A separation system and separation method for ethanol and diethyl acetal
By using acetonitrile as an azeotropic agent in the ethanol and acetal separation system, combined with azeotropic distillation and pressure swing distillation, the problem of difficult separation of ethanol and acetal was solved, and efficient, low-cost separation of high-purity acetal was achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- THE NORTHWEST RES INST OF CHEM IND
- Filing Date
- 2024-01-03
- Publication Date
- 2026-06-19
AI Technical Summary
Existing technologies struggle to effectively separate ethanol and acetal, especially since they form an azeotrope, making separation difficult. Furthermore, existing methods may result in acetal loss or excessively high separation costs.
Acetonitrile was used as an azeotropic agent, and the separation of ethanol and acetal was carried out in an acetal separation tower and an azeotropic agent recovery tower through a combination of one-step azeotropic distillation and pressure swing distillation. The separation of ethanol and acetal was optimized by using different tower settings and operating conditions.
It achieves the separation of high-purity acetal, reduces energy consumption and cost, improves separation efficiency, and the purity of acetal can reach over 99.5%.
Smart Images
Figure CN118022366B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of ethanol-acetal separation, specifically relating to a separation system and method for ethanol and acetal. Background Technology
[0002] Acetaldehyde, also known as diethoxyethane, has the molecular formula C6H. 14 O2, molecular weight: 118, CAS number: 105-57-7, colorless and transparent liquid, melting point -100℃, boiling point 102.7℃; miscible with alcohols and ethers, soluble in heptane, methylcyclohexane, and ethyl acetate, with solubility similar to diethyl ether; its solubility in water at 25℃ is 5%, and it can form an azeotrope with water, with an azeotropic point of 82.66℃ and an azeotropic composition of acetal 85.5% and water 14.5%; it can also form an azeotrope with ethanol, with an azeotropic point of 78℃ and an azeotropic composition of acetal 76% and ethanol 24%. Main uses: used in food additives, fuel additives, dye intermediates, cosmetics, and fragrances.
[0003] The main method for producing acetal currently involves using ethanol and acetaldehyde as raw materials, and carrying out a condensation reaction in a batch reactor under the catalysis of inorganic acids or Lewis acids (calcium chloride, ferric chloride, etc.). The product is then obtained after multiple subsequent separations. However, this reaction process is thermodynamically limited, generates a large amount of water, and acetal can form an azeotrope with ethanol and water, making separation difficult.
[0004] CN 103058837 A only provides a method for producing acetal, but does not provide a specific method for separating acetal and ethanol; CN107324977 A provides a method for purifying acetal by membrane filtration, but the technical cost of the filtration membrane is high. CN 103619791 A and CN 103781749 A mainly involve hydrogenation or hydrolysis to completely convert the acetal, thereby obtaining other substances with high purity, but this results in the complete loss of acetal. If the goal is to obtain acetal as a product for external sale, this technical route is unreasonable.
[0005] Therefore, it is of great significance to effectively separate ethanol and acetal. Summary of the Invention
[0006] To address the shortcomings of existing technologies, this invention provides a separation system and method for ethanol and acetal, using acetonitrile as an azeotropic agent. High-purity acetal is obtained through one-step azeotropic distillation, and then the azeotropic agent acetonitrile and ethanol are separated through pressure swing distillation.
[0007] An ethanol and acetal separation system includes an acetal separation tower. The acetal separation tower has a raw material inlet and an azeotropic agent inlet on its tower wall. The raw material inlet is located in the middle of the tower wall, and the azeotropic agent inlet is located below the raw material inlet. An azeotropic agent recovery tower is connected to the top of the acetal separation tower. Both the acetal separation tower and the azeotropic agent recovery tower have outlets at their bottoms.
[0008] Preferably, one azeotropic agent recovery tower is provided.
[0009] Preferably, there are one or two azeotropic agent recovery towers, namely a first azeotropic agent recovery tower and a second azeotropic agent recovery tower. The top of the acetal separation tower is connected to the first azeotropic agent recovery tower, and the top of the first azeotropic agent recovery tower is connected to the second azeotropic agent recovery tower.
[0010] Preferably, the number of trays in the acetal separation tower is 20-40, and the number of trays in the azeotropic agent recovery tower is 20-30.
[0011] Preferably, the acetal separation tower has 30 trays, starting from the top tray. The raw material inlet is located on the 15th tray of the tower wall, and the azeotropic agent inlet is located on the 20th tray of the tower wall.
