Neutral deinking of the hottest waste newsprint by

Chemical neutral deinking of waste paper

Gao Yujie, doctor, associate professor, main scientific research fields: papermaking additives, special functional paper, waste paper recycling

key points: at present, the vast majority of waste paper chemical deinking plants at home and abroad adopt alkaline deinking method, but alkaline deinking agent has many inevitable shortcomings, such as high COD in wastewater, easy alkaline blackening of pulp, etc. In view of the shortcomings of alkaline deinking, a neutral deinking agent which can deink under neutral conditions is developed, and the application conditions of neutral deinking agent are discussed, and the deinking effect is compared with that of alkaline deinking agent

key words: neutral deinking; Waste paper; Application process; Deinking effect

at present

at present, alkaline deinking is basically the main method of regeneration deinking of various waste papers in China, but alkaline deinking has many disadvantages, such as increasing the COD value of wastewater and increasing the difficulty of wastewater treatment; Peroxide is usually added in the process of waste paper shredding to prevent the alkaline blackening of the pulp; At the same time, sodium silicate is often added as a stabilizer of peroxide, which increases the production cost in the case of low whiteness of pulp, which seems to be caused by the lack of understanding and understanding of material properties. It is very necessary to develop neutral deinking agent and neutral deinking technology. This is because neutral deinking can overcome the above shortcomings

they prepared a unique kind of neutral deinking agent in flexible conductive film 1

1.1 composition of a group of neutral deinking agents

at present, waste paper deinking is to expand the fiber and ink by soaking and wetting in the process of waste paper dissociation, decompose the oil and ink fixed on the fiber, so as to peel the ink from the fiber. The commonly used surfactants in deinking agents are anionic surfactants such as potassium soap, sulfonated oil, sodium linear alkylbenzene sulfonate, sodium fatty alcohol sulfate, sodium fatty alcohol polyoxyethylene ether sulfate, and non-ionic surfactants such as alkyl phenol polyoxyethylene ether, fatty alcohol polyoxyethylene ether, fatty acid polyoxyethylene ester. Fatty acids have a good ability to agglutinate ink particles, and are often used as the main component in the flotation deinking process. However, the penetration of fatty acids is poor, and it is difficult to make the ink particles closely bound to the fiber fall off during the beating process. In order to make up for this shortcoming, other surfactants are often compounded in the formula to improve the penetration of deinking agents. Flotation deinking agent generally does not use non-ionic surfactant as the main component, because it has the property of strongly dispersing ink, so that ink particles are dispersed and emulsified in pulp, which increases the difficulty of flotation. The combination of anionic and non-ionic surfactants has excellent deinking effect. Deinking agent used in flotation method not only requires that the deinking agent be stripped from the fiber, but also requires that the dispersed ink particles can be stably suspended in water without or less reabsorption

at present, chemical neutral deinking has been reported abroad; However, the research and application of neutral deinking in China is still in its infancy. In the process of developing neutral deinking agent, we mainly adapt to flotation deinking and give consideration to washing method. We not only consider having good ability to separate ink, but also appropriately control the foam force and use cost of deinking agent. Therefore, we choose anionic and non-ionic surfactants as the main ingredients. At the same time, in order to strengthen the deinking effect, we add an appropriate amount of inorganic salts and other additives

1.2 performance index of neutral deinking agent in group

current appearance: light yellow translucent viscous liquid current effective content: 20% ~ 50% (depending on requirements) current pH value: 7 ~ 7.5

currently stored at -10 ℃ for 24h, there is no precipitation, and the room temperature is restored without deterioration and stratification. Current shelf life: 1 ~ 2 years. Currently, it is non corrosive and easy to transport and store

1.3 the manufacturing cost of neutral deinking agents

is currently prepared by atmospheric pressure reactor. The required equipment is simple, easy to operate and pollution-free

at present, based on the deinking agent with a concentration of 20%, it costs about 2300 yuan to withdraw from the process first

2 parameter optimization of neutral deinking process parameters

at present, the deinking experiments in this paper are all carried out under neutral conditions. Only neutral deinking agent is added in the pulper, without alkali, sodium silicate and other auxiliary chemicals, and pulping is carried out at 45 ℃ and about 10% concentration for 30min; The deinking environment and deinking wastewater are in the neutral range

at present, through experiments, it is concluded that the best process conditions for neutral deinking when the raw material is American waste paper are: the dosage of self-made neutral deinking agent 801 (or 802) is 1.0%, the pulping time is 20 ~ 30min, the flotation concentration is 0.8 ~ 1.0%, and the flotation time is 10min

at present, the whiteness of deinked pulp obtained by flotation at room temperature is lower than that obtained by flotation at 50 ℃. At low temperature, there are relatively few ink particles and more fiber loss. If conditions permit, appropriately increasing the flotation temperature is conducive to improving the flotation efficiency and the quality of deinked pulp

at present, after the pulping process, the pulp in the hydraulic pulper is kept at constant temperature for a certain time to ensure the full reaction between the deinking agent and the ink, so that the ink particles are fully softened and dispersed, which is conducive to the improvement of deinking effect. In practice, after the waste paper is broken up by the hydraulic pulper, the chemical reaction will be further carried out in the process of pulp storage and transportation, so as to improve the efficiency of ink removal

3 effect and alkaline deinking effect comparison

the use of high-strength thin-walled can reduce the weight of a single piece by 20%