Double-tower rectification method and double-tower rectification system

Abstract

The invention discloses a double-tower rectification method and a double-tower rectification system, and the method comprises the following steps: introducing a material to be separated into a first rectification tower through the middle part of the first rectification tower, and carrying out first rectification treatment to form a first rectification tower top product and a first rectification tower bottom product, the mass content of light key components in the top product of the first rectifying tower is 5%-10%; after the first rectifying tower top product passes through a second reboiler to release heat, the first rectifying tower top product enters a second rectifying tower from the middle of the second rectifying tower through a transmission channel from the top of the first rectifying tower, and second rectifying treatment is performed to form a second rectifying tower top product and a second rectifying tower bottom product. According to the method, the energy consumption can be reduced while an excellent separation result is realized.

Description

TECHNICAL FIELD

[0001] The present application relates to a double-tower rectification method and a double-tower rectification system. BACKGROUND

[0002] The traditional single-tower process of the pyridine debenzene tower is the largest energy consumer in the product rectification system, and the tower kettle reboiler adopts steam heating, so the steam consumption is large and the cost is high. The traditional process debenzene tower top product is benzene and light components, and the kettle product is pyridine and heavy components. The atmospheric boiling point of benzene is 80℃, and the atmospheric boiling point of pyridine is 115℃, which has a large difference. The operating pressure of this tower is 60kPa.G to 80kPa.G, the tower top temperature is 95℃ to 100℃, and the kettle temperature is 145℃ to 155℃, so it is difficult to use differential pressure rectification to realize double-effect rectification.

[0003] The prior art CN102351634A discloses a new energy-saving process for benzene separation by double-effect rectification and heat integration. It is aimed at the system of aromatic hydrocarbons and benzene, and although a multi-stage rectification tower is used, the separation capacity and separation result of each stage are actually the same. If it is applied to the system of pyridine and benzene, the operating pressure difference between the first tower and the second tower is too large due to the large temperature difference between the tower top and the tower bottom, which finally leads to difficulty or inability to realize it, so it cannot achieve the effect of reducing energy consumption on the basis of obtaining excellent separation results.

[0004] Therefore, a refining method for pyridine is needed to achieve excellent separation results while reducing energy consumption. SUMMARY

[0005] In order to solve the problem that the separation method for the system of pyridine and benzene in the prior art cannot achieve the effect of reducing energy consumption on the basis of obtaining excellent separation results, the present application provides a double-tower rectification method and a double-tower rectification system, which can achieve excellent separation results while reducing energy consumption.

[0006] The present application solves the above technical problems by the following technical solutions.

[0007] The present application provides a double-tower rectification method for separating light key components and heavy key components in a material to be separated. The atmospheric boiling point difference between the heavy key component and the light key component is 20-100℃, the mass content of the heavy key component is 10%-30%, and the mass content of the light key component is 50%-80%. The method comprises the following steps:

[0008] S1, a first rectification tower and a second rectification tower are provided, wherein the tower top of the first rectification tower is connected to the middle part of the tower of the second rectification tower through a second reboiler to form a transmission channel;

[0009] S2, heating the first rectifying tower by connecting a first reboiler outside the tower kettle of the first rectifying tower;

[0010] S3, heating the second rectifying tower by the second reboiler connected outside the tower kettle of the second rectifying tower;

[0011] S4, feeding the material to be separated into the first rectifying tower through the middle part of the first rectifying tower to perform first rectifying treatment, forming first rectifying tower top product and first rectifying tower bottom product, the mass content of the light key component in the first rectifying tower top product being 5%-10%;

[0012] S5, feeding the first rectifying tower top product into the second rectifying tower from the middle part of the second rectifying tower through the transmission channel from the top of the first rectifying tower after releasing heat through the second reboiler to perform second rectifying treatment, forming second rectifying tower top product and second rectifying tower bottom product.

[0013] In the present application, the mass content of the heavy key component means the percentage of the mass of the heavy key component in the mass of the material to be separated, and the mass content of the light key component means the percentage of the mass of the light key component in the mass of the material to be separated.

[0014] In the present application, preferably, the heavy key component is benzene, and the light key component is pyridine.

[0015] In the present application, preferably, the top pressure of the first rectifying treatment is 100-160 kPa.G, and the top temperature of the first rectifying treatment is 100-120℃.

