Multi-section membrane embedded coupling rectification device and rectification method

Abstract

The invention belongs to the technical field of chemical engineering, and mainly relates to a multi-section membrane embedded coupling rectification device and a separation method. According to the invention, the multiple sections of membrane units are coupled into the rectifying tower at the same time, different types of membrane units can be embedded according to the characteristics of a separation system, the multi-section structure gives full play to the membrane separation effect, the membrane area is saved, the synergistic effect of the membrane units and the rectifying unit is enhanced, and the separation performance of the membrane embedded coupling device is improved; and the energy consumption of rectification is also reduced.

Description

Technical Field

[0001] The present invention relates to a multi-stage membrane-embedded coupled distillation device and a distillation method, belonging to the field of separation technology. Background Art

[0002] Membrane separation has the advantages of high separation efficiency, good thermal stability, small floor area, etc. Combining membrane separation with distillation technology can produce a synergistic effect, overcome their respective defects, and further improve the separation efficiency. According to the different embedding positions of the membrane unit, the distillation-membrane coupling can be divided into two processes: external coupling and internal coupling. As the main coupling process, external coupling has developed rapidly. However, this method is more like a combination of separation methods, unable to achieve in-situ separation effect, and lacking research on the synergistic mechanism between membrane separation and distillation. Therefore, it is difficult to fully exert the separation potential of the distillation-membrane coupling.

[0003] The distillation-membrane internal coupling process has been proposed for a short time. This process embeds the membrane unit inside the distillation column. Through the in-situ dehydration effect of the membrane unit in the column, it promotes the positive shift of the vapor-liquid equilibrium in the column, thereby improving the distillation separation effect. Compared with the external coupling process, the membrane-embedded coupling process strengthens the synergistic effect between distillation and the membrane unit, reduces the energy cost of separation, and improves the integration of the device. Although the membrane-embedded coupling process improves the distillation separation effect, the influence of the embedding of the membrane unit on the inside of the distillation column lacks research, and the performance improvement of the internal coupling process is limited to a certain extent.

[0004] At present, the internal coupling process embeds the whole membrane unit inside the distillation column. Due to the different vapor-liquid composition distributions and flow rates in the column, the vapor compositions contacted by the membrane unit at different positions are also different. Therefore, it will cause insufficient contact between the membrane unit and the components in the vapor phase or the components contacted cannot be completely removed, and the separation function of the membrane unit cannot be fully exerted. The prior art can further improve the separation effect by increasing the membrane area at the optimal embedding position of the separation system to achieve the separation target. However, it cannot fundamentally solve the problem, which not only increases the process cost but also may cause waste of the membrane area. At the same time, the membrane unit embedded in the column can only separate specific systems. When changing the separation system, the embedded membrane unit needs to be replaced. This problem is more obvious when separating multi-component systems. Because for multi-component systems, only one component can be removed through the membrane unit, and then the subsequent operations are required for further separation, which limits the application scope of this process. Summary of the Invention

[0005] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide a multi-stage membrane-embedded coupled distillation device, which embeds multi-stage membrane units inside the distillation column and can be applied to the separation of ethanol / water system to improve the separation effect.

[0006] A multi-stage membrane-embedded coupled distillation device includes a distillation column and a membrane separation unit; The described membrane separation unit is at least embedded and installed on the trays of at least two distillation columns; and these two trays are respectively located in the trays within the rectifying section and the stripping section; The permeate side of the membrane separation unit is respectively connected to a vacuum pump through the tray interfaces provided in the trays within the rectifying section and the stripping section; The top of the described distillation column is provided with a reflux ratio control system, and the top of the distillation column is connected to a distillate tank through a condenser; The described membrane separation unit is used to separate water or organic substances.

[0007] The hydrophilic membrane or hydrophobic membrane is installed in the membrane separation unit.

[0008] The material of the hydrophilic membrane is one of NaA, T-type, MOR, CHA, NaY or ZSM-5 molecular sieve; the material of the hydrophobic membrane is PDMS.

[0009] The carrier configuration of the separation membrane installed in the membrane separation unit is one of sheet type, tubular type or hollow fiber type.

[0010] The hydrophobic membrane is installed in the membrane separation unit in the rectifying section, and the hydrophilic membrane is installed in the membrane separation unit in the stripping section; the multi-stage membrane embedded coupling distillation device is used to separate the polar organic solvent - non-polar organic solvent - water mixed system.

[0011] A multi-stage membrane embedded coupling distillation method includes the following steps: Using the above-mentioned distillation device, the organic material containing water is fed into the distillation column, and the raw material is heated by an oil bath; the reflux ratio control system controls the reflux ratio of the distillate; the membrane separation units in the rectifying section and the stripping section dehydrate the material in the trays.

