CN110981685B

CN110981685B - Method for separating benzene and isobutanol mixture through heat pump-assisted pressure swing distillation

Info

Publication number: CN110981685B
Application number: CN201911363199.3A
Authority: CN
Inventors: 张治山; 光超; 马艺心; 高军
Original assignee: Shandong University of Science and Technology
Current assignee: Shandong University of Science and Technology
Priority date: 2019-12-26
Filing date: 2019-12-26
Publication date: 2022-05-06
Anticipated expiration: 2039-12-26
Also published as: CN110981685A

Abstract

The invention discloses a method for separating a mixture of benzene and isobutanol by pressure swing rectification assisted by a heat pump, which mainly uses a mechanical vapor recompression type heat pump and a heat integration technology and comprises the following steps: benzene and isobutanol raw material liquid are preheated and then enter a low-pressure stripping tower from the top of the tower, a high-purity isobutanol product is extracted from the tower kettle, a vapor phase at the top of the tower is preheated and compressed to high temperature and high pressure and then enters a high-pressure rectifying tower from the bottom of the tower, steam at the top of the high-pressure rectifying tower is used as a heat source of a reboiler of the low-pressure stripping tower, liquid at the bottom of the low-pressure stripping tower is used as a heat trap of the reboiler, part of the steam at the top of the high-pressure rectifying tower is used as liquid at the top of the tower for reflux after being completely condensed, a high-purity benzene product is extracted, and the liquid at the bottom of the tower is circulated to the top of the low-pressure stripping tower. The invention greatly improves the thermodynamic efficiency and the economy of the separation process of the mixture of the benzene and the isobutanol, and realizes the purposes of energy conservation and emission reduction.

Description

Method for separating benzene and isobutanol mixture through heat pump-assisted pressure swing distillation

Technical Field

The invention belongs to the technical field of separation and purification in the chemical industry, and particularly relates to an energy-saving method for separating binary azeotrope by heat pump-assisted pressure swing distillation, which is particularly suitable for special systems such as benzene and isobutanol, wherein the largest azeotrope is formed at high pressure, the lowest azeotrope is formed at low pressure, and the method can be widened to other similar systems.

Background

Benzene is aromatic hydrocarbon with the simplest composition structure, is colorless, sweet, aromatic and oily transparent liquid at normal temperature, is insoluble in water and has good solubility, so that the benzene is widely used as an adhesive and an industrial solvent. It is an important petrochemical basic material used for synthesizing dyes, rubber, resin, fiber, plastics, medicines, pesticides, films and petrochemical products.

Isobutanol is a colorless transparent liquid at normal temperature, has a special smell, has a density lower than that of water, is slightly soluble in water, and is easily soluble in ethanol and diethyl ether. It is a basic organic chemical raw material, mainly used for producing diisobutyl phthalate plasticizer and isobutyl acetate solvent, and also a small amount of the plasticizer and the isobutyl acetate solvent are used for producing isobutyl butyrate, isobutyl lactate and the like. Isobutanol is also an important organic solvent for dissolving nitrocellulose, ethylcellulose, polyvinyl butyral, rubber and natural resins and various oils.

During the production of certain cellulose nitrate paints, large quantities of mixtures of benzene and isobutanol are produced, which are extremely carcinogenic and environmentally damaging. Therefore, the effective separation and purification of the active carbon has important significance for reducing resource waste and environmental pollution. The mixture of benzene and isobutanol belongs to a special pressure-sensitive azeotropic system and has different azeotropic behaviors under different pressures, as shown in the attached figure 1. The mixture can form a minimum azeotrope when the pressure is less than 380kPa, can form a maximum azeotrope when the pressure is more than 557.3kPa, does not form an azeotrope when the pressure is 380-557.3 kPa, but has small relative volatility, so that the mixture is difficult to completely separate by adopting common rectification. By utilizing the characteristic of azeotropic behavior of the system, a separation method of pressure swing distillation is reported in a patent.

