Low-temperature closed-cycle vertical fluidized bed drying system

Abstract

The invention discloses a low-temperature closed-cycle vertical fluidized bed drying system, relates to drying of dimethyl azodiisobutyrate, and aims to solve the problems that in the prior art, the drying temperature of dimethyl azodiisobutyrate is high, a molten state is extremely easy to form, the crystal form is damaged, the final drying efficiency is low, and the drying quality is difficult to guarantee. A vertical boiling fluidization device in the drying system is used for drying materials, a dust removal device efficiently intercepts solid particles in nitrogen, a low-temperature cooling recovery device sprays low-temperature water and absorbs an organic solvent in the nitrogen, a micro-heat adsorption device removes moisture in the nitrogen, and low-temperature dried nitrogen is obtained and then circulated to the vertical boiling fluidization device. According to the whole drying system, the drying temperature of the dimethyl azobisisobutyrate wet product is controlled to be below 15 DEG C, the drying efficiency of the dimethyl azobisisobutyrate wet product is greatly improved through the drying system, and the quality of the obtained dimethyl azobisisobutyrate wet product is also greatly improved.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical product production, relates to the drying of dimethyl azobisisobutyrate, and in particular to a low-temperature closed-circuit circulation vertical fluidized bed drying system for drying dimethyl azobisisobutyrate. Background Art

[0002] Dimethyl azobisisobutyrate is an important free radical initiator, mainly used in the polymerization of olefins, acrylic acid and its esters; used in styrene polymerization, it can obtain polymers containing ester end groups, and can be hydrolyzed to produce products containing carboxyl end groups. Dimethyl azobisisobutyrate is a heat-sensitive material, easy to decompose at high temperatures, and has a low melting point. Literature reports that the melting point range is 22-28°C.

[0003] The invention patent with application number 201811386205.2 also discloses a method for preparing dimethyl azobisisobutyrate, which comprises first putting 2,2'-azobisisobutyronitrile, methanol and ethylene dichloride into a reactor with a stirring and reflux device; starting stirring, slowly dripping thionyl chloride under cooling, and then controlling the material temperature and keeping warm for reaction; dripping into cold water for hydrolysis reaction after the reaction; standing for the first stratification after the hydrolysis reaction; washing the organic phase obtained after the first stratification with water and performing the second stratification; performing reduced pressure distillation on the organic phase after the second stratification until all the ethylene dichloride is distilled and recovered to obtain liquid dimethyl azobisisobutyrate; low-temperature cooling the liquid dimethyl azobisisobutyrate to obtain a white solid dimethyl azobisisobutyrate product, wherein the content (HPLC) of the white solid dimethyl azobisisobutyrate product is more than 98%, and the yield is 85-95%. The method uses cheaper thionyl chloride to replace hydrogen chloride gas. The thionyl chloride is liquid at room temperature, and it is easy to control the rate and amount when adding it dropwise, and the reaction time is shortened to 6 hours.

[0004] For example, the above-mentioned invention patents, existing literature reports focus on improving the synthesis method of dimethyl azobisisobutyrate. For example, the invention patent with application number 201610526787.4 discloses a method for synthesizing dimethyl azobisisobutyrate, which includes: (1) condensation: adding azobisisobutyronitrile, methanol, and isophorone into a reaction vessel, adding phosphorus trichloride solution for reaction, and centrifuging to obtain azodimine methyl ether hydrochloride solid material; (2) hydrolysis: adding pure water into the hydrolysis vessel, adding azodimine methyl ether hydrochloride solid material into the hydrolysis vessel for hydrolysis; (3) phase separation: placing the hydrolyzed liquid into a phase separation vessel, and using a phase transfer agent hexadecyltrimethylammonium chloride for phase separation; (4) recrystallization; (5) drying. The invention also lies in its synthesis method. By optimizing the process route and raw materials, the raw materials are environmentally friendly and non-toxic, the reaction is stable and easy to control, and the safety of the reaction is greatly improved. As for its drying, it is simply described as placing the wet dimethyl azobisisobutyrate product in a drying room for 24 hours at a drying temperature of ≤25°C.

