A diethyl carbonate heat pump distillation device and process

Abstract

The invention relates to the technical field of diethyl carbonate distillation, in particular to a diethyl carbonate heat pump distillation device and process. The device comprises the following steps: S1: using dimethyl carbonate and ethanol as reaction raw materials, a homogeneous complex formed by potassium carbonate and polyethylene glycol as a catalyst, and nitrogen as a driving gas to push part of the ethanol into a reaction distillation tower; S2: slowly conveying the dimethyl carbonate into the reaction distillation tower, maintaining the temperature at 65-75 DEG C, and reacting for 30-40 minutes. The device allows the dimethyl carbonate to react fully by slowly conveying the dimethyl carbonate into the ethanol and controlling the reaction temperature to be higher than the boiling point of methanol, thereby effectively reducing the concentrations of dimethyl carbonate and methanol, ensuring that the concentration of ethanol in the reaction distillation tower is always higher than that of dimethyl carbonate, facilitating the forward reaction; and volatilizing the generated methanol because the reaction temperature is higher than its boiling point, thereby reducing the chance of the methanol contacting the dimethyl carbonate, thereby reducing the formation of azeotropes, and improving the yield of diethyl carbonate.

Description

Technical Field

[0001] The invention relates to the technical field of diethyl carbonate distillation, in particular to a diethyl carbonate heat pump distillation device and process. Background Art

[0002] Diethyl carbonate is an important organic chemical product, widely used in industries such as synthetic lubricants, synthetic resins, and synthetic coatings. The processes for synthesizing diethyl carbonate include phosgene, transesterification, and methanol oxidative carbonylation. The phosgene method has many problems, such as a long process flow, high toxicity, and severe pollution. The methanol oxidative carbonylation method is prone to catalyst deactivation when synthesizing dimethyl carbonate (DMC), which affects the continuity and stability of production. This makes the method of producing diethyl carbonate through the transesterification reaction of dimethyl carbonate and ethanol safer and more stable. Furthermore, the reaction conditions are mild, and the reaction can be carried out under normal pressure with a reaction temperature not exceeding 80°C. The equipment requirements are not high, making it easy to implement in industry.

[0003] Dimethyl carbonate and ethanol are reacted to prepare diethyl carbonate. The reaction is carried out in the presence of a catalyst. The specific steps are as follows: first, dimethyl carbonate and ethanol are selected as reaction raw materials, with a molar ratio of ethanol to dimethyl carbonate of 6:1; a homogeneous complex formed by an alkali metal carbonate and polyethylene glycol (PEG) is used as a catalyst; the stoichiometric ratio of the catalyst to the reaction raw materials is 0.5%-2%, wherein the molar ratio of the alkali metal carbonate to the polyethylene glycol is 3:1 (the alkali metal carbonate can be one or more of sodium carbonate, potassium carbonate, or lithium carbonate); the reaction raw materials and the catalyst are added to a reactive distillation tower, and the reaction is carried out at atmospheric pressure at a temperature of 65-75°C for a reaction time of 30-60 minutes. After completion of the reaction, the reaction product mainly contains dimethyl carbonate, ethanol, ethyl methyl carbonate, diethyl carbonate, and methanol. Therefore, by distilling the reaction product, more precise separation can be achieved, thereby obtaining a high-purity diethyl carbonate product.

[0004] However, in the production process of diethyl carbonate, the reaction raw materials dimethyl carbonate and ethanol are usually directly added to the reaction distillation tower; this involves two reversible reactions. The first step is the reaction of dimethyl carbonate and ethanol to produce ethyl methyl carbonate and methanol, and the second step is the reaction of ethyl methyl carbonate with ethanol to produce diethyl carbonate and methanol.

[0005] In order to promote the continuous forward progress of the reaction, the reaction temperature needs to be controlled at a level higher than the boiling point of methanol. However, the methanol produced by the reaction easily forms an azeotrope with dimethyl carbonate, and the boiling point of the azeotrope is lower than that of methanol. As a result, during the reaction, the azeotrope formed by dimethyl carbonate and methanol is easily volatilized. As the azeotrope evaporates, the dimethyl carbonate in the reaction system continues to decrease, resulting in insufficient reaction raw materials, which in turn seriously affects the forward progress of the reaction and ultimately leads to a decrease in the yield of diethyl carbonate.

[0006] In view of this, in order to overcome the above technical problems, the present invention proposes a diethyl carbonate heat pump distillation device and process, which solves the above technical problems. Summary of the Invention

[0007] In order to overcome the deficiencies of the prior art, the present invention proposes a diethyl carbonate heat pump distillation device and process. The present invention adopts a method of slowly conveying dimethyl carbonate into ethanol and controls the reaction temperature to be higher than the boiling point of methanol, thereby allowing dimethyl carbonate to fully react and effectively reducing the concentrations of dimethyl carbonate and methanol in a local area. On the one hand, it ensures that the concentration of ethanol in the reaction distillation tower is always significantly higher than that of dimethyl carbonate, which is conducive to the forward reaction and promotes the reaction to more efficiently advance towards the production of diethyl carbonate. On the other hand, the generated methanol volatilizes rapidly because the reaction temperature is higher than its boiling point, greatly reducing the chance of its contact with dimethyl carbonate, thereby reducing the formation of azeotropes to a certain extent, and further improving the yield of diethyl carbonate.

