Continuous preparation method for co-production of acetamide and acetonitrile

Abstract

The invention provides a continuous preparation method for co-production of acetamide and acetonitrile, and belongs to the technical field of acetonitrile synthesis. The preparation method comprises mixing, a route 1, a route 2, a recrystallization system, a mother liquor recovery system and a heat supply system. According to the preparation method for continuously co-producing acetamide and acetonitrile, the yield of the obtained acetonitrile is 93.1-93.7%, the purity is 99.78-99.96%, the yield of acetamide is 89.2-89.7%, the purity is 98.39-98.54%, the service life of the catalyst 1 is 219-235 days, the service life of the catalyst 2 is 254-278 days, the heat consumed for producing 1000 kg of acetonitrile and 1000 kg of acetamide is 1.63 * 10 < 7 >-1.64 * 10 < 7 > kJ, and the heat utilization rate is 78-81%.

Description

Technical Field

[0001] This invention belongs to the field of acetonitrile synthesis technology, specifically relating to a continuous method for the co-production of acetonitrile from acetamide. Background Technology

[0002] Acetamide, acetonitrile, and other fine chemicals are widely used as solvents for organic and inorganic substances. They are also chemical raw materials for the production of anti-acid agents, wetting agents, plasticizers, etc., and have a wide market demand. Currently, the fixed-bed synthesis process using acetic acid ammoniation is commonly used. The main steps of this process are as follows: acetic acid is vaporized and preheated, then mixed with preheated ammonia gas and reacted in a fixed-bed reactor. The fixed-bed reactor is filled with a catalyst, and acetonitrile and acetamide can be flexibly produced at different temperatures. At low temperatures, the reactor effluent enters an acetamide separation tower, with water, a small amount of acetonitrile, and excess ammonia at the top, and acetamide mainly at the bottom. At high temperatures, the reactor effluent is absorbed by ammonia and dehydrated to obtain acetonitrile. The fixed-bed synthesis process using acetic acid ammoniation is simple to operate, has a high yield, and is highly safe. However, the process has poor continuity and cannot produce acetonitrile and acetamide simultaneously.

[0003] Patent CN117567320A discloses a method for preparing acetonitrile and co-producing acetamide by acetic acid amination. In this method, different reaction temperatures are controlled to achieve the purpose of producing acetonitrile and acetamide. The method is simple, has high yield, high purity and high safety. However, this method (1) cannot produce acetonitrile and acetamide at the same time; (2) because the production of acetamide and acetonitrile requires different temperatures, and the catalyst is formed by loading one or more catalytically active metals on γ-Al2O3, the coefficients of thermal expansion of these metals are different. Therefore, when switching the types of products produced, thermal expansion and contraction will cause the metal loaded on γ-Al2O3 to fall off, thereby reducing the service life of the catalyst; (3) when producing acetonitrile, the acetamide production line is not working, and vice versa, which means that the residual heat in the reaction process cannot be fully utilized, resulting in a large loss and low heat utilization rate. Summary of the Invention

[0004] To address the problems existing in the prior art, this invention provides a continuous method for preparing acetamide and acetonitrile, achieving the following objectives: it can simultaneously produce acetonitrile and acetamide, or produce acetonitrile or acetamide alone, reducing the requirements for catalysts, and improving heat utilization efficiency through rational design.

[0005] To solve the above technical problems, the technical solution adopted by the present invention is as follows: A continuous method for preparing acetamide and acetonitrile co-production includes the following steps: 1. Mix Acetic acid and liquid ammonia are vaporized through heat exchanger 1 and heat exchanger 2 respectively, and heated to 160-200°C. After being mixed evenly in a gas mixer, the output mixed gas is divided into two routes, namely route 1 and route 2. The flow rate of the mixed gas through route 1 and route 2 can be controlled by valves. The mass ratio of acetic acid to liquid ammonia is 54–66:17–21.

