Drying method of chlorobenzene

Abstract

The invention provides a method for high-precision removal of water in chlorobenzene. A drying tower is filled with a molecular sieve as a drying agent, chlorobenzene in a chlorobenzene storage tank enters the drying tower at a certain flow speed, the treated chlorobenzene is sampled at an outlet of the drying tower to analyze the water content, qualified chlorobenzene enters a special receiving tank, and unqualified products are returned to the chlorobenzene storage tank. The method solves the problem of poor technical effect of the existing crude salt chlorobenzene drying process, and the produced chlorobenzene with the water content of less than 50ppm can be used for various production occasions with high requirements on the water content.

Description

Technical Field

[0001] The invention belongs to the technical field of organic chemical adsorption and desorption, and particularly relates to a molecular sieve for drying and dehydrating chlorobenzene and an operating method. Background Art

[0002] Chlorobenzene is a colorless liquid with a boiling point of 132.2°C. During World War II, it was mainly used to produce picric acid for explosives. From 1940 to 1960, it was used in large quantities to produce DDT insecticide. After 1960, DDT was gradually replaced by other pesticides with low residual toxicity, and the demand for chlorobenzene gradually decreased. It is mainly used as a solvent for ethyl cellulose and many resins, and to produce a variety of other benzene intermediates, such as nitrochlorobenzene: (1) It is used as an intermediate for dyes, pesticides, and organic synthesis. It is also used to make solvents and rubber additives, paints, quick-drying inks, and dry cleaning agents. (2) It is used as a solvent for nitro spray paints, coatings, and varnishes. In industry, it is used as a raw material for the manufacture of aniline, phenol, picric acid, dyes, fragrances, insecticides, etc. (3) It is used as a solvent, a gas chromatography reference substance, and is used in organic synthesis. It is also used for testing electronic industry products and raw materials. (4) It is an important raw material for organic synthesis.

[0003] The traditional method for drying and dehydrating chlorobenzene is the crude salt drying process. This method is simple to operate and low-cost, but its disadvantage is that the finished chlorobenzene has a high water content (generally around 150 ppm), making it unsuitable for applications requiring a high water content. For example, chlorobenzene is often used as a solvent and heat transfer medium in chemical production. Because it does not react with phosgene, it is a popular solvent in the manufacture of MDI and TDI. However, to reduce phosgene consumption, the chlorobenzene solvent used in MDI and TDI production must contain less than 50 ppm of water. Chlorobenzene with a low water content is sold at a much higher price than chlorobenzene with a high water content.

[0004] It has been reported that a certain chlorobenzene company uses distillation dehydration, adopts a high-plate-count distillation tower, controls the reflux ratio, and reduces the extraction volume, which can simultaneously reduce the content of water and organic impurities in the chlorobenzene finished product. The moisture content of the treated chlorobenzene finished product reaches below 50ppm, and the organic impurities are below 10ppm.

[0005] CN107855004A discloses a method for drying chlorinated liquid in a benzene chlorination reaction using a membrane assembly. The method uses a membrane assembly to separate water from the chlorinated liquid. The chlorinated liquid is passed through the membrane assembly and a certain pressure is applied, so that some of the water remains within the membrane assembly, thereby reducing the water content of the chlorinated liquid from 0.08% to 0.04%. This method is used to treat crude chlorobenzene, but the water content after treatment is still as high as 0.04%, making it impossible to achieve higher-precision dehydration.

[0006] CN209612270U describes a device for molecular sieve drying of chlorobenzene products: a chlorobenzene drying device comprising a chlorobenzene tank, a molecular sieve drying unit, a finished product tank, and a nitrogen heating and purge unit; the molecular sieve drying unit comprises a drying cylinder and a cooling water storage tank. The drying cylinder is filled with an alumina molecular sieve filler to absorb the moisture contained in the chlorobenzene. The discharge port of the drying cylinder is connected to the feed port of the chlorobenzene tank via a pipe, allowing chlorobenzene with a moisture content greater than 0.01% to enter the chlorobenzene tank for repeated drying. The discharge port of the drying cylinder is also connected to the feed port of the finished product tank via a pipe, allowing chlorobenzene with a moisture content of 0.01% after drying to enter the finished product tank. The molecular sieve described in this patent is an alumina molecular sieve, and the moisture content of the dried chlorobenzene product is 0.01% (i.e., 100 ppm).