[0008] The technical solution adopted by the present invention to solve the technical problem is: a diethyl carbonate heat pump distillation process according to the present invention comprises the following steps:

[0009] S1: dimethyl carbonate and ethanol are selected as reaction raw materials, the molar ratio of ethanol to dimethyl carbonate is 6:1, a homogeneous complex formed by potassium carbonate and polyethylene glycol is used as a catalyst, the stoichiometric ratio of the catalyst addition amount to the reaction raw materials is 0.5%-2%, and the molar ratio of the alkali metal carbonate to the polyethylene glycol is 3:1; nitrogen is used as a driving gas to drive the reaction raw materials into the reactive distillation column;

[0010] S2: First, the ethanol in the reaction raw material is divided into two parts in equal proportions, and one of the ethanol parts is added to the reaction distillation tower. At this time, the reaction temperature is controlled to rise to 65-75°C, and then the reaction raw material dimethyl carbonate is slowly transported to the reaction distillation tower. At this time, the first step of the reaction begins, and the reaction time is 30-40 minutes;

[0011] S3: After the first step of the reaction is completed, the temperature is maintained unchanged for 10-15 minutes, and then the reaction temperature is controlled to rise to 75-90°C, and the remaining ethanol is slowly added to the reactive distillation tower. At this time, the second step of the reaction begins, and the reaction time is 20-30 minutes;

[0012] S4: After the second step reaction, the temperature is maintained constant for 5-10 minutes, and then the temperature in the reaction distillation tower is controlled to rise to 110-120 ° C. At this time, distillation begins, and the distillation time is 20-30 minutes;

[0013] S5: After the distillation is completed, the temperature in the reaction distillation tower is controlled to drop to 50° C., and the solid catalyst in the product in the reaction distillation tower is filtered to obtain a high-purity diethyl carbonate product.

[0014] Preferably, in S2, before ethanol is added to the reaction distillation tower, nitrogen is first transported into the reaction distillation tower and the air in the reaction distillation tower is discharged.

[0015] Preferably, in S2, the temperature of the nitrogen is set to 65-75°C.

[0016] Preferably, in S3, the temperature of the nitrogen is set to 75-90°C.

[0017] A diethyl carbonate heat pump distillation device comprises a reaction distillation tower and a first condenser, a second condenser, and a third condenser connected to the reaction distillation tower. A heat exchanger and a heat pump are provided between the reaction distillation tower and the first condenser. A nitrogen tank is provided on one side of the reaction distillation tower; the nitrogen tank is connected to the heat exchanger via the nitrogen pump. The reaction distillation tower also comprises a tower body and a heat pump; the heat pump is used to provide heat to the bottom of the tower body.

[0018] Preferably, an air outlet is provided at the upper end of the tower body; an air inlet is provided at the bottom of the tower body; a raw material box is installed on the side wall of the tower body; a feed port is provided at the upper end of the raw material box; a discharge port is provided at the lower end of the raw material box; a connecting port is provided on the side wall of the tower body; the connecting port is connected to the feed port of the raw material box through a connecting pipe; a stirring rod and a crossbeam are provided inside the tower body; the crossbeam is fixedly connected to the outer wall of the tower body; a cavity is provided inside the crossbeam; the upper end of the stirring rod is rotatably connected to the upper end wall of the cavity; a bevel gear shaft and a bevel gear ring that mesh with each other are provided in the cavity; the bevel gear ring is fixedly connected to the stirring rod; the bevel gear shaft is rotatably and sealedly connected to the crossbeam; a drive motor is fixedly connected to the outer wall of the tower body; the output shaft of the drive motor is fixedly connected to the bevel gear shaft.

[0019] Preferably, the stirring rod includes a rotating rod and a blade; the rotating rod is connected to the bevel gear ring; a support rod is provided inside the tower body; the support rod is connected to the inner wall of the tower body; a circular groove is provided inside the support rod; the rotating rod is sealed in the circular groove; a cylindrical groove is provided inside the support rod; one end of the cylindrical groove is connected to the connecting port, and the other end is connected to the circular groove; an air duct connected to the circular groove is provided inside the rotating rod; and air holes connected to the air duct are provided on the surface of the blade.

[0020] Preferably, an air cavity is opened inside the blade; a rectangular tube connected to the air channel is slidingly and sealed inside the air cavity; a through groove connected to the air hole is opened on the surface of the rectangular tube; an electro-hydraulic push rod is arranged inside the air cavity; one end of the electro-hydraulic push rod is connected to the rectangular tube, and the other end is connected to the inner wall of the air cavity.

[0021] Preferably, the air holes are provided in two groups; one group of the air holes is opened on the upper surface of the blade; the other group of the air holes is opened on the lower surface of the blade; the two groups of the air holes are staggered.

[0022] Preferably, a nitrogen pipeline is installed on the side wall of the raw material box; the end of the nitrogen pipeline away from the raw material box is connected to the air inlet.