[0005] In the prior art, the drying of dimethyl azobisisobutyrate is mostly carried out in a drying chamber, but the drying time of this drying method is long, and the selected drying temperature reaches the melting point of dimethyl azobisisobutyrate, the product is very easy to form a molten state, resulting in the destruction of the crystal form, and the solvent brought into the wet product is wrapped in the molten body and difficult to remove, resulting in low drying efficiency and difficult to ensure drying quality. In addition, the drying method of the drying chamber usually requires manual transportation or auxiliary machinery to transport the wet solid materials in and out of the box. The transportation process is poorly sealed, and the organic solvent in the wet product will volatilize to form unorganized exhaust gas, causing pollution to the environment, high labor intensity, poor operating environment, and low equipment processing capacity. Summary of the invention

[0006] The purpose of the present invention is to provide a low-temperature closed-loop vertical fluidized bed drying system in order to solve the problems in the prior art that dimethyl azobisisobutyrate is dried at a high temperature and easily forms a molten state, the crystal form is destroyed, resulting in low final drying efficiency and difficulty in ensuring drying quality.

[0007] In order to achieve the above-mentioned purpose, the present invention specifically adopts the following technical solutions:

[0008] A low-temperature closed-loop vertical fluidized bed drying system, comprising a vertical boiling fluidizing device, a dust removal device, a low-temperature cooling recovery device, and a micro-heat adsorption device which are sequentially arranged to form a closed loop;

[0009] The vertical boiling fluidized bed device uses low-temperature circulating nitrogen blown in from the bottom to blow up the crystallized material into suspension and fluidize and tumble, thereby drying the crystallized material to obtain dry products and nitrogen, which enters the dust removal device;

[0010] The dust removal device filters the nitrogen to remove solid particles in the nitrogen, and the filtered nitrogen enters the low-temperature cooling recovery device;

[0011] The low-temperature cooling recovery device sprays absorbent into the nitrogen, and the absorbent absorbs the organic solvent in the nitrogen. The nitrogen after the organic solvent is removed enters the micro-heat adsorption device;

[0012] The micro-thermal adsorption device dries the nitrogen at low temperature to obtain low-temperature circulating nitrogen, and the low-temperature circulating nitrogen is circulated to the vertical boiling fluidized bed device for recycling.

[0013] Furthermore, the temperature of the low-temperature circulating nitrogen gas blown into the vertical boiling fluidized bed device does not exceed 15°C, and the material to be dried in the vertical boiling fluidized bed device is a crystalline material at 0-5°C.

[0014] Furthermore, the absorbent sprayed in the low-temperature cooling recovery device is 5°C low-temperature water; after the absorbent absorbs the organic solvent, the nitrogen forms water-saturated nitrogen, and the temperature of the water-saturated nitrogen is 5-8°C.

[0015] Furthermore, the micro-thermal adsorption device dries the nitrogen to obtain low-temperature circulating nitrogen with a dew point below -40°C, and then the low-temperature circulating nitrogen is adjusted to 15°C and circulated to the vertical boiling fluidized bed device.

[0016] Furthermore, it also includes an induced draft device, which is located in a closed loop composed of a vertical boiling fluidization device, a dust removal device, a low-temperature cooling recovery device, and a micro-heat adsorption device, and the induced draft fan of the induced draft device drives the nitrogen to circulate in the closed loop.

[0017] The beneficial effects of the present invention are as follows:

[0018] 1. In the present invention, the drying system adopts a closed and circulating system composed of a vertical boiling fluidized bed device, a dust removal device, a low-temperature cooling recovery device, and a micro-heat adsorption device. The vertical boiling fluidized bed device adopts a fluidized bed structure to dry the material, the dust removal device adopts a bag filter to efficiently intercept solid particles in the nitrogen, the low-temperature cooling recovery device adopts a spray tower to spray low-temperature water from top to bottom and absorb organic solvents in the nitrogen, and the micro-heat adsorption device finally removes the moisture in the nitrogen and obtains low-temperature dry nitrogen, which is then circulated to the vertical boiling fluidized bed device. The entire drying system controls the drying temperature of the dimethyl azobisisobutyrate wet product at 15°C or below, effectively solving the problem that the high drying temperature of dimethyl azobisisobutyrate is very easy to form a molten state, the crystal form is destroyed, resulting in low final drying efficiency and difficult to ensure drying quality. The drying system greatly improves the drying efficiency of the dimethyl azobisisobutyrate wet product, and the quality of the obtained dimethyl azobisisobutyrate wet product is also greatly improved.