[0016] In the present application, preferably, the kettle temperature of the second rectifying treatment is 70-100℃.

[0017] In the prior art, due to the special properties of pyridine and benzene, a single tower is usually used for separation, but the single tower often has the problem of very large energy consumption. In the prior art, for other separation systems (for example, the aromatic hydrocarbon and benzene disclosed in CN102351634A), although multi-stage rectification is used, due to the large difference in physical and chemical properties between the mixture of pyridine and benzene and the mixture of aromatic hydrocarbon and benzene, for example, the atmospheric boiling point of toluene is 110℃, which is closer to the boiling point of benzene than the boiling point of pyridine (115℃); meanwhile, more importantly, the aromatic hydrocarbon and benzene system disclosed in CN102351634A does not have high-boiling unknown heavy impurities, so that the multi-stage rectification with parallel feeding can achieve good results, but in the existing pyridine and benzene system, there are usually high-boiling unknown heavy impurities, which will make the kettle temperature of the rectifying tower higher and cannot directly use the existing multi-stage rectification system (for example, the system disclosed in CN102351634A).

[0018] In the separation system of the present application for pyridine and benzene, the present application selects a series feeding mode, i.e. the total feed is only fed into the middle of the first rectifying tower, and the feed of the second rectifying tower is obtained from the top of the first rectifying tower, so that the top temperature of the first rectifying treatment is 100-120℃, the bottom temperature of the second rectifying treatment is 70-100℃, and the temperature difference between the two is more than 20℃, which breaks the limitation of traditional temperature mismatch and successfully realizes the double-effect process, the top temperature of the first rectifying treatment can completely match the temperature requirement of the heat source of the second reboiler, and the vapor consumption of the reboiler can be further reduced, which not only reduces the difficulty of realizing the double-effect process, but also maximizes energy saving; and high-purity products can also be obtained.

[0019] In the present application, the top and bottom temperatures of the first rectifying treatment and the second rectifying treatment can be controlled by the temperatures of the first reboiler and the second reboiler, and the top and bottom pressures of the first rectifying treatment and the second rectifying treatment can be controlled by a pressure control system, for example, the pressure of the first rectifying treatment can be controlled by a pressure regulating valve system, and the pressure of the second rectifying treatment can be controlled by a combination of a vacuum pump and a pressure regulating valve.

[0020] In the present application, preferably, the mass content of pyridine in the material to be separated is 10%-30%.

[0021] In the present application, preferably, the mass content of benzene in the material to be separated is 50%-80%, for example, 77%.

[0022] In the present application, the material to be separated can be obtained after benzene extraction, wherein the material to be separated is mostly benzene, followed by pyridine, and about 10%-20% of pyridine homologues and heavy impurities; wherein the heavy impurities refer to compounds with a molecular weight of more than 5 times that of pyridine homologues.

[0023] Optionally, the pyridine homologues include 2-methylpyridine, 3-methylpyridine, 3,5-dimethylpyridine, and 2,3,5-trimethylpyridine.

[0024] Optionally, the mass content of the pyridine homologues is 9%-17%.

[0025] In some specific embodiments, the pyridine homologues include 2-methylpyridine, and the mass content of 2-methylpyridine in the material to be separated is 1%-5%.

[0026] In some specific embodiments, the pyridine homologues include 3-methylpyridine, and the mass content of 3-methylpyridine in the material to be separated is 5%-15%.

[0027] In some embodiments, the pyridine homologues include 3,5-dimethylpyridine, and the mass content of 3,5-dimethylpyridine in the material to be separated is 1%-5%.

[0028] In some embodiments, the pyridine homologues include 2,3,5-trimethylpyridine, and the mass content of 2,3,5-trimethylpyridine in the material to be separated is 1%-3%.

[0029] In some embodiments, the pyridine homologues include 2,3,5-trimethylpyridine, and the mass content of 2,3,5-trimethylpyridine in the material to be separated is 1%-3%.

[0030] In some embodiments, the pyridine homologues include 2,3,5-trimethylpyridine, and the mass content of 2,3,5-trimethylpyridine in the material to be separated is 1%-3%.

[0031] In the present application, preferably, the overhead pressure of the first rectification treatment is 120-160 kPa.G, more preferably 140-160 kPa.G.

