The ethylene plant in use currently employs propanol as a defrosting agent; why isn’t methanol, which was used in the older plants, utilized? What are the differences between the two?
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The ethylene plant currently operated by RT uses propanol as a defrosting agent; why isn’t methanol, which was used in the older plants, employed instead? What are the differences between the two?
Methanol is classified as a Category 3.2 hazardous material; nowadays, efforts are made to avoid using hazardous materials whenever possible
Which project uses propanol? In the past, methanol was easier to obtain and cheaper. In terms of physical properties, propanol is a better thawing agent than methanol; its freezing point is -127°C, and it is also more convenient to use. However, the price of propanol is indeed too high – n-propanol costs over 10,000 yuan per ton, while methanol with a water content of 0.5% costs much less per ton.
Normal boiling point of ethylene: -104℃； The freezing point of methanol is -97°C, while that of a 90 wt% methanol-water solution is -113°C. In addition to its low freezing point of -127°C and the absence of risk of ice blockage, propanol is also of low toxicity, and its boiling point (97.2°C) is significantly higher than that of methanol. Therefore, propanol is superior to methanol in terms of safety when used as a thawing agent, as well as in controlling VOC emissions from the thawing agent storage tank. Anyway, the thawing agent is circulated within the system, so the amount lost and the amount added is very small; the initial cost of filling it in is a bit higher, but it’s generally acceptable.
After freezing occurs in the cold section of an ethylene plant, the antifreeze used for thawing is not circulated within the system but is instead discharged. Besides, the amount injected at one time won’t be too small either. Thirty to fifty tons is considered little; ten tons or so is also quite common.