Chinese patent CN 107986928A proposes a method for separating an azeotropic system of benzene and isobutanol by pressure swing distillation, which comprises two sequences: (1) firstly, performing pressure swing rectification under normal pressure and then under pressure, extracting an isobutanol product from the bottom of a normal pressure tower, and feeding tower top material flow into a pressure tower for secondary rectification; benzene products are extracted from the top of the pressurizing tower, and tower bottom material flows circularly enter the atmospheric tower for rectification; (2) firstly pressurizing, then performing pressure swing distillation under normal pressure, extracting a benzene product from the top of a pressurizing tower, feeding a tower bottom material flow into a normal pressure tower for secondary distillation, extracting an isobutanol product from the bottom of the normal pressure tower, and circularly feeding a tower top material flow into the pressurizing tower for distillation. Although the method can obtain high-purity benzene and isobutanol products, the equipment cost and the energy consumption cost are greatly reduced if heat integration and thermal coupling strengthening technologies are adopted. Chinese patent CN 105001056B describes a method for separating an azeotropic system of isobutanol and n-heptane by pressure swing distillation. Pressure-variable rectification of firstly normal pressure and then pressurization is adopted, isobutanol products are obtained at the bottom of a normal pressure tower, and tower top material flow enters a pressurization tower for secondary rectification; and (3) extracting an n-heptane product from the top of the pressurizing tower, and circularly feeding the tower bottom material flow into the atmospheric tower for rectification. The pressure swing rectification process does not consider any energy integration, reboilers at the bottom of the tower use a thermal utility, and condensers at the top of the tower use a cold utility; at the same time, the minimum azeotrope produced at the top of the atmospheric tower and the maximum azeotrope produced at the bottom of the pressurized tower lead to increased equipment and energy costs.

At present, in the field of energy-saving reinforcement in the rectification process, the research and application of the mechanical vapor recompression heat pump technology are increasingly wide. Chinese patent CN 105964007B describes an apparatus and process for separating a mixture of n-butanol and isobutanol. The vapor recompression heat pump technology reported in the patent belongs to self-heating recovery technology, a compressor is arranged like an internal heat integration technology, the whole process can save a large amount of energy, and the separated n-butyl alcohol-isobutyl alcohol mixture belongs to a binary non-azeotropic system. Therefore, the development of an energy-saving, efficient and economical heat pump rectification separation method and device aiming at binary special azeotropic systems such as benzene, isobutanol and the like is of great significance.

Disclosure of Invention

The invention discloses a method for separating a mixture of benzene and isobutanol by pressure swing distillation assisted by a heat pump. The variable pressure rectification adopts the low pressure tower only with the stripping section and the high pressure tower only with the rectification section, thereby reducing the cost of the tower, realizing thorough separation, avoiding the problems of product recontamination and the like, and adopting the technologies of mechanical vapor recompression type heat pump, heat integration, product waste heat recovery and the like, greatly reducing the energy consumption, improving the thermodynamic efficiency and reducing the carbon dioxide emission.

In order to achieve the purpose, the invention adopts the following technical scheme:

the invention provides a method for separating a mixture of benzene and isobutanol by pressure swing distillation assisted by a heat pump, which comprises the following steps: distributing benzene and isobutanol raw material liquid through a distributor II, then respectively entering a heat exchanger I and a heat exchanger II to preheat benzene and isobutanol products, then mixing the benzene and isobutanol raw material liquid with a high-pressure rectifying tower bottom flow, and then entering the tower from the top of a low-pressure stripping tower; high-purity isobutanol products are extracted from the bottom of the low-pressure stripping tower, gas phase at the top of the tower is heated to be in an overheated state through a heat exchanger III, is compressed through a compressor and enters the high-pressure rectifying tower from the bottom of the tower; high-purity benzene steam at the top of the high-pressure rectifying tower enters a reboiler tube side of a tower kettle of the low-pressure stripping tower to exchange heat with an isobutanol product, complete heat integration is realized, the benzene steam is condensed, high-purity isobutanol is gasified, part of the condensed benzene steam is distributed through a distributor I and then flows back as tower top liquid, the rest of the condensed benzene steam is extracted as the benzene product, and the high-pressure rectifying tower liquid enters the top of the low-pressure stripping tower together with the raw material after being throttled and depressurized through a valve.

According to the method for separating benzene and isobutanol by using the embodiment, the matched device comprises the following components in combination with the attached drawings: the system comprises a low-pressure stripping tower (1), a high-pressure rectifying tower (2), a reboiler (3), a heat exchanger I (7), a heat exchanger II (8), a heat exchanger III (4), a compressor (5), a valve (6), a distributor I (9), a distributor II (10), a mixer I (11), a mixer II (12) and a matched pipeline (S101-S119).

According to the method for separating benzene and isobutanol by using the embodiment, the accompanying device is connected with the following steps by combining the attached figure 2:

(1) the feeding pipe (S101) is directly connected with the distributor II (10);

(2) the heat exchanger I (7) and the heat exchanger II (8) are respectively connected with the distributor II (10) and the top of the low-pressure stripping tower (1) through two pipelines;

(3) the bottom of the low-pressure stripping tower (1) is connected with a reboiler through a pipeline and is provided with a discharge pipe;

(4) the top of the low-pressure stripping tower (1) is connected with a heat exchanger III (4) through a pipeline;

(5) the heat exchanger III (4) is connected with the compressor through a pipeline;

(6) the compressor (5) is connected with the bottom of the high-pressure rectification tower (2) through a pipeline;

(7) the top of the high-pressure rectification tower (2) is connected with a reboiler (3) through a pipeline;

(8) the reboiler (3) is connected with the distributor I (9) through a pipeline;

(9) one pipeline of the distributor I (9) is connected with the top (2) of the high-pressure rectifying tower, and the other pipeline is used as a discharge pipe;

(10) the bottom of the high-pressure rectifying tower (2) is connected with the top of the low-pressure stripping tower (1) through a pipeline provided with a valve (6);

(11) other parts requiring pressurization and depressurization are provided with pumps or valves.