[0012] The membrane separation unit is suctioned by a vacuum pump to generate an osmotic pressure, and the working pressure is not higher than 2000 Pa.

[0013] The material at the top of the tower is condensed, and the condensing medium is water.

[0014] The heating medium at the bottom of the tower is dimethyl silicone oil.

[0015] The beneficial effects of the present invention are: The present invention adopts a multi-stage membrane embedded coupling distillation device, which can embed multiple membrane units in the distillation column at the same time. The multi-stage structure can enable the membrane units to contact more water in the vapor phase, improve the overall water driving force, enable the membrane units to remove more water, enhance the role of the packing in the tower, thereby saving part of the membrane area, strengthening the synergistic effect between the membrane units and the distillation unit, and further improving the separation performance of the coupling device. The multi-stage structure also reduces the circulating material in the tower, thereby reducing the energy consumption of distillation.

[0016] The multi-segment membrane units embedded in the tower of the present invention can select the same type of hydrophilic membrane, or different types of membranes can be embedded according to the characteristics of the separation system. In addition to separating binary systems, the multi-segment different types of membranes embedded can selectively separate specific substances in different segments. Therefore, the multi-segment embedded coupling distillation device has a wider application range and also provides a new idea for the separation of multi-component systems. The area of each segment of the membrane unit embedded in the tower can be freely adjusted according to the process simulation results, and the influence of different membrane area distribution methods of each segment of the membrane unit on the separation performance of the device can also be investigated, so as to determine the optimal membrane area ratio and optimize the membrane area according to different feed conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is a schematic diagram of the distillation-membrane internal coupling distillation device and the simulation process applied to ethanol / water in Example 1; Figure 2 is a schematic diagram of the multi-segment membrane embedded coupling distillation device and the simulation process applied to ethanol / water in Example 2; Figure 3 is a diagram of the vapor-liquid composition distribution in the tower of the multi-segment membrane embedded coupling distillation device applied to ethanol / water in Example 2.

[0018] Figure 4 is a schematic diagram of the multi-segment membrane embedded coupling distillation device and the simulation process applied to ethanol / water in Example 3; Figure 5 is a schematic diagram of the small multi-segment membrane embedded coupling distillation device and the experimental process applied to ethanol / water in Example 4; Reference numerals: 1 - raw material tank; 2 - distillation tower section; 3 - hydrophilic membrane (VP 1 ); 4 - hydrophilic membrane (VP 2 ); 5 - hydrophilic membrane (VP 3 ); 6 - hydrophilic membrane (VP 4 ); 7 - condenser; 8 - reflux ratio control system; 9 - distillate tank; 10 - vacuum pump; 11 - VP 1 tower section interface; 12 - VP 2 tower section interface. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0019] The device and working method adopted by the present invention are described in detail as follows: Example 1

[0020] This example is used to illustrate the process simulation and energy consumption analysis of a distillation-membrane internal coupling for the separation of ethanol / water binary system. Taking the feed of 200 kg per hour with a feed composition of 50 wt.% ethanol and 50 wt.% water as an example. The process flow diagram is asFigure 1 As shown in the figure, the NaA molecular sieve membrane 3 is coupled to the upper section of the distillation column. After the combined action of distillation and membrane separation, the ethanol content at the top of the column is 99.00 wt.%, the water content on the permeate side of the molecular sieve membrane is greater than 99.00 wt.%, and the required NaA membrane area is 6.4 m 2 , and the permeate side flow rate is 11.81 kg per hour. This process consumes 1.06 tons of low-pressure steam to obtain one ton of product. Example 2

[0021] This example is used to illustrate the process simulation and energy consumption analysis of a multi-stage membrane-embedded coupled distillation for the separation of ethanol / water binary system. Taking the feed of 200 kg per hour with a feed composition of 50 wt.% ethanol and 50 wt.% water as an example. The process flow diagram is as Figure 2 shown. The differential NaA molecular sieve membrane with a membrane area of 6.4 m 2 is embedded in the distillation column. After the combined action of distillation and separation by membrane units 3, 4, 5, and 6, finally, the ethanol content of the distillate at the top of the column is greater than 99.00 wt.%, the water content on the permeate side of the molecular sieve membrane is greater than 99.00 wt.%, and the water content of the distillate at the bottom of the column is greater than 99.00 wt.%. In the above process flow, the influence of multi-stage embedded coupling on the distillation separation effect is analyzed, and the results are shown in Table 1. The results show that when the membrane area is the same, the multi-stage membrane unit can increase the permeate side flow rate of the membrane unit and increase the ethanol content of the distillate at the top of the column. The influence of multi-stage embedded coupling on the vapor-liquid composition distribution in the column is analyzed as Figure 3 shown. The vapor-liquid composition distribution in the column shows that the multi-stage coupling structure can make the membrane unit contact more water vapor, thereby obtaining a higher water driving force, enabling the membrane unit to remove more water, which is also consistent with the change result of the permeate side flow rate, enhancing the synergistic effect between the membrane unit and distillation, increasing the ethanol content of the distillate at the top of the column, and further improving the separation performance of the coupling device. At the same time, the multi-stage structure enables the membrane unit to remove more water, reducing the material circulation in the column, thereby reducing the distillation energy consumption. Through energy consumption calculation, it can be obtained that for every 1.0 ton of ethanol obtained in this example, 1.03 tons of low-pressure steam are consumed. Compared with the internal coupling process in Example 1 with the same membrane area, 2.8% of low-pressure steam can be saved.