[0012] A method for separating ethanol and acetal, using the above-mentioned separation system, is as follows: The raw material and azeotropic agent enter the acetal separation tower through the raw material inlet and azeotropic agent inlet, respectively. The pressure of the acetal separation tower is 1-10 bar, the top temperature of the acetal separation tower is 90-96℃, the bottom temperature is 120-130℃, and the reflux ratio of the acetal separation tower is 2-20. The bottom product is acetal, which is discharged from the bottom outlet. The top product is a mixture of ethanol and azeotropic agent, which enters the azeotropic agent recovery tower. The raw material is a mixture of ethanol and acetal, and the azeotropic agent is acetonitrile. The feed ratio of the azeotropic agent to ethanol is 0.1-1.
[0013] Preferably, the azeotropic agent recovery tower is provided in one unit, the pressure of the azeotropic agent recovery tower is 30-50 bar, the top temperature of the azeotropic agent recovery tower is 210-220°C, the bottom temperature is 250-270°C, and the reflux ratio of the azeotropic agent recovery tower is 15-30; the top product of the azeotropic agent recovery tower is ethanol, and the bottom product is the azeotropic agent.
[0014] Preferably, the azeotropic agent recovery tower is provided with two towers, namely a first azeotropic agent recovery tower and a second azeotropic agent recovery tower. The top of the acetal separation tower is connected to the first azeotropic agent recovery tower, and the top of the first azeotropic agent recovery tower is connected to the second azeotropic agent recovery tower. The top product of the acetal separation tower enters the first azeotropic agent recovery tower. After separation in the first azeotropic agent recovery tower, a portion of the azeotropic agent is discharged from the bottom outlet of the first azeotropic agent recovery tower, while the ethanol and the remaining azeotropic agent are discharged from the top of the first azeotropic agent recovery tower and enter the second azeotropic agent recovery tower. In the second azeotropic agent recovery tower, the remaining azeotropic agent is discharged from the bottom outlet of the second azeotropic agent recovery tower after separation, and the ethanol is discharged from the top outlet of the second azeotropic agent recovery tower. The pressure of both the first and second azeotropic agent recovery towers is 15-25 bar, the top temperature of both towers is 160-185℃, the bottom temperature of both towers is 195-220℃, and the reflux ratio of both towers is 1-10.
[0015] Preferably, the pressure of the azeotropic agent recovery tower is 40 bar, the top temperature of the azeotropic agent recovery tower is 216°C, the bottom temperature of the azeotropic agent recovery tower is 260°C, and the reflux ratio of the azeotropic agent recovery tower is 20.
[0016] Preferably, the pressure of both the first azeotropic agent recovery tower and the second azeotropic agent recovery tower is 20 bar, the top temperature of both the first azeotropic agent recovery tower and the second azeotropic agent recovery tower is 181°C, the bottom temperature is 205-215°C, the reflux ratio of the first azeotropic agent recovery tower is 5, and the reflux ratio of the second azeotropic agent recovery tower is 10.
[0017] More preferably, the feed ratio of the azeotropic agent to ethanol is 0.5.
[0018] Advantages of this invention:
[0019] This invention uses acetonitrile as an azeotropic agent to obtain high-purity acetal through one-step azeotropic distillation, and then separates the azeotropic agent acetonitrile and ethanol through pressure swing distillation. Attached Figure Description
[0020] Figure 1 A schematic diagram of the structure of one embodiment of the present invention;
[0021] Figure 2 A schematic diagram of another embodiment of the present invention;
[0022] Among them, 1-acetal separation tower, 2-raw material inlet, 3-azeotropic agent inlet, 4-azeotropic agent recovery tower, 5-first azeotropic agent recovery tower, and 6-second azeotropic agent recovery tower. Detailed Implementation
[0023] Example 1
[0024] An ethanol and acetal separation system includes an acetal separation tower 1. The tower wall of the acetal separation tower 1 is provided with a raw material inlet 2 and an azeotropic agent inlet 3. The raw material inlet 2 is located in the middle of the tower wall, and the azeotropic agent inlet 3 is positioned lower than the raw material inlet 2. An azeotropic agent recovery tower 4 is connected to the top of the acetal separation tower. Both the acetal separation tower 1 and the azeotropic agent recovery tower 4 have outlets at their bottoms. One azeotropic agent recovery tower 4 is provided.
[0025] Preferably, the number of trays in the acetal separation tower 1 is 20-40, and the number of trays in the azeotropic agent recovery tower 4 is 20-30.