[0006] 2. Route 1 Route 1 is acetonitrile synthesis. The mixed gas of Route 1 is fed into fixed-bed reactor 1. Under the action of catalyst 1, crude acetonitrile is produced by reaction. The crude acetonitrile is fed into an ammonia absorption tower to remove ammonia, and then fed into an acetonitrile distillation column. Acetonitrile is output from the top of the column. The material from the bottom of the column is discharged into the mother liquor recovery system; The catalyst 1 is La-Zr-γ-Al2O3, which is prepared by adding La(NO3)3, Zr(NO3)4, and γ-Al2O3 to deionized water, stirring until completely mixed, filtering, and calcining the filter cake at 450-550℃ for 0.7-0.9h under a nitrogen atmosphere to obtain La-Zr-γ-Al2O3. The mass ratio of La(NO3)3, Zr(NO3)4, γ-Al2O3, and deionized water is 12-14:6.5-7.5:40-50:170-200; The temperature of the fixed-bed reactor 1 is 345-355℃, and the residence time of the mixed gas in the fixed-bed reactor 1 is 60-100s; The acetonitrile distillation column is configured with a top temperature of 78–82°C, a bottom temperature of 106–113°C, an internal absolute pressure of 68–72 kPa, and a reflux ratio of 2.8–3.2.

[0007] 3. Route 2 Route 2 is for the synthesis of acetamide. The mixed gas of Route 2 is fed into fixed-bed reactor 2. Under the action of catalyst 2, crude acetamide is produced. The crude acetamide is fed into an acetamide distillation column. After the acetamide solution is output from the bottom of the column, it is cooled, crystallized and centrifuged to obtain primary crystalline acetamide and primary mother liquor. Then the primary crystalline acetamide enters the recrystallization system. The material at the top of the tower is recycled to fixed-bed reactor 1 for reuse. The mother liquor enters the mother liquor recovery system; The catalyst 2 is Cu-Zn-γ-Al2O3, which is prepared by adding Cu(NO3)2, Zn(NO3)2, and γ-Al2O3 to deionized water, stirring until completely mixed, filtering, and calcining the filter cake at 550-650℃ for 0.4-0.6h under a nitrogen atmosphere to obtain Cu-Zn-γ-Al2O3. The mass ratio of Cu(NO3)2, Zn(NO3)2, γ-Al2O3, and deionized water is 6-8:10-12:40-50:160-200; The temperature of the fixed-bed reactor 2 is 225-235℃, and the residence time of the mixed gas in the fixed-bed reactor 2 is 40-80s; The acetamide distillation column is configured with a top temperature of 86–93°C, a bottom temperature of 135–142°C, an internal absolute pressure of 55–65 kPa, and a reflux ratio of 3.8–4.1.

[0008] 4. Recrystallization system Acetamide that has undergone primary crystallization and recovered acetamide are added to deionized water. After heating to dissolve, cooling to crystallize, and centrifuging, acetamide and recrystallization mother liquor are obtained. The mass ratio of primary crystallization acetamide, recovered acetamide, and deionized water is 5.5–6.5:1.8–2.2:2–4. The heating and dissolving temperature is 55–65°C. The recrystallization mother liquor enters the mother liquor recovery system.

[0009] 5. Mother liquor recovery system The materials from the bottom of the tower in Route 1, the primary mother liquor from Route 2, and the recrystallization mother liquor are mixed in a mixing vessel and then evaporated and concentrated at 70–80°C. When the solid content reaches 28–32%, the mixture is cooled and crystallized, then centrifuged to obtain recovered acetamide and secondary mother liquor. The recovered acetamide is introduced into the recrystallization system, and 40–60% wt of the secondary mother liquor is reintroduced into the mixing vessel. The remaining portion is removed as waste mother liquor.

[0010] 6. Heating system The heating system is divided into Route 3 and Route 4. Route 3 uses high-temperature molten salt, while Route 4 uses high-pressure steam to provide heat for the entire system. In Route 3, the high-temperature molten salt first enters fixed-bed reactor 1 to provide heat for acetonitrile synthesis, and the remaining heat at the outlet of fixed-bed reactor 1 enters fixed-bed reactor 2 to provide heat for acetamide synthesis. The residual heat at the outlet of fixed-bed reactor 2 provides heat for the acetonitrile distillation column and the acetamide distillation column, and the residual heat at the outlet is combined and used for the recrystallization system; In Route 4, the high-pressure steam first preheats the acetic acid and liquid ammonia respectively through heat exchanger 1 and heat exchanger 2. The remaining heat from the outlets of heat exchanger 1 and heat exchanger 2 is combined and used for the mother liquor recovery system.