[0032] In the present application, preferably, the overhead temperature of the first rectification treatment is 110-120°C, more preferably 113-120°C, for example 116°C.

[0033] In the present application, preferably, the column bottom temperature of the first rectification treatment is 163-173°C, for example 168°C.

[0034] In the present application, preferably, the column bottom pressure of the first rectification treatment is 155-185 kPa.G, for example 165 kPa.G.

[0035] In the present application, preferably, the mass content of pyridine in the overhead product of the first rectification is 5%-10%, for example 6%.

[0036] In the present application, preferably, the mass content of benzene in the bottom product of the first rectification is 0.1% or less.

[0037] In the present application, preferably, the column bottom temperature of the second rectification treatment is 70-90°C, more preferably 78-90°C, for example 81°C.

[0038] In the present application, preferably, the column bottom pressure of the second rectification treatment is -48 kPa.G to -15 kPa.G, for example -37 kPa.G.

[0039] In the present application, preferably, the overhead temperature of the second rectification treatment is 58-72°C, for example 64°C.

[0040] In the present application, preferably, the overhead pressure of the second rectification treatment is -50 kPa.G to -20 kPa.G, for example -40 kPa.G.

[0041] In the present application, preferably, the mass content of benzene in the bottom product of the second rectification is 40%-60%, for example 50% or 55%.

[0042] In the present application, preferably, the mass content of pyridine in the overhead product of the second rectification is 0.1% or less.

[0043] In the present application, the overhead reflux ratio means the ratio of the mass flow rate of the reflux liquid returned from the overhead of the rectification column to the mass flow rate of the overhead product.

[0044] In the present application, preferably, the overhead reflux ratio of the first rectification column is 0.1-0.2, for example 0.123, 0.126, 0.129 or 0.187.

[0045] In the present application, preferably, the overhead reflux ratio of the second rectification column is 0.43-0.55, for example 0.455, 0.456, 0.485 or 0.51.

[0046] In the present application, preferably, the bottom product of the second rectification is recycled to the middle part of the first rectification column as part of the material to be separated.

[0047] In the present application, preferably, the ratio of the flow rate of the material to be separated into the first rectification column to the flow rate of the overhead product of the first rectification column into the second rectification column is (1.1-1.5):1, for example 1.17:1.

[0048] In the present application, preferably, the flow rate of the material to be separated into the first rectification column is 50-60 t / h, for example 55.8 t / h.

[0049] In the present application, preferably, the flow rate of the overhead product of the first rectification column into the second rectification column is 40-50 t / h, for example 47.73 t / h.

[0050] The application also provides a double-tower rectification system for the double-tower rectification method, which comprises a first rectification tower and a second rectification tower in sequence; the first rectification tower is connected with a first reboiler outside the tower kettle, and the first reboiler is used for heating the tower bottom product of the first rectification tower before it flows into the tower kettle of the first rectification tower; the second rectification tower is connected with a second reboiler outside the tower kettle, and the second reboiler is used for heating the tower bottom product of the second rectification tower before it flows into the tower kettle of the second rectification tower.

[0051] The first rectification tower comprises a tower middle feeding port of the first rectification tower, a tower top discharging port of the first rectification tower and a tower kettle discharging port of the first rectification tower.

[0052] The second rectification tower comprises a tower middle feeding port of the second rectification tower, a tower top discharging port of the second rectification tower and a tower kettle discharging port of the second rectification tower.

[0053] The tower top discharging port of the first rectification tower is communicated with the tower middle feeding port of the second rectification tower through the second reboiler and the tower top discharging port of the second rectification tower, forming a transmission channel.

[0054] In the application, preferably, the first rectification tower is further provided with a tower top reflux path of the first rectification tower and a tower top feeding port of the first rectification tower, and the tower top discharging port of the first rectification tower and the tower top feeding port of the first rectification tower are communicated through the tower top reflux path of the first rectification tower.

[0055] In the application, preferably, the second rectification tower is further provided with a tower top reflux path of the second rectification tower and a tower top feeding port of the second rectification tower, and the tower top discharging port of the second rectification tower and the tower top feeding port of the second rectification tower are communicated through the tower top reflux path of the second rectification tower.