[0026] More preferably, the number of trays in the acetal separation tower 1 is 30, starting from the top tray. The raw material inlet 2 is located at the 15th tray on the tower wall, and the azeotropic agent inlet 3 is located at the 20th tray on the tower wall.
[0027] Example 2
[0028] An ethanol and acetal separation system includes an acetal separation tower 1. The tower wall of the acetal separation tower 1 is provided with a raw material inlet 2 and an azeotropic agent inlet 3. The raw material inlet 2 is located in the middle of the tower wall, and the azeotropic agent inlet 3 is positioned lower than the raw material inlet 2. The top of the acetal separation tower is connected to two azeotropic agent recovery towers, namely a first azeotropic agent recovery tower 5 and a second azeotropic agent recovery tower 6. The top of the acetal separation tower is connected to the first azeotropic agent recovery tower 5, and the top of the first azeotropic agent recovery tower 5 is connected to the second azeotropic agent recovery tower 6. The bottoms of the acetal separation tower 1, the first azeotropic agent recovery tower 5, and the second azeotropic agent recovery tower 6 are all provided with outlets.
[0029] Preferably, the number of trays in the acetal separation tower 1 is 20-40, and the number of trays in the first azeotropic agent recovery tower 5 and the second azeotropic agent recovery tower 6 is 20-30.
[0030] More preferably, the number of trays in the acetal separation tower 1 is 30, starting from the top tray. The raw material inlet 2 is located at the 15th tray on the tower wall, and the azeotropic agent inlet 3 is located at the 20th tray on the tower wall.
[0031] Example 3
[0032] A method for separating ethanol and acetal, using the separation system described in Example 1, is as follows: The raw material and azeotropic agent enter the acetal separation tower 1 through the raw material inlet 2 and azeotropic agent inlet 3, respectively. The pressure of the acetal separation tower 1 is 1-10 bar, the top temperature of the acetal separation tower 1 is 90-96℃, the bottom temperature is 120-130℃, and the reflux ratio of the acetal separation tower 1 is 2-20. The bottom product is acetal, which is discharged from the bottom outlet. The top product is a mixture of ethanol and azeotropic agent, which enters the azeotropic agent recovery tower 4. Ethanol is then separated from the azeotropic agent... The azeotropic agent is discharged from the top of the azeotropic agent recovery tower 4, and the azeotropic agent is discharged from the bottom product. The raw material is a mixture of ethanol and acetal, derived from the ethanol dehydrogenation to acetaldehyde process, with feed rates of 95 kg / h for ethanol and 5 kg / h for acetal. The azeotropic agent is acetonitrile. The feed ratio of the azeotropic agent to ethanol is 0.1-1. The pressure of the azeotropic agent recovery tower 4 is 30-50 bar, the top temperature of the azeotropic agent recovery tower 4 is 210-220℃, the bottom temperature is 250-270℃, and the reflux ratio of the azeotropic agent recovery tower 4 is 15-30.
[0033] The acetal separation tower 1 has 30 trays, the raw material inlet 2 is located on the 15th tray of the tower wall, and the azeotropic agent inlet 3 is located on the 20th tray of the tower wall. The bottom temperature of the acetal separation tower 1 is 128℃ and the top temperature is 93℃. The azeotropic agent recovery tower 4 has 30 trays. The separation effect of the acetal separation tower under different process conditions is shown in Table 1.
[0034] Table 1. Different reaction conditions and separation results of the acetal separation tower
[0035] .
[0036] As can be seen from reactions 1-3, the higher the reflux ratio, the higher the purity of acetal at the bottom of acetal separation tower 1. However, an increase in the reflux ratio means an increase in energy consumption. Therefore, the preferred reflux ratio for acetal separation tower 1 is 5.
[0037] As can be seen from reactions 4-8, the purity of acetal at the bottom of acetal separation tower 1 increases with the increase of the acetonitrile feed rate of the azeotropic agent. However, when the acetal feed rate exceeds 50, the change is very small. Therefore, 48 kg / h is preferred, that is, the mass ratio of azeotropic agent to ethanol is preferably 0.5.
[0038] As can be seen from reaction 9-11, the higher the pressure, the higher the purity of acetal at the bottom of acetal separation tower 1. However, the purity of acetal reaches 99.5% at a pressure of 2 bar. Therefore, considering energy consumption, the preferred pressure is 2 bar.
