Separation method of toluene and n-butyl alcohol

Abstract

The invention belongs to the field of chemical engineering, and particularly relates to a separation device and a separation method for separating a toluene and n-butyl alcohol mixture through low-temperature water washing. According to the method, different intersolubility changes of toluene and n-butanol in water at different temperatures are mainly utilized, n-butanol is washed into water in a low-temperature water washing standing layering mode, and then water and n-butanol are separated through rectification; according to the method, a third medium (containing water in a mixed solvent of methylbenzene and n-butyl alcohol) is not introduced, so that the secondary treatment difficulty and potential quality hazards are not increased; the processing mode is simple, the hardware investment cost is low, the low-temperature refrigerant is common in chemical enterprises, and old and existing equipment can be easily utilized in the chemical enterprises; the operation mode is simple, and the operation control difficulty is low.

Description

Technical Field

[0001] The invention belongs to the field of chemical engineering, and in particular relates to a separation device and a separation method for separating a mixture of toluene and n-butanol by low-temperature water washing. Background Art

[0002] As we all know, toluene and n-butanol are widely used as chemical raw materials in chemical production, but they are mutually soluble and azeotropic (azeotropic point is 105℃, and the mass fraction of toluene in the azeotropic is 0.73), so the separation of toluene and n-butanol has become a headache in chemical production. At present, the two methods that are actually used in the industry are mainly extractive distillation separation and pressure swing distillation separation.

[0003] 1. The most common method of separating toluene and n-butanol by extractive distillation is to introduce dimethyl sulfoxide as the extractant. This method uses dimethyl sulfoxide as the extractant, which is introduced from the top of the extractive distillation tower so that it is in full contact with the toluene and n-butanol mixture introduced from the middle of the extractive distillation tower. After extractive distillation, toluene is extracted from the top of the extractive distillation tower, and the extractant and n-butanol mixture enter the extractant recovery tower from the bottom of the extractive distillation tower. After effective separation, n-butanol is extracted from the top of the extractant recovery tower, and the extractant is extracted from the bottom of the extractant recovery tower and recycled. This process has the advantages of low energy consumption, simple process, and high separation purity; but the disadvantages of this process are also obvious, mainly the introduction of a third medium, and the residue of the extractant is not accepted in many chemical reactions, especially in the fine chemical industry. Therefore, there are still certain limitations in the actual application of this method; 2. Pressure swing distillation to separate toluene and n-butanol. This process is theoretically feasible. At present, there is no news of engineering realization in the market. It is mainly based on the feasibility level of system simulation verification. For example, based on technical feasibility and energy saving considerations, the separation of toluene-n-butanol system is systematically studied by pressure swing distillation and heat integration process. Based on the Aspen Plus simulation platform, the NRTL physical property method is used to simulate and calculate the azeotropic data of toluene-n-butanol under different pressures. By examining the degree of deviation of the azeotropic composition under different pressures, it is shown that the system is pressure sensitive, and the pressure swing distillation separation process is determined. For the pressure swing separation of different proportions of toluene and n-butanol under different operating pressures, multi-stage distillation towers are basically used in series with pressure swing distillation. The main reason is that the concentration ratios of the materials to be treated by various companies on the market are different. The initial design investment cost of this method is relatively high, the operating technology requirements are difficult, and the separation purity is also yet to be verified, so few people in the industry give priority to this method. Summary of the invention

[0004] In order to solve the above problems, the present invention discloses a method for separating toluene from n-butanol. The method mainly utilizes the different solubilities of toluene and n-butanol in water. Toluene is slightly soluble in water, and the lower the temperature, the smaller the solubility. On the contrary, n-butanol has a certain solubility in water, and the lower the temperature, the greater the solubility. The method is shown in Table 1 below.

[0005] Table 1 temperature Solubility of n-butanol in water Solubility of toluene in water 0℃ 8.5g / ml / 10℃ 7g / ml / 16℃ / 0.047g / ml 20℃ 5.8g / ml 0.05g / ml 30℃ 4.8g / ml 0.057g / ml 50℃ 3.4g / ml 0.068g / ml 70℃ 2.4g / ml 0.083g / ml The invention mainly utilizes the different mutual solubility changes of toluene and n-butanol in water at different temperatures, adopts the static stratification method of low-temperature water washing to wash n-butanol into water, and then separates water and n-butanol by distillation.