[0056] Preferably, the double-tower rectification system further comprises a second reflux tank and a second condenser, and the tower top discharging port of the second rectification tower is communicated with the tower top feeding port of the second rectification tower through the second condenser and the second reflux tank in sequence, forming the tower top reflux path of the second rectification tower.

[0057] In the application, preferably, the tower kettle discharging port of the second rectification tower is communicated with the tower middle feeding port of the first rectification tower.

[0058] Preferably, the double-tower rectification system further comprises a first reflux tank and a first condenser, and the tower top discharging port of the first rectification tower is communicated with the tower middle feeding port of the second rectification tower through the second reboiler, the first condenser and the first reflux tank in sequence.

[0059] Preferably, in the present application, the first rectifying tower is provided with structured packing above the part of the tower above the feed inlet of the first rectifying tower, and is provided with anti-blocking trays below the part of the tower below the feed inlet of the first rectifying tower.

[0060] Preferably, in the present application, the structured packing is Mellapak Plus. TM .

[0061] Preferably, in the present application, the anti-blocking trays are Sulzer anti-blocking trays.

[0062] Preferably, in the present application, the second rectifying tower is provided with structured packing.

[0063] Preferably, in the present application, the structured packing is Mellapak Plus. TM .

[0064] Preferably, in the present application, the double-tower rectifying system further comprises a first reflux tank and a first condenser, and the overhead outlet of the first rectifying tower is sequentially connected to the second reboiler, the first condenser, the first reflux tank, and then is divided into two paths; one path is connected to the middle feed inlet of the second rectifying tower, and the other path is connected to the overhead feed inlet of the first rectifying tower; wherein the overhead feed inlet of the first rectifying tower is connected to the heat medium connection port of the second reboiler.

[0065] On the basis of common sense in the art, the above-mentioned preferred conditions can be combined arbitrarily, thereby obtaining preferred examples of the present application.

[0066] The reagents and raw materials used in the present application are commercially available.

[0067] The positive progress effect of the present application is that:

[0068] The double-tower rectifying method of the present application successfully realizes the double-effect process by parameter selection, breaks through the limitation of traditional temperature mismatch, the overhead temperature of the first rectifying treatment can completely match the demand of the second reboiler for the temperature of the heat source, which can further reduce the vapor consumption of the reboiler, not only reduces the difficulty of realizing the double-effect process, but also maximizes energy saving; at the same time, high-purity products can also be obtained. BRIEF DESCRIPTION OF DRAWINGS

[0069] Figure 1 FIG. 1 is a structural schematic diagram of the double-tower rectifying system of Example 1.

[0070] The reference signs are as follows:

[0071] 1-First distillation column; 2-Second distillation column; 3-First reboiler; 4-Second reboiler; 5-First condenser; 6-First reflux tank; 7-Second condenser; 8-Second reflux tank;

[0072] 101-Structured packing; 102-Anti-clogging tray. Detailed Implementation

[0073] The present invention is further illustrated below by way of embodiments, but the invention is not limited to the scope of the embodiments described herein. Experimental methods in the following embodiments that do not specify specific conditions were performed according to conventional methods and conditions, or as selected according to the product instructions.

[0074] Example 1

[0075] A schematic diagram of the dual-tower distillation system is shown below. Figure 1 As shown, it sequentially includes a first distillation column 1 and a second distillation column 2; the bottom of the first distillation column 1 is connected to a first reboiler 3, which is used to heat the bottom product of the first distillation column before it flows back into the bottom of the first distillation column 1; the bottom of the second distillation column 2 is connected to a second reboiler 4, which is used to heat the bottom product of the second distillation column 2 before it flows back into the bottom of the second distillation column 2.

[0076] The first distillation column 1 includes a feed inlet, a top outlet, and a bottom outlet.

[0077] The second distillation column 2 includes a feed inlet, a top outlet, and a bottom outlet.

[0078] The top outlet of the first distillation column 1 is connected to the second reboiler 4 and the feed inlet of the second distillation column 2 to form a transmission channel.

[0079] The first distillation column 1 is also provided with a top reflux path and a top feed inlet of the first distillation column 1. The top discharge outlet of the first distillation column 1 and the top feed inlet of 11 are connected through the top reflux path of the first distillation column.