[0011] Compared with the prior art, the beneficial effects of the present invention are as follows: The continuous preparation method of acetamide and acetonitrile of the present invention (1) can control the flow rate of the mixed gas passing through route 1 and route 2 through valves respectively, thereby flexibly controlling the amount of acetamide and acetonitrile produced. It can produce acetamide or acetonitrile alone, or produce acetamide and acetonitrile at the same time, which can meet different production needs. (2) Route 1 produces acetonitrile using catalyst 1 (La-Zr-γ-Al2O3), while Route 2 produces acetamide using catalyst 2 (Cu-Zn-γ-Al2O3). The catalysts operate at a constant temperature, which extends their service life. At the same time, the temperature required for acetamide production is low, and the requirements for the catalyst are also low. The prices of Cu and Zn in catalyst 2 (Cu-Zn-γ-Al2O3) are lower than the prices of La and Zr in catalyst 1 (La-Zr-γ-Al2O3). Using different catalysts can reduce costs. (3) Acetamide and acetonitrile can be produced simultaneously, so the subsequent processes of Route 1 and Route 2 can utilize the residual heat after the reaction, thus improving the heat utilization rate; (4) The continuous acetamide co-production method of the present invention yields acetamide with a yield of 93.1-93.7% and a purity of 99.78-99.96%, acetamide with a yield of 89.2-89.7% and a purity of 98.39-98.54%, catalyst 1 with a lifetime of 219-235 days, catalyst 2 with a lifetime of 254-278 days, and consumes 1.63 × 10⁻⁶ heat to produce 1000 kg acetamide and 1000 kg acetamide. 7 ~1.64×10 7 kJ, with a heat utilization rate of 78-81%. Attached Figure Description

[0012] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the accompanying drawings used in the description of the specific embodiments or the prior art will be briefly introduced below.

[0013] Figure 1 This is a schematic diagram of the production process of acetamide and acetonitrile in a continuous acetamide co-production method of the present invention.

[0014] Figure 2 This is a schematic diagram of the production process of mother liquor recovery and acetamide recrystallization in a continuous acetamide-acetonitrile co-production method of the present invention.

[0015] Figure 3 This is a schematic diagram of the production process of acetamide and acetonitrile in Comparative Example 1. Detailed Implementation

[0016] Example 1 1. Mix Acetic acid and liquid ammonia are vaporized through heat exchanger 1 and heat exchanger 2 respectively, and heated to 180°C. After being mixed evenly in a gas mixer, the output mixed gas is divided into two routes, namely route 1 and route 2. The flow rate of the mixed gas through route 1 and route 2 can be controlled by valves. The mass ratio of acetic acid to liquid ammonia is 3:1.

[0017] 2. Route 1 Route 1 is acetonitrile synthesis. The mixed gas of Route 1 is fed into fixed-bed reactor 1. Under the action of catalyst 1, crude acetonitrile is produced by reaction. The crude acetonitrile is fed into an ammonia absorption tower to remove ammonia, and then fed into an acetonitrile distillation column. Acetonitrile is output from the top of the column. The material from the bottom of the column is discharged into the mother liquor recovery system; The catalyst 1 is La-Zr-γ-Al2O3, which is prepared by adding La(NO3)3, Zr(NO3)4 and γ-Al2O3 to deionized water, stirring until completely mixed, filtering, and calcining the filter cake at 500°C for 0.8 h under a nitrogen atmosphere to obtain La-Zr-γ-Al2O3. The mass ratio of La(NO3)3, Zr(NO3)4, γ-Al2O3, and deionized water is 13:7:45:180; The temperature of the fixed-bed reactor 1 is 350℃, and the residence time of the mixed gas in the fixed-bed reactor 1 is 80s; The acetonitrile distillation column is configured with a top temperature of 80°C, a bottom temperature of 110°C, an internal absolute pressure of 70 kPa, and a reflux ratio of 3.

[0018] 3. Route 2 Route 2 is for the synthesis of acetamide. The mixed gas of Route 2 is fed into fixed-bed reactor 2. Under the action of catalyst 2, crude acetamide is produced. The crude acetamide is fed into an acetamide distillation column. After the acetamide solution is output from the bottom of the column, it is cooled, crystallized and centrifuged to obtain primary crystalline acetamide and primary mother liquor. Then the primary crystalline acetamide enters the recrystallization system. The material at the top of the tower is recycled to fixed-bed reactor 1 for reuse. The mother liquor enters the mother liquor recovery system; The catalyst 2 is Cu-Zn-γ-Al2O3. The preparation method is to add Cu(NO3)2, Zn(NO3)2 and γ-Al2O3 to deionized water, stir until completely mixed, filter, and calcine the filter cake at 600℃ for 0.5h under nitrogen atmosphere to obtain Cu-Zn-γ-Al2O3. The mass ratio of Cu(NO3)2, Zn(NO3)2, γ-Al2O3, and deionized water is 7:11:45:180; The temperature of the fixed-bed reactor 2 is 230°C, and the residence time of the mixed gas in the fixed-bed reactor 2 is 60s; The acetamide distillation column is configured with a top temperature of 90°C, a bottom temperature of 140°C, an internal absolute pressure of 60 kPa, and a reflux ratio of 4.