[0006] To achieve the above object, the technical solution of the present invention is as follows: One object of the present invention is to provide a separation device for separating a mixture of toluene and n-butanol by low-temperature water washing, comprising a low-temperature water washing layered kettle, a distillation tower, a condenser, a reflux tank, and a distillation tower kettle. After the low-temperature water washing layered kettle is treated, the distillation tower kettle is removed. The distillation tower kettle is connected to the distillation tower. The top of the distillation tower is connected to the condenser, the condenser is connected to the reflux tank, the reflux tank is connected to the distillation tower kettle, and the reflux tank is also connected to the distillation tower. The gas phase on the distillation tower kettle enters the distillation tower, the gas phase on the top of the distillation tower is condensed by the condenser and enters the reflux tank, and the n-butanol on the upper layer of the reflux tank is refluxed back to the distillation tower kettle and the lower layer of water is decontaminated.

[0007] A second object of the present invention is to provide a method for separating a mixture of toluene and n-butanol by low-temperature water washing using a separation device as described above, comprising the following steps: Add the mixed solution of toluene and n-butanol into a low-temperature water washing and layering kettle, start stirring after adding water, cool to -5~0°C, continue stirring for 0.5~1h, let stand for 1~1.5h, and separate to obtain the toluene phase on the upper layer and the mixture of water and n-butanol on the lower layer; The mixture of water and n-butanol in the lower layer enters the kettle of the distillation tower, and the water is fully refluxed under normal pressure. The water is discharged through the reflux tank, and the n-butanol in the upper layer continues to return to the kettle of the distillation tower to azeotropize with water. When the kettle temperature of the distillation tower reaches 118°C, the reflux at the top of the distillation tower is stopped. When the top temperature of the distillation tower rises to 115°C, the reflux with water ends, and the kettle contains n-butanol. The distilled water is used as sewage for biochemical treatment.

[0008] Furthermore, in step (1), in the mixed solution of toluene and n-butanol, the mass percentage of toluene is ≥70%, and the mass percentage of n-butanol is ≤30%.

[0009] Furthermore, in step (1), the mass ratio of water to the mixed solution of toluene and n-butanol is 4-6:1.

[0010] Furthermore, step (2) further comprises the following steps: the mixture of water and n-butanol in the lower layer enters the distillation system, and the water is fully refluxed under normal pressure, and the water is discharged through the reflux separator tank, and the n-butanol in the upper layer continues to return to the distillation tower kettle to azeotropize with water until the water content in the system is ≤0.3% and the reflux water is completed.

[0011] The third object of the present invention is to provide an application of water as a separation medium for separating a mixed solution of toluene and n-butanol under low temperature conditions.

[0012] Furthermore, in the application, the mass ratio of water to the mixed solution of toluene and n-butanol is 4~6:1, the separation temperature is -5~0°C, and the separation time is 1~1.5h.

[0013] The beneficial effects of the present invention are: Not introducing a third medium (the mixed solvent of toluene and n-butanol contains water itself) will not increase the difficulty of secondary treatment and quality risks.

[0014] The processing method is simple, the hardware investment cost is small, low-temperature refrigerants are common in chemical companies, and it is easy to achieve by reusing existing equipment in various chemical companies.

[0015] The operation method is simple and the control difficulty is low. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a schematic diagram of a separation device for separating a mixture of toluene and n-butanol by low-temperature water washing according to the present invention; List of Figure Symbols: 1. Low-temperature water-washing stratification kettle; 2. Distillation tower kettle; 3. Distillation tower; 4. Condenser; 5. Reflux tank. DETAILED DESCRIPTION

[0017] The present invention will be further explained below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the following specific embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention.