[0080] The dual-tower distillation system also includes a first reflux tank 6 and a first condenser 5. The top outlet of the first distillation column passes through the second reboiler 4, the first condenser 5, and the first reflux tank 6 in sequence, and then splits into two paths: one path connects to the feed inlet of the second distillation column 2, and the other path connects to the top feed inlet of the first distillation column 1, forming the aforementioned top reflux path of the first distillation column; wherein, the top feed inlet of the first distillation column 1 is connected to the heat medium connection port of the second reboiler 4;

[0081] The second rectifying column 2 is also provided with a column top reflux path of the second rectifying column 2 and a column top feed port of the second rectifying column 2, and the double-column rectifying system further comprises a second reflux tank 8 and a second condenser 7, the column top discharge port of the second rectifying column 2 is communicated with the column top feed port of the second rectifying column 2 in sequence through the second condenser 7 and the second reflux tank 8, thereby forming the column top reflux path of the second rectifying column 2.

[0082] The column bottom discharge port of the second rectifying column 2 is communicated with the middle column feed port of the first rectifying column 1;

[0083] The first rectifying column 1 is provided with structured packing 101 (Sulzer Mellapak Plus TM ) above the first feed port, and is provided with anti-plugging trays 102 (Sulzer anti-plugging trays) below the first feed port, and the second rectifying column 2 is provided with structured packing (Sulzer Mellapak Plus TM ).

[0084] The double-column rectifying method comprises the following steps:

[0085] S1, feeding the material to be separated (the light key component is pyridine, the heavy key component is benzene, the normal pressure boiling point difference between the two is 35℃, the mass content of pyridine is 10%, the mass content of benzene is 77%, the mass content of pyridine homologues (2-methylpyridine 2%, 3-methylpyridine 6%, 3, 5-dimethylpyridine 2% and 2, 3, 5-trimethylpyridine 1%) and heavy impurities (the mass content of unknown substances such as tar generated by upstream reaction is 2%, which can be ignored) is 13%, and the flow rate of the material into the first rectifying column through the first feed port of the first rectifying column is 55800kg / h) into the first rectifying column for first rectifying treatment to form first rectifying column top product (the mass content of pyridine is 5%) and first rectifying column bottom product (the mass content of benzene is 0.1% or less); the column top reflux ratio of the first rectifying column is 0.129;

[0086] The column top pressure of the first rectifying treatment is 140kPa.G, the column top temperature of the first rectifying treatment is 113℃; the column bottom temperature of the first rectifying treatment is 168℃, and the column bottom pressure of the first rectifying treatment is 165kPa.G.

[0087] S2, after the first rectifying column top product is absorbed by the second reboiler, the first rectifying column top product is fed into the second rectifying column through the first feed port of the second rectifying column (the flow rate of the first rectifying column top product into the second rectifying column is 47730kg / h), and the second rectifying treatment is carried out to form second rectifying column top product (the mass content of pyridine is 0.1% or less) and second rectifying column bottom product (the mass content of benzene is 55%); the column top reflux ratio of the second rectifying column is 0.455;

[0088] The column bottom temperature of the second rectification is 81℃, the column bottom pressure is -37kPa.G, the column top temperature is 64℃, and the column top pressure is -40kPa.G.

[0089] The second rectification column bottom product is recycled to the first feed inlet of the first rectification column as part of the material to be separated.

[0090] In this embodiment, the processing capacity is 40,000 tons of pyridine per year, the annual operating time is 7200 hours, the mass content of pyridine in the first rectification column bottom product is 45.9%, and the mass content of benzene is 0.1% or less (the rest is mainly pyridine homologues and unknown heavy impurities); the mass content of benzene in the second rectification column top product is 99%, and the mass content of pyridine is 0.1% or less (the rest is mainly a small amount of light impurities), the energy consumption is 7.89MW, and the steam consumption is 13915kg / h.

[0091] Example 2

[0092] The first rectification column is provided with regular packing (Sulzer Mellapak Plus TM ) above the first feed inlet and below the first feed inlet, forming the first rectification column top product (the mass content of pyridine is 5%) and the first rectification column bottom product (the mass content of benzene is 0.1%), forming the second rectification column top product (the mass content of pyridine is 0.1%) and the second rectification column bottom product (the mass content of benzene is 40%), the top reflux ratio of the first rectification column is 0.187, and the top reflux ratio of the second rectification column is 0.485; the rest of the conditions are the same as in Example 1.

