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Application of supercritical fluid technology(2)——Supercritical printing and dyeing

Overview


Water is an extremely precious resource and cannot be consumed endlessly. Until today, textile dyeing still uses water as the medium. Dyeing and finishing is the industry that consumes the most water in the entire textile industry. The water consumption per 100 meters of printing and dyeing cloths It is (2.5-4)m3. Traditional dyeing methods not only use more water, but also discharge waste water containing unfixed dyes and auxiliaries after dyeing. These substances increase the load on the waste water and are a major source of environmental pollution. The sewage treatment costs of the traditional printing and dyeing industry will increase in the future. Therefore, people began to develop new anhydrous processes, and the supercritical fluid dyeing completely does not use water during the entire dyeing process, does not cause pollution, does not require auxiliaries, and residual dyes can also be recycled.


Among many substances, CO2 is a non-polar molecule and is suitable for the dyeing of hydrophobic synthetic fibers. Among them, polyester is an important synthetic fiber, which has strong hydrophobicity, less dye-up groups, poor moisture absorption, and small puffing in water. Only the dyes with smaller molecular weights are easy to dye, they are difficult to dye with hydrophilic dyes, and they are not easily dyed deep to achieve a firm color. Supercritical CO2 dyeing can make the dyes better penetrate into the fiber polyester, exacerbating the polyester Swelling promotes the diffusion and transfer of dye molecules and accelerates the binding of dye molecules to polyester.

 

 


 Supercritical dyeing technology has a good effect on the dyeing of synthetic fibers. Supercritical dyeing of polar natural fibers is still in the exploratory stage. Research on the dyeing of natural fibers with supercritical dyeing devices has made some progress.


Comprehensive consideration of the environment and the above-mentioned technical factors make supercritical CO2 the best choice for the textile industry. The low viscosity and high solubility of the supercritical fluid give it a high application value and can well enter into very small holes. No convection driving force between holes.


China is a large textile country. There are many enterprises engaged in the textile industry. The water pollution and end treatment brought by traditional dyeing methods have become a barrier to the development of enterprises. The development of dyeing technologies that minimize the use of water has become the development direction of the printing and dyeing industry. The product development team is keenly aware of market conditions. The research and development of the supercritical dyeing device will be another new development point after the supercritical extraction device. The company's development personnel will combine the experience of producing supercritical extraction devices and high-temperature and high-pressure reaction vessels. See also The domestic and foreign literature on supercritical dyeing has formed a complete set of design solutions.

 

1. Dye Kettle: The design pressure is 40MPa, and the maximum design temperature is 350°C. The oil bath is used for heating and the heat transfer medium is silicone oil. There are 3 dyestuff baskets inside, 1 for 2 and the dyestuff kettle is sealed in a special structure. The structure is self-sealing. The higher the pressure is, the better the self-sealing effect is, and the quick opening type is used. Long-term use does not need to replace the seal. Circles need not be replaced within at least one year.


 

2. Coloring kettle: The design pressure is 40MPa, the maximum design temperature is 350°C, and the oil bath is used for heating. The heating medium is silicone oil. There are 3 fabric baskets in total, 1 for 2 and the dyeing kettle is sealed in a special structure. The structure is self-sealing. The higher the pressure is, the better the self-sealing effect is, and the faster the opening type is, the long-term use does not need to replace the sealing ring. At least one year does not need to be replaced.


 

By lowering the temperature and pressure, the residual dye in the supercritical fluid is released from the bottom of the separation vessel. The water bath is used for warming and heat preservation, and a spiral copper coil is set in the water jacket sandwich, which can be circulated through the cooling liquid and synchronized with the water bath to control the temperature. The inlet of the separation kettle is connected to the bottom of the infusion tube, the heating jacket of the kettle body and the insulation layer, and the maximum separation temperature can reach 85°C. The inner wall is processed by a special process. The surface roughness is formed into a mirror surface, which can effectively improve the retention of the inner wall material.

 

There are the following two types of dyeing cycle:



1. The upper end of the dyeing basket basket → Valve 26 → Circulating pump → Observation window → Dye cartridge → Valve 24 → Flowmeter → Valve 29 → Lower end of the dyeing basket


2. The bottom of the dyeing basket basket → Valve 28 → Circulating pump → Observation window → Dye cartridge → Valve 24 → Flowmeter → Valve 27 → Lower end of the dyeing basket

 

 

 

After the corresponding valve is opened according to the above procedure, the circulation pump is started to work again, so that the supercritical fluid containing the dye is repeatedly circulated between the dyeing kettle and the dyeing kettle, so that the solid dye in the dyeing tank continuously dissolves in the fluid while the fluid is circulated. Causes the dye to constantly stain the fiber. After a certain period of dyeing, the dye on the fiber is saturated and the dyeing process is completed.


1. Dye and carbon dioxide recovery process: After the dyeing is completed, the supercritical state is destroyed by the separation tank, residual dye is discharged from the bottom of the separation tank, and carbon dioxide is recycled from above to the loop for recycling.

2. Pressure relief process: Close the valve around the dyeing vessel, open the vent valve, wait until the pressure is zero, remove the autoclave from the oil bath, quickly cool, open the kettle lid after cooling, and remove the fabric.