The effect of sulfate in saline on electrolysis
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This post was last edited by sunjl1981 on 2013-1-6 at 20:00. The requirement for the sulfate content in brine in the chlor-alkali industry was initially set at less than 5 grams per liter; later, it was found that barium ions had a greater impact on the membranes than sulfate did on the electrolysis process. As a result, many manufacturers adjusted the allowable sulfate level to less than 7 grams per liter. Many manufacturers are now using the membrane-based denitration process with KAI membranes. What is the optimal level to maintain for sulfate ions? Here is another issue related to energy consumption. I would like to ask the experts: just how significant is the impact of sulfate ions on electrolysis? Do they affect the membrane, the electrolyzer, or the product? What range should the sulfate concentration in saline be kept within in order to minimize its impact on electrolysis while also maintaining optimal energy consumption? We ask all experts to share their views so that we can all learn together*. Thank you! This post was last edited by haining on 2009-3-27 08:53 ] # ， ， &
It’s certainly better to have a low sulfate level; high sulfate levels lead to low sodium chloride concentrations and reduced anode efficiency. Ideally, the sulfate level should not exceed 5 grams per liter, in order to prevent concentration and crystallization inside the tank
The sulfate ion level should be kept at a low level – exactly how low? Please share your thoughts! Control over the source of sulfate ions also needs to be strengthened; manufacturers that use brine may have higher levels of sulfate ions. Additionally, an excessive amount of sodium sulfite added is also a cause of excessive sulfate levels!
Generally, the sulfate concentration in ion exchange membranes is controlled at 5–6 g/l. The poster said it is necessary to control barium. For a single sulfate ion, it generally does not lose electrons to produce oxygen, as its oxygen evolution potential is high; however, it does have an effect on hydroxide ions. In summary, the sulfate ion has a much smaller impact on the operation of ion exchange membranes compared to metal ions. This post was last edited by limingshuguang on 2009-3-28 09:20]
High SO42- concentrations cause crystallization within the membrane, resulting in membrane pinholes and oxygen evolution corrosion at the anode. It should be kept below 5 g/L, or NaSO4 levels should be below 10 g/L.
Theoretically, the lower the concentration of other impurity ions including sulfate ions, the better. However, setting such low a requirement is not cost-effective or energy-efficient; generally, keeping the sulfate ion concentration at or below 8 is sufficient as it does not have a significant impact on electrolysis.
For ion exchange membranes, a value of less than 7 grams per liter is sufficient; whether the barium method or membrane method is used. Of course, the lower this value, the less energy consumption there will be.
A level between 3.5-5g/l is sufficient; it’s best not to exceed 7g/l. This post was last edited by yzhms on 2009-3-27 17:24]
Here, we require the sulfate level to be less than 5 grams per liter; too high a level can cause crystallization and an increase in oxygen content.
Lowering the amount of sulfate does not necessarily result in lower energy consumption. The sulfate ions must be removed in equal amounts to those that enter; otherwise, the sulfate level in the system will increase. The so-called additional energy consumption refers to the energy required to reduce the sulfate concentration in the system from its initial value to the desired value; thereafter, no further energy consumption occurs.
Sulfate ions pose a certain hazard to electrolysis within the electrolytic system; I don’t quite understand this from a theoretical perspective, so I hope some expert can explain it.
The sulfate content cannot be too high nor too low; if it is too high, oxygen is generated during discharge, reducing the purity of chlorine； Additionally, deposition on the membrane is a common issue; experiments have shown that when the sulfate content is zero, the current efficiency drops sharply, while it reaches its highest level when the sulfate content is between 2–5 g/l. This indicates that sulfates can inhibit the deposition of ions such as strontium and barium; therefore, it is advisable to maintain a certain concentration of sulfates in saline solutions.
Primarily, sulfate ions discharge at the anode during the initial stage of operation, which affects current efficiency and also leads to the release of oxygen, thereby reducing the purity of chlorine. However, after operating for some time, their discharge is suppressed by chloride ions, due to the lower potential of chloride ions. The second is the formation of sulfate precipitates, which attach to the membrane and affect its dialysis rate.
Upper limit: < 10 g/l as Na2SO4; the standard value set by most manufacturers is 5 g/l, but some manufacturers, after consulting experts from Asahi Kasei and drawing on their experience with DuPont membranes, keep this level at 7 g/l. Hazards: 1. A relatively high amount can be tolerated, as ion exchange membranes repel sulfate ions, which leads to a decrease in current efficiency. 2. It deposits in the form of Na2SO4 or polymeric salts on the side of the membrane closest to the cathode. 3. The damage it causes to the membrane is similar to that caused by calcium hydroxide, although the locations where calcium and sulfate ions deposit are different； Calcium ions deposit in the polymers within the reinforcing network. In other words, where there is an electric current flowing, sulfate ions precipitate on the reinforcement mesh, that is, in areas where the current is very weak.