[0022] Table 1 Separation performance of multi-stage membrane-embedded coupled distillation

[0023] Example 3 This example is used to illustrate the process simulation and energy consumption analysis of a multi-stage membrane-embedded coupled distillation for the separation of ethanol / water binary system. Taking the feed of 200 kg per hour with a feed composition of 50 wt.% ethanol and 50 wt.% water as an example. The process flow diagram is as Figure 3 shown. The NaA zeolite membrane with a membrane area of 6.4 m 2 is micro-divided into two membrane units and respectively embedded in the upper section (VP 1 ) 3 and the middle section (VP 2 ) 4 of the distillation column. After the combined action of distillation and the two membrane units, the ethanol content in the overhead distillate is greater than 99.00 wt.%. The above process flow is simulated to analyze the influence of different membrane area distribution schemes on the distillation separation effect and energy consumption when multi-stage membrane units are embedded. The simulation results are shown in Table 2. The results show that when multi-stage membrane units are embedded, although the overall permeate side flow rate of Scheme 1 is the largest because its VP 2 membrane area is the largest and the water content in the vapor phase is relatively high, so more water is removed, but the separation effect is the worst. The energy consumption of Scheme 3 is the highest, while the ethanol content in the distillate of Scheme 2 is the highest and the energy consumption is moderate. Therefore, by comprehensively comparing the energy consumption and distillation separation effects of the three schemes, it is concluded that the optimal solution for multi-stage membrane-embedded coupling is to evenly distribute the membrane area.

[0024] Table 2 Separation performance of different membrane area distribution methods for multi-stage membrane-embedded coupled distillation

[0025] Example 4 This example is used to illustrate a specific implementation experimental case of a small multi-stage membrane-embedded coupled distillation device for the separation of ethanol / water binary system. Taking the feed mass of 1.4 kg with a feed composition of 50 wt.% ethanol and 20 wt.% water as an example, the total membrane area is 7.5 cm 2 . The schematic diagram of the experimental device is as Figure 5 shown, including a raw material tank 1, a distillation column section 2, hydrophilic membranes 3 and 4, a condenser 7, a reflux ratio control system 8, a distillate tank 9, and a vacuum pump 10. The lower part of the distillation column section is connected to the raw material tank, and the upper part is connected to the condenser; the vacuum pump is connected to the hydrophilic membranes 3 and 4 through a cold trap; the hydrophilic membranes 3 and 4 are respectively connected to the interfaces 11 and 12 of the distillation column section; the reflux ratio control system 8 controls the reflux ratio of the distillate; the raw material tank 1 is heated by a heater; the areas of the hydrophilic membranes 3 and 4 embedded in the distillation column can be freely adjusted.

[0026] The above device was used for the separation of the ethanol / water system. The heating temperature was 105 °C, the reflux ratio was set to 5, hydrophilic membranes with different membrane areas were embedded in the middle and upper sections of the distillation column respectively, and the vapor permeation device was turned on. The experimental results are shown in Table 3. Analyzing the experimental results, it can be seen that the mass on the permeate side of Scheme 1 is the largest. This is because in this scheme, 2 the membrane area is the largest. At this time, the water content in the vapor phase is relatively high, so more water is removed, but the separation effect is the worst. The ethanol content in the distillate of Scheme 2 is the highest, and the rectification separation effect is the best. The experimental results are consistent with the simulation, indicating that it is optimal to evenly distribute the membrane area during the multi-stage membrane inlay coupling.