[0023] The beneficial effects of the present invention are as follows:

[0024] 1. The present invention adopts a method of slowly conveying dimethyl carbonate into ethanol and controlling the reaction temperature to be higher than the boiling point of methanol, thereby allowing dimethyl carbonate to fully react and effectively reducing the concentrations of dimethyl carbonate and methanol in a local area. On the one hand, it is ensured that the concentration of ethanol in the reactive distillation tower is always significantly higher than that of dimethyl carbonate, which is conducive to the forward reaction and promotes the reaction to more efficiently advance toward the direction of generating diethyl carbonate. On the other hand, the generated methanol volatilizes rapidly because the reaction temperature is higher than its boiling point, greatly reducing the chance of its contact with dimethyl carbonate, thereby reducing the formation of azeotropes to a certain extent, and further improving the yield of diethyl carbonate.

[0025] 2. The present invention sets a stirring rod so that during the process from the first step reaction to the second step reaction, the driving motor can drive the bevel gear ring through the bevel gear shaft to drive the stirring rod to rotate, so that the blades of the stirring rod rotate, so that the blades can stir the reactants in the tower body. On the one hand, the dimethyl carbonate and ethanol molecules collide with each other more frequently, increasing the chance of intermolecular contact, thereby accelerating the reaction. On the other hand, because the reactant concentration in some areas of the tower body is high, while the product concentration in other areas is low, stirring can effectively break this concentration gradient, so that the reactant concentration in each part of the system remains uniform, thereby avoiding the situation where the reaction rate is slowed down due to the local reactant concentration being too low, ensuring that the reaction can proceed at a relatively stable rate, and further improving the practicality of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0027] Figure 1 It is a process flow chart of the present invention;

[0028] Figure 2 It is a distillation system diagram of the reactive distillation tower used in the present invention;

[0029] Figure 3 is a perspective view of a reactive distillation column used in the present invention;

[0030] Figure 4 Schematic diagram of the structure of the reactive distillation tower used in the present invention;

[0031] Figure 5 yes Figure 4 Enlarged view of point A in the middle;

[0032] Figure 6 yes Figure 4 Enlarged view of point B in the middle;

[0033] Figure 7 is a partial cross-sectional view of the stirring rod used in the present invention;

[0034] Figure 8 yes Figure 7 Enlarged view of point C in the middle.

[0035] In the figure: 1. Reaction distillation tower; 11. Tower body; 111. Air outlet; 112. Air inlet; 12. Heat pump; 13. Raw material box; 131. Feed port; 132. Discharge port; 14. Connecting port; 141. Connecting pipe; 15. Stirring rod; 151. Rotating rod; 152. Blade; 153. Air duct; 154. Air hole; 155. Air cavity; 16. Crossbeam; 161. Cavity; 162. Bevel gear shaft; 163. Bevel gear ring; 164. Drive motor; 17. Support rod; 171. Circular groove; 172. Cylindrical groove; 18. Rectangular cylinder; 181. Through groove; 182. Electro-hydraulic push rod; 19. Nitrogen pipeline; 2. Condenser No. 1; 3. Condenser No. 2; 4. Condenser No. 3; 5. Heat exchanger; 6. Nitrogen tank; 61. Nitrogen pump. DETAILED DESCRIPTION

[0036] In order to make the technical means, creative features, objectives and effects achieved by the present invention easier to understand, the present invention is further described below in conjunction with specific implementation methods.

[0037] like Figures 1 to 8 As shown, the heat pump distillation process of diethyl carbonate described in the present invention comprises the following steps:

[0038] S1: dimethyl carbonate and ethanol are selected as reaction raw materials, the molar ratio of ethanol to dimethyl carbonate is 6:1, a homogeneous complex formed by potassium carbonate and polyethylene glycol is used as a catalyst, the stoichiometric ratio of the catalyst addition amount to the reaction raw materials is 0.5%-2%, and the molar ratio of the alkali metal carbonate to the polyethylene glycol is 3:1; nitrogen is used as a driving gas to drive the reaction raw materials into the reactive distillation column 1;

[0039] S2: First, the ethanol in the reaction raw material is divided into two parts in equal proportion, and one of the ethanol parts is added to the reaction distillation tower 1. At this time, the reaction temperature is controlled to rise to 65-75°C, and then the reaction raw material dimethyl carbonate is slowly transported to the reaction distillation tower 1. At this time, the first step of the reaction begins, and the reaction time is 30-40 minutes;

[0040] S3: After the first step of the reaction is completed, the temperature is maintained unchanged for 10-15 minutes, and then the reaction temperature is controlled to rise to 75-90°C, and the remaining ethanol is slowly added to the reaction distillation tower 1. At this time, the second step of the reaction begins, and the reaction time is 20-30 minutes;

[0041] S4: After the second step reaction is completed, the temperature is maintained unchanged for 5-10 minutes, and then the temperature in the reaction distillation tower 1 is controlled to rise to 110-120°C, at which time distillation begins, and the distillation time is 20-30 minutes;

[0042] S5: After the distillation is completed, the temperature in the reaction distillation tower 1 is controlled to drop to 50° C., and the solid catalyst in the product in the reaction distillation tower 1 is filtered to obtain a high-purity diethyl carbonate product.

[0043] As an embodiment of the present invention, in S2, before ethanol is added to the reaction distillation tower 1, nitrogen is first transported into the reaction distillation tower 1 and the air in the reaction distillation tower 1 is discharged.

[0044] As an embodiment of the present invention, in S2, the temperature of the nitrogen is set to 65-75°C.