Detailed description of the process for separating benzene and isobutanol according to the examples: preheating (such as 84 ℃) of a mixed solution of benzene and isobutanol with pressure (such as 3.5atm), then feeding the preheated mixed solution into the top of a low-pressure stripping tower, producing isobutanol at the bottom of the tower, preheating (such as 140.8 ℃) of an overhead vapor phase, then feeding the preheated vapor phase into a compressor to increase the pressure (such as 7.2atm) and the temperature (such as 176.6 ℃) of the overhead vapor phase, and then feeding the preheated vapor phase into the bottom of a high-pressure rectifying tower. Meanwhile, the steam at the top of the high-pressure rectifying tower exchanges heat with a reboiler of the low-pressure stripping tower, the steam is completely condensed, the steam is circulated to the top of the high-pressure rectifying tower according to a certain proportion (such as 0.723) and the rest is taken out as a benzene product, and the liquid at the bottom of the tower is throttled and depressurized (such as 3.5atm) and then enters the top of the low-pressure stripping tower together with the raw material liquid.

The method specifically comprises the following conditions:

(1) the benzene molar content of the raw material liquid is preferably 0.3-0.7;

(2) the preheating distribution ratio of the raw material liquid is preferably 0.257-0.600;

(3) the number of theoretical plates of the low-pressure stripping tower is preferably 18-20;

(4) the number of theoretical plates of the high-pressure rectifying tower is preferably 20-28;

(5) the operation pressure of the low-pressure stripping tower is preferably 1 atm-4 atm;

(6) the operating pressure of the high-pressure rectifying tower is preferably 7 atm-8 atm;

(7) the preferred tower top temperature of the low-pressure stripping tower is 88-134 ℃, and the preferred tower bottom temperature is 110-148 ℃;

(8) the top temperature of the high-pressure rectifying tower is preferably 160-168 ℃, and the bottom temperature of the high-pressure rectifying tower is preferably 180-187 ℃;

(9) the outlet temperature of the heat exchanger III before the compressor is preferably 140-147 ℃;

(10) the reflux distribution ratio of the condensate at the top of the high-pressure rectifying tower is preferably 0.560-0.724;

(11) the compression ratio of the compressor is preferably 2.0-8.2.

Compared with the prior art, the invention has the following beneficial effects:

(1) the pressure swing distillation of the invention does not need to introduce extra components, the product purity is high and can reach 99.5mol%, and the recovery rate is increased;

(2) the pressure swing rectification separation process of the invention realizes complete heat integration, and saves two condensers and one reboiler compared with the prior process;

(3) the separation process adopts a mechanical vapor recompression type heat pump technology, so that the thermodynamic efficiency is improved, and the carbon dioxide emission is reduced;

(4) the separation process of the invention reduces the operation cost and equipment investment and can obtain good economic benefit.

Drawings

Figure 1 is a depiction of the phase balance of a benzene and isobutanol system for feasibility analysis of the design.

Figure 2 is a separation flow of a benzene and isobutanol system and equipment thereof.

In the figure, the device and the corollary equipment are as follows: 1-low pressure stripping column; 2-high pressure rectification column; 3-a reboiler; 4-heat exchanger III; 5, a compressor; 6, a valve; 7, a heat exchanger I; 8, a heat exchanger II; 9-distributor I; 10-distributor ii; 11-mixer i; 12-mixer ii; S101-S119-pipeline.

Detailed Description

To facilitate understanding of the technical solutions of the present invention, the present invention is further described with reference to the accompanying drawings, and the scope of the present invention is not limited by the claims. The feed and column pressures of the following examples are included in the mixture concentration fluctuation range and pressure setting range described in the present invention.

Example 1:

plant design parameters and operating conditions, feed conditions and product purity are shown in the table.

Example 2:

the plant design parameters and operating conditions, feed conditions and product purity are as indicated.

