Special online pH meter resistant to sulfide corrosion
Thread Content
For the absorption of hydrogen sulfide exhaust gases in our plant, we use primary and secondary liquid alkali absorption systems, and we would like to install online pH meters to monitor the pH value. The meters we used in the past failed after less than half a month; several different brands were tried, but none worked. Is there a specialized meter that can resist sulfide corrosion? ?
Sodium sulfide, which is produced when liquid caustic absorbs hydrogen sulfide, is highly alkaline and is commonly known as caustic sulfide. Therefore, it is meaningless to install first- and second-stage absorption solutions in an online pH meter; even if a pH value is measured, it is not possible to determine whether it is due to excess liquid alkali or to sodium sulfide, the product. Incidentally, the pH of a sodium sulfide solution with a concentration of 0.1 mol/L (7.8 g/L) is as high as about 13 ； The pH value of a 1.0 mol/L sodium sulfide solution is approximately 14.0. Its pH value is approximately equal to that of a sodium hydroxide solution with the same molar concentration.
No matter how advanced the pH meter may be, it only provides measurement results; it still cannot solve the problem of corrosion. Why not focus efforts on anti-corrosion solutions? I would like to recommend a polyaniline-based high-performance anti-corrosion coating to you. Good effect on hydrogen sulfide corrosion. We have carried out anti-corrosion work at the Sichuan Dazhou natural gas purification plant, and the results have been good.
pH meters are made of glass, and strong alkalis can corrode glass; it’s not hydrogen sulfide
But the same pH meter used in liquid caustic has always worked well. It’s never broken
This post was last edited by qugd on 2022-1-25 at 15:41. How long does the pH probe that the original poster is looking for expect to last? In a strongly alkaline medium with a high concentration of sulfur ions (low-valent sulfides), the pH probe (glass electrode) will experience a sodium error (measurement error) due to the effect of the strong alkali ； Furthermore, the penetration of sulfide ions into the reference electrode can cause a drift in its potential, which is also an important source of measurement error. In such cases, it is necessary to select an appropriate pH measurement system based on the specific operating conditions; however, this can only slightly alleviate the issues associated with the use of the electrode probe, as it is not possible to completely overcome them, since the measurement range has reached the limit for using pH electrodes. The interference caused by sulfides is also difficult to completely overcome, as osmosis persists. Although some electrodes with special structures can mitigate this issue to some extent, the effect of sulfides cannot be entirely eliminated. For such samples of highly alkaline, high-concentration sulfides, it is advisable to measure the alkalinity and sulfide concentration separately; chemical titration may be a good solution.