[0019] 4. Recrystallization system Acetamide that has been crystallized once and the recovered acetamide are added to deionized water. After heating to dissolve, cooling to crystallize, and centrifuging, acetamide and recrystallization mother liquor are obtained. The mass ratio of acetamide that has been crystallized once, the recovered acetamide, and the deionized water is 6:2:3. The heating and dissolving temperature is 60°C. The recrystallization mother liquor enters the mother liquor recovery system.

[0020] 5. Mother liquor recovery system The materials from the bottom of the tower in Route 1, the primary mother liquor from Route 2, and the recrystallization mother liquor are mixed in a mixing vessel and then evaporated and concentrated at 75°C. When the solid content reaches 30%, the mixture is cooled and crystallized, then centrifuged to obtain recovered acetamide and secondary mother liquor. The recovered acetamide is sent to the recrystallization system, and 50% wt of the secondary mother liquor is returned to the mixing vessel. The remaining portion is removed as waste mother liquor.

[0021] 6. Heating system The heating system is divided into Route 3 and Route 4. Route 3 uses high-temperature molten salt, while Route 4 uses high-pressure steam to provide heat for the entire system. In Route 3, the high-temperature molten salt first enters fixed-bed reactor 1 to provide heat for acetonitrile synthesis, and the remaining heat at the outlet of fixed-bed reactor 1 enters fixed-bed reactor 2 to provide heat for acetamide synthesis. The residual heat at the outlet of fixed-bed reactor 2 provides heat for the acetonitrile distillation column and the acetamide distillation column, and the residual heat at the outlet is combined and used for the recrystallization system; In Route 4, the high-pressure steam first preheats the acetic acid and liquid ammonia respectively through heat exchanger 1 and heat exchanger 2. The remaining heat from the outlets of heat exchanger 1 and heat exchanger 2 is combined and used for the mother liquor recovery system.

[0022] Example 2 1. Mix Acetic acid and liquid ammonia are vaporized through heat exchanger 1 and heat exchanger 2 respectively, and heated to 160°C. After being mixed evenly in a gas mixer, the output mixed gas is divided into two routes, namely route 1 and route 2. The flow rate of the mixed gas through route 1 and route 2 can be controlled by valves. The mass ratio of acetic acid to liquid ammonia is 54:17.

[0023] 2. Route 1 Route 1 is acetonitrile synthesis. The mixed gas of Route 1 is fed into fixed-bed reactor 1. Under the action of catalyst 1, crude acetonitrile is produced by reaction. The crude acetonitrile is fed into an ammonia absorption tower to remove ammonia, and then fed into an acetonitrile distillation column. Acetonitrile is output from the top of the column. The material from the bottom of the column is discharged into the mother liquor recovery system; The catalyst 1 is La-Zr-γ-Al2O3, which is prepared by adding La(NO3)3, Zr(NO3)4 and γ-Al2O3 to deionized water, stirring until completely mixed, filtering, and calcining the filter cake at 450°C for 0.7 h under a nitrogen atmosphere to obtain La-Zr-γ-Al2O3. The mass ratio of La(NO3)3, Zr(NO3)4, γ-Al2O3, and deionized water is 12:6.5:40:170; The temperature of the fixed-bed reactor 1 is 345℃, and the residence time of the mixed gas in the fixed-bed reactor 1 is 60s; The acetonitrile distillation column is configured with a top temperature of 78°C, a bottom temperature of 106°C, an internal absolute pressure of 68 kPa, and a reflux ratio of 2.8.

