methyl acetate 46.8%, ethyl acetate 24.5%, methyl propionate 15.2%, and ethyl propionate 13.5%.
[0044] S4. Product separation: The same distillation column sequence as in Example 1 was used, with operating parameters adjusted according to the temperature range of each column. Light weight removal tower: pressure 0.7MPa, tower top temperature 30℃; Methyl acetate tower: pressure 0.5MPa, tower top temperature 60℃; Ethyl acetate tower: pressure 0.05MPa, tower top temperature -19℃; Methyl propionate tower: pressure 0.01 MPa, tower top temperature 65℃; Ethyl propionate tower: pressure 0.07MPa, tower top temperature 90℃.
[0045] The obtained ethyl acetate had a purity of 99.1%, methyl propionate had a purity of 99.0%, and ethyl propionate had a purity of 99.2%.
[0046] S5, Closed-loop recycling: The recovered methyl acetate is returned to step S1 for reuse. The system operated continuously for 400 hours, with conversion and selectivity fluctuations in each reactor less than ±2%, demonstrating good catalyst stability. Example 4
[0047] Other aspects are the same as in Example 1, with continuous closed-loop process operation: S1. Hydrogenation of methyl acetate: 20 mL of the above hydrogenation catalyst was packed into a fixed-bed reactor. Hydrogen was introduced for reduction and activation at 120 °C and 2.0 MPa. Then, methyl acetate (recycled material) separated in step S4 was mixed with fresh hydrogen, controlling the hydrogen / methyl acetate molar ratio at 2:1 and the liquid hourly space velocity (LISH) at 5 h⁻¹. -1 The reaction was carried out at a temperature of 120℃ and a pressure of 1.0 MPa. After condensation, the reaction products yielded a mixed alcohol (mainly containing methanol and ethanol), with a methyl acetate conversion rate of 91.6% and an ethanol selectivity of 65.0%.
[0048] S2, Mixed Alcohol Etherification: 20 mL of commercially available sulfonic acid type ion exchange resin (such as Amberlyst-35) is packed into a fixed-bed reactor. The mixed alcohol from step S1 is mixed with fresh methanol at a volume ratio of 0.2:1, and then discharged at an LHSV of 0.5 h⁻¹. -1The mixture was introduced into a reactor at a temperature of 100℃ and a pressure of 0.5 MPa. In the etherification products, the total conversion rate of the mixed alcohol was 44.4%, and the selectivities for dimethyl ether, diethyl ether, and methyl ethyl ether were 27.5%, 45.8%, and 24.1%, respectively.
[0049] S3. Mixed Ether Carbonylation: 15 mL of the modified H-MOR catalyst prepared above was packed into a fixed-bed reactor. The mixed ether from step S2 was mixed with fresh dimethyl ether at a volume ratio of 3:1, and then mixed with carbon monoxide at a volume ratio of 2:1 (CO:total ether = 2:1). The total gas hourly space velocity was 5000 h⁻¹. -1 The reaction was carried out at a temperature of 150℃ and a pressure of 10MPa. The reaction product was a mixed ester, in which the dimethyl ether conversion rate was 44.7%. The composition of the mixed ester was: methyl acetate 42.6%, ethyl acetate 27.1%, methyl propionate 18.2%, and ethyl propionate 14.7%.
[0050] S4. Product Separation: The mixed esters enter a multi-tower series distillation system. The light component removal tower is operated at 0.75 MPa and 35°C at the top to remove the light components; the methyl acetate tower is operated at 0.2 MPa and 80°C at the top to recover unreacted methyl acetate (99.5% purity); the ethyl acetate tower is operated at 0.01 MPa and -18°C at the top to obtain ethyl acetate (99.2% purity); the methyl propionate tower is operated at 0.015 MPa and 70°C at the top to obtain methyl propionate (99.1% purity); and the ethyl propionate tower is operated at 0.07 MPa and 85°C at the top to obtain ethyl propionate (99.3% purity).
[0051] S5. Closed-loop circulation: The methyl acetate recovered from the top of the methyl acetate tower is recycled to the inlet of the hydrogenation reactor in step S1 for use as a feedstock. The system operated continuously and stably for 500 hours, with no significant decrease in the activity of the catalysts, and the product purity remained above 99%.