Example 3:

Example 4:

Example 5:

Example 6:

Example 7:

Example 8:

Example 9:

Example 10:

Example 11:

Example 12:

Claims

1. A method for separating a mixture of benzene and isobutanol by pressure swing distillation assisted by a heat pump is characterized in that a device for realizing the method comprises the following components:

the system comprises a low-pressure stripping tower (1), a high-pressure rectifying tower (2), a reboiler (3), a heat exchanger III (4), a compressor (5), a valve (6), a heat exchanger I (7), a heat exchanger II (8), a distributor I (9), a distributor II (10), a mixer I (11) and a mixer II (12); wherein the feeding pipe (S101) is directly connected with the distributor II (10); the heat exchanger I (7) and the heat exchanger II (8) are respectively connected with the distributor II (10) through two pipelines (S102 and S103), and are also respectively connected with the mixer I (11) through two pipelines (S104 and S105); the mixer I (11) is connected with the mixer II (12) through a pipeline (S106); the mixer II (12) is connected with the top of the low-pressure stripping tower (1) through a pipeline (S107); the bottom of the low-pressure stripping tower (1) is connected with the shell side of the reboiler through a pipeline and is provided with a discharge pipe (S109); the discharge pipe (S109) is connected with the other side and connected with a heat exchanger II (8), and a pipeline (S110) is arranged at the outlet of the heat exchanger II (8); the top of the low-pressure stripping tower (1) is connected with a heat exchanger III (4) through a pipeline (S108); the heat exchanger III (4) is connected with the compressor (5) through a pipeline (S111); the compressor (5) is connected with the bottom of the high-pressure rectifying tower (2) through a pipeline (S112); the tower top is connected with the tube pass of the reboiler (3) through a pipeline (S113); the reboiler (3) is connected with the distributor I (9) through a pipeline (S114); the distributor I (9) is connected with the top of the high-pressure rectifying tower (2) through a pipeline (S116), and the other pipeline is used as a discharge pipe (S115); the discharging pipe (S115) is connected with the other side of the heat exchanger I (7), and a pipeline (S117) is arranged at the outlet of the heat exchanger I (7); the tower bottom of the high-pressure rectifying tower (2) is connected with a throttling valve (6) through a pipeline (S118), and the throttling valve (6) is connected with a mixer II (12) through a pipeline (S119);

the method mainly comprises the following steps:

(1) distributing benzene and isobutanol raw material liquid through a distributor II, then respectively entering a heat exchanger I and a heat exchanger II to preheat benzene and isobutanol products, then mixing with a high-pressure rectifying tower bottom flow, and then entering the tower from the top of a low-pressure stripping tower;

(2) high-purity isobutanol products are extracted from the bottom of the low-pressure stripping tower, gas phase at the top of the tower is heated to be in an overheated state through a heat exchanger III, is compressed through a compressor and enters the high-pressure rectifying tower from the bottom of the tower;

(3) high-purity benzene steam at the top of the high-pressure rectifying tower enters a reboiler tube side of a tower kettle of the low-pressure stripping tower to exchange heat with an isobutanol product, so that complete heat integration is realized, the benzene steam is condensed, the high-purity isobutanol is gasified, part of the condensed benzene steam is distributed by a distributor I and then flows back as tower top liquid, the rest of the condensed benzene steam is extracted as a benzene product, and the high-pressure rectifying tower liquid enters the top of the low-pressure stripping tower together with the raw material after being throttled and depressurized by a valve;

the theoretical plate number of the low-pressure stripping tower is 18-20, the operating pressure is 1 atm-4 atm, the temperature of the top of the tower is 88-134 ℃, and the temperature of the bottom of the tower is 110-148 ℃;

the theoretical plate number of the high-pressure rectifying tower is 20-28, the operating pressure is 7 atm-8 atm, the temperature of the top of the tower is 160-168 ℃, and the temperature of the bottom of the tower is 180-187 ℃;

the distribution ratio of the distributor I is 0.560-0.724; the distribution ratio of the distributor II is 0.257-0.600.

2. The method for separating the mixture of benzene and isobutanol by heat pump-assisted pressure swing distillation according to claim 1, wherein the method comprises the following steps: the molar content of benzene in the raw material liquid is 0.3-0.7.

3. The method for separating the mixture of benzene and isobutanol by heat pump-assisted pressure swing distillation according to claim 1, wherein the method comprises the following steps: the outlet temperature of the heat exchanger III before the compressor is 140-147 ℃, and the compression ratio of the compressor is 2.0-8.2.

4. The method for separating the mixture of benzene and isobutanol by heat pump-assisted pressure swing distillation according to claim 1, wherein the method comprises the following steps: the purity of the separated benzene is more than 99.5 percent, and the recovery rate of the benzene is 98.84 to 99.77 percent; the purity of the isobutanol is more than 99.5 percent, and the recovery rate of the isobutanol is 98.81 to 99.78 percent.