China is a big country of textile printing and dyeing, and the textile printing and dyeing industry is one of the most important industries in the textile industry. According to the statistics of the China Printing and Dyeing Industry Association, the number of printing and dyeing enterprises in the country is more than 2,300, the annual output of printed fabrics is more than 46.721 billion meters, and the processing capacity ranks first in the world. However, in the printing and dyeing process, a large amount of wastewater needs to be discharged, which has high organic pollutant content and deep chroma, which is difficult to effectively recycle, and the cost of environmental protection is high.

According to the data of the State Environmental Protection Administration, the total amount of printing and dyeing wastewater ranks fifth in the total industrial discharge in the country, accounting for 80% of the entire textile industry. With the improvement of national environmental protection standards and the enhancement of people's awareness of environmental protection, environmental protection has become one of the urgent problems to be solved in the printing and dyeing industry. How to reduce water use, reduce the discharge of harmful chemicals and the generation of waste, and achieve clean processing and production is the key to the sustainable development of today's textile printing and dyeing industry.

In the "Technical Guide for Green Development of Printing and Dyeing Industry (2019 edition)" issued by the Ministry of Industry and Information Technology in October 2019, it was proposed that the printing and dyeing industry is an industry that can consume more water and discharge more wastewater in the textile industry chain, and is also a weak link that restricts China's textile industry to the middle and high end. Therefore, it is necessary to develop new technologies to reduce energy consumption and waste water discharge, develop a number of green, intelligent equipment and promote the use of. The waterless printing and dyeing technology meets the current technical needs of the domestic textile industry for energy saving and emission reduction, and also meets the overall trend of domestic textile printing and dyeing industry upgrading.

Waterless printing and dyeing is the selection of non-water dyeing media for dyeing, is a new type of green dyeing technology, with no additives, short process flow, dyeing media can be recycled, no dyeing sewage discharge and other advantages, in line with the guidelines for energy conservation and emission reduction requirements, will be the main development direction of green high-end printing and dyeing in the future.

There are two kinds of real anhydrous dyeing technology, supercritical fluid anhydrous dyeing and solvent dyeing.

Supercritical fluid anhydrous dyeing

In the supercritical state, the supercritical fluid is in the semi-liquid gas state, which makes the supercritical fluid have both the dissolution capacity of a liquid and the diffusion capacity of a gas. In the supercritical fluid anhydrous dyeing process, the supercritical fluid can not only dissolve the dye, but also easily penetrate into the textile interior to complete the process of dye dissolution → adsorption → dyeing.

Supercritical CO2 dyeing technology was invented in 1989 by E. chollmeyer, a textile research center in Northwest Germany. The technology uses supercritical CO2 as the dyeing medium, dissolves the dye to the fiber pores, so that the dye is quickly and evenly dyed on the fabric, and the CO2 can be fully separated from the dye after the end of dyeing, without cleaning, drying and other operations, and the unused dye can be recycled.

CO2 is heated and pressurized to a supercritical fluid state that is neither gas nor liquid, and is continuously circulated between the dye tank and the dyeing tank by circulating pump. The supercritical CO2 fluid dissolves the dye while dyeing the fabric. The dyeing conditions are 20 ~ 30MPa, 80 ~ 160℃, and the dyeing time is about 1h. After dyeing, the remaining dyes and CO2 can be recovered and recycled.

Say no to water pollution in textile industry

In the past, a large number of textile printing and dyeing enterprises gathered in Shantou, Guangdong province, which troubled the people living in the Lianjiang River basin: the chaotic discharge of various kinds of sewage not only gave off odor, but also polluted the soil in the surrounding villages. In recent years, Chaonan District and Chaoyang District of Shantou City have successively built textile printing and dyeing environmental protection comprehensive treatment centers, driving the transformation and upgrading of local textile printing and dyeing enterprises, and making Lianjiang appear clear.

For areas with textile industry as the main industry, water pollution is a problem that must be solved.

"The traditional textile industry is a typical industry with high energy consumption, high water consumption and high pollution, especially in the dyeing and finishing process of textiles, which will produce a lot of wastewater and waste residue." Cao Hongmei, vice president of textile College of Jiangsu Changzhou Textile and Garment Vocational and Technical College, told reporters that printing and dyeing wastewater contains dyes, slurries, additives, oils, fiber impurities and inorganic salts, high content of organic pollutants, large alkaline, water quality changes and high chroma, pollution treatment is difficult. Therefore, in order to fundamentally solve the water pollution caused by textile printing and dyeing, not only must the relevant departments strictly manage the discharge, but also rely on the continuous upgrading of printing and dyeing technology.

"The research and development of waterless dyeing technology is to reduce the production of printing and dyeing wastewater from the source." According to Cao Hongmei, the core of the current domestic research and development of anhydrous dyeing technology is the selection of non-aqueous media for dyeing. "Such as supercritical carbon dioxide dyeing technology, through pressurization, carbon dioxide liquefaction into a fluid medium, in this state after the completion of dyeing and then decompression, carbon dioxide can be recovered, the whole process does not need to wash, does not produce waste water." The other is to use organic solvents instead of water as a medium for dyeing, and after dyeing, the organic solvents can also be recycled."