[0024] 3. Route 2 Route 2 is for the synthesis of acetamide. The mixed gas of Route 2 is fed into fixed-bed reactor 2. Under the action of catalyst 2, crude acetamide is produced. The crude acetamide is fed into an acetamide distillation column. After the acetamide solution is output from the bottom of the column, it is cooled, crystallized and centrifuged to obtain primary crystalline acetamide and primary mother liquor. Then the primary crystalline acetamide enters the recrystallization system. The material at the top of the tower is recycled to fixed-bed reactor 1 for reuse. The mother liquor enters the mother liquor recovery system; The catalyst 2 is Cu-Zn-γ-Al2O3. The preparation method is to add Cu(NO3)2, Zn(NO3)2 and γ-Al2O3 to deionized water, stir until completely mixed, filter, and calcine the filter cake at 550℃ for 0.4h under nitrogen atmosphere to obtain Cu-Zn-γ-Al2O3. The mass ratio of Cu(NO3)2, Zn(NO3)2, γ-Al2O3, and deionized water is 6:10:40:160; The temperature of the fixed-bed reactor 2 is 225°C, and the residence time of the mixed gas in the fixed-bed reactor 2 is 40s; The acetamide distillation column is configured with a top temperature of 86°C, a bottom temperature of 135°C, an internal absolute pressure of 55 kPa, and a reflux ratio of 3.8.

[0025] 4. Recrystallization system Acetamide that has undergone primary crystallization and recovered acetamide are added to deionized water. After heating to dissolve, cooling to crystallize, and centrifuging, acetamide and recrystallization mother liquor are obtained. The mass ratio of primary crystallization acetamide, recovered acetamide, and deionized water is 5.5:1.8:2. The heating and dissolving temperature is 55℃. The recrystallization mother liquor enters the mother liquor recovery system.

[0026] 5. Mother liquor recovery system The materials from the bottom of the tower in Route 1, the primary mother liquor from Route 2, and the recrystallization mother liquor are mixed in a mixing vessel and then evaporated and concentrated at 70–80°C. When the solid content reaches 28%, the mixture is cooled and crystallized, then centrifuged to obtain recovered acetamide and secondary mother liquor. The recovered acetamide is introduced into the recrystallization system, and 40% wt of the secondary mother liquor is reintroduced into the mixing vessel. The remaining portion is removed as waste mother liquor.

[0027] 6. Heating system The heating system is divided into Route 3 and Route 4. Route 3 uses high-temperature molten salt, while Route 4 uses high-pressure steam to provide heat for the entire system. In Route 3, the high-temperature molten salt first enters fixed-bed reactor 1 to provide heat for acetonitrile synthesis, and the remaining heat at the outlet of fixed-bed reactor 1 enters fixed-bed reactor 2 to provide heat for acetamide synthesis. The residual heat at the outlet of fixed-bed reactor 2 provides heat for the acetonitrile distillation column and the acetamide distillation column, and the residual heat at the outlet is combined and used for the recrystallization system; In Route 4, the high-pressure steam first preheats the acetic acid and liquid ammonia respectively through heat exchanger 1 and heat exchanger 2. The remaining heat from the outlets of heat exchanger 1 and heat exchanger 2 is combined and used for the mother liquor recovery system.

[0028] Example 3 1. Mix Acetic acid and liquid ammonia are vaporized through heat exchanger 1 and heat exchanger 2 respectively, and heated to 200°C. After being mixed evenly in a gas mixer, the output mixed gas is divided into two routes, namely route 1 and route 2. The flow rate of the mixed gas through route 1 and route 2 can be controlled by valves. The mass ratio of acetic acid to liquid ammonia is 66:21.

[0029] 2. Route 1 Route 1 is acetonitrile synthesis. The mixed gas of Route 1 is fed into fixed-bed reactor 1. Under the action of catalyst 1, crude acetonitrile is produced by reaction. The crude acetonitrile is fed into an ammonia absorption tower to remove ammonia, and then fed into an acetonitrile distillation column. Acetonitrile is output from the top of the column. The material from the bottom of the column is discharged into the mother liquor recovery system; The catalyst 1 is La-Zr-γ-Al2O3, which is prepared by adding La(NO3)3, Zr(NO3)4 and γ-Al2O3 to deionized water, stirring until completely mixed, filtering, and calcining the filter cake at 550°C for 0.9 h under a nitrogen atmosphere to obtain La-Zr-γ-Al2O3. The mass ratio of La(NO3)3, Zr(NO3)4, γ-Al2O3, and deionized water is 14:7.5:50:200; The temperature of the fixed-bed reactor 1 is 355℃, and the residence time of the mixed gas in the fixed-bed reactor 1 is 100s; The acetonitrile distillation column is configured with a top temperature of 82°C, a bottom temperature of 113°C, an internal absolute pressure of 72 kPa, and a reflux ratio of 3.2.