[0019] 2. In the present invention, the entire system is sealed, there is no environmental pollution, nitrogen is recycled, the problem of explosive organic solvents is solved, and it is suitable for continuous and large-scale industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic diagram of the drying process of the present invention. DETAILED DESCRIPTION

[0021] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments.

[0022] Therefore, based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making any creative inventions shall fall within the scope of protection of the present invention.

[0023] This embodiment provides a low-temperature closed-loop vertical fluidized bed drying system, which is mainly used to process the wet product of dimethyl azobisisobutyrate obtained by purification and crystallization with water or organic solvent, that is, to dry dimethyl azobisisobutyrate with a low melting point under low temperature conditions.

[0024] The drying system comprises a vertical boiling fluidization device, a dust removal device, a low-temperature cooling recovery device, and a micro-heat adsorption device which are arranged in sequence to form a closed loop.

[0025] In the vertical boiling fluidized bed, a vacuum feeding system is used to input the crystallized material (i.e., the wet product of dimethyl azobisisobutyrate) into the vertical boiling fluidized bed, and dry nitrogen is blown in from the bottom of the vertical boiling fluidized bed. The blown-in dry nitrogen gas flow forms a fluidized state, and the crystallized material is blown up and suspended, and fluidized and tumbled like a "boiling state". After the crystallized material is dried, a dry product and nitrogen are obtained, and the nitrogen enters the dust removal device. During the drying process, the "boiling" crystallized material is highly dispersed in the nitrogen, and the nitrogen contacts the surface of the wet material and greatly increases the evaporation area. The nitrogen gas flows through the suspended crystallized material, and heat exchange is performed in a dynamic state, accelerating the vaporization of water and solvent, thereby achieving the purpose of rapid drying. The vaporized water and solvent are discharged from the upper part of the vertical boiling fluidized bed along with the nitrogen and transported to the dust removal device.

[0026] In the dust removal device, the dust removal device (which can be a bag dust collector) uses bags to remove dust and uses a high-efficiency filter to filter the nitrogen, intercepting and filtering out solid particles in the nitrogen. The filtered nitrogen enters the low-temperature cooling recovery device, and the filtered solid particles are collected and taken out.

[0027] The cryogenic cooling recovery device sprays absorbent into the nitrogen, and the absorbent absorbs the organic solvent in the nitrogen. The nitrogen after the organic solvent is removed enters the micro-heat adsorption device. The cryogenic cooling recovery device uses 5°C low-temperature water as an absorbent to absorb the organic solvent in the nitrogen, and absorbs it in the cryogenic cooling recovery device (which can be a spray tower). The cryogenic cooling recovery device is layered with nozzles, and sprays low-temperature water from top to bottom to form highly dispersed mist droplets. The organic solvent in the nitrogen is fully in contact with the mist water and is absorbed, and flows out from the bottom of the cryogenic cooling recovery device and enters the collection tank for collection. The absorbent sprayed in the cryogenic cooling recovery device is 5°C low-temperature water; after the absorbent absorbs the organic solvent, the nitrogen forms water-saturated nitrogen, and the temperature of the water-saturated nitrogen is 5-8°C.

[0028] The micro-thermal adsorption device dries the nitrogen at low temperature to obtain low-temperature circulating nitrogen, which is then circulated to the vertical boiling fluidized bed device for recycling. After the micro-thermal adsorption device dries the nitrogen, low-temperature circulating nitrogen with a dew point below -40°C is obtained, and the low-temperature circulating nitrogen is then adjusted to 15°C and circulated to the vertical boiling fluidized bed device for recycling and drying.

[0029] In addition, in order to better drive and strengthen the flow of nitrogen in the closed loop, the drying system is also provided with an induced draft device, which is located in a closed loop consisting of a vertical boiling fluidization device, a dust removal device, a low-temperature cooling recovery device, and a micro-heat adsorption device, and drives the nitrogen to circulate in the closed loop through the induced draft fan of the induced draft device. The induced draft device can use the induced draft fan to drive the nitrogen to circulate in the entire system.