[0027] Table 3 Rectification separation performance of different membrane area distribution methods

[0028] It demonstrates the feasibility of using this multi-stage membrane inlay coupling device for the separation of the ethanol / water system, proposes a method for multi-stage membrane inlay coupling, and investigates the influence of multi-stage membrane inlay on the rectification separation effect and energy consumption through simulation and experiments. It also examines the influence of different membrane area distribution methods on multi-stage membrane inlay coupling rectification, and at the same time determines that evenly distributing the membrane unit area during multi-stage membrane inlay has the best separation effect. Example 5 Separation process of the ethanol / water / acetone ternary system. A total mass of 200 kg / h with a composition of 30 wt.% ethanol, 40 wt.% water, and 30 wt.% acetone was added to the raw material tank 1 and heated to 110 °C. · The distillation column section 2 was divided into the lower section (stripping section), the middle section (feed section), and the upper section (rectification section). · A hydrophilic NaA zeolite membrane (VP1, membrane area 3.2 m²) was embedded at the lower part of the tower, and the interface 11 was connected to the vacuum pump 10. A PDMS membrane selective for acetone (VP2, membrane area 1.6 m²) was embedded at the upper part of the tower, and the interface 12 was connected to the vacuum pump 10. · The side draw outlet in the middle section was used to collect high-purity ethanol. The temperature at the bottom of the tower was 115 °C (silicone oil heating medium); the pressure at the top of the tower was atmospheric pressure; the reflux ratio was 4; the pressure on the VP1 side of the vacuum pump was 500 Pa, and the pressure on the VP2 side was 800 Pa. During the dehydration process at the lower part of the tower, water molecules in the vapor phase permeated through the VP1 membrane, and water vapor was withdrawn from the permeate side (flow rate 25.3 kg / h, water content > 99.5%); for the removal of acetone at the upper part of the tower: the remaining vapor rose to the upper part of the tower, and acetone permeated through the VP2 membrane, and acetone vapor was withdrawn from the permeate side (flow rate 18.7 kg / h, acetone content > 98.2%); for the side draw of ethanol: the unpermeated ethanol was enriched in the middle section of the tower and withdrawn through the side draw (flow rate 62.0 kg / h, ethanol content > 99.6%, water content < 0.3%, acetone content < 0.1%). In this example, by segmentally embedding a hydrophilic membrane and an acetone-selective membrane, one-step separation of the ethanol / water / acetone ternary system was achieved.

Claims

1. A multi-stage membrane embedded coupled distillation device, characterized in that: It comprises a distillation tower and a membrane separation unit; the membrane separation unit is embedded and installed on at least two tower plates of the distillation tower; and the two tower plates are respectively located in tower sections in the distillation section and the stripping section; the permeation side of the membrane separation unit is respectively connected to a vacuum pump through tower section interfaces arranged in the distillation section and the stripping section; a reflux ratio control system is arranged at the top of the distillation tower, and the top of the distillation tower is connected to a distillate tank through a condenser; the membrane separation unit is used for separating water or organic matter.

2. The multi-stage membrane embedded coupled distillation device according to claim 1, characterized in that: The membrane separation unit is installed with a hydrophilic membrane or a hydrophobic membrane.

3. The multi-stage membrane embedded coupled distillation device according to claim 1, characterized in that: The material of the hydrophilic membrane is one of NaA, T-type, MOR, CHA, NaY or ZSM-5 molecular sieve.

4. The multi-stage membrane embedded coupled distillation device according to claim 1, characterized in that: The material of the hydrophobic membrane is PDMS.

5. The multi-stage membrane embedded coupled distillation device according to claim 1, characterized in that: The carrier configuration of the separation membrane installed in the membrane separation unit is one of sheet type, tube type or hollow fiber type.

6. The multi-stage membrane embedded coupled distillation device according to claim 1, characterized in that: The membrane separation unit in the distillation section is installed with a hydrophobic membrane, and the middle membrane separation unit in the stripping section is installed with a hydrophilic membrane; the multi-stage membrane embedded coupled distillation device is used to separate the polar organic solvent-non-polar organic solvent-water mixed system.

7. A multi-stage membrane embedded coupled distillation method, characterized in that: The method comprises the following steps: using the above-mentioned distillation device, supplying water-containing organic materials into a distillation tower, and heating the raw materials by an oil bath; the reflux ratio control system controls the reflux ratio of the distillate; and the membrane separation units in the distillation section and the stripping section dehydrate the materials in the tower section.

8. The distillation method according to claim 7, characterized in that: The membrane separation unit uses a vacuum pump to generate osmotic pressure, and the working pressure is no higher than 2000Pa.

9. The distillation method according to claim 7, characterized in that: The material at the top of the tower is condensed, and the condensation medium is water.

10. The distillation method according to claim 7, characterized in that: The heating medium of the tower kettle is dimethyl silicone oil.

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