Ethylene glycol chilled water is acidic, with a pH of 4-5. How to solve it
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Our project is a syngas-based ethylene glycol production plant. The chilled water used for ethylene glycol is prepared by mixing desalinated water with polyester-grade ethylene glycol, at a concentration of around 45% w/%, and it has been in use for half a year. Currently, the pH value of the frozen aqueous solution is found to be 4-5. Question 1: Why does acidity appear after running for a while? What causes this? 2. Impact on the equipment. 3. What are the solutions? Are there any practical measures to address this?
1. Ethylene glycol decomposes slowly in the presence of oxygen, producing acid; C2H6O2 + 5O2 = 4CO2 + 6H2O. Carbon dioxide dissolved in water forms carbonic acid
My previous approach was to regularly measure the pH and add a small amount of liquid alkali. At that time, ammonia was used for cooling, which in turn powered the ethylene glycol-based coolant used for air conditioning in the workshops; that was many years ago
Nitrogen seal for the circulating chilled water tank! Measure pH regularly
A corrosion inhibitor specific for ethylene glycol must be added; otherwise, corrosion will be severe. You can consult the professional company in China, Chaoyang Guangda Chemical. In fact, the mixture of ethylene glycol and water is highly corrosive; corrosion intensifies especially after acidification. It’s best to add some alkali first to adjust the pH, and then add a corrosion inhibitor
1. Alkali and corrosion inhibitors need to be added. 2. The chilled water tank should be sealed with N2. 3. When the SS level in the chilled water is high, rust sludge forms; pressure filtration should be used to remove this sludge and reduce the SS level. 4. It is recommended to use DMW during future maintenance, as chilled water causes severe corrosion of pipelines
Ethylene glycol contains hydroxyl groups; when it is exposed to temperatures between 80 and 90 degrees Celsius for an extended period of time, it is first oxidized to glycolic acid, and then further oxidized to oxalic acid, that is, ethanedioic acid (oxalic acid), which has 2 carboxyl groups. Oxalic acid and its byproducts first affect the central nervous system, then the heart, and subsequently the kidneys. Without appropriate treatment, excessive ingestion of ethylene glycol can lead to death. Ethylene glycol oxalate causes corrosion of equipment, leading to leaks. Therefore, the prepared antifreeze must also contain preservatives to prevent corrosion of steel and aluminum as well as the formation of scale.