These water-free dyeing techniques have been applied in practical production. Shandong Qingdao Jifa Group Co., Ltd. has industrialized the supercritical carbon dioxide dyeing technology and established a supercritical carbon dioxide anhydrous dyeing industrialization demonstration line, which has shortened the textile dyeing efficiency from 8 to 12 hours of traditional water dyeing to 3 to 4 hours. Guangdong Yida Textile Co., Ltd. uses organic solvent dyeing technology, in the dyeing process, saving water 100%, reduce energy consumption 39.3%, dye fixation rate of more than 97%, solvent recovery rate of more than 99%.

Not only can the process of "dyeing" save water, but also the washing link after dyeing has also changed due to the emergence of new technologies.

Jiangsu Lianyungang Yingyou Xinlicheng Textile Technology Co., Ltd. developed the flash dyeing no-wash process, "steam instead of washing", to achieve continuous, rapid dyeing and color fixing no-wash processing.

"General fabric dyeing after the need for washing steps, one is to wash away a large number of dyes in the dispersant, suspension agent, flexibility agent, thickener and other additives, the second is to wash away the floating color. So we developed dyes with almost no additives, which dramatically reduced the use of water." Sun Sumei, vice chairman of Jiangsu Lianyungang Yingyou XinLicheng Textile Technology Co., LTD., told reporters that in the flash dyeing production line, when the cloth passes through the pad dyeing unit, it is instantly colored under the action of 200 ° C high temperature, compared with the traditional process, it is removed from the four processes of washing, dehydration, fabric management, drying and setting.

"At present, the flash wash process is mainly applicable to polyester fabrics; The word "flash" in the process name mainly emphasizes the significant increase in production efficiency and production speed." Sun Sumei introduced that in order to calculate the production capacity of a single equipment, the traditional dyeing cylinder equipment can produce 4 tons per day, and the flash dyeing production line can produce 25 tons per day. "The flash dyeing process has been industrialized, and the company has four production lines with a daily output of more than 100 tons of cloth. At the same time, our production costs have also been greatly reduced, in the past to achieve such a output of at least 400 workers, now only more than 100 people. From the perspective of environmental protection, the chemical oxygen demand per ton of wastewater was as high as two or three thousand, and now only in the cleaning machine, the treatment of dark cloth needs to use some water, the water consumption is greatly reduced, the chemical oxygen demand value is also reduced to several hundred, it is easier to deal with, and the pollution is smaller."

Domestic progress

1.Qingdao instant supercritical CO2 anhydrous dyeing industry line:

On June 30, 2021, Jifa supercritical CO2 anhydrous dyeing industrialization demonstration line was started in Jifa Longshan Industrial Park.

Since the industrialization research of "supercritical CO2 anhydrous dyeing technology" began in 2014, we have paid attention to the cooperation between industry, university and research, strengthened the cooperation between school and enterprise, and made a lot of practice and exploration. The completion of the demonstration line will provide a complete technical and equipment standard for the industrialization of waterless dyeing technology.

Since 2014, we have started to research supercritical CO2 anhydrous dyeing technology. After more than six years, we have solved a number of key technical and equipment problems, achieved the successful operation of small test lines and pilot lines, and produced small batches of boxed yarn products that meet the application standards. On July 31, 2019, Recognized by the academicians and experts organized by the China Textile Association as "the overall technology of the project has reached the international leading level". On June 1, 2021, the supercritical CO2 anhydrous dyeing industrialization demonstration line was initially built, and the expected goal was achieved during commissioning and operation.

2, Guangdong Yida reactive dyes anhydrous dyeing industry line:

The research and development team and industrial engineering team of Esquel Environment and Esquel Group have solved a series of material, process and equipment problems for the industrial mass production of 湙 dyeable waterless dyeing technology. After the success of the small laboratory test and 30KG pilot test, the industrialization demonstration base of 500KG per cylinder (2.5 tons per day) of reactive dye anhydrous dyeing began to be built in January 2023, and was officially put into operation on April 26.

3, Zhejiang Lvyu reactive dye non-aqueous medium dyeing:

The "Key technology for zero-discharge dyeing of non-aqueous salt-free wastewater" created by Lvyu Textile puts forward a dyeing mechanism completely different from traditional water bath dyeing in non-aqueous media, and successfully realizes salt-free dyeing of cotton fibers with reactive dyes, with dyeing rate of nearly 100% and color fixing rate greatly increased from 65% of traditional dyeing to 90%. Its "Key technology of zero-discharge dyeing of non-aqueous medium salt-free sewage" was successfully selected as one of the ten typical cases of new mode and new business of Zhejiang textile industry in 2022 by Zhejiang Economic and Information Department.

Article source: National Machinery Group Wuhan Textile you, Watt technology, dyeing and dyeing strict selection