So sodium hypochlorite has oxidation effect.
Chlor-alkali industry is quoted from document No.8 in August 2006.
Study on oxidation of sodium hypochlorite solution in chlor-alkali industry in August 8, 2006
Zhou+,Wang Xiaojun, Wang Wei (School of Environmental Science and Engineering, South China University of Technology, Guangzhou, Guangdong 5 1064 1)
Sodium hypochlorite; Redox potential; Available chlorine content
[Abstract] The effects of temperature, available chlorine content and salt content on the oxidation of sodium hypochlorite solution were studied experimentally. The results show that at normal temperature and pressure, the redox potential of bleaching water is mainly controlled by pH value, and increases with the decrease of pH value. Under the condition of constant pH value, the redox potential of bleaching water has a quadratic function relationship with available chlorine content; The stability of bleach is closely related to temperature and pH value, and it is easy to decompose at high temperature or low pH value. Increasing the salt content is helpful to improve its stability.
[China Library ClassificationNo.] 1Q 124.44 [Document IdentificationNo. A [DocumentNo.1008-133x (2006) 08-0028-03]
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University of Science and Technology of China, Guangzhou, 510641; Redox potential; Abstract: The effects of temperature, available chlorine content and salt content on the oxidation resistance of sodium hydroxide solution were studied by experiments. The following results were found. At room temperature and without pressure, the redox potential of sodium hydroxide solution is mainly affected by pH value, and increases with the decrease of pH value.
Value. Relationship between redox potential of sodium hydroxide solution and active chloride ion content. Ed pH value. The stability of sodium hypochlorite solution depends largely on temperature and pH value. Sodium salt is easy to decompose at high temperature.
Or low ph. The increase of salt content is helpful to improve its stability.
Sodium hypochlorite solution, commonly known as bleach, is a by-product of chlor-alkali industry.
It has a strong oxidation effect and can bleach colored fabrics, which is often called in industry.
For commercial bleaching water, bleaching water and high-efficiency bleaching powder, medical literature also calls it
Hypochlorite soda, sodium hypochlorite and bleach u J are widely used in production.
Laundry, dyeing and finishing, papermaking and other industries use its oxidation to bleach products.
White. The redox potential is ORP (redox po-)
Potential) is the most intuitive parameter reflecting the oxidation of solution.
In this paper, the oxygen content of bleaching wastewater was studied by measuring ORP under different conditions.
Changes in chemistry.
1 experiment
In the experiment, bleach used in clothing washing factory was used. By adding
Nacl changed the salt content, and HCl and H: SO were added drop by drop. Change the pH value, make
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Use portable pH, ORP and temperature produced by EuTECH in Singapore.
Measure pH, ORP and temperature.
2 Results and discussion
The redox potential is usually measured by an inert electrode, such as a platinum electrode.
Platinum electrode and platinum electrode were used in this experiment without applying current.
Silver/silver chloride reference electrode. The drift water level measured by platinum electrode is a kind of
The mixed potential is the result of the interaction of several redox pairs.
It reflects the comprehensive oxidation capacity of bleaching system. Factors affecting measurement
In addition to the properties of platinum electrode surface, elements mainly have the electrical anisotropy of electrode surface.
The properties of the strain and the available chlorine content, temperature and pH value of the bleaching solution.
There are many redox reactions in bleaching water, such as HClO//
[Author Brief Introduction Zhou (1982 I), male, master, now studying in the Department of Environmental Engineering, School of Environmental Science and Engineering, South China University of Technology.
[Fund Project] Key Industrial Plan Project of Guangdong Province in 2005 (ProjectNo.: 200583110/001)
[Date of receipt: April-April 2006]
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8 weeks, etc.: Study on oxidation of sodium hypochlorite solution.
C 12, ClO- 1/cl- 1, 02/oh, etc. Except hclo/c 12 and C 10-/
Except cl- 1, O:/OH- 1, other redox processes are weak and drift.
Because of the dissolved oxygen content in bleaching water, water has little effect on ORP.
Very few, so the ORP of bleaching water is mainly affected by HCLO/Cl:, C 10 ~/Cl-.
Influence. The author mainly studied the factors such as temperature, pH value and salt content.
Effect of elements on ORP of bleaching water.
2. Effect of1temperature on oRP of bleaching solution
Sodium hypochlorite is extremely unstable and will gradually decompose at a slightly higher temperature.