[0093] In this embodiment, the mass content of pyridine in the first rectification column bottom product is 45.9%, and the mass content of benzene is 0.1%; the mass content of benzene in the second rectification column top product is 99%, and the mass content of pyridine is 0.1%; the energy consumption is 8.17MW, and the steam consumption is 14409kg / h.

[0094] In this embodiment, the first rectification column is provided with regular packing, and the heavier components in the material to be separated will affect the distribution performance of the regular packing surface. Compared with Example 1, the separation efficiency will decrease, and the energy consumption will increase.

[0095] Example 3

[0096] The top pressure of the first rectification is 160kPa.G, the top temperature of the first rectification is 116℃, the column bottom pressure of the first rectification is 185kPa.G; the column bottom temperature of the second rectification is 78℃;

[0097] The first rectification tower top product (mass content of pyridine 5%) and the first rectification tower bottom product (mass content of benzene 0.1%) are formed, the second rectification tower top product (mass content of pyridine 0.1%) and the second rectification tower bottom product (mass content of benzene 50%) are formed, the top reflux ratio of the first rectification tower is 0.126, and the top reflux ratio of the second rectification tower is 0.456; the rest of the conditions are the same as in Example 1.

[0098] In this example, the mass content of pyridine in the first rectification tower bottom product is 45.9%, and the mass content of benzene is 0.1%; the mass content of benzene in the second rectification tower top product is 99%, and the mass content of pyridine is 0.1%; the energy consumption is 8.09 MW, and the steam consumption is 14268 kg / h.

[0099] Example 4

[0100] The top pressure of the first rectification process is 100 kPa.G, the top temperature of the first rectification process is 106°C, the bottom pressure of the first rectification process is 125 kPa.G, the bottom temperature of the first rectification process is 161°C, the top pressure of the second rectification process is -20 kPa.G, the top temperature of the second rectification process is 72°C, the bottom pressure of the second rectification process is -15 kPa.G, the bottom temperature of the second rectification process is 90°C, the first rectification tower top product (mass content of pyridine 6%) and the second rectification tower bottom product (mass content of benzene 0.1%) are formed, the second rectification tower top product (mass content of pyridine 0.1%) and the second rectification tower bottom product (mass content of benzene 40%) are formed, the top reflux ratio of the first rectification tower is 0.144, and the top reflux ratio of the second rectification tower is 0.51; the rest of the conditions are the same as in Example 1.

[0101] The first rectification tower top product (mass content of pyridine 5%) and the first rectification tower bottom product (mass content of benzene 0.1%) are formed, the second rectification tower top product (mass content of pyridine 0.1%) and the second rectification tower bottom product (mass content of benzene 50%) are formed, the top reflux ratio of the first rectification tower is 0.126, and the top reflux ratio of the second rectification tower is 0.456; the rest of the conditions are the same as in Example 1.

[0102] In this example, the mass content of pyridine in the first rectification tower bottom product is 45.9%, and the mass content of benzene is 0.1%; the mass content of benzene in the second rectification tower top product is 99%, and the mass content of pyridine is 0.1%; the energy consumption is 8.09 MW, and the steam consumption is 14268 kg / h.

[0103] Example 5

[0104] The top pressure of the first rectification process is 100 kPa.G, the top temperature of the first rectification process is 106°C, the bottom pressure of the first rectification process is 125 kPa.G, the bottom temperature of the first rectification process is 161°C, the top pressure of the second rectification process is -20 kPa.G, the top temperature of the second rectification process is 72°C, the bottom pressure of the second rectification process is -15 kPa.G, the bottom temperature of the second rectification process is 90°C, the first rectification tower top product (mass content of pyridine 6%) and the second rectification tower bottom product (mass content of benzene 0.1%) are formed, the second rectification tower top product (mass content of pyridine 0.1%) and the second rectification tower bottom product (mass content of benzene 40%) are formed, the top reflux ratio of the first rectification tower is 0.144, and the top reflux ratio of the second rectification tower is 0.51; the rest of the conditions are the same as in Example 1.