[0039] As can be seen from reaction 12, when the acetonitrile feed rate is only 19 kg / h, the purity of acetal at the bottom of T1 column can also reach more than 95% by increasing the pressure.
[0040] Based on reaction 2 in Table 1, the top temperature of the azeotropic agent recovery tower 4 is 216℃, the bottom temperature is 260℃, the reflux ratio of the azeotropic agent recovery tower 4 is 20, and the recovery rate and accuracy of ethanol can both reach over 99.5%.
[0041] Example 4
[0042] A method for separating ethanol and acetal, using the separation system described in Example 2, is as follows: The raw material and azeotropic agent enter the acetal separation tower 1 through the raw material inlet 2 and azeotropic agent inlet 3, respectively. The pressure of the acetal separation tower 1 is 2 bar, the top temperature is 93°C, the bottom temperature is 128°C, and the reflux ratio is 5. The bottom product is acetal, which is discharged from the bottom outlet. The top product is a mixture of ethanol and azeotropic agent, which enters the first azeotropic agent recovery tower 5. After separation in the first azeotropic agent recovery tower 5, a portion of the azeotropic agent is discharged from the bottom outlet, while the ethanol and the remaining azeotropic agent are discharged from the top of the first azeotropic agent recovery tower 5 and enter the second azeotropic agent recovery tower 6. After separation in the second azeotropic agent recovery tower 6, the remaining azeotropic agent is discharged from the bottom outlet of the second azeotropic agent recovery tower 6, and ethanol is discharged from the top outlet of the second azeotropic agent recovery tower 6. The raw material is a mixture of ethanol and acetal, derived from the ethanol dehydrogenation to acetaldehyde process, with feed rates of 95 kg / h for ethanol and 5 kg / h for acetal. The azeotropic agent is acetonitrile. The mass ratio of the azeotropic agent to ethanol is 0.5. The pressure of both the first azeotropic agent recovery tower 5 and the second azeotropic agent recovery tower 6 is 20 bar. The top temperature of both towers is 181°C, and the bottom temperature is 205-215°C. The reflux ratio of the first azeotropic agent recovery tower 5 is 5, and the reflux ratio of the second azeotropic agent recovery tower 6 is 10.
[0043] The purity of acetal discharged from the bottom of acetal separation tower 1 is 99.90%; the bottom of the first azeotropic agent recovery tower 5 is mainly acetonitrile, and the remaining acetonitrile and ethanol are mixed and flow out from the top of the first azeotropic agent recovery tower 5; the bottom of the second azeotropic agent recovery tower 6 is mainly residual acetonitrile, and the top is mainly ethanol, which is recycled as a reaction raw material; the recovery rate and recovery accuracy of ethanol can both reach over 99.5%.
[0044] Therefore, in order to reduce the temperature and pressure of the tower and reduce the reflux ratio, two azeotropic agent recovery towers can be set up. The first azeotropic agent recovery tower 5 is equivalent to coarse separation, and the second azeotropic agent recovery tower 6 is equivalent to fine separation. By setting up two towers, the temperature and pressure of the azeotropic agent recovery tower can be reduced, while achieving a separation effect similar to that of a single separation tower.
[0045] Comparative Example 1
[0046] Based on reaction 2 in Table 1 of Example 3, different azeotropic agents were used, and everything else was the same as reaction 2. The effect of different azeotropic agents on the purity of acetal at the bottom of the acetal recovery tower is shown in Table 2.
[0047] Table 2. Effect of different azeotropic agents on the purity of acetal at the bottom of the acetal recovery tower.
[0048] .
[0049] As can be seen from the above comparative examples, the best azeotropic agent is 1,4-dioxane in Comparative Reaction 1, but the purity of the acetal obtained at the bottom of column T1 is only 19.23%, with most of the 1,4-dioxane still being discharged from the top of the column as a mixture with ethanol. Other common azeotropic agents are also difficult to use. Acetonitrile, in particular, is similar; substances containing one or more CN bonds (the extractant in Comparative Reaction 9 contains one CN bond, and the azeotropic agents in Comparative Reaction 7-8 contain two CN bonds) also have virtually no separation effect on the above systems. Acetonitrile has a boiling point of 81℃, which is relatively close to the boiling point of acetal in Comparative Reaction 10-12 (acetal has a boiling point of 103℃, and ethanol has a boiling point of 78℃), but the separation effect is still poor. Therefore, using acetonitrile as an azeotropic agent can achieve the purification and separation of acetal and ethanol.