The reaction equation is as follows (1):
3C 10 for each C 10f for each 2Cl, (1)
2ClO-30 Cl-+02。 (2)
This experiment was carried out at room temperature (about 20℃) and was not considered.
Influence of temperature on experimental results.
2.2
Effect of pH value on redox potential of bleaching water
There are the following equilibrium relationships in floating water:
20H C 12 electrode ClO +Cl +H20. (3)
HClO is very easy to decompose, so in order to prevent it from decomposing, bleaching is guaranteed.
Quality, generally control the mass fraction of free alkali in bleaching water to 0.6%.
~ 1.0%。 See figure 1 for the equilibrium relationship of the bleaching system.
Degradation of nitrite by acidic nitrocellulose
Figure1The concentration of sodium hypochlorite is 0. 1 mol/l at 25℃.
Equilibrium diagram of pH value and bleaching system
As can be seen from Figure 1, when the pH value is less than 2, the solution mainly
The component is Cl: the pH value is greater than 9, and the main component is c 10. pH value
It not only affects the composition of the solution, but also affects its oxidation. HOcl
P 1 has the strongest oxidation ability.
Fig. 2 shows the bleaching water (available chlorine mass) when the pH value is adjusted with hydrochloric acid.
9.59%, salt content is about 7.9%).
8 9 10 Li 12 13
pH value
Fig. 2 Effect of pH value on ORP of bleaching water (adjusted with hydrochloric acid)
As can be seen from Figure 2, with the decrease of pH value of bleaching water,
ORP showed an upward trend, with a mutation at pH = 10.5.
After PH value < 10, the change trend is relatively stable; When the pH value is
The reaction is violent, producing a lot of irritating gas (c 1:), which is difficult to measure.
ORP .
The hydrochloric acid for adjusting the pH value is 1+ 1 hydrochloric acid, which contains Cl-.
In order to avoid its influence on the experimental results, experiments were made with 1+4 sulfuric acid.
Repeat the experiment, and the result is shown in Figure 3. 0RP varies with pH value.
The trend of chemical transformation is almost the same as that of hydrochloric acid, and the mutation point is pH.
Value = 1 1.
8 9 10 Il 12. 13
pH value
Fig. 3 Effect of pH value on oRP of bleaching water (sulfuric acid adjustment)
When hydrochloric acid is added to the bleaching water, the following reactions will occur in the bleaching water:
2H++C 1 +ClO is called C 12+H20. (4)
Reaction (4) greatly increased the concentration of free chlorine in bleaching water and improved the extraction efficiency.
The redox potential is increased. This mutation occurred because of pH >.
At 1 1, most of the added acid is consumed by NaOH. With the addition of acid,
With the increase of dose, the concentration of HclO increased and partially decomposed.
The oxidation ability of HClO is far stronger than the standard of C 10 (HCLO/Cl:).
The electrode potential is 1.6 1 1 V, and the standard electrode potential of ClO- 1/CL- 1
0.89 V), resulting in ORP mutation. This is the same as the result obtained from figure 1.
The conclusion is consistent. Therefore, the pH value of the bleaching solution is in the range of 5-7, and bleaching is carried out.
Cellulose of products (such as clothing, cloth, paper, etc.). ) will be downgraded; In alkali
Bleaching under natural conditions can easily control the damage to cellulose.
2.3 Effect of available chlorine content on oRP of bleaching water
The content of available chlorine does not refer to the content of chlorine, but refers to the oxygen in bleaching water.
The chemical capacity is equivalent to the oxidation capacity of chlorine. That is, a certain amount of floating water
When the reaction is completed, its oxidation capacity is equivalent to how much mass of chlorine gas?
The oxidation capacity of. Therefore, the content of available chlorine can reflect the oxidation degree of bleaching water.
Capacity is an important index to measure the quality of bleach. Available chlorine content in bleaching water
The relationship between quantity and ORP is shown in Figure 4.
As can be seen from Figure 4, when the mass fraction of available chlorine in bleaching water changes from
When lo. 36% decreased to 65438 0.26%, and its ORP first increased and then decreased.
The trend is consistent with the trend that the mass fraction of available chlorine is more than 5% before the change.
Very small; When the mass fraction of available chlorine is less than 5.5%, ORP changes.