[0030] In addition, in the vertical fluidized bed drying device, the material to be dried is an organic crystalline particle at 0 to 5°C. The conventional airflow drying of dry air has the risk of forming explosive mixed dust. Therefore, inert gases such as nitrogen and helium are preferred. From the perspective of economy, nitrogen is undoubtedly the best choice. Different from the existing literature reports, the nitrogen temperature used in this embodiment should not be higher than 15°C through experiments, so that the melting state of the crystal can be effectively avoided during the drying process, and the purpose of rapid drying can be met. Due to the large amount of gas used in airflow drying, the existing process of drying tail gas after dust removal and discharge in fluidized bed drying is not suitable for use in this device. Discharge will cause the gas to be unable to be recycled, and direct circulation will cause the gas moisture content to continue to increase, thereby causing the circulation process to be unable to operate continuously and stably. Therefore, the nitrogen after drying must be dusted, impurity-removed, and dehydrated to achieve the requirement of nitrogen to meet the recycling requirements.

[0031] In this embodiment, after feeding by a vacuum feeding system, the wet material is fluidized by a dry nitrogen gas flow in a vertical fluidized bed. In this state, the crystalline material is highly dispersed in the nitrogen, and the nitrogen contacts the surface of the wet material to accelerate the gasification of water and solvent, thereby achieving the purpose of rapid drying; the gasified water and solvent are discharged from the upper part of the fluidized bed along with the nitrogen, and solid impurities are removed by a dust collector, and methanol organic solvent is removed by absorption using low-temperature water, and dry nitrogen is obtained by dehydration through a micro-thermal adsorption device, which is circulated in the drying system.

Claims

1. A low-temperature closed-circuit vertical fluidized bed drying system, characterized in that: It includes a vertical boiling fluidization device, a dust removal device, a low-temperature cooling recovery device, and a micro-heat adsorption device which are arranged in sequence to form a closed loop; The vertical boiling fluidized bed device uses low-temperature circulating nitrogen blown in from the bottom to blow up the crystallized material into suspension and fluidize and tumble, thereby drying the crystallized material to obtain dry products and nitrogen, which enters the dust removal device; The dust removal device filters the nitrogen to remove solid particles in the nitrogen, and the filtered nitrogen enters the low-temperature cooling recovery device; The low-temperature cooling recovery device sprays absorbent into the nitrogen, and the absorbent absorbs the organic solvent in the nitrogen. The nitrogen after the organic solvent is removed enters the micro-heat adsorption device; The micro-thermal adsorption device dries the nitrogen at low temperature to obtain low-temperature circulating nitrogen, and the low-temperature circulating nitrogen is circulated to the vertical boiling fluidized bed device for recycling.

2. A low-temperature closed-circuit vertical fluidized bed drying system as claimed in claim 1, characterized in that: The temperature of the low-temperature circulating nitrogen gas blown into the vertical boiling fluidized bed device does not exceed 15°C, and the material to be dried in the vertical boiling fluidized bed device is a crystalline material at 0-5°C.

3. A low-temperature closed-circuit vertical fluidized bed drying system as claimed in claim 1, characterized in that: The absorbent sprayed in the low-temperature cooling recovery device is 5°C low-temperature water; after the absorbent absorbs the organic solvent, the nitrogen forms water-saturated nitrogen, and the temperature of the water-saturated nitrogen is 5-8°C.

4. A low-temperature closed-circuit vertical fluidized bed drying system as claimed in claim 1, characterized in that: The micro-heat adsorption device dries the nitrogen to obtain low-temperature circulating nitrogen with a dew point below -40°C. The low-temperature circulating nitrogen is then temperature-adjusted to 15°C and circulated to the vertical boiling fluidized bed device.

5. A low-temperature closed-circuit vertical fluidized bed drying system as claimed in claim 1, characterized in that: It also includes an induced draft device, which is located in a closed loop consisting of a vertical boiling fluidization device, a dust removal device, a low-temperature cooling recovery device, and a micro-heat adsorption device, and drives the nitrogen to circulate in the closed loop through the induced draft fan of the induced draft device.

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