[0045] As an embodiment of the present invention, in S3, the temperature of the nitrogen is set to 75-90°C.

[0046] During operation, in the production process of diethyl carbonate, the reaction raw materials dimethyl carbonate and ethanol are usually directly added to the reaction distillation tower 1; this involves two reversible steps. The first step is the reaction of dimethyl carbonate and ethanol to produce ethyl methyl carbonate and methanol, and the second step is the reaction of ethyl methyl carbonate with ethanol to produce diethyl carbonate and methanol.

[0047] In order to promote the continuous forward progress of the reaction, the reaction temperature needs to be controlled at a level higher than the boiling point of methanol. However, the methanol produced by the reaction easily forms an azeotrope with dimethyl carbonate, and the boiling point of the azeotrope is lower than that of methanol. As a result, during the reaction, the azeotrope formed by dimethyl carbonate and methanol is easily volatilized. As the azeotrope evaporates, the dimethyl carbonate in the reaction system continues to decrease, resulting in insufficient reaction raw materials, which in turn seriously affects the forward progress of the reaction and ultimately leads to a decrease in the yield of diethyl carbonate.

[0048] The present invention adopts a method of slowly conveying dimethyl carbonate into ethanol and controls the reaction temperature to be higher than the boiling point of methanol, thereby allowing dimethyl carbonate to fully react and effectively reducing the concentrations of dimethyl carbonate and methanol in a local area. On the one hand, it ensures that the concentration of ethanol in the reaction distillation tower 1 is always significantly higher than that of dimethyl carbonate, which is conducive to the forward reaction and promotes the reaction to more efficiently advance towards the direction of generating diethyl carbonate. On the other hand, the generated methanol volatilizes rapidly because the reaction temperature is higher than its boiling point, greatly reducing the chance of its contact with dimethyl carbonate, thereby reducing the formation of azeotropes to a certain extent, and further improving the yield of diethyl carbonate.

[0049] In the process of preparing diethyl carbonate by reacting dimethyl carbonate and ethanol, the ethanol used is mostly anhydrous ethanol. This is because in the transesterification reaction, the presence of water will bring many adverse effects. First, water will dilute ethanol and change its actual concentration in the reaction system, thereby interfering with the normal progress of the reaction, making it difficult for the reaction to proceed in the expected direction and rate. Second, water has the characteristic of promoting the hydrolysis reaction of esters, which will cause the generated ester products such as diethyl carbonate to decompose, thereby significantly reducing the yield of the target product. Therefore, before adding ethanol to the reaction distillation tower 1, nitrogen needs to be introduced into the reaction distillation tower 1. The specific method is to use a vacuum pump to extract the air in the reaction distillation tower 1 from the upper end of the reaction distillation tower 1, and nitrogen is added from the bottom of the reaction distillation tower 1, so that the nitrogen is filled in the reaction distillation tower 1. The air in the reaction distillation tower 1 is effectively discharged, so that an inert environment is formed inside the reaction distillation tower 1. This can not only prevent the moisture in the air from interfering with the esterification reaction, but also prevent ethanol from being oxidized to acetaldehyde by the oxygen in the air, thereby improving the purity of the raw materials, and thus improving the yield and purity of diethyl carbonate. Moreover, the temperature of the nitrogen delivered at this time is within the range of 65-75°C, so that the nitrogen at 65-75°C can not only preheat the reaction distillation tower 1, so that the reaction distillation tower 1 can quickly reach the appropriate reaction temperature, reduce the reaction startup time, and improve the reaction efficiency, but also accelerate the process of air discharge. While discharging the air, the inner wall of the reaction distillation tower 1 can also be kept dry, creating a more ideal environment for the reaction, and further ensuring the smooth progress of the reaction and the quality of the product.

[0050] After the nitrogen gas discharges the air in the reaction distillation tower 1, the user controls the nitrogen gas to transport the ethanol into the reaction distillation tower 1. By setting the reaction distillation tower 1 to be a heat pump 12 distillation tower, the heat pump 12 of the heat pump 12 distillation tower can heat the bottom of the tower body 11, so that the ethanol in the tower body 11 is heated to 65-75°C. Then, the nitrogen gas is controlled to slowly push the dimethyl carbonate into the reaction distillation tower 1 to carry out the first step of the reaction. Since the nitrogen temperature is 65-75°C, the nitrogen gas can preheat the pushed dimethyl carbonate, so that the dimethyl carbonate can quickly reach a suitable reaction temperature after entering the reaction distillation tower 1. The reaction temperature is lowered to a low temperature, thereby reducing the reaction startup time and improving the reaction efficiency. At this time, dimethyl carbonate and ethanol can react reversibly to generate ethyl methyl carbonate and methanol. Since the boiling point of methanol is 64.7°C, the rapidly generated methanol will volatilize due to heat, thereby reducing the chance of methanol and dimethyl carbonate coming into contact with each other, and reducing the azeotrope formed by dimethyl carbonate and methanol. In this way, as the amount of azeotrope formed is reduced, the problem of dimethyl carbonate loss caused by the volatilization of the azeotrope will also be significantly improved, allowing more dimethyl carbonate to fully participate in the reaction as a reaction raw material, thereby improving the utilization rate of dimethyl carbonate as a reaction raw material.