[0018] A separation device for separating a mixture of toluene and n-butanol by low-temperature water washing, comprising a low-temperature water washing layering kettle, a distillation tower, a condenser, a reflux tank, and a distillation tower kettle. After the low-temperature water washing layering kettle is treated, the distillation tower kettle is removed. The distillation tower kettle is connected to the distillation tower. The top of the distillation tower is sequentially connected to the condenser, the condenser is connected to the reflux tank, the reflux tank is connected to the distillation tower kettle, and the reflux tank is also connected to the distillation tower. The gas phase on the distillation tower kettle enters the distillation tower, and the gas phase on the top of the distillation tower is condensed by two-stage condensers and enters the reflux tank. The n-butanol on the upper layer of the reflux tank refluxes back to the distillation tower kettle, and part of the water produced on the lower layer is used to return to the top of the distillation tower to cool (reflux) and stabilize the top temperature, and part is produced.

[0019] As a specific embodiment of the present invention, there may be one or more condensers as long as the condensation effect is achieved.

[0020] Example 2 At room temperature, a mixed solution of 90% toluene and 10% n-butanol is introduced into a low-temperature water washing and stratification kettle. After adding water 5 times the mass of the mixed solution, stirring is started after the mixture is finished, and the jacket of the water washing kettle is opened to cool the brine, and the temperature of the mixed solution in the kettle is cooled to 0°C. Stirring is continued at 0°C for 0.5 hours, and stirring is stopped and the kettle is allowed to stand for 1 hour. After 1 hour, stratification begins to occur through the monitoring camera mirror at the bottom of the kettle. The lower layer is the water phase containing n-butanol, and the water phase receiving tank is removed to wait for distillation to recover n-butanol. The organic phase in the kettle is high-content toluene, of which the n-butanol content is ≤0.2%; the toluene recovery rate is 99%.

[0021] The n-butanol aqueous phase separated from the lower layer enters the distillation kettle at room temperature. After the feeding is completed, the temperature is raised to the full reflux state by steam. When the full reflux occurs, the temperature in the kettle is 107°C and the temperature at the top of the tower is 102°C. The upper layer of the reflux separator is n-butanol, and the lower layer is water. Through azeotropic extraction, the lower layer of water is continuously separated, and the water content in the kettle will become lower and lower. At this time, the temperature of the distillation tower kettle and the temperature of the distillation tower top will gradually increase. When the temperature of the distillation tower kettle reaches 118°C, the reflux at the top of the distillation tower is stopped until the top temperature rises to 115°C. The water content of n-butanol in the distillation tower kettle is qualified ≤0.3%, and the reflux with water ends. What is retained in the kettle is high-content n-butanol. The n-butanol in the kettle needs to be used and needs to be distilled out under negative pressure to remove mechanical impurities. The recovered n-butanol content is 99.5%, and the recovery rate is 95%.

[0022] Example 3 At room temperature, a mixed solution of 95% toluene and 5% n-butanol is introduced into a low-temperature water washing and stratification kettle. After adding water 3 times the mass of the mixed solution, stirring is started after the mixture is finished, and the jacket of the water washing kettle is opened to cool the brine, and the temperature of the mixed solution in the kettle is cooled to -5°C. Stirring is continued for 0.5 hour at -5°C, and stirring is stopped and the static stage is entered for 1 hour. After 1 hour, stratification begins to be observed through the monitoring camera mirror at the bottom of the kettle. The lower layer is the water phase containing n-butanol, and the water phase receiving tank is removed to wait for distillation to recover n-butanol; the organic phase in the kettle is high-content toluene, of which the n-butanol content is ≤0.2%; the toluene recovery rate is 99%.

[0023] The n-butanol aqueous phase separated from the lower layer enters the distillation kettle at room temperature. After the feeding is completed, the temperature is raised to the full reflux state by steam. When the full reflux occurs, the temperature in the kettle is 106°C and the temperature at the top of the tower is 101.5°C. The upper layer of the reflux separator is n-butanol, and the lower layer is water. Through azeotropic extraction, the lower layer of water is continuously separated, and the water content in the kettle will become lower and lower. At this time, the temperature of the distillation tower kettle and the temperature of the distillation tower top will gradually increase. When the temperature of the distillation tower kettle reaches 118°C, the reflux at the top of the distillation tower is stopped until the top temperature rises to 115°C. The water content of n-butanol in the distillation tower kettle is qualified ≤0.3%, and the reflux with water ends. What is retained in the kettle is high-content n-butanol. The n-butanol in the kettle needs to be used and needs to be distilled out under negative pressure to remove mechanical impurities. The recovered n-butanol content is 99.5%, and the recovery rate is 95.5%. Comparative Example 1

