Discussion on APMP bleaching effect of the hottest

Discussion on APMP bleaching effect of amidine sulfite poplar

Zhou Xiaolu Zhaoqing, a postgraduate student at Shaanxi University of science and technology, his main research direction is the research and development of processed paper and special paper

key points: the effects of Fas dosage, NaOH/Fas dosage ratio, pulp concentration, bleaching temperature and time on the whiteness of bleached pulp when formamidine sulphonic acid (FAS) is used in the bleaching of poplar alkaline peroxide chemimechanical pulp (APMP) are discussed. The best process conditions are obtained through experiments: Fas dosage 0.6% (mass fraction of absolute dry pulp), bleaching concentration 10%, temperature 70 ℃, time 60min, Fas/NaOH dosage ratio 2, and the whiteness of bleached pulp is 62.3%sbd, Whiteness increased by 9.8% SBD. Through the study of single-stage bleaching of Na2S2O4 and H2O2, the bleaching effect of Fas is compared with that of pulp whiteness, strength, wastewater pollution load and process conditions. It is concluded that FAS is a clean and economical new bleaching agent

key words: formamidine sulfinic acid; Alkaline hydrogen peroxide chemimechanical pulp; Bleaching

adopts formaidine sulphonic acid (FAS), also known as thiourea dioxide, which is the oxidation product of thiourea. The trade name is reductant FM, which was originally used in the dyeing and finishing industry. Its molecular formula (NH2) 2cso2 is white powder, odorless, has no fixed melting point, and can be dissolved in water. The pH value of the aqueous solution with a mass fraction of 10% is 5, which is weakly acidic. It is a relatively safe chemical. It is stable in acidic solution and decomposes into urea and strong reducing hyposulphuric acid when heated, and into urea and sodium hyposulphuric acid in alkaline solution. Because Fas has potential reduction ability (reduction potential 1230mv), it is listed in the category of reducing agents. As a new type of pulp bleach, Fas has convenient bleaching operation, good bleaching effect, no pollution of bleaching wastewater, and the wastewater can be directly discharged into farmland, but it has been rarely used in the domestic paper industry [1] [2]

in this paper, poplar APMP was used for Fas bleaching, and the optimal bleaching conditions were systematically studied. The single-stage bleaching of H2O2 and Na2S2O4 was also studied

1 the real experimental raw material

adopts poplar APMP: it is taken from Hunan Yueyang paper factory, air dried and preserved, whiteness 53.08%sbd, dryness 90.9%, beating degree of raw pulp 17 ° Sr, PFI disc mill beating to 45 ° Sr, and then cutting, tensile index is 37n · m/g, tear index is 4.0mn · m2/g

formamidine sulfurous acid is used, which is provided by Shandong Yantai dastek Chemical Co., Ltd. the appearance electronic universal testing machine is a measuring instrument: loose white crystalline powder, the content of effective components ≥ 99%, the content of thiourea ≤ 0.1%, the content of water ≤ 0.05%, and the content of ash ≤ 0.17%

using this experiment, each cubic meter of vanadium electrolyte will consume 145.61 kg of vanadium pentoxide. The content, dosage and concentration of all substances are calculated by mass fraction

2 results and discussion

2.1 original Fas single-stage bleaching

Fas bleaching is adopted because the secondary situation generated by the decomposition of formamidine sulphonic acid in alkaline solution is not optimistic. Sulfuric acid neutralizes sodium hyposulfite with reducibility, thus changing the structure of chromogenic groups in pulp, reducing the absorption of light, and improving whiteness. The final decomposition products are urea, bisulfate, and sodium hyposulfite. The decomposition reaction is as follows:

ho2sc (NH) NH2 → H2C (o) nh2+h2so2

ho2sc (NH) nh2+2naoh → na2so2+h2c (o) nh2+h2o

2.1.1 the influence of the original Fas dosage on the bleaching effect

the bleaching effect is directly affected by the Fas dosage. When the experimental conditions are as follows: NaOH is half of Fas dosage, pulp concentration is 10%, bleaching time is 60min to reduce energy loss, and the effect of Fas dosage on pulp whiteness under different temperature conditions is shown in Figure 1

Figure 1 Effect of Fas dosage on bleaching effect

Table 1 pH value of different NaOH dosage

NaOH%

initial pH

end point pH

0.2

0.3

0.4

0.5

10.40

11.03

11.24

11.43

5.36

7.10