[0030] 3. Route 2 Route 2 is for the synthesis of acetamide. The mixed gas of Route 2 is fed into fixed-bed reactor 2. Under the action of catalyst 2, crude acetamide is produced. The crude acetamide is fed into an acetamide distillation column. After the acetamide solution is output from the bottom of the column, it is cooled, crystallized and centrifuged to obtain primary crystalline acetamide and primary mother liquor. Then the primary crystalline acetamide enters the recrystallization system. The material at the top of the tower is recycled to fixed-bed reactor 1 for reuse. The mother liquor enters the mother liquor recovery system; The catalyst 2 is Cu-Zn-γ-Al2O3. The preparation method is to add Cu(NO3)2, Zn(NO3)2 and γ-Al2O3 to deionized water, stir until completely mixed, filter, and calcine the filter cake at 650℃ for 0.6h under nitrogen atmosphere to obtain Cu-Zn-γ-Al2O3. The mass ratio of Cu(NO3)2, Zn(NO3)2, γ-Al2O3, and deionized water is 8:12:50:200; The temperature of the fixed-bed reactor 2 is 235°C, and the residence time of the mixed gas in the fixed-bed reactor 2 is 80s; The acetamide distillation column is configured with a top temperature of 93°C, a bottom temperature of 142°C, an internal absolute pressure of 65 kPa, and a reflux ratio of 4.1.

[0031] 4. Recrystallization system Acetamide that has undergone primary crystallization and recovered acetamide are added to deionized water. After heating to dissolve, cooling to crystallize, and centrifuging, acetamide and recrystallization mother liquor are obtained. The mass ratio of primary crystallization acetamide, recovered acetamide, and deionized water is 6.5:2.2:4. The heating and dissolving temperature is 65℃. The recrystallization mother liquor enters the mother liquor recovery system.

[0032] 5. Mother liquor recovery system The materials from the bottom of the tower in Route 1, the primary mother liquor from Route 2, and the recrystallization mother liquor are mixed in a mixing vessel and then evaporated and concentrated at 80°C. When the solid content reaches 32%, the mixture is cooled and crystallized, then centrifuged to obtain recovered acetamide and secondary mother liquor. The recovered acetamide is sent to the recrystallization system, and 60% wt of the secondary mother liquor is returned to the mixing vessel. The remaining portion is removed as waste mother liquor.

[0033] 6. Heating system The heating system is divided into Route 3 and Route 4. Route 3 uses high-temperature molten salt, while Route 4 uses high-pressure steam to provide heat for the entire system. In Route 3, the high-temperature molten salt first enters fixed-bed reactor 1 to provide heat for acetonitrile synthesis, and the remaining heat at the outlet of fixed-bed reactor 1 enters fixed-bed reactor 2 to provide heat for acetamide synthesis. The residual heat at the outlet of fixed-bed reactor 2 provides heat for the acetonitrile distillation column and the acetamide distillation column, and the residual heat at the outlet is combined and used for the recrystallization system; In Route 4, the high-pressure steam first preheats the acetic acid and liquid ammonia respectively through heat exchanger 1 and heat exchanger 2. The remaining heat from the outlets of heat exchanger 1 and heat exchanger 2 is combined and used for the mother liquor recovery system.

[0034] Comparative Example 1 Based on Example 1, route 2 and fixed-bed reactor 2 are omitted, and the catalysts used for the production of acetonitrile and acetamide are both catalyst 1 from Example 1. Specifically, the following modifications are made: 1. Production of acetonitrile Acetic acid and liquid ammonia are vaporized through heat exchanger 1 and heat exchanger 2 respectively, and heated to 180°C. After being mixed evenly in a gas mixer, they are fed into a fixed-bed reactor. Under the action of catalyst 1, they react to produce crude acetonitrile. The crude acetonitrile is fed into an ammonia absorption tower to remove ammonia, and then into an acetonitrile distillation tower. Acetonitrile is output from the top of the tower, and the material in the bottom of the tower is discharged into the mother liquor recovery system. The mass ratio of acetic acid to liquid ammonia is 3:1; The temperature of the fixed-bed reactor is 350℃, and the residence time of the mixed gas in the fixed-bed reactor is 80s; The acetonitrile distillation column is configured with a top temperature of 80°C, a bottom temperature of 110°C, an internal absolute pressure of 70 kPa, and a reflux ratio of 3.