[0024] At room temperature, a mixed solution of 95% toluene and 5% n-butanol is put into a low-temperature water washing and stratification kettle. After adding water 5 times the mass of the mixed solution, stirring is started after the mixture is washed. Stirring is continued for 0.5 hour at room temperature of 25°C. Stirring is stopped and the mixture is allowed to stand for 1 hour. After 1 hour, stratification begins to occur through the monitoring camera mirror at the bottom of the kettle. The lower layer is water containing n-butanol, and the n-butanol content is only 0.2%; the n-butanol content in the organic phase in the kettle is ≥4%, and the toluene content is ≤96%, and the washing effect is not obvious. Comparative Example 2

[0025] At room temperature, a mixed solution of 95% toluene and 5% n-butanol was put into a low-temperature water washing and stratification kettle. After adding water 5 times the mass of the mixed solution, stirring was started after the mixture was completed, and the jacket of the water washing kettle was opened to cool the brine. However, the temperature of the mixed solution in the kettle dropped to <-5.5°C, and ice began to form in the kettle, which was an ice-water mixture, and washing and stratification could not be achieved.

[0026] It should be noted that the above content only illustrates the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. For ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications all fall within the protection scope of the claims of the present invention.

Claims

1. A separation device for separating a mixture of toluene and n-butanol by low-temperature water washing, characterized in that: It includes a low-temperature water washing and stratification kettle, a distillation tower, a condenser, a reflux tank, and a distillation tower kettle. After the low-temperature water washing and stratification kettle is processed, the distillation tower kettle is removed. The distillation tower kettle is connected to the distillation tower. The top of the distillation tower is connected to the condenser. The condenser is connected to the reflux tank. The reflux tank is connected to the distillation tower kettle. The reflux tank is also connected to the distillation tower.

2. A method for separating a mixture of toluene and n-butanol by low-temperature water washing using the separation device as claimed in claim 1, characterized in that: The following steps are involved: Add the mixed solution of toluene and n-butanol into a low-temperature water washing and layering kettle, start stirring after adding water, cool to -5~0°C, continue stirring for 0.5~1h, let stand for 1~1.5h, and separate to obtain the toluene phase on the upper layer and the mixture of water and n-butanol on the lower layer; The mixture of water and n-butanol in the lower layer enters the kettle of the distillation tower, and the water is fully refluxed under normal pressure. The water is discharged through the reflux tank, and the n-butanol in the upper layer continues to return to the kettle of the distillation tower to azeotropize with water. When the kettle temperature of the distillation tower reaches 118°C, the reflux at the top of the distillation tower is stopped. When the top temperature of the distillation tower rises to 115°C, the reflux with water ends, and the kettle contains n-butanol. The distilled water is used as sewage for biochemical treatment.

3. The method for separating a mixture of toluene and n-butanol by low-temperature water washing according to claim 2, characterized in that: In step (1), in the mixed solution of toluene and n-butanol, the mass percentage of toluene is ≥70%, and the mass percentage of n-butanol is ≤30%.

4. The method for separating a mixture of toluene and n-butanol by low-temperature water washing according to claim 2, characterized in that: In step (1), the mass ratio of water to the mixed solution of toluene and n-butanol is 4-6:

1.

5. The method for separating a mixture of toluene and n-butanol by low-temperature water washing according to claim 2, characterized in that: In step (2), when the reflux with water is completed, the water content in the system is ≤0.3%.

6. Use of water as a separation medium for separating a mixed solution of toluene and n-butanol under low temperature conditions.

7. The use of water as a separation medium for separating a mixed solution of toluene and n-butanol under low temperature conditions according to claim 6, characterized in that: The mass ratio of water to toluene n-butanol mixed solution is 4~6:1, the separation temperature is -5~0℃, and the separation time is 1~1.5h.

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