[0007] Therefore, it is necessary to develop a simple and easy-to-operate method to reduce the water content in chlorobenzene products. Summary of the Invention

[0008] In order to solve the problem of poor effect of the crude salt drying process of chlorobenzene in the prior art, the present invention provides a method for removing moisture from chlorobenzene with high precision, namely, a method for drying chlorobenzene.

[0009] The main technical solution of the present invention is a method for drying chlorobenzene, which is characterized in that chlorobenzene is dried using a molecular sieve as a desiccant, wherein the molecular sieve has an A-type molecular sieve crystal structure and an effective pore size of 3-5Å.

[0010] Preferably, the molecular sieve is spherical or strip-shaped, with a particle size of 3-4 mm.

[0011] Preferably, the molecular sieve is loaded in a drying tower, chlorobenzene enters the drying tower from a storage tank, chlorobenzene with qualified water content after drying treatment enters a receiving tank, and chlorobenzene with unqualified water content returns to the storage tank.

[0012] Preferably, the water content of the feed chlorobenzene is controlled to be 150-200 ppm, and the water content of the qualified chlorobenzene after drying is ≤50 ppm.

[0013] Preferably, the molecular sieve is loaded in a drying tower, and inert aluminum balls or porcelain rings, molecular sieve, inert aluminum balls or porcelain rings are loaded in sequence from bottom to top. The ratio of the molecular sieve loading height to the inner diameter of the loading section is 4:1~5:1, and the size of the inert aluminum balls or porcelain rings above and below the molecular sieve is 5-8 mm, preferably 6 mm.

[0014] Preferably, the chlorobenzene is fed from the bottom of the drying tower, and the dried chlorobenzene is taken out from the top of the drying tower.

[0015] Preferably, the chlorobenzene feed space velocity is 0.8-1.5h -1 .

[0016] Preferably, after the molecular sieve is saturated with adsorption, dry hot nitrogen is used to purge the molecular sieve in the drying tower.

[0017] Preferably, the nitrogen gas feed space velocity into the drying tower is 6-10h -1 , nitrogen temperature 180-220℃, nitrogen pressure ≤0.1MPa.

[0018] Preferably, when the drying system is not in operation, the chlorobenzene liquid is vented from the bottom and filled with dry nitrogen. After the nitrogen is filled, the pressure in the drying tower does not exceed 0.1 MPa.

[0019] The beneficial effects of the present invention are as follows: the present invention provides a method for removing moisture from chlorobenzene with high precision, which solves the problem that the existing crude salt drying process technology for chlorobenzene is poor in effect, and the output chlorobenzene with a moisture content of less than 50 ppm can be used in various production occasions with high moisture content requirements. Implementation Method

[0020] The present invention will be described in further detail below with reference to the examples. It should be understood that the following examples are only intended to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made by professionals in this field based on the contents of the present invention still fall within the scope of protection of the present invention. Example 1

[0021] The drying tower barrel has internal dimensions of 1000 x 6000 mm. A grid and screen are used at the bottom of the barrel to support the proppant and molecular sieve loaded into the drying tower. Starting from the bottom, load the tower with 6mm inert aluminum balls or ceramic rings, molecular sieve, and 6mm inert aluminum balls or ceramic rings, respectively. After loading, purge the molecular sieve from bottom to top with hot nitrogen (120-180°C) to remove particulates generated during the loading process and any small amounts of moisture absorbed by the molecular sieve. This purge lasts for 4-8 hours. After the purge is complete, introduce room-temperature dry nitrogen to maintain a nitrogen pressure of 0.1 MPa within the tower before use.

