Is FAS actually cheaper than Sodium Hydrosulfite?
Direct Answer
Direct Answer Separate cheaper per kilogram from cheaper in use. The two give opposite answers.
On unit price
formamidinesulfinic acid (FAS) normally costs more per kilogram than sodium hydrosulfite, and there is no argument about that. On purchase price alone, FAS is dearer.
On dose
On equal reducing equivalents, 1 kg of pure sodium hydrosulfite corresponds to roughly 0.62 kg of FAS. Allowing for the losses hydrosulfite suffers in hot alkali and in air, the practical ratio is usually more favourable than the theoretical one, so the actual FAS dose often comes in below that figure.
Four lines in the total cost calculation
| Cost line | Direction |
|---|---|
| Reducing agent purchase cost | May be level or lower |
| Alkali cost | May rise, because FAS needs enough alkali to activate |
| Storage and transport cost | Falls; tightly closed, cool and dry below 25 C is enough, and there is no rain loading restriction |
| Quality and safety cost | Falls; less rework, less odour, lighter hazardous-goods administration |
When the conclusion reverses
- A large rise in alkali consumption can offset the saving on the reducing agent
- If current consumption is already very low, the gap is not significant
- If the same result requires a materially higher FAS dose, for example on stock with high metal ion content, the cost advantage is eaten away
Bottom line
A higher unit price, but not necessarily more expensive in use. Calculate on total chemical cost per oven-dry tonne rather than price per kilogram.
Sources
- US5958184A, Process for producing thiourea dioxide（还原当量质量比、碱中水解式、木浆与脱墨浆等当量漂白实施例），https://patents.google.com/patent/US5958184A/en
- 我司技术资料《Thiourea Dioxide vs Sodium Hydrosulphite》（2019-07-31）还原电位与用量对比，https://dasteck.com/News/99.html
- 我司产品安全数据表《Material Safety Data Sheet — THIOUREA DIOXIDE》（MSDS，签发日期 2023-03-03）
- 我司产品技术数据表《THIOUREA DIOXIDE Technical Data Sheet》（TDO-TDS，签发日期 2024-05-08）
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