[0105] In the present comparative example, the mass content of pyridine in the first rectification column bottom product is 45.9%, and the mass content of benzene is 0.1%; the mass content of benzene in the second rectification column top product is 99%, and the mass content of pyridine is 0.1%, the energy consumption is 7.93 MW, and the steam consumption is 13986 kg / h. Compared with Example 1, reducing the top pressure of the first rectification column will result in a decrease in the heat transfer temperature difference between the top of the first rectification column and the bottom of the second rectification column, thereby increasing the design difficulty of the reboiler and the heat exchange area.

[0106] Example 6

[0107] The column bottom temperature of the second rectification treatment is 100℃, the top pressure of the second rectification treatment is 10 kPa.G, the top temperature of the second rectification treatment is 82℃, the column bottom pressure of the second rectification treatment is -13 kPa.G, forming the first rectification column top product (the mass content of pyridine is 5%) and the first rectification column bottom product (the mass content of benzene is 0.1%), forming the second rectification column top product (the mass content of pyridine is 0.1%) and the second rectification column bottom product (the mass content of benzene is 40%) The top reflux ratio of the first rectification column is 0.131, and the top reflux ratio of the second rectification column is 0.54; the rest is the same as Example 1.

[0108] In the present comparative example, the mass content of pyridine in the first rectification column bottom product is 45.9%, and the mass content of benzene is 0.1%; the mass content of benzene in the second rectification column top product is 99%, and the mass content of pyridine is 0.1%, the energy consumption is 7.86 MW, and the steam consumption is 13862 kg / h. Compared with Example 1, increasing the column bottom temperature of the second rectification will also result in a decrease in the heat transfer temperature difference between the top of the first rectification column and the bottom of the second rectification column, thereby increasing the design difficulty of the reboiler and the heat exchange area.

[0109] Comparative Example 1

[0110] This comparative example is to separate the material to be separated in Example 1 by using a single rectification column, and the specific operation conditions are as follows:

[0111] The top temperature is 97℃, the top pressure is 70 kPa.G, the column bottom temperature is 151℃, and the column bottom pressure is 80 kPa.G.

[0112] In the present comparative example, the mass content of pyridine in the pyridine product is 45.9%, and the mass content of benzene is 0.3%; the mass content of benzene in the benzene product is 99%, and the mass content of pyridine is 0.3%, the energy consumption is 10.77 MW, and the steam consumption is 18995 kg / h.

[0113] According to the results of the above examples and comparative examples, the double-tower rectification system and the double-tower rectification method of the present application can obtain the first rectification tower bottom product with a mass content of pyridine of 45.9% or more and the second rectification tower top product with a mass content of benzene of 99% or more; it is shown that the examples can obtain products with high purity.

[0114] On this basis, the energy consumption of the examples is only 8.17 MW or less, and the steam consumption is only 14409 kg / h or less.

[0115] Comparative Example 1 uses a single rectification tower, and compared with Example 1, the content of pyridine in the benzene product is reduced from about 0.3wt% to 0.1wt% or less, the content of benzene in the pyridine debenzene product is reduced from about 0.3wt% to 0.1wt% or less, and the energy consumption is greatly reduced. The energy consumption of Comparative Example 1 is as high as 10.77 MW, and the steam consumption is as high as 18995 kg / h. The energy consumption of the examples can be reduced by 25% or more, and according to the calculation of 1.0 MPa.G saturated steam, about 36.6 thousand tons of steam can be saved per year, which is very considerable.

Claims

1. A dual-tower distillation method for separating a light critical component and a heavy critical component from a material to be separated, wherein the difference in atmospheric boiling points between the heavy critical component and the light critical component is 20-100°C, the mass content of the heavy critical component is 10%-30%, and the mass content of the light critical component is 50%-80%, characterized in that... It includes the following steps: S1. A first distillation column and a second distillation column are provided, wherein the top of the first distillation column forms a transfer channel through a second reboiler and the middle of the second distillation column; S2. The first distillation column is heated by connecting a first reboiler to the bottom of the first distillation column; S3. The second distillation column is heated by the second reboiler connected to the bottom of the second distillation column; S4. The material to be separated is passed through the middle of the first distillation column and then into the first distillation column for first distillation treatment to form the top product and the bottom product of the first distillation column. The mass content of the light key components in the top product of the first distillation column is 5%-10%. S5. After the top product of the first distillation column releases heat through the second reboiler, it enters the second distillation column from the top of the first distillation column through the transmission channel from the middle of the second distillation column for second distillation treatment, forming the top product of the second distillation column and the bottom product of the second distillation column.