Claims
1. A process for separating ethanol and diethyl acetal, characterized by: The separation system employs ethanol and acetal, specifically as follows: The raw material and azeotropic agent enter the acetal separation tower through the raw material inlet and azeotropic agent inlet, respectively. The pressure of the acetal separation tower is 1-10 bar, the top temperature is 90-96℃, the bottom temperature is 120-130℃, and the reflux ratio is 2-20. The bottom product is acetal, which is discharged from the bottom outlet. The top product is a mixture of ethanol and azeotropic agent, which enters the azeotropic agent recovery tower. The raw material is a mixture of ethanol and acetal, and the azeotropic agent is acetonitrile. The feed ratio of the azeotropic agent to ethanol is 0.1-1. The ethanol and acetal separation system includes an acetal separation tower. The acetal separation tower has a raw material inlet and an azeotropic agent inlet on its tower wall. The raw material inlet is located in the middle of the tower wall, and the azeotropic agent inlet is located lower than the raw material inlet. An azeotropic agent recovery tower is connected to the top of the acetal separation tower. Both the acetal separation tower and the azeotropic agent recovery tower have outlets at their bottoms.
2. The method for separating ethanol and acetal according to claim 1, characterized in that: One azeotropic agent recovery tower is provided.
3. The separation method of ethanol and acetal according to claim 1, characterized by: The azeotropic agent recovery tower is provided in two parts, namely the first azeotropic agent recovery tower and the second azeotropic agent recovery tower. The top of the acetal separation tower is connected to the first azeotropic agent recovery tower, and the top of the first azeotropic agent recovery tower is connected to the second azeotropic agent recovery tower.
4. The method of separating ethanol and diethyl acetal according to claim 1, characterized in that: The number of trays in the acetal separation tower is 20-40, and the number of trays in the azeotropic agent recovery tower is 20-30.
5. The method of separating ethanol and diethyl acetal according to claim 4, characterized in that: The acetal separation tower has 30 trays, starting from the top tray. The raw material inlet is located on the 15th tray of the tower wall, and the azeotropic agent inlet is located on the 20th tray of the tower wall.
6. The method for separating ethanol and acetal according to claim 1, 4, or 5, characterized in that: The azeotropic agent recovery tower is provided in one unit. The pressure of the azeotropic agent recovery tower is 30-50 bar. The top temperature of the azeotropic agent recovery tower is 210-220℃, the bottom temperature is 250-270℃, and the reflux ratio of the azeotropic agent recovery tower is 15-30. The top product of the azeotropic agent recovery tower is ethanol, and the bottom product is the azeotropic agent.
7. The separation method of ethanol and diethyl acetal according to claim 1 or 4 or 5, characterized in that: The azeotropic agent recovery tower is provided with two towers: a first azeotropic agent recovery tower and a second azeotropic agent recovery tower. The top of the acetal separation tower is connected to the first azeotropic agent recovery tower, and the top of the first azeotropic agent recovery tower is connected to the second azeotropic agent recovery tower. The top product of the acetal separation tower enters the first azeotropic agent recovery tower. After separation in the first azeotropic agent recovery tower, a portion of the azeotropic agent is discharged from the bottom outlet of the first azeotropic agent recovery tower, while ethanol and the remaining azeotropic agent are discharged from the top of the first azeotropic agent recovery tower and enter the second azeotropic agent recovery tower. After separation in the second azeotropic agent recovery tower, the remaining azeotropic agent is discharged from the bottom outlet of the second azeotropic agent recovery tower, and ethanol is discharged from the top of the second azeotropic agent recovery tower. The pressure of both the first and second azeotropic agent recovery towers is 15-25 kcal. The top temperature of both the first and second azeotropic agent recovery towers is 160-185℃, and the bottom temperature is 195-220℃. The reflux ratio of both the first and second azeotropic agent recovery towers is 1-10.
8. The method of separating ethanol and diethyl acetal according to claim 6, characterized in that: The pressure of the azeotropic agent recovery tower is 40 bar, the top temperature of the azeotropic agent recovery tower is 216°C, the bottom temperature of the tower is 260°C, and the reflux ratio of the azeotropic agent recovery tower is 20.
9. The separation method of ethanol and diethyl acetal according to claim 7, characterized by: The pressure of both the first and second azeotropic agent recovery towers is 20 bar. The top temperature of both towers is 181°C and the bottom temperature is 205-215°C. The reflux ratio of the first azeotropic agent recovery tower is 5, and the reflux ratio of the second azeotropic agent recovery tower is 10.