[0051] After the first step of the reaction is completed, the temperature is maintained unchanged for 10-15 minutes. On the one hand, this is to ensure that dimethyl carbonate and ethanol react repeatedly, and on the other hand, this is to allow the generated methanol to volatilize due to heat, thereby reducing the content of methanol in the product after the first step of the reaction is completed. The reaction temperature is then controlled to rise to 75-89°C, and then the second step of the reaction is carried out. Due to the increase in temperature, on the one hand, the chemical reaction rate is accelerated, that is, the thermal motion of the molecules is intensified, the effective collision frequency between the reactant molecules is increased, and the reaction rate is accelerated, thereby increasing the amount of diethyl carbonate generated per unit time. On the other hand, at a higher temperature, methanol will escape from the reaction system faster. According to Le Chatelier's principle, reducing the product concentration can shift the equilibrium toward the direction of generating the product, thereby facilitating the reaction. In the production of diethyl carbonate; in addition, the boiling point of dimethyl carbonate is 90°C, and the reaction temperature is controlled to be slightly lower than the boiling point of dimethyl carbonate in order to avoid the volatilization of dimethyl carbonate in the reaction product due to heat. This is because the first step reaction of dimethyl carbonate and ethanol to produce ethyl methyl carbonate and methanol is a reversible reaction. If the reaction temperature is higher than the boiling point of dimethyl carbonate, a large amount of dimethyl carbonate will be volatilized. If dimethyl carbonate cannot be replenished in time or effectively recycled, the concentration of dimethyl carbonate in the reaction system will decrease, affecting the progress of the first step reaction. Therefore, controlling the reaction temperature to rise to 75-89°C can avoid the decrease in the concentration of dimethyl carbonate, thereby maintaining the stable production of ethyl methyl carbonate and thereby improving the production efficiency of diethyl carbonate.

[0052] The reason why the ethanol in the reaction raw material is divided into two parts in equal proportion is that the boiling point of ethanol is 78.3°C. During the second step reaction, the reaction temperature rises to 75-89°C, which will cause ethanol to volatilize. Therefore, the second part of ethanol is controlled to be continuously filled into the reaction distillation tower 1, which can replenish the volatilized ethanol in time and increase the ethanol concentration, thereby ensuring that ethyl methyl carbonate and ethanol stably generate diethyl carbonate. After the second step reaction is completed, the reaction temperature is maintained unchanged for 10-15 minutes, so that the generated methanol and the ethanol in the tower body 11 are heated and completely volatilized. At this time, the temperature in the reaction distillation tower 1 is controlled to rise to 110-120°C, so that the distillation temperature The boiling point of the reaction distillation tower 1 is higher than that of ethyl methyl carbonate, dimethyl carbonate and ethanol, so that ethyl methyl carbonate and dimethyl carbonate are volatilized by heat. Since methanol is completely volatilized by heat, it is difficult for diethyl carbonate to undergo a reversible reaction. When the distillation is completed, ethyl methyl carbonate and dimethyl carbonate are completely volatilized. At this time, the temperature in the reaction distillation tower 1 is first controlled to drop to 50°C. This is because polyethylene glycol begins to melt between 60-70°C to form a viscous liquid. Therefore, the temperature in the reaction distillation tower 1 is controlled to drop to 50°C to solidify the polyethylene glycol, so as to facilitate the filtration of the homogeneous complex formed by potassium carbonate as a catalyst and polyethylene glycol, thereby obtaining a high-purity diethyl carbonate product.

[0053] A diethyl carbonate heat pump 12 distillation device includes a reaction distillation tower 1 and a first condenser 2, a second condenser 3, and a third condenser 4 connected to the reaction distillation tower 1. A heat exchanger 5 and a heat pump 12 are provided between the reaction distillation tower 1 and the first condenser 2. A nitrogen tank 6 is provided on one side of the reaction distillation tower 1; the nitrogen tank 6 is connected to the heat exchanger 5 via a nitrogen pump 61. The reaction distillation tower 1 also includes a tower body 11 and a heat pump 12; the heat pump 12 is used to provide heat to the bottom of the tower body 11.

[0054] During the first and second step reactions, the gaseous products generated by the reactions are first transported from the top of the reaction distillation tower 1 to the heat exchanger 5, and then transported to the condenser for condensation and separation. The nitrogen pump 61 transports the nitrogen in the nitrogen tank 6 to the heat exchanger 5 for preheating, and then transports it to the heat pump 12 for heating. Finally, the nitrogen heated by the heat pump 12 is transported into the reaction distillation tower 1. The reason for preheating the nitrogen is, on the one hand, to improve the utilization rate of thermal energy and reduce the loss of thermal energy. On the other hand, it is to enable the nitrogen to quickly reach the appropriate heating temperature due to preheating, thereby reducing the heating time of the heat pump 12 and thus reducing the energy consumption of the heat pump 12.

[0055] Since the temperature of the first step reaction is 65-75°C, the reaction temperature is only higher than the boiling point of methanol and the azeotrope of dimethyl carbonate and methanol. Therefore, the gaseous product components produced by the first step reaction are methanol and the azeotrope of dimethyl carbonate and methanol. The temperature of the second step reaction is 75-90°C, which is higher than the boiling point of methanol, dimethyl carbonate and methanol azeotrope and ethanol. Therefore, the gaseous products produced are methanol, dimethyl carbonate and methanol azeotrope and ethanol; the distillation temperature is 110-120°C, which is higher than the temperature of methanol, dimethyl carbonate and methanol azeotrope, ethanol and ethyl methyl carbonate, so the number of condensers is set to three, namely condenser No. 1 2, condenser No. 2 3 and condenser No. 3 4.