[0052] Any aspects not described in this invention are applicable to existing technologies.
[0053] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.
Claims
1. A continuous closed-loop production process for preparing propionate esters using methanol or dimethyl ether as raw materials, characterized in that, Includes the following steps: S1. Hydrogenation of methyl acetate: Methyl acetate undergoes a hydrogenation reaction with hydrogen gas under the action of a hydrogenation catalyst to produce a mixed alcohol of methanol and ethanol. S2. Etherification of Mixed Alcohols: The mixed alcohols obtained in step S1 are mixed with methanol feedstock, and an etherification reaction occurs under the action of an etherification catalyst to generate a mixed ether containing dimethyl ether, diethyl ether, and methyl ethyl ether. S3, Carbonylation of mixed ether: The mixed ether obtained in step S2 is mixed with fresh dimethyl ether raw material, and then mixed with carbon monoxide to carry out a carbonylation reaction to generate a mixed ester containing methyl acetate, ethyl acetate, methyl propionate and ethyl propionate. S4. Product separation: The mixed ester obtained in step S3 is separated by multi-tower continuous distillation and extraction to obtain ethyl acetate, methyl propionate and ethyl propionate products respectively, while methyl acetate is separated. S5. Closed-loop recycling: The methyl acetate separated in step S4 is returned to the methyl acetate hydrogenation step in step S1 to repeat the hydrogenation reaction, thereby achieving the directional closed-loop recycling of methyl acetate.
2. The process according to claim 1, characterized in that, The hydrogenation catalyst in step S1 is a supported metal catalyst, with one or more of alumina, silica or activated carbon as the support, and one or more of Cu, Zn, Ni or Mo as the active component. The loading of the active component is 2% to 50 wt.% based on the mass of the catalyst.
3. The process according to claim 1, characterized in that, The hydrogenation reaction conditions in step S1 are: reaction temperature 120–250℃, reaction pressure 1.0–5.0 MPa, and liquid hourly space velocity 0.5–5 h⁻¹. -1 The molar ratio of hydrogen to methyl acetate is 2 to 20:
1.
4. The process according to claim 1, characterized in that, The etherification catalyst in step S2 is a solid acid catalyst, selected from one or more of sulfonic acid ion exchange resins, supported heteropoly acids, and modified molecular sieves; the modified molecular sieve is one or more of H-MOR, H-ZSM-5, and H-FER.
5. The process according to claim 1, characterized in that, The etherification reaction conditions in step S2 are: reaction temperature 100–250℃, reaction pressure 0.5–5.0 MPa, and liquid hourly space velocity 0.5–3 h⁻¹. -1 .
6. The process according to claim 1, characterized in that, The volume ratio of the mixed alcohol to the fresh methanol feedstock in step S2 is 0.2 to 10:
1.
7. The process according to claim 1, characterized in that, The carbonylation reaction in step S3 uses a modified H-zeolite molecular sieve catalyst. The modified H-zeolite molecular sieve is a zeolite molecular sieve containing eight-membered ring channels and is selected from one or more of H-MOR molecular sieve, H-ZSM-35 molecular sieve, H-FER molecular sieve, and H-MFI molecular sieve.
8. The process according to claim 1, characterized in that, The carbonylation reaction conditions in step S3 are as follows: reaction temperature 150–400 °C, reaction pressure 1.0–10.0 MPa, and gas space velocity of the mixed ether, dimethyl ether, and carbon monoxide mixture 500–5000 h⁻¹. -1 The volume ratio of carbon monoxide to mixed ether is 2 to 50:
1.
9. The process according to claim 1, characterized in that, When dimethyl ether is used as a raw material, the volume ratio of the mixed ether to dimethyl ether in step S3 is 2 to 10:
1.
10. The process according to claim 1, characterized in that, The multi-tower series continuous distillation and extraction process described in step S4 includes a light-removal tower, a methyl acetate tower, an ethyl acetate tower, a methyl propionate tower, and an ethyl propionate tower connected in series.