[0022] The drying tower is filled with spherical molecular sieves with a pore size of 3Å and a particle size of 3-4mm. The height-to-diameter ratio of the molecular sieve filling section in the drying tower is 4:1. The water content of chlorobenzene before entering the tower is 150ppm, and the air velocity of the tower is 0.8h -1 , the water content of chlorobenzene after drying is 36ppm. Example 2

[0023] The drying tower is filled with spherical molecular sieves with a pore size of 5Å and a particle size of 3-4mm. The height-to-diameter ratio of the molecular sieve filling section in the drying tower is 5:1. The water content of chlorobenzene before entering the tower is 200ppm, and the air velocity of the tower is 1.5h -1 , the water content of chlorobenzene after drying is 45ppm. Example 3

[0024] The drying tower is filled with spherical molecular sieves with a pore size of 4Å and a particle size of 3-4mm. The height-to-diameter ratio of the molecular sieve filling section in the drying tower is 5:1. The chlorobenzene water content before entering the tower is 188ppm, and the air velocity before entering the tower is 0.8h -1 , the water content of chlorobenzene after drying is 48ppm. Example 4

[0025] The drying tower is filled with strip molecular sieves with a pore size of 4Å and a particle size of 3-4mm. The height-to-diameter ratio of the molecular sieve filling section in the drying tower is 4:1. The water content of chlorobenzene before entering the tower is 164ppm, and the air velocity of entering the tower is 1h -1 , the water content of chlorobenzene after drying is 44ppm. Example 5

[0026] The drying tower is filled with strip molecular sieves with a pore size of 3Å and a particle size of 3-4mm. The height-to-diameter ratio of the molecular sieve filling section in the drying tower is 4:1. The water content of chlorobenzene before entering the tower is 195ppm, and the air velocity of entering the tower is 0.8h -1 , the water content of chlorobenzene after drying is 36ppm. Example 6

[0027] The drying tower is filled with strip molecular sieves with a pore size of 5Å and a particle size of 3-4mm. The height-to-diameter ratio of the molecular sieve filling section in the drying tower is 5:1. The water content of chlorobenzene before entering the tower is 160ppm, and the air velocity before entering the tower is 1.5h -1 , the water content of chlorobenzene after drying is 50ppm. Example 7

[0028] The drying tower is filled with strip molecular sieves with a pore size of 5Å and a particle size of 3-4mm. The height-to-diameter ratio of the molecular sieve filling section in the drying tower is 4.5:1. The water content of chlorobenzene before entering the tower is 185ppm, and the air velocity of entering the tower is 1.2h -1 , the water content of chlorobenzene after drying is 46ppm.

Claims

1. A drying method for chlorobenzene, characterized in that The molecular sieve is used as a desiccant to dry the chlorobenzene, and the molecular sieve has a type A molecular sieve crystal structure and an effective pore size of 3-5Å.

2. The drying method according to claim 1, characterized in that The molecular sieve is spherical or strip-shaped with a particle size of 3-4 mm.

3. The drying method according to claim 1 or 2, characterized in that The molecular sieve is loaded in the drying tower, and chlorobenzene enters the drying tower from the storage tank. After drying, chlorobenzene with qualified water content enters the receiving tank, and chlorobenzene with unqualified water content returns to the storage tank.

4. The drying method according to claim 3, characterized in that The water content of the feed chlorobenzene is controlled to be 150-200ppm, and the water content of the qualified chlorobenzene after drying is ≤50ppm.

5. The drying method according to claim 3, characterized in that The molecular sieve is loaded in the drying tower, and from bottom to top, 5-8mm inert aluminum balls or ceramic rings are loaded as proppants, molecular sieves, 5-8mm inert aluminum balls or ceramic rings, and the ratio of the molecular sieve loading height to the inner diameter of the loading section tower is 4:1~5:

1.

6. The drying method according to claim 3, characterized in that Chlorobenzene is fed from the bottom of the drying tower, and the dried chlorobenzene is taken out from the top of the drying tower.

7. The drying method according to claim 6, characterized in that Chlorobenzene feed space velocity is 0.8-1.5h -1 .

8. The drying method according to claim 3, characterized in that After the molecular sieve is saturated with adsorption, dry hot nitrogen is used to purge the molecular sieve in the drying tower.

9. The drying method according to claim 8, characterized in that Nitrogen gas feed space velocity into the drying tower is 6-10h -1 , nitrogen temperature 180-220℃, nitrogen pressure ≤0.1MPa.

10. The drying method according to claim 3, characterized in that When the drying system is not in operation, the chlorobenzene liquid is vented from the bottom and filled with dry nitrogen. After filling with nitrogen, the pressure in the drying tower does not exceed 0.1MPa.