[0056] The gaseous product produced by the first step reaction is transported to the first condenser 2 for condensation. Since the boiling point of the azeotrope of dimethyl carbonate and methanol is lower than that of methanol, the condensation temperature of the first condenser 2 is controlled to be between the boiling point of the azeotrope of dimethyl carbonate and methanol and the boiling point of methanol, so that the methanol is condensed into a liquid state, and the methanol and the azeotrope formed by dimethyl carbonate and methanol are separated. The separated liquid methanol is recovered, and the azeotrope formed by dimethyl carbonate and methanol can be transported to a separation device. By adopting an azeotropic distillation method, an entrainer is added to the azeotrope, so that methanol and the entrainer form a new azeotrope with a lower azeotropic temperature than the original azeotrope, and the temperature difference between the new azeotrope and the original azeotrope is more than 10°C, thereby separating the dimethyl carbonate.

[0057] The gaseous products produced by the second step reaction are transported to the No. 2 condenser 3, and the condensation temperature of the No. 2 condenser 3 is 70°C, so that the condensation temperature of the No. 2 condenser 3 is lower than the boiling point of ethanol, thereby separating the ethanol in the gaseous products produced by the second step reaction, and the remaining gaseous methanol and dimethyl carbonate and methanol azeotrope are transported to the No. 1 condenser 2 for condensation and separation. Similarly, the gaseous products produced by distillation are directly transported to the No. 3 condenser 4, and the condensation temperature of the No. 3 condenser 4 is 100°C, so that the condensation temperature of the No. 3 condenser 4 is lower than the boiling point of ethyl methyl carbonate, so that ethyl methyl carbonate is condensed and separated, and the remaining gaseous products are transported to the No. 2 condenser 3 to separate ethanol. After the ethanol is separated, it is transported to the No. 1 condenser 2 to separate methanol.

[0058] As an embodiment of the present invention, the tower body 11 is provided with an air outlet 111 at the upper end; an air inlet 112 is provided at the bottom of the tower body 11; a raw material box 13 is installed on the side wall of the tower body 11; a feed port 131 is provided at the upper end of the raw material box 13; a discharge port 132 is provided at the lower end of the raw material box 13; a connecting port 14 is provided on the side wall of the tower body 11; the connecting port 14 is connected to the feed port 131 of the raw material box 13 through a connecting pipe 141; a stirring rod 15 and a horizontal Beam 16; the crossbeam 16 is fixedly connected to the inner wall of the tower body 11; a cavity 161 is formed inside the crossbeam 16; the upper end of the stirring rod 15 is rotatably connected to the upper end wall of the cavity 161; a bevel gear shaft 162 and a bevel gear ring 163 that mesh with each other are provided in the cavity 161; the bevel gear ring 163 is fixedly connected to the stirring rod 15; the bevel gear shaft 162 is rotatably and sealedly connected to the crossbeam 16; a drive motor 164 is fixedly connected to the outer wall of the tower body 11; the output shaft of the drive motor 164 is fixedly connected to the bevel gear shaft 162.

[0059] As an embodiment of the present invention, the stirring rod 15 includes a rotating rod 151 and a blade 152; the rotating rod 151 is connected to the bevel gear ring 163; a support rod 17 is provided inside the tower body 11; the support rod 17 is connected to the inner wall of the tower body 11; a circular groove 171 is provided inside the support rod 17; the rotating rod 151 is sealed and connected in the circular groove 171; a cylindrical groove 172 is provided inside the support rod 17; one end of the cylindrical groove 172 is connected to the connecting port, and the other end is connected to the circular groove 171; an air duct 153 connected to the circular groove 171 is provided inside the rotating rod 151; and an air hole 154 connected to the air duct 153 is provided on the surface of the blade 152.

[0060] As an embodiment of the present invention, an air cavity 155 is opened inside the blade 152; a rectangular tube 18 connected to the air duct 153 is slidingly and sealedly connected inside the air cavity 155; a through groove 181 connected to the air hole 154 is opened on the surface of the rectangular tube 18; an electro-hydraulic push rod 182 is arranged inside the air cavity 155; one end of the electro-hydraulic push rod 182 is connected to the rectangular tube 18, and the other end is connected to the inner wall of the air cavity 155.

[0061] As an embodiment of the present invention, the air holes 154 are provided in two groups; one group of the air holes 154 is opened on the upper surface of the blade 152; the other group of the air holes 154 is opened on the lower surface of the blade 152; the two groups of the air holes 154 are staggered.

[0062] As an embodiment of the present invention, a nitrogen pipeline 19 is installed on the side wall of the raw material box 13 ; one end of the nitrogen pipeline 19 away from the raw material box 13 is connected to the air inlet 112 .