2. The dual-tower distillation method as described in claim 1, characterized in that, The heavy key component is benzene, and the light key component is pyridine; Wherein, the pressure at the top of the first distillation treatment column is 100-160 kPa.G, and the temperature at the top of the first distillation treatment column is 100-120℃; The temperature of the bottom of the second distillation treatment column is 70-100℃.

3. The dual-tower distillation method as described in claim 2, characterized in that, It meets one or more of the following conditions: (a) The top pressure of the first distillation treatment column is 120-160 kPa·G; (b) The top temperature of the first distillation treatment column is 110-120°C; (c) The temperature of the reboiler in the first distillation process is 163-173°C; (d) The pressure of the bottom column of the first distillation treatment is 155-185 kPa.G.

4. The dual-tower distillation method as described in claim 2, characterized in that, It meets one or more of the following conditions: (a) The pyridine content in the top product of the first distillation column is 6% by mass; (b) The benzene content of the bottom product of the first distillation column is less than 0.1%.

5. The dual-tower distillation method as described in claim 2, characterized in that, It meets one or more of the following conditions: (a) The bottom temperature of the second distillation treatment column is 70-90°C; (b) The reboiler pressure of the second distillation treatment is from -48 kPa.G to -15 kPa.G; (c) The top temperature of the second distillation treatment column is 58-72℃; (d) The top pressure of the second distillation treatment column is from -50 kPa.G to -20 kPa.G.

6. The dual-tower distillation method as described in claim 2, characterized in that, It meets one or more of the following conditions: (a) The benzene content in the bottom product of the second distillation column is 40%-60% by mass; (b) The mass content of pyridine in the top product of the second distillation column is less than 0.1%.

7. The dual-tower distillation method as described in claim 2, characterized in that, It meets one or more of the following conditions: (a) The reflux ratio at the top of the first distillation column is 0.1-0.2; (b) The reflux ratio at the top of the second distillation column is 0.43-0.

55.

8. The dual-tower distillation method as described in claim 1, characterized in that, It meets one or more of the following conditions: (a) The bottom product of the second distillation column is recycled to the middle of the first distillation column as part of the material to be separated; (b) The ratio of the flow rate of the material to be separated into the first distillation column to the flow rate of the top product of the first distillation column into the second distillation column is (1.1-1.5):

1.

9. A dual-tower distillation system for the dual-tower distillation method as described in any one of claims 1-8, comprising a first distillation column and a second distillation column in sequence; a first reboiler is externally connected to the reboiler of the first distillation column, the first reboiler being used to heat the bottom product of the first distillation column before it is refluxed into the reboiler of the first distillation column; a second reboiler is externally connected to the reboiler of the second distillation column, the second reboiler being used to heat the bottom product of the second distillation column before it is refluxed into the reboiler of the second distillation column; The first distillation column includes a feed inlet, a top outlet, and a bottom outlet. The second distillation column includes a feed inlet, a top outlet, and a bottom outlet. The top outlet of the first distillation column is connected to the feed inlet of the second distillation column through the second reboiler, forming a transmission channel.

10. The dual-tower distillation system as described in claim 9, characterized in that, The dual-tower distillation system satisfies one or more of the following conditions: (a) The first distillation column is further provided with a top reflux path and a top feed inlet of the first distillation column, and the top discharge outlet and the top feed inlet of the first distillation column are connected through the top reflux path of the first distillation column. (b) The second distillation column is further provided with a top reflux path and a top feed inlet of the second distillation column, and the top discharge outlet and the top feed inlet of the second distillation column are connected through the top reflux path of the second distillation column. (c) The bottom outlet of the second distillation column is connected to the feed inlet of the first distillation column; (d) The dual-tower distillation system further includes a first reflux tank and a first condenser. The top outlet of the first distillation column is connected to the feed inlet of the second distillation column in sequence through the second reboiler, the first condenser, and the first reflux tank. (e) The first distillation column is provided with structured packing above the feed inlet and with anti-clogging trays below the feed inlet. (f) The second distillation column is equipped with structured packing.

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