[0035] 2. Production of acetamide Acetic acid and liquid ammonia are vaporized through heat exchanger 1 and heat exchanger 2 respectively, and heated to 180°C. After being mixed evenly in a gas mixer, they are fed into a fixed-bed reactor. Under the action of catalyst 1, they react to produce crude acetamide. The crude acetamide is fed into an acetamide distillation column. After the acetamide solution is output from the bottom of the column, it is cooled, crystallized, and centrifuged to obtain primary crystalline acetamide and primary mother liquor. Then the acetamide enters the recrystallization system. The primary mother liquor enters the mother liquor recovery system, and after evaporation, concentration, cooling, crystallization, and centrifugation, the recovered acetamide and secondary mother liquor are obtained. The recovered acetamide also enters the recrystallization system. 50% wt of the secondary mother liquor is reintroduced into the mother liquor recovery system, and the remainder is removed as waste mother liquor. The recrystallization system involves adding primary crystallized acetamide and recovered acetamide to deionized water, heating to dissolve, cooling to crystallize, and centrifuging to obtain acetamide and recrystallization mother liquor. The mass ratio of primary crystallized acetamide, recovered acetamide, and deionized water is 6:2:3, the heating and dissolving temperature is 60°C, and the recrystallization mother liquor enters the mother liquor recovery system. The mass ratio of acetic acid to liquid ammonia is 3:1; The temperature of the fixed-bed reactor is 230°C, and the residence time of the mixed gas in the fixed-bed reactor is 60s. The acetamide distillation column is configured with a top temperature of 90°C, a bottom temperature of 140°C, an internal absolute pressure of 60 kPa, and a reflux ratio of 4.

[0036] 3. Heating system The heating system is divided into Route 3 and Route 4. Route 3 uses high-temperature molten salt, while Route 4 uses high-pressure steam to provide heat for the entire system. In Route 3, the high-temperature molten salt first enters the fixed-bed reactor to provide heat for the synthesis of acetonitrile or acetamide. The residual heat at the outlet of the fixed-bed reactor enters the acetonitrile distillation column or the acetamide distillation column to provide heat. The residual heat at the outlet is then combined and used for the recrystallization system. In Route 4, the high-pressure steam first preheats the acetic acid and liquid ammonia respectively through heat exchanger 1 and heat exchanger 2. The remaining heat from the outlets of heat exchanger 1 and heat exchanger 2 is combined and used for the mother liquor recovery system.

[0037] Test case The yields and purity of acetonitrile and acetamide prepared in Examples 1-3 and Comparative Example 1, the lifetimes of catalyst 1 and catalyst 2, the total heat consumed in producing 1000 kg of acetonitrile and 1000 kg of acetamide, and the heat utilization rate were tested respectively.

[0038] The test results are shown in Table 1.

[0039] Table 1

[0040] The results above show that, compared with Examples 1 to 3, the purity and yield of acetonitrile and acetamide produced by Comparative Example 1 are not much different from those of Examples 1 to 3. However, since Comparative Example 1 uses catalyst 1 to produce both acetonitrile and acetamide, the service life of catalyst 1 is greatly shortened. Because Comparative Example 1 cannot produce acetonitrile and acetamide at the same time, the production time is extended, resulting in heat waste, high heat consumption, and low heat utilization.

Claims

1. A continuous method for preparing acetamide and acetonitrile, characterized in that: The preparation method includes: mixing, route 1, route 2, recrystallization system, mother liquor recovery system, and heating system; The mixing method is as follows: acetic acid and liquid ammonia are vaporized by passing them through heat exchanger 1 and heat exchanger 2 respectively, and heated to 160-200°C. After being mixed evenly in a gas mixer, the output mixed gas is divided into two routes, namely route 1 and route 2. Route 1 is acetonitrile synthesis. The mixed gas of Route 1 is fed into fixed-bed reactor 1. Under the action of catalyst 1, crude acetonitrile is produced by reaction. The crude acetonitrile is fed into an ammonia absorption tower to remove ammonia, and then fed into an acetonitrile distillation tower. Acetonitrile is output from the top of the tower. The material from the bottom of the column is discharged into the mother liquor recovery system; Route 2 is acetamide synthesis. The mixed gas of Route 2 is fed into fixed-bed reactor 2. Under the action of catalyst 2, crude acetamide is produced. The crude acetamide is fed into an acetamide distillation column. After the acetamide solution is output from the bottom of the column, it is cooled, crystallized, and centrifuged to obtain primary crystalline acetamide and primary mother liquor. Then the primary crystalline acetamide enters the recrystallization system. The material at the top of the tower is recycled to fixed-bed reactor 1 for reuse. The mother liquor enters the mother liquor recovery system; The heating system is divided into route 3 and route 4, where route 3 is high-temperature molten salt and route 4 is high-pressure steam, which provide heat for the entire system.