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Chlor-alkali industry in 2006
Very obvious. On the premise of ignoring the influence of pH value and temperature, after
Curve fitting, bleaching ORP and available chlorine mass fraction (range
Yes 1.26%- 1.36%) (scale = 99. 1%, P
O.000 1):
E = 550.72+ 18.55 Xun Yi 1.20 Cui 2. (5)
Among them, E is the ORP(mV) of bleach, which is called bleach available chlorine.
Quality score (%).
The mass fraction of available chlorine in bleaching water sold in the market is mostly lower than that of available chlorine.
12% can be considered as ORP and available chlorine in industrial bleaching water at room temperature.
The content relationship conforms to formula (5).
Fig. 4 Relationship curve between available chlorine content and oRP in bleaching water.
2.4 Influence of salt content on oRP of bleaching water
It can be seen from formula (3) that a large number of products will be produced in the bleaching process.
NaCl, the content of which is only lower than sodium hypochlorite, uses pure caustic soda and
The mass ratio of available chlorine to salt in bleaching water obtained by chlorine reaction is about
1.2: L, with the decomposition of sodium hypochlorite, this ratio gradually decreases. along with
For example, fresh bleached water with a mass fraction of available chlorine of LO% contains salt.
The content fraction is about 8.3%. The solubility of salt in bleached water is about
20%, whether increasing the salt content in bleaching water will affect the balance of formula (3)
Have an impact, thus affecting the ORP of bleach? If it does,
Theoretically, Equation (3) should be shifted to the left, thus increasing.
ORP .
In the experiment, bleach with effective chlorine of 7.23% was mixed.
The salt content increased by 10%, and the available chlorine content was determined as follows.
6.46%, and the redox potential changed from 563 millivolts to 555 millivolts. Visible, mention
After high salt content, the ORP of bleaching water has little change, and its influence can be ignored.
A little. However, the content of available chlorine changes greatly, which should be an increase in salt content.
(Continued from page 27)
It forces papermaking enterprises to use chlorine dioxide produced by sodium chlorate as bleaching agent.
The increasing demand for whitening agent and sodium chlorate has promoted the development of chlorate industry.
Opportunity.
90% sodium chlorate is used to produce chlorine dioxide abroad, and it is also used in China.
The pulp with capacity of 1 10,000 ∑a will be bleached with chlorine dioxide.
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And increase the density of bleaching water, so the reduction of available chlorine content and
It will not change the oxidation of bleach.
The salt content has little influence on the oxidation of bleaching water, but it has influence on its stability.
What's the impact? Raw bleach and salt bleach are also stored in darkness and room temperature.
The available chlorine content of 1 1 day was determined, and the result is shown in Figure 5.
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Fig. 5 Stability of bleaching water with different salinity.
As can be seen from Figure 5, the content of available chlorine in the original bleaching water decreased slightly.
The stability of fast high-salt bleach is higher than that of the original bleach.
3 Conclusion
At normal temperature and pressure, the oRP of bleaching water is mainly controlled by pH value.
The decrease of pH value is increased, which is effective under the condition of constant pH value.
Chlorine content is a quadratic function; Stability, temperature and pH value of bleaching water
Value has a great relationship, and it is easy in the case of high temperature or low pH value.
Decomposition and increasing salt content are helpful to improve its stability.
In the process of industrial use, in order to obtain better bleaching effect and
Easy to control, bleach is usually diluted (dilution multiple of different industries)
Different), and keep the pH above 8. If it takes a short time
In order to preserve bleaching water, it is suggested to increase its salt content before preservation and re-prepare it.
Determination of available chlorine content before use.
refer to
[1] Fan Yuhong. Study on the stability of commercial bleaching water [J]. Chlor-alkali industry,
2003,(8):33—35.
Fang Xianda. Chlorate production technology [M]. Beijing: Chemical Industry Press.
Lv Hongwei. Collection and application of sodium hypochlorite bleaching solution [J]. Paper chemicals,
2004,(4):47.
[Editor: Gao Xudong]
In addition, sodium chlorate can be used to further produce barium chlorate, strontium chlorate and other products.
Products. Further production of perchloric acid compounds with sodium chlorate and sodium perchlorate
Materials and other products to meet the development of modern rocket technology and atomic energy industry.
Need.
[Editor: Gao Xudong]
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