[0063] During operation, electromagnetic valves are installed in the nitrogen pipeline 19, the air inlet 112, the air outlet 111, the feed port 131 and the discharge port 132. The user first controls the nitrogen pump 61 to transport nitrogen through the heat exchanger 5 to the heat pump 12, so that the heat pump 12 heats the nitrogen and heats it to 65-75°C. The electromagnetic valves in the air inlet 112 and the air outlet 111 are opened, and then the heated nitrogen is transported through the air inlet 112 into the reaction distillation tower 1, so that the nitrogen pushes the air in the reaction distillation tower 1 from bottom to top and is discharged from the air outlet 111. When the nitrogen fills the reaction distillation tower 1, the electromagnetic valve in the air outlet 111 is controlled to close, so that the reaction distillation tower 1 is filled with nitrogen. The nitrogen pressure in the tower 1 continues to increase. At this time, the solenoid valves in the feed port 131 and the discharge port 132 are controlled to open, so that the nitrogen in the reaction distillation tower 1 can flow into the air cavity 155 through the air holes 154 on the surface of the blade 152, and then enter the raw material box 13 through the air channel 153, the circular groove 171, the cylindrical groove 172 and the discharge port 132, so that the nitrogen entering the raw material box 13 pushes the air in the raw material box 13 from bottom to top to be discharged from the feed port 131. After the air in the raw material box 13 is completely discharged, the solenoid valves in the feed port 131 and the discharge port 132 are controlled to close. At this time, the air discharge in the reaction distillation tower 1 and the raw material box 13 is completed.

[0064] Then, the filling of raw materials is started. Since there are three raw material boxes 13, the conveying equipment for conveying dimethyl carbonate is connected to the feed port 131 of one of the raw material boxes 13, and then the solenoid valve in the feed port 131 is controlled to open. At this time, dimethyl carbonate is conveyed into the raw material box 13. In the process of dimethyl carbonate entering the raw material box 13, the nitrogen in the raw material box 13 will be squeezed, so that the nitrogen pressure in the raw material box 13 increases. By controlling the solenoid valve in the nitrogen pipeline 19 to open, a pressure relief valve is installed on one side of the nitrogen pipeline 19. Therefore, the user opens the pressure relief valve to allow the nitrogen with increased pressure to escape through the nitrogen pipeline 19 to ensure that the raw materials can flow into the raw material box 13 quickly and stably. Similarly, ethanol divided into two equal parts is added to the remaining two raw material boxes 13 respectively; then, the user first controls the solenoid valve in the discharge port 132 of one of the raw material boxes 13 containing ethanol to open, and controls the solenoid valve in the nitrogen pipeline 19 connected to the raw material box 13 to open, and starts the nitrogen pump 6 1, so that the nitrogen pump 61 delivers nitrogen through the nitrogen pipeline 19 into the raw material box 13, so that the ethanol in the raw material box 13 is pushed by the nitrogen and flows into the feed port 131, so that the ethanol flowing into the feed port 131 can flow into the communication port 14 through the connecting pipe, so that the ethanol flowing into the communication port 14 can flow into the circular groove 171 through the cylindrical groove 172, so that the ethanol entering the circular groove 171 flows into the air cavity 155 through the air channel 153 inside the rotating rod 151, and finally enters the rectangular cylinder 18. The rectangular cylinder 18 is connected to the air holes 154 of the blade 152 through the surface grooves 181, so that the ethanol entering the rectangular cylinder 18 flows into the tower body 11 through the grooves 181 and the air holes 154. When the ethanol in the raw material box 13 completely enters the interior of the tower body 11, the solenoid valve in the nitrogen pipeline 19 is controlled to be closed, and the solenoid valve in the air inlet 112 is controlled to be opened, so that the heat pump 12 transports nitrogen into the tower body 11 and provides heat to the tower body 11, so that the temperature inside the tower body 11 is maintained at 65-75°C.

[0065] When the temperature in the tower body 11 reaches 65-75°C, the solenoid valve in the discharge port 132 of the raw material box 13 containing dimethyl carbonate is controlled to open, and the solenoid valve in the nitrogen pipeline 19 connected to the raw material box 13 is controlled to open, and the nitrogen pump 61 is started, so that the nitrogen pump 61 delivers nitrogen through the nitrogen pipeline 19 into the raw material box 13, so that the ethanol in the raw material box 13 is pushed by the nitrogen and flows into the interior of the tower body 11 through the air holes 154 of the blade 152, starting the first step of the reaction. In the initial state, the through groove 181 at the upper end of the rectangular cylinder 18 is opposite to the air holes 154 at the upper end of the blade 152, so that the dimethyl carbonate can pass through the air holes 154 at the upper end of the blade 152. The nitrogen flows out through the air hole 154, and the nitrogen delivery rate is controlled to adjust the pushing rate of the nitrogen on the dimethyl carbonate, thereby controlling the reaction amount of the dimethyl carbonate entering the tower body 11 per unit time, so as to ensure that the dimethyl carbonate fully reacts. In addition, by arranging the dimethyl carbonate to be ejected through the air hole 154 on the upper end surface of the blade 152, the ejected dimethyl carbonate rises toward the ethanol liquid level, so that the dimethyl carbonate reacts with the ethanol during the rising process, and the methanol obtained by the reaction continues to evaporate upward due to the heat, thereby reducing the chance of methanol and dimethyl carbonate coming into contact, thereby reducing the formation of azeotropes to a certain extent, so that the yield of diethyl carbonate is further improved.