2. The method for preparing acetamide and acetonitrile in a continuous process according to claim 1, characterized in that: In the mixing method, the mass ratio of acetic acid to liquid ammonia is 54-66:17-21.

3. The method for preparing acetamide and acetonitrile in a continuous process according to claim 1, characterized in that: In route 1, the temperature of the fixed-bed reactor 1 is 345–355°C, and the residence time of the mixed gas in the fixed-bed reactor 1 is 60–100 s; the acetonitrile distillation column controls the top temperature to be 78–82°C, the bottom temperature to be 106–113°C, the absolute pressure inside the column to be 68–72 kPa, and the reflux ratio to be 2.8–3.

2.

4. The method for preparing acetamide and acetonitrile in a continuous process according to claim 1, characterized in that: In Route 1, catalyst 1 is La-Zr-γ-Al2O3, which is prepared by adding La(NO3)3, Zr(NO3)4, and γ-Al2O3 to deionized water, stirring until completely mixed, filtering, and calcining the filter cake at 450-550℃ for 0.7-0.9h under a nitrogen atmosphere to obtain La-Zr-γ-Al2O3. The mass ratio of La(NO3)3, Zr(NO3)4, γ-Al2O3, and deionized water is 12-14:6.5-7.5:40-50:170-200.

5. The method for continuous preparation of acetamide and acetonitrile according to claim 1, characterized in that: In route 2, the temperature of the fixed-bed reactor 2 is 225-235℃, and the residence time of the mixed gas in the fixed-bed reactor 2 is 40-80s; the acetamide distillation column controls the top temperature to be 86-93℃, the bottom temperature to be 135-142℃, the absolute pressure inside the column to be 55-65kPa, and the reflux ratio to be 3.8-4.

1.

6. The method for continuous preparation of acetamide and acetonitrile according to claim 1, characterized in that: In route 2, catalyst 2 is Cu-Zn-γ-Al2O3. The preparation method is as follows: Cu(NO3)2, Zn(NO3)2, and γ-Al2O3 are added to deionized water, stirred until completely mixed, filtered, and the filter cake is calcined at 550-650℃ for 0.4-0.6h under a nitrogen atmosphere to obtain Cu-Zn-γ-Al2O3. The mass ratio of Cu(NO3)2, Zn(NO3)2, γ-Al2O3, and deionized water is 6-8:10-12:40-50:160-200.

7. The method for preparing acetamide and acetonitrile in a continuous process according to claim 1, characterized in that: In the heating system, the high-temperature molten salt in route 3 first enters the fixed-bed reactor 1 to provide heat for acetonitrile synthesis, and the remaining heat at the outlet of the fixed-bed reactor 1 enters the fixed-bed reactor 2 to provide heat for acetamide synthesis. The residual heat at the outlet of fixed-bed reactor 2 provides heat for the acetonitrile distillation column and the acetamide distillation column, and the residual heat at the outlet is combined and used for the recrystallization system; In Route 4, the high-pressure steam first preheats the acetic acid and liquid ammonia respectively through heat exchanger 1 and heat exchanger 2. The remaining heat from the outlets of heat exchanger 1 and heat exchanger 2 is combined and used for the mother liquor recovery system.

8. The method for preparing acetamide and acetonitrile in a continuous process according to claim 1, characterized in that: The recrystallization system involves adding primary crystallized acetamide and recovered acetamide to deionized water, heating to dissolve, cooling to crystallize, and centrifuging to obtain acetamide and recrystallization mother liquor. The mass ratio of primary crystallized acetamide, recovered acetamide, and deionized water is 5.5–6.5:1.8–2.2:2–4. The heating and dissolving temperature is 55–65°C. The recrystallization mother liquor enters the mother liquor recovery system.

9. The method for preparing acetamide and acetonitrile in a continuous process according to claim 1, characterized in that: The mother liquor recovery system involves mixing the bottom material of Route 1, the primary mother liquor of Route 2, and the recrystallization mother liquor in a mixing vessel, then evaporating and concentrating them at 70–80°C. When the solid content reaches 28–32%, the mixture is cooled and crystallized, then centrifuged to obtain recovered acetamide and secondary mother liquor. The recovered acetamide enters the recrystallization system, and 40–60 wt% of the secondary mother liquor is reintroduced into the mixing vessel. The remaining portion is removed as waste mother liquor.

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