[0066] Similarly, when the first step of the reaction is completed, the solenoid valve in the discharge port 132 of the raw material box 13 containing the remaining ethanol is controlled to open, and the solenoid valve in the nitrogen pipeline 19 connected to the raw material box 13 is controlled to open, so that the nitrogen pushes the remaining ethanol into the tower body 11 for the second step of the reaction. At this time, it is necessary to control the extension of the electro-hydraulic push rod 182 so that the electro-hydraulic push rod 182 pushes the rectangular cylinder 18 to slide in the air cavity 155, so that the through groove 181 at the lower end of the rectangular cylinder 18 is aligned with the air hole 154 on the lower surface of the blade 152, so that the ethanol can be sprayed into the tower body 11 from the air hole 154 at the lower end of the blade 152, so that the ethanol sprayed into the tower body 11 will first flow toward the bottom of the tower body 11 under the action of inertia. At normal temperature and pressure, the density of dimethyl carbonate is about 1.07 g / cm³, the density of ethanol is about 0.789 g / cm³, and the density of diethyl carbonate is about 0.975 g / cm³. Since ethanol has the lowest density, ethanol will first fall due to inertia and then rise due to buoyancy. Since the reaction temperature in the second step is higher than the boiling point of ethanol, the ethanol that rises to the liquid surface of the reaction mixture will rise due to volatilization. In the present invention, by arranging ethanol to be sprayed from the lower end surface of the blade 152, the residence time of ethanol in the reaction mixture is extended, so that ethanol and the reactants can have more sufficient contact. In this way, the reaction is greatly promoted to proceed in the forward direction, the reaction rate is significantly accelerated, and the yield of diethyl carbonate is further improved.

[0067] The stirring rod 15 is provided so that during the first step reaction and the second step reaction, the driving motor 164 can drive the bevel gear ring 163 through the bevel gear shaft 162 to drive the stirring rod 15 to rotate, so that the blade 152 of the stirring rod 15 rotates, so that the blade 152 can stir the reactants in the tower body 11. On the one hand, the dimethyl carbonate and ethanol molecules collide with each other more frequently, increasing the chance of intermolecular contact, thereby accelerating the reaction. On the other hand, because the reactant concentration in some areas of the tower body 11 is high, while the product concentration in other areas is low, stirring can effectively break this concentration gradient, so that the reactant concentration in each part of the system remains uniform, thereby avoiding the situation where the reaction rate is slowed down due to the local reactant concentration being too low, ensuring that the reaction can proceed at a relatively stable rate, so that the practicality of the present invention is further improved.

[0068] The basic principles, main features, and advantages of the present invention are shown and described above. Those skilled in the art should understand that the present invention is not limited to the foregoing embodiments. The foregoing embodiments and descriptions are merely illustrative of the principles of the present invention. Various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention. Such changes and modifications are intended to fall within the scope of the present invention. The scope of protection claimed in the present invention is defined by the appended claims and their equivalents.

Claims

1. A diethyl carbonate heat pump distillation process, characterized in that: The following steps are involved: S1: dimethyl carbonate and ethanol are selected as reaction raw materials, the molar ratio of ethanol to dimethyl carbonate is 6:1, a homogeneous complex formed by potassium carbonate and polyethylene glycol is used as a catalyst, the stoichiometric ratio of the catalyst addition amount to the reaction raw materials is 0.5%-2%, wherein the molar ratio of alkali metal carbonate to polyethylene glycol is 3:1; nitrogen is used as a driving gas to drive the reaction raw materials into the reaction distillation tower (1); S2: First, the ethanol in the reaction raw material is divided into two parts in equal proportion, and one of the ethanol parts is added to the reaction distillation tower (1). At this time, the reaction temperature is controlled to rise to 65-75°C, and then the reaction raw material dimethyl carbonate is slowly transported to the reaction distillation tower (1). At this time, the first step of the reaction begins, and the reaction time is 30-40 minutes; S3: After the first step of the reaction is completed, the temperature is maintained constant for 10-15 minutes, and then the reaction temperature is controlled to rise to 75-90°C, and the remaining ethanol is slowly added to the reaction distillation tower (1). At this time, the second step of the reaction begins, and the reaction time is 20-30 minutes; S4: After the second step reaction is completed, the temperature is maintained constant for 5-10 minutes, and then the temperature in the reaction distillation tower (1) is controlled to rise to 110-120°C, at which time distillation begins, and the distillation time is 20-30 minutes; S5: After the distillation is completed, the temperature in the reaction distillation tower (1) is controlled to drop to 50° C., and the solid catalyst in the product in the reaction distillation tower (1) is filtered to obtain a high-purity diethyl carbonate product.

2. A diethyl carbonate heat pump distillation process according to claim 1, characterized in that: In the step S2, before ethanol is added to the reaction distillation tower (1), nitrogen is first fed into the reaction distillation tower (1) and the air in the reaction distillation tower (1) is exhausted.

3. A diethyl carbonate heat pump distillation process according to claim 2, characterized in that: In S2, the temperature of the nitrogen gas is set to 65-75°C.

4. A diethyl carbonate heat pump distillation process according to claim 3, characterized in that: In S3, the temperature of the nitrogen gas is set to 75-90°C.

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